GB2167741A - Ceramics-forming composition - Google Patents

Abstract

Slip casting is conducted by using a composition obtained by mixing a resin emulsion with a slip which contains a body for pottery or a ceramic material as a principal constituent. The resulting cast product has mechanical strength of such a degree that it can be subjected to finishing operations without need for its biscuit firing. It is also possible to obtain a new ceramic product of a desired complex shape by bonding two or more formed products, which have in advance been produced from a ceramic material as a raw material in accordance with the process of this invention, with a bond which contains a ceramic material and resin emulsion as principal components, and then firing the thus-bonded formed products.

Description

SPECIFICATION Ceramics-forming composition, process for forming ceramics from the composition, and processing of resulting formed products This invention relates to a ceramics-forming composition, a process for forming ceramics from the composition and a process for processing the resulting formed products. More specifically, it relates to a ceramics-forming composition featuring the addition of a resin emulsion to a body for pottery or a ceramic material (the term "ceramic material" as used herein means a so-called new ceramic material such al alumina, zirconia, silica, ferrite, silicon carbide, silicon nitride or sialon), a process for forming ceramics from the composition, and a process for processing formed products which comprises preparing a jointed formed product from two or more formed products obtained in the above manner and then firing the jointed formed product.

In slip casting processes for the formation of ceramics, cast products have heretofore been produced by adding suitable amounts of water, deflocculants and the like to bodies to prepare slips, pouring the slips into hygroscopic molds such as gypsum molds so as to have deposits of ceramic particles build up on the mold walls owing to the absorption of water by the molds, and after the completion of buildup of the ceramic particles, releasing the cast products from their corresponding molds. These cast products are thereafter processed into ceramics products through such steps as drying, biscuit firing, glazing and firing. When slip casing is relied upon, cast products are required to have mechanical strength of such a degree that they can be successfully handled during their finishing operations and transportation.It is also indispensable that they can be released with ease from their corresponding molds.

When effecting slip casting with a body for pottery, it has conventionally been practiced to incorporate Gairome-clay, Kibushi-clay or the like in a large amount so as to achieve mechanical strength required for proceeding with the slip casting work. It was however still necessary to subject cast products, which have been obtained by casting such bodies, to biscuit firing so that sufficient mechanical strength are imparted to them. In addition, use of clay makes it difficult to produce high-grade porcelain having such translucent appearance as white porcelain. A still more difficult problem has also been encountered due to exhaustion of clay resources of good quality.Under these circumstances, there has been a strong demand for the development of a strength improver which can impart sufficient mechanical strength to cast products without using clay in large volumes.

On the other hand, new ceramic products are expected to find utility in industrial fields owing to their superb mechanical strength, heat resistance, abrasion and wearing resistance and the like, although conventional porcelain products were by no means usable in such industrial fields. However, it can hardly be said under the current circumstances that their applications have proceeded as expected. As one of major reasons for the limited applications of new ceramic products, difficulties in their forming and processing operations may be mentioned.

For the formation of porcelain products, a variety of forming processes may be employed including the above-mentioned slip casting process. Use of such forming processes makes it possible to obtain even products of intricate configurations with ease. In the case of new ceramics, their formation must rely upon sheet forming, extrusion, compression molding orthe like. Hence, it has not been easy to obtain products of intricate configurations. In other words, these forming processes were able to provide products of simple configurations only, such as plate-like products, pipe-like products and the like. It is thus possible to form products of intricate configurations from new ceramic materials provided that slip casting can be applied to them. It was however impossible to form cast products of sufficient strength when usual bodies were employed as they were.There has been a strong demand for the development of a strength improver which can impart sufficient mechanical strengths to cast products so that they may be successfully handled during their final processing operations and transportation.

The present inventors have carried out an extensive research with a view toward solving the above-mentioned problems. As a result, it has been discovered that use of a resin emulsion as a strength improver can improve the mechanical strength of a cast product whether a body for pottery is used or a ceramic material is employed.

By the above-mentioned process, it has become possible to obtain new ceramic products of various configurations besides plate-like and pipe-like products. In order to obtain cast products of more complex configurations, it may be contemplated to form two or more new ceramic cast products separately as parts by the above-mentioned process, jointing them together with a bond, and then firing the thus-jointed cast products. It was however impossible to obtain the intended product from the use of any one of conventionally-known adhesives, because such adhesives are caused to decompose upon firing and the jointed cast products are separated at their jointed surfaces.

The present inventor's research has however found that an intended new ceramic product of any desired shape can be obtained without undergoing the above-mentioned separation by jointing the aforementioned cast products with a jointing medium, which is composed of a ceramic material and a resin emulsion, instead of conventionally-known adhesives and then firing the thus-jointed cast products.

It is desirable to provide a slip composition capable of forming a cast product, which has improved mold releasing characteristics and mechanical strength of such a degree that its finishing operations can be successfully conducted without need for its biscuit firing, upon casting a slip of a body for pottery or a ceramic material, and also to provide a slip casting process making use of such a composition.

It is further desirable to provide a slip composition capable of achieving the first object of this invention without using a clay component as a body for pottery in a large amount upon casting a slip of the body, and also to provide a slip casting process making use of such a composition.

It is also desirable to provide a slip composition which makes it possible to apply a slip casting process, which can impart enough mechanical strength to the resulting cast product so that the cast product can be successfully handled during its finishing operations and transportation, to a ceramic material, and also to provide a slip casting process making use of such a composition.

It is additionally desirable to provide a process for producing a new ceramic product of intricate configurations from a ceramic material as a principal raw material.

According to one aspect of the present invention there is provided: a ceramics-forming composition formed by mixing a resin emulsion with a slip which contains a body for pottery or a ceramic material as a principal constituent.

According to a second aspect of the present invention there is provided a process for forming ceramics, which comprises subjecting the above slip composition to slip casting.

According to a third aspect of the present invention there is provided a process for processing a cast ceramic product, which process comprises the following consecutive steps: a) mixing a resin emulsion with a slip which contains a ceramic material as a principal constituent, thereby preparing a slip composition; b) forming two or more cast products with the slip composition in accordance with a slip casting process, said cast products having the same or different configurations and being in such a matching relation that said cast products include at least one set of matching surfaces to be jointed to each other; c) applying a jointing medium, which contains a ceramic material and a resin emulsion as principa components, to at least one of the matching surfaces of the cast products;; d) jointing the matching surfaces of the cast products so as to joint the cast products into a united cast product; and e) firing the united cast product.

Although the slip casting process of this invention can produce new ceramic products of relatively intricate configurations, new ceramic products of desired intricate configurations can be obtained in accordance with the slip casting process of this invention provided that the process for the processing of cast products, which process comprises such consecutive steps as those described above is applied.

By the term "a body for pottery" as used herein, is meant a body that has conventionally and routinely been used as a body for pottery. Said body typically contains feldspar, siliceous stone, Toseki (pottery stone), kaoline and or clay as its principal constituent or constituents.

On the other hand, the term "a ceramic material" as used herein means raw materials for ceramics; typically including metal oxides such as alumina, zirconia, ferrite, silica, beryllia, magnesia, titania, calsia and zinc oxide, carbides such as silicon carbide and boron carbide, nitrides such as silicon nitride, aluminium nitride and boron nitride, borides such as aluminium boride, the silicates, aluminates and zirconates of various metals, titanates such as barium titanate and strontium titanate, solid solutions such as sialon, and mixtures thereof.

The term "a resin emulsion" means, for example, emulsions of acrylic resins containing (meth)acrylic ester resins, (meth)acrylic ester-vinyl acetate resins, (meth)acrylic ester-styrene resins or (meth)acrylic ester-vinyl chloride resins as principal components, emulsions of vinyl acetate resins containing vinyl acetate resins as principal components, emulsions of ethylene copolymers containing ethylene-acrylic ester resins or ethylene-vinyl chloride resin as principal components, synthetic rubber emulsions containing styrene-butadiene resin, methyl methacrylate-butadiene resin or acrylonitrile-butadiene resin as principal components, natural rubber emulsions, etc. Among these resin emulsions, emulsions of acrylic resins are preferred.

The amount of the resin emulsion to be added to the body for pottery or ceramic material may vary depending on the type of the body or ceramic material, its particle sizes and particle size distribution, the type of the resin emulsion, the type of a ceramic product to be formed, and so on. It cannot thus be specified sweepingly. However, it is generally suitable to add the resin emulsion in an amount of about 0.1 - 20 parts by weight as solids in the emulsion per 100 parts by weight of the dry body or ceramic material.

Resin emulsions useful in the practice of this invention may be prepared by an emulsion polymerization process known perse in the art. Namely, they may each be prepared by using water or a mixed solvent of water and a water-miscible organic solvent such as an alconol or acetone as a medium, dispersing its corresponding monomer, if necessary by adding a surfactant, uniformly in the medium and then subjecting the monomer to emulsion polymerization in the presence of a water-soluble radical polymerization initiator and if desired, a molecular weight regulator and other chemical additives.

As the polymerization initiator, it is possible to use a usual radical polymerization initiator such as a peroxide, redox catalyst, persulfate salt or azo compound.

When the surfactant is employed, it may be any one of anionic, cationic, non-ionic and amphoteric surfactants or a mixture of any combination of such surfactants.

As the molecular weight regulator, may be employed a mercaptan such as tertiary dodecyl mercaptan or normal dodecyl mercaptan, carbon tetrachloride, isopropyl alcohol or the like.

The polymerization is generally conducted at 40 - 90"C in a reactor from which oxygen has been removed.

The monomer, surfactant, molecular weight regulator, polymerization initiator and other desired chemical additives may be added in their entirety to the reaction medium at the start. Alternatively, their partial or entire portions may be added in portions after initiation of the reaction. It is also feasible to change operation conditions such as temperature and stirring conditions as desired in the course of the reaction. The polymerization reaction may be conducted either continuously or batchwise.

The slip composition of this invention, which is prepared by adding the resin emulsion to the body for pottery or the ceramic material, is extremely stable and features a low viscosity and good fluidity, in other words, has excellent formability. Products formed from the slip composition have excellent mechanical strength.

In the slip employed for the preparation of the ceramics-forming composition of this invention and containing the body for pottery or ceramic material as its principal consitiuent, it may be possible to incorporate, besides the above-mentioned body or ceramic material, one or more deflocculants, sintering agents, ceramic raw materials other than those mentioned above, additives and the like as desired.

Illustrative of the deflocculant may include inorganic deflocculants such as water glass, sodium carbonate and phosphate salts such as sodium phosphate and sodium tripolyphosphate and organic deflocculants such as sodium polyacrylate, napthalenesulfonic acid-formaldehyde condensation product and sodium ligninsulfonate. Its content may generally be 0.02 - 2.0 parts by weight as solids per 100 parts by weight of the dry body or ceramic material.

Exemplary sintering agents may include magnesia, boron, the oxides of rare earth metals such as yttrium and lanthanum, etc. Its content may be 0.01 - 5.0 parts by weight per 100 parts by weight of the dry body or ceramic material.

As additives other than those mentioned above, may be mentioned releasing agents such as calcium stearate, zinc stearate and wax emulsions, pH modifiers including ammonia, organic amines such as triethanol amine, and organic acids such as oxalic acid and formic acid, and defoaming agents such as silicone-base and polyether-base defoaming agents. Their contents may each be 0.01 - 10 parts by weight as solids per 100 parts by weight of the dry body or ceramic material. Besides, a wetting agent, an ion scavenger such as chelate agent, a plasticizer andlorthe like may also be used if necessary.

In the ceramics-forming composition of this invention, the body for pottery or ceramic material suitably amounts to 40 - 85 parts by weight as solids per 100 parts by weight of the ceramics-forming composition.

Each cast product formed in accordance with the process of this invention has sufficient green strength so that it can successfully withstand its handling and post processing operations as is, namely, without need for any biscuit firing step. Therefore, it may be glazed and fired into a cast ceramic product as is without any biscuit firing step. If necessary, it may be glazed and fired after the cast product has been colored and then subjected to glazing and decorating firing. Compositions of this invention can bring about excellent results when formed not only by slip casting processes but also by extrusion processes, jiggering processes, jolleying processes, potter's wheeling processes and the like.

As mentioned above, the present invention can bring about the following excellent effects: Biscuit firing step can be omitted.

Post processing operations are easy.

When a body for pottery is used, clay component may be either omitted or reduced.

It permits to apply slip casting to ceramic materials, whereby new ceramic products of rather intricate configurations can be obtained.

It provides cast products having improved green strength.

In order to obtain a new ceramic product of desired intricate configurations in accordance with the present invention, it is necessary to employ the processing process which includes the consecutive steps a through e as mentioned above. Of these consecutive steps, the steps a and b are exactly the same as the corresponding steps described above with respect to ceramic materials. Therefore, the step c and its subsequent steps will hereinafter be described in detail.

Namely, two or more cast new ceramic products formed through the steps a and bare applied at their surfaces, which are to be jointed together, with a jointing medium in the step c. In the step d, they are jointed together into a united cast product. If the jointing medium used in the step c is other than those useful in the practice of this invention, the strength of jointed part will be insufficient even after its firing. The resulting product would thus be separated at the jointed part while it is used.

In the present invention, the jointing medium contains a ceramic material and a resin emulsion as its principal components.

Illustrative of the ceramic material, which makes up the jointing medium, may include the same new ceramics materials as those described above. Any of such new ceramic materials may be used. Although it is not absolutely necessary to use the same new ceramic material as that employed in the step a, it is preferred to use the same new ceramic material. Ceramic materials may generally include fine ceramic materials having particle sizes as small as about 100 and relatively coarse ceramic materials having grain sizes as large as about 5 mm. In the case of sucn coarse ceramic materials, it is preferable to use them after grinding same to a desired particle size.

Illustrative of the resin emulsion, which is the other component of the jointing medium, may include the same resin emulsions as those mentioned above. Any of such emulsions may be used. It is not absolutely necessary to use the same resin emulsion as that employed in the step a, but here again, an emulsion of an acrylic resin is preferred. Two or more resin emulsions of different kinds may also be used in combination.

The bond contains a ceramic material and a resin emulsion as mentioned above. Prior to its application, it may be dispersed in a dispersing medium if desired. Water is preferred as the dispersing medium.

The amount of the resin emulsion to be added to the ceramic material may vary depending on the type of the ceramic material, the type of the resin, the type of a cast ceramic product to be produced, and so on.

Therefore, it cannot be sweepingly specified. However, it is generally suitable to add the resin emulsion in an amount of about 0.1 - 20 parts by weight as solids in the emulsion per 100 parts by weight of the dry ceramic material.

The preferred proportion of the ceramic material in the jointing medium may range from 20 to 90 parts by weight per 100 parts by weight of the jointing medium.

The thus-obtained jointing medium is applied to the surfaces, which are to be jointed together, of the cast products obtained through the steps a and b. Here, it is preferred to wet the surfaces of the cast products, which surfaces are to be jointed together, with the same dispersing medium as that incorporated in the jointing medium prior to the application of the jointing medium thereto. If the surfaces, which are to be jointed together, are not wetted with the dispersing medium, the dispersing medium of the jointing medium is caused to move to the cast products. As a result, the final product which is to be obtained after its firing will have reduced bonding strength. The jointing medium may be applied to both surfaces to be jointed together.

No problem or inconvenience will however be encountered even when it is applied to only one of the surfaces to be jointed together. Although no particular limitation is imposed on the amount of the jointing medium to be applied, it may generally be 0.1 mm - 5 mm as a coat thickness. It is preferred to apply the jointing medium to the surfaces as uniform as possible. As an application method, it may be applied in a usual manner, for example, by a trowel or the like. The cast products with the jointing medium applied on their surfaces to be jointed together are jointed at the surfaces in the step d. Its firing is then effected in the step e under conditions conforming to the ceramic material used, thereby providing the intended ceramic product.As firing conditions for the step e, the firing temperature may generally range from 1000 to 25000C, the firing time may usually be 0.1 - 200 hours, and the firing atmosphere is normally air. However, no problem or inconvenience will be encountered even when an inert gas such as nitrogen is employed as the firing atmosphere.

Unlike conventional porcelain, new ceramics are difficult to form as mentioned above. Namely, due to lack of any suitable binder four new ceramics, formed products have weak strength before their firing. Needless to say, it was virtually impossible under prior art techniques to joint two or more cast products and then to fire the thus-united cast products when various properties required for new ceramics, led by mechanical strength, were taken into consideration.

In the present invention, it has become feasible to produce cast products with improved green strength by slip casting owing to the incorporation of a resin emulsion in a slip which contains a ceramic material as a principal constituent. Furthermore, by jointing two or more cast products with a specific jointing medium, it has also become feasible, after firing, to obtain a new ceramic product having intricate configurations without any reduction to various properties led by mechanical strength.

When conducting slip casting on the ceramics-forming composition of the invention in a gypsum mold, the mold releasing characteristics of the composition are critical characteristics governing whether the slip casting can be successfully performed or not. Here, the term "mold releasing characteristics" pertains to such characteristics as whether a cast product can be readily released from its corresponding gypsum mold or the like and whether the cast product develop cuts or deformation upon its release from the corresponding mold.

For good mold releasing characteristics, it is considered to be necessary that the sticking strength between a mold and its corresponding cast product is weak, the strength of the slip cast product upon its release from the mold, namely, its wet strength is sufficiently high, and the cast product has dry strength of such a degree that it can withstand its handling during its finishing operations and transportation after its release from the mold and its subsequent drying.

The mold releasing characteristics are correlated to the following two parameters. The first parameter is the green strength of a slip cast product. The second parameter is the sticking strength at the interface between the mold and the ceramic material, namely, the force required to separate the slip cast product from the mold surface (which will hereinafter be called "mold releasing strength"). It has been known that this mold releasing strength varies considerably in accordance with the type and amount of a deflocculant to be added to the body. It has also been known that the wall thickness of a gypsum mold decreases to a greater extent, namely, the gypsum mold undergoes more deterioration upon release of its corresponding cast product as a slip having better mold releasing characteristics is employed. In other words, the service life of a gypsum mold decreases as the mold releasing characteristics of a slip becomes better. As one reason for this tendency, it may be contemplated that the deflocculant component in the slip reacts with the gypsum mold at their interface and the reaction product serves to weaken the interfacial sticking strength, but the surface layer of the gypsum mold is destroyed by the reaction.

In order to solve the above-mentioned problem, it has been proposed to incorporate wax-base emulsions in bodies for pottery and ceramic materials. Use of such emulsions are however still insufficient as a method for solving the above-mentioned problem.

As a method for improving the green strength of cast products, a variety of investigations have been carried out, including addition of water-soluble high molecular weight substances such as natural water-soluble high molecular substances, e.g., gum acacia and sodium alginate, semi-synthetic watersoluble high molecular weight substances, e.g., methylcellulose, hydroxyethylcellulose, hydroxypropy Imethylcellulose and carboxymethylcellulose, and synthetic water-soluble high molecular substances, e.g., polyvinyl alcohol and water-soluble acrylic polymers. Since a water-soluble high molecular weight substance moves along with movement of water owing to its inherent nature, the water-soluble high molecular weight substance moves together with water into the surface layer of a gypsum mold when slip casting is conducted.Thus, the mold surface is deteriorated or the fine porous structure of the mold surface is clotted. For these causes, the service life of the mold will be shortened.

During slip casting or its subsequent drying step of the resultant cast product, water moves to the surface of the cast product. Thus, water is absorbed from the surface of the cast product into the corresponding gypsum mold when its slip casting is effected. In the drying step, water is allowed to vaporize and evaporate from the surface of the cast product. Since the water-soluble high molecular weight substance moves together with water as mentioned above, the water-soluble high molecular substance is locally built up in the vicinity of the surface of the cast product while almost no water-soluble high molecular substance is present around the center of the cast product. As a result, the cast product becomes hard near its surface only.Due to this non-uniformity in strength, there has been a possible danger that ceramic products may produce stress and may thus develop warping or cracks subsequent to their firing or sintering.

It has however been found that when an aqueous emulsion of a specific copolymer, which was composed of: A) 0.1 - 15 wt.% of a carboxyl-containing monomer unit and/or B) 0.1 - 5 wt.% of a substituted or unsubstituted carbamoyl-containing monomer unit represented by the following general formula:

wherein R1 and R2 may be the same or different and mean individually a hydrogen atom or methyl group, and R3 denotes a hydrogen atom a Ca-C4 alkyl group or a hydroxymethylene or alkoxymethylene group represented by the following general formula: CH20R4 wherein R4 means a hydrogen atom or a C1-C4 alkyl group; and C) 85 - 99.9 wt.% of one or more other monomer units copolymerizable with the monomer specified in A) and/or B) above, as a resin emulsion upon preparation of a ceramic-forming composition, which is suitable for use in slip casting, by adding the resin emulsion to a slip containing a body for pottery or ceramic material as its principal constituent in accordance with the present invention, the use of the aqueous resin emulsion was able not only to improve the mechanical strength of the cast body but also, surprisingly, to improve its mold releasing characteristics and to prolong the the service life of the gypsum mold.

As preferable examples of the carboxyl-containing monomer (hereinafter referred to as "the monomer A") among the monomer units making up the above specific copolymer, may be mentioned acrylic acid, methacrylic acid, itaconic acid, crotonic acid, fumaric acid and maleic acid, and monoalkyl esters of itaconic acid and maleic acid. Of the constituent units of the copolymer, the proportion of the monomer may amount to 0.1 - 15 wt.% or peferably, 2 - 10 wt.%. If its proportion exceeds 15 wt.%, the viscosity of a slip will be become too high, its fluidity will be impaired and it will not be able to form good cast products when the resulting aqueous emulsion is added to the slip. On the other hand, any proportions smaller than 0.1 wt.% will not permit formation of cast products having sufficient green strength.

As preferable examples of the substituted or unsubstituted, carbamoyl-containing monomer (hereinafter referred to as "the monomer B") out of the monomer units making up the above specific copolymer, may be mentioned acrylic amide, methacrylic amide, dimethyl(meth)acrylic amide, N-methylol(meth)acrylic amide, methoxymethylol(meth)acrylic amide, butoxymethylol(meth)acrylic amide and the like. Of the constituent units of the copolymer, the proportion of this monomer may amount to 0.1 - 5 wt.% or preferably, 0.5 - 4 wt.%. If its amount exceeds 5 wt.%, the viscosity of a slip will become high and its viscosity will increase further as the time goes on, leading to deteriorated fluidity when the resulting aqueous emulsion is added to the slip. It will thus be impossible to form good cast products stably.If its amount is smaller than 0.1 wt.% on the other hand, it will be impossible to form cast products having sufficient green strength.

When the monomer A and monomer B are used in combination as constituent monomer units for a copolymer, the total proportion of these two monomers must be 0.1 - 15 wt.% of the constituent monomers of the copolymer and the proportions of the respective monomers must fall within the above-specified their respective ranges.

As the monomer (hereinafter referred to as "the monomer C") copolymerizable with the monomer A and/or monomer B, a hydroxyl-containing monomer may be used. Illustrative of such a hydroxyl-containing monomer may include 2-hydroxyethyl acrylate, 2-hydroxyethyl methacrylate, hydroxypropyl methacrylate, etc. When such a monomer is used as a constituent unit in an amount of 0.2 - 10 wt.% in the copolymer, the viscosity of a slip is lowered and good fluidity and long-term stability in viscosity (i.e., the viscosity will not increase even along the passage of time) can be obtained if the resulting copolymer is added to the slip. If it is used in any amounts greater than 10 wt.%. the mold releasing characteristics will be lowered upon slip casting and the gypsum mold will be clotted, resulting in a reduction to the service life of the mold.It is thus not preferred to use the monomer C in any amounts outside the above range.

As the monomer C, besides the above-mentioned compounds, it is possible to use, for example, acrylic esters such as methyl acrylate, ethyl acrylate, n-butyl acrylate, 2-ethylhexyl acrylate, octyl acrylate, methoxyethyl acrylate, butoxyethyl acrylate, cyclohexyl acrylate and furfuryl acrylate; methacrylic esters such as methyl methacrylate, ethyl methacrylate, butyl methacrylate, methoxyethyl methacrylate, ethoxy methacrylate, butoxyethyl methacrylate and benzyl methacrylate; aromatic vinyl monomers such as styrene, o-methylstyrene and para-methylstyrene; vinyl esters such as vinyl acetate and vinyl propionate, nitriles such as acrylonitrile and methacrylonitrile; and besides, vinyl chloride, ethylene, butadiene and the like.

The aqueous emulsion of the specific copolymer is an emulsion of a copolymer which contains the monomer C as its principal constituent unit as mentioned above. As a preferable aqueous emulsion, may be mentioned an aqueous emulsion of a copolymer obtained by effecting copolymerization, especially, while using, as the monomer C, an acrylic ester, a styrene-acrylic ester mixture, a styrene-butadiene mixture, a methyl methacrylate-butadiene mixture or a styrene-methyl methacrylate-butadiene mixture.

When a surfactant is incorporated in the aqueous emulsion of the specific copolymer, its amount is preferably limited below 1.0 wt.% based on the total weight of the monomers. The polymer particle of the emulsion may be 0.05 - 0.6 slum, with the range of 0.1 - 0.25 sLm being particularly preferred. If the amount of the surfactant exceeds 1 wt.% or the particle size of the emulsion becomes greater than 0.6 1m, the viscosity of a slip will be lowered, but such effects as excellent mold releasirg characteristics of the resulting cast product and prolonged service life of the gypsum mold will not be fully exhibited when the resultant aqueous emulsion is added to the slip.If the particle size of the emulsion is smaller than 0.05 Fm on the other hand, a slip which contains the resultant aqueous emulsion added thereto may have higher viscosity and its fluidity may thus be reduced.

The ceramics-forming composition prepared by adding the aqeuous emulsion of the specific copolymerto a slip containing a body for pottery or a ceramic material as its principal constituent is extremely stable and has low viscosity and good fluidity, in other words, has excellent formability. Rest ining formed or cast products have excellent mechanical strength. Moreover, when this composition is used in the form of a slip, the mold releasing characteristics are particularly improved upon effecting slip casting and at the same time, the service life of the slip casting gypsum mold can be prolonged to a significant extent.

The above-described excellent effects of the composition, which makes use of the aqueous emulsion of the specific copolymer, may be atributed to the fact that in the composition, some sort of interaction is developed between the inorganic particles of the body for pottery orthe ceramic material and copolymer droplets of the aqueous emulsion and as a result, the copolymer particles are adsorbed on the inorganic particles. This is suggested by the following two phenomena.

As the first phenomenon, the above composition, namely, the slip was added with water to dilute its solid concentration to about 50 - 70%. When the thus-diluted slip was left over for 3 days to 1 week, a colorless and clear water layer was formed as a supernatant. The water layer contained almost no particles of emulsion. It is assumed that the polymer particles of the emulsion were adsorbed on the inorganic particles and were thus caused to precipitate together with the inorganic particles. On the other hand, a similar slip was prepared by using an aqueous emulsion of a copolymer other than the aqueous emulsion of the specific copolymer, namely, an aqueous emulsion of a homopolymer or copolymer which did not contain the monomer A and our monomer B as its constituent monomer unit or units. A similar test was conducted on the slip.A water layer which was formed as a supernatant by allowing the slip to stand was clouded and not clear. It still contained a substantial amount of polymer particles of the emulsion.

As the second phenomenon, the composition making use of the aqueous emulsion of the specific copolymer was compressed in a filter press. Practically colorless and clear water was squeezed out. The thus-obtained water did not contain polymer particles of the emulsion. On the other hand, a similar slip was prepared by using an aqueous emulsion of a copolymer other than the aqueous emulsion of the specific copolymer, namely, an aqueous emulsion of a homopolymer or copolymerwhich did not contain the monomer A andlor monomer B as its constituent monomer unit or units. When the slip composition was compressed in the filter press, clouded and unclear water which contained a substantial amount of polymer particles of the emulsion was squeezed out.

As suggested by the above-described phenomena. carboxyl groups and/or alkoxymethylene groups contained in polymer particles may be serving as a cause for the adsorption phenomenon of polymer particles to inorganic particles although it has not been fully elucidated on what mechanism the interaction induced between the inorganic particles of the body for pottery or the ceramic material and the droplets of the specific copolymer of the aqueous emulsion is dependent.

The present invention will hereinafter be described specifically by the following Examples. Needless to say, the following Examples illustrate a small part of the present invention only. In the Examples, all designations of "%" and "part" and "'parts" mean wt.% and part or parts by weight.

Example 1: To a low-clay pottery body (product of Marui Tohryo Kabushiki Kaisha; Special Grade Body) as a body for pottery, water glass No. 1 was added in an amount of 0.41 % based on dry solids of the body, followed by a further addition, mixing and stirring of water to obtain a slip having a solid content of 68.4%.Portions of the slip were respectively added with resin emulsions A (an acrylic resin emulsion containing a copolymer obtained from styrene and 2-ethylhexyl acrylate as its principal monomer component; solid content: 43%), B (a carboxyl-modified acrylic resin emulsion containing a copolymer obtained from styrene and 2-ethylhexyl acrylate as its principal monomer component; solid content: 43%), C (a synthetic rubber emulsion containing a copolymer obtained from styrene, methyl methacrylate and butadiene as its principal monomer component; solid content: 43%) and D (a vinyl acetate resin emulsion containing polyvinyl acetate as its principal component; solid content" 43%) as shown in Table 1. The resultant mixtures were mixed and stirred to obtain homogeneous slips.

The slips were respectively poured into gypsum molds, each, of 90 mm long, 20 mm wide and 5 mm thick.

After allowing the slips to stand there until deposit of ceramic particles were built up on the corresponding mold surfaces, the thus-cast products were released from the gypsum molds. Thereafter, they were dried respectively at room temperature and 110"C to obtain cast products having the dry bending strength shown in Table 1. The slip cast products were then fired to obtain excellent ceramic products. By the way, the bending strength were measured by means of "Tensilon UTM-lll-500" (trade name; manufactured by Toyo-Baldwin Co., Ltd.).

TABLE 1 Type of Added amount (%) Dry bending strength resin (emulsion/absolute (kgficm2) emulsion dry body) Dried at Dried at room temp. 110 C 1 22 21 A 3 42 44 5 55 57 B 5 50 58 C 3 35 33 D 3 18 20 not added 0 12 13 Besides, a portion of the slip was subjected slip casting without addition of any resin emulsion. The resultant cast product was biscuit-fired at 800"C. The bending strength of the biscuit-fired product was 36 kgf/cm2.

Example 2: To a clay-contained body (product of Marui Tohryo Kabushiki Kaisha; Body No. 30) as a body for pottery, water glass No. 1 was added in an amount of 0.26 % based on dry solids of the body, followed by a further addition, mixing and stirring of water to obtain a slip having a solid content of 69.1%. Portions of the slip were respectively added with the resin emulsion A employed in Example 1 as shown in Table 2 to obtain cast bodies in the same manner as in Example 1. They were then dried to obtain cast products having the dry bending strength shown in Table 2. It was possible to obtain excellent ceramic products by firing the cast products.

TABLE 2 Type of Added amount { /O) Dry ben ding strength resin (emulsion/absolute (kgflcm2) emulsion dry body) Dried at Dried at room temp. 110 C 1 25 24 A 3 46 45 5 54 56 not added 0 17 17 Besides, a portion of the slip was subjected slip casting without addition of any resin emulsion. The resultant cast product was biscuit-fired at 800 C. The dry bending strength of the biscuit-fired product was 41 kgf/cm2.

Example 3: Five kilograms of alumina powder ("A-16 SG, trade name; product of Aluminium Company of America) and 5 kg of alumina powder ("A-32", trade name; product of Nippon Light metal Co., Ltd.) were weighed to obtain 10 kg of an alumina powder mixture. The alumina powder mixture was added with 60 g of a deflocculant ("Seruna D-305", trade name; product of Chukyo Yushi Kabushiki Kaisha) and water. The resultant mixture was then stirred to obtain a slip having a solid content of 81.4%.

To portions of the slip, the resin emulsions A, B, C and D, which were employed in Example 1, and a resin emulsion E (an acrylic resin emulsion containing a polymer obtained from n-butyl methacrylate as its principal monomer component; solid content: 43%) were respectively added as shown in Table 3. Following the procedures of Example 1, cast products were obtained and then dried to obtain cast products having the dry bending strength shown in Table 3. It was able to obtain excellent ceramic products by firing the above cast products.

TABLE 3 Type of Added amount (%) Dry bending strength resin (emulsion/absolute (kgficm2) emulsion dry body) Dried at 11û C A 3 39 1 31 B 3 58 5 84 C 3 41 D 3 45 E 3 86 not added 0 11 Example 4: To silica (siliceous stone imported from Republic of China), a deflocculant ("Seruna D-305", trade name; product of Chukyo Yushi Kabushiki Kaisha) in an amount of 0.6% based on the dry solids of the ceramic material. The resultant mixture was added further with water, followed by its stirring into a slip having a solid content of 68.9%. Portions of the slip were respectively added with the resin emulsions B, C and D, which were employed in Example 1, as shown in Table 4. Following the procedures of Example 1, cast products were obtained. They were then dried to obtain cast products having the dry bending strength shown in Table 4.

TABLE 4 Type of Added amount { /O) Dry bending strength resin {emulsion/absolute (kgf/cm2) emulsion dry body) Dried at 1 110 C B 3 47 C 3 29 D 3 21 not added 0 8 Example 5: To 10 kg of Zirconia ("TZ-3Y, trade name; product of Toyo Soda Mfg. Co., Ltd.), 200 g of a deflocculant ("Seruna D-305", trade name; product of Chukyo Yushi Kabushiki Kaisha) and water were added to obtain a slip having a solid content of 71.4%. Portions of the slip were respectively added with the resin emulsions A and D, which were employed in Example 1, as shown in Table 5. Following the procedures of Example 1, cast products were obtained. They ere then dried to obtain cast products having the dry bending strength shown in Table 5.It was able to obtain excellent ceramic products by firing the cast products.

TABLE 5 Type of Added amount (%) Dry bending strength resin (emulsion/absolute Fkgflcm2) emulsion dry body) Dried at 110 C A 3 44 D 3 42 not added 0 22 Example 6: To 1000 g of p-form silicon carbide powder ("Betarundum Ultrafine", trade name; product of Ibiden Co., Ltd.), 3 g of boron (product of Mitsuwa Kagaku Kabushiki Kaisha), 3 g of a deflocculant ("SMA 1440H", trade name; product of ARCO Chemical Company; ammonium salt of a styrene-monoester of maleic acid copolymer), 10 g of a 70% aqueous solution of monoethylamine (product of Kishida Chemical Co., Ltd.) and water to obtain a slip having a solid content of 65%.

The slip was added with the resin emulsion A, which was employed in Example 1, as shown in Table 6.

Following the procedures of Example 1, a cast product was obtained. It was then dried to obtain a cast product having the dry bending strength shown in Table 6.

TABLE 6 Type of Added amount (%) Dry bending strength resin (emulsion/absolute (kgf'cm2) emulsion dry body) Dried at llO0C A 3 20 not added 0 4 Example 7: A cast product was obtained in the same manner as in Example 6 except that upon preparation of a slip, 100 g of an emulsion of a phenol resin (molar ratio of formaldehyde to phenol: 2; solid content: 50%).

Thereafter, it was sintered at 21 20 C to obtain a sintered product having a density equivalent to 98% of its theoretical density.

Example 8: To 1000 g of rouge ("NSK-500", trade name; product of Morishita Bengara Kogyo Kabushiki Kaisha), 20 g of a deflocculant ("SN Dispersant 5020", trade name; product of Sun Nopco Ltd.) and water were added. The resultant mixture was then stirred to obtain a slip having a solid content of 70%.

Portions of the slip were then added with the resin emulsions A, C and D, which were employed in Example 1, as shown in Table 7. Following the procedures of Example 1, cast products were obtained. They were then dried to obtain cast products having the dry bending strength shown in Table 7.

TABLE 7 Type of Added amount {%) Dry bending strength resin femulsionlabsolute (kgf/cm2) emulsion dry body) Dried at I 110 C A 3 65 C 3 70 D 3 64 notadded 0 35 Example 9: Following the same preparation procedure as that described in Example 3, a slip having a solid content of 81.4% was obtained by using the same raw materials as those described in Example 3.

To the slip, an acrylic resin emulsion F prepared in accordance with the below-described preparation process was added in an amount of 3% based on the dry ceramic material. The resultant mixture was stirred to obtain a homogeneous slip. This slip was poured into a gypsum mold, and it was then allowed to stand there for 0.5 hour so that a deposit of ceramic particles was caused to deposit on the mold wall. The resulting cast product was thereafter released from the mold and dried at 110"C for 1 hour, thereby obtaining a green cast product for a cup portion. The cast product had sufficient green strength.

In the same manner, a green cast product for its matching handle portion was also obtained. The cup portion and handle portions were both wetted with water at surfaces where they were to be jointed together.

Immediately after that, the above slip was coated to the surfaces by a trowel. They were then put together.

Thereafter, the thus-jointed product was dried at 11 out for 30 minutes, followed by its firing at 1 7000C for 4 hours. A alumina-base coffee cup was obtained. The bonding strength between the handle portion and the cup portion of the coffee cup was high. It showed extremely large impact strength.

Preparation of acrylic Resin Emulsion F: Placed in a 5-necked flask fitted with a stirring blade, thermometer, reflux condenser, dropping funnel and nitrogen-feeding line were 500 parts of water and 4 parts of an anionic emulsifier. The internal temperature of the system was raised to 80CC, at which 5 parts of potassium persulfate were added. The contents were stirred until the potassium persulfate was dissolved.

Thereafter, a liquid mixture consisting of 240 parts of methyl methacrylate, 740 parts of ethyl acrylate, 20 parts of hydroxyethyl methacrylate, 1 part of an anionic emulsifier and 500 parts of water was added dropwise over 4 hours from the dropping funnel. After completion of the dropwise addition, the contents were maintained at the temperature of 80 C for further 3 hours. Then, it was cooled. When the internal temperature had become below 30"C, aqueous ammonia was added to adjust the pH to 9. Water was thereafter added to obtain the acrylic resin emulsion having a solid content of 42%.

Comparative Example 1: It was attempted to obtain a cup in the same manner as in Example 9 except that a slip added with no deflocculant and organic binder was used. The cup was separated at its jointed parts. It was thus unable to obtain any satisfactory fired product.

Example 10: Following the same preparation procedure as that described in Example 4, a slip having a solid content of 68.9% was obtained by using the same raw materials as those described in Example 4.

To the slip, an acrylic resin emulsion G prepared in accordance with the below-described preparation process was added in an amount of 3% based on the absolute dry ceramic material. The resultant mixture was stirred to obtain a homogeneous slip. Thereafter, cast products were obtained in the same manner as in Example 9. They were jointed together and were then fired. A coffee cup having high bonding strength between its handle portion and cup portion and showing extremely large impact strength was obtained.

Preparation of acrylic Resin Emulsion G: Following the same procedures as those employed upon preparation of the acrylic resin emulsion F except that the composition of the monomers was changed to 500 parts of styrene and 500 parts of 2-ethylhexyl acrylate, the acrylic resin emulsion G was obtained.

Example 11: A coffee cup was obtained in the same manner as in Example 10 except that a synthetic rubber resin emulsion H, which had been prepared by the below-described preparation process, was used as a resin emulsion. This coffee cup had high bonding strength between its handle portion and cup portion and showed extremely large impact strength.

Preparation ofSynthetic Rubber Resin Emulsion H: Charged in a polymerization pressure tank made of stainless steel and fitted with a stirring blade and thermometer, were 1000 parts of water, 10 parts of sodium dodecylbenzenesulfonate, 7 parts of potassium persulfate, 480 parts of styrene, 200 parts of methyl methacrylate, 300 parts of butadiene and 20 parts of acrylic acid. After maintaining the contents at 700C for 12 hours, they were cooled. When the internal temperature had dropped below 30"C, aqueous ammonia was added to adjust the pH to 9, followed by an addition of water to obtain the synthetic rubber resin emulsion H having a solid content of 42%.

Example 12: Following the same preparation procedure as that described in Example 5, a slip having a solid content of 71.4% was obtained by using the same raw materials as those described in Example 5.

To the slip, the acrylic resin emulsion F was added in an amount of 3% based on the absolute dry ceramic material. The resultant mixture was stirred to obtain a homogeneous slip. Thereafter, cast products were obtained in the same manner as in Example 9. They were jointed together and were then fired at 1 5500C for 3 hours. A coffee cup having high bonding strength between its handle portion and cup portion and showing extremely large impact strength was obtained.

Example 13: Following the same preparation procedure as that described in Example 6, a slip having a solid content of 65% was obtained by using the same raw materials as those described in Example 6.

To the slip, were added the acrylic resin emulsion G in an amount of 3% based on the absolute dry ceramic material and 100 g of a phenol resin emulsion (molar ratio of formaldehyde to phenol: 2; solid content: 50%).

The resultant mixture was stirred to obtain a homogeneous slip. Thereafter, cast products were obtained in the same manner as in Example 9. They were jointed together and were then fired at 21 500C for 15 minutes.

A coffee cup having high bonding strength between its handle portion and cup portion and showing extremely large impact strength was obtained.

Example 14: Following the same preparation procedure as that described in Example 1, a slip having a solid content of 68.4% was obtained by using the same raw materials as those described in Example 1. Portions of the slip were added respectively with aqueous emulsions (solid content: 43%) of copolymers which contained, as their constituent units, the monomers shown in Table 8(1) to Table 8(3) in their respective proportions also given there. The resultant mixtures were stirred to obtain homogeneous slips.

The slips were respectively poured into gypsum molds, each, of 90 mm long, 20 mm wide and 5 mm thick.

After allowing deposits of ceramic particles to build up on the corresponding mold walls, the resultant cast products were released from their corresponding molds. Upon release of the cast products, each of the cast products was investigated whether it showed good mold releasing characteristics or not and whether the thus-released cast product had good shape-retaining characteristics or not (namely, whether it did not develop cuts or deformation). After allowing them to stand at room temperature for their drying, their strength were measured. As to their strength, their bending strength was measured by using "Tensilon UTM-lll-500" (trade name; manufactured by Toyo-Baldwin Co., Ltd.). The thus-obtained cast products were then fired to obtain ceramic products.In the case of ceramic products obtained respectively from cast products resulted from compositions prepared by adding aqueous emulsions of copolymers in which the proportions of their respective monomers given in Table 8 satisfied their corresponding proportion ranges specified in pages 21 - 22 of the present specification, the ceramic products were all superb.

As an evaluation method for the service life of each gypsum mold, the service life was judged by the following 5-stage ranking system on the basis of the upper limit of the number of successful slip casting operations for its corresponding slip.

Excellent: 100 times and up Good: 70 - 99 times Fair: 69 - 40 times Poor: 39 - 20 times Unaccept able: 19 times and less.

In each evaluation, the upper limit of the number of successful slip casting operations was determined by taking, into parallel consideration, the mold releasing characteristics of cast products upon their release from the mold, the shape-retaining characteristics of the cast product after their release, and the extent of roughness of the surface of the gypsum mold after their release. Incidentally, the shape-retaining characteristics were visually determined depending whether cast products contained cuts, deformation and the like which were possibly developed upon their release from their corresponding molds.

Evaluation results are summarized in Tables 9(1) through 9(3), in which A indicates Examples making use of aqueous emulsions of the above-described specific copolymers while B indicates Examples making use of aqueous emulsions of copolymers not meeting the above-described proportion ranges for monomers. In Table 8, the amount of the surfactant contained in each aqueous emulsion which was added to the corresponding slip is expressed per 100 parts by weight of the total amount of the monomers employed for obtaining the corresponding copolymer. Average droplet size of each emulsion is also given there.

TABLE 8(1)

o cu n o; B o n B A B A cu' ci o SC m 0.07 ID 2 5 t 14 16 5 7 Acrylic acid 5 Q amide 0.07 0.2 4 6 o amide 2 3 0f) t ID ~ C O amide 3 .2 Hydroxyethyl b C*l M) m cv s 2-Ethylhexyl 50 50 J 50 50 50 50 50 55 55 55 55 55 55 50 50 55 E CN tr) t E b o methacrylate o Styrene 50 49.93 49.8 48.0 45.0 40.0 36.0 34.0 45 44.93 44.8 44.0 41.0 39.0 43.0 42.0 35 O Sle r co O t surfactant ~ LD 0O 0 b B O to O dv w S O S ~ 1D t 00 O t ~ S O N 00 Sl N SX e O t 1 > cs O O n St (9 &commat; 1 O O O F > Q =s E > > c m (L) c 2 Z X I F cs F m m < uo!X!sodLuoD ja uouoW TABLE 8(2)

A A Methacrylic acid Acrylicacid 5 5 5 5 5 5 5 5 5 5 5 Methacrylicamide 2 2 2 2 2 2 2 2 2 2 2 C Acrylicamide .9 Hydroxyethyl 3 " acrylate B (r) ) 0 m 0 z 2-Ethylhexyl S N 50 50 n c OC n-Butylacrylate O n coc co methacrylate CD 42.9 09 S Z U) N 33 X 33 33 co cr, Amount of 0.4 0.4 0.4 0.4 0.4 0.4 0.4 0.3 0.3 0.3 0.3 surfactant R particle S O r o;o; size (m) a S N O O n cg O t C\l Ln N S O CO LO n D > O t d LD CS LD t l O CS LD sl S B LtS) CoW > > F e > X O X X ss O > > Q F s > s > , > s s > s s a) (3 0 . ~ > z I F N X C E F m 6 uo UO!l!SOdWOD J8W0U0W TABLE 8(3)

o 3 mcu o ni cj n A A hl CU z u) (30) O r ci Ln ~ acid O CS cr, c: cj ~ acid 5 t Methacrylicamide 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 t S N O O o ~ tD /31 o LON O m o: o' u, o CS S LD N O LO b 0 acrylate 6 B uz E 0C CD c ci t Styrene 43 N O 43 43 43 43 43 43 43 43 43 43 43 43 T t(j Ln cu o m cj Ln t co 5:: co u) surfactant 0 size (D X o LD ~ co A S N o n ~ S t oo ~ co o E S cs so e ID CN t 6 t [ o t 4W rO F > F > > ss O F < c c ' , c a) O X > ( C c > , c > r c s > , *,s, O g s t 2 < Z X I cC N X c: m < O) uo!;!sodwos ]3WoUoW TABLE 9(1) Mold Shape Dry Service releasing retaining bending life of charac- charac- stength gypsum teristics teristics (kgflcm2) mold (1) poor poor 35 poor B slightly (2) poor poor 37 fair (3) good good 43 good (4) good good 45 excellent A (5) good good 47 excellent (6) good good 44 excellent (7) good good 45 fair B (8) poor poor 43 unacceptable (9) poor poor 38 poor B slightly (10) poor poor 41 fair (11) good good 43 good A (12) good good 45 excellent (13) good good 47 excellent B (14) poor poor 37 unacceptable (15) good good 47 excellent A (16) good good 45 excellent (17) good good 46 excellent TABLE 9(2) Mold Shape Dry Service releasing retaining bending life of charac- charac- strength gypsum teristics teristics (kgflcm2) mold (18) good good 42 excellent (19) good good 45 excellent (20) good good 46 excellent A (21) good good 44 excellent (22) good good 43 good (23) poor relatively 41 poor good A (24) good good 47 excellent (25) good good 43 excellent (26) good good 40 excellent A (27) good good 41 excellent (28) good good 45 excellent TABLE 9(3) Mold Shape Dry Service releasing retaining bending life of charac- charac- strength gypsum teristics teristics (kgflcm2) mold (29) poor good 49 poor (30) good good 46 fair (31) good good 44 good (32) good good 43 excellent A (33) good good 44 excellent (34) good good 42 excellent (35) good good 40 good (36) slightly relatively 39 fair poor good (37) poor poor 37 poor (38) good good 43 excellent (39) good good 47 excellent (40) good good 45 excellent A (41) good good 43 excellent (42) good good 41 good (43) slightly relatively 38 fair poor good (44) poor poor 35 poor In the above Examples, the preparation of the aqueous emulsions described in Table 8(3) were carried out by effecting emulsion polymerization on reaction mixtures which had been prepared by using anionic surfactants in accordance with a usual reaction mixture for emulsion polymeriziation. The control 6f the droplet size of each emulsion was effected in a usual manner, namely, by adjusting the concentration of the corresponding surfactant at the beginning of the polymerization reaction.

Example 15: Using "No 22 Body" and "No. 30 Body" (trade names; both, products of Marui Tohryo Kabushiki Kaisha) and "New Bone No. 57 Body" and "New Bone No. 60 Body" (trade names. both, products of Yamaka Tohryo Kabushiki Kaisha) as bodies for pottery, Water Glass No. 1 was added in an amount of 0.26% based on the dry solids of the bodies, followed by further addition of water. The resultant mixture were respectively stirred to obtain slips having a solid content of 69.1%. To each of the slips, the aqueous emulsion (solid content: 43%) having the composition given in (5) of Table 8(1) in Example 14was added in an amount of 3% based on the absolute dry weight of the body. Following the procedure of Example 14, cast products were obtained. They were evaluated in the same manner as in Example 14.Results are given in Table 10.

TABLE 10 A (2) (2) (3) (4) Mold releasing good good good good characteristics Shape-retaining good good good good characteristics Dry bending strength 48 46 45 43 (kgf/cm2) Service life of gypsum mold excellent excellent excellent excellent Note: (1) "No. 22 Body" of Marui Tohryo K.K.

(2) "No. 30 Body" of Marui Tohryo K.K.

(3) "New Bone No.57 Body" of Yamaka Tohryo K.K.

(4) "New Bone No.60 Body" of Yamaka Tohryo K.K.

Example 16: In the same preparation method as that described in Example 3, a slip having a solid content of 81.4% was prepared by using the same raw materials as those described in Example 3. Portions of the slip were respectively added with the aqueous emulsions (solid content: 43%) of the compositions given respectively in (1) to (43) of Example 14, each, in an amount of 3% based on the absolutely-dried alumina powder mixture. The slips were subjected to slip casting in the same manner as in Example 14. They were evaluated in the same manner as in Example 14, except that in the present Example, the dry bending strength of each cast product was measured after drying it at 110"C and it was shown as dry bending strength.Results are given in Tables 11(1) through 11(3), in which A also indicates Examples making use of aqueous emulsions of the above-described specific copolymers while B also indicates Examples making use of aqueous emulsions of copolymers not meeting the above-described proportion ranges for monomers.

TABLE 11(1) Mold Shape Dry Service releasing retaining bending life of charac- charac- strength gypsum teristics teristics Rkgflcm2) mold B (1) poor poor 38 poor (2) poor poor 40 fair (3) good good 48 excellent (4) good good 52 excellent A (5) good good 56 excellent (6) good good 55 good (7) good good 50 fair B (8) poor poor 46 unacceptable (9) poor poor 36 poor B (10) poor poor 38 fair (11) good good 51 excellent A (12) good good 55 excellent (13) good good 57 good B (14) poor poor 49 unacceptable (15) good good 58 excellent A (16) good good 56 excellent (17) good good 57 excellent TABLE 11(2) Mold Shape Dry Service releasing retaining bending life of charac- charac- strength gypsum teristics teristics (kgf/cm2) mold (18) good good 55 excellent (19) good good 57 excellent (20) good good 58 excellent A (21) good good 54 excellent (22) good good 52 good (23) poor poor 48 poor A (24) good good 53 excellent (25) good good 56 excellent (26) good good 53 excellent A (27) good good 55 excellent (28) good good 57 excellent TABLE 11(3) Mold Shape Dry Service releasing retaining bending life of charac- charac- strength gypsum teristics teristics (kgflcm2) mold (29) poor good 53 unacceptable (30) good good 54 fair (31) good good 52 good (32) good gqod 55 excellent A (33) good good 58 excellent (34) good good 57 excellent (35) good good 52 good (36) good poor 50 poor (37) poor poor 47 fair (38) good good 53 excellent (39) good good 58 excellent (40) good good 56 excellent A (41) good good 53 excellent (42) slightly relatively 51 good poor good (43) poor poor 47 poor (44) poor poor 45 unacceptable Example 17:: Using silica (siliceous stone imported from Republic of China), zirconia ("TZ-3Y", trade name; product of Toyo Soda Mfg. Co., Ltd.) and form silicon carbide ("Betarundum Ultrafine", trade name; product of Ibiden Co., Ltd.) as ceramic materials, slips suitable for use in slip casting were prepared in the manner described below. Each of the slips was added with the aqueous emulsion (solid content: 43%) of the composition given in (5) of Example 14 in an amount of 3% based on the dry ceramic material. The thus prepared slips were subjected to slip casting in the same manner as in Example 16. Results of their evaluation, which were carried out in the same manner as in Example 16, are given in Table 12.

Preparation Process of Slips for Slip Casting: (a) Silica (siliceous stone imported from Republic of China): To the silica (siliceous stone imported from Republic of China), a deflocculant ("Seruna D-305", trade name; product of Chukyo Yushi Kabushiki Kaisha) was added in an amount of 0.6% based on the dry solids of the ceramic material. Water was also added. The resultant mixture was stirred to obtain a slip having a solid content of 68.9%.

(b) Zirconia: To 10 kg of zirconia ("TZ-3Y", trade name; product of Toyl Soda Mfg. Co., Ltd.), were added 200 g of a deflocculant ("Seruna D-305", trade name; product of Chukyo Yushi Kabushiki Kaisha) and water. The resultant mixture was stirred to obtain a slip having a solid content of 71.4%.

(c) form silicon carbide: Added to 1000 g of p-form silicon carbide ("Betarundum Ultrafine", trade name; product of Ibiden Co., Ltd.) were 3 g of boron (product of Mitsuwa Kagaku Kabushiki Kaisha), 5 g of a deflocculant ("SN Dispersant 5045", trade name; product of Sun Nopco Kabushiki Kaisha), 10 g of a 10% aqueous solution of monoethylamine (product of Kishida Chemical Co., Ltd.) and water. The resultant mixture was stirred to obtain a slip having a solid content of 65%.

TABLE 12 A (a) (b) (c) Mold releasing good good good characteristics Shape-retaining characteristics good good good Dry bending strength 47 44 26 (kgf/cm2) Service life of gypsum mold excellent excellent excellent As demonstrated in Examples 14through 17, by conducting slip casting on slip compositions added with aqueous emulsions of such specific copolymers, cast products having improved dry strength can be obtained. Moreover, when the cast products are released from their corresponding molds, they show excellent mold releasing characteristics and shape-retaining characteristics. It is thus possible to improve the yield of cast products to a significant extent and at the same time, to prolong service life of each gypsum mold. It is therefore feasible to produce excellent cast products with a high degree of efficiency when they are produced by slip casting in accordance with the casting process of this invention.

Claims (10)

1. A ceramics-forming composition formed by mixing a resin emulsion with a slip which contains a body for pottery or a ceramic material as a principal constituent.

2. A ceramics-forming composition as claimed in claim 1, wherein the resin emulsion is an aqueous emulsion of a copolymer composed of: A) 0.1 - 15 wt.% of a carboxyl-containing monomer unit and/or B) 0.1 - 5 wt.% of a substituted or unsubstituted carbamoyl-containing monomer unit represented by the following general formula:

wherein R1 and R2 may be the same or different and mean individually a hydrogen atom or methyl group, and Rg denotes a hydrogen atom, a C1 -C4 alkyl group or a hydroxymethylene or alkoxymethylene group represented by the following general formula: CH2OR4 wherein R4 means a hydrogen atom or C1-C4 alkyl group; and C) 85 - 99.9 wt.% of one or more other monomer units copolymerizable with the monomer specified in A) and/or B) above.

3. A ceramics-forming composition as claimed in claim 2, wherein at least one of said other monomers is a hydroxyl containing monomer.

4. A ceramics-forming composition as claimed in claim 2 or claim 3, wherein the aqueous emulsion has an average droplet particle of 0.05 - 0.6 FLm.

5. A process for forming ceramics, which comprises subjecting the composition of any one of the preceding claims to slip casting.

6. A process for forming ceramics, which comprises subjecting the composition of any one of the preceding claims to jiggering, jolleying or potter's wheeling.

7. A process for processing a cast ceramic product, which process comproses the following consecutive steps: a) mixing a resin emulsion with a slip which contains a ceramic material as a principal constituent, thereby preparing a slip composition; b) forming two or more cast products with the slip composition in accordance with a slip casting process, said cast products having the same or different configurations and being in such a matching relation that said cast products include at least one set of matching surfaces to be jointed to each other; c) applying a jointing medium, which contains a ceramic material and a resin emulsion as principal components, to at least one of the matching surfaces of the cast products; d) jointing the matching surfaces of the cast products so as to joint the cast products into a united cast product; and e) firing the united cast product

8. A ceramics forming composition substantially as described herein.

9. A process for forming ceramics substantially as described herein.

10. A process for processing a cast ceramic product substantially as described herein.