JPH0453814B2 - - Google Patents

Description

[Detailed description of the invention]

(Industrial Application Field) The present invention relates to a method for efficiently dispersing calcium carbonate in an aqueous medium to produce an aqueous dispersion. The present invention relates to a method for producing an aqueous calcium carbonate dispersion, characterized in that polyvinyl alcohol is used in combination as a dispersant. (Prior Art) Calcium carbonate is one of the pigments prized in the paper industry because it is inexpensive and has superior whiteness, ink receptivity, and printability compared to other inorganic pigments. Furthermore, with the spread of neutral paper making, its usage is rapidly increasing. Traditionally, so-called heavy calcium carbonate with an average particle size of around 1 μm has been frequently used as calcium carbonate, but in recent years, with the advancement of paper quality, the average particle size has increased from 0.1 to 1 μm.
The proportion of use of 0.5μ precipitated light calcium carbonate is increasing. However, the smaller the average particle size, the more difficult it becomes to disperse in an aqueous medium.
In addition, it tends to aggregate, which tends to cause problems in the stability of the aqueous dispersion over time. Conventionally used dispersants for calcium carbonate include inorganic condensed phosphates such as pyrophosphate, tripolyphosphate, trimetaphosphate, tetrametaphosphate, and hexametaphosphate, zinc salts,
Silicates, etc. However, these inorganic dispersants have problems with the stability of the resulting aqueous dispersion over time, and they require a large amount to be added to disperse the finely divided precipitated light calcium carbonate, resulting in the water resistance of the coating film. There was a serious drawback in that the sex deteriorated. On the other hand, as organic dispersants, polycarboxylic acid salts such as polyacrylates, polymethacrylates, and polymaleates, and polyvinyl alcohol are known. However, polycarboxylate salts, such as sodium polyacrylate, have a relatively good reputation for dispersing heavy calcium carbonate with an average particle size of around 1 μm. The dispersion of the aqueous dispersion had a high viscosity and there were problems with stability over time. Furthermore, it is described in JP-A-60-262862, for example, that polyvinyl alcohol has a dispersing effect on inorganic pigments. However, the dispersant described in JP-A No. 60-262862 is water-insoluble and has insufficient dispersing effect on calcium carbonate, and when used alone, the viscosity of the aqueous dispersion obtained becomes abnormal. It was completely unsuitable for producing a high-concentration calcium carbonate aqueous dispersion. In order to overcome the drawbacks of such known dispersants, maleic acid copolymers have been developed in Japanese Patent Publication No. 54-36166, Japanese Patent Publication No. 56-47131, Japanese Patent Application Laid-open No. 144499-1982, Japanese Patent Application Laid-open No. 168906-1987, etc. A method using . The dispersant described in Japanese Patent Publication No. 54-36166 has been evaluated as relatively good because the resulting aqueous calcium carbonate dispersion has good flow characteristics (low shear viscosity), but it has a high solid content of 65% by weight or more. There remains a problem with the dispersion. Special Public Service 1976-
The dispersant described in No. 47131 lowers the viscosity of the aqueous fine-particle calcium carbonate dispersion, but requires a large amount to be added, resulting in increased costs and problems with water resistance of the coating film. The dispersant described in JP-A No. 53-144499 yields an aqueous calcium carbonate dispersion with an extremely high solid content of 70% by weight, but it also has a solid content of 1.4% by weight.
% (relative to calcium carbonate). The dispersant described in JP-A-57-168906 is
A serious drawback is that the resulting aqueous calcium carbonate dispersion has poor flow properties (high shear viscosity). Furthermore, a method using an itaconic acid copolymer has been proposed in JP-A No. 59-193964, but problems still remain in dispersing calcite-based cubic calcium carbonate with an average particle size of 0.3μ or less. It is. In addition, the use of hydroxyl group-containing polymers has been proposed in JP-A-59-26131 and JP-A-59-108010, and such polymers have a relatively good reputation for heavy calcium carbonate. However, when dispersing calcium carbonate in the form of extremely fine particles with an average particle size of 0.1 to 0.3μ, the resulting aqueous dispersion has a high viscosity and its stability over time is insufficient, which is a problem. It was something that remained. (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 enables the production of highly concentrated aqueous calcium carbonate dispersions with low viscosity, high fluidity, and good stability over time using a small amount of dispersant for all types of light calcium carbonate. . (Means and effects for solving the problem) The present inventors believe that when used alone,
A polycarboxylic acid-based water-soluble copolymer and a water-soluble anionized modified polyvinyl alcohol, which have a significantly poor dispersion effect in an aqueous medium of light calcium carbonate, are combined with a water-soluble copolymer of a specific molecular weight and a specific degree of polymerization. By selecting a water-soluble polyvinyl alcohol with a characteristic degree of saponification and a specific degree of anionic modification and using it in a specific proportion, the above-mentioned dispersion effect can be significantly improved to a level that could not be obtained with conventional dispersants. The heading completes the invention. That is, the present invention uses an unsaturated monocarboxylic acid monomer selected from acrylic acid, methacrylic acid, and salts thereof as a dispersing agent when dispersing calcium carbonate in an aqueous medium to produce an aqueous dispersion. 60
~99.9 mol% and hydroxyl group-containing monomer
A water-soluble copolymer () with a number average molecular weight of 2,000 to 80,000 obtained using a proportion in the range of 0.1 to 50 mol%
and water-soluble anionized modified polyvinyl alcohol () having a degree of polymerization of 30 to 700, a degree of saponification of 30 to 100 mol%, and a degree of anionic modification of 0.5 to 20 mol%, based on 100 parts by weight of calcium carbonate. The present invention relates to a method for producing an aqueous calcium carbonate dispersion, characterized in that 0.1 to 2 parts by weight of a copolymer () and 0.03 to 1 part by weight of a water-soluble anionized modified polyvinyl alcohol () are used together. The mechanism of action by which excellent calcium carbonate dispersion ability is achieved when the water-soluble copolymer () and the water-soluble anionized modified polyvinyl alcohol () are used together in the above-mentioned ratio is not necessarily clear, but it is explained as follows. It is estimated that. In other words, since the water-soluble copolymer () is strongly adsorbed on the surface of the calcium carbonate particles, the water-soluble anionized modified polyvinyl alcohol () does not exist in an adsorbed form on the surface of the calcium carbonate particles, or exists only in a small amount. The concentration of the water-soluble anionized modified polyvinyl alcohol () in the aqueous medium increases compared to when the water-soluble copolymer () is not used. As a result of the inventors' intensive study of this phenomenon,
Due to the synergistic effect of the water-soluble copolymer () adsorbed on the surface of calcium carbonate particles and the water-soluble anionized modified polyvinyl alcohol () present in the aqueous medium, the viscosity of the resulting calcium carbonate aqueous dispersion is greatly reduced. The present inventors have discovered that this and the stability over time are significantly improved, and have arrived at the present invention. In order to obtain the water-soluble copolymer () used in the present invention, unsaturated monocarboxylic acid monomers (hereinafter simply unsaturated monocarboxylic monomers) selected from acrylic acid, methacrylic acid and their salts are used. ) and a hydroxyl monomer (hereinafter simply referred to as unsaturated hydroxyl monomer) may be polymerized using known techniques. For example, in the case of aqueous polymerization, persulfates such as sodium persulfate and potassium persulfate; hydrogen peroxide; 2,2'-azobis(2-amidinopropane) hydrochloride, 4,4'-azobis-4-
It can be produced by a conventional method using an aqueous azo compound such as cyanovaleric acid as a polymerization catalyst.
In the case of polymerization in organic solvents such as alcohols such as methanol and isopropyl alcohol, ethers such as tetrahydrofuran and dioxane, aromatics such as benzene, xylene and toluene, or ketones such as methyl ethyl ketone and methyl isobutyl ketone, Organic peroxides such as benzoyl peroxide, lauroyl peroxide, and peracetic acid; oil-soluble azo compounds such as azobisisobutyronitrile and 2,2'-azobis(4-methoxy-2,4-dimethylvaleronitrile) etc. can be produced by a conventional method using as a polymerization catalyst. The water-soluble copolymer () contains an unsaturated monocarboxylic acid monomer and an unsaturated hydroxyl monomer,
It is a water-soluble copolymer having a number average molecular weight in the range of 2,000 to 80,000 obtained by copolymerizing the former at a ratio of 50 to 99.9 mol% and the latter at a ratio of 0.1 to 50 mol%. If the proportion of the monomer used or the number average molecular weight is out of this range, the dispersion effect will be insufficient when used in combination with the water-soluble anionized modified polyvinyl alcohol (2). The unsaturated monocarboxylic acid monomer used to obtain the water-soluble copolymer (2) is an acid monomer or an acid form monomer that is neutralized with an alkaline substance to obtain a salt form monomer. Any of the above can be used. When using an acid type monomer, considering the dispersion effect, it is preferable that at least 30 mol% of the carboxyl groups in the resulting water-soluble copolymer (2) be neutralized with an alkaline substance after polymerization. . Such alkaline substances include, for example, hydroxides and carbonates of sodium, potassium, lithium, etc.; ammonia; organic amines; inorganic amines;
Examples include hydroxides and carbonates of calcium, magnesium, aluminum, zinc, and the like. Among them, sodium hydroxide is particularly preferred because it is inexpensive and industrially easily available. Examples of unsaturated monocarboxylic acid monomers in salt form include sodium acrylic acid and methacrylic acid,
Examples include alkali metal salts such as potassium and lithium, ammonium salts, amine salts, and polyvalent metal salts such as calcium, magnesium, aluminum, and zinc. Examples of unsaturated hydroxyl monomers include 3
-Methyl-3-buten-1-ol (isoprenol), 3-methyl-2-buten-1-ol (prenol), 2-methyl-3-buten-2-ol (isoprene alcohol), 2-hydroxyethyl ( meth)acrylate, polyethylene glycol mono(meth)acrylate, polypropylene glycol mono(meth)acrylate, polyethylene glycol monoisoprenol ether,
Polypropylene glycol monoisoprenol ether, polyethylene glycol monoallyl ether, polypropylene glycol monoallyl ether, glycerol monoallyl ether, α-hydroxyacrylic acid (salt), N-methylol (meth)acrylamide, glycerol mono(meth)
Examples include acrylate, vinyl alcohol, allyl alcohol, and 3-allyloxy-2-hydroxypropanesulfonic acid (salt). In addition, when obtaining the water-soluble copolymer (), other monomers that can be copolymerized with the unsaturated monocarboxylic acid monomer and the unsaturated hydroxyl monomer may be used within a range that does not impair the effects of the present invention. It is of course possible to copolymerize. Examples of other copolymerizable monomers include amide monomers such as (meth)acrylamide and t-butyl (meth)acrylamide;
Hydrophobic monomers such as (meth)acrylic acid ester, styrene, 2-methylstyrene, vinyl acetate;
Vinylsulfonic acid, allylsulfonic acid, methallylsulfonic acid, styrenesulfonic acid, 2-acrylamido-2-methylpropanesulfonic acid, sulfomethyl (meth)acrylate, sulfopropyl (meth)acrylate, sulfoethylmaleimide, or a monovalent group thereof. Unsaturated sulfonic acid monomers such as partially or completely neutralized products with metals, divalent metals, ammonia, and organic amines; cationic properties such as dimethylaminoethyl (eth)acrylate, dimethylaminopropyl (meth)acrylamide, etc. Monomers: Nitrile monomers such as (meth)acrylonitrile; (meth)acrylamide methanephosphonic acid, (meth)acrylamide methanephosphonic acid methyl ester, 2-(meth)acrylamido-2-methylpropanephosphonic acid, etc. Examples include phosphorus monomers; unsaturated dicarboxylic acid monomers such as maleic acid, fumaric acid, and itaconic acid; crotonic acid; The water-soluble anionized modified polyvinyl 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 30-100
mol%, preferably 65 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 anionized modified polyvinyl alcohol () is outside the above range, the dispersion effect when used in combination with the water-soluble copolymer () is insufficient. In particular, when the degree of anionic modification of water-soluble anionized modified polyvinyl alcohol () is less than 0.5 mol%, it becomes substantially the same as unmodified polyvinyl alcohol, and the obtained calcium carbonate aqueous dispersion is stable over time. Sexual problems arise. On the other hand, if the degree of anionic modification exceeds 20 mol%,
This is not preferable as it requires a large amount of addition. 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) maleic acid, itaconic acid, fumaric acid, crotonic acid,
Citraconic acid, aconitic acid or one of them
Carboxylic acid monomers such as valent metal salts, ammonium salts, and amine salts; (meth)acrylamide methanephosphonic acid, 2-(meth)acrylamide-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 , phosphonic acid monomers such as amine salts, and the like. 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 may be treated with bromine, iodine, etc. and then sulfonated using a sulfonating agent such as acidic sodium sulfite, or polyvinyl alcohol may be sulfuric acid esterified in a concentrated sulfuric acid aqueous solution.
Furthermore, it is of course possible to saponify a vinyl acetate/(meth)acrylic acid ester copolymer or 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, the water-soluble copolymer () is used in an amount of 0.1 to 2 parts by weight per 100 parts by weight of calcium carbonate, and the water-soluble anionized modified polyvinyl alcohol () is added in an amount of 0.03 to 1 part by weight per 100 parts by weight of calcium carbonate. Used together in a range of proportions. If the amount of water-soluble copolymer () or water-soluble anionized modified polyvinyl alcohol () used is less than the above range,
An aqueous calcium carbonate 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 calcium carbonate aqueous dispersion is decreased, which is not preferable. In the present invention, there is no particular restriction on the order of addition when the water-soluble copolymer () and the water-soluble anionized modified polyvinyl alcohol () are used together as a dispersant. That is, calcium carbonate can be coarsely dispersed in an aqueous medium using a water-soluble copolymer () and then finely dispersed by adding a water-soluble anionized modified polyvinyl alcohol ( After rough dispersion with ), fine dispersion can also be achieved by adding the water-soluble copolymer ( ). It is also possible to add the water-soluble copolymer () and the water-soluble anionized modified polyvinyl alcohol () at the same time and use them together. Additionally, known organic dispersants, such as polyacrylates, polymethacrylates, polymaleates, (meth)acrylic acid/maleic acid copolymers, (meth)acrylic acid, may be used within a range that does not impair the effects of the present invention. / itaconic acid copolymers, known inorganic dispersants, such as hydroxides, carbonates, or halides of polyvalent metals such as calcium, magnesium, aluminum, and zinc, pyrophosphates, tripolyphosphates, hexametaphosphoric acid It is of course possible to use condensed phosphates such as salts in combination. (Effect of the invention) According to the method of the present invention, since a specific water-soluble copolymer and a specific water-soluble anionized modified polyvinyl alcohol are used together as a dispersant in a specific ratio, heavy to light A high-concentration calcium carbonate water-acid solution can be obtained with a small amount of dispersant for all calcium carbonate. In addition, the calcium carbonate aqueous dispersion obtained by the method of the present invention has low viscosity, high fluidity, and excellent stability over time, so it does not adversely affect the water resistance of the resulting coating film. , it can be effectively used for other applications of paint. In addition, the dispersant obtained in the present invention can be used with other inorganic pigments such as clay, titanium oxide, satin white,
It can also be effectively used for aluminum hydroxide, slaked lime, red iron oxide, cement, alumina, zirconia, silica, silicon carbide, silicon titanide, etc. (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, % to calcium carbonate in the examples indicates the solid content weight ratio of the dispersant (water-soluble copolymer or water-soluble anionized modified polyvinyl alcohol) to the solid content of calcium carbonate. Example 1 Capacity 1 (Material SUS 304, inner diameter 90mm, height 160mm)
400 parts of a filter press dehydrated cake (solid content 65.3%) of calcite-based cubic light calcium carbonate (primary particle size 0.15μ) is placed in a beaker of 1.5 mm), and added to it as a dispersant with a number average molecular weight of 14000.
3.26 parts of a 40% aqueous solution of sodium salt (based on calcium carbonate: 0.5%) of a copolymer of acrylic acid/isoprenol = 90/10 (mole ratio), with a degree of polymerization of 250, a degree of saponification of 88 mol%, and p-styrene. Add 2.61 parts of a 20% aqueous solution of anionized modified polyvinyl alcohol with a degree of sulfonation of 3 mol% by a copolymer of sulfonic acid (based on calcium carbonate: 0.2%) and 5.1 parts of water for adjusting the solid content concentration, and mix with a dissolver stirring blade (50 mm).
After kneading at low speed for 3 minutes at φ), the mixture was dispersed at 3000 rpm for 10 minutes to obtain an aqueous dispersion (1) with a solid content concentration of 64%. Viscosity of the obtained aqueous dispersion (1) (B type viscometer, 25℃
Table 1 shows the test results for stability over time (measured by In addition, the flow characteristics of the aqueous dispersion (1) immediately after production were measured using a Hercules viscometer (manufactured by Kumagai Riki Kogyo Co., Ltd., HR-
801C type) (Bob B, sweep time 20 seconds)
The resulting olegram is shown in FIG. Examples 2 to 6 Examples were carried out except that predetermined amounts of the water-soluble copolymer () and water-soluble anionized modified polyvinyl alcohol () shown in Table 1 were used as dispersants, and a predetermined amount of solid content concentration-adjusted water. In the same manner as in Example 1, aqueous dispersions (2) to (6) having a solid content concentration of 64% were obtained. The viscosity and aging stability of the obtained aqueous dispersions (2) to (6) were measured in the same manner as in Example 1, and the test results are shown in Table 1.

【table】

[Table] Comparative Example 1 4.57 parts of a 40% aqueous solution of acrylic acid/maleic acid = 60/40 (mole ratio) copolymer sodium salt with a number average molecular weight of 5200 as a dispersant (based on calcium carbonate 0.7%) and solid content A comparative aqueous dispersion (1) having a solid content concentration of 64% was obtained in the same manner as in Example 1 except that 6.4 parts of water for concentration adjustment was used. The viscosity and aging stability of the obtained comparison aqueous dispersion (1) were measured in the same manner as in Example 1, and the test results are shown in Table 2. Also, a comparative aqueous dispersion immediately after production.
The flow characteristics of (1) were measured using a Hercules viscometer (Bob B, sweep type 20 seconds), and the obtained oleogram is shown in Figure 1. Comparative Examples 2 to 5 Examples except that 0.7% (based on calcium carbonate) of the water-soluble polymer or water-soluble copolymer () shown in Table 2 as a dispersant and a predetermined amount of solid content adjustment water were used. Comparative aqueous dispersions (2) to (5) having a solid content concentration of 64% were obtained in the same manner as in Example 1. The viscosity and aging stability of the obtained comparative aqueous dispersions (2) to (5) were measured in the same manner as in Example 1, and the test results are shown in Table 2. Comparative Examples 6 to 8 Same as Example 1 except that 0.7% (based on calcium carbonate) of water-soluble anionized modified polyvinyl alcohol () shown in Table 2 as a dispersant and a predetermined amount of solid content adjustment water were used. and solid content concentration 64
% comparative aqueous dispersions (6) to (8) were obtained. The viscosity and aging stability of the obtained comparative aqueous dispersions (6) to (8) were measured in the same manner as in Example 1, and the test results are shown in Table 2. Comparative Examples 9 to 23 A water-based polymer or a water-soluble copolymer () shown in Table 2 as a dispersant, a water-soluble polyvinyl alcohol or a water-soluble anionized modified polyvinyl alcohol (), and a predetermined amount of solid content concentration-adjusted water were used as a dispersant. The solid content concentration was determined in the same manner as in Example 1 except that
Comparative aqueous dispersions (9) to (23) of 64% were obtained. The viscosity and aging stability of the obtained comparison aqueous dispersions (9) to (23) were measured in the same manner as in Example 1, and the test results are shown in Table 2.

【table】

[Table] Examples 7 to 12 The water-soluble copolymer (2.5) shown in Table 3 was added as a dispersant to the beaker with a capacity of 1 used in Example 1.
(0.5% relative to calcium carbonate) and 0.5 part (0.1% relative to calcium carbonate) of water-soluble anionized modified polyvinyl alcohol, and add water to bring the total amount up.
170.7 copies. To the obtained aqueous dispersant solution, 500 parts of heavy calcium carbonate (average particle size 10 μm) was added over 2 minutes while stirring at 1000 rpm using the stirring blade used in Example 1 to prepare a premix liquid. Next, this premix liquid was processed using a sand grinder with a Vessel capacity of 1 (glass beads (1.0 to 1.5 mmφ) as media, 0.35, stirring rotation speed 3000 rpm) until the proportion of particles with a particle diameter of 2 μ or less was 90% and the average particle diameter was 0.8 μ. The mixture was dispersed to obtain calcium carbonate aqueous dispersions (7) to (12) with a solid content concentration of 75%. The viscosity and aging stability of the obtained aqueous dispersions (7) to (12) were measured in the same manner as in Example 1, and the test results are shown in Table 3.

【table】

[Table] Comparative Examples 24 to 28 Other than using 3.0 parts of the water-soluble polymer or water-soluble copolymer () shown in Table 4 as a dispersant (0.6% relative to calcium carbonate) and a specified amount of water, the experiment was carried out. Comparative aqueous dispersions (24) to (28) having a solid content concentration of 75% were obtained in the same manner as Examples 7 to 12. The viscosity and aging stability of the obtained comparative aqueous dispersions (24) to (28) were measured in the same manner as in Example 1,
The test results are shown in Table 4. Comparative Examples 29-31 Same as Examples 7-12 except that 0.3 parts of water-soluble anionized modified polyvinyl alcohol () shown in Table 4 (0.6% to calcium carbonate) and a predetermined amount of water were used as a dispersant. Comparative aqueous dispersions (29) to (31) having a solid content concentration of 75% were obtained. The viscosity and aging stability of the obtained comparative aqueous dispersions (29) to (31) were measured in the same manner as in Example 1,
The test results are shown in Table 4. Comparative Examples 32-46 2.5 parts of the water-soluble polymer or water-soluble copolymer () shown in Table 4 as a dispersant (0.5% to calcium carbonate) and water-soluble polyvinyl alcohol or water-soluble anionized modified polyvinyl alcohol () A comparative aqueous dispersion (32) with a solid content concentration of 75% was prepared in the same manner as in Examples 7 to 12, except that 0.5 part (based on calcium carbonate: 0.1%) and a predetermined amount of water were used.
(46) was obtained. The viscosity and aging stability of the obtained comparative aqueous dispersions (32) to (46) were measured in the same manner as in Example 1,
The test results are shown in Table 4.

【table】

[Table] Examples 13 to 18 The water-soluble copolymer () shown in Table 5 was added as a dispersant to the beaker with a capacity of 1 used in Example 1.
0.8 parts (0.2% relative to calcium carbonate) and 0.4 parts (0.1% relative to calcium carbonate) of water-soluble anionized modified polyvinyl alcohol were taken, and water was added to make the total amount 183.5 parts. After adding 400 parts of calcite-based cubic light calcium carbonate fine powder (primary particle size 0.2μ) to the obtained dispersant aqueous solution under low-speed stirring using a dissolver stirring blade (50 mmφ) over 3 minutes,
Dispersion was achieved by stirring at 3000 rpm for 10 minutes. Then, 10% of the same water-soluble anionized modified polyvinyl alcohol () used in preparing the dispersant aqueous solution was added.
% aqueous solution (0.2% to calcium carbonate) and stirred for 2 minutes at 3000 rpm to determine the solid content concentration.
68% calcium carbonate aqueous dispersions (13) to (18) were obtained. The viscosity and aging stability of the obtained aqueous dispersions (13) to (18) were measured in the same manner as in Example 1, and the test results were
Shown in the table.

【table】

[Table] From the above results, water-soluble copolymer () having a specific number average molecular weight as a dispersant and water-soluble anionized modified polyvinyl alcohol ( ) and aqueous calcium carbonate dispersions obtained using the respective dispersants alone, water-soluble copolymers (), or water-soluble anionized modified polyvinyl alcohols (). It can be seen that the viscosity is lower than that of the comparative aqueous dispersion in which either one or both of these dispersions were not used, and the stability over time is also excellent. Furthermore, according to the method of the present invention, an aqueous calcium carbonate dispersion having low viscosity and high fluidity can be obtained with a lower additive amount than the conventionally used dispersant, acrylic acid/maleic acid copolymer. I understand.

[Brief explanation of the drawing]

FIG. 1 is a rheogram showing the flow characteristics of the aqueous dispersion (1) obtained in Example 1 and the comparative aqueous dispersion (1) obtained in Comparative Example 1.

Claims (1)

[Claims] 1. When calcium carbonate is dispersed in an aqueous medium to produce an aqueous dispersion, an unsaturated monocarboxylic acid monomer selected from acrylic acid, methacrylic acid, and their salts is used as a dispersant. The number average molecular weight obtained by using the monomer in the range of 50 to 99.9 mol% and the hydroxyl group-containing monomer in the range of 0.1 to 50 mol% is 2000.
Water-soluble copolymer () which is ~80000 and degree of polymerization 30
~700, a water-soluble anionized modified polyvinyl alcohol () with a saponification degree of 30 to 100 mol% and an anionized modification degree of 0.5 to 20 mol%, and calcium carbonate.
Water-soluble copolymer () 0.1 to 100 parts by weight
2 parts by weight of calcium carbonate and water-soluble anionized modified polyvinyl alcohol () in a ratio ranging from 0.03 to 1 part by weight. 2. The method for producing an aqueous calcium carbonate 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 calcium carbonate dispersion according to claim 1, wherein the water-soluble anionized modified polyvinyl alcohol () is a water-soluble carboxylated modified polyvinyl alcohol.