JPH11278820A - Flexible graphite sheet and sheetlike composite material - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a sealing material having excellent sealing performance and not causing sticking to the opposite metallic material by treating graphite with an acidic material and dispersing porous fine particles capable of adsorbing the acidic material in the resultant expanded graphite. SOLUTION: The expanded graphite is obtd., e.g. by immersing natural graphite or pyrolytic graphite in a soln. of sulfuric acid, a mixed acid or the like to form an intercalation compd., washing the graphite and expanding it by rapid heating. The fine particles capable of adsorbing the residual acidic material which forms rust on the opposite material to cause the sticking of the sealing material are, e.g. silica, an activated clay, a synthetic zeolite or a porous polyimide having >=50 m<2> /g specific surface area. Fine arom. polyimide particles are preferably used. The number average particle diameter is preferably 1-100 μm from the characteristics of the sealing material. The fine particles are added by 1-100 pts.wt. to 100 pts.wt. expanded graphite and they are mixed and rolled in a sheet shape.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a flexible graphite sheet useful as a sealing material and a sheet-like composite material using the same.

[0002]

2. Description of the Related Art Conventionally, asbestos materials having heat resistance, flexibility, and economy have been mainly used as seal materials for places exposed to high temperatures such as engines of automobiles and motorcycles. However, the use of asbestos-based seal materials has decreased due to the problem of carcinogenicity, and seal materials using heat-resistant organic fibers and the like have been developed instead. However, problems remain in cost and the like.

[0003] Therefore, by using an inexpensive graphite which has been subjected to an acid treatment and is heated at a high temperature to have flexibility, so-called expanded graphite is used as a sealing material layer and a metal plate is used as a core material so that it is inexpensive and excellent. A well-balanced sealing material having sealability and heat resistance has been developed. However, if the sealing material is used for a long period of time, it will stick to the sealing partner material (metal), causing a problem when replacing the sealing material and disassembling the engine and the like. I have.

[0004] This is considered to be because acidic substances remaining in the sealing material cause rusting of the mating material (metal). As a method for removing the acidic substance, a method of decomposing and removing the acidic substance by setting the surface of the sealing material to a high temperature state with a burner or the like is considered. However, the acidic substance near the center of the sealing material cannot be removed. It is also conceivable that the surface of the sealing material is covered with a resin or the like to prevent contact between the acidic substance and the counterpart material. However, in this case, the surface of the sealing material is hardened, and the effect of the sealing material is greatly reduced.

[0005]

SUMMARY OF THE INVENTION In view of the above problems, the invention according to claims 1 and 2 is a well-balanced sealing material having excellent sealing properties and heat resistance, and is provided with a mating material (metal).
The present invention provides a flexible graphite sheet useful as a sealing material that hardly causes sticking to the sheet. Claim 3
The described invention provides a sheet-like composite material which is a well-balanced sealing material having excellent sealing properties and heat resistance, and which is useful as a sealing material with almost no sticking to a mating material (metal). Things.

[0006]

SUMMARY OF THE INVENTION The present invention relates to a flexible graphite sheet in which fine particles capable of adsorbing an acidic substance are dispersed in expanded graphite obtained by treating graphite with an acidic substance. The present invention also relates to a flexible graphite sheet wherein the fine particles capable of adsorbing the acidic substance are porous particles having a specific surface area of 50 m ² / g or more. Further, the present invention relates to a sheet-like composite material comprising a core material layer and a sealing material layer made of the above-mentioned flexible graphite sheet bonded to one or both surfaces thereof.

[0007]

DESCRIPTION OF THE PREFERRED EMBODIMENTS In the present invention, expanded graphite itself obtained by treating graphite with an acidic substance is generally known, and is produced, for example, as follows. As the graphite used as a raw material, graphite having a high degree of crystal development such as natural graphite, quiche graphite, and pyrolytic graphite is preferable. Natural graphite is preferred from the viewpoint of the balance between the obtained properties and economy. The natural graphite used is not particularly limited.
F48C (Nippon Graphite Co., Ltd.), H-50 (Chuetsu Graphite Co., Ltd.)
Commercially available products such as A.I.

The acidic substance used for the treatment of graphite is preferably a strongly acidic solution such as sulfuric acid, nitric acid, a mixed solution of sulfuric acid and nitric acid, and a mixed solution of sulfuric acid and hydrogen peroxide solution. As a processing method for forming expanded graphite, for example, by immersing the graphite in a solution of the acidic substance,
A method of generating a graphite intercalation compound, then washing with water and then rapidly heating to expand the c-axis direction of the graphite crystal. This makes it possible to obtain an insect-like expanded graphite having compressive properties.

In the present invention, in order to reduce adsorption of acidic substances (sulfuric acid soul, nitric acid soul, etc.) remaining in the sealing material, which is a cause of rusting of the mating material (metal) which causes sticking of the sealing material. Contains fine particles capable of adsorbing an acidic substance. The fine particles may be fine particles having a function of physically adsorbing or fine particles having a function of chemically adsorbing, and the material may be silica, alumina-based activated clay, silica gel, active silica. Examples thereof include inorganic fine particles such as alumina, synthetic zeolite (molecular sieve) and molecular sieving carbon, and organic fine particles such as porous polyimide fine particles, polyamideimide fine particles, and polyamide fine particles.

Among these, fine particles having a specific surface area of 50 m ² / g or more are preferred because of their large physical adsorbing ability for acidic substances. In terms of the material, polyimide fine particles which can be expected to have a chemical adsorption ability as well as a physical adsorption ability of an acidic substance, do not adversely affect the properties as a sealing material, and have excellent heat resistance are preferable. As the polyimide fine particles, aromatic polyimide fine particles obtained using a material having an aromatic ring are preferable from the viewpoint of excellent heat resistance. Therefore, aromatic polyimide fine particles having a specific surface area of 50 m ² / g or more are particularly preferable. In addition, the specific surface area in the present invention can be measured by a nitrogen substitution method (BET method).

The method for producing the polyimide fine particles having a specific surface area of 50 m ² / g or more is not particularly limited. For example, a material comprising tetracarboxylic dianhydride and diamine, or a material comprising tetracarboxylic dianhydride and diisocyanate material,
Preferably, any of the materials having an aromatic ring is used and, in the presence of a reaction catalyst, if necessary, is dispersed and polymerized in a solvent which does not dissolve the obtained polyimide, whereby porous fine particles can be obtained. Also, commercially available polyimide fine particles for liquid crystal refining and the like can be used.

Although the particle size of the fine particles used in the present invention is not particularly limited, the number average particle size is preferably 1 μm to 100 μm in consideration of the adsorption efficiency, the properties as a sealing material, and the like.
μm to 50 μm are more preferred. The number average particle size can be measured by a particle size distribution analyzer. The shape of the particles to be used is not particularly limited. However, in consideration of the surface area, the adsorption efficiency, and the like, the particles are not flat particles such as phosphorous or scaly, but spherical or nearly spherical (preferably having an aspect ratio of 1 to 1). The particles of 3) are preferred.

The amount of the fine particles used is not particularly limited,
It is preferably 1 to 100 parts by weight, more preferably 5 to 50 parts by weight, based on 100 parts by weight of the expanded graphite. If the mixing amount is less than 1 part by weight, there is not much effect on improving the sticking property. If the mixing amount exceeds 100 parts by weight, it is difficult to uniformly mix the expanded graphite and a sealing material having excellent properties is hardly obtained. Tend.

The production of the flexible graphite sheet of the present invention can be obtained by blending the above-mentioned fine particles with the above-mentioned expanded graphite in a predetermined amount, uniformly containing the particles, rolling, and processing into a sheet. There is no particular limitation on the mixing method, and a method of dry blending fine particles using a mixer or the like under mild conditions that does not cut fibrous graphite in expanded graphite, or a method of spraying fine particles on expanded graphite and vibrating with a vibrator or the like. A method of giving and impregnating, a method of uniformly mixing a resin and fine particles adjusted to a low viscosity that decomposes and sublimates at a low temperature and coating the expanded graphite with a spray gun, etc. And a uniform coating method. In the method of applying a solution containing a resin, the resin is heated in a curing furnace after the application until the resin component is decomposed and sublimated. According to the method as described above, the fine particles cling to the fibrous graphite in the expanded graphite particles, and do not fall with a slight impact or the like. The thickness of the flexible graphite sheet is not particularly limited, but is usually rolled to 0.1 to 3.0 mm into a sheet from the viewpoint of sealing properties.

The sheet-like composite material of the present invention comprises a core material layer,
A sealing material layer made of the above-mentioned flexible graphite sheet, which is bonded to one or both surfaces thereof. As the material of the core material layer, a metal is usually used, and a steel plate or stainless steel is generally used. The lamination of the sealing material on the core layer is not particularly limited, but can be performed by, for example, a roll or a press via an adhesive. The adhesive to be used is not particularly limited, and for example, an adhesive containing a thermosetting resin such as a phenol resin and an epoxy resin as a main component is preferable in terms of heat resistance.

The thickness of the core layer is not particularly limited, but is preferably 0.1 to 1 mm from the viewpoint of sealing properties. Further, the thickness of the entire sheet-like composite material including the core material layer and the seal material layer is not particularly limited.
It is preferably about 3.0 mm. Various gaskets, seals, and the like can be obtained by processing the sheet-shaped composite material produced as described above into a predetermined shape. There is no particular limitation on the processing method, and a method such as punching is used.

[0017]

Next, an embodiment will be described. Example 1 (1) Large particles having a large specific surface area A specific surface area of 100 m ² / g produced by using an aromatic tetracarboxylic dianhydride and an aromatic diamine (BET method, using a Soapomatic 1800 type manufactured by Carlo Elber), Polyimide fine particles for liquid crystal refining (Characterized by Hitachi Chemical Co., Ltd.) having the feature of a number average particle size of 15 μm (using a measuring device, Soapomatic 1800, manufactured by Carlo Elber)
H-2000) was used.

(2) Preparation of flexible graphite sheet containing particles having a large specific surface area 150 g of sulfuric acid (concentration 99% by weight) and 50 g of nitric acid (concentration 99% by weight) were put into a 1-liter glass flask. This was mixed with 100 g of graphite (F48C, manufactured by Nippon Graphite Co., Ltd.), and a Teflon blade was attached to the mixture, followed by a motor.
The mixture was mixed at a rotation speed of rpm for 30 minutes. After the mixing was completed, the acid-treated graphite was taken out, washed with water, transferred to a vat, and dried for 1 hour in a drier heated to 120 ° C. 800 more
The mixture was placed in a heating furnace heated to 5 ° C. for 5 minutes to obtain expanded graphite. The density of the graphite was 0.83 g / cm ³ . The obtained expanded graphite was dispensed into three containers of 20 g each, and the surfaces were made uniform to obtain Sample 1, Sample 2, and Sample 3. Place the sample 1 on the shaking table
Was fixed, and 1 g of the particles of Example 1 (1) was evenly dispersed on the fixed sample 1, and the container was vibrated for 15 minutes using a vibrator to impregnate the particles. This was placed in a 4 cm × 4 cm mold and press-molded to a thickness of 1 mm to obtain a flexible graphite sheet containing fine particles.

(3) Adhesion test The two pieces of cast iron (surface roughness: 5Rz) of 4 cm in length, 4 cm in width and 0.5 cm in thickness, which can be bolted, were prepared by the flexible graphite obtained in Example 1 (2). The sheet was squeezed with bolts so that the surface pressure was 7 MPa. Put this in a dryer heated to 100 ° C.
After leaving it to stand for 0 hour and cooling, the bolt was removed, and the sticking property of a flexible graphite sheet containing particles having a large specific surface area with respect to the metal surface was visually observed.

(4) Sealing test The flexible graphite sheet was press-molded with a special donut-shaped mold having an outer diameter of 50 mm and an inner diameter of 34 mm to obtain a 1 mm-thick sealability measuring sample. This sample was set between two parts of a self-made sealability measuring jig prepared according to the sample shape, and four nuts provided to fix it were set to 20 kg · cm with a torque wrench. 30k
The parts were tightened in three stages of g · cm and 40 kg · cm. At each stage, the side surface of the seal between the jig parts was thoroughly washed, and a developer for checking for seal leakage was applied. At each stage, the antifreeze is poured into a space existing inside the jig until a fixed amount, and the antifreeze is initially compressed from 2 kg / cm ² to 30 kg using an air hose.
The pressure was increased by 0.5 kg / cm ² every minute, and it was confirmed that there was no leakage up to 6.5 kg / cm ² .

Example 2 (1) Preparation of Flexible Graphite Sheet The sample 2 obtained in Example 1 (2) was impregnated with the particles of Example 1 (1) for 20 minutes using the same apparatus. Other than
In the same manner as in Example 1 (2), a flexible graphite sheet containing particles having a large specific surface area was obtained. (2) Sticking Test and Sealing Test The sticking and sealing properties of the flexible graphite sheet containing fine particles were observed in the same manner as in Examples 1 (3) and (4).

Comparative Example 1 (1) Preparation of Flexible Graphite Sheet A flexible graphite sheet was obtained in the same manner as in Example 1 (2) except that no fine particles were used. (2) Sticking property test and sealing property test The sticking property and sealing property of the flexible graphite sheet were observed in the same manner as in Examples 1 (3) and (4).

Table 1 shows the results of the sticking test.

[Table 1]

[0024]

The flexible graphite sheet according to claims 1 and 2 is a well-balanced sealing material having excellent sealing properties and heat resistance, and almost no sticking to a mating material (metal). Absent. The sheet-like composite material according to the third aspect is a well-balanced sealing material having excellent sealing properties and heat resistance, and hardly causes sticking to a mating material (metal).

Claims (3)

[Claims] 1. A flexible graphite sheet in which fine particles capable of adsorbing an acidic substance are dispersed in expanded graphite obtained by treating graphite with an acidic substance. 2. The flexible graphite sheet according to claim 1, wherein the fine particles capable of adsorbing the acidic substance are porous particles having a specific surface area of 50 m ² / g or more. 3. A sheet-like composite material comprising a core material layer and a sealing material layer made of the flexible graphite sheet according to claim 1 bonded to one or both surfaces thereof.