JP4835132B2 - Aqueous pigment dispersion and water-based ink for inkjet recording - Google Patents

Description

  The present invention relates to a water-based ink for inkjet recording which is excellent in both color developability on plain paper and image sharpness on special paper, and an aqueous pigment dispersion which can be easily prepared.

  An aqueous ink for ink-jet recording comprising carbon black or an organic pigment, a styrene- (meth) acrylic acid copolymer, a basic substance, and water as essential components is disclosed in Patent Document 1, for example. Known to.

  An aqueous ink for inkjet recording comprising carbon black or an organic pigment, (meth) acrylic acid ester-acid phosphooxypolyoxyethylene glycol mono (meth) acrylate, a basic substance, and water as essential components is: For example, it is known as in Patent Document 2.

  However, the water-based ink for ink-jet recording as described in Patent Documents 1 and 2 is excellent if only the color developability on plain paper is taken, but the image sharpness on special paper is still unsatisfactory. Met.

JP 2004-217916 A Special table 2003-506536 gazette

  The problem to be solved by the present invention is to provide a water-based ink for ink-jet recording which is excellent in both color developability on plain paper and image sharpness on special paper, and an aqueous pigment dispersion capable of easily preparing the same. It is in.

  The inventors of the present invention have made extensive studies on a water-based ink for inkjet recording excellent in both color development on plain paper and image sharpness on special paper and an aqueous pigment dispersion that can be easily prepared. It has been found that the above problem can be solved by adding a (meth) acrylic acid copolymer and a phosphate group-containing monoethylenically unsaturated monomer copolymer to the dispersion, and the present invention has been completed. It was.

  That is, the present invention relates to a carbon black or organic pigment (A), a copolymer (B) of an acid group-containing ethylenically unsaturated monomer and another copolymerizable ethylenically unsaturated monomer, and a base. In the aqueous pigment dispersion for preparing an aqueous ink for ink-jet recording, which contains the active substance (C) and water (D) as essential components, (meth) acrylic acid as the copolymer (B) A copolymer (b1) obtained by polymerizing another copolymerizable monoethylenically unsaturated monomer as an essential component, a phosphoric acid group-containing monoethylenically unsaturated monomer and other copolymerizable monomers Provided is an aqueous pigment dispersion for preparing an aqueous ink for ink-jet recording, comprising an ethylenically unsaturated monomer and a copolymer (b2) obtained by polymerization as an essential component.

  The present invention also provides an aqueous ink for ink-jet recording comprising the above-described aqueous pigment dispersion.

The aqueous pigment dispersion of the present invention contains both a (meth) acrylic acid copolymer and a phosphoric acid group-containing monoethylenically unsaturated monomer copolymer in the aqueous pigment dispersion. This produces a particularly remarkable effect that it is excellent in both color developability on plain paper and image sharpness on special paper, which cannot be achieved with water-based inks.

Next, the present invention will be described in detail.
The present invention relates to a carbon black or organic pigment (A), a copolymer (B) of an acid group-containing ethylenically unsaturated monomer and another copolymerizable ethylenically unsaturated monomer, basic In the aqueous pigment dispersion for preparing an aqueous ink for ink-jet recording comprising the substance (C) and water (D) as essential components, (meth) acrylic acid and other as the copolymer (B) A copolymer (b1) obtained by polymerizing, as an essential component, a copolymerizable monoethylenically unsaturated monomer, a phosphoric acid group-containing monoethylenically unsaturated monomer and other copolymerizable monoethylene A water-based pigment dispersion for preparing a water-based ink for ink-jet recording, comprising a polymerizable unsaturated monomer and a copolymer (b2) obtained by polymerization as an essential component.

  In the present invention, as a copolymer (B) of an acid group-containing ethylenically unsaturated monomer and another copolymerizable ethylenically unsaturated monomer, (meth) acrylic acid and other copolymerizable can be used. A copolymer (b1) obtained by polymerizing a monoethylenically unsaturated monomer as an essential component, a phosphoric acid group-containing monoethylenically unsaturated monomer and other copolymerizable monoethylenically unsaturated monomers And a copolymer (b2) obtained by polymerization as an essential component.

  In the present invention, by using such a specific copolymer (b1) and a specific copolymer (b2) together as the copolymer (B) to be contained in such an aqueous pigment dispersion, The printed image has both high color development and high image sharpness.

  As the carbon black or organic pigment (A) in the present invention, any known and commonly used carbon black or organic pigment can be used. Specific examples of the organic pigment include insoluble azo pigments, soluble azo pigments, indanthrene pigments, phthalocyanine pigments, quinacridone pigments, perylene pigments, isoindolinone pigments, quinophthalone pigments, anthraquinone pigments. And diketopyrrolopyrrole pigments.

  The copolymer (B) is a copolymer of an acid group-containing ethylenically unsaturated monomer and another copolymerizable ethylenically unsaturated monomer. One copolymer (b1) is a copolymer obtained by polymerizing (meth) acrylic acid and another copolymerizable monoethylenically unsaturated monomer as essential components. The blend (b2) is a copolymer obtained by polymerizing as an essential component with a phosphate group-containing monoethylenically unsaturated monomer and another copolymerizable monoethylenically unsaturated monomer.

  Examples of (meth) acrylic acid in the copolymer (b1) include acrylic acid and methacrylic acid.

  Other copolymerizable monoethylenically unsaturated monomers include styrene monomers such as styrene, α-methylstyrene, dimethylstyrene, tert-butylstyrene, chlorostyrene, and benzyl such as benzyl acrylate and benzyl methacrylate. (Meth) acrylate, phenyl (meth) acrylate, phenylethyl (meth) acrylate, phenylpropyl (meth) acrylate, phenoxyethyl (meth) acrylate, methyl (meth) acrylate, ethyl (meth) acrylate, n-propyl (meth) Acrylate, iso-propyl (meth) acrylate, n-butyl (meth) acrylate, iso-butyl (meth) acrylate, tert-butyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, n-oct (Meth) acrylate, dodecyl (meth) acrylate [lauryl (meth) acrylate], octadecyl (meth) acrylate [stearyl (meth) acrylate], cyclohexyl (meth) acrylate, isobornyl (meth) acrylate, 2-hydroxyethyl (meth) ) Monoethylene such as alkoxypolyalkylene glycol mono (meth) acrylate such as acrylate, 2-hydroxypropyl (meth) acrylate, methoxypolyethylene glycol mono (meth) acrylate, methoxypoly (oxyethyleneoxypropylene) glycol mono (meth) acrylate Unsaturated unsaturated monomers.

  As the other copolymerizable ethylenically unsaturated monomer described above, the hydrophobicity of the copolymer is further increased in the same acid value comparison, and the adsorption of the copolymer onto the pigment surface can be made stronger. For example, styrene monomers such as styrene, α-methylstyrene, dimethylstyrene, tert-butylstyrene, chlorostyrene, benzyl (meth) acrylate, phenyl (meth) acrylate, phenylethyl (meth) acrylate, phenylpropyl ( It is preferable to use a (meth) acrylic acid ester-based monomer having a benzene ring such as (meth) acrylate and phenoxyethyl (meth) acrylate.

  The copolymer (b1) is a copolymer obtained by polymerizing (meth) acrylic acid and a styrene monomer and / or a (meth) acrylic acid ester monomer containing a benzene ring as essential components. It is preferable in that it is more excellent in both color developability on plain paper and gloss on special paper. Among them, a copolymer obtained by polymerizing (meth) acrylic acid and a (meth) acrylic acid ester monomer containing a benzene ring as essential components, and the total of the polymerization units of both monomers on a mass basis Is preferably a copolymer of 85% or more of the total of the polymerization units of all monomers, since the color developability on plain paper and the gloss on special paper are both particularly excellent.

  The copolymer (b1) has, for example, an acid value of 40 to 220 mgKOH / g, and in particular, an acid value of 70 to 160 mgKOH / g in that it is more excellent in dispersibility and dispersion stability when dispersed in water and gloss of printing. It is preferable that Here, the acid value refers to the number of mg of potassium hydroxide necessary to neutralize 1 g of the nonvolatile content of the copolymer. The theoretical acid value can also be obtained arithmetically based on the amount of (meth) acrylic acid used. When the acid value is too low, the pigment dispersibility is lowered, which is not preferable. If the acid value is too high, the water resistance of the colored image is lowered, which is also not preferable. In order to bring the copolymer (b1) within the range of the acid value, (meth) acrylic acid may be included and copolymerized so as to be within the range of the acid value.

  The copolymer (b1) in the present invention is a binary copolymer of the above essential monomers, but also a ternary copolymer of three or more with other copolymerizable monoethylenically unsaturated monomers. It may be a polymer.

  The copolymer (b1) preferably has a hydroxyl value of 10 mgKOH / g or less in order to achieve a high color density on plain paper. Here, the hydroxyl value refers to the number of mg of potassium hydroxide required to neutralize acetic acid produced when acetylating a hydroxyl group having a nonvolatile content of 1 g with acetic anhydride. If it is within the range of the hydroxyl value, the hydrophilicity is improved and there is no excessive penetration, the color development on plain paper becomes better, and the affinity with pigment particles that are generally hydrophobic is also improved. Stability is also more preferable.

  In order to make the copolymer (b1) within the range of the hydroxyl value, the (meth) acrylic acid ester containing a hydroxyl group such as 2-hydroxyethyl (meth) acrylate is within the range of the hydroxyl value. However, from the viewpoint of the technical effect of the present invention, a (meth) acrylic acid ester containing a hydroxyl group copolymerized without including a (meth) acrylic acid ester containing a hydroxyl group. The copolymer (b1) which does not contain the polymerization unit is optimal.

  The copolymer (b1) used in the present invention is a linear copolymer composed only of polymerized units of a monoethylenically unsaturated monomer, but has an ethylenically unsaturated monomer having various crosslinking properties. The copolymer may be a copolymer containing a partially cross-linked portion obtained by copolymerizing the body in a very small amount.

  Examples of the ethylenically unsaturated monomer having such crosslinkability include glycidyl (meth) acrylate, divinylbenzene, ethylene glycol di (meth) acrylate, propylene glycol di (meth) acrylate, polyethylene glycol di ( Examples include poly (meth) acrylates of polyhydric alcohols such as (meth) acrylates, poly (oxyethyleneoxypropylene) glycol di (meth) acrylates, and tri (meth) acrylates of alkylene oxide adducts of glycerol.

  The molecular weight of the copolymer (b1) in the present invention is not particularly limited. For example, from the viewpoint of film formation, the weight average molecular weight is 5,000 to 1,000,000. Among them, the viscosity is low and the handling is easy. It is preferable that it is 5,000-20,000.

  In the present invention, in the copolymer (b1), the reaction rate and the like of each monomer used is considered to be substantially the same, and the charging ratio of each monomer is the content ratio in terms of mass of the polymerization unit of each monomer. Shall be considered. The copolymer in the present invention can be synthesized by various conventionally known reaction methods such as bulk polymerization, solution polymerization, suspension polymerization, and emulsion polymerization. In this case, a known and usual polymerization initiator, chain transfer agent (polymerization degree adjusting agent), surfactant and antifoaming agent can be used in combination.

  On the other hand, the copolymer (b2) is a copolymer obtained by polymerizing a phosphoric acid group-containing monoethylenically unsaturated monomer and another copolymerizable monoethylenically unsaturated monomer as essential components. .

The phosphate group-containing monoethylenically unsaturated monomer is a monomer containing a phosphate group PO ₃ H ₂ and one of polymerizable ethylenically unsaturated double bonds. Examples of such a phosphoric acid group-containing monoethylenically unsaturated monomer include vinylphosphonic acid and those represented by the following general formula (hereinafter collectively referred to as phosphoric acid monomer).

(In the above formula, a is 0 or 1; when a is 1, X is an alkylene group having 1 to 9 carbon atoms; b and c are independently 0 to 10; And R ₃ is a hydrogen atom or a methyl group.)

  Examples of such phosphoric acid monomers include various acid phosphoxypolyoxyalkylene glycol mono (meth) acrylates. From the viewpoint of ease of polymerization control, a preferred phosphoric acid monomer in the present invention is acid phosphoxypolyoxyalkylene glycol mono (meth) acrylate, and examples of such a monomer include acid phosphoxypolyethylene glycol mono ( And (meth) acrylate, acid phosphoxy poly (oxyethyleneoxypropylene) glycol mono (meth) acrylate, and the like. From the viewpoint of enhancing hydrophilicity, the polyoxyalkylene skeleton contained in the acid phosphoxypolyoxyalkylene glycol mono (meth) acrylate is only a polyoxyethylene skeleton or a polyoxyalkylene skeleton mainly composed of polyoxyethylene. Is preferred. Examples of the phosphoric acid monomer include Phosmer M, PE, PP, etc. of Unichemical Co., Ltd., and monomers manufactured by DuPont, USA.

  The copolymer (b2) of the present invention is obtained by separating the functions of a phosphoric acid group and a polyoxyalkylene group, and an acid phosphosiloxane mono (meth) acrylate as a phosphoric acid monomer and the other copolymerizable monoethylene described above. It may be a copolymer containing these polymerized units used in combination with an alkoxypolyalkylene glycol mono (meth) acrylate as a polymerizable unsaturated monomer, but the function of each functional group is integrated, It is a copolymer containing polymer units of acid phosphoxypolyoxyalkylene glycol mono (meth) acrylate, which is a phosphoric acid monomer containing a phosphoric acid group and a polyoxyalkylene group in one molecule. This is preferable in that the glossiness of paper can be further improved. Examples of the acid phosphosiloxane mono (meth) acrylate include acid phosphooxyethyl mono (meth) acrylate and acid phosphooxypropyl mono (meth) acrylate.

  The copolymer (b2) only needs to contain a polymerization unit of a phosphoric acid monomer, but the acid value is 40 to 220 mgKOH / g, and in particular, dispersibility and dispersion stability when dispersed in water, and gloss of printing. It is preferable that the acid value is 140 to 200 mgKOH / g. In the aqueous pigment dispersion of the present invention, the copolymer (b2) may be of an acid value that itself disperses in water, as long as the pigment dispersibility is exclusively assigned to the copolymer (b1). The acid value is as defined above. When the acid value is too low, the storage stability is lowered, and when an aqueous pigment ink for inkjet recording is prepared, the printing stability is deteriorated. If the acid value is too high, the water resistance of the colored image is lowered, which is also not preferable. In order to make the copolymer (b1) within the range of the acid value, a phosphoric acid monomer may be included and copolymerized so as to be within the range of the acid value.

  Examples of other copolymerizable ethylenically unsaturated monomers that can be used in combination with the phosphoric acid monomer include the various monomers described above that can be used in obtaining the copolymer (b1).

  Other copolymerizable ethylenically unsaturated monomers described above in that the hydrophobicity of the copolymer (b1) can be further increased in the same acid value comparison, and the affinity with the copolymer (b1) can be further increased. As, for example, styrene monomers such as styrene, α-methylstyrene, dimethylstyrene, tert-butylstyrene, chlorostyrene, benzyl (meth) acrylate, phenyl (meth) acrylate, phenylethyl (meth) acrylate, It is preferable to use a (meth) acrylic acid ester monomer having a benzene ring, such as phenylpropyl (meth) acrylate and phenoxyethyl (meth) acrylate.

  As the copolymer (b2), acid phosphoxypolyethylene glycol mono (meth) acrylate and a styrene monomer and / or a (meth) acrylic acid ester monomer containing a benzene ring are polymerized as essential components. It is preferable that the copolymer is excellent in both color developability on plain paper and gloss on special paper.

  The copolymer (b2) used in the present invention is the same as the copolymer (b1), even if it is a linear copolymer having only a polymerization unit of a monoethylenically unsaturated monomer. A copolymer containing a partially crosslinked portion obtained by copolymerizing a small amount of such various crosslinkable ethylenically unsaturated monomers may also be used.

  The molecular weight of the copolymer (b2) in the present invention is not particularly limited. For example, from the viewpoint of film formation, the weight average molecular weight is 5,000 to 1,000,000. Among them, the viscosity is low and the handling is easy. It is preferable that it is 5,000-20,000.

  The hydroxyl value, molecular weight, preparation method and the like of the copolymer (b2) are preferably in the same range as the copolymer (b1).

  As a combination of each copolymer in the copolymer (B), (meth) acrylic acid and a styrene monomer and / or a (meth) acrylic acid ester monomer containing a benzene ring are essential components. Polymerized copolymer, acid phosphoxypolyoxyethylene glycol mono (meth) acrylate, styrene monomer and / or (meth) acrylic acid ester monomer containing benzene ring as essential components A combination with a copolymer is preferred. Among them, a copolymer obtained by polymerizing (meth) acrylic acid and a (meth) acrylic acid ester monomer containing a benzene ring as essential components, and the total of the polymerization units of both monomers on a mass basis (Meth) acrylic which contains a copolymer of 85% or more of the total polymerized units of all monomers, acid phosphoxypolyoxyethylene glycol mono (meth) acrylate, styrenic monomer and / or benzene ring A combination with a copolymer obtained by polymerizing an acid ester monomer as an essential component is more preferable.

  The ratio of the copolymer (b1) and the copolymer (b2) in the aqueous pigment dispersion is not particularly limited, but the copolymer (b1) / copolymer ( b2) = 20/80 to 80/20, especially 30/70 to 70/30, it is possible to use both copolymers in combination for excellent color development on plain paper and on special paper in colored images. It is preferable to have high image sharpness.

  When the copolymer (B) is a substantially linear copolymer, it is suitable for the preparation of a water-based ink for an inkjet recording apparatus of a piezo-type nozzle that does not have a thermal history. Is a copolymer (B) containing a partially crosslinked part, it is suitable for the preparation of a water-based ink for an ink jet recording apparatus of a thermal type nozzle with a thermal history.

  In the present invention, the copolymer (b1) and the copolymer (b2) contain a polymer unit containing an acid group-containing ethylenically unsaturated monomer and another monoethylenically unsaturated monomer as essential components. Both are common in that they are copolymers. By neutralizing the carboxyl group or phosphoric acid group in the copolymer with a basic substance (C) described later, solubility and dispersibility in water (D) are ensured.

  The neutralized acid groups in the copolymers (b1) and (b2) are usually set in the range of 30 to 100%, particularly 70 to 100%. This proportion of ionized groups does not mean the molar ratio of anionic groups to basic substances, but takes into account dissociation equilibrium.

  As the basic substance (C) for neutralizing the copolymers (b1) and (b2), any known and conventional substances can be used, for example, inorganic basic substances such as sodium hydroxide, potassium hydroxide and ammonia. Substances and organic basic substances such as triethylamine and alkanolamine can be used.

  The aqueous pigment dispersion of the present invention contains these carbon black or organic pigment (A), copolymers (b1) and (b2), and a basic substance (C) in water (D). As the water (D) in the present invention, for example, distilled water, ion-exchanged water, pure water, ultrapure water, etc., water having a pH of 6.5 to 7.5 and containing no free ions is preferable.

  In the aqueous pigment dispersion of the present invention, [total non-volatile content of copolymer (b1) and copolymer (b2)] / organic pigment (A) is 0.2 to 2.0 on a mass basis. It is preferable. This [total non-volatile content of copolymer (b1) and copolymer (b2)] / organic pigment (A) is more preferably 0.2 to 1.0, and particularly preferably 0.20 to 0. Most preferred is .65. When this ratio is too low, the scratch resistance of the colored image and the storage stability of the water-based ink itself are lowered. On the other hand, when it is too high, the viscosity of the water-based ink is increased, and the ejection stability tends to be impaired. Is not preferable.

  The aqueous pigment dispersion of the present invention is, for example, an aqueous pigment ink for ink jet recording comprising an organic pigment (A), a copolymer (B), a basic substance (C), and water (D). And an aqueous pigment dispersion for mixing can be prepared by mixing as an essential component.

The aqueous pigment dispersion of the present invention can be produced, for example, by the methods 1) to 4) as described later.
1) An aqueous pigment dispersion comprising an organic pigment (A), a copolymer (b1), a basic substance (C), and water (D), an organic pigment (A), and a copolymer (b2 ), An aqueous pigment dispersion composed of a basic substance (C) and water (D).
2) An aqueous pigment dispersion comprising an organic pigment (A), a copolymer (b1), a basic substance (C), and water (D), and only the copolymer (b2) or a copolymer (B2), an aqueous solution or an aqueous dispersion composed of the basic substance (C) and water (D) are mixed.
3) An aqueous pigment dispersion comprising an organic pigment (A), a copolymer (b2), a basic substance (C), and water (D), and a copolymer (b1) alone or a copolymer An aqueous solution or aqueous dispersion composed of (b1), the basic substance (C), and water (D) is mixed.
4) The organic pigment (A), the copolymer (b1), the copolymer (b2), the basic substance (C), and water (D) are mixed using an organic solvent as necessary. And co-disperse to remove the organic solvent.

  In aqueous pigment dispersions and aqueous pigment inks, the carboxyl group based on the copolymer (b1) makes the interaction between the pigment particles and the copolymer stronger, thereby enhancing the dispersion stability of the dispersed particles, and the like. It is more effective to functionally separate each copolymer so as to enhance the image sharpness of the colored image on the dedicated paper by positioning the phosphate group based on (b2) in the outermost layer of the dispersed particles. . Therefore, the aqueous pigment dispersion produced by the above method 2) has not only high dispersion stability of the dispersed particles but also good image sharpness of the colored image as compared with the aqueous pigment dispersion produced by other methods. Therefore, it is preferable. Also, the viscosity of the aqueous pigment dispersion can be lowered. In the ink jet recording system, in order to eject ink droplets from a nozzle, it is desired that the ink droplet has a low viscosity. Therefore, it is preferable that the viscosity of the aqueous pigment dispersion itself for preparing it is also low.

  In the present invention, the step of mixing and dispersing a mixture of the organic pigment (A), the copolymers (b1) and / or (b2), the basic substance (C) and water (D) in any order is essential. It is preferable to include. The water (D) is optimally 100% water, but it may be a mixture of water and an organic solvent and an aqueous medium containing 60% or more of water in terms of mass. By using a water-soluble organic solvent in combination with water, it may be possible to reduce the liquid viscosity in the dispersion step.

  Examples of the water-soluble organic solvent include ketones such as acetone, methyl ethyl ketone (MEK), methyl butyl ketone, and methyl isobutyl ketone; methanol, ethanol, 2-propanol, 2-methyl-1-propanol, 1-butanol, 2 -Alcohols such as methoxyethanol; ethers such as tetrahydrofuran, 1,4-dioxane, 1,2-dimethoxyethane; amides such as dimethylformamide, N-methylpyrrolidone, etc. It is preferable to use a compound selected from the group consisting of 3 to 6 ketones and alcohols having 1 to 5 carbon atoms. These water-soluble organic solvents may be used as the copolymer solution or separately contained in the mixture during the dispersion step.

  In preparation of the aqueous pigment dispersion in the present invention, optimally, an aqueous medium containing 20 to 65 parts of the non-volatile content of the copolymer (B) and a water-soluble organic solvent per 100 parts of the organic pigment (A) in terms of mass. It can manufacture using an above described raw material so that it may become 235-280 parts.

  As a dispersion apparatus that can be used in the dispersion step, any of various known apparatuses can be used and is not particularly limited. Examples of such a dispersing device include a method using kinetic energy of a spherical dispersion medium having a diameter of about 0.1 to 10 mm made of steel, stainless steel, zirconia, alumina, silicon nitride, glass, etc., shearing by mechanical stirring. Examples of the dispersion device include a dispersion method such as a force utilization method, a pressure change of a dispersed flow bundle supplied at high speed, a flow passage change, or a force utilization force generated by a collision.

  By carrying out such a dispersion step, a state in which the organic pigment (A) is dispersed in the liquid medium containing the copolymer (b1) and / or (b2) is formed.

  Subsequent to the dispersion step, when a water-soluble organic solvent is used in the dispersion step, a step of removing this, and a step of removing excess water (distillation step) to obtain a desired solid content concentration can be performed. As the aqueous pigment dispersion of the present invention, those containing no water-soluble organic solvent are preferred because they have no odor and can improve the working environment.

  As described above, the water-based pigment dispersion exhibits excellent properties in all aspects of dispersion achievement level, dispersion time, and dispersion stability. As described above, the organic pigment (A) and the copolymer (B) are: It is preferable that the interaction is stronger and dispersed. This aqueous pigment dispersion is preferably prepared such that the dispersed particle diameter is 200 nm or less in terms of median diameter.

  The aqueous pigment dispersion of the present invention preferably contains an organic pigment (A), a copolymer (b1), a basic substance (C), and water (D) as essential components as described above. The aqueous pigment dispersion obtained can be prepared by mixing the copolymer (b2) or an aqueous solution or aqueous dispersion thereof. As the copolymer (b2) to be mixed with the aqueous pigment dispersion, or an aqueous solution or aqueous dispersion thereof, those containing no organic pigment (A) are preferably used.

  This mixing can be easily prepared by mixing and stirring both. The aqueous pigment dispersion may be prepared by adding and mixing the copolymer (b2) or its aqueous solution or aqueous dispersion to the aqueous pigment dispersion, or by the reverse method. Thus, the post-mixed copolymer (b2) is disposed outside the copolymer (b1) without directly acting on the organic pigment (A) in the aqueous pigment dispersion.

  In the stirring step, for example, an aqueous solution of the copolymer (b2) previously solubilized in water (D) with a basic substance (C) is added to the obtained aqueous pigment dispersion, and a stirrer such as a homodisper is added. It can be carried out by adsorbing the copolymer (b1) used for pigment dispersion with uniform and high interaction. By doing so, an aqueous pigment dispersion for preparing a water-based ink for ink-jet recording having further excellent performance can be obtained. This aqueous pigment dispersion is also preferably prepared such that the dispersed particle diameter is 200 nm or less in terms of median diameter.

  The aqueous pigment dispersion thus obtained can be used as an aqueous ink for ink jet recording by containing various additives and liquid media that are known and commonly used in the technical field of aqueous ink for ink jet recording. . Specifically, the aqueous pigment dispersion can be made into an aqueous ink for inkjet recording by diluting with water or other liquid medium so that the solid content of the pigment becomes 1 to 10% on a mass basis. Ultracentrifugation or filtration with a microfilter may be further performed in order to remove coarse particles and undersized particles and to adjust the particle size distribution of dispersed particles.

  The water-based ink for ink jet recording thus obtained can be recorded on a known recording medium. As the recording medium at this time, for example, plain paper such as PPC paper, exclusive paper for inkjet such as photographic paper (glossy), photographic paper (silk), synthetic resin film such as OHP film, Various films and sheets, such as metal foils, such as aluminum foil, are mentioned.

  Hereinafter, the present invention will be described in more detail with reference to Examples and Comparative Examples. In the following examples and comparative examples, “part” and “%” are both based on mass.

<Synthesis Example 1>
Methyl ethyl ketone in the reaction vessel of an automatic polymerization reaction device (polymerization tester DSL-2AS type, manufactured by Sakai Sangyo Co., Ltd.) having a reaction vessel equipped with a stirring device, a dropping device, a temperature sensor, and a reflux device having a nitrogen introduction device on the top (MEK) 550 parts were charged, and the inside of the reaction vessel was purged with nitrogen while stirring. The temperature in the reaction vessel was raised to 80 ° C. while maintaining a nitrogen atmosphere, and then 439 parts of benzyl methacrylate, 61 parts of methacrylic acid and “Perbutyl (registered trademark) O” (active ingredient peroxy 2-ethylhexanoic acid t -Butyl, manufactured by Nippon Oil & Fats Co., Ltd. (40.0 parts) was added dropwise over 4 hours. After completion of the dropwise addition, the reaction was further continued at the same temperature for 15 hours, and then a part of MEK was distilled off under reduced pressure, the nonvolatile content was adjusted to 50%, an acid value of 80, a weight average molecular weight of 25,800, a glass transition temperature. (Calculated value) A MEK solution of copolymer S-1 at 63 ° C was obtained.

<Synthesis Example 2>
Isopropyl in the reaction vessel of an automatic polymerization reaction device (polymerization tester DSL-2AS type, manufactured by Sakai Sangyo Co., Ltd.) having a reaction vessel equipped with a stirring device, a dropping device, a temperature sensor, and a reflux device having a nitrogen introduction device at the top. 600 parts of alcohol (IPA) was charged, and the inside of the reaction vessel was purged with nitrogen while stirring. The temperature inside the reaction vessel was raised to 80 ° C. while maintaining a nitrogen atmosphere, and then 37.5 parts of 2-hydroxyethyl methacrylate, 221.2 parts of styrene, phosmer PE (in the general formula, R ₃ = methyl group) from a dropping device. A = c = 0, b = 4-5, acid phosphoxypolyethylene glycol monomethacrylate (manufactured by Unichemical Co., Ltd.) 253.5 parts, Blemmer TGL (polymerization degree modifier) 20.0 parts and perbutyl ( (Registered trademark) O (polymerization initiator, both manufactured by NOF Corporation) 40.0 parts of a mixed solution was added dropwise over 4 hours. After completion of dropping, the reaction was further continued at the same temperature for 7 hours to obtain an IPA solution of copolymer K-1 having an acid value of 150, a weight average molecular weight of 8,400, and a nonvolatile content of 43.81%.

<Comparative Example 1> (Production of aqueous pigment dispersion)
Fastgen (registered trademark) Blue TGR [β-type copper phthalocyanine pigment manufactured by Dainippon Ink & Chemicals, Inc.] in a mixing tank equipped with a cooling jacket. C. I. Pigment Blue 15: 3. ] 1000 g, 800 parts of the copolymer S-1 solution obtained in Synthesis Example 1, 160 parts of a 20% aqueous potassium hydroxide solution, 100 parts of MEK, and 2607 parts of water were stirred and mixed. The mixed solution is passed through a dispersion device (SC mill SC100 / 32 type, manufactured by Mitsui Mining Co., Ltd.) filled with zirconia beads having a diameter of 0.3 mm, and a circulation method (a method in which the dispersion liquid discharged from the dispersion device is returned to the mixing tank) For 4 hours. The number of revolutions of the dispersing device was 2,700 rpm, and the temperature of the dispersion liquid was kept at 40 ° C. or less through the cooling jacket through cold water.

  After the dispersion, the dispersion stock solution was extracted from the mixing tank, and then the mixing tank and the dispersion device flow path were washed with 10,000 parts of water, and the diluted dispersion liquid was obtained together with the dispersion stock solution.

  The diluted dispersion was put into a glass distillation apparatus, and the whole amount of MEK and a part of water were distilled off. After allowing to cool to room temperature, it is dispersed with a disper (TK homodisper 20 type, manufactured by Tokushu Kika Kogyo Co., Ltd.), and further, water is added to adjust the non-volatile content. An aqueous pigment dispersion Y-1 was obtained. This dispersion S-1 was copolymer non-volatile matter / pigment = 0.4 / 1.0.

<Comparative Example 2> (Production of aqueous pigment dispersion)
800 parts of the copolymer S-1 solution of Comparative Example 1, 160 parts of 20% potassium hydroxide, 100 parts of MEK, and 2607 parts of water were respectively added to 913 parts of the copolymer K-1 solution, 300 parts of 20% potassium hydroxide, and IPA100. The aqueous pigment dispersion K-1 having an average particle size of 128 nm and a nonvolatile content of 20% was obtained in the same manner as in Comparative Example 1, except that the amount of water was 2454 parts. This dispersion K-1 was copolymer non-volatile matter / pigment = 0.4 / 1.0.

(Preparation of aqueous pigment dispersion of the present invention)
800 parts of the copolymer S-1 solution of Comparative Example 1, 160 parts of 20% potassium hydroxide, and 2607 parts of water, 400 parts of the copolymer S-1 solution, 80 parts of 20% potassium hydroxide, and 2520 parts of water, respectively. Except that, dispersion and preparation were carried out in the same manner as in Comparative Example 1 to obtain an aqueous pigment dispersion S-2 having an average particle diameter of 148 nm and a nonvolatile content of 20%. This dispersion S-2 was copolymer non-volatile matter / pigment = 0.2 / 1.0.
Moreover, after adding 20% potassium hydroxide aqueous solution corresponding to the acid value to 800 parts of K-1 solution to neutralize it and further diluting to 10% non-volatile content with water, a part of IPA and water are distilled off. A K-1 aqueous solution with a nonvolatile content of 20% was prepared by distillation.
Next, 1000 parts of the aqueous K-1 solution was added to 4000 parts of the aqueous pigment dispersion S-2, and the mixture was stirred and homogenized with the disper for 30 minutes to prepare an aqueous pigment dispersion 1 having a nonvolatile content of 20%. This aqueous pigment dispersion 1 had a copolymer non-volatile content / pigment = 0.4 / 1.0.

(Preparation of aqueous pigment dispersion of the present invention)
800 parts of the copolymer S-1 solution of Comparative Example 1, 160 parts of 20% potassium hydroxide, and 2607 parts of water, respectively, 600 parts of the copolymer S-1 solution, 120 parts of 20% potassium hydroxide, and 2613 parts of water, respectively. Except that, dispersion and preparation were performed in the same manner as in Comparative Example 1 to obtain an aqueous pigment dispersion S-3 having an average particle size of 132 nm and a nonvolatile content of 20%. This dispersion S-3 was copolymer non-volatile matter / pigment = 0.3 / 1.0.
Further, 571 parts of K-1 solution was neutralized by adding a 20% aqueous potassium hydroxide solution corresponding to its acid value, and further diluted with water to a non-volatile content of 10%. A K-1 aqueous solution with a nonvolatile content of 20% was prepared by distillation.
Next, 500 parts of the aqueous K-1 solution was added to 4333 parts of the aqueous pigment dispersion S-3, and the mixture was stirred and homogenized with the disper for 30 minutes to prepare an aqueous pigment dispersion 2 having a nonvolatile content of 20%. This aqueous pigment dispersion 2 had a copolymer nonvolatile content / pigment = 0.4 / 1.0.

(Appropriate evaluation of water-based pigment ink for piezo inkjet recording)
With reference to Example 1 described in JP-A-7-228808, an aqueous pigment ink for piezo ink jet recording was prepared using the aqueous pigment dispersion of Example 1 of the present invention. The ink composition is shown below.

Aqueous pigment dispersion (Example 1) 28.0 parts Triethylene glycol monobutyl ether 10.0 parts Diethylene glycol 15.0 parts Surfynol 465 (manufactured by Air Products) 0.8 parts Water 46.2 parts

(Performance evaluation of water-based pigment ink for inkjet recording)
The aqueous pigment ink for ink jet recording prepared above was filled in a cartridge of a commercially available piezo ink jet printer (MJ-8000C type, manufactured by Seiko Epson Corporation), and printed on various recording media.

(Normal paper color evaluation)
The solid density of the printed material on recording paper Xerox 4024 (manufactured by Fuji Xerox Co., Ltd.), which is plain paper, was measured for optical density with a Macbeth reflection densitometer spectrum eye, and the color development was evaluated as the plain paper characteristics. Displayed as OD in the table.
○: (OD) ≧ 1.00
×: (OD) <1.00

(Exclusive paper image sharpness evaluation)
Printing was performed on 60%, 80%, and 100% (solid) Duty 60%, 80%, and 100% on photographic paper (glossy) (manufactured by Seiko Epson Corporation) having an ink receiving layer, which is a dedicated paper. Using a BYK Gardner company's haze gloss meter, the 20 ° gloss value and haze value of the surface of the obtained printed matter were measured, and the image sharpness was determined by substituting it into the following formula. In the table, it is indicated as IC.

  In the present invention, the mapping sharpness defined by the following mathematical formula has a positive correlation with the visual glossiness, and is very useful as a numerical value for glossiness.

[Comparative Example 3]
Instead of the aqueous pigment dispersion of Example 1, an aqueous pigment ink for piezo ink jet recording was prepared using the aqueous pigment dispersion of Comparative Example 1 described above and evaluated in the same manner.

[Comparative Example 4]
Instead of the aqueous pigment dispersion of Example 1, an aqueous pigment ink for piezo ink jet recording was prepared using the aqueous pigment dispersion of Comparative Example 2 described above and evaluated in the same manner.

  Instead of the aqueous pigment dispersion of Example 1, an aqueous pigment ink for piezo ink jet recording was prepared using the aqueous pigment dispersion of Example 2 described above and evaluated in the same manner.

  The measurement results for each of these evaluation items are collectively shown in Table 1.

Table 1

As can be seen from Table 1 above, the aqueous pigment ink for ink-jet recording of Example 3 obtained from the aqueous pigment dispersion of the present invention has a color development (OD) on plain paper above a certain level, and excellent on special paper. It can be seen that a colored image having mapping sharpness (IC) can be obtained.
In particular, regarding the image sharpness, the value of Example 3 shows a value far exceeding the arithmetic average value of Comparative Example 3 and Comparative Example 4 under the condition that the copolymer non-volatile content / pigment is constant. It is clear that the combined use of these different copolymers has a synergistic effect.

Claims (4)

Copolymer (B) of carbon black or organic pigment (A), acid group-containing ethylenically unsaturated monomer and other copolymerizable ethylenically unsaturated monomer, and basic substance (C) And water (D) as an essential component, an aqueous pigment dispersion for preparing an aqueous ink for inkjet recording, wherein the copolymer (B) can be copolymerized with (meth) acrylic acid Copolymer (b1) obtained by polymerizing a novel monoethylenically unsaturated monomer as an essential component, a phosphoric acid group-containing monoethylenically unsaturated monomer and other copolymerizable monoethylenically unsaturated monomers A water-based pigment dispersion for preparing a water-based ink for ink-jet recording, comprising a monomer and a copolymer (b2) obtained by polymerization as an essential component. As the copolymers (b1) and (b2), a copolymer obtained by polymerizing (meth) acrylic acid and a styrene monomer and / or a (meth) acrylate monomer containing a benzene ring as essential components. Copolymer obtained by polymerizing polymer, acid phosphoxypolyoxyethylene glycol mono (meth) acrylate and styrene monomer and / or (meth) acrylate monomer containing benzene ring as essential components The aqueous pigment dispersion according to claim 1, comprising: An aqueous pigment dispersion comprising an organic pigment (A), a copolymer (b1), a basic substance (C), and water (D), and a copolymer (b2) alone or a copolymer (b2 ), A basic substance (C), and an aqueous solution or aqueous dispersion comprising water (D), and the aqueous pigment dispersion according to claim 1 or 2 prepared. A water-based ink for inkjet recording, comprising the water-based pigment dispersion according to any one of claims 1 to 3.