Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Processes of preparing a desired or intentional composition...
Patent
1995-07-19
1996-12-17
Yoon, Tae
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Processes of preparing a desired or intentional composition...
524114, 524210, 524267, 524515, 524451, 525240, C08L 6300, C08L 2300, C08K 334
Patent
active
055854206
DESCRIPTION:
BRIEF SUMMARY
This invention relates to scratch resistant polymer compositions and moulded articles made using such compositions. In particular it relates to such pigmented compositions and articles having aesthetic appeal for example vehicle interior trim components and domestic appliance components, particularly housings.
Plastics materials are used in many applications where aesthetic appearance is important. Indeed, the commercial success of such articles may depend on their aesthetic appeal. In addition, such articles should also possess suitable functional properties.
To maintain a good appearance, it is desirable that plastic articles have good scratch resistance and do not optically stress whiten to any significant extent when scratched. Stress whitening of pigmented plastic articles is aesthetically undesirable because the white marks formed on scratching visually contrast with the colour of the article. This is particularly marked if the plastics article is darkly pigmented for example black, grey, brown or blue, as are commonly used in vehicle interior trim.
Our PCT Application No PCT/GB 92/01400, (published as WO 93/03095 A) (which is incorporated by reference herein) relates to a polypropylene copolymer composition and to articles made from it having improved scratch resistance and including a polyorganosiloxane, particularly a polydimethylsiloxane. This prior development provides an improvement in scratch resistance over conventional compounded polypropylene type materials, but further improvements would be very attractive for industrial uses of compounded polyolefin materials.
The present invention is directed to a filled compounded blend of mainly polypropylene and a minor proportion of low density polyethylene type polymers, in which the filler is mainly a plate like filler such as talc. The filled compounded blend has excellent scratch resistance, retains a desirable combination of impact strength and stiffness and may be produced economically.
Accordingly the present invention provides a filled polymer composition which comprises:
from 70 to 95% by weight of a polypropylene homopolymer, and
from 5 to 30% by weight of a low density polyethylene; and from 5 to 30% by weight of a plate like inorganic filler.
The compositions of the invention can give significantly improved resistance to stress whitening and can be used to produce moulded articles with surfaces having improved scratch resistance. Accordingly, a further aspect of the invention provides for the use of a polymer composition according to the invention as a scratch resistant material.
The polypropylene homopolymer used in the polymer resin blend is a conventional substantially isotactic polypropylene. Typically it will have a MFI of from 2 to 50, more usually 4 to 40 and commonly 5 to 20, dg.min.sup.-1 (at 230.degree. C., 2.16 kg load). As is described in more detail below, within the invention there are compositions having differing relative levels of filler. We have found that within the overall MFI ranges different ranges are appropriate to such different filler levels as is set out below.
The low density polyethylene used in the polymer resin blend is a polyethylene having a density in the range about 0.890 to about 0.935. This range corresponds the polymers commonly described as Low Density PolyEthylene (LDPE) and Very Low Density PolyEthylene (VLDPE). Among LDPE polymers, so-called Linear Low Density PolyEthylene (LLDPE) polymers are particularly useful. The MFI of the low density polyethylene polymer is typically from 2 to 40, more usually from 4 to 35 and most commonly from 15 to 25, dg.min.sup.-1 (at 190.degree. C., 2.16 kg load).
Considered as a two component blend, the polypropylene and low density polyethylene are used in relative proportions within the range about 70 to about 95% by weight polypropylene and about 30 to about 5 by weight polyethylene, more usually 80 to 90% polypropylene and 20 to 10% polyethylene and most commonly about 85% polypropylene and polyethylene.
The "plate like filler" is a filler whose particles have a
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Grasmeder John R.
Lindsay Christopher I.
BASF - Aktiengesellschaft
Yoon Tae
LandOfFree
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