JP2007091910A - Ink for inkjet - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an ink for inkjet, providing excellent jetting stability and decap resistance in an inkjet printer, further providing an image having excellent character quality, resistance to strike through and abrasion resistance, and having excellent curl characteristics of a printed recording material. <P>SOLUTION: The inkjet ink comprising at least a coloring material, an organic solvent, water and a macromolecular compound is characterized by ≥10 and <50 mass% content of the water based on the whole mass of the ink, at least one kind of the water-soluble organic solvent having ≥9.0 and <12.0 SP value in the organic solvents, ≥30 mass% content of the water-soluble organic solvent having ≥9.0 and <12.0 SP value, and the macromolecular compound having two or more side chains on the hydrophilic main chain and crosslinkable between side chains by the irradiation with active energy rays. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a novel inkjet ink.

  In recent years, the inkjet recording method can easily and inexpensively create an image, and thus has been applied to various printing fields such as photographs, various printing, marking, and special printing such as a color filter. In particular, ink jet recording equipment that emits and controls fine dots, ink reproducibility with improved color reproduction range, durability, emissivity, etc. Using specially improved special paper, it is possible to obtain image quality comparable to silver halide photography.

  However, in an inkjet image recording system that requires special paper, there are problems in that the types of recording media that can be used are limited and the cost of the recording media is increased.

  On the other hand, in the office, there is an increasing need for a system capable of performing full color printing at high speed without being restricted by a recording medium (for example, plain paper, coated paper, art paper, plain paper double-sided printing, etc.).

  In addition, the composition of the ink-jet ink used here can be printed at a high speed, has good character reproducibility on plain paper, and shows through when printing (the printed ink passes through the recording medium and the image is printed on the back side). ), Feathering, image blurring, fast penetration into paper, fast drying, and so on.

  As one of the methods, a so-called water-based ink-jet ink having a water content of 50% by mass or more is widely used as an ink-jet ink. An electrophotographic copy paper using such a water-based ink-jet ink is widely used. When inkjet image recording is performed on plain paper such as high-quality paper and medium-quality paper, in addition to problems caused by the ink permeability of the substrate such as through-through of the formed image and feathering, the curl of the plain paper on which the image was recorded And cockling is a big problem.

  In order to solve the above problems, an ink jet recording method using an ink jet ink having improved penetrability by specifying a wetting time and an absorption coefficient for a recording medium in the Bristow method has been disclosed (for example, see Patent Document 1). However, in the method described in Patent Document 1, since the color material in the ink also penetrates into the plain paper at the same time, the decrease in image density and the back-through of the ink become large, which is particularly suitable for double-sided printing. Has the disadvantage of not doing.

  Further, an inkjet ink containing a specific amide compound, pyridine derivative, imidazoline compound or urea compound as an anti-curl agent is disclosed (for example, see Patent Document 2). However, the method described in Patent Document 2 has a problem that clogging is likely to occur in the nozzle portion of the recording head as the ink liquid is dried.

  As a method for improving the curl, an ink jet recording method has been proposed in which a solution containing water is applied to the back side of the image printing surface to optimize the curl balance (see, for example, Patent Document 3). However, the method described in Patent Document 3 does not have double-sided recording suitability, and the strength of plain paper decreases with the increase in the amount of ink jet ink and curl balance liquid attached to plain paper. Etc.

  Further, solvent-based inks that can perform printing at high speed instead of water-based inkjet inks have been studied. That is, by using an oil-based ink (solvent ink jet ink) that contains a volatile solvent and has improved drying properties, even when printing on plain paper, the penetration into the recording medium is fast and the drying time is short. High-speed printing is possible without curling the recording medium. However, solvent-based inks have high penetrability into plain paper, resulting in poor character reproducibility and show-through in recording media, which is a major obstacle especially when printing on both sides of plain paper. It was.

  On the other hand, the present inventors have prescribed the specific solvent and water content in the ink under specific conditions, thereby improving the light emission and decapability at the time of printing. An ink-jet ink excellent in strikethrough resistance, character quality, and curl characteristics has been proposed (see, for example, Patent Document 4).

  However, the method proposed in Patent Document 4 could improve curling resistance while preventing curling, but because more pigment remained on the surface layer of paper, high-speed printing, especially double-sided printing, was considered. In this case, since the conveyance in the ink jet printer becomes severe, it has been found that the scratch resistance of the printed portion is insufficient.

With respect to scratch resistance, for example, a proposal has been made to include a vinyl copolymer in ink (see, for example, Patent Document 5). However, simply adding a polymer to the ink-jet ink does not provide a sufficient effect on scratch resistance. Therefore, an ink using an ultraviolet polymerization monomer as a polymer compound has been proposed (see, for example, Patent Document 6). In these methods, the ink itself is cured with a curing component, so that the scratch resistance is improved. Caused unnaturalness. Furthermore, many of the conventionally known actinic ray curable compounds have safety concerns, and even if safety is cleared, the range of selectable compounds is limited and the characteristics of the resulting image film are also great. You will be restricted.
JP 10-316915 A JP 9-176538 A JP-A-10-272828 JP 2005-220296 A JP 2005-97433 A JP-A-7-224241

  The present invention has been made in view of the above-mentioned problems, and its purpose is excellent in emission stability and decap resistance in an ink jet printer, and excellent in character quality, back-through resistance, and scratch resistance of the formed image, and An object of the present invention is to provide an ink-jet ink excellent in curling characteristics of a printed recording material.

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

  (1) An inkjet ink containing at least a coloring material, an organic solvent, water, and a polymer compound, wherein the water content is 10% by mass or more and less than 50% by mass of the total ink, and the organic solvent At least one is a water-soluble organic solvent having an SP value of 9.0 or more and less than 12.0, and the content of the water-soluble organic solvent having an SP value of 9.0 or more and less than 12.0 is 30% by mass or more of the ink mass, and the polymer compound is a polymer compound having a plurality of side chains in the hydrophilic main chain and capable of crosslinking between the side chains by irradiating active energy rays. An ink-jet ink comprising:

  (2) At least one of the organic solvents is a water-soluble organic solvent having an SP value of 9.0 or more and less than 11.0, and the water-soluble organic solvent having an SP value of 9.0 or more and less than 11.0. The ink-jet ink according to item (1), wherein the content of the ink is 30% by mass or more of the total ink mass.

  (3) The inkjet ink as described in (1) or (2) above, wherein the polymer compound is contained in an amount of 0.8% by mass to 5.0% by mass with respect to the total mass of the ink. .

  (4) The hydrophilic main chain of the polymer compound is a saponified product of polyvinyl acetate, having a saponification degree of 77% or more and 99% or less and a polymerization degree of 200 or more and 4000 or less. The inkjet ink according to any one of (1) to (3) above.

  (5) Any of (1) to (4) above, wherein the modification rate of the side chain with respect to the hydrophilic main chain of the polymer compound is 0.8 mol% or more and 4 mol% or less. Item 2. An ink-jet ink according to item 1.

  (6) The ink for ink-jet recording according to any one of (1) to (5), wherein the coloring material is a pigment.

  According to the present invention, an inkjet ink having excellent emission stability and decap resistance in an ink jet printer, excellent character quality of a formed image, resistance to back-through, and scratch resistance, and excellent curl characteristics of a printed recording material. Could be provided.

  Hereinafter, the best mode for carrying out the present invention will be described in detail.

  As a result of intensive studies in view of the above problems, the present inventor is an inkjet ink containing at least a coloring material, an organic solvent, water, and a polymer compound, and the water content is 10 mass of the total ink mass. % Or more and less than 50% by mass, and at least one of the organic solvents is a water-soluble organic solvent having an SP value of 9.0 or more and less than 12.0, and the SP value of 9.0 or more and 12. The content of the water-soluble organic solvent of less than 0 is 30% by mass or more of the total ink mass, and the polymer compound has a plurality of side chains in the hydrophilic main chain, and is irradiated with active energy rays. Ink jet ink characterized in that it is a polymer compound that can be cross-linked between side chains, has excellent emission stability and decap resistance in an ink jet printer, and character quality, back-through resistance, and resistance to formed images. Scratching Excellent, and found to be able to achieve excellent ink-jet ink to curl properties of printing the recording material is completed the invention.

  The present invention will be described in detail below.

《Polymer Compound》
In the inkjet ink of the present invention (hereinafter, also simply referred to as ink), 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 ( Hereinafter, it is also characterized by containing a polymer compound according to the present invention.

  The active energy ray-crosslinking type polymer compound according to the present invention crosslinks via a crosslink between the side chains of the main chain originally having a certain degree of polymerization. The effect of increasing the molecular weight per photon is significantly greater than that of active energy ray curable resins that polymerize. 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 image film after being cured by irradiating with active energy rays cannot be controlled and are hard. It tends to be a fragile film.

  In the polymer compound according to the present invention, 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.

  Furthermore, in the conventionally known active energy ray-curable ink, almost all the amount other than the color material is a curable polymer component, so that the dots after curing rise and the image quality represented by gloss is greatly deteriorated. The polymer compound according to the present invention requires only a small amount and has a large amount of dry components, so that image quality after drying, for example, improvement in glossiness can be improved and scratch resistance is good.

  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 thereof. Is preferably 200 or more and 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. When it is less than 0.3 mol%, the crosslinkability is insufficient, and the effect of the present invention is reduced.

  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-56-67309 includes a 2-azido-5-nitrophenylcarbonyloxyethylene structure represented by the following general formula (2) in the polyvinyl alcohol structure, or the following general formula. This 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.

  In the ink according to the present invention, the active energy ray-crosslinking polymer compound according to the present invention is preferably contained in an amount of 0.8% by mass or more and 5.0% by mass or less based on the total mass of the ink. The presence of 0.8% by mass or more improves cross-linking efficiency, and beading and color bleeding 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 viewpoints of light emission properties and ink storage stability.

[Photopolymerization initiator, sensitizer]
In the ink according to the present invention, it is also preferable to add a photopolymerization initiator or a sensitizer. These compounds may be dissolved or dispersed in a solvent, or may be chemically bonded to the photosensitive resin.

  Although there is no restriction | limiting in particular about the photoinitiator and photosensitizer which are applied, A water-soluble photoinitiator is preferable from a viewpoint of mixability 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, from the viewpoint of compatibility with the resin, 4- (2-hydroxyethoxy) phenyl- (2-hydroxy-2-propyl) ketone (n = 1, HMPK) represented by the following general formula (7), The ethylene oxide adduct (n = 2 to 5) is more preferable.

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

  Other photopolymerization initiators include 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, isopropoxychlorothioxanthone, anthraquinones such as ethyl anthraquinone, benzanthraquinone, aminoanthraquinone, chloroanthraquinone, benzoin ethers such as acetophenones, benzoin methyl ether 2,4,6-trihalomethyltriazines, 1-hydroxycyclohexyl phenyl ketone, 2- (o-chlorophenol) Nyl) -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, -di (p -Methoxyphenyl) -5-phenylimidazole dimer, 2,4,5-triarylimidazole dimer of 2- (2,4-dimethoxyphenyl) -4,5-diphenylimidazole dimer, benzyldimethyl ketal 2-benzyl-2-dimethylamino-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, methylbenzoin, benzoins such as ethylbenzoin, 9-phenylacridine, 1,7-bis (9,9'-acridinyl) heptane, etc. Acridine derivatives, bisacylphosphine oxides, and mixtures thereof are preferably used, and the above 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 and irradiation method thereof>
The ink jet recording method of the present invention includes an ink jet recording medium containing a polymer compound having a plurality of side chains in the hydrophilic main chain and capable of crosslinking between side chains by irradiating active energy rays. After the recording ink is ejected to record an image, the active energy ray is irradiated onto the recorded image to cure the polymer compound to form an image.

(Active energy irradiation method)
The ink according to the present invention has a water-soluble polymer having a plurality of side chains in the hydrophilic main chain and capable of crosslinking between the side chains by irradiating active energy rays. After spraying, curing is performed by irradiation with active energy rays.

  Hereinafter, a method for irradiating an inkjet ink with an active energy ray will be described.

<Active energy rays>
Examples of the active energy rays in the present invention include electron beams, ultraviolet rays, α rays, β rays, γ rays, X-rays, etc., but they are dangerous to the human body and easy to handle. Electron beams and ultraviolet rays that are widely used are preferred. In the present invention, ultraviolet rays are particularly preferable.

  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 or the like may be deteriorated.

  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 tube having an operating pressure of several hundred Pa to 1 MPa. A conventionally well-known thing, such as LED, is used.

<Light irradiation conditions after ink landing>
As the irradiation condition of the active energy ray, it is preferable that the active energy ray is irradiated for 0.001 to 1.0 seconds after the ink has landed on the recording medium, and more preferably 0.001 to 0.00. 5 seconds. In order to form a high-definition image, it is particularly important that the irradiation timing is as early as possible.

<Irradiation means of active energy rays>
As a method for irradiating active energy rays, a basic method is disclosed in Japanese Patent Application Laid-Open No. 60-132767. According to this, the light source is provided on both sides of the ink jet recording 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. Furthermore, there is a method in which 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 ultraviolet rays by applying a collimated light source to a mirror surface provided on the side surface of the head unit is disclosed. . Any of these irradiation methods can be used in the image recording method of the present invention.

  Also preferred is a method in which the irradiation of active energy rays is divided into two stages, and the active energy rays are first irradiated by the above-described method within 0.001 to 2.0 seconds after ink landing, and further the active energy rays are irradiated. It is one of. By dividing the irradiation of the active energy ray into two stages, it is possible to further suppress the shrinkage of the recording material that occurs during ink curing.

<< Solvent composition >>
The solvent composition in the ink of the present invention contains at least water and an organic solvent, the water content is 10% by mass or more and less than 50% by mass of the total ink mass, and at least one of the organic solvents is SP. A water-soluble organic solvent having a value of 9.0 or more and less than 12.0, and the content of the water-soluble organic solvent having an SP value of 9.0 or more and less than 12.0 is 30% by mass or more of the total ink mass. By using this solvent composition, the emission stability and decap resistance are excellent, the character quality of the formed image and the through-through resistance are good, and the curled characteristics of the printed recording material are good. It becomes possible.

  If the water content in the total ink mass is less than 50 mass%, the occurrence of curling and cockling is suppressed. Moreover, if it is 10 mass% or more, favorable dispersion stability of the pigment can be obtained. The water content in the total ink mass is preferably 20% by mass or more and less than 40% by mass.

  In the ink of the present invention, the water-soluble organic solvent having an SP value of 9.0 or more and less than 12 is contained at 30% by mass or more of the total ink mass. The occurrence of cockling can be drastically suppressed, and it is preferable that the water-soluble organic solvent having an SP value of 9.0 or more and less than 12 is preferably contained in an amount of 50 to 80% by mass of the total ink mass. .

  In the ink of the present invention, the SP value of the main organic solvent is 9.0 or more and less than 12, but if it is 9.0 or more, the compatibility with water is good and the separation from water does not occur. High dispersion stability of the pigment particles can be maintained. Moreover, if SP value is less than 12, the inhibitory effect with respect to the curl resulting from an organic solvent can be acquired. In the present invention, the SP value range of the organic solvent is more preferably 9.0 or more and less than 11.

The solubility parameter (SP value) of the solvent referred to in the present invention is a value represented by the square root of the molecular aggregation energy, and is described in Polymer HandBook (Second Edition) Chapter IV Solubility Parameter Values. The unit is (cal / cm) ^1/2 and refers to the value at 25 ° C. In addition, R.D. F. It can be calculated by the method described in Fedors, Polymer Engineering Science, 14, p147 (1967).

  Hereinafter, examples of the water-soluble organic solvent having an SP value of 9.0 or more and less than 12 according to the present invention include ethylene glycol monomethyl ether (11.6), ethylene glycol monoethyl ether (11.4), and ethylene glycol. Monobutyl ether (9.8), ethylene glycol monoisopropyl ether (9.2), diethylene glycol monomethyl ether (11.6), diethylene glycol monoethyl ether (11.2), diethylene glycol monobutyl ether (9.5), diethylene glycol dimethyl ether ( 9.4), triethylene glycol monomethyl ether (10.5), triethylene glycol monoethyl ether (10.4), triethylene glycol monobutyl ether (9.6), propylene glycol Monomethyl ether (10.4), propylene glycol monophenyl ether (9.4), dipropylene glycol monomethyl ether (9.6), tripropylene glycol monomethyl ether (9.6), etc., but are particularly limited is not. The numerical value in the parenthesis represents the SP value.

  In the ink of the present invention, in addition to a water-soluble organic solvent having an SP value of 9.0 or more and less than 12, conventionally known various water-soluble organic solvents can be used in combination. Among these, ethylene carbonate, propylene carbonate, 1, 3-Dimethyl-2-imidazolidinone is preferable because it does not adversely affect the dispersibility of the pigment and has an effect of lowering the ink viscosity.

《Coloring material》
The ink of the present invention contains a color material, and examples of the color material used in the ink of the present invention include a color material that forms yellow, magenta, cyan, black, blue, green, and red inks. Are preferably used, and particularly preferable are yellow, magenta, cyan, and black color materials.

  In the ink of the present invention, a dye ink whose color material is a dye, or a pigment ink that forms a dispersion containing fine pigment particles, or a color material that is insoluble in a solvent constituting the ink-jet ink, The present invention can be applied to various ink-jet inks such as a dispersion ink composed of a molecular polymer dispersion.

  Examples of the dye that can be used in the present invention include azo dyes, methine dyes, azomethine dyes, xanthene dyes, quinone dyes, phthalocyanine dyes, triphenylmethane dyes, diphenylmethane dyes, and the specific compounds include: For example, the dye illustrated in Unexamined-Japanese-Patent No. 2002-264490 can be mentioned.

  In addition, oil-soluble dyes that form colored fine particles together with polymers, etc., and become colorants, are usually soluble in organic solvents that do not have a water-soluble group such as carboxylic acid and sulfonic acid, and are insoluble in water, such as disperse dyes. Etc. are selected. Also included are dyes that exhibit oil solubility by salting a water-soluble dye with a long-chain base. For example, acid dyes, direct dyes, salt-forming dyes of reactive dyes and long-chain amines are known. .

  However, in the ink of the present invention, it is preferable to use a pigment as the coloring material, and a pigment that does not have solubility in the solvent composition according to the present invention is preferable from the viewpoint of exerting the intended effects of the present invention.

  As the pigment that can be used in the present invention, conventionally known pigments can be used without particular limitation, and any of water-dispersible pigments, solvent-dispersible pigments, and the like can be used, for example, organic pigments such as insoluble pigments and lake pigments, An inorganic pigment such as carbon black can be preferably used. The pigment is present in a dispersed state in the water-based ink. The dispersion method may be any of self-dispersion, activator dispersion, polymer dispersion, and microcapsule dispersion, but the polymer dispersion and microcapsule dispersion are fixed. From the viewpoint of sex.

  The insoluble pigment is not particularly limited. Dioxazine, thiazole, phthalocyanine, diketopyrrolopyrrole and the like are preferable.

  Specific pigments that can be preferably used include the following pigments.

  Examples of the magenta or red pigment 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 pigment for orange or yellow 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 15: 3, C.I. I. Pigment yellow 17, C.I. I. Pigment yellow 74, C.I. I. Pigment yellow 93, C.I. I. Pigment yellow 128, C.I. I. Pigment yellow 94, C.I. I. And CI Pigment Yellow 138.

  Examples of the pigment 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.

  In addition to the above pigments, when red, green, blue and intermediate colors are required, the following pigments are preferably used alone or in combination. I. Pigment Red; 209, 224, 177, 194, C.I. I. Pigment Orange; 43, C.I. I. Vat Violet; 3, C.I. I. Pigment Violet; 19, 23, 37, C.I. I. Pigment Green; 36, 7, C.I. I. Pigment Blue; 15: 6 or the like is used.

  Examples of black pigments include C.I. I. Pigment black 1, C.I. I. Pigment black 6, C.I. I. Pigment black 7 and the like.

  The average particle size of the pigment dispersion used in the ink of the present invention is preferably 50 nm or more and less than 200 nm. When the average particle size of the pigment dispersion is less than 50 nm or 200 nm or more, the stability of the pigment dispersion tends to be poor, and the storage stability of the aqueous ink tends to deteriorate.

  The particle size of the pigment dispersion can be determined by a commercially available particle size measuring instrument using a dynamic light scattering method, an electrophoresis method, or the like. Accurate and often used.

  The pigment used in the present invention is preferably used after being dispersed by a disperser together with a dispersant and other necessary additives according to desired purposes. As the disperser, a conventionally known ball mill, sand mill, line mill, high-pressure homogenizer, or the like can be used. Among them, the dispersion by sand mill is preferable because the particle size distribution is sharp when the dispersion is aimed at an average particle diameter of around 100 nm. The material of the beads used for sand mill dispersion is preferably zirconia or zircon from the viewpoint of contamination of bead fragments and ionic components. Further, the bead diameter is preferably 0.1 mm or more and 0.5 mm.

<Pigment dispersant>
Examples of the polymer dispersant for dispersing the pigment according to the present invention include higher fatty acid salts, alkyl sulfates, alkyl ester sulfates, alkyl sulfonates, sulfosuccinates, naphthalene sulfonates, alkyl phosphates, polyphosphates, and the like. Activators such as oxyalkylene alkyl ether phosphate, polyoxyalkylene alkyl phenyl ether, polyoxyethylene polyoxypropylene glycol, glycerin ester, sorbitan ester, polyoxyethylene fatty acid amide, amine oxide, or styrene, styrene derivatives, vinyl A block copolymer comprising at least two monomers selected from naphthalene derivatives, acrylic acid, acrylic acid derivatives, maleic acid, maleic acid derivatives, itaconic acid, itaconic acid derivatives, fumaric acid, fumaric acid derivatives, and randoma Copolymer and can be exemplified salts thereof.

  In the present invention, the addition amount of the pigment dispersant is preferably 10 to 100% by mass with respect to the pigment.

<Surfactant>
In the dispersion of the pigment according to the present invention, a surfactant can be used as an additive. As the surfactant used in the present invention, any of cationic, anionic, amphoteric and nonionic surfactants can be used, but it is particularly preferable to use a nonionic surfactant from the viewpoint of dispersion stability.

  Nonionic activators include, for example, polyoxyethylene secondary alcohol ether, polyoxyethylene alkylphenyl ether, polyoxyethylene sterol ether, polyoxyethylene lanolin derivative polyoxyethylene polyoxypropylene alkyl ether, polyoxyethylene glycerin fatty acid ester , Polyoxyethylene castor oil, hydrogenated castor oil, polyoxyethylene sorbitol fatty acid ester, polyethylene glycol fatty acid ester, fatty acid monoglyceride, polyglycerin fatty acid ester, sorbitan fatty acid ester, propylene glycol fatty acid ester, sucrose fatty acid ester, fatty acid alkanolamide, poly Oxyethylene fatty acid amide, polyoxyethylene alkylamine, alkylamine oxide , Acetylene glycol, acetylene alcohol, and the like.

  Further, it is preferable to use a surfactant in order to accelerate the penetration of ink droplets after ink ejection into plain paper, and such a surfactant has an adverse effect on the ink, such as storage stability. The surfactant is not limited as long as it does not affect the surface, and the same surfactants as those used as an additive at the time of dispersion can be used.

《Polyvalent metal ion》
In the ink of the present invention, the total content of calcium ions, magnesium ions and iron ions, which are polyvalent metal ions, is preferably 10 ppm or less, more preferably 0.1 to 5 ppm, particularly preferably. 0.1-1 ppm.

  By setting the content of polyvalent metal ions in the inkjet ink to the amount specified above, an ink having high dispersion stability can be obtained. The polyvalent metal ion according to the present invention is contained in sulfates, chlorides, nitrates, acetates, organic ammonium salts, EDTA salts and the like.

《Other additives》
In the ink of the present invention, in addition to the above description, if necessary, the output stability, print head and ink cartridge compatibility, storage stability, image storage stability, and other various performance improvement objectives are known. Various additives such as polysaccharides, viscosity modifiers, specific resistance regulators, film forming agents, ultraviolet absorbers, antioxidants, anti-fading agents, antifungal agents, rust preventives, etc. may be appropriately selected and used. For example, oil droplet fine particles such as liquid paraffin, dioctyl phthalate, tricresyl phosphate, silicon oil, ultraviolet absorbers described in JP-A-57-74193, 57-87988, and 62-261476, As described in Kaisho 57-74192, 57-87989, 60-72785, 61-146591, JP-A-1-95091 and 3-13376, etc. Anti-fading agents, fluorescent whitening agents described in JP-A Nos. 59-42993, 59-52689, 62-280069, 61-242871, and JP-A-4-219266 Can be mentioned.

  In addition, the dissolved oxygen concentration in the ink of the present invention is preferably 2 ppm or less at 25 ° C. By setting this dissolved oxygen concentration condition, the formation of bubbles can be suppressed, and the emission stability even in high-speed printing. An ink jet recording method having excellent properties can be realized. As a method for measuring the dissolved oxygen dissolved in the ink, for example, it can be measured using a dissolved oxygen measuring device DO-14P (manufactured by Toa Radio).

"Recording method"
In the image recording method using the ink of the present invention, for example, an ink jet print can be obtained by ejecting ink as droplets from an ink jet head based on a digital signal and adhering to plain paper by a printer loaded with ink jet ink. .

  When an image is formed by ejecting the ink of the present invention, the inkjet head to be used may be an on-demand system or a continuous system. Also, as a discharge method, an electro-mechanical conversion method (for example, a single cavity type, a double cavity type, a bender type, a piston type, a shear mode type, a shared wall type, etc.), an electro-thermal conversion method (for example, thermal ink jet) Any ejection method such as a mold, a bubble jet (registered trademark) mold, or the like may be used.

  Among them, in the ink jet recording method according to the present invention, the ink of the present invention is ejected from a piezo ink jet recording head having a nozzle diameter of 30 μm or less to perform recording on plain paper, and further, the nozzle diameter is 30 μm or less. It is preferable to perform recording on plain paper by discharging from a piezo-type ink jet recording head having a line head.

  As a printing method of an ink jet printer, the printing characteristics of the ink of the present invention can be sufficiently obtained by printing using a line head type recording head with respect to a shuttle head type recording head. It is possible to achieve a very good dot shape (roundness) and printing accuracy when droplets land on plain paper.

  In particular, it is preferable to apply the ink of the present invention to an ink jet recording system in which images are printed on both sides of plain paper from the viewpoint that the object and effects of the present invention can be exhibited.

  In double-sided printing, after printing on one side, plain paper is turned over and transported with the printing side down, but the ink of the present invention has the above-mentioned characteristics. Since there is no bleeding of characters, high density and excellent character quality on any surface, no conveyance failure occurs, and the conveyance belt is not contaminated with ink.

"recoding media"
The plain paper used in the ink jet recording method using the ink of the present invention is not particularly limited, but non-coated paper, special printing paper, and 80 to 200 μm uncoated paper belonging to a part of information paper are desirable. The construction of the plain paper according to the present invention is made by a conventional method using mainly chemical pulps represented by LBKP and NBKP, sizing agents and fillers, and using other paper making aids as necessary. As the pulp material used for the plain paper according to the present invention, mechanical pulp and recycled paper recycled pulp may be used in combination, and there is no problem even if these are used as the main material.

  Examples of the sizing agent internally added to the plain paper according to the present invention include rosin size, AKD, Alnicel succinic anhydride, petroleum resin-based size, epichlorohydrin, cationic starch, and acrylamide.

  Examples of the filler internally added to the plain paper according to the present invention include finely divided silicic acid, aluminum silicate, diatomaceous earth, kaolin, kaolinite, halloysite, nacrite, dickite, pyrophyllite, sericite, titanium dioxide, bentonite and the like. Is mentioned.

  Further, the plain paper according to the present invention may contain a water-soluble polyvalent metal salt from the viewpoint of enhancing the strike through of the ink of the present invention and the fixability of the pigment. The water-soluble polyvalent metal salt is not particularly limited, but for example, aluminum, calcium, magnesium, zinc, iron, strontium, barium, nickel, copper, scandium, gallium, indium, titanium, zirconium, tin, lead, etc. It is added as a salt such as a metal salt, sulfate, nitrate, formate, succinate, malonate, chloroacetate or p-toluenesulfonate. Further, a water-soluble inorganic polymer such as polyaluminum chloride may be used as a salt of a water-soluble polyvalent metal ion. The water solubility is preferably at least 0.1% by mass, more preferably 1% by mass. Among these, a water-soluble salt composed of aluminum, calcium, aluminum, magnesium, and zinc is preferable because its metal ion is colorless. Particularly preferred are aluminum chloride, aluminum sulfate, aluminum nitrate, aluminum acetate, calcium chloride, calcium sulfate, calcium nitrate, calcium acetate, magnesium chloride, magnesium sulfate, magnesium nitrate, magnesium acetate, zinc chloride, zinc sulfate, zinc nitrate, Zinc acetate.

  In the present invention, in addition to plain paper, high-quality paper, art paper, coated paper, cast-coated paper, glossy paper, ink jet paper, and the like can be widely used.

  EXAMPLES Hereinafter, the present invention will be specifically described with reference to examples, but the present invention is not limited thereto. In addition, although the display of "part" or "%" is used in an Example, unless otherwise indicated, "part by mass" or "mass%" is represented.

<< Preparation of polymer compound >>
[Preparation 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 each put in a reaction vessel and stirred in a hot water bath at 80 ° C. for 8 hours.

  Next, 45 g of a polyvinyl acetate saponified product having a degree of polymerization of 300 and a saponification rate of 88% was dispersed in 225 g of ion-exchanged water, and then 4.5 g of phosphoric acid and p- (3 -Methacryloxy-2-hydroxypropyloxy) benzaldehyde was added under the condition that the modification rate was 3 mol% with respect to polyvinyl alcohol, 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 is filtered, and Irgacure 2959 (manufactured by Ciba Specialty Chemicals) is mixed here as a photopolymerization initiator at a ratio of 0.1 g with respect to 100 g of the above 15% aqueous solution. To obtain a 10% aqueous polymer compound solution.

[Preparation of polymer compounds 2 to 11]
In the preparation of the polymer compound 1, the polymerization degree and saponification degree of the polyvinyl acetate saponified product were changed as shown in Table 1, and the amount of p- (3-methacryloxy-2-hydroxypropyloxy) benzaldehyde charged was changed. Then, 10% aqueous solutions of the polymer compounds 2 to 11 having the modification rate of the main chain PVA described in Table 1 were prepared.

<Preparation of ink>
(Preparation of pigment dispersion)
(Preparation of magenta pigment dispersion)
The following additives are mixed, put together with 200 g of zirconia beads having a diameter of 0.5 mm in a polypropylene plastic bottle, sealed, and dispersed for 5 hours using a paint shaker. A magenta pigment with a magenta pigment content of 15% A dispersion was prepared.

C. I. Pigment Red 122 15 parts Jonkrill 501 (manufactured by Johnson Polymer Co., Ltd.) 5 parts Tripropylene glycol monomethyl ether 40 parts Ion-exchanged water 40 parts (Preparation of yellow pigment dispersion, cyan pigment dispersion, and black pigment dispersion)
In the preparation of the magenta pigment dispersion, C.I. I. Instead of CI Pigment Red 122, C.I. I. Pigment yellow 150 (yellow pigment dispersion), C.I. I. Pigment blue 15: 3 (cyan pigment dispersion), C.I. I. A yellow pigment dispersion, a cyan pigment dispersion, and a black pigment dispersion were prepared in the same manner except that each was changed to CI Pigment Black 7 (black pigment dispersion).

[Preparation of ink]
The types of the pigment dispersion prepared above, the types and addition amounts of the polymer compound, the types and addition amounts of the solvent, and the water content were mixed in the combinations shown in Table 1 and sufficiently stirred. Next, this mixed solution was filtered with a # 3500 mesh metal filter, deaerated with a hollow fiber membrane, and inks 1 to 28 were prepared. Further, 0.2 part of a surfactant (Surfinol 104E, manufactured by Nissin Chemical) was added to each ink.

  The polymer compound 12 used for the preparation of the ink 28 is the vinyl copolymer A1 described in Patent Document 5.

  The solvent content shown in Table 1 is indicated by the total amount of the solvent added at the time of ink preparation and the amount of solvent brought in from each pigment dispersion. In the preparation of inks 17 and 19, diethylene glycol monomethyl ether (DEGME) and dipropylene glycol monobutyl ether (DPGBE) were used for the preparation of each pigment dispersion.

  Similarly, the water content shown in Table 1 is indicated by the total amount of water added at the time of ink preparation and water brought in from each pigment dispersion.

  The details of the solvents described in abbreviations in Table 1 are as follows.

TPGME; tripropylene glycol monomethyl ether DEGME; diethylene glycol monomethyl ether DPGBE; dipropylene glycol monobutyl ether DMI; 1,3-dimethyl-2-imidazolidinone PY150; I. Pigment Yellow 150
PR122; C.I. I. Pigment Red 122
PB15: 3; C.I. I. Pigment Blue 15: 3
PBk7; C.I. I. Pigment Black 7

《Image recording and evaluation》
[Production of image samples]
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 driving frequency of 12 kHz, a nozzle number of 128, and a nozzle density of 180 dpi (hereinafter, dpi represents the number of dots per 2.54 cm). Using a printer, print each color solid image of 10cm x 10cm on business class plain paper (manufactured by Konica Minolta Business Technology Co., Ltd.), then discharge each color ink continuously, and 0.1 seconds after landing, 120W / cm metal halide A lamp (MAL 400NL, power supply power 3 kW · hr, manufactured by Nippon Battery Co., Ltd.) was irradiated.

[Evaluation of through-hole resistance]
For each of the formed solid images, the image density of each of the image portion and the non-image portion on the recording print surface (referred to as A surface) and the back surface (referred to as B surface) was measured with a reflection densitometer, The rate was measured, and the strikethrough resistance was evaluated according to the following evaluation criteria.

Back-through density ratio = (B-side image density−B-side unprinted portion density) / (A-side image density−A-side unprinted portion density) × 100 (%)
A: Back-through density ratio is less than 10% B: Back-through density ratio is 10% or more and less than 20% Δ: Back-through density ratio is 20% or more and less than 30% ×: Back-through density ratio Is 30% or more and less than 50%. XX: Back-through density ratio is 50% or more [Evaluation of curl]
Each sample on which the above solid images were printed was left on a horizontal substrate under the following three conditions for one week, and then evaluated for curl according to the following evaluation criteria.

Condition 1: 23 ° C., 20% RH
Condition 2: 23 ° C., 55% RH
Condition 3: 23 ° C., 80% RH
A: There is no occurrence of floating at the end of 2 mm or higher in any condition, and no cockling is observed. ○: In any condition, the floating height is 2 mm or more and less than 5 mm. In addition, the occurrence of cockling (認 め) is not observed. Δ: The floating height is 5 mm or more and less than 10 mm under any conditions, but the occurrence of slight cockling (皺) is recognized. Even under the above conditions, the height of the float is 10 mm or more and less than 30 mm, but the occurrence of clear cockling (皺) is observed. ×: The end part with a height of 30 mm or more occurs under all conditions. [Evaluation of scratch resistance]
Scratch strength was measured using a scratch strength tester HEIDON-18 (manufactured by HEIDON) and a measuring needle using a 0.8 mmR sapphire needle. The measurement was performed by conducting a 10 cm scratch test at a constant load three times, defining a limit load where no scratched part exists on the recording medium as scratch strength, and evaluating the scratch resistance of the image according to the following criteria.

A: Scratch strength is 200 g or more. O: Scratch strength is 150 g or more and less than 200 g. Δ: Scratch strength is 100 g or more and less than 150 g. X: Scratch strength is less than 100 g.
The gloss difference between each color solid image forming part and the unprinted part (white background part) was visually observed, and the glossiness was evaluated according to the following criteria.

A: There is almost no difference in glossiness between the image-formed surface and the non-printed part, and it has a natural glossiness. ○: A slight difference is observed in the glossiness between the image-formed surface and the non-printed part, but the glossiness is preferable. Yes: A difference in glossiness between the image forming surface and the non-printed portion is recognized, but the glossiness of the image forming surface is higher than that of the non-printed portion, but is within a practically acceptable range. A large difference in glossiness was observed between the surface and the unprinted portion, and the glossiness of the image forming surface was remarkably higher than that of the unprinted portion, and the quality was unbearable. Shown in

  As is apparent from the results shown in Table 2, the ink of the present invention having the configuration defined in the present invention is superior in the back-through resistance, curl characteristics, scratch resistance and gloss to the comparative example. I understand. In addition, using the ink of the present invention, after discharging continuously from all the nozzles of the ink jet recording head for 1 minute, the discharging of all the nozzles is stopped all at once, and after a predetermined time has passed, all the nozzles are discharged again. As a result of performing the operation under the condition of performing continuous emission and evaluating the emission stability and the decap resistance, it was confirmed that they were excellent in both characteristics.

Claims (6)

An ink-jet ink containing at least a coloring material, an organic solvent, water and a polymer compound, wherein the water content is 10% by mass or more and less than 50% by mass of the total ink mass, and at least one of the organic solvents The seed is a water-soluble organic solvent having an SP value of 9.0 or more and less than 12.0, and the content of the water-soluble organic solvent having an SP value of 9.0 or more and less than 12.0 is the total ink mass. 30% by mass or more, and the polymer compound has a plurality of side chains in the hydrophilic main chain, and is a polymer compound that can be cross-linked between the side chains by irradiation with active energy rays. Ink-jet ink characterized. At least one of the organic solvents is a water-soluble organic solvent having an SP value of 9.0 or more and less than 11.0, and the content of the water-soluble organic solvent having an SP value of 9.0 or more and less than 11.0 The inkjet ink according to claim 1, wherein is at least 30 mass% of the total ink mass. The ink-jet ink according to claim 1, wherein the polymer compound is contained in an amount of 0.8% by mass to 5.0% by mass with respect to the total mass of the ink. The hydrophilic main chain of the polymer compound is a saponified product of polyvinyl acetate, having a saponification degree of 77% or more and 99% or less and a polymerization degree of 200 or more and 4000 or less. The ink for inkjet of any one of 1-3. The inkjet according to any one of claims 1 to 4, wherein the modification rate of the side chain with respect to the hydrophilic main chain of the polymer compound is 0.8 mol% or more and 4 mol% or less. For ink. The inkjet ink according to claim 1, wherein the color material is a pigment.