JPH10101437A - Forming of powder assuming sintering - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a forming method of sintering precursor capable of precisely, rapidly, simply and densely forming a body having a complicate shape with thick wall by mixing powder with a volatile liquid, a monomer and a polymerization initiator and polymerizing and curing the mixture and carrying out volatilization treatment of the volatile liquid. SOLUTION: Slip obtained by mixing powder with a volatile liquid, a monomer which is an acrylic acid salt soluble in the liquid and a polymerization initiator for the monomer are injected to a mold. Thereby, polymerization of the monomer is started and the slip is cured. Since the cured product has elasticity, the formed material can be removed from the mold without giving stain and crack thereto. Then, volatilization treatment of the volatile liquid is carried out and cured product causes self-shrinkage with loss of liquid and densified. The coefficient of linear contraction is 2 to 15%. All of material passing through sintering process can be used as the powder and the powder includes alumina, mullite, zirconia, silicon nitride, boron nitride or powdery metallurgy. One or more kinds of substances of water, alcohols, etc., in an amount of 10-50wt.% based on powder are used as the volatile liquid. The monomer is used in an amount of 0.5-15wt.% based on powder.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for obtaining a dense compact as a sintering precursor of powders such as ceramics and metals.

[0002]

2. Description of the Related Art Pressure molding, casting, and injection molding are commonly used as powder molding methods, and each has the following characteristics.

(Pressure molding method) Although it has the advantage of mass production and good dimensional accuracy, it is extremely difficult to mold a complex shape, it is difficult to obtain a uniform product, and variations in density and strength occur. It has the disadvantage of being easy.

(Cast molding) It has the advantage that molding of complicated shapes is possible, the equipment cost is low, and it is suitable for small-quantity production. However, the productivity is poor, the dimensional accuracy is poor, and the molding of thick products is cracked. Has the disadvantage that it is difficult because of

(Injection molding) There is an advantage that a product having a complicated shape can be obtained with high dimensional accuracy, mass productivity is high, and automation is possible. However, since the amount of binder is large, it takes a long time to remove the binder. There is a disadvantage that the compact is hard to densify and the equipment cost is expensive.

As a method for remedying these drawbacks, Japanese Patent Publication No. 7-22931 discloses a method in which a thermosetting resin, a curing agent for the resin and a gas-dispersible liquid are mixed with a powder and self-cured to form a liquid. A self-curing type casting method is described in which a dense molded body is obtained by performing an air diffusion treatment, and when this is sintered, a sintered body having excellent characteristics is obtained. Although this molding method has the advantage of obtaining a uniform-thickness product with a complex shape, in the initial stage of air diffusion treatment from a self-cured body,
Since a large amount of water remains in the cured product and the thermosetting resin film covers the entire cured product, cracks will occur if the air diffusion speed from the surface is faster than the diffusion speed of the liquid from the inside. However, there is a disadvantage that the liquid is easily diffused and takes a long time.

Further, US Pat. No. 4,894,194
A powder is mixed with at least one polyfunctional monomer (for example, hexanediol diacrylate, trimethylolpropane triacrylate, etc.), a gas-dispersible liquid and a polymerization initiator of the monomer, and heated to form a self-adhesive. A gel cast molding method is described in which a dense sintered body is obtained by curing and subjecting a liquid to a gas diffusion treatment, and when this is sintered, a sintered body having excellent properties is obtained. With this molding method, complex and thick products can be molded,
To cure, at least 100-120 ° C, 5-3
0 minute heating is required, and the operation is complicated. As described above, all of the conventional methods have advantages and disadvantages, and a molding method capable of obtaining a complicated shape and a thick product with good dimensional accuracy, quickly and easily has not been developed yet.

[0008]

DISCLOSURE OF THE INVENTION The present invention has been made in view of such a problem.
It is an object of the present invention to provide a novel molding method of a powder sintering precursor for compactly forming a thick complicated shape body with good dimensional accuracy, quickly and easily.

[0009]

Means for Solving the Problems As a result of intensive studies on the above problems, the present inventors have obtained the following new findings. In other words, the air is easily dispersed by injecting a gas-dispersible liquid into the powder for molding, a slip obtained by mixing a soluble monomer and a polymerization initiator of the monomer with the liquid, and curing the mixture by polymerization. A sintered precursor can be obtained, and when this is sintered, an extremely dense sintered body is obtained.
As the above-mentioned soluble monomer, it has been found that acrylates are most preferable.

The present study has been made based on the above findings.

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION When a slip in which a powder is mixed with a gas-dispersible liquid, a soluble monomer and a polymerization initiator of the monomer are injected into a mold, polymerization of the monomer is started,
The slip hardens. This curing mechanism is considered to be due to the fact that the polymerization proceeds while fixing the liquid, or because the produced polymer swells when fixing the gas-dispersible liquid. Since this cured product has elasticity, it is possible to release the molded product without scratching or cracking.

Next, the air-diffusing liquid is subjected to an air diffusion process.
As the liquid disappears, the cured body undergoes self-shrinkage and becomes dense. This shrinkage can be caused by powders, soluble monomers, gaseous liquids,
Although it depends on the type of polymerization initiator and the like and the addition ratio, the linear shrinkage is generally 2 to 15%.

The most important feature of the present invention is that this air diffusion process can be performed quickly. Tokuho 7-22931
In the self-curing molding method described in No. 1, when the air diffusion processing speed is high, cracks are likely to occur, whereas in the present invention, even if the air diffusion processing speed is increased, cracks do not occur in the molded body, The liquid can be quickly diffused, and the cured product can be densified. In this regard, it is conceivable that the cured body has elasticity and thus hardly causes cracks, the generated polymer is phase-separated, and the liquid is easily scattered.

Any powder can be used as long as it is a material that has undergone a sintering process. Typical ones are alumina,
Oxide-based powders such as mullite and zirconia; non-oxide-based powders such as silicon nitride, boron nitride, and aluminum nitride; mixed powders of two or more of these; pottery stones such as tableware, insulators, sanitary ware, feldspars In the powder metallurgy, powders containing clay, silica, etc., stainless steel powder, pure titanium powder, titanium alloy powder, cemented carbide powder and the like can be mentioned.

The gaseous liquid is capable of dissolving soluble monomers,
Use a material that can be easily separated from the cured product during the air diffusion treatment. The most typical one is water. In addition, organic solvents such as alcohol and toluene are used. These liquids can be used singly or as a mixture of two or more air-dispersible liquids such as water + alcohol. Also,
The mixing ratio of the gas-dispersible liquid is preferably approximately 10 to 50% by weight based on the powder. If the liquid amount is less than 10% by weight, the dispersibility of the powder is poor, an uneven structure is generated in the sintered body, and the characteristics of the sintered body such as mechanical strength are reduced. In addition, when the liquid amount is 5
If the content exceeds 0% by weight, it takes a long time for the liquid to be diffused, and the strength of the cured product becomes low, making it difficult to handle.

When a gas-dispersible liquid and a soluble monomer are mixed with a powder, a dispersant is added when the dispersibility of the powder is poor or when it is necessary to reduce the amount of the gas-dispersible liquid. The dispersing agent can be selected as long as it does not adversely affect the sintered body after sintering, in consideration of the dispersibility of the powder and the effect of reducing the amount of the gaseous liquid. Dispersants can be broadly classified into inorganic and organic. Typical organic dispersants include polyamic acid ammonium salts and acrylic acid oligomers for oxide ceramics, and amine dispersants for non-oxide ceramics. As the inorganic dispersant, sodium silicate, sodium pyrophosphate and the like can be appropriately used. The dispersing effect can also be obtained by adjusting the pH of the slip. Various acids such as hydrochloric acid and nitric acid as the pH adjuster,
Bases such as aqueous ammonia can be used.

As the soluble monomer, those which fix a large amount of gas-permeable liquid at the time of polymerization are preferable. For example, metal-containing acrylate monomers (metal species: Li, Na, C)
a, Sr, Ba, Mn, Fe, Co, Ni, Cu, A
g, Zn, Al) Others, metal-containing methacrylate monomers, metal-containing maleate monomers, metal-containing itaconic acid monomers, and the like, among which metal-containing acrylate monomers are most preferred. The mixing ratio of the soluble monomer is preferably from 0.5 to 15% by weight based on the powder. If the amount of the monomer is less than 0.5% by weight, it is no longer possible to fix the slip containing the gaseous liquid and the powder, the strength of the cured product is reduced, and the handling of the molded product becomes difficult. Conversely, if the addition ratio of the soluble monomer exceeds 15% by weight, the amount of resin in the cured product will inevitably become excessive, making degreasing difficult.

To initiate the polymerization of the soluble monomer, a polymerization initiation catalyst is added. A typical example is ammonium persulfate + L-ascorbic acid. In addition, any material that can initiate polymerization of the monomer can be used as appropriate.

In the present invention, first, the powder, the gas-dispersible liquid, the soluble monomer and, if necessary, the dispersant are mixed and dispersed at a predetermined ratio to prepare a slip. The mixing and dispersing method can be suitably used as long as it is a wet dispersing mixer such as a ball mill and a fine particle mill. When bubbles are entrained in the slip during the mixing and dispersing processes and adversely affect the properties after sintering, a defoaming agent under reduced pressure or an antifoaming agent is added.

Next, the polymerization of the soluble monomer is started.
The polymerization is started by adding a polymerization initiator before casting. The polymerization initiator can be added smoothly to the container containing the slip with stirring, or a two-component mixer such as a line mixer can be used for smooth casting.

The mold can be used as long as it has no water absorption and is excellent in dimensional stability. A typical example of a mold material is
There are a mold, a resin mold, a gypsum mold with a seal, or a disintegrating mold. Usually, normal pressure casting is performed, but when the slip is highly viscous, pressure casting is performed.

Although the hardening of the slip accompanying the polymerization reaction is sufficiently possible in a normal temperature range, depending on the shape to be molded, heat casting at 80 ° C. or less is possible. Heating can further reduce the curing time.

The release of the cured product from the mold is easy. When the mold release property between the mold and the cured product is poor, a mold release agent such as a silicon-based, fluorine-based, vaseline-based, or grease can be smoothly removed from the mold surface. In the demolded cured body, the remaining gaseous liquid is removed at room temperature or by a heating operation. This air diffusion treatment is different from the case of the self-curing molding method using the thermosetting resin as described above, and in a short time,
Ends easily without cracking or deformation.

Next, the organic components in the dried compact are degreased and removed. The organic component refers to a produced polymer, a dispersant, and the like. Degreasing is performed in the air or in a non-oxidizing atmosphere. A rough guide is to heat to about 300 ° C or more.

Finally, the degreased body is heated and sintered. Here, sintering refers to both semi-sintering that retains water absorption and sintering for densification. The powder molding method of the present invention is for obtaining a sintering precursor on the premise of undergoing a sintering step.

[0026]

【Example】

Example Molding powder: Ceramic powder (alumina 10% by weight, clay 40)
% By weight, feldspar 30% by weight, silica stone 20% by weight) Air-dispersible liquid: Water Soluble monomer: Zinc acrylate Dispersant: Polycarboxylate ammonium salt Polymerization initiator: Ammonium persulfate + L-alcorbic acid Mold: 200 mmφ × 200 mmL mold Mold with tee

Mixing ratio Ceramic raw material powder: 100 (wt%) Water: 30 Zinc acrylate: 5 Dispersant: 0.9 Ammonium persulfate: 0.03 L-Ascorbic acid: 0.03

A predetermined amount of the above-mentioned ceramic powder, water, zinc acrylate, and a dispersant were mixed in a ball mill to prepare a slip. Ammonium persulfate and L-ascorbic acid were added to the slip, and the mixture was stirred and cast into a mold at normal pressure and normal temperature.
The viscosity of the slip increased after casting and hardened after about 5 minutes. The cured product had elasticity and sufficient strength to be handled by hand, and could be easily removed from the mold without any defects such as cracks. This was dried at 70 ° C. for 2 hours. No cracks, deformation, etc. due to drying were observed. The molded product obtained by casting using the same powder and using a thermosetting resin cracked during drying under the same conditions. Also,
It took 10 hours at 50 ° C. to dry the cast molded body made of the thermosetting resin without causing cracks.

The dried product was placed in a box-type electric furnace, and
The temperature was raised to 12 ° C. at a rate of 12 hours, left for 1 hour, and allowed to cool. Even during this degreasing process, cracking and deformation were not observed,
Organic components had been completely removed. Finally, the temperature is raised at a rate of 10 hours to 1300 ° C. in a CO reducing atmosphere,
The sintering was performed while holding for a time. The density of the obtained sintered body is 2.
46g / cm3, water absorption 0%, bending strength 150MPa
And exhibited excellent mechanical strength values equal to or higher than the bending strength of 146 MPa of a sintered body obtained by casting using a thermosetting resin.

Example Molding powder: Alumina powder (purity 99.9%, average particle size 0.2 micron) Air-dispersible liquid: water Soluble monomer: magnesium acrylate Dispersant: acrylic acid oligomer Polymerization initiator: ammonium persulfate + L -Ascorbic acid mold: Mold having a cavity of 50 mmφ x 300 mmL

Mixing ratio Alumina powder: 100 (wt%) Water: 28 Magnesium acrylate: 3.5 Dispersant: 1.5 Ammonium persulfate: 0.02 L-Ascorbic acid: 0.02

A slip was prepared in the same manner as in the example, a polymerization initiator was added, and the mixture was cast at normal pressure and normal temperature. After casting, the viscosity of the slip increased and hardened after about 5 minutes. The cured body is
Although it has elasticity, it has sufficient strength to be handled by hand, and can be easily removed from the mold without any defects such as cracks. This was dried at 70 ° C. for 2 hours. No cracks, deformation, etc. due to drying were observed. The molded product obtained by casting using the same powder and using a thermosetting resin cracked during drying. Further, it took 9 hours at 50 ° C. to dry the cast molded body using the thermosetting resin without causing cracks.

The dried product was placed in a box-type electric furnace, and
The temperature was raised to 12 ° C. at a rate of 12 hours, left for 1 hour, and allowed to cool. Even during this degreasing process, cracking and deformation were not observed,
Organic components had been completely removed. Finally, in the air, 1
The temperature was raised to 800 ° C. at a rate of 12 hours, and held for 4 hours for sintering. The density of the obtained sintered body is 3.98 g / cm.
3. The water absorption was 0%, and the bending strength was 406 MPa, which was an excellent mechanical strength value equal to or higher than the bending strength of 398 MPa of a sintered body obtained by casting using a thermosetting resin.

Examples Molded powder: tungsten carbide + cobalt-based ultra-hard powder (average particle size: 5 microns) Air-dispersible liquid: ethanol Soluble monomer: cobalt acrylate Dispersant: phthalic acid copolymer Polymerization initiator: Ammonium persulfate + L-ascorbic acid Mold: polyethylene resin mold having an outer diameter of 15 mmφ and a drill cavity of 200 mmL

Blending ratio Carbide powder: 100 (wt%) Ethanol: 12 Cobalt acrylate: 3 Dispersant: 1.1 Ammonium persulfate: 0.02 L-ascorbic acid: 0.02

A slip was prepared in the same manner as in the example,
A polymerization initiator was added, and the mixture was cast at normal pressure and normal temperature. The slip thickened immediately after casting and hardened after about 3 minutes. The cured product had elasticity and sufficient strength for handling, so it could be easily removed from the mold, and no defects such as cracks were observed. This was dried at 50 ° C. for 2 hours. No crack deformation due to drying was observed.

The dried compact was placed in a hydrogen atmosphere at 60
After degreasing at 0 ° C., the temperature was increased to 1260 ° C. in a hydrogen atmosphere at a rate of 6 hours, and the temperature was maintained for 2 hours, followed by sintering. The sintered body was completely densely sintered to obtain a helical carbide drill.

[0038]

As described above, the method of the present invention has a high density,
It is extremely useful as a method for molding a powder sintering precursor for obtaining a high-strength sintered body, and has the following advantages. (1) A complicated shape can be obtained. (2) A thick material can be obtained. (3) Molding is possible in a short time. (4) The manufacturing cost is low. (5) Compatible with most manufacturing industries involving a sintering process.

Claims (2)

[Claims] 1. A method in which an air-dispersible liquid is mixed with a powder, a slip obtained by mixing a soluble monomer and a polymerization initiator of the monomer with the liquid is poured into a mold, and the mixture is cured by polymerization. A method of molding a sintered precursor of a powder, characterized by the following. 2. The method according to claim 1, wherein the soluble monomer is an acrylate.