JPH1112043A - Casting of ceramic powder - Google Patents

Abstract

PROBLEM TO BE SOLVED: To eliminate an inconvenience that water retentivity and shape retentivity have no problem but mold releasability has a problem, when a mixture of a monofunctional acrylic resin with a polyfunctional acrylic resin is used as a binder. SOLUTION: This method for casting powder comprises mixing the ceramic powder with water, a dispersant and a thermosetting acrylic resin as a binder, pouring the obtained slurry into a mold comprising a material not absorbing the water, and subsequently thermally curing the slurry. Therein, the acrylic resin comprises a mixture of at least one kind of water-soluble monofunctional acrylic resin with at least one kind of water-soluble poluyfunctional acrylic resin in a mixing ratio of 99.9:0.1 to 96.0:4.0 in an addition amount of 1-13 vol.% or in a mixing ratio of 96.0:4.0 to 80.0:20.0 in an addition amount of 1-25 vol.%.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for molding ceramic powder, and more particularly to a method for molding ceramic powder in which a slurry is hardened while containing a solvent by heating.

[0002]

2. Description of the Related Art As a method for forming a ceramic powder for obtaining a molded article having a complicated shape, a slurry prepared by adding and mixing water, a binder, and the like to a ceramic powder is poured into a mold made of gypsum or the like. In addition, a casting method for obtaining a molded body by utilizing the fact that the slurry absorbs and hardens the slurry by absorbing water is used. In this casting method,
Since the water in the slurry is absorbed by the mold and hardens, the unevenness in density occurs between the center and the surface of the molded body. As a result, there is a problem that cracks are likely to occur during drying and firing. . In addition, there is also a problem that a crack is generated in a concave portion of the molded body due to shrinkage of the molded body in the mold.

[0003] Therefore, the present inventors have recently poured a slurry prepared using water as a solvent and a binder that cures itself as a binder into a mold made of a material that does not absorb the solvent, and then used the slurry. Is proposed in Japanese Patent Application No. 9-92784. This method
Since the solvent is not absorbed by the mold, density unevenness and shrinkage in the mold due to the movement of the solvent seen in the casting method can be suppressed. Since it uses water-soluble thermosetting resin such as acrylic resin and urea resin, it is possible to prepare a slurry that is stable at room temperature, and to produce a molded body that does not leave resin aggregates in the molded body. It is a method of forming ceramic powder that can be formed.

However, when an acrylic resin is used as the binder, there is no problem in sinterability, but there is a problem in moldability. The problem is that if only a monofunctional acrylic resin having one vinyl group in the molecule is used, the shape retention is poor, and it is difficult for the obtained molded article to have a shape retention that can be handled depending on the shape. Was. When only a polyfunctional acrylic resin having two or more vinyl groups in the molecule is used, water retention is poor, and the solvent is separated from the slurry when the slurry is heated and cured, and depending on the shape, the concave portion is formed by shrinkage in the mold of the molded body. There is a problem that cracks occur in the steel.

For this reason, the present inventors have recently proposed a molding method for solving these problems in Japanese Patent Application No. 9-137377. This method uses a mixture of a monofunctional acrylic resin and a polyfunctional acrylic resin that is water-soluble and thermosetting to the acrylic resin, so that the slurry can be heated and cured without separating the solvent, and has a shape-retaining property that can be handled. An object of the present invention is to provide a method for forming a ceramic powder capable of forming a formed body.

[0006]

However, in this molding method, there is no problem in water retention and shape retention, but there is a problem in mold releasability. This is because the molded article and the mold come into close contact with each other, so even if a mold release agent is used, the molded article has poor mold release properties. There was a problem that the molded body could not be taken out without breaking.

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned problems of the method for forming ceramic powder, and has as its object to provide a method for forming ceramic powder capable of improving the releasability. .

[0008]

Means for Solving the Problems The present inventors have conducted intensive studies in order to achieve the above-mentioned object, and as a result, if the mixing ratio of the monofunctional acrylic resin and the polyfunctional acrylic resin to be used and the amount of addition thereof are made appropriate. The present invention was completed based on the finding that the releasability can be improved.

That is, according to the present invention, (1) a slurry prepared by adding water, a dispersant, and a thermosetting acrylic resin as a binder to a ceramic powder and mixing the resulting mixture is poured into a mold made of a material that does not absorb water. Then, in a method of molding a ceramic powder in which the slurry is cured by heating, the acrylic resin comprises a mixture of at least one water-soluble monofunctional acrylic resin and at least one water-soluble polyfunctional acrylic resin. When the mixture ratio of the mixture is 9
9.9: 0.1 to 96.0: 4.0 and the addition amount is 1 to 13.
% By volume or a mixing ratio of 96.0: 4.0 to 80.0:
(2) The method for molding a ceramic powder (claim 1), wherein the addition amount is 1 to 25% by volume at 20.0, and (2) the acrylic resin is a resin having a lower degree of polymerization than the oligomer. A method of forming a ceramic powder according to claim 1 (claim 2). This will be described in more detail below.

As mentioned above, the binder used in the present invention is a mixture of one or more monofunctional acrylic resins and one or more polyfunctional acrylic resins, which are water-soluble and thermosetting. Mixing ratio of the mixture is 99.9: 0.1 ~
96.0: 4.0, the addition amount is 1 to 13% by volume, or the mixing ratio is 96.0: 4.0 to 80.0: 20.0,
The addition amount was 1 to 25% by volume. By mixing the monofunctional acrylic resin and the polyfunctional acrylic resin in the ratio in this range and adding the mixed mixture in this range, the releasability can be improved for the following reasons.

It is considered that in this range, the surface of the molded article is in an uncured state, and the uncured portion acts as a release agent, so that the mold releasability of the molded article is improved. It is. And, since the molded body after demolding has only a hardened surface, the water retention is poor, and even if the surface properties are poor, if the surface is washed with water, only the uncured portion is washed away, and the surface is smooth. Since a solid cured product having a surface is obtained, there is no problem in water retention and surface shape, as well as in shape retention.

As for the mixing ratio and the addition amount of the monofunctional acrylic resin and the polyfunctional acrylic resin, the mixing ratio is 99.9:
If the addition amount is 0.1 to 80.0: 20.0 and the addition amount is 1 to 25% by volume, only the surface of the molded body is not cured except in a part of the range, so that water retention, surface properties, and The mold releasability is improved without any problem in shape. A part of the range means that the mixture ratio is 9
9.9: 0.1 to 96.0: 4.0, and the added amount is 13 to
It is in the range of 25% by volume. In this range, although there is no problem in terms of curing, since there is no uncured portion on the surface of the molded body, there is a problem in mold release properties.
The range excluding the mixing ratio of 99.9: 0.1 to 80.0: 20.0 and the amount of addition from 1 to 25% by volume is the range of the mixing ratio and the amount of addition of the present invention.

The ratio of the monofunctional acrylic resin is 99.9.
If it is larger than the case where only a monofunctional acrylic resin is used, the strength of the obtained molded article is weak and shape retention is poor,
It is not preferable because it is damaged when the mold is removed. Conversely 8
If it is smaller than 0.0, a part of the solvent is separated when the slurry is cured, as in the case of using only the polyfunctional acrylic resin, and the molded body shrinks in the mold and cracks are generated in the concave portion. It is not preferable.

On the other hand, if the addition amount is less than 1% by volume, the slurry is not cured and a molded body cannot be formed, which is not preferable. If it is more than 25% by volume, the viscosity of the slurry increases, and in some cases, the slurry becomes high. Cannot be prepared, and it is difficult to degrease molded products with thick products.
It is not preferable because cracks occur in the molded body after degreasing,
In order to obtain a dense sintered body, the range of 3 to 20% by volume is particularly desirable.

The degree of polymerization of the acrylic resin is not particularly limited as long as it is a resin showing thermosetting properties, but a resin having a viscosity as low as possible is desirable. A resin having a lower polymerization degree than that of the oligomer was used as the resin capable of being prepared. By using this resin, an excellent low-viscosity slurry having good moldability can be prepared.

[0016]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The molding method of the present invention will be described in more detail. First, oxides such as alumina and zirconia as well as non-oxides such as silicon nitride, sialon and silicon carbide can be used as ceramic powder. Prepare these powders. An appropriate sintering aid may be appropriately added to these powders.

Water and a dispersant are added to the prepared powder, and a monofunctional acrylic resin such as acrylic acid and a polyfunctional acrylic resin such as acrylic acid ester are mixed as a binder so that the mixing ratio is within the above range. The mixture is added and mixed in the ratio described above to prepare a slurry. After degassing the slurry under vacuum, it is poured into a mold that does not absorb the solvent. The mold is heated to a temperature at which the resin is cured together with the mold to cure the slurry, and the cured molded body is dried and degreased,
Sintering is performed at a predetermined temperature and a predetermined firing time in a predetermined atmosphere by a conventional method.

When the ceramic powder is formed by the above-described method, a formed body having excellent releasability can be formed.

[0019]

EXAMPLES Hereinafter, the present invention will be described in more detail with reference to Examples of the present invention and Comparative Examples.

(Examples 1 to 5) (1) Molding of Ceramic Powder Water, a binder, and a dispersant were added to the ceramic powder shown in Table 1 at the ratio shown in Table 1, and blended. After mixing with a pot mill, vacuum degassing was performed to prepare a slurry. The obtained slurry is 20 mm in diameter and 100 mm in thickness.
Was poured into an acrylic resin mold from which the molded article was obtained, and then heated together with the mold at 80 ° C. for 3 hours to cure the slurry. The obtained molded body was removed from the mold, and the surface was washed with water.
Dried in an atmosphere of 0% RH.

(2) Evaluation When the obtained molded product is released from the mold, a product which can be easily released without the close contact of the molded product is regarded as having good releasability (○), and a product which is not easy is regarded as having poor releasability. (X). Also, the molded body was removed from the mold, and the surface was washed with water and visually observed, and those having a smooth surface were evaluated as good surface quality (良), and those having no smooth surface were evaluated as poor surface quality (×). )
And Furthermore, the molded body washed with water is left standing on a horizontal place and visually observed. If the side surface of the molded body does not collapse due to its own weight, it is regarded as good shape retention (性), and if it gradually collapses, poor shape retention (×) ). Furthermore, the obtained molded body was sintered in the air atmosphere in Examples 1 and 2, in a nitrogen atmosphere in Examples 3 and 4, and in vacuum in Example 5 at a temperature shown in Table 1 for 3 hours. The bulk density of the obtained sintered body was measured by the Archimedes method. Table 1 shows the results.

Comparative Examples 1 to 3 Comparative Examples 1 to 3
In Comparative Example 2, only a monofunctional acrylic resin was used as a binder, and in Comparative Example 2, only a polyfunctional acrylic resin was used as a binder. Other than that, a slurry was prepared in the same manner as in Examples 1 and 2, and a molded body was prepared. ,evaluated. In Comparative Example 3, a slurry was prepared in the same manner as in Example 3 except that the mixing ratio of the monofunctional acrylic resin and the polyfunctional acrylic resin was out of the range of the present invention, and a molded body was prepared and evaluated. . Table 1 shows the results.

[0023]

[Table 1]

As is evident from Table 1, in the examples, the releasability, surface properties and shape retention were all satisfactory without any defects. In addition, each of the obtained sintered bodies had a high specific gravity, and a dense sintered body having no defect could be obtained. This indicates that it is possible to form a molded article having excellent surface properties and shape retention as well as excellent releasability.

On the other hand, in Comparative Example 1, since only a monofunctional acrylic resin was used as the binder, the releasability was poor, and the strength of the molded article was low. There was also a problem with gender. In Comparative Example 2, since only the polyfunctional acrylic resin was used as the binder, there were too many uncured portions, and even if the surface was washed, a smooth surface was obtained, but there were irregularities and the surface shape was poor. . Furthermore, in Comparative Example 3, since the mixing ratio was out of the range of the present invention, the surface of the molded body and the mold were in close contact with each other, and the mold releasability was poor. Each of the obtained sintered bodies was a dense sintered body having a high specific gravity and no defects as in the examples. This means that if a mixture of monofunctional acrylic resin and polyfunctional acrylic resin is used,
This shows that although there is no problem with water retention and shape retention, there may be problems with mold release.

[0026]

As described above, according to the molding method of the present invention, the releasability between the molded body and the mold can be improved. This provides a method for molding ceramic powder that can provide a molded article having excellent water retention, shape retention, and even releasability when a water-soluble and thermosetting acrylic resin is used as a binder. Now you can.

Claims (2)

[Claims] 1. A slurry prepared by adding water, a dispersant, and a thermosetting acrylic resin as a binder to a ceramic powder and mixing the resulting mixture is poured into a molding die made of a material that does not absorb water, and then the slurry is removed. In a method for molding a ceramic powder to be cured by heating, the acrylic resin comprises at least one water-soluble monofunctional acrylic resin,
It is composed of a mixture of at least one kind of water-soluble polyfunctional acrylic resin, and the mixture ratio of the mixture is 99.9: 0.1 to 9
6.0: 4.0 at an addition amount of 1 to 13% by volume, or a mixing ratio of 96.0: 4.0 to 80.0: 20.0 and an addition amount of 1 to 25% by volume. Of forming ceramic powder. 2. The method according to claim 1, wherein the acrylic resin is a resin having a lower polymerization degree than the oligomer.