JPH08231906A - Aqueous ink composition for ink jet recording - Google Patents

Abstract

PURPOSE: To obtain an aqueous ink composition suitable for ink jet recording, giving an ink image of high resistance to water by dispersing a pigment, a specific amount of a basic compound and a styrene copolymer having a specific acid value in an aqueous medium. CONSTITUTION: This ink composition is obtained by adding a dispersed pigment (preferably an organic pigment), a basic compound (preferably an alcoholamine compound and its content is 40-120% equivalent to the acid value of the styrene copolymer) and a styrene copolymer with an acid value of 20-170mgKOH/g, preferably 20-100mgKOH/g and a weight-average molecular weight of 900-7,000 (preferably styrene-(meth)acrylic acid-(meth)acrylic ester copolymer) in an aqueous medium.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a pigment-dispersed aqueous ink composition having excellent water resistance, and particularly to a pigment-dispersed aqueous ink composition for ink jet recording.

[0002]

2. Description of the Related Art Among currently known recording methods,
An ink jet recording method that is low in noise, capable of high-speed recording, and capable of recording on plain paper is a very useful recording method.

In this ink jet recording method, a colored liquid called ink is heated to generate bubbles, and the 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 are a method of recording the material by adhering it to a recording material such as paper, and a method of applying pressure to the ink by a piezoelectric element to eject small droplets of the ink from the nozzle.

As an ink applied to this recording method, a pigment-dispersed water-based ink can be mentioned. When an ink jet recording method is carried out using a conventional pigment-dispersed ink,
There is a drawback that the obtained ink image has poor water resistance.
For example, JP-A-56-147860 and JP-A-56-1
47861, JP-A-56-147862, JP-A-5
The styrene-based copolymer used in the aqueous ink composition for ink jet recording proposed in JP-A-6-147863 and JP-A-56-147859 has an acid value of 200 m.
It has a drawback that the ink image is inferior in water resistance when ink jet recording is carried out with an ink composition containing gKOH / g or more, which is easily soluble in water and which contains a pigment dispersed as a dispersant.

Further, in Example 2 of JP-A-4-18461, an aqueous ink composition for ink jet recording containing a pigment, a basic compound and a styrene-based copolymer dispersed in an aqueous medium is used. However, the acid value is 430m
A water-soluble resin, which is a styrene-based copolymer having gKOH / g and a weight average molecular weight of 5,860 and in which the content of the basic compound is 87% of the amount corresponding to the acid value of the copolymer. Aqueous ink compositions for inkjet recording containing the same are described.

Further, in Example 2 of JP-A-4-18467, an aqueous ink composition for ink jet recording containing a pigment, a basic compound and a styrene copolymer dispersed in an aqueous medium is used. The combined value is 12
A styrene-based copolymer having 0 mgKOH / g and 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 inkjet recording containing a water-soluble resin is described.

[0007]

However, in all of the above publications, the focus is on improving the ejection stability,
Although it may give good results in that respect, the ink images obtained therefrom again all had the drawback of insufficient waterfastness. 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.

[0008]

Means for Solving the Problems The present inventor has made diligent studies in view of the above circumstances, and as a result, "resin acid value" which is not considered to contribute to the improvement of water resistance from the description in the above publication.
And a combination of two scales of "basic compound content", 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 the copolymer By designing the amount within a specific range corresponding to the acid value of the coalesced product, the synergistic effect of them makes it possible to obtain an ink image having extremely excellent water resistance, which cannot be predicted from the compositions described in these publications. They have found that an aqueous ink composition can be obtained, and completed the present invention.

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

The present invention will be described in detail below.

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

Examples of the inorganic pigment include carbon black, metal oxides, metal sulfides and metal chlorides. Particularly in the black aqueous ink composition, carbon black is preferable, and examples of the carbon black include furnace black, lamp black, acetylene black and channel black. One 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, anthraquinone pigments, and Examples include quinophthalone pigments. One of these organic pigments may be used, or a plurality of organic pigments may be used in combination. An inorganic pigment can also be used together with the organic pigment. Further, an extender pigment or the like can also be used together for improving fluidity.

According to the formulation of the present invention, the absolute water resistance of the ink image obtained from the prepared composition is similar to that of the carbon black type and the organic pigment type, but the carbon black type has its own water resistance. In terms of the degree of improvement (improvement rate), the organic pigment type tends to be more prominent than the carbon black type in terms of the degree of improvement (improvement rate) because it has good properties and is superior to that of the organic pigment.

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

Further, for the toning of the black aqueous ink composition,
Two or more kinds of other inorganic pigments and / or organic pigments can be used in combination. Further, an extender pigment or the like can be used together for improving fluidity.

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

The styrene-based copolymer (C) used in the present invention contains styrene and / or a styrene derivative, one or more kinds of ionic monomers as essential constituent monomers, and other addition-polymerizable vinyl groups. The acid value may be 20 to
It is a copolymer of 170 mgKOH / g. Among them, acid value 4
Copolymers of 0 to 155 mg KOH / g are preferred.

Further, styrene and / or a styrene derivative, (meth) acrylic acid and one or more kinds of acrylic acid esters are used as the copolymer because of the excellent dispersion stability of the pigment. As an essential constituent monomer,
A styrene- (meth) acrylic acid- (meth) acrylic acid ester-based copolymer, which may contain other addition-polymerizable vinyl group-containing monomers as constituent monomers, is preferable.

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, for example, styrene, a styrene derivative, vinylnaphthalene, a vinylnaphthalene derivative, an α, β-ethylenically unsaturated carboxylic acid aliphatic alcohol ester, acrylonitrile, vinylidene chloride, acetic acid. Mention may be made of vinyl, vinyl chloride, acrylamide, methacrylamide, hydroxyethyl methacrylate, hydroxypropyl methacrylate, glycidyl methacrylate and N-butoxymethyl acrylamide. These constitute the hydrophobic portion of the copolymer (C) that adsorbs to the pigment (A).

Among these nonionic monomers, styrene and / or styrene derivatives such as α-methylstyrene, which are excellent in the adsorptivity to the pigment, are essential. However, a polymer composed only of styrene and / or a styrene derivative has a drawback of lacking flexibility, and therefore, 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, such as carboxylic acid group, sulfonic acid group, and sulfate ester group. The functional group is, 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 α of sulfonated vinylnaphthalene
It is introduced into the copolymer (C) from an ionic monomer such as a β-unsaturated monomer. Among these ionic monomers, (meth) acrylic acid is preferable because of its excellent pigment dispersion stability.

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

As the copolymer (C), one that disperses in water when neutralized has a higher adsorptivity on the pigment surface, and therefore the mechanical stability of the dispersed pigment becomes higher.
More preferred is one that dissolves in water. That is, it is more preferable that the copolymer (C) neutralized with the compound (B) is dispersed in the aqueous medium (I).

The styrene-based copolymer (C) may be used alone or in combination of two or more. It is also possible to combine one or more kinds of resins made of nonionic monomers with the styrene copolymer as an essential component.

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

In order to disperse or dissolve the styrenic 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 compounds include ammonia, monomethylamine, dimethylamine, trimethylamine, monoethylamine, dimethylamine and trimethylamine. Examples of alcohol amine compounds include monoethanolamine, diethanolamine, triethanolamine, monopropanolamine,
Dipropanolamine, tripropanolamine, methylethanolamine, dimethylethanolamine and N
-Methyldiethanolamine.

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

Of these basic compounds (B), alcohol amine compounds are preferable because of their excellent compatibility with an aqueous medium and their appropriate volatility.
When the compound (B) for neutralization has an appropriate volatility, the copolymer (C) is water-soluble because the compound (B) has a low volatility 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). Above all, 50%
It is preferably not less than 110% and not more than 110%. The amount (g) of the basic compound (B), which corresponds to the acid value of the styrene-based copolymer (C) used, is represented by the formula (1).

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

In the present invention, the above-mentioned ionic method can be used for stabilization, but if necessary, a non-ionic method can be used in combination therewith. For this purpose, a compound having a hydrophilic portion and a hydrophobic portion is used, and the hydrophobic portion thereof is adsorbed on the surface of the pigment, and the hydrophilic portion entropically or sterically supplements the dispersion stabilization of the pigment.

Representative compounds useful for this purpose include, for example, polyvinyl alcohol, cellulosics, polyethylene oxide and polypropylene oxide. This non-ionic method is not sensitive to pH changes or ionic contamination, but has the drawback that the ink image is inferior in water resistance, so it should be minimized when used in combination.

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

Therefore, as the styrene-based copolymer (C) used in the present invention, one having an acid value of 170 mgKOH / g or less is used, and the content of the basic compound (B) is the same as that of the copolymer (C ) 120% of the total acid value
If the amount is less than the above, the ink image obtained from the water-based ink composition will have excellent water resistance.

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

In comparison with the copolymers (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 deteriorated, Even if the content of the basic compound (B) is small,
Since the dispersion stability of the pigment is also impaired, the content of the basic compound (B) must be 40% or more of the amount corresponding to the total acid value of the copolymer (C) used.

Therefore, in the aqueous ink composition for ink jet recording containing the pigment (A), the basic compound (B) and the styrene-based copolymer (C) dispersed in the aqueous medium (I), the copolymer ( The acid value of C) is 20 to 170 mg
KOH / g, and the content of the basic compound (B) is 40% or more of the amount corresponding to the acid value of the copolymer (C) 12
The water-based ink composition for inkjet recording having a content of less than 0% is excellent in both good pigment dispersion stability and water resistance of the ink image.

The weight average molecular weight of the styrene copolymer (C) is not particularly limited, and any molecular weight may be used, but it is 3,000 in terms of water resistance of the ink image.
Above all, it is preferable to use 3,000 to 30,000, and particularly preferably 4,000 to 26,000.

With the same acid value and same basic compound used, the larger the weight average molecular weight of the copolymer (C), the more excellent the water resistance of the ink image obtained from the aqueous ink composition. The water-based ink composition of the present invention containing the styrene-based copolymer (C) having a weight average molecular weight of more than 7,000 has a compound (B) content of whatever the acid value of the copolymer (C). However, if the acid value and the content are within the numerical range of the present invention, the water resistance of the obtained ink image will be extremely excellent.

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

On the other hand, the weight average molecular weight is 3,000 to 7,
The ink image obtained from the water-based ink composition of the present invention containing 000 styrene-based copolymers (C) is the compound (B).
When the acid value of the styrene-based copolymer exceeds 100 mgKOH / g, in contrast to that of the styrene-based copolymer (C) having a weight average molecular weight of more than 7,000 in the same content system, the water resistance is slightly It tends to decrease. However, there is no practical problem.

Therefore, the weight average molecular weight is 3,000 to
When a copolymer having a weight average molecular weight of 7,000 is used, the degree of freedom of 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, the acid value is 20 to 100 mgK
It is preferable to prepare the water-based ink composition of the present invention by using an OH / g styrene-based copolymer, and the water resistance of the 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, an acid value of 20 to 170 mg KOH / g,
And using a copolymer (C) having a weight average molecular weight of more than 7,000, and having an acid value equivalent to 40% of the copolymer (C).
A composition having the same ink image water resistance as the composition prepared with the compound (B) content of 120% or more and less than 120% has a weight average molecular weight of 3,000 to 7,000 and an acid value of 20 to 10
In the case of obtaining 0 mgKOH / g of the copolymer (C), the acid value equivalent of the copolymer (C) is 40% or more and 120% or more.
It is preferable to prepare the composition so as to minimize the amount of the compound (B) used in the range of less than the range.

The method for producing the aqueous 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.

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

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

The pigment (A) is added to the aqueous medium (I) containing the styrenic copolymer (C) in the colloidal state,
When dispersed, the styrene copolymer (C) is strongly adsorbed on the surface of the pigment, and an aqueous ink composition having excellent mechanical stability can be obtained.

The 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,
Less likely to be agglomerated and adsorbed on the nozzle part. Therefore, the ink ejection stability of the inkjet printer is excellent.

Next, the pigment (A) is added and the pigment (A) is dispersed. The disperser used for this purpose may be any disperser 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 aqueous ink composition by filtering or centrifuging.

The aqueous ink composition for ink jet recording of the present invention is manufactured by the above manufacturing 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 methyl alcohol, ethyl alcohol, n-propyl alcohol, isopropyl alcohol, n-butyl alcohol, sec-butyl alcohol, tert-butyl alcohol, isobutyl alcohol and the like having 1 to 4 carbon atoms. Alkyl alcohols, ethylene glycol, propylene glycol, 1,3-butanediol, polyhydric alkyl alcohols such as 1,2,6-hexanetriol and glycerin, amides such as dimethylformamide and dimethylacetamide, acetone and diacetone Ketones such as alcohols or keto alcohols, ethers such as tetrahydrofuran and dioxane, polyalkylene glycols such as polyethylene glycol and polypropylene glycol, diet Glycol, triethylene glycol, alkylene glycols the alkylene group contains from 2 to 6 carbon atoms, such as tripropylene glycol ,,
Ethylene glycol monomethyl (or ethyl) ether and triethylene glycol monomethyl (or ethyl)
Lower alkyl ethers of polyhydric alcohols such as ether, N-methyl-2-pyrrolidone, 1,3-dimethyl-
2-imidazolidinone etc. are mentioned.

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

Other additives may 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, ultraviolet absorbers, defoamers, penetrants Can be mentioned.

[0058]

EXAMPLES Examples and comparative examples of the present invention will be shown below, but these examples are for clarifying the present invention and do not limit the scope of the present invention. still,
Unless otherwise specified, parts in the examples and comparative examples are parts by weight.

Synthesis Example 1 (Synthesis of Styrene Copolymer) A separable flask equipped with a stirrer, a thermometer and a reflux condenser is charged with 667 parts of MEK and heated to 70 ° C. while substituting with nitrogen. The internal temperature is kept at 70 ° C., and 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 and reacted for about 2 hours. After the completion of the addition, 2 parts of AIBN is added 4 and 8 hours later, and 1 part of AIBN is added 12 and 16 hours later to continue the reaction. 4 hours after the addition of the monomer mixture, 333 parts of MEK is added. 22 hours after the addition of the monomer mixture was completed, the internal temperature was lowered to terminate the reaction, and a MEK solution of a styrene-based copolymer was obtained.

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

The acid value of the obtained styrene copolymer is 14
It was 7 mgKOH / g, and the weight average molecular weight measured by GPC was 24,000 in terms of polystyrene. Hereinafter, this styrene-based copolymer is abbreviated as resin (a).

Synthesis Example 2 (Synthesis of Styrene Copolymer) Isopropyl alcohol (IPA) 1,000 in a separable flask equipped with a stirrer, thermometer and reflux condenser.
A portion is charged, and the temperature is raised to 70 ° C. while substituting with nitrogen while stirring. Keeping the internal temperature at 70 ° C, 51 parts of acrylic acid, 300 parts of styrene, 149 parts of butyl acrylate and AIBN
(Azobisisobutyronitrile) 30 parts of a mixture of about 2
Add and react over time. 4 and 8 after addition
After a period of time, 2 parts of AIBN is added and the reaction is continued. 12 hours after the completion of addition of the monomer mixture, the internal temperature was lowered to terminate the reaction, and an IPA solution of a styrene-based copolymer was obtained.

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

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

Synthesis Example 3 (Synthesis of Styrene Copolymer) Synthesis Example 2 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. Do the same operation, acid value 120m
A styrene-based copolymer having gKOH / g and a weight average molecular weight of 6,100 was obtained. Hereinafter, this styrene-based copolymer is abbreviated as resin (c).

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

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

The water resistance test method was as follows: the aqueous ink compositions of Examples and Comparative Examples were written on a copy paper with a pen, and the written copy paper was immersed in water for 1 to 2 minutes after writing. Observe the condition of the ink. If the written ink does not run into water at all, the water resistance is extremely good,
It shows with a mark. The water resistance is good if the written ink flows to the water a little and the ink image can be read.
Shown with a circle. When most of the written ink flows into water, the water resistance is poor and is indicated by a cross.

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

[0070]

[Table 1]

Comparative Example 3 A corresponding styrene-based copolymer was obtained by the same procedure 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 by performing the same operation as in Comparative Example 2 except that this was used. The same operation was performed using this composition, but the same result as in Comparative Example 2 was obtained.

As can be seen by comparing Example 1 in Table 1 with Comparative Examples 1 to 3, the content of the compound (B) was 40 even when the copolymers having almost the same weight average molecular weight were used. %
In the composition deviating from ≦ copolymer (C) acid value equivalent amount <120% (Comparative Example 1) 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 cannot be obtained as in Example 1 in which they are combined.

[0073]

[Table 2]

[0074]

[Table 3]

From the comparison between Examples 1 and 7, it was found that the water resistance of the ink image was better when the copolymer having a lower acid value was used at almost the same molecular weight and the same basic compound content. You can see.

Even when any of the compositions of Examples is ejected from an ejection orifice or a nozzle and ink is ejected as a droplet to perform recording by an ink jet printer for recording, a similarly excellent ink image is obtained. Water resistance was obtained. In addition, the composition of Example 4 did not dry the ink at the nozzle portion, did not block the nozzle, and was particularly excellent in ejection stability.

[0077]

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

Claims (8)

[Claims] 1. An aqueous ink composition for ink jet recording comprising a pigment (A), a basic compound (B) and a styrene-based copolymer (C) dispersed in an aqueous medium (I), wherein the copolymer ( The acid value of C) is 20 to 170 mg KO
H / g, and the content of the basic compound (B) is 40% or more and 120% or more of the amount corresponding to the acid value of the copolymer (C).
The water-based ink composition for inkjet recording is characterized by being less than 1. 2. The composition according to claim 1, wherein the styrene copolymer (C) is neutralized with the basic compound (B) and dispersed in the aqueous medium (I). 3. The composition according to claim 1 or 2, wherein the styrene-based copolymer (C) has a weight average molecular weight of more than 7,000. 4. The acid value of the styrene copolymer (C) is 20 to 20.
100 mg KOH / g and weight average molecular weight of 3,000
The composition according to claim 1 or 2, wherein the composition is 7,000. 5. The styrene-based copolymer (C) is styrene-
It is a (meth) acrylic acid- (meth) acrylic acid ester type copolymer, It is characterized by the above-mentioned.
The composition as described. 6. The composition according to claim 1, 2, 3, 4 or 5, wherein the pigment (A) is an organic pigment. 7. The composition according to claim 1, wherein the aqueous medium (I) contains a polyhydric alcohol compound. 8. The composition according to claim 1, wherein the basic compound (B) is an alcohol amine compound.