JP2013075957A - Ink composition, ink set, and method for image forming - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an ink composition that attains suppression of discharge bending when the ink composition is discharged from a discharge head equipped with a nozzle plate provided with a liquid repellent film, and to provide a method for forming an excellent image by suppressing discharge bending when the ink composition is discharged.SOLUTION: The ink composition includes water and a resin-coated pigment whose at least one part of the surface is coated with a water-insoluble polymer, and the total concentration of Mg and phosphate ions in the composition is ≥1 ppm and ≤70 ppm in mass basis.

Description

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

  The ink jet recording system is capable of high-speed and high-definition image recording, and has been rapidly developed in various fields. In an ink jet printer used for such an ink jet recording method, a method of forming an image by ejecting ink droplets from a large number of nozzles formed on an ink jet head is known. Ink jet heads include a type in which glass or silicon is used as a member from the viewpoint of ease of fine processing for recording, processing accuracy, process, and the like.

  On the other hand, inks used in such ink jet printers are generally known to be composed of a coloring material that is a colorant, water, a water-soluble organic solvent, and a surfactant. In recent years, color materials such as pigments have been studied as ink materials that impart properties. Since pigments are generally insoluble in water, when a pigment is used in a water-based ink composition, a polymer that uses a water-soluble resin or the like as a dispersant and mixes the pigment with the dispersant to stably disperse in water. Use an ink that uses a dispersant, an ink that uses a self-dispersing pigment that has been surface-treated with a functional group bonded to the pigment surface, or a resin-coated pigment (encapsulated pigment) that covers the surface of the pigment with a water-insoluble resin. Ink has been proposed.

However, when a water-based ink containing a pigment is used in an ink jet printer, there is a problem in that an ink jet head deteriorates due to an impurity component (for example, phosphoric acid) in the ink derived from the pigment, and good dischargeability cannot be maintained. It was.
In order to solve such a problem, an aqueous ink containing a quinacridone pigment and a block polymer having a carboxylic acid as a solubilizing group is disclosed in an ink using a resin dispersant (see, for example, Patent Document 1). Even when a pigment that has not been purified is used, the clogging resistance of the nozzle is maintained at a high level, and good printing durability can be obtained. Also disclosed is an ink in which the phosphate ion concentration in an aqueous ink containing a self-dispersing pigment whose surface is modified with a sulfonic acid group is 20 ppm or less (see, for example, Patent Document 1), an inkjet head, and the like. It is said that corrosion (rust) of the metal member can be prevented.

JP 2004-269798 A JP2011-74198A

  However, in the water-based ink containing the block polymer described above, kogation of the thermal head caused by the formation of a water-insoluble component by phosphate ions and Ca contained in the ink is prevented, and the nozzle clogging is expected to be eliminated. However, the effect of the presence of impurity components other than Ca has not been clarified. For this reason, when a small amount of Mg in the ink coexists with phosphate ions, a liquid repellent film using, for example, a fluorine compound is provided on the hole forming surface of the nozzle plate in which a plurality of ejection holes are formed. When ejected from an inkjet head, there was a phenomenon that the liquid repellency of the liquid repellent film was lowered.

  In addition, the aqueous ink containing the self-dispersing pigment whose surface is modified with the sulfonic acid group described above is mainly corroded by an ink jet head having a metal member such as a nickel-containing metal in the ink flow path. Prevention is intended. However, here, no consideration is given to the case where Mg and phosphate ions are mixed in the ink, and it is difficult to suppress a decrease in the liquid repellency of the liquid repellent film.

As described above, when the liquid repellency of the liquid repellent film is lowered, a discharge bend (discharge directionality failure) occurs during ink discharge, and an image failure such as white spots may occur, leading to a decrease in image quality. is there.
Therefore, the present invention provides an ink composition and an ink set that can suppress the discharge bending when discharging from a discharge head including a nozzle plate provided with a liquid repellent film, and also suppress the discharge bending during ink discharge. It is an object of the present invention to provide an image forming method capable of forming an excellent image.

  As a result of extensive research, the present inventors have newly found that the cause of the deterioration of the liquid repellent film of the ejection head is the presence of a trace amount of Mg contained in the ink together with phosphate ions. Coating with a water-insoluble polymer reduces the abundance of phosphate ions and Mg in the ink, and prevents a decrease in liquid repellency of the liquid repellent film due to the coexistence of phosphate ions and Mg. Clarified that you can.

Specific means of the present invention for achieving the above object are as follows.
<1> Ink having water and a resin-coated pigment in which at least a part of the surface of the pigment is coated with a water-insoluble polymer and having a total Mg concentration and phosphate ion concentration of 1 ppm to 70 ppm on a mass basis It is a composition.

<2> The ink composition according to <1>, wherein the pigment is a quinacridone pigment.

<3> The ink composition according to <1> or <2>, wherein the water-insoluble polymer includes a structural unit represented by the following general formula (1).

(In General Formula (1), R ¹ represents a hydrogen atom or a methyl group, L ¹ represents a substituted or unsubstituted phenylene group, L ² represents a single bond or a divalent linking group, and Ar ¹ represents carbon. This represents a monovalent group derived from a condensed aromatic ring having a number of 8 or more, a hetero ring in which an aromatic ring is condensed, or a compound in which two or more benzene rings are linked.

<4> The ink composition according to any one of <1> to <3>, wherein the water-insoluble polymer has an acid value of 30 mgKOH / g or more and 100 mgKOH / g or less.

<5> The ink composition according to any one of <1> to <4>, further including polymer particles.

<6> A treatment liquid containing the ink composition according to any one of <1> to <5>, and an aggregation component that aggregates the components contained in the ink composition when contacted with the ink composition; , An ink set.
<7> An image forming method including an ink application step of applying the ink composition according to any one of <1> to <5> onto a recording medium by an inkjet method.

<8> The image according to <7>, further comprising a treatment liquid application step of applying a treatment liquid containing an aggregating component that aggregates the components contained in the ink composition when contacted with the ink composition onto a recording medium. It is a forming method.

<9> The image forming method according to <8>, wherein the aggregation component is an acidic compound.

  According to the present invention, there is provided an ink composition capable of suppressing discharge bending at the time of discharging from a discharge head including a nozzle plate provided with a liquid repellent film, and also excellent in suppressing discharge bending at the time of ink discharge. It is possible to provide an image forming method in which an image is formed.

It is a schematic sectional drawing which shows an example of the internal structure of a discharge head. It is the schematic which shows an example of the discharge port arrangement | sequence of a nozzle plate.

The description of the configuration of the present invention described below may be made based on typical embodiments of the present invention, but the present invention is not limited to such embodiments.
Hereinafter, the ink composition of the present invention and the image forming method using the same will be described in detail.

[Ink composition]
The ink composition of the present invention (hereinafter, also simply referred to as “ink”) is prepared in an aqueous system containing at least water and a resin-coated pigment in which at least a part of the surface of the pigment is coated with a water-insoluble polymer. The total of the Mg concentration and the phosphate ion concentration is 1 ppm or more and 70 ppm or less on a mass basis.
By setting it as the said structure, it can be set as the ink composition which can suppress the discharge bending at the time of discharging from the discharge head provided with the nozzle plate provided with the liquid repellent film. This is considered as follows.

  That is, if Mg and phosphate ions coexist in the ink, the deterioration of the liquid repellent film formed on the ejection head is accelerated, the liquid repellency is lowered, and the ink tends to adhere to the liquid repellent film. Become. As drying of the adhering ink proceeds, deposits are generated in the vicinity of the tip of the nozzle of the ejection head, and “ejection bending” occurs in which the ink ejected from the nozzle is bent. On the other hand, by coating the surface of the pigment with the water-insoluble polymer, the impurity component derived from the pigment is coated with the water-insoluble polymer, so that the abundance of Mg and phosphate ions in the ink is reduced. For this reason, contact between Mg and phosphate ions is reduced, contact between the ejection head and these impurity components is reduced, and deterioration of the liquid repellent film due to the coexistence of phosphate ions and Mg is prevented. It is speculated that you can.

<Mg concentration and phosphate ion concentration>
In the ink composition of the present invention, Mg and phosphate ions are mainly contained as impurity components derived from the pigment described later.
In the present invention, the sum of the Mg concentration and the phosphate ion concentration in the ink composition is 1 ppm to 70 ppm on a mass basis. As a result, even when Mg and phosphate ions coexist in the ink composition, deterioration of the liquid repellent film of the ejection head due to the impurity components is suppressed, and sufficient liquid repellency is maintained. Therefore, it is possible to suppress the discharge bending due to the deterioration of the property. The sum of Mg concentration and phosphate ion concentration of 1 ppm or more means that Mg and phosphate ions are substantially contained in the ink composition. Few. Further, in the range where the total of the Mg concentration and the phosphate ion concentration exceeds 70 ppm, the deterioration of the liquid repellent film cannot be suppressed, and the discharge bend occurs.

The phosphate ion concentration in the ink composition can be determined by an anion chromatography method that can be detected by electrical conductivity (suppressor method), a direct absorbance detection method that captures the ion concentration in the sample by absorbance, and the ion exchange concentration by absorbance. It can be measured by the indirect absorbance detection method.
In the measurement, any commonly used measuring apparatus can be used. For example, trade name “ICS-2000” manufactured by Dionex Co., Ltd., “IC2010” manufactured by Tosoh Corporation, “ICA-2000” manufactured by Toa DKK Corporation, and the like can be mentioned.

Moreover, the supernatant liquid processed by ultracentrifugation (for example, 140,000 rpm, 60 min) is extract | collected, What is necessary is just to use the sample diluted 10 to 1000 times by ultrapure.
The measurement conditions are not particularly limited, and the column to be used, the eluent composition, the flow rate, the column temperature, the injection amount, etc. may be appropriately selected.
For example, as the column, for example, trade names “AS18 4 mm”, “AS15 4 mm”, “AS20 4 mm” manufactured by Dionex Co., Ltd. can be used.
The eluent is not particularly limited, and examples thereof include an aqueous potassium hydroxide solution having a predetermined concentration.
Specific measurement conditions may be, for example, a flow rate of 1 ml / min to 2 ml / min, a column temperature of 38 ° C. to 42 ° C., and a sample injection volume of 50 μL to 200 μL.

The Mg concentration in the ink composition can be measured by ICP-OES.
In the measurement, any commonly used measuring apparatus can be used. For example, the quantification may be performed using Optima 7300 DV manufactured by PerkinElmer.
Further, a sample obtained by collecting an appropriate amount of the ink composition, adding HNO ₃ , and microwave ashing (230 ° C.) may be used.

  As a method for controlling the Mg concentration and phosphate ion concentration in the ink composition within the above ranges, a method of washing the pigment to be used with pure water before preparing a resin-coated pigment dispersion described later, impurities Examples thereof include a method of selecting and using a pigment having a concentration within the above range.

<Resin-coated pigment coated with water-insoluble polymer>
The ink composition of the present invention contains at least one resin-coated pigment (hereinafter also referred to as “resin-coated pigment”) in which at least a part of the pigment surface is coated with a water-insoluble polymer. Thereby, the abundance in the ink composition of Mg and phosphate ions derived from the pigment is reduced. As a result, the deterioration of the liquid repellent film due to the coexistence of Mg and phosphate ions is suppressed, and good liquid repellency is maintained, so that the discharge bending can be reduced.
The resin-coated pigment in the present invention does not necessarily have to be entirely coated with the water-insoluble polymer in the present invention, and may be in a state where at least a part of the pigment surface is coated. It is contained in a dispersed state in the product.

(Water-insoluble polymer)
In the present invention, the water-insoluble polymer for covering the pigment is preferably one containing at least one hydrophilic structural unit (A) and at least one hydrophobic structural unit (B).
Here, the term “insoluble” means that when a polymer is mixed in an aqueous medium at 25 ° C., the amount of the polymer dissolved in the aqueous medium is 10% by mass or less as a mass ratio with respect to all the mixed polymers.

~ Hydrophilic structural unit (A) ~
The hydrophilic structural unit (A) in the water-insoluble polymer is not particularly limited as long as it contains at least one hydrophilic functional group. Even if it contains an ionic hydrophilic group, it is nonionic hydrophilic. It may contain a group.
As the hydrophilic functional group, the water-insoluble polymer can be stably present in the ink composition, from the viewpoint of facilitating the removal of the adhered aggregate by alleviating the adhesion or deposition of the aggregate. Acidic groups are preferred. In this case, even if the hydrophilic structural unit having an acidic group is a structural unit derived from an acidic group-containing monomer, the structural unit having no acidic group (polymer chain after polymerization) is converted into an acidic group by a polymer reaction. May be introduced.

  The acidic group is not particularly limited, and examples thereof include a carboxyl group, a phosphoric acid group, and a sulfonic acid group from the viewpoint of stability in an emulsified or dispersed state. Among them, a viewpoint of dispersion stability when an ink composition is configured. Therefore, a carboxyl group is preferable.

The acidic group-containing monomer is preferably an acidic group-containing monomer having an acidic group and an ethylenically unsaturated bond. Examples of the acidic group-containing monomer include an unsaturated carboxylic acid monomer, an unsaturated sulfonic acid monomer, and an unsaturated phosphoric acid monomer.
Examples of the unsaturated carboxylic acid monomer include acrylic acid, methacrylic acid, crotonic acid, itaconic acid, maleic acid, fumaric acid, citraconic acid, and 2-methacryloyloxymethyl succinic acid. Examples of the unsaturated sulfonic acid monomer include styrene sulfonic acid, 2-acrylamido-2-methylpropane sulfonic acid, 3-sulfopropyl (meth) acrylate, and bis- (3-sulfopropyl) -itaconate. It is done. Examples of the unsaturated phosphoric acid monomer include vinyl phosphonic acid, vinyl phosphate, bis (methacryloxyethyl) phosphate, diphenyl-2-acryloyloxyethyl phosphate, diphenyl-2-methacryloyloxyethyl phosphate, dibutyl-2- Examples include acryloyloxyethyl phosphate.
Among the acidic group-containing monomers, unsaturated carboxylic acid monomers are preferable, and acrylic acid and methacrylic acid are more preferable from the viewpoints of dispersion stability and ejection stability.
That is, the repeating unit having an acidic group is preferably a structural unit derived from (meth) acrylic acid.
The water-insoluble polymer preferably contains either or both of a structural unit derived from acrylic acid and a structural unit derived from methacrylic acid.

Moreover, when the said hydrophilic structural unit (A) contains a basic group, an amino group and an amide group (a nitrogen atom is unsubstituted) can be mentioned as a basic group.
Examples of the hydrophilic structural unit (A) containing a basic hydrophilic group include structural units derived from a monomer having a basic hydrophilic group. Examples of the monomer having a basic hydrophilic group include vinyl monomers such as (meth) acrylates, (meth) acrylamides, and vinyl esters having a basic hydrophilic functional group.

  As a monomer that forms a hydrophilic structural unit having a basic hydrophilic group, it has a functional group capable of forming a polymer such as an ethylenically unsaturated bond and a basic hydrophilic functional group. Are preferred and can be selected from known monomers. Specific examples include (meth) acrylamide, aminoethyl acrylate, aminopropyl acrylate and the like.

  Further, when the hydrophilic structural unit (A) contains a nonionic hydrophilic group, examples of the nonionic hydrophilic group include a hydroxyl group and alkylene oxides such as polyethylene oxide and polypropylene oxide described later.

  Examples of the hydrophilic structural unit containing a nonionic hydrophilic group include a structural unit derived from a monomer having a nonionic hydrophilic group. Examples of the monomer having a nonionic hydrophilic group include vinyl having a hydrophilic functional group such as (meth) acrylates, (meth) acrylamides, and vinyl esters having a nonionic hydrophilic group. Mention may be made of monomers.

  As a monomer that forms a hydrophilic structural unit having a nonionic hydrophilic group, it has a functional group capable of forming a polymer such as an ethylenically unsaturated bond and a nonionic hydrophilic functional group. Preferably, they can be selected from known monomers. Specific examples include hydroxyethyl (meth) acrylate, hydroxybutyl (meth) acrylate, and (meth) acrylate containing an alkylene oxide polymer.

  A hydrophilic structural unit having a nonionic hydrophilic group can be formed by polymerization of a corresponding monomer, but a hydrophilic functional group may be introduced into the polymer chain after polymerization.

  The hydrophilic structural unit having a nonionic hydrophilic group is more preferably a hydrophilic structural unit having an alkylene oxide structure. The alkylene moiety of the alkylene oxide structure is preferably an alkylene moiety having 1 to 6 carbon atoms, more preferably an alkylene moiety having 2 to 6 carbon atoms, and particularly preferably an alkylene moiety having 2 to 4 carbon atoms from the viewpoint of hydrophilicity. Moreover, as a polymerization degree of an alkylene oxide structure, 1-120 are preferable, 1-60 are more preferable, and 1-30 are especially preferable.

  Moreover, it is also a preferable aspect that the hydrophilic structural unit having a nonionic hydrophilic group is a hydrophilic structural unit containing a hydroxyl group. The number of hydroxyl groups in the structural unit is not particularly limited, and is preferably 1 to 4, more preferably 1 to 3, from the viewpoint of hydrophilicity of the water-insoluble polymer and compatibility with the solvent and other monomers during polymerization. 1-2 is particularly preferred.

The content ratio of the hydrophilic structural unit (A) in the water-insoluble polymer differs depending on, for example, the ratio of the hydrophobic structural unit (B) described later. For example, when the water-insoluble polymer is composed only of acrylic acid and / or methacrylic acid [hydrophilic structural unit (A)] and a hydrophobic structural unit (B) described later, acrylic acid relative to the total mass of the water-insoluble polymer. And / or the content rate of methacrylic acid is calculated | required by "100- (mass% of hydrophobic structural unit (B))".
The said hydrophilic structural unit (A) can be used individually by 1 type or in mixture of 2 or more types.

~ Hydrophobic structural unit (B) ~
It is preferable that the water-insoluble polymer in the present invention further includes at least one hydrophobic structural unit (B) in addition to the hydrophilic structural unit (A). The hydrophobic structural unit (B) is not particularly limited as long as it is a structural unit containing a hydrophobic functional group, but preferably contains at least one kind of structural unit having an aromatic ring. It is more preferable that at least 1 type of the structural unit represented by these is included.

In general formula (1), R ¹ represents a hydrogen atom or a methyl group, and L ¹ represents a substituted or unsubstituted phenylene group. L ² represents a single bond or a divalent linking group. Ar ¹ represents a monovalent group derived from a condensed aromatic ring having 8 or more carbon atoms, a hetero ring in which an aromatic ring is condensed, or a compound in which two or more benzene rings are connected.
In the general formula (1), R ¹ represents a hydrogen atom or a methyl group, preferably a methyl group.

L ¹ represents a substituted or unsubstituted phenylene group. L ¹ is preferably an unsubstituted phenylene group.
L ² represents a single bond or a divalent linking group. The divalent linking group is preferably a linking group having 1 to 30 carbon atoms, more preferably a linking group having 1 to 25 carbon atoms, still more preferably a linking group having 1 to 20 carbon atoms, Particularly preferred is a linking group having 1 to 15 carbon atoms.
Among them, most preferably, an alkyleneoxy group having 1 to 25 carbon atoms (more preferably 1 to 10), an imino group (—NH—), a sulfamoyl group, and 1 to 20 carbon atoms (more preferably 1 to 15). A divalent linking group containing an alkylene group, such as an alkylene group or an ethylene oxide group [— (CH 2 CH 2 O) n —, n = 1 to 6], and a group in which two or more of these are combined.

Ar ¹ represents a monovalent group derived from a condensed aromatic ring having 8 or more carbon atoms, a hetero ring in which an aromatic ring is condensed, or a compound in which two or more benzene rings are connected.

  The “condensed aromatic ring having 8 or more carbon atoms” includes an aromatic ring in which at least two benzene rings are condensed, at least one aromatic ring and a condensed alicyclic hydrocarbon ring. Is an aromatic compound having 8 or more carbon atoms. Specific examples include naphthalene, anthracene, fluorene, phenanthrene, acenaphthene and the like.

  The “heterocycle having an aromatic ring condensed” is a compound in which an aromatic compound containing no hetero atom (preferably a benzene ring) and a cyclic compound having a hetero atom are condensed. Here, the cyclic compound having a hetero atom is preferably a 5-membered ring or a 6-membered ring. As a hetero atom, a nitrogen atom, an oxygen atom, or a sulfur atom is preferable. The cyclic compound having a hetero atom may have a plurality of hetero atoms. In this case, the heteroatoms may be the same or different from each other. Specific examples of the heterocyclic ring condensed with an aromatic ring include phthalimide, acridone, carbazole, benzoxazole, and benzothiazole.

  Examples of the compound in which two or more benzene rings are linked include compounds in which two or more benzenes are bonded to each other through a single bond or a linking group having 1 to 2 carbon atoms. Specific examples of the monovalent group derived from a compound in which two or more benzene rings are linked include biphenyl, terphenyl, diphenylmethyl, triphenylmethyl and the like.

  Specific examples of the monomer forming the repeating unit represented by the general formula (1) include, but are not limited to, the following monomers.

Ar ¹ in the repeating unit represented by the general formula (1) is preferably a monovalent group derived from acridone or phthalimide, from the viewpoint of dispersion stability of the coated pigment. A monovalent group derived from is preferable.
Among the repeating units represented by the general formula (1), R ¹ is a methyl group, L ¹ is an unsubstituted phenylene group, and L ² is divalent in view of dispersion stability of the pigment. And Ar ¹ is preferably a monovalent group derived from acridone.

  The content ratio of the repeating unit represented by the general formula (1) in the copolymer is preferably in the range of 5% by mass to 25% by mass, more preferably 10% by mass with respect to the total mass of the copolymer. The range is 18% by mass or less. If the content is 5% by mass or more, the occurrence of image failure such as white spots tends to be remarkably suppressed. If the content is 25% by mass or less, the copolymerization reaction solution (for example, methyl ethyl ketone) is used. This is preferable because a problem in production suitability due to a decrease in solubility is not likely to occur.

  It is also a preferable aspect that the water-insoluble polymer in the present invention has a structural unit represented by the following general formula (2) other than the structural unit represented by the general formula (1).

In the general formula (2), R ² represents a hydrogen atom or a methyl group, preferably a methyl group. Ar ² represents an unsubstituted or substituted aromatic ring group. Examples of the substituent when the aromatic ring is substituted include a halogen atom, an alkyl group, an alkoxy group, a hydroxyl group, a cyano group, and an alkoxycarbonyl group, and may form a condensed ring. . When a condensed ring is formed, for example, a condensed aromatic ring having 8 or more carbon atoms, or an aromatic ring condensed with a hetero ring can be mentioned. Ar ² may be a monovalent group derived from a compound in which two or more aromatic rings (for example, benzene rings) are linked.

  The “condensed aromatic ring having 8 or more carbon atoms” and the “aromatic ring condensed with a heterocycle” in the general formula (2) are the same as the “condensed aromatic ring having 8 or more carbon atoms” in the general formula (1) and It is synonymous with "an aromatic ring condensed with a heterocycle". Moreover, as a monovalent group derived from a compound in which two or more aromatic rings (for example, benzene rings) are linked, a monovalent group derived from a compound in which two or more benzene rings are linked in the general formula (1). Preferable examples can be given.

The aromatic ring group represented by Ar ² is bonded to the main chain of the water-insoluble polymer via the ester group and the ethylene oxide chain, and the aromatic ring is not directly bonded to the main chain. An appropriate distance is maintained between the hydrophilic structural unit and the water-insoluble polymer is likely to interact with the pigment, and is strongly adsorbed to enhance dispersibility.
Among these, as Ar ² , an unsubstituted benzene ring and an unsubstituted naphthalene ring are preferable, and an unsubstituted benzene ring is particularly preferable.

  n represents the number of repetitions obtained by averaging the ethyleneoxy chains in the water-insoluble polymer of the resin-coated pigment contained in the ink composition. The range of n is 1-6, preferably 1-2.

  The following monomers etc. can be mentioned as a specific example of the monomer which forms the structural unit represented by the said General formula (2).

Among the structural units represented by the general formula (2), in terms of dispersion stability, R ² is a methyl group, Ar ² is an unsubstituted benzene ring, and n is 1 to 2. The case is particularly preferred.

  The content ratio of the structural unit represented by the general formula (2) in the water-insoluble polymer is preferably in the range of 30% by mass to 70% by mass with respect to the total mass of the water-insoluble polymer, more preferably 40%. The range is from mass% to 50 mass%. When the content is 30% by mass or more, the dispersibility is excellent, and when the content is 70% by mass or less, adhesion and deposition of aggregates can be suppressed, and occurrence of image failure such as white spots can be suppressed. .

  The water-insoluble polymer in the present invention can exist stably in an aqueous ink, and from the viewpoint of alleviating the adhesion or deposition of aggregates and facilitating the removal of the adhered aggregates, the hydrophilic structural unit (A ) And a hydrophobic structural unit (B). Here, the hydrophobic structural unit (B) includes a structural unit represented by the general formula (1).

  The water-insoluble polymer in the present invention may further have a hydrophobic structural unit other than the structural unit represented by the general formula (1) and the structural unit represented by the general formula (2). Examples of the other hydrophobic structural unit do not belong to the hydrophilic structural unit (A) (for example, have no hydrophilic functional group), such as (meth) acrylates, (meth) acrylamides, styrenes, and vinyl. Examples thereof include structural units derived from vinyl monomers such as esters, and hydrophobic structural units having an aromatic ring via a linking group at the atom forming the main chain. These structural units can be used individually by 1 type or in mixture of 2 or more types.

Examples of the (meth) acrylates include methyl (meth) acrylate, ethyl (meth) acrylate, butyl (meth) acrylate, isobutyl (meth) acrylate, hexyl (meth) acrylate, and the like. ) Acrylate, ethyl (meth) acrylate, and butyl (meth) acrylate are preferable, and methyl (meth) acrylate and ethyl (meth) acrylate are particularly preferable.
Examples of the (meth) acrylamides include N-cyclohexyl (meth) acrylamide, N- (2-methoxyethyl) (meth) acrylamide, N, N-diallyl (meth) acrylamide, N-allyl (meth) acrylamide, and the like. (Meth) acrylamides.
Examples of the styrenes include styrene, methyl styrene, dimethyl styrene, trimethyl styrene, ethyl styrene, isopropyl styrene, n-butyl styrene, tert-butyl styrene, methoxy styrene, butoxy styrene, acetoxy styrene, chlorostyrene, dichlorostyrene, Examples thereof include bromostyrene, chloromethylstyrene, hydroxystyrene protected with a group that can be deprotected by an acidic substance (for example, t-Boc), methyl vinylbenzoate, α-methylstyrene, vinylnaphthalene, and the like. Styrene and α-methylstyrene are preferred.
Examples of the vinyl esters include vinyl esters such as vinyl acetate, vinyl chloroacetate, vinyl propionate, vinyl butyrate, vinyl methoxyacetate, and vinyl benzoate. Of these, vinyl acetate is preferable.

The above-mentioned “hydrophobic structural unit having an aromatic ring via a linking group to an atom forming a main chain” is a copolymer of an aromatic ring linking to an atom forming the main chain of the copolymer via a linking group The structural unit in which the ratio in the interior is 15% by mass or more and 27% by mass or less is preferable, the structural unit that is 15% by mass or more and 25% by mass or less is more preferable, and the structural unit that is 15% by mass or more and 20% by mass or less is more preferable. .
Since the aromatic ring has a structure in which it is bonded to an atom forming the main chain of the copolymer via a linking group and is not directly bonded to an atom forming the main chain of the copolymer, the hydrophobic aromatic ring and the hydrophilic structural unit Since an appropriate distance is maintained between the copolymer and the pigment, interaction between the copolymer and the pigment is likely to occur, and it is strongly adsorbed to further improve dispersibility.

  The “hydrophobic structural unit having an aromatic ring via a linking group in the main chain atom” is a structural unit represented by the following general formula (3) (repeating unit represented by the general formula (1)) And excluding the repeating unit represented by the general formula (2).

In the general formula (3), R ¹¹ represents a hydrogen atom, a methyl group, or a halogen atom.
L ¹¹ represents * —COO—, * —OCO—, * —CONR ¹² — or * —O—, and R ¹² represents a hydrogen atom or an alkyl group having 1 to 10 carbon atoms. Incidentally, * mark in group represented by L ¹¹ represents a connecting point with the main chain.

L ¹² represents a single bond or a divalent linking group having 1 to 30 carbon atoms, and when it is a divalent linking group, it is preferably a linking group having 1 to 25 carbon atoms, more preferably a carbon number. It is a 1-20 linking group, More preferably, it is a C1-C15 linking group.
Among them, particularly preferably, an alkyleneoxy group having 1 to 25 carbon atoms (more preferably 1 to 10), an imino group (—NH—), a sulfamoyl group, and 1 to 20 carbon atoms (more preferably 1 to 15). A divalent linking group containing an alkylene group, such as an alkylene group or an ethylene oxide group [— (CH ₂ CH ₂ O) _n —, n = 1 to 6], and a group in which two or more of these are combined. .

In the general formula (3), Ar ¹¹ represents a monovalent group derived from an aromatic ring.
The aromatic ring represented by Ar ¹¹ is not particularly limited, but a benzene ring, a condensed aromatic ring having 8 or more carbon atoms, an aromatic ring condensed with a hetero ring, or a compound in which two or more benzene rings are connected. Can be mentioned. Details of the condensed aromatic ring having 8 or more carbon atoms, an aromatic ring condensed with a heterocycle, and a compound in which two or more benzene rings are linked are as described above.

  Hereinafter, specific examples of monomers capable of forming “a hydrophobic structural unit having an aromatic ring via a linking group at an atom constituting the main chain” will be given. However, the present invention is not limited to the following specific examples.

Among the above, the water-insoluble polymer in the present invention has a structure in which the hydrophilic structural unit (A) is (meth) acrylic acid and the hydrophobic structural unit (B) is represented by (i) the general formula (1). A unit (preferably a structural unit derived from the aforementioned M-25 / M-27, M-28 / M-29), (ii) a structural unit represented by the general formula (2) (preferably phenoxyethyl (meth) acrylate) Derived structural unit), and (iii) a hydrophobic structural unit other than the above (B) (preferably a structural unit derived from methyl (meth) acrylate, ethyl (meth) acrylate, or benzyl methacrylate). It is preferable that
Further, in the water-insoluble polymer in the present invention, the hydrophilic structural unit (A) is (meth) acrylic acid, and the hydrophobic structural unit (B) contains at least one of the above (i) and (ii). Is preferred.
Particularly, in the water-insoluble polymer in the present invention, the hydrophilic structural unit (A) is (meth) acrylic acid, and the hydrophobic structural unit (B) contains at least one of the above (i) and (ii), And (iii).

The water-insoluble polymer in the present invention includes a hydrophilic structural unit (A) and a hydrophobic structural unit (B) (the structural unit represented by the general formula (2), the structural unit represented by the general formula (1)). The composition with the other hydrophobic structural unit (B) affects the degree of hydrophilicity and hydrophobicity of each, but the ratio of the hydrophilic structural unit (A) is 15% by mass or less. Is preferred. At this time, the proportion of the hydrophobic structural unit (B) is preferably more than 80% by mass and more preferably 85% by mass or more with respect to the total mass of the water-insoluble polymer.
When the content of the hydrophilic structural unit (A) is 15% by mass or less, the amount of the component dissolved alone in the aqueous medium is suppressed, and various properties such as pigment dispersion are improved, which is favorable during ink jet recording. Ink discharge performance is obtained.

  A preferable content ratio of the hydrophilic structural unit (A) is in the range of more than 0% by mass and 15% by mass or less, more preferably 2% by mass to 15% by mass with respect to the total mass of the water-insoluble polymer. It is a range, More preferably, it is the range of 5 to 15 mass%, Most preferably, it is the range of 8 to 12 mass%.

The acid value of the water-insoluble polymer in the present invention is preferably from 30 mgKOH / g to 100 mgKOH / g, more preferably from 30 mgKOH / g to 85 mgKOH / g from the viewpoint of pigment dispersibility and storage stability. It is preferably 50 mgKOH / g or more and 85 mgKOH / g or less.
The acid value is defined as the mass (mg) of KOH required to completely neutralize 1 g of the water-insoluble polymer, and is measured by the method described in JIS standards (JIS K0070, 1992).

The molecular weight of the water-insoluble polymer in the present invention is preferably 30,000 or more, more preferably 30,000 to 150,000, even more preferably 30,000 to 100,000, and particularly preferably 3 in terms of weight average molecular weight (Mw). 10,000 to 80,000. When the molecular weight is 30,000 or more, the steric repulsion effect as a dispersant tends to be good, and the steric effect makes it easy to adsorb to the pigment.
The number average molecular weight (Mn) is preferably in the range of about 1,000 to 100,000, particularly preferably in the range of 3,000 to 50,000. When the number average molecular weight is within the above range, a function as a coating film in the pigment or a function as a coating film of the ink composition can be exhibited. The water-insoluble polymer in the present invention is preferably used in the form of an alkali metal or organic amine salt.

  The molecular weight distribution (weight average molecular weight / number average molecular weight) of the water-insoluble polymer in the present invention is preferably in the range of 1 to 6, and more preferably in the range of 1 to 4. When the molecular weight distribution is within the above range, the dispersion stability and ejection stability of the ink can be improved.

  The number average molecular weight and the weight average molecular weight are detected by a differential refractometer with a solvent THF using a GPC analyzer using columns of TSKgel SuperHZM-H, TSKgel SuperHZ4000, and TSKgel SuperHZ2000 (both manufactured by Tosoh Corp.). It is the molecular weight expressed by converting using polystyrene as a substance.

The water-insoluble polymer in the present invention can be synthesized by various polymerization methods such as solution polymerization, precipitation polymerization, suspension polymerization, bulk polymerization, and emulsion polymerization. The polymerization reaction can be performed by a known operation such as a batch system, a semi-continuous system, or a continuous system. The polymerization initiation method includes a method using a radical initiator, a method of irradiating light or radiation, and the like. These polymerization methods and polymerization initiation methods are described in, for example, the revised version of Tsuruta Junji “Polymer Synthesis Method” (published by Nikkan Kogyo Shimbun, 1971), Takatsu Otsu and Masato Kinoshita, “Experimental Methods for Polymer Synthesis” , Published in 1972, pages 124-154.
Among the polymerization methods, a solution polymerization method using a radical initiator is particularly preferable. Solvents used in the solution polymerization method are, for example, ethyl acetate, butyl acetate, acetone, methyl ethyl ketone, methyl isobutyl ketone, cyclohexanone, tetrahydrofuran, dioxane, N, N-dimethylformamide, N, N-dimethylacetamide, benzene, toluene, acetonitrile And various organic solvents such as methylene chloride, chloroform, dichloroethane, methanol, ethanol, 1-propanol, 2-propanol, 1-butanol and the like. A solvent may be used individually by 1 type or in combination of 2 or more types. Moreover, you may use as a mixed solvent with water. The polymerization temperature needs to be set in relation to the molecular weight of the polymer to be produced, the type of initiator, etc., and is usually about 0 ° C. to 100 ° C., but the polymerization is preferably performed in the range of 50 to 100 ° C. . The reaction pressure may be appropriately selected typically is ^{1kg / cm 2 ~100kg / cm 2} , particularly ^1kg / cm ^{2 ~30kg} / cm 2 is preferably about. The reaction time is about 5 to 30 hours. The obtained resin may be subjected to purification such as reprecipitation.

  Specific examples of preferred water-insoluble polymers in the present invention are shown below. However, the present invention is not limited to the following.

(Pigment)
Next, the pigment coated with the water-insoluble polymer will be described.
There is no restriction | limiting in particular as a pigment in this invention, A conventionally well-known organic pigment and an inorganic pigment can be used. For example, azo pigments such as azo lakes, insoluble azo pigments, condensed azo pigments and chelate azo pigments, phthalocyanine pigments, perylene pigments, perinone pigments, anthraquinone pigments, quinacridone pigments, dioxazine pigments, diketopyrrolopyrrole pigments, thioindigo pigments, isoindolinone pigments , Polycyclic pigments such as quinophthalone pigments, dye lakes such as basic dye type lakes, acid dye type lakes, organic pigments such as nitro pigments, nitroso pigments, aniline black, daylight fluorescent pigments, titanium oxides, iron oxides And inorganic pigments such as carbon black. Any pigment not described in the color index can be used as long as it can be dispersed in the aqueous phase. Further, pigments whose surface is treated with a surfactant, a polymer dispersant, or the like, or graft carbon can also be used. Among the pigments, azo pigments, phthalocyanine pigments, anthraquinone pigments, quinacridone pigments, and carbon black pigments are preferably used, and quinacridone pigments are more preferable.

  The pigments may be used singly or in combination, and a plurality of pigments may be selected from each group or between the groups and used in combination. It can be appropriately selected according to the purpose.

  In the pigment coated with the water-insoluble polymer in the present invention (hereinafter also referred to as “resin-coated pigment”), the ratio (p: r) between the pigment (p) and the water-insoluble polymer (r) in the present invention is: The weight ratio is preferably 100: 25 to 100: 140, more preferably 100: 25 to 100: 50. The ratio (p: r) tends to improve the dispersion stability and abrasion resistance when the water-insoluble polymer is 100: 25 or more, and the ratio (p: r) is dispersed when the water-insoluble polymer is 100: 140 or less. There is a tendency for stability to improve.

The particle diameter (volume average) of the resin-coated pigment particle dispersion in the present invention is preferably 50 nm to 120 nm, more preferably 60 nm to 100 nm, and still more preferably 70 nm to 90 nm.
When the particle diameter is 50 nm or more, deterioration of stability tends to be suppressed, and when the particle diameter is 120 nm or less, droplet ejection characteristics are improved, and the occurrence of white spots in a recorded image tends to be suppressed.
The particle size distribution of the particle size is not particularly limited, and may be either a wide particle size distribution or a monodisperse particle size distribution. Two or more kinds of dispersions having a monodisperse particle size distribution may be mixed and used.
The particle diameter of the dispersion of resin-coated pigment particles is a volume average particle diameter measured by a dynamic light scattering method using a nanotrack particle size distribution analyzer UPA-EX150 (manufactured by Nikkiso Co., Ltd.).

  The resin-coated pigment (microencapsulated pigment) in the present invention can be produced by the conventional physical and chemical methods using the water-insoluble polymer and the pigment. For example, as described in JP-A-9-151342, JP-A-10-140065, JP-A-11-209672, JP-A-11-172180, JP-A-10-25440, or JP-A-11-43636. It can be manufactured by a method. Specific examples include the phase inversion method and acid precipitation method described in JP-A-9-151342 and JP-A-10-140065. Among them, the phase inversion method is preferable from the viewpoint of dispersion stability.

a) Phase Inversion Method The phase inversion method is basically a self-dispersion (phase inversion emulsification) method in which a mixed melt of a resin having a self-dispersing ability or a dissolving ability and a pigment is dispersed in water. The mixed melt may contain the above curing agent or polymer compound. Here, the mixed molten material refers to a mixed state that is not dissolved, a state that is dissolved and mixed, or a state that includes both of these states. A more specific production method of the “phase inversion method” includes the method described in JP-A-10-140065.
b) Acid precipitation method The acid precipitation method prepares a water-containing cake composed of a resin and a pigment, and neutralizes some or all of the anionic groups of the resin in the water-containing cake using a basic compound. This is a method for producing a microencapsulated pigment.
Specifically, the acid precipitation method includes (1) a step of dispersing a resin and a pigment in an alkaline aqueous medium and subjecting the resin to gelation by performing a heat treatment as necessary; Hydrophobizing the resin by making it neutral or acidic, and strongly fixing the resin to the pigment; (3) obtaining a water-containing cake by performing filtration and washing as necessary; and (4) a water-containing cake. A step of neutralizing a part or all of the anionic group of the resin with a basic compound and then redispersing in an aqueous medium, and (5) performing a heat treatment as necessary, And a step of gelling the resin.

  More specific production methods of the above phase inversion method and acid precipitation method include the methods described in JP-A-9-151342 and JP-A-10-140065.

In the ink composition of the present invention, the resin-coated pigment in the present invention comprises a preparation step of preparing a dispersion of the resin-coated pigment by a method comprising the following steps (1) and (2) using the water-insoluble polymer. It can be provided. Further, the ink composition of the present invention can be prepared by a method of providing this preparation step and using the resulting dispersion of the resin-coated pigment together with water and an organic solvent to form an ink composition.
Step (1): Step of dispersing a mixture containing a water-insoluble polymer, an organic solvent, a neutralizing agent, a pigment, and water by stirring or the like to obtain a dispersion Step (2): Removing the organic solvent from the dispersion Process

  The stirring method is not particularly limited, and a commonly used mixing and stirring device, and a dispersing device such as an ultrasonic dispersing device, a high-pressure homogenizer, and a bead mill can be used as necessary.

  Preferred examples of the organic solvent used here include alcohol solvents, ketone solvents, and ether solvents. Examples of the alcohol solvent include isopropyl alcohol, n-butanol, t-butanol, ethanol and the like. Examples of the ketone solvent include acetone, methyl ethyl ketone, diethyl ketone, and methyl isobutyl ketone. Examples of the ether solvent include dibutyl ether and dioxane. Among these solvents, ketone solvents such as methyl ethyl ketone and alcohol solvents such as isopropyl alcohol are preferable, and methyl ethyl ketone is more preferable.

Further, at least one neutralizing agent is contained in the ink composition so that part or all of the dissociable groups are neutralized and the water-insoluble polymer forms a stable emulsified or dispersed state in water. It is preferable.
The neutralizing agent is preferably used in an amount of 0.5 to 1.5 equivalents relative to the acid value of the resin, and preferably in the range of 1 to 1.5 equivalents.

  Examples of the neutralizing agent include alcohol amines (eg, diethanolamine, triethanolamine, 2-amino-2-ethyl-1,3-propanediol), alkali metal hydroxides (eg, lithium hydroxide, hydroxide) Sodium, potassium hydroxide, etc.), ammonium hydroxide (eg, ammonium hydroxide, quaternary ammonium hydroxide), phosphonium hydroxide, alkali metal carbonate, etc. Preferably used.

  In the step (2), the organic solvent is distilled off from the dispersion obtained in the step (1) by a conventional method such as vacuum distillation, and the phase is changed to an aqueous system. A dispersion of resin-coated pigment particles coated with a polymer can be obtained. The organic solvent in the obtained dispersion is substantially removed, and the amount of the organic solvent here is preferably 0.2% by mass or less, and more preferably 0.1% by mass or less.

More specifically, for example, (1) a step of neutralizing a water-insoluble polymer having an anionic group or a solution obtained by dissolving it in an organic solvent and a basic compound (neutralizing agent); ) After the pigment is mixed with the obtained mixture to form a suspension, the pigment is dispersed with a disperser or the like to obtain a pigment dispersion, and (3) the organic solvent is removed by distillation, for example. Coating the pigment with a specific water-insoluble polymer having an anionic group, and dispersing the pigment in an aqueous medium to form an aqueous dispersion.
More specifically, the descriptions in JP-A-11-209672 and JP-A-11-172180 can be referred to.

  In the present invention, the dispersion treatment can be performed using, for example, a ball mill, a roll mill, a bead mill, a high-pressure homogenizer, a high-speed stirring type disperser, an ultrasonic homogenizer, or the like.

  The content of the pigment coated with the water-insoluble polymer is preferably 1% by mass or more and 10% by mass or less, more preferably 2% by mass or more and 8% by mass or less from the viewpoints of dispersion stability and concentration of the ink composition. Preferably, 2 mass% and 6 mass% or less are especially preferable.

<Water>
The ink composition in the present invention contains water. There is no restriction | limiting in particular in content of water. Especially, preferable content of water is 10 mass% or more and 99 mass% or less, More preferably, it is 30 mass% or more and 80 mass% or less, More preferably, it is 50 mass% or more and 70 mass% or less.

<Organic solvent>
The ink composition in the invention can contain at least one organic solvent in addition to the resin-coated pigment and water described above. The organic solvent is used for the purpose of an anti-drying agent, a wetting agent or a penetration accelerator. The anti-drying agent is used for the purpose of preventing the ink from adhering and drying to form aggregates and clogging at the ink discharge port of the ejection nozzle, and the anti-drying agent and wetting agent have a vapor pressure lower than that of water. Low water-soluble organic solvents are preferred. Moreover, as a penetration accelerator, it is used for the purpose of improving the ink permeability to paper.

The organic solvent contained in the ink composition of the present invention can be appropriately selected from known organic solvents in consideration of the function as a drying inhibitor, wetting agent, or penetration enhancer. From the viewpoint of solubility, a water-soluble organic solvent is preferable.
Examples of water-soluble organic solvents include glycerin, 1,2,6-hexanetriol, trimethylolpropane, ethylene glycol, propylene glycol, diethylene glycol, triethylene glycol, tetraethylene glycol, pentaethylene glycol, dipropylene glycol, 2- Butene-1,4-diol, 2-ethyl-1,3-hexanediol, 2-methyl-2,4-pentanediol, 1,2-octanediol, 1,2-hexanediol, 1,2-pentanediol Alkanediols (polyhydric alcohols) such as 4-methyl-1,2-pentanediol; glucose, mannose, fructose, ribose, xylose, arabinose, galactose, aldonic acid, glucitol, maltose, cellobiose, lact Sugars such as sucrose, trehalose and maltotriose; sugar alcohols; hyaluronic acids; so-called solid wetting agents such as ureas; alkyl alcohols having 1 to 4 carbon atoms such as ethanol, methanol, butanol, propanol and isopropanol Ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol monobutyl ether, ethylene glycol monomethyl ether acetate, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, diethylene glycol mono-n-propyl ether, ethylene glycol mono-iso-propyl ether, diethylene glycol Mono-iso-propyl ether, ethylene glycol mono-n-butyl ether, Tylene glycol mono-t-butyl ether, diethylene glycol mono-t-butyl ether, 1-methyl-1-methoxybutanol, propylene glycol monomethyl ether, propylene glycol monoethyl ether, propylene glycol mono-t-butyl ether, propylene glycol mono-n-propyl Glycol ethers such as ether, propylene glycol mono-iso-propyl ether, dipropylene glycol monomethyl ether, dipropylene glycol monoethyl ether, dipropylene glycol mono-n-propyl ether, dipropylene glycol mono-iso-propyl ether; 2 -Pyrrolidone, N-methyl-2-pyrrolidone, 1,3-dimethyl-2-imidazolidinone, formamide, aceto Toamide, dimethyl sulfoxide, sorbit, sorbitan, acetin, diacetin, triacetin, sulfolane and the like can be mentioned, and one or more of these can be used.

  For the purpose of drying inhibitors and wetting agents, polyhydric alcohols are useful, such as glycerin, ethylene glycol, diethylene glycol, triethylene glycol, propylene glycol, dipropylene glycol, tripropylene glycol, 1,3-butanediol. 2,3-butanediol, 1,4-butanediol, 3-methyl-1,3-butanediol, 1,5-pentanediol, tetraethylene glycol, 1,6-hexanediol, 2-methyl-2, Examples include 4-pentanediol, polyethylene glycol, 1,2,4-butanetriol, 1,2,6-hexanetriol, and the like. These may be used individually by 1 type and may use 2 or more types together.

  For the purpose of the penetrant, a polyol compound is preferable, and examples of the aliphatic diol include 2-ethyl-2-methyl-1,3-propanediol, 3,3-dimethyl-1,2-butanediol, 2,2- Diethyl-1,3-propanediol, 2-methyl-2-propyl-1,3-propanediol, 2,4-dimethyl-2,4-pentanediol, 2,5-dimethyl-2,5-hexanediol, Examples include 5-hexene-1,2-diol and 2-ethyl-1,3-hexanediol. Among these, preferred examples include 2-ethyl-1,3-hexanediol and 2,2,4-trimethyl-1,3-pentanediol.

The said organic solvent can be used individually by 1 type or in mixture of 2 or more types.
The content of the organic solvent in the ink composition is preferably 1% by mass to 60% by mass, and more preferably 5% by mass to 40% by mass.

<Polymer particles>
In addition to the above components, the ink composition of the present invention preferably contains polymer particles from the viewpoint of improving abrasion resistance. The polymer particles can be suitably used in the form of latex.
Polymer particles include acrylic resins, vinyl acetate resins, styrene-butadiene resins, vinyl chloride resins, acrylic-styrene resins, butadiene resins, styrene resins, crosslinked acrylic resins, crosslinked styrene resins, and benzoguanamine resins. And particles such as phenol resin, silicone resin, epoxy resin, urethane resin, paraffin resin, and fluorine resin. Among these, acrylic resins, acrylic-styrene resins, styrene resins, cross-linked acrylic resins, and cross-linked styrene resins can be given as preferable examples.

The weight average molecular weight of the polymer particles is preferably 10,000 or more and 200,000 or less, more preferably 100,000 or more and 200,000 or less.
The average particle size of the polymer particles is preferably in the range of 10 nm to 1 μm, more preferably in the range of 10 nm to 200 nm, still more preferably in the range of 20 nm to 100 nm, and particularly preferably in the range of 20 nm to 50 nm.

The content of the polymer particles is preferably 0.5% by mass or more and 20% by mass or less, more preferably 3% by mass or more and 20% by mass or less, and further preferably 5% by mass or more and 15% by mass or less with respect to the ink.
The glass transition temperature Tg of the polymer particles is preferably 30 ° C. or higher, more preferably 40 ° C. or higher, and further preferably 50 ° C. or higher.
Further, the particle size distribution of the polymer particles is not particularly limited, and may be either a wide particle size distribution or a monodispersed particle size distribution. Further, two or more kinds of polymer fine particles having a monodispersed particle size distribution may be mixed and used.

<Surfactant>
The ink composition in the invention may contain at least one surfactant. The surfactant is used as a surface tension adjusting agent, and examples thereof include nonionic, cationic, anionic and betaine surfactants.
The surfactant preferably contains an amount capable of adjusting the surface tension of the ink composition to 20 mN / m to 60 mN / m in order to eject droplets well by the ink jet method. Among them, the content of the surfactant is preferably an amount capable of adjusting the surface tension to 20 mN / m to 45 mN / m, more preferably an amount capable of adjusting to 25 mN / m to 40 mN / m.

  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 Any of the surfactants can be used.

Specific examples of the anionic surfactant include, for example, sodium dodecylbenzenesulfonate, sodium lauryl sulfate, sodium alkyldiphenyl ether disulfonate, sodium alkylnaphthalenesulfonate, sodium dialkylsulfosuccinate, sodium stearate, potassium oleate, Sodium dioctylsulfosuccinate, sodium polyoxyethylene alkyl ether sulfate, sodium polyoxyethylene alkyl ether sulfate, sodium polyoxyethylene alkyl phenyl ether sulfate, sodium dialkylsulfosuccinate, sodium stearate, sodium oleate, t-octylphenoxy Examples include sodium ethoxypolyethoxyethyl sulfate, and one or more of these are selected. Rukoto can.
Specific examples of the nonionic surfactant include, for example, polyoxyethylene lauryl ether, polyoxyethylene octyl phenyl ether, polyoxyethylene oleyl phenyl ether, polyoxyethylene nonyl phenyl ether, oxyethylene / oxypropylene block copolymer, t- Examples include octylphenoxyethyl polyethoxyethanol, nonylphenoxyethyl polyethoxyethanol, and the like, and one or more of these can be selected.
Examples of the cationic surfactant include tetraalkylammonium salts, alkylamine salts, benzalkonium salts, alkylpyridium salts, imidazolium salts, and the like. Specific examples thereof include dihydroxyethyl stearylamine and 2-heptadecenyl. -Hydroxyethyl imidazoline, lauryl dimethyl benzyl ammonium chloride, cetyl pyridinium chloride, stearamide methyl pyridium chloride and the like.

  The content of the surfactant in the ink composition is not particularly limited and is preferably 1% by mass or more, more preferably 1% by mass or more and 10% by mass or less, and further preferably 1% by mass or more and 3% by mass or less. It is.

<Others>
In addition to the above components, the ink composition of the present invention includes, for example, an ultraviolet absorber, an antifading agent, an antifungal agent, an antirust agent, an antioxidant, an emulsion stabilizer, a penetration enhancer, a pH, if necessary. You may contain other components, such as a regulator, a surface tension regulator, antiseptic | preservative, an antifoamer, a viscosity regulator, a dispersion stabilizer, and a chelating agent.
For details of the other components, for example, paragraph numbers [0098] to [0105] of JP2010-155359A, paragraph numbers [0247] to [0248] of JP2011-62999A, JP2010- No. 155359, paragraphs [0099] to [0104] and the like can be mentioned.

<Physical properties of ink composition>
The surface tension (25 ° C.) of the ink composition in the invention is preferably from 20 mN / m to 60 mN / m. More preferably, it is 20 mN or more and 45 mN / m or less, More preferably, it is 25 mN / m or more and 40 mN / m or less.
The surface tension is measured using an automatic surface tensiometer CBVP-Z (manufactured by Kyowa Interface Science Co., Ltd.) and a water-based ink at 25 ° C.

Further, the viscosity at 20 ° C. of the ink composition in the present invention is preferably 1.2 mPa · s or more and 15.0 mPa · s or less, more preferably 2 mPa · s or more and less than 13 mPa · s, and still more preferably. Is 2.5 mPa · s or more and less than 10 mPa · s.
The viscosity is measured using a VISCOMETER TV-22 (manufactured by TOKI SANGYO CO. LTD) under the condition of 20 ° C. of a water-based ink.

The ink composition in the present invention can be used for forming a multicolor image (for example, a full color image). For the formation of a full color image, a magenta tone ink composition, a cyan tone ink composition, and a yellow tone ink composition can be used, and a black tone ink composition is used to further adjust the tone. Can do.
In addition, ink compositions having red (R), green (G), blue (B), and white (W) tones other than yellow (Y), magenta (M), and cyan (C), and so-called printing fields. Ink-colored ink compositions and the like can be used.
The ink composition of each color tone can be prepared by changing the hue of the pigment used as the colorant as desired.

[Ink set]
The ink set of the present invention includes at least one of the ink compositions described above, and at least one treatment liquid containing an aggregating component that aggregates the components contained in the ink composition when in contact with the ink composition. And can be constituted using other components as required.
The ink set can be used as an ink cartridge containing these integrally or independently, and is preferable from the viewpoint of convenient handling. An ink cartridge including an ink set is known in the art, and can be formed into an ink cartridge by appropriately using a known method.

(Processing liquid)
The treatment liquid contains at least one aggregation component that aggregates the pigment in the ink composition. By mixing the treatment liquid with the ink composition ejected by the ink jet method, aggregation of the pigment stably dispersed in the ink composition is promoted.

~ Aggregating component ~
The aggregating component contained in the treatment liquid is not particularly limited as long as it can agglomerate the pigment in the ink composition, and may be an inorganic acid or an organic acid.
Examples of the aggregating component include a phosphoric acid group, a phosphonic acid group, a phosphinic acid group, a sulfuric acid group, a sulfonic acid group, a sulfinic acid group, a compound having a carboxyl group, or an acidic compound such as a salt thereof (for example, a polyvalent metal salt). Is mentioned. Among these, a compound having a phosphate group (H ₂ PO ₄ ⁻ ) is more preferable from the viewpoint of the aggregation speed of the ink composition and uneven gloss of the image area. Examples of the compound having a phosphoric acid group include orthophosphoric acid and pyrophosphoric acid (diphosphoric acid).
Specifically, sulfuric acid, hydrochloric acid, nitric acid, phosphoric acid, polyacrylic acid, acetic acid, glycolic acid, malonic acid, malic acid, maleic acid, ascorbic acid, succinic acid, glutaric acid, fumaric acid, citric acid, tartaric 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 are preferred It is mentioned in.
An acidic compound may be used individually by 1 type, and may use 2 or more types together.

  As the acidic compound, an acidic compound having high water solubility is preferable, and an organic acid is preferable, an organic acid having a valence of 2 or more is more preferable, and a divalent carboxylic acid is more preferable in terms of increasing cohesion and fixing the entire ink. Particularly preferred. The divalent or higher organic acid is preferably an organic acid having a first pKa of 3.5 or less, more preferably an organic acid having a first pKa of 3.0 or less. Specific examples include oxalic acid, malonic acid, and citric acid.

  The content of the acidic compound in the treatment liquid is preferably 1% by mass or more and 50% by mass or less, more preferably 3% by mass or more and 45% by mass or less, and still more preferably from the viewpoint of cohesiveness of the ink composition. It is the range of 5 mass% or more and 40 mass% or less.

The aggregation component may include other aggregation components that are compounds other than the acidic compound and can aggregate the components in the ink composition. Examples of other aggregating components include polyvalent metal salts, polyallylamines, and derivatives thereof.
Examples of the polyvalent metal salt include alkaline earth metals belonging to Group 2 of the periodic table (eg, magnesium, calcium), transition metals belonging to Group 3 of the periodic table (eg, lanthanum), and Group 13 of the periodic table. Mention may be made of salts of cations (for example, aluminum) and lanthanides (for example, neodymium). As these metal salts, carboxylate (formic acid, acetic acid, benzoate, etc.), nitrate, chloride, and thiocyanate are suitable. Among them, preferred are calcium salts or magnesium salts of carboxylic acids (formic acid, acetic acid, benzoates, etc.), calcium salts or magnesium salts of nitric acid, calcium chloride, magnesium chloride, and calcium salts or magnesium salts of thiocyanic acid.

  Examples of the organic acid include polyacrylic acid, acetic acid, glycolic acid, malonic acid, malic acid, maleic acid, ascorbic acid, succinic acid, glutaric acid, fumaric acid, citric acid, tartaric acid, lactic acid, sulfonic acid, and 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 are preferably selected. be able to.

The aggregating components can be used alone or in combination of two or more.
As content of the said aggregation component in the said process liquid, 1 to 20 mass% is preferable, More preferably, it is 5 to 20 mass%, More preferably, it is the range of 10 to 20 mass%. It is.

  The treatment liquid in the present invention can be configured to contain an aqueous solvent (for example, water) or an organic solvent in addition to the aggregation component. Moreover, the said process liquid can contain another additive as needed. Other additives include, for example, anti-drying agents (wetting agents), anti-fading agents, emulsion stabilizers, penetration enhancers, UV absorbers, preservatives, anti-fungal agents, pH adjusters, surface tension adjusters, anti-foaming agents. Well-known additives, such as a foaming agent, a viscosity modifier, a dispersing agent, a dispersion stabilizer, a rust preventive agent, a chelating agent, are mentioned.

Examples of the treatment liquid include a liquid composition capable of generating an aggregate by changing the pH of the ink composition. At this time, pH (25 degreeC) of a process liquid has preferable 6 or less, More preferably, pH is 4 or less. Especially, pH (25 degreeC) has the preferable range of 1-4, Especially preferably, pH is 1-3. In this case, the pH (25 ° C.) of the ink composition is preferably 7.5 or more (more preferably 8 or more).
Among these, in the present invention, from the viewpoint of image density, resolution, and speedup of inkjet recording, the pH (25 ° C.) of the ink composition is 7.5 or more, and the pH (25 ° C.) of the treatment liquid is. The case of 4 or less is preferable.

The viscosity of the treatment liquid is preferably in the range of 1 mPa · s to 30 mPa · s, more preferably in the range of 1 mPa · s to 20 mPa · s, from the viewpoint of the aggregation rate of the ink composition, and more preferably 2 mPa · s to 15 mPa · s. The range of s or less is more preferable, and the range of 2 mPa · s or more and 10 mPa · s or less is particularly preferable. The viscosity is measured under a condition of 25 ° C. using a VISCOMETER TV-22 (manufactured by TOKI SANGYO CO. LTD).
The surface tension of the treatment liquid is preferably in the range of 20 mN / m to 60 mN / m, more preferably in the range of 25 mN / m to 50 mN / m, and more preferably in the range of 30 mN / m to 45 mN / m from the viewpoint of the aggregation rate of the ink composition. The range of is more preferable. The surface tension is measured under conditions of 25 ° C. 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 comprises, on a recording medium, the water of the present invention described above and a resin-coated pigment in which at least a part of the surface of the pigment is coated with a water-insoluble polymer, and Mg and phosphate ions The ink composition is provided with an ink application process in which an ink composition in which the total of the above is suppressed to a predetermined concentration is applied by an inkjet method from an ejection head provided with a nozzle plate provided with a liquid repellent film. Thereby, even when phosphate ions and Mg coexist in the ink, the deterioration of the liquid repellent film can be suppressed, stable liquid repellency can be obtained, and the discharge bending at the time of ink discharge can be suppressed. As a result, a high resolution image is formed.
The water-insoluble polymer in the present invention is as described in the above-mentioned section of the ink composition, and preferred examples are also the same.
The same applies to other components used in the image forming method of the present invention.

<Ink application process>
The image forming method of the present invention is an ink application process in which the ink composition according to the present invention is ejected from a ejection head having a nozzle plate provided with a liquid repellent film and applied onto a recording medium by an inkjet method. Have Thereby, the ink composition can be selectively applied onto the recording medium, and a desired visible image can be formed. At this time, by using the ink composition described above, the liquid repellency of the liquid repellent film is maintained, so that the discharge bending is suppressed. As a result, high-resolution image formation can be performed.

  Specifically, the image recording using the ink-jet method is performed by supplying energy to a desired recording medium, that is, plain paper, resin-coated paper, for example, JP-A-8-169172 and JP-A-8-27693. JP-A-2-276670, JP-A-7-276789, JP-A-9-323475, JP-A-62-238783, JP-A-10-153789, JP-A-10-217473, JP-A-10-235995. No. 10-337947, 10-217597, 10-337947, ink jet paper, film, electrophotographic paper, fabric, glass, metal, ceramics, etc. To form a colored image. As a preferable ink jet recording method for the present invention, the methods described in paragraph numbers [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.
The ink jet method includes a method of ejecting many low-density inks called photo inks in a small volume, a method of improving image quality using a plurality of inks having substantially the same hue and different concentrations, and colorless and transparent inks. The method using is included.

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

(Discharge head)
The discharge head used in the image forming method of the present invention includes a nozzle plate provided with a liquid repellent film at least in part. FIG. 1 is a schematic cross-sectional view showing an example of the internal structure of the ejection head.

~ Nozzle plate ~
As shown in FIG. 1, the ejection head 200 includes a nozzle plate 11 having ejection ports (nozzles) and an ink supply unit 20 provided on the side opposite to the ejection direction of the nozzle plate. The nozzle plate 11 is provided with a plurality of ejection ports 12 for ejecting ink.

  As shown in FIG. 2, the nozzle plate 11 is provided with 32 × 64 discharge ports (nozzles) arranged two-dimensionally. The nozzle plate 11 enables high-definition and high-quality recording of 1200 dpi (dots per inch) by high-speed single pass (recording medium passes once). That is, the plurality of nozzles of the nozzle plate 11 are arranged in a two-dimensional matrix, and the ink supply unit fixed to the nozzle plate 11 discharges a large amount of ink at a high frequency (so-called high duty). It has a flow path configuration that can.

  Part or all of the nozzle plate 11 is made of silicon that can be easily used for semiconductor processes in order to achieve high definition. The nozzle opening of the nozzle plate 11 and the surface on the ink ejection direction side may have a structure in which silicon is exposed. Specifically, when the whole or a part of the nozzle plate 11 is formed of silicon, for example, single crystal silicon or polysilicon can be used as silicon.

~ Liquid repellent film ~
The nozzle plate 11 is configured such that a liquid repellent film formed using fluorinated alkylsilane is provided on the surface as a film containing fluorocarbon (hereinafter referred to as “fluorocarbon film”).

As the liquid repellent film, for example, a silane coupling compound represented by the following general formula (4) is preferably used.
_{C n F 2n + 1 -C m} H 2m -Si-X 3 ··· formula (4)
In the general formula (4), n represents an integer of 1 or more, and m represents 0 or an integer of 1 or more. X represents an alkoxy group, an amino group, or a halogen atom. A part of X may be substituted with an alkyl group.
In the general formula (4), n is an integer of 1 to 14, m is an integer of 0 or 1 to 5, and X is an alkoxy group in terms of liquid repellency and durability of the liquid repellent film. Or it is preferably a halogen atom, more preferably n is an integer of 1 to 12, m is an integer of 0 or 1 and X is an alkoxy group or a halogen atom.

Specific examples of the fluorinated alkylsilane include fluoroalkyltrichlorosilane such as C ₈ F ₁₇ C ₂ H ₄ SiCl ₃ and CF ₃ (CF ₂ ) ₈ C ₂ H ₄ SiCl ₃ , and CF ₃ (CF ₂ ) ₈ C _2. H ₄ Si (OCH ₃ ) ₃ , 3,3,3-trifluoropropyltrimethoxysilane, tridecafluoro-1,1,2,2-tetrahydrooctyltrimethoxysilane, heptadecafluoro-1,1,2 And fluoroalkylalkoxysilanes such as 2-tetrahydrodecyltrimethoxysilane.

  The fluorocarbon film is formed by, for example, fluororesin coating, chemical vapor deposition, eutectoid plating with a fluorine polymer, or liquid repellent treatment such as fluorine silane treatment, aminosilane treatment, or fluorocarbon plasma polymerized film. It is possible to form.

As a method for forming a liquid repellent film using a fluoroalkylsilane, the following methods may be mentioned.
As a first example, there is a method of forming a water-repellent monomolecular film or a polymer film by reacting a fluoroalkyltrichlorosilane such as CF ₃ (CF ₂ ) ₈ C ₂ H ₄ SiCl ₃ with a base material (patent) No. 2500816, Japanese Patent No. 2525536). In the above chemical formula, CF ₃ (CF ₂ ) ₈ C ₂ H ₄ — is a fluoroalkyl group, and —SiCl ₃ is a trichlorosilyl group. In this method, a substrate on which active hydrogen is present is exposed to a solution in which fluoroalkyltrichlorosilane is dissolved, and a chlorosilyl group (—SiCl) and active hydrogen are reacted to form a Si—O bond with the substrate. As a result, the fluoroalkyl chain is fixed to the substrate via Si—O. Here, the fluoroalkyl chain imparts water repellency to the film. Depending on the film formation conditions, the water-repellent film is a monomolecular film or a polymer film.

As a second example, a porous substrate impregnated with a compound containing a fluoroalkyl chain such as a fluoroalkylalkoxysilane such as CF ₃ (CF ₂ ) ₈ C ₂ H ₄ Si (OCH ₃ ) ₃ is heated in a vacuum. Then, there is a method of evaporating the compound to make the substrate surface water-repellent (see JP-A-6-143586). In this method, a method of providing an intermediate layer such as silicon dioxide has been proposed in order to improve the adhesion between the water repellent film and the substrate.

As a third example, there is a method in which a fluoroalkylsilane is formed on the surface of a substrate by a chemical vapor deposition method using a compound such as fluoroalkyltrichlorosilane such as CF ₃ (CF ₂ ) ₈ C ₂ H ₄ SiCl _3. Yes (see JP 2000-282240 A).

  As a fourth example, there is a method in which oxide fine particles such as zirconia and alumina are formed on the surface of a substrate, and then a fluoroalkylchlorosilane, a fluoroalkylalkoxysilane or the like is applied on the surface (see JP-A-6-171094). ).

  As a fifth example, after hydrolyzing and dehydrating polymerization of a mixed solution in which a metal alkoxide is added to a fluoroalkylalkoxysilane, this solution is applied to a substrate and baked, whereby a fluoroalkyl chain in the metal oxide is formed. There is a method of forming a water-repellent film in which molecules having molecules are mixed (see Japanese Patent No. 2687060, Japanese Patent No. 2874391, Japanese Patent No. 2729714, and Japanese Patent No. 25559797). In this method, the fluoroalkyl chain imparts water repellency to the film, and the metal oxide imparts high mechanical strength to the film.

Among the above forming methods, the chemical vapor deposition method mentioned as the third example is preferable. In the case of the chemical vapor deposition method, a container containing a fluorocarbon material such as fluorinated alkylsilane and a silicon substrate are placed in a sealed container made of Teflon (registered trademark) and the whole sealed container is placed in an electric furnace. By evaporating the fluorinated alkylsilane or the like by raising the temperature in the same manner, molecules such as fluorinated alkylsilane are deposited on the surface of the silicon substrate, and chemical vapor deposition can be performed. In this way, for example, a monomolecular film of fluorinated alkylsilane can be formed on the nozzle plate by chemical vapor deposition. In this case, the deposition surface of the silicon substrate is preferably made hydrophilic. Specifically, for example, by cleaning the surface of a silicon substrate using ultraviolet light (wavelength 172 nm), organic impurities are removed, and a clean surface is obtained. At this time, since the silicon surface is naturally oxidized and covered with the SiO ₂ film, water vapor in the atmosphere is immediately adsorbed on the surface and the surface is covered with OH groups to become a hydrophilic surface.

The following method is mentioned as another aspect of the said chemical vapor deposition method.
A liquid repellent film using a fluorinated alkylsilane can be obtained by, for example, introducing a fluoroalkyltrichlorosilane such as CF ₃ (CF ₂ ) ₈ C ₂ H ₄ SiCl ₃ and water vapor into a CVD reactor at a low pressure. It can be deposited on the outer surface of the uncoated substrate. The partial pressure of fluoroalkyltrichlorosilane such as CF ₃ (CF ₂ ) ₈ C ₂ H ₄ SiCl ₃ is 0.05 to 1 torr (6.67 Pa to 133.3 Pa) (for example, 0.1 torr to 0.5 torr ( 13.3 Pa to 66.5 Pa)), and the partial pressure of H ₂ O can be between 0.05 to 20 torr (for example, 0.1 to 2 torr). The deposition temperature can be between room temperature and 100 degrees Celsius. The coating process can be performed, for example, using a Molecular Vapor Deposition (MVD) ™ machine from Applied MicroStructures, Inc.

  The thickness of the liquid repellent film is not particularly limited, but is preferably in the range of 0.2 nm to 30 nm, and more preferably in the range of 0.4 nm to 20 nm. Even if the thickness of the liquid repellent film exceeds 30 nm, there is no particular problem, but if it is 30 nm or less, it is advantageous in terms of film uniformity, and if it is 0.2 nm or more, the water repellency to the ink is good. is there.

The nozzle plate 11 may be formed of a film containing at least one selected from the group consisting of oxides and nitrides of metals (including silicon) and metals (excluding silicon). Specifically, when the whole or a part of the nozzle plate 11 is formed of silicon, for example, single crystal silicon or polysilicon can be used as silicon. When the entire or part of the nozzle plate is formed of silicon, for example, a metal oxide such as silicon oxide, titanium oxide, or chromium oxide, or a metal nitride such as titanium nitride or silicon nitride is formed on a single crystal silicon substrate. Alternatively, a film made of a metal such as zirconium may be provided. The silicon oxide may be, for example, a SiO ₂ film formed by oxidizing all or part of the silicon surface of a nozzle plate made of silicon. A film made of tantalum oxide (preferably tantalum pentoxide (Ta ₂ O ₅ )), zirconium, chromium, titanium, glass, or the like may be formed on all or part of the silicon surface. A part of silicon may be replaced with glass (eg, borosilicate glass, photosensitive glass, quartz glass, soda lime glass). A film made of tantalum oxide such as tantalum pentoxide has very excellent ink resistance to ink, and particularly good erosion resistance can be obtained for alkaline ink.

As a specific aspect of the method for forming the SiO ₂ film, the aspect described in Paragraph No. [0041] of Japanese Patent Application Laid-Open No. 2011-62999 can be applied.

  In addition, as a configuration example of the discharge head including the nozzle plate 11 having a plurality of two-dimensionally arranged discharge ports (nozzles), it is described in paragraph numbers [0042] to [0066] of Japanese Patent Application Laid-Open No. 2011-62999. Things can be mentioned.

<Processing liquid application process>
The image forming method of the present invention preferably further includes a treatment liquid application step for applying a treatment liquid containing an aggregating component for aggregating components such as pigments contained in the ink composition on the recording medium. Moreover, in this invention, it can comprise by further providing another process as needed.

In the treatment liquid application step, the ink composition and a treatment liquid containing an aggregation component that aggregates the components contained in the ink composition when contacted with the ink composition are applied to the recording medium. . As a result, when two liquids of the ink composition and the processing liquid are brought into contact during recording, aggregation of the pigment occurs and image formation becomes possible. At this time, by using the ink composition, the adhesion or deposition of aggregates caused by the contact of the two liquids on the liquid repellent film is alleviated. For this reason, it is possible to prevent a failure in the direction of ink discharge during ink discharge and to prevent an image failure such as a discharge bend, and it is possible to record a high-resolution image.
As the treatment liquid, those already described in the section of the ink set can be used.

  In the treatment liquid application step, the treatment liquid is applied onto the recording medium before or after application of the ink composition. 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 application amount of the treatment liquid can be appropriately selected according to the total droplet ejection amount of the ink composition. Conversely, the total droplet ejection amount of the ink composition may be selected according to the coating amount of the treatment liquid. In the present invention, from the viewpoint of aggregation property of the ink composition, as the application amount of the acidic compound in the area on the recording medium which the treatment liquid has been deposited, it is the average 0.1g ^/ m ² ~1.0g / m 2 it is ^preferred, more preferably ^{0.15g / m 2 ~0.70g / m 2} , further preferably ^{0.25g / m 2 ~0.55g / m 2} .
By setting the application amount of the treatment liquid to 0.1 g / m ² or more, the ink composition to be ejected can be effectively aggregated and fixed, and a higher resolution image can be recorded. Further, when the treatment liquid is applied in an amount of 1.0 g / m ² or less, it is possible to suppress the occurrence of damage to the recording medium, and it is possible to suppress a decrease in abrasion resistance. In particular, when a recording medium having a coating layer is used as the recording medium, the amount of treatment liquid applied is preferably 1.0 g / m ² or less from the viewpoint of suppressing damage to the coating layer.

  In the present invention, an embodiment in which the ink application step is provided after the treatment liquid is applied in the treatment liquid application step is preferable. That is, before applying the ink composition to the recording medium, a processing liquid for aggregating the pigment in the ink composition is applied in advance, and the recording liquid is brought into contact with the processing liquid applied on the recording medium. An embodiment in which an ink composition is applied to form an image 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.

In forming an image, a polymer latex compound may be used in combination for the purpose of imparting glossiness or water resistance or improving weather resistance. The timing of applying the latex compound may be before or after applying the ink composition, or may be applied simultaneously. Therefore, the latex compound may be used in a form applied to the recording medium, may be used in a form added to the ink composition, or may be used in a form in which the polymer latex is made into another liquid.
Specifically, the methods described in JP-A No. 2002-166638, JP-A No. 2002-121440, JP-A No. 2002-154201, JP-A No. 2002-144696, and JP-A No. 2002-080759 are preferable. Can be used.

  The image forming method of the present invention may further include other steps in addition to the ink application step of applying the ink composition and the treatment liquid application step of applying the treatment liquid. There is no restriction | limiting in particular as another process, According to the objective, it can select suitably. For example, a dry removal step of drying and removing an organic solvent in the ink composition applied to the recording medium, a heat fixing step of melting and fixing resin fine particles or polymer latex contained in the ink composition, and the like can be mentioned.

As another example of the image forming method of the present invention, an intermediate transfer member is used as a recording medium for first image formation, and the water-insoluble polymer, pigment, organic solvent and neutralization in the present invention described above are neutralized on the intermediate transfer member. An ink application step for applying an ink composition containing an agent and water by an ink jet method, and a treatment liquid application step for applying a treatment liquid containing an aggregating component for aggregating the pigment in the ink composition on the intermediate transfer member; And a transfer step of transferring the image formed on the intermediate transfer body to a desired final recording medium after forming an image on the intermediate transfer body by bringing the ink composition and the treatment liquid into contact with each other Is mentioned.
In this case as well, other processes such as a drying removal process and a heat fixing process can be further provided in the same manner as described above.

  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, “%” and “part” are based on mass.

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

(Synthesis Example 1)
-Synthesis of monomer (M-25 / M-27) mixture-
37.5 g of 9 (10H) -acridone and 8.84 g of sodium hydroxide were dissolved in 180 ml of dimethyl sulfoxide, 62.5 mg of nitrobenzene was added, and the mixture was heated to 55 ° C. 44 g of chloromethylstyrene (CMS-P manufactured by Seimi Chemical Co., Ltd., a mixture of meta / para form = 50/50 (mol / mol)) was added dropwise thereto, and the mixture was further heated and stirred at 55 ° C. for 7 hours. A mixed solution consisting of 75 ml of methanol and 75 ml of distilled water was poured into this reaction solution with stirring, and the mixture was cooled until the temperature reached 45 ° C. After stirring at this temperature for 30 minutes, the mixture was further cooled to 30 ° C. and stirred at this temperature for 1 hour. The obtained precipitate was separated by filtration and washed with a mixed solution consisting of 60 ml of methanol and 60 ml of distilled water, and the resulting crystal was put into 300 ml of methanol and washed with stirring at 50 ° C. Thereafter, the temperature was lowered and the mixture was stirred at 45 ° C. for 30 minutes, and further stirred at 30 ° C. for 1 hour. The obtained precipitate was separated by filtration and washed repeatedly with 300 ml of methanol three times. The obtained crystals were dried to obtain 49.9 parts of an M-25 / M-27 mixture.

Acridone contained in the obtained monomer (M-25 / M-27) mixture was quantified by the method shown below.
10 mg of the obtained monomer (M-25 / M-27) mixture was weighed, 10 ml of acetonitrile was added and dissolved by stirring to prepare a sample for measurement.
For the measurement, high performance liquid chromatography (manufactured by Shimadzu Corporation, instrument name: LC-2010) was used, the column was TSK-GEL ODS-80Ts manufactured by TOHSO, and the eluent was liquid A (triethylamine and phosphorus). Acid 0.1% by volume aqueous solution) and solution B (a solution prepared by adjusting triethylamine and phosphoric acid to 0.1% by volume in a solution consisting of acetonitrile / water = 9/1 (volume ratio)), The measurement was performed by setting the apparatus so that the composition of the eluent during the measurement from the start of the measurement was as shown below.

<Measurement conditions>
・ Gradient 0 to 15 minutes A solution: 20%, B solution: 80%
15 to 25 minutes A solution: Decrease from 20% to 0%,
Liquid B: Increased from 80% to 100%
25 to 35 minutes B solution: 100%
35-38 minutes A solution: Increased from 0% to 20%,
Liquid B: Decrease from 100% to 80%
45 minutes stop

The column temperature was 40 ° C., the flow rate was 1.0 ml / min, the injection volume was 10 μl, and the detection wavelength was 270 nm. Among the obtained charts, a peak having a retention time of 3.5 minutes was adopted as a peak derived from acridone, and this area was measured.
Separately, several acetonitrile solutions of acridone having different concentrations were prepared and measured under the same conditions, and a calibration curve was prepared by measuring the peak area with a retention time of 3.5 minutes. Using this calibration curve, it was found that the acridone contained in the obtained monomer (M-25 / M-27) mixture was 0.12% based on the monomer (M-25 / M-27) mixture. It was.

(Synthesis Example 2)
-Synthesis of water-insoluble polymer P-1-
To a 1000 ml three-necked flask equipped with a stirrer and a condenser tube, 240 g of methyl ethyl ketone, 30 g of a mixture of M-25 / M-27, 20 g of methacrylic acid and 150 g of ethyl methacrylate were added and heated to 75 ° C. under a nitrogen atmosphere. A solution in which 2.44 g of dimethyl-2,2′-azobisisobutyrate was dissolved in 16 g was added.
After stirring for 2 hours while maintaining the same temperature, a solution of 1.0 g of dimethyl-2,2′-azobisisobutyrate dissolved in 2 g of methyl ethyl ketone was added and reacted for another 2 hours, and then 2 g of methyl ethyl ketone. A solution in which 1.0 g of dimethyl-2,2′-azobisisobutyrate was dissolved was added, heated to 80 ° C. and heated for 4 hours.
74 g of methyl ethyl ketone was added to the obtained reaction solution, and water-insoluble polymer P-1 (monomer (M-25 / M-27) mixture / ethyl methacrylate / methacrylic acid (copolymerization ratio [molar ratio] = 15/75/10) Copolymer) was obtained.

A part of the obtained solution was heat-dried under reduced pressure to obtain a non-volatile content, which was 36.8%.
The composition of the obtained water-insoluble polymer P-1 was confirmed by ¹ H-NMR, and the weight average molecular weight (Mw) determined by GPC was 44200. Furthermore, when the acid value of this polymer was determined by the method described in JIS standard (JIS K 0070: 1992), it was 65.2 mgKOH / g.

(Synthesis Examples 3-5)
-Synthesis of water-insoluble polymers P-2 to P-4-
In the synthesis of the water-insoluble polymer P-1, 15 g of a monomer (M-25 / M-27) mixture, 10 g of methacrylic acid, and 75 g of ethyl methacrylate are respectively shown in Table 1 as shown in Table 1 below. The water-insoluble polymers P-2 to P-4 were synthesized in substantially the same manner as the synthesis of the water-insoluble polymer P-1 except that the water-insoluble polymers P-1 and P-4 were synthesized.

Example 1
-Preparation of dispersion of resin-coated pigment particles-
Pigment Red 122 (Chromophthal Jet Magenta DMQ (manufactured by Ciba Specialty Chemicals; magenta pigment), 10 parts, 4.5 parts of the above water-insoluble polymer P-1, 42 parts of methyl ethyl ketone, 1N aqueous NaOH solution 5 5 parts and 87.2 parts of ion-exchanged water were mixed, dispersed, and further treated for 10 passes with a disperser (Microfluidizer M-140K, 150 MPa). Then, methyl ethyl ketone was removed at 55 ° C., and a part of the water was removed to obtain a dispersion of resin-coated pigment particles having a pigment concentration of 10.2%.

-Measurement of particle diameter of resin-coated pigment particles-
About the obtained dispersion of resin-coated pigment particles, a volume average particle diameter was measured by a dynamic light scattering method using a nanotrack particle size distribution analyzer UPA-EX150 (manufactured by Nikkiso Co., Ltd.).
The measurement was performed by adding 10 ml of ion exchanged water to 10 μl of the resin-coated pigment particle dispersion to prepare a sample solution for measurement, and adjusting the temperature to 25 ° C. The measurement results are shown in Table 1 below.

-Measurement of ion concentration in ink-
The phosphate ion concentration in each of the water-based inks was obtained by collecting the supernatant liquid processed by ultracentrifugation (140,000 rpm, 60 min), and an anion chromatograph obtained by ultrapure and diluting the sample 10 to 1000 times under the following conditions. Measured by the method.
<Measurement conditions>
Measuring device: Product name “ICS-2000”, manufactured by Dionex Co., Ltd.
Column: Product name “AS18 4mm” manufactured by Dionex Co., Ltd.
Guard column: Product name "AG18 4mm", manufactured by Dionex Co., Ltd.
Eluent: 5 mmol / l potassium hydroxide aqueous solution
Flow rate: 1 ml / min
Column temperature: 30 ° C
Injection volume: 25 μl
Detection: Electrical conductivity (suppressor method)

-Measurement of impurity elements in ink-
0.03 ml of the water-based ink is collected, ₃ ml of HNO 3 is added, and a sample subjected to microwave ashing (230 ° C.) is subjected to an all-element survey using ICP-MS (HP-4500, manufactured by Agilent). Elements that may be present in the sample in several mg / l or more were quantified with ICP-OES (Optima 7300 DV, manufactured by Perkin Elmer).

-Preparation of latex-
120 g of water, 19.8 g of latemul ASK (manufactured by Kao Corporation, carboxylate emulsifier), 6 g of 5 mol / l sodium hydroxide aqueous solution, 0.3 g of 2,2′-azobis (2-amidinopropane) dihydrochloride Was added and dissolved uniformly.
The mixture was heated to 70 ° C., and a monomer mixture of 25.9 g of styrene, 26.3 g of butyl acrylate, and 5.1 g of acrylic acid was added over 2 hours under a nitrogen stream. Then, it heated at 70 degreeC for 2 hours and 80 degreeC for 3 hours. After cooling to room temperature, a 1 mol / l sodium hydroxide aqueous solution was added with stirring so that the pH was around 9, and latex PL-01 was obtained.
The volume average particle diameter of the obtained latex was 115 nm. The solid content of the latex dispersion was 33%.

-Preparation of water-based ink-
Next, using the obtained dispersion of resin-coated pigment particles, a magenta-colored aqueous ink having the following composition was prepared. The pH of this water-based ink at 25 ° C. was 8.9.
<Composition>
-Dispersion of the resin-coated pigment particles-38.2 parts-Latex PL-01-15 parts-Glycerin-15 parts-Diethylene glycol monoethyl ether-5 parts-Olphine E1010 (Nisshin Chemical) (Manufactured by Kogyo Co., Ltd.) ・ ・ ・ 1 part ・ Ion-exchanged water ・ ・ ・ 25.8 parts

-Preparation of treatment solution-
Components of the following composition were mixed to prepare an aqueous treatment liquid (aggregated liquid).
<Composition>
・ Citric acid (Wako Pure Chemical Industries) 16.7%
・ Diethylene glycol monoethyl ether (Wako Pure Chemical Industries) 20.0%
・ Zonyl FSN-100 (DuPont) 1.0%
・ Ion exchange water 62.3%
When the physical properties of the reaction solution were measured, the viscosity was 4.9 mPa · s, the surface tension was 24.3 mN / m, and the pH was 1.5.

  As described above, an ink set composed of a magenta-colored water-based ink and an aqueous aggregated liquid was produced.

―Image formation―
6 to 8 of Japanese Patent Application Laid-Open No. 2011-62999, an ejection head provided with a silicon nozzle plate was prepared, and a storage tank connected thereto was refilled with the magenta ink obtained above. The silicon nozzle plate is made of single crystal silicon, and the surface on the ink ejection direction side is a silicon oxide film formed by introducing SiCl ₄ and water vapor into a chemical vapor deposition (CVD) reactor. (SiO ₂ film) is formed. The thickness of the SiO ₂ film is 50 nm. Furthermore, chemical vapor deposition (CVD) is performed using C ₈ F ₁₇ C ₂ H ₄ SiCl ₃ after oxygen plasma treatment, and a liquid repellent film is formed on the SiO ₂ film. A liquid repellent film was formed by introducing C ₈ F ₁₇ C ₂ H ₄ SiCl ₃ and water vapor into the CVD reactor at low pressure. The thickness of the liquid repellent film is 10 nm. Further, as shown in FIG. 2, the silicon nozzle plate has a plurality of nozzles arranged in a two-dimensional matrix so that ink droplets can be ejected with high definition. As a recording medium, Tohishi Art Double Sided N (manufactured by Mitsubishi Paper Industries Co., Ltd.) was prepared.
This recording medium is fixed on a stage movable in a predetermined linear direction at 500 mm / second, the stage temperature is kept at 30 ° C., and the treatment liquid obtained above is fixed to a thickness of about 1.2 μm with a bar coater. It was applied so that it was dried immediately after application at 50 ° C. for 2 seconds. The prepared ejection head is fixedly arranged so that the direction of the line head in which the nozzles are arranged (main scanning direction) is inclined by 75.7 degrees with respect to the direction orthogonal to the moving direction of the stage (sub-scanning direction), and recording is performed. While the medium is moved at a constant speed in the sub-scanning direction, the ink is ejected by a line method under an ink droplet amount of 6.0 pl, an ejection frequency of 25.7 kHz, and a resolution of 1200 dpi × 1200 dpi, and a 50% solid image of 2 cm square and 4 An image containing ˜8 pt “轟” character image and a solid 4 pt “轟” character image was recorded in the solid image.
Immediately after recording, the sample was dried at 60 ° C. for 3 seconds, passed between a pair of fixing rollers heated to 60 ° C., and subjected to a fixing process at a nip pressure of 0.25 MPa and a nip width of 4 mm to obtain an evaluation sample.

―Image evaluation―
1) Discharge bend After the discharge head continuously discharged 600 billion times at 25.7 kHz, an image was recorded, and a line image of 75 × 2400 dpi was drawn with a discharge frequency of 25.7 kHz using 96 nozzles. And the center value of the line was measured for this line image with the dot analyzer DA-6000 made from Oji Scientific Instruments, and the standard deviation (sigma) of the deviation | shift amount of each line was computed. The evaluation results are shown in Table 2 below. In addition, when the standard deviation σ of the deviation amount is smaller than 2 μm, it is normal, and when it is smaller than 5 μm, it indicates that it is at a practical level.
<Evaluation criteria>
A: σ <3 μm
B: 3 μm ≦ σ <5 μm
C: 5 μm ≦ σ <7 μm
D: 7 μm ≦ σ

2) State of liquid repellent film
After the ejection head continuously ejected 600 billion times at 25.7 kHz, an image was recorded and a film (liquid repellency) formed using C ₈ F ₁₇ C ₂ H ₄ SiCl ₃ around 2048 nozzle holes The state of the film) was observed with an optical microscope. And the presence or absence of the change in the said liquid repellent film was evaluated according to the following evaluation criteria. The evaluation results are shown in Table 1 below. In addition, the state where the liquid repellent film state around the nozzle hole is not changed is regarded as a normal state, and if the change is less than 10, it indicates that it is at a practical level.
<Evaluation criteria>
A: Less than 5 changes in the liquid-repellent film state around the nozzle hole.
B: The change of the liquid repellent film state around the nozzle hole is 5 or more and less than 10.
C: 10 or more and less than 20 changes in the liquid-repellent film state around the nozzle hole.
D: 20 or more changes in the liquid-repellent film state around the nozzle hole.

(Examples 2 to 4)
In Example 1, the water-insoluble polymer P-1 (monomer (M-25 / M-27) mixture / ethyl methacrylate / methacrylic acid copolymer) used in “Preparation of dispersion of resin-coated pigment particles” was used as follows. As shown in Table 1, a dispersion of resin-coated pigment particles was obtained in the same manner as in Example 1 except that each of the water-insoluble polymers P-2 to P-4 was changed. Ink preparation and evaluation were performed. The results of measurement and evaluation are shown in Table 1 below.

(Example 5)
Pigment Red (hereinafter abbreviated as “PR”) 122 used as a magenta ink pigment in Example 1 was replaced with Pigment Violet (hereinafter abbreviated as “PV”) 19 ((CINQUASIA MAGENTA RT-355D (Ciba -Specialty Chemicals Co., Ltd .; magenta pigment))) Other than that, in the same manner as in Example 1, a dispersion of resin-coated pigment particles was obtained, and the particle diameter was measured, and the aqueous ink was prepared and evaluated. The results of measurement and evaluation are also shown in Table 1 below.

(Example 6)
In Example 1, the impurity component was added when obtaining the dispersion of the resin-coated pigment particles, and the Mg concentration and the phosphate ion (PO ₄ ²⁻ ) concentration shown in Table 1 below were adjusted. In the same manner as in Example 1, a dispersion of resin-coated pigment particles was obtained, the particle diameter was measured, and the aqueous ink was prepared and evaluated. The results of measurement and evaluation are shown in Table 1 below.

(Comparative Examples 1-3)
In Example 1, the water-insoluble polymer P-1 used in “Preparation of dispersion of resin-coated pigment particles” was prepared as shown in Table 1 below. Water-insoluble polymer P-5 (benzyl methacrylate / methacrylic acid (= 90 / 10 [%]) copolymer) (Comparative Example 1), water-insoluble polymer P-6 (benzyl methacrylate / methacrylic acid (= 80/20 [%]) copolymer) (Comparative Example 2), water-insoluble polymer P-7 (styrene / methacrylic acid (= 90/10 [%]) copolymer) (Comparative Example 3) was changed in the same manner as in Example 1 except that the dispersion of resin-coated pigment particles was changed. In addition, the particle diameter was measured, and the aqueous ink was prepared and evaluated. The results of measurement and evaluation are shown in Table 1 below.

(Comparative Example 4)
PR122 used as a magenta ink pigment in Example 1 was changed to a carbon black self-dispersion (CABOJET300 (manufactured by Cabot; black pigment)), and the surface was a water-insoluble polymer in the same manner as in Example 1 except that. The particle diameter of the pigment not coated with was measured, and the aqueous ink was prepared and evaluated. The results of measurement and evaluation are also shown in Table 1 below.

(Comparative Example 5)
PR122 used as a pigment of magenta ink in Example 1 was used, and “preparation of dispersion of resin-coated pigment particles” in Example 1 was not performed. Otherwise, the surface was a water-insoluble polymer. The particle diameter of the pigment not coated with was measured, and the aqueous ink was prepared and evaluated. The results of measurement and evaluation are also shown in Table 1 below.

As shown in Table 1, in Examples 1 to 6, the discharge bending could be suppressed even after continuous discharge of 600 billion times. This is presumably because the liquid repellency of the liquid repellent film of the ejection head is stably maintained.
On the other hand, Comparative Examples 1 to 3 in which the total of the Mg concentration and the phosphate ion (PO ₄ ²⁻ ) concentration in the ink exceeds 70 ppm, or a pigment whose surface is not coated with a water-insoluble polymer was used. In Comparative Example 4, the liquid-repellent film of the ejection head was significantly deteriorated, and ejection bending occurred. For this reason, high-resolution images could not be obtained.

11 ... Nozzle plate 12 ... Discharge port (nozzle)
23: Ink supply flow path 30: Piezoelectric element (piezoelectric actuator; pressure generating means)
200: Discharge head

Claims (9)

An ink composition comprising water and a resin-coated pigment in which at least a part of the surface of the pigment is coated with a water-insoluble polymer, and having a total Mg concentration and phosphate ion concentration of 1 ppm to 70 ppm on a mass basis. The ink composition according to claim 1, wherein the pigment is a quinacridone pigment. The ink composition according to claim 1, wherein the water-insoluble polymer contains a structural unit represented by the following general formula (1).

(In General Formula (1), R ¹ represents a hydrogen atom or a methyl group, L ¹ represents a substituted or unsubstituted phenylene group, L ² represents a single bond or a divalent linking group, and Ar ¹ represents carbon. This represents a monovalent group derived from a condensed aromatic ring having a number of 8 or more, a hetero ring in which an aromatic ring is condensed, or a compound in which two or more benzene rings are linked.   The ink composition according to any one of claims 1 to 3, wherein the water-insoluble polymer has an acid value of 30 mgKOH / g or more and 100 mgKOH / g or less.   The ink composition according to any one of claims 1 to 4, further comprising polymer particles.   An ink composition according to any one of claims 1 to 5 and a treatment liquid containing an aggregating component that agglomerates the components contained in the ink composition when in contact with the ink composition. Ink set.   An image forming method comprising an ink application step of applying the ink composition according to any one of claims 1 to 5 onto a recording medium by an ink jet method.   The image forming method according to claim 7, further comprising a treatment liquid application step of applying a treatment liquid containing an aggregating component that aggregates the components contained in the ink composition when contacting the ink composition onto a recording medium.   The image forming method according to claim 8, wherein the aggregation component is an acidic compound.