JP2000001313A - Preparation of aqueous gypsum slurry and aqueous gypsum slurry - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a high concn. and low viscosity aq. gypsum slurry easy to handle by wet-grinding coarse gypsum in the presence of calcium carbonate whose average particle diameter is below that of the coarse gypsum and a dispersant. SOLUTION: A mixture is prepd. by mixing 100 pts.wt. coarse gypsum having 5-100 μm average particle diameter with 1-100 pts.wt., preferably 5-50 pts.wt,. calcium carbonate whose average particle diameter is below that of the coarse gypsum, 0.1-10 wt.%, preferably 0.5-5 wt.% (expressed in terms of solid) dispersant based on the total amt. of the coarse gypsum and calcium carbonate and water. The dispersant is, e.g. a (meth)acrylic acid polymer having a wt. average mol.wt. of 500-30,000, preferably 1,000-20,000. The mixture is wet-ground with a sand grinder to obtain the objective aq. gypsum slurry having >=50 wt.% solid concn., <=2,000 cps, preferably <=1,000 cps viscosity and <=5 μm, preferably <=2 μm average particle diameter.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a gypsum water slurry in which gypsum is dispersed and suspended in water, and more particularly to a high-concentration and low-viscosity gypsum which is easy to handle. The present invention relates to a water slurry and a method for obtaining the gypsum water slurry. The gypsum water slurry is useful as a filler for paper, and the present invention belongs to inorganic pigment preparation technology, papermaking technology, and the like.

[0002]

2. Description of the Related Art In addition to natural gypsum, gypsum is produced as a by-product of various chemical reactions, particularly as waste gypsum, and is used in the fields of cement, building materials, resins, paper and the like. recent years,
In these fields, gypsum has been dispersed and suspended in water and used as a water slurry because it is easy to handle. As a recent trend, gypsum water slurries in which fine gypsum is dispersed have been required as gypsum water slurries. Particularly, as a filler for paper, the solid content concentration is 50% by weight or more, the viscosity is 2000 cps or less, and the average Particle size 2
Gypsum water slurries of μm or less have been required. The gypsum water slurry is desirably as high a concentration as possible from the viewpoint of transportation efficiency and efficiency at the time of use. However, when the concentration is made high, the viscosity becomes high and handling becomes extremely difficult. In addition, a wet grinding method is generally used to make solid particles in the slurry finer, but the gypsum water slurry is remarkably thickened as the grinding proceeds, and a practically usable gypsum water slurry having a high concentration and a low viscosity is obtained. Was difficult. For example, Japanese Patent Application Laid-Open No. 2-172529 discloses that a special polymer containing a specific ethylene-based monomer as a constituent monomer is used as a dispersant. Further, the same publication discloses that, as a prior art, sodium polyacrylate was used as a dispersing agent, and gypsum dihydrate was ground in the presence of calcium carbonate. It discloses that it was possible.

[0003]

DISCLOSURE OF THE INVENTION The present inventors have developed a gypsum water slurry which rapidly increases in viscosity under a high concentration without using a dispersant comprising a special polymer as described above. The purpose of the study was to grind gypsum by wet grinding, which is an inexpensive and simple method, to obtain a low-viscosity state even at a high solids concentration of 50% by weight or more.

[0004]

The inventors of the present invention have conducted intensive studies to solve the above-mentioned problem, that is, the problem of increasing the viscosity, and as a result, it has become possible to produce a gypsum water slurry having a high concentration and a low viscosity. They found a method and completed the present invention. That is, the present invention provides a method for producing a gypsum water slurry and an average particle size, wherein the average particle size is prepared by wet-grinding coarse gypsum in the presence of calcium carbonate and a dispersant having an average particle size of the coarse gypsum or less. Contains gypsum and calcium carbonate having a solid content of 50% by weight or more and a viscosity of 2000 cps or less.

[0005]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The gypsum applied to the present invention is classified into anhydrous gypsum, hemihydrate gypsum, dihydrate gypsum and the like according to the state of water of crystallization. However, preferred for the present invention is gypsum. In addition, gypsum includes natural gypsum, excreted gypsum, titanium gypsum and other by-product gypsum with different production states,
All of them apply to the present invention without limitation. In the present invention, the raw gypsum before pulverization, which is a raw material, preferably has an average particle size of 5 to 100 μm.

The calcium carbonate used in the present invention has an average particle size equal to or less than the average particle size of the gypsum, and preferably, when the average particle size is 1 in the coarse gypsum.
0.5 or less. When the average particle size of calcium carbonate is half or less of the average particle size of coarse gypsum (that is, the above numerical value of 0.5 or less), the effect of the present invention is particularly well exhibited, the gypsum water slurry is reduced in viscosity, and gypsum pulverization is also performed. It becomes easy, and the average particle size of the gypsum can be reduced to 5 μm or less and further 2 μm or less in a short time. There is no particular limitation on the form of calcium carbonate, and so-called heavy calcium carbonate obtained by pulverizing natural limestone, chemically synthesized light calcium carbonate, and the like can be used. The form at the time of use is not particularly limited, such as pulverization and water slurry. The amount of calcium carbonate added is preferably 1 to 100 parts by weight, more preferably 5 to 100 parts by weight, based on 100 parts by weight of coarse gypsum.
５０50 parts by weight. If the addition amount is less than 1 part by weight, it becomes difficult to lower the viscosity of the resulting gypsum water slurry,
If it is added in excess of 100 parts by weight, not only the effect cannot be expected to be improved, but also the gypsum concentration in the gypsum water slurry is undesirably reduced.

As the dispersing agent used in the present invention, known and commonly used dispersing agents which have been conventionally used can be used in the same manner as in the prior art, but the dispersing agent which exerts its effects best in the present invention is acrylic. Acid or methacrylic acid (hereinafter collectively referred to as (meth) acrylic acid) as a constituent monomer, and a polymer or copolymer obtained by neutralizing a part or all of carboxyl groups (hereinafter collectively referred to as these). (Referred to as a (meth) acrylic acid polymer). As the (meth) acrylic acid polymer, a monomer other than (meth) acrylic acid may be copolymerized, and as the monomer,
Various monomers can be used as long as they are monomers copolymerizable with (meth) acrylic acid, for example, crotonic acid, fumaric acid,
Maleic acid, unsaturated carboxylic acid monomers such as itaconic acid, 2-acrylamido-2-methylpropanesulfonic acid,
Sulfonic acid monomers such as styrene sulfonic acid, vinyl sulfonic acid, methallyl sulfonic acid, allyl sulfonic acid, or esters thereof, alkyl (meth) acrylates, unsaturated hydroxy esters, unsaturated carboxylic esters, Examples include various (meth) acrylic acid polyalkylene glycol esters, non-ionic monomers such as (meth) acrylamide, acrylonitrile, styrene, and vinyl acetate. Of these monomers, maleic acid, 2-acrylamido-2-methylpropanesulfonic acid, and salts thereof are preferably used in consideration of polymerizability, economic efficiency, and ease of handling. The ratio of the (meth) acrylic acid monomer in the (meth) acrylic acid polymer as a dispersant is 50 to
It is preferably 100 mol%, more preferably 70 to 100 mol%. When the proportion of the (meth) acrylic acid monomer is less than 50 mol%, the ability to reduce the viscosity derived from (meth) acrylic acid is reduced. Examples of the form of the neutralized salt in (meth) acrylic acid include an alkali metal salt and an ammonium salt. Examples of the alkali metal include sodium, potassium, and lithium. In addition, a part of the salt is a polyvalent metal salt within a range not hindering its function,
For example, alkaline earth metals such as calcium and magnesium, and salts of zinc and the like may be used. It is preferable that the (meth) acrylic acid polymer is usually used as an aqueous solution. When the (meth) acrylic acid polymer is used as an aqueous solution, it has excellent dispersing ability. Preferably it is 5-10. The (meth) acrylic acid polymer can be produced by a known method using a polymerization initiator. For example, (meth) acrylic acid and other copolymerizable monomers can be used as usual polymerization initiator systems, such as ammonium or alkali metal persulfate, azobisisobutyronitrile, polymerization initiator such as hydrogen peroxide And approximately 50 to 150 ° C. in a solvent such as water or an alcohol, using an accelerator such as a sulfite or an amine compound if necessary.
At about 1 to 10 hours, and a part or all of the solvent is distilled off as necessary, thereby obtaining a polymer having a predetermined concentration. Also, neutralization of the carboxyl group of the polymer,
An aqueous solution of an alkali metal-containing compound such as sodium hydroxide or the like or an aqueous solution of ammonia is added to the obtained aqueous solution of the polymer to adjust the pH. That is, when a monomer having a carboxyl group and a sulfone group is used in combination, a predetermined amount of the carboxyl group and the sulfone group is neutralized, and an alkali metal salt or an ammonium salt of the polymer can be easily obtained. The formation of the alkali metal salt or ammonium salt of the polymer is generally carried out after the production of the polymer as described above, but the carboxylic acid monomer or sulfonic acid monomer in a monomer state is formed. It is also possible by a method of copolymerizing a monomeric salt, and such a polymer can also be used in the present invention. The (meth) acrylic acid polymer used as a dispersant preferably has a weight average molecular weight of 500 to 30,000, more preferably 1,000 to 20,000. In the present invention, the use ratio of the dispersant is preferably from 0.1 to 10% by weight, more preferably from 0.5 to 5% by weight, based on the total amount of coarse gypsum and calcium carbonate. The effect is particularly remarkable at 2% by weight or more.

The wet pulverization method in the present invention may be any method as long as it can perform processing in a slurry state using a known pulverizer, but it is preferable to use a sand grinder in view of the efficiency of the pulverization processing. Any method may be used for adjusting the coarse gypsum water slurry before performing the wet grinding, but after mixing the dispersant in water,
A method of mechanically dispersing coarse gypsum and calcium carbonate is preferred. According to the invention by these methods, high concentrations,
That is, a fine gypsum aqueous slurry having a solid content of 50% by weight or more and a low viscosity, that is, a viscosity of 2000 cps or less can be easily produced. The preferred particle size of the particles contained in the gypsum water slurry after the wet pulverization is different depending on the purpose of use of the obtained gypsum water slurry, but in many cases, the average particle size is preferably 5 μm or less. More specifically, when a gypsum water slurry is used as a paper filler,
The present invention can provide a gypsum water slurry having a viscosity of 2000 cps or less, particularly preferably 1000 cps or less, and an average particle diameter of 2 μm or less at a solid content concentration of 50 wt% or more.

[0009]

Until now, it was impossible to produce a gypsum water slurry having the above-mentioned properties by a wet pulverization method, as far as the applicant knows. However, the present invention relates to a commercially available dispersant, coarse gypsum and calcium carbonate. By using this method, a gypsum water slurry having a high concentration, a low viscosity, and fine particles, particularly an average particle diameter of 2 μm or less, which has been impossible until now, can be realized. Although the reason why the production of a high-concentration, low-viscosity gypsum aqueous slurry in the present invention has become unclear, in the present invention, the average particle diameter of the raw gypsum is smaller than that of calcium carbonate having a smaller average particle diameter. It is presumed that the main cause is that calcium carbonate particles were adsorbed on the gypsum particles in the process of coarse gypsum being pulverized and dissolved in water, and dissolution of the gypsum was suppressed.

[0010]

The present invention will be described more specifically with reference to examples and comparative examples below, but the present invention is not limited to these examples. In the following, weight% is simply expressed as%. ○ Example 1 The solid content was 2 with respect to the total amount of coarse gypsum and calcium carbonate.
% Dispersant (sodium polyacrylate, average molecular weight 6)
000) in water, and then coarse gypsum (average particle size 20 μm) and 8% of heavy calcium carbonate (average particle size 2 μm)
m) and add 10 with an auto homomixer (manufactured by Tokushu Kakoki).
The mixture was stirred at 00 rpm for 10 minutes to prepare a slurry in which the total amount of coarse gypsum and calcium carbonate was 55%. This slurry was mixed with glass beads having an average particle size of 2 mm, and wet pulverized using a sand grinder (made by AMEX). The viscosity of the slurry before pulverization by a BM type viscometer (60 rpm, 25 ° C.) (hereinafter referred to as the same measurement method) was 370 cps, and the viscosity of the slurry after pulverization was 690 cps. The average particle size in the gypsum water slurry after pulverization was 0.8 μm.

Example 2 16% of heavy calcium carbonate (average particle size: 2
μm) and a dispersant (sodium salt of a copolymer of acrylic acid / 2-acrylamido-2-methylpropanesulfonic acid with a solid content of 3% based on the total amount of both) and a copolymerization ratio of 88/12
(Mol%, average molecular weight 10,000), a slurry having a total amount of coarse gypsum and calcium carbonate of 60% was prepared in the same manner as in Example 1, and wet pulverized. The viscosity of the slurry before pulverization was 270 cps, and the viscosity of the slurry after pulverization was 62 cps.
It was 0 cps. The average particle size of the particles in the gypsum water slurry after pulverization was 0.8 μm.

Example 3 Light calcium carbonate (average particle size: 1.3 μm) in the ratio shown in Table 1 was added to coarse gypsum (average particle size: 31 μm) and dispersed in the ratio shown in Table 1 based on the total amount of both. Sodium polyacrylate (average molecular weight: 6000) was added to prepare a coarse gypsum aqueous slurry in which the total amount of coarse gypsum and light calcium carbonate was 63%. This coarse gypsum water slurry was pulverized for 1 hour using a sand grinder, and the viscosity and average particle size of the ground gypsum water slurry were measured. Table 1 shows the results.

[0013]

[Table 1]

Comparative Example 1 A slurry containing 55% coarse gypsum was prepared in the same manner as in Example 1 except that heavy calcium carbonate was not used.
The viscosity of the slurry before pulverization was 600 cps. When this slurry was subjected to wet pulverization, the viscosity was remarkably increased on the way, and it became impossible to continue pulverization.

[0015]

As can be seen from the above results, according to the present invention, a gypsum water slurry having a low viscosity and a higher concentration can be obtained.

 ──────────────────────────────────────────────────続 き Continued on the front page F-term (reference) 4D063 FF01 FF35 GA07 GA10 GB01 GD27 4G065 AA01 AA07 AA10 AB01Y AB13Y AB18Y AB22Y AB38Y BA07 BB06 CA11 DA06 DA07 EA01 EA03 EA04 4G076 AA14 AA16 A08AG08 AG12 AG71 AG73 AG89 AG98 AH01 AH33 EA16 EA25 FA30

Claims (2)

[Claims] 1. A method for producing a gypsum water slurry, wherein the gypsum is prepared by wet grinding in the presence of calcium carbonate having an average particle size equal to or less than the average particle size of the gypsum and a dispersant. 2. Gypsum having an average particle size of 5 μm or less and calcium carbonate, a solid content concentration of 50% by weight or more and a viscosity of 2% or more.
A gypsum water slurry characterized by being at most 000 cps.