JPH0620533B2 - Method for producing calcium carbonate aqueous dispersion - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method for efficiently dispersing calcium carbonate in an aqueous medium to produce an aqueous dispersion, and more specifically, acrylic acid having a specific molecular weight and / or The present invention relates to a method for producing an aqueous dispersion of calcium carbonate, which comprises using a methacrylic acid polymer and a water-soluble phosphate together in a specific ratio.

(Prior Art) Calcium carbonate is one of the pigments prized in the paper manufacturing industry because it is inexpensive and has excellent whiteness, ink acceptability, gloss, and printability as compared with other inorganic pigments. In addition, the use of neutral papermaking is rapidly increasing.

Conventionally, so-called heavy calcium carbonate having an average particle diameter of about 1 μ has been frequently used as calcium carbonate, but in recent years, as the quality of paper has become higher, the use ratio of sedimentable colloidal calcium carbonate having an average particle diameter of 0.1 to 0.3 μ has been increasing. is there. However, the smaller the average particle size, the more difficult it is to disperse in an aqueous medium, the more likely it is to aggregate, and the more easily the aging stability of the aqueous dispersion is likely to occur.

Conventionally used dispersants for calcium carbonate include condensed phosphates such as pyrophosphate, tripolyphosphate, trimetaphosphate, tetrametaphosphate, hexametaphosphate, zinc salts and silicates in the inorganic system. is there. However, these inorganic dispersants have a problem with respect to the stability of the resulting aqueous dispersion over time, and a large amount of addition is required to disperse the particulate precipitable colloidal calcium carbonate. There was a serious drawback that it deteriorated.

On the other hand, polycarboxylic acid salts such as polyacrylic acid salts, polymethacrylic acid salts, and polymaleic acid salts are known as organic dispersants. However, polycarboxylic acid salts such as sodium polyacrylate have been relatively well evaluated for dispersing heavy calcium carbonate having an average particle size of about 1 μm,
Dispersion of extremely fine particles of calcium carbonate of about 0.1 to 0.3 µ had a problem that the viscosity of the obtained aqueous dispersion was high and the stability over time was poor.

In order to overcome the drawbacks of the known dispersants, maleic acid copolymers are disclosed in JP-B-54-36166, JP-B-56-47131, JP-A-53-144499 and JP-A-57-168906. A method of using is proposed. The dispersant described in JP-B-54-36166 has a relatively good evaluation in that the obtained calcium carbonate aqueous dispersion has good flow characteristics (low high shear viscosity),
Dispersion at a high concentration of 65% by weight or more of solid content remains a problem. The dispersant described in Japanese Examined Patent Publication No. 56-47131 has a low viscosity of an aqueous dispersion of fine particle calcium carbonate, but requires a large amount of addition, resulting in cost increase and water resistance of the coating film. With the dispersant described in JP-A-53-144499, an aqueous dispersion of calcium carbonate having an extremely high solid content of 70% by weight is obtained, but a high addition amount of 1.4% (calcium carbonate) is also required. I am trying. The dispersant described in JP-A-57-168906 has a serious drawback that the obtained calcium carbonate aqueous dispersion has poor flow characteristics (high high shear viscosity).

Further, a method using an itaconic acid copolymer is proposed in JP-A-59-193964, but the average particle size is 0.3.
Dispersion of calcite-based cubic calcium carbonate having a particle size of not more than μ remains a problem.

(Problems to be Solved by the Invention) The present invention solves the above-mentioned problems associated with the lack of dispersion performance of conventional dispersants, and a small amount of dispersion for any heavy to light calcium carbonate. It is intended to provide a method capable of producing an aqueous dispersion of high-concentration calcium carbonate which has a low viscosity, a high fluidity and a good stability with time of an agent.

(Means and Actions for Solving Problems) The inventors of the present invention have found that the water-soluble polycarboxylic acid-based polycarboxylic acid compounds which, when used alone, are significantly inferior in the effect of dispersing light calcium carbonate in an aqueous medium. The combination and the water-soluble phosphates, by using a water-soluble polymer of a specific molecular weight and in combination at a specific ratio, it was found that the above dispersing effect can be significantly improved to a level that cannot be obtained with conventional dispersants, The present invention has been completed.

That is, the present invention is to disperse calcium carbonate having an average particle size of 0.3μ or less in an aqueous medium to produce an aqueous dispersion, and as a dispersant, at least one selected from acrylic acid, methacrylic acid and salts thereof. A water-soluble polymer (I) having a number average molecular weight of 8,000 to 80,000 as an acid form derived from the monomer (1) and a water-soluble phosphate (II), ) Water-soluble phosphates based on 100 parts by weight
(II) The present invention relates to a method for producing an aqueous dispersion of calcium carbonate, which is used in an amount of 5 to 50 parts by weight.

To obtain the water-soluble polymer (I) used in the present invention, a monomer selected from acrylic acid, methacrylic acid and salts thereof (hereinafter referred to as unsaturated monocarboxylic acid-based monomer).
May be polymerized by a known technique. For example, in the case of aqueous solution polymerization, persulfates such as sodium persulfate and potassium persulfate;
Hydrogen peroxide; a water-soluble azo compound such as 2,2'-azobis (2-amidinopropane) hydrochloride or 4,4'-azobis-4-cyanovaleric acid can be produced by a conventional method as a polymerization catalyst. Further, alcohols such as methanol and isopropyl alcohol, tetrahydrofuran,
In the case of polymerization in an organic solvent such as an ether type such as dioxane, an aromatic type such as benzene, xylene and toluene, or a ketone type such as methyl ethyl ketone and methyl isobutyl ketone, organic matter such as benzoyl peroxide, lauroyl peroxide and peracetic acid Peroxide type; azobisisobutyronitrile, 2,
An oil-soluble azo compound such as 2'-azobis (4-methoxy-2,4-dimethylvaleronitrile) can be produced by a conventional method as a polymerization catalyst.

The number average molecular weight of the water-soluble polymer (I) is 8.0 in acid form.
In the range of 80 to 80,000, more preferably 10,000
It is in the range of 0 to 50,000. Those out of this range have an insufficient dispersion effect when used in combination with the water-soluble phosphates (II).

The unsaturated monocarboxylic acid-based monomer used to obtain the water-soluble polymer (I) includes a salt-form monomer obtained by neutralizing an acid-form monomer or an acid-form monomer with an alkaline substance. Any body type can be used. When an acid-type monomer is used, the water-soluble polymer obtained can be obtained by considering the dispersion effect.
It is preferred that at least 30 mol% of the carboxyl groups in (I) are neutralized after polymerization with an alkaline substance before use. Examples of such alkaline substances include hydroxides and carbonates of sodium, potassium, lithium and the like; ammonia; organic amines; inorganic amines; hydroxides and carbonates of calcium, magnesium, aluminum, zinc and the like. You can Among them, sodium hydroxide is particularly preferable because it is inexpensive and industrially available.

Examples of the salt type unsaturated monocarboxylic acid type monomer include alkali metal salts of acrylic acid and methacrylic acid such as sodium, potassium and lithium, ammonium salts, organic amine salts and calcium, magnesium, aluminum and zinc. Mention may be made of polyvalent metal salts.

Further, when obtaining the water-soluble polymer (I), it is of course possible to copolymerize the unsaturated monocarboxylic acid-based monomer with another monomer that is copolymerizable, within a range that does not impair the effects of the present invention. Is. Examples of other copolymerizable monomers include (meth)
Amide-based monomers such as acrylamide and t-butyl (meth) acrylamide; hydrophobic monomers such as (meth) acrylic acid ester, styrene, 2-methylstyrene and vinyl acetate; vinyl sulfonic acid, allyl sulfonic acid, meta Rylsulfonic acid, styrenesulfonic acid, 2-acrylamido-2-methylpropanesulfonic acid, 3-allyloxy-
2-hydroxypropanesulfonic acid, sulfoethyl (meth) acrylate, sulfopropyl (meth) acrylate, 2-hydroxysulfopropyl (meth) acrylate, sulfoethylmaleimide or monovalent metal, divalent metal, ammonia or organic amine thereof Unsaturated sulfonic acid type monomers such as partially neutralized products and fully neutralized products; 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,
Hydroxyl group-containing unsaturated monomers such as N-methylol (meth) acrylamide, glycerol mono (meth) acrylate, vinyl alcohol; dimethylaminoethyl (meth)
Cationic monomers such as acrylate and dimethylaminopropyl (meth) acrylamide; nitrile-based monomers such as (meth) acrylonitrile; (meth) acrylamidomethanephosphonic acid, (meth) acrylamidomethanephosphonic acid methyl ester, 2- ( Phosphorus-containing monomers such as (meth) acrylamido-2-methylpropanephosphonic acid;
Examples thereof include dicarboxylic acid type monomers such as itaconic acid, maleic acid and citraconic acid; and crotonic acid.

As the water-soluble phosphates (II) used in the present invention, either acid form or salt form can be used, but sodium, potassium and ammonium salts which are inexpensive and easy to obtain industrially are preferable. Examples of such water-soluble phosphates (II) include reducing phosphates such as phosphoric acid (sodium), sodium hypophosphite, and sodium phosphite; potassium pyrophosphate, sodium tripolyphosphate, sodium hexametaphosphate. And other condensed phosphates. In the present invention, the water-soluble polymer described above is used as the dispersant.
(I) and water-soluble phosphates (II) are used, but there is no particular limitation on the order and timing of addition. For example, when water-soluble polymer (I) is used to disperse calcium carbonate in an aqueous medium, water-soluble phosphates (II) can be additionally added and used in combination. It is also possible to additionally use the water-soluble polymer (I) when dispersing using, and also to add calcium carbonate by adding the water-soluble polymer (I) and the water-soluble phosphates (II) at the same time. It can also be dispersed.

Furthermore, the water-soluble polymer (I) or the water-soluble phosphates (II) is used alone and dispersed, and then the obtained calcium carbonate aqueous dispersion is mixed with a predetermined amount of the water-soluble polymer (I) or water-soluble phosphorus. It is also possible to add an acid salt (II).

Water-soluble polymer (I) used as a dispersant in the present invention
And the proportion of water-soluble phosphates (II) is
(I) 100 parts by weight of water-soluble phosphates (II) 5-5
It is in the range of 0 parts by weight. If the use ratio of these dispersants is out of this range, the effect of dispersing calcium carbonate in an aqueous medium becomes insufficient, and a high concentration carbon dioxide with low viscosity and high fluidity and good stability over time with a small amount of dispersant added. It becomes impossible to obtain an aqueous dispersion of calcium.

The amount of the water-soluble polymer (I) and the water-soluble phosphates (II) to be used in the present invention with respect to calcium carbonate is not particularly limited as long as the use ratio of these dispersants is within the above range. From the viewpoint of water resistance of the coating film obtained by using the dispersion liquid, it is preferable to make the amount as small as possible. Therefore, the total amount of the water-soluble polymer (I) and the water-soluble phosphates (II) is also taken into consideration in consideration of performance such as viscosity and fluidity of the obtained calcium carbonate aqueous dispersion and their stability over time. Is preferably in the range of 0.1 to 1.0% based on the weight of calcium carbonate.

(Effects of the Invention) According to the method of the present invention, since a specific water-soluble polymer and a water-soluble phosphate salt are used together as a dispersant in a specific ratio, it is possible to use all heavy to light calcium carbonates. It is possible to form a high-concentration calcium carbonate aqueous dispersion with a small amount of dispersant. Further, the calcium carbonate aqueous dispersion obtained by the method of the present invention has a low viscosity and high fluidity and is excellent in their stability over time, so that it does not adversely affect the water resistance of the obtained coating film. It can be effectively used for paints and other applications.

(Examples) The present invention will be specifically described with reference to examples, but the present invention is not limited to these examples. still,
Parts and% in the examples indicate parts by weight and% by weight, respectively.

Example 1 Volume 1 (Material SUS304, inner diameter 90 mm, height 160
(400 mm) of a calcite-based cubic light calcium carbonate (average particle size 0.15μ) filter press dehydrated cake (solid content: 65.3%) into a beaker (mm), and the number average molecular weight as an acid form was added thereto. Aqueous solution 1 in which 1.30 parts of sodium polyacrylate having a content of 14,000 and 0.26 parts of sodium hexametaphosphate (total amount of 1.56 parts, relative to calcium carbonate of 0.6%) are dissolved in 15.5 parts of water.
Add 7.06 parts and dissolver stirring blade (50 mm)
The mixture was kneaded at low speed for 3 minutes and then dispersed at 5000 rpm for 30 minutes to obtain an aqueous dispersion (1) having a solid content concentration of 63%.

Table 1 shows the test results of the viscosity (measured with a B-type viscometer at 25 ° C.) and aging stability of the obtained aqueous dispersion (1). Further, the rheogram obtained by measuring the flow characteristics of the aqueous dispersion (1) immediately after production with a Hercules viscometer (HR-801C type manufactured by Kumagai Riki Kogyo Co., Ltd.) (Bob B, sweep time 20 seconds) Is shown in FIG.

Examples 2 to 3 Water having a solid concentration of 63% was obtained in the same manner as in Example 1 except that the predetermined amounts of the water-soluble polymer (I) and the water-soluble phosphates (II) shown in Table 1 were used. A dispersion was obtained. Table 1 shows the test results of viscosity and aging stability of the obtained aqueous dispersion.

Comparative Example 1 Same as Example 1 except that only 1.56 parts of sodium salt of a copolymer of acrylic acid / maleic acid = 65/35 (molar ratio) having a number average molecular weight of 3,500 as an acid form was used. Similarly, a comparative aqueous dispersion (1) having a solid content concentration of 63% was obtained.

Table 2 shows the test results of viscosity and aging stability of the obtained comparative aqueous dispersion (1). Further, the flow characteristics of the comparative aqueous dispersion (1) immediately after production were measured with a Hercules viscometer (Bob B, sweep time: 20 seconds), and the obtained rheogram is shown in FIG.

Comparative Examples 2 to 5 Comparative water having a solid concentration of 63% was prepared in the same manner as in Example 1 except that only 1.56 parts of the water-soluble polymer or the water-soluble polymer (I) shown in Table 2 was used. A dispersion was obtained. Table 2 shows the test results of viscosity and aging stability of the obtained aqueous dispersion for comparison.

Comparative Example 6 Using only 2.09 parts of the sodium salt of the copolymer used in Comparative Example 1 (vs. calcium carbonate 0.8%), instead of 15.5 parts of water used in Example 1, 15.8 parts. In the same manner as in Example 1 except that was used, a comparative aqueous dispersion having a solid content concentration of 63% was obtained. Table 2 shows the test results of viscosity and aging stability of the obtained aqueous dispersion for comparison.

Comparative Examples 7 to 9 Example 1 except that the predetermined amount of the water-soluble polymer or the water-soluble polymer (I) and the water-soluble phosphates (II) shown in Table 2 were used.
In the same manner as above, a comparative aqueous dispersion having a solid content concentration of 63% was obtained. Table 2 shows the test results of viscosity and aging stability of the obtained aqueous dispersion for comparison.

Comparative Example 10 A comparative aqueous dispersion having a solid content concentration of 63% was obtained in the same manner as in Example 1 except that only 1.56 parts of sodium hexametaphosphate was used. Table 2 shows the test results of viscosity and aging stability of the obtained aqueous dispersion for comparison.

Examples 4 to 7 A water-soluble polymer (I) and a water-soluble phosphate (II) shown in Table 3 were added to a beaker having a capacity of 1 used in Example 1 in a predetermined amount (water-soluble polymer (I)). And the total amount of water-soluble phosphates (II) were 2.0 parts, and calcium carbonate was 0.5%), and water was added to make the total amount 100 parts. To the obtained aqueous dispersant solution, 400 parts of heavy calcium carbonate (average particle size 0.9 μ) was added 10 parts under stirring at 1000 rpm with the stirring blade used in Example 1.
Added in minutes. Then, the mixture was dispersed under stirring at 8000 rpm for 15 minutes to obtain a calcium carbonate aqueous dispersion having a solid content concentration of 80%. Table 3 shows the test results of the viscosity and aging stability of the obtained aqueous dispersion.

Comparative Examples 11 to 12 Comparative water having a solid content concentration of 80% was prepared in the same manner as in Examples 5 to 8 except that only 2 parts of the water-soluble polymer or the water-soluble polymer (I) shown in Table 4 was used. A dispersion was obtained. Table 4 shows the test results of the viscosity and the aging stability of the obtained comparative aqueous dispersion.

Comparative Example 13 Example 5 except that the predetermined amount of the water-soluble polymer or the water-soluble polymer (I) and the water-soluble phosphates (II) shown in Table 4 was used.
In the same manner as in -8, a comparative aqueous dispersion having a solid content concentration of 80% was obtained. Table 4 shows the test results of the viscosity and the aging stability of the obtained comparative aqueous dispersion.

Comparative Example 14 An aqueous dispersion for comparison having a solid content concentration of 80% was obtained in the same manner as in Examples 5 to 8 except that only 2.0 parts of sodium hexametaphosphate was used. Table 4 shows the test results of the viscosity and the aging stability of the obtained comparative aqueous dispersion.

Comparative Example 15 The same operation as in Example 4 was carried out except that calcium hexametaphosphate was used in place of sodium hexametaphosphate in Example 4, and the test results are described below. The viscosity of the aqueous dispersion was 1300 cps immediately after production and 2500 cps after standing at room temperature for 1 week.

From the above results, the calcium carbonate aqueous dispersion obtained by using the water-soluble polymer having a specific number average molecular weight (I) and the water-soluble phosphates (II) in combination at a specific ratio is a water-soluble polymer.
(I) or water-soluble phosphates (II) each has a lower viscosity than the comparative aqueous dispersions used alone or the comparative aqueous dispersions used outside the combined proportion of the present invention, and their stability over time. It turns out that it is also excellent.

Further, according to the method of the present invention, it is possible to obtain an aqueous dispersion of calcium carbonate having a low viscosity and a high fluidity with a small amount of a dispersant, as compared with a conventionally used acrylic acid / maleic acid copolymer. I understand.

[Brief description of drawings]

FIG. 1 is a rheogram of the aqueous dispersion (1) obtained in Example 1 and the comparative aqueous dispersion (1) obtained in Comparative Example 1 (measured with Hercules viscometer, Bob B, sweep time of 20 seconds). Is.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-57-184430 (JP, A) JP-A-59-98723 (JP, A) JP-B-46-23763 (JP, B1) JP-B-46- 14821 (JP, B1) JP-B 49-27507 (JP, B1) JP-B 58-31211 (JP, B2)

Claims (1)

[Claims] 1. When a calcium carbonate having an average particle diameter of 0.3 μm or less is dispersed in an aqueous medium to produce an aqueous dispersion, at least one selected from acrylic acid, methacrylic acid and salts thereof as a dispersant. Water-soluble polymer (I) having a number average molecular weight of 8,000 to 80,000 as an acid form derived from one kind of monomer and water-soluble phosphoric acid which is a potassium salt, sodium salt and / or ammonium salt Production of calcium carbonate aqueous dispersion characterized in that salt (II) is used in combination at a ratio of 5 to 50 parts by weight of water-soluble phosphate (II) with respect to 100 parts by weight of water-soluble polymer (I). Method.