JP2005232360A - Water-based ink composition, inkjet recording method using it, and recorded matter - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a water-based ink composition excellent in storage stability when left alone at a high temperature for long, in ejection stability when used for an inkjet printer, and in color developability regardless of recording media species, which is suitable to ink for inkjet recording. <P>SOLUTION: This water-based ink composition comprises a coloring component, a resin emulsion, a humectant and water, characterized in that the coloring component is a dispersion in which a colorant is made water-dispersive through inclusion by a dispersive polymer which is water-insoluble by itself, and the resin emulsion is subjected to heat treatment at a temperature not lower than the glass transition temperature (Tg) of the resin component constituting the resin emulsion before added to the water-based ink composition. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to an aqueous ink composition, an ink jet recording method, and a recorded matter.

  The ink jet recording method is a printing method in which printing is performed by causing a droplet of an ink composition to fly and adhere to a recording medium such as paper. This method has a feature that a high-resolution and high-quality image can be printed at a high speed with a relatively inexpensive apparatus.

  The ink composition used in the ink jet recording method generally contains water as a main component and contains a moisturizing agent such as glycerin for the purpose of preventing coloring components and clogging. As the colorant used in the ink composition for ink jet recording, many water-soluble dyes are used because of the high saturation of the colorant, the rich variety of colorants that can be used, and the solubility in water. Yes.

  However, the dye may be inferior in various properties such as light resistance and water resistance, and thus a printed matter printed with the dye-based ink composition is inferior in light resistance and water resistance. The water resistance is improved by an ink jet recording medium having an ink absorbing layer, but it is still not sufficient for plain paper.

  In contrast, pigments are superior in light resistance and water resistance compared to dyes, and in recent years, the use of pigments as colorants in ink compositions for ink jet recording has been studied for the purpose of improving light resistance and water resistance. Here, since the pigment is generally insoluble in water, when the pigment is used in the water-based ink composition, the pigment is mixed with a dispersant such as a water-soluble resin and stably dispersed in water. It is necessary to prepare as.

  In order to stably disperse the pigment in the water system, it is necessary to consider the type of pigment, particle size, type of dispersant used, and dispersion means, and so far, many dispersion methods and ink jet recording inks have been proposed. Has been. For example, an aqueous pigment ink in which carbon black is dispersed with a surfactant or a polymer dispersant is known (see Patent Document 1 and Patent Document 2). In addition, an ink composition comprising water, a styrene-maleic acid copolymer, ε-caprolactam, and a pigment has been proposed (see Patent Document 3). An ink composition containing an aqueous medium, a styrene-maleic acid copolymer, and a copper phthalocyanine pigment has been proposed (see Patent Document 4). Also, water-based inks using a resin in which 60 mol% or more of the acid groups of the dispersion polymer are neutralized with an alkaline neutralizing agent have been proposed (see Patent Documents 5 and 6).

  In addition, for the purpose of improving the fixability, water resistance, color development, etc. of ink on a recording medium, or suppressing bleeding, it has been studied to add a resin emulsion having a specific structure to ink containing a pigment. For example, an ink containing a pigment dispersed with a branched polymer dispersant, and an emulsion polymer composed of acrylic and / or methacrylic and / or vinyl monomers has been proposed (see Patent Document 7 and Patent Document 8). Further, inks containing charged pigments and resin emulsions and having the same charge polarity have been proposed (see Patent Document 9 and Patent Document 10).

JP-A 64-6074 JP-A 64-31881 Japanese Patent Laid-Open No. 3-252467 Japanese Patent Laid-Open No. 3-79680 JP-A-8-183920 Japanese Patent Laid-Open No. 9-40895 Japanese Patent Laid-Open No. 10-195354 JP-A-10-195355 JP 2000-351931 A JP 2000-81366 A

  As described above, in order to use a pigment in an ink composition for ink jet recording, it is important to stably disperse it in water and hold it for a long time. 4) was not satisfactory.

  In addition to the colorant, various additives, particularly a water-soluble organic solvent, are added to the ink used in the ink jet recording method in order to optimize various characteristics in the ink jet recording method. The water-soluble organic solvent includes a moisturizing agent that prevents drying, a penetrating solvent or surfactant that controls the permeability to the recording medium by lowering the surface tension of the ink composition, and an organic amine that adjusts the pH of the ink composition. Etc. Some of these solvents affect the dispersibility by affecting the dispersed colorant, which may impair the storage stability of the ink composition. In particular, there is a problem that these effects are likely to occur with a solvent having a strong affinity for the pigment surface having a hydrophobic surface and the hydrophobic portion in the dispersant. In addition, when such an effect occurs, the dispersion polymer as the dispersant is released from the pigment surface and dissolved in the ink, and when this is used as an ink for ink jet recording, the discharge from the printer head is not possible. There was a problem of becoming stable.

  Used in water-based inks using a dispersion polymer in which 60 mol% or more of the acid groups of the dispersion polymer are neutralized with an alkaline neutralizing agent, as described in the above prior art (Patent Documents 5 and 6). Depending on the type of the water-soluble organic solvent, there has been a problem that the storage stability and ejection stability of the ink are lowered due to the influence of the dispersion polymer and the water-soluble organic solvent.

  Further, in the above-described conventional technology (Patent Document 1 to Patent Document 6), a part of the dispersant for dispersing the pigment is dissolved in the ink, and it acts as a penetrant for the ink. The penetration into the recording medium has been increased more than necessary. For this reason, the pigment particles may be dragged into the recording medium and soak into the recording medium, resulting in poor color development of the image. In particular, the effect is remarkable in plain paper and recycled paper, and in some cases, bleeding due to excessive penetration and back-through through which ink penetrates to the back side of the paper are caused, resulting in deterioration of image quality.

  For the purpose of preventing such harmful effects, various additions of a resin emulsion have been studied as shown in Patent Documents 7 to 10, and certain effects can be obtained. However, as a result of detailed studies by the present inventors, it has been found that simply adding a resin emulsion to a pigment ink is not sufficient as an ink for inkjet recording. Specifically, when the ink is left for a long period of time or at a high temperature, there is an increase in viscosity, particle size, or agglomeration that appears to be due to the interaction between the pigment particles and the resin emulsion. It has been found that problems such as unstable ejection, clogging of the head nozzle, and reduction in density occur.

  Accordingly, an object of the present invention is to solve the above-mentioned problems and to provide a water-based ink composition suitable as an ink for ink jet recording which has high storage stability, high ejection stability and excellent color developability.

  The water-based ink composition of the present invention is a water-based ink composition comprising a coloring component, a humectant, a resin emulsion, and water, and the coloring component includes the colorant as a dispersion polymer so that it can be dispersed in water. And the dispersion polymer is a dispersion composed of a substance that is insoluble in water alone, and the glass transition temperature (Tg) of the resin component constituting the resin emulsion before the resin emulsion is added to the aqueous ink composition. The heat treatment is performed at the above temperature.

  The water-based ink composition of the invention further comprises a penetrating solvent.

  The water-based ink composition of the invention is characterized in that the penetrating solvent is selected from the group consisting of monohydric alcohols, glycol monoether derivatives of polyhydric alcohols, and 1,2-alkyldiols.

  The aqueous ink composition of the present invention is characterized by further comprising an acetylene glycol surfactant.

  The water-based ink composition of the present invention is characterized by comprising at least one resin emulsion having a glass transition temperature (Tg) of 30 ° C. or higher of the resin constituting the resin emulsion.

  The water-based ink composition of the invention is characterized in that the colorant is carbon black.

  The water-based ink composition of the invention is characterized in that the colorant is an organic pigment.

  The aqueous ink composition of the present invention further comprises a weak alkalinizing agent and is characterized by being alkaline.

  The water-based ink composition of the invention is characterized in that the weak alkalinizing agent comprises at least one compound selected from an organic acid salt and an organic buffer.

  The inkjet recording method of the present invention is characterized in that recording is performed by discharging droplets of the aqueous ink composition described above and attaching the droplets to a recording medium.

  The recorded matter of the present invention is characterized in that the above-described aqueous ink composition is printed by an inkjet recording method.

  The water-based ink composition of the present invention comprises a coloring component, a resin emulsion, a humectant, and water as essential components, and the coloring component includes the coloring agent as a dispersion polymer so that it can be dispersed in water and the dispersion. A dispersion composed of a polymer which is insoluble in water alone, and the resin emulsion has a temperature equal to or higher than the glass transition temperature (Tg) of the resin component constituting the resin emulsion before being added to the aqueous ink composition. It is heat treated.

  Moreover, the water-based ink composition of the present invention according to another aspect further comprises a penetrating solvent in addition to the above components.

  Furthermore, the aqueous ink composition of the present invention according to another embodiment further comprises an acetylene alcohol surfactant in addition to the above components.

  With such a configuration, it is possible to obtain an aqueous ink composition suitable as an inkjet recording ink that has high storage stability, high ejection stability, and excellent color developability for the inkjet recording method.

  Here, it is essential that the dispersion polymer has both a hydrophobic part and a hydrophilic part as its polymer structure. If the dispersion polymer does not have a hydrophobic portion, the entire polymer is dissolved in water and does not become a dispersion polymer, and a stable colorant dispersion cannot be obtained. Further, the free polymer dissolved in water in this manner makes the discharge of the aqueous ink composition from the printer head unstable. Further, the recording medium, particularly plain paper / recycled paper, excessively penetrates more than necessary, resulting in an image in which bleeding or back-through occurs with poor color development. On the other hand, if the dispersion polymer does not have a hydrophilic portion, the colorant cannot be stably dispersed by the polymer, and the colorant dispersion liquid aggregates and settles.

  In addition, the resin emulsion improves the color developability by suppressing the penetration of the dispersion into the recording medium, and the resin emulsion and the resin emulsion and the dispersion are fused together as it is further dried. Fixing properties are improved by fixing the pigment particles on the recording medium.

  Here, when the resin emulsion is added to the water-based ink composition of the present invention, the resin emulsion is preliminarily heated at a glass transition temperature (hereinafter referred to as “Tg”) of a resin component constituting the resin emulsion. It is essential to do. The present inventors have found that by performing this treatment, the storage stability of the water-based ink composition is dramatically improved (particularly, the rate of change in viscosity and the rate of change in particle size are reduced). In particular, the improvement effect by this treatment was large in a resin emulsion composed of a resin component having a Tg of room temperature or higher (approximately 30 ° C. or higher). The present inventors have made various studies for the purpose of improving color developability on a recording medium, particularly on plain paper and recycled paper, but a resin emulsion is essential to achieve the purpose. It has been found that the Tg of the resin component constituting the resin emulsion has an influence on the existence and the effect, and that the effect is more effective when the Tg is room temperature or higher (approximately 30 ° C. or higher). However, at the same time, if an aqueous ink composition to which a resin emulsion having a Tg of the resin component of room temperature or higher is added is left for a long period of time or at a high temperature, problems such as increased particle size, increased viscosity, and generation of sediment frequently occur. I also found out. Therefore, as a result of various studies to achieve both improvement in color development and ensuring storage stability, it is possible to solve the problem by heat-treating the resin emulsion at Tg or more of the resin component constituting it before adding it to the ink. And the present invention has been established.

  The reason why the color developability is improved by adding the resin emulsion, and the reason why the storage stability is improved by heat-treating the resin emulsion at a temperature equal to or higher than the Tg of the resin component before adding the resin emulsion to the ink, has not yet been determined. Not estimated, but estimated as follows. In other words, when a water-based ink composition containing a resin emulsion adheres to plain paper, recycled paper, etc., the resin emulsion first adheres to the paper fibers or on the surface, preventing the colorant in the ink from seeping into the paper. To do.

  As a colorant suitable for the water-based ink composition of the present invention, a dispersion containing a pigment as a dispersion polymer as described above is used. The pigment is present on the paper surface and has a characteristic of developing color by reflecting light of a specific wavelength. However, if the pigment penetrates into the paper, it is hidden by the paper fiber and cannot sufficiently reflect the light. Therefore, when a resin emulsion is added to the ink, the resin emulsion first fills the gap between the paper fibers and the dispersion is placed on top of it, resulting in the presence of a large amount of dispersion on the paper surface, resulting in plain paper and recycled paper. We believe that the color development on paper will be improved. Moreover, when creating a resin emulsion, neutralizing an unneutralized portion (specifically, a carboxylic acid group, a sulfonic acid group, etc.) of an acid group in a resin constituting the resin emulsion as a dissociating group Although it can be stably dispersed in water, not a few unneutralized groups remain in the resin emulsion particles. If this is added to the ink as it is and stored for a long time or at a high temperature, the unneutralized groups inside the resin emulsion particles will come out on the surface of the resin emulsion particles due to the molecular movement of the resin components, consuming the alkali components in the ink. As a result, the ink itself becomes a neutralizing group, and as a result, the pH of the ink is inclined toward the acidic side. As a result, the colorant contained in the ink, particularly the pigment dispersion, becomes unstable on the acidic side, resulting in interactions between the dispersions or the resin emulsion, resulting in increased particle size, thickening, and aggregation. It is conceivable that problems such as generation of objects will occur. However, if the resin emulsion is heat-treated at Tg or higher of the resin component before being added to the ink, unneutralized groups inside the resin emulsion particles come out on the surface of the resin emulsion particles and stabilize at that stage. Thus, once the non-neutralized groups come out on the surface of the resin emulsion particles by the heat treatment and are stabilized, even if they are added to the ink and allowed to stand for a long time or at a high temperature, there are no more unneutralized groups. Since the ink does not come out on the surface, the pH of the ink is not inclined toward the acidic side from the initial state, and the above-described problem may not occur.

The components of the water-based ink composition of the present invention are described below.
<Water-based ink composition>
[Dispersed polymer]
The dispersion polymer in the water-based ink composition of the present invention is insoluble in water alone and is soluble in an organic solvent (preferably a hydrophilic organic solvent such as acetone or methyl ethyl ketone) used in the method for producing a dispersion described later in the examples. Although there is no restriction | limiting in particular if it is a polymer, It is essential to have both a hydrophobic part and a hydrophilic part as the polymer structure.

  Here, the hydrophobic portion refers to a repeating unit having an alkyl group, a cycloalkyl group, an aromatic ring, or an unneutralized group. An unneutralized group is a group that can be neutralized by a neutralizing agent, and examples thereof include an acid group and an alkaline group. Specific examples of the unneutralized group include a carboxylic acid group and a sulfonic acid group.

  Moreover, as a hydrophilic part, the repeating unit which has a neutralizing group is shown. The neutralizing group is a group formed by neutralizing an unneutralized group, and is preferably an ionic group. The unneutralized group and the neutralized group are preferably anionic groups, and particularly suitable when the unneutralized group is a carboxylic acid group and the neutralized group is a carboxylic acid anion group (carboxylate group). Can be illustrated. Examples of the carboxylate include lithium carboxylate, sodium carboxylate, potassium carboxylate, and ammonium carboxylate.

  Since the dispersion polymer has the above-described structure, the hydrophobic polymer can be firmly adsorbed on the hydrophobic surface of the colorant described later and can include the colorant. Furthermore, since the hydrophilic part is compatible with water, it can be a dispersion that is stably dispersed in water.

  The dispersion polymer having an anionic group is obtained by polymerizing, for example, a monomer having an anionic group (hereinafter referred to as an anionic group-containing monomer) and, if necessary, another monomer that can be copolymerized with these monomers in a solvent. Is obtained. Examples of the anionic group-containing monomer include a monomer having a carboxylic acid group and a monomer having a sulfonic acid group.

  As the monomer having a carboxylic acid group, an acrylic monomer containing one or two carboxylic acid groups in the repeating unit is preferable.

  Specific examples of the monomer having a carboxylic acid group include acrylic acid, methacrylic acid, crotonic acid, ethacrylic acid, propylacrylic acid, isopropylacrylic acid, itaconic acid, fumaric acid, maleic acid and the like. Among these, acrylic acid, methacrylic acid, and maleic acid are preferable.

  Specific examples of the monomer having a sulfonic acid group include styrene sulfonic acid, isoprene sulfonic acid, sulfobutyl methacrylate, and allyl sulfonic acid. Furthermore, after polymerizing the resin, it is also preferable to sulfonate with a sulfonating agent such as sulfuric acid, fuming sulfuric acid, sulfamic acid and the like.

  Specific examples of other monomers that can be copolymerized with the anionic group-containing monomer include methyl acrylate, ethyl acrylate, isopropyl acrylate, acrylic acid-n-propyl, acrylic acid-n-butyl, and acrylic acid-t-. Butyl, 2-ethylhexyl acrylate, n-octyl acrylate, lauryl acrylate, benzyl acrylate, methyl methacrylate, ethyl methacrylate, isopropyl methacrylate, methacrylic acid n-propyl, methacrylic acid n-butyl, (Meth) acrylic esters such as isobutyl methacrylate, tert-butyl methacrylate, 2-ethylhexyl methacrylate, n-octyl methacrylate, lauryl methacrylate, stearyl methacrylate, tridecyl methacrylate, benzyl methacrylate, etc. ; Steer Addition reaction product of oil fatty acid and (meth) acrylic acid ester monomer having oxirane structure such as addition reaction product of acid and glycidyl methacrylate; oxirane compound containing alkyl group having 3 or more carbon atoms and (meth) acrylic Addition reaction product with acid; styrene monomer such as styrene, α-methylstyrene, o-methylstyrene, m-methylstyrene, p-methylstyrene, p-tert-butylstyrene, etc .; such as benzyl itaconate Itaconic acid esters; maleic acid esters such as dimethyl maleate; fumaric acid esters such as dimethyl fumarate; acrylonitrile, methacrylonitrile, vinyl acetate, isobornyl acrylate, isobornyl methacrylate, aminoethyl acrylate, acrylic acid Aminopropyl, aqua Methylaminoethyl acrylate, methylaminopropyl acrylate, ethylaminoethyl acrylate, ethylaminopropyl acrylate, aminoethylamide acrylate, aminopropylamide acrylate, methylaminoethylamide acrylate, methylaminopropylamide acrylate, Acrylic acid ethylaminoethylamide, acrylic acid ethylaminopropylamide, methacrylic acid amide, aminoethyl methacrylate, aminopropyl methacrylate, methylaminoethyl methacrylate, methylaminopropyl methacrylate, ethylaminoethyl methacrylate, ethylamino methacrylate Propyl, methacrylic acid aminoethylamide, methacrylic acid aminopropylamide, methacrylic acid methylaminoethylamide, methacrylic acid methylaminoamide Pyramide, ethyl aminoethylamide methacrylate, ethyl aminopropyl amide methacrylate, hydroxymethyl acrylate, 2-hydroxyethyl acrylate, 2-hydroxypropyl acrylate, hydroxymethyl methacrylate, 2-hydroxyethyl methacrylate, Examples include 2-hydroxypropyl methacrylate, N-methylolacrylamide, and allyl alcohol.

  These dispersion polymers preferably have a weight average molecular weight in the range of 1,000 to 200,000, particularly preferably in the range of 3,000 to 150,000. When the weight average molecular weight of the dispersion polymer is within this range, the function as a coating film in the colorant or as a coating film in the aqueous ink composition can be sufficiently exhibited.

  Examples of the alkaline compound that neutralizes a part of the unneutralized group of the dispersion polymer having an anionic group include organic amines and alkali metal salt compounds. Specific examples of organic amines include salts with volatile amine compounds such as ammonia, triethylamine, tributylamine, dimethylethanolamine, diisopropanolamine and morpholine, diethanolamine, triethanolamine, tripropanolamine and other highly volatile compounds. Examples include salts of boiling organic amines. Specific examples of the alkali metal salt compound include compounds having lithium, sodium and potassium as the alkali metal, preferably an alkali metal hydroxide salt such as sodium hydroxide, potassium hydroxide and lithium hydroxide, more preferably potassium hydroxide. Can be mentioned.

  In the present invention, the hydrophobic part is preferably in the range of 1% to 67% in terms of molar ratio with respect to the sum of the repeating units of the hydrophobic part and the hydrophilic part. The range of 1% to 30% It is particularly preferred that Thereby, an aqueous ink composition having high storage stability can be obtained. If there are too many hydrophobic parts, the dispersion of the colorant and the like by the dispersion polymer is unstable, and the colorant dispersion tends to aggregate and settle. Conversely, if there are too few hydrophobic parts, the entire dispersion polymer will be water-soluble and colored. The amount of free polymer that is not adsorbed by the agent increases and the discharge of the aqueous ink composition from the printer head becomes unstable, and the water-dispersed dispersion polymer acts as a penetrating agent, so that the ink can soak into the recording medium more than necessary. There is a tendency that the image has problems such as bleeding and show-through.

  The amount of the anionic group in the dispersion polymer is such that the acid value is about 30 KOHmg / g or more, preferably about 50 to 250 KOHmg / g. When the acid value of the dispersion polymer is in such a range, the storage stability of the colorant particles formed into a coating is improved, and the water resistance of the recorded image is improved.

  By using a dispersion in which a colorant is dispersed using the dispersion polymer described above, a water-based ink composition suitable as an ink for ink jet recording excellent in storage stability and ejection stability can be realized.

[Colorant]
Examples of the colorant include organic pigments, carbon black, oil-soluble dyes, and disperse dyes as colorants that are insoluble or hardly soluble in an aqueous medium. In particular, carbon black, organic pigments, oil-soluble dyes, and disperse dyes are preferred because they have good color development and are difficult to settle during dispersion due to their low specific gravity.

  In the aqueous ink composition of the present invention, such a colorant is dispersed by the dispersion polymer (preferably a polymer having an anionic group).

  Specific examples of preferred carbon black in the present invention include No. 1 as carbon black manufactured by Mitsubishi Chemical Corporation. 2300, 900, MCF88, no. 20B, no. 33, no. 40, no. 45, no. 52, MA7, MA8, MA100, No2200B and the like. Examples of carbon blacks manufactured by Degussa include color blacks FW1, FW2, FW2V, FW18, FW200, S150, S160, S170, Pretex 35, U, V, 140U, Special Black 6, 5, 4A, 4, 250, etc. It is done. Examples of carbon black manufactured by Columbia Carbon include Conductex SC, Raven 1255, 5750, 5250, 5000, 3500, 1255, 700, and the like. Examples of the carbon black manufactured by Cabot include Regal 400R, 330R, 660R, Mogul L, Monarch 700, 800, 880, 900, 1000, 1100, 1300, 1400, Elftex 12 and the like manufactured by Cabot. Note that these are examples of carbon black suitable for the present invention, and the present invention is not limited to these. These carbon blacks may be used singly or as a mixture of two or more. These pigments are added in an amount of 0.5 to 15% by weight, preferably 1 to 10% by weight, based on the total amount of the aqueous ink composition.

  Preferred organic pigments in the present invention include quinacridone pigments, quinacridone quinone pigments, dioxazine pigments, phthalocyanine pigments, anthrapyrimidine pigments, ansanthrone pigments, indanthrone pigments, flavanthrone pigments, perylene pigments. , Diketopyrrolopyrrole pigments, perinone pigments, quinophthalone pigments, anthraquinone pigments, thioindigo pigments, benzimidazolone pigments, isoindolinone pigments, azomethine pigments or azo pigments.

  Specific examples of the organic pigment used in the water-based ink composition according to the present invention include the following.

  Examples of the pigment used in the cyan ink composition include C.I. I. Pigment blue 1, 2, 3, 15: 3, 15: 4, 15:34, 16, 22, 60, etc .; C.I. I. Bat blue 4, 60 and the like, preferably C.I. I. Pigment Blue 15: 3, 15: 4, and one or a mixture of two or more selected from the group consisting of 60. These pigments are contained in an amount of 0.5 to 15% by weight, preferably about 1 to 10% by weight, based on the cyan ink composition.

  Examples of the pigment used in the magenta ink composition include C.I. I. Pigment Red 5, 7, 12, 48 (Ca), 48 (Mn), 57 (Ca), 57: 1, 112, 122, 123, 168, 184, 202, C.I. I. Pigment violet 19 and the like, preferably C.I. I. Pigment red 122, 202, and 209, C.I. I. One or a mixture of two or more selected from the group consisting of pigment violet 19. These pigments are contained in an amount of about 0.5 to 15% by weight, preferably about 1 to 10% by weight, based on the magenta ink composition.

  Examples of the pigment used in the yellow ink composition include C.I. I. Pigment Yellow 1, 2, 3, 12, 13, 14C, 16, 17, 73, 74, 75, 83, 93, 95, 97, 98, 119, 110, 114, 128, 129, 138, 150, 151, 154, 155, 180, 185, etc., preferably C.I. I. One or a mixture of two or more selected from the group consisting of CI Pigment Yellow 74, 109, 110, 128, and 138. These pigments are contained in an amount of about 0.5 to 15% by weight, preferably about 1 to 10% by weight, based on the yellow ink composition.

  Examples of the pigment used in the orange ink composition include C.I. I. Pigment Orange 36 or 43, or a mixture thereof. These pigments are contained in an amount of about 0.5 to 15% by weight, preferably about 1 to 10% by weight, based on the orange ink composition.

  Examples of the pigment used in the green ink composition include C.I. I. Pigment Green 7 or 36 or a mixture thereof. These pigments are contained in an amount of about 0.5 to 15% by weight, preferably about 1 to 10% by weight, based on the green ink composition.

  In the water-based ink composition of the present invention, the weight ratio of the colorant to the dispersion polymer is preferably 10: 1 to 1:10, and more preferably 4: 1 to 1: 3. Further, the particle size of the colorant at the time of dispersion is such that the maximum particle size when measured by a dynamic light scattering method is less than 500 nm and the average particle size is 300 nm or less, more preferably the average particle size is 200 nm or less.

[Resin emulsion]
The resin emulsion suppresses the above-mentioned dispersion from permeating into the recording medium and improves its color development property. As the resin emulsion is further dried, the resin emulsion and the resin emulsion and the dispersion are fused together to form a pigment. By fixing the particles on the recording medium, the fixing property is improved. Examples of the resin component constituting the resin emulsion having such characteristics include acrylic resins, methacrylic resins, styrene resins, urethane resins, acrylamide resins, epoxy resins, and the like, and a mixture of these resins. A system may be used. Among these resin components, a styrene-acrylic acid copolymer, a styrene-acrylic acid-acrylic acid alkyl ester copolymer, a styrene-maleic acid copolymer, and a styrene-maleic acid-acrylic acid alkyl ester copolymer are more preferable. Examples thereof include a polymer, a styrene-methacrylic acid copolymer, a styrene-methacrylic acid-acrylic acid alkyl ester copolymer, and a styrene-maleic acid-half ester copolymer.

  These resin components are required to have both a hydrophobic part and a hydrophilic part as a structure. Here, the hydrophobic portion refers to a repeating unit having an alkyl group, a cycloalkyl group, an aromatic ring, or an unneutralized group. An unneutralized group is a group that can be neutralized by a neutralizing agent, and examples thereof include an acid group and an alkaline group. Specific examples of the unneutralized group include a carboxylic acid group and a sulfonic acid group.

  Moreover, as a hydrophilic part, the repeating unit which has a neutralizing group is shown. The neutralizing group is a group formed by neutralizing an unneutralized group, and is preferably an ionic group. The unneutralized group and the neutralized group are preferably anionic groups, and particularly suitable when the unneutralized group is a carboxylic acid group and the neutralized group is a carboxylic acid anion group (carboxylate group). Can be illustrated. Examples of the carboxylate include lithium carboxylate, sodium carboxylate, potassium carboxylate, and ammonium carboxylate.

  Since the resin component constituting the resin emulsion has the above-described structure, the hydrophobic part is present inside the resin emulsion and is isolated from water, and the hydrophilic part is present on the surface so that it can become familiar with water. Therefore, it can be a resin emulsion that is stably dispersed in water. Further, when adhering to the recording medium, the resin emulsions or the resin emulsion and the dispersion are both fused and formed into a film, and the hydrophobic part can cover the surface of the film. Since this film is insoluble in water and does not re-disperse, and firmly adheres to the recording medium together with the dispersion, the image has good fixability and water resistance.

  Such resin emulsions may be synthesized and used so as to satisfy various characteristics, but commercially available products may also be used. Specifically as a commercial item, mobile 701 (Tg: -19 degreeC), mobile 743 (Tg: 39 degreeC), mobile 745 (Tg: 21 degreeC), mobile 940 (Tg: 1 degreeC), mobile 1930 (Tg: 1 ° C), mobile 664 (Tg: 6 ° C), mobile DM5 (Tg: -3 ° C), mobile 700 (Tg: -2 ° C), mobile 792 (Tg: -2 ° C), mobile DM772 (Tg: 3 ° C) ), Mobile 865 (Tg: 1 ° C), Mobile 870 (Tg: 19 ° C), Mobile 928 (Tg: 5 ° C), Mobile 1750T (Tg: 16 ° C), Mobile 1751 (Tg: 16 ° C), Mobile 1760 ( Tg: 7 ° C), mobile LDM6316 (Tg: 17 ° C), mobile 7200 (Tg: 24 ° C), mobile 727 ( g: 5 ° C), mobile 752 (Tg: 16 ° C), mobile 837 (Tg: 10 ° C), mobile 860 (Tg: 3 ° C), mobile 864 (Tg: 4 ° C), mobile 864M (Tg: 4 ° C) , Mobile DM60 (Tg: 0 ° C.), Mobile DM 765 (Tg: −19 ° C.), Mobile 937 (Tg: −42 ° C.), Mobile 1906 (Tg: −45 ° C.), Mobile LDM 6300 (Tg: 10 ° C.), Mobile 742N (Tg: 37 ° C.), mobile 749E (Tg: 25 ° C.), mobile 752 (Tg: 16 ° C.), mobile 916 (Tg: −5 ° C.), mobile 1700A (Tg: 37 ° C.), mobile 7210 (Tg: 16 ° C), mobile 747 (Tg: 42 ° C), mobile 6520 (Tg: 40 ° C), mobile 7 02 (Tg: −35 ° C.), mobile LDM7010 (Tg: 34 ° C.), mobile VDM7410 (Tg: −4 ° C.), mobile DM 772 (Tg: 3 ° C.), mobile DM 774 (Tg: 10 ° C.), mobile 947 (Tg) : -55 ° C), mobile LDM6481 (Tg: -22 ° C), mobile LDM6880 (Tg: 9 ° C), mobile DM758 (Tg: -60 ° C), mobile DM765 (Tg: -19 ° C), mobile 650 (Tg: −37 ° C.), mobile 760H (Tg: −17 ° C.), mobile 761HG (Tg: −35 ° C.), mobile 763 (Tg: −18 ° C.), mobile 412 (Tg: −62 ° C.), mobile 490 (Tg: −53 ° C.), mobile S-71 (Tg: −53 ° C.), mobile 987 (Tg: -2 ° C), Mobile 1410 (Tg: -8 ° C), Mobile 630 (Tg: 27 ° C), Mobile 620 (Tg: -22 ° C), Mobile 730L (Tg: -13 ° C), Mobile 735 (Tg: 14) ° C), mobile 747 (Tg: 42 ° C), mobile 767 (Tg: 25 ° C), mobile 790 (Tg: 102 ° C), mobile 9000 (Tg: 46 ° C), mobile 880 (Tg: 3 ° C), mobile DM60 (Tg: 3 ° C), mobile 8020 (Tg: -22 ° C), mobile 8030 (Tg: 17 ° C), mobile 8055 (Tg: 78 ° C), mobile 8201 (Tg: 8 ° C), mobile 787 (Tg: 14) ° C), mobile 710 (Tg: 9 ° C), mobile 718 (Tg: -6 ° C), mobile 776 (Tg: -2) ° C), Mobile 952 (Tg: -38 ° C), Mobile 963A (Tg: -19 ° C), Mobile DM772 (Tg: 6 ° C), Mobile 975A (Tg: 27 ° C), Mobile 3200 (Tg: -21 ° C) Apletan 760H (Tg: −17 ° C.), apletan 2200 (Tg: 19 ° C.), apletan 2000 (Tg: 19 ° C.), apletan 3510 (Tg: 0 ° C.), apletan 3410 (Tg: −32 ° C.) (all above) Trade name, manufactured by Clariant Japan Co., Ltd.), PCL series 0619 (Tg: -4 ° C), PCL series 0623A (Tg: -6 ° C), PCL series 0640 (Tg: 55 ° C), PCL series 0693 (Tg: 20 ° C) ), PCL series 0695 (Tg: -4 ° C), PCL series 0696 (Tg: -12 ° C) PCL series 0850 (Tg: 7 ° C), PCL series 0890 (Tg: -17 ° C), SB series 0561 (Tg: -63 ° C), SB series 0589 (Tg: 0 ° C), SB series 0602 (Tg: 40 ° C) ), SB series 2108 (Tg: −66 ° C.), SB series 0533 (Tg: −20 ° C.), SB series 0545 (Tg: −31 ° C.), SB series 0548 (Tg: −49 ° C.), SB series 0568 ( −23 ° C.), SB series 0569 (Tg: −4 ° C.), SB series 0573 (Tg: −9 ° C.), SB series 0597C (Tg: 28 ° C.), AE series AE116 (Tg: 50 ° C.), AE series AE119 (Tg: 55 ° C.), AE series AE120 (Tg: −10 ° C.), AE series AE121 (Tg: 58 ° C.), AE series AE125 (Tg: 60 ° C), AE series AE134 (Tg: 48 ° C), AE series AE137 (Tg: 48 ° C), AE series AE140 (Tg: 53 ° C), AE series AE173 (Tg: 60 ° C), AE series AE200 (Tg: -45 ° C), AE series AE311 (Tg: -50 ° C), AE series AE318 (Tg: 5 ° C), AE series AE337 (Tg: -30 ° C), AE series 343 (Tg: 0) ° C), AE series 362 (Tg: -5 ° C), AE series AE373B (Tg: 10 ° C), AE series AE379A (Tg: 20 ° C), AE series AE513A (Tg: -48 ° C), AE series AE517 (Tg) : -48 ° C), AE series AE604 (Tg: 5 ° C), AE series AE610C Tg: -62 ° C), AE series AE815 (Tg: 5 ° C), AE series AE945 (Tg: -17 ° C), AE series AE950 (Tg: -20 ° C), AE series AE986A (Tg: 2 ° C) (above) All trade names, manufactured by JSR Corporation), Jonkrill 7100 (Tg: -10 ° C), Jonkrill 390 (Tg: -5 ° C), Jonkrill 1674 (Tg: -4 ° C), Jonkrill 711 (Tg: 0) ), Jonkrill 1695 (Tg: 5 ° C), Jonkrill 511 (Tg: 9 ° C), Jonkrill 7001 (Tg: 12 ° C), Jonkrill 632 (Tg: 12 ° C), Jonkrill 741 (Tg: 15) ° C), Jonkrill 450 (Tg: 16 ° C), Jonkrill 840 (Tg: 16 ° C), Jonkrill 74J (Tg: 22 ° C), PDX-71 1B (Tg: 19 ° C.), HRC-1645 (Tg: 21 ° C.), Jonkrill 734 (Tg: 30 ° C.), Jonkrill 852 (Tg: 31 ° C.), Jonkrill 7600 (Tg: 35 ° C.), Jonkrill 775 (Tg: 37 ° C.), Jonkrill 537 (Tg: 49 ° C.), Jonkrill 1535 (Tg: 50 ° C.), PDX-7630A (Tg: 53 ° C.), Jonkrill 352 (Tg: 56 ° C.), Jonkrill 352D (Tg: 56 ° C.), PDX-7145 (Tg: 56 ° C.), Jonkrill 538 (Tg: 66 ° C.) (all are trade names, manufactured by Johnson Polymer Co., Ltd.) and the like.

  One or a plurality of these resin emulsions can be used in the aqueous ink composition of the present invention, and at least one of them is preferable that the Tg of the resin component constituting it is 30 ° C. or higher. The reason is that by including a resin emulsion in which the Tg of the resin is 30 ° C. or higher, the dispersion, that is, the colorant such as a pigment can be present on the surface of the recording medium, and as a result, the effect of increasing the color developability. Because there is.

  The addition amount of these resin emulsions may be appropriately determined in consideration of fixability, color developability and the like, but is preferably in the range of 0.1% by weight to 20% by weight in terms of solid content in the aqueous ink composition. If the amount of the resin emulsion added is less than 0.1% by weight, the color developability of the image may be poor. On the other hand, if it exceeds 20% by weight, the ink viscosity becomes high and becomes unsuitable as an ink for an ink jet recording system, and the solid content concentration in the ink becomes high, so that clogging of the head nozzle is likely to occur. .

  Here, it is essential that the resin emulsion used in the water-based ink composition of the present invention is previously heat-treated at a temperature equal to or higher than Tg of the resin component constituting the resin emulsion. The reason for this is as described above, because the storage stability (change in particle size, change in viscosity, etc.) of the aqueous ink composition for a long period of time or at a high temperature is dramatically improved. At that time, as a heating condition, it is necessary to heat the resin emulsion at a temperature equal to or higher than Tg of the resin component until the pH of the resin emulsion becomes constant. Specifically, the heating process is completed when the pH becomes constant by continuing the heating at a temperature equal to or higher than the Tg of the resin component. If the heat treatment is completed before the heating time is short, that is, before the pH becomes constant, unneutralized groups such as carboxylic acid remain inside the resin emulsion particles. When this is added to the ink, the same situation as when a resin emulsion that has not been heat-treated is added, and the storage stability of the ink cannot be ensured.

  When the resin emulsion is heat-treated until the pH becomes constant, the finally reached pH differs depending on the resin emulsion to be used and cannot be determined unconditionally. However, other components added to the aqueous ink composition, particularly those of the present invention, From the viewpoint of ensuring the dispersion stability of the pigment dispersion used in the aqueous ink composition, it is preferable to use a resin emulsion having a pH after heat treatment of 7.0 or more at 25 ° C. If a resin emulsion having a pH after the heat treatment of at least this value is used, it is easy to ensure storage stability as a water-based ink composition. When a resin emulsion having a pH of less than 7.0 is used, interaction with the pigment dispersion tends to occur when the resin emulsion is added. If this ink is left for a long period of time or at a high temperature, the viscosity, particle size, Detrimental effects such as sedimentation may occur.

[Humectant]
It is essential that the aqueous ink composition according to the present invention comprises a humectant. The humectant is added to suppress drying of the water-based ink composition, and has an effect of preventing aggregation and solidification of the water-based ink composition by suppressing water evaporation due to drying at the tip of the printer head nozzle.

  The humectant is selected from water-soluble and highly hygroscopic materials such as glycerin, ethylene glycol, diethylene glycol, triethylene glycol, tetraethylene glycol, polyethylene glycol, propylene glycol, dipropylene glycol, polypropylene glycol, 1,3-propanediol. 1,4-butanediol, 1,5-pentanediol, 2,3-butanediol, 2-methyl-2,4-pentanediol, 2-ethyl-1,3-hexanediol, 1,2,6- Polyols such as hexanetriol and pentaerythritol, lactams such as 2-pyrrolidone and N-methyl-2-pyrrolidone, and ureas such as 1,3-dimethylimidazolidinone can be used.

  Furthermore, a water-soluble solid humectant can be used in combination and added for the purpose of assisting the ability of the above materials. Specifically, diols such as 1,6-hexanediol, 1,8-octanediol, 2,2-dimethyl-1,3-propanediol, and 2,2-diethyl-1,3-propanediol, trimethylolethane , Lactams such as ε-caprolactam, urea derivatives such as urea, thiourea and ethylene urea, glucose, mannose, fructose, ribose, xylose, arabinose, galactose, aldonic acid, glucitol (sorbitol), maltose, Monosaccharides such as cellobiose, lactose, sucrose, trehalose, maltotriose, disaccharides, oligosaccharides and polysaccharides, and derivatives of these saccharides include the reducing sugars, oxidized sugars, amino acids, thio sugars, etc. It is done. Sugar alcohol is particularly preferable, and specific examples include maltitol and sorbit.

  The addition amount of these humectants is preferably 1% by weight to 40% by weight, more preferably 1% by weight to 30% by weight, based on the total amount of the aqueous ink composition, alone or in combination. These humectants can be added together with other ink additives in an addition amount that results in an ink viscosity of 25 cPs or less at 25 ° C.

[water]
Water is a medium serving as the center of the aqueous ink composition of the present invention, and preferable water is ion-exchanged water, ultrafiltered water, reverse osmosis water, distilled water for the purpose of reducing ionic impurities as much as possible. Etc. or ultrapure water can be used.

  Further, when water sterilized by ultraviolet irradiation or addition of hydrogen peroxide is used, it is preferable because generation of mold and bacteria can be prevented when the aqueous ink composition is stored for a long period of time.

  The water-based ink composition of the present invention includes a colorant as described above, and can be dispersed in water, and is a dispersion of a dispersion polymer that is insoluble in water alone, and is previously heat-treated at a temperature equal to or higher than Tg of the resin component. Resin emulsion, humectant, and water are essential components. If these components are used, the storage stability and ejection stability of the ink are good, and the color development is excellent regardless of the type of recording medium. Although an image is obtained, various characteristics can be further improved by further including the following components as necessary. Hereinafter, the components will be described.

[Penetration solvent]
According to another aspect, the water-based ink composition according to the present invention can further comprise a penetrating solvent. The permeation solvent here is an additive for accelerating the ink permeability to the recording medium, and is appropriately selected depending on the desired ink drying time.

  As an example of the penetrating solvent, it is preferable to select from glycol monoether derivatives of polyhydric alcohols or 1,2-alkyldiols as having an action of lowering the surface tension of the aqueous ink composition.

  As the 1,2-alkyldiols, 1,2-alkyldiols having 4 to 8 carbon atoms such as butanediol, pentanediol, hexanediol, heptanediol, and octanediol are preferable. Of these, 1,6-hexanediol, 1,2-heptanediol, and 1,2-octanediol having 6 to 8 carbon atoms are particularly preferable because of their high permeability to recording media. The addition amount of these 1,2-alkyl diols is preferably in the range of 0.25 wt% to 5 wt% with respect to the total amount of the aqueous ink composition.

  As the glycol monoether derivative of polyhydric alcohol, a derivative of polyhydric alcohol having 3 or more carbon atoms in alkyl is particularly preferable. Specifically, ethylene glycol monobutyl ether, diethylene glycol mono-n-propyl ether, ethylene glycol mono-iso-propyl ether, diethylene glycol mono-iso-propyl ether, ethylene glycol mono-n-butyl ether, ethylene glycol mono-t-butyl ether Diethylene glycol mono-n-butyl ether, triethylene glycol mono-n-butyl ether, diethylene glycol mono-t-butyl ether, 1-methyl-1-methoxybutanol, propylene glycol mono-t-butyl ether, propylene glycol mono-n-propyl ether, Propylene glycol mono-iso-propyl ether, propylene glycol mono-n-butyl ether, dipropylene Glycol mono -n- butyl ether, dipropylene glycol mono -n- propyl ether, dipropylene glycol monomethyl -iso- propyl ether. The addition amount of the glycol monoether derivative of the polyhydric alcohol is preferably in the range of 0.5 to 15% by weight with respect to the total amount of the aqueous ink composition.

  Moreover, as another example of the osmotic solvent, methanol, ethanol, n-propyl alcohol, iso-propyl alcohol, 2,2-dimethyl-1-propanol, n-butanol, 2-butanol, tert-butanol, iso-butanol Water-soluble ones such as 2-methyl-1-butanol, 3-methyl-1-butanol, 3-methyl-2-butanol, n-pentanol, 2-pentanol, 3-pentanol, tert-pentanol, etc. And monohydric alcohols. The addition amount of these monohydric alcohols is preferably in the range of 0.5 wt% to 10 wt% with respect to the total amount of the aqueous ink composition.

  These penetrating solvents may be used alone or in a mixture of two or more. In particular, when a plurality of types of penetrating solvents having different structures are used in combination, the same image quality can be obtained for various recording medium types exhibiting different penetrability and color developability, which is preferable from the viewpoint of compatibility with recording medium types.

  In the case of an aqueous ink composition having a relatively long drying time, a moisturizing agent having a relatively small surface tension of an aqueous solution can be used as a substitute for the penetrating solvent. In this case, the above penetrating solvent is used. It can also be set as a water-based ink composition without adding.

  The penetrating solvent described above has almost no dissolving action in the dispersion polymer or the resin emulsion, and has an action of stably dispersing and holding the dispersion liquid in which the dispersion polymer or the resin emulsion is dispersed. For this reason, the water-based ink composition of the present invention is highly preserved because there is almost no free dispersion polymer or dissolved resin component that is not adsorbed on the surface of the colorant such as a pigment even if it contains the penetrating solvent as described above. There is an advantage that stability and ejection stability can be secured.

  These penetrating solvents have excellent properties as penetrating components, and water-based ink compositions containing them have excellent penetrability and drying properties because their wettability and penetration rate are improved regardless of the type of recording medium. Indicates. Furthermore, since it also has a function of exhibiting high color developability regardless of the colorant, it also has an effect that a clear printed image with higher color developability can be realized without selecting a paper type.

[Acetylene glycol surfactant]
According to another aspect, the water-based ink composition according to the present invention can further comprise an acetylene glycol surfactant. The acetylene glycol-based surfactant here is an additive for accelerating the ink permeability to the recording medium, like the above-mentioned penetrating solvent. In addition, the acetylene glycol-based surfactant has characteristics with little or no foaming property, and is particularly useful when the aqueous ink composition of the present invention is used in an ink jet recording method. Preferable specific examples of the acetylene glycol surfactants preferable in the present invention include Surfynol 61, 82, 104, 440, 465, 485, or TG (all trade names, manufactured by Air Products and Chemicals, Inc.), Orphine STG, Olphine E1010, etc. (all trade names, manufactured by Nissin Chemical Industry Co., Ltd.) are included.

  The addition amount of the acetylene glycol surfactant may be appropriately determined depending on the desired ink drying time, but is preferably 0.01% by weight to 10% by weight with respect to the total amount of the aqueous ink composition.

  The acetylene glycol surfactant described above has almost no dissolving action in the dispersion polymer and the resin emulsion, and has an action of stably dispersing and holding the dispersion liquid in which the dispersion polymer or resin emulsion is dispersed. . Therefore, the water-based ink composition of the present invention contains almost no free dispersed polymer or dissolved resin component that is not adsorbed on the surface of the colorant such as a pigment even if it contains the acetylene glycol surfactant as described above. Therefore, there is an advantage that high storage stability and ejection stability can be secured.

  In addition, these acetylene glycol surfactants have excellent properties as penetrating components, and aqueous ink compositions containing them have improved wettability and penetration speed regardless of the type of recording medium. Shows excellent properties. Furthermore, since it also has a function of exhibiting high color developability regardless of the colorant type, it has an effect that a clear printed image with higher color developability can be realized without selecting a paper type.

[Weak alkaline agent]
In the ink jet recording apparatus, when a metal is used in the flow path of the water-based ink composition, the water-based ink composition of the present invention may be used because the metal may corrode if the water-based ink composition is acidic. It is desirable to be adjusted to be alkaline or alkaline.

  In order to adjust to neutral or alkaline, according to another aspect, the water-based ink composition preferably further contains a weak alkalinizing agent. Here, when a strongly alkaline compound such as sodium hydroxide is used to adjust the water-based ink composition to neutral or alkaline, an unneutralized group which is a hydrophobic portion in the dispersed polymer is converted into an acid group (carboxylic acid group, In the case of a sulfonic acid group or the like, neutralization of the acid group may proceed. In that case, as described above, the entire dispersion polymer becomes water-soluble, the free polymer that does not adsorb to the colorant such as pigment increases, and the discharge of the aqueous ink composition from the printer head becomes unstable. Problems such as bleeding and show-through occur in the image. In the present invention, by using a weak alkalinizing agent, the aqueous ink composition can be kept neutral or alkaline without greatly changing the neutralization rate of the dispersion polymer, and a more reliable aqueous ink composition is provided. can do.

  Examples of the weak alkalinizing agent include compounds selected from organic acid salts and organic buffering agents. The organic acid salt is preferably an alkyl carboxylic acid salt such as acetate or propionate, or a hydroxy acid salt such as lactate, glycolate or glycerate. Among these, alkali metal salts of alkylcarboxylic acids are preferable, such as sodium acetate, potassium acetate, sodium propionate, potassium propionate, and the like. As the organic buffer, tris (hydroxymethyl) aminomethane, tris-hydrochloride, tris-maleic acid, bis (2-hydroxyethyl) iminotris (hydroxymethyl) methane and the like are preferable.

  The addition amount of the weak alkalinizing agent can be appropriately set according to the desired ink pH, and is preferably in the range of 0.01 to 10% by weight.

[Other ingredients]
The water-based ink composition of the present invention may further contain additives that are usually used in ink jet recording inks, if necessary.

  Additives added as necessary include antioxidants, ultraviolet absorbers, preservatives, fungicides, surfactants, and the like.

  Antioxidants and ultraviolet absorbers include allophanates such as allophanate and methyl allophanate, biurets such as biuret, dimethylbiuret and tetramethylbiuret, L-ascorbic acid and its salts, etc. Tinuvin 328, 900 manufactured by Ciba Geigy 1130, 384, 292, 123, 144, 622, 770, 292, Irgacor 252, 153, Irganox 1010, 1076, 1035, MD1024, or the like, or a lanthanide oxide or the like is used.

  Examples of antiseptics and fungicides include sodium benzoate, sodium pentachlorophenol, sodium 2-pyridinethiol-1-oxide, sodium sorbate, sodium dehydroacetate, 1,2-dibenzisothiazolin-3-one, etc. You can choose from.

  The surfactant is an additive for further accelerating the ink permeability to the recording medium. Suitable materials include anionic surfactants such as fatty acid salts and alkyl sulfate ester salts, polyoxyethylene alkyl ethers, polyoxyethylenes. Nonionic surfactants such as ethylene phenyl ether, acetylene glycol-based nonionic surfactants, cationic surfactants, amphoteric surfactants, silicon-based surfactants, phosphorus-based surfactants, boron-based surfactants Etc. can be used as needed.

  Examples of the silicon surfactant include BYK-307, BYK-331, BYK-333, BYK-347, BYK-348 (all of which are trade names, manufactured by BYK Chemie Co., Ltd.).

[Physical properties of water-based ink composition]
The water-based ink composition of the present invention may be used in the flow path of the water-based ink composition in the viewpoint of ensuring storage stability (change in particle size, change in viscosity, etc.) and dispersion stability, and in an inkjet recording apparatus. From the viewpoint of preventing corrosion of metal parts, the pH is preferably adjusted to neutral or alkaline. More desirably, the pH of the aqueous ink composition at 25 ° C. is in the range of 7.0 to 10.0. Deviating from this range tends to cause problems in terms of storage stability, dispersion stability, and corrosion. In particular, when the pH exceeds 10.0, the dispersion polymer including a colorant such as a pigment becomes water-soluble and functions as a penetrating agent, so that it penetrates into the recording medium more than necessary, resulting in an image. There also occurs a problem that the color developability is inferior due to bleeding and back-through.

  In addition, the water-based ink composition of the present invention preferably has a viscosity of 25 cPs or less at 25 ° C. from the viewpoint of ensuring ejection stability in an ink jet recording apparatus. More preferably, it is 15 cPs or less.

[Colorant dispersion method and selection of water-soluble organic solvent and dispersion polymer]
In the present invention, a preferred method for dispersing a colorant with a dispersion polymer is to dissolve or disperse a polymer containing an anionic group in alkaline water containing an alkaline compound such as an organic amine or an alkali metal salt compound. And a colorant can be mixed and dispersed using a dispersing machine such as a ball mill, a sand mill, an attritor, a roll mill, an agitator mill, a Henschel mixer, a colloid mill, an ultrasonic homogenizer, a jet mill, or an ang mill. More preferably, in order to more firmly adhere the colorant and the dispersion polymer and stabilize the dispersion, JP-A-9-151342, JP-A-10-140065, JP-A-11-209672, JP-A-11-172180, It can also be produced by the methods disclosed in JP-A-10-25440, JP-A-11-43636, or JP-A-2001-247810. The manufacturing methods disclosed in these publications are outlined below.

  JP-A-2001-247810, JP-A-9-151342, and JP-A-10-140065 disclose “phase inversion method” and “acid precipitation method”.

a) "Phase inversion method"
In the present invention, the “phase inversion method” basically refers to a self-dispersion (phase inversion emulsification) method in which a mixed melt of a polymer having self-dispersing ability or solubility and a pigment is dispersed in water. . Here, the mixed melt means a mixed state without dissolving, a mixed state with dissolved, or a state including both of these states.

As one specific example,
(1) A step of preparing a solvent-based slurry by adding a pigment, a neutralizing agent and a small amount of water to a dispersion polymer precursor (a polymer containing an anionic group as described above) / solvent solution,
(2) Dispersing the slurry while adding it to a large amount of water to produce a water-based slurry;
(3) A step of removing the solvent used for dissolving the polymer from the water-based slurry to prepare a pigment-containing polymer particle dispersion including a pigment with a water-dispersible polymer.

b) "Acid precipitation"
In the present invention, the “acid precipitation method” refers to preparing a water-containing cake composed of a polymer and a pigment, and neutralizing a part of the unneutralized groups contained in the polymer in the water-containing cake with a neutralizing agent. This is a method for producing a colorant.

When the unneutralized group is an anionic acid group and the neutralizing agent is a basic compound, specifically, for example,
(1) A step of dispersing a polymer and a pigment in an alkaline aqueous medium, and subjecting the polymer to gelation by performing a heat treatment as necessary, and (2) neutralizing or acidifying the polymer by making the pH neutral or acidic. A step of hydrophobizing to strongly fix the polymer to the pigment, (3) a step of filtering and washing with water as necessary to obtain a water-containing cake, and (4) a polymer in which the water-containing cake is contained. A step of neutralizing a part or all of the anionic group with a basic compound and then redispersing in an aqueous medium; and (5) a step of gelling the polymer by performing heat treatment as necessary. Is included.

  More specific production methods of the above “phase inversion method” and “acid precipitation method” are the same as those disclosed in JP-A-9-151342 and JP-A-10-140065. Good.

Further, JP-A-11-209672 and JP-A-11-172180 disclose a method for producing a colorant. The outline of this production method basically comprises the following production steps.
(1) A polymer having an anionic group or a solution obtained by dissolving it in an organic solvent and a neutral compound are mixed and neutralized. (2) A pigment is mixed into this mixed solution to form a suspension. Later, the pigment is dispersed by a disperser or the like to obtain a pigment dispersion, (3) if necessary, the solvent is distilled off, and (4) a polymer having an anionic group by adding an acidic compound. By coating the pigment with a polymer having an anionic group, (5) filtering and washing with water as necessary, and (6) adding a basic compound to have an anionic group. Neutralizing anionic groups of the polymer and dispersing in an aqueous medium to obtain an aqueous dispersion.

  Moreover, it may be the same as that disclosed in JP-A-11-2096722 and JP-A-11-172180.

  In the aqueous dispersion of the colorant obtained as described above, the above-described 2-ethyl-1,3-hexanediol and water, and the above-described water-soluble organic solvent, weak alkali agent, and other components as necessary. By adding the aqueous ink composition, it can be suitably produced.

<Inkjet recording method and recorded matter>
As the ink jet recording method of the present invention, any method can be used as long as it is a system in which the above-described aqueous ink composition is ejected as droplets from a fine nozzle and the droplets adhere to a recording medium. To explain some of them, there is an electrostatic attraction method. In this method, a strong electric field is applied between the nozzle and the acceleration electrode placed in front of the nozzle, and ink is continuously ejected in the form of droplets from the nozzle. There are a method of recording by supplying a printing information signal to the deflection electrode while the ink droplet flies between the deflection electrodes, or a method of ejecting the ink droplet corresponding to the printing information signal without deflecting the ink droplet.

  The second method is a method in which ink droplets are forcibly ejected by applying pressure to the ink liquid with a small pump and mechanically vibrating the nozzle with a crystal resonator or the like. The ejected ink droplet is charged simultaneously with the ejection, and a printing information signal is given to the deflection electrode and recorded while the ink droplet flies between the deflection electrodes.

  The third method is a method using a piezoelectric element, in which a pressure and a print information signal are simultaneously applied to an ink liquid by a piezoelectric element to eject and record ink droplets.

  The fourth method is a method in which the ink liquid is rapidly expanded in volume by the action of heat energy, and the ink liquid is heated and foamed with a microelectrode in accordance with a print information signal to eject and record ink droplets.

  Of the various ink jet recording methods described above, in particular, by combining the printing method at a relatively low ink discharge speed of 10 m / s or less with the aqueous ink composition of the present invention, ink adhesion to the discharge nozzle is prevented. Ink jet recording can be performed stably, which is preferable.

  The recorded matter of the present invention can be obtained by printing the above-described aqueous ink composition by an ink jet recording method.

  The contents of the present invention will be clearly described by the following examples, but the scope of the present invention is not limited to the following examples. Moreover, the dispersion liquid used for the water-based ink composition of the present invention was prepared by the following method.

<Preparation of dispersion>
(1) Dispersion 1
75 g of MA100 (trade name, manufactured by Mitsubishi Chemical Corporation) as carbon black, Jonkrill 611 (trade name, Johnson Polymer Co., Ltd., weight average molecular weight 8, 100, acid value 53 KOH mg / g) 25 g, potassium hydroxide 1.0 g, and 250 g of ultrapure water purified by an ion exchange method and a reverse osmosis method were mixed and dispersed in a ball mill using zirconia beads for 10 hours. The obtained dispersion stock solution is filtered through a membrane filter having a pore size of about 8 μm (trade name, manufactured by Nihon Millipore Limited) to remove coarse particles, diluted to a pigment concentration of 15% by weight with ultrapure water, and dispersed with a dispersion polymer. Liquid 1 was prepared.

(2) Dispersion 2
A dispersion was prepared in the same manner as dispersion 1, except that carbon black was replaced with color black S160 (trade name, manufactured by Degussa) and the amount of potassium hydroxide added was changed to 1.20 g. This is Dispersion Liquid 2.

(3) Dispersion 3
For dispersion 1, carbon black was converted to C.I. I. A dispersion was prepared in the same manner except that Pigment Blue 15: 3 65 g, the addition amount of the dispersion polymer was changed to 35 g, and the addition amount of potassium hydroxide was changed to 1.70 g. This is Dispersion Liquid 3.

(4) Dispersion 4
For dispersion 1, carbon black was converted to C.I. I. A dispersion was prepared in the same manner except that Pigment Yellow 74 was used. This is Dispersion Liquid 4.

(5) Dispersion 5
75 g of MA100 (trade name, manufactured by Mitsubishi Chemical Co., Ltd.) as carbon black, Jonkrill 678 (trade name, Johnson Polymer Co., Ltd., weight average molecular weight 8, 500, acid value 215 KOH mg / g) 25 g, potassium hydroxide 1.80 g, and ultrapure water 250 g purified by ion exchange method and reverse osmosis method were mixed and dispersed in a ball mill with zirconia beads for 10 hours. The obtained dispersion stock solution is filtered through a membrane filter having a pore size of about 8 μm (trade name, manufactured by Nihon Millipore Limited) to remove coarse particles, diluted to a pigment concentration of 15% by weight with ultrapure water, and dispersed with a dispersion polymer. Liquid 5 was prepared.

(6) Dispersion 6
A dispersion was prepared in the same manner as in dispersion 1, except that carbon black was replaced with color black S160 (trade name, manufactured by Degussa) and the amount of potassium hydroxide added was changed to 3.80 g. This is designated as Dispersion Liquid 6.

(7) Dispersion 7
For dispersion 1, carbon black was converted to C.I. I. A dispersion was prepared in the same manner except that 80 g of Pigment Red 122 was replaced with 20 g of the dispersion polymer and 3.44 g of potassium hydroxide. This is designated as Dispersion Liquid 7.

(8) Dispersion 8
[Synthesis of dispersion polymer]
A reaction vessel equipped with a stirrer, thermometer, reflux tube and dropping funnel was replaced with nitrogen, and then 25 g of styrene, 30 g of n-dodecyl methacrylate, 20 g of methoxypolyethylene glycol methacrylate, 15.5 g of butyl methacrylate, and 9.3 g of methacrylic acid were added to 100 g of methyl ethyl ketone. And was replaced with nitrogen gas.

  The same monomer / methyl ethyl ketone solution was placed in the dropping funnel, and 0.2 g of 2,2'-azobis (2,4-isomethylvaleronitrile) was further added to perform nitrogen gas replacement.

  In a nitrogen atmosphere, the polymerization reaction was carried out while heating to 65 ° C. and adding the dropping funnel solution over 3 hours. The obtained copolymer solution was purified by repeatedly drying under reduced pressure, dissolving methyl ethyl ketone and filtering, and then diluted by adding methyl ethyl ketone so that the solid content of the dispersed polymer was 50% by weight. A dispersion polymer solution A having an acid value of about 70 KOH mg / g and a weight average molecular weight of 50,000 was obtained.

[Preparation of dispersion]
150 g of MA100 (trade name, manufactured by Mitsubishi Chemical Corporation) as carbon black and 100 g of the above dispersion polymer solution A were mixed and stirred to prepare a slurry. To this slurry, 50 g of a 10 wt% aqueous potassium hydroxide solution was added and dispersed with an ultrahigh pressure homogenizer.

  Subsequently, this dispersion solution is gradually added to 400 g of stirring pure water, and all of methyl ethyl ketone and a part of water are removed at 60 ° C. under reduced pressure to further increase the pigment concentration to 15% by weight. Pure water was added to obtain dispersion 8.

(9) Dispersion 9
A dispersion was prepared in the same manner as in dispersion 8, except that carbon black was replaced with color black S160 (trade name, manufactured by Degussa) and the addition amount of 10 wt% potassium hydroxide aqueous solution was changed to 47.5 g. . This is designated as Dispersion Liquid 9.

(10) Dispersion 10
C. of organic pigments I. Pigment Blue 15: 4 50 g and the above-mentioned dispersion polymer solution A 100 g were mixed and stirred to prepare a slurry. To this slurry, 47.5 g of a 10% by weight aqueous potassium hydroxide solution was added and dispersed with an ultrahigh pressure homogenizer.

  Subsequently, this dispersion solution was gradually added to 250 g of stirring pure water, and all of methyl ethyl ketone and a part of water were removed at 60 ° C. under reduced pressure to further increase the pigment concentration to 15% by weight. Pure water was added to obtain dispersion 10.

(11) Dispersion 11
For the dispersion 10, the pigment is an organic pigment C.I. I. Pigment Red 122 was 200 g, and a dispersion was prepared in the same manner except that the amount of 10 wt% potassium hydroxide aqueous solution was changed to 39.5 g. This is designated as Dispersion Liquid 11.

(12) Dispersion 12
For the dispersion 10, the pigment is an organic pigment C.I. I. Pigment Yellow 74 150 g was used, and a dispersion was prepared in the same manner except that the amount of 10 wt% potassium hydroxide aqueous solution was changed to 39.5 g. This is designated as Dispersion Liquid 12.

(13) Dispersion 13
[Synthesis of dispersion polymer]
Each component of n-butyl methacrylate 40% by weight, n-butyl acrylate 5% by weight, styrene 20% by weight, 2-hydroxyethyl methacrylate 15% by weight and methacrylic acid 20% by weight is mixed in a 1 L beaker so that the total amount becomes 500 g. Further, 4 g of tert-butyl peroxyoctoate was added as a polymerization initiator to obtain a polymer synthesis mixture.

  Next, 500 g of methyl ethyl ketone was put into a 1 L flask, and the temperature was raised to 75 ° C. while stirring in a nitrogen atmosphere. The polymer synthesis mixture was added dropwise over 3 hours with stirring at 75 ° C. The reaction was further continued for 8 hours at 75 ° C. with stirring. Thereafter, the reaction product was naturally cooled to 25 ° C., and diluted by adding methyl ethyl ketone so that the solid content was 50% by weight. A dispersion polymer solution B having an acid value of 150 KOH mg / g and a weight average molecular weight of 15,000 was obtained.

[Preparation of dispersion]
150 g of MA100 (trade name, manufactured by Mitsubishi Chemical Corporation) as carbon black, 100 g of the above-mentioned dispersion polymer solution B, 50 g of 10 wt% potassium hydroxide aqueous solution, and 700 g of ultrapure water purified by an ion exchange method and a reverse osmosis method are mixed. In a sand mill (manufactured by Yaskawa Seisakusho), the mixture was dispersed for 2 hours together with glass beads (diameter 1.7 mm, 1.5 times the amount (weight) of the mixture). Thereafter, the glass beads were removed, other components were added, and the mixture was stirred at room temperature for 20 minutes, followed by filtration through a 5 μm membrane filter.

  The obtained filtrate was distilled at 80 ° C. under normal pressure to distill all of methyl ethyl ketone and a part of water. Further, 1N hydrochloric acid solution was added dropwise with stirring to coagulate the dispersed polymer layer. This was subjected to suction filtration while washing with water to obtain a water-containing pigment cake. While stirring the water-containing cake, 1% by weight of potassium hydroxide aqueous solution was redispersed in 375 g, and ultrapure water was further added so that the pigment concentration was 15% by weight, whereby dispersion 13 was obtained.

(14) Dispersion 14
The dispersion liquid was prepared in the same manner as the dispersion liquid 13 except that the carbon black was color black S160 (trade name, manufactured by Degussa) and the amount of the 1 wt% potassium hydroxide aqueous solution added during redispersion was changed to 422 g. Produced. This is referred to as dispersion 14.

(15) Dispersion 15
For the dispersion 13, carbon black was changed to C.I. I. A dispersion was prepared in the same manner as in Pigment Red 122, except that 250 g of the 1% by weight aqueous potassium hydroxide solution was changed to 422 g. This is designated as dispersion 15.

(16) Dispersion liquid 16
[Preparation of dispersion polymer]
50 g of styrene-methyl methacrylate polymer having a weight average molecular weight of 15,000 and a styrene molar ratio of 35%, 500 g of 2-pyrrolidone and 25 g of sulfamic acid were mixed and reacted at 80 ° C. for 3 hours to sulfonate some styrene. The solution was purified by repeated dissolution in 2-pyrrolidone and precipitation with acidic water at pH 5.0, and then dissolved in methyl ethyl ketone so that the solid content was 50% by weight. A dispersion polymer solution C having an acid value of 70 KOH mg / g and a weight average molecular weight of 15,000 was obtained.

[Preparation of dispersion]
150 g of MA100 (trade name, manufactured by Mitsubishi Chemical Corporation) as carbon black, 100 g of the above-mentioned dispersion polymer solution C, 25 g of 10 wt% potassium hydroxide aqueous solution, and 700 g of ultrapure water purified by an ion exchange method and a reverse osmosis method are mixed. In a sand mill (manufactured by Yaskawa Seisakusho), the mixture was dispersed for 2 hours together with glass beads (diameter 1.7 mm, 1.5 times the amount (weight) of the mixture). Thereafter, the glass beads were removed, other components were added, and the mixture was stirred at room temperature for 20 minutes, followed by filtration through a 5 μm membrane filter.

  The obtained filtrate was distilled at 80 ° C. under normal pressure to distill all of methyl ethyl ketone and a part of water. Further, 1N hydrochloric acid solution was added dropwise with stirring to coagulate the dispersed polymer layer. This was subjected to suction filtration while washing with water to obtain a water-containing pigment cake. While stirring the water-containing cake, 1% by weight potassium hydroxide aqueous solution was redispersed in 310 g, and ultrapure water was further added so that the pigment concentration was 15% by weight, whereby dispersion 16 was obtained.

(17) Dispersion 17
For the dispersion 16, carbon black was changed to C.I. I. Pigment Blue 15: 3 A dispersion was prepared in the same manner except that 250 g was used. This is designated as Dispersion Liquid 17.

<Preparation of water-based ink composition>
[Example 1]
In Example 1, Johncrill 734 (trade name, Tg: 30 ° C., solid content: 42% by weight, manufactured by Johnson Polymer Co., Ltd.) was used. The heat treatment method was performed by sealing Joncrill 734 in a sample bottle and leaving it at 40 ° C. until the pH became constant (pH 7.8 at 25 ° C.). 19.1 g of this heat-treated Joncryl 734, 26.7 g of dispersion 1 (using carbon black) obtained by the above-mentioned materials and methods, 15.0 g of glycerin, 7.0 g of triethylene glycol, trimethylolpropane 5.0g, 2-pyrrolidone 5.0g, ultrapure water is added and the total amount is 100g, stirred for 2 hours, filtered through a membrane filter (trade name, manufactured by Nihon Millipore Limited) with a pore size of about 1.2 μm. A water-based ink composition was prepared.

[Example 2] to [Example 18]
An ink was prepared in the same manner as in Example 1 except that the additives and amounts were changed to the compositions shown in Tables 1 and 2. The resin emulsion and heat treatment method used here are shown below.

<Resin emulsion 1>
Resin emulsion; John Krill 734 (trade name, Tg: 30 ° C., solid content: 42% by weight, manufactured by Johnson Polymer Co., Ltd.)
Heat treatment method: Leave until the pH is constant at 40 ° C. (pH 7.8 at 25 ° C.).

<Resin emulsion 2>
Resin emulsion; Mobile 742N (trade name, Tg: 37 ° C., solid content: 43% by weight, manufactured by Clariant Polymer Co., Ltd.)
Heat treatment method: Leave until pH is constant at 40 ° C. (pH 7.5 at 25 ° C.).

<Resin emulsion 3>
Resin emulsion; AE series AE140 (trade name, Tg: 53 ° C., solid content: 48% by weight, manufactured by JSR Corporation)
Heat treatment method: let stand at 60 ° C. until pH is constant (pH 7.2 at 25 ° C.).

<Resin emulsion 4>
Resin emulsion; John Krill 538 (trade name, Tg: 66 ° C., solid content: 45% by weight, manufactured by Johnson Polymer Co., Ltd.)
Heat treatment method: Leave until the pH is constant at 90 ° C. (pH 7.0 at 25 ° C.).

<Resin emulsion 5>
Resin emulsion; Mobile 937 (trade name, Tg: -42 ° C., solid content: 60% by weight, manufactured by Clariant Polymer Co., Ltd.)
Heat treatment method: Leave until the pH is constant at 40 ° C. (pH 7.9 at 25 ° C.).

<Resin emulsion 6>
Resin emulsion; AE series AE343 (trade name, Tg: 0 ° C., solid content: 55% by weight, manufactured by JSR Corporation)
Heat treatment method: Leave until the pH is constant at 40 ° C. (pH 8.0 at 25 ° C.).

<Resin emulsion 7>
Resin emulsion; Mobile 972 (trade name, Tg: 101 ° C., solid content: 50% by weight, manufactured by Clariant Polymer Co., Ltd.)
Heat treatment method: Leave until the pH is constant at 120 ° C. (pH 6.5 at 25 ° C.).

<Resin emulsion 8>
Resin emulsion; Johncrill 631 (trade name, Tg: 87 ° C., solid content: 49.5 wt%, manufactured by Johnson Polymer Co., Ltd.)
Heat treatment method; no heat treatment (pH 7.5 at 25 ° C.).

(Comparative Example 1)
A water-based ink composition was prepared in the same manner as in Example 2 except that the resin emulsion 2 was not added to the composition of Example 2, but 2.6 g of a 1% by weight potassium hydroxide aqueous solution was added instead. did. As a result of adding potassium hydroxide during preparation of the aqueous ink composition, the amount of potassium hydroxide relative to the total amount of carboxylic acid groups in the dispersion polymer was about 125% in molar ratio, and all the carboxylic acid groups were in the state of potassium carboxylic acid. .

(Comparative Example 2)
A water-based ink composition was prepared in the same manner as in Example 7 except that 14.1 g of resin emulsion 8 was added instead of resin emulsion 1 and resin emulsion 5 to the composition of Example 7.

(Comparative Example 3)
A water-based ink composition was prepared in the same manner as in Example 1 except that 30.3 g of resin emulsion 7 was added instead of resin emulsion 1 to the composition of Example 1.

  Each said composition is put together in Table 1-Table 2, and is shown.

<Evaluation method>
(Storage stability)
The aqueous ink compositions of Examples 1 to 18 and Comparative Examples 1 to 3 were allowed to stand at 60 ° C. for 2 weeks, left for 1 month, and frozen for 1 week. Compared. Judgment criteria are as follows.
・ Viscosity judgment AA: Change width is less than ± 3% A: Change width is ± 3% or more, less than ± 6% B: Change width is ± 6% or more, less than ± 10% C: Change width is ± 10% or more Particle size determination AA: Change width is less than ± 5% A: Change width is ± 5% or more, less than ± 10% B: Change width is ± 10% or more, less than ± 20% C: Change width is ± 20% or more

(Discharge stability)
The aqueous ink compositions of Examples 1 to 18 and Comparative Examples 1 to 3 were mounted on PX-V700 (trade name, manufactured by Seiko Epson Corporation), which is an inkjet printer. A4 size Xerox P (trade name, manufactured by Fuji Xerox Office Supply Co., Ltd.) is used for printing paper, and images with mixed characters and fills are continuously printed in an environment of 20-25 ° C / 40-60% RH. Then, the image being printed was visually observed for defects such as flying bends and missing. Judgment criteria are as follows.
Judgment AA: Even if continuous printing is performed up to 200 sheets, no flying bend / missing occurs. A: Flying bend / missing does not occur when printing is performed up to 100 sheets. B: Flying bend / missing occurs after continuous printing up to 100 sheets. Has occurred, but there are less than 10 locations. C: Flying bends / misses occur at 10 locations or more during continuous printing of up to 100 sheets.

(Evaluation of print quality on plain paper and recycled paper)
The aqueous ink compositions of Examples 1 to 18 and Comparative Examples 1 to 3 were mounted on PX-V700 (trade name, manufactured by Seiko Epson Corporation), which is an inkjet printer. Print quality (character quality) due to character blurring when 1 to 20 points of Gothic characters are printed in 1 point increments on plain paper / recycled paper with the print setting “paper type; plain paper, print quality; fine” Evaluated. Further, an image with a different fill density in 5% increments from 5% to 100% with the same print settings was printed, and the print quality (filled image quality) due to the uneven density and the back-through state of the printed matter was evaluated. In this evaluation, Xerox Premium Multipurpose 4024 (trade name, manufactured by Xerox Corporation), Xerox P (trade name, manufactured by Fuji Xerox Office Supply Co., Ltd.), REYMAT (trade name, manufactured by Ausedat Ray Company), Hammermill Copy Plus (plain paper). Evaluation was carried out visually using Xerox R (trade name, manufactured by Fuji Xerox Office Supply Co., Ltd.) as a recycled paper using a product name (available from International Paper). The evaluation criteria are shown below.

[Character quality]
Evaluation AA: bleeding is not recognized in characters at all points A: Bleeding is slightly observed with characters of 5 points or less B: Characters of 5 points or less appear thick due to bleeding C: Bleeding is remarkable 5 points The following characters cannot be distinguished

[Filled image quality]
Evaluation AA: Almost no shading is observed in all filled images. There is no breakthrough.
A: Slight shading unevenness is recognized in an image with a fill density of 100%, but it is a level that causes no problem in practical use. There is almost no see-through.
B: Light and dark unevenness is observed in an image having a fill density of 50% or more. The show-through is also noticeable.
C: Light and shade unevenness is observed in all filled images. Print-through is remarkable and printing density is low.

  Tables 3 to 4 show the results of pH, storage stability (viscosity, particle size), ejection stability, and print quality (character quality, filled image quality) at the time of preparation for each aqueous ink composition. Shown together.

  As shown in Tables 3 and 4, the aqueous ink compositions of Examples 1 to 18 containing the heat-treated resin emulsion have good storage stability (viscosity change, particle size change) when left under the above conditions. In addition, there was no problem with ejection stability in the ink jet printer. The print quality (character quality, filled image quality) was also good regardless of the paper type.

  On the other hand, in Comparative Example 1 in which no resin emulsion was added to Example 2 and potassium hydroxide was further added to neutralize all unneutralized groups of the dispersed polymer, the material of the aqueous ink composition was blended. Immediately after the treatment, the viscosity changed, and the storage stability when left under the above conditions was poor. Dispersion polymer solubilized by the influence of potassium hydroxide with added ejection stability adhered to the head nozzle surface, causing flight bending and slipping. In addition, due to the influence of the water-dispersed dispersion polymer, the print quality is blurred by the character quality, and uneven density and back-through occur in the painted image quality, resulting in a decrease in the print density.

  In Comparative Example 2 in which a resin emulsion that was not heat-treated was added, the storage stability was poor when left under the above conditions. Incidentally, when the pH of the ink after storage stability evaluation was measured, the pH at 25 ° C. was 6.5, indicating acidity. In addition, there was a paper type in which the print quality bleeds at the character quality and the density unevenness occurs at the filled image quality.

  In Comparative Example 3 in which the resin emulsion in which the pH of the heat-treated product became acidic (pH 6.5 at 25 ° C.) was added, the viscosity fluctuated immediately after the water-based ink composition material was blended and left under the above conditions. Storage stability at the time was inferior and ejection stability was also inferior. In addition, there was a paper type in which the print quality bleeds at the character quality and the density unevenness occurs at the filled image quality.

  Although the present invention has been described in detail and with reference to specific embodiments, it will be apparent to those skilled in the art that various changes and modifications can be made without departing from the spirit and scope of the invention.

  The water-based ink composition of the present invention has high storage stability and ejection stability and is excellent in color developability regardless of the type of recording medium, and is particularly suitable for use as an ink for ink jet recording.

Claims (10)

  A water-based ink composition comprising a coloring component, a resin emulsion, a humectant, and water, wherein the coloring component includes the coloring agent in a dispersion polymer so that it can be dispersed in water, and the dispersion polymer alone is in water. It is a dispersion made of an insoluble material, and is heat-treated at a temperature equal to or higher than the glass transition temperature (Tg) of the resin component constituting the resin emulsion before the resin emulsion is added to the aqueous ink composition. A water-based ink composition characterized by the above.   The aqueous ink composition according to claim 1, further comprising a penetrating solvent.   The aqueous ink composition according to claim 2, wherein the penetrating solvent is selected from the group consisting of monohydric alcohols, glycol monoether derivatives of polyhydric alcohols, and 1,2-alkyldiols.   The aqueous ink composition according to any one of claims 1 to 3, further comprising an acetylene glycol surfactant.   5. The water-based ink according to claim 1, comprising at least one resin emulsion having a glass transition temperature (Tg) of a resin constituting the resin emulsion of 30 ° C. or more. Composition.   The water-based ink composition according to claim 1, wherein the colorant is carbon black, an organic pigment, or a combination thereof.   The aqueous ink composition according to any one of claims 1 to 6, further comprising a weak alkalinizing agent and being alkaline.   The aqueous ink composition according to claim 7, wherein the weak alkalinizing agent comprises at least one compound selected from organic acid salts and organic buffering agents.   An ink jet recording method for performing recording by discharging droplets of the water-based ink composition according to claim 1 and attaching the droplets to a recording medium. The recorded matter which printed the water-based ink composition as described in any one of Claims 1-8 with the inkjet recording method.