Inkjet recording ink

Abstract

To provide an inkjet recording ink that can obtain a recorded product excellent in image concentration and scratch resistance and is excellent also in continuous discharge properties even when performing recording on a recording medium with high liquid-absorbing properties.SOLUTION: An inkjet recording ink contains pigments, wax, surfactants, organic solvents, and water, the surfactants comprising a surfactant A that is one or more selected from the group consisting of polyoxyethylene alkyl ether, polyoxyethylene alkenyl ether, polyoxyethylene aryl ether, and an anionic surfactant, and a surfactant B that is one or more selected from the group consisting of an acetylene-based surfactant and a silicone-based surfactant, wherein the content of the surfactant B in the inkjet recording ink is 0.15 mass% or less.SELECTED DRAWING: None

Description

[Technical field]

[0001] The present invention relates to an ink for ink-jet recording. [Background technology]

[0002] Inkjet recording is a method of directly ejecting ink droplets from minute nozzles and depositing them on a recording medium to obtain a recorded matter with characters and images. This method has become extremely popular due to its many advantages, including the ease and low cost of producing full-color images, the ability to use plain paper as a recording medium, and the fact that it does not come into contact with the recording medium. In recent years, the use of inkjet recording methods has expanded beyond consumer printing to commercial printing using plain paper. With the aim of reducing the burden on the environment, there is an increasing demand for water-based inks for inkjet recording that use water primarily as a solvent. In order to meet such demands, various water-based inks for inkjet printing have been proposed that not only satisfy basic performance requirements for inkjet recording inks such as ejection stability, but also enhance the added value of the resulting recorded matter. For example, Patent Document 1 describes an ink containing wax, an organic solvent, and water for the purpose of providing an ink with excellent fixing properties, etc., in which the organic solvent contains a compound having a solubility parameter of 9 or more and 11 or less, and a compound having a saturated vapor pressure at 100°C in a specific range. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2017-8294 A Summary of the Invention [Problem to be solved by the invention]

[0004] However, it has been found that the technique of Patent Document 1 does not provide sufficient image density and abrasion resistance in inkjet recording on a highly liquid-absorbent recording medium such as plain paper. Furthermore, regarding ejection stability, which is a basic performance of an ink for inkjet recording, when producing recorded matter continuously, excellent continuous ejection properties are also required when the ink is continuously ejected from the inkjet nozzles. An object of the present invention is to provide an ink for inkjet recording which can provide a recorded matter having excellent image density and abrasion resistance even when recording on a highly liquid-absorbent recording medium, and which also has excellent continuous ejection properties. [Means for solving the problem]

[0005] The present inventors have found that the above-mentioned problems can be solved by providing an inkjet recording ink containing a pigment, a wax, a surfactant, an organic solvent, and water, wherein the surfactant includes at least two specific surfactants, and the content of the specific surfactant in the inkjet recording ink is equal to or less than a specific value. That is, the present invention provides an ink for ink-jet recording, comprising a pigment, a wax, a surfactant, an organic solvent, and water, the surfactant comprises surfactant A which is one or more selected from the group consisting of polyoxyethylene alkyl ethers, polyoxyethylene alkenyl ethers, polyoxyethylene aryl ethers, and anionic surfactants, and surfactant B which is one or more selected from the group consisting of acetylene-based surfactants and silicone-based surfactants; The inkjet recording ink has a surfactant B content of 0.15% by mass or less. Effect of the Invention

[0006] According to the present invention, it is possible to provide an ink for inkjet recording that can obtain a recorded matter having excellent image density and abrasion resistance even when recording on a highly liquid-absorbent recording medium, and that also has excellent continuous ejection properties. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0007] [Inkjet recording ink] The inkjet recording ink of the present invention (hereinafter also referred to as "the ink of the present invention" or "ink") is an inkjet recording ink containing a pigment, a wax, a surfactant, an organic solvent, and water, wherein the surfactant includes surfactant A which is one or more selected from the group consisting of polyoxyethylene alkyl ethers, polyoxyethylene alkenyl ethers, polyoxyethylene aryl ethers, and anionic surfactants, and surfactant B which is one or more selected from the group consisting of acetylene-based surfactants and silicone-based surfactants, and the content of surfactant B in the inkjet recording ink is 0.15 mass % or less. In the present invention, the term "recording" refers to a concept that includes printing and printing out characters and images, and the term "recorded matter" refers to a concept that includes printed matter and printed matter on which characters and images are recorded. In the present invention, "wax" refers to an organic substance that is solid or semi-solid at room temperature (25°C) and becomes liquid when heated. Here, "wax is semi-solid" means that the wax deforms and flows when force is applied to it, but can maintain a certain shape when no force is applied to it. In addition, the temperature at which the wax becomes liquid, that is, the melting point of the wax, is in the range of 45°C to 160°C. In the present invention, "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 8 g / m 2 In addition, the term "low liquid absorption" is a concept that includes low liquid absorption and non-liquid absorption, and means that the water absorption amount of the recording medium when the recording medium is in contact with pure water for 100 ms is 0 g / m 2 More than 8g / m 2 This means that: In the present invention, the term "continuous ejection property" refers to the ejection property when the ink is ejected continuously from the inkjet nozzle in the case of continuously producing recorded matter, etc. Furthermore, in this specification, the image density and abrasion resistance when recording on a highly liquid-absorbent recording medium are also simply referred to as "image density" and "abrasion resistance", respectively.

[0008] The ink of the present invention can provide a recorded matter having excellent image density and abrasion resistance even when recorded on a highly liquid-absorbent recording medium such as plain paper, and can also provide an ink-jet ink having excellent continuous ejection properties. The reason for this is unclear, but is thought to be as follows. The ink of the present invention contains surfactant B, which is one or more selected from the group consisting of acetylene-based surfactants and silicone-based surfactants. The surfactant B has high adsorption to the ink-gas-liquid interface at the tip of the inkjet nozzle, contributes to the appropriate formation of a meniscus at the ink-gas-liquid interface, and enables the ink to be stably and continuously ejected from the inkjet nozzle, and is therefore considered to have the effect of enhancing continuous ejection. On the other hand, the surfactant B is also partially adsorbed to the pigment, and also has the effect of preventing the effect of aggregation or thickening caused by polyvalent metal salts present on the surface of plain paper commonly used for inkjet recording. Therefore, in the present invention, by setting the content of surfactant B to a specific value or less, it is possible to suppress the adsorption of surfactant B to the pigment and to suppress the effect of preventing the effect of aggregation or thickening caused by polyvalent metal salts present on the surface of plain paper, and it is considered that both excellent continuous ejection and high image density can be achieved. The ink of the present invention also contains surfactant A, which is one or more surfactants selected from the group consisting of polyoxyethylene alkyl ethers, polyoxyethylene alkenyl ethers, polyoxyethylene aryl ethers, and anionic surfactants. It is believed that surfactant A enhances the function of stably dispersing the wax in the ink while exerting the function of improving the abrasion resistance of the wax, thereby contributing to the improvement of continuous ejection properties.

[0009] <Pigments> The pigment may be either an inorganic pigment or an organic pigment, and a lake pigment or a fluorescent pigment may also be used. If necessary, these pigments may also be used in combination with an extender pigment. Specific examples of inorganic pigments include carbon black, metal oxides such as titanium oxide, iron oxide, red iron oxide, and chromium oxide, pearlescent pigments, etc. Examples of carbon black include furnace black, lamp black, acetylene black, and channel black. Specific examples of organic pigments include azo pigments such as azo lake pigments, insoluble monoazo pigments, insoluble disazo pigments, and chelate azo pigments; and polycyclic pigments such as phthalocyanine pigments, perylene pigments, perinone pigments, anthraquinone pigments, quinacridone pigments, dioxazine pigments, thioindigo pigments, isoindolinone pigments, quinophthalone pigments, diketopyrrolopyrrole pigments, benzimidazolone pigments, and threne pigments. In the achromatic ink, achromatic pigments such as white, black, and gray can be used, while in the chromatic ink, chromatic organic pigments such as yellow, magenta, cyan, blue, red, orange, and green can be used. Specific examples of preferred organic pigments include one or more product numbers selected from 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. The pigments can be used alone or in combination of two or more.

[0010] The pigment in the ink of the present invention may be in the form of a pigment dispersed with a polymer dispersant or a surfactant as a dispersant, or in the form of a self-dispersing pigment dispersed without the use of a dispersant. The polymer dispersant may be either a water-soluble polymer or a water-insoluble polymer. Here, the "water-soluble" and "water-insoluble" of a polymer are determined as follows: when a polymer is dried at 105°C for 2 hours and allowed to reach a constant weight, and then dissolved in 100 g of water at 25°C until saturation is reached, if the amount dissolved exceeds 10 g, the polymer is determined to be "water-soluble," and if the amount dissolved is 10 g or less, the polymer is determined to be "water-insoluble." In addition, when a polymer has an anionic group and the anionic group is neutralized with a neutralizer when the polymer is blended into the ink of the present invention, the "water-soluble" and "water-insoluble" are determined based on 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 the polymer is blended into the ink of the present invention.

[0011] Specifically, from the viewpoint of improving the dispersion stability of the pigment and improving the continuous dischargeability, preferred forms of the pigment in the ink of the present invention include (I) a form in which a water-soluble polymer is adsorbed as a polymer dispersant on the pigment surface, (II) a form in which a water-soluble surfactant or a water-dispersible surfactant is adsorbed on the pigment surface, (III) a form of a self-dispersing pigment in which a hydrophilic functional group is chemically or physically introduced on the pigment surface and dispersed without using a polymer dispersant or a surfactant, and (IV) a form in which the pigment is coated with a water-insoluble polymer as a polymer dispersant, etc. Among these, from the viewpoint of the same as above, the form of the pigment in the ink of the present invention is more preferably one or more forms selected from the group consisting of form (III) and form (IV), and even more preferably form (IV). (IV) As a form in which a pigment is coated with a water-insoluble polymer as a polymer dispersant (hereinafter, the water-insoluble polymer is also referred to as "water-insoluble polymer (p)"), a particle of the water-insoluble polymer (p) containing the pigment (hereinafter, also referred to as "pigment-containing polymer particle") is preferable. The form of the pigment-containing polymer particle includes a form in which the water-insoluble polymer (p) encapsulates the pigment, a form in which the pigment is uniformly dispersed in the water-insoluble polymer (p), a form in which the pigment is exposed from the surface of the water-insoluble polymer (p) particle, a form in which the water-insoluble polymer (p) is adsorbed to the pigment, and a mixture thereof.

[0012] As the water-insoluble polymer (p), it is preferable to use those described in paragraphs

[0013] to

[0019] of JP 2022-104084 A, and a vinyl-based polymer obtained by addition polymerization of a vinyl monomer (vinyl compound, vinylidene compound, vinylene compound) is more preferable. From the viewpoint of improving the dispersion stability of the pigment and improving the continuous dischargeability, the water-insoluble polymer (p) is preferably a vinyl-based polymer containing a constituent unit derived from an ionic vinyl monomer, more preferably a vinyl-based polymer containing a constituent unit derived from an ionic vinyl monomer and a constituent unit derived from a hydrophobic vinyl monomer, and even more preferably a vinyl-based polymer containing a constituent unit derived from an ionic vinyl monomer, a constituent unit derived from a hydrophobic vinyl monomer, and a constituent unit derived from a nonionic monomer.

[0013] The ionic monomer is preferably an anionic monomer, more preferably a carboxylic acid monomer or a sulfonic acid monomer, and further preferably a carboxylic acid monomer. The carboxylic acid monomer is preferably one or more selected from (meth)acrylic acid, crotonic acid, itaconic acid, maleic acid, fumaric acid, and citraconic acid, and more preferably (meth)acrylic acid. "(Meth)acrylic acid" means at least one selected from the group consisting of acrylic acid and methacrylic acid. "(Meth)" in the following also has the same meaning.

[0014] The term "hydrophobic" for the hydrophobic monomer 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. Specific examples of the hydrophobic monomer include those described in paragraphs

[0020] to

[0022] of JP 2018-83938 A. Among these, alkyl (meth)acrylates having an alkyl group having 1 to 18 carbon atoms, particularly 1 to 10 carbon atoms, aromatic group-containing monomers having an aromatic group having 6 to 22 carbon atoms, macromonomers having a polymerizable functional group at one end, and the like are preferred, and one or more selected from the group consisting of alkyl (meth)acrylates having an alkyl group having 1 to 10 carbon atoms, styrene, α-methylstyrene, benzyl (meth)acrylate, and styrene-based macromonomers are more preferred.

[0015] The nonionic monomer is a monomer that has high affinity with water or a water-soluble organic solvent, and is, for example, a monomer that contains a hydroxy group or a polyalkylene glycol chain. Specific examples of the nonionic monomer include those described in paragraph

[0018] of JP 2018-83938 A. Among these, one or more selected from the group consisting of methoxypolyethylene glycol (n = 1 to 30, n indicates the average number of moles of oxyalkylene groups added. The same applies below) (meth)acrylate and polypropylene glycol (n = 2 to 30) (meth)acrylate are preferred. The ionic monomer, the hydrophobic monomer, and the nonionic monomer may each be used alone or in combination of two or more kinds of monomer components contained in each component.

[0016] The weight average molecular weight of the water-insoluble polymer (p) is preferably 7,000 or more, more preferably 10,000 or more, even more preferably 30,000 or more, and preferably 100,000 or less, more preferably 80,000 or less, even more preferably 60,000 or less. The weight average molecular weight of the water-insoluble polymer (p) is measured by the method described in the Examples. From the viewpoint of improving the dispersion stability of the pigment and improving the continuous dischargeability, the acid value of the water-insoluble polymer (p) is preferably 60 mgKOH / g or more, more preferably 70 mgKOH / g or more, even more preferably 80 mgKOH / g or more, still more preferably 90 mgKOH / g or more, even more preferably 100 mgKOH / g or more, and is preferably 350 mgKOH / g or less, more preferably 300 mgKOH / g or less, and even more preferably 250 mgKOH / g or less. The acid value of the water-insoluble polymer (p) can be calculated from the mass ratio of the constituent monomers. When using a commercially available product, the published value may be referred to.

[0017] From the viewpoint of improving the dispersion stability of the pigment and improving the continuous dischargeability, the pigment dispersed in the polymer dispersant is preferably one in which the polymer dispersant is crosslinked with a crosslinking agent, i.e., a pigment dispersed in a polymer dispersant having a crosslinked structure (hereinafter also referred to as a "crosslinked polymer dispersant"). When the form of the pigment in the ink of the present invention is form (IV), it is preferably in the form of a water-insoluble crosslinked polymer particle containing the pigment (hereinafter also referred to as a "pigment-containing crosslinked polymer particle"). The pigment-containing crosslinked polymer particle is composed of a pigment and a crosslinked polymer, and the crosslinked polymer is preferably one that has a structure derived from the polymer dispersant and a structure derived from the crosslinking agent, and more preferably one that has a structure derived from the water-insoluble polymer (p) and a structure derived from the crosslinking agent, i.e., one that is crosslinked with the water-insoluble polymer (p) by a crosslinking agent. The crosslinking agent may be a compound having two or more functional groups capable of reacting with the functional group of the polymer dispersant. For example, when the water-insoluble polymer (p) as the polymer dispersant has a carboxy group, the crosslinking agent may preferably be a polyglycidyl ether compound of a polyhydric alcohol.

[0018] When the pigment in the ink of the present invention is in the form of (IV), the pigment is preferably blended as an aqueous dispersion of pigment-containing polymer particles or pigment-containing crosslinked polymer particles (hereinafter also referred to as "pigment dispersion"). The pigment dispersion can be efficiently produced by the method described in paragraphs

[0022] to

[0026] of JP-A-2022-104084.

[0019] From the viewpoint of improving the dispersion stability of the pigment and improving the continuous dischargeability, the average particle size of the pigment-containing polymer particles or pigment-containing crosslinked polymer particles in the pigment dispersion is preferably 60 nm or more, more preferably 70 nm or more, even more preferably 80 nm or more, still more preferably 90 nm or more, and is preferably 200 nm or less, more preferably 170 nm or less, and even more preferably 130 nm or less. The average particle size is measured by the method described in the Examples. It is preferable that the pigment-containing polymer particles or pigment-containing crosslinked polymer particles do not swell or shrink, and do not aggregate with each other, and the average particle size of the pigment-containing polymer particles or pigment-containing crosslinked polymer particles in the ink of the present invention is preferably the same as the average particle size in the pigment dispersion. That is, the preferred embodiment of the average particle size of the pigment-containing polymer particles or pigment-containing crosslinked polymer particles 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 or pigment-containing crosslinked polymer particles in the pigment dispersion.

[0020] The content of the pigment in the ink of the present invention is preferably 2% by mass or more, more preferably 4% by mass or more, and even more preferably 5% by mass or more from the viewpoint of ensuring the image density of the obtained recorded matter, and is preferably 30% by mass or less, more preferably 20% by mass or less, even more preferably 15% by mass or less, and even more preferably 10% by mass or less, from the viewpoint of suppressing thickening of the ink and improving continuous ejection properties, and from the viewpoint of improving the abrasion resistance of the recorded matter. The content of the polymer dispersant or crosslinked polymer dispersant in the ink of the present invention is preferably 1% by mass or more, more preferably 2% by mass or more, and even more preferably 2.5% by mass or more, from the viewpoint of improving the dispersion stability of the pigment and thereby improving the continuous ejection property, and from the viewpoint of improving the scratch resistance of the obtained recorded matter, and is preferably 10% by mass or less, more preferably 7% by mass or less, and even more preferably 5% by mass or less, from the viewpoint of improving the image density. The mass ratio of the content of the pigment in the ink of the present invention to the total content of the pigment and the polymer dispersant or crosslinked polymer dispersant [pigment / (pigment+polymer dispersant or crosslinked polymer dispersant)] is, from the viewpoint of improving image density, preferably 0.3 or more, more preferably 0.5 or more, and even more preferably 0.6 or more, and from the viewpoint of improving the dispersion stability of the pigment and improving the continuous ejection property, and from the viewpoint of improving the abrasion resistance of the obtained recorded matter, it is preferably 0.9 or less, more preferably 0.85 or less, and even more preferably 0.8 or less.

[0021] <Wax> The ink of the present invention contains a wax from the viewpoint of improving abrasion resistance. The wax may be either a natural wax or a synthetic wax. Examples of natural waxes include petroleum waxes such as paraffin wax and microcrystalline wax; vegetable waxes such as carnauba wax, candelilla wax and rice wax; and animal waxes such as lanolin and beeswax. Examples of synthetic waxes include synthetic hydrocarbon waxes such as polyolefin wax and Fischer-Tropsch wax; silicone waxes; and modified waxes such as paraffin wax derivatives, montan wax derivatives, and microcrystalline wax derivatives. The waxes can be used alone or in combination of two or more.

[0022] The melting point of the wax is preferably 80°C or higher, more preferably 100°C or higher, even more preferably 120°C or higher, still more preferably 130°C or higher, and is preferably 160°C or lower, more preferably 155°C or lower, and even more preferably 150°C or lower, from the viewpoint of preventing the wax from sinking into the ink coating when an image consisting of an ink coating formed on a recording medium is dried, thereby improving abrasion resistance. The melting point of the wax is measured by the method described in the Examples.

[0023] Among these, from the viewpoint of improving continuous dischargeability and improving abrasion resistance, it is preferable that the wax contains a polyolefin wax containing an olefin monomer as a main component. Examples of the olefin monomer that is the main component of the polyolefin wax include linear olefins and cyclic olefins. Preferably, the main component is a linear olefin having 2 to 6 carbon atoms. More preferably, the polyolefin wax is mainly composed of ethylene or propylene. Even more preferably, the polyolefin wax is mainly composed of ethylene. Here, "containing ethylene or propylene as a main component" means that the content of ethylene or propylene relative to the total components constituting the wax is preferably 50 mass% or more, more preferably 65 mass% or more, and even more preferably 80 mass% or more. Oxidized polyolefin waxes are included in the category of polyolefin waxes, and can be obtained by introducing oxygen atoms or the like into the molecules of high molecular weight polyolefin polymers while adjusting the molecular weight to a desired value by thermal decomposition or the like. That is, from the viewpoint of improving abrasion resistance, the polyolefin wax is preferably at least one selected from the group consisting of polyethylene wax, polypropylene wax, and oxidized polyethylene wax, and more preferably oxidized polyethylene wax. Suitable examples of commercially available polyethylene waxes include the "Hiwax" series manufactured by Mitsui Chemicals, Inc. and the "Sunwax" series manufactured by Sanyo Chemical Industries, Ltd.

[0024] In the present invention, the wax may contain waxes other than the polyolefin wax within the range that does not impair the effects of the present invention. The content of the polyolefin wax in the wax 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.

[0025] The wax in the ink of the present invention is preferably in the form of wax particles dispersed in an aqueous medium. The wax particles are composed of a wax and a dispersant. The dispersant is preferably a surfactant, more preferably at least one selected from the group consisting of nonionic surfactants and anionic surfactants. In this case, the wax is preferably blended as a dispersion of wax particles dispersed in an aqueous medium (hereinafter also referred to as "wax dispersion"). There are no particular limitations on the method for producing the wax dispersion, and examples include a method of mixing and emulsifying the wax with a known surfactant. Among these, the wax is preferably one dispersed by the surfactant A. In this case, the wax is preferably blended as a dispersion of wax particles (wax dispersion) in which the wax is dispersed in an aqueous medium by the surfactant A. The surfactant A will be described later.

[0026] From the viewpoint of improving continuous dischargeability, the average particle size of the wax particles in the wax dispersion is preferably 20 nm or more, more preferably 30 nm or more, and even more preferably 40 nm or more, and is preferably 130 nm or less, more preferably 100 nm or less, and even more preferably 70 nm or less. The average particle size is measured by the method described in the Examples. It is preferable that the wax particles do not swell or shrink, and do not aggregate with each other. The average particle size of the wax particles in the ink of the present invention is preferably the same as the average particle size in the wax dispersion. The preferred embodiment of the average particle size of the wax particles in the ink of the present invention is the same as the preferred embodiment of the average particle size of the wax particles in the wax dispersion.

[0027] From the viewpoint of improving abrasion resistance, the content of wax in the ink of the present invention is preferably 0.2% by mass or more, more preferably 0.4% by mass or more, even more preferably 0.6% by mass or more, still more preferably 0.8% by mass or more, and still more preferably 1.0% by mass or more, and from the viewpoint of improving image density and continuous jetting ability, the content of wax in the ink of the present invention is preferably 3.0% by mass or less, more preferably 2.4% by mass or less, even more preferably 1.8% by mass or less, and still more preferably 1.2% by mass or less. In the present invention, when the wax is dispersed by surfactant A, the total content of the wax and surfactant A in the ink of the present invention is, from the viewpoint of improving abrasion resistance, preferably 0.4% by mass or more, more preferably 0.8% by mass or more, even more preferably 1.0% by mass or more, and still more preferably 1.2% by mass or more, and from the viewpoint of suppressing a decrease in image density and continuous jetting ability due to surfactant A used as a wax dispersant, preferably 3.6% by mass or less, more preferably 3.0% by mass or less, even more preferably 2.4% by mass or less, and still more preferably 1.8% by mass or less.

[0028] <Surfactant> The ink of the present invention contains a surfactant. The surfactant includes surfactant A which is one or more types selected from the group consisting of polyoxyethylene alkyl ethers, polyoxyethylene alkenyl ethers, polyoxyethylene aryl ethers, and anionic surfactants, and surfactant B which is one or more types selected from the group consisting of acetylene-based surfactants and silicone-based surfactants.

[0029] (Surfactant A) The surfactant A is at least one selected from the group consisting of polyoxyethylene alkyl ethers, polyoxyethylene alkenyl ethers, polyoxyethylene aryl ethers, and anionic surfactants. The surfactant A can be used alone or in combination of two or more kinds. In the present invention, the surfactant A preferably acts as a dispersant in a wax dispersion composed of a wax and a dispersant.

[0030] The alkyl group in the polyoxyethylene alkyl ether preferably has a carbon number of 8 to 22, more preferably 10 to 20, and even more preferably 12 to 18. Preferred examples of the polyoxyethylene alkyl ether include one or more selected from the group consisting of polyoxyethylene lauryl ether, polyoxyethylene myristyl ether, polyoxyethylene cetyl ether, and polyoxyethylene stearyl ether. The alkenyl group in the polyoxyethylene alkenyl ether preferably has a carbon number of 8 to 22, more preferably 10 to 20, and even more preferably 12 to 18. A preferred example of the polyoxyethylene alkenyl ether is polyoxyethylene oleyl ether. Preferred examples of the polyoxyethylene aryl ether include one or more members selected from the group consisting of polyoxyethylene distyrenated phenyl ether and polyoxyethylene tribenzyl phenyl ether. The average number of moles of ethylene oxide added in the polyoxyethylene alkyl ether, polyoxyethylene aryl ether, and polyoxyethylene alkenyl ether is, from the viewpoint of increasing the dispersion stability of the wax and improving continuous dischargeability, preferably 6 or more, more preferably 8 or more, and even more preferably 10 or more, and from the same viewpoint as above, is preferably 20 or less, more preferably 16 or less, and even more preferably 14 or less.

[0031] Preferred examples of the anionic surfactant include one or more selected from the group consisting of polyoxyethylene alkyl ether sulfates, polyoxyethylene alkyl ether carboxylates, polyoxyethylene alkyl ether phosphates, saturated fatty acid salts, and unsaturated fatty acid salts. The counter ion of the anionic group of the anionic surfactant is preferably an alkali metal ion, an ammonium ion (NH + ) and organic ammonium ions. Suitable examples of the organic ammonium ion include the ammonium ion of an alkylamine and the ammonium ion of an alcoholamine. Among these, the organic ammonium ion is preferably the ammonium ion of an alcoholamine, more preferably the ammonium ion of an ethanolamine, and further preferably the ammonium ion of a diethylethanolamine.

[0032] Preferred examples of the anionic surfactant include one or more selected from the group consisting of sodium stearate, potassium stearate, diethylethanolamine stearate, triethanolamine stearate, sodium laurate, potassium laurate, diethylethanolamine laurate, triethanolamine stearate, sodium oleate, potassium oleate, diethylethanolamine oleate, and triethanolamine stearate, and more preferred are one or more selected from the group consisting of diethylethanolamine oleate and potassium oleate.

[0033] (Surfactant B) The ink of the present invention contains, in addition to surfactant A, surfactant B which is at least one type selected from acetylene-based surfactants and silicone-based surfactants. The surfactant B can be used alone or in combination of two or more kinds. As described above, it is believed that Surfactant B has a high adsorptivity to the ink-gas-liquid interface at the tip of the inkjet nozzle, thereby contributing to the appropriate formation of a meniscus at the ink-gas-liquid interface and improving the continuous ejection of ink.

[0034] The HLB value of surfactant B is preferably 13.5 or less, more preferably 10 or less, and even more preferably 7 or less, from the viewpoint of increasing the adsorption to the ink-liquid interface at the tip of the inkjet nozzle and thereby improving the continuous ejection properties of the ink, and from the viewpoint of improving image density. In the present invention, the HLB value is a value indicating the affinity of a surfactant to water and oil as a hydrophilic-lipophilic balance, and can be calculated by the following formula according to the Griffin method. The catalog value of each product can also be referred to. HLB value = 20 x [(molecular weight of hydrophilic group contained in surfactant) / (molecular weight of surfactant)] Examples of the hydrophilic group contained in the surfactant include a hydroxy group and an ethyleneoxy group.

[0035] Preferred examples of the acetylene surfactant include acetylene alcohols such as 2,4,7,9-tetramethyl-5-decyne-4,7-diol, 3,6-dimethyl-4-octyne-3,6-diol, 3,5-dimethyl-1-hexyne-3-ol, 2,4-dimethyl-5-hexyne-3-ol, 2,5-dimethyl-3-hexyne-2,5-diol, and 2,5,8,11-tetramethyl-6-dodecyne-5,8-diol, as well as ethylene oxide adducts of the acetylene alcohols. Among these, from the viewpoint of improving the adsorption to the ink gas-liquid interface at the tip of the inkjet nozzle to improve the continuous ejection properties of the ink, and from the viewpoint of improving image density, the acetylene-based surfactant is more preferably one or more selected from the group consisting of acetylene-based diols and ethylene oxide adducts of the acetylene-based diols, even more preferably one or more selected from the group consisting of 2,4,7,9-tetramethyl-5-decyne-4,7-diol and ethylene oxide adducts of 2,4,7,9-tetramethyl-5-decyne-4,7-diol, and still more preferably an ethylene oxide adduct of 2,4,7,9-tetramethyl-5-decyne-4,7-diol.

[0036] The average number of moles of ethylene oxide added in the acetylene surfactant (hereinafter also referred to as "average number of moles of EO added") is, from the viewpoint of increasing the adsorption to the ink-liquid interface at the tip of the inkjet nozzle to improve the continuous ejection properties of the ink, and from the viewpoint of improving image density, preferably 35 moles or less, more preferably 30 moles or less, even more preferably 25 moles or less, still more preferably 20 moles or less, still more preferably 15 moles or less, still more preferably 10 moles or less, still more preferably 5 moles or less, still more preferably 2 moles or less, and preferably 1 mole or more.

[0037] The HLB value of the acetylene-based surfactant is preferably 13.5 or less, more preferably 10 or less, and even more preferably 7 or less, from the viewpoint of increasing the adsorption to the ink-liquid interface at the tip of the inkjet nozzle and improving the continuous ejection of the ink, and from the viewpoint of improving the image density.

[0038] Commercially available acetylene surfactants include Surfynol 104 (2,4,7,9-tetramethyl-5-decyne-4,7-diol, average EO adduct number: 0, HLB value: 3) from Nissin Chemical Industry Co., Ltd., Surfynol 104E (2,4,7,9-tetramethyl-5-decyne-4,7-diol diluted with 50% ethylene glycol), Surfynol 104PG-50 (2,4,7,9-tetramethyl-5-decyne-4,7-diol diluted with 50% propylene glycol), and Surfynol 420 (2,4,7,9-tetramethyl-5-decyne-4,7-diol with EO adduct (EO) Examples of such compounds include Surfynol 440 (EO adduct of 2,4,7,9-tetramethyl-5-decyne-4,7-diol (average number of moles added by EO: 3.5), HLB value: 8 (catalog value)), Surfynol 465 (EO adduct of 2,4,7,9-tetramethyl-5-decyne-4,7-diol (average number of moles added by EO: 10), HLB value: 13 (catalog value)), and Surfynol 485 (EO adduct of 2,4,7,9-tetramethyl-5-decyne-4,7-diol (average number of moles added by EO: 30), HLB value: 17 (catalog value)).

[0039] As the silicone surfactant, a polyether-modified silicone surfactant is preferred from the viewpoint of improving the adsorption to the ink-liquid interface at the tip of the inkjet nozzle to improve the continuous ejection of the ink, and from the viewpoint of improving image density.

[0040] Polyether-modified silicone surfactants have a structure in which the side chain and / or terminal hydrocarbon groups of silicone oil are replaced with polyether groups.As the polyether group, polyethyleneoxy group, polypropyleneoxy group, polyalkyleneoxy group in which ethyleneoxy group (EO) and propyleneoxy group (trimethyleneoxy group or propane-1,2-diyloxy group; PO) are added in block or random form are suitable, and compounds in which polyether group is grafted to silicone main chain, compounds in which silicone and polyether group are bonded in block form, etc. can be used.

[0041] The HLB (hydrophilic lipophilic balance) value of the polyether-modified silicone surfactant is, from the viewpoint of increasing the adsorption to the ink-air interface at the tip of the inkjet nozzle to improve the continuous ejection of the ink, and from the viewpoint of improving image density, preferably 13.5 or less, more preferably 10 or less, even more preferably 7 or less, and is preferably 2 or more, more preferably 3 or more, even more preferably 4 or more.

[0042] Specific examples of polyether-modified silicone surfactants include PEG-3 dimethicone, PEG-9 dimethicone, PEG-9 methyl ether dimethicone, PEG-10 dimethicone, PEG-11 methyl ether dimethicone, PEG / PPG-20 / 22 butyl ether dimethicone, PEG-32 methyl ether dimethicone, PEG-9 polydimethylsiloxyethyl dimethicone, lauryl PEG-9 polydimethylsiloxyethyl dimethicone, and the like. Commercially available polyether-modified silicone surfactants include the KF series manufactured by Shin-Etsu Chemical Co., Ltd., Silface SAG005 manufactured by Nissin Chemical Industry Co., Ltd., and BYK-348 manufactured by BYK Japan K.K.

[0043] As described above, from the viewpoint of improving continuous ejection properties, surfactant B is preferably an acetylene-based surfactant, more preferably one or more selected from the group consisting of acetylene-based diols and ethylene oxide adducts of the acetylene-based diols, even more preferably one or more selected from the group consisting of 2,4,7,9-tetramethyl-5-decyne-4,7-diol and ethylene oxide adducts of 2,4,7,9-tetramethyl-5-decyne-4,7-diol, and even more preferably an ethylene oxide adduct of 2,4,7,9-tetramethyl-5-decyne-4,7-diol.

[0044] From the viewpoints of improving image density and abrasion resistance, and of improving continuous ejection properties, the content of Surfactant A in the ink of the present invention is preferably 0.1% by mass or more, more preferably 0.2% by mass or more, even more preferably 0.3% by mass or more, and still more preferably 0.4% by mass or more, and from the same viewpoints as above, it is preferably 1% by mass or less, more preferably 0.6% by mass or less, and even more preferably 0.5% by mass or less.

[0045] From the viewpoint of improving continuous ejection properties, the content of Surfactant B in the ink of the present invention is preferably 0.005% by mass or more, more preferably 0.01% by mass or more, even more preferably 0.02% by mass or more, and still more preferably 0.04% by mass or more, and from the viewpoint of improving image density, the content of Surfactant B in the ink of the present invention is 0.15% by mass or less, preferably 0.12% by mass or less, more preferably 0.09% by mass or less, and even more preferably 0.06% by mass or less.

[0046] The mass ratio of the content of surfactant B in the ink of the present invention to the content of pigment [surfactant B / pigment] (hereinafter referred to as "mass ratio [surfactant B / pigment]") is preferably 0.0001 or more, more preferably 0.001 or more, even more preferably 0.003 or more, and still more preferably 0.006 or more, from the viewpoint of improving continuous ejection properties, and is preferably 0.025 or less, more preferably 0.02 or less, even more preferably 0.015 or less, and still more preferably 0.01 or less, from the viewpoint of improving image density.

[0047] The mass ratio of the content of surfactant B to the content of surfactant A in the ink of the present invention [surfactant B / surfactant A] (hereinafter referred to as "mass ratio [surfactant B / surfactant A]") is preferably 0.01 or more, more preferably 0.04 or more, and even more preferably 0.08 or more, from the viewpoint of improving continuous ejection properties, and is preferably 0.3 or less, more preferably 0.25 or less, even more preferably 0.2 or less, still more preferably 0.16 or less, and even more preferably 0.12 or less, from the viewpoint of improving image density.

[0048] The mass ratio of the total content of surfactant A and surfactant B in the ink of the present invention to the content of the pigment [(surfactant A + surfactant B) / pigment] (hereinafter referred to as "mass ratio [(surfactant A + surfactant B) / pigment]") is, from the viewpoint of improving continuous ejection property and abrasion resistance, preferably 0.01 or more, more preferably 0.03 or more, even more preferably 0.04 or more, still more preferably 0.05 or more, still more preferably 0.06 or more, still more preferably 0.07 or more, and still more preferably 0.08 or more, and from the viewpoint of improving image density, is preferably 0.125 or less, more preferably 0.12 or less, still more preferably 0.115 or less, still more preferably 0.11 or less, still more preferably 0.105 or less, and still more preferably 0.10 or less.

[0049] <Organic solvent> The ink of the present invention contains an organic solvent. The organic solvents can be used alone or in combination of two or more. From the viewpoint of improving the continuous dischargeability, the organic solvent preferably contains one or more solvents selected from the group consisting of 1,2-alkanediols and polyalkylene glycols.

[0050] In the present invention, the term "1,2-alkanediol" refers to a compound represented by the general formula C n H 2n+2 (n is an integer of 3 or more), in which the hydrogen atom of the terminal primary carbon atom and the hydrogen atom of the secondary carbon atom adjacent to the terminal primary carbon atom are each substituted with a hydroxy group. Compared to alkanediols other than 1,2-alkanediols with the same number of carbon atoms, 1,2-alkanediols have a structure in which two highly polar hydroxyl groups are unevenly distributed on one side of the molecule, and therefore have excellent interfacial tension reducing ability. Therefore, it is believed that it can contribute to improving continuous ejection by further suppressing the adsorption of the acetylene-based surfactant and silicone-based surfactant of surfactant B to the pigment, while at the same time increasing the dispersion stability of the wax.

[0051] In the present invention, the number of carbon atoms in the 1,2-alkanediol is 3 or more, preferably 4 or more, more preferably 5 or more, and even more preferably 6 or more, from the viewpoints described above, and is preferably 14 or less, more preferably 12 or less, even more preferably 10 or less, and even more preferably 8 or less, from the viewpoints described above. In the present invention, the 1,2-alkanediol is preferably, for example, one or more selected from the group consisting of 1,2-propanediol, 1,2-butanediol, 1,2-pentanediol, 1,2-hexanediol, 1,2-heptanediol, 1,2-octanediol, 1,2-nonanediol, 1,2-decanediol, 1,2-dodecanediol, and 1,2-tetradecanediol. Among these, the 1,2-alkanediol is more preferably one or more selected from the group consisting of 1,2-pentanediol and 1,2-hexanediol, and further preferably 1,2-hexanediol.

[0052] In the present invention, the term "polyalkylene glycol" refers to a compound in which two or more molecules of alkylene glycol are condensed. Since polyalkylene glycol has hydroxy groups at both ends of its molecular structure, it is believed that it can increase the moisture retention of the ink of the present invention and improve the intermittent ejection properties. Here, "intermittent ejection properties" refers to the ejection properties when the ink is ejected again after a predetermined time has elapsed without ejecting the ink from the inkjet nozzle. In the present invention, the number of carbon atoms in the polyalkylene glycol is preferably 4 or more, more preferably 6 or more, from the viewpoint of improving continuous ejection properties and intermittent ejection properties, and from the same viewpoint as above, it is preferably 9 or less, more preferably 8 or less. In the present invention, the number of condensed molecules of alkylene glycol constituting the polyalkylene glycol is preferably 2 or more, and is preferably 4 or less, more preferably 3 or less, and even more preferably 2, from the viewpoint of improving continuous ejection properties and intermittent ejection properties. In the present invention, the polyalkylene glycol is preferably at least one selected from the group consisting of diethylene glycol, triethylene glycol, tetraethylene glycol, dipropylene glycol, and tripropylene glycol. Among these, the polyalkylene glycol is more preferably at least one selected from the group consisting of diethylene glycol and dipropylene glycol, and further preferably dipropylene glycol.

[0053] In the present invention, the organic solvent preferably contains at least 1,2-alkanediol from the viewpoint of improving the continuous dischargeability. In this case, the organic solvent preferably further contains an organic solvent other than 1,2-alkanediol from the viewpoint of improving the continuous dischargeability. As such an organic solvent, the above-mentioned polyalkylene glycol is preferably mentioned. Furthermore, the ink of the present invention may contain an organic solvent other than 1,2-alkanediol and polyalkylene glycol. Preferred examples of such organic solvents include polyhydric alcohols other than 1,2-alkanediol and polyalkylene glycol, glycol ethers, nitrogen-containing heterocyclic compounds, etc. Among these, from the viewpoint of improving the dispersion stability of the pigment dispersion and improving the continuous ejection property, polyhydric alcohols other than 1,2-alkanediol and polyalkylene glycol are preferred.

[0054] From the viewpoint of improving continuous ejection property and intermittent ejection property, the content of the organic solvent 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 5% by mass or more, still more preferably 8% by mass or more, and still more preferably 9% by mass or more, and from the same viewpoint as above, it is preferably 20% by mass or less, more preferably 15% by mass or less, still more preferably 13% by mass or less, and still more preferably 11% by mass or less.

[0055] When the ink of the present invention contains a 1,2-alkanediol, the content of 1,2-alkanediol in the ink of the present invention is, from the viewpoint of improving continuous ejection properties, preferably 1.5% by mass or more, more preferably 2% by mass or more, even more preferably 3% by mass or more, still more preferably 3.5% by mass or more, and still more preferably 4% by mass or more, and from the same viewpoints as above, preferably 20% by mass or less, more preferably 15% by mass or less, even more preferably 13% by mass or less, still more preferably 10% by mass or less, still more preferably 8% by mass or less, and still more preferably 6% by mass or less.

[0056] When the ink of the present invention contains polyalkylene glycol, the content of polyalkylene glycol in the ink of the present invention is, from the viewpoint of improving continuous ejection properties and intermittent ejection properties, preferably 1% by mass or more, more preferably 2% by mass or more, even more preferably 3.5% by mass or more, and even more preferably 4.5% by mass or more, and from the same viewpoints as above, preferably 11% by mass or less, more preferably 9% by mass or less, even more preferably 8% by mass or less, even more preferably 7% by mass or less, and even more preferably 6% by mass or less.

[0057] In the ink of the present invention, when a 1,2-alkanediol and a polyalkylene glycol are contained as the organic solvent, the total content of the 1,2-alkanediol and the polyalkylene glycol in the organic solvent is, from the viewpoint of improving the continuous ejection properties and the intermittent ejection properties, preferably 70% by mass or more, more preferably 80% by mass or more, even more preferably 90% by mass or more, still more preferably 95% by mass or more, still more preferably 99% by mass or more, and still more preferably 100% by mass. When the ink of the present invention contains 1,2-hexanediol as the 1,2-alkanediol and further contains dipropylene glycol as the polyalkylene glycol, the total content of 1,2-hexanediol and dipropylene glycol in the organic solvent in the ink of the present invention is, from the viewpoint of improving the continuous ejection properties and the intermittent ejection properties, preferably 70% by mass or more, more preferably 80% by mass or more, even more preferably 90% by mass or more, still more preferably 95% by mass or more, still more preferably 99% by mass or more, and still more preferably 100% by mass.

[0058] When the ink of the present invention contains a 1,2-alkanediol and a polyalkylene glycol as organic solvents, the mass ratio of the polyalkylene glycol content to the 1,2-alkanediol content in the ink of the present invention [polyalkylene glycol / 1,2-alkanediol] is, from the viewpoint of improving continuous ejection properties and intermittent ejection properties, preferably 0.4 or more, more preferably 0.6 or more, and even more preferably 0.9 or more, and from the same viewpoints as above, is preferably 3 or less, more preferably 2 or less, even more preferably 1.7 or less, even more preferably 1.3 or less, and even more preferably 1.1 or less.

[0059] When the ink of the present invention contains 1,2-hexanediol as the 1,2-alkanediol and further contains dipropylene glycol as the polyalkylene glycol, the mass ratio of the dipropylene glycol content to the 1,2-hexanediol content in the ink of the present invention [dipropylene glycol / 1,2-hexanediol] is, from the viewpoint of improving the continuous ejection properties and the intermittent ejection properties, preferably 0.4 or more, more preferably 0.6 or more, and even more preferably 0.9 or more, and from the same viewpoints as above, is preferably 3 or less, more preferably 2 or less, even more preferably 1.7 or less, even more preferably 1.3 or less, and even more preferably 1.1 or less.

[0060] <Water> The ink of the present invention contains water. The ink of the present invention is preferably a water-based ink for ink-jet printing in which water accounts for the largest proportion by mass of the liquid components of the ink.

[0061] The water content in the ink of the present invention is preferably 50% by mass or more, more preferably 60% by mass or more, even more preferably 70% by mass or more, and preferably 90% by mass or less, more preferably 87% by mass or less, even more preferably 85% by mass or less.

[0062] (Inkjet recording method) The ink of the present invention is preferably used in an inkjet recording method in which the ink is loaded into a known inkjet recording apparatus and ejected as ink droplets onto a recording medium to record an image, etc. Ink droplet ejection methods in inkjet recording methods include a piezoelectric method, a thermal method, and an electrostatic method, with the piezoelectric method being preferred. Examples of the recording medium include highly liquid-absorbent recording media such as plain paper and wood-free paper, low liquid-absorbent recording media such as art paper and coated paper, and non-liquid-absorbent recording media such as synthetic resin films. Among these, from the viewpoints of image density and abrasion resistance, the ink of the present invention is preferably used in an inkjet recording method for recording on a highly liquid-absorbent recording medium. In an ink jet recording method using the ink of the present invention, it is preferable to have a step of drying the image formed on the recording medium after ejecting ink droplets onto the recording medium to form an image. The drying temperature and drying time can be appropriately adjusted depending on the composition of the ink of the present invention and the type of recording medium. Suitable means for drying an image on a recording medium include a method of blowing gas adjusted to a desired temperature, a method of passing an image on a print recording medium through a gas atmosphere adjusted to a desired temperature, a method of irradiating an image on a recording medium with an infrared heater, and a method of heating with a platen heater. EXAMPLES

[0063] 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.

[0064] (1) Measurement of weight average molecular weight of water-insoluble polymer (p) The measurement was performed by gel permeation chromatography under the following conditions. GPC equipment: Tosoh Corporation "HLC-8320GPC" Column: 2 x "TSKgel α-M" (Tosoh Corporation) Eluent: N,N-dimethylformamide (Fujifilm Wako Pure Chemical Industries, Ltd., for high performance liquid chromatography) dissolved with phosphoric acid (Fujifilm Wako Pure Chemical Industries, Ltd., special grade reagent) and lithium bromide (Tokyo Chemical Industry Co., Ltd., reagent) to concentrations of 60 mmol / L and 50 mmol / L, respectively. Flow rate: 1mL / min Standard material: Monodisperse polystyrene with known molecular weight

[0065] (2) Measurement of the average particle size of pigment-containing polymer particles or pigment-containing crosslinked polymer particles in a pigment dispersion, and the average particle size of wax particles in a wax dispersion The particle size was measured by dynamic light scattering using a laser particle analysis system "ELS-8000" (manufactured by Otsuka Electronics Co., Ltd.), and calculated by cumulant method analysis. 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 entered as the refractive index of the dispersion solvent. For the measurement sample, the pigment dispersion was weighed into a screw tube (Maruemu Co., Ltd., No. 5) 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.

[0066] (3) Measurement of solids concentration 10.0 g of sodium sulfate, which had been kept constant in a desiccator, was weighed out into a 30 mL polypropylene container (φ: 40 mm, height: 30 mm), and about 1.0 g of the sample was added thereto and mixed, then accurately weighed, and maintained at 105°C for 2 hours to remove volatile matter, and left in the desiccator for 15 minutes before measuring the mass. The mass of the sample after removing the volatile matter was taken as the solid content, and was divided by the mass of the sample added to obtain the solid content concentration (%).

[0067] (4) Measurement of the melting point of wax The melting point of the wax was measured by an apparatus conforming to JIS K 0064:1992. Specifically, using a differential scanning calorimeter (Q20, manufactured by TA Instruments), the sample was heated to 200°C and cooled from that temperature to 0°C at a rate of 10°C / min. Next, the sample was 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.

[0068] Production Example 1-1 (Production of a solution of water-insoluble polymer p1) 16 parts of methacrylic acid (manufactured by FUJIFILM Wako Pure Chemical Industries, Ltd.), 44 parts of styrene (manufactured by FUJIFILM Wako Pure Chemical Industries, Ltd.), 30 parts (15 parts active content) of styrene macromonomer "AS-6S" (manufactured by Toagosei Co., Ltd., number average molecular weight 6,000, solid content 50%), and 25 parts of methoxypolyethylene glycol methacrylate "BLEMMER PME-200" (NOF Corporation) were mixed to prepare 115 parts of a monomer mixture. Into a reaction vessel, 18 parts of methyl ethyl ketone, 0.03 parts of 2-mercaptoethanol as a chain transfer agent, and 10% (11.5 parts) of the monomer mixture were placed and mixed, and the inside of the vessel was thoroughly purged with nitrogen gas. On the other hand, the remaining 90% (103.5 parts) of the monomer mixture, 0.27 parts of the chain transfer agent, 42 parts of methyl ethyl ketone, and 3 parts of 2,2'-azobis(2,4-dimethylvaleronitrile) "V-65" (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) as a polymerization initiator were mixed and placed in a dropping funnel. Under a nitrogen atmosphere, the mixed solution in the reaction vessel was heated to 75°C while stirring, and the mixed solution in the dropping funnel was dropped over 3 hours. After 2 hours at 75°C from the end of the dropping, a solution in which 3 parts of the polymerization initiator were dissolved in 5 parts of methyl ethyl ketone was added, and the mixture was further aged at 75°C for 2 hours and then at 80°C for 2 hours. After cooling to room temperature, 50 parts of methyl ethyl ketone was added to obtain a solution of water-insoluble polymer p1 (weight average molecular weight: 50,000, acid value: 104 mgKOH / g). The solid content concentration of the solution of water-insoluble polymer p1 was 45%.

[0069] Production Example 2-1 (Production of Water Dispersion P-1' of Pigment-Containing Crosslinked Polymer Particles) 95.2 parts of the solution of the water-insoluble polymer p1 obtained in Production Example 1-1 was mixed with 53.9 parts of methyl ethyl ketone, and 15.0 parts of a 5N aqueous sodium hydroxide solution, 0.5 parts of 25% aqueous ammonia, and 341 parts of ion-exchanged water were added as neutralizing agents, and 100 parts of CI Pigment Black 7 (PB7, manufactured by Cabot Corporation) were added as a pigment to obtain a pigment mixture. The degree of neutralization of the water-insoluble polymer p1 was 78.8 mol%. The resulting pigment mixture was mixed for 1 hour using a disperser blade at 7,000 rpm and 20°C, and then dispersed for 15 passes at a pressure of 180 MPa using a microfluidizer "High Pressure Homogenizer M-140K" (Microfluidics Corporation) to obtain a dispersion. The entire amount of the obtained dispersion was placed in a 2L eggplant flask, and ion-exchanged water was added so that the solid concentration was 15%, and then, using a rotary distillation apparatus (Tokyo Rikakikai Co., Ltd., rotary evaporator: N-1000S), the mixture was heated in a warm bath adjusted to 32°C at a rotation speed of 50 r / min and held at a pressure of 0.09 MPa (abs) for 3 hours to remove methyl ethyl ketone. Next, the warm bath was adjusted to 62°C, the pressure was reduced to 0.07 MPa (abs), and the mixture was concentrated until the solid concentration reached 25%, to obtain a concentrate. The obtained concentrate was placed in a 500 mL angle rotor and centrifuged at 3,660 r / min for 20 minutes using a centrifuge (Hitachi Koki Co., Ltd., high-speed refrigerated centrifuge: himac CR22G, set temperature 20°C). The liquid phase was then recovered and filtered through a filter ``Mini Sart Syringe Filter'' (Sartorius, pore size: 5 μm, material: cellulose acetate) to remove coarse particles, thereby obtaining aqueous dispersion P-1 of pigment-containing polymer particles (solid concentration: 25%). To 100 parts of the obtained aqueous dispersion P-1 of pigment-containing polymer particles, 0.45 parts of trimethylolpropane polyglycidyl ether "Denacol EX321L" (manufactured by Nagase Chemtex Corporation) as a crosslinking agent and 15.23 parts of ion-exchanged water were added, and the mixture was heated at 70 ° C for 3 hours while stirring. Then, after cooling to room temperature, the liquid phase portion was collected and filtered with a filter "Mini Sart Syringe Filter" (manufactured by Sartorius, pore size: 5 μm, material: cellulose acetate) to remove coarse particles, and an aqueous dispersion P-1' of pigment-containing crosslinked polymer particles (solid concentration: 22.0%, pigment content: 15.1%, crosslinked polymer dispersant content: 6.9%) (hereinafter also referred to as "pigment dispersion P-1'"). The average particle size of the pigment-containing crosslinked polymer particles in the pigment dispersion P-1' was 100 nm.

[0070] Production Example 3-1 (Production of Wax Dispersion W-1) In an autoclave equipped with a stirrer, a thermometer, and a temperature controller, 23 parts of oxidized polyethylene wax "A-C316" ​​(manufactured by Honeywell, melting point: 140 ° C., acid value 16 mg KOH / g) as a wax, 12 parts of polyoxyethylene oleyl ether (carbon number of alkyl group: 18, average number of moles of ethylene oxide added: 12) as a surfactant A, 0.76 parts of 48% KOH, and 64.24 parts of ion-exchanged water were added, heated to 160 ° C., and then aged for 2 hours while maintaining the temperature at 160 ° C. Then, it was cooled to 40 ° C. to obtain wax dispersion W-1 (solid concentration 35%, average particle size 60 nm).

[0071] Production Example 3-2 (Production of Wax Dispersion W-2) In an autoclave equipped with a stirrer, a thermometer, and a temperature controller, 23 parts of oxidized polyethylene wax "A-C316" ​​(manufactured by Honeywell, melting point: 140 ° C., acid value 16 mg KOH / g) as a wax, 12 parts of polyoxyethylene stearyl ether (number of carbon atoms in alkyl group: 18, average number of moles of ethylene oxide added: 12) as surfactant A, 0.76 parts of 48% KOH, and 64.24 parts of ion-exchanged water were added, heated to 160 ° C., and then aged for 2 hours while maintaining the temperature at 160 ° C. Then, it was cooled to 40 ° C. to obtain wax dispersion W-2 (solid concentration 35%, average particle size 60 nm).

[0072] Production Example 3-3 (Production of Wax Dispersion W-3) In an autoclave equipped with a stirrer, a thermometer, and a temperature controller, 23 parts of oxidized polyethylene wax "A-C316" ​​(manufactured by Honeywell, melting point: 140°C, acid value 16mgKOH / g) as a wax, 8.5 parts of oleic acid as a fatty acid forming surfactant A, 0.76 parts of 48% KOH, 3.5 parts of diethylethanolamine, and 60.24 parts of ion-exchanged water were added, heated to 160°C, and then aged for 2 hours while maintaining the temperature at 160°C. The mixture was then cooled to 40°C to obtain wax dispersion W-3 (solid concentration 35%, average particle size 60nm).

[0073] Production Example 3-4 (Production of Wax Dispersion W-4) In an autoclave equipped with a stirrer, a thermometer, and a temperature controller, 23 parts of ethylene acrylic acid copolymer wax "A-C540" (manufactured by Honeywell, melting point 105 ° C., acid value 40 mg KOH / g) as a wax, 12 parts of polyoxyethylene oleyl ether (carbon number of alkyl group: 18, average number of moles added of ethylene oxide: 12) as a surfactant A, 1.15 parts of 48% KOH, and 63.85 parts of ion-exchanged water were added, heated to 160 ° C., and then aged for 2 hours while maintaining the temperature at 160 ° C. Then, it was cooled to 40 ° C. to obtain wax dispersion W-4 (solid concentration 35%, average particle size 50 nm).

[0074] Example 1 A water dispersion P-1' of pigment-containing crosslinked polymer particles (pigment dispersion P-1') 39.7 parts (pigment: 6.0 parts, crosslinked polymer dispersant: 2.7 parts), wax dispersion W-1 4.3 parts (wax: 1.0 part, surfactant A: 0.5 parts), 1,2-hexanediol (manufactured by Toyo Gosei Co., Ltd.) (hereinafter referred to as "1,2-HD") 5 parts and dipropylene glycol (manufactured by ADEKA Corporation) (hereinafter referred to as "DPG") 5 parts as organic solvents, acetylene surfactant "Surfynol 420" (manufactured by Nissin Chemical Industry Co., Ltd., HLB value: 4 (catalog value), EO average added mole number: 1) 0.05 parts as surfactant B, and ion-exchanged water were mixed to a total amount of 100 parts, and the resulting mixture was filtered with a filter "Mini Sart Syringe Filter" (manufactured by Sartorius, pore size: 5 μm, material: cellulose acetate) to obtain an inkjet recording ink.

[0075] Examples 2 to 25 and Comparative Examples 1 to 3 Each inkjet recording ink was obtained in the same manner as in Example 1, except that the blending compositions in Example 1 were changed to those shown in Tables 1 to 3. The surfactants other than the acetylene-based surfactant used as the surfactant B in Example 1 are as follows. (Acetylene-based surfactants) Surfynol 440: Nissin Chemical Industry Co., Ltd., HLB value: 8 (catalog value), average number of EO moles added: 3.5 Surfynol 465: Nissin Chemical Industry Co., Ltd., HLB value: 13 (catalog value), average number of EO moles added: 10 (Silicone surfactant) KF-6015: Shin-Etsu Chemical Co., Ltd., HLB value: 4.5 (catalog value)

[0076] <Evaluation> (1) Evaluation of image density A4-sized plain paper "NPi Form Next-IJ" (manufactured by Nippon Paper Industries Co., Ltd.) was used as a recording medium, and each of the inkjet recording inks of the examples and comparative examples was used to prepare and evaluate recorded matter by the following inkjet recording method. In an environment of 25±1° C. temperature and 30±5% relative humidity, the inkjet recording ink was filled into a print evaluation device (manufactured by Tritec Corporation) equipped with an inkjet head “KJ4B-HD06MHG-STDV” (manufactured by Kyocera Corporation, piezo type). The head voltage was set to 26V, the frequency to 10kHz, the amount of the discharged liquid to be used to be 12pL, the head temperature to 25°C, the resolution to be 600dpi, and the negative pressure to be -4.0kPa. 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 an image with a duty of 100% was formed. Immediately after the image formation, the image formed on the recording medium was dried for 1 minute in a constant temperature dryer (model: DVS402, manufactured by Yamato Scientific Co., Ltd.) set at a temperature of 70°C, to obtain a recorded matter. The obtained recorded matter was left to stand at room temperature for 24 hours, and then the image density at any five points was measured using a spectrodensitometer / colorimeter "X-Rite eXact" (manufactured by X-rite) under the conditions of light source D50, viewing angle 2°, CIE color system, and filter T, and the average value of the image densities at the five points was calculated as the image density of the recorded matter. The higher the image density value, the better it is considered to be. The results are shown in Tables 1 to 3.

[0077] (2) Evaluation of abrasion resistance A4-sized plain paper "NPi Form Next-IJ" (manufactured by Nippon Paper Industries Co., Ltd.) was used as a recording medium, and each of the inkjet recording inks of the examples and comparative examples was used to prepare and evaluate recorded matter by the following inkjet recording method. In an environment of 25±1° C. temperature and 30±5% relative humidity, the inkjet recording ink was filled into a print evaluation device (manufactured by Tritec Corporation) equipped with an inkjet head “KJ4B-HD06MHG-STDV” (manufactured by Kyocera Corporation, piezo type). The head voltage was set to 26V, the frequency to 10kHz, the amount of the discharged liquid to be used to be 12pL, the head temperature to 25°C, the resolution to be 600dpi, and the negative pressure to be -4.0kPa. 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 an image with a duty of 100% was formed. Immediately after the image formation, the image formed on the recording medium was dried for 1 minute in a constant temperature dryer (model: DVS402, manufactured by Yamato Scientific Co., Ltd.) set at a temperature of 70°C, to obtain a recorded matter. The resulting printed matter was left to stand at room temperature for 24 hours, and then a 2x2cm piece of unprinted, high-quality plain paper "NPi Form Next-IJ" (manufactured by Nippon Paper Industries Co., Ltd.) was placed on the image-formed surface using a Gakushin-type abrasion tester, and the paper was run back and forth 15 times with a load of 7N. The transfer OD of the ink onto the unprinted, high-quality plain paper was measured using a spectrodensitometer "X-Rite eXact" (manufactured by X-rite) under the conditions of light source D50, viewing angle 2°, CIE color system, and filter T, and the average of the transfer ODs at nine points was calculated as an index of abrasion resistance. The results are shown in Tables 1 to 3. It is determined that the lower the transfer OD, the better the abrasion resistance.

[0078] (3) Evaluation of continuous discharge In an environment of temperature 25±1°C and relative humidity 30±5%, an inkjet recording ink of each of the examples and comparative examples was filled into an inkjet discharge evaluation device (manufactured by Seiko Epson Corporation) equipped with an inkjet head "S800-A1" (manufactured by Seiko Epson Corporation, piezo type). The head voltage was set to 37V, the frequency was 25kHz, the push-pull type driving waveform, and the appropriate amount of discharged liquid was 7.5pL, and an ink discharge command was transferred to the discharge evaluation device, and the number of normal discharge nozzles in the initial stage where the ink was normally discharged was confirmed. Continuous discharge was performed for 30 minutes under the same conditions, and the number of normal discharge nozzles after 30 minutes was confirmed. The continuous discharge property (%) was calculated and evaluated using the following formula. It is judged that the larger the continuous discharge property (%), the better it is. The results are shown in Tables 1 to 3. Continuous dischargeability (%) = (number of nozzles discharging normally after 30 minutes / number of nozzles discharging normally at the beginning) x 100

[0079] (4) Evaluation of intermittent ejection In an environment of temperature 25±1°C and relative humidity 30±5%, an inkjet recording ink of each of the examples and comparative examples was filled into an inkjet discharge evaluation device (manufactured by Seiko Epson Corporation) equipped with an inkjet head "S800-A1" (manufactured by Seiko Epson Corporation, piezo type). The head voltage was set to 37V, the frequency was 25kHz, the push-pull type driving waveform, and the appropriate amount of discharged liquid was 7.5pL, and an ink discharge command was transferred to the discharge evaluation device, and the initial number of normal discharge nozzles in which the ink was normally discharged was confirmed. Under the same conditions, the printing machine was stopped for 15 minutes to expose the inkjet head to the atmosphere. After 15 minutes, an ink discharge command similar to the discharge conditions was transferred to the discharge evaluation device, and the number of normal discharge nozzles after 15 minutes of intermittent discharge was observed. The intermittent discharge property was evaluated by calculating (%) using the following formula. It is determined that the intermittent discharge property is superior as the intermittent discharge property (%) increases. The results are shown in Tables 1 to 3. Intermittent discharge performance (%) = (number of nozzles discharging normally after 15 minutes of interruption / number of nozzles discharging normally at the beginning) x 100

[0080] [Table 1]

[0081] [Table 2]

[0082] [Table 3]

[0083] From Tables 1 to 3, it can be seen that the inkjet recording inks of Examples 1 to 25 can provide recorded matter having excellent image density and abrasion resistance even when recording on a highly liquid-absorbent recording medium, and also have excellent continuous ejection properties, compared to the inkjet recording inks of Comparative Examples 1 to 3.

Claims

1. An inkjet recording ink containing a pigment, wax, surfactant, organic solvent, and water, The surfactant comprises one or more surfactants A selected from the group consisting of polyoxyethylene alkyl ethers, polyoxyethylene alkenyl ethers, polyoxyethylene aryl ethers, and anionic surfactants, and one or more surfactants B selected from the group consisting of acetylene-based surfactants and silicone-based surfactants. An inkjet recording ink in which the content of surfactant B is 0.15% by mass or less.

2. The inkjet recording ink according to claim 1, wherein the wax is dispersed by surfactant A.

3. The inkjet recording ink according to claim 1 or 2, wherein the mass ratio of the content of surfactant B in the inkjet recording ink to the content of pigment [surfactant B / pigment] is 0.0001 or more and 0.025 or less.

4. The inkjet recording ink according to claim 1 or 2, wherein the organic solvent contains a 1,2-alkanediol.

5. The inkjet recording ink according to claim 4, wherein the 1,2-alkanediol is 1,2-hexanediol.

6. The inkjet recording ink according to claim 4, wherein the content of 1,2-alkanediol in the inkjet recording ink is 1.5% by mass or more and 20% by mass or less.

7. The inkjet recording ink according to claim 4, wherein the organic solvent further contains polyalkylene glycol.

8. The inkjet recording ink according to claim 7, wherein the polyalkylene glycol is dipropylene glycol.

9. The inkjet recording ink according to claim 1 or 2, wherein the HLB of surfactant B is 13.5 or less.

10. The inkjet recording ink according to claim 1 or 2, wherein the wax content in the inkjet recording ink is 0.2% by mass or more.