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
2001-03-26
2002-05-28
Seidleck, James J. (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...
C525S064000, C525S193000, C525S240000, C525S232000, C525S285000, C525S324000, C428S402000, C428S403000, C264S302000
Reexamination Certificate
active
06395839
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to a grafted and cross-linkable thermoplastic polyolefin composition which has elasticity and flexibility properties.
The invention relates more especially to a grafted and crosslinkable thermoplastic polyolefin composition which has elasticity and flexibility properties, which is in the form of a powder, for the production of flexible coatings by free flow of the powder over a heated mold, according to either of the molding processes of slush molding or rotational molding.
The invention also relates to the process for the preparation of the said composition.
The invention also relates to the process for making use of the said composition.
Finally, the invention relates to the molded articles produced by making use of the composition.
TECHNICAL BACKGROUND OF THE INVENTION
Numerous parts which are made of polymeric materials are increasingly involved in motor vehicle construction, such as dashboards, door panels, consoles, and the like. Some of them are involved in a highly visible manner in the internal architecture of the vehicle, with the result that they must offer, on the visible surface, a pleasant aesthetic appearance giving, for example, the appearance of leather. This visible surface constitutes the skin of the component. This skin, coloured in bulk, must also have other properties, which are a good resistance to scratching and to chemical agents such as solvents, and a good resistance to temperature variations, ranging from severe cold to prolonged exposure to the sun in an enclosed atmosphere.
The skin thus referred to may relate to any components, (also called inserts) made of polymeric materials, particularly those forming part of the internal architecture of the vehicle, starting with the rigid inserts, generally confined to bottom-range vehicles, as far as foamed inserts fitted to more elaborate vehicles.
In the case of rigid inserts the skin or, at least its appearance, is obtained by virtue of engraving of the mold, either from the material of which the insert consists or else, for example, using a dual injection of two different materials, one for the insert the other for the skin.
In the case of foamed inserts the skin is generally produced independently of the insert itself, in a material which is 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 the polyurethane lacquers deposited on the visible surface of the said skin in order, if need be, to make them conform to the specifications of the motor vehicle manufacturers.
To produce the skin of inserts such as, for example, the dashboard, various processes are proposed, in which one of the concerns is to produce a skin with the least possible residual stress.
In a first type of process which makes use of a prefabricated polypropylene-based sheet, the dashboard skins are produced by means of the positive or negative thermoforming process. However, the thermoforming practiced, whether positive (the surface appearance of the skin exists on the sheet before the thermoforming) or negative (the surface appearance is given to the sheet by the mold at thermoforming) generally makes use of (preheated) sheets which are preferably thin, for both technical and economic reasons.
As a result, the forms of skins which are obtained are very limited because they give rise to very thin skins and to residual stresses which, when they are released by aging, generate aesthetically unsightly small cracks.
In another type of process the dashboard skins are produced according to the slush molding process (referred to above), which allows them to be obtained generally free from residual stresses. In itself the slush molding process is a molding process employing conventional hardware (mold made of electroformed nickel heated, for example, by a hot air system) which allows the desired skins to be produced by making use of a polymer powder based on polyvinyl chloride (PVC) using the free flow technique. The skins thus produced, even if no longer containing any, or hardly any residual stresses, and even though they essentially meet the specifications of the motor vehicle manufacturers, exhibit immediate or potential disadvantages, even in the short term.
One of the real and immediate disadvantages is that, owing to their composition, PVC-based skins are fairly highly laden with volatile materials (in particular plasticizers for PVC). In use and under the effect of the temperature variations in the vehicle's interior, these materials are volatilized and migrate onto the cold regions, to condense thereon; this is the well-known phenomenon of the slow opacifying of vehicle windshields, particularly awkward for the driver's visibility and control of the vehicle.
Among the potential disadvantages, the use of PVC, in the present state of the recycling at the end of the life of materials introduced into the manufacture of motor vehicles, appears to be doomed to a more or less short term, for better protection of the environment. This is because the polymeric materials resulting, from the dissembling of scrap vehicles are at present employed (wholly or partly) as fuel in some types of furnaces, such as, for example, cement works' kilns. Now, when it is burnt, PVC converted into fuel gives off acidic gaseous effluents which are harmful to the environment.
This is why, in order to respond to a dual concern of the motor vehicle manufacturers and of the public authorities, which is firstly that for the protection of the environment (eliminating the harmful gaseous effluents generated by the burning of waste made of polymeric materials and limiting their dumping) and, next, that for the most complete recycling of the waste (made up of polymeric materials) resulting from the destruction of scrap vehicles, motor vehicle manufacturers seriously envisage limiting the number of polymers present in each vehicle but, at the same time increasing their relative quantities, and in particular replacing PVC with polyolefins, to permit easier recycling. Thus, motor vehicles would be fitted with components, such as foamed dashboards, in which the skin, the foam and the rigid insert would be made of polyolefins which can be recycled at the end of the vehicles' life. To do this, thermoplastic polyolefin compositions have already been proposed.
In this context document EP0482778 describes a polyolefin composition which has elastic properties, made up of an extruded mixture of polypropylene and of a polyolefin elastomer [ethylene-propylene rubber (EPR) and ethylene-propylene-diene monomer (EPDM)], which can be employed according to the slush molding process.
However, according to this document:
to promote the melting, in contact with the mold, of the composition which is in the form of a powder, oils such as paraffinic oils are introduced therein in a relatively high proportion in relation to the polyolefin elastomer. These oils constitute a potential risk of giving off volatile substances that pollute the environment and opacify vehicle windshields, as well as a risk of the appearance of the skin deteriorating as it ages;
to impart good heat resistance to the skin which is, by definition, thin, and to limit the presence of interfering volatile materials, crosslinking agents, including organic peroxides in particular, are introduced into the composition;
finally, to permit easy demolding of the skin, mold release agents which are external (for example dimethylsiloxane) deposited on the mold, or internal to the composition (for example methylpolysiloxane), are used; they also constitute a risk of direct pollution of the environment of the manufacturing workshops, but, above all, create greater difficulty in the subsequent operation of lacquering the skins which is at present necessary to make them conform to the motor vehicle manufacturers' specifications (appearance, degree of mattness/gloss and resistance to scratching, abrasion and to chemical agents, including solvents).
Ano
Marciniak Tony
Valligny Dominique
Asinovsky Olga
Millen White Zelano & Branigan P.C.
Seidleck James J.
Visteon Systemes Interieurs S.A.S.
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