JP2009280671A - Inkjet ink and inkjet recording method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an inkjet ink which is satisfactory in ejecting property and can prevent bleeding, beading, feathering and a strike-through phenomenon on a printing paper or a regular paper, and to provide an inkjet recording method. <P>SOLUTION: The inkjet ink includes a coloring material, water and a water-soluble solvent, wherein the ink includes at least an aqueous gelling agent containing a carboxylic acid or its salt having a molecular weight of not more than 1,000. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention is an inkjet ink that gives an image without beading or color bleed to a medium having good feathering and back-through resistance during recording on plain paper, low ink absorbability, or non-ink absorbability, The present invention also relates to an ink jet recording method.

  In recent years, inkjet recording methods are capable of recording high-definition images with a relatively simple apparatus, and have been rapidly developed in various fields. In addition, there are various uses, and a recording medium or ink suitable for each purpose is used. In particular, in recent years, the recording speed has been greatly improved, and printers having performance capable of withstanding light printing applications have been developed.

  Therefore, the demand for printing on printing paper, particularly plain paper, is still high in the light printing field, and there is a high demand for high-speed inkjet recording and clear printing of characters.

  However, as a problem of ink jet recording in the printing field, since only a relatively low viscosity ink can be emitted from the ink jet head, when recording on printing paper with low ink absorbency, the color changes between different colors. A phenomenon called bleed that mixes, and a phenomenon called beading in which the shade of the color looks like a bead between colors occurs, causing the image quality to deteriorate. In addition, when recording on plain paper with a high ink absorption speed, a phenomenon called feathering, in which irregular bleeding occurs along the fibers of the paper, occurs, as well as a phenomenon that the ink penetrates to the back side. However, even plain paper is a major cause of image quality degradation.

  In order to prevent this, various methods have been proposed. Among them, the ink has temperature sensitivity, and a difference between the temperature of the inkjet head and the temperature of the recording medium provides a low viscosity at the time of emission. Thus, there is an attempt of a temperature-sensitive thickening type water-based ink that attempts to prevent bleeding, beading, and feathering while ensuring high emissivity when landing on a recording medium.

  For example, Patent Document 1 proposes a temperature-sensitive thickening type water-based ink containing a high-molecular substance that is thermoreversibly converted to a temperature-sensitive gel at a transition temperature or higher and becomes water-insoluble by drying. However, if a large change in viscosity is expected, the molecular weight of the temperature-sensitive thickening polymer also increases, causing problems in light-emitting properties such as clogging of the head, and has not been put into practical use.

On the other hand, Patent Document 2 discloses a water-based inkjet ink containing, as an aqueous gelling agent, a dialkyl piperazine dione compound, a compound having two or more ureido bonds, such as a compound having a low molecular weight and reversibly sol-gel-transferred by temperature. ing. However, since the disclosed compound is nonionic, it has solubility only in an ink having a low water content, and application to an ink having a high water content has been difficult.
JP 09-012947 A JP 2005-330309 A

  The present invention has been made in view of the above-mentioned problems, and an object of the present invention is to have good emission properties and prevent bleeding, beading, feathering, and back-through with respect to printing paper and plain paper. An inkjet ink and an inkjet recording method are provided.

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

  1. An ink-jet ink comprising a coloring material, water, and a water-soluble solvent, comprising at least an aqueous gelling agent containing a carboxylic acid having a molecular weight of 1000 or less or a salt thereof.

  2. 2. The inkjet ink as described in 1 above, wherein the aqueous gelling agent is a compound represented by the following general formula (1) or general formula (2).

(Wherein R ¹ : alkyl, alkoxy, alkylamino, alkenyl, alkenyloxy, alkenylamino R ² , R ⁴ , R ⁵ , R ⁶ : alkylene X, Y: hydrogen atom, monovalent metal cation, ammonium ion, organic Ammonium ion Y ¹ , Y ² , Y ³ : represents a hydrogen atom or alkylamide, alkenylamide, alkylcarbamoyl, alkenylcarbamoyl)
3. 3. The inkjet ink as described in 1 or 2 above, wherein the content of the aqueous gelling agent with respect to the total amount of the ink is 0.5% by mass or more and 20% by mass or less.

  4). 4. The inkjet ink according to any one of 1 to 3, wherein the colorant contains a pigment.

  5). 5. The inkjet ink according to any one of 1 to 4, wherein the inkjet ink reversibly undergoes a sol-gel phase transition depending on temperature.

  6). 6. The inkjet ink as described in 5 above, wherein the temperature at which the sol-gel phase transition of the inkjet ink is 30 ° C. or more and less than 80 ° C.

  7. An inkjet recording method for recording on a recording medium using the inkjet ink according to any one of 1 to 6, wherein a recording head is heated.

  8). An inkjet recording method for recording on a recording medium using the inkjet ink according to any one of 1 to 6, wherein the recording head is a line head.

  INDUSTRIAL APPLICABILITY According to the present invention, it is possible to provide an ink jet ink and an ink jet recording method that have good light emission properties and can prevent bleeding, beading, feathering, and back-through with respect to printing paper and plain paper.

  The best mode for carrying out the present invention will be described in detail below, but the present invention is not limited thereto.

  The inkjet ink of the present invention (hereinafter also simply referred to as ink) is an aqueous gelling agent containing at least a carboxylic acid having a molecular weight of 1000 or less or a salt thereof in an inkjet ink containing a coloring material, water and a water-soluble solvent. It is characterized by containing.

  As a result of intensive studies in view of the above problems, the present inventors have included a specific aqueous gelling agent that undergoes a sol-gel phase transition reversibly depending on temperature. As a result, the present inventors have found that an inkjet ink can be prepared that prevents bleeding, beading, feathering, and back-through from printing paper and plain paper.

  Hereinafter, the present invention will be described in detail.

<Aqueous gelling agent>
The aqueous gelling agent as used in the present application is a so-called low molecular weight compound having a molecular weight of 1000 or less, reversibly changes sol-gel with temperature change, and is 0.5 mass at 80 ° C. in an inkjet ink containing 50% or more of water. % Or more soluble.

  Specific examples of the aqueous gelling agent include Eur. J. et al. Org. Chem. 2005, 3615-3631, among which, in the present invention, at least one carboxylic acid or a salt thereof is bonded in the molecule.

  The aqueous gelling agent used in the present invention is preferably a compound represented by the general formulas (1) and (2), and further has a structure described in the following general formulas (3) and (4). It is preferable.

Here, R ¹ is a C1 to C22 alkyl group (methyl group, ethyl group, propyl group, n-butyl group, i-butyl group, hexyl group, octyl group, decyl group, dodecyl group, hexadecyl group, octadecyl group). Etc.), C1 to C22 alkoxy groups (methoxy group, ethoxy group, propoxy group, n-butoxy group, hexaoxy group, octaoxy group, denyloxy group, dodecyloxy group, hexadecyloxy group, etc.), C1 to C22 alkyl group Amino group (methylamino group, ethylamino group, propylamino group, n-butylamino group, i-butylamino group, hexylamino group, octylamino group, decylamino group, dodecylamino group, hexadecylamino group, octadecylamino group ), C2 to C22 alkenyl groups (ethynyl group, hex Alkenyloxy group (allyloxy group, butenyloxy group, octadecynyloxy group, etc.), C2 to C22 alkenylamino group (allylamino group, butenylamino group, octaneyl group, etc.) Decynyloxy group and the like).

Alkylene group R ² is C1 to C8 (methylene, ethylene, 1-or 2-propylene, 1-or 2-butylene, pentylene, hexylene, octylene, etc.), and alkyl group of ^{R 3} is C1 to C22 ( Methyl group, ethyl group, propyl group, n-butyl group, i-butyl group, hexyl group, octyl group, decyl group, dodecyl group, hexadecyl group, octadecyl group, etc.), C2 to C22 alkenyl group (ethynyl group, Hexenyl group, hexadecenyl group, octadecynyl group, etc.).

Y ¹ , Y ² and Y ³ are each a hydrogen atom or a C1 to C22 alkylamide group (methylamide group, ethylamide group, propylamide group, n-butylamide group, i-butylamide group, hexylamide group, octylamide group, decylamide Group, dodecylamide group, hexadecylamide group, octadecylamide group, etc.), C1-C22 alkenylamide group (allylamide group, octadecynylamide group, etc.), C1-C22 alkylcarbamoyl group (methylcarbamoyl group, ethylcarbamoyl group) Group, propylcarbamoyl group, n-butylcarbamoyl group, i-butylcarbamoyl group, hexylcarbamoyl group, octylcarbamoyl group, decylcarbamoyl group, dodecylcarbamoyl group, hexadecylcarbamoyl group, octadecylcarbamoyl group Etc.) represent alkenyl carbamoylmethyl group C1 to C22 (allylcarbamoyl group, octene de Senior carbamoyl group).

  X is a hydrogen atom, monovalent metal cation (Li, Na, K cation), ammonium ion, organic ammonium ion (ethanol ammonium cation, triethanol ammonium cation, methyl ammonium ethanol cation, etc.)

R ⁴ , R ⁵ , R ⁶ are C1-C8 alkylene groups (methylene, ethylene, 1- or 2-propylene, 1- or 2-butylene, pentylene, hexylene, octylene, etc.), R ⁷ , R ⁸ are C1 to C22 alkyl groups (methyl group, ethyl group, propyl group, n-butyl group, i-butyl group, hexyl group, octyl group, decyl group, dodecyl group, hexadecyl group, octadecyl group, etc.), C2 to C22 Or an alkenyl group (such as an ethynyl group, a hexenyl group, a hexadecenyl group, and an octadecynyl group).

  X and Y each represent a hydrogen atom, a monovalent metal cation (cation such as Li, Na, or K), an ammonium ion, or an organic ammonium ion (such as ethanolammonium cation, triethanolammonium cation, or methylammoniumethanol cation). X and Y may be the same, but are preferably different in order to further increase the gelation rate. More preferably, either X or Y is a hydrogen atom, and the other is a monovalent metal cation (cation such as Li, Na, or K), ammonium ion, or organic ammonium ion.

<Molecular weight of aqueous gelling agent>
Since the inkjet ink of the present invention is used with a low molecular weight aqueous gelling agent having a molecular weight of 1000 or less, the aqueous gelling agent dissolves and the viscosity of the ink is greatly reduced by increasing the temperature, and the inkjet head When it is emitted and landed on the recording medium, it is cooled quickly by the recording medium, and at the same time it thickens and gels, and there is no fluidity, so an image without bleeding, beading, feathering, and back-through is obtained. It is obtained.

  Here, an aqueous gelling agent having a molecular weight of more than 1000, or a water-soluble polymer compound having a so-called cloud point such as a natural polymer such as agar, polyisopropylacrylamide, partially saponified polyvinyl alcohol, etc. When used as an agent, the viscosity of the ink dissolved at a high temperature is not sufficiently lowered, and emission from the inkjet head is deteriorated. Alternatively, if the amount used is reduced and the ink viscosity at the time of high-temperature dissolution is reduced to a range where it can be ejected, the viscosity will not increase sufficiently even if cooled on the surface of the recording medium, and bleeding, beading, feathering, and back-through will not occur. It cannot be prevented.

  In the aqueous gelling agent used in the present invention, it is necessary that one or more carboxylic acids or salts thereof are present in the molecule. Carboxylic acid or a salt thereof increases the water solubility without increasing the molecular weight of the aqueous gelling agent and allows a large amount to be put in the ink. The difference in viscosity of the ink cooled and thickened and gelled can be increased, and bleeding, beading, feathering, and back-through can be preferably prevented. Further, when an image is formed on a recording medium, it functions to increase water resistance by interaction with a salt or the like present on the surface of the recording medium. An aqueous gelling agent having a hydrophilic nonionic group such as polyethylene oxide instead of carboxylic acid has a high molecular weight in order to increase water solubility, and the light emission from the inkjet head is deteriorated, improving the light emission. Therefore, if the molecular weight is low, bleeding, beading, feathering, and back-through cannot be prevented, which is not preferable. In addition, when an aqueous gelling agent having a sulfonic acid or a salt thereof is used in place of the carboxylic acid or a salt thereof, the water resistance when the image is formed on the recording medium is too high because the water solubility is too high. Is not preferable from the viewpoint of image storage stability.

  Hereinafter, although the specific example of the aqueous | water-based gelatinizer which concerns on this invention is shown, this invention is not limited to this.

<Addition amount of aqueous gelling agent>
The amount of the aqueous gelling agent used in the ink of the present invention is 0.5% by mass or more and 20% by mass in the ink mass in order to prevent bleeding, beading and feathering and to obtain image scratch resistance. It is preferably used in the following. If it is less than 0.5% by mass, the ink does not gel even when the temperature is low, and the solid matter floats, and bleeding, beading, and feathering cannot be prevented. Further, when an amount larger than 20% by mass is used, the adhesiveness is poor particularly in the image recorded on the printing paper, and the phenomenon that the image is peeled off easily occurs. By using the ink in an amount of 0.5% by mass or more and 20% by mass or less in the mass of the ink, it becomes possible to achieve both bleed, beading and feathering prevention and scratch resistance on the printing paper and plain paper.

  Furthermore, in order to improve bleed, beading, feathering prevention and scratch resistance, the content is preferably 3% by mass or more and 15% by mass or less.

《Water-soluble solvent》
An aqueous liquid medium is preferably used as the solvent, and a mixed solvent such as water and a water-soluble organic solvent is more preferably used as the aqueous liquid medium.

  Examples of the water-soluble organic solvent preferably used include alcohols (for example, methanol, ethanol, propanol, isopropanol, butanol, isobutanol, sec-butanol, t-butanol), polyhydric alcohols (for example, ethylene glycol, diethylene glycol) , Triethylene glycol, polyethylene glycol, propylene glycol, dipropylene glycol, polypropylene glycol, butylene glycol, hexanediol, pentanediol, glycerin, hexanetriol, thiodiglycol), polyhydric alcohol ethers (for example, ethylene glycol monomethyl ether, Ethylene glycol monoethyl ether, ethylene glycol monobutyl ether, diethylene glycol monomethyl ether Ter, diethylene glycol monoethyl ether, diethylene glycol monobutyl ether, propylene glycol monomethyl ether, propylene glycol monobutyl ether, ethylene glycol monomethyl ether acetate, triethylene glycol monomethyl ether, triethylene glycol monoethyl ether, triethylene glycol monobutyl ether, ethylene glycol monophenyl Ether, propylene glycol monophenyl ether), amines (eg, ethanolamine, diethanolamine, triethanolamine, N-methyldiethanolamine, N-ethyldiethanolamine, morpholine, N-ethylmorpholine, ethylenediamine, diethylenediamine, triethylenetetramine, tetra Tylenepentamine, polyethyleneimine, pentamethyldiethylenetriamine, tetramethylpropylenediamine), amides (eg, formamide, N, N-dimethylformamide, N, N-dimethylacetamide, etc.), heterocyclics (eg, 2-pyrrolidone, N-methyl-2-pyrrolidone, cyclohexyl pyrrolidone, 2-oxazolidone, 1,3-dimethyl-2-imidazolidinone and the like, and sulfoxides (for example, dimethyl sulfoxide).

  Among them, polyhydric alcohols (for example, ethylene glycol, diethylene glycol, triethylene glycol, polyethylene glycol, propylene glycol, dipropylene glycol, polypropylene glycol, butylene glycol, hexane are used as solvents for promoting the gelation of the aqueous gelling agent. Diol, pentanediol, glycerin, hexanetriol, thiodiglycol). The reason for this is that when the aqueous gelling agent thickens and gels, hydrogen bonds between hydrogen-bonding groups such as amide groups or ureido groups in the molecule, and C4 or higher hydrocarbon groups also in the molecule It is considered that it is preferable not to have a strong hydrogen bond group and a hydrophobic bond group in the solvent molecule because it is considered to be gelled by a mutual hydrophobic bond due to a phenyl group or the like. For this reason, it is particularly preferable that 50% or more with respect to the total amount of the water-soluble solvent in which the polyhydric alcohol is used.

<Surfactant>
In the inkjet ink of the present invention, a surfactant may be used as necessary. As surfactants that may be used,
Anionic surfactants: Anionic surfactants such as alkyl sulfates, alkyl ester sulfates, dialkyl sulfosuccinates, alkyl naphthalene sulfonates, alkyl phosphates, polyoxyalkylene alkyl ether phosphates, fatty acid salts, etc.

  Nonionic surfactants: nonionic surfactants such as polyoxyethylene alkyl ethers, polyoxyalkylene alkylphenyl ethers, acetylene glycols, polyoxyethylene-polyoxypropylene block copolymers, glycerin esters, sorbitan esters, poly Activators such as oxyethylene fatty acid amide, amine oxide, etc.

  Cationic surfactants: Examples include cationic surfactants such as alkylamine salts and quaternary ammonium salts.

<Colorant>
In the inkjet ink of the present invention, it is necessary to add a colorant in order to recognize an image. As the colorant that may be used, various known dyes or pigments may be used in the inkjet ink. However, from the viewpoint of image storage stability, the pigment is preferable.

〔dye〕
There is no restriction | limiting in particular as dye which can be used by this invention, Water-soluble dyes, such as an acid dye, a direct dye, and a reactive dye, a disperse dye, etc. are mentioned. Of these, anionic dyes are preferred.

(Water-soluble dye)
Examples of water-soluble dyes 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 like. The compounds are shown below. However, it is not limited to these exemplified compounds.

<C. I. Acid Yellow>
1, 3, 11, 17, 18, 19, 23, 25, 36, 38, 40, 42, 44, 49, 59, 61, 65, 67, 72, 73, 79, 99, 104, 110, 114, 116, 118, 121, 127, 129, 135, 137, 141, 143, 151, 155, 158, 159, 169, 176, 184, 193, 200, 204, 207, 215, 219, 220, 230, 232, 235, 241, 242, 246
<C. I. Acid Orange>
3, 7, 8, 10, 19, 24, 51, 56, 67, 74, 80, 86, 87, 88, 89, 94, 95, 107, 108, 116, 122, 127, 140, 142, 144, 149, 152, 156, 162, 166, 168
<C. I. Acid Red>
88, 97, 106, 111, 114, 118, 119, 127, 131, 138, 143, 145, 151, 183, 195, 198, 211, 215, 217, 225, 226, 249, 251, 254, 256, 257, 260, 261, 265, 266, 274, 276, 277, 289, 296, 299, 315, 318, 336, 337, 357, 359, 361, 362, 364, 366, 399, 407, 415
<C. I. Acid Violet>
17, 19, 21, 42, 43, 47, 48, 49, 54, 66, 78, 90, 97, 102, 109, 126
<C. I. Acid Blue>
1, 7, 9, 15, 23, 25, 40, 62, 72, 74, 80, 83, 90, 92, 103, 104, 112, 113, 114, 120, 127, 128, 129, 138, 140, 142, 156, 158, 171, 182, 185, 193, 199, 201, 203, 204, 205, 207, 209, 220, 221, 224, 225, 229, 230, 239, 249, 258, 260, 264, 278, 279, 280, 284, 290, 296, 298, 300, 317, 324, 333, 335, 338, 342, 350
<C. I. Acid Green>
9, 12, 16, 19, 20, 25, 27, 28, 40, 43, 56, 73, 81, 84, 104, 108, 109
<C. I. Acid Brown>
2, 4, 13, 14, 19, 28, 44, 123, 224, 226, 227, 248, 282, 283, 289, 294, 297, 298, 301, 355, 357, 413
<C. I. Acid Black>
1, 2, 3, 24, 26, 31, 50, 52, 58, 60, 63, 107, 109, 112, 119, 132, 140, 155, 172, 187, 188, 194, 207, 222
<C. I. Direct yellow>
8, 9, 10, 11, 12, 22, 27, 28, 39, 44, 50, 58, 79, 86, 87, 98, 105, 106, 130, 132, 137, 142, 147, 153
<C. I. Direct orange>
6, 26, 27, 34, 39, 40, 46, 102, 105, 107, 118
<C. I. Direct Red>
2, 4, 9, 23, 24, 31, 54, 62, 69, 79, 80, 81, 83, 84, 89, 95, 212, 224, 225, 226, 227, 239, 242, 243, 254
<C. I. Direct Violet>
9, 35, 51, 66, 94, 95
<C. I. Direct Blue>
1, 15, 71, 76, 77, 78, 80, 86, 87, 90, 98, 106, 108, 160, 168, 189, 192, 193, 199, 200, 201, 202, 203, 218, 225, 229, 237, 244, 248, 251, 270, 273, 274, 290, 291
<C. I. Direct Green>
26, 28, 59, 80, 85
<C. I. Direct Brown>
44, 106, 115, 195, 209, 210, 222, 223
<C. I. Direct Black>
17, 19, 22, 32, 51, 62, 108, 112, 113, 117, 118, 132, 146, 154, 159, 169
<C. I. Basic Yellow>
1, 2, 11, 13, 15, 19, 21, 28, 29, 32, 36, 40, 41, 45, 51, 63, 67, 70, 73, 91
<C. I. Basic Orange>
2, 21, 22
<C. I. Basic Red>
1, 2, 12, 13, 14, 15, 18, 23, 24, 27, 29, 35, 36, 39, 46, 51, 52, 69, 70, 73, 82, 109
<C. I. Basic Violet>
1, 3, 7, 10, 11, 15, 16, 21, 27, 39
<C. I. Basic Blue>
1, 3, 7, 9, 21, 22, 26, 41, 45, 47, 52, 54, 65, 69, 75, 77, 92, 100, 105, 117, 124, 129, 147, 151
<C. I. Basic Green>
1, 4
<C. I. Basic Brown>
1
<C. I. Reactive Yellow>
2, 3, 7, 15, 17, 18, 22, 23, 24, 25, 27, 37, 39, 42, 57, 69, 76, 81, 84, 85, 86, 87, 92, 95, 102, 105, 111, 125, 135, 136, 137, 142, 143, 145, 151, 160, 161, 165, 167, 168, 175, 176
<C. I. Reactive Orange>
1, 4, 5, 7, 11, 12, 13, 15, 16, 20, 30, 35, 56, 64, 67, 69, 70, 72, 74, 82, 84, 86, 87, 91, 92, 93, 95, 107
<C. I. Reactive Red>
2, 3, 5, 8, 11, 21, 22, 23, 24, 28, 29, 31, 33, 35, 43, 45, 49, 55, 56, 58, 65, 66, 78, 83, 84, 106, 111, 112, 113, 114, 116, 120, 123, 124, 128, 130, 136, 141, 147, 158, 159, 171, 174, 180, 183, 184, 187, 190, 193, 194, 195, 198, 218, 220, 222, 223, 228, 235
<C. I. Reactive Violet>
1, 2, 4, 5, 6, 22, 23, 33, 36, 38
<C. I. Reactive Blue>
2, 3, 4, 5, 7, 13, 14, 15, 19, 21, 25, 27, 28, 29, 38, 39, 41, 49, 50, 52, 63, 69, 71, 72, 77, 79, 89, 104, 109, 112, 113, 114, 116, 119, 120, 122, 137, 140, 143, 147, 160, 161, 162, 163, 168, 171, 176, 182, 184, 191, 194, 195, 198, 203, 204, 207, 209, 211, 214, 220, 221, 222, 231, 235, 236
<C. I. Reactive Green>
8, 12, 15, 19, 21
<C. I. Reactive Brown>
2, 7, 9, 10, 11, 17, 18, 19, 21, 23, 31, 37, 43, 46
<C. I. Reactive Black>
5, 8, 13, 14, 31, 34, 39
<C. I. Food Black>
1, 2
[Pigment]
As the pigment that can be used in the present invention, conventionally known organic and inorganic pigments can be used. For example, azo pigments such as azo lakes, insoluble azo pigments, condensed azo pigments, chelate azo pigments, phthalocyanine pigments, perylene and perylene pigments, anthraquinone pigments, quinacridone pigments, dioxazine pigments, thioindigo pigments, isoindolinone pigments, quinophthalone pigments, etc. Examples include cyclic pigments, dye lakes such as basic dye type lakes and acid dye type lakes, organic pigments such as nitro pigments, nitroso pigments, aniline black and daylight fluorescent pigments, and inorganic pigments such as carbon black. Pigments are preferred.

(Organic pigment)
Specific organic pigments are exemplified below.

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

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

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

(Dispersant)
As the water-soluble polymer dispersant for stably dispersing the pigment in the ink, the following water-soluble resin can be used, which is preferable from the viewpoint of ejection stability.

  As the water-soluble resin, styrene-acrylic acid-acrylic acid alkyl ester copolymer, styrene-acrylic acid copolymer, styrene-maleic acid copolymer, styrene-maleic acid-acrylic acid alkyl ester copolymer are preferably used. Styrene-methacrylic acid copolymer, styrene-methacrylic acid-acrylic acid alkyl ester copolymer, styrene-maleic acid half ester copolymer, vinyl naphthalene-acrylic acid copolymer, vinyl naphthalene-maleic acid copolymer It is a water-soluble resin such as.

  The content of the water-soluble resin with respect to the total amount of the ink is preferably 0.1 to 10% by mass, and more preferably 0.3 to 5% by mass.

  Two or more of these water-soluble resins can be used in combination.

(Anionic pigment)
The form of the anionic pigment used in the present invention is preferably a pigment in which the pigment is dispersed with an anionic polymer dispersant or an anion-modified self-dispersing pigment from the viewpoint of dispersion stability.

  The anionic polymer dispersant refers to a dispersant having an anionic group obtained by neutralizing an acidic group in a molecule with a basic compound. Examples of the basic compound used at this time include alkali metal hydroxides such as sodium hydroxide and potassium hydroxide, and amines such as ammonia, alkylamine, and alkanolamine. In the present invention, amines are particularly preferable. .

  The anionic polymer dispersant preferably used in the present invention is not particularly limited as long as the molecular weight is 1000 or more. For example, polyvinyl alcohols, polyvinyl pyrrolidones, polyacrylic acid, and acrylic acid-acrylonitrile copolymers , Acrylic resins such as potassium acrylate-acrylonitrile copolymer, vinyl acetate-acrylic acid ester copolymer, acrylic acid-acrylic acid ester copolymer, styrene-acrylic acid copolymer, styrene-methacrylic acid copolymer Styrene-acrylic resins such as styrene-methacrylic acid-acrylic acid ester copolymer, styrene-α-methylstyrene-acrylic acid copolymer, styrene-α-methylstyrene-acrylic acid-acrylic acid ester copolymer, Styrene-maleic acid copolymer, styrene-maleic anhydride Acid copolymer, vinyl naphthalene-acrylic acid copolymer, vinyl naphthalene-maleic acid copolymer, and vinyl acetate-ethylene copolymer, vinyl acetate-fatty acid vinyl ethylene copolymer, vinyl acetate-maleic acid ester copolymer Polymers, vinyl acetate copolymers such as vinyl acetate-crotonic acid copolymer, vinyl acetate-acrylic acid copolymer, and copolymers or resins such as salts thereof are, for example, carboxylic acid, sulfonic acid or phosphonic acid. Includes homopolymers, copolymers and terpolymers with acid functionality.

  Monomers that give acid functionality include, for example, acrylic acid, methacrylic acid, crotonic acid, maleic acid, maleic anhydride, itaconic acid, mesaconic acid, fumaric acid, citraconic acid, vinyl acetic acid, acrylic oxypropionic acid, vinyl sulfonic acid Styrene sulfonic acid, 2-acrylamido-2-methylpropane sulfonic acid, allyl sulfonic acid, allyl phosphonic acid, vinyl phosphonic acid and vinyl sulfonic acid.

  The anion-modified self-dispersing pigment preferably used in the present invention refers to a pigment having an anionic group on the surface and capable of being dispersed without a dispersant. An anionic self-dispersing pigment is a pigment in which an acidic group is modified on the pigment, and this is neutralized with a basic compound to form an anionic group that can be dispersed in water without a dispersant.

  Pigment particles having acidic groups on the surface are pigments directly modified with acidic groups on the surface of the pigment particles, or organic substances having organic pigment mother nuclei, or those having acidic groups bonded via a joint. Say.

  Examples of the acidic group (also referred to as polar group) include a sulfonic acid group, a carboxylic acid group, a phosphoric acid group, a boric acid group, and a hydroxyl group, preferably a sulfonic acid group and a carboxylic acid group, and more preferably a sulfonic acid group. It is a group.

  Acid group modifiers include sulfuric acid, fuming sulfuric acid, sulfur trioxide, chlorosulfuric acid, fluorosulfuric acid, amidosulfuric acid, sulfonated pyridine salt, sulfamic acid and other treatments containing sulfur atoms, and the pigment particle surface is oxidized. Carboxylating agents such as sodium hypochlorite and potassium hypochlorite that introduce carboxylic acid groups can be mentioned. Among them, a sulfonating agent such as sulfur trioxide, sulfonated pyridine salt or sulfamic acid, or a carboxylating agent is preferable.

  Examples of basic compounds that neutralize acidic groups include alkali metal hydroxides such as sodium hydroxide and potassium hydroxide, and amines such as ammonia, alkylamines, and alkanolamines. In the present invention, amines are used. Is particularly preferred.

  Examples of a method for obtaining pigment particles having a polar group on the surface include, for example, International Publication No. 97/48769 pamphlet, JP-A Nos. 10-110129, 11-246807, 11-57458, and 11-189739. By oxidizing the surface of pigment particles described in JP-A-11-323232, JP-A-2000-265094, etc. with an appropriate oxidizing agent, at least a part of the pigment surface is said to be a sulfonic acid group or a salt thereof. The method of introduce | transducing a polar group is mentioned.

  Specifically, it is prepared by oxidizing carbon black with concentrated nitric acid, or in the case of color pigments by oxidizing with sulfamic acid, sulfonated pyridine salt, amidosulfuric acid, etc. in sulfolane or N-methyl-2-pyrrolidone. Can do. A pigment dispersion can be obtained by removing and purifying a substance that has become too water-soluble due to these reactions. Moreover, when a sulfonic acid group is introduced to the surface by oxidation, the acidic group may be neutralized with a basic compound as necessary.

  As other methods, a method of adsorbing the pigment derivatives described in JP-A-11-49974, JP-A-2000-273383, JP-A-2000-303014, etc. on the pigment particle surface by a treatment such as milling, Examples include a method of dissolving the pigments described in JP-A Nos. 2002-179777 and 2002-201401 together with a pigment derivative in a solvent and then crystallization in a poor solvent. Pigment particles having a polar group can be obtained.

  The average particle size of the pigment dispersion used in the inkjet ink of the present invention is preferably 500 nm or less, more preferably 200 nm or less, preferably 10 to 200 nm, and more preferably 10 to 150 nm. If the average particle size of the pigment dispersion exceeds 500 nm, the dispersion becomes unstable, and even if the average particle size of the pigment dispersion is less than 10 nm, the stability of the pigment dispersion tends to deteriorate, and the storage stability of the ink Tend to deteriorate.

  The particle size of the pigment dispersion can be measured by a commercially available particle size measuring device using a light scattering method, an electrophoresis method, a laser Doppler method or the like. It is also possible to obtain a particle image with a transmission electron microscope on at least 100 particles and perform statistical processing on the image using image analysis software such as Image-Pro (manufactured by Media Cybernetics). Is possible.

  Examples of the dispersing means that can be used in the present invention include a ball mill, a sand mill, an attritor, a roll mill, an agitator, a Henschel mixer, a colloid mill, an ultrasonic homogenizer, a pearl mill, a wet jet mill, a paint shaker, and a high-pressure homogenizer. Various dispersers can be used. It is also preferable to use a centrifugal separator or a filter for the purpose of removing the coarse particles of the pigment dispersion.

(Polymer fine particles)
In the present invention, polymer fine particles may be added in order to improve fixability.

  The fixing fine polymer particles that can be used in the present invention are not particularly limited, and examples thereof include styrene-butadiene copolymer, polystyrene, acrylonitrile-butadiene copolymer, acrylate copolymer, polyurethane, and silicon-acrylic. Examples thereof include latex such as a copolymer and an acrylic-modified fluororesin. The latex may be obtained by dispersing polymer particles using an emulsifier, or may be dispersed without using an emulsifier. A surfactant is often used as an emulsifier, but a polymer having a water-soluble group such as a sulfonic acid group or a carboxylic acid group (for example, a polymer in which a solubilizing group is graft-bonded, a single group having a solubilizing group). It is also preferable to use a polymer obtained from a monomer and a monomer having an insoluble part.

  In the ink of the present invention, soap-free latex may be used. Soap-free latex is a latex that does not use an emulsifier and a polymer having a water-soluble group such as a sulfonic acid group or a carboxylic acid group (for example, a polymer in which a solubilizing group is graft-bonded, a solubilizing group) A polymer obtained from a monomer having an insoluble part and a monomer having an insoluble part).

  In recent years, there are latexes in which core-shell type polymer particles with different compositions at the center and outer edges of the particles are dispersed, in addition to latexes in which the polymer particles are uniform throughout. A type of latex can also be preferably used.

  The average particle size of the fixing fine polymer particles in the present application can be measured by light scattering, is preferably 10 nm or more and 300 nm or less, more preferably 10 nm or more and 200 nm or less. If the average particle diameter of the fixing fine polymer particles by light scattering exceeds 300 nm, the glossiness of the image is deteriorated, and if it is less than 10 nm, the water resistance and scratch resistance become insufficient.

  The fixing polymer fine particles preferably have a glass transition point of -20 ° C or higher and 80 ° C or lower, preferably -10 ° C or higher and 60 ° C or lower. If the glass transition point is too low, the scratching property is improved, but conversely, if the images are left to overlap each other, adhesion occurs and peeling of the image portion occurs. Further, if the glass transition point is too high, the scratching property is inferior.

  The total amount of polymer fine particles having groups capable of generating hydrogen bonds with water molecules and releasing water by a water-soluble solvent, and polymer fine particles for fixing is preferably 3% by mass to 30% by mass from the viewpoint of fixability. . If the amount is less than 3% by mass, a printed matter with insufficient rubbing properties and high fastness cannot be obtained. If the amount is more than 30% by mass, the ink viscosity before drying is too high, making it difficult to emit from the head.

(Other additives)
In addition to the above description, the inkjet ink of the present invention is publicly known depending on the purpose of improving the emission stability, print head and ink cartridge compatibility, storage stability, image storage stability, and other various performances as necessary. Various additives, such as viscosity modifiers, specific resistance regulators, film forming agents, UV absorbers, antioxidants, anti-fading agents, anti-fouling agents, rust inhibitors, etc. can be appropriately selected and used, For example, oil droplet fine particles such as liquid paraffin, dioctyl phthalate, tricresyl phosphate, silicone oil, ultraviolet absorbers described in JP-A-57-74193, JP-A-57-87988, and JP-A-62-261476, 57-74192, 57-87989, 60-72785, 61-146591, JP-A-1-95091 and 3-13376. , Whitening agents described in JP-A-59-42993, JP-A-59-52689, JP-A-62-280069, JP-A-61-228771 and JP-A-4-219266. An agent etc. can be mentioned.

  The ink-jet ink of the present invention has the property of reversibly changing the sol-gel phase depending on the temperature when an aqueous gelling agent is added, but the temperature at which the sol-gel phase transition of the ink is preferably 30 ° C. or higher and lower than 80 ° C. Although it can adjust mainly with the property and addition amount of the said aqueous | water-based gelling agent, it can adjust also with the combination with the kind and addition amount of the various additives mentioned above.

<Inkjet recording method>
The ink jet head used in the ink jet recording method may be an on-demand system or a continuous system. Discharge methods include electro-mechanical conversion methods (single cavity type, double cavity type, bender type, piston type, shear mode type, shared wall type, etc.), electro-thermal conversion methods (thermal ink jet type, bubble type) Specific examples include jet (registered trademark) type, electrostatic suction type (electric field control type, slit jet type, etc.) and discharge type (spark jet type, etc.). You may use. As a printing method, a serial head method, a line head method, or the like can be used without limitation. In the present invention, the line head system is particularly preferable.

  As described above, the ink jet ink of the present invention uses a low molecular weight aqueous gelling agent having a molecular weight of 1000 or less, and the aqueous gelling agent dissolves and the viscosity of the ink is greatly reduced by elevating the temperature. Therefore, it is preferable that the recording head is heated to prevent the ink from solidifying.

  The heating temperature of the recording head is not particularly limited, but it is preferable from the viewpoint of ejection stability that the recording head is heated to 35 to 100 ° C. to eject ink. The recording head is generally heated by a heater with a temperature sensor.

  As recording media applicable to the ink jet recording method, for example, plain paper, high quality paper, art paper, coated paper, cast coated paper, glossy paper, ink jet exclusive paper, and the like are widely used. Among them, it is preferable to use art paper, coated paper, cast coated paper, or glossy paper, which is a support that does not have much ink absorbability, because the excellent characteristics of the ink of the present invention can be exhibited.

The paper coated paper, there is a non-coated paper, the coated paper, the coated amount per 1 m ² are each one side 20g before and after art paper, one surface 10g before and after the coated paper, one surface 5g before and after lightweight coated Examples thereof include paper, finely coated paper, mat-coated paper with matte finish, dull-coated paper with dull finish, and newsprint paper.

  Non-coated paper includes printing paper A using 100% chemical pulp, printing paper B using 70% or more, printing paper C using 40% or more and less than 70%, printing paper D using less than 40%, or mechanical pulp. The gravure paper which contained and performed the calendar process etc. can be mentioned. Further details are described in detail in the “Latest Paper Processing Handbook” edited by the Paper Processing Handbook Editorial Committee, published by Tech Times, “Printing Engineering Handbook” edited by the Japan Printing Society.

  As the plain paper, uncoated paper, special printing paper, and 80 to 200 μm uncoated paper belonging to a part of information paper are used. The plain paper used in the present invention includes advanced printing paper, intermediate printing paper, lower printing paper, thin printing paper, fine coating printing paper, special printing paper such as colored fine paper, foam paper, PPC paper, and other information paper. Specifically, there are the following papers and various modified / processed papers using them, but are not particularly limited thereto.

  OK fine paper, OK Prince fine paper, OK Shikari, OK Everlight, OK sour cream, OK shoe cream, OK soft cream vanilla, OK moonlight cream, OK clear white, OK top coat +, OK top coat S, OK top coat Matt N, OKH, OKH-D, map paper, OK Form Green 100 (above, manufactured by Oji Paper Co., Ltd.), Super Matte Art A, Rhizo Art Double Side N, Rhizo Art Single Side N, Pearl Coat N, New V Matt, Pearl Soft (Above, manufactured by Mitsubishi Paper Industries Co., Ltd.) Esprit To C (above, manufactured by Nippon Paper Industries Co., Ltd.), Mu mat, α mat, Hamming, L book, Kinmari SW, Kinmari V, Cream Kinmari, Maricopy, Semi-quality, S Shiromari (above, manufactured by Hokuetsu Paper Company) Thunderbird Quality, Thunderbird Super Art N, Thunderbird Dalart N, Thunderbird Coat N, Thunderbird Matt Coat N, Regina (Made by Chuetsu Pulp & Co., Ltd.), NIP / KPF, BOD Paper, Fine PPC, Fine FC, Color Inkjet Paper ( Kishu Paper Co., Ltd.), Audrey, Utrillo Plus, Goethe Coat, Canto Excel, Carteto Excel, Dante Excel, Plato Bulky Cream, Dante, Tioubaru (above, Daio Paper Co., Ltd.), New Bright, General PPC Paper, Multi Printer Paper (above, manufactured by Nagoya Pulp), Dream Coats, cherry white dal, cherry white, cherry 1 super, star linden AW, star elm, star laurel, blue gum, yashima 1 (manufactured by Marusumi Paper Co., Ltd.) and the like.

  EXAMPLES The present invention will be specifically described below with reference to examples, but the present invention is not limited to these examples.

Example 1
<Preparation of cyan pigment dispersion 1>
The following additives were mixed, dispersed using a sand grinder filled with 50% by volume of 0.5 mm zirconia beads, and diluted with water to prepare a cyan pigment dispersion having a content of 10%. The average particle diameter of the cyan pigment particles contained in this cyan pigment dispersion was 108 nm, and the ζ potential in water was −41 mV. The particle diameter was measured with Malvern Zetasizer 1000HS, and the ζ potential was measured using ELS-800 (manufactured by Otsuka Electronics Co., Ltd.) after the pigment ink solution was diluted 1000 times with water.

<Cyan pigment dispersion composition>
C. I. Pigment Blue 15: 3 10 parts by mass Polymer dispersant (styrene / n-butyl methacrylate / stearyl acrylate / methacrylic acid, number average molecular weight 8500, acid number 185) 5 parts by mass Glycerin 15 parts by mass Ion-exchanged water 60 parts by mass [ Preparation of ink 1]
30 parts by mass of the cyan pigment dispersion (3 parts solids)
Aqueous gelling agent Exemplary compound A-1 5 parts by mass DEG (diethylene glycol) 20 parts by mass Glycerin 5 parts by mass Triethylene glycol monobutyl ether 10 parts by mass E1010 (Olfin E1010, manufactured by Nissin Chemical) 0.3 parts by mass Pure water was added. Then, 100 parts were added, and once heated and mixed at 80 degrees, ink 1 was obtained.

  The viscosity of the ink 1 was measured between 20 ° C. and 80 ° C. under the condition of a temperature change of 10 ° C./min and a shear rate of 1/10 s using an MCR300 manufactured by Paar PHYSICA and a plate CP75-1. As a result, a reversible sol-gel phase change occurred, which became a gel at 35 ° C. or lower and became a sol at 55 ° C. or higher.

[Preparation of Inks 2 to 13]
Inks 2 to 11 were prepared in the same manner as described in Table 1 except that the aqueous gelling agent A-1 and the amount used for the preparation of ink 1 were changed to other exemplary aqueous gelling agents. The transition temperature was measured. The ink 12 is an ink to which no aqueous gelling agent is added, and the ink 13 is an ink using agar as a comparison with the aqueous gelling agent.

<Inkjet print evaluation>
<Print evaluation>
Nozzle diameter 25 μm, drive frequency 12 kHz, nozzle number 128, nozzle density 180 dpi (dpi represents the number of dots per 2.54 cm), a piezo head with a heating device is mounted, and the maximum recording density is 720 × 720 dpi. An on-demand inkjet printer was prepared. While heating the head to 70 ° C., a cyan image, a solid image, and a density of 80% to 0% on coated paper (OK Kanto, manufactured by Oji Paper Co., Ltd.) and plain paper (First Class paper, manufactured by Konica Minolta Business Technology). Nine gradation images and line drawing images were created.

<Ink emission evaluation>
Create an image under the above conditions, leave it for 2 minutes, then repeat it again for 10 minutes. ○: No difference is observed in the image at the 10th time.

  Δ: Partial blurring is observed at the 6th to 10th times.

  X: Some blurring is already seen in the 5th time.

<Evaluation of beading>
The above-prepared dots of each gradation of each cyan were observed with a loupe, and the image uniformity was evaluated according to the following criteria.

  A: The dot shape is maintained for each gradation.

  Δ: The dot shape is maintained up to a density of 50%, but some dots are deformed at a density of 60% to 80%.

  X: The dot shape is not maintained in the entire region.

<Evaluation of feathering>
The cyan images created above were observed with a magnifying glass and evaluated according to the following criteria.

◎: Thin lines are reproduced without blurring due to bleeding ○: Lines are not thickened due to bleeding, but less than 5 spots, ink bleeding along the paper fiber is observed Δ: Lines are thickened due to bleeding No, but less than 10 spots, ink bleeding along the paper fiber is observed. ×: Line thickening due to bleeding is severe <Evaluation of showthrough>
The reflection density on the back side of the solid image printed sample is measured.

The difference between the reflection density on the back side of the sample on which the solid image was printed and the density of the paper on which printing was not performed is less than 0.03.

Δ: 0.03 to 0.06
X: Greater than 0.08 The results are shown in Table 1.

  From Table 1, it can be seen that the inks 1 to 11 of the present invention are superior in ink ejection properties to the comparative example, and further excellent in beading, feathering, and back-through without depending on the type of the recording medium.

Example 2
(Preparation of ink set of the present invention)
In preparation of ink 1 of Example 1, C.I. I. Instead of pigment blue 15: 3, carbon black, C.I. I. Pigment red 122, C.I. I. Black ink, magenta ink, and yellow ink were prepared using each of Pigment Yellow 74 to obtain an ink set of the present invention.

(Production of comparative ink set)
A similar ink set was prepared except that the aqueous gelling agent was removed.

(Evaluation)
<Evaluation of beading, feathering and behind-the-scenes>
The same evaluation as in Example 1 was performed.

<Bleed evaluation>
A4 output of high-definition color digital standard image data “fruit basket” issued by the Japan Standards Association using the ink set of the present invention and the comparative ink set, using the ink jet printer used in Example 1. I got an image.

Visually observe the boundary between black and cyan with a magnifying glass. ○: Both black and cyan have a dot shape. △: Either black or cyan or the dot shape is slightly broken. ×: Either black or cyan. The dot shape is broken and flowing.

  The results are shown in Table 2.

  As shown in Table 2, the ink set of the present invention has good beading, feathering, and back-through as in Example 1, and “generation of bleed in which colors are mixed between different colors” is remarkably suppressed. I understand that.

Claims (8)

An ink-jet ink comprising a coloring material, water, and a water-soluble solvent, comprising at least an aqueous gelling agent containing a carboxylic acid having a molecular weight of 1000 or less or a salt thereof. The inkjet ink according to claim 1, wherein the aqueous gelling agent is a compound represented by the following general formula (1) or general formula (2).

(Wherein R ¹ : alkyl, alkoxy, alkylamino, alkenyl, alkenyloxy, alkenylamino R ² , R ⁴ , R ⁵ , R ⁶ : alkylene X, Y: hydrogen atom, monovalent metal cation, ammonium ion, organic Ammonium ion Y ¹ , Y ² , Y ³ : represents a hydrogen atom or alkylamide, alkenylamide, alkylcarbamoyl, alkenylcarbamoyl) The inkjet ink according to claim 1 or 2, wherein the content of the aqueous gelling agent with respect to the total amount of the ink is 0.5 mass% or more and 20 mass% or less. The inkjet ink according to any one of claims 1 to 3, wherein the colorant contains a pigment. The inkjet ink according to any one of claims 1 to 4, wherein the inkjet ink reversibly undergoes a sol-gel phase transition depending on temperature. 6. The inkjet ink according to claim 5, wherein the temperature at which the sol-gel phase transition of the inkjet ink is 30 ° C. or more and less than 80 ° C. An inkjet recording method for recording on a recording medium using the inkjet ink according to claim 1, wherein the recording head is heated. An inkjet recording method for performing recording on a recording medium using the inkjet ink according to claim 1, wherein the recording head is a line head.