Stock material or miscellaneous articles – Hollow or container type article – Polymer or resin containing
Reexamination Certificate
1999-12-30
2002-05-21
Dye, Rena L. (Department: 1772)
Stock material or miscellaneous articles
Hollow or container type article
Polymer or resin containing
C428S035700, C220S062110, C220S062220, C220S562000, C206S524100, C206S524200
Reexamination Certificate
active
06391412
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an automobile fuel tank which has good impact resistance as well as good impermeability to automobile fuel, especially gasoline blended with methanol or methyl t-butyl ether (MTBE).
2. Description of the Prior Art
Plastics fuel tanks are coming into general use. Most popular among them are those of single-layer type made of polyethylene. Their disadvantage is a comparatively high permeability to gasoline. Conventional measures against this were sulfonation of the polyethylene tank (Japanese Patent Publication No. 23914/1971), fluorination of the polyethylene tank (Japanese Patent Publication Nos. 21877/1972 and 15862/1978), and blending of polyethylene with nylon as a barrier material (Japanese Patent Laid-open No. 296331/1992). There has also been proposed a plastics fuel tank of five-layer construction in which the inner and outer layers are made of high-density polyethylene and the middle layer is made of nylon and they are bonded together with adhesive resin layers.
It has been found that these prior art technologies do not cope with the recent situation arising from the use of the gasoline which contains oxygenated compounds such as methanol, ethanol or MTBE (referred to as oxygen-containing gasoline hereinafter) which started in the U.S. to prevent air pollution, to reduce gasoline consumption, to improve the octane number of gasoline, and to lower the amount of unburnt hydrocarbon in exhaust gas. Unfortunately, the above-mentioned sulfonation or fluorination of the single-layered polyethylene fuel tank does not provide sufficient barrier properties for oxygen-containing gasoline. Likewise, the combination of nylon with polyethylene (in the form of multi-layer or dispersion) does not completely prevent permeation of oxygen-containing gasoline through the fuel tank.
To address this problem, there has been proposed a multi-layer fuel tank composed of polyethylene and ethylene-vinyl alcohol copolymer (EVOH for short hereinafter) which exhibits good gasoline barrier properties. Although it is superior in barrier properties to the conventional fuel tanks, there still is room for improvement to meet the future environmental regulations. Improvement in impact resistance is another subject to be considered.
One way to approach problems involved in the fuel tank having an intermediate layer of EVOH is by blending EVOH with polyolefin or polyamide (as proposed in Japanese Patent Laid-open Nos. 218891/1994 and 52333/1995). However, the problems still remain unsolved because such blending appreciably impairs the gasoline barrier properties and adversely affects the melt stability of the raw material.
SUMMARY OF THE INVENTION
The present invention was completed in view of the foregoing. It is an object of the present invention to provide a multi-layered fuel tank composed of high-density polyethylene and EVOH layers, which is superior in gasoline barrier properties (especially for oxygen-containing gasoline) and impact resistance.
This object could be achieved on the basis of the surprising finding that a fuel tank of multi-layer construction which comprises (a) inner and outer layers of high-density polyethylene, (b) intermediate layers of adhesive resin, and (c) a core layer of ethylene-vinyl alcohol copolymer shows the above-mentioned desired properties if the total thickness of the layers positioned inside the layer (c) is smaller than the total thickness of the layers positioned outside of the layer (c).
According to a preferred embodiment of the present invention, the layer (c) has a thickness which satisfies the formula below.
0.005
≦A/B≦
0.13 (1)
where
A is the thickness of the layer (c), and
B is the thickness of all the layers.
The present invention especially produces its noticeable effect when the fuel tank is used for gasoline comprising oxygene-containing compounds.
According to the present invention, the multi-layer construction is characterized in that the total thickness of the layers positioned inside the layer (c) is smaller than the total thickness of the layers positioned outside of the layer (c). This arrangement contributes to the superior barrier properties (especially for oxygen-containing gasoline) and good impact resistance. These characteristics make the fuel tank to meet the environmental and safety regulations. The multi-layer construction provides as good barrier properties and impact resistance as the conventional one even though the EVOH layer is reduced in thickness. This leads to cost reduction and thickness reduction (and hence weight reduction) These effects are enhanced when the formula (1) above is satisfied.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
The fuel tank of the present invention is constructed of (a) inner and outer layers of high-density polyethylene, (b) intermediate layers of adhesive resin, and (c) a core layer of ethylene-vinyl alcohol copolymer. It is extremely important in the present invention that the ratio (I/O) is smaller than 50/50, where I is the total thickness of the layers positioned inside of the layer (c), and O is the total thickness of the layers positioned outside of the layer (c), in other words that the core layer (c) is shifted to the inside of the fuel tank wall.
(Incidentally, the thickness of each layer is an average measured at the bulge of the fuel tank.)
Shifting the EVOH layer (c) to the inside improves the gasoline barrier properties and impact resistance, as demonstrated in Example 1 and Comparative Examples 3 to 5. It is to be noted that the value of gasoline barrier properties is increased more than four-fold by moving the EVOH layer (c) from the outermost position (as in Comparative Example 5) to the innermost position (as in Comparative Example 3), with the layers (a), (b), and (c) being the same in thickness. It is also noted that the value of gasoline barrier properties is increased about 1.5-fold by moving the EVOH layer (c) from the center (as in Comparative Example 4) to the position where the ratio (I/O) is 20/80 (as in Example 1). It is significant that the performance of the fuel tank of multi-layer construction greatly varies as mentioned above although the materials and their amount are substantially the same.
The reason for the above-mentioned effect of improving gasoline barrier properties is not known. It is believed that the degree of swelling of the high-density polyethylene layer (a) and EVOH layer (c) due to gasoline, methanol, and MTBE varies depending on the position of the EVOH layer (c).
Also, shifting the EVOH layer (c) to the inside improves the impact resistance of the fuel tank, as demonstrated in Example 1 and Comparative Example 4. That is, the height for breakage in drop test is 5.7 m in the case where the EVOH layer (c) is positioned at the center (as in Comparative Example 4), whereas the height for breakage in drop test is increased to 7.6 m in the case where the EVOH layer (c) is shifted to the position where the ratio (I/O) is 20/80 (as in Example 1). Presumably, the improvement in impact resistance is due to the soft, thick HDPE layer placed outside. Incidentally, although shifting the EVOH layer (c) to the inside improves the impact resistance of the fuel tank, there is an optimum position for the most desired effect.
As mentioned above, shifting the EVOH layer (c) to the inside improves the gasoline barrier properties and impact resistance of the fuel tank. The greater the distance of shifting, the better the result. Thus, the position for shifting should be such that the ratio (I/O) is equal to or smaller than 45/55, preferably 40/60, more preferably 35/65, and most desirably 30/70.
According to the present invention, the fuel tank of multi-layer construction comprises (a) inner and outer layers of high-density polyethylene, (b) intermediate layers of adhesive resin, and (c) a core layer of ethylene-vinyl alcohol copolymer. The core layer (c) should be shifted to the inside but should not be at the innermost position. In other words, the innermost layer should
Hata Nobuhiro
Negi Taichi
Dye Rena L.
Kuraray Co. Ltd.
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
LandOfFree
Fuel tank does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Fuel tank, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Fuel tank will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2832786