JPH0582254B2 - - Google Patents

Description

[Detailed description of the invention]

(Industrial Application Field) The present invention relates to a method for efficiently dispersing talc in an aqueous medium to produce a highly concentrated aqueous dispersion. Specifically, the present invention relates to a method for efficiently dispersing talc in an aqueous medium to produce a highly concentrated aqueous dispersion. The present invention relates to a method for producing an aqueous talc dispersion characterized by the following. (Prior art) Talc is used as a coating pigment because it is inexpensive and has excellent abrasion resistance, ink receptivity, and gloss compared to other inorganic pigments, and it is also used as a pulp material because it has an excellent gummy adsorption ability. It is one of the pigments that is used as a pitch control agent in the paper manufacturing industry. Conventionally, coarse talc with an average particle size of around 5 μm has been frequently used, but in recent years, as paper quality has become more sophisticated, the proportion of fine-grained talc used has been increasing with the average particle size of 1 to 3 μm. However, the smaller the average particle diameter, the more difficult it becomes to disperse in an aqueous medium, and the more likely it is to aggregate, causing problems in the stability of the aqueous dispersion over time. Conventionally known dispersants for talc include pyrophosphate, tripolyphosphate, trimetaphosphate,
Examples include condensed phosphates such as tetrametaphosphate and hexametaphosphate; polycarboxylate salts such as polyacrylate, polymethacrylate, and polymaleate; and polyvinyl alcohol. However, although these condensed phosphates and polycarboxylate salts have a relatively good reputation for dispersing coarse talc, they require high viscosity of the resulting aqueous dispersion for dispersing fine talc. There were also problems with stability over time. Furthermore, it is described that polyvinyl alcohol has a dispersing effect on inorganic pigments, such as in JP-A-60-262862. However, Tokukai Akira
The dispersant described in No. 60-262862 is water-insoluble,
The viscosity of the talc aqueous dispersion obtained using this as a dispersant was abnormally high, and it was completely unsuitable for producing a high concentration talc aqueous dispersion. On the other hand, especially effective for dispersing talc,
The use of salts of sulfated alkylphenol ethylene oxide adducts (JP-A-53-102882) and dialkyl sulfosuccinates (JP-A-59-55336) has been proposed. However, JP-A-53-102882
The dispersant described in the above issue requires a relatively large amount to be added, which has serious drawbacks such as increased cost and poor water resistance of the coating film.Furthermore, foaming during dispersion production significantly impairs workability. Problems remained.
In addition, the dispersant described in JP-A No. 59-55336 has a relatively good reputation for coarse talc with an average particle size of 5μ or more, but for fine talc with an average particle size of 1 to 3μ. Problems still remained regarding the dispersion of . (Problems to be Solved by the Invention) The present invention solves the above-mentioned problems associated with insufficient dispersion performance of conventional dispersants.
The present invention provides a method that makes it possible to produce highly concentrated aqueous talc dispersions with low viscosity and good stability over time using a small amount of dispersant for all fine-grained talc. (Means and effects for solving the problem) The present inventors have discovered that by using a specific amount of water-soluble polyvinyl alcohol having a specific degree of polymerization, a specific degree of saponification, and a specific degree of anionic modification to talc, They discovered that the dispersion effect could be significantly improved to a level that could not be obtained with conventional dispersants, and completed the present invention. That is, in the present invention, when dispersing talc in an aqueous medium to produce an aqueous dispersion, a dispersant having a degree of polymerization of 30 to 700, a degree of saponification of 65 to 100 mol%, and a degree of anionic modification of 0.5 to 20 is used as a dispersant. The present invention relates to a method for producing an aqueous talc dispersion, characterized in that mol% of water-soluble anionized modified polyvinyl alcohol () is used in an amount ranging from 0.3 to 3 parts by weight per 100 parts by weight of talc. The water-soluble anionized modified pyrivinyl alcohol () used in the present invention is, for example, vinyl acetate/
It is a polyvinyl alcohol having an anionic group in the molecule, which is obtained by saponifying an anionic monomer copolymer using a known technique, and has a degree of polymerization of 30 to 30.
700, preferably 100-300, saponification degree 65-100
mol%, preferably 80 to 100 mol%, and degree of anionic modification 0.5 to 20 mol%, preferably 1 to 100 mol%.
A range of 10 mol% is effectively used. If any one of the degree of polymerization, degree of saponification, and degree of anionic modification of the water-soluble anionically modified polyvinyl alcohol () is outside the above range, the dispersion effect is insufficient. In particular, when the degree of anionization modification of the water-soluble anionized modified polyvinyl alcohol () is less than 0.5 mol%, the degree of anionization modification is substantially the same as that of unmodified polyvinyl alcohol, and the stability over time of the obtained talc aqueous dispersion is A problem arises.
On the other hand, if the degree of anionic modification exceeds 20 mol %, a large amount is required to be added, which is not preferable. Examples of anionic monomers used for anionization modification when obtaining water-soluble anionization modified polyvinyl alcohol () include allylsulfonic acid, methallylsulfonic acid, styrenesulfonic acid, vinylsulfonic acid, 3-allyloxy- 2-
Hydroxypropanesulfonic acid, sulfoethyl (meth)acrylate, 2-acrylamide-2
- Sulfonic acid monomers such as methylpropanesulfonic acid, sulfoethylmaleimide, sulfoalkylmaleate, or their monovalent metal salts, ammonium salts, and amine salts; acrylic acid, methacrylic acid, α-hydroxyacrylic acid, (anhydrous ) Sulfonic acid monomers such as maleic acid, itaconic acid, fumaric acid, crotonic acid, citraconic acid, afnitic acid or their monovalent metal salts, ammonium salts, and amine salts; (meth)acrylamidomethanephosphonic acid, 2- (meth)acrylamido-2-methylpropanephosphonic acid, mono[2-hydroxyethyl (meth)acrylate] acid phosphate, mono(3-chloro-2-hydroxypropyl (meth)acrylate) acid phosphate or their Monovalent metal salts, ammonium salts,
Examples include phosphonic acid monomers such as amine salts. In order to obtain water-soluble anionized modified polyvinyl alcohol (), it is not limited to that obtained by saponifying a vinyl acetate/anionic monomer copolymer. For example, polyvinyl alcohol can be treated with bromine, iodine, etc. and then sulfonated using a sulfonating agent such as acidic sodium sulfite, or polyvinyl alcohol can be modified with sulfuric acid esterification in a concentrated sulfuric acid aqueous solution. Of course, it is also possible to saponify vinyl acetate (meth)acrylic acid ester copolymer and the like to modify it by carboxylation. Among such water-soluble anionized modified polyvinyl alcohols, water-soluble sulfonated modified polyvinyl alcohols or water-soluble carboxylated modified polyvinyl alcohols, which are inexpensive and easily produced industrially, are particularly preferred. In the present invention, water-soluble anionized modified polyvinyl alcohol () is used at 0.3 parts by weight per 100 parts by weight of talc.
-3 parts by weight. If the amount of water-soluble anionized modified polyvinyl alcohol () used is less than the above range, an aqueous talc dispersion with low viscosity and good stability over time cannot be obtained. Further, even if the amount used is increased beyond the above range, a dispersion effect commensurate with the increased amount cannot be obtained, and on the contrary, the water resistance of the coating film using the obtained talc aqueous dispersion is undesirably reduced. In the present invention, in order to produce an aqueous talc dispersion, talc may be dispersed in an aqueous medium using a predetermined amount of the above-mentioned dispersant. Talc can be dispersed using various conventional mixing devices, such as a container equipped with a stirrer such as a dissolver stirring blade, or a mixer such as a ball mill or paint shaker.
This can be achieved by adding an aqueous medium and a dispersant and stirring or mixing. The order of addition of talc, aqueous medium, and dispersant is not particularly limited. For example, talc may be added to an aqueous medium in which a dispersant is dissolved, or the dispersant may be added to a talc slurry obtained by kneading talc and an aqueous medium. May be added. Known organic dispersants such as polyacrylates, polymethacrylates, polymaleates, (meth)acrylic acid/maleic acid copolymers, sulfated alkylphenol ethylene oxide additions may be used within the range not impairing the effects of the present invention. salts, dialkyl sulfosuccinates, polyethylene glycol, oxyethylene/oxypropylene block copolymers, and known inorganic dispersants such as calcium.
Hydroxides, carbonates, or halides of polyvalent metals such as magnesium, aluminum, and zinc,
It is of course possible to use condensed phosphates such as pyrophosphate, tripolyphosphate, and hexametaphosphate in combination. (Effects of the Invention) According to the method of the present invention, since a specific amount of water-soluble anionized modified polyvinyl alcohol is used as a dispersant, high-concentration talc water dispersion is possible for all coarse to fine talc particles. It can be made into a liquid. In addition, the talc aqueous dispersion obtained by the method of the present invention has low viscosity, high fluidity, and excellent stability over time, and furthermore, the water resistance of the coating film obtained using the talc aqueous dispersion is It can be effectively used in paints and other applications without having any adverse effects on the product. (Examples) Hereinafter, the present invention will be specifically explained with reference to Examples, but the present invention is not limited to these Examples. Note that parts and % in the examples indicate parts by weight and % by weight, respectively. In addition, % of talc in the example
represents the solid content weight ratio of the dispersant to the talc solid content. Example 1 Capacity 1 (Material SUS 304, inner diameter 90mm, height 160mm)
mm) in a beaker with a degree of polymerization of 250 as a dispersant.
Add 10 parts of a 20% aqueous solution of anionized modified polyvinyl alcohol (based on 1% talc) having a degree of saponification of 88 mol % and a degree of sulfonation of 3 mol % due to copolymerization of allyl sulfonic acid and water to bring the total amount to 133.3 parts. And so. Fine-grained talc powder with an average particle size of 2.6μ is added to it while stirring at low speed using a dissolver stirring blade (50mmφ).
200 parts were added over 3 minutes. then 10 at 3000rpm
Dispersion was carried out for a minute to obtain an aqueous dispersion (1) with a solid content concentration of 60%. Viscosity of the obtained aqueous dispersion 1 (B type viscometer, 25℃
Table 1 shows the test results for stability over time (measured by Examples 2 to 7 An aqueous dispersion with a solid content concentration of 60% was prepared in the same manner as in Example 1, except that the water-soluble anionized modified polyvinyl alcohol () shown in Table 1 was used as a dispersant.
(2) to (7) were obtained. The viscosity and aging stability of the obtained aqueous dispersions (2) to (7) were measured in the same manner as in Example 1, and the test results are shown in Table 1.

[Table] ×: Large amount of sediment, solid sediment Comparative Examples 1 to 6 Predetermined amounts of condensed phosphates, polycarboxylic acid salts, and sulfated alkylphenol ethylene oxide adducts shown in Table 2 as dispersants The solid content concentration was 60% in the same manner as in Example 1 except that one or two types of salts and dialkyl sulfosuccinates were used.
Aqueous dispersions (1) to (6) for comparison were obtained. The viscosity and aging stability of the obtained comparative aqueous dispersions (1) to (6) were measured in the same manner as in Example 1, and the test results are shown in Table 2.

【table】

[Table] ×: The amount of sediment is large and the sediment is hard Comparative Examples 7 to 16 The same procedure as Example 1 was carried out except that the polyvinyl alcohol shown in Table 3 was used as a dispersant, and the solid content concentration was 60%. Comparative aqueous dispersions (7) to (16) were obtained. The viscosity and aging stability of the obtained comparative aqueous dispersions (7) to (16) were measured in the same manner as in Example 1, and the test results are shown in Table 3.

【table】

[Table] ×: Large amount of sediment, solid sediment Example 8 In the same stainless steel beaker as used in Example 1, a dispersant with a polymerization degree of 250 and a saponification degree of
4 parts of a 20% aqueous solution of anionized modified polyvinyl alcohol (based on 0.4% talc) containing 88 mol% and a degree of sulfonation of 3 mol% by copolymerization of allylsulfonic acid.
and water were added to make the total amount 107.7 parts. While stirring at low speed using a dissolver stirring blade (50 mmφ), 200 parts of coarse talc powder with an average particle size of 10 μm was added over 3 minutes. Next, dispersion was performed at 3000 rpm for 10 minutes to obtain an aqueous dispersion (8) with a solid content concentration of 65%. Viscosity of the obtained aqueous dispersion (8) (B-type viscometer, 25℃
Table 4 shows the test results for stability over time. Examples 9 to 14 An aqueous dispersion with a solid content concentration of 65% was prepared in the same manner as in Example 8, except that the water-soluble anionized modified polyvinyl alcohol () shown in Table 4 was used as a dispersant.
(9) to (14) were obtained. The viscosity and aging stability of the obtained aqueous dispersions (9) to (14) were measured in the same manner as in Example 8, and the test results are shown in Table 4.

【table】

[Table] ×: Large amount of sediment, solid sediment Comparative examples 17-22 Condensed phosphates, polycarboxylic acid salts, and sulfated alkylphenol ethylene oxide adducts in the specified amounts shown in Table 5 as dispersants The solid content concentration was 65% in the same manner as in Example 8 except that one or two types of salts and dialkyl sulfosuccinates were used.
Aqueous dispersions (17) to (22) for comparison were obtained. The viscosity and aging stability of the obtained comparative aqueous dispersions (17) to (22) were measured in the same manner as in Example 8, and the test results are shown in Table 5.

[Table] ×: The amount of sediment is large and the sediment is hard Comparative Examples 23-32 The same procedure as Example 8 was carried out except that the polyvinyl alcohol shown in Table 6 was used as a dispersant, and the solid content concentration was 65%. Comparative aqueous dispersions (23) to (32) were obtained. The viscosity and aging stability of the obtained comparative aqueous dispersions (23) to (32) were measured in the same manner as in Example 8, and the test results are shown in Table 6.

[Table] ×: Large amount of sediment, solid sediment

Claims (1)

[Claims] 1. When dispersing talc in an aqueous medium to produce an aqueous dispersion, as a dispersant, a polymer with a degree of polymerization of 30 to 700,
Saponification degree 65-100 mol% and anionic modification degree
0.5 to 20 mol% of water-soluble anionized modified polyvinyl alcohol () per 100 parts by weight of talc
A method for producing an aqueous talc dispersion, characterized in that it is used in an amount ranging from 0.3 to 3 parts by weight. 2. The method for producing an aqueous talc dispersion according to claim 1, wherein the water-soluble anionized modified polyvinyl alcohol () is a water-soluble sulfonated modified polyvinyl alcohol. 3. The method for producing an aqueous talc dispersion according to claim 1, wherein the water-soluble anionized modified polyvinyl alcohol () is a water-soluble carboxylated modified polyvinyl alcohol.