CERAMICS BINDER AND PRODUCTION OF CERAMICS ARTICLES

Abstract: Disclosed are a ceramics binder comprising an organic binding agent and adamantane and/or trimethylene-norbor­ nane as a binding-auxiliary, and a method for producing a ceramics article comprising mixing a ceramics raw material powder with a ceramics binder comprising an organic bind­ ing agent and adamantane and/or trimethylenenorbornane as a binding auxiliary, molding the resulting mixture by an injection molding method or an extrusion molding method to obtain a molded article, and sintering the molded article. When the ceramics binder is used in a dough for injection molding, the time required for eliminating the ceramics binder can be shortened and the content of the ceramics binder which remains in the molded articles after eliminat­ ing treatment can be reduced to a negligibly low level.

Description: FIELD OF THE INVENTION The present invention relates to a ceramic binder which enables upon production of ceramic articles as by injection molding to mold under mild conditions, shorten period of time required for the elimination of the organic compound and reduce the amount of the remaining binder in molded articles, and ceramic articles produced using such a ceramic binder. BACKGROUND OF THE INVENTION One of the conventional methods according to which ceramic articles are produced is a method in which ceramic raw material powder and a binder are mixed to form a plastic dough, which is injection molded into a desired shape, and the molded article is heated, e.g., at a temperature of from 400 to 500°C to eliminate the organic compounds, and then the article is sintered at a temperature of from 800 to 1800°C. Conventional binders comprise a mixture of a thermoplastic resin as a main ingredient and an organic compound such as naphthalene, anthracene, camphor, and phenanthrene. However, this type of binder is disadvantageous in that after the elimination treatment of organic compounds from the molded articles they remain in the article in a considerable amount and ceramic articles obtained by sintering molded articles tend to show a poor appearance since cracks and voids occur on the surface of the articles. In addition, when the above-described dough is injection molded, molding pressure becomes too high to continue injection molding. When the molding temperature is elevated in order to decrease the molding pressure, not only decomposition of binder occurs giving rise to defective molding, but also it takes a long time to eliminate the organic compounds from the molded articles, resulting in poor productivity. Ceramic binder compositions exhibiting the above-mentioned deficiencies are described in JP-A-56157474 and EP-A-0125912. SUMMARY OF THE INVENTION An object of the present invention is to provide a binder whose content in molded articles after elimination of organic compounds can be further reduced to a minimum when it is mixed with ceramic raw material powder and the resulting mixture is molded and heated for elimination of organic compounds. Another object of the present invention is to provide a binder which can give rise to ceramic articles having no cracks or voids on the surface thereof when it is mixed with ceramic raw material powder and the resulting mixture is molded, heated for elimination of organic compounds and sintered. Still another object of the present invention is to provide a binder which can be removed from molded articles in a short period of time when it is mixed with ceramic raw material powder and the resulting mixture is molded and heated for elimination of organic compounds. Further, an object of the present invention is to provide a method for producing a ceramic article by injection molding or extrusion molding at a lower molding temperature and pressure than is used conventionally to produce ceramic articles having a good appearance. These objects of the present invention can be attained by a ceramic binder comprising an organic binding agent and adamantane and/or trimethylenenorbornane (hereinafter, sometimes referred to as "a binding auxiliary"), wherein said organic binding agent is contained in an amount of from 0.5 to 50 parts by weight per 100 parts by weight of the ceramic raw material powder to be mixed, and said adamantane and/or trimethylenenorbornane is contained in an amount of from 0.1 to 15 parts by weight per 100 parts by weight of the ceramic raw material powder to be mixed. BRIEF DESCRIPTION OF DRAWING The single figure is a perspective view of a molded ceramic article according to a preferred embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION A ceramic binder comprising an organic binding agent and a binding auxiliary is mixed with ceramic raw material powder to form a dough. As the organic binding agent, any conventional binding agent can be used. Suitable examples thereof include thermoplastic resins such as polyethylene, atactic polypropylene, polybutene, polystyrene, ethylene-vinyl acetate copolymer, polybutyl methacrylate, cellulose acetate and acrylic resin, water-soluble binders such as polyvinyl alcohol, sugar, carboxymethylcellulose, starch, dextrin, gelatin, molasses, pulp waste liquor, peptone and polyvinyl ether; organic solvent-soluble binders such as ethylcellulose, acetylcellulose, wax, liquid paraffin, heavy oil, machine oil, phenol resins and ethyl silicate. When the ceramic binder of the present invention is used in a dough for injection molding, it is preferred to use as the organic binding agent at least one member selected from the group consisting of polyethylene, atactic polypropylene, polystyrene, ethylene-vinyl acetate copolymer, polybutyl methacrylate and wax. These binding agents can be used singly or in admixture. In the present invention, it is essential that the ceramic binder comprises a mixture of the above-described organic binding agent with adamantane and/or trimethylene-norbornane, preferably endotrimethylenenorbornane, as a binding auxiliary. The blend ratio of the organic binding agent to the binding auxiliary varies depending on the kind of the ceramic raw material powder. The organic binding agent is used in an amount of from 0.5 to 50 parts by weight, preferably from 5 to 30 parts by weight, per 100 parts by weight of the ceramic raw material powder, while the binding auxiliary is used in an amount of from 0.1 to 15 parts by weight, preferably from 2 to 8 parts by weight, per 100 parts by weight of the ceramic raw material powder. The ceramic binder of the present invention can contain various additives such as a plasticizer and a lubricant, in addition to the organic binding agent and the binding auxiliary. Suitable examples of the plasticizer include diethyl phthalate, dibutyl phthalate, dioctyl phthalate and fatty acid esters. As for the lubricant, there can be illustrated aluminum stearate, magnesium stearate, diglycol stearate, flour and mineral oil. In the case of injection molding, a dough obtained by mixing the ceramic raw material powder with the ceramic binder of the present invention has an excellent flowability on heating without the addition of additives such as the plasticizer and the lubricant, resulting in injection-molded articles having an excellent surface appearance. Suitable examples of the ceramic raw material include non-plastic materials such as silica, feldspar, toseki (pottery stone), lithium minerals, sillimanite, alumina, zirconia, silicon carbide and silicon nitride; and plastic materials such as kaolin, plastic clay and fire clay. Of course, the ceramic raw material must be subjected to pulverization, wet mixing, sifting, removal of impurities, and the like prior to mixing with the ceramic binder of the present invention in the same manner as in the case of producing conventional ceramic articles. Mixing of the ceramic raw material with the ceramic binder of the present invention can be carried out by kneading, which can be performed, for example, at a temperature of from 80 to 160°C, preferably from 100 to 120°C, for from 0.5 to 3 hours, preferably from 0.5 to 1 hour. Kneading can be carried out using a ball mill, a plastomill, a hot kneader, a cokneader or a kneader which can heat and give a shearing force to a material to be processed. Mixing can be carried out in various manners. For example, at first a binding agent and a binding auxiliary are mixed with each other sufficiently to prepare a ceramic binder, and then the ceramic binder is mixed with a ceramic raw material powder. Alternatively, a ceramic raw material powder, a binding agent and a binding auxiliary are mixed simultaneously or subsequently. The dough thus obtained can be molded into a desired shape by a conventional method for molding ceramics such as a soft mud method, a semi-soft mud method, a plastic pressure molding method, a driven potter's wheel method, a roller machine method, an extrusion molding method, a hard mud method, a hydrostatic press method (a rubber press method), a stuffing method, a hot press method and an injection molding method. Among these methods, an injection molding method is particularly preferred since a dough containing the ceramic binder of the present invention can be injection molded sufficiently at such a temperature and pressure that a dough which does not contain the ceramic binder of the present invention cannot be molded satisfactorily, and the of time required for elimination of organic compounds can be shortened considerably. The method for producing ceramic articles using an injection molding in acordance with the present invention is described in detail below. That is, the ceramic raw material powder and the ceramic binder are hot kneaded to obtain a dough, which then is converted into pellets or powders for use as a molding material by granulation using rolls, pelletization using a pelletizer, size reduction by cold grinding using a kneader and pulverization by extruding the dough in the form of sheet using rolls. This molding material is supplied to a plunger type, preplasticating type or screw in-line type injection molding machine to give an molded article. The injection molding can be carried out at a temperature of from 80 to 205°C and at a pressure of from 943 to 14715 N/cm² (300 to 1,500 kg/cm²). Then the molded article is subjected to elimination treatment to remove the ceramic binder. The eliminating treatment can be carried out by heating the molded articles usually at a temperature of from 20 to 450°C for from 15 to 40 hours. It should be noted that in this eliminating treatment, the ceramic binder of the present invention can be removed in a time much shorter than that required for removing a conventional binder and the amount of the remaining ceramic binder of the present invention is very small. After the eliminating treatment, the molded article is sintered to produce a ceramic article. The ceramic binder of the present invention comprises a mixture of a conventional binding agent with a specific compound as a binding auxiliary, and as a result, when a dough prepared by mixing it with a ceramic raw material powder is molded into an article and the ceramic binder in this molded article is eliminated, the amount of the ceramic binder remaining in the molded article is small as compared with articles molded from a dough using a conventional binder and subjected to a eliminating treatment giving rise to ceramic articles having a beautiful surface without defects such as cracks and voids. The above-described advantages of the ceramic binder of the present invention are attainable not only in the case of ceramic articles produced using injection molding but also in the case of ceramic articles produced using other molding methods. Particularly, when the ceramic binder of the present invention is used in a dough for injection molding, the time required for the elimination treatment of the ceramic binder can be shortened and the content of the ceramic binder which remains in the molded articles after degreasing treatment can be reduced to a negligibly small level. Hereinafter, the present invention will be described in greater detail with reference to the examples and comparative examples. However, the present invention is not to be construed as being limited to these examples. EXAMPLES 1 TO 6 AND COMPARATIVE EXAMPLES 1 TO 4 Various kinds of ceramic raw materials shown in Tables 1 and 2, various kinds of binding agents shown in Table 1 and various kinds of binding auxiliaries were kneaded in ratios shown in Table 1 at a temperature of 100 ∼±10°C for 30 minutes using a laboratory plastomill at a torque of 400.5 Ncm (50 kg.cm). Then, the thus-kneaded material was reduced in size using a hand press and then further ground to form a bulk material of from 5 to 7 mm . The bulk material was injection molded using an injection molding machine (produced by Yamashiro Seiki Co., Ltd., vertical plunger type) under molding conditions shown in Table 1 to form molded articles having a shape shown in Table 1. The ceramic binder in molded articles was eliminated under the conditions shown in Table 1, and thereafter sintered at a temperature of 1,620°C (temperature increase rate: 100 C/h) to form ceramic articles. The appearance of the ceramic articles was evaluated by naked eye. The results obtained are shown in Table 1.

Claims: A ceramic binder comprising an organic binding agent in an amount of from 0.5 to 50 parts by weight per 100 parts by weight of the ceramic raw material powder to be mixed, and an adamantane and/or trimethylenenorbornane as a binding auxiliary in an amount of 0.1 to 15 parts by weight per 100 parts by weight of the ceramic raw material powder to be mixed. The ceramic binder as claimed in Claim 1, wherein said binding agent is at least one member selected from the group consisting of a thermoplastic resin, a watersoluble binder and an organic solvent-soluble binder. The ceramic binder as claimed in Claim 1, wherein said organic binding agent is at least one member selected from the group consisting of an ethylene-vinyl acetate copolymer, a polybutyl methacrylate, a polystyrene, a polyethylene, a polypropylene and wax. The ceramic binder as claimed in Claim 1, wherein said trimethylenenorbornane is endotrimethylenenorbonane. The ceramic binder as claimed in Claim 1, wherein said ceramic binder further contains a plasticizer and/or a lubricant. A method for producing a ceramic article comprising mixing a ceramic raw material powder with a ceramic binder according to any one of claims 1 to 5, molding the resulting mixture by an injection molding method or an extrusion molding method to obtain a molded article, and sintering the molded article. The method as claimed in Claim 6, wherein said ceramic binder is blended with said ceramic powder at a temperature of from 80 to 150°C. The method as claimed in Claim 6, wherein said ceramic raw material powder is at least one member selected from the group consisting of alumina, zirconia, silicon nitride and silicon carbide.

Inventors: SAITOH, KATSUYOSHI, SAKAI, TSUNENORI
Applicants: IDEMITSU PETROCHEMICAL CO. LTD.
Application year: 1986
Main classification: C04B35
IPC codes: C04B35