JPH0891943A - Ceramic composition and production of ceramic product - Google Patents

Abstract

PURPOSE: To produce a ceramic product excellent in mass production, having stable qualities free from defects such as burn-off, crack and weld line. CONSTITUTION: Ceramic powder is mixed with ice of water made into fine particles having the same particle size as that of the ceramic powder or ice of water mixed with 1-5 pts.wt. of polyvinyl alcohol based on 100 pts.wt. of water in an atmosphere at <=0 deg.C to form a ceramic composition. The ceramic composition is injected from an injection molding machine laid in an atmosphere at <=0 deg.C to a mold similarly laid in an atmosphere at <=0 deg.C to form a green molded article. The green molded article is dried and baked to give the objective ceramic product.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a ceramic composition and a method for producing a ceramic product. More specifically, the present invention relates to a ceramic composition comprising a mixture of ceramic powder and a binder, and a green compact from the ceramic composition. The present invention relates to a method for producing a ceramic product, in which a binder is removed from the green molded body and then fired to obtain a ceramic product.

[0002]

2. Description of the Related Art Ceramics are mechanically wear-resistant,
It has been widely used in recent years because it is excellent in heat resistance, heat insulation, and the like, electrically excellent in insulation, and chemically stable. As a method for manufacturing a ceramic product, an injection molding method is also known, as is well known in the art and disclosed in Japanese Patent Laid-Open No. 3-290374. According to this injection molding method, it is possible to mass-produce a product having a complicated shape as compared with, for example, a hot pressing method, a rubber pressing method, a casting molding method, etc. Moreover, since finishing machining is hardly required, This injection molding method is a very advantageous manufacturing method. The injection molding method is carried out by using an organic binder such as polyethylene, in order to give the ceramic powder a fluidizing action, a plasticizing action, a wetting action, a hardening action and the like.
Polystyrene, polypropylene, etc. are added and kneaded, and the resulting mixture is injected into a mold to form a green molded body having a desired shape. The organic binder is removed from the green molded body, and then the green molded body is baked. We are obtaining ceramic products. By the way, as is clear from the above explanation,
The organic binder has various functions, but one of the main functions is to keep the green molded body in a predetermined shape until the obtained green molded body is fired in a furnace. If it remains in the body, it reacts with the ceramic powder during firing or softens and melts, or the gas generated by decomposition is trapped inside,
Defects such as swelling, cracking, or deformation occur, which adversely affects the ceramic products. Therefore, a degreasing step of removing the organic binder from the green compact is performed before firing.

The degreasing method for removing the organic binder from the green molded body is well known without mentioning the name of the literature, and it is a method of degreasing by heating in an inert atmosphere or a vacuum atmosphere, a method of degreasing in a solvent, and infrared rays. There is known a method of irradiating with and decomposing the organic binder.

[0004]

As described above, by using the organic binder, the ceramic powder can be imparted with fluidity, plasticizing action, hardening action and the like, and a green molded body can be formed by injection. . Further, before firing the green compact, it is possible to remove the organic binder harmful to the ceramic product by appropriately adopting a known degreasing method for the organic binder. However, the method of manufacturing a ceramic product using an organic binder has various problems or drawbacks. For example, when a thermoplastic resin is used as the organic binder, the ceramic powder added with a sintering aid as necessary, the thermoplastic resin as the organic binder, the lubricant and the plasticizer, the melting temperature of the thermoplastic resin There is a drawback that it is necessary to mix and knead at a high temperature in the vicinity for a long time, for example, several tens minutes to 2 hours. Moreover, if the order of introducing the organic binder is changed or the mixing and kneading time is changed, the fluidity of the composition of the ceramic powder and the organic binder is changed, and other molding conditions are the same,
There is a problem that the quality of ceramic products changes and the quality is not stable.

When a composition of ceramic powder and an organic binder is injection-molded, the organic binder is used as described above in order to provide appropriate heat fluidity and moldability. Is difficult to select, and defects such as sink marks, cracks, and welds may occur in the ceramic product depending on the type of organic binder. Further, since the thermoplastic resin used as the organic binder generally has a high melt viscosity, it has a low affinity with the ceramic powder having a small particle diameter, and the addition rate of the organic binder cannot be lowered. That is, the amount of organic binder added must be increased. When the addition amount increases,
In the degreasing step of removing the organic binder from the green compact, defects are likely to occur, and the shrinkage dimension of the ceramic product also becomes large, resulting in variation in dimension. Further, it becomes impossible to obtain a high-density ceramic product.

The constituent elements of the organic binder are carbon, hydrogen,
Nitrogen, oxygen, and the like, which are degreased when they remain in the green molded body, since they hinder the characteristics of the ceramic product, but there is also a problem in degreasing. As for degreasing, as described above, a method of degreasing in a solvent, a method of decomposing an organic binder by irradiating infrared rays, etc. are known, but there are problems of solvent treatment, cost problems, etc. It is generally advantageous to heat the organic binder to pyrolyze the organic binder and to volatilize it. When the green molded body is rapidly heated by this method, the green molded body is locally heated, and the organic binder in the green molded body is softened and melted, or the gas generated by the decomposition is trapped inside. As a result, defects such as swelling, cracks, and deformation may occur in the green molded body. Therefore, degreasing must be performed at an extremely slow rate of temperature rise per unit time of about 0.5 to 10 ° C / H, and it takes a long time of several tens to several hundreds of hours, and the rate of temperature rise is high. Must be carefully controlled and degreased. As described above, the degreasing process is complicated, and as a result, it is a major impediment factor in industrially mass-producing ceramic products. Also,
In the degreasing step, since a large amount of green compacts are degreased at once, there is a problem of environmental pollution of a large amount of harmful gas generated from the organic binder.

Accordingly, the present invention provides a ceramic composition and a method for producing a ceramic product, which solves the conventional problems as described above, even though the present invention is produced by an injection molding method which is advantageous as a method for producing a ceramic product. Specifically, the ceramic product obtained is stable in quality, has no defects such as sink marks, cracks, and well lands, and the degreasing step can be omitted. Furthermore, the ceramic composition is excellent in mass production. And it aims at providing the manufacturing method of a ceramic product.

[0008]

In the present invention, most of the above-mentioned conventional problems are caused by the organic binder,
Focusing on the fact that most of the problems can be solved if a green molded body can be molded using a volatile liquid such as water or alcohol as a binder, and when the liquid freezes, it has the necessary binding force for the green molded body. It was done by finding out things. And, ice of water which is made into fine particles having the same particle size as the ceramic powder or ice of water obtained by adding polyvinyl alcohol to water is used as a binder, or 1 to 5 parts by weight of polyvinyl alcohol is added to 100 parts by weight of water. It is intended to achieve the object of the invention by using ice of added water as a binder. That is, in order to achieve the above-mentioned object, the present invention provides a mixture of ceramic powder and a binder,
The binder is composed of water ice which is finely divided into particles having a particle size similar to that of the ceramic powder, or water ice obtained by adding polyvinyl alcohol to water. The invention according to claim 2 is a mixture of ceramic powder and a binder,
1 part per 100 parts by weight of ice, or water of which the binder is atomized to a particle size similar to that of ceramic powder
~ 5 parts by weight of polyvinyl alcohol added water ice. According to a third aspect of the present invention, a mixture of ceramic powder and a binder is injected into a mold by an injection molding machine to form a green molded body having a predetermined shape, and the binder is removed from the green molded body, followed by firing. When obtaining a ceramics product, as the binder, ice of water that has been atomized to a particle size similar to that of ceramics powder,
Alternatively, a green molded body is formed by using ice of water obtained by adding polyvinyl alcohol to water in an atmosphere of 0 ° C. or lower. In the invention according to claim 4, a mixture of ceramic powder and a binder is injected into a mold by an injection molding machine to make a green molded body having a predetermined shape, and after removing the binder from the green molded body, When a ceramic product is obtained by firing, as the binder, ice of water that has been made into fine particles with a particle size similar to that of the ceramic powder, or ice of water to which 1 to 5 parts by weight of polyvinyl alcohol is added per 100 parts by weight of water. Using 0
It is configured to make a green compact in an atmosphere of ° C or below.

[0009]

The ceramic powder in the present invention is not limited to Al ₂ O ₃ , ZrO ₂ and BeO for oxide type, SiC, TiC and WC for carbide type,
The nitride type includes Si ₃ N ₄ , BN, AlN and the like, and refers to one kind or a mixture of two or more kinds thereof. Each of these ceramic powders is a powder that can be injected into a mold from an injection molding machine to obtain a green compact by using water ice or water ice containing polyvinyl alcohol as a binder.

The ceramic powder applied to the present invention is
It can be obtained by a conventionally known method, but its particle size is not particularly limited as long as it can be calcined. However, considering the strength of the green compact, the cost of obtaining the ceramic powder, and the like, 0.1 to 5 μm, preferably 0.3 to 2 μm
It is preferred to apply m powders. Further, the type of ceramic powder does not matter. That is, the ceramic powder may be the above-mentioned simple substance or one or a mixture of two or more thereof.

Although the grain size of ice as a binder is not strictly limited, it is about 0.1 to about the same as that of the ceramic powder.
5 μm, preferably 0.3 to 2 μm is desirable. This is because the ice and the ceramic powder are uniformly mixed. Ice having such a grain size can be produced, for example, as shown in Japanese Patent Publication No. 28443/1990. That is, ultrasonic vibration is applied to water to atomize the water. And it can be made by instantly cooling atomized water. It is also possible to use water prepared by adding polyvinyl alcohol to the above-mentioned water that is the raw material of ice. The use of water added with polyvinyl alcohol has the effect of increasing the strength of the green molded body after drying.

The ceramic powder selected as described above and ice are mixed in a conventionally known kneader placed in an atmosphere of 0 ° C. or lower. As a result, a ceramic composition is obtained, which is a mixture of iced water having a particle size similar to that of the ceramics powder, or 1 to 5 parts by weight of polyvinyl alcohol added to 100 parts by weight of water. To be This ceramic composition is injected into a mold from an injection molding machine as described below to obtain a green molded body. The amount of ice added to the ceramic powder varies depending on the type, particle size and shape of the ceramic powder, but is 8 to 15 wt% with respect to the ceramic powder.

As a hopper, an injection molding machine, a mold device and the like necessary for injection molding, those having a conventionally known structure are applied, but these devices are placed at 0 ° C. or lower. The composition, which is a mixture of ice and ceramics, is placed in the hopper of an injection molding machine.
The screw of the injection molding machine is rotationally driven and the tip of the cylinder is weighed in a conventional manner. During measurement, the ceramic composition is pressurized in the process of being sent to the tip by the screw. When pressurized, the binder ice moves in a direction of decreasing volume to maintain equilibrium. That is, a part becomes liquid. Since the binder is ice, the frictional resistance is small and the rotational drive resistance of the screw at the time of measurement is small, but since a part of the ice becomes liquid, it becomes a composition with fluidity, and the resistance becomes smaller, Weighed on the tip.

A predetermined amount of the composition is injected into a mold by driving the screw in the axial direction to obtain a green molded body. Open the mold and take out the green compact. At the time of injection, the composition is flowing, but at the end of the injection, the flow stops and the pressure becomes slightly lower, so that the liquid water becomes solid ice again. Therefore, the strength of the green molded body is increased, and the green molded body can be taken out from the mold without being deformed. As described above, a green molded body having a complicated shape such as a turbocharger rotor which is a mechanical component, an optical fiber connector ferrule which is a photoelectric component, etc. is obtained.

Next, the green molded body obtained as described above is dehydrated. According to the present invention, since the binder is water, the dehydration step can be carried out in various ways, for example, it can be placed in a heating chamber and dried by heating, or can be naturally dried at room temperature. At this time, in order to promote evaporation, the pressure inside the room can be reduced. 90% or more of the added water is dehydrated using the above method. The dehydrated green compact is fired by a conventionally known method to obtain a ceramic product.

[0016]

【Example】

Example 1: [Preparation of ceramic powder] Alumina and Al, which are typical oxide-based ceramics
Conducted with ₂ O ₃ . As this alumina powder, a commercially available product was used. The average particle size was 0.4 μm. [Production of ice] An ultrasonic transducer was put in water to atomize the water to obtain a mist. This mist was introduced into an atmosphere of -30 ° C and frozen. Since the size of the fog is about 0.2 μm, the grain size of ice was estimated to be 0.3 to 0.5 μm, which is slightly larger than this. Alumina powder and 10 Wt% ice were mixed in an atmosphere of 0 ° C. or lower to obtain an alumina composition. [Injection molding] The alumina composition was weighed with a 50 ton injection molding machine installed in an atmosphere of -5 ° C. On a 50 ton injection molding machine, the alumina composition is 700-1000.
Since it is pressurized to about kg / cm ² , it is considered that part of the ice as the binder is liquid water in the atmosphere of −5 ° C. Then, the screw was driven by driving the screw into a mold placed in an atmosphere of −20 ° C. The mold was opened to obtain a plate-shaped green molded body having a length of 45 mm, a width of 4.8 mm and a thickness of 3.6 mm. The water became ice in the mold, and the green compact had a predetermined strength. Similarly, a plurality of green molded bodies were obtained. [Drying] (1) The green molded body was naturally dried for 15 hours in an atmosphere of room temperature of 25 ° C and humidity of 60%. The green molded body weighed 2.3 grams before drying and 2.09 grams after drying. Therefore, it means 90% dehydration. (2) Another green molded body was dried in a drying oven at 120 ° C for 3 hours. At this time, the temperature rise control was not performed. Similarly, as a result of measuring the weight before drying and the weight after drying, 3
It was 92% dehydrated after drying for an hour. 90 above sea urchin
It was dehydrated by 92%, but the green molded body had sufficient strength and did not hinder the subsequent handling. [Firing] The green molded body dehydrated by the methods (1) and (2) was fired in a firing furnace at a temperature of 1600 ° C for 2 hours to obtain a product. No defects such as cracks or deformations were found in any of the obtained products. From this, it was found that any drying method can be adopted in consideration of the drying time, the drying cost and the like.

Example 2: [Preparation of ceramic powder] Silicon nitride Si, which is a typical nitride ceramics
Conducted for ₃ N ₄ . As this silicon nitride powder, a commercially available product was used. The average particle size was 0.6 μm. [Production of ice] An ultrasonic oscillator was put into water to which 5 parts by weight of polyvinyl alcohol was added per 100 parts by weight of water, and the water was atomized to obtain a mist. This mist was introduced into an atmosphere of -35 ° C and frozen. Since the size of the fog is about 0.2 μm, the particle size of ice is slightly larger than 0.3 to 0.3.
It was estimated to be 5 μm. A silicon nitride powder was mixed with 13 Wt% of ice in an atmosphere of 0 ° C or lower to obtain a silicon nitride composition. [Injection molding] The above silicon nitride composition was weighed with a 100 ton injection molding machine installed in an atmosphere of -5 ° C. 10
On a 0 ton injection molding machine, the silicon nitride composition is 700-
Since it is pressurized to about 1000 kg / cm ² , -5 ° C
In the atmosphere of, part of the ice as the binder is considered to be liquid water. Then, the screw was driven by driving the screw into a mold placed in an atmosphere of −20 ° C. The mold was opened to obtain a cylindrical green molded body having a diameter of 15 mm and a length of 50 mm. The water became ice in the mold, and the green compact had a predetermined strength. Similarly, a plurality of green molded bodies were obtained. [Drying] (1) Green molded body at room temperature 25 ° C and humidity 60% 2
It was naturally dried for 4 hours. The green compact weighed 20.3 grams before drying and 17.8 grams after drying.
Therefore, it means 95% dehydration. (2) Other green compacts were dried in a drying oven at 120 ° C for 5 hours. At this time, temperature rise control was not performed unlike the conventional degreasing process. Similarly, as a result of measuring the weight before drying and the weight after drying, it was found that 97% of the water was dehydrated after drying for 5 hours. Although 95 to 97% of the water was dehydrated as described above, the strength of the green molded body was sufficient because ice of water containing polyvinyl alcohol was used. [Firing] The green molded body dehydrated by the methods (1) and (2) was fired in a firing furnace at a temperature of 1750 ° C for 1 hour to obtain a product. No defects such as cracks or deformations were found in any of the obtained products. When using water ice with polyvinyl alcohol added, it is 95-97.
The quality of the product was good, as% could be dehydrated.

The reason why polyvinyl alcohol is added to water is to increase the strength of the green molded body. However, if the added amount is too large, the influence of polyvinyl alcohol on the ceramic product is not preferable. On the other hand, if the amount is too small, the effect becomes small. Therefore, the addition amount of polyvinyl alcohol is preferably 1 to 5 parts by weight per 100 parts by weight of water, but it is obvious that the present invention can be carried out without being limited to this addition amount.

[0019]

As described above, according to the present invention, since fine particles of ice are used as the binder of the ceramic composition, injection molding can be performed with a smaller addition rate than that of the organic binder conventionally used. However, defects such as sink marks and cracks do not occur in the green molded body. Therefore, the effect peculiar to the present invention that a high-quality ceramic product can be obtained despite using inexpensive ice is obtained. Further, since the binder temporarily becomes water during molding, the viscous resistance is small, the density distribution of the ceramic powder in the green molded body becomes uniform, and defects such as surface peeling that occur during firing can be eliminated. Furthermore, since the binder is water, it is possible to use an inexpensive drying process, and it is not necessary to use an expensive degreasing furnace as when using a conventional organic binder, and in the time required for the degreasing process. In comparison, it can be dried in a short time.
Therefore, according to the present invention, the manufacturing time of ceramic products can be significantly shortened, and industrial mass production is possible. Moreover, since the binder is water, it does not pollute the environment like an organic binder. Also,
Use of water ice obtained by adding polyvinyl alcohol to water has the effect of increasing the strength of the green molded body and facilitating handling in addition to the above effects.

Claims (4)

[Claims] 1. A mixture of a ceramic powder and a binder, wherein the binder is ice of water that has been atomized to a particle size similar to that of the ceramic powder, or ice of water obtained by adding polyvinyl alcohol to water. A characteristic ceramic composition. 2. A mixture of ceramic powder and a binder, wherein the binder is finely divided into particles of the same size as the ceramic powder, or ice of water, or 1 to 5 parts by weight of polyvinyl alcohol per 100 parts by weight of water. A ceramic composition characterized by being ice of water to which is added 3. A mixture of ceramic powder and a binder is injected into a mold by an injection molding machine to form a green molded body having a predetermined shape, and after removing the binder from the green molded body, the ceramic is fired. When a product is obtained, as the binder, ice of water finely divided into particles having a particle size similar to that of ceramic powder, or ice of water obtained by adding polyvinyl alcohol to water is used, and a green compact is formed in an atmosphere of 0 ° C. or lower. A method for manufacturing a ceramic product, which comprises: 4. A mixture of ceramic powder and a binder is injected into a mold by an injection molding machine to form a green molded body having a predetermined shape, and the binder is removed from the green molded body, followed by firing. When obtaining a product, as the binder, ice of water finely divided into particles having a particle size similar to that of ceramic powder, or ice of water to which 1 to 5 parts by weight of polyvinyl alcohol is added per 100 parts by weight of water is used. A method for producing a ceramic product, comprising producing a green compact in an atmosphere of 0 ° C or lower.