JPH0433611B2 - - 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.

(Problem to be solved by the invention) On the other hand, the amount of binder mixed with ceramic powder is 35 times that of other molding methods (for example, press molding or extrusion molding) (10 times the amount of binder mixed with ceramic powder). ~20wt%), 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.

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 three days or more 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 solvent 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 does not contain an organic binder that essentially provides shapeability, Not only can the conventional degreasing process be almost omitted, but 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, the present invention is not limited only to the injection molding method, but can be sufficiently applied to other molding methods such as the mud casting method.

In the present invention, ceramic powder is made into a slurry using a surfactant in a solvent such as water, is injected into a mold by an injection molding machine, and then frozen. A ceramic sintered body can be obtained. Also,
This manufacturing method becomes more effective when the volume concentration of the solvent in the slurry is within 60% and the amount of surfactant added is within 0.01% to 6% relative to the ceramic powder.

The present invention will be explained in detail below.

Ceramic powders used in the present invention include alumina, silicon nitride, silicon carbide, sialon, titanium, barium oxide, zirconium oxide, magnesium oxide, beryllium oxide, titanium oxide,
Zinc oxide, yttrium oxide, calcium oxide,
Hafnium oxide, boron nitride, titanium nitride, zirconium carbide, forsterite, steatite, mullite, cordierite, tungsten carbide, silicon dioxide, carbon, montmorillonite, vermiculite, kaolin, talc, seviolite, attapulgite, wood knot viscosity, Examples include white china clay and feldspar. Furthermore, the composition of the ceramic powder may be used as a single composition or compound as described above, or as a solid solution or eutectic, or a mixture of a plurality thereof. 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 subdivision process obtained through the steps of pulverization and classification using various mills, or may be provided by a solid phase reaction method, a solid phase gas phase reaction method, a liquid phase method, or a gas phase method. It may be any one provided by a fine ceramics forming process such as a 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 finally achieved sintered body, and the maximum particle size is approximately 30μ. If the particle size is larger than this, the molded body will melt in the firing process after freezing and removal, which will be described later, and will be unable to maintain its shape. In addition, in order to maximize quality characteristics such as strength in a sintered body of ceramic powder, the particle size distribution of ceramic powder is narrow, the particle shape is isotropic, and the particle size is 1μ or less. It is preferable.

Surfactants that can be used in the present invention include anionic surfactants, nonionic surfactants, cationic surfactants, and amphoteric surfactants.

Examples of anionic surfactants include salts of sodium, potassium, lithium, ammonium or organic bases such as alkylarylsulfonic acids, alkylsulfonic acids, α-sulfonated fatty acids, or alkali metal soaps of natural or synthetic fatty acids. Alternatively, a sulfate salt type anionic surfactant such as polyoxyethylene alkyl sulfate can be used. However, in cases where metallic elements such as sodium enter the sintered body of the ceramic powder and significantly deteriorate quality characteristics, the above-mentioned compounds containing metallic elements should be avoided.

The nonionic surfactants mentioned above include polyol ethers, long chain alcohols, fatty acids, aliphatic amines, fatty acid amides, alkylphenols,
Condensates of sulfonic acids, etc., addition products of polyoxyethylene or polypropylene glycol, reaction products of polyhydroxyalkylamines and polyhydroxycarboxylic acids or polyhydroxycarboxylic acid amides, long-chain tertiary amine oxides , long-chain tertiary phosphine oxide, and the like.

Examples of the above-mentioned cationic surfactants include ester-type, amide-type, and ether-type alkylamine salts such as laurylamine acetate, stearylamine acetate, polyoxyethylene stearylamine, distearyldimethylammonium chloride, and cetyltrimethylammonium chloride. I can list things.

Examples of the above-mentioned amphoteric surfactants include alkyl sulfhopetaine, carboxyl, phosphate,
Examples thereof include aliphatic amines substituted with groups such as phosphino, and derivatives thereof.

The surfactants mentioned above can be used alone or as a mixture of two or more, and the amount added is determined based on the weight of the ceramic powder.
The content is preferably within 0.01% to 6%. If it is less than 0.01%, not only will it be difficult to reduce the volume concentration of the solvent in the ceramic powder slurry to 60% or less, but even if the solvent concentration is achieved within 60%, it will be difficult to desorb after freezing as described below. During the process of molding and firing, the molded body melts and is no longer able to maintain its predetermined shape. Also, the amount of surfactant added is 6%.
In the above case, the amount of organic matter in the ceramic powder becomes large, and if the sintering process is rapidly started after demolding and the temperature is raised at a considerable speed, decomposition gas will be generated and cracks and blisters will occur in the sintered body. ,
This makes it impossible to simplify the degreasing process after molding, which is one of the objectives of the present invention.

Why the slurry is created using a surfactant and the shaped product maintains its shape even when it is heated after freezing, the mechanism and the effect of the surfactant at that time are not clear, but in the example As explained in detail, this is a fact.

Among the solvents that can be used in the present invention, water is most preferred. In addition to water, alcohols such as methanol, ethanol, n-prebanol, and isopropanol, ketones such as acetone, methyl ethyl ketone, methyl isobutyl ketone, and ethyl butyl ketone, esters such as methyl cellosolve acetate, cellosolve acetate, and ethyl acetate, and methyl Ethers such as cellosolve, butyl cellosolve and butyl carbitol, aromatic hydrocarbons such as benzene, toluene and xylene, aliphatic hydrocarbons such as n-hexane, etc. can be added as long as the gist of the present invention is not obstructed. However, those with extremely low freezing temperatures are not desirable from the viewpoint of energy costs.

It is not preferable that the amount of the above-mentioned solvent exceeds 60 vol % in the volume of the slurry obtained by kneading ceramic powder and surfactant in a solvent. At 60vol% or more, even if the slurry is molded by injection molding and frozen in the mold, the shape of the molded product will be destroyed and melted during sintering after demolding, resulting in the molded product not retaining the desired shape. It becomes difficult to manufacture a sintered body with

In the present invention, first, ceramic powder is sufficiently dispersed in a solvent such as water using a surfactant using a mixing and dispersing device to prepare a slurry. At this time, the following additives can 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, carboxymethylcellulose, polyvinyl alcohol, gum arabic, modified maleic acid resin, dextrin. , guar gum, polyethylene, wax, polypropylene ethylene vinyl acetate copolymer resin, acrylic acid ester resin, polybutadiene, styrene acrylic acid ester copolymer resin, urethane resin, and other organic polymer compound powders, varnishes, or emulsions. .

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 temperature of the slurry injected into the mold is kept below the freezing point of the slurry for a while until the entire slurry freezes, and then the frozen molding method body is removed from the mold by an ejector rod mechanism or the like. However, when designing a mold, if a solvent such as water that expands when frozen is used, it is preferable to take into account the release of expansion pressure as necessary. The frozen molded body taken out of the mold is first dried at a temperature slightly higher than the boiling point of the solvent, and then the sintered body is obtained by furnace sintering at an appropriate time. A method of obtaining a sintered body using a one-stage method of furnace sintering may also be used.
In this case, the greatest feature of the present invention is that the temperature increase rate during drying or furnace sintering can be increased to an extent that is completely impossible with conventional methods. When a raw molded body is mixed with a large amount of binder as in the conventional method, the binder decomposes during firing and generates a large amount of gas, and oxides are generated near the surface, which prevents gas from escaping from inside. However, in the present invention,
Since the solvent used is removed by evaporation without being decomposed, there is no volumetric expansion due to decomposed gas, and therefore the temperature can be increased at a very high rate. 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 1 100 parts by weight of aluminum oxide (purity 99.9%, average particle size 0.5μ) as ceramic powder was dispersed at high speed in 25 parts by weight of water to which 3 parts by weight of nonionic surfactant was added using a high-speed impeller mill. After making a slurry and defoaming with a vacuum degassing device,
The injection temperature is set to room temperature, and the injection molding machine is used to inject into a mold that can form parts with complex shapes such as gears.
Thereafter, the slurry was frozen in a mold, taken out as a frozen molded body, and raised to 1700°C at a heating rate of 70°C/hour in an atmospheric furnace to obtain a sintered body. The dimensional accuracy and density of this sintered body were very good.

Example 2 A frozen molded body obtained in the same manner as in Example 1 except that 100 parts by weight of aluminum oxide in Example 1 was replaced with 140 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 firing at 1500°C for 2 hours had very good dimensional accuracy and density.

Example 3 Silicon carbide (purity 99.5
%, average particle size 0.2μ) containing 100 parts by weight of anionic surfactant, water:ethanol 3:1
Dispersed in 25 parts by weight of a mixed solution of
The frozen molded body obtained in the same manner as in Example 1 was then heated to 2000°C at a rate of 70°C/hour in a vacuum furnace to obtain a sintered body. The dimensional accuracy and density of this sintered body were very good.

Comparative Example 1 A frozen compact was obtained in the same manner as in Example 1, except that the surfactant in Example 1 was not added and water was 50 parts by weight to 100 parts by weight of aluminum oxide, but At the initial stage of firing, the shape of the molded body completely collapsed.

Comparative Example 2 0.12% by weight of nonionic surfactant in Example 1
A slurry was prepared in which 60 parts by weight of water was changed from 25 parts by weight, and 3 parts by weight of methylcellulose was added as a thickener, and a frozen molded body was obtained in the same manner as in Example 1, but this was also furnace fired. At the initial stage, the shape of the molded product completely collapsed.

Comparative Example 3 A ceramic powder slurry was prepared using 3 parts by weight of the surfactant in Example 1 and 30 parts by weight of the surfactant aqueous solution, and the rest was carried out in the same manner as in Example 1 to obtain a frozen molded body. The result of furnace firing was a sintered body with cracks.

Comparative Example 4 A slurry of ceramic powder was prepared by replacing the water in Example 1 with 25 parts by weight of xylene, and the rest was carried out in the same manner as in Example 1 to obtain an agglomerated body and fired in a furnace. Cracks appeared in the molded product at an early stage.

(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. A manufacturing method for obtaining a ceramic sintered body in which ceramic powder is made into a slurry, molded using an injection molding machine, taken out and sintered in a furnace as it is, wherein the solvent used in the slurry is mainly water. Yes, the volume concentration of the solvent in the slurry is within 60%, the slurry contains a surfactant within 0.01 to 6% by weight based on the ceramic powder, and is frozen in a molding machine. A method for producing a ceramic sintered body, characterized in that it is a molded body.