JPH06287055A - Production of sintered article of ceramic - Google Patents

Abstract

PURPOSE:To provide production of a sintered article of ceramic slightly causing defects such as deformation and cracking in a production process, capable of greatly improving qualities, yield of product and mass productivity even in the case of a large-sized product of a complicate shape. CONSTITUTION:Raw material powder of ceramic is blended with an organic binder comprising 5-50wt.% of a thermosetting resin based on the whole amount of a binder and the rest of a component to be readily de-fatted at a low temperature of 100-200 deg.C to give a raw material mixture. The prepared raw material mixture is molded by injection molding to form an injection molded article of a given shape. The injection molded article is heat-treated to >= the curing temperature of the thermosetting resin, the thermosetting resin is cured, the raw material powder of ceramic is cross-linked with the thermosetting resin to form the cured molded article and the cured molded article is defatted and sintered.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a ceramics sintered body, and more particularly to a method for manufacturing a ceramics sintered body in which defects such as deformation and cracks are less likely to occur even when the ceramics is large and has a complicated shape.

[0002]

2. Description of the Related Art Conventionally, as a general method for producing a ceramics sintered body, a raw material mixture consisting of a ceramic raw material powder and an organic binder is molded into a predetermined shape by a die molding method or an injection molding method, and the obtained molding is carried out. A method of manufacturing by degreasing and sintering a body is widely adopted.

In the conventional mold forming method, since the raw material mixture is prepared by adding a relatively small amount of the organic binder of about 5 to 10% by weight to the ceramic raw material powder, degreasing of the formed body is performed. Is relatively easy and can be performed in a short time. However, in the mold forming method, the raw material mixture is pressed in a uniaxial direction to form the formed body,
There are many restrictions on the shape of the molded body, and it is not suitable for manufacturing a ceramic molded body having a complicated shape.

On the other hand, the injection molding method was originally developed to mass-produce plastic products with high dimensional accuracy, but in recent years, its application range has been expanded to the field of powder metallurgy of ceramics and metals. ing.

When a ceramic product is manufactured by an injection molding method, an organic binder mainly composed of a thermoplastic resin such as polyethylene or polystyrene, which has been conventionally used for modeling an engineering plastic, or a wax such as paraffin is the main component. The organic raw material mixture is mixed with the ceramic raw material powder as a binder, and the raw material mixture homogenized by kneading is heated and pressed into a mold of a predetermined shape in a state of good fluidity to form a molded body, and this shape is given. It was manufactured by heating the molded body in a degreasing process to remove organic components and then sintering.

According to the injection molding method, even a complicatedly shaped product can be easily molded, the molding operation is simple, the molding time is short, and the mass productivity is excellent.

[0007]

However, in the injection molding method, the amount of the organic binder added is 20 to 60% by weight with respect to the ceramic raw material powder in order to ensure good fluidity of the raw material for molding, particularly in the molding die. Extremely many.

Therefore, it is extremely difficult to remove the unnecessary binder component in the degreasing step after the predetermined shape is formed by injection molding, and defects such as cracks and foaming are apt to occur, resulting in a problem that the product yield is lowered. It was In particular, it is extremely difficult to remove the binder from a large-sized molded body having a large wall thickness. Further, the heating operation during degreasing tends to further soften and deform the molded body, and this tendency becomes more remarkable in the case of the molded body having a complicated shape.
Therefore, there is a problem that the manufacturing yield of the final product is significantly reduced when a ceramics sintered body having a large size and a complicated shape is manufactured by an injection molding method.

A molding material containing a thermoplastic resin or the like as an organic binder which has been conventionally used has a property that fluidity is imparted by heating the thermoplastic resin or the like and solidifies at a low temperature in a mold. However, an organic binder is used that allows the molded body to be easily removed from the mold.

Generally, in an injection molding method in which fluidity is imparted by heating, an organic binder is used which solidifies under low temperature conditions and softens and exhibits fluidity under high temperature conditions. Therefore, under high temperature conditions during degreasing, the kneaded product of the ceramic raw material powder and the organic binder has almost no structural strength. That is, it is considered that the conventional binder composition has almost no binder strength under high temperature conditions, and the shape retention strength is maintained only by the entanglement of powder particles and the interparticle working force. Therefore, if it is attempted to degrease by rapidly heating to a high temperature in this state, defects such as cracks will occur in the molded body due to the gas pressure of the decomposed and volatile components of the binder. It is said that this tendency becomes more remarkable as the wall thickness of the molded product increases, and that when the wall thickness exceeds 20 mm, degreasing becomes difficult rapidly.

Under these circumstances, the wall thickness is usually 20 mm.
In order to obtain a large-sized molded body as described above, the molded body is placed in a degreasing heating furnace in which a gas flow and a temperature pattern are controlled with high accuracy, and based on a heating schedule of 150 to 200 hours, which is extremely long. However, there is a problem in that it is necessary to perform degreasing at a slow speed, which inevitably greatly reduces the production efficiency of ceramic products and thus impairs mass productivity. Moreover, even when the careful degreasing operation is continued for a long period of time as described above, the rate of defects such as cracks occurring after degreasing is still high, and it cannot be a practical industrial method.

The present invention has been made to solve the above-mentioned problems, and even in the case of a large size and a complicated shape, defects such as deformation and cracks are less likely to occur in the manufacturing process, and the quality and the product yield are improved. And it aims at providing the manufacturing method of the ceramics sintered compact which can improve mass productivity sharply.

[0013]

In order to achieve the above object, in the method for producing a ceramics sintered body according to the present invention, a thermosetting resin of 5 to 50% by weight with respect to the total amount of binder and a balance of 100 to 100% are used. An organic binder composed of an easily degreasing component that can be degreased at a low temperature of 200 ° C. is added and kneaded to a ceramic raw material powder to prepare a raw material mixture, and the obtained raw material mixture is molded by an injection molding method to obtain a predetermined shape. An injection-molded body is formed, and the thermosetting resin is cured by heating the injection-molded body to a temperature not lower than the curing temperature of the thermosetting resin, and the ceramic raw material powder is crosslinked with the thermosetting resin to cure the molded body. Is prepared, and then the cured molded body is degreased and sintered.

Here, the ceramic raw material powder used in the above-mentioned manufacturing method is a mixture mainly composed of an inorganic compound. Among them, particularly typical ones are alumina, zirconia, titania and mullite. One or a mixture of oxide-based and non-oxide-based general-purpose ceramic raw materials such as beryllium, beryllia, cordierite, zircon, sialon, silicon nitride, silicon carbide, aluminum nitride, boron nitride or ferrite, and magnesium carbonate. , Known conventional sintering aids such as calcium carbonate, calcium carbonate, yttrium oxide, cerium oxide or silicic acid, Li ₂ O, BaO, T
Various additives such as a ₂ O ₃ , Pt or Pd that change the electrical properties are added.

The organic binder (binder) is added in order to bond the ceramic raw material powders to each other and maintain the shape of the molded body. In the present invention, in addition to the conventional general-purpose thermoplastic resin, 5 A major feature is to use a composition containing ˜50 wt% of thermosetting resin as an organic binder.

That is, the organic binder used in the method of the present invention is a thermosetting resin in an amount of 5 to 50% by weight based on the total amount of the binder, and the rest is an easily degreasing component which can be degreased at a low temperature of 100 to 200 ° C. It consists of and.

The thermosetting resin contained in the molded body is cured by the heat treatment described later to crosslink between the ceramic raw material powders to enhance the shape retention strength of the molded body and to form a gap between the crosslinked ceramic raw material powders. To form. This gap serves as a volatilization path of the above-mentioned easily degreasing component during degreasing heating, and the easily degreasing component is efficiently removed from the molded body through this volatilization path, so that a high quality ceramic sintered body can be obtained.

When the content of the thermosetting resin in the organic binder composition is less than 5% by weight, the above-mentioned crosslinking is small,
The amount of volatilization route produced is small and the degreasing property is reduced. on the other hand,
When the content exceeds 50% by weight, curing degreasing having a high decomposition temperature tends to remain in the molded body and cracks are likely to occur during sintering of the molded body. Therefore, the content of the thermosetting resin in the organic binder is set in the range of 5 to 50% by weight.

As the thermosetting resin constituting the organic binder, unsaturated polyester resin, phenol resin, amino resin, epoxy resin, diallyl phthalate resin,
A thermosetting urethane resin or a thermosetting acrylic resin is typical, but a diallyl phthalate resin is particularly preferable.

In addition to the above thermosetting resin, the organic binder component has various physical properties such as dispersibility of raw materials, lubricity, prevention of shrinkage, releasability, adjustment of melt viscosity or adjustment of porosity. Is added as an easily degreasing component.

Specific examples of the additive include waxes such as paraffin and kerosene, fats and oils or their derivatives, solvents such as ethylene glycol, dibutyl phthalate or dioctyl phthalate, and plasticizers,
Various thermoplastic resins such as polyethylene, polypropylene, ethylene-vinyl acetate copolymer, chlorinated polyethylene, polysiloxane, acrylic acid-based polymer, polystyrene, polyoxyethylene or polyoxypropylene are adopted. In particular, these additives are 100 to 200
It is an easily degreasing component that decomposes easily at a low temperature of ℃.

As the organic binder used in the method of the present invention, it is desirable to use a resin composition having an average particle size of 1 mm or less. That is, the present inventors have conducted extensive research on the size of the particle size of the organic binder component capable of obtaining a homogeneous ceramics sintered body having no defects. As a result, in ceramic injection molding materials,
It has been found that the size of the particle size with which the organic binder component is most compatible with the ceramic powder is 1 mm or less.

In the ceramic injection molding material used in the method of the present invention, the particle size of each component particle such as resin and lubricant constituting the organic binder component before heating is adjusted to 1 mm or less, the component of the organic binder and the ceramic powder. And are mixed so that they are uniformly dispersed. It is considered that when the particle size of the component of the organic binder is this size, it is well compatible with the ceramic raw material powder and uniformly dispersed and mixed with the ceramic raw material powder. Therefore, since the powder of the organic binder is well compatible with the ceramic powder, it is easily and uniformly dispersed and mixed in the mixing process.

In carrying out the method of the present invention, the operation of kneading the ceramic raw material powder and the organic binder to prepare an injection molding material can be carried out by any mixer or stirrer, but a pressure kneader, A heating type vacuum extruder, a vacuum mixing agitator, a double-arm type kneader, a roll, a single-axis or multi-axis mixer, or the like is suitable. This kneading operation is carried out at a temperature of 80 to 90 ° C. at which the material does not harden.

In preparing the above mixture, the mixing ratio is 8 to 60 parts by weight, preferably 20 to 60 parts by weight of the organic binder with respect to 100 parts by weight of the ceramic raw material powder.
It may be set to be 40 parts by weight.

When the amount of the above organic binder is too small, the fluidity of the mixture tends to deteriorate, and molding defects tend to occur. On the contrary, when the amount is too large, problems such as cracks and shrinkage deformation occur in the degreasing process or the firing process. It will be easier.

The raw material mixture prepared by the kneading operation is granulated and made into a pellet-shaped injection molding material having a diameter of about 5 to 10 mm, which is further charged into an injection molding machine to form an injection molding having a predetermined shape. To be done. The injection molding temperature is a temperature at which the pellets are sufficiently softened and fluidized, and the temperature at which the thermosetting resin does not cure, specifically, 80 to 120.
It is set to about ℃.

Next, the obtained injection-molded body is heat-treated at a temperature not lower than the curing temperature of the thermosetting resin in a short time. This heat treatment cures the thermosetting resin contained in the injection-molded body, crosslinks between the ceramic raw material powders, and enhances the shape retention strength of the injection-molded body. By this heat treatment, a cured molded article having high shape retention strength is formed, and the easily degreased component contained in the cured molded article is removed by about 4% by weight of the total amount of the binder, so that the cured molded article excluding the crosslinked portion is formed. A porous volatilization route is formed inside the body.

The heat treatment conditions for the injection molded article are set within a range of 120 to 200 ° C. within 1 hour.
If the heating temperature is lower than 120 ° C., the molded body will not be sufficiently cured, while if the heating temperature exceeds 200 ° C., the curing will proceed rapidly and the hardness adjustment will become difficult.

On the other hand, if the heat treatment temperature is too high, the constituent components of the organic binder such as polystyrene aggregate with each other and the dispersibility deteriorates. Therefore, it is necessary to set the heat treatment temperature below the decomposition temperature of the organic binder.

Here, the hardness of the ceramic molded body after the heat treatment may be adjusted to a rubber hardness of 50 or more, preferably 80 or more as measured by a spring hardness meter (HD-100N series, manufactured by Ueshima Seisakusho). When the hardness of the molded body is less than 50, the structural strength of the molded body is insufficient and cracks are likely to occur due to the pressure of the decomposition gas generated during degreasing. Further, it is important to set the time for hardening the ceramic molded body to a short time such as within 1 hour. This is because if the curing time exceeds 1 hour, cracks are likely to occur in the molded body.

Next, the obtained cured molded article is degreased. In the first half of this degreasing operation, the decomposition gas of the easily degreasing component contained in the cured molded article is smoothly discharged to the outside of the system through the volatilization route. During this time, the shape of the cured molded article maintains a predetermined shape and does not deform due to the shape-retaining function in the cross-linking portion, even under high temperature conditions. Here, when the removal rate of the easily degreased component is less than 4% by weight, the amount of the vaporization route produced is insufficient. Furthermore, in the latter half of the degreasing operation, the resin component forming the crosslinked portion is volatilized when the degreasing temperature rises and exceeds the decomposition temperature of the thermosetting resin forming the crosslinked portion,
The compact is almost completely degreased.

The degreased compact is subsequently sintered in a sintering step for a predetermined time at a sintering temperature according to the type of the ceramic raw material powder, and is finished as a product such as various industrial ceramics or electronic material ceramics. .

[0034]

According to the method for manufacturing a ceramics sintered body having the above structure, a predetermined amount of thermosetting resin is contained as an organic binder component, and the injection molded body is heat-treated and cured before the degreasing step. Since the ceramic raw material powders are cross-linked with each other, the structural strength of the molded body can be increased more than before.
Therefore, it is less likely that the injection molded body is cracked or deformed or damaged by the gas pressure of the binder component that is decomposed and volatilized during degreasing of the injection molded body,
It is possible to greatly improve the manufacturing yield of large-sized and complicated ceramic products.

By the heat treatment, the thermosetting resin contained in the injection molded body crosslinks between the ceramic raw material powders to enhance the shape retention strength, and the volatilization path of the organic binder is porous between the crosslinked portions. Therefore, even when the molded body is degreased at a high temperature, no deformation occurs, and the decomposition gas of the organic binder is efficiently removed to the outside of the molded body through the above volatilization route to improve the degreasing efficiency. Become.

[0036]

Next, one embodiment of the present invention will be described more specifically with reference to the drawings and further together with a comparative example.

Examples 1 to 3 50% by volume of each binder solution having the composition shown in Table 1 was added to silicon nitride powder having an average particle size of 1 μm, and the mixture was heated with a pressure kneader set to 80 ° C. Three kinds of injection molding materials were prepared by crushing and kneading for 60 minutes.

Next, using each of the prepared molding materials, the cylinder temperature was 100 ° C., the mold temperature was 40 ° C.,
In addition, injection molding was performed under the condition that the injection pressure was 1000 kg / cm ² , and the diameter for model rotor was 250 mm and the maximum thickness was 50.
A large number of large-diameter disk-shaped thick-walled injection-molded bodies (green bodies) were formed.

Next, the obtained injection-molded body was subjected to a furnace temperature of 18
Put in an electric furnace (oven) set at 0 ° C for 1 hour,
Heat treatment was applied to cure. The hardness of the molded product after the heat curing treatment was 91 to 96 as a result of measurement with the spring hardness meter. The binder removal rate (weight reduction rate) was 6 to 9% by weight. At this time, no defects such as cracks and pores were observed in the molded body.

Next, the heat-treated cured molded body is placed in a degreasing heating furnace set to a temperature of 180 ° C., heated to a temperature of 350 ° C. at a temperature rising rate of 5 ° C./Hr, and further heated to 10 ° C./H.
It was heated to 600 ° C. at a heating rate of r. The degreasing treatment was performed in a nitrogen gas atmosphere. The binder weight loss rate in the molded body after degreasing was 99.5 to 99.7%, and visual inspection was conducted, but cracks, pores and deformation were hardly found in the molded body.

Next, the obtained molded body was sintered in a nitrogen gas atmosphere at a normal pressure at a temperature of 1750 ° C. for 6 hours to manufacture a disc-shaped ceramic sintered body for a model rotor. An X-ray inspection and an appearance inspection were performed on the obtained sintered body, but no pores were observed inside the sintered body, and defects such as cracks and deformation examples on the outer surface portion were hardly recognized.

Comparative Example 1 On the other hand, as Comparative Example 1, the injection-molded article prepared in Example 1 was placed directly in a degreasing heating furnace at room temperature without being cured by heat treatment, and the temperature rising rate was 5 ° C./Hr. From room temperature to 3
Heat to 50 ° C, then 6 at a heating rate of 10 ° C / Hr.
The degreasing treatment was performed according to the conventional degreasing temperature pattern of heating to 00 ° C. However, since the temperature rising operation was started from room temperature, it took about 20 hours for the molded body to harden, and the strength of the molded body during degreasing was low.
Since the molded product had a low hardness and a low shape retention strength, 85% of the samples were deformed and the yield of the final product was significantly reduced. The above results are shown in Table 1 below.

[0043]

[Table 1]

As is clear from the results shown in Table 1, in the injection-molded articles in Examples 1 to 3, the organic binder containing a predetermined amount of the thermosetting resin was used, and the thermosetting treatment was performed in advance. The structural strength of the molded product is high, and there is almost no deformation or cracking. In particular, the thermosetting resin contained in the injection-molded body by the above heat treatment crosslinks between the ceramic raw material powders to enhance the shape retention strength, and a volatilization path of the organic binder is formed between the crosslinked portions in a porous form. Therefore, even if a thick injection molded product is degreased at high temperature, no deformation occurs, and the decomposed gas of the organic binder passes through the above volatilization path and is efficiently removed to the outside of the molded product to significantly improve the degreasing efficiency. To be improved. Therefore, the total time required for the degreasing treatment can be significantly reduced from the conventional 120 hours to about 90 hours even if the time required for the heat curing treatment before the degreasing (within 1 hour) and the cooling time after the degreasing are added. did it. Therefore, high-quality large-sized (ceramics) products could be efficiently manufactured with a high yield.

In order to investigate the relationship between the temperature at which the injection molded body is heated and cured before degreasing and the hardness of the cured molded body, the temperature of the heating furnace is changed from 110 ° C. to 170 ° C. The hardness of the cured molded article after being treated for 1 hour was measured using the spring type hardness tester. When the heat treatment temperature was less than 120 ° C, the injection molded article did not cure sufficiently, while the temperature It was confirmed that when the temperature exceeds 200 ° C., the curing proceeds rapidly, which makes it difficult to adjust the hardness and causes swelling and cracking.

Further, when the removal rate (reduction rate) of the organic binder in the cured molded article was measured under the above heat treatment temperature conditions, the results shown in Table 2 below were obtained.

[0047]

[Table 2]

As is clear from the results shown in Table 2, when the heat treatment temperature is 150 ° C. or higher, the removal rate of the organic binder is 4% by weight or more, and the volatilization route of the organic binder is formed around the crosslinked portion of the cured molded article. It was found that the degreasing was sufficiently performed and the degreasing proceeded smoothly.

In the above examples, the method for producing a ceramics sintered body using the injection molding method is described, but the method of the present invention is not limited to the injection molding but other plasticizing methods such as the extrusion molding method. It can be similarly applied to a method for producing a ceramics sintered body using a molding method.

[0050]

As described above, according to the method for producing a ceramics sintered body of the present invention, a predetermined amount of a thermosetting resin is contained as an organic binder component, and an injection molded body is formed before the degreasing step. Since the ceramic raw material powders are cross-linked by heat treatment and hardening, the structural strength of the molded body can be increased more than before. Therefore, it is less likely that cracks will occur in the injection-molded product or the injection-molded product will be deformed or damaged due to the gas pressure of the binder component that has decomposed or volatilized during degreasing of the injection-molded product. Can be greatly improved.

Further, by the above heat treatment, the thermosetting resin contained in the injection molded body crosslinks between the ceramic raw material powders to enhance the shape retention strength, and the volatilization path of the organic binder is porous between the crosslinked portions. Therefore, even when the molded body is degreased at a high temperature, no deformation occurs, and the decomposition gas of the organic binder is efficiently removed to the outside of the molded body through the above volatilization route to improve the degreasing efficiency. Become.

Claims (1)

[Claims] 1. An organic binder consisting of 5 to 50% by weight of the total amount of binder and a rest of an easily degreasing component which can be degreased at a low temperature of 100 to 200 ° C. is added and kneaded to the ceramic raw material powder. To prepare a raw material mixture, and the obtained raw material mixture is molded by an injection molding method to form an injection molded body having a predetermined shape, and the injection molded body is heat-treated at a temperature not lower than the curing temperature of the thermosetting resin. Of the ceramic sintered body characterized by curing the thermosetting resin to crosslink the ceramic raw material powder with the thermosetting resin to prepare a cured molded body, and then degreasing and sintering the cured molded body. Production method.