JPH0656505A - Ceramic composition for low pressure forming - Google Patents

Abstract

PURPOSE:To enhance ease of the handling and the dimensional accuracy of a ceramic sintered compact by preventing breakage of the forming at the time of dewaxing by reducing a content to be solidified added as a gelling agent as much as possible and enhancing the strength of a ceramic forming. CONSTITUTION:An alkali metallic salt of an organic compound incorporating a carboxylic group or an alkaline earth metallic salt of an organic compound incorporating a carboxylic group as a modifier is added to a slurry consisting of ceramic powder, an organic solvent, a dispersant and a gelling agent to prepare the ceramic composition for low pressue forming. The gel strength is enhanced by the modifier and is sufficient to produce a stabilized ceramic forming in spite of using a less solid content.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a ceramic composition mainly used in a low pressure molding method.

[0002]

2. Description of the Related Art As a ceramics molding method, an injection molding method in which a ceramics kneaded material is injected into a mold at high pressure is widely used. However, this injection molding method has problems such as wear of the mold by hard ceramic powder, generation of distortion due to internal stress of the molded body, and long degreasing time.

As a method for solving these problems, Japanese Unexamined Patent Publication No. 2-188460 discloses a method in which an organic solvent is used to reduce the viscosity of a ceramic slurry to improve the fluidity,
A new molding method is disclosed in which the slurry is injected into a mold at a pressure of about ² to 8 kg / cm ² and then cooled and solidified.

[0004]

By the way, in the low-pressure molding method as described above, it is possible to increase the strength of the ceramic molded body and improve the shape-retaining property in order to facilitate the handling of the ceramic molded body and the ceramic sintered body. Is also important for achieving high accuracy. In order to increase the strength of the ceramics compact, a method of increasing the concentration of the ceramic powder in the slurry and a method of increasing the addition amount of the gelling agent can be considered.

However, increasing the concentration of the ceramic powder is limited in terms of the particle size of the ceramic powder. That is, the larger the particle diameter of the ceramic powder is, the more advantageous it is to increase the powder concentration, but on the other hand, the sinterability of the powder is lowered, which is disadvantageous in improving the strength of the ceramic sintered body. On the other hand, although the method of increasing the addition amount of the gelling agent can effectively increase the strength of the ceramic molded body, the merit of the low pressure molding method using an organic solvent that the degreasing time is shortened is reduced. . That is, when the addition amount of the gelling agent is increased, during degreasing, the gelling agent gasifies from the solid due to thermal decomposition and expands in volume, so that cracks frequently occur in the molded body, and in order to prevent this, There is no choice but to lengthen the degreasing time.

The present invention has been made in view of the above circumstances, and the amount of solidification added as a gelling agent is reduced as much as possible to prevent cracking of the compact during degreasing, while increasing the strength of the ceramic compact, The purpose is to facilitate handling and improve the dimensional accuracy of the ceramic sintered body.

[0007]

A low-pressure molding ceramic composition of the present invention for solving the above-mentioned problems is a low-pressure molding ceramic composition comprising ceramic powder, an organic solvent, a dispersant and a gelling agent, An alkali metal salt of an organic compound containing a carboxyl group or an alkaline earth metal salt of an organic compound containing a carboxyl group is added as a modifier.

As the ceramic powder, silicon nitride,
Various ceramics such as silicon carbide, alumina, yttria, silica, and spinel can be used alone or in combination. The amount of the ceramic powder can be set to about 40 to 70 vol% and is preferably set to 45 to 65 vol% although it depends on the particle size distribution of the powder.

As the organic solvent, various kinds of organic solvents can be used, and it is necessary to select one that can obtain the gelling action of the gelling agent. Specific examples include mineral oils, animal and vegetable oils, hydrocarbon solvents, ketones, esters, amides, alcohols and the like. Moreover, you may use these 2 or more types in mixture. Among these, petroleum hydrocarbon solvents having a small polarity can be mentioned as preferable organic solvents. Examples of the petroleum-based hydrocarbon solvent include paraffinic hydrocarbons (iso-paraffin, n-paraffin), aromatic hydrocarbons (alkylbenzene, etc.), naphthene-based solvents and the like. However, a polar solvent such as alcohol may be preferable in view of good wettability with Si ₃ N ₄ powder and good handleability (washability with water).

The amount of the organic solvent can be 30-60 vol% minus the amount of the gelling agent, the dispersant and the modifier added. When the amount of the organic solvent is more than 60 vol%, the shrinkage during firing is large, and the possibility of cracking increases, and a denser sintered body cannot be obtained. Again 3
If it is less than 0 vol%, the slurry viscosity becomes too high, and pores remain, which is not preferable for molding.

The dispersant promotes the dispersion of the ceramic powder in the organic solvent, enables a high powder concentration, and exhibits a viscosity reducing effect. As the dispersant, any compound having a function of dispersing ceramic powder in an organic solvent can be used, and a compound having a higher solubility in the organic solvent is preferable. For example, for petroleum hydrocarbon solvents, polyoxyethylene alkyl ether phosphates,
Examples thereof include polyethylene alkyl ether phosphates, polyethylene glycol alkyl ethers, and copolymers of polyoxypropylene monoallyl monostearyl ether with maleic anhydride and styrene.

The addition amount of the dispersant is 1 to 25 vol% when the ceramic powder and the dispersant are 100 vol%.
It is preferable that If the amount of the dispersant is more than 25 vol%, the viscosity of the slurry increases, and if it is less than 1 vol%, it may not be possible to form a slurry. The optimum addition amount depends on the type of dispersant and the characteristics of the ceramic powder (particularly the specific surface area).

The gelling agent may be any compound that can gelate the above organic solvent. Although the mode of the gelling agent is not limited,
Typically, a compound that is liquefied in a heated state with a mixture with an organic solvent and gelated when cooled in a mold can be used. Examples of such a compound include a hydroxy group-containing fatty acid (in particular, an alkyl fatty acid having 10 to 30 carbon atoms, for example, 12 hydroxystearic acid), or N-lauroyl-L-glutamic acid-α, γ-di-n-.
Amino acid derivatives such as butyramide, dihydrolanosterol derivatives, dibenzylidene sorbitol and the like can be used.

The addition amount of the gelling agent is preferably 2 to 30 vol% when the organic solvent and the gelling agent are 100 vol%. When the amount of the gelling agent is more than 30 vol%, the degreasing time becomes long, and when it is less than 2 vol%, the desired gelling ability cannot be obtained. The greatest feature of the present invention is that
Further, it contains a modifier. In this specification,
The modifier refers to an alkali metal salt or an alkaline earth metal salt of an organic compound containing a carboxyl group, and this modifier is added together with a gelling agent to enhance the strength of the molded body when gelled. Specific examples thereof include alkali metal salts or alkaline earth metal salts such as carboxymethyl cellulose, alginic acid, polyacrylic acid, fatty acid, benzoic acid, stearic acid and acetic acid. Examples of the ion pair that constitutes the alkali metal salt of the organic compound containing a carboxyl group include lithium, sodium and potassium. In addition, examples of the ion pair that constitutes the alkaline earth metal salt of the organic compound containing a carboxyl group include calcium, strontium, barium, and magnesium.

Here, when the ceramics sintered body obtained from the composition of the present invention is used only at room temperature, it is not necessary to limit the above ion pair, but the above sintered body is 1000 ° C.
When used at a high temperature of about a certain level or higher, it is preferable to select ions that can be crystallized even if they remain in the sintered body, such as magnesium and calcium. As a result, it is possible to obtain a sintered body with a small decrease in strength even at high temperatures.

The amount of an alkali metal salt or an alkaline earth metal salt of an organic compound containing a carboxyl group as a modifier is 1 to 50 vol% when the gelling agent and the modifier are 100 vol%. It is preferable that the amount is 3 to 10% by volume. If the added amount of the modifier is more than 50%, it is not possible to secure the amount of the gelling agent to fulfill the required gelling ability, and the added amount of the modifier is 1
If it is less than%, the effect of adding the modifier is not exerted.

[0017]

[Function] To increase the strength of the ceramic molded body,
As described above, it is effective to increase the addition amount of the gelling agent such as 12-hydroxystearic acid, but in this case, the merit of the low pressure molding method that the degreasing time can be shortened is reduced. The ceramic composition for low pressure molding of the present invention contains an alkali metal salt or an alkaline earth metal salt of an organic compound containing a carboxyl group as a modifier. This modifier has a function of increasing gel strength.
Therefore, it is possible to obtain a stable ceramic molded body without increasing the amount of gelling agent, that is, to obtain sufficient gel strength with a small solid content.

[0018]

EXAMPLES The present invention will be specifically described below with reference to examples. Example 1 A ceramic powder composed of 92% by weight of silicon nitride, 4% by weight of yttria and 4% by weight of alumina was used.
In a ball mill, vol%, a polymer of maleic anhydride and a polyoxypropylene as a dispersant (NOF, trade name Marialim AAS-0851) is 7.9 vol%, and isoparaffin as an organic solvent is 62.1 vol%. The mixture was put into a container, and wet mixed for 24 hours or more to prepare a slurry.

This slurry was heated to 80 ° C. or higher, and 12 hydroxystearic acid as a gelling agent and sodium acetate as a modifier as shown in Table 1 were added and dissolved. Then, a part of the organic solvent was evaporated to adjust the powder concentration to 45 vol% to obtain a ceramic composition of this example. The composition ratio of each component is as follows.

Ceramic powder 45 vol% Polymer of maleic anhydride and polyoxypropylene (dispersing agent) 8.9 vol% Isoparaffin (organic solvent) 36.1 vol% 12 Hydroxystearic acid (gelling agent) 8 vol% Sodium acetate ( Modifier) 2 vol% Next, the above ceramic composition is placed in a cooled mold for 2 k.
It was injected at a pressure of g / cm ² and, after 15 minutes, demolded. The hardness of the obtained ceramic molded body is SRIS-0101.
(Japan Rubber Association standard). The results are shown in Table 1.
Shown in.

After the molded body was dried at 50 ° C. for 72 hours, the temperature was raised to 600 ° C. at a heating rate of 50 ° C./hr to degrease it, and it was sintered at 1700 ° C. in a nitrogen gas atmosphere.
No defects were found in the obtained sintered body. (Examples 2 to 7) As shown in Table 1, the same as Example 1 except that the modifier was replaced with sodium benzoate, sodium stearate, potassium stearate, sodium carboxymethyl cellulose, sodium alginate, and sodium polyacrylate. Similarly, each of Examples 2 to 7 is performed.
A ceramic molded body according to was obtained. The hardness of each obtained ceramic molded body was measured in the same manner as in Example 1. The results are shown in Table 1.

Each ceramic compact was sintered in the same manner as in Example 1. No defects were found in each of the obtained sintered bodies. (Comparative Example) 12 as a gelling agent in a ceramic composition
A ceramic compact according to a comparative example was obtained in the same manner as in Example 1 and Example 1 except that the composition ratio of hydroxystearic acid was 10 vol% and no modifier was added. The hardness of the obtained ceramic molded body was measured in the same manner as in Example 1. The results are shown in Table 1. Further, the ceramic molded body was sintered in the same manner as in Example 1. Defects were found in the obtained sintered body.

[0023]

[Table 1] (Evaluation) From Table 1, the hardness of the ceramic molded body according to the example to which the modifier is added is 1.5 to 2 times or more the hardness of the ceramic molded body according to the comparative example to which the modifier is not added. Therefore, it can be seen that the strength of the ceramic molded body is improved by adding the modifier according to the present invention.

The amount of organic solids (gelling agent and modifier) in the ceramic composition of the example is the same as the amount of organic solids (gelling agent) in the ceramic composition of the comparative example. In this case, the time required for degreasing is also the same. Therefore, it is understood that by adding the modifier, it is possible to increase the strength of the ceramic molded body while preventing the degreasing time from being prolonged.

[0025]

As described in detail above, according to the ceramic composition for low pressure molding of the present invention, the strength of the ceramic molded body can be enhanced while ensuring the advantage of the low pressure injection molding method that the degreasing time is shortened. It will be possible. Therefore, by using the ceramic composition for low-pressure molding of the present invention, it is possible to manufacture a sintered body that is dense, has little dimensional variation, and has excellent performance such as strength in a short time.

Claims (1)

[Claims] 1. A ceramic composition for low-pressure molding, comprising ceramic powder, an organic solvent, a dispersant, and a gelling agent, wherein the modifier is an alkali metal salt of an organic compound containing a carboxyl group, or a carboxyl group. A ceramic composition for low-pressure molding, to which an alkaline earth metal salt of an organic compound containing is added.