JP2007138093A - Inkjet ink - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide inkjet ink excellent in storage stability and ejection stability and capable of giving a printed matter excellent in gloss and color density. <P>SOLUTION: The inkjet ink is inkjet ink containing a pigment, a polymeric dispersant, and water, wherein a polymer compound composed of a hydrophilic skeleton and a plurality of side chains attached thereto and being capable of being crosslinked among the side chains when irradiated with an actinic radiation is contained, and that portion of the polymer dispersant which remains not adsorbed on the pigment and free accounts for 1.0 mass% or smaller of the entire ink. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an inkjet ink.

  The ink jet recording method is capable of recording a high-definition image with a relatively simple device, and has been rapidly developed in various fields. In addition, there are various uses, and a recording medium or ink suitable for each purpose is used.

  In particular, in recent years, the recording speed has been greatly improved, and printers having performance capable of withstanding light printing applications have been developed.

  However, in order to draw out the performance of the ink jet printer, an ink jet dedicated paper having ink absorbability is required.

  When recording on coated paper or art paper that does not absorb much ink, or on plastic film that does not absorb ink at all, there is a problem such as so-called bleeding in which different color ink liquids mix on the recording medium and cause color turbidity. In addition, there has been a problem in providing a variety of recording media to the inkjet.

  In the above problems, a hot-melt ink composition made of a wax that is solid at room temperature is used, liquefied by heating, etc., sprayed with some energy applied, cooled and solidified while adhering to the recording medium, and recorded A hot-melt ink jet recording method for forming dots has been proposed. However, an image recorded by such a method has problems such as deterioration in quality and lack of scratching performance due to the rising of the dots because the ink dots are in the form of soft wax.

  On the other hand, an inkjet recording ink that is cured by exposure to ultraviolet rays is disclosed (for example, see Patent Document 1). In addition, a so-called non-aqueous ink containing a pigment as an essential component and a triacrylate or higher polyacrylate as a polymerizable material and using a ketone and an alcohol as a main solvent has been proposed (for example, Patent Document 2). reference.). Further, an ink using a water-based ultraviolet polymerization monomer has been proposed (for example, see Patent Document 3).

  In these methods, since the ink itself is cured with a curing component, recording is possible even on a non-absorbing medium. However, since the curing component other than the colorant is contained in a large amount and does not volatilize, the recording surface is reduced. The ink dots swelled up, causing unnaturalness in image quality, especially gloss. Furthermore, there is a safety concern for the conventionally known curable components, and there is a problem that even if the safety is cleared, there is a narrow selection of substances, and the material and physical properties cannot be designed freely. .

In actinic ray curable inkjet ink containing a photopolymerizable compound, a pigment, and a dispersant, a technique for improving the ink storage stability and the emission stability by setting the released polymer dispersant to 1% by mass or less is disclosed. (For example, see Patent Document 4) This technique is only for solvent-based inks, and does not describe any ink containing water.
U.S. Pat. No. 4,228,438 Japanese Patent Publication No. 5-64667 JP-A-7-224241 JP 2005-263898 A

  An object of the present invention is to supply an inkjet ink that is excellent in storage stability and emission stability of an ink, and that can provide a printed matter with excellent gloss and high density.

  The above object of the present invention is achieved by the following configurations.

  1. In an inkjet ink containing a pigment, a polymer dispersant, and water, a polymer compound having a plurality of side chains in a hydrophilic main chain and capable of crosslinking between side chains by irradiation with active energy rays An ink-jet ink characterized in that the free polymer dispersant contained therein and not adsorbed on the pigment is 1.0% by mass or less of the total ink.

  2. 2. The ink-jet ink as described in 1 above, wherein a mass ratio of the pigment to the liberated polymer dispersant is 4: 1 to 200: 1.

  3. 3. The inkjet ink as described in 1 or 2 above, wherein the polymer dispersant has a weight average molecular weight of 5,000 to 50,000.

  4). 4. The inkjet ink according to any one of 1 to 3, wherein the polymer dispersant has an acid value of 20 to 250.

  5. The inkjet ink according to any one of 1 to 4, wherein the polymer compound is contained in an amount of 0.8 to 5.0% by mass based on the total mass of the ink.

  6). The hydrophilic main chain is a saponified product of polyvinyl acetate, has a saponification degree of 77 to 99%, and a polymerization degree of 200 to 4000. Ink for inkjet.

  7). 7. The inkjet ink according to any one of 1 to 6, wherein a modification rate of the side chain with respect to the hydrophilic main chain is 0.8 mol% or more and 4 mol% or less.

  According to the present invention, it is possible to supply an ink jet ink that is excellent in storage stability and emission stability of an ink, and that can provide a printed matter with excellent gloss and high density.

  When highly polar water is present as in the ink jet ink of the present invention, it is important to sufficiently disperse the pigment by sufficiently wetting the pigment to improve the dispersion stability. Excess free polymer dispersant not adsorbed on the pigment deteriorates the emission stability, and the fixing property to plain paper becomes insufficient, making it difficult to obtain a high-quality printed matter with high concentration. Conceivable.

  This is presumably because the liberated polymer dispersant causes deterioration in ink repellency around the nozzle outlet of the recording head, which lowers the emission stability. In addition, when such ink is printed on a recording medium such as plain paper, it is estimated that the fixability to cellulose fibers is deteriorated, and as a result, it is difficult to obtain a high density.

  In addition, as a method for quantifying the released polymer dispersant, for example, using a centrifugal separator, the pigment component and the polymer dispersant adsorbed on the pigment are precipitated, and the supernatant liquid (which can be cross-linked with the released polymer dispersant is cross-linked). A polymer compound is taken out), an acid is added to the supernatant, and only the released polymer dispersant is settled and evaporated to dryness to measure the mass.

  Various methods are conceivable as means for adjusting the amount of the released polymer dispersant. For example, the type of pigment, the surface treatment method of the pigment, the composition of the polymer dispersant, the molecular weight, the acid value, the ratio of the pigment to the polymer dispersant, the dispersion conditions, and the like are also related. Among these, it is important to select the composition, weight average molecular weight, and acid value of the polymer dispersant.

(Active energy ray crosslinkable polymer compound)
The polymer compound having a plurality of side chains in the hydrophilic main chain according to the present invention and capable of crosslinking between the side chains by irradiating with active energy rays is a saponified product of polyvinyl acetate, polyvinyl acetal, polyethylene Oxide, polyalkylene oxide, polyvinylpyrrolidone, polyacrylamide, polyacrylic acid, hydroxyethyl cellulose, methyl cellulose, hydroxypropyl cellulose, or a derivative of the hydrophilic resin, and at least one hydrophilic selected from the group consisting of these copolymers In the resin, a modified group such as a photodimerization type, a photodecomposition type, a photopolymerization type, a photomodification type, or a photodepolymerization type is introduced into the side chain. Photopolymerizable crosslinkable groups are desirable from the viewpoints of sensitivity and performance of the generated image.

  In the hydrophilic main chain, a saponified product of polyvinyl acetate is preferable from the viewpoint of ease of introduction of side chains and handling, and the degree of saponification is preferably 77% or more and 99% or less, and the degree of polymerization is 200. It is preferably 4000 or less and more preferably 200 or more and 2000 or less from the viewpoint of handling. The modification rate of the side chain with respect to the main chain is preferably 0.3 mol% or more and 4 mol% or less, and more preferably 0.8 mol% or more and 4 mol% or less from the viewpoint of reactivity. If it is less than 0.3 mol%, the crosslinkability is insufficient and the effect of the present invention is reduced. If it is more than 4 mol%, the crosslink density is increased and the film is hard and brittle, and the strength of the film is lowered.

  As the photodimerization-type modifying group, those in which a diazo group, a cinnamoyl group, a stilbazonium group, a stilquinolium group or the like is introduced are preferable. For example, a photosensitive resin described in JP-A-60-129742 (Composition).

  The photosensitive resin described in JP-A-60-129742 is a compound represented by the following general formula (1) in which a stilbazonium group is introduced into a polyvinyl alcohol structure.

In the formula, R ₁ represents an alkyl group having 1 to 4 carbon atoms, and A ⁻ represents a counter anion.

  The photosensitive resin described in JP-A No. 56-67309 contains a 2-azido-5-nitrophenylcarbonyloxyethylene structure represented by the following general formula (2) or the following general formula ( It is a resin composition represented by 3) and having a 4-azido-3-nitrophenylcarbonyloxyethylene structure.

  Further, a modifying group represented by the following general formula (4) is also preferably used.

  In the formula, R represents an alkylene group or an aromatic ring. A benzene ring is preferred.

  As the photopolymerization type modifying group, for example, a resin represented by the following general formula (5) shown in JP-A Nos. 2000-181062 and 2004-189841 is preferable from the viewpoint of reactivity.

In the formula, R ₂ represents a methyl group or a hydrogen atom, n represents 1 or 2, X represents — (CH ₂ ) _m —COO— or —O—, and Y represents an aromatic ring or a single bond. And m represents an integer from 0 to 6.

  Moreover, it is also preferable to use the photopolymerization type | mold modified group represented by following General formula (6) described in Unexamined-Japanese-Patent No. 2004-161942 for a conventionally well-known water-soluble resin.

In the formula, R ₃ represents a methyl group or a hydrogen atom, and R ₄ represents a linear or branched alkylene group having 2 to 10 carbon atoms.

  Such an active energy ray crosslinkable polymer compound is preferably contained in an amount of 0.8% by mass to 5.0% by mass with respect to the total mass of the ink. The presence of 0.8% by mass or more improves cross-linking efficiency, and beading and color bleed are more preferable due to a rapid increase in ink viscosity after cross-linking. In the case of 5.0% by mass or less, it is difficult to adversely affect the physical properties of the ink and the state in the ink head, which is preferable from the viewpoint of the light emission property and the ink storage property. Further, crosstalk in the recording method is less likely to occur. Further, since printing and swell are reduced, it is preferable in terms of gloss.

  In such an active energy ray crosslinkable polymer compound, the main chain originally having a certain degree of polymerization is crosslinked via a crosslink between side chains, and thus polymerized via a general chain reaction. The effect of increasing the molecular weight per photon is significantly greater than the active energy ray curable resin. On the other hand, in the conventionally known active energy ray curable resins, the number of crosslinking points cannot be controlled, so the physical properties of the cured film cannot be controlled, and the film tends to be hard and brittle.

  In such an active energy ray crosslinkable polymer compound, the number of crosslinking points can be completely controlled by the length of the hydrophilic main chain and the amount of side chains introduced, and the physical properties of the ink film can be controlled according to the purpose.

  In addition, conventionally known active energy ray-curable inks (radical polymerizable compounds and cationic polymerization compounds) are almost all components other than the colorant, so that the dots after curing rise and the image quality typified by gloss is inferior. On the other hand, the active energy ray crosslinkable polymer compound used in the present invention requires a small amount, and since there are many dry components, the image quality after drying can be improved and the fixing property is also good. In addition, since the conventionally known active energy ray-curable ink is also a solvent-based ink, there are problems such as difficulty in feathering and density with respect to plain paper, but the inkjet ink of the present invention is a water-based ink. Therefore, such a fault is also eliminated.

(Photopolymerization initiator, photosensitizer)
In the present invention, it is also preferable to add a photopolymerization initiator or a photosensitizer. These compounds may be dissolved or dispersed in a solvent, or may be chemically bonded to the photosensitive resin.

  There is no restriction | limiting in particular about the photoinitiator and photosensitizer which are applied, A conventionally well-known thing can be used. Although there is no restriction | limiting in particular about the photoinitiator and photosensitizer which are applied, A water-soluble thing is preferable from a viewpoint of mixing property and reaction efficiency. In particular, 4- (2-hydroxyethoxy) phenyl- (2-hydroxy-2-propyl) ketone (HMPK), thioxanthone ammonium salt (QTX), and benzophenone ammonium salt (ABQ) are preferable from the viewpoint of miscibility with an aqueous solvent.

  Furthermore, 4- (2-hydroxyethoxy) phenyl- (2-hydroxy-2-propyl) ketone (n = 1, HMPK) represented by the following general formula (7) from the viewpoint of compatibility with the resin, An ethylene oxide adduct (n = 2 to 5) is more preferable.

  In the formula, n represents an integer of 1 to 5.

  In addition, benzophenones such as benzophenone, hydroxybenzophenone, bis-N, N-dimethylaminobenzophenone, bis-N, N-diethylaminobenzophenone, 4-methoxy-4'-dimethylaminobenzophenone. Thioxanthones such as thioxatone, 2,4-diethylthioxanthone, isopropylthioxanthone, chlorothioxanthone, and isopropoxychlorothioxanthone. Anthraquinones such as ethyl anthraquinone, benzanthraquinone, aminoanthraquinone and chloroanthraquinone. Acetophenones. Benzoin ethers such as benzoin methyl ether. 2,4,6-trihalomethyltriazines, 1-hydroxycyclohexyl phenyl ketone, 2- (o-chlorophenyl) -4,5-diphenylimidazole dimer, 2- (o-chlorophenyl) -4,5-di ( m-methoxyphenyl) imidazole dimer, 2- (o-fluorophenyl) -4,5-phenylimidazole dimer, 2- (o-methoxyphenyl) -4,5-phenylimidazole dimer, 2- (P-methoxyphenyl) -4,5-diphenylimidazole dimer, 2,4-di (p-methoxyphenyl) -5-phenylimidazole dimer, 2- (2,4-dimethoxyphenyl) -4, 2,4,5-triarylimidazole dimer of 5-diphenylimidazole dimer, benzyldimethyl ketal, 2-benzyl-2-dimethyl Ruamino-1- (4-morpholinophenyl) butan-1-one, 2-methyl-1- [4- (methylthio) phenyl] -2-morpholino-1-propanone, 2-hydroxy-2-methyl-1-phenyl -Propan-1-one, 1- [4- (2-hydroxyethoxy) -phenyl] -2-hydroxy-2-methyl-1-propan-1-one, phenanthrenequinone, 9,10-phenanthrenequinone, Benzoins such as methylbenzoin and ethylbenzoin, 9-phenylacridine, acridine derivatives such as 1,7-bis (9,9'-acridinyl) heptane, bisacylphosphine oxide, and mixtures thereof are preferably used. May be used alone or in combination.

  In addition to these photopolymerization initiators, accelerators and the like can also be added. Examples of these include ethyl p-dimethylaminobenzoate, isoamyl p-dimethylaminobenzoate, ethanolamine, diethanolamine, triethanolamine and the like.

  Even if these photoinitiators are grafted to the side chain with respect to the hydrophilic main chain.

(Active energy rays, irradiation method)
Examples of active energy rays in the present invention include electron beams, ultraviolet rays, α rays, β rays, γ rays, and X-rays. However, there are dangers to the human body, and handling is easy and industrial use. Electron beams and ultraviolet rays are widely used.

  When using an electron beam, the amount of the electron beam to be irradiated is preferably in the range of 0.1 to 30 Mrad. If it is less than 0.1 Mrad, a sufficient irradiation effect cannot be obtained, and if it exceeds 30 Mrad, the support may be deteriorated, which is not preferable.

  When ultraviolet rays are used, the light source is, for example, a low pressure, medium pressure, high pressure mercury lamp, metal halide lamp, xenon lamp having a light emission wavelength in the ultraviolet region, cold cathode tube, hot cathode having an operating pressure of 0.1 kPa to 1 MPa. Conventionally known materials such as tubes and LEDs are used.

(Light irradiation conditions after ink landing)
As the irradiation condition of actinic rays, actinic rays are preferably irradiated between 0.001 and 1.0 seconds after ink landing, and more preferably 0.001 to 0.5 seconds. In order to form a high-definition image, it is particularly important that the irradiation timing is as early as possible.

(Installation of lamp)
As a method for irradiating actinic rays, the basic method is disclosed in JP-A-60-132767. According to this, a light source is provided on both sides of the head unit, and the head and the light source are scanned by the shuttle method. Irradiation is performed after a certain period of time after ink landing. Further, the curing is completed by another light source that is not driven. In US Pat. No. 6,145,979, as an irradiation method, a method using an optical fiber or a method of irradiating a recording unit with UV light by applying a collimated light source to a mirror surface provided on the side of the head unit is disclosed. ing. Any of these irradiation methods can be used in the image forming method according to the present invention.

  In another preferred embodiment, irradiation with actinic rays is divided into two stages, and actinic rays are first irradiated by the above-described method between 0.001 and 2.0 seconds after ink landing, and further irradiated with actinic rays. It is. By dividing the irradiation of actinic rays into two stages, it is possible to further suppress the shrinkage of the recording material that occurs during ink curing.

(Pigment)
As the pigment that can be used in the present invention, conventionally known organic and inorganic pigments can be used. Examples of the anionic pigment include azo pigments such as azo lakes, insoluble azo pigments, condensed azo pigments, chelate azo pigments, phthalocyanine pigments, and perylenes. Perylene pigments, anthraquinone pigments, quinacridone pigments, dioxazine pigments, thioindigo pigments, isoindolinone pigments, quinophthaloni pigments, dye lakes such as acid dye lakes, nitro pigments, nitroso pigments, aniline black Organic pigments such as daylight fluorescent pigments, and inorganic pigments such as carbon black.

  Specific organic pigments are exemplified below.

  Examples of pigments for magenta or red include C.I. I. Pigment red 2, C.I. I. Pigment red 3, C.I. I. Pigment red 5, C.I. I. Pigment red 6, C.I. I. Pigment red 7, C.I. I. Pigment red 15, C.I. I. Pigment red 16, C.I. I. Pigment red 48: 1, C.I. I. Pigment red 53: 1, C.I. I. Pigment red 57: 1, C.I. I. Pigment red 122, C.I. I. Pigment red 123, C.I. I. Pigment red 139, C.I. I. Pigment red 144, C.I. I. Pigment red 149, C.I. I. Pigment red 166, C.I. I. Pigment red 177, C.I. I. Pigment red 178, C.I. I. And CI Pigment Red 222.

  Examples of the orange or yellow pigment include C.I. I. Pigment orange 31, C.I. I. Pigment orange 43, C.I. I. Pigment yellow 12, C.I. I. Pigment yellow 13, C.I. I. Pigment yellow 14, C.I. I. Pigment yellow 15, C.I. I. Pigment yellow 17, C.I. I. Pigment yellow 74, C.I. I. Pigment yellow 93, C.I. I. Pigment yellow 94, C.I. I. Pigment yellow 128, C.I. I. And CI Pigment Yellow 138.

  Examples of pigments for green or cyan include C.I. I. Pigment blue 15, C.I. I. Pigment blue 15: 2, C.I. I. Pigment blue 15: 3, C.I. I. Pigment blue 16, C.I. I. Pigment blue 60, C.I. I. And CI Pigment Green 7.

  As a method for dispersing the pigment, for example, various dispersing machines such as a ball mill, a sand mill, an attritor, a roll mill, an agitator, a Henschel mixer, a colloid mill, an ultrasonic homogenizer, a pearl mill, a wet jet mill, and a paint shaker can be used. It is also preferable to use a centrifugal separator or a filter for the purpose of removing the coarse particles of the pigment dispersion.

  Examples of the polymer dispersant according to the present invention include styrene, styrene derivatives, vinyl naphthalene derivatives, acrylic acid, acrylic acid derivatives, methacrylic acid, methacrylic acid derivatives, maleic acid, maleic acid derivatives, itaconic acid, itaconic acid derivatives, Examples thereof include a polymer composed of a single monomer selected from fumaric acid and fumaric acid derivatives, a copolymer composed of two or more monomers, and salts thereof. Water-soluble polymers such as polyvinyl alcohol, polyvinyl pyrrolidone, cellulose derivatives, gelatin, and polyethylene glycol can also be used. Preferred polymer dispersants include styrene, styrene derivatives, vinyl naphthalene derivatives, acrylic acid, acrylic acid derivatives, methacrylic acid, methacrylic acid derivatives, maleic acid, and a single monomer selected from maleic acid derivatives. Copolymers or copolymers composed of two or more monomers and their salts are water-soluble.

  The content of these polymer dispersants with respect to the total amount of ink is preferably 0.1 to 10% by mass, and more preferably 0.3 to 5% by mass. Two or more types can be used in combination.

  The mass ratio between the pigment in the ink and the liberated polymer dispersant is more preferably in the range of 4: 1 to 200: 1 from the viewpoint of gloss of the printed matter. Although the details are not clear, it is speculated that the presence of an appropriate amount of the free polymer dispersant may cause the pigments to bind well and contribute to the improvement of gloss.

  The weight average molecular weight of the polymer dispersant according to the present invention is preferably in the range of 5000 to 50000 in terms of the dispersion stability of the ink. Similarly, the acid value of the polymer dispersant is in the range of 25 to 250 for the ink dispersion stability. Preferred for sex.

(Water-soluble solvent)
A water-soluble solvent is preferably used as the solvent according to the present invention, and a mixed solvent such as water and a water-soluble organic solvent is more preferably used as the water-soluble solvent. The content of water with respect to the total amount of ink is preferably 20 to 70% by mass. Examples of the water-soluble organic solvent preferably used include alcohols (for example, methanol, ethanol, propanol, isopropanol, butanol, isobutanol, secondary butanol, tertiary butanol), polyhydric alcohols (for example, ethylene glycol, diethylene glycol). , Triethylene glycol, polyethylene glycol, propylene glycol, dipropylene glycol, polypropylene glycol, butylene glycol, hexanediol, pentanediol, glycerin, hexanetriol, thiodiglycol), polyhydric alcohol ethers (for example, ethylene glycol monomethyl ether, Ethylene glycol monoethyl ether, ethylene glycol monobutyl ether, diethylene glycol Monomethyl ether, diethylene glycol monoethyl ether, diethylene glycol monobutyl ether, propylene glycol monomethyl ether, propylene glycol monobutyl ether, ethylene glycol monomethyl ether acetate, triethylene glycol monomethyl ether, triethylene glycol monoethyl ether, triethylene glycol monobutyl ether, ethylene glycol Monophenyl ether, propylene glycol monophenyl ether), amines (eg, ethanolamine, diethanolamine, triethanolamine, N-methyldiethanolamine, N-ethyldiethanolamine, morpholine, N-ethylmorpholine, ethylenediamine, diethylenediamine, triethylenete) Lamin, tetraethylenepentamine, polyethyleneimine, pentamethyldiethylenetriamine, tetramethylpropylenediamine), amides (eg, formamide, N, N-dimethylformamide, N, N-dimethylacetamide, etc.), heterocycles (eg, 2 -Pyrrolidone, N-methyl-2-pyrrolidone, cyclohexyl pyrrolidone, 2-oxazolidone, 1,3-dimethyl-2-imidazolidinone), sulfoxides (for example, dimethyl sulfoxide) and the like.

(Surfactant)
Surfactants preferably used in the inkjet ink of the present invention include alkyl sulfates, alkyl ester sulfates, dialkyl sulfosuccinates, alkyl naphthalene sulfonates, alkyl phosphates, and polyoxyalkylene alkyl ether phosphates. , Anionic surfactants such as fatty acid salts, nonionic surfactants such as polyoxyethylene alkyl ethers, polyoxyalkylene alkyl phenyl ethers, acetylene glycols, polyoxyethylene-polyoxypropylene block copolymers, glycerin esters , Surfactants such as sorbitan esters, polyoxyethylene fatty acid amides and amine oxides, and cationic surfactants such as alkylamine salts and quaternary ammonium salts.

(Various additives)
In the present invention, other conventionally known additives can be contained. For example, fluorescent brighteners, antifoaming agents, lubricants, preservatives, thickeners, antistatic agents, matting agents, water-soluble polyvalent metal salts, acid bases, pH adjusters such as buffers, antioxidants, surfaces These are tension modifiers, non-resistance modifiers, rust inhibitors, inorganic pigments, and the like.

(Recording sheet)
The paper includes coated paper and non-coated paper. As the coated paper, art paper having a coating amount per m ^{2 of} about 20 g on one side, coated paper having a coating amount per m ^{2 of} about 10 g on one side, Examples include a light-weight coated paper having a coating amount per 1 m ^{2 of} about 5 g on one side, a finely coated paper, a mat-like finished mat-coated paper, a dull-like finished dull-coated paper, and newsprint paper. Non-coated paper includes printing paper A using 100% chemical pulp, printing paper B using 70% or more chemical pulp, printing paper C using 40% or more and less than 70% chemical pulp, and printing using less than 40% chemical pulp. Examples thereof include paper D, gravure paper containing mechanical pulp and subjected to calendar treatment. Further details are described in detail in the “Latest Paper Processing Handbook” edited by the Paper Processing Handbook Editorial Committee, published by Tech Times, “Printing Engineering Handbook” edited by the Japan Printing Society.

  As the plain paper, uncoated paper, special printing paper, and 80 to 200 μm uncoated paper belonging to a part of information paper are used. The plain paper used in the present invention includes, for example, high-grade printing paper, intermediate-grade printing paper, low-grade printing paper, thin-like printing paper, fine-coating printing paper, special printing paper such as fine-quality printing paper, foam paper, PPC paper, and others There are information sheets and the like. Specifically, there are the following sheets and various modified / processed sheets using these sheets, but the present invention is not particularly limited thereto.

  High quality paper and colored high quality paper, recycled paper, copy paper / colored paper, OCR paper, carbonless paper / colored paper, synthetic paper such as YUPO 60, 80, 110 microns, YUPO COAT 70, 90 microns, etc. Coated paper 90kg, Foam mat paper 70, 90, 110kg, Foamed PET 38 microns, Mitsuori-kun (above, Kobayashi recording paper), OK fine paper, New OK fine paper, Sunflower, Phoenix, OK Royal White, Export fine paper ( NPP, NCP, NWP, Royal White) OK Book Paper, OK Cream Book Paper, Cream Premium Paper, OK Map Paper, OK Ishikari, Cucumber, OK Foam, OKH, NIP-N (above, Shin Oji Paper), Gold Wang, Toko, export quality paper, special demand quality paper, book paper, book paper L, light cream book paper, elementary textbook Paper, continuous slip paper, high quality NIP paper, silver ring, gold yang, gold yang (W), bridge, capital, silver ring book, harp, harp cream, SK color, securities paper, opera cream, opera, KYP medical record, silvia HN, Excellent Foam, NPI Foam DX (Nippon Paper), Pearl, Kinryo, Uscream fine paper, Special Book Paper, Super Book Paper, Book Paper, Diamond Foam, Inkjet Foam (Mitsubishi Paper), Carpet V, carpet SW, white elephant, luxury publication paper, cream carpet, cream white elephant, securities / voucher paper, book paper, map paper, copy paper, HNF (above, Hokuetsu), phone book cover, Book paper, cream shirairai, cream shirairaifu, cream shirairaifu, DSK (above, Daishowa Paper), Sendai MP fine paper, Jiang, Thunderbird quality, hanging paper, colored paper base, dictionary paper, cream book, white book, cream quality paper, map paper, continuous slip paper (above, Chuetsu Pulp), OP gold cherry (Chuetsu), gold sand, reference book paper, Replacement certificate paper (white), form printing paper, KRF, white foam, color foam, (K) NIP, fine PPC, Kishu inkjet paper (above, made by Kishu Paper), Taiou, Bright Foam, Kant, Kant White, Dante , CM paper, Dante comic, Heine, paperback book paper, Heine S, New AD paper, Utrilo Excel, Excel Super A, Kant Excel, Excel Super B, Dante Excel, Heine Excel, Excel Super C, Excel Super D, AD Excel, Excel Super E, New Bright Foam, New Bright NI P (above, made by Daio Paper), Sun Ring, Moon Ring, Cloud Pass, Galaxy, Baiyun, Wyeth, Moon Ring Ace, Baiyun Ace, Cloud Pass Ace (above, Nippon Paper Industries), Taiou, Bright Foam, Bright Nip (Nagoya Pulp), Peony A, Golden Pigeon, Special Peony, White Peony A, White Peony C, Silver Pigeon, Super White Peony A, Light Cream White Peony, Special Medium Quality Paper, White Pigeon, Super Medium Quality Paper, Blue Pigeon, Red Pigeon, Gold Pigeon M Snow Vision, Snow Vision, Gold Pigeon Snow Vision, White Pigeon M, Super DX, Hamanasu O, Red Pigeon M, HK Super Printing Paper (Made by Honshu Paper), Stalinden (A・ AW), Star Elm, Star Maple, Star Laurel, Star Poplar, MOP, Star Cherry I, Cherry I Super, Cherry II Super, Star Cherry III, Star Cherry IV, Cherry III Super, Cheri -IV Super (above, made by Maruzumi Paper), SHF (above, made by Toyo Pulp), TRP (above, made by Tokai Pulp), etc.

(Various films)
As the various films, all commonly used films can be used. For example, there are a polyester film, a polyolefin film, a polyvinyl chloride film, a polyvinylidene chloride film, and the like. Resin-coated paper that is photographic printing paper or YUPO paper that is synthetic paper can also be used.

(Various ink jet recording media)
As the various ink jet recording media, an ink receiving layer is formed on the surface using an absorbent support or a non-absorbent support as a base material. Examples of the ink receiving layer include a coating layer, a swelling layer, and a fine void layer.

  The swelling layer absorbs ink when the ink receiving layer made of a water-soluble polymer swells. The fine void layer is composed of inorganic or organic fine particles having a secondary particle size of about 20 to 200 nm and a binder, and fine voids of about 100 nm absorb ink.

  In recent years, an ink jet recording medium in which the fine void layer is provided using RC paper in which both surfaces of a paper base material are coated with an olefin resin is preferably used in terms of a photographic image.

  EXAMPLES Hereinafter, the present invention will be specifically described with reference to examples, but the present invention is not limited thereto.

Example 1
(Synthesis of polymer compound 1)
56 g of glycidyl methacrylate, 48 g of p-hydroxybenzaldehyde, 2 g of pyridine, and 1 g of N-nitroso-phenylhydroxyamine ammonium salt were put in a reaction vessel and stirred in a hot water bath at 80 ° C. for 8 hours.

  Next, 45 g of saponified polyvinyl acetate having a polymerization degree of 400 and a saponification degree of 88% was dispersed in 225 g of ion-exchanged water, and then 4.5 g of phosphoric acid and p- (3-methacryloxy-2) obtained by the above reaction were added to this solution. -Hydroxypropyloxy) benzaldehyde was added to PVA so that the modification rate was 3 mol%, and the mixture was stirred at 90 ° C. for 6 hours. After cooling the obtained solution to room temperature, 30 g of basic ion exchange resin was added and stirred for 1 hour. Thereafter, the ion exchange resin was filtered, and Irgacure 2959 (manufactured by Ciba Specialty Chemicals) as a photopolymerization initiator was mixed at a rate of 0.1 g with respect to 100 g of 15% aqueous solution, and then diluted with ion exchange water. A 10% aqueous solution of polymer compound 1 was obtained.

(Synthesis of polymer compounds 2 and 3)
In addition, the modification rate was adjusted by changing the polymerization degree and the saponification degree of the polyvinyl acetate saponified product as needed and changing the amount of p- (3-methacryloxy-2-hydroxypropyloxy) benzaldehyde charged.

(Preparation of pigment dispersion A)
The following additives were mixed and dispersed using a sand grinder filled with 50% by volume of 0.5 mm zirconia beads to prepare Pigment Dispersion A having a pigment content of 20%.

Carbon black MA7 (Mitsubishi Chemical) 20 parts Styrene-acrylic acid-methyl acrylate copolymer (weight average molecular weight 10,000, acid value 140) 10 parts Ethylene glycol 20 parts Glycerin 10 parts Ion-exchanged water 40 parts Table 1 lists polymer dispersants Pigment dispersions B to F were prepared in the same manner except for the changes as described.

[Preparation of Ink-1]
10% aqueous solution of polymer compound 1 20 parts Diethylene glycol 20 parts Glycerin 10 parts Triethylene glycol monobutyl ether 10 parts Pigment dispersion A 20 parts Surfinol 465 (manufactured by Air Products) 0.5 parts Was 100 parts to prepare an ink.

  This ink is precipitated in a centrifugal separator to precipitate the pigment and the polymer dispersant adsorbed on the pigment, thereby obtaining a supernatant. A small amount of hydrochloric acid was added dropwise to the supernatant, and only the released polymer dispersant was precipitated, evaporated to dryness, and the mass was measured. From this result, the mass% in the ink was obtained.

[Preparation of Inks-2 to 12]
In the preparation of ink-1, an ink was prepared in the same manner except that the kind of 10% aqueous solution of polymer compound 1 and the addition amount, as well as the type of dispersion liquid were changed (if the addition amount was different, ion exchange was performed). Prepared by changing the amount of water).

[Preparation of Comparative Inks-13 and 14]
Comparative ink-13 was prepared in the same manner as ink-1, except that polymer compound 1 was not contained. Also, Comparative Ink-14 having the following composition containing a solvent-based UV curable cationic polymerization monomer was prepared.

Carbon black MA7 (manufactured by Mitsubishi Chemical) 4 parts Polymer dispersing agent (Solpers 3200 manufactured by Avecia) 10 parts Cationic polymerization monomer OXT221 (manufactured by Oxetane Toagosei) 80 parts Photoacid generator CS5102 (manufactured by Nippon Soda) 5 parts Initiator assistant C17001 (made by Nippon Soda) 1 part

[Evaluation of ink]
(Storage stability)
Each of the inks prepared above was put in a glass bottle, sealed, and allowed to stand at 60 ° C. for 7 days, and then the pigment sedimentation state was visually observed, and the storage stability of the ink was evaluated according to the following criteria.

○: No pigment settling is observed Δ: No settling is observed, but when the liquid is shaken, some aggregates of pigment particles are observed on the wall surface of the glass bottle ×: Clear sediment is observed at the bottom of the glass bottle.

(Continuous emission)
In an environment of 20 ° C. and 30% RH, each ink set was mounted on an ink jet printer equipped with a piezo-type head having a nozzle hole diameter of 20 μm, a driving frequency of 10 kHz, and a nozzle number of 128, and under the condition of discharging 12 pl per drop, The state after the discharge was continuously continued for 1 hour without cleaning was visually observed, and the discharge stability was evaluated according to the following criteria.

◎: Normal emission from all nozzles ○: Clogging is observed in 1 to 3 nozzles, but recovered by suction cleaning from the nozzle surface △: Clogging occurs in 4 or more nozzles and cannot be recovered by suction cleaning Clogging occurs in one nozzle, but is in a practically acceptable range. X: Clogging occurs in 7 or more nozzles, and clogging that cannot be recovered by suction cleaning occurs in 2 nozzles. Xx: Clogging in 10 or more nozzles. Occurred, and clogging that cannot be recovered by suction cleaning occurs for 3 nozzles or more.

[Evaluation of inkjet image]
(concentration)
An on-demand ink jet with a maximum recording density of 720 × 720 dpi using a piezo head having a nozzle diameter of 25 μm, a drive frequency of 12 kHz, a nozzle count of 128, and a nozzle density of 180 dpi (dpi represents the number of dots per 2.54 cm). Using a printer, print a 10cm x 10cm black solid on plain paper (Ricoh's full color PPC paper type 6000), measure the black density with an X-Rite reflection densitometer, and follow the criteria below. evaluated. Each ink was continuously ejected and landed, and 0.1 seconds later, 120 W / cm metal halide lamps (MAL 400NL power supply power 3 kW · hr, manufactured by Nippon Battery Co., Ltd.) disposed at both ends of the piezo-type head were irradiated.

◎: Black density 1.5 or more ○: Black density 1.4 or more, less than 1.5 △: Black density 1.2 or more, less than 1.4 ×: Black density 0.8 or more, less than 1.2 XX: Black density less than 0.8.

(Glossy)
Using an on-demand type ink jet printer with a maximum recording density of 720 × 720 dpi, using a piezo head having a nozzle diameter of 25 μm, a drive frequency of 12 kHz, a nozzle number of 128, and a nozzle density of 180 dpi, art paper (NK Art Kongo N, manufactured by Oji Paper) ) Was printed with a solid black of 10 cm × 10 cm, visually observed, and glossiness was evaluated according to the following criteria. Each ink was continuously ejected and landed, and 0.1 seconds after landing, a 120 W / cm metal halide lamp (MAL 400NL power supply power 3 kW · hr, manufactured by Nippon Battery Co., Ltd.) was irradiated.

◎: Natural difference between glossiness of recording surface and background is almost natural ○: Glossiness of recording surface and background is slightly different, but acceptable level Δ: Visual observation that glossiness of recording surface and background is slightly different And the glossiness of the recording surface is remarkably higher than that of the background. X: It is possible to visually observe that the glossiness of the recording surface and the background is clearly different, and the glossiness of the recording surface is remarkably higher than that of the background. It can be visually observed that the glossiness of the recording medium is different, and the glossiness of the recording surface is significantly lower than that of the base.

  From Table 3, 1 to 7 and 9 to 12, which are the inks for inkjet of the present invention, are excellent in storage stability and continuous emission as inks, and also excellent in density and gloss as inkjet images. I understand that.

Claims (7)

In an inkjet ink containing a pigment, a polymer dispersant, and water, a polymer compound having a plurality of side chains in a hydrophilic main chain and capable of crosslinking between side chains by irradiation with active energy rays An ink-jet ink characterized in that the free polymer dispersant contained therein and not adsorbed on the pigment is 1.0% by mass or less of the total ink. The inkjet ink according to claim 1, wherein a mass ratio of the pigment to the liberated polymer dispersant is 4: 1 to 200: 1. The inkjet ink according to claim 1 or 2, wherein the polymer dispersant has a weight average molecular weight of 5,000 to 50,000. The inkjet ink according to any one of claims 1 to 3, wherein the polymer dispersant has an acid value of 20 to 250. The inkjet ink according to any one of claims 1 to 4, wherein the polymer compound is contained in an amount of 0.8 to 5.0% by mass with respect to the total mass of the ink. 6. The hydrophilic main chain is a saponified product of polyvinyl acetate, has a saponification degree of 77 to 99%, and a polymerization degree of 200 to 4000. Inkjet ink. The inkjet ink according to any one of claims 1 to 6, wherein the modification rate of the side chain with respect to the hydrophilic main chain is 0.8 mol% or more and 4 mol% or less.