JP2002012485A - Surface coating method of graphite sheet - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a thermoconductive flexible graphite sheet whose surface has the properties of less peeling-off of the graphite powder, excellent insulation, chemical stability and less thermal resistance. SOLUTION: The graphite sheet with excellent electrical insulation and flexibility, less peeling-off of the graphite powder and low thermal resistance is realized by arranging a coated resin film on the surface of the sheet.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for coating the surface of a graphite sheet.

[0002]

2. Description of the Related Art As a graphite sheet, there is known a sheet obtained by mixing graphite powder with a binder resin, or by rolling expanded graphite into a sheet. Also,
A method for directly obtaining a flexible graphite sheet by heat treatment and rolling treatment using a polyimide film as a raw material has already been disclosed in Japanese Patent Publication No. 1-96442. These graphite sheets are excellent in properties such as electric conductivity and heat conductivity. In particular, those using a polyimide film as a raw material can provide a graphite sheet having high quality, high resistance to bending and high flexibility, and excellent heat conductivity.

On the other hand, in recent years, as electronic devices have become smaller and higher in performance, thermal problems generated from CPUs and the like which are integrated at a high density, and thermal problems are also important in semiconductor manufacturing equipment requiring fine control. Are becoming important considerations.
Regarding heat, not only heat dissipation but also heat uniformity, which is how to reduce temperature variations depending on the location, is important.

Heretofore, at present, a metal plate such as an aluminum plate or a copper plate having excellent heat conductivity is appropriately processed or combined with a cooling fan to take measures against heat radiation.

Under such circumstances, the graphite sheet is
Compared to a metal plate, it has good thermal conductivity, and is light and flexible. Therefore, it is beginning to be expected as a heat conductive material for electronic devices, devices and equipment.

[0006]

However, when the graphite sheet is used as it is as a heat conductive material inside an electronic device, the graphite sheet has electrical conductivity, so that an electrical short circuit between the electronic components occurs. Carbon powder may be dispersed from the surface due to wear and abrasion, and the carbon powder may similarly have an adverse electrical effect.

Further, in terms of mechanical strength, depending on the method of use, the breaking strength, tensile strength, etc. may not be sufficient.

To prevent these disadvantages, it has been proposed to cover the surface of the graphite sheet with a polymer film. However, when the graphite sheet surface is used in contact with a heat source or a cooling portion, the thermal resistance of the polymer film on the surface is low, so that the thermal resistance increases as the thickness of the polymer film increases. For this reason, it is desirable to use a polymer film as thin as possible, but it is difficult to handle a polymer film of 10 μm or less.

When a polymer film is bonded to the surface of a graphite sheet to be integrated, an adhesive layer or an adhesive layer is present, and these layers also have a low thermal conductivity. Become.

[0010] Therefore, there is a demand for a graphite sheet having a surface having excellent insulating properties, being chemically stable, preventing carbon powder from being detached from the surface, and having a small increase in thermal resistance.

[0011]

Means for Solving the Problems To solve the above problems, the present invention is a method for coating a surface of a graphite sheet, wherein a resin coating film is provided on the surface of the graphite sheet.

The resin coating film may be made of an epoxy resin, a polyimide resin, a fluororesin, or the like, or a laminate of two or more of these resins.
As the coating method, a method such as dipping, spin coating, screen printing, brush coating, spraying and the like is desirable. As a graphite sheet, a sheet made of a polyimide film as a raw material is excellent in thermal conductivity and flexibility, and is suitable for high performance. With such a configuration, a chemically stable graphite sheet having excellent insulation properties is realized.

[0013]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention according to claim 1 is characterized in that a resin coating film is provided by applying a solution-type resin to one or both surfaces of a graphite sheet made of a polyimide film as a raw material. This is a method for coating the surface of a graphite sheet.

[0014] With such a configuration, the surface of the graphite sheet is insulated, the mechanical strength is improved, and the graphite powder is prevented from desorbing.

According to a second aspect of the present invention, by using an epoxy resin as the resin coating film, the graphite sheet has the functions of insulating the surface, improving the mechanical strength, and preventing the graphite powder from being detached. Can be.

Further, as described in claim 3, a polyimide resin can be used as the resin coating film. Such a polyimide resin coating film has the functions of insulating the surface of the graphite sheet, improving the mechanical strength, and preventing the graphite powder from being detached, and exhibits further excellent heat resistance.

As described in claim 4, a fluorine resin can be used as the resin coating film. Such a fluororesin coating film has the functions of insulating the surface of the graphite sheet, improving the mechanical strength, and preventing the graphite powder from desorbing, and exhibits features that are excellent in chemical resistance.

As described in claim 5, the resin coating film may be formed by laminating two or more types of epoxy resin, polyimide resin and fluororesin. With such a configuration, in addition to the functions of insulating the surface of the graphite sheet, improving the mechanical strength, and preventing the desorption of the graphite powder, it is possible to provide functions such as heat resistance, chemical resistance, and flexibility. .

As the coating method, it is desirable to use any one of dipping, spin coating, screen printing, and brush coating.

Further, spraying can be used as a coating method.

It is desirable that the thickness of the resin coating film be 10 μm or less. This is because a thin coating film is preferable in order to exhibit the basic characteristics of the graphite sheet. When the thickness of the resin coating film exceeds 10 μm,
This is because the thermal resistance due to the coating film is increased, the good thermal conductivity of the graphite sheet is impaired, and the flexibility and flexibility are reduced.

A pretreatment step in which the graphite sheet is heated from room temperature to 1000 ° C. to 1600 ° C. in an inert gas using a polyimide film as a raw material in the inert gas according to claim 9; The graphite sheet surface coating method according to any one of claims 1 to 9, wherein a graphite sheet produced by heating from room temperature to a temperature of 2500 ° C or higher after the treatment step is used.

By using the graphite sheet prepared in this way, a heat conductive material having excellent flexibility and flexibility can be used as a surface having excellent insulation, being chemically stable, and having low thermal resistance. It becomes possible to realize a graphite sheet having

With such a configuration, the thickness of the coating film having a small thermal conductivity can be reduced as compared with the case of coating with a polymer film, so that the thermal resistance can be reduced, and the graphite sheet has excellent properties. The effect on thermal conductivity can be reduced.

Furthermore, in such a configuration, since the adhesion between the coating film and the graphite sheet is good, it is not necessary to use an adhesive or an adhesive, and the workability is good. Hereinafter, description will be made in more detail in accordance with each embodiment of the present invention.

(Embodiment 1) In the first embodiment of the present invention, an experiment was carried out using a 75 μm-thick Toray Dupont (Kapton) polyimide film as a starting material for a graphite sheet. went. As a preliminary heat treatment, the maximum treatment temperature was increased to 1200 ° C. in a nitrogen atmosphere, and then the temperature was lowered to room temperature, and then taken out. Further, as a high temperature heat treatment, a maximum treatment temperature of 2 in an Ar gas atmosphere.
After the temperature was raised to 700 ° C., the temperature was lowered to room temperature and firing was performed. Thereafter, the graphite sheet produced by rolling had flexibility and flexibility that can be repeatedly bent, and had a thickness of about 100 μm.

The conditions for forming the graphite sheet described above are typical examples, and the conditions are not limited as long as they are flexible and flexible enough to be graphitized and repeatedly bent. Of course.

On both surfaces of the thus obtained graphite sheet, an epoxy resin (a two-part epoxy compounded resin manufactured by Three Bond Co., Ltd., this agent 2022, a curing agent 2104) was coated by brushing. Then, it was cured by holding at 100 ° C. for 1 hour. The thickness of the epoxy resin coating film on the graphite sheet thus formed is 8 μm.
m, the surface was insulative, and no desorption of graphite powder was observed.

In order to evaluate the thermal conductivity of the graphite sheet coated on the surface, a graphite sheet was sandwiched between a heat source and a heat sink, and the temperature difference between the heat source and the heat sink was measured.

In the present embodiment, a graphite sheet having a size of 2 × 1.5 cm and both sides of the graphite sheet as described above are provided between a heat source having a size of 2 × 1.5 cm and a heat sink. Those coated with an epoxy resin film having a thickness of 8 μm were fixed to each other. The fixing was performed with M3 screws at a tightening torque of 1 MPa. 4 W of electric power was applied to the heat source to generate heat, and the temperature difference between the heat source and the heat sink at the time of the steady state was measured.

As a result, the temperature difference between the heat source and the heat sink was 4.8 ° C. when only the graphite sheet was used, and 5.8 ° C. when the graphite sheet coated with the epoxy resin film was used. The increase in difference is 1.0
° C.

Further, the graphite sheet having the coating film formed on both sides has the same flexibility and flexibility as the single graphite sheet.

Further, in the graphite sheet having the coating film formed on both surfaces, no breakage such as peeling or crack occurred at all even when the graphite sheet was bent 100 times in the front and back directions.

Accordingly, the graphite sheet according to the present embodiment, whose both surfaces are covered with the epoxy resin coating film, has improved mechanical strength and graphite while maintaining the original thermal conductivity, flexibility and flexibility of the graphite sheet. It can be said that it has realized prevention of powder desorption and insulation of the surface.

When the graphite sheet of the present embodiment is cut, trimmed, drilled for mounting, etc. in order to mount the graphite sheet in the electronic device, it is needless to say that the processing is the same as the processing of the graphite sheet. is there.

(Embodiment 2) In a second embodiment of the present invention, an epoxy resin (a two-component epoxy compound resin manufactured by Three Bond Co., Ltd.) is provided on both surfaces of a graphite sheet obtained in the same manner as in the first embodiment. , This agent 2022, curing agent 210
4) was diluted 1: 2 with methyl ethyl ketone, coated by dipping, and then cured by holding at 100 ° C. for 1 hour. The thickness of the epoxy resin coating film on the graphite sheet thus formed was 6 μm, the surface was insulative, and no desorption of the graphite powder was observed.

In order to evaluate the heat conduction characteristics of the graphite sheet coated with the epoxy resin in this manner, the graphite sheet is interposed between the heat source and the heat sink in the same manner as in the first embodiment. The temperature difference from the heat sink was measured.

As a result, the temperature difference between the heat source and the heat sink was 4.8 ° C. in the case of only the graphite sheet, and 5.6 ° C. in the case of the graphite sheet coated with the epoxy resin. 0.8 ° C.

(Embodiment 3) In a third embodiment of the present invention, an epoxy resin (a two-part epoxy compounded resin manufactured by Three Bond Co., Ltd.) is provided on both sides of a graphite sheet obtained in the same manner as in the first embodiment. , This agent 2022, curing agent 210
4) was diluted 1: 3 with methyl ethyl ketone, coating was performed by spin coating, and the coating was cured at 100 ° C. for 1 hour. The thickness of the epoxy resin coating film on the graphite sheet thus formed was 5 μm, the surface was insulative, and no desorption of the graphite powder was observed.

In order to evaluate the thermal conductivity of the graphite sheet coated with the epoxy resin in this manner, the graphite sheet is sandwiched between the heat source and the heat sink in the same manner as in the first embodiment. The temperature difference from the heat sink was measured.

As a result, the temperature difference between the heat source and the heat sink was 4.8 ° C. in the case of only the graphite sheet, and 5.3 ° C. in the case of the graphite sheet coated with the epoxy resin. 0.5 ° C.

(Embodiment 4) In a fourth embodiment of the present invention, a polyimide varnish (Trenice # 3000 manufactured by Toray Industries, Inc.) is applied to both surfaces of a graphite sheet obtained in the same manner as in the first embodiment. After diluting 1: 3 with acetamide and coating by dipping, heat treatment was performed at 120 ° C. for 10 minutes, at 220 ° C. for 10 minutes, and at 300 ° C. for 30 minutes. The thickness of the polyimide resin coating film on the graphite sheet thus formed was 9 μm, the surface was insulative, and no desorption of the graphite powder was observed.

In order to evaluate the heat conduction characteristics of the graphite sheet coated with the polyimide resin in this way, as in the first embodiment, the graphite sheet is sandwiched between the heat source and the heat sink, and the heat source and the heat sink Was measured.

As a result, the temperature difference between the heat source and the heat sink was 4.8 ° C. in the case of the graphite sheet alone, and 6.0 ° C. in the case of the graphite sheet coated with the polyimide resin by dipping. The increase was 1.2 ° C.

(Embodiment 5) In a fifth embodiment of the present invention, a polyimide varnish (Trenice # 3000 manufactured by Toray Industries, Inc.) is applied to both sides of a graphite sheet obtained in the same manner as in the first embodiment. 1:10 with acetamide
After coating by spraying,
After heat treatment at 120 ° C. for 10 minutes and 220 ° C. for 10 minutes, coating is performed again by spraying.
The heat treatment was performed by holding at 220 ° C. for 10 minutes and at 300 ° C. for 30 minutes. The thickness of the polyimide resin coating film on the graphite sheet thus prepared is 6 μm.
The surface was insulative and no graphite powder was detached.

In order to evaluate the thermal conductivity of the graphite sheet coated with the polyimide resin in this manner, the graphite sheet is sandwiched between the heat source and the heat sink in the same manner as in the first embodiment. The temperature difference from the heat sink was measured.

As a result, the temperature difference between the heat source and the heat sink was 4.8 ° C. in the case of only the graphite sheet, and 5.6 ° C. in the case of the graphite sheet coated with the polyimide resin. 0.8 ° C.

(Embodiment 6) In a sixth embodiment of the present invention, polyimide varnish (Semico Fine SP-110 manufactured by Toray Industries, Inc.) is provided on both surfaces of a graphite sheet obtained in the same manner as in the first embodiment. After coating by screen printing, 80 ° C, 150 ° C, 200 ° C,
Heat treatment was carried out at 350 ° C. for 30 minutes each. The thickness of the polyimide resin coating film on the graphite sheet thus formed was 8 μm, the surface was insulating, and no desorption of the graphite powder was observed.

In order to evaluate the heat conduction characteristics of the graphite sheet coated with the polyimide resin in this manner, the graphite sheet is sandwiched between the heat source and the heat sink in the same manner as in the first embodiment. The temperature difference from the heat sink was measured.

As a result, the temperature difference between the heat source and the heat sink was 4.8 ° C. in the case of only the graphite sheet, and 5.5 ° C. in the case of the graphite sheet coated with the polyimide resin. 0.7 ° C.

(Embodiment 7) In a seventh embodiment of the present invention, a fluororesin (Cytop CTX-809 manufactured by Asahi Glass Co., Ltd.) is applied to both surfaces of a graphite sheet obtained in the same manner as in the first embodiment. Was brushed and then held at 50 ° C. for 1 hour and at 180 ° C. for 1 hour to cure. The thickness of the fluororesin coating film on the graphite sheet thus formed was 10 μm, the surface was insulative, and no desorption of the graphite powder was observed.

In order to evaluate the thermal conductivity of the graphite sheet coated with the fluororesin,
As in the first embodiment, a graphite sheet was interposed between the heat source and the heat sink, and the temperature difference between the heat source and the heat sink was measured.

As a result, the temperature difference between the heat source and the heat sink was 4.8 ° C. in the case of only the graphite sheet, and 6.2 ° C. in the case of the graphite sheet coated with the fluororesin. 1.4 ° C.

(Eighth Embodiment) In an eighth embodiment of the present invention, as a method for producing a graphite sheet, a preliminary firing using a polyimide film is performed in a nitrogen atmosphere at a heating rate of 5%.
The heat treatment was performed in the same manner as in the first embodiment except that the temperature was raised at a rate of ° C./min and the maximum processing temperature was set to 1600 ° C.

The film after firing is a graphite sheet, in a foamed state, and has a thickness of 200 μm.
It was not flexible and was hard and brittle. Thereafter, the graphite sheet produced by rolling is flexible and flexible so that it can be repeatedly bent, and has a thickness of about 1 mm.
It was 00 μm.

The graphite sheets thus produced were provided with a resin coating film on the surface in the same manner as in the first to seventh embodiments, and all showed good characteristics.

Further, the maximum processing temperature of the pre-firing is 1400
When the same experiment as above was performed at a temperature of ° C., the same result as above was obtained.

[0058]

As described above, according to the present invention, by providing a resin coating film on the surface of a graphite sheet, it is possible to obtain excellent electrical insulation and flexibility, hardly detach graphite powder, and low thermal resistance. A good quality graphite sheet having characteristics can be obtained.

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) B05D 7/24 302 B05D 7/24 302L // C01B 31/04 101 C01B 31/04 101Z (72) Inventor Yasuo Kudo 1006 Kadoma Kadoma, Kadoma City, Osaka Prefecture F-term (reference) 4D075 AE03 BB28Z BB57Z DA03 DB11 EB16 EB33 EB39 4G046 EB06 EC03 EC05

Claims (9)

[Claims] 1. A method for coating a surface of a graphite sheet, wherein a resin coating film is provided on one or both surfaces of the surface of the graphite sheet by applying a resin in solution. 2. The method for coating a surface of a graphite sheet according to claim 1, wherein the resin coating film contains an epoxy resin. 3. The method for coating a surface of a graphite sheet according to claim 1, wherein the resin coating film contains a polyimide resin. 4. The method for coating a surface of a graphite sheet according to claim 1, wherein the resin coating film contains a fluororesin. 5. A resin coating film comprising: an epoxy resin;
The surface coating method for a graphite sheet according to any one of claims 1 to 4, wherein two or more kinds of polyimide resin or fluorine resin are laminated. 6. The method for coating a surface of a graphite sheet according to claim 1, wherein the coating method is any one of dipping, spin coating, screen printing and brush coating. 7. The method for coating a surface of a graphite sheet according to claim 1, wherein the coating method is spraying. 8. The method for coating a surface of a graphite sheet according to claim 1, wherein the thickness of the resin coating film is 10 μm or less. 9. The graphite sheet is heated from room temperature in an inert gas to 100
A pre-treatment step of firing at a temperature in the range of 0 ° C. or more and 1600 ° C. or less;
9. The graphite sheet surface coating method according to claim 1, wherein the graphite sheet is formed by firing at a temperature of 00 ° C. or higher.