JP7413809B2 - Inkjet printing method - Google Patents

Description

The present invention relates to an ink set and an inkjet textile printing method.

In the inkjet textile printing method, for example, an inkjet ink containing pigment particles and a dispersant is used. Inkjet inks using pigment particles are required to have excellent ejection stability and to be able to form images with excellent image density.

As an inkjet ink with excellent ejection stability, for example, an inkjet ink containing pigment particles having an aspect ratio of 1.0 or more and 2.0 or less has been proposed (Patent Document 1). Further, as an inkjet ink that can form an image with excellent image density, for example, an inkjet ink containing pigment particles having an aspect ratio of 5.0 or more and 7.0 or less has been proposed (Patent Document 2).

Japanese Patent Application Publication No. 2017-141387 JP2009-029888A

However, the inkjet ink described in Patent Document 1 tends to result in images formed with insufficient image density. Further, the inkjet ink described in Patent Document 2 tends to have insufficient ejection stability.

The present invention has been made in view of the above problems, and an object of the present invention is to provide an ink set and an inkjet textile printing method that can form an image with excellent ejection stability of inkjet ink and excellent image density. .

The ink set according to the present invention includes an inkjet ink and a pretreatment liquid. The inkjet ink contains pigment particles and an anionic dispersant. The long axis of the pigment particles is 50 nm or more and 200 nm or less. The aspect ratio of the pigment particles is 2.0 or more and 3.0 or less. The pretreatment liquid contains water and a cationic material.

An inkjet textile printing method according to the present invention is an inkjet textile printing method in which an image is formed on an image forming area of a fabric using the above-described ink set, and the method includes a pretreatment step of applying the pretreatment liquid to the image forming area; and an ink ejection step of ejecting the inkjet ink onto the image forming area using a head.

According to the ink set and inkjet textile printing method according to the present invention, it is possible to form an image with excellent ejection stability of inkjet ink and excellent image density.

Embodiments of the present invention will be described below. Note that the "longer diameter" of the pigment particles is the average value of the longer diameters of 100 pigment particles measured using an electron microscope. The "breadth axis" of the pigment particles is the average value of the short diameters of 100 pigment particles measured using an electron microscope. The "aspect ratio" of a pigment particle is the ratio of the major axis of the pigment particle (average value of the major axis of 100 pigment particles) to the minor axis of the pigment particle (average value of the minor axis of 100 pigment particles) (major axis/short axis). diameter).

In this specification, acrylic and methacrylic may be collectively referred to as "(meth)acrylic". Each component described in this specification may be used alone or in combination of two or more.

<First embodiment: Ink set>
An ink set according to a first embodiment of the present invention will be described below. The ink set of the present invention includes an inkjet ink (hereinafter sometimes simply referred to as ink) and a pretreatment liquid. The ink contains pigment particles and an anionic dispersant. The long axis of the pigment particles is 50 nm or more and 200 nm or less. The aspect ratio of the pigment particles is 2.0 or more and 3.0 or less. The pretreatment liquid contains water and a cationic material.

The ink set of the present invention is suitable, for example, as an ink set used in an inkjet textile printing method described below.

By having the above-described configuration, the ink set of the present invention can form an image with excellent ink ejection stability and excellent image density. The reason is presumed to be as follows. Generally, pigment particles tend to have anionic properties. Since the ink included in the ink set of the present invention uses pigment particles that tend to have anionic properties in combination with a dispersant that has anionic properties, the pigment particles have relatively strong anionic properties. On the other hand, the pretreatment liquid included in the ink set of the present invention contains a cationic material. The cationic material promotes adsorption of pigment particles to the fabric by imparting cationic properties to the fabric. Moreover, the cationic material causes the pigment particles to aggregate on the fabric by suppressing electrostatic repulsion between the pigment particles. Furthermore, since the pigment particles contained in the ink included in the ink set of the present invention have a relatively large aspect ratio of 2.0 or more, they tend to remain on the surface of the fabric without penetrating into the interior of the fabric. As described above, the ink set of the present invention can form images with excellent image density.

Additionally, in general, ink containing pigment particles with an excessively large aspect ratio (for example, pigment particles with an aspect ratio of more than 3.0) increases in viscosity when the concentration of pigment particles increases due to drying. It tends to be easy. However, the pigment particles contained in the ink provided in the ink set of the present invention have an aspect ratio of 3.0 or less, and the aspect ratio is not excessively large. Therefore, the ink provided in the ink set of the present invention dries while adhering to the nozzle portion of the inkjet textile printing apparatus, and its viscosity is unlikely to increase even when the concentration of pigment particles increases. As described above, the ink set of the present invention has excellent ink ejection stability.

[ink]
The ink contains pigment particles and an anionic dispersant. Preferably, the ink further contains at least one of water, a water-soluble organic solvent, and a nonionic surfactant.

(pigment particles)
Pigment particles include pigment. Pigment particles exist, for example, dispersed in a solvent. The major axis of the pigment particles is 50 nm or more and 200 nm or less, preferably 100 nm or more and 200 nm or less, and more preferably 150 nm or more and 180 nm or less. By setting the major axis of the pigment particles to 50 nm or more, the image density of the formed image can be improved. By setting the major axis of the pigment particles to 200 nm or less, the ejection stability of the ink can be improved.

The aspect ratio of the pigment particles is 2.0 or more and 3.0 or less, preferably 2.3 or more and 2.9 or less. By setting the aspect ratio of the pigment particles to 2.0 or more, the image density of the formed image can be improved. By setting the aspect ratio of the pigment particles to 3.0 or less, the ejection stability of the ink can be improved.

Examples of pigments include yellow pigments, orange pigments, red pigments, blue pigments, violet pigments, and black pigments. Examples of yellow pigments include C.I. I. pigment yellow (74, 93, 95, 109, 110, 120, 128, 138, 139, 151, 154, 155, 173, 180, 185, and 193). Examples of orange pigments include C.I. I. Pigment Orange (34, 36, 43, 61, 63, and 71). Examples of red pigments include C.I. I. Pigment Red (122 and 202). Examples of blue pigments include C.I. I. Pigment Blue (15, more specifically 15:3). Examples of the purple pigment include C.I. I. pigment violet (19, 23, and 33). Examples of black pigments include C.I. I. Pigment Black (7).

The content of pigment particles in the ink is preferably 1.0% by mass or more and 15.0% by mass or less, more preferably 5.0% by mass or more and 10.0% by mass or less. By setting the content of pigment particles to 1.0% by mass or more, the image density of the formed image can be improved. By controlling the content of pigment particles to 15.0% by mass or less, the fluidity of the ink can be improved.

(Dispersant with anionic properties)
Examples of the anionic dispersant include anionic surfactants, polymers having acid groups, and salts of polymers having acid groups. Examples of the acid group include a carboxy group and a sulfo group.

Anionic surfactants include, for example, fatty acid soaps (eg, sodium stearate and sodium dodecanoate) and sulfonate compounds (eg, sodium dodecyl sulfate and sodium dodecylbenzene sulfonate).

Examples of the polymer having acid groups include copolymers having repeating units derived from polycarboxylic acid and (meth)acrylic acid. Examples of the polycarboxylic acid include poly(meth)acrylic acid, polymaleic acid, polyphthalic acid, and a copolymer of (meth)acrylic acid and maleic acid. Examples of copolymers having repeating units derived from (meth)acrylic acid include copolymers having repeating units derived from (meth)acrylic acid and repeating units derived from vinyl compounds other than (meth)acrylic acid. Examples include polymers. Examples of vinyl compounds other than (meth)acrylic acid include styrene and (meth)acrylic acid alkyl esters.

Examples of salts of polymers having acid groups include alkylolammonium salts of polymers having acid groups, and metal salts (eg, sodium salts) of polymers having acid groups. Examples of the alkylol ammonium salt of a polymer having an acid group include "DISPERBYK (registered trademark) 180", "DISPERBYK (registered trademark) 181" and "DISPERBYK (registered trademark) 187" manufactured by BYK Chemie Japan Co., Ltd. Can be mentioned.

As the anionic dispersant, an alkylol ammonium salt of a polymer having an acid group is preferable.

In the ink, the content of the anionic dispersant is preferably 0.1% by mass or more and 3.0% by mass or less, more preferably 0.3% by mass or more and 1.0% by mass or less. By setting the content of the anionic dispersant to 0.1% by mass or more, the dispersibility of pigment particles in the ink can be improved. By controlling the content of the anionic dispersant to 3.0% by mass or less, the ejection properties of the ink can be improved.

(water)
When the ink contains water, the content of water in the ink is preferably 30.0% by mass or more and 70.0% by mass or less, and preferably 40.0% by mass or more and 60.0% by mass or less.

(Water-soluble organic solvent)
Examples of water-soluble organic solvents include glycol compounds, ether compounds of polyhydric alcohols, lactam compounds, nitrogen-containing compounds, acetate compounds, thiodiglycol, glycerin, and dimethyl sulfoxide.

Examples of glycol compounds include ethylene glycol, 1,3-propanediol, 1,2-propanediol, diethylene glycol, triethylene glycol, and tetraethylene glycol.

Examples of ether compounds of polyhydric alcohols include diethylene glycol diethyl ether, diethylene glycol monobutyl ether, ethylene glycol monomethyl ether, ethylene glycol monobutyl ether, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, diethylene glycol diethyl ether, triethylene glycol monomethyl ether, and triethylene. Examples include glycol monoethyl ether and propylene glycol monomethyl ether.

Examples of lactam compounds include 2-pyrrolidone and N-methyl-2-pyrrolidone.

Examples of nitrogen-containing compounds include 1,3-dimethylimidazolidinone, formamide, and dimethylformamide.

Examples of the acetate compound include diethylene glycol monoethyl ether acetate.

The water-soluble organic solvent is preferably a glycol compound, a lactam compound, or glycerin, and more preferably 1,3-propanediol, triethylene glycol, 2-pyrrolidone, or glycerin.

When the ink contains a water-soluble organic solvent, the content of the water-soluble organic solvent in the ink is preferably 20.0% by mass or more and 60.0% by mass or less, and 30.0% by mass or more and 50.0% by mass or less. is more preferable.

When the ink contains a glycol compound, the content of the glycol compound in the ink is preferably 10.0% by mass or more and 45.0% by mass or less, more preferably 25.0% by mass or more and 35.0% by mass or less.

When the ink contains a lactam compound, the content of the lactam compound in the ink is preferably 0.5% by mass or more and 10.0% by mass or less, more preferably 1.5% by mass or more and 5.0% by mass or less.

When the ink contains glycerin, the content of glycerin in the ink is preferably 1.0% by mass or more and 15.0% by mass or less, more preferably 3.0% by mass or more and 8.0% by mass or less.

(Nonionic surfactant)
The nonionic surfactant improves the compatibility and dispersion stability of each component contained in the ink. Moreover, the nonionic surfactant improves the permeability (wettability) of the ink to the fabric.

Examples of nonionic surfactants include polyoxyethylene dodecyl ether, polyoxyethylene hexadecyl ether, polyoxyethylene nonylphenyl ether, polyoxyethylene sorbitan monooleate ether, monodecanoyl sucrose, and ethylene oxide addition of acetylene glycol. Things can be mentioned. As the nonionic surfactant, an ethylene oxide adduct of acetylene glycol is preferred.

When the ink contains a nonionic surfactant, the content of the nonionic surfactant in the ink is preferably 0.1% by mass or more and 5.0% by mass or less, and 0.5% by mass or more and 2.0% by mass or less. is more preferable.

(other ingredients)
The ink may further contain known additives (for example, a solubility stabilizer, a drying inhibitor, an antioxidant, a viscosity modifier, a pH adjuster, and a fungicide) as necessary.

[Ink preparation method]
The ink can be prepared, for example, by uniformly mixing the pigment dispersion and other components (for example, water, a water-soluble organic solvent, and a nonionic surfactant) blended as necessary using a stirrer. In preparing the ink, after uniformly mixing each component, foreign substances and coarse particles may be removed by filtration treatment or centrifugation treatment.

(Pigment dispersion)
The pigment dispersion is a dispersion containing pigment particles and an anionic dispersant. Water is preferred as the dispersion medium for the pigment dispersion.

The content ratio of pigment particles in the pigment dispersion is, for example, 5.0% by mass or more and 25.0% by mass or less. The content of the anionic dispersant in the pigment dispersion is, for example, 5.0% by mass or more and 15.0% by mass or less.

The pigment dispersion liquid can be prepared by wet-dispersing pigment particles, an anionic dispersant, a dispersion medium (for example, water), and optionally added components using a media-type wet dispersion machine. In wet dispersion using a media-type wet dispersion machine, for example, small diameter beads (for example, beads having a D ₅₀ of 0.5 mm or more and 1.5 mm or less) can be used as the media. The material of the beads is not particularly limited, but hard materials (eg, glass and zirconia) are preferred.

When a pigment dispersion is used in the production of ink, the ratio of the pigment dispersion to the total raw materials of the ink is, for example, 30.0% by mass or more and 70.0% by mass or less.

(Method for preparing pigment particles)
Pigment particles having the above-mentioned major axis and aspect ratio can be obtained, for example, by salt milling. A specific example of salt milling will be described below. First, the raw material pigment (hereinafter sometimes referred to as pigment raw material), salt (e.g., sodium chloride), solvent, and optional additives (e.g., dispersion aid) are prepared. Mix and get a mixture. Next, the mixture is kneaded using a kneader (eg, a double-arm kneader). Next, the mixture after kneading is washed with water to remove salt and solvent, and then dried. Pigment particles are thereby obtained. In salt milling, the major axis and aspect ratio of pigment particles can be adjusted by changing the kneading conditions and the amount of salt used.

The kneading conditions are, for example, a temperature of 50° C. or more and 100° C. or less, a rotation speed of 1000 rpm or more and 4000 rpm or less, and a treatment time of 1 hour or more and 10 hours or less.

Examples of salts used in salt milling include sodium chloride, calcium chloride, and potassium chloride. As the salt, sodium chloride is preferred. In salt milling, as the amount of salt used increases, the longer diameter and aspect ratio of the resulting pigment particles tend to become smaller. The amount of salt used is preferably 300 parts by mass or more and 600 parts by mass or less, more preferably 350 parts by mass or more and 450 parts by mass or less, based on 100 parts by mass of the pigment raw material. When the amount of salt used is 300 parts by mass or more and 600 parts by mass or less, pigment particles having the above-mentioned major axis and aspect can be easily obtained.

As the solvent used for salt milling, for example, a water-soluble organic solvent can be used. Examples of water-soluble organic solvents used in salt milling include compounds similar to those exemplified as water-soluble organic solvents used in ink. The water-soluble organic solvent used in salt milling is preferably a glycol compound, and more preferably diethylene glycol. The amount of the solvent used is preferably 100 parts by mass or more and 400 parts by mass or less, more preferably 150 parts by mass or more and 250 parts by mass or less, based on 100 parts by mass of the pigment raw material.

Dispersion aids improve the dispersibility of pigment particles. Examples of the dispersion aid include pigment derivatives (compounds in which a polar functional group is introduced into a pigment). When using a pigment derivative in salt milling, the amount of the pigment derivative used is preferably 3.0 parts by mass or more and 15.0 parts by mass or less based on 100 parts by mass of the pigment.

[Pre-treatment liquid]
The pretreatment liquid contains water and a cationic material. Although the pretreatment liquid may contain components other than water and the cationic material (for example, a binder resin and a water-soluble organic solvent), it is preferable to contain only water and the cationic material. In the pretreatment liquid, the total content of water and cationic material is preferably 90% by mass or more, more preferably 100% by mass.

Cationic materials include, for example, metal salts, cationic polymers, and cationic surfactants. As the cationic material, metal salts are preferred.

Examples of the cation in the metal salt include monovalent metal ions and polyvalent metal ions. Examples of monovalent metal ions include sodium ions and potassium ions. Examples of polyvalent metal ions include calcium ions, magnesium ions, copper ions, nickel ions, zinc ions, barium ions, aluminum ions, titanium ions, strontium ions, chromium ions, cobalt ions, and iron ions. As the cation in the metal salt, calcium ions are preferred.

Examples of the anion in the metal salt include chloride ion, bromide ion, iodide ion, nitrate ion, sulfate ion, acetate ion, carbonate ion, and hydroxide ion. The anion in the metal salt is preferably a chloride ion.

Examples of metal salts include calcium chloride, calcium nitrate, calcium sulfate, calcium acetate, calcium hydroxide, calcium carbonate, magnesium chloride, magnesium acetate, magnesium sulfate, magnesium carbonate, barium sulfate, barium chloride, zinc sulfide, zinc carbonate, and Examples include copper nitrate. Calcium chloride is preferred as the metal salt.

The content of the cationic material in the pretreatment liquid is preferably 1.0% by mass or more and 10.0% by mass or less, more preferably 3.0% by mass or more and 7.0% by mass or less. Further, the content of the cationic material in the solid content of the pretreatment liquid is preferably 80.0% by mass or more and 100.0% by mass or less, more preferably 95.0% by mass or more and 100.0% by mass or less.

(water)
The content of water in the pretreatment liquid is preferably 50.0% by mass or more and 90.0% by mass or less, and preferably 60.0% by mass or more and 80.0% by mass or less.

[Preparation method of pretreatment liquid]
The pretreatment liquid can be prepared, for example, by mixing water and a cationic material. Note that natural water with high hardness can also be used as it is as the pretreatment liquid.

<Second embodiment: Inkjet textile printing method>
Next, an inkjet textile printing method according to a second embodiment of the present invention will be described. The inkjet textile printing method of the present invention forms an image in an image forming area of a fabric using the ink set according to the first embodiment. The inkjet textile printing method of the present invention includes a pretreatment step of applying a pretreatment liquid to an image forming area, and an ink ejection step of ejecting ink to the image forming area with a head. Since the inkjet textile printing method of the present invention uses the ink set according to the first embodiment, it is possible to form an image with excellent ink ejection stability and excellent image density.

The material of the fabric used in the inkjet printing method of the present invention is not particularly limited, but includes, for example, cotton, silk, linen, acetate resin, rayon, nylon resin, polyurethane resin, and polyester resin. Cotton is preferred as the material for the fabric.

[Pre-treatment process]
In this step, a pretreatment liquid is applied to the image forming area of the fabric. The method of applying the pretreatment liquid to the image forming area is not particularly limited, but examples include a method of discharging the pretreatment liquid with a head, a method of dispersing the pretreatment liquid with a spray, and a method of storing the pretreatment liquid. An example of this method is to immerse the fabric in a tank. In this step, it is preferable to dry the fabric after applying the pretreatment liquid to the image forming area of the fabric.

[Ink discharge process]
In this step, a head discharges ink onto the image forming area of the fabric to form a desired image. Examples of the head include, but are not limited to, a piezo head and a thermal inkjet head.

In this step, the amount of ink ejected is preferably 1.0 g/m ² or more and 10.0 g/m ² or less.

Examples of the present invention will be described below. However, the present invention is not limited to the following examples.

[Preparation of pigment particles]
Pigment particles (p-1) to (p-16) were prepared by the following method. First, the pigment raw material and the dispersion aid will be explained.

(pigment raw material)
・Pigment raw material (B): "Heliogen (registered trademark) Blue D7088" manufactured by BASF Corporation, Cyan pigment / Pigment raw material (M): "Magenta D4550" manufactured by BASF Corporation, Magenta pigment / Pigment raw material (Y): BASF stock "Palcohol Yellow D1115J" manufactured by the company, yellow pigment/pigment raw material (K): "MONARCH (registered trademark) 800" manufactured by Cabot Co., Ltd., black pigment (carbon black)

(Dispersion aid)
・Dispersion aid (A-1): "BYK-SYNERGIST 2100" manufactured by BYK Chemie Japan Co., Ltd., pigment derivative ・Dispersion aid (A-2): "BYK-SYNERGIST 2105" manufactured by BYK Chemie Japan Co., Ltd., pigment derivative

(Preparation of pigment particles (p-1))
250 parts by mass of the above pigment raw material (B), 20 parts by mass of dispersion aid (A-1), 1000 parts by mass of sodium chloride as a salt, and 500 parts by mass of diethylene glycol as a solvent were mixed. The obtained mixture was filled into a double-arm kneader (“S5-2” manufactured by Moriyama Co., Ltd.) (ratio of volume of mixture to capacity of kneader: approximately 50% by volume), and heated at a temperature of 80°C, normal humidity, and a rotation speed of 2000 rpm. The mixture was kneaded (salt milled) for 5 hours under the following conditions. After washing the obtained kneaded material with water, it was dehydrated using a filter press machine ("Manual Filter Press SQ" manufactured by Kurita Kikai Seisakusho Co., Ltd.). The dehydrated kneaded product was dried in a vacuum dryer for 24 hours and coarsely ground to obtain pigment particles (p-1).

(Preparation of pigment particles (p-2) to (p-16))
Pigment particles (p-2) to (p-16) were prepared in the same manner as in the preparation of pigment particles (p-1), except for the following changes. In the preparation of pigment particles (p-2) to (p-16), the types and amounts of raw materials used were changed as shown in Tables 1 and 2 below. In addition, in Tables 1 and 2 below, "-" indicates that the corresponding raw material was not used.

[Preparation of pigment dispersion]
Pigment dispersions (P-1) to (P-17) were prepared by the following method. First, the dispersant used in preparing the pigment dispersion will be explained.

(dispersant)
- Anionic dispersant: "DISPERBYK (registered trademark) 180" manufactured by BYK Chemie Japan Co., Ltd. (alkylolammonium salt of a polymer having an acid group, non-volatile content 81% by mass)
- Cationic dispersant: "DISPERBYK (registered trademark) 161" manufactured by BYK Chemie Japan Co., Ltd. (high molecular weight block copolymer with pigment affinity group, non-volatile content 30% by mass)

(Preparation of pigment dispersion (P-1))
After adding 760 parts by mass of ion-exchanged water to 90 parts by mass of the above-mentioned anionic dispersant, 150 parts by mass of pigment particles (p-1) were further added. The resulting mixture was premixed by stirring at 5000 rpm for 1 hour using a high-speed rotating disper (T.K. Robomix+T.K. Homodisper 2.5 model, manufactured by Primix). Next, a dispersion treatment was performed using a bead mill ("MSC50" manufactured by Nippon Coke Industry Co., Ltd.). In the dispersion process, zirconia beads (diameter 0.2 mm) were used as the media. In addition, in the dispersion treatment, the media filling rate in the bead mill vessel was 80% by volume. As a result, a pigment dispersion (P-1) was obtained.

(Preparation of pigment dispersions (P-2) to (P-17))
Pigment dispersions (P-2) to (P-17) were prepared in the same manner as in the preparation of pigment dispersion (P-1), except for the following changes. In the preparation of pigment dispersions (P-2) to (P-17), the types of raw materials used were changed as shown in Tables 3 and 4 below.

[Preparation of ink]
(Preparation of ink (I-1))
50 parts by mass of pigment dispersion (P-1), 10 parts by mass of ion-exchanged water, 5 parts by mass of glycerin, 15 parts by mass of 1,3-propanediol, 16 parts by mass of triethylene glycol, 3 parts by mass of 2-pyrrolidone. parts by mass and a nonionic surfactant (Nissin Chemical Industry Co., Ltd. "Surfynol (registered trademark) 420" (acetylene glycol surfactant)) were mixed and stirred. In this way, ink (I-1) was prepared.

(Preparation of inks (I-2) to (I-17))
Inks (I-2) to (I-17) were prepared in the same manner as ink (I-1) except for the following changes. In the preparation of inks (I-2) to (I-17), the types of pigment dispersions were changed as shown in Tables 5 and 6 below.

[Preparation of major axis and aspect ratio of pigment particles]
The major axis and aspect ratio of the pigment particles were measured by the following method. The measurement results are shown in Tables 5 and 6 below. First, a mesh substrate ("4110S-CF" manufactured by Alliance Biosystems) was immersed in a tank storing the measurement target (specifically, any of the inks (I-1) to (I-17)). Next, the mesh substrate to which the measurement target had been adsorbed was frozen using liquid nitrogen. Next, the pigment particles adsorbed on the above-mentioned mesh substrate were observed using a transmission electron microscope ("JEM2200FS" manufactured by JEOL Ltd.). The average value of the major axis of 100 pigment particles was measured, and the obtained average value was taken as the major axis of the pigment particle. The average value of the breadth of 100 pigment particles was measured, and the obtained average value was taken as the breadth of the pigment particle. The ratio (major axis/breadth axis) of the major axis of the pigment particle (average value of the major axis of 100 pigment particles) to the minor axis of the pigment particle (average value of the minor axis of 100 pigment particles) is calculated as the aspect ratio of the pigment particle. It was compared.

In the measurement of the major axis of the pigment particles, the distance between two imaginary parallel lines that can sandwich the pigment particle to be measured and is set so that the distance is the maximum is taken as the measured value of the major axis. In addition, when measuring the minor axis of pigment particles, the width measured at the point where it intersects with the third virtual parallel line that is set to be equidistant from each of the two virtual parallel lines described above is shortened. This was taken as the measured value of the diameter.

In Tables 5 and 6 below, the colors "C", "M", "Y" and "K" represent cyan, magenta, yellow and black, respectively.

<Ink set>
A 5% by mass calcium chloride aqueous solution was prepared and used as a pretreatment liquid. Any one of inks (I-1) to (I-17) and a pretreatment liquid were combined to form an ink set.

<Evaluation>
Inkjet printing was performed using each ink set or ink according to the following method. Then, the ejection stability of the ink and the image density of the formed image were evaluated. The evaluation results are shown in Tables 7 and 8 below. As the fabric, cotton broadcloth (manufactured by Irosensha Co., Ltd.) was used. Note that the evaluation was performed at a temperature of 23° C. and a humidity of 50% RH (normal temperature and normal humidity environment).

[Evaluation machine]
A prototype machine manufactured by Kyocera Document Solutions Co., Ltd. was used as an evaluation machine. The evaluation machine was equipped with a recording head ("KJ4B-YH" manufactured by Kyocera Corporation) having a plurality of nozzles. This recording head had a nozzle cleaning function for purging ink from the nozzles. The evaluation machine had a function of wiping ink adhering to the nozzles of the recording head. Further, the evaluation machine was equipped with a conveyance device below the recording head that could convey the fabric in the horizontal direction. The recording head was filled with ink (specifically, any one of inks (I-1) to (I-17)) included in the ink set to be evaluated.

[Preprocessing]
In the inkjet printing of Comparative Examples 3 to 4, 7 to 8, 11 to 12, and 15 to 16, the above fabrics were used as they were without pretreatment. That is, in the inkjet printing of Comparative Examples 3 to 4, 7 to 8, 11 to 12, and 15 to 16, ink was used alone instead of using an ink set.

On the other hand, in the inkjet printing of Examples 1 to 8, Comparative Examples 1 to 2, 5 to 6, 9 to 10, 13 to 14, and 17, the above-mentioned fabrics were pretreated. Specifically, the above-mentioned fabric was immersed in a pretreatment liquid (5% by mass aqueous calcium chloride solution) and then dried. The pretreated fabric thus obtained was used in the following evaluation.

[Image density]
While the fabric was being conveyed using a conveyance device, ink was ejected onto the image forming area of the fabric using a recording head in which ink was set (ejection amount: 6.3 g/m ² ). As a result, a 3 cm x 4 cm rectangular solid image was formed in the image forming area of the fabric. The optical density (OD) of the formed solid image was measured using a reflection densitometer ("FD-9" manufactured by Konica Minolta, Inc.) (observation light source: D50 light source, illumination condition: M2, field of view: 2°, Concentration status: I).

The standard of image density was changed depending on the color of the formed image. Specifically, for cyan images, magenta images, and yellow images (Examples 1 to 6, Comparative Examples 1 to 12 and 17), when the OD is 1.2 or more, the image density is determined to be "good (A)", When the OD was less than 1.2, the image density was determined to be "poor (B)". For black images (Examples 7 to 8 and Comparative Examples 13 to 16), when the OD is 1.3 or more, the image density is judged to be "good (A)", and when the OD is less than 1.3, the image density is judged as "good (A)". The density was determined to be "poor (B)".

[Discharge stability]
While the fabric was being conveyed using a conveyance device, ink was ejected onto the image forming area of the fabric using a recording head in which ink was set (ejection amount: 6.3 g/m ² ). As a result, a solid image was formed on the entire surface of the fabric. This operation was repeated 100 times in total to form solid images on each of 100 pieces of fabric. Thereafter, ink was ejected from all nozzles of the recording head to form a check pattern image for checking the occurrence of nozzle clogging. By observing the check pattern image, the number of nozzles in which nozzle clogging occurred (defective nozzles) was counted. The ejection stability of the ink was evaluated based on the following criteria.
A (especially good): 0 defective nozzles B (good): 1 to 5 defective nozzles C (poor): 6 or more defective nozzles

In Tables 7 and 8 below, "Y" in the pretreatment section indicates that pretreatment was performed. "N" in the pretreatment section indicates that no pretreatment was performed.

As shown in Tables 7 and 8, the ink sets used in inkjet textile printing in Examples 1 to 8 included ink and a pretreatment liquid. The ink contained pigment particles and an anionic dispersant. The major axis of the pigment particles was 50 nm or more and 200 nm or less. The aspect ratio of the pigment particles was 2.0 or more and 3.0 or less. The pretreatment liquid contained water and a cationic material. The ink sets used in the inkjet textile printing of Examples 1 to 8 had excellent ink ejection stability and were able to form images with excellent image density.

On the other hand, the ink sets or inks used in the inkjet textile printing of Comparative Examples 1 to 17 did not satisfy the above-mentioned configuration. Therefore, the inkjet textile printing of Comparative Examples 1 to 17 did not have sufficient ink ejection stability or the image density of the formed images.

Specifically, the inks used in the inkjet printing of Comparative Examples 1, 5, 9, and 13 had pigment particle aspect ratios of less than 2.0. Therefore, in the inkjet printing of Comparative Examples 1, 5, 9, and 13, the image density of the formed images was poor.

The inks used in the inkjet printing of Comparative Examples 2, 6, 10, and 14 had an aspect ratio of pigment particles of more than 3.0. Therefore, in the inkjet textile printings of Comparative Examples 2, 6, 10, and 14, the ink ejection stability was poor.

In the inkjet printing of Comparative Examples 3 to 4, 7 to 8, 11 to 12, and 15 to 16, no pretreatment liquid was used. Therefore, in the inkjet printing of Comparative Examples 3 to 4, 7 to 8, 11 to 12, and 15 to 16, the image density of the formed images was poor.

In the inkjet printing of Comparative Example 17, the dispersant contained in the ink did not have anionic properties. Therefore, in the inkjet textile printing of Comparative Example 17, the image density of the formed image was poor.

The ink set and inkjet textile printing method of the present invention can be used to form printed objects.

Claims (5)

An inkjet textile printing method for forming an image in an image forming area of a fabric using an ink set comprising an inkjet ink and a pretreatment liquid, the method comprising:
The inkjet ink contains pigment particles and an anionic dispersant,
The major axis of the pigment particles is 50 nm or more and 200 nm or less,
The aspect ratio of the pigment particles is 2.0 or more and 3.0 or less,
The pretreatment liquid contains water and a cationic material,
a pretreatment step of applying the pretreatment liquid to the image forming area;
An inkjet textile printing method comprising: an inkjet step of discharging the inkjet ink onto the image forming area using a head. The inkjet textile printing method according to claim 1, wherein the cationic material contains a metal salt. The inkjet textile printing method according to claim 2, wherein the metal salt includes calcium chloride. The inkjet textile printing method according to any one of claims 1 to 3, wherein the content of the cationic material in the pretreatment liquid is 1.0% by mass or more and 10.0% by mass or less. The inkjet textile printing method according to any one of claims 1 to 4, wherein the dispersant contains an alkylol ammonium salt of a polymer having an acid group.