JP7632033B2 - Colorant dispersions, inks, ink sets, and coatings - Google Patents

Description

The present invention relates to a colorant dispersion for use in aqueous inkjet inks, etc., and to an ink, ink set, and coating that contain the same.

Among the inkjet inks used in inkjet printing, inks that use pigments as colorants contain the pigments in a finely dispersed state.
Paper is often used as the recording medium for inkjet printing. Paper can be broadly divided into coated paper, such as art paper and coated paper, and uncoated paper, such as foam paper and fine paper. However, while coated paper has a smooth recording surface, uncoated paper has relatively many bumps and grooves, and the ink absorption of the two types of paper differs greatly, so printed matter with high print density was created by forming an ink-receiving layer on the surface. To reduce costs, there was a demand for inkjet inks for uncoated paper that do not have an ink-receiving layer.
Normally, to increase print density, it is sufficient to use ink with finely dispersed colorants, but the print density of uncoated paper, which easily absorbs ink, decreases if there is no ink-receiving layer, as the ink penetrates into the paper. In contrast, if the dispersed particle size of the colorant is increased, the colorant will remain on the surface of the uncoated paper, increasing the print density, but on the other hand, the storage stability of the ink decreases.

As an ink for increasing print density, Patent Document 1 discloses an ink that uses a random copolymer of styrene macromer/styrene/benzyl methacrylate/alkyleneoxy chain-containing methacrylate/methacrylic acid as a dispersant. Patent Document 2 discloses an ink that uses a block polymer composed of benzyl methacrylate in the A block and methacrylic acid/butyl methacrylate in the B block as a dispersant.

JP 2009-108115 A JP 2020-125452 A

However, conventional inks were unable to achieve both storage stability and high print density.

The present invention aims to provide a colorant dispersion that can be used to produce an inkjet ink with good storage stability and that allows for high-density printing on uncoated paper that does not have an ink-receiving layer.

The colorant dispersion of the present invention is a colorant dispersion containing a dispersant, a colorant, and water,
the dispersant is a polymer containing a colorant adsorptive group-containing monomer unit, a maleic acid unit, and a maleimide unit or an N-substituted maleimide unit;
The colorant-adsorptive-group-containing monomer unit contains at least one of an α-olefin unit and a (meth)acrylic acid ester monomer unit having an alkyl group.

First, the terms used in this specification are defined. "C.I." stands for Color Index (C.I.). Monomer and monomer are ethylenically unsaturated group-containing monomers. (Poly)alkyleneoxy groups include both polyalkyleneoxy groups and alkyleneoxy groups. Alkyleneoxy groups include, for example, ethyleneoxy groups, propyleneoxy groups, butyleneoxy groups, etc. A monomer that has been polymerized to become a part of a polymer is called a monomer unit. A dispersant is a compound used to disperse a colorant that has been previously finely divided.

The colorant dispersion of the present invention is a colorant dispersion containing a dispersant, a colorant, and water,
the dispersant is a polymer containing a colorant adsorptive group-containing monomer unit, a maleic acid unit, and a maleimide unit or an N-substituted maleimide unit;
The colorant-adsorptive-group-containing monomer unit contains at least one of an α-olefin unit and a (meth)acrylic acid ester monomer unit having an alkyl group.
The colorant dispersion is preferably used for applications such as inkjet ink, flexographic printing ink, stationery, textile printing agents, and paints.

The dispersant contained in the colorant dispersion is characterized by containing a colorant adsorptive group-containing monomer unit, a maleic acid unit, and a maleimide unit or an N-substituted maleimide unit, which improves storage stability and dramatically improves print density on uncoated paper and coated paper while maintaining fine dispersion that enables inkjet ejection.
It is speculated that these effects are due to the repulsive effect of the two carboxyl groups derived from the maleic acid unit and the phenomenon of chelating traces of metal ions such as Ca ions contained in paper, which are significantly improved by including maleimide units or N-substituted maleimide units. It is also speculated that the adsorption of various pigment types to the dispersant can be significantly improved by including a colorant adsorptive group-containing monomer unit and a highly polar and hydrophobic maleimide unit or N-substituted maleimide unit. It is speculated that this allows the dispersant to have excellent dispersibility for various pigment types while also exhibiting a phenomenon of insolubilization by chelating with traces of metal ions in paper, and that the colorant dispersion remains on the paper surface during printing, thereby realizing high print density.

<Coloring Agent>
The colorant is a compound in the form of particles, and may be an aggregate. The colorant may be appropriately selected from organic pigments, inorganic pigments, and dyes.

Examples of organic pigments include azo pigments, diazo pigments, phthalocyanine pigments, quinacridone pigments, isoindolinone pigments, dioxazine pigments, perylene pigments, perinone pigments, thioindigo pigments, anthraquinone pigments, and quinophthalone pigments.

In terms of the color index of organic pigments, for example, C.I. Pigment Red 1, 2, 3, 4, 5, 6, 7, 9, 10, 14, 17, 22, 23, 31, 32, 38, 41, 48:1, 48:2, 48:3, 48:4, 49, 49:1, 49:2, 52:1, 52:2, 53:1, 57:1, 60:1, 63:1, 66, 67, 81:1, 81:2, 81:3, 83, 88, 90, 105, 112, 119, 122, 123, 144, 1 46, 147, 148, 149, 150, 155, 166, 168, 169, 170, 171, 172, 175, 176, 177, 178, 179, 184, 185, 187, 188, 19 0, 200, 202, 206, 207, 208, 209, 210, 216, 220, 224, 226, 242, 246, 254, 255, 264, 266, 269, 270, 272, 279,
C. I. PigmentYellow1, 2, 3, 4, 5, 6, 10, 11, 12, 13, 14, 15, 16, 17, 18, 20, 24, 31, 32, 34, 35, 35:1, 36, 36:1, 37, 37:1, 40, 42, 4 3, 53, 55, 60, 61, 62, 63, 65, 73, 74, 77, 81, 83, 86, 93, 94, 95, 97, 98, 100, 101, 104, 106, 108, 109, 110, 113, 114, 115, 116 , 117, 118, 119, 120, 123, 125, 126, 127, 128, 129, 137, 138, 139, 147, 148, 150, 151, 152, 153, 154, 155, 156, 161, 162, 1 64, 166, 167, 168, 169, 170, 171, 172, 173, 174, 175, 176, 177, 179, 180, 181, 182, 185, 187, 188, 193, 194, 199, 213, 214,
C. I. PigmentOrange2, 5, 13, 16, 17:1, 31, 34, 36, 38, 43, 46, 48, 49, 51, 52, 55, 59, 60, 61, 62, 64, 71, 73,
C. I. PigmentGreen7, 10, 36, 37, 58, 59, 62, 63,
C. I. PigmentBlue1, 2, 15, 15:1, 15:2, 15:3, 15:4, 15:6, 16, 22, 60, 64, 66, 79, 79, 80
C. I. PigmentViolet1, 19, 23, 27, 32, 37, 42
C. I. PigmentBrown25, 28
C. I. PigmentBlack1, 7
C.I. Pigment White 1, 2, 4, 5, 6, 7, 11, 12, 18, 19, 21, 22, 23, 26, 27, 28 and the like.

Among these, C.I. Pigment Red 31, 48:1, 48:2, 48:3, 48:4, 57:1, 122, 146, 147, 148, 150, 170, 176, 177, 184, 185, 202, 242, 254, 255, 264, 266, 269,
C. I. PigmentYellow12, 13, 14, 17, 74, 83, 108, 109, 120, 150, 151, 154, 155, 180, 185, 213
C. I. PigmentOrange36, 38, 43, 64, 73
C. I. PigmentGreen7, 36, 37, 58, 62, 63,
C. I. PigmentBlue15:1, 15:3, 15:6, 16, 22, 60, 66,
C. I. PigmentViolet19, 23, 32,
C. I. PigmentBrown25,
C. I. PigmentBlack1, 7
C.I. Pigment White 6 is preferred.

Examples of inorganic pigments include carbon black, metal oxides, metal complexes, and other inorganic pigments. Examples of carbon black include furnace black, thermal lamp black, acetylene black, and channel black. Examples of metal oxides include titanium oxide, iron oxide, iron hydroxide, zirconia, and alumina. Examples of other inorganic pigments include ultramarine, yellow lead, zinc sulfide, and cobalt blue.

The carbon black preferably has properties such as an average primary particle size of 11 to 50 nm, a specific surface area by BET method of 50 to 400 ^{m 2} /g, and a pH of 2 to 10. Commercially available carbon black products include, for example, No. 25, 30, 33, 40, 44, 45, 52, 850, 900, 950, 960, 970, 980, 1000, 2200B, 2300, 2350, 2600; MA7, MA8, MA77, MA100, MA230 (manufactured by Mitsubishi Chemical Corporation), RAVEN760UP, 780UP, 860UP, 900P, 1000P, 1060UP, 1080UP, 1255 (manufactured by Columbian Carbon Co., Ltd.), Examples of such resins include REGAL 330R, 400R, 660R, MOGULL (manufactured by Cabot Corporation), Nipex 160IQ, 170IQ, 35, 75; PrinteX 30, 35, 40, 45, 55, 75, 80, 85, 90, 95, 300; Special Black 350, 550; Nerox 305, 500, 505, 600, 605 (manufactured by Orion Engineered Carbons).

Examples of the titanium oxide include anatase type and rutile type. Among these, the rutile type is preferred in terms of improving the hiding power of printed matter. Titanium oxide can be synthesized by the chlorine method, sulfuric acid method, etc., with the chlorine method being preferred in terms of improving whiteness.

The activity of titanium oxide is preferably suppressed by treating the surface with an inorganic compound. After the treatment with the inorganic compound, the surface is preferably further treated with an organic compound. This improves the dispersion stability of titanium oxide. Examples of inorganic compounds include compounds of silicon, aluminum, zirconium, tin, antimony, and titanium, as well as hydrated oxides of these elements. Examples of organic compounds include polyhydric alcohols, alkanolamines and derivatives thereof, higher fatty acids and metal salts thereof, and organometallic compounds.

The dye is preferably a disperse dye. A disperse dye is a dye that has the property of sublimating when heated. Examples of disperse dyes include
C.I. Disperse Yellow 3, 7, 8, 23, 39, 51, 54, 60, 71, 86; C.I. Disperse Orange 1, 1:1, 5, 20, 25, 25:1, 33, 56, 76; C.I. Disperse Brown 2; C.I. Disperse Red 11, 50, 53, 55, 55:1, 59, 60, 65, 70, 75, 93, 146, 158, 190, 190:1, 207, 239, 240, 343; C.I. Vat Red 41; C.I. Disperse Violet 8, 17, 23, 27, 28, 29, 36, 57; C.I. Disperse Blue 19, 26, 26:1, 35, 55, 56, 58, 60, 64, 64:1, 72, 72:1, 81, 81:1, 91, 95, 108, 131, 141, 145, 165, 359, and 360.

Colorants can be used alone or in combination of two or more types.

The average primary particle diameter of the colorant is usually preferably 5 to 1,000 nm. The average primary particle diameter is, for example, the average value of approximately 20 particles randomly selected from an enlarged image selected from a range of 2,000 to 100,000 times using a transmission electron microscope. When the particles are elliptical, the length of the vertical axis is used.

<Dispersant>
The dispersant is a polymer containing a colorant-adsorptive group-containing monomer unit, a maleic acid unit, and a maleimide unit or an N-substituted maleimide unit. The dispersant can be synthesized, for example, by emulsion polymerization, solution polymerization, bulk polymerization, suspension polymerization, etc. The polymerization method can be, for example, random polymerization, alternating copolymerization, block polymerization, etc. The polymerization reaction can be, for example, radical polymerization, anionic polymerization, cationic polymerization, etc. In this specification, the dispersant can be synthesized by appropriately combining these methods.
In the present specification, a dispersant that undergoes random polymerization or alternating copolymerization in a solution using a radical polymerization initiator will be described below as an example.

The dispersant is preferably synthesized by copolymerizing a monomer mixture containing a colorant-adsorbing group-containing monomer, maleic acid, and maleimide or N-substituted maleimide, and a (meth)allyl monomer.

<Colorant Adsorption Group-Containing Monomer>
The colorant-adsorptive-group-containing monomer may be any monomer that contains a structure that is adsorbed to a colorant, and contains at least one of an α-olefin unit and a (meth)acrylic acid ester monomer unit having an alkyl group.
Among these, α-olefins are preferred from the viewpoints of copolymerizability with maleic acid (anhydride) and (meth)allyl monomers and adsorption rate to the colorant surface.

The α-olefin is preferably an α-olefin having 6 to 50 carbon atoms, more preferably having 8 to 30 carbon atoms, and further preferably having 12 to 28 carbon atoms.
Examples of α-olefins include 1-hexene (carbon number: 6), 1-heptene (carbon number: 7), 1-octene (carbon number: 8), 1-nonene (carbon number: 9), 1-decene (carbon number: 10), 1-dodecene (carbon number: 12), 1-tetradecene (carbon number: 14), 1-hexadecene (carbon number: 16), 1-octadecene (carbon number: 18), 1-eicosene (carbon number: 20), 1-docosene (carbon number: 22), 1-tetracosene (carbon number: 24), 1-octacosene (carbon number: 28), 1-triacontene (carbon number: 30), 1-dotriacontene (carbon number: 32), 1-tetratriacontene (carbon number: 34), 1-hexatriacontene (carbon number: 36), and 1-octatriacontene (carbon number: 38).

α-Olefins can be used alone or in combination of two or more types.

The alkyl chain of the (meth)acrylic acid ester monomer having an alkyl group preferably has 6 to 50 carbon atoms, more preferably 8 to 30 carbon atoms, and even more preferably 10 to 24 carbon atoms.
Examples of (meth)acrylic acid ester monomers having an alkyl group include decyl (meth)acrylate, undecyl (meth)acrylate, lauryl (meth)acrylate, tridecyl (meth)acrylate, tetradecyl (meth)acrylate, pentadecyl (meth)acrylate, hexadecyl (meth)acrylate, heptadecyl (meth)acrylate, stearyl (meth)acrylate, isostearyl (meth)acrylate, and behenyl (meth)acrylate.

The (meth)acrylic acid ester monomers having an alkyl group can be used alone or in combination of two or more types.

<Maleic acid>
To form the maleic acid unit, at least one of maleic acid and maleic anhydride is used, of which maleic anhydride is preferred from the viewpoint of excellent copolymerizability.

<Maleimide, N-substituted maleimide>
Since the maleimide unit and the N-substituted maleimide unit are dispersants containing a colorant adsorptive group-containing monomer unit and a maleic acid unit, the print density on uncoated paper and coated paper can be dramatically improved while maintaining the storage stability of the colorant dispersion and the fine dispersion that enables inkjet ejection. It is speculated that this effect is significantly improved by the inclusion of a maleimide unit or an N-substituted maleimide unit, due to the repulsive effect of the two carboxyl groups derived from the maleic acid unit and the phenomenon of chelating a small amount of metal ions such as Ca ions contained in the paper. It is also speculated that the adsorption rate for various pigment types can be significantly improved because the dispersant contains a colorant adsorptive group-containing monomer unit and a maleimide unit or an N-substituted maleimide unit that has a highly polar imide bond and is hydrophobic. As a result, the dispersant has excellent dispersibility for various pigment types, but is insolubilized by chelating with a small amount of metal ions in the paper, and a high print density can be achieved by the colorant dispersion remaining on the paper surface during printing. Furthermore, by changing the substituent of the N-substituted maleimide unit, it is possible to adjust the compatibility and the adsorption rate to the colorant.
Among the substituents, examples of the hydrocarbon groups include a methyl group, an ethyl group, a propyl group, an isopropyl group, a butyl group, an isobutyl group, a s-butyl group, a t-butyl group, an amyl group, a hexyl group, a heptyl group, an octyl group, a nonyl group, a decyl group, a lauryl group, a myristyl group, a cetyl group, a stearyl group, an oleyl group, and the like;
Examples of the cyclic hydrocarbon group include a cyclohexyl group;
Examples of the aromatic group include a phenyl group, an o-tolyl group, an m-tolyl group, a p-tolyl group, a 2-ethylphenyl group, a 2-fluorophenyl group, an o-methoxyphenyl group, an m-hydroxyphenyl group, a p-hydroxyphenyl group, a p-carboxylphenyl group, and a benzyl group;
From the viewpoints of storage stability and compatibility with the binder, preferred are cyclic hydrocarbon groups and aromatic groups, more preferred are cyclohexyl groups or phenyl groups, and particularly preferred are phenyl groups.

To form the maleimide unit or N-substituted maleimide unit, commercially available monomers may be used, or they may be obtained by modification from maleic anhydride.

The maleimide or N-substituted maleimide units can be used alone or in combination of two or more types.

Amines are used to form N-substituted maleimide units, and may be obtained by modifying maleic anhydride. Examples of amines include, but are not limited to, methylamine, ethylamine, propylamine, isopropylamine, butylamine, amylamine, hexylamine, heptylamine, octylamine, nonylamine, decylamine, laurylamine, myristylamine, cetylamine, stearylamine, oleylamine, aniline, o-toluidine, 2-ethylaniline, 2-fluoroaniline, o-anisidine, m-toluidine, m-anisidine, m-phenetidine, p-toluidine, 2,3-dimethylaniline, 5-aminoindan, aspartic acid, glutamic acid, and γ-aminobutyric acid.

Amines can be used alone or in combination of two or more types.

In this specification, the maleimide unit or N-substituted maleimide unit may be hydrolyzed in the form of an aqueous pigment dispersion to become either an imide bond state or an amide bond state. These forms are also included in the maleimide unit or N-substituted maleimide unit.

(Meth)allyl Monomer
The (meth)allyl monomer is a monomer containing a (meth)allyl group. The (meth)allyl monomer is not particularly limited, but is preferably a (meth)allyl ether monomer represented by the following general formula (1).

In the general formula (1), R ₁ represents a hydrogen atom or a methyl group. R ₂ O represents an alkyleneoxy group, and two or more types of alkyleneoxy groups may be added randomly or in a block form. The alkyleneoxy group represented by R ₂ O is preferably an alkyleneoxy group having 2 to 5 carbon atoms from the viewpoint of dispersion stability, for example.
Examples of the alkyleneoxy group having 2 to 5 carbon atoms include an ethyleneoxy group, a propyleneoxy group, a butyleneoxy group, and a tetramethyleneoxy group. Among these, from the viewpoint of dispersibility, a single addition of an ethyleneoxy group or a propyleneoxy group, or a block or random addition of an ethyleneoxy group and a propyleneoxy group is preferred, and a single addition of a propyleneoxy group, or a block or random addition of an ethyleneoxy group and a propyleneoxy group is more preferred.

In general formula (1), m is the average number of moles of alkyleneoxy groups and is either 0 or an integer from 1 to 100. From the viewpoint of the copolymerizability of the monomer and the adsorption rate of the dispersant to the colorant, it is preferably 1 to 60, more preferably 3 to 50, and even more preferably 5 to 40.

In the general formula (1), R ₃ represents a hydrogen atom, a linear or branched alkyl group, a saturated acyl group, or a phenyl group which may be substituted with an alkyl group. The linear or branched alkyl group may be, for example, a linear or branched alkyl group having 1 to 20 carbon atoms, and a methyl group, an ethyl group, an isopropyl group, or the like is preferred. The saturated acyl group may be, for example, a saturated acyl group having 1 to 10 carbon atoms, and a substituent derived from ethanoic acid, butanoic acid, propionic acid, or butyric acid is preferred. The phenyl group which may be substituted with an alkyl group may be, for example, a phenyl group, a naphthyl group, a p-methylphenyl group, or the like.
Among these, _R3 is preferably a linear or branched alkyl group, and from the viewpoint of dispersion stability, a methyl group is most preferable.

Examples of the (meth)allyl ether monomer represented by the general formula (1) include alkyl (meth)allyl ethers such as methyl (meth)allyl ether and ethyl (meth)allyl ether; ring-containing (meth)allyl ethers such as phenyl (meth)allyl ether and cyclohexyl (meth)allyl ether; hydroxyalkyl (meth)allyl ethers such as 2-hydroxyethyl (meth)allyl ether and 4-hydroxybutyl (meth)allyl ether; and (meth)allyl esters such as (meth)allyl propionate, (meth)allyl hexanoate, and (meth)allyl cyclohexanepropionate.
In addition, the (meth)allyl ether monomer represented by the general formula (1) preferably has a (poly)alkyleneoxy group. For example, (poly)alkyleneoxy group-containing (meth)allyl ethers such as polyalkylene glycol (meth)allyl ether, alkyleneoxy glycol (meth)allyl ether, and alkoxy polyalkylene glycol (meth)allyl ether can be mentioned. Among these, from the viewpoint of compatibility with the binder resin, it is preferable to contain a (poly)alkyleneoxy group, and more preferably an alkoxy polyalkylene glycol (meth)allyl ether.

Examples of alkoxy polyalkylene glycol (meth)allyl ethers include methoxyethylene glycol (meth)allyl ether, methoxypolyethylene glycol (meth)allyl ether, methoxypropylene glycol (meth)allyl ether, methoxypolypropylene glycol (meth)allyl ether, ethoxyethylene glycol (meth)allyl ether, ethoxypolyethylene glycol (meth)allyl ether, ethoxypropylene glycol (meth)allyl ether, ethoxypolypropylene glycol (meth)allyl ether, propoxyethylene glycol (meth)allyl ether, propoxypolyethylene glycol (meth)allyl ether, propoxypropylene glycol (meth)allyl ether, and propoxypolypropylene glycol (meth)allyl ether. From the viewpoint of compatibility with the binder resin, methoxypolyethylene glycol (meth)allyl ether and methoxypolypropylene glycol (meth)allyl ether are more preferable, and methoxypolypropylene glycol (meth)allyl ether is even more preferable.

The (meth)allyl ethers can be used alone or in combination of two or more types.

The dispersant may contain other monomer units other than colorant adsorption group-containing monomer units, maleic acid units, and maleimide units or N-substituted maleimide units, as well as (meth)allyl monomer units. Examples of other monomer units include, but are not limited to, aromatic ring-containing monomers (excluding heterocyclic ring-containing monomers), alicyclic ring-containing monomers, heterocyclic ring-containing monomers (excluding aromatic ring-containing monomers), and other vinyl monomers.

Examples of aromatic ring-containing monomers include styrene, benzyl (meth)acrylate, phenoxyethyl (meth)acrylate, and styrene macromers.

Examples of alicyclic monomers include isobornyl (meth)acrylate, cyclohexyl (meth)acrylate, dicyclopentanyl (meth)acrylate, 3,3,5-trimethylcyclohexyl (meth)acrylate, and 4-tert-butylcyclohexyl (meth)acrylate.

Examples of heterocycle-containing monomers include N-vinyl-2-pyrrolidone, N-vinylcaprolactam, N-vinylpyridine, N-vinylpyrimidine, N-vinylpiperidone, N-vinylpyrrole, N-vinylimidazole, N-vinyloxazole, N-vinylpiperazine, and (meth)acryloylmorpholine.

The dispersant can be synthesized by adding a radical polymerization initiator and, if necessary, a chain transfer agent to a monomer mixture containing a colorant adsorption group-containing monomer, (maleic anhydride), maleimide or N-substituted maleimide, and (meth)allyl monomer, and polymerizing the mixture. The resulting dispersant is essentially an alternating polymer in which maleic anhydride is alternately arranged between randomly arranged colorant adsorption group-containing monomer units and (meth)allyl monomers.

The content of the colorant-adsorbing group-containing monomer unit is preferably 20 to 60 mol %, more preferably 25 to 55 mol %, and even more preferably 30 to 50 mol % of the total monomer units of the dispersant. When an appropriate amount is contained, the dispersant is easily adsorbed to the surface of the colorant, and storage stability is further improved.

The content of maleic acid units is preferably 5 to 60 mol %, more preferably 10 to 50 mol %, and even more preferably 15 to 40 mol % of the total monomer units of the dispersant. When an appropriate amount is contained, it is possible to increase the print density on uncoated paper while maintaining the storage stability of the colorant dispersion.

The content of maleimide units or N-substituted maleimide units is preferably 5 to 60 mol %, more preferably 10 to 50 mol %, and even more preferably 15 to 40 mol % of the total monomer units of the dispersant. When an appropriate amount is contained, it is possible to increase the print density on uncoated paper while maintaining the storage stability of the colorant dispersion.

The content of (meth)allyl monomer units is preferably 1 to 30 mol %, more preferably 1 to 20 mol %, and even more preferably 2 to 15 mol % of the total monomer units of the dispersant. When an appropriate amount is contained, the compatibility of the dispersant with the binder resin, etc. is improved, and the print density is further improved.

The radical polymerization initiator may be an azo compound or a peroxide. Examples of the azo compound include azobisisobutyronitrile and azobis2,4-dimethylvaleronitrile. Examples of the peroxide include cumene hydroperoxide, t-butyl hydroperoxide, benzoyl peroxide, diisopropyl peroxycarbonate, di-t-butyl peroxide, lauroyl peroxide, t-butyl peroxybenzoate, and t-butyl peroxy-2-ethylhexanoate.

The radical polymerization initiator can be used alone or in combination of two or more types.

The organic solvents used in solution polymerization include, but are not limited to, ethyl acetate, n-butyl acetate, isobutyl acetate, toluene, xylene, acetone, hexane, methyl ethyl ketone, and cyclohexanone. These polymerization solvents may be used in combination of two or more types.

Organic solvents can be used alone or in combination of two or more types.

<Sites Modified by Hydroxycarboxylic Acid>
The maleic acid unit of the dispersant is preferably a unit having a modified site by an oxycarboxylic acid having a divalent or trivalent carboxyl group. It is preferable to form an ester bond site by an oxycarboxylic acid having a divalent or trivalent carboxyl group (hereinafter referred to as oxycarboxylic acid). Specifically, an ester bond site is formed by reacting an acid anhydride group in the maleic anhydride unit with an oxycarboxylic acid. It is preferable to form the ester bond site at a ratio of 30 to 100% in 100 mol% of the acid anhydride group. By esterification, it is possible to impart a divalent or trivalent carboxyl group site to the dispersant, and an excellent electrostatic repulsion effect can be obtained, and at the same time, a small amount of metal ions such as Ca ions contained in the paper can be chelated by the adjacent carboxyl group. The dispersant becomes insoluble by chelating the metal ions, and the colorant dispersion does not penetrate into the paper surface and remains in large amounts on the surface, dramatically improving the print density. In addition, by esterification, compatibility with binder resins and the like is improved, and the print density is further improved.

A preferred method for obtaining an esterified dispersant is, for example, to polymerize a monomer mixture containing a colorant-adsorbing group-containing monomer, maleic anhydride, and maleimide or N-substituted maleimide, and a (meth)allyl monomer, and then react it with water or an oxycarboxylic acid having a divalent or trivalent carboxyl group.

Examples of oxycarboxylic acids having a divalent carboxyl group include aminocarboxylic acid chelating agents such as tartronic acid, malic acid, 4-hydroxyphthalic acid, and N,N-bis(carboxymethyl)ethanolamine.

Examples of oxycarboxylic acids with a trivalent carboxyl group include citric acid.

In particular, water or oxycarboxylic acids having a divalent or trivalent carboxyl group with a molecular weight of 80 to 350 are preferred, with water being more preferred. When the molecular weight of the oxycarboxylic acid having a divalent or trivalent carboxyl group is 80 to 350, the esterification reaction is more likely to proceed, and a dispersant with an excellent balance of hydrophilicity and hydrophobicity is obtained, which tends to enhance the pigment dispersion stabilization effect. Furthermore, dispersants obtained by esterification reaction with water have significantly improved storage stability, fine dispersion properties that enable inkjet ejection, and print density. This is thought to be because the adjacent carboxyl groups derived from maleic acid are highly effective as dispersion sites, as well as excellent reactivity with metal ions in paper.

The esterification reaction is carried out at 50 to 300°C, and may be carried out in the presence of a suitable solvent as necessary. Furthermore, an esterification catalyst may be added as necessary. The esterification catalyst is not particularly limited, and examples thereof include sulfuric acid, hydrogen chloride, p-toluenesulfonic acid, triethylamine, dimethylbenzylamine, tetrabutylammonium bromide, and 1,8-diazabicyclo[5.4.0]undecene-7. It is preferable to use about 0.03 to 5% by mass of the esterification catalyst relative to 100 parts by mass of the reactant.

The acid anhydride value of the dispersant is preferably small. For example, 0 to 50 mgKOH/g is preferable, 0 to 30 mgKOH/g is more preferable, and 0 to 10 mgKOH/g is even more preferable. A moderate acid anhydride value further improves the dispersibility of the colorant.

The compounds used for forming the ester bond site may be used alone or in combination of two or more kinds.

The acid value of the dispersant is preferably 35 to 400 mgKOH/g, more preferably 50 to 300 mgKOH/g, and even more preferably 65 to 200 mgKOH/g. With a moderate acid value, excellent electrostatic repulsion effects are obtained, storage stability and fine dispersion are improved, and reactivity to minute metal ions in paper is increased, improving print density.

The number average molecular weight of the dispersant is preferably 2,000 to 35,000, more preferably 3,000 to 15,000, and the polydispersity (Mw/Mn) is preferably 1.2 to 4.0. If the dispersant has an appropriate number average molecular weight and polydispersity, the adsorption rate to the colorant is improved, and the storage stability and fine dispersion properties are improved.

<Colorant Dispersion>
The colorant dispersion of the present specification contains at least a dispersant, a basic compound, a colorant, and water, and preferably contains an appropriate component selected from a binder resin, a crosslinking agent, and the like.

<Basic Compound>
The basic compound neutralizes the carboxyl group derived from the dispersant, and can stably disperse the colorant particles. Furthermore, the basic compound is used to adjust the pH of the colorant dispersion to about 7 to 10. Examples of the basic compound include organic amines such as ammonia, dimethylaminoethanol, diethanolamine, and triethanolamine; inorganic alkalis such as alkali metal hydroxides such as sodium hydroxide, lithium hydroxide, and potassium hydroxide; organic acids, and mineral acids.

From the viewpoint of dispersion stability of the colorant dispersion, the neutralization degree of the dispersant is preferably 10 to 200 mol %, more preferably 40 to 160 mol %, of the carboxyl groups. Here, the neutralization degree is obtained by dividing the molar equivalent of the basic compound by the molar amount of the carboxyl groups of the dispersant. It can be calculated by the following formula.
{(weight (g) of basic compound/equivalent of basic compound)/[(acid value of dispersant (KOH
mg/g × weight of dispersant (g)/(56.1 × 1000) × 100

The basic compounds can be used alone or in combination of two or more types.

<Crosslinking Agent>
In the colorant dispersion, it is preferable to crosslink the dispersant with a crosslinking agent. The crosslinking agent is used to crosslink the carboxyl groups derived from the dispersant in the colorant dispersion. The crosslinking agent is a compound having two or more functional groups (hereinafter referred to as reactive functional groups) capable of reacting with carboxyl groups. The dispersant tightly coats the colorant by crosslinking, and the dispersion stability of the colorant dispersion is further improved. The reactive functional group is preferably, for example, an isocyanate group, an aziridine group, a carbodiimide group, an oxetane group, an oxazoline group, or an epoxy group, more preferably an aziridine group, a carbodiimide group, or an epoxy group, and even more preferably an epoxy group. The addition of a crosslinking agent is also preferable from the viewpoint of improving the dispersion stability as an inkjet ink. Examples of the crosslinking agent include an isocyanate compound, an aziridine compound, a carbodiimide compound, an oxetane compound, an oxazoline compound, and an epoxy compound.

The isocyanate compound may be, for example, an organic polyisocyanate or an isocyanate-terminated prepolymer. Examples of the organic polyisocyanate include aliphatic diisocyanates such as hexamethylene diisocyanate and 2,2,4-trimethylhexamethylene diisocyanate; aromatic diisocyanates such as tolylene-2,4-diisocyanate and phenylene diisocyanate; alicyclic diisocyanates; aromatic triisocyanates; and modified products thereof, such as urethane modified products. The isocyanate-terminated prepolymer may be obtained by reacting an organic polyisocyanate or a modified product thereof with a low molecular weight polyol or the like.

Examples of the aziridine compound include N,N'-diphenylmethane-4,4'-bis(1-aziridinecarboxite), N,N'-toluene-2,4-bis(1-aziridinecarboxite), bisisophthaloyl-1-(2-methylaziridine), tri-1-aziridinylphosphine oxide, N,N'-hexamethylene-1,6-bis(1-aziridinecarboxite), 2,2'-bishydroxymethylbutanol-tris[3-(1-aziridinyl)propionate], trimethylolpropane tri-β-aziridinylpropionate, tetramethylolmethane tri-β-aziridinylpropionate, tris-2,4,6-(1-aziridinyl)-1,3,5-triazine, and 4,4'-bis(ethyleneiminocarbonylamino)diphenylmethane.

The carbodiimide compound may be, for example, a high molecular weight polycarbodiimide produced by subjecting a diisocyanate compound to a decarboxylation condensation reaction in the presence of a carbodiimide catalyst. Examples of such high molecular weight polycarbodiimides include the Carbodilite series manufactured by Nisshinbo Industries, Inc.

Oxetane compounds, for example, 4,4'-(3-ethyloxetan-3-ylmethyloxymethyl)biphenyl (OXBP), 3-ethyl-3-hydroxymethyloxetane (EHO), 1,4-bis[{(3-ethyl-3-oxetanyl)methoxy}methyl]benzene (XDO), di[1-ethyl(3-oxetanyl)]methyl ether (DOX), di[1-ethyl(3-oxetanyl)]methyl ether (DOE), 1,6-bis[(3-ethyl-3-oxetanyl)methoxy]hexane (HDB), 9,9-bis[2-methyl-4-{2-(3-oxetanyl)}butoxyphenyl]fluorene, 9,9-bis[4-[2-{2-(3-oxetanyl)}butoxy]ethoxyphenyl]fluorene, etc.

Examples of oxazoline compounds include compounds in which two or more, preferably two to three, oxazoline groups are bonded to an aliphatic or aromatic group, more specifically, bisoxazoline compounds such as 2,2'-bis(2-oxazoline), 1,3-phenylenebisoxazoline, and 1,3-benzobisoxazoline, and compounds having a terminal oxazoline group obtained by reacting such compounds with polybasic carboxylic acids.

Examples of epoxy compounds include polyglycidyl ethers such as ethylene glycol diglycidyl ether, polyethylene glycol diglycidyl ether, polypropylene glycol diglycidyl ether, glycerin triglycidyl ether, glycerol polyglycidyl ether, polyglycerol polyglycidyl ether, trimethylolpropane polyglycidyl ether, sorbitol polyglycidyl ether, pentaerythritol polyglycidyl ether, resorcinol diglycidyl ether, neopentyl glycol diglycidyl ether, and hydrogenated bisphenol A diglycidyl ether.

Of these, ethylene glycol diglycidyl ether and trimethylolpropane polyglycidyl ether are preferred.

Crosslinking agents can be used alone or in combination of two or more types.

The molecular weight (formula weight or number average molecular weight Mn) of the crosslinking agent is preferably 100 to 2,000, more preferably 120 to 1,500, and particularly preferably 150 to 1,000, from the viewpoints of ease of reaction and storage stability of the colorant dispersion. The number of reactive functional groups contained in the crosslinking agent is preferably 2 to 6, from the viewpoints of controlling the molecular weight of the dispersant after crosslinking and improving storage stability.

The crosslinking agent preferably has a suitable water solubility so that it can react efficiently with the carboxyl groups of the dispersing agent in water. The water solubility is preferably 0.1 to 50 g, more preferably 0.2 to 40 g, and even more preferably 0.5 to 30 g, of the crosslinking agent in 100 g of water at 25°C.

The amount of crosslinking agent used is preferably about 10 to 150 mol % of reactive functional groups relative to 100 mol % of the carboxyl groups of the dispersant, more preferably 20 to 120 mol %, and even more preferably 30 to 100 mol %.

It is preferable to adjust the non-volatile content of the colorant dispersion with water to 5 to 80% by mass.

The content of the colorant and dispersant is preferably 5 to 40% by mass, and more preferably 10 to 30% by mass, out of 100% by mass of the colorant dispersion. The storage stability is further improved when an appropriate amount is contained.

The D50 average particle size (median diameter) of the colorant in the colorant dispersion is preferably 20 to 200 nm, more preferably 25 to 150 nm, even more preferably 30 to 130 nm, and particularly preferably 35 to 90 nm. Having an appropriate particle size improves ejection stability from the nozzle, and further improves the storage stability of the colorant dispersion. The D50 average particle size is measured using a laser diffraction/scattering method.

<Production of Colorant Dispersion>
Examples of the method for producing the colorant dispersion include, but are not limited to, the following methods: First, the colorant is added to an aqueous medium in which at least a dispersant, a basic compound, and water are mixed, and the mixture is stirred. After that, a dispersion treatment is carried out using a dispersing means described below, and a centrifugation treatment is carried out as necessary to obtain a desired colorant dispersion.

The above-mentioned colorant dispersion means is carried out using a commonly used dispersing machine. Examples of the dispersion means include a ball mill, a roll mill, a sand mill, a bead mill, and a nanomizer. Among these, a bead mill is preferably used. Examples of such a means include a super mill, a sand grinder, an agitator mill, a grain mill, a dyno mill, a pearl mill, and a cobol mill (all of which are product names).

In addition, if a micronization treatment is performed before the above dispersion treatment, the colorant can be finely dispersed. In particular, a method in which the colorant is covered with a dispersant by a salt milling method and then micronized is preferred. The salt milling method includes, for example, a process of kneading a water-soluble solvent, a water-soluble inorganic salt, a colorant, and a dispersant to cover the surface of the colorant with the dispersant, and then removing the water-soluble inorganic salt and the water-soluble solvent. First, the water-soluble solvent, the water-soluble inorganic salt, the colorant, and a dispersant are kneaded to cover the surface of the colorant with the dispersant. The colorant is micronized by the kneading, and its surface is covered with the dispersant. Kneading by the salt milling method can efficiently micronize the colorant. Examples of kneading devices used in the salt milling method include a kneader, a two-roll mill, a three-roll mill, a ball mill, an attritor, a horizontal sand mill, a vertical sand mill, and/or an annular bead mill. Among these, a kneader is preferred in terms of efficiently covering the surface of the colorant. The kneading conditions can be appropriately adjusted depending on the type of colorant, the degree of micronization, and the like. It can also be heated or cooled as needed.

The water-soluble inorganic salt acts as a crushing aid, and the high hardness of the water-soluble inorganic salt is used to crush the colorant. Examples of water-soluble inorganic salts include sodium chloride, potassium chloride, and sodium sulfate. From the standpoint of cost, it is preferable to use sodium chloride (table salt).

The water-soluble solvent moistens the colorant and the water-soluble inorganic salt. The water-soluble solvent is a compound that dissolves (mixes) in water but does not dissolve the water-soluble inorganic salt. Examples of the water-soluble solvent include glycols such as ethylene glycol, diethylene glycol, triethylene glycol, tetraethylene glycol, propylene glycol, polyethylene glycol, and polypropylene glycol; diols such as butanediol, pentanediol, and hexanediol; glycol esters such as propylene glycol laurate; ethers such as diethylene glycol monoethyl, diethylene glycol monobutyl, and diethylene glycol monohexyl; glycol ethers such as cellosolve including propylene glycol ether, dipropylene glycol ether, and triethylene glycol ether; alcohols such as methanol, ethanol, isopropyl alcohol, 1-propanol, 2-propanol, 1-butanol, 2-butanol, butyl alcohol, and pentyl alcohol; sulfolane; lactones such as γ-butyrolactone; lactams such as N-(2-hydroxyethyl)pyrrolidone; and glycerin. Among these, glycols such as diethylene glycol and triethylene glycol are preferred.

Water-soluble solvents can be used alone or in combination of two or more types.

The amount of the water-soluble solvent used is preferably 5 to 1,000 parts by mass, more preferably 50 to 500 parts by mass, per 100 parts by mass of the colorant. The amount of the water-soluble inorganic salt used is preferably 50 to 2,000 parts by mass, more preferably 300 to 1,000 parts by mass, per 100 parts by mass of the colorant. The amount of the dispersant used is preferably 5 to 100 parts by mass, more preferably 10 to 80 parts by mass, per 100 parts by mass of the colorant. Using an appropriate amount further improves storage stability and fine dispersion.

Then, the water-soluble inorganic salt and the water-soluble solvent are removed from the mixture containing the colorant obtained. First, the mixture is removed from the kneading device, ion-exchanged water is added, and the mixture is stirred to obtain a suspension. The amount of ion-exchanged water used is preferably 10 to 10,000 times the mass of the mixture added to the kneading device. The stirring temperature is preferably 25 to 90°C. Next, filtration is performed to obtain the colorant. These operations can remove the water-soluble solvent and the water-soluble inorganic salt. A further step of removing the ion-exchanged water may be performed. The water is preferably removed by a drying process. Drying conditions include, for example, a method of drying at normal pressure in the range of 80 to 120°C for about 12 to 48 hours, and a method of drying at reduced pressure in the range of 25 to 80°C for about 12 to 60 hours. The drying process is preferably performed using a spray dryer. In addition, a grinding process can be performed simultaneously with or after the drying process.

The colorant dispersion is preferably used in inks (inkjet inks, flexographic printing inks, etc.), paints, stationery, textile printing agents, etc.
The ink is preferably an inkjet ink.

<Inkjet ink>
The inkjet ink of the present specification contains a colorant dispersion, water, and a water-soluble solvent. The inkjet ink of the present specification uses water as a solvent (medium), but it is preferable to use a water-soluble solvent in combination to prevent the ink from drying. The water-soluble solvent has a lower surface tension than water, and therefore improves the permeability and wettability and spreadability of the ink into the substrate after printing.

Examples of water-soluble solvents include polyhydric alcohols, polyhydric alcohol alkyl ethers, polyhydric alcohol aryl ethers, nitrogen-containing heterocyclic compounds, amides, amines, sulfur-containing compounds, propylene carbonate, ethylene carbonate, and other water-soluble solvents.

Examples of polyhydric alcohols include glycerin, ethylene glycol, diethylene glycol, triethylene glycol, tetraethylene glycol, polyethylene glycol, 1,2-propanediol, 1,3-propanediol, dipropylene glycol, tripropylene glycol, polypropylene glycol, 1,2-butanediol, 1,3-butanediol, 1,4-butanediol, 1,2-pentanediol, 1,3-pentanediol, 1,4-pentanediol, 1,5-pentanediol, 1,2-hexanediol, 1,3-hexanediol, 1,4-hexanediol, 1,5-hexanediol, 1, 6-hexanediol, 3-methyl-1,3-butanediol, trimethylolethane, trimethylolpropane, 1,2,6-hexanetriol, 1,2,4-butanetriol, 1,2,3-butanetriol, petriol, 2-ethyl-2-methyl-1,3-propanediol, 3,3-dimethyl-1,2-butanediol, 2,2-diethyl-1,3-propanediol, 2-methyl-2-propyl-1,3-propanediol, 2,4-dimethyl-2,4-pentanediol, 2,5-dimethyl-2,5-hexanediol, 5-hexene-1,2-diol, 2-ethyl-1,3-hexanediol, and the like. Among these, 2-ethyl-1,3-hexanediol, 2,2,4-trimethyl-1,3-pentanediol, 1,2-propanediol, 1,2-butanediol, 1,3-butanediol, 1,2-pentanediol, 1,5-pentanediol, 1,2-hexanediol, 1,6-hexanediol, and 1,2-heptanediol are preferred.

Examples of polyhydric alcohol alkyl ethers include ethylene glycol monoethyl ether, ethylene glycol monobutyl ether, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, diethylene glycol monobutyl ether, tetraethylene glycol monomethyl ether, propylene glycol monoethyl ether, and propylene glycol monobutyl ether. Examples of polyhydric alcohol aryl ethers include ethylene glycol monophenyl ether, diethylene glycol monophenyl ether, tetraethylene glycol chlorophenyl ether, ethylene glycol monobenzyl ether, and ethylene glycol monoallyl ether.

Examples of nitrogen-containing heterocyclic compounds include 2-pyrrolidone, N-methyl-2-pyrrolidone, N-hydroxyethyl-2-pyrrolidone, 1,3-dimethylimidazolidinone, ε-caprolactam, and γ-butyrolactone. Examples of amides include formamide, N-methylformamide, and N,N-dimethylformamide. Examples of amines include monoethanolamine, diethanolamine, triethanolamine, monoethylamine, diethylamine, and triethylamine. Examples of sulfur-containing compounds include dimethyl sulfoxide, sulfolane, and thiodiethanol.

As the other water-soluble solvent, sugar is preferable. Examples of sugars include monosaccharides, disaccharides, oligosaccharides (including trisaccharides and tetrasaccharides), polysaccharides, etc. Examples of sugars include glucose, mannose, fructose, ribose, xylose, arabinose, galactose, maltose, cellobiose, lactose, sucrose, trehalose, maltotriose, etc. Here, polysaccharides means sugar in a broad sense, and includes substances widely present in nature such as α-cyclodextrin and cellulose. In addition, derivatives of these sugars include, for example, reduced sugars of the sugars (for example, sugar alcohols [represented by the general formula: HOCH ₂ (CHOH) _n CH ₂ OH (wherein n represents an integer of 2 to 5)], oxidized sugars (for example, aldonic acid, uronic acid, etc.), amino acids, thioacids, etc.). Among these, sugar alcohols are preferable, and maltitol and sorbitol are more preferable.

Water-soluble solvents can be used alone or in combination of two or more types.

The content of the water-soluble solvent in the inkjet ink is preferably 3 to 60% by mass, and more preferably 3 to 50% by mass. The content of water in the inkjet ink is preferably 10 to 90% by mass, and more preferably 30 to 80% by mass. The inclusion of an appropriate amount of water-soluble solvent improves the stability of ink ejection from the head.

The inkjet ink preferably contains a binder resin. This improves the water resistance, solvent resistance, abrasion resistance, gloss, etc. of the printed coating film. Examples of binder resins include (meth)acrylic resins, styrene-(meth)acrylic resins, polyurethane resins, styrene-butadiene resins, vinyl chloride resins, polyolefin resins, polyester resins, polyurethane resins, alkyd resins, fluororesins, silicone-containing resins, etc.

The content of the binder resin is preferably 1 to 30% by mass, and more preferably 2 to 20% by mass, of the non-volatile content of the coloring composition.

Binder resins can be used alone or in combination of two or more types.

The inkjet ink of this specification may contain additives as necessary. Examples of additives include surfactants, defoamers, waxes, and preservatives. The content of the additives in the inkjet ink is preferably 0.05 to 10% by mass, and more preferably 0.2 to 5% by mass.

The inkjet ink of this specification can be used in various inkjet printers. Examples of inkjet systems include charge-controlled, continuous-jet, such as spray, on-demand, such as piezo, thermal, and electrostatic suction systems.

<Flexographic printing ink>
The flexographic printing ink of the present specification more preferably contains a colorant, a dispersant, and a binder resin. Examples of the binder resin include an acrylic resin and a urethane resin. The flexographic printing ink may also contain additives, a solvent, and a crosslinking agent.

(Acrylic resin)
Examples of the acrylic resin include an acrylic copolymer, an acrylic acid-styrene copolymer resin, an acrylic acid-maleic acid resin, an acrylic acid-styrene-maleic acid resin, etc. The acrylic copolymer is a copolymer using two or more monomers of (meth)acrylic acid and (meth)acrylic acid ester.

The weight-average molecular weight of the acrylic resin is preferably in the range of 200,000 to 800,000. If the weight-average molecular weight is less than 200,000, the strength of the resin film decreases, and the laminate's adhesion to the substrate, water friction resistance, scratch resistance, and blocking resistance may decrease. On the other hand, if it exceeds 800,000, the mobility of the molecular chain decreases, so that under low-temperature drying conditions, fusion between the ink film layers becomes insufficient, and the laminate's adhesion to the substrate and water friction resistance may decrease. In addition, resolubility is also likely to decrease.

The glass transition temperature (Tg) of the acrylic resin is preferably about -30°C to 30°C. A moderate Tg improves water abrasion resistance, blocking resistance, and adhesion to the substrate.

(urethane resin)
Examples of urethane resins include polyurethane-urea resins in addition to polyurethane resins. From the viewpoint of film-forming properties, it is preferable that the urethane resin has an acid value. The weight-average molecular weight of the urethane resin is preferably 10,000 to 100,000. If the urethane resin has an appropriate molecular weight, the adhesion to the substrate, water friction resistance, scratch resistance, and blocking resistance are further improved.

The acid value of the binder resin is preferably 20 to 180 mgKOH/g, and more preferably 40 to 150 mgKOH/g. A moderate acid value improves resolubility during printing, adhesion to the substrate, water abrasion resistance, and blocking resistance.

The amount of binder resin contained in flexographic printing ink is preferably 1 to 50% by mass, based on 100% by mass of flexographic printing ink. If the amount is moderate, the strength of the ink coating is improved, and adhesion to the substrate and water abrasion resistance are further improved.

Flexographic printing inks can contain additives as needed. Additives include leveling agents, wetting agents, water repellents, defoamers, waxes, crosslinking agents, etc.

Solvents used in flexographic printing inks include water or the water-soluble solvents mentioned above. Solvents can be used alone or in combination of two or more types.

The content of the colorant is preferably an amount sufficient to ensure the concentration and coloring power of the flexographic printing ink, i.e., 1 to 50% by mass in 100% by mass of the flexographic printing ink. The viscosity of the flexographic printing ink composition is preferably in the range of 10 mPa·s or more from the viewpoint of preventing settling of the colorant and dispersing it appropriately, and 1000 mPa·s or less from the viewpoint of workability during ink production and printing. The above viscosity is measured at 25°C using a Tokimec B-type viscometer.

Flexographic printing ink can be prepared by mixing and dispersing the above-mentioned components. For example, in addition to the colorant dispersion of the present invention, optional components such as wax and wetting agents can be added and mixed and stirred to produce an aqueous flexographic ink. Dispersion and stirring can be performed using, for example, a high-speed mixer, homogenizer, planetary mixer, trimix, kneader, extruder, horizontal sand mill, vertical sand mill and/or annular bead mill, paint shaker, ball mill, disperser equipped with an ultrasonic oscillator, two-roll mill, three-roll mill, etc.

<Ink set>
The ink set of the present invention includes inks of two or more colors, at least one of which includes the colorant dispersion of the present invention. Examples of the colors included in the ink set include cyan, yellow, magenta, black, orange, green, and white.

<Ink manufacturing method>
The method for producing the ink of the present invention will be described below, although the method for producing the ink of the present invention is not limited to the following.

(Adjustment)
The colorant dispersion, the water-soluble organic solvent, water, and optionally a binder resin, a surfactant, and other additives are added and stirred and mixed. If necessary, the mixture may be stirred and mixed while being heated in the range of 40 to 100° C.

(Removal of coarse particles)
The coarse particles contained in the mixture are removed by a method such as filtration separation or centrifugation to obtain an ink. As the filtration separation method, a known method can be appropriately used. The filter pore size is not particularly limited as long as it can remove coarse particles and dust, but in the case of inkjet ink, it is preferably 0.3 to 5 μm, more preferably 0.5 to 3 μm. When performing filtration, a single type of filter may be used, or multiple types may be used in combination.

<Method of manufacturing coated product>
The coated article of the present invention preferably comprises a substrate and a printed layer formed from an ink or an ink set.
Examples of the substrate include paper substrates such as fine paper, recycled paper, coated paper, art paper, cast paper, lightly coated paper, and synthetic paper, as well as polyvinyl chloride sheets, polyester films, polypropylene films, and polyethylene films. The substrate may also be a laminate of a plurality of materials. Among these, uncoated paper such as fine paper is preferred.
The thickness of the substrate is about 20 to 300 μm, and the basis weight of the substrate is about 30 to 300 g/m ² .
The thickness of the printed layer is preferably 0.01 to 5 μm, more preferably 0.1 to 4 μm, and further preferably 0.5 to 3 μm. By setting the thickness of the printed layer within the above range, it is possible to obtain sufficient color development as a printed matter, while allowing the solvent to be sufficiently evaporated in the drying step during the preparation of the printed layer, thereby forming a strong film.
The printing layer may be formed using a printing machine suitable for each ink, such as an inkjet printer, a flexographic printer, a gravure printer, or an offset printer.
After printing the ink, a drying step can be added as necessary. Examples of the dryer used in the drying step include a hot air dryer and an infrared heater.

<Paint>
In this specification, the paint preferably contains a colorant dispersion and a binder resin, and more preferably contains a crosslinking agent. The paint is preferably an aqueous paint containing a colorant dispersion and a binder resin. The ratio of the colorant dispersion to the binder resin varies depending on the required application and is not particularly limited.

(Binder resin)
Examples of the binder resin include acrylic resin, polyester resin, alkyd resin, fluororesin, urethane resin, silicone-containing resin, etc., which contain a crosslinkable functional group. Examples of the crosslinking agent include melamine resin, urea resin, polyisocyanate compound, blocked polyisocyanate compound, epoxy compound, carboxyl group-containing compound, acid anhydride, alkoxysilane group-containing compound, etc. Among these, a combination of acrylic resin and melamine resin is preferable.

The coating material may further contain water, organic solvents, rheology control agents, pigment dispersants, anti-settling agents, curing catalysts, defoamers, antioxidants, UV absorbers, surface conditioners, crosslinking agents, extender pigments, etc. as necessary.

Paint can be made by mixing and dispersing the above materials.

The paint can be applied to a variety of substrates. Examples of substrates include metal substrates such as iron, stainless steel, aluminum, and surface-treated materials thereof; cement-based substrates such as cement, lime, and gypsum; and plastic substrates such as polyvinyl chlorides, polyesters, polycarbonates, and acrylics.

The paint can be applied, for example, by brushing, roller coating, or spray coating. After application, the coating is dried at room temperature or by heating to form a film. The thickness of the coating is usually about 5 to 70 μm.

＜Stationery＞
The stationery ink of the present specification contains a colorant dispersion and can be used for applications such as writing instruments, recorders, printers, etc. The stationery preferably contains a binder. The stationery can optionally contain a water-soluble organic solvent, a thickener, a dispersant, a lubricant, an anti-rust agent, an antiseptic, an antibacterial agent, etc. depending on each application (e.g., ballpoint pen, marking pen, etc.). The ratio of the colorant to the binder resin varies depending on the required application and is not particularly limited.

The stationery is preferably prepared by preparing a high-concentration colorant dispersion, diluting it with water, and adding the binder resin and, if necessary, other additives. The method for dispersing the colorant dispersion is not particularly limited and may be any of the known dispersion methods described above. The stationery is more preferably used for, for example, thixotropic inks (e.g., gel inks for water-based ballpoint pens) and Newtonian inks (e.g., low-viscosity water-based ballpoint pen inks). The pH (25°C) of the stationery is preferably adjusted to 5 to 10 with a pH adjuster or the like, more preferably 6 to 9.5, from the standpoints of usability, safety, the stability of the ink itself, and compatibility with the ink container.

The colorant content can be adjusted as appropriate depending on the line density of the stationery, but is preferably about 0.1 to 40% by mass of the total stationery ink composition.

<Textile printing agents>
The printing agent of the present specification preferably contains a colorant dispersion, water, and a binder resin. The printing agent can record images such as characters, pictures, and patterns on fabrics such as woven fabrics, nonwoven fabrics, and knitted fabrics. The ratio of the covering colorant to the binder resin varies depending on the desired application and is not particularly limited.

The binder resin may be any of the binder resins described above. The binder resin may be in the form of water-dispersed particles, water-soluble resin, etc. Examples of the binder resin include urethane resin and acrylic resin.

After preparing the colorant dispersion, the printing agent can be prepared by further mixing water, a binder resin, and other additives as necessary, according to the fiber to be colored, and according to the preferred processing method such as dip dyeing or printing. The printing agent for screen recording preferably contains additives such as preservatives, viscosity adjusters, pH adjusters, chelating agents, antioxidants, UV absorbers, flame retardants, crosslinking agents, etc. The colorant concentration of the printing agent for screen recording is preferably 1 to 10 mass %. The printing agent for dip dyeing preferably contains additives such as preservatives, viscosity adjusters, pH adjusters, chelating agents, antioxidants, UV absorbers, flame retardants, crosslinking agents, etc. The colorant concentration of the printing agent for dip dyeing is preferably in the range of 1 to 10 mass %. The viscosity of the printing agent for dip dyeing is set arbitrarily in the range of 1 mPa·s to 100 mPa·s in accordance with the printing device. The printing agent for spray printing preferably contains, as additives, a viscosity adjuster, a pH adjuster, a chelating agent, a plasticizer, an antioxidant, an ultraviolet absorbing agent, and the like. The colorant concentration of the printing agent for spray recording is preferably 1% by mass to 10% by mass. The viscosity of the printing agent for spray recording is set arbitrarily in the range of 1 mPa·s to 100 mPa·s in accordance with the device. The printing agent for inkjet recording preferably contains, as additives, a preservative, a viscosity adjuster, a pH adjuster, a chelating agent, an antioxidant, an ultraviolet absorbing agent, a flame retardant, and the like. The colorant concentration of the printing agent for inkjet recording is preferably 1% by mass to 20% by mass. The additives are preferably added to the aqueous dispersion of the coating colorant together with the binder resin. Examples of preservatives include sodium benzoate, sodium pentachlorophenol, sodium 2-pyridinethiol-1-oxide, sodium sorbate, sodium dehydroacetate, 1,2-dibenzisothiazolin-3-one (Proxel GXL, Proxel XL-2, Proxel LV, Proxel AQ, Proxel BD20, and Proxel DL, manufactured by Arch Chemicals). Specific examples of viscosity modifiers include mainly water-soluble natural or synthetic polymers such as carboxymethylcellulose, sodium polyacrylate, polyvinylpyrrolidone, gum arabic, and starch. Examples of pH adjusters include collidine, imidazole, phosphoric acid, 3-(N-morpholino)propanesulfonic acid, tris(hydroxymethyl)aminomethane, and boric acid. Examples of the chelating agent include ethylenediaminetetraacetic acid, ethylenediaminediacetic acid, nitrilotriacetic acid, 1,3-propanediaminetetraacetic acid, diethylenetriaminepentaacetic acid, N-hydroxyethylethylenediaminetriacetic acid, iminodiacetic acid, uramildiacetic acid, 1,2-diaminocyclohexane-N,N,N',N'-tetraacetic acid, malonic acid, succinic acid, glutaric acid, maleic acid, and salts thereof (including hydrates). Examples of the antioxidant include hindered phenol compounds, hydroquinone compounds, phosphite compounds and their substitution products, copper halides, and alkali metal halides. Examples of the ultraviolet absorbing agent include organic compound ultraviolet absorbing agents such as benzotriazoles and benzophenones; and inorganic compound ultraviolet absorbing agents such as titanium oxide and zinc oxide. When the printing agent is applied to an inkjet recording method, it is preferable to adjust the surface tension to 20 mN/m or more and 60 mN/m or less. More preferably, the viscosity is 20 mN or more and 45 mN/m or less, and even more preferably, 20 mN/m or more and 40 mN/m or less. If the surface tension is less than 20 mN/m, the liquid may overflow onto the nozzle surface, making it impossible to print normally. On the other hand, if the surface tension exceeds 60 mN/m, there is a tendency for the liquid to be easily repelled by non-absorbent substrates. The viscosity is also preferably 1.2 mPa·s or more and 20.0 mPa·s or less, more preferably 2.0 mPa·s or more and less than 15.0 mPa·s, and even more preferably 3.0 mPa·s or more and less than 12.0 mPa·s. When the viscosity is in this range, excellent ejection properties and good jetting properties can be maintained for a long period of time. The surface tension can be appropriately adjusted by the surfactant.

The printing agent of the present invention can be used for printing on fabrics, artificial leather, natural leather, etc. It is particularly excellent for printing on fabrics. The fabric is preferably a medium composed of fibers, and may be a woven fabric or a nonwoven fabric. Examples of materials include cotton, silk, wool, hemp, nylon, polyester, polyurethane, rayon, etc.

The present invention will be described in more detail below with reference to examples and comparative examples. It goes without saying that the present invention is not limited to the examples. In the following, "parts" means "parts by mass" and "%" means "% by mass". In this specification, Examples 10, 14 and 15 are reference examples.

(Mass average molecular weight (Mw), number average molecular weight (Mn))
The mass average molecular weight (Mw) and number average molecular weight (Mn) are polystyrene-equivalent mass average molecular weight (Mw) and number average molecular weight (Mn) measured using a TSK-GELSUPERHZM-N column (manufactured by Tosoh Corporation) at a column temperature of 40° C. with a GPC (manufactured by Tosoh Corporation, HLC-8320GPC) equipped with an RI detector, using THF as a developing solvent at a flow rate of 0.35 ml/min.

(Dispersion Degree)
The dispersity is calculated from the following formula:
Dispersity = mass average molecular weight (Mw) / number average molecular weight (Mn)

(Acid value)
Approximately 1 g of sample was precisely weighed and placed in an Erlenmeyer flask, and 50 ml of a mixture of distilled water and dioxane (weight ratio: distilled water/dioxane = 1/9) was added to dissolve. The above sample solution was titrated with 0.1 mol/L potassium hydroxide-ethanol solution (titer F) using a potentiometer (manufactured by Kyoto Electronics Manufacturing Co., Ltd., device name "potentiometric automatic titrator AT-710M"), and the amount of potassium hydroxide-ethanol solution (α (mL)) required to reach the titration end point was measured. The acid value (mg KOH/g) was calculated as the value of the dispersant in a dry state using the following formula.
Acid value (mg KOH/g) = {(5.611 x α x F)/S}/(non-volatile content/100)
Where S is the amount of sample taken (g)
α: consumption of 0.1 mol/L potassium hydroxide ethanol solution (ml)
F: Potency of 0.1 mol/L potassium hydroxide/ethanol solution

The (meth)allyl monomers used in the synthesis of the dispersants are shown in Table 1. The (meth)allyl monomers were obtained according to known synthesis methods such as those described in JP-A-01-000109.

<Production of Dispersant>
(Preparation of Dispersant 1)
In a reaction vessel equipped with a gas inlet tube, a thermometer, a condenser, and a stirrer, 19.5 parts (35 mol%) of 1-octene as a pigment-adsorptive group-containing monomer, 19.5 parts (30 mol%) of maleic anhydride, 34.5 parts (30 mol%) of N-phenylmaleimide, 26.5 parts (5 mol%) of monomer M4 as an allyl monomer, and 100 parts of methyl ethyl ketone as a solvent were charged, substituted with nitrogen, and then heated and stirred at 130° C. To this, 1.0 part of t-butylperoxy-2-ethylhexanoate as a radical polymerization initiator was added dropwise over 2 hours while stirring. Thereafter, the mixture was reacted for another 1 hour while maintaining the temperature at 130° C. by stirring. After that, after confirming that the polymerization conversion rate was 95-100%, the reaction temperature was lowered to 60°C, 16.8 parts of water (5 equivalents relative to the amount of maleic anhydride charged) and 0.01 parts of diazabicycloundecene as a catalyst were added, and the mixture was heated to 80°C while stirring and held for 4 hours to complete the reaction. The solvent was concentrated under reduced pressure to completely remove it. The number average molecular weight of the obtained dispersant was 6,400 and the acid value was 203.2 mgKOH/g. Then, dimethylaminoethanol was added so that the degree of neutralization was 100% based on the acid value of the obtained dispersant, and ion-exchanged water was added so that the non-volatile content was 30%, and the mixture was stirred at 50°C for 1 hour to obtain dispersant 1.

(Preparation of Dispersants 2 to 23)
Dispersants 2 to 23 were obtained by synthesizing in the same manner as Dispersant 1, except that the raw materials and the amounts charged of Dispersant 1 were changed as shown in Table 2. Dispersants 14 to 15 were prepared by modifying the acid anhydride group in the maleic anhydride unit using a compound shown in Table 2 in an amount of 1 equivalent to the amount of maleic anhydride charged. The amounts in Tables 2 to 4 are in mol %.

The abbreviations in Tables 2-1 to 2-3 are as follows.
HIDA: N-(2-hydroxyethyl)iminodiacetic acid

<Production of Colorant Dispersion>
(Preparation of Colorant Dispersion Set 1)
20 parts of Printex 85 (carbon black, manufactured by Orion Engineered Carbons), 20 parts of dispersant 1, and 60 parts of water were mixed and premixed with a stirrer, and then main dispersion was carried out using a 0.6 L Dyno Mill filled with 1800 g of zirconia beads with a diameter of 0.5 mm to obtain a black colorant dispersion. Colorant dispersion set 1 (K, C, M, Y) was obtained using the same method except that the pigment was changed to the following.
Cyan: LIONOGEN BLUE FG-7358G (C.I. Pigment) manufactured by Toyo Color Co., Ltd.
Blue 15: 3)
Magenta: TOSHIKI RED150TR (C.I. Pigment Red 150) manufactured by Tokyo Color Materials Co., Ltd.
Yellow: LIONOL YELLOW TT1405G (C.I. Pigment Yellow 14) manufactured by Toyo Color Co., Ltd.

(Production Examples of Colorant Dispersion Sets 2 to 23)
Colorant Dispersion Sets 2 to 23 were obtained in the same manner as in Colorant Dispersion Set 1, except that the dispersant used was changed according to Table 3.

<Production of Inkjet Ink Set>
(Inkjet ink set 1 production)
Of the obtained colorant dispersion set 1, 20.0 parts of black colorant dispersion, 20.0 parts of propylene glycol, 5.0 parts of 1,2-hexanediol, 10.0 parts of Joncryl 780 as a binder resin, 43.9 parts of ion-exchanged water, 0.1 parts of Surfynol DF110D (manufactured by Air Products Japan Co., Ltd.) as an activator, 0.5 parts of BYK-349 (manufactured by BYK Corporation), 0.5 parts of triethanolamine as a pH adjuster, and Proxel GXL (s) (manufactured by Arch Chemical Co., Ltd.) as a preservative were mixed to obtain a black inkjet ink. Inkjet ink set 1 (K, C, M, Y) was obtained by using the same method except that the color of the colorant dispersion used in the colorant dispersion set 1 was changed.

<Production of Inkjet Ink Sets 2 to 23>
Inkjet ink sets 2 to 23 were obtained in the same manner as inkjet ink set 1, except that the colorant dispersions used were changed according to Tables 4-1 to 4-3.

The abbreviations in Tables 4-1 to 4-3 are as follows.
1,2-HD: 1,2-hexanediol PG: 1,2-propanediol SF DF110D: Surfynol DF110D (manufactured by Nissin Chemical Industry Co., Ltd.)
TEA: Triethanolamine

<Production of coated products>
(Production of coated product)
The obtained inkjet ink set 1 was loaded into an inkjet printer (Seiko Epson Corporation, model number: EM-930C, piezo type), and black ink, cyan ink, magenta ink, and yellow ink were used for full-surface solid printing (fine mode) on fine paper (Nippon Paper Industries Co., Ltd., NPi Form NEXT-IJ, 64 g/m2 per gram) and coated paper (Oji Paper Co., Ltd., OK Topcoat, 104.7 g/m2 per gram). After that, the ink was left to stand for 24 hours at 25°C and a relative humidity of 50%, and then coated product 1 was obtained.

<Production of Coatings 2 to 23>
Coatings 2 to 23 were obtained in the same manner as for Coating 1, except that the inkjet inks used were changed to 2 to 23.

<Examples 1 to 20 and Comparative Examples 1 to 3>
The colorant dispersions, inkjet inks, and coatings produced above were subjected to the following evaluations 1 to 4.

<Evaluation 1: Storage stability evaluation>
The storage stability of the obtained colorant dispersion set was evaluated using the black colored dispersion as follows. The colorant dispersion was stored in a thermostatic chamber at 70°C to accelerate aging, and then the change in viscosity of the colorant dispersion before and after aging was evaluated. The viscosity was measured using an E-type viscometer (Toki Sangyo Co., Ltd. TVE-20L, standard cone) at 25°C and a rotation speed of 50 rpm, and the value after 1 minute was taken as the viscosity value. The evaluation criteria were as follows. A score of 2 or more was considered to be in the practical range.
5: Viscosity change rate after four weeks of storage is less than ±10%; 4: Viscosity change rate after two weeks of storage is less than ±10%; 3: Viscosity change rate after one week of storage is less than ±10%; 2: Viscosity change rate after one week of storage is ±10-20%.
1: Viscosity change rate after one week of storage is more than ±20%

<Evaluation 2: Evaluation of coarse particle amount>
The amount of coarse particles in the colorant dispersion was evaluated using the black colorant dispersion from the obtained colorant dispersion set as follows. Specifically, the amount of coarse particles in the colorant dispersion was evaluated based on the time it took for a fixed amount of the colorant dispersion to pass through a 25 mmφ glass fiber filter (manufactured by GF/BGE Healthcare Life Sciences). If there were many coarse particles, the filter would become clogged and the time to pass would be longer. If there were even more coarse particles, the filter would become clogged and the entire amount of the colorant dispersion could not be filtered. Generally, the filters used in the path for supplying ink to an inkjet head are larger than 1 μm, and the colorant concentration of ink for inkjet recording is generally lower than that of the colorant dispersion. It can be said that passing through the filter by this test method is sufficient, but it can be said that a faster filtration rate leads to higher re-dissolution and disintegration of the colorant particles and superior productivity. Specific evaluation conditions are shown below. 15 ml of water was poured into a suction vessel equipped with a vacuum pump via a cock.
A funnel with ml graduations and a 25 mm diameter filter holder (manufactured by ADVANTEC) with a 25 mm diameter glass fiber filter (manufactured by GF/BGE Healthcare Life Sciences) are placed on the vessel. A pressure reducing pump is operated using a cock so that the pressure inside the suction vessel is not reduced. 15 g of colorant dispersion is weighed into the funnel. The pump and suction vessel are started by opening the pressure, and the time it takes for the entire amount of colorant dispersion to pass through the filter is measured. The pressure inside the suction vessel at this time is 0.05 MPa to 0.07 MPa. A rating of 2 or higher was considered to be in the practical range.
5: Filtration possible in less than 30 seconds 4: Filtration possible in 30 to less than 45 seconds 3: Filtration possible in 45 to less than 60 seconds 2: Filtration possible in 60 to less than 90 seconds 1: Filtration not possible in less than 90 seconds

<Evaluation 3: Evaluation of density on fine paper>
The obtained inkjet ink was loaded into an inkjet printer (Seiko Epson Corporation, model number: EM-930C, piezoelectric type), and 100% solid images were printed on fine paper (Nippon Paper Industries Co., Ltd., NPi Form NEXT-IJ, 64 g/m ² per square meter) using black ink, cyan ink, magenta ink, and yellow ink. The printed matter was left for 24 hours at 25° C. and 50% relative humidity, and the obtained test piece was measured using a densitometer, eXactAdvance, manufactured by X-rite Corporation. The color measurement conditions were ISO status T, viewing angle 2°, and light source D50 as the density standard. The higher the print density, the higher the print density. The evaluation criteria were as follows. A score of 2 or more was considered to be in the practical range.
5: For each of the OD values K, C, M, and Y, the density is higher by 0.3 or more than that of Comparative Example 3; 4: For each of the OD values K, C, M, and Y, the density is higher by 0.2 or more and less than 0.3 than that of Comparative Example 3; 3: For each of the OD values K, C, M, and Y, the density is higher by 0.1 or more and less than 0.2 than that of Comparative Example 3; 2: For each of the OD values K, C, M, and Y, the density is higher by less than 0.1 than that of Comparative Example 3; 1: For each of the OD values K, C, M, and Y, the density is equal to or less than that of Comparative Example 3.

<Evaluation 4: Coated Paper Density Evaluation>
The obtained inkjet ink was loaded into an inkjet printer (Seiko Epson Corporation, model number: EM-930C, piezoelectric type), and 100% solid images were printed on coated paper (Oji Paper Co., Ltd. OK Topcoat, 104.7 g/ ^m2 per square meter) using black ink, cyan ink, magenta ink, and yellow ink. The printed matter was left for 24 hours at 25°C and 50% relative humidity, and the obtained test piece was then measured using a densitometer, eXactAdvance, manufactured by X-rite Corporation. The color measurement conditions were ISO status T, viewing angle 2°, and light source D50, based on density. The higher the print density, the higher the print density. The evaluation criteria were as follows. A score of 2 or more was considered to be in the practical range.
5: For each of the OD values K, C, M, and Y, the density is higher by 0.7 or more than that of Comparative Example 3; 4: For each of the OD values K, C, M, and Y, the density is higher by 0.5 or more and less than 0.7 than that of Comparative Example 3; 3: For each of the OD values K, C, M, and Y, the density is higher by 0.2 or more and less than 0.5 than that of Comparative Example 3; 2: For each of the OD values K, C, M, and Y, the density is higher by less than 0.2 than that of Comparative Example 3; 1: For each of the OD values K, C, M, and Y, the density is equal to or lower than that of Comparative Example 2

The evaluation results for the examples and comparative examples are shown in Table 5 above.

From the results in Table 5, it can be seen that Examples 1 to 20 are capable of printing at high density on uncoated paper having no ink-receiving layer, and provide colorant dispersions from which inkjet inks having good storage stability can be prepared.

Claims (6)

A colorant dispersion comprising a dispersant, a colorant, and water,
the dispersant is a polymer containing a colorant-adsorptive-group-containing monomer unit, a maleic acid unit, a (meth)allyl monomer unit, and a maleimide unit or an N-substituted maleimide unit,
the colorant-adsorptive-group-containing monomer unit contains at least one of an α-olefin unit and a (meth)acrylic acid ester monomer unit having an alkyl group,
The colorant dispersion , wherein the N-substituted maleimide unit is a unit having a ring structure at a substitution site . 2. The colorant dispersion according to claim 1, wherein the maleic acid unit is a maleic acid unit modified with an oxycarboxylic acid having a divalent or trivalent carboxyl group. The colorant dispersion according to claim 1 or 2 , wherein the (meth)allyl monomer unit is a unit having an alkyleneoxy moiety. An ink comprising the colorant dispersion according to any one of claims 1 to 3 . An ink set comprising the ink of claim 4 . A coated product comprising a substrate and a printed layer formed from the ink according to claim 4 or the ink set according to claim 5 .