Inkjet recording ink

Abstract

To provide an inkjet recording ink or the like having excellent discharge stability and capable of obtaining a recorded matter having excellent image fastness in an inkjet recording method which comprises a step of heating and holding an ink coating film on a recording medium after inkjet recording under a temperature environment of 100°C or more.SOLUTION: There is provided an inkjet recording ink or the like which contains a pigment, an organic solvent (B), cross-linked polymer particles (C) containing no pigment, polymer particles (D) containing wax and water, wherein the organic solvent (B) includes one or more organic solvents (b1) selected from the group consisting of a propylene glycol monomethyl ether, 3-methoxy-1-butanol, a propylene glycol monobutyl ether, an ethylene glycol monobutyl ether, 3-methoxy-3-methyl-1-butanol and a dipropylene glycol monomethyl ether.SELECTED DRAWING: None

Description

[Technical field]

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

[0002] Inkjet recording is a recording method in which ink droplets are directly ejected from a fine nozzle and deposited on a recording medium to obtain a recorded matter on which characters or images are recorded. Inkjet recording is characterized by not requiring plate-making and easy operation of the printing device, and is used in offices and homes, and in recent years, the demand for inkjet recording has been increasing in industrial applications as well. Conventionally, plain paper was the main recording medium, but in recent years, there has been an increasing demand for printing on low-absorbency recording media such as coated paper and art paper, and there is a demand for the development of inkjet recording inks that can print sharply on various recording media. Among them, in recent years, from the viewpoint of reducing environmental load, the importance of inkjet recording methods using water-based inks for inkjet recording, which mainly use water as a solvent, has been increasing. However, when using water-based inks for ink-jet printing, repelling of the ink occurs when printing on a low-liquid-absorbency recording medium, which causes problems such as bleeding and distortion of the image. As one of the measures for solving such a problem, a pretreatment of the recording medium using a treatment liquid is known. For example, Patent Document 1 discloses that by combining a treatment liquid, which uses a predetermined amount of calcium nitrate as a flocculant and has a high boiling point solvent amount and a treatment liquid viscosity and pH within specific ranges, with an inkjet ink, it is possible to produce high-quality prints that have excellent image uniformity and image density on various recording media, regardless of printing conditions such as printing speed, and are free of image defects such as color mixing and insufficient filling.

[0003] In addition, when the vicinity of the inkjet recording head is exposed to very dry conditions, a phenomenon in which ink coagulation and thickening occurs around the nozzle holes when ink ejection is temporarily stopped may occur. Furthermore, there are problems such as a decrease in ejection stability due to an increase in ejection frequency associated with an increase in the recording speed and a decrease in the stress that can be applied to each droplet, which makes nozzle chipping and ejection distortion more likely to occur, and a decrease in image robustness due to a reduction in the amount of resin components blended into the ink, which is a measure to suppress the generation of the coagulation and thickening. Therefore, attempts have been made to improve these problems. For example, Patent Document 2 discloses an aqueous ink containing water-insoluble polymer particles, an organic solvent, and water, in which the water-insoluble polymer particles are crosslinked polymers, the organic solvent contains a polyhydric alcohol ether, and the viscosity change rate of the organic solvent is set within a specific range, thereby making it possible to obtain a printed matter that has excellent ejection stability and excellent drying properties and abrasion resistance when printed on a low water-absorbent printing medium. Furthermore, Patent Document 3 discloses that by incorporating crosslinked polymer particles, in which a polyolefin wax is incorporated into a specific crosslinked polymer, into a water-based ink for inkjet printing, it is possible to obtain recorded matter that is excellent in storage stability and ejection stability, and also excellent in image fastness, even when recording on a low liquid-absorbent recording medium. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2020-70334 A [Patent Document 2] JP 2019-116598 A [Patent Document 3] Patent Publication No. 2022-085430 Summary of the Invention [Problem to be solved by the invention]

[0005] When recording on a low-absorbency recording medium such as coated paper using the inkjet recording method, the ink needs to be dried quickly in order to increase the recording speed. Therefore, after inkjet recording, an operation is generally performed in which the ink coating film on the recording medium is heated and maintained in an environment with a temperature higher than room temperature. In order to increase the recording speed, it is becoming common for the environment to be higher than room temperature in this operation to be a temperature environment of 100°C or higher. However, it has been found that the techniques of Patent Documents 1 to 3 do not provide sufficient image fastness when using an inkjet recording method in which an ink coating film on a recording medium is heated and maintained in a temperature environment of 100° C. or higher. An object of the present invention is to provide an ink for inkjet recording, an inkjet recording set, and an inkjet recording method which are excellent in ejection stability and which are capable of obtaining recorded matter with excellent image fastness in an inkjet recording method including a step of heating and maintaining an ink coating film on a recording medium after inkjet recording in an environment at a temperature of 100°C or higher. [Means for solving the problem]

[0006] The present inventors have found that the above-mentioned problems can be solved by providing an inkjet recording ink that contains a pigment, an organic solvent, crosslinked polymer particles that do not contain a pigment, polymer particles that contain a wax, and water, wherein the organic solvent contains one or more selected from specific monohydric alcohols. That is, the present invention provides the following [1] to [3]. [1] A pigment, an organic solvent (B), crosslinked polymer particles not containing a pigment (C), polymer particles containing a wax (D), and water; The organic solvent (B) comprises one or more organic solvents (b1) selected from the group consisting of propylene glycol monomethyl ether, 3-methoxy-1-butanol, propylene glycol monobutyl ether, ethylene glycol monobutyl ether, 3-methoxy-3-methyl-1-butanol, and dipropylene glycol monomethyl ether. [2] An inkjet recording set comprising the inkjet recording ink according to [1] above and a low liquid-absorbent recording medium having a component derived from a treatment liquid on its surface. [3] An inkjet recording method using the inkjet recording set according to [2] above, A step 1 of forming an ink coating film on a low liquid-absorbent recording medium having a component derived from the treatment liquid on its surface by an ink jet recording method using the ink for ink jet recording; and step 2 of heating and maintaining the ink coating film formed on the low liquid-absorbent recording medium in an environment at a temperature of 100° C. or higher to obtain a recorded matter. Effect of the Invention

[0007] According to the present invention, it is possible to provide an ink for inkjet recording, an inkjet recording set, and an inkjet recording method which are excellent in ejection stability and which are capable of obtaining recorded matter with excellent image fastness in an inkjet recording method including a step of warming and maintaining the ink coating film on a recording medium after inkjet recording in an environment at a temperature of 100°C or higher. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0008] [Inkjet recording ink] The inkjet recording ink of the present invention (hereinafter also referred to as "the ink of the present invention" or "ink") contains a pigment, an organic solvent (B), crosslinked polymer particles (C) not containing a pigment, polymer particles (D) containing a wax, and water, and the organic solvent (B) contains one or more organic solvents (b1) selected from the group consisting of propylene glycol monomethyl ether, 3-methoxy-1-butanol, propylene glycol monobutyl ether, ethylene glycol monobutyl ether, 3-methoxy-3-methyl-1-butanol, and dipropylene glycol monomethyl ether. From the viewpoint of reducing the environmental load, the ink of the present invention is preferably a so-called water-based ink in which water accounts for the largest proportion by mass. Note that, in the present invention, "water-based" means that water accounts for the largest proportion by mass of the medium. In the present invention, "wax" refers to an organic substance that is solid at room temperature (25°C) and becomes liquid when heated. At this time, the temperature at which the wax becomes liquid, that is, the melting point of the wax, is in the range of 45°C to 150°C. In the present invention, the term "recording" refers to a concept including printing and printing out characters and images, and the term "recorded matter" refers to a concept including printed matter and printed matter on which characters and images are recorded. In addition, the term "low liquid absorption" is a concept that includes low liquid absorption and non-liquid absorption, and the amount of water absorption of the recording medium when the recording medium is in contact with pure water for 100 ms is 0 g / m 2 More than 10g / m 2 "Highly absorbent" means that the amount of water absorbed by the recording medium when the recording medium is in contact with pure water for 100 ms is 10 g / m 2 It means to be super. Hereinafter, the image fastness of a recorded matter in an inkjet recording method including a step of warming and maintaining the ink coating film on a recording medium after inkjet recording in a temperature environment of 100° C. or higher will also be simply referred to as "image fastness".

[0009] The ink of the present invention has excellent ejection stability, and can provide a recorded matter having excellent image fastness in an inkjet recording method including a step of heating and maintaining the ink coating film on a recording medium after inkjet recording in a temperature environment of 100° C. or higher. The reason for this is not clear, but is thought to be as follows. The organic solvent (b1) contained in the ink of the present invention is a monohydric alcohol having a linear or branched aliphatic saturated hydrocarbon chain having from 3 to 5 carbon atoms and one oxygen atom of an ether group, or a monohydric alcohol having two chains of propanediyl groups and two oxygen atoms of an ether group. When the ink of the present invention is an aqueous ink in which water accounts for the largest proportion by mass, the organic solvent (b1) contributes to stable dispersion of the pigment, the pigment-free crosslinked polymer particles (C), and the wax-containing polymer particles (D) due to its strong hydrophobicity derived from the short-chain aliphatic saturated hydrocarbon chain, weak hydrophilicity derived from the oxygen of the ether group, and strong hydrophilicity derived from the hydroxyl group, and is considered to be able to suppress the occurrence of ink aggregation and thickening in the vicinity of the nozzle and improve ejection stability. In addition, in the present invention, since the crosslinked polymer particles (C) containing no pigment have a crosslinked structure, it is considered that even in the case of a water-based ink for ink-jet printing in which an organic solvent (b1) is present, excessive swelling can be suppressed and good ejection stability can be ensured. Furthermore, after inkjet recording, the content ratio of the organic solvent (b1) in the ink coating increases due to the evaporation of water. Thereafter, until the organic solvent (b1) evaporates, the organic solvent (b1) having various functional groups ranging from hydrophobic to hydrophilic as described above acts to moderately swell the crosslinked polymer particles (C) not containing a pigment and the polymer particles (D) containing a wax in the ink coating, and bond the particles together, which is considered to contribute to improving the image fastness of the resulting recorded matter. In addition, in order to remove volatile components from the ink coating film as soon as possible after inkjet recording, the ink coating film on the recording medium after inkjet recording is heated and held in a temperature environment of 100° C. or higher. The ink of the present invention contains a wax component as wax-containing polymer particles (D), so it is possible to suppress the generation of ink aggregation thickening products near the nozzle and improve the ejection stability. In addition, even if the ink coating film on the recording medium is heated and held in a temperature environment of 100° C. or higher, the wax component can maintain its particle shape for a long time, and even if the wax component dissolves, the wax component can be made to exist evenly in the smoothly formed ink coating film, making it difficult for the wax component to become extremely unevenly distributed. In addition, the wax component is prevented from sinking into the ink coating film and remains on the surface of the ink coating film, thereby enabling the friction reduction effect to be expressed, and therefore it is considered that high image robustness can be expressed.

[0010] <Pigments> Pigments are advantageous over dyes in terms of water resistance and weather resistance of recorded materials. The pigment may be either an inorganic pigment or an organic pigment, and may be used in combination with an extender pigment, if necessary. The pigments may be used alone or in combination of two or more kinds. Specific examples of inorganic pigments include carbon black and metal oxides. In particular, carbon black is preferred for black inks. Examples of carbon black include furnace black, thermal black, acetylene black, and channel black. In white inks, titanium oxide is preferred. Specific examples of organic pigments include azo pigments, diazo pigments, phthalocyanine pigments, quinacridone pigments, isoindolinone pigments, dioxazine pigments, perylene pigments, perinone pigments, thioindigo pigments, anthraquinone pigments, and quinophthalone pigments. In the achromatic ink, achromatic pigments such as white, black, and gray can be used, while in the chromatic ink, chromatic pigments such as yellow, magenta, cyan, blue, red, orange, and green can be used. Specific examples of preferred organic pigments include one or more products having product numbers selected from the group consisting of CI Pigment Yellow, CI Pigment Red, CI Pigment Orange, CI Pigment Violet, CI Pigment Blue, and CI Pigment Green. Examples of the extender pigment include silica, calcium carbonate, and talc.

[0011] In the present invention, the pigment is dispersed in the liquid medium of the ink. The form of the pigment in the ink of the present invention is preferably at least one selected from the group consisting of a pigment dispersed without a dispersant (hereinafter also referred to as a "self-dispersed pigment"), a pigment dispersed with a low molecular weight dispersant, and a pigment dispersed with a polymer dispersant. Among these, from the viewpoint of improving the ejection stability and image fastness, the pigment is more preferably contained as a pigment dispersed with a polymer dispersant, and further preferably contained as polymer particles (A) containing the pigment (hereinafter also referred to as "pigment-containing polymer particles (A)").

[0012] (Polymer (a)) The polymer (a) constituting the pigment-containing polymer particles (A) (hereinafter also referred to as "polymer (a)") may have a dispersing ability to stably disperse the pigment in the inkjet recording ink. From the viewpoint of improving the ejection stability, the polymer (a) preferably has an acid group, more preferably has a carboxy group. The polymer skeleton of the polymer (a) is preferably one or more selected from the group consisting of polyester, polyurethane, and vinyl-based polymer. Among these, from the viewpoint of improving the ejection stability and image fastness, the vinyl-based polymer obtained by addition polymerization of a vinyl monomer (vinyl compound, vinylidene compound, vinylene compound) described in paragraphs

[0017] to

[0024] of JP-A-2017-119845 is more preferable. The number average molecular weight of the polymer (a) is preferably 5,000 or more, more preferably 7,000 or more, even more preferably 10,000 or more, and is preferably 50,000 or less, more preferably 40,000 or less, even more preferably 30,000 or less. The number average molecular weight of the polymer (a) can be measured by the method described in the Examples. From the same viewpoint as above, the acid value of the polymer (a) is preferably 100 mgKOH / g or more, more preferably 150 mgKOH / g or more, even more preferably 200 mgKOH / g or more, and preferably 320 mgKOH / g or less, more preferably 280 mgKOH / g or less, even more preferably 260 mgKOH / g or less. The acid value of the polymer (a) can be measured by the method described in the Examples. It may also be calculated from the mass ratio of the constituent monomers, and when using a commercially available product, published values ​​may be referred to.

[0013] The polymer (a) constituting the pigment-containing polymer particles (A) preferably has a crosslinked structure from the viewpoint of improving discharge stability and image fastness. As the polymer (a) having a crosslinked structure, a polymer crosslinked with a crosslinking agent is preferably mentioned, and more preferably a vinyl polymer obtained by addition polymerization of a vinyl monomer (vinyl compound, vinylidene compound, vinylene compound) with a crosslinking agent as described in paragraphs

[0017] to

[0024] of JP-A-2017-119845 is more preferably a vinyl polymer obtained by crosslinking with a crosslinking agent. The crosslinking agent is preferably a compound having two or more functional groups capable of reacting with the functional groups of the polymer (a) constituting the pigment-containing polymer particle (A). For example, when the polymer (a) constituting the pigment-containing polymer particle (A) has a carboxyl group as an acid group, the crosslinking agent is preferably a polyglycidyl ether compound of a polyhydric alcohol. When the polymer (a) constituting the pigment-containing polymer particle (A) has a crosslinked structure, from the viewpoint of improving the ejection stability and image fastness, the acid value is preferably 40 mgKOH / g or more, more preferably 60 mgKOH / g or more, even more preferably 80 mgKOH / g or more, and is preferably 150 mgKOH / g or less, more preferably 130 mgKOH / g or less, even more preferably 110 mgKOH / g or less. When the polymer (a) constituting the pigment-containing polymer particle (A) has a crosslinked structure, the acid value of the polymer (a) having a crosslinked structure can be measured by the method described in the Examples using an aqueous dispersion of the pigment-containing polymer particle (A) as a measurement sample. It can also be calculated from the acid value of the polymer before crosslinking and the degree of crosslinking.

[0014] In the present invention, when the polymer (a) constituting the pigment-containing polymer particle (A) has an acid group, it is preferable that a part of the acid group of the polymer (a) is neutralized with a neutralizing agent from the viewpoint of improving the ejection stability and image fastness. Examples of the neutralizing agent include an alkali metal hydroxide and an amine compound. Among these, the neutralizing agent is preferably an alkali metal hydroxide, more preferably sodium hydroxide.

[0015] (Production of Pigment-Containing Polymer Particles (A)) In the present invention, the pigment-containing polymer particles (A) are preferably blended in the form of an aqueous dispersion. The method for producing the aqueous dispersion of the pigment-containing polymer particles (A) can be any known method, but the method described in paragraphs

[0031] to

[0039] of JP-A-2017-119845 is preferred. When the polymer (a) constituting the pigment-containing polymer particles (A) has a crosslinked structure, the method described in paragraphs

[0031] to

[0044] of JP-A-2017-119845 is preferred.

[0016] The average particle size of the pigment-containing polymer particles (A) in the water dispersion is preferably 30 nm or more, more preferably 50 nm or more, even more preferably 70 nm or more, and is preferably 200 nm or less, more preferably 150 nm or less, even more preferably 130 nm or less. The average particle size of the pigment-containing polymer particles (A) in the water dispersion is measured by the method described in the Examples. The pigment-containing polymer particles (A) contained in the ink of the present invention are preferably ones that are unlikely to swell or shrink, or to aggregate with each other. In this case, the average particle size of the pigment-containing polymer particles (A) in the ink of the present invention is considered to be the same as the average particle size of the pigment-containing polymer particles (A) in the aqueous dispersion. From this viewpoint, the preferred embodiment of the average particle size of the pigment-containing polymer particles (A) in the ink of the present invention is the same as the preferred embodiment of the average particle size of the pigment-containing polymer particles (A) in the dispersion. The average particle size of the pigment-containing polymer particles (A) in the ink of the present invention is also measured by the same method as that described in the Examples.

[0017] <Organic solvent (B)> The ink of the present invention contains an organic solvent (B) from the viewpoint of improving ejection stability and image fastness, and the organic solvent (B) contains one or more organic solvents (b1) selected from the group consisting of propylene glycol monomethyl ether, 3-methoxy-1-butanol, propylene glycol monobutyl ether, ethylene glycol monobutyl ether, 3-methoxy-3-methyl-1-butanol, and dipropylene glycol monomethyl ether.

[0018] (Organic solvent (b1)) From the viewpoint of improving ejection stability and image fastness, the organic solvent (b1) is at least one selected from the group consisting of propylene glycol monomethyl ether, 3-methoxy-1-butanol, propylene glycol monobutyl ether, ethylene glycol monobutyl ether, 3-methoxy-3-methyl-1-butanol, and dipropylene glycol monomethyl ether. The organic solvent (b1) may be used alone or in combination of two or more kinds. Of these, from the same viewpoint as above, the organic solvent (b1) is preferably a combination of two or more kinds, more preferably contains two or more kinds selected from the group consisting of propylene glycol monomethyl ether, ethylene glycol monobutyl ether, and dipropylene glycol monomethyl ether, and even more preferably contains three kinds of propylene glycol monomethyl ether, ethylene glycol monobutyl ether, and dipropylene glycol monomethyl ether.

[0019] When two or more organic solvents (b1) are used in combination, the weighted average boiling point of the organic solvent (b1) is preferably 145°C or higher. When the weighted average boiling point of the organic solvent (b1) is 145°C or higher, the organic solvent (b1), which also acts as an ink component to keep the ink moist, does not volatilize excessively around the nozzle hole, suppressing the occurrence of ink aggregation and thickening in the vicinity of the nozzle, suppressing the occurrence of non-ejection and ejection distortion, and further improving ejection stability. From this viewpoint, the weighted average boiling point of the organic solvent (b1) is more preferably 150°C or higher, even more preferably 155°C or higher, even more preferably 160°C or higher, even more preferably 165°C or higher, even more preferably 170°C or higher, and even more preferably 175°C or higher. In the present invention, the weighted average boiling point of organic solvent (b1) is the sum (unit: °C) of the values ​​calculated by multiplying the boiling point (unit: °C) of each organic solvent constituting organic solvent (b1) by the value obtained by dividing the content (mass %) of each organic solvent constituting organic solvent (b1) in the ink by the content (mass %) of organic solvent (b1) in the ink (i.e., the total content of organic solvents constituting organic solvent (b1) contained in the ink). That is, in this case, the weighted average boiling point of organic solvent (b1) is obtained by weighting the boiling points of each organic solvent constituting organic solvent (b1) by their mass ratios, and is an index of the volatility of organic solvent (b1).

[0020] (Organic solvent (b2)) From the viewpoint of improving the ejection stability and image fastness, the organic solvent (B) preferably contains an organic solvent other than the organic solvent (b1). Preferred examples of the organic solvent other than the organic solvent (b1) (hereinafter, also referred to as "organic solvent (b2)") include diol compounds, triol compounds, and polyalkylene glycols having an added mole number of 3 or more. The organic solvent (b2) may be used alone or in combination of two or more kinds. Among these, the organic solvent (b2) is preferably a diol compound, more preferably an alkanediol having 3 to 6 carbon atoms, even more preferably one or more selected from the group consisting of 1,2-propanediol, 1,3-propanediol, 1,2-butanediol, 1,3-butanediol, 1,4-butanediol, 1,2-pentanediol, 1,3-pentanediol, 1,5-pentanediol, 1,2-hexanediol, and 1,6-hexanediol, even more preferably one or more selected from the group consisting of 1,2-propanediol, 1,2-butanediol, and 1,2-hexanediol, and even more preferably 1,2-propanediol.

[0021] The boiling point of the organic solvent (b2) is preferably 150°C or higher and 225°C or lower. When the boiling point of the organic solvent (b2) is 150°C or higher, the organic solvent (b2), which plays a strong role in moisturizing the ink as an ink component, does not volatilize excessively around the nozzle hole, suppressing the occurrence of ink aggregation and thickening in the vicinity of the nozzle, suppressing the occurrence of non-ejection and ejection distortion, and improving ejection stability. When the boiling point of the organic solvent (b2) is 225°C or lower, the amount of the organic solvent (b2) remaining in the ink coating film on the recording medium can be reduced when the ink coating film on the recording medium is heated and maintained in a temperature environment of 100°C or higher, and it is considered that the image fastness can be further improved. From this viewpoint, the boiling point of the organic solvent (b2) is more preferably 160°C or higher, even more preferably 170°C or higher, even more preferably 180°C or higher, and more preferably 220°C or lower, even more preferably 210°C or lower, and even more preferably 200°C or lower. In the present invention, when only one organic solvent is used as the organic solvent (b2), the boiling point of the organic solvent (b2) refers to the boiling point of that organic solvent. When two or more organic solvents (b2) are used in combination, the boiling point of the organic solvent (b2) refers to the sum (unit: ° C) of the values ​​calculated by multiplying the boiling points (unit: ° C) of the organic solvents constituting the organic solvent (b2) by the content (mass %) of the organic solvents constituting the organic solvent (b2) in the ink divided by the content (mass %) of the organic solvent (b2) in the ink (i.e., the total content of the organic solvents constituting the organic solvent (b2) contained in the ink), that is, the weighted average value of the boiling points. That is, in this case, the weighted average value of the boiling points of the organic solvent (b2) is obtained by weighting the boiling points of the organic solvents constituting the organic solvent (b2) by the mass ratio, and is an index of the volatility of the organic solvent (b2).

[0022] When two or more kinds of organic solvents (B) are used in combination, the weighted average value of the boiling points of the organic solvents (B) is preferably 200° C. or lower. When the weighted average boiling point of the organic solvent (B) is 200°C or less, the amount of organic solvent (B) remaining in the ink coating film on a recording medium can be reduced when the ink coating film is heated and maintained in a temperature environment of 100°C or higher, and embrittlement of the ink coating film can be suppressed, so that a recorded matter with excellent image fastness can be obtained. In addition, when two or more organic solvents (B) are used in combination, the weighted average boiling point of the organic solvent (B) is preferably 160° C. or higher. When the weighted average boiling point of the organic solvent (B) is 160° C. or higher, when the ink coating film on the recording medium is heated and maintained in a temperature environment of 100° C. or higher, the evaporation rate of the organic solvent (B) from the ink coating film is in a moderate range, the generation of voids in the ink coating film is suppressed, the smoothness of the ink coating film can be improved, and good image fastness can be obtained. From these viewpoints, the weighted average boiling point of the organic solvent (B) is more preferably 170° C. or higher, even more preferably 180° C. or higher, and more preferably 195° C. or lower, even more preferably 190° C. or lower, and even more preferably 185° C. or lower. The weighted average boiling point of organic solvent (B) is the sum (unit: °C) of the values ​​calculated by multiplying the boiling point (unit: °C) of each organic solvent constituting organic solvent (B) by the value obtained by dividing the content (mass %) of each organic solvent constituting organic solvent (B) in the ink by the content (mass %) of organic solvent (B) in the ink (i.e., the total amount of organic solvent contained in the ink). In other words, the weighted average boiling point of organic solvent (B) is obtained by weighting the boiling points of each organic solvent constituting organic solvent (B) by their mass ratios, and is an index of the volatility of organic solvent (B).

[0023] <Crosslinked polymer particles not containing pigment (C)> The ink of the present invention contains crosslinked polymer particles (C) that do not contain a pigment, from the viewpoint of improving the ejection stability and image fastness. From the viewpoint of improving the discharge stability and image fastness, the polymer (c) constituting the pigment-free crosslinked polymer particles (C) is preferably one obtained by crosslinking the polymer (c') having no crosslinked structure with a crosslinking agent. That is, the polymer (c) constituting the pigment-free crosslinked polymer particles (C) preferably has a constitutional unit derived from the polymer (c') having no crosslinked structure and a constitutional unit derived from the crosslinking agent. The polymer (c') not having a crosslinked structure is preferably a water-insoluble polymer. In the present invention, a "water-insoluble polymer" means a polymer that, when dried at 105° C. for 2 hours to reach a constant weight and then dissolved to saturation in 100 g of water at 25° C., dissolution amount is 10 g or less. If the polymer has an ionic group and the ionic group is neutralized with a neutralizer when it is blended into the ink of the present invention, the water-insoluble polymer is judged from the amount of dissolution measured under conditions in which the neutralizer is mixed in such a way that the mass ratio of the polymer to the neutralizer is the same when it is blended into the ink of the present invention. When checking the water insolubility, if the dispersion is in a dispersed state, the dispersion is subjected to solid-liquid separation by centrifugation, and the water insolubility is judged based on the amount of dissolution in the liquid phase. Even if the dispersion state cannot be visually confirmed and the polymer appears transparent, it is judged to be in a dispersed state if the particle diameter is measured in the same manner as in the measurement of the particle diameter of the polymer particles described in the Examples.

[0024] The polymer (c') that does not have a crosslinked structure has a reactive group that can react with a crosslinking agent. Examples of the reactive group include acid groups such as carboxyl groups, sulfonic acid groups, and phosphoric acid groups; amino groups; hydroxyl groups; isocyanate groups; and epoxy groups. Among these, acid groups are preferred, and carboxyl groups are more preferred. Examples of the polymer (c') not having a crosslinked structure include one or more selected from the group consisting of condensation polymers such as polyurethane and polyester, and vinyl resins such as acrylic resins, styrene resins, acrylic-styrene resins, butadiene resins, styrene-butadiene resins, vinyl chloride resins, vinyl acetate resins, and acrylic silicone resins. Among these, vinyl polymers using a vinyl compound as a monomer are preferred. When the polymer (c') not having a crosslinked structure is a vinyl polymer, from the viewpoint of improving the ejection stability and image fastness, the polymer (c') is preferably a polymer containing (c-1) a structural unit derived from an ionic monomer, and more preferably a polymer containing (c-1) a structural unit derived from an ionic monomer and (c-2) a structural unit derived from a hydrophobic monomer.

[0025] (Polymer (c') having no crosslinked structure) [(c-1) Ionic Monomer] The (c-1) ionic monomer (hereinafter also referred to as "component (c-1)") is preferably an anionic monomer. The component (c-1) may be used alone or in combination of two or more kinds. Examples of the anionic monomer include carboxylic acid monomers, sulfonic acid monomers, and phosphoric acid monomers, with the carboxylic acid monomers being preferred. The carboxylic acid monomer is preferably, for example, one or more selected from the group consisting of acrylic acid, methacrylic acid, crotonic acid, itaconic acid, maleic acid, fumaric acid, and citraconic acid. Among these, the (c-1) component is more preferably one or more selected from the group consisting of acrylic acid and methacrylic acid, and even more preferably acrylic acid, from the viewpoint of improving the ejection stability and image fastness.

[0026] [(c-2) Hydrophobic Monomer] The hydrophobic monomer (c-2) (hereinafter also referred to as "component (c-2)") is preferably used as a monomer component of the polymer (c') not having a crosslinked structure, in addition to the component (c-1). The component (c-2) may be used alone or in combination of two or more kinds. The term "hydrophobic" in the hydrophobic monomer (c-2) means that when the monomer is dissolved in 100 g of ion-exchanged water at 25° C. until saturation, the amount of the monomer dissolved is less than 10 g. The (c-2) component is preferably, for example, one or more selected from the group consisting of alkyl (meth)acrylates and aromatic group-containing monomers such as styrene, α-methylstyrene, benzyl (meth)acrylate, etc. Among these, from the viewpoint of improving the ejection stability and image fastness, the (c-2) component is more preferably one or more selected from the group consisting of alkyl (meth)acrylates having an alkyl group having 1 to 22 carbon atoms and styrene.

[0027] From the viewpoint of improving ejection stability and image fastness, the acid value of the polymer (c') not having a crosslinked structure is preferably 5 mgKOH / g or more, more preferably 10 mgKOH / g or more, even more preferably 20 mgKOH / g or more, still more preferably 25 mgKOH / g or more, and is preferably 320 mgKOH / g or less, more preferably 240 mgKOH / g or less, even more preferably 120 mgKOH / g or less, still more preferably 80 mgKOH / g or less. The acid value of the polymer (c') having no crosslinked structure can be measured by the method described in the Examples. It may also be calculated from the mass ratio of the constituent monomers, and when using a commercially available product, the published values ​​may be referred to.

[0028] The crosslinking agent used for crosslinking the polymer (c') having no crosslinked structure has a water solubility (mass ratio) of preferably 50% or less, more preferably 40% or less, and even more preferably 35% or less, from the viewpoint of efficiently forming a crosslinked structure. Here, the water solubility (mass ratio) refers to the solubility (%) when 10 parts by mass of the crosslinking agent is added to 90 parts by mass of water at 25°C.

[0029] The crosslinking agent is preferably a compound having two or more epoxy groups in the molecule, more preferably a compound having two or more glycidyl ether groups in the molecule, and even more preferably a polyglycidyl ether compound of a polyhydric alcohol having a hydrocarbon group having 3 to 8 carbon atoms. From the viewpoints of ease of reaction, ejection stability, and image fastness, the molecular weight of the crosslinking agent is preferably 120 or more, more preferably 150 or more, and even more preferably 200 or more, and is preferably 2,000 or less, more preferably 1,500 or less, and even more preferably 1,000 or less. The epoxy equivalent of the crosslinking agent is preferably 90 or more, more preferably 100 or more, even more preferably 110 or more, and is preferably 300 or less, more preferably 200 or less, even more preferably 150 or less. The number of epoxy groups in the crosslinking agent is 2 or more per molecule from the viewpoint of efficiently reacting with the uncrosslinked polymer to improve ejection stability and image fastness, and is preferably 6 or less per molecule, and more preferably 4 or less from the viewpoint of market availability. Examples of preferred crosslinking agents include polyglycidyl ethers of polyhydric alcohols such as polypropylene glycol diglycidyl ether (water soluble rate: 31%), glycerol polyglycidyl ether, polyglycerol polyglycidyl ether, trimethylolpropane polyglycidyl ether (water soluble rate: 27%), sorbitol polyglycidyl ether, pentaerythritol polyglycidyl ether (water insoluble), resorcinol diglycidyl ether, neopentyl glycol diglycidyl ether, 1,6-hexanediol diglycidyl ether, and hydrogenated bisphenol A diglycidyl ether. Among these, the crosslinking agent is more preferably one or more selected from the group consisting of trimethylolpropane polyglycidyl ether, pentaerythritol polyglycidyl ether, and 1,6-hexanediol diglycidyl ether.

[0030] In the present invention, when the polymer (c') having no crosslinked structure has an acid group, it is preferable that a part of the acid groups of the polymer (c') having no crosslinked structure is neutralized with a neutralizing agent, and further a part of the acid groups of the polymer (c') having no crosslinked structure is crosslinked with a crosslinking agent to have a crosslinked structure. When the polymer (c') having no crosslinked structure has an acid group, suitable examples of the neutralizing agent include those exemplified for the pigment-containing polymer particles (A).

[0031] (Production of pigment-free crosslinked polymer particles (C)) In the present invention, the pigment-free crosslinked polymer particles (C) are preferably blended in the form of an aqueous dispersion. The aqueous dispersion of the pigment-free crosslinked polymer particles (C) can be obtained by reacting the polymer particles (C') having no crosslinked structure with a crosslinking agent. Suitable examples of the method for producing the aqueous dispersion of the polymer particles (C') that do not have a crosslinked structure include a method of adding water in which the polymer (c') that does not have a crosslinked structure is insoluble to the solution of the polymer (c') that does not have a crosslinked structure to obtain an aqueous dispersion of the polymer particles (C') that do not have a crosslinked structure, and a method of adding a so-called neutralizing agent that generates ion repulsion to the polymer (c') that does not have a crosslinked structure in the presence of water in which the polymer (c') that does not have a crosslinked structure is insoluble to obtain an aqueous dispersion of the polymer particles (C') that do not have a crosslinked structure.Then, a crosslinking agent is added to the aqueous dispersion of the polymer particles (C') that do not have a crosslinked structure, and the polymer particles (C') that do not have a crosslinked structure are reacted with the crosslinking agent to form a crosslinked structure in the polymer particles (C') that do not have a crosslinked structure, and an aqueous dispersion of the crosslinked polymer particles (C) that does not contain a pigment can be obtained. The acid value of the crosslinked polymer (c) constituting the pigment-free crosslinked polymer particles (C) (i.e., the acid value after crosslinking) is, from the viewpoint of improving ejection stability and image fastness, preferably 5 mgKOH / g or more, more preferably 10 mgKOH / g or more, even more preferably 15 mgKOH / g or more, and is preferably 100 mgKOH / g or less, more preferably 80 mgKOH / g or less, even more preferably 60 mgKOH / g or less. The acid value of the crosslinked polymer (c) can be measured by the method described in the Examples using an aqueous dispersion of the crosslinked polymer particles (C) that does not contain a pigment as a measurement sample. It can also be calculated from the acid value of the polymer before crosslinking and the degree of crosslinking.

[0032] The average particle size of the pigment-free crosslinked polymer particles (C) in the water dispersion is preferably 5 nm or more, more preferably 10 nm or more, even more preferably 15 nm or more, and is preferably 200 nm or less, more preferably 150 nm or less, even more preferably 130 nm or less. The average particle size of the pigment-free crosslinked polymer particles (C) in the water dispersion is measured by the method described in the Examples. Since the crosslinked polymer particles (C) not containing a pigment contained in the ink of the present invention have a crosslinked structure, swelling or shrinkage of the particles and aggregation between the particles are unlikely to occur, and the average particle size of the crosslinked polymer particles (C) not containing a pigment in the ink of the present invention is considered to be the same as the average particle size of the crosslinked polymer particles (C) not containing a pigment in the aqueous dispersion. From this viewpoint, the preferred embodiment of the average particle size of the crosslinked polymer particles (C) not containing a pigment in the ink of the present invention is the same as the preferred embodiment of the average particle size of the crosslinked polymer particles (C) not containing a pigment in the dispersion. The average particle size of the crosslinked polymer particles (C) not containing a pigment in the ink of the present invention is also measured by the same method as that described in the Examples.

[0033] <Wax-containing polymer particles (D)> The ink of the present invention contains wax-containing polymer particles (D) (hereinafter also referred to as "wax-containing polymer particles (D)") from the viewpoint of improving the ejection stability and image fastness. The wax-containing polymer particles (D) are composed of a wax (w) and a polymer (d).

[0034] (Wax (w)) Suitable examples of the wax (w) include unmodified wax and oxidized wax. The wax (w) may be used alone or in combination of two or more kinds. Preferred examples of the wax (w) include polyolefin wax and paraffin wax. Among these, the wax (w) more preferably contains one or more selected from the group consisting of polyolefin wax and paraffin wax, and even more preferably contains polyolefin wax. The polyolefin wax is preferably one whose main component is an olefin monomer. Here, the polyolefin wax "mainly containing an olefin monomer" refers to one in which the content of the olefin monomer is preferably 50% by mass or more, more preferably 65% ​​by mass or more, and even more preferably 80% by mass or more, based on the total components constituting the polyolefin wax. A preferred example of a polyolefin wax "mainly containing an olefin monomer" is a polyethylene wax whose main component is ethylene. The content of the polyolefin wax in the wax (w) is preferably 70% by mass or more, more preferably 80% by mass or more, even more preferably 90% by mass or more, and still more preferably 100% by mass. The melting point of the wax (w) is preferably 60°C or higher, more preferably 80°C or higher, even more preferably 100°C or higher, even more preferably 115°C or higher, even more preferably 120°C or higher, and preferably 150°C or lower, more preferably 140°C or lower, even more preferably 130°C or lower.

[0035] (Polymer (d)) The wax-containing polymer particles (D) are composed of a wax (w) and a polymer (d), and the polymer (d) preferably has a dispersing ability that stably disperses the wax (w) in the ink, which allows the wax-containing polymer particles (D) to be stably dispersed in the ink, compared with the case of using a wax dispersed by a low-molecular surfactant or a wax dispersed without a polymer dispersant.

[0036] From the viewpoint of enhancing the effect of stably dispersing the wax-containing polymer particles (D) in the ink, the polymer (d) constituting the wax-containing polymer particles (D) is preferably a vinyl polymer containing (d-1) a constituent unit derived from an ionic monomer and (d-2) a constituent unit derived from a hydrophobic monomer.

[0037] [(d-1) Ionic Monomer] The (d-1) ionic monomer (hereinafter also referred to as "component (d-1)") is preferably an anionic monomer. The component (d-1) may be used alone or in combination of two or more kinds. Suitable anionic monomers include the same monomers as those exemplified as (c-1) ionic monomers. Among these, the (d-1) ionic monomer is more preferably a carboxylic acid monomer, even more preferably one or more selected from the group consisting of acrylic acid and methacrylic acid, and even more preferably acrylic acid.

[0038] [(d-2) Hydrophobic Monomer] It is preferable that a hydrophobic monomer (d-2) (hereinafter also referred to as "component (d-2)") is further used as a monomer component of the polymer (d) in addition to the component (d-1). The term "hydrophobic" in the hydrophobic monomer (d-2) means that when the monomer is dissolved in 100 g of ion-exchanged water at 25° C. until saturation, the amount of the monomer dissolved is less than 10 g. The component (d-2) may be used alone or in combination of two or more kinds. Preferred examples of the component (d-2) include one or more selected from the group consisting of alkyl (meth)acrylates and aromatic group-containing monomers such as styrene, α-methylstyrene, benzyl (meth)acrylate, etc. Among these, one or more selected from the group consisting of alkyl (meth)acrylates having an alkyl group with 1 to 22 carbon atoms and styrene are more preferred, and it is even more preferred to use an alkyl (meth)acrylate having an alkyl group with 1 to 22 carbon atoms in combination with styrene.

[0039] The acid value of the polymer (d) is preferably 80 mgKOH / g or more, more preferably 100 mgKOH / g or more, even more preferably 120 mgKOH / g or more, and preferably 320 mgKOH / g or less, more preferably 240 mgKOH / g or less, even more preferably 200 mgKOH / g or less, even more preferably 160 mgKOH / g or less, even more preferably 130 mgKOH / g or less. The acid value of the polymer (d) can be measured by the method described in the Examples. It may also be calculated from the mass ratio of the constituent monomers, and when using a commercially available product, published values ​​may be referred to.

[0040] When the wax-containing polymer particles (D) are composed of a polymer (d) containing a structural unit derived from an ionic monomer (d-1), it is preferable that a portion of the ionic groups contained in the wax-containing polymer particles (D) are neutralized with a neutralizing agent. When the wax-containing polymer particles (D) have an acid group as the ionic group, suitable examples of the neutralizing agent include those exemplified for the pigment-containing polymer particles (A).

[0041] The polymer (d) is preferably a non-crosslinked polymer that does not have a crosslinked structure. The reason why the polymer (d) is preferably a non-crosslinked polymer is unclear, but it is considered that when the ink coating film on the recording medium after inkjet recording is heated and held in a temperature environment of 100°C or higher, the wax (w) constituting the wax-containing polymer particles (D) dissolves and the wax (w) diffuses into the ink coating film, causing the ink coating film to be smoothed, thereby reducing the friction resistance and allowing good image fastness to be exhibited. Furthermore, when the polymer (d) is a non-crosslinked polymer, the polymer (d) does not have a crosslinked structure, so that the polymer (d) forms a film and contributes to the toughening of the ink coating film, and it is considered that the image fastness can be further improved.

[0042] (Production of wax-containing polymer particles (D)) The wax-containing polymer particles (D) are preferably blended in the form of an aqueous dispersion. A suitable example of a method for producing an aqueous dispersion of the wax-containing polymer particles (D) is a method in which a polymer (d) obtained by copolymerizing raw material monomers including the (d-1) component, the (d-2) component, and other monomer components as required, a wax (w), and a neutralizing agent as required are subjected to mechanical stress using a dispersing device in the presence of an aqueous medium to be atomized. The average particle size of the wax-containing polymer particles (D) in the aqueous dispersion is preferably 20 nm or more, more preferably 30 nm or more, even more preferably 40 nm or more, and preferably 200 nm or less, more preferably 150 nm or less, even more preferably 120 nm or less, and even more preferably 100 nm or less. The average particle size of the wax-containing polymer particles (D) in the aqueous dispersion is measured by the method described in the Examples. The wax-containing polymer particles (D) contained in the ink of the present invention are preferably those which are unlikely to swell or shrink or to aggregate with each other. In this case, the average particle size of the wax-containing polymer particles (D) in the ink of the present invention is considered to be the same as the average particle size of the wax-containing polymer particles (D) in the aqueous dispersion.

[0043] <Surfactant (E)> The ink of the present invention preferably further contains a surfactant (E). The surfactant (E) may be used alone or in combination of two or more kinds. The surfactant (E) is preferably one or more selected from the group consisting of silicone-based surfactants and acetylene glycol-based surfactants, and more preferably a combination of a silicone-based surfactant and an acetylene glycol-based surfactant.

[0044] The silicone surfactant is preferably, for example, one or more selected from the group consisting of polyether-modified silicones and amino-modified silicones, with polyether-modified silicones being more preferred. When the silicone surfactant is a polyether-modified silicone, its HLB is preferably 5 or more, more preferably 6 or more, and preferably 13 or less, more preferably 12 or less, and even more preferably 11 or less.

[0045] Preferred examples of the acetylene glycol surfactant include one or more surfactants selected from the group consisting of acetylene glycol and ethylene oxide adducts of the acetylene glycol. The HLB value of the acetylene glycol surfactant is preferably 2 or more, more preferably 3 or more, and is preferably 18 or less, more preferably 16 or less, and further preferably 14 or less. It is preferable to use one or more acetylene glycol surfactants (e1) having an HLB value of preferably 2 or more, more preferably 3 or more, and preferably 7 or less, more preferably 6 or less in combination with one or more acetylene glycol surfactants (e2) having an HLB value of preferably 8 or more, more preferably 9 or more, and preferably 18 or less, more preferably 16 or less, and even more preferably 14 or less. As the surfactant (E), it is more preferable to use a combination of a silicone surfactant, an acetylene glycol surfactant (e1), and an acetylene glycol surfactant (e2). The HLB value is the hydrophile-lipophile balance according to Griffin, and is a value that indicates the degree of affinity of a surfactant to water and oil. The definition of the HLB value is described in WC Griffin: J. Soc. Comestic Chemists, 1, 311 (1949), Takahashi Kotami, Namba Yoshiro, Koike Motoo, and Kobayashi Masao, "Surfactant Handbook", 3rd Edition, Kogaku Tosho Publishing Co., Ltd., November 25, 1972, pp. 179-182, etc. It is also listed in surfactant catalogs.

[0046] <Water> The ink of the present invention contains water. The water used in the ink of the present invention is preferably pure water or ion-exchanged water from the viewpoint of preventing the inclusion of unintended substances.

[0047] The ink of the present invention may contain various additives as optional components, such as a pH adjuster, a viscosity adjuster, a defoamer, a preservative, and a rust inhibitor, if necessary. In this case, a part of the water content may be replaced with the various additives.

[0048] (Content of each component in the ink of the present invention) From the viewpoint of improving ejection stability and image fastness, the content of the pigment in the ink of the present invention is preferably 1% by mass or more, more preferably 2% by mass or more, even more preferably 3% by mass or more, still more preferably 4% by mass or more, and is preferably 15% by mass or less, more preferably 10% by mass or less, and even more preferably 8% by mass or less. From the viewpoint of improving ejection stability and image fastness, the content of the pigment-containing polymer particles (A) in the ink of the present invention is preferably 2 mass % or more, more preferably 3 mass % or more, even more preferably 4 mass % or more, still more preferably 5 mass % or more, and is preferably 16 mass % or less, more preferably 11 mass % or less, and even more preferably 9 mass % or less. The mass ratio of the pigment content to the total content of the pigment and polymer (a) in the ink of the present invention [pigment / (pigment+polymer (a))] is, from the viewpoint of improving ejection stability and image fastness, preferably 0.3 or more, more preferably 0.5 or more, even more preferably 0.7 or more, and is preferably 0.9 or less, more preferably 0.85 or less, even more preferably 0.8 or less.

[0049] From the viewpoint of improving ejection stability and image fastness, the content of the organic solvent (B) in the ink of the present invention is preferably 10% by mass or more, more preferably 15% by mass or more, even more preferably 20% by mass or more, and is preferably 40% by mass or less, more preferably 35% by mass or less, even more preferably 30% by mass or less, and still more preferably 25% by mass or less.

[0050] From the viewpoint of improving ejection stability and image fastness, the content of the organic solvent (b1) in the ink of the present invention is preferably 5 mass % or more, more preferably 7 mass % or more, even more preferably 10 mass % or more, still more preferably 12 mass % or more, and is preferably 30 mass % or less, more preferably 25 mass % or less, even more preferably 20 mass % or less, still more preferably 18 mass % or less, and still more preferably 16 mass % or less.

[0051] From the viewpoint of improving ejection stability and image fastness, the content of the organic solvent (b2) in the ink of the present invention is preferably 0 mass % or more, more preferably 1 mass % or more, even more preferably 3 mass % or more, and is preferably 20 mass % or less, more preferably 15 mass % or less, even more preferably 12 mass % or less, and still more preferably 10 mass % or less.

[0052] From the viewpoint of improving ejection stability and image fastness, the mass ratio of the content of organic solvent (b1) to the content of organic solvent (B) in the ink of the present invention [organic solvent (b1) / organic solvent (B)] is preferably 0.30 or more, more preferably 0.35 or more, even more preferably 0.40 or more, still more preferably 0.45 or more, still more preferably 0.50 or more, still more preferably 0.55 or more, still more preferably 0.60 or more, and is preferably 0.90 or less, more preferably 0.85 or less, still more preferably 0.80 or less, still more preferably 0.75 or less, and still more preferably 0.70 or less.

[0053] The content of the organic solvent having a boiling point of 180° C. or less in the ink of the present invention is preferably 0.5% by mass or more, more preferably 1% by mass or more, and even more preferably 1.3% by mass or more from the viewpoint of improving image fastness, and is preferably 20% by mass or less, more preferably 15% by mass or less, even more preferably 10% by mass or less, still more preferably 7% by mass or less, still more preferably 5% by mass or less, still more preferably 4% by mass or less, and even more preferably 3% by mass or less, from the viewpoint of improving ejection stability.

[0054] The mass ratio of the content of the organic solvent having a boiling point of 180°C or less to the content of organic solvent (B) in the ink of the present invention [organic solvent having a boiling point of 180°C or less / organic solvent (B)] is, from the viewpoint of achieving both ejection stability and image fastness, preferably 0.01 or more, more preferably 0.05 or more, and even more preferably 0.10 or more, and from the viewpoint of improving the ejection stability, is preferably 0.70 or less, more preferably 0.50 or less, even more preferably 0.40 or less, still more preferably 0.30 or less, and even more preferably 0.20 or less.

[0055] From the viewpoint of improving ejection stability and image fastness, the content of the crosslinked polymer particles (C) not containing a pigment in the ink of the present invention is preferably 1 mass % or more, more preferably 2 mass % or more, even more preferably 3 mass % or more, still more preferably 4 mass % or more, even more preferably 5 mass % or more, and is preferably 10 mass % or less, more preferably 8 mass % or less, and even more preferably 7 mass % or less.

[0056] From the viewpoint of improving ejection stability and image fastness, the content of the wax-containing polymer particles (D) in the ink of the present invention is preferably 0.1 mass % or more, more preferably 0.2 mass % or more, even more preferably 0.5 mass % or more, still more preferably 0.7 mass % or more, still more preferably 1 mass % or more, and is preferably 10 mass % or less, more preferably 5 mass % or less, even more preferably 3 mass % or less, still more preferably 2 mass % or less, and still more preferably 1.5 mass % or less.

[0057] From the viewpoint of improving ejection stability and image fastness, the content of the surfactant (E) in the ink of the present invention is preferably 0.11 mass % or more, more preferably 0.2 mass % or more, even more preferably 0.5 mass % or more, still more preferably 0.8 mass % or more, still more preferably 1 mass % or more, and is preferably 5 mass % or less, more preferably 3 mass % or less, and even more preferably 2 mass % or less.

[0058] From the viewpoint of improving ejection stability and image fastness, the content of the silicone surfactant in the ink of the present invention is preferably 0.01% by mass or more, more preferably 0.02% by mass or more, even more preferably 0.05% by mass or more, still more preferably 0.08% by mass or more, still more preferably 0.1% by mass or more, and is preferably 0.5% by mass or less, more preferably 0.3% by mass or less, and even more preferably 0.25% by mass or less. From the viewpoint of improving ejection stability and image fastness, the content of the acetylene glycol surfactant in the ink of the present invention is preferably 0.1 mass % or more, more preferably 0.2 mass % or more, even more preferably 0.5 mass % or more, still more preferably 0.8 mass % or more, still more preferably 1 mass % or more, and is preferably 4.5 mass % or less, more preferably 3 mass % or less, and even more preferably 2.5 mass % or less.

[0059] When the ink of the present invention contains a silicone surfactant, an acetylene glycol surfactant (e1), and an acetylene glycol surfactant (e2), the content of the silicone surfactant in the ink of the present invention is preferably 0.01% by mass or more, more preferably 0.02% by mass or more, even more preferably 0.05% by mass or more, still more preferably 0.08% by mass or more, still more preferably 0.1% by mass or more, and is preferably 0.5% by mass or less, more preferably 0.3% by mass or less, and even more preferably 0.25% by mass or less, and the content of the acetylene glycol surfactant (e1) in the ink of the present invention is The content of the acetylene glycol surfactant (e2) in the ink of the present invention is preferably 0.05% by mass or more, more preferably 0.1% by mass or more, even more preferably 0.2% by mass or more, still more preferably 0.25% by mass or more, and preferably 1% by mass or less, more preferably 0.7% by mass or less, and even more preferably 0.5% by mass or less, and the content of the acetylene glycol surfactant (e2) in the ink of the present invention is preferably 0.05% by mass or more, more preferably 0.1% by mass or more, even more preferably 0.3% by mass or more, still more preferably 0.5% by mass or more, and preferably 2% by mass or less, more preferably 1% by mass or less, and even more preferably 0.7% by mass or less.

[0060] From the viewpoint of improving ejection stability and image fastness, the water content in the ink of the present invention is preferably 40% by mass or more, more preferably 50% by mass or more, even more preferably 60% by mass or more, and is preferably 85% by mass or less, more preferably 80% by mass or less, even more preferably 75% by mass or less.

[0061] [Inkjet recording method] The inkjet recording method using the inkjet recording ink of the present invention (hereinafter also referred to as "the inkjet recording method of the present invention") can further improve its performance by forming an inkjet recording set with the inkjet recording ink together with a low liquid-absorbent recording medium having a component derived from a treatment liquid on its surface. That is, it is preferable to use the inkjet recording ink of the present invention as an inkjet recording set including a low liquid-absorbent recording medium having a component derived from a treatment liquid on its surface. The inkjet recording set of the present invention contains the inkjet recording ink of the present invention and a low liquid-absorbent recording medium having a component derived from a treatment liquid on its surface, and therefore can obtain a recorded product with excellent image fastness in an inkjet recording method including a step of heating and maintaining the ink coating film on the recording medium after inkjet recording in a temperature environment of 100°C or higher. The reason is unclear, but the inkjet recording ink according to the present invention contains one or more organic solvents (b1) selected from specific monohydric alcohols, and the solvent (b1) can moderately swell the crosslinked polymer particles (C) that do not contain a pigment and the polymer particles (D) that contain a wax in the ink coating film to make each particle bond firmly, and further enhances the fixing effect of the treatment liquid to the recording medium, so that a strong ink coating film can be formed, and when the surface of the resulting recorded matter is rubbed, the pigment is unlikely to peel off, and image fastness is improved. Also, as described above, even if the ink coating film on the recording medium is heated and held in a temperature environment of 100°C or higher, the wax component is unlikely to be extremely unevenly distributed, and the wax component is prevented from sinking into the ink coating film and remains on the surface of the ink coating film, thereby exhibiting a friction reduction effect, and therefore it is believed that high image fastness can be exhibited.

[0062] The inkjet recording method of the present invention preferably includes a step 1 of forming an ink coating film on a low liquid-absorbent recording medium having a component derived from the treatment liquid on its surface by an inkjet recording method using the ink for inkjet recording according to the present invention, and a step 2 of warming and maintaining the ink coating film on the low liquid-absorbent recording medium formed in the step 1 in a temperature environment of 100° C. or higher to obtain a recorded matter. According to the ink jet recording method of the present invention, the printing time can be reduced by shortening the drying operation of the ink coating, and further, a recorded matter exhibiting good image fastness can be obtained.

[0063] (Process 1) Step 1 is a step of forming an ink coating film on a low liquid-absorbent recording medium having a component derived from a treatment liquid on its surface by an inkjet recording method using the inkjet recording ink according to the present invention.

[0064] <Low-liquid-absorbent recording medium having a component derived from a processing liquid> [Processing solution] The low liquid-absorbent recording medium having a component derived from the treatment liquid used in step 1 is preferably one that has been treated with the treatment liquid constituting the inkjet recording set of the present invention. The treatment liquid according to the present invention is applied to the surface of a low-absorbent recording medium, and then the recording medium is dried, so that a component derived from the treatment liquid becomes one of the components constituting the surface-treated recording medium. That is, the surface-treated recording medium according to the present invention is a recording medium having a component derived from the treatment liquid on at least one surface of the low-absorbent recording medium. In the low-absorbent recording medium having a surface containing a component derived from the treatment liquid according to the present invention, the component derived from the treatment liquid is preferably a divalent or trivalent metal cation. When the divalent or trivalent metal cation applied to the low-absorbent recording medium comes into contact with the ink of the present invention on the recording medium, the crosslinked polymer particles (C) not containing a pigment in the ink of the present invention, the wax-containing polymer particles (D), and, if the pigment is in the form of pigment-containing polymer particles (A), the pigment-containing polymer particles (A) can exert an effect of enhancing the effect of firmly binding them to the low-absorbent recording medium by degenerating the electric double layer that exerts the dispersion stability of those particles, causing aggregation.

[0065] The divalent or trivalent metal cation is preferably at least one selected from the group consisting of calcium salts, magnesium salts, and aluminum salts. In the present invention, the component derived from the treatment liquid preferably contains an anion that forms a pair with the metal cation. The anion affects the solubility of the metal cation in the treatment liquid. The anion that is combined with the metal cation is preferably one or more anions selected from the group consisting of nitrate ion, halide ion, and sulfate ion, and more preferably nitrate ion. That is, the component derived from the treatment liquid according to the present invention is preferably one or more selected from the group consisting of calcium nitrate, magnesium nitrate, and aluminum nitrate. In other words, the low liquid-absorbent recording medium having a component derived from the treatment liquid according to the present invention on its surface is preferably a low liquid-absorbent recording medium treated with a treatment liquid containing one or more metal salts selected from the group consisting of calcium nitrate, magnesium nitrate, and aluminum nitrate.

[0066] In the low liquid-absorbing recording medium according to the present invention having on its surface a component derived from the treatment liquid, the component derived from the treatment liquid is preferably a water-soluble polymer. In the present invention, the term "water-soluble polymer" refers to a polymer that dissolves in an amount of more than 10 g when the polymer is dried at 105° C. for 2 hours to reach a constant weight and then dissolved in 100 g of water at 25° C. If the polymer has an ionic group and the ionic group is neutralized with a neutralizing agent when the polymer is blended into the treatment liquid of the present invention, the amount of dissolution is determined by measuring the amount of dissolution under conditions in which the neutralizing agent is mixed in such a way that the mass ratio of the polymer to the neutralizing agent is the same when the polymer is blended into the treatment liquid of the present invention. When the water-soluble polymer applied to a low-liquid-absorbing recording medium comes into contact with the ink of the present invention on the recording medium, the water-soluble polymer becomes dissolved in the liquid medium of the ink and combines with the pigment-free crosslinked polymer particles (C), the wax-containing polymer particles (D), and the pigment in the ink of the present invention. When a portion of the water and organic solvent (B) subsequently evaporates and the water-soluble polymer dries up, the water-soluble polymer is able to exert the effect of firmly binding them to the low-liquid-absorbing recording medium.

[0067] The water-soluble polymer is preferably at least one selected from the group consisting of polyvinyl alcohol, partially saponified polyvinyl alcohol, polyvinylpyrrolidone, carboxymethyl cellulose, and hydroxyethyl cellulose. Among these, the water-soluble polymer is more preferably at least one selected from the group consisting of polyvinyl alcohol, partially saponified polyvinyl alcohol, and polyvinylpyrrolidone. That is, the component derived from the treatment liquid according to the present invention is preferably one or more selected from the group consisting of polyvinyl alcohol, partially saponified polyvinyl alcohol, polyvinylpyrrolidone, carboxymethyl cellulose, and hydroxyethyl cellulose. In other words, the low liquid-absorbing recording medium having a component derived from the treatment liquid according to the present invention on its surface is preferably one that has been treated with a treatment liquid containing one or more selected from the group consisting of polyvinyl alcohol, partially saponified polyvinyl alcohol, polyvinylpyrrolidone, carboxymethyl cellulose, and hydroxyethyl cellulose.

[0068] The treatment liquid according to the present invention preferably further contains a water-soluble organic solvent. By further containing a water-soluble organic solvent, the moisturizing property and drying property of the treatment liquid, as well as the wettability to the low liquid-absorbing recording medium, can be more suitably adjusted. Suitable organic solvents that can be used in the treatment liquid include monohydric alcohols, glycols, glycol ethers, trihydric or higher polyhydric alcohols, polyalkylene oxides, etc.

[0069] The treatment liquid according to the present invention preferably further contains a surfactant. Examples of the surfactant include nonionic surfactants, anionic surfactants, cationic surfactants, etc., and preferably the nonionic surfactants.

[0070] The treatment liquid according to the present invention can be produced by a known method, for example, by mixing a metal salt or a water-soluble polymer that provides a divalent or trivalent metal cation, a water-soluble organic solvent, a surfactant, and, if necessary, water and other components.

[0071] [Low liquid-absorbent recording medium] The low-absorbency recording medium used in the inkjet recording method of the present invention is preferably, for example, coated paper or resin film, and more preferably coated paper. The water absorption amount of the low-absorbency recording medium when in contact with pure water for 100 msec is preferably 0 g / m 2 More preferably, 0.05 g / m2 More preferably, 0.1 g / m 2 More preferably, 1 g / m 2 and preferably 10 g / m 2 Less than 7g / m, more preferably 2 More preferably, 6 g / m or less 2 Less than 5 g / m 2 The amount of water absorption can be measured using an automatic scanning absorptivity meter.

[0072] The method of applying the treatment liquid to the low-absorbency recording medium is not particularly limited, and includes known methods such as coating, immersion, and inkjet recording. Examples of the coating and immersion methods include methods using a roll coater, gravure coater, die coater, curtain coater, spray coater, blade coater, wire bar coater, rod coater, impregnation coater, cast coater, air knife coater, reverse coater, lip coater, kiss coater, etc. Among these, one or more selected from the group consisting of coating and inkjet recording methods are preferred, and the coating method is more preferred.

[0073] The amount of the treatment liquid applied to the low-absorbency recording medium is preferably 0.1 g / m in terms of solid content. 2 More preferably, 0.2 g / m 2 More preferably, 0.3 g / m 2 and preferably 10 g / m 2 Less than or equal to 8 g / m 2 More preferably, 5 g / m or less 2 More preferably, 3 g / m or less 2 More preferably, 2 g / m or less 2 The following is the result.

[0074] After the treatment liquid is applied to the low-absorbent recording medium, it is preferable to dry the treatment liquid on the low-absorbent recording medium. The drying method is not particularly limited, and known methods such as natural drying and hot air drying can be used. The temperature for drying the treatment liquid on the low liquid-absorbent recording medium is preferably 30°C or higher, more preferably 40°C or higher, even more preferably 50°C or higher, and preferably 200°C or lower, more preferably 150°C or lower, even more preferably 120°C or lower, and even more preferably 90°C or lower. The drying time for drying the treatment liquid on the low liquid-absorbent recording medium is preferably 1 second or more, more preferably 10 seconds or more, and from the viewpoint of suppressing deformation of the recording medium due to heat and reducing energy, is preferably 45 minutes or less, more preferably 30 minutes or less.

[0075] <Inkjet recording> In step 1, the ink for ink-jet recording of the present invention is used to form an ink coating film on a low liquid-absorbent recording medium having a component derived from a treatment liquid on its surface by an ink-jet recording method. As the ejection method in the ink jet recording method, either a piezoelectric method or a thermal method can be preferably adopted. When inks of two or more colors are used to form an image by the inkjet recording method, the inkjet recording apparatus used for the inkjet recording method preferably has a plurality of inkjet recording heads that eject inks of two or more colors.

[0076] (Process 2) Step 2 is a step of obtaining a recorded matter by heating and holding the ink coating film on the low liquid-absorbent recording medium in a temperature environment of 100° C. or higher. By including Step 2, the inkjet recording method of the present invention can obtain a recorded matter having good image fastness. In step 2, the temperature of the environment in which the ink coating film on the recording medium after inkjet recording is heated and maintained is preferably 110°C or higher, more preferably 120°C or higher, even more preferably 130°C or higher, still more preferably 135°C or higher, even more preferably 140°C or higher, and is preferably 170°C or lower, more preferably 160°C or lower, and even more preferably 150°C or lower. The temperature of the environment for warming and maintaining the ink coating on the recording medium after inkjet recording is preferably a value obtained by measuring the temperature of the surface of the recording medium on which the ink coating is formed using a non-contact thermometer. Alternatively, the temperature of a means for warming and maintaining the ink coating on the recording medium, which will be described later, may be measured and used as the temperature of the surface of the recording medium on which the ink coating is formed. The time for which the ink coating film on the recording medium after inkjet recording is kept warm is preferably 10 seconds or more, more preferably 15 seconds or more, and even more preferably 20 seconds or more, and from the viewpoint of improving the recording speed, is preferably 180 seconds or less, more preferably 120 seconds or less, even more preferably 90 seconds or less, still more preferably 60 seconds or less, still more preferably 40 seconds or less, still more preferably 30 seconds or less, and still more preferably 20 seconds or less. Suitable means for warming and maintaining the ink coating film on the recording medium include a method of blowing gas adjusted to the above-mentioned temperature onto the ink coating film on the recording medium, a method of passing the ink coating film on the recording medium through a gas atmosphere adjusted to the above-mentioned temperature, a method of irradiating the ink coating film on the recording medium with an infrared heater, and a method of heating with a platen heater. EXAMPLES

[0077] In the following Production Examples, Examples and Comparative Examples, "parts" and "%" are "parts by mass" and "% by mass" unless otherwise specified. The methods for measuring each physical property are as follows.

[0078] (1) Measurement of polymer number average molecular weight The measurement was performed by gel permeation chromatography under the following conditions. GPC equipment: Tosoh Corporation "HLC-8320GPC" Columns: Tosoh Corporation's "TSKgel SuperAWM-H", "TSKgel SuperAW3000", and "TSKgel guardcolum Super AW-H" Eluent: N,N-dimethylformamide with phosphoric acid and lithium bromide dissolved at concentrations of 60mmol / L and 50mmol / L, respectively. Flow rate: 0.5mL / min Standard material: Monodisperse polystyrene kits with known molecular weights "PStQuick B (F-550, F-80, F-10, F-1, A-1000)" and "PStQuick C (F-288, F-40, F-4, A-5000, A-500)" (both manufactured by Tosoh Corporation) Measurement sample: 0.1 g of polymer was mixed with 10 mL of the eluent in a glass vial, stirred with a magnetic stirrer at 25° C. for 10 hours, and filtered with a syringe filter (DISMIC-13HP, made of PTFE, 0.2 μm, manufactured by Advantec Co., Ltd.) before use.

[0079] (2) Measurement of the acid value of the polymer The resin was dissolved in a titration solvent of toluene and acetone (2:1) in an automatic potentiometric titrator (Kyoto Electronics Manufacturing Co., Ltd., electric burette, model number: APB-610), and titrated with 0.1N potassium hydroxide / ethanol solution by potentiometric titration, with the inflection point on the titration curve as the end point. The acid value (mgKOH / g) was calculated from the titration amount of potassium hydroxide solution up to the end point.

[0080] (3) Measurement of solids concentration 10.0 g of sodium sulfate that had been kept at a constant weight in a desiccator was weighed out into a 30 mL ointment container, and approximately 1.0 g of the sample was added and mixed, then accurately weighed, kept at 105°C for 2 hours to remove volatile matter, and left in the desiccator for a further 15 minutes, after which the mass was measured. The mass of the sample after the volatile matter was removed was taken as the solid content, and was divided by the initial mass of the sample to obtain the solid content concentration (%).

[0081] (4) Measurement of the average particle size of pigment-containing polymer particles (A) Using a laser particle analysis system (ELS-8000, manufactured by Otsuka Electronics Co., Ltd.), the average particle size of the pigment dispersion was measured by dynamic light scattering, and calculated by cumulant analysis. The measurement conditions were a temperature of 25°C, an angle of 90° between the incident light and the detector, and 100 cumulative measurements. The refractive index of water (1.333) was entered as the refractive index of the dispersion solvent. For the measurement sample, pigment-containing polymer particles (A) were weighed into a screw tube (No. 5, manufactured by Maruemu Co., Ltd.) and the solids concentration was 2×10 -4 Water was added so as to obtain the desired mass %, and the mixture was stirred at 25° C. for 1 hour using a magnetic stirrer.

[0082] (5) Measurement of the average particle size of the crosslinked polymer particles (C) not containing a pigment The cumulant average particle size measured using a laser particle analysis system (ELS-8000 manufactured by Otsuka Electronics Co., Ltd.) was taken as the average particle size of the crosslinked polymer particles (C) that did not contain a pigment. The measurement conditions were a temperature of 25°C, an angle between the incident light and the detector of 90°, and 100 cumulative measurements. The refractive index of water (1.333) was input as the refractive index of the dispersion solvent. The solids concentration of the measurement sample was 5×10 -3 It is expressed as mass %.

[0083] (6) Measurement of the melting point of wax (w) The melting point of the wax (w) was measured using a measuring device conforming to JIS K 0064. Specifically, using a differential scanning calorimeter (TA Instruments, "Q20"), the sample was heated to 200°C and cooled to 0°C at a rate of 10°C / min. The sample was then heated at a rate of 10°C / min, and the amount of heat was measured up to 200°C. Among the observed heat of fusion peaks, the temperature of the peak with the largest peak area was determined as the maximum peak temperature of melting, and this peak temperature was determined as the melting point.

[0084] (7) Measurement of the average particle size of wax-containing polymer particles (D) The average particle size of the wax-containing polymer particles (D) was measured using a Microtrack particle size analyzer ("UPA" manufactured by Nikkiso Co., Ltd.).

[0085] (Polymer synthesis) Synthesis Example 1 (Synthesis of polymer (p1)) A monomer mixture was prepared by mixing 31 parts of acrylic acid and 69 parts of styrene. 10 parts of methyl ethyl ketone (hereinafter referred to as "MEK"), 0.2 parts of 2-mercaptoethanol as a polymerization chain transfer agent, and 10% of the monomer mixture were mixed in a reaction vessel, and the vessel was thoroughly purged with nitrogen gas. Separately, a mixture of the remainder of the monomer mixture (90% of the monomer mixture), 0.13 parts of the polymerization chain transfer agent, 30 parts of MEK, and 1.1 parts of 2,2'-azobis(2,4-dimethylvaleronitrile) ("V-65" manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) as a radical polymerization initiator was placed in a dropping funnel, and the monomer mixture in the reaction vessel was heated to 65°C while stirring under a nitrogen atmosphere, and the mixture in the dropping funnel was dropped over 3 hours. After 2 hours had passed from the end of the dropping while maintaining the temperature at 65°C, a solution in which 0.1 parts of the polymerization initiator was dissolved in 2 parts of MEK was added, and the mixture was further aged at 65°C for 2 hours and 70°C for 2 hours, and then dried under reduced pressure to obtain a polymer (p1) (number average molecular weight: 19,000, acid value: 240 mgKOH / g).

[0086] Synthesis Example 2 (Synthesis of polymer (p2)) A monomer mixture was prepared by mixing 16 parts of acrylic acid, 63 parts of styrene, and 21 parts of ethyl acrylate. In a reaction vessel, 10 parts of MEK, 0.2 parts of 2-mercaptoethanol as a polymerization chain transfer agent, and 10% of the monomer mixture were mixed and thoroughly purged with nitrogen gas. Separately, a mixture of the remainder of the monomer mixture (90% of the monomer mixture), 0.2 parts of the polymerization chain transfer agent, 30 parts of MEK, and 1.1 parts of 2,2'-azobis(2,4-dimethylvaleronitrile) ("V-65" manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) as an azo-based radical polymerization initiator was placed in a dropping funnel, and the monomer mixture in the reaction vessel was heated to 65°C while stirring under a nitrogen atmosphere, and the mixture in the dropping funnel was dropped over 3 hours. After 2 hours had passed from the end of the dropping while maintaining the temperature at 65°C, a solution in which 0.1 parts of the polymerization initiator was dissolved in 2 parts of MEK was added, and the mixture was further aged at 65°C for 2 hours and at 70°C for 2 hours, and then dried under reduced pressure to obtain a polymer (p2) (number average molecular weight: 32,000, acid value: 125 mgKOH / g).

[0087] (Production of Pigment-Containing Polymer Particles (A)) Manufacturing Example 1-1 100 parts of the polymer (p1) obtained in Synthesis Example 1 was mixed with 78.6 parts of MEK, and 41.2 parts of a 5N aqueous sodium hydroxide solution (sodium hydroxide content: 16.9%) was added as a neutralizing agent to neutralize (neutralization degree: 40 mol%). 800 parts of ion-exchanged water was further added, and 400 parts of a black pigment (CI Pigment Black 7, Cabot Corporation's "Monarch 717") was added thereto, and the mixture was stirred for 60 minutes at 20°C using a disperser (Asada Iron Works Co., Ltd.'s "Ultra Disperser") with the disperser blade rotating at 7000 rpm. The resulting mixture was dispersed 10 times using a Microfluidizer (Microfluidics Corporation, trade name) at a pressure of 200 MPa. 250 parts of ion-exchanged water was added to the obtained dispersion and stirred. After that, MEK was completely removed at 60°C under reduced pressure. Further, some of the water was removed to make the pigment concentration 15%. Then, 35.7 parts of trimethylolpropane polyglycidyl ether ("Denacol EX-321" manufactured by Nagase ChemteX Corporation, epoxy equivalent: 140) was added as an epoxy crosslinking agent, the mixture was sealed, and heated at 70°C for 5 hours while stirring with a stirrer. The mixture was then cooled to room temperature to obtain an aqueous dispersion of pigment-containing crosslinked polymer particles A1 (crosslinking rate 60 mol%) (solid concentration: 20%, acid value: 96 mgKOH / g, pigment concentration: 14.9%, average particle size: 99 nm).

[0088] (Production of pigment-free crosslinked polymer particles (C)) Manufacturing Example 2-1 100 parts (solid concentration: 44%) of acrylic resin emulsion (BASF "Joncryl8211", Tg: 60 ° C., acid value: 26 mg KOH / g) was taken in a screw-top glass bottle, 0.84 parts (crosslinking rate 30%) of Denacol EX-321 (trimethylolpropane polyglycidyl ether) as a crosslinking agent and 123.4 parts of ion-exchanged water were added, the bottle was sealed, and the bottle was heated at 70 ° C. for 5 hours while stirring with a stirrer. After 5 hours, the temperature was lowered to room temperature, and the bottle was filtered with a 25 mL needleless syringe (Terumo Corporation) equipped with a 5 μm filter (acetyl cellulose membrane, outer diameter: 2.5 cm, Fujifilm Corporation) to obtain an aqueous dispersion of crosslinked polymer particles C1 that does not contain a pigment (solid concentration: 20%, acid value: 18 mg KOH / g, average particle size 108 nm).

[0089] Manufacturing Example 2-2 100 parts (solid concentration: 46%) of acrylic resin emulsion (BASF "Joncryl538", Tg: 64 ° C., acid value: 70 mg KOH / g) was taken in a screw-top glass bottle, 2.17 parts (crosslinking rate 25%) of Denacol EX-212 (1,6-hexanediol diglycidyl ether) as a crosslinking agent and 138.7 parts of ion-exchanged water were added, the bottle was sealed, and the bottle was heated at 70 ° C. for 5 hours while stirring with a stirrer. After 5 hours, the temperature was lowered to room temperature, and the bottle was filtered with a 25 mL needleless syringe (Terumo Corporation) equipped with a 5 μm filter (acetyl cellulose membrane, outer diameter: 2.5 cm, Fujifilm Corporation) to obtain an aqueous dispersion of crosslinked polymer particles C2 not containing a pigment (solid concentration: 20%, acid value: 50 mg KOH / g, average particle size 112 nm).

[0090] (Production of wax-containing polymer particles (D)) Manufacturing Example 3-1 As a polymer dispersant, 10 parts of the polymer (p2) obtained in Synthesis Example 2 was neutralized by adding 2 parts of a 5N aqueous sodium hydroxide solution (NaOH solid content: 16.9%) as a neutralizing agent for neutralizing the carboxyl groups of the polymer (p2) (neutralization degree 38 mol %). Further, 240 parts of ion-exchanged water was added, and polyethylene wax (melting point: 122°C, density: 0.970 g / cm 3 100 parts of a cellulose acetate polymer (p2) having a weight average molecular weight of 2,000 and manufactured by Mitsui Chemicals, Inc., "Hiwax 200P") was heated to 85 to 95°C, and the resulting mixture was dispersed for 30 minutes using an ultrasonic homogenizer while being maintained at 90 to 95°C. The mixture was then cooled to room temperature and dispersed three times using a Microfluidizer (manufactured by Microfluidics, product name) at a pressure of 200 MPa to obtain an aqueous dispersion of wax-containing polymer particles D1 (wax content: 20%, polymer (p2) content: 2%, average particle size: 88 nm, pH: 7.3).

[0091] Manufacturing Example 3-2 In Production Example 3-1, polyethylene wax (melting point: 122°C, density: 0.970 g / cm 3 , weight average molecular weight: 2,000, "Hiwax 200P" manufactured by Mitsui Chemicals, Inc.) was mixed with polyethylene wax (melting point: 109°C, density: 0.920g / cm 3 An aqueous dispersion of wax-containing polymer particles D2 (wax content: 20%, polymer (p2) content: 2%, average particle size: 94 nm, pH: 7.3) was obtained in the same manner as in Production Example 3-1, except that the aqueous dispersion was changed to "Hiwax 110P" manufactured by Mitsui Chemicals, Inc. (wax content: 20%, polymer (p2) content: 2%, average particle size: 94 nm, pH: 7.3).

[0092] Manufacturing Example 3-3 In Production Example 3-1, polyethylene wax (melting point: 122°C, density: 0.970 g / cm 3An aqueous dispersion of wax-containing polymer particles D3 (wax content: 20%, polymer (p2) content: 2%, average particle size: 84 nm, pH: 7.3) was obtained in the same manner as in Production Example 3-1, except that the wax (melting point: 69°C, weight average molecular weight: 2,000, "Hiwax 200P" manufactured by Mitsui Chemicals, Inc.) was changed to paraffin wax (melting point: 69°C, "Paraffin Wax 155" manufactured by Nippon Seiro Co., Ltd.).

[0093] Manufacturing Example 3-4 100 parts of the aqueous dispersion of wax-containing polymer particles D1 obtained in Production Example 3-1 (wax content: 20%, polymer (p2) content: 2%) was placed in a glass container that could be sealed, and 0.09 parts of 1,6-hexanediol diglycidyl ether ("Denacol EX-212" manufactured by Nagase ChemteX Corporation, epoxy equivalent: 151) (corresponding to a crosslinking degree of 13.2 mol%) and 55 parts of ion-exchanged water were added, and the container was sealed. The container was heated at 70°C for 5 hours while stirring with a stirrer to obtain an aqueous dispersion of wax-containing crosslinked polymer particles D1' (wax content: 19.98%, crosslinked polymer (p2) content: 2.09% (of which crosslinking agent component: 0.09%), average particle size: 92 nm, pH: 8.3).

[0094] Manufacturing Example 3-5 10 parts of the polymer (p2) obtained in Synthesis Example 2 as a polymer dispersant was neutralized by adding 2 parts of a 5N aqueous sodium hydroxide solution (sodium hydroxide content: 16.9%) as a neutralizing agent for neutralizing the carboxyl groups of the polymer (p2). Further, 54 parts of ion-exchanged water and 286 parts by mass of oxidized high-density polyethylene wax emulsion dispersed with a nonionic surfactant ("AQUACER 515" manufactured by BYK-Chemie, melting point: 130°C) were added, and the mixture was treated nine times with a Microfluidizer (manufactured by Microfluidics, product name) at a pressure of 200 MPa to obtain an aqueous dispersion of wax-containing polymer particles D4 (wax content: 12%, nonionic surfactant content: 8%, polymer (p2) content: 2%, average particle size: 43 nm, pH: 7.3).

[0095] (Preparation of recording medium coated with treatment liquid) Preparation example 1 [Preparation of Processing Solution] 43 parts of magnesium nitrate hexahydrate (manufactured by FUJIFILM Wako Pure Chemical Industries, Ltd.), 4 parts of 2-propanol (manufactured by FUJIFILM Wako Pure Chemical Industries, Ltd.), and 0.05 parts of an acetylene glycol surfactant (2,4,7,9-tetramethyl-5-decyne-4,7-diol, "Surfynol 104" manufactured by Air Products and Chemicals, Inc.) were mixed, and ion-exchanged water was added so that the total amount became 100 parts. The mixture was filtered with a 25 mL needleless syringe (manufactured by Terumo Corporation) equipped with a 5 μm filter (acetyl cellulose membrane, outer diameter: 2.5 cm, manufactured by FUJIFILM Wako Pure Chemical Industries, Ltd.) to obtain treatment liquid U1. [Preparation of low liquid-absorbent recording medium having a component derived from a treatment liquid on its surface] The treatment solution U1 prepared above was applied to coated paper ("OK Topcoat+" manufactured by Oji Paper Co., Ltd., water absorption: 4.9 g / m) using a non-wire bar coater (manufactured by OSG System Products Co., Ltd., model number: OSP-03, film thickness: 3 μm). 2 The mixture was placed in an air oven at 50° C. and dried for 30 minutes to remove volatile matters, thereby obtaining a low liquid-absorbent recording medium 1 having a surface containing a component derived from the treatment liquid.

[0096] Example 2 [Preparation of Processing Solution] 100 parts of polyvinyl alcohol ("Poval 3-80" manufactured by Kuraray Co., Ltd., saponification degree 79-81%, polymerization degree 300) was placed in a screw-top glass bottle, 300 parts of ion-exchanged water was added, the bottle was sealed, and the mixture was stirred with a stirrer at room temperature for 1 hour, then heated to 90°C and heated for 1 hour. After 1 hour, the temperature was lowered to room temperature to obtain a PVA3-80 solution. 10 parts of the obtained PVA3-80 solution, 43 parts of calcium nitrate tetrahydrate (manufactured by FUJIFILM Wako Pure Chemical Industries, Ltd.), 4 parts of 2-propanol (manufactured by FUJIFILM Wako Pure Chemical Industries, Ltd.), and 0.05 parts of 2,4,7,9-tetramethyl-5-decyne-4,7-diol (manufactured by Air Products and Chemicals, Inc., "Surfynol 104") as an acetylene glycol surfactant were mixed, and ion-exchanged water was added so that the total amount became 100 parts. The mixture was filtered with a 25 mL needleless syringe (manufactured by Terumo Corporation) equipped with a 5 μm filter (acetyl cellulose membrane, outer diameter: 2.5 cm, manufactured by FUJIFILM Wako Pure Chemical Industries, Ltd.) to obtain a treatment liquid U2. [Preparation of low liquid-absorbent recording medium having a component derived from a treatment liquid on its surface] A low liquid absorbing recording medium 2 having a component derived from the treatment liquid on its surface was obtained in the same manner as in Preparation Example 1, except that the treatment liquid U1 in Preparation Example 1 was changed to treatment liquid U2.

[0097] Example 1 (Production of inkjet recording ink) 33.6 parts of an aqueous dispersion of pigment-containing crosslinked polymer particles A1 obtained in Production Example 1-1 (solid concentration: 20%, pigment concentration: 14.9%), 28.5 parts of an aqueous dispersion of pigment-free crosslinked polymer particles C1 obtained in Production Example 2-1 (solid concentration: 20%), 5.0 parts of an aqueous dispersion of wax-containing polymer particles D1 obtained in Production Example 3-1 (wax content: 20%), 3.0 parts of ethylene glycol monobutyl ether (manufactured by FUJIFILM Wako Pure Chemical Industries, Ltd.), 16.0 parts of dipropylene glycol monomethyl ether (manufactured by FUJIFILM Wako Pure Chemical Industries, Ltd.), 12.5 parts of 1,2-propanediol (manufactured by FUJIFILM Wako Pure Chemical Industries, Ltd.), 2,5,8,11-tetramethyl ether as an acetylene glycol surfactant (e1), Inkjet recording ink I-1 was obtained by adding 0.5 parts of -6-dodecyne-5,8-diol ("Surfynol DF110D" manufactured by Nissin Chemical Industry Co., Ltd., HLB: 3) (hereinafter referred to as "Surfynol DF110D"), 0.6 parts of an EO adduct of 2,4,7,9-tetramethyl-5-decyne-4,7-diol ("Surfynol 465" manufactured by Nissin Chemical Industry Co., Ltd., average number of moles of EO added = 10, HLB: 13) (hereinafter referred to as "Surfynol 465") as an acetylene glycol surfactant (e2), 0.2 parts of a silicone surfactant ("BYK-348" manufactured by BYK-Chemie, HLB: 11) (hereinafter referred to as "BYK348"), and ion-exchanged water to a total amount of 100 parts. The water content in 100 parts of the total amount of the water-based ink for inkjet printing I-1 was 52.3 parts, including water derived from the water dispersion of the pigment-containing crosslinked polymer particles A1, the water dispersion of the pigment-free crosslinked polymer particles C1, and the water dispersion of the wax-containing polymer particles D1. Using the obtained water-based ink for inkjet printing I-1, the ejection stability was evaluated by the following method.

[0098] (Inkjet recording) [Process 1] In an environment of 25±1°C temperature and 30±5% relative humidity, a print evaluation device (manufactured by Tritec Co., Ltd.) equipped with an inkjet recording head (Kyocera Corporation's "KJ4B-HD06MHG-STDV", piezo type) was filled with the inkjet recording ink I-1. The head voltage was set to 26V, the driving frequency to 30kHz, the amount of ejected liquid to be ejected to 12pl, the head temperature to 32°C, the resolution to 600dpi, the number of flushings before ejection to 200, and the negative pressure to -4.0kPa. The recording medium 1 was fixed to the conveying table under reduced pressure so that the longitudinal direction of the recording medium 1 was the same as the conveying direction. A print command was transferred to the print evaluation device, and a solid ink coating film with a duty of 100% was formed on the recording medium 1. [Process 2] Within 10 seconds after carrying out step 1, the ink coating film on recording medium 1 was heated and held in an air oven at 110° C. for 30 seconds, thereby obtaining a recorded matter P1-1. Furthermore, a recorded matter P2-1 was obtained in the same manner, except that the ink coating film on Recording Medium 1 was heated and held in an air oven at 140° C. for 20 seconds instead of being heated and held in an air oven at 110° C. for 30 seconds. The image fastness of the obtained recorded matter was evaluated by the following method.

[0099] Examples 2 to 21 and 23 (Production of inkjet recording ink) Water-based inks for ink-jet printing I-2 to I-22 were obtained in the same manner as in Example 1, except that the compositions of the water-based inks in Example 1 were changed to those shown in Table 1 or Table 2. Using each of the obtained water-based inks for ink-jet printing, ejection stability was evaluated by the following method. The numerical values ​​of the compositions of the water-based inks in Tables 1 and 2 are effective amounts (solid contents (however, for wax-containing polymer particles (D), these are the solid contents of the wax (w) and polymer (d))). The same applies below. (Inkjet recording) Recorded matters P1-2 to P1-21, P1-23 and recorded matters P2-2 to P2-21, P2-23 were obtained in the same manner as in Example 1, except that the water-based ink for ink-jet printing I-1 was changed to the water-based ink for ink-jet printing I-2 to I-22, respectively. Using each of the obtained recorded matters, the image fastness was evaluated by the following method.

[0100] Example 22 (Production of inkjet recording ink) A water-based ink for ink-jet printing I-3 was obtained in the same manner as in Example 3. Using each of the water-based inks for ink-jet printing thus obtained, the ejection stability was evaluated by the following method. The numerical values ​​for the composition of the water-based ink in Table 2 are the effective amounts (solid amounts (however, for wax-containing polymer particles (D), this is the solid amount of wax (w) and polymer (d))). (Inkjet recording) Recorded matter P1-22 and recorded matter P2-22 were obtained in the same manner as in Example 1, except that the water-based ink for inkjet printing I-1 was changed to the water-based ink for inkjet printing I-3, and the low-absorbent recording medium 1 having a component derived from the treatment liquid on its surface was changed to the low-absorbent recording medium 2 having a component derived from the treatment liquid on its surface. Using the obtained recorded matter, the image fastness was evaluated by the following method.

[0101] Comparative Examples 1 to 4 (Production of inkjet recording ink) Water-based inks for ink-jet printing CI-1 to CI-4 were obtained in the same manner as in Example 1, except that the composition of the water-based ink in Example 1 was changed to that shown in Table 3. Using each of the obtained water-based inks for ink-jet printing, the ejection stability was evaluated by the following method. Note that, since the ejection stability of Comparative Examples 1 to 3 was poor, the image fastness was not evaluated. (Inkjet recording) Recorded matter PC1-4 and recorded matter PC2-4 were obtained in the same manner as in Example 1, except that the water-based ink for ink-jet printing I-1 was changed to the water-based ink for ink-jet printing CI-4. Image fastness was evaluated by the following method using each of the obtained recorded matters.

[0102] 〔evaluation〕 (Discharge stability) Using each of the water-based inks for ink-jet printing obtained in the Examples and Comparative Examples, ink was printed on A4-sized coated paper ("OK Topcoat+" manufactured by Oji Paper Co., Ltd., water absorption: 4.9 g / m) by the following ink-jet printing method. 2 The nozzle recovery rate and nozzle chipping were evaluated as ejection stability. The results are shown in Tables 1 to 3. [Evaluation of nozzle recovery rate] Each water-based ink for inkjet printing was filled into a print evaluation device (manufactured by Tritec Co., Ltd.) equipped with an inkjet recording head (Kyocera Corporation's "KJ4B-HD06MHG-STDV", piezo type) under an environment of 25±1°C temperature and 30±5% relative humidity. The head voltage was set to 26V, the driving frequency to 30kHz, the amount of ejected liquid to be ejected to 12pL, the head temperature to 32°C, the resolution to 600dpi, the number of flushings before ejection to 200, and the negative pressure to -4.0kPa, and the recording medium was fixed to the conveying table under reduced pressure so that the longitudinal direction of the recording medium was the same as the conveying direction. A print command was transferred to the print evaluation device, and a solid image with a duty of 100% was printed. After that, the printing evaluation device was stopped for 30 minutes, and the recording head was exposed to the atmosphere. After 30 minutes had passed, the ink was purged from the recording head once, and the state of nozzle chipping when printing was resumed after wiping was observed, and the nozzle recovery rate (%) was calculated using the following formula to evaluate the ejection stability. The results are shown in Tables 1 to 3. Nozzle recovery rate (%) = (number of normal nozzles / total number of nozzles) x 100 The higher the nozzle recovery rate (%), the better the nozzle recovery is judged to be, and a value of 85% or higher is usable for practical use.

[0103] [Evaluation of nozzle chipping] Each water-based ink for inkjet printing was filled into an inkjet ejection evaluation device (ImageXpert's "Jetexpert") equipped with an inkjet recording head (FUJIFILM's "Samba G3L", piezo type) under an environment of 25±1°C temperature and 30±5% relative humidity. The head voltage was set to 30V, the frequency to 50kHz, the push-pull type driving waveform, the appropriate amount of ejected liquid to 2.5pL, and the negative pressure to -4.0kPa, and an ink ejection command was transferred to the ejection evaluation device to confirm the number of nozzles from which each water-based ink for inkjet printing was ejected normally. Continuous ejection was performed for 30 minutes under the same conditions, and the number of nozzles from which the inkjet printing ink was ejected normally after 30 minutes was reconfirmed. The nozzle dropout rate (%) was calculated by the following formula to evaluate the ejection stability. The results are shown in Tables 1 to 3. Nozzle chipping rate (%) = 100 - (number of nozzles that discharge normally after 30 minutes / number of nozzles that discharge normally at the beginning) x 100 The smaller the rate of nozzle chipping (%), the better the ejection stability is judged to be, and a value of 10% or less is usable for practical purposes.

[0104] (Image robustness) The obtained recordings P1-1 to P1-23 and PC1-4, and recordings P2-1 to P2-23 and PC2-4 were each rubbed 20 times with a Gakushin-type abrasion tester (RT-300, manufactured by Daiei Scientific Instruments Manufacturing Co., Ltd.) using an untreated, unprinted piece of the above coated paper cut to a size of 2 x 2 cm, placed on the printed surface, and rubbed back and forth with a load of 10 N.While rubbing, the presence or absence of exposure of the recording medium was confirmed, and the concentration of the transferred ink after 20 rubs was measured using a spectrophotometer (Spectro-Eye, manufactured by Sakata Inx Engineering Co., Ltd.). The more the number of reciprocating movements until the recording medium was exposed and the lower the density of the transferred ink, the better the image fastness was judged to be, and the image was evaluated according to the following criteria. The results are shown in Tables 1 to 3. [Evaluation Criteria] A: Even after 20 reciprocal rubs, the recording medium is not exposed and the density of the transferred ink is 0.1 or less. B: Even after 20 reciprocating rubs, the recording medium is not exposed and the density of the transferred ink is 0.2 or less. C: The recording medium was not exposed even after 10 reciprocal rubbings, but after 20 reciprocal rubbings, the recording medium was exposed and the density of the transferred ink was 0.2 or less. D: The recording medium was not exposed even after 10 reciprocating rubs, but after 20 reciprocating rubs, the recording medium was exposed and the density of the transferred ink was more than 0.2. E: The recording medium was exposed after 10 double rubs. When the evaluation result was E (that is, when the recording medium was exposed after 10 reciprocating rubs), the density of the transferred ink after 20 reciprocating rubs was not measured.

[0105] [Table 1] [Table 2]

[0106] [Table 3]

[0107] It can be seen from Tables 1 to 3 that the inkjet recording inks I-1 to I-22 used in Examples 1 to 23 are excellent in ejection stability. On the other hand, Comparative Example 1 uses non-crosslinked polymer particles containing no pigment instead of crosslinked polymer particles containing no pigment, so it is inferior in ejection stability compared to the Examples, and Comparative Example 2 uses a wax emulsion in which the wax is dispersed with a nonionic surfactant, and the wax is not dispersed with a polymer, so it is inferior in ejection stability compared to the Examples. In addition, Comparative Example 3 does not contain an organic solvent (b1), so it is inferior in ejection stability. From the above, as described above, Comparative Examples 1 to 3 are not evaluated for image fastness because they have inferior ejection stability. Furthermore, from Tables 1 to 3, it can be seen that the inkjet recording sets of the inks for inkjet recording of Examples 1 to 23 and the recording media having components derived from each treatment liquid have excellent ejection stability, and can provide recorded products with excellent image fastness in an inkjet recording method including a step of heating and maintaining the ink coating film on the recording medium after inkjet recording in a temperature environment of 100°C or higher. On the other hand, it is seen from Comparative Example 4 that when the wax-containing polymer particles (D) are not contained, the image fastness is poor.

Claims

1. A method for producing a coating composition comprising: a pigment, an organic solvent (B), pigment-free crosslinked polymer particles (C), wax-containing polymer particles (D), and water; the organic solvent (B) contains one or more organic solvents (b1) selected from the group consisting of propylene glycol monomethyl ether, 3-methoxy-1-butanol, propylene glycol monobutyl ether, ethylene glycol monobutyl ether, 3-methoxy-3-methyl-1-butanol, and dipropylene glycol monomethyl ether.

2. 2. The ink jet recording ink according to claim 1, wherein the organic solvent (b1) is a mixture of two or more kinds, and the weighted average boiling points of the organic solvents (b1) are 145° C. or higher.

3. 3. The ink jet recording ink according to claim 1, wherein the organic solvent (B) is a mixture of two or more kinds, and the weighted average boiling points of the organic solvents (B) are 200°C or less.

4. 3. The inkjet recording ink according to claim 1, wherein the mass ratio of the content of the organic solvent having a boiling point of 180°C or less to the content of the organic solvent (B) [organic solvent having a boiling point of 180°C or less / organic solvent (B)] is 0.01 or more and 0.70 or less.

5. The ink for ink-jet recording according to claim 1 or 2, wherein the content of the organic solvent (B) is from 10% by mass to 40% by mass.

6. 3. The ink for inkjet recording according to claim 1, wherein the mass ratio of the content of the organic solvent (b1) to the content of the organic solvent (B) [organic solvent (b1) / organic solvent (B)] is 0.30 or more and 0.90 or less.

7. An inkjet recording set comprising the inkjet recording ink according to claim 1 or 2 and a low-liquid-absorbent recording medium having a component derived from the treatment liquid on its surface.

8. An inkjet recording method using the inkjet recording set according to claim 7, a step 1 of forming an ink coating film on a low liquid-absorbent recording medium having a surface containing a component derived from the treatment liquid by an inkjet recording method using the ink for inkjet recording; and step 2 of heating and maintaining the ink coating film formed on the low-liquid-absorbent recording medium in an environment at a temperature of 100° C. or higher to obtain a recorded matter.