Pigment dispersants and pigment dispersions

Abstract

To provide a pigment dispersant that enables efficient dispersion without causing local shades of pigment even when the pigment concentration is high, and a pigment dispersion using this pigment dispersant.SOLUTION: Provided is a pigment dispersant that contains a polyalkylene ether glycol having a number average molecular weight of 200 or more and 5000 or less as determined from a hydroxyl value. Polytetramethylene ether glycol is preferred as the polyalkylene ether glycol. A pigment dispersion that contains the pigment dispersant, a pigment and a medium.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a pigment dispersant and a pigment dispersion. More specifically, the present invention relates to a dispersant that enables efficient dispersion without causing local variations in pigment density even when the pigment concentration is high, and a pigment dispersion using the dispersant. [Background technology]

[0002] Pigment dispersions (also called "pigment pastes") with high pigment concentrations are used in paints and inks. For example, multiple pigment pastes containing different pigments are mixed to prepare a desired color, and then the resulting mixture is mixed with the main binder of the paint or ink to obtain the desired paint or ink.

[0003] Conventionally, polymer compounds such as polyethylene glycol have been used as pigment dispersants for dispersing pigments such as carbon black in a medium to prepare pigment dispersions (see, for example, Patent Documents 1 and 2). Also, dioctyl phthalate and dibutyl phthalate have been used as lubricating dispersants (see, for example, Patent Document 3).

[0004] Pigment dispersions are widely used as ink or paint concentrates in various fields such as papermaking, the rubber industry, and plastics. However, if the dispersion of the pigment in a pigment dispersion is uneven, the quality of the coating film, print, etc. formed by the ink or paint produced using this pigment dispersion will be significantly impaired, for example, the desired color tone will not be expressed and the gloss will be impaired. For this reason, when used as a pigment paste, a pigment dispersion is desired to have a higher pigment concentration from the viewpoint of production efficiency of inks and paints, and a pigment dispersant is required to exhibit excellent uniform pigment dispersibility even at high pigment concentrations. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Publication No. 2018-035283 [Patent Document 2] Japanese Patent Application Laid-Open No. 2014-070119 [Patent Document 3] Japanese Patent Application Laid-Open No. 2007-119721 Summary of the Invention [Problem to be solved by the invention]

[0006] However, conventionally known dispersants do not disperse pigments sufficiently, and particularly when the pigment concentration is high, the degree of pigment dispersion becomes uneven, making it impossible to obtain the desired color tone and gloss.

[0007] The present invention aims to solve the above-mentioned conventional problems and to provide a dispersant that enables efficient dispersion without causing local variations in pigment density even when the pigment concentration is high, and a pigment dispersion using this dispersant. [Means for solving the problem]

[0008] The present inventors have conducted extensive research to solve the above problems and have found that polyalkylene ether glycols having a specific number average molecular weight exhibit excellent dispersing effects even for high-concentration pigments, thereby solving the above problems.

[0009] That is, the present invention is summarized as follows.

[0010] [1] A pigment dispersant containing a polyalkylene ether glycol having a number average molecular weight calculated from a hydroxyl value of 200 to 5,000.

[0011] [2] The pigment dispersant according to [1], wherein the polyalkylene ether glycol comprises polytetramethylene ether glycol.

[0012] [3] A pigment dispersion comprising the pigment dispersant according to [1] or [2], a pigment, and a medium.

[0013] [4] The pigment dispersion according to [3], wherein the pigment is an inorganic pigment.

[0014] [5] The pigment dispersion according to [3], wherein the pigment is carbon black.

[0015] [6] Use of the pigment dispersion according to [5] as a paint concentrate.

[0016] [7] Use of the pigment dispersion described in [5] in an ink concentrate. [Effects of the Invention]

[0017] The pigment dispersant of the present invention can efficiently disperse pigments without causing local variations in pigment density even when the pigment concentration is high. Therefore, when a pigment dispersion using the pigment dispersant of the present invention is used as a concentrate for paints or inks, high-quality coating films or printed matter with excellent color tone and gloss can be obtained. [Brief explanation of the drawings]

[0018] [Figure 1] 1 is a TEM photograph showing the dispersion state of carbon black in Dispersion 2 of Example 2. [Figure 2] 1 is a TEM photograph showing the dispersion state of carbon black in Dispersion 3 of Comparative Example 1. [Figure 3] 1 is a TEM photograph showing the dispersion state of carbon black in Dispersion 5 of Comparative Example 3. DETAILED DESCRIPTION OF THE INVENTION

[0019] Hereinafter, an embodiment of the present invention will be described in detail.

[0020] [Pigment dispersant] The pigment dispersant of the present invention contains a polyalkylene ether glycol having a number average molecular weight calculated from a hydroxyl value (hereinafter, sometimes simply referred to as "number average molecular weight") of 200 or more and 5000 or less.

[0021] Polyalkylene ether glycols are generally polyhydroxy compounds having one or more ether bonds in the main backbone of the molecule.

[0022] Examples of the repeating units in the main skeleton of the polyalkylene ether glycol include a 1,2-ethylene glycol unit, a 1,2-propylene glycol unit, a 1,3-propanediol (trimethylene glycol) unit, a 2-methyl-1,3-propanediol unit, a 2,2-dimethyl-1,3-propanediol unit, a 1,4-butanediol (tetramethylene glycol) unit, a 2-methyl-1,4-butanediol unit, a 3-methyl-1,4-butanediol unit, a 3-methyl-1,5- Examples of the repeating unit include saturated hydrocarbon groups having 1 to 20 carbon atoms, such as pentanediol units, neopentyl glycol units, 1,6-hexanediol units, 1,7-heptanediol units, 1,8-octanediol units, 1,9-nonanediol units, 1,10-decanediol units, and 1,4-cyclohexanedimethanol units. A single repeating unit may form a polyalkylene ether glycol, or two or more repeating units may form a copolymerized polyalkylene ether glycol. While the raw materials providing these repeating units are not particularly limited, cyclic ethers are preferred. Furthermore, the raw materials providing these repeating units may be derived from petroleum or biomass.

[0023] As the polyalkylene ether glycol, among polyalkylene ether glycols having the above repeating units in the main skeleton, from the viewpoint of pigment dispersibility, polytetramethylene ether glycol, polytrimethylene ether glycol, copolymer polyether polyols obtained by reacting 1 to 20 mol % of 3-methyltetrahydrofuran with tetrahydrofuran (for example, "PTG-L1000," "PTG-L2000," and "PTG-L3500" manufactured by Hodogaya Chemical Co., Ltd.), and copolymer polyether glycols obtained by reacting neopentyl glycol with tetrahydrofuran are preferred, with polytetramethylene ether glycol being more preferred.

[0024] These polyalkylene ether glycols may be used alone or in combination of two or more.

[0025] In the present invention, the molecular weight of the polyalkylene ether glycol used as the pigment dispersant, in terms of number average molecular weight, has a lower limit of usually 200 or more, and preferably 230 or more, and an upper limit of usually 5000 or less, preferably 4000 or less, more preferably 3000 or less, and particularly preferably 2000 or less, and further preferably 1000 or less, 800 or less, 700 or less, 600 or less, 500 or less, and 400 or less, in that order, and is most preferably 300 or less.

[0026] When the number-average molecular weight of the polyalkylene ether glycol is equal to or less than the upper limit, the viscosity of the pigment dispersion is reduced, making it easier to work with, whereas when the number-average molecular weight of the polyalkylene ether glycol is equal to or more than the lower limit, efficient dispersion is possible even when the pigment concentration is high.

[0027] Here, the number average molecular weight of the polyalkylene ether glycol can be determined by the hydroxyl value (KOH (mg) / g) measurement method using the acetylation method in accordance with JIS K1557-1:2007, as described in the Examples section below.

[0028] The pigment dispersant of the present invention may contain any polyalkylene ether glycol having the above-mentioned specific number average molecular weight, and may also contain other components. However, it is preferred that the pigment dispersant of the present invention contains 20% by mass or more, and particularly 50 to 100% by mass, of polyalkylene ether glycol.

[0029] The pigment dispersant may contain pigment dispersing components other than the polyalkylene ether glycol having the specific number-average molecular weight (hereinafter referred to as "other pigment dispersing components") as long as the effects of the present invention are not impaired. Examples of other pigment dispersing components include dispersing agents such as phthalic acid, fatty acid salts, α-sulfofatty acid ester salts, alkylbenzene sulfonates, alkyl sulfates, alkyl ether sulfate ester salts, alkyl triethanolamine sulfates, fatty acid diethanolamides, alkyl trimethyl ammonium salts, dialkyl dimethyl ammonium chloride, alkyl pyridinium chloride, and alkyl carboxybetaine, as well as polymer dispersing agents such as polyoxyethylene alkyl phenyl ethers, polyvinylpyrrolidone (hereinafter also abbreviated as "PVP"), polyvinyl alcohol (hereinafter also abbreviated as "PVA"), polyethylene oxide (hereinafter also abbreviated as "PEO"), styrene-acrylic acid copolymers, oxyethylene-oxypropylene block polymers, poly(meth)acrylic acid esters, and PVP-acrylic acid graft polymers.

[0030] [Pigment dispersion] The pigment dispersion of the present invention contains the above-described pigment dispersant of the present invention, a pigment, and a medium.

[0031] The pigment contained in the pigment dispersion of the present invention is not particularly limited and can be appropriately selected depending on the purpose. For example, either an organic pigment or an inorganic pigment can be selected.

[0032] Examples of organic pigments include azo pigments, condensed polycyclic pigments, dye lake pigments, nitro pigments, nitroso pigments, and aniline black. Among these, azo pigments and condensed polycyclic pigments are more preferred.

[0033] Examples of azo pigments include soluble azo pigments, insoluble azo pigments, and condensed azo pigments. Examples of condensed polycyclic pigments include phthalocyanine pigments, quinacridone pigments, isoindolinone pigments, dioxazine pigments, perylene pigments, perinone pigments, thioindigo pigments, anthraquinone pigments, pyrrocholine pigments, fluorubine pigments, quinophthalene pigments, and metal complex pigments. Examples of dye lake pigments include acid dye lake and basic dye lake.

[0034] Examples of inorganic pigments include titanium oxide, iron oxide, calcium carbonate, barium sulfate, aluminum hydroxide, barium yellow, cadmium red, chrome yellow, and carbon black. Among these, carbon black is particularly preferred. Examples of carbon black include those produced by known methods such as the contact method, furnace method, and thermal method.

[0035] The pigment dispersant of the present invention exhibits excellent effects in dispersing inorganic pigments, particularly carbon black, which are pigments that tend to aggregate and are difficult to disperse.

[0036] The above pigments may be used alone or in combination of two or more.

[0037] The pigment content (pigment concentration) in the pigment dispersion is preferably 0.01 to 10% by mass, and more preferably 0.03 to 1% by mass, based on the total mass of the pigment dispersion, from the viewpoints of coloring properties and storage stability.

[0038] The content of the pigment dispersant in the pigment dispersion is usually 0.1 to 10 parts by mass, and preferably 1 to 7 parts by mass, per 100 parts by mass of the pigment. When the content of the pigment dispersant is equal to or greater than the lower limit, excellent uniform dispersibility and stability can be obtained, and when it is equal to or less than the upper limit, excellent uniform dispersibility and stability can be obtained.

[0039] As the medium, various media can be used depending on the application. That is, in the case of solvent-based paints and inks, organic solvents are used, and in the case of water-based paints and inks, water-based solvents are used as liquid media.

[0040] Examples of organic solvents that can be used include soybean oil, toluene, xylene, thinner, butyl acetate, methyl acetate, methyl isobutyl ketone, methyl cellosolve, ethyl cellosolve, propyl cellosolve, butyl cellosolve, glycol ether solvents such as propylene glycol monomethyl ether, ester solvents such as ethyl acetate, butyl acetate, and amyl acetate, aliphatic hydrocarbon solvents such as hexane, heptane, and octane, alicyclic hydrocarbon solvents such as cyclohexane, petroleum solvents such as mineral spirits, ketone solvents such as acetone and methyl ethyl ketone, alcohol solvents such as methyl alcohol, ethyl alcohol, propyl alcohol, and butyl alcohol, and aliphatic hydrocarbons, which are commonly used in solvent-based paints.

[0041] The aqueous solvent may be a mixture of water and water-soluble organic solvents such as alcohol solvents typically used in aqueous paints, such as ethyl alcohol, propyl alcohol, and butyl alcohol; glycol ether solvents, such as methyl cellosolve, ethyl cellosolve, propyl cellosolve, and butyl cellosolve; oxyethylene or oxypropylene addition polymers, such as diethylene glycol, triethylene glycol, polyethylene glycol, dipropylene glycol, tripropylene glycol, and polypropylene glycol; alkylene glycols, such as ethylene glycol, propylene glycol, and 1,2,6-hexanetriol; and glycerin and 2-pyrrolidone.

[0042] These liquid media may be used alone or in combination of two or more.

[0043] Among these, organic solvents are preferred because they have good compatibility with the pigment dispersant of the present invention and have a viscosity that makes them easy to handle when made into a pigment dispersion, and thinner, butyl alcohol, butyl cellosolve, etc. can be suitably used.

[0044] In addition to the solvent as the liquid medium, the pigment dispersion may contain at least some of the paint or ink components as other media depending on the type of paint or ink used. These paint or ink components may be added to the pigment dispersion when preparing the paint or ink from the pigment dispersion.

[0045] Additives other than solvents include resins that serve as binders, oils and fats, antifoaming agents, extender pigments, drying accelerators, surfactants, hardening accelerators, auxiliaries, chelating agents, preservatives, viscosity adjusters, and pH adjusters.

[0046] Examples of resins that can be used include acrylic resins, alkyd resins, polyester resins, polyurethane resins, epoxy resins, phenolic resins, melamine resins, amino resins, vinyl chloride resins, silicone resins, rosin-based resins such as gum rosin and lime rosin, maleic acid resins, polyamide resins, nitrocellulose, ethylene-vinyl acetate copolymer resins, rosin-modified resins such as rosin-modified phenolic resins and rosin-modified maleic acid resins, and petroleum resins, which are commonly used in solvent-based paints and oil-based printing inks. For water-based paints, water-soluble acrylic resins, water-soluble styrene-maleic acid resins, water-soluble alkyd resins, water-soluble melamine resins, water-soluble urethane emulsion resins, water-soluble epoxy resins, water-soluble polyester resins, and the like, which are commonly used for water-based paints and water-based inks, can be used.

[0047] As the fat or oil, boiled oil obtained by processing drying oil such as linseed oil, tung oil, oiticica oil, safflower oil, etc. can be used.

[0048] In producing the pigment dispersion of the present invention, kneading and dispersion treatment can be performed while applying strong shear force using a two-roll mill, three-roll mill, ball mill, tron ​​mill, disperser, kneader, co-kneader, homogenizer, blender, single-screw or twin-screw extruder, etc. Furthermore, if necessary, fine dispersion treatment can also be performed using beads made of glass, zirconia, etc., with a particle size of 0.01 to 3 mm, using a vertical or horizontal sand grinder, pin mill, slit mill, ultrasonic disperser, etc. In such a dispersion treatment, the pigment dispersant may be added to the liquid medium in advance, and then the pigment may be added and dispersed, or the pigment may be mixed with a medium such as a liquid medium, and then the pigment dispersant may be added and dispersed.

[0049] [Paints and inks] The pigment dispersion of the present invention is suitably used as a paint concentrate or ink concentrate, that is, a pigment paste, for producing paints or inks.

[0050] Examples of methods for producing paints and inks include mixing a pigment dispersion and a primary binder and, if necessary, diluting the mixture with a solvent. Depending on the purpose, the pigment dispersion and the primary binder may be used alone or in combination.

[0051] Examples of primary binders for paints include aliphatic solvent-based long-chain alkyd resins, aromatic solvent-based long-chain alkyd resins, medium-chain alkyd resins, short-chain alkyd resins, modified cellulose resins, polyester resins, acrylic resins, polyurethane resins, and epoxy resins. Examples of primary binders for inks include modified rosin resins, hydrocarbon resins, modified cellulose resins, acrylic resins, polyamide resins, and polyurethane resins. Furthermore, by mixing the pigment dispersion with a UV-curable monomer or oligomer, it can be used to produce UV-curable paints or inks. [Example]

[0052] The present invention will be explained in more detail below by way of examples and comparative examples, but the present invention is not limited to these examples as long as it does not depart from the gist of the invention.

[0053] [Hydroxyl value and number average molecular weight of polyalkylene ether glycol] In the examples, the number average molecular weight of the polyalkylene ether glycol used as a dispersant was measured by the following method. The hydroxyl value of the polyalkylene ether glycol was measured by a method using an acetylation reagent in accordance with JIS K1557-1. The number average molecular weight (Mn) was calculated from the measured hydroxyl value according to the following formula (I). Number average molecular weight = 2 × 56.1 / (hydroxyl value × 10 -3 ) …(I)

[0054] [Dispersant] In the following examples and comparative examples, the following pigment dispersants were used. PTMG1: Polytetramethylene ether glycol manufactured by Mitsubishi Chemical Corporation (Number average molecular weight: 230) DOP: Dioctyl phthalate

[0055] [Examples 1-2 and Comparative Examples 1-3] <Preparation of Carbon Black Dispersion> A container was charged with 16.0 g of Amilac (trade name) No. 1026 Clear (amino alkyd resin manufactured by Kansai Paint Co., Ltd.), 10.0 g of thinner, 2.6 g of carbon black (CB), and a dispersant shown in Table 1 to prepare a dispersion. To the dispersion, 2.0 mm diameter zirconia beads of the same weight as the dispersion were added, and dispersion treatment was carried out twice for 30 minutes each using a Paint Shaker 5400 (manufactured by RED DEVIL Co., Ltd.) After dispersion treatment was completed, the beads were separated using a filter, and then 50 g of No. 1026 Clear was added and mixed to prepare Dispersions 1 to 5, respectively.

[0056] [Table 1]

[0057] <Evaluation of Carbon Black Dispersion> Dispersions 1 to 5 were evaluated for dispersibility as follows.

[0058] (Evaluation of dispersibility (part 1)) For Dispersions 1 to 5, L*, a*, and b* were measured using a colorimeter NF333 (manufactured by Nippon Denshoku Industries Co., Ltd.) under Illuminant C. The results are shown in Table 2. The L* value is used as an index of the dispersibility of carbon black; the smaller the L* value, the darker the black, and the better the dispersibility of the carbon black is evaluated to be.

[0059] [Table 2]

[0060] (Evaluation of dispersibility (part 2)) Dispersions 2, 3, and 5 were selected and observed under a transmission electron microscope (TEM) at a magnification of 2000x. Figure 1 is a TEM photograph of Dispersion 2, Figure 2 is a TEM photograph of Dispersion 3, and Figure 3 is a TEM photograph of Dispersion 5. As is clear from Figures 1 to 3, carbon black in Dispersion 2 has less aggregation than the other dispersions, indicating that it is more efficiently dispersed.

[0061] As is clear from TEM photographs, the pigment dispersants of the present invention exhibit little carbon black aggregation, and the carbon black is efficiently dispersed even in a finely divided state. This micro-dispersion is also shown by the L* value evaluated macroscopically, and the dispersions of the Examples have lower L* values ​​and a stronger blackness than the Comparative Examples.

Claims

1. A pigment dispersant containing polytetramethylene ether glycol having a number average molecular weight of 200 or more and 800 or less, calculated from a hydroxyl value.

2. A pigment dispersion comprising the pigment dispersant according to claim 1, a pigment, and a medium.

3. The pigment dispersion according to claim 2, wherein the pigment is an inorganic pigment.

4. 3. The pigment dispersion according to claim 2, wherein the pigment is carbon black.

5. Use of the pigment dispersion according to claim 4 as a paint concentrate.

6. Use of the pigment dispersion according to claim 4 in an ink concentrate.

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