JP2011038018A - Method for producing aqueous dispersion of self-dispersing polymer, aqueous ink composition, ink set, and method for forming image - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for producing an aqueous dispersion of a self-dispersing polymer excellent in dispersion stability. <P>SOLUTION: The aqueous dispersion of a self-dispersing polymer is produced by a production method including: a polymerization step in which a copolymer including a hydrophilic component and a hydrophobic component is produced in a reaction mixture containing less than 10 mass% of an organic solvent in the total mass; a copolymer solution preparation step in which after a copolymer solution is obtained by adding the organic solvent to the copolymer obtained from the polymerization step, absorbance measurement at 660 nm with a sample length of 10 mm is performed at room temperature (25°C) for a solution sample having 25 mass% of solid concentration of the copolymer prepared from the copolymer solution, and when the obtained absorbance is greater than 0.10, insoluble matter contained in the copolymer solution are removed, thereby reducing the absorbance measured for the copolymer solution after removing the insoluble matter on the same conditions as the previous absorbance measurement to 0.10 or less; and a dispersion step in which water is added to the copolymer solution obtained from the copolymer solution preparation step to obtain the aqueous dispersion of the copolymer. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a method for producing a self-dispersing polymer aqueous dispersion, an aqueous ink composition, an ink set, and an image forming method.

  The ink jet recording method performs recording by ejecting ink droplets from a large number of nozzles formed on an ink jet head, and the noise during the recording operation is low, the running cost is low, and various recording media are used. On the other hand, it is widely used because it can record high-quality images.

  Ink-jet inks use carbon black pigments for black inks, but color inks are mainly water-soluble dyes, which require improved weather resistance (light resistance, ozone resistance, water resistance). Yes. In particular, when considering application to the printing field, improvement in weather resistance is particularly important. The pigment is inherently high in fastness due to its high crystallinity, and has excellent light resistance and water resistance compared to dyes. However, there are problems such as dischargeability due to clogging of the nozzle part, storage stability such as coagulation sedimentation, and further fixing of printed matter such as abrasion resistance and glossiness due to particles remaining on the surface of the recording medium. It is left.

  As a technique for preventing clogging of a nozzle part in an inkjet head, an inkjet ink composition containing a hydrosol polymer in which a water-insoluble polymer synthesized in an organic solvent is dispersed in an aqueous carrier medium is disclosed (for example, Patent Document 1). The ink composition is said to have good storage stability, low viscosity, excellent print quality, excellent stain resistance after drying and sufficiently long blockage or coagulation time.

  As an ejection property improving technique in ink jet recording, an aqueous ink jet recording liquid having a small content of a serum fraction of a unit derived from a hydrophilic monomer derived from a polymer binder emulsion has been disclosed (for example, see Patent Document 2). The aqueous ink jet recording liquid is said to be able to improve the optical density and to overcome the problem of printing life occurring in the ink jet ink containing a certain polymer emulsion binder.

Japanese Patent No. 3069543 JP 2006-131900 A

  However, the ink-jet ink composition containing the hydrosol polymer described in Patent Document 1 has an effect of improving fixability, but when applied to an ink-jet ink using an ink solvent with little paper curl generation, at the time of high-speed printing, Dischargeability may not be sufficient.

  In addition, the method for producing a polymer binder emulsion described in Patent Document 2 requires dialysis and ultrafiltration after emulsion polymerization, and has a problem of poor productivity. In addition, when the polymer binder emulsion is applied to an inkjet ink, the stability of the ink may be inferior, or the ejection property may not be sufficient during high-speed printing.

  The present invention has been made in view of such circumstances, and includes a method for producing an aqueous dispersion of a self-dispersing polymer excellent in dispersion stability, an aqueous dispersion obtained by the production method, and is stable over time. It is an object of the present invention to provide an ink composition and an ink set that exhibit excellent discharge stability and good ejection stability when applied to an inkjet, and an image recording method using the ink composition or the ink set.

Specific means for solving the above problems are as follows.
<1> A polymerization step for producing a copolymer containing a hydrophilic constituent unit and a hydrophobic constituent unit in a reaction mixture containing less than 10% by mass of an organic solvent in the total mass;
After an organic solvent is added to the copolymer obtained by the polymerization step to obtain a copolymer solution, the copolymer prepared from the copolymer solution has a solid content concentration of 25% by mass with respect to a solution sample. 660 nm absorbance measurement with a sample length of 10 mm is performed at room temperature (25 ° C.), and when the obtained absorbance is greater than 0.10, the insoluble matter contained in the copolymer solution is removed to remove the insoluble matter. A copolymer solution preparation step of making the absorbance measured under the same conditions as the above-mentioned absorbance measurement in the copolymer solution after removal to be 0.10 or less,
A dispersion step of adding water to the copolymer solution obtained by the copolymer solution preparation step to obtain an aqueous dispersion of the copolymer;
A process for producing an aqueous dispersion of a self-dispersing polymer comprising

<2> The method for producing a self-dispersing polymer aqueous dispersion according to <1>, wherein the polymerization step is a polymerization step to which a bulk polymerization method or a suspension polymerization is applied.
<3> The method for producing an aqueous self-dispersing polymer dispersion according to <1> or <2>, wherein at least one of the hydrophilic structural units is a structural unit having a carboxyl group.
<4> At least one of the hydrophobic structural units is any one of the above <1> to <3>, which is a structural unit derived from at least one of an acrylic ester monomer and a methacrylic ester monomer. A process for producing the aqueous dispersion of a self-dispersing polymer as described.

  <5> Water-insoluble colored particles containing a colorant, and a self-dispersing polymer aqueous dispersion produced by the method for producing an aqueous self-dispersing polymer dispersion according to any one of <1> to <4>, A water-based ink composition containing

<6> An ink set comprising at least one water-based ink composition according to <5>.
<7> Image formation including an ink application step of applying the aqueous ink composition onto a recording medium using the water-based ink composition according to <5> or the ink set according to <6>. Method.

  According to the present invention, a method for producing an aqueous dispersion of a self-dispersing polymer having excellent dispersion stability, an aqueous dispersion obtained by the production method, and excellent in stability over time and good in application to inkjet recording An ink composition and an ink set exhibiting excellent ejection stability, and an image recording method using the ink composition or the ink set can be provided.

<Method for producing aqueous dispersion of self-dispersing polymer>
The method for producing an aqueous dispersion of a self-dispersing polymer of the present invention (hereinafter also simply referred to as “the method of production of the present invention”) comprises a copolymer containing a hydrophilic structural unit and a hydrophobic structural unit, an organic solvent. A polymerization step for producing in a reaction mixture containing less than 10% by mass in the total mass;
After an organic solvent is added to the copolymer obtained by the polymerization step to obtain a copolymer solution, the copolymer prepared from the copolymer solution has a solid content concentration of 25% by mass with respect to a solution sample. 660 nm absorbance measurement with a sample length of 10 mm is performed at room temperature (25 ° C.), and when the obtained absorbance is greater than 0.10, the insoluble matter contained in the copolymer solution is removed to remove the insoluble matter. In the copolymer solution after the removal, a copolymer solution preparation step for reducing the absorbance measured under the same conditions as the above-mentioned absorbance measurement to 0.10 or less, and the copolymer solution obtained by the copolymer solution preparation step A dispersion step of adding water to obtain an aqueous dispersion of the copolymer.
The production method of the present invention can efficiently produce an aqueous dispersion of a self-dispersing polymer having excellent dispersion stability by having such a configuration.

[Self-dispersing polymer]
In the present invention, the self-dispersing polymer is a copolymer containing a hydrophilic structural unit and a hydrophobic structural unit, and in the absence of a surfactant, the hydrophilic functional group of the polymer itself (preferably, A water-insoluble polymer that can be dispersed in an aqueous medium by a dissociable group or a salt thereof. The self-dispersing polymer is preferably a copolymer derived from a monomer having an ethylenically unsaturated bond. In addition, the dispersion state here means an emulsified state (emulsion) in which a water-insoluble polymer is dispersed in an aqueous medium, and a dispersed state (suspension) in which a water-insoluble polymer is dispersed in an aqueous medium. ) Including both states.
The self-dispersing polymer is preferably a self-dispersing polymer that can be in a dispersed state in which a water-insoluble polymer is dispersed in a solid state, for example, from the viewpoint of ink fixability when contained in an aqueous ink composition.

  Further, the dispersion state of the self-dispersing polymer in the present invention means a solution obtained by dissolving 30 g of a water-insoluble polymer in 70 g of an organic solvent (for example, methyl ethyl ketone), and a neutralizing agent capable of neutralizing 100% of the dissociable group of the water-insoluble polymer. (If the salt-forming group is anionic, sodium hydroxide, acetic acid if it is cationic) and 200 g of water were mixed and stirred (apparatus: stirring apparatus with stirring blades, rotation speed 200 rpm, 30 minutes, 25 ° C.). After that, even after removing the organic solvent from the mixed solution, it means a state in which it can be visually confirmed that the dispersion state exists stably at 25 ° C. for at least one week.

  The water-insoluble polymer means a polymer having a dissolution amount of 10 g or less when the polymer is dissolved in 100 g of water at 25 ° C., and the dissolution amount is preferably 5 g or less, more preferably 1 g or less. is there. The dissolution amount is the dissolution amount when 100% neutralized with sodium hydroxide or acetic acid depending on the type of dissociable group of the water-insoluble polymer.

  Hereinafter, each process in the manufacturing method of this invention is demonstrated sequentially.

[Polymerization process]
The polymerization step is a step of producing a copolymer containing a hydrophilic constituent unit and a hydrophobic constituent unit in a reaction mixture containing less than 10% by mass of an organic solvent in the total mass, and is produced in this step. This copolymer constitutes the self-dispersing polymer in the present invention described above.
Hereinafter, the synthesis of the copolymer constituting the self-dispersing polymer will be described.

The synthesis of the copolymer in the polymerization step is performed in a reaction mixture containing less than 10% by mass of an organic solvent in the total mass. For the polymerization step, various polymerization methods such as an emulsion polymerization method, a suspension polymerization method, a bulk polymerization method, a solid phase polymerization method, and a precipitation polymerization method can be used.
These polymerization methods are used when synthesizing a polymer with the same weight average molecular weight as the polymerization rate is high and the amount of residual monomer is small compared to the general solution polymerization method that has been applied to the production of aqueous polymer dispersions. In that a polymer having a small molecular weight distribution can be obtained.

  When the residual monomer is small, the present inventors have stabilized the dispersion of the copolymer (self-dispersing polymer) in the dispersion step, and as a result, the self-dispersing polymer obtained by the production method of the present invention is used as an ink for inkjet. When it is used in the composition, the ejection property is improved, and when the molecular weight distribution of the copolymer is small, the content of low molecular weight components in the ink composition is reduced, so that the ejection property is further improved. I found it.

  Among the above polymerization methods, the polymerization method applied to the polymerization step is preferably an emulsion polymerization method, a suspension polymerization method, or a bulk polymerization method, and since the use of a low molecular surfactant is not essential, A combined method or a bulk polymerization method is more preferable, and a suspension polymerization method is particularly preferable because a copolymer having a high glass transition temperature can be synthesized.

  In the case of the emulsion polymerization method and the suspension polymerization method, the main component of the polymerization medium is water. However, in the emulsion polymerization method, in order to increase the solubility and diffusibility of the monomer in the polymerization medium or to control the molecular weight. In the suspension polymerization method, when a solid monomer is used, the organic solvent may be used in an amount of less than 10% by mass in order to keep the monomer droplets in a liquid state or to control the molecular weight.

  The copolymer (self-dispersing polymer) obtained in the polymerization step contains at least one hydrophilic structural unit and at least one hydrophobic structural unit.

  At least one of the hydrophobic structural units is preferably a structural unit derived from a monomer having an ethylenically unsaturated bond from the viewpoint of dispersion stability, and is preferably an acrylic acid ester monomer or a methacrylic acid ester monomer. More preferably, it is a structural unit derived from at least one.

  Specific examples of the monomer constituting the hydrophobic structural unit include styrene, α-methylstyrene, methyl acrylate, ethyl acrylate, n-propyl acrylate, isopropyl acrylate, n-butyl acrylate, isobutyl acrylate, sec-butyl acrylate, tert -Butyl acrylate, amyl acrylate, hexyl acrylate, 2-ethylhexyl acrylate, octyl acrylate, tert-octyl acrylate, 2-chloroethyl acrylate, 2-bromoethyl acrylate, 4-chlorobutyl acrylate, cyanoethyl acrylate, 2-acetoxyethyl acrylate, Benzyl acrylate, methoxybenzyl acrylate, 2-chlorocyclohexyl acrylate, cyclohexylacetate Rate, furfuryl acrylate, tetrahydrofurfuryl acrylate, phenyl acrylate, 2-phenoxyethyl acrylate, 5-hydroxypentyl acrylate, 2,2-dimethyl-3-hydroxypropyl acrylate, 2-methoxyethyl acrylate, 3-methoxybutyl acrylate, 2-ethoxyethyl acrylate, 2-butoxyethyl acrylate, 2- (2-methoxyethoxy) ethyl acrylate, 2- (2-butoxyethoxy) ethyl acrylate, glycidyl acrylate, 1-bromo-2-methoxyethyl acrylate, 1,1 -Dichloro-2-ethoxyethyl acrylate, 2,2,2-tetrafluoroethyl acrylate, 1H, 1H, 2H, 2H-perfluorodecyl acrylate, methyl Tacrylate, ethyl methacrylate, n-propyl methacrylate, isopropyl methacrylate, n-butyl methacrylate, isobutyl methacrylate, sec-butyl methacrylate, tert-butyl methacrylate, amyl methacrylate, hexyl methacrylate, benzyl methacrylate, chlorobenzyl methacrylate, octyl methacrylate, stearyl methacrylate, 2- (3-phenylpropyloxy) ethyl methacrylate, furfuryl methacrylate, tetrahydrofurfuryl methacrylate, phenyl methacrylate, 2-phenoxyethyl methacrylate, cresyl methacrylate, naphthyl methacrylate, 2-hydroxyethyl methacrylate, 4-hydroxybutyl methacrylate, triethyle Glycol monomethacrylate, dipropylene glycol monomethacrylate, 2-methoxyethyl methacrylate, 3-methoxybutyl methacrylate, 2-ethoxyethyl methacrylate, methoxydiethylene glycol methacrylate, 2-iso-propoxyethyl methacrylate, 2-butoxyethyl methacrylate, 2- (2 -Methoxyethoxy) ethyl methacrylate, 2- (2-ethoxyethoxy) ethyl methacrylate, 2- (2-butoxyethoxy) ethyl methacrylate, 2-acetoxyethyl methacrylate, 2-acetoacetoxyethyl methacrylate, allyl methacrylate, glycidyl methacrylate, 2, 2,2-tetrafluoroethyl methacrylate, 1H, 1H, 2H, 2H-perfluorodecylme Acrylate and the like.

  Further, as other specific examples of the monomer constituting the hydrophobic structural unit, cyclohexyl, cyclohexylmethyl, 3-cyclohexenylmethyl, 4-isopropylcyclohexyl, 1-methylcyclohexyl, 2-methylcyclohexyl, acrylic acid and methacrylic acid, 3-methylcyclohexyl, 4-methylcyclohexyl, 1-ethylcyclohexyl, 4-ethylcyclohexyl, 2-tert-butylcyclohexyl, 4-tert-butylcyclohexyl, menthyl, 3,3,5-trimethylcyclohexyl, cycloheptyl, cyclooctyl , Nonyl, cyclodecyl, 2-norbornyl, isobornyl, 3-methyl-2-norbornyl, dicyclopentanyl, dicyclopentenyl, dicyclopentenyloxyethyl, adamanty -1-yl, adamantane-2-yl, 2-methyladamantan-2-yl, 2-ethyladamantan-2-yl and 3,5-dimethyladamantan-1-yl, 1,1′-bisadamantane-3- Each ester, such as il.

  In addition, the hydrophilic structural unit contained in the copolymer (self-dispersing polymer) is derived from a monomer having a hydrophilic group and an ethylenically unsaturated bond (hereinafter also referred to as “hydrophilic group-containing monomer”). Those that do are preferred. The hydrophilic group-containing monomer may be a monomer containing one kind of hydrophilic group or a monomer containing two or more kinds of hydrophilic groups. Moreover, there is no restriction | limiting in particular as a hydrophilic group which a hydrophilic group containing monomer has, A dissociative group or a nonionic hydrophilic group may be sufficient.

  In the present invention, the hydrophilic group is preferably a dissociable group and more preferably an anionic dissociable group from the viewpoint of promoting self-dispersion and the stability of the formed emulsified or dispersed state. Examples of the dissociable group include a carboxyl group, a phosphoric acid group, and a sulfonic acid group. Among these, from the viewpoint of fixability when a self-dispersing polymer aqueous dispersion constitutes an aqueous ink composition, the carboxyl group is preferable.

The hydrophilic group-containing monomer in the present invention is preferably a dissociable group-containing monomer from the viewpoint of self-dispersibility, and preferably a dissociable group-containing monomer having a dissociable group and an ethylenically unsaturated bond. .
Examples of the dissociable group-containing monomer include an unsaturated carboxylic acid monomer, an unsaturated sulfonic acid monomer, and an unsaturated phosphoric acid monomer.

Specific examples of the unsaturated carboxylic acid monomer include acrylic acid, methacrylic acid, crotonic acid, itaconic acid, maleic acid, fumaric acid, citraconic acid, and 2-methacryloyloxymethyl succinic acid. Specific examples of the unsaturated sulfonic acid monomer include styrene sulfonic acid, 2-acrylamido-2-methylpropane sulfonic acid, 3-sulfopropyl (meth) acrylate, and bis- (3-sulfopropyl) -itaconate. It is done. Specific examples of unsaturated phosphoric acid monomers include vinylphosphonic acid, vinyl phosphate, bis (methacryloxyethyl) phosphate, diphenyl-2-acryloyloxyethyl phosphate, diphenyl-2-methacryloyloxyethyl phosphate, dibutyl-2- Examples include acryloyloxyethyl phosphate.
Among the dissociable group-containing monomers, unsaturated carboxylic acid monomers are preferable and acrylic acid and methacrylic acid are more preferable from the viewpoints of dispersion stability and dischargeability.

The molecular weight range of the copolymer (self-dispersing polymer) obtained in the polymerization step is preferably 3000 to 200,000, more preferably 5000 to 150,000, and more preferably 10,000 to 100,000 in terms of weight average molecular weight. More preferably. By setting the weight average molecular weight of the copolymer to 3000 or more, the amount of the water-soluble component can be effectively suppressed. Moreover, self-emulsification stability can be improved by making the weight average molecular weight of a copolymer into 200,000 or less.
The weight average molecular weight can be measured by gel permeation chromatography (GPC).

  Specific examples of the self-dispersing polymer are listed below as exemplary compounds B-01 to B-12, but the present invention is not limited thereto. In addition, the parenthesis represents the mass ratio of the copolymerization component.

B-01: Methyl methacrylate / 2-methoxyethyl acrylate / benzyl methacrylate / methacrylic acid copolymer (47/10/34/9)
B-02: Methyl methacrylate / styrene / benzyl methacrylate / methacrylic acid copolymer (63/10/20/7)
B-03: Phenoxyethyl acrylate / methyl methacrylate / acrylic acid copolymer (50/45/5)
B-04: Methyl methacrylate / dicyclopentanyl methacrylate / benzyl methacrylate / methacrylic acid copolymer (43/17/30/10)
B-05: Methyl methacrylate / isobornyl methacrylate / methacrylic acid copolymer (38/52/10)
B-06: Styrene / phenoxyethyl acrylate / methyl methacrylate / acrylic acid copolymer (10/49/35/6)
B-07: benzyl acrylate / methyl methacrylate / acrylic acid copolymer (50/45/5)
B-08: Phenoxyethyl methacrylate / benzyl acrylate / ethyl methacrylate / methacrylic acid copolymer (32/20/40/8)
B-09: Methyl methacrylate / isobornyl methacrylate / hydroxyethyl methacrylate / methacrylic acid copolymer (40/48/5/7)
B-10: benzyl methacrylate / isobutyl methacrylate / cyclohexyl methacrylate / methacrylic acid copolymer (35/30/30/5)
B-11: Phenoxyethyl acrylate / ethyl acrylate / acrylic acid copolymer (30/65/5)
B-12: Methyl methacrylate / tert-butyl methacrylate / isobornyl methacrylate / methacrylic acid copolymer (35/10/45/10)

[Copolymer solution preparation process]
In the copolymer solution preparation step, an organic solvent is added to the copolymer obtained in the polymerization step to obtain a copolymer solution, and then the solid content concentration of the copolymer prepared from the copolymer solution is When a 660 nm absorbance measurement at a sample length of 10 mm is performed on a 25 mass% solution sample at room temperature (25 ° C.) and the obtained absorbance is greater than 0.10, insoluble matter contained in the copolymer solution Is a step of reducing the absorbance measured under the same conditions as the above-mentioned absorbance measurement in the copolymer solution after removing insoluble matter to 0.10 or less.

  In this step, first, an organic solvent is added to the copolymer obtained in the polymerization step to obtain a copolymer solution. That is, the copolymer solution obtained here is obtained by dissolving the copolymer (self-dispersing polymer) obtained in the polymerization step in an organic solvent that dissolves the copolymer.

  There is no restriction | limiting in particular as a method of melt | dissolving a copolymer in an organic solvent, The melt | dissolution method used normally can be applied.

  The organic solvent is not particularly limited as long as it can dissolve the copolymer. For example, the organic solvent (henceforth an "organic good solvent") whose solubility (25 degreeC) of a copolymer is 10 mass% or more can be mentioned.

Examples of the organic good solvent include ketone solvents such as methyl ethyl ketone and acetone, ether solvents such as 1,3-dioxane, 1,4-dioxane, 1,3-oxolane and tetrahydrofuran, ester solvents such as ethyl acetate, Examples include amide solvents such as dimethylacetamide, dimethylformamide, and N-methylpyrrolidone. In the present invention, at least one selected from ketone solvents, ether solvents, and ester solvents is preferable, and at least one selected from ketone solvents, ether solvents, and ester solvents having a boiling point of 100 ° C. or less. It is more preferable that it is at least one selected from methyl ethyl ketone, acetone, 1,3-dioxane, 1,4-dioxane, tetrahydrofuran and ethyl acetate.
The organic good solvents may be used alone or in combination of two or more.

  Further, as the solvent for dissolving the copolymer, a good organic solvent and a solvent having a low solubility of the copolymer (hereinafter sometimes referred to as “organic poor solvent”) may be used in combination. Here, the organic poor solvent having low copolymer solubility means an organic solvent having a copolymer solubility (25 ° C.) of less than 10% by mass.

Examples of the organic poor solvent include alcohol solvents such as ethanol, isopropyl alcohol, n-butanol, s-butanol, t-butanol, and 2-ethylhexanol. Especially, it is preferable that it is an alcohol solvent whose boiling point is 100 degrees C or less, and it is more preferable that it is at least 1 sort (s) chosen from ethanol, isopropyl alcohol, and t-butanol.
The organic poor solvent may be used alone or in combination of two or more.

  In the present invention, when the organic poor solvent is used in combination, the content of the organic poor solvent in the organic solvent dissolving the copolymer is 30 to 70% by mass from the viewpoint of dispersion stability of the self-dispersing polymer aqueous dispersion. Preferably, it is 30-60 mass%.

  As described above, the polymerization step in the present invention is a polymer having a low molecular weight distribution when a polymer having a similar polymerization weight average molecular weight is obtained with a high polymerization rate and a small amount of residual monomer compared to the case where a conventional polymerization method is applied. Is obtained. However, the copolymer obtained from the polymerization step may contain a trace component insoluble in the organic solvent. That is, when producing a copolymer (self-dispersing polymer) in the polymerization step, for example, a surfactant is used if an emulsion polymerization method is applied, and if a suspension polymerization method is applied. Since an additive such as a water-soluble polymer compound is used, each of these components remains as an insoluble matter (insoluble component) together with the copolymer, and the insoluble in the copolymer solution obtained in this step. Turbidity (hereinafter also referred to as “turbidity component”) may occur depending on the object.

  The present inventors have clarified that this insoluble matter affects the physical properties of the self-dispersing polymer aqueous dispersion obtained by the production method of the present invention. Specifically, if the aqueous dispersion of a self-dispersing polymer contains a large amount of turbid components (insoluble matter), the stability of the self-dispersing polymer in the dispersion decreases, the particle size increases, and the filterability deteriorates. I will do. For this reason, when there is a turbid component, it is necessary to remove the turbid component.

  Here, “the turbidity of the copolymer solution” refers to a value obtained by measuring the absorbance at 660 nm with a sample length of 10 mm and a solution having a copolymer concentration of 25% by mass at room temperature (25 ° C.). The absorbance, which is an index of turbidity of the copolymer solution, is preferably 0.10 or less, more preferably 0.04 or less, and particularly preferably 0.02 or less.

  Specifically, in the copolymer solution preparation step, the presence or absence of turbidity in the copolymer solution obtained by adding an organic solvent to the copolymer is determined, and turbidity caused by insoluble matter has occurred. If determined, the insoluble matter contained in the copolymer solution is removed. The insoluble matter contained in the copolymer solution is removed as follows.

  First, the presence or absence of turbidity in the copolymer solution is determined. The determination was made by preparing a solution sample having a copolymer solid content concentration of 25 mass% from the copolymer solution, and measuring the absorbance at 660 nm with a sample length of 10 mm at room temperature (25 ° C.). It is determined that “there is turbidity” when the obtained absorbance is 0.10 or more.

  In preparing the solution sample, when the copolymer solution needs to be diluted, the organic solvent added to the copolymer solution may be further added.

  When the obtained absorbance is greater than 0.10 and it is determined that the copolymer solution is “turbid”, the insoluble matter contained in the copolymer solution is removed. The insoluble matter is removed so that the absorbance measured under the same conditions as the absorbance measurement performed on the copolymer solution before removal of the insoluble matter is 0.10 or less. .

  As a method for removing the insoluble matter, a method of filtering the copolymer solution is preferable. As a filtration method, conventionally known methods such as natural filtration, vacuum filtration, pressure filtration, and centrifugal filtration can be used. As the filter medium, cellulose, nylon, glass fiber, celite, metal, sand and the like can be used. The form of the filter medium may be any of a sheet, a cartridge type, a spool type, a roll type, a pleat type, and the like.

The copolymer solution after the insoluble matter is removed is subjected to a dispersion step described later.
On the other hand, when the obtained absorbance is 0.10 or less and it is determined that the copolymer solution is “no turbidity”, the dispersion step described later may be performed without removing the insoluble matter.

[Dispersion process]
The dispersion step is a step of adding water to the copolymer solution obtained by the copolymer solution preparation to obtain an aqueous dispersion of the copolymer, while adding at least water to the copolymer solution, A step of preparing an aqueous dispersion by mixing and stirring is preferred.
Thus, by adding water to the copolymer solution in which the copolymer is dissolved in an organic solvent, a self-dispersing polymer aqueous dispersion having better dispersion stability can be obtained without requiring strong shearing force. Can do.

  The method of mixing and stirring in the dispersion step is not particularly limited, and a commonly used mixing and stirring device, and a dispersing machine such as an ultrasonic dispersing machine or a high-pressure homogenizer can be used as necessary.

In the dispersion step, at least water is added to the copolymer solution, but a neutralizer and / or a water-soluble electrolyte may be added in addition to water. In addition, you may perform the addition to the copolymer solution of a neutralizing agent and / or a water-soluble electrolyte after completion | finish of a dispersion | distribution process.
In the dispersion step, an organic solvent (preferably an organic poor solvent) may be further added in addition to water.

In the dispersion step, by adding a neutralizing agent to the copolymer solution, some or all of the dissociable groups that the copolymer (self-dispersing polymer) may have are neutralized, and the copolymer (self-dispersing) Polymer) can form a stable dispersion in an aqueous medium.
In addition, by adding a water-soluble electrolyte to the copolymer solution in the dispersion step, for example, the thickness of the electric double layer contributing to dispersion is controlled, and the dispersed particle size of the copolymer particles becomes a particle size suitable for dispersion. Excellent dispersion stability, viscosity and particle size can be controlled.

  As the neutralizing agent, if the copolymer (self-dispersing polymer) has an anionic dissociating group as a dissociating group, the neutralizing agent used is an organic amine compound, ammonia, or an alkali metal hydroxide. And basic compounds such as Examples of organic amine compounds include monomethylamine, dimethylamine, trimethylamine, monoethylamine, diethylamine, triethylamine, monopropylamine, dipropylamine, monoethanolamine, diethanolamine, triethanolamine, N, N-dimethyl-ethanolamine, N, N-diethyl-ethanolamine, 2-dimethylamino-2-methyl-1-propanol, 2-amino-2-methyl-1-propanol, N-methyldiethanolamine, N-ethyldiethanolanine, monoisopropanolamine, di Examples include isopropanolamine and triisopropanolamine. Examples of the alkali metal hydroxide include lithium hydroxide, sodium hydroxide, and potassium hydroxide. Among these, sodium hydroxide, potassium hydroxide, triethylamine, and triethanolamine are preferable from the viewpoint of stabilizing the dispersion of the self-dispersing polymer particles of the present invention in water.

  These neutralizing agents (preferably basic compounds) are preferably used in an amount of 5 to 120 mol%, based on 100 mol% of the dissociable group of the copolymer (self-dispersing polymer), and 10 to 110 mol%. Is more preferable, and it is still more preferable that it is 15-100 mol%. By making it 15 mol% or more, the effect of stabilizing the dispersion of particles in water is remarkably exhibited, and by making it 100 mol% or less, water-soluble components in the dispersed state are remarkably reduced, There is an effect of suppressing an increase in viscosity.

  The water-soluble electrolyte is not particularly limited as long as it is a compound selected from an acidic compound and a salt thereof and having a functional group that can be dissolved and dissociated in water, and may be an organic compound or an inorganic compound. The term “water-soluble” as used herein means that 5 g or more is dissolved in 100 g of water at 25 ° C. Furthermore, the water-soluble electrolyte is a compound that does not substantially function as the neutralizing agent.

  Examples of the water-soluble electrolyte include acidic compounds such as carboxylic acid derivatives, sulfonic acid derivatives, phosphoric acid derivatives, and inorganic acids, and compounds in which these acidic functional groups form a salt. The molecular weight of the acidic compound is not particularly limited, but from the viewpoint of dispersion stability, it is preferably 1000 or less, more preferably 500 or less, and even more preferably 300 or less.

Moreover, as a cation which forms a salt with an acidic compound, an alkali metal ion such as sodium ion or potassium ion, an ammonium ion (NH ₄ ⁺ ), and a monoethanol ammonium ion (HOCH ₂ CH ₂ NH ₃ ⁺ ) An amino alcohol ion etc. can be mentioned. The cation forming the salt may be one kind or a combination of two or more kinds.
The water-soluble electrolyte may be a mixture of an acidic compound and a salt. That is, the thing in which the acidic functional group of an acidic compound forms the salt partially is mentioned.

Specific examples of water-soluble electrolytes include acidic compounds containing carboxyl groups such as acrylic acid, methacrylic acid, maleic acid, malic acid, tartaric acid, fumaric acid, and lactic acid, and salts thereof, methanesulfonic acid, and p-toluenesulfonic acid. Examples thereof include acidic compounds containing a sulfonyl group and salts thereof, and inorganic acid salts such as NaCl, KCl, Na ₂ SO ₄ , CaCl ₂ , and AlCl ₃ .
Among these, from the viewpoint of dispersion stability, it is preferably at least one selected from acidic compounds containing carboxyl groups and salts thereof, and inorganic acid salts, and acidic compounds containing carboxyl groups having a molecular weight of 500 or less and More preferably, at least one selected from those salts and inorganic acid salts, and at least one selected from maleic acid, malic acid, tartaric acid, and their Na salts, and NaCl, Na ₂ SO _4. It is more preferable.
The water-soluble electrolyte may be used alone or in combination of two or more.

The addition amount of the water-soluble electrolyte is such that the content of the water-soluble electrolyte is 0 to 10% by mass with respect to the self-dispersing polymer resin from the viewpoint of dispersion stability of the self-dispersing polymer aqueous dispersion. Is preferable, and it is more preferable to add so that it may become 0-5 mass%.
When the content of the water-soluble electrolyte is 10% by mass or less, aggregation, fusion, and precipitation of the self-dispersing polymer aqueous dispersion can be suppressed.

  In the present invention, when a carboxylic acid derivative or a salt thereof is used as the water-soluble electrolyte, the content of the water-soluble electrolyte is preferably 0 to 8% by mass with respect to the self-dispersing polymer resin, and 0 to 5% by mass. It is more preferable that Moreover, when using an inorganic acid or its salt as a water-soluble electrolyte, it is also preferable that the content rate of a water-soluble electrolyte is 0-7 mass%, and it is more preferable that it is 0-4 mass%.

[Solvent removal step]
In the manufacturing method of this invention, it is preferable to include a solvent removal process after a dispersion | distribution process.
The solvent removal step is not particularly limited as long as at least a part of the solvent remaining in the aqueous dispersion after the dispersion step can be removed. As a method for removing the solvent, a commonly used method such as distillation, vacuum distillation or the like can be applied.

  In the production method of the present invention, a self-dispersing polymer aqueous dispersion having better dispersion stability can be obtained by including a solvent removal step. Furthermore, the above-mentioned water-soluble electrolyte may be added to the self-dispersing polymer aqueous dispersion after the solvent removing step.

  In the solvent removal step, at least part of the solvent is removed, but part of water may be removed together with the solvent.

  The solvent removal step is a step of removing the solvent so that the solvent content in the aqueous dispersion of the self-dispersing polymer is 0.05% by mass or more and 10% by mass or less of the solid content mass of the copolymer. It is preferably 0.08% by mass or more and 8% by mass or less.

  The average particle size of the self-dispersing polymer particles in the self-dispersing polymer aqueous dispersion obtained by the production method of the present invention is preferably in the range of 0.1 nm to 80 nm, more preferably 0.2 nm to 60 nm, and More preferably, it is 3 nm to 40 nm. When the average particle diameter is 0.1 nm or more, the production suitability is improved, and the viscosity of the aqueous dispersion can be suppressed. To do. Moreover, storage stability improves by setting it as an average particle diameter of 80 nm or less. On the other hand, when it is less than 0.1 nm, the interaction between particles is greatly increased, the viscosity of the aqueous dispersion is increased, and the production efficiency may be lowered. Moreover, it is not suitable for a water-based ink composition from the viewpoint of ejection properties. On the other hand, if it exceeds 80 nm, the fusion between polymer particles and the number of micron-sized coarse particles increase, and it becomes difficult to maintain a stable dispersion state.

In the present invention, the particle size distribution of the self-dispersing polymer particles is not particularly limited, and may have a wide particle size distribution or a monodispersed particle size distribution. Moreover, two or more kinds of self-dispersing polymer resins (copolymers) may be mixed and contained.
The average particle size and particle size distribution of the self-dispersing polymer particles can be measured using, for example, a dynamic light scattering method.

The aqueous self-dispersing polymer dispersion produced by the production method of the present invention has excellent dispersion stability. Accordingly, for example, an ink composition containing the aqueous dispersion of a self-dispersing polymer can exhibit excellent storage stability (stability over time) and can exhibit better ink fixability. Further, by applying the aqueous self-dispersing polymer dispersion to the ink composition for inkjet, it is possible to exhibit excellent ejection properties in addition to storage stability and ink fixing properties.
The self-dispersing polymer aqueous dispersion in the invention may be used singly or in combination of two or more when applied to an aqueous ink composition or the like.

<Water-based ink composition>
The aqueous ink composition of the present invention contains at least one kind of water-insoluble colored particles containing a colorant and at least one kind of the above-mentioned self-dispersing polymer aqueous dispersion. The aqueous ink composition of the present invention contains the self-dispersing polymer aqueous dispersion produced by the production method of the present invention, so that the storage stability of the ink composition is excellent and the fixability of the formed image is improved. .

  The water-based ink composition of the present invention can be used not only for the formation of a single color image but also for the formation of a multicolor image (for example, a full color image). In order to form a full color image, a magenta color ink, a cyan color ink, and a yellow color ink can be used, and a black color ink may be further used to adjust the color tone. Further, red, green, blue, and white inks other than yellow, magenta, and cyan color inks, and so-called special color inks (for example, colorless) in the printing field can be used.

  The method for recording an image using the water-based ink composition of the present invention is not particularly limited, and a known image recording method can be used. For example, the image is coated by means such as an inkjet method, a copying method, a printing method, and the like. Examples thereof include a method of applying a water-based ink composition to a recording medium.

[Water-insoluble colored particles]
The water-insoluble colored particles in the present invention contain at least one colorant. As the colorant, known dyes, pigments and the like can be used without particular limitation. Among these, from the viewpoint of ink colorability, a colorant that is almost insoluble or hardly soluble in water is preferable. Specific examples include various pigments, disperse dyes, oil-soluble dyes, dyes forming J aggregates, and the like, and pigments are more preferable.
In the present invention, the water-insoluble pigment itself or the pigment itself surface-treated with a dispersant can be used as water-insoluble colored particles.

  There is no restriction | limiting in particular as a pigment in this invention, A conventionally well-known organic and inorganic pigment can be used. For example, polycyclic pigments such as azo lakes, azo pigments, phthalocyanine pigments, perylene and perinone pigments, anthraquinone pigments, quinacridone pigments, dioxazine pigments, diketopyrrolopyrrole pigments, thioindigo pigments, isoindolinone pigments, quinophthalone pigments, basic Examples include dye lakes such as dye-type lakes and acid dye-type lakes, organic pigments such as nitro pigments, nitroso pigments, aniline black, and daylight fluorescent pigments, and inorganic pigments such as titanium oxide, iron oxide, and carbon black. Any pigment not described in the color index can be used as long as it can be dispersed in the aqueous phase. Further, it is of course possible to use a pigment obtained by surface-treating the above pigment with a surfactant, a polymer dispersing agent or the like, or graft carbon. Among the above pigments, it is particularly preferable to use an azo pigment, a phthalocyanine pigment, an anthraquinone pigment, a quinacridone pigment, or a carbon black pigment.

-Dispersant-
When the colorant in the present invention is a pigment, it is preferably dispersed in an aqueous solvent by a dispersant. The dispersant may be a polymer dispersant or a low molecular surfactant type dispersant. The polymer dispersant may be either a water-soluble dispersant or a water-insoluble dispersant.
The low molecular surfactant type dispersant (hereinafter sometimes referred to as “low molecular dispersant”) may be added for the purpose of stably dispersing the organic pigment in an aqueous solvent while keeping the ink at a low viscosity. it can. The low molecular dispersant herein is a low molecular dispersant having a molecular weight of 2000 or less. Moreover, 100-2000 are preferable and, as for the molecular weight of a low molecular dispersing agent, 200-2000 are more preferable.

  The low molecular weight dispersant has a structure including a hydrophilic group and a hydrophobic group. In addition, the hydrophilic group and the hydrophobic group may be independently contained in one molecule or more, and may have a plurality of types of hydrophilic groups and hydrophobic groups. In addition, a linking group for linking a hydrophilic group and a hydrophobic group can be appropriately included.

Examples of the hydrophilic group possessed by the low molecular dispersant include an anionic property, a cationic property, a nonionic property, and a betaine type combining these.
The anionic group is not particularly limited as long as it has a negative charge, but may be a phosphoric acid group, a phosphonic acid group, a phosphinic acid group, a sulfuric acid group, a sulfonic acid group, a sulfinic acid group, or a carboxylic acid group. Preferably, it is a phosphoric acid group or a carboxylic acid group, and more preferably a carboxylic acid group.

The cationic group is not particularly limited as long as it has a positive charge, but is preferably an organic cationic substituent, more preferably a cationic group containing nitrogen or phosphorus, and nitrogen. More preferably, it is a cationic group. Among these, a pyridinium cation or an ammonium cation is particularly preferable.
The nonionic group is not particularly limited as long as it has no negative or positive charge. For example, a polyalkylene oxide, polyglycerin, a part of sugar unit, etc. are mentioned.

The hydrophilic group in the low molecular weight dispersant in the present invention is preferably an anionic group from the viewpoint of dispersion stability and aggregation of the pigment.
Moreover, when a low molecular weight dispersing agent has an anionic hydrophilic group, it is preferable that the pKa is 3 or more from a viewpoint of making it contact with an acidic process liquid and promoting aggregation reaction. The pKa of the low molecular dispersant in the present invention is determined experimentally from a titration curve by titrating a solution of 1 mol / L of the low molecular dispersant in tetrahydrofuran-water = 3: 2 (V / V) solution with an acid or alkaline aqueous solution. It is the calculated value.
Theoretically, if the pKa of the low molecular dispersant is 3 or more, 50% or more of the anionic groups are in a non-dissociated state when in contact with a treatment solution having a pH of about 3. Accordingly, the water solubility of the low molecular weight dispersant is remarkably lowered, and an agglomeration reaction occurs. That is, the aggregation reactivity is improved. From this viewpoint, it is preferable that the low molecular dispersant has a carboxylic acid group as an anionic group.

  On the other hand, the hydrophobic group possessed by the low molecular dispersant may have any structure such as hydrocarbon, fluorocarbon, and silicone, but is particularly preferably hydrocarbon. Further, these hydrophobic groups may have a linear structure or a branched structure. The hydrophobic group may have a single chain structure or two or more chain structures, and may have a plurality of types of hydrophobic groups in the case of a structure having two or more chains.

  The hydrophobic group is preferably a hydrocarbon group having 2 to 24 carbon atoms, more preferably a hydrocarbon group having 4 to 24 carbon atoms, and further preferably a hydrocarbon group having 6 to 20 carbon atoms.

  Among the polymer dispersants in the present invention, a hydrophilic polymer compound can be used as the water-soluble dispersant. For example, natural hydrophilic polymer compounds include plant polymers such as gum arabic, tragan gum, guar gum, karaya gum, locust bean gum, arabinogalactone, pectin, quince seed starch, seaweeds such as alginic acid, carrageenan and agar. Examples include molecules, animal polymers such as gelatin, casein, albumin and collagen, and microorganism polymers such as xanthene gum and dextran.

  In addition, as hydrophilic polymer compounds chemically modified from natural products, fiber polymers such as methyl cellulose, ethyl cellulose, hydroxyethyl cellulose, hydroxypropyl cellulose, carboxymethyl cellulose, sodium starch glycolate, sodium starch phosphate, etc. And seaweed polymers such as alginic acid propylene glycol ester.

  Synthetic water-soluble polymer compounds include vinyl polymers such as polyvinyl alcohol, polyvinyl pyrrolidone, and polyvinyl methyl ether, acrylic polymers such as polyacrylamide, polyacrylic acid or alkali metal salts thereof, and water-soluble styrene acrylic resins. Resin, water-soluble styrene maleic acid resin, water-soluble vinyl naphthalene acrylic resin, water-soluble vinyl naphthalene maleic resin, polyvinyl pyrrolidone, polyvinyl alcohol, alkali metal salt of β-naphthalene sulfonic acid formalin condensate, quaternary ammonium, amino group, etc. And a polymer compound having a cationic functional group salt in the side chain.

  Among these, from the viewpoint of dispersion stability of the pigment, a polymer compound containing a carboxyl group is preferable. For example, an acrylic resin such as a water-soluble styrene acrylic resin, a water-soluble styrene maleic acid resin, a water-soluble vinyl naphthalene acrylic resin, A polymer compound containing a carboxyl group such as a water-soluble vinyl naphthalene maleic resin is particularly preferable.

  As the water-insoluble dispersant among the polymer dispersants, a polymer having both a hydrophobic part and a hydrophilic part can be used. For example, styrene- (meth) acrylic acid copolymer, styrene- (meth) acrylic acid- (meth) acrylic acid ester copolymer, (meth) acrylic acid ester- (meth) acrylic acid copolymer, polyethylene glycol ( Examples thereof include a meth) acrylate- (meth) acrylic acid copolymer and a styrene-maleic acid copolymer.

  The weight average molecular weight of the polymer dispersant in the present invention is preferably 3,000 to 200,000, more preferably 5,000 to 100,000, still more preferably 5,000 to 80,000, and particularly preferably 10,000. 000-60,000.

  Further, the mixing mass ratio of the pigment and the dispersant (pigment: dispersant) is preferably in the range of 1: 0.06 to 1: 3, more preferably in the range of 1: 0.125 to 1: 2. Preferably it is 1: 0.125 to 1: 1.5.

In the present invention, when a dye is used as the colorant, a water-insoluble carrier can be used as a water-insoluble colored particle. As the dye, known dyes can be used without particular limitation. For example, the dyes described in JP-A-2001-115066, JP-A-2001-335714, JP-A-2002-249677 and the like can be used in the present invention. It can be used suitably. The carrier is not particularly limited as long as it is insoluble in water or hardly soluble in water, and inorganic materials, organic materials, and composite materials thereof can be used. Specifically, the carriers described in JP-A-2001-181549, JP-A-2007-169418, etc. can be suitably used in the present invention.
The carrier holding the dye (water-insoluble colored particles) can be used as an aqueous dispersion using a dispersant. As the dispersant, the above-described dispersants can be suitably used.

  The water-insoluble colored particles in the present invention preferably contain a pigment and a dispersant, more preferably contain an organic pigment and a polymer dispersant, from the viewpoint of light resistance and quality of the image, and the organic pigment and the carboxyl group. It is particularly preferable to include a polymer dispersant.

In the present invention, the average particle size of the water-insoluble colored particles is preferably 10 to 200 nm, more preferably 10 to 150 nm, and still more preferably 10 to 100 nm. When the average particle size is 200 nm or less, the color reproducibility is good, and in the case of the ink jet method, the droplet ejection characteristics are good. Moreover, light resistance becomes favorable because an average particle diameter is 10 nm or more.
The particle size distribution of the water-insoluble colored particles is not particularly limited, and may be either a wide particle size distribution or a monodisperse particle size distribution. Further, two or more kinds of water-insoluble colored particles having a monodisperse particle size distribution may be mixed and used.
The average particle size and particle size distribution of the water-insoluble colored particles can be measured using, for example, a light scattering method.

In the present invention, the water-insoluble colored particles may be used alone or in combination of two or more.
Further, the content of the water-insoluble colored particles is preferably 1 to 25% by mass, more preferably 2 to 20% by mass, and more preferably 5 to 20% by mass with respect to the aqueous ink composition from the viewpoint of image density. % Is more preferable, and 5 to 15% by mass is particularly preferable.

The solid content of the self-dispersing polymer in the aqueous ink composition of the present invention is preferably 1 to 30% by mass with respect to the aqueous ink composition from the viewpoint of image glossiness, and 5 to 15%. More preferably, it is mass%.
In addition, the content ratio of the water-insoluble colored particles to the water-insoluble particles (water-insoluble colored particles / water-insoluble particles) in the water-based ink composition of the present invention is 1 / 0.5 to from the viewpoint of image scratch resistance. 1/10 is preferable, and 1/1 to 1/4 is more preferable.

-Water-soluble organic solvent-
The aqueous ink composition of the present invention contains water as a solvent, but can further contain a water-soluble organic solvent. The water-soluble organic solvent can be contained as a drying inhibitor and a penetration enhancer.
The anti-drying agent can effectively prevent nozzle clogging that may occur due to drying of ink at the ink ejection port, particularly when the aqueous ink composition of the present invention is applied to an image recording method using an ink jet method. .

  The drying inhibitor is preferably a water-soluble organic solvent having a vapor pressure lower than that of water. Specific examples of the drying inhibitor include ethylene glycol, propylene glycol, diethylene glycol, polyethylene glycol, thiodiglycol, dithiodiglycol, 2-methyl-1,3-propanediol, 1,2,6-hexanetriol, Polyvalent alcohols typified by acetylene glycol derivatives, glycerin, trimethylolpropane, etc., polyvalent alcohols such as ethylene glycol monomethyl (or ethyl) ether, diethylene glycol monomethyl (or ethyl) ether, triethylene glycol monoethyl (or butyl) ether Lower alkyl ethers of alcohols, 2-pyrrolidone, N-methyl-2-pyrrolidone, 1,3-dimethyl-2-imidazolidinone, heterocyclic rings such as N-ethylmorpholine, sulfolane, dimethyls Sulfoxide, sulfur-containing compounds such as sulfolane, diacetone alcohol, polyfunctional compounds such as diethanolamine, and urea derivatives. Of these, polyhydric alcohols such as glycerin and diethylene glycol are preferred as the drying inhibitor. Moreover, said drying inhibitor may be used independently or may be used together 2 or more types. These drying inhibitors are preferably contained in the ink in an amount of 10 to 50% by mass.

  Further, the penetration accelerator is preferably used for the purpose of allowing the ink to penetrate better into the recording medium (printing paper). Specific examples of penetration enhancers include alcohols such as ethanol, isopropanol, butanol, di (tri) ethylene glycol monobutyl ether, 1,2-hexanediol, sodium lauryl sulfate, sodium oleate, and nonionic surfactants. Etc. can be used suitably. These penetration enhancers exhibit a sufficient effect when contained in the ink composition in an amount of 5 to 30% by mass. Further, it is preferable that the penetration enhancer is used within a range of an addition amount that does not cause printing bleeding and paper loss (print through).

In addition to the above, the water-soluble organic solvent can be used for adjusting the viscosity. Specific examples of water-soluble organic solvents that can be used to adjust the viscosity include alcohols (eg, methanol, ethanol, propanol, isopropanol, butanol, isobutanol, sec-butanol, t-butanol, pentanol, hexanol, Cyclohexanol, benzyl alcohol), polyhydric alcohols (for example, ethylene glycol, diethylene glycol, triethylene glycol, polyethylene glycol, propylene glycol, dipropylene glycol, polypropylene glycol, butylene glycol, hexanediol, pentanediol, glycerin, hexanetriol, Thiodiglycol), glycol derivatives (eg, ethylene glycol monomethyl ether, ethylene glycol monoethyl ether) Ter, ethylene glycol monobutyl ether, diethylene glycol monomethyl ether, diethylene glycol monobutyl ether, propylene glycol monomethyl ether, propylene glycol monobutyl ether, dipropylene glycol monomethyl ether, triethylene glycol monomethyl ether, ethylene glycol diacetate, ethylene glycol monomethyl ether acetate, Triethylene glycol monomethyl ether, triethylene glycol monoethyl ether, ethylene glycol monophenyl ether), amine (eg, ethanolamine, diethanolamine, triethanolamine, N-methyldiethanolamine, N-ethyldiethanolamine, morpholine, N-ethylmorpholine, Tylenediamine, diethylenetriamine, triethylenetetramine, polyethyleneimine, tetramethylpropylenediamine) and other polar solvents (eg, formamide, N, N-dimethylformamide, N, N-dimethylacetamide, dimethylsulfoxide, sulfolane, 2-pyrrolidone, N-methyl-2-pyrrolidone, N-vinyl-2-pyrrolidone, 2-oxazolidone, 1,3-dimethyl-2-imidazolidinone, acetonitrile, acetone).
In addition, a water-soluble organic solvent may be used individually by 1 type, or may use 2 or more types together.

-Other additives-
The water-based ink composition in the invention may contain other additives in addition to the above components.
Examples of other additives in the present invention include, for example, antifading agents, emulsion stabilizers, penetration enhancers, ultraviolet absorbers, preservatives, antifungal agents, pH adjusters, surface tension adjusters, antifoaming agents, and viscosity adjusters. Well-known additives, such as an agent, a dispersing agent, a dispersion stabilizer, a rust preventive agent, and a chelating agent, are mentioned. These various additives may be added directly after the aqueous ink composition is prepared, or may be added when the aqueous ink composition is prepared.

  The ultraviolet absorber is used for the purpose of improving image storability. Examples of ultraviolet absorbers include benzotriazoles described in JP-A Nos. 58-185677, 61-190537, JP-A-2-782, JP-A-5-97075, JP-A-9-34057, and the like. Compounds, benzophenone compounds described in JP-A No. 46-2784, JP-A No. 5-194433, US Pat. No. 3,214,463, etc., JP-B Nos. 48-30492, 56-211141, Cinnamic acid compounds described in, for example, Kaihei 10-88106, JP-A-4-298503, 8-53427, 8-239368, 10-182621, JP-A-8- No. 501291, etc., triazine compounds, Research Disclosure No. Compounds described in No. 24239, compounds that emit fluorescence by absorbing ultraviolet rays typified by stilbene-based and benzoxazole-based compounds, so-called fluorescent brighteners, can also be used.

  The anti-fading agent is used for the purpose of improving image storage stability. As the antifading agent, various organic and metal complex antifading agents can be used. Organic anti-fading agents include hydroquinones, alkoxyphenols, dialkoxyphenols, phenols, anilines, amines, indanes, chromans, alkoxyanilines, heterocycles, etc. Complex, zinc complex and the like. More specifically, Research Disclosure No. No. 17643, Nos. VII to I, J; 15162, ibid. No. 18716, page 650, left column, ibid. No. 36544 at page 527, ibid. No. 307105, page 872, ibid. The compounds described in the patent cited in US Pat. No. 15,162, and the compounds included in the general formulas and compound examples of representative compounds described in JP-A-62-215272, pages 127 to 137 can be used.

Examples of the antifungal agent include sodium dehydroacetate, sodium benzoate, sodium pyridinethione-1-oxide, p-hydroxybenzoic acid ethyl ester, 1,2-benzisothiazolin-3-one and salts thereof. These are preferably used in the water-based ink composition in an amount of 0.02 to 1.00% by mass.
As the pH adjuster, a neutralizer (organic base, inorganic alkali) can be used. For the purpose of improving the storage stability of the aqueous ink composition, the pH adjuster is preferably added so that the aqueous ink composition has a pH of 6 to 10, and more preferably added to have a pH of 7 to 10. .

Examples of the surface tension adjusting agent include nonionic surfactants, cationic surfactants, anionic surfactants, betaine surfactants, and the like.
The addition amount of the surface tension adjusting agent is preferably an addition amount for adjusting the surface tension of the water-based ink composition to 20 to 60 mN / m in order to achieve good droplet ejection by the ink jet method, and is adjusted to 20 to 45 mN / m. The addition amount to be adjusted is more preferable, and the addition amount adjusted to 25 to 40 mN / m is more preferable. On the other hand, when ink is applied by a method other than the inkjet method, a range of 20 to 60 mN / m is preferable, and a range of 30 to 50 mN / m is more preferable.
The surface tension of the water-based ink composition can be measured using, for example, a plate method.

Specific examples of surfactants include fatty acid salts, alkyl sulfate esters, alkylbenzene sulfonates, alkyl naphthalene sulfonates, dialkyl sulfosuccinates, alkyl phosphate esters, naphthalene sulfonate formalin condensation in hydrocarbons. Products, anionic surfactants such as polyoxyethylene alkyl sulfates, polyoxyethylene alkyl ethers, polyoxyethylene alkyl allyl ethers, polyoxyethylene fatty acid esters, sorbitan fatty acid esters, polyoxyethylene sorbitan fatty acid esters, polyoxy Nonionic surfactants such as ethylene alkylamine, glycerin fatty acid ester and oxyethyleneoxypropylene block copolymer are preferred. Further, SURFYNOLS (Air Products & Chemicals), which is an acetylene-based polyoxyethylene oxide surfactant, is also preferably used. An amine oxide type amphoteric surfactant such as N, N-dimethyl-N-alkylamine oxide is also preferred.
Furthermore, pages (37) to (38) of JP-A-59-157636, Research Disclosure No. The surfactants described in 308119 (1989) can also be used.
Also, fluorine (fluorinated alkyl) surfactants, silicone surfactants, and the like described in JP-A Nos. 2003-322926, 2004-325707, and 2004-309806 are disclosed. By using, the abrasion resistance can be improved.
These surface tension modifiers can also be used as an antifoaming agent, and fluorine compounds, silicone compounds, chelating agents represented by EDTA, and the like can also be used.

The viscosity of the aqueous ink composition of the present invention is preferably in the range of 1 mPa · s to 30 mPa · s from the viewpoint of droplet ejection stability and agglomeration speed when ink is applied by an ink jet method. 1 mPa · s to 20 mPa The range of s is more preferable, the range of 2 mPa · s to 15 mPa · s is more preferable, and the range of 2 mPa · s to 10 mPa · s is particularly preferable.
When the ink is applied by a method other than the ink jet method, the viscosity of the aqueous ink composition is preferably in the range of 1 mPa · s to 40 mPa · s, more preferably in the range of 5 mPa · s to 20 mPa · s. .
The viscosity of the water-based ink composition can be measured using, for example, a Brookfield viscometer.

<Ink set>
The ink set of the present invention includes at least one water-based ink composition. The ink set of the present invention is used in a recording method using the aqueous ink composition described above, and is particularly preferable as an ink set used in an ink jet recording method. Further, the ink set of the present invention can be used as an ink cartridge in which these are integrally or independently accommodated, and is preferable from the viewpoint of easy handling. An ink cartridge including an ink set is known in the art, and can be formed into an ink cartridge by appropriately using a known method.

<Image forming method>
The image forming method of the present invention includes an ink application step of applying the water-based ink composition onto a recording medium using the water-based ink composition or the ink set.
The water-based ink composition and ink set of the present invention can be used for general writing instruments, recorders, pen plotters, and the like, but are particularly preferably used for inkjet recording methods. The ink jet recording method in which the ink set or the ink cartridge of the present invention can be used includes any recording method in which the ink composition is ejected as droplets from a thin nozzle and the droplets are attached to a recording medium. Specific examples of the ink jet recording method in which the aqueous ink composition of the present invention can be used will be described below.

  The first method is a method called an electrostatic attraction method. In the electrostatic suction method, a strong electric field is applied between the nozzle and the acceleration electrode arranged in front of the nozzle, and droplet-like ink is continuously ejected from the nozzle, and the ink droplet passes between the deflection electrodes. In the meantime, by supplying a printing information signal to the deflection electrode, the ink droplets are blown toward the recording medium and the ink is fixed on the recording medium, or the image is recorded, or the ink droplets are not deflected, In this method, an image is fixed on a recording medium by ejecting ink droplets from a nozzle onto the recording medium in accordance with a print information signal. The ink set or ink cartridge of the present invention is preferably used in a recording method using this electrostatic suction method.

  The second method is a method for forcibly ejecting ink droplets from the nozzles by applying pressure to the ink liquid with a small pump and mechanically vibrating the ink jet nozzles with a quartz vibrator or the like. The ink droplet ejected from the nozzle is charged at the same time as it is ejected, and while the ink droplet passes between the deflection electrodes, a print information signal is given to the deflection electrode to fly the ink droplet toward the recording medium, This is a method for recording an image on a recording medium. The ink set or ink cartridge of the present invention is preferably used for this recording method.

  The third method is a method (piezo) in which an image is recorded on a recording medium by simultaneously applying a pressure and a printing information signal to the ink liquid by a piezoelectric element and ejecting ink droplets from a nozzle toward the recording medium. The ink set or ink cartridge of the present invention is preferably used for this recording method.

  In the fourth method, the ink liquid is heated and foamed using microelectrodes according to the print signal information, and the bubbles are expanded to eject the ink liquid from the nozzle toward the recording medium, thereby forming an image on the recording medium. It is a method of recording. The ink set or ink cartridge of the present invention is preferably used for this recording method.

  The recording medium in the present invention is not particularly limited, and examples thereof include plain paper, high-quality paper, and coated paper.

  The ink set or ink cartridge of the present invention is particularly preferable as an ink composition used when an image is recorded on a recording medium using an image recording method based on an ink jet recording method including the four methods described above. The recorded matter recorded using the ink set of the present invention has an excellent image quality, and further has excellent ink fixing properties.

  EXAMPLES The present invention will be specifically described below with reference to examples, but the present invention is not limited to these examples. Unless otherwise specified, “part” and “%” are based on mass.

<Example 1>
1. Preparation of self-dispersing polymer aqueous dispersion -polymerization process-
A 1 liter separable flask equipped with a stirrer, a reflux condenser, and a nitrogen gas introduction tube was charged with 5.3 g of polyvinyl alcohol (degree of polymerization 1,000) and 300 g of water, and the temperature was raised to 65 ° C. While stirring, a mixed solution consisting of 128.1 g of methyl methacrylate, 166.4 g of isobornyl methacrylate, 27.2 g of methacrylic acid, 1.1 g of dodecyl mercaptan, 4.06 g of benzoyl peroxide (70%), and 170 g of water was added. It was. After stirring for 1 hour, the temperature was raised to 85 ° C. and stirred for 1 hour. Subsequently, the temperature was raised to 90 ° C. and stirred for 2 hours, and copolymer particles were taken out by filtration. Furthermore, the operation of stirring and washing the copolymer particles with 500 ml of hot water and filtering was repeated three times to obtain 300 g of copolymer (P-01). The weight average molecular weight (Mw) of the copolymer is 87000, the dispersity (Mw / Mn) is 1.9 (calculated in terms of polystyrene by gel permeation chromatography (GPC), the columns used are TSKgel SuperHZM-H, TSKgel SuperHZ4000, TSKgel SuperHZ200 (manufactured by Tosoh Corporation)). Since the acid value of the copolymer (P-01) was 53 KOH mg / g, the copolymerization ratio of methyl methacrylate / isobornyl methacrylate / methacrylic acid after correcting the acid value was 40 / 51.9 / 8.1. (Mass ratio).

-Copolymer solution preparation process-
To 300 g of copolymer (P-01), 450 g of methyl ethyl ketone and 250 g of isopropanol were added to dissolve the copolymer to obtain a copolymer solution (solution P-01a). The solution P-01a was slightly turbid by visual observation.
In order to measure the absorbance of the solution P-01a, a part of the solution P-01a was separated, and methyl ethyl ketone was added thereto to make the solid content concentration of the copolymer (P-01) 25% by mass. Samples were prepared. Using the solution sample, the absorbance at 660 nm was measured at room temperature (25 ° C.) using a cell having a sample length of 10 mm, and the value was 0.12.
Furthermore, a part of the obtained solution P-01a was collected and filtered with each material shown in Table 1 to obtain solutions (solution P-01b) to (solution P-01d). Further, the absorbance of solutions (P-01b) to (solution P-01d) was measured in the same manner as in solution P-01a. The results are shown in Table 1.

-Dispersing process-
Next, 83.3 g (solid content concentration 30%) of the obtained copolymer solution (Solution P-01a) was weighed, 12.5 g of methyl ethyl ketone, 4.2 g of isopropanol, and a 2 mol / L sodium hydroxide aqueous solution 7 0.0 g was added, and the temperature in the reaction vessel was raised to 75 ° C. Next, 77 g of distilled water was added dropwise at a rate of 2 ml / min to disperse in water. Thereafter, 90 g in total of isopropanol, methyl ethyl ketone, and distilled water was distilled off under reduced pressure to obtain an aqueous dispersion (L-01) of a self-dispersing polymer (P-01) having a solid content concentration of 26.5%.
The copolymer solution (solution P-01a) was changed to (solution P-01b) to (solution P-01d), and in the same manner as the aqueous dispersion (L-01), the dispersion polymer aqueous dispersion (L- 02) to (L-04) were obtained.
Table 1 shows the physical properties of the obtained self-dispersing polymer aqueous dispersions (L-01) to (L-04).

2. Evaluation of Self-Dispersing Polymer Aqueous Dispersion About the self-dispersing polymer aqueous dispersions (L-01) to (L-04) obtained above, the appearance, storage stability, and filterability were evaluated as follows. went.

(appearance)
10 mL of each aqueous dispersion was put in a 15 mL glass bottle and sealed, and the appearance was visually observed. Evaluation was performed according to the following evaluation criteria. ○ and Δ are levels that have no practical problem.
~Evaluation criteria~
○: Almost transparent to pale milky white.
Δ: Milky white.
×… cloudiness.

(Stability)
For each aqueous dispersion, the average particle size was measured before and after leaving at 60 ° C. for 7 days, and the change rate of the average particle size before and after being left [(average particle size after being left-average particle size before being left)] / Average particle diameter before standing] was calculated.
The stability (storage stability) of the aqueous dispersion was evaluated by the rate of change of the average particle size obtained. The evaluation criteria are as follows. ○ and Δ are levels that have no practical problem.
The particle diameter is a volume average particle diameter measured using a dynamic scattering method within 24 hours after preparing an aqueous dispersion, and using Microtrac UPA EX-150 (manufactured by Nikkiso Co., Ltd.). It is a value measured by a conventional method.
~Evaluation criteria~
◯: The change rate of the average particle size change rate was less than 5%.
Δ: The rate of change of the average particle size was 5% or more and less than 10%.
X: The change rate of the average particle size change rate was 10% or more.

(Filterability)
Filterability was evaluated according to the following evaluation criteria by filtering each aqueous dispersion with a 5 μm syringe filter (25 mmφ).
○ and Δ are levels that have no practical problem.
~Evaluation criteria~
○: 10 mL or more.
Δ: 2 mL or more and less than 10 mL.
X: Less than 2 mL.

First, as can be seen from Table 1, the copolymer (P-01) polymerized by suspension polymerization has an absorbance greater than 0.10 when the copolymer solution is used, and the insoluble matter is not removed. The self-dispersing polymer aqueous dispersion (L-01) produced using the copolymer solution is inferior in appearance, stability and filterability.
On the other hand, after preparing a copolymer solution containing the copolymer (P-01), a self-dispersing polymer aqueous solution prepared using a copolymer solution from which insoluble matters were removed by filtration so that the absorbance was 0.10 or less. Dispersions (L-02) to (L-04) were good in appearance, stability and filterability. In particular, the aqueous dispersion (L-03) having an absorbance of 0.04 or less has better appearance and stability than the aqueous dispersion (L-02), and the aqueous dispersion (L-04) having an absorbance of 0.02 or less. ) Was superior in appearance, stability and filterability to the aqueous dispersion (L-01).

<Example 2>
-Polymerization process-
In the synthesis of the copolymer (P-01) of Example 1, the mass ratio of the copolymers P-02 to P-05 shown below is used instead of methyl methacrylate, isobornyl methacrylate, and methacrylic acid. Example 1 except that the type and mixing ratio of each monomer were changed, the copolymer solution was filtered with filter paper, and the type and amount of the neutralized base species were changed as shown in Table 2. Thus, the following copolymers (P-02) to (P-05), which are self-dispersing polymers, were obtained. Furthermore, self-dispersed polymer aqueous dispersions (L-04) to (L-09) were obtained using these copolymers. The physical properties of the obtained self-dispersing polymer aqueous dispersions (L-04) to (L-09) are shown in Table 2.

P-02: Methyl methacrylate / dicyclopentanyl methacrylate / methacrylic acid copolymer (40/50/10)
P-03: Methyl methacrylate / styrene / benzyl methacrylate / methacrylic acid copolymer (62/10/20/8)
P-04: Methyl methacrylate / phenoxyethyl acrylate / acrylic acid copolymer (50/44/6)
P-05: Methyl methacrylate / isobornyl methacrylate / methacrylic acid copolymer (38/52/10)

<Example 3>
-Polymerization process-
In a 0.3 L three-necked flask equipped with a stirrer, thermometer, reflux condenser, and nitrogen gas inlet tube, 50.0 g methyl methacrylate, 45.0 g phenoxyethyl acrylate, 5.0 g acrylic acid, 2-ethylhexyl thioglycolate A mixed solution consisting of 1.0 g and 0.5 g of 2,2′-azobisisobutyronitrile was added and heated at 80 ° C. for 5 hours and then at 100 ° C. for 5 hours to obtain a copolymer (P-06). Got. The copolymer had a weight average molecular weight (Mw) of 68,000 and a dispersity (Mw / Mn) of 2.0.

-Copolymer solution preparation process-
The copolymer (P-06) was dissolved in methyl ethyl ketone / isopropanol so as to have a solid content of 30% by mass to obtain a copolymer solution (solution P-06). The obtained solution P-06 was fractionated, and the absorbance of the solution sample prepared by adding methyl ethyl ketone so that the solid content concentration was 25% by mass was measured in the same manner as in Example 1. Since the measured absorbance was 0.02, no filtration was performed.

-Dispersing process-
Example 1 except that the dispersion step used (solution P-06) instead of (solution P-01a) in Example 1 and the amount of neutralized base species was changed as shown in Table 2. In this manner, an aqueous self-dispersing polymer dispersion (L-10) was obtained. Table 2 shows the physical properties of the obtained self-dispersing polymer aqueous dispersion (L-10).

  P-06: Methyl methacrylate / phenoxyethyl acrylate / acrylic acid copolymer (50/45/5)

<Example 4>
In Example 1, the solution obtained in the step of obtaining the copolymer solution is filtered with a filter paper, and in the dispersion step, 3.7 g of 20% malic acid aqueous solution is added after adding sodium hydroxide aqueous solution (water-soluble electrolyte: A self-dispersing polymer aqueous dispersion (L-11) was obtained in the same manner as in Example 1 except that the addition was 0.3% equivalent to the copolymer). Table 2 shows the physical properties of the obtained self-dispersing polymer aqueous dispersion (L-11).

<Comparative Example 1>
360.0 g of methyl ethyl ketone was charged into a 2-liter three-necked flask equipped with a stirrer, a thermometer, a reflux condenser, and a nitrogen gas inlet tube, and the temperature was raised to 75 ° C. While maintaining the temperature in the reaction vessel at 75 ° C., 180.0 g of methyl methacrylate, 162.0 g of phenoxyethyl acrylate, 18.0 g of acrylic acid, 72 g of methyl ethyl ketone, and “V-601” (manufactured by Wako Pure Chemical Industries, Ltd.) A mixed solution consisting of 44 g was added dropwise at a constant speed so that the addition was completed in 2 hours. After completion of the dropwise addition, a solution consisting of 0.72 g of “V-601” and 36.0 g of methyl ethyl ketone was added, stirred for 2 hours at 75 ° C., and then a solution consisting of 0.72 g of “V-601” and 36.0 g of isopropanol was added. After stirring at 75 ° C. for 2 hours, the temperature was raised to 85 ° C., and stirring was further continued for 2 hours. After cooling, methyl ethyl ketone was added to adjust the solid content to 30% to obtain a copolymer solution (solution PH-01). The weight average molecular weight (Mw) of the obtained copolymer was 64000, and dispersion degree (Mw / Mn) was 3.1.

The dispersion step was the same as in Example 1 except that (Solution PH-01) was used instead of (Solution P-01a) in Example 1 and the amount of the neutralized base species was changed as shown in Table 1. Thus, an aqueous dispersion of a self-dispersing polymer was obtained. The physical properties of the obtained self-dispersing polymer aqueous dispersion (LH-01) are shown in Table 2.
PH-01: Copolymer of methyl methacrylate / phenoxyethyl acrylate / acrylic acid (50/45/5)

<Comparative Example 2>
A self-dispersing polymer aqueous dispersion (LH-02) was produced according to Example 30 of Japanese Patent No. 3069543. The physical properties of the obtained self-dispersing polymer aqueous dispersion (LH-02) are shown in Table 2.
PH-02: Methyl methacrylate / ethoxytriethylene glycol methacrylate / methacrylic acid copolymer (25/72/3)

<Example 5>
[Preparation of water-based ink composition]
<< Preparation of Cyan Ink C-1 >>
(Preparation of cyan dispersion as water-insoluble colored particles)
In a reaction vessel, 6 parts of styrene, 11 parts of stearyl methacrylate, 4 parts of styrene macromer AS-6 (manufactured by Toagosei Co., Ltd.), 5 parts of Blenmer PP-500 (manufactured by NOF Corporation), 5 parts of methacrylic acid, 2-mercaptoethanol A mixed solution of 0.05 part and 24 parts of methyl ethyl ketone was prepared.
On the other hand, 14 parts of styrene, 24 parts of stearyl methacrylate, 9 parts of styrene macromer AS-6 (manufactured by Toa Gosei), 9 parts of Blenmer PP-500 (manufactured by NOF Corporation), 10 parts of methacrylic acid, 2-mercaptoethanol A mixed solution consisting of 13 parts, 56 parts of methyl ethyl ketone and 1.2 parts of 2,2′-azobis (2,4-dimethylvaleronitrile) was prepared and placed in a dropping funnel.

  Next, under a nitrogen atmosphere, the mixed solution in the reaction vessel was heated to 75 ° C. while stirring, and the mixed solution in the dropping funnel was gradually dropped over 1 hour. 2 hours after the completion of the dropwise addition, a solution prepared by dissolving 1.2 parts of 2,2′-azobis (2,4-dimethylvaleronitrile) in 12 parts by mass of methyl ethyl ketone was added dropwise over 3 hours, and further at 75 ° C. for 2 hours. And aged at 80 ° C. for 2 hours to obtain a polymer dispersant solution.

  A part of the obtained polymer dispersant solution was isolated by removing the solvent, the obtained solid content was diluted to 0.1% by mass with tetrahydrofuran, and the weight average molecular weight was measured by GPC. As a result, the isolated solid had a polystyrene equivalent weight average molecular weight of 25,000.

  Moreover, 5.0 g of the obtained polymer dispersant solution in terms of solid content, 10.0 g of cyan pigment pigment blue 15: 3 (manufactured by Dainichi Seika), 40.0 g of methyl ethyl ketone, 8.0 g of 1 mol / L sodium hydroxide, Ion-exchanged water 82.0 g and 0.1 mm zirconia beads 300 g were supplied to the vessel and dispersed with a ready mill disperser (manufactured by Imex) at 1000 rpm for 6 hours. The obtained dispersion was concentrated under reduced pressure using an evaporator until methyl ethyl ketone could be sufficiently distilled off, and concentrated until the pigment concentration became 10%, and a cyan dispersion C1 as water-insoluble colored particles was prepared. The average particle diameter of the obtained cyan dispersion liquid C1 was 77 nm.

  Then, using cyan dispersion C1 as water-insoluble colored particles and L-01 as a self-dispersing polymer aqueous dispersion, ink was prepared so as to have the following ink composition. After the preparation, coarse particles were removed with a 5 μm filter, and cyan ink C-1 was prepared as an aqueous ink composition.

<Ink composition of cyan ink C-1>
・ Cyan pigment (Pigment Blue 15: 3, manufactured by Dainichi Seika) 4%
・ The above polymer dispersant: 2%
・ L-04 (converted to solid content): 8%
・ Diethylene glycol monoethyl ether: 10%
(Water-soluble solvent, manufactured by Wako Pure Chemical Industries)
・ Sanix GP250 ... 5%
(Water-soluble solvent, manufactured by Sanyo Chemical Industries, Ltd.)
・ Orphine E1010 (Nisshin Chemical)… 1%
・ Ion-exchanged water: added so that the total is 100%

<< Preparation of Cyan Inks C-2 to C-9, CH-1 to CH-2 >>
A water-based ink was prepared in the same manner as in the cyan ink C-1, except that each of the polymer aqueous dispersions shown in Table 2 below was used instead of the self-dispersing polymer aqueous dispersion L-04 in the cyan ink C-1. Cyan inks C-2 to C-8 and CH-1 to CH-2 of the composition were prepared, respectively.

  The cyan inks C-1 to C-8 and CH-1 to CH-2 all showed good values of 5 mPa · s to 6 mPa · s.

[Evaluation]
Each cyan ink prepared as described above (hereinafter sometimes simply referred to as “ink”) was subjected to an ink stability test and a droplet ejection test (ejection stability test).
The ink aging stability test is an evaluation of the stability of the particle size and viscosity before ink is ejected, that is, when the ink is stored in the ink storage tank (or cartridge). When discharging from the droplet ejection nozzle of the ink jet apparatus, problems such as clogging of the droplet ejection nozzle occur.
Further, the droplet ejection test (ejection stability test) is an evaluation relating to the ejection directionality, and if the ink viscosity is high, the nozzles are clogged and a directionality defect occurs.

(Ink stability test over time)
Each 10 mL of ink was sealed in a 15 mL glass bottle and allowed to stand at 60 ° C. for 14 days, and then the average particle size and viscosity were measured. Change rate of average particle size before and after standing [(average particle size after leaving-average particle size before leaving) / average particle size before leaving] and change rate of viscosity [(viscosity after leaving-before leaving) Viscosity) / viscosity before standing] was calculated. The evaluation criteria are as follows. The particle size is a volume average particle size measured using a dynamic scattering method within 24 hours after preparing an aqueous dispersion, and is a conventional method using Microtrac UPA EX-150 (manufactured by Nikkiso Co., Ltd.). It is the value measured by.

~Evaluation criteria~
A: The change rate of the average particle diameter or the change rate of the viscosity was less than 5%.
Δ: The change rate of the average particle diameter or the change rate of the viscosity was 5% or more and less than 10%.
X: The change rate of the average particle diameter or the change rate of the viscosity was 10% or more.
And evaluation of x was judged to be unusable. The results are shown in Table 2.

(Discharge stability test)
The discharge stability test was performed as follows. On Tokuhishi Double-sided Art N (Mitsubishi Paper Co., Ltd.), using a GELJETG717 printer head manufactured by Ricoh, in an environment of 30 ° C and 50% humidity, the resolution is 1200 x 600 dpi and the ink droplet ejection volume is 3 pL. Dripped. The discharge stability was evaluated by observing the state after 75 minutes after hitting continuously. Table 3 shows the discharge stability test results. The evaluation criteria for the ejection stability test in Table 2 are as follows. In addition, it was judged that evaluation of x was unusable.
~Evaluation criteria~
○: No discharge failure and no direction failure.
○ △: There was no ejection failure and a little direction failure occurred.
Δ: Almost no ejection failure and some direction failure occurred.
×: There were many ejection failures.

The abbreviations shown in Table 2 are as follows.
NaOH: sodium hydroxide Amm: aqueous ammonia (2.8% solution)
TEA: Triethylamine

  As can be seen from Table 2, the cyan ink of the present invention is excellent in both stability and ejection properties, but unlike the polymerization step of the examples, the comparative example in which a copolymer was produced using an organic solvent. The cyan ink CH-1 had a tendency to be inferior in droplet ejection stability, and the cyan ink CH-2 in the comparative example was inferior in ink stability and had insufficient ejection properties.

  As described above, by using the ink composition containing the self-dispersing polymer aqueous dispersion of the present invention, which is characterized by the production method, an ink composition having unprecedented high ink stability and stable ejection properties is provided. I understand that I was able to.

Claims (7)

A polymerization step for producing a copolymer containing a hydrophilic structural unit and a hydrophobic structural unit in a reaction mixture containing less than 10% by mass of an organic solvent in the total mass;
After an organic solvent is added to the copolymer obtained by the polymerization step to obtain a copolymer solution, the copolymer prepared from the copolymer solution has a solid content concentration of 25% by mass with respect to a solution sample. 660 nm absorbance measurement with a sample length of 10 mm is performed at room temperature (25 ° C.), and when the obtained absorbance is greater than 0.10, the insoluble matter contained in the copolymer solution is removed to remove the insoluble matter. A copolymer solution preparation step of making the absorbance measured under the same conditions as the above-mentioned absorbance measurement in the copolymer solution after removal to be 0.10 or less,
A dispersion step of adding water to the copolymer solution obtained by the copolymer solution preparation step to obtain an aqueous dispersion of the copolymer;
A process for producing an aqueous dispersion of a self-dispersing polymer comprising   The method for producing a self-dispersing polymer aqueous dispersion according to claim 1, wherein the polymerization step is a polymerization step to which a bulk polymerization method or a suspension polymerization method is applied.   The method for producing a self-dispersing polymer aqueous dispersion according to claim 1 or 2, wherein at least one of the hydrophilic structural units is a structural unit having a carboxyl group.   The self-dispersion according to any one of claims 1 to 3, wherein at least one of the hydrophobic structural units is a structural unit derived from at least one of an acrylate monomer and a methacrylic acid monomer. A method for producing an aqueous polymer dispersion.   An aqueous solution containing water-insoluble colored particles containing a colorant and a self-dispersing polymer aqueous dispersion produced by the method for producing an aqueous self-dispersing polymer dispersion according to any one of claims 1 to 4. Ink composition.   An ink set comprising at least one water-based ink composition according to claim 5.   An image forming method including an ink application step of applying the aqueous ink composition onto a recording medium using the aqueous ink composition according to claim 5 or the ink set according to claim 6.