Water-based ink for inkjet recording

Abstract

To provide a water-based ink for inkjet recording having excellent long-term discharge reliability and discharge recovery properties in inkjet recording while suppressing degradation of water repellency of an inkjet head using a silicon member or a silicon oxide member and to provide an inkjet recording method using the same.SOLUTION: There is provided [1] a water-based ink for inkjet recording which contains a polymer particles containing carbon black, an organic solvent, a silicic acid compound and water, wherein the content of the silicic acid compound is 1 mass ppm or more and 450 mass ppm or less in the ink. There is provided [2] an inkjet recording method which discharges the ink from an inkjet head using one or more selected from silicon and a silicon oxide for a nozzle plate member using the water-based ink for inkjet recording of [1].SELECTED DRAWING: None

Description

[Technical field]

[0001] The present invention relates to a water-based ink for ink-jet printing and an ink-jet recording method using the same. [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 the field of commercial printing, in addition to printing on conventional highly water-absorbent recording media such as plain paper and copy paper, there is a demand for printing on less water-absorbent recording media such as offset coated paper. In recent years, inkjet heads with dramatically improved ejection accuracy have come into use by using MEMS (Micro Electro Mechanical Systems) technology to process nozzle plates and other components made of silicon or silicon oxide materials.

[0003] Water-based pigment inks with good light and water resistance are commonly used as colorants in inkjet printers; however, when such water-based pigment inks are filled into inkjet heads that use silicon or silicon oxide components and are used or left for long periods of time, the silicon and other materials in contact with the ink dissolve, causing deterioration of components such as the nozzle plate, reducing the water repellency of the inkjet head, decreasing the printer's ejection accuracy and resulting in reduced image quality. Various proposals have been made to alleviate the above problems. For example, Patent Document 1 describes an aqueous ink that contains a colorant, a resin, water glass, and an organic solvent, and in which the colorant is self-dispersing carbon black having anionic hydrophilic groups on its surface, for the purpose of providing an aqueous ink that has improved ejection stability and clogging resistance from the nozzle or pen tip without reducing the fixability, abrasion resistance, water resistance, and marker resistance of the formed image. Furthermore, Patent Document 2 describes an ink composition that contains water, a colorant, a water-soluble organic solvent, a surfactant, and a water-soluble silicate in an amount of 0.0001% by mass or more and 0.5% by mass or less with respect to the total mass, for the purpose of providing an ink composition that has good ink ejection reliability and can suppress a decrease in the water repellency of an inkjet head. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2003-342501 A [Patent Document 2] JP 2011-63725 A Summary of the Invention [Problem to be solved by the invention]

[0005] The water-based ink of the cited document 1 is insufficient in terms of ejection recovery caused by drying of the nozzle when printing is stopped.In addition, the ejection property deteriorates due to deterioration of the ink over time, so that the ink is insufficient in terms of long-term ejection reliability. Furthermore, the ink composition of Patent Document 2, in the case of a black ink using carbon black, does not sufficiently suppress the decrease in water repellency of the inkjet head, and is insufficient in terms of long-term ejection reliability. An object of the present invention is to provide a water-based ink for ink-jet printing which is excellent in long-term ejection reliability and ejection recovery property in ink-jet recording while suppressing a decrease in water repellency of an ink-jet head which uses a silicon member or a silicon oxide member, and an ink-jet 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 incorporating a specific amount of silicic acid compound into a water-based ink for ink-jet printing, which contains polymer particles containing carbon black, an organic solvent, and a silicic acid compound, because the ink has excellent water repellency against ink-jet heads that use silicon members or silicon oxide members. That is, the present invention provides the following [1] and [2]. [1] A water-based ink for ink-jet printing, comprising polymer particles containing carbon black, an organic solvent, a silicic acid compound, and water, wherein the content of the silicic acid compound in the ink is from 1 ppm by mass to 450 ppm by mass. [2] An ink-jet recording method comprising the steps of: using the water-based ink for ink-jet recording according to [1] above, and ejecting the ink from an ink-jet head having a nozzle plate member made of at least one material selected from the group consisting of silicon and silicon oxide. Effect of the Invention

[0007] According to the present invention, it is possible to provide a water-based ink for ink-jet printing which is excellent in long-term ejection reliability and ejection recovery property in ink-jet recording while suppressing a decrease in water repellency of an ink-jet head which uses a silicon member or a silicon oxide member, and an ink-jet recording method using the same. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0008] [Water-based ink for inkjet printing] The water-based ink for ink-jet printing of the present invention (hereinafter also referred to as "the ink of the present invention") is a water-based ink for ink-jet printing containing polymer particles containing carbon black, an organic solvent, a silicic acid compound and water, characterized in that the content of the silicic acid compound in the ink is 1 ppm by mass or more and 450 ppm by mass or less.

[0009] In this specification, the term "aqueous system" means that water accounts for the largest proportion by mass of the medium in which carbon black is dispersed. In addition, "recording" is a concept that includes printing and printing out characters and images, and "recorded matter" is a concept that includes printed matter and printed matter on which characters and images are recorded.

[0010] The ink of the present invention suppresses the deterioration of the water repellency of an ink-jet head using a silicon member or a silicon oxide member, and is also excellent in long-term ejection reliability and ejection recovery property in ink-jet recording. The reason for this is not clear, but is thought to be as follows. In inkjet heads in which nozzle plates using silicon or silicon oxide materials are processed using MEMS technology, silicate ions are usually eluted from the silicon, etc., but the ink of the present invention contains silicate compounds such as sodium silicate and colloidal silica, which suppresses the elution of silicate ions from silicon or silicon oxide, and is therefore thought to be able to suppress the decrease in water repellency of the inkjet head that is caused by corrosion of the nozzle plate, even when the ink is in contact with the ink for a long period of time. On the other hand, in a general inkjet recording ink that uses carbon black as a colorant, because the carbon black has a strong substance trapping power, even if a silicic acid compound is contained in the ink, the balance of the content of the silicic acid compound in the ink is lost over a long period of time, and therefore the effect of suppressing the decrease in water repellency of the inkjet head described above cannot be achieved, and the inkjet ink cannot exhibit long-term ejection reliability or ejection recovery properties. In the ink of the present invention, the polymer particles containing carbon black are used, and the carbon black is at least partially covered with the polymer, so that the ability of the carbon black to capture silicic acid compounds and the like can be set within an appropriate range, and it is believed that the balance of the content of the silicic acid compounds in the ink can be appropriately maintained. Therefore, the effect of suppressing the decrease in water repellency of the inkjet head described above can be exhibited, and the ink of the present invention can improve long-term ejection reliability and ejection recovery. In addition, the use of the polymer particles containing carbon black allows the carbon black to be stably dispersed in the ink, so that the generation of coarse particles due to the aggregation of carbon black is controlled, and it is believed that this contributes to further improvement of long-term ejection reliability and ejection recovery in inkjet recording.

[0011] <Polymer particles containing carbon black> The carbon black-containing polymer particles are composed of carbon black and a polymer (hereinafter also referred to as "polymer (a)") that has a function of dispersing the carbon black in a medium mainly composed of water. There are no particular limitations on the polymer (a) as long as it is a polymer that has a function of dispersing carbon black in an aqueous medium mainly composed of water. The polymer (a) is preferably a water-insoluble polymer. In this specification, the term "water-insoluble polymer" refers to a polymer that dissolves in an amount of less than 10 g when the polymer is dried at 105° C. for 2 hours, reaches a constant weight, and is dissolved in 100 g of water at 25° C. When the polymer is an anionic polymer, the amount of dissolution is the amount of dissolution when polymer (a) is neutralized with sodium hydroxide to the same degree of neutralization as the degree of neutralization of the polymer constituting the polymer particles containing carbon black in the state contained in the ink of the present invention. When checking whether or not the polymer is water-insoluble, if it is in a dispersed state, the dispersion is precipitated by centrifugation and the amount of the polymer dissolved in the aqueous phase is used for the determination. Even if the polymer does not appear to be in a dispersed state and appears transparent, it is determined to be in a dispersed state if the particle size is measured in the same manner as in the measurement of the particle size of the polymer particles described in the Examples.

[0012] (Carbon Black) In the ink of the present invention, the carbon black contained in the polymer particles containing carbon black may be any known carbon black such as channel black, furnace black, acetylene black, thermal black, ketjen black, etc. Among these, from the viewpoints of long-term ejection reliability and ejection recovery, one or more types selected from channel black and furnace black are preferred, and channel black is more preferred. The carbon black may be used alone or in combination of two or more kinds. Specific examples of carbon black include Regal 400R, 660R, Monarch 717, 800, 880, 900, and 1100 (all manufactured by Cabot Corporation), ColorBlack FW1, FW18, S160, S170, Nipex 180IQ, 170IQ, 160IQ, Printex 55, 70, 80, 90, L6, U, V, and 150T (all manufactured by Orion Engineered Carbon Corporation), No. 45, 47, 900, 2200B, 2300, 2600, 990, 980, 970, 960, 950, 850, MCF-88, MA8, 600, and 100 (all manufactured by Mitsubishi Chemical Corporation). However, the carbon black is not limited to these.

[0013] The specific surface area of ​​the carbon black is preferably 100 m 2 / g or more 450m 2 In the present invention, the specific surface area of ​​the carbon black used is 100 m 2 / g or more 450m 2 / g or less, a predetermined amount of the silicic acid compound dissolved in the ink can be captured by the carbon black, so that the concentration of the silicic acid compound in the ink can be kept below a concentration at which recrystallization does not occur, and it is considered that the long-term ejection reliability of the ink of the present invention can be improved and the ejection recovery property can be improved. From the viewpoint of improving the long-term ejection reliability and the ejection recovery property, the specific surface area of ​​the carbon black is more preferably 110 m 2 / g or more, more preferably 180m 2 / g or more, and even more preferably 230m2 The specific surface area of ​​the carbon black is more preferably 400 m / g or more from the viewpoint of suppressing aggregation of carbon black particles and improving long-term discharge reliability and discharge recovery. 2 / g or less, more preferably 340m 2 / g or less, and even more preferably 280m 2 / g or less. The specific surface area of ​​the carbon black is measured by the method described in the Examples.

[0014] The pH of the carbon black is preferably from 3.0 to 9.5. When the pH of the carbon black used in the present invention is from 3.0 to 9.5, it is believed that the affinity between the carbon black and the polymer (a) in the polymer particles containing the carbon black can be strengthened, the dispersion stability of the polymer particles containing the carbon black in an aqueous medium can be improved, and the long-term ejection stability and ejection recovery property of the ink of the present invention can be improved. Carbon black also contains an acid component, and it is known that hydrogen ions are continuously supplied from the carbon black surface into the ink during storage. The lower the pH of the carbon black, the more pronounced this hydrogen ion supplying ability becomes. The presence of hydrogen ions supplied from the carbon black surface in the ink can suppress hydrolysis of silicon in the nozzle plate, etc., and can further suppress the deterioration of the water repellency of the inkjet head. From the viewpoints of suppressing a decrease in the water repellency of the inkjet head and improving long-term ejection reliability and ejection recovery, the pH of the carbon black is preferably 9.5 or less, more preferably 8.5 or less, even more preferably pH 7.0 or less, and still more preferably pH 5.5 or less. The pH of the carbon black is measured by the method described in the Examples.

[0015] In this specification, the morphology of polymer particles containing carbon black means particles in which the polymer encompasses the carbon black, particles consisting of a polymer and carbon black, on the surface of which part of the carbon black is exposed, particles in which the polymer is adsorbed to part of the carbon black, and mixtures thereof. In the ink of the present invention, the polymer particles containing carbon black are preferably "crosslinked polymer particles containing carbon black" described below, from the viewpoint of improving long-term jetting reliability and jetting recovery properties.

[0016] (Polymer (a)) Polymer (a) of any composition can be used, but from the viewpoint of improving the long-term ejection reliability and ejection recovery property of the ink of the present invention, 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-1) a polymer containing a structural unit derived from an ionic monomer is preferable, and (a-2) a copolymer having a structural unit derived from an ionic monomer and a structural unit derived from a hydrophobic monomer is more preferable.

[0017] [(a-1) Ionic Monomer] As the (a-1) ionic monomer (hereinafter also referred to as "component (a-1)"), an anionic monomer is preferred from the viewpoint of improving the dispersion stability of carbon black. Examples of the anionic monomer include a carboxylic acid monomer, a sulfonic acid monomer, a phosphoric acid monomer, etc. Examples of the carboxylic acid monomer include an acrylic acid, a methacrylic acid, a crotonic acid, an itaconic acid, a maleic acid, a fumaric acid, a citraconic acid, etc. Among these, carboxylic acid monomers are more preferable, one or more selected from acrylic acid and methacrylic acid are more preferable, and acrylic acid is more preferable.

[0018] [(a-2) Hydrophobic Monomer] From the viewpoint of improving the dispersion stability of carbon black, it is preferable to use the hydrophobic monomer (a-2) (hereinafter also referred to as "component (a-2)") as an additional monomer component in addition to the component (a-1). Specific examples of the (a-2) component include those described in paragraphs

[0020] to

[0022] of JP 2018-83938 A. Among these, one or more selected from alkyl (meth)acrylates having an alkyl group having 1 to 22 carbon atoms, styrene, α-methylstyrene, and benzyl (meth)acrylate are preferred, and styrene is more preferred.

[0019] [(a-3) Nonionic Monomer] The (a-3) nonionic monomer (hereinafter also referred to as "component (a-3)") can be used from the viewpoint of further improving the dispersion stability of carbon black. The component (a-3) is a monomer that has a high affinity for water or a water-soluble organic solvent, such as a monomer that contains a hydroxyl group or a polyalkylene glycol chain. Specific examples of the (a-3) component include those described in paragraph

[0018] of JP 2018-83938 A. Among these, one or more selected from methoxypolyethylene glycol (n = 1 to 30) (meth)acrylate and polypropylene glycol (n = 2 to 30) (meth)acrylate are preferred. Here, n represents the average number of moles of oxyalkylene groups added. The monomer components contained in each of the above components (a-1) to (a-3) can be used alone or in combination of two or more kinds.

[0020] From the above viewpoints, the polymer (a) preferably has an (a-1) component of at least one selected from acrylic acid and methacrylic acid, and an (a-2) component of at least one selected from styrene and α-methylstyrene, and is more preferably a styrene-(meth)acrylic acid copolymer.

[0021] [Content of each structural unit in polymer (a)] The content of each component in the monomer mixture during production of polymer (a) (content as unneutralized amount; the same applies below) or the content of structural units derived from each component in polymer (a) is as follows, from the viewpoint of improving the long-term ejection reliability and ejection recovery property of the ink of the present invention. The content of the (a-1) component is preferably 10 mass% or more, more preferably 15 mass% or more, even more preferably 20 mass% or more, and preferably 60 mass% or less, more preferably 50 mass% or less, even more preferably 40 mass% or less. The content of the (a-2) component 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, even more preferably 75% by mass or less.

[0022] When the (a-3) component is contained, the content of the (a-3) component is preferably 30 mass % or less, more preferably 20 mass % or less, even more preferably 10 mass % or less, and still more preferably 5 mass % or less. The mass ratio of [component (a-1) / component (a-2)] is preferably 0.2 or more, more preferably 0.3 or more, even more preferably 0.35 or more, still more preferably 0.38 or more, and is preferably 2 or less, more preferably 1.5 or less, even more preferably 1 or less, still more preferably 0.8 or less, and particularly preferably 0.6 or less.

[0023] [Production of polymer (a)] The polymer (a) is produced by copolymerizing a monomer mixture containing the above-mentioned components (a-1) and (a-2), and further the component (a-3) as required, by a known polymerization method such as solution polymerization, bulk polymerization, suspension polymerization, emulsion polymerization, etc. Among these polymerization methods, the solution polymerization method is preferred.

[0024] The acid value of the polymer (a) is derived from the carboxy group, and from the viewpoint of improving the long-term ejection reliability and storage stability of the ink of the present invention, the acid value is preferably 160 mgKOH / g or more, more preferably 180 mgKOH / g or more, even more preferably 200 mgKOH / g or more, and is preferably 300 mgKOH / g or less, more preferably 280 mgKOH / g or less, even more preferably 260 mgKOH / g or less. The acid value of the polymer (a) can be measured by the method described in the Examples, or can be calculated from the mass ratio of the constituent monomers. From the viewpoint of improving the long-term jetting reliability and the jetting recovery property of the ink of the present invention, the number average molecular weight of the polymer (a) is preferably 4,000 or more, more preferably 6,000 or more, even more preferably 8,000 or more, and is preferably 80,000 or less, more preferably 50,000 or less, even more preferably 30,000 or less. The number average molecular weight is measured by the method described in the Examples.

[0025] [Neutralization] At least a portion of the carboxy groups of the polymer (a) is preferably neutralized with an alkali metal compound or the like. Examples of the alkali metal compound include one or more selected from alkali metal hydroxides such as lithium hydroxide, sodium hydroxide, potassium hydroxide, and cesium hydroxide; alkali metal salts of carbonate such as sodium carbonate, sodium bicarbonate, and potassium 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.

[0026] From the viewpoint of ensuring the dispersion stability of carbon black, 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 is preferably 150 mol % or less, more preferably 100 mol % or less, even more preferably 80 mol % or less. In the present invention, when the degree of neutralization of the polymer (a) is 100 mol % or less, the degree of neutralization is synonymous with the equivalent amount of the neutralizing agent used, and the equivalent amount (mol %) of the neutralizing agent used for the polymer (a) is calculated by the following formula. Equivalent amount of neutralizing agent used for polymer (a) (mol %)=[[mass (g) of neutralizing agent added to neutralize polymer (a) / equivalent amount of neutralizing agent] / [acid value of polymer (a) (mg KOH / g)×mass (g) of polymer (a) / (56×1000)]]×100 In the present invention, when the neutralizing agent is used in excess of the number of moles of carboxy groups in polymer (a), this means that the neutralizing agent is in excess of the carboxy groups in polymer (a), and the degree of neutralization in this case is considered to be 100 mol %.

[0027] [Crosslinked structure of polymer (a)] The polymer (a) is preferably one that has been crosslinked using a crosslinking agent to form a crosslinked structure. That is, in the present invention, the polymer particles containing carbon black preferably have a crosslinked structure, i.e., the polymer particles are preferably crosslinked polymer particles containing carbon black. The crosslinked polymer constituting the crosslinked polymer particles containing carbon black is preferably a crosslinked polymer (A) consisting of a component derived from the polymer (a) and a component derived from a crosslinking agent. The crosslinked polymer (A) constituting the crosslinked polymer particles containing carbon black (hereinafter also simply referred to as "crosslinked polymer (A)") has a three-dimensional structure, which is firmly adsorbed or fixed on the carbon black surface. Therefore, it is considered that the aggregation of carbon black in the ink of the present invention is suppressed, and further the swelling of the polymer is suppressed, thereby improving the long-term ejection reliability and storage stability of the ink of the present invention. The crosslinking agent is preferably a compound having two or more epoxy groups in the molecule (hereinafter also referred to as "epoxy compound"). The crosslinking agent may be water-soluble or water-insoluble, but from the viewpoint of more efficiently crosslinking with the carboxyl group of the polymer (a) in a medium mainly composed of water, 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, the 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 of 25°C. The water solubility (mass%) can be specifically measured by the method described in the Examples.

[0028] The compound having two or more epoxy groups in the molecule is preferably a compound having two or more glycidyl ether groups in the molecule, more preferably a polyglycidyl ether compound of a polyhydric alcohol having a hydrocarbon group having 3 to 8 carbon atoms. The epoxy equivalent of the compound having two or more epoxy groups in the molecule is preferably 90 or more, more preferably 100 or more, even more preferably 110 or more, and is preferably 300 or less, more preferably 200 or less, even more preferably 170 or less, from the viewpoint of more efficiently crosslinking with the carboxy group of the polymer (a) in a medium mainly composed of water.

[0029] Specific examples of the compound having two or more epoxy groups in the 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 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.

[0030] From the viewpoint of improving the long-term ejection reliability and storage stability of the ink of the present invention, the acid value of the crosslinked polymer (A) is preferably 90 mgKOH / g or more, more preferably 95 mgKOH / g or more, even more preferably 100 mgKOH / g or more, and is preferably 200 mgKOH / g or less, more preferably 180 mgKOH / g or less, even more preferably 160 mgKOH / g or less. From the viewpoint of ensuring the dispersion stability of carbon black, the degree of neutralization of the crosslinked polymer (A) is preferably 20 mol % or more, more preferably 40 mol % or more, even more preferably 60 mol % or more, and is preferably 150 mol % or less, more preferably 120 mol % or less, even more preferably 100 mol % or less. The acid value of the crosslinked polymer (A) can be calculated from the charge ratio based on the acid value of the polymer (a).

[0031] (Production of polymer particles containing carbon black) The polymer particles containing carbon black can be efficiently produced by a method including the following steps 1 and 2. Step 1: neutralizing at least a portion of the carboxy groups of the polymer (a) with an alkali metal compound to obtain an aqueous dispersion of the polymer (a). Step 2: A step of dispersing the aqueous dispersion of the polymer (a) obtained in step 1 and carbon black to obtain an aqueous dispersion of polymer particles containing carbon black. Furthermore, when the polymer particles containing carbon black are crosslinked polymer particles containing carbon black, the crosslinked polymer particles containing carbon black can be efficiently produced by a method including the following step 3 in addition to the above steps 1 and 2. Step 3: A step of adding a crosslinking agent to the aqueous dispersion of polymer particles containing carbon black obtained in step 2, and subjecting the mixture to a crosslinking treatment to obtain an aqueous dispersion of crosslinked polymer particles containing carbon black.

[0032] The neutralization in step 1 is preferably carried out so that the pH is from 7 to 11. The degree of neutralization of the alkali metal compound and polymer (a) used for neutralization is as described above. In the dispersion treatment in step 2, the carbon black particles can be atomized to a desired particle size only by main dispersion using shear stress, but from the viewpoint of obtaining a uniform carbon black aqueous dispersion, it is preferable to carry out the dispersion treatment in two or more stages, in which a mixture containing carbon black and polymer (a) is preliminarily dispersed and then further main dispersion is carried out. As a disperser used for the preliminarily dispersion, a commonly used mixing and stirring device such as an anchor blade or a disperser blade can be used. Examples of dispersing machines used in the dispersion include kneading machines such as roll mills and kneaders, high-pressure homogenizers such as microfluidizers, and media-type dispersing machines 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 carbon black. When the dispersion treatment is performed using a high-pressure homogenizer, the average particle size of the carbon black particles in the carbon black aqueous dispersion can be adjusted by controlling the treatment pressure and the number of passes. From the viewpoints of productivity and economy, the treatment pressure is preferably 60 MPa or more and 300 MPa or less, and the number of passes is preferably 3 or more and 30 or less.

[0033] In step 3, the polymer (a) dispersing the carbon black in the carbon black aqueous dispersion is crosslinked by a crosslinking agent to form a crosslinked polymer (A) having a three-dimensional structure, thereby obtaining an aqueous dispersion in which particles of the crosslinked polymer (A) containing carbon black are dispersed in an aqueous medium. Preferred crosslinking agents are as described above. From the viewpoints of completion of the crosslinking reaction and economic efficiency, the temperature of the crosslinking treatment is preferably 50° C. or higher, more preferably 70° C. or higher, and preferably 95° C. or lower, more preferably 92° C. or lower. From the same viewpoints as above, the time of the crosslinking treatment is preferably 0.5 hours or higher, more preferably 1 hour or higher, and preferably 10 hours or lower, more preferably 6 hours or lower.

[0034] The acid value of the polymer (a) constituting the carbon black-containing polymer particles is preferably 160 mgKOH / g or more, more preferably 180 mgKOH / g or more, even more preferably 200 mgKOH / g or more, and is preferably 300 mgKOH / g or less, more preferably 280 mgKOH / g or less, even more preferably 260 mgKOH / g or less.

[0035] The acid value of the crosslinked polymer (A) constituting the crosslinked polymer particles containing carbon black is preferably 90 mgKOH / g or more, more preferably 95 mgKOH / g or more, even more preferably 100 mgKOH / g or more, and is preferably 200 mgKOH / g or less, more preferably 180 mgKOH / g or less, even more preferably 160 mgKOH / g or less.

[0036] From the viewpoint of facilitating the preparation of the ink of the present invention, the non-volatile component concentration (solids concentration) of the obtained aqueous dispersion of polymer particles containing carbon black or aqueous dispersion of crosslinked polymer particles containing carbon black is preferably 10% by mass or more, more preferably 15% by mass or more, and is preferably 30% by mass or less, more preferably 25% by mass or less.

[0037] From the viewpoint of improving the color development of recorded matter, the carbon black content in the obtained aqueous dispersion of polymer particles containing carbon black or aqueous dispersion of crosslinked polymer particles containing carbon black is preferably 2% by mass or more, more preferably 5% by mass or more, even more preferably 8% by mass or more, and is preferably 25% by mass or less, more preferably 20% by mass or less, even more preferably 18% by mass or less.

[0038] From the viewpoint of improving the long-term ejection reliability and ejection recovery properties of the ink of the present invention, the crosslinking rate of the crosslinked polymer (A) is preferably 20 mol % or more, more preferably 30 mol % or more, even more preferably 40 mol % or more, and is preferably 80 mol % or less, more preferably 70 mol % or less, even more preferably 60 mol % or less. When an epoxy compound is used as the crosslinking agent, the crosslinking rate (mol %) of the crosslinked polymer (A) is calculated by the following formula. Crosslinking rate (mol%) of crosslinked polymer (A)=[molar equivalent number of epoxy groups of epoxy compound in preparation of crosslinked polymer (A)] / [molar equivalent number of carboxyl groups of polymer (a) in preparation of crosslinked polymer (A)]×100 When the crosslinking rate of the crosslinked polymer (A) is within the above-mentioned suitable range, the three-dimensional structure is appropriately formed and the crosslinked polymer (A) exhibits water-insolubility regardless of the type of polymer (a) or the type of crosslinking agent.

[0039] The average particle size of the carbon black-containing polymer particles in the aqueous dispersion of the carbon black-containing polymer particles, or the average particle size of the carbon black-containing crosslinked polymer particles in the aqueous dispersion of the carbon black-containing crosslinked polymer particles, is preferably 60 nm or more, more preferably 70 nm or more, even more preferably 80 nm or more, and is preferably 200 nm or less, more preferably 160 nm or less, even more preferably 120 nm or less, from the viewpoint of improving the long-term jetting reliability and jetting recovery property of the ink of the present invention using the aqueous dispersion. The average particle size is measured by the method described in the Examples. The average particle size of the carbon black-containing polymer particles or the average particle size of the carbon black-containing crosslinked polymer particles in the water-based ink after preparation of the water-based ink is substantially the same as the average particle size of the carbon black-containing crosslinked polymer particles in the water dispersion.

[0040] <Organic solvent> The organic solvent used in the ink of the present invention mainly serves to improve the long-term ejection reliability and ejection recovery of the ink of the present invention. The organic solvent may be liquid or solid at 25° C., but a water-soluble organic solvent that dissolves in 100 mL of water at 25° C. in an amount of 10 mL or more is preferred. From the viewpoint of improving the long-term ejection reliability and ejection recovery property of the ink of the present invention, the boiling point of the water-soluble organic solvent is preferably 90°C or higher, more preferably 110°C or higher, even more preferably 130°C or higher, still more preferably 150°C or higher, and is preferably 250°C or lower, more preferably 240°C or lower, and even more preferably 235°C or lower. From the same viewpoint as above, the water-soluble organic solvent preferably contains one or more selected from polyhydric alcohols and polyhydric alcohol alkyl ethers. Examples of polyhydric alcohols 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, and propylene glycol is more preferred.

[0041] Examples of polyhydric alcohol alkyl ethers 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, dipropylene glycol monobutyl 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, dipropylene glycol monobutyl ether, diethylene glycol monoisopropyl ether, and diethylene glycol monobutyl ether are preferred, and diethylene glycol monoisopropyl ether is more preferred. Of the above organic solvents, one or more selected from propylene glycol, dipropylene glycol monomethyl ether, dipropylene glycol monobutyl ether, diethylene glycol monoisopropyl ether, and diethylene glycol monobutyl ether are preferred, and one or more selected from propylene glycol and diethylene glycol monoisopropyl ether are more preferred. The organic solvent may further contain organic solvents other than those mentioned above, within the range that does not impair the effects of the present invention. The organic solvent used herein preferably contains one or more water-soluble organic solvents having a boiling point of 90° C. or higher, and more preferably contains two or more water-soluble organic solvents having a boiling point of 90° C. or higher. When the organic solvent contains two or more water-soluble organic solvents, the weighted average boiling point of the organic solvents is preferably 150° C. or higher, more preferably 180° C. or higher, and preferably 250° C. or lower, more preferably 240° C. or lower, even more preferably 220° C. or lower, and even more preferably 200° C. or lower. When two or more water-soluble organic solvents are used as the organic solvent, the weighted average boiling point of the organic solvents is a weighted average weighted by the content (mass%) of each water-soluble organic solvent.

[0042] <Silicate compounds> The ink of the present invention contains a silicic acid compound from the viewpoints of suppressing the elution of silicate ions from silicon or silicon oxide, suppressing a decrease in the water repellency of the ink-jet head, and improving the long-term ejection reliability and ejection recovery properties of the ink of the present invention. The silicic acid compound may be broadly selected from silicic acid and silicates, but is particularly preferably at least one selected from alkali metal or alkaline earth metal silicates of silicic acid, such as sodium silicate, potassium silicate, calcium silicate, and magnesium silicate, and silicic anhydride (silica). As the silicate, an alkali metal salt of silicic acid called water glass is preferable. As the silicic anhydride (silica), colloidal silica is preferred. Of these silicic acid compounds, from the viewpoints of improving the stability over time during storage of the ink of the present invention and improving the long-term jetting reliability and jetting recovery properties of the ink of the present invention, one or more alkali metal salts of silicic acid selected from sodium silicate and potassium silicate are more preferred, and from the viewpoints of suppressing a decrease in the water repellency of the inkjet head and improving the long-term jetting reliability and jetting recovery properties of the ink of the present invention, it is even more preferred to use sodium silicate. When the alkali metal salt is a sodium salt or a potassium salt, the rational formula of the alkali metal salt of silicic acid is X2O·nSiO2 (X represents sodium or potassium, and n represents the molar ratio). In the ink of the present invention, the mass ratio of the SiO2 content to the X2O content in the alkali metal salt of silicate [(SiO2 (mass %)) / (X2O (mass %))] is, from the viewpoints of suppressing a decrease in the water repellency of the inkjet head and improving the long-term ejection reliability of the ink of the present invention, preferably 1.0 or more, more preferably 1.5 or more, even more preferably 2.0 or more, and still more preferably 3.0 or more, and from the same viewpoints, is preferably 5.0 or less, more preferably 4.0 or less, and even more preferably 3.5 or less. In addition, when sodium silicate and potassium silicate are contained as the alkali metal salt of silicic acid, the SiO2 content and X2O content in the alkali metal salt of silicic acid are the total amounts of the SiO2 content and X2O content contained in the sodium silicate and potassium silicate, respectively.

[0043] As the sodium silicate, industrially used sodium silicate is preferred. The standard of sodium silicate is stipulated in the group standard (sodium silicate (sodium silicate)) of the Japan Inorganic Chemicals Association, and any of sodium silicate No. 1, sodium silicate No. 2, and sodium silicate No. 3 in solution state, and sodium metasilicate in solid state can be used. Among these, from the viewpoint of blending stability in ink, it is preferable to use any of sodium silicate No. 1, sodium silicate No. 2, and sodium silicate No. 3 in solution state. Moreover, from the viewpoint of suppressing the decrease in water repellency of the inkjet head and improving the long-term discharge reliability of the ink of the present invention, sodium silicate No. 3 is more preferred.

[0044] <Polymer particles not containing pigment>

[0043] From the viewpoints of improving the fixation of the ink of the present invention to a recording medium and imparting image fastness to recorded matter while maintaining the long-term ejection reliability and ejection recovery properties of the ink of the present invention, it is preferred that the ink of the present invention further contains polymer particles that do not contain a pigment. Examples of the polymer constituting the pigment-free polymer particles (hereinafter also referred to as "polymer (b)") include (meth)acrylic resins, styrene resins, styrene-(meth)acrylic resins, urethane resins, polyester resins, butadiene resins, vinyl chloride resins, etc. Among these, from the viewpoint of improving the fixability of the ink of the present invention, one or more types selected from (meth)acrylic resins and styrene-(meth)acrylic resins are preferred, and styrene-(meth)acrylic resins are more preferred. The polymer particles not containing a pigment are preferably used as an aqueous dispersion in which they are dispersed in water. The polymer (b) may be a suitably synthesized product or a commercially available product. In addition, from the viewpoint of improving the long-term ejection reliability of the ink of the present invention, it is preferable that the polymer (b) has a crosslinked structure. That is, the pigment-free polymer particles are preferably pigment-free crosslinked polymer particles. The pigment-free crosslinked polymer particles are preferably crosslinked polymer (B) composed of a component derived from the polymer (b) and a component derived from the crosslinking agent.

[0045] [Polymer (b)] The (meth)acrylic resin as polymer (b) preferably has (b-1) a structural unit derived from a carboxyl group-containing vinyl monomer (hereinafter also referred to as "component (b-1)") and (b-2) a structural unit derived from a hydrophobic vinyl monomer (hereinafter also referred to as "component (b-2)"). Examples of the component (b-1) include the same carboxylic acid monomers as those of the component (a-1). Among them, from the viewpoint of improving the image fastness of the recorded matter while maintaining the long-term ejection reliability and ejection recovery property of the ink of the present invention, one or more selected from acrylic acid and methacrylic acid are preferred, and acrylic acid is more preferred. As the (b-2) component, the alkyl (meth)acrylate and aromatic group-containing monomers similar to those of the (a-2) component can be preferably used. Vinyl chloride monomers can also be used. Among them, styrene-based monomers are preferred, and one or more selected from styrene and α-methylstyrene are preferred, with styrene being more preferred. The monomer components contained in each of the above components (b-1) and (b-2) can be used alone or in combination of two or more kinds.

[0046] [Content of each structural unit in polymer (b)] The content of the structural units derived from the components (b-1) and (b-2) in the polymer (b) is as follows, from the viewpoint of improving the image fastness of the recorded matter while maintaining the long-term ejection reliability and ejection recoverability of the ink of the present invention. The content of the (b-1) component is preferably 15 mass% or more, more preferably 20 mass% or more, even more preferably 25 mass% or more, and preferably 70 mass% or less, more preferably 60 mass% or less, even more preferably 50 mass% or less. The content of the (b-2) component 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, even more preferably 75% by mass or less.

[0047] The polymer (b) can be produced by copolymerizing a monomer mixture containing the components (b-1) and (b-2) by a known solution polymerization method or the like. The production method, neutralization method, and crosslinking method of the polymer (b) are the same as those of the polymer (a) described above, and therefore the description thereof will be omitted.

[0048] From the viewpoint of improving image fastness of recorded matter while maintaining the long-term ejection reliability and ejection recoverability of the ink of the present invention, the acid value of the polymer (b) is preferably 180 mgKOH / g or more, more preferably 200 mgKOH / g or more, even more preferably 220 mgKOH / g or more, and is preferably 320 mgKOH / g or less, more preferably 300 mgKOH / g or less, and even more preferably 280 mgKOH / g or less. The number average molecular weight of the 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, even more preferably 30,000 or less. The acid value and number average molecular weight of the polymer (b) can be measured in the same manner as in the case of the polymer (a).

[0049] From the viewpoints of improving the fixation of the ink of the present invention to a recording medium and imparting image fastness to recorded matter while maintaining the long-term ejection reliability and ejection recovery properties of the ink of the present invention, the acid value of the crosslinked polymer (B) is preferably 90 mgKOH / g or more, more preferably 95 mgKOH / g or more, even more preferably 100 mgKOH / g or more, and is preferably 200 mgKOH / g or less, more preferably 180 mgKOH / g or less, even more preferably 160 mgKOH / g or less. The acid value of the crosslinked polymer (B) can be calculated from the charge ratio based on the value of the polymer (b).

[0050] From the viewpoints of improving the fixation of the ink of the present invention to a recording medium and imparting image fastness to a recorded matter while maintaining the long-term ejection reliability and ejection recovery properties of the ink of the present invention, the crosslinking rate of the crosslinked polymer (B) is preferably 20 mol % or more, more preferably 30 mol % or more, even more preferably 40 mol % or more, and is preferably 80 mol % or less, more preferably 70 mol % or less, even more preferably 60 mol % or less. When an epoxy compound is used as the crosslinking agent, the crosslinking rate (mol %) of the crosslinked polymer (B) is calculated by the following formula. Crosslinking rate (mol%) of crosslinked polymer (B)=[molar equivalent number of epoxy groups of epoxy compound in preparation of crosslinked polymer (B)] / [molar equivalent number of carboxyl groups of polymer (b) in preparation of crosslinked polymer (B)]×100

[0051] The average particle size of the pigment-free polymer particles is, from the viewpoint of improving the image fastness of recorded matter while maintaining the long-term ejection reliability and ejection recovery properties of the ink of the present invention, preferably 20 nm or more, more preferably 30 nm or more, even more preferably 40 nm or more, and is preferably 150 nm or less, more preferably 100 nm or less, even more preferably 70 nm or less. The average particle size of the polymer particles not containing a pigment is measured by the method described in the Examples. The average particle size of the non-pigmented polymer particles in the ink of the present invention after preparation of the ink of the present invention is substantially the same as the average particle size of the non-pigmented polymer particles prepared before preparation of the water-based ink.

[0052] Polymer (a) and polymer (b) may be the same or different, that is, polymer (a) and polymer (b) may have different compositions (structures), or may be the same polymer including the composition (structure) and differ only in the presence or absence of a pigment. The polymer (a) and the polymer (b) may be commercially available products. Examples of commercially available dispersions of the polymers (a) and (b) that can be used include Neocryl A1127 (anionic self-crosslinking water-based acrylic resin) manufactured by DSM Neo Resins, Joncryl 390 (acrylic resin) and Joncryl PDX-7775 (styrene-acrylic resin) manufactured by BASF, and Vinyblan 700 (vinyl chloride-acrylic resin) manufactured by Nissin Chemical Industry Co., Ltd. When the polymer particles containing carbon black and the polymer particles not containing a pigment are both crosslinked polymer particles, it is preferred that the components derived from the crosslinking agent among the components constituting the crosslinked polymer are the same. In addition, when the polymer particles containing carbon black and the polymer particles not containing a pigment are both crosslinked polymer particles, it is preferable that the polymer (a) component and the polymer (b) component among the components constituting the crosslinked polymer are the same, and that the components derived from the crosslinking agent among the components constituting the crosslinked polymer are also the same. When the carbon black constituting the ink of the present invention is a crosslinked polymer particle containing carbon black, the polymer particles not containing a pigment are crosslinked polymer particles not containing a pigment, and the polymer (a) component and the polymer (b) component among the components constituting the crosslinked polymer are the same, and the components derived from the crosslinking agent among the components constituting the crosslinked polymer are also the same, not only is image fastness improved, but long-term ejection reliability and ejection recovery are also significantly improved. The details of the reason for this are unclear, but it is thought that when the type of polymer is the same, the coating of the carbon black with the polymer becomes more stable, which makes it easier to express the performance of keeping the amount of silicic acid compound in the ink constant.

[0053] <Wax> The ink of the present invention may contain a wax separately from the viewpoint of improving image fastness of the recorded matter. From the viewpoint of improving image fastness of the recorded matter while maintaining the long-term ejection reliability and ejection recovery property of the ink of the present invention, the melting point of the wax is preferably 95° C. or higher, more preferably 100° C. or higher, even more preferably 105° C. or higher, and is preferably 150° C. or lower, more preferably 145° C. or lower, even more preferably 140° C. or lower. Examples of the wax include polyolefin waxes containing an olefin monomer as a main component, petroleum-based paraffin waxes consisting of a mixture of linear saturated hydrocarbons having 20 to 30 carbon atoms, and synthetic waxes such as Fischer-Tropsch wax. Among these, one or more waxes selected from polyolefin waxes and paraffin waxes are preferred. The wax is preferably contained in the ink in the form of wax particles obtained by dispersing the wax in an aqueous medium.

[0054] <Surfactant> The ink of the present invention may contain a surfactant. The surfactant that may be contained in the ink of the present invention means a surfactant other than that brought in from a wax emulsion or a resin emulsion when the ink of the present invention contains the wax emulsion or the resin emulsion, and examples of nonionic surfactants include polyoxyalkylene alkyl ether type surfactants, acetylene glycol type surfactants, polyhydric alcohol type surfactants, fatty acid alkanolamides, etc. Among these, polyoxyalkylene alkyl ether type surfactants and acetylene glycol type surfactants are preferred, and for example, it is more preferred to use 2,4,7,9-tetramethyl-5-decyne-4,7-diol in combination with a polyoxyalkylene alkyl ether type surfactant. Commercially available examples of nonionic surfactants include the "Surfynol" series manufactured by Nissin Chemical Industry Co., Ltd. and Air Products & Chemicals, the "Acetylenol" series manufactured by Kawaken Fine Chemicals Co., Ltd., and the "Emulgen" series manufactured by Kao Corporation. The above surfactants can be used alone or in combination of two or more.

[0055] <Method of manufacturing the ink of the present invention> The ink of the present invention can be obtained by mixing the above-mentioned carbon black-containing polymer particles, an organic solvent, a silicic acid compound, water, and, if necessary, pigment-free polymer particles and wax, as well as various additives typically used in inks, such as a humectant, wetting agent, penetrant, surfactant, viscosity adjuster, defoamer, preservative, antifungal agent and rust inhibitor.

[0056] <Contents of each component of the ink of the present invention> The contents of the various components in the ink of the present invention are as follows, from the viewpoint of suppressing a decrease in the water repellency of the ink-jet head and from the viewpoint of improving the long-term ejection reliability and ejection recovery properties of the ink of the present invention.

[0057] (Carbon black content) The content of carbon black 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. The content of polymer particles containing carbon black 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.

[0058] The content of the silicic acid compound in the ink of the present invention is 1 ppm by mass or more, preferably 3 ppm by mass or more, more preferably 5 ppm by mass or more, even more preferably 10 ppm by mass or more, and even more preferably 25 ppm by mass or more, from the viewpoint of suppressing a decrease in the water repellency of the inkjet head. Also, from the viewpoint of improving the long-term ejection reliability of the ink of the present invention, the content of the silicic acid compound in the ink is 450 ppm by mass or less, preferably 300 ppm by mass or less, more preferably 200 ppm by mass or less, even more preferably 150 ppm by mass or less, even more preferably 100 ppm by mass or less, even more preferably 75 ppm by mass or less, and even more preferably 50 ppm by mass or less.

[0059] (Organic solvent content) The content of the organic solvent in the ink of the present invention is preferably 15% by mass or more, more preferably 18% by mass or more, and even more preferably 20% by mass or more, from the viewpoints of suppressing a decrease in the water repellency of the inkjet head and improving the long-term ejection reliability and ejection recovery property, and from the same viewpoints, is preferably 35% by mass or less, more preferably 30% by mass or less, and even more preferably 28% by mass or less.

[0060] When the ink of the present invention contains polymer particles that do not contain a pigment, the content thereof 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, even more preferably 10% by mass or less.

[0061] (The ratio of the content of the silicic acid compound in the ink to the product of the specific surface area of ​​the carbon black in the ink and the content of the carbon black) In the ink of the present invention, the ratio of the content of the silicic acid compound in the ink to the product of the specific surface area of ​​the carbon black in the ink and the content of the carbon black [(content of the silicic acid compound (ppm by mass)) / (specific surface area of ​​the carbon black (m 2 It is preferable that the ratio ((g)×(carbon black content (mass %)) / 100) is 0.1 or more and 30 or less. In the above ratio, the product of the specific surface area of ​​the carbon black in the ink and the content of the carbon black is an index showing how much of the silicic acid compound the carbon black in the ink of the present invention supplements. That is, the above ratio is an index showing how much of the silicic acid compound is contained in the ink relative to the ability of the carbon black in the ink to supplement the silicic acid compound dissolved in the ink, and it is considered that the larger the above ratio, the more the silicic acid compound dissolved in the ink becomes excessive, which recrystallizes and becomes coarse particles, thereby adversely affecting the long-term ejection reliability. Also, if the above ratio is too small, it indicates that the ink does not contain enough silicic acid compound to maintain the water repellency of the inkjet head. From the viewpoints of suppressing a decrease in the water repellency of the inkjet head and improving long-term ejection reliability and ejection recovery, the above ratio is more preferably 0.3 or more, even more preferably 1 or more, still more preferably 1.5 or more, and even more preferably 2 or more, and from the viewpoints of suppressing aggregation of the particles containing carbon black and improving long-term ejection reliability, the ratio is more preferably 15 or less, even more preferably 10 or less, still more preferably 7 or less, still more preferably 5 or less, still more preferably 4 or less, and even more preferably 3 or less.

[0062] 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 is preferably 80% by mass or less, more preferably 70% by mass or less.

[0063] <Ink properties> From the viewpoint of improving the long-term jetting reliability and jetting recovery property of the ink of the present invention, 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 is preferably 10 mPa s or less, more preferably 7 mPa s or less, even more preferably 6 mPa s or less. In the present invention, the viscosity of the ink can be measured using an E-type viscometer. From the viewpoint of improving the long-term ejection reliability and ejection recovery of the ink of the present invention, the pH of the ink of the present invention is preferably 7.0 or more, more preferably 7.2 or more, and even more preferably 7.5 or more. Also, from the viewpoint of suppressing the decrease in the water repellency of the inkjet head, the pH is preferably 10 or less, more preferably 9.5 or less, and even more preferably 9.0 or less. The pH of the water-based ink can be measured by the method described in the Examples.

[0064] [Inkjet recording method] The inkjet recording method of the present invention is characterized in that the water-based ink for inkjet printing of the present invention is used and the ink is ejected from an inkjet head using one or more materials selected from silicon and silicon oxide as a nozzle plate member. Nozzle plates using silicon and silicon oxide as components have a water-repellent film formed on the surface of the nozzle plate, thereby improving the ink repellency of the surface of the nozzle plate. Inkjet heads that use silicon or the like as a nozzle plate member include, for example, Samba G3L and Samba G5L manufactured by Fujifilm Dimatix Corporation, and S3200, S800, I3200, I1600, and D3000 manufactured by Seiko Epson Corporation.

[0065] The ink of the present invention can be loaded into a known inkjet recording device such as a piezoelectric type, and ejected as ink droplets onto a recording medium to obtain a recorded matter. As the inkjet recording medium, highly water-absorbent plain paper, low water-absorbent coated paper, and non-water-absorbent resin film can be used. Examples of plain paper include "4200" (manufactured by Fuji Xerox Co., Ltd.) and "NPi Form NEXT-IJ" (manufactured by Nippon Paper Industries Co., Ltd.). Examples of coated papers include the 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). The resin film may be a transparent synthetic resin film, such as a film of polyester, polyvinyl chloride, polyolefin, nylon, etc. Among these, a polyester film or a stretched polypropylene film is preferred, and a film that has been subjected to a corona discharge treatment is more preferred.

[0066] Even when the ink of the present invention is used in an inkjet head equipped with a nozzle plate using a silicon member or a silicon oxide member, it is possible to suppress the elution of the silicon member and the like and to suppress the generation of agglomerated foreign matter in the ink, thereby suppressing the decrease in water repellency of the inkjet head and improving long-term ejection reliability and ejection recovery performance. EXAMPLES

[0067] In the following Preparation Examples, 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.

[0068] <Measurement> (1) Measurement of polymer number average molecular weight The measurement was performed by gel permeation chromatography (GPC apparatus (HLC-8320GPC) manufactured by Tosoh Corporation, columns (TSKgel SuperAWM-H, TSKgel SuperAW3000, TSKgel guardcolumn Super AW-H) manufactured by Tosoh Corporation, flow rate: 0.5mL / min) using a solution of phosphoric acid and lithium bromide dissolved in N,N-dimethylformamide to a concentration of 60mmol / L and 50mmol / L, respectively, as an eluent, and using a monodisperse polystyrene kit with known molecular weight (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) as a standard substance. 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 with a syringe filter (DISMIC-13HP, made of PTFE, 0.2 μm, manufactured by Advantec Co., Ltd.).

[0069] (2) Measurement of solids concentration of aqueous dispersions of polymer particles containing carbon black and polymer particles not containing pigment 10.0 g of sodium sulfate that had been kept at a constant weight in a desiccator was weighed out into a 30 mL ointment container, and approximately 1.0 g of the sample was added and mixed, then accurately weighed, kept at 105°C for 2 hours to remove volatile matter, and left in the desiccator for a further 15 minutes, after which the mass was measured. The mass of the sample after volatile matter removal was taken as the solid content, and was divided by the initial mass of the sample to obtain the solid content concentration.

[0070] (3) Measurement of the average particle size of polymer particles containing carbon black and polymer particles not containing pigment Using a laser particle analysis system (Otsuka Electronics Co., Ltd., product name: ELS-8000), the average particle size of the polymer particles was measured from the aqueous dispersion of the polymer particles by dynamic light scattering, and calculated by cumulant 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, and the refractive index of water (1.333) was input as the refractive index of the dispersion solvent. For the measurement sample, the aqueous dispersion of the polymer particles 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.

[0071] (4) Measurement of the acid value of the polymer The resin was dissolved in a titration solvent of toluene and acetone (2:1) in an automatic potentiometric titrator (Kyoto Electronics Manufacturing Co., Ltd., electric burette, model number: APB-610), and titrated with 0.1N potassium hydroxide / ethanol solution by potentiometric titration, with the inflection point on the titration curve as the end point. The acid value (mgKOH / g) was calculated from the titration amount of potassium hydroxide solution up to the end point.

[0072] (5) Measurement of pH of carbon black In accordance with JIS K 5101-17-2:2004, a mixture of carbon black and distilled water was measured using a glass electrode pH meter. The measurement temperature was 23°C ± 1°C.

[0073] (6) Measurement of the specific surface area of ​​carbon black The amount of nitrogen adsorption was calculated using the BET equation in accordance with ASTM D 6556.

[0074] (7) Measurement of water solubility of crosslinking agent At room temperature 25°C, 90 parts by mass of ion-exchanged water and 10 parts by mass of crosslinking agent (W1) were added to a glass tube (25mmφ×250mmh), and the glass tube was left to stand for 1 hour in a thermostatic bath adjusted to a water temperature of 25°C. Next, the glass tube was vigorously shaken for 1 minute, and then left to stand again in the thermostatic bath for 12 hours. Next, the undissolved matter that separated from the water and precipitated or floated was collected, dried for 6 hours under an environment of 40°C and a gauge pressure of -0.08MPa, and then weighed (W2). The water solubility rate (mass%) was calculated by the following formula (1). Water solubility (mass%)={(W1-W2) / W1}×100 (1)

[0075] (8) Measuring pH of water-based ink The pH of the water-based ink at 25° C. was measured using a tabletop pH meter “F-71” (manufactured by Horiba, Ltd.) that uses a pH electrode “6337-10D” (manufactured by Horiba, Ltd.).

[0076] Preparation Example 1 (Preparation of Polymer (a1)) A monomer mixture was prepared by mixing 31 parts of acrylic acid (reagent manufactured by FUJIFILM Wako Pure Chemical Industries, Ltd.) and 69 parts of styrene (reagent manufactured by FUJIFILM Wako Pure Chemical Industries, Ltd.). In a reaction vessel, 10 parts of methyl ethyl ketone (MEK, reagent manufactured by FUJIFILM Wako Pure Chemical Industries, Ltd.), 0.2 parts of 2-mercaptoethanol (polymerization chain transfer agent, reagent manufactured by FUJIFILM Wako Pure Chemical Industries, Ltd.), and 10% of the monomer mixture were mixed and thoroughly substituted with nitrogen gas. Meanwhile, a mixture of the remaining 90% of the monomer mixture, 0.13 parts of 2-mercaptoethanol, 30 parts of MEK, and 1.1 parts of 2,2'-azobis-(2,4-dimethylvaleronitrile) (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd., product name: V-65 polymerization initiator) was placed in a dropping funnel, and the contents in the reaction vessel were heated to 65°C while stirring under a nitrogen atmosphere, and the contents in the dropping funnel were dropped over 3 hours. The reaction vessel was maintained at 65°C for 2 hours after the end of the dropping from the dropping funnel, and then a solution in which 0.1 parts of the polymerization initiator was dissolved in 2 parts of MEK was added, and the mixture was further held at 65°C for 2 hours, and further aged at 70°C for 2 hours, and then dried under reduced pressure to obtain polymer (a1) (non-crosslinked) (number average molecular weight: 12000, acid value: 240mgKOH / g).

[0077] Production Example 1 (Production of Water Dispersion of Carbon Black-Containing Polymer Particles (Polymer Constituting the Particles=Crosslinked Polymer (A1))) (Process 1) 25 parts of the polymer (a1) obtained in Preparation Example 1 was mixed with 78.6 parts of MEK, and 10.2 parts of a 5N aqueous sodium hydroxide solution (sodium hydroxide solid content 16.9%, Fujifilm Wako Pure Chemical Industries, Ltd., for volumetric titration) was added to neutralize the mixture so that the ratio of the moles of sodium hydroxide to the moles of carboxyl groups in the polymer was 40% (neutralization degree 40%). 400 parts of ion-exchanged water was added, and 100 parts of carbon black pigment (CI Pigment Black 7, Orion Engineered Carbons, Inc., product name: NIPex 180IQ) was added thereto, and the mixture was stirred for 60 minutes at 20°C with a disper blade rotating at 7000 rpm using a disper (Asada Iron Works, Inc., product name: Ultra Disper). (Process 2) Next, the mixture was subjected to 15 passes of dispersion treatment at a pressure of 150 MPa using a Microfluidizer (trade name, manufactured by Microfluidics). 250 parts of ion-exchanged water was added to the resulting dispersion, and the mixture was stirred. MEK was then completely removed at 60°C under reduced pressure, and some of the water was then removed. The liquid phase of the resulting dispersion was collected using a centrifuge and filtered through a membrane filter made of cellulose acetate with a pore size of 5 μm to obtain an aqueous dispersion of polymer particles containing carbon black. At this time, the solid content of the aqueous dispersion of polymer particles containing carbon black was 25%. (Step 3) 100 parts of the aqueous dispersion of polymer particles containing carbon black was placed in a screw-top glass bottle, 31 parts of ion-exchanged water was added, 1.5 parts of trimethylolpropane polyglycidyl ether (manufactured by Nagase Chemtex Corporation, trade name: Denacol EX-321LT, epoxy equivalent: 140, water solubility: 27%) was added, the bottle was sealed, and the bottle was heated at 70°C for 5 hours while stirring with a stirrer (crosslinking rate: 50 mol%). After 5 hours, the dispersion was cooled to room temperature (25°C) and filtered through a membrane filter made of cellulose acetate with a pore size of 5 μm to obtain aqueous dispersion I-1 (solid concentration: 20%, carbon black 15.1%, polymer 4.9%, average particle size 107 nm) of polymer particles containing carbon black (polymer = crosslinked polymer (A1), acid value 120 mg KOH / g, neutralization degree 80%).

[0078] Production Examples 2 to 6 (Production of Water Dispersion of Polymer Particles (Polymer = Crosslinked Polymer (A1)) Containing Carbon Black) Aqueous dispersions I-2 to I-6 of polymer particles containing carbon black were obtained in the same manner as in Production Example 1, except that the carbon black in Production Example 1 was changed to that shown in Table 1. The carbon blacks used in Production Examples 1 to 6 and shown in Table 1 are as follows. NIPex180IQ (Orion Engineered Carbons, pH 4.5, specific surface area 260 m 2 / g, Channel Black) NIPex160IQ (Orion Engineered Carbons, pH 4.5, specific surface area 180m 2 / g, Channel Black) COLOUR BLACK FW 1 (Orion Engineered Carbons, pH 3.5, specific surface area 320m 2 / g, Channel Black) MA8 (Mitsubishi Chemical Corporation, pH 3.0, specific surface area 120 m 2 / g, furnace black) Monarch 717 (Cabot Corporation, pH 8.5, specific surface area 183 m 2 / g, furnace black) Printex55 (Orion Engineered Carbons, pH 9.5, specific surface area 110 m 2 / g, furnace black)

[0079] Production Example 7 (Production of Water Dispersion of Polymer Particles Containing Carbon Black (Polymer = Polymer (a1) (Non-Crosslinked))) In the procedure of Production Example 1, the operations of (Step 1) and (Step 2) were performed, but the operation of (Step 3) was not performed. In (Step 1), 25 parts of the polymer (a1) obtained in Preparation Example 1 was changed to 33.3 parts, and 10.2 parts of 5N sodium hydroxide aqueous solution was changed to 20.2 parts so that the ratio of the moles of sodium hydroxide to the moles of carboxyl groups of the polymer was 80% (neutralization degree 80%), and an aqueous dispersion I-7 of polymer particles containing carbon black (polymer = polymer (a1) (non-crosslinked), acid value 240 mg KOH / g, neutralization degree 80%) was obtained (solid concentration: 20%, carbon black 15.1%, polymer 4.9%, average particle size 105 nm).

[0080] [Table 1]

[0081] Production Example 8 (Production of Water Dispersion of Polymer Particles Containing No Pigment) 15.3 parts of the polymer (a1) obtained in Preparation Example 1 was mixed with 63.5 parts of ion-exchanged water, and 6.2 parts of a 5N aqueous sodium hydroxide solution (solid content: 16.9%) was further added to neutralize the mixture so that the ratio of the moles of sodium hydroxide to the moles of carboxyl groups in the polymer became 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 this polymer dispersion to room temperature, 4.6 parts of trimethylolpropane polyglycidyl ether (Nagase ChemteX Corporation, trade name: Denacol EX-321LT, epoxy equivalent: 140, water solubility: 27%) was added, the mixture was sealed, and heated at 90°C for 1.5 hours while stirring with a stirrer (crosslinking rate: 50 mol%). Thereafter, the polymer dispersion was cooled to room temperature (25°C) and filtered through a cellulose acetate membrane filter with a pore size of 5 μm to obtain water dispersion II-1 (solid concentration: 20%, average particle size 51 nm) containing no pigment (crosslinked polymer, acid value 120 mgKOH / g, neutralization degree 80%).

[0082] Example 1 (Preparation of Water-Based Ink) 28.2 parts of an aqueous dispersion I-1 of polymer particles containing carbon black obtained in Production Example 1 (solid content concentration: 20% by mass) (breakdown: 4.2 parts of carbon black, 1.4 parts of crosslinked polymer A1, 22.6 parts of ion-exchanged water), 25 parts of an aqueous dispersion II-1 of polymer particles not containing a pigment obtained in Production Example 8 (solid content concentration: 20% by mass) (breakdown: 5.0 parts of polymer, 20.0 parts of ion-exchanged water), propylene glycol (PG, manufactured by FUJIFILM Wako Pure Chemical Industries, Ltd. Reagent) 20 parts, diethylene glycol monoisopropyl ether (iPDG, Nippon Nyukazai Co., Ltd.) 5 parts, Surfynol 104PG-50 (Nissin Chemical Industry Co., Ltd., 2,4,7,9-tetramethyl-5-decyne-4,7-diol in propylene glycol 50% solution) 2 parts (2,4,7,9-tetramethyl-5-decyne-4,7-diol solid content 1 part), Emulgen 120 (Kao Corporation, lauryl alcohol ethylene oxide adduct, active content 100%) 0.5 parts, No. 3 sodium silicate (Fuji Chemical Co., Ltd., sodium silicate aqueous solution, active content 38 mass%, (SiO2 (mass%)) / (Na2O (mass%)) = 3.2) 0.0079 parts (sodium silicate active content 0.003 parts), and 1N sodium hydroxide aqueous solution (Fujifilm Wako Pure Chemical Co., Ltd. A suitable amount of carbon black-containing polymer particles (for volumetric analysis) was mixed so that the ink pH became 8.5, and ion-exchanged water was added so that the total amount became 100 parts. The mixture was filtered through a cellulose acetate membrane filter having a pore size of 5 μm to obtain a water-based ink III-1 (polymer particles containing carbon black: 5.6% by mass (including 4.0% by mass of carbon black, 5.0% by mass of polymer particles not containing a pigment, and 30 ppm by mass of silicic acid compound).

[0083] Examples 2 to 11 and Comparative Examples 1 to 3 (Production of Water-Based Inks) Water-based inks III-2 to III-11 and III-12 to III-14 were obtained in the same manner as in Example 1, except that the conditions in Example 1 were changed to those shown in Table 2. The results are shown in Table 2. In Comparative Example 1, a water dispersion of modified carbon black (CAB-O-JET200: product name, manufactured by Cabot Corporation, solid content 20%, no polymer, average particle size 130 nm) was used in place of the polymer particles containing carbon black.

[0084] <Evaluation> Using the water-based inks obtained in the Examples and Comparative Examples, the water repellency of an inkjet head using a silicon oxide nozzle plate was evaluated, as well as the long-term ejection reliability and ejection recovery of the water-based ink in the inkjet head, were evaluated by the following methods. The results are shown in Table 2.

[0085] (1) Evaluation of water repellency of inkjet heads using silicon oxide nozzle plates A Samba G3L inkjet head manufactured by FUJIFILM Dimatix Corporation was used as a test specimen for an inkjet head using a silicon oxide nozzle plate, and the contact angle of water on the water-repellent film was measured as described below to evaluate the effect of the ink composition on the liquid repellency of the water-repellent film. 300 ml of the water-based ink obtained in each of the examples and comparative examples was weighed into a 500 ml wide-mouth bottle (500 ml i-boy wide-mouth bottle (manufactured by AS ONE Corporation)). The test piece was then immersed in the water-based ink, and the container was sealed and then left to stand in a thermostatic chamber set at 50°C for 28 days. The test piece was then removed and washed with ion-exchanged water, and the contact angle of water on the water-repellent film surface of the nozzle plate was measured. Ion-exchanged water was used to measure the contact angle of water, and measurements were made in a normal manner using a contact angle measuring device (DM-500, manufactured by Kyowa Interface Science Co., Ltd.) at 25°C and a relative humidity of 50%. Regarding the water repellency of the silicon nozzle plate, if the contact angle is 80° or more, there is no practical problem, and if the contact angle is 90° or more, it can be used preferably. (2) Evaluation of long-term discharge reliability The water-based inks obtained in the examples and comparative examples were placed in glass containers, sealed, and left to stand in a thermostatic chamber at 50°C for 28 days, and then left to stand at room temperature for another 24 hours. The inks were then filled into a Samba G3L inkjet head manufactured by Fujifilm Dimatix, and a jetXpert inkjet liquid observation device (manufactured by imageXpert) was used to conduct a discharge test in an environment at a temperature of 25±1°C and a relative humidity of 30±5% to confirm the flying behavior. The discharge conditions were a single pulse standard waveform, the voltage was adjusted so that the droplet volume was 2.4 pL, and continuous discharge was performed for 30 minutes. After that, drop 1, located about 0.2 mm from the nozzle, and drop 2, located about 0.6 mm from the nozzle, were photographed simultaneously using a strobe, and the angle of the line connecting drop 1 and drop 2, which are about 0.4 mm apart, was measured for deviation from perpendicular (90 degrees) 1,000 times for each nozzle, and the standard deviation σ was calculated and used as an index of disturbance in the ejection direction. The standard deviation σ was taken as the average value for 30 nozzles for one ink. If the two drops are ejected completely perpendicularly from the nozzle plate, the standard deviation σ = 0. On the other hand, if the positions of drop 1 and drop 2 deviate to the left or right of the perpendicular line from the nozzle plate, the value of the standard deviation σ increases, and it is evaluated that disturbance in the ejection direction has occurred. If the standard deviation σ is less than 15 mrad, there is no problem in practical use, but if it is less than 10 mrad, it can be used preferably, and if it is less than 5 mrad, it can be used more preferably.

[0086] (3) Evaluation of ejection recovery In an environment of 25±1° C. temperature and 30±5% relative humidity, the water-based inks obtained in the examples and comparative examples were filled into a print evaluation device (manufactured by Altec Corporation) equipped with a Samba G3L inkjet head manufactured by Fujifilm Dimatix. The recording medium was a coated paper "OK ​​Topcoat+" (Oji Paper Co., Ltd., product name, water absorption 4.9 g / m 2 ) was fixed to the conveying table of the printing evaluation device under reduced pressure so that the longitudinal direction of the recording medium was aligned with the conveying direction. The ejection conditions were a single pulse standard waveform, the voltage was adjusted to a droplet volume of 2.4 pL, the drive frequency was 20 kHz, the resolution was 1200 x 1200 dpi, and a solid image of 2 cm square with a duty of 100% was printed in one pass. After that, the printer was stopped for 10 minutes and the inkjet head was exposed to the atmosphere. After 10 minutes, the printing substrate was changed to a new one, and printing was resumed again under conditions of 20 kHz without flushing, and the same image printed before the inkjet head was exposed to the atmosphere was printed. The ejection recovery rate (%) was calculated based on the following criteria by observing the obtained print, and the ejection stability was evaluated. Discharge recovery rate (%) = (discharge area of ​​solid printing after 10 minutes of air exposure / discharge area of ​​solid printing before 10 minutes of air exposure) x 100 The higher the ejection recovery rate (%), the better the ejection stability is judged to be.

[0087] [Table 2]

[0088] From Table 2, it can be seen that the water-based inks obtained in Examples 1 to 11 are superior in suppressing the decrease in water repellency of the inkjet head, and in long-term ejection reliability and ejection recovery in inkjet recording, compared to the water-based inks obtained in Comparative Examples 1 to 3.

Claims

1. An aqueous ink for inkjet recording containing polymer particles containing carbon black, an organic solvent, a silicic acid compound, and water, wherein the content of the silicic acid compound is 1 ppm by mass or more and 450 ppm by mass or less in the ink. The aqueous ink for inkjet recording.

2. The aqueous ink for inkjet recording according to claim 1, wherein the polymer particles containing carbon black are crosslinked polymer particles containing carbon black.

3. The aqueous ink for inkjet recording according to claim 2, wherein the acid value of the crosslinked polymer constituting the crosslinked polymer particles containing carbon black is 90 mgKOH / g or more and 200 mgKOH / g or less.

4. The aqueous ink for inkjet recording according to claim 1, wherein the organic solvent is at least one selected from polyhydric alcohols and polyhydric alcohol alkyl ethers.

5. The aqueous ink for inkjet recording according to claim 1, further containing polymer particles not containing a pigment.

6. The pH of the carbon black is 3.0 or more and 9.5 or less, and the specific surface area of the carbon black is 100 m 2 / g or more and 450 m 2 / g or less. The aqueous ink for inkjet recording according to claim 1.

7. The ratio [(content of silicic acid compound (ppm by mass)) / {specific surface area of carbon black (m 2 / g) × content of carbon black (mass%)} / 100] of the content of the silicic acid compound in the ink to the product of the specific surface area of the carbon black and the content of the carbon black in the ink is 0.1 or more and 30 or less. The aqueous ink for inkjet recording according to claim 1.

8. An inkjet recording method of discharging the ink from an inkjet head using, as a nozzle plate member, one or more selected from silicon and silicon oxide, the inkjet recording water-based ink according to any one of claims 1 to 7.