Ink set, inkjet recording method, and inkjet recording apparatus

Abstract

The present invention provides an ink set containing water-based ink and a reaction solution, which is less prone to clouding of the reaction solution due to heat and over time, and which can record images with good scratch resistance and water scratch resistance. [Solution] An ink set comprising an aqueous ink and a reaction solution used in an inkjet recording method for recording an image on a recording medium using an aqueous ink and an aqueous reaction solution containing a reactant that reacts with the aqueous ink. The aqueous ink contains a resin. The reactant contains at least one selected from the group consisting of polyvalent metal salts and cationic resins. The reaction solution further contains an ionic surfactant and a crosslinking agent that can form a bond with the resin in the aqueous ink.

Description

[Technical Field]

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

[0002] An inkjet recording device is a device that records images onto a recording medium by ejecting tiny ink droplets from the ejection port of a recording head. In recent years, there has been a demand for recording media that have low absorption of water-based ink, or recording media that hardly absorb water-based ink at all. Examples of recording media with low absorption of water-based ink (hereinafter also referred to as "low-absorption recording media") include recording media with a coating layer, such as art paper or coated paper. Examples of recording media that hardly absorb water-based ink (hereinafter also referred to as "non-absorbent recording media") include plastic film.

[0003] As for inks, the use of water-based inks containing pigments (hereinafter also referred to as "pigment inks") is being considered from the perspective of environmental impact and safety. Until now, high-definition image quality has been obtained using pigment inks on recording media that readily absorb water-based inks, such as recording media without a coating layer (e.g., plain paper). In contrast, with low-absorption and non-absorption recording media, the applied ink droplets do not easily penetrate the recording media, and adjacent ink droplets are applied before ink fixation through penetration has almost occurred. As a result, the ink droplets merge together, causing bleeding and unevenness, making it difficult to obtain high-definition image quality.

[0004] To address the above issues, for example, Patent Document 1 proposes a reaction solution containing a polyvalent metal salt that reacts with components such as pigments in ink to cause aggregation and thickening.

[0005] In addition, in the recorded matter recorded by an inkjet recording method using aqueous ink on the above low-absorbency recording medium or non-absorbency recording medium, an image is formed by the presence of an image layer formed of ink or the like on the surface of the recording medium. Therefore, higher requirements are placed on the abrasion resistance and fixing property of the image than ever before.

[0006] On the other hand, Patent Document 2 proposes an ink set including a first liquid composition containing a crosslinking agent and water, and an aqueous ink as a second liquid composition containing a pigment and a resin capable of reacting with the crosslinking agent.

Prior Art Documents

Patent Documents

[0007]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0008] In the crosslinking agent described in Patent Document 2, the higher the concentration in the reaction solution, the higher the crosslinking density of the image layer formed by the ink and the reaction solution on the recording medium, and high fastness such as good abrasion resistance and water abrasion resistance can be expected. In addition, in order to obtain a high-quality image, it is necessary to contain a high concentration of polyvalent metal salt in the reaction solution. However, the reaction solution containing a high concentration of the crosslinking agent and the polyvalent metal salt becomes cloudy depending on the temperature and separates into two layers over time. It has been found that due to this layer separation, the crosslinking agent is localized at a high concentration, and the crosslinking agents self-crosslink and become gel-like. It is considered that in such a reaction solution partially gelled, the effect of improving the fastness of the image expected by containing the crosslinking agent cannot be sufficiently exhibited. In addition, the fastness of the image may be an important factor in the ratio of the amount of resin and the amount of crosslinking agent on the recording medium. However, in the reaction solution gelled into two layers as described above, it becomes difficult to control the application to the recording medium.

[0009] Therefore, an object of the present invention is to provide an ink set containing aqueous ink and a reaction solution that is less prone to clouding of the reaction solution due to heat and over time, and that can record images with good scratch resistance and water scratch resistance. Another object of the present invention is to provide an inkjet recording method and an inkjet recording apparatus that can use this ink set. [Means for solving the problem]

[0010] In other words, the present invention provides an ink set for use in an inkjet recording method that records an image on a recording medium using an aqueous ink and an aqueous reaction solution containing a reactant that reacts with the aqueous ink, wherein the aqueous ink contains a resin, the reactant contains at least one selected from the group consisting of polyvalent metal salts and cationic resins, and the reaction solution further contains an ionic surfactant and a crosslinking agent that can form a bond with the resin in the aqueous ink. [Effects of the Invention]

[0011] According to the present invention, an ink set comprising aqueous ink and a reaction solution can be provided that is less prone to clouding of the reaction solution due to heat and over time, and that can record images with good scratch resistance and water scratch resistance. Furthermore, according to the present invention, an inkjet recording method and an inkjet recording apparatus that can use this ink set can be provided. [Brief explanation of the drawing]

[0012] [Figure 1] This is a schematic diagram showing one embodiment of the inkjet recording apparatus of the present invention. [Figure 2] This is a perspective view showing an example of a liquid dispensing device. [Modes for carrying out the invention]

[0013] The present invention will be described in more detail below with reference to preferred embodiments. In the present invention, when a compound is a salt, the salt exists in the ink dissociated into ions, but for convenience, it will be expressed as "contains a salt." Also, the aqueous ink and reaction solution for inkjet printers may be simply referred to as "ink" and "reaction solution." Unless otherwise specified, the physical properties are values ​​at room temperature (25°C). When "(meth)acrylic acid" and "(meth)acrylate" are written, they mean "acrylic acid, methacrylic acid" and "acrylate, methacrylate," respectively.

[0014] When recording an image using a two-component reaction system that employs a reaction solution and ink, the reaction solution is generally applied to the recording medium first, followed by the ink. In the inkjet recording method of the present invention, the order in which the reaction solution and ink are applied is not limited to the above order. However, it is preferable to apply the reaction solution to the recording medium first, followed by the ink, in order to further enhance the effects of the present invention. The following explanation will use the order in which the reaction solution is applied to the recording medium first, followed by the ink, as an example.

[0015] The inventors of the present invention have been working to obtain recording materials that achieve both high image quality and durability by using a reaction solution containing a high concentration of a crosslinking agent and a polyvalent metal salt and / or a cationic resin, and an aqueous ink containing a pigment.

[0016] Specifically, in a two-component reaction system consisting of an aqueous ink and a reaction solution containing a flocculant that causes a rapid viscosity change upon contact with the aqueous ink, we investigated incorporating a resin into the ink and a crosslinking agent into the reaction solution that can form bonds with the resin in the ink. This is expected to create a crosslinked structure in the image layer formed by the ink and reaction solution, thereby improving the robustness of the recorded image, such as scratch resistance and water resistance. Furthermore, within a certain range of the ratio of resin to crosslinking agent in the image layer, it is thought that the image robustness tends to improve as the amount of crosslinking agent increases.

[0017] However, the inventors' investigations revealed that in a reaction solution containing high concentrations of polyvalent metal salts and / or cationic resins, as well as a crosslinking agent, each material could not be sufficiently hydrated. The crosslinking agent, which has relatively weak interactions with water molecules, eluted, causing the entire reaction solution to become cloudy. It was also found that the degree of cloudiness became more pronounced with increasing temperature of the reaction solution. Furthermore, it was found that the cloudy solution, over time, caused the crosslinking agent to gel, making it prone to layer separation.

[0018] The inventors considered that promoting the hydration of the crosslinking agent is important in order to suppress the elution of the crosslinking agent in the reaction solution. Through investigation, it was found that by further including an ionic surfactant in the reaction solution, the hydration of the crosslinking agent in the reaction solution is promoted, and the turbidity of the reaction solution can be suppressed. The inventors believe the reason for this is as follows.

[0019] Generally, polyvalent metal salts, cationic resins, and surfactants used in aqueous reaction solutions dissolve by hydrating with water molecules in the reaction solution. Similarly, crosslinking agents, except in special cases such as emulsion types, also achieve water solubility through hydration with water molecules. Therefore, the higher the concentration of polyvalent metal salts and / or cationic resins in the reaction solution, the more easily crosslinking agents, which have relatively weaker interactions with water molecules, will dissolve. To address this, ionic surfactants are added to the reaction solution as solubilizing agents. In the reaction solution, ionic surfactants form aggregates such as micelles, with their hydrophobic parts facing inward and their hydrophilic parts facing outward. It is believed that the encapsulation of the crosslinking agent within these aggregates improves the solubility of the crosslinking agent in the reaction solution, enabling higher concentrations of the crosslinking agent.

[0020] <Ink Set> The ink set of the present invention is a set containing an aqueous ink and an aqueous reaction liquid. This ink set is used in an inkjet recording method for recording an image on a recording medium using the aqueous ink and the reaction liquid. The reaction liquid contains a reactant that reacts with the aqueous ink. And the reactant contains at least one selected from the group consisting of a polyvalent metal salt and a cationic resin. Further, the ink contains a resin. By the ink containing a resin, a resin film can be formed on the recording medium. In order to enhance the abrasion resistance of the image, the strength of this resin film is increased to make the image less likely to be damaged. Therefore, the reaction liquid contains a crosslinking agent that can form a bond with the resin in the ink and the above-described ionic surfactant. As the resin to be contained in the ink, a resin that can form a bond with the crosslinking agent is used. In the recording medium, when the reaction liquid and the ink come into contact with each other, the resin in the ink and the crosslinking agent in the reaction liquid can react. Hereinafter, the reaction liquid and the ink constituting the ink set will be described.

[0021] <Reaction Liquid> The reaction liquid is an aqueous reaction liquid containing a reactant that reacts with the aqueous ink. Hereinafter, each component used in the reaction liquid and the like will be described in detail.

[0022] (Reactant) The reaction liquid reacts with the ink when coming into contact with the ink, and aggregates components (components having an anionic group such as a resin and a self-dispersing pigment) in the ink, and contains a reactant. As the reactant, at least one selected from the group consisting of a polyvalent metal salt and a cationic resin is used.

[0023] As the polyvalent metal salt, a polyvalent metal salt (which may be a hydrate) formed by bonding a polyvalent metal ion and an anion can be used. Examples of the polyvalent metal ion include divalent metal ions such as Ca 2+ , Cu 2+ , Ni 2+ , Mg 2+ , Sr 2+ , Ba 2+ , and Zn 2+ and the like, and Fe 3+ , Cr 3+ , Y3+ , and Al 3+ Examples of trivalent metal ions include Cl. - , Br - , I - , - ClO2 - ClO3 - ClO4 - NO2 - NO3 - SO4 2- CO3 2- , HCO3 - , PO4 3- HPO4 2- , and H2PO4 - Inorganic anions such as HCOO - , (COO - )2, COOH(COO - ), CH3COO - CH3CH(OH)COO - , C2H4(COO - )2, C6H5COO - , C6H4(COO - )2, and CH3SO3 - Examples of organic anions include the following. The reaction solution may contain one or more polyvalent metal salts. When polyvalent metal ions are used as reactants, the content (mass%) of polyvalent metal salts in the reaction solution is preferably 1.0% by mass or more and 30.0% by mass or less, and more preferably 2.0% by mass or more and 30.0% by mass or less, based on the total mass of the reaction solution. In this specification, when the polyvalent metal salt is a hydrate, the "content (mass%) of polyvalent metal salt" in the reaction solution means the "content (mass%) of anhydrous polyvalent metal salt" excluding water as the hydrate.

[0024] Furthermore, from the viewpoint of the compatibility of the components in the reaction solution, which reduces the likelihood of turbidity occurring in the reaction solution due to heat and over time, the standard enthalpy of formation of the anions constituting the polyvalent metal salt is -1,000 kJ / mol. -1 -200kJmol -1The following is preferable. For the calculation method of the standard enthalpy of formation of anions, refer to "Chemical Handbook Basic Edition" (Maruzen Publishing) and calculate using 298.15K. Note that the standard enthalpy of formation of a typical anion is SO4 2- -909.34kJmol -1 Cl - -167.08 kJ / mol -1 , PO4 3- -1018.7kJmol -1 That is the case.

[0025] If the reaction solution contains a polyvalent metal salt, from the viewpoint of easily improving the scratch resistance and water resistance of the image, the polyvalent metal salt contains sulfate ions (SO4 2- It is preferable that the polyvalent metal salt is magnesium sulfate, as this makes it easier to improve the scratch resistance and water resistance of the image, and also makes it less likely for the reaction solution to become cloudy due to heat and over time.

[0026] Examples of cationic resins include resins having the structure of primary to tertiary amines and resins having the structure of quaternary ammonium salts. Specifically, examples include resins having the structures of vinylamine, allylamine, vinylimidazole, vinylpyridine, dimethylaminoethyl methacrylate, ethyleneimine, and guanidine. The reaction solution may contain one or more cationic resins. To improve solubility in the reaction solution, a cationic resin may be used in combination with an acidic compound, or the cationic resin may be subjected to quaternization treatment. When a cationic resin is used as a reactant, the content (mass%) of the cationic resin in the reaction solution is preferably 1.0% by mass or more and 10.0% by mass or less, based on the total mass of the reaction solution.

[0027] Furthermore, in addition to the polyvalent metal salt and / or cationic resin used as a reactant, the reaction solution may optionally contain other reactants. Examples of other reactants include organic acids. The reaction solution containing organic acids has buffering capacity in the acidic range (pH less than 7.0, preferably pH 2.0 to 5.0), which efficiently converts the anionic groups of components present in the ink into acidic forms and causes aggregation.

[0028] Examples of organic acids include monocarboxylic acids and their salts, such as formic acid, acetic acid, propionic acid, butyric acid, benzoic acid, glycolic acid, lactic acid, salicylic acid, pyrrole carboxylic acid, furoic acid, picolinic acid, nicotinic acid, thiophene carboxylic acid, levulinic acid, and coumaric acid; dicarboxylic acids and their salts or hydrogen salts, such as oxalic acid, malonic acid, succinic acid, glutaric acid, adipic acid, maleic acid, fumaric acid, itaconic acid, sebacic acid, phthalic acid, malic acid, and tartaric acid; tricarboxylic acids and their salts or hydrogen salts, such as citric acid and trimellitic acid; and tetracarboxylic acids and their salts or hydrogen salts, such as pyromellitic acid. The reaction solution may contain one or more organic acids. When an organic acid is used as a reactant, the content (mass%) of the organic acid in the reaction solution is preferably 1.0% by mass or more and 40.0% by mass or less, based on the total mass of the reaction solution.

[0029] The amount of reactant (mass%) in the reaction solution is preferably 1.0% by mass or more and 35.0% by mass or less, and more preferably 2.0% by mass or more and 30.0% by mass or less, based on the total mass of the reaction solution. From the viewpoint of easily suppressing the phenomenon of ink bleeding along the fibers of the recording medium in the image (feathering), the above amount of reactant is more preferably 2.0% by mass or more, and even more preferably 2.5% by mass or more. On the other hand, from the viewpoint of further easily improving the scratch resistance and water resistance of the image, the above amount of reactant is more preferably 30.0% by mass or less, and even more preferably 25.0% by mass or less. The above amount of reactant is the total amount of reactants such as polyvalent metal salts, cationic resins, and organic acids.

[0030] (Crosslinking agent) The reaction solution contains a crosslinking agent that can form a bond with the resin in the ink, as described later. The crosslinking agent is a component that can form a three-dimensional network structure by reacting with the resin in the ink. The crosslinking agent is a different component from the reaction agent. The bond formed between the resin in the ink and the crosslinking agent is preferably a covalent bond. The crosslinking agent may be dissolved in the aqueous medium in the reaction solution, or it may be dispersed as particles in the aqueous medium in the reaction solution. Since the crosslinking agent is contained in the reaction solution, it is separated from the resin in the ink before the reaction solution and ink are applied to the recording medium, thus improving the shelf life of the reaction solution. Furthermore, since the crosslinking agent is contained in the reaction solution, it is not necessary to use a separate liquid containing the crosslinking agent, which is advantageous in terms of the number of ink cartridge types that can be used in inkjet recording devices.

[0031] When the reaction solution is used in an inkjet recording method that includes a drying step in which an ink-coated recording medium is heated, it is preferable that the glass transition temperature of the crosslinking agent is lower than the heating temperature of the recording medium in the drying step. When the glass transition temperature of the crosslinking agent is lower than the heating temperature of the recording medium, the crosslinking agent softens more easily and comes into contact with the resin in the ink more easily. This makes it easier for the crosslinking agent in the reaction solution and the resin in the ink to crosslink, which tends to increase the strength of the resin film and thus improves the scratch resistance of the image. On the other hand, from the viewpoint of image adhesion resistance, it is preferable that the glass transition temperature of the crosslinking agent be above 50°C, and more preferably above 51°C. This improves the image adhesion resistance. The glass transition temperature can be measured by conventional methods, for example, using a thermal analysis device such as a differential scanning calorimeter (DSC).

[0032] The reaction start temperature between the crosslinking agent and the resin in the ink is preferably lower than the drying temperature after recording, and more preferably 25°C or lower.

[0033] The crosslinking agent is not particularly limited as long as it can form a bond with the resin in the ink, and an appropriate one can be selected and used depending on the intended use, drying conditions, and type of recording medium. The crosslinking agent is a compound having two or more functional groups (hereinafter sometimes referred to as "crosslinkable groups") that can form a bond with the resin or other components in the ink. When these functional groups bond with the resin in the ink, a crosslinked structure (three-dimensional network structure) can be introduced into the image layer formed by the ink and reaction solution. Furthermore, if these bonds are covalent bonds, the number of hydrophilic groups in the material of the image layer is irreversibly reduced, improving the hydrophobicity of the image layer and tending to increase its water resistance and ethanol resistance.

[0034] Examples of functional groups (crosslinkable groups) that a crosslinking agent may possess include carbodiimide groups, epoxy groups, amino groups, isocyanate groups, oxazoline groups, silyl groups, halides, aziridine groups, melanin groups, azo groups, and bismaleimide groups. Compounds having two or more functional groups selected from these can be used as crosslinking agents. Furthermore, a crosslinking agent may have one of the above functional groups, or two or more. In addition, a single crosslinking agent may be used, or two or more may be used in combination.

[0035] Among the functional groups listed above, from the viewpoint of improving the shelf life of the reaction solution and the robustness of the image, it is preferable that the crosslinking agent has two or more functional groups selected from the group consisting of carbodiimide groups, isocyanate groups, and oxazoline groups. In particular, from the viewpoint of further improving the scratch resistance of the image, it is even more preferable that the crosslinking agent has two or more carbodiimide groups. Therefore, it is preferable to use at least one selected from the group consisting of carbodiimide-based crosslinking agents having carbodiimide groups, isocyanate-based crosslinking agents having isocyanate groups, and oxazoline-containing crosslinking agents having oxazoline groups. In particular, it is even more preferable to use a carbodiimide-based crosslinking agent. As these crosslinking agents, commercially available products can preferably be used due to their availability.

[0036] Examples of carbodiimide-based crosslinking agents include the trade name "Carbodilite" (model numbers: V-02, V-02-L2, SV-02, V-04, V-10, E-02, E-03, E-05, manufactured by Nisshinbo Chemical). Examples of isocyanate-based crosslinking agents include the trade name "Elastron" (model numbers: BN-69, BN-77, BN-27, manufactured by Daiichi Kogyo Seiyaku). Examples of oxazoline group-containing crosslinking agents include the trade name "Epocross" (model numbers: K-2010E, K-2020E, K-2035E, WS-300, WS-500, WS-700, manufactured by Nippon Shokubai).

[0037] The crosslinking agent having the functional groups described above can form bonds with the resin in the ink, and optionally with components other than the resin in the ink, or with hydrophilic groups present on the surface of the recording medium. Examples of hydrophilic groups that can react with the crosslinking agent include carboxyl groups, phenolic hydroxyl groups, alcoholic hydroxyl groups, amino groups, amide groups, aromatic thiol groups, epoxy groups, caprolactam groups, and acid anhydride groups. Among these, carboxyl groups or alcoholic hydroxyl groups are preferred.

[0038] The reaction between the functional groups of the crosslinking agent in the reaction solution and the carboxyl groups of the resin in the ink will be explained with an example. When the crosslinking agent in the reaction solution has an oxazoline group, the oxazoline group and the carboxyl group of the resin form an amide ester bond, thereby crosslinking the resin film on the recording medium. Also, when the crosslinking agent in the reaction solution has a carbodiimide group (-N=C=N-), the carbodiimide group and the carboxyl group of the resin form an N-acylurea structure, thereby crosslinking the resin film on the recording medium. As a result, the strength of the resin film formed on the recording medium is increased, and the scratch resistance and water resistance of the image can be improved.

[0039] Regarding the number of functional groups (crosslinkable groups) in the molecule of the crosslinking agent, from the viewpoint of further improving the scratch resistance and water resistance of the image, it is preferable that the crosslinking agent has 1 mole of functional groups per molecular weight of 350 to 550. In other words, the chemical formula weight per mole of functional groups of the crosslinking agent, i.e., the functional group equivalent, is preferably 350 or more and 550 or less.

[0040] The content (mass%) of the crosslinking agent in the reaction solution is preferably 1.0% by mass or more and 25.0% by mass or less, and more preferably 2.0% by mass or more and 20.0% by mass or less, based on the total mass of the reaction solution. From the viewpoint of further improving the scratch resistance and water scratch resistance of the image, the above content of the crosslinking agent is more preferably 2.0% by mass or more, and more preferably 5.0% by mass or more. On the other hand, from the viewpoint of easily suppressing image feathering and improving the compatibility of the components in the reaction solution, the above content of the crosslinking agent is more preferably 20.0% by mass or less, and more preferably 15.0% by mass or less.

[0041] (Ionic surfactant) The reaction solution contains an ionic surfactant. Examples of ionic surfactants include cationic surfactants, anionic surfactants, and amphoteric surfactants. One of these ionic surfactants may be used alone, or two or more may be used in combination. It is preferable to use a compound that has a hydrophilic part containing a cationic group, an anionic group, or both, and a hydrophobic part that is an aliphatic hydrocarbon group. In particular, it is more preferable that the ionic surfactant has at least one cationic hydrophilic part (a hydrophilic part containing a cationic group).

[0042] The anionic group that the ionic surfactant may contain is preferably at least one selected from the group consisting of carboxylic acid groups, carboxylic acid ester groups, sulfonic acid groups, sulfate ester groups, phosphoric acid groups, phosphoric acid ester groups, phosphonic acid groups, and phosphonic acid ester groups. These anionic groups may form salts with alkali metal ions, ammonium ions, or organic ammonium ions. The hydrophilic portion may be alkylene groups, amide groups, sulfonyl groups, imino groups, carbonyl groups, ester groups, ether groups, alkylene oxide groups, and combinations thereof, which have these anionic groups.

[0043] Cationic groups that ionic surfactants may contain include amino groups and pyridine groups.

[0044] Examples of aliphatic hydrocarbon groups constituting the hydrophobic portion include linear, branched, and cyclic aliphatic hydrocarbon groups. However, aliphatic hydrocarbon groups do not have aromatic rings. Specific examples of aliphatic hydrocarbon groups include alkyl groups, alkenyl groups, alkynyl groups, cycloalkyl groups, and cycloalkenyl groups.

[0045] Specific examples of anionic surfactants include alkyl sulfonic acid, polyoxyethylene alkyl ether sulfate, polyoxyethylene lauryl ether sulfate, alkyl sulfate ester, alkyl taurine, alkyl sulfoacetic acid, carboxylated polyoxyethylene alkyl ether, alkyl phosphoric acid, polyoxyethylene alkyl ether phosphoric acid, alkyl phosphate ester, aliphatic carboxylic acid, polyoxyethylene alkyl ether carboxylic acid, N-acyl sarcosine, and N-acyl glutamic acid. One of these anionic surfactants may be used alone, or two or more may be used in combination.

[0046] Specific examples of cationic surfactants include stearamidopropyldimethylamine, steartrimonium chloride, stearoxypropyltrimonium chloride, distearyldimonium chloride, dicocoylethylhydroxyethylmonium methosulfate, and benzalkonium chloride. One of these cationic surfactants may be used alone, or two or more may be used in combination.

[0047] Specific examples of amphoteric surfactants include amino acid-type amphoteric surfactants, betaine-type amphoteric surfactants, sulfate ester-type amphoteric surfactants, sulfonate-type amphoteric surfactants, and phosphate ester-type amphoteric surfactants. One of these amphoteric surfactants may be used alone, or two or more may be used in combination.

[0048] From the viewpoint of antibacterial and antifungal properties in the reaction solution, it is preferable that the ionic surfactant also contains a cationic surfactant. Furthermore, the inclusion of a cationic surfactant in the ionic surfactant of the reaction solution tends to further improve the water resistance of the image and the compatibility of the components in the reaction solution.

[0049] The content (by mass) of the ionic surfactant in the reaction solution is preferably 0.1% by mass or more and 4.0% by mass or less, and more preferably 0.2% by mass or more and 3.0% by mass or less, based on the total mass of the reaction solution. From the viewpoint of further improving the water resistance of the image and suppressing feathering of the image, the above content of the ionic surfactant is even more preferably 0.3% by mass or more and 1.5% by mass or less.

[0050] The reaction solution may, in addition to the ionic surfactant, optionally further contain a nonionic surfactant. When the reaction solution contains a nonionic surfactant, the content (mass%) of the nonionic surfactant in the reaction solution is preferably 0.1% by mass or more and 2.0% by mass or less, based on the total mass of the reaction solution.

[0051] Furthermore, when the reaction solution is based on the total mass of the reaction solution, and the content of the reactant (mass%) in the reaction solution is A, the content of the crosslinking agent (mass%) is B, and the content of the ionic surfactant (mass%) is C, it is preferable that (A+B) / C is between 5.0 and 50.0. When (A+B) / C is 5.0 or higher, the water resistance of the image is more easily improved and feathering of the image is more easily suppressed. From these viewpoints, it is more preferable that (A+B) / C be 5.5 or higher, and even more preferable that it be 6.0 or higher. On the other hand, when (A+B) / C is 50.0 or lower, the compatibility of the components in the reaction solution is more easily improved and feathering of the image is more easily suppressed. From these viewpoints, it is more preferable that (A+B) / C be 40.0 or lower, and even more preferable that it be 30.0 or lower.

[0052] (aqueous medium) The reaction solution is an aqueous reaction solution containing at least water as an aqueous medium. Examples of aqueous mediums used in the reaction solution include those similar to those that can be contained in ink, as described later. The water content (mass%) in the reaction solution is preferably 50.0% by mass or more and 95.0% by mass or less, based on the total mass of the reaction solution. The water content (mass%) in the reaction solution is preferably 1.0% by mass or more and 45.0% by mass or less, based on the total mass of the reaction solution. Furthermore, from the viewpoint of further improving the scratch resistance and water scratch resistance of the image, it is preferable that the reaction solution contains a water-soluble organic solvent with a boiling point of 250°C or less.

[0053] Examples of water-soluble organic solvents with a boiling point of 250°C or lower include ethylene glycol (boiling point 197°C), 1,2-propanediol (boiling point 188°C), 1,3-propanediol (boiling point 210°C), 1,2-butanediol (boiling point 193°C), 1,3-butanediol (boiling point 208°C), 1,4-butanediol (boiling point 230°C), 1,3-butanediol (boiling point 182°C), 1,2-pentanediol (boiling point 206°C), 1,2-hexanediol (boiling point 223°C), and 2-methyl-1,3-propanediol. Examples include ol (boiling point 214°C), diethylene glycol monomethyl ether (boiling point 194°C), diethylene glycol monoethyl ether (boiling point 202°C), diethylene glycol monoisopropyl ether (boiling point 207°C), diethylene glycol monoisobutyl ether (boiling point 229°C), diethylene glycol monobutyl ether (boiling point 230°C), 1,5-pentanediol (boiling point 242°C), diethylene glycol (boiling point 245°C), and 2-pyrrolidone (boiling point 245°C). One or more of these can be used.

[0054] (Other ingredients) The reaction solution may contain various other components as needed. These other components are similar to those that can be included in the ink, as described later.

[0055] (Physical properties of the reaction solution) The reaction solution is preferably an aqueous reaction solution suitable for use in an inkjet system. Therefore, from the viewpoint of reliability, it is preferable to appropriately control its physical properties. Specifically, the surface tension of the reaction solution at 25°C is preferably 20 mN / m or more and 60 mN / m or less. The viscosity of the reaction solution at 25°C is preferably 1.0 mPa·s or more and 10.0 mPa·s or less. The pH of the reaction solution at 25°C is preferably 5.0 or more and 9.5 or less, and more preferably 6.0 or more and 9.0 or less.

[0056] <ink> The ink is a water-based inkjet ink containing resin. The following provides a detailed explanation of the various components used in the ink.

[0057] (Colorants) The ink preferably contains a colorant. Pigments and dyes can be used as the colorant. The colorant content (by mass) in the ink is preferably 0.5% 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.

[0058] Specific examples of pigments include inorganic pigments such as carbon black and titanium dioxide; and organic pigments such as azo, phthalocyanine, quinacridone, isoindolinone, imidazolon, diketopyrrolopyrrole, and dioxazine. Pigments may be used individually or in combination of two or more.

[0059] As for the dispersion method of the pigment, resin-dispersed pigments using a resin as a dispersant, and self-dispersing pigments in which hydrophilic groups are bonded to the surface of the pigment particles can be used. In addition, resin-bonded pigments in which a resin containing organic groups is chemically bonded to the surface of the pigment particles, and microcapsule pigments in which the surface of the pigment particles is coated with a resin or the like can be used. It is also possible to use a combination of pigments with different dispersion methods from among these. In particular, it is preferable to use resin-dispersed pigments in which the resin as a dispersant is physically adsorbed to the surface of the pigment particles, rather than resin-bonded pigments or microcapsule pigments.

[0060] For the resin dispersant used to disperse the pigment in an aqueous medium, it is preferable to use one that can disperse the pigment in the aqueous medium through the action of anionic groups. As the resin dispersant, a resin having anionic groups can be used, and it is preferable to use a resin such as those described later, and among them, a water-soluble resin. The pigment content (mass%) in the ink is preferably 0.3 times or more and 10.0 times or less in mass ratio to the resin dispersant content (mass%).

[0061] As self-dispersing pigments, those in which anionic groups are bonded directly to the surface of the pigment particles or via other atomic groups (-R-) can be used. Specific examples of other atomic groups (-R-) include linear or branched alkylene groups having 1 to 12 carbon atoms; arylene groups such as phenylene and naphthylene groups; carbonyl groups; imino groups; amide groups; sulfonyl groups; ester groups; and ether groups. Alternatively, combinations of these groups may also be used.

[0062] It is preferable to use dyes that have anionic groups. Specific examples of dyes include azo, triphenylmethane, (aza)phthalocyanine, xanthene, and anthrapyridone. Dyes may be used individually or in combination of two or more.

[0063] Examples of the anionic groups described in the descriptions of resin dispersants, self-dispersing pigments, and dyes include carboxylic acid groups, sulfonic acid groups, and phosphonic acid groups. The anionic group may be either an acid type or a salt type, and if it is a salt type, it may be in a partially dissociated state or a fully dissociated state. When the anionic group is a salt type, examples of cations that become counterions include alkali metal cations, ammonium, and organic ammonium. The colorant to be contained in the ink is preferably a pigment, and more preferably a resin-dispersed pigment.

[0064] (resin) The ink contains resin. The resin content (by mass) in the ink is preferably 0.1% by mass or more and 20.0% by mass or less, and more preferably 0.5% by mass or more and 15.0% by mass or less, based on the total mass of the ink.

[0065] Resins can be added to ink (i) to stabilize the dispersion state of pigments, i.e., as a resin dispersant or its auxiliary agent. They can also be added to ink (ii) to improve various properties of the recorded image. Examples of resin forms include block copolymers, random copolymers, graft copolymers, and combinations thereof. The resin may be a water-soluble resin that can dissolve in an aqueous medium, or it may be resin particles dispersed in an aqueous medium. The ink may contain one or more types of resins, and may contain both water-soluble resins and resin particles. From the viewpoint of further improving the scratch resistance and water resistance of the image, and from the viewpoint of the storage properties of the ink, it is preferable that the resin in the ink contains resin particles.

[0066] [Composition of the resin] Examples of resins include acrylic resins, urethane resins, and olefin resins. Among these, acrylic resins and urethane resins are preferred, and acrylic resins composed of units derived from (meth)acrylic acid and (meth)acrylate are even more preferred.

[0067] As for acrylic resins, those having hydrophilic units and hydrophobic units as constituent units are preferred. Among these, resins having hydrophilic units derived from (meth)acrylic acid and hydrophobic units derived from at least one of a monomer having an aromatic ring and a (meth)acrylic acid ester monomer are preferred. In particular, resins having hydrophilic units derived from (meth)acrylic acid and hydrophobic units derived from at least one of a monomer of styrene and α-methylstyrene are preferred. Because these resins readily interact with pigments, they can be suitably used as resin dispersants for dispersing pigments.

[0068] Hydrophilic units are units that have hydrophilic groups, such as anionic groups. Hydrophilic units can be formed, for example, by polymerizing hydrophilic monomers that have hydrophilic groups. Specific examples of hydrophilic monomers that have hydrophilic groups include acidic monomers having carboxylic acid groups, such as (meth)acrylic acid, itaconic acid, maleic acid, and fumaric acid, and anionic monomers such as anhydrides and salts of these acidic monomers. Cations that constitute salts of acidic monomers include ions such as lithium, sodium, potassium, ammonium, and organic ammonium. Hydrophobic units are units that do not have hydrophilic groups, such as anionic groups. Hydrophobic units can be formed, for example, by polymerizing hydrophobic monomers that do not have hydrophilic groups, such as anionic groups. Specific examples of hydrophobic monomers include monomers having aromatic rings, such as styrene, α-methylstyrene, and benzyl (meth)acrylate; and (meth)acrylic acid ester monomers, such as methyl (meth)acrylate, butyl (meth)acrylate, and 2-ethylhexyl (meth)acrylate.

[0069] Urethane resins can be obtained, for example, by reacting polyisocyanate with a polyol. Alternatively, they may be obtained by further reacting with a chain extender. Examples of olefin resins include polyethylene and polypropylene.

[0070] Furthermore, the resin in the ink must have functional groups (hereinafter sometimes referred to as "reactive groups") that can react with the functional groups (crosslinkable groups) of the crosslinking agent. Examples of functional groups (reactive groups) that the resin may have include hydroxyl groups, carboxyl groups, thiol groups, and amino groups. It is preferable that the resin has one or more of these functional groups.

[0071] [Properties of the resin] In this specification, "water-soluble resin" means that when the resin is neutralized with an equivalent amount of alkali to its acid value, it exists in an aqueous medium without forming particles whose particle size can be measured by dynamic light scattering. Whether or not a resin is water-soluble can be determined according to the following method. First, prepare a liquid containing the resin (resin solids content: 10% by mass) neutralized with an alkali equivalent to its acid value (sodium hydroxide, potassium hydroxide, etc.). Next, prepare a sample solution by diluting the prepared liquid 10 times (by volume) with pure water. Then, when the particle size of the resin in the sample solution is measured by dynamic light scattering, if no particles with a particle size are measured, the resin can be determined to be water-soluble. The measurement conditions in this case can be, for example, SetZero: 30 seconds, Number of measurements: 3, Measurement time: 180 seconds. In addition, a particle size analyzer using dynamic light scattering (for example, product name "UPA-EX150", manufactured by Nikkiso) can be used as the particle size distribution analyzer. Of course, the particle size distribution measuring devices and measurement conditions used are not limited to those mentioned above.

[0072] The acid value of the water-soluble resin is preferably 100 mg KOH / g or more and 250 mg KOH / g or less. In this specification, the acid value of the resin may be measured by a potentiometric titrator using a potassium hydroxide-ethanol titration solution. The weight-average molecular weight of the water-soluble resin is preferably 3,000 or more and 15,000 or less. In this specification, the weight-average molecular weight of the resin may be measured as a value equivalent to standard polystyrene, measured by gel permeation chromatography (GPC).

[0073] The acid value of the resin constituting the resin particles is preferably 5 mg KOH / g or more and 100 mg KOH / g or less. The weight-average molecular weight of the resin constituting the resin particles is preferably 1,000 or more and 2,000,000 or less. The volume-based cumulative 50% particle diameter (D) of the resin particles measured by dynamic light scattering is... 50The particle diameter is preferably between 50 nm and 500 nm. The volume-based cumulative 50% particle diameter of the resin particles is the diameter of the particle at which the volume of the particles accumulates to 50% of the total volume of the measured particles in the particle diameter integration curve, starting from the smallest particle diameter. The volume-based cumulative 50% particle diameter of the resin particles can be measured using the dynamic light scattering particle size analyzer and measurement conditions described above. The resin particles do not need to contain colorants.

[0074] (aqueous medium) The ink is an aqueous ink containing at least water as an aqueous medium. The ink may contain an aqueous medium which is water or a mixed solvent of water and a water-soluble organic solvent. Deionized water or ion-exchanged water is preferably used as the water. The water content (mass%) in the aqueous ink is preferably 50.0% by mass or more and 95.0% by mass or less based on the total mass of the ink. The water-soluble organic solvent content (mass%) in the aqueous ink is preferably 2.0% by mass or more and 40.0% by mass or less based on the total mass of the ink. As the water-soluble organic solvent, any of those usable for inkjet inks, such as alcohols, (poly)alkylene glycols, glycol ethers, nitrogen-containing solvents, and sulfur-containing solvents, can be used. One type of water-soluble organic solvent may be used alone, or two or more types may be used in combination.

[0075] (Other ingredients) The ink may contain various other components as needed. Examples of other components include various additives such as defoamers, surfactants, pH adjusters, viscosity modifiers, rust inhibitors, preservatives, fungicides, antioxidants, and reduction inhibitors. However, it is preferable that the ink does not contain the reactants included in the reaction solution. Furthermore, it is preferable that the ink does not contain the crosslinking agents included in the reaction solution.

[0076] (Physical properties of ink) The ink is an aqueous ink for use in inkjet systems. Therefore, from the viewpoint of reliability, it is preferable to appropriately control its physical properties. Specifically, the surface tension of the ink at 25°C is preferably 20 mN / m or more and 60 mN / m or less. The viscosity of the ink at 25°C is preferably 1.0 mPa·s or more and 10.0 mPa·s or less. The pH of the ink at 25°C is preferably 7.0 or more and 9.5 or less, and more preferably 8.0 or more and 9.5 or less.

[0077] <Inkjet recording method and inkjet recording device> The present invention relates to an inkjet recording method (hereinafter also simply referred to as the "recording method") which is a method of recording an image on a recording medium using an aqueous reaction solution containing an aqueous ink and a reactant that reacts with the aqueous ink. This recording method includes a reaction solution application step of applying the reaction solution to the recording medium and an ink application step of applying aqueous ink to the recording medium by ejecting it from an inkjet ejection head so as to overlap with at least a portion of the area on the recording medium to which the reaction solution is applied.

[0078] Furthermore, the inkjet recording apparatus of the present invention (hereinafter also simply referred to as "recording apparatus") is an apparatus used in an inkjet recording method that records an image on a recording medium using an aqueous reaction solution containing aqueous ink and a reactant that reacts with the aqueous ink. This recording apparatus comprises a reaction solution application means for applying the reaction solution to the recording medium, and an ink application means for applying aqueous ink to the recording medium by ejecting it from an inkjet ejection head so as to overlap with at least a portion of the area on the recording medium to which the reaction solution is applied. This recording apparatus is preferably used in the inkjet recording method of the present invention.

[0079] The aqueous ink used in the recording method and recording device described above contains a resin. The reaction solution used in the recording method and recording device contains at least one reactant selected from the group consisting of polyvalent metal salts and cationic resins, an ionic surfactant, and a crosslinking agent that can form a bond with the resin in the aqueous ink. The ink and reaction solution described above are preferred as the ink and reaction solution used in this recording method and recording device, and it is preferable to use the ink set described above that contains them.

[0080] (Inkjet recording device) The details of the inkjet recording device will be described below with reference to the drawings. Figure 1 is a schematic diagram showing an example of the general configuration of an inkjet recording device. The inkjet recording device of this embodiment is an inkjet recording device that records an image on a recording medium using a reaction liquid containing a reactant that reacts with ink, and ink. The X, Y, and Z directions represent the width (overall length), depth, and height directions of the inkjet recording device, respectively. The recording medium is transported in the X direction.

[0081] The inkjet recording apparatus 100 of the embodiment shown in Figure 1 is configured to include a recording unit 1000, a heating unit 2000, a fixing unit 3000, a cooling unit 4000, a reversing unit 5000, and a paper discharge unit 6000. In the recording unit 1000, various liquids are applied to the recording medium 1100, which has been transported from the paper feed device 1400 by the transport member 1300, by the liquid application device 1200. In the heating unit 2000, the liquid applied to the recording medium 1100 is heated by the heating device 2100 to evaporate volatile components such as water in the liquid and dry it. In the fixing unit 3000, the fixing member 3100 is brought into contact with the area of ​​the recording medium 1100 to which the liquid has been applied and heated to promote the fixing of the image to the recording medium 1100. After that, the recording medium 1100 is cooled by the cooling member 4100 of the cooling unit 4000. When recording an image on the reverse side following the front side (recording side), the recording medium 1100 is first inverted by the inversion device 5100 of the inversion unit 5000. Then, after the image is recorded on the reverse side in the same manner as on the front side, it is transported by the transport member 6100 of the paper discharge unit 6000 and loaded into the recording medium storage unit 6200. Here, a configuration having a heating unit 2000, a fixing unit 3000, a cooling unit 4000, and an inversion unit 5000 is used as an example for explanation, but depending on the recording conditions (type of ink and recording medium, recording speed, etc.), the heating unit, fixing unit, cooling unit, and inversion unit may be omitted.

[0082] Any recording medium 1100 can be used. For example, recording media with ink absorption (permeability), such as plain paper or uncoated paper without a coating layer, or glossy paper or art paper with a coating layer, can be used. Alternatively, recording media without permeability, such as films or sheets made of resin materials like polyvinyl chloride (PVC) or polyethylene terephthalate (PET), can be used.

[0083] [Records Department] The recording unit 1000 has a liquid application device 1200. The liquid application device 1200 is configured with a reaction liquid application device 1201 and an ink application device 1202. The reaction liquid application device 1201 shown in Figure 1 is an example of a unit using an inkjet ejection head. In addition, the reaction liquid application device may be configured using a gravure coater, offset coater, die coater, blade coater, etc. The application of the reaction liquid by the reaction liquid application device 1201 may be before or after ink application, as long as it can come into contact with the ink on the recording medium 1100. However, in order to record high-quality images on various recording media with different liquid absorption characteristics, it is preferable to apply the reaction liquid before ink application. An inkjet ejection head (recording head) is used as the ink application device 1202. Examples of ejection methods for the ejection head as the liquid application device 1200 include a method in which a film boiling is generated in the liquid using an electro-thermal converter to form bubbles and eject the liquid, and a method in which a liquid is ejected using an electro-mechanical converter.

[0084] The liquid dispensing device 1200 is a line head extending in the Y direction, with discharge ports arranged to cover the image recording area of ​​the maximum usable width of the recording medium. The discharge head has a discharge port surface (not shown) with discharge ports formed below it (towards the recording medium 1100), and the discharge port surface faces the recording medium 1100 at a very small distance of a few millimeters.

[0085] Multiple ink dispensers 1202 may be provided to dispense each color of ink onto the recording medium 1100. For example, when recording color images using yellow ink, magenta ink, cyan ink, and black ink, four ink dispensers 1202, each dispensing one of the four types of ink, are arranged in a line in the X direction. Hereinafter, the ink and reaction solution may be collectively referred to as "liquid".

[0086] Figure 2 is a perspective view showing an example of a liquid dispensing device. The liquid dispensing device 1200 shown in Figure 2 is an example of a line head. The liquid dispensing device 1200 as a line head has multiple discharge element substrates 1203, each having a row of discharge ports, arranged in a straight line. Multiple rows of discharge ports are arranged on the discharge element substrate 1203.

[0087] [Conveyor System] As shown in Figure 1, the recording unit 1000 is configured to include a liquid application device 1200 and a transport member 1300 for transporting the recording medium 1100. The liquid application device 1200 applies reaction liquid and ink to desired positions on the recording medium 1100 transported by the transport member 1300. Each liquid application device receives an image signal of the recorded data and applies the necessary reaction liquid and ink to each position. Figure 1 shows the transport member 1300 in the form of a transport belt, but spurs, transport cylinders, etc., may be used as long as they have the function of transporting the recording medium 1100. To improve transport accuracy, the transport member 1300 can be made of a material that can fix the recording medium 1100 in place. Specifically, methods include providing holes in the transport member 1300 and fixing the recording medium 1100 by suction from the back side, or forming the transport member 1300 from an appropriate material and fixing the recording medium 1100 by electrostatic attraction.

[0088] [Heating section] As shown in Figure 1, the heating unit 2000 is configured to include a heating device 2100 and a transport member 2200. The recording medium 1100, to which the reaction liquid and ink have been applied and an image has been recorded, is transported by the transport member 2200 and heated by the heating device 2100 to evaporate the liquid component of the image and dry it. Preferably, between the ink application step and the fixing step, there is further a drying step in which the ink-applied recording medium is heated non-contact to dry the ink. Having such a drying step makes it possible to effectively suppress deformation (cockling and curling) of the recording medium 1100.

[0089] The heating device 2100 can have any configuration as long as it can heat the recording medium 1100, and various conventionally known devices such as hot air dryers and heaters can be used. Among these, the use of non-contact heaters such as electric heating wires and infrared heaters is preferable from the standpoint of safety and energy efficiency. Furthermore, by incorporating a fan to spray the heated gas onto the recording medium 1100 and using a mechanism to send hot air, drying efficiency can be easily improved.

[0090] Regarding the heating method, the recording medium 1100 may be heated from the side to which the reaction liquid and ink are applied (the recording surface (front)), from the back side, or from both sides. The transport member 2200 may also be provided with a heating function. Figure 1 shows a transport member 2200 using a transport belt, but spurs, transport cylinders, etc., may be used as long as they have the function of transporting the recording medium 1100. From the viewpoint of suppressing deformation of the recording medium 1100 due to heating, it is preferable to have a configuration in which the recording medium 1100 is transported while being in close contact with the transport member 2200 by blowing air from the heating unit 2000, or to provide a mechanism for fixing the recording medium to the transport member 2200. Specifically, examples include a method of providing holes in the transport member 2200 and fixing the recording medium 1100 by suction from the back side, or a method of forming the transport member 2200 with an appropriate material and fixing the recording medium 1100 by electrostatic attraction.

[0091] The heating temperature should be set so as not to over-dry the recording medium 1100, while rapidly evaporating the liquid components and suppressing deformation of the recording medium 1100. The temperature of the drying means can be set so that the recording medium reaches the desired temperature, taking into account the transport speed and ambient temperature. Specifically, the temperature of the drying means (such as hot air) is preferably 40°C to 100°C, and more preferably 60°C to 80°C. When heating the recording medium 1100 by blowing heated gas, the wind speed is preferably 1 m / s to 100 m / s. The temperature of the wind, such as hot air, can be measured using a K-type thermocouple thermometer. A specific measuring instrument could be, for example, the product name "AD-5605H" (manufactured by A&D).

[0092] [Fixing section] As shown in Figure 1, the fixing unit 3000 is a contact-type heating and pressurizing mechanism having a fixing member 3100 as a fixing belt such as an endless belt and a transport member 3200. In the fixing unit 3000, the transport member 3200 transports the recording medium 1100, and the fixing member 3100 is brought into contact with the recording medium 1100 under pressure, heating the liquid such as reaction solution or ink applied to the recording medium 1100. This allows the image to be fixed to the recording medium 1100. After the image is recorded on the recording medium 1100, the liquid components of the reaction solution or ink penetrate the recording medium 1100 or evaporate after passing through the heating unit 2000, and then are fixed in the fixing unit 3000 to complete the image. By heating and pressurizing the recording medium 1100 while it is sandwiched between the fixing member 3100 and the transport member 3200, the image on the recording medium 1100 and the fixing member 3100 come into close contact, and the image is fixed to the recording medium 1100. By using a liquid such as ink containing resin particles and colorants, the resin particles soften and form a film mainly by heating in the fixing unit 3000, and the colorants can be bonded onto the recording medium 1100.

[0093] One method for heating the fixing member 3100 is to install a heat source, such as a halogen heater, inside the roller that drives the fixing member 3100 as a fixing belt. Another method is to install a heat source, such as an infrared heater, in a location separate from the fixing member 3100. Furthermore, these methods may be combined. The transport member 3200 may also be heated as needed. The temperature of the fixing member 3100 can be set so that the surface of the recording medium reaches a desired temperature, taking into account the transport speed and ambient temperature. Specifically, it is preferable to set the temperature of the fixing member 3100 to 50°C or more and 120°C or less, and more preferably to 60°C or more and 110°C or less. The temperature of the contact-type heating and pressing mechanism (fixing member 3100) and the surface temperature of the recording medium immediately after passing through the contact-type heating and pressing mechanism can both be measured using a radiation thermometer. The radiation thermometer should be installed near the end (terminal) of the contact-type heating and pressing mechanism. A specific example of a radiation thermometer is the product name "Radiation Thermometer IT-545S" (manufactured by Horiba, Ltd.).

[0094] [Cooling section] The cooling unit 4000 is comprised of a cooling element 4100 and a transport element 4200 (Figure 1). The cooling unit 4000 cools the recording medium 1100, which has become hot after passing through the heating unit 2000 and the fixing unit 3000. The cooling element 4100 can have any configuration as long as it can cool the recording medium 1100, and methods such as air cooling and water cooling can be used. Among these, blowing an unheated gas is preferable from the standpoint of safety and energy efficiency. Furthermore, using a mechanism that incorporates a fan to blow gas onto the recording medium 1100 makes it easier to improve cooling efficiency. The temperature of the cooling means can be set so that the image on the recording medium reaches the desired temperature, taking into account the transport speed and ambient temperature. Specifically, it is preferable to set the temperature of the cooling means (such as blowing air) to 20°C or more and 60°C or less, and more preferably to 25°C or more and 50°C or less. When cooling by blowing gas, it is preferable to set the wind speed to 1 m / s or more and 100 m / s or less. By implementing these conditions, deformation of the recording media 1100 and image sticking (blocking) of the data loaded in the paper output section 6000, which will be described later, can be suppressed.

[0095] [Reversal section] When performing double-sided recording, the recording medium 1100 is inverted using the inversion unit 5000 (Figure 1). The recording medium 1100, with the image recorded on its recording surface (front), passes through the cooling unit 4000, then branches off and is transported, and inverted by the inversion device 5100. The inverted recording medium 1100 is then transported to the paper feed device 1400 of the recording unit 1000 with liquid applied to its back surface (the side opposite to the recording surface (front)).

[0096] [Paper output section] After image recording, the recording medium 1100 is placed in the paper discharge unit 6000 (Figure 1). After single-sided or double-sided recording is performed, the recording medium 1100 passes through the cooling unit 4000, is transported by the transport member 6100, and is finally placed in the recording medium storage unit 6200 in a stacked state. Two or more recording medium storage units 6200 may be provided to accommodate different recording materials, for example.

[0097] (Reaction solution application process) The reaction solution application step is a step of applying a reaction solution containing a reactant that reacts with the ink to the recording medium. As mentioned above, various coating devices such as coaters can be used as means of applying the reaction solution to the recording medium, but preferably, the reaction solution is applied to the recording medium by ejecting it from an inkjet type ejection head (recording head). By using an inkjet type ejection head to apply the reaction solution to the recording medium, the amount of reaction solution ejected can be finely adjusted. When applying the reaction solution using an ejection head, it is possible to control the application so that the reaction solution is not applied to the blank areas of the recording medium where ink is not applied, and the reactant is less likely to remain on the surface of the blank areas. Therefore, if the reactant remains on the surface of the blank areas, it is possible to suppress the damage of the image layer by the residual reactant, thereby further improving the scratch resistance of the image.

[0098] (Ink application process) The ink application process involves applying aqueous ink to the recording medium by ejecting it from an inkjet-type ejection head so that it overlaps with at least a portion of the area on the recording medium to which the reaction solution is applied. This process makes it possible to react functional groups such as carboxyl groups in the resin in the ink with functional groups such as carbodiimide groups or oxazoline groups in the crosslinking agent in the reaction solution. As a result, a crosslinked structure can be formed in the image layer formed by the ink and the reaction solution, improving the robustness of the recorded image, such as scratch resistance and water resistance. As mentioned above, an inkjet-type ejection head (recording head) is used as the ink application means for applying ink to the recording medium. Also, as mentioned above, it is preferable to apply ink to the recording medium after applying the reaction solution to the recording medium.

[0099] (drying process) The recording method described above preferably includes a drying step in which the recording medium to which the reaction solution and ink have been applied is dried by heating. By performing the drying step after the step of applying the reaction solution and ink to the recording medium, the aqueous medium of the image layer is evaporated and the residual components in the image layer are minimized, thereby further improving scratch resistance. In addition, by forming a film of resin particles through heating, the strength of the image layer is improved, further improving scratch resistance.

[0100] (Composition of image layers) The solid components remaining in the image layer obtained by applying the reaction solution and ink to the recording medium 1100 using the recording unit 1200 of the aforementioned inkjet recording device 100, and drying it with the heating unit 2000 as needed, include polyvalent metal salts, crosslinking agents, colorants, and resins. Among these, the resin amount and crosslinking agent amount are factors that greatly affect the robustness of the image, such as scratch resistance and water resistance. In the image layer, the amount of functional groups (crosslinkable groups, μmol / m²) of the crosslinking agent per unit area of ​​the recording medium is important. 2 ) is E, and the amount of functional groups (reactive groups, μmol / m³) that the resin has 2 If D is denoted by the following relationship, it is preferable that the following relationship is satisfied: That is, from the viewpoint of further improving the scratch resistance and water resistance of the image, it is preferable that the D / E ratio in the image layer formed by the reaction solution and aqueous ink applied to the recording medium is 0.5 or more and 6.0 or less.

[0101] The amount of crosslinkable groups E (μmol / m²) of the crosslinking agent in the reaction solution per unit area of ​​the recording medium. 2 ), and the amount of reactive groups D (μmol / m³) in the resin in the ink 2 The following can be calculated: First, based on the value (%) of the recording duty cycle and its definition, the amount of reaction solution and ink applied per unit area of ​​the recording medium (g / m²) 2 Next, the amount of crosslinking agent and resin particles per unit area of ​​the recording medium (g / m²) is calculated based on the crosslinking agent content (mass%) in the reaction solution and the resin (resin particles) content (mass%) in the ink. 2) is calculated. Then, the amount of crosslinking agent to be applied (g / m) is calculated. 2 Based on the crosslinking group equivalents of the crosslinking agent (e.g., carbodiimide group equivalents, epoxy group equivalents, or oxazoline group equivalents), the amount of crosslinking groups E (μmol / m²) per unit area of ​​the recording medium is determined. 2 ) is calculated. Also, the amount of resin particles to be applied (g / m³) is calculated. 2 Based on the amount of reactive groups in the resin particles (carboxyl group equivalent (μmol / g), etc.), the amount of reactive groups D (μmol / m²) per unit area of ​​the recording medium is determined. 2 ) is calculated. In the embodiment described below, the value of D / E was calculated using D and E calculated as described above. [Examples]

[0102] The present invention will be described in more detail below with reference to examples and comparative examples, but the present invention is not limited in any way by the following examples unless it exceeds the gist of the invention. Unless otherwise specified, amounts of components indicated in "parts" and "%" are based on mass.

[0103] <Preparation of reaction solution> Each reaction solution was prepared by mixing the components (in %) shown in the upper section of Table 1 (Tables 1-1 to 1-3), stirring thoroughly, and then pressure filtering through a 3.0 μm pore size cellulose acetate filter (manufactured by Advantec). The lower section of Table 1 shows the characteristics of the reaction solutions, including the content of the reactant A (%), the crosslinking agent B (%), the ionic surfactant C (%), and the (A+B) / C value. The amount of polyvalent metal salt hydrate shown in the upper section of Table 1 is the amount in terms of polyvalent metal salt equivalent. The amounts of cationic resin and crosslinking agent are the amounts in terms of solid content, which are the active ingredients. Furthermore, the amount of ion-exchanged water includes the amount of water contained in the polyvalent metal salt hydrate, as well as the amount of water contained in the cationic resin product and the crosslinking agent product.

[0104] The details of the materials used in preparing the reaction solution, as shown in Table 1, are as follows: (Reactive agent) Magnesium sulfate heptahydrate (solubility in water at 25°C: 25g / 100g) Calcium chloride dihydrate (solubility in water at 25°C: 74.5g / 100g) Calcium nitrate tetrahydrate (solubility in water at 25°C: 121.2g / 100g) Calcium sulfate dihydrate (solubility in water at 25°C: 0.21g / 100g) • PAS-H-5L: Product name of cationic resin manufactured by Nitto Boseki Medical (solids content 28%)

[0105] (Surfactants) • Acetylenel E100: A nonionic surfactant manufactured by Kawaken Fine Chemicals (acetylene glycol ethylene oxide adduct). • Nissan Cation EQ-01D: Product name of a cationic surfactant manufactured by NOF Corporation (Dicocoylethyl Hydroxyethylmonium Methosulfate) • 2-Ethylhexyl sulfate sodium: Anionic surfactant • Anchitol 20HD: A brand name for an amphoteric surfactant manufactured by Kao Corporation (lauryl hydroxysulfobetaine).

[0106] (Crosslinking agent) • CarbodiLite SV-02: A trade name for a carbodiimide-based crosslinking agent for water-based resins manufactured by Nisshinbo Chemical, containing two or more carbodiimide groups (Solid content: 40%, Crosslinkable group (carbodiimide group) equivalent: 430). • Denacol EX-313: Trade name of an epoxy crosslinking agent manufactured by Nagase ChemteX, containing two or more epoxy groups (Solid content: 100%, Crosslinkable group (epoxy group) equivalent: 141) • Epocross WS-300: A trade name for a water-soluble polymer containing two or more oxazoline groups, manufactured by Nippon Shokubai (Solid content: 10%, Crosslinkable group (oxazoline group) equivalent: 130). • Elastron BN-69: Trade name of a water-based polyisocyanate crosslinking agent manufactured by Daiichi Kogyo Seiyaku, containing two or more isocyanate groups (Solid content: 40%, Crosslinking group (isocyanate group) equivalent: Unknown) • CarbodiLite V-02: A trade name for a carbodiimide-based crosslinking agent for aqueous resins manufactured by Nisshinbo Chemical, containing two or more carbodiimide groups (Solid content: 40%, Crosslinkable group (carbodiimide group) equivalent: 590). (The above crosslinking group equivalents refer to the chemical formula weight per mole of crosslinking group.)

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[0110] <Preparation of Pigment Dispersion> (Pigment dispersion 1) A styrene-ethyl acrylate-acrylic acid copolymer (resin 1 having a carboxyl group) with an acid value of 150 mg KOH / g and a weight-average molecular weight of 8,000 was prepared. 20.0 parts of resin 1 were neutralized with potassium hydroxide equimolar to its acid value, and then an appropriate amount of pure water was added to prepare an aqueous solution of resin 1 with a resin (solids) content of 20.0%. 10.0 parts of pigment (carbon black), 15.0 parts of the aqueous solution of resin 1, and 75.0 parts of pure water were mixed to obtain a mixture. The obtained mixture and 200 parts of 0.3 mm diameter zirconia beads were placed in a batch-type vertical sand mill (manufactured by AIMEX) and dispersed for 5 hours while cooling with water. After removing coarse particles by centrifugation, the mixture was pressure filtered through a cellulose acetate filter (manufactured by Advantec) with a pore size of 3.0 μm to prepare pigment dispersion 1 with a pigment content of 10.0% and a resin dispersant (resin 1) content of 3.0%.

[0111] (Pigment dispersion 2) Pigment dispersion 2 was prepared using the same procedure as described above for pigment dispersion 1, except that the pigment was changed to CI Pigment Blue in a 15:3 ratio. The pigment dispersion 2 contained 10.0% pigment and 3.0% resin dispersant (resin 1).

[0112] (Pigment dispersion 3) Pigment dispersion 3 was prepared using the same procedure as described above for pigment dispersion 1, except that the pigment was changed to CI Pigment Red 122, with a pigment content of 10.0% and a resin dispersant (resin 1) content of 3.0%.

[0113] (Pigment dispersion 4) Except for changing the pigment to CI Pigment Yellow 74, pigment dispersion 4 was prepared using the same procedure as described above for pigment dispersion 1, with a pigment content of 10.0% and a resin dispersant (resin 1) content of 3.0%.

[0114] <Preparation of resin particles> (Resin particle dispersion) A solution was prepared by mixing 0.2 parts potassium persulfate and 74.0 parts deionized water. An emulsion was prepared by mixing 19.0 parts ethyl methacrylate (EMA), 5.0 parts n-butyl methacrylate (nBMA), 1.5 parts methacrylic acid (MAA), and 0.3 parts reactive surfactant as the monomer components. The reactive surfactant used was "ADEKA Soap ER20" (manufactured by ADEKA, nonionic surfactant, 20 ethylene oxide groups). The emulsion was added dropwise to the solution over 1 hour under a nitrogen atmosphere, polymerized at 80°C with stirring, and then stirred for a further 2 hours. After cooling to room temperature, deionized water and potassium hydroxide aqueous solution were added to obtain a resin particle dispersion with a carboxyl group (carboxylic acid group) content of 25.0% and a carboxyl group equivalent of 300 μmol / g.

[0115] <Ink preparation> Each ink was prepared by mixing the components (in %) shown in Table 2, stirring thoroughly, and then pressure filtering through a 3.0 μm pore size cellulose acetate filter (manufactured by Advantec). "Joncryl 819" in Table 2 is the trade name of an aqueous solution of acrylic copolymer resin, a water-soluble resin manufactured by BASF (solids (resin) content: 32.1%). "Acetylenel E100" is the trade name of a nonionic surfactant manufactured by Kawaken Fine Chemicals. The "resin particles" in Table 2 refer to resin particles obtained by drying the above resin particle dispersion.

[0116] TIFF2026070478000004.tif73170

[0117] <Rating> Sets of reaction solutions and inks were created by combining the types (numbers) of reaction solutions and inks shown on the left side of Table 3. The reaction solutions and inks constituting these sets were filled into the reaction solution dispenser 1201 and the ink dispenser 1202 of the inkjet recording device 100 having the configuration shown in Figure 1. Using the above inkjet recording device 100, a 5cm x 5cm solid image was recorded on a recording medium. In this case, for Examples 1 to 23 and Comparative Examples 1 to 3, the recording duty cycle of the reaction solution was set to 30% and the recording duty cycle of the ink to 100% to record the solid image. In Example 25, the recording duty cycle of the reaction solution was set to 30% and the recording duty cycle of the ink to 50%, in Example 26, the recording duty cycle of the reaction solution was set to 5% and the recording duty cycle of the ink to 100%, and in Example 27, the recording duty cycle of the reaction solution was set to 4% and the recording duty cycle of the ink to 100% to record the solid image. In this inkjet recording device 100, an image recorded under the condition that one 3.0 ng droplet (ink droplet or reaction droplet) is applied to a unit area of ​​1 / 1200 inch x 1 / 1200 inch is defined as having a recording duty cycle of 100%.

[0118] For recording conditions, in all examples except Example 24 and in the comparative examples, the reaction solution and ink were applied to the recording medium by ejecting them from an inkjet ejection head in the order shown, overlapping each other (indicated as "IJ ejection" in Table 3). In Example 24, the reaction solution was applied to the recording medium using a bar coater (indicated as "bar coater" in Table 3), and then the ink was applied to the recording medium by ejecting it from an inkjet ejection head. Furthermore, the amount of reaction solution and ink applied to the recording medium was set to the amount of D / E shown in Table 3. D / E is the amount of crosslinkable groups E (μmol / m²) of the crosslinking agent in the reaction solution per unit area of ​​the recording medium in the image layer formed by the reaction solution and ink applied to the recording medium. 2 The amount of reactive groups D (μmol / m³) in the resin in the ink relative to ) 2 This is the ratio of ).

[0119] In this embodiment, the evaluation criteria for each item below stipulated that "5", "4", "3", and "2" were acceptable levels, and "1" was an unacceptable level. The evaluation results are shown on the right side of Table 3.

[0120] (Abrasion resistance) After applying the reaction solution and ink to the recording medium under the recording conditions using the inkjet recording device 100 described above, the recording was dried for 6 minutes with 80°C hot air using the heating device 2100 of the inkjet recording device 100 to obtain the recorded material. At this time, fixing in the fixing unit 3000 and cooling in the cooling unit 4000 were not performed. Subsequently, the obtained recorded material was left for 24 hours under conditions of a temperature of 23°C and a relative humidity of 50%. White polyester film (product name "PET WH50", manufactured by Lintec) was used as the recording medium. The recording medium on which the image was recorded was cut into strips 25 mm wide, and evaluated using the abrasion resistance tester (manufactured by Imoto Seisakusho), a JSPS testing machine, under the following conditions. The cut recording medium was placed on the abrasion stand, and the JSPS test cloth (Kanakin No. 3, manufactured by the Japanese Standards Association) was placed on the abrasion tool, and a friction test was performed 50 times with a load of 500 g. The abrasion resistance of the image was evaluated according to the following evaluation criteria based on the degree of visual visibility of the recording medium's substrate (hereinafter referred to as the damage rate of the recording surface) and whether or not the image was transferred to the JSPS test cloth. 5: No changes were observed in either the recording surface or the test cloth. 4: The recording surface showed no change, but the test cloth had an image transfer. 3: The damage rate of the recording surface was less than approximately 10%. 2: The damage rate of the recording surface was between approximately 10% and 50%. 1: The damage rate of the recording surface was approximately 51% or higher.

[0121] (Water abrasion resistance) The friction test was conducted in the same manner as the above-described method for evaluating abrasion resistance, except that 100 μL of pure water was dropped onto the JSPS test cloth used in the above-described method to wet it, and then friction was performed using the wetted area. The water abrasion resistance of the images was then evaluated according to the above-described criteria for evaluating abrasion resistance.

[0122] (compatibility) The compatibility of the components in the reaction solutions used in each example and comparative example was evaluated. Specifically, 10 g of the reaction solution shown in Table 1 was heated for 2 hours under the temperature conditions specified in the evaluation criteria below, then stirred for 10 seconds and allowed to stand for 10 seconds. After that, the presence or absence of turbidity in the reaction solution was checked visually, and the compatibility of the reaction solution was evaluated according to the evaluation criteria below based on the temperature at which turbidity began to occur. 5. It did not become cloudy even at temperatures above 81℃. 4. It became cloudy at temperatures between 61°C and 80°C. 3. It became cloudy at temperatures between 41°C and 60°C. 2: It became cloudy at temperatures between 26°C and 40°C. 1: It became cloudy at temperatures below 25°C.

[0123] (Image feathering) Using the inkjet recording device 100 described above, 36 points of ruled lines were recorded on the recording medium (product name "PET WH50", manufactured by Lintec) at a recording medium transport speed of 40 m / min to prepare a sample for feathering evaluation. The obtained image was dried for 6 minutes with 80°C hot air using the heating device 2100 of the inkjet recording device 100. After leaving this feathering evaluation sample at a temperature of 23°C and a relative humidity of 50% for 24 hours, the roughness value Ra was measured. The roughness value Ra was measured using the Personal Image Quality Evaluation System Personal IAS (manufactured by Quality Engineering Associates). The degree of feathering of the image was then evaluated according to the following evaluation criteria based on the Ra value. In this evaluation, the degree of variation in the width of the ruled lines is measured using the above evaluation system, and a small Ra value means that the width of the ruled lines is constant and excellent. 5: Ra was 5.0 or less. 4: Ra was between 5.1 and 9.0. 3: Ra was between 9.1 and 13.0. 2: Ra was between 13.1 and 15.0. 1: Ra was 15.1 or higher.

[0124] TIFF2026070478000005.tif201170

Claims

1. An ink set comprising an aqueous ink and a reaction solution, used in an inkjet recording method for recording an image on a recording medium using an aqueous ink and an aqueous reaction solution containing a reactant that reacts with the aqueous ink, The aforementioned water-based ink contains a resin, The reactant comprises at least one selected from the group consisting of polyvalent metal salts and cationic resins. The ink set is characterized in that the reaction solution further contains an ionic surfactant and a crosslinking agent capable of forming a bond with the resin in the aqueous ink.

2. The ink set according to claim 1, wherein the resin comprises resin particles.

3. The ink set according to claim 1, wherein the ionic surfactant has at least one cationic hydrophilic portion.

4. The ink set according to claim 1, wherein the ionic surfactant comprises a cationic surfactant.

5. The standard enthalpy of formation of the anion constituting the polyvalent metal salt is -1,000 kJ mol. －１ -200 kJ mol －１ The ink set according to claim 1, which is as follows:

6. The ink set according to claim 1, wherein the polyvalent metal salt comprises sulfate ions.

7. The ink set according to claim 1, wherein the polyvalent metal salt is magnesium sulfate.

8. The ink set according to claim 1, wherein the reaction solution contains a water-soluble organic solvent having a boiling point of 250°C or lower.

9. The ink set according to claim 1, wherein the crosslinking agent has two or more functional groups selected from the group consisting of a carbodiimide group, an isocyanate group, and an oxazoline group.

10. The ink set according to claim 1, wherein the crosslinking agent has two or more carbodiimide groups.

11. The ink set according to claim 10, wherein the crosslinking agent has 1 mol of functional groups per molecular weight of 350 to 550.

12. The content (by mass) of the reactant in the reaction solution is 2.0% by mass or more and 30.0% by mass or less, based on the total mass of the reaction solution. The ink set according to claim 1, wherein the content (by mass) of the crosslinking agent in the reaction solution is 2.0% by mass or more and 20.0% by mass or less, based on the total mass of the reaction solution.

13. The ink set according to claim 1, wherein when the content of the reactant in the reaction solution (mass%) is A, the content of the crosslinking agent (mass%) is B, and the content of the ionic surfactant (mass%) is C, based on the total mass of the reaction solution, (A + B) / C is 5.0 or more and 50.0 or less.

14. An inkjet recording method for recording an image on a recording medium using an aqueous reaction solution containing an aqueous ink and a reactant that reacts with the aqueous ink, A reaction solution application step of applying the reaction solution to the recording medium, The process includes an ink application step of applying the aqueous ink to the recording medium by ejecting it from an inkjet ejection head so as to overlap with at least a portion of the area of ​​the recording medium to which the reaction solution is applied, The aforementioned water-based ink contains a resin, The reactant comprises at least one selected from the group consisting of polyvalent metal salts and cationic resins. An inkjet recording method characterized in that the reaction solution further contains an ionic surfactant and a crosslinking agent capable of forming a bond with the resin in the aqueous ink.

15. The inkjet recording method according to claim 14, wherein the reaction solution application step is a step of applying the reaction solution to the recording medium by ejecting it from an inkjet ejection head.

16. In the image layer formed by the reaction solution and aqueous ink applied to the recording medium, the amount of functional groups (μmol / m²) of the crosslinking agent per unit area of ​​the recording medium is ２ ) is E, and the amount of functional groups (μmol / m) in the resin ２ The inkjet recording method according to claim 14, wherein D is 0.5 or more and 6.0 or less.

17. An inkjet recording apparatus used in an inkjet recording method for recording an image on a recording medium using an aqueous ink and an aqueous reaction solution containing a reactant that reacts with the aqueous ink, A reaction solution application means for applying the reaction solution to the recording medium, The system includes an ink application means for dispensing the aqueous ink from an inkjet ejection head and applying it to the recording medium such that it overlaps with at least a portion of the area of ​​the recording medium to which the reaction solution is applied, The aforementioned water-based ink contains a resin, The reactant comprises at least one selected from the group consisting of polyvalent metal salts and cationic resins. An inkjet recording apparatus characterized in that the reaction solution further contains an ionic surfactant and a crosslinking agent capable of forming a bond with the resin in the aqueous ink.

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