Pigment dispersion for aqueous inkjet and method for producing same

Abstract

The present invention relates to a pigment dispersion for aqueous inkjet, which contains a black pigment, a dispersant, an organic solvent and water, and is characterized in that: the black pigment is carbon black having a dibutyl phthalate (DBP) absorption amount of 80-150 cm3 / 100 g, and the dispersant contains a benzyl acrylate copolymer as an active ingredient; the organic solvent contains at least one selected from the group consisting of C4-10 glycol ethers, monohydric alcohols and polyhydric alcohols, the monohydric alcohols and the polyhydric alcohols are C4-10 chain saturated alcohols, and the total amount of the organic solvent is 1-8 wt% of the total amount of the aqueous inkjet pigment dispersion. The present invention can provide a pigment dispersion capable of producing an aqueous inkjet ink having good filter filterability, and a method for producing the pigment dispersion.

Description

Technical Field

[0001] The present invention relates to a pigment dispersion for aqueous inkjet and a method for producing the same, and in particular to a pigment dispersion for aqueous inkjet using carbon black as a pigment and a method for producing the same. Background Art

[0002] In recent years, due to the improvement of image quality and printing speed, inkjet printers are used not only for home printing but also for printing of various businesses such as business documents. On the other hand, in printing for commercial and industrial purposes such as the latter, there is a further demand for higher image quality and higher speed printing, and various studies have been conducted to cope with these (e.g., Patent Documents 1 to 3).

[0003] Patent document 1 proposes that in addition to being able to record images with excellent text quality, images that are not easily smudged even when drawn with a marker and have excellent fastness such as marking resistance can be recorded. In the aqueous ink for inkjet containing a pigment and a polyurethane resin, a specific polyurethane resin is used, and the dynamic surface tension of the aqueous ink is set within a specified range.

[0004] In Patent Document 2, as the properties required for a coloring composition (ink) become higher, the dispersibility of the coloring material in the existing dispersant is insufficient, and when the amount of the dispersant used is increased, heat resistance such as hue change caused by heating during or after ink ejection becomes a problem. Therefore, a dispersant having excellent dispersibility even in a small amount is provided, and a polymerization product in which a specific block copolymer has a content ratio within a specified range and a coloring composition containing the polymerization product are proposed.

[0005] Patent document 3 provides an aqueous ink for inkjet recording that improves the abrasion resistance of coated paper recording, and proposes that the resin particles contained in the aqueous ink for inkjet recording be composed of a specified polymer and that the storage modulus of the dried ink film at 25°C be set within a specified range.

[0006] Prior art literature

[0007] Patent Literature

[0008] Patent Document 1: Japanese Patent Application Publication No. 2018-150514

[0009] Patent Document 2: Japanese Patent Application Publication No. 2021-98835

[0010] Patent Document 3: Japanese Patent Application Publication No. 2022-156109 Summary of the invention

[0011] Technical problem to be solved by the invention

[0012] The above-mentioned prior art is believed to be able to meet the market demand for high-quality images and high-speed printing in inkjet printing. However, according to the research of the inventors of the present invention, it has been found that in these prior art, in the filter filtration process usually performed in the final stage of manufacturing inkjet ink, the filter sometimes has poor filterability and needs to increase the filtration pressure or the filter is easily clogged and needs to be frequently replaced, which sometimes increases power consumption, the amount of filter used, the workload of filter replacement, and the amount of ink loss.

[0013] Therefore, an object of the present invention is to provide a pigment dispersion capable of producing an aqueous inkjet ink having good filterability and a method for producing the pigment dispersion.

[0014] Technical solutions for solving technical problems

[0015] In order to solve the above technical problems, the inventors of the present invention have conducted intensive research. As a result, it has been found that by using specific compounds for the pigment, dispersant, and organic solvent in the aqueous inkjet pigment dispersion and setting the total amount of the organic solvent to a specified range, a pigment dispersion capable of manufacturing an aqueous inkjet ink having good filterability can be obtained. The present invention relates to the following (1) to (4).

[0016] (1) A pigment dispersion for aqueous inkjet, comprising a black pigment, a dispersant, an organic solvent and water, wherein:

[0017] The black pigment is dibutyl phthalate (DBP) with an absorption of 80 to 150 cm 3 / 100g of carbon black,

[0018] The above dispersant contains a benzyl acrylate copolymer as an active ingredient.

[0019] The organic solvent contains at least one selected from glycol ethers having 4 to 10 carbon atoms, monohydric alcohols and polyhydric alcohols, and the monohydric alcohols and polyhydric alcohols are chain saturated alcohols having 4 to 10 carbon atoms.

[0020] The total amount of the organic solvent is 1 to 8% by weight of the entire aqueous inkjet pigment dispersion.

[0021] (2) The aqueous inkjet pigment dispersion according to the above item (1), wherein the dispersant is contained in an amount of 15 to 60 parts by weight based on solid content, relative to 100 parts by weight of the black pigment.

[0022] (3) A method for producing an aqueous inkjet pigment dispersion, which is used to produce the aqueous inkjet pigment dispersion described in the above item (1) or (2), the method comprising:

[0023] A step of obtaining a mixed solution containing the black pigment, the dispersant, the organic solvent and the water, adjusting the content of the organic solvent in the entire mixed solution to 1 to 8% by weight, and then dispersing the mixed solution.

[0024] (4) An aqueous inkjet ink comprising the aqueous inkjet pigment dispersion according to the above item (1) or (2).

[0025] Effects of the Invention

[0026] According to the present invention, it is possible to provide a pigment dispersion capable of producing an aqueous inkjet ink having excellent filterability and a method for producing the pigment dispersion. DETAILED DESCRIPTION

[0027] (Pigment dispersion for aqueous inkjet)

[0028] The aqueous inkjet pigment dispersion (hereinafter sometimes referred to as "pigment dispersion") according to the embodiment of the present invention contains a black pigment, a dispersant, an organic solvent and water. The components contained in the pigment dispersion are as follows. The black pigment is dibutyl phthalate (DBP) with an absorption of 80 to 150 cm 3 / 100g of carbon black. The dispersant contains a benzyl acrylate copolymer as an effective ingredient. The organic solvent contains at least one selected from glycol ethers having 4 to 10 carbon atoms, monohydric alcohols and polyhydric alcohols. In addition, the monohydric alcohol and the polyhydric alcohol are chain saturated alcohols having 4 to 10 carbon atoms. In addition, the total amount of the organic solvent is 1 to 8% by weight in the entire aqueous inkjet pigment dispersion.

[0029] Thus, by using specific compounds as black pigment, dispersant, and organic solvent, setting the total amount of organic solvent to a predetermined range, and performing a dispersion treatment, good filterability can be achieved when preparing an aqueous inkjet ink. The filterability of the pigment dispersion can be evaluated by the method described in the Examples section described later.

[0030] Hereinafter, the components of the pigment dispersion will be described.

[0031] As long as the black pigment has a DBP absorption of 80 to 150 cm 3 / 100g of carbon black is sufficient. As long as the carbon black has a DBP absorption within the specified range, channel black, furnace black, acetylene black, etc. can be used. The size of the carbon black can be any size suitable for inkjet ink applications, for example, the average primary particle size can be 13 to 25nm, preferably 15 to 20nm. The average primary particle size can be calculated as the average value of the major diameter and minor diameter when more than 100 pigment particles are observed using a transmission electron microscope (the average value of the number of measurements of 1 / 2 of the sum of the major diameter (nm) and minor diameter (nm) of one particle). The DBP absorption can be measured based on JIS K6221. In addition, the average particle size of the secondary particles formed by the aggregation of primary particles is generally 50 to 200nm. The average particle size can be measured, for example, using general methods such as dynamic light scattering and laser diffraction. More specifically, for example, the measurement can be performed using a zeta potential / particle size / molecular weight measurement system (manufactured by Otsuka Electronics Co., Ltd., ELSZ-2000ZS).

[0032] The pH of carbon black is not particularly limited, but is preferably pH 6.0 to 9.0.

[0033] Commercially available carbon blacks can be used, for example, MA600, MA600B, #750B, #650B, #40, #40B, MA100, MA100R, #3230B manufactured by Mitsubishi Chemical Corporation, HIBLACK890, HIBLACK30, COLOUR BLACK FW1, COLOUR BLACK S160, COLOUR BLACK S170, NEROX510, NEROX600, SPECIAL BLACK 4, SPECIAL BLACK 5, SPECIAL BLACK 6, NIPex60, NIPex 90, NIPex 160IQ, NIPex 170IQ, NIPex 180IQ, PRINTEX U, TOKABLACK #3855 manufactured by Tokai Carbon Co., Ltd., SUNBLACK 305, SUNBLACK 320, SUNBLACK X15 manufactured by Asahi Carbon Co., Ltd., Niteron #300IH ISAF-HS, Niteron #300ISAF, Niteron #200IS HAF-HS manufactured by Nippon Steel Carbon Co., Ltd., etc.

[0034] As the carbon black, one kind of carbon black having predetermined properties may be used alone, or two or more kinds thereof may be used in combination.

[0035] The content of the black pigment is preferably as high as possible within a range in which stability is maintained, and is preferably 15.0 to 25.0% by weight in the pigment dispersion.

[0036] As long as the dispersant contains a benzyl acrylate copolymer as an active ingredient as described above. As long as the benzyl acrylate copolymer is a copolymer composed of a structural unit from benzyl acrylate and a structural unit from a monomer that can be polymerized with benzyl acrylate. The copolymer can be a random copolymer or a block copolymer. From the viewpoint of further improving the filterability of the filter, a block copolymer is preferred. In addition, as a block copolymer, it is preferred to contain a hydrophilic block (hereinafter sometimes referred to as "block A"). And a hydrophobic block (hereinafter sometimes referred to as "block B".). Wherein, the hydrophilic block refers to a block with a relatively large affinity for water compared to the hydrophobic block. For example, the hydrophilic block includes a hydrophilic monomer described later, and the copolymer is formed in a manner that the hydrophilic block does not contain a hydrophilic monomer or the ratio of the hydrophilic functional group contained in the hydrophobic block is less than that of the hydrophilic block. The hydrophobic block preferably does not contain a hydrophilic monomer.

[0037] As the monomer polymerizable with benzyl acrylate, there can be mentioned, as described above, a hydrophilic monomer and a monomer other than a hydrophilic monomer (hereinafter sometimes referred to as a "hydrophobic monomer").

[0038] Examples of hydrophilic monomers include: (meth)acrylic acid, unsaturated polycarboxylic acids such as maleic acid, maleic anhydride and other monomers containing carboxyl or anhydride groups; styrene sulfonic acid, 4-(methacryloyloxy)butyl sulfonic acid and other monomers containing sulfonic acid groups; ethylene oxide-modified (meth)acrylate monomers such as ethylene oxide-modified (meth)acrylate alkyl esters, etc. Among these, unsaturated polycarboxylic acids such as (meth)acrylic acid and maleic anhydride are preferred, and (meth)acrylic acid is more preferred. Hydrophilic monomers can be used alone or in combination of two or more. When two or more are combined, the structures of blocks A and B can be random polymers or block polymers, respectively. In addition, (meth)acrylic acid refers to methacrylic acid and / or acrylic acid.

[0039] Examples of the hydrophobic monomer include styrene monomers such as styrene, α-methylstyrene, and vinyltoluene; α-olefin monomers such as ethylene, propylene, and 1-butene; vinyl monomers having phenyl, biphenyl, and naphthyl groups, etc. The hydrophobic monomer may be used alone or in combination of two or more. When two or more are combined, the structures of blocks A and B may be random polymers or block polymers, respectively. In addition, benzyl acrylate is equivalent to the hydrophobic monomer.

[0040] The structure of the benzyl acrylate copolymer is preferably composed of a block A composed of structural units derived from benzyl acrylate and a hydrophilic monomer, and a block B composed of structural units derived from a hydrophobic monomer, more preferably composed of a block A composed of structural units derived from benzyl acrylate and a hydrophilic monomer, and a block B composed of structural units derived from one or more hydrophobic monomers including benzyl acrylate, further preferably composed of a block A composed of structural units derived from benzyl acrylate and (meth)acrylic acid, and a block B composed of structural units derived from benzyl acrylate, and particularly preferably composed of a block A composed of structural units derived from benzyl acrylate, methacrylic acid, and acrylic acid, and a block B composed of structural units derived from benzyl acrylate.

[0041] The content ratio of block A to block B (weight ratio A / B) can be appropriately determined according to the types and contents of the components, and is preferably 30 / 70 to 70 / 30. In addition, when block A is composed of structural units derived from benzyl acrylate (X) and (meth)acrylic acid (Y), the content ratio in block A (weight ratio X / Y) is preferably 1 / 1 to 3 / 1. In addition, when (meth)acrylic acid is acrylic acid (Y1) and methacrylic acid (Y2), the content ratio in block A (weight ratio Y1 / Y2) is preferably 200 / 1 to 100 / 1.

[0042] The peak molecular weight of the benzyl acrylate copolymer is not particularly limited, but is preferably 5000 to 20000, and more preferably 6000 to 15000, from the viewpoint of further improving the filterability of the filter. The peak molecular weight of the benzyl acrylate copolymer can be measured by GPC (gel permeation chromatography). The acid value of the benzyl acrylate copolymer is not particularly limited, but is preferably 100 to 200 mgKOH / g from the viewpoint of further improving the filterability of the filter. The acid value (acid value when converted to solid content) can be obtained, for example, by a method based on DIN EN ISO 2114.

[0043] The amine value of the benzyl acrylate copolymer is not particularly limited, but is preferably 10 mgKOH / g or less, particularly preferably 0 mgKOH / g. The amine value (amine value in terms of solid content) can be determined by a method based on DIN 16945, for example.

[0044] The method for synthesizing the block copolymer composed of block A and block B is not particularly limited, and for example, the block copolymer can be obtained by subjecting the monomer of block A to living polymerization to obtain a polymer and then subjecting the polymer to living polymerization with the monomer of block B. The polymerization is not limited to living polymerization, and may be free radical polymerization.

[0045] When the benzyl acrylate copolymer contains block A, it is preferred that after isolating the polymer, the polymer, a base such as sodium hydroxide and pure water are mixed to prepare a polymer solution having a pH of 7.5 to 10.0. This polymer solution can be used as a dispersant.

[0046] The content of the dispersant is not particularly limited, but is preferably 15 to 60 parts by weight, more preferably 20 to 55 parts by weight, and even more preferably 25 to 45 parts by weight based on solid content, relative to 100 parts by weight of the black pigment.

[0047] As described above, the organic solvent only needs to contain at least one selected from glycol ethers having 4 to 10 carbon atoms, monohydric alcohols and polyhydric alcohols, and the monohydric alcohols and polyhydric alcohols are chain saturated alcohols having 4 to 10 carbon atoms. One of these organic solvents may be used alone, or two or more of them may be used in combination. From the viewpoint of further improving the filterability of the filter, the organic solvent is preferably one or more selected from glycol ethers having 4 to 10 carbon atoms, specified monohydric alcohols and polyhydric alcohols, more preferably one or more selected from specified monohydric alcohols and polyhydric alcohols, further preferably one or more selected from polyhydric alcohols, and particularly preferably one or more selected from glycols.

[0048] The organic solvent may contain any compound as long as it contains the above-defined compound, and may contain other organic solvents within a range that does not impair the filterability of the filter, but preferably contains substantially no organic solvent.

[0049] Examples of the glycol ethers having 4 to 10 carbon atoms include alkylene glycol monoalkyl ethers having 4 to 10 carbon atoms. Examples of such alkylene glycol monoalkyl ethers include ethylene glycol monoethyl ether, ethylene glycol monobutyl ether, ethylene glycol mono-tert-butyl ether, ethylene glycol monopropyl ether, ethylene glycol monoisopropyl ether, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, diethylene glycol monoisopropyl ether, diethylene glycol monobutyl ether, diethylene glycol mono-tert-butyl ether, triethylene glycol monoethyl ether, triethylene glycol monobutyl ether, propylene glycol monomethyl ether, propylene glycol monoethyl ether, propylene glycol monobutyl ether, propylene glycol tert-butyl ether, propylene glycol monopropyl ether, dipropylene glycol monomethyl ether, dipropylene glycol monoethyl ether, dipropylene glycol monobutyl ether, dipropylene glycol monopropyl ether, and dipropylene glycol monoisopropyl ether.

[0050] The glycol ether may have 4 to 10 carbon atoms, and more preferably 8 to 10 carbon atoms from the viewpoint of filterability.

[0051] Monohydric alcohol is a chain saturated alcohol having 4 to 10 carbon atoms, and is an organic compound having a structure in which one hydrogen atom of a saturated aliphatic hydrocarbon having 4 to 10 carbon atoms is replaced by a hydroxyl group. The chain structure of the alcohol may be straight chain or branched. In addition, the position of the hydroxyl group is not particularly limited, and may be any of primary alcohol, secondary alcohol, and tertiary alcohol. The number of carbon atoms is preferably 4 to 8. Examples of such chain saturated monohydric alcohols having 4 to 10 carbon atoms include: 1-butanol, 2-butanol, 2-methyl-1-propanol, 2-methyl-2-propanol butanol;

[0052] Pentanols such as 1-pentanol, 2-pentanol, 3-pentanol, 2-methyl-1-butanol, 2-methyl-2-butanol, 3-methyl-2-butanol, and 2,2-dimethyl-1-propanol;

[0053] Hexanols such as 1-hexanol, 2-hexanol, 3-hexanol, 2-methyl-1-pentanol, 3-methyl-1-pentanol, 4-methyl-1-pentanol, 2-methyl-2-pentanol, 3-methyl-2-pentanol, 4-methyl-2-pentanol, 2-methyl-3-pentanol, 3-methyl-3-pentanol, 2,2-dimethyl-1-butanol, 2,3-dimethyl-1-butanol, 3,3-dimethyl-1-butanol, 2,3-dimethyl-2-butanol, 3,3-dimethyl-2-butanol, and 2-ethyl-1-butanol;

[0054] Heptanols such as 1-heptanol, 2-heptanol, 3-heptanol, 4-heptanol, and 2-methyl-1-hexanol;

[0055] Octanols such as 1-octanol, 2-octanol, 3-octanol, 2-methyl-1-heptanol, and 2-ethyl-1-hexanol;

[0056] Nonanols such as 1-nonanol, 2-nonanol, 3-nonanol, 2-methyl-1-octanol, 3-methyl-3-octanol;

[0057] Decyl alcohols such as 1-decanol, 2-decanol, 3-decanol, 2-methyl-1-nonanol and 3-methyl-3-nonanol.

[0058] Polyols are chain saturated alcohols having 4 to 10 carbon atoms, and are organic compounds having a structure in which two or more hydrogen atoms of a saturated aliphatic hydrocarbon having 4 to 10 carbon atoms are substituted with hydroxyl groups. The chain structure of the alcohol may be straight chain or branched. In addition, the position of the hydroxyl group is not particularly limited. The number of carbon atoms is preferably 4 to 8. The valence is not particularly limited, but preferably divalent. Examples of such chain saturated polyols having 4 to 10 carbon atoms include butanediols such as 1,2-butanediol, 1,3-butanediol, 1,4-butanediol, 2,3-butanediol, and 2-methyl-1,3-propanediol;

[0059] Pentanediols such as 1,2-pentanediol, 1,5-pentanediol, and 2-methyl-1,3-butanediol;

[0060] Hexanediols such as 1,2-hexanediol, 1,5-hexanediol, 3-methyl-1,5-pentanediol, and 2-methyl-2,4-pentanediol;

[0061] Heptanediols such as 1,2-heptanediol and 1,7-heptanediol;

[0062] Octanediols such as 1,2-octanediol, 1,8-octanediol, 2-ethyl-1,3-hexanediol, 2,2,4-trimethyl-1,3-pentanediol, and 2,2-dimethyl-1,3-propanediol;

[0063] Nonanediols such as 1,2-nonanediol, 1,9-nonanediol, and 2-butyl-2-ethyl-1,3-propanediol;

[0064] Decanediols such as 1,2-decanediol and 1,10-decanediol;

[0065] Tetratols such as erythritol and threitol;

[0066] Pentosans such as xylitol;

[0067] Mannitol and other hexitols, etc.

[0068] Among these, as the polyhydric alcohol, 1,2-butanediol, 1,2-pentanediol, 1,2-hexanediol, 1,2-heptanediol, and 1,2-octanediol are particularly preferred, and 1,2-hexanediol is more preferred.

[0069] The total amount of the organic solvent is 1 to 8% by weight of the pigment dispersion as a whole, preferably 2 to 5% by weight. By making the content in the pigment dispersion within such a range, the effect of the organic solvent in the manufacturing method described below can be obtained, and there is a tendency to easily obtain the effect of improving the filterability of the aqueous inkjet ink prepared from the pigment dispersion.

[0070] Water is not particularly limited, and is preferably water after impurities have been removed. For example, pure water such as ion exchange water, distilled water, and RO water (purified water obtained by reverse osmosis membrane) can be cited. The content of water can be appropriately determined, for example, it can be 51.6 to 80.6% by weight in the entire pigment dispersion. In addition, when water is contained in the dispersant or other components described later, the water is contained.

[0071] In addition to the above-mentioned components, other components may be added to the pigment dispersion as required. Such other components include, for example, pH adjusters, pigment derivatives, antioxidants, anti-agglomeration agents, surface adjusters (leveling agents), defoamers, etc. As pH adjusters, aqueous solutions containing alkalis such as sodium hydroxide may be included.

[0072] For example, in the filter filterability test described later, the pigment dispersion composed of the above components has a large filter throughput of the particles in the pigment dispersion, which can give good filter filterability to the inkjet ink. In the filter filtration process usually performed in the final stage of the manufacturing process of the inkjet ink, good filterability can be achieved, so the pressure during filtration, the amount of filter used and the number of exchanges, the loss of ink, etc. can be reduced, and the filtration process can be labor-saving, and the inkjet ink can be provided environmentally friendly and cheaply. In addition, the pigment dispersion has a normal viscosity that can be applied to aqueous inkjet ink. The viscosity can be measured at 25°C using an E-type viscometer (manufactured by Toki Sangyo Co., Ltd., TV-22), for example.

[0073] (Method for producing a pigment dispersion for aqueous inkjet)

[0074] The above-mentioned pigment dispersion can be produced, for example, as follows.

[0075] First, a mixed solution containing the above-mentioned black pigment, dispersant, organic solvent and water (other components as needed) is prepared, and the content of the organic solvent in the whole mixed solution is adjusted to 1 to 8% by weight. Preferably, it is 2 to 5% by weight, and more preferably 3.5 to 5% by weight. It is believed that by the content of the organic solvent being such a specified range in the dispersion process described later, the pigment is easily dissolved in water using the organic solvent, and it is helpful for the adsorption of the pigment and the dispersant. Regardless of the size of the average particle size after the dispersion treatment, the permeability of the pigment to the filter becomes good, and the filterability of the filter of the final aqueous inkjet ink is improved. It is speculated that when the content of the organic solvent is more than 8% by weight, the adsorption of the dispersant to the pigment begins to desorb. As a result, although the mechanism is not clear, it is considered that the filterability of the aqueous inkjet ink made by the obtained pigment dispersion is reduced due to the destruction of the pigment aggregation during dispersion, or due to the occurrence of aggregation after dispersion.

[0076] As long as the organic solvent that can be used contains one or more of glycol ethers, monohydric alcohols and polyhydric alcohols selected from 4 to 10 carbon atoms as described above, it is preferred to be selected from one or more of the monohydric alcohols and polyhydric alcohols specified, and more preferably selected from one or more of the polyhydric alcohols, from the viewpoint of the filterability of the inkjet ink obtained using the pigment dispersion. In addition, the content of the organic solvent can be appropriately adjusted according to the composition of other components contained in the pigment dispersion. For example, when a chain saturated diol (diol) with 4 to 8 carbon atoms is used as an organic solvent, the content during the dispersion treatment is preferably 2 to 5% by weight in the pigment dispersion. In addition, when the diol is 1,2-hexanediol, the content during the dispersion treatment is preferably 3.5 to 5% by weight in the pigment dispersion.

[0077] Next, a process (dispersion process) of dispersing the mixture 1 in which the concentration of the organic solvent is adjusted in this way is performed. The dispersion process can be performed using a general dispersion process device in accordance with a conventional method. As a dispersion process device, for example, a bead mill, a sand mill, a grinder, a disperser, a paint conditioner, a kneader, etc. can be cited. When a dispersion medium (media) is used, its type is not particularly limited, and glass beads, zirconium oxide beads, aluminum oxide beads, stainless steel beads, etc. can be used. The size of the medium is not particularly limited, and can be appropriately selected according to various conditions. For example, a medium below φ1.00 mm can be used. In addition, as required, the dispersion process can also be performed in a manner that the size of the medium is gradually reduced. In addition, in the case of performing the dispersion process as described above, it is also possible to perform a pre-dispersion process with a load smaller than the load during the dispersion process after preparing the mixed solution. In the case of performing the pre-dispersion process, the concentration of the organic solvent in the mixed solution can be adjusted within the above-mentioned specified range, or it may not be adjusted.

[0078] After the dispersion treatment process, as required, in order to adjust the pigment concentration, etc., it is also possible to add water and stir the process (adjustment process). By dispersion treatment, the black pigment has been evenly dispersed, so the stirring at this time can be a simple stirring operation, and it is also possible to use the above-mentioned dispersion treatment device to carry out. Afterwards, when using a medium to carry out dispersion treatment, the medium can be removed to obtain a desired pigment dispersion. The removal of the medium can be carried out before the adjustment process, but from the viewpoints of the adjustment accuracy of the concentration, it is preferably carried out after the adjustment process.

[0079] (Aqueous inkjet ink)

[0080] The aqueous inkjet ink involved in the embodiment of the present invention contains the above-mentioned aqueous inkjet pigment dispersion. That is, it contains the above-mentioned black pigment, dispersant, organic solvent and water constituting the pigment dispersion, and may contain other components added as needed in the pigment dispersion. In addition, it may also contain an organic solvent commonly used in inkjet ink (hereinafter referred to as an organic solvent for ink), and may contain a surfactant and other additives. The concentration of the above-mentioned black pigment in the aqueous inkjet ink can be 1.0 to 10.0 weight %, preferably 3.0 to 7.0 weight % in the aqueous inkjet ink. The combination of the pigment dispersion and the organic solvent for ink, etc. is adjusted so that the concentration of the black pigment is within this range.

[0081] As organic solvents for ink, in addition to the glycol ethers specified above and the specified monohydric or polyhydric alcohols, general organic solvents used for ink applications can also be used. As such organic solvents for ink, water-soluble organic solvents can be cited, for example, compounds described in Japanese Patent Documents 1 to 3 can be used. Specifically, they can be listed: monohydric alcohols; glycols, polyhydric alcohols such as glycols other than glycols and glycerol; glycol ethers; ketones such as acetonyl acetone; esters such as γ-butyrolactone, diacetin, and triethyl phosphate; lower alkoxy alcohols such as 2-methoxyethanol and 2-ethoxyethanol; amines such as ethanolamine, diethanolamine, triethanolamine, N-methyldiethanolamine, N-ethyldiethanolamine, triethylenetetramine, tetraethylenepentamine, and pentamethyldiethylenetriamine; formamide, N,N- Amides such as dimethylformamide, N-methylformamide, and N,N-dimethylacetamide; heterocyclics such as 2-pyrrolidone, N-ethylpyrrolidone, N-methyl-2-pyrrolidone, cyclohexylpyrrolidone, morpholine, N-ethylmorpholine, 2-oxazolidinone, 1,3-dimethyl-2-imidazolidinone, imidazole, methylimidazole, hydroxyimidazole, dimethylaminopyridine, 1,3-propanesultone, hydroxyethylpiperazine, and piperazine; sulfoxides such as dimethyl sulfoxide; sulfones such as cyclopentane, etc. These may be used alone or in combination of two or more.

[0082] The content of the organic solvent in the aqueous inkjet ink can be appropriately determined in consideration of the pigment concentration, etc. For example, the total content of the organic solvent in the aqueous inkjet ink together with the above-mentioned pigment dispersion can be 10.0 to 30.0% by weight.

[0083] The surfactant is not particularly limited, and examples thereof include anionic surfactants, cationic surfactants, amphoteric surfactants, nonionic surfactants, silicone surfactants, fluorine surfactants, etc. Specific examples of these surfactants include compounds described in Japanese Patent Document 2. The content of the surfactant may be, for example, 0.01 to 5.0% by weight in the entire aqueous inkjet ink.

[0084] Examples of other additives include antioxidants, anti-agglomeration agents, surface conditioners (leveling agents), preservatives, pH adjusters, rust preventives, and defoaming agents.

[0085] The aqueous inkjet ink can be obtained by mixing the above-mentioned pigment dispersion with an organic solvent for ink, a surfactant as required, and other additives and stirring them uniformly, and then filtering them with a common filter to remove particles of a certain size or more that can be contained in the ink. The mesh size (pore size) and material of the filter can be appropriately determined according to the purpose, etc.

[0086] The above aqueous inkjet ink contains the above pigment dispersion, so that it has good filterability even after being prepared into ink. Therefore, as mentioned above, labor can be saved during filtering, and the inkjet ink can be provided in an environmentally friendly and low-cost manner.

[0087] Example

[0088] Hereinafter, embodiments of the present invention will be described in detail based on examples.

[0089] (Example 1)

[0090] Carbon black (manufactured by Mitsubishi Chemical Corporation, MA600, average primary particle size 20 nm, DBP absorption 131 cm 3 / 100g) 20 parts by weight, 22.22 parts by weight of a dispersant A2 described later as a dispersant, 6.4 parts by weight of 1,2-hexanediol (1,2-HD) as an organic solvent, 0.4 parts by weight of a 30% by weight NaOH aqueous solution, and 30.98 parts by weight of pure water were mixed to obtain 80.00 parts by weight of a mixed solution 1. The concentration of the organic solvent in the mixed solution 1 was 8% by weight. 336 parts by weight of zirconia beads (bead diameter φ 0.65 mm) were added to the mixed solution 1, and a dispersion treatment was performed at 2000 rpm for 120 minutes using a sand mill to obtain a dispersion (dispersion step).

[0091] 20.00 parts by weight of pure water was added to the obtained dispersion to obtain 100.00 parts by weight (excluding zirconium oxide beads) of mixed solution 2. After stirring the mixed solution 2, the zirconium oxide beads were removed to obtain a pigment dispersion in which the black pigment was uniformly dispersed (adjustment step). The concentration of the organic solvent in the pigment dispersion of the final composition was 6.4% by weight. In addition, the average particle size and viscosity of the obtained pigment dispersion were measured by the above-mentioned general method.

[0092] (Examples 2 to 11, Comparative Examples 1 to 10)

[0093] The dispersion process was carried out in the same manner as in Example 1 except that the dispersion composition was set to the composition shown in Tables 1 and 2. Next, the pigment dispersion having the final composition was obtained in the same manner as in Example 1 except that the concentration of the organic solvent was set to the concentration shown in Tables 1 and 2.

[0094] (Dispersant A)

[0095] Dispersant A contains a benzyl acrylate copolymer as an active ingredient. The benzyl acrylate copolymer is a diblock copolymer consisting of a block of benzyl acrylate / acrylic acid / methacrylic acid = 34.6 / 15.3 / 0.1 (weight ratio) and a block of benzyl acrylate = 50 (weight ratio) in terms of monomer composition ratio. The acid value of the copolymer is 128 mgKOH / g and the peak molecular weight is 8000.

[0096] Dispersant A is a polymer aqueous solution composed of the copolymer, sodium hydroxide and ion-exchanged water, and is adjusted to have a solid content of 27.0% by weight and a pH of 8.2. Dispersant A does not contain an organic solvent.

[0097] (Dispersant B)

[0098] Dispersant B contains a benzyl acrylate copolymer as an active ingredient. The benzyl acrylate copolymer is a diblock copolymer consisting of a block of benzyl acrylate / acrylic acid / methacrylic acid = 34.6 / 15.3 / 0.1 (weight ratio) and a block of benzyl acrylate = 50 (weight ratio) in terms of monomer composition ratio. The copolymer has an acid value of 124 mgKOH / g, an amine value of 0 mgKOH / g, and a peak molecular weight of 12,400.

[0099] Dispersant B is a polymer aqueous solution composed of the copolymer, sodium hydroxide and ion-exchanged water, and is adjusted to have a solid content of 26.2% by weight and a pH of 8.4. Dispersant B does not contain an organic solvent.

[0100] (Dispersant C)

[0101] Dispersant C contains a benzyl methacrylate copolymer obtained by polymerizing benzyl methacrylate instead of benzyl acrylate as its constituent monomer as an active ingredient. The benzyl methacrylate copolymer is a diblock copolymer composed of a block of methyl methacrylate / acrylic acid = 61.7 / 11.1 (weight ratio) and a block of benzyl methacrylate = 27.2 (weight ratio) in terms of monomer composition ratio. The copolymer has an acid value of 93 mgKOH / g, an amine value of 0 mgKOH / g, and a peak molecular weight of 8920.

[0102] Dispersant C is a polymer aqueous solution composed of the copolymer, sodium hydroxide and ion-exchanged water, and is adjusted to have a solid content of 21.4% by weight and a pH of 8.2. Dispersant C does not contain an organic solvent.

[0103] (evaluate)

[0104] <Filterability test>

[0105] <<Preparation of test sample A>>

[0106] To each of the pigment dispersions obtained in Examples and Comparative Examples, 400 parts by weight of pure water was added so that the pigment concentration corresponding to the ink composition became 4%, and the mixture was stirred to prepare a test sample A in which a black pigment was uniformly dispersed.

[0107] <<Preparation of test sample B>>

[0108] 397 parts by weight of pure water and 3 parts by weight of 1,2-hexanediol were added to the pigment dispersion of Comparative Example 1 so that the pigment concentration of the ink composition became 4%, and the mixture was stirred to prepare a test sample B in which the black pigment was uniformly dispersed. The test sample B was compared with the test sample A using the pigment dispersion of Example 2 to confirm the effect of the organic solvent when the organic solvent was added later during the preparation of the ink composition.

[0109] <<Test>>

[0110] The filterability test of each of the obtained test samples A and B was carried out by the following method.

[0111] The 500mL sample bottle with the weight measured in advance is placed in an apparatus for vacuum filtration system (Advantec manufacture, VT-500). The upper part has a membrane filter (manufactured by Japan PALL Co., Ltd., NNG29325, mesh 1.2μm) and is provided with a filter holder for vacuum filtration (Advantec manufacture, KGS-47). 500g of test sample is put into the state of suction with pressure 0.08MPa and filtered. After 3 minutes, stop suction, and after returning to normal pressure, take out the 500mL sample bottle and measure the weight. By calculating the weight difference before and after filtration, the weight (filtration amount) of the filtrate passed through the filter every 3 minutes is obtained. About the evaluation criteria of filtration amount, it is qualified when 90.0g / 3 minutes or more, good when 150g / 3 minutes or more, and excellent when 200g / 3 minutes or more. The evaluation results using test sample A are shown in Tables 1 and 2. In addition, the result when using test sample B is 26.1g / 3 minutes. In addition, about Comparative Examples 9 and 10, since the filterability test could not be performed due to high viscosity, they are indicated by "-" in Table 2.

[0112] [Table 1]

[0113]

[0114] 1) Manufactured by Orion Engineered Carbons Co., Ltd., average primary particle size 15nm, DBP absorption 95cm 3 / 100g

[0115] 2) Manufactured by Mitsubishi Chemical Corporation, average primary particle size 18nm, DBP absorption 55cm 3 / 100g

[0116] 3) Manufactured by Mitsubishi Chemical Corporation, average primary particle size 50nm, DBP absorption 175cm 3 / 100g

[0117] 4) 1,2-Butanediol

[0118] 5) 1,2-Octanediol

[0119] 6) Diethylene glycol monobutyl ether

[0120] 7) Triethylene glycol monobutyl ether

[0121] [Table 2]

[0122]

[0123] 1) Manufactured by Orion Engineered Carbons Co., Ltd., average primary particle size 15nm, DBP absorption 95cm 3 / 100g

[0124] 2) Manufactured by Mitsubishi Chemical Corporation, average primary particle size 18nm, DBP absorption 55cm 3 / 100g

[0125] 3) Manufactured by Mitsubishi Chemical Corporation, average primary particle size 50nm, DBP absorption 175cm 3 / 100g

[0126] 4) 1,2-Butanediol

[0127] 5) 1,2-Octanediol

[0128] 6) Diethylene glycol monobutyl ether

[0129] 7) Triethylene glycol monobutyl ether

[0130] As shown in Tables 1 and 2, it can be seen that the pigment dispersion obtained by using a dispersant containing a specified copolymer as an effective ingredient and a specified carbon black, containing a specified organic solvent and making it within a specified content range, and performing a dispersion treatment, has a significantly larger filter throughput than the pigment dispersion of the comparative example, and has excellent filterability. It can also be seen that compared with the result of the test sample B using comparative example 1, when no organic solvent is used in preparing the pigment dispersion, and when the organic solvent is added for the first time when preparing the ink composition, the filter filterability is significantly worse than that of the embodiment, and the effect of the organic solvent cannot be obtained. In addition, in comparative examples 9 and 10, which do not contain a benzyl acrylate copolymer as a dispersant but contain a benzyl methacrylate copolymer as an effective ingredient, the viscosity is large and it is difficult to use it as an ink.

[0131] Therefore, the pigment dispersion of the predetermined structure can provide an aqueous inkjet ink having good filterability. As a result, an environmentally friendly and inexpensive inkjet ink can be provided.

Claims

1. A pigment dispersion for aqueous inkjet, characterized in that: Contains black pigment, dispersant, organic solvent and water, wherein: The black pigment is dibutyl phthalate (DBP) with an absorption of 80 to 150 cm 3 / 100g of carbon black, The dispersant contains a benzyl acrylate copolymer as an effective ingredient. The organic solvent comprises at least one selected from glycol ethers having 4 to 10 carbon atoms, monohydric alcohols and polyhydric alcohols, and the monohydric alcohols and polyhydric alcohols are chain saturated alcohols having 4 to 10 carbon atoms. The total amount of the organic solvent is 1 to 8% by weight in the entire aqueous inkjet pigment dispersion.

2. The aqueous inkjet pigment dispersion according to claim 1, wherein: The dispersant is contained in an amount of 15 to 60 parts by weight based on solid content, relative to 100 parts by weight of the black pigment.

3. A method for producing a pigment dispersion for aqueous inkjet, which is used to produce the pigment dispersion for aqueous inkjet according to claim 1 or 2, the method comprising: A step of obtaining a mixed solution containing the black pigment, the dispersant, the organic solvent and the water, adjusting the content of the organic solvent in the entire mixed solution to 1 to 8% by weight, and then subjecting the mixed solution to a dispersion treatment.

4. An aqueous inkjet ink, characterized in that: Contains the pigment dispersion for aqueous inkjet according to claim 1 or 2.

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