JP4692505B2 - Water-based ink composition for inkjet recording - Google Patents

Description

  The present invention relates to a pigment-dispersed water-based ink composition having excellent water resistance, and more particularly to a pigment-dispersed water-based ink composition for inkjet recording.

  Among various recording methods currently known, an inkjet recording method that is low in noise, capable of high-speed recording, and capable of recording on plain paper is an extremely useful recording method.

  In this ink jet recording method, heat is applied to a colored liquid called ink to generate bubbles, and ink is ejected in the form of small droplets from a nozzle having a diameter of 30 to 50 microns by the pressure generated when the bubbles are generated. The main recording methods include a method of recording by adhering to a recording member such as paper and a method of applying pressure to the ink with a piezoelectric element and ejecting small droplets of ink from the nozzles.

  Examples of the ink applied to this recording method include pigment-dispersed water-based ink. However, when an ink-jet recording method is performed using a conventional pigment-dispersed ink, there is a defect that the obtained ink image is inferior in water resistance. . For example, the styrene copolymer used in the water-based ink composition for ink jet recording proposed in Patent Document 1, Patent Document 2, Patent Document 3, Patent Document 4, and Patent Document 5 has an acid value of 200 mgKOH / g. As described above, when ink jet recording is performed with an ink composition that is easily soluble in water and contains a pigment dispersed as a dispersant, there is a drawback that the ink image is inferior in water resistance.

  In Example 2 of Patent Document 6, an aqueous ink composition for ink jet recording containing a pigment, a basic compound and a styrene copolymer dispersed in an aqueous medium, the polymer has an acid value of 430 mgKOH / g. Ink jet including a water-soluble resin, which is a styrene copolymer having a weight average molecular weight of 5,860 and the content of the basic compound is 87% of the amount corresponding to the acid value of the copolymer A water-based ink composition for recording is described.

Further, in Example 2 of Patent Document 7, an aqueous ink composition for ink jet recording comprising a pigment, a basic compound and a styrene copolymer dispersed in an aqueous medium, the copolymer has an acid value of 120 mgKOH. / G, a water-soluble resin, which is a styrene copolymer having a weight average molecular weight of 6,100, and the content of the basic compound is 125% of the amount corresponding to the acid value of the copolymer An aqueous ink composition for ink jet recording is described.
JP-A-56-147860 Japanese Patent Application Laid-Open No. 56-147861 JP-A-56-147862 JP-A-56-147863 Japanese Unexamined Patent Publication No. 56-147859 JP-A-4-018461 JP-A-4-018467

  However, all of the above publications are focused on improving ejection stability, and may give good results in that respect, but the ink images obtained therefrom are still insufficient in water resistance. It had the fault of being. The present invention solves the drawback that the pigment-dispersed water-based ink composition used in the conventional ink jet recording method is inferior in water resistance.

  The water-based ink composition for ink-jet recording of the present invention has a particularly remarkable effect that water resistance is extremely high as compared with an ink image obtained from a conventional ink composition.

  As a result of intensive studies in view of the above situation, the present inventor has found that “resin acid value” and “basic compound content” are not considered to contribute to improvement of water resistance from the description in the above publication. By combining the two scales, a styrene copolymer having an acid value in a specific range is used as the styrene copolymer, and the content of the basic compound is specified in an amount corresponding to the acid value of the copolymer. By carrying out the design within the range, a pigment-dispersed water-based ink composition capable of obtaining an ink image with extremely excellent water resistance, which cannot be predicted from the composition described in these publications, due to their synergistic effect. As a result, the present invention has been completed.

  That is, in the aqueous ink composition for ink jet recording containing the pigment (A), the basic compound (B), and the styrene copolymer (C) dispersed in the aqueous medium (I), the copolymer (C) The acid value is 20 to 170 mgKOH / g, and the content of the basic compound (B) is 40% or more and less than 120% of the amount corresponding to the acid value of the copolymer (C). A water-based ink composition for inkjet recording.

  The present invention is described in detail below.

  The pigment (A) used in the present invention is not particularly limited, and examples thereof include inorganic pigments, organic pigments, and extender pigments as necessary.

  Examples of the inorganic pigment include carbon black, metal oxide, metal sulfide, and metal chloride. In particular, carbon black is preferable in the black aqueous ink composition, and examples of the carbon black include furnace black, lamp black, acetylene black, and channel black. One kind of these carbon blacks may be used, or a plurality of carbon blacks may be used in combination.

  Examples of organic pigments include soluble azo pigments, insoluble azo pigments, insoluble diazo pigments, condensed azo pigments, phthalocyanine pigments, quinacridone pigments, isoindolinone pigments, dioxazine pigments, perylene pigments, perinone pigments, thioindigo pigments, anthoraquinone pigments and quinophthalone pigments. Can be mentioned. One of these organic pigments may be used, or a plurality of organic pigments may be used in combination. Moreover, an inorganic pigment can also be used for an organic pigment. In addition, extender pigments and the like can also be used for improving fluidity.

  According to the prescription of the present invention, the water resistance absolute value of the ink image obtained from the prepared composition is comparable in both the carbon black type and the organic pigment type, but the carbon black type has good water resistance itself. In view of the fact that it is superior to that of organic pigments, organic pigments tend to be more prominent than carbon blacks in terms of the degree of improvement (improvement rate).

  Examples of extender pigments include silica, calcium carbonate, and talc. These extender pigments are rarely used alone and are used in combination with inorganic pigments or organic pigments.

  In addition, two or more kinds of other inorganic pigments and / or organic pigments can be used in combination for toning the black aqueous ink composition. In addition, extender pigments and the like can also be used for improving fluidity.

  The amount of the pigment (A) added is preferably 1-30% by weight of the finally obtained aqueous ink composition, and more preferably 1-10% by weight.

  The styrene copolymer (C) used in the present invention comprises styrene and / or a styrene derivative and one or more ionic monomers as essential constituent monomers, and other monomers having addition polymerizable vinyl groups. It is a copolymer having an acid value of 20 to 170 mgKOH / g, which may be contained as a constituent monomer. Among them, a copolymer having an acid value of 40 to 155 mgKOH / g is preferable.

  Furthermore, as a copolymer, styrene and / or a styrene derivative, (meth) acrylic acid, and one or two or more kinds of acrylic esters are essential constituent monomers because they are excellent in pigment dispersion stability. And a styrene- (meth) acrylic acid- (meth) acrylic acid ester-based copolymer which may contain another monomer having an addition polymerizable vinyl group as a constituent monomer.

  In the present invention, acrylic acid and methacrylic acid are collectively referred to as (meth) acrylic acid.

  The monomer for obtaining the copolymer (C) is a nonionic monomer having an addition-polymerizable vinyl group, such as styrene, styrene derivatives, vinyl naphthalene, vinyl naphthalene derivatives, α, β-ethylenically unsaturated carboxylic acid. Aliphatic alcohol esters, acrylonitrile, vinylidene chloride, vinyl acetate, vinyl chloride, acrylamide, methacrylamide, hydroxyethyl methacrylate, hydroxypropyl methacrylate, glycidyl methacrylate and N-butoxymethylacrylamide. These constitute the hydrophobic part of the copolymer (C) adsorbed on the pigment (A).

  Of these nonionic monomers, styrene and / or styrene derivatives such as α-methylstyrene, which are excellent in adsorptivity to pigments, are essential. However, since a polymer composed only of styrene and / or a styrene derivative has a drawback of lacking flexibility, a copolymer with another nonionic monomer is preferable.

  Examples of the ionic monomer that can be used to obtain the copolymer (C) include monomers having an addition-polymerizable vinyl group. For example, ionic groups such as a carboxylic acid group, a sulfonic acid group, and a sulfate group can be used. For example, (meth) acrylic acid, crotonic acid, itaconic acid, itaconic acid monoester, maleic acid, maleic acid monoester, fumaric acid, fumaric acid monoester, vinyl sulfonic acid, sulfoethyl methacrylate, sulfopropyl methacrylate and sulfonation It is introduced into the copolymer (C) from an ionic monomer such as an α, β-unsaturated monomer of vinyl naphthalene. Of these ionic monomers, (meth) acrylic acid is preferred from the viewpoint of excellent dispersion stability of the pigment.

  The composition of the present invention containing the copolymer (C) can be stabilized by an ionic method. In this ionic method, the pigment (A) particles can be stabilized by neutralization of the copolymer (C) obtained by polymerizing the above-described ionic monomer as an essential component and the basic compound (B). That is, the pigment (A) particles are stabilized through an electric double layer formed by dissociation of the neutralized copolymer (C), whereby the repulsive force of ions prevents the aggregation of the pigment particles. Yes.

  As the copolymer (C), the one that is dispersed in water when neutralized has a higher adsorptivity to the pigment surface, and therefore the mechanical stability of the dispersed pigment is higher, so that it is more soluble than water. preferable. That is, it is more preferable that the copolymer (C) neutralized with the compound (B) is dispersed in the aqueous medium (I).

  One type of styrene copolymer (C) may be used, or a plurality of types may be combined. One or more resins made of nonionic monomers can be combined with a styrene copolymer as an essential component.

  The addition amount of the styrenic copolymer (C) is preferably 1:10 to 5: 1 by weight ratio of the copolymer (C) and the pigment (A), and more preferably 1: 5 to 3: 1. Is preferred.

  In order to disperse or dissolve the styrene copolymer (C) in the aqueous medium, it is necessary to add the basic compound (B). Examples of the basic compound (B) include aliphatic amine compounds, alcohol amine compounds, alkali metal hydroxides and alkaline earth metal hydroxides.

  Examples of the aliphatic amine compound include ammonia, monomethylamine, dimethylamine, trimethylamine, monoethylamine, dimethylamine and trimethylamine. Examples of the alcohol amine compound include monoethanolamine, diethanolamine, triethanolamine, monopropanolamine, dipropanolamine, tripropanolamine, methylethanolamine, dimethylethanolamine and N-methyldiethanolamine.

  Examples of the alkaline earth metal hydroxide include lithium hydroxide, sodium hydroxide, and potassium hydroxide. Examples of the alkaline earth metal hydroxide include beryllium hydroxide, magnesium hydroxide, calcium hydroxide, and strontium hydroxide. These basic compounds (B) may be used alone or in combination.

  Of these basic compounds (B), alcohol amine compounds are preferred because of their excellent compatibility with aqueous media and appropriate volatility. When the neutralizing compound (B) has an appropriate volatility, the copolymer (C) is water-soluble because it is less volatile in the storage state and tends to evaporate after ink image formation. The composition can be designed so that the water resistance of the ink image is improved.

  In the present invention, the content of the basic compound (B) in the composition is adjusted to 40% or more and less than 120% of the amount corresponding to the acid of the copolymer (C). Especially, it is preferable to set it as 50% or more and 110% or less. The amount (g) of the basic compound (B) corresponding to the acid value of the used styrene copolymer (C) is represented by the formula (1).

Corresponding amount (g) = A × Wp × M / 56110 Equation (1)
A: Acid value of styrene copolymer (C) (mgKOH / g)
Wp: Weight of the styrene copolymer (C) used (g)
M: Molecular weight of the basic compound (B)

  In the present invention, stabilization is possible by the above ionic method, but if necessary, a nonionic method can be used in combination. For this purpose, a compound having a hydrophilic part and a hydrophobic part is used, and the hydrophobic part adsorbs it on the pigment surface, and the hydrophilic part supplements the dispersion stabilization of the pigment entropically or sterically.

  Representative compounds useful for this purpose include, for example, polyvinyl alcohol, cellulosic derivatives, polyethylene oxide and polypropylene oxide. This non-ionic method is not sensitive to pH changes or ionic contamination, but has the disadvantage that the ink image is poorly water-resistant and must be minimized when used in combination.

  The water resistance of the ink image obtained from the aqueous ink composition for ink jet recording containing the pigment (A), the basic compound (B) and the styrene copolymer (C) dispersed in the aqueous medium (I) is the same. In comparison of the copolymer (C) having a molecular weight, the higher the acid value of the copolymer (C) and the higher the content of the basic compound (B), the worse.

  Accordingly, as the styrene copolymer (C) used in the present invention, an acid value of 170 mgKOH / g or less is used, and the content of the basic compound (B) is set to the total amount of the copolymer (C) used. If prepared so as to be less than 120% of the amount corresponding to the acid value, the ink image obtained from the water-based ink composition has excellent water resistance.

  However, when the acid value of the copolymer (C) is lowered, the dispersion stability of the pigment is impaired. Therefore, it is necessary to use a copolymer (C) having an acid value of 20 mgKOH / g or more.

  Further, in the comparison with the copolymer (C) having the same molecular weight, if the content of the basic compound (B) is as large as 120% or more as described above, the water resistance of the ink image is inferior and the basic compound is inferior. Even if the content of (B) is small, the dispersion stability of the pigment is also impaired. Therefore, the content of the basic compound (B) is an amount corresponding to the total acid value of the copolymer (C) used. % Or more is required.

  Therefore, in the aqueous ink composition for ink jet recording containing the pigment (A), the basic compound (B) and the styrene copolymer (C) dispersed in the aqueous medium (I), the copolymer (C) Aqueous ink for inkjet recording having an acid value of 20 to 170 mgKOH / g and a content of the basic compound (B) of 40% or more and less than 120% of an amount corresponding to the acid value of the copolymer (C). The composition is excellent in both good pigment dispersion stability and water resistance of the ink image.

  The weight average molecular weight of the styrenic copolymer (C) is not particularly limited, and any molecular weight may be used. However, from the viewpoint of the water resistance of the ink image, it is 3,000 or more, particularly 3,000 to It is preferable to use 30,000, particularly preferably 4,000 to 26,000.

  In addition, at the same acid value and the same basic compound use amount, the water resistance of the ink image obtained from the water-based ink composition is excellent as the weight average molecular weight of the copolymer (C) is large. The water-based ink composition of the present invention containing a styrene copolymer (C) having a weight average molecular weight exceeding 7,000 has a compound (B) content regardless of the acid value of the copolymer (C). However, the water resistance of the obtained ink image is extremely excellent as long as the acid value and the content thereof are within the numerical limit range of the present invention.

  The weight average molecular weight of the copolymer (C) referred to here is a polystyrene equivalent weight average molecular weight measured by GPC (gel permeation chromatography).

  On the other hand, the ink image obtained from the aqueous ink composition of the present invention containing the styrene copolymer (C) having a weight average molecular weight of 3,000 to 7,000 is the weight of the compound (B) in the system having the same content. In contrast to that of the styrene copolymer (C) having an average molecular weight exceeding 7,000, when the acid value of the styrene copolymer exceeds 100 mgKOH / g, the water resistance tends to be slightly lowered. However, there is no practical problem.

  Therefore, when a copolymer having a weight average molecular weight of 3,000 to 7,000 is used, the degree of freedom in the acid value range is narrower than when a copolymer having a weight average molecular weight of more than 7,000 is used. That is, it is preferable to prepare the aqueous ink composition of the present invention using a styrene copolymer having an acid value of 20 to 100 mgKOH / g, and the water resistance of an ink image obtained therefrom is extremely excellent. When the weight average molecular weight of the styrene copolymer (C) is less than 3,000, the dispersion stability of the pigment tends to be impaired, which is not preferable.

  That is, a compound (C) having an acid value of 20 to 170 mgKOH / g and a weight average molecular weight exceeding 7,000, and having an acid value equivalent of 40% to less than 120% of the copolymer (C) ( B) A composition having an ink image water resistance equivalent to the composition prepared in the content is a copolymer (C) having a weight average molecular weight of 3,000 to 7,000 and an acid value of 20 to 100 mgKOH / g. When trying to obtain the composition, the amount of the compound (B) corresponding to the acid value of the copolymer (C) in the range of 40% or more and less than 120% of the compound (B) content should be minimized as much as possible. Is preferably prepared.

  The production method of the water-based ink composition for ink jet recording of the present invention is shown below, but this production method is for clarifying the present invention and does not limit the scope of the present invention.

  A basic compound (B) and a styrene copolymer (C) are added to the aqueous medium (I), and the styrene copolymer (B) is dispersed or dissolved. When the styrene copolymer (C) is difficult to disperse or dissolve, it is dispersed or dissolved while heating the aqueous medium. When the styrene copolymer (C) is dispersed or dissolved, a stirrer such as a homomixer may be used.

  The styrene copolymer (C) is not completely dissolved in the aqueous medium (I) containing the basic compound (B), and a part or most of the styrene copolymer (C) is dispersed, so that the styrene copolymer (C) May be colloidal. In particular, when the acid value of the styrene copolymer (C) is low, the weight average molecular weight is large, and the content of the basic compound is small, the styrene copolymer (C) tends to be in a colloidal state.

  When the pigment (A) is added to and dispersed in the aqueous medium (I) containing the colloidal styrene copolymer (C), the styrene copolymer (C) is strongly adsorbed on the pigment surface, and mechanically. A water-based ink composition having excellent stability can be obtained.

  A water-based ink composition having excellent mechanical stability is stable against a large shear stress generated when it is rapidly sent to the nozzle portion of an ink jet printer, and hardly aggregates and adsorbs on the nozzle portion. Therefore, the ink discharge stability of the ink jet printer is excellent.

  Next, the pigment (A) is added, and the pigment (A) is dispersed. The disperser used for this may be any disperser that is generally used, and examples thereof include a paint shaker, a ball mill, a roll mill, a speed line mill, a homomixer, and a sand grinder. Coarse particles can be removed from the obtained pigment-dispersed water-based ink composition by filtering, centrifugation, or the like.

  The aqueous ink composition for ink jet recording of the present invention is produced by the above production method.

  The aqueous medium (I) of the present invention is a solvent containing water as a main component. As water, it is preferable to use ion-exchanged water (deionized water) instead of general water containing various ions. The aqueous medium (I) of the present invention may contain a water-soluble organic solvent.

  Examples of the aqueous organic solvent include alkyl alcohols having 1 to 4 carbon atoms such as methyl alcohol, ethyl alcohol, n-propyl alcohol, isopropyl alcohol, n-butyl alcohol, sec-butyl alcohol, tert-butyl alcohol, and isobutyl alcohol. Polyhydric alkyl alcohols such as ethylene glycol, propylene glycol, 1,3-butanediol, 1,2,6-hexanetriol and glycerol, amides such as dimethylformamide and dimethylacetamide, acetone and diacetone alcohol, etc. Ketones or ketoalcohols, ethers such as tetrahydrofuran and dioxane, polyalkylene glycols such as polyethylene glycol and polypropylene glycol, diethylene glycol , Alkylene glycols containing 2 to 6 carbon atoms such as triethylene glycol and tripropylene glycol, polyhydric alcohols such as ethylene glycol monomethyl (or ethyl) ether and triethylene glycol monomethyl (or ethyl) ether Lower alkyl ethers, N-methyl-2-pyrrolidone, 1,3-dimethyl-2-imidazolidinone and the like.

  Among these water-soluble organic solvents, polyhydric alcohol compounds such as polyhydric alkyl alcohols, polyalkylene glycols, and alkylene glycols in which the alkylene group contains 2 to 6 carbon atoms are water-based for inkjet recording of the present invention. Acts as a wetting agent for the ink composition. That is, in order to prevent the ink from drying and blocking the nozzle in the nozzle portion of the ink jet recording apparatus, the ink is prevented from drying. Therefore, it is preferable to use these polyhydric alcohol compounds. These polyhydric alcohol compounds may be used alone or in combination. The addition amount of these polyhydric alcohol compounds is preferably 0 to 50% by weight, more preferably 5 to 30% by weight of the aqueous ink composition for ink jet recording.

  Other additives can be added to the water-based ink composition for ink-jet recording of the present invention depending on the purpose. For example, dispersion aids, thickeners, fluidity improvers, surfactants, conductivity adjusters, pH adjusters, acid value inhibitors, preservatives, bactericides, UV absorbers, antifoaming agents, penetrants Can be mentioned.

  In the following, examples and comparative examples of the present invention will be shown. However, these examples are for clarifying the present invention and do not limit the scope of the present invention. In the examples and comparative examples, parts are by weight unless otherwise specified.

(Synthesis Example 1) (Synthesis of styrene copolymer)
MEK667 parts are charged into a separable flask equipped with a stirrer, a thermometer, and a reflux condenser, and the temperature is raised to 70 ° C. while purging with nitrogen under stirring. While maintaining the internal temperature at 70 ° C., a mixture of 230 parts of methacrylic acid, 590 parts of styrene, 150 parts of methyl methacrylate and 10 parts of AIBN (azobisisobutylnitrile) is added over about 2 hours and reacted. After completion of the addition, 2 parts of AIBN are added 4 and 8 hours later, and 1 part of AIBN is added 12 and 16 hours later, and the reaction is continued. Also, 433 parts of MEK is added 4 hours after the addition of the monomer mixture. 22 hours after the completion of the addition of the monomer mixture, the internal temperature was lowered to complete the reaction, whereby a MEK solution of a styrene copolymer was obtained.

  The MEK solution of the styrene copolymer is poured into a large amount of methanol and stirred. The styrene copolymer precipitated in methanol is separated from the solvent using a glass filter and further washed with methanol. The styrenic copolymer containing methanol is put into a heating and vacuum dryer and dried until reaching a constant weight.

  The acid value of the obtained styrene copolymer was 147 mgKOH / g, and the weight average molecular weight measured by GPC was 24,000 in terms of polystyrene. Hereinafter, this styrene copolymer is abbreviated as resin (a).

(Synthesis Example 2) (Synthesis of styrene copolymer)
1,000 parts of isopropyl alcohol (IPA) is charged into a separable flask equipped with a stirrer, a thermometer, and a reflux condenser, and the temperature is raised to 70 ° C. while purging with nitrogen under stirring. While maintaining the internal temperature at 70 ° C., a mixture of 51 parts of acrylic acid, 300 parts of styrene, 149 parts of butyl acrylate and 30 parts of AIBN (azobisisobutylnitrile) is added over about 2 hours and reacted. At the end of the addition, 4 parts and 8 hours later, 2 parts of AIBN are added and the reaction is continued. 12 hours after the completion of the monomer mixture addition, the internal temperature was lowered to complete the reaction, whereby an IPA solution of a styrene copolymer was obtained.

  The IPA solution of the styrene copolymer is poured into a large amount of methanol and stirred. The styrene copolymer precipitated in methanol is separated from the solvent using a glass filter and further washed with methanol. The styrenic copolymer containing methanol is put into a heating and vacuum dryer and dried until reaching a constant weight.

  The acid value of the obtained styrene copolymer was 77 mgKOH / g, and the weight average molecular weight measured by GPC was 5,600 in terms of polystyrene. Hereinafter, this styrene copolymer is abbreviated as resin (b).

(Synthesis Example 3) (Synthesis of styrene copolymer)
The same operation as in Synthesis Example 2 was performed except that 51 parts of acrylic acid was replaced with 80 parts of acrylic acid, and 149 parts of butyl acrylate was replaced with 120 parts of butyl acrylate. , 100 styrene copolymer was obtained. Hereinafter, this styrene copolymer is abbreviated as resin (c).

(Examples and Comparative Examples)
Table 1 shows the compositions and blending amounts and water resistance of Examples and Comparative Examples. The production methods of the pigment-dispersed water-based ink compositions of Examples and Comparative Examples shown in Table 1 are shown below.

  A 250 ml stainless beaker is charged with the aqueous medium, styrene copolymer and basic compound described in Table 1, and heated to around 90 ° C. while stirring with a stirrer to dissolve or disperse the copolymer. However, about Example 1, it stirred with the homomixer, heating, and the copolymer was disperse | distributed. After cooling, add a reduced amount of water by evaporation and transfer to a 250 ml wide mouthed polybin. Furthermore, 200 parts of pigment and glass beads (3 mmφ) were added to wide-mouthed polybin, and dispersed for 4 hours with a paint conditioner to obtain aqueous ink compositions of Examples and Comparative Examples.

  The water resistance test method was to write the water-based ink compositions of Examples and Comparative Examples on a copy paper with a pen, immerse the copy paper written between 1 and 2 minutes after writing in water, and Observe the condition. If the written ink does not flow in water at all, the water resistance is very good and is indicated by ◎. The water resistance is good if the ink image can be read to the extent that the written ink flows slightly into the water, and is indicated by a circle. When most of the written ink flows into the water, the water resistance is poor and is indicated by a cross.

  Each “Joncry” in the table is a styrene copolymer containing (meth) acrylic acid manufactured by Johnson Polymer Co., Ltd. as a copolymerization component.

(Comparative Example 3)
A corresponding styrene copolymer was obtained in the same manner as in Synthesis Example 3 except that the acid value was 430 and the weight average molecular weight was 5860. An ink composition was obtained in the same manner as in Comparative Example 2 except that this was used. Although the same operation was performed using this composition, it was the same result as the comparative example 2.

  As can be seen from the comparison between Example 1 and Comparative Examples 1 to 3 in Table 1, the content of the compound (B) is 40% ≦ copolymer even if a copolymer having a substantially equivalent weight average molecular weight is used. In the composition (Comparative Example 1) deviating from the polymer (C) acid value equivalent amount <120% and the composition deviating from 20 ≦ acid value ≦ 170 (Comparative Examples 2 to 3), It is clear that an ink image having excellent water resistance as in Example 1 is not obtained.

  From the comparison between Examples 1 and 7, it is found that the water resistance of the ink image is more excellent when a copolymer having a lower acid value is used at substantially the same molecular weight and the same basic compound content. Recognize.

  In addition, even when any of the compositions in the examples was ejected from the ejection orifice or nozzle and the ink was ejected as droplets and printing was performed by an ink jet printer, the excellent water resistance of the ink image was similarly obtained. Obtained. In addition, the composition of Example 4 had little ink drying at the nozzle portion, and was particularly excellent in ejection stability without blocking the nozzle.

Claims (7)

A method for producing an aqueous ink composition for ink-jet recording comprising a pigment (A), a basic compound (B), and a styrene copolymer (C) dispersed in an aqueous medium (I) , the styrene copolymer and acid value of the polymer (C) is a 20~170mgKOH / g, and the basic compound (B) content is more than 40% of the amount corresponding to the acid value of the styrene-based copolymer (C) of less than 120% der is, the aqueous medium (I), the basic compound (B) and styrene copolymer (C) was added styrene copolymer (C) was dispersed, styrenic became colloidal state A method for producing a water-based ink composition for ink-jet recording , which comprises adding and dispersing the pigment (A) to an aqueous medium (I) containing a copolymer (C) . The method for producing a water-based ink composition for ink-jet recording according to claim 1, wherein the weight average molecular weight of the styrene copolymer (C) exceeds 7,000 . The water-based ink composition for ink jet recording according to claim 1 or 2, wherein the styrene copolymer (C) has an acid value of 20 to 100 mgKOH / g and a weight average molecular weight of 3,000 to 7,000. Manufacturing method. The inkjet recording according to any one of claims 1 to 3 , wherein the styrene copolymer (C) is a styrene- (meth) acrylic acid- (meth) acrylic ester copolymer. For producing a water-based ink composition for use. The method for producing an ink composition for ink jet recording according to any one of claims 1 to 4 , wherein the pigment (A) is an organic pigment . The method for producing an ink composition for ink jet recording according to any one of claims 1 to 5, wherein the aqueous medium (I) contains a polyhydric alcohol compound . The method for producing an ink composition for ink jet recording according to any one of claims 1 to 6, wherein the basic compound (B) is an alcohol amine compound .