JP4973917B2 - Carbon material manufacturing method - Google Patents

Description

  The present invention relates to a method for producing a carbon material for firing a molded body produced by injection molding, injection compression molding or transfer molding, and more particularly to a method for producing a carbon material that suppresses phenomena such as blistering and cracking that occur during firing.

  Furthermore, it is possible to produce a carbon material that approximates the target final product shape. For example, when producing a carbon material having an irregular shape or a complicated shape, the carbon material that can reduce the number of parts to be machined in post-processing as much as possible. It relates to the manufacturing method.

  Carbon materials have excellent heat resistance and high temperature strength in a non-oxidizing atmosphere, and have high conductivity, thermal conductivity, and chemical stability, and are widely used as various industrial materials. Conventionally, this carbon material is made of carbonaceous powder such as coke powder, combined with a binder such as pitch and tar, heated and kneaded, and the raw material powder obtained by pulverizing the kneaded product is extruded or subjected to cold isostatic pressure. It is manufactured by molding by isotropic pressure molding, etc., firing the molded body, repeating pitch impregnation and refiring, and graphitizing as necessary.

  In this manufacturing process, particularly in the firing process, a large amount of volatile gas mainly derived from the binder is generated, and deformation and cracking such as swelling are likely to occur unless the generated gas is smoothly volatilized and discharged from the molded body. For this reason, it is necessary to heat the heating rate very slowly in the firing process, and the firing cycle usually requires a long period of one month or more. Further, in order to obtain a final product having a three-dimensional shape, machining is performed from a block-shaped carbon material to a desired shape, and thus there is a difficulty in that it becomes expensive.

  On the other hand, carbon powder such as graphite and a thermosetting resin with a relatively high carbonization rate are mixed and kneaded as a binder, then dried and pulverized to form a molded powder, and a molded body obtained by molding the molded powder into a desired shape is fired. There is a method to carbonize.

  As a molding method, an injection molding method capable of producing a molded body having a relatively complicated shape is useful. For example, Patent Document 1 discloses a paste-like composition in which a resin is highly bonded to the particle surface of carbon fine powder due to a mechanochemical phenomenon by adding high mechanical energy when carbon fine powder and a thermosetting resin are mixed. A manufacturing method is disclosed in which the composition is cast or injection molded and fired.

  However, the fluidity of the paste-like composition is important at the time of molding, and the amount of thermosetting resin is inevitably increased because it is necessary to maintain high fluidity particularly in injection molding. For example, in Patent Document 1, the carbon powder has an average particle size of 100 μm or less, and the amount of thermosetting resin as a binder increases. Swelling and cracking are likely to occur, and it is difficult to produce a thick carbon product.

  Therefore, in Patent Document 2, 10 to 50 parts by weight of a benzylic ether type phenol resin is added to and kneaded with 100 parts by weight of carbon powder, and this kneaded product is injection molded or extruded to form a molded body, which is made into a non-oxidizing atmosphere. A method for producing a carbon molded body that is heat-treated at a temperature of 600 ° C. or higher has been proposed.

  Patent Document 2 uses a benzylic ether type phenolic resin that can obtain a kneaded material having good fluidity even if the amount of resin added is small, and it is said that a molded body having a complicated shape can be efficiently produced by injection molding. However, benzylic ether type phenolic resins have poor mold releasability, so it is necessary to add a mold release agent. Furthermore, there is a problem that the amount of volatile gas generated during firing carbonization is larger than that of ordinary phenolic resins. It is difficult to produce a thick molded body.

  Patent Document 3 discloses a method for producing a mesocarbon powder molded body in which a uniform mixture of mesocarbon powder and an organic binder is heated and injection molded. However, since the mesocarbon powder used has a small particle size of 1 to 80 μm and a plasticizer is added to improve the fluidity during molding, the amount of gas generated during the firing process increases, and the density of the carbon sintered body There is a drawback that the strength is lowered.

Patent Document 4 injects a resin composition mainly composed of 50 to 95% by mass of a novolac phenol resin having an ortho bond / para bond abundance ratio of 3 or more and 50 to 5% by mass of a carbonaceous material. An amorphous carbon molded body obtained by carbonizing and firing a molded body is disclosed, but since a fine powder having a carbonaceous material particle size of 100 μm or less is used, the resin amount ratio of the resin composition is high, and the amount of gas generated during firing There are many difficulties.
JP 59-195515 A Japanese Patent Laid-Open No. 01-115869 Japanese Patent Laid-Open No. 08-113668 JP 2004-131527 A

  Therefore, the inventor conducted various studies on the resin composition that is an injection molding material in order to solve the above problems, and a molded body obtained by injection molding or the like of a resin composition in which carbon powder and a thermosetting resin that is a binder are mixed. Found that a resin-rich layer is formed on the surface layer, and this resin-rich layer becomes a dense carbon layer during firing carbonization, which inhibits the emission of gas generated during decomposition carbonization of the resin component. It was.

  This tendency becomes prominent when the average particle size of the carbon powder is small, the mixing ratio of the thermosetting resin is large, and the thickness of the molded body is thick, and the volatile decomposition gas generated from the thermosetting resin The discharge does not proceed smoothly and blisters and cracks occur during firing carbonization. Furthermore, since the bonding force between the carbon powder and the thermosetting resin is reduced when the molded body is fired, it cannot withstand the pressure of the decomposition gas, and the occurrence of swelling and cracking is promoted.

  The inventor uses a carbon powder having a relatively large particle size, and adds a molding aid for improving the fluidity and mold release of the resin composition when mixing the thermosetting resin by a conventional method. Furthermore, the removal of the resin-rich layer formed on the surface of the molded body prevents the phenomenon of blistering and cracking during firing and carbonization of the molded body, and the nearness is such that machining to the target shape is almost unnecessary in post-processing. It was confirmed that a net-shaped carbon material was obtained.

  That is, the present invention has been completed based on these findings, and its purpose is to suppress phenomena such as blistering and cracking that occur during firing in a method for producing a carbon material for firing a molded body produced by injection molding or the like. An object of the present invention is to provide a method for producing a carbon material close to the intended final product shape.

In order to achieve the above object, the method for producing a carbon material according to the present invention comprises 100 parts by weight of carbon powder having an average particle diameter of 0.2 to 2 mm and a thermosetting resin of 10 to 40 weights with a residual carbon ratio of 40% or more. Part, the raw material consisting of 0.1 to 5 parts by weight of a molding aid with a residual carbon ratio of 10% or less, mixed and dried, pulverized molding powder is formed by injection molding, injection compression molding or transfer molding Then, by removing a part of the surface layer surface of the obtained molded body and removing the resin rich layer formed on the surface layer surface of the molded body, the gas permeability coefficient of the molded body is 1.0 to 5.0 × 10 ^−10. After adjusting to mol · mm ⁻² · s ⁻¹ · MPa ⁻¹ , curing treatment is performed at a temperature of 180 to 280 ° C., and then baking treatment is performed at a temperature of 800 ° C. or higher in a non-oxidizing atmosphere. Features.

  According to the present invention, a carbon powder having a large particle size is used, and a molding powder comprising a resin composition in which a thermosetting resin and a molding aid are mixed in a specific quantity ratio is obtained by injection molding, injection compression molding, transfer molding, or the like. By removing the resin-rich layer formed on the surface layer of the molded body and setting the gas permeability coefficient of the molded body to a predetermined range, the pyrolysis gas of the thermosetting resin generated during firing is effectively reduced. Emission and volatilization can be removed. As a result, it becomes possible to manufacture a carbon material with less blistering and cracking efficiently and with high productivity even if the firing time is shortened.

  The carbon material thus produced has characteristics such as a bending strength of 15 MPa or more, a specific resistance of 0.5 Ω · m or less, and a thermal conductivity of 30 W / mK or more, an antistatic material, an electromagnetic shielding material, and a sliding member. It can be used in a wide range of fields such as heat dissipating bases, far-infrared radiators, various heating elements including heating elements for cooking appliances, crucibles for metal deposition.

  Various carbonaceous powders are used as the raw material carbon powder, but graphite powder with a high degree of graphitization has high fluidity during injection, and there is little nozzle clogging or short shot. And natural graphite powder are preferred.

  The carbon powder having a mean particle size of 0.2 to 2 mm, preferably 0.4 to 2 mm, is used. If the average particle diameter is less than 0.2 mm, the fluidity of the molding powder is reduced, so that the moldability is deteriorated. If the resin amount is relatively increased in order to maintain the moldability, the resin formed on the surface of the molded body The rich layer becomes thick, and the amount of gas generated when the molded body is fired increases, which causes blistering and cracking. On the other hand, if the average particle diameter exceeds 2 mm, the gas permeability coefficient of the molded body increases, so that the firing process is easy, but the strength of the carbon material is reduced, and clogging easily occurs during injection molding.

  The thermosetting resin used as the binder for carbon powder is phenol resin, epoxy resin, polyimide resin, furan resin, unsaturated polyester resin, etc. with a residual carbon ratio of 40% or more, which is commonly used. Resins or epoxy resins are preferred.

In the present invention, in addition to the above-mentioned carbon powder and thermosetting resin that are commonly used as raw materials, a molding aid having a residual carbon ratio of 10% or less in order to improve fluidity, moldability and mold release during molding. Is an essential requirement. Residual charcoal ratio was determined by placing a resin sample in a magnetic crucible, heating at 135 ° C. for 1 hour, further heating at 250 ° C. for 5 hours, then covering the magnetic crucible and further in a non-oxidizing atmosphere at 1000 ° C. It is measured by heating for 30 minutes and dividing the weight of the sample after heating for 30 minutes at 1000 ° C. by the weight of the resin sample put in the porcelain crucible.
Residual carbon ratio (%) = (weight of sample after heating at 1000 ° C. for 30 minutes) / (weight of resin sample put in porcelain crucible) × 100

  As the molding aid, stearic acid, stearate, oleic acid, polyethylene wax, carnauba wax, organic phosphate ester, cross-linked polyolefin and the like, or an organic substance that is a mixture of two or more of these are preferably exemplified. The

  The mixing ratio of these raw materials is set to a ratio of 100 parts by weight of the carbon powder, 10 to 40 parts by weight of the thermosetting resin, and 0.1 to 5 parts by weight of the molding aid. When the mixing amount ratio of the thermosetting resin is less than 10 parts by weight, the fluidity of the raw material that is the mixed resin composition is low, and the moldability is deteriorated, whereas when it exceeds 40 parts by weight, the moldability is good. The resin-rich layer formed on the surface of the molded body becomes thick, and the amount of resin decomposition gas generated during firing increases, which causes the carbon material to swell and crack.

  On the other hand, when the mixing amount ratio of the molding aid to be added is less than 0.1 parts by weight, the fluidity of the mixed raw material is lowered, and a short shot is likely to occur, and the releasability is deteriorated. However, when the mixing ratio exceeds 5 parts by weight, the amount of generated gas increases because many decomposition components are generated from the molding aid during firing, and blistering and cracking are likely to occur during firing.

  In addition, it is preferable to add a firing aid in these raw material systems. The firing aid is decomposed and generated along with the carbonization of the resin component before the resin component is decomposed and carbonized by firing the thermosetting resin. It functions to facilitate gas volatilization and emission by forming a gas outflow passage. Examples of the baking aid include cellulose fiber, rayon fiber, acrylic resin, polystyrene resin, corn starch, and walnut powder.

  In addition, the addition amount of the firing aid is the above mixed raw material, that is, the mixing amount ratio of carbon powder 100 parts by weight, thermosetting resin 10 to 40 parts by weight, and molding aid 0.5 to 1 part by weight. It is added in an amount ratio of 0 to 10 parts by weight. Note that the firing aid is not required to be added if no blistering or cracking occurs during firing, but if the added amount ratio exceeds 10 parts by weight, the physical properties of the carbon material become non-uniform and the strength also decreases.

  The thermosetting resin is dissolved in an appropriate organic solvent to form a resin solution, and then carbon powder, the thermosetting resin, a molding aid, and, if necessary, a firing aid are mixed so as to have the above weight ratio. Mixing is carried out with an appropriate kneader such as a kneader, pressure type kneader, or twin screw kneader. The kneaded product is dried by vacuum drying or air drying to remove the organic solvent, and then pulverized to obtain a molding powder. Prepare.

  The molding powder is preferably pulverized into particles of 5 mm or less, and the molding method is preferably an injection method with high productivity, and molding methods such as injection molding, injection compression molding, and transfer molding are applied.

  In the molded body thus obtained, a resin-rich layer is formed on the surface, and this resin-rich layer is carbonized during the firing process and converted into a dense carbon layer (glassy carbon layer). . Therefore, the carbon layer formed on the surface of the molded body prevents the permeation of the decomposition gas of the resin generated along with the carbonization of the resin component during the curing process and the baking process, particularly the baking process, and causes the carbon material to expand and crack. Cause. Therefore, in the present invention, gas is smoothly removed by removing a part of the surface of the molded body to remove the resin rich layer, and it is essential to remove the resin rich layer on the surface of the molded body. It becomes a requirement.

The removal amount of the resin-rich layer varies depending on the average particle size of carbon powder, raw material components, composition, etc., but the gas permeability coefficient of the molded product after removal is 1.0 to 5.0 × 10 ⁻¹⁰ mol · mm ^−2. -It is necessary to remove so that it may become the range of s < ^{-1 >} * MPa- ¹ . If the gas permeability coefficient is less than 1.0 × 10 ⁻¹⁰ mol · mm ⁻² · s ⁻¹ · MPa ⁻¹ , gas permeation and volatilization are not sufficient, while the gas permeability coefficient is 5.0 × 10 ⁻¹⁰ mol. This is because there is no significant difference in the effect of gas permeation and volatilization even if the surface layer is removed to a degree exceeding mm ⁻² · s ⁻¹ · MPa ⁻¹ .

The gas permeability coefficient is measured by the following method.
Measured by the following method in accordance with JIS K7126 method A (differential pressure method).
A molded body having a thickness of 5 mm was cut from one side to a thickness of 1 mm, the surface layer of the molding surface on the other side was removed, and a 74φ × 1 t size test piece was used. Pressure change on the low pressure side after 60 minutes from closing the exhaust valve on the low pressure side under the conditions that the diameter of the permeation surface is 55 mm, the gas type is helium gas, and the low pressure side volume is 15 cm ^{3 and the} differential pressure is 0.2 MPa. (Room temperature 25 ° C.)

  The removal amount of the resin-rich layer depends on conditions such as the production conditions of the molded body, the size of the molded body, the curing process, and the baking process, but usually the surface layer is removed by 10 μm or more, preferably about 40 to 50 μm. The resin-rich layer can be removed by polishing or grinding using sand paper or sand blasting, or by burning off the surface resin layer with a burner or the like.

  After removing the resin-rich layer formed on the surface of the molded body and adjusting to a predetermined gas permeability coefficient, the resin component is cured by heating to a temperature of 180 to 280 ° C. by a conventional method. In a non-oxidizing atmosphere such as active gas or nitrogen gas, the resin component is heated and carbonized by heating to a temperature of 800 ° C. or higher. Further, depending on the purpose of use, it may be heated to a temperature of about 3000 ° C. A carbon material is manufactured by converting.

  With this manufacturing method, it is possible to efficiently and efficiently produce a carbon material having characteristics of a bending strength of 15 MPa or more, a specific resistance of 0.5 Ω · m or less, and a thermal conductivity of 30 W / mK or more. Become.

  These carbon materials are used in a wide range of application fields such as antistatic materials, electromagnetic shielding materials, sliding members, heat dissipation bases, far-infrared radiators, various heating elements including heating elements for cookers, and crucibles for metal deposition. be able to.

  Examples of the present invention will be specifically described below in comparison with comparative examples.

Examples 1-3, Comparative Examples 1-7
As the carbon powder, artificial graphite powder having an average particle size adjusted by pulverizing artificial graphite and having a different average particle diameter was used, and a phenol resin (manufactured by Gunei Chemical Industry Co., Ltd., PSM-) having a residual carbon ratio of 55% was used as the thermosetting resin. 2222), a resin solution was prepared by dissolving in acetone so that the resin solid content was 50 wt%. At this time, 10% of hexamine, which is a curing agent for the phenol resin, was added to the resin solid content. Further, stearic acid was used as a molding aid and added to the resin solution, and the mixture was stirred for 60 minutes to be completely compatible with the resin solution.

  In these raw material systems of artificial graphite powder, phenol resin solution, and stearic acid, the components were mixed at different weight ratios, and kneaded for 60 minutes with a biaxial kneader to prepare a mixed raw material. Next, after air-drying at room temperature to remove acetone and volatile components, the powder was pulverized to a particle size of 3 mm or less to obtain a molding powder.

Examples 4 to 5 and Comparative Example 8
Using ultrafine fibers made of cellulose as a baking aid, adding and mixing the raw material system consisting of the above artificial graphite powder, phenol resin solution and stearic acid while changing the mixing parts by weight, and then molding in the same manner as in Example 3 Powder was prepared.

  These molding powders were injection-molded with a single plate of 150 × 150 × 5 tmm using a 150-t general-purpose injection molding machine. The injection conditions were a cylinder temperature of 90 ° C., a mold temperature of 170 ° C., and the injection pressure and speed were selected according to the raw material composition of the molding powder.

  The surface layer surface of the obtained molded body was ground with a # 1000 paper file, and a part of the resin rich layer formed on the surface layer surface was removed by grinding to produce molded bodies having different gas permeability coefficients.

  Next, after curing by heating at a temperature of 250 ° C. for 5 hours, the temperature was once returned to room temperature, followed by baking at a temperature of 1000 ° C. for 5 hours in a nitrogen atmosphere to produce a carbon material. These production conditions are shown in Table 1.

  About these carbon materials, bulk specific gravity, bending strength, specific resistance, thermal conductivity, etc. were measured by the following method, and the obtained results are shown in Table 2.

(1) Bulk specific gravity;
The dry weight of the sample and the weight in water were measured (at room temperature of 25 ° C.) by the Archimedes method.

(2) Bending strength (MPa);
A three-point bending test was performed according to JIS K7203 under the conditions of a test piece size of 90 × 10 × 5 t (mm), a fulcrum distance of 80 mm, and a crosshead speed of 0.5 mm / min.

(3) Specific resistance (Ω.m);
Calculated by measuring the voltage drop at a terminal distance of 67 mm (room temperature 25 ° C.) by passing a direct current of 0.5 A in the longitudinal direction of the test piece size 90 × 10 × 5 t (mm) by the voltage drop method of JIS R7202. .

(4) Thermal conductivity (Wm ⁻¹ .K ⁻¹ );
Measured by laser flash method. TC-7000 type manufactured by Vacuum Riko Co., Ltd. is used as a measuring device. A laser beam with a predetermined energy is applied to a test piece size 10φ × 2t (mm), and the temperature change of the test piece and the temperature change of the laser light and the back surface of the projection surface The specific heat capacity and the thermal diffusivity in the thickness direction were measured and calculated from thermal conductivity = specific heat capacity × thermal diffusivity × density.

  In Examples 1 to 5, the moldability is good in any case, and by removing the surface resin-rich layer, gas permeation generated during firing is good. It did not occur and the bending strength could be used as a graphite material.

  In Comparative Example 1, since the graphite powder particle size was small, the flowability of the molding material was poor, and the mold could not be filled during injection molding. In Comparative Example 2, since the graphite powder particle size was large, injection molding was possible by increasing the spool diameter and the gate structure, but the fired molded article had low strength and could be used as a graphite material. There wasn't.

  In Comparative Example 3, since the resin amount was small, the fluidity of the molding powder was poor, and a remarkable weld line was observed in the molded product. In addition, breakage occurred at the weld line during firing, and the molded body was cracked, and the bending strength was lowered in other portions. In Comparative Example 4, since the amount of resin was large, the flowability of the molding powder was good and the moldability was good. However, the amount of gas generated by the resin decomposition was large, and many blisters occurred during firing.

  In Comparative Example 5, although the flowability of the molding material was improved by increasing the amount of the molding aid, the molding aid floated on the surface layer of the molded body to form a film, and the gas generated during molding The injection molded body swelled without being discharged. In Comparative Example 6, since no molding aid was added, the fluidity of the molding powder was poor, and short molding occurred frequently. Further, remarkable weld lines were observed in the obtained molded body.

  In Comparative Example 7, the injection molded body that was injection molded under the same conditions as in Example 3 was fired without removing the surface layer. Unfortunately, numerous blisters occurred during firing. In Comparative Example 8, molding was performed by increasing the amount of the firing aid. Molding could be performed without problems, but the dispersion of the firing aid could not be made uniform, and the pores formed when the firing aid was decomposed during firing became non-uniform, resulting in a local decrease in strength, Cracks entered during firing.

Claims (3)

100 parts by weight of carbon powder having an average particle size of 0.2 to 2 mm, 10 to 40 parts by weight of thermosetting resin having a residual carbon ratio of 40% or more, and molding aid 0.1 to 5 having a residual carbon ratio of 10% or less. Molded powder obtained by mixing raw materials with a weight ratio of parts by weight, drying and pulverizing is molded by injection molding, injection compression molding or transfer molding, and a part of the surface layer surface of the resulting molded body is removed. After removing the resin-rich layer formed on the surface layer, the gas permeability coefficient of the molded body was adjusted to 1.0 to 5.0 × 10 ⁻¹⁰ mol · mm ⁻² · s ⁻¹ · MPa ⁻¹ , A method for producing a carbon material, characterized by performing a curing treatment at a temperature of 180 to 280 ° C and then performing a baking treatment at a temperature of 800 ° C or higher in a non-oxidizing atmosphere.   2. The carbon material according to claim 1, wherein the molding aid is a compound such as stearic acid, stearate, oleic acid, polyethylene wax, carnauba wax, organic phosphate ester, cross-linked polyolefin, or a mixture of two or more thereof. Production method.   The method for producing a carbon material according to claim 1, wherein 0 to 10 parts by weight of a baking aid such as cellulose fiber, rayon fiber, acrylic resin, polystyrene resin, corn starch or walnut powder is added to the raw material.