JP5055753B2 - Inkjet ink - Google Patents

Description

  The present invention relates to an inkjet ink used in an inkjet recording system.

  In recent years, the inkjet recording method can create images easily and inexpensively, and thus has been applied to various printing fields such as photographs, various printing, marking, and special printing such as color filters. In particular, ink jet recording devices that emit and control fine dots, ink with improved color reproduction range, durability, and emission suitability, ink absorbency, colorant color development, surface gloss, etc. are dramatically improved. It is also possible to obtain image quality comparable to silver halide photography using special paper.

  However, in an inkjet image recording system that requires dedicated paper, there are problems in that the 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 that can perform full color printing at high speed without being restricted by recording media (for example, plain paper, coated paper, art paper).

  In particular, it is desired to perform high-quality printing at high speed on plain paper (for example, PPC paper, non-coated paper for printing, etc.) that is inexpensive and easily available. When water-based ink is used, curling and cockling after printing have been a major issue. On the other hand, when oil-based ink is used, there is no problem with curling and cockling, but there are problems such as higher penetrating power than aqueous ink, character image quality, blurring, and low reflection density. Various studies have been conducted so far, including the composition of the recording liquid, in order to solve the problem of printing on plain paper, but ink that satisfies all of curling, cockling, image density, and character quality has not been obtained. It was.

  As a method for preventing curling and cockling during recording on plain paper using water-based ink, a technique of adding a specific diol to the ink is disclosed (see Patent Document 1). However, even in this method, there is a problem that curling and cockling occur when an image with a large amount of ink is printed. Further, a technique for preventing curling and cockling by adding caseins into the ink is disclosed (see Patent Document 2). However, this method has a problem of deteriorating dispersion stability with respect to ink containing a pigment.

  As a technology that pays attention to the occurrence of curl when using plain paper, a technology that suppresses the occurrence of curl and improves the character quality and light output by including a specific organic solvent in a specific ratio has been released. (See Patent Documents 3 to 5).

Although the technologies disclosed in these patent specifications have been confirmed to be effective in curl suppression, they have reached the level at which performances related to image quality, such as character quality and optical density, are expected. Turned out to have no difficulties. In addition, it has become clear that there is a problem that the color material moves to the pen tip portion of the marker when overwritten with the marker. In addition, when using special glossy paper for the purpose of so-called photographic image quality, there is a problem that the gloss difference between the image area and the non-image area of the formed image is large and the formed image looks unnatural. It became clear to do.
JP-A-6-157955 JP-A-5-208547 JP 2005-220296 A Japanese Patent Laid-Open No. 2005-220297 Japanese Patent Laid-Open No. 2005-220298

  The present invention has been made in view of the above problems, and its purpose is to provide excellent curling characteristics of a printed recording medium, excellent image quality, and color material that moves even when overwritten with a marker on a printed image. It is an object of the present invention to provide an ink-jet ink that can form a stable image and gives uniform gloss even when printed on glossy paper.

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

  1. In an inkjet ink that contains at least water, a water-soluble organic solvent, and a pigment, and the water content is 10% by mass or more and less than 50% by mass of the total ink, the SP value of the water-soluble organic solvent is 16.5. An inkjet comprising at least 30% by weight of a water-soluble organic solvent of less than 24.6 and dispersed with an alkali-soluble polymer dispersant neutralized with an organic base. For ink.

  2. 2. The inkjet ink according to 1, wherein the water-soluble organic solvent having an SP value of 16.5 or more and less than 24.6 has a vapor pressure at 25 ° C. of 0.01 Pa or more and 133 Pa or less.

3. 3. The inkjet ink according to 1 or 2, wherein the water content is 20% by mass or more and less than 40% by mass of the total ink.
4). The inkjet ink according to any one of 1 to 3, comprising 1.05 to 1.2 times equivalent of the organic base in an amount necessary for neutralizing the polymer dispersant.
5). The inkjet ink according to any one of 1 to 4, wherein the pH of the ink is 8.05 to 10.0.
6). The polymer dispersant is styrene, styrene derivative, vinyl naphthalene derivative, acrylic acid, acrylic acid derivative, methacrylic acid, methacrylic acid derivative, maleic acid, maleic acid derivative, itaconic acid, itaconic acid derivative, fumaric acid, fumaric acid derivative. The inkjet ink according to any one of 1 to 5, which is a polymer composed of a single monomer selected from the above or a copolymer composed of two or more monomers.
7). At least water, a water-soluble organic solvent, a pigment, a pigment dispersant comprising an alkali-soluble polymer dispersant, and an organic equivalent of 1.05 to 1.2 times the amount necessary to neutralize the polymer dispersant In an inkjet ink that contains a base and the water content is 20% by weight or more and less than 40% by weight of the total ink,
The ink has a pH of 8.05 to 10.0;
Among the water-soluble organic solvents, a water-soluble organic solvent having an SP value of 16.5 or more and less than 24.6 is contained by 30% by mass or more of the total ink, and
The polymer dispersant is styrene, styrene derivative, vinyl naphthalene derivative, acrylic acid, acrylic acid derivative, methacrylic acid, methacrylic acid derivative, maleic acid, maleic acid derivative, itaconic acid, itaconic acid derivative, fumaric acid, fumaric acid derivative. An ink-jet ink , which is a polymer comprising a single monomer selected from the above or a copolymer comprising two or more monomers .

  According to the present invention, a curled characteristic of a printed recording medium is excellent, a stable image in which a color material does not move even when overwritten with a marker on a printed image can be formed, and even when printed on glossy paper It is possible to provide an ink-jet ink that gives high glossiness.

  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 has at least water, a water-soluble organic solvent, and a pigment, and the water content is 10% by mass or more and less than 50% by mass of the total ink. In the water-soluble organic solvent, the water-soluble organic solvent having an SP value of 16.5 or more and less than 24.6 is 30% by mass or more of the total ink, and the pigment is neutralized with an organic base. Ink-jet ink, characterized by being dispersed with a polymer dispersant, excels in curling characteristics of the printed recording medium, further improves image quality, and allows the color material to move even when overwritten with a marker on the printed image As a result, the present inventors have found that an ink-jet ink that can form a stable image with no gloss and can provide uniform gloss even when printed on glossy paper is achieved.

  Hereinafter, the present invention will be described in detail.

  In the inkjet ink of the present invention, at least water, a water-soluble organic solvent and a pigment are contained, and the water content is 10% by mass or more and less than 50% by mass of the total amount of the water-soluble organic solvent. Among them, a water-soluble organic solvent having an SP value of 16.5 or more and less than 24.6 is contained by 30% by mass or more of the total ink, and the pigment is dispersed by an alkali-soluble polymer dispersant neutralized with an organic base. It is characterized by being.

  When the water content in all the inks is 50% by mass or more, curling and cockling are inferior. If it is less than 10% by mass, the dispersion stability of the pigment becomes poor even with other solvent compositions.

  The water content in all inks is more preferably 20% by mass or more and less than 40% by mass.

  The ink-jet ink of the present invention (hereinafter also simply referred to as ink) contains a water-soluble organic solvent having an SP value of 16.5 or more and less than 24.6 at 30% by mass or more of the total ink. When the addition amount is less than 30% by mass, curling and cockling during recording on plain paper become extremely large.

  If the SP value of the organic solvent is also less than 16.5, the compatibility with water is deteriorated and separation occurs. Conversely, an organic solvent having an SP value of 24.6 or more has an insufficient curl suppressing effect.

  The range of the SP value of the organic solvent is more preferably 16.5 or more and less than 22.5.

  The solvent solubility parameter (SP value) in the present invention is a value represented by the square root of the molecular cohesive energy. F. It can be calculated by the method described in Fedors, Polymer Engineering Science, 14, p147 (1974). The unit is (MPa) 1/2, and refers to the value at 25 ° C.

  Hereinafter, examples of water-soluble organic solvents having an SP value of 16.5 or more and less than 24.6 are shown together with the SP value. Needless to say, the present invention is not limited to this.

Ethylene glycol monomethyl ether (SP value: 24.5)
Ethylene glycol monoethyl ether (23.5)
Ethylene glycol monobutyl ether (22.1)
Ethylene glycol monoisopropyl ether (22.3)
Diethylene glycol monomethyl ether (23.0)
Diethylene glycol monoethyl ether (22.4)
Diethylene glycol monobutyl ether (21.5)
Diethylene glycol diethyl ether (16.8)
Triethylene glycol monomethyl ether (22.1)
Triethylene glycol monoethyl ether (21.7)
Triethylene glycol monobutyl ether (21.1)
Propylene glycol monomethyl ether (23.0)
Propylene glycol monophenyl ether (24.2)
Dipropylene glycol monomethyl ether (21.3)
Tripropylene glycol monomethyl ether (20.4)
1,3-dimethyl-2-imidazolidinone (21.8)
Further, among water-soluble organic solvents having an SP value of 16.5 or more and less than 24.6, a water-soluble organic solvent having a vapor pressure at 20 ° C. of 0.01 Pa or more and 133 Pa or less is contained by 30% by mass or more of the total ink. It is preferable to contain an organic solvent of 0.01 Pa or more and 66 Pa or less. Examples of water-soluble organic solvents corresponding to this include tripropylene glycol monomethyl ether (vapor pressure: 3.99 Pa), triethylene glycol monomethyl ether (less than 1.33 Pa), triethylene glycol monobutyl ether (less than 1.33 Pa) , Diethylene glycol monomethyl ether (24.00 Pa), diethylene glycol monoethyl ether (17.33 Pa), and the like.

  In the present invention, various water-soluble organic solvents can be used in combination with the water-soluble organic solvent.

  Examples of water-soluble organic solvents preferably used include alcohols (eg, methanol, ethanol, propanol, isopropanol, butanol, isobutanol, secondary butanol, tertiary butanol, pentanol, hexanol, cyclohexanol, benzyl alcohol, etc.), 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, 1,3 -Propanediol, 1,4-butanediol, 1,5-pentanediol, 1,2-pentanediol 1,2-hexanediol, 1,2,6-hexanetriol, etc.), amines (eg, ethanolamine, diethanolamine, triethanolamine, N-methyldiethanolamine, N-ethyldiethanolamine, morpholine, N-ethylmorpholine, ethylenediamine) , Diethylenediamine, triethylenetetramine, tetraethylenepentamine, polyethyleneimine, pentamethyldiethylenetriamine, tetramethylpropylenediamine, etc.), amides (eg, formamide, N, N-dimethylformamide, N, N-dimethylacetamide, etc.), Heterocycles (eg 2-pyrrolidone, N-methyl-2-pyrrolidone, cyclohexyl pyrrolidone, 2-oxazolidone etc.), sulfoxides (eg dimethyl sulfoxide) ), Sulfones (e.g., sulfolane), urea, acetonitrile, ketones (e.g., acetone, methyl ethyl ketone, etc.).

  Of the water-soluble organic solvents in the ink of the present invention, it is preferable to use an organic solvent that exhibits a maximum viscosity by mixing ratio when mixed with water, and water and the water-soluble at a ratio in the vicinity of the maximum. Mixing with an organic solvent is one of the more preferable aspects in terms of light output and decap. The vicinity mentioned here means within 10% above and below the ratio indicating the maximum when the total mass of water and the water-soluble organic solvent is 100%. For example, when the ratio of water to the organic solvent is 50:50 and indicates the maximum, 40:60 to 60:40 is set as the vicinity.

  Examples of the solvent that shows the maximum viscosity by the mixing ratio when mixed with water include ethylene glycol monoalkyl ethers (eg, ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol monobutyl ether), Diethylene glycol monoalkyl ethers (eg, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, diethylene glycol monobutyl ether, etc.), triethylene glycol monoalkyl ethers (eg, triethylene glycol monomethyl ether, triethylene glycol monoethyl ether, triethylene glycol monoethyl ether) Butyl ether), propylene glycol monoalkyl ethers (eg, propylene glycol) Coal monomethyl ether, propylene glycol monoethyl ether, propylene glycol monobutyl ether, etc.), dipropylene recall monoalkyl ethers (eg, dipropylene glycol monomethyl ether, dipropylene glycol monoethyl ether, dipropylene glycol monobutyl ether, etc.), tripropylene Recall monoalkyl ethers (for example, tripropylene glycol monomethyl ether, tripropylene glycol monoethyl ether, tripropylene glycol monobutyl ether) and the like, preferably dialkylene glycol monoalkyl ethers or trialkylene glycol monoalkyl Ethers.

  As the pigment 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 insoluble pigment is not particularly limited, for example, azo, azomethine, methine, diphenylmethane, triphenylmethane, quinacridone, anthraquinone, perylene, indigo, quinophthalone, isoindolinone, isoindoline, azine, oxazine, thiazine, 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. Pigment red 202, C.I. I. Pigment red 222, C.I. I. Pigment violet 19 and the like.

  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. Pigment yellow 138, C.I. I. And CI Pigment Yellow 150.

  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 15: 4, C.I. I. Pigment blue 15: 6, C.I. I. Pigment blue 16, C.I. I. Pigment blue 60, C.I. I. And CI Pigment Green 7.

  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 dispersed state of the pigment contained in the ink of the present invention is preferably 50 nm or more and less than 200 nm. If the average particle diameter 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 recording liquid 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 various desired purposes. As the disperser, a conventionally known ball mill, sand mill, line mill, high-pressure homogenizer, or the like can be used. In particular, the particle size distribution of the ink produced by dispersion with a sand mill is sharp and preferable. 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. Furthermore, the bead diameter is preferably 0.3 to 3 mm.

  In the present invention, the pigment is dispersed by an alkali-soluble polymer dispersant neutralized with an organic base.

  Neutralizing the pigment dispersant with an organic base is a well-known technique. By using an organic base, dispersion stability can be improved, and by using a volatile amine compound, the amine volatilizes after printing and drying, and the dispersant becomes insoluble. It is known to have.

  In the study leading to the present invention, the present inventors examined the use of an organic base for the purpose of improving the dispersion stability. Certainly, although some improvement was observed, a notable effect was not obtained, and the expected known effect was not obtained.

  On the other hand, it has been found from the above examination that the neutralizing agent of the dispersant greatly affects the performance such as image quality, for example, character quality and optical density. It has also been clarified that the neutralizing agent of the dispersant affects the phenomenon that the color material moves to the pen tip portion of the marker when overwritten with the marker. In addition, it has been found that the glossiness when printed on glossy paper is also affected, causing a large difference in glossiness between the image area and the non-image area, resulting in an unnatural image. .

  In the solvent composition that is the feature of the present invention, these performances are inferior to inorganic bases as neutralizers, but it is found that organic bases can be greatly improved by using organic bases as neutralizers and give superior performances. did.

  The reason for this is not out of the scope of estimation, but is considered as follows. In the so-called plain paper, which is considered as a main recording medium in the present invention, a material having a water-repellent action called a sizing agent is internally added, and thereby designed to suppress excessive penetration of water-based ink. Has been. In the present invention, the hydrophobicity of the pigment dispersant increases by using an organic base as a neutralizing agent for the dispersant. By adsorbing such a dispersant on the surface, the hydrophobicity of the pigment itself, which is a coloring material, is also increased. For this reason, the pigment interacts with the sizing agent in the plain paper, particularly near the surface, so that it does not easily penetrate into the inside, giving sharp characters and high optical density. For the same reason, the coloring material is sufficiently fixed on the paper surface, and it is considered that a stable image can be formed without moving the coloring material to the pen tip of the marker even when the marker is used.

  Furthermore, when so-called photo-quality glossy paper is used, when an inorganic base is used as a neutralizing agent, the exchange neutralization reaction between the mordant and the neutralizing agent in the glossy paper proceeds rapidly, so that the pigment particles Gloss is deteriorated because they are randomly aggregated. On the other hand, by using an organic base as a neutralizing agent, the exchange neutralization reaction with the mordant proceeds slowly, so that the pigment particles can be orderedly aggregated, the smoothness of the image surface is improved, and excellent gloss is achieved. I think that it shows.

  Examples of these polymer dispersants 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, fumaric acid. , A polymer composed of a single monomer selected from fumaric acid derivatives, or a copolymer composed of two or more monomers and salts thereof (hereinafter abbreviated as acrylic polymer). To do). Further, a polyester derivative formed from a polyvalent carboxylic acid and a polyhydric alcohol, and a polyurethane / polyurea derivative formed from a polyvalent isocyanate and a polyhydric alcohol / polyamine are also included. Furthermore, water-soluble polymer dispersants such as polyvinyl alcohol, polyvinyl pyrrolidone, cellulose derivatives, gelatin, and polyethylene glycol can also be used.

  As these polymer dispersants, acrylic polymer dispersants are preferably used from the viewpoints of easy molecular structure design and easy performance as a dispersant.

  Of the acrylic polymer dispersants, a polymer dispersant containing at least 30 mol% of an acrylic monomer is preferable. Moreover, it is preferable to have both the hydrophobic partial structure which controls the adsorption | suction to the pigment surface, and the hydrophilic partial structure which controls the stability in a solvent. Such a polymer dispersant can be synthesized by copolymerization of a hydrophobic monomer and a hydrophilic monomer.

  Examples of the hydrophobic monomer include styrene, α-methylstyrene, vinyl naphthalene, phenyl methacrylate, p-tolyl methacrylate, 2-phenoxyethyl methacrylate, benzyl methacrylate, lauryl methacrylate (LMA), stearyl methacrylate (SMA), 2-octyldodecyl methacrylate, behenyl methacrylate, phenyl acrylate, p-tolyl acrylate, 2-phenoxyethyl acrylate, benzyl acrylate, lauryl acrylate, stearyl acrylate (SA), 2-octyldodecyl acrylate, behenyl acrylate, methyl methacrylate (MMA), Ethyl methacrylate (EMA), propyl methacrylate, n-butyl methacrylate (BMA), hexyl Tacrylate, 2-ethylhexyl methacrylate (EHMA), octyl methacrylate, hydroxylethyl methacrylate (HEMA), hydroxypropyl methacrylate, 2-ethoxyethyl methacrylate, methacrylonitrile, 2-trimethylsiloxyethyl methacrylate, glycidyl methacrylate (GMA), methyl acrylate, Examples include, but are not limited to, ethyl acrylate, propyl acrylate, butyl acrylate, hexyl acrylate, 2-ethylhexyl acrylate, octyl acrylate, hydroxyethyl acrylate, hydroxypropyl acrylate, acrylonitrile, 2-trimethylsiloxyethyl acrylate, and glycidyl acrylate. It is not a thing.

  Examples of the hydrophilic monomer include methacrylic acid (MAA), acrylic acid (AA), maleic acid, dimethylaminoethyl methacrylate (DMAEMA), diethylaminoethyl methacrylate, 3-butylaminoethyl methacrylate, dimethylaminoethyl acrylate. , Diethylaminoethyl acrylate, dimethylaminopropyl methacrylamide, methacrylamide, acrylamide, dimethylacrylamide and the like, but are not limited thereto. The hydrophilic monomer is preferably methacrylic acid, acrylic acid or dimethylaminoethyl methacrylate.

  Polymers containing acids can be produced directly from unsaturated acids or from blocked monomers with blocking groups that can be removed after polymerization. Examples of blocked monomers that yield acrylic acid or methacrylic acid after removal of the blocking group include trimethylsilyl methacrylate (TMS-MAA), trimethylsilyl acrylate, 1-butoxyethyl methacrylate, 1-ethoxyethyl methacrylate, 1-butoxyethyl Examples include acrylate, 1-ethoxyethyl acrylate, 2-tetrahydropyranyl acrylate, and 2-tetrahydropyranyl methacrylate.

  Examples of the structure of these polymers include random polymers, random copolymers, block copolymers, branched polymers or copolymers, graft polymers, and copolymers. Among these, block copolymers and branched copolymers have the advantage that the hydrophilic portion and the hydrophobic portion can be easily designed and controlled.

  Examples of the block polymer include AB, BAB, and ABC type structures (here, A, B, and C schematically indicate polymer blocks having different structures from each other), but there is a block portion. If there is, there is no structural restriction. In particular, a block polymer having a hydrophobic block and a hydrophilic block, and having a balanced block size that contributes to dispersion stability is preferable. Functional groups can be incorporated into the hydrophobic block (the block to which the colorant is attached), thereby enhancing the specific interaction between the dispersant and the pigment to improve dispersion stability.

  These polymers can be synthesized by a conventionally known method. For example, US Pat. Nos. 5,085,698, 5,221,334, 5,272,201, Nos. 519,085 and 6,117,921, JP-A-10-279873, JP-A-11-269418, JP-A-2001-115065, 2001-13949, 2001-247796, It can be synthesized by the methods disclosed in JP-A-2003-260348, particularly in the examples.

  As a monomer which can be used for a block copolymer, the monomer similar to the monomer which can be used for the said acrylic polymer dispersing agent can be mentioned, for example.

  As the monomer that can be used in the branched polymer or copolymer, and the graft polymer or copolymer, those listed as monomers that can be used in the acrylic polymer dispersant are used. be able to. In addition, a macromer having a polymerizable functional group at one end, for example, a silicone macromer, a styrenic macromer, a polyester macromer, a polyurethane macromer, a polymer or copolymer easily branched by using a polyalkyl ether macromer, and a graft A polymer or copolymer can be synthesized. Examples of the macromer include styrene macromers AS-6 and AN-6 manufactured by Toagosei, silicone macromers FM-0711 and FM-0721 manufactured by Chisso, polyethylene glycol acrylate, polyethylene glycol methacrylate, and the like.

  These polymers preferably have a weight average molecular weight in the range of 1,000 to 100,000, and more preferably in the range of 2,500 to 50,000. The acid value is preferably in the range of 10 to 500, and more preferably in the range of 50 to 250.

  In the present invention, these polymers are characterized by being neutralized with an organic base. Examples of the organic base include general organic bases such as alkanolamines (ethanolamine, monomethylethanolamine, monoethylethanolamine, dimethylaminoethanol, diethylaminoethanol, triethanolamine, propanolamine, etc. ), Amino acid esters (glycine methyl ester, alanine ethyl ester, etc.), alkylamines (diethylamine, triethylamine, 2,2,2-diazabicyclooctane, etc.), anilines (dimethylaniline, diethylaniline, etc.) , Heterocyclic amines (imidazole, pyridine, pyrrole, 1,4-diazabicyclo [2.2.2] octane, 1,8-diazabicyclo [5.4.0] -7-undecene, etc.), hydroxylated quaternary Ammonium salt La methyl ammonium hydroxide, tetrabutyl hydroxide, etc.), and the like.

  The amount of these organic bases added is preferably not less than the amount (equivalent) required to neutralize the polymer, and more preferably 1.05 to 1.2 times the equivalent.

  In the present invention, these polymers are characterized by alkali solubility. Here, the alkali-soluble means that the polymer and the neutralizing agent are 1% by mass as a neutralized polymer in a mixed solvent of tripropylene glycol monomethyl ether and water (mixing ratio = 70: 30). When it is added, it means that it dissolves completely.

  In the ink of the present invention, together with the above polymer dispersant, known pigment dispersants such as higher fatty acid salts, alkyl sulfates, alkyl ester sulfates, alkyl sulfonates, sulfosuccinates, naphthalene sulfonates, alkyls. Combined use of surfactants such as phosphate, polyoxyalkylene alkyl ether phosphate, polyoxyalkylene alkyl phenyl ether, polyoxyethylene polyoxypropylene glycol, glycerin ester, sorbitan ester, polyoxyethylene fatty acid amide, amine oxide It does not prevent.

  Next, each component of the ink of the present invention other than those described above will be described.

  The pH of the ink of the present invention is preferably 7.0 or more, more preferably 8.05 to 10.0. By setting the above pH, the emission stability is good and the concentration is high. It is preferable from the viewpoint that an image having a preferable gloss can be obtained.

  Examples of the pH adjuster used in the ink of the present invention include various organic amines such as monoethanolamine, diethanolamine, and triethanolamine, alkali metal hydroxides such as sodium hydroxide, lithium hydroxide, and potassium hydroxide. Inorganic alkali agents, organic acids, and mineral acids.

  The surface tension of the ink of the present invention is preferably 25 to 50 mN / m at 25 ° C. More preferably, it is 25-40 mN / m, More preferably, it is 25-35 mN / m. When the surface tension of the ink is less than 25 mN / m, the absorption speed to the recording medium is increased, causing aggregation due to the pigment particles, resulting in the occurrence of bronzing, reduction in gloss and abrasion resistance. On the other hand, when the surface tension of the ink exceeds 50 mN / m, the ink droplets that have landed on the recording medium cause color turbidity due to staying for a long time, and a high-definition image cannot be obtained.

The surface tension referred to in the present invention can be adjusted to a desired surface tension by appropriately adjusting the type and addition amount using, for example, various water-soluble organic solvents and the following various surfactants. The method for measuring tension is described in general interface chemistry and colloid chemistry reference books. For example, New Experimental Chemistry Course Vol. 18 (Interface and Colloid), edited by The Chemical Society of Japan, published by Maruzen Co., Ltd. : P. 68-117 can be referred to, and specifically, it can be determined by using a ring method (Dunoi method) or a vertical plate method (Wilhelmy method).

  Various surfactants can be used as one means for achieving the surface tension. Each surfactant that can be used in the present invention is not particularly limited, and examples thereof include anionic surfactants such as dialkyl sulfosuccinates, alkyl naphthalene sulfonates, fatty acid salts, polyoxyethylene alkyl ethers, polyoxy Nonionic surfactants such as ethylene alkylallyl ethers, acetylene glycols, polyoxyethylene / polyoxypropylene block copolymers, and cationic surfactants such as alkylamine salts and quaternary ammonium salts. In particular, an anionic surfactant and a nonionic surfactant can be preferably used.

  In the present invention, an acetylene-based surfactant is used as the surfactant from the viewpoint of obtaining an image having good emission stability, favorable gloss at a high concentration, and excellent uniformity. preferable.

  The acetylene surfactant is not particularly limited, and examples thereof include acetylene glycols and acetylene alcohols. More preferable are surfactants having an acetylene group and an alkylene oxide chain. Nord 465 (manufactured by Nissin Chemical Industry Co., Ltd.) can be mentioned.

  In the ink of the present invention, the ink viscosity is preferably 1 to 40 mPa · s at 25 ° C., more preferably 5 to 40 mPa · s, and further preferably 5 to 15 mPa · s. Further, in the ink according to the present invention, the dissolved oxygen concentration in the ink is preferably 2 ppm or less at 25 ° C. By using this dissolved oxygen concentration condition, the formation of bubbles can be suppressed, and in high-speed printing. In addition, an ink jet recording method having excellent emission stability 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).

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

  By setting the content of the polyvalent metal ions in the 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.

  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 a viscosity modifier, a specific resistance modifier, a film forming agent, an ultraviolet absorber, an antioxidant, a fading inhibitor, an antifungal agent, a rust inhibitor, etc. can be appropriately selected and used. Oil droplets such as liquid paraffin, dioctyl phthalate, tricresyl phosphate, silicon oil, ultraviolet absorbers described in JP-A-57-74193, JP-A-57-87988, and JP-A-62-261476, JP-A-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-59-42993, JP-A-59-52689, JP-A-62-280069, JP-A-61-228771, JP-A-4-219266, etc. be able to.

  In the image forming method using the ink of the present invention, for example, an ink jet print is obtained by ejecting ink as droplets from an ink jet recording head based on a digital signal and adhering to a recording medium by an ink jet printer loaded with the ink. It is done.

  When an image is formed by ejecting the ink of the present invention, the ink jet recording head used may be an on-demand system or a continuous system. In addition, 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, a thermal type) Any discharge method such as an ink jet type or a bubble jet (registered trademark) type may be used.

  Among them, when using the ink of the present invention, recording is performed on a recording medium by discharging from a piezo-type ink jet recording head having a nozzle diameter of 30 μm or less, and further, a line head system having a nozzle diameter of 30 μm or less. It is preferable to perform recording on a recording medium by ejecting from a piezo-type inkjet recording head, and to record an image on a recording medium at a printing speed of 20 ppm or more using a piezo-type inkjet recording head having a nozzle diameter of 30 μm or less. .

  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 the droplets land on the recording medium.

  In addition, the ink of the present invention has characteristics excellent in emission stability and decap resistance, has excellent characteristics in high-speed printing, and is preferably printed at a high speed of 20 ppm or more as a printing speed, More preferably, it is 20-100 ppm, More preferably, it is 25-50 ppm. In the present invention, ppm refers to the number of pages printed per minute (Page Per Minute) on an A4 size recording medium.

  The recording medium used for the ink of the present invention can be used without limitation as long as it has the absorptivity and retentivity of the ink to be printed. For example, it can be used on a non-absorbent support or an absorbent support. Ink jet recording media provided with an ink absorbing layer that absorbs and retains ink, and paper supports such as coated paper and non-coated paper can be used, but image printing is performed using plain paper as the recording medium. However, this is preferable from the viewpoint of obtaining the effect of preventing the show-through and high quality image according to the present invention.

  Such plain paper 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, nalite, 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 improving the penetration of the ink of the present invention and the fixability of the colorant.

  The water-soluble polyvalent metal salt that can be used in the present invention is not particularly limited. For example, aluminum, calcium, magnesium, zinc, iron, strontium, barium, nickel, copper, scandium, gallium, indium, titanium, Metal salts such as zirconium, tin, and lead, sulfates, nitrates, formates, succinates, malonates, chloroacetates, and p-toluenesulfonates are added as salts. 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.

  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.

Examples Preparation of polymer dispersant
Monomers were mixed at the following composition ratio, and polymer dispersants 1 to 5 were synthesized by solution polymerization.

(Polymer dispersant 1)
Acrylic acid / methyl acrylate / styrene = 30/38/32 (mass ratio) (average molecular weight 20,000, acid value 230)
(Polymer dispersant 2)
Acrylic acid / methyl acrylate / stearyl acrylate = 30/34/36 (mass ratio) (average molecular weight 12,000, acid value 230)
(Polymer dispersant 3)
Acrylic acid / methyl acrylate / 2-hydroxyethyl methacrylate / 2-ethylhexyl methacrylate = 20/25/40/15 (mass ratio) (average molecular weight 13,000, acid value 150)
(Polymer dispersant 4)
Methacrylic acid / 2-hydroxyethyl methacrylate / styrene = 12/30/58 (mass ratio) (average molecular weight 22,000, acid value 70)
(Polymer dispersant 5)
Acrylic acid / styrene / α-methylstyrene = 40/25/35 (mass ratio) (average molecular weight 9,500, acid value 200)
(Evaluation of neutralization and solubility of neutralized polymer dispersant)
After completion of the reaction, the reaction solvent was removed under reduced pressure, and triethylene glycol monobutyl ether was added to the residue to obtain a solution having a solid content ratio of 20%. Next, it neutralized with the neutralizing agent shown in Table 1, and the neutralized polymer dispersing agents 1-5 were prepared from the solution containing the polymer dispersing agents 1-5, respectively. The solubility of the neutralized polymer dispersant was visually evaluated according to the following criteria. The neutralizing agent was added in an amount 1.1 times the equivalent of the polymer dispersant.

<Solubility>
○: The solution is clear and no turbidity is observed. Δ: Although it is slightly turbid, it is almost clear. ×: The solution is white turbid.

  The evaluation results are shown in Table 1.

  The details of the neutralizing agents described in abbreviated names in Table 1 are as follows.

<Inorganic base>
NaOH: Sodium hydroxide KOH: Potassium hydroxide <Organic base>
DMAE: Dimethylaminoethanol TEA: Triethanolamine TBAOH: Tetra-n-butylammonium hydroxide DABCO: 1,4-diazabicyclo [2.2.2] octane ImH: Imidazole (Preparation of pigment dispersions 1 to 17)
A horizontal bead mill (system zeta mini manufactured by Ashizawa) filled with 60% by volume of zirconia beads having a diameter of 0.5 mm by mixing the dispersion solvent and the pigment in the ratio shown in Table 2 using the prepared neutralized polymer dispersant. Then, the zirconia beads were removed to obtain pigment dispersions 1 to 17.

  The details of each additive described in Table 2 with the abbreviations are as follows.

<Water-soluble organic solvent>
DPGmME: Dipropylene glycol monomethyl ether TEGmBE: Triethylene glycol monobutyl ether 1,3-BDO: 1,3-butanediol t-BuOH: Tertiary butanol DEG: Diethylene glycol <Vapor pressure, viscosity, and SP value of each solvent alone >
DPGmME: Viscosity = 3.3 mPa · s, Vapor pressure = 53 Pa, SP value = 20.4
TEGmBE: Viscosity = 9.9 mPa · s, Vapor pressure <1.3 Pa, SP value = 23.0
1,3-BDO: Viscosity = 98 mPa · s, vapor pressure = 8 Pa, SP value = 30.3
t-BuOH: Viscosity = 3.6 mPa · s, Vapor pressure = 4080 Pa, SP value = 22.3
DEG: Viscosity = 30 mPa · s, vapor pressure <1.3 Pa, SP value = 27.1
Water: Viscosity = 0.87 mPa · s, Vapor pressure = 3.16 kPa
The above characteristic values are all values at 25 ° C.

<Pigment>
Y: C.I. I. Pigment Yellow 139
C: C.I. I. Pigment Blue 15: 3
M: C.I. I. Pigment Red 122
K: Carbon black << Preparation of ink >>
[Preparation of inks 1 to 17]
Ink 1 to 17 were prepared by adding a water-soluble organic solvent and water to the prepared pigment dispersion so as to have the addition amounts shown in Table 3, followed by degassing treatment under reduced pressure.

<Viscosity characteristics of solvent and water mixed solvent>
For the solvent set of the water-soluble organic solvent and water, a solvent was prepared by changing the mixing ratio by 10% by mass from 100: 0 to 0: 100, with the water-soluble organic solvent: water, The viscosity was measured. The obtained results are as follows.

  DPGmME / water solvent composition: DPGmME: Water showed a maximum viscosity (6.2 mPa · s) under a mixing condition of 80:20.

  TEGmBE / water solvent composition: TEGmBE: Water showed a maximum viscosity (9.8 mPa · s) under a mixing condition of 80:20.

  Viscosity increased monotonically as the ratio of 1,3-BDO / water solvent composition: 1,3-BDO increased. Under a mixing condition of 1,3-BDO / water of 60:40, the viscosity was 11.1 mPa · s.

  Solvent composition of t-BuOH / water: The maximum viscosity (4.0 mPa · s) was exhibited under a mixing condition of 60:40 of t-BuOH: water.

  As the ratio of DEG / water solvent composition: DEG increased, the viscosity increased monotonically. Under a mixing condition of DEG / water of 60:40, the viscosity was 6.6 mPa · s.

<Evaluation of ink>
[Evaluation of formed image]
(Evaluation of curl characteristics after printing)
Ten share mode piezo-type recording heads having a nozzle diameter of 25 μm, a discharge ink droplet amount of 4 pl, and a number of nozzles of 256 are arranged in parallel in the width direction of the recording medium, and the nozzle resolution per color is 1440 dpi In this case, dpi represents the number of dots per 2.54 cm), and a line head type ink jet printer having a total number of nozzles of 2560 was used. Each ink prepared above was loaded into this ink jet printer, and the droplet speed was 8 m / sec. The drive voltage of the recording head was adjusted so that the ink droplet amount was 4 pl.

  Next, A4 size Konica Minolta Business Technology business class plain paper is used as the recording medium, and the short side length of A size in the transport direction is 10 ppm in an environment of 23 ° C. and 30% RH. A solid image of 200 mm × 280 mm was printed at a resolution of 1440 dpi × 1440 dpi at a printing speed of 1 (speed of printing 10 sheets of A4 size plain paper per minute). The printed plain paper was then allowed to stand for 1 week on a flat surface in an environment of 23 ° C. and 20% RH for 1 week, and then the heights of the four corners were measured. For the negative curl sample with the central part floating upside down, the sample was allowed to stand for another day after being turned upside down. The raised heights of the four corners were measured as described above, and the curl characteristics were evaluated according to the following criteria.

A: Almost flat, even at the most floating part at the four corners, the lifting height is less than 5 mm. O: The lifting height at the most floating part at the four corners is 5 mm or more and less than 10 mm. Δ: Most floating at the four corners. The height of the raised portion is 10 mm or more and less than 20 mm. X: The height of the raised portion of the most floating portion at the four corners is 20 mm or more, or it is rounded into a cylindrical shape and cannot be measured (evaluation of character quality).
Using the above method, the characters “Mouth, Fourth, Day, Time, Cause, Hard, Country, Eye, Figure, Country” are printed in 4 and 6 point MS Mincho style with a recording resolution of 1440 × 1440 dpi. The printed character image was visually observed, and character quality was evaluated according to the following evaluation criteria.

◎: All 4-point character images are clearly recorded in detail ○: 4-point character images can be read △: 4-point character images are difficult to read, but 6-point character images are read Possible x: It is difficult to interpret a character image of 6 points (evaluation of optical density)
By the above method, a solid image of 50 mm × 50 mm was printed at a resolution of 1440 dpi × 1440 dpi. The obtained image was subjected to density measurement using an optical densitometer (X-Rite 938 manufactured by X-Rite), and the maximum reflection density value was measured. The reflection density (reflectance coefficient density) was evaluated according to the following criteria.

◎: Concentration value is 1.0 or more ○: Concentration value is 0.9 or more and less than 1.0 △: Concentration value is 0.8 or more and less than 0.9 ×: Concentration value is less than 0.8 (marker resistance Evaluation)
According to the above method, the recording resolution is 1440 x 1440 dpi and the 4 characters, 6 points, and 8 points of MS Mincho in the Chinese character "mouth, fourth, day, times, cause, trouble, solid, country, eye, figure, country" Printed characters. This printed plain paper is left on a flat table in an environment of 23 ° C. and 20% RH for 1 hour with the printed surface facing up, then traced over the characters using a commercially available fluorescent marker, and the subsequent character image The marker resistance was evaluated according to the following evaluation criteria.

◎: No change in image is recognized ○: No change in image is observed, but transfer of the color material to the pen tip of the marker can be confirmed △: The image density of the rubbed portion is reduced and the outline of the character is also Although it is smudged, there is no practical problem. X: The image density of the rubbed portion is reduced, and it is difficult to interpret the 4-point character image. Furthermore, the color material on the marker's pen tip has been greatly transferred (evaluation of gloss uniformity)
A solid image of 50 mm × 50 mm was printed at a resolution of 1440 dpi × 1440 dpi in the same manner except that a thick glossy inkjet photographic paper manufactured by Konica Minolta Photo Imaging was used as the recording medium. About the obtained image, the gloss difference with an unprinted part was evaluated visually according to the following reference | standard.

◎: The entire surface has a uniform and high gloss feeling, and there is almost no difference in gloss between the printed and unprinted portions. ○: The entire surface has a uniform and high gloss feeling, but between the printed and unprinted portions. A slight difference in gloss is observed. Δ: A difference in gloss between the printed part and the unprinted part can be recognized, but there is no problem in practical use. X: There is a significantly large difference in gloss. Table 4 shows the evaluation results obtained as described above. .

  As is apparent from the results shown in Table 4, when an inorganic base was used as the neutralizing agent, curl was good, but the character quality, optical density, marker resistance, and gloss uniformity were inferior. Even if the neutralized dispersant is alkali-soluble, good results were not obtained when an inorganic base was used.

  Even when the dispersant of the range of the present invention was used, good results were not obtained when the SP value of the solvent was out of the range.

  On the other hand, when a solvent having an SP value defined in the present invention is used and a dispersant that is neutralized with an organic base and further soluble in alkali is used, good character quality, optical density, marker resistance, and gloss uniformity It turns out that sex is obtained.

Claims (7)

In an inkjet ink containing at least water, a water-soluble organic solvent, and a pigment, and the water content is 10% by mass or more and less than 50% by mass of the total ink,
Among these water-soluble organic solvents, an alkali-soluble polymer comprising a water-soluble organic solvent having an SP value of 16.5 or more and less than 24.6% by mass or more based on the total amount of ink, and wherein the pigment is neutralized with an organic base An inkjet ink, characterized by being dispersed by a dispersant.   The inkjet ink according to claim 1, wherein the water-soluble organic solvent having an SP value of 16.5 or more and less than 24.6 has a vapor pressure at 25 ° C of 0.01 Pa or more and 133 Pa or less. The inkjet ink according to claim 1 or 2, wherein the water content is 20 mass% or more and less than 40 mass% of the total ink. The inkjet ink according to any one of claims 1 to 3, comprising 1.05 to 1.2 equivalents of the organic base in an amount necessary to neutralize the polymer dispersant. The inkjet ink according to any one of claims 1 to 4, wherein the pH of the ink is 8.05 to 10.0. The polymer dispersant is styrene, styrene derivative, vinyl naphthalene derivative, acrylic acid, acrylic acid derivative, methacrylic acid, methacrylic acid derivative, maleic acid, maleic acid derivative, itaconic acid, itaconic acid derivative, fumaric acid, fumaric acid derivative. The inkjet ink according to any one of claims 1 to 5, which is a polymer composed of a single monomer selected from the above or a copolymer composed of two or more monomers. At least water, a water-soluble organic solvent, a pigment, a pigment dispersant comprising an alkali-soluble polymer dispersant, and an organic equivalent of 1.05 to 1.2 times the amount necessary to neutralize the polymer dispersant In an inkjet ink that contains a base and the water content is 20% by weight or more and less than 40% by weight of the total ink,
The ink has a pH of 8.05 to 10.0;
Among the water-soluble organic solvents, a water-soluble organic solvent having an SP value of 16.5 or more and less than 24.6 is contained by 30% by mass or more of the total ink, and
The polymer dispersant is styrene, styrene derivative, vinyl naphthalene derivative, acrylic acid, acrylic acid derivative, methacrylic acid, methacrylic acid derivative, maleic acid, maleic acid derivative, itaconic acid, itaconic acid derivative, fumaric acid, fumaric acid derivative. An ink-jet ink , which is a polymer comprising a single monomer selected from the above or a copolymer comprising two or more monomers .