JPH0329740B2 - - Google Patents

Description

Detailed Description of the Invention (Industrial Application Field) The present invention provides a method for injection molding ceramics.
The present invention relates to a manufacturing method that can increase the density of a sintered body by simplifying the degreasing process after molding and significantly reducing the amount of binder that has conventionally been used in large amounts.

(Conventional technology) There are a wide variety of methods for molding ceramics, but
In recent years, processing methods using injection molding machines have been actively studied. Advantages of this processing method include good dimensional accuracy, the ability to produce products with complex shapes, and the ability to produce in large quantities or in small quantities.

(Problems to be Solved by the Invention) On the other hand, the amount of binder mixed with ceramic powder is 3 to 5 times that of other molding methods (for example, press molding or extrusion molding) (relative to ceramic powder). (10 to 20 wt%), which not only has an economic disadvantage, but also reduces the packing density of the ceramic powder, increases the shrinkage rate after firing, and makes it difficult to maintain sufficient dimensional accuracy. Ta.

Furthermore, in order to avoid rapid decomposition and evaporation of the binder and breakage and cracking of the molded product, heating in the degreasing process to remove this binder by firing is carried out at a slow heating rate of 1 to 10°C/hour. It is necessary to do it. This process usually takes more than three days and has been a major problem in terms of productivity.

In conventional injection molding methods, in order to give fluidity and formability to ceramic powder, (1) a material that melts with heat, such as a thermoplastic resin, paraffin, or wax, is used as a binder, or (2) water, etc. is used as a binder. A method has been used in which fluidity is imparted by using as a solution and shapeability is imparted by using a water-soluble binder together, but in the former method,
The latter method also has the above-mentioned problems, and although the amount of organic binder can be reduced, it must have a viscosity that can be removed from the mold, which ultimately increases the discharge pressure and causes wear on the molding machine. Moreover, since the amount of water-soluble binder cannot be made close to 0, it has been impossible to omit the degreasing step.

(Means for Solving the Problems) The present invention has been made by focusing on such conventional problems, and because it uses a small amount of organic binder that essentially provides shapeability, it is difficult to Not only can the previously performed degreasing step be almost omitted, the packing density of the ceramic powder can be improved, and molding can be performed at low discharge pressure, so there is less wear on the molding machine. Furthermore, considering the essential constituent factors of the present invention, it is not limited to merely injection molding processing methods, but can be sufficiently applied to other molding methods such as slurry casting molding methods.

In the present invention, the ceramic powder contains an ester resin emulsion and an ester solvent as essential components,
Add a surfactant to make a slurry, adjust the pH to 8 or higher, and inject it into a mold using an injection molding machine.Then, heat the temperature inside the mold to 50-100℃ to solidify the slurry and form a molded product. A ceramic sintered body can be obtained by taking it out and performing furnace sintering.
In addition, in this manufacturing method, the amount of the ester resin emulsion and ester solvent added is 0.5 to 10% by weight and 0.1 to 10% by weight based on the ceramic powder.
5% by weight is suitable.

The present invention will be explained in detail below.

Ceramic powders used in the present invention include alumina, silicon nitride, silicon carbide, sialon, barium titanate, zirconium oxide, magnesium oxide, beryllium oxide, titanium oxide, zinc oxide, yttrium oxide, calcium oxide, hafnium oxide, and nitride. Boron, titanium nitride, zirconium carbide, forsterite, steatite,
Mullite, cordierite, tungsten carbide, silicon dioxide, carbon, montmorillonite,
Examples include vermiculite, kaolin, talc, sepiolite, attapalgite, kibushi clay, white china clay, and feldspar. In addition, the composition of the ceramic powder may be a single composition or a compound as described above,
Alternatively, there is no problem in using a solid solution or a eutectic alone or in a mixture of a plurality of them. Further, in order to improve the characteristics of the sintered body of the above-mentioned substances, a system in which a plurality of additives are added can also be used. In addition, these ceramic powders may be provided by a fragmentation process obtained through a process of pulverization and classification using various mills, or may be obtained by a solid phase reaction method, a solid phase gas phase reaction method, a liquid phase method, It may be any one provided by a fine ceramics formation process such as a gas phase method, or a mixture thereof. Furthermore, in addition to the powders mentioned above, metal or alloy powders can also be used.
The finer the particle size of these powders, the better the quality of the final sintered body, and the maximum particle size is
It is approximately 30μ. If the particle size is larger than this, the molded body will melt in the firing process after being heated and solidified and taken out, which will be described later, and will be unable to maintain its shape. In addition, in order to maximize the quality characteristics such as strength in the fired body of ceramic powder, the particle size distribution of ceramic powder is narrow, the particle size shape is isotropic, and the particle size is 1μ or less. It is preferable.

The ester resin emulsion used in the present invention is a water-dispersed emulsion whose resin composition consists of an ester-based synthetic resin. Examples of this ester-based synthetic resin include ester derivatives of unsaturated carboxylic acids such as acrylic acid, methacrylic acid, itaconic acid, maleic acid, and fumaric acid. Examples of acrylic acid include methyl acrylate,
Examples include ethyl acrylate, butyl acrylate, 2-ethylhexyl acrylate, glycidyl acrylate, 2-hydroxyethyl acrylate, and hydroxypropyl acrylate. In addition, these resins may be copolymerized with divinyl compounds or thermosetting resins, or copolymerized with resins such as N-methylol acrylamide, glycidyl methacrylate, hydroxyethyl methacrylate, and acrylic acid. Reactive curability can be obtained.

The ester solvents used in the present invention are mostly esters of lower fatty acids and various alcohols,
Examples include methyl acetate, ethyl acetate, butyl acetate, ethylene glycol monomethyl acetate, ethylene glycol monoethyl acetate, diethylene glycol monomethyl acetate, diethylene glycol monoethyl acetate, and the like.

The appropriate amount of the ester resin emulsion or ester solvent used is 0.5 to 10% by weight and 0.1 to 5% by weight, respectively, based on the ceramic powder. The amount of ester resin emulsion used is 0.5
If it is less than 10% by weight, the strength of the molded product cannot be obtained when the ceramic slurry is solidified, and if it is more than 10% by weight, it will not be an improvement over the prior art and a degreasing step will be required. The amount of ester solvent used is 0.1% by weight.
In the following cases, the ceramic slurry does not solidify, or even if it solidifies, its strength is insufficient. Moreover, if it is more than 5% by weight, it will gel even at room temperature, resulting in poor storage stability.

In the present invention, after dispersing the ceramic powder, the pH is adjusted to 8 or higher; however, if the pH is lower than 8, solidification of the slurry does not occur. Volatile compounds such as ammonia and amines are desirable for this pH adjustment.

In the present invention, ceramic slurry is injected into a mold by an injection molding machine and then heated. The heating time varies depending on the shape of the molded product, but the heating time is 10 seconds after reaching a predetermined temperature. Any above is sufficient.

In the present invention, first, ceramic powder is sufficiently dispersed in a solvent consisting of water, an ester resin emulsion, and an ester solvent using a mixing and dispersing device using a surfactant to create a slurry.
Adjust PH. At this time, the following additives may be used within a range that does not impair the essence of the present invention. That is, in order to improve the viscosity of the slurry, methylcellulose, ethylmethylcellulose, hydroxypropylmethylcellulose, ethylcellulose acetate, hydroxymethylcellulose, hydroxypropylcellulose, starch, glue,
Casein, carboxymethyl cellulose, polyvinyl alcohol, gum arabic, modified maleic acid resin, dextrin, guar gum, ethylene vinyl acetate copolymer resin, acrylic ester resin,
Examples include powders, varnishes, and emulsions of organic polymer compounds such as polybutadiene and styrene acrylate copolymer resins.

The slurry prepared in the above manner is preferably sufficiently defoamed in a vacuum before injection molding.
If defoaming is not performed, the molded body may not only crack due to crystallization of the solvent upon freezing, but also have a negative effect on the strength of the sintered body after sintering. Next, the slurry is molded using an injection molding machine, and the cylinder temperature of the injection molding machine at this time is preferably room temperature, specifically a temperature above the melting point and below the boiling point of the slurry. One of the major features of the present invention is that sufficient molding can be achieved even if the injection pressure at this time is relatively low. The slurry injected into the mold is heated to a mold temperature of 50 to 100°C, held at that temperature for 10 seconds or more, and then the solidified molded body is removed from the mold using an ejector rod mechanism or the like. However, when designing the mold, it is preferable to take into consideration the escape of steam pressure as necessary, since water and the like evaporate during heating and generate steam.

The solidified molded body taken out from the mold can be sintered in a single stage of furnace sintering from the beginning. In this case, the temperature increase rate during furnace sintering can be increased to a level that is completely impossible with conventional methods.
This is the greatest feature of the present invention. When a raw molded body is mixed with a large amount of binder as in the conventional method, the binder decomposes during sintering and generates a large amount of gas, and oxides are generated near the surface, which causes gas to escape from the inside. However, in the present invention, the amount of binder used is small and the added solvent is removed by evaporation without being decomposed. Volumetric expansion due to gas is small, and therefore the heating rate can be very high. Specifically, a temperature increase rate of 50° C./hour or more is possible, and in the case of thin molded objects, a temperature increase rate of about 2 to 4 times is also possible.

This will be explained in detail below using examples.

Example 1 An ester resin emulsion (solid content 50%) was added to 460 parts by weight of aluminum oxide (purity 99.9%, average particle size 0.5μ) as ceramic powder in 90 parts by weight of water to which 8 parts by weight of a surfactant was added. Add 10 parts by weight and 3 parts by weight of butyl carbitol acetate (ethylene glycol monoethyl ether acetate),
High-speed dispersion is made into a slurry using a high-speed impeller mill, and 2 parts by weight of ammonia water is added and mixed. After defoaming using a vacuum defoaming device, the injection temperature is set to room temperature, and the molding material is made into a slurry that can be molded into complex-shaped parts such as gears. The slurry is injected into a mold using an injection molding machine, and then heated and solidified in the mold, taken out as a solidified molded product, and heated to 1700°C at a heating rate of 70°C/hour in an atmospheric furnace. A sintered body was obtained. The dimensional accuracy and density of this sintered body were very good.

Example 2 A solidified molded body obtained in the same manner as in Example 1 except that 460 parts by weight of aluminum oxide in Example 1 was replaced with 600 parts by weight of zirconium oxide (center particle size 0.8μ) containing 3 mol% of yttrium oxide. The temperature was raised to 150°C at a heating rate of 80°C/hour in an inert gas atmosphere furnace, and then the calcined compact was heated to 150°C.
The sintered body obtained by sintering at 1500°C for 2 hours had very good dimensional accuracy and density.

Comparative Example 1 Butyl carbitol acetate in Example 1 was not added, but 10 parts by weight of ester resin emulsion was added to 90 parts by weight of water to which 8 parts by weight of surfactant was added to 100 parts by weight of aluminum oxide. A solidified molded product was obtained in the same manner as in Example 1, but the shape of the molded product completely collapsed when taken out from the mold.

Comparative Example 2 The ester resin emulsion in Example 1 was replaced with vinyl acetate resin emulsion, and the rest was as in Example 1.
A solidified molded product was obtained in the same manner as above, but the shape of the molded product completely collapsed when it was removed from the mold.

Comparative Example 3 A frozen molded product was obtained in the same manner as in Example 1 except that the addition of ammonia water in Example 1 was set to 0.
The shape of the molded product also collapsed when it was removed from the mold.

Comparative Example 4 A ceramic slurry was prepared by changing the amount of butyl carbitol acetate added from 3 parts by weight in Example 1 to 30 parts by weight, but it solidified during storage at room temperature (3 days after preparation of the slurry). However, if the slurry is degassed and injection molded immediately after making the slurry,
A sintered body could be obtained by subsequent firing.

(Effects of the Invention) As is clear from the above examples, if a ceramic sintered body is produced using the method of the present invention, the amount of organic binder can be significantly reduced and the temperature increase rate can be extremely fast. Not only is this possible, but the density of the sintered body can be increased and its quality characteristics can be improved.

Claims (1)

[Claims] 1 0.5 to 10% by weight of ester resin emulsion and 0.1% of ester solvent based on ceramic powder
Disperse ceramic powder with ~5% by weight as an essential component in an aqueous solvent using a surfactant, then adjust the pH to 8 or higher, and inject the resulting slurry into a mold using an injection molding machine. Thereafter, the temperature inside the mold is heated to 50 to 100°C, the slurry is solidified, and the molded body is taken out and sintered in a furnace.