Pigment dispersion for ultraviolet-curable inkjet ink, method for producing same, and ultraviolet-curable inkjet ink

Abstract

To provide a pigment dispersion liquid used for preparing a UV-curable inkjet ink, which uses a yellow pigment or an orange pigment but yet allows these pigments to be dispersed suitably and stored stably.SOLUTION: The present invention provides a pigment dispersion liquid used for preparing a UV-curable inkjet ink, which comprises a pigment comprising at least either a yellow pigment or an orange pigment, a pigment derivative, an aminated polymer dispersant, and a UV-curable monomer. The pigment derivative has a structure represented by the general formula (1) (where X is OH or OCH3, and at least two of four X are OH).SELECTED DRAWING: None

Description

[Technical field]

[0001] The present invention relates to a pigment dispersion for an ultraviolet-curable inkjet ink, a method for producing the same, and an ultraviolet-curable inkjet ink. [Background technology]

[0002] Inkjet printing does not require a plate and is capable of printing images on demand by data output from a personal computer. Inkjet printing uses water-based inkjet ink, solvent-based inkjet ink, ultraviolet-curable inkjet ink, etc. Among them, ultraviolet-curable inkjet ink, which does not require a drying process and can produce prints with excellent durability, has attracted attention for industrial applications such as sign displays, packaging, and printing on plastic containers.

[0003] Inkjet printing methods are shifting from single-pass printing to high-speed printing, where ink is ejected from a line head at once to print a large-area image at once. This has created a need for the development of ultraviolet-curable inkjet (hereinafter also referred to as "UVIJ ink") that can handle such high-speed printing.

[0004] UVIJ ink is prepared by, for example, using a pigment dispersion liquid in which an ultraviolet-curable monomer is used as a liquid medium, and blending an oligomer, a photoinitiator, and the like. UVIJ inks usually include the three primary color inks of cyan ink, magenta ink, and yellow ink, as well as black ink and white ink. In addition, complementary color inks such as green ink, orange ink, and blue ink are also used. When preparing each of these color inks, a pigment dispersion liquid in which the pigment of each color is dispersed in a liquid medium is used.

[0005] Pigment dispersions and inks prepared using the same are required to have finely dispersed pigment particles and low viscosity so that they can be stably discharged from an inkjet recording head. Furthermore, they are required to be resistant to aggregation and have stable viscosity even when stored for a long period of time, that is, the pigment dispersion state is required to be maintained at a constant state without fluctuating. However, when the pigment is finely dispersed, the surface energy increases, making it more likely to aggregate. As a result, there are issues such as an increase in viscosity and an increase in particle size during storage.

[0006] The liquid medium used in the pigment dispersion for UVIJ ink is an ultraviolet-curable monomer, which is an oil-based organic compound. The yellow pigment, which is an azo-based pigment used in each color of UVIJ ink, and the orange pigment, which is also used as a vat dye, have lower solvent resistance than blue pigments such as copper phthalocyanine, which is a highly crystalline metal salt, and magenta pigments such as quinacridone pigments, which are highly crystalline due to the influence of high hydrogen bonds. In addition, highly polar monomers such as ether-based monomers such as 2-(2-vinyloxyethoxy)ethyl acrylate; and monomers having amide bonds such as acryloylmorpholine, N-vinylpyrrolidone, and N-vinylcaprolactam; are used as ultraviolet-curable monomers in recent UVIJ inks. These ultraviolet-curable monomers have strong solubility for organic compounds. Therefore, when a pigment is dispersed in these ultraviolet-curable monomers, the dispersibility of the pigment is likely to decrease because crystals tend to grow. Therefore, the viscosity increases during dispersion, and the dispersibility decreases during storage, which tends to cause aggregation of pigment particles and an increase in viscosity. Therefore, there is a demand for pigment dispersions for UVIJ inks that use yellow and orange pigments and that have excellent pigment dispersibility as well as excellent storage stability.

[0007] As pigment dispersions for UVIJ inks with improved pigment dispersibility, various pigment dispersions using, for example, yellow pigments or orange pigments have been proposed (Patent Documents 1 to 3). [Prior art documents] [Patent documents]

[0008] [Patent Document 1] JP 2006-282758 A [Patent Document 2] JP 2004-2528 A [Patent Document 3] JP 2014-145053 A Summary of the Invention [Problem to be solved by the invention]

[0009] However, even the pigment dispersions proposed in Patent Documents 1 to 3 are still not sufficient in terms of pigment dispersibility and storage stability as pigment dispersions for preparing UVIJ inks that are more suitable for high-speed printing, and there is still room for further improvement.

[0010] The present invention has been made in consideration of the problems associated with the conventional techniques, and an object of the present invention is to provide a pigment dispersion liquid used for preparing an ultraviolet-curable ink-jet ink that has excellent dispersibility and storage stability for a yellow or orange pigment, even though the pigment is used. Another object of the present invention is to provide a method for producing the pigment dispersion liquid, and an ultraviolet-curable ink-jet ink that uses the pigment dispersion liquid. [Means for solving the problem]

[0011] That is, according to the present invention, there is provided a pigment dispersion liquid as shown below. [1] A pigment dispersion for use in an ultraviolet-curable inkjet ink, comprising a pigment including at least one of a yellow pigment and an orange pigment, a pigment derivative, a polymer dispersant having an amino group, and an ultraviolet-curable monomer, wherein the pigment derivative has a structure represented by the following general formula (1):

[0012] TIFF0007637606000001.tif49170 (In the general formula (1), X represents OH or OCH3, and two or more of the four Xs are OH.)

[0013] [2] The pigment dispersion according to [1], wherein the content of the pigment derivative is 3 to 20 parts by mass per 100 parts by mass of the pigment. [3] The pigment dispersion liquid according to the above [1] or [2], wherein the polymer dispersant is a polymer having an amine value of 0.5 to 100 mgKOH / g and a number average molecular weight of 5,000 to 20,000, the polymer comprising 3 to 50 mass% of structural units (1) derived from at least one member selected from the group consisting of dimethylaminoethyl methacrylate, diethylaminoethyl methacrylate, 2-vinylpyridine, 4-vinylpyridine, and vinylimidazole, some amino groups of which may be converted to quaternary ammonium salts, 40 to 90 mass% of structural units (2) derived from a macromonomer represented by the following general formula (2), and 0.5 to 20 mass% of structural units (3) derived from other monomers:

[0014] TIFF0007637606000002.tif36170 (In the general formula (2), R1 represents a hydrogen atom or a methyl group, A represents O or NH, Q represents an ethylene group or a methylethylene group, Y represents O, NHCOO, or NHCONH, m and n each independently represent an average number of repeating units of 0 or more, and m+n=20 to 100, and R2 represents a hydrogen atom, an alkyl group having 1 to 18 carbon atoms, an aryl group, or an alkylaryl group.)

[0015] [4] The pigment dispersion according to any one of [1] to [3], wherein the yellow pigment is at least one selected from the group consisting of CI Pigment Yellow 74, 128, 138, 139, 150, 155, 180, and 185, and the orange pigment is at least one selected from the group consisting of CI Pigment Orange 16, 34, 43, and 64.

[0016] According to the present invention, there is also provided a method for producing a pigment dispersion liquid as described below. [5] A method for producing a pigment dispersion liquid according to any one of [1] to [4] above, comprising the steps of mixing the pigment with an aqueous solution of an alkali neutralization product of the pigment derivative, and then adding an acid to precipitate the pigment derivative, thereby obtaining a pigment-derivative-treated pigment.

[0017] Furthermore, according to the present invention, there is provided the following ultraviolet-curable ink-jet ink. [6] An ultraviolet-curable inkjet ink containing the pigment dispersion liquid according to any one of [1] to [4] above. Effect of the Invention

[0018] According to the present invention, it is possible to provide a pigment dispersion liquid used for preparing an ultraviolet-curable ink-jet ink that has excellent dispersibility and storage stability for a yellow pigment or an orange pigment, even though the pigment is used. Furthermore, according to the present invention, it is possible to provide a method for producing the pigment dispersion liquid, and an ultraviolet-curable ink-jet ink that uses the pigment dispersion liquid. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0019] <Pigment dispersion> Hereinafter, an embodiment of the present invention will be described, but the present invention is not limited to the following embodiment. The pigment dispersion of the present invention is a pigment dispersion used in an ultraviolet-curable inkjet ink, which contains a pigment including at least one of a yellow pigment and an orange pigment, a pigment derivative, a polymer dispersant having an amino group, and an ultraviolet-curable monomer. The pigment derivative has a structure represented by the following general formula (1). Hereinafter, the pigment dispersion of the present invention will be described in detail.

[0020] TIFF0007637606000003.tif49170 (In the general formula (1), X represents OH or OCH3, and two or more of the four Xs are OH.)

[0021] (Pigments) The pigment includes at least one of a yellow pigment and an orange pigment. The pigment is preferably either a yellow pigment or an orange pigment. The hue (yellow) of the pigment derivative does not significantly interfere with the hue of the pigment used. Examples of yellow pigments include CI Pigment Yellow 1, 2, 3, 4, 5, 6, 7, 10, 11, 12, 13, 14, 16, 17, 24, 34, 35, 37, 53, 55, 65, 73, 74, 75, 81, 83, 93, 94, 95, 97, 98, 99, 108, 109, 110, 113, 114, 117, 120, 124, 128, 129, 133, 138, 139, 147, 150, 151, 153, 154, 155, 167, 172, 180, and 185. Furthermore, examples of orange pigments include CI Pigment Orange 1, 2, 5, 7, 13, 14, 15, 16, 24, 34, 36, 38, 40, 43, 63, and 64.

[0022] Among them, since the color development and light resistance are good, the yellow pigment is preferably at least one selected from the group consisting of CI Pigment Yellow 74, 128, 138, 139, 150, 155, 180, and 185. Also, the orange pigment is preferably at least one selected from the group consisting of CI Pigment Orange 16, 34, 43, and 64. In particular, since the hue range is wide, the yellow pigment is preferably at least one selected from the group consisting of CI Pigment Yellow 138, 150, 155, 180, and 185. Also, the orange pigment is preferably at least one selected from the group consisting of CI Pigment Orange 43 and 64.

[0023] (Pigment derivatives) The pigment derivative has a structure represented by the following general formula (1).

[0024] TIFF0007637606000004.tif49170 (In the general formula (1), X represents OH or OCH3, and two or more of the four Xs are OH.)

[0025] The pigment derivative is a compound having a skeleton similar to that of the pigment or a structure that is adsorbed to the pigment. The pigment dispersion of the present invention contains an ultraviolet-curable monomer, which is an oil-based compound, as a liquid medium. The pigment is an oil-based organic compound, and the polymeric dispersant used to finely disperse the pigment in the liquid medium and increase the storage stability of the pigment dispersion is also oil-based. The polymeric dispersant needs to be adsorbed to the pigment without dissolving in the liquid medium. The pigment derivative is a component that mediates the adsorption of the polymeric dispersant to the pigment. Since the liquid medium is an organic compound, the polymeric dispersant is adsorbed to the pigment by ionic bonding to suppress the detachment of the polymeric dispersant. For this reason, the pigment derivative has an acidic carboxy group as an active group in its molecular structure. In addition, a basic polymer having an amino group is used as the polymeric dispersant. For this reason, the polymeric dispersant adsorbed to the pigment imparts a carboxy group, which is an active group, to the surface of the pigment particles. Then, the carboxy group imparted to the surface of the pigment particles and the amino group in the polymeric dispersant are ionic bonded, and the pigment is stably adsorbed to the polymeric dispersant. This allows the pigment to be finely dispersed in the ultraviolet-curable monomer, which is the liquid medium, to provide a pigment dispersion having excellent storage stability.

[0026] Since the pigment derivative has an aromatic ring and an amide bond in its molecular structure, it is strongly adsorbed to the yellow pigment or orange pigment. In addition, since the pigment derivative has two or more carboxyl groups in its molecular structure, it can impart carboxyl groups to the pigment particle surface by adsorbing to the pigment. In the general formula (1), the number of "OH" groups represented by "X" may be expressed as an average value. That is, the pigment derivative represented by the general formula (1) may be a mixture of a plurality of compounds having different numbers of "OH" groups represented by "X". In the general formula (1), the number of "OH" groups represented by "X" is preferably "4". That is, by using a pigment dispersant represented by the general formula (1) in which the number of carboxyl groups in one molecule is 4, it is possible to effectively impart carboxyl groups to the pigment particle surface. In addition, since the number of carboxyl groups imparted is increased, the polarity can be further increased and the pigment becomes more difficult to dissolve in the ultraviolet curable monomer used as the liquid medium.

[0027] The pigment derivative represented by the general formula (1) can be produced according to a conventionally known method. For example, the pigment derivative can be produced by azo coupling. In particular, the pigment derivative represented by the general formula (1) can be easily produced by using CI Pigment Yellow 155 (hereinafter also referred to as "PY-155") having the structure represented by the following formula (A) as a raw material and hydrolyzing the methyl ester in the molecular structure under alkaline conditions, for example.

[0028] TIFF0007637606000005.tif47170

[0029] After dispersing PY-155 in water, an alkali metal hydroxide such as sodium hydroxide or potassium hydroxide is added. When all methyl esters are to be hydrolyzed, an alkali metal hydroxide in an amount equal to or greater than the molar amount of the methyl esters may be used. The ester bonds are hydrolyzed by heating at room temperature, preferably at about 80°C, to form alkali metal salts of carboxy groups. The progress of the hydrolysis reaction can be tracked by confirming the decrease in the absorption peak derived from the ester bonds and the increase in the absorption peak derived from the carboxy groups, or by confirming the pH change, by IR analysis using an infrared spectrophotometer.

[0030] After the hydrolysis, an acidic substance such as hydrochloric acid or acetic acid is added to neutralize the solution, preferably until the pH becomes 3 or less. This allows the pigment derivative represented by general formula (1) that is now water-insoluble to precipitate. The precipitated pigment derivative can be extracted as a solid by filtering and drying. However, when the number of carboxy groups in one molecule is "4", it may become very hard and difficult to dissolve in a solvent, making it difficult to handle. For this reason, it is preferable to extract the precipitated pigment derivative in the form of a water paste without drying it.

[0031] In the pigment dispersion, the content of the pigment derivative relative to 100 parts by mass of the pigment is preferably 3 to 20 parts by mass, and more preferably 5 to 15 parts by mass. If the content of the pigment derivative is less than 3 parts by mass relative to 100 parts by mass of the pigment, the amount of active groups derived from the pigment derivative imparted to the pigment surface may be insufficient. On the other hand, if the content of the pigment derivative is more than 20 parts by mass relative to 100 parts by mass of the pigment, the hue derived from the pigment derivative is easily reflected, and the desired hue may not be obtained.

[0032] (Polymer dispersant) The polymer dispersant is a basic polymer dispersant having an amino group. Examples of the polymer dispersant include long-chain alkyl monoamines; polyalkylene glycol adducts of long-chain alkyl amines; amide amine salts of polyesters such as poly12-hydroxysaric acid and polyethyleneimine, polyvinylamine, polyallylamine, etc.; reactants of compounds having tertiary and primary amino groups such as polyethylene glycol, polyesters, and diethylaminopropylamine with isocyanate polynuclear compounds; vinyl polymers having vinylimidazole, vinylpyridine, etc. as constituents; polymers in which tertiary amino groups such as AB block copolymers having (meth)acrylic acid monomers as constituents, A chains soluble in solvents, and B chains containing amino group-containing (meth)acrylates such as dimethylaminoethyl methacrylate, are converted into quaternary ammonium salts with quaternizing agents such as methyl chloride and benzyl chloride; and the like.

[0033] As the polymer dispersant, it is preferable to use a polymer having a structural unit (1) derived from at least one member selected from the group consisting of dimethylaminoethyl methacrylate, diethylaminoethyl methacrylate, 2-vinylpyridine, 4-vinylpyridine, vinylimidazole, and quaternary ammonium salts thereof, in which some amino groups may be converted to quaternary ammonium salts, a structural unit (2) derived from a macromonomer represented by the following general formula (2), and a structural unit (3) derived from another monomer.

[0034] TIFF0007637606000006.tif36170 (In the general formula (2), R1 represents a hydrogen atom or a methyl group, A represents O or NH, Q represents an ethylene group or a methylethylene group, Y represents O, NHCOO, or NHCONH, m and n each independently represent an average number of repeating units of 0 or more, and m+n=20 to 100, and R2 represents a hydrogen atom, an alkyl group having 1 to 18 carbon atoms, an aryl group, or an alkylaryl group.)

[0035] [Constituent unit (1)] The structural unit (1) is a structural unit derived from at least one member selected from the group consisting of dimethylaminoethyl methacrylate, diethylaminoethyl methacrylate, 2-vinylpyridine, 4-vinylpyridine, and vinylimidazole, in which some of the amino groups may be converted to quaternary ammonium salts.

[0036] A part of the amino group in the structural unit (1) may be converted to a quaternary ammonium salt in order to adjust the solubility in the ultraviolet-curable monomer. That is, the structural unit (1) may have a quaternary ammonium salt group. The quaternary ammonium salt group can be formed by reacting an amino group with a quaternizing agent. Examples of the quaternary salt agent include methyl chloride, benzyl chloride, benzyl bromide, dimethyl sulfate, diethyl sulfate, methyl p-toluenesulfonate, methyl methylsulfonate, and methyl trifluoromethylsulfonate. Examples of the counter ion of the quaternary ammonium salt group include chloride ion, bromide ion, and sulfate ester ion. The counter ion may be changed by reacting with a metal cation. Examples of the metal cation include bis(fluorosulfonyl)imide lithium salt, (fluorosulfonyl)(trifluoromethylsulfone)imide lithium salt, bis(trifluoromethylsulfone)imide lithium salt, sodium tetrafluoroborate, and sodium hexafluorophosphate.

[0037] The content of the structural unit (1) in the polymer dispersant (polymer) is preferably 3 to 50 mass %, more preferably 10 to 30 mass %, based on the total of the structural units (1) to (3). If the content of the structural unit (1) in the polymer is less than 3 mass %, the amount of amino groups is insufficient, so that the adsorption to the pigment is likely to decrease, and the dispersibility of the pigment may decrease slightly. On the other hand, if the content of the structural unit (1) in the polymer is more than 50 mass %, the amount of amino groups may be too large. As a result, the polymerization reaction during production may be easily inhibited, and the pigment may be more likely to aggregate.

[0038] [Constituent unit (2)] The structural unit (2) is a structural unit derived from a macromonomer represented by the following general formula (2).

[0039] TIFF0007637606000007.tif36170 (In the general formula (2), R1 represents a hydrogen atom or a methyl group, A represents O or NH, Q represents an ethylene group or a methylethylene group, Y represents O, NHCOO, or NHCONH, m and n each independently represent an average number of repeating units of 0 or more, and m+n=20 to 100, and R2 represents a hydrogen atom, an alkyl group having 1 to 18 carbon atoms, an aryl group, or an alkylaryl group.)

[0040] The structural unit (2) is a structural unit having a polyalkylene glycol chain. The polymer dispersant containing this structural unit (2) has a structure in which a polyalkylene glycol chain is grafted. The polyalkylene glycol chain is a molecular chain that can be dissolved in an ultraviolet-curable monomer, which is a liquid medium (dispersion medium). When the polymer dispersant is adsorbed to the pigment, the polyalkylene glycol chain has steric repulsion to suppress the aggregation of the pigment, and the pigment is less likely to aggregate even after a long period of time has passed, thereby improving storage stability. In addition, O (oxygen atom), NHCOO (urethane bond), and NHCONH (urea bond) represented by Y in the general formula (2) have the function of adsorbing to the pigment by hydrogen bonding with hydrogen atoms constituting carboxyl groups, hydroxyl groups, etc. on the surface of the pigment. This allows the pigment to be well and stably dispersed in the liquid medium for a long period of time.

[0041] In the general formula (2), m is the average number of repeating units of a propyleneoxy group (-CH(CH3)CHO-), and n is the average number of repeating units of an ethyleneoxy group (-CH2CHO-). m and n each independently represent an average number of repeating units of 0 or more, and m+n=20 to 100, preferably m+n=35 to 100. That is, the molecular weight of the polyalkylene glycol chain is preferably 880 to 5,800, more preferably 1,540 to 5,800. In addition, in the general formula (2), the alkyl group having 1 to 18 carbon atoms represented by R2 is preferably a methyl group, an ethyl group, a propyl group, a butyl group, a dodecyl group, a stearyl group, a phenyl group, a naphthyl group, or a nonylphenyl group.

[0042] Examples of the macromonomer represented by general formula (2) include a macromonomer in which Y is a urethane bond (NHCOO) obtained by reacting (meth)acryloyloxyethyl isocyanate with a glycol ether monoalkyl ether such as polyethylene glycol monomethyl ether, polyethylene glycol polypropylene glycol monobutyl ether, polypropylene glycol monomethyl ether, or polyethylene glycol monododecyl ether; and a macromonomer in which Y is a urea bond (NHCONH) obtained by reacting (meth)acryloyloxyethyl isocyanate with a monoether monoamine such as polyethylene glycol polypropylene glycol monoamine.

[0043] In the general formula (2), Y is preferably a urea bond (NHCONH) that does not require a catalyst when reacting an isocyanate with an amine. In addition, the polyalkylene glycol chain in the general formula (2) is preferably a random copolymer of propylene oxide and ethylene oxide. Furthermore, in the general formula (2), R2 is preferably a methyl group. The molecular weight of the polyalkylene glycol chain is preferably 2,000 to 4,000, and m+n=36 to 90.

[0044] The content of the structural unit (2) in the polymer dispersant (polymer) is preferably 40 to 90 mass %, more preferably 45 to 85 mass %, based on the total of the structural units (1) to (3). The structural unit (2) is a structural unit contained in a relatively large amount in the polymer. By using a polymer containing a large amount of such structural unit (2) as a polymer dispersant, the densely arranged polyalkylene glycol chains act as steric hindrance, preventing the pigments from approaching each other, and the pigment can be stably dispersed.

[0045] [Constituent unit (3)] The structural unit (3) is a structural unit derived from another monomer capable of copolymerizing with each monomer constituting the structural units (1) and (2). As the other monomer, a conventionally known vinyl-based monomer or the like can be used. As the other monomer, (meth)acrylic acid-based monomers such as (meth)acrylic acid and (meth)acrylic acid esters; vinyl monomers such as styrene, vinyl toluene, vinyl pyridine, vinyl caprolactone, vinyl imidazole, α-methyl styrene, and vinyl acetate; and the like can be mentioned. Among them, α-methyl styrene is preferred from the viewpoint of easy control of the molecular weight.

[0046] The content of the structural unit (3) in the polymer dispersant (polymer) is preferably 0.5 to 20 mass% and more preferably 0.6 to 16 mass% based on the total of the structural units (1) to (3). If the content of the structural unit (3) in the polymer exceeds 20 mass%, the content of other structural units is relatively reduced, and the function as a dispersant may be slightly reduced.

[0047] [polymer] The amine value of the polymer used as the polymer dispersant is 0.5 to 100 mgKOH / g, preferably 10 to 90 mgKOH / g, and more preferably 20 to 80 mgKOH / g. The number average molecular weight (Mw) of the polymer is 5,000 to 20,000, and preferably 10,000 to 15,000. If the number average molecular weight of the polymer is less than 5,000, the content of the structural unit (2) is somewhat low, and thus the dispersion stability may be insufficient. On the other hand, if the number average molecular weight of the polymer is more than 20,000, the amount of the polymer dispersant required to disperse the pigment may be too large, and the viscosity of the pigment dispersion may be excessively high. In this specification, the number average molecular weight (Mn) and the weight average molecular weight (Mw) are both values ​​calculated in terms of polystyrene measured by gel permeation chromatography (GPC).

[0048] (Method of synthesizing polymer dispersants) The polymer used as the polymer dispersant can be synthesized by a conventionally known method. For example, it can be synthesized by a conventionally known radical polymerization method; a polymerization method in which a molecular weight is adjusted using a chain transfer agent such as thiol, an atom transfer radical polymerization method (ATRP method), a reversible addition-fragmentation chain transfer polymerization method (RAFT method), a nitroxide method (NMP method), an organotellurium method (TERP method), an iodine transfer polymerization method (ITP method), a reversible transfer catalyst polymerization method (RTCP method), a reversible catalyst-mediated polymerization method (RCMP method), or the like; a living radical polymerization method. Among them, the living radical polymerization method is preferred because it is possible to make the molecular weight of the main chain more uniform and to make an AB block copolymer by the addition method.

[0049] The polymerization may be either thermal polymerization or photopolymerization, and an azo-based radical generator, a peroxide-based radical generator, a photosensitizer, etc. may be added to the polymerization reaction system. The polymerization method may be any of solventless polymerization, solution polymerization, and emulsion polymerization, and among them, solution polymerization is preferred.

[0050] The UVIJ ink prepared using the pigment dispersion of the present invention is an environmentally friendly ink that does not substantially contain volatile components, and the components ejected and applied to the substrate are cured by ultraviolet light to form an image. For this reason, it is preferable that the solution containing the polymer dispersant obtained by the above-mentioned synthesis method or the like does not substantially contain volatile components. For example, after solution polymerization, it is preferable to precipitate the solution in a poor solvent or volatilize the solvent used. In order to obtain a polymer dispersant that does not substantially contain volatile components, the polymer dispersant may be synthesized in a non-volatile solvent.

[0051] (UV-curable monomer) The ultraviolet curable monomer is a component that can also function as a liquid medium for dispersing the pigment. The ultraviolet curable monomer may be a monofunctional monomer having one ultraviolet curable reactive group, a polyfunctional monomer having two or more reactive groups, or a mixture of these. Furthermore, an oligomer (photocurable oligomer) or a polymer (photocurable polymer) having an ultraviolet curable reactive group may be coexisted.

[0052] Among the ultraviolet curable monomers, examples of monofunctional monomers include methyl (meth)acrylate, ethyl (meth)acrylate, butyl (meth)acrylate, n-butyl (meth)acrylate, isobutyl (meth)acrylate, t-butyl (meth)acrylate, hexyl (meth)acrylate, cyclohexyl (meth)acrylate, trimethylcyclohexyl (meth)acrylate, t-butylcyclohexyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, isodecyl (meth)acrylate, lauryl (meth)acrylate, stearyl (meth)acrylate, isobornyl (meth)acrylate, dicyclopentenyl (meth)acrylate, adamantyl (meth)acrylate, adamantyl methyl (meth)acrylate, 2-hydroxyethyl ... Examples of the radical polymerizable monomer include propyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, glycidyl (meth)acrylate, dimethylaminoethyl (meth)acrylate, diethylaminoethyl (meth)acrylate, polyethylene glycol mono(meth)acrylate, polyethylene glycol monomethyl ether (meth)acrylate, 2-ethoxyethyl (meth)acrylate, tetrahydrofurfuryl (meth)acrylate, allyl (meth)acrylate, benzyl (meth)acrylate, phenoxyethyl (meth)acrylate, (3-ethyloxetan-3-yl)methyl (meth)acrylate, an adduct of phthalic anhydride and 2-hydroxyethyl (meth)acrylate, acryloylmorpholine, N-vinylpyrrolidone, and N-vinylcaprolactam. Among them, (meth)acrylate-based compounds having good ultraviolet curing properties are preferred.

[0053] Examples of polyfunctional monomers and photocurable oligomers include vinyloxyethoxyethyl (meth)acrylate, neopentyl glycol di(meth)acrylate, ethylene glycol di(meth)acrylate, poly(n=2 or more) ethylene glycol di(meth)acrylate, polypropylene glycol (n=2 or more) di(meth)acrylate, polybutylene glycol (n=2 or more) di(meth)acrylate, 2,2-bis(4-(meth)acryloxyethoxyphenyl)propane, 2,2-bis(4-(meth)acryloxydiethoxyphenyl)propane, trimethylolpropane diacrylate, bis(2-( Epoxy poly(meth)acrylates such as epoxy di(meth)acrylate obtained by reacting bisphenol A diepoxy with (meth)acrylic acid, 1,Urethane tri(meth)acrylate obtained by reacting 2-hydroxyethyl(meth)acrylate with a trimer of 6-hexamethylene diisocyanate, urethane di(meth)acrylate obtained by reacting isophorone diisocyanate with 2-hydroxypropyl(meth)acrylate, urethane hexa(meth)acrylate obtained by reacting isophorone diisocyanate with pentaerythritol tri(meth)acrylate, urethane di(meth)acrylate obtained by reacting dicyclohexyl diisocyanate with 2-hydroxyethyl(meth)acrylate, dicyclo Examples of suitable poly(meth)acrylates include urethane di(meth)acrylates obtained by reacting 2-hydroxyethyl (meth)acrylate with a urethane reaction product of hexyl diisocyanate and poly(n=6-15)tetramethylene glycol; polyester (meth)acrylates obtained by reacting trimethylolethane with succinic acid and (meth)acrylic acid; and polyester poly(meth)acrylates obtained by reacting trimethylolpropane with succinic acid, ethylene glycol, and (meth)acrylic acid. Among these, polyfunctional (meth)acrylate monomers and photocurable oligomers having good ultraviolet curability are preferred.

[0054] Examples of photocurable polymers include polymers having a plurality of radically polymerizable (meth)acryloyloxy groups at the terminals or side chains of polymers such as poly(meth)acrylate, polyurethane, polyester, polyamide, polyimide, and polyepoxy resin.

[0055] (Additives) The pigment dispersion may further contain various additives other than the above-mentioned components. Examples of additives include polymerization inhibitors, surfactants, antioxidants, UV absorbers, light stabilizers, leveling agents, thickeners, viscosity adjusters, preservatives, antifungal agents, dyes, waxes, fillers, acid generators, and alkali generators. Since the pigment dispersion of the present invention is used to produce UVIJ ink, it may contain a photopolymerization initiator in advance.

[0056] The polymerization inhibitor is a component that prevents the ultraviolet-curable monomer from polymerizing and solidifying during dispersion or storage. Examples of the polymerization inhibitor include phenol compounds such as p-methoxyphenol, t-butylcatechol, di-t-butyl-para-cresol, hydroquinone monomethyl ether, 3,5-di-t-butyl-4-hydroxytoluene, 2,2'-methylenebis(4-methyl-6-t-butylphenol); quinone compounds such as p-benzoquinone; amine compounds such as p-benzylaminophenol, di-β-naphthyl-para-phenylenediamine, phenylhydroxylamine, diethylhydroxylamine; oxime compounds such as quinone dioxime and cyclohexanone oxime; and sulfur compounds such as phenothiazine.

[0057] (Pigment dispersion) The preferred contents of each component in the pigment dispersion are as follows. That is, the total content of the pigment and pigment derivative (content of pigment treated with pigment derivative) in the pigment dispersion is preferably 5 to 30 mass %, and more preferably 10 to 25 mass %. The content of the polymer dispersant having an amino group in the pigment dispersion is preferably 0.5 to 30 mass %, and more preferably 1 to 25 mass %. Furthermore, the content of the ultraviolet-curable monomer in the pigment dispersion is preferably 40 to 94.5 mass %, and more preferably 60 to 90 mass %.

[0058] The viscosity of the pigment dispersion may be adjusted to a viscosity suitable for inkjet printing while taking into consideration the properties of the pigment, etc. The viscosity of the pigment dispersion at 25°C is preferably 3 to 100 mPa s. The surface tension of the pigment dispersion at 25°C is preferably 15 to 45 mN / m, and more preferably 20 to 40 mN / m.

[0059] <Method of manufacturing pigment dispersion> The pigment dispersion can be produced according to a conventional method. For example, a mixture is obtained by mixing an ultraviolet curable monomer, a pigment, a pigment derivative, and a polymer dispersant, and adding an organic solvent as necessary. The mixture is finely dispersed in the pigment using a paint shaker, a ball mill, an attritor, a sand mill, a horizontal media mill, a colloid mill, a roll mill, or the like to prepare a dispersion. Next, the ultraviolet curable monomer is added to the prepared dispersion to adjust the concentration, and other additives are further added as necessary, to obtain a pigment dispersion. It is preferable to remove coarse particles using a centrifuge or a filter as necessary.

[0060] In order to set the number average particle size (particle size distribution) of the pigment within the desired range, techniques such as reducing the size of the grinding media used during dispersion, increasing the packing rate of the grinding media, lengthening the treatment time, slowing down the discharge speed, and classifying the pigment using a filter or a centrifuge after grinding may be employed.

[0061] When producing a pigment dispersion, it is preferable to mix a pigment with an aqueous solution of an alkali neutralized pigment derivative, add an acid, and precipitate the pigment derivative to obtain a pigment-derivative-treated pigment. That is, the method for producing a pigment dispersion of the present invention preferably includes a step of mixing a pigment with an aqueous solution of an alkali neutralized pigment derivative, add an acid, and precipitate the pigment derivative to obtain a pigment-derivative-treated pigment. In addition, it is preferable that the pigment dispersion of the present invention is obtained by a production method including a step of mixing a pigment with an aqueous solution of an alkali neutralized pigment derivative, add an acid, and precipitate the pigment derivative to obtain a pigment-derivative-treated pigment. In this way, by going through the step of obtaining a pigment-derivative-treated pigment, a pigment dispersion having excellent pigment dispersibility and storage stability can be obtained. In addition, since the pigment derivative is hard and poorly soluble in organic solvents, it is preferable to handle it as described above.

[0062] Specifically, first, the pigment is peptized with water. The pigment may be in the form of a water paste immediately after synthesis, or in the form of a water paste of a finely divided pigment. The amount of the pigment is preferably 10% by mass or less of the amount of water, more preferably 5% by mass or less. To peptize the pigment with water, a stirrer such as a disperser or homogenizer, or a dispersing machine such as a bead mill can be used. Next, the water paste of the pigment derivative is diluted with water so that the content of the pigment derivative is 10% by mass or less, preferably 3% by mass or less, and then an alkali component is added to neutralize the carboxyl group of the pigment derivative, to prepare an aqueous solution of the alkali neutralized pigment derivative. Examples of the alkali component that can be used include ammonia, organic amines, and alkali metal hydroxides. The amount of the alkali component may be an amount that allows the pigment derivative to dissolve in water, and it is preferable to use an alkali component with a molar number equal to or greater than the number required to neutralize all the carboxyl groups of the pigment derivative.

[0063] After mixing the water slurry in which the pigment has been sufficiently peptized with an aqueous solution of an alkali neutralized product of the pigment derivative, an acid is gradually added to precipitate the pigment derivative. As the acid, an acid component such as hydrochloric acid or acetic acid can be used. These acid components are preferably used in the form of an aqueous solution of 10% by mass or less. By adding the acid, the pigment derivative is precipitated on the surface of the pigment in units of one molecule or several molecules, and a pigment derivative-treated pigment in which the pigment derivative is adsorbed on at least a part of the surface of the pigment can be obtained. The obtained pigment derivative-treated pigment (hereinafter also simply referred to as "treated pigment") can be filtered and washed, and then further dried and pulverized for use.

[0064] The resulting treated pigment is dispersed in an ultraviolet-curable monomer, which is a dispersion medium, using a polymer dispersant having an amino group. By using the polymer dispersant, the pigment particles can be finely dispersed. Furthermore, the amino group of the polymer dispersant ionically bonds to the carboxy group derived from the pigment derivative present on the surface of the pigment, and the polymer dispersant is adsorbed to the pigment. This suppresses pigment aggregation, making it possible to produce a pigment dispersion with excellent storage stability.

[0065] The treated pigment may be prepared by a method other than the above-mentioned method. For example, the treated pigment can be obtained by mixing an aqueous paste of the pigment and an aqueous paste of the pigment derivative, followed by filtration and drying. Alternatively, when the pigment is milled in the presence of a salt and a water-soluble organic solvent to be finely divided, an aqueous paste of the pigment derivative is allowed to coexist, or an aqueous paste of the pigment derivative is added after the finely divided pigment is milled. The treated pigment can then be obtained by washing with water, desalting, removing the solvent, and drying.

[0066] <UV-curable inkjet ink> By using the above-mentioned pigment dispersion, it is possible to produce an ultraviolet-curable inkjet ink that has excellent dispersibility and storage stability for a yellow or orange pigment. That is, the ultraviolet-curable inkjet ink of the present invention is an ultraviolet-curable inkjet ink that contains the above-mentioned pigment dispersion.

[0067] The UVIJ ink contains, as components other than the pigment dispersion liquid described above, for example, a photopolymerization initiator, an ultraviolet-curable polymer, and the above-mentioned additives. The photopolymerization initiator is a component for photopolymerizing the ultraviolet-curable monomer by irradiating ultraviolet light onto the ink applied to the substrate by the inkjet method, thereby forming a cured image. The photopolymerization initiator may be any that generates active species such as radicals or cations and initiates polymerization of the ultraviolet-polymerizable monomer. As the photopolymerization initiator, a photoradical polymerization initiator or a photocationic polymerization initiator can be used. Among these, it is preferable to use a photoradical polymerization initiator.

[0068] Examples of photopolymerization initiators include benzophenone-based photopolymerization initiators, thioxanthone-based photopolymerization initiators, ketoxime ester-based photopolymerization initiators, and acylphosphine oxide-based photopolymerization initiators. The content of the photopolymerization initiator in the UVIJ ink is preferably 3 to 12% by mass based on the entire UVIJ ink. If the content of the photopolymerization initiator is less than 3% by mass, the curing property may be slightly insufficient. On the other hand, if the content of the photopolymerization initiator is more than 12% by mass, the photopolymerization initiator may remain or the cured film may become colored.

[0069] The components are mixed and thoroughly stirred, and then filtered as necessary to remove coarse particles and foreign matter to obtain a UVIJ ink. The obtained UVIJ ink can be used to record (print) images on various substrates by inkjet recording. Examples of substrates include paper, photographic paper, glossy photographic paper, plastic film, fabric, ceramics, and metal. The above UVIJ ink can be used to form an image that is a printing film with high saturation and color development, as well as excellent durability such as adhesion and abrasion resistance. EXAMPLES

[0070] The present invention will be described in detail below with reference to examples, but the present invention is not limited to these examples. In the examples and comparative examples, "parts" and "%" are by mass unless otherwise specified.

[0071] <Synthesis of pigment derivatives> (Synthesis Example 1) 50 parts of CI Pigment Yellow 155 (PY-155, trade name "Ingjet Yellow 4GC", manufactured by Clariant) and 1,000 parts of ion-exchanged water were put into a flask and stirred to obtain a mixed solution. When a drop of the obtained mixed solution was spotted on a filter paper (No. 2), it remained on the surface of the filter paper without showing through. 500 parts of a 5% aqueous sodium hydroxide solution was added to the obtained mixed solution, which was then heated to 80°C and reacted for 4 hours to obtain a yellow reaction solution with a slight greenish tinge. When a drop of the obtained reaction solution was spotted on a filter paper, it showed showing through. This confirmed that the obtained reaction solution was in a dissolved state.

[0072] After cooling to room temperature, 5% hydrochloric acid was gradually added dropwise while measuring the pH. Viscosity increased at around pH 3.5. Further hydrochloric acid was added dropwise to make the reaction solution pH 2.8. When a drop of the resulting reaction solution was spotted on filter paper, there was no bleed-through, and reddish yellow powder remained on the surface of the filter paper. After filtering the reaction solution, it was thoroughly washed with ion-exchanged water to obtain an aqueous paste with a solid content of 11.0%.

[0073] One part of the obtained water paste was dried in a dryer at 100 ° C for 24 hours and then pulverized to obtain a hard powder with a strong reddish color. When analyzed using an infrared spectrophotometer, the 1,713 cm -1 The absorption peak at 1,695 cm originating from the carboxyl group almost disappeared. -1 This confirmed that all of the methyl esters in the structure of PY-155 had been hydrolyzed to carboxy groups, and the desired pigment derivative (hereinafter also referred to as "SYN") had been obtained.

[0074] 0.1 g of SYN ground using a grinder was added to 10 mL each of toluene, methyl ethyl ketone, tetrahydrofuran, dimethylformamide, phenoxyethyl acrylate (PEA), and isobornyl acrylate (IBXA) and stirred. As a result, it was confirmed that SYN was hardly dissolved in any of the liquid media.

[0075] <Manufacture of treated pigments> (Production Example 1) 2.5 parts of sodium hydroxide and 900 parts of water were put into a flask and stirred, and then 90.9 parts of the water paste of SYN obtained in Synthesis Example 1 was added to obtain an aqueous solution of SYN. ​​When a part of the aqueous solution of SYN was spotted on a filter paper, it bleed through to the back. This confirmed that SYN had dissolved. 100 parts of PY-155 and 2,000 parts of water were put into a flask, and while stirring at 2,000 rpm using a disper, an aqueous solution of SYN was added, and the mixture was stirred for 2 hours to obtain a pigment slurry with a pH of 79. When a drop of the obtained pigment slurry was spotted on a filter paper, the pigment remained on the surface of the filter paper, and SYN bled yellow and bled through to the back. 5% hydrochloric acid was gradually added to the obtained pigment slurry to make it pH 2.8. It was slightly thickened around pH 3.0. When a drop of the pigment slurry was spotted on a filter paper, SYN that had become water-insoluble and precipitated remained on the surface of the filter paper. The pigment slurry was filtered and washed, then dried at 100°C for 24 hours, and further pulverized in a pulverizer to obtain a treated yellow pigment (treated Y-1). The non-volatile content (constant weight at 120°C) was 99.4%.

[0076] (Production Examples 2 to 5) Treated yellow pigments (Treatment Y-2 and Treatment Y-3) and treated orange pigments (Treatment O-1 and Treatment O-2) were obtained in the same manner as in Production Example 1 above, except that the formulations were as shown in Table 1. The meanings of the abbreviations in Table 1 are as follows. PY-180: CI Pigment Yellow 180 (manufactured by Dainichi Seika Color & Chemicals Co., Ltd.) PO-43: CI Pigment Orange 43 (manufactured by Dainichi Seika Chemicals Co., Ltd.)

[0077] TIFF0007637606000008.tif42170

[0078] <Synthesis of polymer dispersant> (Synthesis Example 2) One-terminated aminated polypropylene glycol polyethylene glycol monomethyl ether (M2005, trade name "Jeffamine M2005", Huntsman, m+n=35 (m=29, n=6), actual amine value 28.05mgKOH / g) 100 parts (0.05mol) was placed in a reactor and placed in a water bath at 10°C. Methacryloyloxyethyl isocyanate (MOI, trade name "Kalends MOI", Showa Denko) 7.75 parts (0.05mol) was dropped into the reactor over 30 minutes and reacted. A part of the reaction solution was sampled and subjected to IR measurement to confirm the disappearance of the isocyanate group derived from MOI and the formation of urea bonds. In addition, the amine value of the product measured using a 0.1mol / L 2-propanol hydrochloric acid solution using a potentiometric automatic titrator was 0.1mgKOH / g. This confirmed that the reaction between the amino group and the isocyanate group was almost complete. The obtained product was a macromonomer with a methacryloyl group bonded to one end of polypropylene glycol polyethylene glycol monomethyl ether (PPG / PEG). The number average molecular weight (Mn) of the macromonomer in terms of polystyrene, measured by gel permeation chromatography (GPC) using tetrahydrofuran (THF) as a developing solution, was 3,400.

[0079] Next, 86.7 parts of polyalkylene glycol monoalkyl ether (Unilube, trade name "Unilube 50MB-26", NOF Corp., average molecular weight 2,000), 3.0 parts of α-methylstyrene, 10 parts of methyl methacrylate (MMA), and 35 parts of 2-(N,N-dimethylamino)ethyl methacrylate (DMAEMA) were added, and the mixture was heated while bubbling nitrogen. When the internal temperature reached 75°C, 5.0 parts of 2,2'-azobis(isobutyric acid) dimethyl (V-601, trade name "V-601", Fujifilm Wako Pure Chemical Industries, Ltd.) were added, and the mixture was heated to 75°C and polymerized for 4 hours. 0.5 parts of V-601 were further added, and the mixture was polymerized at 75°C for 4 hours. The Mn of the product measured by sampling a portion of the reaction solution was 15,600, and the polydispersity (PDI = weight average molecular weight (Mw) / number average molecular weight (Mn)) was 1.96. The polymer concentration in the reaction solution calculated from the peak area ratio of the polymer and the solvent (Unilube) in the GPC chart was 64.3%. The amine value (polymer equivalent) of the polymer in the reaction solution was 77.4 mg KOH / g. From the above, a solution (D-1S) containing a dispersant (D-1), which is a polymer dispersant (polymer) having a main chain with an amino group and a graft chain in which a polypropylene glycol polyethylene glycol monomethyl ether chain is grafted to this main chain, was obtained.

[0080] (Synthesis Example 3) In the same manner as in Synthesis Example 2, a Unilube solution of a polymer having a main chain with an amino group and a graft chain in which a polypropylene glycol polyethylene glycol monomethyl ether chain was grafted to the main chain was obtained. After the obtained solution was cooled to room temperature, a mixture of 14.1 parts of benzyl chloride and 14.1 parts of Unilube was dropped over 1 hour. The mixture was heated to 80°C and reacted for 5 hours to convert the amino group into a quaternary ammonium salt. A part of the reaction solution was sampled, and the Mn of the polymer measured by GPC using 0.1 mol / L lithium chloride-dimethylformamide (Li-DMF) solvent as the developing solvent was 18,600, and the PDI was 2.36. The content of the polymer in the reaction solution was 63.0%, and the amine value of the polymer (polymer equivalent) was 35.1 mgKOH / g. As a result of the above, a solution (D-2S) was obtained containing a dispersant (D-2), which is a polymer dispersant (polymer) having a main chain having an amino group and a quaternary ammonium base and a graft chain in which a polypropylene glycol polyethylene glycol monomethyl ether chain is grafted to this main chain.

[0081] (Synthesis Example 4) 341 parts of diethylene glycol monobutyl ether (BDG), 3.0 parts of iodine, 9 parts of 2,2'-azobis(2,4-dimethylvaleronitrile) (V-65, trade name "V-65", Fujifilm Wako Pure Chemical Industries, Ltd.), 52 parts of MMA, 52.6 parts of butyl methacrylate, 52 parts of 2-ethylhexyl methacrylate, 94.2 parts of tetrahydrofurfuryl methacrylate, and 0.1 parts of N-iodosuccinimide were put into a reactor, stirred, and polymerized at 62 ° C for 4 hours while flowing nitrogen. A part of the reaction solution was sampled and measured for the polymer's Mn, which was 9,500, and the PDI was 1.21. The non-volatile content that reached a constant weight in a 150 ° C dryer was 42.9%, confirming that the polymerization was almost 100%.

[0082] 108.3 parts of DMAEMA and 3 parts of V-65 were added, and polymerization was carried out at 62°C for 5 hours. After cooling to room temperature, a mixture of 21.8 parts of benzyl chloride and 157.7 parts of BDG was added dropwise over 1 hour, and the mixture was reacted at 80°C for 5 hours to obtain a polymerization solution containing a polymer. The polymerization rate and reaction rate calculated from the non-volatile content were both about 100%, and the non-volatile content was 43.2%. The Mn of the obtained polymer was 14,600, the PDI was 1.36, and the amine value (polymer equivalent) was 75.6 mgKOH / g. The obtained polymer was an AB block copolymer having a polymer block A that is compatible with the solvent and a polymer block B having an amino group and a quaternary ammonium base.

[0083] 1,178 parts of ion-exchanged water was placed in a flask and stirred at 2,000 rpm using a disperser. When 149.6 parts of the polymerization solution were added, the polymer dissolved in the water, and a slightly blue translucent polymer aqueous solution was obtained. When a mixture of 6.7 parts of bis(trifluoromethanesulfonyl)imide lithium (TFSI lithium salt) and 20 parts of water was gradually added dropwise, a polymer precipitated. It is believed that the chloride ions of the quaternary ammonium base and the TFSI ions exchanged ions, and the polymer became insoluble in water and precipitated. After filtering the polymerization solution, it was thoroughly washed with ion-exchanged water and dried in a dryer at 100°C to obtain dispersant (D-3), which is a solid polymer dispersant (polymer). The Mn of the obtained polymer was 17,600, the PDI was 1.44, the non-volatile content was 99.8%, and the amine value was 68.7 mgKOH / g. The obtained polymer was an AB block copolymer having a polymer block A that was soluble in the solvent and a polymer block B that had an amino group and a quaternary ammonium base. The quaternary ammonium salt group of this polymer block B has chloride ions and TFSI ions as counter ions.

[0084] <Production of pigment dispersion> Example 1 20 parts of treatment Y-1, 6.2 parts of D-1S (4 parts of dispersant), 73.8 parts of phenoxyethyl acrylate (PEA), and 0.25 parts of p-methoxyphenol (HP) were placed in a resin container and thoroughly stirred using a disperser to obtain a pigment slurry. 300 parts of zirconia beads with a diameter of 0.5 mm were added, the container was sealed, and a dispersion was performed using a Scandex for 60 minutes to obtain a dispersion. After filtering through a 0.5 μm filter to remove coarse particles, PEA was added to adjust the concentration, and yellow pigment dispersion-1 (pigment content 15%) was obtained. The viscosity (initial viscosity) of yellow pigment dispersion-1 measured using an E-type viscometer at 60 rpm and 25 °C was 29.3 mPa s. In addition, the number average particle size (initial number average particle size) of pigment particles measured using a dynamic light scattering particle size distribution measuring device was 111.0 nm. A storage test was conducted in which Yellow Pigment Dispersion-1 was left to stand for one week at 60°C. After the storage test, the viscosity of Yellow Pigment Dispersion-1 (viscosity after storage) was 28.4 mPa s, and the number average particle diameter of the pigment particles (number average particle diameter after storage) was 110 nm.

[0085] Comparative Example 1 18.2 parts of PY-155, 1.8 parts of a pigment derivative (trade name "Solsperse 22000", manufactured by Lubrizol, pigment-similar structure), 6.2 parts of D-1S (4 parts of dispersant), 73.8 parts of PEA, and 0.25 parts of HP were placed in a resin container. The pigment derivative used does not have a structure represented by general formula (1). Thereafter, a yellow pigment dispersion was obtained in the same manner as in Example 1 described above. The initial viscosity of the obtained pigment dispersion was 69.3 mPa·s, and the initial number average particle diameter of the pigment particles was 201 nm. In addition, the pigment dispersion had no fluidity after the storage test and did not maintain a dispersed state.

[0086] Example 2 Into a resin container, 18.2 parts of PY-155, 1.8 parts of the powder of the pigment derivative (SYN) obtained in Synthesis Example 1, 6.2 parts of D-1S (4 parts of dispersant), 73.8 parts of PEA, and 0.25 part of HP were placed. Thereafter, in the same manner as in Example 1 described above, a yellow pigment dispersion was obtained. The initial viscosity of the obtained pigment dispersion was 36.4 mPa·s, and the initial number average particle diameter of the pigment particles was 156 nm. Further, red coarse particles were confirmed in the residue of the filter. The viscosity of the pigment dispersion after storage was 49.3 mPa·s, and the number average particle diameter of the pigment particles after storage was 186 nm. Although the viscosity and the particle diameter of the pigment particles increased upon storage, the fluidity as a pigment dispersion was maintained to some extent.

[0087] (Examples 3 to 15) Except that the compounding formulations shown in Tables 2 to 4 were used, each pigment dispersion was obtained in the same manner as in Example 1 described above. The meanings of the abbreviations in Table 4 are shown below. ·BzA: Benzyl acrylate ·IBXA: Isobornyl acrylate ·ACMO: Acryloyl morpholine ·VEEA: Vinyl oxyethoxyethyl acrylate

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[0089] TIFF0007637606000010.tif116170

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[0091] <Manufacture of <UVIJ Ink> (Example 16) 18 parts of the yellow pigment dispersion-1 obtained in Example 1, 53.5 parts of PEA, 19 parts of VEEA, 5 parts of photopolymerization initiator 1 (trade name "Lucirin TPO", manufactured by BASF), and 4.5 parts of photopolymerization initiator 2 (trade name "Irgacure 819", manufactured by BASF) were mixed and thoroughly stirred, and then filtered through a 5 μm filter to obtain a UVIJ ink. The number average particle diameter of the pigment particles in the obtained UVIJ ink was 108 nm, and the viscosity of the UVIJ ink was 4.9 mPa s. In addition, the number average particle diameter of the pigment particles in the UVIJ ink after the storage test was 107.1 nm, and the viscosity of the UVIJ ink after storage was 4.8 mPa s.

[0092] The obtained UVIJ ink was filled into an ink cartridge and loaded into an inkjet printer (product name "EB100", manufactured by Konica Minolta). Using this inkjet printer, a solid image was recorded continuously for one hour on a polyethylene terephthalate (PET) film. As a result, the image was recorded smoothly without clogging of the recording head. Furthermore, the recorded image had no streaks or wrinkles, and the ink discharge stability was good.

[0093] The image recorded using a UV lamp was irradiated with ultraviolet light, hardening the image to obtain a print sample. The print sample obtained was cut into a checkerboard pattern using a cutter, and then cellophane tape was applied and then quickly peeled off to perform an adhesion (fixation) test. As a result, the hardened image did not peel off at all, and was in good adhesion to the film. Furthermore, instead of the PET film, images were recorded using polyvinyl chloride film and surface-treated polypropylene film, and a similar adhesion (fixation) test was performed. As a result, the images recorded on both films did not peel off, and were in good adhesion to the film.

[0094] Furthermore, when UVIJ inks were similarly prepared using the pigment dispersions obtained in Examples 3 to 15, each UVIJ ink had good fine dispersion properties, storage stability, and ejection stability. [Industrial Applicability]

[0095] The pigment dispersions of the present invention are particularly useful as raw materials for preparing UVIJ inks for printing on substrates such as transparent plastic films.

Claims

1. A pigment dispersion liquid for use in an ultraviolet-curable inkjet ink, the pigment dispersion liquid containing a pigment including at least one of a yellow pigment and an orange pigment, a pigment derivative, a polymer dispersant having an amino group, and an ultraviolet-curable monomer, The pigment derivative has a structure represented by the following general formula (1): The pigment dispersion liquid is a polymer having an amine value of 0.5 to 100 mgKOH / g and a number average molecular weight of 5,000 to 20,000, the polymer comprising 3 to 50 mass% of structural units (1) derived from at least one member selected from the group consisting of dimethylaminoethyl methacrylate, diethylaminoethyl methacrylate, 2-vinylpyridine, 4-vinylpyridine, and vinylimidazole, some amino groups of which may be converted to quaternary ammonium salts, 40 to 90 mass% of structural units (2) derived from a macromonomer represented by the following general formula (2), and 0.5 to 20 mass% of structural units (3) derived from other monomers: (In the general formula (1), X is OH or OCH ３ and two or more of the four X's are OH. (In the general formula (2), R 1 represents a hydrogen atom or a methyl group, A represents O or NH, Q represents an ethylene group or a methylethylene group, Y represents O, NHCOO, or NHCONH, m and n each independently represent an average number of repeating units of 0 or more, and m+n=20 to 100, and R 2 represents a hydrogen atom, an alkyl group having 1 to 18 carbon atoms, an aryl group, or an alkylaryl group.)

2. 2. The pigment dispersion according to claim 1, wherein the content of the pigment derivative is 3 to 20 parts by mass based on 100 parts by mass of the pigment.

3. The yellow pigment is at least one selected from the group consisting of C.I. Pigment Yellow 74, 128, 138, 139, 150, 155, 180, and 185; 3. The pigment dispersion according to claim 1, wherein the orange pigment is at least one selected from the group consisting of C.I. Pigment Orange 16, 34, 43, and 64.

4. A method for producing the pigment dispersion liquid according to any one of claims 1 to 3, comprising the steps of: A method for producing a pigment dispersion liquid, comprising the steps of: mixing the pigment with an aqueous solution of an alkali neutralization product of the pigment derivative; and then adding an acid to precipitate the pigment derivative, thereby obtaining a pigment-derivative-treated pigment.

5. 4. An ultraviolet-curable ink-jet ink comprising the pigment dispersion liquid according to claim 1.

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