JP3245678B2 - Method for producing carbon material coated with carbon coating - Google Patents

Description

Description: FIELD OF THE INVENTION The present invention relates to a method for producing a carbon material coated with a carbon coating, and more particularly to a mandrel or / and a molding mold for producing a carbon / carbon composite, metal The present invention relates to a method for producing a carbon material which is extremely suitably used for a melting crucible, a glass sealing jig, a brazing jig, a graphite material part for an electric furnace, a continuous casting die, and the like.

[Conventional technology]

Conventionally, when carbon or graphite materials are used, particles fall off from the surface of these materials, causing contamination of the place of use and adhesion of dust to the products, resulting in a serious problem of lowering the product yield. That is, the dust generated from these materials is a serious problem, and in addition to the above-mentioned difficulties, there is also a problem of environmental hygiene for workers and the like. In addition, since these materials react with metals to form carbides, their use as metal melting crucibles is greatly limited.

As a means for preventing such carbon or graphite particles from falling off, a method of coating these materials with pyrolytic carbon is conventionally known. However, this method requires a complicated apparatus, which is a great difficulty for industrial implementation. Further, for example, when a fine hole of about 0.1 to 1 mm is required as in a jig for sealing a diode, there is also a problem that the fine hole is filled with the deposited pyrolytic carbon.

As another method, a method of firmly covering these materials with a glassy carbon film is also known, but it is still impossible to solve the disadvantage of filling small holes.

[Problems to be solved by the invention]

The problem to be solved by the present invention is to solve the problem of particles falling off in these materials. In addition, by modifying the surface of the graphite material, in the field where fine holes are required, fineness is required. It is an object of the present invention to develop measures for preventing carbon particles from falling off, suppressing reactivity with metal, and prolonging the life of graphite parts without filling the holes.

[Means for solving the problem]

The problem is to form a film of the resin on the surface of carbon or graphite using an organic solvent solution of an aromatic polyamideimide resin, and after curing, calcinate in a non-oxidizing atmosphere to carbonize or further graphitize. Solved by

According to the study of the present inventor, a specific resin called aromatic polyamide-imide resin is dissolved in a solvent and impregnated or applied to the surface of carbon or graphite material, and then cured and carbonized. It has been found that the carbon or graphite material having a carbon coating to be obtained has greatly improved particle detachment and hardly generates dust. In addition, even when fine holes are present in the carbon or graphite material, it is clear that the organic solvent solution of the resin penetrates into the fine holes and does not cover the fine holes on the surface, so that the fine holes almost remain as they are. Was.

Further, according to the study of the present inventor, when an organic solvent solution of the aromatic polyamide-imide resin is used, the concentration of the solution is reduced, or the molecular weight of the resin used is reduced to a lower molecular weight, thereby causing the particles to fall off. It has been clarified that the effect of preventing occlusion of small holes is further enhanced.

[Function and Configuration of the Invention]

The resin used in the present invention needs to penetrate deep into the carbon base material to be coated and cover the carbon fine particles constituting the base material.

For that purpose, it is necessary to lower the viscosity of the polymer solution to improve the permeability. In such a case, the method of lowering the viscosity includes (a) a method of diluting with a large amount of a solvent,
(B) There is a method of using a resin having a small molecular weight, in other words, using the resin in a state close to an oligomer state.

However, according to the method (a), a very small amount of the polymer component remains after the solvent is removed by evaporation, and the polymer layer itself has many holes from which the solvent has escaped and is rough. Therefore, there is a disadvantage that the coating effect is substantially reduced. In the case of the method (b), if the molecular weight is too small, it is thermally unstable, decomposes and evaporates at a slight temperature rise, and the coating effect is reduced. It was also found that (c) a resin having a heat resistance as much as possible is desirable.

The inventors changed the type and molecular weight of the resin to be used, the concentration in the solvent, and the like, and searched for the condition with the best impregnation state, and completed the present invention.

As a result of various tests, an aromatic polyamideimide resin was found to be optimal as the resin used in the present invention. Its structural formula is as follows.

This resin is known as a heat-resistant resin like the polyimide resin and the polybenzimidazole resin. In general, it is advantageous because it has a surface which is hard but has elasticity, has good adhesion to a carbon substrate, and has a property of not easily peeling off once a surface layer is formed.

As the molecular weight, 10 to 100 mer (n is 1 in the above formula)
When the molecular weight is about 1,000 to 10,000, it is difficult to dissolve in a solvent, the solution tends to be viscous, and the permeability to a graphite base material is deteriorated. Ten
If it is less than 1, the surface hardness is low and the coating effect is low. As the solvent, dimethylacetamide, dimethylformamide,
Dimethyl sulfoxide, N-methyl-2-pyrrolidone and the like are mentioned as preferred solvents.

Although the viscosity of the polyamideimide resin in the solvent varies depending on the solvent, the concentration of the resin component (solid content) must be adjusted in order to maintain a suitable viscosity for spraying or coating for surface treatment. 10-50% by weight, preferably 20-
It is about 35%. If the resin component is too small, the viscosity is low,
Although it has good permeability, the formed resin layer after the solvent is volatilized is rough, and the base material sealing property is low.

Conversely, if the amount of the resin component is too large, there is a disadvantage in that the resin becomes viscous and the permeability to the base material is deteriorated, and the stability in the solvent is poor, and white turbidity is reduced. Is not preferred.

There is a correlation between the molecular weight of the resin and the resin concentration in the solvent,
In order to maintain good workability, restrictions were imposed on the molecular weight and the solvent concentration as described above.

 The method of the present invention will be described below in the order of the manufacturing steps.

First, a carbon material is coated or immersed in an organic solvent solution of an aromatic polyamide-imide resin to coat or partially impregnate the solution. The raw carbon material used at this time is not particularly limited. Preferred is an isotropic carbon material. Further, a carbon / carbon composite material or the like can be used as the carbon material.

An organic solvent solution of the resin is applied or impregnated on the carbon material. These methods are brushing, spraying,
Any method such as immersion is adopted. The coating amount of the resin is usually 1 to 20 μm, preferably about 5 to 10 μm as the thickness of the coating layer. It doesn't need to be too thick and can be rather harmful. The coating is then heated at 300-400 ° C. to remove the solvent by volatilization and to cure the resin, and then fired in a non-oxidizing atmosphere to carbonize or further graphitize the coating.

Since the carbon material or the graphite coating of the aromatic polyamide-imide resin is firmly formed in the carbon material obtained in this way, no particle separation occurs and almost no dust is generated, and various difficulties based on this are prevented beforehand. Can be. Also, in the case of carbon materials that require fine holes, the resin has a low molecular weight or the solvent solution thereof has a low concentration (low viscosity), so that it hardly penetrates into the fine holes and coats the surface thereof. , A small hole almost remains.

〔Example〕

 Hereinafter, the present invention will be described in detail with reference to examples.

Example 1 A carbon material (an isotropic graphite material “IG-
11 ") with an aromatic polyamide-imide resin (Ohara Kako Co., Ltd.)
30% n-methyl-2-pyrrolidone solvent solution (resin concentration 20%, viscosity 1.1 poise)
After immersion for a minute and lifting, the adhered liquid was removed, dried at 300 ° C., and baked at 1000 ° C. for 24 hours in a nitrogen gas to obtain a target carbon material coated with a carbonaceous film. However, the thickness of this coating was 5 μm. No graphite powder was present on the surface of the obtained carbon product, and the element was not stained by touching the element. The presence or absence of the graphite powder could be determined by attaching an adhesive tape to the surface of the product, leaving the tape for a short time, peeling the tape, and measuring whether or not the graphite powder adhered to the tape. The result was also good. The fine holes present in the product did not cause clogging.

Example 2 The procedure of Example 1 was repeated except that the concentration of the solvent solution of the aromatic polyamideimide resin was changed to 35%. The obtained product was similarly subjected to a graphite powder shedding test. As a result, it was almost the same as Example 1.

Example 3 Example 1 on one side of a graphite material (“IG-11”) 25 × 25 × 15 mm
Polyamideimide resin dissolved in organic solution (concentration 35
%), And then cured at 300 ° C. in a drier, and further carbonized by heating in a nitrogen gas at 1000 ° C. for 24 hours.

The reactivity of the obtained graphite material with iron was measured. As shown in Fig. 1, the measuring method is as follows:
10mm), place the above graphite material (3) through the copper foil (2) (thickness 0.1mm) with the resin coating surface facing the iron plate (1) side, and up to 1100 ° C under N ₂ gas. The temperature was raised (20 ° C./min), kept for 4 minutes, and then cooled, and the state of bonding was observed.

In this measurement, a graphite material not using any polyamide-imide resin was treated in the same manner.

As a result, the graphite material of Example 3 was not bonded to the iron plate.
On the other hand, the graphite material alone (without the application of the polyamide-imide resin) was strongly bonded to the iron plate.

Originally, it has been known that when a graphite material is heated in a furnace by a method as shown in FIG. 1, a special alloy is precipitated between the graphite material and an iron plate to maintain a strong bonding state. However, as described above, no chemical reaction occurred on the surface on which the polyamideimide resin solution was applied and heat-treated. This indicates that the surface treatment by the method of the present invention modifies the graphite surface and has the effect of eliminating the reaction with certain metals (for example, Fe-based).

This effect is practically achieved by improving the product quality by preventing graphite powder from being separated and reacting with certain metals by performing this treatment on a graphite jig for sealing glass, a graphite crucible for melting metal, etc. The effect of preventing deterioration of the crucible material due to the prevention effect is added, and the life of the graphite jig and the crucible is greatly extended.

[Brief description of the drawings]

FIG. 1 is an explanatory view of a method for measuring the reactivity between a graphite material and a metal. 1. Iron plate 2. Copper foil 3. Graphite material

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-60-195014 (JP, A) JP-A-54-21984 (JP, A) JP-A-64-9866 (JP, A) (58) Field (Int. Cl. ⁷ , DB name) C04B 35/52 CA (STN)

Claims (3)

(57) [Claims] 1. An aromatic polyamide-imide resin is dissolved in an organic solvent, and this solution is applied or impregnated on a carbon material.
A method for producing a carbon material coated with a carbon film, characterized in that the material is cured at 400 ° C. and then fired in a non-oxidizing atmosphere to be carbonized or further graphitized. 2. The method according to claim 1, wherein the concentration of the aromatic polyamideimide resin in the organic solvent is 10 to 50%. 3. The method according to claim 1, wherein the aromatic polyamide-imide resin is about 10 to
The method according to claim 1, wherein the resin is a low molecular weight resin of about 100 mer.