Water-based ink for inkjet recording.

Abstract

The present invention provides an inkjet water-based ink that exhibits excellent water repellency for recording heads using silicon or glass components, long-term ejection reliability in inkjet recording, and excellent wetting and spreading of ink dots on a recording medium, as well as an inkjet recording method using the same. [Solution] [1] An inkjet water-based ink for inkjet recording containing a pigment, polymer particles without pigment, an organic solvent, a silicate compound, and water, wherein the solubility of the organic solvent in water is less than 20% by mass, its content is 1 to 15% by mass, and the content of the silicate compound is 2.5 to 250 ppm by mass; and [2] An inkjet recording method using the water-based ink, wherein the ink is ejected from a recording head using one or more selected from silicon and silicon oxide as the nozzle plate member.

Description

Technical Field

[0001] The present invention relates to an aqueous ink for inkjet recording and an inkjet recording method using the same.

Background Art

[0002] The inkjet recording method is a recording method in which ink droplets are directly ejected from fine nozzles and adhered to a recording medium to obtain a recording in which characters and images are recorded. This method has many advantages such as being easily full-color and inexpensive, being able to use plain paper as a recording medium, and being non-contact with the recording medium, so it has become extremely popular. In the commercial printing field, in addition to printing on conventional highly absorbent recording media such as plain paper and copy paper, printing on low-absorbent coated papers such as offset coated paper is also required. In recent years, by using MEMS (Micro Electro Mechanical Systems) technology to process nozzle plates and the like using silicon members and glass members, recording heads with dramatically improved ejection accuracy have come to be used.

[0003] As the ink used in inkjet printers, water-based pigment inks having good light resistance and water resistance as colorants are widely used. However, when such water-based pigment inks are filled in inkjet recording heads using silicon members or glass members, and used or left for a long time, silicon or the like in contact with the ink elutes, the water repellency of the nozzle plate or the like decreases, the ejection design accuracy of the printer decreases, and the image quality may deteriorate. Various proposals have been made to improve the above problems. For example, Patent Document 1 proposes an inkjet ink composition containing a water-soluble alkali metal silicate, self-dispersing polymer particles, and a pigment as an ink composition excellent in dispersion stability and suppressing the decrease in liquid repellency of inkjet recording head members.

Prior Art Documents

Patent Documents

[0004] [Patent Document 1] Japanese Patent Publication No. 2011-057754 [Overview of the project] [Problems that the invention aims to solve]

[0005] The ink composition described in Patent Document 1 suffered from deterioration of ejection performance due to the degradation of the ink over time, and also had insufficient wetting and spreading properties of ink dots on low-water-absorbent recording media. The present invention aims to provide an inkjet water-based ink that exhibits excellent water repellency for recording heads using silicon or glass components, long-term ejection reliability in inkjet recording, and excellent wetting and spreading of ink dots on a recording medium, as well as an inkjet recording method using the same. [Means for solving the problem]

[0006] The present inventors have found that the above-mentioned problems can be solved by including specific amounts of an organic solvent having a specific solubility and a silicate compound in an aqueous inkjet recording ink containing a pigment, polymer particles, an organic solvent, and a silicate compound. In other words, the present invention provides the following [1] and [2]. [1] An inkjet water-based ink containing a pigment, polymer particles without pigment, an organic solvent (C-1), a silicate compound, and water, wherein the solubility of the organic solvent (C-1) in water is less than 20% by mass, the content of the organic solvent (C-1) is 1% by mass or more and 15% by mass or less in the ink, and the content of the silicate compound is 2.5 ppm by mass or more and 250 ppm by mass or less in the ink. [2] An inkjet recording method comprising using the water-based inkjet recording ink described in [1] above, and ejecting ink from a recording head using one or more selected from silicon and silicon oxide as the nozzle plate member. [Effects of the Invention]

[0007] According to the present invention, it is possible to provide an inkjet water-based ink that exhibits excellent water repellency for recording heads using silicon or glass components, excellent long-term ejection reliability in inkjet recording, and excellent wetting and spreading of ink dots on a recording medium, as well as an inkjet recording method using the same. [Modes for carrying out the invention]

[0008] [Water-based ink for inkjet recording] The present invention provides an aqueous inkjet recording ink (hereinafter also referred to as "the present invention ink") which contains a pigment, pigment-free polymer particles, an organic solvent (C-1), a silicate compound, and water, characterized in that the solubility of the organic solvent (C-1) in water is less than 20% by mass, the content of the organic solvent (C-1) in the ink is 1% by mass or more and 15% by mass or less, and the content of the silicate compound in the ink is 2.5 ppm by mass or more and 250 ppm by mass or less.

[0009] In this specification, "aqueous system" means a medium in which water accounts for the largest proportion by mass of the pigment dispersion medium. Furthermore, "record" is a concept that includes printing and printing of text and images, while "record material" is a concept that includes printed materials and printed objects on which text and images are recorded.

[0010] The ink of this invention exhibits excellent water repellency for recording heads using silicon or glass components, long-term ejection reliability in inkjet recording, and superior wetting and spreading of ink dots on recording media. The reason for this is not entirely clear, but it is thought to be as follows. In recording heads where nozzle plates and other components using silicon or glass materials are processed using MEMS technology, silicate ions are normally released from silicon, etc. However, since the ink of the present invention contains silicate compounds such as colloidal silica and sodium silicate, it is believed that the release of silicate ions from silicon, etc. can be suppressed, and even after long-term contact with the ink, the decrease in surface water repellency due to corrosion of the nozzle plate can be suppressed. Another method to improve the wettability and spreadability of ink dots on a recording medium is to include a low-water-soluble organic solvent in the ink. In other words, to improve the wetting spread of dots on the recording medium and suppress the decrease in water repellency of the nozzle plate when in contact with ink for a long period of time, it would be sufficient to include both a low-water-soluble organic solvent and a silicate compound in the ink. However, the solubility of the silicate compound decreases due to the influence of the highly hydrophobic low-water-soluble organic solvent, and the recrystallization and Ostwald aging of the silicate compound are promoted, leading to the significant generation of coarse particles, which in turn creates a new problem of degraded ejection performance. Therefore, the present invention's ink contains an organic solvent (C-1) with a low water solubility of less than 20% by mass, with a content of 1% to 15% by mass, and a silicate compound content of 2.5 ppm to 250 ppm by mass. This is thought to improve the wetting spread of ink dots on the recording medium while suppressing the dissolution of nozzle plate members into the ink and the generation of coarse particles due to the recrystallization of silicate compounds and Ostwald maturation. Furthermore, the present invention's ink contains a sufficient amount of organic solvent (C-1) to promote the wetting spread of ink dots on the recording medium, thereby improving the wetting spread of ink dots after printing, reducing the graininess of the recorded material, and reducing streaks during solid printing.

[0011] <Pigments> The pigments used in the present invention may be either inorganic or organic pigments. 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 slene pigments. The hue is not particularly limited, and any chromatic pigment such as yellow, magenta, cyan, blue, red, orange, and green can be used. Specific examples of preferred pigments include one or more products from each product code selected from CI Pigment Yellow, CI Pigment Red, CI Pigment Orange, CI Pigment Violet, CI Pigment Blue, and CI Pigment Green. Examples of inorganic pigments include metal oxides such as titanium dioxide and zinc oxide, metal salts such as calcium carbonate and calcium sulfate, and carbon black. Among these, carbon black is preferred. The above pigments can be used individually or in combination of two or more.

[0012] The forms of pigments include (i) pigments that can maintain a dispersed state without a dispersant, i.e., self-dispersing pigments; (ii) pigment particles in which the pigment is dispersed with a surfactant; and (iii) polymer particles containing pigment. Among these, the form of "polymer particles containing pigment" is preferred from the viewpoint of improving the long-term ejection reliability of the ink of the present invention and the wettability and spreadability of ink dots on a recording medium, and from the same viewpoint, the form of "crosslinked polymer particles containing pigment" described later is more preferred. In this specification, the form of a pigment-containing polymer particle means a particle in which the polymer encapsulates the pigment, a particle in which a portion of the pigment is exposed on the surface of a particle composed of polymer and pigment, a particle in which the polymer is adsorbed onto a portion of the pigment, and mixtures thereof.

[0013] [Polymer particles containing a pigment] The polymer particles containing a pigment are composed of the above pigment and a polymer (hereinafter also referred to as "polymer (a)") having a function of dispersing the pigment in a medium mainly composed of water. Polymer (a) is not particularly limited as long as it is a polymer having a function of dispersing a pigment in an aqueous medium mainly composed of water. Polymer (a) is preferably a water-insoluble polymer. As used herein, the "water-insoluble polymer" means a polymer that, when a polymer dried at 105 °C for 2 hours to reach a constant weight is dissolved in 100 g of water at 25 °C, has a dissolution amount of less than 10 g. When the polymer is an anionic polymer, the dissolution amount is the dissolution amount when the anionic groups of the polymer are neutralized with sodium hydroxide at 100 mol%.

[0014] [Polymer (a)] Polymer (a) can have any structure, but from the viewpoint of improving the long-term ejection reliability of the ink of the present invention and the wet spreading property of ink dots on a recording medium, vinyl polymers obtained by addition polymerization of vinyl monomers such as vinyl compounds, vinylidene compounds, and vinylene compounds are preferred. As the vinyl polymer, a polymer containing a structural unit derived from an (a-1) ionic monomer is preferred, and a copolymer polymer having a structural unit derived from an (a-1) ionic monomer and a structural unit derived from an (a-2) hydrophobic monomer is more preferred. [(a-1) Ionic monomer] As the (a-1) ionic monomer, anionic monomers are preferred from the viewpoint of improving the dispersion stability of the pigment. Examples of the anionic monomer include carboxylic acid monomers, sulfonic acid monomers, phosphoric acid monomers, etc. Examples of the carboxylic acid monomer include acrylic acid, methacrylic acid, crotonic acid, itaconic acid, maleic acid, fumaric acid, citraconic acid, etc. ​​​Among these, carboxylic acid monomers are more preferred, and one or more selected from acrylic acid and methacrylic acid are even more preferred.

[0016] [[(a - 2) hydrophobic monomer]] (a - 2) hydrophobic monomer is preferably further used as a monomer component in addition to the (a - 1) component from the viewpoint of improving the dispersion stability of the pigment. Specific examples of the (a - 2) component include those described in paragraphs

[0020] to

[0022] of JP - A No. 2018 - 83938. Among these, one or more selected from alkyl (meth) acrylates having an alkyl group with 1 to 22 carbon atoms, styrene, α - methylstyrene, and benzyl (meth) acrylate are preferred.

[0017] [[(a - 3) non - ionic monomer]] (a - 3) non - ionic monomer can be used from the viewpoint of further improving the dispersion stability of the pigment. (a - 3) component is a monomer having a high affinity with water or a water - soluble organic solvent, for example, a monomer containing a hydroxyl group or a polyalkylene glycol chain. Specific examples of the (a - 3) component include those described in paragraph

[0018] of JP - A No. 2018 - 83938. Among these, one or more selected from methoxypolyethylene glycol (n = 1 - 30) (meth) acrylate and polypropylene glycol (n = 2 - 30) (meth) acrylate are preferred. The above (a - 1) to (a - 3) components can be used by using the monomer components contained in each component alone or by mixing two or more of them.

[0018] From the above viewpoints, for polymer (a), it is preferable that the (a - 1) component is one or more selected from acrylic acid and methacrylic acid, and the (a - 2) component is one or more selected from styrene and α - methylstyrene, and it is more preferably a styrene - (meth) acrylic acid copolymer.

[0019] [[Content of each structural unit in polymer (a)]] The content of each component in the monomer mixture during the production of polymer (a) (content as unneutralized amount; the same applies hereinafter) or the content of constituent units derived from each component in polymer (a) is as follows, from the viewpoint of improving the long-term ejection reliability of the ink of the present invention and the wettability of ink dots on the recording medium. The content of component (a-1) is preferably 15% by mass or more, more preferably 20% by mass or more, even more preferably 25% by mass or more, and preferably 70% by mass or less, more preferably 60% by mass or less, and even more preferably 50% by mass or less. The content of component (a-2) is preferably 30% by mass or more, more preferably 40% by mass or more, even more preferably 50% by mass or more, and preferably 85% by mass or less, more preferably 80% by mass or less, and even more preferably 75% by mass or less.

[0020] If component (a-3) is present, the content of component (a-3) is preferably 30% by mass or less, more preferably 20% by mass or less, even more preferably 10% by mass or less, and even more preferably 5% by mass or less. The mass ratio of [(a-1) component / (a-2) component] is preferably 0.2 or more, more preferably 0.3 or more, even more preferably 0.35 or more, and even more preferably 0.38 or more, and preferably 2 or less, more preferably 1.5 or less, even more preferably 1 or less, and even more preferably 0.8 or less.

[0021] [Production of polymer (a)] Polymer (a) is produced by copolymerizing a monomer mixture containing component (a-1) and component (a-2), and optionally further component (a-3), using known polymerization methods such as bulk polymerization, solution polymerization, suspension polymerization, and emulsion polymerization. Among these polymerization methods, solution polymerization is preferred.

[0022] The acid value of polymer (a) is derived from the carboxyl group, but from the viewpoint of improving the long-term ejection reliability of the ink of the present invention and the wettability of ink dots on the recording medium, the acid value is preferably 180 mg KOH / g or more, more preferably 200 mg KOH / g or more, even more preferably 220 mg KOH / g or more, and preferably 320 mg KOH / g or less, more preferably 300 mg KOH / g or less, and even more preferably 280 mg KOH / g or less. The acid value of polymer (a) can be measured by the method described in the examples. It can also be calculated from the mass ratio of the constituent monomers. The number-average molecular weight of polymer (a) is preferably 4,000 or more, more preferably 6,000 or more, even more preferably 8,000 or more, and preferably 80,000 or less, more preferably 50,000 or less, and even more preferably 30,000 or less, from the viewpoint of improving the long-term ejection reliability of the ink of the present invention and the wettability of ink dots on the recording medium. The number-average molecular weight is measured by the method described in the examples.

[0023] [Neutralization] Preferably, at least a portion of the carboxyl groups of polymer (a) are neutralized with an alkali metal compound or the like. Examples of alkali metal compounds include one or more selected from alkali metal hydroxides such as lithium hydroxide, sodium hydroxide, potassium hydroxide, and cesium hydroxide; alkali metal salts of carbonic acid such as disodium carbonate, sodium bicarbonate, and dipotassium carbonate; and alkali metal salts of boric acid such as sodium borate. Among these, alkali metal hydroxides are preferred, sodium hydroxide and potassium hydroxide are more preferred, and sodium hydroxide is even more preferred.

[0024] The degree of neutralization of polymer (a) is preferably 15 mol% or more, more preferably 20 mol% or more, even more preferably 30 mol% or more, and preferably 150 mol% or less, more preferably 100 mol% or less, and even more preferably 80 mol% or less, from the viewpoint of ensuring the dispersion stability of the pigment. The degree of neutralization (mol%) is calculated using the following formula. Degree of neutralization (mol %) = [Number of moles of alkali metal compound / Number of moles of carboxyl groups in polymer (a)] × 100 In this invention, if an excess of alkali metal compound is used compared to the number of moles of carboxyl groups in polymer (a), the degree of neutralization may exceed 100 mol%.

[0025] [Crosslinking of polymer (a)] It is preferable that polymer (a) is crosslinked using a crosslinking agent to form a crosslinked structure. That is, in the present invention, the pigment is preferably a crosslinked polymer particle containing the pigment. In this case, the polymer constituting the crosslinked polymer particle consists of a component derived from polymer (a) and a component derived from the crosslinking agent. This crosslinking treatment causes polymer (a), which has a two-dimensional structure, to become a three-dimensional structure, and the polymer is firmly adsorbed or fixed to the pigment surface, suppressing the aggregation of the pigment in the ink of the present invention and further suppressing the swelling of the polymer. As a result, it is believed that the long-term ejection reliability of the ink of the present invention and the wettability and spreadability of ink dots on recording media are improved, and further, the color development and scratch resistance of the recorded material are improved. The crosslinking agent is preferably a compound having two or more epoxy groups in its molecule. The crosslinking agent may be water-soluble or water-insoluble, but from the viewpoint of more efficiently crosslinking with the carboxyl groups of polymer (a) in a water-based medium, its water solubility is preferably 50% by mass or less, more preferably 40% by mass or less, and even more preferably 35% by mass or less. Here, water solubility (mass%) refers to the solubility (mass%) of the crosslinking agent when 10 parts by mass of the crosslinking agent are dissolved in 90 parts by mass of water at room temperature (25°C). Specifically, the water solubility (mass%) can be measured by the method described in the examples.

[0026] Compounds having two or more epoxy groups in the molecule are preferably compounds having two or more glycidyl ether groups in the molecule, and more preferably polyglycidyl ether compounds of polyhydric alcohols having hydrocarbon groups with 3 to 8 carbon atoms. The epoxy equivalent of a compound having two or more epoxy groups in its molecule is preferably 90 or more, more preferably 100 or more, even more preferably 110 or more, and preferably 300 or less, more preferably 200 or less, and even more preferably 170 or less, from the viewpoint of more efficiently crosslinking with the carboxyl groups of polymer (a) in a water-based medium.

[0027] Specific examples of compounds having two or more epoxy groups in their molecule include one or more selected from polyglycidyl ethers such as cyclohexanedimethanol diglycidyl ether, polyethylene glycol diglycidyl ether, 1,6-hexanediol diglycidyl ether, diethylene glycol diglycidyl ether, glycerol polyglycidyl ether, polyglycerol polyglycidyl ether, trimethylolpropane polyglycidyl ether, sorbitol polyglycidyl ether, pentaerythritol polyglycidyl ether, resorcinol diglycidyl ether, neopentyl glycol diglycidyl ether, and hydrogenated bisphenol A type diglycidyl ether. Among these, one or more selected from cyclohexanedimethanol diglycidyl ether, 1,6-hexanediol diglycidyl ether, diethylene glycol diglycidyl ether, trimethylolpropane polyglycidyl ether, and pentaerythritol polyglycidyl ether are preferred.

[0028] (Manufacturing of cross-linked polymer particles containing pigments) Crosslinked polymer particles containing pigments can be efficiently manufactured by a method comprising the following steps 1 to 3. Step 1: A step to obtain an aqueous dispersion of polymer (a) by neutralizing at least a portion of the carboxyl groups of polymer (a) with an alkali metal compound. Step 2: Disperse the aqueous dispersion of polymer (a) obtained in Step 1 with the pigment to obtain an aqueous pigment dispersion of polymer particles containing the pigment dispersed in polymer (a). Step 3: Add a compound having two or more epoxy groups in its molecule to the pigment aqueous dispersion obtained in Step 2, and perform a crosslinking treatment to obtain an aqueous dispersion of crosslinked polymer particles containing the pigment.

[0029] In step 1, neutralization is preferably carried out so that the pH is between 7 and 11. The degree of neutralization of the alkali metal compound and polymer (a) used for neutralization is as described above. In step 2, the dispersion treatment can be performed solely by shear stress to finely atomize the pigment particles to the desired particle size. However, from the viewpoint of obtaining a uniform aqueous pigment dispersion, it is preferable to pre-disperse the pigment mixture before further pre-dispersion. For pre-dispersion, commonly used mixing and stirring devices such as anchor blades and disperser blades can be used. Dispersion machines used for this dispersion include kneaders such as roll mills and kneaders, high-pressure homogenizers such as microfluidizers, and media-type dispersants such as paint shakers and bead mills. Among these, it is preferable to use a high-pressure homogenizer from the viewpoint of reducing the particle size of the pigment. When performing dispersion processing using a high-pressure homogenizer, the average particle size of pigment particles in the aqueous pigment dispersion can be adjusted by controlling the processing pressure and the number of passes. From the viewpoint of productivity and economic efficiency, the processing pressure is preferably 60 MPa to 300 MPa, and the number of passes is preferably 3 to 30.

[0030] In step 3, a polymer (a) in which the pigment is dispersed in an aqueous pigment dispersion is crosslinked by a compound having two or more epoxy groups in its molecule to form a crosslinked polymer, and an aqueous dispersion in which particles of the crosslinked polymer containing the pigment are dispersed in an aqueous medium can be obtained. From the viewpoint of completion of the crosslinking reaction and economic efficiency, the temperature in step 3 is preferably 50°C or higher, more preferably 70°C or higher, and preferably 95°C or lower, more preferably 92°C or lower. Also, from the same viewpoint as above, the crosslinking treatment time is preferably 0.5 hours or more, more preferably 1 hour or more, and preferably 10 hours or lower, more preferably 6 hours or lower.

[0031] The acid value of the crosslinked polymer constituting the pigment-containing crosslinked polymer particles is preferably 90 mgKOH / g or more, more preferably 95 mgKOH / g or more, even more preferably 100 mgKOH / g or more, and preferably 200 mgKOH / g or less, more preferably 180 mgKOH / g or less, and even more preferably 160 mgKOH / g or less.

[0032] The concentration of nonvolatile components (solids) in the resulting aqueous pigment dispersion is preferably 10% by mass or more, more preferably 15% by mass or more, and preferably 30% by mass or less, more preferably 25% by mass or less, from the viewpoint of facilitating the preparation of the ink of the present invention. The solid content concentration of the pigment aqueous dispersion is measured by the method described in the examples.

[0033] The pigment content in the resulting aqueous pigment dispersion is preferably 2% by mass or more, more preferably 5% by mass or more, even more preferably 8% by mass or more, and preferably 25% by mass or less, more preferably 20% by mass or less, and even more preferably 18% by mass or less, from the viewpoint of improving the color development of the recorded material.

[0034] The crosslinking ratio of polymer (a) is preferably 20 mol% or more, more preferably 30 mol% or more, even more preferably 40 mol% or more, and preferably 80 mol% or less, more preferably 70 mol% or less, and even more preferably 60 mol% or less, from the viewpoint of improving the long-term ejection reliability of the ink of the present invention and the wettability of ink dots on the recording medium. Here, the crosslinking rate (mol%) is calculated as "(number of moles of epoxy groups in a compound having two or more epoxy groups in the molecule / number of moles of carboxyl groups in polymer (a)) × 100".

[0035] The average particle size of the polymer particles containing the pigment in the aqueous pigment dispersion is preferably 60 nm or larger, more preferably 80 nm or larger, even more preferably 100 nm or larger, and also preferably 200 nm or smaller, more preferably 160 nm or smaller, and even more preferably 150 nm or smaller, from the viewpoint of reducing coarse particles and improving the long-term ejection reliability of the ink of the present invention and the wettability of ink dots on the recording medium. The average particle size is measured by the method described in the examples. Furthermore, the average particle size of the pigment-containing polymer particles in the ink of the present invention after ink preparation is substantially the same as the average particle size of the pigment-containing polymer particles in the pigment aqueous dispersion.

[0036] <Pigment-free polymer particles> The ink of the present invention contains polymer particles that do not contain pigment, from the viewpoint of improving the long-term ejection reliability of the ink and the wettability and spreadability of ink dots on the recording medium. Examples of polymers constituting polymer particles that do not contain pigments (hereinafter also referred to as "polymer (b)") include (meth)acrylic resins, styrene resins, urethane resins, polyester resins, butadiene resins, and vinyl chloride resins. Among these, (meth)acrylic resins are preferred, and styrene-(meth)acrylic resins are more preferred, from the viewpoint of improving the long-term ejection reliability of the ink of the present invention and the wettability of ink dots on recording media due to their affinity with organic solvents (C-1) with a water solubility of less than 20% by mass, as described later. Polymer particles that do not contain pigments are preferably used as an aqueous dispersion in which they are dispersed in water. Polymer (b) may be synthesized or commercially available. Furthermore, from the viewpoint of improving the long-term ejection reliability of the ink of the present invention and the wettability and spreadability of ink dots on the recording medium, it is preferable that polymer (b) has a crosslinked structure crosslinked with a crosslinking agent, i.e., is a crosslinked polymer particle that does not contain pigment. This pigment-free crosslinked polymer particle consists of components derived from polymer (b) and components derived from the crosslinking agent.

[0037] [Polymer (b)] The (meth)acrylic resin as polymer (b) preferably has (b-1) a constituent unit derived from a carboxyl group-containing vinyl monomer and (b-2) a constituent unit derived from a hydrophobic vinyl monomer. Component (b-1) can be a carboxylic acid monomer similar to that of component (a-1) above. Among these, one or more selected from acrylic acid and methacrylic acid are preferred from the viewpoint of improving the long-term ejection reliability of the ink of the present invention and the wettability of the ink dots on the recording medium. (b-2) Component is preferably an alkyl (meth)acrylate or aromatic group-containing monomer similar to component (a-2) above. Among these, styrene monomers are preferred, and one or more selected from styrene and α-methylstyrene are preferred. The above components (b-1) and (b-2) can be used by using the monomer components contained in each component individually or by mixing two or more of them.

[0038] [Content of each constituent unit in polymer (b)] The content of constituent units derived from components (b-1) and (b-2) in polymer (b) is as follows, from the viewpoint of improving the ejection stability of the ink of the present invention. The content of component (b-1) is preferably 15% by mass or more, more preferably 20% by mass or more, even more preferably 25% by mass or more, and preferably 70% by mass or less, more preferably 60% by mass or less, and even more preferably 50% by mass or less. The content of component (b-2) is preferably 30% by mass or more, more preferably 40% by mass or more, even more preferably 50% by mass or more, and preferably 85% by mass or less, more preferably 80% by mass or less, and even more preferably 75% by mass or less.

[0039] Polymer (b) can be produced by copolymerizing a monomer mixture containing component (b-1), component (b-2), etc., using a known solution polymerization method or the like. The method for producing polymer (b), the neutralization method, and the crosslinking treatment method are preferably the same as those described above for producing polymer (a).

[0040] The acid value of polymer (b) is preferably 180 mg KOH / g or more, more preferably 200 mg KOH / g or more, even more preferably 220 mg KOH / g or more, and preferably 320 mg KOH / g or less, more preferably 300 mg KOH / g or less, and even more preferably 280 mg KOH / g or less, from the viewpoint of improving the long-term ejection reliability of the ink of the present invention and the wettability of ink dots on the recording medium. The number-average molecular weight of polymer b is preferably 4,000 or more, more preferably 6,000 or more, even more preferably 8,000 or more, and preferably 80,000 or less, more preferably 50,000 or less, and even more preferably 30,000 or less. The acid value and number-average molecular weight of polymer (b) can be measured in the same manner as for polymer (a).

[0041] The average particle size of the pigment-free polymer particles is preferably 60 nm or larger, more preferably 80 nm or larger, even more preferably 100 nm or larger, and preferably 200 nm or smaller, more preferably 160 nm or smaller, and even more preferably 150 nm or smaller, from the viewpoint of improving the long-term ejection reliability of the ink of the present invention and the wettability of the ink dots on the recording medium. The average particle size of the pigment-free polymer particles is measured by the method described in the examples. The average particle size of pigment-free polymer particles in the ink of the present invention after ink preparation is substantially the same as the average particle size of pigment-free polymer particles prepared before ink preparation.

[0042] Polymers (a) and (b) may be the same or different. That is, polymers (a) and (b) may have different compositions (structures), or they may be the same polymer including their composition (structure), differing only in the presence or absence of pigment. Polymers (a) and (b) can also be commercially available. Examples of commercially available dispersions of polymers (a) and (b) that can be used include Neocryl A1127 (anionic self-crosslinked aqueous acrylic resin) from DSM Neo Resins, Joncryl 390 etc. (acrylic resin) from BASF, Joncryl PDX-7775 etc. (styrene-acrylic resin), and Vinibran 700 etc. (vinyl chloride-acrylic resin) from Nisshin Chemical Industry Co., Ltd. When both pigment-containing polymer particles and pigment-free polymer particles are crosslinked polymer particles containing pigments and crosslinked polymer particles not containing pigments, it is preferable that the crosslinking agent is the same. Furthermore, if both the polymer particles containing pigment and the polymer particles not containing pigment are crosslinked polymer particles containing pigment and crosslinked polymer particles not containing pigment, it is preferable that polymer (a) and polymer (b) are the same, and that the crosslinking agent is also the same.

[0043] <wax> The ink of the present invention may contain a wax separately from the viewpoint of improving its fixation properties. The wax is preferably one that has a melting point of 95°C or higher, more preferably 100°C or higher, even more preferably 105°C or higher, and preferably 150°C or lower, more preferably 145°C or lower, and even more preferably 140°C or lower, from the viewpoint of not adversely affecting the ejection properties. Examples of waxes include polyolefin waxes, which are mainly composed of olefin monomers; petroleum-based paraffin waxes, which consist of a mixture of chain-type saturated hydrocarbons with 20 to 30 carbon atoms; and synthetic waxes such as sazole waxes. Among these, one or more selected from polyolefin waxes and paraffin waxes are preferred. It is preferable to use the wax as an emulsion in which the wax is dispersed in an aqueous medium.

[0044] <Organic solvents> [Organic solvent (C-1)] The organic solvent (C-1) used in the ink of the present invention has a solubility in water of less than 20% by mass and plays a role in improving the wettability of ink dots on the recording medium. In the present invention, the solubility of the organic solvent (C-1) in water is expressed by the mass of the organic solvent at which phase separation occurs when the organic solvent is added in small amounts to 100 g of ion-exchanged water at 20°C and stirred, as described in the example. The solubility of the organic solvent (C-1) in water 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 the wettability and spreadability of ink dots on the recording medium, and preferably 1% by mass or more, more preferably 2% by mass or more, and even more preferably 3% by mass or more, from the viewpoint of improving the ejection stability of the ink of the present invention.

[0045] Specific examples of organic solvents (C-1) include ethylene glycol-based glycol ethers, propylene glycol-based glycol ethers, and dialkyl glycol ethers. Examples of ethylene glycol-based glycol ethers include ethylene glycol monohexyl ether (solubility in water 0.99% by mass), diethylene glycol monohexyl ether (solubility in water 1.7% by mass), ethylene glycol mono-2-ethylhexyl ether (solubility in water 0.2% by mass), diethylene glycol mono-2-ethylhexyl ether (solubility in water 0.3% by mass), ethylene glycol monophenyl ether (solubility in water 2.7% by mass), diethylene glycol monophenyl ether (solubility in water 3.4% by mass), and ethylene glycol monobenzyl ether (solubility in water 0.4% by mass). Examples of propylene glycol-based glycol ethers include dipropylene glycol monopropyl ether (solubility in water: 4.8% by mass), propylene glycol monobutyl ether (solubility in water: 6.4% by mass), dipropylene glycol monobutyl ether (solubility in water: 3.0% by mass), tripropylene glycol monobutyl ether (solubility in water: 0.4% by mass), and propylene glycol monophenyl ether (solubility in water: 0.2% by mass). Examples of dialkyl glycol ethers include diethylene glycol dibutyl ether (solubility in water: 0.3% by mass). Among these, the organic solvent (C-1) is preferably one or more selected from propylene glycol monobutyl ether, dipropylene glycol monopropyl ether, and dipropylene glycol monobutyl ether, with propylene glycol monobutyl ether being more preferred, from the viewpoint of improving the long-term ejection reliability of the ink of the present invention and the wettability of ink dots on the recording medium.

[0046] The boiling point of the organic solvent (C-1) is preferably 120°C or higher, more preferably 140°C or higher, even more preferably 160°C or higher, and preferably 250°C or lower, more preferably 240°C or lower, and even more preferably 235°C or lower, from the viewpoint of improving the long-term ejection reliability of the ink of the present invention and the wettability of the ink dots on the recording medium. [Water-soluble organic solvents] In the ink of the present invention, the organic solvent preferably further contains, in addition to the organic solvent (C-1), a water-soluble organic solvent having a solubility in water of 20% by mass or more at 20°C. The water-soluble organic solvent uniformly dissolves the organic solvent (C-1), which has a solubility in water of less than 20% by mass, in the ink of the present invention, and plays a role in improving the long-term ejection reliability of the ink of the present invention and the wettability of the ink dots on the recording medium. The water-soluble organic solvent may be a liquid or a solid at 25°C. Preferably, the water-soluble organic solvents are glycol-based solvents (C-2) with a solubility in water of 20% by mass or more, and glycol ether-based solvents (C-3) with a solubility in water of 20% by mass or more. These may be used individually or in combination.

[0047] (Glycol-based solvent (C-2) with a solubility in water of 20% by mass or more) Specific examples of glycol-based solvents (C-2) with a solubility in water of 20% by mass or more include ethylene glycol, propylene glycol, 1,2-butanediol, 1,2-hexanediol, 1,2-octanediol, 1,8-octanediol, 1,2-decanediol, 1,3-propanediol, 1,4-butanediol, 2-ethyl-1,3-hexanediol, diethylene glycol, dipropylene glycol, and glycerin. Among these, one or more selected from propylene glycol, 1,2-butanediol, 1,3-propanediol, and 1,4-butanediol are preferred, with propylene glycol being more preferred.

[0048] (Glycol ether-based solvent (C-3) with a solubility in water of 20% by mass or more) Examples of glycol ether solvents (C-3) with a solubility in water of 20% by mass or more include ethylene glycol ether, propylene glycol ether, and dialkyl glycol ether. Specific examples of glycol ether solvents (C-3) with a solubility in water of 20% by mass or more include ethylene glycol monoethyl ether, ethylene glycol monoisopropyl ether, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, diethylene glycol monopropyl ether, dipropylene glycol monomethyl ether, diethylene glycol monoisopropyl ether, diethylene glycol monobutyl ether, tetraethylene glycol monomethyl ether, propylene glycol monomethyl ether, propylene glycol monoethyl ether, and tripropylene glycol monomethyl ether. Among these, one or more selected from dipropylene glycol monomethyl ether, diethylene glycol monoisopropyl ether, and diethylene glycol monobutyl ether are preferred, with diethylene glycol monoisopropyl ether being more preferred.

[0049] In the ink of the present invention, it is preferable to use in combination an organic solvent (C-1) and one or more glycol-based solvents (C-2) selected from propylene glycol, 1,2-butanediol, 1,3-propanediol, and 1,4-butanediol, as a glycol-based solvent (C-2) having a solubility in water of 20% by mass or more, and one or more glycol ether-based solvents (C-3) selected from dipropylene glycol monomethyl ether, diethylene glycol monoisopropyl ether, and diethylene glycol monobutyl ether, as a glycol-based solvent (C-3) having a solubility in water of 20% by mass or more. It is more preferable to use in combination an organic solvent (C-1) and propylene glycol as a glycol-based solvent (C-2) having a solubility in water of 20% by mass or more, and diethylene glycol monoisopropyl ether as a glycol ether-based solvent (C-3) having a solubility in water of 20% by mass or more.

[0050] The boiling point of the water-soluble organic solvent is preferably 110°C or higher, more preferably 130°C or higher, even more preferably 150°C or higher, and preferably 250°C or lower, more preferably 240°C or lower, and even more preferably 235°C or lower, from the viewpoint of uniformly dissolving the organic solvent (C-1) in the ink of the present invention and improving the long-term ejection reliability of the ink of the present invention and the wettability of the ink dots on the recording medium.

[0051] The ink of the present invention may further contain organic solvents other than those mentioned above, as long as they do not impair the effects of the present invention.

[0052] <Silicate compounds> The ink of the present invention contains a silicate compound, from the viewpoint of improving long-term ejection reliability and suppressing the decrease in water repellency of the nozzle plate surface when the ink of the present invention comes into contact with it. Because the ink of the present invention contains a silicate compound, it suppresses the elution of silicate ions from inkjet recording heads using glass or silicon as materials, and also suppresses the decrease in surface water repellency due to corrosion of the nozzle plate even when in contact with the ink for a long period of time. The silicate compound can be broadly selected from silicic acid and silicates. Anhydrous silicic acid is preferred as the silicic acid, and colloidal silica is more preferred. As silicates, alkali metal salts and alkaline earth metal salts of silicic acid are preferred, and alkali metal salts are more preferred. Among these, the silicate compound is preferably one or more selected from sodium silicate, potassium silicate, calcium silicate, magnesium silicate, and anhydrous silicic acid. Among these silicate compounds, it is more preferable to use one or more water-soluble inorganic silicate compounds selected from sodium silicate and potassium silicate, from the viewpoint of improving the long-term stability of the ink of the present invention when stored, by suppressing recrystallization and Ostwald aging of the silicate compounds and suppressing the generation of coarse particles. It is even more preferable to use sodium silicate from the viewpoint of improving the long-term ejection reliability of the ink of the present invention and suppressing the decrease in water repellency of the nozzle plate surface when the ink comes into contact with it.

[0053] As sodium silicate, industrially used sodium silicate can be used, and its standard is specified in JIS K 1408. It can be used in any form, including sodium silicate No. 1, sodium silicate No. 2, and sodium silicate No. 3 in solution state, or sodium metasilicate in solid state. Among these, from the viewpoint of ink formulation stability, it is preferable to use any of sodium silicate No. 1, sodium silicate No. 2, or sodium silicate No. 3 in aqueous solution state. Furthermore, from the viewpoint of improving the long-term ejection reliability of the ink of the present invention and suppressing the decrease in water repellency of the nozzle plate surface when the ink of the present invention comes into contact with it, it is even more preferable to use sodium silicate No. 3. These industrially used sodium silicates can be added directly to the ink, or they can be diluted with water beforehand.

[0054] <Surfactants> The ink of the present invention may further contain a surfactant, if necessary. Examples of surfactants include nonionic surfactants and cationic surfactants, but it is preferable that the product contains a nonionic surfactant. Examples of nonionic surfactants include polyoxyalkylene alkyl ether type surfactants, acetylene glycol-based surfactants, polyhydric alcohol type surfactants, and fatty acid alkanolamides. Among these, polyoxyalkylene alkyl ether type surfactants and acetylene glycol-based surfactants are preferred. Preferred examples of polyoxyalkylene alkyl ether type surfactants include alkylene oxide adducts of alcohols having 10 to 22 carbon atoms, and more preferred examples include ethylene oxide adducts of lauryl alcohol. Preferred examples of acetylene glycol-based surfactants include 2,4,7,9-tetramethyl-5-decine-4,7-diol and its alkylene oxide adduct. Examples of commercially available nonionic surfactants include the "Surfinol" series from Nisshin Chemical Industry Co., Ltd. and Air Products & Chemicals, the "Acetyleneol" series from Kawaken Fine Chemical Co., Ltd., and the "Emulgen" series from Kao Corporation.

[0055] The above-mentioned surfactants can be used individually or in combination of two or more. From the viewpoint of widening the dot diameter of water-based inks, it is more preferable to use two or more nonionic surfactants, and it is even more preferable to use a polyoxyalkylene alkyl ether type surfactant and an acetylene glycol type surfactant in combination.

[0056] <Ink manufacturing method> The ink of the present invention can be obtained by mixing the aforementioned pigment, polymer particles that do not contain the pigment, an organic solvent, a silicate compound, water, and, if necessary, the aforementioned wax and various additives commonly used in inks, such as humectants, wetting agents, penetrating agents, surfactants, viscosity modifiers, defoamers, preservatives, antifungal agents, and rust inhibitors.

[0057] <Content of each component in the ink> The content of each component in the ink of the present invention is as follows, from the viewpoint of improving the long-term ejection reliability of the ink of the present invention and the wettability and spreadability of ink dots on the recording medium.

[0058] (Pigment content) The pigment content in the ink of the present invention is preferably 1% by mass or more, more preferably 2% by mass or more, even more preferably 2.5% by mass or more, and preferably 15% by mass or less, more preferably 10% by mass or less, even more preferably 8% by mass or less, and even more preferably 6% by mass or less. The content of pigment-containing polymer particles in the ink of the present invention is preferably 2% by mass or more, more preferably 3% by mass or more, even more preferably 4% by mass or more, and preferably 15% by mass or less, more preferably 10% by mass or less, even more preferably 8% by mass or less, and even more preferably 7% by mass or less.

[0059] (Content of polymer particles that do not contain pigments) The content of pigment-free polymer particles 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, and preferably 15% by mass or less, more preferably 12% by mass or less, and even more preferably 10% by mass or less.

[0060] (Wax content) The wax content in the ink of the present invention is preferably 0.5% by mass or more, more preferably 0.6% by mass or more, even more preferably 0.8% by mass or more, and preferably 3% by mass or less, more preferably 2.5% by mass or less, and even more preferably 2.0% by mass or less.

[0061] (Organic solvent content) The content of the organic solvent in the ink of the present invention is preferably 35% by mass or less, more preferably 30% by mass or less, even more preferably 28% by mass or less, and preferably 16% by mass or more, more preferably 18% by mass or more, and even more preferably 20% by mass or more.

[0062] (Content of organic solvent (C-1)) The content of the organic solvent (C-1) in the ink of the present invention, which has a solubility in water of less than 20% by mass, is 15% by mass or less, preferably 12% by mass or less, more preferably 8% by mass or less, even more preferably 6% by mass or less, and 1% by mass or more, preferably 2% by mass or more, and more preferably 3% by mass or more.

[0063] (Content of glycol-based solvent (C-2) with a solubility in water of 20% by mass or more) The content of glycol-based solvent (C-2) in the ink of the present invention, which has a solubility in water of 20% by mass or more, is preferably 30% by mass or less, more preferably 25% by mass or less, and preferably 1% by mass or more, more preferably 10% by mass or more, and even more preferably 15% by mass or more.

[0064] (Content of glycol ether-based solvent (C-3) with a solubility in water of 20% by mass or more) The content of glycol ether-based solvent (C-3) with a water solubility of 20% by mass or more in the ink is preferably 20% by mass or less, more preferably 10% by mass or less, even more preferably 6% by mass or less, and even more preferably 4% by mass or less.

[0065] (Mass ratio of organic solvent (C-1) to total organic solvents) The mass ratio of organic solvent (C-1) to total organic solvent in the ink of the present invention [mass of organic solvent (C-1) / mass of total organic solvent] is preferably 0.05 or more, more preferably 0.1 or more, even more preferably 0.18 or more, and preferably 0.35 or less, more preferably 0.3 or less, and even more preferably 0.25 or less. When the mass ratio of the organic solvent (C-1) to the total organic solvent in the ink of the present invention is within the above range, the solubility of the silicate compound in the ink can be optimally maintained, making it easier to further improve the long-term ejection reliability of the ink of the present invention and the wettability and spreadability of the ink dots on the recording medium.

[0066] (Mass ratio of glycol-based solvents (C-2) with a solubility in water of 20% by mass or more relative to the total organic solvents) The mass ratio of glycol-based solvent (C-2) with a water solubility of 20% by mass or more to the total organic solvent in the ink of the present invention [mass of glycol-based solvent (C-2) with a water solubility of 20% by mass or more / mass of total organic solvent] is preferably 0.5 or more, more preferably 0.6 or more, and preferably 0.95 or less, more preferably 0.9 or less, and even more preferably 0.85 or less.

[0067] (Mass ratio of glycol ether-based solvents (C-3) with a solubility in water of 20% by mass or more relative to the total organic solvent) The mass ratio of glycol ether-based solvent (C-3) with a solubility in water of 20% by mass or more to the total organic solvent in the ink of the present invention [mass of glycol ether-based solvent (C-3) with a solubility in water of 20% by mass or more / mass of total organic solvent] is preferably 0.2 or less, more preferably 0.15 or less.

[0068] (Silicate compound content) The silicate compound content in the ink of the present invention is 2.5 ppm by mass or more, preferably 3 ppm by mass or more, more preferably 3.5 ppm by mass or more, even more preferably 4 ppm by mass or more, even more preferably 30 ppm by mass or more, and even more preferably 50 ppm by mass or more, from the viewpoint of suppressing a decrease in the water repellency of the nozzle plate surface when the ink comes into contact with it. Furthermore, from the viewpoint of improving the time stability of the ink of the present invention when it is stored and suppressing disturbances in the discharge direction of the ink of the present invention, by suppressing the recrystallization and Ostwald maturation of the silicate compound and suppressing the generation of coarse particles, the content is 250 ppm by mass or less, preferably 230 ppm by mass or less, more preferably 200 ppm by mass or less, even more preferably 170 ppm by mass or less, even more preferably 150 ppm by mass or less, even more preferably 120 ppm by mass or less, and even more preferably 100 ppm by mass or less.

[0069] The water content in the ink of the present invention is preferably 30% by mass or more, more preferably 40% by mass or more, even more preferably 50% by mass or more, and preferably 90% by mass or less, more preferably 80% by mass or less, and even more preferably 70% by mass or less.

[0070] <Ink properties> The viscosity of the ink of the present invention at 32°C is preferably 2 mPa·s or more, more preferably 3 mPa·s or more, even more preferably 4 mPa·s or more, and preferably 10 mPa·s or less, more preferably 7 mPa·s or less, and even more preferably 6 mPa·s or less, from the viewpoint of improving the long-term ejection reliability of the ink of the present invention and the wettability of ink dots on the recording medium. In the present invention, the viscosity of the ink can be measured using an E-type viscometer. The pH of the ink of the present invention is preferably 7.0 or higher, more preferably 7.2 or higher, and even more preferably 7.5 or higher, from the viewpoint of improving the long-term ejection reliability of the ink and the wettability of the ink dots on the recording medium. Furthermore, from the viewpoint of suppressing the decrease in water repellency of the nozzle plate surface when the ink of the present invention comes into contact with it, the pH is preferably 10 or lower, more preferably 9.5 or lower, and even more preferably 9.0 or lower. In the present invention, the pH of the ink can be measured by conventional methods.

[0071] [Inkjet recording method] The inkjet recording method of the present invention is characterized by ejecting the above-described ink of the present invention from a recording head that uses one or more materials selected from silicon and silicon oxide as a nozzle plate member. Nozzle plates using silicon and silicon oxide as materials improve ink repellency on the nozzle plate surface by forming a water-repellent film on the nozzle plate surface. Commercially available recording heads can be used as recording heads that use silicon materials as nozzle plate materials, such as the Samba G3L and Samba G5L from Fujifilm Dimatix, and the S3200, S800, I3200, I1600, and D3000 from Seiko Epson.

[0072] The ink of the present invention can be loaded into a known inkjet recording device such as a piezo type, and ejected as ink droplets onto a recording medium to obtain a recorded material. As inkjet recording media, highly absorbent plain paper, low absorbent coated paper, and non-absorbent resin film can be used. Examples of coated papers include general-purpose glossy paper "OK ​​Topcoat Plus" (manufactured by Oji Paper Co., Ltd.), multicolor foam gloss paper (manufactured by Oji Paper Co., Ltd.), UPM Finesse Gloss (manufactured by UPM), UPM Finesse Matt (manufactured by UPM), TerraPress Silk (manufactured by Stora Enso), and LumiArt (manufactured by Stora Enso). Examples of resin films include transparent synthetic resin films, such as polyester, polyvinyl chloride, polyolefin, and nylon films. Among these, polyester films and stretched polypropylene films are preferred, and those treated with corona discharge are even more preferred. The ink of the present invention, even when used in a recording head equipped with a nozzle plate or the like that uses a silicon component or a glass component, can achieve both long-term ejection reliability by suppressing the elution of silicon components and the generation of aggregated foreign matter in the ink, and good wettability and spreading of ink dots on the recording medium. [Examples]

[0073] In the following preparation examples, manufacturing examples, examples, and comparative examples, "parts" and "%" refer to "parts by mass" and "mass%" unless otherwise specified. The measurement methods for each physical property are as follows.

[0074] <Measurement> (1) Measurement of the number-average molecular weight of polymers The solutions prepared by dissolving phosphoric acid and lithium bromide in N,N-dimethylformamide at concentrations of 60 mmol / L and 50 mmol / L, respectively, were used as eluents. The measurements were performed using gel permeation chromatography (GPC instrument (HLC-8320GPC) manufactured by Tosoh Corporation, columns manufactured by Tosoh Corporation (TSKgel SuperAWM-H, TSKgel SuperAW3000, TSKgel guardcolumn Super AW-H), flow rate: 0.5 mL / min) and monodisperse polystyrene kits with known molecular weights as standard substances (PStQuick B (F-550, F-80, F-10, F-1, A-1000), PStQuick C (F-288, F-40, F-4, A-5000, A-500), manufactured by Tosoh Corporation). The measurement sample was prepared by mixing 0.1 g of polymer with 10 mL of the eluent in a glass vial, stirring at 25°C for 10 hours, and filtering through a syringe filter (DISMIC-13HP, made of PTFE, 0.2 μm, manufactured by Advantec Co., Ltd.).

[0075] (2) Measurement of the solid content concentration of the pigment dispersion 10.0 g of sodium sulfate, which had been stabilized in a desiccator, was weighed into a 30 mL ointment container. Approximately 1.0 g of the sample was added and mixed, then accurately weighed. The mixture was kept at 105°C for 2 hours to remove volatile components, and then left in the desiccator for another 15 minutes. The mass was then measured. The mass of the sample after removal of volatile components was taken as the solid content, and the solid content concentration was obtained by dividing it by the mass of the initial sample.

[0076] (3) Average particle size of pigment dispersions and polymer particles that do not contain pigments The average particle size of the pigment dispersion was measured by dynamic light scattering using a laser particle analysis system (Otsuka Electronics Co., Ltd., product name: ELS-8000), 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 integration cycles. The refractive index of water (1.333) was input as the refractive index of the dispersion solvent. For the measurement sample, a pigment dispersion or polymer particles without pigment were weighed into a screw tube (Maruemu Co., Ltd., No. 5), and the solid content concentration was 2 × 10⁻⁶. -4 A solution was used in which water was added to achieve a mass percentage, and the mixture was stirred at 25°C for 1 hour.

[0077] (4) Measurement of the acid value of polymers The resin was dissolved in a titration solvent of toluene and acetone (2:1) using a potentiometric automatic titrator (manufactured by Kyoto Electronics Manufacturing Co., Ltd., electric burette, model number: APB-610). The titration was performed using potentiometric titration with a 0.1N potassium hydroxide / ethanol solution, and the inflection point on the titration curve was defined as the endpoint. The acid value (mgKOH / g) was calculated from the amount of potassium hydroxide solution titrated to the endpoint.

[0078] (5) Measurement of the solubility of organic solvents in water 100g of deionized water was placed in a container, and organic solvents were added in small amounts at 20°C while stirring. This process was repeated until phase separation occurred, and the solubility of various organic solvents in water was calculated using the following equation (1). Solubility in water (mass %) = (mass of dissolved organic solvent (g) / mass of water (g)) × 100 (1) Furthermore, the solubility in water of a water-soluble solvent that can be completely miscible with water in any proportion is denoted as ∞. A solvent with a solubility in water of 20% by mass or less is defined as a low-water-soluble solvent, while a solvent with a solubility in water exceeding 20% ​​by mass is defined as a water-soluble solvent.

[0079] (6) Measurement of the water solubility of the crosslinking agent 90 parts by mass of deionized water and 10 parts by mass of crosslinking agent (W1) were added to a glass tube (25 mmφ × 250 mmh) at room temperature (25°C), and the glass tube was left to stand for 1 hour in a constant temperature bath adjusted to a water temperature of 25°C. Next, the glass tube was shaken vigorously for 1 minute, and then left to stand again in the constant temperature bath for 12 hours. Then, the undissolved material that separated from the water and settled or floated was collected, dried for 6 hours at 40°C and a gauge pressure of -0.08 MPa, and weighed (W2). The water solubility (mass%) was calculated using the following formula (2). Water solubility (mass%)={(W1-W2) / W1}×100 (2)

[0080] (7) Measurement of pH of water-based ink The pH of water-based ink at 25°C was measured using a benchtop pH meter "F-71" (manufactured by Horiba, Ltd.) equipped with a pH electrode "6337-10D" (manufactured by Horiba, Ltd.).

[0081] Preparation Example 1 (Preparation of Polymer (a)) A monomer mixture was prepared by mixing 31 parts acrylic acid and 69 parts styrene. 10 parts MEK, 0.2 parts 2-mercaptoethanol (polymerization chain transfer agent), and 10% of the monomer mixture were added to the reaction vessel and mixed, followed by thorough nitrogen gas purging. Meanwhile, a mixture of the remaining 90% of the monomer mixture, 0.13 parts of the polymerization chain transfer agent, 30 parts of MEK, and 1.1 parts of the radical polymerization initiator (2,2'-azobis(2,4-dimethylvaleronitrile), manufactured by Fujifilm Wako Pure Chemical Industries, Ltd., trade name: V-65) was placed in a dropping funnel. Under a nitrogen atmosphere, the monomer mixture in the reaction vessel was heated to 65°C while stirring, and the mixture in the dropping funnel was added dropwise over 3 hours. After 2 hours at 65°C following the completion of the dropwise addition, a solution of 0.1 parts of the polymerization initiator dissolved in 2 parts of MEK was added, and the mixture was aged for a further 2 hours at 65°C and 2 hours at 70°C before being dried under reduced pressure to obtain polymer (a) (number average molecular weight: 12000, acid value: 240 mgKOH / g).

[0082] Manufacturing Example I-1 (Production of an aqueous dispersion of cross-linked polymer particles containing pigments) (Process 1) 32 parts of polymer (a) obtained in Preparation Example 1 were mixed with 202 parts of deionized water, and then 12.8 parts of 5N sodium hydroxide aqueous solution (sodium hydroxide solids content 16.9%) were added to neutralize the mixture so that the ratio of moles of sodium hydroxide to moles of carboxyl groups in polymer (a) was 40% (degree of neutralization 40 mol%). The mixture was then heated to 90°C using a warm bath and stirred for 1 hour to completely disperse the polymer in water, thereby obtaining a polymer dispersion. (Process 2) Step 1: After cooling the obtained polymer dispersion to room temperature (25°C), 100 parts of cyanide pigment (CI Pigment Blue 15:3, manufactured by DIC Corporation, product name: TGR-SD) were added, and the mixture was stirred for 3 hours at 20°C with the disperser blades rotating at 6,000 rpm using a disperser (manufactured by Asada Iron Works Co., Ltd., product name: Ultra Disperser). Next, 124 parts of deionized water were added, and the mixture was dispersed in 15 passes at a pressure of 150 MPa using a microfluidizer (manufactured by Microfluidics, product name). The obtained dispersion was placed in a 500 mL angle rotor and centrifuged at 3,660 rpm for 20 minutes using a high-speed refrigerated centrifuge (manufactured by Hitachi Koki Co., Ltd., product name: himac CR22G, set temperature 20°C). The liquid layer was then collected and filtered through a 5 μm membrane filter (manufactured by Sartorius, product name: Minisart) to obtain a pigment aqueous dispersion. At this time, the solid content concentration of the pigment aqueous dispersion was 25%. (Step 3) 100 parts of the pigment aqueous dispersion were placed in a screw-top glass bottle, 32 parts of deionized water were added, and 1.8 parts of trimethylolpropane polyglycidyl ether (manufactured by Nagase ChemteX Corporation, trade name: Denacol EX-321LT, epoxy equivalent: 140, water solubility 27%) was added as a water-insoluble crosslinking agent. The bottle was then sealed tightly and heated at 70°C for 5 hours while stirring with a stirrer. At this time, the crosslinking treatment was performed with an amount of crosslinking agent that could react with 50% of the total number of carboxyl groups contained in the polymer (crosslinking rate: 50 mol%). After 5 hours, the dispersion was cooled to room temperature (25°C), and filtered using a 25 mL needleless syringe (manufactured by Terumo Corporation) fitted with the aforementioned 5 μm filter to obtain an aqueous dispersion of crosslinked polymer particles containing pigment (acid value 120 mg KOH / g) (solid content concentration: 20%, pigment 14.2%, polymer 5.8%, average particle size 105 nm).

[0083] Manufacturing Example I-2 (Preparation of an aqueous dispersion of cross-linked polymer particles without pigments) 15.3 parts of polymer (a) obtained in Preparation Example 1 were mixed with 63.5 parts of deionized water, and then 6.2 parts of 5N sodium hydroxide aqueous solution (solids content: 16.9%) were added to neutralize the mixture so that the ratio of moles of sodium hydroxide to moles of carboxyl groups of the polymer was 40% (degree of neutralization: 40 mol%). The mixture was heated to 90°C using a warm bath and stirred for 1 hour to completely disperse the polymer in water, thereby obtaining a polymer dispersion. After cooling the polymer dispersion to room temperature, 4.6 parts of trimethylolpropane polyglycidyl ether (Denacol EX-321LT, manufactured by Nagase ChemteX Corporation, epoxy equivalent: 140) were added as a crosslinking agent, the container was sealed, and heated at 90°C for 1.5 hours while stirring with a stirrer. At this time, the crosslinking treatment was performed with an amount of crosslinking agent that could react with 50% of the total number of carboxyl groups contained in the polymer (crosslinking rate 50 mol%). Subsequently, the polymer dispersion was cooled to room temperature (25°C), and filtered using a 25 mL needleless syringe (manufactured by Terumo Corporation) fitted with a 5 μm membrane filter (product name: Minisart) to obtain an aqueous dispersion of crosslinked polymer particles without pigment (solid content concentration: 20%).

[0084] Example 1 (Manufacturing of water-based ink) 28.2 parts of an aqueous dispersion of crosslinked polymer particles containing the pigment obtained in Production Example I-1 (PB15:3, solids content: 20%) (breakdown: pigment 4.0 parts, crosslinked polymer 1.6 parts, ion-exchanged water 22.6 parts), 25 parts of an aqueous dispersion of crosslinked polymer particles without the pigment obtained in Production Example I-2 (solids content: 20%) (breakdown: crosslinked polymer 5.0 parts, ion-exchanged water 20.0 parts), 20.0 parts propylene glycol, 5.0 parts propylene glycol monobutyl ether (BFG, manufactured by Nippon Emulsifier Co., Ltd.), 2.0 parts Surfinol 104PG-50 (manufactured by Nisshin Chemical Industry Co., Ltd., acetylene glycol active content 50%), Emulgen 120 (manufactured by Kao Corporation, ethyl lauryl alcohol) 0.5 parts of lenooxide adduct, 0.0197 parts of sodium silicate (manufactured by Fuji Chemical Co., Ltd., aqueous sodium silicate solution, effective content 38% by mass), and an appropriate amount of 1N sodium hydroxide aqueous solution were mixed to make the ink pH 8.5. Then, ion-exchanged water was added to make a total volume of 100 parts, and the mixture was filtered using a 25 mL needleless syringe (manufactured by Terumo Corporation) fitted with a 5 μm filter (acetylcellulose membrane, outer diameter: 2.5 cm, manufactured by Fujifilm Wako Pure Chemical Corporation) to obtain aqueous ink II-1 (crosslinked polymer particles containing pigment: 5.6% (of which pigment is 4.0%), crosslinked polymer particles without pigment: 5.0%, low water-soluble solvent: 5.0%, silicate compound content: 75 ppm).

[0085] Examples 2-10 and Comparative Examples 1-3 (Manufacturing of water-based inks) In Example 1, water-based inks II-2 to II-10 and II-11 to II-13 were obtained in the same manner as in Example 1, except that the conditions shown in Table 1 were changed. The results are shown in Table 1. The solvents listed in Table 1 are as follows: • PG: Propylene glycol, infinite solubility in water iPDG: Diethylene glycol monoisopropyl ether, solubility in water ∞ BFG: Propylene glycol mono-n-butyl ether, solubility in water 6.4% by mass PFDG: Dipropylene glycol monopropyl ether, solubility in water 4.8% by mass BFDG: Dipropylene glycol mono-n-butyl ether, solubility in water 3.0% by mass • BDG: Diethylene glycol monobutyl ether, solubility in water is infinite. • BTG: Triethylene glycol monobutyl ether, solubility in water is infinite. iPDG, BFG, PFDG, BFDG, BDG, and BTG are manufactured by Nippon Emulsifier Co., Ltd.

[0086] <Rating> Using the aqueous inks obtained in the examples and comparative examples, the water repellency of the silicon nozzle plate used in the MEMS processed recording head, the long-term ejection reliability of the MEMS processed recording head, and the dot diameter of the aqueous ink were evaluated using the following methods. The results are shown in Table 1.

[0087] (1) Evaluation of water repellency of silicone nozzle plates As a recording head using a silicon oxide nozzle plate, a Samba G3L inkjet recording head manufactured by Fujifilm Dimatex Corporation was used as a test specimen. The water contact angle on the water-repellent film was measured as follows, and the effect of water-based ink on the liquid repellency of the water-repellent film was evaluated. 300 mL of the aqueous ink obtained in the examples and comparative examples were each measured into 500 mL wide-mouth bottles (iBoy wide-mouth bottle 500 mL (manufactured by AS ONE Corporation)). The test pieces were then immersed in the aqueous ink, the containers were sealed tightly, and left to stand in a constant temperature bath set to 50°C for 28 days. After that, the test pieces were removed, washed with deionized water, and the water contact angle of the water-repellent film surface of the nozzle plate was measured. Deionized water was used to measure the water contact angle, and the measurement was performed by a conventional method using a contact angle measuring device (Kyowa Interface Science Co., Ltd., DM-500) in an environment of 25°C and 50% relative humidity. Regarding the water repellency of the silicone nozzle plate, there are no practical problems if the contact angle is 80° or more, and it can be used suitably if the contact angle is 90° or more.

[0088] (2) Evaluation of long-term discharge reliability The aqueous inks obtained in the examples and comparative examples were placed in glass containers, sealed tightly, and left to stand in a constant temperature bath at 50°C for 28 days as an accelerated test, followed by a further 24 hours of standing at room temperature. Subsequently, the aqueous inks were filled into a Samba G3L inkjet recording head manufactured by Fujifilm Dimatex Corporation, and ejection tests were conducted using a jetXpert inkjet liquid observation device (manufactured by imageXpert) in an environment of 25±1°C and 30±5% relative humidity to confirm the flight behavior. Using a single-pulse standard waveform, the voltage was adjusted so that the droplet volume was 2.4 pL, and continuous ejection was performed for 30 minutes. Subsequently, two droplets, one approximately 0.2 mm from the nozzle and the other approximately 0.6 mm from the nozzle, were simultaneously photographed using a strobe light. The angle of the straight line connecting the two droplets, separated by approximately 0.4 mm, was measured 1000 times per nozzle to determine the deviation from the vertical (90 degrees). The standard deviation σ was calculated and used as an indicator of ejection direction turbulence. The standard deviation σ was the average value of 30 nozzles for each ink. If two drops are dispensed perfectly perpendicularly from the nozzle plate, the standard deviation σ = 0. On the other hand, if the positions of the first and second drops are shifted to the left or right relative to the perpendicular from the nozzle plate, the value of the standard deviation σ increases, and it is evaluated that there is a disturbance in the direction of dispensing. If the standard deviation σ is less than 15 mrad, there are no practical problems. If it is less than 10 mrad, it can be used favorably, and if it is less than 5 mrad, it can be used even more favorably. If it is 15 mrad or more, there is a high probability that the ink landing position will be off by 15 μm or more when the gap between the recording head and the paper surface is 1 mm, so it cannot be used in practical terms.

[0089] (3) Evaluation of dot diameter of water-based ink (wetting spread of ink dots) In an environment of 25±1℃ and 30±5% relative humidity, a printing evaluation device (manufactured by Altec Co., Ltd.) equipped with an inkjet recording head (Samba G3L, manufactured by Fujifilm Dimatex Co., Ltd.) was filled with the water-based inks obtained in the examples and comparative examples. The ejection conditions were set using a single-pulse standard waveform, and the voltage was adjusted to produce a droplet volume of 2.4 pL. Coated paper "OK ​​Topcoat+" (manufactured by Oji Paper Co., Ltd., product name, water absorption 4.9 g / m²) was used as the recording medium.2 The recording medium was fixed to the transport table under reduced pressure using a device such that its longitudinal direction and transport direction were the same. A print command was transferred to the aforementioned print evaluation device, and a 2cm square area (image area for dot diameter measurement) with a duty cycle of 5% was printed in a single pass to obtain a printed material using the aforementioned recording medium. After the obtained printed material was left to stand for 24 hours, the ink dot diameter was measured using the handheld image evaluation system "PIAS-II" manufactured by Quality Engineering Associates Inc. under conditions of a threshold of 50%, a minimum dot diameter of 10μm, and a maximum dot diameter of 100μm. Larger dot diameters reduce the graininess of the recorded material and also reduce streaks during solid color printing. A dot diameter of 35 μm or larger per 2.4 pL of ink droplet is considered excellent, and 40 μm or larger is even better.

[0090] [Table 1]

[0091] Table 1 shows that the water-based inks obtained in Examples 1 to 10 exhibit superior water-repellency retention of the nozzle plate, long-term ejection reliability in inkjet recording, and superior wetting and spreading of ink dots on the recording medium compared to the water-based inks obtained in Comparative Examples 1 to 5.

Claims

1. An inkjet water-based ink containing a pigment, polymer particles without pigment, an organic solvent (C-1), a silicate compound, and water, The solubility of the organic solvent (C-1) in water is less than 20% by mass. An inkjet water-based ink for recording, wherein the content of the organic solvent (C-1) is 1% by mass or more and 15% by mass or less in the ink, and the content of the silicate compound is 2.5 ppm by mass or more and 250 ppm by mass or less in the ink.

2. The water-based inkjet recording ink according to claim 1, wherein the silicate compound is one or more selected from sodium silicate, potassium silicate, calcium silicate, magnesium silicate, and anhydrous silicic acid.

3. The water-based inkjet recording ink according to claim 1 or 2, wherein the organic solvent (C-1) is one or more selected from propylene glycol monobutyl ether, dipropylene glycol monopropyl ether, and dipropylene glycol monobutyl ether.

4. The water-based ink for inkjet recording according to any one of claims 1 to 3, further containing a glycol-based solvent (C-2) having a solubility in water of 20% by mass or more.

5. The water-based inkjet recording ink according to any one of claims 1 to 4, further containing a glycol ether solvent (C-3) having a solubility in water of 20% by mass or more.

6. The water-based inkjet recording ink according to any one of claims 1 to 5, wherein the pigment is in the form of polymer particles containing the pigment.

7. The water-based inkjet recording ink according to any one of claims 1 to 5, wherein the pigment is in the form of cross-linked polymer particles containing the pigment.

8. The water-based inkjet recording ink according to claim 7, wherein the acid value of the polymer constituting the cross-linked polymer particles containing the pigment is 90 mg KOH / g or more and 200 mg KOH / g or less.

9. The water-based ink for inkjet recording according to any one of claims 1 to 8, further comprising a nonionic surfactant.

10. An inkjet recording method comprising using an inkjet water-based inkjet recording ink according to any one of claims 1 to 9, and ejecting ink from a recording head using one or more selected from silicon and silicon oxide as the nozzle plate member.

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