JP2023057384A - Inkjet recording method and inkjet recording device - Google Patents

Abstract

To provide an inkjet recording method capable of recording an image having excellent color development and scratch resistance on a low to non-absorptive recording medium even in the case where ink containing quinacridone solid solution pigment is used as pigment.SOLUTION: An inkjet recording method has a process of ejecting aqueous ink from a recording head of an inkjet method and recording an image by imparting the ink onto a recording medium. Furthermore, the method has a process of heating the recording medium onto which aqueous ink is imparted, where the aqueous ink contains pigment, resin dispersant, fluorine-based surfactant and polyoxyethylene alkyl ether, the pigment is quinacridone solid solution pigment, the polyoxyethylene alkyl ether has hydrocarbon group of carbon number 10 or more and 18 or less, and HLB value obtained by Griffin method is 15.0 or less, and the water absorption amount of the recording medium from contact start to 30 msec1/2 in Bristow method is 10 mL/m2 or less.SELECTED DRAWING: None

Description

The present invention relates to an inkjet recording method and an inkjet recording apparatus.

In recent years, the inkjet recording method has been increasingly used in the field of signs and displays, such as recording of posters and large-sized advertisements. In this field, polyvinyl chloride sheets, polyethylene terephthalate (PET) sheets, and the like are often used as recording media from the viewpoint of durability and cost of recording media. These recording media have no or almost no water-based ink absorbing layer on the recording surface of the recording medium. recording medium (recording medium with low water-based ink absorption). Solvent-based inks, curable inks, and the like have conventionally been used to record images on these recording media. However, from the viewpoint of reducing environmental load and odor, there is an increasing need for water-based inks using water-based media.

The recording surface of a non-absorbent recording medium has the property that ink does not spread easily. In order to improve the wetting and spreading properties of the ink on non-absorbent recording media, for example, an ink containing at least one of a fluorosurfactant and a siloxane surfactant having 5 or more siloxane units has been proposed (Patent Reference 1).

Further, images used in the field of signs and displays are required to be brighter and capable of color reproduction in highly saturated areas, and to have excellent abrasion resistance. Conventionally, quinacridone pigments have been used as magenta pigments. For example, an ink using a quinacridone solid solution pigment having a hue closer to yellow has been proposed in order to reproduce bright and highly saturated colors (Patent Document 2). Further, an ink containing a water-soluble resin, a fluorosurfactant, and a polyoxyethylene alkyl ether has been proposed for recording images having scratch resistance (Patent Document 3).

JP 2014-077072 A JP-A-11-049998 WO2011/136000

However, C.I. I. When Pigment Blue 15:3 is used, a good solid image can be recorded, but when a quinacridone solid solution pigment is used, the color developability tends to be insufficient. In addition, when a quinacridone solid solution pigment is used as a coloring material for the ink proposed in Patent Document 3, the resulting image tends to have white spots and the like, resulting in insufficient color developability and scratch resistance. Furthermore, it has been found that when an image is recorded by applying the ink proposed in Patent Document 2 to a non-absorbent recording medium, the ink tends to be repelled, resulting in a lower color development of the resulting image.

Accordingly, it is an object of the present invention to record an image excellent in color developability and abrasion resistance on a low to non-absorbent recording medium even when using an ink containing a quinacridone solid solution pigment as a pigment. To provide a possible ink jet recording method. Another object of the present invention is to provide an inkjet recording apparatus for use in this inkjet recording method.

That is, according to the present invention, there is provided an inkjet recording method comprising a step of ejecting water-based ink from an ink-jet recording head and applying it to a recording medium to record an image, further comprising: a step of heating a recording medium, wherein the water-based ink contains a pigment, a resin dispersant for dispersing the pigment in the water-based ink, a fluorosurfactant, and a polyoxyethylene alkyl ether; , a quinacridone solid solution pigment, wherein the polyoxyethylene alkyl ether has a hydrocarbon group having 10 or more and 18 or less carbon atoms, and an HLB value determined by the Griffin method is 15.0 or less, and the recording medium is a Bristol An ink jet recording method characterized in that the amount of water absorption from the start of contact to 30 msec ^1/2 is 10 mL/m ² or less according to the method.

According to the present invention, even when an ink containing a quinacridone solid solution pigment as a pigment is used, it is possible to record an image excellent in color developability and scratch resistance on low to non-absorbent recording media. An inkjet recording method can be provided. Further, according to the present invention, it is possible to provide an inkjet recording apparatus used for this inkjet recording method.

1 is a perspective view schematically showing an embodiment of an inkjet recording apparatus of the present invention; FIG. 1 is a side view schematically showing an embodiment of an inkjet recording apparatus of the present invention; FIG.

The present invention will be further described in detail below with reference to preferred embodiments. In the present invention, when the compound is a salt, the salt is dissociated into ions in the ink, but for convenience, it is expressed as "containing the salt." In addition, water-based ink for inkjet is sometimes simply referred to as "ink". Unless otherwise specified, physical property values are values at normal temperature (25° C.) and normal pressure (1 atm). In this specification, low-absorption to non-absorption recording media may be collectively referred to as "non-absorption recording medium". A low-absorption to non-absorption recording medium is defined as having a water absorption of 10 mL/m ² or less from the start of contact to 30 msec ^1/2 in the Bristow method.

The present inventors have developed an inkjet recording method capable of recording an image with excellent color development and scratch resistance on low to non-absorptive recording media even when using an ink containing a quinacridone solid solution pigment as a pigment. investigated. As a result, the inventors have found that it is important to satisfy the following requirements, and have completed the present invention.
- It has a step of heating the recording medium to which the ink is applied.
• The ink contains a quinacridone solid solution pigment, a resin dispersant that disperses the quinacridone solid solution pigment in the ink, a fluorosurfactant, and a polyoxyethylene alkyl ether.
- The polyoxyethylene alkyl ether has a hydrocarbon group with 10 to 18 carbon atoms and an HLB value of 15.0 or less as determined by the Griffin method.

The present inventors first recorded an image on a non-absorbing recording medium using an ink containing a quinacridone solid solution pigment dispersed with a resinous dispersant. However, it has been found that even if a fluorosurfactant, which is a component that imparts wettability, is contained in the ink, the color developability of the recorded image is not improved.

Since the quinacridone solid solution pigment contains a plurality of quinacridone molecules with different substituents in its crystal, sites with different polarities are present on the particle surface of the pigment. In general, the pigment is dispersed in the ink by the adsorption of the hydrophobic site of the resin dispersant to the hydrophobic site of the particle surface of the pigment. The resin dispersant repeatedly adsorbs and desorbs from the particle surface of the pigment, and maintains a state of adsorption equilibrium to maintain the dispersion stability of the pigment. However, in the case of a quinacridone solid solution pigment having sites with different polarities on its surface, it is difficult to maintain the adsorption equilibrium of the resin dispersant, and other components in the ink tend to destabilize the dispersion state.

As volatile components such as water and water-soluble organic solvents in the ink applied to the non-absorbent recording medium evaporate, the remaining non-volatile components concentrate the ink. Non-volatile components in ink include solid components such as pigments and resins, as well as high-boiling water-soluble organic solvents, surfactants, preservatives, and the like. When an ink containing a quinacridone solid solution pigment is used, the resin dispersant is detached from the pigment particle surface due to the action of the fluorosurfactant with increased concentration, destabilizing the dispersed state of the pigment. A pigment whose dispersed state is destabilized tends to form aggregates on the surface of a recording medium. Therefore, even if the ink is applied to the recording medium at a uniform density, when the ink is concentrated, there are areas where the pigment is relatively high and areas where the pigment is relatively low. As a result, fine irregularities are formed on the surface of the image to be formed, and it is thought that the distribution of the pigment becomes non-uniform and the color developability of the image deteriorates.

The inventors of the present invention presumed that by maintaining a stable dispersion state of the quinacridone solid solution pigment in the ink that has dried on the recording medium, it is possible to suppress the deterioration of the color development of the image, and conducted various studies. gone. As a result, by using a polyoxyethylene alkyl ether having a hydrocarbon group having 10 or more and 18 or less carbon atoms and having an HLB value of 15.0 or less as determined by the Griffin method, not only the color developability of the image but also the durability can be improved. It was found that the abrasion resistance was also improved.

Polyoxyethylene alkyl ether is a component that functions as a so-called surfactant. A polyoxyethylene alkyl ether having an HLB value of 15.0 or less has relatively low hydrophilicity among polyoxyethylene alkyl ether surfactants. Surfactants with low hydrophilicity tend to be oriented at the air-liquid interface, so they exist on the surface of ink droplets applied to the recording medium. However, when the water content in the ink droplets decreases due to drying, the hydrophobicity of the ink droplets as a whole increases. easier to get along with. Hydrophobic components in the ink include the particle surfaces of pigments and the hydrophobic sites of resin dispersants. The hydrophobic part of the polyoxyethylene alkyl ether that has entered the inside of the ink droplet acts on the particle surface of the pigment to keep the dispersed state of the pigment stable. As a result, it is considered that the dispersion state of the quinacridone solid solution pigment is less likely to be destabilized by the fluorosurfactant, and the color developability of the image is improved.

On the other hand, highly hydrophilic polyoxyethylene alkyl ethers (HLB value exceeding 15.0) are difficult to penetrate into the inside of the ink droplets even if the water content in the ink droplets is reduced. It is considered that the effect of keeping the dispersion state stable cannot be obtained. In addition, when a quinacridone pigment that is not a solid solution (for example, Pigment Red 122) is used, the problem of lowering the color developability of the image hardly occurs.

<Inkjet recording method and inkjet recording apparatus>
The inkjet recording method of the present invention has a step of ejecting water-based ink from an inkjet recording head and applying it to a recording medium to record an image. The inkjet recording method of the present invention further includes a step of heating the recording medium to which the water-based ink has been applied. The water-based ink contains a pigment, a resin dispersant that disperses the pigment in the water-based ink, a fluorosurfactant, and a polyoxyethylene alkyl ether, and the pigment is a quinacridone solid solution pigment. The polyoxyethylene alkyl ether has a hydrocarbon group with 10 to 18 carbon atoms and an HLB value of 15.0 or less as determined by the Griffin method. Further, the inkjet recording apparatus of the present invention is an apparatus used in an inkjet recording method having a step of ejecting water-based ink from an inkjet recording head and applying it to a recording medium to record an image. The inkjet recording apparatus of the present invention is an apparatus suitable for use in the above recording method. The inkjet recording method and inkjet recording apparatus (hereinafter also simply referred to as "recording method and recording apparatus") of the present invention will be described in detail below.

(water-based ink)
The ink contains a pigment, a resin dispersant that disperses the pigment in the ink, a fluorosurfactant, and a specific polyoxyethylene alkyl ether. Each component constituting the ink will be described in detail below.

[Pigment and Resin Dispersant]
The pigment used in the ink is a quinacridone solid solution pigment. Examples of quinacridone solid solution pigments include C.I. I. Pigment Red 202 and C.I. I. Pigment Violet 19 solid solution, C.I. I. Pigment Red 122 and C.I. I. A solid solution of Pigment Violet 19 and the like can be mentioned. A combination of multiple types of pigments may be used for the ink. Pigments other than the quinacridone solid solution pigment (other pigments) may be further contained.

The content (% by mass) of the pigment in the ink is preferably 0.2% by mass or more and 10.0% by mass or less based on the total mass of the ink. If the content of the pigment is less than 0.2% by mass, the color developability of the recorded image may slightly deteriorate. On the other hand, if the content of the pigment exceeds 10.0% by mass, the viscosity of the ink tends to increase, which may slightly lower the ejection properties.

The pigment is a resin-dispersed pigment using a resin as a dispersant. By using an ink containing a resin-dispersed pigment as a coloring material, an image having excellent scratch resistance can be recorded. Pigments dispersed in ink by such a dispersion method include resin-dispersed pigments and microcapsule pigments. Microcapsule pigments are obtained by coating the particle surfaces of pigments with a resin and dispersing them.

A resin dispersant usually has a hydrophilic unit having an anionic group and a hydrophobic unit having no anionic group. A hydrophilic unit is a unit that ensures affinity to an aqueous medium. A hydrophobic unit is a unit that adsorbs to the pigment particle surface through hydrophobic interactions. A water-soluble resin is preferably used as the resin dispersant. When a water-dispersible resin (water-insoluble resin, resin particles) is used as a resin dispersant, the storage stability of the ink tends to be slightly lowered in some cases.

Examples of resin dispersants include acrylic resins and urethane resins. Among them, acrylic resins are preferable, and acrylic resins composed of units derived from (meth)acrylic acid or (meth)acrylic acid ester are more preferable.

As the acrylic resin, one having a hydrophilic unit and a hydrophobic unit as structural units is preferable. Among them, a resin having a hydrophilic unit derived from (meth)acrylic acid and a hydrophobic unit derived from at least one of a monomer having an aromatic ring and a (meth)acrylic acid ester is preferable. In particular, a resin having a hydrophilic unit derived from (meth)acrylic acid and a hydrophobic unit derived from at least one monomer of styrene and α-methylstyrene is preferred. Since these resins easily interact with pigments, they can be suitably used as resin dispersants for dispersing pigments.

A hydrophilic unit is a unit having a hydrophilic group such as an anionic group. A hydrophilic unit can be formed, for example, by polymerizing a hydrophilic monomer having a hydrophilic group. Specific examples of hydrophilic monomers having a hydrophilic group include acidic monomers having a carboxylic acid group such as (meth)acrylic acid, itaconic acid, maleic acid and fumaric acid, and anhydrides of these acidic monomers. and anionic monomers such as compounds and salts. Examples of cations constituting salts of acidic monomers include ions such as lithium, sodium, potassium, ammonium and organic ammonium. A hydrophobic unit is a unit that does not have a hydrophilic group such as an anionic group. A hydrophobic unit can be formed, for example, by polymerizing a hydrophobic monomer that does not have a hydrophilic group such as an anionic group. Specific examples of hydrophobic monomers include monomers having aromatic rings such as styrene, α-methylstyrene, and benzyl (meth)acrylate; methyl (meth)acrylate, butyl (meth)acrylate, (meth)acrylate, ) (meth)acrylate monomers such as 2-ethylhexyl acrylate.

The volume-based cumulative 50% particle size (D50) of the pigment in the ink is preferably 10 nm or more and 300 nm or less, more preferably 20 nm or more and 200 nm or less. The volume-based cumulative 50% particle size (D50) of the pigment can be measured using, for example, a dynamic light scattering particle size measuring device.

[Resin particles]
The ink preferably contains resin particles. If a water-soluble resin is contained in place of the resin particles, the volume of the water-soluble resin rapidly shrinks when the ink dries, which may result in a slight decrease in the color developability of the image.

As used herein, the term “resin particles” refers to a resin that is insoluble in the aqueous medium that constitutes the ink. means a resin that may be present in On the other hand, "water-soluble resin" refers to a resin that is soluble in the aqueous medium that constitutes the ink. means a resin that may be present in "Resin particles" can also be rephrased as "water-dispersible resin (water-insoluble resin)".

Whether or not a certain resin is a "resin particle" can be determined according to the method described below. First, a liquid containing a resin to be determined (resin content: 10% by mass) is prepared. Next, a sample is prepared by diluting the prepared liquid 10-fold (by volume) with deionized water. Then, when the particle size of the resin in the sample is measured by the dynamic light scattering method, if particles having a particle size are measured, the particles are determined to be "resin particles" (water-dispersible resin). . On the other hand, if particles having a particle size are not measured, it is determined that the resin is not a "resin particle" (is a "water-soluble resin"). The measurement conditions at this time can be, for example, SetZero: 30 seconds, number of measurements: 3, measurement time: 180 seconds, shape: spherical, refractive index: 1.59. As the particle size distribution analyzer, a particle size analyzer using dynamic light scattering (for example, trade name “Nanotrack UPA-EX150” manufactured by Nikkiso Co., Ltd.) can be used. Of course, the particle size distribution measuring device and measurement conditions are not limited to those described above.

The volume-based cumulative 50% particle diameter (D50) of the resin particles in the ink is preferably 50 nm or more and 500 nm or less, more preferably 100 nm or more and 300 nm or less. If the volume-based cumulative 50% particle diameter (D50) of the resin particles is less than 100 nm, the ink dischargeability may slightly deteriorate. On the other hand, if the volume-based cumulative 50% particle diameter (D50) of the resin particles exceeds 300 nm, light scattering may occur on the surface of the recording medium, and the color development of the image may slightly deteriorate.

The content (% by mass) of the resin particles in the ink is preferably 1.0 times or more as a mass ratio to the content (% by mass) of the pigment. If the mass ratio is less than 1.0 times, the effect of improving the scratch resistance of the image may be slightly reduced.

Examples of resin particles include acrylic resin particles, polyolefin resin particles, polyurethane resin particles, and polyester resin particles. Among them, polyester resin particles are preferred. Surfactants are likely to be adsorbed on the surfaces of resin particles other than polyester resin particles (other resin particles). For this reason, if other resin particles are used, the effect of imparting wettability by the fluorosurfactant and the effect of stabilizing the dispersed state of the pigment by the polyoxyethylene alkyl ether may be reduced, resulting in poor image color development. And the effect of improving scratch resistance may be slightly reduced.

[Constituent material of polyester resin]
A polyester resin is usually composed of a unit derived from a polyhydric alcohol and a unit derived from a polycarboxylic acid. An unreacted hydroxy group or carboxylic acid group exists at the end of the polyester resin. The sum of the proportion (% by mass) of the units derived from the polyhydric alcohol and the proportion (% by mass) of the units derived from the polycarboxylic acid in the polyester resin is preferably 90.0% by mass or more. Moreover, it is more preferably 95.0% by mass or more, and may be 100.0% by mass.

(1) Polyhydric alcohol Examples of polyhydric alcohols include dihydric to tetrahydric polyhydric alcohols. Examples of polyhydric alcohols include polyhydric alcohols having an aliphatic group, polyhydric alcohols having an aromatic group, and sugar alcohols. Examples of polyhydric alcohols include ethylene glycol [1,2-ethanediol], neopentyl glycol [2,2-dimethyl-1,3-propanediol], 1,3-propanediol, and 1,4-butanediol. , benzenediol, 2,2-bis (4-hydroxyphenyl) propane [bisphenol A] and other dihydric alcohols; glycerin, trimethylolethane, trihydric alcohols such as trimethylolpropane; tetrahydric alcohols such as pentaerythritol; can be mentioned. As the polyhydric alcohol, an oligomer (low molecular weight polymer having a molecular weight of 1,000 or less) can also be used. The ratio (% by mass) of units derived from polyhydric alcohol in the polyester resin is preferably 40.0% by mass or more and 60.0% by mass or less.

(2) Polyvalent carboxylic acid Examples of the polyvalent carboxylic acid include divalent to tetravalent polycarboxylic acids. Examples of polyvalent carboxylic acids include polyvalent carboxylic acids having an aliphatic group, polyvalent carboxylic acids having an aromatic group, and nitrogen-containing polyvalent carboxylic acids. Examples of polyvalent carboxylic acids include divalent carboxylic acids such as glutaric acid, adipic acid, terephthalic acid, isophthalic acid, and 2,6-naphthalenedicarboxylic acid; trivalent carboxylic acids such as trimellitic acid; tetravalent carboxylic acid; and the like. Oligomers (low-molecular-weight polymers with a molecular weight of 1,000 or less) can also be used as polyvalent carboxylic acids. The ratio (% by mass) of units derived from polyvalent carboxylic acid in the polyester resin is preferably 40.0% by mass or more and 60.0% by mass or less.

[Analysis of polyester resin particles]
The composition of the polyester resin that constitutes the resin particles can be analyzed, for example, by the method shown below. First, a sample is prepared by dissolving the resin particles in an organic solvent such as tetrahydrofuran that can dissolve the resin particles. The resin particles to be dissolved in the organic solvent may be in an aqueous dispersion state or in a dry state. The prepared sample is analyzed by analysis methods such as nuclear magnetic resonance (NMR) spectroscopy and matrix-assisted laser desorption/ionization mass spectrometry (MALDI-MS) to determine the type of unit (monomer) that constitutes the resin. and the ratio can be known. Also, by analyzing the resin particles by pyrolysis gas chromatography, it is possible to detect the units (monomers) that constitute the resin. When preparing a sample, if an insoluble matter that does not dissolve in an organic solvent is generated, the generated insoluble matter can be analyzed by pyrolysis gas chromatography to detect the units (monomers) that constitute the resin.

[Other resins]
The ink may further contain a resin (another resin) other than the resin particles. The type and form of other resins may be those that can stably exist in the water-based ink. Examples of other resins include (meth)acrylic resins, polyamide resins, polyester resins, polyvinyl alcohol resins, and polyolefin resins. A base may be added to the ink to improve the solubility of these resins. Examples of bases that can be used include organic amines such as monoethanolamine, diethanolamine, triethanolamine, aminemethylpropanol, and N,N-dimethylethanolamine; inorganic bases such as potassium hydroxide and sodium hydroxide;

[Fluorine-based surfactant]
The ink contains a fluorosurfactant. The fluorosurfactant preferably has a perfluoroalkyl group having 6 or less carbon atoms. When the number of carbon atoms in the perfluoroalkyl group exceeds 6, the hydrophobicity of the perfluoroalkyl group is strong, so that it is likely to be adsorbed by pigments and resin particles due to hydrophobic interaction, and the effect of imparting wettability to the ink is reduced. As a result, the effect of improving the color developability of the image may slightly decrease. The number of carbon atoms in the perfluoroalkyl group of the fluorosurfactant is preferably 4 or more. Nonionic fluorine-based surfactants are preferred, and perfluoroalkylethylene oxide adducts are more preferred. Ionic fluorine-based surfactants tend to lose hydrophilicity due to evaporation of water, so the effect of imparting wettability to ink is weak, and the effect of improving the color development of images may be somewhat reduced.

The content (% by mass) of the fluorosurfactant in the ink is preferably 0.1% or more based on the total mass of the ink. If the content of the fluorosurfactant is less than 0.1%, the effect of imparting wettability to the ink may be slightly reduced.

The content (% by mass) of the fluorosurfactant in the ink is preferably 0.40 times or less as a mass ratio with respect to the content (% by mass) of the pigment. If the mass ratio is more than 0.40, the amount of the fluorosurfactant acting on the surface of the pigment particles tends to be excessive, and the effect of stably maintaining the dispersed state of the pigment by the polyoxyethylene alkyl ether is slightly reduced. sometimes.

[Polyoxyethylene alkyl ether]
The ink contains a polyoxyethylene alkyl ether having a hydrocarbon group with 10 to 18 carbon atoms. Polyoxyethylene alkyl ether is represented, for example, by the following general formula (1). If the number of carbon atoms in the hydrocarbon group is 9 or less, the hydrophobic portion will be too short, and the effect of keeping the quinacridone solid solution pigment in a stable state of dispersion will be insufficient. On the other hand, if the number of carbon atoms in the hydrocarbon group is 19 or more, the hydrophobic portion is too long to act on the pigment in the dried ink on the recording medium.
R—O—(CH ₂ CH ₂ O) _n —H (1)
(In general formula (1), R represents a branched or linear hydrocarbon group having 10 to 18 carbon atoms, and n represents a natural number)

The number of carbon atoms in the hydrocarbon group constituting the polyoxyethylene alkyl ether is preferably 16 or less, more preferably 12 or less, from the viewpoint of further improving the color developability and scratch resistance of the recorded image. Hydrocarbon groups include alkyl groups and alkenyl groups. n is preferably 5 or more and 50 or less, more preferably 5 or more and 25 or less.

The HLB value of polyoxyethylene alkyl ether determined by the Griffin method is 15.0 or less. When the HLB value of the polyoxyethylene alkyl ether exceeds 15.0, the hydrophilicity is too high, so that it becomes difficult to act on the quinacridone solid solution pigment, and the effect of keeping the dispersed state of the pigment stably becomes insufficient. The HLB value of the polyoxyethylene alkyl ether is preferably 13.0 or less from the viewpoint of further improving the color developability and scratch resistance of the recorded image. The HLB value is preferably 10.0 or more.

The HLB value according to the Griffin method can be calculated from the following formula (2). The HLB value determined by the Griffin method is a physical property value representing the degree of hydrophilicity or lipophilicity of a surfactant, and ranges from 0.0 to 20.0. The smaller the HLB value, the higher the lipophilicity, and the larger the HLB value, the higher the hydrophilicity.
HLB value = 20 x (formula weight of hydrophilic group of surfactant/molecular weight of surfactant) (2)

The content (% by mass) of the polyoxyethylene alkyl ether in the ink is preferably 0.08 times or more and 0.40 times or less as a mass ratio to the content (% by mass) of the pigment. If the mass ratio is less than 0.08 times, the effect of stably maintaining the dispersed state of the pigment may be reduced, and the effect of improving the color developability may be slightly reduced. On the other hand, when the mass ratio is more than 0.40 times, the amount of polyoxyethylene alkyl ether acting on the pigment particle surface tends to be excessive, and adsorption of the resin dispersant to the pigment particle surface is inhibited. It may be difficult to stably maintain the dispersed state of the pigment.

[Aqueous medium]
The ink is an aqueous ink containing at least water as an aqueous medium. The ink can contain water or an aqueous medium that is a mixed solvent of water and a water-soluble organic solvent. As water, it is preferable to use deionized water or ion-exchanged water. The water content (% by mass) in the ink is preferably 50.0% by mass or more and 95.0% by mass or less based on the total mass of the ink. As the water-soluble organic solvent, alcohols, (poly)alkylene glycols, glycol ethers, nitrogen-containing compounds, sulfur-containing compounds, and the like, which can be used for inkjet inks, can be used.

The ink preferably contains a first water-soluble organic solvent having a boiling point of 190° C. or higher. However, if all of the water-soluble organic solvent contained in the ink is the first water-soluble organic solvent, the liquid component tends to decrease rapidly when the ink dries. As a result, the effect of stably maintaining the dispersed state of the pigment by the polyoxyethylene alkyl ether is reduced, and the effect of improving the color developability may be slightly reduced.

The ratio of the second water-soluble organic solvent having a boiling point of 250° C. or more to all the water-soluble organic solvents in the ink is preferably 40.0% by mass or less. If the ratio of the second water-soluble organic solvent to all the water-soluble organic solvents is more than 40.0% by mass, the liquid component may tend to remain in the image formed by drying, resulting in poor durability of the image. In some cases, the effect of improving scratch resistance is slightly reduced. Boiling points of main water-soluble organic solvents are shown below. 2-pyrrolidone (246°C), 2-hydroxyethyl-2-pyrrolidone (309°C), 1,3-propanediol (213°C), 1,2-butanediol (193°C), 1,3-butanediol ( 207°C), 2,3-butanediol (177°C), 1,2-pentanediol (207°C), 1,2-hexanediol (224°C), 2-methyl-1,3-propanediol (214°C ), propylene glycol (1,2-propanediol 188 ° C.), glycerin (290 ° C.), triethylene glycol (287 ° C.), diethylene glycol (245 ° C.), dipropylene glycol dimethyl ether (171 ° C.), diethylene glycol monoethyl ether (202 °C).

The content (% by mass) of the water-soluble organic solvent in the ink is preferably 3.0% by mass or more and 40.0% by mass or less, and 15.0% by mass or more and 30.0% by mass, based on the total mass of the ink. % by mass or less is more preferable. If the content of the water-soluble organic solvent in the ink is out of the above range, ejection failure may easily occur.

[Other ingredients]
In addition to the above components, the ink may optionally contain water-soluble organic compounds that are solid at 25° C., such as polyhydric alcohols such as trimethylolpropane and trimethylolethane; urea derivatives such as urea and ethyleneurea; may be included. Furthermore, if necessary, the ink may contain surfactants other than the above two types (other surfactants), pH adjusters, antifoaming agents, rust inhibitors, antiseptics, antifungal agents, oxidizing agents. Various additives such as inhibitors, anti-reduction agents, and chelating agents may also be included. The content (% by mass) of the surfactant (including the fluorine-based surfactant and polyoxyethylene alkyl ether described above) in the ink is 0.1% by mass or more and 5.0% by mass based on the total mass of the ink. The following are preferable. Moreover, it is more preferable that it is 0.1 mass % or more and 2.0 mass % or less.

(recoding media)
In the recording method and recording apparatus of the present invention, a non-absorbent recording medium (low to non-absorbent recording medium) is used as the recording medium. The non-absorbent recording medium is tested according to JAPAN TAPPI Paper Pulp Test Method No. 51, "Liquid absorption test method for paper and paperboard", the recording medium has a water absorption of 10 mL/m ² or less from the start of contact to 30 msec ^1/2 according to the Bristow method.

Examples of low to non-absorbent recording media include plastic films; recording media in which a plastic film is adhered to the recording surface of a substrate; and recording media in which an organic resin coating layer is provided on the recording surface of a substrate containing cellulose pulp. ; and the like can be used. Among these, a plastic film is preferable, and a recording medium in which an organic resin coat layer as an organic resin layer is provided on the recording surface of a substrate containing cellulose pulp is also preferable.

(Inkjet recording device)
FIG. 1 is a perspective view schematically showing one embodiment of the inkjet recording apparatus of the present invention. FIG. 2 is a side view schematically showing an embodiment of the inkjet recording apparatus of the invention. As shown in FIGS. 1 and 2, the printing apparatus of this embodiment includes an inkjet printing head 22 that ejects ink. Examples of the printhead include a printhead that ejects ink by the action of mechanical energy and a printhead that ejects ink by the action of thermal energy. Among them, a recording head that ejects ink by the action of thermal energy is preferable. A print head that ejects ink by the action of thermal energy is a thermal print head that applies thermal energy to ink by applying an electric pulse to an electrothermal conversion element and ejects ink from an ejection port. The thermal print head preferably has a mechanism (temperature control mechanism) for heating the water-based ink ejected from the print head and applied to the print medium to a predetermined temperature.

[Thermal fixing treatment]
The recording method of the present invention has a step of heating (thermal fixing processing) a recording medium to which ink has been applied. By heating the recording medium to which the ink has been applied, film formation is accelerated, and an image with excellent color developability and scratch resistance can be recorded. The heating temperature of the ink-applied recording medium is preferably 40° C. or higher and 120° C. or lower, more preferably 50° C. or higher and 90° C. or lower, from the viewpoints of drying efficiency and suppression of deformation of the recording medium.

The thermal fixing treatment is not particularly limited, and can be performed by thermal fixing means such as known heating means such as a heater, air blowing means such as a dryer, and a combination thereof. That is, the recording apparatus includes a mechanism (thermal fixing means) that heats the recording medium to which ink is applied. Examples of the heat fixing means include the above heating means, air blowing means, and means combining these. Examples of heat fixing methods include a method of applying heat from a heater or the like from the opposite side of the recording surface (ink application surface) of the recording medium, a method of applying warm air or hot air to the recording surface of the recording medium, and an infrared heater. and the like can be mentioned. Moreover, you may combine these plural.

In the printing apparatus shown in FIGS. 1 and 2, a heater 25 supported by a frame (not shown) is located downstream in the sub-scanning direction A from the position where the print head 22 reciprocates in the main scanning direction B. are placed. A heater 25 can heat the recording medium 1 to which ink has been applied. Specific examples of the heater 25 include sheathed heaters and halogen heaters. The heater 25 is covered with a heater cover 26 . The heater cover 26 is a member for efficiently irradiating the recording medium 1 with heat generated from the heater 25 . Furthermore, the heater cover 26 is also a member that protects the heater 25 . The recording medium 1 to which the ink ejected from the recording head 22 is applied is wound up by the winding spool 27 to form a roll-shaped winding medium 24 .

EXAMPLES The present invention will be described in more detail below with reference to examples and comparative examples, but the present invention is not limited by the following examples as long as the gist thereof is not exceeded. "Parts" and "%" regarding component amounts are based on mass unless otherwise specified.

<Preparation of resin particle dispersion>
(Dispersion of resin particles 1)
60.0 parts of ethylene glycol, 40.0 parts of neopentyl glycol, 54.5 parts of terephthalic acid, and 54.5 parts of isophthalic acid are placed in a reaction vessel installed in an autoclave and heated at 220° C. for 4 hours to form an ester. reaction was carried out. The temperature was raised to 240° C., and the pressure inside the autoclave was reduced to 13 Pa over 90 minutes. After the esterification (dehydration-condensation) reaction was continued at 240° C. and a reduced pressure of 13 Pa for 5 hours, nitrogen gas was introduced into the autoclave to restore the normal pressure. After lowering the temperature in the reaction vessel to 220° C., a catalyst (tetra-n-butyl titanate) and 1.0 part of trimetic acid were added, and the mixture was heated at 220° C. for 2 hours to carry out a transesterification reaction. The amount (mol) of the catalyst was defined as “3×10 ⁻⁴ ×total amount (mol) of polyvalent carboxylic acid used”. Thereafter, nitrogen gas was introduced into the autoclave to pressurize it, and the sheet-like resin was taken out. After the resin was taken out and cooled to 25° C., it was pulverized with a crusher to obtain a polyester resin.

A stirrer (trade name “Tornado Stirrer Standard SM-104” manufactured by AS ONE) was set in a 2 L beaker. 200 g of polyester resin and methyl ethyl ketone (MEK) were put into this beaker and stirred at 30° C. to dissolve the polyester resin. Then, 15.9 g of 5% potassium hydroxide aqueous solution was added and stirred for 30 minutes. While stirring at 30° C., 500 g of deionized water was added dropwise at a rate of 20 mL/min. After heating to 60° C., MEK and some water were distilled off. After cooling to 25° C., the mixture was filtered through a 150-mesh wire mesh, and deionized water was added to obtain a dispersion liquid of resin particles 1 having a resin particle content of 30.0%.

(Dispersion of resin particles 2)
1,160 mL of water was heated to 90° C. in the reactor. Further, 1.39 g of potassium persulfate as a polymerization initiator was mixed with 160 mL of water to prepare an initiator solution. 32 mL of the prepared initiator solution was added to the reactor and stirred. Separately, 159.4 mL of water was mixed with 183 g of styrene, 80 g of benzyl acrylate, 1.5 g of methacrylic acid, 1.6 g of isooctylthioglycolate as a chain transfer agent, and 9.98 g of a 30% aqueous solution of an emulsifier. to prepare a monomer mixture. As the emulsifier, an aliphatic phosphate ester (addition mole number of ethylene oxide group: 10), trade name "Rhodafac RS 710" (manufactured by Rhodia Novecare) was used. The prepared monomer mixed solution was dropped into the reactor over 30 minutes, and at the same time, 129.4 g of the initiator solution was dropped into the reactor over 30 minutes and stirred. The resulting reaction was stirred and maintained at 90° C. for 3 hours. After cooling to 50° C., a 50% potassium hydroxide aqueous solution was added to adjust the pH to 8.5. After the contents were cooled to ambient temperature, they were filtered through a 200 mesh filter and deionized water was added to obtain a dispersion of resin particles 2 with a resin particle content of 30.0%.

(Dispersion of resin particles 3)
An appropriate amount of ion-exchanged water was added to a commercially available aqueous dispersion containing urethane resin particles (trade name “U-coat UWS-145”, manufactured by Sanyo Chemical Industries, Ltd., resin content 35.0%), and the resin particle content was A 30.0% dispersion of resin particles 3 was prepared.

<Aqueous solution of acrylic resin>
A styrene-acrylic copolymer (trade name “Joncryl 690”, manufactured by BASF) having a weight average molecular weight of 16,500 and an acid value of 240 mgKOH/g was prepared. Neutralize and dilute the styrene-acrylic copolymer with an aqueous potassium hydroxide solution having an acid value 0.95 times (on a molar basis) to prepare an aqueous acrylic resin solution with a resin content of 25.0%. bottom.

<Preparation of pigment dispersion>
(Pigment dispersion liquid 1)
A styrene-ethyl acrylate-acrylic acid copolymer (resin 1) having an acid value of 150 mgKOH/g and a weight average molecular weight of 8,000 was prepared. 20.0 parts of resin 1 is neutralized with potassium hydroxide having an equimolar acid value, and an appropriate amount of pure water is added to prepare an aqueous solution of resin 1 having a resin (solid content) content of 20.0%. was prepared. A quinacridone solid solution pigment 1 (trade name “CROMOPHTAL Jet Magenta 2BC”, manufactured by BASF, a solid solution of CI Pigment Red 202 and CI Pigment Violet 19) was prepared. A mixture was obtained by mixing 20.0 parts of quinacridone solid solution pigment 1, 50.0 parts of aqueous solution of resin 1, and 30.0 parts of ion-exchanged water. Using Nanomizer (manufactured by Yoshida Kikai Kogyo Co., Ltd.), the obtained mixture was subjected to 50 pass dispersion treatment at a pressure of 150 MPa, and then centrifuged at a rotation speed of 5,000 rpm for 30 minutes to remove coarse particles. After pressure filtration through a cellulose acetate filter (manufactured by Advantech) with a pore size of 3.0 μm, the mixture was diluted with ion-exchanged water to obtain a pigment content of 15.0% and a resin dispersant (resin 1) content of 7. Pigment Dispersion 1 was prepared at 0.5%.

(Pigment dispersion liquid 2)
The same amount (by mass) of C.I. I. Pigment Red 122 presscake and C.I. I. After the press cake of Pigment Violet 19 was ground, it was treated with a water-soluble organic solvent in accordance with a conventional method to obtain a quinacridone solid solution pigment 2. The quinacridone solid solution pigment 2 obtained was used instead of the quinacridone solid solution pigment 1, and the content of the pigment was 15.0%, and the resin dispersant (resin A pigment dispersion 2 containing 7.5% of 1) was prepared.

(Pigment dispersion liquid 3)
Instead of quinacridone solid solution pigment 1, C.I. I. Pigment Red 122 (trade name “Ink Jet Magenta E02”, manufactured by Clariant) was used. Pigment Dispersion 3 containing 15.0% pigment and 7.5% resin dispersant (Resin 1) was prepared in the same manner as Pigment Dispersion 1 except for this. prepared.

<Surfactant>
A surfactant having the properties shown in Table 1 was prepared.

<Ink preparation>
Each component (unit: %) shown in Tables 2-1 to 2-4 was mixed, thoroughly stirred, and filtered under pressure through a cellulose acetate filter (trade name “Minisart”, manufactured by Sartorius) with a pore size of 1.2 μm. to prepare each ink. The properties of each prepared ink are shown in the lower part of Tables 2-1 to 2-4. In Tables 2-1 to 2-4, "Proxel GXL (S)" is a trade name of a preservative manufactured by Arch Chemicals.

<Evaluation>
An ink jet recording apparatus (trade name “image PROGRAF PRO-2000”, manufactured by Canon Inc.) with a built-in heating mechanism was used for the following evaluations. This inkjet recording apparatus is defined to have a recording duty of 100% for a solid image recorded under the condition that one droplet of 4 ng of ink is applied to a unit area of 1/1,200 inch×1/1,200 inch. In the present invention, in the following evaluation criteria for each item, "A" and "B" were defined as acceptable levels, and "C" was defined as an unacceptable level. Table 3 shows the evaluation results. The heating temperature in the heat fixing process for each evaluation was 80°C.

(chromogenic)
Each ink was filled in an ink cartridge and installed in an inkjet recording apparatus. A pattern containing an image of 2 cm×2 cm with a recording duty of 20% to 200% was recorded in increments of 20% on a recording medium (trade name “Scotchcal Graphic Film IJ1220N Glossy”, manufactured by 3M) to obtain a recorded matter. L ^* a ^* b ^* defined by CIE (International Commission on Illumination) using a fluorescence spectrodensitometer under the conditions of light source D50, viewing angle of 2 degrees, incident angle of 45 degrees, reflection angle of 0 degrees, and filter ANSI A. L ^* , a ^* , and b ^* in the color system were measured. As a fluorescence spectrodensitometer, trade name "FD-7" (manufactured by Konica Minolta) was used. Chroma (C ^* ) was calculated from the obtained measured values according to the following formula (A).
C ^* =((a ^* ) ²⁺ (b ^* ) ² ) ^1/2 (A)

Then, the maximum value of C* at a duty of 10 to 100% was defined as "maximum chroma", and the color development of the image was evaluated according to the evaluation criteria shown below.
A: The maximum chroma was 75 or more.
B: The maximum saturation was 70 or more and less than 75.
C: The maximum chroma was less than 70.

(Scratch resistance)
Each ink was filled in an ink cartridge and installed in an inkjet recording apparatus. A pattern containing an image of 3 cm×12 cm with a recording duty of 200% was printed on a recording medium (trade name “Scotchcal IJ1220N Glossy”, manufactured by 3M) at intervals of 20% to obtain a printed matter. Using a wear resistance tester (manufactured by Tester Sangyo), which is a Gakushin type testing machine according to JIS L0849, a white friction cloth (cotton) specified in JIS L0803 is used to test the surface of the recorded image with a load of 500 g. A friction test was conducted by reciprocating 50 times and then reciprocating 150 times. The images after the friction test were visually observed, and the abrasion resistance of the images was evaluated according to the evaluation criteria shown below. In addition, among the evaluation results of "scratch resistance" in Table 3, "B-" means that the performance is relatively inferior among "B".
A: No scratch marks were observed on the image after 50 reciprocations.
B: Scratches were observed on the image after 50 reciprocations, but the white background of the recording medium was not visible.
C: Scratches were observed on the image after 50 reciprocations, and the white background of the recording medium was visible.

Claims (15)

An inkjet recording method comprising a step of ejecting water-based ink from an inkjet recording head and applying it to a recording medium to record an image,
further comprising heating the recording medium to which the water-based ink has been applied;
the water-based ink contains a pigment, a resin dispersant for dispersing the pigment in the water-based ink, a fluorosurfactant, and a polyoxyethylene alkyl ether;
the pigment is a quinacridone solid solution pigment,
The polyoxyethylene alkyl ether has a hydrocarbon group having 10 or more and 18 or less carbon atoms and has an HLB value of 15.0 or less as determined by the Griffin method,
An inkjet recording method, wherein the recording medium has a water absorption amount of 10 mL/m ² or less from the start of contact to 30 msec ^1/2 in the Bristow method. 2. The inkjet recording method according to claim 1, wherein the content (% by mass) of the fluorosurfactant in the water-based ink is 0.1% by mass or more based on the total mass of the ink. 3. The inkjet according to claim 1, wherein the content (% by mass) of the fluorosurfactant in the water-based ink is 0.40 times or less as a mass ratio with respect to the content (% by mass) of the pigment. Recording method. The inkjet recording method according to any one of claims 1 to 3, wherein the fluorosurfactant is a nonionic fluorosurfactant. 5. The inkjet recording method according to any one of claims 1 to 4, wherein the fluorosurfactant has a perfluoroalkyl group having 6 or less carbon atoms. The content (% by mass) of the polyoxyethylene alkyl ether in the water-based ink is 0.08 times or more and 0.40 times or less as a mass ratio with respect to the content (% by mass) of the pigment. 6. The inkjet recording method according to any one of 5. 7. The inkjet recording method according to any one of claims 1 to 6, wherein the polyoxyethylene alkyl ether has an HLB value determined by the Griffin method of 13.0 or less. The inkjet recording method according to any one of claims 1 to 7, wherein the polyoxyethylene alkyl ether has a hydrocarbon group having 16 or less carbon atoms. 9. The inkjet recording method according to claim 8, wherein the hydrocarbon group of the polyoxyethylene alkyl ether has 12 or less carbon atoms. The inkjet recording method according to any one of claims 1 to 9, wherein the water-based ink further contains a first water-soluble organic solvent having a boiling point of 190°C or higher. the water-based ink further contains a water-soluble organic solvent,
The second water-soluble organic solvent having a boiling point of 250° C. or higher accounts for 40.0% by mass or less of the water-soluble organic solvent in the water-based ink. Inkjet recording method. The inkjet recording method according to any one of claims 1 to 11, wherein the water-based ink further contains resin particles. 13. The inkjet recording method according to claim 12, wherein the content (% by mass) of the resin particles in the water-based ink is 1.0 times or more as a mass ratio with respect to the content (% by mass) of the pigment. 14. The ink jet recording method according to claim 12 or 13, wherein the resin particles are polyester resin particles. An inkjet recording apparatus for use in an inkjet recording method having a step of ejecting water-based ink from an inkjet recording head and applying it to a recording medium to record an image,
A mechanism for heating the recording medium to which the water-based ink has been applied,
the water-based ink contains a pigment, a resin dispersant for dispersing the pigment in the water-based ink, a fluorosurfactant, and a polyoxyethylene alkyl ether;
the pigment is a quinacridone solid solution pigment,
The polyoxyethylene alkyl ether has a hydrocarbon group having 10 or more and 18 or less carbon atoms and has an HLB value of 15.0 or less as determined by the Griffin method,
An inkjet recording apparatus, wherein the recording medium has a water absorption amount of 10 mL/m ² or less from the start of contact to 30 msec ^1/2 in the Bristow method.

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