JP2006274141A - Aqueous dispersion for preparing ink-jet printing water-based ink and the resultant ink-jet printing water-based ink - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an ink-jet printing water-based ink having a combination of regular paper color developability, the scratch resistance of printed images on exclusive paper and storage stability, and to provide an aqueous dispersion for preparing the ink. <P>SOLUTION: The aqueous dispersion is such that colored polymer particles(C) with pigment particles(A) coated with a styrene-based polymer(B), a self-water-dispersible styrene-based polymer(D) compatible with the polymer(B) and a polymeric dispersant(E) for dispersing the particles(C) other than the polymers B and D are included in water. The ink-jet printing water-based ink containing the aqueous dispersion is also provided. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an aqueous dispersion for preparing an inkjet recording aqueous ink and an inkjet recording aqueous ink.

  As a method for obtaining a desired colored image on a recording medium such as paper or film, for example, an aqueous pigment dispersion in which an organic pigment is dispersed in an aqueous medium with various polymer dispersants is adjusted to have a predetermined pigment concentration. There is known an ink jet recording method in which diluted aqueous ink for ink jet recording is ejected from a piezo-type or thermal-type micro nozzle to form an image on a recording medium.

  In the inkjet recording method, with the widespread use of printers and the diversification of consumer needs for recording formats, recently, not only general-purpose plain paper such as PPC paper, which is mainly used for printing, but also high quality like silver halide photographs. A recording medium (dedicated paper) having an ink receiving layer such as photographic glossy paper for obtaining an image has also been used. Under such circumstances, the water-based ink used for inkjet recording is required to obtain an excellent colored image on any recording medium.

  In addition, the water-based ink for inkjet recording is only used in a small amount in a short time when the printer is operating, and remains stored in the printer cartridge for a long time when the printer is stopped. Therefore, before and after long-term storage, it must have excellent storage stability that does not change the particle size and viscosity of the dispersed particles, and excellent storage stability without ink ejection failure before and after long-term storage Have to have.

  Examples of water-based pigment dispersions having excellent water resistance, scratch resistance and storage stability that satisfy these characteristics, and water-based inks for ink jet recording prepared therefrom include, for example, organic pigment particles such as styrene- (meth). An aqueous pigment dispersion of colored polymer particles coated with an acrylic acid copolymer and a self-water dispersible styrene- (meth) acrylic acid copolymer itself having the same monomer composition as described above. A water-based ink for inkjet recording in which a dispersion and a wetting agent are mixed is known (see Patent Documents 1 and 2).

Patent Document 1 discloses an aqueous pigment dispersion obtained by a phase inversion emulsification method containing colored polymer particles in which pigment particles are coated with a styrene- (meth) acrylic acid copolymer, and the same amount as that. An aqueous ink for inkjet recording prepared by mixing with an aqueous dispersion of a copolymer having a body composition and then using a wetting agent or the like is described.
In Patent Document 2, a styrene- (meth) acrylic acid copolymer, pigment particles, a basic compound, water, and an organic solvent are kneaded, and after removing the solvent, an acidic compound is added to acidify the copolymer. After filtration and intimate contact with the pigment particles, the same copolymer and basic compound as described above are added and redispersed to coat the pigment particles with the styrene- (meth) acrylic acid copolymer. Inkjet recording water-based inks prepared by a wetting agent or the like prepared from an aqueous pigment dispersion obtained according to an acid precipitation method, containing colored polymer particles and a copolymer similar thereto are described.

  Although these techniques of Patent Documents 1 and 2 employ different production methods such as a phase inversion emulsification method or an acid precipitation method in terms of the production method of colored polymer particles, they do not contain colored polymer particles and pigments. This is common in that the coalescence itself is contained in an aqueous medium. In both Patent Documents 1 and 2, polymerization of monomers such as (meth) acryl having high affinity for water is performed on both the polymer in the colored polymer particles and the copolymer containing no pigment. Copolymers containing units are employed.

However, when an aqueous ink for inkjet recording is prepared from such a copolymer, the solid print reflection density (OD value) on a recording medium having no ink receiving layer, that is, plain paper is high, but the ink receiving layer is provided. There is a drawback in that either the scratch resistance of the printed image on the recording medium, for example, a special paper or the storage stability of the ink cannot be satisfied.
In other words, none of the water-based inks obtained from the conventional techniques as described above have both plain paper colorability, scratch resistance of printed images on special paper, and excellent storage stability of the water-based ink itself. .

JP 2001-329199 A JP 2004-83786 A

  An object of the present invention is to provide a water-based ink for ink-jet recording, which has both the color developability of plain paper and the scratch resistance and storage stability of printed images on special paper, and an aqueous dispersion for preparing the same.

As a result of intensive studies in view of the above circumstances, the present inventors have found that when the aqueous polymer contains the colored polymer particles and the copolymer itself containing no pigment, the weight in the former colored polymer particles is reduced. The polymer composition is made hydrophobic so that self-water dispersibility is not manifested, and the water dispersibility of the colored polymer particles, which is impaired by this, is compensated by the combined use with the polymer dispersant. By adopting a polymer that is compatible with the polymer in the coalesced particles, it has been found that the above-mentioned problems can be solved, and the present invention has been completed.
That is, the present invention relates to a colored polymer particle (C) in which pigment particles (A) are coated with a styrene polymer (B), and a self-water dispersible styrene polymer compatible with the polymer (B) ( D) and a polymer dispersant (E) other than (B) and (D) for dispersing the colored polymer particles (C) in water for preparing an aqueous ink for ink jet recording. An aqueous dispersion of is provided.
The present invention also provides a water-based ink for ink-jet recording in which the above-mentioned aqueous dispersion is diluted to 1 to 10% of an organic pigment in terms of mass.

  In the water dispersion of the present invention, the polymer composition in the conventional self-water dispersible colored polymer particles is functionally separated, and the polymer composition itself is made hydrophobic instead of making the polymer composition hydrophobic. As a copolymer used in combination with the colored polymer particles, a compatible polymer is adopted, so that the ink is excellent in color development on plain paper and printed images on special paper and has excellent storage stability. The recording water-based ink can be prepared.

Details of the present invention will be described below.
The aqueous dispersion of the present invention comprises colored polymer particles (C) in which pigment particles (A) are coated with a styrene polymer (B), and a self-water dispersible styrene system compatible with the polymer (B). The polymer (D) and a polymer dispersant (E) other than the (B) and (D) for dispersing the colored polymer particles (C) are contained in water.

  As the pigment particles (A) in the present invention, any known and commonly used carbon black and organic pigments can be used. Specifically, for example, carbon black, insoluble azo pigment, soluble azo pigment, indanthrene pigment, phthalocyanine pigment, quinacridone pigment, perylene pigment, isoindolinone pigment, quinophthalone pigment, anthraquinone pigment, etc. Is mentioned. The particle diameter of the organic pigment is not particularly limited, but is made to be particles in an aqueous dispersion for polymerization. At this time, the average particle diameter of the pigment particles (A) is, for example, 5 to 600 nm, preferably 20 to 300 nm. In the present invention, the “average particle size” means a volume-based average particle size. The organic pigment particles are preferably single fine particles, but may be aggregates in which a plurality of fine particles are aggregated or associated. As the aggregates of organic pigment particles, those within the above-described exemplary average particle diameter can be used.

  In the present invention, 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 regarded as the content ratio in terms of mass of the polymerization unit of each monomer. The styrene polymer (B) and the styrene polymer (D) 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, known and commonly used polymerization initiators, chain transfer agents, surfactants and antifoaming agents can be used in combination.

  As the styrenic polymer (B) in the present invention, for example, a homopolymer of a styrenic monomer, a copolymer of a styrenic monomer or a styrenic monomer and other water at 25 ° C. Examples thereof include a copolymer with a monoethylenically unsaturated polymerizable monomer having a solubility of 2.5% by mass or less. The molecular weight of the styrenic polymer (B) is not particularly limited. For example, from the viewpoint of compatibility with the styrenic polymer (D) described later and film formation, a polystyrene-converted weight average molecular weight of 10,000 to 40,000. It is preferable that it is an average molecular weight equivalent to a styrene-type polymer (D). The styrenic polymer (B) is substantially hydrophobic and itself is neither water-soluble nor water-dispersible.

  The styrene monomer in the present invention means styrene that may have a substituent selected from the group consisting of an alkyl group, an alkoxyl group, and a halogen atom on the benzene ring. Examples of such styrene monomers include styrene, methyl styrene, iso-propyl styrene, tert-butyl styrene, methoxy styrene, propoxy styrene, chlorostyrene, bromostyrene, and the like. Such a styrene monomer generally has a solubility in water at 25 ° C. of 2.5% by mass or less. These styrene monomers can be used alone or in combination of two or more.

  Examples of other monoethylenically unsaturated polymerizable monomers having a solubility in water at 25 ° C. of 2.5% by mass or less that can be used in combination with a styrenic monomer include (meth) acrylic acid. Examples include methyl, n-butyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, cyclohexyl (meth) acrylate, and fluorinated alkyl (meth) acrylate.

  Styrene monomers are either styrene alone or styrene and other water at 25 ° C. because of its excellent properties such as its availability and optical properties such as hydrophobicity and high refractive index. It is preferably a mixture with a monoethylenically unsaturated polymerizable monomer having a solubility in water of 2.5% by mass or less. Among them, when the total of the monoethylenically unsaturated polymerizable monomer having a solubility in water at 25 ° C. of 2.5% by mass or less in terms of mass is 100% in terms of mass, styrene It is particularly preferable that the monomer content is 70 to 100%. By polymerizing only a styrenic monomer or a styrene monomer and a monoethylenically unsaturated polymerizable monomer having a solubility in water at 25 ° C. of 2.5% by mass or less, It can be a polymer.

  Homopolymers of styrene monomers and other monoethylenically unsaturated polymerizable monomers having a solubility in water at 25 ° C. of 2.5% by mass or less with a polymerization unit of styrene monomers of 70% or more Copolymer has a large amount of benzene rings in the molecule, so it has excellent affinity with aromatic rings and heterocyclic rings contained in the pigment structure. Especially when the pigment particles (A) are organic pigment particles, The coating of the pigment particles (A) with the styrene polymer (B) becomes more sufficient.

  In the polymerization process of the styrenic polymer (B), a radical polymerization initiator is used. However, the terminal group of the styrene polymer (B) is terminated by the addition of a cleavage radical of the radical polymerization initiator. The When the radical polymerization initiator is azo, the radical is generated by decomposition and elimination of nitrogen. A chemical structure fragment generated by elimination of nitrogen becomes a denitrification residue and acts as a radical. The terminal group of the styrene polymer (B) is a denitrogen residue of an azo polymerization initiator having a non-salt polar group containing a non-salt polar group and having solubility in a specific water. It is preferable because the colored polymer particles (C) exhibit better dispersion stability in water in a specific pH range. The function and the like of the nonionic azo polymerization initiator containing a polar group that is not a salt and having a specific solubility in water will be described later.

  The average particle diameter of the colored polymer particles (C) in which the pigment particles (A) are coated with the styrene polymer (B) is, for example, 5 to 600 nm, preferably 20 to 300 nm, like the pigment particles (A). is there. The ratio of the pigment particles (A) and the styrene polymer (B) constituting the colored polymer particles (C) is not particularly limited. For example, the styrene polymer (100 parts by weight in terms of pigment particles (A)) B) 5 to 100 parts, preferably 10 to 50 parts.

  Since the colored polymer particles (C) are coated with a styrene polymer (B) having substantially no water solubility or water dispersibility on the surface of the pigment particles (A), the styrene polymer ( Similar to B), it is neither water-soluble nor water-dispersible. Therefore, in order to disperse the colored polymer particles (C), a polymer dispersant (E) described later is used in combination.

  The styrenic polymer (D) in the present invention has a property of being stably dispersed in water by itself without using a surfactant or a polymer dispersant (this property is referred to as self-water dispersibility), and the polymer. (B) and a compatible property. The average particle diameter of the styrenic polymer (D) is, for example, 5 to 600 nm, preferably 20 to 300 nm, like the pigment particles (A) and the colored polymer particles (C). The styrenic polymer (D) and the styrenic polymer (B) in the colored polymer particles (C) can be clearly distinguished in terms of the presence or absence of this self-water dispersibility.

  In order to impart self-water dispersibility to the polymer to obtain a styrene polymer (D), there is a method in which a styrene polymer that can become self-water dispersible by neutralization and a neutralizing agent are used in combination. According to this method, for example, a styrene- (meth) acrylic acid copolymer obtained by copolymerizing (meth) acrylic acid and a styrene monomer as essential monomers may be used in combination with a basic substance. I can do it.

As this styrene- (meth) acrylic acid copolymer, those having a polymer unit based on a styrene monomer of 20 to 50% in terms of mass are preferable. Within this range, the abrasion resistance of the printed image on the special paper and the storage stability of the water-based ink are better, and the dispersibility in water is also excellent. Moreover, as this styrene- (meth) acrylic acid copolymer, what has an acid value of 50-200 is preferable. Here, the acid value means the number of mg of potassium hydroxide necessary to neutralize 1 g of the nonvolatile content of the copolymer, and the unit is mg KOH / g. The theoretical acid value can also be obtained arithmetically based on the anionic group-containing monomer used and the amount used. When the acid value is too low, pigment dispersion and storage stability are lowered, and when an aqueous ink for ink jet recording is prepared, printing stability is deteriorated, 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.
As the basic substance, any known and commonly used substances can be used. For example, inorganic basic substances such as sodium hydroxide and ammonia, and organic basic substances such as triethylamine and alkanolamine can be used.

  The neutralized carboxyl group in the styrenic polymer (D) is preferably set in the range of usually 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.

  On the other hand, the compatibility between the styrenic polymer (D) and the polymer (B) can be ensured by making the monomer compositions of both polymers substantially the same. Specifically, as the styrene polymer (B), a homopolymer of a styrene monomer or a styrene monomer having a polymer unit of 70% or more and a solubility in water at 25 ° C. of 2.5%. When a copolymer with a monoethylenically unsaturated polymerizable monomer of less than mass% is used, a styrene- (meth) acrylic acid copolymer is used as the styrene polymer (D), The monomer composition other than (meth) acrylic acid can be made substantially the same as that of the polymer (B). More specifically, the styrene polymer (D) contains 20 to 65%, particularly 25 to 55%, of the content of the polymerization unit of the styrene monomer in the styrene polymer (B). It is preferable.

  Further, as the styrene polymer (D), various styrene polymers can be used as compared with the styrene polymer (B). It may be a styrene polymer copolymerized by using a known and commonly used monoethylenically unsaturated monomer in addition to the styrene monomer and (meth) acrylic acid as necessary. Examples of such a monomer include methyl (meth) acrylate, ethyl (meth) acrylate, n-propyl (meth) acrylate, isopropyl (meth) acrylate, n-butyl (meth) acrylate, Isobutyl (meth) acrylate, tert-butyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, n-octyl (meth) acrylate, dodecyl (meth) acrylate, octadecyl (meth) acrylate, (meta ) Cyclohexyl acrylate, isobornyl (meth) acrylate, benzyl (meth) acrylate, and the like.

  The styrenic polymer (D) is preferably a styrenic polymer containing polymer units of styrene monomer, (meth) acrylic acid, and benzyl (meth) acrylate as essential polymer units.

  As the styrenic polymer (D), a weight average in terms of polystyrene is ensured from the viewpoints of ensuring its own self-water dispersibility, compatibility with the styrenic polymer (B), film-forming property, and printing stability over time. The molecular weight is preferably 2,000 to 100,000, more preferably 5,000 to 50,000, and an average molecular weight equivalent to that of the styrenic polymer (B). Further, since the glass transition temperature (Tg) of the styrene polymer (B) is relatively high, from the viewpoint of film properties such as film formation and scratch resistance, the styrene polymer (D) is styrene. A styrene polymer having a Tg lower than that of the polymer (B), particularly a styrene polymer having a Tg of 40 to 100 ° C., particularly Tg of 20 to 70 ° C. is preferred.

  The polymer dispersant (E) in the present invention is a polymer dispersant that works effectively in an aqueous system, which is different from any of the polymers (B) and (D), and any known and commonly used one can be used. . As such a polymer dispersing agent (E), those having a small amount and a large dispersion effect are preferable, and examples thereof include various polymers in which the dispersion function in an aqueous medium and the adsorption function on fine particles are separated. Specifically, ethylene oxide-propylene oxide block copolymer, ethylene oxide-tetrahydrofuran block copolymer, styrene- (meth) acrylic acid block copolymer, (meth) acrylic acid ester- (meth) acrylic acid block copolymer. Polymer, styrene- (meth) acrylic acid polyethylene glycol ester block copolymer, styrene-maleic acid copolymer polyethylene glycol ester, styrene-maleic acid copolymer ethylene glycol propylene glycol ester, (meth) acrylic acid ester- ( (Meth) acrylic acid polyethylene glycol ester block copolymer, styrene or comb polymer composed of (meth) acrylic acid ester and polyethylene glycol macromer, styrene or (meth) acrylic It includes comb polymers consisting of a macromer and polyethylene glycol esters. In addition, a polymer having an affinity for an organic pigment and having a functional group such as a primary to tertiary amino group bonded to a terminal or a side chain can also be used. Of these, styrene-maleic acid copolymer alkylene oxide adducts such as styrene-maleic acid copolymer polyethylene glycol ester and styrene-maleic acid copolymer polyethylene glycol polypropylene glycol ester are preferable.

  Such polymer dispersant (E) includes, for example, each item number of Solsperse (registered trademark) manufactured by Avicia Co., each product number of DISPER BIC manufactured by BYK Chemie, each product number of EFKA manufactured by EFKA Chemical Co., each product number of the same polymer, Ajinomoto ( Each product number manufactured by Ajisper (registered trademark) manufactured by Kyoeisha Chemical Co., Ltd., each product number manufactured by Floren (registered trademark), each manufactured by Johnson Polymer Co., Ltd. These can be used alone or in combination of two or more.

  The aqueous dispersion of the present invention comprises these colored polymer particles (C), a styrene polymer (D), and a polymer dispersant (E) in water. As the water in the present invention, for example, distilled water, ion-exchanged water, pure water, ultrapure water, or the like, water having a pH of 6.5 to 7.5 and containing no free ions is preferable.

  The aqueous dispersion of the present invention contains, for example, colored polymer particles (C) and a polymer dispersant (E), and the colored polymer particles (C) are submerged in water by the action of the polymer dispersant (E). It can be prepared by mixing a stably dispersed aqueous dispersion and an aqueous dispersion of a styrene polymer (D).

  The ratio of the colored polymer particles (C), the styrene polymer (D), and the polymer dispersant (E) in the aqueous dispersion of the present invention is not particularly limited. In terms of mass, per 100 parts of the colored polymer particles (C), the styrene polymer (D) may be 15 to 40 parts and the polymer dispersant (E) may be 2 to 20 parts.

  When the total amount of the organic pigment particles (A) is 100 parts, the total of the styrene polymer (D) and the styrene polymer (B) in the colored polymer particles (C) is 10 to 100 parts. It is preferable to do so. If this ratio is too low, the scratch resistance of the colored image from the water-based ink and the storage stability of the water-based ink itself will decrease, and conversely, if it is too high, the viscosity of the water-based ink will increase and its ejection stability. Tends to be damaged, which is not preferable.

  The nonvolatile content of the aqueous dispersion of the present invention is not particularly limited, but is, for example, more than 5% and 30%, preferably more than 7% and 20% in terms of mass.

  An aqueous dispersion containing colored polymer particles (C) and a polymer dispersant (E), wherein the colored polymer particles (C) are stably dispersed in water by the action of the polymer dispersant (E) [ Hereinafter, it is referred to as an aqueous dispersion (X). Can be produced by a known and commonly used technique. For example, pigment particles (A) and non-ionic azo compounds having a non-salt polar group and having the aforementioned solubility in water. System polymerization initiator, polymer dispersant (E), an organic solvent, an aqueous dispersion containing water, and a styrene monomer, and the monomer exists as droplets in the aqueous dispersion It is possible to prepare by preparing an aqueous dispersion of pigment particles (A) coated with a styrenic polymer (B), followed by distillation under reduced pressure.

The aqueous dispersion (X) can be produced, for example, by sequentially performing the following steps.
First step: Pigment particles (A), a nonionic salt-containing polar group and a water-soluble azo polymerization initiator, polymer dispersant (E) and organic An aqueous dispersion containing a solvent and water is prepared.
Second step: The aqueous dispersion and the styrene monomer are mixed and polymerized so that the monomer does not exist as droplets in the aqueous dispersion, and colored polymer particles (C) An aqueous dispersion of is prepared.
Third step: The aqueous dispersion is distilled to remove the organic solvent and, if necessary, water to obtain an aqueous dispersion of colored polymer particles (C).

  In the first step, an aqueous dispersion containing pigment particles (A), a nonionic and water-soluble azo polymerization initiator, a polymer dispersant, an organic solvent, and water is prepared.

  In order to obtain the styrenic polymer (B) in the present invention, various known and commonly used radical polymerization initiators can be used. As this radical polymerization initiator, an azo polymerization initiator having a nonionic salt-containing polar group and solubility in water [hereinafter simply referred to as a polymerization initiator]. ] Is preferably used. Although this polymerization initiator contains a polar group in its chemical structure, it does not have a salt structure, exhibits nonionic properties, and has solubility in specific water. This polymerization initiator can be decomposed into terminal groups of the styrenic polymer (B), contributing to dispersibility of the colored polymer particles (C) in water, and styrene not coated with a pigment in the polymerization process. There is a specific property that the particles of the polymer (B) itself are not substantially generated.

  The solubility of this specific water means that when 100 mg of a polymerization initiator is placed in a container and 21 ° C. ion-exchanged water is added to this while stirring, the crystals of the azo polymerization initiator disappear and the liquid is transparent. The amount of ion-exchanged water that was measured when the amount of ion-exchanged water that was not filtered when the liquid was filtered through a 0.1 μm filter was 10 mg or less, and the amount of the polymerization initiator dissolved in 100 g of ion-exchanged water was expressed as M (unit: g). In this case, 0.005 g ≦ M ≦ 3 g is satisfied. If the solubility is smaller than the lower limit value, a large amount of coarse aggregated particles tends to be formed after the formation reaction of the colored polymer particles (C). On the other hand, if the solubility is larger than the upper limit value, the styrenic polymer (B) itself. There is a tendency that a large amount of fine particles are generated, which is not preferable.

  Examples of such a polymerization initiator include 2,2′-azobis [2- (2-imidazolin-2-yl) propane], dimethyl 2,2′-azobis (2-methylpropionate), 4, 4-azobis (4-cyanopentanoic acid) is mentioned. The aqueous dispersion of colored polymer particles (C) containing the styrene polymer (B) containing these denitrogenated residues as terminal groups is preferably used when preparing the aqueous dispersion of the present invention. Used.

  As radical polymerization initiators, compounds having a wide variety of chemical structures are known. In order to utilize the specific properties as described above, azobisisobutyronitrile (AIBN), 2, 2 ′ Use of -azobis [2- (2-imidazolin-2-yl) propane] hydrochloride, potassium persulfate and the like is not preferable in terms of producing an aqueous dispersion of suitable colored polymer particles (C).

  Examples of the organic solvent in the present invention include non-reactive organic compounds that are liquid at room temperature, such as lower alcohols such as methanol and isopropyl alcohol; alkylene glycols such as ethylene glycol and polyethylene glycol; mono- or dialkyl ethers of alkylene glycols; Ether acetates; Ketones such as acetone and methyl ethyl ketone; Cyclic ethers such as tetrahydrofuran; Nitrogen-containing compounds such as dimethylformamide and methyl pyrrolidone; Acetic esters such as ethyl acetate and butyl acetate; Aromatic hydrocarbons such as toluene and xylene; And aliphatic hydrocarbons. These can be used alone or in combination of two or more. However, this organic solvent is preferable because a hydrophilic organic solvent is miscible with water without being separated, and a lower alcohol is particularly preferable because it can be removed at a low temperature by distillation described later.

  An aqueous dispersion containing pigment particles (A), a polymerization initiator, a polymer dispersant (E), an organic solvent, and water is prepared by mixing the respective raw materials in an arbitrary mass ratio and in an arbitrary order. However, for example, the pigment particles (A) are sufficiently dispersed in advance to prepare an organic solvent dispersion of the pigment particles (A), and the polymerization initiator and the polymer dispersion. It is preferable to prepare a polymerization initiator aqueous solution by mixing the agent (E) and water, and to mix and prepare these organic solvent dispersion and the polymerization initiator aqueous solution. Any known and commonly used means can be used for the dispersion. Specifically, a mechanical stirring process using a paint shaker, an attritor, a ball mill, or the like, a sonication process using an ultrasonic homogenizer, a pressure dispersion process using a pressure homomixer, or the like can be given.

  The concentration (amount used) of the pigment particles (A) in this aqueous dispersion is appropriately adjusted according to the type and amount used of the polymer dispersant (E). As 100%, for example, it is in the range of 0.1 to 80%, preferably 1 to 50%. When the concentration range is as described above, the polymerization described later can suppress the generation of particles consisting only of the styrene polymer (B), and the pigment particles (A) coated with the styrene polymer (B), that is, The yield of the colored polymer particles (C) can be further increased.

  The amount of the polymerization initiator used is, in terms of mass, a monoethylenic monomer having a solubility in water at 25 ° C. of 2.5% by mass or less other than the styrene monomer and the styrene monomer used as necessary. It is 0.05-10 parts with respect to a total of 100 parts of a saturated polymerizable monomer, Preferably it is 0.5-5 parts. Within this range, the unreacted raw material monomer hardly remains, and the amount of particles made of only the styrene polymer (B) is extremely small.

  The amount of the polymer dispersant (E) used is, for example, 0.1 to 50 parts, preferably 3 to 20 parts by nonvolatile matter with respect to 100 parts of the pigment particles (A) in terms of mass.

  The aqueous dispersion described above can be prepared by using water as a main liquid medium and using an organic solvent in combination. The liquid medium of this aqueous dispersion is an aqueous medium. The aqueous medium is a mixture of water and an organic solvent, and refers to a liquid medium having a water content of 60% or more in terms of mass. By using a small amount of an organic solvent in combination with water, an aqueous dispersion that tends to be unstable only with water can be made more stable. The amount of the aqueous medium used in preparing the aqueous dispersion is not particularly limited, but the total mass conversion of the pigment particles (A), the polymerization initiator, the polymer dispersant (E), the organic solvent, and water is 100%. The balance excluding the pigment particles (A), the polymerization initiator, and the polymer dispersant (E) is an aqueous medium.

  In the second step, the aqueous dispersion obtained above and the solubility in water at 25 ° C. other than the styrene monomer and the styrene monomer used as necessary are 2.5 as described above. A colored polymer containing a polymer dispersant (E) and an organic solvent coated with pigment particles (A) by mixing and polymerizing a monoethylenically unsaturated polymerizable monomer of less than mass%. An aqueous dispersion of particles (C) is produced.

  When an aqueous dispersion of colored polymer particles (C) containing a polymer dispersant (E) and an organic solvent is produced by polymerizing a styrene monomer and coating the pigment particles (A), This polymerization is performed so that the styrene monomer does not exist as droplets in the aqueous dispersion of the raw material. In order to mix and polymerize the styrenic monomer so that it does not exist as droplets in the aqueous dispersion of the raw material, if necessary, an amount of surfactant that is less than the critical micelle concentration can be used in combination. .

  Here, “does not exist as droplets in the aqueous dispersion” means that the amount of the styrene monomer supplied to the aqueous dispersion is the saturated dissolution amount of the styrene monomer in the aqueous dispersion at the polymerization temperature. The following is maintained. That is, the polymerization of the styrene monomer is carried out in a state where it is diffused and dissolved in the aqueous dispersion. By doing so, the pigment particles (A) can be precisely coated with the styrenic polymer (B) to obtain colored polymer particles (C). On the other hand, when the styrenic monomer is present in the aqueous dispersion in the form of droplets, the pigment particles (A) may be taken into these droplets, and as a result, the pigment particles (A) are converted into styrene-based monomers. Not only can it not be precisely coated with the coalesced (B), it can also be the cause of the generation of coarse particles. As a method of supplying the styrene monomer in such a small amount, for example, a method in which a styrene monomer is dropped in a very small amount into the aqueous dispersion, a two-phase of a styrene monomer and the aqueous dispersion. The method of superposing | polymerizing in a separation state is mentioned. Generally, a method of performing polymerization in a two-phase separation state is employed. According to this method, the styrene monomer concentration in the aqueous dispersion is maintained below the above-mentioned solubility by gently stirring so as to maintain the phase separation state of the aqueous phase and the monomer phase. Can do. On the other hand, if the two phases are suspended, coarse particles may be generated, which is not preferable.

  In performing the above-described polymerization, a surfactant can be used in combination as necessary. As the surfactant, for example, any of an anionic surfactant, a nonionic surfactant, and a cationic surfactant can be used. When the surfactant is used in combination, the amount used is preferably an amount that is less than the critical micelle concentration of the surfactant in the aqueous dispersion, from the viewpoint of less foaming due to distillation or the like described later. .

  The polymerization reaction of the styrenic monomer can be carried out by cleaving the polymerization initiator and generating radicals. In order to carry out the polymerization reaction, an aqueous dispersion containing a styrene monomer as an essential component and a surfactant as necessary may be heated to a temperature equal to or higher than the cleavage temperature of the polymerization initiator. Although depending on the polymerization initiator and the molecular weight of the styrene polymer (B) to be obtained, the heating temperature at this time is, for example, 50 to 80 ° C., and the heating time is, for example, 30 minutes to 20 hours.

  This polymerization reaction can be performed, for example, in an atmosphere of an inert gas such as nitrogen or helium. Moreover, this polymerization reaction can be performed under normal pressure or under pressure. However, it is conveniently carried out at normal pressure in an inert gas atmosphere.

  By performing the first step and the second step as described above, even if the pigment particles (A) are aggregated for any reason, the styrenic monomer enters the void portion of the aggregate, and the void As a result of the polymerization being carried out in the interior to form a styrene polymer (B) and coating, the agglomeration is dissolved and the aqueous dispersion after passing through the second step is compared with the aqueous dispersion obtained in the first step. It is also possible to reduce the average particle size.

  By the formation of the reaction field state such as the kind of the polymerization initiator and the styrenic monomer as described above, the aqueous dispersion obtained in this second step has a conventional content ratio of the colored polymer particles (C). It becomes possible to make it higher remarkably compared with. That is, when the total number of the total dispersed particles in the aqueous dispersion is 100%, the colored polymer particles (C) can be at least 60% or more, preferably 85% or more.

  The monomer composition of the styrenic polymer (B) is a monoethylenic unsaturated compound having a solubility in water of not more than 2.5% by mass only at the styrenic monomer or at 25 ° C. According to the monomer mixture which is a mixture with the polymerizable monomer and the styrene monomer accounts for 70% or more, the pigment particles (A) not coated with the styrene polymer (B) or the styrene It is possible to easily obtain an aqueous dispersion containing 85% or more of colored polymer particles (C) substantially free from the particles of the polymer (B) itself. The number of colored polymer particles (C) in the total dispersed particles in the aqueous dispersion is determined from observation within the field of view of a two-dimensional image of an electron micrograph taken by developing the aqueous dispersion on a glass plate. I can do it. In aqueous dispersions for preparing water-based inks for ink jet recording, pigment particles that are not covered with the styrenic polymer contained therein are stable in dispersion at long periods of room temperature or in a humid heat environment, and optical properties. Since the discharge characteristics may be adversely affected, the content thereof is preferably as small as possible.

  Further, the particle diameter of the colored polymer particles (C) in the aqueous dispersion obtained in the second step is generally slightly larger than the average particle diameter of the pigment particles (A) used. The average particle diameter of the colored polymer particles (C) is as described above. As described above, this aqueous dispersion may have a small content of dispersed particles other than the colored polymer particles (C), and the average particle size of the colored polymer particles (C) is determined in the third step described later. Even before and after distillation concentration, there is no change or even if there is a change, the difference is very small.

  Depending on the type of the end group of the polymerization initiator exposed on the surface of the dispersed particles, it is possible to disperse the colored polymer particles (C) in water at a pH of 7 to 11, for example. The colored polymer particles (C) having a terminal group on the surface obtained by using a suitable polymerization initiator can be stably dispersed in water, for example, at a pH of 8 to 10 without the presence of an organic solvent.

  In this second step, in an aqueous medium containing a polymer dispersant (E), an organic solvent, and optionally a surfactant, colored polymer particles having excellent dispersion stability once in a certain pH range ( If the aqueous dispersion of C) is obtained, even if the organic solvent that contributes to dispersion stability is removed from the aqueous medium in the subsequent third step, only the colored polymer particles (C) are used in the pH range. A water dispersion in which it is stably dispersed in water is obtained.

  The aqueous dispersion obtained in the second step is an aqueous dispersion of colored polymer particles (C) containing a polymer dispersant (E) and an organic solvent. If the aqueous dispersion containing the polymer dispersant (E) and the organic solvent is used as it is for various applications, the excellent properties of the colored polymer particles (C) can be used effectively. Absent. Therefore, in the next step, an aqueous dispersion of colored polymer particles (C) containing no organic solvent is prepared.

  In the third step, the aqueous dispersion of colored polymer particles (C) containing the polymer dispersant (E) and the organic solvent is distilled to remove the organic solvent and, if necessary, water. Thus, an aqueous dispersion of colored polymer particles (C) is obtained. In the method through the first step to the second step described above, the aqueous dispersion may be produced in a state where the concentration of the pigment particles (A) is dilute due to the kind of the monomer used therein and the reaction field. Many. Accordingly, an aqueous dispersion having a relatively low content of the colored polymer particles (C) is likely to be obtained as the obtained aqueous dispersion. Therefore, the solvent removal by distillation can be performed with the aim of increasing the content of the colored polymer particles (C) and obtaining a odorless dispersion. Further, in order to increase the content of the colored polymer particles (C), water can be distilled off by a required amount to concentrate the nonvolatile content.

  In addition, although distillation at the time of manufacturing water dispersion (X) should just be performed so that it may become a required non volatile matter, the handling is easy and it becomes applicable to various application uses. Thus, it is preferable to make an aqueous dispersion having a nonvolatile content of more than 10% and 30% in terms of mass. This distillation is preferably performed so as not to affect the coating state of the styrenic polymer (B) in the colored polymer particles (C). For example, the distillation is performed below Tg of the styrenic polymer (B). Is preferred. Distillation of the styrene polymer (B) below Tg can be performed, for example, by distillation under reduced pressure.

  As described above, the aqueous dispersion of the present invention is, for example, an aqueous dispersion (X) and an aqueous dispersion of a styrene polymer (D) [referred to as an aqueous dispersion (Y). ] Can be prepared by mixing. This mixing can be performed by stirring in the absence of a grinding medium such as a metal bead or a rod so that the dispersibility of the dispersed particles in the mixture is not destroyed. In this case, a known and commonly used dispersing device can be used.

  The self-water dispersible styrenic polymer (D) and the aqueous dispersion (Y) that are compatible with the styrenic polymer (B) can be prepared by using the colored polymer particles (A) described above without using the pigment particles (A). It can be produced according to the production method of the aqueous dispersion (X) of C). The styrenic polymer (D) may not be a polymer produced by using an azo polymerization initiator other than a suitable polymerization initiator or an organic peroxide, and the first step to the third step. An aqueous dispersion of the styrenic polymer (D) can also be produced by conventional solution polymerization or emulsion polymerization without passing.

  The styrenic polymer (D) is preferably an aqueous dispersion as in the case of the colored polymer particles (C). The aqueous dispersion (Y) of the styrene polymer (D) is preferably an aqueous dispersion having a nonvolatile content exceeding 10% in terms of mass.

  As described above, the aqueous dispersion of the present invention comprises an aqueous dispersion (X) of colored polymer particles (C) and an aqueous dispersion (Y) of a styrene polymer (D) from which an organic solvent has been removed in advance. However, as an alternative method, an aqueous dispersion of colored polymer particles (C) and an aqueous dispersion of styrenic polymer (D) are mixed and then distilled. Any organic solvent of each dispersion is removed at once and water is also removed if necessary to obtain an aqueous dispersion of the present invention, or an aqueous dispersion of colored polymer particles (C) and a styrenic polymer (D ), And then distilled to remove the organic solvent and, if necessary, water to remove the organic solvent. In this case, the Tg of the styrene polymer (B) or the styrene polymer (D) is taken into account in distillation.

  In the conventional phase inversion emulsification method and acid precipitation method, if the ratio (R / P) of pigment and polymer non-volatile content contained in the aqueous dispersion is increased beyond 0.3, only the scratch resistance is improved. On the other hand, although there was a tendency for the plain paper color development and gloss to be lowered, in the case of the aqueous dispersion of the present invention obtained based on the above production method, even if R / P is increased beyond 0.3, Since the color development and gloss of plain paper are not greatly reduced, it is possible to further increase the degree of freedom in the R / P design of the aqueous dispersion while ensuring the color development and gloss of plain paper.

  The aqueous ink for inkjet recording of the present invention contains the water dispersion. Such an aqueous ink can be prepared from an aqueous dispersion so that the organic pigment content is 1 to 10% in terms of mass. The portion related to the coloration is the charged organic pigment itself, and there are colored polymer particles (C) contained in the aqueous dispersion and pigment particles (A) remaining in an uncoated state. Is a pigment component including that, and its content is 1 to 10%.

  In the preparation of the water-based ink for inkjet recording, water or a water-soluble organic solvent is added to the concentrated aqueous dispersion exceeding the above-mentioned dispersed particle content as necessary, and the necessary dispersed particles in the above range. Various additives necessary for the preparation of water-based inks for ink jet recording such as surfactants, wetting agents, fungicides, pH adjusters, etc. can be used in combination.

  In addition, the obtained water-based ink for ink-jet recording is subjected to ink-jet recording with extremely small nozzle clogging in which dispersed particles are contained within the required particle size distribution by filtering through a microfilter or ultracentrifugating as necessary. Water-based ink can be obtained.

  Further, by appropriately selecting and preparing the composition according to the ejection method, it is possible to obtain an aqueous ink for ink jet recording that can be applied to either the piezo method or the thermal method from the aqueous dispersion.

  The water-based ink for ink-jet recording of the present invention can be printed and recorded on any known recording medium. Examples of such a recording medium include plain paper, dedicated paper for inkjet recording such as photographic paper, a surface-treated resin film, a surface-treated resin sheet, and the like. However, since the water-based ink for inkjet recording of the present invention is excellent in high color development on plain paper, high scratch resistance on special paper and its own storage stability, it is suitable for application to plain paper and special paper for inkjet recording. .

EXAMPLES Hereinafter, although this invention is demonstrated in detail based on an Example, this invention is not limited to these Examples.

  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.

[Preparation of aqueous dispersion of colored polymer particles (C)]
Fastogen (registered trademark) Blue TGR wet cake (CI Pigment Blue 15: 3 manufactured by Dainippon Ink and Chemicals, Inc., non-volatile content of 44.9%) 35.2 g, BYK190 (polymer manufactured by Big Chemie Japan) Dispersant: Styrene-maleic acid copolymer alkylene oxide adduct.) 8.0 g, BYK024 (anti-foaming agent manufactured by Big Chemie Japan) 0.8 g and 36.0 g of water are placed in a 200 ml glass bottle, and zirconia is added. 250 g of beads (diameter 1.5 mm, pulverized media) were added and dispersed with a paint shaker for 2 hours.
Next, 0.16 g of VA-061 (a polymerization initiator manufactured by Wako Pure Chemical Industries, Ltd., 2,2′-azobis [2- (2-imidazolin-2-yl) propane]) was added, and further with a paint shaker. Dispersed for 1 hour.
The above dispersion was diluted with 224 g of 0.05% aqueous sodium dodecylbenzenesulfonate (anionic surfactant), and then 16 g of isopropanol was further mixed. This solution was divided into two equal parts and transferred to 200 ml vials. Further, 1.6 g of styrene was added to each, and the tube was sealed to replace the inside with nitrogen. Next, polymerization was carried out in an oil bath at 70 ° C. for 20 hours while stirring at a speed that maintained two-layer separation.
Thus, an aqueous dispersion in which colored polymer particles in which copper phthalocyanine pigment particles are coated with a styrene homopolymer, and a polymer dispersant are dispersed in an aqueous medium containing an organic solvent, an antifoaming agent and water. Manufactured.

  The content of all pigment particles in the aqueous dispersion in terms of mass is 5% on the basis of the mass of the charged amount, and the ratio of the styrene polymer (B) / pigment particles (A) in the colored polymer particles is: The styrene homopolymer in the colored polymer particles is 16.8 / 83.2 on the basis of the mass of the charged amount, and is dissolved in acetone at Tg = 82 ° C., and the weight average molecular weight in terms of polystyrene is in the range of 10,000 to 40,000. It was in. From observation of the obtained aqueous dispersion by a TEM (scanning electron microscope) photograph, no styrene homopolymer particles were observed, and it was determined that the colored polymer particles were 90% or more of the total number of particles. The average particle diameter of the colored polymer particles was in the range of 80 to 200 nm.

The aqueous dispersion obtained above was distilled under reduced pressure at 60 to 70 torr and 60 ° C. to remove all of the organic solvent and a small amount of water and concentrated to obtain an aqueous dispersion (X ₁ ). The content of all pigment particles in the aqueous dispersion (X ₁ ) was 13.4% based on the mass of the charged amount due to this concentration. By this concentration, the average particle diameter of the colored polymer particles hardly changed.

[Preparation of aqueous dispersion of styrenic polymer (D)]
<Synthesis Example 1>
Methyl ethyl ketone in a 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 (Hereafter, MEK) 550 parts was charged, and the inside of the reaction vessel was purged with nitrogen while stirring. The temperature was raised to 80 ° C. while maintaining the inside of the reaction vessel in a nitrogen atmosphere, and then 37.5 parts of 2-hydroxyethyl methacrylate, 69.0 parts of methacrylic acid, 143.5 parts of benzyl methacrylate, 250. A mixed solution of 0 part and 40.0 parts of “Perbutyl (registered trademark) O” (active ingredient t-butyl 2-ethylhexanoate, manufactured by NOF Corporation) was dropped over 4 hours. After completion of the dropwise addition, the reaction was further continued at the same temperature for 15 hours to obtain a MEK solution of a copolymer having an acid value of 150, a weight average molecular weight of 22,000, and Tg (calculated value) −10 ° C. After completion of this reaction, a part of MEK was distilled off under reduced pressure, the nonvolatile content was adjusted to 50%, and a MEK solution of a styrene copolymer was obtained.

12 parts of the MEK solution of the copolymer having a nonvolatile content of 50% obtained above was neutralized with 2.1 parts of a 25% aqueous potassium hydroxide solution and diluted with ion-exchanged water. A neutralized styrene copolymer D ₁ water-MEK mixed solvent solution was obtained. The aqueous dispersion of styrene polymer particles obtained by distilling off MEK from this solution was in the range of an average particle size of 50 to 200 nm.

<Synthesis Example 2>
Except for using 37.5 parts of 2-hydroxyethyl methacrylate, 69.0 parts of methacrylic acid, 93.5 parts of butyl acrylate, 150.0 parts of benzyl methacrylate, and 150.0 parts of styrene as monomers, In the same manner as in Synthesis Example 1, a MEK solution of a styrene copolymer having an average molecular weight of 23,000, Tg (calculated value) of 45 ° C., and a non-volatile content of 50% was obtained.

12 parts of the MEK solution of the copolymer having a nonvolatile content of 50% obtained above was neutralized with 2.1 parts of a 25% aqueous potassium hydroxide solution and diluted with ion-exchanged water. A neutralized styrene copolymer D ₂ water-MEK mixed solvent solution was obtained. The aqueous dispersion of styrene polymer particles obtained by distilling off MEK from this solution was in the range of an average particle size of 50 to 200 nm.

<Synthesis Example 3>
Except for using 37.5 parts of 2-hydroxyethyl methacrylate, 99.5 parts of methacrylic acid, 263.0 parts of butyl methacrylate, and 100.0 parts of styrene as monomers, A MEK solution of a styrene copolymer having an acid value of 130, a weight average molecular weight of 23,000, Tg (calculated value) of 55 ° C., and a nonvolatile content of 50% was obtained.

12 parts of the MEK solution of the copolymer having a nonvolatile content of 50% obtained above was neutralized with 3.1 parts of a 25% aqueous potassium hydroxide solution and diluted with ion-exchanged water. A neutralized styrene copolymer D ₃ water-MEK mixed solvent solution was obtained. The aqueous dispersion of styrene polymer particles obtained by distilling off MEK from this solution was in the range of an average particle size of 50 to 200 nm.

<Synthesis Example 4>
The same procedure as in Synthesis Example 1 except that 112.5 parts of 2-hydroxyethyl methacrylate, 115.0 parts of methacrylic acid, 122.5 parts of butyl acrylate, and 150.0 parts of dodecyl methacrylate were used as monomers. Thus, a MEK solution of a copolymer having an average molecular weight of 19,000, a Tg (calculated value) of 87 ° C., and a nonvolatile content of 50% was obtained.

12 parts of the MEK solution of the copolymer having a nonvolatile content of 50% obtained above was neutralized with 3.6 parts of a 25% aqueous potassium hydroxide solution and diluted with ion-exchanged water. A neutralized copolymer D ₄ water-MEK mixed solvent solution was obtained.

Styrene copolymer D of Synthesis Example 1 15 parts of a _1- water-MEK mixed solvent solution, 74.6 parts of an aqueous dispersion (X ₁ ), and 10.4 parts of water are mixed, and a Dispermat CV disperser (VMA-GETZMANN) is mixed. For 30 minutes. The aqueous pigment dispersion thus obtained was distilled under reduced pressure at 60 to 70 torr and 60 ° C. to remove contained MEK and further concentrated. After concentration, the sum of the colored polymer particles and pigment particles contained in the dispersion was diluted to 10% with deionized water to obtain an aqueous dispersion Z ₁ of the present invention.

Example 1 except that the same amount of the styrene copolymer D ₂ water-MEK mixed solvent solution of Synthesis Example 2 was used instead of the styrene copolymer D ₁ water-MEK mixed solvent solution of Synthesis Example 1. Similarly, a total of 10% of the colored polymer particles and pigment particles contained in the dispersion to obtain an aqueous dispersion Z ₂ of the present invention that the pH is 8-10.

Example 1 except that the same amount of the styrene copolymer D ₃ water-MEK mixed solvent solution of Synthesis Example 3 was used instead of the styrene copolymer D ₁ water-MEK mixed solvent solution of Synthesis Example 1. Similarly, a total of 10% of the colored polymer particles and pigment particles contained in the dispersion to obtain an aqueous dispersion Z ₃ of the present invention that the pH is 8-10.

<Comparative Example 1>
The same amount of the copolymer D ₄ water-MEK mixed solvent solution of Synthesis Example 4 was used instead of the styrene copolymer D ₁ water-MEK mixed solvent solution of Synthetic Example 1 in the same manner as in Example 1. Te, total of the colored polymer particles and pigment particles contained in the dispersion at 10% to obtain an aqueous dispersion Z ₄ which pH is 8-10.

<Comparative example 2>
Styrene copolymer _{D 1} water -MEK mixed solvent solution 12 parts of Synthesis Example 1, Fastgen (registered trademark) Blue TGR (produced by Dainippon Ink & Chemicals Co., Ltd. C.I. Pigment Blue 15:. 3 nonvolatile content 100%.) 12 parts, 51 parts of water and 200 parts of zirconia beads were added and dispersed for 2 hours with a paint shaker. After removing the zirconia beads from the aqueous pigment dispersion thus obtained by filtration, distillation under reduced pressure was performed at 60 to 70 torr and 60 ° C. to remove the MEK contained therein and further concentrated. Thus, the sum of the colored polymer particles and pigment particles contained in the dispersion to obtain an aqueous dispersion Z ₅ is 10%.

<Comparative Example 3>
74.6 parts of an aqueous dispersion (X ₁ ) was diluted with ion-exchanged water so that the total of the colored polymer particles and the pigment particles contained in the dispersion was 10% to obtain an aqueous dispersion Z ₆ .

[Preparation of water-based ink for inkjet recording]
And Example 1 of JP-A-7-228808 JP reference, the water-based ink for ink jet recording were prepared for aqueous dispersion Z ₁ of the first embodiment. The ink composition is shown below.

Water dispersion Z ₁ 40.0 parts Triethylene glycol monobutyl ether 10.0 parts Diethylene glycol 15.0 parts Surfinol 465 (manufactured by Air Products) 0.8 parts Water 34.2 parts

(Performance evaluation of water-based ink for inkjet recording)
1. Evaluation of printed matter The above-prepared water-based ink for ink-jet recording, which has not been subjected to storage stability test, is filled in a cartridge of a commercially available piezo-type ink jet printer (MJ-8000C type, manufactured by Seiko Epson Corporation) Printed on a recording medium.

1-1. Plain Paper Coloring The solid density of the printed material on the recording paper Xerox 4024 (Fuji Xerox Co., Ltd.), which is plain paper, was measured with a Macbeth reflection densitometer spectrum eye.

1-2. Evaluation was made using a photographic paper (silk tone) [manufactured by Seiko Epson Corporation], which is a special paper for scratch resistance. Solid printing was performed on the same photographic paper, and after printing for 10 minutes, after drying for 1 hour, each printed part was rubbed with a finger, and the rubbing condition was visually evaluated. The evaluation criteria are described below.
◎: Printing is not taken at all ○: Printing is hardly taken and the surroundings are not dirty △: Printing is rubbed and the surroundings are dirty ×: Printing is rubbed considerably and the surroundings are also heavily stained

2. Storage stability (storage stability)
About the aqueous ink for inkjet recording prepared above, the average particle diameter before and behind storing for 7 days in a 70 degreeC thermostat was measured. The average particle diameter was defined as the volume average particle diameter measured with a laser Doppler particle size analyzer Microtrac (UPA150 type, manufactured by Leeds & Northrop). The average particle diameter after storage was compared with that before storage, and the storage stability was evaluated according to the following criteria.
○: Change rate before and after storage is less than 110% △: Same as below 110-120% ×: Same as 120% or more

  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 dispersion of the present invention has excellent storage stability even before ink preparation, and as a result, excellent storage stability even when viewed from an aqueous inkjet recording ink prepared therefrom. Have.
It can also be seen that the water-based ink for ink jet recording of the present invention has both high color developability on plain paper and high scratch resistance of printed images on special paper.
On the other hand, the water-based ink for ink jet recording prepared from the conventional aqueous dispersion as in the comparative example has any of storage stability, color developability on plain paper, and scratch resistance of printed images on special paper. However, it will be inferior.
Also, using the same self-water dispersible styrenic polymer as in Example 1, an aqueous dispersion of colored polymer particles was prepared by a phase inversion emulsification method or an acid precipitation method according to the background art. Even if the water dispersion of the water-dispersible styrene polymer itself is added, the styrene polymer in the colored polymer particles and the styrene polymer to be added must have the same composition. From the aqueous dispersion, it has excellent storage stability, high color developability on plain paper, and high scratch resistance of printed images on special paper, as in the case of functional separation in the composition of the styrene polymer. A water-based ink for inkjet recording was not obtained.

Claims (6)

Colored polymer particles (C) in which pigment particles (A) are coated with a styrene polymer (B), a self-water dispersible styrene polymer (D) compatible with the polymer (B), An aqueous dispersion for preparing a water-based ink for ink-jet recording, comprising, in water, a polymer dispersant (E) other than the above (B) and (D) for dispersing the colored polymer particles (C). The styrenic polymer (B) contains, as a terminal group, a deionized residue of an azo polymerization initiator that is nonionic and contains a non-salt polar group and has solubility in water as described below. The aqueous dispersion according to claim 1, which is a styrene polymer.
When 100 mg of the azo polymerization initiator was put into a container and ion exchange water at 21 ° C. was added to the container while stirring, the crystals of the azo polymerization initiator disappeared and the liquid was transparent (the liquid with a 0.1 μm filter). When the amount of azo polymerization initiator dissolved in 100 g of ion-exchanged water was measured as M (unit: g), 0.005 g ≦ M ≦ 3 g is satisfied. Colored polymer particles (C) in which pigment particles (A) are coated with a styrenic polymer (B) and a polymer other than (B) and (D) for dispersing the colored polymer particles (C) An aqueous dispersion containing a dispersant (E) is an organic pigment particle, a nonionic salt-containing azo polymerization initiator having a non-salt polar group, , Polymer dispersion, organic solvent, aqueous dispersion containing water, and styrene monomer are mixed and polymerized so that the monomer does not exist as droplets in the aqueous dispersion The aqueous dispersion according to claim 1, which is an aqueous dispersion obtained by preparing an aqueous dispersion of organic pigment particles coated with a styrene-based polymer and then performing distillation under reduced pressure. Colored polymer particles (C) in which pigment particles (A) are coated with a styrenic polymer (B) and a polymer other than (B) and (D) for dispersing the colored polymer particles (C) The aqueous dispersion according to claim 4, wherein the colored polymer particles (C) in the aqueous dispersion containing the dispersant (E) are 85% or more of the total number of dispersed particles. The aqueous dispersion according to any one of claims 1 to 4, which has a pH of 8 to 10. A water-based ink for ink-jet recording, comprising the water dispersion according to any one of claims 1 to 5.