JP4735586B2 - Manufacturing method of ceramic sintered body - Google Patents

Description

  The present invention relates to a method for manufacturing a ceramic sintered body for easily manufacturing a ceramic product.

  In recent years, ceramic parts having complicated shapes have been required for machine structural parts, decorative parts, electronic parts, and the like. In particular, for wet complex shapes, several wet forming methods called casting and gel casting methods have been proposed. For example, in casting of alumina, zirconia, or a composite ceramic thereof, a cross-linking mainly composed of a mixture of a cross-linking component comprising a water-soluble epoxy resin and a cross-linking agent comprising an amine compound. A method for producing a ceramic molded body in which a water-soluble binder and a mixture of alumina, zirconia, or a composite ceramic powder thereof are filled in a mold and reaction-cured to form a molded body, wherein the crosslinkable water-soluble binder is formed. The amount of curing agent added to the binder is added so that the curing agent is 1 to 4 parts by weight with respect to 10 parts by weight of the crosslinkable water-soluble binder, and the reaction-cured molded body is dehumidified or humidified after demolding. There has been proposed a method for producing a ceramic molded body characterized in that the ceramic molded body is dried in an atmosphere. (Patent Document 1) However, this method has a problem that cracks and deformations occur if the shape is thick or the shape is complicated such that the thickness is extremely different.

  In addition, a method for producing a ceramic molded body is proposed in which a mixture containing ceramic powder, a curable resin, a solvent, and a compound that aggregates with the solvent is molded and sintered. (Patent Document 2) However, although the shape retention was improved, cracks occurred during drying, and physical properties after sintering were sometimes lowered.

In addition, regarding the method for producing an aluminum oxide sintered body, a method of adding silicon oxide, magnesium oxide or calcium oxide as a sintering aid is proposed as a method for improving the sintered body characteristics such as wear resistance. . (Patent Document 3) However, the sintered body prepared by the method of promoting the sintering by forming a glass phase in this way has a drawback of being weak in chemical resistance, particularly alkali resistance. In addition, this method requires that the ceramic particles have a BET specific surface area value of 5 m ² / g or more, and there is a problem that dry cracking may occur when cast molding or gel casting is performed.
Japanese Patent No. 3692682 JP 2005-53716 A JP 2003-321270 A

  The objective of this invention is providing the manufacturing method of the ceramic sintered compact which can manufacture a ceramic product of a large sized complicated shape easily without a crack.

The present invention employs the following means in order to solve such problems. That is, in a method for producing an aluminum oxide sintered body in which a solvent-containing ceramic molded body is prepared from a mixture containing aluminum oxide powder, a solvent, and a curable resin, and the solvent is removed, degreased, and sintered, the BET ratio of the aluminum oxide powder is This is a method for producing a ceramic sintered body having a surface area of 1 to 4 m ² / g and adding at least one of Cr ₂ O ₃ and Fe ₂ O ₃ and CoO as a sintering aid.

  According to the present invention, a sintered body can be easily produced without cracking during drying. It is particularly suitable for the production of large complex ceramics.

The present invention provides a method for producing a ceramic sintered body by preparing a solvent-containing ceramic molded body from a mixture containing aluminum oxide powder, a solvent, a curable resin, and a sintering aid, and then desolvating, degreasing and sintering. It is important that the aluminum oxide powder has a BET specific surface area of 1 to 4 m ² / g and contains at least one of Cr ₂ O ₃ and Fe ₂ O ₃ and CoO as a sintering aid. The BET specific surface area of the aluminum oxide powder can be determined by a method for measuring the specific surface area of the JIS R1626 (1996) fine ceramic powder by the gas adsorption BET method.

In general, a casting method that does not use a solvent-absorbing mold such as a gypsum mold creates a mixture containing ceramic powder, a solvent, a curable resin, etc., and cures the mixture while pouring it into a non-solvent mold. A solvent molded body is obtained. Next, it consists of the steps of removing the mold and removing the solvent from the solvent-containing ceramic molded body, followed by degreasing and sintering. However, in a complicated shape having a thick shape or an extreme difference in thickness, it is very difficult to remove the solvent from the solvent-containing ceramic, that is, to control the drying, and cracking occurs. In order to eliminate this crack, it is important that the BET specific surface area value of the aluminum oxide powder is in the range of 1 to 4 m ² / g. If it exceeds 4 m ² / g, cracks in drying occur. If it is less than 1 m ² / g, cracking does not occur, but the sinterability is poor, and even if a sintering aid is added, there is no effect. Preferably, it is in the range of 1 to ³ m ² / g. Aluminum oxide having a BET specific surface area value in the range of 1 to 4 m ² / g is inferior in sinterability, so it is necessary to add a sintering aid. The sintering aids are Cr ₂ O ₃ and Fe ₂ O _3. It is necessary to be at least one of these and CoO. These sintering aids are preferably in the form of fine powder. The average particle size is 10 μm or less, preferably 5 μm or less.
The average particle diameter here refers to a value obtained by measurement using a particle size distribution measuring device or the like.

CoO can promote the growth of crystal grains and increase the density of the sintered body. However, the addition of CoO alone makes it difficult to control the growth of crystal grains, resulting in the formation of large particles, which degrades mechanical properties such as bending strength. Therefore, it is necessary to add at least one of Cr ₂ O ₃ or Fe ₂ O ₃ that suppresses the growth of particles to satisfy both sinterability and mechanical properties. When Cr ₂ O ₃ is added, the bending strength tends to increase, and when Fe ₂ O ₃ is added, the sintered density tends to increase and both are more preferably added.

The addition amount of the sintering aid is 0.05 to 1.0% by weight of CoO, 0.1 to 1.3% by weight of Cr ₂ O ₃ , and Fe ₂ O ₃ 0 based on the total amount of aluminum oxide and the sintering aid. 0.01 to 1.0% by weight, and the total addition amount is preferably 0.5 to 1.5% by weight.

If the amount of CoO added is less than 0.05% by weight, the effect of promoting grain growth is small, and if it exceeds 1.0% by weight, the mechanical properties of the sintered body such as bending strength and hardness may be lowered. Preferably 0.07 to 0.3% by weight is more desirable. If Cr ₂ O ₃ is less than 0.1% by weight, the effect of suppressing grain growth is small, and if it exceeds 1.3% by weight, the mechanical properties of the sintered body may be lowered. Preferably 0.3 to 1.0% by weight is more desirable. If Fe ₂ O ₃ is less than 0.01% by weight, the effect of suppressing grain growth is small, and if it exceeds 1.0%, the mechanical properties of the sintered body may be lowered. Preferably 0.1 to 0.5 weight% is more desirable.

  Moreover, if the total amount of sintering aids added is less than 0.5 weight, the effect of promoting grain growth and the mechanical properties of the sintered body may be inferior. Characteristics may be degraded. Preferably 0.5 to 1.0% by weight is more desirable.

Further sintering properties, the effect of improving the mechanical properties of the sintered body, the composition ratio in the sintering aid is the total parts by weight of _Cr 2 _{O 3} and _Fe 2 _{O 3} relative to CoO1 parts 3-10 A part by weight is desirable. More preferably, 4 to 7 times is desirable.

  When preparing a mixture by mixing aluminum oxide powder, a sintering aid, a solvent, and a curable resin, a dispersant may be added to prepare a highly fluid mixture suitable for casting. For an oxide system such as aluminum oxide, dispersion of a polycarboxylic acid system is effective, but not limited thereto. Any mixing method may be used as long as wet mixing is possible, such as a medium agitation mill such as a ball mill, a planetary agitator without a pulverizing medium, or an agitator with a stirring blade. Methods and conditions that have a pulverizing effect that greatly increases the specific surface area are not preferred.

  The curable resin is preferably a water-soluble epoxy resin. Examples of such curable resins include melamine resins, phenol resins, epoxy resins, acrylic resins, urethane resins, and the like. Among these, an epoxy resin is preferably used in order to improve the shape retention of the molded body. The solvent is preferably aqueous based on the influence on the environment. Therefore, the curable resin is preferably water-soluble, and glycidyl ether type epoxy resin, glycidyl ester type epoxy resin, methyl glycidyl ether type epoxy resin, and cyclohexene oxide type epoxy resin are preferable. An ether type epoxy resin is more preferable because it cures smoothly even at room temperature.

  The addition amount of the curable resin is preferably 2 to 6 parts by weight with respect to the total of aluminum oxide and sintering aid. If the addition amount is less than 2 parts by weight, the strength of the solvent-containing molded body and the dried molded body may be insufficiently cracked, and if it exceeds 6 parts by weight, the degreasing process and the sintering process for converting the dried molded body into a sintered body In the process of removing the cured resin, such as cracking may occur, which is not preferable.

  The solvent in the mixture is desirably 20 parts by weight or less in order to facilitate drying.

  The curing agent is preferably amine-based because it can be cured at room temperature. When a curing agent is added, the amount added can be appropriately determined depending on the combination with the curable resin. That is, the preferred compounding ratio differs depending on the functional group equivalent of the curable resin and the active group equivalent of the curing agent. For example, when using an epoxy resin as the curable resin and a polyamine curing agent as the curing agent, The active hydrogen equivalent ratio of the amine curing agent is preferably about 0.8 to 1.5 from the viewpoint of curability.

By humidifying and drying the produced solvent-containing molded product, a good molded product free from cracks and warpage can be obtained. Although the drying conditions vary depending on the powder used and the shape of the molded body, it is desirable to dry while gradually decreasing the relative humidity from the conditions of room temperature and relative humidity of 60 to 90%.
Degreasing and sintering are performed to make the obtained ceramic molded body into a sintered body. The degreasing conditions may be appropriately determined depending on the type and amount of the binder, the shape of the formed body, and the sintering temperature depending on the ceramic material to be used and the shape of the ceramic formed body. In particular, a large molded body or a thick molded body may be heated to a temperature of 30 ° C./hour or less up to about 600 ° C. so as to prevent cracking due to degreasing to remove the binder. Sintering conditions are good to hold | maintain at 1600-1700 degreeC for 2 hours-3 hours.

Examples will be described below.
The physical properties of the examples were measured and evaluated as follows.
(1) BET specific surface area value The BET specific surface area value was measured by the BET single point method according to JIS-R1626 (1996) "Method for measuring specific surface area by gas adsorption BET method of fine ceramic powder".
(2) Cracking at the time of drying The produced solvent-containing molded sample having a size of 100 mm × 70 mm and a thickness of 30 mm was humidified and dried at a temperature of 30 ° C. and a relative humidity of 60% for 24 hours, and the presence or absence of cracks was confirmed. A constant temperature and humidity dryer was used for drying.
(3) Relative density of sintered body The sintered density of the sintered body was measured by the Archimedes method. A value obtained by dividing the sintered density by the theoretical density as a percentage was taken as the relative density. Here, each theoretical density was as follows.
Aluminum oxide: 3.98 g / cm ³
(4) Bending strength of sintered body The bending strength of the sintered body was determined in accordance with JIS-R1601 (1995) “Method for testing the bending strength of fine ceramics”.

Example 1
14 parts by weight of distilled water, 0.35 parts by weight of dispersant, 4 parts by weight of curability for the powder formulation shown in Example 1 of Table 1 and 100 parts by weight of the total amount of aluminum oxide and sintering aid. The resin was placed in a ball mill and mixed for 12 hours.
The BET specific surface area of the aluminum oxide powder was 3 m ² / g. A polycarboxylate was used as the dispersant, and a water-soluble epoxy resin (glycidyl ether type) was used as the curable resin. Next, the mixture was taken out from the ball mill, mixed with a curing agent with a rotary evaporator, poured into a mold, and allowed to cure at 20 ° C. for 24 hours to obtain a water-containing molded body. As the curing agent, 1- (2-aminoethyl) piperazine was used. As the mold, PP 100 mm × 70 mm, thickness 30 mm, PP 50 mm × 40 mm, and thickness 10 mm were used.

  A water-containing molded sample of 100 mm × 70 mm and a thickness of 30 mm was humidified and dried for 24 hours at a temperature of 30 ° C. and a relative humidity of 60%, and the presence or absence of cracks was confirmed. In addition, a 50 mm × 40 mm, 10 mm thick water-containing molded product sample was cooled to a relative humidity of 90% from a relative humidity of 90% at a relative humidity of 0.6% / hour. The molded body was obtained by drying with hot air at 100 ° C. for 24 hours. Further, the temperature was raised to 600 ° C. at a temperature raising rate of 25 ° C./hour in an electric furnace, and the temperature was further raised and sintered at 1600 ° C. for 2 hours to obtain a sintered body sample. After the density was measured with the obtained sintered body sample, it was processed into a bent piece and the bending strength was measured. As a result, as shown in Table 1, there was no dry crack, the relative density of the 1600 ° C. sintered body was 99% or more, and the bending strength was 400 MPa or more.

Example 2
14 parts by weight of distilled water, 0.35 parts by weight of dispersant and 4 parts by weight of curable resin are ball milled with respect to the total amount of the powder formulation and the aluminum oxide and sintering aid shown in Example 2 of Table 1. And mixed for 12 hours.
The BET specific surface area of the aluminum oxide powder was 1.7 m ² / g. A polycarboxylate was used as the dispersant, and a water-soluble epoxy resin (glycidyl ether type) was used as the curable resin. Next, the mixture was taken out from the ball mill, mixed with a curing agent with a rotary evaporator, poured into a mold, and allowed to cure at 20 ° C. for 24 hours to obtain a water-containing molded body. As the curing agent, 1- (2-aminoethyl) piperazine was used. As the mold, PP 100 mm × 70 mm, thickness 30 mm, PP 50 mm × 40 mm, and thickness 10 mm were used.
A water-containing molded sample of 100 mm × 70 mm and a thickness of 30 mm was humidified and dried for 24 hours at a temperature of 30 ° C. and a relative humidity of 60%, and the presence or absence of cracks was confirmed. In addition, a 50 mm × 40 mm, 10 mm thick water-containing molded product sample was cooled to a relative humidity of 90% from a relative humidity of 90% at a relative humidity of 0.6% / hour. The molded body was obtained by drying with hot air at 100 ° C. for 24 hours. Further, the temperature was raised to 600 ° C. at a temperature raising rate of 25 ° C./hour in an electric furnace, and the temperature was further raised and sintered at 1600 ° C. for 2 hours to obtain a sintered body sample. A sample sintered at 1650 ° C. for 2 hours was also prepared. After the density was measured with the obtained sintered body sample, it was processed into a bent piece and the bending strength was measured. As a result, as shown in Table 1, there was no dry crack and the bending strength of the 1600 ° C. sintered body was 300 MPa or less, but the relative density of the 1650 ° C. sintered body was 96% or more and the bending strength was 320 MPa or more.

Example 3
Except for the prescription shown in Example 3 of Table 1, it was prepared and evaluated in the same manner as in Example 2. The BET specific surface of the aluminum oxide powder was 1.7 m ² / g. As shown in Table 1, there were no dry cracks, and the relative density was 97% or more and the bending strength was 370 MPa or more in the 1650 ° C. sintered body.

Example 4
Except for the formulation shown in Example 4 of Table 1, it was prepared and evaluated in the same manner as Example 2. The BET specific surface of the aluminum oxide powder was 1.7 m ² / g. As shown in Table 1, the results show no dry cracking, the relative density of the 1600 ° C. sintered body is 96% or less, and the bending strength is 300 MPa or less. It was 310 MPa or more.

Example 5
Except for the formulation shown in Example 5 of Table 1, it was prepared and evaluated in the same manner as in Example 2. The BET specific surface of the aluminum oxide powder was 1.7 m ² / g. As a result, as shown in Table 1, there was no dry crack. The relative density of the sintered body at 1650 ° C. was 97% or more, and the bending strength was 284 MPa.

Example 6
Except for the prescription shown in Example 6 of Table 1, it was prepared and evaluated in the same manner as in Example 2. The BET specific surface of the aluminum oxide powder was 2.2 m ² / g. As a result, as shown in Table 1, there was no dry crack. The relative density of the sintered body at 1650 ° C. was 96% or more, and the bending strength was 276 MPa.

Example 7
Except for the prescription shown in Example 7 in Table 1, it was prepared and evaluated in the same manner as in Example 2. The BET specific surface of the aluminum oxide powder was 2.2 m ² / g. As a result, as shown in Table 1, there was no dry crack. The relative density of the sintered body at 1650 ° C. was 97% or more, and the bending strength was 263 MPa.

Example 8
Except for the prescription shown in Example 8 in Table 1, it was prepared and evaluated in the same manner as in Example 2. The BET specific surface of the aluminum oxide powder was 2.2 m ² / g. As a result, as shown in Table 1, there was no dry crack. The relative density of the 1650 ° C. sintered body was 97% or more, and the bending strength was 340 MPa or more.

Comparative Example 1
Except for the prescription shown in Comparative Example 1 in Table 2, it was prepared and evaluated in the same manner as in Example 1. The BET specific surface of the aluminum oxide powder was 4.5 m ² / g. As shown in Table 2, the results showed that the relative density at 1600 ° C. was 98% or more and the bending strength was 330 MPa or more, but dry cracking occurred.

Comparative Example 2
Except for the prescription shown in Comparative Example 2 in Table 2, it was prepared and evaluated in the same manner as in Example 2. The BET specific surface of the aluminum oxide powder was 1.7 m ² / g. As shown in Table 2, there were no dry cracks, but in the 1650 ° C. sintered body, the relative density was 95% or less and the bending strength was 230 MPa or less.

Comparative Example 3
Except for the prescription shown in Comparative Example 3 in Table 2, it was prepared and evaluated in the same manner as in Example 2. The BET specific surface of the aluminum oxide powder was 1.7 m ² / g. As a result, as shown in Table 2, there was no dry cracking, but the bending strength of the 1650 ° C. sintered body was a low value of 230 MPa or less.

Comparative Example 4
Except for the prescription shown in Comparative Example 4 in Table 2, it was prepared and evaluated in the same manner as in Example 2. The BET specific surface of the aluminum oxide powder was 1.7 m ² / g. As shown in Table 2, the results were as low as 1650 ° C. sintered body with a relative density of 95% or less and a bending strength of 230 MPa or less.

Comparative Example 5
Except for the prescription shown in Comparative Example 5 in Table 2, it was prepared and evaluated in the same manner as in Example 2. The BET specific surface of the aluminum oxide powder was 1.7 m ² / g. As shown in Table 4, there were no dry cracks, but the relative density of the sintered body was 96% or less and the bending strength was as low as 230 MPa or less.

Comparative Example 6
Except for the prescription shown in Comparative Table 6 in Table 2, it was prepared and evaluated in the same manner as in Example 2. The BET specific surface of the aluminum oxide powder was 0.6 m ² / g. As shown in Table 4, there were no dry cracks, but the relative density of the sintered body was as low as 95% or less and the bending strength was as low as 230 MPa or less.

As shown in Examples 1 to 8 in Table 1, according to the production method of the present invention, there is no dry crack, and a sintered body having a high relative density and bending strength can be obtained.

  The method for producing a sintered body according to the present invention can be suitably applied to large structural parts and the like because it can suitably provide complex shapes, large complex shapes, etc., but the scope of application is not limited to these. Absent.

Claims (3)

In a method for producing a ceramic sintered body by producing a solvent-containing ceramic molded body from a mixture containing aluminum oxide powder, a solvent, a curable resin, and a sintering aid, and then removing the solvent, degreasing, and sintering. A ceramic having a BET specific surface area of 1 to 4 m ² / g and containing at least one of Cr ₂ O ₃ and Fe ₂ O ₃ as a sintering aid and CoO. A method for producing a sintered body. 0.05 to 1.0 wt% of CoO with respect to the total amount of aluminum oxide powder and sintering aid, the _Cr 2 _{O 3} 0.1 to 1.3 wt% and _Fe 2 _{O 3} 0.01 was added to 1.0 wt%, the total addition amount is 0.5 to 1.5 wt%, the composition ratio in the sintering aid is, _Cr 2 _{O 3} with respect CoO1 parts by weight _Fe 2 O method of manufacturing a ceramic sintered body of claim 1, wherein the total parts by weight of ₃ is 3 to 10 parts by weight. The method for producing a ceramic sintered body according to claim 1 or 2 , wherein the curable resin is a water-soluble epoxy resin.