WO2013083956A1

WO2013083956A1 - Radiation curable inks

Info

Publication number: WO2013083956A1
Application number: PCT/GB2012/052921
Authority: WO
Inventors: Nigel Gould
Original assignee: Sericol Limited
Priority date: 2011-12-08
Filing date: 2012-11-27
Publication date: 2013-06-13
Also published as: GB201406708D0; GB201121139D0; GB2510733A; GB2510733B

Abstract

A radiation-curable ink having low nozzle blocking, good solvent and water rub resistance and good adhesion, the ink having a viscosity of 1 to 80 mPa⋅s and being suitable for use in ink jet printing and comprising: Component A: a water-soluble, radiation-curable polymer; Component B: a colorant; Component C: water; and Component D: a water-dispersible, radiation-curable polyurethane.

Description

RADIATION CURABLE INKS

This invention relates to radiation-curable inks, to a printing method and to an ink jet printer cartridge.

Ink jet printing is a commonly used technique for printing substrates with an ink composition. The inks used vary depending on the properties required for the printed substrate. Water-based, solvent-based and radiation-curable ink jet printing inks are commercially available.

Many radiation-curable inkjet inks suffer from the problem of nozzle blocking, typically as a result of the ink forming an insoluble film within or over the very small nozzles used in ink jet printers. Furthermore, the resultant cured inks can suffer from poor adhesion to the substrate and low water- and/or solvent-resistance.

There exists a need for inks suitable for use in ink jet printing which have a low tendency to block nozzles and, when cured, provide prints having good adhesion, water- and solvent-resistance.

According to a first aspect of the present invention, there is provided a radiation-curable ink having a viscosity of 1 to 80 mPa-s comprising:

Component A: a water-soluble, radiation-curable polymer;

Component B: a colorant;

Component C: water; and

Component D: a water-dispersible, radiation-curable polyurethane.

In this document (including its claims), the verb "comprising" and its conjugations is used in its non-limiting sense to mean that items following the word are included, but items not specifically mentioned are not excluded. In addition, reference to an element by the indefinite article "a" or "an" does not exclude the possibility that more than one of the elements is present, unless the context clearly requires that there be one and only one of the elements. The indefinite article "a" or "an" thus usually mean "at least one".

Component A typically comprises a water-solubilising group. The identity of the water-solubilising group is not particularly limited as long as it (or they) impart water-solubility to Component A. Preferred water-solubilising groups are acidic groups, e.g. carboxylic, sulfonic, phosphoric and, phosphonic acid groups and combinations comprising two or more thereof, more preferably carboxylic and sulfonic acid groups, especially a carboxylic acid groups. Such acidic groups may be in the free acid form or, more preferably, in salt form. Preferred salts are alkali metal salts, especially lithium, sodium and potassium, ammonium and substituted ammonium salts (including quaternary amines such as ((CH3)₄N+) and mixtures thereof. Especially preferred are salts with sodium, lithium, ammonia and/or volatile amines, more especially sodium salts.

Acidic groups may be converted into various salt forms using known techniques, e.g. ion exchange or simply adding a base or alkali.

Preferably 1 g of Component A is soluble in an amount of less than 30 ml, more preferably in an amount of less than 20 ml, and further more preferably in an amount of 10 ml of deionised water at 25°C.

From the viewpoints of solvent resistance and adhesiveness to a base material after the ink composition has been cured, Component A is preferably a high-molecular-weight compound having an average molecular weight of 5,000 or more.

Preferably Component A comprises at least one maleimide group, e.g. of Formula (1 ):

Formula (1 )

wherein:

R^a and R^b are each independently H or an optionally substituted Ci_-4- alkyl group, or

R^a and R^b together with the carbon atoms to which they are attached form an optionally substituted 4- to 6-membered ring.

Preferably R^a and R^b are each independently a Ci_-4- alkyl group. When R^a or R^b is a Ci-₄- alkyl group it may be substituted or, more preferably, unsubstituted.

The Ci-₄- alkyl groups represented by R^a and R^b may each independently have a linear or branched structure. Specific examples thereof include a methyl, ethyl, propyl, isopropyl, butyl, iso-butyl, sec-butyl, t-butyl.

The optionally substituted 4- to 6-membered ring which may be formed by R^a and R^b together with the carbon atoms to which they are attached (i.e. the carbon atoms shown in Formula (1 )) may be substituted or unsubstituted, but it is preferably unsubstituted. Preferably the ring is a 5-membered ring or, more preferably, a 6-membered ring.

From the viewpoints of physical properties of a cured ink film, such as solvent resistance and adhesiveness to a base material after the ink composition has been cured, it is preferable that R^a and R^b are each independently methyl or ethyl, especially methyl.

Component A preferably has a molecular weight of 5,000 or more and comprises at least two maleimide groups (preferably each independently of Formula (1 )) and a water-solubilising group.

In one embodiment the molecular weights referred to in this specification are weight average molecular weights. In another embodiment the molecular weights referred to in this specification are number average molecular weights.

The number of groups each represented by Formula (1 ) is not particularly limited, but is preferably from 2 to 500, and more preferably from 10 to 200. In one embodiment at least one of the groups each represented by Formula (1 ) is present at a side chain of the polymer, and more preferable that at least two of the groups each represented by Formula (1 ) are present at one or more side chains of the polymer.

From the viewpoints of ejection properties and the like at the time of ejecting an ink by an inkjet method, the average molecular weight of Component A is preferably from 5,000 to 200,000, more preferably from 7,000 to 100,000, further more preferably from 10,000 to 50,000, and particularly preferably from 10,000 to 40,000.

The average molecular weight may be measured by gel permeation chromatography (GPC). In the invention, the GPC measurement is carried out using HLC-8020GPC (trade name, manufactured by Tosoh Corporation) with TSK GEL SUPER HZM-H, TSK GEL SUPER HZ4000, and TSK GEL SUPER HZ200 (all trade names, manufactured by Tosoh Corporation; 4.6 mm ID χ 15cm) as columns and tetrahydrofuran (THF) as an eluting solvent.

Preferably Component A is a polyacrylate, polyester, polyethyleneimine, polystyrene, or the like or a copolymer comprising two or more of the foregoing. From the viewpoints of ejection property of an ink composition by an inkjet method, solvent resistance and adhesiveness to a base material after the ink composition has been cured, and the like, Component A preferably has a polyacrylate structure.

Preferably the group of Formula (1 ) is present in Component (A) as part of a group of Formula (1 '):

wherein in Formula (1 '): each R^c independently is H or methyl;

each Z independently is -COO- or -CONR^d-, in which R^d is H or Ci_-4-alkyl; each X independently is a divalent organic group; and

each R^a and R^b independently is as hereinbefore defined.

In Formula (V), Z is preferably -COO-.

In other words, Component A preferably comprises a group of Formula (1 ') as defined above.

The Ci-4-alkyl represented by R^d may have a linear structure or a branched structure. Specific examples thereof include a methyl, ethyl, propyl, isopropyl, butyl, isobutyl, sec-butyl, and t-butyl. R^d is preferably H, methyl or ethyl, especially H. It should be noted that R^d may be substituted or unsubstituted, but is preferably unsubstituted.

In Formula (V), X represents a divalent organic group. The divalent organic group is preferably an alkylene group which has 2 to 20 carbon atoms and which may have a linear structure, a branched structure, or a cyclic structure. The alkylene group may contain an ether bond, an ester bond, an amide bond, a urethane bond, or an arylene group. When X represents an alkylene group, the alkylene group preferably has 2 to 20 carbon atoms, more preferably has 2 to 12 carbon atoms, and further more preferably has 2 to 8 carbon atoms.

In Formula (1 '), it is preferred that R^a and R^b are each independently methyl or ethyl, R^c is methyl, Z is -COO-, and X is an alkylene group having 2 to 12 carbon atoms.

When Component A comprises the group of Formula (1 ') mentioned above,

Component A is preferably obtained by process comprising the polymerisation of a composition comprising a monomer represented by Formula (1 '-1 ) shown below and a monomer havin

R^a, R , R^c, Z, and X in Formula (1 '-1 ) have the same definitions as those of Formula (1 ') mentioned above, respectively, and examples (including preferable examples) thereof are also the same.

From the viewpoint of controlling the physical properties of a film of cured ink composition, it is preferable that the composition further comprises another monomer (hereinafter, also referred to as additional monomer).

Examples of preferred monomers represented by (1 '-1 ) include the following compou 1

(1-1-1) (1-1-2) (1-1-3)

(1-1-4) (1-1-5) (1-1-6)

(1-1-7) (1-1-8) (1-1-9)

(1-1-10) (1-1-11) (1-1-12)

(1-1-13) (1-1-14)

(1-1-15) (1-1-16)

Preferably Component A further comprises a group of Formula (2), in addition to the group of Formula

wherein in Formula (2):

each R^cy independently is H or methyl;

each Z^y independently is -COO-, -CONR^dy-, or a single bond, in which R^dy is H or C i_-4alkyl;

each R^y independently is a single bond or a divalent organic group; and each A independently is a water-solubilising group.

In Formula (2), R^cy is preferably H.

In Formula (2), Z^y is preferably -COO-.

When R^dy is C i_-4alkyl it may have a linear structure or a branched structure. Specific examples thereof include a methyl, ethyl, propyl, isopropyl, butyl, isobutyl, sec-butyl, and t-butyl. R^dy is preferably H, methyl or ethyl, especially H. It should be noted that R^dy may be substituted or unsubstituted, but is preferably unsubstituted.

When R^y is a divalent organic group, the divalent organic group is preferably a substituted or unsubstituted alkylene group having 1 to 20 carbon atoms, a substituted or unsubstituted arylene group having 6 to 20 carbon atoms, or a substituted or unsubstituted aralkylene group having 7 to 20 carbon atoms. These groups may each contain an ether bond, an ester bond, an amide bond, or a urethane bond.

When R^y is an alkylene group having 1 to 20 carbon atoms, the alkylene group may have a linear structure, a branched structure, or a cyclic structure. When R^y is an alkylene group, the alkylene group preferably has 2 to 12 carbon atoms, and more preferably has 2 to 8 carbon atoms. Specific examples of alkylene group represented by R^y include -CH₂-, -C2H4-, -C(CH₃)2-CH₂-, -CH₂C(CH₃)2CH₂-, -C₆Hi2-, C₄H7(C4H9)C₄H8-, Ci₈H₃₆, a 1 ,4-trans-cyclohexylene group, -C₂H -OCO-C₂H -, -C₂H -OCO-, -C₂H -O-C₅Hi₀-, -ΟΗ₂-0-0₅Η₉(0₅Ηιι)-, -C₂H₄-CONH-C₂H₄-, -C₂H₄-CONH-, -C H₈-OCONH-C₆H₁₂-, and

-CH₂-OCONHCioH₂₀-.

When R^y is an arylene group having 6 to 20 carbon atoms, the arylene group preferably has 6 to 18 carbon atoms, more preferably has 6 to 14 carbon atoms, and most preferably has 6 to 10 carbon atoms. Specific examples of arylene group represented by R^y include a phenylene group, a biphenylene group, -C6H₄-CO-C6H₄-, and a naphthylene group.

When R^y is an aralkylene group having 7 to 20 carbon atoms, the aralkylene group preferably has 7 to 18 carbon atoms, more preferably has 7 to 14 carbon atoms, and most preferably has 7 to 10 carbon atoms. Specific examples of aralkylene group represented by R^y include -C3H₆-C6H₄-, -C₂H₄-C6H₄-C6H₄-, -CH₂-C₆H -C₆H -C₂H -, and -C₂H -OCO-C₆H .

In Formula (2), A represents a water-solubilising group, preferably represents -COOM¹, -SO3M¹ , -P(0)(OM²)₂, or -OP(0)(OM²)₂, more preferably represents -COOM¹ or -SO3M¹ , and most preferably represents -COOM¹.

M¹ represents an alkali metal or an onium ion, and preferably an alkali metal. Specific examples of M¹ include a lithium atom, a sodium atom, a potassium atom, and an ammonium ion.

M² represents a H atom, an alkali metal, or an onium ion, and preferably a H atom. Specific examples of M² include a H atom, a lithium atom, a sodium atom, a potassium atom, and an ammonium ion.

It is preferable that A represents -COOM¹ or -SO3M¹ , in which M¹ represents an alkali metal, and more preferable that A represents -COOM¹, in which M¹ represents an alkali metal.

In Formula (2), it is preferable that R^cy is a H atom, Z^y is -COO-, R^y is a single bond, an alkylene group having 2 to 8 carbon atoms, or an arylene group having 6 to 10 carbon atoms, and A is -COOM¹ or -SO3M¹.

The group of Formula (2) may be incorporated into Component A by including a monomer of Formula (2-1 ) in the aforementioned polymerisation process:

In Formula (2-1 ), R^cy, Z^y, R^y, and A have the same definitions as those in Formula (2), respectively, and preferable ranges thereof are also the same.

Preferred examples of monomers of Formula (2-1 ) include following compounds (2-1 -1 ) to (2-1 -15):

Examples of the additional monomers which are copolymerizable with a monomers of (1 '-1 ) and Formula (2-1 ) include styrene, p-methoxystyrene, methyl (meth)acrylate, ethyl (meth)acrylate, allyl (meth)acrylate, butyl (meth)acrylate, hexyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, octyl (meth)acrylate, decyl (meth)acrylate, stearyl (meth)acrylate, cyclohexyl (meth)acrylate, bornyl (meth)acrylate, isobornyl (meth)acrylate, benzyl (meth)acrylate, 2-ethylhexyl diglycol (meth)acrylate, butoxyethyl (meth)acrylate, butoxymethyl (meth)acrylate, 3-methoxybutyl (meth)acrylate, 2-(2-methoxyethoxy)ethyl (meth)acrylate, 2-(2-butoxyethoxy)ethyl (meth)acrylate, 2,2,2-tetrafluoroethyl (meth)acrylate, 1 Η, Ι H,2H,2H-perfluorodecyl (meth)acrylate, 4-butylphenyl (meth)acrylate, phenyl (meth)acrylate, 2,4,5-tetramethylphenyl (meth)acrylate, 4-chlorophenyl (meth)acrylate, phenoxymethyl (meth)acrylate, phenoxyethyl (meth)acrylate, glycidyl (meth)acrylate, glycidyloxybutyl (meth)acrylate, glycidyloxyethyl (meth)acrylate, glycidyloxypropyl (meth)acrylate, tetrahydrofurfuryl (meth)acrylate,

2- hydroxyethyl (meth)acrylate, 3-hydroxypropyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 2-hydroxybutyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate,

3- hydroxypropyl (meth)acrylate, butoxydiethylene glycol (meth)acrylate, trifluoroethyl (meth)acrylate, perfluorooctylethyl (meth)acrylate, 2-hydroxy-3-phenoxypropyl (meth)acrylate, (meth)acrylamide, N-butyl (meth)acrylamide, N-p-hydroxyphenyl (meth)acrylamide, and p-sulfamoylphenyl (meth)acrylamide and combinatiosn comprising two or more thereof. Preferable examples of monomers which are copolymerizable with a monomer represented by Formula (1 '-1 ) include alkyl (meth)acrylates having about 1 to 8 carbon atoms, such as methyl (meth)acrylate, ethyl (meth)acrylate, butyl (meth)acrylate, hexyl (meth)acrylate, or 2-ethylhexyl (meth)acrylate. Any of known monomers other than mentioned above may be additionally used, is necessary.

Component A is preferably of Formula (A):

wherein:

each R^cx independently is H or methyl;

each Z^x independently is -COO-, -CONR^dx-, or a single bond, in which R^dx is H or C-i-4-alkyl;

each R^x independently is H atom, Ci-10-alkyl, an aryl group having 6 to 20 carbon atoms, or an aralkyl group having 7 to 20 carbon atoms;

a, b, and c each independently have a value greater than zero; and each R^a, R^b, R^c and Z independently is as defined in relation to Formula (1 ') (and preferable ranges thereof are also the same) and each R^cy, Z^y, R^y, and A independently is as defined in relation to Formula (2) (and preferable ranges thereof are also the same).

In Formula (A), R^cx is preferably H.

In Formula (A), Z^x is preferably -COO-.

The C-i-4-alkyl group which may be represented by R^dx may have a linear structure or a branched structure. Specific examples thereof include a methyl group, an ethyl group, a propyl group, an isopropyl group, a butyl group, an isobutyl group, a sec-butyl group, and a t-butyl group. R^dx is preferably H, methyl or ethyl, and particularly preferably H. It should be noted that R^dx may be substituted or unsubstituted, but is preferably unsubstituted.

The groups represented by R^x may each be substituted or unsubstituted, and may each contain an ether bond, an ester bond, an amide bond, or a urethane bond.

When R^x is Ci-10-alkyl, the alkyl group may have a linear structure, a branched structure, or a cyclic structure. R^x is preferably d-8-alkyl, more preferably C-i-6-alkyl.

Specific examples of R^x include -CH₃, -C₂H₅, -CH(CH₃)₂, -CH₂C(CH₃)3, -C₆H i 3, a cyclohexyl group, -C2H4-OCO-C2H5, -C2H4-O-C5H11 , -C2H4-CONH-C2H5, and -C₄H8-OCONH-C6H₁₃.

When R^x represents an aryl group having 6 to 20 carbon atoms, the aryl group has 6 to 20 carbon atoms, preferably 6 to 18 carbon atoms, further more preferably 6 to 14 carbon atoms, and most preferably 6 to 10 carbon atoms. Specific examples of aryl group represented by R^x include a phenyl group, a biphenyl group, -C6H₄-CO-C6H₅, and a naphthyl group.

When R^x represents an aralkyl group having 7 to 20 carbon atoms, the aralkyl group has 7 to 20 carbon atoms, preferably 7 to 18 carbon atoms, further more preferably 7 to 14 carbon atoms, and most preferably 7 to 10 carbon atoms. Specific examples of aralkyl group represented by R^x include -C3H6-C6H5, -C2H₄-C6H₄-C6H5, -CH2^_C6H₄-C6H₄-C2H5, and -C2H₄-OCO-C6Hs.

In Formula (Α'), a, b, and c indicate copolymerization ratios in a polymer compound, and the sum of the numbers represented by a, b, and c, respectively, is preferably 100. It should be noted that the copolymerization ratios are in molar ratios. It is preferable that 30 < a + b < 90 and 10 < c < 70, and more preferable that 40 < a + b < 90 and 10 < c < 60.

In Formula (Α'), it is preferable that R^a and R^b are each independently methyl or ethyl; R^c is methyl; Z is -COO-; X is an alkylene group having 2 to 12 carbon atoms; R^cy represents is H; Z^y is -COO-; R^y is a single bond, an alkylene group having 2 to 8 carbon atoms, or an arylene group having 6 to 10 carbon atoms; A is -COOM¹ or -SO3M¹ ; R^cx is H; Zx is -COO-; R^x is C_1-6-alkyl or an aryl group having 6 to 10 carbon atoms; and a, b, and c each independently represent a number that satisfies following expressions: 40 < a + b < 90 and 10 < c < 60.

Examples of Component A include following compounds (A-1 ) to (A-1 1 ), but the present invention is not limited thereto.

In the invention, compounds (A-1 ) to (A-9) may be preferably used as Component A, and compounds (A-1 ) to (A-3) and (A-7) to (A-9) are particularly preferable.

In general, Component A used in the invention and precursors thereof may be produced by a known method. Acrylates usable as precursors of a polymer compound such as Exemplary Compounds (1 -1 -1 ) to (1 -1 -16) may be produced in accordance with the methods disclosed in Japanese Patent Application Laid-Open (JP-A) Nos. 52-988 and 4-251258, and the like. Compounds usable as precursors of a polymer compound such as Exemplary Compounds (2-1 -1 -) to (2-1 -15) may be commercially-available compounds, or may be compounds obtained by neutralizing an acid group of the commercially-available compounds with a hydroxide or the like of an alkali metal. Polymer compounds such as Exemplary Compounds (A-1 ) to (A-1 1 ) may be obtained by polymerizing the above precursors by a known polymerization method, followed by, if necessary, neutralization of acid group thereof with a hydroxide or the like of an alkali metal. For example, such polymer compounds may be produced by a method in accordance with the polymerization methods disclosed in JP-A Nos. 52-988 and 55-154970, Langmuir Vol. 18, 14, pp. 5414-5421 , 2002, and the like.

The content of Component A in the ink composition is preferably from 1 to 50% by mass, more preferably from 2 to 35% by mass, and further more preferably from 3 to 30% by mass. When the content of Component A is 1 % by mass or more, favorable physical properties of a cured film may be obtained, and when the content is 50% by mass or less, ink viscosity may be maintained at an appropriate degree.

The colorant usable in the invention is not particularly limited, and may be selected from known colorants such as pigments, water-soluble dyes, and disperse dyes. Of these, the colorant preferably is or comprises a pigment.

Preferred colorants comprise a coloured, water-insoluble core and a polymer (e.g. acrylate polymer) shell having water-dispersing groups (e.g. carboxy and/or sulpho groups). Such colorants may be obtained, if desired, by dispersing a pigment in a liquid medium comprising a dispersant having carboxy groups and a crosslinking agent and cross-linking the dispersant with the crosslinking agent, thereby forming a polymer shell having water-dispersing groups around a water-insoluble, pigment core. Suitable methods for making such colorants are described in more detail in, for example, WO 2006/064193 and WO 201 1008810.

Suitable pigment-based colorants are also available commercially, in the form of aqueous dispersions, from FUJIFILM Imaging Colorants, e.g. the Pro-Jet™ APD range of pigment-based colorants. Examples include Pro-Jet™ APD 1000 yellow, magenta cyan and black.

When component (B) is included in the ink as an aqueous dispersion the water is not included when calculating the amount of component (B) present.

The pigment is not particularly limited, and may be appropriately selected depending on the purpose. Examples of pigment include known organic pigments and inorganic pigments, for example as listed in the Colour Index. Examples of pigments include yellow, magenta, cyan, green, orange, purple, brown, black, and white pigments.

Examples of yellow pigments include: C. I. Pigment Yellow 1 , 2, 3, 4, 5, 10, 65, 73, 74, 75, 97, 98, 1 1 1 , 1 16, 130, 167, 205, 61 , 62, 100, 168, 169, 183, 191 , 206, 209, 212, 12, 13, 14, 16, 17, 55, 63, 77, 81 , 83, 106, 124, 126, 127, 152, 155, 170,

172, 174, 176, 214, 219, 24, 99, 108, 193, 199; 60, 93, 95, 128, 166, 109, 1 10, 139,

173, 185, 120, 151 , 154, 175, 180, 181 , 194, 1 17, 129, 150, 153, 138, and 213.

Examples of magenta pigments include: C. I. Pigment Red 193, 38, 2, 5, 8, 9, 10, 1 1 , 12, 14, 15, 16, 17, 18, 22, 23, 31 , 32, 1 12, 1 14, 146, 147, 150, 170, 184, 187, 188, 210, 213, 238, 245, 253, 256, 258, 266, 268, 269, 3, 4, 6, 49, 53, 68; 237, 239, 247, 41 , 48, 52, 57, 58, 63, 64: 1 , 200, 81 : 1 , 169, 172, 88, 181 , 279, 123, 149, 178, 179, 190, 224, 144, 166, 214, 220, 221 , 242, 262, 168, 177, 182, 226, 263, 83, 171 , 175, 176, 185, 208, 122, 202 (including a mixture thereof with C. I. Pigment Violet 19), 207, 209, 254, 255, 264, 270, 272, 257 and 271 .

Examples of cyan pigments include: C. I. Pigment Blue 25, 26, 15, 15: 1 , 15:2, 15:3, 15:4, 15:6, 16, 17: 1 , 75, 79, 1 , 24: 1 , 56, 61 , 62, 60, 63 and 80.

Examples of green pigments include C. I. Pigment Green 1 , 4, 7, 36 and 8. Examples of orange pigments include C. I. Pigment Orange 1 , 2, 3, 5, 4, 24, 38, 74, 13, 34, 36, 60, 62, 64, 72, 15, 16, 17, 46, 19, 43, 48, 49, 51 , 61 , 66, 68, 71 , 73 and 81 .

Examples of brown pigments include C. I. Pigment Brown 5, 23, 41 , 42, 25 and 32.

Examples of purple pigments include C. I. Pigment Violet 1 , 2, 3, 27, 13, 17, 25, 50, 5: 1 , 19, 23, 37 29, 32, and 38.

Examples of black pigments include: C. I. Pigment Black 1 , 7, 10, 1 1 , 20, 31 and 32.

Examples of white pigments include: C. I. Pigment White 4; 6, 7, 12, 18, 19, 21 , 22, 23, 27 and 28.

Preferably the pigment, dispersing agent and dispersing conditions are selected such that the pigment particles have a volume average particle diameter of 0.005 pm to 0.5 pm, more preferably 0.01 pm to 0.45 pm, and especially 0.015 pm to 0.4 pm. When the average particle diameter is within the above ranges, the effect of the invention may be further exerted.

The average particle diameter and particle size distribution of particles may be determined by measuring a volume average particle diameter by dynamic light scattering method using a commercially-available particle size analyzer such as a Nanotrac particle size analyzer UPA-EX150 (trade name, manufactured by Nikkiso Co., Ltd.).

Examples of water-soluble dye usable in the invention include acid dyes and direct dyes. Acid dyes and direct dyes have structures containing an acid group as a solubilizing group. Such dyes are listed in the Colour Index International and many are available commercially.

The ink optionally comprises only one type of colorant, or a combination of two or more colorants may be used.

The content of Component B is preferably from 0.1 to 30% by mass, and more preferably from 0.5 to 20% by mass, with respect to the total mass of the ink.

Preferably the ink contains water as the main solvent, especially deionised water.

The content of Component C, water, in the ink is preferably from 10 to 97% by mass, more preferably from 30 to 95% by mass, and further more preferably from 35 to 93% by mass.

Component D preferably has an MFFT of below 0°C.

Preferably the wt% of Component D present in the ink of the invention is greater than the wt% of Component A, more preferably the wt% of Component D is at least double the wt% of Component A. Component D is water-dispersible and typically is included in the ink as a dispersion in water. When Component D is included in the ink as a dispersion in water, the water (and any other solvent which may be present) is not included when calculating the amount of Component D present. For example, 10g of a 35% solids aqueous dispersion of water-dispersible, radiation-curable polyurethane would count as 3.5g of Component D. The same principle applies to Component A, which may also be included in the ink in the form of a solution and the solvent (typically water) is not included when calculating the amount of Component D present.

Of course Component D has a lower solubility water at 25°C than Component A.

Preferably Component forms a clear solution when mixed with water at 25°C in a weight ratio of 10: 1 and when mixed with water at 25°C in a weight ratio of 1 : 10. In contrast, Component D typically forms a turbid mixture when mixed with water at 25°C in one or both of the aforementioned ratios (1 : 10 and/or 10: 1 ).

Water-dispersible, radiation-curable polyurethanes are commercially available from a number of sources for use in wood and floor finishes. For example, Cytec sell such polyurethanes as aqueous dispersions under the Ucecoat™ trade mark. Examples of commercially available water-dispersible, radiation-curable polyurethanes include Alberdingk™ Lux 399 and Lux 515 from Alberdingk Boley, Laromer™ 8949 from BASF and Ucecoat™ 7571 , 7655, 7689, 7699 and 7890 from Cytec, with Ucecoat™ 7655 being preferred.

In one embodiment Component D is a filtered, water-dispersible polyurethane having ethylenically unsaturated groups. In this way one may remove particles which might otherwise block the fine nozzles used in ink jet printheads.

Preferably Component D is free from maleimide groups, e.g. free from groups of Formula (1 ) as hereinbefore defined. Thus in a preferred embodiment Component A comprises a maleimide groups and Component D is free from maleimide groups, and such maleimide groups are preferably of Formula (1 ) as hereinbefore defined.

In another embodiment, Component A comprises a maleimide groups and is free from urethane groups and Component D comprises urethane groups and is free from maleimide groups, and such maleimide groups are preferably of Formula (1 ) as hereinbefore defined.

The radiation-curable ink of the invention optionally further contains a water-miscible organic solvent as Component E, especially a water-miscible organic solvent having a solubility in water at 25°C of 10% by mass or more.

Examples of water-miscible organic solvent which may be used in the invention include the following: a monohydric alcohol; e.g. methanol, ethanol, propanol, isopropanol, butanol, isobutanol, secondary butanol, tertiary butanol, pentanol, hexanol, cyclohexanol, or benzyl alcohol;

a polyhydric alcohol, e.g. as ethylene glycol, diethylene glycol, triethylene glycol, polyethylene glycol, propylene glycol, dipropylene glycol, polypropylene glycol, butylene glycol, hexanediol, pentanediol, glycerin, hexanetriol, thiodiglycol, or 2-methylpropanediol;

a polyhydric alcohol ether, e.g. ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol monobutyl ether, diethylene glycol monoethyl ether, diethylene glycol monomethyl ether, diethylene glycol monobutyl ether, propylene glycol monomethyl ether, propylene glycol monobutyl ether, tripropylene glycol monomethyl ether, dipropylene glycol monomethyl ether, dipropylene glycol dimethyl ether, ethylene glycol monomethyl ether acetate, triethylene glycol monomethyl ether, triethylene glycol monoethyl ether, triethylene glycol monobutyl ether, ethylene glycol monophenyl ether, or propylene glycol monophenyl ether;

an amide, e.g. formamide, Ν,Ν-dimethyl formamide, or N,N-dimethyl acetamide;

a heterocyclic compound, e.g. 2-pyrrolidone, N-methyl-2-pyrrolidone, cyclohexylpyrrolidone, 2-oxazolidone, 1 ,3-dimethyl-2-imidazolidinone, or γ-butyrolactone;

a sulfoxide, e.g. dimethyl sulfoxide;

a sulfone, e.g. sulfolane;

another compound such as urea, acetonitrile, or acetone; and

a combination comprising two or more of the foregoing.

When present, the water-miscible organic solvent comprises a polyhydric alcohol ether or a heterocyclic compound, more preferably a combination thereof. Among polyhydric alcohol ethers, glycol ethers are preferable, and specifically, tripropylene glycol monomethyl ether, dipropylene glycol monomethyl ether, and dipropylene glycol dimethyl ether are preferable. Among heterocyclic compounds, 2-pyrrolidone, N-methyl pyrrolidone, γ-butyrolactone, and the like are preferable, and 2-pyrrolidone is particularly preferable. In particular, a high-boiling solvent is preferable from the viewpoint of improvement in ejection property, and the high-boiling solvent has a boiling temperature at normal pressure of preferably 120°C or more, and more preferably 150°C or more.

The water-miscible organic solvent may consist of a single solvent or a combination of two or more thereof may be used.

The total amount of water-miscible organic solvent included in the ink is preferably from 1 to 60% by mass, more preferably from 2 to 35% by mass.

The ink optionally contains the water-miscible organic solvent as Component E in addition to Components A to D.

Preferably the radiation-curable ink comprises:

0.25 to 30% of Component A;

0.1 to 30% of Component B;

10 to 97% of Component C

5 to 20% of Component D; and

0 to 60% of Component E;

wherein all % are by mass relative to the total mass of components A, B, C, D and E.

More preferably the radiation-curable ink comprises:

0.5 to 20% of Component A;

0.5 to 20% of Component B;

30 to 95% of Component C;

5 to 15% of Component D; and

2 to 40 % of Component E;

In an especially preferred embodiment the radiation-curable ink comprises:

1 to 12% of Component A;

0.5 to 20% of Component B;

35 to 93% of Component C;

5 to 10% of Component D; and

2 to 35% of Component E;

The mass ratio of Component C to Component E, when present, is preferably from 1 :0.1 to 1 : 10, more preferably from 1 :0.2 to 1 :5, further more preferably from 1 :0.2 to 1 :2, and most preferably from 1 :0.3 to 1 :0.6.

The ink optionally contains a further additive in addition to the Components A, B, C, D and E.

Optionally the ink further comprises a dispersing agent. Examples of pigment dispersing agents which may be used include surfactants, e.g. higher fatty acid salts, alkyl sulfate salts, alkyl ester sulfate salts, alkyl sulfonate salts, sulfosuccinic acid salts, naphthalene sulfonate salts, alkyl phosphate salts, polyoxyalkylene alkyl ether phosphate salts, polyoxyalkylene alkyl phenyl ether, polyoxyethylene polyoxypropylene glycol, glycerin ester, sorbitan ester, polyoxyethylene fatty acid amide, or amine oxide; and block copolymers, random copolymers, and salts thereof formed from at least two types of monomers selected from the group consisting of styrene, a styrene derivative, a vinyl naphthalene derivative, acrylic acid, an acrylic acid derivative, maleic acid, a maleic acid derivative, itaconic acid, an itaconic acid derivative, fumaric acid, and a fumaric acid derivative; and combinations comprising two or more of the foregoing.

The pigment is optionally a self-dispersive pigment, i.e. a pigment capable of being dispersed without a dispersing agent, e.g. a pigment comprising coloured particles and surface polar groups.

Examples of surface polar groups include a sulfonic, carboxylic, phosphoric, boric acid groups, and hydroxyl groups, with sulfonic and carboxylic acid groups being preferable, and sulfonic acid groups being more preferable. Such groups may be in free acid or salt form.

Pigments having surface polar groups are commercially available, e.g. from Cabot Corporation under the Cabojet trade mark.

Typically the pigment is dispersed with one or more of the other ink components using a dispersing apparatus, e.g. a ball mill, a sand mill, an attritor, a roll mill, an agitator, a henschel mixer, a colloidal mill, an ultrasonic homogenizer, a pearl mill, a wet-type jet mill, and/or a paint shaker. Furthermore, it is preferable to use a centrifugal separator or a filter to remove coarse particles of pigment dispersion.

Regarding a preferable amount of dispersing agent added to an ink composition, it is preferable that the mass ratio D/P, in which P represents a mass of pigment in an ink composition and D represents a mass of a polymer dispersing agent in an ink composition, satisfies following equation: 0.01 < D/P < 2.0, more preferably 0.03 < D/P < 1 .5, and further more preferably 0.05 < D/P < 0.6. When a dispersing treatment is carried out, a dispersing aid which is generally called a synergist (e.g., SOLSPERSE™ series such as SOLSPERSE™ 5000, 12000, or 22000 (trade marks of Lubrizol Corporation), and EFKA™ 6745 (trade mark of BASF)), and various surfactants and defoaming agents may preferably be added in addition to the dispersing agent, to increase dispersibility of pigment or wettability.

When bead mill dispersing is carried out, beads having a volume average particle diameter of preferably from 0.01 mm to 3.0 mm, more preferably from 0.05 mm to 1 .5 mm, and further more preferably from 0.1 mm to 1 .0 mm are preferably used to obtain a pigment dispersion which can then be incorporated into the ink.

The ink composition of the invention may additionally contain a surfactant. Examples of preferable surfactant include anionic surfactants (e.g. a dialkyl sulfosuccinates, alkyl naphthalene sulfonates, or fatty acid salts); nonionic surfactants (e.g. polyoxyethylene alkyl ethers, polyoxyethylene alkyl allyl ethers, acetylene glycols, or polyoxyethylene-polyoxypropylene block copolymers); and cationic surfactants (e.g. alkyl amine salts or quaternary ammonium salts). Among theses, an anionic surfactant and a nonionic surfactant are preferred.

A latex may be included in the ink composition of the invention. Examples of latex which may be used in the invention include styrene-butadiene copolymers, polystyrene, acrylonitrile-butadiene copolymers, acrylic acid ester copolymers, polyurethane, silicone-acrylic copolymers, and acryl-modified fluorine resins.

The radiation-curable ink optionally further comprises a polymerization initiator as Component F. The polymerization initiator is preferably water-soluble, e.g. having a solubility in distilled water at 25°C of at least 0.5%, more preferably at least 1 %, and particularly preferably at least 3%, by mass, or water-dispersible.

Preferred polymerization initiators are a-aminoketones and acylphosphine oxides.

Examples of a-aminoketones include

2-methyl-1 -phenyl-2-morpholinopropan-1 -one,

2-methyl-1 -[4-(hexyl)phenyl]-2-morpholinopropan-1 -one, and 2-ethyl-2-dimethylamino-1 -(4-morpholinophenyl)-butanone-1 . Furthermore, such compounds are available as commercial products as IRGACURE series (trade name, manufactured by Ciba Geigy) such as IRGACURE 907, IRGACURE 369, or IRGACURE 379. Examples of acylphosphine oxides include

[2,4,6-trimethylbenzoyl-diphenyl-phosphineoxide] which is available under a product name of DAROCUR TPO (trade name, manufactured by BASF Japan.), and [bis(2,4,6-trimethylbenzoyl)-phenylphosphineoxide] which is available under a product name of IRGACURE 819 (trade name, manufactured by BASF Japan.). Although the acylphosphine oxides are preferably used as a polymerization initiator, other polymerization initiator may be used in the radiation-curable ink of the invention. Alternatively, other polymerization initiator may be used in combination with an acylphosphine oxide. In this case, a water-soluble polymerization initiator is preferably used.

The total content of polymerization initiator(s) in the radiation-curable ink is preferably 0 to 10 %, more preferably 0 to 5 %, and further more preferably from 0 to 3 %, relative to the total mass of the ink.

Optionally the ink also includes a sensitizing agent, especially such an agent having a solubility in distilled water at 25°C of at least 0.5%, more preferably at least 1 %, and particularly at least 3%, by mass.

Examples of suitable sensitizing agents include benzophenone, thioxanthone, and especially, isopropyl thioxanthone, anthraquinone and 3-acylcoumarine derivatives, terphenyl, styrylketone and 3-(aroylmethylene)thiazoline, camphorquinone, eosin, rhodamine, and erythrosine. A compound represented by formula (i) disclosed in JP-A No. 2010-24276, a compound represented by formula (I) disclosed in JP-A No. 6-107718, or the like may preferably be used.

The method for producing inks of the invention is not particularly limited, for example the ink may be prepared by stirring, mixing, and/or dispersing the respective components, e.g. using a container-driven medium mill such as a ball mill, a centrifugal mill, or a planetary balls mill, a high-speed rotary mill (e.g. a sand mill), a medium agitating mill (e.g. a mixing vessel-type mill), or a simple dispersion apparatus (e.g. a disper).

The ink preferably has a surface tension at 25°C of 20 to 40 mN/m. The surface tension may be measured using an automatic surface tensiometer CBVP-Z (trade name, manufactured by Kyowa Interface Science Co., Ltd.).

The ink preferably has a viscosity of 1 to 60 mPa-s, more preferably 1 to 50 mPa-s, especially 1 to 40 mPa-s, and more especially from 3 to 30 mPa-s. Typically viscosities are measured at 25°C. The viscosity may be measured using a Brookfield DV-1 rheometer using a UL-A spindle and adapter kit with a spindle speed of 60 RPM. The desired viscosity may be achieved by selecting the identity and relative amounts of components A to D as appropriate.

According to a second aspect of the present invention there is provided a process for printing an image on a substrate comprising applying an ink according to the first aspect of the present invention to the substrate by means of an ink jet printer and curing the ink.

The inkjet printer may be any of the known types, for example thermal, piezo and paddle-type ink jet printer. Thermal printheads are commonly used in HP and Canon printers, while piezo printheads are common in Epson printers. Paddle-type printers are disclosed in the numerous patents filed by Silverbrook.

The identity of the image is not critical to the present invention. For example, the image may be text, numbers, a picture or a combination of two or more thereof. The image may cover all or just a part of the substrate and may be any colour or combination of colours.

The ink may be cured by irradiating it. The source of radiation may be any source which provides the wavelength and intensity of radiation necessary to cure the ink, with curing by irradiation with UV light being particularly preferred. A typical example of a UV light source for curing is an H-bulb with an maximum linear power density of 600 Watts/inch (240 W/cm) as supplied by Fusion UV Systems which has emission maxima around 220nm, 255nm, 300nm, 310nm, 365nm, 405nm, 435nm, 550nm and 580nm. Alternatives are the V-bulb and the D-bulb which have a different emission spectrum with main emissions between 350 and 450nm and above 400nm respectively.

In a preferred embodiment the curing is performed using an irradiation source having linear power density below 1 W/cm, more preferably below 0.5W/cm.

An irradiation source having its emissions maximum in the range 253 to 254nm is especially preferred.

Preferably the irradiation is performed using a low pressure mercury or amalgam lamp. Low pressure mercury and amalgam lamps have a much lower linear power density than the typical 80 to 240 W/cm of medium pressure mercury lamps and the spectral profile is different. Historically such lamps are typically used for disinfection purposes.

Examples of low pressure mercury lamps include low output class (0.02 to below 0.1 W/cm2), standard output class (0.1 to below 0.17 W/cm2), high output class (0.17 to below 0.4 W/cm2) and ultra-high output class (0.4 to below 1 W/cm2). The figures in W/cm2 may be measured at a distance of either 0.3 metres or 1 metre from the lamp, although it will be understood that during the process the actual distance between the lamp and the transparent composition will almost certainly be different from this distance.

Crystec Technology Trading GmbH provide low pressure mercury lamps in all of the aforementioned output classes, e.g. the "UVL" low output range of lamps, the "SUV" standard output range of lamps, the "EUV" high output range of lamps and the FUV400U ultra-high output lamp. Low pressure mercury lamps may also be obtained from Heraeus Noblelight.

The choice of low pressure mercury lamp depends to some extent on the speed required for cure, with fast printing methods typically requiring a higher linear power density lamp than slower printing methods. Furthermore, when the lamp is included in an ink jet printer a lower linear power density lamp is preferred to avoid the printer from over-heating and to avoid the need to include cooling fans within the printer.

Low pressure mercury lamps are preferred over medium pressure mercury lamps because they are much more efficient in the present process. Approximately 35% of the energy input is converted to UV radiation, 85% of which has a wavelength of 254 nm (UVC). These lamps therefore generate less heat in use than medium pressure mercury lamps, which means that they are more economical to run and less likely to damage temperature-sensitive substrates. Furthermore, low pressure mercury lamps can be manufactured in such a way as not to generate ozone in use and are therefore safer to use than medium pressure mercury lamps. Although low pressure mercury lamps are used extensively in the water purification industry, they have not yet found widespread application in the printing industry.

Typical medium pressure mercury lamps have linear power density in the range of 80 to 240 W/cm. In contrast, the maximum linear power density for low pressure mercury lamps is around 30 to 440 mW/cm, which means that the peak irradiance of low pressure mercury lamps is also low.

A single low pressure mercury lamp or two or more low pressure mercury lamps can be used for curing the ink. Low pressure mercury lamps are used extensively in the water purification industry and are therefore widely available.

According to a third aspect of the present invention there is provided an ink jet printer cartridge comprising a chamber and an ink, wherein the ink is present in the chamber and is as defined in the first aspect of the present invention.

The invention is illustrated by the following non-limiting examples. The following ingredients were used in the Examples:

Irgacure™ 2959 is a photoinitiator

Ucecoat™ 6558 is a 50% solids solution in water of an acrylated polyurethane having an MFFT of below 0°C.

Ucecoat™ 7655 is a 35% solids dispersion in water of an acrylated polyurethane having an MFFT of below 0°C.

Pro-Jet™ APD 1000 yellow, magenta, cyan and black are colorants, available from FUJIFILM Imaging Colorants. Each has a 14wt% pigment solids content except for the magenta which has a 16.6% solids content.

Zonyl™ FSN is a fluorosurfactant.

(A-1 ) has the structure shown earlier in this specification and has a molecular weight of approximately 25,000 and a solids content of 20wt%.

All viscosities were measured at 25°C using a Brookfield DV-1 rheometer fitted with a UL-A spindle and adapter kit with a spindle speed of 60 RPM.

Examples 1 to 4 and Comparative Example 1

Inks were prepared by mixing the ingredients indicated in Tables 1 and 2 using a high speed silverson stirrer. Components A, D and C were stirred for 10 minutes at 2000 RPM. The 2-pyrollidone (Component E) was added and mixed for 5 minutes. The photoinitiator (Irgacure™ 2959) was added and stirred until fully dissolved. The colorant (Component B) was then added and dispersed at 2000 rpm for 10 minutes. The stirrer speed was reduced to 1000 rpm before adding the Zonyl™ FSN surfactant and stirring for 5 minutes. Table 1

Table 2 (Comparative, due to no Component A)

Comparative Example 1

Ingredient Amount (parts)

Component A - -

Component B Pro-Jet™ APD 1000 Cyan 10.0

Component C Deionised water 37.3

Component D Ucecoat™ 7655 28.6

Component E 2-pyrollidinone 20.0

Photoinitiator Irgacure™ 2959 4.0

Surfactant Zonyl™ FSN 0.1 Comparative Example 1 had a viscosity of 4.5 cP. Results

Water-Re-solubility Before Cure

Water-re-solubility of each radiation-curable ink was measured as follows.

An ink film was drawn down on Mactac™ JT5929 self adhesive PVC using a 12 micron K bar. The film was dried for 3 minutes at 60°C (without UV cure). The solubility of the dry film in water was then measured by rubbing with a soft cloth soaked in water and the result noted in Table 3.

Water and Solvent Rub Resistance

An ink film was drawn down on Mactac™ JT5929 self adhesive PVC using a 12 micron K bar. The film was dried for 3 minutes at 60°C. The dried film was then irradiated with UV light using a low pressure mercury UV lamp at a rate equivalent to a print speed of 16 m²/hour to give a cured film. This equates to UV dose of approximately 750 mJ/cm².

Solvent rub resistance was measured by rubbing the cured film with a soft cloth impregnated with isopropyl alcohol. The number of double rubs required to remove the cured film is shown in Table 3.

Water rub resistance was measured in the same way as solvent rub resistance except that the cloth was impregnated with water instead of isopropyl alcohol.

Adhesion was measured by applying 3M scotch tape securely to the cured film and then removing the tape with a sharp tug. The degree of film removal was scored 1 for complete removal and 5 for no visible removal. The results are shown in Table 3.

Table 3 - Results

Example 5

The ink described in Table 4 below was prepared using an analogous procedure to Examples 1 to 4. The ink had a viscosity of 6.0 cP.

Table 4

Example 5

Ingredient Amount (parts)

Ucecoat 6558

Component A 6.6

(50% solids)

Component B Pro-Jet™ APD 1000 Cyan 10

Component C deionised water 39.28

Component D Ucecoat™ 7655 20.02

Component E 2-pyrollidone 20

Surfactant Zonyl™ FSN 0.1

Photoinitiator Irgacure™ 2959 4

Claims

1 . A radiation-curable ink having a viscosity of 1 to 80 mPa-s comprising:

Component A: a water-soluble, radiation-curable polymer;

Component B: a colorant;

Component C: water; and

Component D: a water-dispersible, radiation-curable polyurethane.

2. A radiation-curable ink according to claim 1 , wherein Component A comprises at least one maleimide group.

3. A radiation-curable ink according to any one of the preceding claims, wherein Component D is free from maleimide groups

4. A radiation-curable ink according to any one of the preceding claims, wherein Component A comprises one or more urethane groups.

5. A radiation-curable ink according to any one of the preceding claims, wherein Component A comprises a copolymer having the structure represented by following Formula (A).

wherein in Formula (A):

R^a and R^b < each independently represents H or an optionally substituted Ci_-4- alkyl group, or

R^a and R^b together with the carbon atoms to which they are attached form an optionally substituted 4- to 6-membered ring;

each R^cx, R^cy and R^c independently represent H or methyl;

each Z^x independently is -COO-, -CONR^dx-, or a single bond, in which R^dx is H or Ci- -alkyl;

each Z^y independently is -COO-, -CONR^dy-, or a single bond, in which R^ay is H or Ci-₄-alkyl;

each R^y independently is a single bond or a divalent organic group; each A independently is a water-solubilising group;

each Z independently is -COO- or -CONR^d-, in which R^d is H or

C-i-4-alkyl;

each X independently is a divalent organic group;

each R^x independently is H atom, Ci-10-alkyl, an aryl group having 6

20 carbon atoms, or an aralkyl group having 7 to 20 carbon atoms; and

a, b, and c each independently have a value greater than zero.

6. A radiation-curable ink according to claim 5 wherein 30 < a + b < 90 and 10 < c < 70.

7. A radiation-curable ink according to any one of the preceding claims, wherein Component B comprises a coloured, water-insoluble core and a polymer shell having water-dispersing groups.

8. A radiation-curable ink according to any one of the preceding claims, further comprising Component E: a water-miscible organic solvent.

9. A radiation-curable ink according to claim 8 which comprises:

0.25 to 30% of Component A;

0.1 to 30% of Component B;

10 to 97% of Component C

5 to 10% of Component D; and

1 to 60% of Component E;

10. A radiation-curable ink according to any one of the preceding claims which has a viscosity of 1 to 60 mPa-s.

1 1 . A radiation-curable ink according to any one of the preceding claims which has a viscosity of 1 to 40 mPa-s.

12. A process for printing an image on a substrate comprising applying an ink according to the any one of the preceding claims to the substrate by means of an ink jet printer and curing the ink.

13. A process according to claim 12 wherein the curing comprises irradiation with UV light.

14. An ink jet printer cartridge comprising a chamber and an ink, wherein the ink is present in the chamber and is as defined in any one of claims 1 to 1 1 .