JP2010188661A - Ink set for inkjet recording, and inkjet image recording method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an ink set for inkjet recording capable of providing a uniform image with uniform dot diameters, and an inkjet image recording method using the same. <P>SOLUTION: This ink set for the inkjet recording includes an aqueous ink composition containing at least a pigment, and a reaction liquid containing a polyvalent organic acid and at least one kind of a polyphosphoric acid and metaphosphoric acid. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an ink set for inkjet recording and an inkjet image recording method.

  Various recording media have been studied as recording media for inkjet recording, and a technique capable of forming high-quality images is required. Also, various ink materials have been studied for inks from the viewpoints of water resistance and light resistance.

  For example, a pigment is widely used for a colorant that is one of the components of the ink material, and the pigment is used by being dispersed in a medium such as water. When pigments are used in a dispersed manner, the dispersed particle size when dispersed, the stability after dispersion, size uniformity, etc., and ejection properties from the ejection head are important. It is done.

  On the other hand, when recording on plain paper or the like, sufficient performance may not be obtained in terms of fixability (for example, scratch resistance) and resolution in addition to the color density. In particular, there is a case where the speed of ink-jet recording is increased, and there is a demand for recording suitability in the case of performing high-speed recording by a single pass method capable of recording by one head operation instead of the shuttle scan method.

  As a technique related to the above, an ink set including a pigment ink and a treatment liquid containing an acidic compound is disclosed (for example, see Patent Document 1).

JP 2007-261206 A

However, with the ink set described in Patent Document 1, it is difficult to say that the quality of the formed image is sufficient.
It is an object of the present invention to provide an ink set for ink jet recording that can provide a homogeneous image with uniform dot diameters and that can provide good physical strength of a drawn image, and an ink jet image recording method using the ink set. To do.

<1>
An ink set for inkjet recording, comprising: an ink composition containing at least a pigment; and a reaction liquid containing a polyvalent organic acid and at least one of polyphosphoric acid and metaphosphoric acid.
<2>
The polyvalent organic acid contained in the reaction solution contains at least one selected from tartaric acid, DL-malic acid, maleic acid, 4-methylphthalic acid, glutaric acid, and malonic acid. The ink set for inkjet recording as described in <1>.
<3>
The ink set for inkjet recording according to <1> or <2>, wherein the concentration of the polyvalent organic acid is 10 to 30% by mass with respect to the total mass in the reaction solution.
<4>
The ink set for inkjet recording according to any one of <1> to <3>, wherein the reaction solution contains 1 to 30% by mass of an organic solvent based on the total mass.
<5>
The ink set for inkjet recording according to any one of <1> to <4>, wherein the pH of the reaction solution is 3.5 or less.

<6>
The ink set for inkjet recording according to <5>, wherein the pH of the reaction solution is 0.5 to 2.5.
<7>
The ink set for inkjet recording according to any one of <1> to <6>, wherein the reaction liquid contains an anionic surfactant or a nonionic surfactant.
<8>
A reaction liquid application step of applying a reaction liquid containing a polyvalent organic acid and at least one of polyphosphoric acid and metaphosphoric acid onto a recording medium, and an ink composition containing a pigment were applied to the reaction liquid. An ink jet image recording method comprising: an ink droplet ejecting step of ejecting droplets onto a recording medium by an ink jet method.
<9>
The ink droplet ejection step is the inkjet image recording method according to <8>, wherein the droplet ejection is started within 10 seconds after the reaction liquid application step.
<10>
The ink jet image recording method according to <8> or <9>, wherein the ink droplet ejection step ejects ink droplets with a droplet amount of 1.5 to 3.0 pL.

  According to the present invention, it is possible to provide an ink set for ink jet recording capable of providing a uniform image with uniform dot diameters and obtaining good physical strength of a drawn image, and an ink jet image recording method using the ink set. it can.

<Ink set for inkjet recording>
The ink set for inkjet recording of the present invention has at least one aqueous ink composition containing at least a pigment and a reaction solution containing a polyvalent organic acid and containing at least one of polyphosphoric acid and metaphosphoric acid. .
By forming an image using the ink set having such a configuration, a homogeneous image having a uniform dot diameter can be obtained.

(Ink composition)
The ink composition in the present invention contains at least one pigment as a water-insoluble colorant. Furthermore, the ink composition may comprise a pigment dispersant, polymer particles, an organic solvent, a neutralizing agent, water and other components as necessary.

-Pigment-
The ink composition in the present invention contains at least one pigment as a water-insoluble colorant. In the present invention, a water-insoluble pigment itself or a water-insoluble pigment surface-treated with a dispersant can be contained as a water-insoluble colorant.

The type of the pigment is not particularly limited, and conventionally known organic and inorganic pigments can be used. For example, polycyclic pigments such as azo lakes, azo pigments, phthalocyanine pigments, perylene and perinone pigments, anthraquinone pigments, quinacridone pigments, dioxazine pigments, diketopyrrolopyrrole pigments, thioindigo pigments, isoindolinone pigments, quinophthalone pigments, basic Examples include dye lakes such as dye-type lakes and acid dye-type lakes, organic pigments such as nitro pigments, nitroso pigments, aniline black, and daylight fluorescent pigments, and inorganic pigments such as titanium oxide, iron oxide, and carbon black. Further, any pigment that is not described in the color index can be used as long as it is dispersible in the aqueous phase. Further, pigments whose surface is treated with a surfactant, a polymer dispersant, or the like, or graft carbon can also be used.
Of these pigments, azo pigments, phthalocyanine pigments, anthraquinone pigments, quinacridone pigments, and carbon black pigments are particularly preferable.

~ Dispersant ~
In the present invention, the pigment is preferably dispersed in an aqueous solvent by a dispersant. The dispersant may be a polymer dispersant or a low molecular surfactant type dispersant. Further, the polymer dispersant may be either a water-soluble dispersant or a water-insoluble dispersant.

  The low molecular surfactant type dispersant (hereinafter sometimes referred to as “low molecular dispersant”) can stably disperse an organic pigment in an aqueous solvent while maintaining a low viscosity of the ink. The low molecular dispersant herein is a low molecular dispersant having a molecular weight of 2000 or less. Moreover, 100-2000 are preferable and, as for the molecular weight of a low molecular dispersing agent, 200-2000 are more preferable.

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

Examples of the hydrophilic group include an anionic group, a cationic group, a nonionic group, and a betaine type combining these.
The anionic group is not particularly limited as long as it has a negative charge, but may be a phosphoric acid group, a phosphonic acid group, a phosphinic acid group, a sulfuric acid group, a sulfonic acid group, a sulfinic acid group, or a carboxylic acid group. Preferably, it is a phosphoric acid group or a carboxylic acid group, and more preferably a carboxylic acid group.
The cationic group is not particularly limited as long as it has a positive charge, but is preferably an organic cationic substituent, more preferably a cationic group containing nitrogen or phosphorus, and nitrogen. More preferably, it is a cationic group. Among these, a pyridinium cation or an ammonium cation is particularly preferable.
The nonionic group is not particularly limited as long as it has no negative or positive charge, and examples thereof include polyalkylene oxide, polyglycerin, and a part of sugar unit.

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

On the other hand, the hydrophobic group may have any structure such as hydrocarbon, fluorocarbon, and silicone, but is preferably hydrocarbon. Further, these hydrophobic groups may have a linear structure or a branched structure. The hydrophobic group may have a single-chain structure or two or more chain structures, and may have a plurality of types of hydrophobic groups in the case of a structure having two or more chains.
The hydrophobic group is preferably a hydrocarbon group having 2 to 24 carbon atoms, more preferably a hydrocarbon group having 4 to 24 carbon atoms, and still more preferably a hydrocarbon group having 6 to 20 carbon atoms.

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

  Examples of hydrophilic polymer compounds that are chemically modified from natural products include fiber polymers such as methylcellulose, ethylcellulose, hydroxyethylcellulose, hydroxypropylcellulose, carboxymethylcellulose, starches such as sodium starch glycolate and sodium starch phosphate And seaweed polymers such as propylene glycol alginate and the like.

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

  Among these, from the viewpoint of pigment dispersion stability and aggregation, a polymer compound containing a carboxyl group is preferable. For example, an acrylic resin such as a water-soluble styrene acrylic resin, a water-soluble styrene maleic resin, and a water-soluble vinyl naphthalene. High molecular compounds containing a carboxyl group such as an acrylic resin and a water-soluble vinyl naphthalene maleic resin are particularly preferred.

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

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

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

The ink composition in the present invention preferably contains a pigment and a dispersant, more preferably contains an organic pigment and a polymer dispersant, from the viewpoint of light resistance and quality of the image, and the organic pigment and the carboxyl group. It is particularly preferable to include a polymer dispersant. Among them, the water-insoluble colorant is preferably a water-insoluble colorant in which the pigment is coated with a polymer dispersant (preferably having a carboxyl group) from the viewpoint of agglomeration and eventually ink fixing properties. A water-insoluble one coated with a polymer is preferred. As the acrylic polymer, for example, an acrylic resin such as a water-soluble styrene acrylic resin, a water-soluble styrene maleic acid resin, a water-soluble vinyl naphthalene acrylic resin, and a water-soluble vinyl naphthalene maleic resin are preferable.
Furthermore, from the viewpoint of cohesiveness, it is preferable that the acid value of the polymer dispersant is larger than the acid value of the polymer particles (preferably self-dispersing polymer particles) described later.

The average particle size of the water-insoluble colorant containing the pigment is preferably 10 to 200 nm, more preferably 10 to 150 nm, and still more preferably 10 to 100 nm. When the average particle size is 200 nm or less, the color reproducibility is good, the droplet ejection characteristics when droplets are ejected by the ink jet method are good, and when it is 10 nm or more, the light resistance is good. Further, the particle size distribution of the color material is not particularly limited, and may be either a wide particle size distribution or a monodisperse particle size distribution. Two or more color materials having a monodisperse particle size distribution may be mixed and used.
The average particle size and particle size distribution of the coloring material are determined by measuring the volume average particle size by a dynamic light scattering method using a nanotrack particle size distribution measuring device UPA-EX150 (manufactured by Nikkiso Co., Ltd.). It is what

In the present invention, the content of the pigment in the ink composition is preferably 1 to 25% by mass, more preferably 2 to 20% by mass with respect to the ink composition from the viewpoint of image density. 10 mass% is especially preferable.
You may use a water-insoluble coloring material individually by 1 type or in combination of 2 or more types.

-Polymer particles-
The ink composition in the invention preferably contains at least one polymer particle. Thereby, the scratch resistance of the formed image is improved more effectively.
Examples of the polymer particles in the present invention include thermoplastic, thermosetting or modified acrylic, epoxy, polyurethane, polyether, polyamide, unsaturated polyester, phenol, silicone, or fluorine. Resins, polyvinyl resins such as vinyl chloride, vinyl acetate, polyvinyl alcohol or polyvinyl butyral, polyester resins such as alkyd resins and phthalic resins, melamine resins, melamine formaldehyde resins, aminoalkyd cocondensation resins, urea resins, urea resins And the like, or particles of a resin having an anionic group such as a copolymer or a mixture thereof. Among these, anionic acrylic resins include, for example, an acrylic monomer having an anionic group (anionic group-containing acrylic monomer) and, if necessary, other monomers copolymerizable with the anionic group-containing acrylic monomer. Obtained by polymerization in a solvent. Examples of the anionic group-containing acrylic monomer include an acrylic monomer having one or more selected from the group consisting of a carboxyl group, a sulfonic acid group, and a phosphonic group. Among them, an acrylic monomer having a carboxyl group (for example, acrylic acid) Methacrylic acid, crotonic acid, ethacrylic acid, propylacrylic acid, isopropylacrylic acid, itaconic acid, fumaric acid and the like), and acrylic acid or methacrylic acid is particularly preferred.

  The polymer particles in the present invention are preferably self-dispersing polymer particles from the viewpoints of ejection stability and liquid stability (particularly dispersion stability) when the above-described coloring materials (particularly pigments) are used. Self-dispersing polymer particles having are more preferable. Self-dispersing polymer particles are water-insoluble polymers that can be dispersed in an aqueous medium by the functional groups (particularly acidic groups or salts thereof) of the polymer itself in the absence of other surfactants, By means of water-insoluble polymer particles containing no free emulsifier.

Here, the dispersed state means both an emulsified state (emulsion) in which a water-insoluble polymer is dispersed in an aqueous medium and a dispersed state (suspension) in which a water-insoluble polymer is dispersed in an aqueous medium. It includes the state of.
The water-insoluble polymer in the invention is preferably a water-insoluble polymer that can be in a dispersed state in which the water-insoluble polymer is dispersed in a solid state from the viewpoint of aggregation rate and fixing property when incorporated in the ink composition.

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

  The water-insoluble polymer means a polymer having a dissolution amount of 10 g or less when the polymer is dried at 105 ° C. for 2 hours and then dissolved in 100 g of water at 25 ° C., and the dissolution amount is preferable. Is 5 g or less, more preferably 1 g or less. The dissolution amount is the dissolution amount when neutralized with sodium hydroxide or acetic acid according to the kind of the salt-forming group of the water-insoluble polymer.

  The aqueous medium is configured to contain water, and may contain a hydrophilic organic solvent as necessary. In the present invention, it is preferably composed of water and 0.2% by mass or less of a hydrophilic organic solvent with respect to water, and more preferably composed of water.

  The main chain skeleton of the water-insoluble polymer is not particularly limited. For example, a vinyl polymer or a condensation polymer (epoxy resin, polyester, polyurethane, polyamide, cellulose, polyether, polyurea, polyimide, polycarbonate, etc.) is used. it can. Of these, vinyl polymers are particularly preferred.

Preferable examples of the vinyl polymer and the monomer constituting the vinyl polymer include those described in JP-A Nos. 2001-181549 and 2002-88294. In addition, a radical transfer of a vinyl monomer using a chain transfer agent, a polymerization initiator or an iniferter having a dissociable group (or a substituent that can be derived from the dissociable group), or a dissociable group in either the initiator or the terminator. A vinyl polymer in which a dissociable group is introduced at the end of a polymer chain by ionic polymerization using a compound having (or a substituent that can be derived from a dissociable group) can also be used.
Moreover, as a suitable example of the monomer which comprises a condensation type polymer and a condensation type polymer, what is described in Unexamined-Japanese-Patent No. 2001-247787 can be mentioned.

  The self-dispersing polymer particles in the present invention preferably contain a water-insoluble polymer containing a hydrophilic constituent unit and a constituent unit derived from an aromatic group-containing monomer from the viewpoint of self-dispersibility.

The hydrophilic structural unit is not particularly limited as long as it is derived from a hydrophilic group-containing monomer, and even if it is derived from one kind of hydrophilic group-containing monomer, it contains two or more hydrophilic groups. It may be derived from a monomer. The hydrophilic group is not particularly limited, and may be a dissociable group or a nonionic hydrophilic group.
In the present invention, the hydrophilic group is preferably a dissociable group and more preferably an anionic dissociable group from the viewpoint of promoting self-dispersion and the stability of the formed emulsified or dispersed state. Examples of the dissociable group include a carboxyl group, a phosphoric acid group, and a sulfonic acid group. Among them, a carboxyl group is preferable from the viewpoint of fixability when an ink composition is configured.

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

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

The self-dispersing polymer particles in the present invention preferably contain a polymer having a carboxyl group from the viewpoint of self-dispersibility and the aggregation rate when coming into contact with the reaction solution, and have a carboxyl group and an acid value (mgKOH / g It is more preferable that the polymer contains 25-100. Furthermore, the acid value is more preferably from 25 to 80, and particularly preferably from 30 to 65, from the viewpoints of self-dispersibility and agglomeration rate when contacted with the reaction solution.
In particular, when the acid value is 25 or more, the stability of self-dispersibility is good, and when it is 100 or less, the cohesiveness is improved.

The aromatic group-containing monomer is not particularly limited as long as it is a compound containing an aromatic group and a polymerizable group. The aromatic group may be a group derived from an aromatic hydrocarbon or a group derived from an aromatic heterocycle. In the present invention, an aromatic group derived from an aromatic hydrocarbon is preferable from the viewpoint of particle shape stability in an aqueous medium.
The polymerizable group may be a condensation polymerizable polymerizable group or an addition polymerizable polymerizable group. In the present invention, from the viewpoint of particle shape stability in an aqueous medium, an addition polymerizable group is preferable, and a group containing an ethylenically unsaturated bond is more preferable.

  The aromatic group-containing monomer in the present invention is preferably a monomer having an aromatic group derived from an aromatic hydrocarbon and an ethylenically unsaturated bond. The aromatic group-containing monomer may be used alone or in combination of two or more.

Examples of the aromatic group-containing monomer include phenoxyethyl (meth) acrylate, benzyl (meth) acrylate, phenyl (meth) acrylate, and a styrene monomer. Of these, aromatic group-containing (meth) acrylate monomers are preferred from the viewpoint of the balance between the hydrophilicity and hydrophobicity of the polymer chain and the ink fixability, and include phenoxyethyl (meth) acrylate, benzyl (meth) acrylate, and phenyl (meth). At least one selected from acrylates is more preferable, and phenoxyethyl (meth) acrylate and benzyl (meth) acrylate are more preferable.
“(Meth) acrylate” means acrylate or methacrylate.

The self-dispersing polymer particles in the present invention include a structural unit derived from an aromatic group-containing (meth) acrylate monomer, and the content is preferably 10% by mass to 95% by mass. When the content of the aromatic group-containing (meth) acrylate monomer is 10% by mass to 95% by mass, the stability of the self-emulsification or dispersion state can be improved, and further the increase in ink viscosity can be suppressed.
In the present invention, from the viewpoints of stability in a self-dispersing state, stabilization of particle shape in an aqueous medium due to hydrophobic interaction between aromatic rings, and reduction in the amount of water-soluble components due to appropriate hydrophobicization of particles. More preferably, the content is from mass% to 90 mass%, more preferably from 15 mass% to 80 mass%, and particularly preferably from 25 mass% to 70 mass%.

  The self-dispersing polymer particles in the present invention can be constituted using, for example, a structural unit derived from an aromatic group-containing monomer and a structural unit derived from a dissociable group-containing monomer. Furthermore, other structural units may be further included as necessary.

The monomer that forms the other structural unit is not particularly limited as long as it is a monomer copolymerizable with the aromatic group-containing monomer and the dissociable group-containing monomer. Among these, an alkyl group-containing monomer is preferable from the viewpoint of flexibility of the polymer skeleton and ease of control of the glass transition temperature (Tg).
Examples of the alkyl group-containing monomer include methyl (meth) acrylate, ethyl (meth) acrylate, isopropyl (meth) acrylate, n-propyl (meth) acrylate, n-butyl (meth) acrylate, isobutyl (meth) acrylate, alkyl (meth) acrylates such as t-butyl (meth) acrylate, hexyl (meth) acrylate, ethylhexyl (meth) acrylate; hydroxymethyl (meth) acrylate, 2-hydroxyethyl (meth) acrylate, 2-hydroxypropyl (meth) Ethylenically unsaturated monomers having a hydroxyl group such as acrylate, 4-hydroxybutyl (meth) acrylate, hydroxypentyl (meth) acrylate, hydroxyhexyl (meth) acrylate; Dialkylaminoalkyl (meth) acrylates such as ru (meth) acrylate; N-hydroxyalkyl (meth) such as N-hydroxymethyl (meth) acrylamide, N-hydroxyethyl (meth) acrylamide, N-hydroxybutyl (meth) acrylamide Acrylamide; N-methoxymethyl (meth) acrylamide, N-ethoxymethyl (meth) acrylamide, N- (n-, iso) butoxymethyl (meth) acrylamide, N-methoxyethyl (meth) acrylamide, N-ethoxyethyl (meta And (meth) acrylamides such as N-alkoxyalkyl (meth) acrylamides such as acrylamide and N- (n-, iso) butoxyethyl (meth) acrylamide.

  The molecular weight range of the water-insoluble polymer constituting the self-dispersing polymer particles in the present invention is preferably 3000 to 200,000, more preferably 5000 to 150,000, and more preferably 10,000 to 100,000 in terms of weight average molecular weight. More preferably it is. By setting the weight average molecular weight to 3000 or more, the amount of water-soluble components can be effectively suppressed. Moreover, self-dispersion stability can be improved by making a weight average molecular weight into 200,000 or less.

  The weight average molecular weight is measured by gel permeation chromatography (GPC). For GPC, HLC-8020GPC (manufactured by Tosoh Corporation) is used, TSKgel, Super Multipore HZ-H (manufactured by Tosoh Corporation, 4.6 mm ID × 15 cm) are used as columns, and THF (tetrahydrofuran) is used as an eluent. ) Is used. As conditions, the sample concentration is 0.45% by mass, the flow rate is 0.35 ml / min, the sample injection amount is 10 μl, the measurement temperature is 40 ° C., and an IR detector is used. In addition, the calibration curve is “standard sample TSK standard, polystyrene” manufactured by Tosoh Corporation: “F-40”, “F-20”, “F-4”, “F-1”, “A-5000”, It is prepared from 8 samples of “A-2500”, “A-1000”, “n-propylbenzene”.

The water-insoluble polymer constituting the self-dispersing polymer particle in the present invention is a structural unit derived from an aromatic group-containing (meth) acrylate monomer (preferably phenoxyethyl (meth) acrylate) from the viewpoint of controlling the hydrophilicity / hydrophobicity of the polymer. It is preferable that 15-80 mass% of the total mass of a self-dispersing polymer particle is included as a copolymerization ratio for the structural unit derived from and / or the structural unit derived from benzyl (meth) acrylate.
In addition, the water-insoluble polymer has a constitution derived from a carboxyl group-containing monomer having a copolymerization ratio of 15 to 80% by mass of a constitutional unit derived from an aromatic group-containing (meth) acrylate monomer from the viewpoint of controlling the hydrophilicity / hydrophobicity of the polymer. And a structural unit derived from an alkyl group-containing monomer (preferably a structural unit derived from an alkyl ester of (meth) acrylic acid), and a structural unit derived from phenoxyethyl (meth) acrylate and / or Alternatively, a structural unit derived from benzyl (meth) acrylate as a copolymerization ratio of 15 to 80% by mass, a structural unit derived from a carboxyl group-containing monomer, and a structural unit derived from an alkyl group-containing monomer (preferably (meth) A structural unit derived from an alkyl ester having 1 to 4 carbon atoms of acrylic acid) More preferably, the acid value is 25 to 100 and the weight average molecular weight is preferably 3000 to 200,000, the acid value is 25 to 95, and the weight average molecular weight is 5000 to 150,000. It is more preferable that

  Specific examples of the water-insoluble polymer constituting the self-dispersing polymer particles are listed below as exemplary compounds B-01 to B-19, but the present invention is not limited thereto. In addition, the parenthesis represents the mass ratio of the copolymerization component.

B-01: Phenoxyethyl acrylate / methyl methacrylate / acrylic acid copolymer (50/45/5)
B-02: Phenoxyethyl acrylate / benzyl methacrylate / isobutyl methacrylate / methacrylic acid copolymer (30/35/29/6)
B-03: Phenoxyethyl methacrylate / isobutyl methacrylate / methacrylic acid copolymer (50/44/6)
B-04: Phenoxyethyl acrylate / methyl methacrylate / ethyl acrylate / acrylic acid copolymer (30/55/10/5)
B-05: benzyl methacrylate / isobutyl methacrylate / methacrylic acid copolymer (35/59/6)
B-06: Styrene / phenoxyethyl acrylate / methyl methacrylate / acrylic acid copolymer (10/50/35/5)
B-07: benzyl acrylate / methyl methacrylate / acrylic acid copolymer (55/40/5)
B-08: Phenoxyethyl methacrylate / benzyl acrylate / methacrylic acid copolymer (45/47/8)
B-09: Styrene / phenoxyethyl acrylate / butyl methacrylate / acrylic acid copolymer (5/48/40/7)
B-10: benzyl methacrylate / isobutyl methacrylate / cyclohexyl methacrylate / methacrylic acid copolymer (35/30/30/5)
B-11: Phenoxyethyl acrylate / methyl methacrylate / butyl acrylate / methacrylic acid copolymer (12/50/30/8)
B-12: benzyl acrylate / isobutyl methacrylate / acrylic acid copolymer (93/2/5)
B-13: Styrene / phenoxyethyl methacrylate / butyl acrylate / acrylic acid copolymer (50/5/20/25)
B-14: Styrene / butyl acrylate / acrylic acid copolymer (62/35/3)
B-15: Methyl methacrylate / phenoxyethyl acrylate / acrylic acid copolymer (45/51/4)
B-16: Methyl methacrylate / phenoxyethyl acrylate / acrylic acid copolymer (45/49/6)
B-17: Methyl methacrylate / phenoxyethyl acrylate / acrylic acid copolymer (45/48/7)
B-18: Methyl methacrylate / phenoxyethyl acrylate / acrylic acid copolymer (45/47/8)
B-19: Methyl methacrylate / phenoxyethyl acrylate / acrylic acid copolymer (45/45/10)

  The method for producing the water-insoluble polymer constituting the self-dispersing polymer particles in the present invention is not particularly limited. For example, emulsion polymerization is carried out in the presence of a polymerizable surfactant to obtain a surfactant and a water-insoluble polymer. Examples include a method of covalent bonding, and a method of copolymerizing a monomer mixture containing the hydrophilic group-containing monomer and the aromatic group-containing monomer by a known polymerization method such as a solution polymerization method or a bulk polymerization method. Among the polymerization methods, a solution polymerization method is preferable and a solution polymerization method using an organic solvent is more preferable from the viewpoint of aggregation rate and droplet ejection stability when an ink composition is used.

  The self-dispersing polymer particles in the present invention include a polymer synthesized in an organic solvent from the viewpoint of aggregation rate, and the polymer has a carboxyl group (preferably having an acid value of 20 to 100). Part or all of the carboxyl groups of the polymer are preferably neutralized and prepared as a polymer dispersion having water as a continuous phase. That is, the production of the self-dispersing polymer particles in the present invention includes a step of synthesizing a polymer in an organic solvent and a dispersion step of making an aqueous dispersion in which at least a part of the carboxyl groups of the polymer is neutralized. It is preferable to do so.

The dispersion step preferably includes the following step (1) and step (2).
Step (1): Step of stirring a mixture containing a polymer (water-insoluble polymer), an organic solvent, a neutralizing agent, and an aqueous medium Step (2): Step of removing the organic solvent from the mixture

The step (1) is preferably a treatment in which a polymer (water-insoluble polymer) is first dissolved in an organic solvent, then a neutralizing agent and an aqueous medium are gradually added, mixed and stirred to obtain a dispersion. In this way, by adding a neutralizing agent and an aqueous medium to a water-insoluble polymer solution dissolved in an organic solvent, a self-dispersing polymer having a particle size with higher storage stability without requiring strong shearing force. Particles can be obtained.
There is no restriction | limiting in particular in the stirring method of this mixture, Dispersing machines, such as a generally used mixing stirring apparatus and an ultrasonic disperser, a high-pressure homogenizer, can be used as needed.

Preferred examples of the organic solvent include alcohol solvents, ketone solvents, and ether solvents.
Examples of the alcohol solvent include isopropyl alcohol, n-butanol, t-butanol, ethanol and the like. Examples of the ketone solvent include acetone, methyl ethyl ketone, diethyl ketone, and methyl isobutyl ketone. Examples of ether solvents include dibutyl ether and dioxane. Among these solvents, ketone solvents such as methyl ethyl ketone and alcohol solvents such as isopropyl alcohol are preferable. It is also preferable to use isopropyl alcohol and methyl ethyl ketone in combination for the purpose of moderating the polarity change during the phase inversion from oil to water. By using this solvent in combination, it is possible to obtain self-dispersing polymer particles having a fine particle size with high dispersion stability without aggregation and sedimentation and fusion between particles.

  The neutralizing agent is used so that a part or all of the dissociable group is neutralized and the self-dispersing polymer forms a stable emulsified or dispersed state in water. When the self-dispersing polymer of the present invention has an anionic dissociative group (for example, a carboxyl group) as a dissociable group, the neutralizing agent used is basic such as an organic amine compound, ammonia, or an alkali metal hydroxide. Compounds. Examples of organic amine compounds include monomethylamine, dimethylamine, trimethylamine, monoethylamine, diethylamine, triethylamine, monopropylamine, dipropylamine, monoethanolamine, diethanolamine, triethanolamine, N, N-dimethyl-ethanolamine, N, N-diethyl-ethanolamine, 2-dimethylamino-2-methyl-1-propanol, 2-amino-2-methyl-1-propanol, N-methyldiethanolamine, N-ethyldiethanolamine, monoisopropanolamine, diisopropanol Examples include amines and triisopropanolamine. Examples of the alkali metal hydroxide include lithium hydroxide, sodium hydroxide, and potassium hydroxide. Among these, sodium hydroxide, potassium hydroxide, triethylamine, and triethanolamine are preferable from the viewpoint of stabilizing the dispersion of the self-dispersing polymer particles of the present invention in water.

  These basic compounds are preferably used in an amount of 5 to 120 mol%, more preferably 10 to 110 mol%, still more preferably 15 to 100 mol%, based on 100 mol% of the dissociable group. . By setting it as 15 mol% or more, the effect which stabilizes dispersion | distribution of the particle | grains in water expresses, and there exists an effect which reduces a water-soluble component by setting it as 100 mol% or less.

  In the step (2), the aqueous dispersion of the self-dispersing polymer particles is obtained by distilling off the organic solvent from the dispersion obtained in the step (1) by a conventional method such as distillation under reduced pressure and phase-inversion into an aqueous system. A dispersion can be obtained. The organic solvent in the obtained aqueous dispersion has been substantially removed, and the amount of the organic solvent is preferably 0.2% by mass or less, more preferably 0.1% by mass or less.

The average particle size of the polymer particles (particularly self-dispersing polymer particles) is preferably in the range of 10 to 400 nm, more preferably in the range of 10 to 200 nm, still more preferably in the range of 10 to 100 nm, and particularly preferably in terms of volume average particle size. It is the range of 10-50 nm. Manufacturability is improved by having an average particle diameter of 10 nm or more. Moreover, storage stability improves by setting it as an average particle diameter of 400 nm or less. Moreover, there is no restriction | limiting in particular regarding the particle size distribution of a polymer particle, Any of what has a wide particle size distribution or a monodispersed particle size distribution may be sufficient. Further, two or more kinds of polymer particles may be mixed and used.
The average particle size and particle size distribution of the polymer particles are determined by measuring the volume average particle size by a dynamic light scattering method using a nanotrack particle size distribution measuring device UPA-EX150 (manufactured by Nikkiso Co., Ltd.). It is what

The content of the polymer particles (particularly self-dispersing polymer particles) in the ink composition is preferably 1 to 30% by mass with respect to the ink composition from the viewpoint of glossiness of the image, and 3 to More preferably, it is 15 mass%.
The polymer particles (particularly self-dispersing polymer particles) can be used singly or in combination of two or more.

-Organic solvent-
The ink composition in the invention preferably contains water as a solvent, and more preferably further contains at least one organic solvent (preferably a water-soluble organic solvent). By containing an organic solvent, in particular, a water-soluble organic solvent, drying prevention and penetration promotion can be achieved.
When a water-soluble organic solvent is used as an anti-drying agent, nozzle clogging that may occur due to ink drying at the ink discharge port is effectively prevented when an ink composition is discharged by an inkjet method to record an image. be able to.

In order to prevent drying, a water-soluble organic solvent having a vapor pressure lower than that of water is preferable. Specific examples of water-soluble organic solvents suitable for preventing drying include ethylene glycol, propylene glycol, diethylene glycol, polyethylene glycol, thiodiglycol, dithiodiglycol, 2-methyl-1,3-propanediol, 1,2 , 6-hexanetriol, acetylene glycol derivative, glycerin, polyhydric alcohols represented by trimethylolpropane, ethylene glycol monomethyl (or ethyl) ether, diethylene glycol monomethyl (or ethyl) ether, triethylene glycol monoethyl (or butyl) ) Lower alkyl ethers of polyhydric alcohols such as ethers, heterocyclic rings such as 2-pyrrolidone, N-methyl-2-pyrrolidone, 1,3-dimethyl-2-imidazolidinone, N-ethylmorpholine, Horan, dimethyl sulfoxide, sulfur-containing compounds such as sulfolane, diacetone alcohol, polyfunctional compounds such as diethanolamine, and urea derivatives.
Of these, polyhydric alcohols such as glycerin and diethylene glycol are preferred. Moreover, these may be used individually by 1 type, or may use 2 or more types together. These water-soluble organic solvents are preferably contained in the ink composition in an amount of 10 to 50% by mass.

  In order to promote penetration, a water-soluble organic solvent is preferably used from the viewpoint of allowing the ink composition to penetrate better into the recording medium. Specific examples of water-soluble organic solvents suitable for promoting penetration include alcohols such as ethanol, isopropanol, butanol, di (tri) ethylene glycol monobutyl ether, 1,2-hexanediol, sodium lauryl sulfate, and sodium oleate. And nonionic surfactants. A good effect is acquired by containing these 5-30 mass% in an ink composition. Further, these water-soluble organic solvents are preferably used within a range of addition amounts that do not cause printing / image bleeding and paper loss (print-through).

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

-Surfactant-
The ink composition in the invention preferably contains at least one surfactant. The surfactant is used as a surface tension adjusting agent. Examples of the surface tension adjusting agent include nonionic surfactants, cationic surfactants, anionic surfactants, betaine surfactants, and the like. In the present invention, from the viewpoint of aggregation rate, an anionic surfactant or a nonionic surfactant is preferable, and an anionic surfactant is more preferable.

  The surfactant preferably contains an amount capable of adjusting the surface tension of the ink composition to 25 mN / m or more and 40 mN / m or less in order to perform good droplet ejection by the inkjet method. Among them, the content of the surfactant is preferably an amount capable of adjusting the surface tension to 27 to 37 mN / m.

  These surface tension modifiers can also be used as antifoaming agents, and fluorine compounds, silicone compounds, chelating agents represented by EDTA, and the like can also be used.

-Other additives-
The ink composition in the invention may further contain other additives in addition to the above components. Examples of other additives include antifading agents, emulsion stabilizers, penetration enhancers, ultraviolet absorbers, antiseptics, antifungal agents, pH adjusters, antifoaming agents, viscosity modifiers, dispersants, and dispersion stabilizers. And known additives such as rust preventives and chelating agents. These various additives may be added directly after the ink composition is prepared, or may be added when the ink composition is prepared.

  As the pH adjuster, a neutralizer (organic base, inorganic alkali) can be used. From the viewpoint of improving the storage stability of the ink composition, the pH adjuster is preferably added so that the pH of the ink composition is 6 to 10, and more preferably added so that the pH is 7 to 10. .

The viscosity of the ink composition in the present invention is preferably in the range of 1 to 30 mPa · s, and preferably 1 to 20 mPa, from the viewpoint of ejection stability when ejected by an inkjet method and the aggregation rate when using a reaction liquid described later. -The range of s is more preferable, the range of 2-15 mPa * s is further more preferable, and the range of 2-10 mPa * s is especially preferable.
The viscosity is measured using a VISCOMETER TV-22 (manufactured by TOKI SANGYO CO. LTD) under conditions of 25 ° C. of the ink composition.

  The ink composition in the present invention includes a pigment coated with a polymer dispersant having a carboxyl group, and polymer particles, and has a solid content of 7 to 10% by mass, and a solid content other than the pigment relative to the pigment. The content ratio is preferably 0.8 to 1.6, and includes a pigment coated with an acrylic polymer and self-dispersing polymer particles, and has a solid content of 7 to 9% by mass. It is more preferable that the solid content other than the pigment is 1.0 to 1.4.

(Reaction solution)
The ink set for inkjet recording of the present invention contains at least one reaction solution. The reaction liquid in the present invention causes the ink composition to aggregate when it comes into contact with the ink composition.
As a result, it is possible to increase the speed of ink jet recording, and it is possible to form an image with high density and resolution even in high speed recording.

-Polyvalent organic acid, polyphosphoric acid and metaphosphoric acid-
The reaction liquid in the present invention contains at least one polyvalent organic acid and contains at least one polyphosphoric acid and metaphosphoric acid (hereinafter also referred to as a specific inorganic acid).
By including a compound selected from these acids as a component for aggregating the ink composition, the monochromatic dot diameter in the image portion formed using the ink composition and the secondary color dot diameter obtained by overprinting two colors are used. The difference is small, and as a result, each color is uniform and a homogeneous image can be drawn.
That is, with the above-described reaction liquid configuration, the difference between the dot diameter of the single color drawing and the dot diameter of the secondary color is small, and when the image is recorded using the ink composition, the image drawing property is excellent and the drawing is good. The physical intensity of the image is obtained.

  As the polyvalent organic acid, tartaric acid, DL-malic acid, maleic acid, 4-methylphthalic acid, glutaric acid, among others, in terms of the difference in dot diameter between the dot diameter of the single color drawing and the dot diameter of the secondary color And at least one organic acid selected from malonic acid (hereinafter also referred to as “specific organic acid”), and preferably contains at least one organic acid selected from maleic acid and DL-malic acid. Preferably it contains seeds.

In the present invention, the concentration of the polyvalent organic acid in the reaction solution is preferably 10 to 30% by mass in terms of the difference in dot diameter between the dot diameter of the single color drawing and the dot diameter of the secondary color, It is more preferably 12 to 28% by mass, and particularly preferably 15 to 25% by mass.
By setting the concentration of the polyvalent organic acid in the reaction solution in the range of 10 to 30% by mass, the difference between the dot diameter of the single color drawing and the dot diameter of the secondary color is small, and the image drawing property is excellent and good. The physical strength of the drawn image can be obtained.

Although the reaction liquid in the present invention contains the specific inorganic acid, the concentration of the specific inorganic acid in the reaction liquid is 1 to 20 in terms of the difference in dot diameter between the dot diameter of the single color drawing and the dot diameter of the secondary color. It is preferably mass%, more preferably 3 to 17 mass%, and particularly preferably 5 to 15 mass%.
By setting the concentration of the specific inorganic acid in the reaction solution in the range of 1 to 20% by mass, the difference between the dot diameter of the single color drawing and the dot diameter of the secondary color is small, the image drawing property is excellent, and the drawing is good. The physical intensity of the image is obtained.
In the present invention, since the reaction solution contains the polyvalent organic acid and at least one of polyphosphoric acid and metaphosphoric acid is used in combination, the coating amount of the flocculant can be reduced. Adhesion with the composition is also improved. In addition, when the ink composition is ejected onto the recording medium to which the reaction liquid is applied, the difference between the dot diameter of the single color drawing and the dot diameter of the secondary color can be reduced. A drawn image is obtained.

  In addition to the polyvalent organic acid and the specific inorganic acid, the reaction liquid in the present invention comprises other aggregating components, water, a water-soluble organic solvent, a surfactant, and other additives as necessary. be able to.

-Organic solvent-
The reaction solution in the present invention preferably contains at least one organic solvent, and is preferably an organic solvent (hereinafter also referred to as a water-soluble organic solvent) that dissolves 5 g or more in 100 g of water at 20 ° C.
As the water-soluble organic solvent, a water-soluble organic solvent that can be specifically contained in the ink composition described above can be used in the reaction liquid as well. Among these, from the viewpoint of curling suppression, polyalkylene glycol or a derivative thereof is preferable. Diethylene glycol monoalkyl ether, triethylene glycol monoalkyl ether, dipropylene glycol, tripropylene glycol monoalkyl ether, polyoxypropylene glyceryl ether, polyoxypropylene More preferably, it is at least one selected from oxyethylene polyoxypropylene glycol.
The content of the organic solvent in the reaction solution is not particularly limited, but from the viewpoint of curl suppression, it is preferably 1 to 30% by mass, more preferably 5 to 15% by mass with respect to the entire reaction solution. preferable.

-Surfactant-
The reaction solution in the present invention preferably contains at least one surfactant. The surfactant can be used as a surface tension adjusting agent. Examples of the surface tension adjusting agent include nonionic surfactants, cationic surfactants, anionic surfactants, betaine surfactants, and the like.
Among these, a nonionic surfactant or an anionic surfactant is preferable from the viewpoint of the aggregation rate of the ink composition.

  Specific examples of surfactants include fatty acid salts, alkyl sulfate esters, alkylbenzene sulfonates, alkyl naphthalene sulfonates, dialkyl sulfosuccinates, alkyl phosphate esters, naphthalene sulfonate formalin condensation in hydrocarbons Products, anionic surfactants such as polyoxyethylene alkyl sulfates, polyoxyethylene alkyl ethers, polyoxyethylene alkyl allyl ethers, polyoxyethylene fatty acid esters, sorbitan fatty acid esters, polyoxyethylene sorbitan fatty acid esters, polyoxy Nonionic surfactants such as ethylene alkylamine, glycerin fatty acid ester and oxyethyleneoxypropylene block copolymer are preferred. Further, SURFYNOLS (Air Products & Chemicals), which is an acetylene-based polyoxyethylene oxide surfactant, is also preferably used. An amine oxide type amphoteric surfactant such as N, N-dimethyl-N-alkylamine oxide is also preferred.

Furthermore, pages (37) to (38) of JP-A-59-157636, Research Disclosure No. The surfactants described in 308119 (1989) can also be used.
Further, fluorine (fluorinated alkyl type) surfactants, silicone type surfactants and the like described in JP-A Nos. 2003-322926, 2004-325707, and 2004-309806 are also included.

  The addition amount of the surfactant in the reaction solution is not particularly limited, but the addition amount is preferably such that the surface tension of the reaction solution is 40 mN / m or more, and the addition is 40 to 60 mN / m. The amount is more preferable, and the addition amount is more preferably 42 to 50 mN / m.

-Other aggregation components-
Unless the effect of this invention is impaired, the reaction liquid in this invention can contain another aggregation component in addition to the said polyvalent organic acid and specific inorganic acid. Examples of other flocculants include polyvalent metal salts and polyallylamine.
Examples of the polyvalent metal salt include alkaline earth metals belonging to Group 2 of the periodic table (eg, magnesium, calcium), transition metals belonging to Group 3 of the periodic table (eg, lanthanum), and cations from Group 13 of the periodic table. (For example, aluminum), salts of lanthanides (for example, neodymium), polyallylamine, and polyallylamine derivatives. As the metal salt, carboxylate (formic acid, acetic acid, benzoate, etc.), nitrate, chloride, and thiocyanate are suitable. Among them, preferred are calcium salts or magnesium salts of carboxylic acids (formic acid, acetic acid, benzoates, etc.), calcium salts or magnesium salts of nitric acid, calcium chloride, magnesium chloride, and calcium salts or magnesium salts of thiocyanic acid.
The content of the polyvalent metal salt in the reaction solution can be, for example, 1 to 10% by mass.

-Other additives-
The reaction liquid in the present invention can be configured to contain other additives in addition to the above components. Other additives in the reaction liquid are the same as other additives in the ink composition.

There is no restriction | limiting in particular as surface tension of the said reaction liquid, For example, it can be 40 mN / m or more. Among these, from the viewpoint of suppressing the occurrence of curling in the recording medium, it is more preferably 40 to 60 mN / m, more preferably 42 to 50 mN / m, and further preferably 42 to 47 mN / m.
The surface tension of the reaction solution can be adjusted, for example, by adding a surfactant. Further, the surface tension of the reaction solution is measured under a condition of 25 ° C. by a plate method using an Automatic Surface Tensiometer CBVP-Z (manufactured by Kyowa Interface Science Co., Ltd.).

The reaction liquid in the present invention preferably has a pH (25 ° C. ± 1 ° C.) of 3.5 or less, more preferably 0.5 to 2.5, from the viewpoint of the aggregation rate of the ink composition. More preferably, it is 0.5 to 2.0.
The viscosity of the reaction liquid is preferably in the range of 1 to 30 mPa · s, more preferably in the range of 1 to 20 mPa · s, and still more preferably in the range of 2 to 15 mPa · s, from the viewpoint of the aggregation rate of the ink composition. A range of 2 to 10 mPa · s is particularly preferable. In addition, a viscosity is measured on 25 degreeC conditions using VISCOMETER TV-22 (product made from TOKI SANGYO CO.LTD).

  The reaction solution in the present invention contains 10 to 30% by mass of an organic acid selected from tartaric acid, DL-malic acid, maleic acid, 4-methylphthalic acid, glutaric acid, and malonic acid, and contains at least the specific inorganic acid. 1 type is contained and it is preferable that pH is 0.5-2.5 or less, and at least 1 sort (s) of the organic acid chosen from maleic acid and DL-malic acid is 12-28 mass% ( More preferably, the content is 15 to 25% by mass), and the pH is more preferably 0.5 to 2.0 or less.

<Inkjet image recording method>
The inkjet image recording method of the present invention includes a reaction liquid application step of applying a reaction liquid containing a polyvalent organic acid and containing at least one of polyphosphoric acid or metaphosphoric acid onto a recording medium, and a pigment. An ink droplet ejecting step of ejecting the ink composition onto the recording medium provided with the reaction liquid by an ink jet method.
By forming an image by the inkjet image recording method having such a configuration, it is possible to provide a homogeneous image having excellent dot physical strength and a uniform dot diameter.

(Reaction solution application process)
The reaction liquid application step is a step of applying the above-described reaction liquid capable of forming an aggregate when it comes into contact with the ink composition onto the recording medium, and bringing the ink composition and the reaction liquid into contact for imaging. It can be set as the structure to do. In this case, when the reaction liquid comes into contact with, for example, an ink composition containing pigment particles, the dispersed particles containing the pigment particles in the ink composition aggregate to fix the image on the recording medium.
Details and preferred embodiments of the reaction solution are as described above.

  The application of the reaction solution can be performed by applying a known method such as a coating method, an ink jet method, or an immersion method. As a coating method, a known coating method using a bar coater, an extrusion die coater, an air doctor coater, a bread coater, a rod coater, a knife coater, a squeeze coater, a reverse roll coater, a bar coater or the like can be used. Details of the inkjet method will be described later.

  The reaction liquid application step is provided before the ink droplet ejection step using the ink composition. That is, before the ink composition is deposited on the recording medium, a reaction liquid for aggregating the pigment in the ink composition is applied in advance, and the reaction liquid applied on the recording medium is brought into contact with the recording medium. The ink composition is dropped into an image. Thereby, inkjet recording can be speeded up, and an image with high density and resolution can be obtained even at high speed recording.

  In the present invention, there is further provided a heat drying step for heating and drying the reaction liquid on the recording medium after the reaction liquid is applied on the recording medium and before the ink composition is applied. By heating and drying the reaction liquid in advance before the ink droplet ejection step, ink coloring properties such as bleeding prevention are improved, and a visible image with good color density and hue can be recorded.

  Heating and drying can be performed by a known heating means such as a heater, a blowing means using blowing air such as a dryer, or a combination of these. As the heating method, for example, a method of applying heat with a heater or the like from the side opposite to the reaction liquid application surface of the recording medium, a method of applying warm air or hot air to the reaction liquid application surface of the recording medium, or an infrared heater was used. The heating method etc. are mentioned, You may heat combining these two or more.

(Ink droplet ejection process)
In the ink droplet ejection step, the above-described ink composition is applied onto the recording medium to which the reaction liquid is applied by an inkjet method. In this step, the ink composition can be applied on the recording medium, and a desired visible image can be formed. The details of the ink composition are as described above.

The inkjet method is not particularly limited, and is a known method, for example, a charge control method that discharges ink using electrostatic attraction, a drop-on-demand method (pressure pulse method) that uses vibration pressure of a piezoelectric element, an electric method An acoustic ink jet system that converts a signal into an acoustic beam, irradiates the ink with ink and ejects the ink using radiation pressure, and a thermal ink jet (bubble jet (registered trademark)) that heats the ink to form bubbles and uses the generated pressure. )) Any method may be used. As an ink jet method, in particular, the method described in Japanese Patent Application Laid-Open No. Sho 54-59936 causes an abrupt volume change of the ink subjected to the action of thermal energy, and the ink is ejected from the nozzle by the action force due to this state change. Ink jet method can be used effectively.
The ink jet method includes a method of ejecting many low-density inks called photo inks in a small volume, a method of improving image quality using a plurality of inks having substantially the same hue and different concentrations, and colorless and transparent inks. The method using is included.

Further, the ink jet head used in the ink jet method may be an on-demand method or a continuous method. In addition, as a discharge method, an electro-mechanical conversion method (for example, a single cavity type, a double cavity type, a bender type, a piston type, a shear mode type, a shared wall type, etc.), an electro-thermal conversion method (for example, a thermal type) Specific examples include an ink jet type, a bubble jet (registered trademark) type, an electrostatic attraction type (for example, an electric field control type, a slit jet type, etc.) and a discharge type (for example, a spark jet type). However, any discharge method may be used.
There are no particular restrictions on the ink nozzles used when recording by the ink jet method, and they can be appropriately selected according to the purpose.

As an inkjet head, a single serial head is used, and a shuttle system that performs recording while scanning the head in the width direction of the recording medium, and a line in which recording elements are arranged corresponding to the entire area of one side of the recording medium. There is a line system using a head. In the line system, an image can be recorded on the entire surface of the recording medium by scanning the recording medium in a direction orthogonal to the arrangement direction of the recording elements, and a carriage system such as a carriage for scanning a short head is not necessary. Further, since complicated scanning control of the carriage movement and the recording medium is not required and only the recording medium moves, the recording speed can be increased as compared with the shuttle system.
The ink jet image recording method of the present invention can be applied to any of these, but generally, when applied to a line system that does not use a dummy jet, the effect of improving ejection accuracy and image scratch resistance is great.

The ink droplet ejection step in the present invention is preferably started within 10 seconds after the reaction liquid application step, and more preferably within 0.1 seconds to 10 seconds. Thereby, an image can be recorded at high speed. In the inkjet image recording method of the present invention, by using the above-described ink set for inkjet recording, even when an image is recorded at high speed, landing interference can be suppressed and a high-definition image can be formed.
Here, “starts within 10 seconds after the reaction liquid application step” means that the time from the completion of application / drying of the reaction liquid to the first ink droplet landing on the recording medium is within 10 seconds. Means.

Further, in the ink droplet ejection step in the present invention, from the viewpoint of high-definition printing, it is preferable that the amount of ink droplets ejected is 1.5 to 3.0 pL, and 1.5 to 2.5 pL. It is more preferable.
The amount of ink droplets can be adjusted by appropriately selecting the ejection conditions in the ink jet method according to the ink composition to be ejected.

Furthermore, the ink droplet ejection step in the present invention includes 50 halftone dots (monochromatic dot diameter) drawn as single color dots of one ink composition and a solid image on the solid image of the other one ink composition. About 50 secondary color dots (dots of two-color overprinted dots) in which the above-mentioned one ink composition is ejected in a dot shape and overprinted with dots, the dots of the single-color dot diameter and the dots of two-color overprinted dots The smaller the difference in diameter (Δdot diameter), the more uniform the dot diameter of each color and the more preferable it is possible to draw a uniform image. It is a practical level that the Δ dot diameter is 3 μm or less, more preferably 2 μm or less, and still more preferably 0 to 1 μm.
The dot diameter is obtained by measuring the equivalent circle diameter using a dot analyzer DA-6000 manufactured by Oji Scientific Instruments Co., Ltd., and measuring the average value of 50 dots as the dot diameter.

-Recording media-
The inkjet image recording method of the present invention records an image on a recording medium.
The recording medium is not particularly limited, and general printing paper mainly composed of cellulose, such as so-called high-quality paper, coated paper, and art paper, used for general offset printing and the like can be used. General printing paper mainly composed of cellulose is relatively slow in ink absorption and drying in image recording by a general ink jet method using water-based ink, and color material movement is likely to occur after droplet ejection, and image quality is likely to deteriorate. However, according to the inkjet image recording method of the present invention, it is possible to record a high-quality image excellent in color density and hue by suppressing the movement of the coloring material.

  As the recording medium, commercially available media can be used. For example, “OK Prince fine quality” manufactured by Oji Paper Co., Ltd., “Shiorai” manufactured by Nippon Paper Industries Co., Ltd., and Nippon Paper Industries ( Fine coated paper such as “New NPI fine quality” manufactured by Co., Ltd., “OK Everlight Coat” manufactured by Oji Paper Co., Ltd., and “Aurora S” manufactured by Nippon Paper Industries Co., Ltd., Oji Lightweight coated paper (A3) such as “OK Coat L” manufactured by Paper Industries Co., Ltd. and “Aurora L” manufactured by Nippon Paper Industries Co., Ltd. “OK Top Coat +” manufactured by Oji Paper Co., Ltd. and Nippon Paper Industries Co., Ltd. ) Coated paper (A2, B2) such as “Aurora Coat” manufactured by Oji Paper Co., Ltd. Art paper (A1) such as “OK Kanfuji +” manufactured by Oji Paper Co., Ltd. Is mentioned. It is also possible to use various photographic papers for ink jet recording.

Among these, from the viewpoint of obtaining a high-quality image having a large color material movement suppression effect and better color density and hue than before, the water absorption coefficient Ka is preferably 0.05 to 0.5. a recording medium mL ^/ m 2 ^{· ms 1/2,} more preferably recording medium 0.1~0.4mL ^/ m 2 ^{· ms 1/2,} more preferably 0.2-0.3 ml / It is a recording medium of m ² · ms ^1/2 .

  The water absorption coefficient Ka is synonymous with that described in JAPAN TAPPI paper pulp test method No. 51: 2000 (issued by Japan Paper Pulp Technology Association). Specifically, the absorption coefficient Ka is an automatic scanning absorption meter. It is calculated from the difference in the amount of water transferred between the contact time of 100 ms and the contact time of 900 ms using KM500Win (manufactured by Kumagai Riki Co., Ltd.).

  In the present invention, the application amount of the treatment liquid and the application amount of the water-based ink are preferably adjusted as necessary. For example, the application amount of the treatment liquid may be changed according to the recording medium in order to adjust the physical properties such as the viscoelasticity of the aggregate formed by mixing the treatment liquid and the water-based ink.

  The present invention will be described more specifically with reference to the following examples. The scope of the present invention is not limited to the specific examples shown below. Unless otherwise specified, “part” and “%” are based on mass.

  The weight average molecular weight was measured by gel permeation chromatography (GPC). GPC uses HLC-8020GPC (manufactured by Tosoh Corporation), TSKgel, Super Multipore HZ-H (manufactured by Tosoh Corporation, 4.6 mm ID × 15 cm) as columns, and THF (tetrahydrofuran) as an eluent. ) Was used. The conditions were as follows: the sample concentration was 0.45 mass%, the flow rate was 0.35 ml / min, the sample injection amount was 10 μl, the measurement temperature was 40 ° C., and an IR detector was used. In addition, the calibration curve is “standard sample TSK standard, polystyrene” manufactured by Tosoh Corporation: “F-40”, “F-20”, “F-4”, “F-1”, “A-5000”, It produced from eight samples of "A-2500", "A-1000", and "n-propylbenzene".

(Synthesis of polymer dispersant P-1)
According to the following scheme, a polymer dispersant P-1 was synthesized as shown below.

To a 1000 ml three-necked flask equipped with a stirrer and a condenser, 88 g of methyl ethyl ketone was added and heated to 72 ° C. in a nitrogen atmosphere. Then, a solution in which 10 g of methacrylic acid and 30 g of methyl methacrylate were dissolved was dropped over 3 hours. After completion of the dropwise addition, the reaction was further continued for 1 hour, and then a solution of 0.42 g of dimethyl 2,2′-azobisisobutyrate in 2 g of methyl ethyl ketone was added, heated to 78 ° C. and heated for 4 hours. The obtained reaction solution was reprecipitated twice in a large excess amount of hexane, and the precipitated resin was dried to obtain 96 g of a polymer dispersant P-1.
The composition of the obtained resin was confirmed by ¹ H-NMR, and the weight average molecular weight (Mw) determined by GPC was 44,600. Furthermore, when the acid value was calculated | required by the method as described in JIS specification (JISK0070: 1992), it was 65.2 mgKOH / g.

<Preparation of pigment dispersion>
(Preparation of cyan dispersion)
Pigment Blue 15: 3 (phthalocyanine bull-A220, manufactured by Dainichi Seika Co., Ltd.), 5 parts of the polymer dispersant P-1, 42 parts of methyl ethyl ketone, 5.5 parts of 1N NaOH aqueous solution, 87.2 parts of ion-exchanged water was mixed and dispersed with a bead mill using 0.1 mmφ zirconia beads for 2 to 6 hours.
After removing methyl ethyl ketone at 55 ° C. under reduced pressure and further removing a part of water, the obtained dispersion was further used with a high-speed centrifugal cooler 7550 (manufactured by Kubota Seisakusho), using a 50 mL centrifuge tube, Centrifugation was performed at 8000 rpm for 30 minutes, and the supernatant liquid other than the precipitate was collected. Thereafter, the pigment concentration was determined from the absorbance spectrum, and a dispersion (cyan dispersion C) of resin-coated pigment particles (pigment coated with a polymer dispersant) having a pigment concentration of 10.2% by mass was obtained. The average particle size of the obtained Cyan Dispersion C was 105 nm.

(Preparation of magenta dispersion)
In the preparation of the cyan dispersion, a resin was prepared in the same manner as the preparation of the cyan dispersion except that Pigment Red 122 was used instead of Pigment Blue 15: 3 (Phthalocyanine-A220, manufactured by Dainichi Seika Co., Ltd.). A dispersion (magenta dispersion M) of coated pigment particles (pigment coated with a polymer dispersant) was prepared. The average particle size of the obtained magenta dispersion M was 85 nm.

(Preparation of yellow dispersion)
In the preparation of the cyan dispersion, resin-coated pigment particles (in the same manner as described above) except that Yellow Pigment Pigment Yellow 74 was used instead of Pigment Blue 15: 3 (Phthalocyanine-A220, manufactured by Dainichi Seika Co., Ltd.) A dispersion (pigment coated with polymer dispersant) (yellow dispersion Y) was prepared. The average particle size of the obtained yellow dispersion Y was 82 nm.

(Preparation of black dispersion)
In the preparation of the cyan dispersion, the same method was used except that carbon black (NIPEX 160-IQ, manufactured by Degussa) was used instead of Pigment Blue 15: 3 (Phthalocyanine-A220, manufactured by Dainichi Seika Co., Ltd.). A dispersion (black dispersion K) of resin-coated pigment particles (pigment coated with a polymer dispersant) was prepared. The average particle size of the obtained black dispersion K was 130 nm.

[Preparation of self-dispersing polymer particles]
-Synthesis Example 1
360.0 g of methyl ethyl ketone was charged into a 2-liter three-necked flask equipped with a stirrer, a thermometer, a reflux condenser, and a nitrogen gas inlet tube, and the temperature was raised to 75 ° C. While maintaining the temperature in the reaction vessel at 75 ° C., 180.0 g of phenoxyethyl acrylate, 162.0 g of methyl methacrylate, 18.0 g of acrylic acid, 72 g of methyl ethyl ketone, and “V-601” (manufactured by Wako Pure Chemical Industries, Ltd.) A mixed solution consisting of 44 g was added dropwise at a constant speed so that the addition was completed in 2 hours. After completion of the dropwise addition, a solution consisting of 0.72 g of “V-601” and 36.0 g of methyl ethyl ketone was added, stirred for 2 hours at 75 ° C., and then a solution consisting of 0.72 g of “V-601” and 36.0 g of isopropanol was added. After stirring at 75 ° C. for 2 hours, the temperature was raised to 85 ° C., and stirring was further continued for 2 hours. The weight average molecular weight (Mw) of the obtained copolymer was 64000 (calculated in terms of polystyrene by gel permeation chromatography (GPC), columns used were TSKgel SuperHZM-H, TSKgel SuperHZ4000, TSKgel SuperHZ200 (manufactured by Tosoh Corporation)), The acid value was 38.9 (mgKOH / g).
Next, 668.3 g of the polymerization solution was weighed, 388.3 g of isopropanol and 145.7 ml of 1 mol / L NaOH aqueous solution were added, and the temperature in the reaction vessel was raised to 80 ° C. Next, 720.1 g of distilled water was added dropwise at a rate of 20 ml / min to disperse in water. Thereafter, the temperature in the reaction vessel was maintained at 80 ° C. for 2 hours, 85 ° C. for 2 hours, and 90 ° C. for 2 hours under atmospheric pressure, and then the reaction vessel was depressurized, and isopropanol, methyl ethyl ketone, and distilled water totaled 913. 7 g was distilled off to obtain an aqueous dispersion (emulsion) of self-dispersing polymer fine particles (B-01) having a solid content concentration of 28.0%. In addition, the number of each structural unit of the compound example (B-01) shown below represents a mass ratio. Hereinafter, the same applies to each structural formula.

<Preparation of ink>
Using the pigment dispersion (cyan dispersion C, magenta dispersion M, yellow dispersion Y, black dispersion K, and self-dispersing polymer particles B-01) obtained above, An ink composition was prepared by mixing the components, and the prepared ink composition was filtered with a plastic disposable syringe through a PVDF 5 μm filter (Millex SV, Millipore, diameter 25 mm) to obtain a finished ink.
About each color ink, pH was measured using the Toa DKK Co., Ltd. pH meter WM-50EG. Moreover, surface tension was measured by Kyowa Interface Science Co., Ltd. FASE Automatic Surface Tensionmeter CBVP-Z. The results are shown in Table 1.

<Preparation of reaction solution>
(Reaction solution 1)
The following materials were mixed to prepare Reaction Solution 1.
・ DL-malic acid 29.0g
・ Anionic surfactant A (10%) 0.2g
・ New Pole GP-250 (manufactured by Sanyo Chemical Co., Ltd.) 10.0 g
・ Ion exchange water 60.8g
When the pH was measured with a pH meter WM-50EG manufactured by Toa DDK Co., Ltd., the pH value was 0.97. Moreover, it was 44.3 mN / m when surface tension was measured in Kyowa Interface Science Co., Ltd. product FASE Automatic Surface Tensionmeter CBVP-Z.
The structure of the anionic surfactant A used in the reaction solution is shown below.

(Reaction solution 2)
The following materials were mixed to prepare Reaction Solution 2.
・ DL-malic acid 14.5g
・ Anionic surfactant A (10%) 0.2g
・ New Pole GP-250 (manufactured by Sanyo Chemical Co., Ltd.) 10.0 g
・ Ion-exchanged water 75.3g
The pH and surface tension were measured in the same manner as in the reaction solution 1. The pH value was 1.63, and the surface tension was 42.2 mN / m.

(Reaction solution 3)
The following materials were mixed to prepare a reaction solution 3.
・ DL-malic acid 14.5g
・ Phosphoric acid (85%) 12.5g
・ Anionic surfactant A (10%) 0.1g
・ New Pole GP-250 (manufactured by Sanyo Chemical Co., Ltd.) 10.0 g
・ Ion exchange water 62.8g
The pH and surface tension were measured in the same manner as in the reaction solution 1. The pH value was 0.62, and the surface tension was 40.7 mN / m.

(Reaction solution 4)
The following materials were mixed to prepare a reaction solution 4.
・ DL-malic acid 14.5g
-Polyphosphoric acid 8.7g
・ Anionic surfactant A (10%) 0.1g
・ New Pole GP-250 (manufactured by Sanyo Chemical Co., Ltd.) 10.0 g
・ Ion exchange water 66.7g
The pH and surface tension were measured in the same manner as in the reaction solution 1. The pH value was 0.41, and the surface tension was 41.0 mN / m.

(Reaction solution 5)
The following materials were mixed to prepare a reaction solution 5.
・ DL-malic acid 14.5g
・ Metaphosphoric acid (37%) 8.7g
・ Anionic surfactant A (10%) 0.1g
・ New Pole GP-250 (manufactured by Sanyo Chemical Co., Ltd.) 10.0 g
・ Ion exchange water 66.7g
The pH and surface tension were measured in the same manner as in the reaction solution 1. The pH value was 0.80, and the surface tension was 40.3 mN / m.

(Reaction liquid 6)
The following materials were mixed to prepare a reaction solution 6.
・ DL-malic acid 14.5g
・ Metaphosphoric acid (37%) 8.7g
・ Anionic surfactant A (10%) 0.1g
・ Diethylene glycol monobutyl ether 2.5g
・ Tripropylene glycol monomethyl ether 7.5g
・ Ion exchange water 66.7g
The pH and surface tension were measured in the same manner as in the reaction solution 1. The pH value was 0.89, and the surface tension was 41.2 mN / m.

(Reaction solution 7)
The following materials were mixed to prepare a reaction solution 7.
・ DL-malic acid 23.18g
・ Metaphosphoric acid (37%) 3.46 g
・ Anionic surfactant A (10%) 0.2g
・ New Pole GP-250 (manufactured by Sanyo Chemical Co., Ltd.) 10.0 g
・ Ion exchange water 63.36g
The pH and surface tension were measured in the same manner as in the reaction solution 1. The pH value was 0.92, and the surface tension was 40.9 mN / m.

(Reaction liquid 8)
The following materials were mixed to prepare a reaction solution 8.
・ DL-malic acid 23.2g
・ 1mol-sulfuric acid 10.8g
・ Anionic surfactant A (1%) 0.2g
・ New Pole GP-250 (manufactured by Sanyo Chemical Co., Ltd.) 10.0 g
・ Ion exchange water 55.8g
The pH and surface tension were measured in the same manner as in the reaction solution 1. The pH value was 0.33, and the surface tension was 41.0 mN / m.

(Reaction liquid 9-12, 14-16)
Reaction liquids 9 to 12 and 14 to 16 were prepared in the same manner as in the reaction liquid 6 except that DL-malic acid in the reaction liquid 6 was replaced with the acid species and mol amount shown in Table 2.
The pH and surface tension were measured in the same manner as in the reaction solution 1. Each pH value is as shown in the table. The surface tension was 41.7-43.0 mN / m.

(Reaction solution 13)
The following materials were mixed to prepare a reaction solution 13.
・ Polyphosphoric acid 17.3g
・ Anionic surfactant A (1%) 0.1g
・ New Pole GP-250 (manufactured by Sanyo Chemical Co., Ltd.) 10.0 g
・ Ion exchange water 66.7g
The pH and surface tension were measured in the same manner as in the reaction solution 1. The pH value was 0.33, and the surface tension was 37.2 mN / m.

<Inkjet image recording>
Using A4 size Tokuhishi art (manufactured by Mitsubishi Paper Industries) as a recording medium, the reaction liquid and ink shown in Table 1 below were combined and an image was drawn and recorded under the following image recording conditions.
Ink droplet ejection was started within 10 seconds after the reaction liquid application step.

-Reaction liquid application process-
Immediately before ink drawing on the medium, the reaction liquid shown in Table 1 was applied to the surface of the medium so as to be 1.7 g / m ² using a coating bar.

Next, the recording medium provided with the reaction liquid was dried under the following conditions.
-Drying conditions for reaction liquid (fan drying)-
Wind speed: 15m / s
Temperature: The recording medium was heated from the back side of the recording surface with a contact type flat heater so that the surface temperature of the recording medium was 60 ° C.
Air blowing area: 450 mm (drying time 0.7 seconds)

-Ink drop process-
Using the cyan pigment ink C, magenta pigment ink M, yellow pigment ink Y, and black pigment ink K obtained above as the ink composition, four-color single-pass image formation was performed under the following conditions.
The ink composition was applied on the recording medium to which the reaction solution was applied under the following conditions.
Head: 1,200 dpi / 20 inch wide piezo full line heads were arranged for four colors.
The amount of ejected droplets was 2.4 pL.
Drive frequency: 30 kHz (recording medium conveyance speed 635 mm / sec)
Ink application is as follows: (1) Yellow pigment ink Y is drawn as halftone dots, (2) First, cyan pigment ink C is drawn as a uniform solid image, and then yellow pigment ink Y is the same as (1). Drawing was performed as halftone dots under the conditions, and Y dot images on Y single color dots and cyan solids were obtained.

Next, the recording medium provided with ink was dried under the following conditions.
--Drying conditions for ink (air drying)-
Wind speed: 15m / s
Temperature: The recording medium was heated from the back side of the recording surface with a contact type flat heater so that the surface temperature of the recording medium was 60 ° C.
Air blowing area: 640 mm (drying time 1 second)

Next, a heat fixing process was performed under the following conditions to prepare a sample in which an image was formed on a recording medium.
--Fixing--
Silicone rubber roller (hardness 50 °, nip width 5mm)
Roller temperature: 90 ° C
Pressure: 0.8 MPa

<Evaluation>
1. Evaluation of drawing dot diameter Dot analyzer made by Oji Scientific Instruments Co., Ltd. for 50 halftone dots drawn as monochromatic yellow dots and 50 secondary color dots with halftone dots overlaid on a cyan solid image The equivalent circle diameter was measured using DA-6000, and the average value of 50 dots was taken as the dot diameter.
The smaller the difference (Δ dot diameter) between the single color dot diameter and the dot diameter of the two-color overprinted dots, the more uniform the dot diameters of the respective colors, and the more homogeneous images can be drawn. In particular, the Δ dot diameter is 3 μm or less (practical level), more preferably 1 μm to 2 μm, and still more preferably 0 to less than 1 μm.

2. 2. Evaluation of abrasion resistance and tape peelability of drawn image 2-1. Evaluation of abrasion resistance of drawn image For the recording medium on which the secondary color produced in the evaluation of the drawing dot diameter is drawn, the recording medium which has not been drawn is applied 10 times with a weight of 240 g / cm ² after the drawing and drying at room temperature and humidity for 1 day. The degree of ease of scratching the drawn image at that time was examined. Evaluation was made according to the following criteria.
<Evaluation criteria>
A: The level where the rubbed part is not scratched is the same as the non-rubbed part.
B: The surface of the rubbed part is slightly scratched, but the image is not damaged and has no problem.
C: The surface of the rubbed part is slightly peeled off, extremely fine scratches are seen, and the practical lower limit level.
D: The ink is peeled off and the white background of the medium is partially exposed, which is not practical.

2-2. Evaluation of tape peelability of drawn image When the cellophane (registered trademark) is pasted on the secondary color solid image portion of the recording medium on which the secondary color produced in the drawing dot diameter evaluation has been drawn for 2 days, and then peeled off immediately after the cellophane (registered trademark) is applied. The degree of ink peeling of the drawn image was evaluated. The evaluation criteria were 1 for almost all peeling and 5 for no peeling at all, and a five-step evaluation was performed according to the degree of peeling during that time.
<Evaluation criteria>
5: Not peeled off 4: As an image, peeling is not known, but the adhesive surface of the peeled tape is slightly colored.
3: When looked closely, a white background can be seen slightly, and a slight color can be seen on the adhesive surface of the peeled tape (practical limit).
2: Many white spot-like peelings are visually observed in the drawn image, and the level is not practical.
1: The entire surface peeled and the paper background was exposed.

  From the results in Table 2, the reaction solution No. In the comparative example using 1 to 3, 8, and 13, the difference (Δ dot diameter) between the single color dot diameter and the secondary color dot diameter is large. On the other hand, in the Example which satisfy | fills the structure of this invention using the samples 4-7, 9-12, and 14-16, all can make the dot diameter difference ((DELTA) dot diameter) of a single color and a secondary color small. I understand. It can also be seen that the physical strength of the drawn image is good in the example satisfying the configuration of the present invention.

Claims (10)

An ink set for ink-jet recording, comprising: an ink composition containing at least a pigment; and a reaction liquid containing a polyvalent organic acid and at least one of polyphosphoric acid and metaphosphoric acid. The polyvalent organic acid contained in the reaction solution contains at least one selected from tartaric acid, DL-malic acid, maleic acid, 4-methylphthalic acid, glutaric acid, and malonic acid. Item 2. An ink set for inkjet recording according to Item 1. The ink set for ink jet recording according to claim 1 or 2, wherein the concentration of the polyvalent organic acid is 10 to 30% by mass with respect to the total mass in the reaction solution. The ink set for inkjet recording according to any one of claims 1 to 3, wherein the reaction solution contains 1 to 30% by mass of an organic solvent based on the total mass. The ink set for inkjet recording according to any one of claims 1 to 4, wherein the pH of the reaction solution is 3.5 or less. The ink set for inkjet recording according to claim 5, wherein the pH of the reaction solution is 0.5 to 2.5. The ink set for inkjet recording according to any one of claims 1 to 6, wherein the reaction liquid contains an anionic surfactant or a nonionic surfactant. A reaction liquid application step of applying a reaction liquid containing a polyvalent organic acid and at least one of polyphosphoric acid and metaphosphoric acid onto a recording medium, and an ink composition containing a pigment were applied to the reaction liquid. An ink jet image recording method comprising: an ink droplet ejection step of ejecting ink onto a recording medium by an ink jet method. 9. The ink jet image recording method according to claim 8, wherein the ink droplet ejection step starts the droplet ejection within 10 seconds after the reaction liquid application step. 10. The ink jet image recording method according to claim 8, wherein in the ink droplet ejection step, ink droplet ejection is performed with a droplet amount of 1.5 to 3.0 pL.