ASA molding compounds for producing shaped parts

Details ASA molding compounds for producing shaped parts ASA molding compounds for producing shaped parts

2001-02-14

2004-01-27

Mullis, Jeffrey (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...

C525S067000, C525S068000, C525S069000, C525S070000

Reexamination Certificate

active

06683133

ABSTRACT:

The invention relates to thermoplastic molding compositions made from a polystyrene-acrylonitrile polymer and from a crosslinked rubber having two or more phases, and to molded materials produced therefrom, and also to a process for producing molded materials by coextrusion.
In certain application sectors for thermoplastic polymer materials, in particular in the internal fitting of automobiles and in household, electrical and sport equipment, there is increasing demand for a non-reflective, matt surface. This may be for decorative or safety reasons, e.g. reduced glare for the driver of the automobile, or to improve performance characteristics—fingerprints are difficult to see on matt surfaces. However, most commercially available impact-modified molding compositions give moldings with glossy surfaces.
Matt moldings can be achieved by surface-treatment of a finished molding with normal gloss, for example by mechanical roughening, such as grinding or brushing, or by etching, solvation or swelling, or by applying a matt coating. However, a factor common to all of these processes is a disadvantageous additional operation on the finished molding.
Moldings with a matt surface may also be produced using tools or molds with a structured surface, but the structuring of the mold wears away comparatively quickly. Inorganic matting agents, such as silica gel or chalk, can be added to polymers, but the disadvantage is impairment of the mechanical properties of the molding.
This adverse effect can be avoided by addition of suitable organic matting agents. They are composed of particles of comparatively large diameter (D>about 0.5 &mgr;m) dispersed in matrix polymers. The particles protrude to some extent from the smooth and therefore glossy surface of the matrix polymer and thus create a diffuse reflection of incident light (scattering), so that to an observer the surface appears matt.
Many applications require polymers which are simultaneously matt and impact-resistant. If a rigid, brittle polymer is to be modified in this way in a single operation the large matting particles must simultaneously have elastomeric properties. To make the matting rubber particles compatible at least to some extent with the nonelastic matrix polymer the former usually have to be provided with a graft shell made from a polymer with some degree of compatibility.
EP-A 269 324 discloses graft polymers of this type which have large particle diameters and are elastomeric and also have matting action. However, the process to prepare the particles is very laborious. A first step prepares elastomeric core particles, and in a subsequent step these are swollen with freshly added monomer, and the polymerization is then continued. This procedure is repeated, if desired, until the required particle size has been achieved, and the graft shell is then produced.
EP-A 576 960 gives another way of achieving matt and impact-resistant molded material compositions, by producing relatively large particles through the agglomeration of small particles of graft polymers whose graft core comprises acid groups and whose shell comprises basic groups, or vice versa. However, in some cases only a limited matting effect is attainable by this route.
A further requirement placed upon the surface properties of polymer molded materials is generally that these are uniform, free from flow lines, streaks and marks.
It is an object of the present invention to provide thermoplastic molding compositions whose surface properties are improved and which are both matt and free from flow lines.
We have found that this object is achieved by means of thermoplastic molding compositions comprising
A) from 20 to 90% by weight, preferably from 30 to 80% by weight, particularly preferably from 40 to 75% by weight, of a thermoplastic polymer composed of units deriving from
a1) from 60 to 85% by weight, preferably from 63 to 81% by weight, particularly preferably from 65 to 80% by weight, of styrene and/or substituted styrene, in particular &agr;-methylstyrene,
a2) from 15 to 40% by weight, preferably from 19 to 37% by weight, particularly preferably from 20 to 35% by weight, of acrylonitrile, and
a3) from 0 to 25% by weight, preferably from 0 to 20% by weight, particularly preferably from 0 to 18% by weight, of other monomers copolymerizable with a1 and a2, and
B) from 10 to 80% by weight, preferably from 20 to 70% by weight, particularly preferably from 25 to 60% by weight, of a crosslinked graft rubber having two or more phases and composed of
b1) from 30 to 90% by weight, preferably from 40 to 70% by weight, particularly preferably from 45 to 70% by weight, of a phase prepared by emulsion or miniemulsion polymerization of
b1.1) from 80 to 100% by weight, preferably from 90 to 100% by weight, particularly preferably from 95 to 100% by weight, of an acrylate, and
b1.2) from 0 to 20% by weight, preferably from 0 to 10% by weight, particularly preferably from 0 to 5% by weight, of other monomers, and
b2) from 10 to 70% by weight, preferably from 30 to 60% by weight, particularly preferably from 30 to 55% by weight, of at least one other phase prepared by polymerizing
b2.1) from 60 to 85% by weight, preferably from 70 to 80% by weight, of styrene,
b2.2) from 15 to 35% by weight, preferably from 20 to 30% by weight, of acrylonitrile and
b2.3) from 90 to 20% by weight of other monomers, in the presence of the first phase.
In the thermoplastic molding compositions the polymer A has a viscosity number, measured on a 0.5% strength solution in dimethylformamide at 23° C., of from 50 to 70 ml/g, preferably from 55 to 65 ml/g, and at least 80% by number, preferably at least 85% by number, particularly preferably at least 90% by number, of the rubber particles B in the dispersion, after the preparation thereof, have a diameter of <0.2 &mgr;m, preferably <0.18 &mgr;m, particularly preferably <0.15 &mgr;m.
This class of products is known as ASA since it is composed of acrylonitrile, styrene and an acrylate.
Surprisingly, it has been found that by processing molding compositions made from a polystryrene-acrylonitrile matrix and, embedded into this, crosslinked rubber particles, a rough surface is obtained which scatters light and therefore has a matt appearance, with small-diameter rubber particles dispersed in the polystyrene-acrylonitrile matrix. It has also been found that the surface of the resultant molded materials after coextrusion with other plastics, in particular ABS, is free from flow lines if a free-flowing polystyrene-acrylonitrile matrix is used.
Component A in the novel thermoplastic molding compositions is from 20 to 90% by weight, preferably from 30 to 80% by weight, particularly preferably from 40 to 75% by weight, of a thermoplastic polymer composed of units deriving from
a1) from 60 to 85% by weight, preferably from 63 to 81% by weight, particularly preferably from 65 to 80% by weight, of styrene and/or substituted styrene, in particular &agr;-methylstyrene,
a2) from 15 to 40% by weight, preferably from 19 to 37% by weight, particularly preferably from 20 to 35% by weight, of acrylonitrile, and
a3) from 0 to 25% by weight, preferably from 0 to 20% by weight, particularly preferably from 0 to 18% by weight, of other monomers copolymerizable with a1 and a2.
Other monomers a3) whose use is preferred are (meth)acrylic acid and/or its derivatives, in particular methyl methacrylate, acrylamide and/or methacrylamide, and also maleic anhydride and/or phenylmaleimide.
Component B in the thermoplastic molding compositions is from 10 to 80% by weight, preferably from 20 to 70% by weight, particularly preferably from 25 to 60% by weight, of a crosslinked graft rubber having two or more phases and composed of
b1)from 30 to 90% by weight, preferably from 40 to 70% by weight, particularly preferably from 45 to 70% by weight, of a phase prepared by emulsion or miniemulsion polymerization of
b1.1) from 80 to 100% by weight, preferably from 90 to 100% by weight, particularly preferably from 95 to 100% by weight, of an acrylate, and
b1.2) from 0 to 20% by weight,

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