JP2024051578A - Inkjet printing method - Google Patents

Abstract

[Problem] An inkjet textile printing method that can obtain a printed material with excellent image quality and excellent durability against external stress such as rubbing, even when the printing medium is a fabric with low hydrophilicity. [Solution] The inkjet textile printing method includes a printing step of inkjet printing an ink composition containing a pigment, pigment-free (meth)acrylic resin particles, a blocked isocyanate compound, a water-soluble organic solvent, and water onto a fabric having a temperature of 40° C. or higher where the ink composition lands, and the (meth)acrylic resin that constitutes the pigment-free (meth)acrylic resin particles has a functional group that can react with an isocyanate group. [Selected Figure] None

Description

The present invention relates to an inkjet printing method.

Textile printing is a coloring method in which colors or patterns are applied directly to fabric. Screen printing and roller printing are widely used, but in recent years, inkjet printing methods that utilize inkjet printing have been under study.
The inkjet printing textile printing method has the advantage that it is possible to form high-definition, high-quality images on fabrics without requiring skill by ejecting ink droplets and depositing them on the fabric to perform printing. In addition, unlike conventional methods, it does not require plate making, making it easy to handle small-lot, high-mix production, and it also has the characteristic of having only a small impact on the environment because only the amount of ink necessary to form an image is used.

There are two types of ink for textile printing: dye ink and pigment ink. Pigment ink has the advantage over dye ink in that it has high light resistance and does not require post-processing such as washing after printing.
However, unlike dye inks, which can be bound by chemical bonding between the dye molecules and the fabric, pigment inks have poor bonding strength between the pigment particles and the fabric, and therefore have the disadvantage of being less able to resist external forces when the printed area is subjected to them.In addition, pigment inks tend to flow before they are fixed on the fabric, which can lead to problems with image bleeding and color mixing.

In view of this, various proposals have been made as ink-jet printing methods for improving the image quality and durability of textiles printed with pigment inks.
For example, Patent Literature 1 discloses an inkjet ink composition for textile printing, which has an objective of achieving both good washing fastness and texture, and contains a pigment, a water-dispersible resin, a crosslinking agent, and water, in which the water-dispersible resin has specific tensile properties, and the ratio of the water-dispersible resin to the pigment or the crosslinking agent is within a specific range.

JP 2019-31611 A

However, the inkjet textile printing ink composition of Patent Document 1 does not have sufficient durability against external stress such as rubbing when applied to fabrics with low hydrophilicity, such as polyester and nylon.
The present invention relates to an ink-jet textile printing method that can provide a printed material that has excellent image quality and excellent durability against external stress such as rubbing, even when the print medium is a fabric with low hydrophilicity.

The present inventors have found that the above-mentioned problems can be solved by using an ink composition containing a pigment, (meth)acrylic resin particles not containing a pigment, a blocked isocyanate compound, a water-soluble organic solvent, and water, and performing inkjet printing on a fabric in which the temperature of the portion where the ink composition lands is 40° C. or higher.
The present invention relates to the following [1].
[1] An inkjet textile printing method, comprising: a printing step of inkjet printing an ink composition containing a pigment, pigment-free (meth)acrylic resin particles, a blocked isocyanate compound, a water-soluble organic solvent, and water onto a fabric having a temperature of 40° C. or higher at a portion where the ink composition lands, wherein the (meth)acrylic resin constituting the pigment-free (meth)acrylic resin particles has a functional group capable of reacting with an isocyanate group.

The present invention provides an inkjet printing method that can produce printed matter with excellent image quality and excellent durability against external stress such as rubbing, even when the printing medium is a fabric with low hydrophilicity.

[Inkjet printing method]
The inkjet textile printing method of the present invention includes a printing step of inkjet printing an ink composition containing a pigment, pigment-free (meth)acrylic resin particles, a blocked isocyanate compound, a water-soluble organic solvent, and water onto a fabric having a temperature of 40° C. or higher at a portion where the ink composition lands, and the (meth)acrylic resin constituting the pigment-free (meth)acrylic resin particles has a functional group capable of reacting with an isocyanate group.
The ink composition used in the present invention may be simply referred to as an "ink composition" or "ink."

In the present invention, "(meth)acrylic" means acrylic or methacrylic, and "(meth)acrylic resin" means a resin containing one or more selected from the group consisting of structural units derived from acrylic esters and structural units derived from methacrylic esters, and which may contain structural units other than the structural units derived from acrylic esters and the structural units derived from methacrylic esters.
In the present invention, "(meth)acrylic resin particles not containing a pigment" means that the (meth)acrylic resin has the function of maintaining itself in a dispersed state in the ink, but does not have the function of maintaining the pigment in a dispersed state in the ink.
In this specification, the term "landing" refers to the adhesion of an ink composition to a print medium by inkjet printing.
In this specification, the term "printed textile" refers to a material on which an ink composition is applied (printed) onto the surface of a fabric, which is a printing medium, to form an image.

According to the inkjet textile printing method of the present invention, even if the printing medium is a fabric with low hydrophilicity such as polyester or nylon, it is possible to obtain a printed textile with excellent image quality and excellent durability against external stress such as rubbing. The reason for this is not clear, but is thought to be as follows.
In general, when a low-hydrophilic fabric such as polyester or nylon is used as a printing medium, ink does not easily penetrate into the printing medium. Therefore, in order to obtain a printed product with good image quality, it is necessary to quickly dry and harden the ink dots to prevent the ink dots from mixing and bleeding on the surface of the printing medium.
On the other hand, in the inkjet printing method of the present invention, inkjet printing is performed on a fabric where the temperature of the part where the ink composition lands is 40°C or higher. This promotes evaporation of the water and water-soluble organic solvent contained in the ink composition after landing, and the ink composition quickly thickens, preventing the ink dots from mixing and bleeding. This is thought to result in a printed material with good image quality.

In general, when pigment inks are used on ordinary fabrics such as cotton, the colorant components and the components that bind them become entangled with the fibers relatively easily. However, when synthetic fibers with low hydrophilicity such as polyester or nylon are used as the printing medium, as described above, the ink hardly penetrates into the interior of the printing medium, so that entanglement with the fibers is weak and durability against external stresses such as rubbing is likely to decrease.
On the other hand, in the inkjet printing method of the present invention, the pigment-free (meth)acrylic resin particles contained in the ink composition have higher hydrophobicity than polyurethane resins having many urethane groups in the polymer main chain or polyester resins having many ester groups in the polymer main chain. Therefore, when a fabric with low hydrophilicity such as polyester or nylon is used as the printing medium, the ink composition exhibits a relatively strong interaction with the printing medium, and the interaction with the printing medium resulting from the hydrophobicity becomes stronger even in a wet state in the drying process after inkjet printing, which is considered to enhance the durability of the printed material against external stress such as rubbing.
Furthermore, in the inkjet textile printing method of the present invention, the pigment-free (meth)acrylic resin particles on the fabric after inkjet printing are crosslinked by the blocked isocyanate compound, which is thought to enhance the durability of the coating film and improve the durability of the printed fabric against external stresses such as rubbing.
Furthermore, in the present invention, the (meth)acrylic resin constituting the pigment-free (meth)acrylic resin particles contains a structural unit derived from a (meth)acrylic acid ester, and the hydrocarbon group derived from the alcohol of the structural unit can take the form of an extended side chain branching off from the main chain, thereby enabling stronger hydrophobicity to be expressed, and it is considered that the effect of the present invention based on the above-mentioned hydrophobicity is further enhanced.

<Ink composition>
In the ink-jet printing method of the present invention, the ink composition contains a pigment, (meth)acrylic resin particles not containing a pigment, a blocked isocyanate compound, a water-soluble organic solvent, and water.

<Pigments>
In the present invention, the pigment may be either an inorganic pigment or an organic pigment.
Examples of inorganic pigments include carbon black and metal oxides. In the case of black ink, carbon black is preferred. Examples of carbon black include furnace black, thermal black, acetylene black, and channel black. In the case of white ink, examples of metal oxides include titanium dioxide, zinc oxide, silica, alumina, and magnesium oxide, and among these, titanium dioxide is preferred.
Examples of organic pigments include azo pigments, diazo pigments, phthalocyanine pigments, quinacridone pigments, isoindolinone pigments, dioxazine pigments, perylene pigments, perinone pigments, thioindigo pigments, anthraquinone pigments, and quinophthalone pigments.
The hue is not particularly limited, and in the chromatic ink, any chromatic pigment such as yellow, magenta, cyan, red, blue, orange, green, etc. can be used.
The pigments may be used alone or in combination of two or more kinds.

In the present invention, the pigment may be dispersed with a resin or surfactant having pigment dispersing ability as a dispersant, or may be a self-dispersing pigment dispersed without using a dispersant. Among these, from the viewpoint of improving the image quality of the printed matter and durability against external stress, it is preferable that the pigment is in the form of a resin particle containing the pigment (hereinafter also referred to as "pigment-containing resin particle"). In the present invention, the resin particle containing the pigment means any one of the following: a particle consisting of the pigment and a resin having pigment dispersing ability (hereinafter also referred to as "pigment dispersion resin"), in which the pigment dispersion resin contains the pigment; a particle consisting of the pigment dispersion resin and the pigment, in which a part of the pigment is exposed on the surface of the particle; a particle in which the pigment dispersion resin is adsorbed to a part of the pigment, or a mixture of these.

(Pigment dispersion resin)
The pigment dispersion resin is a resin having a pigment dispersing ability to disperse a pigment in an aqueous medium mainly composed of water. Examples of the pigment dispersion resin include vinyl polymers, polyester polymers, and polyurethane polymers. Among these, vinyl resins obtained by addition polymerization of vinyl monomers such as vinyl compounds, vinylidene compounds, and vinylene compounds are preferred from the viewpoint of improving the image quality of printed matter and durability against external stress.
From the viewpoint of improving the image quality of the printed matter and durability against external stress, the pigment dispersion resin preferably has an ionic group. When the pigment dispersion resin is a vinyl resin, the ionic group is preferably introduced into the skeleton of the pigment dispersion resin by (a-1) an ionic vinyl monomer having an ionic group (hereinafter also referred to as "ionic monomer" or "component (a-1)").
In addition, the pigment dispersion resin preferably has a hydrophobic group. When the pigment dispersion resin is a vinyl resin, the hydrophobic group is preferably introduced into the skeleton of the pigment dispersion resin by (a-2) a hydrophobic vinyl monomer having a hydrophobic group (hereinafter also referred to as "hydrophobic monomer" or "component (a-2)"), from the same viewpoint as above.
That is, in the present invention, the pigment dispersing resin is preferably a vinyl resin containing (a-1) a structural unit derived from an ionic monomer and (a-2) a structural unit derived from a hydrophobic monomer.
From the same viewpoint as above, the pigment dispersion resin may further have a nonionic group. When the pigment dispersion resin is a vinyl resin, the nonionic group may be introduced into the skeleton of the pigment dispersion resin by (a-3) a nonionic vinyl monomer having a nonionic group (hereinafter also referred to as "nonionic monomer" or "component (a-3)").

[Component (a-1)]
The component (a-1) may be both anionic and cationic, but is preferably anionic. The ionic group that exhibits anionicity is preferably an acid group, and the acid group is preferably a carboxylic acid group.
Specific examples of the component (a-1) include those described in paragraph [0017] of JP-A-2018-80255. Among them, one or more selected from acrylic acid and methacrylic acid are preferred.
In the present invention, it is preferable that the ionic groups introduced by the component (a-1) of the pigment dispersion resin constituting the pigment-containing resin particles are partially or entirely neutralized with a basic compound or an acidic compound. When the pigment dispersion resin is in a neutralized state, the pigment dispersion resin is ionic and can disperse the pigment in an aqueous medium.

[Component (a-2)]
The hydrophobicity of the component (a-2) means that when the monomer is dissolved in 100 g of ion-exchanged water at 25° C. until saturation, the dissolution amount is less than 10 g, and the dissolution amount is preferably 5 g or less, and more preferably 1 g or less.
Preferred examples of the hydrophobic group of the component (a-2) include one or more groups selected from the group consisting of alkyl groups, aromatic groups, and silicone groups.
The component (a-2) is preferably at least one selected from the group consisting of alkyl (meth)acrylates, aromatic group-containing monomers, aromatic group-containing macromonomers, and silicone macromonomers, more preferably at least one selected from the group consisting of aromatic group-containing monomers and aromatic group-containing macromonomers, and even more preferably an aromatic group-containing monomer.
Specific examples of the (a-2) component include those described in paragraph [0018] of JP-A-2018-80255. Among these, one or more selected from the group consisting of styrene-based monomers such as styrene and α-methylstyrene, benzyl (meth)acrylate, and styrene macromers are preferred, styrene-based monomers are more preferred, and one or more selected from the group consisting of styrene and α-methylstyrene are even more preferred.

[Component (a-3)]
Examples of the nonionic group of the component (a-3) include a hydroxy group and a polyoxyalkylene group.
The component (a-3) is preferably at least one selected from the group consisting of hydroxyalkyl (meth)acrylates, polyalkylene glycol (meth)acrylates, alkoxypolyalkylene glycol (meth)acrylates, and phenoxypolyalkylene glycol (meth)acrylates.
Specific examples of the component (a-3) include those described in paragraph [0022] of JP-A-2018-80255. Among them, one or more selected from polyethylene glycol (n = 2 to 30) (meth)acrylate and phenoxy (ethylene glycol / propylene glycol copolymer) (meth)acrylate are preferred.
The monomer components contained in each of the above components (a-1) to (a-3) can be used alone or in combination of two or more kinds.

In addition, when the pigment dispersion resin has a functional group that can react with an isocyanate group, the pigment dispersion resin in the ink composition is also crosslinked, which can further improve the durability of the coating film and produce a printed material with superior durability against external stress. The functional group is preferably one or more selected from the group consisting of a hydroxy group, a carboxy group, and an amino group, and more preferably one or more selected from the group consisting of a hydroxy group and a carboxy group. The functional group is contained in one or more selected from the group consisting of the (a-1) component and the (a-3) component, and can be introduced into the skeleton of the pigment dispersion resin by these components.

(Content of each structural unit in pigment dispersion resin)
From the viewpoint of improving the dispersion stability of the pigment-containing resin particles, the contents of the structural units derived from the components (a-1) to (a-3) in the pigment dispersion resin are as follows.
The content of the (a-1) component is preferably 10% by mass or more, more preferably 20% by mass or more, even more preferably 25% by mass or more, and is preferably 50% by mass or less, more preferably 40% by mass or less, even more preferably 35% by mass or less.
The content of the (a-2) component is preferably 30% by mass or more, more preferably 40% by mass or more, even more preferably 50% by mass or more, and is preferably 90% by mass or less, more preferably 80% by mass or less, even more preferably 75% by mass or less.
When the component (a-3) is contained, the content thereof is preferably 5% by mass or more, more preferably 10% by mass or more, and preferably 30% by mass or less, more preferably 25% by mass or less.
The mass ratio of the component (a-1) to the component (a-2), [(a-1)/(a-2)], is preferably 0.1 or more, more preferably 0.2 or more, and is preferably 1.2 or less, more preferably 1.0 or less, and even more preferably 0.8 or less.

In the present invention, the content of the structural units derived from components (a-1) to (a-3) in the pigment dispersion resin can be determined by measurement, and can also be substituted by the charging ratio of the raw material monomers containing components (a-1) to (a-3) during the production of the pigment dispersion resin.

(Production of pigment dispersion resin)
When the pigment dispersion resin is a vinyl resin, it can be produced by polymerizing the components (a-1) to (a-3) by a known method. Specifically, the procedure of the production method described in paragraphs [0027] to [0028] of JP-A-2018-80255 is preferred.

From the viewpoint of improving the dispersion stability of the pigment-containing resin particles, the weight average molecular weight of the pigment dispersing resin is preferably 6,000 or more, more preferably 8,000 or more, even more preferably 10,000 or more, and is preferably 300,000 or less, more preferably 100,000 or less, even more preferably 50,000 or less, even more preferably 30,000 or less.
The weight average molecular weight of the pigment dispersing resin is measured by the method described in the examples.

From the viewpoint of improving the dispersion stability of the pigment-containing resin particles, the acid value of the pigment dispersing resin is preferably 100 mgKOH/g or more, more preferably 150 mgKOH/g or more, even more preferably 200 mgKOH/g or more, and is preferably 350 mgKOH/g or less, more preferably 300 mgKOH/g or less, even more preferably 270 mgKOH/g or less.
The acid value of the pigment dispersing resin can be calculated from the mass ratio of the constituent monomers.

Commercially available pigment dispersion resins may be used. Commercially available pigment dispersion resins include styrene/acrylic resins such as "Joncryl 67", "Joncryl 611", "Joncryl 678", "Joncryl 680", "Joncryl 690", and "Joncryl 819" (all manufactured by BASF Japan Ltd.).

In the present invention, the pigment dispersion resin constituting the resin particles containing a pigment (pigment-containing resin particles) preferably has at least a crosslinked structure in a part thereof. In the present invention, the pigment dispersion resin having a crosslinked structure preferably further has a compound having two or more functional groups capable of reacting with the component (a-1), i.e., a component derived from a crosslinking agent, in addition to the structural units derived from the above-mentioned components (a-1), (a-2), and, if necessary, (a-3).
In the present invention, the amount of the component derived from the crosslinking agent in the pigment dispersion resin constituting the pigment-containing resin particles can be calculated from the amount charged when the resin is produced.

In the present invention, when the pigment-dispersing resin constituting the pigment-containing resin particles has a crosslinked structure, it is preferable that the pigment-containing resin particles are prepared using the above-mentioned pigment, pigment-dispersing resin, and crosslinking agent.

Specific examples of crosslinking agents include those described in paragraph [0041] of JP 2018-80255 A. Among them, water-insoluble compounds are preferred, polyglycidyl ether compounds of polyhydric alcohols having a hydrocarbon group with 3 to 8 carbon atoms are more preferred, one or more selected from the group consisting of pentaerythritol polyglycidyl ether and trimethylolpropane polyglycidyl ether are even more preferred, and trimethylolpropane polyglycidyl ether is even more preferred.

In the present invention, the ratio of the molar equivalent number of the crosslinkable functional groups of the crosslinking agent to the molar equivalent number of the ionic groups of the pigment dispersing resin, i.e., the crosslinking rate, is preferably 10 mol% or more, more preferably 20 mol% or more, even more preferably 30 mol% or more, and is preferably 80 mol% or less, more preferably 70 mol% or less, even more preferably 60 mol% or less.

When the pigment dispersing resin constituting the pigment-containing resin particles has a crosslinked structure, the acid value of the pigment dispersing resin is, from the viewpoint of improving the dispersion stability of the pigment-containing resin particles, preferably 50 mgKOH/g or more, more preferably 55 mgKOH/g or more, even more preferably 60 mgKOH/g or more, and is preferably 175 mgKOH/g or less, more preferably 150 mgKOH/g or less, even more preferably 135 mgKOH/g or less.
When the pigment dispersing resin constituting the pigment-containing resin particles has a crosslinked structure, the acid value of the pigment dispersing resin can be calculated from the mass ratio of the pigment dispersing resin and the crosslinking agent used.

In the present invention, the mass ratio of the pigment dispersing resin to the pigment constituting the pigment-containing resin particles [pigment dispersing resin content/pigment content] is preferably 0.25 or more, more preferably 0.30 or more, even more preferably 0.35 or more, and is preferably 0.70 or less, more preferably 0.60 or less, even more preferably 0.50 or less, from the viewpoint of improving the dispersion stability of the pigment-containing resin particles.

[Production of pigment-containing resin particles]
The pigment-containing resin particles can be produced by any known method. Specifically, the procedure of the production method described in paragraphs [0030] to [0039] of JP-A-2018-80255 is preferred.

<(Meth)acrylic resin particles not containing pigment>
The ink composition used in the ink-jet textile printing method of the present invention contains (meth)acrylic resin particles that do not contain a pigment, from the viewpoint of improving the image quality of the printed matter and durability against external stress.
In the present invention, the (meth)acrylic resin constituting the pigment-free (meth)acrylic resin particles has a functional group capable of reacting with an isocyanate group, which is preferably at least one selected from the group consisting of a hydroxy group, a carboxy group, and an amino group, and more preferably at least one selected from the group consisting of a hydroxy group and a carboxy group.
In the present invention, the definitions of "(meth)acrylic", "(meth)acrylic resin" and "pigment-free (meth)acrylic resin particles" are as described above.

((Meth)acrylic resin)
In the present invention, the (meth)acrylic resin constituting the pigment-free (meth)acrylic resin particles contains a structural unit derived from a (meth)acrylic acid ester (hereinafter also referred to as "component (b-1)").
The (meth)acrylic acid ester is not particularly limited as long as it has a hydrocarbon group derived from an alcohol, and examples thereof include esters of a linear, branched, or alicyclic aliphatic alcohol and (meth)acrylic acid, and esters of an aromatic ring-containing alcohol and (meth)acrylic acid.
The ester of a linear, branched, or alicyclic aliphatic alcohol with (meth)acrylic acid is preferably one having an alkyl group having 1 to 22 carbon atoms, such as methyl (meth)acrylate, ethyl (meth)acrylate, (normal or iso)propyl (meth)acrylate, (normal, iso, or tertiary)butyl (meth)acrylate, (normal or iso)amyl (meth)acrylate, cyclohexyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, (normal or iso)octyl (meth)acrylate, (normal or iso)decyl (meth)acrylate, (normal or iso)dodecyl (meth)acrylate, (normal or iso)stearyl (meth)acrylate, etc. Among these, from the viewpoint of improving the image quality of the printed matter and durability against external stress, one or more selected from the group consisting of methyl (meth)acrylate, ethyl (meth)acrylate, and (normal, iso, or tertiary)butyl (meth)acrylate are preferred.
Examples of the ester of an aromatic ring-containing alcohol and (meth)acrylic acid include benzyl (meth)acrylate, phenoxyethyl (meth)acrylate, etc. Among these, benzyl (meth)acrylate is preferred from the viewpoint of improving the image quality of the printed matter and durability against external stress.

In the present invention, the (meth)acrylic resin preferably contains a structural unit derived from an ionic vinyl monomer having an ionic group (hereinafter also referred to as "component (b-2)").
From the viewpoint of reacting the (meth)acrylic resin with an isocyanate compound, the ionic vinyl monomer having an ionic group is preferably an anionic monomer, more preferably a carboxylic acid monomer, and may further include a sulfonic acid vinyl monomer as another ionic vinyl monomer.
Preferred examples of the ionic vinyl monomer having an ionic group include (meth)acrylic acid, crotonic acid, itaconic acid, maleic acid, fumaric acid, citraconic acid, 2-methacryloyloxymethylsuccinic acid, styrenesulfonic acid, 2-acrylamido-2-methylpropanesulfonic acid, and 3-sulfopropyl(meth)acrylate.
Among these, from the viewpoint of improving the image quality of the printed matter and durability against external stress, one or more selected from the group consisting of (meth)acrylic acid, maleic acid, styrenesulfonic acid, and 2-acrylamido-2-methylpropanesulfonic acid are more preferable, and (meth)acrylic acid is even more preferable.

In the present invention, the (meth)acrylic resin may contain structural units derived from monomers other than the (meth)acrylic acid ester and the ionic vinyl monomer having an ionic group.
Specific examples of monomers other than (meth)acrylic acid esters and ionic vinyl monomers having an ionic group include styrene-based monomers, acrylamide-based monomers, and vinyl ester-based monomers. Among these, styrene-based monomers are preferred. Specific examples of styrene-based monomers include styrene, α-methylstyrene, vinyltoluene, and vinylnaphthalene, with styrene being preferred.

(Content of each structural unit in (meth)acrylic resin)
The content of the structural units derived from the components (b-1) and (b-2) in the (meth)acrylic resin is as follows, from the viewpoint of improving the durability of the printed matter against external stress.
The content of the (b-1) component is preferably 80% by mass or more, more preferably 90% by mass or more, even more preferably 95% by mass or more, and is preferably 99.5% by mass or less, more preferably 99% by mass or less.
The content of the (b-2) component is preferably 0.5 mass% or more, more preferably 1.0 mass% or more, even more preferably 1.2 mass% or more, and is preferably 3.0 mass% or less, more preferably 2.5 mass% or less, even more preferably 2.0 mass% or less.
The mass ratio of the component (b-1) to the component (b-2), [(b-1)/(b-2)], is preferably 25 or more, more preferably 30 or more, and even more preferably 40 or more, and is preferably 100 or less, more preferably 80 or less, and even more preferably 70 or less.
The total content of the components (b-1) and (b-2) is preferably 85% by mass or more, more preferably 90% by mass or more, even more preferably 95% by mass or more, and still more preferably 100% by mass.

[Production of pigment-free (meth)acrylic resin particles]
The pigment-free (meth)acrylic resin particles can be produced by copolymerizing a (meth)acrylic acid ester and, if necessary, an ionic vinyl monomer having an ionic group, and, if necessary, a monomer other than the (meth)acrylic acid ester and the ionic vinyl monomer having an ionic group, by a known polymerization method. For example, the polymerization method can be an emulsion polymerization method, a suspension polymerization method, or the like, and is preferably an emulsion polymerization method.

In the polymerization, a polymerization initiator can be used. Examples of the polymerization initiator include persulfates and water-soluble azo polymerization initiators, and persulfates such as ammonium persulfate and potassium persulfate are preferred.
In addition, a surfactant can be used during the polymerization. Examples of the surfactant include anionic surfactants, cationic surfactants, and nonionic surfactants.
Among these, from the viewpoint of stably emulsifying the raw material monomers, preferably, one or more types selected from the group consisting of anionic surfactants and nonionic surfactants are used, and emulsifiers for emulsion polymerization can be used.
From the viewpoint of improving the dispersion stability of the resin particles not containing a pigment, the anionic surfactant is preferably at least one selected from the group consisting of fatty acid salts, alkylbenzenesulfonates, polyoxyethylene alkylphenyl ether sulfates, polyoxyethylene aralkylaryl ether sulfates, and polyoxyethylene alkyl ether sulfates, more preferably polyoxyethylene alkyl ether sulfates. Commercially available anionic surfactants include "Latemul" and "EMAL" (manufactured by Kao Corporation).
Examples of the nonionic surfactant include polyoxyethylene alkyl ethers, polyoxyethylene alkylaryl ethers, polyoxyethylene fatty acid esters, oxyethylene/oxypropylene block copolymers, and the like. From the viewpoint of improving the dispersion stability of the resin particles not containing a pigment, polyoxyethylene alkyl ethers are preferred.

As for preferred polymerization conditions, the polymerization temperature is preferably 50°C or higher and 90°C or lower, and the polymerization time is preferably 1 hour or higher and 20 hours or lower. In addition, the polymerization atmosphere is preferably an inert gas atmosphere such as a nitrogen gas atmosphere or argon atmosphere.

The resulting pigment-free (meth)acrylic resin particles can be purified by reprecipitation, membrane separation, chromatography, extraction, etc. to remove unreacted monomers, etc.

In terms of being incorporated into an ink composition in the inkjet printing method of the present invention, the (meth)acrylic resin particles that do not contain a pigment are preferably used as an aqueous dispersion (emulsion) of resin particles in which water is the main dispersion medium.

In the present invention, the weight average molecular weight of the pigment-free (meth)acrylic resin particles is preferably 100,000 or more, more preferably 200,000 or more, even more preferably 300,000 or more, and is preferably 1,500,000 or less, more preferably 1,000,000 or less, even more preferably 800,000 or less, and even more preferably 600,000 or less, from the viewpoint of improving the image quality of the printed matter and durability against external stress.

In the present invention, from the viewpoint of improving the image quality of a printed matter and durability against external stress, the glass transition temperature of the (meth)acrylic resin particles not containing a pigment is preferably 30° C. or lower, more preferably 20° C. or lower, even more preferably 15° C. or lower, still more preferably 5° C. or lower, and is preferably −30° C. or higher, more preferably −20° C. or higher, and even more preferably −10° C. or higher.
When the glass transition temperature is -30°C or higher, it is easy to prevent the pigment-free (meth)acrylic resin particles from becoming too soft in a system in which a pigment and a water-soluble organic solvent are mixed in the ink, and it is easy to improve the durability of the printed material against external stress. On the other hand, when the glass transition temperature is 30°C or lower, it is easy to prevent the pigment-free (meth)acrylic resin particles from becoming too hard in the above system, and it is easy to improve the durability of the printed material against external stress.
In the present invention, the degree of mixing of the water-soluble organic solvent in the ink composition varies somewhat depending on the printing conditions and the type of the water-soluble organic solvent. However, as long as the glass transition temperature of the pigment-free (meth)acrylic resin particles is within the above-mentioned range, a printed material having excellent durability against external stress can be obtained.

From the viewpoint of improving the image quality of the printed matter and durability against external stress, the average particle size of the (meth)acrylic resin particles that do not contain pigment is preferably 80 nm or more, more preferably 100 nm or more, even more preferably 110 nm or more, and is preferably 160 nm or less, more preferably 150 nm or less, even more preferably 140 nm or less.

(Other resins)
In the present invention, the ink composition may contain other resins (hereinafter also referred to as "other resins") other than the pigment-free (meth)acrylic resin particles in the form of pigment-free resin particles, within the scope of not impairing the effects of the present invention. In the present invention, when the pigment is in the form of pigment-containing resin particles, the resin constituting the pigment-containing resin particles is not included in the other resins.
Examples of other resins include polyurethane resins such as polycarbonate-based polyurethane resins, polyester-based polyurethane resins, and polyether-based polyurethane resins; polyester resins, and the like.

In the ink composition of the present invention, the mass ratio of the content of the pigment-free (meth)acrylic resin particles to the total content of the pigment-free (meth)acrylic resin particles and the other resins [content of the pigment-free (meth)acrylic resin particles/total content of the pigment-free (meth)acrylic resin particles and the other resins] is preferably 75% by mass or more, more preferably 85% by mass or more, even more preferably 90% by mass or more, even more preferably 95% by mass or more, and even more preferably 100% by mass, from the viewpoint of not impairing the effects of the present invention.

<Blocked isocyanate compound>
In the present invention, the ink composition contains a blocked isocyanate compound from the viewpoint of obtaining a printed matter having excellent durability against external stress.
A blocked isocyanate compound is a compound in which an isocyanate group in a polyisocyanate compound is blocked with a blocking agent. In a blocked isocyanate compound, a protecting group by a blocking agent is bonded to a highly reactive isocyanate group, and the blocked isocyanate compound is stabilized without reacting at room temperature. On the other hand, the protecting group is dissociated by heating after inkjet printing, and the isocyanate group acquires reactivity, so that a resin component having a functional group capable of reacting with an isocyanate group in the ink composition is crosslinked, and the durability of the coating film can be improved. As a result, a printed material having excellent durability against external stress can be obtained.

A polyisocyanate compound is a compound having two or more isocyanate groups in one molecule. Examples of the polyisocyanate compound include aliphatic polyisocyanates, alicyclic polyisocyanates, aliphatic polyisocyanates having an aromatic ring, aromatic polyisocyanates, and modified products thereof. Modified products of polyisocyanate compounds include polymers such as isocyanurates; biuret products; and adducts with polyhydric alcohols such as trimethylolpropane and pentaerythritol.

The aliphatic polyisocyanate is preferably a diisocyanate having a linear or branched aliphatic hydrocarbon group between two isocyanate groups. The carbon number of the aliphatic hydrocarbon group is preferably 2 or more, more preferably 3 or more, and preferably 12 or less, more preferably 10 or less, even more preferably 9 or less, and still more preferably 8 or less. Specific examples include tetramethylene diisocyanate, pentamethylene diisocyanate, hexamethylene diisocyanate (HDI), heptamethylene diisocyanate, octamethylene diisocyanate, decamethylene diisocyanate, dodecamethylene diisocyanate, 2,2,4- or 2,4,4-trimethylhexamethylene diisocyanate, and the like.
Examples of the alicyclic polyisocyanate include hydrogenated xylylene diisocyanate (H6XDI), 1,4-cyclohexane diisocyanate, 4,4'-dicyclohexylmethane diisocyanate (H12MDI), isophorone diisocyanate (IPDI), and 2,5- or 2,6-norbornane diisocyanate.
Examples of the aliphatic polyisocyanate having an aromatic ring include m- or p-xylylene diisocyanate (XDI), tetramethylxylylene diisocyanate (TMXDI), and the like.
Examples of aromatic polyisocyanates include 1,3- or 1,4-phenylene diisocyanate, 2,4- or 2,6-tolylene diisocyanate (TDI), 4,4'- or 2,4'-diphenylmethane diisocyanate (MDI), m- or p-isocyanatophenylsulfonyl isocyanate, 4,4'-diisocyanatobiphenyl, 4,4'-diisocyanato-3,3'-dimethylbiphenyl, 1,5-naphthylene diisocyanate, and 2,6-dimethylbenzene-1,4-diisocyanate.
Among these, the polyisocyanate compound is preferably one or more selected from the group consisting of aliphatic polyisocyanates, alicyclic polyisocyanates, and modified products thereof, more preferably one or more selected from the group consisting of aliphatic polyisocyanates, alicyclic polyisocyanates, and multimers thereof, and even more preferably a multimer of an aliphatic polyisocyanate or alicyclic isocyanate.

Blocking agents for blocked isocyanate compounds include compounds such as 3,5-dimethylpyrazole, methyl ethyl ketoxime, and ε-caprolactam, but 3,5-dimethylpyrazole is preferred from the standpoints of stability at room temperature, reactivity at coating drying temperatures, and the safety of the dissociated blocking agent.

The dissociation temperature of the blocked isocyanate compound is preferably 90° C. or higher, more preferably 100° C. or higher, from the viewpoint of improving the durability of the printed fabric against external stress, and is preferably 200° C. or lower, more preferably 180° C. or lower, even more preferably 160° C. or lower, still more preferably 150° C. or lower, and even more preferably 140° C. or lower, from the viewpoint of suppressing damage such as deformation of the fabric.
From the viewpoint of improving the durability of the printed matter against external stress, the isocyanate group equivalent of the blocked isocyanate compound is preferably 300 or more, more preferably 500 or more, even more preferably 700 or more, and is preferably 4,000 or less, more preferably 3,000 or less, even more preferably 2,000 or less, still more preferably 1,500 or less, and even more preferably 1,200 or less. The isocyanate group equivalent means the mass of the blocked isocyanate compound per mole of isocyanate group.

Commercially available blocked isocyanate compounds using 3,5-dimethylpyrazole as a blocking agent include Trixene Aqua BI200 and BI220 manufactured by GSI Creos Co., Ltd.; Bayhydur BL2867 and Bayhydur BL xp 2706 manufactured by Sumika Covestro Urethane Co., Ltd.

<Water-soluble organic solvent>
In the present invention, the ink composition contains a water-soluble organic solvent.
In the present invention, the term "water-soluble organic solvent" means an organic solvent that can be mixed with water in any ratio.
The water-soluble organic solvent is used from the viewpoint of exhibiting an appropriate affinity with the resin constituting the resulting printed textile, promoting film formation of the resin, and improving the image quality and durability against external stress of the printed textile.
From the above viewpoints, in the present invention, it is preferable that the water-soluble organic solvent contains one or more selected from the group consisting of alkylene glycols and polyalkylene glycols.

The alkylene glycol is preferably an aliphatic diol having from 2 to 6 carbon atoms, more preferably one or more selected from the group consisting of propylene glycol, 1,2-butanediol, and 1,3-butanediol, and even more preferably propylene glycol.
In the present invention, the term "polyalkylene glycol" refers to a compound having a structure in which alkylene glycols are condensed.
Suitable examples of polyalkylene glycols include diethylene glycol, triethylene glycol, dipropylene glycol, etc., with dipropylene glycol being more preferred.

From the above viewpoint, the water-soluble organic solvent may contain an alkylene glycol alkyl ether. Examples of the alkylene glycol alkyl ether include alkylene glycol monoalkyl ethers having an alkyl group with 1 to 6 carbon atoms, preferably 3 to 6 carbon atoms. Suitable examples of the alkylene glycol monoalkyl ether include ethylene glycol monobutyl ether, diethylene glycol monobutyl ether, triethylene glycol monobutyl ether, propylene glycol monomethyl ether, and dipropylene glycol monomethyl ether.
In the present invention, the water-soluble organic solvents may be used alone or in combination of two or more kinds.

<Water>
In the present invention, the ink composition contains water. In the present invention, the ink composition is preferably a so-called water-based ink in which water accounts for the largest proportion by mass.

<Surfactant>
In the present invention, the ink composition preferably contains a surfactant from the viewpoint of improving the image quality of the printed matter by allowing the ink dots to blend well with the print medium. The surfactant is preferably a nonionic surfactant, and more preferably at least one selected from the group consisting of silicone-based surfactants and acetylene glycol-based surfactants.

From the viewpoint of allowing the ink dots to blend well with the printing medium and improving the image quality of the printed matter, the silicone-based surfactant preferably has an HLB value of 5 or more, more preferably 6 or more, and preferably 12 or less, more preferably 11 or less, and even more preferably 10 or less.
As the acetylene glycol-based surfactant, from the viewpoint of allowing the ink dots to blend well with the printing medium and improving the image quality of the printed material, it is preferable to use in combination one having an HLB value of preferably 2 or more, more preferably 3 or more, and preferably 18 or less, more preferably 16 or less, and even more preferably 14 or less, and from the viewpoint of allowing the ink droplets to be ejected well, one having an HLB value of preferably 3 or more, more preferably 4 or more, and preferably 7 or less, and more preferably 6 or less.
It is more preferable to use a combination of at least one of the above acetylene glycol surfactants having different HLB values, totaling two or more of each, and at least one of the above silicone surfactants.

The HLB value is Griffin's Hydrophile-Lipophile Balance, which indicates the degree of affinity of a surfactant for water and oil. The definition of the HLB value is described in W. C. Griffin: J. Soc. Cosmetic Chemists, 1, 311 (1949), and in "Surfactant Handbook," 3rd Edition, Kogaku Tosho Publishing Co., Ltd., November 25, 1972, pp. 179-182, co-authored by Takahashi Etsutami, Namba Yoshiro, Koike Motoo, and Kobayashi Masao. It is also listed in surfactant catalogs.

Commercially available silicone surfactants include the "Silface" series manufactured by Nissin Chemical Industry Co., Ltd., the "KF" series manufactured by Shin-Etsu Chemical Co., Ltd., and the "BYK" series manufactured by BYK-Chemie.
Commercially available acetylene glycol surfactants include the "Surfynol" series and "Olfine" series manufactured by Nissin Chemical Industry Co., Ltd., and the "Acetylenol" series manufactured by Kawaken Fine Chemicals Co., Ltd.

[Preparation of Ink Composition]
In the present invention, the ink composition can be efficiently produced by mixing a pigment, (meth)acrylic resin particles not containing a pigment, a blocked isocyanate compound, a water-soluble organic solvent, water, and, if necessary, a surfactant, etc. There are no particular limitations on the method of mixing them.
The pigment is preferably mixed in the form of a pigment dispersing resin or a surfactant, or in the form of a self-dispersing pigment dispersed without using a dispersant, and more preferably in the form of resin particles containing the pigment.

[Content of each component in the ink composition]
In the present invention, the content and mass ratio of each component of the ink composition are as follows, from the viewpoint of improving the image quality of the printed matter and durability against external stress.

(Pigment content)
In the present invention, the content of the pigment in the ink composition is preferably 1% by mass or more, more preferably 2% by mass or more, even more preferably 3% by mass or more, and is preferably 12% by mass or less, more preferably 10% by mass or less, even more preferably 8% by mass or less.

(Content of resin particles containing pigment)
In the present invention, when the pigment is in the form of pigment-containing resin particles, the content of the pigment-containing resin particles in the ink composition is preferably 2 mass % or more, more preferably 3 mass % or more, even more preferably 4 mass % or more, and is preferably 10 mass % or less, more preferably 9 mass % or less, even more preferably 8 mass % or less.

(Content of non-pigmented (meth)acrylic resin particles)
In the present invention, the content of the (meth)acrylic resin particles not containing a pigment in the ink composition is preferably 1% by mass or more, more preferably 2% by mass or more, even more preferably 4% by mass or more, and is preferably 15% by mass or less, more preferably 10% by mass or less, even more preferably 8% by mass or less.

In the present invention, when the pigment in the ink composition is in the form of pigment-containing resin particles, the mass ratio of the pigment-containing resin particles to the pigment-free (meth)acrylic resin particles [content of pigment-containing resin particles/content of pigment-free (meth)acrylic resin particles] is preferably 0.5 or more, more preferably 0.7 or more, even more preferably 0.8 or more, and is preferably 3 or less, more preferably 2.5 or less, even more preferably 2 or less, even more preferably 1.5 or less, even more preferably 1 or less.

In the present invention, the mass ratio of the total amount of resin to pigment in the ink composition [total content of resin in ink composition/content of pigment] is preferably 1 or more, more preferably 1.2 or more, even more preferably 1.5 or more, and is preferably 10 or less, more preferably 6 or less, even more preferably 4 or less, and even more preferably 3 or less.

(Blocked isocyanate compound content)
In the present invention, the content of the blocked isocyanate compound in the ink composition is preferably 0.2% by mass or more, more preferably 0.5% by mass or more, even more preferably 0.7% by mass or more, still more preferably 0.9% by mass or more, and is preferably 5% by mass or less, more preferably 4% by mass or less, even more preferably 3% by mass or less, and still more preferably 2% by mass or less.

(Mass ratio of blocked isocyanate compound to pigment-free (meth)acrylic resin particles)
In the present invention, the mass ratio of the blocked isocyanate compound to the pigment-free (meth)acrylic resin particles in the ink composition [blocked isocyanate compound content/pigment-free (meth)acrylic resin particles content] is preferably 0.03 or more, more preferably 0.05 or more, even more preferably 0.07 or more, still more preferably 0.13 or more, and is preferably 0.60 or less, more preferably 0.50 or less, still more preferably 0.40 or less, still more preferably 0.30 or less, and still more preferably 0.20 or less.

(Content of Water-soluble Organic Solvent)
In the present invention, the content of the water-soluble organic solvent in the ink composition is preferably 5% by mass or more, more preferably 10% by mass or more, even more preferably 15% by mass or more, and is preferably 45% by mass or less, more preferably 40% by mass or less, even more preferably 30% by mass or less.
When the water-soluble organic solvent contains an alkylene glycol, the ratio of the alkylene glycol to the entire water-soluble organic solvent is preferably 50 mass % or more, more preferably 55 mass % or more, even more preferably 60 mass % or more, and preferably 80 mass % or less, more preferably 75 mass % or less, even more preferably 70 mass % or less.
When the water-soluble organic solvent contains polyalkylene glycol, the ratio of the polyalkylene glycol to the entire water-soluble organic solvent is preferably 10 mass % or more, more preferably 20 mass % or more, even more preferably 30 mass % or more, and is preferably 50 mass % or less, more preferably 40 mass % or less.

(Surfactant content)
In the present invention, when the ink composition contains a surfactant, the content thereof is preferably 0.5% by mass or more, more preferably 0.7% by mass or more, even more preferably 0.9% by mass or more, and is preferably 2% by mass or less, more preferably 1.7% by mass or less, even more preferably 1.5% by mass or less.
In the present invention, when the ink composition contains a silicone-based surfactant, the content thereof is preferably 0.01% by mass or more, more preferably 0.02% by mass or more, and preferably 0.2% by mass or less, more preferably 0.1% by mass or less, and even more preferably 0.05% by mass or less.
In the present invention, when the ink composition contains an acetylene glycol-based surfactant, the content thereof is preferably 0.3 mass % or more, more preferably 0.4 mass % or more, even more preferably 0.5 mass % or more, and preferably 1.5 mass % or less, more preferably 1.3 mass % or less, even more preferably 1.2 mass % or less.

(Water Content)
In the present invention, the water content in the ink composition is preferably 40% by mass or more, more preferably 50% by mass or more, even more preferably 55% by mass or more, and is preferably 80% by mass or less, more preferably 75% by mass or less, even more preferably 70% by mass or less.

<Printing process>
In the inkjet printing method of the present invention, there is no limitation on the inkjet printing, and any inkjet printing can be used, among which drop-on-demand inkjet printing is preferred.
Examples of drop-on-demand printing devices include a piezoelectric type using a piezoelectric element disposed in an inkjet head, a thermal type using thermal energy from a heater or the like disposed in an inkjet head, etc. Among these, inkjet printing using a piezoelectric type inkjet printing device is more preferable.
From the viewpoint of improving image quality, the resolution of inkjet printing is preferably 600 dpi (dots per inch) or more, and more preferably 720 dpi or more.

(Fabric)
The fabric used in the inkjet printing method of the present invention is not particularly limited. For example, it may be made of natural fibers such as cotton, hemp, or silk, semi-synthetic fibers such as rayon or acetate, or synthetic fibers such as nylon, polyester, or polyurethane. It may also be a mixed fabric containing two or more of these fibers.
Among these, from the viewpoint of improving the image quality and durability against external stress of the printed material, a fabric containing one or more selected from the group consisting of nylon, polyester, polyurethane, and cotton is preferred, and a fabric containing one or more selected from polyester and nylon is more preferred. When one or more selected from the group consisting of nylon and polyester is used in the blended fabric containing two or more types of fibers listed above, a printed material having excellent image quality and durability against external stress can be obtained by the inkjet printing method of the present invention.
Furthermore, as the fabric containing polyurethane, artificial leather or synthetic leather having a surface resin layer containing polyurethane is also preferred.

In the present invention, the temperature of the portion where the ink composition lands on the fabric by inkjet printing is, from the viewpoint of obtaining a printed material with excellent image quality, 40° C. or higher, preferably 45° C. or higher, more preferably 50° C. or higher, even more preferably 55° C. or higher, and preferably 120° C. or lower, more preferably 100° C. or lower, even more preferably 95° C. or lower, and still more preferably 70° C. or lower.
By setting the temperature of the portion where the ink composition lands on the fabric to 40°C or higher, evaporation of the water and water-soluble organic solvent contained in the ink composition after landing is promoted, the ink composition quickly thickens, bleeding is suppressed, and a printed material with excellent image quality is obtained.

In the inkjet printing method of the present invention, there is no limitation on the method of measuring the temperature of the part where the ink composition lands on the fabric, and any known method can be used. Specifically, the temperature measured by placing a temperature sensor on the platen part supporting the fabric located directly under the inkjet head may be the temperature of the part where the ink lands, or the temperature measured by using a radiation type thermometer using infrared rays at any point on the fabric within a distance of 30 cm from the part where the ink lands may be the temperature of the part where the ink lands. In addition, the temperature of the part where the ink lands can be measured using a radiation type thermometer on a surface other than the surface where the ink lands with the inkjet head, and used as the temperature of the part where the ink lands.

In the inkjet printing method of the present invention, methods for raising the temperature of the portion of the fabric where the ink composition lands to 40°C or higher include a method of heating the fabric before the ink is supplied from the inkjet head and a method of heating the fabric directly under the inkjet head. Of these, from the viewpoint of reliably raising the temperature of the fabric to 40°C or higher and improving the image quality of the printed fabric, the method of heating the fabric before the ink is supplied from the inkjet head is preferred. Examples of heating equipment include infrared lamps, sheet heaters, and devices for blowing heated air. These may be used alone or in combination. Of these, sheet heaters are preferred from the viewpoint of reliably raising the temperature of the fabric to 40°C or higher and improving the image quality of the printed fabric.

<Heating process>
In the ink-jet textile printing method of the present invention, it is preferable to include a heating step of heating the ink-jet printed portion of the fabric to a temperature of 100° C. or higher after the printing step.
By including a heating step after the printing step, in which the surface temperature of the inkjet-printed portion of the fabric is raised to 100°C or higher, in cases where the pigment-free (meth)acrylic resin particles and the pigment in the ink dots applied to the surface of the fabric are in the form of pigment-containing resin particles, and in cases where the pigment dispersing resin constituting the pigment-containing resin particles has a functional group capable of reacting with an isocyanate group, a crosslinking reaction between the pigment dispersing resin and a blocked isocyanate compound is promoted, and the crosslinked resin coating firmly bonds the pigment particles to the fabric, thereby improving durability against external stress.

In the present invention, the temperature at which the inkjet-printed portion of the fabric is adjusted after inkjet printing is preferably 100°C or higher, more preferably 110°C or higher, and even more preferably 120°C or higher, from the viewpoint of improving the durability of the printed fabric against external stress, and is preferably 200°C or lower, more preferably 170°C or lower, more preferably 160°C or lower, and even more preferably 140°C or lower, from the same viewpoint as above.

In the heating step, the equipment for raising the temperature of the fabric after the printing step to 100° C. or higher is preferably an infrared lamp, a sheet heater, a device for blowing heated air, a device for maintaining the fabric under a heated air atmosphere, etc. These may be used alone or in combination.
There is no limitation on the method of measuring the temperature of the fabric in the heating step, and any known method can be used. Specifically, it may be a method of measuring the temperature of the fabric at a point more than 30 cm away from the site where the ink lands using a radiation type thermometer using infrared rays, or a method of measuring using a temperature sensor installed on a platen part supporting the fabric. In addition, the temperature of a surface other than the inkjet printed surface at a site more than 30 cm away from the inkjet printed portion may be measured using a radiation type thermometer.

The time for which the temperature of the fabric in the heating step is raised to 100°C or higher is preferably 1 second or more, more preferably 10 seconds or more, even more preferably 30 seconds or more, and even more preferably 1 minute or more, from the viewpoint of improving the durability of the printed fabric against external stress, and is preferably 40 minutes or less, more preferably 30 minutes or less, and even more preferably 20 minutes or less, from the viewpoint of productivity.
By setting the time for which the temperature of the fabric in the heating step is kept at 100°C or higher for 1 second or longer, when the non-pigment-containing (meth)acrylic resin particles in the ink dots and the pigment are in the form of pigment-containing resin particles, and when the pigment dispersion resin constituting the pigment-containing resin particles has a functional group capable of reacting with an isocyanate group, the pigment dispersion resin is crosslinked with a blocked isocyanate compound, and the crosslinked resin coating firmly bonds the pigment particles to the fabric, thereby improving the durability of the obtained printed fabric against external stress.

<Pretreatment process>
In the present invention, a pretreatment step may be included before the printing step, in which a treatment liquid containing a compound that bonds pigment or pigment-free (meth)acrylic resin particles to the fabric through a chemical reaction is applied. Examples of the compound that bonds pigment or pigment-free (meth)acrylic resin particles to the fabric through a chemical reaction include cationic compounds and polyvalent metal salts. Examples of the cationic compound include quaternary salts of alkylamines and polymers having amino groups. Examples of the polyvalent metal salt include nitrates and halides of alkaline earth metals.
In the present invention, from the viewpoint of durability of the printed matter against external stress and from the viewpoint of productivity, it is preferable not to include the pretreatment step.

In the following manufacturing examples, preparation examples, working examples, and comparative examples, "parts" and "%" are "parts by mass" and "% by mass" unless otherwise specified. The methods for measuring each physical property are as follows.

(1) Measurement of weight average molecular weight of pigment dispersion resin and (meth)acrylic resin Using a solution of phosphoric acid and lithium bromide dissolved in N,N-dimethylformamide to concentrations of 60 mmol/L and 50 mmol/L, respectively, as an eluent, measurement was performed by gel permeation chromatography (GPC apparatus manufactured by Tosoh Corporation (HLC-8120GPC), columns manufactured by Tosoh Corporation (TSK-GEL, α-M × 2), flow rate: 1 mL/min) using monodisperse polystyrene with known molecular weight as a standard substance.

(2) Measurement of solid content concentration of aqueous dispersion 10.0 g of sodium sulfate, which had been brought to a constant weight in a desiccator, was weighed out into a 30 ml polypropylene container (φ=40 mm, height=30 mm), and about 1.0 g of the sample was added thereto and mixed, and then accurately weighed, and the mixture was maintained for 2 hours under an environment of 105° C. and a gauge pressure of −0.08 MPa to remove volatile matter, and was then left in a desiccator at room temperature (25° C.) for another 15 minutes, after which the mass was measured. The mass of the sample after removal of volatile matter was taken as the solid content, and was divided by the mass of the sample added to obtain the solid content concentration.

(3) Measurement of the average particle size of pigment-containing resin particles and pigment-free (meth)acrylic resin particles Using a laser particle analysis system "ELS-8000" (manufactured by Otsuka Electronics Co., Ltd.), a solution diluted with water was used so that the concentration of the particles to be measured was 5 x ^10-3 mass% (solid content concentration equivalent). The measurement conditions were a temperature of 25°C, an angle between the incident light and the detector of 90°, and 100 cumulative measurements. The refractive index of water (1.333) was input as the refractive index of the dispersion solvent, and the average particle size obtained by the cumulant analysis was used as the average particle size of the pigment-containing resin particles and the pigment-free (meth)acrylic resin particles.

(4) Measurement of Glass Transition Temperature of Pigment-Free (Meth)acrylic Resin Particles A water dispersion of pigment-free (meth)acrylic resin particles was freeze-dried at -10°C for 9 hours using a freeze dryer "FDU-2100" manufactured by Tokyo Rikakikai Co., Ltd., to prepare a sample. Using a differential scanning calorimeter (manufactured by Perkin Elmer, product name: Pyris 6 DSC), 5 mg of the sample was weighed into an aluminum pan, heated to 150°C, cooled from that temperature to -50°C at a temperature drop rate of 10°C/min, and then heated at a temperature increase rate of 10°C/min. The glass transition temperature was determined as the temperature at the intersection of an extension of the baseline below the maximum endothermic peak temperature and a tangent line showing the maximum slope from the rising part of the peak to the apex of the peak.

[Production of pigment dispersion resin]
Production Example a1 (Production of Resin a1)
62 parts of acrylic acid, 129 parts of styrene, and 9 parts of α-methylstyrene were mixed to prepare a monomer mixture. 20 parts of methyl ethyl ketone, 0.3 parts of 2-mercaptoethanol (polymerization chain transfer agent), and 10% of the monomer mixture were mixed in a reaction vessel, and nitrogen gas replacement was thoroughly performed. Separately, a mixture of the remainder of the monomer mixture (i.e., 90% of the prepared monomer mixture), 0.27 parts of the polymerization chain transfer agent, 60 parts of methyl ethyl ketone, and 2.2 parts of an azo-based radical polymerization initiator (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd., product name: V-65, 2,2'-azobis(2,4-dimethylvaleronitrile)) was placed in a dropping funnel, and the monomer mixture in the reaction vessel was heated to 65°C while being stirred under a nitrogen atmosphere, and the mixture in the dropping funnel was dropped over 3 hours. After 2 hours had elapsed at 65° C. from the end of the dropwise addition, a solution in which 0.3 parts of the polymerization initiator was dissolved in 5 parts of methyl ethyl ketone was added, and the mixture was further aged at 65° C. for 2 hours and at 70° C. for 2 hours to obtain a solution of resin a1 (weight average molecular weight: 12,500).
The acid value of the resin a1 is calculated to be 241 mgKOH/g from the charge ratio of the raw material monomers.

[Preparation of Water Dispersion of Pigment-Containing Resin Particles]
Preparation Example I-1 (Preparation of Water Dispersion I-1 of Pigment-Containing Resin Particles)
(1) 32 parts of resin a1 obtained by completely removing the solvent from the resin a1 solution obtained in Production Example a1 by drying under reduced pressure was mixed with 202 parts of ion-exchanged water. 12.8 parts of a 5N aqueous sodium hydroxide solution (sodium hydroxide solid content: 16.9%) (neutralization degree: 40 mol%) was further added thereto, and the mixture was heated to 90°C using a warm bath, stirred for 1 hour to disperse the resin a1 in water, and cooled to room temperature (25°C) to obtain a dispersion of resin a1 (solid content concentration: 12.8%).
(2) 246.8 parts of the dispersion of resin a1 obtained in (1) above was added with 100 parts of carbon black pigment (C.I. Pigment Black 7, manufactured by Cabot Corporation, trade name: Monarch717), and stirred for 3 hours using a disperser (manufactured by Asada Iron Works Co., Ltd., trade name: Ultra Disperser) at 20 ° C. with a disperser blade rotating at 6,000 rpm. Next, 124 parts of ion-exchanged water was added, and the mixture was dispersed 15 times at a pressure of 150 MPa using a microfluidizer (manufactured by MICROFLUIDICS, trade name). The obtained dispersion was placed in a 500 mL angle rotor, centrifuged at 3,660 rpm for 20 minutes using a high-speed cooling centrifuge (manufactured by Hitachi Koki Co., Ltd., trade name: himac CR22G, set temperature 20 ° C.), and the liquid phase portion was then collected. The collected liquid phase was filtered through a 5 μm membrane filter (Minisart, product name, manufactured by Sartorius) to obtain a pigment-containing aqueous dispersion I'-1 of resin particles. At this time, the solid content of the pigment-containing aqueous dispersion I'-1 of resin particles was 25%.
(3) 100 parts of the aqueous dispersion I'-1 of the pigment-containing resin particles obtained in (2) above was placed in a screw-top glass bottle, 32 parts of ion-exchanged water and 1.78 parts of trimethylolpropane polyglycidyl ether (Nagase ChemteX Corporation, product name: Denacol EX-321LT, epoxy value: 139) were added, the bottle was sealed, and the bottle was heated at 70°C for 5 hours while stirring with a stirrer. At this time, crosslinking treatment was performed with an amount of crosslinking agent of an epoxy amount capable of reacting with 50% of the total number of carboxyl groups contained in the resin (crosslinking rate 50 mol%). After 5 hours, the temperature was lowered to room temperature (25°C) and filtered with a 25 mL needleless syringe (Terumo Corporation) equipped with the 5 μm filter to obtain an aqueous dispersion I-1 of the pigment-containing resin particles containing crosslinked pigment (solid content concentration: 20%). The acid value of the crosslinked resin constituting the resin particles containing the crosslinked pigment is calculated to be 120.5 mgKOH/g. The average particle size of the resin particles containing the crosslinked pigment contained in the water dispersion I-1 was 99 nm. The mass ratio of the pigment dispersion resin to the pigment of the resin particles containing the crosslinked pigment contained in the water dispersion I-1 was 0.41.

Preparation Example I-2 (Preparation of Water Dispersion I-2 of Pigment-Containing Resin Particles)
In the preparation example of the aqueous dispersion I-1 of the resin particles containing a pigment, 100 parts of the carbon black pigment was replaced with 100 parts of a cyan pigment (C.I. Pigment Blue 15:3, copper phthalocyanine, manufactured by DIC Corporation, product name: TGR-SD), and the same method was used to obtain an aqueous dispersion I-2 of the resin particles containing a crosslinked pigment (solid content concentration: 20% by mass). The acid value of the resin constituting the pigment-containing resin particles contained in the aqueous dispersion I-2 of the resin particles containing a crosslinked pigment is calculated to be 120.5 mg KOH/g. The average particle size of the pigment-containing resin particles contained in the aqueous dispersion I-2 of the resin particles containing a pigment was 105 nm. In addition, the mass ratio of the pigment dispersion resin to the pigment of the resin particles containing a crosslinked pigment contained in the aqueous dispersion I-2 was 0.41.

[Production of pigment-free (meth)acrylic resin particles]
Production Example b1 (Production of Pigment-Free (Meth)acrylic Resin Particles b1)
A separable flask was charged with 3 parts of acrylic acid, 60 parts of methyl methacrylate, 110 parts of n-butyl acrylate, 27 parts of methyl acrylate, 18.5 parts of an aqueous solution of sodium polyoxyethylene (18) lauryl ether sulfate as an emulsifier (manufactured by Kao Corporation, product name: LATEMULU E-118B, solids content 26%), 96 parts of ion-exchanged water, and 0.4 parts of potassium persulfate, and the mixture was stirred with a stirring blade (300 rpm) to obtain a monomer emulsion.
On the other hand, 4.6 parts of an aqueous solution of sodium polyoxyethylene (18) lauryl ether sulfate, 186 parts of ion-exchanged water, and 0.08 parts of potassium persulfate were placed in a reaction vessel, and the vessel was thoroughly purged with nitrogen gas. Under a nitrogen atmosphere, the temperature in the reaction vessel was raised to 80° C. while stirring (200 rpm) with a stirring blade, and the monomer emulsion was added dropwise over 3 hours, followed by reaction for 1 hour to obtain a water dispersion (solid concentration: 40%) of pigment-free (meth)acrylic resin particles b1 (weight average molecular weight: 470,000).
The pigment-free (meth)acrylic resin particles b1 had an average particle size of 130 nm and a glass transition temperature of 0° C. The pigment-free (meth)acrylic resin particles b1 were composed of a (meth)acrylic resin having acrylic acid, methyl methacrylate, n-butyl acrylate, and methyl acrylate as structural units.

Production Example b2 (Production of Pigment-Free (Meth)acrylic Resin Particles b2)
A water dispersion (solids concentration: 40%) of pigment-free (meth)acrylic resin particles b2 (weight average molecular weight: 490,000) was obtained in the same manner as in Production Example b1, except that the amount of methyl methacrylate and the amount of n-butyl acrylate charged in the separable flask were changed to 74 parts and 96 parts, respectively.
The pigment-free (meth)acrylic resin particles b2 had an average particle size of 127 nm and a glass transition temperature of 11° C. The pigment-free (meth)acrylic resin particles b2 were composed of a (meth)acrylic resin having acrylic acid, methyl methacrylate, n-butyl acrylate, and methyl acrylate as structural units.

[Preparation of Water-Based Inks II-1 to II-8]
Preparation Examples 1 to 8
Into a glass container, as shown in the column of ink formulation in Table 1, an aqueous dispersion I-1 or I-2 of pigment-containing resin particles, an aqueous dispersion of pigment-free resin particles b1 or b2, a dispersion of other resin particles (resin particles not containing pigment), a dispersion of a blocked isocyanate compound, a water-soluble organic solvent, a surfactant, and ion-exchanged water were added, and then stirred for 1 hour. Note that the ion-exchanged water was added so that the total amount of the ink formulation was 100 parts. Thereafter, filtration was performed using a 5 μm disposable membrane filter (manufactured by Sartorius, product name "Minisart") to obtain water-based inks II-1 to II-8.

Details of the dispersion of other resin particles (resin particles not containing a pigment), the blocked isocyanate compound, the water-soluble organic solvent, and the surfactant described in Table 1 are as follows.
(Dispersion of other resin particles (resin particles not containing pigment))
Superflex 300 (manufactured by Daiichi Kogyo Seiyaku Co., Ltd., dispersion of polyester ether-based polyurethane resin particles, solid content 30%)
(Blocked isocyanate compound dispersion)
Bayhydur BL2867 (manufactured by Sumika Covestro Urethane Co., Ltd., aqueous dispersion of dimethylpyrazole type blocked isocyanate compound, solid content 37.9%, isocyanate equivalent 960)
(Water-soluble organic solvent)
・Propylene glycol, dipropylene glycol (surfactant)
[Silicone-based surfactant]
Silface SAG005 (manufactured by Nissin Chemical Industry Co., Ltd., polyether modified silicone, active ingredient 100%)
[Acetylene-based surfactants]
Surfynol 465 (manufactured by Nissin Chemical Industry Co., Ltd., ethylene oxide (EO) adduct of 2,4,7,9-tetramethyl-5-decyne-4,7-diol, average number of moles of EO added: 10, active content 100%)
Surfynol 420 (manufactured by Nissin Chemical Industry Co., Ltd., EO adduct of 2,4,7,9-tetramethyl-5-decyne-4,7-diol, average number of moles of EO added: 1.3, active content 100%)

<Preparation of printed matter>
Examples 1 to 5, 7 to 12, Comparative Examples 1 to 3
Using the obtained water-based inks II-1 to II-8, printed materials were produced and evaluated under the conditions shown in Table 1 and in the following procedure. The results are shown in Table 1.
(Printing process)
The obtained water-based ink was filled into a print evaluation device (manufactured by Tritec Co., Ltd.) equipped with an inkjet head (manufactured by Kyocera Corporation, product name: KJ4B-HD06MHG-STDV, piezo type) in an environment of temperature 25±1°C and relative humidity 30±5%. The head voltage was 26V, frequency 15kHz, head temperature 32°C, ejection droplet volume 5pL, resolution 600×600dpi, number of flushings before ejection 200 shots, and negative pressure -4.0kPa were set. At this time, one-pass printing was performed using two inkjet heads for one type of ink, and the total resolution was 1200dpi in the horizontal direction×600dpi in the feed direction. An A4-sized film heater (manufactured by Kawai Electric Manufacturing Co., Ltd.) was fixed on the transport table, and the fabric shown in Table 1 as the printing medium was fixed on the heater with double-sided tape in a direction in which the longitudinal direction of the printing medium and the transport direction were the same. A print command was transferred to the print evaluation device while adjusting the heater strength so that the temperature of the part where the ink landed would be the temperature shown in Table 1, as measured by an infrared radiation thermometer MT-4 (manufactured by Raytec Corporation). For evaluating image quality (bleeding), a print pattern having 50 Japanese hiragana characters (MS Mincho), 24 alphabet characters (Times New Roman), and numbers 1 to 30 (Times New Roman) with a font size of 8 pt, and for evaluating friction fastness, a print pattern with a duty of 30% of 2 cm in the transport direction were inkjet printed, to obtain inkjet prints.
(Heating process)
The obtained inkjet printed matter was placed in a constant temperature dryer adjusted to 120° C. except for Example 7, and 170° C. for Example 7, and the temperature of the inkjet-printed surface of the fabric was measured with the infrared radiation thermometer described above, and after it was confirmed that the inkjet-printed surface of the fabric was maintained at each temperature for 20 minutes, the temperature was returned to room temperature of 23±1° C., and a printed textile was obtained. The obtained printed textile was subjected to each evaluation.

Example 6
A treatment liquid containing a polyvalent metal salt prepared as described below was uniformly sprayed onto the fabric in such an amount that the amount of polyvalent metal salt applied to the fabric was 5.0 g/ ^m2 , and then the fabric was dried by heating in a constant temperature dryer at 100°C for 5 minutes and then returned to room temperature of 23±1°C. Using the water-based ink II-1, a printed fabric was obtained in the same manner as in Example 1. The obtained printed fabric was subjected to each evaluation.

(Preparation of treatment solution containing polyvalent metal salt)
A glass container was charged with 8% calcium nitrate tetrahydrate (manufactured by FUJIFILM Wako Pure Chemical Industries, Ltd., solid content 100%), 0.1% silicone surfactant (manufactured by BYK Japan K.K., product name: BYK-348, active content 100%), 5.6% styrene/acrylic emulsion (manufactured by Japan Coating Resins Co., Ltd., product name: Mowinyl 966A, solid content 45%), and 86.3% ion-exchanged water, and the mixture was stirred with a magnetic stirrer for 10 minutes to obtain a treatment liquid containing a polyvalent metal salt.

The print media shown in Table 1 are as follows. All the fabrics were cut to A5 size before use.
PES (polyester): Polyester Tropical Toray (120 g/m ² , manufactured by Shikisensha Co., Ltd.)
Nylon: Nylon 6 taffeta (70 g/m ² , manufactured by Shikisen Co., Ltd.)
Cotton: Cotton broadcloth 40 with mercerized finish (122 g/ ^m2 , manufactured by Shikisen Co., Ltd.)

<Evaluation>
(1) Evaluation of Image Quality (Bleeding) The print patterns of the printed materials for evaluating image quality (bleeding) obtained in the Examples and Comparative Examples were visually observed to evaluate the image quality.
If the evaluation standard is A or B, there is no problem in practical use.
(Evaluation criteria)
A: There is no bleeding or crushing of any of the letters or numbers, and they are completely legible.
B: Some bleeding is observed in some of the letters and numbers, and the sharpness is inferior to that of A, but not so much that the letters and numbers cannot be distinguished.
C: The letters and numbers are partially or entirely blurred by ink bleeding and cannot be identified.

(2) Evaluation of dry rub fastness The prints for evaluating rub fastness obtained in the examples and comparative examples were subjected to a dry rub test in accordance with JIS L0849:2013 using a type II rub tester, and were evaluated using a discoloration gray scale. Grade 3 or higher for dry rub fastness is acceptable, grades 3-4 or higher are excellent, and grade 4 or higher is even better.
(3) Evaluation of Wet Rub Fastness The printed materials for evaluating rub fastness obtained in the Examples and Comparative Examples were subjected to a wet rub test in accordance with JIS L0849:2013 using a type II rub tester, and were evaluated using a discoloration gray scale. Grade 3 or higher for wet rub fastness is acceptable, grades 3-4 or higher are excellent, and grade 4 or higher is even better.

From Table 1, it can be seen that the printed materials obtained in Examples 1 to 12 have superior image quality and durability against external stress such as rubbing, compared to the printed materials obtained in Comparative Examples 1 to 3.

Claims (6)

The method includes a printing step of ink-jet printing an ink composition containing a pigment, (meth)acrylic resin particles not containing a pigment, a blocked isocyanate compound, a water-soluble organic solvent, and water onto a fabric having a temperature of 40° C. or higher at a portion where the ink composition lands,
The (meth)acrylic resin constituting the pigment-free (meth)acrylic resin particles has a functional group capable of reacting with an isocyanate group. The inkjet printing method according to claim 1, wherein the glass transition temperature of the pigment-free (meth)acrylic resin particles is 30°C or lower. The inkjet printing method according to claim 1 or 2, further comprising a heating step for heating the inkjet-printed portion of the fabric to 100°C or higher after the printing step. The inkjet printing method according to any one of claims 1 to 3, wherein the water-soluble organic solvent contains one or more selected from the group consisting of alkylene glycols and polyalkylene glycols. The inkjet printing method according to any one of claims 1 to 4, wherein the fabric contains at least one material selected from polyester and nylon. The inkjet printing method according to any one of claims 1 to 5, wherein the pigment is in the form of resin particles containing the pigment.