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
1998-08-19
2001-04-17
Foelak, Morton (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...
C264S302000, C525S240000
Reexamination Certificate
active
06218474
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to a polyolefin thermoplastic composition having elastic properties, being in the form of fine particles conferring on it the character of a powder.
The invention relates more especially to a polyolefin thermoplastic composition having elastic properties, being in the form of a powder, for the production of skins by the process of powder slush moulding on conventional equipment.
The invention also relates to the process for preparing the said composition.
Finally, the invention relates to the moulded articles produced by the use of the composition.
TECHNICAL BACKGROUND OF THE INVENTION
Many components made of polymer materials are increasingly being used in the construction of motor vehicles: such as dashboards, door panels, consoles, etc. Some of them are used very visibly in the internal architecture of the vehicle, in such a way that they must have, on the visible surface, a pleasing aesthetic appearance which reproduces, for example, the appearance of leather. This visible surface constitutes the skin of the component. This skin, bulk coloured, must also have other properties, which are good scratch resistance and good resistance to chemicals such as solvents, as well as the ability to withstand thermal variations, ranging from the very cold to the prolonged exposure to sunshine in a confined atmosphere.
The abovementioned skin may concern all components (also called inserts) made of polymer materials, particularly those involved in the internal architecture of the vehicle—from the rigid inserts generally reserved for bottom-of-the-range vehicles to the foamed inserts with which more sophisticated vehicles are equipped.
In the case of rigid inserts, the skin, or at very least its appearance, is obtained by the etching of the mould, either as a result of the constituent material of the insert or else, for example, by the co-injection moulding of two different materials, one for the insert and the other for the skin.
In the case of foamed inserts, the skin is generally made, independently of the insert itself, of a material compatible, on the one hand, with the foam subsequently developed between the said skin and the insert and, on the other hand, with the finishing lacquers, such as polyurethane lacquers, deposited on the visible surface of the said skin in order to make them comply, where necessary, with the specifications of motor-vehicle manufacturers.
In order to produce the skin of inserts, such as the dashboard for example, various processes have been proposed, one of the preoccupations of which is to produce a skin with the lowest possible residual stress.
In a first type of process which uses a premanufactured polypropylene-based sheet, the skins of dashboards are produced by means of the process of positive or negative thermoforming. However, the thermo-forming employed, whether positive (the surface appearance of the skin exists on the sheet before thermoforming) or negative (the surface appearance is given to the sheet by the mould during thermoforming), generally involves, both for technical and economic reasons, sheets (preheated) which are preferably thin. Consequently, the shapes of the skins obtained are very limited and contain residual stresses which, when they are relieved by ageing, generate crazes which are very unattractive.
In one type of process, the skins of dashboards are produced using the slush moulding process (mentioned above) which generally allows them to be obtained free of residual stresses. By itself, the slush moulding process is a moulding process using conventional equipment (electroformed nickel mould heated by a hot-air system) which allows the production of the desired skins using a polymer powder based on polyvinyl chloride (PVC) by the technique of powder slush moulding. The skins thus produced, although they no longer include residual stresses, or very few residual stresses, and although they meet for the most part the specifications of motor-vehicle manufacturers, do have immediate or potential drawbacks, even in the short term.
Among the immediate drawbacks, the PVC-based skins are quite highly loaded, owing to their composition, with volatile substances (in particular, PVC plasticizers). These materials, in use and due to the effect of temperature variations in the passenger compartment of the vehicle, are volatilized and migrate to cold areas, where they condense—this is the well-known phenomenon of slow opacification of the windscreen of a vehicle, which is a particular impediment to the driver's view and to the proper control of the vehicle.
Among the potential drawbacks, the use of PVC appears, in the current situation of end-of-life recycling of materials used in the manufacture of motor vehicles, to be prohibited in the relatively short term for better environmental protection.
Polymer materials resulting from grinding up worn-out vehicles are currently used (completely or partly) as fuel in certain types of furnaces, such as, for example, furnaces in cement works. However, PVC converted into a fuel material emits, when it is burnt, acid-gas effluents which are harmful to the environment.
This is why, in order to meet the twin concern of motor-vehicle manufacturers and the public authorities, which is firstly that of protecting the environment (removing harmful gaseous effluents generated by the combustion of waste made of polymer materials and limiting the dumping thereof) and then that of more completely recycling the waste (formed from polymer materials) resulting from the destruction of worn-out vehicles by grinding, motor-vehicle manufacturers seriously envisage limiting the number of polymers present in each vehicle, but at the same time increasing their relative amounts, and in particular substituting PVC with polyolefins in order to allow easier recycling. Thus, motor vehicles would be equipped with components, such as foamed dashboards, whose skin, foam and rigid insert would be made of polyolefins which can be recycled at the end of the life of the vehicles.
To do this, polyolefin thermoplastic compositions have already been proposed.
By way of example, document EP 0,508,801 describes a powder composition of thermoplastic elastomers for powder moulding, which comprises:
either (i) a powder of a thermoplastic elastomer comprising a composition composed of an ethylene-alpha-olefin copolymer rubber and of a polyolefin resin;
or (ii) a powder of a thermoplastic elastomer comprising a partially crosslinked composition composed of an ethylene-alpha-olefin copolymer rubber and of a polyolefin resin,
this powder composition being able to be used in the slush moulding process.
However, according to this document:
in order to increase melt flow and at the same time to improve the flexibility of the moulded article, the olefin copolymer rubber is diluted with oil and thus comprises an ethylene-alpha-olefin copolymer rubber with the addition of a mineral oil as a flexibilizer with a relatively high content with respect to the polyolefin elastomer. These oils constitute, in fact, a risk of emitting volatile substances which pollute the environment and opacify vehicle windscreens, and also a risk of impairing the appearance of the skin during its ageing—the phenomenon of exudation is not eliminated.
finally, in order to allow the skin to be easily demoulded, external mould-release agents (for example, dimethylsiloxane) deposited on the mould or mould-release agents internal to the composition.
(for example, methylpolysiloxane) are employed: they also constitute a risk of directly polluting the environment of the manufacturing workshops, but above all they make it more difficult to carry out the subsequent operation of lacquering the skins, this currently being necessary in order to make them comply with the specifications of motor-vehicle manufacturers (appearance, matt-gloss level, scratch resistance, abrasion resistance and resistance to chemicals, including solvents).
Another document, U.S. Pat. No. 5,302,454, also describes a thermoplastic polyolefin composition, having
Marciniak Tony
Valligny Dominique
Foelak Morton
Millen White Zelano & Branigan P.C.
Plastic Comnium Auto Interieur
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