JP2003171590A - Water-based pigment ink for ink-jet recording - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a water-based pigment ink for ink-jet recording excellent enough in preservation stability not to suffer from aggregation and sedimentation of pigment particles and deposition of the solid content during a long-term storage, exhibiting excellent redissolvability of the ink at a printer head and good jetting stability at a nozzle while giving a printed matter excellent in quality, water resistance and fixing properties. <P>SOLUTION: The water-based pigment ink for ink-jet recording comprises at least a self-dispersible acidic pigment, a water-soluble resin, which resin comprises a copolymer, having a hydrophilic portion, a hydrophobic portion and an acidic group, of a monomer bearing an α,β-ethylenically unsaturated group constituting the hydrophilic portion with a monomer bearing an α,β- ethylenically unsaturated group constituting the hydrophobic portion and has a specific weight-average molecular weight Mw and a specific acid value with at least 50% of the acidic group neutralized by a specific basic organic compound, a water-soluble organic solvent in an amount of at most 30 wt.% and water as the remainder. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an aqueous pigment ink for inkjet recording, which is suitable for use in an inkjet recording apparatus and which uses a pigment as a colorant.

[0002]

2. Description of the Related Art A water-based ink for ink jet recording is a composition containing a dye or pigment as a colorant and an aqueous medium for dissolving or dispersing the dye or pigment as main components. Of these, inks using pigments have weather resistance, water resistance, and
Regarding the fixability, it is remarkably superior to the ink using a dye, but the pigment is essentially insoluble in water, and in order to stably disperse the pigment in the water-based ink, use a polymer dispersant or the like. Distributed processing is required.

As the polymer dispersant, polyvinyl alcohol, β-naphthalenesulfonic acid formalin condensate salt,
Water-soluble resin such as styrene-acrylic acid copolymer salt,
A hydrophobic resin dispersion of an acrylic-urethane copolymer has been proposed. Among these, many proposals have been made regarding a polyacrylic acid-based copolymer and a styrene-acrylic acid-based copolymer, each of which has a hydrophobic portion having a high affinity with a pigment and a hydrophilic portion having a high affinity with an aqueous medium. ing.
For example, Japanese Patent No. 2714240 discloses an ink containing a specific acidic carbon black and a specific styrene-acrylic acid-based water-soluble resin, and Japanese Patent Application Laid-Open No. 8-253716 discloses an acrylic acid-styrene-α-methylstyrene 3 Inks using the original copolymer are disclosed.

Further, as the copolymerization form of the polymer dispersant, a block copolymer, a graft copolymer, a random copolymer and the like have been reported. Block copolymers and graft copolymers composed of a hydrophobic block and a hydrophilic block are generally ideal as dispersants, but there are restrictions on the monomers that can be used for the blocks, which may complicate synthesis. In many cases, it cannot always be said that it is optimal as a dispersion aid for self-dispersion pigments. In addition, random copolymers are relatively easy to synthesize, and there are many commercially available products, and many of them exhibit a sufficient dispersing effect when combined with a specific pigment.

On the other hand, many attempts have been made to modify the pigment to make it hydrophilic as a means for dispersing the pigment without using a polymer dispersant. Above all, the development of carbon black used for the black pigment, which is the most in demand, is being actively conducted. For example, carbon black-water-soluble peroxide-water-soluble polyacrylic ester reaction adduct, ink using modified carbon black by reaction of carbon black-diazonium salt, oxidation treatment of carbon black with nitric acid, etc. have been reported. ing.

Among these modification treatments, a reaction between carbon black and a diazonium salt (see, for example, Table 10-5).
No. 10862) has a wide variety of diazonium salts used in the reaction, and the reaction is relatively easy to control. That is, a modified carbon black having a desired water dispersibility can be obtained by appropriately selecting the number and charge of ionic functional groups added by the reaction. The modified carbon black has sufficient self-dispersibility that does not require addition of a polymer dispersant.

In the water-based pigment ink for ink-jet recording, it is necessary to secure good water resistance and fixability of the printed matter, which are the advantages of the pigment, while at the same time ensuring the ejection stability and the storage stability which are the drawbacks. For this reason, it is important to improve the dispersibility of the pigment particles, and various methods as described above have been proposed. However, in the conventional method using a water-soluble polymer dispersant, it is necessary to add a relatively large amount of dispersant in order to obtain sufficient dispersibility. Therefore, there is a problem that the water content of the ink evaporates in the vicinity of the nozzle, the ink is ejected abnormally due to the increase in viscosity, and in the worst case, the nozzle is clogged.

Further, even when a specific copolymer is used as the polymer dispersant, selection of the type of monomer, physical properties such as molecular weight, acid value, glass transition temperature and the like are insufficient. Furthermore, when a self-dispersion pigment is used, there is a problem that the hydrophilic functional group added to the pigment surface in order to obtain sufficient dispersibility deteriorates the water resistance of the printed matter and impairs the original advantage of the pigment. It was

[0009]

DISCLOSURE OF THE INVENTION The present invention provides excellent print quality, water resistance, and fixability, but does not cause aggregation, sedimentation, or solid content precipitation of pigment particles during long-term storage, thus improving storage stability. An object of the present invention is to provide a water-based pigment ink for inkjet recording which is excellent, has excellent re-dissolvability of ink in a printer head, and has good ejection stability at a nozzle.

[0010]

As a result of intensive studies to solve the above problems, the present inventors have found that by combining a specific self-dispersible acidic pigment, a water-soluble resin and a water-soluble organic solvent. In addition, it is possible to obtain a water-based pigment ink for inkjet recording which is excellent in storage stability while being excellent in print quality, water resistance, and fixability, excellent in redissolvability of ink in a printer head, and good in ejection stability at a nozzle. It was found that the present invention has been completed.

Thus, according to the present invention, there is provided a water-based pigment ink for ink jet recording containing at least a self-dispersible acidic pigment, a water-soluble resin and a water-soluble organic solvent, and the balance being water, wherein the water-soluble resin is hydrophilic. Having a hydrophilic portion, a hydrophobic portion and an acidic group, and having an α, β-ethylenically unsaturated group constituting the hydrophilic portion, and an α, β-ethylenically unsaturated group constituting the hydrophobic portion A copolymer having a weight average molecular weight M _W of 15,000 or less and an acid value of 300 mgKOH / g or less,
50% or more of the acidic groups are neutralized with a basic organic compound selected from ammonia and amines, and the content of the water-soluble organic solvent is 30% by weight or less. A pigmented ink is provided.

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION The aqueous pigment ink for ink jet recording of the present invention (hereinafter abbreviated as "ink") contains at least a self-dispersible acidic pigment, a water-soluble resin and a water-soluble organic solvent, and the balance is water. And the water-soluble resin has a hydrophilic portion, a hydrophobic portion and an acidic group,
A copolymer composed of a monomer having an α, β-ethylenically unsaturated group constituting a hydrophilic part and a monomer having an α, β-ethylenically unsaturated group constituting a hydrophobic part. ,
Having a weight average molecular weight M _W of 15,000 or less, 300 m
It has an acid value of gKOH / g or less, 50% or more of the acidic groups are neutralized by a basic organic compound selected from ammonia and amines, and the content of the water-soluble organic solvent is 30% by weight or less. Is characterized in that. By combining such a self-dispersible acidic pigment, a water-soluble resin and a water-soluble organic solvent, an ink having good dispersibility, redissolvability and excellent physical properties of the pigment (especially carbon black) can be obtained.

As the self-dispersible acidic pigment used in the present invention, commercially available or newly produced neutral, basic or acidic pigments are treated by various methods and the surface thereof is modified to be acidic, and Examples include commercially available self-dispersion acidic pigments. As such a self-dispersion acidic pigment, one having an anionic functional group selected from a sulfonic acid group, a sulfinic acid group, a carboxylic acid group, a phosphoric acid group and salts thereof on the surface is preferable. These functional groups impart sufficient hydrophilicity to the pigment.

Examples of the pigment to be subjected to the surface modification treatment include various known organic pigments and inorganic pigments. As the organic pigment, azo type, acridine type, phthalocyanine type, quinacridone type, anthraquinone type, indanthrene type, dioxazine type, indigo type, thioindigo type,
Perylene-based, perinone-based, isoindolenine-based, etc.
Examples of the pigment include a pigment having a structure having an aromatic ring in the molecule, and examples of the inorganic pigment include carbon black. Further, these pigments may be commercially available ones or newly produced ones.

Examples of the modification treatment method include oxidation treatment with an oxidizing agent such as sulfuric acid, nitric acid, hypochlorous acid, and peroxide, addition reaction treatment of diazonium salt, oxidation treatment with plasma, and oxidation treatment with the plasma. The subsequent graft copolymerization treatment with a hydrophilic polymer may be mentioned.

Generally, in the modification treatment with an oxidizing agent, it is difficult to control the oxidation reaction, the pigment itself may be deteriorated (for example, discolored) by a treatment for a long time, and a large amount of the modified pigment ( 15 to 20 times by weight) of the oxidizer is required, the waste liquid treatment cost is high, continuous treatment cannot be performed, and the treatment is batch type, which is not preferable because the treatment efficiency is low. On the other hand, the addition reaction treatment with a diazonium salt is relatively easy to control the addition reaction and can introduce various functional groups such as an alkylcarboxylic acid group, an arylcarboxylic acid group, a sulfonic acid group, an amino group and a phosphoric acid group. It is preferable since a modified pigment having a desired hydrophilicity (particularly carbon black) can be easily obtained.

Examples of commercially available self-dispersing acidic pigments (surface modified pigments) include CAB-O- manufactured by Cabot Corporation.
Examples include JET200 and CAB-O-JET300. These are acidic carbon blacks to which a sulfonic acid group and a carboxylic acid group have been added, respectively, and are preferably used in the ink of the present invention.

The average particle size of the self-dispersing acidic pigment is 0.0
It is preferably 5 to 3 μm. An ink using a pigment having such an average particle size can be expected to have further long-term storage stability at high temperature and further improved print quality. The particle size distribution of the self-dispersion acidic pigment is 60 to less than 0.2 μm.
It is preferable that the content is 98% by volume, the particle size of 0.2 to 0.6 μm is 0.5 to 40% by volume, and the particle size of 0.6 μm or more is 5% by volume or less. In the ink using the pigment having such a particle size distribution, a small amount of coarse particles form a rough film layer on the printer head to prevent the pigment particles from further adhering to improve the long-term ejection stability of the ink. To do. Further, when particles having a narrow particle size distribution are used, the particles are likely to aggregate with each other, but in the ink using the pigment having the above particle size distribution, aggregation of particles is prevented, dispersibility is further improved, and high temperature The long-term storage stability of the ink is improved.

The water-soluble resin used in the present invention acts as a dispersion aid to further improve the stabilization of the dispersed state of the pigment, and forms a hydrophobic film in a printed matter in a short time. It acts as a binder that brings about improvements in the properties and water resistance. In general, in a dye ink, a dye of a coloring material (colorant) penetrates into a printing medium such as paper, whereas in a pigment ink, the pigment of the coloring material is only fixed on the surface of the medium, and a binder or the like is used. Often added to improve fixability. In particular, in the case of an ink using a self-dispersion type pigment, while sufficient hydrophilicity can be obtained due to the hydrophilic group on the surface, the water resistance in the printed matter may be sacrificed. Is preferably added.

It is considered that the action of stabilizing the dispersion includes both the repulsive action by the electric double layer and the steric repulsive action based on the thermodynamic stabilization. The water-soluble resin used in the present invention is composed of a hydrophilic portion and a hydrophobic portion, and a part of the hydrophilic portion is bonded to the anionic functional group added to the pigment surface, but most of the hydrophilic portion surrounds the pigment particles. It is believed that the particles come into contact with the aqueous medium around the particles and give an electrical and three-dimensional repulsive force. Further, it is considered that the hydrophobic portion of the water-soluble resin is adsorbed to the aromatic ring in the pigment molecule by the hydrophobic bond based on Van der Waals force.

The hydrophilic portion surrounding the outside of the water-soluble resin particles needs to have mobility so that the particles can be easily dissolved in a solvent in order to prevent the particles from aggregating, and a vinyl compound having a carboxyl group or a sulfone group that gives electric repulsive force is used. Are suitable. Such a vinyl compound is also excellent in the function of providing anti-drying on the surface of the nozzle, non-adhesiveness with a water-repellent surface, re-dissolvability in a medium, and the like. On the other hand, the hydrophobic portion needs a binding force that is easily adsorbed to the self-dispersion acidic pigment (particularly, a pigment having an aromatic ring), and does not need mobility. Therefore, acrylic acid esters, styrene derivatives, vinylnaphthalene derivatives and the like are suitable.

Examples of the monomer having an α, β-ethylenically unsaturated group constituting the hydrophilic portion include (meth) acrylic acid, crotonic acid, itaconic acid, itaconic acid monoester, (anhydrous) maleic acid, and maleic acid. Acid monoester, fumaric acid, fumaric acid monoester, vinylsulfonic acid, styrenesulfonic acid, sulfonated vinylnaphthalene, N,
N-dimethylaminoethyl methacrylate and N, N
-At least one selected from diethylaminoethyl methacrylate.

The functional group contained in the above monomer is an anionic functional group selected from sulfonic acid group, sulfinic acid group, carboxylic acid group, phosphoric acid group and salts thereof present on the surface of the self-dispersion acidic pigment. It is considered that, in addition to forming a hydrogen bond with the group, most of the constituents not involved in this bond provide water solubility, and the electrical and steric repulsive forces enhance the dispersion stability of the pigment.

As the monomer having an α, β-ethylenically unsaturated group constituting the hydrophobic portion, styrene, α-methylstyrene, vinyltoluene, vinylnaphthalene and its derivatives, (meth) acrylic acid alkyl ester,
At least one selected from (meth) acrylic acid aryl ester, crotonic acid alkyl ester, itaconic acid dialkyl ester, and maleic acid dialkyl ester is included. Among these, a monomer having an aromatic ring that is well compatible with the pigment is particularly preferable. In the present invention, “(meth) acrylic” means acrylic or methacrylic.

The water-soluble resin used in the present invention is a monomer having an α, β-ethylenically unsaturated group constituting the hydrophilic portion and an α, β-ethylenically unsaturated constituting a hydrophobic portion. It can be obtained by polymerizing a monomer having a group by a known method. The combination of the above monomers is preferable in that not only the polymerization thereof is easy, but also an ink having excellent physical properties is obtained.

The water-soluble resin used in the present invention is preferably a random copolymer or an alternating copolymer. In such a polymerization (bonding) form, the monomers constituting the hydrophilic part and the hydrophobic part are randomly present in the polymer chain, so that the surface of the self-dispersible acidic pigment (modified pigment) is It is believed that it is capable of forming bonds with both the hydrophilic functional groups present and the hydrophobic polynuclear aromatic rings. In the present invention, not only the water-soluble resin to be copolymerized but also a commercially available product corresponding to the above water-soluble resin can be used.

The water-soluble resin used in the present invention is
20 to 60 mol% of a monomer having an α, β-ethylenically unsaturated group constituting a hydrophilic part, and 40 to 8 a monomer having an α, β-ethylenically unsaturated group constituting a hydrophobic part
It is preferably a copolymer with 0 mol%.

When the composition ratio of the monomer is out of the above range and the ratio of the hydrophilic portion (the former monomer) is high, the adsorptivity for the hydrophobic pigment particles is lowered and the dispersion of the pigment particles is reduced. It is not preferable because the stability may be deteriorated, the water solubility may be too high, the water resistance of the printed matter may be reduced, and the printing density may be reduced. On the other hand, when the ratio of the hydrophobic portion (the latter monomer) is high, the solubility in the aqueous medium decreases and the dispersion stability of the pigment particles deteriorates, or the resin aggregates in the aqueous medium together with the pigment particles. It is not preferable because it may cause precipitation or sedimentation.

The water-soluble resin has a weight average molecular weight M _W of 15,000 or less, preferably 3,000 to 15,000. M _W and M _N can be measured by GPC (gel permeation chromatography) or the like.

When the copolymers constituting the water-soluble resin have the same structure, the binder function of the ink is improved with an increase in M _W , but the ink is thickened and the ink is easy to handle and stable. Dischargeability deteriorates. Therefore, considering these balances, it is preferable that M _W does not exceed 15,000. On the other hand, when M _W is less than 3000, the water-soluble resin has a small steric repulsion action and does not contribute much to the dispersion stability of the pigment, or has an effect as a dispersion aid but an effect as a binder. This is not preferable because it is sufficient and the fastness of the printed matter is deteriorated.

The ratio of the weight average molecular weight M _{W of} the water-soluble resin to the number average molecular weight M _N (dispersion degree M _W / M _N ) is related to the dispersibility of the pigment in the ink and the fastness of the printed matter. In order to obtain stable dispersibility, M _W / M _N is preferably 1 to 2.5, and particularly preferably 1 to 1.5. M _W
When / M _N is less than 1, it is not preferable because the fastness of the printed matter is insufficient, and when M _W / M _N exceeds 2.5, the viscosity of the ink increases and the dispersibility deteriorates. It is not preferable.

The water-soluble resin has an acid value of 300 mgKOH / g or less, preferably 50 to 300 mgKOH / g, more preferably 100 to 300 mgKOH / g,
More preferably 100-250 mg KOH / g. When the acid value of the water-soluble resin is within the above range, a good balance between the water solubility of the water-soluble resin and the fastness of the printed matter can be obtained, which is preferable.

The water-soluble resin used in the present invention comprises 50% or more of the acidic groups of the copolymer, which are neutralized with a basic organic compound selected from ammonia and amines. The copolymer can maintain good water solubility.

The neutralization treatment is carried out, for example, by adding an excessive amount (1.2 to 2.5 equivalents) of the above basic organic compound to the water-soluble resin with respect to the acid value of the water-soluble resin and heating for several hours. It can be performed by stirring.

Amines that can be used for the neutralization treatment include aliphatic amine, ethanolamine, diethanolamine, triethanolamine, propanolamine, methylethanolamine, N, N-dimethylethanolamine (N, N-dimethylamino). ethanol),
Examples thereof include alcohol amines such as N, N-diethylethanolamine (N, N-diethylaminoethanol), morpholine, N-methylmorpholine and the like.

By the above neutralization treatment, the copolymer constituting the water-soluble resin is made water-soluble, and the water-soluble resin is stably present in the ink. On the other hand, in the printed matter on which the ink is ejected, ammonia and amines evaporate (volatilize) in a short time, so that the water solubility of the copolymer is lost and a hydrophobic film is formed. Therefore, since the pigment is coated on the resin, a printed matter having excellent water resistance (fastness) can be obtained. For this reason, the neutralization process requires a medium (0.1 to 1 m
Amines having a vapor pressure of mHg) are preferably used.

The glass transition temperature Tg of the water-soluble resin is 50 to
It is preferably 100 ° C. Tg of water-soluble resin is 50
When the temperature is higher than 0 ° C, even if the printer head is dried and the ink components are solidified, the surface of the solidified material is soft and the ink itself is redissolved, which is preferable. Further, if the Tg of the water-soluble resin exceeds 100 ° C., the film-forming ability at room temperature becomes insufficient and the printed matter is inferior in quick-drying property and fastness, which is not preferable.

The water-soluble organic solvent used in the present invention acts as a dispersion medium for the pigment and a wetting agent for the ink, and a water-soluble organic solvent usually used for dye-based and pigment-based inks can be used. Further, the water-soluble organic solvent also has an adjusting effect on the drying property of the ink and the penetrability into the printing medium. Among the water-soluble organic solvents, at least one selected from (poly) alkylene glycol, polyhydric alcohol, ester, amide, carboxylic acid, organic sulfide, organic sulfoxide, sulfone and ketone is particularly preferable. These water-soluble organic solvents have a high surface tension, a boiling point higher than that of water, and a low vapor pressure, and improve the nozzle clogging property.

The ink of the present invention has a self-dispersion type acidic pigment of 1 to 10% by weight, similarly to the composition of a usual aqueous pigment ink.
Water-soluble resin 0.5 to 10% by weight and water-soluble organic solvent 5
It is preferable to contain ˜30% by weight. If the content of the self-dispersion acidic pigment is less than 1% by weight, the optical density of the printed matter will be insufficient, and if it exceeds 10% by weight, the ink viscosity will be high and the dispersion stability of the pigment will be poor. It may decrease, which is not preferable.

When the content of the water-soluble resin is less than 0.5%, the dispersion stabilization and the binder effect are not observed, which is not preferable, and when it exceeds 10% by weight, the ink viscosity remarkably increases. Aggregation and nozzle clogging may occur frequently, which is not preferable. In particular, when recording is performed using a thermal jet printer that applies thermal energy to the thin film resistor to generate and eject ink droplets, if excess water-soluble resin for the pigment is present in the ink, the thin film resistor The ink does not foam even if a predetermined amount of heat energy is applied to it, or the excess water-soluble resin becomes insoluble due to the heat when the pulse is applied, and it accumulates on the thin film resistor, causing ink ejection failure and disturbance in the ejection direction. Sometimes.

If the content of the water-soluble organic solvent is less than 5% by weight, nozzle clogging tends to occur, which is not preferable, and if it exceeds 30% by weight, the viscosity becomes too high and the drying property is high. And the print quality deteriorates, which is not preferable.

The pH of the ink of the present invention is preferably 7-11. For example, by adjusting the pH of the ink to the above range with amines, the electric repulsion of the acidic pigment and the repulsion of the water-soluble resin due to the electric double layer can be maintained in a good balance.

When the pH of the ink is less than 7, it is expected that the electric repulsive force of the pigment in the dispersed state will decrease and the dispersed state will become unstable. It is not preferable because it tends to occur. Further, when the pH of the ink exceeds 11, the electric repulsion action of the water-soluble resin is hindered and precipitation easily occurs, which may hinder the dispersion stability and induce deterioration of the ink performance, which is preferable. Absent. On the other hand, since the ink of the present invention has a high possibility of coming into contact with the human body, p is preferable in terms of stability and safety.
It is preferable to adjust H to near neutral.

Additives may be added, if necessary, in order to impart desired physical properties to the ink of the present invention. In order to adjust the surface tension, viscosity, moisturizing property, drying property, etc. of the ink, a solvent other than the above water-soluble organic solvent can be added to the ink. Specifically, in order to adjust the drying property and fixing property, highly volatile monohydric alcohols such as ethanol, 1-propanol, 2-propanol and 1-butanol, and low volatile alcohols such as 1-hexanol are used. An organic solvent having high water solubility can be added.

Examples of other additives include a pH adjusting agent, antifungal agent, antiseptic agent, antirust agent, nozzle drying inhibitor and the like. Examples of the pH adjuster include inorganic salts such as potassium hydrogenphosphate and sodium hydrogenphosphate in addition to the above amines. Examples of the antifungal, antiseptic and antirust agents include benzoic acid, dichlorophen, sorbic acid, p-hydroxybenzoic acid ester and ethylenediaminetetraacetic acid (EDTA). Examples of the nozzle drying inhibitor include urea, thiourea, ethylene urea and the like.

To the ink of the present invention, an anionic surfactant, a cationic surfactant, a nonionic surfactant, an amphoteric surfactant or a dispersant is added for the purpose of improving the dispersibility of the pigment and the printing quality. Good.

As the anionic surfactant, a (higher) fatty acid salt, an alkyl sulfate salt, an alkyl aryl sulfonate, an alkyl naphthalene sulfonate, a dialkyl sulfonate, a dialkyl sulfosuccinate, an alkyl diaryl ether disulfonate, Examples thereof include alkyl phosphates, polyoxyethylene alkyl ether sulfates, polyoxyethylene alkyl aryl ether sulfates, and polyoxyethylene alkyl phosphate ester salts.

Examples of the cationic surfactant include an alkylamine salt, a quaternary ammonium salt, an alkylpyridinium salt, an alkylimidazolium salt and the like.

As the nonionic surfactant, polyoxyethylene alkyl ether, polyoxyethylene alkylaryl ether, polyoxyethylene oxypropylene block copolymer, sorbitan fatty acid ester, polyoxyethylene sorbitan fatty acid ester, glycerin fatty acid ester, polyoxyethylene. Nonionic surfactants such as fatty acid esters, polyoxyethylene alkylamines, fluorine-based and silicon-based are included.

Examples of the zwitterionic surfactant include alkylbetaine, alkylamine oxide, phosphadylcholine and the like.

[0051]

EXAMPLES The present invention will be specifically described based on synthetic examples, comparative synthetic examples, examples and comparative examples, but the present invention is not limited to these synthetic examples and examples.

(Synthesis Examples 1 to 6 and Comparative Synthesis Examples 1 and 2)
According to a known acrylic resin synthesis method, a copolymer (water-soluble resin) having a monomer composition (% by weight) shown in Table 1 was synthesized,
The molecular weight M _W and the acid value were measured by a predetermined method. The obtained measurement results are shown in Table 1.

[0053]

[Table 1]

In a water bath adjusted to about 80 ° C,
The obtained water-soluble resin was heated and mixed with pure water (distilled water) about 5 times the weight of the resin and an excess (about 1.2 times the weight of the resin) of amine to completely dissolve the resin. The obtained solution was mixed with carbon black (dispersion liquid), an organic solvent and distilled water shown in each of the following Examples and Comparative Examples, and sufficiently stirred. Further, if necessary, dust filtration and coarse particles were removed by vacuum filtration with a 2 μm membrane filter to obtain an aqueous pigment ink.

[0055] (Example 1) Carbon black 5% by weight (Carboxylic acid group adduct, manufactured by Cabot Corporation, CAB-O-JET300) Water-soluble resin of Synthesis Example 1 3% by weight Ammonia 5% by weight Ethylene glycol 15% by weight Glycerin 5% by weight Distilled water balance

[0056] (Example 2) Carbon black 5% by weight (Sulfonic acid group adduct, manufactured by Cabot Corporation, CAB-O-JET200) Water-soluble resin of Synthesis Example 2 3% by weight N, N-dimethylaminoethanol 2% by weight Diethylene glycol 5% by weight Glycerin 5% by weight Isopropyl alcohol 2% by weight Distilled water balance

[0057] (Example 3) Carbon black 5% by weight (Carboxylic acid group adduct, manufactured by Cabot Corporation, CAB-O-JET300) Water-soluble resin of Synthesis Example 3 3% by weight N, N-dimethylaminoethanol 2% by weight 2-pyrrolidone 10% by weight PEG400 4% by weight Isopropyl alcohol 2% by weight Distilled water balance

(Examples 4 to 6) An aqueous pigment ink was obtained in the same manner as in Example 3 except that the water-soluble resins of Synthesis Examples 1 to 6 were used instead of the water-soluble resins of Synthesis Example 1. .

[0059] (Comparative Example 1) Example in which ordinary acidic carbon black that is not a self-dispersion type is used Carbon black (Mitsubishi Chemical Co., MA7) 5% by weight Water-soluble resin of Synthesis Example 1 4% by weight N, N-dimethylaminoethanol 2% by weight Diethylene glycol 8% by weight 2-pyrrolidone 8% by weight Distilled water balance

[0060] (Comparative Example 2) Example using other water-soluble resin Carbon black 5% by weight (Carboxylic acid group adduct, manufactured by Cabot Corporation, CAB-O-JET300) Polyvinylpyrrolidone (K-30, manufactured by ISP) 3% by weight N, N-dimethylaminoethanol 2% by weight Diethylene glycol 8% by weight 2-pyrrolidone 8% by weight Distilled water balance

[0061] (Comparative Example 3) Example using a water-soluble resin neutralized with sodium hydroxide Carbon black 5% by weight (Carboxylic acid group adduct, manufactured by Cabot Corporation, CAB-O-JET300) Water-soluble resin of Synthesis Example 3 3% by weight NaOH 3% by weight Diethylene glycol 8% by weight 2-pyrrolidone 8% by weight Distilled water balance

[0062] (Comparative Example 4) Example using a water-soluble resin having an acid value of more than 300 Carbon black 5% by weight (Carboxylic acid group adduct, manufactured by Cabot Corporation, CAB-O-JET300) Water-soluble resin of Comparative Synthesis Example 2 3% by weight N, N-dimethylaminoethanol 2% by weight Diethylene glycol 8% by weight 2-pyrrolidone 8% by weight Distilled water balance

[0063] (Comparative Example 5) Example in which a water-soluble resin whose neutralization with respect to an acid value is less than 50% is used Carbon black 5% by weight (Carboxylic acid group adduct, manufactured by Cabot Corporation, CAB-O-JET300) Resin of Synthesis Example 3 3% by weight Triethanolamine 0.2% by weight Diethylene glycol 8% by weight 2-pyrrolidone 8% by weight Distilled water balance

Comparative Example 6 An example using a water-soluble resin having a weight average molecular weight M _W of more than 15000 Carbon black 5% by weight (carboxylic acid group adduct, manufactured by Cabot Corporation, CAB-O-JET300) Comparative Synthesis Example 1 Resin 3% by weight triethanolamine 0.2% by weight 2-pyrrolidone 12% by weight ethanol 2% by weight distilled water balance

[0065] (Comparative Example 7) Example in which the total amount of water-soluble organic solvents exceeds 30% by weight Carbon black 5% by weight (Carboxylic acid group adduct, manufactured by Cabot Corporation, CAB-O-JET300) 2% by weight of resin of Synthesis Example 3 Triethanolamine 3% by weight PEG400 15% by weight 2-pyrrolidone 15% by weight Ethanol 3% by weight Distilled water balance

Each of the aqueous pigment inks obtained in Examples 1 to 6 and Comparative Examples 1 to 7 was filled in a cartridge of an ink jet printer (DeskJet970C manufactured by Hewlett-Packard Co.) to perform recording, and nozzle clogging resistance was obtained. The water resistance, fixability and print quality of the recorded matter were evaluated by the following methods.

(Clogging resistance) After cleaning the cartridge head and performing predetermined printing, the state of the nozzle was observed with an optical microscope, and the clogging resistance was evaluated according to the following criteria. ○: No clogging ×: There is clogging

(Water resistance) Commercially available PPC paper (manufactured by Oji Paper Co., Ltd.) was subjected to predetermined printing, allowed to stand for 6 hours, and then the printed matter was immersed in tap water for 5 minutes to obtain a densitometer (R, Macbeth, R
The optical density value was measured using D-918). The residual rate (%) was obtained from the obtained results and the optical density value before immersion measured in advance.

(Fixability) Solid printing was performed on art paper, the printed matter was rubbed with a damp cotton swab three times, and changes in the printed area were visually observed, and the fixability was evaluated according to the following criteria. ○: No rubbing ×: Rub

(Printing Quality) Predetermined characters and image samples were printed on a commercially available PPC paper (manufactured by Oji Paper Co., Ltd.), the obtained printed matter was visually observed, and the printing quality was evaluated according to the following criteria. : Good (those whose 3pt alphabet can be identified) x: Poor (those whose 3pt alphabet cannot be identified)

(Storage Stability) Each aqueous pigment ink was put in a glass sample bottle and sealed in a constant temperature bath at 60 ° C. for 1 hour.
After storage for a month, the presence or absence of aggregates of pigment particles after storage and the presence or absence of precipitation of precipitates were visually observed, and the storage stability was evaluated according to the following criteria. ◯: No agglomerates or precipitates ×: Agglomerates or precipitates are shown in Table 2 below.

[0072]

[Table 2]

With respect to the water-based pigment inks of Examples 1 to 6, good results were obtained in all evaluation items.
On the other hand, the water-based pigment inks of Comparative Examples 1 to 4 were inferior in any of water resistance, fixability and storage stability. In addition, the water-based pigment inks of Comparative Examples 5 to 7 have a resistance to clogging,
The print quality and the storage stability were poor, and in particular, when the print quality was changed, the ink was warped.

[0074]

EFFECTS OF THE INVENTION According to the present invention, the printed matter is excellent in quality, water resistance, and fixability, but is free from pigment particle aggregation, sedimentation, and solid content precipitation during long-term storage, and is excellent in storage stability. It is possible to provide an ink which has excellent re-dissolvability of ink in a printer head and good ejection stability at a nozzle and which satisfies all required characteristics.

   ─────────────────────────────────────────────────── ─── Continued front page    F-term (reference) 2C056 EA13 EA14 EA26 FA03 FC01                 2H086 BA52 BA55 BA59 BA60 BA62                 4J039 AD13 AD14 BE01 BE12 GA24

Claims (8)

[Claims] 1. A water-based pigment ink for inkjet recording, comprising at least a self-dispersible acidic pigment, a water-soluble resin and a water-soluble organic solvent, and the balance being water, wherein the water-soluble resin is a hydrophilic portion or a hydrophobic portion. And a monomer having an acidic group and having an α, β-ethylenically unsaturated group constituting a hydrophilic portion, and a monomer having an α, β-ethylenically unsaturated group constituting a hydrophobic portion. A copolymer having a weight average molecular weight M _W of 15,000 or less, and 3
Has an acid value of 00 mgKOH / g or less and 50% of acidic groups
The above is neutralized with a basic organic compound selected from ammonia and amines, and the content of the water-soluble organic solvent is 30% by weight or less, and an aqueous pigment ink for inkjet recording. 2. The water-soluble resin is (meth) acrylic acid, crotonic acid, itaconic acid, itaconic acid monoester, (anhydrous) maleic acid, maleic acid monoester, fumaric acid,
Α constituting at least one hydrophilic moiety selected from fumaric acid monoester, vinylsulfonic acid, styrenesulfonic acid, sulfonated vinylnaphthalene, N, N-dimethylaminoethyl methacrylate and N, N-diethylaminoethyl methacrylate, Monomer having β-ethylenically unsaturated group, styrene, α-methylstyrene, vinyltoluene, vinylnaphthalene and its derivatives, (meth) acrylic acid alkyl ester, (meth) acrylic acid aryl ester, crotonic acid alkyl ester 2. A copolymer with a monomer having an α, β-ethylenically unsaturated group constituting at least one kind of hydrophobic moiety selected from dialkyl esters of itaconic acid and dialkyl esters of maleic acid. Water-based pigment for inkjet recording Link. 3. A water-soluble resin constitutes a hydrophilic portion.
Monomers 20 to 60 having α, β-ethylenically unsaturated groups
mol% and α, β-ethylenic component which constitutes the hydrophobic part
It is a copolymer with a saturated group of 40 to 80 mol%, and its weight
Weight average molecular weight M _WIs 3000 to 15000, and
Its weight average molecular weight M_WAnd number average molecular weight M _NRatio with (min
Dispersion M_W/ M_N) Is 1 to 2.5.
The water-based pigment ink for inkjet recording described. 4. The water-based pigment ink for inkjet recording according to claim 1, wherein the water-soluble resin is a random copolymer or an alternating copolymer. 5. The water-soluble resin is 50 to 300 mg KOH.
The aqueous pigment ink for inkjet recording according to any one of claims 1 to 4, which has an acid value of / g. 6. The self-dispersion acidic pigment has, on its surface, a functional group selected from a sulfonic acid group, a sulfinic acid group, a carboxylic acid group, a phosphoric acid group and salts thereof.
5. The water-based pigment ink for inkjet recording according to any one of items 1 to 5. 7. The water-soluble organic solvent is at least one selected from (poly) alkylene glycols, polyhydric alcohols, esters, amides, carboxylic acids, organic sulfides, organic sulfoxides, sulfones and ketones. 7. The water-based pigment ink for inkjet recording according to any one of 6. 8. A self-dispersible acidic pigment 1 to 10% by weight, a water-soluble resin 0.5 to 10% by weight, and a water-soluble organic solvent 5 to 5.
The aqueous pigment ink for inkjet recording according to any one of claims 1 to 7, which contains 30% by weight.