Field of the Invention

The present invention relates to compositions, in particular compositions for forming an image on or within a substrate.

Background of the Invention

In-line digital printing is a process known for the formation of greyscale, single- coloured (monochromic), or multi-coloured images on or within substrates. Radiation from a laser source(s) effects laser-reactive compound in compositions applied on or incorporated within substrates such that they change colour upon application of the radiation. However, problems arise in that when using these laser-reactive compounds, access to a full colour gamut and the full range of primary colours required to form multi-coloured images is difficult to achieve.

There is therefore a desire to provide laser-reactive compositions for use in the formation of an image on or within a substrate that can provide a broad colour gamut for in-line digital printing via laser excitation, enabling real-time marketing and personalisation response capabilities for users. In order to achieve this, it is necessary to have compositions that have components able to form stable predictable colours upon application of radiation or other stimuli.

Summary of the Invention

According to a first aspect of the present invention, there is provided a composition comprising a keto acid compound and an acid-generating agent, wherein the keto acid compound is capable of transitioning from a non-coloured state to a coloured state, the transition being effected by the application of an applied transition stimulus, wherein the keto acid compound is of formula (I):

wherein Xi _a , X _2a , and X _3a are independently selected from C, N, B and S; the two R groups may be the same or different, and are independently selected from: hydrogen; Ci-i ₈ alkyl; Ce-^aryl optionally substituted with Ci-i ₈ alkoxy, -CN, - CF ₃ , -NO2, halogen, or CMS alkyl; halogen; -N0 ₂ ; -CF ₃ ; -OR ³ ; -NR CN; -SR

COR ³ ; -C0 ₂ R ³ ; and -CONR ³ ₂ ; wherein R ³ is selected from an alkali metal; hydrogen; Ci-i ₈ alkyl; and Ce-^ aryl optionally substituted with Ci-i ₈ alkoxy, -CN, - CF ₃ , -N0 ₂ , halogen, or CMS alkyl; or both R groups, together with the nitrogen atom to which they are attached, join together to form a cyclic amino group, wherein the cyclic amino group is optionally substituted with CMS alkoxy, -CN, - CF ₃ , -N0 ₂ , halogen, or CMS alkyl;

A may be the same as or different to B’ (defined below), and is independently selected from: hydrogen; Ci-i ₈ alkyl; C _6- 12 aryl optionally substituted with CM S alkoxy, -CN, -CF ₃ , -N0 ₂ , halogen, or CMS alkyl; a heterocyclic ring; a heteroaryl; halogen; -N0 ₂ ; -CF ₃ ; -OR ³ ; -NR ³ ₂ ; -CN; -SR ³ ; -COR ³ ; -C0 ₂ R ³ ; -CONR ³ ₂ ; wherein R ³ is selected from an alkali metal; hydrogen; Ci-i ₈ alkyl; and C _6- 12 aryl optionally substituted with CMS alkoxy, -CN, -CF ₃ , -N0 ₂ , halogen, or CMS alkyl; and

R ¹ is selected from

wherein Xi _b , X _2b , X3 _b and X _4b are independently selected from C, N, B and S; and B’ is the same or different to A and is independently selected from hydrogen; C1-18 alkyl; C _6- 12 aryl optionally substituted with C _1-18 alkoxy, -CN, -CF ₃ , -N0 ₂ , halogen, or CMS alkyl; a heterocyclic ring; a heteroaryl; halogen; -N0 ₂ ; -CF ₃ ; - OR ³ ; -NR ³ ₂ ; -CN; -SR ³ ; -COR ³ ; -C0 ₂ R ³ ; -CONR ³ ₂ ; wherein R ³ is selected from an alkali metal; hydrogen; Ci-i ₈ alkyl; and C ₆ -i ₂ aryl optionally substituted with Ci_ 18 alkoxy, -CN, -CF ₃ , -N0 ₂ , halogen, CMS alkyl, hydroxyl (-OH), or -NR ₂ wherein R is as defined above. According to a second aspect of the present invention, there is provided a substrate comprising a composition applied to or incorporated within, the composition comprising a keto acid compound and an acid-generating agent, wherein the keto acid compound is capable of transitioning from a non-coloured state to a coloured state, the transition being effected by the application of an applied transition stimulus, wherein the keto acid compound is of formula (I):

wherein Xi _a , X _2a , and X _3a are independently selected from C, N, B and S; the two R groups may be the same or different, and are independently selected from: hydrogen; Ci-i ₈ alkyl; C ₆ -i ₂ aryl optionally substituted with CMS alkoxy, -CN, - CF ₃ , -N0 ₂ , halogen, or CMS alkyl; halogen; -N0 ₂ ; -CF ₃ ; -OR ³ ; -NR CN; -SR

COR ³ ; -C0 ₂ R ³ ; and -CONR ³ ₂ ; wherein R ³ is selected from an alkali metal; hydrogen; Ci-i ₈ alkyl; and C ₆ -i ₂ aryl optionally substituted with CMS alkoxy, -CN, - CF ₃ , -N0 ₂ , halogen, or CMS alkyl; or both R groups, together with the nitrogen atom to which they are attached, join together to form a cyclic amino group, wherein the cyclic amino group is optionally substituted with CMS alkoxy, -CN, - CF ₃ , -N0 ₂ , halogen, or CMS alkyl; A may be the same as or different to B’ (defined below), and is independently selected from: hydrogen; Ci-i ₈ alkyl; C _6- 12 aryl optionally substituted with C _1-18 alkoxy, -CN, -CF ₃ , -N0 ₂ , halogen, or CMS alkyl; a heterocyclic ring; a heteroaryl; halogen; -N0 ₂ ; -CF ₃ ; CONR wherein R ³ is selected from an alkali metal; hydrogen; Ci-i ₈ alkyl; and C _6- 12 aryl optionally substituted with CMS alkoxy, -CN, -CF ₃ , -N0 ₂ , halogen, or CMS alkyl; and

R ¹ is selected from

wherein Xi _b , X _2b , X3 _b and X _4b are independently selected from C, N, B and S; and B’ is the same or different to A and is independently selected from hydrogen; Ci-is alkyl; C _6- 12 aryl optionally substituted with CMS alkoxy, -CN, -CF ₃ , -N0 ₂ , halogen, or CMS alkyl; a heterocyclic ring; a heteroaryl; halogen; -N0 ₂ ; -CF ₃ ; - OR ³ ; -NR ³ ₂ ; -CN; -SR ³ ; -COR ³ ; -C0 ₂ R ³ ; -CONR ³ ₂ ; wherein R ³ is selected from an alkali metal; hydrogen; Ci-i ₈ alkyl; and C _6- 12 aryl optionally substituted with Ci_ 18 alkoxy, -CN, -CF ₃ , -N0 ₂ , halogen, CMS alkyl, hydroxyl (-OH), or -NR ₂ wherein R is as defined above.

According to a third aspect of the present invention, there is provided a method of forming a substrate comprising applying to or incorporating within a substrate a composition comprising a keto acid compound and an acid-generating agent, wherein the keto acid compound is capable of transitioning from a non-coloured state to a coloured state, the transition being effected by the application of an applied transition stimulus, wherein the keto acid compound is of formula (I):

wherein Xi _a , X _2a , and X _3a are independently selected from C, N, B and S; the two R groups may be the same or different, and are independently selected from: hydrogen; Ci-i ₈ alkyl; Ce-^aryl optionally substituted with Ci-i ₈ alkoxy, -CN, - CF ₃ , -NO2, halogen, or Ci-i ₈ alkyl; halogen; -N0 ₂ ; -CF ₃ ; -OR ³ ; -NR CN; -SR

COR ³ ; -C0 ₂ R ³ ; and -CONR ³ ₂ ; wherein R ³ is selected from an alkali metal; hydrogen; Ci-i ₈ alkyl; and Ce-^ aryl optionally substituted with Ci-i ₈ alkoxy, -CN, - CF ₃ , -N0 ₂ , halogen, or CMS alkyl; or both R groups, together with the nitrogen atom to which they are attached, join together to form a cyclic amino group, wherein the cyclic amino group is optionally substituted with CMS alkoxy, -CN, - CF ₃ , -N0 ₂ , halogen, or CMS alkyl;

A may be the same as or different to B’ (defined below), and is independently selected from: hydrogen; Ci-i ₈ alkyl; C _6- 12 aryl optionally substituted with CM S alkoxy, -CN, -CF ₃ , -N0 ₂ , halogen, or CMS alkyl; a heterocyclic ring; a heteroaryl; halogen; -N0 ₂ ; -CF ₃ ; -OR ³ ; -NR ³ ₂ ; -CN; -SR ³ ; -COR ³ ; -C0 ₂ R ³ ; -CONR ³ ₂ ; wherein R ³ is selected from an alkali metal; hydrogen; Ci-i ₈ alkyl; and C _6- 12 aryl optionally substituted with CMS alkoxy, -CN, -CF ₃ , -N0 ₂ , halogen, or CMS alkyl; and

R ¹ is selected from

wherein Xi _b , X _2b , X3 _b and X _4b are independently selected from C, N, B and S; and B’ is the same or different to A and is independently selected from hydrogen; C1-18 alkyl; C _6- 12 aryl optionally substituted with C _1-18 alkoxy, -CN, -CF ₃ , -N0 ₂ , halogen, or CMS alkyl; a heterocyclic ring; a heteroaryl; halogen; -N0 ₂ ; -CF ₃ ; - OR ³ ; -NR ³ ₂ ; -CN; -SR ³ ; -COR ³ ; -C0 ₂ R ³ ; -CONR ³ ₂ ; wherein R ³ is selected from an alkali metal; hydrogen; Ci-i ₈ alkyl; and C ₆ -i ₂ aryl optionally substituted with Ci_ 18 alkoxy, -CN, -CF ₃ , -N0 ₂ , halogen, CMS alkyl, hydroxyl (-OH), or -NR ₂ wherein R is as defined above. According to a fourth aspect of the present invention, there is provided a method of forming colour on or within a substrate comprising a composition applied to or incorporated within, the composition comprising a keto acid compound and an acid-generating agent, wherein the keto acid compound is capable of transitioning from a non-coloured state to a coloured state, the transition being effected by the application of an applied transition stimulus, wherein the keto acid compound is of formula (I):

wherein Xi _a , X _2a , and X _3a are independently selected from C, N, B and S; the two R groups may be the same or different, and are independently selected from: hydrogen; Ci-i ₈ alkyl; C ₆ -i ₂ aryl optionally substituted with CM _S alkoxy, -CN, -

CF ₃ , -N0 ₂ , halogen, or CMS alkyl; halogen; -N0 ₂ ; -CF ₃ ; -OR ³ ; -NR CN; -SR

COR ³ ; -C0 ₂ R ³ ; and -CONR ³ ₂ ; wherein R ³ is selected from an alkali metal; hydrogen; Ci-i ₈ alkyl; and C ₆ -i ₂ aryl optionally substituted with CMS alkoxy, -CN, - CF ₃ , -N0 ₂ , halogen, or CMS alkyl; or both R groups, together with the nitrogen atom to which they are attached, join together to form a cyclic amino group, wherein the cyclic amino group is optionally substituted with CMS alkoxy, -CN, - CF ₃ , -N0 ₂ , halogen, or CMS alkyl; A may be the same as or different to B’ (defined below), and is independently selected from: hydrogen; Ci-i ₈ alkyl; C _6- 12 aryl optionally substituted with C _1-18 alkoxy, -CN, -CF ₃ , -N0 ₂ , halogen, or CMS alkyl; a heterocyclic ring; a heteroaryl; halogen; -N0 ₂ ; -CF ₃ ; CONR wherein R ³ is selected from an alkali metal; hydrogen; Ci-i ₈ alkyl; and C _6- 12 aryl optionally substituted with CMS alkoxy, -CN, -CF ₃ , -N0 ₂ , halogen, or CMS alkyl; and

R ¹ is selected from

wherein Xi _b , X _2b , X3 _b and X _4b are independently selected from C, N, B and S; and B’ is the same or different to A and is independently selected from hydrogen; Ci-is alkyl; C _6- 12 aryl optionally substituted with CMS alkoxy, -CN, -CF ₃ , -N0 ₂ , halogen, or CMS alkyl; a heterocyclic ring; a heteroaryl; halogen; -N0 ₂ ; -CF ₃ ; - OR ³ ; -NR ³ ₂ ; -CN; -SR ³ ; -COR ³ ; -C0 ₂ R ³ ; -CONR ³ ₂ ; wherein R ³ is selected from an alkali metal; hydrogen; Ci-i ₈ alkyl; and C _6- 12 aryl optionally substituted with Ci_ 18 alkoxy, -CN, -CF ₃ , -N0 ₂ , halogen, CMS alkyl, hydroxyl (-OH), or -NR ₂ wherein R is as defined above, wherein the method comprises applying the applied transition stimulus to the composition on or within the substrate as required to develop the coloured state of the keto acid compound of formula (I) of the composition.

According to a fifth aspect of the present invention, there is provided a method of forming an image on or within a substrate comprising a composition applied to or incorporated within, the composition comprising a keto acid compound and an acid-generating agent, wherein the keto acid compound is capable of transitioning from a non-coloured state to a coloured state, the transition being effected by the application of an applied transition stimulus, wherein the keto acid compound is of formula (I):

wherein Xi _a , X _2a , and X _3a are independently selected from C, N, B and S; the two R groups may be the same or different, and are independently selected from: hydrogen; Ci-i ₈ alkyl; C ₆ -i ₂ aryl optionally substituted with Ci-i ₈ alkoxy, -CN, - CF ₃ , -N0 ₂ , halogen, or C _{M S} alkyl; halogen; -N0 ₂ ; -CF ₃ ; -OR ³ ; -NR ³ ₂ ; -CN; -SR ³ ; - COR ³ ; -C0 ₂ R ³ ; and -CONR ³ ₂ ; wherein R ³ is selected from an alkali metal; hydrogen; Ci-i ₈ alkyl; and C ₆ -i ₂ aryl optionally substituted with Ci-i ₈ alkoxy, -CN, - CF ₃ , -N0 ₂ , halogen, or C _{M S} alkyl; or both R groups, together with the nitrogen atom to which they are attached, join together to form a cyclic amino group, wherein the cyclic amino group is optionally substituted with C _{M S} alkoxy, -CN, - CF ₃ , -N0 ₂ , halogen, or C _{M S} alkyl;

A may be the same as or different to B’ (defined below), and is independently selected from: hydrogen; Ci-i ₈ alkyl; C _6-i2 aryl optionally substituted with C _{M S} alkoxy, -CN, -CF ₃ , -N0 ₂ , halogen, or C _{M S} alkyl; a heterocyclic ring; a heteroaryl; halogen; -N0 ₂ ; -CF ₃ ; -OR ³ ; -NR ³ ₂ ; -CN; -SR ³ ; -COR ³ ; -C0 ₂ R ³ ; -CONR ³ ₂ ; wherein R ³ is selected from an alkali metal; hydrogen; Ci-i ₈ alkyl; and C _6-i2 aryl optionally substituted with C _{M S} alkoxy, -CN, -CF ₃ , -N0 ₂ , halogen, or C _{M S} alkyl; and

R ¹ is selected from wherein Xi _b , X _2b , X3 _b and X _4b are independently selected from C, N, B and S; and B’ is the same or different to A and is independently selected from hydrogen; C1-18 alkyl; C ₆ -12 aryl optionally substituted with Ci-i ₈ alkoxy, -CN, -CF ₃ , -N0 ₂ , halogen, or Ci-i ₈ alkyl; a heterocyclic ring; a heteroaryl; halogen; -N0 ₂ ; -CF ₃ ; - OR ³ ; -NR ³ ₂ ; -CN; -SR ³ ; -COR ³ ; -C0 ₂ R ³ ; -CONR ³ ₂ ; wherein R ³ is selected from an alkali metal; hydrogen; Ci-i ₈ alkyl; and C ₆ -i ₂ aryl optionally substituted with Ci_ 18 alkoxy, -CN, -CF ₃ , -N0 ₂ , halogen, Ci-i ₈ alkyl, hydroxyl (-OH), or -NR ₂ wherein R is as defined above; and wherein the method comprises applying the applied transition stimulus to the composition on or within the substrate as required to develop the coloured state of the keto acid compound of formula (I) of the composition, and thereby form an image on or within the substrate.

According to a sixth aspect of the present invention, there is provided a use of a composition in the formation of colour on or within a substrate, the composition comprising a keto acid compound and an acid-generating agent, wherein the keto acid compound is capable of transitioning from a non-coloured state to a coloured state, the transition being effected by the application of an applied transition stimulus, wherein the keto acid compound is of formula (I):

wherein Xi _a , X _2a , and X _3a are independently selected from C, N, B and S; the two R groups may be the same or different, and are independently selected from: hydrogen; Ci-i ₈ alkyl; Ce-^aryl optionally substituted with Ci-i ₈ alkoxy, -CN, -

CF ₃ , -NO2, halogen, or CMS alkyl; halogen; -N0 ₂ ; -CF ₃ ; -OR ³ ; -NR CN; -SR

COR ³ ; -C0 ₂ R ³ ; and -CONR ³ ₂ ; wherein R ³ is selected from an alkali metal; hydrogen; Ci-i ₈ alkyl; and Ce-^ aryl optionally substituted with Ci-i ₈ alkoxy, -CN, - CF ₃ , -N0 ₂ , halogen, or CMS alkyl; or both R groups, together with the nitrogen atom to which they are attached, join together to form a cyclic amino group, wherein the cyclic amino group is optionally substituted with CMS alkoxy, -CN, - CF ₃ , -N0 ₂ , halogen, or CMS alkyl; A may be the same as or different to B’ (defined below), and is independently selected from: hydrogen; Ci-i ₈ alkyl; C _6- 12 aryl optionally substituted with CM S alkoxy, -CN, -CF ₃ , -N0 ₂ , halogen, or CMS alkyl; a heterocyclic ring; a heteroaryl; halogen; -N0 ₂ ; -CF ₃ ; -OR ³ ; -NR ³ ₂ ; -CN; -SR ³ ; -COR ³ ; -C0 ₂ R ³ ; -CONR ³ ₂ ; wherein R ³ is selected from an alkali metal; hydrogen; Ci-i ₈ alkyl; and C _6- 12 aryl optionally substituted with CMS alkoxy, -CN, -CF ₃ , -N0 ₂ , halogen, or CMS alkyl; and

R ¹ is selected from

wherein Xi _b , X _2b , X3 _b and X _4b are independently selected from C, N, B and S; and B’ is the same or different to A and is independently selected from hydrogen; Ci-i ₈ alkyl; C _6- 12 aryl optionally substituted with CMS alkoxy, -CN, -CF ₃ , -N0 ₂ , halogen, or CMS alkyl; a heterocyclic ring; a heteroaryl; halogen; -N0 ₂ ; -CF ₃ ; - OR ³ ; -NR ³ ₂ ; -CN; -SR ³ ; -COR ³ ; -C0 ₂ R ³ ; -CONR ³ ₂ ; wherein R ³ is selected from an alkali metal; hydrogen; Ci-i ₈ alkyl; and Ce-^ aryl optionally substituted with Ci_ is alkoxy, -CN, -CF ₃ , -N0 ₂ , halogen, CMS alkyl, hydroxyl (-OH), or -NR ₂ wherein

R is as defined above. According to a seventh aspect of the present invention, there is provided a use of a composition in the formation of an image on or within a substrate, the composition comprising a keto acid compound and an acid-generating agent, wherein the keto acid compound is capable of transitioning from a non-coloured state to a coloured state, the transition being effected by the application of an applied transition stimulus, wherein the keto acid compound is of formula (I):

wherein Xi _a , X _2a , and X _3a are independently selected from C, N, B and S; the two R groups may be the same or different, and are independently selected from: hydrogen; Ci-i ₈ alkyl; C ₆ -i ₂ aryl optionally substituted with Ci-i ₈ alkoxy, -CN, - CF ₃ , -NO2, halogen, or C _{M S} alkyl; halogen; -N0 ₂ ; -CF ₃ ; -OR ³ ; -NR ³ ₂ ; -CN; -SR ³ ; - COR ³ ; -C0 ₂ R ³ ; and -CONR ³ ₂ ; wherein R ³ is selected from an alkali metal; hydrogen; Ci-i ₈ alkyl; and C ₆ -i ₂ aryl optionally substituted with Ci-i ₈ alkoxy, -CN, - CF ₃ , -N0 ₂ , halogen, or C _{M S} alkyl; or both R groups, together with the nitrogen atom to which they are attached, join together to form a cyclic amino group, wherein the cyclic amino group is optionally substituted with C _{M S} alkoxy, -CN, - CF ₃ , -N0 ₂ , halogen, or C _{M S} alkyl;

A may be the same as or different to B’ (defined below), and is independently selected from: hydrogen; Ci-i ₈ alkyl; C _6-i2 aryl optionally substituted with C _{M S} alkoxy, -CN, -CF ₃ , -N0 ₂ , halogen, or C _{M S} alkyl; a heterocyclic ring; a heteroaryl; halogen; -N0 ₂ ; -CF ₃ ; -OR ³ ; -NR ³ ₂ ; -CN; -SR ³ ; -COR ³ ; -C0 ₂ R ³ ; -CONR ³ ₂ ; wherein R ³ is selected from an alkali metal; hydrogen; Ci-i ₈ alkyl; and C _6-i2 aryl optionally substituted with C _{M S} alkoxy, -CN, -CF ₃ , -N0 ₂ , halogen, or C _{M S} alkyl; and R is selected from

wherein Xi _b , X _2b , X3 _b and X _4b are independently selected from C, N, B and S; and B’ is the same or different to A and is independently selected from hydrogen; C1-18 alkyl; C ₆ -12 aryl optionally substituted with Ci-i ₈ alkoxy, -CN, -CF ₃ , -N0 ₂ , halogen, or Ci-i ₈ alkyl; a heterocyclic ring; a heteroaryl; halogen; -N0 ₂ ; -CF ₃ ; - OR ³ ; -NR ³ ₂ ; -CN; -SR ³ ; -COR ³ ; -C0 ₂ R ³ ; -CONR ³ ₂ ; wherein R ³ is selected from an alkali metal; hydrogen; Ci-i ₈ alkyl; and C ₆ -i ₂ aryl optionally substituted with Ci_ 18 alkoxy, -CN, -CF ₃ , -N0 ₂ , halogen, Ci-i ₈ alkyl, hydroxyl (-OH), or -NR ₂ wherein R is as defined above.

According to an eighth aspect of the present invention, there is provided a substrate having applied thereon a plurality of discrete layers, wherein at least one of the discrete layers comprises a keto acid compound and an acid- generating agent, the keto acid compound being capable of transitioning from a non-coloured state to a coloured state, the transition being effected by the application of an applied transition stimulus, wherein the keto acid compound is of formula (I):

wherein Xi _a , X _2a , and X _3a are independently selected from C, N, B and S; the two R groups may be the same or different, and are independently selected from: hydrogen; Ci-i ₈ alkyl; C ₆ -i ₂ aryl optionally substituted with Ci-i ₈ alkoxy, -CN, - CF ₃ , -NO2, halogen, or CMS alkyl; halogen; -N0 ₂ ; -CF ₃ ; -OR ³ ; -NR CN; -SR

COR ³ ; -C0 ₂ R ³ ; and -CONR ³ ₂ ; wherein R ³ is selected from an alkali metal; hydrogen; Ci-i ₈ alkyl; and Ce-^ aryl optionally substituted with Ci-i ₈ alkoxy, -CN, - CF ₃ , -N0 ₂ , halogen, or CMS alkyl; or both R groups, together with the nitrogen atom to which they are attached, join together to form a cyclic amino group, wherein the cyclic amino group is optionally substituted with CMS alkoxy, -CN, - CF ₃ , -N0 ₂ , halogen, or CMS alkyl;

A may be the same as or different to B’ (defined below), and is independently selected from: hydrogen; Ci-i ₈ alkyl; C _6- 12 aryl optionally substituted with CM S alkoxy, -CN, -CF ₃ , -N0 ₂ , halogen, or CMS alkyl; a heterocyclic ring; a heteroaryl; halogen; -N0 ₂ ; -CF ₃ ; -OR ³ ; -NR ³ ₂ ; -CN; -SR ³ ; -COR ³ ; -C0 ₂ R ³ ; -CONR ³ ₂ ; wherein R ³ is selected from an alkali metal; hydrogen; Ci-i ₈ alkyl; and C _6- 12 aryl optionally substituted with CMS alkoxy, -CN, -CF ₃ , -N0 ₂ , halogen, or CMS alkyl; and R ¹ is selected from

wherein Xi _b , X _2b , X3 _b and X _4b are independently selected from C, N, B and S; and B’ is the same or different to A and is independently selected from hydrogen; Ci-i ₈ alkyl; C _6- 12 aryl optionally substituted with CMS alkoxy, -CN, -CF ₃ , -N0 ₂ , halogen, or CMS alkyl; a heterocyclic ring; a heteroaryl; halogen; -N0 ₂ ; -CF ₃ ; - OR ³ ; -NR ³ ₂ ; -CN; -SR ³ ; -COR ³ ; -C0 ₂ R ³ ; -CONR ³ ₂ ; wherein R ³ is selected from an alkali metal; hydrogen; Ci-i ₈ alkyl; and Ce-^ aryl optionally substituted with Ci_ is alkoxy, -CN, -CF ₃ , -N0 ₂ , halogen, CMS alkyl, hydroxyl (-OH), or -NR ₂ wherein R is as defined above; and wherein at least one of the discrete layers comprises at least one additional compound capable of transitioning from a non-coloured state to a coloured state, the transition being effected by the application of an additional applied stimulus; wherein, if formed, the coloured state of the keto acid compound of formula (I) and the at least one additional compound are different in colour, and the discrete layer comprising the keto acid compound of formula (I) is a different layer to the discrete layer comprising the at least one additional compound.

According to a ninth aspect of the present invention there is provided a method of forming a substrate having applied thereon a plurality of discrete layers, wherein at least one of the discrete layers comprises a keto acid compound and an acid-generating agent, the keto acid compound being capable of transitioning from a non-coloured state to a coloured state, the transition being effected by the application of an applied transition stimulus, wherein the keto acid compound is of formula (I):

wherein Xi _a , X _2a , and X _3a are independently selected from C, N, B and S; the two R groups may be the same or different, and are independently selected from: hydrogen; Ci-i ₈ alkyl; Ce-^aryl optionally substituted with Ci-i ₈ alkoxy, -CN, -

CF ₃ , -N0 ₂ , halogen, or CMS alkyl; halogen; -N0 ₂ ; -CF ₃ ; -OR ³ ; -NR CN; -SR

COR ³ ; -C0 ₂ R ³ ; and -CONR ³ ₂ ; wherein R ³ is selected from an alkali metal; hydrogen; Ci-i ₈ alkyl; and Ce-^ aryl optionally substituted with Ci-i ₈ alkoxy, -CN, - CF ₃ , -N0 ₂ , halogen, or CMS alkyl; or both R groups, together with the nitrogen atom to which they are attached, join together to form a cyclic amino group, wherein the cyclic amino group is optionally substituted with CMS alkoxy, -CN, - CF ₃ , -N0 ₂ , halogen, or CMS alkyl;

A may be the same as or different to B’ (defined below), and is independently selected from: hydrogen; Ci-i ₈ alkyl; C _6- 12 aryl optionally substituted with CM S alkoxy, -CN, -CF ₃ , -N0 ₂ , halogen, or Ci-i ₈ alkyl; a heterocyclic ring; a heteroaryl; halogen; -N0 ₂ ; -CF ₃ ; -OR ³ ; -NR ³ ₂ ; -CN; -SR ³ ; -COR ³ ; -C0 ₂ R ³ ; -CONR ³ ₂ ; wherein R ³ is selected from an alkali metal; hydrogen; Ci-i ₈ alkyl; and C _6- 12 aryl optionally substituted with C _{1 -18} alkoxy, -CN, -CF ₃ , -N0 ₂ , halogen, or C _{1 -18} alkyl; and

R ¹ is selected from

wherein Xi _b , X _2b , X3 _b and X _4b are independently selected from C, N, B and S; and B’ is the same or different to A and is independently selected from hydrogen; Ci-is alkyl; C _6- 12 aryl optionally substituted with C _1-18 alkoxy, -CN, -CF ₃ , -N0 ₂ , halogen, or C _{M S} alkyl; a heterocyclic ring; a heteroaryl; halogen; -N0 ₂ ; -CF ₃ ; - OR ³ ; -NR ³ ₂ ; -CN; -SR ³ ; -COR ³ ; -C0 ₂ R ³ ; -CONR ³ ₂ ; wherein R ³ is selected from an alkali metal; hydrogen; Ci-i ₈ alkyl; and Ce-^ aryl optionally substituted with Ci_ 18 alkoxy, -CN, -CF ₃ , -N0 ₂ , halogen, C _{M S} alkyl, hydroxyl (-OH), or -NR ₂ wherein R is as defined above; and wherein at least one of the discrete layers comprises at least one additional compound capable of transitioning from a non-coloured state to a coloured state, the transition being effected by the application of an additional applied stimulus; wherein, if formed, the coloured state of the keto acid compound of formula (I) and the at least one additional compound are different in colour, and the discrete layer comprising the keto acid compound of formula (I) is a different layer to the discrete layer comprising the at least one additional compound; and wherein the method comprises applying to a substrate the plurality of discrete layers. According to a tenth aspect of the present invention, there is provided a method of forming colour on a substrate having a plurality of discrete layers applied thereon, wherein at least one of the discrete layers comprises a keto acid compound and an acid-generating agent, the keto acid compound being capable of transitioning from a non-coloured state to a coloured state, the transition being effected by the application of an applied transition stimulus, wherein the keto acid compound is of formula (I):

wherein Xi _a , X _2a , and X _3a are independently selected from C, N, B and S; the two R groups may be the same or different, and are independently selected from: hydrogen; Ci-i ₈ alkyl; C ₆ -i ₂ aryl optionally substituted with Ci-i ₈ alkoxy, -CN, -

CF ₃ , -N0 ₂ , halogen, or CMS alkyl; halogen; -N0 ₂ ; -CF ₃ ; -OR ³ ; -NR CN; -SR

COR ³ ; -C0 ₂ R ³ ; and -CONR ³ ₂ ; wherein R ³ is selected from an alkali metal; hydrogen; Ci-i ₈ alkyl; and C ₆ -i ₂ aryl optionally substituted with Ci-i ₈ alkoxy, -CN, - CF ₃ , -N0 ₂ , halogen, or CMS alkyl; or both R groups, together with the nitrogen atom to which they are attached, join together to form a cyclic amino group, wherein the cyclic amino group is optionally substituted with CMS alkoxy, -CN, - CF ₃ , -N0 ₂ , halogen, or CMS alkyl; A may be the same as or different to B’ (defined below), and is independently selected from: hydrogen; Ci-i ₈ alkyl; C _6-i2 aryl optionally substituted with CM S alkoxy, -CN, -CF ₃ , -N0 ₂ , halogen, or CMS alkyl; a heterocyclic ring; a heteroaryl; halogen; -N0 ₂ ; -CF ₃ ; -OR ³ ; -NR ³ ₂ ; -CN; -SR ³ ; -COR ³ ; -C0 ₂ R ³ ; -CONR ³ ₂ ; wherein R ³ is selected from an alkali metal; hydrogen; Ci-i ₈ alkyl; and C _6-i2 aryl optionally substituted with CMS alkoxy, -CN, -CF ₃ , -N0 ₂ , halogen, or CMS alkyl; and

R ¹ is selected from wherein Xi _b , X _2b , X3 _b and X _4b are independently selected from C, N, B and S; and B’ is the same or different to A and is independently selected from hydrogen; C1-18 alkyl; C _6- 12 aryl optionally substituted with C _1-18 alkoxy, -CN, -CF ₃ , -N0 ₂ , halogen, or C _{M S} alkyl; a heterocyclic ring; a heteroaryl; halogen; -N0 ₂ ; -CF ₃ ; - OR ³ ; -NR ³ ₂ ; -CN; -SR ³ ; -COR ³ ; -C0 ₂ R ³ ; -CONR ³ ₂ ; wherein R ³ is selected from an alkali metal; hydrogen; Ci-i ₈ alkyl; and C ₆ -i ₂ aryl optionally substituted with Ci_ 18 alkoxy, -CN, -CF ₃ , -N0 ₂ , halogen, C _{M S} alkyl, hydroxyl (-OH), or -NR ₂ wherein R is as defined above; and wherein at least one of the discrete layers comprises at least one additional compound capable of transitioning from a non-coloured state to a coloured state, the transition being effected by the application of an additional applied stimulus; wherein, if formed, the coloured state of the keto acid compound of formula (I) and the at least one additional compound are different in colour, and the discrete layer comprising the keto acid compound of formula (I) is a different layer to the discrete layer comprising the at least one additional compound; and wherein the method comprises applying the applied transition stimulus and additional applied stimulus to the substrate as required to develop the coloured state of the keto acid compound of formula (I) and the at least one additional compound.

According to an eleventh aspect of the present invention, there is provided a method of forming an image on a substrate having a plurality of discrete layers applied thereon, wherein at least one of the discrete layers comprises a keto acid compound and an acid-generating agent, the keto acid compound being capable of transitioning from a non-coloured state to a coloured state, the transition being effected by the application of an applied transition stimulus, wherein the keto acid compound is of formula (I):

wherein Xi _a , X _2a , and X _3a are independently selected from C, N, B and S; the two R groups may be the same or different, and are independently selected from: hydrogen; Ci-i ₈ alkyl; C ₆ -i ₂ aryl optionally substituted with Ci-i ₈ alkoxy, -CN, - CF ₃ , -N0 ₂ , halogen, or C _{M S} alkyl; halogen; -N0 ₂ ; -CF ₃ ; -OR ³ ; -NR ³ ₂ ; -CN; -SR ³ ; - COR ³ ; -C0 ₂ R ³ ; and -CONR ³ ₂ ; wherein R ³ is selected from an alkali metal; hydrogen; Ci-i ₈ alkyl; and C ₆ -i ₂ aryl optionally substituted with Ci-i ₈ alkoxy, -CN, - CF ₃ , -N0 ₂ , halogen, or C _{M S} alkyl; or both R groups, together with the nitrogen atom to which they are attached, join together to form a cyclic amino group, wherein the cyclic amino group is optionally substituted with C _{M S} alkoxy, -CN, - CF ₃ , -N0 ₂ , halogen, or C _{M S} alkyl;

A may be the same as or different to B’ (defined below), and is independently selected from: hydrogen; Ci-i ₈ alkyl; C _6-i2 aryl optionally substituted with C _{M S} alkoxy, -CN, -CF ₃ , -N0 ₂ , halogen, or C _{M S} alkyl; a heterocyclic ring; a heteroaryl; halogen; -N0 ₂ ; -CF ₃ ; -OR ³ ; -NR ³ ₂ ; -CN; -SR ³ ; -COR ³ ; -C0 ₂ R ³ ; -CONR ³ ₂ ; wherein R ³ is selected from an alkali metal; hydrogen; Ci-i ₈ alkyl; and C _6-i2 aryl optionally substituted with C _{M S} alkoxy, -CN, -CF ₃ , -N0 ₂ , halogen, or C _{M S} alkyl; and

R ¹ is selected from wherein Xi _b , X _2b , X3 _b and X _4b are independently selected from C, N, B and S; and B’ is the same or different to A and is independently selected from hydrogen; C1-18 alkyl; C _6- 12 aryl optionally substituted with C _1-18 alkoxy, -CN, -CF ₃ , -N0 ₂ , halogen, or C _{M S} alkyl; a heterocyclic ring; a heteroaryl; halogen; -N0 ₂ ; -CF ₃ ; - OR ³ ; -NR ³ ₂ ; -CN; -SR ³ ; -COR ³ ; -C0 ₂ R ³ ; -CONR ³ ₂ ; wherein R ³ is selected from an alkali metal; hydrogen; Ci-i ₈ alkyl; and C ₆ -i ₂ aryl optionally substituted with Ci_ 18 alkoxy, -CN, -CF ₃ , -N0 ₂ , halogen, C _{M S} alkyl, hydroxyl (-OH), or -NR ₂ wherein R is as defined above; and wherein at least one of the discrete layers comprises at least one additional compound capable of transitioning from a non-coloured state to a coloured state, the transition being effected by the application of an additional applied stimulus; wherein, if formed, the coloured state of the keto acid compound of formula (I) and the at least one additional compound are different in colour, and the discrete layer comprising the keto acid compound of formula (I) is a different layer to the discrete layer comprising the at least one additional compound; and wherein the method comprises applying the applied transitions stimulus and additional applied stimulus to the substrate as required to develop the coloured state of the keto acid compound of formula (I) and the at least one additional compound, and thereby form an image on a substrate.

According to a twelfth aspect of the present invention, there is provided a use of a keto acid compound in the formation of colour on a substrate, the keto acid compound capable of transitioning from a non-coloured state to a coloured state, the transition being effected by the application of an applied transition stimulus, wherein the keto acid compound is of formula (I):

wherein Xi _a , X _2a , and X _3a are independently selected from C, N, B and S; the two R groups may be the same or different, and are independently selected from: hydrogen; Ci-i ₈ alkyl; Ce-^aryl optionally substituted with Ci-i ₈ alkoxy, -CN, - CF ₃ , -NO2, halogen, or Ci-i ₈ alkyl; halogen; -N0 ₂ ; -CF ₃ ; -OR ³ ; -NR CN; -SR

COR ³ ; -C0 ₂ R ³ ; and -CONR ³ ₂ ; wherein R ³ is selected from an alkali metal; hydrogen; Ci-i ₈ alkyl; and Ce-^ aryl optionally substituted with Ci-i ₈ alkoxy, -CN, - CF ₃ , -N0 ₂ , halogen, or CMS alkyl; or both R groups, together with the nitrogen atom to which they are attached, join together to form a cyclic amino group, wherein the cyclic amino group is optionally substituted with CMS alkoxy, -CN, - CF ₃ , -N0 ₂ , halogen, or CMS alkyl;

A may be the same as or different to B’ (defined below), and is independently selected from: hydrogen; Ci-i ₈ alkyl; C _6- 12 aryl optionally substituted with CM S alkoxy, -CN, -CF ₃ , -N0 ₂ , halogen, or CMS alkyl; a heterocyclic ring; a heteroaryl; halogen; -N0 ₂ ; -CF ₃ ; -OR ³ ; -NR ³ ₂ ; -CN; -SR ³ ; -COR ³ ; -C0 ₂ R ³ ; -CONR ³ ₂ ; wherein R ³ is selected from an alkali metal; hydrogen; Ci-i ₈ alkyl; and C _6- 12 aryl optionally substituted with CMS alkoxy, -CN, -CF ₃ , -N0 ₂ , halogen, or CMS alkyl; and

R ¹ is selected from

wherein Xi _b , X _2b , X3 _b and X _4b are independently selected from C, N, B and S; and B’ is the same or different to A and is independently selected from hydrogen; C1-18 alkyl; C _6- 12 aryl optionally substituted with C _1-18 alkoxy, -CN, -CF ₃ , -N0 ₂ , halogen, or C _{M S} alkyl; a heterocyclic ring; a heteroaryl; halogen; -N0 ₂ ; -CF ₃ ; - OR ³ ; -NR ³ ₂ ; -CN; -SR ³ ; -COR ³ ; -C0 ₂ R ³ ; -CONR ³ ₂ ; wherein R ³ is selected from an alkali metal; hydrogen; Ci-i ₈ alkyl; and C ₆ -i ₂ aryl optionally substituted with Ci_ 18 alkoxy, -CN, -CF ₃ , -N0 ₂ , halogen, C _{M S} alkyl, hydroxyl (-OH), or -NR ₂ wherein R is as defined above. According to a thirteenth aspect of the present invention, there is provided a use of a keto acid compound in the formation of an image on a substrate, the keto acid compound capable of transitioning from a non-coloured state to a coloured state, the transition being effected by the application of an applied transition stimulus, wherein the keto acid compound is of formula (I):

wherein Xi _a , X _2a , and X _3a are independently selected from C, N, B and S; the two R groups may be the same or different, and are independently selected from: hydrogen; Ci-i ₈ alkyl; C ₆ -i ₂ aryl optionally substituted with C _{M S} alkoxy, -CN, - CF ₃ , -N0 ₂ , halogen, or C _{M S} alkyl; halogen; -N0 ₂ ; -CF ₃ ; -OR ³ ; -NR ³ ₂ ; -CN; -SR ³ ; - COR ³ ; -C0 ₂ R ³ ; and -CONR ³ ₂ ; wherein R ³ is selected from an alkali metal; hydrogen; Ci-i ₈ alkyl; and C ₆ -i ₂ aryl optionally substituted with C _{M S} alkoxy, -CN, - CF ₃ , -N0 ₂ , halogen, or C _{M S} alkyl; or both R groups, together with the nitrogen atom to which they are attached, join together to form a cyclic amino group, wherein the cyclic amino group is optionally substituted with C _{M S} alkoxy, -CN, - CF ₃ , -N0 ₂ , halogen, or C _{M S} alkyl;

A may be the same as or different to B’ (defined below), and is independently selected from: hydrogen; Ci-i ₈ alkyl; C _6-i2 aryl optionally substituted with C _{M S} alkoxy, -CN, -CF ₃ , -N0 ₂ , halogen, or Ci-i ₈ alkyl; a heterocyclic ring; a heteroaryl; halogen; -N0 ₂ ; -CF ₃ ; -OR ³ ; -NR ³ ₂ ; -CN; -SR ³ ; -COR ³ ; -C0 ₂ R ³ ; -CONR ³ ₂ ; wherein R ³ is selected from an alkali metal; hydrogen; Ci-i ₈ alkyl; and C _6- 12 aryl optionally substituted with C _{1 -18} alkoxy, -CN, -CF ₃ , -N0 ₂ , halogen, or C _{1 -18} alkyl; and

R ¹ is selected from

wherein Xi _b , X _2b , X3 _b and X _4b are independently selected from C, N, B and S; and B’ is the same or different to A and is independently selected from hydrogen; Ci-is alkyl; C _6- 12 aryl optionally substituted with C _1-18 alkoxy, -CN, -CF ₃ , -N0 ₂ , halogen, or C _{M S} alkyl; a heterocyclic ring; a heteroaryl; halogen; -N0 ₂ ; -CF ₃ ; - OR ³ ; -NR ³ ₂ ; -CN; -SR ³ ; -COR ³ ; -C0 ₂ R ³ ; -CONR ³ ₂ ; wherein R ³ is selected from an alkali metal; hydrogen; Ci-i ₈ alkyl; and Ce-^ aryl optionally substituted with Ci_ 18 alkoxy, -CN, -CF ₃ , -N0 ₂ , halogen, C _{M S} alkyl, hydroxyl (-OH), or -NR ₂ wherein R is as defined above.

Detailed description of the Invention

The intention of the present invention is to provide a laser-reactive composition that is capable of providing colour or an image on or with a substrate using a laser source(s) to manipulate colour changes in the compounds of the laser- reactive composition at localised positions so as to create single- or multi- coloured images on or within a substrate.

The present invention is of particular use in in-line printing, and allows compositions to be prepared with components that can respond to radiation or other stimuli to generate predictable colours for image formation. The compound of formula (I) of the present invention may therefore have use independently or in combination with other colour-forming compounds, depending on desired use. A broad colour gamut can therefore be achieved using these laser-reactive components.

It has been surprisingly and advantageously found that the keto acid compound of formula (I) can advantageously form colour upon exposure to an applied transition stimulus.

"Non-coloured state" and like terms as used herein, refers to the natural state (non-coloured state) of a keto acid compound before the applied transition stimulus is applied to it. The non-coloured state of the compound may be white, off-white or colourless i.e. clear, or has reduced or low visible colour, i.e. is paler in colour (a lighter shade or less intense colour) than a coloured state of the same colour. Alternatively, the natural state (non-coloured state) of a compound may possess an initial colour which will change following application of the applied transition stimulus to a more intense colour (coloured state), or a different colour. It will therefore be appreciated that, in the natural state (non- coloured state), the compound may often appear to display a colour, but that when compared with a coloured state of the same compound, it will be paler in colour, i.e. less intensely coloured, or a different colour. It will be appreciated by a skilled person that when the non-coloured state of a compound is colourless, any underlying colour of the substrate on which the compound is applied to or incorporated within will be visible.

"Coloured state" and like terms as used herein, refers to the state of a keto acid compound in which the compound displays a colour, i.e. is substantially or highly coloured, in the visible spectrum and to a human eye. The "coloured state" will be more intensely coloured than the "non-coloured state" of the same compound. This may be a more intense colouration of the same colour, but may also be a more intense colouration of a different colour to that of the non- coloured state as discussed above. In relation to the term "coloured state", the singular encompasses the plural and vice versa. For example, although reference is made herein to "a" coloured state, the term encompasses one or more coloured states. It will be appreciated that some compounds may have more than one coloured state, such as a first and a second coloured state, each of the first and second coloured states having a different colour. By the term "colour" and like terms as used herein, is meant the colours and hues of the visible light colour spectrum, i.e. red, orange, yellow, green, blue and violet, in addition to magenta, pink, purple, cyan, turquoise, brown and black, and mixtures thereof. Both primary and secondary colours are encompassed, i.e. the coloured state of a compound may have a primary or secondary colour. In the context of the present invention, the term may also be used to describe differing shades of each of the colours of the visible light colour spectrum, in addition to magenta, pink, purple, turquoise, brown, cyan and black.

"Stable coloured state" and like terms as used herein, refers to the coloured state of a keto acid compound that is stable under ambient conditions, i.e. maintains essentially its colour under ambient conditions. "Ambient conditions" and like terms as used herein, refers to the normal range of conditions of the surrounding environment to which the compounds are exposed, i.e. the range of temperatures, pressures and atmospheric conditions to which the compounds are exposed during use, storage and otherwise. This includes solar radiation including electromagnetic radiation of X-rays, ultraviolet (UV) and infrared (IR) radiation. Typically, ambient conditions include a temperature of from 10 to 35 °C, a pressure of from 20 to 100 kPa, and the environment is typically an oxygen-containing atmosphere. It will be appreciated by a skilled person that the required stability of the coloured state of a compound will be dependent upon the application for which a substrate having the composition and therefore the compound applied to or incorporated within is intended to be used. For example, if the composition comprising the compound is to be utilised in a laser reactive patch for a disposable item such as a hot or cold beverage container, the required stability of a coloured state of the compound will only need to be for a relatively short period of time, for example, a number of hours such as 6 to 12 hours, or a number of days such as 3 or 4 days. Whereas, if the composition comprising the compound is to be utilised in a laser-reactive composition applied on or incorporated within a cosmetic container or outdoor signage, the required stability of a coloured state of the compound will be greater, for example, a number of months, or even a number of years for outdoor signage uses. In general however, stable under ambient conditions is meant that when exposed to ambient conditions for at least a number of hours or a number of days, such as for at least two weeks, the coloured state maintains essentially its colour. Preferably, the compound will permanently remain in the particular coloured state. Accordingly, it is preferred that the compound remains in a coloured state for at least 3 days, preferably for at least 4 days, more preferably for at least 1 or even at least 2 weeks, and most preferably, for at least 2 months.

"Monochromic" or "single-coloured image" and like terms used herein, refer to an image that is human or machine readable and has a single colour that is visible to the human eye. In the context of the present invention, the non- coloured state can form part of a monochromic image. In particular, when the non-coloured state of a compound is non-colour i.e. white, off-white or colourless, the non-coloured state can form part of the monochromic image.

"Multi-coloured image" and like terms as used herein, refers to an image or text that is human or machine readable having multiple colours, i.e. displaying 2 or more colours that are visible to the human eye. In the context of the present invention, the non-coloured state can form part of a multi-coloured image. In particular, when the non-coloured state of a compound is non-colour, i.e. white, off-white or colourless, the non-coloured state can form part of the multi-coloured image.

The term "image" incorporates, but is not limited to: text, logos, graphics, symbols and pictures. The term also incorporates both single- and multi- coloured images. It will be appreciated that in the context of the present invention, for both single- and multi-coloured images, it is the manipulation of the compounds that facilitates the formation of an image.

"Transitioning" and "transition" and like terms as used herein, refer to a keto acid compound changing irreversibly from a non-coloured state to a coloured state upon application of the applied transition stimulus. It will be appreciated by a skilled person that these are intentional transitions facilitated by the application of the applied transition stimulus. Such a transition may also occur from, for example, a first coloured state to a second coloured state if a compound has two coloured states. By the term "irreversibly" is meant that once the coloured state of the compound has been formed, the coloured state of the compound will be stable under ambient conditions.

"Printing", "in-line digital printing" or "laser printing" and like terms as used herein, refer to the process of using radiation to achieve colour and form an image on a substrate.

Radiation" and like terms as used herein, refers to energy in the form of waves or particles, and in particular, refers to electromagnetic radiation such as ultraviolet (UV), visible, near-infrared (NIR), and infrared (IR) particle radiation, e.g. alpha (a) radiation, beta (b) radiation, neutron radiation and plasma. It will be appreciated that, in the context of the present invention, a distinction is made between radiation of greater than 400 nm, e.g. near-infrared radiation, which causes vibrational, conductive and radiative excitation to the components upon application and therefore provides a‘temperature’, and radiation of 400 nm or less (e.g. ultraviolet radiation), or microwave radiation, which does not. In the context of the present invention, the "temperature" applied to the compositions and compounds is intended to include the temperature provided to the compositions and compounds through the application of thermal energy in different conductive, radiative and vibrational forms. As discussed, this may be through application of radiation of greater than 400 nm.

By the term "laser source(s)" and like terms as used herein includes any suitable commercial or non-commercial laser source(s).

All references to particular chemical compounds herein are to be interpreted as covering the compounds per se, and also, where appropriate, derivatives, hydrates, solvates, complexes, isomers, tautomers thereof.

Regarding all aspects of the present invention, it will be appreciated that A and B’ may constitute a substituent at a single position on the benzene ring to which each of A and B’ relates, or A and B’ may constitute multiple independently selected substituents at any of the available positions on the benzene ring to which each of A and B’ relates. For example, the benzene ring to which B’ relates may be substituted with a single substituent or up to 4 independently selected substituents.

Preferably, the keto acid compound is of formula (II):

wherein Xi _a , X _2a , X3 _a , Xi _b , X2 _b , X3 _b and X _4b , R, A and B’ are as described above for formula (I).

Preferably, the keto acid compound is of formula (III):

wherein R and B’ are as described above for formula (I). Preferably, the two R groups are the same and are selected from Ci-i ₈ alkyl; and C ₆ -i ₂ aryl optionally substituted with C _{M S} alkoxy, -CN, -CF ₃ , -N0 ₂ , halogen, or C _{M S} alkyl. More preferably, the two R groups are the same and are C _{M S} alkyl. Most preferably, the two R groups are the same and are Ci _-6 alkyl.

Preferably, B’ is independently selected from hydrogen; -N0 ₂ and halogen, more preferably, hydrogen and chlorine, and most preferably hydrogen.

Preferably, the keto acid compound is selected from 2-(4-(dimethylamino)-2- hydroxybenzoyl)benzoic acid, 2-(4-(dibutylamino)-2-hydroxybenzoyl)benzoic acid, 2-(4-(diethylamino)-2-hydroxybenzoyl)benzoic acid, and 2, 3,4,5- tetrachloro-6-(4-(diethylamino)-2-hydroxybenzoyl)benzoic acid. More preferably, 2-(4-(dimethylamino)-2-hydroxybenzoyl)benzoic acid, 2-(4-(dibutylamino)-2- hydroxybenzoyl)benzoic acid, and 2-(4-(diethylamino)-2-hydroxybenzoyl)benzoic acid.

Keto acid compounds of formula (I) according to the present invention are commercially available, for example, they can be sourced from Chameleon Speciality Chemicals Limited.

It is noted that in one embodiment, the keto acid compound may be in the form of a‘dimer’, whereby B’ denotes a -C0 ₂ R ³ group (where R ³ is hydrogen such that the benzene ring carries two carboxyl groups) and also, an independently selected -COR ³ group, where R ³ is a C _6- 12 aryl substituted with hydroxyl (-OH) and NR ₂ , wherein R is as defined above for formula (I). Preferably, the -C0 ₂ R ³ group (where R ³ is hydrogen such that the benzene ring carries two carboxyl groups) is at X _2b and the -COR ³ group is at X _3b .

Suitable acid-generating agents for use in the composition according to the first aspect of the present invention include any suitable commercially available or chemically synthesisable acid-generating agents. Suitable acid-generating agents include, but are not limited to the following: thermal acid-generating agents (TAGs) based on amine salts of borobenzilate and tri-n-butylammonium borodisalicylate; photoacid-generating agents such as but not limited to triphenylsulfonium triflate, triphenylsulfonium hexafluorophosphate, triphenylsulfonium perluorobutane sulfonate, triphenylsulfonium trifluoromethylsulfonate, N-phenylbis(trifluoromethanesulfonimide), Bisphenol derivatives including but not limited to bisphenol A, bisphenol F, bisphenol S, bisphenol E, bisphenol B, bisphenol AF, bisphenol AP, and bisphenol BP. Suitable photoacid-generating agents include those described in US 8932797, the content of which is incorporated herein by reference.

It will be appreciated by the skilled person that the acid-generating agent and the keto acid compound of formula (I) interact to achieve colour formation. The acid- generating agent is present in the composition according to the first aspect of the present invention to facilitate a pH change through generation of acid upon application of the applied transition stimulus. This acid generation facilitates the transition of the keto acid compound from the non-coloured state to a coloured state. By‘acid’ is meant any molecular entity or chemical species capable of donating a hydrogen (proton) or capable of forming a covalent bond with an electron pair.

The applied transition stimulus may be selected from radiation and temperature, as outlined below.

It will be appreciated that the applied transition stimulus will differ depending upon the components of the composition according to the first aspect of the present invention. In particular, the selection of radiation or temperature as the applied transition stimulus will differ depending on whether the acid-generating agent is a photoacid-generating agent or a thermal acid-generating agent. It will be appreciated that if the keto acid compound of formula (I) is accompanied by a photoacid-generating agent, radiation will be utilised to facilitate the transition of the keto acid compound of formula (I) from the non-coloured to a coloured state, and alternatively, if the keto acid compound of formula (I) is accompanied by a thermal acid-generating agent, temperature will be utilised to facilitate the transition of the keto acid compound of formula (I) from the non-coloured to a coloured state.

The applied transition stimulus may be radiation. It will be appreciated that the radiation selected will be the radiation required to facilitate a transition of the keto acid compound of formula (I) from the non-coloured to a coloured state. The radiation selected will therefore be dependent upon the keto acid compound of formula (I) and the acid-generating present in the composition according to the first aspect of the present invention. As discussed above, if the keto acid compound of formula (I) is accompanied by a photoacid-generating agent, radiation will be utilised to facilitate the transition of the keto acid compound of formula (I) from the non-coloured to a coloured state. It will be appreciated by a skilled person that given the interaction between the acid-generating agent and the keto acid compound of formula (I), the radiation is selected to achieve the acid generation of the acid-generating agent. The radiation may be selected from gamma radiation with a wavelength of less than 0.01 nm, X-ray radiation with a wavelength of from 0.01 to 10 nm, ultraviolet (UV) radiation with a wavelength of from 10 to 400 nm, and microwave radiation with a wavelength of from 1 mm to 1 m. Preferably, the radiation is ultraviolet (UV) radiation with a wavelength of from 10 to 400 nm, preferably with a wavelength of from 100 to 400 nm.

It will be appreciated that from the radiation and wavelength ranges detailed herein for the applied transition stimulus, a skilled person would select radiation of a specific wavelength as required to achieve the desired transition of the keto acid compound from the non-coloured state to a coloured state. It will be appreciated that the specifically selected radiation will differ depending upon the components of the composition according to the first aspect of the present invention.

The radiation may be applied to the keto acid compound of formula (I) of the composition by any suitable means. Suitable means include laser excitation through application of radiation to the composition and thus the keto acid compound by a laser source(s). It will be understood by a skilled person that the radiation may be applied to the composition at localised positions to selectively develop the coloured state of the keto acid compound at these localised positions in the composition. These localised positions may overlap with each other. Alternatively, it will be appreciated by a skilled person that the radiation may be applied to the composition on or within a substrate by flood illumination, meaning that the composition as a whole is flooded with radiation. This can be done using any suitable lamp or bulb, such as a UV lamp, or medium pressure mercury or amalgam lamp or microwave powered UV lamp, a Xe, Hg or XeHg arc (broadband UV sources); a germicidal lamp, a diode bar; or LED(s). Where a broadband UV source is utilised, it will be appreciated that a range of wavelengths over the 10 to 400 nm range will be emitted. It will also be understood by a skilled person that the radiation is applied to the composition for an appropriate amount of time required to facilitate the transition of the keto acid compound from the non-coloured state to a coloured state. Typically the time required to deliver sufficient radiation will depend upon the power of the means used to apply radiation and the method of application i.e. at localised positions, or by flood illumination. For example, in one embodiment, the radiation may be applied to the keto acid compound of formula (I) for less than 120 seconds (such as between 30 to 110 seconds, or even between 75 to 105 seconds), or for less than 60 seconds, such as for less than 20 seconds, or even less than 10 seconds.

It will be appreciated that when applied using a laser source(s), the radiation dosage applied can be controlled by alteration of the time for which the radiation is applied, the power of the means used to apply the radiation (wattage) and thus, the fluence (amount of energy delivered per unit area) delivered by a laser source(s), i.e. J/cm ²

The applied transition stimulus may be temperature. It will be appreciated by a skilled person that the temperature will be the temperature required to facilitate a transition of the keto acid compound of formula (I) from the non-coloured state to a coloured state. The temperature selected will therefore be dependent upon the keto acid compound of formula (I) and acid-generating agent present in the composition according to the first aspect of the present invention. As discussed above, if the keto acid compound of formula (I) is accompanied by a thermal acid-generating agent, temperature will be utilised to facilitate the transition of the keto acid compound of formula (I) from the non-coloured to a coloured state. It will be appreciated by a skilled person that given the interaction between the acid-generating agent and the keto acid compound of formula (I), the temperature is selected to achieve the acid generation of the acid-generating agent. The temperature may be a temperature of from 80 to 300 °C, such as from 80 to 250 °C.

The temperature may be applied using any suitable means. Suitable means include laser excitation through application of keto acid compound of formula (I) using radiation from a laser source(s). It will be understood by a skilled person that the temperature may be applied to the composition at localised positions to selectively develop the coloured state of the keto acid compound of formula (I) at these localised positions in the composition. These localised positions may overlap with each other. Alternatively, it will be appreciated by a skilled person that the temperature may be applied to the composition on or within a substrate by flood illumination, meaning that the composition as a whole is flooded with radiation. This can be done using a lamp or bulb, such as an IR lamp; a diode bar; or LED(s). It will further be appreciated that the temperature may be applied to the keto acid compound of formula (I) using a conductive temperature source. Conductive temperature sources include but are not limited to: sources of steam and hot air, lamps, heat tunnels, hotplates, LED(s), thermal print heads, thermal conductors, hot liquids and heated substrates. It will also be understood by a skilled person that the radiation is applied to the composition for an appropriate amount of time required to reach the temperature required to facilitate the transition of the keto acid compound of formula (I) from the non-coloured state to a coloured state. Typically the time required to deliver sufficient temperature will depend upon the means used to apply radiation and the method of application i.e. at localised positions, or by flood illumination. For example, in one embodiment, the temperature may be applied to the keto acid compound of formula (I) for less than 120 seconds (such as between 30 to 110 seconds, or even between 75 to 105 seconds), or for less than 60 seconds, such as for less than 20 seconds, or even less than 10 seconds.

It will be appreciated that when applied using a laser source(s), the temperature applied can be controlled by alteration of the time for which the radiation is applied, the power of the means used to apply the radiation (wattage) and thus, the fluence (amount of energy delivered per unit area) delivered by a laser source(s), i.e. J/cm ²

It will be appreciated by a skilled person that the temperature may be applied using a combination of the means listed above, i.e. combinations of laser excitation at localised positions, flood illumination and a conductive temperature source. For example, in one embodiment, the temperature may be applied to the keto acid compound of formula (I) using laser excitation at localised positions, in addition to a conductive temperature source.

In addition, it will be appreciated that where the temperature is applied using radiation, i.e. at localised positions using a laser source(s) or by flood illumination, the composition and thus the keto acid compound of formula (I) may be exposed to a temperature in excess of the stated temperature ranges for a very short period of time, i.e. microseconds. It will be understood that this will not have any significant effect on the result to be achieved.

The temperature may be applied to the keto acid compound of formula (I) using radiation selected from visible radiation with a wavelength of from 400 to 700 nm, infrared (IR) radiation with a wavelength of from 700 nm to 1 mm, including near-infrared (NIR) radiation with a wavelength of from 700 to 1600 nm. Preferably, the temperature is selected from visible radiation with a wavelength of from 400 to 700 nm, infrared (IR) radiation with a wavelength of 10600 nm (using a C0 ₂ laser), infrared radiation with a wavelength of from 700 nm to 1 mm, and near-infrared (NIR) radiation with a wavelength of 700 to 1600 nm.

It will be appreciated that from the temperature and wavelength ranges detailed herein for the applied transition stimulus, a skilled person would select temperature as required to achieve the desired transition of the keto acid compound of formula (I) from the non-coloured state to a coloured state. It will be appreciated that the specifically selected temperature will differ depending upon the components of the composition according to the first aspect of the present invention.

It will be understood by a skilled person that the coloured state of the keto acid compound of formula (I) is stable under ambient conditions.

The coloured state of the keto acid compound of formula (I) may have any colour. Preferably, the colour of the coloured state of the keto acid compound of formula (I) is selected from yellow, orange and red. It will be appreciated by a skilled person that the means used to apply the applied transition stimulus will affect the colour of the coloured state formed. For example, where a laser source(s) is used to apply the applied transition stimulus, the fluence (amount of energy delivered per unit area) may affect the colour, intensity or lightness of the coloured state formed. In the context of the present invention, the fluence is dependent upon the power of the means used to apply the applied transition stimulus (wattage) and the time for which the applied transition stimulus is applied to a particular localised position on the substrate, which may be controlled by the scanning speed of the laser or the speed of the moving stage. These two variables can be altered to change the fluence. Where the fluence is low (e.g. lower power and/or shorter irradiation times), the coloured state of the keto acid compound of formula (I) will be of a less intense colour, and where the fluence is high (e.g. higher power and/or longer irradiation times), the coloured state of the keto acid compound of formula (I) will be of a more intense colour. Changing the fluence may also result in a coloured state of the keto acid compound of formula (I) changing colour. For example, low fluence may form a coloured state of the keto acid compound of formula (I) having a yellow colour, and higher fluence may form the same coloured state of the keto acid compound of formula (I) having an orange or red colour. In the context of the present invention, fluence values may range from 0.01 to 20 J/cm ² , such as from 0.1 to 10 J/cm ² and even from 0.5 to 5 J/cm ² .

Preferably, the applied transition stimulus is temperature as defined above.

The keto acid compound may be present in the composition according to the first aspect of the present invention in any suitable amount. Preferably, the composition comprises from 0.1 to 50%, such as from 0.1 to 40 %, or even from 3 to 30 % of the keto acid compound based on the total solid weight of the composition. Most preferably, the composition comprises from 5 to 25 % of the keto acid compound based on the total solid weight of the composition.

The acid-generating agent may be present in the composition in any suitable amount. Preferably, the composition comprises from 0.1 to 50 %, such as from 5 to 40 % of the acid-generating agent based on the total solid weight of the composition. Most preferably, the composition comprises from 5 to 30 % of the acid-generating agent based on the total solid weight of the composition.

The ratio of the acid-generating agent to the keto acid compound based on the total solid weight of the composition may be from 4:1 to 1 :4, preferably from 3: 1 to 1 :3, and more preferably from 2:1 to 1 :2.

The composition according to the first aspect of the present invention may further comprise a binder. Suitable binders will be well known to a person skilled in the art. Examples of suitable binders include, but are not limited to the following: polymeric binders such as acrylic polymers, styrene polymers and hydrogenated products thereof; vinyl polymers; polyolefins and hydrogenated or epoxidised products thereof; aldehyde-containing polymers; epoxide-containing polymers; polyamides; polyesters; polyurethanes; sulphone-containing polymers; natural products and derivatives thereof; and combinations thereof. The binder may be present in the composition in any suitable amount. Preferably, the composition comprises from 1 to 50 %, such as from 5 to 40 % and most preferably, from 10 to 35 % of binder based on the total solid weight of the composition.

The composition according to the first aspect of the present invention may further comprise a near-infrared radiation (NIR) absorber. It will be appreciated that an NIR absorber may be utilised when NIR radiation is to be utilised, the Nlr absorber capable of enhancing the absorption of the NIR radiation. Examples of suitable NIR absorbers include, but are not limited to the following: inorganic copper salts such as copper (II) hydroxyl phosphate; organic NIR dyes and pigments such as N,N,N’,N’-tetrakis(4-dibutylaminophenyl)-p-benzoquinone bis(iminium hexafluoro-antimonate); non-stoichiometric inorganic compounds such as reduced indium tin oxide, reduced zinc oxide, reduced tungsten oxide (tungsten bronze), reduced doped tungsten oxide, reduced antimony tin oxide, or doped metal oxides such as aluminium-doped zinc oxide (AZO) and fluorine- doped tin oxide (FTO); conductive polymers such as poly polystyrene sulfonate (PEDOT); and combinations thereof. Preferably, the NIR absorber is a non- stoichiometric inorganic compound. Preferably, the composition comprises from 0.05 to 25 %, such as from 0.05 to 20 % of an NIR absorber based on the total solid weight of the composition.

The composition according to the first aspect of the present invention may further comprise a curable compound. Suitable curable compounds will be well known to a person skilled in the art. Examples of suitable curable compounds include, but are not limited to: any commercially available monomers, oligomers, monomer and oligomer mixtures, or photoinitiators. The curable compound may be present in the composition in any suitable amount. The composition according to the first aspect of the present invention may further comprise an additive or combination of additives. Suitable additives will be well known to a person skilled in the art. Examples of suitable additives include, but are not limited to the following: polymers; light or energy absorbing agents; UV absorbers; surfactants; wetting agents; drying promoters; colourants such as pigments; tinting agents; fluorescent agents; plasticisers; optical brighteners; oxidising or reducing agents; stabilisers; light stabilising agents such as hindered amines; rheology modifiers such as thickening or thinning agents; slip agents; humectants; adhesion promotors; acid or base scavenging agents; retarders; defoamers; antifoaming agents; and combinations thereof. Preferably, the composition comprises 0.1 to 9 %, such as from 0.1 to 8%, or even from 0.1 to 7 % of additives based on the total solid weight of the composition.

The composition according to the first aspect of the present invention may further comprise a solvent. The composition may comprise a single solvent or a mixture of solvents. The solvent may comprise water, an organic solvent, a mixture of water and an organic solvent, or a mixture of organic solvents. Suitable organic solvent include, but are not limited to the following: alcohols such as ethanol, n-propanol, isopropanol and n-butanol; esters such as ethyl acetate, butyl acetate, and n-hexyl acetate; aromatic hydrocarbons such as benzene, toluene, xylene, and solvent naphtha 100, 150, 200; ketones such as acetone, cyclohexanone, methylisobutyl ketone, and methyl ethyl ketone; glycols such as butyl glycol; glycol ethers such as methoxy propanol, ethylene glycol monomethyl ether, ethylene glycol monobutyl ether; and combinations thereof. Preferably, the solvent is present in the composition in amounts of from 15 to 70 %, such as from 15 to 60 %, or even from 20 to 55 % based on the total solid weight of the composition.

The composition according to the first aspect of the present invention may have a viscosity of from 14 to 120 Zahn seconds (efflux time), suitably measured using a Zahn cup #2 viscosity measurement device at a temperature of 16 to 30 °C. It will be appreciated that the viscosity of the composition is dependent upon a number of factors, including the number, type and amount of the components present in the composition, in addition to the printing application and, if applied to a substrate, the desired coat weight of the composition on the substrate.

The composition according to the first aspect of the present invention preferably comprises, in addition to the keto acid compound of formula (I) and acid- generating agent, a binder, an additive or combination of additives, and a solvent or combination of solvents. If NIR is to be used as the applied transition stimulus, an NIR absorber is preferably present in the composition.

It will be appreciated that the composition according to the first aspect of the present invention may be formed through the combination of formulations containing different components of the composition, for example the keto acid compound of formula (I) may be in a separate formulation to the acid-generating agent, these two formulations then being combined to form the composition according to the first aspect of the present invention.

The composition according to the first aspect of the present invention may further comprise at least one additional compound capable of transitioning from a non-coloured state to a coloured state, the transition being effected by the application of an additional applied stimulus, wherein, if formed, the coloured state of the keto acid compound and at least one additional compound are different in colour. The coloured state of the at least one additional compound may have any colour. Preferably, the coloured state of the at least one additional compound is selected from blue, black and red. Preferably, the coloured state of the at least one additional compound is stable.

It will be appreciated that the at least one additional compound and the keto acid compound of formula (I) will be selected based on the colour(s) of their coloured states that can be achieved. Furthermore, the at least one additional compound and the compound of formula (I) will be selected such that their colour formation is triggered by different conditions. Preferably, the applied transition stimulus and additional applied stimulus are different. It will be understood by this that even if the applied transition stimulus and the additional applied stimulus are selected so as to be temperature and additional temperature, the temperature and additional temperature will be different. ‘Different conditions’ encompasses the differing orders of application of the applied transition stimulus and additional applied stimulus, as required, for the formation of colour for the at least one additional compound and the keto acid compound of formula (I).

Examples of suitable additional compounds include diacetylene compounds comprising a diacetylene moiety ( ' c=c-c=c— \ ) _a leuco dye, and oxyanions of a multivalent metal.

The terms "non-coloured state", "coloured state", "stable coloured state" as defined above in relation to the keto acid compound of formula (I) are applicable to the at least one additional compound. The term "transition" as defined above in relation to the keto acid compound of formula (I) is also applicable to the at least one additional compound, the applied transitions stimulus being replaced by the additional applied stimulus.

If present, the at least one additional compound may be present in the composition according to the first aspect of the present invention in any suitable amount. Preferably, the composition comprises from 0.1 to 50%, such as from 0.1 to 40 %, or even from 3 to 30 % of the at least one additional compound based on the total solid weight of the composition. Most preferably, the composition comprises from 5 to 25 %, or even from 15 to 25% of the at least one additional compound based on the total solid weight of the composition.

It will be appreciated by a skilled person that if the at least one additional compound is present in the composition according to the first aspect of the present invention, the composition may be formed through the combination of formulations containing the different components of the composition, for example, the keto acid compound of formula (I), the acid-generating agent, and the at least one additional compound may be each in separate formulations, which are combined together to form the composition according to the first aspect of the present invention.

The at least one additional compound may be an oxyanion of a multivalent metal. The use of oxyanions of multivalent metals in laser-markable compositions are disclosed in US7485403, the content of which is incorporated herein by reference. A particularly preferred oxyanion is ammonium octamolybdate (NH ₄ ) ₄ Mo _s 0 ₂ e or ‘AOM’, which is a commercially available molybdenum composition with the CAS number 12411-64-2. The AOM pigment will typically be formulated together with a binder, e.g. a polymeric binder, in the compositions of the invention. Suitable oxyanions include molybdate, tungstate or analogous transition metal compounds, including di- and hept-molybdates.

Preferably, the oxyanion of a multivalent metal is ammonium octamolybdate (AOM).

The at least one additional compound may be a diacetylene compound. Diacetylene compounds are well known to a skilled person as compounds capable of forming colour. Typical diacetylene compounds are disclosed for this purpose in WO 2012/114121. Suitable examples are taught in W02009/093028, WO2010/001171 , W02010/029329, and WO2013/068729, the content of each of which is incorporated herein by reference. Known methods of synthesis of diacetylene compounds include the formation of a reactive acid chloride and subsequent addition of an amine or alcohol, or the formation of a mixed anhydride and subsequent reactions with an amine or alcohol. Diacetylene compounds typically have two coloured states, such as a first and a second coloured state, each of the first and second coloured states having a different colour. It will be appreciated by a skilled person that when diacetylene compounds are in the non-coloured state, they are considered to be monomers. It will be appreciated that to access the first coloured state of the diacetylene compound, an additional applied stimulus will be required, and to access the second coloured state of the diacetylene compound, a different additional applied stimulus will be required. The first and second coloured states of diacetylene compounds are formed on account of polymerisation of these monomers upon exposure to the additional applied stimulus. Polymerisation of at least a portion of the monomers enables the formation of the coloured states. In addition, without being bound by theory, it is considered that the different first and second coloured states are achieved through changes in conjugation of the diacetylene polymer, i.e. a structural change. The at least one additional compound may be any suitable diacetylene compound.

The at least one additional compound may be a diacetylene compound having the following formula (III):

T- (CH ₂ ) _X - L - Q wherein x is from 2 to 12, preferably 2 to 10, and more preferably 2 to 8; o

L is selected from an amide having the formula: v H \ and an ester having

° 9

, A ₀ , _{x N} _ _f the formula: ^u ¾, preferably L is an amide having the formula H ,

Q is selected from a cyclopropyl and a -(CH ₂ ) _y -CH ₃ linear alkyl chain, y being selected from 1 to 20, preferably 5 to 19, and more preferably 7 to 17; and

T is selected from hydrogen, a -(CH ₂ ) _X (CH ₃ ) linear alkyl chain wherein x is defined as above for formula (I), and -(CH ₂ ) _X -L-Q, wherein x, L and Q are as defined above for formula (I).

It will be appreciated by a skilled person that the diacetylene compound can be either symmetrical or unsymmetrical, i.e. T is -(CH ₂ ) _X -L-Q and the values of x, L and Q are the same as those on the other side of the diacetylene moiety (symmetrical), or T is hydrogen, a -(CH ₂ ) _X (CH ₃ ) linear alkyl chain, or -(CH ₂ ) _X -L-Q and the values of x, L and Q are not the same on both sides of the diacetylene moiety (unsymmetrical). Preferably, T is -(CH ₂ ) _X -L-Q and the values of x, L and Q are the same on both side of the diacetylene moiety, such that the diacetylene compound is symmetrical.

The at least one additional compound may be a diacetylene compound of formula (IV): wherein x is from 4 to 8, and Q is selected from cyclopropyl and a -(CH ₂ ) _y (CH ₃ ) linear alkyl chain wherein y is 7 to 17.

Examples of suitable diacetylene compounds include, but are not limited to the following: N1 ,N22-dioctadecyldocosa-10,12-diynediamide, N1 ,N22- dihexadecyldocosa-10-12-diynediamide, N 1 , N22-ditetradecyldocoda-10,12- diynediamide, N1 ,N22-didodecyldocosa-10,12-diynediamide, N1 ,N22- didecyldocosa-10, 12-diynediamide, N 1 , N22-dioctyldocosa-10, 12-diynediamide, N 1 , N22-dihexyldocosa-10, 12-diynediamide, N 1 , N22-dicyclopropyldocosa- 10,12-diynediamide.

Preferably, the diacetylene compound is a diacetylene compound selected from N 1 , N22-dioctadecyldocosa-10, 12-diynediamide, N 1 , N22-dihexadecyldocosa-

10,12-diynediamide, N 1 , N22-ditetradecyldocosa-10, 12-diynediamide, N 1 , N22- didodecyldocosa-10,12-diynediamide, and N1 ,N22-dicyclopropyldocosa-10,12- diynediamide.

It will be appreciated by a skilled person that the non-coloured state of certain diacetylene compounds may preferably need to be‘activated; (i.e. made capable of undergoing a transition to a coloured state) prior to exposure to the additional applied stimulus to enable a transition from the non-coloured state to a coloured state to be possible. If required, activation can be facilitated by exposure of the non-coloured state of the diacetylene compound to an activation temperature. It will be appreciated by a skilled person that this activation may take place prior to the exposure to the additional applied stimulus to effect the transition from the non-coloured state to a coloured state, or alternatively, the non-coloured state of the diacetylene compound may be activated during this exposure. If the activation takes place prior to the exposure to the additional applied stimulus, the activation temperature is a temperature between ambient temperatures (10 to 35 °C) and the decomposition temperature of the diacetylene compound. The activation temperature may be from 40 to 150 °C. The diacetylene compound may be exposed to the activation temperature using any suitable means, including radiation source(s) such as laser source(s). The radiation may be selected from visible light with a wavelength of from 400 to 700nm, infrared radiation with a wavelength of from 700nm to 1 mm, in particular 100nm, and near-infrared radiation with a wavelength of from 700 to 1600nm.

The at least one additional compound may be a leuco dye. Leuco dyes are well known to a skilled person as compounds capable of forming colour. They can be photochromic (change colour on exposure to light such as UV light), chemochromic, thermochrmoic, or halochromic (change colour on exposure to change in environmental pH). Halochromic leuco dyes can be used in combination with an acid-generating agent such as a Lewis acid compound, or acid-generating agent such as a thermal acid generating (TAG) agent or a photoacid-generating agent. Examples of suitable leuco dyes are contained in WO2015/015200 and WO2013/068729, the content of each of which is incorporated herein by reference. Examples of suitable acid-generating agents are as discussed above in relation to the acid-generating agents relating to the compound of formula (I) or (II). Preferably, the halochromic lecuo dyes are used in combination with an acid- or base-generating agent.

The at least one additional compound may be a leuco dye, including any commercially available or chemically synthesisable leuco dye, including but not limited: commercially available photochromic, thermochromic, chemochromic, and halochromic lecuo dyes. Examples of suitable leuco dyes include, but are not limited to: spiroxazines, naphthopyrans, phthalides, fluorans, triarylmethanes, benzoxazines, quinazolines, spiropyrans, quinones, tetrazolium salts, thiazines, phenazines and oxazines.

Suitable suppliers of leuco dyes include, but are not limited to: Yamada Chemical Company Limited, Chameleon Speciality Chemicals Limited, and Connect Chemicals.

The leuco dye may be selected from: 2-Anilino-3-diethylamino-6-methylfluoran (Chameleon Black 1 ), 2-Anilino-6-dibutylamino-3-methylfluoran (Chameleon Black 2), 6-(Dimethylamino)-3,3-bis [4-(dimethylamino) phenyl] phthalide (Chameleon Blue 3), 4,4'-[(9-butyl-9H-carbazol-3-yl)methylene]bis[N-methyl-N- phenylaniline] (Chameleon Blue 4), 3,3'-Bis(1 -n-octyl-2-methylindol-3- yl)phthalide (Chameleon Red 5), 6'-(Diethylamino)-3-oxo-spiro [isobenzofuran- 1 (3H),9'-[9H] xanthene]-2'-carboxylic acid ethyl ester (Chameleon Orange 6), 7- [4-(diethylamino)-2-ethoxyphenyl]-7-(2-methyl-1 -octyl-1 H-indol-3-yl) Furo[3,4- b]pyridin-5(7H)-one (Chameleon Blue 8),

2'-(Dibenzylamino)-6'- (diethylamino)fluoran (Chameleon Blue 9), N,N-dimethyl-4-[2-[2-(octyloxy)phenyl]-6-phenyl-4-pyridinyl] - Benzenamine (Chameleon Yellow 10), and 6'-(diethylamino)-2'-[(dimethylphenyl) amino]-3'- methylspiro [isobenzofuran-1 (3H),9'-[9H]xanthene]-3-one (chameleon Black 15).

Preferably, the leuco dye is a halochromic leuco dye. Preferably, the leuco dye is a halochromic leuco dye in combination with an acid- or base-generating agent.

Preferably, if the at least one additional compound is present, the composition comprises a keto acid compound of formula (I), a diacetylene compound.

Preferably, if the at least one additional compound is present, the composition comprises a keto acid compound of formula (I), a diacetylene compound and an oxyanion of a multivalent metal.

It will be appreciated that a composition comprising a keto acid compound of formula (I) and at least one additional compound enables the production of a broad range of colours in the formation of an image. The different applied transition stimulus and additional applied stimulus can be applied in different combinations at particular localised positions, enabling the formation of desired single- and multi-coloured images with a broad colour gamut.

The additional applied stimulus may be selected from additional radiation and additional temperature, as discussed below.

It will be appreciated by a skilled person that the selection of the additional applied stimulus is dependent upon the nature of the at least one additional compound. For example, if the at least one additional compound is a diacetylene compound, the application of the additional radiation effects the transition of the at least one compound from the non-coloured state to a coloured state, and the additional radiation will be selected to achieve this transition. Further, if the at least one additional compound is a leuco dye, the application of additional radiation or additional temperature effects the transition of the at least one compound from the non-coloured state to a coloured state. It will be appreciated by a skilled person that the selection of the additional radiation or additional temperature will be dependent upon the type of leuco dye selected for use, and if present, the nature of the acid-generating agent utilised such as a thermal acid generating agent or a photoacid-generating agent. For example, if the at least one additional compound is a halochromic leuco dye accompanied by a photoacid- generating agent, additional radiation is utilised to facilitate a transition from the non-coloured to a coloured state of the leuco dye, and if the at least one additional compound is a halochromic leuco dye accompanied by a thermal acid- generating agent, additional temperature is utilised to facilitate a transition from the non-coloured to a coloured state of the leuco dye. It will be appreciated by a skilled person that given the interaction between the acid-generating agent and the leuco dye to form colour, the radiation or temperature will be selected to achieve the acid generation of the acid-generating agent. These selections are well within the capabilities of a skilled person.

In addition, if the at least one additional compound is an oxyanion of a multivalent metal such as AOM, the application of the additional temperature effects the transition of the at least one compound from the non-coloured state to a coloured state, and the additional temperature will be selected to achieve this transition. It will be appreciated that, in the context of the present invention, the diacetylene compounds typically have two coloured state, such as a first and a second coloured state, each of the first and second coloured states having a different colour. For such diacetylene compounds, the application of the additional radiation effects the transition of the at least one additional compound from the non-coloured to the first coloured state, and the application of the additional temperature effects the transition from the first coloured to the second coloured state. The additional applied stimulus may be additional radiation. It will be appreciated that the additional radiation selected will be the radiation required to facilitate a transition of the at least one additional compound from the non- coloured to a coloured state. The additional radiation selected will therefore be dependent upon the at least one additional compound present in the composition. The additional radiation may be selected from gamma radiation with a wavelength of less than 0.01 nm, X-ray radiation with a wavelength of from 0.01 to 10 nm, ultraviolet (UV) radiation with a wavelength of from 10 to 400 nm, and microwave radiation with a wavelength of from 1 mm to 1 m. Preferably, the additional radiation is ultraviolet (UV) radiation with a wavelength of from 10 to 400 nm, preferably with a wavelength of from 100 to 400 nm.

The additional radiation may be applied to the at least one additional compound of the composition according to the first aspect of the present invention by any suitable means. Suitable means include laser excitation through application of radiation to the composition and thus the at least one additional compound by a laser source(s). It will be understood by a skilled person that the additional radiation may be applied to the composition at localised positions to selectively develop the coloured state of the at least one additional compound at these localised positions in the composition. These localised positions may overlap with each other. Alternatively, it will be appreciated by a skilled person that the radiation may be applied to the composition on or within a substrate by flood illumination, meaning that the composition as a whole is flooded with radiation. This can be done using any suitable lamp or bulb, such as a UV lamp, or medium pressure mercury or amalgam lamp or microwave powered UV lamp, a Xe, Hg or XeHg arc (broadband UV sources); a germicidal lamp, a diode bar; or LED(s). Where a broadband UV source is utilised, it will be appreciated by a skilled person that a range of wavelengths will be emitted over the 10 to 400 nm range. It will also be understood by a skilled person that the additional radiation is applied to the composition for an appropriate amount of time required to facilitate the transition of the at least one additional compound from the non- coloured state to a coloured state. Typically the time required to deliver sufficient additional radiation will depend upon the means used to apply radiation and the method of application i.e. at localised positions, or by flood illumination. For example, in one embodiment, the additional radiation may be applied to the at least one additional compound for less than 120 seconds (such as between 30 to 110 seconds, or even between 75 to 105 seconds), or for less than 60 seconds, such as for less than 20 seconds, or even less than 10 seconds.

It will be appreciated that from the additional radiation and wavelength ranges detailed herein for the additional applied stimulus, a skilled person would select additional radiation of a specific wavelength as required to achieve the desired transition of the at least one additional compound from the non-coloured state to a coloured state. It will be appreciated that the specifically selected additional radiation will differ depending upon the components of the composition.

It will be appreciated that when applied using a laser source(s), the additional radiation dosage applied can be controlled by alteration of the time for which the additional radiation is applied, the power of the means used to apply the additional radiation (wattage) and thus, the fluence (amount of energy delivered per unit area) delivered by a laser source(s), i.e. J/cm ²

The additional applied stimulus may be an additional temperature. It will be appreciated by a skilled person that the additional temperature will be a temperature required to facilitate a transition of the at least one additional compound from the non-coloured to a coloured state, or from a first coloured state to a second coloured state when a diacetylene compound is utilised. The additional temperature selected will therefore be dependent upon the at least one additional compound present in the composition. The additional temperature may be a temperature of from 50 to 300 °C, such as from 50 to 280 °C, or even 80 to 200 °C.

The additional temperature may be applied to the at least one additional compound of the composition by any suitable means. Suitable means include laser excitation through application of radiation to the composition and thus the at least one additional compound by a laser source(s). It will be understood by a skilled person that the additional temperature may be applied to the composition at localised positions to selectively develop the coloured state of the at least one additional compound, or the second coloured state from the first coloured state, at these localised positions in the composition. These localised positions may overlap with each other. Alternatively, it will be appreciated by a skilled person that the additional temperature may be applied to the at least one additional compound by flood illumination, meaning that the composition as a whole is flooded with radiation. This may be done using a lamp or bulb, such as an IR, UV or mercury lamp; diode bar; or LED(s). It will further be appreciated that the additional temperature may be applied to the at least one additional compound using a conductive temperature source. Conductive temperature sources include sources of steam and hot air, lamps, heat tunnels, hotplates LED(s), thermal print heads, thermal conductors, hot liquids and heated substrates. It will be understood by a skilled person that the radiation is applied to the composition for an appropriate amount of time required to reach the additional temperature and facilitate the transition of the at least one additional compound from the non-coloured state to the coloured state. Typically the time required to deliver sufficient temperature will depend upon the power of the means used to apply radiation and the method of application i.e. at localised positions, by flood illumination, or using a conductive temperature source. For example, in one embodiment, the additional temperature may be applied to the at least one additional compound for less than 120 seconds (such as between 30 to 110 seconds, or even between 75 to 105 seconds), or for less than 60 seconds, such as for less than 20 seconds, or even less than 10 seconds.

It will be appreciated that when applied using a laser source(s), the additional temperature applied can be controlled by alteration of the time for which the radiation is applied, the power of the means used to apply the radiation (wattage) and thus, the fluence (amount of energy delivered per unit area) delivered by a laser source(s), i.e. J/cm ²

It will be appreciated by a skilled person that the additional temperature may be applied to the at least one additional compound using a combination of the suitable means listed above, i.e. using combinations of laser excitation at localised positions, flood illumination, and a conductive temperature source. For example, in one embodiment, the additional temperature may be applied to the at least one additional compound using laser excitation at localised positions, in addition to using a conductive temperature source.

In addition, it will be appreciated that where the additional temperature is applied using radiation, i.e. at localised positions using a laser source(s) or by flood illumination, the composition and thus the at least one additional compound may be exposed to a temperature in excess of the stated temperature ranges for a very short period of time, i.e. microseconds. It will be understood that this will not have any significant effect on the result to be achieved.

The additional temperature may be applied to the at least one additional compound using radiation selected from visible radiation with a wavelength of from 400 to 700 nm, infrared (IR) radiation with a wavelength of from 700 nm to 1 mm, including near-infrared (NIR) radiation with a wavelength of from 700 to 1600 nm. Preferably, the additional temperature is selected from visible radiation with a wavelength of from 400 to 700 nm, infrared (IR) radiation with a wavelength of 10600 nm (using a C0 ₂ laser), infrared radiation with a wavelength of from 700 nm to 1 mm, and near-infrared (NIR) radiation with a wavelength of 700 to 1600 nm.

It will be appreciated that from the temperature and wavelength ranges detailed herein for the additional temperature, a skilled person would select a specific additional temperature as required to achieve the desired transition of the at least one additional compound from the non-coloured state to a coloured state. It will be appreciated that the specifically selected additional temperature will differ depending upon the components of the composition. It will further be appreciated that for diacetylene compounds, the additional temperature may be the temperature required to achieve a transition of the at least one additional compound from the first coloured state to a second coloured state.

It will be appreciated by a skilled person that the means used to apply the additional applied stimulus will affect the colour of the coloured state of the at least one additional compound that is formed. For example, where a laser source(s) is used to apply the additional applied stimulus, the fluence (amount of energy delivered per unit area) will affect the colour, intensity or lightness of the coloured state formed. In the context of the present invention, the fluence is a measure of the power of means used to apply the additional applied stimulus (wattage), and the time for which the additional applied stimulus is applied to a particular position on the substrate, which may be controlled by the scanning speed of the laser or the speed of the moving stage. These two variables can be altered to change the fluence. Where the fluence is low (e.g. lower power and/or shorter irradiation times), the coloured state of the at least one additional compound will be of a less intense colour, and where the fluence is high (e.g. higher power and/or longer irradiation times), the coloured state of the at least one additional compound will be of a more intense colour. In the context of the present invention, fluence values may range from 0.01 to 20 J/cm ² , such as from 0.1 to 10 J/cm ² and even from 0.5 to 5 J/cm ² .

Further, it will be appreciated by a skilled person that the required fluence from the additional applied stimulus necessary to facilitate a transition from the non- coloured state to a coloured state of the at least one additional compound may be different to the required fluence from the applied transition stimulus necessary to facilitate a transition from the non-coloured state to a coloured state of the keto acid compound of formula (I). Preferably, the required fluence from the additional applied stimulus necessary to facilitate a transition from the non-coloured state to a coloured state of the at least one additional compound will be different to the required fluence from the applied transition stimulus necessary to facilitate a transition from the non-coloured state to a coloured state of the keto acid compound of formula (I).

It will further be appreciated that the composition according to the first aspect of the present invention may not comprise more than one acid- or base-generating agent. As the keto acid compound of formula (I) or (II) is accompanied by an acid-generating agent, either the at least one additional compound will be selected so as to not require an acid- or base-generating agent, or in certain instances, the acid-base-generating agent associated with the keto acid compound of formula (I) will also interact with the at least one additional compound as discussed above. It will be appreciated by a skilled person that the composition according to the first aspect of the present invention may comprise more than one at least one additional compound.

The composition according to the first aspect of the present invention may be applied to or incorporated within any suitable substrate. It will be appreciated by a skilled person that the components of the composition will likely vary depending on the substrate to which the composition is to be applied to or incorporated within.

Thus, according to a second aspect of the present invention, there is provided a substrate comprising the composition according to the first aspect of the present invention applied to or incorporated within.

The composition according to the first aspect of the present invention, or the substrate of the second aspect of the present invention may be suitable for end use as labels (adhesive and wraparound) and/or, in fast-moving consumer goods; packaging such as disposable packaging including food and hot or cold beverage containers; hygiene and personal care product packaging such as shampoo bottles; cosmetic product packaging; medical and diagnostic devices and associated packaging; and outdoor products such as signage.

Examples of suitable substrates to which the composition may be applied, include, but are not limited to: polymers and recycled polymer materials such as polyethylene terephthalate (PET), polyethylene (PE), low density polyethylene (LDPE), high density polyethylene (HDPE), polystyrene (PS), polypropylene (PP), orientated polypropylene (OPP), biaxially orientated polypropylene (BOPP), cast polypropylene (CPP), polyamide (PA) such as nylon, polyvinyl chloride (PVC), or combinations thereof; cellulose; glass; plastic; metal and metal foils; textiles; paper; corrugated paperboard, cardboard, and equivalent recycled analogues, or combinations thereof; ceramics; foodstuffs and pharmaceutical preparations; or combinations thereof, e.g. polymer lined paper. The polymer and recycled polymer materials may be in the form of polymer film substrates. Examples of suitable substrates within which the composition may be incorporated include, but are not limited to: polymers and recycled polymer materials such as polyethylene terephthalate (PET), polyethylene (PE), low density polyethylene (LDPE), high density polyethylene (HDPE), polystyrene (PS), polypropylene (PP), orientated polypropylene (OPP), biaxially orientated polypropylene (BOPP), cast polypropylene (CPP), polyamide (PA) such as nylon, polyvinyl chloride (PVC), or combinations thereof; and any thermoplastic material such as plastic; or combinations thereof. The polymer and recycled polymer materials may be in the form of polymer film substrates.

Preferably, the substrate to which the composition may be applied or incorporated within is a polymer film substrate. Preferably, the substrate is colourless (i.e. transparent or translucent), white, or off-white.

It will be appreciated by a skilled person that the substrate to which the composition has been applied to or incorporated within may itself be applied to a further substrate. Examples of further substrates include, but are not limited to the following: polymers and recycled polymer materials such as polyethylene terephthalate (PET), polyethylene (PE), low density polyethylene (LDPE), high density polyethylene (HDPE), polystyrene (PS), polypropylene (PP), orientated polypropylene (OPP), biaxially orientated polypropylene (BOPP), cast polypropylene (CPP), polyamide (PA) such as nylon, polyvinyl chloride (PVC), or combinations thereof; cellulose; glass; plastic; metal and metal foils; textiles; paper; corrugated paperboard, cardboard, and equivalent recycled analogues, or combinations thereof; ceramics; foodstuffs and pharmaceutical preparations; or combinations thereof, e.g. polymer lined paper. The polymers and recycled polymer materials may be in the form of polymer film substrates.

Preferably, the substrate comprises an additional adhesive layer. It will be appreciated that this additional adhesive layer is operable to apply the substrate to a further substrate or any other material and is therefore on an exterior surface of the substrate. The adhesive layer may cover all, substantially all, or part of the surface area of an exterior surface of the substrate. When the composition is applied to the substrate, the additional adhesive layer is preferably on an exterior surface of the substrate other than that to which the composition is applied.

Preferably, the composition according to the first aspect of the present invention is applied on a substrate.

When the composition according to the first aspect of the present invention is applied on a substrate, the substrate may further comprise an at least one additional compound either incorporated within or applied to the substrate. Preferably, this further at least one additional compound is applied to the substrate. If the at least one additional compound is applied to the substrate, this may be in a layer on the substrate formed from a composition comprising the at least one additional compound, the composition being as defined above for the composition according to the first aspect of the present invention, the keto acid compound of formula (I) and the acid-generating agent replaced by the at least one additional compound. This layer comprising the at least one additional compound may be applied to the substrate underneath the composition applied to the substrate, or applied over the composition applied on the substrate. If an at least one additional compound is present in the composition according to the first aspect of the present invention, the at least one additional compound in the separate composition will be different. By different is meant that the at least one additional compound in the composition according to the present invention and the further at least one additional compound are selected either from different groups of (a) a diacetylene compound, (b) oxyanion of a multivalent metal or (c) leuco dye as defined above, or are selected from the same group (a), (b) or (c), but are selected so as to be different compounds in that group, e.g. two different leuco dyes. Preferably, the at least one additional compound in the composition according to the present invention and the further at least one additional compound are selected from different groups of (a) a diacetylene compound, (b) oxyanion of a multivalent metal or (c) leuco dye as defined above. Preferably, the further at least one additional compound (other than that in the composition according to the first aspect of the present invention) is a leuco dye or oxyanion of a multivalent metal and applied to the substrate as a composition. Thus, according to a third aspect of the present invention, there is provided a method of forming a substrate comprising applying to or incorporating within the substrate a composition according to the first aspect of the present invention.

The composition may be applied to the substrate by any suitable method. Methods of applying the composition to a substrate will be well known to a person skilled in the art. Suitable application methods include, but are not limited to the following: flexographic printing, gravure printing, screen printing, offset printing and meyer bar coating. The composition may be applied to all, substantially all or part of the surface area of an exterior surface of the substrate.

The composition may be applied on a substrate to any suitable coat weight dependent upon both the substrate to which the composition is applied and the application method. It will be appreciated by a skilled person that the coat weight of the composition on the substrate will affect the intensity of the colour of the coloured state of the keto acid compound and, if present, the at least one additional compound. Preferably, the composition is applied to a coat weight of from 0.1 to 50 gsm (grams per square metre), more preferably from 0.1 to 25 gsm and most preferably, 0.1 to 15 gsm. This coat weight is per individual layer of the composition that is applied to the substrate.

The coat weight may be measured by any suitable method. Suitable measuring methods will be well known to those skilled in the art. Preferably, the coat weight is measured by weighing the same area of substrate with and without the composition applied thereto, and comparing the two weights.

The composition may be applied to the substrate as a single layer or as part of a multi-layer system. The composition may be applied to the substrate as an undercoat or an overcoat, on top of a primer or as a primer layer. The composition may be applied to the substrate once or multiple times. The composition may be applied to at least part, or all, of an exterior surface of the substrate. As discussed above in relation to the second aspect of the present invention, a layer comprising an at least one additional compound may be applied underneath the composition applied to the substrate, or applied over the composition applied on the substrate. The composition according to the present invention may be incorporated within the substrate by any suitable method. Methods of incorporating the composition within a substrate will be well known to a person skilled in the art. Suitable incorporation methods include, but are not limited to: extrusion methods including melt extrusion; injection molding; blow molding; compression molding; film insert molding; gas assisted molding; rotational molding; structural foam molding; thermoforming; and combinations thereof.

It will be appreciated by a skilled person that the composition may be incorporated within the substrate on its own or as part of a solid and/or liquid masterbatch.

The composition may be incorporated within a substrate to any suitable weight percentage of the total solid weight of the substrate. Preferably, the substrate comprises 0.001 to 50 % of the composition incorporated within, based on the total solid weight of the substrate. More preferably, the substrate comprises 0.002 to 30 % of the composition incorporated within, based on the total solid weight of the substrate. Most preferably, the substrate comprises 0.003 to 20 % of the composition incorporated within, based on the total solid weight of the substrate.

Preferably, the composition according to the first aspect of the present invention is applied to the substrate.

The application to, or incorporation of the composition within the substrate enables an image to be formed on or within the substrate.

Thus, according to a fourth aspect of the present invention, there is provided a method of forming colour on or within a substrate comprising the composition according to the first aspect of the present invention applied to or incorporated within, the method comprising applying the applied transition stimulus to the composition on or within the substrate as required to develop the coloured state of the keto acid compound of formula (I) of the composition.

According to a fifth aspect of the present invention, there is provided a method of forming an image on or within a substrate comprising the composition according to the first aspect of the present invention applied to or incorporated within, the method comprising applying the applied transition stimulus to the composition on or within the substrate as required to develop the coloured state of the keto acid compound of formula (I) of the composition, and thereby form an image on or within the substrate.

It will be understood by a skilled person that the applied transition stimulus may be applied to the composition such that the non-coloured state and/or coloured state of the keto acid compound are present at different localised positions of the composition to create an image. The coloured state of the keto acid compound may be selectively developed at localised positions. Suitable means for applying the applied transition stimulus are as discussed above.

It will also be appreciated that if the composition further comprises at least one additional compound, the method of forming an image on the substrate comprising the composition may include the application of an additional applied stimulus to effect the transition of the at least one additional compound from its non-coloured state to a coloured state. In addition, if the composition comprises at least one additional compound, it will be appreciated that the application of the applied transition stimulus and the additional applied stimulus will be conducted in the appropriate order as required to selectively develop the non-coloured and/or coloured states of the keto acid compound and at least one additional compound at localised positions of the composition. When the composition comprises at least one additional compound, suitable means for applying the additional applied stimulus or additional temperature are as discussed above.

It will be understood by a skilled person that more than one of the applied transition stimulus and additional applied stimulus may be applied at the same localised position. For example, in order to form a colour resulting from the mixing of two colours (i.e. the mixing of the colours of a coloured state of the keto acid compound and a coloured state of an at least one additional compound of a different colour), the applied transition stimulus and additional applied stimulus may be applied at that particular localised position of the composition. It will further be appreciated by a skilled person that the specific applied transition stimulus and additional applied stimulus will be selected dependent upon the colours required in the image to be formed. The radiation or temperature for each of the two stimuli will be selected so as to facilitate the formation of the desired image.

Optionally, a separate conductive source of temperature may be provided to the composition before, during or after the formation of the image. Conductive sources include, but are not limited to the following: sources of steam and hot air, lamps, heat tunnels, LED(s), thermal print heads, hotplates, thermal conductors, hot liquids and heated substrates.

According to a sixth aspect of the present invention, there is provided a use of the composition according to the first aspect of the present invention in the formation of colour on or within a substrate.

According to a seventh aspect of the present invention, there is provided a use of the composition according to the first aspect of the present invention in the formation of an image on or within a substrate.

According to an eighth aspect of the present invention, there is provided a substrate having applied thereon a plurality of discrete layers, wherein at least one of the discrete layers comprises a keto acid compound and an acid- generating agent, the keto acid compound being capable of transitioning from a non-coloured state to a coloured state, the transition being effected by the application of an applied transition stimulus, wherein the keto acid compound is of formula (I):

wherein Xi _a , X _2a , and X _3a are independently selected from C, N, B and S; the two R groups may be the same or different, and are independently selected from: hydrogen; Ci-i ₈ alkyl; Ce-^aryl optionally substituted with Ci-i ₈ alkoxy, -CN, -

CF ₃ , -NO2, halogen, or CMS alkyl; halogen; -N0 ₂ ; -CF ₃ ; -OR ³ ; -NR CN; -SR

COR ³ ; -C0 ₂ R ³ ; and -CONR ³ ₂ ; wherein R ³ is selected from an alkali metal; hydrogen; Ci-i ₈ alkyl; and Ce-^ aryl optionally substituted with Ci-i ₈ alkoxy, -CN, - CF ₃ , -N0 ₂ , halogen, or CMS alkyl; or both R groups, together with the nitrogen atom to which they are attached, join together to form a cyclic amino group, wherein the cyclic amino group is optionally substituted with CMS alkoxy, -CN, - CF ₃ , -N0 ₂ , halogen, or CMS alkyl; A may be the same as or different to B’ (defined below), and is independently selected from: hydrogen; Ci-i ₈ alkyl; C _6- 12 aryl optionally substituted with CM S alkoxy, -CN, -CF ₃ , -N0 ₂ , halogen, or CMS alkyl; a heterocyclic ring; a heteroaryl; halogen; -N0 ₂ ; -CF ₃ ; -OR ³ ; -NR ³ ₂ ; -CN; -SR ³ ; -COR ³ ; -C0 ₂ R ³ ; -CONR ³ ₂ ; wherein R ³ is selected from an alkali metal; hydrogen; Ci-i ₈ alkyl; and C _6- 12 aryl optionally substituted with CMS alkoxy, -CN, -CF ₃ , -N0 ₂ , halogen, or CMS alkyl; and

R ¹ is selected from

wherein Xi _b , X _2b , X3 _b and X _4b are independently selected from C, N, B and S; and B’ is the same or different to A and is independently selected from hydrogen; Ci-i ₈ alkyl; C _6- 12 aryl optionally substituted with CMS alkoxy, -CN, -CF ₃ , -N0 ₂ , halogen, or CMS alkyl; a heterocyclic ring; a heteroaryl; halogen; -N0 ₂ ; -CF ₃ ; - OR ³ ; -NR ³ ₂ ; -CN; -SR ³ ; -COR ³ ; -C0 ₂ R ³ ; -CONR ³ ₂ ; wherein R ³ is selected from an alkali metal; hydrogen; Ci-i ₈ alkyl; and Ce-^ aryl optionally substituted with Ci_ is alkoxy, -CN, -CF ₃ , -N0 ₂ , halogen, CMS alkyl, hydroxyl (-OH), or -NR ₂ wherein R is as defined above; and wherein at least one of the discrete layers comprises at least one additional compound capable of transitioning from a non-coloured state to a coloured state, the transition being effected by the application of an additional applied stimulus; wherein, if formed, the coloured state of the keto acid compound of formula (I) and the at least one additional compound are different in colour, and the discrete layer comprising the keto acid compound of formula (I) is a different layer to the discrete layer comprising the at least one additional compound.

In the eighth aspect of the present invention, the keto acid compound of formula (I), acid-generating agent and at least one additional compound are as defined above throughout the first to seventh aspects of the present invention. In addition, the applied transition stimulus and additional applied stimulus are as defined above throughout the first to seventh aspects of the present invention. It will further be appreciated that the substrate according to the eighth aspect of the present invention is based upon the substrate according to the second aspect of the present invention, the substrate according to the second aspect of the present invention having a composition layer applied to or incorporated within and the substrate according to the eighth aspect of the present invention having a plurality of discrete layers applied thereon.

The plurality of discrete layers may further comprise one or more additional layers. Suitable additional layers may be selected from, but not limited to: thermal insulating layers; polymer layers; radiation blocking layers such as layers comprising UV absorbing components or layers comprising UV absorbing components; primers; adhesion promoting layers; overprint varnish layers; barrier layers; diffusion barrier layers; quenching layers; layers comprising hindered amine light stabilisers; and combinations thereof.

It will be appreciated by a skilled person that the plurality of discrete layers may comprise more than one at least one additional compound. The plurality of discrete layers may further comprise a second of an at least one additional compound. This second of an at least one additional compound may be present in the discrete layer comprising the keto acid compound of formula (I), the different discrete layer comprising the at least one additional compound, or a separate different discrete layer of the plurality of discrete layers. Preferably, the second of the at least one additional compound is present in a separate discrete layer of the plurality of discrete layers. Accordingly, the substrate may comprise a first discrete layer comprising the keto acid compound of formula (I) and an acid-generating agent, a second different discrete layer comprising an at least one additional compound, and a third different discrete layer comprising the second of an at least one additional compound. It will be understood that the at least one additional compound and the second of an least one additional compound will be selected dependent upon the colours required, and will be different. By different is meant that the two at least one additional compounds are selected either from different groups of (a) a diacetylene compound, (b) oxyanion of a multivalent metal or (c) leuco dye as defined above, or are selected from the same group (a), (b) or (c), but are selected so as to be different compounds in that group, e.g. two different leuco dyes. Preferably, the two at least one additional compounds are selected from different groups of (a) a diacetylene compound, (b) oxyanion of a multivalent metal or (c) leuco dye as defined above.

It will be further appreciated that the discrete layer comprising the keto acid compound of formula (I) and the acid-generating agent may be formed of a composition applied to the substrate. In this regard, the composition is as defined above for the first aspect of the present invention. The at least one additional compound present in a different discrete layer of the plurality of discrete layers applied to the substrate according to the eighth aspect of the present invention may be present as a composition that forms the different layer of the plurality of discrete layers. When the at least one additional compound is present in a composition in a separate layer of the plurality of discrete layers, the at least one additional compound may be present in any suitable amount, preferably from 5 to 60% of the total solid weight of the composition, more preferably from 5 to 50%, or 5 to 35% of the total solid weight of the composition, or even from 5 to 15% of the total solid weight of the composition. Such compositions are formulated with other components such as NIR absorbers, binders, solvents and additives as defined above in relation to the composition of the first aspect of the present invention, the keto acid compound of formula (I) being replaced by the at least one additional compound.

Preferably, the plurality of discrete layers comprises a keto acid compound of formula (I) and a diacetylene compound, the two compounds being in different discrete layers.

Preferably, the plurality of discrete layers comprises comprises a keto acid compound of formula (I), a diacetylene compound and an oxyanion of a multivalent metal. Preferably, the three components are each in a different discrete layer.

It will be appreciated by a skilled person that if the plurality of discrete layers comprises one or more additional layers and these one or more additional layers are positioned between the discrete layer comprising the keto acid compound of formula (I) and the discrete layer comprising the at least one additional compound, the one or more additional layers mean that the applied transition stimulus and additional applied stimulus can be applied to the substrate from both sides in order to form multi-coloured images, the two sides being defined by the one or more additional layers.

The plurality of discrete layers may have any suitable overall coat weight. Preferably, the plurality of discrete layers individually have a coat weight as set out above in relation to the composition according to the first aspect of the present invention. Further, preferably the plurality of discrete layers have an overall coat weight (encompassing all layers) of less than 100 gsm (grams per square metre), more preferably less than 50 gsm, and most preferably less than 30 gsmlt will be appreciated by a skilled person that the overall coat weight of the plurality of discrete layers will be dependent upon the layer formation and the substrate. The substrate according to the eighth aspect of the present invention may be suitable for end use as labels (adhesive and wraparound) and/or, in fast-moving consumer goods; packaging such as disposable packaging including food and hot or cold beverage containers; hygiene and personal care product packaging such as shampoo bottles; cosmetic product packaging; medical and diagnostic devices and associated packaging; and outdoor products such as signage.

The plurality of discrete layers may be applied to any suitable substrate. It will be appreciated by a skilled person that the layer structure of the plurality of discrete layers may vary depending on the substrate to which it is to be applied. The substrates to which the plurality of discrete layers may be applied are as described above in relation to the substrate according to the second aspect of the present invention.

Examples of suitable substrates to which the plurality of discrete layers may be applied to, include, but are not limited to: polymers and recycled polymer materials such as polyethylene terephthalate (PET), polyethylene (PE), low density polyethylene (LDPE), high density polyethylene (HDPE), polystyrene (PS), polypropylene (PP), orientated polypropylene (OPP), biaxially orientated polypropylene (BOPP), cast polypropylene (CPP), polyamide (PA) such as nylon, polyvinyl chloride (PVC), or combinations thereof; cellulose; glass; plastic; metal and metal foils; textiles; paper; corrugated paperboard, cardboard, and equivalent recycled analogues, or combinations thereof; ceramics; foodstuffs and pharmaceutical preparations; or combinations thereof, e.g. polymer lined paper. The polymers and recycled polymer materials may be in the form of polymer film substrates.

Preferably, the substrate to which the plurality of discrete layers is applied is a polymer film substrate. Preferably, the substrate is colourless (i.e. transparent or translucent), off-white or white.

It will be appreciated by a skilled person that the substrate to which the plurality of discrete layers has been applied to may itself be applied to a further substrate. Examples of further substrates include, but are not limited to the following: polymers and recycled polymer materials such as polyethylene terephthalate (PET), polyethylene (PE), low density polyethylene (LDPE), high density polyethylene (HDPE), polystyrene (PS), polypropylene (PP), orientated polypropylene (OPP), biaxially orientated polypropylene (BOPP), cast polypropylene (CPP), polyamide (PA) such as nylon, polyvinyl chloride (PVC), or combinations thereof; cellulose; glass; plastic; metal and metal foils; textiles; paper; corrugated paperboard, cardboard, and equivalent recycled analogues, or combinations thereof; ceramics; foodstuffs and pharmaceutical preparations; or combinations thereof, e.g. polymer line paper. The polymers and recycled polymer materials may be in the form of polymer film substrates. Preferably, the substrate to which the plurality of discrete layers is applied comprises an additional adhesive layer. It will be appreciated that this additional adhesive layer is operable to apply the substrate to a further substrate and is therefore on an exterior surface of the substrate. The adhesive layer may cover all, substantially all, or part of the surface area of an exterior surface of the substrate.

Thus, according to a ninth aspect of the present invention there is provided a method of forming the substrate according to the eighth aspect of the present invention, the method comprising applying to a substrate a plurality of discrete layers. The plurality of discrete layers may be applied to the substrate by any suitable method. Methods of applying the plurality of discrete layers to the substrate will be well known to a person skilled in the art. Suitable application methods include, but are not limited to the following: flexographic printing, gravure printing, screen printing, offset printing and meyer bar coating. The plurality of discrete layers may be applied to all, substantially all or part of the surface area of the substrate. The plurality of discrete layers are applied to the substrate layer by layer in the required order.

The application of the plurality of discrete layers to the substrate enables an image to be formed on the substrate. Thus, according to a tenth aspect of the present invention, there is provided a method of forming colour on the substrate according to the eighth aspect of the present invention, the method comprising applying the applied transition stimulus and additional applied stimulus to the substrate as required to develop the coloured state of the keto acid compound of formula (I) and at least one additional compound.

According to an eleventh aspect of the present invention, there is provided a method of forming colour on the substrate according to the eighth aspect of the present invention, the method comprising applying the applied transition stimulus and additional applied stimulus to the substrate as required to develop the coloured state of the keto acid compound of formula (I) and the at least one additional compound, and thereby form an image on the substrate.

It will be appreciated that the methods of forming colour and an image according to the tenth and eleventh aspects of the present invention required similar considerations to those defined above for the fourth and fifth aspects of the present invention.

It will be understood by a skilled person that the applied transition stimulus and additional applied stimulus may be applied to the substrate such that the non- coloured state and/or coloured state of the keto acid compound of formula (I) and the at least one additional compound are present at different localised positions of the composition to create an image. The coloured state of the keto acid compound of formula (I) and the at least one additional compound may be selectively developed at localised positions. Suitable means for applying the applied transition stimulus and additional applied stimulus are as defined above. The application of the applied transition stimulus and the additional applied stimulus will be conducted in the appropriate order as required to selectively develop the coloured states of the keto acid compound of formula (I) and at least one additional compound. It will also be appreciated that when the at least one additional compound is a diacetylene compound, different additional applied stimulus (additional radiation and additional temperature) may be applied at the same localised position to facilitate a transition from the non-coloured to the first coloured state, as well as a transition from the first coloured state to the second coloured state. Multi-coloured images can be formed.

It will be understood by a skilled person that more than one of the applied transition stimulus and additional applied stimulus may be applied at the same localised position. For example, in order to form a colour resulting from the mixing of two colours (i.e. the mixing of the colours of a coloured state of the keto acid compound and a coloured state of an at least one additional compound of a different colour), the applied transition stimulus and additional applied stimulus may be applied at that particular localised position.

It will be appreciated by a skilled person that the ordering of the plurality of discrete layers on the substrate according to the eighth aspect of the present invention can have an effect on colour formed. When the means used to apply the applied transition stimulus or additional applied stimulus is a laser source(s), the fluence received by each layer varies dependent upon the position of the keto acid compound of formula (I) and the at least one additional compound in the layer structure of the plurality of discrete layers relative to the means.

It will further be appreciated by a skilled person that dependent upon the required image to be formed, the relationship between the applied transition stimulus and the additional applied stimulus will vary. The specific applied transition stimulus and additional applied stimulus will be selected dependent upon the colours required in the image to be formed. The radiation or temperature for each of the two stimuli will be selected so as to facilitate the formation of the desired image.

Optionally, a separate conductive source of temperature may be provided to the composition before, during or after the formation of the image. Conductive sources include, but are not limited to the following: sources of steam and hot air, lamps, heat tunnels, LED(s), thermal print heads, hotplates, thermal conductors, hot liquids and heated substrates.

According to a twelfth aspect of the present invention, there is provided a use of a keto acid compound in the formation of colour on a substrate, the keto acid compound capable of transitioning from a non-coloured state to a coloured state, the transition being effected by the application of an applied transition stimulus, wherein the keto acid compound is of formula (I):

wherein Xi _a , X _2a , and X _3a are independently selected from C, N, B and S; the two R groups may be the same or different, and are independently selected from: hydrogen; Ci-i ₈ alkyl; C ₆ -i ₂ aryl optionally substituted with Ci-i ₈ alkoxy, -CN, -

CF ₃ , -NO2, halogen, or CMS alkyl; halogen; -N0 ₂ ; -CF ₃ ; -OR ³ ; -NR CN; -SR

COR ³ ; -C0 ₂ R ³ ; and -CONR ³ ₂ ; wherein R ³ is selected from an alkali metal; hydrogen; Ci-i ₈ alkyl; and C ₆ -i ₂ aryl optionally substituted with Ci-i ₈ alkoxy, -CN, - CF ₃ , -N0 ₂ , halogen, or CMS alkyl; or both R groups, together with the nitrogen atom to which they are attached, join together to form a cyclic amino group, wherein the cyclic amino group is optionally substituted with CMS alkoxy, -CN, - CF ₃ , -N0 ₂ , halogen, or CMS alkyl; A may be the same as or different to B’ (defined below), and is independently selected from: hydrogen; Ci-i ₈ alkyl; C _6-i2 aryl optionally substituted with CM S alkoxy, -CN, -CF ₃ , -N0 ₂ , halogen, or CMS alkyl; a heterocyclic ring; a heteroaryl; halogen; -N0 ₂ ; -CF ₃ ; -OR ³ ; -NR ³ ₂ ; -CN; -SR ³ ; -COR ³ ; -C0 ₂ R ³ ; -CONR ³ ₂ ; wherein R ³ is selected from an alkali metal; hydrogen; Ci-i ₈ alkyl; and C _6-i2 aryl optionally substituted with CMS alkoxy, -CN, -CF ₃ , -N0 ₂ , halogen, or CMS alkyl; and

R ¹ is selected from wherein Xi _b , X _2b , X3 _b and X _4b are independently selected from C, N, B and S; and B’ is the same or different to A and is independently selected from hydrogen; C1-18 alkyl; C ₆ -12 aryl optionally substituted with Ci-i ₈ alkoxy, -CN, -CF ₃ , -N0 ₂ , halogen, or Ci-i ₈ alkyl; a heterocyclic ring; a heteroaryl; halogen; -N0 ₂ ; -CF ₃ ; - OR ³ ; -NR ³ ₂ ; -CN; -SR ³ ; -COR ³ ; -C0 ₂ R ³ ; -CONR ³ ₂ ; wherein R ³ is selected from an alkali metal; hydrogen; Ci-i ₈ alkyl; and C ₆ -i ₂ aryl optionally substituted with Ci_ 18 alkoxy, -CN, -CF ₃ , -N0 ₂ , halogen, Ci-i ₈ alkyl, hydroxyl (-OH), or -NR ₂ wherein R is as defined above. According to a thirteenth aspect of the present invention, there is provided a use of a keto acid compound in the formation of an image on a substrate, the keto acid compound capable of transitioning from a non-coloured state to a coloured state, the transition being effected by the application of an applied transition stimulus, wherein the keto acid compound is of formula (I):

wherein Xi _a , X _2a , and X _3a are independently selected from C, N, B and S; the two R groups may be the same or different, and are independently selected from: hydrogen; Ci-i ₈ alkyl; C ₆ -i ₂ aryl optionally substituted with Ci-i ₈ alkoxy, -CN, -

CF ₃ , -N0 ₂ , halogen, or Ci-i ₈ alkyl; halogen; -N0 ₂ ; -CF ₃ ; -OR ³ ; -NR CN; -SR COR ³ ; -C0 ₂ R ³ ; and -CONR ³ ₂ ; wherein R ³ is selected from an alkali metal; hydrogen; Ci-i ₈ alkyl; and C ₆ -i ₂ aryl optionally substituted with Ci-i ₈ alkoxy, -CN, - CF ₃ , -NO2, halogen, or C _1-18 alkyl; or both R groups, together with the nitrogen atom to which they are attached, join together to form a cyclic amino group, wherein the cyclic amino group is optionally substituted with C _{M S} alkoxy, -CN, - CF ₃ , -NO2, halogen, or C _{M S} alkyl; A may be the same as or different to B’ (defined below), and is independently selected from: hydrogen; Ci-i ₈ alkyl; C _6- 12 aryl optionally substituted with C _{M S} alkoxy, -CN, -CF ₃ , -N0 ₂ , halogen, or C _{M S} alkyl; a heterocyclic ring; a heteroaryl; halogen; -N0 ₂ ; -CF ₃ ; -OR ³ ; -NR ³ ₂ ; -CN; -SR ³ ; -COR ³ ; -C0 ₂ R ³ ; -CONR ³ ₂ ; wherein R ³ is selected from an alkali metal; hydrogen; Ci-i ₈ alkyl; and C _6- 12 aryl optionally substituted with C _{M S} alkoxy, -CN, -CF ₃ , -N0 ₂ , halogen, or C _{M S} alkyl; and

R ¹ is selected from

wherein Xi _b , X _2b , X3 _b and X _4b are independently selected from C, N, B and S; and B’ is the same or different to A and is independently selected from hydrogen; Ci-is alkyl; C _6- 12 aryl optionally substituted with C _{M S} alkoxy, -CN, -CF ₃ , -N0 ₂ , halogen, or C _{M S} alkyl; a heterocyclic ring; a heteroaryl; halogen; -N0 ₂ ; -CF ₃ ; - OR ³ ; -NR ³ ₂ ; -CN; -SR ³ ; -COR ³ ; -C0 ₂ R ³ ; -CONR ³ ₂ ; wherein R ³ is selected from an alkali metal; hydrogen; Ci-i ₈ alkyl; and Ce-^ aryl optionally substituted with Ci_ is alkoxy, -CN, -CF ₃ , -N0 ₂ , halogen, C _{M S} alkyl, hydroxyl (-OH), or -NR ₂ wherein R is as defined above.

It will be appreciated by a skilled person that for the twelfth and thirteenth aspects of the present invention, the keto acid compound of formula (I) is as described above for the first aspect of the present invention. In addition, the applied transition stimulus is as described above for the first aspect of the present invention. It will be appreciated by a skilled person that the radiation applied to the compositions or substrates disclosed herein as any of the applied transition stimulus, applied additional stimulus or additional temperature, whether by a laser source(s) or flood illumination, is applied using an apparatus suitable for such purpose, i.e. suitable for calculating the radiation required relating to the different stimuli and temperatures required to produce a desired image and applying it to a composition on or within a substrate or substrate having a plurality of discrete layers. It will be appreciated that the apparatus will be programmed to effect the application of the different stimuli and temperature to the compositions or substrates in the required order and facilitate the formation of an image.

Chemical Definitions

The term "C _{M S} alkyl" demotes a straight or branched saturated alkyl group having from 1 to 18 carbon atoms; optionally "C _{M S} alkyl" groups can contain some degree of unsaturation (partial unsaturation) i.e. may contain one or more alkene/alkenyl moiety(s). For parts of the range C _{M S} alkyl, all sub-groups thereof are contemplated, such as C _{M O} alkyl, C _{5-i 5} alkyl, C _{5-i 0} alkyl, and Ci _-6 alkyl. Examples of said Ci _-4 alkyl groups include methyl, ethyl, n-propyl, iso- propyl, n-butyl, iso-butyl, sec-butyl, and tert-butyl. The alkyl groups may be optionally substituted with one or more functional groups, including C _{M S} alkyl groups, "C _6-12 aryl", and "C _{M S} alkoxy", halogen, and "C _3-i8 cycloalkyl".

The term "C _6-12 aryl" denotes a monocyclic or polycyclic conjugated unsaturated ring system having from 6 to 12 carbon atoms. For parts of the range C _6-12 aryl, all sub-groups thereof are contemplated, such as C _6-i o aryl, C _10-12 aryl, and C ₆ -s aryl. An aryl group includes condensed ring groups such as monocyclic ring groups, or bicyclic ring groups. Examples of C _6-12 aryl groups include phenyl, biphenyl, indenyl, naphthyl or azulenyl. Condensed rings such as indan and tetrahydro naphthalene are also included in the C _6-12 aryl group. The aryl groups may be optionally substituted with other functional groups. The aryl groups may be optionally substituted with one or more functional groups, including C _{M S} alkyl groups, halogen, and "C _{M S} alkoxy". The aryl groups may be substituted with these substituents at a single position on their unsaturated ring system, or may be substituted with these substituents at multiple positions on their unsaturated ring system.

The term "C _{M S} alkoxy" denotes a straight of branched C _{M S} alkyl group which is attached to the remainder of the molecule through an oxygen atom. For parts of the range C _{M S} alkoxy, all sub-groups thereof are contemplated such as C _{M O} alkoxy, C _{5-i 5} alkoxy, C _5-i0 alkoxy, and Ci _-6 alkoxy. Examples of said Ci _-4 alkoxy groups include methoxy, ethoxy, n-propoxy, iso-propoxy, n-butoxy, iso-butoxy, sec-butoxy, and tert-butoxy. The alkoxy groups may be optionally substituted with other functional groups. The alkoxy groups may be optionally substituted with one or more functional groups, including C _{M S} alkyl groups, "C _6- 12 aryl", and "Ci-is alkoxy", halogen, and "C _3-i8 cycloalkyl".

The term "C _3-i8 cycloalkyl" denotes a non-aromatic, saturated or partially saturated (i.e. may contain one or more alkene or alkenyl moiety(s)) monocyclic ring system having from 3 to 18 carbon atoms. For parts of the range C _{3-i 8} cycloalkyl, all sub-groups thereof are contemplated, such as C _3-8 cycloalkyl, C _{5-i 5} cycloalkyl, and C _5-i0 cycloalkyl. Examples of suitable C _3-i0 cycloalkyls include cyclopropyl, cyclobutyl, cyclopentyl, cyclohexyl and cycloheptyl. The cycloalkyl groups may be optionally substituted with other functional groups. The cycloalkyl groups may be optionally substituted with one or more functional groups, including Ci _-20 alkyl groups, "C _5-2 o aryl", "Ci _-20 alkoxy", "hydroxylCi _-2 o alkoxy" and "C _{3-i 8} cycloalkyl".

The terms“unsaturated” and“partially saturated” refer to rings wherein the ring structure(s) contains atoms sharing more than one valence bond i.e. the ring contains at least one multiple bond e.g. a C=C, CºC or N=C bond. The term “fully saturated” refers to rings where there are no multiple bonds between ring atoms.

“Optional” or “optionally” means that the subsequently described event or circumstance may but need not occur, and that the description includes instances where the event or circumstance occurs and instances in which it does not.

"Halogen" refers to fluorine, chlorine, bromine or iodine.

The term "heterocycle" and "heterocyclic ring" denotes a non-aromatic, saturated or partially saturated monocyclic or polycylic ring system having from 4 to 18 ring atoms in which one or more of the ring atoms is not carbon, e.g. nitrogen, sulphur or oxygen. The said ring system may be attached to the rest of the molecule through either a heteroatom or a carbon atom of the ring system. Examples of heterocyclic groups include but are not limited to: piperidinyl, morpholinyl, homomorpholinyl, azepanyl, piperazinyl, oxo-piperazinyl, diazepinyl, tetrahydropyridinyl, tetrahydropyranyl, pyrrolidinyl, tetrahydrofuranyl and dihydropyrrolyl.

The terms “heteroaryl” and “heteroaromatic ring” denote a monocyclic or polycyclic hetero-aromatic group comprising 5 to 18 atoms in which one or more of the atoms are other than carbon, such as nitrogen, phosphorus, sulphur or oxygen. The said hetero-aromatic ring may be attached to the rest of the molecule through either a heteroatom or a carbon atom of the ring system. Examples of heteroaryl groups include but are not limited to furyl, pyrrolyl, thienyl, oxazolyl, isoxazolyl, oxadiazolyl, imidazolyl, oxatriazoly, thiazolyl, isothiazolyl, tetrazolyl, pyrazolyl, pyridinyl, pyrimidinyl, pyridazinyl, pyrazinyl, triazinyl and thiadiazolyl. In some embodiments, the heteroaryl group contains at least one ring nitrogen atom. The nitrogen atoms in the heteroaryl groups can be basic, as in the case of an imidazole or pyridine, or essentially non-basic as in the case of an indole or pyrrole nitrogen. In general the number of basic nitrogen atoms present in the heteroaryl group, including any amino group substituents of the ring, will be less than five.

The term “cyclic amino group” refers to a non-aromatic, fully saturated or partially unsaturated monocyclic ring system having from 4 to 18 ring atoms in which one of the ring atoms is nitrogen and the group is attached to the rest of the molecule via this nitrogen atom. In such cyclic amino groups, one or more of the remaining ring atoms may be other than carbon, such as nitrogen, sulphur or oxygen. Examples of such cyclic amino groups include piperidine (1 -piperidinyl), pyrrolidine (1 -pyrrolidinyl), pyrrolidone, morpholine or piperazine.

All of the features contained herein may be combined with any of the above aspects and in any combination.

For a better understanding of the present invention, and to show how embodiments of the same may be carried into effect, reference will now be made, by way of example, to the following experimental data.

Examples

The keto acid compounds of formula (I) used in the following examples can be purchased from Chameleon Speciality Chemicals Ltd, or formulated according to the following syntheses.

Generic Synthesis of a Keto Acid Compound of Formula (I)

The amino-phenol (1 equivalent) and anhydride (1 equivalent) are weighed into a round bottom flask fitted with a stirrer bar, thermometer and reflux condenser. The solids are suspended in toluene (0.3 to 2.0 molar solution) and refluxed for 18 hours. The reaction mixture is allowed to cool to room temperature and the solvent removed on a roto-evaporator. The product is isolated by flash column chromatography eluting with a polarity gradient from Heptane/DCM 1 :1 to DCM 20 % ethyl acetate. The column fractions are concentrated on a roto-evaporator to ~0.5 L and precipitated by adding the solution to a beaker of stirred Heptane (1 to 2 L). The precipitate is vacuum filtered onto paper, dried by suction for around 10 minutes then transferred to a drying dish and dried in a vacuum oven (20 °C) overnight yielding the product as a pale coloured powder.

Specific Synthesis of (2-(4-(dimethylamino)-2-hvdroxybenzoyl)benzoic acid

3-(Dimethylamino)phenol (26.0 g, 190 mmol) and Phthalic anhydride (28.07 g, 189.5 mmol) were weighed into a round bottom flask fitted with a stirrer bar, thermometer and reflux condenser. The solids were suspended in toluene (100 ml_) and reflux for 18 hours. The reaction mixture was allowed to cool to room temperature and the solvent removed on a roto-evaporator. The residue was extracted into ethyl acetate (500 ml_) with sonication and heating. The mixture was filtered through sintered glass. The filtrate was precipitated by addition of heptane (500 ml_) and the dark solids vacuum filtered onto paper. The solids were dissolved in dichloromethane (300 ml_) and passed through a silica pad eluting with dichloromethane until the filtrate ran clear. The dichloromethane solution was concentrated on a roto-evaporator to ~0.5 L and was precipitated by adding the dichloromethane solution to a beaker of stirred Heptane (1 L). The precipitate was vacuum filtered onto paper, dried by suction for around 10 minutes then transferred to a drying dish and dried in a vacuum oven (20 °C) overnight yielding the product as a beige coloured powder (22.23 g, 77.92 mmol, 41.1 %).

Specific Synthesis of (2-(4-(diethylamino)-2-hvdroxybenzoyl)-5-nitrobenzoic acid

3-(Diethylamino)phenol (21.47 g, 129.9 mmol) and 4-nitro-phthalic anhydride (25.07 g, 129.8 mmol) were weighed into a round bottom flask fitted with a stirrer bar, thermometer and reflux condenser. The solids were suspended in toluene (100 ml_) and reflux for 18 hours. The reaction mixture was allowed to cool to room temperature and the solvent removed on a roto-evaporator. The product was isolated by flash column chromatography eluting with a polarity gradient from Heptane/DCM 1 :1 to DCM 10 % ethyl acetate. The column fractions were concentrated on a roto-evaporator to -0.5 L and was precipitated by adding the solution to a beaker of stirred heptane (1 L). The precipitate was vacuum filtered onto paper, dried by suction for around 10 minutes then transferred to a drying dish and dried in a vacuum oven (20 °C) overnight yielding the product as a pale-yellow coloured powder (7.60 g, 21.2 mmol, 16.3 %).

Specific _ Synthesis _ of _ (2,3,4,5-tetrachloro-6-(4-(diethylamino)-2- hvdroxybenzovDbenzoic acid

3-(Diethylamino)phenol (22.00 g, 131.1 mmol) and tetrachloro-phthalic anhydride (38.06 g, 131.1 mmol) were weighed into a round bottom flask fitted with a stirrer bar, thermometer and reflux condenser. The solids were suspended in toluene (100 ml_) and reflux for 18 hours. The reaction mixture was allowed to cool to room temperature and the solvent removed on a roto-evaporator. The product was isolated by flash column chromatography eluting with a polarity gradient from Heptane/DCM 1 :1 to DCM 10 % ethyl acetate. The column fractions were concentrated on a roto-evaporator to ~0.5 L and was precipitated by adding the solution to a beaker of stirred heptane (1 L). The precipitate was vacuum filtered onto paper, dried by suction for - 10 mins then transferred to a drying dish and dried in a vacuum oven (20 °C) overnight yielding the product as a yellow coloured powder (15.63 g, 34.65 mmol, 26.02 %). Specific Synthesis of (2,5-bis(4-(diethylamino)-2-hvdroxybenzoyl)terephthalic acid

3-(Diethylamino)phenol (39.3 g, 230 mmol) and pyromellitic anhydride (25.0 g, 1 14.6 mmol) were weighed into a round bottom flask fitted with a stirrer bar, thermometer and reflux condenser. The solids were suspended in toluene (400 mL) and reflux for 18 hours. The reaction mixture was allowed to cool to room temperature and the solvent removed on a roto-evaporator. The product was isolated by flash column chromatography eluting with a polarity gradient from Heptane/DCM 1 :1 to DCM 20 % ethyl acetate. The column fractions were concentrated on a roto-evaporator to ~0.5 L and was precipitated by adding the solution to a beaker of stirred heptane (2 L). The precipitate was vacuum filtered onto paper, dried by suction for - 10 mins then transferred to a drying dish and dried in a vacuum oven (20 °C) overnight yielding the product as a yellow coloured powder (5.84 g, 10.6 mmol, 9.29 %).

Colour Formation Using the Keto Acid Compounds of Formula (I)

For each of the examples, unless otherwise stated, the natural state (non- coloured state) of the keto acid compound of formula (I) and at least one additional compound is either off-white or white. For each of the examples, unless otherwise indicated, the 10.6 pm C0 ₂ laser is set at a speed of 5350 /s and at 38% power. The speed or power of the laser can be altered to vary the fluence applied by the laser source. Marking speeds within the 2600-5350 mm/s range are 2600, 2975, 3325, 3600, 3850, 4100, 4300, 4750, 5050 and 5350 mm/s. Example 1

A composition according to the first aspect of the present invention comprising a keto acid compound of formula (I) and acid-generating agent was formulated according to Table 1. All amounts are provided in weight percentage (wt%).

Table 1

A layer of the composition was applied to a PET using a 16 pm K-bar applicator. The keto acid compound of formula (I) is in its non-coloured state prior to application of the applied transition stimulus. An applied transition stimulus (temperature) was applied to the composition and thus the keto acid compound of formula (I) using a C0 ₂ laser (IR radiation of 1060 nm) to effect a transition from the non-coloured state to a coloured state of the keto acid compound of formula (I). The colour of the coloured state, and intensity thereof, could be changed between yellow or orange by variation of the fluence applied by the C0 ₂ laser.

An image having yellow and orange colours can therefore be formed.

Example 2

A composition according to the first aspect of the present invention comprising a keto acid compound of formula (I) was formulated according to Table 2. All amounts are provided in weight percentage (wt%).

Table 2

A layer of the composition was applied to a PET substrate using a 16 pm K-bar applicator. The keto acid compound of formula (I) is in its non-coloured state prior to application of the applied transition stimulus. An applied transition stimulus (temperature) was applied to the composition and thus the keto acid compound of formula (I) using a C0 ₂ laser (IR radiation of 1060 nm) to effect a transition from the non-coloured to a coloured state of the keto acid compound of formula (I). The colour of the coloured state, and intensity thereof, could be changed between yellow or orange by variation of the fluence applied by the C0 ₂ laser.

An image having yellow and orange colours can therefore be formed.

Example 3 A composition according to the first aspect of the present invention comprising a keto acid compound of formula (I) and acid-generating agent was formulated according to Table 3. All amounts are provided in weight percentage (wt%). Table 3

A layer of the composition was applied to a paper substrate using a K2 K-bar applicator. The keto acid compound of formula (I) is in its non-coloured state prior to application of the applied transition stimulus. An applied transition stimulus (temperature) was applied to the composition and thus the keto acid compound of formula (I) using a 10.6 pm C0 ₂ laser (38% power) to apply IR radiation and effect a transition from the non-coloured to a coloured state of the keto acid compound of formula (I). The colour of the coloured state, and intensity thereof, could be changed between yellow or orange by variation of the fluence applied by the C0 ₂ laser.

An image having yellow and orange colours can therefore be formed. Example 4

A composition according to the first aspect of the present invention comprising a keto acid compound of formula (I) and acid-generating agent was formulated according to Table 4. All amounts are provided in weight percentage (wt%).

Table 4

A composition comprising a diacetylene compound (an‘at least one additional compound’) was formulated according to Table 7, using the millbase formulations of Tables 5 and 6. All amounts are provided in weight percentage (wt%).

Table 5 - Millbase formulation of diacetylene compound

Table 6 - Millbase formulation of NIR absorber

Table 7

A layer of the composition comprising a keto acid compound of formula (I) formulated according to Table 4 was applied to a PET substrate using a 16 pm K-bar applicator. A layer of the composition comprising a diacetylene compound was formulated according to Table 7 was then applied using a 16 pm k-bar applicator on top of the layer of the composition comprising a keto acid compound of formula (I).

The keto acid compound of formula (I) and diacetylene compound are in their non-coloured states. It is noted that the diacetylene compound utilised in this example has a non-coloured state that requires‘activation’, i.e. application of an activation temperature to make it capable of transitioning from the non-coloured to a coloured state.

(Note: The composition comprising a keto acid compound of formula (I) and the composition comprising an additional compound formulated can also be combined and applied to the substrate as a single layer, i.e. a composition according to the first aspect of the present invention).

An applied transition stimulus (temperature) was applied to the substrate at localised positions using a 1070 nm NIR fibre laser to facilitate a transition from the non-coloured to a coloured state of the keto acid compound of formula (I). As discussed above, the colour of the coloured state, and intensity thereof, could be changed between yellow or orange by variation of the fluence applied by the C0 ₂ laser.

The non-coloured state of the diacetylene compound is also‘activated’ at these localised positions by the application of the NIR radiation. It is noted that the activation temperature required to activate the non-coloured state of the diacetylene compound is lower than that required to facilitate the transition of keto acid compound of formula (I) from the non-coloured to a coloured state. Following application of the NIR radiation, UV radiation (an additional applied stimulus: additional radiation) is applied to the substrate by flood illumination using a 254 nm germicidal lamp to effect a transition from the activated non- coloured state of the diacetylene compound to a blue coloured state solely at the localised positions at which the non-coloured state of the diacetylene compound had been activated. As the coloured state of the diacetylene compound is formed at the same localised position at which the coloured state of the keto acid compound of formula (I) has been formed, the final colour displayed at these localised positions is dependent upon the colour of the coloured state of keto acid compound of formula (I), and the blue colour of the coloured state of the diacetylene compound, i.e. the final colour at these localised positions results from the combination of colours of the coloured states of these two components. Accordingly, orange, yellow and green colours may be formed.

To provide a blue colour, prior to the application of the NIR radiation, an activation temperature of around 95 °C can be applied at different localised positions using a 1070 NIR fibre laser to‘activate’ the non-coloured state of the diacetylene compound at those localised positions. The coloured state of the keto acid compound of formula (I) upon application of the NIR radiation is not formed as the activation temperature is lower than the temperature of the applied transition stimulus such that the transition of the keto acid compound of formula (I) is not facilitated. Following further application of UV radiation as the additional applied stimulus (additional radiation) by flood illumination using a 254nm germicidal lamp, the diacetylene compound transitions from the non- coloured to the blue coloured state at the localised positions.

A multi-coloured image may therefore be formed displaying yellow, orange, blue and green colours.

Example 5

A composition according to the first aspect of the present invention comprising a keto acid compound of formula (I) and acid-generating agent was formulated according to Table 3. All amounts are provided in weight percentage (wt%).

A composition comprising an oxyanion of a multivalent metal (an‘at least one additional compound’) was formulated according to Table 8. All amounts are provided in weight percentage (wt%).

Table 8

A composition comprising a leuco dye (an‘at least one additional compound’) was formulated according to Table 9. All amounts are provided in weight percentage.

Table 9

Table 10

A layer of the composition comprising an oxyanion of a multivalent metal was applied to a paper substrate using a K2 K-bar applicator. A layer of the composition comprising a keto acid compound of formula (I) was then applied on top of the layer of the composition comprising an oxyanion of a multivalent metal using a K2 k-bar applicator. A layer of the composition comprising a leuco dye formulated was then applied on top of the layer of the composition comprising a keto acid compound of formula (I) using a K2 k-bar applicator.

The oxyanion of a multivalent metal, keto acid compound of formula (I) and leuco dye are in their non-coloured states.

An additional applied stimulus (additional temperature) was applied to the substrate at localised positions using a 10.6 pm C0 ₂ laser at 20% power to provide IR radiation. At these localised positions, the leuco dye transitions from the non-coloured to a blue coloured state and a blue colour is formed. The intensity of this colour can be varied by variation of the fluence of the laser source(s). It is noted that the applied transition stimulus (temperature) required to facilitate a transition of the keto acid compound of formula (I) from the non-coloured to a coloured state and the additional applied stimulus (additional temperature) required to facilitate a transition of the oxyanion of a multivalent metal from the non-coloured to a coloured state is higher than that of the additional applied stimulus (additional temperature) applied using the C0 ₂ laser at 20% power. It is noted that the temperatures required for the transitions of the keto acid compound of formula (I) and the oxyanion of a multivalent metal are close together. Accordingly, upon application of the applied transition stimulus (additional temperature) using the C0 ₂ laser at 20% power, the transition from the non-coloured to a coloured state of the keto acid compound of formula (I) or the oxyanion of a multivalent metal does not occur.

Alternatively, an applied transition stimulus (additional temperature) was applied to the substrate at localised positions using a 10.6 pm C0 ₂ laser at increased power (38% power). It will be appreciated that this provides a higher temperature to the localised positions than that supplied at 20% power. At these localised positions, the leuco dye again transitions from the non-coloured state to a blue coloured state, the colour formed being more intense given the higher power of the laser source(s) utilised. Increased fluence has thus been applied. In addition, at these localised positions, the additional applied stimulus (additional temperature) required for the transition of the oxyanion of a multivalent metal is achieved, and the applied transition stimulus (temperature) required for the transition of the keto acid compound of formula (I) is achieved. The oxyanion of a multivalent metal transitions from the non-coloured state to a black coloured state. The intensity of this colour can be varied by variation of the fluence of the C0 ₂ laser. Additionally, the keto acid compound transitions from a non-coloured to a coloured state. As discussed above, the colour of the coloured state of the keto acid compound of formula (I), and intensity thereof, can be varied between orange or yellow by variation of the fluence applied by the C0 ₂ laser.

As the coloured state of the leuco dye is formed at the same localised position at which the coloured state of the oxyanion of a multivalent metal and the keto acid compound of formula (I) are formed, the final colour displayed at these localised positions is dependent upon the black coloured state of the oxyanion of a multivalent metal, the blue colour of the coloured state of the leuco dye, and the colour of the coloured state of the keto acid compound of formula (I), i.e. the final colour at these localised positions results from the combination of colours of the coloured states of these three components. Accordingly, blue and black colours can be formed.

A multi-coloured image may therefore be formed displaying blue and black colours. Example 6

A composition according to the first aspect of the present invention comprising a keto acid compound of formula (I) and acid-generating agent was formulated according to Table 3 above. A composition comprising an oxyanion of a multivalent metal (an ‘at least additional compound’) was formulated according to Table 8 above.

A composition comprising a diacetylene compound (an‘at least one additional compound’) was formulated according to Table 13, using the millbase formulations of Tables 1 1 and 12. All amounts are provided in weight percentage (wt%).

Table 11 - Millbase formulation of diacetylene compound

Table 12 - Millbase formulation of NIR absorber

Table 13

A layer of the composition comprising an oxyanion of a multivalent metal was applied to a paper substrate using a K2 K-bar applicator. A layer of the composition comprising a keto acid compound of formula (I) was then applied on top of the layer of the composition comprising an oxyanion of a multivalent metal using a K2 k-bar applicator. A layer of the composition comprising a diacetylene compound was then applied on top of the layer of the composition comprising a keto acid compound of formula (I) using a K2 k-bar applicator.

The oxyanion of a multivalent metal, keto acid compound of formula (I) and diacetylene compound are in their non-coloured states.

Following application of the layers to the substrate, an applied transition stimulus (temperature) is applied to localised positions by IR radiation using a 10.6 pm C0 ₂ laser (20% power). The keto acid compound of formula (I) transitions from the non-coloured state to a yellow coloured state at the localised positions. The intensity of the yellow colour can be varied by alteration of the fluence provided by the C0 ₂ laser.

It is noted that the temperature of the applied transition stimulus required to facilitate a transition of the keto acid compound of formula (I) from the non- coloured state to a coloured state is slightly lower than the additional applied stimulus (additional temperature) required to facilitate a transition of the oxyanion of a multivalent metal from a non-coloured to a coloured state. To provide such an additional temperature to facilitate the transition of the oxyanion of a multivalent metal from a non-coloured to a coloured state, the power of the C0 ₂ laser is increased to 38%. This facilitates the formation of the black coloured state of the oxyanion of a multivalent metal. The intensity of the black colour formed can be made to vary by variation of the fluence provided by the C0 ₂ laser. If the 38% power is utilised, as the coloured state of the oxyanion of a multivalent metal is formed at the same localised position at which the coloured state of the keto acid compound of formula (V) has been formed, the final colour displayed at these localised positions is dependent upon the black colour of the coloured state of the oxyanion of a multivalent metal, and the yellow colour of the coloured state of the keto acid compound of formula (V), i.e. the final colour at these localised positions results from the combination of colours of the coloured states of the two components. Accordingly, different yellow and black coloured states can be formed. It is noted that the activation temperature of the diacetylene compound is lower than both the applied transition stimulus (temperature) and additional applied stimulus (additional temperature) required to facilitate the transitions of the oxyanion of a multivalent metal and the keto acid compound of formula (I). Accordingly, upon application of the IR radiation at the localised positions of the substrate, the non-coloured state of the diacetylene compound is activated at these localised positions.

Upon application of UV radiation to the substrate by flood illumination using a germicidal lamp (additional applied stimulus: additional radiation), the diacetylene compound transitions from the non-coloured state to a first blue coloured state at the localised positions at which the non-coloured state has been‘activated’.

If the UV radiation has been applied following only the application of IR radiation using the C0 ₂ laser at 20% power, the colour displayed at the localised positions will be a combination of the blue of the first coloured state of the diacetylene compound and the yellow coloured state of the keto acid compound of formula (V). Accordingly, different blue and green colours can be formed. If further IR radiation (additional applied stimulus: additional temperature) is applied using the C0 ₂ laser at 20% power at the localised positions at which the first coloured state of the diacetylene compound have been formed, the diacetylene compound transitions from the blue first coloured state to a red second coloured state. The intensity of the colour can be varied by variation of the fluence applied by the C0 ₂ laser. The colour displayed at the localised positions will be a combination of the red of the second coloured state of the diacetylene compound and the yellow coloured state of the keto acid compound of formula (V). Accordingly, different orange and red colours can be formed. It is noted that the temperature required to facilitate the transition of the diacetylene compound from the first coloured state to a second coloured state is lower than the additional temperature of the additional applied stimulus required to facilitate a transition of the oxyanion of a multivalent metal from the non-coloured to the coloured state. Accordingly, if instead the further IR radiation is applied using the C0 ₂ laser at 38% power, the additional temperature of the additional applied stimulus is reached and the oxyanion of a multivalent metal transitions from the non-coloured to a black coloured state. The intensity of the colour can be varied by variation of the fluence applied by the C0 ₂ laser. The colour displayed at the localised positions will be a combination of the red of the second coloured state of the diacetylene compound, the yellow coloured state of the keto acid compound of formula (V), and the black coloured state of the oxyanion of a multivalent metal. Accordingly, different red, brown and black colours can be formed.

Alternatively, if the UV radiation (additional applied stimulus: additional radiation) has been applied following the application of IR radiation using a C0 ₂ laser at 38% power, the colour display at the localised positions will be a combination of the blue of the first coloured state of the diacetylene compound, the yellow coloured state of the keto acid compound of formula (V), and the black coloured state of the oxyanion of a multivalent metal. Accordingly, different green and black colours can be formed.

A multi-coloured image displaying yellow, black, green, blue, red, orange and brown colours can therefore be formed.

Example 7 A composition according to the first aspect of the present invention comprising a keto acid compound of formula (I) and acid-generating agent was formulated according to Table 3 above.

A composition comprising a leuco dye (an‘at least one additional compound’) was formulated according to Table 9 above.

A layer of the composition comprising a keto acid compound of formula (I) was applied to a paper substrate using a K2 k-bar applicator. A layer of the composition comprising a leuco dye was then applied on top of the layer of the composition comprising a keto acid compound of formula (I) using a K2 k-bar applicator.

The keto acid compound of formula (I) and leuco dye are in their non-coloured states.

An additional applied stimulus (additional temperature) was applied to the substrate at localised positions using a 10.6 pm C0 ₂ laser at 20% power. At these localised positions, the leuco dye transitions from the non-coloured to a blue coloured state and a blue colour is formed. The intensity of this colour can be varied by variation of the fluence applied by the laser.

It is noted that the applied transition stimulus (temperature) required to facilitate a transition of the keto acid compound of formula (I) from the non-coloured to a coloured state is higher than that of the additional applied stimulus (additional temperature) applied using the C0 ₂ laser at 20% power. Accordingly, upon application of the additional temperature using the C0 ₂ laser at 20% power, the transition from the non-coloured to a coloured state of the keto acid compound of formula (I) does not occur.

Alternatively, an additional applied stimulus (additional temperature) is applied to the substrate at localised positions using a 10.6 pm C0 ₂ laser at 38% power to provide IR radiation. It will be appreciated that this provides a higher temperature than that supplied at 20% power. At these localised positions, the leuco dye transitions from the non-coloured state to a blue coloured state, the colour formed being more intense given the higher power of the laser source(s) utilised. Increased fluence has thus been applied. In addition, upon application of the IR radiation using a C0 ₂ laser at 38% power, the applied transition stimulus (temperature) required for the transition of the keto acid compound of formula (I) is achieved, and the keto acid compound transitions from a non- coloured to a coloured state. As discussed above, the colour of the coloured state, and intensity thereof, can be changed between yellow or orange by variation of the fluence applied by the C0 ₂ laser.

As the coloured state of the leuco dye is formed at the same localised position at which the coloured state of the keto acid compound of formula (I) is formed, the final colour displayed at these localised positions is dependent upon the colour of the blue coloured state of the leuco dye, and the colour of the coloured state of the keto acid compound of formula (I), i.e. the final colour at these localised positions results from the combination of colours of the coloured states of the two components. Accordingly, light to dark turquoise colours can be formed.

A multi-coloured image may be formed displaying light to dark turquoise colours.

Example 8

A composition according to the first aspect of the present invention comprising a keto acid compound of formula (I) and acid-generating agent was formulated according to Table 3 above.

A composition comprising a diacetylene compound (an‘at least one additional compound’) was formulated according to Table 13 above, using the millbase formulations of Tables 11 and12.

A layer of the composition comprising a keto acid compound of formula (I) was applied to a paper substrate using a K2 k-bar applicator. A layer of the composition comprising a diacetylene compound was then applied on top of the layer of the composition comprising a keto acid compound of formula (I) using a K2 k-bar applicator. The keto acid compound of formula (I) and diacetylene compound are in their non-coloured states.

Upon application of an activation temperature using a C0 ₂ laser (20% power) to provide IR radiation at localised positions, the non-coloured state of the diacetylene compound is activated.

It is noted that the applied transition stimulus (temperature) required to facilitate a transition of the keto acid compound of formula (I) from the non-coloured to a coloured state is higher than that of the activation temperature applied using the C0 ₂ laser at 20% power, and thus there is no transition from the non-coloured state to a coloured state of the keto acid compound of formula (I). If following application of the activation temperature, UV radiation is applied by flood illumination to the substrate using a germicidal lamp, the non-coloured state of the diacetylene compound transitions to a first blue coloured state solely at the localised positions at which the non-coloured state of the diacetylene compound has been‘activated’. A blue colour can therefore be formed.

Subsequent application of IR radiation using a 10.6 pm C0 ₂ laser (20% power) to the localised positions at which the first blue coloured state has been formed then acts as the additional applied stimulus (additional temperature) and the diacetylene compound transitions at these localised positions from the first blue coloured state to a second red coloured state. The intensity of the colour formed can be varied by altering the fluence applied by the C0 ₂ laser. Again, as discussed above, there is no transition from the non-coloured state to a coloured state of the keto acid compound of formula (I).

Alternatively, following application of the layers to the substrate, the activation temperature is applied using a C0 ₂ laser (38% power), i.e. at increased fluence, to provide IR radiation at localised positions. It will be appreciated that a higher temperature is applied such that as well as activating the non-coloured state of the diacetylene compound at these localised positions, the transition of the keto acid compound of formula (I) from the non-coloured state to a coloured state is facilitated, i.e. the applied transition stimulus (additional temperature) is reached. The colour of the coloured state of the keto acid compound of formula (I), and the intensity thereof, can be changed between yellow or orange by variation of the fluence applied by the C0 ₂ laser.

If following application of the additional applied stimulus (additional temperature) that formed the coloured state of the keto acid compound of formula (I) at those localised positions, UV radiation is applied by flood illumination using a germicidal lamp as the additional applied stimulus (additional radiation), the ‘activated’ non-coloured state of the diacetylene compound transitions to a blue coloured state solely at these localised positions that have been‘activated’. As the coloured state of the diacetylene compound is formed at the same localised position at which the coloured state of the keto acid compound of formula (I) has been formed, the final colour displayed at these localised positions is dependent upon the blue coloured state of the diacetylene compound, and the colour of the coloured state of the keto acid compound of formula (I), i.e. the final colour at these localised positions results from the combination of colours of the coloured states of the two components. Accordingly, blue, green and orange coloured states can be formed.

A multi-coloured image may therefore be formed displaying yellow, orange, red, green and blue colours.

Example 9 A composition comprising a keto acid compound of formula (I) and an acid- generating agent was formulated according to Table 14.

Table 14

The composition was applied to a paper substrate using a k2 k-bar applicator.

The keto acid compound of formula (I) is in its non-coloured state prior to application of the applied transition stimulus.

An applied transition stimulus (temperature) was applied to the composition and thus the keto acid compound of formula (I) using a 10.6 pm C0 ₂ laser (38% power) to provide IR radiation and effect a transition from the non-coloured state to a yellow coloured state of the keto acid compound of formula (I). The intensity of the colour of the coloured stated of the keto acid compound of formula (I) can by varied by altering the fluence applied by the C0 ₂ laser. Example 10

A composition comprising an oxyanion of a multivalent metal (an‘at least one additional compound’) was formulated according to Table 8 above.

A composition comprising a keto acid compound of formula (I) and an acid- generating agent was formulated according to Table 14. A layer of the composition comprising an oxyanion of a multivalent metal was applied to a paper substrate using a k2 k-bar applicator. A layer of the composition comprising a keto acid compound of formula (I) and an acid- generating agent was applied using a k2 k-bar applicator over the layer of the composition comprising an oxyanion of a multivalent metal. Upon application of IR radiation using a 10.6 pm C0 ₂ laser (20% power) to localised positions of the substrate (applied transition stimulus: temperature), the compound of formula (I) transitions from the non-coloured to a yellow coloured state. The intensity of the colour formed can be varied by altering the fluence of the C0 ₂ laser. It is noted that the additional applied stimulus: temperature required to facilitate the transition of the oxyanion of a multivalent metal is a higher temperature than the applied transition stimulus: temperature required to facilitate the transition of the compound of formula (I) from the non-coloured to a coloured state. Accordingly, the application of the IR radiation using a C0 ₂ laser at 20% power does not facilitate a transition of the oxyanion of a multivalent metal from the non-coloured to a coloured state. However, when the power of the C0 ₂ laser is increased to 38%, in addition to the transition of the keto acid compound of formula (I) from the non-coloured to a yellow coloured state, the oxyanion of a multivalent metal transitions from the non-coloured state to a black coloured state. The intensity of the colour of the coloured state can be made to vary by variation of the fluence of the C0 ₂ laser. As the coloured state of the oxyanion of the multivalent metal is formed at the same localised position at which the coloured state of the keto acid compound of formula (I) is formed, the final colour displayed at these localised positions is dependent upon the black coloured state of the oxyanion of a multivalent metal, and the yellow coloured state of the keto acid compound, i.e. the final colour at these localised positions results from the combination of colours of the coloured states of these two components. Accordingly, different yellow and black colours can be formed.

A multi-coloured image displaying yellow and black colours can therefore be formed.

Example 1 1

A composition comprising a keto acid compound of formula (I) and an acid- generating agent was formulated according to Table 14.

A composition comprising a diacetylene compound (an‘at least one additional compound’) was formulated according to Table 13, using the millbase formulations of Tables 1 1 and 12.

A layer of the composition comprising a keto acid compound of formula (I) and acid-generating agent was applied to a paper substrate using a k2 k-bar applicator. A layer of the composition comprising a diacetylene compound was applied using a k2 k-bar applicator over the layer of the composition comprising a keto acid compound of formula (I) and acid-generating agent.

Following application of the layers to the substrate, IR radiation is applied using a 10.6 pm C0 ₂ laser (20% power) (activation temperature) to localised positions of the substrate so as to‘activate’ the non-coloured state of the diacetylene compound. It is noted that this activation temperature is lower than the applied transition stimulus: temperature required to facilitate a transition of the non- coloured state of the keto acid compound of formula (I) from the non-coloured to a coloured state. Accordingly, when a coloured state of the keto acid compound of formula (I) is also required at the localised positions, the power of the laser is increased to 38% power, such that a higher temperature is provided and the keto acid compound of formula (I) transitions from the non-coloured state to a yellow coloured state. The intensity of the yellow coloured state formed can be varied by alteration of the fluence applied by the C0 ₂ laser. At these localised positions, the non-coloured state of the diacetylene compound is‘activated’.

Upon further application of UV radiation using a germicidal lamp, the‘activated’ non-coloured state of the diacetylene compound at the localised positions transition to a blue first coloured state. If the coloured state of the keto acid compound of formula (I) has been formed, the final colour displayed at the localised positions will be a combination of the blue first coloured state of the diacetylene compound and the yellow coloured state of the keto acid compound of formula (I). Accordingly, blue and green colours can be formed.

Upon application of the additional applied stimulus (additional temperature) by flood illumination using a heat gun, the first blue coloured states formed will transition from the first blue coloured state to the second red coloured state. Again, if the coloured state of the keto acid compound of formula (I) has been formed, the final colour displayed at these localised positons will be a combination of the colour of the red second coloured state of the diacetylene compound and the yellow coloured state of the keto acid compound of formula (I). Accordingly, red and orange colours can be formed. A multi-coloured image displaying red, yellow, blue, orange and green colours may therefore be formed.

Example 12

A composition comprising a keto acid compound of formula (I) and an acid- generating agent was formulated according to Table 14, but the keto acid compound of formula (I) was replaced with 2,5-bis(4-(diethylamino)-2- hydroxybenzoyl)terephthalic acid.

A layer of the composition comprising a keto acid compound of formula (I) and acid-generating agent was applied to a paper substrate using a k2 k-bar applicator.

Following application of the composition to the substrate, the keto acid compound of formula (I) is in the non-coloured state. The non-coloured state of the keto acid compound is yellow, and therefore the substrate displays this colour. Following application of the composition to the substrate, IR radiation is applied using a 10.6 pm C0 ₂ laser (applied transition stimulus: temperature) to localised positions of the substrate to facilitate a transition of the non-coloured state of the keto acid compound of formula (I) to a coloured state. The colour of the coloured state, and intensity thereof, can be changed between yellow, orange and red by variation of the fluence applied by the C0 ₂ laser.

A multi-coloured image having yellow, orange and red colours can therefore be formed.

Example 13

A composition comprising a keto acid compound of formula (I) and an acid- generating agent was formulated according to Table 14, but the keto acid compound of formula (I) was replaced with 2,5-bis(4-(diethylamino)-2- hydroxybenzoyl)terephthalic acid. A composition comprising a diacetylene compound (an‘at least one additional compound’) is formulated according to Table 13, using the millbase formulations of Tables 1 1 and 12, but the diacetylene compound is replaced with N1 ,N22- ditetradecyldocosa-10, 12-diynediamide.

A layer of the composition comprising a keto acid compound of formula (I) and an acid generating agent is applied to a paper substrate using a k2 k-bar applicator. A layer of the composition comprising a diacetylene compound was applied using a k2 k-bar applicator over the layer of the composition comprising a keto acid compound of formula (I) and an acid-generating agent.

Following application of the layers to the substrate, the keto acid compound of formula (I) and the diacetylene compound are in their non-coloured states. The non-coloured state of the keto acid compound of formula (I) is yellow in colour and therefore the substrate displays this colour. It is noted that the diacetylene compound utilised in this example has a non-coloured state that requires ‘activation’, i.e. application of an activation temperature to make it capable of transitioning from the non-coloured to a coloured state.

Following application of the layers to the substrate, IR radiation is applied at localised positions using a 10.6 pm C0 ₂ laser (applied transition stimulus: temperature) to localised positions of the substrate to facilitate a transition of the non-coloured state of the keto acid compound of formula (I) to a coloured state. The colour of the coloured state, and intensity thereof, can be changed between yellow, orange and red by variation of the fluence applied by the C0 ₂ laser. It is noted that the activation temperature of the diacetylene compound is lower than the applied transition stimulus: temperature. Accordingly, the IR radiation also provides an activation temperature at these localised positions such that the non-coloured state of the diacetylene compound is activated and capable of undergoing a transition.

Upon further application of UV radiation using a germicidal lamp (additional applied stimulus: additional radiation), the non-coloured state of the diacetylene compound transitions to a blue first coloured state at the localised positions at which the non-coloured state of the diacetylene compound has been activated. As the coloured state of the first blue coloured state of the diacetylene compound is formed at the same localised position at which the coloured state of the keto acid compound of formula (I) has been formed, the final colour displayed at these localised positions is dependent upon the blue colour of the first coloured state of the diacetylene compound, and the colour of the coloured state of the keto acid compound of formula (I), i.e. the final colour at these localised positions results from the combination of colours of the coloured states of these two components. Accordingly, blue, green and purple colours can be formed. Upon further application of an additional applied stimulus (additional temperature) to the substrate by flood illumination using a heat gun, the first blue coloured state of the diacetylene compound transitions to a second red coloured state. As before, in light of the combination of the red second coloured state of the diacetylene compound and the colour of the coloured state of the keto acid compound of formula (I), red, orange and purple colours can be formed. A multi-coloured image displaying yellow, orange, red, blue, green and purple colours may therefore be formed.