Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Mixing of two or more solid polymers; mixing of solid...
Reexamination Certificate
2000-06-27
2001-12-25
Nutter, Nathan M. (Department: 1711)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Mixing of two or more solid polymers; mixing of solid...
C525S214000, C525S217000, C525S232000, C525S233000, C525S235000, C525S238000, C525S239000, C524S847000, C524S849000
Reexamination Certificate
active
06333386
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a rubber composition, a hose of low fuel permeation, and an electroconductive hose of low fuel permeation. More particularly, it relates to a rubber composition of good fuel impermeability and low-temperature flexibility, and a hose of low fuel permeation utilizing this rubber composition, and also to a rubber composition of good fuel impermeability, low-temperature flexibility and electroconductivity, and an electroconductive hose of low fuel permeation utilizing this rubber composition.
2. Description of the Related Art
Control on the leakage of fuel by permeation from an automobile, which is similar to the SHED control (Shield Housing for Evaporative Determinations) in the United States, is put into practice in Japan and Europe in 2000 A.D. A fuel transporting hose is required to be highly impermeable to fuel, since it is greatly responsible for the leakage of fuel by permeation from an automobile, as is well known.
In Japan and Europe, NBR (acrylonitrile-butadiene rubber) or blend rubber of NBR and PVC (polyvinyl chloride) of general specifications is used for a fuel hose in an automobile, such as a filler, breather or evaporation hose. However, that type of hose fails to achieve any fuel impermeability conforming to the strengthened domestic control as stated above. In addition, the rubber material noted above often releases a plasticizer, a vulcanizing agent or its reaction product, when dipped in fuel. In particular, the vulcanizing agent or its reaction product, if released, will corrode the metallic members of a fuel pump or will clog the valves in fuel piping.
In the United States in which the SHED control is already in force, FKM (fluororubber) or resin is used for the inner layer of a hose, and NBR-PVC (blend rubber of NBR and PVC), ECO (epichlorohydrin rubber), CSM (chlorosulfonated polyethylene rubber), etc. for its outer layer. These United States specifications can be expected to achieve the fuel impermeability conforming to the control. There are, however, problems, since FKM and fluororesins are expensive, and the inner layer of FKM or resin is difficult to bond to the outer layer.
It has heretofore been said that increasing the AN content (combined acrylonitrile content) of NBR in NBR-PVC to a range falling between 36 and 42% by weight or so could improve the fuel swelling resistance of NBR-PVC. The inventors of this invention, however, have found that the fuel impermeability of NBR-PVC in which the AN content of NBR falls within that range is still poor.
The inventors have further found that increasing the AN content of NBR to a range falling between 43 to 50% by weight or so realizes good fuel impermeability of NBR which is comparable to that of FKM.
However, increasing the AN content thereof to such a high level will decrease the low-temperature properties of the rubber material necessary to fuel hoses (for example, the flexibility of hoses used in cold districts where the ambient temperature often reaches −30° C. or so). To improve the low-temperature properties of rubber materials for hoses, in general, the amount of the plasticizer to be added thereto will be increased, which, however, adversely affects the fuel impermeability of the hoses formed of such rubber materials.
Apart from the problems of fuel impermeability and low-temperature flexibility of hoses noted above, it is also advantageous to make fuel hoses have electroconductivity. While an automobile is driven or refueled, fuel flows in the fuel hose to generate static electricity. If kept charged with static electricity, the fuel hose will give sparks dangerous to fuel when it is contacted with a metallic refueling gun or the like. To avoid the dangerous trouble, for example, an earth wire may be disposed between a filler hose and the body of an automobile thereby to remove static electricity through it, which, however, requires some specific members and an additional step for fitting it. It will be rather reasonable to use a filler or breather hose having electroconductivity. However, FKM and fluororesins essentially have large electric resistance, and hoses having the inner layer formed of these materials could hardly have electroconductivity.
SUMMARY OF THE INVENTION
The inventors of this invention have evaluated fuel impermeability and electroconductivity of various types of inexpensive NBR-PVC-based rubber compositions using gasoline for practical use. The gasoline for practical use includes Phase-II gasoline for evaporation control evaluation in the United States, and gasoline for evaporation control evaluation in Europe.
The results of evaluation have revealed that even NBR-PVC can realize a rubber composition having the following properties (1) to (4).
(1) It has fuel impermeability comparable to that of FKM.
(2) It keeps flexibility even at low temperatures.
(3) The release of a vulcanizing agent and its reaction product therein into fuel is reduced.
(4) It will also have good electroconductivity, if desired.
A first aspect of this invention resides in a rubber composition for hoses of low fuel permeation, which comprises NBR having a combined acrylonitrile content (AN content) of from 43 to 50% by weight, PVC blended with the NBR, and a plasticizer having a solubility parameter (SP) value of at least 8.8 and a molecular weight of at most 550 added to the NBR-PVC blend.
In the first aspect, the AN content of NBR in the NBR-PVC blend is controlled to fall between 43 and 50% by weight, and therefore the fuel impermeability of the NBR-PVC blend is comparable to that of FKM. To improve the low-temperature properties of the rubber composition, a plasticizer having an SP value of at least 8.8 and a molecular weight of at most 550 is added to the NBR-PVC blend. The plasticizer having a molecular weight of at most 550 has low viscosity at low temperatures, and therefore significantly improves the low-temperature properties of the NBR-PVC blend. The plasticizer having an SP value of at least 8.8 is highly miscible with the NBR-PVC blend in which NBR has a high AN content, hardly affecting the fuel impermeability of the rubber composition. Accordingly, adding the plasticizer as above to the NBR-PVC blend improves the low-temperature properties of the rubber composition, effectively maintaining the fuel impermeability thereof.
The AN content of smaller than 43% by weight will give the rubber composition of insufficient fuel impermeability; and the AN content of larger than 50% by weight will decrease the low-temperature properties of the rubber composition to such a degree that they cannot be improved even by the addition of a plasticizer. A plasticizer having an SP value of smaller than 8.8 is poorly miscible with NBR-PVC and will bleed out of the rubber composition, which makes it difficult to improve low-temperature properties. A plasticizer having a molecular weight of larger than 550 increases the low-temperature viscosity of the rubber composition, which also makes it difficult to improve low-temperature properties.
In addition to the above, in the first aspect of the invention, the amount of the vulcanizing agent and its reaction product to be released from the rubber composition when dipped in fuel is small. Therefore, hoses formed of the rubber composition are free from the troubles to be caused by the released ingredients that may corrode the metallic members of fuel pumps and may clog the valves in fuel piping.
A second aspect of the invention resides in a hose of low fuel permeation, which comprises the rubber composition of the first aspect.
The advantages of the hose of the second aspect are that it is inexpensive and impermeable to fuel and has good low-temperature properties, and the amount of the vulcanizing agent and its reaction product to be released from it is small. The hose is especially suitable for automobiles.
A third aspect of the invention resides in a rubber composition for electroconductive hoses of low fuel permeation, which comprises NBR having an AN content of from 43 to 50% by
Kanbe Shinobu
Kato Kazuhiro
Miyajima Atsuo
Nishiyama Takahiro
Jacobson & Holman PLLC
Nutter Nathan M.
Tokai Rubber Industries Ltd.
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