JP2000264710A - Casting composition for section - Google Patents

Abstract

PROBLEM TO BE SOLVED: To ensure superior moldability, to enhance strength and wear resistance, to considerably increase the service frequency of a gypsum mold and to simplify a tail end process because a used section is crushed to an appropriate block shape by adding a specified amount of cayboxymethylcellulose having a specified average molecular weight to hemihydrate gypsum. SOLUTION: Carboxymethylcellulose having a weight average molecular weight of 2,500-140,000, preferably 2,500-95,000 is added by 0.1-5.0 pts.wt. to 100 pts.wt. hemihydrate gypsum. The hemihydrate gypsum is preferably α- hemihydrate gypsum produced as a byproduct in the production of phosphoric acid by a wet process using a phosphate ore and sulfuric acid, in particular α-hemihydrate gypsum obtained by drying and comminuting the byproduct and adding an alkali, particularly an inorganic alkali compound. It is also preferable that a fluidizer, a retarder, an accelerator, a defoaming agent, etc., are optionally used.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a casting composition for moldings containing hemihydrate gypsum as a main component.

[0002]

2. Description of the Related Art Conventionally, plaster for moldings, especially plaster for ceramics and magnetic moldings, has a mixed water volume of 60 mainly containing β hemihydrate gypsum and partially containing α hemihydrate gypsum depending on the method of molding the ceramics. Disclosed is a method using 〜85% by weight of hemihydrate gypsum or α-hemihydrate gypsum alone and an additive (JP-A-53-74526).

[0003] As a gypsum-type material in the rokuro method or press method requiring high strength and abrasion resistance, gypsum having a mixed water content of about 60% by weight, that is, a high α-hemihydrate gypsum content is used. . On the other hand, as a gypsum molding material in the casting method, which has restrictions on the water absorption properties of gypsum in addition to strength, the amount of mixed water is as large as 65 to 85% by weight. Less plaster is used.
In addition, setting hardening is possible with a small amount of water and good strength is obtained,
A molding method using only α-hemihydrate gypsum which is excellent in wear resistance has been proposed (JP-A-53-74526). The method is characterized by reducing the particle diameter of α-hemihydrate gypsum to an appropriate particle size. The setting speed and the sedimentation speed are adjusted by restricting within the range. The reason is that α used in this method
Since hemihydrate gypsum is gypsum produced by pressurized hydrothermal reaction, the size of the produced particles is coarse and the true specific gravity is larger than that of β-hemihydrate gypsum. In the case of cast molding, even if the slurry is formed with a required amount of mixed water, the flowability is poor and the work of pouring into a mold is troublesome. Further, there is a problem that the gypsum particles settle during the casting operation, water is separated on the surface, the properties of the surface of the cured product are deteriorated, and the dimensional accuracy of the gypsum mold becomes poor. Therefore, in order to solve these disadvantages, the particle size of α-hemihydrate gypsum is reduced to an appropriate particle size, and the setting speed and the sedimentation speed are adjusted.

However, these conventional products need to be properly used depending on the type and content of gypsum hemihydrate according to the method of molding the ceramic. There are restrictions on the shape of the gypsum used, such as the particle size distribution, and there is also a problem in economics. These are kneaded with water and poured into a mold. However, in the case of a complicated shape due to a problem in fluidity, the slurry often does not flow into every corner of the mold, resulting in a defective product. Also, when processing used molds, when crushed using a hammer or the like, the destruction state of the molds is broken into small pieces, the workability of the post-processing process is poor, and there is a lot of dust and an environmental problem. .

[0005]

SUMMARY OF THE INVENTION The present invention has been intensively studied in view of these problems, and as a result, it can be used without restricting the type, mixing ratio and particle size of hemihydrate gypsum, and has excellent moldability, strength and strength. Abrasion resistance is improved, the number of times the gypsum mold can be used is greatly improved, and when a used mold is crushed, it is broken into an appropriate block to obtain a casting composition for a mold that can be easily processed after the process. Was.

[0006]

SUMMARY OF THE INVENTION The present invention is directed to carboxymethyl cellulose (CMC) among various soluble polymers.
By using, it is possible to obtain a casting composition for a mold material which has excellent moldability, has high performance, greatly improves the number of uses, and is easy to dispose.

That is, the present invention is characterized in that 0.1 to 5.0 parts by weight of carboxymethylcellulose having an average molecular weight of 2,500 to 140,000 is added to 100 parts by weight of hemihydrate gypsum. Composition.

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in detail.
Hemihydrate gypsum is not particularly limited, but in consideration of the desired strength, abrasion resistance, etc., productivity and economy, by-products are produced when phosphoric acid and sulfuric acid are used to produce phosphoric acid by the wet phosphoric acid production method. It is more preferable to use α-hemihydrate gypsum. Further, α-hemihydrate gypsum obtained by adding alkali after drying and pulverizing the α-hemihydrate gypsum is more preferable.

The alkali to be added to the α-hemihydrate gypsum is not particularly limited as long as it is both organic and inorganic. N, which is preferably an inorganic compound,
hydroxides such as aOH, KOH, Ca (OH) ₂ , and CaC
Examples include carbonates such as O ₃ and K ₂ CO ₃ and basic oxides such as Na ₂ O, CaO and MgO, which form hydroxides in an aqueous solution, and ammonia gas / solution. You may. As a matter of course, as the inorganic alkali, a hardening inorganic material exhibiting alkalinity such as cement may be added and mixed. The addition amount of the alkali is preferably 0.1 to 5.0 parts by weight based on 100 parts by weight of α-hemihydrate gypsum.

CMC used to adjust the strength, abrasion resistance, and crushing state at the time of breaking of a mold material is a representative of water-soluble synthetic resins as well as polyvinyl alcohol (hereinafter abbreviated as PVA). The practical underlying properties of CMC are that it is soluble in water, high in viscosity, compatible with other water-soluble substances, dispersible, stable, adhesive, non-toxic, It is widely used because it emits no odor or no toxic gas when burned. In the case of gypsum mold casting, products have conventionally been produced by reducing the viscosity using water glass or the like, but since water glass is alkaline, the consumption of gypsum mold material is severe and has a large effect on manufacturing costs.
If CMC is used instead, a peptizing effect is obtained, and casting is facilitated and moldability is improved.

As a result of various studies in the present invention, a CMC having a polymerization degree and a molecular weight lower than those conventionally used has been found. That is, CMC having an average molecular weight of 2,500 to 140,000 is added to hemihydrate gypsum.
0.1 to 5.0 parts by weight per 100 parts by weight of hemihydrate gypsum,
More preferably, it is added in an amount of 0.5 to 3.0 parts by weight, and in addition, it is a casting composition for a molding material comprising a fluidizing agent, a retarder, an accelerator, and a defoaming agent. By using the low-molecular-weight, low-viscosity CMC according to the present invention, the resulting slurry can be improved in fluidity without hindering the setting and curing time. Therefore, it is possible to cope with complicated molds, and since strength and abrasion resistance are improved, it is possible to prevent quality deterioration such as cracks and cracks generated during the mold removal process, and press molding by peptizing action. By improving the (base density), the compressive strength is improved, and the rotation rate used is also improved. In addition, when the used mold material is post-treated, the material is broken into blocks when crushed with a hammer or the like, so that the handling becomes easy and the environment can be improved without dust.

[0012] Regarding the type of CMC used, if the average molecular weight is less than 2,500, the viscosity is low, the strength of the mold decreases, and the desired performance cannot be obtained. Average molecular weight 140,0
If it exceeds 00, the viscosity of the CMC is high and the fluidity becomes poor, so that the work of pouring into the mold is hindered and the desired performance of the mold cannot be obtained. Also, when the amount of addition is out of the range of 0.1 to 5.0 parts by weight with respect to 100 parts by weight of hemihydrate gypsum, the same phenomenon occurs, and the desired mold material cannot be obtained.

[0013] A polymer substance such as CMC is generally a mixture of simple substances having various molecular weights, and the molecular weight and the degree of polymerization naturally give only average values, and various values may be given depending on the measuring method. is there. The measuring method is a viscosity method,
There are an osmotic pressure method, an ultracentrifugation method, a light scattering method and the like, and the viscosity method is the most frequently employed, and the molecular weight display of the present invention is a numerical value using the viscosity method.

The fluidizing agent is not particularly limited,
The following can be used: For example, oxycarboxylic acid-based and / or polycarboxylic acid-based include Marialim A
KM60F, Tupole HP-11 or the like is used.
The amount added for obtaining good fluidity is preferably 0.1 to 5 parts by weight, more preferably 0.5 to 3 parts by weight, per 100 parts by weight of hemihydrate gypsum. If the amount is less than 0.1 part by weight, a slurry having a high fluidity cannot be obtained at an appropriate amount of water. If the amount exceeds 5 parts by weight, a remarkable retardation of solidification is caused, which adversely affects the development of strength. In addition, salts of highly condensed products of β-naphthalenesulfonic acid formaldehyde, salts of melaminesulfonic acid formaldehyde condensate, salts of aminosulfonic acid condensate, and lignin-based fluidizing agents are used.

[0015] A retarder can be used to further reduce the decrease in the fluidity of the obtained slurry over time. Although there is no particular limitation on the retarder, hydroxycarboxylic acids and / or salts thereof (hereinafter, referred to as hydroxycarboxylic acids) are desirable. Examples of the hydroxycarboxylic acids used include malic acid, sodium malate, citric acid, sodium citrate and the like. The addition amount is based on 100 parts by weight of hemihydrate gypsum.
It is preferably 0.01 to 5 parts by weight, more preferably 0.1 to 5 parts by weight.
03 to 3 parts by weight are preferred. If the amount is less than 0.01 part by weight, a substantial retarding effect cannot be obtained, and if it exceeds 5 parts by weight, the setting time becomes extremely long and the strength development is undesirably adversely affected.

After pouring into a mold while maintaining the fluidity for a certain period of time, it is desirable to set as quickly as possible. As the accelerator used for that purpose, an alkali metal carbonate or the like is effective. The addition amount is 0.02 to 2 parts by weight, preferably 0.1 to 1 part by weight, per 100 parts by weight of hemihydrate gypsum.
Parts by weight are preferred. If it is less than 0.02 parts by weight, the effect of accelerating the curing is small, and if it exceeds 2 parts by weight, the curing speed is too high and the workability is deteriorated. Examples of the alkali metal of carbonate or bicarbonate include lithium, sodium, potassium and the like.

Since foaming due to slurry stirring or the like impairs surface properties such as blistering and dents on the molded body, a known defoaming agent such as a silicone-based or nonionic surfactant can be generally used as a preventive measure. . The amount used is hemihydrate gypsum 100
The amount is 0.01 to 0.6 parts by weight with respect to parts by weight, and the effect is not improved even if the added amount is larger than this, which is uneconomical. Usually, it is preferable to use it in the range of 0.05 to 0.4 parts by weight.

[0018]

The present invention will be described below in detail with reference to examples. Parts represent parts by weight unless otherwise specified. Example 1 0.4 parts of slaked lime was added to 100 parts of α-hemihydrate gypsum by-produced when phosphoric acid was produced by wet phosphoric acid production using phosphate rock and sulfuric acid. Molecular weight 2
One part of CMC (Daiichi Kogyo Seiyaku Co., Ltd .: Cellogen 1A) having 7,000 to 33,000 was added. Similarly, "Mariarim AKM60F" (trade name of Takemoto Yushi Co., Ltd.) containing a polycarboxylic acid (maleic anhydride) as a main component as a fluidizing agent.
0.5 part, 1 part of sodium citrate as a retarder, 0.2 part of potassium sulfate as a hardening accelerator, SN as an antifoaming agent
0.05 parts of a deformer and 40 parts of water were blended, and the mixture was stirred at 1,500 rpm for 30 seconds using a stirrer. The impact-free flow values of these slurries, the evaluation of moldability of the cured body (cylindrical type), the drop fracture test, and the compressive strength were measured. Table 1 shows the results.

The evaluation of each physical property was measured as follows. (1) Flow value: In a room with a temperature of 20 ° C and a relative humidity of 60%, use a flow cone specified in JIS R5201 and place it on a smooth acrylic resin plate, pour the kneaded slurry into the flow cone, and immediately apply no impact The spreading diameter in the state was measured. (2) Moldability evaluation: A cylindrical (vase) mold was made of silicone rubber, the slurry was poured into the mold, and the fluidity and moldability (appearance) were compared visually. (3) Drop breaking test: The mold prepared in (2) was dropped from a certain height, and the broken height and the state (visual) were evaluated. (4) Compressive strength: Performed in accordance with JIS T 6604. A test piece (20 × 20 × 20 mm) was cured in a room at a temperature of 20 ° C. and a relative humidity of 60% for 24 hours, and measured using a tester for compressive strength (Shimadzu Autograph AG10TD).

Example 2 The CMC of Example 1 was used to obtain an average molecular weight of 47,000 to 54,0
The procedure was performed in the same manner as in Example 1 except that CMC (Daiichi Kogyo Seiyaku Co., Ltd .: Cellogen PR) was changed to 00. Table 1 shows the evaluation results of the physical properties.

Example 3 The CMC of Example 1 was prepared using the average molecular weight of 100,000 to 11
000 CMC (Daiichi Kogyo Seiyaku Co., Ltd .: Cellogen WS-
Except having changed to A), it carried out similarly to Example 1. Table 1 shows the evaluation results of the physical properties.

Example 4 The amount of CMC added in Example 1 was 3.0 parts, and the amount of the fluidizing agent was 1.0.
The procedure was performed in the same manner as in Example 1 except that the parts were changed. Table 1 shows the evaluation results of the physical properties.

COMPARATIVE EXAMPLE 1 The CMC of Example 1 was prepared by adding an average molecular weight of 210,000 to 25.
The same procedure as in Example 1 was carried out except that the amount of CMC (Daiichi Kogyo Seiyaku Co., Ltd., cellogen 3H) having 000 was changed to 0.1 part. Table 1 shows the evaluation results of the physical properties.

[0024]

[Table 1]

[0025]

As a result of intensive studies in view of these problems, the present invention can be used without restricting the type, mixing ratio, and particle size of hemihydrate gypsum, and has excellent moldability, strength and abrasion resistance. Thus, a cast composition for a mold material was obtained, which was able to significantly improve the number of times the gypsum mold could be used and, when the used mold material was crushed, cracked into an appropriate block and the post-treatment process was simple.

Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat II (Reference) C08K 3/28 C08K 3/28 3/30 3/30 C08L 1/26 C08L 1/26 // (C04B 28/14 24 : 38) 111: 00

Claims (4)

[Claims] 1. A casting composition for a molding material, wherein 0.1 to 5.0 parts by weight of carboxymethyl cellulose having an average molecular weight of 2,500 to 140,000 is added to 100 parts by weight of hemihydrate gypsum. 2. The hemihydrate gypsum is formed using phosphate rock and sulfuric acid.
2. The casting composition according to claim 1, wherein the composition is α-hemihydrate gypsum by-produced when phosphoric acid is produced by wet phosphoric acid production. 3. An average molecular weight of 2,500 to 95,0.
2. The casting composition for a molding material according to claim 1, wherein carboxymethylcellulose which is 00 is used. 4. The casting composition for a mold according to claim 2, wherein an alkali is added to the α-hemihydrate gypsum.