JPH0597527A - Molding of graphite-dispersing ceramics - Google Patents

Abstract

PURPOSE:To provide a method for molding a complicated-shape graphite- dispersing ceramic molding of high density with high dimensional accuracy by using a thermosetting resin prepolymer as a molding binder. CONSTITUTION:A mixture composed of a thermosetting resin prepolymer as a molding binder and a powdery ceramics in a volume ratio of (30:70) to (5:95) is molded in a mold at the flow point of the prepolymer and organic materials contained in the resin are subsequently decomposed in an inert gas and then sintered in an inert gas to obtain the objective graphite-dispersing ceramic molding. Use of the thermosetting resin prepolymer enables use of a solvent for mixing the ceramic raw materials therewith and, therefore, uniform blending. By decomposition of the thermosetting resin, graphite remains in the sintered material and thereby a sliding effect is exhibited.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for molding high density, high dimensional precision ceramics, and more particularly to a method for molding graphite-dispersed ceramics.

[0002]

2. Description of the Related Art As a ceramics molding method, a powder press molding method, an injection molding method, an extrusion molding method, a casting molding method and the like are known. This molding process is extremely important,
Affects product performance. For example, in the injection molding method,
It can be molded with high dimensional accuracy, but it is difficult to prevent the occurrence of voids or cracks due to air entrapment. Also,
The flow of material by injection causes weld lines in the compact, which leads to mechanical strength defects after sintering. Also,
In a usual molding method, since the particle filling rate in the molded body is as low as 60% or less, it is greatly contracted and deformed during sintering. A thermoplastic binder is often used in the above molding method. This is because the thermoplastic binder can be fluidized by heating and can be easily uniformly mixed with the ceramic powder. However, the thermoplastic binder has the following drawbacks. 1) Gas is generated at the time of removing the binder, which causes blisters and cracks, resulting in mechanical strength defects after sintering. 2) It is necessary to heat the mold or the raw material during molding and to take out the product after cooling, which requires a long molding process. 3) The mold becomes brittle by heating and cooling the mold. 4) Distortion occurs when the molded product (product) is cooled. 5) It takes time to cool the molded product before taking it out.

On the other hand, a thermoplastic resin can be cured after it has been made fluid by heating. It can be taken out without cooling the molded product. However, since the thermosetting resin is insoluble in the solvent, it is difficult to uniformly mix it with the ceramic powder, resulting in uneven filling. Further, when the amount of the thermosetting resin is increased, the ceramic particle filling rate becomes small, and the product shape collapses when the binder is removed. Further, even if the thermosetting resin was used, it was not possible to obtain a molded article in which graphite was dispersed in ceramics because the sintering was performed in the atmosphere.

[0004]

SUMMARY OF THE INVENTION An object of the present invention is to provide a method for molding a graphite-dispersed ceramic compact with high density and high dimensional accuracy by using a prepolymer of thermosetting resin as a molding binder. There is.

[0005]

In order to achieve the above object, in the present invention, a mixture of a thermosetting resin prepolymer and a ceramic powder is molded in a mold having a prepolymer flow starting temperature or higher, After that, the organic component in the resin is decomposed in an inert gas, and the resin is further sintered in an inert gas to obtain a graphite-dispersed ceramics molding method. Further, in the present invention, a mixture in which the surface of the ceramic powder is covered with a prepolymer of a thermosetting resin is molded in a mold having a temperature above the flow starting temperature of the prepolymer, and then the resin is treated in an inert gas in a resin. Decomposes the organic content of
Further, the method is a method for forming a graphite-dispersed ceramic, which is characterized by sintering in an inert gas.

In the above-described molding method of the present invention, the ratio of the prepolymer of the thermosetting resin to the ceramic powder in the raw material mixture was in the range of 30:70 to 5:95 vol% and was obtained by sintering. The particle filling rate of the graphite-dispersed ceramic compact is 70 vol% or more. Moreover, the ceramic powder for molding in which the surface of the raw material is covered with the prepolymer of the thermoplastic resin has an apparent viscosity of 0.1 MPa · s to 0.3 MPa · s by the flow tester (however, the nozzle shape φ6 × 6 It is preferable that the pressure is 0.8 mm and the pressure is 39 MPa). The molding method of the present invention includes the following steps. (A) A step of mixing the prepolymer of the thermosetting resin before cross-linking with the ceramic powder and the solvent, (b) a step of removing the solvent, (c) a crushing step, (d) pressure molding in a room temperature mold , A step of producing a preformed body, (e) a step of decomposing organic components in the resin in an inert gas, (f) a step of sintering in an inert gas, and the above steps.

In the above, the ceramic powder is
It comprises at least one of inorganic compound and / or metal particles, short fibers and long fibers. The metal particles are changed to nitrides, oxides, carbides, etc. in the final sintered body. In the present invention, the prepolymer of the thermosetting resin is soluble in the solvent,
Easy to mix and disperse with particles, short fibers and long fibers. As the particles, particles having a particle size of about 10 nm to 1 mm can be used, but the particle size is not limited to this range. Further, it is preferable to use fibers having a diameter of about 0.1 μm to 1 mm and an aspect ratio of 10 to 100, but not limited to this range. The thermosetting resin, at least one of addition reaction type polyimide resin, epoxy resin, urea resin, melamine resin, phenol resin, unsaturated polyester resin, alkyd resin, urethane resin, urea resin, diallyl phthalate resin, if necessary , Mix the curing agent. In particular, the epoxy resin is effective for high dimensional precision molding because the shrinkage upon curing is small. At the time of molding, it is necessary to carry out pressure molding in the mold at a flow starting temperature or higher and then cure. By combining the thermosetting resin and the curing agent, the curing time can be controlled within tens of seconds to several minutes, which is effective for shortening the molding process. Further, since the mold temperature can be kept constant, it is possible to prevent the mold from becoming brittle. The mold temperature is preferably a temperature at which the mixture of the thermosetting resin prepolymer and the ceramic powder has fluidity and is cured. The curing time can also be controlled by controlling the mold temperature. Generally, it is preferable to set the temperature in the range of 100 ° C to 200 ° C.

When the mixture of the thermosetting resin prepolymer and the ceramic powder is cured, the shrinkage rate is 0.5% or less,
Especially when high dimensional accuracy is required, it is preferably 0.1% or less. This curing shrinkage facilitates release from the mold. In the present invention, the prepolymer of the thermosetting resin and the ceramic powder may be mixed by adhering the prepolymer of the thermosetting resin to the surface of the ceramic powder by a method such as a pot mill, a ladle machine, or spray drying. Therefore, the method is not bound by the general concept.
In the present invention, in the case of producing a product having a complicated shape, it is also possible to prepare a preformed body at a temperature at which it is not heat-cured and perform a ceramics molding method in which the final molded body is a combination of one or more preformed bodies.

[0009]

In the present invention, the ratio of the thermosetting resin prepolymer to the ceramic powder is 30:70 to 5:95.
The reason for using a mixture of vol% will be described. Since the ceramic raw material powder itself is composed of brittle solid particles, it is difficult to fill it by pressing as it is, and it is necessary to help the fluidity by adding a binder. The strength of the sintered body depends on the added amount of the binder. For example,
FIG. 1 shows the relationship between the bending strength of the Si ₃ N ₄ sintered body obtained by the reaction sintering method of metallic Si and the addition amount of the prepolymer of the thermosetting resin. Further, FIG. 2 shows the relationship between the filling rate of the molded particles and the addition amount of the prepolymer of the thermosetting resin. As described above, the particle filling rate of the compact and the strength of the sintered body depend on the amount of the prepolymer added of the thermosetting resin. A high-strength product can be obtained only with the optimum addition amount. This is because as the amount of the binder added to the raw material powder increases, the fluidity of the mixture becomes better and the molding becomes easier. As a result, the density of the molded body is improved.
However, if the binder is added in an amount higher than the ratio of the voids when the raw material powder is in an ideal close packing, the raw material powder will be in an isolated state in the binder. In this case, the fluidity of the mixture is improved, and injection molding is possible, but the packing rate of particles in the molded article is reduced. When the binder removal treatment is performed, the thermosetting resin that is the binding component is decomposed, which may cause a phenomenon that the shape of the product collapses. Thus, by adding an optimum amount of the prepolymer of the thermosetting resin, the particle filling rate of the molded body can be 70 vol% or more.

In the present invention, the apparent viscosity of the molding ceramic powder whose surface is covered with the thermosetting resin is from 0.1 MPa · s to 0.3 MPa by a flow tester.
・ S (however, nozzle shape φ6 × 6.8mm, pressure 39M
Pa). FIG. 3 shows the relationship between the apparent viscosity of the flow tester and the packing rate of the molded particles. This has the same tendency as in FIG. 2, and it can be seen that the viscosity of the raw material affects the packing rate of the molded particles. The reason is exactly the same as above. As described above, by adjusting the apparent viscosity to the optimum value, the particle filling rate of the molded product can be 70 vol% or more. For the above-mentioned final molded product, after thermally decomposing the contained thermosetting resin in an inert gas, it is further sintered by a method such as pressure sintering or hot press sintering in an inert gas. Make a body. Here, when the contained thermosetting resin is pyrolyzed, it remains as graphite and is scattered in the sintered body, which is effective for improving the sliding characteristics, and is therefore suitable for a sliding member. The method for forming the ceramic molded body is selected according to the shape of the molded body and the properties required for the sintered body, such as press molding, casting molding, rubber press molding, extrusion molding, and die powder molding.

[0011]

EXAMPLES The present invention will be described in more detail below with reference to examples, but the present invention is not limited thereto. Example 1 SiC particles having an average particle size of 2 μm and metallic Si having an average particle size of 0.1 μm were mixed into a mixed powder having a raw material compounding ratio of 20:80 vol%, and a prepolymer of an epoxy resin was used as a binder for molding in an amount of 1 to 50 vol%. Acetone was added as a solvent and mixed in a pot mill for 24 hours. Then, after the solvent in the mixture is dried and removed, the raw material is mechanically pressed with a molding pressure of 1000 kgf / cm ² and a temperature of 1 kg.
Pressure is maintained for 2 minutes at 60 ℃, diameter 50mm, thickness 20mm
Was molded. The relationship between the particle volume filling rate of the obtained molded product and the amount of prepolymer of the epoxy resin is shown in FIG.
From this, the prepolymer amount of epoxy resin is 5 to 30v
It can be seen that the particle filling rate of the molded product is 70 vol% or more when it is ol%. The organic content in the molding binder was removed from each of the molded bodies in an inert gas to leave the free carbon content, and the molded body was heated at 1100 ° C to 1350 ° C at a temperature rising rate of 3 ° C / h for a long time in a nitrogen atmosphere. By this, free carbon 1-6v
ol%, Si ₃ N ₄ whiskers / particles = 5/95 vol%
A sintered body of was obtained. The relationship between the three-point bending test strength and the amount of epoxy resin prepolymer is shown in FIG. With an epoxy resin having a prepolymer amount of 20 vol%, a bending strength of 620 MPa was obtained. The pore shape in the sintered body was as small as 5 μm or less, and it was found that the raw material and the binder were uniformly mixed. The prepolymer amount of epoxy resin is 40v
The shape of the molded body of ol% or more collapsed after removing the binder.

For comparison, 20 vol% of the epoxy resin powder after cross-linking was added to the above raw material powder, and acetone was mixed and mixed in a pot mill for 24 hours. After the solvent in the mixture is dried and removed, the raw material is mechanically pressed with a molding pressure of 1000 kgf / cm ² and a temperature of 160 ° C.
Then, the pressure was held for 2 minutes to form a product having a diameter of 50 mm and a thickness of 20 mm. After removing the molding binder from this molded body, the temperature is changed from 1100 ° C to 1350 ° C at 3 ° C / h in a nitrogen atmosphere.
The heating was performed for a long time at a heating rate of. The three-point bending strength of the obtained sintered body was 230 MPa, which is 1/2 of that of the present invention.
It is below. This is because large pores (50 μm) remained as defects because the raw material and the binder could not be uniformly mixed.

Example 2 TiN particles having an average particle size of 1 μm and metallic Si having an average particle size of 0.1 μm were mixed into a powder mixture having a raw material compounding ratio of 20:80 vol%, and a prepolymer of a phenol novolac resin was used as a molding binder. 20 vol% was added, acetone was added as a solvent, and the mixture was mixed in a pot mill for 24 hours. After the solvent in the mixture is dried and removed, the raw material is mechanically pressed at a molding pressure of 1000 kgf / c.
m ² , temperature 160 ° C., holding pressure for 2 minutes, diameter 50 mm,
A product having a thickness of 20 mm was molded. From this, a particle filling rate of the molded body of 77 vol% was obtained. Organic matter in the molding binder was removed from this molded body in an inert gas to leave free carbon content, and the temperature was changed from 1100 ° C to 1350 ° C at 3 ° C in a nitrogen atmosphere.
The heating was performed at a heating rate of / h for a long time. The dimensional change rate during sintering was as small as 0.12 vol%. As a result of the three-point bending test, a bending strength of 630 MPa was obtained. The pore shape in the sintered body was as small as 1 μm or less, and it was found that the raw material and the binder were uniformly mixed.

Example 3 AlN particles having an average particle size of 1 μm and metallic Si having an average particle size of 0.2 μm were mixed into a mixed powder having a raw material mixing ratio of 50:50 vol%, and 19 vol of an epoxy resin prepolymer was used as a molding binder. %, Tetraphenylphosphonium as a curing catalyst was added in an amount of 1 vol%, acetone was added as a solvent, and they were mixed in a pot mill for 24 hours. Then, after the solvent in the mixture is dried and removed, the raw material is mechanically pressed with a molding pressure of 1000 kgf / cm ² and a temperature of 1 kg.
Pressure is maintained for 30 seconds at 60 ° C, diameter 50 mm, thickness 20 mm
Was molded. From this, the particle packing ratio of the molded body is 7
5 vol% was obtained. From this molded body, the organic content in the molding binder was removed in an inert gas to leave the free carbon content, and the mixture was heated in a nitrogen atmosphere at 1100 ° C to 1350 ° C at a temperature rising rate of 4 ° C / h for a long time. As a result of 3-point bending test, 63
A bending strength of 0 MPa was obtained. The pore shape in the sintered body was as small as 2 μm or less, and it was found that the raw material and the binder were uniformly mixed. It was also found that the molding time can be shortened by adding a curing catalyst. In the present invention, the fluidity (moldability) can be improved by adding a small amount of a thermoplastic resin such as polyethylene or a lubricant such as stearic acid. In the present invention, a method of molding a mixture of a prepolymer of a thermoplastic resin, ceramic powder and a solvent by a casting molding method and removing the solvent with gypsum or the like is also possible, which is effective for molding a complicated shape.

Example 4 A mixed powder of SiC fibers having a diameter of 1 μm and an aspect ratio of 100 and Si ₃ N ₄ having an average particle diameter of 0.1 μm in a raw material mixture ratio of 25:75 vol% was used as a sintering aid Y. ₂ O
₂ vol% of ₃ and ₂ vol% of Al ₂ O ₃ were added, and 25 vol% of a prepolymer of a phenol novolac resin was added as a molding binder, and acetone was added as a solvent, and the mixture was mixed in a pot mill for 24 hours. Then, after the solvent in the mixture is dried and removed, the raw material is mechanically pressed with a molding pressure of 1000 kgf / cm ² and a temperature of 1 kg.
Pressure is maintained at 50 ° C for 3 minutes, diameter 50mm, thickness 20mm
Was molded. From this, the particle packing ratio of the molded body is 7
3 vol% was obtained. The molded binder was removed from this molded body, leaving the free carbon content, and heat-treated at 1450 ° C. for 2 hours in a nitrogen atmosphere. And 5 at 1750 ° C. in a nitrogen atmosphere
It was treated for a time to produce a sintered body. A sintered body having characteristics of three-point bending strength of 630 MPa and K _1C = 11.3 was obtained.
The shrinkage amount at the time of sintering is about 7%, which is less than 1/2 of that of a general pressureless sintered product.

Example 5 TiN particles having an average particle size of 3 μm and metallic Si having an average particle size of 0.5 μm were mixed into a mixed powder having a raw material compounding ratio of 50:50 vol%, and 19 vol of an epoxy resin prepolymer was used as a molding binder. %, Tetraphenylphosphonium as a curing catalyst was added in an amount of 1 vol%, acetone was added as a solvent, and they were mixed in a pot mill for 24 hours. Then, after the solvent in the mixture was dried and removed, the raw material was mechanically pressed at a molding pressure of 500 kgf / cm ² to a diameter of 40.
A preform having a thickness of 10 mm and a thickness of 10 mm is prepared. Similarly, Al ₂ O ₃ particles having an average particle size of 10 μm and an average particle size of 0.
19 vol% of epoxy resin prepolymer as a molding binder, 1 vol% of tetraphenylphosphonium as a curing catalyst, and 1% by volume of acetone as a solvent are added to a mixed powder having a raw material mixing ratio of 50:50 vol% of 5 μm metal Si. And mixed in a pot mill for 24 hours. After the solvent in the mixture is dried and removed, the raw material is mechanically pressed at a molding pressure of 500 kgf / cm ^2.
Then, a preform having a diameter of 40 mm and a thickness of 10 mm is prepared. Then, the preforms (1) and (2) were overlaid on a mold and kept at a temperature of 160 ° C. for 30 seconds, a diameter of 40 mm and a thickness of 2
A product having a diameter of 0 mm was molded. After removing the molding binder from this composite molded body, the temperature was changed from 1100 ° C.
0 ° C. was heated at a heating rate of 4 ° C./h for a long time. As a result, a structure having conductivity and insulation could be manufactured. The joint (interface) part of the composite material was bonded by Si ₃ N ₄ which is a nitride of Si.

Example 6 SiC particles having an average particle size of 1 μm and metallic Si having an average particle size of 0.2 μm were mixed into a mixed powder having a raw material compounding ratio of 25:75 vol%, and 19 vol of an epoxy resin prepolymer was used as a molding binder. %, Tetraphenylphosphonium as a curing catalyst was added in an amount of 1 vol%, acetone was added as a solvent, and they were mixed in a pot mill for 24 hours. Then, after the solvent in the mixture is dried and removed, the raw material is mechanically pressed with a molding pressure of 1000 kgf / cm ² and a temperature of 1 kg.
Hold pressure at 60 ° C for 30 seconds, outer diameter 60 mm, inner diameter 50 m
A ring having a diameter of m and a thickness of 20 mm was formed. From this, a particle filling rate of the molded body of 72 vol% was obtained. The molding binder was removed from this molded body, leaving the free carbon content, and heated in a nitrogen atmosphere at 1100 ° C to 1350 ° C at a temperature rising rate of 4 ° C / h for a long time. Result of 3-point bending test: 570MP
The bending strength of a was obtained. The pore shape in the sintered body is 3μ
It was as small as m or less, and it was found that the raw material and the binder were uniformly mixed. After polishing the sliding surface, Al ₂
A sliding test was conducted using O ₃ (relative density: 98%). The sliding conditions were a surface pressure of 10 kgf / cm ² and a sliding speed of 3 m / sec in the atmosphere. As a result, the friction coefficient of 0.005, the wear amount of 0.01mg / cm ^2/100
h and small. In addition, as a comparative example, Si ₃ N ₄ / Al ₂ O
₃ combined sliding test results, the friction coefficient is 0.15, the wear amount was 0.21mg / cm ² / 100h, inferior to the present invention.

[0018]

As compared with the conventional ceramics molding method using a thermoplastic resin, the dimensional stability of the product is improved, the life of the mold is extended, and cracks due to degreasing can be prevented. By using the prepolymer of the thermosetting resin, a solvent can be used for mixing with the ceramic raw material, and uniform mixing is possible. From the above points, it is an excellent molding method for mass-produced products. Furthermore, when the prepolymer thermosetting resin is decomposed, graphite remains in the sintered body and brings about a sliding effect, so it can be applied to sliding members such as bearings, guide rails, gears, Oldham rings, bearings, and floating seals. ..

[Brief description of drawings]

FIG. 1 is a graph showing the relationship between the bending strength of a Si ₃ N ₄ sintered body obtained by the reaction sintering method of metallic Si and the addition amount of a prepolymer of a thermosetting resin.

FIG. 2 is a graph showing the relationship between the packing rate of molded particles and the amount of prepolymer added to the thermosetting resin.

FIG. 3 is a graph showing the relationship between the apparent viscosity by a flow tester and the packing rate of molded particles.

Claims (9)

[Claims] 1. A mixture of a thermosetting resin prepolymer and a ceramic powder is molded in a mold having a temperature above the flow initiation temperature of the prepolymer, and then the organic component in the resin is decomposed in an inert gas, Furthermore, a method for forming graphite-dispersed ceramics, characterized by sintering in an inert gas. 2. A mixture in which the surface of ceramic powder is covered with a prepolymer of a thermosetting resin is molded in a mold having a temperature above the flow initiation temperature of the prepolymer, and then the mixture is heated in an inert gas in the resin. A method for forming graphite-dispersed ceramics, which comprises decomposing organic matter and further sintering in an inert gas. 3. The graphite-dispersed ceramics according to claim 1, wherein the ratio of the prepolymer of the thermosetting resin to the ceramic powder in the mixture is 30:70 to 5:95 vol%. Molding method. 4. The method for molding graphite-dispersed ceramics according to claim 3, wherein the graphite-dispersed ceramics molded body obtained by sintering has a particle packing rate of 70 vol% or more. 5. A mixture in which the surface of ceramic powder is covered with a prepolymer of thermosetting resin has an apparent viscosity of 0.1 MPa · s to 0.3 M measured by a flow tester.
Pa · s (however, nozzle shape φ6 × 6.8 mm, pressure 3
9 MPa), The method for molding a graphite-dispersed ceramic according to claim 2. 6. (a) a step of mixing a prepolymer of thermosetting resin with ceramic powder and a solvent, (b) a step of removing the solvent, (c) a pulverizing step, (d) pressurization in a room temperature mold Graphite characterized by including a step of molding and producing a preformed body, (e) a step of decomposing an organic component in a resin in an inert gas, and (f) a step of sintering in an inert gas. Forming method of dispersed ceramics. 7. The graphite-dispersed ceramics according to claim 1, wherein the ceramic powder is made of at least one of inorganic compound and / or metal particles, short fibers and long fibers. Molding method. 8. The prepolymer of the thermosetting resin is at least one of polyimide resin, epoxy resin, urea resin, melamine resin, phenol resin, unsaturated polyester resin, alkyd resin, urethane resin, urea resin and diallyl phthalate resin. The method for forming a graphite-dispersed ceramic according to any one of claims 1 to 6, comprising: 9. The prepolymer of the thermosetting resin is at least one of polyimide resin, epoxy resin, urea resin, melamine resin, phenol resin, unsaturated polyester resin, alkyd resin, urethane resin, urea resin, diallyl phthalate resin. 7. The method for forming a graphite-dispersed ceramics according to claim 1, which comprises: