Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – At least one aryl ring which is part of a fused or bridged...
Reexamination Certificate
2001-05-25
2002-05-21
Sanders, Kriellion A. (Department: 1714)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
At least one aryl ring which is part of a fused or bridged...
C428S036800, C428S039000, C428S492000, C428S522000, C138S137000, C138S140000
Reexamination Certificate
active
06391963
ABSTRACT:
TECHNICAL FIELD
This invention relates to a rubber composition and a fuel transporting hose for a vehicle. More particularly, this invention relates to a fuel transporting hose for a vehicle which is simple and inexpensive in construction and is satisfactory for fuel impermeability and a certain level of conductivity as required of a fuel transporting hose for a vehicle, and to a rubber composition used therefor.
BACKGROUND ART
Regulations concerning the permeation of fuel in a vehicle, which are similar to the so-called SHED regulation in the United States, are put into effect in A.D. 2000 in Japan and Europe. As is well known, a fuel transporting hose is highly responsible for the permeation of fuel in a vehicle, and measures have been sought for controlling the permeation of fuel from a fuel transporting hose.
It has been a common practice in Japan to use FKM (fluororubber) of high fuel impermeability and sour resistance to form an inner wall layer of a fuel hose used in what is called a liquid line, such as a feed or return circuit in a vehicle fuel line. Generally used NBR (acrylonitrile-butadiene rubber), or NBR-PVC which is a blend of NBR and PVC (polyvinyl chloride), has been used for a filler neck hose connecting a filler hole and a gasoline tank, or a breather or evaporation hose forming a vapor line. In the United States having the SHED regulation already in effect, the specifications for a filler neck hose or an evaporation hose employ FKM or a resinous material such as a polyamide resin or fluororesin for its inner wall layer and NBR-PVC, ECO (epichlorohydrin rubber), CSM (chlorosulfonated polyethylene rubber) or the like for its outer wall layer.
The specifications adopted in Japan for the filler neck, breather and evaporation hoses as mentioned above, however, fail to attain any fuel impermeability conforming to the national regulation going to be put into effect as stated above. The filler neck or evaporation hose having an inner wall layer formed from FKM or a resinous material as in the United States can be expected to satisfy the regulation in fuel impermeability. FKM or a fluororesin is, however, expensive, and is so low in reactivity that its bonding to an outer layer material requires an additional level of technical skill and an additional amount of processing cost. Another drawback is that a complicated manufacturing process is required for shaping a hose having a layer of FKM like bellows.
It has also been pointed out that a filler neck or breather hose may be charged with static electricity as a result of e.g. the flow of gasoline during fill-up or body vibration and may produce a spark when contacted by a metallic fill-up gun, resulting in the ignition of gasoline. It is, thus, hoped that conductivity will be imparted to any such hose (for example, to the extent giving it a volume specific resistance not exceeding 10
8
&OHgr;·cm) to prevent any electrical charging thereof. It is, however, difficult to impart any satisfactory conductivity, since FKM or a resinous material essentially has a high electric resistance.
Under these circumstances, it is an object of this invention to make a fuel transporting hose for a vehicle having high fuel impermeability and conductivity by using a simple and inexpensive rubber composition. The inventor of this invention has evaluated various rubber compositions containing NBR or NBR-PVC as a base material, and has conceived a compound design for a rubber composition which is comparable to FKM in fuel impermeability and exhibits high conductivity, while ensuring the necessary properties including low temperature properties.
DISCLOSURE OF THE INVENTION
It has been pointed out that NBR or NBR-PVC having a relatively high AN content of, say, 36 to 42 percent by weight has an improved fuel swelling resistance. However, the inventor's experiment conducted by using PHASE 11 gasoline for evaluation (gasoline for a permeation test as specified by the U.S. CARB, i.e. SHED test) indicates that NBR or NBR-PVC having such an content is apparently unsatisfactory in fuel impermeability.
During the process of research work, on the other hand, the inventor has found that NBR or NBR-PVC having a specific AN content in an ultrahigh nitrite range (for example, 43 percent by weight or higher) has a high fuel impermeability comparable to that of FKM. The inventor has also found that, while it is feared that NBR or NBR-PVC having an content in an ultrahigh nitrite range may be undesirably poor in low temperature properties as required of a fuel hose for a vehicle (the flexibility of a hose used in a very cold place having a temperature of as low as, say, −30° C.), the addition of a properly selected plasticizer in a properly selected amount makes it possible to realize a satisfactory level of low temperature properties while ensuring a high fuel impermeability, and that the proper addition of carbon black (CB) makes it possible to realize satisfactory conductivity while ensuring the properties mentioned above.
Moreover, the inventor has found very interesting matters, as shown at (1) to (4) below, about the technical meaning of PVC as a material blended for such a rubber composition.
(1) PVC is basically a component contributing to fuel impermeability, and it is necessary or beneficial to blend PVC with NBR to impart weatherability and ozone resistance to a rubber composition used for making an outer layer for a fuel hose having a multilayer wall structure, or a fuel hose having a single-layer wall. A rubber composition containing 25 percent by weight or more of PVC relative to NBR is practically satisfactory in weatherability and ozone resistance.
(2) It is, therefore, not necessary to blend 25 percent by weight or more of PVC with NBR to make any rubber composition not used for the purpose as stated at (1) above. On the other hand, it is feared that PVC as a resinous component may lower the low temperature properties of the composition. While it is effective in this connection to increase the proportion of the plasticizer, the excessive increase of the plasticizer in the rubber composition results in a reduction of its fuel impermeability. Thus, an increase in the blend ratio of PVC brings about a narrowing in the range of proportions which can be selected for achieving a good balance between the fuel impermeability of the rubber composition and its low temperature properties.
(3) If the amount of PVC blended is less than 25 percent by weight relative to NBR, it is possible to secure a broad range of proportions which can be selected for making a rubber composition having a good balance between fuel impermeability and low temperature properties, while maintaining the contribution of PVC to fuel impermeability as stated above. The amount of PVC is preferably not more than 5 percent by weight if the balance between the fuel impermeability of the rubber composition and its low temperature properties is more important than the contribution of PVC to its fuel impermeability.
(4) If NBR has an content set in a really ultrahigh range not lower than 46 percent by weight, the contribution of PVC to fuel impermeability as stated above can hardly be obtained. In such a case, therefore, it is preferable in view of the foregoing (1) to (3) to use NBR as a base material without blending any PVC.
According to a first aspect of this invention, there is, thus, provided a rubber composition for a fuel transporting hose for a vehicle which comprises NBR having an AN (combined acrylonitrile) content of 46 to 52 percent by weight as a base material, and 15 to 30 parts by weight of a plasticizer having an SP value (solubility parameter) of 8.8 or more and a molecular weight of 550 or less, relative to 100 parts by weight of the base material.
According to the first aspect of this invention in which NBR having an AN content of 46 to 52 percent by weight is used as a base material, NBR having such an ultrahigh AN content makes it possible to obtain a high fuel impermeability comparable to that of FKM. The composition contains 15 to 30 parts by weight
Jacobson & Holman PLLC
Sanders Kriellion A.
Tokai Rubber Industries Ltd.
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