JPH0461826B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Application Field] The present invention relates to an optimal binder composition for ceramics in a degreasing method for removing binder from a ceramic molded body using a supercritical fluid or a pressurized liquefied fluid. In particular, the present invention relates to a binder composition for a ceramic molded body that is optimized for supercritical extraction by combining specific components such as an eluting binder component, a difficult-to-elute binder component, and an additive auxiliary thereof. [Prior Art] Conventionally, binder extraction from green ceramic molded bodies before firing using the unique extraction characteristics of supercritical fluids has been carried out using a predetermined pressure or pressure in an extraction tank.
The target binder component is extracted under temperature conditions. Generally speaking, the method of obtaining a ceramic sintered body by injection molding is to heat and mix ceramic powder and an organic binder (thermoplastic resin, wax, etc.) to impart fluidity, and then injection mold the resulting material. A well-known method is to heat and degrease the green ceramic body over a long period of time, decompose and remove the binder, and then sinter it. , it takes a very long time (several days). Moreover, the thicker the product, the more difficult it is to do, and there are many problems such as a high defective rate. From this point of view, the supercritical extraction method was proposed (Japanese Patent Applications No. 59-273487 and No. 59-59 by the present applicant).
No. 273488), but it was also discovered that the binder composition used in conventional heat degreasing was unsuitable for this supercritical extraction method. Specifically, when carrying out supercritical extraction, if a binder with a low melting point and low strength is used, the mixture of ceramic powder and binder will rapidly solidify or soften beyond the melting point of the binder. The problem is that injection molding is not easy because the viscosity is low in the molten state. From this point of view, the binder composition of the present invention was invented. In this specification, "supercritical fluid extraction" refers to a method of extracting a substance by utilizing an increase in the vapor pressure of the substance and a difference in chemical affinity in the presence of a supercritical fluid or pressurized liquefied fluid. says. [Problems to be Solved by the Invention] The present invention seeks to provide a binder composition suitable for supercritical extraction that utilizes the unique extraction characteristics of supercritical or near-supercritical fluids.
The object of the present invention is to provide an optimal binder composition for ceramic moldings to be subjected to supercritical extraction by a combination of components with four different functions. Furthermore, the present invention makes injection molding of a ceramic molded body relatively easy, and when the ceramic molded body is brought into contact with a supercritical or pressurized fluid such as carbon dioxide or fluorocarbon gas, injection molding can be carried out in an extremely short time of 1 to 3 hours. It is extracted, falls off, cracks, swells,
It is an object of the present invention to provide a binder composition that is less likely to cause defects such as deformation. Accordingly, an object of the present invention is to provide an optimal binder composition for ceramic molded bodies that can simplify production and save energy in the production of ceramic molded bodies. [Means for Solving the Problems] The present invention provides a binder composition for ceramic molded bodies that can be degreased using a supercritical or pressurized liquefied fluid. Elution binder component (component A); B: hard-to-elute binder component (component B) that is relatively difficult to extract by supercritical or pressurized liquefied fluid but gives strength to the molded product; C: gives flexibility and fluidity to component B The above-mentioned binder composition is characterized by combining a plasticity imparting component (component C) and a lubricity imparting component (component D) that improves the slippage of ceramic powder. Furthermore, in the binder composition of the present invention, component A is contained in an amount of 30 to 95% by weight, and component B is contained in an amount of 30 to 95% by weight.
is preferably 5 to 70% by weight, component C is preferably 0 to 30% by weight, and component D is preferably 0 to 25% by weight.
In the present invention, component A can be one to three selected from higher alcohols, paraffin waxes, fatty acids, and fatty acid salts, and component B can be polypropylene, polyethylene, polystyrene, ethylene vinyl acetate. Those composed of one or more of copolymers, acrylic resins such as polymethacrylic esters or polyacrylic esters, wax, atactic polpropylene, and polyethylene glycol can be used. [Function] The optimal binder composition for the ceramic molded body for extraction treatment with a supercritical or near-supercritical fluid of the present invention is a new binder composition that can best utilize the characteristics of supercritical extraction, and is a binder composition that can best utilize the characteristics of supercritical extraction. This is a novel binder composition that combines various components.
That is, the optimal binder composition for the supercritical fluid extracted ceramic molded body of the present invention is one that makes good use of supercritical extraction technology. Generally speaking, in extraction with supercritical or near-supercritical fluids, the ability of the supercritical gas as a solvent is highly dependent on its density. That is, the density of a gas in a supercritical or near-supercritical state is considerably higher than that in a normal gas state, and near the critical temperature, it is almost comparable to the density in a liquid state.
Such an increase in density increases the chemical affinity with the solute, allowing the supercritical or nearly supercritical gas to function as a separation medium. Therefore, under conditions of constant temperature, as the pressure increases, the density of supercritical or near-supercritical gas also increases, and the solvent capacity increases accordingly. In fluid extraction near supercriticality, when the pressure is very high, the solubility increases as the temperature rises; This is because the increase in the vapor pressure of the extracted material is more remarkable than the decrease in the density of the gas, and the dissolution into a supercritical or nearly supercritical gas due to the increase in vapor pressure makes a large contribution. On the other hand, when the pressure is not so high, the solubility decreases as the temperature increases. In this case, while the vapor pressure of the material to be extracted is only slightly increased, the density of the supercritical or nearly supercritical gas is significantly reduced. As described above, the solvent ability of supercritical or nearly supercritical liquids is remarkable. For example, when carbon dioxide gas (CO ₂ ) is used for supercritical extraction, the specific gravity (density) changes greatly near the critical point, making fluid extraction extremely efficient. Able to drive. Gases or fluids suitable for use as such fluids include those shown in the following table, such as carbon dioxide gas and Freon (trademark) gas.

[Table] In general, the substances listed in Table 1 are used as solvents for supercritical fluid extraction, but carbon dioxide, chlorofluorocarbon gas, etc. are mainly used from the viewpoint of operability of temperature and pressure, cost, and safety. It will be done. The use of these substances in the debinding of the binder composition for ceramic molded bodies according to the present invention is convenient because the critical temperature is lower than the melting point or softening point of the substance generally used as a binder, and the molded body does not deform during debinding. Good. Furthermore, the removal rate of the binder depends on the contact flow rate between the ceramic molded body and the supercritical fluid, and the removal rate can also be increased by increasing the flow rate of the fluid in the examples described below. The binder composition for ceramic moldings that can be degreased using a supercritical or pressurized liquefied fluid according to the present invention is a binder composition that can be degreased using a supercritical or pressurized liquefied fluid. Alternatively, in addition to the binder that can be extracted and degreased by pressurized liquefied fluid, there is also a difficult-to-elute binder component (component B);
By combining the plasticity-imparting component (component C) and the lubricity-imparting component (component D), the injection moldability of the ceramic molded product is improved, and even if supercritical degreasing is performed in an extremely short period of time, the molded product does not have any defects. Make it difficult for it to occur. Next, each component of the binder composition of the present invention will be explained. Elution binder component according to the present invention (component A)
is a binder material that is relatively easily extracted by supercritical or pressurized liquefied fluid and has been commonly used as a binder in the past. For this purpose, one or more types may be selected from, for example, higher alcohols (eg, octadecanol), fatty acids, fatty acid salts (eg, magnesium stearate, aluminum stearate), wax, and the like. This eluted binder component is used in an amount of about 50 to 95% by weight of the total binder amount. The hard-to-elute binder component (component B) according to the present invention is relatively difficult to extract with supercritical or pressurized liquefied fluid, and at the same time imparts good fluidity to ceramic powder to facilitate injection molding and to form a molded product. It is a binder component that provides strength and prevents defects such as cracks and deformation that occur during extraction and degreasing using supercritical or pressurized liquefied fluids. This ingredient is
The temperature and pressure at which it dissolves in a supercritical or pressurized liquefied fluid is higher than that of the eluted binder component, that is, it is poorly soluble. This component is selected from one or more of thermoplastic resins (eg, polyethylene, polystyrene, polypropylene, APP, EVA, acrylic resins, etc.), wax, polyethylene glycol, and the like. This difficult-to-elute binder component ranges from 5 to 40% by weight of the total binder. The relationship between component A and component B is as shown in the graph showing the solubility trends of components A and B shown in the attached figure. Component A is relatively easily dissolved and is easily dissolved when it comes into contact with a supercritical fluid. On the other hand, component B remains in the molded product and plays a role in maintaining the strength of the molded product. The plasticity imparting component (component C) imparts flexibility and fluidity to the hard-to-elute binder component. This flexibility-imparting component is selected from phthalic acid esters or fatty acid esters, such as diethyl phthalate (DEP), dibutyl phthalate (DBP), and dioctyl phthalate (DOP). This flexibility imparting component ranges from 0 to 30% by weight of the total binder amount. The lubricity-imparting component (component D) is a component that improves the slippage of ceramic powder, and this component D
improves pressure transmission properties and mold release properties, and is selected from, for example, stearic acid, metal salts of stearic acid, polyethylene oxide, and the like. This lubricity-imparting component accounts for 0 of the total binder amount.
Contains in the range of ~25% by weight. The solubility of the above-mentioned eluted binder component (component A) and difficult-to-elute binder component (component B) in supercritical or near-supercritical fluids has the characteristics shown in the figure, and the eluted binder component has a relatively low temperature,
The binder component, which is dissolved and eluted at low pressure and difficult to be eluted, is not dissolved and eluted even at relatively high temperature and pressure. The binder composition according to the present invention uses a combination of components A, B, C, and D as described above, and components C and D are added incidentally to components A and B to improve fluidity and mold release properties. Ingredient A is added to the ceramic powder because it improves the properties and makes injection molding easier.
If the desired properties can be obtained from components C and B alone, there is no need to add components C and D. Furthermore, each of the components A, B, C, and D can be composed of a plurality of substances. In the binder composition of the present invention, component A is 50 to 95% by weight, component B is 5 to 40% by weight, component C is 0 to 30% by weight, and component D is 0 to 25% by weight.
A range of % by weight is preferred. If component A is less than 50% by weight, the amount of binder extracted will be small and defects will occur due to the influence of the remaining binder (mainly component B), making it difficult to sinter as is. 95
If the weight percentage is exceeded, component A generally has a low melting point and low strength, making it difficult to maintain its shape. If component B is less than 5% by weight, it will not be possible to impart good fluidity to the ceramic powder, making injection molding difficult and resulting in insufficient strength of the molded product. In addition, if component B exceeds 40% by weight, if the supercritical resin is directly transferred to the sintering process,
This causes cracking and blistering, and there is a problem in that conventional heat degreasing is further required. Component A can be one to three selected from higher alcohols, waxes, fatty acids, and fatty acid salts, and component B can be polypropylene, polystyrene, polyethylene, ethylene-vinyl acetate copolymer, polymethacrylate ester, or A material composed of one or more selected from acrylic resins such as polyacrylic esters, wax, atactic polypropylene, and polyethylene glycol can be used. Next, a method for treating ceramic molded bodies using the binder composition according to the present invention will be described. 5 to 30% by weight of the binder composition of the present invention containing components A, B, C, and D as described above is added to ordinary ceramic powder (silicon nitride, silicon carbide, alumina, zirconia, etc.) and thoroughly heated. Mix. The mixture of ceramic powder and binder composition has good fluidity due to the action of components B, C and D according to the present invention, and can be easily molded using a common injection molding machine. Next, this molded body is brought into contact with a supercritical or pressurized liquefied fluid such as carbon dioxide or chlorofluorocarbon gas for 1 to 3 hours to perform extraction degreasing. Since the supercritical or pressurized liquefied fluid extracts the binder through the gaps between the particles of the compact, component A will come out in a very short time, but at that time component B will provide the strength of the compact, preventing cracks, etc. be able to. Further, if the softening point of component B is higher than the critical point, deformation during extraction and degreasing in a supercritical state can be prevented. Next, if the temperature or pressure is increased, component B is similarly extracted in a short time, but cracks no longer occur because component A has already been degreased and a loophole exists. Furthermore, even if extraction degreasing with a supercritical or pressurized liquefied fluid is completed while component B remains, and normal firing is performed as is, component B will easily escape from the molded body as a gas through the loophole in component A. No defects such as cracks or blisters will occur due to vaporization. For the same reason, components C and D may not be able to be extracted and degreased using supercritical or pressurized liquefied fluids, but those that can be extracted and degreased are preferred. The heated fluid, which becomes a solvent in a supercritical state, is pressurized to a predetermined pressure and flows through the green ceramic molded object to be extracted, dissolving the binder composition from the extracted object as it passes. It is preferable that the critical temperature is lower than the melting point or softening point of the binder material that is generally used and that does not deform the molded product during degreasing. Also,
Since the binder removal rate depends on the contact flow rate between the ceramic molded body and the supercritical fluid, the removal rate can be improved by increasing the flow rate of the fluid. The binder composition of the present invention can be used for injection molding of engineering ceramics such as silicon nitride, silicon carbide, alumina, and zirconia, as well as injection molding and degreasing of powders such as electronic materials, magnetic materials, metal powders, cemented carbide, and graphite powder. All of them can be applied.
Moreover, there are products that can be applied not only to powder injection molding but also to extrusion molding and degreasing of press molded products. It is possible to degrease powders that would change the physical properties of the powder using conventional thermal degreasing, and the strength of the molded product can be maintained. [Example] Next, specific examples of the binder composition of the present invention will be explained in more detail in the following Examples, but the present invention is limited to the following Examples unless the gist thereof is changed. isn't it. Example 1 Consisting of 55% by weight of octadecanol as component A, 18% by weight of ethylene vinyl acetate copolymer and 15% by weight of wax as component B, 3% by weight of dibutyl phthalate as component C, and 9% by weight of stearic acid as component D. 16% by weight of the binder mixture was added to the alumina powder (average particle size 0.6 μm), heated and kneaded, formed into pellets, and molded into 10×20× pellets using an injection molding machine.
A block-shaped molded body with a diameter of 30 m/m was obtained. Next, this is extracted using a supercritical extraction and degreasing device at a temperature of 60℃ and a pressure of 200℃.
When exposed to CO ₂ supercritical fluid at Kgf/cm ² for 1.5 hours, the binder removal rate was 78%, cracking, blistering,
A degreased body without defects such as deformation was obtained. continue,
This degreased body was heated at a rate of 180°C/h and held at 1600°C for 2 hours to sinter it. No defects such as cracks or blisters were observed in this sintered body, and the results were extremely good.Example 2: 65% by weight of octadecanol as component A, 29% by weight of polyethylene as component B, and dibutyl as component C. A mixture consisting of 6% by weight of phthalate was added to 16% by weight of alumina powder (average particle size 0.6 μm).
The CO ₂
Extractive degreasing was performed using supercritical fluid. A degreased body with a binder removal rate of 65% and no defects such as cracks, blisters, or deformations was obtained. Next, this degreased body was heated to 150
When the temperature was raised at a rate of °C/h and sintered at 1600 °C for 2 hours, no defects such as cracks or blisters were observed in the sintered body. Example 3 63% by weight of paraffin wax as component A, 25% by weight of polymethacrylate as component B,
4% by weight of dibutyl phthalate as component C component D
A mixture consisting of 8% by weight of stearic acid as
Silicon nitride powder (contains Al ₂ O ₃ and Y ₂ O ₃ as auxiliaries),
was added in an amount of 21% by weight, and kneading, molding, and degreasing was performed under the same conditions as in Example 1. Binder removal rate 71
%, no defects were observed in the degreased body. Next, this degreased body was heated at 180°C/h for 1100°C in a nitrogen stream.
℃, then nitrogen pressure 9Kg/cm ² and 1800℃
When the sintered body was sintered for 2 hours, no defects were observed in the sintered body. [Effects of the Invention] The binder composition for ceramics suitable for supercritical extraction and supercritical fluid extraction of the present invention contains an eluting binder component (component A) that is relatively easily extracted by supercritical or pressurized liquefied fluid; A hard-to-elute binder component (component B) that is relatively difficult to be extracted by pressurized fluid but gives strength to the molded body; a plasticity-imparting component (component C) that gives flexibility and fluidity to component B; and improves the slippage of ceramic powder. This is a binder composition for ceramics, which combines a lubricity-imparting component (component D) that
In addition, compared to conventional binders made of higher alcohols, fatty acids, etc., injection molding is easier because it gives ceramic powder good fluidity, and the strength of the molded product can be maintained sufficiently. Even if extraction and degreasing is performed with liquefied fluid, cracks, deformation,
The second is that products with fewer defects such as blisters can be obtained.
Second, the degreasing time can be significantly reduced compared to conventional heat degreasing treatment, the degreasing time can be shortened even compared to conventional ordinary binders, and even if the degreasing time is shortened, defects are less likely to occur. 3. Compared to conventional thermal degreasing treatment, the degreasing temperature can be lowered.
Therefore, gasification of the binder can be prevented, and there is almost no internal stress caused by expansion or movement of the binder, and therefore defects such as cracking, blistering, deformation, etc. do not occur.Fourthly, the above From this point of view, technological advantages were obtained, such as the ability to apply the supercritical fluid extraction method to ceramic molded bodies with complex shapes and thick-walled molded bodies.

[Brief explanation of drawings]

The figure is a graph showing the solubility trends of components A and B used in the binder composition of the present invention.

Claims (1)

[Claims] 1. A eluting binder component (component A) that is relatively easy to extract with a supercritical or pressurized liquefied liquid; B. A binder component that is relatively difficult to extract with a supercritical or pressurized liquefied liquid, but that provides strength to the molded product. A combination of a binder component that is difficult to elute (component B) that gives the component B; a plasticity-imparting component (component C) that gives flexibility and fluidity to component B; Component A is 50 to 90% by weight, component B is 5 to 40% by weight, and component C is 30% by weight.
% by weight or less, component D is 25% by weight or less of a binder composition for ceramic molded bodies to form a ceramic molded body, and the molded body is degreased using a supercritical or pressurized liquefied liquid. A method for manufacturing ceramics, characterized by: 2 Early component A is higher alcohol, wax,
The method for producing ceramics according to claim 1, wherein the ceramics are one to three selected from fatty acids and fatty acid salts. 3. Component B is composed of one or more of polypropylene, polyethylene, polystyrene, ethylene vinyl acetate copolymer, acrylic resin such as polymethacrylate or polyacrylate, wax, atactic polypropylene, and polyethylene glycol. A method for manufacturing ceramics according to claim 1, characterized in that the method comprises: