Plastic and nonmetallic article shaping or treating: processes – Pore forming in situ – Composite article making
Reexamination Certificate
1999-07-09
2001-06-26
Kuhns, Allan R. (Department: 1732)
Plastic and nonmetallic article shaping or treating: processes
Pore forming in situ
Composite article making
C164S045000, C164S157000, C164S209000, C164S210000, C164S505000
Reexamination Certificate
active
06251320
ABSTRACT:
FIELD OF THE INVENTION
The invention concerns a process for producing a cover skin for the instrument panel of a motor vehicle.
BACKGROUND OF THE INVENTION
A motor vehicle usually has an instrument panel, which can also be referred to as a dashboard, extending beneath the windshield at the front part of the passenger compartment of such a nature that the structure involves a support body which carries the necessary instruments and fittings and which can extend for example in the region in front of the front seats over almost the entire width of the vehicle. The support body is covered by a separately produced skin or covering which is adapted to the contour of the support body and which at least predominantly comprises thermoplastic polyurethane. The gauge of the cover skin does not exceed or only slightly exceeds a dimension for example of 1 mm. That skin is not self-supporting and can therefore be changed in shape virtually without limitation.
Covers of a skin or film configuration of that kind can be produced by a process referred to as the slush process in which thermoplastic polyurethane in powder form is introduced into a mold of suitable configuration in which, while being heated, it is distributed over the surface of the mold by a biaxial fling movement or by other suitable movements, being raised to the melting temperature. The powder which is distributed in the form of a uniform layer over the inside surface of the mold gels due to the increase in temperature thereof so that the individual particles of the powder combine together to form a continuous wall portion or skin which, after adequate cooling, is then removed from the mold and subjected to suitable cutting operations to put it into the appropriate shape required for it to be mounted on the holding arrangement for the instruments. That process is extremely time-consuming and therefore expensive, in particular by virtue of the fact that between three and seven minutes are required for an operating cycle for the production of such a cover skin, depending on the size of the cover skin to be produced.
Having regard to the extremely large numbers in which cover skins of that kind are required, there is an urgent need for a more economical production process.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a process for producing a cover skin for a motor vehicle instrument panel in large numbers and economically, with ease of adaptability of the product configuration.
Another object of the present invention is to provide a process for producing a cover skin for a motor vehicle instrument panel which is such that it can be employed for producing the cover skin virtually irrespective of the extent of the instrument panel generally transversely with respect to the longitudinal axis of the motor vehicle and thus irrespective of the length of the cover skin.
Still another object of the present invention is to provide a process for producing a cover skin of thermoplastic polyurethane for a motor vehicle instrument panel, which permits the cover skin produced to be of any suitable length of between about 0.8 meter and 1.80 meter.
Yet a further object of the present invention is to provide a process for producing a cover skin for a motor vehicle instrument panel such that the result can satisfy virtually all reasonable demands in terms of quality and more specifically capacity to withstand mechanical loadings, appearance and other properties required for the intended function.
Yet a further object of the present invention is to provide a process for producing a cover skin of thermoplastic polyurethane for an instrument panel for a motor vehicle, which is at least comparable to the cover skins produced by the above-mentioned slush process.
Yet another object of the present invention is a process for producing a cover skin for a motor vehicle instrument panel such that the resulting cover skin can be soft and elastic as required.
In accordance with the present invention the foregoing and other objects are attained by a process for producing a cover skin of thermoplastic polyurethane for an instrument panel for a motor vehicle, wherein firstly a preform is produced by extrusion from thermoplastic polyurethane and thereafter the preform is expanded in a blow molding mold by an increased internal pressure in the preform.
It has been found that, although thermoplastic polyurethane cannot be readily processed using an extrusion blow molding procedure, production of the cover skins is possible in spite of the requirements which are unfavourable in regard to that procedure, more especially in terms of the dimensions, namely length and thin gauge, large diameter of the preform, and the expanded product to be produced therefrom, such production being considerably more economical than when using the conventional procedures in which the hollow body produced in the blow molding mold is normally required to undergo a finishing operation in order to arrive at the desired end product.
In this respect, the process can be particularly economical by producing in the blow molding mold a hollow body which constitutes a plurality of cover skins for respective instrument panels, so that the hollow body is divided up into the respective individual cover skins by suitable dividing processes such as cutting operations. It will be appreciated that this requires a blow molding mold of appropriate size. Nonetheless, the increased costs that this entails do not constitute a disadvantage, having regard to the large numbers in which cover skins of this kind are required. The blow-molded hollow body can be such that it comprises first and second portions which after a cutting operation represent respective cover skins, and, between the first and second portions, a region which represents waste or surplus and which consequently defines a spacing between the two portions for constituting the respective cover skins, on the inflated hollow body, prior to the hollow body being cut into the respective portions for affording the respective cover skins. That region representing waste on the blow-molded hollow body also takes account of the fact that the boundary edges of the end products may extend in an irregular configuration.
In order to take account of the particular features and aspects of thermoplastic polyurethane, it is advantageous for the processing procedure, that is to say including plasticising and shaping the starting material to constitute the preform, to be implemented under specific conditions in terms of for example pressure and temperature, with the starting material desirably being introduced in granule form into the extruder for extrusion of the preform. More particularly, in accordance with a preferred feature of the invention, it is advantageous for the preform which can be of a length of 1.80 m or more, to be produced by means of discontinuous extrusion which is known in relation to plastic processing operations, wherein the plasticised material is firstly conveyed into a storage space or chamber and then expelled by means of a piston or some other suitable manner in the form of a tubular portion through the generally annular outlet opening of the extrusion head. In that respect, the endeavour is for the preform to be extruded within a short period of time, for example within a period of one minute or less, with a preform length of between 1.30 m and 1.80 m. That has the advantage that the very thin-walled preform, the wall thickness or gauge of which can be about 2 mm, is subjected to a loading under its own weight by virtue of hanging from the extrusion head, only for a short period of time, and thus reaches the required length before it could uncontrolledly tear away under the effect of its own weight and the tensile loading applied thereto as a result. It has been found particularly advantageous in accordance with a preferred feature of the invention for the preform comprising thermoplastic polyurethane to be extruded at a speed of between about 10 and 40 cm/second, more particularly between about 10 and 35 cm/
Hänsel Bruno
Moitzheim Jürgen
Drinker Biddle & Reath LLP
Kautex Textron GmbH & Co. KG.
Kuhns Allan R.
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