Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – At least one aryl ring which is part of a fused or bridged...
Reexamination Certificate
2001-03-21
2003-01-21
Yoon, Tae H. (Department: 1714)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
At least one aryl ring which is part of a fused or bridged...
C524S284000, C524S504000, C523S201000, C523S202000, C525S064000
Reexamination Certificate
active
06509402
ABSTRACT:
The invention provides antistatic, thermoplastic moulding compositions with improved properties, based on optionally rubber-modified polymers of vinyl aromatics, e.g. styrene and/or &agr;-methyl styrene and acrylonitrile and/or acrylates, which contain a special acid-reacting polyether as the antistatic agent.
Most plastics, because of their chemical constitution, are electrical insulators with a high electrical surface resistance. This readily leads to the electrostatic charging of the plastics surfaces during the processing and use of such compositions. This results in various problems and drawbacks in practice, e.g. rapid soiling and accumulation of dust on plastics parts, with characteristic dust patterns forming on the surface. This is also true to a particular extent for optionally rubber-modified polymers of vinyl aromatics and acrylonitrile used as moulding compositions, e.g. styrene-acrylonitrile copolymers (SAN) and graft copolymers of styrene and acrylonitrile on polybutadiene (ABS).
The provision of antistatic properties in such moulding compositions is known. Alkyl and aryl sulfonates (DE-OS 1 544 652), amines (DE-PS 1 258 083), quaternary ammonium salts, amides, phosphoric acids and alkyl and aryl phosphonates, for example, are recommended as antistatic agents.
These antistatic moulding compositions still have drawbacks. Many of the antistatic agents mentioned are of low effectiveness and have to be used in high concentrations; many of these low molecular-weight compounds migrate to the surface. Mouldings with inhomogeneous and stained surfaces, or even surface deposits, are therefore often obtained. In many cases, mechanical properties such as e.g. heat resistance or modulus of elasticity are also severely impaired.
Even pure polyethers, as proposed e.g. in DE-PS 1 244 398 as high molecular-weight antistatic agents, have to be used in quantities of approx. 5 wt. % or more for the reliable provision of antistatic properties in styrene polymers. This leads to stained and greasy surfaces and even surface deposits on the finished parts.
Although the antistatic effect can be improved by graft copolymerisation of styrene and acrylonitrile on these polyethers, as described in EP-A-0 061 692, yellow to brown discolorations occur when processing styrene polymers containing such antistatic agents at temperatures of >150° C.
The use of polyethers modified with radical formers according to EP-A-0 278 349 to impart antistatic properties to styrene polymers leads to improved effectiveness compared with the unmodified polyether, but the application is critical in respect of a quantitative decomposition of the radical former, characterised by high energy requirements and long reaction times, during the modification of the polyether to avoid undesirable side effects, especially discolorations and negative effects on the flow properties when soft and on the toughness of the moulding compositions containing them.
The object of the present invention was therefore to provide thermoplastic moulding compositions based on vinyl aromatic polymers with polyethers as antistatic agents without the above-mentioned disadvantages.
Surprisingly, it was found that the desired thermoplastic moulding compositions are obtained with very good antistatic properties if certain acid-reacting polyethers, preferably polyethers treated with certain carboxylic acids, are used as antistatic agents.
The invention provides antistatic, thermoplastic moulding compositions containing
I.) 99.8 to 95 parts by weight, preferably 99.5 to 96 parts by weight and particularly preferably 99 to 97 parts by weight of an optionally rubber-modified polymer of vinyl aromatics and optionally other vinyl monomers consisting of
A) 0 to 100 wt. % of one or more graft copolymers of 10 to 95 wt. % (based on A) rubber and 90 to 5 wt. % (based on A) monomers graft copolymerised on to the rubber, with styrene, &agr;-methyl styrene, ring-substituted styrene, methyl methacrylate, (meth)acrylonitrile, maleic anhydride, N-substituted maleimides or mixtures thereof being graft copolymerised as the monomers and the rubbers having glass transition temperatures of <10° C. and being present in the form of at least partially crosslinked particles with an average particle diameter (d
50
) of 0.05 to 20 &mgr;m and
B) 100 to 0 wt. % of one or more thermoplastic vinyl polymers, the monomers being selected from the series styrene, &agr;-methyl styrene, ring-substituted styrene, methyl methacrylate, acrylonitrile, methacrylonitrile, maleic anhydride, N-substituted maleimides or mixtures thereof, and
II.) 0.2 to 5 parts by weight, preferably 0.5 to 4 parts by weight and particularly preferably 1 to 3 parts by weight of a polyalkylene ether with molecular weights (number average) of between 500 and 15,000 and a pH of 2.5 to 5.5, preferably of 3.0 to 5.0 (measured as a 5% dispersion in water), which preferably contains carboxyl groups.
The invention also provides a process for imparting antistatic properties to optionally rubber-modified polymers of vinyl aromatics and other vinyl monomers, as described above, which is characterised in that 0.2 to 5 parts of a polyalkylene ether with molecular weights (number average) of between 500 and 15,000 and a pH of 2.5 to 5.5 (measured as a 5% dispersion in water), which is a reaction product of polyols with one or more alkylene oxides and which is preferably prepared by mixing with 0.01 to 3 wt. %, preferably 0.02 to 2 wt. % and particularly preferably 0.05 to 1 wt. % (based on the quantity of polyalkylene ether) of at least one carboxylic acid and/or carboxylic anhydride and stirring at temperatures greater than or equal to room temperature, preferably at 20° C. to 100° C., particularly preferably 25 to 90° C. and especially 30° C. to 80° C., are added to 99.8 to 95 parts by weight of polymer I.).
Optionally rubber-modified copolymers of vinyl aromatics and other vinyl monomers (I) within the meaning of the invention are mixtures of (A) 0 to 100, preferably 1 to 60, especially 5 to 50 wt. % of one or more graft copolymers and (B) 100 to 0, preferably 40 to 99, especially 50 to 95 wt. % of one or more thermoplastic vinyl polymers.
Graft copolymers (A) within the meaning of the invention are those in which either styrene, &agr;-methyl styrene, methyl methacrylate or a mixture of 95 to 50 wt. % styrene, &agr;-methyl styrene, ring-substituted styrene, methyl methacrylate or mixtures thereof and 5 to 50 wt. % (meth)acrylonitrile, maleic anhydride, N-substituted maleimides or mixtures thereof are graft copolymerised on to a rubber.
Suitable rubbers are practically all rubbers with glass transition temperatures of <10° C. Examples are polybutadiene, polyisoprene, styrene-butadiene copolymers, acrylonitrile-butadiene copolymers, acrylic rubbers, EPM rubbers (ethylene-propylene rubbers) and EPDM rubbers (ethylene-propylene-diene rubbers) containing an unconjugated diene, such as e.g. 1,5-hexadiene or norbornadiene, in small quantities as the diene. Diene rubbers are preferred.
The graft copolymers (A) contain 10 to 95 wt. %, especially 20 to 70 wt. %, rubber and 90 to 5 wt. %, especially 80 to 30 wt. %, graft copolymerised monomers. The rubbers are present in these graft copolymers in the form of at least partially crosslinked particles with an average particle diameter (d
50
) of 0.05 to 20 &mgr;m, preferably 0.1 to 2 &mgr;m and particularly preferably 0.1 to 0.8 &mgr;m.
Graft copolymers of this type may be produced by radical graft copolymerisation of styrene, &agr;-methyl styrene, ring-substituted styrene, (meth)acrylonitrile, methyl methacrylate, maleic anhydride, N-substituted maleimide in the presence of the rubbers to be grafted. Preferred production processes are emulsion, solution, bulk or suspension polymerisation.
The average particle diameter d
50
is the diameter above and below which 50 wt. % of the particles lie. It can be determined by ultracentrifuge measurement (W. Scholtan, H. Lange, Kolloid-Z. und Z. Polymere 250 (1972), 782-796).
The production of the copolymers and graft copolymers is g
Bayer Aktiengesellschaft
Gil Joseph C.
Mrozinski John E.
Preis Aron
Yoon Tae H.
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