Water-based ink for inkjet printing

Abstract

To provide an aqueous ink for ink jet recording capable of obtaining recorded materials of almost the same image qualities both on gross coat paper having a smooth surface which is difficult to get wet and on which ink is difficult to spread, and on mat coat paper which has irregularities on the surface and which is easily wet and on which ink is easily spread due to a capillary phenomenon.SOLUTION: An aqueous ink for ink jet recording contains pigment, propylene glycol mono n-butyl ether, and polyether-modified silicone. A content of the propylene glycol mono n-butyl ether is 0.5-10 mass% in the ink, and an HLB value of the polyether-modified silicone is 7-14.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a water-based ink for ink-jet printing. [Background technology]

[0002] Inkjet recording is a method of printing characters and images by ejecting ink droplets directly from minute nozzles onto a recording medium. This method has many advantages, including the ease of full-color printing, low cost, the ability to use plain paper as a recording medium, and non-contact printing. In recent years, the spread of digital printing has expanded its use beyond consumer printing to commercial and industrial printing using low-absorbency coated paper, etc., and there has been an increasing demand for water-based inkjet inks with the aim of increasing printing speed, improving image quality, and reducing the environmental impact. In order to meet such demands, various water-based inks have been proposed, provided that they satisfy basic performance requirements such as ejection stability and storage stability. For example, Patent Document 1 discloses an ink composition that has the ejection stability and other properties required of an ink composition and can produce images that are excellent in abrasion resistance and other properties on specialty paper. The ink composition contains an alkali-soluble copolymer, water, a colorant, and a wax, and the copolymer is a copolymer having an acid value of 40 or less obtained by polymerizing an ethylenically unsaturated carboxylic acid monomer and another monomer in the presence of a polymer compound or a copolymerizable surfactant. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2003-261805 Summary of the Invention [Problem to be solved by the invention]

[0004] To achieve the color and texture that users envision, they use a variety of recording media with different surface properties. For coated paper, which is in high demand for high image quality and quality as a recording medium, gloss coated paper with an excellent glossy finish and matte coated paper with a matte finish are used. When ink jet recording is performed using pigment ink, it is advisable to change the recording conditions appropriately depending on the surface characteristics of the recording medium used, but this affects productivity. Therefore, there is a demand for a versatile water-based ink that can produce printed matter of substantially the same image quality regardless of the type of recording medium, such as gloss-coated paper, matte-coated paper, etc. However, when printing on coated paper with different surface conditions, the appearance of the printed matter varies due to differences in wetting properties, and this has not yet been sufficiently improved. The ink composition described in Patent Document 1 has improved to some extent in terms of basic performance as a water-based ink for inkjet printing, but it has problems such as poor wetting and spreading of the ink on gloss-coated paper, resulting in noticeable white voids, and has not improved the problem of excessive wetting and spreading of the ink on matte-coated paper, resulting in different image quality of the recorded material between the two paper types. An object of the present invention is to provide a water-based ink for ink-jet printing that can produce recorded images of substantially the same image quality on either gloss coated paper, which has a smooth surface and thus makes it difficult for the ink to wet and spread, or matte coated paper, which has an uneven surface and therefore makes it easy for the ink to wet and spread due to capillary action. [Means for solving the problem]

[0005] The present inventors have discovered that the above-mentioned problems can be solved by an aqueous ink containing a specific amount of propylene glycol mono-n-butyl ether as an organic solvent and further having a polyether-modified silicone with an HLB value within a specific range. That is, the present invention provides a water-based ink for ink-jet printing containing a pigment, propylene glycol mono-n-butyl ether, and a polyether-modified silicone, The water-based ink for ink-jet printing is provided, in which the content of propylene glycol mono-n-butyl ether in the ink is 0.5% by mass or more and 10% by mass or less, and the HLB value of the polyether-modified silicone is 7 or more and 14 or less. [Effects of the Invention]

[0006] According to the present invention, it is possible to provide a water-based ink for ink-jet printing that can produce recorded images of substantially the same image quality on both gloss coated paper, which has a smooth surface and thus makes it difficult for the ink to wet and spread, and matte coated paper, which has an uneven surface and therefore makes it easy for the ink to wet and spread due to capillary action. DETAILED DESCRIPTION OF THE INVENTION

[0007] [Water-based ink for inkjet printing] The water-based ink for ink-jet printing of the present invention is a water-based ink for ink-jet printing containing a pigment, propylene glycol mono-n-butyl ether, and polyether-modified silicone (hereinafter also simply referred to as "the ink of the present invention"); The content of propylene glycol mono-n-butyl ether in the ink is 0.5% by mass or more and 10% by mass or less, and the HLB value of the polyether-modified silicone is 7 or more and 14 or less. In this specification, "recording" is a concept that includes printing and printing characters or images, and "recorded matter" is a concept that includes printed matter and printed matter on which characters or images are recorded. "Water-based" means that water accounts for the largest proportion of the medium contained in the ink.

[0008] The water-based ink for ink-jet printing of the present invention can produce printed matter of substantially the same image quality on both gloss coated paper, which has a smooth surface and therefore the ink does not wet or spread easily, and matte coated paper, which has an uneven surface and therefore the ink wets or spreads easily due to capillary action. The reason for this is not clear, but is thought to be as follows. The reason why water-based inks do not wet and spread easily on gloss-coated paper is thought to be because the surface of gloss-coated paper is smooth and has low surface free energy. On the other hand, matte-coated paper has the same low surface free energy as gloss-coated paper, but because the surface is uneven, water-based inks penetrate into these unevenness and are thought to wet and spread easily due to capillary action. Furthermore, in terms of liquid absorption, matte-coated paper absorbs organic solvents more easily than gloss-coated paper. Generally, in order for ink to wet and spread on a recording medium with low surface free energy, it is necessary to lower the surface tension of the ink. Because propylene glycol mono-n-butyl ether has low solubility in water, it is thought to orient at the interface between the ink and the recording medium at an early stage after the ink is ejected from the head nozzle and lands on the recording medium. This rapidly reduces the surface tension near the interface, allowing it to wet the coated paper surface, which has low surface free energy. Furthermore, propylene glycol mono-n-butyl ether that orients at the paper surface is absorbed into the matte coated paper surface and quickly detaches from the ink. As a result, it contributes little to the spread of the ink due to capillary action on the matte coated paper, and it is thought that wetting and spreading on the matte coated paper is somewhat suppressed. On the other hand, polyether-modified silicones with an HLB value of 7 to 14 are thought to orient at the interface between the ink and the recording medium once the aqueous ink has spread to a certain extent on the paper surface. Therefore, on matte-coated paper, they are thought to orient at the edge of the ink droplet when the ink begins to spread due to penetration into the surface irregularities by capillary action. However, since the ink droplets are drying at their edges, the polyether-modified silicones bleed out, turning into microscopic oil droplets and being repelled, further suppressing spreading. As a result, it is thought that printed materials with nearly the same image quality can be obtained on both gloss-coated and matte-coated paper.

[0009] <Pigments> The pigment used in the present invention may be either an inorganic pigment or an organic pigment. Examples of inorganic pigments include carbon black and metal oxides, and carbon black is preferred for black inks. Examples of carbon black include furnace black, lamp black, acetylene black, and channel black. Examples of white inks include titanium dioxide, zinc oxide, silica, alumina, and metal oxides such as magnesium oxide. Examples of organic pigments include azo pigments, diazo pigments, phthalocyanine pigments, quinacridone pigments, isoindolinone pigments, dioxazine pigments, perylene pigments, perinone pigments, thioindigo pigments, anthraquinone pigments, and quinophthalone pigments. The hue is not particularly limited, and in the chromatic ink, any chromatic pigment such as yellow, magenta, cyan, red, blue, orange, or green can be used. The pigments can be used alone or in combination of two or more.

[0010] Suitable forms of the pigment include (i) a pigment that can maintain a dispersed state without a dispersant, i.e., a self-dispersing pigment, (ii) a pigment particle form in which the pigment is dispersed with a low-molecular-weight or high-molecular-weight surfactant, and (iii) a polymer particle form containing the pigment. Of these, the polymer particle form containing the pigment is preferred from the viewpoint of the dispersion stability and fixability of the pigment. Here, "pigment-containing polymer particles" (hereinafter also referred to as "pigment-containing polymer particles") means particles in which a polymer encapsulates a pigment, particles consisting of a polymer and a pigment with part of the pigment exposed on the surface, particles in which a polymer is adsorbed to part of the pigment, or a mixture thereof. Of these, particles in which a polymer encapsulates a pigment are more preferred.

[0011] [Pigment-containing polymer particles] The polymer constituting the pigment-containing polymer particles (hereinafter also referred to as "polymer a") may be either water-soluble or water-insoluble, as long as it has at least the pigment dispersibility to disperse the pigment in an aqueous medium, and is preferably a water-insoluble polymer. Here, "water-insoluble" means that when a polymer that has been dried at 105°C for 2 hours and has reached a constant weight is dissolved in 100 g of water at 25°C until saturation is reached, the amount of dissolution is 10 g or less. When the water-insoluble polymer is an anionic polymer, the amount of dissolution is the amount of dissolution when the anionic groups of the polymer are 100% neutralized with sodium hydroxide.

[0012] Examples of polymer a include vinyl resins, polyester resins, polyurethane resins, etc. Among these, vinyl polymers obtained by addition polymerization of vinyl monomers are preferred from the viewpoint of improving the storage stability and ejection stability of the ink of the present invention. The vinyl polymer preferably contains (a-1) a structural unit derived from an ionic monomer, and further preferably contains (a-2) a structural unit derived from a hydrophobic monomer and / or (a-3) a nonionic monomer.

[0013] [(a-1) Ionic Monomer] The (a-1) ionic monomer is preferably an anionic monomer, and examples thereof include carboxylic acid monomers and sulfonic acid monomers, with carboxylic acid monomers being more preferred. The carboxylic acid monomer may be at least one selected from (meth)acrylic acid, crotonic acid, itaconic acid, maleic acid, fumaric acid, and citraconic acid, with at least one selected from acrylic acid and methacrylic acid being more preferred.

[0014] [(a-2) Hydrophobic Monomer] (a-2) The term "hydrophobic" in the hydrophobic monomer means that when the monomer is dissolved in 100 g of ion-exchanged water at 25° C. until saturation, the amount of the dissolved monomer is less than 10 g. Specific examples of the (a-2) hydrophobic monomer include those described in paragraphs

[0020] to

[0022] of JP 2018-83938 A. Among these, alkyl(meth)acrylates having an alkyl group with 1 to 18 carbon atoms, particularly 1 to 10 carbon atoms, aromatic group-containing monomers having an aromatic group with 6 to 22 carbon atoms, and macromonomers having a polymerizable functional group at one end are preferred, with one or more selected from styrene, α-methylstyrene, and benzyl(meth)acrylate being more preferred. The macromonomer having a polymerizable functional group at one end is a compound having a number average molecular weight of 500 or more and 100,000 or less, preferably 1,000 or more and 10,000 or less, and the polymerizable functional group can be an acryloyloxy group or a methacryloyloxy group. The macromonomer is preferably an aromatic group-containing monomer-based macromonomer, and examples of the aromatic group-containing monomer constituting the macromonomer include the aromatic group-containing monomers described above. Specific examples of commercially available styrene-based macromonomers include AS-6(S), AN-6(S), and HS-6(S) manufactured by Toagosei Co., Ltd.

[0015] [(a-3) Nonionic Monomer] (a-3) The nonionic monomer is a monomer that has a high affinity with water or a water-soluble organic solvent, and is, for example, a monomer that contains a hydroxyl group or a polyalkylene glycol chain. Specific examples of the component (a-3) include those described in paragraph

[0018] of JP-A No. 2018-83938. 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. 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.

[0016] (Content of each structural unit in polymer a) The content of the structural units derived from components (a-1) to (a-3) in polymer a is as follows, from the viewpoints of the dispersion stability of the pigment, the storage stability of the ink of the present invention, and obtaining recorded materials of substantially the same image quality on both gloss coated paper and matte coated paper. The content of component (a-1) is preferably 5% by mass or more, more preferably 10% by mass or more, even more preferably 12% by mass or more, and preferably 45% by mass or less, more preferably 40% by mass or less, even more preferably 35% 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 95% by mass or less, more preferably 90% by mass or less, even more preferably 80% by mass or less, and even more preferably 70% by mass or less.

[0017] When the component (a-3) is contained, the content thereof is preferably 2% by mass or more, more preferably 5% by mass or more, even more preferably 10% by mass or more, and preferably 45% by mass or less, more preferably 40% by mass or less, even more preferably 35% by mass or less. The mass ratio of component (a-1) to component (a-2) [component (a-1) / component (a-2)] is preferably 0.1 or more, more preferably 0.2 or more, even more preferably 0.25 or more, and is preferably 1.2 or less, more preferably 0.8 or less, even more preferably 0.5 or less. In the present invention, the content of the structural units derived from the components (a-1) to (a-3) in polymer a can be determined by measurement, or can be substituted by the charging ratio of the raw material monomers including the components (a-1) to (a-3) during the production of polymer a.

[0018] (Production of polymer a) Polymer a can be produced by copolymerizing the mixture of the above-mentioned monomers by a known polymerization method, preferably a solution polymerization method. There are no limitations on the solvent used in the solution polymerization method, but polar solvents such as water, lower aliphatic alcohols, ketones such as methyl ethyl ketone, ethers, and esters are preferred. During polymerization, a polymerization initiator such as an azo compound or a persulfate, or a polymerization chain transfer agent such as a mercaptan, can be used. The polymerization temperature varies depending on the type of polymerization initiator, monomer, and solvent used, but is preferably 30°C or higher, more preferably 50°C or higher, and preferably 95°C or lower, more preferably 80°C or lower. The polymer a is preferably neutralized with a neutralizing agent as described below.

[0019] From the viewpoint of improving dispersion stability, etc., the weight average molecular weight of polymer a is preferably 5,000 or more, more preferably 8,000 or more, even more preferably 10,000 or more, and is preferably 150,000 or less, more preferably 100,000 or less, even more preferably 80,000 or less. From the same viewpoint as above, the acid value of polymer a is preferably 50 mgKOH / g or more, more preferably 70 mgKOH / g or more, even more preferably 90 mgKOH / g or more, and is preferably 400 mgKOH / g or less, more preferably 300 mgKOH / g or less, even more preferably 200 mgKOH / g or less. The weight average molecular weight and acid value of the polymer can be measured by the method described in the Examples.

[0020] <Production of Pigment-Containing Polymer Particles> The pigment-containing polymer particles can be efficiently produced as a pigment aqueous dispersion by a method including the following steps 1 and 2. Step 1: A step of dispersing a pigment mixture containing a pigment, polymer a, an organic solvent, and water to obtain a dispersion. Step 2: A step of removing the organic solvent from the dispersion obtained in Step 1 to obtain an aqueous dispersion of pigment-containing polymer particles (hereinafter also referred to as "pigment aqueous dispersion (i)"). In the present invention, if necessary, the pigment water dispersion (i) obtained in step 2 can be further subjected to a crosslinking treatment with a crosslinking agent.

[0021] (Process I) The pigment mixture in step 1 is preferably obtained by a method in which polymer a is dissolved in an organic solvent, and then the pigment, water, and, if necessary, a neutralizer, a surfactant, etc. are added to the obtained organic solvent solution and mixed to obtain an oil-in-water dispersion. Although there are no restrictions on the organic solvent used in step 1, ketones, ethers, esters, aliphatic alcohols having from 1 to 3 carbon atoms, etc. are preferred, and from the viewpoint of improving the wettability to the pigment and the adsorption of polymer a to the pigment, ketones having from 4 to 8 carbon atoms are more preferred, methyl ethyl ketone and methyl isobutyl ketone are even more preferred, and methyl ethyl ketone is even more preferred. When a vinyl resin is synthesized as polymer a by solution polymerization, the solvent used in the polymerization may be used as is.

[0022] (Neutralization of polymer a) When polymer a has acid groups, it is preferable that at least a portion of the acid groups be neutralized with a neutralizing agent, which is believed to increase the charge repulsion force that occurs after neutralization, thereby suppressing aggregation of pigment particles in aqueous inks and improving the dispersion stability of the pigment. When neutralizing, it is preferable to neutralize so that the pH is 7 or more and 11 or less. Examples of the neutralizing agent include bases such as sodium hydroxide, potassium hydroxide, ammonia, and various amines, with sodium hydroxide and ammonia being preferred. The polymer a may be neutralized in advance. From the viewpoint of improving dispersion stability, the amount of neutralizing agent used is preferably 20 mol% or more, more preferably 30 mol% or more, even more preferably 40 mol% or more, and is preferably 150 mol% or less, more preferably 120 mol% or less, even more preferably 100 mol% or less. Here, the equivalent amount of the neutralizing agent used can be calculated by the following formula, where polymer a before neutralization is "polymer a'". Equivalent amount of neutralizing agent used (mol %)=[{weight (g) of neutralizing agent added / equivalent amount of neutralizing agent} / [{acid value of polymer a' (mg KOH / g) × weight (g) of polymer a'} / (56 × 1,000)]] × 100

[0023] (Dispersion of pigment mixture) In the dispersion treatment in step 1, the pigment particles can be atomized to a desired particle size by main dispersion using shear stress alone. However, from the viewpoint of obtaining a uniform aqueous pigment dispersion, it is preferable to pre-disperse the pigment mixture and then further carry out main dispersion. As a dispersing machine used for preliminary dispersion, a commonly used mixing and stirring device such as an anchor blade or a disperser blade can be used. Examples of means for applying shear stress used in this dispersion include kneaders such as roll mills and kneaders, high-pressure homogenizers such as microfluidizers, and media-type dispersers such as paint shakers and bead mills. Among these, it is preferable to use high-pressure homogenizers and bead mills from the viewpoint of reducing the particle size of the pigment. When a dispersion treatment is carried out using a high-pressure homogenizer, the pigment can be controlled to have a desired particle size by controlling the number of passes at a dispersion pressure of 50 MPa or more, preferably 100 MPa or more.

[0024] (Process 2) The organic solvent can be removed by a known method in step 2. It is preferable that the organic solvent in the obtained pigment water dispersion (i) has been substantially removed, but it may remain in an amount of, for example, 0.1 mass % or less as long as the object of the present invention is not impaired. Furthermore, in order to remove coarse particles and the like, it is preferable that the aqueous dispersion from which the organic solvent has been removed is further centrifuged, and then the liquid layer portion is filtered through a filter or the like, and the pigment aqueous dispersion (i) is obtained by passing through the filter or the like.

[0025] The non-volatile component concentration (solid content concentration) of the resulting pigment water dispersion (i) is preferably 10% by mass or more, more preferably 15% by mass or more, and preferably 45% by mass or less, more preferably 40% by mass or less, from the viewpoint of dispersion stability. From the viewpoint of dispersion stability, the content of the pigment in the pigment water dispersion (i) is preferably 5% by mass or more, more preferably 10% by mass or more, even more preferably 12% by mass or more, and is preferably 45% by mass or less, more preferably 40% by mass or less, even more preferably 30% by mass or less. The average particle size of the pigment-containing polymer particles in the pigment water dispersion (i) is preferably 50 nm or more, more preferably 70 nm or more, even more preferably 80 nm or more, and is preferably 350 nm or less, more preferably 250 nm or less, even more preferably 150 nm or less, from the viewpoint of reducing coarse particles and improving the ejection stability of the water-based ink. The average particle size of the pigment-containing polymer particles in the water-based ink is substantially the same as the average particle size in the pigment water dispersion. The solid content concentration and average particle size of the pigment aqueous dispersion are measured by the method described in the examples.

[0026] <Propylene glycol mono-n-butyl ether> The ink of the present invention contains water-insoluble propylene glycol mono-n-butyl ether, the content of which in the ink is 0.5% by mass or more and 10% by mass or less, in order to obtain printed matter of substantially the same image quality on both gloss coated paper and matte coated paper. The content of propylene glycol mono-n-butyl ether in the ink is preferably 1% by mass or more, more preferably 1.5% by mass or more, even more preferably 2% by mass or more, and preferably 9% by mass or less, more preferably 8% by mass or less, even more preferably 6% by mass or less.

[0027] <Other organic solvents> The ink of the present invention may contain organic solvents other than propylene glycol mono-n-butyl ether (hereinafter also referred to as "other organic solvents") to the extent that the effects of the present invention are not impaired. The other organic solvent is preferably one that is miscible with water in any ratio. The inclusion of other solvents improves the stability of propylene glycol mono-n-butyl ether and polyether-modified silicone in water, and can increase the dot diameter of the ejected ink. Specific examples of other organic solvents include polyhydric alcohols, glycol ethers, nitrogen-containing heterocyclic compounds, etc. Among these, one or more selected from polyhydric alcohols and glycol ethers are preferred, and polyhydric alcohols are more preferred. The boiling point of the other organic solvent is preferably 100°C or higher, more preferably 120°C or higher, even more preferably 140°C or higher, and preferably 260°C or lower, more preferably 250°C or lower, even more preferably 240°C or lower.

[0028] Preferred polyhydric alcohols include diols such as ethylene glycol, propylene glycol, dipropylene glycol, 1,3-butanediol, 1,2-butanediol, 1,4-butanediol, 3-methyl-1,3-butanediol, 1,4-butanediol, 1,5-pentanediol, 2-methyl-2,4-pentanediol, 1,2-hexanediol, 1,6-hexanediol, 2-methyl-2,4-pentanediol, 1,2-octanediol, and 1,8-octanediol. Among these, preferred are at least one selected from propylene glycol, dipropylene glycol, 1,2-butanediol, 1,4-butanediol, and 1,2-hexanediol, more preferred are at least one selected from propylene glycol, dipropylene glycol, and 1,2-butanediol, and even more preferred is propylene glycol. When the ink of the present invention contains propylene glycol, the propylene glycol suppresses the evaporation of propylene glycol mono-n-butyl ether, thereby enhancing the effect of obtaining printed matter of substantially the same image quality on both gloss coated paper and matte coated paper.

[0029] Examples of glycol ethers include ethylene glycol monomethyl ether, diethylene glycol monomethyl ether, triethylene glycol monomethyl ether, polyethylene glycol monomethyl ether, ethylene glycol monoisopropyl ether, diethylene glycol monoisopropyl ether, ethylene glycol monobutyl ether, diethylene glycol monobutyl ether, triethylene glycol monobutyl ether, ethylene glycol monoisobutyl ether, diethylene glycol monoisobutyl ether, diethylene glycol monobenzyl ether, propylene glycol methyl ether, dipropylene glycol methyl ether, tripropylene glycol methyl ether, propylene glycol monopropyl ether, ethylene glycol dimethyl ether, diethylene glycol dimethyl ether, triethylene glycol dimethyl ether, and diethylene glycol methyl ethyl ether. Of these, one or more selected from diethylene glycol monoisopropyl ether, diethylene glycol monobutyl ether, diethylene glycol monoisobutyl ether, and dipropylene glycol methyl ether are preferred, and diethylene glycol monoisopropyl ether is more preferred.

[0030] <Polyether-modified silicone> The polyether-modified silicone used in the ink of the present invention has an HLB value of 7 or more and 14 or less, from the viewpoint of obtaining printed matter of substantially the same image quality on both gloss coated paper and matte coated paper. The HLB value of the polyether-modified silicone is preferably 8 or more, more preferably 9 or more, even more preferably 10 or more, and is preferably 13 or less, more preferably 12 or less, even more preferably 11 or less. Here, the "HLB value" is a value that indicates the affinity of the polyether-modified silicone to water and oil, and can be calculated using the Griffin method according to the following formula: HLB = 20 × [(molecular weight of hydrophilic groups contained in polyether-modified silicone) / (molecular weight of polyether-modified silicone)]

[0031] Polyether-modified silicones have a structure in which the hydrocarbon groups on the side chains and / or terminals of silicone oil are substituted with polyether groups. Suitable polyether groups include polyethyleneoxy groups, polypropyleneoxy groups, and polyalkyleneoxy groups in which ethyleneoxy groups (EO) and propyleneoxy groups (PO) are added in a block or random fashion. Compounds in which polyether groups are grafted onto a silicone main chain, compounds in which silicone and polyether groups are bonded in a block fashion, etc. can be used. Specific examples of polyether-modified silicones include PEG-9 dimethicone, PEG-9PEG-9 dimethicone, PEG-9 methyl ether dimethicone, PEG-10 dimethicone, PEG-11 methyl ether dimethicone, PEG / PPG-20 / 22 butyl ether dimethicone, PEG-32 methyl ether dimethicone, PEG-9 polydimethylsiloxyethyl dimethicone, and lauryl PEG-9 polydimethylsiloxyethyl dimethicone. Commercially available examples of polyether-modified silicones include the BYK series manufactured by BYK Japan K.K., the KF series manufactured by Shin-Etsu Chemical Co., Ltd., Silface SAG manufactured by Nissin Chemical Industry Co., Ltd., and TEGO WET 240 and TEGO WET 270 manufactured by Evonik.

[0032] <Wax> The ink of the present invention preferably contains wax, which is thought to suppress ink bleeding because the wax tends to aggregate with other dispersants as the ink spreads and is easily fixed on the recording medium. The wax may be either a natural wax or a synthetic wax. Examples of natural waxes include petroleum waxes such as paraffin wax and microcrystalline wax; vegetable waxes such as carnauba wax, candelilla wax and rice wax; and animal waxes such as lanolin and beeswax. Examples of synthetic waxes include synthetic hydrocarbon waxes such as polyolefin wax and Fischer-Tropsch wax, silicone waxes, and modified waxes such as paraffin wax derivatives, montan wax derivatives, and microcrystalline wax derivatives. The above waxes can be used alone or in combination of two or more.

[0033] Among the waxes mentioned above, one or more selected from paraffin wax and polyolefin wax are preferred, polyolefin wax which has a large molecular weight and is prone to aggregation is more preferred, and polyethylene wax containing ethylene as the main component is more preferred. Oxidized polyethylene wax can be obtained by adjusting high molecular weight polyethylene to a desired molecular weight by thermal decomposition or the like while introducing oxygen atoms or the like into the molecule, and can be used as polyethylene wax.

[0034] From the viewpoint of ink storage stability and obtaining printed images of substantially the same image quality on both gloss coated paper and matte coated paper, the melting point of the wax is preferably 80°C or higher, more preferably 85°C or higher, and is preferably 150°C or lower, more preferably 145°C or lower. The melting point of the wax is measured by the method described in the Examples.

[0035] The wax is preferably used as a wax emulsion dispersed in an aqueous medium. To ensure dispersibility, the wax emulsion preferably has an anionic or cationic surface charge, or is nonionic. Among these, nonionic wax emulsions are more preferred from the viewpoint of suppressing the influence on other dispersants and reducing the influence of other dispersants to achieve good ink performance. A nonionic wax emulsion can be obtained, for example, by mixing and emulsifying wax with a known nonionic surfactant.

[0036] The average particle size of the wax particles in the wax emulsion, particularly the average particle size of the paraffin wax particles and / or polyolefin wax particles, is preferably 300 nm or less, more preferably 250 nm or less, even more preferably 150 nm or less, from the viewpoint of wax dispersion stability and obtaining printed matter of substantially the same image quality on both gloss coated paper and matte coated paper, and is preferably 20 nm or more, preferably 40 nm or more. The average particle size of the wax particles can be measured by dynamic light scattering, for example, using a Microtrac particle size analyzer UPA manufactured by Nikkiso Co., Ltd. according to the method described in the Examples. The average particle size of the wax particles in the water-based ink is substantially the same as the average particle size of the wax particles in the wax emulsion.

[0037] <Other surfactants> The ink of the present invention may contain other surfactants besides the polyether-modified silicone as long as the effects of the present invention are not impaired. As such other surfactants, nonionic surfactants are preferred, and examples thereof include acetylene glycol surfactants, fluorine-based surfactants, and alkylene surfactants. However, from the viewpoint of obtaining printed matter of substantially the same image quality on both gloss coated paper and matte coated paper, acetylene glycol surfactants are preferred.

[0038] Acetylene glycol surfactants are surfactants with relatively low molecular weights, and therefore have relatively low dynamic surface tension in the short-term range, which is thought to assist the function of propylene glycol mono-n-butyl ether in the present invention. Examples of acetylene glycol surfactants include acetylene glycols having 8 to 22 carbon atoms and ethylene adducts of the acetylene glycols, and 2,4,7,9-tetramethyl-5-decyne-4,7-diol, 3,6-dimethyl-4-octyne-3,6-diol, or 3,5-dimethyl-1-hexyn-3-ol, 2,4-dimethyl-5-hexyn-3-ol, and ethylene oxide adducts thereof are preferred. The HLB value of the acetylene glycol surfactant is preferably 8 or less, more preferably 6 or less, and even more preferably 5 or less, from the viewpoints of suppressing solubility in water and enabling ink droplets to quickly orient on the dot surface after landing on a recording medium, thereby improving the wettability of the ink on the recording medium, and is preferably 12 or more, more preferably 2 or more, and even more preferably 3 or more. Examples of commercially available acetylene glycol surfactants include the Surfynol series manufactured by Air Products & Chemicals and the Acetylenol series manufactured by Kawaken Fine Chemicals Co., Ltd.

[0039] [Production of the ink of the present invention] The ink of the present invention can be efficiently produced by mixing the pigment aqueous dispersion (i) containing the pigment-containing polymer particles, propylene glycol mono-n-butyl ether, polyether-modified silicone, and, if necessary, other organic solvents, other surfactants, water, and various additives. There are no particular limitations on the method for mixing the above components. Examples of the additives include fixing aids, humectants, wetting agents, penetrating agents, viscosity adjusters, antifoaming agents, preservatives, antifungal agents, and antirust agents. The fixing aid may be an emulsion containing water-insoluble polymer particles. Examples of the water-insoluble polymer particles include particles of condensation resins such as polyurethane and polyester; and vinyl resins such as (meth)acrylic resins, styrene resins, styrene-(meth)acrylic resins, butadiene resins, styrene-butadiene resins, vinyl chloride resins, vinyl acetate resins, and acrylic silicone resins.

[0040] The content of each component of the ink of the present invention and the ink properties are as follows, from the viewpoint of improving ejection stability and obtaining recorded images of substantially the same image quality on both gloss coated paper and matte coated paper. (Pigment content) The content of the pigment in the ink of the present invention is preferably 1% by mass or more, more preferably 2% by mass or more, even more preferably 4% by mass or more, and is preferably 15% by mass or less, more preferably 10% by mass or less, even more preferably 8% by mass or less. (polymer content) The polymer content in the ink of the present invention is preferably 0.5% by mass or more, more preferably 1% by mass or more, even more preferably 1.5% by mass or more, and preferably 10% by mass or less, more preferably 6% by mass or less, even more preferably 4% by mass or less. (Content of pigment-containing polymer particles) The content of the pigment-containing polymer particles in the ink of the present invention, in terms of the total of the pigment and polymer, is preferably 2% by mass or more, more preferably 4% by mass or more, even more preferably 6% by mass or more, and is preferably 20% by mass or less, more preferably 15% by mass or less, even more preferably 10% by mass or less.

[0041] (Propylene glycol mono-n-butyl ether content) As described above, the content of propylene glycol mono-n-butyl ether in the ink of the present invention is 0.5% by mass or more, preferably 1% by mass or more, more preferably 1.5% by mass or more, even more preferably 2% by mass or more, and is 10% by mass or less, preferably 9% by mass or less, more preferably 8% by mass or less, even more preferably 6% by mass or less. (Content of other organic solvents) From the viewpoint of stably retaining propylene glycol mono-n-butyl ether in the ink, the content of other organic solvents in the ink of the present invention is preferably 5% by mass or more, more preferably 10% by mass or more, more preferably 15% by mass or more, and is preferably 30% by mass or less, more preferably 28% by mass or less, and even more preferably 25% by mass or less.

[0042] (Polyether-modified silicone content) The content of polyether-modified silicone in the ink of the present invention is preferably 0.005% by mass or more, more preferably 0.01% by mass or more, even more preferably 0.02% by mass or more, and still more preferably 0.1% by mass or more, and is preferably 0.9% by mass or less, more preferably 0.7% by mass or less, and even more preferably 0.5% by mass or less.

[0043] (Wax content) The wax content in the ink of the present invention is preferably 0.1% by mass or more, more preferably 0.2% by mass or more, even more preferably 0.3% by mass or more, and preferably 1.5% by mass or less, more preferably 1.2% by mass or less, even more preferably 1% by mass or less.

[0044] (Content of other surfactants) The content of other surfactants, particularly acetylene glycol surfactants, in the ink of the present invention is preferably 0.1% by mass or more, more preferably 0.2% by mass or more, even more preferably 0.3% by mass or more, and preferably 1.5% by mass or less, more preferably 1.2% by mass or less, even more preferably 1% by mass or less.

[0045] (Water content) The water content in the ink of the present invention is preferably 35% by mass or more, more preferably 45% by mass or more, even more preferably 55% by mass or more, and preferably 95% by mass or less, more preferably 90% by mass or less, even more preferably 85% by mass or less.

[0046] (Physical properties of ink of the present invention) From the viewpoint of improving the storage stability of the ink, the viscosity of the ink of the present invention at 32°C is preferably 2 mPa·s or more, more preferably 4 mPa·s or more, and preferably 12 mPa·s or less, more preferably 9 mPa·s or less. The pH of the ink of the present invention is preferably 7 or more, more preferably 7.5 or more, from the viewpoint of improving the storage stability of the ink, and is preferably 10 or less, more preferably 9.5 or less, from the viewpoint of component resistance and skin irritation.

[0047] [Inkjet recording method] The ink of the present invention can be loaded into a known ink jet recording apparatus and ejected as ink droplets onto a recording medium to obtain a recorded image or the like. Ink jet recording apparatuses include those of the piezo-driven type and those of the thermal-driven type, but it is more preferable to use water-based ink for ink jet printing of the piezo-driven type. Usable recording media include highly water-absorbent plain paper, low water-absorbent coated paper, art paper, and non-water-absorbent resin films such as polyester film and polypropylene film. By using the ink of the present invention, inkjet recordings of substantially the same image quality can be obtained on both gloss coated paper, which has a particularly smooth surface and thus the ink does not easily wet and spread, and matte coated paper, which has an uneven surface and therefore the ink easily wets and spreads due to capillary action. [Example]

[0048] In the following Production Examples, Examples and Comparative Examples, "parts" and "%" are "parts by mass" and "% by mass" unless otherwise specified. The methods for measuring each physical property are as follows.

[0049] (1) Measurement of weight-average molecular weight of water-insoluble polymers The measurement was performed using a gel chromatography method (Tosoh GPC system (HLC-8120GPC), Tosoh columns (TSK-GEL, α-M × 2), flow rate: 1 mL / min) with a solution of phosphoric acid (Fujifilm Wako Pure Chemical Industries, Ltd., special grade reagent) and lithium bromide (Tokyo Chemical Industry Co., Ltd., reagent) dissolved in N,N-dimethylformamide (Fujifilm Wako Pure Chemical Industries, Ltd., for high performance liquid chromatography) to concentrations of 60 mmol / L and 50 mmol / L, respectively, as the eluent, using monodisperse polystyrene of known molecular weight as a standard substance.

[0050] (2) Measurement of the acid value of the polymer The resin was dissolved in a titration solvent consisting of a mixture of toluene and acetone (2:1 by mass) in an automatic potentiometric titrator (Kyoto Electronics Manufacturing Co., Ltd., electric burette, model number: APB-610), and titrated with a 0.1 N potassium hydroxide / ethanol solution by potentiometric titration. The inflection point on the titration curve was taken as the endpoint. The acid value (mg KOH / g) was calculated from the titration volume of the potassium hydroxide solution up to the endpoint.

[0051] (3) Measurement of the average particle size of pigment-containing polymer particles The particle size was measured by dynamic light scattering using a laser particle analysis system (manufactured by 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 times. The refractive index of water (1.333) was input as the refractive index of the dispersion solvent. The measured concentration was 5 × 10 -3 The measurement was carried out in mass % (converted into solid content concentration), and the obtained cumulant average particle size was taken as the average particle size of the polymer particles.

[0052] (4) Measurement of solids concentration of pigment water dispersion 10.0 g of sodium sulfate, brought to a constant weight in a desiccator, was weighed into a 30 mL polypropylene container (φ: 40 mm, height: 30 mm), and approximately 1.0 g of the sample was added and mixed. The mixture was then accurately weighed and maintained at 105°C for 2 hours to remove volatiles. The mixture was then left in the desiccator for another 15 minutes and the mass was measured. The mass of the sample after volatiles removal was taken as the solid content and divided by the mass of the added sample to obtain the solid content concentration.

[0053] (5) Measurement of the melting point of wax The melting point of the wax was measured using a measuring device conforming to JIS K 0064. Specifically, using a differential scanning calorimeter (Q20, manufactured by TA Instruments), the sample was heated to 200°C and then cooled to 0°C at a rate of 10°C / min. The sample was then heated at a rate of 10°C / min, and the calorific value was measured up to 200°C. The temperature of the peak with the largest peak area among the observed heat of fusion peaks was taken as the maximum peak temperature of melting, and this peak temperature was taken as the melting point.

[0054] (6) Measurement of the average particle size of wax particles in a wax emulsion The average particle size of wax particles in the wax emulsion was measured using a Nikkiso Microtrac particle size analyzer UPA at a laser wavelength of 780 nm, a laser output of 3 mW, and a sample concentration of 5 × 10 -3 The median value of the volume average particle size distribution (D 50 ) was taken as the average particle size of the wax particles in the wax emulsion.

[0055] Production Example 1 (Production of aqueous dispersion of pigment-containing polymer particles) (1) Production of water-insoluble polymers 16 parts of methacrylic acid, 44 parts of styrene, 30 parts of styrene macromonomer (manufactured by Toagosei Co., Ltd., trade name: AS-6S, number average molecular weight: 6,000, solid content concentration: 50%), and 25 parts of methoxypolyethylene glycol methacrylate (manufactured by NOF Corporation, trade name: Blemmer PME-200) were mixed to prepare 115 parts of a monomer mixture. In a reaction vessel, 18 parts of methyl ethyl ketone (MEK), 0.03 parts of 2-mercaptoethanol (chain transfer agent), and 10% (11.5 parts) of the monomer mixture were placed and mixed, and the atmosphere was thoroughly replaced with nitrogen gas. Meanwhile, a mixture of the remaining 90% (103.5 parts) of the monomer mixture with 0.27 parts of the chain transfer agent, 42 parts of MEK, and 3 parts of a polymerization initiator (2,2'-azobis(2,4-dimethylvaleronitrile), manufactured by Fujifilm Wako Pure Chemical Industries, Ltd., product name: V-65) was placed in a dropping funnel. The mixture in the reaction vessel was heated to 75°C under a nitrogen atmosphere while stirring, and the mixture in the dropping funnel was added dropwise over 3 hours. After 2 hours at 75°C from the end of the dropping, a solution of 3 parts of the polymerization initiator in 5 parts of MEK was added, and the mixture was further aged at 75°C for 2 hours and then at 80°C for 2 hours. 50 parts of MEK was then added to obtain a solution of a water-insoluble polymer (weight average molecular weight: 50,000, acid value: 104 mgKOH / g) (solids concentration: 45%).

[0056] (2) Preparation of aqueous dispersion of pigment-containing polymer particles 95.2 parts of the water-insoluble polymer solution obtained in (1) above was dissolved in 53.9 parts of MEK, and 135.0 parts of a 5N aqueous solution of sodium hydroxide, 0.5 parts of 25% aqueous ammonia, and 341.3 parts of ion-exchanged water were added as neutralizing agents to the solution. 100 parts of CI Pigment Black 7 (manufactured by Cabot Corporation) was then added as a carbon black pigment to obtain a pigment mixture (degree of neutralization: 78.8 mol%). The resulting pigment mixture was mixed for 1 hour using a disperser blade at 7000 rpm and 20°C, and the resulting dispersion was subjected to a dispersion treatment using a Microfluidizer (manufactured by Microfluidics, product name: M-140K) for 15 passes at a pressure of 180 MPa. The obtained dispersion of pigment-containing polymer particles was cooled under reduced pressure at 60°C to remove MEK, and then some of the water was removed. The mixture was then centrifuged, and the liquid phase was filtered through a filter (manufactured by Sartorius, trade name: Mini Sart Syringe Filter, pore size: 5 μm, material: cellulose acetate) to remove coarse particles, yielding an aqueous dispersion of pigment-containing polymer particles (solid concentration: 25%, pigment: 17.5%, polymer: 7.5%, average particle size: 100 nm).

[0057] Example 1 (Production of Water-Based Ink 1) 30.0 parts of the aqueous dispersion of pigment-containing polymer particles obtained in Production Example 1 [solid content: 7.5 parts (pigment: 5.25 parts, polymer: 2.25 parts)], 3.0 parts of propylene glycol mono-n-butyl ether (manufactured by Nippon Nyukazai Co., Ltd., trade name: BFG), 0.1 parts of polyether-modified silicone (manufactured by Shin-Etsu Chemical Co., Ltd., trade name: KF-353A, HLB: 10), 20.0 parts of propylene glycol (manufactured by AGC Corporation), 20.0 parts of polyethylene wax (manufactured by Toho Chemical Industry Co., Ltd., trade name: Hi-Tec E-6500, nonionic polyethylene wax emulsion, melting point 1.7 parts of a water-based ink containing 100 parts of a cellulose acetate copolymer (product name: Surfynol 104PG50, HLB: 4, active ingredient: 50% by mass), 1.2 parts of an acetylene-based surfactant (manufactured by Nissin Chemical Industry Co., Ltd., trade name: Surfynol 104PG50, HLB: 4, active ingredient: 50% by mass), and ion-exchanged water were added to bring the total amount to 100 parts, and the mixture was stirred with a magnetic stirrer for 30 minutes. The mixture was then filtered using a syringe equipped with a 5 μm acetylcellulose filter to obtain Water-based Ink 1 [solid concentration: 8.1%, pigment-containing polymer particles: 7.5% (pigment: 5.25%, polymer: 2.25%), average particle size: 95 nm].

[0058] Examples 2 to 12 and Comparative Examples 1 to 3 (Production of Water-Based Inks 2 to 12 and Comparative Examples 21 to 23) In the same manner as in Example 1, water-based inks 2 to 12 and 21 to 23 were obtained according to the formulations shown in Table 1. The results are shown in Table 1. The amount of each component in Table 1 is the amount of solid content (active content).

[0059] The details of each component in Table 1 are as follows: [Polyether-modified silicone] KF-6011: Shin-Etsu Chemical Co., Ltd., product name, HLB: 12 KF-640: Shin-Etsu Chemical Co., Ltd., product name, HLB: 14 SAG005: Manufactured by Nissin Chemical Industry Co., Ltd., Product name: Silface SAG005, HLB: 7 KF-6014: Shin-Etsu Chemical Co., Ltd., product name, HLB: 5 [Paraffin wax] AQUACER 539: BYK, product name, nonionic paraffin wax emulsion, melting point: 90°C, average particle size: 220 nm, solid content: 35% by mass

[0060] Using the water-based inks obtained in the examples and comparative examples, dot diameters and the difference in line width between matte coated paper and gloss coated paper were measured by the following methods. The results are shown in Table 1.

[0061] <Measurement of dot diameter> An inkjet printer (ImageXpert, product name: Jetxpert) equipped with a Fujifilm Dimatix piezo-driven inkjet head (product name: Samba G3L) was filled with water-based ink. After adjusting the head voltage to 30 V, frequency to 20 kHz, push-pull drive waveform, and ink ejection volume to 2.0 pL, printing was performed at a resolution of 1200 x 1200 dpi on gloss-coated paper (Oji Paper, product name: OK Topcoat+) and matte-coated paper (GRAFICAS Y FORMULARIOS, product name: Fitnes Matt), with an image density of 6%. The resulting print was observed under an optical microscope, and the diameter of the ink dots was measured and recorded as the dot diameter. To print evenly on paper at a resolution of 1200 dpi, a dot diameter of 30 μm is required, but due to the impact accuracy of the inkjet head, a dot diameter of 30 μm can cause streaks (white spaces), etc. Therefore, a dot diameter of 31 μm or more was deemed acceptable.

[0062] <Measurement of the difference in line width between matte coated paper and gloss coated paper> The same gloss-coated paper and matte-coated paper as above were prepared, and an inkjet printer (manufactured by Tritec Corporation) equipped with a piezo-driven inkjet head, product name: KJ4B-600, manufactured by Kyocera Corporation, was filled with water-based ink, and a line five dots wide was printed on each of the gloss-coated paper and matte-coated paper. The resulting prints were observed under an optical microscope and the line widths were measured. The difference in line width was calculated by subtracting the line width of the gloss coated paper from the line width of the matte coated paper. The smaller this difference, the more equivalent the image quality of the gloss coated paper and matte coated paper. The difference in line width is preferably 100 μm or less, more preferably 50 μm or less, and even more preferably 35 μm or less.

[0063] [Table 1]

[0064] Table 1 shows that the water-based inks of Examples 1 to 12 produced larger dot diameters on gloss-coated paper than the water-based ink of Comparative Example 1, and that the difference in line width between matte-coated paper and gloss-coated paper was smaller than that of the water-based ink of Comparative Example 2, which contained propylene glycol mono-n-butyl ether but no polyether-modified silicone. Furthermore, it can be seen that when the HLB value of the polyether-modified silicone is less than 7, as in Comparative Example 3, a repellency phenomenon occurs, resulting in uneven printing.

Claims

1. A water-based ink for ink-jet printing, comprising a pigment, propylene glycol mono-n-butyl ether, and a polyether-modified silicone, Further comprising a wax, the content of propylene glycol mono-n-butyl ether in the ink is 0.5% by mass or more and 10% by mass or less, and the HLB value of the polyether-modified silicone is 7 or more and 14 or less, a water-based ink for inkjet printing, the water-based ink comprising: a pigment in the form of polymer particles containing the pigment; a polymer constituting the pigment-containing polymer particles is a vinyl polymer; the vinyl polymer contains a structural unit derived from a hydrophobic monomer; and the hydrophobic monomer consists of only one or more monomers selected from the group consisting of alkyl(meth)acrylate having an alkyl group having from 1 to 18 carbon atoms, styrene, α-methylstyrene, and a macromonomer having a polymerizable functional group at one end.

2. 2. The water-based ink for ink-jet printing according to claim 1, wherein the content of the polyether-modified silicone is from 0.005% by mass to 0.9% by mass.

3. 3. The water-based ink for ink-jet printing according to claim 1, further comprising an organic solvent other than propylene glycol mono-n-butyl ether.

4. 4. The water-based ink for ink-jet printing according to claim 3, wherein the organic solvent other than propylene glycol mono-n-butyl ether is at least one selected from the group consisting of polyhydric alcohols and glycol ethers.

5. 5. The water-based ink for ink-jet printing according to claim 1, further comprising an acetylene glycol surfactant.

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