JP5523687B2 - Ink set for inkjet recording and inkjet image recording method - Google Patents

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). In addition, an ink set comprising a pigment ink having a solid content of 4.2 to 8.5% by mass and a treatment liquid containing a polyvalent metal salt is disclosed (for example, see Patent Document 2).
JP 2007-261206 A JP 2005-22329 A

However, in the ink sets described in Patent Documents 1 to 25, the glossiness of the formed image changes depending on the image density, so the glossiness of the image is partially different, and the image quality as a whole image is sufficient. It was hard to say. Further, depending on the solid content concentration of the ink, stickiness derived from the processing liquid component may occur, and an improvement has been desired.
An object of the present invention is to provide an ink set for ink jet recording capable of obtaining uniform glossiness from low to high image density and suppressing the occurrence of stickiness in the image area, and an ink jet recording method using the same. And

Specific means for solving the above problems are as follows.
<1> at least a pigment and a surface comprising an active agent and an organic solvent and a self-dispersing polymer particles and water, the ink composition solids content of from 7 to 10 wt%, D L-malic acid, and 4- An ink set for inkjet recording, comprising: a reaction liquid containing at least one organic acid selected from methylphthalic acid .

<2> The ink set for ink jet recording according to <1>, wherein the ink composition has a solid content ratio other than the pigment to the pigment of 0.8 to 1.6.
<3> The ink set for inkjet recording according to <1> or <2>, wherein the ink composition has a solid content ratio other than the pigment to the pigment of 1.0 to 1.4.

<4> The ink set for ink jet recording according to any one of <1> to <3>, wherein the reaction liquid has a content of the organic acid of 15 to 40% by mass.
<5> The ink set for inkjet recording according to any one of <1> to <4>, wherein the reaction liquid further includes a water-soluble organic solvent having a content rate of 1 to 30% by mass.

<6> The ink set for ink-jet recording according to any one of <1> to <5>, wherein the reaction solution has a pH of 3.5 or less.
<7> The ink set for inkjet recording according to any one of <1> to <6>, wherein the reaction solution has a pH of 0.5 to 2.5.
<8> The ink set for inkjet recording according to any one of <1> to <7>, wherein the reaction liquid further contains an anionic surfactant or a nonionic surfactant.

<9> D L-malic acid, and 4 a reaction solution containing at least one organic acid selected from among methyl phthalic acid, a reaction liquid applying step is applied onto the recording medium, drying, and at least a pigment An ink composition containing a surfactant, an organic solvent, self-dispersing polymer particles, and water and having a solid content of 7 to 10% by mass on a recording medium to which the reaction solution is applied is obtained by an inkjet method. An ink jet image recording method comprising: an ink droplet ejecting step for ejecting droplets.

<10> The inkjet image recording method according to <9>, wherein the ink droplet ejection step is started within 10 seconds after the reaction liquid application step.
<11> The inkjet image recording method according to <9> or <10>, wherein the ink droplet ejection step has a droplet amount of an ink droplet ejected of 1.5 to 3.0 pL.
<12> In the ink droplet ejection step, the ratio of the diameter of the pixel dots formed on the recording medium by one ink droplet to the diameter of the ink droplet is 1.7 to 2.0. <9> The inkjet image recording method of any one of-<11>.

  According to the present invention, there are provided an ink set for ink jet recording capable of obtaining uniform glossiness from low to high image density and suppressing the occurrence of stickiness in an image portion, and an ink jet recording method using the same. Can do.

<Ink set for inkjet recording>
The ink set for inkjet recording of the present invention comprises at least one ink composition containing at least a pigment and having a solid content of 7 to 10% by mass, tartaric acid, DL-malic acid, maleic acid, 4-methylphthalic acid. And at least one reaction solution containing at least one organic acid selected from glutaric acid.
By forming an image using an ink set having such a configuration, from a low image density (low halftone dot%) to an intermediate density part (intermediate halftone dot%) and a high density part (high halftone dot%). (Particularly in the middle density area), uniform glossiness can be obtained, and the occurrence of stickiness in the image area derived from the processing liquid components can be suppressed, so that a high-quality image can be formed as a whole. Can do.
However, in the present invention, at least a pigment, a surfactant, an organic solvent, self-dispersing polymer particles, and water are applied as the ink composition, and DL-malic acid and 4 are used as the reaction liquid. -Those containing at least one organic acid selected from methylphthalic acid are applied.

(Ink composition)
The ink composition in the present invention contains at least one pigment as a water-insoluble colorant and has a solid content of 7 to 10% by mass. With this configuration, a uniform gloss level that does not depend on the density of the formed image can be obtained.
In addition, the ink composition may include a pigment dispersant, polymer particles, a water-soluble organic solvent, a surfactant, water, and other components as necessary.

The solid content of the ink composition in the present invention is 7 to 10% by mass, and more preferably 7 to 9% by mass from the viewpoint of obtaining uniform gloss.
When the solid content of the ink composition exceeds 10% by mass, when the ink composition is ejected onto a recording medium, the spread of the deposited ink tends to be relatively small, and particularly the glossiness at a halftone is high. There is a tendency to decrease.
On the other hand, if the solid content of the ink composition is less than 7% by mass, the cohesiveness of the ink is lowered, and bleeding between colors is likely to occur and the formed image may be deteriorated.

Moreover, it is preferable that the content ratio (B / A) of solid content (B) other than a pigment with respect to a pigment (A) is 0.8-1.6, and the said ink composition is 1.0-1.4. More preferably, it is more preferably 1.0 to 1.3. When the ratio of the solid content other than the pigment within the above range is within the above range, the glossiness of the formed image becomes more effective and uniform, and the scratch resistance and image density of the image are improved.
Here, the solid content is the total amount of nonvolatile components remaining after removing volatile components such as water and water-soluble organic solvent contained in the ink composition. Examples of the solid content in the ink composition include pigments, pigment dispersants, polymer particles, and other components, and pigments, pigment dispersants, and polymer particles are preferable.

-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.

Specific examples of the organic pigment used in the present invention are shown below.
Examples of organic pigments for orange or yellow include C.I. I. Pigment orange 31, C.I. I. Pigment orange 43, C.I. I. Pigment yellow 12, C.I. I. Pigment yellow 13, C.I. I. Pigment yellow 14, C.I. I. Pigment yellow 15, C.I. I. Pigment yellow 17, C.I. I. Pigment yellow 74, C.I. I. Pigment yellow 93, C.I. I. Pigment yellow 94, C.I. I. Pigment yellow 128, C.I. I. Pigment yellow 138, C.I. I. Pigment yellow 151, C.I. I. Pigment yellow 155, C.I. I. Pigment yellow 180, C.I. I. And CI Pigment Yellow 185.

  Examples of organic pigments for magenta or red include C.I. I. Pigment red 2, C.I. I. Pigment red 3, C.I. I. Pigment red 5, C.I. I. Pigment red 6, C.I. I. Pigment red 7, C.I. I. Pigment red 15, C.I. I. Pigment red 16, C.I. I. Pigment red 48: 1, C.I. I. Pigment red 53: 1, C.I. I. Pigment red 57: 1, C.I. I. Pigment red 122, C.I. I. Pigment red 123, C.I. I. Pigment red 139, C.I. I. Pigment red 144, C.I. I. Pigment red 149, C.I. I. Pigment red 166, C.I. I. Pigment red 177, C.I. I. Pigment red 178, C.I. I. Pigment red 222C. I. Pigment violet 19 and the like.

  Examples of organic pigments for green or cyan include C.I. I. Pigment blue 15, C.I. I. Pigment blue 15: 2, C.I. I. Pigment blue 15: 3, C.I. I. Pigment blue 15: 4, C.I. I. Pigment blue 16, C.I. I. Pigment blue 60, C.I. I. Pigment Green 7 and siloxane-crosslinked aluminum phthalocyanine described in US Pat. No. 4,311,775.

  Examples of organic pigments for black include C.I. I. Pigment black 1, C.I. I. Pigment black 6, C.I. I. Pigment black 7 and the like.

~ 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 co-condensation 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 present 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 a liquid composition is used.

  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, radical transfer of vinyl monomers using dissociable groups (or substituents that can be induced to dissociable groups), polymerization initiators, and iniferters, or dissociable groups on either initiators or terminators 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 unsaturated phosphoric acid monomers include vinylphosphonic acid, vinyl phosphate, bis (methacryloxyethyl) phosphate, diphenyl-2-acryloyloxyethyl phosphate, diphenyl-2-methacryloyloxyethyl phosphate, dibutyl-2- Examples include acryloyloxyethyl phosphate.
Among the dissociable group-containing monomers, unsaturated carboxylic acid monomers are preferable and acrylic acid and methacrylic acid are more preferable from the viewpoints of dispersion stability and 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). 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. ) Is used. The conditions are as follows: the sample concentration is 0.35 / min, 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-ethyldiethanolanine, monoisopropanolamine, di Examples include isopropanolamine and triisopropanolamine. Examples of the alkali metal hydroxide include lithium hydroxide, sodium hydroxide, and potassium hydroxide. Among these, sodium hydroxide, potassium hydroxide, triethylamine, and triethanolamine are preferable from the viewpoint of stabilizing the dispersion of the self-dispersing polymer particles of the present invention in water.

  These 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.

-Water-soluble organic solvent-
The ink composition in the invention preferably contains water as a solvent, and more preferably contains at least one water-soluble organic solvent. By containing a water-soluble organic solvent, it is possible to prevent drying and promote penetration. 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) Tellurium, 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 eject ink droplets favorably by the ink jet method. Among them, the content of the surfactant is preferably an amount capable of adjusting the surface tension to 27 to 37 mN / m.

  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.
In addition, fluorine (fluorinated alkyl-based) surfactants, silicone-based surfactants and the like described in JP-A Nos. 2003-322926, 2004-325707, and 2004-309806 are also included. Scratch resistance can also be improved.

  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.

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

  By containing the anti-fading agent, image storability can be improved. As the antifading agent, various organic and metal complex antifading agents can be used. Examples of organic anti-fading agents include hydroquinones, alkoxyphenols, dialkoxyphenols, phenols, anilines, amines, indanes, chromans, alkoxyanilines, heterocycles, etc. There are nickel complexes and zinc complexes. More specifically, Research Disclosure No. No. 17643, Nos. VII to I, J; 15162, ibid. No. 18716, page 650, left column, ibid. No. 36544, page 527, ibid. No. 307105, page 872, ibid. The compounds described in the patent cited in Japanese Patent No. 15162 and the compounds represented by the general formulas and compound examples of the representative compounds described on pages 127 to 137 of JP-A-62-215272 can be used.

  Examples of the antifungal agent include sodium dehydroacetate, sodium benzoate, sodium pyridinethione-1-oxide, p-hydroxybenzoic acid ethyl ester, 1,2-benzisothiazolin-3-one and salts thereof. These are preferably used in the ink composition in an amount of 0.02 to 1.00% by mass.

  As the pH adjuster, a neutralizer (organic base, inorganic alkali) can be used. 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 content ratio of solids other than the pigment is 1.0 to 1.4.

(Reaction solution)
The ink set for ink jet recording of the present invention contains at least one kind of reaction liquid. 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.

The reaction solution in the present invention contains at least one organic acid selected from tartaric acid, DL-malic acid, maleic acid, 4-methylphthalic acid, and glutaric acid (hereinafter sometimes referred to as “specific organic acid”). However, it is preferable to include at least one organic acid selected from maleic acid and DL-malic acid.
By including a compound selected from these specific organic acids as a component for aggregating the ink composition, it is possible to effectively suppress the occurrence of stickiness in the image area formed using the ink composition. Furthermore, it is possible to effectively suppress bleeding of an image formed using the ink composition.
In the present invention, the content of the specific organic acid in the reaction solution is not particularly limited, but is preferably 15 to 40% by mass from the viewpoint of the aggregation rate of the ink composition, and is 15 to 35% by mass. More preferably.

  In addition to the specific organic acid, the reaction liquid in the present invention can comprise other aggregating components, water, a water-soluble organic solvent, a surfactant, and other additives as necessary.

-Water-soluble organic solvent-
The reaction solution in the present invention preferably contains at least one water-soluble organic solvent. The water-soluble organic solvent in the present invention is not particularly limited as long as it is an organic solvent capable of dissolving 5 g or more in 100 g of water at 20 ° C. Specifically, the water-soluble organic solvent that can be contained in the ink composition described above can be used in the reaction solution 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 water-soluble organic solvent in the reaction solution is not particularly limited. However, from the viewpoint of curling suppression, the content is preferably 1 to 30% by mass, and 5 to 15% by mass. Is more 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-
The reaction solution in the present invention can contain other aggregating components in addition to the specific organic acid as long as the effects of the present invention are not impaired. 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 solution in the present invention can be configured to contain other additives in addition to the organic acid and the water-soluble organic solvent. Other additives in the reaction liquid are the same as other additives in the ink composition described later.

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 (made by TOKI SANGYO CO.LTD).

  The reaction solution in the present invention contains 15 to 40% by mass of at least one organic acid selected from tartaric acid, DL-malic acid, maleic acid, 4-methylphthalic acid, and glutaric acid, and has a pH of 0.5. It is preferable that the surface tension is 40 to 60 mN / m, and at least one organic acid selected from maleic acid and DL-malic acid is 15 to 40% by mass (further, More preferably, the content is 15 to 35% by mass), the pH is 0.5 to 2.0 or less, and the surface tension is more preferably 42 to 50 mN / m.

<Inkjet image recording method>
In the inkjet image recording method of the present invention, a reaction liquid containing at least one organic acid selected from tartaric acid, DL-malic acid, maleic acid, 4-methylphthalic acid, and glutaric acid is applied onto a recording medium. Then, a reaction liquid application step for drying and an ink composition containing at least a pigment and having a solid content of 7 to 10% by mass are ejected onto the recording medium provided with the reaction liquid by an ink jet method. An ink droplet ejection step.
By forming an image by the ink jet image recording method having such a configuration, uniform glossiness can be obtained from a low image density to a high image density (particularly in a halftone portion), and the occurrence of stickiness in the image area can be suppressed. Can do. Furthermore, it is possible to suppress the occurrence of bleeding of the formed image.
However, in the inkjet image recording method of the present invention, the ink composition containing at least a pigment, a surfactant, an organic solvent, self-dispersing polymer particles and water is applied, and DL- The thing containing at least 1 sort (s) of the organic acid chosen from malic acid and 4-methylphthalic acid is applied.

(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 selectively applied onto 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. 54-59936 causes a sudden volume change of the ink subjected to the action of thermal energy, and the ink is ejected from the nozzle by the action force caused by 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.

In addition, an 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 suction 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 is moved, the recording speed can be increased as compared with the shuttle system. The ink jet 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.

Further, in the ink droplet ejection step according to the present invention, from the viewpoint of print density and image gloss, the diameter (C) of the ink droplet of the diameter (D) of the pixel dot formed on the recording medium by one ink droplet. The ratio (D / C) to is preferably 1.7 to 2.0, and more preferably 1.7 to 1.9.
The diameter of the ink droplet can be appropriately changed depending on, for example, the amount of the ink droplet. Moreover, the diameter of the pixel dot formed by one ink droplet can be appropriately changed depending on, for example, the solid content of the ink composition.

-Recording media-
The inkjet 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 ink jet 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 color 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. and “Tokuhishi Art” manufactured by Mitsubishi Paper Industries 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). 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.

EXAMPLES The present invention will be specifically described below with reference to examples, but the present invention is not limited to these examples. Unless otherwise specified, “part” and “%” are based on mass.
However, an ink set to which a reaction liquid containing at least one organic acid selected from DL-malic acid and 4-methylphthalic acid is applied corresponds to this embodiment.

  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 0.35 / min, 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".

<Example 1>
~ Preparation of ink composition ~
[Preparation of pigment dispersion]
(Preparation of polymer dispersant P-1)
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. under a nitrogen atmosphere. 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 in which 0.42 g of dimethyl 2,2′-azobisisobutyrate was dissolved 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 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 1H-NMR, and the weight average molecular weight (Mw) determined by GPC was 44600. Furthermore, when the acid value of this polymer was calculated | required by the method of JIS specification (JISK0070: 1992), it was 65.2 mgKOH / g.

(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 removing a part of water in the obtained dispersion, using a high-speed centrifugal cooler 7550 (manufactured by Kubota Seisakusho), using a 50 mL centrifuge, 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) of resin-coated pigment particles (pigment coated with a polymer dispersant) having a pigment concentration of 10.2% by mass was obtained.

(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) of coated pigment particles (pigment coated with a polymer dispersant) was prepared.

(Preparation of yellow dispersion)
In the preparation of the cyan dispersion, resin-coated pigment particles (with a polymer dispersant) were prepared in the same manner as the preparation of the cyan dispersion except that yellow pigment pigment yellow 74 was used instead of cyan pigment pigment blue 15: 3. Coated pigment) dispersion (yellow dispersion) was prepared.

(Preparation of black dispersion)
In the preparation of the cyan dispersion, resin-coated pigment particles (in the same manner as in the preparation of the cyan dispersion, except that carbon black (NIPEX 160-IQ manufactured by Degussa) was used instead of cyan pigment Pigment Blue 15: 3. A dispersion (black dispersion) of a pigment coated with a polymer dispersant was prepared.

(Preparation of self-dispersing polymer particles)
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%.

<Preparation of ink composition>
Using the pigment dispersion liquid of each color and the self-dispersing polymer fine particles obtained above, each component was mixed so as to have the ink composition (solid content) shown in Table 1 below to prepare an ink composition. . The prepared ink composition was filtered with a plastic disposable syringe through a PVDF 5 μm filter (Millex SV manufactured by Millipore, diameter 25 mm) to obtain a finished ink composition.
About each color ink composition, pH (25 degreeC) was measured using the Toa DKK Co., Ltd. product pH meter WM-50EG. Further, the surface tension at 25 ° C. was measured with FASE Automatic Surface Tensionmeter CBVP-Z manufactured by Kyowa Interface Science Co., Ltd. The results are shown in Table 1.

  In the composition of the magenta ink composition M1, the amount of self-dispersing polymer particles added was changed to the amount shown in Table 2 below, and the amount of water added was changed to M1 so that the finished total amount was 100 g. Similarly, ink compositions M2 to M7 were prepared.

[Preparation of reaction solution]
(Reaction solution 1)
The following materials were mixed to prepare reaction solution 1.
・ Citric acid 22.5g
・ Anionic surfactant A (10%) ... 1g
・ Diethylenecricol monoethyl ether 20g
・ Ion-exchanged water: 56.5g
When the pH (25 ° C.) was measured with a pH meter WM-50EG manufactured by Toa DDK Co., Ltd., the pH value was 1.29.
The anionic surfactant A is a compound represented by the following structural formula.

(Reaction solution 2)
The following materials were mixed to prepare reaction solution 2.
・ Malonic acid 22.5g
・ Anionic surfactant A (10%) ... 1g
・ Diethylenecricol monoethyl ether 20g
・ Ion-exchanged water: 56.5g
When the pH (25 ° C.) was measured with a pH meter WM-50EG manufactured by Toa DDK Co., Ltd., the pH value was 1.00.

(Reaction solution 3)
The following materials were mixed to prepare reaction solution 3.
・ Tartaric acid 22.5g
・ Anionic surfactant A (10%) ... 1g
・ Diethylenecricol monoethyl ether 20g
・ Ion-exchanged water 54g
When the pH (25 ° C.) was measured with a pH meter WM-50EG manufactured by Toa DDK Co., Ltd., the pH value was 1.06.

(Reaction solution 4)
The following materials were mixed to prepare reaction solution 4.
・ Glutaric acid 22.5g
・ Anionic surfactant A (10%) ... 1g
・ Diethylenecricol monoethyl ether 20g
・ Ion-exchanged water: 56.5g
When the pH (25 ° C.) was measured with a pH meter WM-50EG manufactured by Toa DDK Co., Ltd., the pH value was 2.01.

(Reaction solution 5)
The following materials were mixed to prepare a reaction solution 5.
・ Maleic acid 22.5g
・ Anionic surfactant A (10%) ... 1g
・ Diethylenecricol monoethyl ether 20g
・ Ion-exchanged water: 56.5g
When the pH (25 ° C.) was measured with a pH meter WM-50EG manufactured by Toa DDK Co., Ltd., the pH value was 0.67.

(Reaction liquid 6)
The following materials were mixed to prepare a reaction solution 6.
・ 4-methylphthalic acid 22.5g
・ Anionic surfactant A (10%) ... 1g
・ Diethylenecricol monoethyl ether 20g
・ Ion-exchanged water: 64g
When the pH was measured with a pH meter WM-50EG manufactured by Toa DDK Corporation, the pH value was 1.45.

(Reaction solution 7)
The following materials were mixed to prepare a reaction solution 7.
・ DL-malic acid 22.5g
・ Anionic surfactant A (10%) ... 1g
・ Diethylenecricol monoethyl ether 20g
・ Ion-exchanged water: 56.5g
When the pH (25 ° C.) was measured with a pH meter WM-50EG manufactured by Toa DDK Co., Ltd., the pH value was 1.32.

(Reaction liquid 8)
The following materials were mixed to prepare a reaction solution 8.
・ Maleic acid ... 11.25g
・ DL-malic acid ... 11.25g
・ Anionic surfactant A (10%) ... 1g
・ Triethylene glycol monomethyl ether 20g
・ Ion-exchanged water: 56.5g
When pH (25 degreeC) was measured with Toa DDK Co., Ltd. product pH meter WM-50EG, pH value was 0.78.

(Reaction solution 9)
The following materials were mixed to prepare a reaction solution 9.
・ Calcium nitrate tetrahydrate 22.5g
・ Anionic surfactant A (10%) ... 1g
・ Triethylene glycol monomethyl ether 20g
・ Ion-exchanged water: 56.5g
When pH (25 degreeC) was measured with Toa DDK Co., Ltd. product pH meter WM-50EG, pH value was 3.0.

<Inkjet image recording>
An image was drawn and recorded under the following image recording conditions using the above ink compositions M1 to M7 and reaction liquids 1 to 9 using A4 size Tokuhishi art (manufactured by Mitsubishi Paper Industries) as the recording medium.
Ink droplet ejection was started within 10 seconds after the reaction liquid application step.

-Reaction liquid application process-
Prior to ink drawing on the recording medium, the reaction liquid shown in Table 2 was applied to the surface of the recording medium so as to be 2.3 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 magenta pigment ink M1 obtained above as the ink composition, 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 set to 2.0 pL.
Halftone dot area ratio: It was set to be 0 to 100%.
Drive frequency: 30 kHz (recording medium conveyance speed 635 mm / sec)

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>
In order to confirm that the halftone dot% (halftone dot area ratio) drawn is correctly drawn, Oji Measuring Instruments stocks for 50 dots of each halftone dot (pixel dots formed by one ink droplet) The equivalent circle diameter was measured using a company-made dot analyzer DA-6000, and the average value was taken as the dot diameter.
In addition, millions of ink droplets were ejected, the mass thereof was measured, and the diameter (ink diameter) of one ink droplet was calculated in consideration of the specific gravity of the ink measured in advance.

1. Glossiness of image For a drawn portion having a halftone dot area ratio of 50% and a white background portion (halftone dot area ratio 0%), the glossiness is set to HOROBA GLOSS CHECKER IG-331 (manufactured by Horiba Ltd.) and an incident angle of 60 °. Each was measured with.

~Evaluation criteria~
A: The difference between the glossiness of white background and the glossiness of 50% part was less than 5%.
B: The difference between the glossiness of the white background and the glossiness of 50% was 5% or more and less than 10%, which was an acceptable limit.
C: The difference between the glossiness of the white background and the glossiness of the 50% part was 10% or more and less than 15%, and the glossiness difference was a level that could be clearly seen visually, and there was a problem in practical use.
D: The difference between the glossiness of the white background and the glossiness of the 50% portion was 15% or more, which was an unusable level.

2. Image surface stickiness A uniform image was formed on a recording medium by printing so that the dot area ratio was 50%.
After the fixing process, the stickiness of the surface when the surface of the recording medium was touched with a finger was evaluated according to the following evaluation criteria.

~Evaluation criteria~
A: It did not adhere to the finger at all.
B: The finger moved by touching the surface of the recording medium had a slight resistance, but there was no adhesion.
C: When the finger was moved by touching the surface of the recording medium, it was a practical limit level with a feeling of being slightly dragged by the finger.
D: The level of adhesion to the finger when touching the surface of the recording medium was not practical.

From Table 2, it can be seen that the sample of the present invention can provide an ink set having good gloss and good performance without any problem of stickiness.
Further, Sample No. 101 having a solid content of less than 7% in the ink composition was severely sticky and had a practical problem. On the other hand, Sample No. 107 having a solid content of more than 10% had a low halftone gloss, and a uniform glossiness not depending on the image density was not obtained.
Even when the solid content in the ink composition was within the range of the present application, Samples Nos. 108 and 109 using organic acids other than the specific organic acid had stickiness and had practical problems.

<Example 2>
Instead of the magenta inks M1 to M7 in Example 1, the composition of the cyan ink C1 was changed to C1 except that the addition amount of the self-dispersing polymer fine particles and the addition amount of water were changed in the same manner as the magenta inks M2 to M7. Similarly, inks C2 to C7 were prepared and evaluated in the same manner as in Example 1. As a result, the present invention showed favorable results in both glossiness and stickiness in the same tendency as in the case of magenta ink in cyan ink.

<Example 3>
The tartaric acid in the reaction solution 6 of Example 1 of the present invention is a mixture of two or three kinds selected from tartaric acid, DL-malic acid, maleic acid, 4-methylphthalic acid, and glutaric acid (the total acid content is the reaction solution 6). As a result of testing in the same manner as in Example 1, the same performance as in the present invention in Example 1 was obtained.

<Example 4>
In the preparation of the ink composition of Example 1 of the present invention, B-07 synthesized in the same manner as B-01 was used instead of B-01 as the self-dispersing polymer particles added to the ink composition. Except for the above, the ink composition produced in the same manner as in Example 1 was evaluated in the same manner as in Example 1. As a result, it was as good as the sample of this application in Example 1.

Claims (12)

An ink composition comprising at least a pigment, a surfactant, an organic solvent, self-dispersing polymer particles and water, and having a solid content of 7 to 10% by mass;
A reaction solution containing at least one organic acid selected from among D L-malic acid, and 4-methylphthalic acid,
An ink set for inkjet recording comprising:   The ink set for ink-jet recording according to claim 1, wherein the ink composition has a solid content ratio other than the pigment to the pigment of 0.8 to 1.6.   The ink set for ink jet recording according to claim 1 or 2, wherein the ink composition has a solid content ratio other than the pigment to the pigment of 1.0 to 1.4.   The ink set for inkjet recording according to any one of claims 1 to 3, wherein the reaction liquid has a content of the organic acid of 15 to 40% by mass.   The ink set for inkjet recording according to any one of claims 1 to 4, wherein the reaction liquid further contains a water-soluble organic solvent having a content of 1 to 30% by mass.   The ink set for inkjet recording according to any one of claims 1 to 5, wherein the reaction solution has a pH of 3.5 or less.   The ink set for inkjet recording according to any one of claims 1 to 6, wherein the reaction solution has a pH of 0.5 to 2.5.   The ink set for inkjet recording according to any one of claims 1 to 7, wherein the reaction liquid further contains an anionic surfactant or a nonionic surfactant. D L-malic acid, and 4-methylphthalic reaction solution containing at least one organic acid selected from the acid, and applied onto the recording medium, a reaction liquid applying step of drying,
An ink composition containing at least a pigment, a surfactant, an organic solvent, self-dispersing polymer particles, and water and having a solid content of 7 to 10% by mass on a recording medium provided with the reaction liquid, An ink ejection process for ejecting ink by an inkjet method;
An inkjet image recording method comprising:   The ink jet image recording method according to claim 9, wherein the ink droplet ejection step is started within 10 seconds after the reaction liquid application step.   11. The ink jet image recording method according to claim 9, wherein in the ink droplet ejection step, the amount of ink droplets ejected is 1.5 to 3.0 pL.   The ratio of the diameter of pixel dots formed on the recording medium by one ink droplet to the diameter of the ink droplet is 1.7 to 2.0 in the ink droplet ejection step. The inkjet image recording method according to any one of the above.