JPH01107836A - Production of aqueous dispersion liquid of aluminum hydroxide - Google Patents

Abstract

PURPOSE:To enhance the dispersion effect of aluminum hydroxide by preparing an aq. dispersion liq. with water soluble condensed phosphates and water soluble PVA having specified degrees of polymn., saponification and anionic modification. CONSTITUTION:Water soluble condensed phosphates and water soluble anionic- modified PVA having 30-700 degree of polymn., 30-100% degree of saponification and 0.5-20mol% degree of anionic modification are used as dispersants in combination and added to an aq. dispersion liq. of aluminum hydroxide by 0.1-2pts.wt. and 0.03-1pt.wt. per 100pts.wt. aluminum hydroxide, respectively, to prepare an aq. dispersion liq. of aluminum hydroxide having superior aging stability, low viscosity and high flowability. The water soluble condensed phosphates may be hexametaphosphates or pyrophosphates.

Description

Detailed Description of the Invention (Field of Industrial Application) The present invention relates to a method for efficiently dispersing aluminum hydroxide in an aqueous medium to produce an aqueous dispersion. The present invention relates to a method for producing an aqueous aluminum hydroxide dispersion, which is characterized by using a specific water-soluble anionized modified polyvinyl alcohol as a dispersant.

(Prior Art) Aluminum hydroxide is one of the MFLs that is prized in the paper industry because it is inexpensive and provides superior whiteness, smoothness, and gloss compared to other inorganic pigments.

Traditionally, so-called fine-grained aluminum hydroxide with an average particle size of over 1μ has been frequently used as aluminum hydroxide, but in recent years, with the advancement of paper quality, the proportion of fine-grained aluminum hydroxide with an average particle size of 1μ or less has been increasing. be. However, the smaller the average particle size, the more difficult it becomes to disperse in a high concentration in an aqueous medium, and the more likely it is to aggregate, causing problems in the oral stability of the aqueous dispersion.

Conventionally used dispersants for aluminum hydroxide include:
Inorganic types include condensed phosphates such as biroline Mm, tripolyphosphate, trimetaphosphate, tetrametaphosphate, and hexametaline M salt, zinc salts, and silicates. However, these inorganic dispersants have problems with the oral stability of the resulting aqueous dispersion, and the dispersion of fine aluminum hydroxide requires repeated additions, resulting in poor water resistance of the coating film. There was a serious drawback.

On the other hand, among organic dispersants, polyacrylate/polymethacrylate IS! Polycalrevo 2M salts such as salts and polymaleates, polyvinyl alcohol, and the like are known.

However, polycarboxylate salts, such as sodium polyacrylate, have a relatively good reputation for dispersing fine-grained aluminum hydroxide, but the viscosity of the resulting aqueous dispersion is There were also problems with oral stability. Furthermore, it is described in, for example, JP-A-60-262862 that polyvinyl alcohol has a dispersing effect on non-n pigments. However,
The dispersant described in No. 0-262862 is water-insoluble,
It has an insufficient dispersing effect on aluminum hydroxide, and when used alone, the resulting aqueous dispersion has an abnormally high viscosity, making it completely unsuitable for producing a highly concentrated aluminum hydroxide aqueous dispersion.

In order to overcome the drawbacks of such known dispersants, for example, a copolymer of an α,β unsaturated carboxylic acid and a hydrophobic vinyl monobase was disclosed in Japanese Patent Publication No. 50-23850, and
No. 144498 proposes the use of a copolymer of an unsaturated monocarboxylic acid and an unsaturated dicarboxylic acid. However, when dispersing fine particles of aluminum hydroxide with an average particle size of 1μ or less using the dispersant described in Japanese Patent Publication No. 50-23850, no matter how large the amount of dispersant is used, the concentration is as high as 75fflQ%, for example. Therefore, an aqueous dispersion having a viscosity of 800 cps or less, which is the upper limit that can be practically handled, cannot be obtained. In addition, the dispersant described in JP-A No. 53-144498 has obtained a relatively good evaluation as a highly concentrated aqueous dispersion of 70% by weight or more, but a highly concentrated aqueous dispersion of 75% by weight The viscosity of the aqueous dispersion exceeded 800 cps, and problems still remained.

(Problems to be Solved by the Invention) The present invention solves the above-mentioned problems associated with the insufficient dispersion performance of conventional dispersants. The present invention provides a method for producing a highly concentrated aqueous dispersion of aluminum hydroxide having low viscosity, high fluidity, and good oral stability using a dispersant.

(Means and effects for solving the problem) The present inventors have discovered that water-soluble condensed phosphates and water-soluble condensed phosphates have a significantly poor dispersion effect in an aqueous medium when used alone. By using water-soluble polyvinyl alcohol with a specific degree of polymerization, a specific degree of saponification, and a specific degree of anionic modification in a specific ratio, the above-mentioned dispersion effect can be significantly improved to a level that cannot be obtained with conventional dispersants. They discovered this and completed the present invention.

That is, in the present invention, when aluminum hydroxide is dispersed in an aqueous medium to produce an aqueous dispersion, water-soluble condensed phosphates (I) and a polymerization degree of 30 to 700 and a saponification degree of 30 to 30 are used as dispersants. 100 mol% and degree of anionic modification 0.5~
20 mol% of water-soluble anionized modified polyvinyl alcohol (II) is added to 100% of aluminum hydroxide, 0.1 to 2 times of water-soluble condensed phosphates (I), and water-soluble anionized. Modified polyvinyl alcohol (II
) It relates to a method for producing an aqueous aluminum hydroxide dispersion, characterized in that the aluminum hydroxide aqueous dispersion is used in combination at a ratio of 0.03 to 1 part.

Although the mechanism of action by which excellent aluminum hydroxide dispersion ability is developed when water-soluble condensed phosphates (I) and water-soluble anionized modified polyvinyl alcohol (IF>) are used together in the ratio within the above range is not necessarily clear. It is assumed that water-soluble condensed phosphates (I
) is strongly adsorbed on the surface of aluminum hydroxide particles, so water-soluble anionized modified polyvinyl alcohol (n)
is not present in an adsorbed form on the aluminum hydroxide particle surface or can exist only in a small amount, and water-soluble anionized modified polyvinyl alcohol (II) in an aqueous medium.
concentration increases compared to the case where water-soluble condensed phosphorus M salt (1) is not used. As a result of intensive investigation into this phenomenon, the present inventors found that the relationship between water-soluble condensed phosphates (I) adsorbed on the surface of aluminum hydroxide particles and water-soluble anionized modified polyvinyl alcohol (II) present in the aqueous medium It was discovered that the viscosity of the obtained aqueous aluminum hydroxide dispersion was significantly reduced and the stability over time was significantly improved due to a synergistic effect, and the present invention was achieved.

Examples of the water-soluble condensed phosphates (I) used in the present invention include alkali metal salts such as cum, potassium, and lithium, ammonium salts, and amine salts of pyrophosphoric acid, hexametaphosphoric acid, and tripolyphosphoric acid. Among these, particularly preferred are sodium salts, potassium salts, and amine salts of birophosphoric acid or hexametaphosphoric acid, which have excellent dispersion performance, are inexpensive, and are easily available industrially.

The water-soluble anionized modified polyvinyl alcohol (II) used in the present invention is a polyvinyl alcohol having an anionic group in the molecule, such as the one obtained by saponifying a vinyl acetate/anionic monomer copolymer using a known technique. It is an alcohol and has a degree of polymerization of 30 to 700, preferably 100 to 30.
0, the degree of saponification is 30 to 100 mol%, preferably 65
~100 mol% and degree of anionic modification 0.5~2
A range of 0 mol %, preferably 1 to 10 mol %, is effectively used. If any one of the degree of polymerization, degree of saponification, and degree of anionization modification of water-soluble anionized modified polyvinyl alcohol (ff) is outside the above range, when used in combination with water-soluble condensed phosphates (I>), In particular, when the degree of anionic modification of the water-soluble anionized modified polyvinyl alcohol (II) is less than 0.5 mol%, it becomes substantially the same as that of unmodified polyvinyl alcohol, A problem arises in the stability of the obtained aluminum hydroxide aqueous dispersion over time.On the other hand, if the degree of anionic modification exceeds 20 mol%, it is not preferable because it requires repeated additions.

Examples of anionic bases used for anionization modification when obtaining water-soluble anionization-modified polyvinyl alcohol (If) include allylsulfonic acid, methallylsulfonic acid, styrenesulfonic acid, vinylsulfonic acid,
-Aryloxy-2-hydroxypropanesulfonic acid, sulfoethyl (meth)acrylate, 2-acrylamido-2-methylpropanesulfonic acid, sulfoethylmaleimide, sulfoalkylmaleate, or their monovalent gold salts, ammonium salts, amine salts, etc. The sulfonic acid monomers nialic acid, methacrylic acid, α-hydroxyacrylic acid, (anhydrous) maleic acid, itaconic acid, fumaric acid, crotonic acid, citraconic acid, aconitic acid or their monovalent metal salts, ammonium salts, Carboxylic acid monomers such as amine salts: (meth)acrylamide methanephosphonic acid, 2-(meth)acrylamide-2-methylpropanephosphonic acid, mono[2-hydroxyethyl (meth)acrylate acid phosphate, mono[ Phosphonic acids such as 3-chloro-2-hydroxybrobyl (meth)acrylate coacid phosphate or their monovalent metal salts, ammonium salts, and amine salts 111ff
Examples include i-body.

The method of obtaining water-soluble anionized modified polyvinyl alcohol (II) is not limited to that obtained by saponifying a vinyl acetate/anionic monolithic 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 by sulfuric acid esterification in a concentrated aqueous sulfuric acid 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 (It), 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 condensed phosphorus M salt (I) is 0.1 to 2 parts per 1001 parts of aluminum hydroxide, and the water-soluble anionized modified polyvinyl alcohol (II) is per 100 parts of aluminum hydroxide. They are used together in a proportion ranging from 0.03 to 1 part by weight. If ω of the water-soluble condensed phosphates (I) or the water-soluble anionized modified polyvinyl alcohol ([) is less than the above range, an aqueous aluminum hydroxide dispersion with low viscosity and good stability over time cannot be obtained. In addition, even if the amount used is increased beyond the above range, the dispersion effect commensurate with the increased amount will not be obtained, and on the contrary, the water resistance of the coating film using the obtained aluminum hydroxide aqueous dispersion will decrease. Undesirable.

In the present invention, water-soluble condensed phosphorus lli! 2 Salts (I)
and water-soluble anionized modified polyvinyl alcohol (II)
There is no particular restriction on the order of addition when these are used together as a dispersant. That is, aluminum hydroxide can be coarsely dispersed in an aqueous medium using water-soluble condensed phosphates (I) and then finely dispersed by adding water-soluble anionized modified polyvinyl alcohol (II); After rough dispersion with modified polyvinyl alcohol (II), water-soluble condensed phosphates (I) can be added to finely disperse the mixture. It is also possible to add the water-soluble condensed phosphates (I) and the water-soluble anionized modified polyvinyl alcohol (II) 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 copolymer, etc., and known inorganic dispersants, such as hydroxides of polyvalent metals such as calcium, magnesium, aluminum, and zinc,
It is of course possible to use carbonates or halides, surfactants, wetting agents such as polyethylene glycol, polyoxyethylene/polyoxypropylene block copolymers, etc. in combination.

(Effects of the Invention) According to the method of the present invention, since water-soluble condensed phosphates and a specific water-soluble anionized modified polyvinyl alcohol are used together as a dispersant in a specific ratio, fine to fine particles can be A high-degree aluminum hydroxide aqueous dispersion can be obtained with a small amount of parent dispersant relative to all aluminum hydroxide. In addition, the aluminum hydroxide aqueous dispersion obtained by the method of the present invention has low viscosity, high fluidity, and excellent oral stability, so it does not adversely affect the water resistance of the resulting coating film. , can be effectively used in paints and other applications.

The dispersant obtained in the present invention is also effective for inorganic pigments such as clay, titanium oxide, satin white, calcium carbonate, slaked lime, red iron, cement, alumina, zirconia, silica, silicon carbide, and silicon nitride. used for.

(Examples) Hereinafter, the present invention will be specifically explained with reference to Examples, but the present invention is not limited to these Examples. still,
Parts and % in examples are fffffi parts and lf, respectively.
Indicates f1%. In addition, the % to aluminum hydroxide in the examples indicates the solid content 1ffi ratio of the dispersant (water-soluble condensed phosphates or water-soluble anionized modified polyvinyl alcohol) to the solid content of aluminum hydroxide.

Example 1 Number of customers: 11 (Material: SUS 304, inner diameter: 90 m.

3.0 parts of a 20% aqueous solution of sodium hexametaphosphate (0.2% to aluminum hydroxide) as a dispersant and water were added to a beaker with a height of 160 m to make the total amount 97 parts. Aluminum hydroxide fine powder (average particle size 0.8μ) was stirred at low speed with a Daysilver stirring blade (50Mφ).
300 parts were added over 3 minutes. then 3000 rpm
After roughly dispersing for 10 minutes, a 20% aqueous solution of anionized modified polyvinyl alcohol with a degree of polymerization of 250, a degree of saponification of 88 mol%, and a degree of sulfonation of 3.0 mol% by copolymerization of p-styrene sulfonic acid was added. (0.2% of aluminum hydroxide) and a daysilver stirring blade (50 parts M
φ) for 2 minutes at 3000 rpra to obtain an aqueous dispersion (1) with a solid content of 81 degrees and 75%.

Table 1 shows the viscosity (measured with a Type B viscometer at 25°C) and oral stability test results of the obtained aqueous dispersion (1).

Examples 2 to 6 The same procedure as in Example 1 was carried out except that the predetermined amounts of water-soluble condensed phosphates (I) and water-soluble anionized modified polyvinyl alcohol (I) shown in Table 1 were used as dispersants. Aqueous dispersions (2) to (6) having a solid content concentration of 75% were obtained.

The viscosity and oral stability of the aqueous dispersions (2) to (6) were measured in the same manner as in Example 1, and the test results were
Shown in the table.

Comparative Example 1 In the same stainless steel beaker as used in Example 1, acrylic M having a number average molecular weight of 5.200 was added as a dispersant.
/ Maraine! = 60/40 (molar ratio) 3 parts of a 40% aqueous solution of copolymer sodium salt (to aluminum hydroxide: 0.
4%) and 97 parts of water, and stirred with a day silver stirring blade (5%) and 97 parts of water.
0sφ), 300 parts of the fine aluminum hydroxide powder used in Example 1 was added over 3 minutes while stirring at low speed. then 30
Dispersion was carried out at 00 rpm for 12 minutes to obtain a comparative aqueous dispersion (1) with a solid content concentration of 75%.

The viscosity and aging stability of the obtained comparative aqueous dispersion (1) were measured in the same manner as in Example 1, and the test results are shown in Table 2.

Comparative Examples 2 to 4 Comparative Examples 2 to 4 were carried out in the same manner as in Comparative Example 1, except that the predetermined amount of the water-soluble polymer or water-soluble condensed phosphates (I) shown in Table 2 was used as the dispersant, and the solid content concentration was 75%. Comparative aqueous dispersion (2)
~(4) was obtained.

The viscosity and oral stability of the obtained comparative aqueous dispersions (2) to (4) were measured in the same manner as in Example 1, and the test results are shown in Table 2.

Comparative Examples 5 to 7 A comparative aqueous dispersion with a solid content concentration of 75% was prepared in the same manner as in Comparative Example 1, except that a predetermined amount of water-soluble anionized modified polyvinyl alcohol (II) shown in Table 2 was used as a dispersant. (
5) to (1) were obtained.

The viscosity and oral stability of the obtained comparative aqueous dispersions (5) to (7) were measured in the same manner as in Example 1, and the test results are shown in Table 2.

Comparative Examples 8 to 10 The same procedure as in Example 1 was used except that the predetermined amounts of water-soluble condensed phosphates (I) and water-soluble polyvinyl alcohol shown in Table 2 were used as dispersants, and the solid content concentration was 75%. Comparative aqueous dispersions (8) to (10) were obtained.

The viscosity and aging stability of the obtained comparative aqueous dispersions (8) to (10) were measured in the same manner as in Example 1, and the test results are shown in Table 2.

Claims (1)

[Claims] 1. When dispersing aluminum hydroxide in an aqueous medium to produce an aqueous dispersion, water-soluble condensed phosphates (I) with a degree of polymerization of 30 to 700 and a degree of saponification are used as a dispersant. 30-1
00 mol% and degree of anionic modification 0.5 to 20 mol%
water-soluble anionized modified polyvinyl alcohol (II), 0.1 to 2 parts by weight of water-soluble condensed phosphates (I), and water-soluble anionized modified polyvinyl alcohol (II) per 100 parts by weight of aluminum hydroxide. ) A method for producing an aqueous dispersion of aluminum hydroxide, characterized in that the aluminum hydroxide aqueous dispersion is used in combination in a proportion ranging from 0.03 to 1 part by weight. 2. The method for producing an aqueous aluminum hydroxide dispersion according to claim 1, wherein the water-soluble condensed phosphate (I) is a hexametaphosphate or a pyrophosphate. 3. Water-soluble anionized modified polyvinyl alcohol (II)
The method for producing an aqueous aluminum hydroxide dispersion according to claim 1, wherein is water-soluble sulfonated modified polyvinyl alcohol. 4. Water-soluble anionized modified polyvinyl alcohol (II)
The method for producing an aqueous aluminum hydroxide dispersion according to claim 1, wherein is water-soluble carboxylated modified polyvinyl alcohol.