JP2008094058A - Inkjet printing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an inkjet printing method capable of obtaining printed matter with high print density and an ink set. <P>SOLUTION: (1) This inkjet printing method includes the steps of printing a recording medium with a water ink having a colorant by an inkjet recording method, and then overprinting a coating ink including a particle having an average particle diameter of 30 to 400 nm and an index of refraction1 of 0 to 2.2 on the printed part by the inkjet recording method. (2) The ink set is made up of the water ink having the colorant and the coating ink having a particle with an average particle diameter of 30 to 400 nm and an index of refraction of 1.0 to 2.2. The ink set is printed on the recording medium by the inkjet recording method and the coating ink is overprinted on the printed part. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an ink jet printing method and an ink set that can obtain a printed matter with excellent print density when printing on plain paper or the like.

The ink jet recording method is a recording method in which characters and images are obtained by ejecting ink droplets directly from a very fine nozzle onto a recording member and attaching them. This method is easily spread at a full color and is inexpensive, and can be used as a recording member, and can be used as a recording member.
For example, Patent Documents 1 and 2 are known as ink jet printing methods.
Patent Document 1 discloses a step of adhering an ink composition containing a resin emulsion and / or an inorganic oxide colloid in addition to water and a colorant and having a specific surface tension to a recording medium, and a polyvalent metal salt thereon. Alternatively, a method having a step of applying a reaction solution containing a polyallylamine derivative and having a specific surface tension is disclosed. According to this method, agglomerates are formed on the recording medium from the reaction between the colorant component in the ink composition and the reaction liquid, and as a result, a high-quality color image having a high print density and no color bleeding is obtained. It is supposed to be done.
Patent Document 2 prints a first liquid containing water and a colorant, and a second liquid containing protein, alginate, polyacrylate, polyacrylamide, or a cationic activator as a thickener. Thus, a method for obtaining a good image is disclosed.

Regarding ink-jet recording ink, for example, Patent Document 3 discloses a liquid composition containing light or white water-insoluble fine particles (resin emulsion), a water-soluble organic solvent and water, a colorant, a water-soluble organic solvent and water. An ink containing an ink containing is disclosed.
Regarding the ink set, for example, Patent Document 4 discloses an ink set for printing two liquids of a color ink composition and a clear ink composition.
However, with the ink jet printing method, ink, and ink set disclosed in the above-mentioned patent document, the print density when printing on plain paper is still not sufficient.

Japanese Patent Laid-Open No. 11-115303 JP-A-3-240558 JP 2000-034342 A JP 2003-286428 A

  It is an object of the present invention to provide an ink jet printing method and an ink set capable of obtaining a printed matter having an excellent print density.

In the inkjet printing method for printing two liquids, the present inventors print a coating ink containing a step of printing a water-based ink containing a colorant and particles (i) having a specific particle size and refractive index. It has been found that by combining the steps, a printed matter having an excellent print density can be obtained.
That is, the present invention provides the following (1) and (2).
(1) An ink jet printing method in which the following steps 1 and 2 are sequentially performed on a recording medium using an aqueous ink and a coating ink.
Step 1: A step of printing a water-based ink containing a colorant on all or part of the recording medium by an ink jet recording method Step 2: An average particle size of 30 on the printed portion of the recording medium obtained in Step 1 Step (2) A step of printing a coating ink containing particles (ii) having a refractive index of 1.0 to 2.2 at ˜400 nm by an ink jet recording method (2) A water-based ink containing a colorant and an average particle diameter Is an ink set composed of a coating ink containing particles (ii) having a refractive index of 1.0 to 2.2 and a water-based ink printed on a recording medium by an inkjet recording method. An ink set for printing the coating ink on the printed portion.

  According to the ink jet printing method and ink set of the present invention, a printed matter (printed matter, photograph) having an excellent print density can be obtained even if plain paper or copy paper is used as a recording medium.

  In order to achieve a high print density by the ink jet recording method, the present inventors have (1) to reduce the reflected light from the surface of the printing surface, and (2) in a printing method by two-component printing, a recording medium The present inventors have found that by coating or laminating particles having a specific particle size and refractive index on the colorant printed on, the reflected light can be effectively reduced and the print density can be improved.

The inkjet printing method of the present invention is characterized by sequentially performing the following steps 1 and 2 on a recording medium using an aqueous ink and a coating ink. Step 1: A colorant is contained in all or part of the recording medium. Step of printing water-based ink to be printed by inkjet recording method Step 2: Particles having an average particle size of 30 to 400 nm and a refractive index of 1.0 to 2.2 on the printed portion of the recording medium obtained in Step 1 Step of Overprinting Coating Ink Containing (A) by Inkjet Recording Method Each component used in the printing method of the present invention will be described below.

[Particles (a) having an average particle size of 30 to 400 nm and a refractive index of 1.0 to 2.2] (hereinafter also simply referred to as “particles (a)”)
In order to reduce the reflectance of light from the surface of the printing surface, the present inventors are effective in reducing the surface scattering of light on the colorant surface and improving the light absorption rate to the colorant. In view of this, in order to achieve a high printing density in the ink jet recording method, the optimum range of the refractive index and average particle diameter of the particles was found.
In the present invention, particles (A) having a refractive index of 1.0 to 2.2 are used from the viewpoint of efficiently reducing reflected light from the printed matter and improving the print density.
The refractive index of the particles (A) used in the present invention is 1.0 or more, preferably 1.1 or more, more preferably 1.2 or more, and particularly preferably 1.3 or more. 2 or less, preferably 1.8 or less, more preferably 1.7 or less, particularly preferably 1.65 or less, and most preferably 1.6 or less. From the above viewpoint, the refractive index of the particles (A) is preferably 1.0 to 1.8, more preferably 1.1 to 1.7, still more preferably 1.2 to 1.65, and particularly preferably 1. 3 to 1.6.
The refractive index can be measured by an optical interference type film thickness measuring device (manufactured by Dainippon Screen Co., Ltd., product name: Lambda Ace VM-1000) described later. When the particles (I) are powders, about 0.01 parts by weight of a polyacrylate (for example, Pois 530A manufactured by Kao Corporation) with respect to 1 part by weight of the particles (I), water, ethanol, etc. A dispersion dispersed in a dispersion medium can be applied to the measurement method.

The average particle diameter of the particles (a) used in the present invention is preferably 30 nm or more, more preferably 50 nm or more, and particularly preferably from the viewpoint of efficiently reducing reflected light and improving printing density and dispersion stability. It is 70 nm or more, and the upper limit is 400 nm or less, preferably 350 nm or less, more preferably 300 nm or less, still more preferably 280 nm or less, and particularly preferably 250 nm or less. From the above viewpoint, the average particle diameter of the particles (a) is 30 to 400 nm, preferably 30 to 350 nm, more preferably 30 to 300 nm, still more preferably 50 to 300 nm, particularly preferably 50 to 280 nm, and most preferably 70 to 250 nm.
The average particle diameter of the particles (A) can be measured by a laser particle analysis system ELS-8000 (cumulant analysis) manufactured by Otsuka Electronics Co., Ltd. The measurement conditions are a temperature of 25 ° C., an angle between incident light and a detector of 90 °, and an integration count of 100. The refractive index of water (1.333) is input as the refractive index of the dispersion solvent. The concentration of the measurement solution is usually about 5 × 10 ⁻³ wt%.

In the present invention, when an aqueous ink containing particles (I) and a colorant (particularly pigment) is printed on a recording medium by an inkjet recording method, the particles (I) It is considered that the print density can be improved by the aggregate covering the colorant of the printed matter and performing the same function as the antireflection film of the printed matter.
In general, when substances having different refractive indexes are present, the refractive index R of air is n ₀ , the refractive index of the colorant is n ₂ , and the refractive index of the substance present on the colorant is n _1. It is represented by the following formula.
Reflectivity R = [(n ₀ n ₂ -n ₁ n ₁ ) / (n ₀ n ₂ + n ₁ n ₁ )] ²
Here, if the refractive index n _{0 of} air is 1.00, the reflectance R may be minimized to improve the print density, and n ₁ = √n ₂ to minimize the value of the above equation. It is preferable that
Considering that the refractive index of the quinacridone pigment is about 2 and the refractive index of the phthalocyanine pigment is about 1.4, the above range is appropriate for the refractive index of the particles (A) used in the present invention. I understand that.

In addition, the intensity of the reflected light is most weakened because the light reflected on the surface of the colorant and the light reflected on the surface of the material present on the colorant are reversed in phase. The film thickness d of the substance is preferably represented by the following formula where λ is the wavelength of light.
Film thickness d = λ / [(2 + 2√2) × n ₁ ]
The film thickness d is a calculated value when the light incident angle is 45 ° and the light receiving angle is 0 ° (measurement condition of Macbeth densitometer).
The magenta measurement wavelength (λ) is 536 nm (half width ± 20 nm), the cyan measurement wavelength (λ) is 624 nm (half width ± 20 nm), and the yellow measurement wavelength (λ) is 432 nm (half width ± 20 nm). Considering the aforementioned n ₁ , it can be seen that the above range is appropriate for the average particle diameter of the particles (A) used in the present invention.

The particles (a) may be either organic particles or inorganic particles, but inorganic particles and / or polymer particles are preferable, and one kind selected from the group consisting of inorganic particles, polystyrene particles, and polymer particles having fluorine atoms. It is still more preferable that it is above.
Inorganic fine particles include silicon oxide (hereinafter referred to as silica), aluminum oxide (hereinafter referred to as alumina), metal oxides such as magnesium fluoride, manganese oxide, and magnesium oxide, calcium carbonate, magnesium carbonate, barium sulfate, and aluminum silicate. , Alumina white, talc, clay, titanium mica, those obtained by modifying or surface-modifying the surface of these fine particles with a functional group such as a carboxy group or an amino group, or those formed into composite particles with a surfactant. Among these, from the viewpoint of dispersibility, metal oxide particles are preferable, colloidal particles are more preferable, and at least one selected from the group consisting of colloidal silica and colloidal alumina is particularly preferable. Colloidal silica obtained by the manufacturing method is most preferable.

Polymer particles include polystyrene, styrene- (meth) acrylic copolymer, polymethyl methacrylate, (meth) acrylic acid alkyl ester copolymer, styrene-butadiene copolymer, polybutadiene, acrylonitrile-butadiene copolymer, silicon- Examples thereof include particles made of (meth) acrylic ester copolymer, fluorine- (meth) acrylic ester copolymer, polytetrafluoroethylene, silicone polymer and the like. Among these, polystyrene particles and particles made of a polymer having a fluorine atom such as a fluorine- (meth) acrylic ester copolymer or polytetrafluoroethylene are preferable from the viewpoint of having a low refractive index.
The glass transition temperature (Tg) of the polymer constituting the polymer particles is preferably 20 ° C. or higher, more preferably 30 ° C. or higher, and the upper limit is not particularly limited, but is preferably 250 ° C. or lower. From the above viewpoint, the Tg of the polymer is preferably 20 to 250 ° C, more preferably 30 to 250 ° C. When the Tg of the polymer is in the range of 20 ° C. or higher, the polymer fine particles are hardly formed into a film by heat received in the drying process of the ink after printing, and can be present in the form of particles on the colorant. The Tg of the polymer is measured by the method described in the examples.
The weight average molecular weight of the polymer is preferably from 5,000 to 500,000, more preferably from 10,000 to 400,000, particularly preferably from 10,000 to 300,000, from the viewpoint of glossiness of the recording medium. . The weight average molecular weight of the polymer is measured by a gel permeation chromatography method using dimethylformamide containing 60 mmol / L phosphoric acid and 50 mmol / L lithium bromide as a solvent, using polystyrene as a standard substance.
The constituent unit of the polymer constituting the polymer particle and the constituent unit of the polymer constituting the water-insoluble polymer particle (b) containing the colorant described later may be the same or different. It does not contain a colorant.

[Coating ink]
The coating ink in the present invention is a liquid composition mainly composed of particles (i), water, and preferably water containing a water-soluble organic solvent, and if necessary, a wetting agent, a dispersing agent, and an antifoaming agent. Further, additives such as antifungal agents and chelating agents can be contained. There is no restriction | limiting in particular in the mixing method of each of these components. The content of the particles (A) in the coating ink is preferably 0.1% by weight or more, more preferably 1% by weight or more, particularly preferably 2% by weight or more from the viewpoint of dispersion stability and ejection stability, and the upper limit thereof. Is preferably 20% by weight or less, more preferably 15% by weight or less, and particularly preferably 10% by weight or less. From these viewpoints, 0.1 to 20% by weight is preferable, 1 to 15% by weight is more preferable, and 2 to 10% by weight is particularly preferable. Further, the viscosity (20 ° C.) of the coating ink is preferably 2 to 12 mPa · s, and more preferably 2.5 to 10 mPa · s, in order to maintain good ejection properties. The surface tension (20 ° C.) of the coating ink is preferably 23 to 50 mN / m, more preferably 23 to 40 mN / m, and particularly preferably 23 to 30 mN / m.

[Colorant]
As the colorant, either a hydrophobic dye or a pigment can be used. Moreover, both can be used in combination at an arbitrary ratio. Among them, it is preferable to use a pigment for the development of high weather resistance, which has been in strong demand in recent years.
In the present invention, the pigment means an organic pigment and / or carbon black.
Examples of the organic pigment include azo pigments, diazo pigments, phthalocyanine pigments, quinacridone pigments, isoindolinone pigments, dioxazine pigments, perylene pigments, perinone pigments, thioindigo pigments, anthraquinone pigments, and quinophthalone pigments.
Specific examples of preferred organic pigments include C.I. I. Pigment Yellow 13, 17, 74, 83, 97, 109, 110, 120, 128, 139, 151, 154, 155, 174, 180; I. Pigment Red 48, 57: 1, 122, 146, 176, 184, 185, 188, 202; I. Pigment violet 19, 23; C.I. I. Pigment Blue 15, 15: 1, 15: 2, 15: 3, 15: 4, 16, 60; I. Pigment Green 7, 36 etc.
Examples of carbon black include furnace black, thermal lamp black, acetylene black, and channel black.

As the dye, a hydrophobic dye is preferably used because it can be contained in a water-insoluble polymer. Examples of hydrophobic dyes include oily dyes and disperse dyes. The solubility of the hydrophobic dye in the organic solvent is 2 g / in the organic solvent used for dissolving the hydrophobic dye during the production of the aqueous dispersion from the viewpoint of efficiently incorporating the dye into the water-insoluble polymer. L or more is preferable, and 20 to 500 g / L (25 ° C.) is more preferable.
Examples of oil-based dyes include C.I. I. Solvent Black, C.I. I. Solvent Yellow, C.I. I. Solvent Red, C.I. I. Solvent Violet, C.I. I. Solvent Blue, C.I. I. Solvent Green, C.I. I. One or more types of products selected from the group consisting of Solvent Orange are listed, which are commercially available from Orient Chemical Co., Ltd., BASF Corp. and others.
Examples of disperse dyes include C.I. I. Disperse Yellow, C.I. I. Disperse Orange, C.I. I. Disperse Red, C.I. I. Dispers Violet, C.I. I. Disperse Blue, C.I. I. One or more types of products selected from the group consisting of Disperse Green are listed. Of these, C.I. I. Solvent Yellow 29 and 30, C.I. I. Solvent Blue 70, C.I. I. Solvent Red 18 and 49, C.I. I. Solvent blacks 3 and 7 and nigrosine-based black dyes are preferred.
The above colorants can be used alone or in admixture of two or more at any ratio.

[Water-based ink containing colorant]
The water-based ink in the present invention is a liquid composition mainly comprising water containing a colorant, water, and preferably a water-soluble organic solvent, and if necessary, a wetting agent, a dispersing agent, an antifoaming agent, and an antifungal agent. An additive such as an agent and a chelating agent can be contained. There is no restriction | limiting in particular in the mixing method of each of these components.
The content of the colorant in the water-based ink is preferably 1 to 20% by weight, and more preferably 3 to 10% by weight from the viewpoint of improving dispersion stability, printing density, and the like.
In the present invention, it is preferable to use water-insoluble polymer particles containing a colorant. In this case, the weight ratio of the water-insoluble polymer to the colorant [colorant / water-insoluble polymer] , Preferably 50/50 to 90/10, more preferably 50/50 to 80/20, still more preferably 55/45 to 78/22. Further, the viscosity (20 ° C.) of the water-based ink is preferably 2 to 12 mPa · s, and more preferably 2.5 to 10 mPa · s, in order to maintain good ejection properties. The surface tension (20 ° C.) of the water-based ink is preferably 23 to 50 mN / m, more preferably 23 to 40 mN / m, and particularly preferably 23 to 30 mN / m.

(Water-insoluble polymer)
Examples of the water-insoluble polymer constituting the water-insoluble polymer particles include a water-insoluble vinyl polymer, a water-insoluble ester polymer, and a water-insoluble urethane polymer. Among these, a water-insoluble vinyl polymer is preferable from the viewpoint of the stability of the aqueous dispersion.
Here, the water-insoluble polymer is a polymer having a dissolution amount of 10 g or less, preferably 5 g or less, more preferably 1 g or less, after being dried at 105 ° C. for 2 hours and then dissolved in 100 g of water at 25 ° C. Say. When the water-insoluble polymer has a salt-forming group, the above-mentioned dissolution amount is a dissolution amount when the salt-forming group of the water-insoluble polymer is neutralized 100% with acetic acid or sodium hydroxide, depending on the type.
The water-insoluble polymer is preferably a water-insoluble graft polymer containing a structural unit derived from the macromer (b) from the viewpoint of sufficient printing density and improvement in dispersion stability. In particular, the water-insoluble polymer has a polymer containing a structural unit derived from the salt-forming group-containing monomer (a) and a structural unit derived from the hydrophobic monomer (c) in the main chain, and the structural unit derived from the macromer (b). A water-insoluble graft polymer having a side chain is preferred.
Examples of such a water-insoluble graft polymer include a salt-forming group-containing monomer (a) (hereinafter sometimes referred to as “(a) component”), a macromer (b) (hereinafter sometimes referred to as “(b) component”), And a water-insoluble vinyl polymer obtained by copolymerizing a monomer mixture (hereinafter also referred to as “monomer mixture”) containing a hydrophobic monomer (c) (hereinafter also referred to as “component (c)”) is preferable.

(Salt-forming group-containing monomer (a))
The component (a) is used from the viewpoint of enhancing the dispersion stability of the resulting dispersion, and examples thereof include a cationic monomer and an anionic monomer. Specifically, those described in JP-A-9-286939, page 5, column 7, line 24 to page 8, column 8 line 29 can be used. Examples of the salt-forming group include a carboxy group, a sulfonic acid group, a phosphoric acid group, an amino group, and an ammonium group.
Representative examples of the cationic monomer include unsaturated amine-containing monomers and unsaturated ammonium salt-containing monomers. Among these, N, N-dimethylaminoethyl (meth) acrylate, N- (N ′, N '-Dimethylaminopropyl) (meth) acrylamide is preferred.

Representative examples of anionic monomers include unsaturated carboxylic acid monomers, unsaturated sulfonic acid monomers, unsaturated phosphoric acid monomers, and the like.
Examples of the unsaturated carboxylic acid monomer include acrylic acid, methacrylic acid, crotonic acid, itaconic acid, maleic acid, fumaric acid, citraconic acid, and 2-methacryloyloxymethyl succinic acid.
Examples of unsaturated sulfonic acid monomers include styrene sulfonic acid, 2-acrylamido-2-methylpropane sulfonic acid, 3-sulfopropyl (meth) acrylate, and bis- (3-sulfopropyl) -itaconate.
Examples of unsaturated phosphoric acid monomers include vinylphosphonic acid, vinyl phosphate, bis (methacryloxyethyl) phosphate, diphenyl-2-acryloyloxyethyl phosphate, diphenyl-2-methacryloyloxyethyl phosphate, dibutyl-2-acryloyloxy Examples thereof include ethyl phosphate.
Among the anionic monomers, an unsaturated carboxylic acid monomer is preferable and acrylic acid or methacrylic acid is more preferable from the viewpoints of dispersion stability, ejection reliability, and the like.

(Macromer (b))
The component (b) is used from the viewpoint of improving the dispersion stability of the water-insoluble polymer particles and improving the printing density, and has a number average molecular weight of 500 to 100,000, preferably 1,000 to 10,000. Examples thereof include a macromer which is a monomer having a polymerizable functional group such as an unsaturated group at the terminal.
The number average molecular weight of the component (b) can be measured by gel permeation chromatography using polystyrene as a standard substance and tetrahydrofuran containing 50 mmol / L acetic acid as a solvent.
Specifically, as the macromer of the component (b), the following (b-1) styrene-based macromer, (b-2) alkyl (meth) acrylate-based macromer, (b-3) aromatic ring-containing (meth) acrylate-based Macromers, (b-4) silicone-based macromers, and the like.

(B-1) Styrenic Macromer The styrene macromer means a macromer having a styrene monomer (referred to as a b-1 monomer) such as styrene, α-methylstyrene, vinyltoluene and the like. Of the styrenic monomers, styrene is preferred.
Examples of the styrenic macromer include a styrene homopolymer having a polymerizable functional group at one end, and a copolymer of styrene and another monomer having a polymerizable functional group at one end. The polymerizable functional group present at one end is preferably an acryloyloxy group or a methacryloyloxy group, and by copolymerizing these, a water-insoluble graft polymer having a structural unit derived from a styrenic macromer can be obtained. Examples of the other monomer include acrylonitrile, an alkyl (meth) acrylate (b-2 monomer) described later, and an aromatic ring-containing (meth) acrylate (b-3 monomer) other than styrene.
In the side chain or in the styrenic macromer, the content of the structural unit derived from the styrenic monomer is preferably 60% by weight or more, more preferably 70% by weight or more, and particularly preferably 90% by weight from the viewpoint of high print density. % Or more.
Examples of commercially available styrenic macromers include Toa Gosei Co., Ltd. trade name, AS-6 (S), AN-6 (S), HS-6 (S), and the like.

(B-2) Alkyl (meth) acrylate-based macromer An alkyl (meth) acrylate-based macromer has an alkyl group that may have a hydroxy group, preferably 1 to 22 carbon atoms, preferably 1 to 18 carbon atoms. , Means a macromer having an alkyl (meth) acrylate (b-2 monomer).
Specifically, as the b-2 monomer, methyl (meth) acrylate, ethyl (meth) acrylate, (iso) propyl (meth) acrylate, 2-hydroxyethyl (meth) acrylate, (iso or tertiary) butyl ( Examples include (meth) acrylate, 2-ethylhexyl (meth) acrylate, (iso) octyl (meth) acrylate, (iso) decyl (meth) acrylate, (iso) stearyl (meth) acrylate, and the like.
The side chain containing the structural unit derived from the b-2 monomer is obtained by copolymerizing an alkyl (meth) acrylate macromer having a polymerizable functional group at one end, for example, methyl methacrylate macromer, butyl acrylate macromer. , Isobutyl methacrylate-based macromer, lauryl methacrylate-based macromer, and the like.
The alkyl (meth) acrylate-based macromer is composed of an alkyl (meth) acrylate homopolymer having a polymerizable functional group at one end, and an alkyl (meth) acrylate having another polymerizable functional group at one end and another monomer. A copolymer may be mentioned, and the polymerizable functional group is preferably an acryloyloxy group or a methacryloyloxy group. Examples of the other monomer include the styrene monomer (b-1 monomer) and aromatic ring-containing (meth) acrylate (b-3 monomer) other than styrene described below.
In the side chain or in the alkyl (meth) acrylate macromer, the content of the structural unit derived from (meth) acrylic acid ester is the largest, and from the viewpoint of high printing density, it is preferably 60% by weight or more, more preferably 70%. % By weight or more, particularly preferably 90% by weight or more.

(B-3) Aromatic ring-containing (meth) acrylate-based macromer The aromatic ring-containing (meth) acrylate-based macromer means a macromer having an aromatic ring-containing (meth) acrylate (b-3 monomer). As an aromatic ring containing (meth) acrylate, the monomer represented by following formula (1) is preferable.
CH ₂ = CR ² COOR ³ (1)
(In the formula, R ² represents a hydrogen atom or a methyl group, and R ³ represents an arylalkyl group having 7 to 22 carbon atoms or an aryl group having 6 to 22 carbon atoms, which may have a substituent.)
Specifically, benzyl (meth) acrylate, phenyl (meth) acrylate, 2-phenylethyl (meth) acrylate, phenoxyethyl (meth) acrylate, 1-naphthyl acrylate, 2-naphthyl (meth) acrylate, phthalimidomethyl (meta ) Acrylate, p-nitrophenyl (meth) acrylate, 2-hydroxy-3-phenoxypropyl (meth) acrylate, 2-methacryloyloxyethyl-2-hydroxypropyl phthalate, 2-acryloyloxyethyl phthalate, and the like. Among these, benzyl (meth) acrylate is particularly preferable. These can be used alone or in admixture of two or more.

A side chain containing a structural unit derived from an aromatic ring-containing (meth) acrylate can be obtained by copolymerizing an aromatic ring-containing (meth) acrylate-based macromer having a polymerizable functional group at one end.
An aromatic ring-containing (meth) acrylate-based macromer is a homopolymer of an aromatic ring-containing (meth) acrylate having a polymerizable functional group at one end, and an aromatic ring-containing (meth) acrylate having a polymerizable functional group at one end And other monomers, and the polymerizable functional group is preferably an acryloyloxy group or a methacryloyloxy group. Examples of the other monomer include the styrene monomer (b-1 monomer) and (meth) acrylic acid ester (b-2 monomer).
In the side chain or the aromatic ring-containing (meth) acrylate macromer, the content of the structural unit derived from the aromatic ring-containing (meth) acrylate is the largest.

(B-4) Silicone Macromer The water-insoluble graft polymer used in the present invention may have an organopolysiloxane chain as a side chain. This side chain can be obtained, for example, by copolymerizing a silicone macromer having a polymerizable functional group at one end, preferably represented by the following formula (2).
_{CH 2 = C (CH 3)} -COOC 3 H 6 - [Si (CH _{3) 2} -O] _{t -Si (CH 3) 3 (} 2)
(Wherein t represents a number of 8 to 40)
When the polymer used in the present invention is a water-insoluble graft polymer, the weight ratio of [main chain / side chain] is preferably 1/1 to 20/1 from the viewpoint of improving storage stability and the like. 3/2 to 15/1 is more preferable, and 2/1 to 10/1 is particularly preferable. The weight ratio is calculated assuming that the polymerizable functional group is contained in the side chain.
Among the above, a styrenic macromer having a polymerizable functional group at one end is preferable from the viewpoint of high affinity with the pigment and improving storage stability.

(Hydrophobic monomer (c))
The component (c) is used from the viewpoint of improving the printing density, and examples thereof include alkyl (meth) acrylate, alkyl (meth) acrylamide, and aromatic ring-containing monomers.
Alkyl (meth) acrylates include (iso) propyl (meth) acrylate, (iso or tertiary) butyl (meth) acrylate, (iso) amyl (meth) acrylate, cyclohexyl (meth) acrylate, 2-ethylhexyl (meth) Acrylate, (iso) octyl (meth) acrylate, (iso) decyl (meth) acrylate, (iso) dodecyl (meth) acrylate, (iso) cetyl (meth) acrylate, (iso) stearyl (meth) acrylate, (iso) Examples include (meth) acrylic acid esters having an alkyl group having 3 to 30 carbon atoms such as behenyl (meth) acrylate. Among these, (meth) acrylates having an alkyl group having 3 to 22 carbon atoms, preferably 3 to 18 carbon atoms, are preferable from the viewpoint of dispersion stability.

Examples of the aromatic ring-containing monomer include styrene monomers (c-1) such as styrene, 2-methylstyrene and vinyltoluene, aryl esters of (meth) acrylic acid such as benzyl (meth) acrylate and phenoxyethyl (meth) acrylate, Preferred examples include an aromatic group-containing vinyl monomer (c-2) having 6 to 22 carbon atoms such as ethyl vinyl benzene, 4-vinyl biphenyl, 1,1-diphenyl ethylene, vinyl naphthalene and chlorostyrene. Among these, benzyl (meth) acrylate is particularly preferable.
In the present specification, “(iso or tertiary)” and “(iso)” mean that both of these groups are present and not present, and these groups are present. If not, it indicates normal. In addition, “(meth) acrylate” indicates that both acrylate and methacrylate are included.
The component (c) is preferably an aromatic ring-containing monomer from the viewpoint of improving the printing density.
The components (a) to (c) can be used alone or in combination of two or more.

In the present invention, the monomer mixture containing the components (a), (b), and (c) further contains a hydroxyl group-containing monomer (d) (hereinafter sometimes referred to as “component (d)”). Is preferred.
The component (d) enhances dispersion stability. As the component (d), for example, 2-hydroxyethyl (meth) acrylate, 3-hydroxypropyl (meth) acrylate, polyethylene glycol (n = 2 to 30, n represents the average number of moles of oxyalkanediyl group added. The same shall apply hereinafter.) (Meth) acrylate, polypropylene glycol (n = 2 to 30) (meth) acrylate, poly (ethylene glycol (n = 1 to 15) / propylene glycol (n = 1 to 15)) (meth) acrylate, etc. Is mentioned. Among these, 2-hydroxyethyl (meth) acrylate, polyethylene glycol monomethacrylate, and polypropylene glycol methacrylate are preferable.

The monomer mixture may further contain a monomer (e) represented by the following formula (3) (hereinafter sometimes referred to as “component (e)”).
^{_{CH 2 = C (R 4)}} COO (R 5 O) p R 6 (3)
(Wherein R ⁴ is a hydrogen atom or an alkyl group having 1 to 5 carbon atoms, R ⁵ is a divalent hydrocarbon group having 1 to 30 carbon atoms which may have a hetero atom, and R ⁶ is a hetero atom. A monovalent hydrocarbon group having 1 to 30 carbon atoms, p may represent an average added mole number, and is 1 to 60, preferably 1 to 30.)
The component (e) exhibits excellent effects such as enhancing the ejection reliability of the water-based ink and suppressing the occurrence of twisting even when continuous printing is performed.
In the formula (3), examples of the hetero atom that R ⁵ or R ⁶ may have include a nitrogen atom, an oxygen atom, a halogen atom, and a sulfur atom.
Typical examples of the group represented by R ⁵ or R ⁶ include aromatic groups having 6 to 30 carbon atoms, heterocyclic groups having 3 to 30 carbon atoms, alkanediyl groups having 1 to 30 carbon atoms, and the like. May have a substituent. These groups may be a combination of two or more. Examples of the substituent include an aromatic group, a heterocyclic group, an alkyl group, a halogen atom, and an amino group.

As R ⁵ , a phenylene group optionally having a substituent having 1 to 24 carbon atoms, an aliphatic alkanediyl group having 1 to 30 carbon atoms, preferably 1 to 20 carbon atoms, or a carbon having an aromatic ring. Preferred examples include an alkanediyl group having 7 to 30 carbon atoms and an alkanediyl group having 4 to 30 carbon atoms having a heterocyclic ring. Particularly preferred specific examples of the R ⁵ O group include an oxyethylene group, an oxy (iso) propylene group, an oxytetramethylene group, an oxyheptamethylene group, an oxyhexamethylene group, or a carbon composed of one or more of these oxyalkanediyl groups. The oxyalkanediyl group and oxyphenylene group of several 2-7 are mentioned.
R ⁶ is a phenyl group, an aliphatic alkyl group having 1 to 30 carbon atoms, preferably a branched chain having 1 to 20 carbon atoms, or an alkyl group having 7 to 30 carbon atoms having an aromatic ring. Or a C4-C30 alkyl group which has a heterocyclic ring is mentioned preferably. More preferable examples of R ⁶ include alkyl groups having 1 to 12 carbon atoms such as methyl group, ethyl group, (iso) propyl group, (iso) butyl group, (iso) pentyl group, and (iso) hexyl group, phenyl Groups and the like.

Specific examples of the component (e) include methoxypolyethylene glycol (p is 1 to 30 in the above formula (3)) (meth) acrylate, methoxypolytetramethylene glycol (p = 1 to 30) (meth) acrylate, and ethoxypolyethylene. Glycol (p = 1-30) (meth) acrylate, (iso) propoxypolyethylene glycol (p = 1-30) (meth) acrylate, butoxypolyethylene glycol (p = 1-30) (meth) acrylate, octoxypolyethylene glycol (P = 1-30) (meth) acrylate, methoxypolypropylene glycol (p = 1-30) (meth) acrylate, methoxy (ethylene glycol / propylene glycol copolymer) (p = 1-30, ethylene glycol moiety therein 1 to 29) (meta Acrylate, and the like. Among these, methoxypolyethylene glycol (p = 2 to 20) (meth) acrylate and octoxypolyethylene glycol (p = 2 to 20) (meth) acrylate are preferable.
Specific examples of commercially available (d) and (e) components include Shin-Nakamura Chemical Co., Ltd. polyfunctional acrylate monomer (NK ester) M-40G, 90G, 230G, EH-4E, Nippon Oil & Fat Co., Ltd. Blemmer Series, PE-90, 200, 350, PME-100, 200, 400, 1000, PP-500, 800, 1000, AP-150, 400, 550, 800, 50PEP-300, 50POEP-800B, and the like.
The component (d) and the component (e) can be used alone or in combination of two or more.

Components (a) to (e) in the monomer mixture of the above components (a) to (e) at the time of production of the water-insoluble polymer (contents as an unneutralized amount; the same applies hereinafter) The content of the structural unit derived from is as follows.
The content of the component (a) is preferably 1 to 50% by weight, more preferably 2 to 40% by weight, more preferably 3 to 30% by weight, particularly preferably from the viewpoint of dispersion stability of the resulting dispersion. Is 5 to 20% by weight.
The content of the component (b) is preferably 1 to 50% by weight, more preferably 3 to 40% by weight, and particularly preferably 5 to 35% by weight from the viewpoint of dispersion stability of the obtained dispersion, improvement in printing density, and the like. %.
The content of the component (c) is preferably 5 to 90% by weight, more preferably 5 to 80% by weight, and still more preferably 10 to 60% by weight from the viewpoint of printing density and the like.
The weight ratio ((a) / [(b) + (c)]) of the content of the component (a) and the total content of the components (b) and (c) is the long-term storage of the resulting water-based ink. From the viewpoints of stability, ejection reliability, etc., it is preferably 0.01 to 1, more preferably 0.02 to 0.7, and still more preferably 0.05 to 0.5.

The content of the component (d) is preferably 1 to 40% by weight, more preferably 2 to 30% by weight, and further preferably 3 to 15% by weight from the viewpoints of redispersibility and dispersion stability.
The content of the component (e) is preferably 1 to 50% by weight, more preferably 2 to 30% by weight, and further preferably 5 to 30% by weight from the viewpoints of ejection reliability, dispersion stability, and the like.
The total content of the component (a) and the component (d) is preferably 5 to 60% by weight, more preferably 7 to 50% by weight, and still more preferably 10 from the viewpoints of stability in water and water resistance. -40% by weight.
The total content of the component (a) and the component (e) is preferably 5 to 75% by weight, more preferably 7 to 50% by weight, from the viewpoint of dispersion stability in water, ejection reliability, and the like. Preferably it is 10 to 40% by weight.
The total content of the component (a), the component (d), and the component (e) is preferably 5 to 60% by weight, more preferably 7 to 50% by weight from the viewpoints of dispersion stability in water and ejection reliability. %, More preferably 10 to 40% by weight.

(Production of water-insoluble polymer)
The water-insoluble polymer constituting the water-insoluble polymer particles is produced by copolymerizing the monomer mixture by a known polymerization method such as a bulk polymerization method, a solution polymerization method, a suspension polymerization method, an emulsion polymerization method, Among these polymerization methods, effects such as high gloss and high printing density can be suitably obtained in the case of the solution polymerization method.
The solvent used in the solution polymerization method is preferably a polar organic solvent having a high affinity with the water-insoluble polymer, and preferably has a solubility in water of 20% by weight or less, preferably 5% by weight or more. Examples of the polar organic solvent include aliphatic alcohols such as butoxyethanol; aromatics such as toluene and xylene; ketones such as methyl ethyl ketone and methyl isobutyl ketone; esters such as ethyl acetate. Among these, methyl ethyl ketone, methyl isobutyl ketone, toluene, xylene, butoxyethanol, or a mixed solvent of one or more of these with water is preferable.

In the polymerization, azo compounds such as 2,2′-azobisisobutyronitrile and 2,2′-azobis (2,4-dimethylvaleronitrile), tert-butyl peroxyoctoate, dibenzoyl oxide, etc. Known polymerization initiators such as organic peroxides can be used.
The amount of the polymerization initiator is preferably 0.001 to 5 mol, more preferably 0.01 to 2 mol, per mol of the monomer mixture.
In the polymerization, a known polymerization chain transfer agent such as mercaptans such as octyl mercaptan and 2-mercaptoethanol and thiuram disulfide can be further added.
The polymerization conditions of the monomer mixture vary depending on the type of polymerization initiator, monomer, and solvent used, but the polymerization temperature is usually 30 to 100 ° C., preferably 50 to 80 ° C., and the polymerization time is 1 to 20 hours. is there. The polymerization atmosphere is preferably a nitrogen gas atmosphere or an inert gas atmosphere such as argon.
After completion of the polymerization reaction, the produced polymer can be isolated from the reaction solution by a known method such as reprecipitation or solvent distillation. Further, the obtained polymer can be purified by repeating reprecipitation or by removing unreacted monomers and the like by membrane separation, chromatographic method, extraction method and the like.

  The weight average molecular weight of the obtained water-insoluble polymer is preferably from 5,000 to 500,000, more preferably from 8,000 to 400,000, from the viewpoint of dispersion stability of the colorant, water resistance, ejection reliability and the like. 1,000 to 300,000 are particularly preferred. The weight-average molecular weight of the water-insoluble polymer is measured using polystyrene as a standard substance by gel chromatography using dimethylformamide containing 60 mmol / L phosphoric acid and 50 mmol / L lithium bromide as a solvent. .

When the water-insoluble polymer has a salt-forming group derived from the salt-forming group-containing monomer (a), it is neutralized with a neutralizing agent. As the neutralizing agent, an acid or a base can be used depending on the kind of the salt-forming group in the polymer. For example, hydrochloric acid, acetic acid, propionic acid, phosphoric acid, sulfuric acid, lactic acid, succinic acid, glycolic acid, Examples include acids such as gluconic acid and glyceric acid, bases such as lithium hydroxide, sodium hydroxide, potassium hydroxide, ammonia, methylamine, dimethylamine, trimethylamine, ethylamine, diethylamine, triethylamine, triethanolamine, and tributylamine It is done.
The degree of neutralization of the salt-forming group is preferably 10 to 200%, more preferably 20 to 180%, and particularly preferably 50 to 150%. Here, the degree of neutralization can be determined by the following formula when the salt-forming group is an anionic group.
{[Weight of neutralizing agent (g) / equivalent of neutralizing agent] / [acid value of polymer (KOH mg / g) × polymer weight (g) / (56 × 1000)]} × 100
When the salt-forming group is a cationic group, it can be determined by the following formula.
{[Weight of neutralizer (g) / equivalent of neutralizer] / [amine value of polymer (HCL mg / g) × polymer weight (g) / (36.5 × 1000)]} × 100
The acid value and amine value can be calculated from the structural unit of the polymer, but can also be determined by a method of titrating by dissolving the polymer in an appropriate solvent (for example, methyl ethyl ketone).

[Water-insoluble polymer particles containing colorant (b)]
The water-insoluble polymer particles (B) containing a colorant are preferably obtained as an aqueous dispersion by the following steps (1) and (2).
Step (1): A step of dispersing a mixture containing a water-insoluble polymer, an organic solvent, a colorant, water and, if necessary, a neutralizing agent Step (2): a step of removing the organic solvent In the step (1) First, the water-insoluble polymer is dissolved in an organic solvent, and then a colorant, water, and, if necessary, a neutralizing agent, a surfactant and the like are added to the organic solvent and mixed to obtain an oil-in-water dispersion. It is preferable to obtain a body.
In the mixture, the colorant is preferably 5 to 50% by weight, the organic solvent is preferably 10 to 70% by weight, the water-insoluble polymer is preferably 2 to 40% by weight, and the water is 10 to 70% by weight. preferable. When the water-insoluble polymer has a salt-forming group, it is preferable to use a neutralizing agent, but the degree of neutralization is not particularly limited. Usually, it is preferable that the liquid dispersion of the finally obtained water dispersion is neutral, for example, pH is 4.5 to 10. The pH can also be determined by the desired degree of neutralization of the water-insoluble vinyl polymer.

Preferred examples of the organic solvent include alcohol solvents, ketone solvents, and ether solvents, and those having a solubility in water of 50% by weight or less and 10% by weight or more at 20 ° C. are preferable.
Examples of alcohol solvents include ethanol, isopropanol, n-butanol, tertiary butanol, isobutanol, diacetone alcohol and the like. Examples of the ketone solvent include acetone, methyl ethyl ketone, diethyl ketone, and methyl isobutyl ketone. Examples of the ether solvent include dibutyl ether, tetrahydrofuran, dioxane and the like. Among these solvents, isopropanol, acetone and methyl ethyl ketone are preferable, and methyl ethyl ketone is particularly preferable. These solvents can be used alone or in admixture of two or more.
As the neutralizing agent, an acid or a base can be used depending on the kind of the salt-forming group in the water-insoluble polymer.
Examples of neutralizers include hydrochloric acid, acetic acid, propionic acid, phosphoric acid, sulfuric acid, lactic acid, succinic acid, glycolic acid, gluconic acid, glyceric acid, and other acids, lithium hydroxide, sodium hydroxide, potassium hydroxide, ammonia, methyl Examples include bases such as amine, dimethylamine, trimethylamine, ethylamine, diethylamine, triethylamine, and triethanolamine.

There is no restriction | limiting in particular in the dispersion method of the mixture in the said process (1). It is preferable to carry out the main dispersion by applying a shear stress after preliminarily dispersing. In step (2), atomization is performed so that water-insoluble polymer particles having a desired average particle diameter are obtained.
When preliminarily dispersing the mixture, a commonly used mixing and stirring device such as an anchor blade can be used. Among the mixing and stirring devices, Ultra Disper [Asada Steel Co., Ltd., trade name], Ebara Milder [Ebara Manufacturing Co., Ltd., trade name], TK homomixer, TK pipeline mixer, TK homo jetter, TK homomic line flow, High-speed agitating and mixing devices such as Filmix [Special Machine Industry Co., Ltd., trade name], Clear Mix [M Technique Co., Ltd., trade name], KD Mill [Kinetic Dispersion Co., Ltd., trade name] and the like are preferable.
As means for giving the shear stress of this dispersion, for example, a kneader such as a roll mill, a bead mill, a kneader, an extruder, a high-pressure homogenizer (Izumi Food Machinery Co., Ltd., trade name), a minilab 8.3H type (Rannie Co., trade name) Representative homo-valve type high-pressure homogenizer, microfluidizer (Microfluidics, trade name), nanomizer (Nanomizer, trade name), optimizer (Sugino Machine Co., trade name), Genus PY (Shiramizu Chemical Co., Ltd.) Product name], DeBEE2000 [Japan EE Co., Ltd., product name] and the like chamber type high-pressure homogenizer. Among these, a high-pressure homogenizer is preferable from the viewpoint of reducing the particle size of the pigment contained in the mixture.

  In the step (2), water of the water-insoluble polymer particles containing a colorant having a desired average particle size is obtained by distilling the organic solvent from the dispersion obtained in the step (1) to make an aqueous system. A dispersion can be obtained. The organic solvent contained in the aqueous dispersion can be removed by a general method such as distillation under reduced pressure. The organic solvent in the aqueous dispersion containing the obtained water-insoluble polymer particles is substantially removed, and the amount of the organic solvent is preferably 0.1% by weight or less, more preferably 0.01% by weight or less. is there. It is preferable to remove coarse particles by filtering the obtained aqueous dispersion containing water-insoluble polymer particles. Coarse particles are not present, or even if they are present, the amount of the filter is preferably 1 to 10 μm, more preferably 3 to 7 μm, in order to prevent clogging of the printer nozzles.

The water dispersion of water-insoluble polymer particles containing a colorant is a dispersion in which a solid content of a water-insoluble polymer containing a colorant is dispersed in water as a main medium. Here, the form of the water-insoluble polymer particles containing the colorant is not particularly limited as long as the particles are formed of at least the colorant and the water-insoluble polymer. For example, a particle form in which a colorant is included in a water-insoluble polymer, a particle form in which a colorant is uniformly dispersed in a water-insoluble polymer, a particle form in which a colorant is exposed on the surface of a water-insoluble polymer particle, and the like are included.
The average particle diameter of the water-insoluble polymer particles containing the colorant is preferably 50 to 200 nm, more preferably 70 to 170 nm, and particularly preferably 90 to 150 nm, from the viewpoints of dispersion stability and dischargeability. From the viewpoint of increasing the storage stability of the dispersion by reducing the coarse particles, D90 of the water-insoluble polymer particles containing the colorant (the cumulative 90% value calculated from the small particle side in the frequency distribution of the scattering intensity). 350 nm or less is preferable, 300 nm or less is more preferable, and 270 nm or less is particularly preferable. The lower limit is preferably 100 nm or more from the viewpoint of ease of production. The D10 of the water-insoluble polymer particles containing the colorant (the cumulative 10% value calculated from the small particle side in the frequency distribution of the scattering intensity) is preferably 10 nm or more from the viewpoint of printing density and ease of production, 20 nm or more is further preferable, and 30 nm or more is particularly preferable.
In addition, average particle diameter, D90, D10 can be measured by the laser particle analysis system ELS-8000 (cumulant analysis) of the said Otsuka Electronics Co., Ltd. The measurement conditions are the same as described above.

〔recoding media〕
The recording medium used in the present invention is not particularly limited as long as it can be applied to the ink jet recording method, and examples thereof include paper, plastic, and composites thereof.
The recording medium may have a void-type ink receiving layer or an alumina-based ink receiving layer and is usually called glossy paper or photographic paper. However, in order to exert the effects of the present invention, the recording medium has an ink receiving layer. Usually, what is called plain paper or copy paper is suitable.
Here, the ink receiving layer means a void-type ink receiving layer composed of porous inorganic particles such as alumina and silica and a water-soluble resin (binder). A recording medium having such an ink receiving layer is, for example, “ “Applications and Materials of Inkjet Printer” (issued by CMC Corporation 2002), p174 to p181.
Specific examples of the recording medium that can be suitably used in the present invention include commercially available ordinary products such as trade names of Xerox Co., Ltd., Xerox 4024, PB paper manufactured by Canon Inc., and PPC paper My Paper manufactured by Ricoh Co., Ltd. Paper is an example.

[Inkjet printing method]
The inkjet printing method of the present invention is characterized in that the following steps 1 and 2 are sequentially performed on a recording medium using a water-based ink and a coating ink.
Step 1: A step of printing a water-based ink containing a colorant on all or part of the recording medium by an ink jet recording method Step 2: An average particle size of 30 on the printed portion of the recording medium obtained in Step 1 A step of printing a coating ink containing particles (A) having a refractive index of 1.0 to 2.2 at ˜400 nm by using an ink jet recording method. Volume ratio of coating to recording medium [volume of particles (A) (Cm ³ ) / volume of colorant (cm ³ )] is a volume ratio of the abundance ratio of particles (A) and colorants per unit area of the recording medium. From the viewpoint of covering properties and prevention of wrinkling of the recording medium, it is preferably ¼ or more, more preferably ３ or more, and particularly preferably ½ or more. The upper limit is 4/1 or less, preferably 3/1 or less, and more preferably 2/1 or less. From these viewpoints, 1/4 to 4/1 is preferable, 1/3 to 3/1 is more preferable, and 1/2 to 2/1 is particularly preferable.
In the present invention, the ink jet recording method is not limited, but is particularly suitable for a piezo ink jet printer.

[Ink set]
The ink set of the present invention is an ink composed of a water-based ink containing a colorant and a coating ink containing particles (i) having an average particle diameter of 30 to 400 nm and a refractive index of 1.0 to 2.2. In the ink set, the water-based ink is printed on a recording medium by an ink jet recording method, and the coating ink is printed over the printed portion.
The ink set includes two or more different colors, preferably chromatic inks, as the water-based ink. Here, the “different color” means that the reflected light is measured at a wavelength of light of D65 / 2 using a spectral color difference meter SE-2000 manufactured by Nippon Denshoku Industries Co., Ltd., and L ^* a ^* b ^{* A} color in which a ^* (chromaticity in the red-green direction) and b ^* (chromaticity in the yellow-blue direction) are not the same when displayed in the color system. Examples thereof include two or more chromatic colors selected from the group consisting of cyan, yellow, magenta, light cyan, dark yellow, and light magenta.
The ink set of the present invention preferably includes a combination of two or more water-based inks selected from these chromatic colors. A three-color ink set, a four-color ink set, a five-color ink set, a six-color ink set, and seven colors Any of ink set and higher may be used.
More preferably, the ink set includes two or more different colors of water-based inks selected from magenta ink, yellow ink, and cyan ink, which are the three subtractive primary colors, and the ink set including these three colors of ink is provided. Particularly preferred. The ink set of the present invention may further include black ink such as self-dispersing carbon black.

In the following production examples, preparation examples, examples and comparative examples, “parts” and “%” are “parts by weight” and “% by weight” unless otherwise specified.
Production Example 1 (Production of water-insoluble polymer for dispersing pigment)
In a reaction vessel, 20 parts of methyl ethyl ketone and 0.03 part of a polymerization chain transfer agent (2-mercaptoethanol), 10% of 200 parts of the monomer mixture shown in Table 1 were mixed and mixed, and nitrogen gas substitution was sufficiently performed. A mixed solution was obtained.
On the other hand, the remaining 90% of the monomer mixture shown in Table 1 was charged into the dropping funnel, and 0.27 part of the polymerization chain transfer agent, 60 parts of methyl ethyl ketone and a radical polymerization initiator (2,2′-azobis (2,4- 1.2 parts of (dimethylvaleronitrile) was added and mixed, and nitrogen gas substitution was sufficiently performed to obtain a mixed solution.
Under a nitrogen atmosphere, the mixed solution in the reaction vessel was heated to 65 ° C. while stirring, and the mixed solution in the dropping funnel was gradually dropped over 3 hours. After 2 hours at 65 ° C. from the end of dropping, a solution obtained by dissolving 0.3 part of the radical polymerization initiator in 5 parts of methyl ethyl ketone was added, and further aged at 65 ° C. for 2 hours and 70 ° C. for 2 hours to obtain a polymer solution. It was.

The details of the compounds shown in Table 1 are as follows.
Styrene macromer: manufactured by Toa Gosei Co., Ltd., trade name: AS-6S, number average molecular weight: 6000, polymerizable functional group: methacryloyloxy group, pure content 50%
Polyethylene glycol monomethacrylate (ethylene oxide average addition mole number = 9): Shin-Nakamura Chemical Co., Ltd., trade name: NK ester M-90G Terminal: hydrogen atom / polypropylene glycol monomethacrylate (propylene oxide average addition mole number = 9) : Made by Nippon Oil & Fats Co., Ltd., Trade name: Blemmer PP-500 End: Hydrogen atom

Production Example 2 (Production of water dispersion of water-insoluble polymer particles containing pigment)
25 parts of the polymer obtained by drying the polymer solution obtained in Synthesis Example 1 under reduced pressure was dissolved in 70 parts of methyl ethyl ketone, and 4.1 parts of neutralizing agent (5N aqueous sodium hydroxide solution) was contained therein (degree of neutralization 75%). ) And 230 parts of ion-exchanged water to neutralize the salt-forming group, and further add 75 parts of dimethylquinacridone pigment (CI Pigment Violet 19, Clariant Japan, trade name: Hostaperm Red E5B02) Mix at 20 ° C. for 1 hour. The obtained mixture was subjected to 10-pass dispersion treatment at a pressure of 200 MPa with a microfluidizer (trade name, manufactured by Microfluidics).
After adding 250 parts of ion-exchanged water to the obtained dispersion and stirring, methyl ethyl ketone was removed at 60 ° C. under reduced pressure, a part of water was further removed, and a 5 μm filter (acetylcellulose membrane, outer diameter: Pigment-containing vinyl polymer particles having a solid content concentration of 20% by filtering with a 25 mL needleless syringe (made by Terumo Co., Ltd.) attached with 2.5 cm, manufactured by Fuji Photo Film Co., Ltd., and removing coarse particles An aqueous dispersion was obtained. The average particle diameter of the pigment-containing vinyl polymer particles was 110 nm.

Preparation Example 1 (Preparation of water-based ink)
To 40 parts of the aqueous dispersion of pigment-containing vinyl polymer particles obtained in Production Example 1, 7 parts of triethylene glycol monobutyl ether, 1 part of Surfynol 465 (manufactured by Nissin Chemical Industry Co., Ltd., nonionic activator), Proxel XL2 (Abyssia Co., Ltd., antibacterial agent) 0.3 parts are mixed, and glycerin and ion-exchanged water are added so that the E-type viscosity at 20 ° C. is 4 mPa · s. Adjusted as follows. By filtering the obtained mixed solution with a syringe having a capacity of 25 mL equipped with a 1.2 μm filter (acetylcellulose membrane, outer diameter: 2.5 cm, manufactured by Fuji Photo Film Co., Ltd.), and removing coarse particles. A water-based ink was obtained.
Preparation Example 2 (Preparation of coating ink)
Colloidal silica MP-1040 (manufactured by Nissan Chemical Industries, Ltd., trade name, average particle size 110 nm) 15 parts (purified equivalent value 6 parts), 7 parts of triethylene glycol monobutyl ether and 1 part of Surfynol 465 were mixed. Glycerin and ion-exchanged water were added so that the E-type viscosity at 20 ° C. was 4 mPa · s, and the mixture was stirred well to adjust the total to 100 parts. The obtained mixed liquid was filtered in the same manner as in Preparation Example 1 to obtain a coating ink.

Example 1
The water-based ink obtained in Preparation Example 1 was commercially available on plain paper (XEROX Corporation, trade name: 4024) using a printer manufactured by Seiko Epson Corporation (model number: EM-930C, piezo system) by an inkjet recording system. ) (Printing condition = paper type: plain paper, mode setting: photo (4 passes)), and then the coating ink obtained in Adjustment Example 2 is overlaid on the printed portion of the recording medium under the same conditions. Printed.
Example 2
Using colloidal silica MP-2040 (manufactured by Nissan Chemical Industries, Ltd., trade name, average particle size 210 nm) pure equivalent 6 parts instead of colloidal silica MP-1040, coating is performed in the same manner as in Preparation Example 2. An ink was prepared. The obtained coating ink was used in place of the coating ink used in Example 1, and the same printing process as in Example 1 was performed.
Example 3
Instead of colloidal silica MP-1040, a colloidal silica SI-45P (catalyst chemical industry Co., Ltd., cataloid SI-45P, average particle size 60 nm) pure equivalent 6 parts was used, and the same process as in Preparation Example 2 was performed. A coating ink was prepared. The obtained coating ink was used in place of the coating ink used in Example 1, and the same printing process as in Example 1 was performed.

Example 4
Instead of colloidal silica MP-1040 in Preparation Example 2, colloidal silica SI-50 (catalyst chemical industry Co., Ltd., Cataloid SI-50, average particle size 30 nm), 6 parts pure value, was used. A coating ink was prepared by the same process. The obtained coating ink was used in place of the coating ink used in Example 1, and the same printing process as in Example 1 was performed.
Example 5
Instead of colloidal silica MP-1040 in Preparation Example 2, 3 parts of polystyrene (manufactured by ZEON Corporation, PS, average particle size 120 nm) pure conversion value was used, and the coating ink was applied in the same process as in Preparation Example 2. Prepared. The obtained coating ink was used in place of the coating ink used in Example 1, and the same printing process as in Example 1 was performed.
Example 6
Instead of colloidal silica MP-1040 in Preparation Example 2, fluorine polymer emulsion (manufactured by Nissin Chemical Industry Co., Ltd., trade name: VINYBRAN FJ-310, average particle size 180 nm, Tg 35 ° C.) pure equivalent 4.4 parts A coating ink was prepared by the same process as in Preparation Example 2. The obtained coating ink was used in place of the coating ink used in Example 1, and the same printing process as in Example 1 was performed.
Example 7
In place of colloidal silica MP-1040 in Preparation Example 2, polytetrafluoroethylene (manufactured by Asahi Glass Co., Ltd., PTFE, trade name: AD911, average particle size of 270 nm), a pure equivalent value of 4.3 parts, was used, and Preparation Example 2 A coating ink was prepared by the same process as described above. The obtained coating ink was used in place of the coating ink used in Example 1, and the same printing process as in Example 1 was performed.
Example 8
In place of colloidal silica MP-1040 in Preparation Example 2, 9 parts of magnesium fluoride (MgF ₂ , average particle size 190 nm) pure conversion value was used, and a coating ink was prepared by the same process as in Preparation Example 2. The obtained coating ink was used in place of the coating ink used in Example 1, and the same printing process as in Example 1 was performed.

Comparative Example 1
In place of colloidal silica MP-1040 in Preparation Example 2, colloidal silica MP-4540M (manufactured by Nissan Chemical Industries, Ltd., trade name: average particle size: 460 nm) pure equivalent 6 parts was used, and the same as in Preparation Example 2 The coating ink was prepared by the process of. The obtained coating ink was used in place of the coating ink used in Example 1, and the same printing process as in Example 1 was performed.
Comparative Example 2
In place of colloidal silica MP-1040 in Preparation Example 2, titanium oxide (manufactured by Nippon Aerosil Co., Ltd., SiO ₂ , trade name: AEROXIDE-P25, average particle size: 220 nm) 11 parts pure conversion value was used, Preparation Example 2 A coating ink was prepared by the same process as described above. The obtained coating ink was used in place of the coating ink used in Example 1, and the same printing process as in Example 1 was performed.
Comparative Example 3
In the printing process of Example 1, only the printing with the water-based ink was performed, and the printing process with the coating ink was not performed.

(1) After the printed matter subjected to the printing density printing process is left at 25 ° C. for 24 hours, the printing density is measured at the center of the printed matter (5.1 cm × 8.0 cm) using a Macbeth densitometer (product number: RD914, manufactured by Gretag Macbeth). And a total of 5 points at the four corners were measured, and the average value was obtained.
(2) Refractive index measurement method The liquid in which the particles (A) are dispersed is spin-coated to form a thin film (about 100 μm), and then the dispersion medium is used in a vacuum dryer (105 ° C., −8000 Pa, 10 hours drying). Was measured by JIS K7142-1996 (method B, 589 nm) using an optical interference film thickness measuring device (product name: Lambda Ace VM-1000, manufactured by Dainippon Screen Co., Ltd.).
(3) Measuring method of glass transition temperature (Tg) In this invention, Tg of a polymer says the value measured using the differential scanning calorimeter [Seiko Instruments Inc., DSC6200]. Specifically, the measurement was performed under the conditions of the following continuous temperature programs 1 to 4, and the value measured by the temperature program 3 was defined as Tg. The reason for performing the measurement in the temperature program for temperature rise and cooling and using the measured value of the temperature program 3 is to ensure the reproducibility of the measured value.
Temperature program:
1.30 to 250 ° C .: Temperature rising rate 30 ° C./min, holding time 1 min
2.250 to -100 ° C .: cooling rate 30 ° C./min, holding time 30 min
3. −100 to 250 ° C .: Temperature rising rate 5 ° C./min, holding time 1 min
4.250 to 30 ° C .: cooling rate 30 ° C./min, holding time 2 min
(4) Measuring method of E type viscometer The measuring condition of E type viscosity is RE80 manufactured by Toki Sangyo Co., Ltd., measuring temperature 20 ° C., measuring time 1 minute, rotation speed 100 rpm, rotor is standard (1 ° 34 ′ × R24) was used.

(5) Measuring method of coating volume ratio The coating volume ratio [volume of particles (i) (cm ³ ) / volume of colorant (cm ³ )] in the printing process of this example is as follows. Since the discharge amount (weight) of the working ink and the water-based ink can be regarded as the same, [the volume of particles (ii) per gram of coating ink (cm ³ / g) / the volume of colorant per gram of water-based ink (cm ³ / g)].
Volume (cm ³ / g) of particles (g) per gram of coating ink = content (g / g) of particles (a) in coating ink / true density (g / cm ³ ) of particles (a)
Colorant volume per gram of water-based ink (cm ³ / g) = content of colorant in water-based ink (wt%) / true density of colorant (g / cm ³ )
The pigment content in the water-based ink described in Preparation Example 1 is 6% by weight, and the true density of this pigment is 2.0 (g / cm ³ ). Therefore, the volume of the pigment per 1 g of water-based ink is 0.03 (cm ³ / g).
On the other hand, the content of the particles (I) in the coating ink of Example 1 is 6% by weight, and the true density of the particles (I) is 2.1 (g / cm ³ ). The volume of the particles (g) per 1 g of ink is 0.029 (cm ³ / g).
Therefore, the coating volume ratio of Example 1 is 0.029 / 0.03 = 0.97.

From the results of Table 2, Examples 1 to 8 in which a printing process using a coating ink was performed after printing a water-based ink containing a colorant were compared with Comparative Example 3 in which a process using a coating ink was not performed. It can also be seen that the print density is improved. It was also confirmed that the printing density was highest when the refractive index of the particles (a) in the coating ink was about 1.4 and the particle size was about 100 nm.
In Comparative Example 1, the particle size of the particles (A) is too high, and in Comparative Example 2, the refractive index of the particles (A) is too high, so that none of the print density improvement effects can be obtained.

Claims (7)

An ink jet printing method in which the following steps 1 and 2 are sequentially performed on a recording medium using an aqueous ink and a coating ink.
Step 1: A step of printing a water-based ink containing a colorant on all or part of the recording medium by an ink jet recording method Step 2: An average particle size of 30 on the printed portion of the recording medium obtained in Step 1 A step of printing a coating ink containing particles (ii) having a refractive index of 1.0 to 2.2 at ˜400 nm by using an inkjet recording method.   The inkjet printing method according to claim 1, wherein the particles (a) are inorganic particles and / or polymer particles.   The inkjet printing method according to claim 1 or 2, wherein the content of the particles (I) in the coating ink is 0.1 to 20% by weight. The volume ratio of coating to the recording medium [volume of particles (A) (cm ³ ) / volume of colorant (cm ³ )] is 1/4 to 4/1. Inkjet printing method.   The inkjet printing method according to any one of claims 1 to 4, wherein the colorant in the water-based ink is contained in the water-insoluble polymer particles (b). The water-insoluble polymer constituting the water-insoluble polymer particle (b) has a polymer containing a structural unit derived from the salt-forming group-containing monomer (a) and a structural unit derived from the hydrophobic monomer (c) in the main chain, and is a macromer. The inkjet printing method according to claim 5, which is a water-insoluble graft polymer having a structural unit derived from (b) in the side chain.   An ink set comprising a water-based ink containing a colorant and a coating ink containing particles (ii) having an average particle diameter of 30 to 400 nm and a refractive index of 1.0 to 2.2, and inkjet recording An ink set in which the water-based ink is printed on a recording medium by a method, and the coating ink is printed over the printed portion.