JP2011195686A - Ink set for inkjet recording and image formation method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an ink set for inkjet recording that is free from decrease in detergency according to pH decrease while stored, maintains stable discharge performance of an ink discharge head, and suppresses corrosion of the ink discharge head, and an image formation method that maintains stable discharge performance over a long period of time and forms a desired image.SOLUTION: The ink set for inkjet recording includes an ink composition including water, a pigment, and polymer particles, and a maintenance liquid including n-propanol. The image formation method uses the ink set for inkjet recording.

Description

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

  With the rapid development of the information technology industry in recent years, various information processing systems have been developed, and recording methods and recording apparatuses suitable for each information processing system have been put into practical use. Among these, the ink jet recording method is widely used because it can record on various recording materials, the hardware (device) is relatively inexpensive and compact, and has excellent quietness. ing. In the recording using the ink jet recording method, it has become possible to obtain a so-called photographic-like high quality recorded matter.

In general, an ink jet recording method using a pigment ink is considered to have excellent storability as compared with an ink jet recording method using a dye ink.
In addition, when the moisture in the ink evaporates and solidifies, the pigment ink does not re-dissolve while it is solidified, causing clogging at the nozzle tip of the ink ejection head of the ink jet recording apparatus, etc. It was generated. Further, when the ink is solidified at the cap, the wiped portion, etc., it is difficult to wipe and remove the solidified ink, and there is a problem that the maintenance of the ink jet recording apparatus is burdened.

A liquid used for wiping or cleaning solidified ink attached to an ink discharge head or the like is called a cleaning liquid, a maintenance liquid, or a cleaning liquid.
As a maintenance liquid used in the inkjet recording method, an inkjet maintenance liquid containing water and 0.3% by mass to 15% by mass of an alkylene glycol monoalkyl ether is disclosed (for example, see Patent Document 1).
In addition, an inkjet cleaning liquid containing a surfactant, a basic compound, and water and having a pH of 9 or more is disclosed, and is said to be effective for cleaning pigment ink (see, for example, Patent Document 2). In order to make pH 9 or more, adding basic compounds, such as a triethanolamine and potassium hydroxide, is indicated.

Japanese Patent Laid-Open No. 2005-7703 JP 2000-127419 A

However, the maintenance liquids described in Patent Documents 1 and 2 have revealed a phenomenon that the pH decreases during storage.
There are various factors that cause a decrease in pH. For example, there is a decrease in pH due to carbon dioxide by absorbing carbon dioxide in the air, or a decrease in pH due to decomposition due to dissolved oxygen. In particular, a maintenance liquid containing a glycol ester or an alkylene glycol alkyl ether tends to be decomposed by dissolved oxygen to lower the pH. Lowering the pH not only reduces the cleaning ability of the maintenance liquid, but also makes these pigments and polymer particles easily aggregate when used in combination with an ink composition containing pigments and polymer particles. Further, after the ink jet recording, if the ink discharge head is washed with a maintenance liquid having a lowered pH, the ink pigment and polymer particles are aggregated, and the detergency is remarkably deteriorated.

  In addition, depending on the type of solvent used in the maintenance liquid, the ink discharge head of the ink jet recording apparatus may be corroded, and particularly in the maintenance liquid having a pH of 9 or more by adding a basic compound, This tendency is remarkable. An ink discharge head of an ink jet recording apparatus is manufactured by a semiconductor process using a silicon wafer as a substrate when processing the nozzle portion of the head more precisely. For this reason, a silicon dioxide film is formed on the ink discharge head for the purpose of preventing the portions in contact with various liquids such as ink and maintenance liquid from being corroded by the various liquids. Furthermore, an ink-repellent film may be formed to prevent ink from adhering to the ink discharge head. However, the silicon dioxide film and the ink repellent film are corroded by the above maintenance liquid, and the life of the ink discharge head is shortened.

  The present invention has been made in view of the above, and there is no deterioration in cleaning properties due to a decrease in pH during storage, the discharge performance of the ink discharge head can be kept stable, and corrosion of the ink discharge head is suppressed. An object is to provide an ink set for inkjet recording. Another object of the present invention is to provide an image forming method capable of maintaining a stable ejection performance over a long period of time and forming a desired image over a long period of time.

Specific means for solving the above problems are as follows.
<1> An ink set for ink-jet recording comprising an ink composition containing water, a pigment, and polymer particles, and a maintenance liquid containing n-propanol.
<2> The ink set for inkjet recording according to <1>, wherein the maintenance liquid contains a surfactant.
<3> The ink set for inkjet recording according to <2>, wherein the surfactant is a nonionic surfactant.
<4> The ink set for inkjet recording according to any one of <1> to <3>, wherein the polymer particles are derived from a polymer latex.
<5> The ink set for inkjet recording according to any one of <1> to <4>, wherein the polymer particles have an I / O value of 0.2 or more and 0.55 or less.

<6> The ink set for inkjet recording according to any one of <1> to <5>, wherein the ink composition has a pH of 7.5 to 12.
<7> Furthermore, the ink set for inkjet recording as described in any one of <1>-<6> containing the process liquid containing the coagulant | flocculant which aggregates at least one of the pigment and polymer particle which are contained in the said ink composition. .
<8> The ink set for inkjet recording according to <7>, wherein the treatment liquid has a pH of 1 to 6.
<9> The ink set for inkjet recording according to <7> or <8>, wherein the treatment liquid contains water and an organic acid.

<10> The ink set for inkjet recording according to any one of <1> to <6> is used,
Image formation comprising: an ink application step of applying the ink composition in a pattern from a discharge head for inkjet recording onto a recording medium; and an ink removal step of removing the ink composition attached to the discharge head by the maintenance liquid Method.
<11> The ink set for inkjet recording according to any one of <7> to <9> is used,
An ink application step of applying the ink composition in a pattern from a discharge head for inkjet recording onto a recording medium;
A treatment liquid application step of applying the treatment liquid onto a recording medium;
An ink removing step of removing the ink composition adhering to the ejection head by the maintenance liquid;
An image forming method comprising:
<12> The image forming method according to <10> or <11>, wherein at least one of the inkjet recording ejection heads has an ink-repellent film.

  According to the present invention, an ink set for ink-jet recording in which the cleaning performance associated with a decrease in pH during storage is not reduced, the ejection performance of the ink ejection head can be kept stable, and the corrosion of the ink ejection head is suppressed. Is provided. In addition, according to the present invention, there is provided an image forming method capable of maintaining a stable ejection performance over a long period of time and forming a desired image over a long period of time.

Hereinafter, the ink composition and maintenance liquid contained in the ink set for inkjet recording according to the present invention, and the treatment liquid contained as desired will be described.
1. Ink Composition The ink composition according to the present invention includes water, a pigment, and polymer particles.

(Pigment)
There is no restriction | limiting in particular as a pigment, According to the objective, it can select suitably, For example, any of an organic pigment and an inorganic pigment may be sufficient.
Examples of the organic pigment include azo pigments, polycyclic pigments, dye metal chelates, nitro pigments, nitroso pigments, and aniline black. Among these, azo pigments and polycyclic pigments are more preferable. Examples of the azo pigments include azo lakes, insoluble azo pigments, condensed azo pigments, and metal chelate azo pigments. Examples of the polycyclic pigment include phthalocyanine pigments, perylene pigments, perinone pigments, anthraquinone pigments, quinacridone pigments, dioxazine pigments, indigo pigments, thioindigo pigments, isoindolinone pigments, and quinofullerone pigments. Examples of the dye metal chelate include basic dye type metal chelates and acidic dye type metal chelates.
Examples of the inorganic pigment include titanium oxide, iron oxide, calcium carbonate, barium sulfate, aluminum hydroxide, barium yellow, cadmium red, chrome yellow, and carbon black. Among these, carbon black is particularly preferable. In addition, as said carbon black, what was manufactured by well-known methods, such as a contact method, a furnace method, and a thermal method, is mentioned, for example.
The above pigments may be used alone or in combination of a plurality selected from the above-mentioned groups or between the groups.

  Pigments are color developing properties, granularity, ink stability (dispersed state of the pigment and properties of liquid properties such as ink viscosity, surface tension, pH, etc.), ejection reliability (from the ink ejection head) In view of the property that the discharge performance is kept constant for a long period of time, it is preferably contained in the ink composition according to the present invention in the range of 0.1% by mass or more and 15% by mass or less. It is contained in the range of 5% by mass to 12% by mass, particularly preferably in the range of 1% by mass to 10% by mass.

From the viewpoint that the pigment is stable in the dispersed state and liquid physical properties for a long time in the ink composition according to the present invention, and that the discharge performance from the ink discharge head is maintained constant for a long time, It is preferably used in the form of at least one pigment aqueous dispersion selected from the following (1) to (4).
(1) Encapsulated pigment aqueous dispersion, that is, a polymer emulsion in which a pigment is contained in water-insoluble resin particles. More specifically, the pigment is coated with a hydrophilic and water-insoluble resin to form a resin layer on the pigment surface. The pigment is dispersed in water by making it hydrophilic.
(2) Self-dispersed pigment aqueous dispersion, that is, a pigment having at least one hydrophilic group on the surface and exhibiting water dispersibility in the absence of a dispersant, more specifically, mainly carbon black. It is hydrophilized by oxidation treatment, and a simple pigment is dispersed in water.
(3) A resin-dispersed pigment aqueous dispersion, that is, a pigment dispersed in water with a water-insoluble polymer compound having a weight average molecular weight of 50,000 or less.
(4) A surfactant-dispersed pigment aqueous dispersion, that is, a pigment dispersed in water with a surfactant.
Among these, preferred are (1) encapsulated pigment aqueous dispersion, (2) self-dispersed pigment aqueous dispersion, and (3) resin-dispersed pigment aqueous dispersion, and particularly preferred is (1) encapsulated pigment. An aqueous dispersion and (3) a resin-dispersed pigment aqueous dispersion.

Hereinafter, the pigment aqueous dispersions (1) to (4) will be described.
<Encapsulated pigment aqueous dispersion>
An encapsulated pigment aqueous dispersion is a pigment particle coated with a hydrophilic and water-insoluble resin (hereinafter also referred to as “water-insoluble resin”), and is uniformly dispersed in water by this coating resin. is there.
Here, “water-insoluble” means that the resin is “water-insoluble” when the resin is dissolved in 100 g of water at 25 ° C. and the dissolved amount is 10 g or less.
As such a water-insoluble resin for coating a pigment, a hydrophilic and water-insoluble resin having self-dispersing ability or solubility ability in a mixed solvent of water and a water-soluble organic solvent and having an anionic group (acidic) Is preferred.
The water-insoluble resin may be either thermoplastic or thermosetting, modified acrylic, epoxy, polyurethane, polyether, polyamide, unsaturated polyester, phenol, silicone, fluorine. Polymer compounds, polyvinyl chloride, polyvinyl acetate, polyvinyl alcohol, polyvinyl butyral, etc., polyesters such as alkyd resin, phthalic acid resin, melamine resin, melamine formaldehyde resin, amino alkyd cocondensation resin, urea resin, etc. And materials having an anionic group such as copolymers and mixtures thereof.

Among the water-insoluble resins, an anionic acrylic resin is copolymerized with, for example, an acrylic monomer having an anionic group (hereinafter referred to as an anionic group-containing acrylic monomer) and, if necessary, these monomers. It is obtained by polymerizing the other monomers obtained in a solvent.
Examples of the anionic group-containing acrylic monomer include acrylic monomers having one or more anionic groups selected from the group consisting of a carboxyl group, a sulfonic acid group, and a phosphonic group. An acrylic monomer is particularly preferable.
Specific examples of the acrylic monomer having a carboxyalkyl group include acrylic acid, methacrylic acid, crotonic acid, ethacrylic acid, propylacrylic acid, isopropylacrylic acid, itaconic acid, and fumaric acid. Among these, acrylic acid and methacrylic acid can be mentioned as preferable ones.

  The water-insoluble resin is preferably a hydrophilic and water-insoluble resin having a hydrophilic structural unit (a) and a hydrophobic structural unit (b). The water-insoluble resin may further contain other structural units that are not included in the hydrophilic structural unit (a) and the hydrophobic structural unit (b), if necessary.

-Hydrophilic structural unit (a)-
The hydrophilic structural unit (a) is not particularly limited as long as it is derived from a hydrophilic group-containing monomer, and even if it is derived from one kind of hydrophilic group-containing monomer, it contains two or more hydrophilic groups. It may be derived from a monomer. The hydrophilic group is not particularly limited, and may be a dissociable group or a nonionic hydrophilic group, or may contain both of them.
By synthesizing the water-insoluble resin in the present invention using the monomer having the hydrophilic group as described above, the water-insoluble resin having the hydrophilic group as described above can be prepared.
The hydrophilic group is preferably a dissociable group from the viewpoint of stability in an emulsified or dispersed state. Examples of the dissociable group include a carboxyl group, a phosphoric acid group, and a sulfonic acid group. Among them, the ink composition is excellent in dispersion stability in that the initial dispersion state is maintained for a long period of time. And a carboxyl group is preferred.

The monomer having hydrophilicity is preferably a dissociable group-containing monomer, more preferably a dissociable group-containing monomer having a dissociable group and an addition polymerizable unsaturated bond such as an ethylenically unsaturated bond. Examples of the dissociable group-containing monomer include an unsaturated carboxylic acid monomer, an unsaturated sulfonic acid monomer, and an unsaturated phosphoric acid monomer.
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 (methacryloyloxyethyl) phosphate, diphenyl-2-acryloyloxyethyl phosphate, diphenyl-2-methacryloyloxyethyl phosphate, and dibutyl-2-acryloyloxy. Examples thereof include ethyl phosphate.
Among the dissociable group-containing monomers, unsaturated carboxylic acid monomers are preferable, and acrylic acid and methacrylic acid are more preferable from the viewpoints of dispersion stability and ejection stability.
That is, the hydrophilic structural unit (a) preferably includes a structural unit derived from (meth) acrylic acid.
Here, the term “(meth) acrylic acid” is a term used when collectively describing acrylic acid and methacrylic acid. The same applies to terms such as “(meth) acrylate” and “(meth) acrylamide”.

  As other hydrophilic structural unit (a), a structural unit derived from a monomer having a nonionic hydrophilic group can be used. As a monomer that forms a 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. There is no particular limitation, and it can be selected from known monomers. From the viewpoints of availability, handleability, and versatility, vinyl monomers are preferred.

Examples of the hydrophilic structural unit (a) include vinyl monomers having a hydrophilic functional group such as (meth) acrylates, (meth) acrylamides, and vinyl esters having a hydrophilic functional group. it can.
Here, examples of the “hydrophilic functional group” include a hydroxyl group, an amino group, an amide group (unsubstituted nitrogen atom), and alkylene oxides such as polyethylene oxide and polypropylene oxide described later.
Specific examples of the hydrophilic structural unit (a) include hydroxyethyl (meth) acrylate, hydroxybutyl (meth) acrylate, (meth) acrylamide, aminoethyl acrylate, aminopropyl acrylate, and an alkylene oxide polymer (meth). An acrylate can be mentioned preferably.

The hydrophilic structural unit having a nonionic hydrophilic group can be formed by polymerization of the 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 resin and compatibility with the solvent and other monomers during polymerization. 1-2 is particularly preferred.
The hydrophilic structural unit (a) may be contained alone or in combination of two or more.

In the above, for example, the content ratio of the hydrophilic structural unit differs depending on the ratio of the hydrophobic structural unit (b) described later. For example, when the water-insoluble resin is composed only of acrylic acid and / or methacrylic acid [hydrophilic structural unit (a)] and a hydrophobic structural unit (b) described later, the content ratio of acrylic acid and / or methacrylic acid Is determined by “100- (mass% of hydrophobic structural unit)”.
The content ratio of the hydrophilic structural unit (a) is preferably in the range of more than 0% by mass and 15% by mass or less, more preferably in the range of 2% by mass to 15% by mass with respect to the total mass of the water-insoluble resin. The range of 5% by mass to 15% by mass is more preferable, and the range of 8% by mass to 12% by mass is particularly preferable.

-Hydrophobic structural unit (b)-
The hydrophobic structural unit (b) preferably includes a structural unit having an aromatic ring bonded to an atom forming the main chain via a linking group.
In such a structural unit having an aromatic ring, the aromatic ring has a structure in which the aromatic ring is bonded to an atom forming the main chain of the water-insoluble resin through a linking group and is not directly bonded to an atom forming the main chain of the water-insoluble resin. Therefore, the hydrophobic aromatic ring and the hydrophilic structural unit are kept at an appropriate distance, and the water-insoluble resin and the pigment are likely to interact with each other. Is further improved.
Among the “structural units having an aromatic ring bonded to the atom forming the main chain via a linking group”, the structural unit represented by the following structural formula (2) is preferable in that the pigment can be easily dispersed. preferable.

In the structural formula (2), R ¹ represents a hydrogen atom, a methyl group, or a halogen atom.
L ¹ represents ^* —COO—, ^* —OCO—, ^* —CONR ² —, ^* —O—, or a substituted or unsubstituted phenylene group, and R ² represents a hydrogen atom having 1 to 10 carbon atoms. Represents an alkyl group. In addition, the * mark in the group represented by L ¹ indicates a bond position linked to the carbon atom of the main chain. Although it does not specifically limit as a substituent in case the phenylene group is substituted, For example, a halogen atom, an alkyl group, an alkoxy group, a hydroxyl group, a cyano group etc. are mentioned.
L ² represents a simple 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 carbon. A linking group having 1 to 20 carbon atoms, more preferably a linking group having 1 to 15 carbon atoms. 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], etc., and a group in which two or more of these are combined is there.
Ar ¹ represents a monovalent group derived from an aromatic ring.
The aromatic ring represented by Ar ¹ is not particularly limited, and examples thereof include a benzene ring, a condensed aromatic ring having 8 or more carbon atoms, a hetero ring in which an aromatic ring is condensed, or a benzene ring in which two or more are connected. .

Of the structural units represented by the structural formula (2), R ¹ is a hydrogen atom or a methyl group, L ¹ is ^* —COO—, and L ² is a carbon containing an alkyleneoxy group and / or an alkylene group. A combination of structural units that are divalent linking groups of 1 to 25 is preferable, and more preferably, R ¹ is a hydrogen atom or a methyl group, L ¹ is ^* —COO—, and L ² is ^* — ( CH ₂ -CH _{2 -O) n} - [n represents the number of repetitions of the average, which is n = 1 to 6. ] Is preferred.

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 aromatic ring condensed with a heterocycle include phthalimide, acridone, carbazole, benzoxazole, and benzothiazole.
Hereinafter, specific examples of monomers capable of forming the structural unit represented by the structural formula (2) are listed. However, the present invention is not limited to these specific examples.

Among the structural units represented by the structural formula (2), a structural unit derived from a compound selected from benzyl methacrylate, phenoxyethyl acrylate, and phenoxyethyl methacrylate is preferable from the viewpoint of dispersion stability. The water-insoluble resin in the present invention preferably has one or more structural units selected from these as the hydrophobic structural unit (b).
The content ratio of the “structural unit having an aromatic ring bonded to the atom forming the main chain via a linking group” in the water-insoluble resin is the dispersion stability of the pigment in the ink composition according to the present invention, the ink From the viewpoint of the stability of ink ejection from the ejection head (the property that the performance of ejecting ink from the nozzles of the ejection head is maintained at a constant level) and the cleaning properties with the maintenance liquid described later, It is preferable that it is 40 mass% or more. The content ratio of the structural unit is preferably 40% by mass or more and less than 75% by mass, more preferably 40% by mass or more and less than 70% by mass, and further preferably 40% by mass or more and less than 60% by mass.
In addition, the ratio of the aromatic ring bonded to the atom forming the main chain via a linking group is 15% by mass or more and 27% by mass or less with respect to the total mass of the water-insoluble resin in terms of improving the abrasion resistance. Preferably, 15 mass% or more and 25 mass% or less are more preferable, and 15 mass% or more and 20 mass% or less are especially preferable.
When adjusted to the above range, the rub resistance (characteristic that the ink pattern formed on the recording medium can withstand because the pattern is peeled off by friction), ink stability, and ejection reliability are improved.

Moreover, the case where the hydrophobic structural unit (b) has a structural unit derived from an alkyl ester having 1 to 4 carbon atoms of (meth) acrylic acid is preferable from the viewpoint of dispersion stability of the pigment.
Specific examples of alkyl esters of (meth) acrylic acid include, for example, methyl (meth) acrylate, ethyl (meth) acrylate, propyl (meth) acrylate, isopropyl (meth) acrylate, and isobutyl (meth) acrylate. , (Meth) acrylic acid tertiary butyl and the like. The alkyl moiety of the alkyl ester has 1 to 4 carbon atoms, preferably 1 to 2 carbon atoms.
The content ratio in the water-insoluble resin of the “structural unit derived from an alkyl ester having 1 to 4 carbon atoms of (meth) acrylic acid” is 15% by mass or more based on the total mass of the water-insoluble resin. This is preferable because of excellent dispersion stability of the pigment. The content ratio of the structural unit is more preferably 20 to 60% by mass, and particularly preferably 20 to 50% by mass.

  As described above, from the viewpoint of further improving the dispersion stability of the pigment, the hydrophobic structural unit (b) is a water-insoluble structural unit having an aromatic ring bonded to the atom forming the main chain through a linking group. 40% by mass or more (more preferably 40 to 75% by mass, still more preferably 40 to 70% by mass, particularly preferably 40 to 60% by mass) with respect to the total mass of the resin, and the carbon number of (meth) acrylic acid. It is preferable that the structural unit derived from the alkyl ester of 1-4 is 15 mass% or more (more preferably 20-60 mass%, especially preferably 20-50 mass%) with respect to the total mass of the water-insoluble resin.

Examples of other hydrophobic structural units (b) other than those described above include, for example, those that do not belong to the hydrophilic structural unit (a) (for example, have no hydrophilic functional group), such as (meth) acrylamides, styrenes, and vinyl Examples include structural units derived from vinyl monomers such as esters, (meth) acrylates such as alkyl (carbon number 1 to 4) esters of (meth) acrylic acid, and the like. These structural units can be used individually by 1 type or in mixture of 2 or more types.
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 include bromostyrene, chloromethylstyrene, hydroxystyrene protected with a group deprotectable by an acidic substance (for example, t-Boc), methyl vinylbenzoate, α-methylstyrene, vinylnaphthalene, and the like. α-methylstyrene is 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.
Examples of the (meth) acrylates include methyl (meth) acrylate, ethyl (meth) acrylate, (iso) propyl (meth) acrylate, and (iso or tertiary) butyl (meth) acrylate.

  The composition of the hydrophilic structural unit (a) and the hydrophobic structural unit (b) depends on the degree of hydrophilicity and hydrophobicity, but the content of the hydrophobic structural unit (b) is water-insoluble. A case where the composition exceeds 80% by mass is preferable with respect to the total mass of the resin, and a case where the composition exceeds 85% by mass is more preferable. In other words, the content ratio of the hydrophilic structural unit (a) is preferably in the range of 15% by mass or less with respect to the total mass of the water-insoluble resin. When the hydrophilic structural unit (a) is 15% by mass or less, the component dissolved alone in the aqueous liquid medium without contributing to the dispersion of the pigment is reduced, and the dispersion state of the pigment can be efficiently and satisfactorily maintained. Since an increase in viscosity can be suppressed, an ink composition having excellent ejection properties can be obtained.

  The water-insoluble resin may be either a random copolymer in which each structural unit is irregularly introduced or a block copolymer in which the structural units are regularly introduced. Each structural unit in the case of a block copolymer may be synthesized in any order of introduction, and the same component may be used twice or more. From the viewpoint of versatility and manufacturability, the water-insoluble resin is preferably a random copolymer.

The acid value of the water-insoluble resin in the present invention is preferably 100 or less, more preferably 30 mgKOH / g or more and 100 mgKOH / g or less, more preferably 30 mgKOH / g or more and 85 mgKOH / g from the viewpoint of pigment dispersibility and storage stability. More preferably, it is more preferably 50 mgKOH / g or more and 85 mgKOH / g or less.
The acid value is defined by the mass (mg) of KOH required to completely neutralize 1 g of the water-insoluble resin, and is measured by the method described in JIS standards (JISK0070, 1992).

The molecular weight of the water-insoluble resin in the present invention is preferably 30,000 or more in terms of weight average molecular weight (Mw), more preferably 30,000 to 150,000, still more preferably 30,000 to 100,000, particularly preferably 30,000 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.
Further, the number average molecular weight (Mn) is preferably in the range of 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, the function of the coating film as a pattern formed on the recording medium can be sufficiently exhibited as a coating film for coating the pigment particles. The anionic group contained in the water-insoluble resin is preferably used in the form of an alkali metal or organic amine salt.

Moreover, as molecular weight distribution (weight average molecular weight / number average molecular weight) of water-insoluble resin, the range of 1-6 is preferable, and the range of 1-4 is more preferable. 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 GMHxL, TSKgel G4000HxL, and TSKgel G2000HxL (both manufactured by Tosoh Corporation) as a standard substance. It is the molecular weight expressed by converting using polystyrene.

The water-insoluble resin can be synthesized by various polymerization methods such as solution polymerization, precipitation polymerization, suspension polymerization, precipitation 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, Masaaki Kinoshita, “Experimental Methods for Polymer Synthesis” , Published in 1972, pages 124-154.
Specifically, the water-insoluble resin can be produced by copolymerizing a monomer mixture and, if necessary, a mixture containing an organic solvent and a radical polymerization initiator in an inert gas atmosphere. 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 , Various organic solvents such as methylene chloride, chloroform, dichloroethane, methanol, ethanol, 1-propanol, 2-propanol, and 1-butanol. 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 can be carried out in the range of 50 ° C. to 100 ° C. preferable. 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.
Hereinafter, preferred specific examples of the water-insoluble resin in the present invention will be shown. However, the present invention is not limited to the following.

When producing the encapsulated pigment aqueous dispersion, the ratio of the water-insoluble resin to the pigment is preferably selected from the range of the pigment: water-insoluble resin mass ratio of 100: 20 to 100: 140. As a result, a pigment dispersion state in the ink composition according to the present invention that is stable for a long period of time can be obtained, and the discharge performance from the ink discharge head can be maintained constant over a long period of time. The ratio is more preferably selected from the range of 100: 25 to 100: 50. The encapsulated pigment aqueous dispersion can be produced by the conventional physical and chemical methods using the above-described components. According to a preferred embodiment of the present invention, 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 Manufactured by a method described in each publication.
Specific examples include the phase inversion emulsification method and the acid precipitation method described in JP-A-9-151342 and JP-A-10-140065.

The phase inversion emulsification 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 further contain at least one of a curing agent and a polymer compound different from the resin. 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.
More specific methods of the above phase inversion emulsification method and acid precipitation method are described in JP-A-9-151342 and JP-A-10-140065, and can be referred to.

<Self-dispersed pigment aqueous dispersion>
Self-dispersed pigment aqueous dispersion means that a large number of hydrophilic functional groups and / or salts thereof (hereinafter referred to as dispersibility-imparting groups) are directly or via an alkyl group, alkyl ether group, aryl group, etc. on the pigment surface. This is a dispersion in which an indirectly bonded product is dispersed in water. In this dispersion, the pigment can be dispersed in an aqueous medium without a dispersant.
Inks containing a self-dispersing pigment as a colorant do not need to contain a dispersant as described above that is contained in order to disperse a normal pigment. It is easy to prepare ink that is excellent in ejection stability.
Examples of dispersibility-imparting groups to be bonded to the surface of the self-dispersion _{pigment, -COOH, -CO, -OH, -SO} 3 H, -PO 3 H 2 and can quaternary ammonium and exemplary salts thereof, these Is produced by bonding (grafting) an active species having a dispersibility-imparting group or a dispersibility-imparting group to the surface of the pigment by subjecting the pigment as a raw material to physical treatment or chemical treatment. Examples of the physical treatment include vacuum plasma treatment. Examples of the chemical treatment include a wet oxidation method in which the pigment surface is oxidized with an oxidizing agent in water, and a method in which a carboxyl group is bonded via a phenyl group by bonding p-aminobenzoic acid to the pigment surface. It can be illustrated.
In the present invention, preferred examples include self-dispersing pigments that are surface-treated by oxidation treatment with hypohalous acid and / or hypohalite or oxidation treatment with ozone. Commercially available products can also be used as the self-dispersing pigment, such as MicroJet CW-1 (trade name; manufactured by Orient Chemical Co., Ltd.), CAB-O-JET200, CAB-O-JET300 (above trade names). ; Manufactured by Cabot Corporation).
A self-dispersion type pigment may be used individually by 1 type, and may be used in combination of 2 or more type.

<Resin dispersion pigment water dispersion>
In the present invention, the “pigment coated with a water-insoluble resin” may be prepared by using, for example, a water-insoluble resin as a dispersant, and dispersing the pigment with the dispersant. It can also be made by preparing a dispersion.
By doing so, the pigment particles can be present in a fine particle size, and high dispersion stability can be obtained after dispersion. In this case, since it is not necessary to coat the entire surface of the pigment particles with the water-insoluble resin, the use ratio of the water-insoluble resin to the pigment can be reduced. Specifically, the mass ratio of pigment: water-insoluble resin is preferably selected from the range of 100: 15 to 100: 100. As a result, a pigment dispersion state in the ink composition according to the present invention that is stable for a long period of time can be obtained, and the discharge performance from the ink discharge head can be maintained constant over a long period of time. The ratio is more preferably selected from the range of 100: 20 to 100: 40.

  The dispersion can be performed by using a known method, a mixing / stirring device, a dispersing device, or the like in which stirring and dispersion can be performed after mixing desired components. The dispersion can be performed using, for example, a ball mill, a roll mill, a bead mill, a high-pressure homogenizer, a high-speed agitation disperser, an ultrasonic homogenizer, or the like.

-Pigment dispersant-
When preparing the pigment dispersion, the above-mentioned water-insoluble resin can be used as a dispersant. At this time, other pigment dispersants other than the water-insoluble resin may be used in combination.
The other pigment dispersant can be appropriately selected from compounds having a function of dispersing a pigment in an aqueous phase. Examples of such other pigment dispersants include nonionic compounds, anionic compounds, cationic compounds, and amphoteric compounds.

  For example, a homopolymer or copolymer of a monomer having an α, β-ethylenically unsaturated group may be mentioned. Examples of monomers having an α, β-ethylenically unsaturated group include ethylene, propylene, butene, pentene, hexene, vinyl acetate, allyl acetate, acrylic acid, methacrylic acid, crotonic acid, crotonic acid ester, itaconic acid, itacone Acid monoester, maleic acid, maleic acid monoester, maleic acid diester, fumaric acid, fumaric acid monoester, vinyl sulfonic acid, styrene sulfonic acid, sulfonated vinyl naphthalene, vinyl alcohol, acrylamide, methacryloxyethyl phosphate, bismethacryloxy Styrene derivatives such as ethyl phosphate, methacryloxyethyl phenyl acid phosphate, ethylene glycol dimethacrylate, diethylene glycol dimethacrylate, styrene, α-methylstyrene, vinyltoluene , Vinylcyclohexane, vinylnaphthalene, vinylnaphthalene derivatives, alkyl acrylates that may be substituted with aromatic groups, phenyl esters of acrylate, alkyl methacrylates that may be substituted with aromatic groups, phenyl esters of methacrylic acid, methacryl Examples include acid cycloalkyl esters, crotonic acid alkyl esters, itaconic acid dialkyl esters, maleic acid dialkyl esters, and derivatives of these compounds.

  Specific examples of the homopolymer or copolymer of the monomer having an α, β-ethylenically unsaturated group include acrylic acid alkyl ester-acrylic acid copolymer, methacrylic acid alkyl ester-methacrylic acid copolymer, and styrene. -Acrylic acid alkyl ester-Acrylic acid copolymer, Styrene-Methacrylic acid phenyl ester-Methacrylic acid, Styrene-Methacrylic acid cyclohexyl ester-Methacrylic acid copolymer, Styrene-Styrene sulfonic acid copolymer, Styrene-Maleic acid copolymer Polymer, styrene-methacrylic acid copolymer, styrene-acrylic acid copolymer, vinyl naphthalene-maleic acid copolymer, vinyl naphthalene-methacrylic acid copolymer, vinyl naphthalene-acrylic acid copolymer, polystyrene, polyvinyl alcohol, Various cyclic lactones and And polyester polymers obtained by ring-opening polymerization with a cyclic lactam and a base.

When preparing the resin-dispersed pigment aqueous dispersion, at least one water-insoluble volatile solvent can be used. Since water-insoluble volatile solvents have little effect on dispersibility, while maintaining good dispersibility in the dispersion process, the water-insoluble volatile solvent is finally concentrated to remove the non-water-soluble volatile solvent while maintaining good dispersibility. Thus, a pigment dispersion having excellent storage stability over a long period of time can be obtained. Also, when an ink composition is prepared and used for recording, it is excellent in ejection stability, and image recording with curl generation suppressed can be performed.
Here, “water-insoluble” means a property that the solubility in water is 80 g / 100 mL or less at 20 ° C. “Volatile” means a property having a boiling point of 200 ° C. or lower.
In the present invention, the water-insoluble volatile solvent is preferably selected from those having a water solubility of 50 g / 100 mL or less and a boiling point of 150 ° C. or less.

  The water-insoluble volatile solvent can be selected as desired from water-insoluble and volatile organic solvents. Specific examples of the water-insoluble volatile solvent include ketone solvents (for example, methyl ethyl ketone and diethyl ketone) and ether solvents (for example, dibutyl ether). Of these, ketone solvents are preferable from the viewpoint of imparting dispersion stability, and methyl ethyl ketone is most preferable among them.

The average particle diameter of the particles is preferably in the range of 30 to 200 nm, more preferably in the range of 50 to 150 nm. When the average particle size is 30 nm or more, the production suitability is improved, and when it is 200 nm or less, the storage stability is improved. In addition, there is no restriction | limiting in particular regarding the particle size distribution of resin-coated pigment particle | grains, Any of what has a wide particle size distribution or a monodispersed particle size distribution may be sufficient.
The average particle size and particle size distribution of the pigment particles are determined by measuring the volume average particle size by a dynamic light scattering method using a nanotrack particle size distribution analyzer UPA-EX150 (manufactured by Nikkiso Co., Ltd.). It is done.

  When the pigment in the ink composition of the present invention is contained in the form of the pigment aqueous dispersion of (1) or (3) as described above, the total content of the pigment and the water-insoluble resin is included in the present invention. The amount is preferably 0.05% by mass to 30% by mass based on the ink composition. By setting such a range, it is possible to obtain an appropriate pattern density, ink composition viscosity, and ink ejection stability by ink ejected and formed on a recording medium. The content is more preferably 0.1% by mass to 20% by mass, and particularly preferably 0.15% by mass to 15% by mass.

<Surfactant-dispersed pigment aqueous dispersion>
The surfactant-dispersed pigment aqueous dispersion is obtained by dispersing a pigment in water using a surfactant as a dispersant. The surfactant used as the dispersant is not particularly limited, and may be any of an anionic surfactant, a nonionic surfactant, a cationic surfactant, and an amphoteric surfactant. And an ionic surfactant such as a cationic surfactant is preferable because the pigment can be dispersed in a smaller amount.
Two or more kinds of surfactants may be used in combination.
The ratio of the surfactant to the pigment is preferably in the range of 100: 5 to 100: 50 in terms of the pigment: surfactant mass ratio. By setting it within this range, a pigment dispersion state in the ink composition according to the present invention that is stable for a long period of time can be obtained, and the dischargeability from the ink discharge head can be maintained constant over a long period of time. The ratio is more preferably selected from the range of 100: 5 to 100: 20.

(Polymer particles)
The ink composition of the present invention preferably contains at least one kind of polymer particles from the viewpoint of improving abrasion resistance, blocking resistance, and offset resistance.
As the polymer particles, polymer latex in which the particles are dispersed in water can be preferably used.
The polymer particles having an I / O value of 0.20 or more and 0.55 or less are preferable in terms of blocking resistance and stability of the ink composition.

  The polymer particles are not particularly limited. For example, thermoplastic acrylic, epoxy, polyurethane, polyether, polyamide, unsaturated polyester, phenol, silicone, or fluorine resin, vinyl chloride And polymer particles composed of polyvinyl resins such as vinyl acetate, polyvinyl alcohol, or polyvinyl butyral, polyester resins such as alkyd resins and phthalic resins, or resins such as copolymers or mixtures thereof.

  The polymer particles are formed by aggregating or destabilizing the ink when contacted with a treatment liquid capable of forming an aggregate by contact with the ink composition described later, or by drying the liquid, thereby increasing the viscosity of the ink. The ink composition preferably has a function of fixing an image. Such polymer particles are preferably dispersed in at least one of water and an organic solvent.

The weight average molecular weight of the polymer particles in the present invention is preferably 10,000 or more and 200,000 or less, more preferably 100,000 or more and 200,000 or less, from the viewpoint of the stability of the ink composition.
The average particle size of the polymer particles in the present invention 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.
Moreover, there is no restriction | limiting in particular regarding the particle size distribution of a polymer particle, What has a wide particle size distribution or a thing with a monodispersed particle size distribution may be sufficient. Two or more kinds of latexes having a monodispersed particle size distribution may be mixed and used.

The glass transition temperature (Tg) of the polymer particles in the present invention is preferably 50 ° C. or higher. By including polymer particles having a Tg of 50 ° C. or higher, the fixability of the ink composition to the recording medium and the abrasion resistance can be effectively improved. The Tg of the polymer particles is more preferably 50 ° C. or higher and 180 ° C. or lower, still more preferably 70 ° C. or higher and 170 ° C. or lower.
The Tg of the polymer particles can be appropriately controlled by a commonly used method. For example, the Tg of the polymer particle can be set to a desired value by appropriately selecting the type of polymerizable group of the monomer constituting the polymer, the type and composition ratio of the substituent on the monomer, the molecular weight of the polymer molecule constituting the polymer particle, and the like. The range can be controlled.

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

  In the ink composition of the present invention, the content of polymer particles (mass of resin solids) is the content of pigment (mass of pigment solids) from the viewpoint of improving the scratch resistance, blocking resistance, and offset resistance. Is preferably exceeded. In the present invention, the solid content mass ratio (a) / (b) between the polymer particles (a) and the pigment (b) is preferably 1 to 10, and more preferably 1.2 to 5.

<Self-dispersing polymer particles>
The polymer particles in the present invention are preferably self-dispersing polymer particles from the viewpoint of imparting ejection stability, liquid stability when using a pigment (particularly dispersion stability), and high-speed droplet ejection printing suitability. More preferred are self-dispersing polymer particles having
The self-dispersing polymer particles in the present invention are water-insoluble which can be dispersed in an aqueous medium by a functional group (particularly an acidic group or a salt thereof) of the resin itself in the absence of other surfactants. A polymer particle (also referred to as “first polymer”) means a fine particle of a water-insoluble resin that does not contain a free emulsifier.

Here, the dispersed state means an emulsified state (emulsion) in which water-insoluble polymer particles are dispersed in an aqueous medium and a dispersed state (suspension) in which water-insoluble polymer particles are dispersed in an aqueous medium in a solid state. It includes both states.
In the ink composition according to the present invention, the water-insoluble polymer particles are dispersed in a solid state in the ink composition from the viewpoint of the aggregation rate of the pigment and the water-insoluble polymer particles and the ink fixing property. preferable.

  The self-dispersing polymer particles used in the ink composition according to the present invention include a solution in which 30 g of a water-insoluble resin is dissolved in 70 g of an organic solvent (for example, methyl ethyl ketone), and 100% neutralization of salt-forming groups of the water-insoluble resin. A neutralizing agent (sodium hydroxide if the salt-forming group is anionic, acetic acid if it is cationic) and 200 g of water are mixed and stirred (apparatus: stirring device with stirring blades, rotation speed 200 rpm, 30 minutes, 25 After the removal of the organic solvent from the mixed solution, it is preferable that it can be visually confirmed that the dispersion state exists stably at 25 ° C. for at least one week.

  The “water-insoluble polymer particles” means polymer particles having a dissolution amount of 10 g or less when the polymer particles are dried at 105 ° C. for 2 hours and then dissolved in 100 g of water at 25 ° C. . In the present invention, the water-insoluble polymer particles preferably have a dissolution amount of preferably 5 g or less, and more preferably have a dissolution amount of 1 g or less. In addition, the said dissolution amount is a dissolution amount when neutralizing 100% with sodium hydroxide or acetic acid according to the kind of salt formation group of a water-insoluble polymer.

  The aqueous medium is configured to contain water, and may contain a hydrophilic organic solvent as necessary. When a hydrophilic organic solvent is included, the amount is preferably 0.2% by mass or less with respect to water. In the present invention, the aqueous medium is more preferably composed of 100% water.

The main chain skeleton of the water-insoluble polymer particles is not particularly limited. For example, a vinyl polymer or a condensation polymer (epoxy resin, polyester, polyurethane, polyamide, cellulose, polyether, polyurea, polyimide, polycarbonate, etc.) is used. Can do. Of these, vinyl polymers are particularly preferred.
Preferable examples of the vinyl polymer and the monomer constituting the vinyl polymer include those described in JP-A Nos. 2001-181549 and 2002-88294. In addition, radical transfer of vinyl monomers using dissociable groups (or substituents that can be induced to dissociable groups), polymerization initiators, and iniferters, or dissociable groups on either initiators or terminators A vinyl polymer in which a dissociable group is introduced at the end of a polymer chain by ionic polymerization using a compound having (or a substituent that can be derived from a dissociable group) can also be used.
Moreover, as a suitable example of the monomer which comprises a condensation type polymer and a condensation type polymer, what is described in Unexamined-Japanese-Patent No. 2001-247787 can be mentioned.

The self-dispersing polymer particles in the present invention include a hydrophilic constituent unit and a constituent unit derived from an aromatic group-containing monomer or a cycloaliphatic group-containing monomer as a hydrophobic constituent unit from the viewpoint of self-dispersibility. It is preferable to contain water-insoluble polymer particles. The hydrophobic structural unit is a cyclic aliphatic group-containing (meth) acrylate (hereinafter sometimes referred to as “alicyclic (meth) acrylate”) from the viewpoints of blocking resistance, abrasion resistance, and dispersion stability. More preferred.
The alicyclic (meth) acrylate includes a structural site derived from (meth) acrylic acid and a structural site derived from alcohol, and the structural site derived from alcohol is unsubstituted or substituted. It has a structure containing at least one hydrocarbon group (cycloaliphatic group). The alicyclic hydrocarbon group may be a structural site derived from alcohol itself or may be bonded to a structural site derived from alcohol via a linking group.
In addition, “alicyclic (meth) acrylate” means methacrylate or acrylate having an alicyclic hydrocarbon group.

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

The hydrophilic group-containing monomer in the present invention is preferably a dissociable group-containing monomer from the viewpoint of self-dispersibility and aggregation of the polymer particles, and contains a dissociable group having a dissociable group and an ethylenically unsaturated bond. A monomer is preferred.
Examples of the dissociable group-containing monomer include an unsaturated carboxylic acid monomer, an unsaturated sulfonic acid monomer, and an unsaturated phosphoric acid monomer.

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

The self-dispersing polymer particles in the present invention are a first polymer having a carboxyl group and an acid value (mgKOH / g) of 25 to 100 from the viewpoints of self-dispersibility and agglomeration speed when contacting with the treatment liquid. It is preferable to contain. Furthermore, the acid value is more preferably from 25 to 80, and particularly preferably from 30 to 65, from the viewpoints of self-dispersibility and agglomeration rate when contacted with the treatment liquid.
When the acid value is 25 or more, the stability of the polymer particles in the ink composition is improved, and when the acid value is 100 or less, the aggregation property of the polymer particles is improved. Furthermore, the acid value of the self-dispersing polymer particles is smaller than the acid value of the water-insoluble resin used for the dispersion of the pigment, so that both the dispersion stability of the pigment and the aggregation rate when in contact with the treatment liquid can be achieved. From the viewpoint, the difference is more preferably 5 to 70, and 10 to 70 is particularly preferable.

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

The aromatic group-containing monomer in the present invention is preferably a monomer having an aromatic group derived from an aromatic hydrocarbon and an ethylenically unsaturated bond, and more preferably an aromatic group-containing (meth) acrylate monomer. preferable.
In the present invention, the aromatic group-containing monomers may be used singly or in combination of two or more.
Examples of the aromatic group-containing monomer include phenoxyethyl (meth) acrylate, benzyl (meth) acrylate, phenyl (meth) acrylate, and a styrene monomer. Among them, from the viewpoint of the balance between the hydrophilicity and hydrophobicity of the polymer chain and the ink fixing property, it is preferably at least one selected from phenoxyethyl (meth) acrylate, benzyl (meth) acrylate, and phenyl (meth) acrylate. More preferred is phenoxyethyl (meth) acrylate, and particularly preferred is phenoxyethyl acrylate.
“(Meth) acrylate” means acrylate or methacrylate.

The alicyclic hydrocarbon group is not particularly limited as long as it contains a cyclic non-aromatic hydrocarbon group, and is a monocyclic hydrocarbon group, a bicyclic hydrocarbon group, a tricyclic or more polycyclic group. A hydrocarbon group is mentioned. Examples of the alicyclic hydrocarbon group include a cycloalkyl group such as a cyclopentyl group and a cyclohexyl group, a cycloalkenyl group, a bicyclohexyl group, a norbornyl group, an isobornyl group, a dicyclopentanyl group, a dicyclopentenyl group, and an adamantyl group. , Decahydronaphthalenyl group, perhydrofluorenyl group, tricyclo [5.2.1.0 ^2,6 ] decanyl group, and bicyclo [4.3.0] nonane.

  The alicyclic hydrocarbon group may further have a substituent. Examples of the substituent include an alkyl group, an alkenyl group, an aryl group, an aralkyl group, an alkoxy group, a hydroxyl group, a primary amino group, a secondary amino group, a tertiary amino group, an alkyl or arylcarbonyl group, and a cyano group. Is mentioned. Further, the alicyclic hydrocarbon group may further form a condensed ring. As an alicyclic hydrocarbon group in this invention, it is preferable that carbon number of an alicyclic hydrocarbon group part is 5-20 from a viscosity or a soluble viewpoint.

  Examples of the linking group that connects the alicyclic hydrocarbon group and the structural portion derived from alcohol include alkyl groups, alkenyl groups, alkylene groups, aralkyl groups, alkoxy groups, mono- or oligoethylene groups having 1 to 20 carbon atoms. Preferable examples include a coal group, a mono- or oligopropylene glycol group, and the like.

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

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

  The self-dispersing polymer in the present invention is preferably an acrylic resin containing a structural unit derived from a (meth) acrylate monomer, and contains a structural unit derived from an aromatic group-containing (meth) acrylate or alicyclic (meth) acrylate. Acrylic resins are preferable, and further, it includes a structural unit derived from aromatic group-containing (meth) acrylate or alicyclic (meth) acrylate, and the content ratio is preferably 10% by mass to 95% by mass. When the content ratio of the aromatic group-containing (meth) acrylate or alicyclic (meth) acrylate is 10% by mass to 95% by mass, self-emulsification or dispersion stability is improved, and ink viscosity is further increased. Can be suppressed. In the present invention, self-dispersed state stability, stabilization of particle shape in an aqueous medium due to hydrophobic interaction between aromatic rings or alicyclic hydrocarbon groups, water-soluble component due to appropriate hydrophobicization of particles From the viewpoint of lowering the amount, a range of 15% by mass to 90% by mass is more preferable, a range of 15% by mass to 80% by mass is more preferable, and a range of 25% by mass to 70% by mass is particularly preferable.

The self-dispersing polymer in the present invention can be constituted using, for example, a structural unit derived from an aromatic group-containing monomer or a cycloaliphatic group-containing monomer and a structural unit derived from a dissociable group-containing monomer. Furthermore, other structural units may be further included as necessary.
The monomer that forms the other structural unit is not particularly limited as long as it is a monomer copolymerizable with the aromatic group-containing monomer or the cyclic aliphatic group-containing monomer and the dissociable group-containing monomer. Among these, an alkyl group-containing monomer is preferable from the viewpoint of flexibility of the polymer skeleton and ease of control of the glass transition temperature (Tg).
Examples of the alkyl group-containing monomer include methyl (meth) acrylate, ethyl (meth) acrylate, isopropyl (meth) acrylate, n-propyl (meth) acrylate, n-butyl (meth) acrylate, isobutyl (meth) acrylate, Alkyl (meth) acrylates such as t-butyl (meth) acrylate, hexyl (meth) acrylate, ethylhexyl (meth) acrylate, and hydroxymethyl (meth) acrylate, 2-hydroxyethyl (meth) acrylate, 2-hydroxypropyl (meth) ) Ethylenically unsaturated monomers having hydroxyl groups such as acrylate, 4-hydroxybutyl (meth) acrylate, hydroxypentyl (meth) acrylate, hydroxyhexyl (meth) acrylate, and dimethyl (Meth) acrylic ester monomers such as dialkylaminoalkyl (meth) acrylates such as ruaminoethyl (meth) acrylate; N-hydroxymethyl (meth) acrylamide, N-hydroxyethyl (meth) acrylamide, N-hydroxybutyl (meth) N-hydroxyalkyl (meth) acrylamide such as acrylamide, N-methoxymethyl (meth) acrylamide, N-ethoxymethyl (meth) acrylamide, N- (n-, iso) butoxymethyl (meth) acrylamide, N-methoxyethyl (Meth) acrylamide, such as (meth) acrylamide, N-ethoxyethyl (meth) acrylamide, N-alkoxyalkyl (meth) acrylamide such as N- (n-, iso) butoxyethyl (meth) acrylamide, etc. And (meth) acrylamide-based monomers like.

The molecular weight range of the water-insoluble polymer particles constituting the self-dispersing polymer in the present invention is preferably 3000 to 200,000, more preferably 5000 to 150,000, and more preferably 10,000 to 100,000 in terms of weight average molecular weight. More preferably it is. By setting the weight average molecular weight to 3000 or more, the amount of water-soluble components can be effectively suppressed. Moreover, self-dispersion stability can be improved by making a weight average molecular weight into 200,000 or less.
The weight average molecular weight is measured by gel permeation chromatography (GPC). For GPC, HLC-8220GPC (manufactured by Tosoh Corporation) is used, and as columns, TSKgeL SuperHZM-H, TSKgeL SuperHZ4000, TSKgeL SuperHZ2000 (manufactured by Tosoh Corporation, 4.6 mm ID × 15 cm) are used as eluents. Use THF (tetrahydrofuran).

The water-insoluble polymer particles constituting the self-dispersing polymer particles in the present invention are structural units derived from aromatic group-containing (meth) acrylate or alicyclic (meth) acrylate (preferably from the viewpoint of controlling the hydrophilicity / hydrophobicity of the polymer. , Structural units derived from phenoxyethyl (meth) acrylate and / or structural units derived from benzyl (meth) acrylate, or isobornyl (meth) acrylate and / or adamantyl (meth) acrylate and / or dicyclopentanyl (meth) It is preferable that 15 to 80% by mass of the total mass of the self-dispersing polymer particles is included as a copolymerization ratio of (acrylate).
In addition, the water-insoluble polymer particles are 15 to 80% by mass as a copolymerization ratio of a structural unit derived from an aromatic group-containing (meth) acrylate or alicyclic (meth) acrylate, from the viewpoint of controlling the hydrophilicity / hydrophobicity of the polymer. It is preferable to include a structural unit derived from a carboxyl group-containing monomer and a structural unit derived from an alkyl group-containing monomer (preferably a structural unit derived from an alkyl ester of (meth) acrylic acid). Furthermore, a structural unit derived from phenoxyethyl (meth) acrylate and / or a structural unit derived from benzyl (meth) acrylate, isobornyl (meth) acrylate and / or adamantyl (meth) acrylate and / or dicyclopentanyl ( 15 to 80% by mass of a structural unit derived from a (meth) acrylate as a copolymerization ratio, a structural unit derived from a carboxyl group-containing monomer, and a structural unit derived from an alkyl group-containing monomer (preferably (meth) acrylic acid In addition, it is preferable that the acid value is 25 to 100 and the weight average molecular weight is 3000 to 200,000. The acid value is 25 to 95 and the weight average molecular weight is 5,000 to 150,000. More preferable.

Specific examples of the water-insoluble polymer particles constituting the self-dispersing polymer particles are listed below as exemplary compounds C-01 to C-24, but the present invention is not limited thereto. The values in parentheses represent the mass ratio of the copolymer component.
C-01: Phenoxyethyl acrylate / methyl methacrylate / acrylic acid copolymer (50/45/5)
C-02: Phenoxyethyl acrylate / benzyl methacrylate / isobutyl methacrylate / methacrylic acid copolymer (30/35/29/6)
C-03: Phenoxyethyl methacrylate / isobutyl methacrylate / methacrylic acid copolymer (50/44/6)
C-04: Phenoxyethyl acrylate / methyl methacrylate / ethyl acrylate / acrylic acid copolymer (30/55/10/5)
C-05: benzyl methacrylate / isobutyl methacrylate / methacrylic acid copolymer (35/59/6)
C-06: Styrene / phenoxyethyl acrylate / methyl methacrylate / acrylic acid copolymer (10/50/35/5)
C-07: benzyl acrylate / methyl methacrylate / acrylic acid copolymer (55/40/5)
C-08: Phenoxyethyl methacrylate / benzyl acrylate / methacrylic acid copolymer (45/47/8)
C-09: Styrene / phenoxyethyl acrylate / butyl methacrylate / acrylic acid copolymer (5/48/40/7)
C-10: benzyl methacrylate / isobutyl methacrylate / cyclohexyl methacrylate / methacrylic acid copolymer (35/30/30/5)
C-11: Phenoxyethyl acrylate / methyl methacrylate / butyl acrylate / methacrylic acid copolymer (12/50/30/8)
C-12: benzyl acrylate / isobutyl methacrylate / acrylic acid copolymer (93/2/5)
C-13: Styrene / phenoxyethyl methacrylate / butyl acrylate / acrylic acid copolymer (50/5/20/25)
C-14: Styrene / butyl acrylate / acrylic acid copolymer (62/35/3)
C-15: Methyl methacrylate / phenoxyethyl acrylate / acrylic acid copolymer (45/51/4)
C-16: Methyl methacrylate / phenoxyethyl acrylate / acrylic acid copolymer (45/49/6)
C-17: Methyl methacrylate / phenoxyethyl acrylate / acrylic acid copolymer (45/48/7)
C-18: Methyl methacrylate / phenoxyethyl acrylate / acrylic acid copolymer (45/47/8)
C-19: Methyl methacrylate / phenoxyethyl acrylate / acrylic acid copolymer (45/45/10)

C-20: Methyl methacrylate / isobornyl methacrylate / methacrylic acid copolymer (20/72/8)
C-21: Methyl methacrylate / isobornyl methacrylate / methacrylic acid copolymer (40/52/8)
C-22: Methyl methacrylate / isobornyl methacrylate / methacrylic acid copolymer (10/13/2)
C-23: Methyl methacrylate / isobornyl methacrylate / dicyclopentanyl methacrylate / methacrylic acid copolymer (20/62/10/8)
C-24: Methyl methacrylate / dicyclopentanyl methacrylate / methacrylic acid copolymer (20/72/8)

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

The self-dispersing polymer particles in the present invention include a first polymer synthesized in an organic solvent from the viewpoint of aggregation rate, and the first polymer has a carboxyl group and has an acid value of 25 to 100. In addition, it is preferable that at least a part of the carboxyl groups of the first polymer is neutralized and prepared as a polymer dispersion having water as a continuous phase.
That is, the method for producing self-dispersing polymer particles in the present invention includes a step of synthesizing the first polymer in an organic solvent, and an aqueous dispersion in which at least a part of the carboxyl groups of the first polymer is neutralized. And a dispersion step.

The dispersion step preferably includes the following step (1) and step (2).
Step (1): A step of stirring the mixture containing the first polymer (water-insoluble polymer), the organic solvent, the neutralizing agent, and the aqueous medium.
Step (2): A step of removing the organic solvent from the mixture.
The step (1) is a treatment in which the first polymer (water-insoluble polymer) is first dissolved in an organic solvent, and then a neutralizer and an aqueous medium are gradually added, mixed and stirred to obtain a dispersion. It is preferable. In this way, by adding a neutralizing agent and an aqueous medium to a water-insoluble polymer solution dissolved in an organic solvent, a self-dispersing polymer having a particle size with higher storage stability without requiring strong shearing force. Particles can be obtained.
There is no restriction | limiting in particular in the stirring method of this mixture, Dispersing machines, such as a generally used mixing stirring apparatus and an ultrasonic disperser, a high-pressure homogenizer, can be used as needed.

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

The neutralizing agent is used so that a part or all of the dissociable group is neutralized and the self-dispersing polymer forms a stable emulsified or dispersed state in water. When the self-dispersing polymer has an anionic dissociative group (for example, a carboxyl group) as a dissociable group, examples of the neutralizing agent used include basic compounds such as organic amine compounds, ammonia, and alkali metal hydroxides. It is done. Examples of organic amine compounds include monomethylamine, dimethylamine, trimethylamine, monoethylamine, diethylamine, triethylamine, monopropylamine, dipropylamine, monoethanolamine, diethanolamine, triethanolamine, N, N-dimethyl-ethanolamine, N, N-diethyl-ethanolamine, 2-dimethylamino-2-methyl-1-propanol, 2-amino-2-methyl-1-propanol, N-methyldiethanolamine, N-ethyldiethanolanine, monoisopropanolamine, di Examples include isopropanolamine and triisopropanolamine. Examples of the alkali metal hydroxide include lithium hydroxide, sodium hydroxide, and potassium hydroxide. Among these, sodium hydroxide, potassium hydroxide, triethylamine, and triethanolamine are preferable from the viewpoint of stabilizing the dispersion of the self-dispersing polymer particles in water.
These basic compounds are preferably used in an amount of 5 to 120 mol%, more preferably 10 to 110 mol%, still more preferably 15 to 100 mol%, based on 100 mol% of the dissociable group. . By setting it as 15 mol% or more, the effect which stabilizes dispersion | distribution of the particle | grains in water expresses, and there exists an effect which reduces a water-soluble component by setting it as 100 mol% or less.

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

The average particle size of the self-dispersing polymer particles in the present invention is preferably in the range of 10 nm to 400 nm, more preferably 10 nm to 200 nm, further preferably 10 nm to 100 nm. Manufacturability is improved when the average particle diameter is 10 nm or more. Moreover, storage stability improves by setting it as an average particle diameter of 400 nm or less.
Further, the particle size distribution of the self-dispersing 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 water-insoluble particles may be mixed and used.
The average particle size and particle size distribution of the self-dispersing polymer particles can be measured using, for example, a light scattering method.
The self-dispersing polymer particles of the present invention can be suitably contained in an aqueous ink composition, for example, and can be used alone or in combination of two or more.

(Water-soluble organic solvent)
The ink composition contains water as a solvent, but preferably contains at least one water-soluble organic solvent.
Examples of the water-soluble organic solvent 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-pentane Alkanediols (polyhydric alcohols) such as diol and 4-methyl-1,2-pentanediol; C1-C4 alkyl alcohols such as ethanol, methanol, butanol, propanol and isopropanol; ethylene glycol monomethyl alcohol 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, ethylene 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 Recall mono-n-propyl 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, etc. 2-pyrrolidone, N-methyl-2-pyrrolidone, 1,3-dimethyl-2-imidazolidinone, formamide, acetamide, dimethyl sulfoxide, sorbit, sorbitan, acetin, diacetin, triacetin, sulfolane and the like It is done. These may be used alone or in combination of two or more.

  In addition, polyhydric alcohols are useful in terms of preventing drying and imparting moisture. For example, 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-2,4-pentanediol, polyethylene glycol, 1,2,4-butanetriol, 1,2 , 6-hexanetriol and the like. These may be used alone or in combination of two or more. From the viewpoint of permeability, 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 , 5-hexene-1,2-diol, 2-ethyl-1,3-hexanediol, and the like. Of these, 2-ethyl-1,3-hexanediol and 2,2,4-trimethyl-1,3-pentanediol are preferable. These may be used alone or in combination of two or more.

  An alkylene oxide adduct of glycerin can be preferably used. A commercial item may be used for the alkylene oxide adduct of glycerol. Commercially available products include, for example, polyoxypropylated glycerin (ether of polypropylene glycol and glycerin), Sanniks GP-250 (average molecular weight 250), GP-400 (average molecular weight 400), GP-600 (average 600) [Above, Sanyo Chemical Industries, Ltd.], Reocon GP-250 (average molecular weight 250), GP-300 (average molecular weight 300, GP-400 (average molecular weight 400), GP-700 (average molecular weight 700) Lion Co., Ltd.], polypropylene triol glycol triol type average molecular weight 300, average molecular weight 700 [more, Wako Pure Chemical Industries, Ltd.] and the like.

  The content of the water-soluble organic solvent contained in the ink composition is preferably 1.0% by mass to 50% by mass, and preferably 5.0% by mass to 40% from the viewpoint of preventing drying of the ink and imparting wetness. More preferably, the content is 10% by mass to 30% by mass.

(water)
The ink composition in the present invention contains water, but the amount of water is not particularly limited. Especially, the preferable content of water is 10 to 99% by mass, more preferably 30 to 80% by mass, and still more preferably 50 to 70% by mass.

(Other ingredients)
In addition to each of the components described above, the ink composition may include, for example, a surfactant, an ultraviolet absorber, an antifading agent, an antifungal agent, a pH adjuster, a rust inhibitor, an antioxidant, and an emulsifier. You may contain other components, such as a stabilizer, antiseptic | preservative, an antifoamer, a viscosity modifier, a dispersion stabilizer, a chelating agent, and a solid wetting agent.
The surfactant is used as a surface tension adjusting agent, and examples thereof include nonionic surfactants, cationic surfactants, anionic surfactants, 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.
There is no restriction | limiting in particular in content in the ink composition of surfactant, 1 mass% or more is preferable, More preferably, it is 1-10 mass%, More preferably, it is 1-3 mass%.

(Physical properties of ink composition)
The surface tension of the ink composition according to the present invention is preferably 20 mN / m or more and 60 mN / m or less from the viewpoint of ejection stability when used in an ink jet recording method. 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 viscosity of the ink at 20 ° C. is preferably from 1.2 mPa · s to 15.0 mPa · s, more preferably from 2 mPa · s to less than 13 mPa · s, still more preferably from 2.5 mPa · s to 10 mPa · s. -Less than s.

  The ink composition according to the present invention preferably has a pH of 7.5 or more and 12 or less at 25 ° C. from the viewpoint of preventing aggregation of pigments and cleaning properties with a maintenance liquid described later. It is more preferable to have the following pH. In order to adjust the pH of the water-soluble ink composition to the above range, a pH adjuster such as the above-mentioned water-soluble basic substance can be used as necessary.

The ink can be used for forming a multicolor image (for example, a full color image). For the formation of a full-color image, it can be used as a magenta tone ink, a cyan tone ink, or a yellow tone ink by changing the hue of the pigment used in the ink composition as desired. Furthermore, in order to adjust the color tone, black color tone ink can be used.
In addition, the ink may be red (R), green (G), blue (B), or white (W) ink other than yellow (Y), magenta (M), and cyan (C). It can be used as a special color ink in the printing field.

2. Maintenance Liquid The maintenance liquid according to the present invention (hereinafter also simply referred to as “maintenance liquid”) contains n-propanol. Here, “maintenance” includes maintaining the discharge head for discharging the ink composition and its discharge performance at or close to the desired state and maintaining it, and cleaning (cleaning) the recording head. This includes maintenance and maintenance in good condition. Therefore, a solution having such performance that contributes to maintenance is referred to as “maintenance liquid”.
The maintenance liquid according to the present invention may be composed of 100% n-propanol, but more preferably contains n-propanol and water, and particularly preferably contains a surfactant.
The surfactant has a function of allowing the maintenance liquid to permeate the ink composition (ink-solidified product) attached to the ink ejection head and effectively promote re-dispersion / re-dissolution.
As the surfactant used in the maintenance liquid according to the present invention, a cationic surfactant, a nonionic surfactant, an anionic surfactant, as long as the pH of the maintenance liquid can be used in a neutral to weak alkaline state, Although amphoteric surfactants can be used, nonionic surfactants are preferred from the viewpoint of suppressing the corrosion of the silicon dioxide film and water repellent film of the head. Specifically, polyoxyethylene alkyl ether, polyoxy Nonionic surfactants such as ethylene alkyl allyl ether, polyoxyethylene fatty acid ester, sorbitan fatty acid ester, polyoxyethylene sorbitan fatty acid ester, acetylenic diol derivative, polyoxyethylene alkylamine, glycerin fatty acid ester, oxyethyleneoxypropylene block copolymer It is. Of these, particularly preferred nonionic surfactants are polyoxyethylene alkyl ethers and acetylenic diol derivatives.

The maintenance liquid according to the present invention contains 5% by mass or more of n-propanol with respect to the total mass of the maintenance liquid, and has high cleaning properties, and the discharge performance of the ink discharge head is maintained for a long time. Therefore, it is preferable. The amount of n-propanol contained in the maintenance liquid according to the present invention is preferably in the range of 5% by mass to 100% by mass, and more preferably in the range of 10% by mass to 50% by mass.
When the maintenance liquid according to the present invention contains a surfactant, the content thereof is preferably in the range of 0.01% by mass to 10% by mass with respect to the total mass of the maintenance liquid, and is 0.3% by mass to 5% by mass. A range is more preferred.
When the maintenance liquid according to the present invention contains water, the content thereof is preferably in the range of 0.1% by mass to 95% by mass, and more preferably in the range of 50% by mass to 90% by mass with respect to the total mass of the maintenance liquid. .

(Physical properties etc. of maintenance liquid)
The maintenance liquid is preferably a liquid that does not cause aggregation when mixed with the ink composition of the present invention. If aggregation occurs, components such as pigments in the ink composition are further fixed to the ink jet head or the like, and the effect of the present invention is reduced. From such a viewpoint, the pH of the maintenance liquid preferably has a pH of 7.0 or more and 8.8 or less at 25 ° C.

From the viewpoint of workability, the viscosity at 20 ° C. of the maintenance liquid is preferably 1 mPa · s or more and 1000 mPa · s or less, more preferably 1 mPa · s or more and less than 500 mPa · s, further preferably 2 mPa · s or more and 100 mPa · s. -Less than s.
The measurement of the viscosity in the present invention is the same as the measurement method described in the section of the aggregate liquid.

The maintenance liquid of the present invention is preferably a colorless liquid containing no pigment.
Further, the content of the solid content (25 ° C.) in the maintenance liquid is not particularly limited, but is preferably 5% by mass or less from the viewpoint of preventing solids remaining after washing, and 2% by mass or less. It is more preferable that

Moreover, in this invention, you may use another solvent together in the range which does not impair the effect of this invention from a viewpoint of drying prevention, wettability improvement, and a permeability improvement.
The water-soluble organic solvent that can be used in combination can be appropriately selected from those other than n-ppanol described above as the water-soluble organic solvent.

  When the other solvent is used in combination, it is used in a range of 50% by mass or less, more preferably in a range of 0.1% by mass to 20% by mass with respect to n-ppanol contained in the maintenance liquid.

  Further, the content of the solid content (25 ° C.) in the maintenance liquid is not particularly limited, but is preferably 5% by mass or less from the viewpoint of preventing solids remaining after washing, and 2% by mass or less. It is more preferable that

  The ink set for ink-jet recording of the present invention comprises the ink composition and a maintenance liquid, and further includes a treatment liquid (hereinafter also referred to as “aggregated liquid”) described below. It is preferable to include.

3. Aggregating liquid The aggregating liquid used in the present invention is a liquid containing a component having a property of aggregating at least a pigment among the components contained in the ink composition by contacting with the ink composition.
The aggregating liquid contains at least one aggregating agent (hereinafter also referred to as “aggregation promoting agent”) capable of forming an agglomerate when contacted with the ink composition. By mixing the ink composition and the flocculant on the recording medium, aggregation of pigments and the like stably dispersed in the ink composition is promoted. Such an aggregating agent is preferably at least one selected from a cationic polymer, an acidic compound, and a polyvalent metal salt from the viewpoint of image quality to be formed.

As the cationic polymer, a polymer having a primary to tertiary amino group or a quaternary ammonium base as a cationic group is preferably used.
Examples of the cationic polymer include a homopolymer of a monomer having a primary to tertiary amino group and a salt thereof, or a quaternary ammonium base (cationic monomer), the cationic monomer and another monomer ( Those obtained as copolymers or condensation polymers with non-cationic monomers) are preferred. These polymers can be used in any form of water-soluble polymer or water-dispersible latex particles.
Specifically, poly (vinyl pyridine) salts, polyalkylaminoethyl acrylate, polyalkylaminoethyl methacrylate, poly (vinyl imidazole), polyethyleneimine, polybiguanide, polyguanide, and copolymers comprising epihalohydrin derivatives and amine derivatives, and It is selected from combinations thereof.

The aggregating liquid in the present invention may further comprise an aqueous solvent (for example, water) in addition to the cationic polymer.
The content of the cationic polymer in the aggregate liquid is preferably 5 to 95 mass%, more preferably 10 to 80 mass% with respect to the total mass of the aggregate liquid from the viewpoint of the aggregation effect.

Examples of the aggregation liquid containing an acidic compound include a liquid that can generate an aggregation by changing the pH of the ink composition. At this time, the pH (25 ° C.) of the aggregation liquid is preferably 1 or more and 6 or less, more preferably 2 or more and 5 or less, and more preferably 3 to 5 from the viewpoint of the aggregation rate of the ink composition. Is more preferable.
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 aggregate liquid is. The case of 3-5 is preferable.
The aggregating components can be used alone or in combination of two or more.

  The aggregation liquid can be constituted using at least one acidic compound as an aggregation accelerator. As the acidic compound, a compound having a phosphoric acid group, a phosphonic acid group, a phosphinic acid group, a sulfuric acid group, a sulfonic acid group, a sulfinic acid group, or a carboxyl group, or a salt thereof (for example, a polyvalent metal salt) may be used. it can. Among these, from the viewpoint of the aggregation rate of the ink composition, a compound having a phosphate group or a carboxyl group is more preferable, and a compound having a carboxyl group is still more preferable.

The compound having a carboxyl group includes 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 (for example, polyvalent metal salts), etc. It is preferable to be selected from among These compounds may be used alone or in combination of two or more.
The content of the acidic compound in the aggregate liquid is preferably 5 to 95 mass%, more preferably 10 to 80 mass%, based on the total mass of the aggregate liquid, from the viewpoint of the aggregation effect.

Moreover, what contains a polyvalent metal salt can be mentioned as a preferable example of the aggregation liquid which improves high-speed aggregation property. Examples of the polyvalent metal salt include salts of alkaline earth metals of the second group of the periodic table (for example, magnesium, calcium), transition metals of the third group of the periodic table (for example, lanthanum), and group 13 of the periodic table. And salts of lanthanides (for example, neodymium). As such a polyvalent metal salt, carboxylate (formic acid, acetic acid, benzoate, etc.), nitrate, chloride, and thiocyanate are suitable. Among them, preferred are calcium and magnesium salts of carboxylic acids (formic acid, acetic acid, benzoate, etc.), calcium nitrate, magnesium nitrate, calcium chloride, magnesium chloride, calcium thiocyanate, and magnesium thiocyanate.
The content of the metal salt in the aggregate liquid is preferably 1 to 10% by mass, more preferably 1.5 to 7% by mass, and still more preferably 2 to 6% by mass.

The viscosity of the aggregation 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. The range is more preferable, and the range of 2 mPa · s to 10 mPa · s is particularly preferable. The viscosity is measured under a condition of 20 ° C. using VISCOMETER TV-22 (manufactured by TOKI SANGYO CO. LTD).
In addition, the surface tension of the aggregation liquid is preferably 20 mN / m to 60 mN / m, more preferably 20 mN / m to 45 mN / m, and more preferably 25 mN / m from the viewpoint of the aggregation rate of the ink composition. More preferably, it is ˜40 mN / m. The surface tension is measured under conditions of 25 ° C. using an Automatic Surface Tensiometer CBVP-Z (manufactured by Kyowa Interface Science Co., Ltd.).

4). Image Forming Method An image forming method according to the present invention includes an ink application step of applying the ink composition in a pattern on a recording medium with an inkjet recording discharge head using the inkjet recording ink set, and the maintenance liquid. An ink removing step of removing the ink composition adhering to the ejection head.
Here, the “ink composition adhering to the ejection head” includes not only the “ink composition” itself but also “fixed matter” derived from the ink and adhered to the ejection head.

-Pattern formation process-
The pattern formation step in the present invention includes an ink application step in which the ink composition contained in the ink set for ink jet recording is ejected in a pattern onto a recording medium by the ink jet recording ejection head.
As an ink jet recording method, energy is supplied to the ink composition, and a known image receiving material, that is, plain paper, resin-coated paper, such as JP-A-8-169172, JP-A-8-27693, and JP-A-2-276670. Gazettes, 7-276789, 9-323475, JP-A-62-238783, JP-A-10-153898, 10-217473, 10-235995, 10- An image is formed on ink-jet exclusive paper, film, electrophotographic co-paper, fabric, glass, metal, ceramics, etc. described in JP-A Nos. 337947, 10-217597, and 10-337947. In addition, the description of paragraph numbers 0093 to 0105 in JP-A No. 2003-306623 can be applied as an ink jet recording method preferable for the present invention.

  As a discharge head for ink jet recording (hereinafter also simply referred to as a head), a known one can be applied, and a continuous type or a dot on demand type can be used. Among the dot-on-demand types, the thermal head is preferably a type having an operation valve as described in JP-A-9-323420 for discharging. As the piezo head, for example, the heads described in European Patent A277,703, European Patent A278,590 and the like can be used. The head preferably has a temperature control function so that the temperature of the ink can be controlled. In the ink ejection step, it is preferable to control the ink temperature so that the fluctuation range of the ink viscosity is within ± 5%. Moreover, as a drive frequency, it is preferable to operate | move at 1-500 kHz. The shape of the nozzle does not necessarily need to be circular, and is not particular about the shape such as an ellipse or a rectangle. The nozzle diameter is preferably in the range of 10 to 100 μm. The nozzle opening itself is not necessarily a perfect circle. In this case, the nozzle diameter is assumed to be a circle equivalent to the area of the opening.

  The temperature of the ink at the time of ink ejection in the ink ejection process is preferably 30 ° C. or higher from the viewpoint of controlling the temperature of the ink at the time of ejection and improving the wiping property, and more preferably 35 ° C. or higher. Further, from the viewpoint of ink stability and ejection reliability, 70 ° C. or lower is preferable.

  An ink repellent film is provided on the area of the ink discharge head where ink may adhere, particularly the nozzle surface (the surface of the nozzle plate on which the head discharge port is formed) in order to reduce ink adhesion. It is preferable. Preferred materials for forming the ink repellent film include perfluoropolymers such as PTFE, PFA, and FEP. In areas where such ink repellent films are formed, even if ink unintentionally flies at the time of printing, it is suppressed from adhering, and even if adhering ink is further dried, it can be wiped lightly. Can be easily removed.

-Ink removal process-
In the ink removing step, a maintenance liquid is applied to the ink jet head (for example, the periphery of the head and the ink flow path; hereinafter also referred to as the head) in order to remove the ink or the fixed matter derived from the ink from the nozzle surface of the head. To do.
By applying the maintenance liquid to the head or the like, the ink fixed matter derived from the ink on the nozzle surface is easily dissolved or swelled and removed.
In addition, before or after applying the maintenance liquid, scraping with a blade, wiping with a cloth or paper, or ink solid matter may be removed. Preferably, after applying the maintenance liquid, the nozzle surface is rubbed with a wiper blade (wiping), the ink adhering matter is scraped off, the air pressure or the maintenance liquid is removed, etc., and wiped with cloth or paper. A method is preferable, and among these, scraping with a blade and wiping with a cloth or paper are preferable.
The wiper blade is preferably made of rubber having elasticity, and specific materials include butyl rubber, chloroprene rubber, ethylene propylene rubber, silicone rubber, urethane rubber, nitrile rubber, and the like. In order to impart ink repellency to the wiper blade, a wiper blade coated with a fluorine resin or the like may be used.
Since the predetermined ink composition is used in the image forming method of the present invention, the ink fixed matter derived from the ink composition on the nozzle surface can be easily scraped off as a solid.

The image forming method of the present invention further includes a step (heat fixing step) of fixing the image by heating the recording medium after the image is formed by ejecting ink onto the recording medium in the ink applying step. May be.
The drying and removing step is not particularly limited except that the ink solvent (water and solvent) contained in the ink composition discharged onto the recording medium is removed by drying, and can be appropriately selected according to the purpose.
The heat fixing step is not particularly limited except that the polymer particles contained in the ink composition are softened to impart image abrasion resistance, and can be appropriately selected according to the purpose.
The recording medium in the present invention is not particularly limited, and examples thereof include plain paper, high-quality paper, and coated paper.

-Treatment liquid application process-
In the pattern forming step according to the image forming method of the present invention, a treatment liquid application step for applying the above-described treatment liquid on a recording medium before or after the above-described ink application step using the ink composition. It is preferable to contain.
The treatment liquid is applied onto the recording medium by applying the above-described treatment liquid to the entire recording medium using, for example, a roll coater, bar coater, spray coater, gravure coater, blade coater, air knife coater, or the like. In addition, an aggregating liquid discharge port is provided, and the aggregating liquid is discharged onto the recording medium from the aggregating liquid discharge port.

  In the present invention, an embodiment in which the ink application process is provided after the aggregation liquid is applied in the aggregation liquid application process is preferable. That is, before applying the ink composition on the recording medium, an aggregation liquid for aggregating particles such as pigments contained in the ink composition in advance is applied, and the treatment system applied on the recording medium An embodiment in which an ink composition is applied so as to come into contact with each other 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 the image forming method of the present invention, an intermediate transfer member is used as a recording medium for first recording an image, and an ink application step of applying the ink composition of the present invention to the intermediate transfer member by an ink jet method; And an aggregating liquid application step for providing an aggregating liquid capable of forming an agglomerate when contacted with the ink composition, and forming an image on the intermediate transfer body by bringing the ink composition and the aggregating liquid into contact with each other. Alternatively, a method may be provided in which a transfer step for transferring the image formed on the intermediate transfer member to a desired final recording medium is provided. Also in this case, an embodiment in which the ink application process is provided after the aggregation liquid is applied in the aggregation liquid application process is preferable.

The recording medium used in the image forming method according to the present invention includes general printing paper mainly composed of cellulose, such as so-called high-quality paper, coated paper, and art paper, used for general offset printing.
As the recording medium, commercially available media can be used. For example, “OK Prince fine quality” manufactured by Oji Paper Co., Ltd., “Shiorai” manufactured by Nippon Paper Industries Co., Ltd., and Nippon Paper Industries ( Fine coated paper such as “New NPI fine quality” manufactured by Co., Ltd., “OK Everlight Coat” manufactured by Oji Paper Co., Ltd., and “Aurora S” manufactured by Nippon Paper Industries Co., Ltd., Oji Lightweight coated paper (A3) such as “OK Coat L” manufactured by Paper Industries Co., Ltd. and “Aurora L” manufactured by Nippon Paper Industries Co., Ltd. “OK Top Coat +” manufactured by Oji Paper Co., Ltd. and Nippon Paper Industries Co., Ltd. ) Coated paper (A2, B2) such as “Aurora Coat” manufactured by Oji Paper Co., Ltd. Art paper (A1) such as “OK Kanfuji +” manufactured by Oji Paper Co., Ltd. and “Tokuhishi Art” manufactured by Mitsubishi Paper Industries Co., Ltd. Is mentioned. It is also possible to use various photographic papers for ink jet recording.

EXAMPLES The present invention will be specifically described below with reference to examples, but the present invention is not limited to these examples. Unless otherwise specified, “parts” and “%” are based on mass.
The weight average molecular weight was measured by gel permeation chromatography (GPC). GPC uses HLC-8220GPC (manufactured by Tosoh Corporation), and three columns are connected in series using TSKgeL SuperHZM-H, TSKgeL SuperHZ4000, and TSKgeL SuperHZ2000 (all are trade names of Tosoh Corporation). , THF (tetrahydrofuran) was used as an eluent. The conditions were as follows: the sample concentration was 0.35% by mass, the flow rate was 0.35 ml / min, the sample injection amount was 10 μl, the measurement temperature was 40 ° C., and an IR detector was used. In addition, the calibration curve is “standard sample TSK standard, polystyrene” manufactured by Tosoh Corporation: “F-40”, “F-20”, “F-4”, “F-1”, “A-5000”, It produced from eight samples of "A-2500", "A-1000", and "n-propylbenzene".

<Preparation of inkjet ink composition>
(Synthesis of water-insoluble resin B)
To a 1000 ml three-necked flask equipped with a stirrer and a condenser tube, 88 g of methyl ethyl ketone was added and heated to 72 ° C. in a nitrogen atmosphere. Here, 50 g of methyl ethyl ketone was mixed with 0.85 g of dimethyl 2,2′-azobisisobutyrate and 60 g of benzyl methacrylate. Then, a solution in which 10 g of methacrylic acid and 30 g of methyl methacrylate were dissolved was dropped over 3 hours. After completion of the dropwise addition, the mixture was further reacted for 1 hour, and then a solution of 0.42 g of dimethyl 2,2′-azobisisobutyrate in 2 g of methyl ethyl ketone was added, heated to 78 ° C. and heated for 4 hours. The obtained reaction solution was poured into a large excess of hexane and reprecipitated twice, and then the precipitated resin was dried to obtain 96 g of water-insoluble polymer dispersant B.
The composition of the obtained resin was confirmed by 1H-NMR to be a copolymer of benzyl methacrylate, methacrylic acid, and methyl methacrylate. Moreover, the weight average molecular weight (Mw) calculated | required by GPC was 44,600. Furthermore, when the acid value was calculated | required by the method as described in JIS specification (JISK0070: 1992), it was 65.2 mgKOH / g.

(Preparation of colored particle dispersion C)
Pigment Blue 15: 3 (phthalocyanine blue A220, manufactured by Dainichi Seika Kogyo Co., Ltd .; cyan pigment), 5 parts of the water-insoluble resin B, 42 parts of methyl ethyl ketone, and 1 mol / L aqueous NaOH solution 5 0.5 part and 87.2 parts of ion-exchanged water were mixed and dispersed by a bead mill using 0.1 nmφ zirconia beads for 2 to 6 hours.
After removing methyl ethyl ketone at 55 ° C. under reduced pressure and further removing a part of the water under reduced pressure, using a high-speed centrifugal cooler 7550 (manufactured by Kubota Seisakusho), using a 50 mL centrifuge tube, Centrifugation was performed at 8000 rpm for 30 minutes, and the supernatant liquid other than the precipitate was collected. Thereafter, the pigment concentration was determined from the absorbance spectrum, and colored particle dispersion C was obtained as a dispersion of resin-coated pigment particles (pigment coated with a polymer dispersant) having a pigment concentration of 10.2% by mass.

(Preparation of self-dispersing polymer particles)
In a 2 liter three-necked flask equipped with a stirrer, a thermometer, a reflux condenser, and a nitrogen gas introduction tube, 540.0 g of methyl ethyl ketone was charged, and the temperature was raised to 75 ° C. in a nitrogen-free atmosphere. While maintaining the temperature in the reaction vessel at 75 ° C., 216 g of methyl methacrylate (MMA), 280.8 g of isobornyl methacrylate (IBOMA), 43.2 g of methacrylic acid (MAA), 108 g of methyl ethyl ketone, and “V-601” (Wako Pure) A mixed solution consisting of 2.16 g (manufactured by Yakuhin Kogyo Co., Ltd.) was added dropwise at a constant speed so that the addition was completed in 2 hours. After completion of the dropwise addition, a solution consisting of 1.08 g of “V-601” and 15.0 g of methyl ethyl ketone was added, stirred for 2 hours at 75 ° C., and then a solution consisting of 0.54 g of “V-601” and 15.0 g of methyl ethyl ketone was added. after stirring for 2 hours at 75 ° C., further stirred for 2 hours by heating to 85 ° C., to obtain a copolymer solution M MA / IBOMA / MAA = 40 /52/8 by weight ratio.
The weight average molecular weight (Mw) of the obtained copolymer was 63000, and the acid value was 52.1 (mgKOH / g).

  Next, 588.2 g of the copolymer solution was weighed, 165 g of isopropanol and 120.8 ml of 1 mol / L NaOH aqueous solution were added, and the temperature in the reaction vessel was raised to 80 ° C. Next, 718 g of distilled water was added dropwise at a rate of 20 ml / min to disperse in water. Then, the solvent was distilled off by keeping the reaction vessel internal temperature at 80 ° C. for 2 hours, 85 ° C. for 2 hours and 90 ° C. for 2 hours under atmospheric pressure. Furthermore, the pressure in the reaction vessel was reduced, and isopropanol, methyl ethyl ketone, and distilled water were distilled off to obtain an aqueous dispersion P of the above copolymer having a solid content concentration of 26.0%.

The I / O value of the copolymer contained in the obtained aqueous dispersion P was 0.50. Moreover, it was 160 degreeC when the glass transition temperature was measured with the following method.
The amount of the copolymer solution after the above polymerization, which was 0.5 g as a solid content, was particularly dried under reduced pressure at 50 ° C. for 4 hours to obtain a polymer solid content. Using the obtained polymer solid content, Tg was measured with a differential scanning calorimeter (DSC) EXSTAR 6220 manufactured by SII Nanotechnology. Measurement conditions were such that a sample amount of 5 mg was sealed in an aluminum pan, and the peak top value of DDSC of the measurement data at the second temperature increase in the following temperature profile was defined as Tg in a nitrogen atmosphere.
30 ° C to -50 ° C (cooled at 50 ° C / min)
−50 ° C. → 230 ° C. (temperature rise at 20 ° C./min)
230 ° C → -50 ° C (cooled at 50 ° C / min)
−50 ° C. → 230 ° C. (temperature rise at 20 ° C./min)

(Preparation of ink-jet ink composition)
Using the dispersion C of the resin-coated pigment particles obtained above and the aqueous dispersion P, each component was mixed so as to have the following ink composition. This was packed in a plastic disposable syringe and filtered through a PVDF 5 μm filter (Millex-SV, diameter 25 mm, manufactured by Millipore) to obtain cyan ink (inkjet ink composition) C-01. The pH of this cyan ink C-01 was 8.6.

~ Ink composition ~
・ Cyan pigment (Pigment Blue 15: 3): 4%
-Water-insoluble resin B (solid content): 2%
Aqueous dispersion P (solid content): 8%
・ Sanix GP250: 10%
(Sanyo Chemical Industries, hydrophilic organic solvent, I / O value 1.30)
Tripropylene glycol monomethyl ether (TPGmME): 6%
(Wako Pure Chemical Industries, Ltd., hydrophilic organic solvent, I / O value 0.80)
・ Orphine E1010 (manufactured by Nissin Chemical Industry Co., Ltd., surfactant): 1%
・ Ion exchange water: 69%

  In the preparation of the cyan ink C-01, the yellow ink Y-01 (pH) was prepared in the same manner as above except that the pigment was changed from Pigment Blue 15: 3 to Pigment Yellow 74, Pigment Red 122, and Carbon Black. = 8.4), magenta ink M-01 (pH = 8.7), and black ink K-01 (pH = 8.6), respectively.

(Preparation of inkjet head cleaning solution)
An inkjet head cleaning liquid A comprising the following components was prepared.
When the viscosity, surface tension, and pH of the cleaning liquid were measured, the viscosity was 2.0 mPa · s, the surface tension was 27.7 mN / m, and the pH was 8.5.
The viscosity was measured under the condition of 25 ° C. using VISCOMETER Tv-22 (manufactured by TOKI SANGYO CO. LTD). The surface tension was measured using an Automatic Surface Tensiometer CBVP-Z (Kyowa Interface Science Co., Ltd.) at 25 ° C. The pH was measured at 25 ° C. ± 1 ° C.

~ Composition of maintenance liquid A ~
・ N-propanol (Wako Pure Chemical Industries, Ltd.): 20.0g
・ Orphine E1010 (Nisshin Chemical Industry Co., Ltd., surfactant): 1.0 g
・ Ion-exchanged water: 79.0 g

  In the preparation of the maintenance liquid A, maintenance liquids B to I were prepared in the same manner as described above except that the solvent type, the solvent amount, the surfactant type, and the surfactant amount were changed as shown in Table 1 below.

(Evaluation of ink washability)
After cutting the silicon wafer into 1.2 cm x 3.0 cm, each 30 μL of inkjet ink Y-01, M-01, C-01, K-01 containing polymer particles is weighed with a micropipette and placed on the silicon wafer. Dripping into. The ink spread on the silicon wafer is left as it is at room temperature for 16 hours to dry the ink. After the silicon wafer with the dried ink is attached to a glass sample bottle for 25 ml, add 20 ml of inkjet head cleaning liquids A to I to the sample bottle, close the lid, and soak the dried ink in the cleaning liquid. Leave for 16 hours at room temperature. After the lapse of 16 hours, the silicon wafer is taken out, and the glass sample bottle is shaken 2 to 3 times to make the cleaning solution uniform, and then the absorbance of the cleaning solution is measured. Assuming that the dried ink solid solution was completely dissolved and redispersed, the ink solution that was dropped into 20 ml of ion-exchanged water without drying and solidifying the ink (type), the ratio of the absorbance of the cleaning liquid to the absorbance of the type: The evaluation of the cleaning ability of the maintenance liquid was evaluated according to the following evaluation criteria. ◎ means the highest detergency.

-Evaluation criteria for ink washability-
A: Rabs is 95% or more. B: Rabs is 80% or more and less than 95%. Δ: Rabs is 50% or more and less than 80%. X: Rabs is less than 50%.

表２の結果から、本発明のメンテナンス液は、イエロー、マゼンタ、シアン、ブラックの全てのインクに対して良好な洗浄性を有することがわかる。

From the results in Table 2, it can be seen that the maintenance liquid of the present invention has good cleaning properties for all the inks of yellow, magenta, cyan and black.

(Storage stability of maintenance liquid)
Each of the maintenance liquids A to I was stored under the following environment, and the pH (25 ° C.) after storage was measured and compared with the pH (25 ° C.) immediately after preparation. The obtained results are shown in Table 3.
Storage condition 1: 14 days in 60 ° C incubator Storage condition 2: 28 days at room temperature (about 25 ° C)

Based on the amount of pH change represented by the following formula, storage stability was evaluated according to the following evaluation criteria.
ΔpH = (pH immediately after preparation) − (pH after storage)
~Evaluation criteria~
AA: When ΔpH is within 0.3 A: When ΔpH is larger than 0.3 and smaller than 0.5 B: When ΔpH is larger than 0.5 and smaller than 2.0 C: When ΔpH is larger than 2.0

(Erosion of maintenance liquid on ink repellent film)
a) Preparation of silane coupling layer (ink repellent film) The surface of a silicon substrate with a thermally oxidized silicon film formed on the surface is etched with oxygen gas in Ar gas to activate the surface, and then contains fluorine atoms The silane coupling agent (product name: manufactured by NANOS-B T & K Co., Ltd.) was used to form a silane coupling layer with a thickness of 20 nm on the surface to form an ink repellent film. .

b) Contact angle evaluation with respect to ink repellent film Contact angle: α of the cyan ink C-01 obtained in the above example with respect to the surface of the ink repellent film prepared above was measured using a contact angle meter drop master DM700 (Kyowa Interface Science ( It was calculated | required using Co., Ltd. product.
Separately from this, the silicon substrate having the ink repellent film obtained above was cut into 2 cm × 4 cm, and then immersed in 50 ml of the maintenance liquid prepared in Examples and Comparative Examples, and sealed at 45 ° C. × Left for 100 hours. Thereafter, the silicon substrate is taken out of the maintenance liquid, and the contact angle: β with respect to cyan ink C-01 is obtained in the same manner as the measurement of the contact angle before immersion, and the value obtained by subtracting the contact angle α from the contact angle β: The erodibility was evaluated according to the evaluation criteria. A indicates the least erosion.
~Evaluation criteria~
A: γ ≦ 15 °
B: 15 ° <γ ≦ 30 °
C: 30 ° <γ ≦ 50 °
D: 50 ° <γ
The ink contact angle before immersion was 85 °. Similar results were obtained even when other color inks Y-01, M-01, and K-01 were used. For G and I where the results of the detergency test are not preferable, the contact angle of the surface after immersion in the nozzle plate is not measured.
The obtained results are shown in Table 3.

  From the results in Table 3, it can be seen that the maintenance liquid used in the present invention has excellent storage stability and does not corrode the discharge head.

(Image formation and evaluation)
The ink composition, the treatment liquid, and the maintenance liquid obtained above were combined to make an ink set.

Tokishi Art Double Sided N (84.9 g / m ² , manufactured by Mitsubishi Paper Industries Co., Ltd.) as a recording medium is fixed on a stage that can move in a predetermined linear direction at 500 mm / second, and the agglomerated liquid is attached to the wire bar. The coating was applied to a thickness of about 5 μm with a coater, and was dried at 50 ° C. for 2 seconds immediately after coating.

[Evaluation of maintainability]
As ink-jet recording apparatus, using an inkjet printer was modified by Ricoh Co. GELJET GX5000 printer, Dashizukuryou 3.5 pL, an ink coating amount is below the ink composition in an amount of ^{5g / m 2 (1) ~} (3 ) After discharging under the conditions of the above, the maintenance liquid loaded in the inkjet printer is applied to the nozzle surface of the head with a roller, and then the nozzle surface of the inkjet head is wiped with a wiper blade (hydrogenated NBR). The pass / fail was determined from the result of the evaluation of the dischargeability. Subsequently, the maintainability was evaluated according to the following evaluation criteria. The results are shown in Table 4.
Note that an ink repellent film formed using a fluorine-based silane coupling agent is formed on the surface of the nozzle plate of the head.

-Evaluation criteria for re-ejectability evaluation-
(1) Immediately after the end of continuous ejection for 60 minutes, blade wipe is performed once.
(2) Pause for 30 minutes after ejection for 1 minute, perform blade wipe once after the suspension, and pass if the subsequent ink ejection rate is 90% or more.
(3) When the blade wipe is performed once immediately after the end of the discharge for 10 minutes and no image unevenness is observed in the image formed thereafter, it is passed.

-Measurement method of ink discharge rate-
After confirming that all nozzles were discharging at the start of the experiment, the number of discharge nozzles after the experiment including maintenance was counted, and the discharge rate was calculated as follows.
Discharge rate (%) = [number of discharge nozzles after maintenance] / [total number of nozzles] x 100 (%)
~Evaluation criteria~
A: When all three items pass B: When two items pass C: When only one item passes D: When all three items fail

  From the results of Table 4, when the ink set for ink jet recording according to the present invention is used, even when a maintenance liquid stored for a long period of time is used, the performance immediately after manufacture is maintained, and an image with excellent image quality over a long period of time. Can be understood.

Claims (12)

  An ink set for ink jet recording, comprising: an ink composition containing water, a pigment and polymer particles; and a maintenance liquid containing n-propanol.   The ink set for inkjet recording according to claim 1, wherein the maintenance liquid contains a surfactant.   The ink set for inkjet recording according to claim 2, wherein the surfactant is a nonionic surfactant.   The ink set for inkjet recording according to any one of claims 1 to 3, wherein the polymer particles are derived from a polymer latex.   The ink set for inkjet recording according to any one of claims 1 to 4, wherein the polymer particles have an I / O value of 0.2 or more and 0.55 or less.   The ink set for inkjet recording according to any one of claims 1 to 5, wherein the ink composition has a pH of 7.5 or more and 12 or less.   Furthermore, the ink set for inkjet recording as described in any one of Claims 1-6 containing the process liquid containing the coagulant | flocculant which aggregates at least one of the pigment and polymer particle which are contained in the said ink composition.   The ink set for inkjet recording according to claim 7, wherein the treatment liquid has a pH of 1 or more and 6 or less.   The ink set for inkjet recording according to claim 7 or 8, wherein the treatment liquid contains water and an organic acid. The ink set for inkjet recording according to any one of claims 1 to 6, is used,
Image formation comprising: an ink application step of applying the ink composition in a pattern from a discharge head for inkjet recording onto a recording medium; and an ink removal step of removing the ink composition attached to the discharge head by the maintenance liquid Method. The ink set for inkjet recording according to any one of claims 7 to 9, is used,
An ink application step of applying the ink composition in a pattern from a discharge head for inkjet recording onto a recording medium;
A treatment liquid application step of applying the treatment liquid onto a recording medium;
An ink removing step of removing the ink composition adhering to the ejection head by the maintenance liquid;
An image forming method comprising:   The image forming method according to claim 10, wherein at least a part of the inkjet recording ejection head has an ink repellent film.