Inkjet recording method and inkjet recording device

Abstract

To provide an inkjet recording method capable of recording an image having good scratch resistance by using an aqueous ink and a reaction liquid.SOLUTION: In the inkjet recording method, an aqueous ink containing resin particles and a reaction liquid containing a reactant for flocculating a component in the aqueous ink are applied to a recording medium by being discharged from a recording head of an inkjet system. The reaction liquid contains a compound represented by the following general formula (1) (where n represents an integer of 0-3). At least one of the aqueous ink and the reaction liquid contains a surfactant having an HLB value of 15 or less.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to an inkjet recording method and an inkjet recording apparatus. [Background technology]

[0002] In recent years, inkjet recording methods have been increasingly used in the sign and display field, such as for recording posters and large advertisements. In this field, polyvinyl chloride sheets and polyethylene terephthalate (PET) sheets are often used as recording media due to their durability and cost. These recording media have no or almost no water-based ink absorbing layer on the recording surface, and are known as non-absorbent recording media (recording media that do not absorb water-based ink) or low-absorbent recording media (recording media with low water-based ink absorption). There is a demand for inkjet recording methods that can directly record on these recording media.

[0003] Known methods for recording images on the above-mentioned non-absorbent or low-absorbent recording media (hereinafter collectively referred to as "non-absorbent recording media") include recording methods using non-aqueous inks primarily composed of organic solvents or inks that are cured by energy rays such as UV light. However, these recording methods present many challenges in terms of environmental impact and odor, as non-aqueous inks use volatile organic solvents and therefore have an odor, and UV-curable inks require the use of polymerizable monomers and UV irradiation for fixation. Furthermore, records made by these recording methods contain decomposition products such as organic solvents and polymerizable monomers remaining within the image, and the odor can become a significant problem depending on the environment in which the record is used, for example, when the record is displayed indoors.

[0004] For these reasons, studies are being conducted on a recording method that can record on non-absorbent recording media using aqueous ink. Non-absorbent recording media have no or almost no ink-absorbing layer, making it difficult to achieve high-resolution image quality. As a method for improving image quality on non-absorbent recording media, an inkjet recording method has been proposed in which a reaction liquid containing an aggregating agent that aggregates the components in the ink is applied to the recording medium, and then aqueous ink is applied (see Patent Document 1).

[0005] Furthermore, when recorded materials in the sign and display field are displayed on walls, the surface of the recorded material is strongly scratched with tools such as scrapers, and when displayed outdoors, they are touched by many people, so higher scratch resistance is required than for photographs and graphic art recorded with conventional inkjet technology.As a method for improving the scratch resistance of images recorded on non-absorbent recording media, a method has been proposed in which a reaction liquid and an aqueous ink containing resin particles are used, and further a nitrogen-containing solvent is added to the aqueous ink (see Patent Document 2).

[0006] In addition, a method has been proposed in which a reaction liquid is applied to a recording medium, and then an ink containing an inorganic oxide colloid is applied to the recording medium to record an image in white or the like (see Patent Document 3). Patent Document 3 also describes that a nitrogen-containing solvent may be added to the reaction liquid. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Japanese Patent Application Laid-Open No. 2018-138353 [Patent Document 2] Japanese Patent Application Publication No. 2018-154805 [Patent Document 3] Japanese Patent Application Laid-Open No. 2002-103783 Summary of the Invention [Problem to be solved by the invention]

[0008] Images in the above-mentioned fields are required to have a higher level of abrasion resistance than ever before. As a result of investigations by the present inventors, it was found that the abrasion resistance of images does not reach a sufficiently high level in conventional inkjet recording methods using aqueous inks and reaction liquids, and there is still room for improvement.

[0009] Therefore, an object of the present invention is to provide an inkjet recording method capable of recording an image with good scratch resistance using a water-based ink and a reaction liquid, and another object of the present invention is to provide an inkjet recording apparatus that can be used in the inkjet recording method. [Means for solving the problem]

[0010] The above object can be achieved by the present invention, which provides an inkjet recording method in which an aqueous ink containing resin particles and a reaction liquid containing a reactant that aggregates components in the aqueous ink are ejected from an inkjet recording head onto a recording medium, wherein the reaction liquid contains a compound represented by the following general formula (1), and at least one of the aqueous ink and the reaction liquid contains a surfactant with an HLB value of 15 or less:

[0011] TIFF2023029244000001.tif33170 (n in the general formula (1) represents an integer of 0 to 3.) [Effects of the Invention]

[0012] According to the present invention, there is provided an inkjet recording method capable of recording an image with good scratch resistance using a water-based ink and a reaction liquid, and an inkjet recording apparatus that can be used in the inkjet recording method. [Brief explanation of the drawings]

[0013] [Figure 1]1 is a perspective view schematically illustrating an embodiment of an inkjet recording apparatus of the present invention. [Figure 2] 1 is a side view schematically illustrating an embodiment of an inkjet recording apparatus of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0014] The present invention will be described in further detail below with reference to preferred embodiments. In the present invention, when the compound is a salt, the salt is present in the ink as dissociated ions, but for convenience, it will be expressed as "containing a salt." Furthermore, aqueous inkjet inks may be simply referred to as "ink." Physical property values ​​are values ​​at room temperature (25°C) unless otherwise specified.

[0015] The present inventors have investigated a method for obtaining images with good abrasion resistance using an inkjet recording method that uses an aqueous ink containing resin particles and a reaction liquid containing a reactant that aggregates the components in the ink. As a result, it was found that desired images can be obtained by adding a compound represented by general formula (1) described below to the reaction liquid and by adding a surfactant with an HLB value of 15 or less to at least one of the ink and the reaction liquid. The present inventors believe that the reason why images with good abrasion resistance can be obtained by the above means is as follows.

[0016] First, solid images recorded using ink containing resin particles and a reaction liquid were observed, and many white areas (whiteouts) were found where the recording medium was not colored by the ink colorant. On the other hand, when an image was recorded using only the ink and reaction liquid, no whiteouts were observed. The reaction liquid contains a reactant that aggregates the colorant and resin particles in the ink, and acts to fix the ink when the ink and reaction liquid react on the recording medium. Therefore, when ink and a reaction liquid are used, the ink is less likely to wet and spread compared to when ink is used without a reaction liquid. As a result, it is speculated that whiteouts are more likely to occur when ink and a reaction liquid are used.

[0017] The inventors suspected that whiteouts reduce the contact area between the ink dots and the recording medium, thereby reducing the adhesion of the ink dots to the recording medium, making it difficult to obtain images with good abrasion resistance. Therefore, they considered whether adding a surfactant with a low HLB value to the ink would lower the ink's surface tension, thereby increasing the ink's wettability to the recording medium and improving abrasion resistance. As a result of their investigation, they found that increasing the ink's wettability and suppressing the occurrence of whiteouts slightly improved abrasion resistance, but did not achieve a sufficiently high level. Therefore, detailed observation of the image surface of the recorded product revealed that the film-forming properties of the resin particles were insufficient. It is believed that poor film-forming properties of the resin particles result in a weaker fusion force between the resin particles, which would cause the ink to dry and result in the image formed lacking strength.

[0018] Heating a recording medium to which ink has been applied can easily improve the film-forming properties of the resin particles. However, this would require the addition of a heating means and increased power consumption for heating. Therefore, to improve the film-forming properties of the resin particles without heating, 2-pyrrolidone, a water-soluble organic solvent that highly dissolves resin particles, was added to the ink. However, no improvement in the scratch resistance of the image was observed. Detailed observation of the image surface in the recorded material revealed that the film-forming properties of the resin particles were improved, but white spots occurred. The reason for this is thought to be as follows: 2-pyrrolidone has a high affinity with surfactants with low HLB values, and these surfactants suppress the orientation at the interface between the ink dots and the recording medium and the interface between the air layer and the ink dots (hereinafter collectively referred to as the "interface"). As a result, the ink's wettability to the recording medium was not improved, resulting in white spots, which is thought to be the reason why the scratch resistance of the image was not improved.

[0019] Based on the above findings, the inventors of the present invention conducted various studies to suspect that the abrasion resistance of images could be improved by reducing the affinity between the water-soluble organic solvent and the surfactant. As a result, they discovered that the abrasion resistance of images could be dramatically improved by adding a surfactant with an HLB value of 15 or less to the ink and / or reaction solution and adding a compound represented by general formula (1) to the reaction solution as a water-soluble organic solvent. The compound represented by general formula (1) has a pyrrolidone skeleton that can enhance the solubility of resin particles. In addition, the compound represented by general formula (1) has a hydrophilic group, such as a hydroxy group (when n in general formula (1) is 0) or a hydroxyalkyl group (when n in general formula (1) is an integer of 1 to 3). Therefore, since the compound has an HLB value of 15 or less, it has low affinity with highly hydrophobic surfactants. It is presumed that this facilitates orientation of the surfactant at the interface, thereby improving the wettability of the ink to the recording medium.

[0020] Furthermore, detailed observation of the image surface of the recorded material revealed a significant improvement in the film-forming properties of the resin particles. The reasons for this are thought to be as follows: As described above, the compound represented by general formula (1) easily increases the solubility of the resin particles. In addition, due to the low affinity between the surfactant and the compound represented by general formula (1), the surfactant orients not only at the interface but also at the resin particles. As a result, it is presumed that the surfactant penetrates into the molecular chains of the resin that form the resin particles, loosening the entanglement of the molecular chains and improving the film-forming properties of the resin particles. As described above, the use of the compound represented by general formula (1) efficiently orients the surfactant at the interface and at the resin particles, thereby improving the ink wettability to the recording medium and the film-forming properties of the resin particles. This is thought to have dramatically improved the scratch resistance of the image.

[0021] It has been found that adding the compound represented by general formula (1) to the ink rather than the reaction liquid does not provide the same effect of improving abrasion resistance as adding it to the reaction liquid. The inventors speculate that the reason for this is as follows: If the compound represented by general formula (1) is present only in the ink, the resin particles in the ink tend to incorporate the compound represented by general formula (1) into the resin molecular chains, causing the resin particles to swell in the ink. As a result, the rapid dissolution of the resin particles that would occur when the recording medium comes into contact with the compound represented by general formula (1) provided by the reaction liquid becomes somewhat less likely to occur, and it is therefore speculated that the abrasion resistance effect is not achieved. As described above, it is important to add the compound represented by general formula (1) to the reaction liquid.

[0022] <Inkjet recording method and inkjet recording apparatus> The inkjet recording method of the present invention is a recording method comprising a step of ejecting an aqueous ink containing resin particles and a reaction liquid that aggregates components in the aqueous ink from an inkjet recording head and applying them to a recording medium. The inkjet recording apparatus of the present invention is equipped with the aqueous ink, the reaction liquid, and an inkjet recording head that ejects and applies them to a recording medium. It is not necessary to perform a step of curing the image by irradiation with actinic energy rays or the like. The inkjet recording method and inkjet recording apparatus of the present invention are described in detail below. The present invention is not limited by the following description as long as it does not deviate from the gist of the invention.

[0023] [Water-based ink] The inkjet recording method and inkjet recording apparatus of the present invention use an aqueous ink containing resin particles. The resin particles form a film by forming a film, and have the role of imparting physical strength to an image. Each component of the ink is described in detail below.

[0024] (resin particles) The ink contains resin particles. In this specification, "resin particles" refers to a resin that is present in a state in which it is not dissolved in the aqueous medium that constitutes the ink, and specifically refers to a resin that can be present in the aqueous medium in the form of particles whose particle diameter can be measured by dynamic light scattering. On the other hand, "water-soluble resin" refers to a resin that is present in a state in which it is dissolved in the aqueous medium that constitutes the ink, and specifically refers to a resin that can be present in the aqueous medium in the form of particles whose particle diameter cannot be measured by dynamic light scattering. Resin particles can be expressed as a "water-dispersible resin (water-insoluble resin)" in contrast to "water-soluble resin."

[0025] Whether a resin corresponds to the above-defined "resin particle" can be determined according to the following method. First, a liquid containing the resin to be determined (resin content: 10% by mass) is prepared. Next, this liquid is diluted 10 times (by volume) with pure water to prepare a sample. Then, when the particle size of the resin in the sample is measured by dynamic light scattering, if particles having a particle size are measured, the resin can be determined to be a "resin particle" (i.e., a "water-dispersible resin"). On the other hand, if particles having a particle size are not measured, the resin can be determined not to be a "resin particle" (i.e., a "water-soluble resin"). A particle size analyzer (e.g., the "UPA-EX150" manufactured by Nikkiso) can be used as a particle size distribution analyzer using dynamic light scattering. The measurement conditions can be, for example, Set Zero: 30 seconds, number of measurements: 3, measurement time: 180 seconds, shape: spherical, and refractive index: 1.59. Of course, the particle size analyzer and measurement conditions are not limited to those described above.

[0026] Examples of resin materials that form the resin particles include acrylic resins, urethane resins, polyester resins, olefin resins, and styrene resins. Among these, acrylic resins, urethane resins, and polyester resins are preferred. In the following description, "(meth)acrylic acid" refers to "acrylic acid, methacrylic acid," and "(meth)acrylate" refers to "acrylate, methacrylate."

[0027] [Acrylic resin] The acrylic resin in this specification is a resin containing units derived from at least one acrylic monomer selected from (meth)acrylic acid and (meth)acrylic acid ester monomers, and obtained by (co)polymerizing a monomer component containing an acrylic monomer. As the acrylic resin, a resin composed of units having an acid group and units not having an acid group, obtained by copolymerizing a monomer having an acid group and a monomer not having an acid group, is preferably used.

[0028] Examples of monomers having an acid group that become units having an acid group upon polymerization include monomers having a carboxylic acid group such as (meth)acrylic acid, maleic acid, itaconic acid, and fumaric acid; monomers having a sulfonic acid group such as styrenesulfonic acid; monomers having a phosphonic acid group such as 2-ethyl phosphonate (meth)acrylic acid; and anhydrides and salts of these monomers. Examples of salts include alkali metal salts such as lithium, sodium, and potassium, ammonium salts, and organic ammonium salts. Among these, alkali metal salts such as lithium, sodium, and potassium are preferred. As the monomer having an acid group, monomers having a carboxylic acid group are preferred, and (meth)acrylic acid is more preferred.

[0029] Examples of monomers that do not have an acid group and that become units that do not have an acid group upon polymerization include monomers that have a hydroxy group, such as 2-hydroxyethyl (meth)acrylate, 3-hydroxypropyl (meth)acrylate, and 3-methyl-5-hydroxypentyl (meth)acrylate; monomers that have an aromatic group, such as styrene, α-methylstyrene, and benzyl (meth)acrylate; and alkyl (meth)acrylates, such as methyl (meth)acrylate, ethyl (meth)acrylate, isopropyl (meth)acrylate, n-butyl (meth)acrylate, isobutyl (meth)acrylate, tert-butyl (meth)acrylate, and 2-ethylhexyl (meth)acrylate. As the monomer that does not have an acid group, monomers that have an aromatic group and alkyl (meth)acrylates are preferred, and monomers that have an aromatic group are more preferred.

[0030] [Urethane resin] The urethane resin is a resin synthesized using at least a polyisocyanate and a component that reacts with it (a polyol or a polyamine), and optionally a crosslinking agent or a chain extender. Preferably, a urethane resin obtained by polymerizing a polyisocyanate, a polyol that does not have an acid group, and a polyol that has an acid group is used.

[0031] Polyisocyanates are compounds having two or more isocyanate groups in their molecular structure. Examples of polyisocyanates include aliphatic polyisocyanates and aromatic polyisocyanates. Examples of aliphatic polyisocyanates include polyisocyanates having a chain structure such as tetramethylene diisocyanate and hexamethylene diisocyanate; and polyisocyanates having a cyclic structure such as isophorone diisocyanate and hydrogenated xylylene diisocyanate. Examples of aromatic polyisocyanates include tolylene diisocyanate and 1,5-naphthylene diisocyanate. Of these, isophorone diisocyanate is preferred.

[0032] A polyol is a compound having two or more hydroxy groups in its molecular structure. Examples of polyols include polyols without acid groups, such as polyether polyols, polyester polyols, and polycarbonate polyols; and polyols with acid groups. Polyamines are compounds having two or more "amino groups or imino groups" in their molecular structure. Examples of polyether polyols include addition polymers of alkylene oxides and polyols; and glycols such as (poly)alkylene glycols. Examples of polyester polyols include acid esters. Examples of polycarbonate polyols include alkanediol-based polycarbonate diols. The number average molecular weight of the polyol without acid groups is preferably 400 or more and 4,500 or less.

[0033] Examples of polyols having an acid group include those having an acid group such as a carboxylic acid group, a sulfonic acid group, a phosphoric acid group, or a phosphonic acid group. The acid group may form a salt, and examples of the salt include alkali metal salts such as lithium, sodium, and potassium, ammonium salts, and organic ammonium salts. Of these, alkali metal salts such as lithium, sodium, and potassium are preferred. Examples of monomers having an acid group include polyols having a carboxylic acid group such as dimethylolacetic acid, dimethylolpropionic acid, dimethylolbutanoic acid, and dimethylolbutyric acid, with dimethylolpropionic acid and dimethylolbutanoic acid being more preferred.

[0034] Examples of polyamines include monoamines having multiple hydroxy groups, such as dimethylolethylamine and diethanolmethylamine; bifunctional polyamines, such as ethylenediamine and propylenediamine; and trifunctional or higher polyamines, such as diethylenetriamine and triethylenetetramine. For convenience, compounds having multiple hydroxy groups and one "amino group or imino group" are also listed as "polyamines."

[0035] When synthesizing a urethane resin, a crosslinking agent or a chain extender can be used. Typically, a crosslinking agent is used when synthesizing a prepolymer, and a chain extender is used when carrying out a chain extension reaction on a prepolymer that has already been synthesized. Basically, the crosslinking agent or chain extender can be appropriately selected from water, polyisocyanate, polyol, polyamine, etc. depending on the purpose, such as crosslinking or chain extension.

[0036] [Polyester Resin] Polyester resins are resins composed of units derived from polyhydric alcohols and units derived from polycarboxylic acids. Examples of polyhydric alcohols that constitute the polyhydric alcohol-derived units of polyester resins include dihydric to tetrahydric alcohols. Examples of polyhydric alcohol structures include polyhydric alcohols having an aliphatic group, polyhydric alcohols having an aromatic group, and sugar alcohols. Specific examples of polyhydric alcohols include dihydric alcohols such as ethylene glycol (also known as 1,2-ethanediol), neopentyl glycol (also known as 2,2-dimethyl-1,3-propanediol), 1,3-propanediol, 1,4-butanediol, benzenediol, and 2,2-bis(4-hydroxyphenyl)propane (also known as bisphenol A); trihydric alcohols such as glycerin, trimethylolethane, and trimethylolpropane; and tetrahydric alcohols such as pentaerythritol. Furthermore, oligomers (low-molecular polymers having a molecular weight of 1,000 or less) can also be used as polyhydric alcohols.

[0037] Since it is easy to adjust the weight-average molecular weight of the polyester resin, it is preferable to use dihydric or trihydric polyhydric alcohols. Furthermore, from the viewpoint of structure, it is preferable to use polyhydric alcohols having an aliphatic group or polyhydric alcohols having an aromatic group. As polyhydric alcohols having an aliphatic group, polyhydric alcohols having a linear or branched aliphatic group having 1 to 6 carbon atoms are more preferable. In particular, ethylene glycol, neopentyl glycol, bisphenol A, and glycerin are preferable, and it is also preferable to use two or more of these in combination.

[0038] Examples of polycarboxylic acids that form the polycarboxylic acid-derived units that constitute the polyester resin through reaction include divalent to tetravalent polycarboxylic acids. Examples of polycarboxylic acid structures include polycarboxylic acids having an aliphatic group, polycarboxylic acids having an aromatic group, and nitrogen-containing polycarboxylic acids. Specific examples of polycarboxylic acids include dicarboxylic acids such as glutaric acid, adipic acid, terephthalic acid, isophthalic acid, and 2,6-naphthalenedicarboxylic acid; tricarboxylic acids such as trimellitic acid; and tetracarboxylic acids such as ethylenediaminetetraacetic acid. Furthermore, oligomers (low-molecular polymers having a molecular weight of 1,000 or less) can also be used as the polycarboxylic acid.

[0039] It is preferable to use divalent or trivalent polycarboxylic acids because it is easy to adjust the weight average molecular weight and acid value of the polyester resin. Also, from the viewpoint of structure, it is preferable to use polycarboxylic acids having an aliphatic group or polycarboxylic acids having an aromatic group. In particular, it is preferable to use adipic acid, terephthalic acid, isophthalic acid, or trimellitic acid, and it is also preferable to use two or more of these in combination.

[0040] [Analysis method] The analysis of resin particles is preferably carried out by analyzing the constituent units of the resin forming the resin particles. Examples of methods for analyzing the constituent units of a resin include the following: First, resin particles are dissolved in an organic solvent (e.g., tetrahydrofuran) capable of dissolving the resin particles to prepare a sample. The resin particles used here may be in the form of an aqueous dispersion or in a dried state. The obtained sample is analyzed by nuclear magnetic resonance (NMR) spectroscopy, matrix-assisted laser desorption / ionization mass spectrometry (MALDI-MS), or the like. This allows the types and proportions of the units (monomers) constituting the resin to be determined. Alternatively, the resin particles themselves can be analyzed by pyrolysis-gas chromatography to detect the units (monomers) constituting the resin. Furthermore, if insoluble matter that does not dissolve in the organic solvent is generated during the preparation of the sample, this insoluble matter can be analyzed by pyrolysis-gas chromatography to detect the units (monomers) constituting the resin.

[0041] [Physical Properties] The amount of anionic groups in the resin particles is preferably 350 μmol / g or less. Using resin particles with such an amount of anionic groups facilitates orientation of surfactants with an HLB value of 15 or less to the resin particles, improving the film-forming properties of the resin particles and further enhancing the scratch resistance of images. The amount of anionic groups in the resin particles is preferably 50 μmol / g or more. The anionic groups are groups contained in units derived from the above-mentioned monomers, such as carboxylic acid groups, sulfonic acid groups, and phosphonic acid groups. The amount of anionic groups in the resin particles can be determined by colloid titration. In the examples described below, the amount of anionic groups in the resin particles was measured by colloid titration using potential difference using an automatic potentiometric titrator (product name "AT-510" manufactured by Kyoto Electronics Manufacturing Co., Ltd.) equipped with a streaming potential titration unit (PCD-500). Methyl glycol chitosan was used as the titration reagent. The glass transition temperature (Tg) of the resin particles is preferably 0° C. or higher and 100° C. or lower, and more preferably 20° C. or higher and 90° C. or lower. The glass transition temperature of the resin particles can be determined for the resin particles themselves using a differential scanning calorimeter.

[0042] [Content] The content (mass %) of resin particles in the ink is preferably 1.0% to 20.0% by mass, more preferably 2.0% to 15.0% by mass, and even more preferably 5.0% to 10.0% by mass, based on the total mass of the ink.

[0043] (Other resins) The ink may further contain a resin (other resin) other than the above-mentioned resin particles. The type and form of the other resin may be any as long as it can be stably present in the aqueous ink. Examples of other resins include acrylic resins, urethane resins, polyester resins, olefin resins, polyamide resins, polyvinyl alcohol resins, and styrene resins. These resins preferably have a salt-type anionic group to improve their solubility. Examples of cations that form salts of anionic groups include cations of organic amines such as monoethanolamine, diethanolamine, triethanolamine, amine methylpropanol, and N,N-dimethylethanolamine; and alkali metal ions such as potassium and sodium. Among these, alkali metal ions are preferred. Furthermore, the form of the other resin is preferably a water-soluble resin.

[0044] (aqueous medium) The ink is an aqueous ink containing at least water as an aqueous medium. The ink may contain an aqueous medium that is a mixed solvent of water and a water-soluble organic solvent. From the viewpoint of odor, etc., the ink preferably contains 50.0% by mass or more of water as an aqueous medium. As the water, deionized water or ion-exchanged water is preferably used. The content (mass %) of water in the ink is more preferably 50.0% by mass or more and 90.0% by mass or less, based on the total mass of the ink.

[0045] The water-soluble organic solvent may be any solvent suitable for use in inkjet inks, such as alcohols, polyols, (poly)alkylene glycols, glycol ethers, other nitrogen-containing compounds, and sulfur-containing compounds. The ink may contain one or more of these water-soluble organic solvents. The content (mass %) of the water-soluble organic solvent in the ink is preferably 5.0% to 40.0% by mass, and more preferably 15.0% to 30.0% by mass, based on the total mass of the ink. By ensuring that the content of the water-soluble organic solvent in the ink is within the above range, the ink's ejection properties can be stably maintained. The content of the water-soluble organic solvent includes the content of the compound represented by general formula (1), which may be added to the ink as needed.

[0046] The ink preferably further contains a compound represented by general formula (1). In an ink containing a compound represented by general formula (1), the resin particles incorporate the compound represented by general formula (1) into the interior of the resin molecular chain, and the resin particles tend to swell in the ink. When the swollen resin particles come into contact with the compound represented by general formula (1) in the reaction solution on the recording medium, the resin particles rapidly dissolve, improving film-forming properties and further improving the scratch resistance of the image. The content (mass %) of the compound represented by general formula (1) in the ink is preferably 1.0 mass % or more and 20.0 mass % or less, based on the total mass of the ink. When the ink contains a compound represented by general formula (1), it preferably also contains a water-soluble organic solvent other than the compound represented by general formula (1).

[0047] (colorant) The ink does not need to contain a colorant, but it can contain a colorant such as a pigment or dye. When the ink contains a colorant, the content (mass %) of the colorant in the ink is preferably 0.1% by mass or more and 15.0% by mass or less, and more preferably 1.0% by mass or more and 10.0% by mass or less, based on the total mass of the ink.

[0048] When a pigment is used as a coloring material, the type of pigment is not particularly limited. Specific examples of pigments include inorganic pigments such as carbon black and titanium oxide; and organic pigments such as azo, phthalocyanine, quinacridone, isoindolinone, imidazolone, diketopyrrolopyrrole, and dioxazine. The ink can contain one or more pigments. Of these, carbon black and organic pigments are preferred. Inks containing these pigments have a black or color hue.

[0049] When a pigment is used as a colorant, the pigment can be dispersed in a manner such as a resin-dispersed pigment using a resin (resin dispersant) as a dispersant, or a self-dispersed pigment in which hydrophilic groups are bonded to the pigment particle surface. Alternatively, a resin-bonded pigment in which an organic group containing a resin is chemically bonded to the pigment particle surface, or a microencapsulated pigment in which the pigment particle surface is coated with a resin, can be used. It is also possible to combine pigments dispersed in different ways. It is preferable to use a resin-dispersed pigment, as this tends to improve the scratch resistance of the image.

[0050] When a dye is used as a coloring material, the type of dye is not particularly limited. Specific examples of dyes include direct dyes, acid dyes, basic dyes, disperse dyes, and food dyes. Specific examples of dye skeletons include azo, triphenylmethane, phthalocyanine, azaphthalocyanine, xanthene, and anthrapyridone. The ink can contain one or more dyes.

[0051] (Other ingredients) In addition to the components described above, the ink may contain, as necessary, water-soluble organic compounds that are solid at room temperature (25° C.), such as urea or its derivatives, trimethylolpropane, and trimethylolethane. The ink may also contain various additives, such as other surfactants, pH adjusters, antifoaming agents, rust inhibitors, preservatives, antifungal agents, antioxidants, antireducing agents, evaporation accelerators, chelating agents, and water-soluble resins.

[0052] [Reaction solution] The inkjet recording method and inkjet recording apparatus of the present invention use a reaction liquid containing a reactant that aggregates components in the ink and a compound represented by general formula (1). The reaction liquid is preferably colorless and does not need to contain a colorant. Furthermore, the reaction liquid preferably does not contain a resin (water-soluble resin, resin particles).

[0053] (reactant) The reactant is not particularly limited, and examples thereof include polyvalent metal ions, cationic resins, and acid-type organic carboxylic acids, and one or more of these can be used. These reactants react with anionic groups possessed by the components of the ink to aggregate the components. Examples of components having anionic groups that react with the reactant include resin dispersants for dispersing pigments, self-dispersing pigments in which anionic groups are bonded to the particle surface directly or via other atomic groups, resin particles, and water-soluble resins.

[0054] Examples of polyvalent metal ions include ions of calcium, magnesium, copper, nickel, zinc, barium, aluminum, titanium, strontium, chromium, cobalt, and iron. Examples of cationic resins include polyallylamine hydrochloride, polyamine sulfone hydrochloride, polyvinylamine hydrochloride, and chitosan acetate.

[0055] Examples of acid-type organic carboxylic acids, with the pKa indicated in parentheses (for compounds with multiple pKas, the pKa of the first dissociation reaction in which a hydrogen ion is released from the acid), include monocarboxylic acids such as formic acid (3.8), acetic acid (4.8), propionic acid (4.9), butyric acid (4.8), benzoic acid (4.2), glycolic acid (3.8), lactic acid (3.9), salicylic acid (3.0), pyrrolecarboxylic acid (4.6), furancarboxylic acid (3.2), nicotinic acid (4.9), levulinic acid (4.4), and coumaric acid (2.8); malonic acid (2.7), succinic acid (4.0), glutaric acid (4.3), and adipic acid (2.8); Examples of dicarboxylic acids include carboxylic acids such as carboxylic acid (4.4), maleic acid (1.8), fumaric acid (2.9), itaconic acid (3.9), sebacic acid (4.6), phthalic acid (2.9), malic acid (3.2), and tartaric acid (3.0); tricarboxylic acids such as citric acid (2.8), trimellitic acid (2.5), and 1,2,3-propanetricarboxylic acid (3.5); and tetracarboxylic acids such as pyromellitic acid (1.9).

[0056] Acid-type organic carboxylic acids are compact molecules among reactants, and therefore prone to precipitation (bleed-out) on the image surface. Precipitation of organic carboxylic acids on the image surface can cause roughness, resulting in a perceived reduction in abrasion resistance. In this case, using a reaction solution containing a compound represented by general formula (1) can prevent a decrease in abrasion resistance due to the precipitation of organic carboxylic acids. The reason for this is believed to be as follows: Compounds represented by general formula (1) not only have affinity for resin particles, but also form hydrogen bonds with the carboxylic acid groups of the organic carboxylic acid through their hydroxyl groups. Furthermore, compounds represented by general formula (1) have a sufficiently high boiling point and low vapor pressure compared to the water-soluble organic solvents used in aqueous inkjet inks, and therefore are less likely to evaporate in a short period of time like water. Therefore, the compound represented by general formula (1) facilitates the close proximity of resin particles and organic carboxylic acids, preventing the precipitation of organic carboxylic acids on the image surface and preventing a decrease in abrasion resistance.

[0057] Among the reactants, it is preferable to use an acid-type organic carboxylic acid with a pKa of 1.8 or higher. Acid-type organic carboxylic acids convert the anionic groups of the ink components from ionic dissociation to H-type, thereby reducing the hydrophilicity of the components and causing them to aggregate. In this case, acid-type organic carboxylic acids with a pKa of 1.8 or higher tend to react more slowly. In addition, compared to polyvalent metal ions and cationic resins, acid-type organic carboxylic acids have fewer reaction sites with anionic groups, making the aggregates formed by the reaction smaller. Furthermore, because the reaction proceeds more slowly and the aggregates formed by the reaction tend to be smaller, the image surface tends to be smoother, thereby further improving the abrasion resistance of the image. Here, pKa represents the ease of dissociation of the acid proton and is the negative common logarithm of the acid dissociation constant (Ka) (pKa = -log10Ka). The amount of acid dissociated in the reaction solution primarily depends on the pKa of the first-stage dissociation reaction in which hydrogen ions are released from the acid. Therefore, in the case of a compound having multiple pKa values, the pKa of the acid-form organic carboxylic acid in the present invention refers to the pKa value of the first dissociation reaction in which a hydrogen ion is released from the acid. The pKa value of the acid-form organic carboxylic acid is preferably 4.9 or less.

[0058] Among the organic carboxylic acids described above, polycarboxylic acids having multiple (two or more) carboxylic acid groups are preferred because they can more easily improve the abrasion resistance of the image. Since polycarboxylic acids tend to be more water-soluble than monocarboxylic acids, it is believed that they are less likely to precipitate due to evaporation of the aqueous medium or evaporation of the acid before being applied to the recording medium, and as a result, their acid function is less likely to be impaired. Furthermore, since polycarboxylic acids have two or more carboxylic acid groups, they form stronger hydrogen bonds with the compound represented by general formula (1). This makes the polycarboxylic acid more likely to be present in the vicinity of the compound represented by general formula (1), which is believed to further suppress bleeding of the organic carboxylic acid onto the surface of the image and further improve the abrasion resistance of the image. The number of carboxylic acid groups in the polycarboxylic acid is preferably four or less.

[0059] The content (mass %) of the reactant in the reaction liquid is preferably 0.1 mass % or more and 5.0 mass % or less, more preferably 0.5 mass % or more and 5.0 mass % or less, and even more preferably 1.0 mass % or more and 5.0 mass % or less, based on the total mass of the reaction liquid.

[0060] (aqueous medium) From the viewpoint of odor, the reaction liquid is preferably an aqueous reaction liquid containing water, and more preferably contains 50.0% by mass or more of water as an aqueous medium. As the water, deionized water or ion-exchanged water is preferably used. The content (mass %) of water in the reaction liquid is more preferably 50.0% by mass or more and 90.0% by mass or less, based on the total mass of the reaction liquid.

[0061] The reaction liquid may further contain a water-soluble organic solvent as an aqueous medium. The water-soluble organic solvent contained in the reaction liquid may be any of the water-soluble organic solvents listed in the description of the ink above. The content (mass %) of the water-soluble organic solvent in the reaction liquid is preferably 5.0 mass % or more and 40.0 mass % or less, and more preferably 15.0 mass % or more and 30.0 mass % or less, based on the total mass of the reaction liquid. By keeping the content of the water-soluble organic solvent in the reaction liquid within the above range, ejection defects of the reaction liquid can be reduced.

[0062] The reaction liquid contains a compound represented by the following general formula (1) as a water-soluble organic solvent.

[0063] TIFF2023029244000002.tif33170

[0064] In general formula (1), n ​​represents an integer of 0 to 3. When n is 0, it represents a single bond, indicating that a hydroxy group is directly bonded to the nitrogen atom. The compound represented by general formula (1) has a structure having both a pyrrolidone skeleton moiety and an N-position substituent moiety having a hydroxy group. The N-position substituent having a hydroxy group in the compound represented by general formula (1) has 0 to 3 carbon atoms. Specific examples of the compound represented by general formula (1) that can be used include N-hydroxy-2-pyrrolidone, N-hydroxymethyl-2-pyrrolidone, N-(2-hydroxyethyl)-2-pyrrolidone, and N-(3-hydroxypropyl)-2-pyrrolidone.

[0065] When a compound equivalent to the compound represented by general formula (1) but lacking an N-position substituent, i.e., 2-pyrrolidone, is used instead of the compound represented by general formula (1), the effect of improving the scratch resistance of the image is not obtained. On the other hand, when a compound in which n in general formula (1) is 4 or greater is used instead of the compound represented by general formula (1), the hydrophobicity of the hydroxyalkyl moiety increases, and the affinity with surfactants having an HLB value of 15 or less decreases. As a result, the surfactant is less likely to orient at the interface or resin particles, and the effect of improving the scratch resistance of the image is not obtained.

[0066] The content (mass %) of the compound represented by general formula (1) in the reaction liquid is preferably 7.0 mass % or more and 31.0 mass % or less, and more preferably 10.0 mass % or more and 30.0 mass % or less, based on the total mass of the reaction liquid.

[0067] (Other ingredients) In addition to the above-mentioned components, the reaction liquid may contain various additives, such as other surfactants, pH adjusters, rust inhibitors, preservatives, antifungal agents, antioxidants, antireducing agents, evaporation promoters, chelating agents, and water-soluble resins, as needed.

[0068] [Surfactant] At least one of the aqueous ink and the reaction liquid contains a surfactant with an HLB value of 15 or less. If neither the aqueous ink nor the reaction liquid contains a surfactant, white spots will appear in the resulting image, and adhesion between the recording film and the recording medium will be reduced, resulting in an inability to improve the abrasion resistance of the image. Since the surfactant only needs to be oriented at the interface in the ink dots where the ink and the reaction liquid are mixed, it is sufficient for the surfactant to be contained in either the ink or the reaction liquid, or it may be contained in both. If the HLB value of the surfactant is greater than 15, it will dissolve in water and the surfactant will not be oriented at the interface or to the resin particles, thereby failing to improve the abrasion resistance of the image. It is more preferable that the HLB value of the surfactant be 12 or less. Using a surfactant with an HLB value of 12 or less will facilitate the surfactant's orientation at the interface or to the resin particles, making it easier to improve the abrasion resistance of the image. It is preferable that the HLB value of the surfactant be 10 or more.

[0069] In this specification, the HLB value is a value determined by the Griffin method. The HLB value according to the Griffin method can be determined from the formula weight and molecular weight of the hydrophilic group of a surfactant using the following formula (A). The HLB value according to the Griffin method represents the degree of hydrophilicity or lipophilicity of a surfactant, and takes a value from 0 to 20. The lower the HLB value, the higher the lipophilicity of the surfactant, and the higher the HLB value, the higher the hydrophilicity. HLB value = 20 × formula weight of hydrophilic group of surfactant / molecular weight of surfactant (A)

[0070] Surfactants with an HLB value are nonionic surfactants. Examples of surfactants with an HLB value of 15 or less include hydrocarbon surfactants such as polyoxyethylene alkyl ethers and ethylene oxide adducts of acetylene glycol; fluorine-based surfactants such as perfluoroalkyl ethylene oxide adducts; and silicone surfactants such as polyether-modified siloxane compounds. One or more surfactants with an HLB value of 15 or less can be used.

[0071] The surfactant preferably contains a hydrocarbon surfactant, and more preferably contains a polyoxyethylene alkyl ether. In polyoxyethylene alkyl ether, the hydrophilic ethylene oxide group and the hydrophobic long-chain alkyl group are clearly separated, and the long-chain alkyl group is easily oriented to the resin particles, which further improves the scratch resistance of the image.

[0072] The content (% by mass) of surfactants with an HLB value of 15 or less is preferably 1.0% by mass or less, based on the total mass of the ink or reaction liquid containing the surfactant. This makes it difficult for surfactants to aggregate together in the ink or reaction liquid to form micelles, which makes it easier for the surfactants to orient at interfaces and resin particles, thereby further improving the scratch resistance of images. Furthermore, the content (% by mass) of surfactants with an HLB value of 15 or less is preferably 0.1% by mass or more, and more preferably 0.2% by mass or more.

[0073] [ΔSP value] It is preferable that the resin particles, the compound represented by general formula (1), and the surfactant having an HLB value of 15 or less are used so that the relationship described below is satisfied with respect to their respective SP values. The SP value (δ: solubility parameter) in this specification is a value calculated by the Fedors method based on the following formula (B) (unit: (cal / cm 3 ) 1 / 2 ) when converting to the SI unit system, use "(cal / cm 3 ) 1 / 2 =2.046×10 3 (J / m 3 ) 1 / 2 In the following description, the unit of SP value (cal / cm 3 ) 1 / 2 ) may be omitted. δ = (ΔE vap / V) 1 / 2 (B) (In formula (B), ΔE vap represents the molar heat of vaporization of the compound (cal / mol), and V is the molar volume of the compound at 25°C (cm3 / mol).

[0074] (ΔSP Value of Compound Represented by General Formula (1) and Resin Particles) The difference (ΔSP value) between the SP value of the compound represented by general formula (1) and the SP value of the resin particles is 5.0 (cal / cm 3 ) 1 / 2 It is preferable that the ΔSP value of the compound represented by general formula (1) and the resin particles is 5.0 or less. When the ΔSP value of the compound represented by general formula (1) and the resin particles is 5.0 or less, the film-forming properties of the resin particles are likely to be improved, and the effect of improving the scratch resistance of the image is likely to be obtained. The ΔSP value of the compound represented by general formula (1) and the resin particles can be determined by subtracting the SP value of the resin particles from the SP value of the compound represented by general formula (1). The ΔSP value of the compound represented by general formula (1) and the resin particles is preferably 1.0 or more, and more preferably 1.5 or more.

[0075] (ΔSP value of resin particles and surfactants with HLB values ​​of 15 or less) The difference (ΔSP value) between the SP value of resin particles and the SP value of surfactants with an HLB value of 15 or less is 3.0 (cal / cm 3 ) 1 / 2 It is preferable that the ΔSP value of the resin particles and the surfactant having an HLB value of 15 or less is 3.0 or less, which makes it easier to improve the film-forming properties of the resin particles and to obtain the effect of improving the scratch resistance of the image. The ΔSP value of the resin particles and the surfactant having an HLB value of 15 or less can be calculated by subtracting the SP value of the surfactant from the SP value of the resin particles. The ΔSP value of the resin particles and the surfactant having an HLB value of 15 or less is preferably 0.5 or more, and more preferably 1.0 or more.

[0076] [Mass ratio of each component] It is preferable that the water-based ink and the predetermined components in the reaction liquid satisfy the following relationship.

[0077] (mass ratio of resin particles to surfactant with an HLB value of 15 or less) The content (mass %) of resin particles in the aqueous ink is preferably 5.0 to 40.0 times the content (mass %) of surfactant in the aqueous ink or reaction liquid containing a surfactant with an HLB value of 15 or less. This mass ratio of 40.0 or less ensures that the amount of surfactant on the recording medium is sufficient relative to the resin particles, which further improves the film-forming properties of the resin particles and improves the abrasion resistance of the image. On the other hand, this mass ratio of 5.0 or more reduces the amount of surfactant remaining in the resin film after recording, which increases the strength of the image and improves the abrasion resistance of the image.

[0078] (mass ratio of the compound represented by general formula (1) to the surfactant with an HLB value of 15 or less) The content (mass %) of the compound represented by general formula (1) in the reaction liquid is preferably 60.0 times or less in mass relative to the content (mass %) of the surfactant in the aqueous ink or reaction liquid containing a surfactant with an HLB value of 15 or less. This mass ratio of 60.0 times or less reduces the dissolution of the surfactant in the compound represented by general formula (1) and facilitates orientation of the surfactant at interfaces and resin particles, thereby improving the scratch resistance of the image. The mass ratio is preferably 10.0 times or more.

[0079] (Mass ratio of compound represented by general formula (1) to resin particles) The content (mass %) of the compound represented by general formula (1) in the reaction liquid is preferably 1.0 to 5.0 times the content (mass %) of the resin particles in the aqueous ink. When this mass ratio is 1.0 or more, the amount of the compound represented by general formula (1) relative to the resin particles is sufficient, which makes it easier to improve the film-forming properties of the resin particles and improve the abrasion resistance of the image. On the other hand, when this mass ratio is 5.0 or less, the compound represented by general formula (1) is less likely to remain in the resin film after recording, or its amount is reduced, which makes it easier to increase the strength of the image and improve the abrasion resistance of the image.

[0080] [Recording Media] The recording medium used in the inkjet recording method and inkjet recording device of the present invention is not particularly limited, but it is preferable to use a non-absorbent recording medium. The non-absorbent recording medium is a recording medium that is non-absorbent in a state where the recording medium ... 1 / 2 Water absorption up to 10mL / m 2 In the present invention, a recording medium that satisfies the above-mentioned condition of water absorption amount is defined as a "non-absorbent recording medium." Inkjet recording media (glossy paper, matte paper, etc.) having an ink-receiving layer formed of inorganic particles and plain paper without a coating layer have a water absorption amount of 10 mL / m or less. 2 When a recording medium other than a non-absorbent recording medium is used, the liquid component is easily absorbed by the recording medium. On the other hand, when a non-absorbent recording medium is used, the absorption of the liquid component is suppressed and the surfactant is easily oriented at the interface and resin particles, which makes it easier to improve the scratch resistance of the image.

[0081] Among non-absorbent recording media, those having a resin layer are preferred. The compound represented by general formula (1) has affinity not only with the resin particles contained in the ink, but also with the constituent materials of the general resin layer of non-absorbent recording media on which an image is recorded by applying an aqueous inkjet ink. This tends to increase the adhesion between the resin particles and the recording medium, further improving the scratch resistance of the image.

[0082] Any non-absorbent recording medium having a resin layer may be used as long as it satisfies this condition. For example, a plastic film; a recording medium in which a plastic film is adhered to the recording surface side of a substrate; a recording medium in which an organic resin coating layer is provided on the recording surface side of a substrate containing cellulose pulp; etc. can be used. Among these, a plastic film is preferred, and a recording medium in which an organic resin coating layer is provided as an organic resin layer on the recording surface side of a substrate containing cellulose pulp is also preferred. For the organic resin layer such as the plastic film and the organic resin coating layer, for example, organic resins such as polyesters such as polyvinyl chloride and PET, polyethylene, polypropylene, and polycarbonate can be used.

[0083] [Discharge method] Methods for ejecting ink or reaction liquid from a recording head include a method of applying mechanical energy to the ink or reaction liquid and a method of applying thermal energy to the ink or reaction liquid. Of these, it is preferable to adopt a method of ejecting ink or reaction liquid by applying thermal energy to the ink or reaction liquid. Examples of recording heads include a recording head that ejects ink or reaction liquid by the action of mechanical energy and a recording head that ejects ink or reaction liquid by the action of thermal energy. Of these, a recording head that ejects ink or reaction liquid by the action of thermal energy is preferable. The order in which the ink and reaction liquid are applied to the recording medium is not particularly limited, but it is preferable to apply the ink after the reaction liquid.

[0084] [Heating process] After applying the ink and reaction liquid to the recording medium, the recording medium is heated to form a film of resin particles, thereby increasing the strength of the image and further improving the scratch resistance of the image.

[0085] The heating means is not particularly limited, and can be, for example, heating with a heater, blowing hot air using a dryer or the like, or a combination of these. The inkjet recording apparatus can be equipped with the above-mentioned heater, dryer, or a combination of these as a heating means. Examples of heating methods include applying heat from the side opposite (backside) the recording surface (ink application surface) of the recording medium using a heater or the like, applying hot or warm air to the recording surface (front side) of the recording medium, and applying heat from the recording surface or back side using an infrared heater. A combination of these methods may also be used. The heating temperature (image temperature) is preferably 60°C or higher and 120°C or lower, and more preferably 70°C or higher and 100°C or lower.

[0086] The difference (T-Tg) between the heating temperature T (°C) of the recording medium and the glass transition temperature Tg (°C) of the resin particles is preferably -10°C or higher (heating temperature ≥ Tg of resin particles - 10°C), and more preferably 0°C or higher (i.e., Tg of resin particles or higher). When the difference (T-Tg) is -10°C or higher, the resin particles are more likely to fuse together, and the effect of improving the scratch resistance of the image is more likely to be obtained. Furthermore, the difference (T-Tg) between the heating temperature T (°C) and the glass transition temperature Tg (°C) is preferably +30°C or lower, and more preferably +20°C or lower.

[0087] [Example of inkjet recording device] FIG. 1 is a perspective view schematically illustrating one embodiment of an inkjet recording apparatus of the present invention. FIG. 2 is a side view schematically illustrating one embodiment of an inkjet recording apparatus of the present invention. In the recording apparatus shown in FIGS. 1 and 2, a heater 25 supported by a frame (not shown) is disposed downstream in a sub-scanning direction A from a position where a recording head 22 reciprocates in a main scanning direction B. The recording medium 1 to which a reaction liquid and ink have been applied can be heated by the heater 25. The heater 25 is covered by a heater cover 26. The heater cover 26 is a member for efficiently irradiating the heat generated by the heater 25 onto the recording medium 1. The heater cover 26 also serves as a member for protecting the heater 25. The recording medium 1 to which ink ejected from the recording head 22 has been applied is wound around a take-up spool 27 to form a roll-shaped wound medium 24. [Example]

[0088] The present invention will be described in more detail below with reference to examples and comparative examples, but the present invention is not limited to the following examples as long as the gist of the invention is not exceeded. The terms "parts" and "%" used to describe the amounts of components are based on mass unless otherwise specified.

[0089] <Preparation of pigment dispersion> A water-soluble resin, styrene / acrylic acid copolymer (composition (mole) ratio = 84.6 / 15.4, acid value 120 mg KOH / g), was dissolved in ion-exchange water with sodium hydroxide in an amount equimolar to the acid value to prepare a resin dispersant solution with a resin content of 20.0%. A mixture of 30.0 parts pigment (carbon black), 30.0 parts aqueous resin dispersant solution, and 40.0 parts water was placed in a sand grinder and dispersed for 1 hour. The mixture was then centrifuged to remove coarse particles, pressure-filtered through a 3.0 μm pore-size microfilter (Fujifilm), and an appropriate amount of ion-exchange water was added to obtain a pigment dispersion. The pigment content in the pigment dispersion was 30.0%, and the resin content was 6.0%.

[0090] <Physical properties of resin particles> The aqueous dispersion of resin particles was dried at 60°C to obtain solid resin particles. 2 mg of the resulting resin particles were placed in an aluminum container and sealed to prepare a sample for measurement. The sample was subjected to thermal analysis using a differential scanning calorimeter (product name "Q1000" manufactured by TA Instruments) according to the temperature program shown below, and a temperature rise curve was created. The temperature at the intersection of a line extending from two points on the low-temperature side of the curve to the high-temperature side and a tangent drawn at the point where the gradient of the step-like change in the curve is maximum (horizontal axis: temperature, vertical axis: heat quantity) was determined as the "glass transition temperature (Tg) of the resin (particles)." [Temperature Program]: (1) Heat up to 200°C at 10°C / min (2) Decrease the temperature from 200°C to -50°C at a rate of 5°C / min. (3) Heat from -50°C to 200°C at 10°C / min

[0091] The amount of anionic groups in the resin particles was determined by colloid titration. Using an automatic potentiometric titrator (product name "AT-510", manufactured by Kyoto Electronics Manufacturing Co., Ltd.) equipped with a streaming potential titration unit (PCD-500), the amount of anionic groups in the resin particles (μmol / g) was measured by colloid titration utilizing potential difference. Methyl glycol chitosan was used as the titration reagent. The SP value ((cal / cm 3 ) 1 / 2 ) was calculated from the SP value of the unit constituting the resin and the mass ratio of the unit.

[0092] <Synthesis of resin particles> (Resin particles 1) Approximately 1160 mL of water was heated to 90°C in a reactor. 1.39 g of potassium persulfate was mixed with 160 mL of water to prepare a solution. 32 mL of this initiator solution was added to the reactor and stirred. Separately, a monomer mixture was prepared by mixing 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 with 159.4 mL of water. The emulsifier used was Rhodafac RS 710 (manufactured by Rhodia Novecare). The monomer mixture was added dropwise to the reactor over 30 minutes, and simultaneously, 129.4 g of the initiator solution was added dropwise to the reactor over the same time period and stirred. The resulting reaction mixture was stirred and maintained at 90°C for 3 hours. The reaction mixture was then cooled to 50°C. Potassium hydroxide was then added to adjust the pH of the solution to 8.5. After cooling the solution to 25°C, it was filtered using a 200-mesh filter, and an appropriate amount of deionized water was added to adjust the resin particle content to 30.0%. In this way, an aqueous dispersion of resin particles 1, which are resin particles formed from an acrylic resin, was obtained. The amount of anionic groups in resin particles 1 was 71 μmol / g, the Tg was 67°C, and the SP value was 10.8.

[0093] (Resin particles 2) A 1-L separable flask equipped with a stirrer, thermometer, and reflux condenser was prepared. A mixture of 100 g of polycarbonate diol, 4.2 g of 2,2-bis(hydroxymethyl)propionic acid, 41 g of 4,4'-dicyclohexylmethane diisocyanate, 2.2 g of triethylamine, and 80 g of acetone (solvent) was prepared. The polycarbonate diol used was "T-5650E" manufactured by Asahi Kasei. Under a nitrogen atmosphere, this mixture was placed in the flask, and one drop of catalyst (tin(II) di(2-ethylhexanoate)) was added. The reaction was carried out at 80°C for 15 hours. After cooling to 40°C, water was added to the flask while stirring at 300 rpm to form urethane resin particles. After stirring at 40°C for 30 minutes, 1.2 g of diethylenetriamine was added and the mixture was stirred at 40°C for 6 hours. After distilling off the solvent, deionized water was added to adjust the resin content to 30.0%. In this way, an aqueous dispersion of resin particles 2, which are resin particles formed from a urethane resin, was obtained. The amount of anionic groups in resin particles 2 was 125 μmol / g, Tg was 64°C, and SP value was 11.5.

[0094] (Resin particles 3 to 9) A mixture of the components (units: parts) listed in the "Esterification Reaction" section of Table 1 was placed in a reaction vessel installed inside the autoclave and heated at 220°C for 4 hours to carry out the esterification reaction. The abbreviations for the components in Table 1 are EG: ethylene glycol, NPG: neopentyl glycol, BPA: bisphenol A, tPA: terephthalic acid, iPA: isophthalic acid, and BTA: trimellitic acid. The temperature was then raised to 240°C, and the pressure inside the autoclave was reduced to 13 Pa over 90 minutes. The esterification (dehydration condensation) reaction was continued by maintaining the reduced pressure at 240°C and 13 Pa for 5 hours, after which nitrogen gas was introduced into the autoclave to return to normal pressure. The temperature inside the reaction vessel was lowered to 220°C, and a catalyst (tetra-n-butyl titanate) and the components (units: parts) listed in the "Transesterification Reaction" section of Table 1 were added. The transesterification reaction was carried out by heating at 220°C for 2 hours. The amount of catalyst used (mol) is 3 x 10 -4× the total amount (mol) of polycarboxylic acids used. Nitrogen gas was then introduced into the autoclave to create a pressurized state, and a sheet-like resin was removed. This resin was cooled to 25°C and then crushed in a crusher to obtain a resin.

[0095] A stirrer (product name: "Tornado Stirrer Standard SM-104" manufactured by AS ONE) was placed in a 2-L beaker. 210 g of the resin obtained above and methyl ethyl ketone were placed in the beaker and stirred at 30°C to dissolve the resin. Next, a 5% aqueous potassium hydroxide solution was added in an amount corresponding to the neutralization rate (mol%) based on the acid value corresponding to the acid groups of the resin, and the mixture was stirred for 30 minutes. While stirring at 30°C, 500 g of deionized water was added dropwise at a rate of 20 mL / min. The mixture was then heated to 60°C, and the methyl ethyl ketone was distilled off, followed by partial distillation of the water. After cooling to 25°C, the mixture was filtered through a 150-mesh wire screen, and the resin content was adjusted to 30.0% with deionized water. In this way, aqueous dispersions of resin particles 3 to 9, which are resin particles formed from polyester resins, were obtained. The properties of resin particles 3 to 9 are listed in the "Properties" section of Table 1.

[0096] TIFF2023029244000003.tif58170

[0097] <SP value of water-soluble organic solvent> The SP values ​​of the water-soluble organic solvents used in preparing the ink and reaction liquid are shown below. N-(2-hydroxyethyl)-2-pyrrolidone: 14.3 N-hydroxymethyl-2-pyrrolidone: 15.2 N-(3-hydroxypropyl)-2-pyrrolidone: 13.7 N-hydroxy-2-pyrrolidone: 16.4 N-(4-hydroxybutyl)-2-pyrrolidone: 13.2 2-pyrrolidone: 12.6 N-methyl-2-pyrrolidone: 11.5 3-Methoxy-N,N-dimethylpropionamide: 9.2 γ-butyrolactone: 9.9 1,2-butanediol: 12.8

[0098] <Surfactant> The commercially available surfactants shown by the following trade names were used to prepare the inks and reaction solutions described below. NIKKOL BL-4.2 (Nikko Chemicals): HLB value 10, SP value 9.6 EMALEX 1615 (manufactured by Nippon Emulsion): HLB value 15, SP value 9.4 TERGITOL 15-S-7 (Dow Chemical): HLB value 11, SP value 9.4 TERGITOL 15-S-9 (Dow Chemical): HLB value 12, SP value 9.4 NIKKOL BC-10 (Nikko Chemicals): HLB value 13, SP value 9.4 Zonyl FS-3100 (Chemours): HLB value 10, SP value 8.7 Acetylenol E60 (Kawaken Fine Chemicals): HLB value 11, SP value 9.9 NIKKOL BC-20 (Nikko Chemicals): HLB value 16, SP value 9.4 Of the above surfactants, "Zonyl FS-3100" is a fluorine-based surfactant, "Acetylenol E60" is an ethylene oxide adduct of acetylene glycol, and the others are polyoxyethylene alkyl ethers.

[0099] <Ink Preparation> Each ink was prepared by mixing the components (unit: %) shown in the upper row of Table 2 (Tables 2-1 and 2-2), thoroughly stirring, and then filtering under pressure through a cellulose acetate filter (trade name "Minisart", manufactured by Sartorius) with a pore size of 1.2 μm. "Proxel GXL(S)" in Table 2 is a commercially available preservative (trade name; manufactured by Arch Chemicals), which was also used in preparing the reaction solution described below.

[0100] TIFF2023029244000004.tif117170

[0101] TIFF2023029244000005.tif117170

[0102] <Preparation of reaction solution> The components (unit: %) shown in the upper row of Table 3 (Tables 3-1 to 3-5) were mixed, thoroughly stirred, and then pressure-filtered through a 1.2 μm pore size cellulose acetate filter (trade name "Minisart", manufactured by Sartorius) to prepare each reaction solution. "PDT-2" in Table 3 is the trade name for an aqueous solution of dimethylamine-epichlorohydrin condensate (60% pure content) manufactured by Yokkaichi Chemical. "PAS-92" is the trade name for an aqueous solution of diallylamine hydrochloride-sulfur dioxide copolymer (20% pure content) manufactured by Nittobo Medical.

[0103] TIFF2023029244000006.tif181170

[0104] TIFF2023029244000007.tif179170

[0105] TIFF2023029244000008.tif179170

[0106] TIFF2023029244000009.tif183170

[0107] TIFF2023029244000010.tif176170

[0108] <Evaluation> The following recording medium was used for recording images. The "amount of water absorption" was measured 30 msec after the start of contact in the Bristow method. 1 / 2 This indicates the amount of water absorbed up to Recording medium 1 (product name "Scotchcal Graphic Film IJ1220", manufactured by 3M, material: polyvinyl chloride, water absorption: 10 mL / m 2 below) Recording medium 2 (product name: "Canon Photo Paper - Glossy Pro [Platinum Grade] PT-201", manufactured by Canon, no resin layer, water absorption: 10 mL / m 2 super) Recording medium 3 (product name "LX Gloss Coat 157 LXGC54", manufactured by Sakurai, no resin layer, water absorption: 10 mL / m 2 below)

[0109] The following evaluations were performed using an inkjet recording device (product name "imagePROGRAF PRO-2000," manufactured by Canon) equipped with an infrared heater located downstream of the recording head in the recording medium transport direction, facing the recording medium. In the inkjet recording device, an image recorded under conditions in which one 4 ng droplet of ink was applied to a unit area of ​​1 / 1200 inch x 1 / 1200 inch was defined as having a recording duty of 100%. Each ink prepared above was filled into an ink cartridge. Recording conditions were an environment of 25°C and 50% relative humidity. Using the recording device, the reaction liquid (30% recording duty) and the ink (120% recording duty) were applied in layers to the recording medium in the combinations of reaction liquid, ink, and recording medium shown in Table 4 (Tables 4-1 and 4-2). The reaction liquid and ink were then applied to the recording medium in this order using the infrared heater, and the area on the recording medium to which the reaction liquid and ink had been applied was heated to the temperature shown in Table 4, thereby recording a solid image.

[0110] The abbreviations in Tables 2 to 4 represent the following: ·R I : Resin particle content in ink (%) ·S I : Content (%) of surfactants with an HLB value of 15 or less in the ink L R : Content (%) of the compound represented by general formula (1) in the reaction solution ·S R : Content (%) of surfactants with an HLB value of 15 or less in the reaction solution S:S I or S R , i.e., the content (%) of surfactant in the ink or reaction liquid

[0111] The "mass ratio" column in Table 4 indicates the mass ratio of each component. The "ΔSP value" column in Table 4 indicates the difference in SP value between each component. In this column, "resin particle - surfactant" indicates the difference between the SP value of the resin particle and the SP value of the surfactant, and "general formula (1) - resin particle" indicates the difference between the SP value of the compound represented by general formula (1) and the SP value of the resin particle.

[0112] (Abrasion resistance) The resulting print was subjected to a 20-cycle back-and-forth rub test at a load of 500 g using a Gakushin-type abrasion tester (manufactured by Tester Sangyo Co., Ltd.) conforming to JIS L0849 and a white cotton rubbing cloth as specified in JIS L0803. The image after the rub test was visually inspected, and the abrasion resistance of the image was evaluated according to the following evaluation criteria. In the present invention, "A+," "A," and "B" were considered acceptable levels, and "C" was considered unacceptable. The evaluation results are shown in Table 4. A+: No scratches were observed in the image after 10 times. A: Scratch marks were observed in the image after 10 times, but no scratches were observed in the image after 5 times. B: Scratches were observed on the image after 5 times, but the white background of the recording medium was not visible. C: Scratches were observed on the image after 5 times, and the white background of the recording medium was visible.

[0113] TIFF2023029244000011.tif249170

[0114] TIFF2023029244000012.tif77170

[0115] The disclosure of this embodiment includes the following methods and configurations. (Method 1) An inkjet recording method in which an aqueous ink containing resin particles and a reaction liquid containing a reactant that aggregates components in the aqueous ink are ejected from an inkjet recording head onto a recording medium, The reaction solution contains a compound represented by the following general formula (1): an inkjet recording method, wherein at least one of the aqueous ink and the reaction liquid contains a surfactant having an HLB value of 15 or less;

[0116] TIFF2023029244000013.tif33170 (n in the general formula (1) represents an integer of 0 to 3.)

[0117] (Method 2) The inkjet recording method according to Method 1, wherein the content (mass %) of the resin particles in the aqueous ink is 5.0 times or more and 40.0 times or less in mass ratio to the content (mass %) of the surfactant in the aqueous ink or the reaction liquid containing the surfactant. (Method 3) The inkjet recording method according to Method 1 or 2, wherein the content (mass %) of the compound represented by General Formula (1) in the reaction liquid is 60.0 times or less in mass ratio relative to the content (mass %) of the surfactant in the aqueous ink or the reaction liquid containing the surfactant. (Method 4) The inkjet recording method according to any one of Methods 1 to 3, wherein the content (mass%) of the compound represented by General Formula (1) in the reaction liquid is 1.0 to 5.0 times, in mass ratio, relative to the content (mass%) of the resin particles in the aqueous ink. (Method 5) The inkjet recording method according to any one of Methods 1 to 4, wherein the content (mass %) of the surfactant is 1.0 mass % or less based on the total mass of the aqueous ink or the reaction liquid containing the surfactant. (Method 6) The inkjet recording method according to any one of Methods 1 to 5, wherein the HLB value of the surfactant is 12 or less. (Method 7) The inkjet recording method according to any one of Methods 1 to 6, wherein the surfactant comprises polyoxyethylene alkyl ether. (Method 8) The difference between the SP value of the resin particles and the SP value of the surfactant is 3.0 (cal / cm 3 ) 1 / 2 8. The inkjet recording method according to any one of Methods 1 to 7, wherein the inkjet recording method is: (Method 9) The difference between the SP value of the compound represented by the general formula (1) and the SP value of the resin particles is 5.0 (cal / cm 3 ) 1 / 2 9. The inkjet recording method according to any one of Methods 1 to 8, wherein the inkjet recording method is: (Method 10) The inkjet recording method according to any one of Methods 1 to 9, wherein the amount of anionic groups in the resin particles is 350 μmol / g or less. (Method 11) The inkjet recording method according to any one of Methods 1 to 10, wherein the aqueous ink further contains a compound represented by formula (1). (Method 12) The inkjet recording method according to any one of Methods 1 to 11, wherein the reactant is an acid-type organic carboxylic acid having a pKa of 1.8 or more. (Method 13) The inkjet recording method according to Method 12, wherein the acid-type organic carboxylic acid has a plurality of carboxylic acid groups. (Method 14) 30 msec from the start of contact of the recording medium in the Bristow method 1 / 2 Water absorption up to 10mL / m 2 14. The inkjet recording method according to any one of Methods 1 to 13, wherein the inkjet recording method is: (Method 15) The inkjet recording method according to Method 14, wherein the recording medium has a resin layer. (Method 16) The inkjet recording method according to any one of Methods 1 to 15, wherein the recording medium is heated after the aqueous ink and the reaction liquid are applied to the recording medium. (Method 17) The inkjet recording method according to Method 16, wherein the difference (T-Tg) between the heating temperature T (°C) of the recording medium and the glass transition temperature Tg (°C) of the resin particles is -10°C or more. (Configuration 1) A printing apparatus comprising: an aqueous ink containing resin particles; a reaction liquid containing a reactant that aggregates components in the aqueous ink; and an inkjet recording head that ejects the aqueous ink and the reaction liquid onto a recording medium; The reaction solution contains a compound represented by the following general formula (1): An inkjet recording apparatus, wherein at least one of the aqueous ink and the reaction liquid contains a surfactant having an HLB value of 15 or less.

[0118] TIFF2023029244000014.tif33170 (n in the general formula (1) represents an integer of 0 to 3.)

Claims

1. An inkjet recording method in which an aqueous ink containing resin particles and a reaction liquid containing a reactant for aggregating components in the aqueous ink are ejected from an inkjet recording head and applied to a recording medium, wherein the reaction liquid contains a compound represented by the following general formula (1), and at least one of the aqueous ink and the reaction liquid contains a surfactant having an HLB value of 15 or less. (In the general formula (1), n represents an integer of 0 to 3.)

2. The inkjet recording method according to claim 1, wherein the content (mass%) of the resin particles in the aqueous ink is 5.0 times or more and 40.0 times or less the mass ratio to the content (mass%) of the surfactant in the aqueous ink or the reaction liquid containing the surfactant.

3. The inkjet recording method according to claim 1, wherein the content (mass%) of the compound represented by the general formula (1) in the reaction liquid is 60.0 times or less the mass ratio to the content (mass%) of the surfactant in the aqueous ink or the reaction liquid containing the surfactant.

4. The inkjet recording method according to claim 1, wherein the content (mass%) of the compound represented by the general formula (1) in the reaction liquid is 1.0 times or more and 5.0 times or less the mass ratio to the content (mass%) of the resin particles in the aqueous ink.

5. The inkjet recording method according to any one of claims 1 to 4, wherein the content (mass%) of the surfactant is 1.0 mass% or less based on the total mass of the aqueous ink or the reaction liquid containing the surfactant.

6. The inkjet recording method according to any one of claims 1 to 4, wherein the HLB value of the surfactant is 12 or less.

7. The inkjet recording method according to any one of claims 1 to 4, wherein the surfactant includes a polyoxyethylene alkyl ether.

8. The difference between the SP value of the resin particles and the SP value of the surfactant is 3.0 (cal / cm ３ ) １／２ The inkjet recording method according to any one of claims 1 to 4, wherein the difference is 3.0 or less.

9. The difference between the SP value of the compound represented by the general formula (1) and the SP value of the resin particles is 5.0 (cal / cm ３ ) １／２ The inkjet recording method according to any one of claims 1 to 4, wherein the difference is 5.0 or less.

10. The inkjet recording method according to any one of claims 1 to 4, wherein the amount of anionic groups in the resin particles is 350 μmol / g or less.

11. The inkjet recording method according to any one of claims 1 to 4, wherein the resin forming the resin particles is at least one selected from the group consisting of an acrylic resin, a urethane resin, and a polyester resin.

12. The inkjet recording method according to any one of claims 1 to 4, wherein the compound represented by the general formula (1) in the reaction liquid and the resin particles in the aqueous ink first come into contact with each other on the recording medium.

13. The inkjet recording method according to any one of claims 1 to 4, wherein the aqueous ink further contains the compound represented by the general formula (1).

14. The inkjet recording method according to any one of claims 1 to 4, wherein the reactant is an acid-type organic carboxylic acid and its pKa is 1.8 or more.

15. The inkjet recording method according to claim 14, wherein the acid-type organic carboxylic acid has a plurality of carboxylic acid groups.

16. The water absorption amount of the recording medium from the start of contact in the Bristol method to 30 msec １／２ is 10 mL / m ２ The inkjet recording method according to any one of claims 1 to 4, wherein the amount is 10 mL / m or less.

17. The inkjet recording method according to claim 16, wherein the recording medium has a resin layer.

18. The inkjet recording method according to any one of claims 1 to 4, wherein after applying the aqueous ink and the reaction liquid to the recording medium, the recording medium is heated.

19. The inkjet recording method according to claim 18, wherein the difference (T - Tg) between the heating temperature T (°C) of the recording medium and the glass transition temperature Tg (°C) of the resin particles is -10°C or more.

20. An inkjet recording apparatus comprising: an aqueous ink containing resin particles; a reaction liquid containing a reactant for aggregating components in the aqueous ink; and an inkjet recording head for discharging the aqueous ink and the reaction liquid and applying them to a recording medium, wherein the reaction liquid contains a compound represented by the following general formula (1), and at least one of the aqueous ink and the reaction liquid contains a surfactant having an HLB value of 15 or less. (In the general formula (1), n represents an integer from 0 to 3.)

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