The present invention relates to the use of highly sterically hindered nitroxyl radicals as in- can stabilizers for UV-curable resins.

The present invention further relates to the use of quinone methides as in-can stabilizers for UV-curable resins and to mixtures of highly sterically hindered nitroxyl radicals and quinone methides as in-can stabilizers for UV-curable resins.

UV-curable inks and varnishes have been one of the fastest growing technologies in the past two decades. This growth is forecast to continue well into the future with the development of new applications for UV curing, such as inks for food packaging. New raw materials are required to ensure that UV-technology can meet the challenging demands of low odor and low migration, low yellowing while maintaining high reactivity.

The UV-curable resins are composed of a monofunctional or multifunctional monomer, oligomer or polymer molecule and a photoinitiating compound. Monomers, oligomers or polymers typically used for UV curing have at least one ethylenically unsaturated group like an acrylate or methacrylate functional groups. Polymerization is achieved by exposure to UV radiation.

UV-curable resins frequently have to be stabilised against undesired polymerisation or crosslinking of the ethylenically unsaturated group in order that they have adequate storage stability without reducing the cure-speed when radiated. The stabilizers should be compatible with a wide range of commercially available oligomers such as epoxy-, urethane-, polyester- and acrylate- systems.

In the prior art, for example in WO01/42313, there are proposed for that purpose sterically hindered nitroxyl radicals of 2,2,6,6-tetramethylpiperidine in general. Examples of typical radical scavenger that prevent the geling of UV curable compositions while having minimal impact on curing speed are bis(1-oxy-2,2J6,6-tetramethylpiperidin-4-yl) sebacate (Irgastab® UV 10) and 4-hydroxy-1-oxy-2,2,6,6-tetramethylpiperidine. The problem underlying the present invention is therefore to provide in-can stabilizers which are radical scavengers that have a high affinity to radicals formed in UV curable resins containing ethylenically unsaturated monomers, oligomers and/or polymers and a photoinitiator during storage without reducing the cure-speed when radiated and which radical scavengers prevent the geling of UV curable resins and thus increase the storage stability throughout their life cycle from manufacturing to curing compared to the state of art stabilizers, especially in pigmented systems. Some pigments, for instance orange, green and black pigments are known to have a negative influence on the storage stability. A specific problem occurs when Orange 34 is used.

It has now been found that this problem is solved by adding to the ethylenically unsaturated monomer-, oligomer- or polymer molecules stable highly sterically hindered nitroxyl radicals and/or by adding compounds from the class of the quinone methides and/or by adding mixtures thereof.

The present invention relates to the use of stable highly sterically hindered nitroxyl radicals of the formulae I or Il as in-can stabilizers for UV-curable resins

I II, wherein Ra> Rb Ro Rd are independently of each other optionally substituted CrCi8alkyl or benzyl, optionally substituted C5-Ci2cycloalkyl or C6-Ci0-aryl; or Ra, Rb Rc, Rd together with the carbon atom form a C5-Ci2cycloalkyl ring, A and D are groups required to complete the open chain nitroxyl radical; RΘ, Rf, Rg, Rh are independently of each other optionally substituted CrCi8alkyl or benzyl, optionally substituted C5-Ci2cycloalkyl or C6-Cio-aryl; or RΘ, Rf, R9, Rh together with the carbon atom form a C5-Ci2cycloalkyl ring, with the proviso that at least one group is different from methyl; T is a group to complete a ring nitroxyl radical.

By the term "highly sterically hindered" is meant that ring nitroxyl radicals of the formula Il are more hindered than ring nitroxyl radicals having 4 methyl groups in the alpha position to the N-atom, for example more hindered than TEMPO (2,2,6,6-tetramethylpiperidinyl-i-oxy- radical). This condition is expressed by the proviso that at least one group in the alpha position is different from methyl.

Concerning open chain nitroxyl radicals of the formula I the highly sterically hindrance is due to the groups A and/or D.

By the term "in can stabilizer" is meant a stabilizer that improves the storage stability. In-can stabilizers are radical scavengers that have a high affinity to radicals formed in UV curable resins during storage without reducing the cure-speed when radiated. In-can stabilizers prevent the geling of UV curable resins and thus increase the storage stability throughout their life cycle from manufacturing to curing.

By the term "UV-curable resin" is meant a coating or ink which achieves the desired degree of hardness upon exposure to ultraviolet radiation. This occurs due to the presence of a photo initiating compound which absorbs UV light (light of wavelength from about 200 nm to about 600 nm), generates a free radical, and causes polymerization or cross-linking of functional groups on resin monomers, oligomers or polymers.

The UV-curable resins are composed of a monofunctional or multifunctional monomer, oligomer or polymer molecule and a photoinitiating compound. Monomers, oligomers or polymers typically used for UV curing have at least one ethylenically unsaturated group like an acrylate or methacrylate functional groups.

The UV curable resin is a pigmented or unpigmented urethane resins, acrylic resins, polyester resins, and epoxy resins. These resins are known in the art. Pigmented systems are preferred.

Among those resins especially inks and overprint varnishes are stabilized. Inks are especially offset inks. Printing ink and overprint varnish formulations are well known. Examples of suitable formulations are described, for example in "Printing Ink and Overprint Varnish Formulations" (2nd Edition), published by William Andrew Publishing/Noyes, 1999, which are incorporated by reference herein. Suitable photoinitiators are known to those skilled in the art. For example, α-hydroxyketones and α-aminoketones, phenylglyoxalates or phospinoxides are photoinitiators commonly used in graphic arts applications.

Especially preferred are, for example, the following commercially available photoinitiators: Darocur 1173: 2-hydroxy-2-methyl-1-phenyl-1-propanone (HMPP) and Oligomeric HMPP, lrgacure 184: 1 -hydroxy-cyclohexyl-phenyl ketone, lrgacure 2959: 2-hydroxy-1 -[4-(2-hydroxyethoxy)phenyl]-2-methyl-1 -propanone, lrgacure 369: 2-benzyl-2-(dimethylamino)-1 -[4-(4-morpholinyl)phenyl]-1 -butanone, lrgacure 1300: lrgacure 369 + lrgacure 651 (benzildimethylketal), lrgacure 379: 2-(4-Methylbenzyl)-2-(dimethylamino)-1 -[4-(4-morpholinyl)phenyl]-1 -butanone, lrgacure 127: 2-Hydroxy-1 -{4-[4-(2-hydroxy-2-methyl-propionyl)-benzyl]-phenyl}-2-meth yl- propan-1-one, lrgacure 754: oxo-phenyl-acetic acid 1-methyl-2-[2-(2-oxo-2-phenyl-acetoxy)-propoxy]-ethyl ester, lrgacure 819: bis(2,4,6-trimethylbenzoyl)-phenylphosphine oxide, lrgacure 2100: a mixture of lrgacure 819 and Lucerin TPO (2,4,6-Trimethylbenzoyl-phenyl phosphinic acid ethyl ester), lrgacure 2022: a mixture of lrgacure 819 and Lucerin TPO and Darocur 1173, lrgacur 250: 4-isobutylphenyl-4'-methylphenyl iodonium hexafluorophosphate, Darocur ITX: 2-isopropylthioxanthone and 4-isopropylthioxanthone, Darocur EDB: ethyl-4-dimethylamino benzoate, Darocur EHA: 2-ethylhexyl-4-dimethylamino benzoate.

The above examples of photoinitiators are not limiting.

Pigments which may be used in the invention include organic and inorganic pigments, alone or in combination. The exact choice of pigments will depend upon the specific application and performance requirements such as color reproduction and image stability. Pigments suitable for use in the present invention include, for example, azo pigments, monoazo pigments, disazo pigments, azo pigment lakes, beta-Naphthol pigments, Naphthol AS pigments, benzimidazolone pigments, disazo condensation pigments, metal complex pigments, isoindolinone and isoindoline pigments, polycyclic pigments, phthalocyanine pigments, quinacridone pigments, perylene and perinone pigments, thioindigo pigments, anthrapyrimidone pigments, flavanthrone pigments, anthanthrone pigments, dioxazine pigments, triarylcarbonium pigments, quinophthalone pigments, diketo pyrrol o pyrrole pigments, titanium oxide, iron oxide, and carbon black. Typical examples of pigments which may be used include Color Index (C.I.) Pigment Yellow 1 , 2, 3, 5, 6, 10, 12, 13, 14, 16, 17, 62, 65, 73, 74, 75, 81, 83, 87, 90, 93, 94, 95, 97, 98, 99, 100, 101 , 104, 106, 108, 109, 110, 111 , 113, 114, 116, 117, 120, 121 , 123, 124, 126, 127, 128, 129, 130, 133, 136, 138, 139, 147, 148, 150, 151 , 152, 153, 154, 155, 165, 166, 167, 168, 169, 170, 171 , 172, 173, 174, 175, 176, 177, 179, 180, 181 , 182, 183, 184, 185, 187, 188, 190, 191 , 192, 193, 194; C.I. Pigment Orange 1 , 2, 5, 6, 13, 15, 16, 17, 17:1 , 19, 22, 24, 31 , 34, 36, 38, 40, 43, 44, 46, 48, 49, 51 , 59, 60, 61, 62, 64, 65, 66, 67, 68, 69; C.I. Pigment Red 1 , 2, 3, 4, 5, 6, 7, 8, 9, 10, 11 , 12, 13, 14, 15, 16, 17, 18, 21 , 22, 23, 31 , 32, 38, 48:1 , 48:2, 48:3, 48:4, 49:1, 49:2, 49:3, 50:1 , 51 , 52:1, 52:2, 53:1 , 57:1, 60:1 , 63:1, 66, 67, 68, 81, 95, 112, 114, 119, 122, 136, 144, 146, 147, 148, 149, 150, 151, 164, 166, 168, 169, 170, 171, 172, 175, 176, 177, 178, 179, 181 , 184, 185, 187, 188, 190, 192, 194, 200, 202, 204, 206, 207, 210, 211, 212, 213, 214, 216, 220, 222, 237, 238, 239, 240, 242, 243, 245, 247, 248, 251, 252, 253, 254, 255, 256, 258, 261 , 264; C.I. Pigment Violet 1, 2, 3, 5:1 , 13, 19, 23, 25, 27, 29, 31 , 32, 37, 39, 42, 44, 50; C.I. Pigment Blue 1, 2, 9, 10, 14, 15:1 , 15:2, 15:3, 15:4, 15:6, 15, 16, 18, 19, 24:1 , 25, 56, 60, 61 , 62, 63, 64, 66; C.I. Pigment Green 1, 2, 4, 7, 8, 10, 36, 45; C.I. Pigment Black 1, 7, 20, 31, 32, and C.I. Pigment Brown 1, 5, 22, 23, 25, 38, 41, 42. In a preferred embodiment of the invention, the pigment employed is C.I. Pigment Blue 15:3, C.I. Pigment Red 122, C.I. Pigment Yellow 155, C.I. Pigment Yellow 74, bis(phthalocyanylalumino)tetraphenyldisiloxane or C.I. Pigment Black 7.

If desired, the resin composition of the present invention can further contain additives commonly employed in the art.

The present invention further relates to the use of quinone methides of the formula III as in- can stabilizers for UV-curable resins

wherein

Ri and R2 independently of each other are CrCi8alkyl, C5-Ci2cycloalkyl, C7-Ci5phenylalkyl, optionally substituted C6-Ci0 arγl; R3 and R4 independently of each other are H, optionally substituted C6-Ci0-aryl, 2-,3-,4- pyridyl, 2-,3-furyl or thienyl, COOH, COORI0, CONH2, CONHR10, CONR10R11, -CN, -COR10, -OCOR10, -OPO(OR1o)2, wherein R10 is CrC8alkyl or phenyl.

The present invention relates to the use of mixtures of stable highly sterically hindered nitroxyl radicals of the formulae I or Il as described above and of quinone methides of the formula III as described above as in-can stabilizers for UV-curable resins.

The mole ratio of the highly sterically hindered nitroxyl radical to the quinone methide in the blend is from 1-99mol% to 99 to 1mol%, preferably 1-20mol% to 99-80mol%.

The stabilizer blend also increases the storage stability of a coating or an ink composition which does not contain a photoinitiator. The storage stabilisation of resins not containing a photo initiator is especially important if a reactive binder such as an amine acrγlate is present.

Furthermore, the invention relates to a method for increasing the storage stability of a radiation curable coating composition or ink composition by adding to the coating- or the ink composition, optionally comprising a photoinitiator, a stabilizer blend of a sterically hindered nitroxyl radical, a quinone methide or mixtures thereof Radiation is electromagnetic radiation, such as near infrared (NIR, wavelength range from about 750 nm to about 1500 nm), visible light, UV radiation or X-radiation, especially UV radiation, and corpuscular radiation such as electron beams.

The stabilizer is added in an amount of from 0.0001 to 10% by weight, based on the total amount of coating composition or ink composition, preferably 0.01 to 5%.

Highly sterically hindered nitroxyl radicals and quinone methides as well as acrylic resins containing them are known per se and are described for various applications in the prior art.

A well known application is the use as flame retardant. WO03/054073 WO03/07605 and WO 03/085039 describe acrylic resins containing highly sterically nitroxyl radicals and their use as flame retardants. The use to increase the storage stability is not disclosed therein. US 6,518,326 (Ciba) relates to compounds of formulae

I2

These compounds may be used together with a radical source to effect polymerization of ethylenically unsaturated monomers or oligomers.

WO96/24620 (EIf Atochem) describes compounds of the formula

used for controlled polymerization of ethylenically unsaturated monomers.

US 6,353,107 (Ciba describes sterically highly hindered piperidine nitoxides

used for controlled polymerisation.

WO20022048205 (Ciba) describes compounds of the formula

used for controlled polymerisation. US6,479,608 (Ciba) describes compounds of the formulae

used for controlled polymerisation.

EP 744392 (Ciba) describes quinone methide compounds and their preparation.

In other words the invention relates the use of stable highly sterically hindered nitroxyl radicals of the formulae I or Il to improve the storage stability by preventing the geling of a resin being composed of monomers-, oligomer- or polymer-molecules that have at least one ethylenically unsaturated group,

I II, wherein Ra> Rb Ro Rd are independently of each other optionally substituted CrCi8alkyl or benzyl, optionally substituted C5-Ci2cycloalkyl or C6-Ci0-aryl; or Ra, Rb Rc, Rd together with the carbon atom form a C5-Ci2cycloalkyl ring, A and D are groups required to complete the open chain nitroxyl radical; RΘ, Rf, Rg, Rh are independently of each other optionally substituted CrCi8alkyl or benzyl, optionally substituted C5-Ci2cycloalkyl or C6-Ci0-aryl; or RΘ, Rf, R9, Rh together with the carbon atom form a C5-Ci 2cycloalkyl ring, with the proviso that at least one group is different from methyl; T is a group to complete a ring nitroxyl radical.

In one aspect the invention relates to the use of open chain stable highly sterically hindered nitroxyl radicals of the formulae Ia-Ie

wherein in formula Ia Y is O or CH2; Ri is tertiary C4-Ci8alkyl or C6-Ci0aryl, which are unsubstituted or substituted by halogen, OH, COOR51 or C(O)-R52 wherein R51 is hydrogen, an alkali metal atom or d-Ci8alkyl and R52 is CrCi8alkyl; or Ri is C5-Ci2cycloalkyl, C5-Ci2cycloalkyl which is interrupted by at least one O or N atom, a polycyclic alkyl radical or a polycyclic alkyl radical which is interrupted by at least one O or N atom; R2 and R3 are independently optionally substituted Ci-d8alkyl, benzyl, C5-Ci2cycloalkyl or C6-Ci0aryl; or together with the carbon atom form a C5-Ci2cycloalkyl ring; if Y is O, R4 is OH, O(al kali-metal) Ci-Ci8alkoxy, benzyloxy, NR53R54, wherein R53 and R54 are independently from each other hydrogen, CrCi8alkyl or C6-Ci0aryl, which are unsubstituted or substituted by halogen, OH, C00R5i or C(O)-R52, wherein R51 and R52 is as defined above; if Y is CH2, R4 is OH, CrC18alkoxy, benzyloxy, 0-C(O)-(C1 -C18)alkyl or NR53R54, wherein R53 and R54 is as defined above;

in formula Ib Y1 is O or CH2; R5, R6, R7 and R8 are independently of each other optionally substituted Ci-Ci8alkyl, benzyl, C5-Ci2cycloalkyl or C6-Ci0aryl, with the proviso that not more than two are aryl; or R5 and R6 and/or R7 and R8 together with the carbon atom form a C5-Ci2cycloalkyl ring; R9 is formyl, C2-Ci 8alkylcarbonyl, benzoyl, CrCi8alkyl, C5-Ci2cycloalkyl, C5-Ci 2cycloalkyl which is interrupted by at least one O or N atom, benzyl or C6-Ci0aryl, which are unsubstituted or substituted by halogen, OH, COOR5i or C(O)-R52, wherein R51 and R52 is as defined above;

Rio is OH, O(alkali-metal) CrCi8alkoxy, benzyloxy, NR53R54, wherein R53 and R54 are as defined above; If Y1 Is CH2 Rio is a group C(O)R55, wherein R55 is OH, CrCi8alkoxy, benzyloxy, NR53R54, wherein R53 and R54 are as defined above;

in formula Ic Q is O or NH or N-CrCi8alkyl; Rii, Ri2, Ri3 and Ri4 are independently of each other optionally substituted Ci-d8alkyl, benzyl, C5-Ci2cycloalkyl or C6-Ci0aryl, with the proviso that not more than two are aryl; or Rn and Ri2 and/or R13 and Ri4 together with the carbon atom form a C5-Ci2cycloalkyl ring; Ri5 and Ri6 are independently from each other hydrogen, formyl, C2-Ci8alkylcarbonyl, benzoyl, CrCi8alkyl, C5-Ci2cycloalkyl, C5-Ci2cycloalkyl which is interrupted by at least one O or N atom, benzyl or C6-Ci0aryl which are unsubstituted or substituted by halogen, OH, COOR5I or C(O)-R52, wherein R51 and R52 is as defined above;

in formula Id

Ri8 and Ri9 independently of one another are hydrogen or d-C4alkyl;

in formula Ie R20 and R2i independently of one another are hydrogen or CrC4alkyl;

In another aspect the invention relates to the use of stable highly sterically hindered ring- nitroxyl radicals of the formula Na-IId

wherein in formula Ha R22, R23, R24, R25 are independently of each other d-C4alkyl with the proviso that at least one group is different from methyl; or R22and R23 and/or R24and R25 form together with the C-atom to which they are bound a C5-C8 cycloalkyl ring; R26, R27 are independently of each other H or CrCi8alkoxy;if R26 is H, R27 is additionally OH, -O-(Ci-Ci8)acyl, -NHR56 or N(R46J2, wherein R56 is H, CrCi8alkyl, C5-C7cycloalkyl, C7- C9phenylalkyl, C6-Ci0aryl or Ci-Ci8acyl; or R26 and R27 together with the C-atom to which they are bonded form a cyclic ketale group

wherein k is 0, 1 or 2 and R57 is CrCi8alkyl, -CH2-OH,

-CH2-O-(Ci -Ci8)alkyl or -CH2-O-(Ci -Ci8)acyl; if k is 2, then the two R47 group may be different; or R26 and R27 together form the group =0, =N-O-R58 or =N-N-R59R60, wherein R58, R59, R60 independently are H, CrCi8alkyl, C5-C7cycloalkyl, C7-C9phenylalkyl, C6-Ci0aryl or

R28 is hydrogen or methyl;

in formula Hb A is O and E is -CH2- or A is NR61 and E is -C(O)-, -CH2- or a direct bond; wherein R61 is H, CrCi8alkyl, C5-C8cycloalkyl, C7-C9phenylalkyl, C6-Ci0aryl or CrCi8acyl; R29, R3o, R31, R32 are independently of each other CrC4alkyl; or R29 and R20 and/or R31 and R32 form together with the C-atom to which they are bound a C5-C8 cycloalkyl ring; or R29, R3o> R3i, R32 can have inserted oxygen or bear functional groups to give compounds like

in formula Hc R33, R34, R35, R36 are independently of each other d-C4alkyl; or R33 and R34 and/or R35 and R36 form together with the C-atom to which they are bound a C5-C8 cycloalkyl ring; or R33, R34, R35, R36 can have inserted oxygen or bear functional groups to give compounds like

R37 is H, Ci-Ci8alkyl, C5-C7cycloalkyl, C7-C9phenylalkyl, C6-Ci oaryl or CrCi8acyl; R38 is H, CrC4 alkyl;

in formula Hd R39 is H, CrCi8alkyl, C5-C7cycloalkyl, C7-C9phenylalkyl, C6-Ci oaryl or CrCi8acyl; R40 is H, CrC4 alkyl; R4I, R42, R43, R44are independently of each other CrC4alkyl; or R33 and R34 and/or R35 and R36 form together with the C-atom to which they are bound a C5-C8 cycloalkyl ring.

Definitions Halogen is Fluorine, Chlorine, Bromine or Iodine, preferably Chlorine or Bromine.

The alkyl radicals in the various substituents may be linear or branched. Examples of alkyl containing 1 to 18 carbon atoms are methyl, ethyl, propyl, isopropyl, butyl, 2-butyl, isobutyl, t- butyl, pentyl, 2-pentyl, hexyl, heptyl, octyl, 2-ethylhexyl, t-octyl, nonyl, decyl, undecyl, dodecyl, tridecyl, tetradecyl, hexadecyl and octadecyl. C5-Ci2cycloalkyl is typically, cyclopentyl, methylcyclopentyl, dimethylcyclopentyl, cyclohexyl, methylcyclohexyl.

Cycloalkyl which is interrupted by at least one O or N atom is for example 2-tetrahydropyran- yl, tetrahydrofurane-yl, 1,4 dioxan-yl, pyrrolidin-yl, tetrahydrothiophen-yl, pyrazolidin-yl, imidazolidin-yl, butyrolactone-yl, caprolactame-yl

Substituted CrCi8alkyl or benzyl, substituted C5-Ci2cycloalkyl or C6-Ci0-aryl which are substituted by CrCi2alkyl, halogen, CrCi2alkoxy, OH, COOR51, C(O)-R52 or -0-CO-R52; wherein R51 is hydrogen, an alkali metal atom or CrCi8alkyl and R52 is CrCi8alkyl. Examples for alkali metal are lithium, sodium or potassium.

C1-C18 alkoxy is for example methoxy, ethoxy, propoxy, butoxy, pentoxy, octoxy, dodecyloxy or octadecyloxy.

C2-Ci8 alkylcarbonyl is for example acetyl, propionyl, butyryl, pentylcarbonyl, hexylcarbonyl or dodecylcarbonyl.

An acyl residue is derived from an aliphatic, cycloaliphatic or aromatic monocarboxylic acid having up to 18 carbon atoms.

The C6-Ci0aryl groups are phenyl or naphthyl, preferrably phenyl.

Polycyclic alkyl radicals which may also be interrupted by at least one oxygen or nitrogen atom are for example adamantane, cubane, twistane, norbomane, bycyclo[2.2.2]octane

Preferences Preferred are: in formula Ia Y is O; Ri is tertiary C4-Ci8alkyl; or C5-Ci2cycloalkyl or C5-Ci2cycloalkyl which is interrupted by at least one O or N atom; R2 and R3 are independently CrCi8alkyl; or together with the carbon atom form a C5- C6cycloalkyl ring; R4 is CrCi8alkoxy, benzyloxy or NR53R54, wherein R53 and R54 are independently from each other hydrogen, d-Ci8alkyl;

in formula Ib

R5, R6, R7 and R8 are independently of each other CrCi8alkyl; or R5 and R6 and/or R7 and R8 together with the carbon atom form a C5-C6cycloalkyl ring; R9 is formyl, C2-C8alkylcarbonyl, benzoyl, CrCi8alkyl, benzyl or phenyl; Rio is Ci-Ci8alkoxy, benzyloxy, NR53R54, wherein R53 and R54 are as defined above;

in formula Ic Q is O; Rii, Ri2, Ri3 and R14 are independently of each other CrCi8alkyl or phenyl; or Rn and R12 and/or R13 and R14 together with the carbon atom form a C5-C6cycloalkyl ring; Ri5 and Ri6 are independently from each other formyl, C2-Ci8alkylcarbonyl, benzoyl, d- Ci8alkyl, benzyl or phenyl;

in formula Id Ri7 is phenyl; Ri8 and Ri9 independently of one another are CrC4alkyl;

in formula Ie R20 and R2i independently of one another are d-C4alkyl;

in formula Ha R22, R23, R24, R25 are independently d-C4alkyl with the proviso that at least one group is different from methyl; R26, R27 are independently H or d-d8alkoxy; if R26 is H, R27 is additionally OH, -O-(d- d8)acyl, -NH-Ci-Ci8alkyl; or R26 and R27 together with the datom to which they are bonded form a cyclic ketale group

wherein k is 0, 1 or 2 and R57 is d-d8alkyl, -CH2-OH,

-CH2-O-(Ci -Ci8)alkyl or -CH2-O-(Ci -Ci8)acyl; if k is 2, then the two R47 group may be different; or R26 and R27 together form the group =0; R28 is hydrogen or methyl;

in formula Hb A is O and E is -CH2- or A is NR61 and E is -CH2- or a direct bond; wherein R61 is H, d- Ci8alkyl, C5-C8cycloalkyl or C7-C9phenylalkyl; R29, R30, R31, R32 are independently of each other Ci-C4alkyl; or R29 and R20 and/or R31 and R32 form together with the C-atom to which they are bound a C5-C8 cycloalkyl ring; or R29> R3o> R31, R32 can have inserted oxygen or bear functional groups to give

compounds like

in formula Mc R33, R34, R35, R36 are independently of each other d-C4alkyl; or R29 and R20 and/or R31 and R32 form together with the C-atom to which they are bound a C5-C8 cycloalkyl ring; or R29, R3o> R31, R32 can have inserted oxygen or bear functional groups to give

compounds - R37 is H, d-Ciβalkyl; R38 is H, CrC4 alkyl;

in formula Hd R39 is H, d-dβalkyl; R40 is CrC4 alkyl; R41, R42, R43, R^are independently of each other d-C4alkyl;

in formula III R1 and R2 are tert. butyl; R3 is H; R4 is optionally substituted phenyl, COOH, COOR10, CONH2, CONHR10, CONR10R11, -CN, COR10, -OCOR10, -OPO(OR1o)2, wherein R10 is CrC8alkyl or phenyl.

Especially preferred are: in formula Ia Y is O; Ri is tertiary C4-C8alkyl; R2 and R3 are independently of each other methyl or ethyl; or together with the carbon atom form a C5-C6cycloalkyl ring; R4 is C1-C18alkoxy or N H-C1-C18alkyl; in formula Ib

R5, R6, R7 and R8 are independently of each other methyl or ethyl; or R5 and R6 and/or R7 and R8 together with the carbon atom form a C5-C6cycloalkyl ring; Rg C2-C8alkylcarbonyl, benzoyl, d-Ci8alkyl or benzyl; Rio is CrCi8alkoxy or NH-CrCi8alkyl;

in formula Ic Q is O; Rii, Ri2, Ri3 and Ri4 are independently of each other methyl or ethyl or phenyl; or Rn and Ri2 and/or R13 and Ri4 together with the carbon atom form a C5-C6cycloalkyl ring; Ri5 and Ri6 are independently from each other C2-C8alkylcarbonyl, benzoyl, CrC8alkylor benzyl;

in formula Id Ri7 is phenyl; Ri8 and Ri9 independently of one another are methyl or ethyl;

in formula Ie R20 and R2i independently of one another are methyl or ethyl;

in formula Ha R22 and R24 are methyl and R23, and R25 are ethyl; R26, R27 are independently H or Ci-Ci8alkoxy; if R26 is H, R27 is additionally OH; or R26 and R27 together with the C-atom to which they are bonded form a cyclic ketale group

wherein k is 0, 1 or 2 and R47 is CrCi8alkyl, -CH2-OH,

-CH2-O-(Ci -Ci8)alkyl or -CH2-O-(Ci -Ci8)acyl; if k is 2, then the two R47 group may be different; or R26 and R27 together form the group =0; R28 is hydrogen or methyl;

in formula Hb A is O and E is -CH2- or A is NH or N-CrCi8alkyl; R29, R3o, R31, R32 are independently of each other are methyl or ethyl; or R29 and R20 and/or R31 and R32 form together with the C-atom to which they are bound a C5-C6 cycloalkyl ring;

in formula Hc R33, R34, R35, R36 are independently of each other methyl or ethyl; or R29 and R20 and/or R31 and R32 form together with the C-atom to which they are bound a C5-C6 cycloalkyl ring; R37 is H, CrCi8alkyl; R38 is H;

in formula Hd R39 is H; R40 is methyl; R41, R42, R43, R^are independently of each other methyl or ethyl.

Preparation The compounds of the formula Ia, Ib and Ic can be prepared by known methods. The methods are described in US6,518,326 (Ciba).

The compounds of the formula Id and Ie are can be prepared as described in WO96/24620.

The compounds of the formula Na can be prepared as described in US6,353,107 (Ciba). The compounds of the formula Na having a cyclic ketal group can be prepared as described in WO20022048205 (Ciba).

The compounds of the formula Nb, Mc and Md can be prepared as described in US6,479,608 (Ciba)

The compound of formula III can be prepared as described in EP 744392 (Ciba)

Examples: a) prepared according to US6,518,326 Formula Ia

tert-butyl-(dimethyl-methylanninocarbonyl-nnethyl)-annine -N-oxyl

tert-butyl-(dimethyl-tert-butylaminocarbonyl-nnethyl)-ann ine-N-oxyl

tert-butyl-(dimethyl-n-butylaminocarbonyl-nnethyl)-annine -N-oxyl

tert-butyl-(dimethyl-methoxycarbonyl-nnethyl)-annine-N-ox yl

tert-butyl-^ert-butylaminocarbonyl-cyclopentyliden-nnethy lJ-annine-N-oxyl

Formula Ib

(dimethyl-acetoxymethyl-nnethyl)-(dinnethyl-propylanninoc arbonyl-nnethyl)-annine-N-oxyl

(dimethyl-ethoxymethyl-nnethyl)-(dinnethyl-ethoxycarbonyl -nnethyl)-annine-N-oxyl

0 ' T O- Formula Ic

bis-(dimethyl-acetoxymethyl-nnethyl)-annine-N-oxyl

N-(2-benzyloxy-1 , 1 -dimethyl-ethyl)-Nl-(1 -benzyloxymethyl-1 -phenyl-propyl)-amine-N-oxyl

bis-(dimethyl-benzoyloxymethyl-nnethyl)-annine-N-oxyl

b) prepared according to WO96724620 Formula Id tert-butyl-(1-phenyl-2-methyl-propyl)-amine-N-oxyl

Formula Ie tert-butyl-(1-dietylphosphono-2,2-dimethyl)-annine-N-oxyl

c) prepared according to US6,353,107 Formula Ha 2,6-diethyl-2,3,6-trinnethyl-piperidine-1-oxyl

2,2,6-trinnethyl-6-ethyl-pipericline-1-oxyl

2J6-diethyl-2J3J6-trinnethyl-4-hydroxypiperidine-1-oxyl

2J2,6-trimethyl-6-ethyl-4-hydroxypiperidine-1-oxyl

2J2J3-dimethyl-6J6-diethyl-4-hydroxypiperidine-1-oxyl

,6-dipropyl-2,6-dinnethyl-3-ethyl-4-hyclroxypipericline

,6-diethyl-2,3,6-trimethyl-4-propyloxypiperidine-1oxyl

,6-diethyl-2,3,6-trinnethyl-4-lauroyloxypiperidine-1-oxyl

,2-dimethyl-6,6-diethyl-4-stearoyloxypiperidine-1-oxyl

,2-dimethyl-6,6-diethyl-4-benzoyloxypiperidine-1-oxyl

,6-diethyl-2,3,6-trinnethyl-4-oxopiperidine-1-oxyl

2,6-dipropyl-2,6-dimethyl-3-ethyl-4-oxypiperidine-1-oxyl

d) prepared according to WO2002048205, Formula Ha 2,6-diethyl-4,4-dimethoxy-2,3,6-trimethyl-piperidin-1-oxyl

4J4-diethoxy-2J6-diethyl-2J3,6-trimethyl-piperidin-1-oxyl

2,6-Ddethyl-2,3,6-trinnethyl-4,4-dipropoxy-piperidin-1-ox yl

4J4-Dibutoxy-2J6-diethyl-2J3,6-trimethyl-piperidin-1-oxyl

2,6-diethyl-4,4-diisobutoxy-2,3,6-trinnethyl-piperidin-1- oxyl

2,6-diethyl-2J3,6-trinnethyl-4J4-bis-octyloxy-piperidin-1 -oxyl

,4-bis-allyloxy-2,6-diethyl-2,3,6-trinnethyl-piperidin-1- oxyl

J4-bis-cyclohexyloxy-2J6-diethyl-2J3J6-trinnethyl-piperid in-1-oxyl

,4-bis-benzyloxy-2J6-diethyl-2J3J6-trinnethyl-piperidin-1 -oxyl

,9-Diethyl-6,7,9-trinnethyl-1 ,4-dioxa-8-aza-spiro[4.5]decan-8-oxyl

,9-Diethyl-2,6,7,9-tetrannethyl-1,4-dioxa-8-aza-spiro[4.5 ]decan-8-oxyl

,9-Diethyl-2-hydroxymethyl-6,7,9-trinnethyl-1,4-dioxa-8-a za-spiro[4.5]decan-8-oxyl

8,10-Diethyl-7,8,10-trimethyl-1 ,5-dioxa-9-aza-spiro[5.5]undecan-9-oxyl

δ.iO-Diethyl-a.S.Z.δ.iO-pentannethyl-I .S-dioxa-θ-aza-spiroIS.Slundecan-θ-oxyl

2,4-Diethyl-1J2,4-trinnethyl-7J16-dioxa-3-aza-dispiro[5.2 .5.2]hexadec-11-en-3-oxyl

δ.iO-Diethyl-S-hydroxymethyl-Sy.δ.iO-tetrannethyl-I .S-dioxa-θ-aza-spiroIS.SJundecan-θ-oxyl

acetic acid 3,6,10-triethyl-7,δ,10-trinnethyl-1,5-dioxa-9-aza-spiro[5.5 ]undec-3-yl-nnethyl ester- 9-oxyl

octadecanoic acid 3,8, 10-triethyl-7,8, 10-trimethyl-1 ,5-dioxa-9-aza-spiro[5.5]undec-3-ylmethyl ester-9-oxyl

Formula Mb prepared according to US6,479,608, 2,2J5J5-tetraethylimidazolidine-4-on-1-oxyl

3-ethyl-3,3,5-trimethylmorpholin-2-on-4-oxyl

3,3-diethyl-5,5-dimethylmorpholin-2-on-4-oxyl

S.S.S.S-tetraethyl-morpholin^-on^-oxyl

3,3,5-trimethyl-5-pivaloyloxymethylmorpholin-2-on-4-oxyl

3,3-diethyl-5-methyl-5-pivaloyloxymethylmorpholin-2-on-4- oxyl

3,3,5-triethyl-5-pivaloyloxymethylmorpholin-2-on-4-oxyl

3,3-diethyl-5,5,6,6-tetramethylpiperazine-2-on-4-oxyl

-isopropyl-3-ethyl-3,5,5-trinnethylpiperazine-2-on-4-oxyl

-isopropyl-3,3-diethyl-5,5-dinnethylpiperazine-2-on-4-oxy l

-t-butyl-3,3-diethyl-5,5-dinnethylpiperazine-2-on-4-oxyl

-t-butyl-3-ethyl-3,5,5-trimethyl-piperazin-2-on-4-oxyl

-t-butyl-3,5-diethyl-3,5-dimethyl-piperazin-2-on-4-oxyl

-t-butyl-5,5-diethyl-3,3-dinnethyl-piperazin-2-on-4-oxyl

1-t-butyl-3,5,5-triethyl-3-nnethyl-piperazin-2-on-4-oxyl

1-t-butyl-3,3,5-triethyl-5-nnethyl-piperazin-2-on-4-oxyl

1-t-Butyl-3,3,5,5-tetraethyl-piperazin-2-on-4-oxyl

i-t-butyl-S.S-cyclohexyliden-S.S-diethyl-piperazin^-on^-o xyl

1-t-butyl-3,3-dipropyl-5,5-dinnethyl-piperazin-2-on-4-oxy l

-t-butyl-3,3-dipropyl-5,5-diethyl-piperazin-2-on-4-oxyl

-t-butyl-3,3-dibutyl-5,5-dinnethyl-piperazin-2-on-4-oxyl

-t-octyl-3,3-diethyl-5,5-dimethyl-piperazin-2-on-4-oxyl

-(2-hydroxyethyl)-3,3-diethyl-5,5-dimethyl-piperazin-2-on -4-oxyl

-(1 , 1 -dimethyl^-hydroxyethylJ-S^-diethyl-S.S-dinnethyl-piperazin^ -on^-oxyl

-phenyl-3,3-diethyl-5,5-dinnethyl-piperazin-2-on-4-oxyl

1-methyl-3,3-diethyl-5,5-dinnethyl-piperazin-2-on-4-oxyl

1-t-butyl-3-isobutyl-3,5,5-trimethyl-piperazin-2-on-4-oxy l

Formula Hc 1 -butyl-S.S.S.Sy-pentamethyl-II ,4]diazepan-2-one-4-oxyl

1 -butyl-3-ethyl-3,5,5,7-tetrannethyl-[1 ,4]diazepan-2-one-4-oxyl

Formula Hd 2J3,7-trimethyl-2,7-diethyl-[1 ,4]diazepan-5-one-1 -oxyl

2J3J4J7-tetramethyl-2J7-diethyl-[1 ,4]diazepan-5-one-1 -oxyl 2J3J7-trimethyl-2J7-diethyl-4-t-butyloxycarbonyl-[1J4]diazep an-5-one-1-oxyl 4-benzyl-2,3,7-trimethyl-2,7-diethyl-[1,4]diazepan-5-one-1-o xyl

Formula III 4-Benzylidene-2,6-di-tert-butyl-cyclohexa-2,5-dienone and (3,5-Di-tert-butyl-4-oxo-cyclohexa- 2,5-dienylidene)-acetonitrile

Application examples Preparation of the tested in-can stabilizers

a) compound of the formula Na, prepared according to US6,353,107 Example 1

2,6-diethyl-2,3,6-trimethyl-4-hydroxypiperidine-1-oxyl

To a solution of 118.2g (O.θmol) 2,6-diethyl-2J3,6-trimethyl-4-oxopiperidine in 1000ml ethanol 18.2g (0.4 mol) sodium borohydride are added in portions and the temperature is kept below 30 0C. Subsequently the solution is stirred for 2 hours at 500C. Ethanol is distilled off, 500 ml water are added to the residue which is subsequently extracted several times with CH2CI2. The extract is dried over Na2SO4 and the solution is filtered. After removing the solvent 116g (97%) 2,6-diethyl-2,3,6-trimethyl-4-hydroxypiperidin are obtained as yellowish liquid. Elemental analysis calculated for Ci2H25NO: C 72,31%; H 12.64%; N 7.03%. Found: C 71.44%; H 12.71%; N 6.87%.

To a solution of 25.7g (0.13 mol) 2,6-diethyl-2,3,6-trimethyl-4-hydroxypiperidine in 120 ml tetrahydrofurane a solution of a solution of 54.5g (0.22 mol) m-chlor-perbenzoic acid (70%) in 230 ml tetrahydrofurane is droppwise added under stirring within 2 hours at 0°C. The red to brown solution is stirred over night at room temperature and 500 ml hexane, are added. The solution is neutralized by shaking several times with 1 N NaHCO3 and finally with water. The solvent is evaporated and 27.Og (97%) 2,6-diethyl-2J3,6-trimethyl-4-hydroxypiperidine-1-oxyl are obtained as red liquid. Elemental analysis calculated for Ci2H24NO2: C 67.25%; H 11.29%; N 6.54%. Found: C 67.10%; H 11.42%; N 6.68%. Example 2

2J6-diethyl-2J3J6-trimethyl-4-oxopiperidine-1-oxyl

2J6-diethyl-2J3J6-trinnethyl-4-oxopiperidine is prepared in analogy to example 1 by oxidizing 16g (0.08 mol) 2,6-diethyl-2,3,6-trimethyl-4-oxopiperidine with m-chlor-perbenzoic acid. 1Og 2J6-diethyl-2J3J6-trimethyl-4-oxypiperidine-1-oxyl are obtained as red liquid. Elemental analysis calculated for Ci2H22NO2: C 67.89%; H 10.44%; N 6.60%. Found: C 68.00%; H 10.42%; N 6.61%.

b) compounds of the formula Ma prepared according to WO20002048205 Example 3 Z.Θ-Diethyl-e.Z.Θ-trimethyl-i ^-dioxa-δ-aza-spiroμ.SJderøn-δ-oxyl

According to Example 5 in US4, 105,626 δ-aza-βy.θ-trimethyl-Z.Θ-diethyl-i ^-dioxaspiro [4.5]decane are dissolved in 100 ml methylene chloride. Into this solution is dropped a solution of 42.6 g of m-chloroperbenzoic acid in 300 ml methylene chloride within 2 hours. The reaction mixture becomes red and m-chlorobenzoic acid is precipitating gradually. After stirring the mixture for 12 hours the precipitate is filtered off by suction. The filtrate is washed with 200 ml of 2 n sodium hydroxide followed by 200 ml of water. After drying over sodium sulfate the methylene chloride is evaporated and the residue is distilled in vacuo. At 12O.degree. C at 0.65 mm Hg there distills pure δ-aza-β.Z.Θ-trimethyl-Z.Θ-diethyl-i ^- dioxaspiro[4.5]decane-8-oxyl Example 4 octadecanoic acid 3,8, 10-triethyl-7,8, 10-trimethyl-1 ,5-dioxa-9-aza-spiro[5.5]undec-3-ylmethyl ester-9-oxyl

The title compound is prepared by oxidizing octadecanoic acid 3,8, 10-triethyl-7,8, 10- trimethyl-1,5-dioxa-9-aza-spiro[5.5]undec-3-yl-methyl ester (prepared in analogy to US 4,105,626, Example 4) as a red oil. MS (Cl): MH+=595 (C36H68NO5 = 594.95).

c) compound of the formula Mb, prepared according to US6,479,608, Example 5 1-t-Butyl-3,3,5,5-tetraethyl-piperazin-2-on-4-oxyl

40 g (1 mol) of finely ground NaOH are added, with stirring, to a solution of 0.189 mol of 1,1- diethyl-2-t-butylaminoethylamin, (prepared in accordance with M. Senkus.: J.Am. Chem. Soc. 68, 10 (1946)) and 25 ml (0.3 mol) of chloroform in 250 ml of diethyl ketone at 10 0C. The reaction mixture is stirred for 16 hours at room temperature and is then filtered. The filtrate, concentrated by evaporation in a rotary evaporator, is chromatographed over silica gel with hexane/ethyl acetate (3:2). The pure fractions are concentrated by evaporation, to give 1-t-butyl-3,3,5,5-tetraethyl-piperazin-2-on (52%) as a yellow oil.

The compound is transformed into the title compound as red crystals, m.p. 34-37 0C. 45.3 g (0.2 MoI) of raw compound are dissolved in 450 ml of ethylacetate and 51.1 ml (0.3 MoI) of peracetic acid (39% in acetic acid) are added to the stirred solution under cooling within 20 minutes. The solution is stirred for another 2.5 hours, then diluted with 100 ml of hexane and washed with NaHCO3 solution till neutral. The title compound is obtained after evaporation of hexane, chromatography of the residue on Silica gel with hexane-EtOAc (5:1) and crystallization from pentane. Example 6 1-t-octyl-3,3-diethyl-5,5-dinnethyl-piperazin-2-on-4-oxyl

In analogy to Example 5 I J-dimethyl^-t-octylaminoethylamin, diethyl keton, chloroform and NaOH are reacted to give 1-t-octyl-3,3-diethyl-5,5-dimethyl-piperazin-2-on compound as a yellow oil.

0.4 g of sodium tungstate, 2 g of sodium carbonate and then, at 10 0C, 27.5 ml of hydrogen peroxide (35%, in water) are added to a solution of 0.064 mol of 1-t-octyl-3,3-diethyl-5,5- dimethyl-piperazin-2-on in 50 ml of methanol. The reaction mixture is stirred for 40 hours at room temperature and is then diluted with 100 ml of saturated NaCI solution and extracted with 5 x 50 ml of methyl-tert-butyl ether. The extracts are dried over MgSO4, concentrated by evaporation and chromatographed over silica gel with hexane/ ethyl acetate (3:1). The pure fractions are concentrated by evaporation, giving the title compound as red crystals, m.p. 54- 56 0C.

Example 7: tert-butyl-(1-dietylphosphono-2,2-dimethyl)-amine-N-oxyl

prepared as described in WO96/24620.

Preparation of the quinone methides according to EP744392 2,6-Di-tert-butyl-4-benzylidene-cyclohexa-2,5-dienone

To a solution of 23.7 g (0.28 mol) of piperidine, 106.1 g (1.0 mol) of benzaldehyde and 206.3 g (1.0 mol) of 2,6-di-tert-butylphenol in 20 ml of toluene is added slowly 70 g (0.82 mol) of piperidine over a one-hour period at 135 DEG C-140 DEG C. The reaction mixture is then heated for another three hours with a continuous separation of water occurring. The resulting Mannich base prepared in situ is diluted with 200 ml of xylene and hydrogen chloride gas is bubbled into the reaction mixture at about 140 DEG C till a state of saturation is reached in about 45 minutes. The mixture is heated for another hour to ensure that the reaction is complete as seen by thin layer chromatography (tic) and gas liquid chromatography (glc) tests. The piperidine hydrochloride formed is removed by filtration. The dark red filtrate obtained is washed thrice with 200 ml of water and finally stirred with 100 g of Kieselgur for 30 minutes. Removal of the Kieselgur by filtration and evaporation of the solvent afford 285.6 g of a dark red viscous oil which contains about 90% (glc) of the title compound. This product is purified further by distillation under vacuum (10 bar) giving 253.4 g (86.1% yield) of a fraction boiling between 160 DEG C-168 DEG C which is 96% pure in glc. This yellow viscous product slowly crystallizes on standing at room temperature.

(S.S-Di-tert-butyM-oxocyclohexa^S-dienylideneJacetonitril e This compound can be made by the procedure of V. V. Ershov et al., Izv. Akad. Nauk. SSSR, Ser. Khim. (5), 928 (1966)

Methyl ^S-Di-tert-butyM-oxocyclohexa^S-dienylideneJacetate This compound can be made by the procedure of F. R. Hewgill et al., Aust. J. Chem. 30, 2565 (1977) Two technical parameters of the new stabilizers were tested:

1. Stabilization efficiency at 70 °C a) in TMPTA (Trimethylolpropane triacrylate) which contains 5% photoinitiator IRGACURE 369 (2-benzyl-2-(dimethylamino)-1-[4-(4-morpholinyl)phenyl]-1-bu tanone) b) in UV-curable offset ink, which contains Pigment Orange 34. 2. Influence of the presence of the new In-can stabilizer on the curing efficiency of blue UV-curable offset ink.

Experimental details

Storage stability of TMPTA 5 g IRGACURE 369 were added to 95 g TMPTA (UCB) and stirred to give a clear, yellowish solution with an initiator concentration of 5 wt-%. 0.1 g stabilizer were added to the solution and stirred until the substance was dissolved completely. 2 ml of the solutions were filled into 2.5 ml-analytical vials and placed in a drying oven (2 samples per substance and concentration). The samples were stored at 70 0C and the polymerization (usually starting at the bottom, to the top) was checked visually (reported as days until the polymerization started).

Storage stability of orange offset ink 0.2 g of a TMPTA solution containing 2.5 wt-% stabilizer were added to 5.0 g of a commercial orange offset ink (w/o previously added stabilizer) and were distributed homogeneously in a muller. 2.4 g of the ink were filled into a weighing container (glass, diameter 13 mm) and placed in a drying oven. The samples were stored at 70 °C and the polymerization of the ink (usually starting at the bottom, to the top) was checked with a spatula (reported as days until the polymerization started).

Influence of the stabilizer on the curing efficiency of a blue offset ink For the assessment of the influence on curing efficiency, a blue UV offset ink was selected as appropriate testing system. Composition of the blue offset ink:

0.2 g of a TMPTA solution containing 2.5 wt-% stabilizer were added to 5.0 g of the blue offset ink and were distributed homogeneously in a muller. The inks were printed with a Prϋfbau multipurpose printability tester on white Lumiart paper (1.5 g/m2) and were exposed to the radiation of one medium-pressure mercury lamp, at 150 W/cm in an UV curing unit from IST-Metz. The through cure (line speed in m/min) and the surface cure (y/n) of the ink were assessed after the exposure.

Results

Start of Line speed for Start of TMPTA Concentration polymerization of curing of blue Stabilizer polymerization at [wt-%] orange offset ink offset ink 70 0C [days] at 70 0C [days] [m/min]

References

Blank - 1-2 3 130 Florstab 1.02 13 >24 120 UV-11

lrgastab 0.1 18 3 90 UV103

Nitroxyl radicals 1 ) Kromachem. 2) Commonly used concentration of Florstab UV1 in UV inks.

3) Irgastab UV IO Ciba Specialty Chemicals.

The high sterically hindered nitroxyl radicals show a higher stabilization effect like the commercial products Florstab UV1 and lrgastab UV10, in particular in the TMPTA / lrgacure 369 mixture. They have no or only a small negative influence on the curing efficiency of the blue offset ink. Storage stability using a mixture of a highly sterically hindered nitroxyl radical and a quinine methide.

Mixture used:

in 16g OTA 480 UCB. This corresponds to a 20% solution of stabilizer.

Formulation 1 : TMPTA (Trimethylol propane triacrylate monomer UCB) which contains 5% photoinitiator IRGACURE 369 (2-benzyl-2-(dimethylamino)-1-[4-(4-morpholinyl)phenyl]-1- butanone)

0.05g or 0.1 g of the stabilizer mixture in OTA 480 (as a 20% solution) were added to 1Og of the Formulation 1 and stirred until the substance was dissolved completely. 2 ml of the solutions were filled into 2.5 ml-analytical vials and placed in a drying oven (2 samples per substance and concentration). The samples were stored at 70 0C and the polymerization (usually starting at the bottom, to the top) was checked visually (reported as days until the polymerization started).

There was no gelation after 15 days. Without stabilization polymerization starts after two days.

Formulation 2: Orange ink from SICPA Security Inks which contains 5% photoinitiator IRGACURE 369.

0.025g or 0.5g of the stabilizer mixture in OTA 480 (as a 20% solution) were added to 10g of the Formulation 2 and mixed using a pigment mill. 2,4 g samples were stored at 70 °C and the polymerization (usually starting at the bottom, to the top) was checked visually (reported as days until the polymerization started).

There was no gelation after 15 days. Without stabilization polymerization starts after two days.