JPH0123433B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for producing a green body for producing a ceramic sintered body for producing a high-density and high-strength ceramic sintered body. A conventional method for producing a ceramic sintered body is a method in which a powder raw material is molded into a product having a desired shape and then sintered. Various means are known for molding the powder raw material into a product having a desired shape. For example, methods such as slurry casting, extrusion, potter's wheel molding, rocking molding, and dry pressure molding are known. The above-mentioned molding means can be roughly classified into wet molding means and dry molding means depending on the liquid content during molding. Among these methods, wet molding methods require that the formed body be sufficiently dried after molding, and shrinkage due to drying must be taken into consideration.
Defects such as warping and cracking are likely to occur during drying. On the other hand, dry molding is an advantageous molding method as it has excellent dimensional accuracy, but when using fine powder, it is difficult to fill the mold uniformly and pressurize it because the powder has poor fluidity. This is difficult and may cause variations in the bulk density of the formed body or the pressure distribution during molding, and defects due to bridging are likely to occur in the formed body. These defects during molding remain in the sintered body even after sintering, causing a significant decrease in the physical properties, especially the mechanical strength, of the sintered body. When molding, it is used after being granulated in advance to improve fluidity. Incidentally, from the viewpoint of handling such as fluidity, it is preferable that the granules have a high bulk density and are hard. It is extremely important that the individual granules are completely crushed during compression molding to obtain a unified product, and soft granules with relatively low bulk density are usually required. This is because when the bulk density of the granules is high and hard, the granules are difficult to crush and require extremely high molding pressure during molding. Furthermore, pores tend to remain in the formed body, making it difficult to obtain a high-strength sintered body. Because it will be. However, granules with too low bulk density are easily broken and re-powdered during handling, and are significantly compressed during molding, causing lamination due to air trapped in the mold and requiring long molding times. However, it has the disadvantage that it is difficult to efficiently produce a green body. As a method for improving the above-mentioned drawbacks, a lubricant is usually added to improve the transmission of molding pressure and improve the moldability. The lubricants include, for example, carbo wax, diglycol stearate, stearic acid, magnesium stearate, zinc stearate, barium stearate, aluminum stearate, mixtures of mineral oil and fat, paraffin emulsion, wax emulsion, glycerin or polyethylene. Watkus is known. As an example, according to JP-A-50-78609, which claimed priority based on patent application No. 409073 filed in the United States on October 24, 1973, silicon carbide with submicron particle size is pressure-molded. A method is described in which aluminum stearate is added and mixed as a lubricant when molding the resulting body. However, according to this method, the die press
The density of the formed body molded at a molding pressure of 5000 psi (approximately 351.5 kg/cm ² ) is equivalent to 55% of the theoretical density, and the density of the formed body molded at a molding pressure of 5000 psi (approx.
The density of the green body molded at a molding pressure of 2109 Kg/cm ² ) is equivalent to 59% of the theoretical density, and this method requires an extremely high molding pressure to obtain a green body with high density. . As mentioned above, it is important that the sintering ceramic powder molded by dry molding means has excellent moldability, and is usually used by adding and mixing a lubricant and granulating it. When using extremely fine powder as ceramic powder for sintering, the powder has strong mutual cohesiveness and is extremely difficult to crush when granulated, and conventionally known lubricants have the disadvantage of not being able to improve formability to that extent. However, it has been difficult to obtain a high-density and high-strength sintered body by molding extremely fine ceramic powder for sintering using dry molding means. By the way, as a result of various studies on the effects of conventionally known lubricants, the present inventors found that it was difficult to improve the formability of extremely fine ceramic powder for sintering with conventionally known lubricants. The conclusion was reached that the cause was due to the following mechanism. In other words, conventionally known lubricants are liquid, grease-like, or relatively soft semi-solid.
When used with fine powders that have a large number of contact points between particles, the lubricant present between the particles does not exert a lubricating effect, but rather causes the particles to adhere to each other and weakens the lubricating effect. Furthermore, when mixing conventional lubricants with extremely fine powders such as those used in the present invention, the lubricant dissolved in a solvent is generally added and mixed for the purpose of uniform mixing, so drying is not necessary. When the lubricant is used, the particles appear to be stuck together. As mentioned above, when conventional lubricants are mixed into extremely fine powders, rather than providing lubricity between the particles, the particles stick or stick to each other, causing friction between the particles. It is difficult to reduce the resistance, and extremely high molding pressure is required to create a formed body with a high theoretical density. Therefore, conventionally, in order to obtain a high-density formed body, extremely high molding pressure is required, which not only requires a strong mold that can withstand high molding pressure, but also causes wear and tear of the mold. It had the disadvantage of a significantly short lifespan. By the way, the present inventors have conventionally used a ball mill in which fluororesin balls were charged as a mixing medium as a mixing means for obtaining a raw material mixture for sintering. However, fluororesin is extremely expensive, and since the fluororesin balls wear out and get mixed into the mixture, the fluororesin balls are replaced with balls made of sintered silicon carbide during the mixing process. As a result, it was discovered that the moldability of the produced mixture was significantly worse than that of a mixture produced using fluororesin balls. As a result of various studies on the above-mentioned phenomenon, the present inventors inferred that the fluororesin mixed in the mixture may have some influence on the molding process, and so they mixed the fluororesin with ceramic fine powder and made the mixture. When the material was pressure-molded, it was found that the hard fluororesin, which had not previously been thought to have a lubricating effect that improves the moldability of fine powder, had an extremely excellent lubricating effect, and it was found to be a lubricant that was not previously known. The present inventors discovered that it has the surprising effect of significantly improving the moldability compared to No. 57-25997 describes ``Ceramics sintering in which a mixture mainly composed of ceramic fine powder composed of one or more components is pressure-molded to form a formed body with a density equivalent to at least 55% of the theoretical density. A method for producing a green body for producing a ceramic sintered body, characterized in that the mixture is made by adding 0.5 to 15 parts by weight of a fluororesin to 100 parts by weight of ceramic fine powder and uniformly mixing the mixture. The present invention proposes an invention related to "a method for manufacturing a formed body." According to the invention, the mixture obtained by mixing ceramic fine powder and fluororesin has extremely excellent moldability, so it is relatively easy to produce extremely high-density formed bodies, which have been difficult to obtain in the past. It can be easily obtained with low molding pressure. The reason why the moldability of the ceramic fine powder mixed with fluororesin in the invention is extremely good is that fluororesin is an extremely hard and highly tough resin, and unlike conventional lubricants, it does not cause particles to stick to each other. This is thought to be because it does not have a sticking effect, has an extremely small surface friction coefficient, and has good lubricating properties because it is powder-like. By the way, the mixture used in the invention includes:
During the manufacturing process or handling, relatively coarse foreign matter may get mixed in, or the fluororesin may form coarse aggregates. When a sintered body is manufactured using a mixture containing It has been found that this is a cause of significant deterioration of the physical properties, especially the bending strength. Therefore, especially when attempting to obtain a sintered body with high strength and reliability, it is important that the mixture does not contain coarse foreign matter or coarse aggregates of fluororesin. However, no suitable method is known for removing coarse foreign matter from the mixture containing the fluororesin and preventing the fluororesin contained in the mixture from agglomerating and achieving a uniform dispersion state. Ta. Therefore, the present inventors conducted various studies to remove coarse foreign substances from the mixture and to make the fluororesin contained in the mixture into a uniformly dispersed state. A mixture of resins is put into a dispersion medium, subjected to uniform dispersion treatment, and then passed through a sieve having a mesh size of 65 μm or less to remove coarse foreign substances contained in the mixture. The present invention has been completed based on the new finding that the present invention has the surprising effect of being able to disperse the fluororesin contained in the mixture by loosening the agglomeration of the fluororesin and making it uniformly dispersed. The present invention further improves the method previously proposed by the present inventors, and enables a high density to be obtained even at a relatively low compacting pressure. It is an object of the present invention to provide a method for producing a green body for producing a ceramic sintered body that does not contain coarse foreign matter or coarse aggregates of fluororesin. According to the present invention, a mixture containing ceramic fine powder as a main component consisting of one or more components is added into a dispersion medium to form a suspension, and then the suspension is sieved and then optionally In the method for producing a green body for producing a ceramic sintered body, which is pressure-molded into the shape of The volume ratio of solid content consisting of ceramic fine powder and fluororesin in the liquid is 5 to 5.
A sieve having a sieve opening of 65 μm or less, with a pressure difference within the range of 50% and a pressure difference to overcome the stagnation of sieving action due to pressure loss occurring between the front side of the sieve and the rear side of the sieve of the suspension. The above object can be achieved by a method for producing a green body for producing a high-strength ceramic sintered body, which is characterized by passing through a sintered body. Next, the present invention will be explained in detail. In the present invention, it is necessary to mix 100 parts by weight of ceramic fine powder consisting of one or more components with 0.5 to 15 parts by weight of fluororesin.
The reason for this is that if the amount of the fluororesin mixed is less than 0.5 parts by weight, the mixture will be significantly inferior in moldability, and not only will extremely large pressure be required to produce the formed body, but also the bulk density of the formed body will be reduced. This tends to cause variations in the pressure distribution during molding and molding, making it difficult to obtain a uniform shaped body with few defects.On the other hand, if the amount exceeds 15 parts by weight, the amount of fluororesin present in the shaped body increases and the formed body This is because it becomes difficult to obtain a high-density sintered body because the density of the sintered body becomes low, and a range of 2 to 10 parts by weight is especially preferable. The fluororesin is preferably at least one selected from polytetrafluoroethylene, polytrifluorochloroethylene, tetrafluoroethylene-hexafluoropropylene copolymer, and polyvinylidene fluoride, and among them, Polytetrafluoroethylene is most suitable. In the present invention, the fluororesin has an average particle size of
Preferably, it is a fine powder of 3 μm or less. The reason for this is that if the average particle size of the fluororesin is larger than 3 μm, it cannot be uniformly dispersed considering the amount of the fluororesin mixed, and the effect of the lubricant becomes uneven. This is because pores are generated in the sintered body, making it difficult to produce a high-strength sintered body. Various types of ceramic fine powder can be used in the present invention, but among them, it is preferable that the ceramic powder has at least one type selected from carbides, nitrides, oxides, or compounds thereof as a main component. Preferably, carbides include silicon carbide, boron carbide, aluminum carbide,
Tungsten carbide, titanium carbide, tantalum carbide,
Zirconium carbide, nitrides such as silicon nitride, boron nitride, aluminum nitride, titanium nitride, tantalum nitride, zirconium nitride, oxides such as steatite, forsterite,
Alumina, zircon, beryllia, magnesia, mullite, cordierite, aluminum titanate, zirconia, etc. can be used. In the present invention, the ceramic fine powder preferably has an average particle size of 2 μm or less.
Ceramic powder with an average particle size larger than 2 μm has relatively few contact points between particles, and conventionally known lubricants can sufficiently improve moldability.
This is because it is difficult to produce a high-density sintered body due to the poor sinterability of the powder. The ceramic fine powder in the present invention is 5
It is most preferable to use a material whose main components are silicon carbide fine powder having a specific surface area of ~100 m ² /g and a sintering aid added if necessary. As the silicon carbide fine powder, silicon carbide fine powder consisting of one or more types selected from α-type crystal, β-type crystal, and amorphous can be used. In particular, in order to produce high-strength silicon carbide pressureless sintered bodies, it is advantageous to use silicon carbide fine powder containing mainly β-type crystals, especially silicon carbide containing 80% by weight or more of β-type crystals. It is more suitable than fine powder. The sintering aid added as necessary is usually at least one of a densification aid and a carbonaceous additive. It is advantageous to use mainly boron-containing additives as the densification aid, and other additives such as beryllium,
Additives containing aluminum and the like can also be used. As the boron-containing additive, for example, at least one selected from boron and boron carbide is converted into silicon carbide fine powder in terms of boron content.
It is advantageous to add from 0.1 to 3.0 parts by weight per 100 parts by weight. The carbonaceous additive can be used as long as it exists in a carbon state at the start of sintering, such as phenolic resin, coal tar pitch, polyphenylene, polymethylphenylene, carbon black, and acetylene black. The fixed carbon content of at least one selected one is 0.3 parts by weight per 100 parts by weight of silicon carbide fine powder.
It is advantageous to add up to 4.0 parts by weight. According to the present invention, the mixture of ceramic fine powder and fluororesin powder can be obtained by charging the ceramic fine powder and fluororesin powder into a conventionally known mixer and mechanically mixing them. can be done, but
In addition, ceramic fine powder is charged into a mixer made of fluororesin or a mixer having a mixing medium made of fluororesin, and during mixing, fine fluororesin powder generated by wear is mixed from the mixer or the mixing medium. You can also. As the mixer, it is advantageous to use, for example, a ball mill, a vibration mill, or an attritor using Teflon balls as a mixing medium. According to the present invention, the volume ratio of the solid content consisting of fine ceramic powder and fluororesin in the suspension is within the range of 5 to 50%, and if necessary, a dispersant is added to perform uniform dispersion treatment. After that, a pressure difference is applied to overcome the stagnation of the sieving action due to the pressure loss that occurs between the front side of the sieve and the rear side of the sieve, and if necessary, the suspension is passed through a sieve of 65 μm or less while being vibrated. The cause of relatively large defects such as pores and inclusions in the sintered body, which significantly deteriorate the strength of the sintered body by passing through a sieve having meshes, is eliminated. According to the present invention, a mixture of ceramic fine powder and fluororesin is added to a dispersion medium, and the volume ratio of the solid content of ceramic fine powder and fluororesin in the suspension is in the range of 5 to 50%. It is necessary to do this internally. The reason for this is that if the volume ratio is higher than 50%, it is difficult to uniformly disperse the ceramic fine powder and the fluororesin, and the viscosity of the suspension also increases, making it difficult to pass through the sieve efficiently. On the other hand, if it is lower than 5%, the uniform dispersibility of ceramic fine powder and fluororesin in the suspension improves, but a large amount of suspension must be sieved, resulting in a substantial throughput per unit equipment. This is because the ratio is small and not economical, and a preferable result can be obtained within the range of 10 to 40%. According to the present invention, acetone, methanol, ethanol, hexane, heptane, nonane, toluene, xylene, ethyl methyl ketone, methyl isobutyl ketone, ethyl benzene,
It is preferable to use at least one selected from ethylene glycol, trichloroethylene, cyclohexane, nitromethane, nitroethane, isopropyl alcohol, benzene, carbon tetrachloride, and water. According to the present invention, a dispersant is added to the suspension if necessary. When water is mainly used as the dispersion medium, the dispersant may be an amine, an organic compound having a carboxyl group, an organic compound having a sulfo group, an ester, an ammonium compound, an organic compound having an ether bond, a carboxylic acid salt, or an aluminic acid. salts, phosphates, phosphate complexes, sulfonates,
It is advantageous to use at least one selected from silicates, such as tetramethylammonium hydroxide, monoethanolamine, monoethylamine, diethylamine, trimethylamine, propylamine, isobutylamine, monobutylamine, di-n- Propylamine, tannic acid, sodium alginate, ammonium alginate, polyacrylic acid, polyacrylic acid amine,
Polyacrylic ester, ammonium polyacrylate, sodium lignosulfonate, ammonium lignosulfonate, sodium aluminate, ammonium aluminate, water glass, fatty acid salt, alkylbenzene sulfonate, linear alkylbenzene sulfonate, α-olefin sulfone There are acid salts, sulfonate salts of naphthalene-formalin condensates, and polyoxyethylene alkyl phenyl ethers, and these can be used alone or in combination. Note that the dispersion state can also be improved by adjusting the pH value of the suspension with aqueous ammonia or the like. The PH value of the suspension is
Advantageously, it is in the range 5.5 to 11. On the other hand, when an organic liquid is mainly used as the dispersion medium, it is advantageous to use at least one selected from amines, organic compounds having a carboxyl group, organic compounds having a sulfo group, and esters. Fatty acid amine, sorbitan fatty acid ester, dialkyl sulfosuccinic acid ester salt, fatty acid, alkyl amine salt, benzene sulfonic acid, polyoxysorbitan fatty acid ester, polyoxyethylene glycerin fatty acid ester, polyethylene glycol fatty acid ester, pentaerythritol fatty acid ester, propylene glycolic acid ester, sucrose fatty acid ester, polyglycerin fatty acid ester,
There are fatty acid alkanolamides and amine oxides, and these can be used alone or in combination. The dispersant has the effect of loosening the agglomeration of ceramic fine powder and fluororesin in the suspension, improving the uniform dispersibility of ceramic fine powder and fluororesin having different specific gravity and particle size, and It has the effect of lowering the viscosity of the material and making it easier to pass through the sieve. According to the present invention, the amount of the dispersant added is preferably within the range of 0.05 to 15 parts by weight based on 100 parts by weight of the total weight of the ceramic fine powder and the fluororesin. The reason for this is that if the amount of the dispersant added is less than the above range, it will not be possible to sufficiently loosen the agglomeration of ceramic fine powder and fluororesin in the suspension and maintain a uniformly dispersed state, making it difficult to sieve efficiently. If the amount exceeds the above range, it is not only uneconomical to add more dispersant than necessary, but it also remains in the sintering raw material and causes problems during sintering. This is because it will have an adverse effect. According to the present invention, the suspension needs to be uniformly dispersed before passing through a sieve. The reason for this is that the ceramic fine powder and fluororesin used in the present invention have strong aggregation properties and remain in a relatively strong agglomerated state even when added to the dispersion medium. This is because the fluororesin cannot be passed through efficiently or the fluororesin cannot be uniformly dispersed. The uniform dispersion treatment is carried out using a vibrating mill, an attritor,
It is advantageous to carry out the dispersion using at least one dispersion device selected from a ball mill, a colloid mill, a Henschel mixer, or a high-speed mixer. This is because conventionally commonly used dispersion methods such as stirring, such as methods using impellers or screws, have difficulty in sufficiently loosening agglomerates and are unable to efficiently pass through a sieve. This is because the dispersing device can apply an extremely strong shearing force, so the dispersing force is extremely strong, and a uniformly dispersed suspension, which is the object of the present invention, can be easily obtained in a short time. According to the present invention, the suspension can be sieved more efficiently and quickly by providing a pressure difference to overcome the stagnation of the sieving action due to the pressure loss occurring between the sieve front side and the sieve back side of the suspension. can be passed through. According to the present invention, it is preferable that the pressure applied to the front side of the suspension to be sieved is varied at a period of 1/400 to 5 seconds. The advantage of varying the pressure applied to the sieve front side of the suspension is that the flow of the suspension in the sieve can be significantly disturbed by pressure fluctuations, which improves the dispersibility of ceramic fine powder and fluororesin in the sieve. This is because particles can be further improved to prevent particles from coagulating with each other, allowing them to pass through the sieve efficiently. The reason why it is preferable to set the period of the pressure fluctuation within the range of 1/400 to 5 seconds is because if the period is shorter than 1/400 second, the transmission force of the pressure fluctuation in the suspension deteriorates significantly. This is because it is difficult to pass through the sieve efficiently, and on the other hand, if it is longer than 5 seconds, the flow of the suspension in the sieve cannot be disturbed so much, so the effect of pressure fluctuation becomes small. Optimal results are obtained within ~2 seconds. According to the present invention, the difference between the maximum and minimum pressures applied to the front side of the suspension is at least 0.3Kg/
^cm2 , and when the pressure applied to the front side of the suspension is maximum, the pressure difference between the front side of the sieve and the back side of the sieve is 0.2
~5Kg/ ^cm2 , and when the pressure applied to the front side of the sieve is the minimum, the pressure difference between the front side of the sieve and the back side of the sieve is within the range of -0.5 to 2Kg/ ^cm2 . The most favorable results are obtained. Note that the pressure difference is a value obtained by subtracting the pressure value on the back side of the sieve from the pressure value on the front side of the sieve. Various means can be considered as a means for applying pressure to the suspension, but among them, a means using a pulsating pump is capable of applying pressure to the suspension while applying pressure fluctuations, and at the same time applying vibration. This is extremely advantageous. For example, a diaphragm pump can be used as the pulsating pump. Further, according to the present invention, vibrations are applied to the suspension if necessary. By applying vibration to the suspension, it is possible to prevent the ceramic fine powder and fluororesin in the suspension from agglomerating and maintain a uniform dispersion state, and furthermore, it is possible to maintain a uniform dispersion state by applying vibration to the suspension. By applying this vibration, the viscosity of the suspension can be significantly reduced, allowing it to pass through the sieve easily. The vibration applied to the suspension is preferably within the range of 1 to 400 Hz. The reason for this is that if the frequency is lower than 1Hz, it will be difficult to maintain uniform dispersion of the suspension or reduce the viscosity, while if it is higher than 400Hz, This is because the transmission of vibrations deteriorates significantly, making it difficult to maintain uniform dispersion of the suspension or reduce the viscosity, as in the case of low vibration frequencies. Optimal results are obtained when vibration is applied. As the vibration to be imparted to the suspension, it is advantageous to use at least one selected from, for example, mechanically imparted vibration, electromagnetic force-induced vibration, and pulsating pump-induced vibration. According to the present invention, it is necessary that the mesh size of the sieve is 65 μm or less. If the mesh size of the sieve is larger than 65 μm, it is possible to remove coarse foreign substances that significantly affect the physical properties of the sintered body, and to uniformly disperse the fluororesin, which is the high strength object of the present invention. This is because it becomes difficult to obtain a sintered body with high reliability.In order to obtain a sintered body with high strength and high reliability, it is advantageous to set the sieve size to 44 μm or less. In addition, from the purpose of removing foreign matter in the mixture, it is advantageous for the sieve mesh to be as small as possible, but foreign matter that is small enough to pass through a 5 μm sieve has little effect on the strength of the sintered body. It does not cast shadows, and the sieve mesh is 5 μm.
Using a smaller sieve would significantly increase the time required to pass through the sieve, making it impractical;
Advantageously, the mesh size is within the range of 5 to 44 μm. According to the present invention, the suspension that has passed through the sieve is dried to remove the dispersion medium, and then a product form is produced in the form of a dry mixture by a dry molding method such as a dry pressure molding method. Ru. According to the invention, it is advantageous for the dry mixture to contain shaping aids. By blending the molding aid into the sintering raw material powder, it acts as a lubricant or binder during molding, and exhibits the effect of reducing molding defects that occur in the formed body. Among the above-mentioned molding aids, those having the effect as a lubricant include carbowax, magnesium stearate, barium stearate, aluminum stearate, zinc stearate, stearic acid, etc., and those having the effect as a binder include Starch, dextrin, gum arabic, casein, molasses, Na-carboxymethyl cellulose, methyl cellulose, polyvinyl alcohol, polyvinyl methyl ether, polyacrylic acid amide, tannic acid, liquid paraffin, wax emulsion, ethyl cellulose, polyvinyl acetate, phenol resin, etc. Cellulose acetate, glycerin, polyethylene glycol, etc. have both effects, and one or more of these can be contained. According to the present invention, the mixture is used after being granulated to improve its fluidity. The mixture has a powder bulk density of 5 to 46% of the theoretical density.
Preferably, the granules have a density corresponding to . The reason why the bulk density of the powder is set within the above range is that if the bulk density of the powder is less than 5%, the compression ratio during molding becomes extremely large, making molding difficult. If the size is larger, the particle size distribution of the granules may be relatively wide or the apparent granule density may be high, but in the former case, the fluidity deteriorates, and in the latter case, the crushing strength of the granules is extremely strong. This is because it may remain in the same shape without being crushed during molding, resulting in areas with extremely low density in the sintered body. Among these, a range of 10 to 40% is preferable. Note that the powder bulk density is the volume of ceramic fine powder that occupies a certain volume of granules, that is, the volume of ceramic fine powder that occupies in a unit volume that includes solids, internal voids, and external voids,
The apparent granule density
Density refers to the volume of ceramic fine powder in a unit bulk volume, and bulk volume is the volume including the ceramic fine powder and internal voids in the granule. Preferably, the mixture is in the form of granules with an average particle size within the range of 0.02 to 0.8 mm. The reason for this is that if the average particle size of the granules is smaller than 0.02 mm, the fluidity will drop significantly, resulting in variations in the bulk density of the formed body and pressure distribution during molding, and defects caused by bridging in the formed body. On the other hand, if it is larger than 0.8 mm, it is difficult to mold a small and complex shaped product. As a method for granulating the mixture, any one selected from, for example, a tablet method, a direct granulation method, a granulation method by spray drying, or a granulation method comprising spray freezing and then freeze drying can be used. . According to the invention, it is advantageous for the mixture to be pressed into a shaped body having a density corresponding to at least 45% of the theoretical density. The reason for this is that when the density is lower than 45%, there are relatively few contact points between the ceramic fine powder particles, making it difficult to uniformly progress the firing shrinkage during sintering, and making it difficult to obtain a high-density sintered body. This is because it becomes difficult to obtain a high-strength sintered body due to variations in physical properties such as the density of the sintered body.In particular, when a high-strength sintered body is required, the density should be increased by 50%. It is effective to do the above. In addition, as a method for pressure molding the mixture, it is advantageous to use, for example, a die press molding method or an isostatic molding method. According to the present invention, a ceramic sintered body having high density and high strength can be manufactured by charging the green body manufactured as described above into a sintering furnace and sintering it. Next, the present invention will be explained with reference to examples. Example 1 97.3% by weight consists of β-type crystals, contains 0.40% by weight of free carbon, 0.17% by weight of oxygen, 15.6 m ² /
500 g of silicon carbide fine powder having a specific surface area of 1.5 g, and 6.5 g of boron carbide powder obtained by crushing commercially available 200-mesh boron carbide particles and adjusting the specific surface area to 22.7 m ² /g by particle size classification, and an average particle size of about 210 Å, Specific surface area 124
260 ml of benzene and 28 g of polytetrafluoroethylene powder with an average particle size of 0.05 μm for ceramic fine powder made of a mixture with 10 g of carbon black of m ² /g.
was added and mixed for 4 hours using a vibration mill, and then dried while being mixed in the vibration mill.
Next, add 210 ml of distilled water, 8 g of cellulose acetate, and 2 ml of tetramethylammonium hydroxide to 200 g of the above mixture.
After dispersing for 10 hours using a ball mill, the suspension was discharged from the ball mill, and an electric vibrator was used to mix the suspension with
The suspension was passed through the sieve by applying pressure to the front side of the sieve using a diaphragm pump while applying Hz vibration.
The sieve used has a sieve mesh of 25 μm and a sieve frame diameter of 200 mmφ.
600W of ultrasonic vibration was applied. The maximum value of the pressure applied to the suspension is 2.0Kg/cm ² , and the maximum value is 0Kg/cm ²
The period of fluctuation was 1 second, and the pressure applied to the suspension on the back side of the sieve was released to the atmosphere. The passage speed of the suspension was 0.13 g/cm ² ·sec. In addition,
The viscosity of the suspension discharged from the ball mill is B
When measured with a type viscometer (rotation speed: 60 rpm, rotor: No. 4), it was 130 g/cm·sec. The suspension under the sieve passed through the sieve was heated to -60 to -70℃.
The average particle size is 0.10mm when sprayed into a container maintained at
Frozen granules were obtained. Next, the frozen granules are placed in a container maintained at 0.01 to 20 mmHg and -5 to -10°C, and freeze-dried to reduce the bulk density of the powder.
A granular dry mixture of 0.53 g/cm ² was obtained. An appropriate amount of the granules was taken and molded using a metal die at a pressure of 0.15 t/cm ² , and then using a hydrostatic press at a pressure of 1.8 t/cm ² . The density of the formed body obtained by the above molding is 1.93 g/cm ³
It was recognized that The raw material was placed in a Tammann-type firing furnace and sintered in an argon gas flow. The heating rate is from room temperature to
The temperature was raised at a rate of 5°C/min up to 1650°C, and after being held at 1650°C for 45 minutes, the temperature was further raised at a rate of 5°C/min, and the maximum temperature was held at 2100°C for 30 minutes. The density of the obtained sintered body was 3.10 g/cm ³ (corresponding to 96.6% of the theoretical density). This sintered body is
It was processed into a bar shape of 3 x 30 mm, and finally polished with 2 μm diamond abrasive grains. The three-point bending strength was measured at a span of 20 mm and a crosshead speed of 0.5 mm/min. It was 73 Kg/mm ² at room temperature. It was confirmed that the sintered body had an average strength of , and a Weibull coefficient of 12, making it an extremely strong and highly reliable sintered body. The three-point bending strength was measured at 30
The Weibull coefficient was determined using Weibull probability paper. The Weibull coefficient is a numerical value determined from the relationship between fracture stress and survival probability in Weibull statistics, which is used as a statistical representation of ceramic strength, and is used as a measure of reliability of strength. Example 2 A green body was prepared using the same formulation and operation as in Example 1, but using the fluororesin shown in Table 1, and a sintered body was obtained. The results were measured in the same manner as in Example 1 and are shown in Table 1.

[Table] Example 3 Ceramic fine powder and benzene similar to Example 1
260 ml was mixed for 30 hours in a ball mill equipped with polytetrafluoroethylene balls having a diameter of 15 to 20 mm, and then dried while being mixed in the mill. The mixture contained about 6% by weight of polytetrafluoroethylene powder having an average particle size of about 0.01 μm. Next, 210 ml of distilled water, 24 g of polyacrylic acid ester, and 3 g of condensed naphthalene sulfonic acid ammonium salt were added to 200 g of the above mixture, and after performing a dispersion treatment for 10 hours using an attritor, a suspension was obtained from the attritor. The same procedure as in Example 1 was carried out, except that the vibration applied to the suspension was 10 Hz, the maximum value of the pressure applied to the suspension was 1.8 Kg/cm ² , and the minimum value was -0.2 Kg/cm ² . The sieving process was carried out under the conditions that the fluctuation period was 1/2 second and the passing speed was 0.25 g/cm ² ·sec. The viscosity of the suspension measured in the same manner as in Example 1 was 180 g/cm·sec. The under-sieve suspension passed through the sieve was spray-dried to give an average particle size of 0.12 mm and a powder bulk density of 0.79 g/cm ³
granules were obtained. An appropriate amount of the granules was taken and the same procedure as in Example 1 was performed to obtain a product. The density of the generated body is
It was found to be 2.01 g/cm ³ . Next, the formed body was sintered in the same manner as in Example 1. The density of the obtained sintered body was 3.17 g/cm ³ (corresponding to 98.7% of the theoretical density). In addition, the three-point bending strength measured in the same manner as in Example 1 was 87Kg/3 at room temperature.
It has an average intensity of mm ² and its Weibull coefficient is
It was 13. Example 4, Comparative Example 1 A sintered body was produced in the same manner as in Example 3, but by changing the fluororesin content, sieving conditions, and molding pressure as shown in Table 2. The results were measured in the same manner as in Example 1 and are shown in Table 2.

【table】

[Table] As can be seen from the results shown in Table 2, when the content of fluororesin in Comparative Example 1-1 is small,
Not only did extremely high compacting pressures be required to obtain a high-density green body, but the bending strength of the sintered bodies was also relatively low. On the other hand, when the content of fluororesin in Comparative Example 1-2 was high, the density of the formed body was relatively low, and the strength of the sintered body was not so high. Furthermore, in Comparative Examples 1-3 shown in the same table, the viscosity of the suspension was extremely high and it was extremely difficult to pass through the sieve. Example 5 The formulation and operation were the same as in Example 1, but as silicon carbide fine powder, 96.1% by weight consisted of β-type crystals, contained 0.42% by weight of free carbon, 0.20% by weight of oxygen, and 36.8 m ² Using silicon carbide fine powder having a specific surface area of /g, a green body was prepared by varying the fluororesin content and molding pressure as shown in Table 2, and a sintered body was obtained. The results were measured in the same manner as in Example 1 and are shown in Table 2. As can be seen from the results shown in Table 2, all the sintered bodies had extremely high strength and high reliability. Example 6, Comparative Example 2 The formulation was the same as in Example 1, but a fluororesin with a particle size as shown in Table 2 was used, the amount of the compound was changed, and after sieving, the same formulation as in Example 3 was used. A sintered body was obtained by granulation using the method described above. The results were measured in the same manner as in Example 1 and are shown in Table 2. Example 7 Ceramic fine powder consisting of 300 g of silicon nitride powder with a purity of 98.2% by weight and a specific surface area of 7.3 m ² /g and 36 g of yttrium oxide with an average particle size of 0.8 μm was mixed with 200 ml of distilled water and an average particle size of 0.05 μm. Add 18g of polytetrafluoroethylene powder and use a ball mill to
After mixing for 16 hours, it was dried while being mixed in the mill. Then add benzene to 300g of the above mixture.
After adding 150 ml, 3 g of sorbitan monooleate, and 1.5 g of polyethylene glycol, and carrying out dispersion treatment for 6 hours using a vibration mill, the mixture was discharged from the vibration mill and sieved in the same manner as in Example 3. Average particle size is 0.14mm, powder bulk density is 0.85g/ ^cm3
granules were obtained. An appropriate amount of the granules was collected and subjected to the same procedure as in Example 1 to obtain a product weighing 1.93 g/cm ³ . Next, the green body was placed in a Tammann-type firing furnace and sintered in a nitrogen gas stream. Sintering at 5℃/
The temperature was raised at 1,650° C. for 1 hour. The obtained sintered body had a theoretical density of 3.16 g/cm ³ (98.7
%). In addition, the three-point bending strength measured in the same manner as in Example 1 was 84.5Kg/
It had an average strength of mm ² . Example 8 Calcined α- with a purity of 99.9% by weight and an average particle size of 5 μm
For ceramic fine powder consisting of 300 g of alumina powder and 6 g of magnesium fluoride with an average particle size of 3 μm,
200 ml of water and 15 g of polytetrafluoroethylene having an average particle size of 0.05 μm were added, mixed for 16 hours using a ball mill, and then dried while being mixed in the mill. Next, 200 ml of acetone, 1.5 g of polyethylene glycol, and 1.5 g of sodium dioctyl sulfosuccinate were added to 250 g of the above mixture, and after performing a dispersion treatment for 5 hours using an attritor, the mixture was discharged from the attritor and prepared as in Example 3. In the same way, the average particle size was 0.09 mm, and the bulk density of the powder was
Granules of 1.05 g/cm ³ were obtained. An appropriate amount was taken from the granules and subjected to the same procedure as in Example 1 to obtain a product weighing 2.38 g/cm ³ . Next, the formed body was placed in a Tanmann-type firing furnace and maintained at 1900°C for 1 hour. The obtained sintered body had a theoretical density of 3.92 g/cm ³ (98.7
%). In addition, the three-point bending strength measured in the same manner as in Example 1 was 35.7Kg/35.7Kg at room temperature.
It had an average intensity of cm ³ . As described above, according to the method of the present invention, it is possible to produce a green body with high density and few molding defects even at a relatively low molding pressure, and by sintering this green body, it is possible to produce a green body with few defects and high quality. A ceramic sintered body with high density and high strength can be produced.

Claims (1)

[Scope of Claims] 1. A mixture of one or more components, the main component of which is ceramic fine powder, is added to a dispersion medium to form a suspension, and then the suspension is sieved. In the method for producing a green body for producing a ceramic sintered body which is pressure-molded into an arbitrary shape, the mixture is mainly made by adding 0.5 to 15 parts by weight of a fluororesin to 100 parts by weight of ceramic fine powder, and The volume ratio of the solid content consisting of ceramic fine powder and fluororesin in the suspension is 5 to 5.
A sieve having a sieve opening of 65 μm or less, with a pressure difference within the range of 50% and a pressure difference to overcome the stagnation of sieving action due to pressure loss occurring between the front side of the sieve and the rear side of the sieve of the suspension. 1. A method for producing a green compact for producing a high-strength ceramic sintered body with few pores, inclusions, etc. 2 The fluororesin is polytetrafluoroethylene,
Polytrifluorochloroethylene, tetrafluoroethylene
The manufacturing method according to claim 1, wherein at least one selected from hexafluorinated propylene copolymers is used. 3. The manufacturing method according to claim 1 or 2, wherein the fluororesin is a fine powder with an average particle size of 3 μm or less. 4. The manufacturing method according to any one of claims 1 to 3, wherein the ceramic fine powder contains at least one selected from carbides, nitrides, oxides, or compounds thereof as a main component. . 5. The manufacturing method according to any one of claims 1 to 4, wherein the ceramic fine powder is a fine powder having an average particle size of 2 μm or less. 6. Claim 1, wherein the ceramic fine powder is mainly composed of silicon carbide fine powder having a specific surface area of 5 to 10 m ² /g or a material to which a sintering aid is added.
- The manufacturing method according to any one of Item 5. 7 The dispersion medium liquid includes acetone, methanol, ethanol, hexane, heptane, nonane, toluene, xylene, ethyl methyl ketone, methyl isobutyl ketone, ethylbenzene, ethylene glycol, trichloroethylene, cyclohexane, nitromethane, nitroethane, isopropyl alcohol, benzene, Claim 1 which is at least one selected from carbon chloride and water
- The manufacturing method according to any one of Item 6. 8 A patent characterized in that when applying a pressure difference between the front side of the sieve and the back side of the suspension, the pressure difference is varied at a period within a range of 1/400 to 5 seconds. The manufacturing method according to any one of claims 1 to 7.