Automobile fuel tank

Details Automobile fuel tank Automobile fuel tank

2000-06-19

2001-09-25

Pyon, Harold (Department: 1772)

Stock material or miscellaneous articles

Hollow or container type article

Polymer or resin containing

C428S036700, C428S036800, C428S036920

Reexamination Certificate

active

06294235

ABSTRACT:

BACKGROUND TO THE INVENTION
The present invention relates to a blow moulded automobile fuel tank composed of high density polyethylene.
DESCRIPTION OF THE PRIOR ART
Such fuel tanks are required to exhibit high safety performance, particularly with regard to fire resistance and impact resistance. Plastics automobile fuel tanks are required to meet minimum statutory and industry specified performance criteria both with respect to creep resistance when the tank is subjected to a fire and crash test resistance when the tank is subjected to an impact. Known blow moulded automobile fuel tanks suffer from the disadvantage that in order to meet the specified criteria the fuel tanks are required by automobile manufacturers to have a minimum wall thickness of at least 3 mm so as to provide sufficient impact strength and creep resistance for the fuel tank as a whole. However, the use of such high wall thicknesses leads to a number of disadvantages. First the high wall thickness increases the weight of the fuel tank, although there is a general desirability to reduce the weight of automobile components. Second, the high wall thickness increases the amount of plastics material employed to produce a fuel tank of a given volume, thereby increasing the material cost of the fuel tank. Finally, the high wall thickness increases the moulding time of the plastics fuel tank, thereby increasing the production cost.
U.S. Pat. No. 4,719,135 discloses a fuel tank having a polymer substrate, e.g. of HDPE, coated with a particular cured varnish agent. The tank is blow moulded. The HDPE has a density of from 0.935 to 0.950 g/cm
3
and an HLMI of less than about 10 g/10 min.
DE-A-3435992 discloses an extrusion blown fuel tank of HDPE, the HDPE also having a density of from 0.935 to 0.950 g/cm
3
and an HLMI of less than about 10 g/10 min.
WO-A-91/09732 discloses a multi-layer container for use as a fuel tank having an interlayer of highly sulphonated high density polyethylene. The tank is blow moulded. A central interlayer is provided between inner and outer layers of HDPE each of thickness 1.5 to 5 mm. It is stated that with a thickness less than 1.5 mm the inner and outer layers do not provide the multi-layer container with sufficient mechanical strength and impact resistance.
SUMMARY OF THE INVENTION
It is an aim of the present invention at least partially to overcome these disadvantages of known fuel tanks.
It is also an aim of the invention to provide a blow moulded automobile fuel tank which may have a lower weight than those using high density polyethylene of standard fuel tank grades yet still meeting stringent industry test specifications, in particular with regard to fire resistance and impact resistance.
Accordingly, the present invention provides a blow moulded automobile fuel tank having a wall defining a fuel chamber wherein the minimum wall thickness of the wall is from 2.4 mm to less than 3 mm, the tank being composed of a high density polyethylene having a density of from 0.945 to 0.955 g/cm
3
and a high load melt index of from 5 to 9.5 g/10 min, the high density polyethylene optionally having a carbon black content of up to 0.5 wt %, and the fuel tank having a fire resistance and an impact resistance both complying with the respective standards defined in ECE 34, ANNEX 5.
Preferably, the density is around 0.95 g/cm
3
. In this specification, the density is measured at 23° C. using the procedures of ASTM D 1505.
Preferably, the high load melt index is around 8 g/10 min. In this specification, the high load melt index is measured using the procedures of ASTM D 1238 at 190° C. using a load of 21.6 kg.
The preferred high density polyethylene has a stress crack resistance (F50) measured in accordance with the procedures of ASTM D 1693 of greater than 360 hours. The preferred high density polyethylene has a flexural modulus measured in accordance with the procedures of ISO 178 at a temperature of 23° C. of 1100 MPa. The preferred high density polyethylene has a stress and an elongation at yield of 25 MPa and 11% respectively, both measured in accordance with the procedures of ISO 527.
The preferred high density polyethylene is produced by a low pressure slurry loop polymerisation process. Typically, the catalyst is a chromium-based catalyst incorporating titanium and having a pore volume of from 1.0 to 3 cm
3
/g and a specific surface area of from 350 to 700 m
2
/g. The preferred chromium-based catalyst may be obtained by deposition of chromium onto a support matrix comprising a blend of silica and titania; the co-deposition of chromium and titanium compounds onto a silica support-matrix; the deposition of a titanium compound onto a support matrix comprising a blend of chromia and silica; or the terprecipitation of silicon, titanium and chromium compounds.


REFERENCES:
patent: 4719135 (1988-01-01), Gerdes et al.
patent: 5384172 (1995-01-01), Takado et al.

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