JP2015180710A - Ink set and image formation method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an ink set and an image formation method with which the viscosity-reducing change of ink and the surface roughening of a formed image are inhibited.SOLUTION: An ink set comprises: an ink composition comprising water, pigment covered with resin, resin particles, and at least one inorganic salt selected from hydrochloride and nitrate, the ink composition having pH of 7.5 or more at 25°C; and process liquid comprising an acidic compound to generate agglomerate on contact with the ink composition, the process liquid having pH of 0.1 or more and 0.5 or less at 25°C.

Description

  The present invention relates to an ink set and an image forming method.

  The ink jet recording method is a method of performing recording by ejecting droplet-like ink from a large number of nozzles formed on an ink jet recording head toward a recording medium and fixing the ink to the recording medium.

  In recent years, an image formed by an ink jet recording method is required to have high resolution and high quality. For example, as an ink that can adjust the texture of an image portion and a non-image portion, and has excellent storage stability. An ink containing a photopolymerizable monomer, a triarylsulfonium salt as a photopolymerization initiator, and a polymerization inhibitor is known (for example, see Patent Document 1).

In addition, as a technique for quickly fixing ink to a recording medium in order to obtain a high-definition and high-quality image, a processing liquid (also referred to as a fixing liquid or a reaction liquid) containing a compound that promotes ink aggregation is used. For example, as an ink set that has good liquid stability and dischargeability and can suppress curling and image deformation of the recording medium after ink application, it includes a pigment, a water-soluble solvent, and resin fine particles. An ink composition, which is a pigment coated with a polymer, obtained through a step in which a pigment is dispersed with a water-soluble dispersant and then crosslinked with a crosslinking agent, and an aggregation accelerator for promoting aggregation of the ink composition There is known an ink set having a colorless ink composition containing a liquid (see, for example, Patent Document 2).
In addition, it is excellent in ink cohesiveness using a treatment liquid containing water, an organic acid compound, and an inorganic acid compound and having a pH of 0.5 to 2.0, and uneven glossiness in the image area is generated. There is known an image forming method that is suppressed and the adverse effect of the treatment liquid on the recording medium is suppressed (for example, see Patent Document 3).

JP 2005-178330 A JP 2009-190379 A JP 2012-196822 A

  A conventional ink composition containing an organic salt (for example, see Patent Document 1) or an ink composition containing a carbonate (for example, see Patent Document 2), a recording medium having a coating layer containing a base paper and an inorganic pigment (hereinafter referred to as “Patent Document 2”) When an image is formed by inkjet recording on a “coated paper”), particularly when a coating layer is locally thin and a region with a small amount of acid due to application of a treatment liquid occurs, such as a low-grade paperboard, the amount of acid is small. In the area, the dots of the ejected ink composition are likely to spread, and the density of the white background portion is locally reduced to increase the density, which may cause “surface alignment” that appears as unevenness.

In addition, an ink composition containing a pigment coated with a polymer may exhibit a phenomenon that the viscosity of the ink composition decreases (“thinning of ink”) when the ink composition is exposed to a high temperature for a long time.
When such a thinning phenomenon occurs, the above-described surface alignment tends to occur, and the frequency of occurrence tends to become remarkable.

  The present invention has been made in view of the above, and an object of the present invention is to provide an ink set and an image forming method in which a change in the viscosity of ink and a surface alignment of an image to be formed are suppressed.

Specific means for achieving the above-described problems are as follows.
<1> an ink composition having a pH of 7.5 or more at 25 ° C., comprising a pigment coated with water, a resin, resin particles, and at least one inorganic salt selected from hydrochloride and nitrate; An ink set comprising: a treatment liquid containing an acidic compound that forms an aggregate when contacted with a composition and having a pH at 25 ° C. of 0.1 to 0.5.
<2> The ink set according to <1>, wherein the inorganic salt is at least one selected from lithium chloride, lithium nitrate, potassium chloride, and potassium nitrate.
<3> The ink set according to <1> or <2>, wherein the resin particles are resin particles selected from an acrylic resin and a urethane resin.
<4> The ink set according to any one of <1> to <3>, wherein the ink composition further includes a polyfunctional (meth) acrylamide compound.
<5> The content of at least one inorganic salt selected from hydrochloride and nitrate is 0.01% by mass to 0.1% by mass with respect to the total mass of the ink composition. The ink set according to any one of the above.
<6> The ink set according to any one of <1> to <5>, wherein the mass ratio of the coating resin of the pigment coated with the resin to the inorganic salt (coating resin / inorganic salt) is 10 to 250. .
<7> The ink set according to any one of <1> to <6>, which is used for forming an image on a recording medium having a base paper and a coating layer containing an inorganic pigment.

<8> An ink composition of the ink set according to any one of <1> to <7> is applied to a recording medium having a base paper and a coating layer containing an inorganic pigment by an inkjet method to form an image. An image forming method comprising: an ink application step for forming; and a treatment liquid application step for applying a treatment liquid of an ink set on a recording medium having a base paper and a coating layer containing an inorganic pigment.
<9> The image forming method according to <8>, wherein after applying the treatment liquid to the recording medium in the treatment liquid application process, the ink composition is applied in the ink application process.

  ADVANTAGE OF THE INVENTION According to this invention, the ink set and the image formation method in which the thinning change of the ink and the surface arrangement | sequence of the image formed are suppressed are provided.

It is a schematic block diagram which shows the structural example of the inkjet recording device used for implementation of image formation.

Hereinafter, the ink set and the image forming method of the present invention will be described in detail.
In this specification, the numerical range indicated using “to” indicates a range including the numerical values described before and after “to” as the minimum value and the maximum value, respectively.

In this specification, “surface area” means that a high-density part and a low-density part of the ink composition are unevenly distributed in a middle area (halftone area) between a bright area (highlight) and a dark area (shadow) of an image. It is a phenomenon that looks rough.
“Surface alignment” is not a phenomenon caused by insufficient local agglomeration of ink compositions such as conventional “bleeding” or “streak”, but non-aggregation due to non-uniform distribution of processing liquid on the recording medium. It is a phenomenon caused by

<Ink set>
The ink set according to the present invention includes water, a resin-coated pigment, resin particles, and at least one inorganic salt selected from hydrochloride and nitrate (hereinafter also referred to as “specific inorganic salt”). And a treatment liquid having a pH of 0.1 or more and 0.5 or less containing an acidic compound that forms an aggregate when contacted with the ink composition.

Although the action mechanism of the present invention is not clear, the present inventor presumes as follows.
That is, the pigment coated with the resin contained in the ink composition undergoes volume shrinkage by heating, and the intermolecular interaction between the pigment coated with the resin or other contained components decreases. This is considered to cause ink viscosity reduction. By including a specific inorganic salt in the ink composition, the volume of the pigment coated with the resin becomes stable in a contracted state before heating, so that the volume change due to heating is suppressed and the ink viscosity is suppressed. It is thought that it is done.
In addition, when the ink composition stabilized by containing a specific inorganic salt comes into contact with the treatment liquid having a pH of 0.1 or more and pH 0.5 or less, the ink composition is uniformly aggregated. It is thought to be suppressed.

≪Ink composition≫
The ink composition according to the present invention contains water, a pigment coated with a resin, resin particles, and at least one inorganic salt selected from hydrochloride and nitrate, and has a pH of 7.5 or more.

-Inorganic salt-
The inorganic salt in the present invention is at least one selected from hydrochloride and nitrate. Among these, monovalent salts are preferable, alkali metal salts are more preferable, and lithium chloride, lithium nitrate, potassium chloride, and potassium nitrate are more preferable from the viewpoint of excellent ink viscosity reduction and surface areal suppression.
An inorganic salt can be used individually or in combination of 2 or more types.
The content of the inorganic salt in the ink composition of the present invention (the total content in the case of two or more types) is not particularly limited, but is 0.01% by mass to 0% based on the total mass of the ink composition. 0.1% by mass is preferable, 0.02% by mass to 0.1% by mass is more preferable, and 0.03% by mass to 0.1% by mass is particularly preferable.

-Pigment coated with resin-
The ink composition according to the present invention contains a pigment coated with at least one resin. Thereby, the dispersion stability of the ink composition is improved, and the quality of the formed image is improved.

(Pigment)
There is no restriction | limiting in particular as a pigment, According to the objective, it can select suitably, For example, any of an organic pigment and an inorganic pigment may be sufficient. Further, a carbon black pigment, a magenta pigment, a cyan pigment, and a yellow pigment may be used as the coloring pigment. The pigment is preferably a pigment that is almost insoluble or hardly soluble in water from the viewpoint of ink colorability.

  Examples of organic pigments include azo pigments, polycyclic pigments, dye chelates, nitro pigments, nitroso pigments, and aniline black. Among these, azo pigments and polycyclic pigments are more preferable. Examples of the inorganic pigment include titanium oxide, iron oxide, calcium carbonate, barium sulfate, aluminum hydroxide, barium yellow, cadmium red, chrome yellow, and carbon black. Among these, carbon black is particularly preferable.

  When an organic pigment is used, the average particle diameter of the organic pigment is preferably small from the viewpoint of transparency and color reproducibility, but is preferably large from the viewpoint of light resistance. From the viewpoint of achieving both of these, the average particle size is preferably 10 nm to 200 nm, more preferably 10 nm to 150 nm, and even more preferably 10 nm to 120 nm. The particle size distribution of the organic pigment is not particularly limited, and may be either a wide particle size distribution or a monodispersed particle size distribution. Two or more kinds of organic pigments having a monodispersed particle size distribution may be mixed and used.

You may use a pigment individually by 1 type or in combination of 2 or more types.
The content of the pigment in the ink composition is preferably 1% by mass to 20% by mass and more preferably 2% by mass to 10% by mass with respect to the ink composition from the viewpoint of image density.

(Coating resin)
In the pigment contained in the ink composition according to the present invention, at least a part of the pigment surface is coated with a resin (dispersant) and dispersed in an aqueous medium.
The pigment dispersant may be either a polymer dispersant or a low molecular surfactant type dispersant. The polymer dispersant may be either a water-soluble dispersant or a water-insoluble dispersant.
Here, “water-soluble” means that it can be dissolved in water at a certain concentration or more. Specifically, the solubility in water at 25 ° C. is preferably 5% by mass or more, and more preferably 10% by mass or more.

  As the low molecular surfactant type dispersant, for example, known low molecular surfactant type dispersants described in paragraphs 0047 to 0052 of JP2011-178029A can be used.

  Among polymer dispersants, water-soluble dispersants include hydrophilic polymer compounds. For example, natural hydrophilic polymer compounds include plant polymers such as gum arabic, tragacanth 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.

In addition, in hydrophilic polymer compounds modified from natural products, fiber polymers such as methylcellulose, ethylcellulose, hydroxyethylcellulose, hydroxypropylcellulose, carboxymethylcellulose, starch such as sodium starch glycolate and sodium starch phosphate And seaweed polymers such as sodium alginate, propylene glycol alginate, and the like.
Further, synthetic hydrophilic polymer compounds include vinyl polymers such as polyvinyl alcohol, polyvinyl pyrrolidone, and polyvinyl methyl ether, non-crosslinked polyacrylamide, polyacrylic acid or alkali metal salts thereof, water-soluble styrene acrylic resins, and the like. Acrylic 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 salts of β-naphthalene sulfonic acid formalin condensate, quaternary ammonium and amino And a polymer compound having a salt of a cationic functional group such as a group in the side chain, a natural polymer compound such as shellac, and the like.

  Among these, water-soluble dispersants introduced with carboxyl groups are hydrophilic polymers such as homopolymers of acrylic acid, methacrylic acid, styrene acrylic acid, and copolymers with monomers having other hydrophilic groups. Preferred as a compound.

Among the polymer dispersants, as the water-insoluble dispersant, a polymer having both a hydrophobic portion and a hydrophilic portion can be used. The hydrophilic structural unit is preferably a structural unit having an acidic group, and more preferably a structural unit having a carboxyl group. Examples of the water-insoluble resin include styrene- (meth) acrylic acid copolymer, styrene- (meth) acrylic acid- (meth) acrylic acid ester copolymer, (meth) acrylic acid ester- (meth) acrylic acid copolymer. Examples thereof include a polymer, a polyethylene glycol (meth) acrylate- (meth) acrylic acid copolymer, a vinyl acetate-maleic acid copolymer, and a styrene-maleic acid copolymer.
More specifically, for example, the water-insoluble resins described in JP-A-2005-41994, JP-A-2006-238991, JP-A-2009-084494, JP-A-2009-191134, and the like are preferably used in the present invention. Can be used.

  The weight average molecular weight of the polymer dispersant is preferably 3,000 to 100,000, more preferably 5,000 to 50,000, still more preferably 5,000 to 40,000, and particularly preferably 10,000. 000 to 40,000.

  The weight average molecular weight of the polymer dispersant 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 0.45 mass%, the flow rate is 0.35 ml / min, the sample injection amount is 10 μl, the measurement temperature is 40 ° C., and the RI 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 polymer dispersant preferably contains a polymer having a carboxyl group from the viewpoints of self-dispersibility and aggregation rate when the treatment liquid comes into contact. The polymer dispersant has a carboxyl group and has an acid value of 130 mgKOH / g or less. It is preferable that the polymer has an acid value of 25 mgKOH / g to 120 mgKOH / g. In particular, when the ink composition of the present invention is used with a treatment liquid that aggregates the components in the ink composition, a polymer dispersant having a carboxyl group and an acid value of 25 mgKOH / g to 100 mgKOH / g is effective. It is. The processing liquid will be described later.

  The mixing mass ratio (p: s) between the pigment (p) and the dispersant (s) 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 content of the coating resin for coating the pigment with respect to the total mass of the ink composition is preferably 0.5% by mass to 3.0% by mass, more preferably 1.0% by mass to 2.8% by mass, and 1.2% by mass. % To 2.5% by mass is particularly preferred.

  The mass ratio of the coating resin and the inorganic salt (coating resin / inorganic salt) is preferably 10 to 250, more preferably 15 to 200, and more preferably 30 to 150, from the viewpoints of ink viscosity reduction and image surface roughness suppression. Is particularly preferred.

  It is preferable that at least a part of the pigment surface includes a pigment coated with a resin coated with a polymer dispersant having a carboxyl group, and the ink composition has at least a part of the pigment surface from the viewpoint of cohesiveness. It is more preferable that the encapsulated pigment is coated with a water-insoluble resin and coated with a polymer dispersant having the following formula.

The volume average particle size (secondary particle size) of the pigment (pigment coated with resin) in the dispersed state is preferably 10 nm to 200 nm, more preferably 10 nm to 150 nm, and even more preferably 10 nm to 100 nm. When the volume average particle diameter is 200 nm or less, the color reproducibility is good, and the droplet ejection characteristics when droplets are ejected by the ink jet method are good. When the volume average particle diameter is 10 nm or more, light resistance is improved. 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 monodispersed particle size distribution may be mixed and used. Here, the volume average particle diameter of the pigment in the dispersed state indicates the average particle diameter in the ink state, but the same applies to the so-called concentrated ink dispersion in the previous stage before the ink is formed.
The average particle size and particle size distribution of the resin-coated pigment were measured by the dynamic light scattering method using Nanotrac particle size distribution analyzer UPA-EX150 (manufactured by Nikkiso Co., Ltd.). Is required.

(Encapsulated pigment)
The encapsulated pigment will be described in detail. The encapsulated pigment resin is not limited, but a polymer compound having self-dispersing ability or dissolving ability in a mixed solvent of water and a water-soluble organic solvent and having an anionic group (acidic) is used. preferable.

  The pigment coated with a water-insoluble resin having an acidic group (preferably a carboxyl group) is, for example, a mixture containing a pigment, a water-insoluble resin (dispersant), and a solvent (preferably an organic solvent) as necessary. It can be obtained by performing dispersion processing with a disperser.

Specifically, for example, a step of adding an aqueous solution containing a basic substance to a mixture of a pigment, a water-insoluble resin (dispersing agent), and an organic solvent capable of dissolving or dispersing the water-insoluble resin to perform a dispersion treatment (mixing / water A pigment dispersion in which at least a part of the surface of the pigment is coated with a water-insoluble resin can be produced by a production method comprising a step of removing the organic solvent and a step of removing at least part of the organic solvent (solvent removal step). . Thereby, a pigment dispersion in which the pigment is finely dispersed and excellent in storage stability can be produced.
More specifically, for example, a pigment dispersion in which at least a part of the pigment surface is coated with a water-insoluble resin can be produced by the method for producing a pigment dispersion described in JP-A-10-140065.
Examples of the dispersant include polyvinyls, polyurethanes, polyesters, etc. Among them, polyvinyls are preferable.
The dispersant needs to have a functional group that can be crosslinked by a crosslinking agent in the molecule. The crosslinkable functional group is not particularly limited, and examples thereof include a carboxyl group or a salt thereof, an isocyanate group, and an epoxy group, but preferably have a carboxyl group or a salt thereof from the viewpoint of improving dispersibility. .

-Resin particles-
The ink composition of the present invention contains at least one resin particle.
The resin particles are particles that exist separately from the pigment coated with the resin. As the resin particles, for example, resin particles formed of a resin selected from a thermoplastic resin and a thermosetting resin can be used. These resins may be further modified resins. Examples of the resin used for forming the resin particles include acrylic resins, epoxy resins, urethane resins, polyether resins, polyamide resins, unsaturated polyester resins, phenol resins, silicone resins, and fluorine resins. , Polyvinyl resins (eg, vinyl chloride, vinyl acetate, polyvinyl alcohol, or polyvinyl butyral), alkyd resins, polyester resins (eg, phthalic acid resins, etc.), amino materials (eg, melamine resins, melamine formaldehyde resins, Aminoalkyd co-condensation resin, urea resin, urea resin, etc.). The resin forming the resin particles may be a copolymer containing two or more structural units constituting the resin exemplified above, or may be a mixture of two or more resins. In addition, the resin particles themselves may be composite resin particles in which two or more resins are laminated like a core / shell, for example, as well as a mixture of two or more resins.
When resin particles are used in the ink composition, only one type may be used, or two or more types may be used in combination.

  Among the above, as the resin particles, acrylic resin, urethane resin, polyether resin, polyester resin, and polyolefin resin particles are preferable. From the viewpoint of film quality and stability, acrylic resin and / or urethane resin are preferable. Particles are particularly preferred.

In the ink composition of the present invention, the glass transition temperature (Tg) of the resin particles is preferably 40 ° C. or higher from the viewpoint of improving the abrasion resistance of the image and suppressing surface roughness, and the upper limit of the glass transition temperature of the resin particles is 250 ° C. is preferable.
The glass transition temperature of the resin particles is preferably in the range of 50 ° C. or higher and 230 ° C. or lower.
For example, when an image is formed by applying the ink composition onto a recording medium together with a treatment liquid described later, the resin particles are contained in the ink composition when contacting the treatment liquid or a region where the treatment liquid is dried. The ink composition has a function of fixing the ink composition by destabilizing and agglomerating and thickening. Thereby, the abrasion resistance of the image is further improved, and image unevenness is further suppressed. Furthermore, the adhesion of the ink composition to the recording medium and the scratch resistance of the image are further improved.

  The glass transition temperature of the resin particles can be appropriately controlled by a commonly used method. For example, the glass transition temperature of the resin particles can be controlled within a desired range by appropriately selecting the type of monomer (polymerizable compound) constituting the resin particles, the composition ratio thereof, the molecular weight of the polymer constituting the resin particles, and the like. Can do.

In the present invention, the measurement Tg obtained by actual measurement is applied as the glass transition temperature of the resin particles.
Specifically, the measurement Tg means a value measured under normal measurement conditions using a differential scanning calorimeter (DSC) EXSTAR 6220 manufactured by SII Nanotechnology. However, when measurement is difficult due to polymer decomposition or the like, calculation Tg calculated by the following calculation formula is applied. The calculation Tg is calculated by the following equation (1).
1 / Tg = Σ (X _i / Tg _i ) (1)
Here, it is assumed that n types of monomer components from i = 1 to n are copolymerized in the polymer to be calculated. X _i is the weight fraction of the i-th monomer (ΣX _i = 1), and Tg _i is the glass transition temperature (absolute temperature) of the homopolymer of the i-th monomer. However, Σ is the sum from i = 1 to n. The homopolymer glass transition temperature value (Tg _i ) of each monomer is the value of Polymer Handbook (3rd Edition) (by J. Brandrup, EH Immergut (Wiley-Interscience, 1989)).

The resin particles are preferably resin particles obtained by a phase inversion emulsification method, and the following self-dispersing polymer particles (self-dispersing polymer particles) are more preferable.
Here, the self-dispersing polymer is dispersed in an aqueous medium by a functional group (particularly an acidic group or a salt thereof) possessed by the polymer itself when it is dispersed by a phase inversion emulsification method in the absence of a surfactant. A water-insoluble polymer that can be in a state.
Here, the dispersed state refers to 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 both states.
“Water-insoluble” means that the amount dissolved in 100 parts by mass of water (25 ° C.) is 5.0 parts by mass or less.

  As the phase inversion emulsification method, for example, a polymer is dissolved or dispersed in a solvent (for example, a water-soluble solvent) and then poured into water as it is without adding a surfactant. For example, there is a method of obtaining an aqueous dispersion in an emulsified or dispersed state after stirring and mixing in a state where the acidic group) is neutralized and removing the solvent.

  Examples of the self-dispersing polymer particles include glass transitions from the self-dispersing polymer particles described in paragraphs 0090 to 0121 of JP2010-64480A and paragraphs 0130 to 0167 of JP2011-066805A. Those having a temperature of 40 ° C. or higher can be selected and used.

The acrylic resin that can be suitably used for the resin particles in the present invention will be described in detail. The acrylic resin of the present invention is a polymer mainly composed of acrylates and methacrylates, and styrenes, acrylamides, and methacrylamides may be further used as copolymerization components.
The polymer constituting the resin particles (specific polymer; the same shall apply hereinafter) preferably has at least one of a structural unit having an aromatic group and a structural unit having an alicyclic group. Here, the alicyclic group is synonymous with the cyclic aliphatic group.
Thereby, the strength of the formed image can be further improved (for example, scratch resistance and blocking resistance).
In the present specification, the structural unit contained in the specific polymer may be referred to as “constituent component”.

(Structural unit having an aromatic group)
Examples of the structural unit having an aromatic group include a structural unit having a phenyl group, a structural unit having a benzyl group, a structural unit having a phenoxy group, and a structural unit having a phenethyl group. The unit is preferably a structural unit having a phenoxy group (preferably a structural unit having a phenoxyethyl group).

The structural unit having an aromatic group is preferably a structural unit derived from a monomer having an aromatic group (hereinafter also referred to as “aromatic group-containing monomer”).
The aromatic group-containing monomer 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 aromatic group-containing (meth) acrylate monomers (for example, phenoxyethyl (meth) acrylate, benzyl (meth) acrylate, phenyl (meth) acrylate, etc.), styrene monomers, and the like. It is done. 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.

(Structural unit having an alicyclic group)
The structural unit having an alicyclic group is preferably a structural unit derived from a monomer having an alicyclic group (hereinafter also referred to as “alicyclic group-containing monomer”).
The alicyclic group-containing monomer is preferably a monomer having an alicyclic group and an ethylenically unsaturated bond, and a (meth) acrylate having an alicyclic group (hereinafter referred to as “alicyclic (meth) acrylate”). Are also preferred.
The alicyclic (meth) acrylate includes a structural site derived from (meth) acrylic acid and a structural site derived from alcohol, and the structural site derived from alcohol is unsubstituted or substituted. It has a structure containing at least one hydrogen group. The alicyclic hydrocarbon group may be a structural site derived from alcohol itself, or may be bonded to a structural site derived from alcohol via a linking group.

The alicyclic hydrocarbon group is not particularly limited as long as it includes a cyclic non-aromatic hydrocarbon group, and is a monocyclic hydrocarbon group, a bicyclic hydrocarbon group, a tricyclic or more polycyclic ring. And a formula hydrocarbon group. Examples of the alicyclic hydrocarbon group include a cycloalkyl group such as a cyclopentyl group and a cyclohexyl group, a cycloalkenyl group, a bicyclohexyl group, a norbornyl group, an isobornyl group, a dicyclopentanyl group, a dicyclopentenyl group, and an adamantyl group. , Decahydronaphthalenyl group, perhydrofluorenyl group, tricyclo [5.2.1.0 ^2,6 ] decanyl group, and bicyclo [4.3.0] nonane.
The alicyclic hydrocarbon group may further have a substituent. Examples of the substituent include an alkyl group, an alkenyl group, an aryl group, an aralkyl group, an alkoxy group, a hydroxyl group, a primary amino group, a secondary amino group, a tertiary amino group, an alkyl or arylcarbonyl group, and a cyano group. Can be mentioned. Further, the alicyclic hydrocarbon group may further form a condensed ring. As an alicyclic hydrocarbon group in this invention, it is preferable that the carbon atom number of an alicyclic hydrocarbon group part is 5-20 from a viscosity or a soluble viewpoint.

Specific examples of the alicyclic (meth) acrylate are shown below, but the present invention is not limited thereto.
Monocyclic (meth) acrylates include cyclopropyl (meth) acrylate, cyclobutyl (meth) acrylate, cyclopentyl (meth) acrylate, cyclohexyl (meth) acrylate, cycloheptyl (meth) acrylate, cyclooctyl (meth) acrylate, and cyclononyl. Examples thereof include cycloalkyl (meth) acrylates having 3 to 10 carbon atoms in the cycloalkyl group such as (meth) acrylate and cyclodecyl (meth) acrylate.
Examples of the bicyclic (meth) acrylate include isobornyl (meth) acrylate and norbornyl (meth) acrylate.
Examples of the tricyclic (meth) acrylate include adamantyl (meth) acrylate, dicyclopentanyl (meth) acrylate, and dicyclopentenyloxyethyl (meth) acrylate.
These can be used alone or in admixture of two or more.

  Among these, from the viewpoints of dispersion stability, fixability, and blocking resistance of the self-dispersing polymer particles, at least one bicyclic (meth) acrylate or a tricyclic or higher polycyclic (meth) acrylate is used. Preferably, it is at least one selected from isobornyl (meth) acrylate, adamantyl (meth) acrylate, and dicyclopentanyl (meth) acrylate.

  In the polymer constituting the resin particles in the present invention, the total content of the structural unit having the aromatic group and the structural unit having the alicyclic group is preferably 3% by mass to 95% by mass. The content is more preferably 5% by mass to 75% by mass, and particularly preferably 10% by mass to 50% by mass. When the total content is in the above range, the stability of the self-emulsification or dispersion state is improved, and further, the increase in ink viscosity can be suppressed.

  In consideration of the removability (maintenance) of the ink composition from the nozzle and the re-discharge property after the removal, the resin particles more preferably have a structural unit having an aromatic group.

In a more preferred form of the resin particles, the polymer constituting the resin particles includes a structural unit having an aromatic group, and the content of the structural unit having an aromatic group is 3% by mass to 45% by mass (relative to the total amount of the polymer). More preferably, it is in the form of 3 mass% to 40 mass%, particularly preferably 5 mass% to 30 mass%.
With this form, it becomes easier to adjust the glass transition temperature of the resin particles to 40 ° C. or higher.

(Hydrophilic structural unit)
The polymer constituting the resin particles preferably contains a hydrophilic constituent unit from the viewpoint of dispersibility in the ink composition (self-dispersibility in the case of self-dispersing polymer particles).
The hydrophilic structural unit is preferably a structural unit derived from a monomer having a hydrophilic group (hereinafter also referred to as “hydrophilic group-containing monomer”).
In this case, the hydrophilic structural unit may be derived from one type of hydrophilic group-containing monomer or may be derived from two or more types of hydrophilic group-containing monomers.
The hydrophilic group is not particularly limited, and may be a dissociable group or a nonionic hydrophilic group.
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 these, a carboxyl group is preferable from the viewpoint of fixability when an ink composition is configured.

The hydrophilic group-containing monomer is preferably a dissociable group-containing monomer from the viewpoint of self-dispersibility and aggregability, and is preferably a dissociable group-containing monomer having a dissociable group and an ethylenically unsaturated bond. .
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 (meth) acrylic 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. Can be mentioned.
Specific examples of the unsaturated phosphoric acid monomer include vinylphosphonic acid, vinyl phosphate, bis (methacryloxyethyl) phosphate, diphenyl-2-acryloyloxyethyl phosphate, diphenyl-2-methacryloyloxyethyl phosphate, dibutyl-2-acryloyloxy Examples thereof include ethyl phosphate.
Among the dissociable group-containing monomers, an unsaturated carboxylic acid monomer is preferable and (meth) acrylic acid is more preferable from the viewpoints of dispersion stability and ejection stability.

  The content of the hydrophilic structural unit in the polymer constituting the resin particles is not particularly limited, but from the viewpoint of dispersion stability, the content is 2% by mass to 30% by mass with respect to the total amount of the resin particles. Preferably, 5 mass%-20 mass% are more preferable, and 5 mass%-15 mass% are especially preferable.

(Structural unit having an alkyl group)
The polymer constituting the resin particles preferably includes a structural unit having an alkyl group from the viewpoint of flexibility of the polymer skeleton and easy control of the glass transition temperature (Tg).
As for the carbon atom number of the alkyl group in the structural unit which has an alkyl group, 1-4 are preferable.
The structural unit having an alkyl group is preferably a structural unit derived from a monomer having an alkyl group (hereinafter also referred to as “alkyl group-containing monomer”).

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, t -Alkyl (meth) acrylates such as butyl (meth) acrylate, hexyl (meth) acrylate, ethylhexyl (meth) acrylate; hydroxymethyl (meth) acrylate, 2-hydroxyethyl (meth) acrylate, 2-hydroxypropyl (meth) acrylate Ethylenically unsaturated monomers having a hydroxyl group such as 4-hydroxybutyl (meth) acrylate, hydroxypentyl (meth) acrylate, and hydroxyhexyl (meth) acrylate; dimethylaminoethyl Dialkylaminoalkyl (meth) acrylates such as meth) acrylate; N-hydroxyalkyl (meth) acrylamides such as N-hydroxymethyl (meth) acrylamide, N-hydroxyethyl (meth) acrylamide, N-hydroxybutyl (meth) acrylamide; N-methoxymethyl (meth) acrylamide, N-ethoxymethyl (meth) acrylamide, N- (n-, iso) butoxymethyl (meth) acrylamide, N-methoxyethyl (meth) acrylamide, N-ethoxyethyl (meth) acrylamide And (meth) acrylamides such as N-alkoxyalkyl (meth) acrylamides such as N- (n-, iso) butoxyethyl (meth) acrylamide.
Among them, alkyl (meth) acrylate is preferable, alkyl (meth) acrylate having 1 to 4 carbon atoms in the alkyl group is more preferable, methyl (meth) acrylate, ethyl (meth) acrylate, isopropyl (meth) acrylate, or Butyl (meth) acrylate is more preferred, and methyl (meth) acrylate is particularly preferred.

  Although there is no restriction | limiting in particular in content of the structural unit which has an alkyl group in the polymer which comprises resin particle, From a viewpoint of dispersion stability, content is 5 mass%-90 mass% with respect to the whole quantity of resin particle. Is preferable, 10% by mass to 85% by mass is more preferable, 20% by mass to 80% by mass is further preferable, 30% by mass to 75% by mass is particularly preferable, and 40% by mass to 75% by mass is most preferable.

  The polymer which comprises the resin particle may contain structural units other than the structural unit mentioned above as needed.

  As a more preferable form of the resin particles, the polymer constituting the resin particles contains at least 10% by mass to 50% by mass of structural units having an alicyclic group and 20% by mass to 80% by mass of structural units having an alkyl group. The form which contains 5 mass%-20 mass% of structural units which have an anionic dissociative group is mentioned.

Specific examples of the self-dispersing polymer particles are listed below as exemplary compounds P-1 to P-5, but the present invention is not limited thereto. In addition, the parenthesis represents the mass ratio of the copolymerization component.
P-1: Methyl methacrylate / isobornyl methacrylate / methacrylic acid copolymer (48/42/10)
P-2: Methyl methacrylate / isobornyl methacrylate / methacrylic acid copolymer (70/20/10)
P-3: Methyl methacrylate / benzyl methacrylate / methacrylic acid copolymer (65/25/10)
P-4: Isopropyl methacrylate / isobornyl methacrylate / methacrylic acid copolymer (50/40/10)
P-5: butyl methacrylate / dicyclopentanyl methacrylate / methacrylic acid copolymer (60/30/10)

In the present invention, urethane resin can also be preferably used as the resin particles. The reason why the urethane resin is preferable is estimated as follows.
In other words, the urethane resin is formed from urethane parts capable of strong interactions such as hydrogen bonding between polymers and non-urethane parts that have relatively weak interactions between polymers, forming an ink film. In this case, it is presumed that as a micro structure, a part having relatively strong interaction and a part having relatively weak interaction are gathered to construct a sea-island structure. Thereby, it is presumed that polyurethane has flexibility. Since polyurethane inherently has flexibility as described above, it is presumed that the formed film is flexible, can relieve stress, and can form an ink image having excellent abrasion resistance.

  Examples of the urethane resin used for forming the resin particles in the present invention include those that can be obtained by reacting a diol compound and a diisocyanate compound. For details of the diol compound and the diisocyanate compound, reference can be made, for example, to the descriptions in paragraph numbers [0031] to [0036] of JP-A No. 2001-247787. Among them, it is preferable to use a polyester urethane resin or a polyether urethane resin having an ester bond in the main chain structure.

  The diisocyanate compound is not particularly limited, but examples thereof include aliphatic diisocyanate compounds such as hexamethylene diisocyanate and 2,2,4-trimethylhexamethylene diisocyanate; isophorone diisocyanate, 1,4-cyclohexane diisocyanate, 4,4 Examples thereof include alicyclic diisocyanate compounds such as' -dicyclohexylmethane diisocyanate; aromatic aliphatic diisocyanate compounds such as xylylene diisocyanate and tetramethylxylene diisocyanate; aromatic diisocyanate compounds such as tolylene diisocyanate and phenylmethane diisocyanate. Moreover, these diisocyanate compounds can use 2 or more types together.

  Although it does not specifically limit as a diol compound, For example, the polyether diol compound obtained by polymerizing heterocyclic ethers, such as alkylene oxides, such as ethylene oxide, propylene oxide, butylene oxide, and tetrahydrofuran, is mentioned. The polyether diol compound may be a homopolymer or a copolymer. Specific examples of the polyether diol compound include polyether diols such as polyethylene glycol, polypropylene glycol, polybutylene oxide, polytetramethylene ether glycol, polyhexamethylene ether glycol, polyethylene adipate, polybutylene adipate, polyneopentylene adipate, Polylactone diols such as poly-3-methylpentylene adipate, polyethylene / butylene adipate, polyneopentyl / hexyl adipate, polycaprolactone diol, polyvalerolactone diol, polycaprolactone / polyvalerolactone diol, polyalkylene carbonate And polycarbonate diols such as Among these, polyether diol and polycarbonate diol are preferable from the viewpoint of the effect of the present invention, and polyalkylene carbonate diol is particularly preferable.

  In the present invention, it is preferable to use a diol compound having a carboxylic acid group in combination as the diol compound to enhance hydrophilicity. Examples of the diol compound having a carboxylic acid group include dimethylolacetic acid, dimethylolpropionic acid, and dimethylolbutanoic acid, and dimethylolpropionic acid is particularly preferable.

  The form of the urethane resin used for the resin particles in the present invention is not particularly limited. Typical forms include emulsion types such as self-emulsifying emulsions and self-stabilizing types. In particular, in the compound constituting the urethane, a urethane resin using a diol compound having an acidic group such as a carboxylic acid group or a sulfonic acid group, a urethane resin obtained by adding a low molecular weight polyhydroxy compound as a raw material, Or the urethane resin which introduce | transduced the acidic group is mentioned, The urethane resin which has a carboxyl group among these is desirable.

The weight average molecular weight of the urethane resin used in the present invention is preferably from 5,000 to 200,000, more preferably from 8,000 to 30,000, from the viewpoints of scratch resistance and ink storage stability.
The acid value of the urethane resin is not particularly limited, but is preferably 5 mgKOH / g or more and 100 mgKOH / g or less, and particularly preferably 10 mgKOH / g or more and 80 mgKOH / g or less.

  The weight average molecular weight is measured by gel permeation chromatography (GPC). As GPC, HLC-8220GPC (manufactured by Tosoh Corporation) is used, and TSKgel Super HZM-H, TSKgel Super HZ4000, TSKgel Super HZ2000 (manufactured by Tosoh Corporation, 4.6 mm ID × 15 cm) are used as columns. Details of GPC are described in paragraph [0076] of Japanese Patent Application Laid-Open No. 2010-155359.

As the urethane resin, those synthesized by a known synthesis method or commercially available products can be used.
As a commercial item, if it is a urethane resin, there will be no restriction | limiting in particular, It is preferable to use a polyester-type urethane resin or a polyether-type urethane resin especially. For example, NeoRez R-960 (manufactured by Nihon Lubrizol), NeoRez R-989 (manufactured by Nihon Lubrizol), NeoRez R-9320 (manufactured by Nihon Lubrizol), NeoRad NR-440 (manufactured by Nihon Lubrizol), Hydran AP-30 (made by DIC Corporation), Hydran APX-601 (made by DIC Corporation), Hydran SP-510 (made by DIC Corporation), Hydran SP-97 (made by DIC Corporation), Hydran HW140 (Manufactured by DIC Corporation), Takerak W-5025 (manufactured by Mitsui Takeda Chemical Co., Ltd.), Elastron MF-60 (manufactured by Daiichi Kogyo Seiyaku Co., Ltd.), Elastron MF-9 (manufactured by Daiichi Kogyo Seiyaku Co., Ltd.), M-1064 (Daiichi Kogyo Seiyaku Co., Ltd.), Iselux S-1020 (Hodogaya Chemical Co., Ltd.), Iselux S-1040 (Hodogaya Chemical Co., Ltd.), Iserax S-1085C (Hodogaya Chemical Co., Ltd.), Iserlux S-4040N (Hodogaya Chemical Co., Ltd.), Neotan UE-5000 (Toagosei Co., Ltd.) Manufactured), RU-40 series (manufactured by Stahl Japan), U-coat UWS-145 (manufactured by Sanyo Chemical Co., Ltd.), Permarin UA-150 (manufactured by Sanyo Chemical Co., Ltd.), WF-41 series (manufactured by Stahl Japan) , WPC-101 (manufactured by Nippon Urethane Industry Co., Ltd.), ACRITT WBR-016U, WEM-321U, WBR-2018, WBR-2000U, WBR-601U, WBR-2101 (manufactured by Taisei Fine Chemical Co., Ltd.).

Hereinafter, specific examples of the urethane resin constituting the resin particles that can be suitably used in the present invention will be given. However, the present invention is not limited to this.
B-1) Sodium hydroxide partially neutralized salt of reaction product of isophorone diisocyanate / polycarbonate diol (Duranol T5661, manufactured by Asahi Kasei Chemicals) / dimethylolpropionic acid B-2) dicyclohexylmethane-4,4′-diisocyanate / polycarbonate diol ( Duranol T5660, manufactured by Asahi Kasei Chemicals) / sodium hydroxide partially neutralized salt of reaction product of dimethylolpropionic acid B-3) Isophorone diisocyanate / polycarbonate diol (Duranol T5661, manufactured by Asahi Kasei Chemicals) / triethylamine of reaction product of dimethylolpropionic acid Partially neutralized salt B-4) Xylylene diisocyanate / polycarbonate diol duranol T 5661, manufactured by Asahi Kasei Chemicals) / dimethylol propionic acid, a reaction product of sodium hydroxide B-5) Isophorone diisocyanate / ethylene glycol (reaction product of isophorone diisocyanate / polyethylene glycol (molecular weight 300, manufactured by Wako Pure Chemical Industries) / dimethylol propionic acid) B-5) Isophorone diisocyanate / ethylene glycol Sodium hydroxide partially neutralized salt of dimethylolpropionic acid reactant B-7) Sodium hydroxide partially neutralized salt of isophorone diisocyanate / polypropylene glycol / dimethylolpropionic acid reactant B-8) Dicyclohexylmethane-4,4 Sodium hydroxide partially neutralized salt of reaction product of '-diisocyanate / 1,2-butanediol / dimethylolpropionic acid

  The molecular weight range of the polymer constituting the resin particles is preferably 3000 to 200,000 in terms of weight average molecular weight, more preferably 5000 to 150,000, and still more preferably 10,000 to 100,000. 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 of the resin particles is measured in the same manner as the weight average molecular weight of the polymer dispersant constituting the pigment coated with the resin.

  The resin particles are preferably a polymer having an acid value of 100 mgKOH / g or less from the viewpoint of self-dispersibility and agglomeration rate when the treatment liquid comes into contact, and the acid value is 25 mgKOH / g to 100 mgKOH / g. More preferred.

The average particle diameter of the resin particles (particularly self-dispersing polymer particles) in the present invention is preferably in the range of 1 nm to 400 nm, more preferably in the range of 1 nm to 200 nm, and still more preferably in the range of 1 nm to 100 nm. Especially preferably, it is the range of 1 nm-50 nm. Manufacturability is improved when the volume average particle diameter is 1 nm or more. Moreover, storage stability improves that a volume average particle diameter is 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 volume average particle size of the pigment in the dispersed state is obtained in the same manner as the average particle size and particle size distribution of the pigment coated with the resin.

There is no particular limitation on the content of the resin particles (preferably self-dispersing polymer particles) in the ink composition (total content when there are two or more types), but with respect to the total amount of the ink composition, 0.3 mass%-10.0 mass% are preferable, 0.5 mass%-7.0 mass% are more preferable, 1.0 mass%-5.0 mass% are especially preferable.
When the content is 0.3% by mass or more, the abrasion resistance of the image can be further improved, and image unevenness can be further suppressed.
When the content is 10.0% by mass or less, the ink ejection property can be further improved, and it is advantageous in that the generation of precipitates in a low temperature environment is suppressed.

-Water-
The ink composition of the present invention contains water.
Although there is no restriction | limiting in particular in content in the ink composition of water, Content of water can be 50 mass% or more.
In general, in an ink composition having a water content of 50% by mass or more, precipitation tends to occur. However, as described above, the ink composition of the present invention can suppress the generation of precipitates even under a low temperature environment.
Therefore, the ink composition of the present invention can contain 50% by mass or more of water.
The preferable content of water in the ink composition is preferably 50% by mass or more and 80% by mass or less, more preferably 50% by mass or more and 75% by mass or less, and still more preferably 50% by mass with respect to the total amount of the ink composition. It is not less than 70% by mass.

-Polymerizable compound-
The ink composition according to the present invention may contain at least one polymerizable compound.
In the case of an ink composition containing a polymerizable compound, it is imparted on a recording medium and has high polymerizability and polymerization efficiency when curing an image by irradiation with active energy rays, and the formed image has abrasion resistance and scratch resistance. It can be increased and can contribute to the suppression of surface roughness.

From the above points, polyfunctional (meth) acrylamide compounds are preferred.
Among polyfunctional (meth) acrylamide compounds, a (meth) acrylamide compound represented by the following general formula (1) (hereinafter simply represented by “general formula (1)” in that it has high polymerization ability and curing ability. Are also particularly preferred.
This compound has four acrylamide groups or methacrylamide groups as polymerizable groups in the molecule. In addition, this compound exhibits curability based on a polymerization reaction due to application of energy such as active energy rays such as α rays, γ rays, X rays, ultraviolet rays, visible rays, infrared rays, and electron beams, and heat. The compound represented by the general formula (1) exhibits water solubility and dissolves well in water-soluble solvents such as water and alcohol.
Further, the compound represented by the general formula (1) is also preferable from the viewpoint of ink dischargeability (particularly, continuous dischargeability).

((Meth) acrylamide compound represented by general formula (1))
In the ink composition of the present invention, as described above, at least one of the polymerizable compounds is preferably a (meth) acrylamide compound represented by the following general formula (1).

In general formula (1), R ¹ represents a hydrogen atom or a methyl group. R ² represents a linear or branched alkylene group having 2 to 4 carbon atoms. However, R ² does not have a structure in which an oxygen atom and a nitrogen atom bonded to both ends of R ² are bonded to the same carbon atom of R ² . R ³ represents a divalent linking group. k represents 2 or 3. x, y, and z each independently represent an integer of 0 to 6, and x + y + z satisfies 0 to 18.

In general formula (1), R ¹ represents a hydrogen atom or a methyl group. Several R < ¹ > may mutually be same or different. R ¹ is preferably a hydrogen atom.

In the general formula (1), R ² represents a linear or branched alkylene group having 2 to 4 carbon atoms. A plurality of R ² may be the same as or different from each other. R ² is preferably an alkylene group having 3 to 4 carbon atoms, more preferably an alkylene group having 3 carbon atoms, and particularly preferably a linear alkylene group having 3 carbon atoms. The alkylene group for R ² may further have a substituent, and examples of the substituent include an aryl group and an alkoxy group.
However, R ² does not have a structure in which an oxygen atom and a nitrogen atom bonded to both ends of R ² are bonded to the same carbon atom of R ² . R ² is a linear or branched alkylene group that connects the oxygen atom and the nitrogen atom of the (meth) acrylamide group. When the alkylene group has a branched structure, it takes an —O—C—N— structure (hemaminal structure) in which the oxygen atoms at both ends and the nitrogen atom of the (meth) acrylamide group are bonded to the same carbon atom in the alkylene group. It is also possible. However, the compound represented by the general formula (1) does not include a compound having such a structure. Thereby, the decomposition at the position of the carbon atom of the —O—C—N— structure is suppressed, and the storage stability of the ink composition can be further improved.

In general formula (1), R ³ represents a divalent linking group. Examples of the divalent linking group for R ³ include an alkylene group, an arylene group, a heterocyclic group, or a group composed of a combination thereof, and an alkylene group is preferable. When the divalent linking group includes an alkylene group, the alkylene group may further include at least one group selected from —O—, —S—, and —NR ^a —. R ^a represents a hydrogen atom or an alkyl group having 1 to 4 carbon atoms.

When R ³ contains an alkylene group, examples of the alkylene group include a methylene group, an ethylene group, a propylene group, a butylene group, a pentylene group, a hexylene group, a heptylene group, an octylene group, and a nonylene group. The number of carbon atoms of the alkylene group of R ³ is preferably 1 to 6, more preferably 1 to 3, and particularly preferably 1.
The alkylene group for R ³ may further contain at least one selected from —O—, —S—, and —NR ^a —. Examples of the alkylene group containing —O— include — C ₂ H ₄ —O—C ₂ H ₄ —, —C ₃ H ₆ —O—C ₃ H ₆ — and the like can be mentioned.
The alkylene group for R ³ may further have a substituent, and examples of the substituent include an aryl group and an alkoxy group.

When R ³ includes an arylene group, examples of the arylene group include a phenylene group and a naphthylene group. The number of carbon atoms of the arylene group of R ³ is preferably 6 to 14, and is 6 to 10 More preferably, 6 is particularly preferable.
The arylene group for R ³ may further have a substituent, and examples of the substituent include an alkyl group and an alkoxy group.

When R ³ contains a heterocyclic group, the heterocyclic group is preferably a 5-membered or 6-membered ring, and they may be further condensed. Further, it may be an aromatic heterocyclic ring or a non-aromatic heterocyclic ring. Specific examples of the heterocyclic group when R ³ includes a heterocyclic group include pyridine, pyrazine, pyrimidine, pyridazine, triazine, quinoline, isoquinoline, quinazoline, cinnoline, phthalazine, quinoxaline, pyrrole, indole, furan, benzofuran, and thiophene. , Benzothiophene, pyrazole, imidazole, benzimidazole, triazole, oxazole, benzoxazole, thiazole, benzothiazole, isothiazole, benzisothiazole, thiadiazole, isoxazole, benzisoxazole, pyrrolidine, piperidine, piperazine, imidazolidine, thiazoline, etc. Is mentioned. Of these, an aromatic heterocyclic group is preferable, and pyridine, pyrazine, pyrimidine, pyridazine, triazine, pyrazole, imidazole, benzimidazole, triazole, thiazole, benzothiazole, isothiazole, benzisothiazole, and thiadiazole are preferable. In addition, although the heterocyclic group shown above is illustrated in a form in which the substitution position is omitted, the substitution position is not limited. For example, in the case of pyridine, substitution is made at the 2-position, 3-position, and 4-position. It is possible to include all of these substitutions. The heterocyclic group may further have a substituent, and examples of the substituent include an alkyl group, an aryl group, and an alkoxy group.

In general formula (1), k represents 2 or 3. Several k may mutually be same or different. C _k H _2k may have a linear structure or a branched structure.

  In general formula (1), x, y, and z each independently represent an integer of 0 to 6, preferably an integer of 0 to 5, and more preferably an integer of 0 to 3. x + y + z satisfies 0-18, is preferably 0-15, and is more preferably 0-9.

  Specific examples (polymerizable compounds a to f) of the compound represented by the general formula (1) are shown below. However, the compound represented by General formula (1) is not limited to these.

  Although there is no restriction | limiting in particular in the synthesis | combining method of the compound represented by General formula (1), For example, it can synthesize | combine by the method described in Unexamined-Japanese-Patent No. 2013-18846 Paragraph 0028-0033 and Paragraph 0123-0139.

When the ink composition according to the present invention contains the compound represented by the general formula (1) described above, the ink composition may contain only one type of the compound represented by the general formula (1). And you may contain 2 or more types.
When the ink composition contains the compound represented by the general formula (1), the content of the compound represented by the general formula (1) is 0.1% by mass with respect to the total amount of the ink composition. -45 mass% is preferable, 1 mass%-30 mass% is more preferable, 2 mass%-20 mass% is especially preferable. When the content of the compound represented by the general formula (1) is within the above range, the curability and storage stability of the ink composition are further improved.
From the viewpoint of curability, the content is more preferably 3% by mass or more, further preferably 5% by mass, and particularly preferably 7% by mass or more.

Further, the proportion of the (meth) acrylamide compound represented by the general formula (1) in the total polymerizable compound contained in the ink composition is 50% by mass or more (more preferably 70% by mass or more, further preferably. Is preferably 80% by mass or more, particularly preferably 90% by mass or more.
This form is remarkably excellent in curability and continuous ink ejection.

((Meth) acrylamide compound represented by general formula (2))
The ink composition according to the present invention includes at least one monofunctional (meth) acrylamide compound represented by the following general formula (2) (hereinafter also referred to as “compound represented by the general formula (2)”). Can be contained. Thereby, the flexibility of an image can be improved more.
In the ink composition according to the present invention, for example, the compound represented by the general formula (1) described above and the compound represented by the following general formula (2) may be used in combination.

In General Formula (2), R ¹⁰ represents a hydrogen atom or a methyl group, R ¹¹ represents a hydrogen atom, a methyl group, or an ethyl group, and R ¹² represents a substituted or unsubstituted alkyl group. R ¹¹ and R ¹² may be bonded to each other to form a 5- to 8-membered ring. The 5-membered ring to 8-membered ring may further contain at least one selected from —O—, —S—, and —NR ^b —. R ^b represents a hydrogen atom or an alkyl group having 1 to 4 carbon atoms.

In the general formula (2), R ¹⁰ represents a hydrogen atom or a methyl group, a hydrogen atom is preferable.
R ¹¹ represents a hydrogen atom, a methyl group or an ethyl group, preferably a hydrogen atom or a methyl group, more preferably a hydrogen atom.
R ¹² represents a substituted or unsubstituted alkyl group. As the alkyl group for R ¹² , a linear or branched alkyl group having 1 to 6 carbon atoms (for example, methyl group, ethyl group, propyl group, butyl group, pentyl group, hexyl group) is preferable, and the number of carbon atoms is 2 An alkyl group having ˜4 is more preferable, and an alkyl group having 2 or 3 carbon atoms is particularly preferable.

Specific examples of the compound represented by the general formula (2) include the following exemplary compounds (C-1) to (C-13). However, the compound represented by the general formula (2) is not limited thereto.
(C-1): Diacetone acrylamide (manufactured by Nippon Kasei Co., Ltd.)
(C-2): Hydroxyethylacrylamide (manufactured by Kojinsha)
(C-3): Hydroxypropylacrylamide (manufactured by Fluka)
(C-4): N- [1,1-bis (hydroxymethyl) -2-hydroxyethyl] propenamide (manufactured by Aldrich)
(C-5): N- (2-dimethylaminoethyl) acrylamide (manufactured by Aldrich)
(C-6): Dimethylaminopropylacrylamide (manufactured by Kojinsha)
(C-7): 2- (acryloyloxy) -N, N, N-trimethylethaneaminium chloride (manufactured by Kojin Co., Ltd.)
(C-8): (3-acrylamidopropyl) trimethylammonium chloride (manufactured by Kojin Co., Ltd.)
(C-9): 2-acrylamido-2-methylpropanesulfonic acid (manufactured by Toa Gosei Co., Ltd.)
(C-10): N- [1,1-dimethyl-2- (sodiooxysulfonyl) ethyl] acrylamide (manufactured by Aldrich)
(C-11): N, N-dimethylacrylamide (manufactured by Kojinsha)
(C-12): N, N-diethylacrylamide (manufactured by Kojinsha)
(C-13): 4-acryloylmorpholine (manufactured by Kojin Co., Ltd.)

When the ink composition contains the compound represented by the above general formula (2), the ink composition may contain only one kind of the compound represented by the general formula (2), or two kinds thereof. You may contain above.
When the ink composition contains the compound represented by the above general formula (2), the preferred range of the content of the compound represented by the general formula (2) is represented by the above general formula (1). This is the same as the preferred range of the compound content.

In the ink composition according to the present invention, as described above, the compound represented by the general formula (1) and the compound represented by the following general formula (2) may be contained in combination.
However, from the viewpoint of further improving the continuous ejection property of the ink, the mass ratio [the compound represented by the general formula (1): the compound represented by the general formula (2)] is preferably 100: 0 to 50:50. 100: 0 to 70:30 is more preferable, 100: 0 to 80:20 is more preferable, 100: 0 to 90:10 is particularly preferable, and 100: 0 is most preferable.
If the said mass ratio is 100: 0-50: 50, the characteristic of the compound represented by General formula (1) will be maintained more effectively.

Examples of the polymerizable compound also include other polymerizable compounds other than the compound represented by the general formula (1) and the compound represented by the general formula (2).
In addition, it goes without saying that the compound represented by the general formula (1) described above (and the compound represented by the general formula (2) if necessary) and other polymerizable compounds may be used in combination. is there.
Examples of other polymerizable compounds include nonionic polymerizable monomers and cationic polymerizable monomers described in paragraphs 0149 to 0169 of JP-A-2011-46872.

  The content of the polymerizable compound in the ink composition (in the case of two or more types, the total content) is preferably 0.1% by mass to 45% by mass with respect to the total amount of the ink composition, and is 1% by mass. -30% by mass is more preferable, and 2% by mass to 20% by mass is particularly preferable. When the content of the polymerizable compound is within the above range, the curability and storage stability of the ink composition are further improved.

-Polymerization initiator-
When the ink composition according to the present invention contains a polymerizable compound, it is preferable to further contain a polymerization initiator.
The polymerization initiator has a function of initiating polymerization of the polymerizable compound by active energy rays.
A polymerization initiator can be used individually by 1 type or in mixture of 2 or more types. The polymerization initiator may be used in combination with a sensitizer.

  As a polymerization initiator, the compound which can start the polymerization reaction of a polymeric compound with an active energy ray can be selected suitably, and can be contained. Examples of the polymerization initiator include polymerization initiators (for example, photopolymerization initiators) that generate active species (radicals, acids, bases, etc.) by radiation or light, or electron beams.

  Examples of the photopolymerization initiator include acetophenone, 2,2-diethoxyacetophenone, p-dimethylaminoacetophenone, p-dimethylaminopropiophenone, benzophenone, 2-chlorobenzophenone, p, p′-dichlorobenzophenone, p, p′-bisdiethylaminobenzophenone, Michler's ketone, benzyl, benzoin, benzoin methyl ether, benzoin ethyl ether, benzoin isopropyl ether, benzoin n-propyl ether, benzoin isobutyl ether, benzoin n-butyl ether, benzyldimethyl ketal, tetramethylthiuram monosulfide, Thioxanthone, 2-chlorothioxanthone, 2-methylthioxanthone, azobisisobutyronitrile, benzoin peroxide , Di-tert-butyl peroxide, 1-hydroxycyclohexyl phenyl ketone, 1- [4- (2-hydroxyethoxy) -phenyl] -2-hydroxy-2-methyl-1-propan-1-one, 2-hydroxy 2-methyl-1-phenyl-1-one, 2-hydroxy-2-methyl-1-phenyl-propan-1-one, 1- (4-isopropylphenyl) -2-hydroxy-2-methylpropane-1 -On, methylbenzoyl formate. Furthermore, for example, aromatic diazonium salts, aromatic halonium salts, aromatic sulfonium salts, metallocene compounds such as triphenylsulfonium hexafluorophosphate, diphenyliodonium hexafluoroantimonate and the like can be mentioned. The 1- [4- (2-hydroxyethoxy) -phenyl] -2-hydroxy-2-methyl-1-propan-1-one can be obtained as a commercial product, for example, Irgacure 2959 (BASF Japan Ltd.). Manufactured). Moreover, as a commercial item marketed on the said 2-hydroxy-2-methyl-1-phenyl-1-one, Darocur 1173 (made by BASF Japan) etc. can be mentioned, for example.

  The ink composition of the present invention contains at least one polymerization initiator represented by the following general formula (X) (specific polymerization initiator; hereinafter also referred to as “compound represented by general formula (X)”). It is more preferable.

In general formula (X), R ^X1 , R ^X2 , R ^X3 , and R ^X4 each independently represent a hydrogen atom, a halogen atom, an alkyl group, an alkoxy group, a hydroxy group, an alkylthio group, a mercapto group, an acyl group, or Represents an amino group. In general formula (X), n represents an integer of 1 or more and 4 or less.

  In addition, when the ink composition of the present invention includes a polymerization initiator represented by the general formula (X), a phenomenon in which resin particles in the ink aggregate due to the polymerization initiator represented by the general formula (X) In addition, the phenomenon in which the discharge property is lowered due to the aggregation is suppressed.

As described above, R ^{X1 to} R ^X4 are a hydrogen atom, a halogen atom, an alkyl group, an alkoxy group, a hydroxy group, an alkylthio group, a mercapto group, an acyl group, or an amino group.

In R ^{X1 to} R ^X4 , the halogen atom is preferably a fluorine atom, a chlorine atom, a bromine atom, or an iodine atom, more preferably a chlorine atom or a bromine atom, and particularly preferably a chlorine atom.

In R ^{X1 to} R ^X4 , the number of carbon atoms of the alkyl group is preferably 1 to 6 carbon atoms, and more preferably 1 to 3 carbon atoms.
In R ^{X1 to} R ^X4 , the alkyl group may be a linear alkyl group or a branched alkyl group. Moreover, the alkyl group may have an alicyclic structure.
^Examples of the alkyl group in R ^{X1 to} R ^X4 include a methyl group, an ethyl group, an n-propyl group, an isopropyl group, an n-butyl group, an s-butyl group, a t-butyl group, an n-pentyl group, an n-hexyl group, A cyclohexyl group is mentioned, A methyl group, an ethyl group, n-propyl group, and an isopropyl group are preferable.

In R ^{X1 to} R ^X4 , the number of carbon atoms of the alkoxy group is preferably 1 to 6 carbon atoms, and more preferably 1 to 3 carbon atoms.
In R ^{X1 to} R ^X4 , the alkoxy group may be a linear alkoxy group or a branched alkoxy group. Moreover, the alkoxy group may have an alicyclic structure.
As an alkoxy group in R ^{< X1} > -R < ^X4 >, a methoxy group, an ethoxy group, n-propyloxy group, isopropyloxy group, n-butoxy group, s-butoxy group, t-butoxy group, n-pentyloxy group, n- A hexyloxy group and a cyclohexyloxy group are mentioned, and a methoxy group, an ethoxy group, an n-propyloxy group, and an isopropyloxy group are preferable.

In R ^{X1 to} R ^X4 , the number of carbon atoms of the alkylthio group is preferably 1 to 6 carbon atoms, and more preferably 1 to 4 carbon atoms.
In R ^{X1 to} R ^X4 , the alkylthio group may be a linear alkylthio group or a branched alkylthio group. Moreover, the alkylthio group may have an alicyclic structure.
^Examples of the alkylthio group in R ^{X1 to} R ^X4 include methylthio group, ethylthio group, n-propylthio group, isopropylthio group, n-butylthio group, s-butylthio group, t-butylthio group, n-pentylthio group, and n-hexylthio group. And a cyclohexylthio group, and a methylthio group, an ethylthio group, an n-propylthio group, and an isopropylthio group are preferable.

In R ^{X1 to} R ^X4 , the number of carbon atoms of the acyl group is preferably 1 to 6 carbon atoms, and more preferably 1 to 3 carbon atoms.
In R ^{X1 to} R ^X4 , the acyl group may be a straight chain acyl group or a branched chain acyl group.
Examples of the acyl group in R ^{X1 to} R ^X4 include a formyl group, an acetyl group, an ethylacyl group, an n-propylacyl group, and an isopropylacyl group, and a formyl group, an acetyl group, and an ethylacyl group are preferable.

R ^{X1 to} R ^X4 are preferably a hydrogen atom, a halogen atom, an alkyl group, an alkoxy group, or an alkylthio group, more preferably a hydrogen atom, an alkoxy group, or an alkylthio group, and most preferably a hydrogen atom.

Moreover, as a preferable form of the compound represented by general formula (X), the form whose 2 or more (preferably 3 or more, most preferably 4) is a hydrogen atom among R ^{< X1} > -R < ^X4 > is mentioned. .

  Hereinafter, specific examples (exemplary compounds) of the compound represented by the general formula (X) are shown. However, the compound represented by general formula (X) is not limited to these.

  The compound represented by the general formula (X) (specific polymerization initiator) can be synthesized, for example, according to the method described in paragraphs 0067 to 0071 and 0112 to 0115 of JP-A No. 2000-186242.

Although there is no restriction | limiting in particular in content of the compound (specific polymerization initiator) represented by general formula (X) in the ink composition of this invention, 0.05 mass%-10. 0% by mass is preferable, 0.08% by mass to 10.0% by mass is more preferable, 0.1% by mass to 10.0% by mass is further preferable, and 0.1% by mass to 8.0% by mass is further preferable. 0.1 mass% to 5.0 mass% is particularly preferable.
When the content is 0.05% by mass or more, sensitivity is further improved, and image abrasion resistance is further improved.
When the content is 10.0% by mass or less, the high temperature aging stability of the ink composition is further improved. Furthermore, when the content is 10.0% by mass or less, the total amount of non-volatile components can be lowered, thereby further improving the abrasion resistance of the image.

The ink composition of the present invention may contain a polymerization initiator other than the above.
Other polymerization initiators may be selected as appropriate from compounds that can initiate a polymerization reaction with active energy rays. ) Can be used. For example, a photoinitiator or the like can be used.
Examples of other polymerization initiators include hydroxyalkylphenone initiators, acetophenone initiators, benzophenone initiators, benzoin initiators, benzoin ether initiators, aminoalkylphenone initiators, xanthone initiators, Examples include oxime initiators.
For example, examples of the hydroxyalkylphenone-based initiator include 1-hydroxycyclohexyl phenyl ketone, 1- (4-isopropylphenyl) -2-hydroxy-2-methylpropan-1-one, and the like.
Examples of acetophenone-based initiators include acetophenone, 2,2-diethoxyacetophenone, p-dimethylaminoacetophenone, and the like.
Examples of the benzophenone initiator include benzophenone, 2-chlorobenzophenone, p, p′-dichlorobenzophenone, p, p′-bisdiethylaminobenzophenone, Michler's ketone, and the like.
Examples of the benzoin initiator and benzoin ether initiator include benzoin, benzoin methyl ether, benzoin ethyl ether, benzoin isopropyl ether, benzoin n-propyl ether, benzoin isobutyl ether, benzoin n-butyl ether and the like.

The content of the total polymerization initiator in the ink composition of the present invention (the total content when there are two or more polymerization initiators) is preferably 0.1% by mass to 15.0% by mass, 1 mass%-10.0 mass% are more preferable, 0.15 mass%-8.0 mass% are still more preferable, 0.2 mass%-5.0 mass% are especially preferable.
When the content of the total polymerization initiator is 0.1% by mass or more, the sensitivity is further improved and the image strength is further improved.
When the content is 15.0% by mass or less, the high temperature aging stability of the ink can be further improved. Furthermore, the total amount of non-volatile components can be reduced, thereby further improving the image intensity.

-Polymerization inhibitor-
In the present invention, a polymerization inhibitor that suppresses polymerization by heat or actinic rays is preferably added to the ink. As the polymerization inhibitor, various compounds are known, and those widely blended in general polymerizable compositions can be used as they are.

  As a polymerization inhibitor, it is possible to use phenolic antioxidants, amine compounds, phosphorus antioxidants, hydroquinone monomethyl ether widely used for (meth) acrylic monomers, hydroquinone, t-butylcatechol, pyrogallol, water, etc. Is possible. These are detailed in “Development Technology of Polymer Additives” (issued by CMC). Since phenolic compounds with double bonds derived from acrylic acid in the molecule can capture R radicals from their reaction mechanism, they can suppress polymerization even when heated in a system without sealed oxygen. Is preferable. Specifically, Sumitizer Chemical's Sumilizer GA-80, Sumilizer GM, Sumilizer GS, etc. can be mentioned.

  These polymerization inhibitors are preferably added at the time of preparing the pigment dispersion, but excessive addition of the polymerization inhibitor causes a decrease in sensitivity as an ink, while maintaining the storage stability as an ink, It is desirable that the amount capable of preventing polymerization at the time of pigment dispersion is appropriately set and blended. Or it is preferable to mix | blend excessively and to extract after dispersion | distribution and to reduce the quantity of a polymerization inhibitor.

  When the photopolymerization is cationic polymerizable, the polymerization inhibitor is preferably an amine compound or water. In the case of an amine compound, it is preferable to add 0.01% by mass to 1% by mass of the whole ink. If it is less than 0.01% by mass, storage stability cannot be obtained. When it is larger than 1% by mass, the curing sensitivity is lowered. In the case of water, 1.0 mass%-3.5 mass% are preferable.

  Among amine compounds, a quaternary ammonium salt has a good balance between sensitivity and storage stability, and is particularly preferable for a transparent cationic polymerizable ink having no pigment.

-Others-
The ink composition according to the present invention may further contain a water-soluble polymer compound, a water-soluble organic solvent, a surfactant, an antifoaming agent, colloidal silica, and wax particles. Hereinafter, these components will be described.

(Water-soluble polymer compound)
The ink composition according to the present invention preferably contains at least one water-soluble polymer compound as necessary. The water-soluble polymer compound is not particularly limited, and known water-soluble polymer compounds such as polyvinyl alcohol, polyacrylamide, polyvinyl pyrrolidone, and polyethylene glycol can be used.
Further, as the water-soluble polymer compound, a specific polymer compound that may be contained in a treatment liquid described later, or a water-soluble polymer compound described in paragraphs 0026 to 0080 of JP2013-001854A is also suitable. is there.

(Water-soluble solvent)
As the water-soluble solvent, known ones can be used without particular limitation.
Examples of the water-soluble solvent include glycols such as glycerin, 1,2,6-hexanetriol, trimethylolpropane, ethylene glycol, propylene glycol, diethylene glycol, triethylene glycol, tetraethylene glycol, pentaethylene glycol, and dipropylene glycol. 2-butene-1,4-diol, 2-ethyl-1,3-hexanediol, 2-methyl-2,4-pentanediol, 1,2-octanediol, 1,2-hexanediol, 1, In addition to polyhydric alcohols such as alkanediols such as 2-pentanediol and 4-methyl-1,2-pentanediol, saccharides, sugar alcohols, and hyaluronic acids described in paragraph 0116 of JP2011-42150A , Alkyl having 1 to 4 carbon atoms Alcohols, glycol ethers, 2-pyrrolidone, N- methyl-2-pyrrolidone. One or more of these solvents can be appropriately selected and used. Polyhydric alcohols are also useful as drying inhibitors and wetting agents, and examples include the examples described in paragraph 0117 of JP-A-2011-42150. Moreover, a polyol compound is preferable as a penetrant, and examples of the aliphatic diol include those described in paragraph 0117 of JP2011-42150A.
As other water-soluble solvents, for example, water-soluble solvents described in paragraphs 0176 to 0179 of JP2011-46872A, and paragraphs 0063 to 0074 of JP2013-18846A are described. It is also possible to appropriately select from the water-soluble solvents that are present.

When the ink composition of the present invention contains a water-soluble solvent, the content of the water-soluble solvent (the total content when there are two or more) is 2% by mass to 20% by mass with respect to the total amount of the ink composition. % Is preferred.
When the total content is 2% by mass or more, the solubility of the polymerization initiator in the ink composition can be further increased.
Moreover, since the polymerizable compound can be sufficiently contained in the ink composition when the total content is 20% by mass or less, the curability of the ink composition can be improved.
The total content is more preferably 3% by mass to 18% by mass and further preferably 4% by mass to 15% by mass with respect to the total amount of the ink composition.

The ink composition of the present invention contains a solvent A represented by the following structural formula (I) as a solvent and a solvent B selected from ethylene glycol, diethylene glycol, triethylene glycol, tetraethylene glycol, and pentaethylene glycol. More preferably. By setting it as such a composition, favorable abrasion resistance is obtained and curling and stacker blocking of the recording medium after image formation is suppressed.
Here, stacker blocking means that recording media on which images are formed are stacked, and the front surface (the surface on which the image is formed) of the recording media and the back surface of another recording medium (the image is formed). This refers to a phenomenon in which an image formed on a recording medium is destroyed by contact with a non-contact surface. The destruction of the image occurs, for example, when the image is transferred to the back surface of the recording medium or between the recording media.
Stacker blocking is described in, for example, Japanese Patent Application Laid-Open No. 2011-088323.
In the present invention, the content of the solvent A with respect to the total amount of the ink composition is 1.0% by mass to 10.0% by mass, and the content of the solvent B with respect to the total amount of the ink composition (mass basis) is the ink composition with the solvent A. It is preferably 0.05 to 20.0 times the content (mass basis) with respect to the total amount of the product.
In the present invention, the content (mass basis) of the solvent B with respect to the total amount of the ink composition is a times to b times (for example, 0.05 times to 20.0 times) the content (mass basis) of the solvent A with respect to the total amount of the ink composition. That the ratio [mass of solvent B / mass of solvent A] is a to b (for example, 0.05 to 20.0).

  The ratio [mass of solvent B / mass of solvent A] is preferably 0.1 to 15.0, and more preferably 0.2 to 10.0.

  In the present invention, the total content of the solvent A and the solvent B is preferably 2.0% by mass to 30.0% by mass, and preferably 3.0% by mass to 20% by mass with respect to the total amount of the ink composition. It is more preferably 0% by mass, and particularly preferably 5.0% by mass to 15.0% by mass.

  In the present invention, the content of the solvent B is preferably 0.5% by mass to 20.0% by mass, and 1.0% by mass to 15.0% by mass with respect to the total amount of the ink composition. It is more preferable that it is 2.0 mass%-10.0 mass%.

<Solvent A>
The solvent A in the present invention is at least one selected from compounds represented by the following structural formula (I). The solvent A may be a single (single component) solvent selected from the compounds represented by the following structural formula (I), or may be selected from the compounds represented by the following structural formula (I). It may be a mixed solvent composed of two or more kinds.

In Structural Formula (I), l, m, and n each independently represent an integer of 0 or more and satisfy l + m + n = 0-15. Especially, l + m + n has the preferable range of 3-12, and the range of 3-10 is more preferable. In Structural Formula (I), AO represents an ethyleneoxy group or a propyleneoxy group. Of these, a propyleneoxy group is preferable. When l + m + n ≧ 2, two or more AOs may be the same or different.
As the compound represented by the structural formula (I), glycerin and an alkylene oxide adduct of glycerin are preferable.

  Examples of the compound represented by the structural formula (I) are shown below. However, the present invention is not limited to these. Hereinafter, the numbers in parentheses represent SP values.

_{· NC 4 H 9 O (AO} ) 4 -H
(AO = EO or PO (EO: PO = 1: 1), SP value = 20.1)
_{· NC 4 H 9 O (AO} ) 10 -H
(AO = EO or PO (EO: PO = 1: 1), SP value = 18.8)
・ HO (A'O) ₄₀ -H
(A′O = EO or PO (EO: PO = 1: 3), SP value = 18.7)
・ HO (A''O) ₅₅ -H
(A ″ O = EO or PO (EO: PO = 5: 6), SP value = 18.8)
・ HO (PO) ₃ −H (SP value = 24.7)
HO (PO) ₇ -H (SP value = 21.2)
1,2-hexanediol (SP value = 27.4)
In addition, EO and PO represent an ethyleneoxy group and a propyleneoxy group, respectively.

  As the alkylene oxide adduct of glycerin, a commercially available product may be used. For example, as polyoxypropylated glycerin (ether of polypropylene glycol and glycerin), Sanix GP-250 (average molecular weight 250), GP-400 (average molecular weight 400), GP-600 (average molecular weight 600) Sanyo Chemical Industries, Ltd.], Reocon GP-250 (average molecular weight 250), GP-300 (average molecular weight 300, GP-400 (average molecular weight 400), GP-700 (average molecular weight 700) , Lion Corp.], polypropylene triol glycol triol type (average molecular weight 300, average molecular weight 700) [above, manufactured by Wako Pure Chemical Industries, Ltd.].

<Solvent B>
The solvent B in the present invention is at least one selected from ethylene glycol, diethylene glycol, triethylene glycol, tetraethylene glycol, and pentaethylene glycol. Of these, triethylene glycol and tetraethylene glycol are preferable. The solvent B may be a single (single component) solvent or a mixed solvent of two or more.

  You may use the commercial item marketed. For example, PEG-200 (average molecular weight 200), PEG-300 (average molecular weight 300), PEG-400 (average molecular weight 400) [manufactured by Sanyo Chemical Industries, Ltd.], PEG # 200 (average molecular weight 200), PEG # 300 (average molecular weight 300), PEG # 400 (average molecular weight 400) (manufactured by Lion Corporation), PEG # 200 (average molecular weight 200), PEG # 300 (average molecular weight 300), PEG # 400 (average molecular weight) 400) [manufactured by NOF Corporation], PEG 200 (average molecular weight 200), PEG 300 (average molecular weight 300), PEG 400 (average molecular weight 400) [manufactured by Daiichi Kogyo Seiyaku Co., Ltd.], etc. Is mentioned.

(Surfactant)
The ink composition according to the present invention can contain at least one surfactant as required. The surfactant can be used as a surface tension adjusting agent, for example.
As the surfactant, a compound having a structure having both a hydrophilic part and a hydrophobic part in the molecule can be used effectively. Anionic surfactant, cationic surfactant, amphoteric surfactant, nonionic surfactant Either a surfactant or a betaine surfactant can be used. Further, the above water-soluble polymer (polymer dispersant) may be used as a surfactant.

In the present invention, a nonionic surfactant is preferable from the viewpoint of suppressing ink droplet ejection interference, and an acetylene glycol derivative (acetylene glycol surfactant) is more preferable.
Examples of acetylene glycol surfactants include 2,4,7,9-tetramethyl-5-decyne-4,7-diol and 2,4,7,9-tetramethyl-5-decyne-4,7. -Alkylene oxide adduct of diol etc. can be mentioned, It is preferable that it is at least 1 sort (s) chosen from this. Examples of commercially available products of these compounds include E series such as Olphine E1010 manufactured by Nissin Chemical Industry Co., Ltd.
As the surfactant other than the acetylene glycol surfactant, a fluorine surfactant is preferable. Examples of the fluorine surfactant include an anionic surfactant, a nonionic surfactant, and a betaine surfactant, and among these, an anionic surfactant is more preferable. Examples of anionic surfactants include Capstone FS-63, Capstone FS-61 (manufactured by Dupont), Footent 100, Footent 110, Footent 150 (manufactured by Neos), CHEMGUARD S-760P (Chemguard) Inc.).

When a surfactant (surface tension adjusting agent) is contained in the ink composition, the surfactant has a surface tension of 20 mN / m to 60 mN / m from the viewpoint of satisfactorily discharging the ink composition by an ink jet method. It is preferable to contain the quantity of the range which can be adjusted to m, More preferably, it is 20 mN / m-45 mN / m from the point of surface tension, More preferably, it is 25 mN / m-40 mN / m.
Here, the surface tension of the ink composition refers to a value measured using an Automatic Surface Tensiometer CBVP-Z (manufactured by Kyowa Interface Science Co., Ltd.) at a liquid temperature of 25 ° C.

  When the ink composition according to the present invention contains a surfactant, the specific amount of the surfactant is not particularly limited, but is preferably 0.1% by mass or more, more preferably based on the total amount of the ink composition. Is 0.1% by mass to 10% by mass, more preferably 0.2% by mass to 3% by mass.

(Defoamer)
The ink composition according to the present invention may contain at least one antifoaming agent as necessary.
Examples of the antifoaming agent include silicone compounds (silicone defoaming agents) and pluronic compounds (pluronic defoaming agents). Among these, silicone antifoaming agents are preferable.
As the silicone-based antifoaming agent, a silicone-based antifoaming agent having a polysiloxane structure is preferable.

A commercial item can be used as an antifoamer.
Examples of commercially available products include BYK-012, 017, 021, 022, 024, 025, 038, 094 (above, manufactured by Big Chemie Japan Co., Ltd.), KS-537, KS-604, KM-72F (above, Shin-Etsu Chemical). Kogyo Co., Ltd.), TSA-739 (Momentive Performance Materials Japan GK), Olfin AF104 (Nisshin Chemical Co., Ltd.), and the like.
Among these, BYK-017, 021, 022, 024, 025, 094, KS-537, KS-604, KM-72F, and TSA-739, which are silicone-based antifoaming agents, are preferable. In view of this, BYK-024 is most preferred.

  When the ink composition according to the present invention contains an antifoaming agent, the content of the antifoaming agent is preferably 0.0001% by mass to 1% by mass, and 0.001% by mass to 0% with respect to the total amount of the ink composition. More preferably, 1% by mass.

(Colloidal silica)
The ink composition according to the present invention may contain colloidal silica as necessary.
Thereby, the stability at the time of continuous discharge of ink can be improved more.
Colloidal silica is a colloid composed of fine particles of inorganic oxide containing silicon having an average particle size of several hundred nm or less. Colloidal silica contains silicon dioxide (including hydrates thereof) as a main component, and may contain aluminate (sodium aluminate, potassium aluminate, etc.) as a minor component.
In addition, colloidal silica may contain inorganic salts such as sodium hydroxide, potassium hydroxide, lithium hydroxide and ammonium hydroxide, and organic salts such as tetramethylammonium hydroxide. These inorganic salts and organic salts act, for example, as colloid stabilizers.
About colloidal silica, the description of Paragraphs 0043-0050 of JP, 2011-202117, A can be referred to suitably, for example.
In addition, the ink composition of the present invention may contain an alkali metal silicate salt instead of or in addition to colloidal silica, if necessary. Regarding the alkali metal silicate, the description in paragraphs 0052 to 0056 of JP-A-2011-202117 can be appropriately referred to.

  When the ink composition according to the present invention contains colloidal silica, the content of colloidal silica is preferably 0.0001% by mass to 10% by mass, and 0.01% by mass to 3% by mass with respect to the total amount of the ink composition. Is more preferable, 0.02% by mass to 0.5% by mass is further preferable, and 0.03% by mass to 0.3% by mass is particularly preferable.

(Wax particles)
The ink composition according to the present invention may contain at least one wax particle. Thereby, abrasion resistance can be improved more.

  As wax particles, for example, plant waxes such as carnauba wax, candeli wax, beeswax, rice wax, lanolin, petroleum waxes such as animal wax, paraffin wax, microcrystalline wax, polyethylene wax, oxidized polyethylene wax, petrolatum, Particles of natural wax or synthetic wax such as montan wax, mineral wax such as ozokerite, synthetic wax such as carbon wax, Hoechst wax, polyolefin wax, stearamide, α-olefin / maleic anhydride copolymer, etc. A mixed particle etc. are mentioned.

The wax is preferably added in the form of a dispersion. For example, the wax can be contained in the ink composition as a dispersion such as an emulsion. As a solvent in the case of a dispersion, water is preferable, but it is not limited thereto. For example, a commonly used organic solvent can be appropriately selected and used during dispersion. Regarding the organic solvent, reference can be made to the description of paragraph number [0027] of JP-A-2006-91780.
Wax particles can be used singly or in combination.

  As the wax particles, commercially available products may be used. Examples of commercially available products include Nopcoat PEM17 (manufactured by Sannopco), Chemipearl W4005 (manufactured by Mitsui Chemicals), AQUACER 515, AQUACER 593 (all of which are manufactured by Big Chemie Japan).

  Among the above, preferable waxes are carnauba wax and polyolefin wax, and carnauba wax is particularly preferable from the viewpoint of abrasion resistance.

  When the ink composition according to the present invention contains wax particles, the content ratio of the resin particles to the wax particles is a range of resin particles: wax particles = 1: 5 to 5: 1 (solid content ratio). Is preferred. When the content ratio is within the above range, the image has excellent abrasion resistance.

(Other additives)
The ink composition of the present invention may contain other additives as necessary.
Other components include, for example, anti-drying agents (wetting agents), anti-fading agents, emulsion stabilizers, penetration enhancers, ultraviolet absorbers, preservatives, anti-fungal agents, viscosity modifiers, dispersion stabilizers, and rust inhibitors. And known additives such as chelating agents.

-Physical properties of ink composition-
The ink composition has a pH of 7.5 or more at 25 ° C. (± 1 ° C.) from the viewpoints of the aggregation rate and the dispersion stability of the composition.
When the pH of the ink composition is less than 7.5, the dispersibility is deteriorated, and the storage stability of the ink composition is lowered. The pH (25 ° C. ± 1 ° C.) of the ink composition is preferably pH 7.5 to 13, and more preferably 7.5 to 10.

  The viscosity of the ink composition is preferably in the range of 0.5 mPa · s to 10 mPa · s, more preferably in the range of 1 mPa · s to 7 mPa · s, from the viewpoint of the aggregation rate. The viscosity is measured under a condition of 30 ° C. using VISCOMETER TV-22 (manufactured by TOKI SANGYO CO. LTD).

  The surface tension of the ink composition at 25 ° C. (± 1 ° C.) is preferably 60 mN / m or less, more preferably 20 mN / m to 50 mN / m, and 25 mN / m to 45 mN / m. More preferably. When the surface tension of the ink composition is within the range, the occurrence of curling in the recording medium is advantageously suppressed. The surface tension is measured at 25 ° C. by a plate method using an Automatic Surface Tensiometer CBVP-Z (manufactured by Kyowa Interface Science Co., Ltd.).

Among the above, preferable embodiments of the ink composition in the invention include the following (1) first embodiment to (3) third embodiment. That is,
(1) As a first aspect,
A mode in which the inorganic salt contained in the ink composition is an alkali metal salt of hydrochloride or nitrate, and the pH of the ink composition is 7.5 to 13.
(2) As a second aspect,
A mode in which the inorganic salt contained in the ink composition is at least one selected from lithium chloride, lithium nitrate, potassium chloride, and potassium nitrate, and the pH of the ink composition is 7.5 to 10.
(3) As a third aspect,
An embodiment in which the inorganic salt contained in the ink composition is potassium nitrate and the pH of the ink composition is 7.5 to 9.

≪Processing liquid≫
The treatment liquid in the present invention contains at least one acidic compound and has a pH at 25 ° C. of 0.1 or more and 0.5 or less. When the treatment liquid having such a configuration is brought into contact with an ink composition having a pH of 7.5 or more containing at least one inorganic salt selected from water, a resin-coated pigment, resin particles, hydrochloride and nitrate, It is possible to agglomerate the dispersed particles in the composition.
In the present invention, by using a treatment liquid containing at least one kind of acidic compound and having a pH of 0.1 or more and pH 0.5 or less, the ink is excellent in cohesiveness and the occurrence of uneven glossiness and surface alignment in the image area is suppressed. The

-Acidic compounds-
Examples of the acidic compound include acidic substances that can lower the pH of the ink composition. Either an organic acidic compound or an inorganic acidic compound may be used, and two or more organic acidic compounds and inorganic acidic compounds are used in combination. May be.

(Organic acidic compounds)
When the treatment liquid contains an organic acidic compound, the organic acidic compound can aggregate components in the ink composition.
There is no restriction | limiting in particular as an organic acidic compound contained in a processing liquid. Examples of acidic groups include phosphoric acid groups, phosphonic acid groups, phosphinic acid groups, sulfuric acid groups, sulfonic acid groups, sulfinic acid groups, and carboxy groups. In the invention, the acidic group is preferably a phosphoric acid group or a carboxy group, more preferably a carboxy group, from the viewpoint of the aggregation rate of the ink composition.

  Organic compounds having a carboxy group (organic carboxylic acid) are polyacrylic acid, acetic acid, glycolic acid, malonic acid, malic acid (preferably DL-malic acid), maleic acid, ascorbic acid, succinic acid, glutaric acid, fumaric acid. Acid, citric acid, tartaric acid, phthalic acid, 4-methylphthalic acid, lactic acid, sulfonic acid, orthophosphoric acid, pyrrolidone carboxylic acid, pyrone carboxylic acid, pyrrole carboxylic acid, furan carboxylic acid, pyridine carboxylic acid, coumaric acid, thiophene carboxylic acid, Nicotinic acid, derivatives of these compounds, or salts thereof (for example, polyvalent metal salts) are preferred. These compounds may be used alone or in combination of two or more.

  The organic carboxylic acid is preferably a divalent or higher carboxylic acid (hereinafter also referred to as polyvalent carboxylic acid) from the viewpoint of the aggregation rate of the ink composition, and malonic acid, malic acid, maleic acid, and succinic acid. , Glutaric acid, fumaric acid, tartaric acid, 4-methylphthalic acid, and citric acid are more preferable, and malonic acid, malic acid, tartaric acid, and citric acid are particularly preferable.

  The organic acidic compound contained in the treatment liquid preferably has a low pKa. Dispersion stability is reduced by bringing the surface charge of particles such as pigments and polymer particles in the ink composition, which is stabilized by a weakly acidic functional group such as a carboxy group, into contact with an organic acidic compound having a lower pKa. Can be reduced.

  The organic acidic compound contained in the treatment liquid preferably has a low pKa, a high solubility in water, and a valence of 2 or more, and a functional group that stabilizes the particles in the ink composition (for example, More preferably, it is a divalent or trivalent acidic substance having a high buffer capacity in a pH range lower than the pKa of a carboxy group or the like.

(Inorganic acidic compounds)
When the treatment liquid contains an inorganic acidic compound, the inorganic acidic compound can agglomerate components in the ink composition.
Examples of the inorganic acidic compound contained in the treatment liquid include phosphoric acid, nitric acid, nitrous acid, sulfuric acid, and hydrochloric acid, but are not particularly limited thereto. As the inorganic acidic compound, phosphoric acid is most preferable from the viewpoint of suppressing the occurrence of uneven glossiness in the image area and the ink aggregation rate.

  Phosphoric acid has a low water solubility (25 ° C.) of 0.0018 g / 100 g of water when a calcium salt (calcium phosphate) is used. Therefore, when the inorganic acidic compound contained in the treatment liquid is phosphoric acid, the calcium salt is not dissolved but is fixed, and the effect of suppressing the occurrence of uneven gloss on the surface of the image area is excellent. In particular, when a recording medium having a coating layer containing calcium carbonate is used as the recording medium, phosphoric acid is advantageous as the inorganic acidic compound contained in the treatment liquid.

The total amount of acidic compounds contained in the treatment liquid is not particularly limited, but is preferably 5% by mass to 40% by mass from the viewpoint of the aggregation speed of the ink composition, and is 10% by mass to 30% by mass. Is more preferable.
The content ratio between the organic acidic compound and the inorganic acidic compound is preferably 5 to 50 mol% of the inorganic acidic compound content relative to the organic acidic compound content from the viewpoint of aggregation rate and gloss unevenness suppression. It is more preferably 10 mol% to 40 mol%, and further preferably 15 mol% to 35 mol%.

In addition to the acidic compound, the treatment liquid may use other aggregating components such as a polyvalent metal salt and a cationic polymer as necessary.
As for the polyvalent metal salt and the cationic polymer, for example, the polyvalent metal salt and the cationic polymer described in paragraphs 0155 to 0156 of JP2011-042150A can be used.

-Water-soluble polymer compounds-
The treatment liquid preferably contains at least one water-soluble polymer compound.
The water-soluble polymer compound is not particularly limited, and known water-soluble polymer compounds such as polyvinyl alcohol, polyacrylamide, polyvinyl pyrrolidone, and polyethylene glycol can be used.
As the water-soluble polymer compound, a specific polymer compound described later and water-soluble polymer compounds described in paragraphs 0026 to 0080 of JP2013-001854A are also suitable.

  Although there is no limitation in particular in the weight average molecular weight of a water-soluble high molecular compound, For example, it can be set as 10000-100,000, Preferably it is 20000-80000, More preferably, it is 30000-80000.

Further, the content of the water-soluble polymer compound in the treatment liquid in the present invention is not particularly limited, but is preferably 0.1% by mass to 10% by mass, and preferably 0.1% by mass to 0.1% by mass with respect to the total amount of the treatment liquid. 4 mass% is more preferable, 0.1 mass%-2 mass% is further more preferable, and 0.1 mass%-1 mass% is especially preferable.
If the content is 0.1% by mass or more, spreading of the ink droplets can be further promoted, and if the content is 10% by mass or less, the thickening of the treatment liquid can be further suppressed. Moreover, if content is 10 mass% or less, the application | coating nonuniformity of the process liquid resulting from the bubble in a process liquid can be suppressed more.

As the water-soluble polymer compound, a polymer compound containing a hydrophilic structural unit having an ionic group (preferably an anionic group) (hereinafter also referred to as “specific polymer compound”) is preferable. Thereby, the spread of the ink droplets applied to the recording medium can be further promoted, and the roughness of the image is further suppressed.
Examples of the ionic group in the specific polymer compound include a carboxyl group, a sulfonic acid group, a phosphoric acid group, a boronic acid group, an amino group, an ammonium group, and salts thereof. Among them, preferred is a carboxyl group, a sulfonic acid group, a phosphoric acid group, or a salt thereof, more preferred is a carboxyl group, a sulfonic acid group, or a salt thereof, and still more preferred is a sulfonic acid group or a salt thereof. Salt.
The hydrophilic structural unit having an ionic group (preferably an anionic group) is preferably a structural unit derived from a (meth) acrylamide compound having an ionic group (preferably an anionic group).
The content of the hydrophilic structural unit having an ionic group (preferably an anionic group) in the water-soluble polymer compound is, for example, 10% by mass to 100% by mass in the total mass of the water-soluble polymer compound. It is preferably 10% by mass to 90% by mass, more preferably 10% by mass to 70% by mass, still more preferably 10% by mass to 50% by mass, and further preferably 20% by mass to 40% by mass. It is particularly preferable that the content is% by mass.

The specific polymer compound includes at least one hydrophobic structural unit in addition to at least one hydrophilic structural unit having the above-described ionic group (preferably an anionic group, particularly preferably a sulfonic acid group). Is more preferable. By including the hydrophobic structural unit, the specific polymer compound is more likely to be present on the surface of the treatment liquid, so that the spread of the ink droplets applied to the recording medium is further promoted, and the roughness of the image is further suppressed.
As the hydrophobic structural unit, a structural unit derived from (meth) acrylic acid ester (preferably, alkyl ester having 1 to 4 carbon atoms of (meth) acrylic acid) is preferable.

  Content of the hydrophobic structural unit in a specific polymer compound can be made into 10 mass%-90 mass% in the total mass of a specific polymer compound, for example, It is preferable that it is 30 mass%-90 mass%. 50 mass% to 90 mass% is more preferable, and 60 mass% to 80 mass% is particularly preferable.

-Water-
The treatment liquid preferably contains water. The content of water is preferably 50% by mass to 90% by mass and more preferably 60% by mass to 80% by mass with respect to the total mass of the treatment liquid.

-Water-soluble organic solvent-
The treatment liquid preferably contains at least one water-soluble organic solvent.
The water-soluble organic solvent 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, a water-soluble organic solvent that can be contained in the ink composition described later can be used in the treatment liquid as well. Among them, 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, and More preferably, it is at least one selected from polyoxyethylene polyoxypropylene glycol.

  As content in the processing liquid of a water-soluble organic solvent, it is preferable that it is 3 mass%-20 mass% with respect to the whole processing liquid from viewpoints, such as applicability | paintability, and it is 5 mass%-15 mass%. More preferred.

-Surfactant-
The treatment liquid may contain 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.

  As the surfactant, JP-A-59-157636, pages 37-38 and Research Disclosure No. The compounds listed as surfactants in 308119 (1989) are also included. Further, fluorine (fluorinated alkyl) -based surfactants and silicone-based surfactants described in JP-A Nos. 2003-322926, 2004-325707, and 2004-309806 are also included.

  Although there is no restriction | limiting in particular as content of surfactant in a processing liquid, It is preferable that it is content so that the surface tension of a processing liquid will be 50 mN / m or less, and it will become 20 mN / m-50 mN / m. The content is more preferable, and the content is more preferably 30 mN / m to 45 mN / m.

-Other additives-
The treatment liquid can be configured to contain other additives in addition to the acidic compound and the water-soluble organic solvent. The other additives in the treatment liquid are the same as the other additives in the ink composition described above.

-Physical properties of treatment liquid-
The treatment liquid has a pH of 0.1 or more and 0.5 or less at 25 ° C. (± 1 ° C.) from the viewpoint of the aggregation rate of the ink composition. When the pH of the treatment liquid is less than 0.1, the adverse effect on the recording medium, for example, the roughness of the paper surface is increased, and the adhesion of the image area is deteriorated. On the other hand, if the pH of the treatment liquid exceeds 0.5, the aggregation rate is too slow, and dot coalescence occurs and the graininess deteriorates. The pH (25 ° C. ± 1 ° C.) of the treatment liquid is more preferably 0.2 to 0.4.

  The viscosity of the treatment liquid is preferably in the range of 0.5 mPa · s to 10 mPa · s, more preferably in the range of 1 mPa · s to 5 mPa · s, from the viewpoint of the aggregation rate of the ink composition. The viscosity is measured under a condition of 25 ° C. using a VISCOMETER TV-22 (manufactured by TOKI SANGYO CO. LTD).

  The surface tension at 25 ° C. (± 1 ° C.) of the treatment liquid is preferably 60 mN / m or less, more preferably 20 mN / m to 50 mN / m, and 30 mN / m to 45 mN / m. Is more preferable. When the surface tension of the treatment liquid is within the range, the occurrence of curling in the recording medium is suppressed, which is advantageous. The surface tension of the treatment liquid is measured under a condition of 25 ° C. by the plate method using an Automatic Surface Tensiometer CBVP-Z (manufactured by Kyowa Interface Science Co., Ltd.).

<Image forming method>
The image forming method of the present invention includes an ink applying step of forming an image by applying the ink composition of the ink set described above onto a recording medium by an ink jet method, and applying the treatment liquid of the ink set onto the recording medium. A treatment liquid application step.
According to the image forming method of the present invention, even when an image is formed over a long period of time and / or on a large amount of recording medium, aggregates are less likely to accumulate at the discharge port, and excellent discharge properties are achieved. Is secured for a long time. Furthermore, since surface alignment is suppressed, an image having excellent image quality is formed.

-Recording media-
The image forming method of the present invention records an image on a recording medium having a coating layer containing a base paper and an inorganic pigment. The coated paper is obtained by applying a coating material to the surface of high-quality paper, neutral paper, or the like that is mainly surface-treated with cellulose as a main component and is not generally surface-treated. The coated paper tends to cause quality problems such as image gloss and scratch resistance in image formation by a normal water-based inkjet. However, in the image forming method of the present invention, surface roughness and gloss unevenness are suppressed and gloss is reduced. Images with good resistance and abrasion resistance can be obtained. In particular, a coated paper having a base paper and a coating layer containing an inorganic pigment is preferably used, and a coated paper having a base paper and a coating layer containing at least one of kaolin and calcium bicarbonate is more preferably used. Specifically, art paper, coated paper, lightweight coated paper, or finely coated paper is more preferable.

  As the recording medium, commercially available media can be used. For example, “OK Prince Quality” manufactured by Oji Paper Co., Ltd., “Shiraoi” manufactured by Nippon Paper Industries Co., Ltd., and Nippon Paper Industries Co., Ltd. Fine paper (A) such as “New NPI Fine” manufactured by Oji Paper Co., Ltd., “OK Everlight Coat” manufactured by Oji Paper Co., Ltd., and “Aurora S” manufactured by Nippon Paper Industries Co., Ltd., Oji Paper Co., Ltd. Lightweight coated paper (A3) such as “OK Coat L” manufactured by Nippon 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 Kanto +” manufactured by Oji Paper Co., Ltd. and “Tokuhishi Art” manufactured by Mitsubishi Paper Industries Co., Ltd. Can be mentioned. It is also possible to use various photographic papers for ink jet recording.

  Among the recording media, so-called coated paper used for general offset printing is preferable.

≪Ink application process≫
In the ink application step, the above-described ink composition is applied to a recording medium by an ink jet 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, such as details and preferred embodiments of the ink composition, are as described above in the description of the ink composition.

  In the image formation by the ink jet method, by applying energy, the ink composition described above is ejected onto a desired recording medium to form a colored image. As a preferable inkjet method for the present invention, the method described in paragraphs 0093 to 0105 of JP-A No. 2003-306623 can be applied.

  The inkjet method is not particularly limited, and is a known method, for example, a charge control method that ejects ink using electrostatic attraction, a drop-on-demand method (pressure pulse method) that uses vibration pressure of a piezoelectric element, An acoustic ink jet system that converts an electrical signal into an acoustic beam, irradiates the ink with ink, and ejects the ink using radiation pressure, and a thermal ink jet that forms bubbles by heating the ink and uses the generated pressure (bubble jet (registered) Trademark)) method or the like. As an ink jet method, in particular, the method described in Japanese Patent Application Laid-Open No. Sho 54-59936 causes an abrupt volume change of the ink subjected to the action of thermal energy, and the ink is ejected from the nozzle by the action force due to this state change. Ink jet method can be used effectively.

  As an inkjet head, a short 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 head in which recording elements are arranged corresponding to the entire area of one side of the recording medium There is a line system using. In the line method, an image can be recorded on the entire surface of the recording medium by scanning the recording medium in a direction crossing 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 image forming 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 abrasion resistance is great.

  The amount of ink droplets ejected from the inkjet head is preferably 1 pl (picoliter) to 10 pl, more preferably 1.5 pl to 6 pl, from the viewpoint of obtaining a high-definition image. In addition, from the viewpoint of improving the unevenness of the image and the continuous gradation, it is also effective to discharge different amounts of liquids in combination, and even in such a case, the present invention can be suitably used.

≪Processing liquid application process≫
The image forming method of the present invention includes a treatment liquid application step for applying the treatment liquid to the recording medium.
In the treatment liquid application step, a treatment liquid containing an acidic compound that aggregates the components in the ink composition is applied to the recording medium, and the treatment liquid is brought into contact with the ink composition to form an image. In this case, the dispersed particles including the resin particles in the ink composition are aggregated, and the image is fixed on the recording medium. The treatment liquid contains at least an aggregating component, and details and preferred embodiments of each component are as described above.

  The treatment liquid can be applied 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 blade coater, a rod coater, a knife coater, a squeeze coater, a reverse roll coater, a bar coater or the like can be used. The details of the inkjet method are as described above.

The treatment liquid application step may be provided either before or after the ink application step using the ink composition. In the present invention, an embodiment in which an ink application process is provided after the treatment liquid application process is preferable.
Specifically, before applying the ink composition onto the recording medium, a treatment liquid is applied in advance to agglomerate the components (the above-mentioned dispersed particles) in the ink composition, and then applied onto the recording medium. An embodiment in which an ink composition is applied so as to come into contact with the treated liquid and imaged is preferable. Thereby, inkjet recording can be speeded up, and an image with high density and resolution can be obtained even at high speed recording.

The application amount of the treatment liquid is not particularly limited as long as the ink composition can be aggregated. However, it is preferable that the application amount of the aggregation component is 0.1 g / m ² or more. The amount of the applied aggregating component is 0.2g ^{/ m 2} ~2.0g ^/ m 2 is preferred. When the application amount of the aggregating component is 0.1 g / m ² or more, good high-speed aggregating property can be maintained according to various usage forms of the ink composition. Moreover, it is preferable that the application amount of the aggregating component is 2.0 g / m ² or less because it does not affect the surface properties (gloss change, etc.) of the applied recording medium.

  In the present invention, an ink application step is provided after the treatment liquid application step, and the treatment liquid on the recording medium is heated and dried after the treatment liquid is applied on the recording medium and before the ink composition is applied. It is preferable to further provide a heat drying step. By heating and drying the treatment liquid in advance before the ink application step, ink colorability such as bleeding prevention is improved, and a visible image with good color density and hue can be recorded.

  Heating and drying can be performed by known heating means such as a heater, air blowing means using air blowing 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 treatment liquid application surface of the recording medium, a method of applying warm air or hot air to the treatment 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.

<Inkjet recording apparatus>
The image forming apparatus that can be used in the image forming method of the present invention is not particularly limited, and is publicly known as described in JP 2010-830221 A, JP 2009-234221 A, JP 10-175315 A, and the like. The image forming apparatus can be used.
The image forming apparatus preferably includes an active energy ray (for example, ultraviolet ray) irradiation unit. For the configuration of other means including the active energy ray irradiation means, for example, a known configuration described in JP 2011-184628 A can be referred to as appropriate.

Hereinafter, an example of an image forming apparatus that can be used in the image forming method of the present invention will be described with reference to FIG.
Next, an example of an ink jet recording apparatus suitable for carrying out the image forming method of the present invention will be specifically described with reference to FIG.
FIG. 1 is a schematic configuration diagram illustrating a configuration example of the entire inkjet recording apparatus.

  As shown in FIG. 1, the ink jet recording apparatus includes an anilox roller 20 and a coating roller 22 in contact with the anilox roller 20 as roller materials for coating the processing liquid sequentially in the recording medium conveyance direction (arrow direction in the figure). The provided treatment liquid application unit 12, the treatment liquid drying zone 13 provided with a heating means (not shown) for drying the applied treatment liquid, the ink ejection unit 14 that ejects various ink compositions, and the ejected ink An ink drying zone 15 for drying the composition is provided. Further, an ultraviolet irradiation unit 16 including an ultraviolet irradiation lamp 16S is disposed on the downstream side of the ink drying zone 15 in the conveyance direction of the recording medium.

  The recording medium supplied to the ink jet recording apparatus includes a processing liquid application unit 12, a processing liquid drying zone 13, and an ink discharging unit by a conveying roller from a paper feeding unit that feeds the recording medium from a case loaded with the recording medium. 14, the ink drying zone 15, and the ultraviolet irradiation unit 16 are sequentially sent and accumulated in the accumulation unit. In addition to the method using a conveyance roller, the conveyance may be performed by a drum conveyance method using a drum-shaped member, a belt conveyance method, a stage conveyance method using a stage, or the like.

  Among the plurality of transport rollers, at least one roller may be a driving roller to which the power of a motor (not shown) is transmitted. By rotating a driving roller rotated by a motor at a constant speed, the recording medium is conveyed in a predetermined direction by a predetermined conveyance amount.

The treatment liquid application unit 12 is provided with an anilox roller 20 that is arranged by immersing a part in a storage dish in which the treatment liquid is stored, and an application roller 22 that is in contact with the anilox roller 20. The anilox roller 20 is a roller material for supplying a predetermined amount of processing liquid to the application roller 22 disposed to face the recording surface of the recording medium. The treatment liquid is uniformly applied onto the recording medium by the application roller 22 supplied with an appropriate amount from the anilox roller 20.
The application roller 22 is configured to be able to convey a recording medium in a pair with the opposing roller 24, and the recording medium passes between the application roller 22 and the opposing roller 24 and is sent to the treatment liquid drying zone 13.

  A treatment liquid drying zone 13 is disposed downstream of the treatment liquid application unit 12 in the recording medium conveyance direction. The treatment liquid drying zone 13 can be configured by using a known heating means such as a heater, an air blowing means using air blowing such as a dryer, or a combination of these. The heating means is a method of installing a heating element such as a heater on the side opposite to the treatment liquid application surface of the recording medium (for example, below the conveyance mechanism that carries the recording medium when conveying the recording medium automatically), Examples include a method of applying warm air or hot air to the treatment liquid application surface of the recording medium, a heating method using an infrared heater, and the like.

Also, since the surface temperature of the recording medium varies depending on the type (material, thickness, etc.) of the recording medium and the environmental temperature, the surface temperature of the recording medium measured by the measuring unit that measures the surface temperature of the recording medium and the measuring unit It is preferable to apply the treatment liquid while providing a control mechanism that feeds back the value to the heating control unit. As a measurement part which measures the surface temperature of a recording medium, a contact or non-contact thermometer is preferable.
Further, the solvent may be removed using a solvent removal roller or the like. As another embodiment, a method of removing excess solvent from the recording medium with an air knife is also used.

  The ink discharge unit 14 is disposed downstream of the treatment liquid drying zone 13 in the recording medium conveyance direction. The ink discharge section 14 includes a recording head (ink discharge head) 30K connected to each of the ink storage sections that store black (K), cyan (C), magenta (M), and yellow (Y) color inks. 30C, 30M, and 30Y are arranged. Each ink storage section (not shown) stores an ink composition containing a pigment corresponding to each hue, polymer particles, a water-soluble solvent, and water. The heads 30K, 30C, 30M, and 30Y are supplied. Further, as shown in FIG. 1, a recording head 30A for spot color ink discharge is provided on the downstream side in the transport direction of the ink discharge heads 30K, 30C, 30M, and 30Y so that spot color ink can be discharged as needed. 30B can be further provided.

  The ink ejection heads 30K, 30C, 30M, and 30Y each eject ink corresponding to an image from ejection nozzles arranged to face the recording surface of the recording medium. Thus, each color ink is applied on the recording surface of the recording medium, and a color image is recorded.

  The ink discharge heads 30K, 30C, 30M, 30Y, 30A, and 30B are all full in which a large number of discharge ports (nozzles) are arranged over the maximum recording width (maximum recording width) of an image recorded on the recording medium. It is a line head. Compared to the serial type in which recording is performed while reciprocating a short shuttle head in the width direction of the recording medium (direction perpendicular to the conveying direction on the recording medium conveying surface), it is possible to record an image on the recording medium at a higher speed. it can. In the present invention, either a serial type recording or a system capable of relatively high speed recording, for example, a single pass system in which one line is formed by one scan may be employed. According to this image recording method, a high-quality image with high reproducibility can be obtained even with the single pass method.

  Here, the ink ejection heads 30K, 30C, 30M, 30Y, 30A, and 30B all have the same structure.

  The application amount of the treatment liquid and the application amount of the ink composition 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 ink composition.

  The ink drying zone 15 is disposed downstream of the ink discharge unit 14 in the recording medium conveyance direction. The ink drying zone 15 can be configured in the same manner as the treatment liquid drying zone 13.

The ultraviolet irradiation unit 16 is arranged further downstream in the recording medium conveyance direction of the ink drying zone 15, and is irradiated with ultraviolet rays by an ultraviolet irradiation lamp 16S provided in the ultraviolet irradiation unit 16, and in the image after image drying. The monomer component is polymerized and cured. The ultraviolet irradiation lamp 16S irradiates the entire recording surface with a lamp disposed opposite to the recording surface of the recording medium, so that the entire image can be cured. The ultraviolet irradiation unit 16 is not limited to the ultraviolet irradiation lamp 16S, and a halogen lamp, a high-pressure mercury lamp, a laser, an LED, an electron beam irradiation device, or the like can also be employed.
The ultraviolet irradiation unit 16 may be installed either before or after the ink drying zone 15, or may be installed both before and after the ink drying zone 15.

  Further, in the ink jet recording apparatus, a heating unit that performs a heat treatment on the recording medium can be arranged in a conveyance path from the paper feeding unit to the stacking unit. For example, the temperature of the recording medium is raised to a desired temperature by disposing a heating unit at a desired position such as the upstream side of the treatment liquid drying zone 13 or between the ink discharge unit 14 and the ink drying zone 15. Thus, drying and fixing can be effectively performed.

  EXAMPLES Hereinafter, the present invention will be described more specifically with reference to examples. However, the present invention is not limited to the following examples unless it exceeds the gist thereof. Unless otherwise specified, “part” is based on mass.

<Preparation of ink composition>
<< Synthesis of water-soluble polymer dispersant Q-1 >>
A monomer supply composition was prepared by mixing methacrylic acid (172 parts), benzyl methacrylate (828 parts), and isopropanol (375 parts). In addition, an initiator supply composition was prepared by mixing 2,2-azobis (2-methylbutyronitrile) (22.05 parts) and isopropanol (187.5 parts).
Next, isopropanol (187.5 parts) was heated to 80 ° C. under a nitrogen atmosphere, and the mixture of the monomer supply composition and the initiator supply composition was dropped therein over 2 hours. After the completion of dropping, the mixture was further maintained at 80 ° C. for 4 hours, and then cooled to 25 ° C.
After cooling, the solvent was removed under reduced pressure to obtain a water-soluble polymer dispersant Q-1 having a weight average molecular weight of about 30,000 and an acid value of 112 mgKOH / g.

<< Preparation of Cyan Pigment Dispersion C-1 >>
After neutralizing 0.8 equivalent of the amount of methacrylic acid in the water-soluble polymer dispersant Q-1 (150 parts) obtained above with an aqueous potassium hydroxide solution, the water-soluble polymer dispersant concentration is 25 masses. % Was further adjusted by adding ion-exchanged water to obtain a water-soluble polymer dispersant aqueous solution.
This water-soluble polymer dispersant aqueous solution (124 parts), Pigment Blue 15: 3 (cyan pigment) (48 parts), water (75 parts) and dipropylene glycol (30 parts) are mixed, and a bead mill ( A dispersion of polymer-coated cyan pigment particles having a pigment concentration of 15% by mass (uncrosslinked dispersion C-1) was obtained by dispersing with a bead diameter of 0.1 mmφ and zirconia beads) until a desired volume average particle size was obtained.
To this uncrosslinked dispersion C-1 (136 parts), Denacol EX-321 (manufactured by Nagase ChemteX Corporation, crosslinking agent) (1.3 parts) and boric acid aqueous solution (boric acid concentration: 4% by mass) (14.3 parts) was added and reacted at 50 ° C. for 6 and a half hours, and then cooled to 25 ° C. to obtain a crosslinked dispersion C-1. Next, ion-exchanged water was added to the obtained crosslinked dispersion C-1, and a stirring type ultra holder (manufactured by ADVANTEC Co., Ltd.) and an ultrafiltration filter (manufactured by ADVANTEC Co., Ltd., molecular weight cut off 50,000, Q0500076E ultra). Filter) and purifying the dispersion so that the dipropylene glycol concentration in the dispersion is 0.1% by mass or less, and then concentrating until the pigment concentration is 15% by mass. Dispersion C-1 was obtained. The pigment contained in the cyan pigment dispersion C-1 is a polymer-coated pigment (encapsulated pigment) whose surface is coated with a crosslinked polymer obtained by crosslinking the water-soluble polymer dispersant Q-1 with a crosslinking agent.

<< Preparation of Magenta Pigment Dispersion M-1 >>
In the preparation of the cyan pigment dispersion C-1, except that Pigment Red 122 (magenta pigment) was used instead of Pigment Blue 15: 3 (cyan pigment) used as the pigment, In the same manner as in the preparation, a magenta pigment dispersion M-1 was obtained.

<< Preparation of Yellow Pigment Dispersion Y-1 >>
In the preparation of cyan pigment dispersion C-1, except that Pigment Yellow 74 (yellow pigment) was used instead of Pigment Blue 15: 3 (cyan pigment) used as the pigment, cyan pigment dispersion C-1 In the same manner as in the preparation, a yellow pigment dispersion Y-1 was obtained.

<< Preparation of Black Pigment Dispersion K-1 >>
In the preparation of cyan pigment dispersion C-1, cyan pigment dispersion C- was used except that carbon black MA-100 (black pigment) was used instead of pigment blue 15: 3 (cyan pigment) used as the pigment. In the same manner as in Preparation 1, a black pigment dispersion K-1 was obtained.

≪Synthesis of polymerizable compound≫
A polymerizable compound a, which is an exemplary compound of the (meth) acrylamide compound represented by the general formula (1), was synthesized. The synthesis was performed according to the method described in paragraphs 0123 to 0128 of JP2013-18846A.

<< Synthesis of self-dispersing polymer particles P-1 (resin 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. Thereafter, while maintaining the temperature in the flask at 75 ° C., 151.2 g of isobornyl methacrylate, 172.8 g of methyl methacrylate, 36.0 g of methacrylic acid, 72 g of methyl ethyl ketone, and “V-601” (manufactured by Wako Pure Chemical Industries, Ltd.) ) A mixed solution consisting of 1.44 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 composed of 0.72 g of “V-601” and 36.0 g of methyl ethyl ketone was added thereto, stirred at 75 ° C. for 2 hours, and further a solution composed of 0.72 g of “V-601” and 36.0 g of isopropanol. And stirred at 75 ° C. for 2 hours. Thereafter, the temperature was raised to 85 ° C., and stirring was further continued for 2 hours to obtain a polymer solution of an isobornyl methacrylate / methyl methacrylate / methacrylic acid (= 42/48/10 [mass ratio]) copolymer.
The weight average molecular weight (Mw) measured in the same manner as described above of the obtained copolymer was 58000 (calculated in terms of polystyrene by gel permeation chromatography (GPC)), and the acid value was 32.6 mgKOH / g. It was.

  Next, 668.3 g of the obtained polymer solution was weighed, 388.3 g of isopropanol and 145.7 ml of 1 mol / L NaOH aqueous solution were added thereto, 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, and then the reaction vessel internal temperature was 80 ° C. for 2 hours, 85 ° C. for 2 hours, and 90 ° C. for 2 hours under atmospheric pressure. Kept. Thereafter, the inside of the reaction vessel is evacuated, and 913.7 g of isopropanol, methyl ethyl ketone, and distilled water are distilled off in total, and self-dispersing polymer particles P-1 (resin particles) having a solid content concentration (polymer particle concentration) of 28.0% by mass. ) Was obtained.

It was 150 degreeC when the glass transition temperature (Tg) of the said self-dispersing polymer particle P-1 was measured with the following method.
-Measurement of glass transition temperature (Tg)-
An aqueous dispersion of self-dispersing polymer particles having a solid content of 0.5 g was dried under reduced pressure at 50 ° C. for 4 hours to obtain a polymer solid content. Using the obtained polymer solid content, Tg was measured with a differential scanning calorimeter (DSC) EXSTAR 6220 manufactured by SII Nanotechnology. The measurement condition was that a sample amount of 5 mg was sealed in an aluminum pan, and the DSC peak top value of the measurement data at the second temperature increase was defined as Tg under the following temperature profile in a nitrogen atmosphere.
30 ° C to -50 ° C (cooled at 50 ° C / min)
−50 ° C. → 220 ° C. (temperature rising at 20 ° C./min)
120 ° C to -50 ° C (cooled at 50 ° C / min)
−50 ° C. → 220 ° C. (temperature rising at 20 ° C./min)

≪Synthesis of water-soluble polymer (water-soluble polymer) ≫
A water-soluble polymer compound (water-soluble polymer 1) used as a component in the treatment liquid was synthesized. This synthesis was performed according to paragraphs 0200 to 0204 and 0229 of JP2013-001854A.
The structure of the water-soluble polymer 1 is shown below.
In the water-soluble polymer 1 shown below, the number on the lower right of each structural unit represents a mass ratio (mass%), and Mw represents a weight average molecular weight.

[Examples 1 to 3]
As Examples 1 to 3, experiments were conducted on the types and addition amounts of inorganic salts and the pH of the treatment liquid in the ink composition.

<Ink No. 1>
Ink No. As No. 1, a black ink was prepared, the stability of the prepared black ink over time at high temperatures was evaluated, and the surface roughness of an image formed using the prepared black ink was evaluated. Details will be described below.

≪Preparation of black ink≫
Components of the following composition were mixed and coarse particles were removed through a membrane filter (pore size 0.5 μm) to obtain a black ink (ink composition).
The physical properties of the produced black ink were a viscosity of 5.0 mPa · s (30 ° C.), a surface tension of 36.0 mN / m (25 ° C.), and a pH of 8.5 (25 ° C.).
Here, the viscosity, surface tension, and pH are respectively VISCOMETER TV-22 (manufactured by TOKI SANGYO CO. LTD), Automatic Surface Tensiometer CBVP-Z (manufactured by Kyowa Interface Science Co., Ltd.), and pH meter WM-50EG (manufactured by Kyowa Interface Science Co., Ltd.). Measured using Toa DDK Co., Ltd.

≪Black ink composition (ink No. 1) ≫
Black pigment dispersion K-1: 15.0% by mass
-Magenta pigment dispersion M-1: 4.0% by mass
Cyan pigment dispersion C-1: 4.0% by mass
Polymerizable compound a (specific example of compound represented by general formula (1)): 1.0% by mass
Polymerization initiator (Exemplary compound (X-1); specific example of compound represented by general formula (X))
... 0.2% by mass
・ 2-Pyrrolidone: 0.5% by mass
・ Glycerin: 3.0% by mass
・ Propylene glycol (made by ADEKA): 9.0% by mass
・ MFTG (manufactured by Nippon Emulsifier Co., Ltd.) 2.0% by mass
・ Orphine E1010 (manufactured by Nissin Chemical Industry Co., Ltd., surfactant): 0.3% by mass
・ Orphine E1020 (manufactured by Nissin Chemical Industry Co., Ltd., surfactant): 1.0% by mass
Self-dispersing polymer particle P-1 (resin particle): 8.0% by mass
・ PVP K-15 (manufactured by ISB Japan Co., Ltd.)… 0.2% by mass
・ Urea: 5.0% by mass
・ Cerosol 524 (manufactured by Chukyo Yushi Co., Ltd.): 1.5% by mass
・ Lithium chloride (inorganic salt): 0.01% by mass
・ Snowtex XS (Nissan Chemical Co., Ltd., colloidal silica): 0.3% by mass
・ Capstone FS-63 (manufactured by Dupont, surfactant): 0.01% by mass
-BYK-024 (Bic Chemie Japan Co., Ltd., antifoaming agent) ... 0.01% by mass
・ Ion-exchanged water: Remaining amount when 100% by mass as a whole

<Preparation of treatment liquid 1>
The component of the following composition was mixed and the processing liquid 1 was obtained.
The physical properties of the prepared treatment liquid 1 were a viscosity of 4.5 mPa · s (25 ° C.), a surface tension of 41.0 mN / m (25 ° C.), and a pH of 0.1 (25 ° C.).
Here, the viscosity, surface tension, and pH are respectively VISCOMETER TV-22 (manufactured by TOKI SANGYO CO. LTD), Automatic Surface Tensiometer CBVP-Z (manufactured by Kyowa Interface Science Co., Ltd.), and pH meter WM-50EG (manufactured by Kyowa Interface Science Co., Ltd.). Measured using Toa DDK Co., Ltd.

<Composition of treatment liquid 1>
・ TPGmME (Tripropylene glycol monomethyl ether) 4.8% by mass
・ DEGmBE (diethylene glycol monobutyl ether) 4.8% by mass
・ Malonic acid: 16.0% by mass
・ Malic acid: 7.8% by mass
・ Propanetricarboxylic acid: 3.5% by mass
・ 85 mass% phosphoric acid aqueous solution ... 15.0 mass%
・ The above-mentioned water-soluble polymer 1 0.6 mass%
・ Antifoamer (Momentive Performance Materials Japan TSA-739 (15%); emulsion type silicone antifoam)
… 0.01% by mass as silicone oil
・ Ion-exchanged water: Total remaining amount of 100% by mass

<Processing liquid 2 and processing liquid 3>
In the above treatment liquid 1, the blending amount of malonic acid and 85% by mass aqueous solution of phosphoric acid is changed to 14.0% by mass and 13.0% by mass in the treatment liquid 2, respectively, and the pH is set to 0.3. 3, the treatment liquid 2 and the treatment liquid 3 were prepared in the same manner as the treatment liquid 1 except that the pH was changed to 10.0 mass% and 8.0 mass%, respectively, and the pH was set to 0.5.

<Image formation>
A GELJET GX5000 printer head manufactured by Ricoh Co., Ltd. was prepared.
This printer head is a line head in which 96 nozzles are arranged.
This printer head was fixedly arranged in an ink jet recording apparatus having the same configuration as the ink jet recording apparatus shown in FIG.
The arrangement at this time was such that the direction in which the 96 nozzles were aligned was inclined by 75.7 ° with respect to the direction orthogonal to the moving direction of the stage of the inkjet apparatus.

  An OK top coat (manufactured by Oji Paper Co., Ltd.) was prepared as a recording medium, and the following treatment liquid application step, drying step, and ink application step were sequentially performed to form (record) an image on the recording medium.

-Treatment liquid application process-
An OK top coat was fixed on a stage movable in a linear direction at 500 mm / second, and each of the treatment liquids obtained above was applied thereto with a wire bar coater so as to be about 1.7 g / m ² .

-Drying process-
At the place where the application of the treatment liquid is completed, the drying of the recording medium is started at 50 ° C. using a dryer after 1.5 seconds from the end of the application of the treatment liquid to this place. After 3.5 seconds from the end of drying. The drying time at this time is 2 seconds.

-Ink application process-
Within 2 seconds after the drying step, ink droplet ejection was started by the following droplet ejection method.
(Dropping method)
While moving the recording medium at a constant speed in the moving direction of the stage, the black ink prepared above from the printer head is subjected to an ink droplet amount of 3.5 pL, an ejection frequency of 24 kHz, a resolution of 1200 dpi × 1200 dpi (dot per inch), Discharge was performed in a line system under a discharge condition of a stage speed of 50 mm / s, and a 40% halftone image of 100 mm × 150 mm was printed. The black ink used was deaerated through a deaeration filter and temperature-controlled at 30 ° C.
The halftone image immediately after printing was dried at 60 ° C. for 3 seconds, and the halftone image was cured by irradiating the dried halftone image with UV (ultraviolet rays).

Irradiation of the above UV (ultraviolet light) is performed by using a metal halide lamp (maximum irradiation wavelength: 365 nm) manufactured by Eye Graphics Co., Ltd., and controlling the light source power and the conveyance speed to achieve an illuminance of 1.5 W / cm ² (integrated irradiation). (Amount: 0.75 J / cm ² )

<Evaluation of high temperature aging stability (60 ° C. aging stability) of ink composition>
25 g of the black ink (ink composition) obtained above was placed in a 30 ml polybin, and the polybin was stored in Thermocelco set at 60 ° C. for 2 weeks. The viscosity of the ink was measured before and after the storage, and the Δ viscosity was calculated according to the following formula.
Δ viscosity = (ink viscosity after storage at 60 ° C. for 2 weeks) − (ink viscosity immediately after ink preparation)

Based on the obtained Δ viscosity, the high temperature aging stability (60 ° C. aging stability) of the ink was evaluated according to the following evaluation criteria. The evaluation results are shown in Table 1 below.
The smaller the Δ viscosity, the better the high temperature aging stability of the ink, which is preferable. In addition, the greater the Δ viscosity, the poorer the stability of the ink at high temperatures with time.
In the following evaluation criteria, A to C are within a practically acceptable range.

-Evaluation criteria for high-temperature stability over time (60 ° C stability over time)-
A: Δ viscosity ≦ 0.3 mPa · s
B: 0.3 mPa · s <Δ viscosity ≦ 0.6 mPa · s
C: 0.6 mPa · s <Δ viscosity ≦ 1 mPa · s
D: Δ viscosity> 1 mPa · s

<Evaluation of surface area>
According to the above <image formation>, a 40% halftone dot image of 100 mm × 150 mm was recorded on a recording medium. Immediately thereafter (immediately after the end of the UV irradiation process), the recorded halftone image (hereinafter also referred to as “recorded image”) was visually observed, and surface alignment was evaluated according to the following evaluation criteria.
The evaluation results are shown in Table 1.
In the following evaluation criteria, A to C are within a practically acceptable range.

-Evaluation criteria for surface alignment-
A: No surface alignment was observed on all 10 images.
B: Surface alignment was observed on 1 out of 10 images.
C: Surface alignment was observed on 2 to 4 of 10 images.
D: Surface alignment was observed on 5 or more of 10 images.

<Evaluation of blocking resistance>
In the above <image formation>, a 100% solid image of 100 mm × 150 mm was recorded on a recording medium. Immediately after completion of the UV irradiation process, the recorded image surfaces were brought into contact with each other, and held at a temperature environment of 45 ° C. under a load of 8 MPa for 60 seconds. Thereafter, the contact surface was visually observed to evaluate the degree of sticking.

<Evaluation of abrasion resistance of image>
According to the above <image formation>, a 100% solid image of 100 mm × 150 mm was recorded on a recording medium. Immediately thereafter (immediately after the end of the UV irradiation process), an operation in which an unrecorded recording medium (the same recording medium used for recording) is superimposed on the recorded solid image and rubbed 500 times with a load of 5 kg / m ^2. Went.
After this operation, scratches on the recorded image and the degree of ink transfer to the recording medium not recorded were visually observed to evaluate the abrasion resistance of the image.

<Evaluation of curls>
In accordance with the above <image formation>, a curl evaluation sample having a size of 254 × 127 mm in which a 100% solid image was recorded on the entire area of one side of the recording medium was prepared. This curl evaluation sample was allowed to stand for 24 hours under conditions of a temperature of 25 ° C. and a humidity of 55% RH, and the degree of curling at that time was evaluated.

[Examples 4 to 91, Comparative Examples 1 to 3]
For Examples 4 to 91 and Comparative Examples 1 to 3, as in Examples 1 to 3, experiments on the type and amount of inorganic salt in the ink composition and the pH of the treatment liquid were conducted. went.

<Ink No. 2-30, 34-35>
Ink No. 1 except that the types and amounts of inorganic salts, types and amounts of resin particles, presence / absence of a polymerizable compound, and presence / absence of a polymerization initiator were changed as shown in Table 1. Evaluation similar to 1 was performed. The evaluation results are shown in Table 1 below. Ink containing no polymerizable compound does not require a UV irradiation step, but UV irradiation was performed on all samples in order to meet the conditions.
Ink No. in Table 1 Details of WBR-2101 used as resin particles in 18-19 and 21-22 are as follows.
-WBR-2101: Aclit WBR-2101 manufactured by Taisei Fine Chemical Co., Ltd. (self-emulsifying urethane emulsion, solid content concentration: 25% by mass)

<Ink No. 31-33, 36-39>
Ink No. 1 except that the pigment dispersion was changed as shown in Table 1. Evaluation similar to 1 was performed.
The evaluation results are shown in Table 1 below.

≪Magenta ink composition (ink No. 31) ≫
-Pigment dispersion M: 42.0% by mass
Polymerizable compound a (specific example of compound represented by general formula (1)): 1.0% by mass
Polymerization initiator (Exemplary compound (X-1); specific example of compound represented by general formula (X))
... 0.2% by mass
・ 2-Pyrrolidone: 0.5% by mass
・ Glycerin: 3.0% by mass
・ Propylene glycol (made by ADEKA): 13.0% by mass
・ MFTG (manufactured by Nippon Emulsifier Co., Ltd.) 2.0% by mass
・ Orphine E1010 (manufactured by Nissin Chemical Industry Co., Ltd., surfactant): 0.3% by mass
・ Orphine E1020 (manufactured by Nissin Chemical Industry Co., Ltd., surfactant): 1.0% by mass
Self-dispersing polymer particle P-1 (resin particle): 8.0% by mass
・ PVP K-15 (manufactured by ISB Japan Co., Ltd.)… 0.2% by mass
・ Urea: 5.0% by mass
・ Cerosol 524 (manufactured by Chukyo Yushi Co., Ltd.): 1.5% by mass
-Potassium nitrate (inorganic salt): 0.03 mass%
・ Snowtex XS (Nissan Chemical Co., Ltd., colloidal silica): 0.3% by mass
・ Capstone FS-63 (manufactured by Dupont, surfactant): 0.01% by mass
-BYK-024 (Bic Chemie Japan Co., Ltd., antifoaming agent) ... 0.01% by mass
・ Ion-exchanged water: Remaining amount when 100% by mass as a whole

<< Cyan ink composition (No. 32) >>
Pigment dispersion C: 20.0% by mass
Polymerizable compound a (specific example of compound represented by general formula (1)): 1.0% by mass
Polymerization initiator (Exemplary compound (X-1); specific example of compound represented by general formula (X))
... 0.2% by mass
・ 2-Pyrrolidone: 0.5% by mass
・ Glycerin: 3.0% by mass
・ Propylene glycol (made by ADEKA): 9.0% by mass
・ MFTG (manufactured by Nippon Emulsifier Co., Ltd.) 2.0% by mass
・ Orphine E1010 (manufactured by Nissin Chemical Industry Co., Ltd., surfactant): 0.3% by mass
・ Orphine E1020 (manufactured by Nissin Chemical Industry Co., Ltd., surfactant): 1.0% by mass
Self-dispersing polymer particle P-1 (resin particle): 8.0% by mass
・ PVP K-15 (manufactured by ISB Japan Co., Ltd.)… 0.2% by mass
・ Urea: 5.0% by mass
・ Cerosol 524 (manufactured by Chukyo Yushi Co., Ltd.): 1.5% by mass
-Potassium nitrate (inorganic salt): 0.05% by mass
・ Snowtex XS (Nissan Chemical Co., Ltd., colloidal silica): 0.3% by mass
・ Capstone FS-63 (manufactured by Dupont, surfactant): 0.01% by mass
-BYK-024 (Bic Chemie Japan Co., Ltd., antifoaming agent) ... 0.01% by mass
・ Ion-exchanged water: Remaining amount when 100% by mass as a whole

<< Composition of yellow ink (ink No. 33) >>
Pigment dispersion Y: 35.0% by mass
Polymerizable compound a (specific example of compound represented by general formula (1)): 1.0% by mass
Polymerization initiator (Exemplary compound (X-1); specific example of compound represented by general formula (X))
... 0.2% by mass
・ 2-Pyrrolidone: 0.5% by mass
・ Glycerin: 3.0% by mass
・ Propylene glycol (made by ADEKA): 10.0% by mass
・ MFTG (manufactured by Nippon Emulsifier Co., Ltd.) 2.0% by mass
・ Orphine E1010 (manufactured by Nissin Chemical Industry Co., Ltd., surfactant): 0.3% by mass
・ Orphine E1020 (manufactured by Nissin Chemical Industry Co., Ltd., surfactant): 1.0% by mass
Self-dispersing polymer particle P-1 (resin particle): 8.0% by mass
・ PVP K-15 (manufactured by ISB Japan Co., Ltd.)… 0.2% by mass
・ Urea: 5.0% by mass
・ Cerosol 524 (manufactured by Chukyo Yushi Co., Ltd.): 1.5% by mass
-Potassium nitrate (inorganic salt): 0.05% by mass
・ Snowtex XS (Nissan Chemical Co., Ltd., colloidal silica): 0.3% by mass
・ Capstone FS-63 (manufactured by Dupont, surfactant): 0.01% by mass
-BYK-024 (Bic Chemie Japan Co., Ltd., antifoaming agent) ... 0.01% by mass
・ Ion-exchanged water: Remaining amount when 100% by mass as a whole

≪Black ink composition (ink No. 36) ≫
Black pigment dispersion K-1: 15.0% by mass
-Magenta pigment dispersion M-1: 4.0% by mass
Cyan pigment dispersion C-1: 4.0% by mass
・ Sanix GP-250 (manufactured by Sanyo Chemical Industries, Ltd.): 5.0% by mass
・ PEG-200 (manufactured by Sanyo Chemical Industries, Ltd.): 5.0% by mass
・ Propylene glycol (made by ADEKA): 9.0% by mass
・ MFTG (manufactured by Nippon Emulsifier Co., Ltd.) 2.0% by mass
・ Orphine E1010 (manufactured by Nissin Chemical Industry Co., Ltd., surfactant)
... 0.3% by mass
・ Orphine E1020 (manufactured by Nissin Chemical Industry Co., Ltd., surfactant)
... 1.0% by mass
Self-dispersing polymer particle P-1 (resin particle): 8.0% by mass
・ PVP K-15 (manufactured by ISB Japan)… 0.2% by mass
・ Urea: 5.0% by mass
・ Cerosol 524 (manufactured by Chukyo Yushi Co., Ltd.): 1.5% by mass
・ Potassium nitrate (inorganic salt): 0.05% by mass
・ Snowtex XS (Nissan Chemical Co., Ltd., colloidal silica)
... 0.3% by mass
・ Capstone FS-63 (manufactured by Dupont, surfactant): 0.01% by mass
・ BYK-024 (Bic Chemie Japan Co., Ltd., antifoaming agent)
… 0.01% by mass
・ Ion-exchanged water: Remaining amount when 100% by mass as a whole

≪Magenta ink composition (ink No. 37) ≫
-Pigment dispersion M: 42.0% by mass
・ Sanix GP-250 (manufactured by Sanyo Chemical Industries, Ltd.): 5.0% by mass
・ PEG-200 (manufactured by Sanyo Chemical Industries, Ltd.): 5.0% by mass
・ Propylene glycol (made by ADEKA): 13.0% by mass
・ MFTG (manufactured by Nippon Emulsifier Co., Ltd.) 2.0% by mass
・ Orphine E1010 (manufactured by Nissin Chemical Industry Co., Ltd., surfactant)
... 0.3% by mass
・ Orphine E1020 (manufactured by Nissin Chemical Industry Co., Ltd., surfactant)
... 1.0% by mass
Self-dispersing polymer particle P-1 (resin particle): 8.0% by mass
・ PVP K-15 (manufactured by ISB Japan)… 0.2% by mass
・ Urea: 5.0% by mass
・ Cerosol 524 (manufactured by Chukyo Yushi Co., Ltd.): 1.5% by mass
-Potassium nitrate (inorganic salt): 0.05% by mass
・ Snowtex XS (Nissan Chemical Co., Ltd., colloidal silica)
... 0.3% by mass
・ Capstone FS-63 (manufactured by Dupont, surfactant): 0.01% by mass
・ BYK-024 (Bic Chemie Japan Co., Ltd., antifoaming agent)
… 0.01% by mass
・ Ion-exchanged water: Remaining amount when 100% by mass as a whole

<< Cyan ink composition (No. 38) >>
Pigment dispersion C: 20.0% by mass
・ Sanix GP-250 (manufactured by Sanyo Chemical Industries, Ltd.): 5.0% by mass
・ PEG-200 (manufactured by Sanyo Chemical Industries, Ltd.): 5.0% by mass
・ Propylene glycol (made by ADEKA): 9.0% by mass
・ MFTG (manufactured by Nippon Emulsifier Co., Ltd.) 2.0% by mass
・ Orphine E1010 (manufactured by Nissin Chemical Industry Co., Ltd., surfactant)
... 0.3% by mass
・ Orphine E1020 (manufactured by Nissin Chemical Industry Co., Ltd., surfactant)
... 1.0% by mass
Self-dispersing polymer particle P-1 (resin particle): 8.0% by mass
・ PVP K-15 (manufactured by ISB Japan)… 0.2% by mass
・ Urea: 5.0% by mass
・ Cerosol 524 (manufactured by Chukyo Yushi Co., Ltd.): 1.5% by mass
-Potassium nitrate (inorganic salt): 0.05% by mass
・ Snowtex XS (Nissan Chemical Co., Ltd., colloidal silica)
... 0.3% by mass
・ Capstone FS-63 (manufactured by Dupont, surfactant): 0.01% by mass
・ BYK-024 (Bic Chemie Japan Co., Ltd., antifoaming agent)
… 0.01% by mass
・ Ion-exchanged water: Remaining amount when 100% by mass as a whole

<< Composition of yellow ink (ink No. 39) >>
Pigment dispersion Y: 35.0% by mass
・ Sanix GP-250 (manufactured by Sanyo Chemical Industries, Ltd.): 5.0% by mass
・ PEG-200 (manufactured by Sanyo Chemical Industries, Ltd.): 5.0% by mass
・ Propylene glycol (made by ADEKA): 10.0% by mass
・ MFTG (manufactured by Nippon Emulsifier Co., Ltd.) 2.0% by mass
・ Orphine E1010 (manufactured by Nissin Chemical Industry Co., Ltd., surfactant)
... 0.3% by mass
・ Orphine E1020 (manufactured by Nissin Chemical Industry Co., Ltd., surfactant)
... 1.0% by mass
Self-dispersing polymer particle P-1 (resin particle): 8.0% by mass
・ PVP K-15 (manufactured by ISB Japan)… 0.2% by mass
・ Urea: 5.0% by mass
・ Cerosol 524 (manufactured by Chukyo Yushi Co., Ltd.): 1.5% by mass
-Potassium nitrate (inorganic salt): 0.05% by mass
・ Snowtex XS (Nissan Chemical Co., Ltd., colloidal silica)
... 0.3% by mass
・ Capstone FS-63 (manufactured by Dupont, surfactant): 0.01% by mass
・ BYK-024 (Bic Chemie Japan Co., Ltd., antifoaming agent)
… 0.01% by mass
・ Ion-exchanged water: Remaining amount when 100% by mass as a whole

From the results in Table 1, the following can be understood.
Examples 1 to 91 are excellent in suppressing the surface areal of the formed image and have little change in the viscosity of the ink composition after storage at 60 ° C. for 2 weeks.
On the other hand, Comparative Examples 1 and 2 in which the salt component contained in the ink composition is not a specific inorganic salt are effective in suppressing the surface areal of the formed image and the high temperature aging stability of the ink composition after storage at 60 ° C. for 2 weeks. Inferior.
Further, Comparative Example 3 in which the pH of the treatment liquid is outside the range of the present invention is inferior in suppressing surface roughness of the formed image.
Furthermore, Examples 88 to 91 containing Solvent A represented by Structural Formula (I) as a solvent and Solvent B selected from ethylene glycol, diethylene glycol, triethylene glycol, tetraethylene glycol, and pentaethylene glycol. Was excellent in both good curb resistance and blocking resistance of the recording medium after image formation.

DESCRIPTION OF SYMBOLS 12 ... Treatment liquid provision part 13 ... Treatment liquid drying zone 14 ... Ink discharge part 15 ... Ink drying zone 16 ... Ultraviolet irradiation part 16S ... Ultraviolet irradiation lamp 30K, 30C, 30M, 30Y ... Ink ejection head

Claims (9)

An ink composition having a pH of 7.5 or more at 25 ° C., comprising water, a pigment coated with a resin, resin particles, and at least one inorganic salt selected from hydrochloride and nitrate;
A treatment liquid containing an acidic compound that forms aggregates when contacted with the ink composition and having a pH at 25 ° C. of 0.1 to 0.5;
Ink set containing.   The ink set according to claim 1, wherein the inorganic salt is at least one selected from lithium chloride, lithium nitrate, potassium chloride, and potassium nitrate.   The ink set according to claim 1, wherein the resin particles are particles of a resin selected from an acrylic resin and a urethane resin.   The ink set according to any one of claims 1 to 3, wherein the ink composition further contains a polyfunctional (meth) acrylamide compound.   The ink set according to any one of claims 1 to 4, wherein the content of the inorganic salt is 0.01% by mass to 0.1% by mass with respect to the total mass of the ink composition.   The ink set according to any one of claims 1 to 5, wherein a mass ratio of the coating resin of the pigment coated with the resin to the inorganic salt is 10 to 250.   The ink set according to any one of claims 1 to 6, which is used for forming an image on a recording medium having a base paper and a coating layer containing an inorganic pigment. An ink for forming an image by applying the ink composition of the ink set according to any one of claims 1 to 7 on a recording medium having a base paper and a coating layer containing an inorganic pigment by an inkjet method. Granting process;
A treatment liquid applying step of applying a treatment liquid of the ink set on a recording medium having a base paper and a coating layer containing an inorganic pigment;
An image forming method comprising:   The image forming method according to claim 8, wherein after the treatment liquid is applied to the recording medium in the treatment liquid application step, the ink composition is applied in the ink application step.