JP2000095573A - Production of powder-formed body and production of sintered body from the formed body - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a production method of a powder-formed body, which enables uniformization of carbon distribution in the product. SOLUTION: This production method of a powder-formed body comprises: a slurry preparation stage for preparing a slurry by mixing a powdery raw material consisting of powdery carbon or a powdery carbon mixture with a polyethylene-imine that is a crosslinkable polymer and water that is a vaporizable dispersion medium, wherein the powdery carbon mixture is obtained by mixing a powdery ceramic material, refractory material or metal with powdery carbon; a curing agent mixing stage for mixing a curing agent into the slurry; a forming stage for casting the slurry contg. the mixed curing agent into a mold and curing the slurry, to form a formed body; and a drying stage for withdrawing the formed body from the mold and drying the withdrawn formed body.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a carbon mixed powder or a carbon powder compact obtained by mixing a carbon powder with a ceramic, refractory or metal powder, and a method for producing a sintered compact thereof.

[0002]

2. Description of the Related Art Conventionally, as a method for producing a powder compact of this type, there is known a method for densifying a powder compact on the premise of sintering described in Japanese Patent Publication No. 2592288. In this method, a raw material powder composed of a carbon mixed powder obtained by mixing a carbon powder with a silicon carbide powder is mixed with polyvinyl alcohol as a crosslinkable polymerizable resin, ammonium polycarboxylate as a dispersant, and water compatible with the resin. A slurry preparation step of preparing a slurry, and a curing agent mixing step of mixing the slurry with formaldehyde as a curing agent,
A molding step of injecting the slurry mixed with the curing agent into a mold to cure the molded article; and a drying step of removing the molded article and drying (spraying water) to obtain a powder molded article. Degreasing and firing in an argon gas atmosphere
A sintered body is obtained by performing a firing step. In this method, a self-hardening reaction by cross-linking polymerization occurs in a slurry mixed with a curing agent injected into a mold, and a molded article is obtained.

[0003]

However, in a conventional method for producing a powder compact and a sintered compact thereof, when polyvinyl alcohol is used as a resin and water is used as a dispersion medium, ammonium polycarboxylate or humic acid is used as a dispersant. Even if ammonium acid is mixed, these dispersants have a low ability to disperse carbon powder, cannot disperse carbon powder uniformly in slurry, and cause carbon powder to concentrate locally in slurry. I will. For this reason, the carbon distribution in the molded body tends to be uneven, and the carbon distribution in the sintered body obtained by firing the molded body tends to be uneven, and there is a problem that the quality of the product varies. Such a problem becomes remarkable when the amount of carbon in the raw material powder increases. On the other hand, as a resin other than polyvinyl alcohol, an epoxy resin, a phenol resin, a melanin resin, a urethane resin, or the like may be used, and water may be used as a dispersion medium. In this case, those resins have high lipophilicity. Therefore, carbon powder with high lipophilicity is selectively taken in, separated from water, and adheres to the inner surface of the slurry mixing container or the inner surface of the mold for pouring the slurry, or the carbon powder concentrates locally in the slurry. Would. For this reason, the amount of carbon powder in the compact and the sintered body is reduced, and the carbon distribution in the compact and the sintered body is likely to be uneven, which causes a problem that the quality of the product varies. Therefore, an object of the present invention is to provide a powder compact capable of making carbon distribution uniform in a product, and a method for producing a sintered compact thereof.

[0004]

In order to solve the above-mentioned problems, a method for producing a powder compact according to the present invention is directed to a method of producing a powder mixture of carbon, which is obtained by mixing carbon powder with ceramic, refractory or metal powder. A slurry preparation step of mixing the powder with polyethyleneimine that is a cross-linkable polymerizable polymer and water that is a gas-dispersing dispersion medium to prepare a slurry, a curing agent mixing step of mixing a curing agent with the slurry, and a curing agent It is characterized by comprising a molding step of injecting the mixed slurry into a mold and curing, and a drying step of removing and drying the molded body. The number average molecular weight of the polyethylene imine is preferably 2000 or more. Further, the curing agent is preferably a water-soluble polyfunctional epoxy compound. On the other hand, the manufacturing method of the sintered body is ceramic,
A slurry is prepared by mixing polyethyleneimine, which is a cross-linkable polymerizable polymer, and water, which is a gas-dispersible dispersion medium, with a carbon mixed powder obtained by mixing a carbon powder with a refractory or metal powder, or a raw material powder made of a carbon powder. A slurry preparation step, a curing agent mixing step of mixing a curing agent into the slurry, a molding step of injecting and curing the slurry mixed with the curing agent into a mold, a drying step of removing the molded body and drying, and drying. And a degreasing / firing step of degreased and fired in a non-oxidizing atmosphere. The number average molecular weight of the polyethylene imine is preferably 2000 or more. Further, the curing agent is preferably a water-soluble polyfunctional epoxy compound.

[0005] Regarding the slurry preparation process: Polyethyleneimine has cross-linking polymerizability, exhibits extremely high dispersibility in carbon powder and other raw material powders, and is optional in water as a gas-dispersible dispersion medium. Can be dissolved in the ratio of Therefore, the carbon powder can be uniformly dispersed in the slurry. As a result, the carbon distribution in the obtained molded body becomes uniform, and the carbon distribution in the sintered body obtained by firing the formed body can be made uniform. As polyethyleneimine, general linear polymers and branched polymers,
A polymer obtained by cross-linking a branched polymer or a polymer obtained by modifying another polymer compound with polyethyleneimine can be used. Polyethyleneimine can be used with any molecular weight, but has good shape retention, that is, in order to obtain a molded article having sufficient strength, the number average molecular weight is preferably 2000 or more, more preferably The number average molecular weight is 8000 or more. When it is desired to obtain a molded product having a high flexibility, for example, a sheet-shaped product, a product having a small number average molecular weight is used. In addition, since polyethyleneimine has high dispersibility in the raw material powder, it is not necessary to add a dispersant, but it may be added as appropriate.

[0006] The amount of polyethyleneimine to be added to the raw material powder is set in accordance with the desired degree of shape retention. Generally, the larger the amount of addition, the more the shape retention is improved.
As described above, since it depends on the number average molecular weight of polyethyleneimine used, the number is set in consideration of the number average molecular weight of polyethyleneimine. The amount of polyethyleneimine added is desirably 0.5 to 50 parts by weight based on 100 parts by weight of the raw material powder. The amount of polyethyleneimine added is
If the amount is less than 0.5 part by weight based on 100 parts by weight of the raw material powder, the strength of the obtained molded body is reduced. On the other hand, if it exceeds 50 parts by weight, cracks may occur in the degreasing step,
In order to prevent this, it is necessary to reduce the degreasing speed. Therefore, it is desirable that the amount of polyethyleneimine added is as small as possible. Also, when the amount of polyethyleneimine added exceeds 100 parts by weight with respect to 100 parts by weight of water, the same problem occurs in the degreasing step.
It is desirable to use less than 00 parts by weight.

If the amount of water added to the raw material powder is too large, drying shrinkage increases in the drying step, which breaks the molded body or prolongs the drying time. It is desirable to use a small amount as long as fluidity capable of defoaming can be ensured. On the other hand, as described above, since polyethyleneimine exhibits high dispersibility in the raw material powder, the fluidity of the slurry can be ensured even when the amount of added water is reduced, as compared with the case where other crosslinked polymerizable resins are used. (When another resin is used, the fluidity of the slurry is ensured by increasing the amount of water added.) As a result, drying shrinkage in the drying step can be reduced, cracking of the molded body can be prevented, and the drying time can be shortened. Further, the amount of water to be added to the raw material powder cannot be unequivocally specified because the viscosity (fluidity) of the slurry changes depending on the particle size, specific gravity, etc. of the raw material powder. Desirably 100 parts by weight. If the amount of water added is less than 5 parts by weight with respect to 100 parts by weight of the raw material powder, the fluidity of the slurry decreases, making it difficult to inject into a mold and remove bubbles.
If the amount is more than 00 parts by weight, drying shrinkage in the drying step of the molded article becomes large, resulting in cracks and a long drying time.

[0008] Regarding the curing agent mixing step: The amount of the curing agent to be added to polyethyleneimine is considered to be an amount equivalent to the reaction with polyethyleneimine in consideration of the number of functional groups, molecular weight and reactivity of the added curing agent. As the curing agent, any one of a water-soluble epoxy compound, a dialdehyde compound, a halogen compound and the like can be used as long as the curing agent causes a cross-linking polymerization reaction with polyethyleneimine.
In order to obtain a molded article having good shape retention, a water-soluble polyfunctional epoxy compound having two or more epoxy groups is particularly preferable, and a water-soluble polyfunctional epoxy compound having four or more epoxy groups is more preferable. It is valid.

Regarding the molding process: The slurry mixed with the curing agent is poured into a mold before fluidity is lost,
Curing due to cross-linking polymerization occurs in the mold, and a molded article containing water as a gas-dispersing dispersion medium is obtained. Curing can be carried out at room temperature, but it is preferable to carry out sealing in such a manner that drying does not occur or to carry out in a humid environment. In addition, heating or cooling can be performed for the purpose of controlling the curing speed.

Regarding the drying step: Drying can be left at room temperature or using a general hot air drier. Particularly, a molded article having a large thickness or a molded article having a large change in thickness is preferably used in a humid environment. It is desirable to carry out drying. The drying temperature is
100 ° C. or less is desirable, and 60 ° C. or less is more desirable.

Regarding the degreasing / firing step: Degreasing can be performed in either a non-oxidizing atmosphere or an oxidizing atmosphere. However, when performed in an oxidizing atmosphere, the degreasing is performed at 600 ° C. or lower so that the carbon powder is not oxidized and removed. Temperature. It is also possible to degrease the molded body by burying the same in a powder similar to the raw material powder, a carbon powder, a commonly used filling powder, or the like. Examples of the non-acid oxidizing atmosphere in the degreasing step and the firing step include an inert gas atmosphere such as argon, nitrogen gas, and hydrogen gas, and a vacuum atmosphere. The firing temperature is appropriately set according to the type of the raw material powder.

[0012]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be described below with reference to specific examples and comparative examples. Example 1 First, a raw material powder composed of 5 parts by weight of carbon black as carbon powder and 100 parts by weight of silicon carbide powder as ceramic powder was mixed with 3 parts by weight of polyethyleneimine, which is a crosslinkable polymer having a number average molecular weight of 8000 to 10500,
And 15 parts by weight of ion-exchanged water as an air-dispersing dispersion medium, and mixed all day and night with a ball mill to prepare a slurry. Next, 1 part by weight of sorbitol polyglycidyl ether (functional group: about 4), which is a water-soluble epoxy resin, was added as a curing agent to the obtained slurry and mixed by vacuum degassing and stirring. Then, the slurry mixed with the curing agent is poured into a polyethylene mold before its fluidity is lost,
Leave at room temperature, demold after curing by cross-linking polymerization in the mold,
Dried for 1 day in a humidifying dryer at a humidity of 90% and a temperature of 40 ° C. for 1 day, and then for 1 day in a hot air dryer at a temperature of 40 ° C. to form a 200 mm square, 40 mm thick powder as shown in FIGS. Two bodies were obtained. After degreasing one of the obtained powder compacts at a temperature of 600 ° C. in a nitrogen gas atmosphere, a surface portion and a middle portion in a thickness direction at a central portion of the degreased body, and a surface portion in a thickness direction at a peripheral corner portion of the degreased body From the intermediate portion, test pieces 2a, 2b and 3a, 3b (20 mm square, 2 mm thick) were cut out, and each test piece was heat-treated at a temperature of 800 ° C. in an air atmosphere, and the weight loss caused in each test piece was determined. When the carbon content was measured, it was as shown in Table 1. In addition, the carbon content was shown as an external ratio to the silicon carbide amount. After the other powder compact was degreased by the same method as that of the first powder compact, it was fired at a temperature of 1900 ° C. in an argon gas atmosphere to obtain a sintered body. A test piece was obtained from the obtained sintered body by the same method as that for the degreased body, and heat treatment was performed to measure the carbon content. As a result, the result was almost the same as that of the degreased body.

[0013]

[Table 1]

Comparative Example 1 First, a raw material powder composed of 5 parts by weight of carbon black as a carbon powder and 100 parts by weight of a silicon carbide powder as a ceramic powder, and 3 parts by weight of a water-soluble epoxy resin, sorbitol polyglycidyl ether, as a cross-linkable polymerizable resin. Department,
And 15 parts by weight of ion-exchanged water as an air-dispersing dispersion medium, and mixed all day and night with a ball mill to prepare a slurry. Next, 0.8 parts by weight of iminobispropylamine as a curing agent was added to the obtained slurry, and the mixture was mixed by vacuum degassing and stirring. Next, the slurry mixed with the curing agent is
Before the fluidity is lost, the mixture is poured into a polyethylene mold, cured by cross-linking polymerization in the mold, demolded, and dried to obtain a 200 mm square, 40 mm thick powder compact in the same manner as in Example 1. I got one. One of the obtained powder compacts was degreased in the same manner as in Example 1 to obtain a test piece, heat-treated, and measured for the carbon content. The results are shown in Table 1. In addition, the other powder compact was degreased and fired in the same manner as in Example 1 to obtain a sintered body, obtain a test piece, heat-treat, and measure the carbon content. Was the result. From Table 1, it can be seen that the distribution of carbon in the powder compact and the sintered compact can be homogenized by performing Example 1 according to the present invention.

Examples 2 to 23 First, as shown in Table 2, cross-linking polymerizable materials having different number average molecular weights were mixed with a raw material powder composed of 5 parts by weight of carbon black as carbon powder and 100 parts by weight of silicon carbide powder as ceramic powder. The respective parts by weight of polyethyleneimine as a polymer and 15 parts by weight of ion-exchanged water as an air-dispersible dispersion medium were added to each other in a ball mill to prepare respective slurries. Next, sorbitol polyglycidyl ether (functional group: about 4), which is a water-soluble epoxy resin, was added as a curing agent to each of the obtained slurries by weight as shown in Table 2, followed by vacuum defoaming and mixing. Then
Each of the slurries mixed with the curing agent is poured into a polyethylene mold before the fluidity of each is lost, left at room temperature, cured by cross-linking polymerization in the mold, and demolded.
%, 1 day in a humidifying dryer at a temperature of 40 ° C.
It dried for one day with the warm air dryer of ° C, and each powder compact 4 of 200 mm square and 10 mm in thickness was obtained as shown in Drawing 3 and Drawing 4. As shown in FIGS. 3 and 4, each of the obtained powder compacts 4 is equidistant from a center line passing through the center parallel to one side of the compact 4 and is equidistant from two support rods 5 parallel to the center line. By 150
It was supported at intervals of mm, the amount of flexure was measured, and the shape retention was investigated. The shape retention was defined as good when the amount of deflection was 2 mm or less, and flexible when the amount exceeded 2 mm.

[0016]

[Table 2]

As can be seen from Table 2, when the number average molecular weight of the polyethyleneimine is less than 2,000, the shape retention of the powder compact is not improved even when the amount thereof is increased, and the powder shows flexibility. The polyethyleneimine has a number average molecular weight of 20.
In the case of 00 or more, the shape retention can be improved by the addition amount.

Examples 24 to 35 First, a raw material powder consisting of 5 parts by weight of carbon black as carbon powder and 100 parts by weight of silicon carbide powder as ceramic powder was mixed with polyethylene as a crosslinkable polymer having a number average molecular weight of 8000 to 10500. 3 parts by weight of imine,
And 15 parts by weight of ion-exchanged water as an air-dispersing dispersion medium, and mixed all day and night with a ball mill to prepare a slurry. Next, a water-soluble epoxy resin having a different number of functional groups as a curing agent was added to each of the obtained slurries by weight as shown in Table 3 and mixed by vacuum defoaming and stirring. Then, each slurry obtained by mixing the respective curing agents was poured into a polyethylene mold before the fluidity was lost, left at room temperature, cured by cross-linking polymerization in the mold, and then released from the mold.
%, 1 day in a humidifying dryer at a temperature of 40 ° C, and then a temperature of 4%
It was dried with a hot air drier at 0 ° C. for one day to obtain each powder compact of 200 mm square and 10 mm thickness in the same manner as in Examples 2 to 23. Each of the obtained powder compacts was equidistant from a center line passing through the center in parallel with one side of the compact in the same manner as in Examples 2 to 23, and was spaced at an interval of 150 mm by two support rods parallel to the center line. Table 3 shows the results obtained by supporting and measuring the amount of deflection and examining the shape retention. As for shape retention, the deflection amount is 2m
m or less was defined as good, and the case exceeding 2 mm was defined as flexibility.

[0019]

[Table 3]

As can be seen from Table 3, the shape retention of the powder compact is good when the number of functional groups of the water-soluble epoxy compound as a curing agent is 4 or more, and when the number of functional groups is 2 or 3, Shape retention can be improved by the amount added. When the number of functional groups is 4 or more, sufficient shape retention can be obtained even if the amount of the curing agent is reduced, so that the amount of the curing agent is reduced and degreasing is facilitated.

In the above-described embodiment, the case where the carbon powder mixed with the ceramic powder and the carbon powder is used as the raw material powder has been described. However, the present invention is not limited to this. It was also found that the same function and effect can be obtained by using carbon powder as refractory powder or carbon powder mixed with metal powder.

[0022]

As described above, according to the method for producing a powder compact and a sintered compact of the present invention, polyethyleneimine having cross-linking polymerizability is very high relative to carbon powder and other raw material powders. Shows dispersibility, and can be dissolved at an arbitrary ratio in water as a gas-dispersing dispersion medium, so that the carbon powder can be uniformly dispersed in the slurry, and in the powder compact or sintered compact The carbon distribution can be homogenized.

[Brief description of the drawings]

FIG. 1 is a plan view showing an example of an embodiment of a powder compact according to the present invention.

FIG. 2 is a side view of the powder compact of FIG. 1;

FIG. 3 is a plan view showing another example of the embodiment of the powder compact according to the present invention.

FIG. 4 is a side view of the powder compact of FIG. 3;

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Powder compact 2a Test piece 2b Test piece 3a Test piece 3b Test piece 4 Powder compact 5 Support rod

Continued on the front page F term (reference) 4G030 AA47 AA60 GA14 GA20 PA21 4J002 CD002 CM011 DA017 DA037 DA066 DM006 EB008 EE018 FD142 FD148 GT00 HA07 4J036 AB03 FA02 FA06 FB14

Claims (6)

[Claims] Claims 1. To a carbon mixed powder obtained by mixing a carbon powder with a ceramic, refractory or metal powder or a raw material powder composed of a carbon powder, polyethyleneimine which is a cross-linkable polymerizable polymer and water which is a gas-dispersible dispersion medium are mixed. A slurry preparation step of mixing and preparing a slurry, a curing agent mixing step of mixing a curing agent into the slurry, a molding step of injecting the slurry mixed with the curing agent into a mold and curing, and demolding the molded body. A method for producing a powder compact, comprising: a drying step of drying. 2. The method according to claim 1, wherein the polyethyleneimine has a number average molecular weight of 2,000 or more. 3. The method according to claim 1, wherein the curing agent is a water-soluble polyfunctional epoxy compound. 4. A crosslinked polymerizable polymer, polyethyleneimine, and water, which is a gas-dispersible dispersion medium, are mixed with a carbon mixed powder obtained by mixing a carbon powder with a ceramic, refractory or metal powder, or a raw material powder made of a carbon powder. A slurry preparation step of mixing and preparing a slurry, a curing agent mixing step of mixing a curing agent into the slurry, a molding step of injecting the slurry mixed with the curing agent into a mold and curing, and demolding the molded body. A method for producing a sintered body, comprising: a drying step of drying; and a degreasing / firing step of degreasing the dried molded body and firing in a non-oxidizing atmosphere. 5. The method for producing a sintered body according to claim 4, wherein the number average molecular weight of the polyethyleneimine is 2,000 or more. 6. The method according to claim 4, wherein the curing agent is a water-soluble polyfunctional epoxy compound.