JPH04240295A - Production of expanded graphite sheet - Google Patents

Abstract

PURPOSE:To produce an expanded graphite sheet having an extremely high mechanical strength and used for gaskets. CONSTITUTION:Expanded graphite expanded into an average volume of >=50 times is compressed to give a specific high density, followed by crushing. The crushed product is mixed with fibrillated aramide pulp fibers, etc., to prepare an aqueous slurry for the production of paper, and the slurry is processed into wet paper.

Description

[Detailed description of the invention]

0001

[Industrial Application Field] The present invention relates to an expanded graphite sheet.
More specifically, the present invention relates to a method for manufacturing a heat-resistant asbestos-free graphite sheet for use in general industry and gaskets for sealing various joint surfaces of internal combustion engines.

0002

[Prior Art] Joint sheets and beater sheets made of asbestos have been used as conventional gaskets. However, due to the toxicity of asbestos to the human body, the use of asbestos is being regulated. -Flexible expanded graphite sheets are also known, and although they have excellent sealing properties and heat resistance, they have low mechanical strength and are difficult to handle in actual use. However, it has the disadvantage of poor water resistance and oil resistance.

As an alternative to these, sheets have been developed in which fillers are added to aramid pulp or inorganic fibers, and a rubber-like elastic material is used as a binder. These sheets are manufactured by a dry method or a wet method, but they have the disadvantage that they are inferior to asbestos sheets in mechanical strength, heat resistance, and sealing properties.

[0004] For this reason, attempts have been made to improve these flexible expanded graphite sheets. For example, JP-A-2-124767
As in the publication, a rubber-like binder is applied to expanded graphite particles in an attempt to improve the folding durability and oil resistance of the sheet, but this method has not reached the point where it can be used as a single molded product. Also, JP-A-62-
As in Japanese Patent No. 288180, an expanded graphite molded body is impregnated with a water-soluble thermosetting resin and the resin is heated and hardened to improve mechanical strength and liquid impermeability, but the most important properties are It has lost some flexibility and handling problems have not yet been solved. Furthermore, as in JP-A-60-71578 and JP-A-63-72780, a method of blending reinforcing fibers and a binder with expanded graphite particles is disclosed.
The effect is not sufficient, and it is not possible to fully compensate for brittleness and mechanical strength.

[0005]

[Problems to be Solved by the Invention] The problems to be solved by the present invention are to eliminate the drawbacks of conventional graphite sheets of this type, especially expanded graphite sheets, and to create a new asbestos-free expanded graphite sheet with excellent mechanical strength. The goal is to develop

[0006]

[Means for solving the problem] This problem involves compressing expanded graphite that has expanded more than 50 times to a bulk density of 0.02 to 0.3 g/cm3, crushing it, and then fibrillating it with aramid pulp fibers. This problem was solved by producing a slurry for papermaking by suspending it in water in the presence of a binder together with reinforcing fibers that have a specific surface area of 3.0 m2/g or more, and wet-processing this slurry to form a sheet. Ru.

[0007]

In the present invention, expanded graphite is first compressed to a predetermined bulk density. Expanded graphite, which has expanded more than 50 times as much as conventional graphite, cannot be homogeneously suspended in water and made into a slurry even if it is pulverized, and it floats on the surface of the water, making it impossible to make paper. A method using a small amount of a hydrophilic solvent such as acetone is also known, but even with this method, the graphite particles tend to float on water, so it is by no means a desirable method. Therefore, even if paper is made in this state, it is not possible to obtain a uniform sheet, and even if it were possible, the mechanical strength is extremely low and it cannot be put to practical use at all. Therefore, in the present invention, the expanded graphite particles are first compressed to a bulk density of 0.02 to 0.3 g/cm3, preferably 0.05 to 0.15 g/cm3. When the bulk density is lower than 0.02 g/cm3, it is difficult for the expanded gas in the cavities of the expanded graphite particles to escape, and the raw material remains in a floating state even if it is stirred and pulverized in water. Furthermore, if the bulk density is greater than 0.3 g/cm3, it becomes difficult to crush in water, and the crushed raw material becomes granular and loses the properties of expanded graphite. When a raw material with the above-mentioned bulk density is pulverized, it is suspended in water and fixed to aramid pulp fibers without losing the properties of expanded graphite, making it an ideal raw material for papermaking.

[0008] In the present invention, the means for compressing the expanded graphite that has expanded more than 50 times may be any means in principle as long as it can achieve a predetermined bulk density, but in particular horizontal conveyors and inclined conveyors are suitable. Compression means that are continuously tightened by a combination are preferred. In this case, for example, in the conventionally known method of using a wire mesh case shown in Japanese Patent Application No. 53-71694, the bulk density is 0.05 to 0.1 g.
/cm3, but mass production is difficult. As the expanded graphite, one used is one that has expanded 50 times or more on average. Therefore, only graphite particles expanded 50 times or more may be used, or expanded graphite particles 50 times or less and 50 times expanded graphite particles may be used.
It may be used by mixing it with 0 times or more expanded graphite so that the total amount becomes 50 times or more. However, if it is less than 50 times on average, the flexibility and sealing properties of the target sheet will deteriorate.

In the present invention, the compressed graphite is then crushed. Both wet and dry crushing methods can be used. In the case of the wet method, compressed graphite is mixed with water beforehand and ground, and the resulting ground material does not separate from the water.
Use it as is for the next slurry preparation. As the crushing means, a mixer type crusher is usually preferably used, but a beating machine used in the paper making field may also be used. The size of the crushed material is usually 50 mesh or less, preferably 60 to 100 mesh.
It is about the size of a mesh. In the case of dry pulverization, compressed graphite is pulverized in the absence of water to the same size as in the case of wet pulverization. As the pulverizer, a pulverizer using shear force is preferable, such as a high-speed mixer. The dry pulverized product may be mixed with water in advance and then used for slurry preparation, or the pulverized product may be used directly for slurry preparation.

The reinforcing fiber used in the present invention has the function of fixing expanded graphite particles in water and uniformly dispersing them without separating even when diluted to a concentration required for paper making. This is an important point in obtaining a high-strength expanded graphite sheet. In order to meet this condition, reinforcing fibers must have the following properties. (1) The reinforcing fibers must be ionically neutral or positive in water. Expanded graphite particles exhibit anionic properties in water, so
Even if fibers with the same ions, such as cellulose fibers, are beaten and fibrillated, they cannot be completely fixed. (2) Beating the fibers to promote fibrillation so that the specific surface area of the fibers is 3.0 m2/g or more. Since the expanded graphite particles have a large specific surface area, the fibers to which they are fixed must also be fibrillated to have a specific surface area of 3.0 m2/g or more to facilitate physical adsorption. For this reason, inorganic fibers and metal fibers similar to monofilaments cannot exhibit the effect of reinforcing agents. The most effective reinforcing fibers that meet the above conditions are those made by pulping para- and meta-aramid fibers that have excellent heat resistance.

[0011] Aramid fiber itself is known;
In the present invention, various conventionally known aramid fibers can be used. This conventional aramid fiber is used after being fibrillated to have a predetermined specific surface area. The fibrillation means at this time is not particularly limited, and ordinary means may be employed. The specific surface area is 3.0 m2/g or more, preferably 5.
Must be 0-8.0m2/g, 3.0m2/g
If it is less than that, graphite particles cannot be sufficiently fixed, which is not desirable. The amount of aramid fiber used in the slurry is about 3 to 25 parts by weight, preferably about 5 to 15 parts by weight.

In the present invention, a binder is used to improve the mechanical strength of the object sheet. The binder can be used in a water-soluble, emulsion or powder form, but an emulsion type is particularly preferred since it is fine particles and easily dispersed in water, and is gradually fixed. As these binders, latexes of NR, NBR, SBR, CR, and acrylic rubber can be used depending on the properties such as strength, heat resistance, and oil resistance. If further heat resistance is required, phenol resin and NBR latex may be used in combination, and emulsions of silicone rubber and fluororubber may also be used.

[0013] In the present invention, each of the above-mentioned materials is suspended in water to form a slurry for paper making, and the mixing ratio of each material at this time is as follows: Expanded graphite particles: 60-95 parts by weight Aramid pulp: 3-95 parts by weight 25 parts by weight Binder: In order to have a high strength sheet with a tensile strength of 1.0 kg/mm2 or more and sufficient heat resistance, it is composed of 1 to 20 parts by weight.
Expanded graphite particles: 70 to 85 parts by weight Aramid pulp: 10 to 20 parts by weight Binder: 5 to 10 parts by weight. In addition, these raw material liquids have expanded graphite particles fixed to the pulp core, so even if the raw material liquid is diluted to a concentration of 1 to 2%, it will not separate and be uniformly dispersed, and will not float on water. Therefore, high-strength sheets can be obtained using papermaking equipment.

[0014] When making paper from a papermaking slurry, a wet papermaking method is usually adopted, and the conventional conditions and equipment for the wet papermaking method itself can be used as appropriate. Although the sheet thus obtained is made of expanded graphite, it has extremely high mechanical strength, excellent heat resistance, flexibility, and extremely excellent sealing properties. It is extremely suitable as a gasket for general industrial use and for sealing various joint surfaces of internal combustion engines. In the present invention, the specific surface area is measured by the following method. In the present invention, the specific surface area is measured by the BET method using a mixed gas of N2 (30%) and He (70%).

[0015]

EXAMPLES The present invention will be explained in more detail below based on Examples, but the present invention is not limited thereto. All units are parts by weight unless otherwise specified.

[Example 1] Add 200 parts of water and 10 parts of aramid fiber pulp (Twaron Pulp 1096 manufactured by Akzo) to a mixer, stir for about 5 minutes to beat the pulp, and drop 3000 parts of water together into the blended cheese ( The specific surface area of the pulp at this time is 7.5 m2/g). On the other hand, 85 parts of graphite particles expanded 150 times were compressed into a sponge shape to have a bulk density of 0.08 g/cm3. This raw material was mixed with 2000 parts of water in a mixer for about 10 minutes, pulverized, and dropped into a blended cheese, where it was mixed with aramid pulp. After stirring for just 1 to 2 minutes, the expanded graphite particles agglomerated around the aramid pulp, and a uniform dispersion was obtained. Furthermore, NB as a binder
R latex (Nippol 1571 manufactured by Nippon Zeon Co., Ltd.)
5 parts of ▲C▼) were added by changing the solid content, and the mixture was stirred for 3 to 4 minutes to be fixed. In this case, since the amount of aramid pulp blended was small, the NBR latex could be fixed only by stirring. Also, a small amount of zinc white, which is a crosslinking agent for NBR, was added. This raw material was placed in a tank equipped with a paper mesh, uniformly dispersed, and then drained to form a sheet. Furthermore, water was squeezed out using a suction pump, and the material was sandwiched between felts and compressed using a press to remove water. Place this sheet in an oven at 120°C to dry it.
The density of the sheet is 1.3g/c through a calender roll.
Adjusted to m3. Finally, crosslinking was performed at 150°C for 20 minutes.

[0016]

[Example 2] 15 parts of aramid pulp, 75 parts of expanded graphite,
A sheet was formed in the same manner as in Example 1 except that 10 parts of NBR latex solid was used. However, since the amount of pulp and binder used has increased, the fixation of latex is not good. Cationic flocculants such as Sunfloc CH799
An aqueous solution containing 0.1 part of P (manufactured by Sanyo Chemical Co., Ltd.) was added for fixation.

[0017]

Examples 3 to 8 Sheets were produced in the same manner as in Examples 1 and 2, except that the blending ratios of expanded graphite, aramid pulp, and NBR latex were changed as shown in Table 1.

[Table 1] The properties of the flexible expanded graphite sheets obtained in Example 1 and Example 2 were measured according to JISR3453. The measurement results are shown in Table 2 and compared with the standard values of JISR3453 Type 1, Type 2, and Type 3.

[Table 2] As is clear from Table 2, the characteristics of each sheet of Examples 1 and 2 substantially satisfy the standard values of JISR3453.

For each sheet obtained in Examples 1 to 8 above (that is, for each sheet when the amount of reinforcing agent and binder added was changed), the relationship between the amount of change and the tensile strength of the sheet, and the same change. The relationship between the amount and stress relaxation rate was investigated. The results are shown in Figure 1 (tensile strength) and Figure 2 (
(stress relaxation rate). However, in FIGS. 1 and 2, the dotted line indicates the case where the NBR content is 10%, and the solid line indicates the case where the NBR content is 5%. As is clear from FIGS. 1 and 2, when the amounts of reinforcing material and binder added change, the tensile strength and stress relaxation rate of the target sheet change. That is, as the proportion of these additives increases, the tensile strength increases, but the stress relaxation rate, which is one of the indicators of heat resistance, decreases. Therefore, a desired sheet can be obtained by appropriately selecting the amount of reinforcing material and binder added depending on the intended use of the sheet.

[0019]

[Effects of the Invention] Compared to flexible expanded graphite sheets, the sheet of the present invention has greatly improved mechanical strength and flexibility, and is easier to handle in actual use. The water and oil resistance properties have also been improved, and asbestos joint sheet JI
The S standard is also almost satisfied. The sheet of the present invention having the above characteristics can be used in general industrial gaskets and gaskets around internal combustion engines in the same way as asbestos joint sheets.

[0020]

[Brief explanation of the drawing]

1 and 2 are graphs showing the relationship between the raw material blending ratio of graphite sheets and the tensile strength or stress relaxation rate.

Claims (3)

[Claims] Claim 1: (A) graphite particles obtained by compressing expanded graphite that has expanded more than 50 times on average to a bulk density of 0.02 to 0.3 g/cm3 and pulverizing it; (B) aramid pulp; Fibrillate the fibers and increase the specific surface area to 3.0m
2/g or more reinforcing fibers, (C) a binder, and (D) water are suspended to form a papermaking slurry, and this slurry is wet-processed to form a sheet. Method for manufacturing graphite sheets. 2. The blending ratio of (A), (B) and (C) is (A) 60 to 95 parts by weight, (B) 5 to 25 parts by weight,
and (C) 1 to 15 parts by weight. Claim 3: Claim 1 in which the compressed product of expanded graphite is wet-pulverized.
The manufacturing method described in.