Material for a gasket coated with foam rubber and manufacturing process of the same

Abstract: In order to improve the sealing property and the resistance to pressure of a gasket coated with foam rubber, a material for the gasket coated with foam rubber is formed by disposing foam rubber layers on both surfaces of a metal plate. The rubber has the property that it is swollen by the medium which is intended to be sealed by the gasket, eg a rubber having a great oil swelling property or an NBR, is used. In this way the sealing property thereof is improved. A preferred rubber composition comprises an NBR having a nitrile amount lower than 30% and a Mooney viscosity greater than 60.

Description: The present invention relates to a material for a gasket coated with foam rubber, in which foam rubber layers are formed on both surfaces of a metal plate, and, in particular, to an improved gasket which has a good sealing property in a wide temperature range owing to the fact that the sealing property after exposure to a high temperature environment is improved. Heretofore there are known gaskets coated with rubber, in each of which rubber layers are formed on both surfaces of a metal plate, for example non asbestos type gaskets. However, since these kinds of prior art gaskets have small amounts of compression and resiliency in the rubber layers, it has been necessary to subject them to mechanical working, such as embossing, in order to deal with deformation of a flange or an abnormal gap between flanges, on which they are mounted. Therefore gaskets coated with foam rubber, in which foam rubber layers are formed on both surfaces of a metal plate, have been used. The foam rubber layers of these gaskets exhibit considerable amounts of compression and resilience in a temperature range around room temperature and therefore it is possible to obtain a good seal with deformations of a flange or an abnormal gap between flanges, on which they are mounted, without any special work, such as embossing, for example. However, since materials for prior art gaskets coated with foam rubber have small amounts of resiliency and large permanent deformation of the foam rubber layers after exposure to a high temperature, they were unable to deal with displacements of flanges or an abnormal gap therebetween due to vibration or application of pressure. Accordingly, a drawback was that leaks occurred. Further, since a high superficial pressure was applied thereto directly below screws, because they were mounted on a flange by means of the screws, they had a drawback that flow of the foam rubber occurred after exposure to a high temperature, which gave rise to torque-down or leakage of a sealed liquid. EP-A-0 693 645 relates to a gasket for refrigerant compressors. US-A-4 728 111 relates to a sheet gasket that comprises a swelling sheet. An object of the present invention is, therefore, to provide a material for a gasket coated with foam rubber, which is improved in the resiliency (sealing property) and the resistance to pressure of the foam rubber layers after exposure to a high temperature atmosphere. Accordingly, the present invention provides a gasket for sealing a medium, the gasket comprising a metal plate having foam rubber layers formed on both sides thereof, wherein the foam rubber layers are formed from a rubber having the property that it is swollen by the medium to be sealed, wherein carbon having a low reinforcing property and an inorganic filler are blended in the rubber. In the material for a gasket coated with foam rubber according to the present invention a rubber having a great oil swelling property may be used as the base rubber for the foam rubber layers. In the material for a gasket coated with foam rubber according to the present invention the base rubber for the foam rubber layers may be an NBR having a nitride amount lower than 30% and a Mooney viscosity greater that 60. In the material for a gasket coated with foam rubber according to the present invention the rubber may further comprise one or more of a deterioration preventing agent, a bridging agent and a thermal decomposition foaming agent. Further, in the material for a gasket coated with foam rubber according to the present invention, MT or FT carbon from 40 to 150 PHR (Parts Hundred Rubber) as the carbon and clay or calcium carbonate from 0 to 80 PHR as the inorganic filler, in total more than 60 PHR, may be blended therein. A further object of the invention relates to the manufacturing process of such a gasket as defined by independent claim 10. Figs. 1 and 2 are schematical diagrams showing embodiments of the present invention by way of example. As a mode of realization of the present invention, in order to improve resiliency (sealing property) and resistance to pressure of the material for a gasket coated with foam rubber after exposure to a high temperature atmosphere, in which foam rubber layers are formed on both surfaces of a metal plate, rubber having a property that it is swollen by medium to be sealed is used for the base rubber of the foam rubber layers. For the base rubber, e.g. in case where the medium to be sealed is oil, NBR or SBR having a low nitrile amount, a rubber having a great oil swelling property such as natural rubber, etc., or a rubber obtained by blending them can be used. For this NBR it is suitable to use a nitrile amount below 30% and a Mooney viscosity greater than 60. Elasticity and hardness of the foam rubber layers can be increased so that their buckling characteristics are improved by blending a carbon having a low reinforcing property, e.g. MT or FT carbon from 40 to 150 PHR and clay or calcium carbonate from 0 to 80 PHR, in total more than 60 PHR in the base rubber. Hereinbelow several preferred embodiments of the present invention will be explained. At first, as indicated in Figs. 1 and 2, grease is removed from both surfaces of a metal base member 1 (0.15 to 0.8 mm thick, made of a cold pressed steel plate, aluminium, stainless steel, etc.) and they are roughened. After having subjected them to a phosphorating processing, primer 2, whose main component is phenol resin, is applied thereto and dried. A rubber compound obtained by blending MT carbon of 80 PHR, clay of 40 PHR, a deterioration preventing agent, a bridging agent, a thermal decomposition type foaming agent, etc. in an NBR having a nitrile amount of 18% and a Mooney viscosity of 72 is dissolved in a mixed solvent of toluene/n-propyl acetic acid, which is applied to both the surfaces of the primer processed metal member 2 to be dried so as to form rubber coat layers 3, each of which is 100 µm thick. Further a not viscous layer such as graphite is applied to each of the rubber coat metal layer 3 and vulcanized at a temperature from 180 to 240°C in a duration from 10 to 20 min. In this way the material for a gasket coated with foam rubber is obtained. Materials for a gasket coated with foam rubber of EMBODIMENTS 2 and 3 and EXAMPLES FOR COMPARISON 1 to 4 as indicated in TABLE 1 were prepared by specifications similar to that used in EMBODIMENT 1, changing rubber blend. Results obtained by measuring resistance to pressure (application of 800 kgf/cm 2 ), resiliency (gap between flanges capable of holding a sealing pressure of 1 kgf/cm 2 ), and swelling ratio of these materials in high temperature ATF oil are indicated in the same table. NUMBER EMBODIMENTS EXAMPLES FOR COMPARISON 1 2 3 1 2 3 4 KIND OF RUBBER NBR NBR NBR/NR NBR NBR NBR NBR NITRILE AMOUNT (%) 18 25 -- 34 18 18 34 MOONEY VISCOSITY 72 68 -- 56 32 72 56 KIND OF CARBON MT MT FT MT MT SRF MT (PHR AMOUNT) 80 120 50 80 80 60 50 KIND OF FILLER CLAY -- CALCIUM CARBONATE CLAY CLAY CLAY -- (PHR AMOUNT) 40 -- 50 40 40 40 -- RESISTANCE TO PRESSURE GOOD GOOD GOOD GOOD GOOD GOOD BAD RESILIENCY (µm) 40 35 40 5 5 -- 20 SWELLING RATIO (%) +10.3 +9.0 +11.1 ±0 ±0 -- +5.0 REMARKS HARDLY FOAMED As clearly seen from TABLE 1, it can be admitted that an effect of increasing resiliency of the foam layers after exposure to a high temperature and improving fitness to the flanges can be obtained by using a rubber having a property that it is swollen by medium to be sealed as the base rubber for the foam rubber layers. It is clear that an effect of increasing elasticity and hardness of the foam layers and an action of improving resistance to heat can be obtained by blending carbon having a low reinforcing property and inorganic filler therein, because the reinforcing property is low and blend of a large amount is possible. As explained above, according to the present invention, an effect of improving the sealing property can be exhibited by improvement of resiliency of the foam layers and fitness to flanges after exposure to high temperature oil owing to increase in the amount of swelling by using a rubber having a property that it is swollen by medium to be sealed. In addition, an effect of improving resistance to pressure owing to increase in elasticity and hardness of the foam layers and an effect of improving resistance to pressure at exposure to a high temperature atmosphere owing to improvement of the resistance to pressure can be exhibited by blending carbon having a low reinforcing property and inorganic filler therein.

Claims: A gasket for sealing a medium, the gasket comprising a metal plate (1) having foam rubber layers (3) formed on both sides thereof, characterized in that the foam rubber layers (3) are formed from a rubber having the property that it is swollen by the medium to be sealed, wherein carbon having a low reinforcing property and an inorganic filler are blended in the rubber. A gasket according to claim 1, wherein the rubber has the property that it is swollen by oil. A gasket according to claim 1 or claim 2, wherein the rubber comprises a nitrile-butadiene rubber (NBR) having a nitrile amount lower than 30% and a Mooney viscosity greater than 60. A gasket according to any one of claims 1 to 3, wherein the rubber further comprises one or more of a deterioration preventing agent, a bridging agent and a thermal decomposition foaming agent. A gasket according to claim 4, wherein from 40 to 150 parts hundred rubber (PHR) of MT and/or FT carbon and from 0 to 80 parts hundred rubber (PHR) of clay and/or calcium carbonate are blended in the rubber, the total of MT and/or FT carbon and clay and/or calcium carbonate being greater than 60 parts hundred rubber (PHR). A gasket according to any one of claims 3 to 5, wherein the rubber comprises a nitrile-butadiene rubber (NBR) having a nitrile amount of 25 or less, preferably 20 or less. A gasket according to any one of claims 3 to 6, wherein the rubber comprises a nitrile-butadiene rubber (NBR) having a Mooney viscosity of greater than 65, preferably greater than 70. A gasket as claimed in any one of claims 1 to 7, further comprising a primer layer (2) between each foam rubber layer (3) and the metal plate (1). Use of a gasket as defined in any one of claims 1 to 8 for sealing high temperature oil, preferably ATF oil. A process of manufacturing a gasket for sealing a medium, which process comprises: i) providing a metal plate (1); ii) applying a liquid rubber composition to both sides of the metal plate, which composition comprises a nitrile-butadiene rubber (NBR) having a nitrile amount lower than 30% and a Mooney viscosity greater than 60 provided in a suitable solvent, wherein carbon having a low reinforcing property and an inorganic filler are blended in the rubber; and iii) drying the liquid rubber composition to result in a foam rubber layer (3) on both sides of the metal plate (1), wherein the foam rubber layer has the property that it is swollen by the medium to be sealed.

Inventors: OMURA ATSUSHI, OMURA, ATSUSHI
Applicants: NICHIAS CORP, NICHIAS CORPORATION
Application year: 1998
Main classification: F16J15
IPC codes: F16J15, C08K3, C09K3, C08L9