Polymer Mixtures With a Mat Surface

The invention relates to polymer mixtures with a mat surface, based on graft polymers with acid functions and thermoplastic resins with basic functions.

Polymer blends with elastic-thermoplastic properties and a mat surface are of increasing interest for fields of application where high toughness and at the same time low gloss is required, thus, for example, for components in automobile interiors or for equipment coverings.

Attempts have hitherto been made to prepare such polymer blends by using large rubber particles (compare, for example, U.S. Pat. No. 4,169,869) or using rubbers which are not crosslinked or only slightly cross-linked (compare, for example, DE-OS (German Published Specification No. 2,057,936), as the graft base for the graft polymers.

However, in all these attempts the desired nature of the surface is acquired with the loss of product qualities which are similarly desirable, such as, for example, notched impact strength, hardness or processability.

The invention relates to mat polymer mixtures of (A) 99.95 to 0.05% by weight, preferably 85 to 15% by weight, of a graft product of a mixture of 40 to 99.9 parts by weight of styrene, .alpha.-methylstyrene, p-methylstyrene, vinyltoluene, methyl methacrylate or mixtures thereof, 40 to 0.1 parts by weight of a monoacid or diacid containing a polymerisable double bond and 0 to 49 parts by weight of acrylonitrile on a rubber in particle form with an average particle diameter (d.sub.50) of 0.05 to 20.0 .mu.m and a glass transition temperature of .ltoreq.10.degree. C., with a total rubber content of 5 to 80% by weight, and (B) 0.05 to 99.95% by weight, preferably 15 to 85% by weight, of a thermoplastic resin containing 0.1to 40% by weight of incorporated units of a basic monomer containing vinyl groups.

Virtually all the rubbers with glass transition temperatures of .ltoreq.10.degree. C. can be used as the graft base for the graft product (A). Examples are polybutadiene, polyisoprene, styrene/butadiene copolymers, acrylonitrile/butadiene copolymers, acrylate rubbers, EPM rubbers (ethylene/propylene rubbers) and EPDM rubbers (ethylene/propylene/diene rubbers which contain small amounts of a nonconjugated diene, such as, for example, hexa-1,5-diene or norbornadiene, as the diene).

These rubbers must be in the form of particles with an average diameter (d.sub.50) of 0.05 to 20.0 .mu.m, preferably 0.1 to 2.0 .mu.m and particularly preferably 0.1 to 0.8 .mu.m.

The graft product (A) is prepared in a manner which is known per se by grafting polymerisation in emulsion, suspension or solution or by a combination of these processes.

It contains 5 to 80% by weight of rubber, in particular 20 to 60% by weight, and has a gel content, measured in acetone at 25.degree. C., of 30 to 90% by weight, in particular 40 to 80% by weight.

Examples of suitable grafting monomers are styrene, .alpha.-methylstyrene, p-methylstyrene, vinyltoluene, acrylonitrile, methacrylonitrile, methyl methacrylate, vinylacetate or mixtures thereof, in particular mixtures of acrylonitrile with styrene.

The graft product (A) is prepared by polymerisation of these monomers in the presence of the diene or acrylate rubbers, a polymerisable monoacid or diacid, for example acrylic acid, methacrylic acid, maleic acid, fumaric acid, itaconic acid, crotonic acid, cinnamic acid, vinylsulphonic acid, vinylbenzenesulphonic acid or mixtures thereof, being required as further monomer components, aliphatic C.sub.3 -C.sub.10 -or aromatic C.sub.9 -C.sub.18 -mono- or di-carboxylic acids being pre- ferred.

Examples of monomer components which are suitable for building up the thermoplastic resin (B) are styrene, .alpha.methylstyrene, p-methylstyrene, vinyltoluene, acrylonitrile, methacrylonitrile, methyl methacrylate, vinyl acetate, N-phenylmaleimide and mixtures thereof, in particular mixtures of acrylonitrile and styrene.

The thermoplastic resin (B) is preferably prepared by polymerisation of these monomers in emulsion, suspension or solution in a manner which is known per se, a basic compound containing vinyl groups (for example 2-vinylpyridine, 3-vinylpyridine, 4-vinylpyridine, N-vinylimidazole, p-dimethylaminostyrene, 4-vinylpyrimidine, N-vinylcarbazole, N-vinylpyrrole, N-vinylindole, dimethylaminoethyl methacrylate or mixtures thereof), being required as a further monomer component.

In the preparation of the graft product (A) and the thermoplastic resin (B) by emulsion polymerisation, it is necessary to take into consideration the acid or basic monomer when choosing the emulsifiers. If acid monomers are present, the polymerisation must be carried out in an acid medium, and thus using emulsifiers which are still effective at pH values below 7. Care must also be taken during working up, that is to say during precipitation of the latices, that the acid or basic character of the graft polymers is retained.

The polymer blends according to the invention can be obtained by mixing their constituents (A) and (B) with one another at elevated temperatures, in particular at temperatures of 100.degree. C. to 280.degree. C., for example in kneaders or on roll mills or screw machines. If (A) and (B) are obtained as dispersions, suspensions or solutions, these can be mixed and worked up together.

The customary amounts of the usual additives, such as antioxidants, anti-ageing agents, lubricants, flameproofing agents, fillers, pigments and antistatics, can be added to the blends.

The blends according to the invention are mat, flexible, thermoplastic moulding materials with good flow properties during processing by extrusion, calendering and injection moulding. They can be processed to mat moulded articles, but are also suitable as modifiers for other plastics, in particular for thermoplastics, such as acrylonitrile/butadiene/styrene terpolymers (ABS), methyl methacrylate/butadiene/styrene terpolymers (MBS), styrene/acrylonitrile copolymers (SAN), .alpha.-methylstyrene/acrylonitrile copolymers, polystyrene, h:gh impact polystyrene (HIPS), polymethyl methacrylate, polyvinyl chloride, polycarbonate, polycarbonate/ABS mixtures, polyphenylene oxide, polyphenylene oxide/HIPS mixtures, polyamides, for example polyamide 6 and polyamide 66, and polyesters, for example polyethylene terephthalate and polybutylene terephthalate. Those mixtures according to the invention which contain a large amount of rubber--about 50 to 70%--are preferably used as "matting modifiers". Their amount is in general 5 to 40% by weight, based on the total modified product.

The following examples illustrate the invention. Parts are parts by weight and always relate to the solid constituents or polymerisable constituents.

G parts of rubber base (in the form of a latex with a solids content of between 35 and 50% by weight) are warmed to 65.degree. C. in a reactor, after which 0.5 part of potassium persulphate (dissolved in 20 parts of water) is added. M parts of the monomer mixture stated in Table 1 and 2 parts of the sodium salt of C.sub.9 -C.sub.18 -alkylsulphonic acids, as an emulsifier (dissolved in 25parts of water), are then metered in over a period of 4 hours, during which the grafting reaction takes place. After an after-reaction time, the graft latex is coagulated, after addition of 1.2 parts of antioxidant, in an aqueous magnesium sulphate/acetic acid solution. The resulting powder is washed with water, an acid solution and again with water and dried at 70.degree. C. in vacuo.

250 parts of water, 2 parts of the sodium salt of disproportionated abietic acid, as the emulsifier, and 0.3 part of potassium sulphate are warmed to 65.degree. C. in a reactor, after which 100 parts of the monomer mixture stated in Table 2 and the amount of tert.-dodecylmercaptan required to establish an average molecular (Mw) of about 80,000 to 90,000 are metered in over a perid of 4 hours. After an after-reaction time, the latex is coagulated, after addition of 1.2 parts of autioxidant, in an aqueous magnesium sulphate/acetic solution. The resulting powder is washed with water, a basic solution and again with water and dried at 70.degree. C. in vacuo.

P parts of the graft product (A) and H parts of the thermoplastic resin (B) are mixed with 3 parts of a lubricant in a kneader and the mixture is then injection-moulded to a small standard bars, a sheet (for evaluation of the surface) and a helix (for evaluation of the flow distance). Some of the material was processed to sheets by extrusion. The notched impact strength was measured at room temperature (a.sub.k.sup.RT) and at -40.degree. C. (a.sub.k.sup.-40.degree. C.) in accordance with DIN 53 453 (units: kJ/m.sup.2), the ball indentation hardness (H.sub.c) was measured in accordance with DIN 53 456 (units: N/mm.sup.2), the heat distortion point (Vicat B) was measured in accordance with DIN 53 460 (units: .degree. C.) and the flow distance was measured at 220.degree. C. on a helix about 8 mm wide and about 2 mm thick (units: cm). The gloss was measured in accordance with DIN 67 530 on a flat sheet with a reflecting angle of 60.degree. (reflectometer value), with the aid of a "Multi-Gloss" multi-angle reflectometer from Byk-Mallinckrodt (see Table 3).

As can be seen from Table 3, only a mixture of graft products with copolymerised acid monomer components and thermoplastic resins with incorporated basic monomers leads to uniformly mat surfaces, both by injection moulding and by extrusion processing, without an adverse influence on the other properties. In addition, an improved heat distortion point and a greater hardness (moulding materials 5 to 9) are thereby achieved. A mixture with a thermoplastic resin modified by basic monomers with an unmodified graft product leads to high-gloss mouldings (moulding materials 1 to 3), and although a mixture of a graft product modified by acid monomers with an unmodified thermoplastic resin also gives a mat surface, reduced flow properties and a decrease in the notched impact strength occur at the same time (moulding material 4).