JPH0465860B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a novel pigment dispersant. More specifically, it relates to a pigment dispersant obtained by copolymerizing a specific sulfonic acid group-containing monomer. Traditionally, clay, calcium carbonate, titanium oxide,
Inorganic pigments such as zinc white, barium sulfate, and talc as well as various organic pigments are used. Generally, these pigments are made into an aqueous dispersion using various dispersants, and various pigment binders such as synthetic resin emulsion, synthetic rubber latex, PVA, and casein are added to this for use. Recently, in the fields where these pigment dispersions are used, various pigments are used in combination in order to obtain better coating film performance at lower cost, and it is necessary to prepare highly concentrated pigment dispersions with low water content. Furthermore, as coating methods become faster, pigment dispersions with good flow characteristics have become desirable.
From this point of view, the conditions that are widely required for pigment dispersants are: (a) they must exhibit good dispersion effects for various pigments; and (b) they must be better in terms of economy and coating performance. It must have a high dispersion effect even when added in a small amount (c) It must be able to reduce the viscosity of a high-concentration pigment dispersion, have excellent viscosity stability over time, and provide good fluidity properties, etc. can be mentioned. Sodium pyrophosphate, sodium hexametaphosphate, sodium naphthalene sulfonate formalin condensate, sodium polyacrylate, etc. are conventionally known as pigment dispersants, but none of them fully satisfies the above-mentioned requirements. Not yet. In view of the above-mentioned circumstances, the present inventors have made extensive studies and found that an unsaturated amidophenyl-substituted alkanesulfonic acid group-containing monomer represented by the following general formula and an α,β-monoethylenically unsaturated carboxylic acid or It has been discovered that a pigment dispersant obtained by copolymerizing the pigment with a salt thereof exhibits an excellent dispersion effect that satisfies the above requirements, and the present invention has been achieved. general formula (In the formula, R ₁ and R ₂ are hydrogen or a lower alkyl group, and X represents hydrogen, an alkali metal ion, an alkaline earth metal ion, or an ammonium ion.) Although the present invention has poor homopolymerizability, it has poor copolymerizability. Unsaturated amidophenyl-substituted alkanesulfonic acid group-containing monomers with rich and specific properties, especially 2-acrylamido-2-phenylpropanesulfonic acid or its salts and one type of α,β-monoethylenically unsaturated carboxylic acid. Or it relates to a pigment dispersant comprising an aqueous solution of an alkali metal salt or the like copolymerized with two or more types. The α,β-monoethylenically unsaturated carboxylic acids used in the present invention include acrylic acid, methacrylic acid, itaconic acid, maleic acid, fumaric acid, crotonic acid, or alkali metal salts and ammonium salts thereof. . The quantitative relationship between these two types of monomers is, for example, the copolymerization ratio of 2-acrylamide-2phenylpropanesulfonic acid (hereinafter abbreviated as APPS) and α,β-monoethylenically unsaturated carboxylic acid. Expressed on a molar basis, it ranges from 1/100 to 90/100. If the ratio of APPS is less than 1/100, a sufficient effect cannot be obtained, and if it is more than 90/100, the dispersion effect will deteriorate, which is not preferable. Moreover, a nonionic monomer can be used in combination with the water-soluble ionic monomer. Examples of such monomers include esters of acrylic acid or methacrylic acid such as methyl acrylate, ethyl acrylate, methyl methacrylate, and 2-hydroxyethyl methacrylate, acrylonitrile, acrylamide, methacrylamide, N- Examples include methylol acrylamide and N-methylol methacrylamide. Next, in order to suitably carry out the present invention, an alkali metal salt or an alkaline earth metal salt of APPS and α, β
- A method in which a monoethylenically unsaturated carboxylic acid, such as acrylic acid, is copolymerized in an aqueous medium and then neutralized, or an alkali metal salt or an alkaline earth metal salt and an α,β-monoethylenically unsaturated carboxylic acid A method of copolymerizing alkali metal salts of 1 and 2 in an aqueous medium can be adopted. The polymerization catalyst may be any water-soluble catalyst, and specifically, inorganic peroxides, organic peroxides, combinations of these peroxides and reducing agents, or azo compounds can be used. Specifically, there are ammonium persulfate, potassium persulfate, hydrogen peroxide, t-butyl peroxide, benzoyl peroxide, cumene hydroxy peroxide, perbutyl oxide, etc. Reducing agents used in combination with these include sulfite and hydrogen sulfite. salts, salts with low ionic valences such as iron, copper, and cobalt, organic amines such as aniline, and even aldoses,
Examples include reducing sugars such as ketose. In addition, examples of azo compounds include azobisisobutyronitrile, 2,2'-azobis-2-amidinopropane hydrochloride, 2,2'-azobis-2,4-dimethylvaleronitrile, 4,4'-azobis- 4-cyanovaleric acid etc. can be applied. It is also possible to use two or more of these initiators in combination. The amount added may be in accordance with usual polymerization conditions, and is, for example, 0.01 to 5% by weight, preferably 0.05 to 2% by weight, based on the monomer. Further, water is usually used as a polymerization solvent, such as ion-exchanged water, distilled water, etc. Also,
Water-miscible solvents such as alcohols and ketones can be used together with water. Examples of alcohols include methyl alcohol, ethyl alcohol, propyl alcohol, isopropyl alcohol, n-butyl alcohol, and sec-butyl alcohol, and examples of ketones include acetone and methyl ethyl ketone. The amount of the organic solvent added to the water may be within a range that does not cause precipitation of the polymerized polymer, and the content of the organic solvent in the mixed solution is usually 90% by volume or less, preferably 80% by volume or less. There is no particular restriction on the monomer concentration, but if the concentration is too high, the solution will become too viscous and a large amount of energy will be consumed for stirring, liquid transfer, etc. Furthermore, if the concentration is too low, the polymerization rate will be low and it will take a lot of time. Usually 0.5
-80% by weight, preferably 1-70% by weight. In addition, during implementation, polymerization containers, polymerization solvents,
It is preferable to replace the polymerization initiator solution, monomer, etc. with an inert gas such as nitrogen gas to deoxygenate the polymerization reaction in order to quickly carry out the polymerization reaction. Often, for convenience, the polymerization is carried out under an oxygen-containing gas such as air. In such a case, the amount of polymerization initiator, or in the case of a redox initiator, the amount of reducing agent may be increased. On the other hand, α,β-monoethylenically unsaturated carboxylic acid can be
Alternatively, the copolymer may be subjected to the polymerization reaction in the form of a salt such as an alkali metal salt or an ammonium salt, and if it is polymerized in the form of a carboxylic acid, it is necessary to neutralize the copolymer. The neutralizing agent may be any agent that can neutralize carboxylic acid, and usually alkali metal hydroxides such as sodium hydroxide and potassium hydroxide, alkali metal carbonates such as sodium carbonate and potassium carbonate, or ammonia are mixed with water. A method is adopted in which the compound is dissolved in and added. On the other hand, when an organic solvent is used in combination, the solvent is usually separated by a method such as distillation. The product may be an aqueous solution as it is after completion of polymerization, or it may be diluted by adding water or the like. The dispersant of the present invention obtained as described above is
In various pigment dispersions, compared to conventional dispersants such as sodium polyacrylate and other sulfonic acid group-containing monomer-modified sodium polyacrylates,
The purpose is to provide a pigment dispersion that exhibits a high dispersion effect even when added in a smaller amount, and has a high concentration, low viscosity, good viscosity stability over time, and good flow characteristics. Hereinafter, the present invention will be explained in more detail with reference to Examples. Example 1 Manufacture of dispersant: 140 g of acrylic acid and 120 g of sodium 2-acrylamido-2-phenylpropanesulfonate (hereinafter abbreviated as APPS-Na) were added to a mixed solvent of 400 g of water and 160 g of isopropyl alcohol, and the mixture was heated with Chitsuso gas. After the substitution, 2 g of potassium persulfate was added and the temperature was raised to 80°C to start polymerization. After polymerizing at 80℃ for 3 hours with sufficient stirring, the isopropyl alcohol was removed, 50% sodium hydroxide was added to adjust the pH to 9.0, and the mixture was diluted with water to a concentration of 20% by weight.
It was made into a product. Evaluation of dispersant: Add 2g of the above dispersant to 60g of water, stir thoroughly to dissolve, then add 140g of heavy calcium carbonate,
The mixture was sufficiently kneaded to obtain a uniform dispersion. The viscosity of the dispersion was measured at 25°C immediately after kneading and after being left at room temperature for 1 day, and the results are shown in Table 1. Comparative Examples 1 and 2 In Comparative Example 1, 200 g of acrylic acid was used instead of the monomer mixture of Example 1, and in Comparative Example 2, a mixture of 60 g of acrylic acid and 220 g of sodium 2-acrylamido-2-methylpropanesulfonate was used. A dispersant was produced in exactly the same manner as in Example 1, except that . The obtained dispersant was evaluated by preparing a pigment slurry in exactly the same manner as in Example 1 and measuring its viscosity. Table 1 shows the results obtained.

[Table] Example 2 Production of dispersant: 45 g of APPS-Na and 105 g of sodium acrylate were added to 600 g of water, and after thorough stirring, 2 g of ammonium persulfate and 3 g of sodium bisulfite were added, and the temperature was raised to 50°C to polymerize. started. 6 at 50℃
Polymerization was carried out with sufficient stirring for a long time, and a viscous liquid after polymerization was obtained as a product. Production of pigment dispersion and its evaluation: Add 1.5g of the dispersant prepared above to 36.5g of water, stir thoroughly to make a uniform aqueous solution, then add 20g of heavy calcium carbonate and clay (Ultra White).
80 g of UW-90 (manufactured by Engelhard) were mixed and thoroughly kneaded. To this clay mixture, 25 g of a 20% starch aqueous solution and then 20 g of 50% SBR latex were added and thoroughly kneaded to form a pigment dispersion.
The stability of this dispersion was evaluated by measuring the viscosity immediately after kneading and after being left at room temperature for one day. Table of results obtained.
Shown in 3. Coating of pigment dispersion and evaluation of coated paper: The pigment dispersion prepared above was hand-coated onto the surface of high-quality paper using a coating rod, and after drying at room temperature, supercalendering was performed to obtain coated paper. .
The coating amount was calculated from the weight increase of the coated paper, and the obtained results are shown in Table 3. The obtained coated paper was evaluated by the following blank paper test and printing test. Blank paper test: (1) Gloss: Measured using a gloss meter manufactured by Murakami Color Co., Ltd. at a measurement angle of 75°C. Large numbers are better. (2) Whiteness and opacity: Measured using a Hunter colorimeter. Large numbers are better. Printing test: (1) Dry pick, wet pick; Mei Seisakusho PI
It was evaluated using a testing machine. Evaluation is done on a 10-point scale, with higher numbers being better. (2) Gloss: The same method as above was used. The results obtained are shown in Table 3. Examples 3 and 4 With the combinations and amounts of monomers shown in Table 2,
A dispersant was produced in exactly the same manner as in Example 2.

【table】

[Table] Next, a pigment dispersion was produced and evaluated in exactly the same manner as in Example 2. The pigment dispersion was used to coat the surface of high-quality paper, and the coated paper was evaluated. The above evaluation results are shown in Table-3. Comparative Examples 3 to 5 With the combinations and amounts of monomers shown in Table 2,
A dispersant was produced in exactly the same manner as in Example 2. A pigment dispersion was then produced and evaluated in exactly the same manner as in Example 2. The pigment dispersion was used to coat the surface of high-quality paper, and the coated paper was evaluated. The above evaluation results are shown in Table-3.

Claims (1)

[Claims] 1. A pigment dispersant obtained by copolymerizing α,β-monoethylenically unsaturated carboxylic acid or its salt and 2-acrylamido-2-phenylpropanesulfonic acid or its alkali metal salt.