JPS58101006A - Casting molding method for ceramic product - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a casting method for ceramic products.

The cast molding method has been widely used for molding ceramics, tableware, microporcelain, and ceramics for physical and chemical use since ancient times, and is the most common method for molding ceramic products.

Powder is charged in water, but at certain pHs there is a point where neither ■ nor OK is charged (this is called the isoelectric point). This isoelectric point is involved in creating a stable slurry. In other words, in the conventional casting molding method, the pH is adjusted to acidic or alkaline with HCl or NaOH to give an electric charge to the powder surface, and the repulsion between the electric charges causes the secondary particles to become primary particles and peptize. However, in the conventional method, slurry is created using acidic or alkaline conditions and poured into the mold, and the reaction between the slurry and the mold causes wear and tear on the mold, shortening its lifespan and reducing the dimensional accuracy of the molded product. There are drawbacks.

On the other hand, the so-called neutral casting method, in which slurry is cast in a neutral slurry, has the advantage that there is very little wear and tear on the formwork due to reaction with the formwork, which is the case when casting is carried out in an acidic or alkaline solution. have. However, in the neutral casting method, materials whose isoelectric points are in the neutral range (e.g. alumina, zirconia, chromium oxide, titanium oxide, etc.)
Even if PR was adjusted using Hcj or NaOH, the repulsion between the charges was very small, and the particles did not deflocculate well, so casting could not be performed.

The present inventors have made extensive studies to enable a neutral cast molding method, and have accomplished the present invention.

The gist of this is that a polyacrylic acid oligomer or an ammonium salt of a polyacrylic acid oligomer (both with a molecular size of about 3000
12,000), an organic binder, and water to make the slurry neutral.

Ceramic powders to which the present invention is applicable include oxides such as alumina, titanium oxide, barium titanate, zircon, zirconia, and spinel, as well as carbides and nitrides such as silicon carbide and silicon nitride.

As the deflocculant, which is one of the constituent elements of the present invention, polyacrylic acid oligomer or ammonium salt obtained by neutralizing this oligomer with liquid ammonia or aqueous ammonia is used depending on the powder of yuzu.

Unlike single molecules such as Hcj and NaOH, polyacrylic acid oligomers have a large molecular weight and a suitably large molecular structure in water, so they do not enter the hydrated film, and even if they do, +OH, The lyophobicity of the -CjH+ structure and the lyotropic property of 000 present in the molecule work to stabilize the powder surface, so polyacrylic acid oligomers can easily keep the pH neutral in water. It has the property of being able to maintain a peptized state regardless of the isoelectric point of the powder without causing agglomeration.

The molecular weight of polyacrylic acid oligomer or ammonium salt of polyacrylic acid oligomer is 3000~] 200
The reason why we limited it to 0 is because those with a molecular weight of 3000 or less only have a peptizing effect on ceramic powder, have no effect at all to prevent particle sedimentation, and on the contrary promote sedimentation and cause decomposition over a long period of time. The sticky particles will coagulate again. 1200 again
This is because when it is 0 or more, the peptizing effect is weak and the bonding force that binds the powder particles is large.

The amount of the deflocculant added in the present invention is preferably 0.2 to 2.5 parts, particularly 0.4 to 1.5 parts, and preferably 0.4 to 1.5 parts or less, as a peptizer based on 0.00 parts of the ceramic powder. is not effective and the slurry does not deflocculate well. Moreover, if it exceeds 2.5 parts, the peptizing property will hardly change, and the density of the sintered body will be adversely affected.

The organic binder, which is another component, imparts strength to the molded product, and includes polyvinyl alcohol, starch, polyvinylpyrrolidone, water-soluble acrylic polymers, polyhydric alcohols such as glycerin, methylcellulose, gelatin, and the like.

The amount added is 0.01 to 2 parts per 100 parts of ceramic powder.
．． 0 part, especially 0.05 to 1.0 part is preferred.

If it is less than 0.01 part, it will not be effective as a binder and the strength of the molded article will not be obtained. Further, if the amount is 2.0 parts or more, no significant increase in strength is observed, which adversely affects drying conditions.

It is also possible to add colloids, wetting agents, etc., if necessary, for the purpose of increasing the stability of the viscosity of the slurry, adjusting the deposition rate, or improving demoldability.

The following description will be given with reference to examples; however, the present invention is not limited to these examples.

Example 1 77M powder (purity 99.5%, average particle size 0.5Aa3
35 parts of water per 100 parts, 0.44 ffl of polyacrylic acid oligomer (molecular weight 5500) as a deflocculant, and polyvinyl alcohol (degree of polymerization 500) as an organic binder.
0.15 parts and 0.08 parts of a silicone polyether nonionic activator as an m* agent were added and stirred in a ball mill for 6 hours to form a uniform slurry. This slurry was cast into a 146φ x 120 mold and left for 3.0 minutes. After that, the frame is 6
After drying at 0°C for 2 hours, and then at 120°C for 2 hours,
The temperature was raised to 1600°C over 8 hours, maintained at 1600°C for 2 hours, and then allowed to cool. Table 1 shows a comparison between the method of the present invention and the acid casting method described above.

Table 1 The degree of formwork wear is expressed as erosion thickness/number of uses.

Example 2 Zirconia powder stabilized with Ittria 3mo 1% (
40 parts of water, 1.5 parts of ammonium salt of polyacrylic acid oligomer (molecular weight 5500) as a peptizer, methoxymethyl methacrylate and acrylic silver as an organic binder, per 100 parts (particle size: 0.3 parts%). A copolymer (4 parts of molecular weight 20,000 JO, 0.] part of a polyalkylene derivative as a wetting agent) was added and stirred in a ball mill for 6 hours to make a uniform slurry.
Pour into a mold of XIOIII did. Table 2 shows a comparison of the above method of the present invention and the alkaline casting method.
Table 2 From the above examples, it can be seen that the present invention is a method for casting ceramic products, which has the characteristics that the life of the mold is improved compared to the conventional casting method, and the mechanical properties of the sintered body are excellent. O is obvious

Claims (1)

[Claims] (1) Ammonium salts of poly, acrylic acid oligomers or polyacrylic butyric oligomers (both with molecular weights of about 3000 to 3200) are used as deflocculants for ceramic powder.
0), an organic binder, and water to make the slurry neutral.