BACKGROUND

[0001] Printing processes such as electrostatic printing involve creating an image using toner particles. In some examples, the toner particles may be suspended in a carrier fluid providing a liquid print agent, which may be used in liquid electrophotographic printing (LEP) processes. A LEP print agent (also referred to as a “liquid ink” herein) may be formed by mixing a resin particle (which may be a thermoplastic resin particle) with a carrier fluid to create the suspension.

BRIEF DESCRIPTION OF DRAWINGS

[0002] Non-limiting examples will now be described with reference to the accompanying drawings, in which: [0003] Figure 1 is a simplified schematic of an example of thermoplastic resin ink particles and an ink resin block formed therefrom;

[0004] Figure 2 is a flowchart of an example of a method of compressing printing toner particles;

[0005] Figures 3A, 3B and 3C are schematic representations of an apparatus for forming an ink resin block from a powder;

[0006] Figure 4 is a flowchart of an example of a method of forming a liquid ink;

[0007] Figure 5 shows a schematic representation of an apparatus for forming a liquid ink;

[0008] Figure 6 is a flowchart of another example of a method of forming a liquid ink; and

[0009] Figure 7 shows distribution times for dispersing ink resin blocks formed according to examples set out herein in a carrier fluid. DETAILED DESCRIPTION

[0010] As used herein, “carrier fluid”, “carrier liquid,” “carrier,” or “carrier vehicle” refers to the fluid in which pigment particles, resin, charge directors and other additives can be dispersed to form a liquid electrostatic ink composition or liquid electrophotographic ink composition. The carrier liquid may include a mixture of a variety of different agents, such as surfactants, co-solvents, viscosity modifiers, and/or other possible ingredients. The carrier fluid may be a non-polar carrier fluid. Examples of non-polar carrier fluids comprise dielectric liquids, non-oxidative water immiscible liquids (e.g., petroleum distillates), hydrocarbon-based carriers (e.g., aliphatic (i.e. , linear/acyclic or cyclic) hydrocarbons, branched-chain aliphatic hydrocarbons, etc.), silicone oil, soy bean oil, vegetable oil, plant extracts, etc. In one example, the non-polar carrier is an alkane or a cycloalkane having from 6 to 14 carbon atoms (e.g., n-hexanes, heptanes, octane, dodecane, cyclohexane etc.), t-butylbenzene, 2,2,4-trimethylpentane, or combinations thereof. Examples of a non-polar carrier fluid comprise at least one substituted or unsubstituted hydrocarbon. The hydrocarbon may be linear, cyclic, or branched, and may be substituted with any suitable functional group. Examples of such hydrocarbons comprise any of dielectric liquids, non-oxidative water immiscible liquids, paraffins, isoparaffins, and oils. Examples of paraffins and isoparaffins comprise those in the ISOPAR ^® family (Exxon Mobil Corporation, USA), including, for example, ISOPAR ^® -G, ISOPAR ^® -H, ISOPAR ^® -K, ISOPAR ^® -L, ISOPAR ^®" M, and ISOPAR ^®" V. Additional examples of a suitable carrier fluid include NORPAR 13™, NORPAR 15™, Exxol D40™, Exxol D80™, Exxol D100™, Exxol D130™, and Exxol D140™, also available from Exxon Mobil Corporation, USA. Some additional examples of a suitable carrier fluid include Teclen N- 16™, Teclen N-20™, Teclen N-22™, Nisseki Naphthesol L™, Nisseki Naphthesol M™, Nisseki Naphthesol H™, #0 Solvent L™, #0 Solvent M™, #0 Solvent H™, Nisseki Isosol 300™, Nisseki Isosol 400™, AF- 4™, AF-5™, AF-6™ and AF-7™ (each available from NIPPON OIL CORPORATION); IP Solvent 1 620™ and IP Solvent 2028™ (each sold by IDEMITSU PETROCHEMICAL CO., LTD.); Amsco OMS™ and Amsco 460™ (each sold by AMERICAN MINERAL SPIRITS CORP.); and Electron, Positron, New II, Purogen HF (100% synthetic terpenes) (sold by ECOLINK™). In other examples of a suitable carrier fluid, other hydrocarbons that may be used as the non-polar carrier fluid comprise those in the SOLTROL ^® family (available from Chevron Phillips Chemical Company, USA) or SHELLSOL ^® (available from Shell Chemicals, USA). [0011] As used herein, “liquid electrostatic ink”, “liquid electrostatic ink composition” or “liquid electrophotographic composition” generally refers to an ink composition that is typically suitable for use in an electrostatic printing process, sometimes termed an electrophotographic printing process. It may comprise pigment particles comprising, at least in part, a thermoplastic resin. The electrostatic ink composition may be a liquid electrostatic ink composition, in which the pigment particles are suspended in a carrier liquid. The pigment particles may be charged or capable of developing charge in an electric field, such that they display electrophoretic behaviour. A charge director may be present to impart a charge to the pigment particles. [0012] If a standard test is mentioned herein, unless otherwise stated, the version of the test to be referred to is the most recent at the time of filing this patent application.

[0013] As used herein, “electrostatic printing” or “electrophotographic printing” generally refers to the process that provides an image that is transferred from a photo imaging substrate either directly or indirectly via an intermediate transfer member to a substrate, such as a paper or plastic substrate. As such, it may be the case that the image is not substantially absorbed into the photo imaging substrate on which it is applied. Additionally, “electrophotographic printers” or “electrostatic printers” generally refer to those printers capable of performing electrophotographic printing or electrostatic printing, as described above. “Liquid electrostatic printing” is a type of electrostatic printing in which a liquid composition is employed in the electrophotographic process rather than a powder toner. An electrostatic printing process may involve subjecting the electrostatic composition to an electric field, for example, an electric field having a field gradient of 50- 400 V/pm, or more, in some examples, 600-900V/pm, or more.

[0014] As used herein, the term “about” is used to provide flexibility to a numerical range endpoint by providing that a given value may be a little above or a little below the endpoint to allow for variation in test methods or apparatus. The degree of flexibility of this term can be dictated by the particular variable and would be within the knowledge of those skilled in the art to determine based on experience and the associated description herein.

[0015] Concentrations, amounts, and other numerical data may be expressed or presented herein in a range format. It is to be understood that such a range format is used merely for convenience and brevity and thus should be interpreted flexibly to include not just the numerical values explicitly recited as the limits of the range, but also to include all the individual numerical values or sub-ranges encompassed within that range as if each numerical value and sub-range is explicitly recited. As an illustration, a numerical range of “about 1 wt.% to about 5 wt.%” should be interpreted to include not just the explicitly recited values of about 1 wt.% to about 5 wt.%, but also to include individual values and sub ranges within the indicated range. Thus, included in this numerical range are individual values such as 2, 3.5, and 4 and sub-ranges such as from 1-3, from 2-4, and from 3-5, etc. This same principle applies to ranges reciting a single numerical value. Furthermore, such an interpretation should apply regardless of the breadth of the range or the characteristics being described.

[0016] Unless otherwise stated, any feature described herein can be combined with any aspect or any other feature described herein. [0017] Toner particles may be prepared for use in a liquid ink, such as a liquid electrostatic ink, in the form of a powder. To form the liquid ink, the particles may be mixed with a liquid such as a carrier fluid. Before the powder is mixed with the liquid, it is prone to dispersing into the atmosphere unless care is taken in handling and packaging the powder. The powder could be transported from its site of manufacture to a customer, and the liquid ink could be prepared at or near the customer’s location by mixing the toner particles with the liquid after, rather than before, shipping. This would reduce the weight to be transported. However, the powder may have a relatively low density and therefore be bulky to ship. In addition, the tendency for the particles to become airborne means that careful handling should be employed. In other examples, a concentrated ink may be transported and diluted at its destination. Wetting the powder particles prevents them from dispersing, and therefore increases ease of transport, but the weight to be transported is higher than for dry powders as an appropriate amount of carrier fluid is included in the concentrated ink.

[0018] Figure 1 shows an example of an ink resin block 100 comprising thermoplastic resin particles 102, the block having a structural integrity provided by the mutual enmeshing of the thermoplastic resin ink particles which are substantially unfused with one another. The block has ‘structural integrity’ in that it is able to keep its form without a supporting structure. For example, the block would not change while falling through space. The block may appear to be ‘solid’ (albeit that it is made up of unfused particles). Moreover, in some examples, the block has ‘structural integrity’ in that it has an ability to withstand stress, as is further set out below. This may be an ability to withstand a measurable stress, for example as described below. In some examples, the block has ‘structural integrity’ in that it has the ability to withstand stresses associated with manual handling without additional packaging. For example, the block may have ‘structural integrity’ in that it has the ability to withstand being dropped from an expected working height, for example from height between 1 and 5 meters, or between 1 and 10 meters. This may be a ‘drop test’ onto a hard surface from a specified height. In some examples, the block may be deemed to pass the test if it sustains little or no damage in such a test.

[0019] The size of the block 100 may be selected to be appropriate for forming an ink with a given optical density within a mixing reservoir. For example, the block may be a relatively small ‘pellet’ weighing around 5-15 grams, for example around 10 grams although it may be larger in other examples.

[0020] Figure 1 also shows a ‘powder’ 104 comprising loose thermoplastic resin ink particles 102. A magnified view of the powder is shown circle 106, in which examples of thermoplastic resin ink particles 102 are visible. It may be noted that, in this example, the particles are ‘tentacular’, or in other words the particles have a number of extending appendages 108 (which form extending arms, or ‘tentacles’) which are elastically deformable and may become intermeshed or entangled. While in the example of the Figures, the extending appendages extend substantially equally in all dimensions, in some examples, the particles may have more of a ‘plate-like’ or ‘flake-like’ form, with the appendages extending more in one plane than another. Entangling or enmeshing of the thermoplastic resin particles 102, for example using compression as described below, can cause them to be held together and form the ink resin block 100. This means that the resin ink particles 102 do not become dispersed in the air in the same way as loose powder particles. The particles 102 may have an average diameter in the range of 5 to 10 micrometres, or an average diameter in the range from 6 to 7 micrometres. The particles 102 may be asymmetrical, for example they may be flat or ‘plate-like’. For example, the particles 102 may have a diameter of around 5pm in one dimension and have a thickness of 200nm in another dimension. In some examples, the edges of the plates may have a tentacular form. Tentacular particles have been utilised in electrophotographic printing, including in liquid inks, to provide particles which are readily charged. In some examples the particles have a porous structure such that liquid may be absorbed into the pores of the particles 102. In some examples the particles increase in size when they absorb a liquid. [0021] The thermoplastic resin ink particles within the block 100 may be discrete particles in that they are not irreversibly bonded to one another and so may be dispersed within a fluid. In examples, the particles 102 within the block 100 are ‘substantially’ unfused in that the majority of particles 102 are unfused from any other particle 102. This means that it is possible to disentangle the majority of the particles 102, in particular when added to a carrier fluid to form a liquid ink as described below, and the particles 102 will be separate from one another such that they can move independently in the liquid and the ink will have substantially the same qualities as if formed directly from the powder form. As will be described in greater detail below, the block 100 may be formed in such a way that phase change (e.g. melting) of the particles 102 is avoided in order that the particles remain substantially unfused from one another.

[0022] The resin particles may comprise a polymeric resin, for example a resin selected from the Nucrel family of toners available from DuPont (e.g. Nucrel 699, Nucrel 599, Nucrel 925) or may comprise for example Elvax 210W by DuPont, A-C 5120 or A-C 580 available from Honeywell, USA, Poly(ethylene-co-glycidyl methacrylate) available from Sigma-Aldrich (Product Code 430862). In some examples the electrostatic ink composition may comprise more than one of these resins, for example it may comprise two or more of these resins.

[0023] The ink resin block 100 may be formed by application of a force or pressure to the powder 104, as described in more detail with reference to Figure 2. The applied force may be controlled or selected so as to cause elastic deformation of the particles 102, wherein elastic deformation means that the deformed particles are able to return to their shape they had prior to application of the force. Alternatively or additionally, applied force may be controlled or selected so as to avoid plastic deformation, and/or phase change in the particles. This means that even after the particles 102 are formed into ink resin block 100 they retain their physical properties. In particular, if the ink resin block 100 is broken up into its constituent particles 102, these particles 102 have comparable, or the same, properties as the particles 102 had before they were formed in to the block 100. This may be contrasted with ‘plastic’ deformation, which may be less readily reversed. In some examples, the ink resin block 100 may be referred to as an ‘agglomerate’ formed using pressure agglomeration, or compaction.

[0024] In some examples, the block may be considered to be an ink resin block having structural integrity if it has an ultimate tensile strength such that it withstands stresses of at least 10 kiloPascals (kPa), or at least 20kPa, or up to around 30kPa (although the ultimate tensile strength may be greater in other examples). [0025] In some examples, the tensile strength may be related to the pressure of compression. For example, for some resins, if a powder is compressed with a pressure of around 5 or 6 bar, this may result in an ultimate tensile strength in the range 50 to 80kPa. However, if the particles are compressed with a pressure of around 150 bar, this may result in an ultimate tensile strength in the range of 500 to lOOOkPa. Therefore, higher levels of compression may be associated with more robust blocks. An ultimate tensile strength in the above ranges allows normal handling without damaging the structural integrity of the ink resin block. While it may be possible to obtain very robust blocks by using high compression forces in this way, which still comprise unfused particles, in some examples the strength of the block may be chosen at least in part considering the shear force to be used to break the block apart. For example, when the ultimate tensile strength is significantly greater than 30kPa then the shear force to disperse the ink resin block may be too large for some practical applications, as is further set out below. In some examples, as set out in greater detail below, pressures of around 3 - 6 bar may be used to obtain a block which are relatively robust without leading to high forces to disperse/long dispersion times when added to a fluid.

[0026] The ultimate tensile strength of a body (in present examples, an ink resin block) may be measured by applying a force to the body. The applied force is precisely measured, and the ultimate tensile strength is determined by measuring the force at which the body breaks. The force may be applied to substantially the whole of a face of the body in some examples. In some examples, the force may be applied to one face. In other examples, an average force applied to a plurality of faces may be determined.

[0027] In the ink resin block 100, the appendages 108 of adjacent particles are entangled, or overlap in space. The entangling of the appendages 108 allows adjacent particles to bond together, such that many individual particles are held together in a single mass, while remaining unfused from one another. This may exploit the elasticity of the resin particles which are deformed by the pressure and, when the pressure is removed seek to resume their initial shape, thus acting on one another in a manner which holds the particles together. Alternatively or additionally, in some examples, it may be the case that compression of the particles 102 brings them sufficiently close together such that Van-Der-

Waals forces provide attractive forces between the particles 102 assisting in holding the particles 102 together.

[0028] The particles 102 are reversibly bonded such that the ink resin block 100 can be dispersed in a carrier fluid by application of agitation to said fluid and the ink resin block 100. Reversible bonding means that it is possible for the process of forming the ink resin block 100 from a loose powder-like state, shown herein as powder 104 to be reversed, that is for the ink resin block 100 to be broken up into its constituent particles 102, wherein said particles are substantially unchanged after (i) being formed into the block 100 and (ii) being broken up into individual particles from the block 100. To assist in reversing the bonding in the ink resin block 100, the ink resin block 100 may be mixed with a liquid. The liquid may assist in breaking the ink resin block 100 into its constituent particles 102 for example by acting as a lubricant thereby reducing the shear forces to separate the particles. The particles 102 may additionally or alternatively absorb a portion of the liquid which may aid dispersion as the particles 102 swell. [0029] To consider a particular example, when allowed to form a loose pile, thermoplastic ink particles may have a density of around 0.15g/cm ³ , but when compressed into an ink resin block, the density may be increased to around 1g/cm ³ _. This increases the ease of transport as the material is less bulky, and in addition, the powder is held within the ink resin block 100 and is not prone to dispersing. Therefore, packaging specifications may be simplified and/or reduced.

[0030] In some examples, the thermoplastic resin particles 102 are ink particles. These particles 102 may be used to form a liquid ink when mixed with a liquid such as a carrier fluid. Liquid inks are used in printing processes such as LEP printing. In LEP printing an image is created on a photoconductive surface by applying the ink to the photoconductive surface. The ink comprises particles which are charged in preparation for printing and the photoconductive surface is selectively charged such that the particles selectively bind to the photoconductive surface to form the predetermined image. The photoconductive surface is selectively charged with a latent electrostatic image with image areas and background areas having different potentials, such that the charged particles adhere to the image areas and not to the background areas. The ink is then transferred to a print substrate, such as paper, directly or by first being transferred to an intermediate transfer member then to the print substrate.

[0031] When in ‘liquid’ form, carrier fluid may constitute about 20% to about 99.5% by weight of the ink composition, in one example about 50% to about 99.5% by weight of the ink composition. The carrier fluid may constitute about 40% to about 90 % by weight of the ink composition. The carrier fluid may constitute about 60% to about 80% by weight of the ink composition. The carrier fluid may constitute about 90% to about 99.5% by weight of the ink composition, in one example about 95% to about 99% by weight of the ink composition. When the ink composition is printed on a print substrate, it may be substantially free from carrier fluid. For example, in an electrostatic printing process and/or afterwards, the carrier fluid may be removed, e.g. by an electrophoresis process(es) during printing and/or evaporation, such that substantially just solids are transferred to the print substrate. Substantially free from carrier fluid may indicate that the ink composition printed on the print substrate contains less than 5 wt% carrier fluid, in one example, less than 2 wt% carrier fluid, in one example less than 1 wt% carrier fluid, in one example less than 0.5 wt% carrier fluid. In one example, the printing composition printed on the print substrate is free from carrier fluid.

[0032] In the example shown in Figure 1, the ink resin block 100 is formed in the shape of a cube, however the ink resin block 100 may be formed in any shape or size, for example different shapes and/or sizes may be used for increasing packing efficiency or depending on the intended use. For example, if intended for use with a high-volume printing/mixing apparatus, the size of the ink resin block 100 may be larger than if intended for use with a lower volume printing/mixing apparatus.

[0033] Figure 2 shows an example of a method, which may be a method of compressing printing toner particles and/or a method of forming an ink resin block from toner particles. In this example block 202 comprises applying a force to toner particles (which may comprise tentacular particles, for example comprising at least one resin described above), and block 204 comprises forming an ink resin block as a result of the applied force. The force applied in block 202 is determined so as to cause elastic deformation of toner particles such that, when the force is removed, the toner particles are mutually enmeshed. The force applied depends therefore on the physical properties of the particles. For a given toner particle, there will be a range of pressures, which may for example be determined experimentally or theoretically, which result in elastic (or reversible) deformation but not plastic (or irreversible) deformation, or in reversible, and not irreversible, bonding. Temperature may also be considered, as this may have an impact on the pressure at which irreversible bonding occurs. Moreover, there will be a range of pressures, which may for example be determined experimentally or theoretically, which provide deformation to an extent that the particles become enmeshed. Alternatively or additionally, there may be a range of pressures, which may for example be determined experimentally or theoretically, which result in a level of hardness which is appropriate for a given apparatus to break up the ink resin block to disperse the particles in a carrier fluid, for example to form liquid ink. Alternatively or additionally, there may be a range of pressures, which may for example be determined experimentally or theoretically, which result in a level of hardness or structural integrity to provide an intended robustness. The pressure applied may be determined with consideration of any or all such ranges/intentions, and in some in examples maybe related to the choice of material (e.g. the resin used), temperatures and the like.

[0034] In some examples, the block may be considered to be an ink resin block having structural integrity if it has a hardness such that it withstands stresses (for example, applied orthogonally to a surface of the block) of at least 20 kiloPascals (kPa), or at least 20kPa, or up to or around 30kPa, or up to around 50kPa. A block for testing may comprise a prism having a flat base and a flat top and the stress may be applied to the top (for example over the whole top) when the base is resting on a surface. In some examples, the base and the top may be of substantially the same form and the cross-section of the block may also have the same constant form. For example, the block may be a right cylinder or a cuboid. Such a block may be used to determine the hardness, and the pressures used to generate a block having the intended hardness may be used to generate blocks having different shapes.

[0035] As has been noted above, the tensile strength may be related to the pressure of compression in forming the block. For an example resin, if the resin powder is compressed with a pressure of around 5 or 6 bar, this may result in an ultimate tensile strength in the range 50 to 80kPa. However, if the example powder is compressed with a pressure of around 150 bar, this may result in an ultimate tensile strength in the range of 500 to lOOOkPa. [0036] An example of an apparatus 300 for performing the method shown in

Figure 2 is depicted in Figures 3A, 3B and 3C. The apparatus 300 is a die tool and comprises a hopper 302, a plunger 304, a body 306 and an outlet door 308. The printing toner particles 310a, also referred to as a powder below, to distinguish from the particles once a block is formed, are loaded into the body 306 via the hopper 302. The outlet door 308 is movable between an open position and a closed position. The interior of the body 306 forms an enclosed chamber when the outlet door 308 is in a closed position, as depicted in Figure 3A. The apparatus 300 may comprise a vent to allow air to escape the chamber, but prevents powder 310a from escaping from the chamber. Such a vent may comprise a filter with a hole, ora plurality of holes, in the range from 10 to 100 micrometres (or more generally with hole(s) smaller than the particle size).

[0037] After the printing toner particle powder 310a are loaded into the body 306 of the apparatus 300 as depicted in Figure 3A, the plunger 304 is moved by application of a force 312 to the plunger 304. The applied force 312 is in the direction towards the body 306 of the apparatus 300 to cause compression of the powder 310a. The applied force 312 causes pressure within the chamber to increase resulting in compression and a decrease in volume of the powder 310a. The applied force 312 is sufficiently large that the pressure causes the powder 310a to form an ink resin block 310b by causing elastic deformation of the toner particles and/or without causing phase change such that, when the force is removed, the toner particles are mutually enmeshed but substantially unfused with one another. [0038] In some examples applying the force to the printing toner particles comprises compressing the printing toner particles at a pressure and temperature such that the toner particles stay below a temperature at which the particles change phase. The change in phase may for example be a change from solid to liquid, which is to be avoided to prevent permanent bonding between the particles. In some examples compressing the printing toner particles is performed at a pressure and temperature below the pressure and temperature at which the toner particles deform plastically. This prevents the particles from forming permanent or irreversible bonds with other toner particles and allows the resulting ink resin block 310b to be broken up again into its constituent particles. If the process is performed at a higher temperature and/or pressure, the probability of such permanent bonding increases, and therefore the temperature and pressure conditions may be significantly lower than those at which such bonding occurs.

[0039] The compression force 312 may cause the volume of the powder 310a to decrease significantly. In some examples compressing the printing toner particles comprises applying a force which is sufficient to provide an ink resin block with a density at least four times the density of the toner particles prior to compressing. For example the powder 310a may have a density of 0.15g/cm ³ before the compression force 312 is applied. After the compression force is applied the density of the ink resin block 310b which is formed may be in the range from 0.7g/cm ³ to 1g/cm ³ . For comparison a non-powdered solid material formed from the same thermoplastic resin as the powder may have a density of 1.05g/cm ³ (for example, plastically deformed resin, or resin which is melted to form a cohesive whole) and so the ink resin block 310b which is formed by compressing the powder 310a so as to elastically deform the particles achieves a density approaching that of a solid formed from the same material. [0040] In some examples compressing the printing toner particles comprises applying a force 312 to provide a pressure in the range from 3 bar to 150 bar (where 1 bar is 100kPa). In some examples, the pressure may be within the range 3 to 10 bar, or 3 to 20bar, or 8-10bar. When a pressure of 150 bar is applied to an example printing toner particles with a density of 0.15g/cm3 the ink resin block 310b which is formed comprises a density of 1 g/cm ³ and is capable of withstanding a stress well in excess of 50kPa. An ink resin block 310b with a tensile strength of around 50kPa will not readily break up when handled and can withstand a 2m drop test (in which it is dropped onto a hard surface from a 2m height) while maintaining the ability to be dispersed in a carrier fluid to form a liquid ink. If a pressure of 5 bar is applied the density of the example ink resin block 310b formed is 0.7g/cm ³ . Although such a block has a lower density and reduced strength when comparted to a block compressed at around higher pressures, it may nevertheless be easier to store and handle when compared to loose particles, forming relatively robust blocks, and may also be relatively easier to disperse in a carrier fluid when forming a liquid ink when compared to blocks formed at higher pressures, as is further explained below with reference to Figure 7.

[0041] The concentration of resin by weight in the loose particles and in the ink resin block will be substantially the same, for example being at least 95% and in some examples being around 98%. The remaining weight may comprise carrier liquid and/or impurities, and/or may be associated with measurement inaccuracies. [0042] In some examples compressing the printing toner particles 310a comprises applying a force to provide a pressure in the range from 5 bar to 10 bar. This provides a compromise between strength and higher density achieved at higher pressures and ease of dispersion of the ink resin block 310b provided at lower pressures.

[0043] As mentioned above, in some examples compressing the powder 310a is performed at a temperature of less than the melting temperature of the powder 310a. The melting temperature of toner particles may for example be in the range from 60 to 70°C. Therefore by performing the compression at a temperature of less than 70°C, or less than 60°C depending on the melting temperature, the process is performed at a sufficiently low temperature that melting and/or plastic deformation of the particles of the powder 310a is avoided.

[0044] In some examples compressing the toner particles 310a is performed at a temperature of 40°C or less, for example in the range from 20°C to 40°C. For example the compression may be performed at room temperature, for example at around 20°C. At lower temperatures, unwanted reactions such as condensation may occur and at higher temperatures, a glass transition may occur. Such conditions may be particularly suited for particles used in liquid electrophotographic printing. For other types of powder, such as that used in dry electrophotography, or xerography, the powder is a harder and more heat- resistant resin and so higher temperatures may be used.

[0045] After the force 312 has been applied and the ink resin block 310b is formed, the outlet door 308 is moved from the closed position to the open position and the ink resin block 310b is ejected from the apparatus 300 as depicted in Figure 3C.

[0046] In some examples, after the ink resin block 310b is formed, and possibly following storage and/or shipping thereof, it is added to a carrier fluid. The carrier fluid containing the ink resin block may be agitated to disperse particles of the toner particles in the fluid to form a liquid ink. By forming the ink resin block 310b handing of the toner particles is simplified. Adding the toner particles to the carrier fluid may occur at a different location from forming of the ink resin block 31 Ob, for example after shipping to a customer. Moreover, forming the ink resin block 310b allows easier storage due to the smaller volume and increased density relative to the powder 310a. Furthermore the ink resin block 310b provides ease of packaging, for example the ink resin block 310b may be strong enough that it can be transported with no packaging or with minimal packaging, thereby eliminating complex and costly packaging used when shipping powder. Providing the toner as an ink resin block 310b may further simplify any apparatus which is used to disperse the ink resin block 310b in a liquid, as such an apparatus will not need systems to handle (for example, contain) powder.

[0047] Figure 4 shows an example of a method, which may be a method of forming a liquid ink. In this example block 402 comprises adding an ink resin block comprising entangled thermoplastic resin particles (which may be tentacular particles, and/or ink particles) to a carrier fluid, the particles being held together by elastic forces due to particle deformation. The block may for example be formed, or have any of the qualities of the blocks 100, 310b described above.

[0048] In this example block 404 comprises agitating the carrier fluid containing the ink resin block to disperse the particles thereof in the carrier fluid to form a liquid ink. [0049] Figure 5 depicts a schematic representation of an apparatus 500 for performing the method of Figure 4. The apparatus 500 comprises a first mixing reservoir 502 and a second mixing reservoir 504. The first mixing reservoir comprises a mixer 506. The first mixing reservoir 502 and the second mixing reservoir 504 are connected via a flow controller 508. The ink resin block 510, which may be the ink resin block 100 depicted in Figure 1 or the ink resin block 310b of Figures 3B and 3C, is added to carrier fluid 512 in the first mixing reservoir 502. The first and/or second mixer may comprise a mixer type known as a ‘high shear mixer’. The mixer may for example be similar to mixers used to mix powdered resin particles. Examples of suitable mixers include Kady mills and Ross mills. [0050] The flow controller 508 may be a pump such as an electric pump, or a valve, and is to control flow of fluid from the first mixing reservoir 502 to the second mixing reservoir 504. Liquid ink may be supplied from the second mixing reservoir to a printing apparatus via an outlet 516 to print an image. Therefore to ensure the ink provided for printing is at a predetermined concentration, the concentration of particles in the second mixing reservoir 504 is maintained at the predetermined concentration. The second mixing reservoir 504 may comprise a sensor to measure the concentration of particles in the fluid 514 in the second mixing reservoir 504. The fluid 514 may be intended to have a concentration for use in a printing apparatus as a liquid ink. The sensor may be an optical sensor that measures concentration by measuring the quantity of light transmitted through the fluid. The concentration may be relatively higher in the first mixing reservoir 502 than in the second mixing reservoir 504. If the concentration falls below a predetermined threshold in the second mixing reservoir 504, as measured by the sensor, then the flow controller 508 is controlled to allow fluid 512 to flow from the first mixing reservoir 502 to the second mixing reservoir 504. For example, if the flow controller 508 is a pump, the pump is activated to pump fluid from the first mixing reservoir 502 to the second mixing reservoir 504. In other examples the flow controller 508 comprises a valve, which may be opened in response to determining the concentration in the fluid 514 in the second mixing reservoir is lower than intended, allowing fluid to flow from the first mixing reservoir 502 to the second mixing reservoir under the force of gravity. If the concentration is too high, carrier fluid may be added to the second mixing reservoir 504.

[0051] The mixer 506 is to mix the fluid 512 and the ink resin block 510 added to the fluid 512. The mixer 506 may mix by agitating the fluid for example by applying a shear force to the fluid. A shear force may be effective at separating the ink resin block 510 into smaller pieces, and/or, as has been noted above, the particles may absorb fluid which may assist in the mutual separation (disentanglement) thereof. In this example mixer 506 comprises four blades which rotate to agitate the fluid 512. However, in other examples the mixer may have any number of blades, and/or may agitate the fluid by other means for example it may comprise a vibrating means within the first mixing reservoir 502. In other examples the mixer 506 may be integral with the first mixing reservoir, for example the first mixing reservoir may rotate or vibrate to mix the fluid 512 and the ink resin block 510. In this way the mixer 506 causes the ink resin block 510 to break up into its constituent particles which are dispersed throughout the fluid 512 to form a suspension.

[0052] Figure 6 shows an example of a method, which may be a method of forming a liquid ink. In this example block 602 comprises adding the ink resin block to a carrier fluid and block 604 comprises disposing the carrier fluid containing the ink resin block in a mixing reservoir. This may be performed manually by an operator dropping the ink resin block into the first mixing reservoir 502, or by some automated means which is capable of determining when to add the ink resin block 510 (for example, in response to a measure of concentration and/or fluid level). The apparatus 500 may also comprise a supply means for supplying fluid to the first mixing reservoir 502, which again may be operated manually or may be automated.

[0053] Block 606 comprises agitating the carrier fluid by applying a shear force within the mixing reservoir. As described above this may be performed by a mixer 506. In some examples the mixer 506 operates at shear forces in the range 100 to 200kPa. In other examples the mixer 506 may be capable of operating at up to 10MPa. In some examples, agitating the carrier fluid containing the ink resin block is performed in a first mixing reservoir, for example the first mixing reservoir 502 depicted in Figure 5.

[0054] Block 608 comprises, after agitation, adding the fluid to a second mixing reservoir 504. This may be controlled by a control means such as a flow controller 508 as described above. Block 610 comprises mixing the liquid ink with additional carrier fluid to achieve an intended concentration of liquid ink in the second mixing reservoir 504. The intended concentration of ink may be the concentration at which ink is supplied to a printing apparatus. Therefore achieving the correct concentration may allow correct operation of the printing apparatus and improve print quality. As mentioned above, carrier fluid may be added until it constitutes about 40 to about 90, or 95, or 98% by weight of the ink composition. In some examples, it may be determined that the intended concentration has been reached by optically measuring the ink to determine if it has an intended optical density. [0055] Figure 7 shows the effect of the density of the ink resin block on dispersion time into carrier fluid to form liquid ink. In this example, the same high shear mixer was used to obtain each data point for a given resin. The left-hand point on the graph shows the dispersion time of an example uncompressed resin toner particles- i.e. loose ‘powder- like’ particles, having a density of around 0.15g/cm ³ . The remaining data points relate to blocks formed of the resin and as the graph shows, as density increases (and correspondingly, the pressure used to form the ink resin block increases), the time to disperse the particles also increases, albeit gradually until the block is compressed to around 0.8g/cm ³ . After that, dispersion (while still possible) takes more time, and therefore a balance may be struck between ease of transport (e.g. in terms of density and/or robustness) and ease of dispersion. The rate of dispersion may only have a weak correlation, or no correlation, with the size of the ink resin block. The size of the ink resin block may be selected to be appropriate for forming an ink with a given optical density within a mixing reservoir 504. For example, the block may be a relatively small ‘pellet’ weighing around 10 grams. [0056] In other words, a relatively lower pressure (say, 3-10bars) may be used to compress loose particles to form blocks having a density of around 0.5-0.8g/cm ³ in this example, and there may be little increase in mixing time. However, a higher pressure (for example, 150 bar) may provide a higher density of around 1g/cm ³ , increasing shipping efficiency (and in some examples, providing a more robust or harder block, which may therefore be associated with less sensitive handling), at the cost of a longer dispersion time.

[0057] The present disclosure is described with reference to flow charts and/or block diagrams of the method, devices and systems according to examples of the present disclosure. Although the flow diagrams described above show a specific order of execution, the order of execution may differ from that which is depicted. Blocks described in relation to one flow chart may be combined with those of another flow chart.

[0058] While the method, apparatus and related aspects have been described with reference to certain examples, various modifications, changes, omissions, and substitutions can be made without departing from the spirit of the present disclosure. It is intended, therefore, that the method, apparatus and related aspects be limited only by the scope of the following claims and their equivalents. It should be noted that the above- mentioned examples illustrate rather than limit what is described herein, and that those skilled in the art will be able to design many alternative implementations without departing from the scope of the appended claims.

[0059] The word “comprising” does not exclude the presence of elements other than those listed in a claim, “a” or “an” does not exclude a plurality, and a single processor or other unit may fulfil the functions of several units recited in the claims.

[0060] The features of any dependent claim may be combined with the features of any of the independent claims or other dependent claims.