JP7122177B2 - Method for producing oil-based inkjet ink - Google Patents

Description

Embodiments of the present invention relate to methods for producing oil-based inkjet inks.

The inkjet recording method ejects droplets of highly fluid inkjet ink from fine nozzles to record an image on a recording medium placed facing the nozzles, enabling high-speed printing with low noise. Therefore, it has spread rapidly in recent years. The inks used in such an inkjet recording method include water-based inks containing water as the main solvent, ultraviolet curable inks (UV inks) containing a high content of polymerizable monomers as the main component, and high inks containing wax as the main component. A so-called non-aqueous ink containing a non-aqueous solvent as a main solvent is known together with a hot-melt ink (solid ink) that contains a content. Non-aqueous ink can be classified into solvent ink (solvent-based ink) whose main solvent is a volatile organic solvent, and oil-based ink (oil-based ink) whose main solvent is a low-volatile or non-volatile organic solvent. Solvent ink dries on the recording medium mainly by evaporation of the organic solvent, whereas oil-based ink dries mainly by permeation into the recording medium.

Improving ink performance by enclosing a coloring material in a resin to form colored resin particles has been studied.
Patent Document 1 discloses the use of an oil-based inkjet ink in which a compound having an α value of 5 to 60 is added as a side chain and a capsule-type pigment surface-treated with a solvent-miscible comb-shaped polyurethane compound is used. there is Patent Document 1 discloses a method for producing this oil-based inkjet ink by mixing a comb-shaped polyurethane compound dissolved in a low-boiling aprotic solvent such as methyl ethyl ketone with a pigment or the like, dispersing the mixture, and then volatilizing the low-boiling solvent. discloses a method.

JP 2011-57812 A

The ink used in Patent Document 1 uses a volatile organic solvent in the ink manufacturing process. In such a case, equipment corresponding to explosion protection is usually required, and there is a problem in safety during manufacturing.
An object of an embodiment of the present invention is to provide a method for producing an oil-based inkjet ink containing colored resin particles that does not require the use of a volatile organic solvent and is excellent in safety.

An embodiment of the present invention includes a step of producing a water-in-oil emulsion comprising a continuous phase containing a non-aqueous solvent and a dispersant, and a dispersed phase containing water, a coloring material, and a water-dispersible resin; and a step of removing the water from the aqueous emulsion.

According to the embodiment of the present invention, it is possible to provide a method for producing an oil-based inkjet ink containing colored resin particles, which does not require the use of a volatile organic solvent and is excellent in safety.

Embodiments of the present invention will be described below, but the following embodiments do not limit the present invention.
Hereinafter, the oil-based inkjet ink may be referred to as "ink" or "oil-based ink".

A method for producing an oil-based inkjet ink according to an embodiment of the present invention prepares a water-in-oil emulsion containing a continuous phase containing a non-aqueous solvent and a dispersant, and a dispersed phase containing water, a coloring material, and a water-dispersible resin. and a step of removing water from the water-in-oil emulsion (hereinafter sometimes referred to as “step 2”).

Methods for producing oil-based inkjet inks containing colored resin particles are generally classified broadly into methods using chemical techniques and methods using physicochemical techniques. For example, chemical methods include an interfacial polycondensation method, an interfacial reaction method (in situ polymerization method), a liquid curing film method (orifice method), and the like. Physicochemical techniques include a liquid drying method (water drying method, oil drying method), a coacervation method, a melting dispersion cooling method, and the like.

For example, the method of producing oil-based inkjet ink by the coacervation method uses volatile organic solvents in the production process, which requires explosion-proof facilities and safety considerations during production. becomes. In the coacervation method, the resin is dissolved in a mixed solvent of a non-aqueous solvent and a volatile organic solvent, and the volatile organic solvent is removed by reducing pressure and/or heating, thereby precipitating the resin around the pigment. However, there are problems such as the generation of unadsorbed resin on the pigment and the variation in the size of the precipitated resin, which limits the amount of resin to be blended.

The ink manufacturing method of the present embodiment uses a method of drying a water-in-oil emulsion in oil. This method does not require the use of volatile organic solvents and is highly safe.

A step (“step 1”) of preparing a water-in-oil emulsion containing a continuous phase containing a non-aqueous solvent and a dispersant and a dispersed phase containing water, a coloring material, and a water-dispersible resin will be described.

The dispersed phase can contain pigments, dyes, or combinations thereof as colorants.

Examples of pigments that can be used include organic pigments such as azo pigments, phthalocyanine pigments, polycyclic pigments and dyed lake pigments, and inorganic pigments such as carbon black and metal oxides.
Examples of azo pigments include soluble azo lake pigments, insoluble azo pigments and condensed azo pigments. Examples of phthalocyanine pigments include metal phthalocyanine pigments and metal-free phthalocyanine pigments. Polycyclic pigments include quinacridone-based pigments, perylene-based pigments, perinone-based pigments, isoindoline-based pigments, isoindolinone-based pigments, dioxazine-based pigments, thioindigo-based pigments, anthraquinone-based pigments, quinophthalone-based pigments, and metal complex pigments. and diketopyrrolopyrrole (DPP). Examples of carbon black include furnace carbon black, lamp black, acetylene black, channel black and the like. Examples of metal oxides include titanium oxide and zinc oxide. These pigments may be used alone or in combination of two or more.

From the viewpoint of ejection stability and storage stability, the average particle size of the pigment is preferably 300 nm or less, more preferably 200 nm or less.
The amount of the pigment is usually 0.01 to 20% by mass, preferably 1 to 15% by mass, based on the total amount of the ink, from the viewpoint of image density and ink viscosity.

The pigment can be preferably used in the form of an aqueous dispersion dispersed in water.
As the pigment, a self-dispersing pigment may be used in which a water-solubilizing group such as a carboxy group, a carbonyl group, a hydroxy group, a sulfo group, or the like is bonded to the surface of the pigment so that the pigment itself is dispersed in water. . For example, an aqueous dispersion of a self-dispersing pigment can be preferably used.
Alternatively, it is also preferable to disperse the pigment in water using, for example, a pigment dispersant such as a water-soluble nonionic dispersant described later.

Any dyes commonly used in the art can be used as the dye. As the dye, it is preferable to use a dye that dissolves or disperses in water. From the viewpoint of reducing strike-through, it is preferable to use a material that is difficult or insoluble in the non-aqueous solvent contained in the ink.
Dyes include basic dyes, acid dyes, direct dyes, soluble vat dyes, acid mordant dyes, mordant dyes, reactive dyes, vat dyes, sulfur dyes, etc. Sexual dyes can be preferably used. Disperse dyes such as azo, anthraquinone, azomethine, and nitro dyes are also preferably used. You may use these individually or in combination of multiple types.
The amount of the dye is usually 0.01 to 20% by mass, preferably 1 to 15% by mass, more preferably 5 to 10% by mass, based on the total amount of the ink, from the viewpoint of image density and ink viscosity. .

The amount of the coloring material is preferably 1 to 50% by mass, more preferably 5 to 40% by mass, based on the total amount of the dispersed phase. The amount of the coloring material is preferably 1 to 30% by mass, more preferably 2 to 20% by mass, relative to the total amount of the water-in-oil emulsion.

The dispersed phase can include a water-dispersible resin. A water-dispersible resin has the property of being able to be dispersed in a particulate form without being dissolved in water. The water-dispersible resin is desirably added in the form of a resin particle dispersion (resin emulsion) preliminarily dispersed in a liquid such as water.

Water-dispersible resins include water-dispersible resins having acidic groups, water-dispersible resins having basic groups, and water-dispersible resins having neither acidic groups nor basic groups (nonionic water-dispersible resins). Any of them can be used, but it is preferable to contain a water-dispersible resin having an acidic group. As the acidic group, a carboxy group, a sulfo group, and the like are preferable.
A water-dispersible resin having an acidic group is considered to have a function of, for example, facilitating suppression of aggregation when shear is applied during ink production. When a water-dispersible resin having an acidic group is used, it tends to be excellent in fixability, ink viscosity, and storage stability.

Examples of water-dispersible resins include water-dispersible urethane resins, water-dispersible polyester resins, water-dispersible (meth)acrylic resins, water-dispersible (meth)acrylic silicone resins, water-dispersible vinyl chloride resins, water-dispersible Styrene (meth)acrylic resin and the like can be mentioned. Among these, water-dispersible urethane resins and water-dispersible (meth)acrylic resins are preferred from the viewpoint of fixability and storage stability, water-dispersible urethane resins having acidic groups, and water-dispersible urethane resins having acidic groups. (Meth)acrylic resins are more preferred. A (meth)acrylic resin means a resin containing a methacrylic unit, a resin containing an acrylic unit, or a resin containing both of these units. The same applies to (meth)acrylic resins below.

A water-dispersible urethane resin has a urethane group (“—NH—CO—O—”). In general, urethane groups (“—NH—CO—O—”) of urethane resins can be obtained by reacting polyols with polyisocyanates.
As the water-dispersible urethane resin, for example, a water-dispersible urethane (meth)acrylic resin can be used. As the water-dispersible urethane (meth)acrylic resin, for example, it is also preferable to use a resin using a (meth)acrylic resin having a plurality of hydroxyl groups as a polyol.
In addition, as the water-dispersible urethane resin, in addition to the urethane group ("-NH-CO-O-"), there is also a water-dispersible urethane urea resin that further has a urea group ("-NH-CO-NH-"). preferable.
The urethane urea resin can be produced, for example, by reacting a urethane prepolymer obtained from a material containing a polyol and a polyisocyanate with water and/or a polyamine compound so that the isocyanate groups of the urethane prepolymer and the water and/or the polyamine compound are It can be obtained by chain extension by generating a urea group through reaction.

From the viewpoint of storage stability and weather resistance, the water-dispersible urethane resin preferably uses an aliphatic polyisocyanate as the polyisocyanate.

The solubility of the water-dispersible resin in the non-aqueous solvent of the ink is preferably 1 g or less as the amount of urethane urea resin that can be dissolved in 100 g of the non-aqueous solvent of the ink at 23°C. It is thought that when the solubility of the water-dispersible resin in the non-aqueous solvent becomes low, the colored resin particles are likely to leave the non-aqueous solvent and remain on the surface of the recording medium when the non-aqueous solvent penetrates into the recording medium. . Therefore, when the solubility of the ink in the non-aqueous solvent is 1 g or less as the amount of the water-dispersible resin that can be dissolved in 100 g of the non-aqueous solvent of the ink at 23° C., the strike-through is reduced and the image density is obtained. tend to be vulnerable. Furthermore, it is thought that the fact that the water-dispersible resin is difficult to dissolve in the non-aqueous solvent also contributes to lowering the viscosity of the ink.

The weight average molecular weight of the water-dispersible resin varies depending on the type of resin, but is preferably 5,000 to 200,000, more preferably 10,000 to 150,000. For example, the weight average molecular weight of the water-dispersible urethane resin is preferably 5,000 to 50,000, more preferably 10,000 to 30,000. The weight average molecular weight of the water-dispersible (meth)acrylic resin is preferably 10,000 to 200,000, more preferably 30,000 to 150,000.
The weight-average molecular weight of the water-dispersible resin is a value obtained by standard polystyrene conversion by the GPC method. The same applies to the weight-average molecular weight of resins and the like described below.

Examples of commercially available water dispersions of water-dispersible resins include, for example, WS5984 and WS4022 manufactured by Mitsui Chemicals, Inc., and supermarkets manufactured by Daiichi Kogyo Seiyaku Co., Ltd. Flex 740, Super Flex 150H, Super Flex 500M, Super Flex 620, TW1262 manufactured by Daicel Allnex Co., Ltd., and the like. These are aqueous dispersions of water-dispersible urethane urea resins. Among these, TW1262 manufactured by Daicel Allnex Co., Ltd. is a commercial product of water dispersion of water-dispersible urethane (meth)acrylic resin using (meth)acrylic resin having a plurality of hydroxyl groups as a polyol. Examples of commercial products of water dispersions of water-dispersible (meth)acrylic resins include Movinyl 6969D manufactured by The Nippon Synthetic Chemical Industry Co., Ltd., and the like.
Examples of commercially available products of aqueous dispersions of water-dispersible resins having acidic groups include WS5984 and WS4022 manufactured by Mitsui Chemicals, Inc.; TW1262 manufactured by Allnex Co., Ltd., Movinyl 6969D manufactured by Nippon Synthetic Chemical Industry Co., Ltd., and the like.

A water-dispersible resin can be used individually by 1 type or in combination of 2 or more types.
The amount of water-dispersible resin can be adjusted appropriately. The amount of the water-dispersible resin is, for example, preferably 0.1% by mass or more, more preferably 0.5% by mass or more, based on the total amount of the ink, from the viewpoints of reducing strike-through, fixability, and storage stability. % by mass or more is more preferable, and 3% by mass or more is even more preferable. On the other hand, from the viewpoint of ink viscosity, the amount of the water-dispersible resin is preferably 30% by mass or less, more preferably 20% by mass or less, further preferably 15% by mass or less, and 10% by mass or less, relative to the total amount of the ink. is more preferred. The amount of the water-dispersible resin is, for example, preferably 0.1 to 30% by mass, more preferably 0.5 to 20% by mass, more preferably 1 to 15% by mass, and 3 to 10% by mass with respect to the total amount of the ink. % is more preferred.

The amount of the water-dispersible resin is preferably 0.1-40% by mass, more preferably 1-30% by mass, relative to the total amount of the dispersed phase. The amount of the water-dispersible resin is preferably 0.1 to 20% by mass, more preferably 1 to 15% by mass, relative to the total amount of the water-in-oil emulsion.

As water, tap water, ion-exchanged water, deionized water, or the like can be used.
In the water-in-oil emulsion, the amount of water is preferably 40-90% by mass, more preferably 50-80% by mass, based on the total amount of the dispersed phase. The amount of water is preferably 1 to 50% by mass, more preferably 5 to 50% by mass, even more preferably 10 to 40% by mass, relative to the total amount of the water-in-oil emulsion.

The dispersed phase may further comprise a pigment dispersant. Preferably, the colorant contains a pigment, and the dispersed phase may further contain a pigment dispersant. Examples of pigment dispersants include water-soluble basic (cationic) dispersants, water-soluble acidic (anionic) dispersants, and water-soluble nonionic dispersants. preferable.
A water-soluble nonionic dispersant is a dispersant in which the hydrophilic group does not have ionic dissociation. Water-soluble nonionic dispersants include, for example, ester-type water-soluble nonionic dispersants, ether-type water-soluble nonionic dispersants, ester/ether-type water-soluble nonionic and polydispersants.
Ester-type water-soluble nonionic dispersants have structures in which polyhydric alcohols such as glycerin, sorbitol and sucrose are ester-bonded with fatty acids, and examples thereof include glycerin fatty acid esters, sorbitan fatty acid esters and sucrose fatty acid esters.
Ether-type water-soluble nonionic dispersants can be prepared, for example, by mainly adding ethylene oxide to raw materials having hydroxyl groups such as higher alcohols, alkylphenols, arylphenols, and arylalkylphenols. aryl polyglycol ethers, alkyl polyglycol ethers). More specifically, there are polyoxyethylene alkyl ethers, polyoxyethylene alkylphenyl ethers, polyoxyethylene arylphenyl ethers, polyoxyethylene arylalkylphenyl ethers and the like.
The ester/ether type water-soluble nonionic dispersant is obtained by adding ethylene oxide to an ester composed of a polyhydric alcohol such as glycerin or sorbitol and a fatty acid. It has both an ester bond and an ether bond in its molecule. Examples include fatty acid polyethylene glycol ether esters.
Moreover, as a water-soluble nonionic dispersant, for example, a polycarboxylic acid polymer, a polysiloxane copolymer, or the like can be used.
These water-soluble nonionic dispersants can be used singly or in combination of two or more.

Fatty acid polyethylene glycol ether esters, polyglycol ethers (eg, arylpolyglycol ethers) and the like are more preferable as water-soluble nonionic dispersants.

By using a water-soluble nonionic dispersant, the pigment can be made finer in the ink production process, and the polymer compound efficiently covers the pigment, thereby controlling the particle size of the colored resin particles. is considered possible. In addition, it is believed that the image density can also be improved by this.
In addition, when a water-soluble nonionic dispersant is used, if the water-dispersible resin has an acidic group, it is easy to prevent pigment aggregation, and there is a tendency that an ink with even better storage stability can be produced.

A pigment dispersant can be used individually by 1 type or in combination of 2 or more types.
The amount of pigment dispersant can be set appropriately. For example, the weight ratio of the pigment dispersant to 1 part of the pigment can be 0.1 to 5, preferably 0.1 to 1. Also, the pigment dispersant can be blended in an amount of, for example, 0.01 to 10% by mass, preferably 0.01 to 5% by mass, based on the total amount of the ink.

The amount of the pigment dispersant is preferably 0.1 to 20% by mass, more preferably 1 to 10% by mass, relative to the total amount of the dispersed phase. The amount of the pigment dispersant is preferably 0.1 to 10% by mass, more preferably 0.5 to 5% by mass, relative to the total amount of the water-in-oil emulsion.
When the water-soluble nonionic dispersant is included, the water-soluble nonionic dispersant is preferably 50 to 100% by mass, more preferably 70 to 100% by mass, based on the total amount of the pigment dispersant.

The components of the continuous phase are explained.

The continuous phase can contain a dispersant (hereinafter sometimes referred to as "dispersant A"). Dispersant A is not particularly limited, and for example, dispersant A may include an ionic dispersant, a nonionic dispersant, or both. Ionic dispersants are dispersants with basic or acidic groups. Examples of the ionic dispersant include a basic dispersant that is a dispersant having a basic (cationic) group, and an acidic dispersant that is a dispersant having an acidic (anionic) group without having a basic group. However, dispersant A preferably contains an ionic dispersant, more preferably a basic dispersant.
It is believed that Dispersant A can act as an emulsifier. Further, when the dispersant A contains an ionic dispersant, the image density and storage stability of the ink tend to be improved, and the ink viscosity tends to be reduced. It is believed that the ionic dispersant contributes to the dispersion stability of the colored resin particles and also contributes to the storage stability of the ink. In addition, the basic dispersing agent can reduce the average particle size of the colored resin particles and narrow the particle size distribution, thereby contributing to the reduction of the ink viscosity.

The dispersant A preferably dissolves in the non-aqueous solvent contained in the ink. It is preferable to dissolve uniformly without separating into two phases.

A basic dispersant is a dispersant having a basic group. Basic groups include amino group, amido group, imino group, pyrrolidone group, morpholino group, nitrile group and the like. For example, examples of amino groups include unsubstituted amino groups and substituted amino groups such as mono- or dialkylamino groups (e.g., dimethylamino group, etc.). , may be substituted with a substituent such as an aryl group. Examples of amide groups similarly include unsubstituted amide groups and substituted amide groups such as mono- or dialkylamide groups (e.g., dimethylamide group, etc.). It may be substituted with a substituent such as a group. The basic dispersant may contain only one type of basic group, or two or more types.
An acidic dispersant is a dispersant that has acidic groups and no basic groups. Examples of acidic groups include a carboxy group (--COOH) and a sulfo group. The acidic dispersant may contain only one, or two or more acidic groups.
The basic dispersant may or may not have an acidic group.

Examples of the basic dispersant include, for example, a linear or branched dispersant having a basic group at the end of the main chain, and a polymer having a plurality of side chains containing a polyester portion having a basic group. A basic dispersant (hereinafter sometimes referred to as a "basic dispersant having a comb structure" or a "basic comb-shaped dispersant"), and a basic (meth)acrylic resin basic dispersant (hereinafter referred to as a "base It may be referred to as a "poly(meth)acrylic dispersant".) and the like.

From the viewpoint of improving storage stability by stabilizing the dispersion, the basic dispersant has a basic group and is a polymer having a plurality of side chains containing a polyester moiety (basic comb dispersant). preferably included.
As the side chain polyester portion of the basic dispersant (basic comb dispersant) having a plurality of side chains containing a polyester portion having a basic group, for example, a hydroxycarboxylic acid, or a hydroxycarboxylic acid and a hydroxy group structure derived from a mixture with a carboxylic acid that does not contain, a polymer having a carbonyl-C3-C6-alkyleneoxy group as a unit, and the like. Examples of structures derived from a mixture of a hydroxycarboxylic acid and a carboxylic acid containing no hydroxy group include a carbonyl-C17-alkyleneoxy group derived from a self-condensate of 12-hydroxystearic acid. The carbonyl-C3-C6-alkyleneoxy group includes, for example, a carbonyl-C5-alkyleneoxy group. For example, a polymer having a carbonyl-C5-alkyleneoxy group as a unit can be obtained by ring-opening polymerization of ε-caprolactone. Obtainable.
The degree of polymerization of the polyester portion is not particularly limited, and may be, for example, about 2-80.

The basic comb dispersant may contain basic groups, for example, in the backbone in the form of a polyamine backbone, and/or have basic groups bonded directly to the backbone or via a linking group. may contain.
When the basic comb dispersant contains a basic group bonded directly to the main chain or via a linking group, the basic comb dispersant may have one or more basic groups, but may have two or more. is preferred. In addition, the type of basic group bonded to the main chain directly or via a linking group is not particularly limited, and for example, the basic groups described above can be used. Amino groups are more preferred.
Examples of the basic comb-shaped dispersant include, for example, a basic dispersant that is a polymer having a main chain containing a polyamine skeleton and a plurality of side chains containing a polyester portion (hereinafter referred to as "basic comb-shaped dispersant a" ), And a basic dispersant that is a polymer having a basic group linked directly or via a linking group to the main chain and having a plurality of side chains containing a polyester moiety (hereinafter referred to as "basic Comb-shaped dispersant b" may be mentioned.) and the like.

A polymer (basic comb-shaped dispersant a) having a main chain containing a polyamine skeleton and a plurality of side chains containing a polyester portion will be described.
In the basic comb-shaped dispersant a, the polyamine skeleton of the main chain includes, for example, a polyalkyleneimine skeleton. Examples of polyalkyleneimine having a polyalkyleneimine skeleton include alkyleneimine having 2 to 8 carbon atoms such as ethyleneimine, propyleneimine, butyleneimine, dimethylethyleneimine, pentyleneimine, hexyleneimine, heptyleneimine, and octyleneimine; Preferred are polymers obtained by polymerizing one or more alkyleneimines having 2 to 4 carbon atoms by conventional methods, and polymers chemically modified by reacting them with various compounds.
Examples of basic comb dispersants a include graft polymers in which the main chain comprises a polyamine skeleton such as a polyalkyleneimine and the graft chains comprise polyester chains. Although the weight-average molecular weight of the polymer containing a polyamine skeleton, which is the main chain, is not particularly limited, it is preferably 600,000 or less.

In the basic comb-shaped dispersant a, the side chain containing the polyester moiety is preferably bonded to the nitrogen atom of the polyamine skeleton of the main chain via an amide bond.
The method for producing the basic comb-shaped dispersant a is not particularly limited. A basic comb dispersant containing a main chain containing a polyamine skeleton such as a polyalkyleneimine skeleton and a side chain containing a polyester moiety includes, for example, a reaction between a polyamine such as a polyalkyleneimine and a polyester having a free carboxyl group. method.
Basic comb-shaped dispersant a has a polyamine skeleton, but may further have basic groups other than this, for example, may have basicity bonded directly to the main chain or via a linking group. .

A basic dispersant (“basic comb-shaped dispersant b”), which is a polymer having a basic group bonded directly or via a linking group to the main chain and having a plurality of side chains containing polyester moieties, will now be described.
Basic group The comb-shaped dispersant b may have one or more basic groups bonded directly or via a linking group to the main chain, but preferably has two or more. The type of basic group is not particularly limited, and for example, the basic groups described above can be used, but among them, amino group and morpholino group are preferable, and amino group is more preferable. The basic comb dispersant b may contain only one type or two or more types of basic groups.
Examples of the basic comb-shaped dispersant b include, for example, a unit having a basic group bonded directly to the main chain or via a linking group (hereinafter sometimes referred to as "unit Xa") and a side containing a polyester part a copolymer containing a unit having a chain (hereinafter sometimes referred to as "unit Xb").

In the unit Xa, the basic group is not particularly limited, and for example, the basic groups described above can be used. Among them, an amino group, an amido group and a morpholino group are preferable, and an amino group is more preferable.
The units Xa can be, for example, acrylic or methacrylic units.
Examples of units Xa include units in which a carbonyl group is bonded to the carbon chain of the main chain and a basic group is bonded to the carbonyl group directly or via a linking group. Examples of such units include units derived from monomers containing an acryloyl group or a methacryloyl group and a basic group. The basic group is preferably bonded to the carbonyl (CO) carbon atom of the acryloyl group or methacryloyl group directly or via a linking group.
Examples of the monomer containing an acryloyl group or a methacryloyl group and a basic group include (meth)acrylate having a basic group, (meth)acrylamide having a basic group, (meth)acryloylmorpholine and the like. Specific examples of monomers containing an acryloyl group or methacryloyl group and a basic group include dimethylaminoethyl (meth)acrylate, diethylaminoethyl (meth)acrylate, (meth)acryloylmorpholine, dimethyl(meth)acrylamide, and dimethylaminopropyl. (Meth)acrylamide and the like. (Meth)acrylate means acrylate, methacrylate or combinations thereof. (Meth)acrylamide means acrylamide, methacrylamide or combinations thereof. Hereinafter, the same applies to (meth)acrylate and (meth)acrylamide.

Unit Xa may be, for example, a unit derived from a monomer obtained by adding an amine compound to a monomer having an epoxy group. As the monomer having an epoxy group, for example, a monomer having an acryloyl group or a methacryloyl group and an epoxy group is preferable. Examples of the monomer containing an acryloyl group or methacryloyl group and a basic group include monomers obtained by adding an amine compound to a monomer having an acryloyl group or methacryloyl group and an epoxy group.
In the monomer having an acryloyl group or methacryloyl group and an epoxy group, the epoxy group is preferably bonded to the carbonyl (CO) carbon atom of the acryloyl group or methacryloyl group directly or via a linking group. Examples of monomers having an acryloyl group or methacryloyl group and an epoxy group include glycidyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate glycidyl ether, 3,4-epoxycyclohexylmethyl (meth)acrylate, and the like. .
As the amine compound to be added to the monomer having an epoxy group, an amine compound having a hydroxyl group (for example, alkanolamine, etc.) is preferable. Examples of the amine compound having a hydroxy group include benzylethanolamine, monoethanolamine, diethanolamine and the like, with diethanolamine being particularly preferred.
Examples of the monomer obtained by adding an amine compound to a monomer having an acryloyl group or a methacryloyl group and an epoxy group include a diethanolamine adduct of glycidyl (meth)acrylate and a benzylethanolamine adduct of glycidyl (meth)acrylate.
A unit derived from a monomer obtained by adding an amine compound to a monomer having an epoxy group can also be obtained, for example, by adding an amine compound to a unit derived from a monomer having an epoxy group, and the unit thus obtained may be

Units having side chains containing polyester moieties (units Xb) may be, for example, acrylic units or methacrylic units.
Examples of the unit Xb include a unit in which a carbonyl group is bonded to the carbon chain of the main chain, and a polyester moiety is bonded to the carbonyl group directly or via a linking group. Such units include, for example, units derived from monomers containing an acryloyl group or a methacryloyl group and a polyester moiety. The polyester moiety is preferably bonded to the carbonyl (CO) carbon atom of the acryloyl group or methacryloyl group directly or via a linking group.
A monomer containing an acryloyl group or methacryloyl group and a polyester moiety can be obtained, for example, by reacting a monomer containing an acryloyl group or methacryloyl group and an epoxy group with a hydroxycarboxylic acid condensate or the like. As the monomer having an acryloyl group or methacryloyl group and an epoxy group, for example, those listed above as examples of the monomer having an acryloyl group or methacryloyl group and an epoxy group can be used. As the hydroxycarboxylic acid condensate, for example, a 12-hydroxystearic acid 6-condensate can be used. For the reaction, for example, a catalyst such as tetrabutylammonium bromide and/or a polymerization inhibitor such as N-nitrosophenylhydroxyamine aluminum salt may be used.

The basic comb dispersant b may, for example, contain other units. Other units include, for example, a unit having an alkyl group having 1 to 8 carbon atoms (hereinafter sometimes referred to as "unit Xc"). As the alkyl group having 1 to 8 carbon atoms, an alkyl group having 1 to 4 carbon atoms is more preferable. Examples of the alkyl group having 1 to 8 carbon atoms include methyl group, ethyl group, butyl group, 2-ethylhexyl group and the like.
A unit having an alkyl group having 1 to 8 carbon atoms (unit Xc) may be, for example, an acrylic unit or a methacrylic unit.
Examples of the unit Xc include, for example, a unit in which a group represented by —COOR ^d is bonded to a carbon atom of the main chain of a (meth)acrylic resin, wherein R ^d has 1 to 8 carbon atoms (more preferably A unit that is an alkyl group having 1 to 4 carbon atoms can be mentioned.
As the unit Xc, for example, a unit derived from a monomer Xc described later can be used.

The basic comb dispersant b may contain only one type of unit Xa, or two or more types. Similarly, the basic comb dispersant b may contain only one, or two or more units Xb, respectively. Also, for example, when the basic dispersant contains the unit Xc, the unit Xc may be contained alone or in two or more.

Unit Xa is, for example, preferably 1 to 50% by mass, more preferably 2 to 40% by mass, and even more preferably 2 to 30% by mass, relative to the entire polymer.
Unit Xb is, for example, preferably 10 to 95% by mass, more preferably 20 to 90% by mass, and even more preferably 40 to 85% by mass, relative to the total polymer.
Unit Xc is, for example, preferably 1 to 90% by mass, more preferably 5 to 50% by mass, even more preferably 5 to 30% by mass, relative to the total polymer.
Here, the polymer as a whole is based on all units constituting basic comb dispersant b.

The basic comb-shaped dispersant b is, for example, a monomer having a basic group (hereinafter sometimes referred to as "monomer Xa") and a monomer having a side chain containing a polyester moiety (hereinafter sometimes referred to as "monomer Xb"). It can be obtained by polymerizing a monomer mixture containing and.
Examples of monomers having a basic group (monomer Xa) include, for example, the above-mentioned monomers containing an acryloyl group or a methacryloyl group and a basic group. Examples of the monomer having a side chain containing a polyester portion (monomer Xb) include, for example, the above-described monomers containing an acryloyl group or methacryloyl group and a polyester portion.
The monomer mixture contains, for example, in addition to or instead of the monomer having a basic group (monomer Xa), the above monomer having an epoxy group (for example, a monomer having an acryloyl group or a methacryloyl group and an epoxy group). After polymerization of the monomer mixture, the structure derived from the monomer having an epoxy group may be reacted with an amine compound to obtain a unit having a basic group (unit Xa).
The monomer mixture may contain other monomers, and examples of other monomers include monomers having an alkyl group having 1 to 8 carbon atoms (hereinafter sometimes referred to as "monomer Xc"). As the monomer having an alkyl group having 1 to 8 carbon atoms (monomer Xc), for example, a monomer having an acryloyl group or a methacryloyl group and an alkyl group having 1 to 8 carbon atoms is preferable. Preferred examples of the monomer Xc include alkyl (meth)acrylates having an alkyl group having 1 to 8 carbon atoms. Specific examples of the monomer Xc include methyl (meth)acrylate, ethyl (meth)acrylate, butyl (meth)acrylate, 2-ethylhexyl (meth)acrylate and the like.
The blending amount of each monomer in the monomer mixture can be adjusted, for example, so as to obtain a preferable proportion of each unit described above.

The monomer mixture can be polymerized by known radical copolymerization. As a reaction system, solution polymerization or dispersion polymerization is preferred.
In the polymerization reaction, a polymerization initiator, a chain transfer agent, a polymerization inhibitor, a polymerization accelerator, a dispersant, etc. can be appropriately added to the reaction system in order to adjust the reaction rate.
As the polymerization initiator, AIBN (azobisisobutyronitrile), 2,2'-azobis(2,4-dimethylvaleronitrile), 2,2'-azobis(4-methoxy-2,4-dimethylvaleronitrile) ), and thermal polymerization initiators such as peroxides such as t-butylperoxybenzoate and t-butylperoxy-2-ethylhexanoate. In addition, a photopolymerization initiator that generates radicals upon exposure to active energy rays can be used.
Moreover, the molecular weight of the obtained (meth)acrylic resin can be adjusted by using a chain transfer agent in the reaction system. As the chain transfer agent, thiols such as n-butyl mercaptan, lauryl mercaptan, stearyl mercaptan, cyclohexyl mercaptan and the like can be preferably used.
A polymerization solvent (reaction solvent) used for solution polymerization is not particularly limited, but a solvent capable of dispersing or dissolving a resin obtained by polymerization is preferable.

The weight average molecular weight of the basic comb dispersant b is preferably 5,000 to 50,000, more preferably 10,000 to 30,000.

The basic dispersant preferably contains, for example, a basic (meth)acrylic resin dispersant (basic (meth)acrylic dispersant) from the viewpoint of lowering the viscosity of the ink. A basic (meth)acrylic resin is a (meth)acrylic resin having a basic group.
The basic (meth)acrylic dispersant contains a basic group and more preferably has a β-dicarbonyl group and/or an alkyl group. The basic dispersant preferably contains, for example, a basic (meth)acrylic dispersant having a basic group, a β-dicarbonyl group, and an alkyl group from the viewpoint of lowering the viscosity of the ink. Examples of such basic (meth)acrylic dispersants include units having a basic group (hereinafter sometimes referred to as "unit Ya"), units having a β-dicarbonyl group (hereinafter sometimes referred to as "unit Yb" (sometimes referred to as "unit Yc"), and basic (meth)acrylic dispersants containing units having an alkyl group (hereinafter sometimes referred to as "unit Yc").
Basic (meth)acrylic dispersants include, for example, a monomer having a basic group (hereinafter sometimes referred to as "monomer Ya"), a monomer having a β-dicarbonyl group (hereinafter sometimes referred to as "monomer Yb") ), and a copolymer of a monomer mixture containing a monomer having an alkyl group (hereinafter sometimes referred to as "monomer Yc"), or a copolymer obtained using such a copolymer. be done.

When using a basic (meth)acrylic dispersant having a basic group, a β-dicarbonyl group and an alkyl group, the adsorption to the colored resin particles is further improved, and the dispersant is free in the non-aqueous solvent. It is believed that the amount can be reduced to further reduce ink viscosity.
In addition, by reducing the amount of the free dispersant, the decrease in interaction between the colored resin particles and the polar groups of the recording medium caused by the interaction of the free dispersant with the polar groups of the recording medium is suppressed. Particles tend to remain on the surface of the recording medium, which is thought to contribute to improvement in image density and reduction in strike-through.

The basic group is not particularly limited, and for example, the basic groups described above can be used. The basic (meth)acrylic dispersant may contain only one type or two or more types of basic groups. The basic group is preferably bonded to the main chain directly or via a linking group.

As the unit having a basic group (unit Ya), for example, the unit described above as the unit Xa can be used. The basic (meth)acrylic dispersant may contain only one type or two or more types of units Ya.

As the alkyl group, an alkyl group having 8 to 22 carbon atoms is preferable, and an alkyl group having 12 to 22 carbon atoms is more preferable. The alkyl group having 8 to 22 carbon atoms may be linear or branched. Specific examples include octyl group, nonyl group, decyl group, undecyl group, dodecyl group, tridecyl group, tetradecyl group, pentadecyl group, hexadecyl group, heptadecyl group, octadecyl group, nonadecyl group, eicosyl group and docosyl group. . The basic (meth)acrylic dispersant may contain one or more of these alkyl groups.

A unit having an alkyl group (unit Yc) may be, for example, an acrylic unit or a methacrylic unit.
An example of the unit Yc is, for example, a unit in which a group represented by —COOR ^e is bonded to a carbon atom of the main chain of a basic (meth)acrylic dispersant, and R ^e is an alkyl group (preferably is an alkyl group having 8 to 22 carbon atoms, more preferably 12 to 22 carbon atoms).
As the unit Yc, for example, a unit derived from a monomer Yc described later can be used.
The basic (meth)acrylic dispersant may contain only one type or two or more types of the unit Yc.

The β-dicarbonyl group includes β-diketone groups such as acetoacetyl group and propionacetyl group, and β-keto acid ester groups such as acetoacetoxy group and propionacetoxy group. The basic (meth)acrylic dispersant may contain one or more of these β-dicarbonyl groups.

A unit having a β-dicarbonyl group (unit Yb) may be, for example, an acrylic unit or a methacrylic unit.
Examples of the unit Yb include units in which a carbonyl group is bonded to the carbon atom of the main chain and a β-dicarbonyl group is bonded to the carbon atom of the carbonyl group directly or via a linking group.
As the unit Yb, a unit derived from (meth)acrylate having a β-dicarbonyl group, a unit derived from (meth)acrylamide having a β-dicarbonyl group, and the like are preferable. (Meth)acrylates having a β-dicarbonyl group include, for example, a β-diketone group or a β-keto acid ester group indirectly bonded to the carbon atom of the carbonyl (CO) of an acryloyl group or a methacryloyl group (meth) ) acrylates are preferred examples. (Meth)acrylamides having a β-dicarbonyl group include, for example, a β-diketone group or a β-keto acid ester group indirectly bonded to the carbonyl (CO) carbon atom of an acryloyl group or a methacryloyl group (meth) ) Acrylamide is a preferred example. As the unit Yb, for example, a unit derived from a monomer Yb described later can be used.
The basic (meth)acrylic dispersant may contain one or more units Yb.

Basic (meth)acrylic dispersants may contain other units.

The unit having a basic group (unit Ya) is preferably 5 to 30% by mass, more preferably 10 to 20% by mass or more, based on the total polymer.
The unit having an alkyl group (unit Yc) is preferably 40 to 90% by mass, more preferably 50 to 90% by mass, and even more preferably 60 to 80% by mass or more based on the total polymer.
The unit having a β-dicarbonyl group (unit Yb) is preferably 5 to 30% by mass, more preferably 10 to 20% by mass, based on the total polymer.
Here, the entire polymer is based on all units constituting the basic (meth)acrylic dispersant.

The basic (meth)acrylic dispersant is, for example, a monomer having a basic group (monomer Ya), a monomer having a β-dicarbonyl group (monomer Yb), and a monomer having an alkyl group (monomer Yc). It can be obtained by polymerizing the mixture.
Examples of the monomer Ya include, for example, the monomers exemplified above for the monomer Xa.
Monomer Yc is preferably a monomer having, for example, an acryloyl group or a methacryloyl group and an alkyl group. Examples of the monomer Yc include alkyl (meth)acrylates, etc., preferably alkyl (meth)acrylates having an alkyl group having 8 to 22 carbon atoms, and alkyl (meth)acrylates having an alkyl group having 12 to 22 carbon atoms. Acrylates are more preferred. Specific examples of the monomer Yc include behenyl (meth)acrylate, lauryl (meth)acrylate, and the like.
Monomer Yb is preferably a monomer having, for example, an acryloyl group or a methacryloyl group and a β-dicarbonyl group. Preferred examples of the monomer Yb include (meth)acrylates having a β-dicarbonyl group and (meth)acrylamides having a β-dicarbonyl group. Specific examples of the monomer Yb include acetoacetoxyalkyl (meth)acrylates such as acetoacetoxyethyl (meth)acrylate, hexadione (meth)acrylate, and acetoacetoxyalkyl (meth)acrylamides such as acetoacetoxyethyl (meth)acrylamide. mentioned.
The monomer mixture may contain other monomers.
The monomer mixture contains, for example, in addition to or instead of the monomer having a basic group (monomer Ya), the above monomer having an epoxy group (for example, a monomer having an acryloyl group or a methacryloyl group and an epoxy group). After polymerization of the monomer mixture, the structure derived from the monomer having an epoxy group is reacted with an amine compound described as an amine compound that can be added to the monomer having an epoxy group to have a basic group. A unit (unit Ya) may be obtained.
The blending amount of each monomer in the monomer mixture can be adjusted, for example, so as to obtain a preferable proportion of each unit described above. The monomer mixture can be polymerized by known radical copolymerization. As the polymerization method, for example, the method described as the method for synthesizing the basic comb-shaped dispersant b can be used.

Although the weight average molecular weight of the basic (meth)acrylic dispersant is not particularly limited, it is preferably 5,000 to 30,000 from the viewpoint of ink stability and ink viscosity.

Examples of commercially available basic dispersants include Solsperse 17000, Solsperse 16000, Solsperse 13940 manufactured by Nippon Lubrizol Co., Ltd., and HYPERMER KD11 manufactured by CRODA. Among these, for example, commercially available examples of basic comb dispersants a include Solsperse 13940 and HYPERMER KD11.
Examples of commercially available acidic dispersants include Solsperse 21000 manufactured by Nippon Lubrizol Co., Ltd., and the like.

Dispersant A may be used alone or in combination of two or more.
For example, from the viewpoint of image density and storage stability, it is also preferable to use a basic comb-shaped dispersant and a basic (meth)acrylic dispersant together.
The amount of dispersant A can be adjusted as appropriate. The amount of dispersant A is preferably 0.1% by mass or more, more preferably 1% by mass or more, and even more preferably 2% by mass or more, relative to the total amount of the ink. On the other hand, the amount of dispersant A is preferably 10% by mass or less, more preferably 5% by mass or less, relative to the total amount of ink. The amount of the dispersant is, for example, preferably 0.1 to 10% by mass, more preferably 1 to 10% by mass, and even more preferably 2 to 5% by mass, relative to the total amount of the ink.

The amount of dispersant A is preferably 0.1 to 10% by mass, more preferably 0.2 to 5% by mass, relative to the total amount of the continuous phase. The amount of dispersant A is preferably 0.1 to 10% by mass, more preferably 0.5 to 5% by mass, relative to the total amount of the water-in-oil emulsion.
When an ionic dispersant is included, the content of the ionic dispersant is preferably 50 to 100% by mass, more preferably 70 to 100% by mass, based on the total amount of dispersant A.
When a basic dispersant is included, the basic dispersant is preferably 50 to 100% by mass, more preferably 70 to 100% by mass, based on the total amount of dispersant A.

Both non-polar organic solvents and polar organic solvents can be used as non-aqueous solvents. These may be used alone or in combination of two or more as long as they form a single phase. In this embodiment, the non-aqueous solvent is preferably a non-water-soluble organic solvent that does not uniformly mix with the same volume of water at 1 atmospheric pressure and 20°C.

Preferred examples of non-polar organic solvents include petroleum hydrocarbon solvents such as aliphatic hydrocarbon solvents, alicyclic hydrocarbon solvents, and aromatic hydrocarbon solvents.
Examples of aliphatic hydrocarbon solvents and alicyclic hydrocarbon solvents include non-aqueous solvents such as paraffinic, isoparaffinic and naphthenic solvents. Commercially available products include No. 0 Solvent L, No. 0 Solvent M, No. 0 Solvent H, Cactus Normal Paraffin N-10, Cactus Normal Paraffin N-11, Cactus Normal Paraffin N-12, Cactus Normal Paraffin N-13, Cactus Normal Paraffin N-14, Cactus Normal Paraffin N-15H, Cactus Normal Paraffin YHNP, Cactus Normal Paraffin SHNP, Isosol 300, Isosol 400, Techlene N-16, Techlene N-20, Techlene N-22, AF Solvent No. 4, AF Solvent No. 5, AF Solvent No. 6, AF Solvent No. 7, Naphthesol 160, Naphthesol 200, Naphthesol 220 (all manufactured by JXTG Nippon Oil & Energy Corporation); Isopar G, Isopar H, Isopar L, Isopar M, Exol D40, Exol D60, Exol D80, Exol D95, Exsol D110, Exsol D130 (all manufactured by ExxonMobil); Moresco White P-40, Moresco White P-60, Moresco White P-70, Moresco White P-80, Moresco White P-100, Moresco White P-120, Moresco White P-150, Moresco White P-200, Moresco White P-260, Moresco White P-350P (all manufactured by MORESCO Co., Ltd.) and the like are preferred. be able to.
Preferred examples of the aromatic hydrocarbon solvent include Grade Alkene L, Grade Alkene 200P (both manufactured by JXTG Nippon Oil & Energy Corporation), Solvesso 100, Solvesso 150, Solvesso 200, and Solvesso 200ND (both manufactured by ExxonMobil). can.
The initial boiling point of the petroleum-based hydrocarbon solvent is preferably 100°C or higher, more preferably 150°C or higher, and even more preferably 200°C or higher. The distillation initial boiling point can be measured according to JIS K0066 "Distillation test method for chemical products".

Preferred examples of polar organic solvents include fatty acid ester solvents, higher alcohol solvents, higher fatty acid solvents, and the like.
For example, isononyl isononanoate, isodecyl isononanoate, isotridecyl isononanoate, methyl laurate, isopropyl laurate, hexyl laurate, isopropyl myristate, isopropyl palmitate, hexyl palmitate, isooctyl palmitate, isostearyl palmitate, methyl oleate , ethyl oleate, isopropyl oleate, butyl oleate, hexyl oleate, methyl linoleate, ethyl linoleate, isobutyl linoleate, butyl stearate, hexyl stearate, isooctyl stearate, isopropyl isostearate, 2-octyl pivalate Fatty acid ester solvents having 13 or more, preferably 16 to 30, carbon atoms in one molecule such as decyl, methyl soybean oil, isobutyl soybean oil, methyl tall oil, isobutyl tall oil; isomyristyl alcohol, isopalmityl alcohol, stearyl Higher alcohol solvents having 6 or more, preferably 12 to 20 carbon atoms per molecule such as alcohol, isostearyl alcohol, oleyl alcohol, isoeicosyl alcohol, decyltetradecanol; lauric acid, isomyristic acid, palmitic acid , isopalmitic acid, α-linolenic acid, linoleic acid, oleic acid, isostearic acid and the like, and higher fatty acid solvents having 12 or more, preferably 14 to 20, carbon atoms per molecule.
The boiling point of polar organic solvents such as fatty acid ester solvents, higher alcohol solvents, and higher fatty acid solvents is preferably 150° C. or higher, more preferably 200° C. or higher, and further preferably 250° C. or higher. preferable. Non-aqueous solvents having a boiling point of 250° C. or higher also include non-aqueous solvents having no boiling point.
When using a solvent with a high boiling point or distillation initial boiling point, it tends to be easy to prevent drying of the ink at the nozzle of the inkjet printhead, but the solvent causes show-through in printed matter and increases the ink viscosity. Sometimes. It is preferable to select a solvent or use a plurality of solvents in combination, taking into consideration the drying property of the ink at the nozzle, the strike-through of the printed matter, and the balance of the ink viscosity.

The amount of the non-aqueous solvent is preferably 70-99% by mass, more preferably 80-99% by mass, relative to the total amount of the continuous phase. The amount of the non-aqueous solvent is preferably 30-80% by mass, more preferably 40-70% by mass, relative to the total amount of the water-in-oil emulsion.

In step 1, the water-in-oil emulsion can be produced, for example, by mixing and emulsifying the above dispersed phase and continuous phase.
The continuous phase and dispersed phase are preferably prepared separately in advance. Then, the dispersed phase is preferably added to the continuous phase and emulsified. The emulsification treatment may be performed, for example, by using an ultrasonic homogenizer or the like while adding the dispersed phase to the continuous phase, or may be performed, for example, after adding the dispersed phase to the continuous phase.
In step 1, the water-in-oil emulsion has a disperse phase of 20 to 50% by mass and a continuous phase of 80 to 50% by mass with respect to the entire water-in-oil emulsion, as a mass ratio of the state before water is removed. is preferred.

The step of removing water from the water-in-oil emulsion (step 2) will be described.

In step 2, water in the dispersed phase of the water-in-oil emulsion is removed. It is believed that this yields colored resin particles containing dispersed phase components from which water has been removed.
As a method for removing water, for example, a method of decompressing and/or heating, or a method of blowing gas into the liquid and bubbling to promote evaporation, or a combination thereof can be used. Conditions for reducing the pressure and/or heating may be such that water is removed but the non-aqueous solvent in the continuous phase remains. For example, an evaporator can be used for reducing the pressure. The heating temperature is preferably 30°C or higher, more preferably 40°C to 100°C, and even more preferably 60°C to 90°C.
In step 2, water in the dispersed phase is preferably removed by 80% by mass or more, preferably by 90% by mass or more, more preferably by 95% by mass or more, relative to the amount before removal. More preferably, 99% by mass or more is removed.

The oil-based inkjet ink produced by the above production method will be described.

In addition to the above components, the oil-based ink may contain various additives. As additives, nozzle clogging inhibitors, antioxidants, conductivity modifiers, viscosity modifiers, surface tension modifiers, oxygen absorbers, and the like can be added as appropriate. These types are not particularly limited, and those used in the relevant field can be used.

The amount of water in the ink is preferably 1% by mass or less, more preferably less than 1% by mass, even more preferably 0.5% by mass or less, and even more preferably 0.1% by mass or less, relative to the total amount of the ink.

The average particle size of the colored resin particles in the ink is preferably 50-300 nm, more preferably 80-200 nm. The amount of the colored resin particles in the ink is preferably 1 to 40% by mass, more preferably 5 to 30% by mass, based on the solid content of the dispersed phase component relative to the total amount of the ink. The average particle size of the colored resin particles is the volume-based average particle size measured by the dynamic scattering method. can be measured.

The appropriate range of the viscosity of the oil-based inkjet ink varies depending on the nozzle diameter of the ejection head of the inkjet recording system, the ejection environment, and the like. It is more preferably about 10 mPa·s, and even more preferably about 10 mPa·s.

The printing method using the oil-based inkjet ink is not particularly limited, and may be any method such as a piezo method, an electrostatic method, or a thermal method. When using an inkjet recording apparatus, it is preferable to eject the ink according to the present embodiment from an inkjet head based on a digital signal, and cause the ejected ink droplets to adhere to the recording medium.

In the present embodiment, the recording medium is not particularly limited, and printing paper such as plain paper, coated paper, and special paper, cloth, inorganic sheet, film, OHP sheet, etc. may be used as a base material with an adhesive layer on the back. can be used. Among these, from the viewpoint of ink permeability, printing paper such as plain paper and coated paper can be preferably used.

Here, plain paper is ordinary paper on which an ink-receiving layer, a film layer, or the like is not formed. Examples of plain paper include high-quality paper, medium-quality paper, PPC paper, rough paper, recycled paper, and the like. Plain paper has paper fibers with a thickness of several μm to several tens of μm forming voids of several tens to several hundreds of μm, so that the ink easily permeates the paper.

As the coated paper, inkjet coated paper such as matte paper, glossy paper, semi-glossy paper, and so-called coated printing paper can be preferably used. Here, coated printing paper is printing paper conventionally used in letterpress printing, offset printing, gravure printing, etc., and inorganic pigments such as clay and calcium carbonate are applied to the surface of high-quality paper or medium-quality paper. , a printing paper provided with a coating layer containing a binder such as starch. Coated printing paper can be lightly coated paper, high-quality lightweight coated paper, medium-quality lightweight coated paper, high-quality coated paper, medium-quality coated paper, art paper, cast coated paper, etc., depending on the coating amount and coating method. being classified.

EXAMPLES The present invention will be described in detail below with reference to examples. The invention is not limited to the following examples.
Common components are the same throughout the following examples and comparative examples unless otherwise specified. "%" indicates "% by mass" unless otherwise specified.

<Ink material>
Materials for the inks of Examples and Comparative Examples are shown below.

Carbon black: MOGAL L (manufactured by Cabot Specialty Chemicals) (powder)
Phthalocyanine blue: Lionol BGFJ (manufactured by Toyo Ink Co., Ltd.) (powder)
Self-dispersing pigment: Bonjet Black CW-1 (manufactured by Orient Chemical Industry Co., Ltd.) (self-dispersing carbon black, water dispersion, solid content 20%)

Pigment dispersant: borchiGenDFN (manufactured by Borchers) (water-soluble nonionic dispersant, allyl alkylbiphenyl polyglycol ether, active ingredient 100%)
Acidic urethane 1: WS5984 (manufactured by Mitsui Chemicals, Inc.) (aqueous dispersion of water-dispersible urethane urea resin having acidic group, 40% active ingredient)
Acidic urethane 2: Superflex 740 (manufactured by Daiichi Kogyo Seiyaku Co., Ltd.) (aqueous dispersion of water-dispersible urethane urea resin having acidic group, active ingredient 40%)
Acidic urethane 3: WS4022 (manufactured by Mitsui Chemicals, Inc.) (aqueous dispersion of water-dispersible urethane urea resin having acidic group, 30% active ingredient)
Acidic urethane 4: Superflex 150H (manufactured by Daiichi Kogyo Seiyaku Co., Ltd.) (aqueous dispersion of urethane urea resin having acidic group, active ingredient 38%)
Acidic urethane 5: TW1262 (manufactured by Daicel Allnex Co., Ltd.) (aqueous dispersion of urethane urea having an acidic group and acrylic hybrid resin, active ingredient 35%)
Basic urethane 1: Superflex 620 (manufactured by Daiichi Kogyo Seiyaku Co., Ltd.) (aqueous dispersion of water-dispersible urethane urea resin having basic group, 30% active ingredient)
Nonionic urethane 1: Superflex 500M (manufactured by Daiichi Kogyo Seiyaku Co., Ltd.) (aqueous dispersion of urethane urea resin, nonionic type, active ingredient 45%)
Acidic (meth)acrylic 1: Movinyl 6969D (manufactured by Nippon Synthetic Chemical Industry Co., Ltd.) (aqueous dispersion of water-dispersible (meth)acrylic resin having acidic group, active ingredient 40%)

Urethane resin c1: synthesized by the method described below (urethane resin solution, active ingredient 50%, solvent methyl ethyl ketone)
Urethane resin c2: synthesized by the method described below (urethane resin solution, active ingredient 50%, solvent methyl ethyl ketone)
Urethane urea resin c1: synthesized by the method described below (urethane urea resin solution, active ingredient 50%, solvent methyl ethyl ketone)

Basic dispersant 1: Solsperse 17000 (manufactured by Nippon Lubrizol Co., Ltd.) (active ingredient 100%)
Basic dispersant 2: Solsperse 16000 (manufactured by Nippon Lubrizol Co., Ltd.) (active ingredient 100%)
Basic comb dispersant 1: HYPERMER KD11 (manufactured by CRODA) (solution of basic comb dispersant a, active ingredient 40%, solvent is high-boiling paraffin oil)
Basic comb dispersant 2: Solsperse 13940 (solution of basic comb dispersant a, manufactured by Nippon Lubrizol Co., Ltd.) (active ingredient 40%, solvent is petroleum solvent)
Acidic dispersant 1: Solsperse 21000 (manufactured by Nippon Lubrizol Co., Ltd.) (100% active ingredient)

Fatty acid ester solvent 1: Methyl oleate (manufactured by FUJIFILM Wako Pure Chemical Industries, Ltd.)
Fatty acid ester solvent 1: Isopropyl myristate (manufactured by FUJIFILM Wako Pure Chemical Industries, Ltd.)
Petroleum-based hydrocarbon solvent 1: Exsol D110 (manufactured by ExxonMobil)
Petroleum-based hydrocarbon solvent 2: Exsol D130 (manufactured by ExxonMobil)

<Urethane resin c1, urethane resin c2, and urethane urea resin c1>
Table 1 shows the formulations of diols a and b. Diethanolamine was charged at the ratio shown in Table 1, and the temperature was raised to 110°C. To this, the monomers shown in the table were added dropwise in respective blending amounts to complete the Michael addition reaction to obtain a diol.

Table 2 shows the formulations of the urethane resin solutions (urethane resin c1, urethane resin c2 and urethane urea resin c1) used in Comparative Examples.
Urethane resin c1 and urethane resin c2 were produced as follows.
According to the compounding amounts shown in Table 2, the diol solution obtained above, propylene glycol as other diol components, and MEK (methyl ethyl ketone) were charged, a tin-based catalyst (dibutyltin dilaurate) was added, and the mixture was heated to 78°C. heated up. Then, diisocyanate (hexamethylene diisocyanate) was added dropwise to obtain a resin solution having a solid content of 50.0% by mass.
Urethane urea resin c1 was produced as follows.
According to the compounding amounts shown in Table 2, the diol solution obtained above, propylene glycol as other diol components, and MEK (methyl ethyl ketone) were charged, a tin-based catalyst (dibutyltin dilaurate) was added, and the mixture was heated to 78°C. heated up. Diisocyanate (hexamethylene diisocyanate) was added dropwise, and finally diamine (N,N'-dimethylethylenediamine) was added dropwise to obtain a resin solution having a solid content of 50.0% by mass.
The weight average molecular weight (GPC method, standard polystyrene conversion) of each resin is shown in the table.

The materials listed in Tables 1 and 2 are as follows.
Diethanolamine: manufactured by Nippon Shokubai Co., Ltd. Diethylacrylamide: manufactured by KJ Chemicals Corporation Methoxypolyethylene glycol (PEG9) acrylate: manufactured by NOF Corporation Hexamethylene diisocyanate: manufactured by FUJIFILM Wako Pure Chemical Industries, Ltd.
Propylene glycol: manufactured by FUJIFILM Wako Pure Chemical Industries, Ltd.
Dibutyltin laurate: manufactured by Tokyo Fine Chemicals Co., Ltd.
N,N'-Dimethylethylenediamine: Koei Chemical Industry Co., Ltd. Methyl ethyl ketone: FUJIFILM Wako Pure Chemical Industries, Ltd.

<Ink production>
The inks of Examples 1-15 were prepared as follows.
A continuous phase was prepared by mixing a non-aqueous solvent and a dispersant in the amounts shown in Tables 3 and 4. Next, a coloring material, a pigment dispersant, and water were mixed in the amounts shown in Tables 3 and 4, and dispersed in a bead mill (manufactured by Shinmaru Enterprises Co., Ltd., Dyno Mill Multi LAB) to obtain a dispersion composition. After adding the resin emulsion shown in Tables 3 and 4 to the product in the compounding amount shown in Tables 3 and 4, the mixture was stirred with a magnetic stirrer.
While the continuous phase was stirred with a magnetic stirrer, the dispersed phase premixed as described above was added dropwise to the continuous phase, and an ultrasonic homogenizer "Ultrasonic processor VC-750" (Sonics Co., Ltd.) was used under ice cooling. ) was irradiated for 10 minutes to obtain a water-in-oil (W/O) emulsion.
Water in the dispersed phase and volatile matter contained in the resin emulsion were removed from the obtained emulsion while the pressure was reduced by an evaporator to obtain a colored resin particle dispersion. The removal rate of volatile matter was almost 100% by weight. This colored particle dispersion was used as an ink as it was.
The compositions of the inks of Examples 1-15 after devolatilization (desolventization) are shown in Tables 6 and 7.

Inks for Comparative Examples 1-4 were prepared as follows.
Each component was mixed according to the ink formulation in Table 5 and dispersed by a bead mill (Dyno Mill Multi LAB manufactured by Shinmaru Enterprises Co., Ltd.). After dispersion, the low boiling point solvent (methyl ethyl ketone) in the dispersion was removed using an evaporator. Thus, the pigment was encapsulated with the urethane resin to obtain an ink containing the encapsulated pigment. The resin of urethane resin c1 used in Comparative Example 1 was dissolved in the non-aqueous solvent of Comparative Example 1, but the resin of urethane resin c2 used in Comparative Examples 2 and 3 was dissolved in the non-aqueous solvents of Comparative Examples 2 and 3. didn't.
Table 8 shows the compositions of the inks of Comparative Examples 1 to 4 after solvent removal.

<Evaluation method>
Evaluation was performed according to the following evaluation methods. The results are shown in Tables 6-8.

(1) Viscosity of Ink The viscosity of the ink was evaluated according to the following criteria. The viscosity of the ink is the viscosity at 23° C., and was measured using a rheometer AR-G2 (manufactured by TA Instruments Japan Co., Ltd.) with a cone angle of 2° and a diameter of 40 mm. The results are shown in Tables 6-8.
(Evaluation criteria)
AA: Ink viscosity of less than 12 mPa·s A: Ink viscosity of 12 mPa·s or more and less than 13 mPa·s B: Ink viscosity of 13 mPa·s or more and less than 15 mPa·s C: Ink viscosity of 15 mPa·s or more

(2) Image density and image strike-through A solid image was printed on plain paper "Riso Paper Multi" (manufactured by Riso Kagaku Corporation) using an inkjet printer "ORPHIS GD9630" (manufactured by Riso Kagaku Corporation). After 24 hours from printing, using a spectral density/colorimeter (eXact, manufactured by X-rite), measure the OD value of the surface of the printed matter (front OD value) and the OD value of the back side of the printed matter (back OD value). did. The image density was evaluated from the OD values in the table according to the following criteria. Image strike-through was evaluated from the back OD value according to the following criteria.

(Image density evaluation criteria)
AA: Table OD value is 1.20 or more A: Table OD value is 1.10 or more and less than 1.20 B: Table OD value is less than 1.10 (image strike-through evaluation criteria)
AA: Back OD value is less than 0.25 A: Back OD value is 0.25 or more and less than 0.35 B: Back OD value is 0.35 or more and less than 0.45 C: Back OD value is 0.45 or more

(3) Storage stability (70°C, 4 weeks)
First, the viscosity of the ink immediately after ink preparation was measured.
Next, the ink was placed in a sealed container and left at 70° C. for 4 weeks. After that, the ink was sampled and the ink viscosity was measured.
The ink viscosity is the viscosity at 23° C., and was measured using a rheometer AR-G2 (manufactured by TA Instruments Japan Co., Ltd.) with a cone angle of 2° and a diameter of 40 mm.
From the viscosity of the ink immediately after preparation and the viscosity of the ink before and after being left for 4 weeks, the viscosity change rate was obtained by the following formula, and the storage stability was evaluated according to the following criteria.
Viscosity change rate (%) = [(ink viscosity after standing for 4 weeks x 100)/(viscosity immediately after preparation)] - 100 (%)
(Evaluation criteria)
AA: Viscosity change rate is less than ±3% A: Viscosity change rate is ±3% or more and less than ±6% B: Viscosity change rate is ±6% or more

In each example, an oil-based inkjet ink could be produced without the need to use a volatile organic solvent.

Claims (6)

A step of preparing a water-in-oil emulsion comprising a continuous phase containing a non-aqueous solvent and a dispersant and a dispersed phase containing water, a coloring material, and a water-dispersible resin;
removing the water from the water-in-oil emulsion to produce a colored resin particle dispersion ;
The dispersant is an emulsifier for the water-in-oil emulsion, and dissolves uniformly without dividing into two phases when mixed in the same volume with the non-aqueous solvent at 1 atmospheric pressure 20 ° C.
A method for producing an oil-based inkjet ink containing colored resin particles . The method for producing an oil-based inkjet ink according to claim 1, wherein the water-dispersible resin contains a water-dispersible resin having an acidic group. The method for producing an oil-based inkjet ink according to claim 1 or 2, wherein the water-dispersible resin comprises a water-dispersible urethane resin, a water-dispersible (meth)acrylic resin, or a combination thereof. 4. The production of an oil-based inkjet ink according to any one of claims 1 to 3, wherein the water-in-oil emulsion contains water in an amount of 1 to 50% by mass with respect to the total amount of the water-in-oil emulsion. Method. 5. The method for producing an oil-based inkjet ink according to claim 1, wherein the amount of water in the oil-based inkjet ink is 1% by mass or less with respect to the total amount of the oil-based inkjet ink. The method for producing an oil-based inkjet ink according to any one of claims 1 to 5, wherein the coloring material contains a pigment, and the dispersed phase further contains a pigment dispersant.