JP2009249195A - Method for producing carbon molded product - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for producing a carbon molded product having a small shrinkage anisotropy at the time of burning and a reduced anisotropy of physical properties by reducing the anisotropy of the molded product accompanying a flow of a molding compound at the time of injection molding and suppressing the distortion due to the shrinkage at the time of burning. <P>SOLUTION: Carbon powder containing 0.01-5 pts.wt. of an organic compound or a synthetic resin compound is subjected to mechanical grinding to smooth a particle surface. 100 pts.wt. of the carbon powder and a resin solution in which 10-40 pts.wt. of a thermosetting resin solid content having a residual carbon ratio of 40% or more are mixed and kneaded , and the resulting mixture is dried, and thereafter crushed to obtain a molding powder. The molding powder is molded by injection molding, injection compression molding, or transfer moulding. The resulting molded product is cured at a temperature of 180-280°C and then burned at a temperature of 800°C or higher in a non-oxidizing atmosphere. <P>COPYRIGHT: (C)2010,JPO&INPIT

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 in particular, production of a carbon molded body with reduced variation in physical properties within the carbon material after firing. Regarding the method.

  Furthermore, it is possible to produce a carbon molded body approximating the target final product shape, for example, an antistatic material, an electromagnetic shielding material, a sliding member, a heat radiation base, a far-infrared radiator, a heating element, an electromagnetic induction and a direct current. The present invention relates to a method for producing a carbon molded body that can reduce the number of parts to be machined in post-processing as much as possible even when producing a carbon molded body having an irregular shape or a three-dimensional complex shape, such as a heating element and a container for a cooker.

  Carbon materials have excellent heat resistance and high temperature strength in a non-oxidizing atmosphere, and also have high electrical conductivity, thermal conductivity and chemical stability, and from such unique properties, electric, electronic, mechanical, metallurgical, Widely used in a wide range of fields such as chemistry. Conventionally, this carbon material is made of carbonaceous powder such as coke powder, blended with a binder such as pitch or tar, heated and kneaded, then pulverized to produce the raw material powder, and the raw material powder is extruded. It is molded by molding, cold isostatic pressing or the like, and is fired, further pitch impregnated, and refired repeatedly, and graphitized as necessary to produce a block-like carbon material.

  This manufacturing process is complicated, and especially in the firing process, a large amount of volatile gas derived mainly from the binder is generated, and if the generated gas is not smoothly volatilized and discharged from the molded body, deformation such as blistering and cracking will occur. Is likely to occur. Therefore, it is necessary to heat the heating rate very slowly during the firing process, and the firing cycle usually requires a long period of one month or more. In addition, 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, so that there is a problem that it becomes expensive.

  In order to eliminate such a problem and obtain a carbon molded body approximate to the final product shape, carbon powder such as graphite and a thermosetting resin having a relatively high carbonization rate are mixed and kneaded as a binder, then dried, There is a method of pulverizing into a molding powder and firing, carbonizing, and optionally graphitizing a molded body obtained by molding the molding powder into a desired shape by a molding method such as injection molding, transfer molding or compression molding. By this molding method, a molded body having a particularly complicated shape can be produced, and an injection molding method having a short molding cycle time 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 average particle size of the carbon powder may be a fine powder of 100 μm or less, and the amount of thermosetting resin that is a binder is increased to 30 to 95%, and the surface of the molded body is increased. Is easy to form a resin-rich layer, especially in thick carbon products with a thickness of 3 mm or more, it is difficult to discharge the decomposition gas during firing. It is difficult to manufacture.

  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. is there. However, because the amount of resin is small, the injection material spreads when it enters the mold cavity and is filled with air, and further filled so as to crush the air embraced by the material filled later, The carbon material after firing has anisotropy of physical properties such as low strength in the injection direction (high electrical resistance) and high strength in the perpendicular direction (low electrical resistance).

  In addition, since the injection molded product is forcibly filled in the mold at a high pressure, a large residual stress is accumulated in the molded product, and the residual stress is released during the subsequent curing and firing processes, and is caused by springback. It may expand greatly in the injection flow direction, and may be distorted and cracked during curing and firing.

  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 However, there is a problem that blisters and cracks occur.
JP 59-195515 A Japanese Patent Laid-Open No. 01-115869 Japanese Patent Laid-Open No. 08-113668 JP 2004-131527 A

  Therefore, the inventors suppress the above problems, that is, the anisotropy of the molded body due to the flow of the injection material at the time of injection molding, and suppress the distortion due to shrinkage at the time of firing, thereby preventing the carbon molded body from being swollen or cracked. In order to achieve this, the injection molding material was intensively studied from various aspects.

  Then, a synthetic resin compound is added to and mixed with the raw material graphite powder, and the resin-mixed graphite powder is cured and infusibilized by heat treatment or the like, and then mechanically milled to agglomerate secondary particles. When the mixed carbon powder is crushed and the surface of the mixed carbon powder is smoothed to have a rounded shape, the filling property of the rounded carbon powder particles in the resin binder is improved, and the moldability is improved. I found that it improved dramatically.

  As a result, it is confirmed that there is little variation in the physical properties of the fired carbon molded body without causing blistering or cracking during firing, and that a three-dimensional net-shaped carbon molded body requiring almost no machining is obtained. did.

  The present invention was developed based on these findings, and reduces the anisotropy of the molded body due to the flow of the molding material at the time of injection molding and the like, and suppresses distortion due to shrinkage at the time of firing. In addition to providing a method for producing a carbon molded body in which the shrinkage anisotropy of the carbon material is small and the anisotropy of the physical properties of the carbon material is reduced, the strain at the time of firing is reduced to reduce the mechanical strength, thermal conductivity, etc. The purpose is to improve the thermal properties.

  Furthermore, the present invention is a method for producing a carbon material that approximates the shape of a final product and has a portion that is machined in a post-processing as much as possible even when producing a deformed or complex shaped carbon molded body, and also occurs during firing. It aims at providing the manufacturing method of the carbon molded object which can reduce phenomena, such as a swelling and a crack.

  In order to achieve the above object, the method for producing a carbon molded body according to the present invention comprises: curing (infusibilizing) a graphite powder mixed with 0.01 to 10 parts by weight of a synthetic resin compound; The surface of the particles was smoothed by mechanical grinding, and the powder after grinding and 10 to 40 parts by weight of a thermosetting resin solid content having a residual carbon ratio of 40% or more with respect to 100 parts by weight of the powder were dissolved. After mixing with a resin solution, kneading and drying, the pulverized molding powder is molded by injection molding, injection compression molding or transfer molding, and the resulting molded body is cured at a temperature of 180 to 280 ° C. A structural feature is that a baking treatment is performed at a temperature of 800 ° C. or higher in an oxidizing atmosphere.

  As the synthetic resin compound, a thermosetting resin, a thermoplastic resin, pitch, or a mixture of two or more of these is preferably used.

  According to the present invention, the anisotropy of the molded body due to the flow of the molding material at the time of injection molding is reduced, and the distortion due to the shrinkage at the time of firing is suppressed, so that the shrinkage anisotropy at the time of firing is small. It is possible to produce a carbon molded body that has a small anisotropy and that approximates the final product shape with as few as possible parts to be machined in post-processing.

  The carbon molded body produced according to the present invention includes a wide variety of heating elements such as antistatic materials, electromagnetic wave shielding materials, sliding members, heat dissipation bases, far-infrared radiators, electromagnetic induction, and various heating elements and containers. Can be used in application fields.

  Since raw material powder is required to improve mechanical strength and thermal conductivity, graphite powder is applied, and graphite powder with high degree of graphitization has high fluidity at injection and good moldability. Since there is little nozzle clogging or short shot, artificial graphite powder or natural graphite powder is preferred from the viewpoint of moldability.

  As the graphite powder, one having an average particle size adjusted to 0.05 to 2 mm by pulverization with an appropriate pulverizer is preferably used. If the average particle size is less than 0.05 mm, the fluidity of the kneaded product is lowered and the injection moldability is deteriorated. If the amount of resin is increased in order to improve the injection property, the injected molded body becomes dense and occurs during firing. Since the amount of gas to be increased also increases, it causes swelling and cracking in the produced carbon molded body. Further, when the average particle diameter is larger than 2 mm, the strength of the carbon molded body is lowered, and clogging is likely to occur near the gate of the mold during injection molding.

  A synthetic resin compound is added to the graphite powder and mixed with an appropriate mixer. At this time, mixing is performed without applying a large share, and the mixture is cured and infusibilized by heat treatment or the like, and then mechanically ground. As the synthetic resin compound, a thermosetting resin, a thermoplastic resin, pitch, or a mixture of two or more of these is preferably used.

  Specifically, as the thermoplastic resin, polyethylene, polypropylene, fluororesin, polyamide, polyacetal, saturated polyester, polyvinyl chloride, polyvinyl butyral, polybutyl alcohol, polyvinylidene chloride, polyvinyl acetate, polyvinyl formal, polyvinyl acetal, Examples thereof include polystyrene, AS resin, ABS resin, methacrylic resin, polycarbonate, polyphenylene oxide, polysulfone, and celluloid.

  Examples of thermosetting resins include phenolic resin, epoxy resin, polyimide, furan resin, and unsaturated polyester. Examples of pitch powder include petroleum pitch, coal pitch, synthetic pitch, coal tar pitch, soft pitch, and hard pitch. It can be illustrated.

  These synthetic resin compounds are added and mixed at a ratio of 0.01 to 10 parts by weight with respect to the graphite powder. When the amount is less than 0.01 part, shrinkage anisotropy occurs when the injection-molded product is baked, and the physical properties such as strength and thermal conductivity are lowered. When the amount exceeds 10 parts by weight, the decomposition components increase, so that not only blisters and cracks are likely to occur during firing, but the synthetic resin compound peels off from the graphite powder during mechanical grinding and is finely pulverized. , The fluidity at the time of injection molding is lowered, and a short shot tends to occur.

  The graphite powder obtained by adding, mixing and curing these synthetic resin compounds is subjected to mechanical grinding treatment, and the graphite powder aggregated by the cured product of the synthetic resin compound breaks the primary particles while the synthetic resin compound adheres to the graphite powder. Smooth the particle surface of the powder to make it round. Normally, graphite powder has an angular shape, and a kneaded product with resin, which is a material to be injection-molded, has a short distance between carbon powder particles, and in the injection direction when injecting at a high pressure, particularly the interparticle distance in the vicinity of the gate. Is injected in a close state, so that a large residual stress exists in the molded body.

  Therefore, when the molded body is cured and fired, the residual stress is relaxed when the binding force of the binder resin is weakened, so-called springback occurs, and the shrinkage anisotropy increases during firing by expanding in the injection direction.

On the other hand, when the synthetic resin compound is added, mixed, and cured, and the particle surface of the graphite powder that has been mechanically milled is smoothed and rounded, the synthetic resin compound is converted into graphite powder. When mixed and cured, the unevenness of the graphite powder surface is covered, and when this mixture is mechanically milled and spheronized, the cured product of the attached synthetic resin compound is rounded with strong adhesion. Since it becomes smoother and the filling property at the time of injection molding is improved and it is spheroidized with the hardened synthetic resin compound attached, the graphite particles are destroyed when filled in the mold cavity with a large force Is suppressed, springback hardly occurs, and anisotropy is remarkably reduced.
In addition, graphite powder has poor wettability with thermosetting resin with a residual carbon ratio of 40% or more, which becomes a binder during injection molding, but graphite powder with a synthetic resin compound cured product is a mechano-mechanical material for mechanical grinding treatment. The chemical change improves the wettability with the thermosetting resin as the injection molding binder, and as a result, the mechanical characteristics and the thermal characteristics are improved.

  Furthermore, since the spread of the molding material at the moment of exiting from the cylinder nozzle during injection molding is reduced, the amount of air that is embraced during molding is reduced, the anisotropy of the molded product is reduced, and the strength is also improved. Can do.

  The method of the mechanical attrition treatment is not particularly limited as long as the corners of the carbon powder can be removed and the particle surface can be smoothed into a rounded shape, for example, compression mainly including impact force, including particle interaction, A device that repeatedly gives mechanical action such as friction and shearing force can be used, and it has a rotor with a large number of blades installed inside the casing. When the rotor rotates at high speed, it impacts the carbon powder introduced inside. A device that repeatedly gives mechanical action such as compression, friction, and shearing force can be preferably used.

  Specific examples include a hybridization system manufactured by Nara Machinery Co., Ltd., a mechanofusion apparatus manufactured by Hosokawa Micron Corporation, and the like.

  In this way, 0.01 to 10 parts by weight of the synthetic resin compound was added, mixed, and 100 parts by weight of the carbon powder obtained by mechanically grinding the hardened graphite powder and a heat with a residual carbon ratio of 40% or more. A curable resin is mixed with a resin solution in which the solid content of the resin is 10 to 40 parts by weight in an organic solvent.

  Thermosetting resin is a binder for carbon powder, and phenol resin, epoxy resin, polyimide, furan resin, unsaturated polyester, etc. with a residual carbon ratio of 40% or more are used. Or an epoxy resin is suitable.

  The residual charcoal rate was measured by placing a sample in a crucible, heating at 135 ° C. for 1 hour, further heating at 250 ° C. for 5 hours, then covering the magnetic crucible and heating at 1000 ° C. for 30 minutes in a non-oxidizing atmosphere. It is measured by dividing the weight of the later sample by the weight of the sample put in the porcelain crucible.

  As the organic solvent, an appropriate solvent capable of dissolving a resin such as acetone or alcohol is used, and the carbon powder and the resin solution are sufficiently kneaded by an appropriate kneader such as a kneader, a pressure type kneader, or a twin screw kneader. . Then, after drying by vacuum drying or air drying to remove the organic solvent and volatile components that volatilize at a low temperature, the powder is pulverized to obtain a molding powder.

  In addition, when the resin solid content in the resin solution is less than 10 parts by weight, it is difficult to obtain a uniform molded product due to the decrease in fluidity of the molding powder at the time of injection molding, while when the resin solid content exceeds 40 parts by weight. Although the moldability is good, gas outflow is poor during injection molding, and blisters and cracks are likely to occur during firing.

  The molding powder is preferably pulverized to a particle size of 5 mm or less, and the molding powder is molded by injection molding, injection compression molding, transfer molding, or the like. In consideration of productivity and mold structure, injection molding is preferable.

  It should be noted that when producing molding powder, a molding aid that improves fluidity, moldability, releasability, etc. during injection molding, and a firing aid that volatilizes and disappears before the thermosetting resin decomposes during the firing process. An agent can also be added.

  Examples of the molding aid include fatty acid compounds such as stearic acid, stearate, oleic acid, polyethylene wax, carnauba wax, organic phosphate esters, cross-linked polyolefins, and the like, and is added at a ratio of 0.1 to 5 parts by weight. It is preferable. If the amount is less than 0.1 parts by weight, the fluidity of the molding powder is reduced and short shots are likely to occur, and the releasability is also deteriorated. On the other hand, if the amount exceeds 5 parts by weight, the decomposition components during firing increase, and blisters and cracks are likely to occur.

  Examples of firing aids include fibers such as cellulose and rayon, acrylic resins such as polymethylmethacrylate, polystyrene resins, corn starch, walnut powder, etc. Addition is always necessary if no swelling or cracking occurs during firing. However, when added, the amount is preferably less than 10 parts by weight.

  In addition, a resin-rich layer is easily formed on the surface layer of the molded body thus obtained, and this resin-rich layer is a carbon layer (glass-like) whose structure is dense due to carbonization of the resin during firing. Carbon layer). This carbon layer prevents the permeation of the resin decomposition gas generated by the carbonization of the resin component during the curing treatment and the firing treatment, and the gas emitted from the molding aid and firing aid, and the swelling of the carbon material. Cause cracks. Therefore, in order to smoothly volatilize these gases, it is preferable to remove a part of the surface layer of the molded body and remove the resin rich layer in advance.

  The removal of the resin-rich layer depends on the conditions for forming the molded body, the size of the molded body, the curing process, the firing process, etc., but usually the surface of the surface layer is removed by 10 μm or more, preferably about 40-50 μm. The removal of the resin-rich layer can also be carried out by polishing or grinding with sandpaper or sandblast, or by burning the surface resin layer with a burner or the like.

  After removing the resin-rich layer formed on the surface of the molded body, the resin component is cured by heating to a temperature of 180 to 280 ° C. by a conventional method, and then non-oxidizing such as inert gas or nitrogen gas A carbon molded body is manufactured by heating to a temperature of 800 ° C. or higher in an atmosphere and baking the resin component to carbonize. Depending on the purpose of use, it is further graphitized by heat treatment to a temperature of about 3000 ° C.

  Hereinafter, the present invention will be specifically described by way of examples and comparative examples.

Examples 1-3, Comparative Examples 1-4
As the carbon powder, graphite powder obtained by pulverizing artificial graphite and adjusting the particle size was used, and stearic acid was added to this graphite powder at different ratios. However, in Comparative Examples 1 and 4, it was not added.

  This graphite powder was mechanically ground using a hybridization system manufactured by Nara Machinery Co., Ltd. at a rotational speed of 6000 rpm for 3 minutes.

About these graphite powder, the tapping density was measured by JISR1628.
The tapping density was measured under the condition that the tapping cell was filled with graphite powder, the stroke length at tapping was 10 mm, and the tapping frequency was 1000 times.

  Moreover, the average particle diameter of the graphite powder was measured using a laser diffraction particle size distribution analyzer (manufactured by Shimadzu Corporation, SALD-2100).

  A phenol resin having a residual carbon ratio of 50% (manufactured by Gunei Chemical Industry Co., Ltd., Residtop PG-2411) was used as the thermosetting resin, and dissolved in acetone so that the resin concentration was 50 wt% to prepare a resin solution.

  The resin solution was added to the graphite powder in different quantitative ratios and kneaded for 60 minutes with a biaxial kneader. At that time, 10% of hexamine was added to the resin solid content as a phenol resin curing agent. Thereafter, it was air-dried at room temperature to remove acetone and volatile components, and pulverized to produce a molding powder having a particle size of 3 mm or less. The production conditions for this molding powder are shown in Table 1.

  Next, these molding powders were injection-molded by taking a single plate with a 150 × 150 × 5 tmm mold using a 150-t general-purpose injection molding machine. The injection molding conditions were a cylinder temperature of 90 ° C., a mold temperature of 170 ° C., and the injection pressure and speed were selected in accordance with the raw material composition of the molding powder. The surface layer surface of the molded body was ground with a # 1000 paper file, and the resin-rich layer formed on the surface layer surface was removed by 30 μm.

  Next, after curing by heating at a temperature of 250 ° C. for 5 hours, the temperature was once returned to normal temperature, and then heated at 1000 ° C. for 5 hours in a nitrogen atmosphere to perform a baking treatment to produce a carbon molded body.

  Next, these carbon molded bodies were measured for bulk specific gravity, bending strength, specific resistance, thermal conductivity and the like by the following methods. In order to evaluate the anisotropy of physical properties, a test piece in the injection direction and a test piece in a direction perpendicular to the injection direction are cut out from one plane, and the injection direction (X direction) and the injection direction And the physical properties in the direction perpendicular to (Y direction) were measured. The results are shown in Table 2.

Bulk specific gravity;
It was determined by measuring the dry weight of the sample and the weight in water (at room temperature of 25 ° C.) by the Archimedes method.

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.

Specific resistance (mΩ · cm);
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 of 90 × 10 × 5 t (mm) by the voltage drop method of JIS R7202. .

Thermal conductivity (Wm ⁻¹ K ⁻¹ );
Measured by laser flash method. TC-7000 type manufactured by Vacuum Riko Co., Ltd. is used as the measuring device. A laser beam with a predetermined energy is applied to a test piece size of 10φ × 2t (mm). From 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 and 2, 1 part by weight of stearic acid was added to the graphite powder, and in Example 3, 0.03 part by weight was added to perform mechanical grinding. In Examples 1 to 3, the moldability was good, the anisotropy of shrinkage during firing was suppressed, and the anisotropy of the physical properties of the carbon molded body was small.

  In Comparative Example 1 in which stearic acid was not added and the mechanical grinding treatment was not performed, the moldability and the appearance of the carbon molded body were good, but it expanded in the injection direction due to the springback phenomenon during curing and firing. As a result, the shrinkage anisotropy of the carbon molded body increased. In addition, the spread of the molding material could not be suppressed during injection molding, and the anisotropy of the physical properties of the carbon molded body increased due to air inclusion.

  In Comparative Example 2 where the amount of stearic acid added was as large as 6 parts by weight, the moldability was good, but the decomposition component of stearic acid increased and swelling occurred during firing.

  Comparative Example 3 uses graphite powder with a small particle size and increased the amount of phenolic resin in order to ensure the fluidity of the molding material. Therefore, the moldability was good, but the injection-molded body became dense and generated during firing. Permeation and volatilization of the decomposition gas of the resin were not sufficiently performed, and the carbon molded body was swollen and cracked.

  In Comparative Example 4 in which the amount of phenol resin is small, the fluidity of the molding material was lowered and short molding was achieved.

Claims (2)

  After the graphite powder mixed with 0.01 to 10 parts by weight of the synthetic resin compound is cured (infusibilized), the resin-mixed graphite powder is mechanically ground to smooth the particle surface. A powder and a resin solution in which 10 to 40 parts by weight of a solid content of a thermosetting resin having a residual carbon ratio of 40% or more with respect to 100 parts by weight of the powder are mixed, kneaded, dried, and then pulverized molding powder is injection molded. Carbon obtained by molding by injection compression molding or transfer molding, and curing the resulting molded body at a temperature of 180 to 280 ° C., followed by firing at a temperature of 800 ° C. or higher in a non-oxidizing atmosphere. Manufacturing method of a molded object.   The method for producing a carbon molded body according to claim 1, wherein the synthetic resin compound is a thermosetting resin, a thermoplastic resin, pitch, or a mixture of two or more of these.