JPH02202576A - Graphite soft gasket material - Google Patents

Abstract

PURPOSE:To provide the subject gasket material having excellent flexibility, sealability and strength and used for seals and gaskets by subjected a mixture if swelled graphite particles, soft rubber, carbon black, etc., to a thermal press- molding process. CONSTITUTION:A mixture comprising swelled graphite particles, soft rubber component (preferably a synthetic rubber such as NBR, fluorinated rubber, SBR or CR) and carbon black and/or graphite powder (preferably the carbon black has particle sizes of <=1mum and the graphite powder is scaly one having sizes of approximately 100mum) is subjected to a thermal press-molded to provide the objective gasket material.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a graphite soft gasket material used for flexible seals and gaskets.

(Prior technology) Various types of rubber plates and molded products are commonly used as soft gasket materials, but since rubber alone has poor gas and liquid sealing properties when the temperature exceeds 80°C, asbestos that is a mixture of rubber and asbestos is used. Sheets (defined as asbestos joint sheets in JIS-R3453) are used because they have high strength and are inexpensive. However, asbestos is harmful to humans.

Attempts have been made to use non-asbestos sheets made of aramid fibers or glass fibers instead of asbestos, but aramid fibers and glass fibers have extremely small aspect ratios compared to asbestos and are not compatible with rubber. These non-asbestos sheets containing asbestos as a binder have low strength.

In addition, since the asbestos sheet and non-asbestos sheet have many fine voids between the fibers, when used as a gasket, the fluid that should be sealed by sewing through these fine voids leaks out to the outside, reducing sealing performance. There are drawbacks to doing so.

Natural graphite is a solution to the above drawbacks.

There is a flexible graphite sheet made by pressure-molding expanded graphite particles obtained by immersing graphite powder such as Quiche graphite in a mixture of sulfuric acid and oxidizing agent such as nitric acid, washing with water, dehydrating, and rapidly heating. This flexible graphite sheet is composed of graphite particles that are oriented in a plane with each other, so it has extremely excellent sealing properties, and it also has excellent heat resistance because it does not contain any organic matter such as rubber or resin.

(Problem to be solved by the invention) However, sheets made by simply press-molding expanded graphite particles have lower tensile strength and other properties than asbestos sheets containing binders such as rubber or non-asbestos sheets. It has the disadvantage of low mechanical strength, brittleness, and cracks when bent. Therefore, attempts have been made to combine binders and reinforcing materials in order to improve the strength of sheets formed by pressure-forming expanded graphite particles. JP-A No. 60-24201 proposes a method of impregnating an expanded graphite sheet with a thermosetting resin and curing it by heating. However, if more than a few inches of resin is impregnated, the sheet loses its flexibility and becomes hard. , cannot be used as a seal material or soft gasket material. On the other hand, if the resin impregnation rate is such that flexibility remains, hardly any improvement in strength can be expected. Japanese Patent Publication No. 1986-715
No. 78 and JP-A-63-72780 disclose expanded graphite.

A method has been proposed in which fibers and a binder are mixed and pressure molded, but the method involves uniformly dispersing and mixing fibers into expanded graphite, which is an extremely light powder with a bulk density of 0.01 g/cm or less. In addition, wet mixing with the addition of a binder solvent destroys the extremely brittle expanded graphite particles, which actually reduces the strength after pressure forming, and the effect of the binder and reinforcing material is almost negligible. Furthermore, as mentioned above, adding fibers deteriorates the sealing properties.Furthermore, conventional asbestos sheets or non-asbestos sheets often contain inorganic powder fillers such as talc in addition to fibers and binders. However, in the case of flexible graphite sheets, the powder tends to become a source of destruction of expanded graphite particles, which has the disadvantage of reducing strength.

An object of the present invention is to provide a graphite soft gasket material that eliminates the drawbacks of the flexible graphite sheet described above.

(l! Means for Solving the Problem) The present invention relates to a graphite soft gasket material formed by hot-pressing a mixture of expanded graphite particles, a soft rubber component, and carbon black and/or graphite powder.

In the present invention, expanded graphite particles obtained by a known method are used, and the expansion ratio, that is, the bulk density is not particularly limited. The soft rubber is blended to increase the strength due to the entanglement K of expanded graphite particles, and artificial rubbers such as NBR, fluororubber, SBR, and CR are preferable. The soft rubber component is made by adding a vulcanizing agent such as sulfur and a vulcanization accelerator to the above-mentioned rubber raw material such as NBR, and is vulcanized during hot press molding of the mixture with expanded graphite particles, carbon black, and/or graphite powder. The vulcanization temperature is preferably 140°C or higher. Further, the amount of the vulcanizing agent is preferably 151 i or less based on the rubber. Too much vulcanizing agent reduces the flexibility of the rubber and makes it hard. The rubber component is usually used after being dissolved in a rubber solvent.

When the amount of carbon black and/or graphite powder is less than that of soft rubber, it acts as a reinforcing agent for the rubber.

When the amount is greater than that of soft rubber, the strength of the resulting gasket material decreases and it acts as a sink filler. The carbon black preferably has a particle size not exceeding 1 μm, and the graphite powder is not particularly limited in particle size, but flaky graphite powder with an average particle size of about 100 μm is preferable.

The optimum composition of each component of the graphite soft gasket material in the present invention is 1, all of which are 5 to 35 pieces of soft rubber.

5 to 35 grams of carbon black and/or graphite powder.

The remainder is considered to be expanded graphite particles.

If the amount of soft rubber is too small, the absolute amount of the binder will be insufficient, resulting in insufficient improvement in mechanical strength, and if it is too large, the resulting gasket material will lack heat resistance.

In terms of the balance between mechanical strength and heat resistance, if the amount of carbon black and/or graphite powder is relatively small, the amount of soft rubber may be relatively small, and the amount of carbon black and/or graphite powder is relatively large. In such cases, it is preferable to increase the amount of soft rubber. Naori - As mentioned above, the addition of carbon black and/or graphite powder acts as a reinforcing agent for the rubber or a filler for the gasket material, so if the amount is small, the effect will be small, but if it is too large, the seal will be damaged. In the case of graphite powder, the strength decreases.

The method of mixing expanded graphite particles, soft rubber components, and carbon black and/or graphite powder is not limited in percentage, but
Components other than the expanded graphite particles are sufficiently dissolved or dispersed in advance in an organic solvent that is a solvent for rubber, and the expanded graphite particles are immersed in this liquid and mixed gently to the extent that the expanded graphite particles are not destroyed. Preferably, the organic solvent is removed by drying to form a mixture.

The mixture is hot-pressed at 140°C, which is the temperature at which the rubber is vulcanized.
It is preferable to carry out the heating at a temperature of 170° C. or lower.

If the temperature is too low or too high, the strength and heat resistance of the resulting gasket material will decrease. There are no particular restrictions on the pressure.

(Example) Next, the present invention will be explained in detail.

Example I 60 parts by weight of NBR powder (acrylonitrile butadiene rubber manufactured by Nihon Gosei Rubber ■), sulfur powder type 5 needle, and 5 parts by weight of tetramethylthiuram disulfide powder as a vulcanization accelerator were dissolved in 10.000 parts by weight of trichlorethylene. 1st carbon black (Tokai Carbon Fissure, Geast 116
．． After dispersing and suspending 70 parts by weight (average particle size 50 μm) in the rubber solution, 60 parts by weight of expanded graphite particles with a bulk density of 0.01 g/cm' were prepared. A portion of the solution was added and immersed, and trichlorethylene was removed by drying to obtain a mixture. This mixture was hot-press molded using a calendar roll heated to 150°C to a thickness of 1++ m.
A graphite soft gasket material having a bulk density of 1.49/an3 was obtained. This gasket material has 30% by weight of expanded graphite particles.
, 35% by weight of soft rubber and 35% by weight of carbon black.
The tensile strength is 200 as the average value of 10 tests.
kgf/an''.Long life coolant liquid (LLC liquid) When applied at a pressure of L kgf Am'', liquid leakage occurred, but no liquid leakage occurred at pressures of 0.7 to 9f/an. .

Example 2 17 parts by weight of the same NBR powder, 2 parts by weight of sulfur powder and 1 part by weight of tetramethylthiuram disulfide powder as in Example 1 were dissolved in 2000 parts by weight of acetone, and scaly graphite powder (manufactured by Nippon Graphite Industries, CB150) was added to the above solution. After being dispersed and suspended in a rubber solution, expanded graphite particles 3606 with a bulk density of o, oig/am3
0 parts by weight were added and mixed gently, and then acetone was removed by drying to obtain a mixture. This mixture was hot-pressed at 145° C. using a calendar roll to obtain a graphite soft gasket material having a thickness of 0.5 rra and a bulk density of 1.5 g 7 cm”.

This gasket material consists of 90% by weight of expanded graphite particles, 5% by weight of soft rubber, and 5% by weight of natural graphite.

The tensile strength is the average value of the number of tests x2ok+;+f/
cm2 was shown. Further, even when the LLC liquid was applied at a pressure of 1 kg/an'', no liquid leakage occurred.

Comparative Example 1 Only expanded graphite particles with a bulk density of 0.01 g/cm3 were molded through a pressure roll to obtain an expanded graphite sheet with a bulk density of 1.49 g/cm3. The tensile strength of this sheet is 65
kgf/Cl1112, and the LLC liquid is 11<gf/
No liquid leakage occurred even when it was added in cm2.

Comparative Example 2 When LLC liquid was added to a commercially available asbestos joint sheet and a non-asbestos sheet containing aramid fibers,
Liquid leakage occurred at a pressure of 0.2 kgf/am''.

(Effects of the Invention) The graphite gasket material of the present invention has superior sealing performance compared to conventional gasket materials containing asbestos or aramid fibers, and is superior in strength to gasket materials formed by pressure molding only expanded graphite particles. .

Claims (1)

[Claims] 1. A graphite soft gasket material obtained by hot-pressing a mixture of expanded graphite particles, a soft rubber component, and carbon black and/or graphite powder.