Pigment dispersion for aqueous inkjet and method for producing the same

Abstract

To provide a pigment dispersion by which aqueous inkjet ink having excellent filtration performance of filter can be produced, and a method for producing the pigment dispersion.SOLUTION: Pigment dispersion for aqueous inkjet contains black pigment, dispersant, organic solvent and water, where the black pigment is carbon black having a dibutylphthalate (DBP) absorption amount of 80 to 150 cm3 / 100 g, the dispersant contains benzyl acrylate-based copolymer as an active ingredient, the organic solvent contains at least one kind selected from glycol ethers of carbon number 4 to 10, monohydric alcohol and polyhydric alcohol, and the monohydric alcohol and polyhydric alcohol are straight-chain saturated alcohol of carbon number 4 to 10, and the total amount of the organic solvent is 1 to 8 wt.% in the total pigment dispersion for aqueous inkjet.SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention relates to a pigment dispersion for aqueous inkjet and a method for producing the same, and more particularly 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, inkjet printers have been used not only for printing at home but also for printing in various business operators such as the creation of business documents due to the improvement of image quality and printing speed. On the other hand, for example, in the printing for business and industrial applications such as the latter, further improvement in image quality and high-speed printing are required, and various studies have been conducted to meet these requirements (for example, Patent Documents 1 to 3).

[0003] In Patent Document 1, in addition to being able to record an image with excellent character quality, in order to be able to record an image with excellent fastness such as marker resistance that is not easily soiled even when traced with a marker pen, in an aqueous ink for inkjet containing a pigment and a urethane resin, it is proposed to use a specific urethane resin and to set the dynamic surface tension of the aqueous ink within a predetermined range.

[0004] In Patent Document 2, as the characteristics required for the coloring composition (ink) become more advanced, the dispersibility of the coloring material is not sufficient with conventional dispersants, and when the amount of the dispersant used is increased, problems such as changes in hue due to heating during or after ink ejection occur. Therefore, in order to provide a dispersant having excellent dispersibility even in a small amount, a polymerization product in which a specific block copolymer has a content within a predetermined range, and a coloring composition containing the same have been proposed.

[0005] In Patent Document 3, in order to provide an aqueous ink for inkjet recording that improves the rub resistance during recording on coated paper, the resin particles contained in the aqueous ink for inkjet recording are composed of a predetermined polymer, and the storage elastic modulus of the dried ink film at 25°C is set within a predetermined range. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] JP 2018-150514 A [Patent Document 2] Patent Publication No. 2021-98835 [Patent Document 3] JP 2022-156109 A Summary of the Invention [Problem to be solved by the invention]

[0007] It is believed that the above-mentioned conventional techniques can meet the market demand for higher image quality and faster printing in inkjet printing. However, according to the study by the present inventor, it has been found that some of these conventional techniques have poor filter filterability, such as the need to increase the filtration pressure in the filter filtration process that is usually performed in the final stage of the production of inkjet ink, or the filter is easily clogged and needs to be replaced frequently, resulting in increased power consumption, filter usage, filter replacement labor, ink loss, etc.

[0008] Therefore, an object of the present invention is to provide a pigment dispersion capable of producing a water-based ink-jet ink having excellent filterability, and a method for producing the pigment dispersion. [Means for solving the problem]

[0009] The present inventors have conducted extensive research to solve the above-mentioned problems. As a result, they have found that by using specific pigments, dispersants, and organic solvents and by controlling the total amount of the organic solvent within a specific range in a pigment dispersion for aqueous inkjet printing, a pigment dispersion can be obtained that can produce an aqueous inkjet ink with good filterability. The present invention relates to the following (1) to (4).

[0010] (1) In a pigment dispersion for aqueous inkjet containing a black pigment, a dispersant, an organic solvent, and water, the black pigment is carbon black having a dibutyl phthalate (DBP) absorption of 80 to 150 cm 3 / 100 g, the dispersant contains a benzyl acrylate copolymer as an active ingredient, 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 alcohol and the polyhydric alcohol are linear saturated alcohols having 4 to 10 carbon atoms, and the total amount of the organic solvent is 1 to 8% by weight in the entire pigment dispersion for aqueous inkjet. A pigment dispersion for aqueous inkjet. (2) The pigment dispersion for aqueous inkjet according to the above (1), which contains 15 to 60 parts by weight of the dispersant based on the solid content with respect to 100 parts by weight of the black pigment. (3) In the method for producing the pigment dispersion for aqueous inkjet according to the above (1) or (2), a step of obtaining a mixed liquid containing the black pigment, the dispersant, the organic solvent, and the water, adjusting the content of the organic solvent in the entire mixed liquid to 1 to 8% by weight, and then subjecting the mixed liquid to a dispersion treatment. A manufacturing method. (4) An ink for aqueous inkjet containing the pigment dispersion for aqueous inkjet according to the above (1) or (2).

Effects of the Invention

[0011] According to the present invention, it is possible to provide a pigment dispersion capable of producing an ink for aqueous inkjet having good filterability and a method for producing the pigment dispersion.

Modes for Carrying Out the Invention

[0012] (Pigment Dispersion for Aqueous Inkjet) The pigment dispersion for aqueous inkjet according to an embodiment of the present invention (hereinafter, may be simply referred to as "pigment dispersion") contains a black pigment, a dispersant, an organic solvent, and water. And each component contained in the pigment dispersion is as follows. The black pigment is carbon black with a dibutyl phthalate (DBP) absorption amount of 80 to 150 cm 3 / 100 g. The dispersant contains a benzyl acrylate copolymer as an active ingredient. 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 alcohol and the polyhydric alcohol are linear saturated alcohols having 4 to 10 carbon atoms. Further, the total amount of the organic solvent is 1 to 8% by weight in the whole pigment dispersion for aqueous inkjet.

[0013] Thus, by adopting specific ones as the black pigment, the dispersant, and the organic solvent, and setting the total amount of the organic solvent within a predetermined range and performing dispersion treatment, it becomes possible to realize good filterability when made into an ink for aqueous inkjet. The filterability of the pigment dispersion can be evaluated by the method described in the column of the examples described later.

[0014] Hereinafter, the components of the pigment dispersion will be described.

[0015] As described above, the black pigment has a DBP absorption amount of 80 to 150 cm 3It may be carbon black at 100 g. As long as the DBP absorption amount of the carbon black is within a predetermined range, channel black, furnace black, acetylene black, etc. can be used. The size of the carbon black only needs to be a general one applicable to inkjet ink applications. For example, the average primary particle diameter can be 13 to 25 nm, preferably 15 to 20 nm. The average primary particle diameter can be calculated as the average value of the major axis and the minor axis (the average value of the measurement number of 1 / 2 of the sum of the major axis (nm) and the minor axis (nm) of one particle) when observing 100 or more pigment particles by a transmission electron microscope. The DBP absorption amount can be measured according to JIS K6221. Also, the average particle diameter of the secondary particles formed by aggregation of the primary particles is usually 50 to 200 nm. This average particle diameter can be measured by general methods such as the dynamic light scattering method and the laser diffraction method. More specifically, for example, it can be measured using a zeta potential, particle size, molecular weight measurement system (manufactured by Otsuka Electronics Co., Ltd., ELSZ-2000ZS).

[0016] Regarding the pH of the carbon black, there is no particular limitation, but those with a pH of 6.0 to 9.0 are preferred.

[0017] Such carbon black can use commercially available products. 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, NIPex 60, NIPex 90, NIPex 160IQ, NIPex 170IQ, NIPex 180IQ, PRINTEX U manufactured by Orion Engineered Carbons S.A., TOKABLACK #3855 manufactured by Tokai Carbon Co., Ltd., SUNBLACK305, SUNBLACK320, SUNBLACK X15 manufactured by Asahi Carbon Co., Ltd., Nitron #300IH ISAF-HS, Nitron #300 ISAF, Nitron #200IS HAF-HS manufactured by Nippon Carbon Co., Ltd., etc. can be mentioned.

[0018] Carbon black having predetermined characteristics may be used alone or in combination of two or more.

[0019] The content of the black pigment is preferably as high as possible within a range where stability can be maintained, and 15.0 to 25.0% by weight in the pigment dispersion is preferred.

[0020] The dispersant may contain, as an active ingredient, a benzyl acrylate copolymer as described above. The benzyl acrylate copolymer may be a copolymer composed of a structural unit derived from benzyl acrylate and a structural unit derived from a monomer copolymerizable with benzyl acrylate. The copolymer may be a random copolymer or a block copolymer, but a block copolymer is preferred from the viewpoint of further improving the filterability. Further, as the block copolymer, it is preferably composed of a hydrophilic block (hereinafter sometimes referred to as "block A") and a hydrophobic block (hereinafter sometimes referred to as "block B"). Here, the hydrophilic block means a block having a relatively greater affinity for water than the hydrophobic block. For example, the hydrophilic block contains a hydrophilic monomer described later, and the hydrophobic block is composed of a copolymer such that it does not contain a hydrophilic monomer or the proportion of the hydrophilic functional group contained therein is less than that of the hydrophilic block and contains a hydrophilic monomer. It is preferable that the hydrophobic block does not contain a hydrophilic monomer.

[0021] Examples of the monomer copolymerizable with benzyl acrylate include the hydrophilic monomers and monomers other than the hydrophilic monomers (hereinafter sometimes referred to as "hydrophobic monomers") as described above. Examples of the hydrophilic monomers include unsaturated polyvalent carboxylic acids such as (meth)acrylic acid and maleic acid, monomers containing a carboxyl group or acid anhydride group such as maleic anhydride; monomers containing a sulfonic acid group such as styrene sulfonic acid and 4-(methacryloyloxy)butyl sulfonic acid; ethylene oxide-modified (meth)acrylic acid ester monomers such as ethylene oxide-modified (meth)acrylic acid alkyl ester. Among these, unsaturated polyvalent carboxylic acids such as (meth)acrylic acid and maleic anhydride are preferred, and (meth)acrylic acid is more preferred. The hydrophilic 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 each be a random polymer or a block polymer. Incidentally, (meth)acrylic acid means methacrylic acid and / or acrylic acid.

[0022] Examples of the hydrophobic monomer include styrene-based monomers such as styrene, α-methylstyrene, and vinyltoluene; α-olefin-based monomers such as ethylene, propylene, and 1-butene; and vinyl-based monomers having a phenyl group, biphenyl group, naphthyl group, etc. The hydrophobic monomer may be used alone or in combination of two or more. When combining two or more, the structures of blocks A and B may each be a random polymer or a block polymer. Note that benzyl acrylate corresponds to the hydrophobic monomer.

[0023] The structure of the benzyl acrylate copolymer is preferably composed of block A composed of structural units derived from benzyl acrylate and a hydrophilic monomer, and block B composed of structural units derived from a hydrophobic monomer. More preferably, it is composed of block A composed of structural units derived from benzyl acrylate and a hydrophilic monomer, and block B composed of structural units derived from one or more hydrophobic monomers including benzyl acrylate. Even more preferably, it is composed of block A composed of structural units derived from benzyl acrylate and (meth)acrylic acid, and block B composed of structural units derived from benzyl acrylate. Particularly preferably, it is composed of block A composed of structural units derived from benzyl acrylate, methacrylic acid, and acrylic acid, and block B composed of structural units derived from benzyl acrylate.

[0024] The content ratio (weight ratio A / B) of block A and block B can be appropriately determined according to the types and contents of the components, but 30 / 70 to 70 / 30 is preferable. When block A is composed of structural units derived from benzyl acrylate (X) and (meth)acrylic acid (Y), the content ratio (weight ratio X / Y) in block A is preferably 1 / 1 to 3 / 1. Further, when (meth)acrylic acid is acrylic acid (Y1) and methacrylic acid (Y2), the content ratio (weight ratio Y1 / Y2) in block A is preferably 200 / 1 to 100 / 1.

[0025] The peak top molecular weight of the benzyl acrylate copolymer is not particularly limited, but from the viewpoint of further improving the filterability, it is preferably 5,000 to 20,000, more preferably 6,000 to 15,000. The peak top 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 from the viewpoint of further improving the filterability, it is preferably 100 to 200 mgKOH / g. The acid value (acid value in terms of solid content) can be determined, for example, by a method conforming to DIN EN ISO 2114. The amine value of the benzyl acrylate copolymer is not particularly limited, but those having an amine value of 10 mgKOH / g or less are preferred, and 0 mgKOH / g is particularly preferred. The amine value (amine value in terms of solid content) can be determined, for example, by a method conforming to DIN 16945.

[0026] The method for synthesizing the block copolymer composed of block A and block B is not particularly limited. For example, after living polymerization of the monomer of block A to obtain a polymer, this polymer and the monomer of block B can be obtained by living polymerization. The polymerization is not limited to living polymerization and may be radical polymerization.

[0027] When the benzyl acrylate copolymer contains block A, after isolating the polymer, it is preferable to mix the polymer, a base such as sodium hydroxide, and pure water to obtain a polymer solution having a pH of 7.5 to 10.0. This polymer solution can be used as a dispersant.

[0028] The content of the dispersant is not particularly limited, but based on the solid content, it 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 with respect to 100 parts by weight of the black pigment.

[0029] As described above, 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 alcohol and polyhydric alcohol may be linear saturated alcohols having 4 to 10 carbon atoms. These organic solvents may be used alone or in combination of two or more. From the viewpoint of further improving the filterability, the organic solvent is preferably one or more selected from glycol ethers having 4 to 10 carbon atoms, a predetermined monohydric alcohol, and polyhydric alcohols, more preferably one or more selected from a predetermined monohydric alcohol and polyhydric alcohols, still more preferably one or more selected from polyhydric alcohols, and particularly preferably one or more selected from dihydric alcohols.

[0030] The organic solvent only needs to contain the aforementioned predetermined ones, and other organic solvents may be contained as long as the filterability is not impaired, but it is preferably not substantially contained.

[0031] Examples of 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-t-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-t-butyl ether, triethylene glycol monoethyl ether, triethylene glycol monobutyl ether, propylene glycol monomethyl ether, propylene glycol monoethyl ether, propylene glycol monobutyl ether, propylene glycol -t- butyl ether, propylene glycol monopropyl ether, dipropylene glycol monomethyl ether, dipropylene glycol monoethyl ether, dipropylene glycol monobutyl ether, dipropylene glycol monopropyl ether, dipropylene glycol monoisopropyl ether, and the like.

[0032] The carbon number of the glycol ethers may be 4 to 10, but from the viewpoint of filterability, 8 to 10 is more preferable.

[0033] The monohydric alcohol is a linear 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 substituted with a hydroxyl group. The linear structure of the alcohol may be linear or may have a branched chain. Also, the position of the hydroxyl group is not particularly limited, and any of primary to tertiary alcohols may be used. The carbon number is preferably 4 to 8. Examples of such linear saturated monohydric alcohols having 4 to 10 carbon atoms include 1-butanol, 2-butanol, 2-methyl-1-propanol, 2-methyl-2-propanol (butanol); Pentanols such as 1-pentanol, 2-pentanol, 3-pentanol, 2-methyl-1-butanol, 2-methyl-2-butanol, 3-methyl-2-butanol, 2,2-dimethyl-1-propanol; 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, 2-ethyl-1-butanol; Heptanols such as 1-heptanol, 2-heptanol, 3-heptanol, 4-heptanol, 2-methyl-1-hexanol; Octanols such as 1-octanol, 2-octanol, 3-octanol, 2-methyl-1-heptanol, 2-ethyl-1-hexanol; Nonanols such as 1-nonanol, 2-nonanol, 3-nonanol, 2-methyl-1-octanol, 3-methyl-3-octanol; Decanols such as 1-decanol, 2-decanol, 3-decanol, 2-methyl-1-nonanol, 3-methyl-3-nonanol can be mentioned.

[0034] The polyhydric alcohol is a chain saturated alcohol having 4 to 10 carbon atoms, and is an organic compound 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 linear or may have a branched chain. Also, 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 a divalent one is preferred. Examples of such chain saturated polyhydric alcohols having 4 to 10 carbon atoms include butanediols such as 1,2-butanediol, 1,3-butanediol, 1,4-butanediol, 2,3-butanediol, 2-methyl-1,3-propanediol; Pentanediols such as 1,2-pentanediol, 1,5-pentanediol, 2-methyl-1,3-butanediol; Hexanediols such as 1,2-hexanediol, 1,5-hexanediol, 3-methyl-1,5-pentanediol, 2-methyl-2,4-pentanediol; Heptanediols such as 1,2-heptanediol, 1,7-heptanediol; Octanediols such as 1,2-octanediol, 1,8-octanediol, 2-ethyl-1,3-hexanediol, 2,2,4-trimethyl-1,3-pentanediol, 2,2-dimethyl-1,3-propanediol; Nonanediols such as 1,2-nonanediol, 1,9-nonanediol, 2-butyl-2-ethyl-1,3-propanediol; Decanediols such as 1,2-decanediol, 1,10-decanediol; Tetritols such as erythritol, threitol; Pentitols such as xylitol; Hexitols such as mannitol; etc. may be mentioned.

[0035] Among these, as the polyhydric alcohol, particularly, 1,2-butanediol, 1,2-pentanediol, 1,2-hexanediol, 1,2-heptanediol, 1,2-octanediol are preferable, and 1,2-hexanediol is more preferable.

[0036] The content of the organic solvent is such that its total amount is 1 to 8% by weight in the whole pigment dispersion. Preferably it is 2 to 5% by weight. By setting the content in the pigment dispersion within such a range, the effect of the organic solvent in the manufacturing method described later can be enjoyed, and the effect of improving the filterability of the aqueous inkjet ink prepared from the pigment dispersion is likely to be obtained.

[0037] The water is not particularly limited, but water from which impurities have been removed is preferred. For example, pure water such as ion-exchanged water, distilled water, RO water (purified water by reverse osmosis membrane), etc. can be mentioned. The water content can be determined as appropriate. For example, it can be 51.6 to 80.6% by weight in the whole pigment dispersion. In addition, when water is contained in the dispersant and other components described later, these are included.

[0038] In addition to the aforementioned components, other components can be added to the pigment dispersion as necessary. Examples of such other components include pH adjusters, pigment derivatives, antioxidants, anti-aggregation agents, surface conditioners (leveling agents), defoaming agents, etc. Examples of the pH adjuster include an aqueous solution containing a base such as sodium hydroxide.

[0039] The pigment dispersion having the above component composition, for example, in the filterability test described later, has a large filter passing amount of particles in the pigment dispersion, and it becomes possible to impart good filterability to the inkjet ink. In the filter filtration process generally performed at the final stage of the manufacturing process of the inkjet ink, good filterability can be realized, so the pressure during filtration, the usage amount and replacement frequency of the filter, the loss of the ink, etc. can be reduced, and labor saving during the filtration process becomes possible, and the inkjet ink can be provided in consideration of the environment and at low cost. In addition, the pigment dispersion has a normal viscosity applicable to aqueous inkjet ink. This viscosity can be measured at 25 °C using, for example, an E-type viscometer (manufactured by Toki Sangyo Co., Ltd., TV-22).

[0040] (Method for producing a pigment dispersion for aqueous inkjet) The aforementioned pigment dispersion can be produced, for example, as follows. First, prepare a mixed solution containing the aforementioned black pigment, dispersant, organic solvent, and water (and other components as necessary), and adjust the content of the organic solvent in the entire mixed solution to be 1 to 8% by weight. Preferably, it is 2 to 5% by weight, and more preferably 3.5 to 5% by weight. When the content of the organic solvent is within such a predetermined range in the dispersion process described later, the pigment is more likely to be compatible with water due to the organic solvent, and further helps the adsorption of the pigment and the dispersant. Regardless of the size of the average particle diameter after the dispersion treatment, the permeability of the pigment to the filter becomes good, and it is considered that the effect of improving the filterability of the finally obtained aqueous inkjet ink can be obtained. When the content of the organic solvent exceeds 8% by weight, it is speculated that the adsorption of the dispersant to the pigment may start to come off. As a result, although the mechanism is not necessarily clear, it is considered that the filterability of the aqueous inkjet ink prepared from the obtained pigment dispersion decreases due to preventing the disintegration of pigment aggregation during dispersion or generating aggregation after dispersion.

[0041] As described above, the organic solvent that can be used may include one or more selected from glycol ethers having 4 to 10 carbon atoms, a predetermined monohydric alcohol, and polyhydric alcohols. However, from the perspective of the filterability of the inkjet ink obtained using the pigment dispersion, it is preferably one or more selected from a predetermined monohydric alcohol and polyhydric alcohols, and more preferably one or more selected from polyhydric alcohols. In addition, the content of the organic solvent may be appropriately adjusted according to the composition of other components contained in the pigment dispersion. For example, when using a linear saturated dihydric alcohol (diol) having 4 to 8 carbon atoms as the organic solvent, the content during the dispersion treatment is preferably 2 to 5% by weight in the pigment dispersion. Further, 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.

[0042] Next, perform a step of dispersing the mixture 1 in which the concentration of the organic solvent is adjusted in this way (dispersion step). The dispersion treatment can be carried out according to a conventional method using a general dispersion treatment apparatus. Examples of the dispersion treatment device include a bead mill, a sand mill, an attritor, a disper, a paint conditioner, a kneader, and the like. When using a dispersion medium, the type thereof is not particularly limited, and glass beads, zirconia beads, alumina beads, stainless steel beads, and the like can be used. The size of the medium is not particularly limited and can be appropriately selected according to various conditions. For example, those with a diameter of 1.00 mm or less can be used. Further, if necessary, the dispersion treatment may be performed so that the size of the medium is gradually reduced. When performing the dispersion treatment as described above, after preparing the mixed solution, a preliminary dispersion treatment may be performed at a load smaller than the load during the dispersion treatment. When performing the preliminary dispersion treatment, the concentration of the organic solvent in the mixed solution may or may not be adjusted so as to be within the above-mentioned predetermined range.

[0043] After the dispersion treatment step, if necessary, in order to adjust the pigment concentration and the like, a step of adding water and stirring may be performed (adjustment step). At this time, since the black pigment is uniformly dispersed by the dispersion treatment, a simple stirring operation may be sufficient, but it may also be performed using the above-mentioned dispersion treatment device. Thereafter, when the dispersion treatment is performed using a medium, the medium can be removed to obtain a desired pigment dispersion. The removal of the medium may be performed before the adjustment step, but from the viewpoint of the accuracy of concentration adjustment and the like, it is preferably performed after the adjustment step.

[0044] (Ink for aqueous inkjet) The ink for aqueous inkjet according to an embodiment of the present invention contains the above-described pigment dispersion for aqueous inkjet. That is, it contains the above-described black pigment, dispersant, organic solvent, and water that constitute the pigment dispersion, and may contain other components added as necessary in the pigment dispersion. Further, it further contains an organic solvent generally used in inkjet inks (hereinafter referred to as an organic solvent for ink), and may contain a surfactant and other additives. The concentration of the above-described black pigment in the ink for aqueous inkjet can be, for example, 1.0 to 10.0% by weight, preferably 3.0 to 7.0% by weight in the ink for aqueous inkjet. The blending of the pigment dispersion, the organic solvent for ink, etc. is adjusted so that the black pigment concentration falls within this range.

[0045] As the organic solvent for ink, in addition to the above-described predetermined glycol ethers and predetermined monohydric or polyhydric alcohols, general organic solvents used for ink can be used. Such organic solvents for ink include water-soluble organic solvents, and for example, those described in Patent Documents 1 to 3 and the like can be adopted. Specifically, monohydric alcohols; glycols, diols other than glycols, polyhydric alcohols such as glycerin; glycol ethers; ketones such as acetonylacetone; 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; amides such as formamide, N,N-dimethylformamide, N-methylformamide, and N,N-dimethylacetamide; 2-pyrrolidone, N-ethylpyrrolidone, N-methyl-2- Heterocyclic compounds such as pyrrolidone, cyclohexylpyrrolidone, morpholine, N-ethylmorpholine, 2-oxazolidone, 1,3-dimethyl-2-imidazolidinone, imidazole, methylimidazole, hydroxyimidazole, dimethylaminopyridine, 1,3-propanesultone, hydroxyethylpiperazine, piperazine, etc.; Sulfoxides such as dimethyl sulfoxide; Sulfones such as sulfolane, etc. These may be used alone or in combination of two or more.

[0046] The content of the organic solvent for ink in the aqueous inkjet ink can be appropriately determined in consideration of the concentration of the pigment and the like. For example, the total amount with the predetermined organic solvent contained in the above-mentioned pigment dispersion can be 10.0 to 30.0% by weight in the aqueous inkjet ink.

[0047] There is no particular limitation on the surfactant. For example, anionic surfactants, cationic surfactants, amphoteric surfactants, nonionic surfactants, silicone-based surfactants, fluorine-based surfactants, etc. can be mentioned. Specific examples thereof include those described in Patent Document 2, for example. The content of the surfactant can be, for example, 0.01 to 5.0% by weight in the whole aqueous inkjet ink.

[0048] Other additives include antioxidants, anti-aggregation agents, surface conditioners (leveling agents), preservatives, pH adjusters, rust preventives, defoamers, etc.

[0049] The aqueous inkjet ink is obtained by mixing the above-mentioned pigment dispersion, the organic solvent for ink, and, if necessary, a surfactant and other additives, stirring them to make them uniform, and then usually filtering them through a filter to remove particles having a size equal to or larger than a certain size that can be contained in the ink. The mesh size (pore diameter) and material of the filter can be appropriately determined according to the use and the like.

[0050] The ink for aqueous inkjet as described above contains the pigment dispersion mentioned above, and thus has good filterability even after being made into ink. Therefore, as described above, labor can be saved during the filtration process, and the ink for inkjet can be provided in an environmentally friendly and inexpensive manner.

Example

[0051] Hereinafter, embodiments of the present invention will be described in detail based on examples.

[0052] (Example 1) As the black pigment, 20 parts by weight of carbon black (manufactured by Mitsubishi Chemical Corporation, MA600, average primary particle diameter 20 nm, DBP absorption 131 cm 3 / 100 g), 22.22 parts by weight of Dispersant A (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 30% 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 this mixed solution 1 is 8% by weight. 336 parts by weight of zirconia beads (bead diameter φ0.65 mm) were added to this mixed solution 1, and dispersion treatment was performed at 2000 rpm for 120 minutes using a sand mill to obtain a dispersion (dispersion step). 20.00 parts by weight of pure water was added to the obtained dispersion to obtain 100.00 parts by weight of a mixed solution 2 (excluding zirconia beads). After stirring this mixed solution 2, the zirconia 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 having the final composition is 6.4% by weight. Incidentally, the average particle diameter and viscosity of the obtained pigment dispersion were measured by the general method described above.

[0053] (Examples 2 to 11, Comparative Examples 1 to 10) The dispersion step was performed in the same manner as in Example 1 except that the formulations during dispersion shown in Tables 1 and 2 were used. Next, a pigment dispersion having the final composition was obtained in the same manner as in Example 1 except that the organic solvent concentration shown in Tables 1 and 2 was achieved.

[0054] (Dispersant A) Dispersant A contains a benzyl acrylate copolymer as the active ingredient. This benzyl acrylate copolymer is a diblock copolymer composed of a block with a monomer composition ratio of benzyl acrylate / acrylic acid / methacrylic acid = 34.6 / 15.3 / 0.1 (weight ratio) and a block with benzyl acrylate = 50 (weight ratio). The copolymer had an acid value of 128 mgKOH / g and a peak top molecular weight of 8000. Dispersant A is an aqueous polymer solution composed of the copolymer, sodium hydroxide, and ion-exchanged water, 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.

[0055] (Dispersant B) Dispersant B contains a benzyl acrylate copolymer as the active ingredient. This benzyl acrylate copolymer is a diblock copolymer composed of a block with a monomer composition ratio of benzyl acrylate / acrylic acid / methacrylic acid = 34.6 / 15.3 / 0.1 (weight ratio) and a block with benzyl acrylate = 50 (weight ratio). The copolymer had an acid value of 124 mgKOH / g, an amine value of 0 mgKOH / g, and a peak top molecular weight of 12400. Dispersant B is an aqueous polymer solution composed of the copolymer, sodium hydroxide, and ion-exchanged water, 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.

[0056] (Dispersant C) Dispersant C contains, as its active ingredient, a benzyl methacrylate copolymer polymerized using benzyl methacrylate instead of benzyl acrylate as its constituent monomer. This benzyl methacrylate copolymer is a diblock copolymer composed of a block with a monomer composition ratio of methyl methacrylate / acrylic acid = 61.7 / 11.1 (weight ratio) and a block with benzyl methacrylate = 27.2 (weight ratio). The copolymer had an acid value of 93 mgKOH / g, an amine value of 0 mgKOH / g, and a peak top molecular weight of 8920. Dispersant C is an aqueous polymer solution composed of the copolymer, sodium hydroxide, and ion-exchanged water, 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.

[0057] (Evaluation) <Filtration property test> (Preparation of test sample A) For each pigment dispersion obtained in the examples and comparative examples, 400 parts by weight of pure water was added so that the pigment concentration corresponding to the ink composition was 4%, and the mixture was stirred to prepare test sample A in which the black pigment was uniformly dispersed.

[0058] (Preparation of test sample B) To the pigment dispersion of Comparative Example 1, 397 parts by weight of pure water and 3 parts by weight of 1,2 - hexanediol were added so that the pigment concentration corresponding to the ink composition was 4%, and the mixture was stirred to prepare test sample B in which the black pigment was uniformly dispersed. Test sample B is used to confirm the effect of the organic solvent when the organic solvent is added later during the preparation of the ink composition, in comparison with test sample A using the pigment dispersion of Example 2.

[0059] (Test) The obtained test samples A and B were subjected to a filtration property test by the following method. A 500 mL sample bottle, whose weight had been measured in advance, was placed stationary inside an apparatus for a vacuum filtration system (VT-500 manufactured by Advantec). A filter holder for vacuum filtration (KGS-47 manufactured by Advantec), equipped with a membrane filter (NNG29325 manufactured by Nippon Pall Co., Ltd., with an aperture of 1.2 μm), was installed on top. With suction applied at a pressure of 0.08 MPa, 500 g of the test sample was introduced and filtered. After 3 minutes, the suction was stopped and the pressure was returned to normal pressure. Then, the 500 mL sample bottle was taken out and its weight was measured. By calculating the difference in weight before and after filtration, the weight of the filtrate (filtration volume) that passed through the filter per 3 minutes was determined. The evaluation criteria for the filtration volume were set as follows: passing if it was 90.0 g / 3 minutes or more, good if it was 150 g / 3 minutes or more, and excellent if it was 200 g / 3 minutes or more. The evaluation results using test sample A are shown in Tables 1 and 2. Also, the result when using test sample B was 26.1 g / 3 minutes. Note that for Comparative Examples 9 and 10, since the viscosity was too high and the filtration test could not be performed, they are indicated by "-" in Table 2.

[0060]

Table 1

[0061]

Table 2

[0062] As shown in Tables 1 and 2, a pigment dispersion obtained by using a dispersant containing a predetermined copolymer as an active ingredient and a predetermined carbon black, and containing a predetermined organic solvent so as to be within a predetermined content range and performing a dispersion treatment has a significantly larger filter throughput compared to the pigment dispersion of the comparative example, and it can be seen that the filter filtration property is excellent. Further, from the results of test sample B using Comparative Example 1, when no organic solvent is used during the preparation of the pigment dispersion and the organic solvent is added for the first time when preparing the ink composition, the filter filtration property is significantly worse compared to the examples, and it can be seen that the effect of the organic solvent cannot be obtained. Further, in Comparative Examples 9 and 10 using a benzyl methacrylate copolymer as an active ingredient instead of a benzyl acrylate copolymer as a dispersant, the viscosity was high and it was difficult to use as an ink. Therefore, a pigment dispersion having a predetermined configuration can provide an ink for water-based inkjet with good filter filtration property. As a result, the ink for inkjet can be provided inexpensively while considering the environment.

Claims

1. A water-based pigment dispersion for inkjet printing, comprising a black pigment, a dispersant, an organic solvent and water, The black pigment has a dibutyl phthalate (DBP) absorption of 80 to 150 cm ３ / 100g of carbon black, The dispersant contains a benzyl acrylate copolymer as an active ingredient, 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; The total amount of the organic solvent is 1 to 8% by weight based on the entire pigment dispersion for water-based inkjet.

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

3. 3. The method for producing the pigment dispersion for water-based inkjet according to claim 1 or 2, a step of obtaining a mixed liquid containing the black pigment, the dispersant, the organic solvent, and the water, the mixed liquid having an adjusted content of the organic solvent in the entire mixed liquid being 1 to 8 wt %, and then dispersing the mixed liquid.

4. 3. A water-based ink-jet ink comprising the water-based ink-jet pigment dispersion according to claim 1 or 2.

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