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
2001-10-12
2003-10-28
Wu, David W. (Department: 1713)
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...
C525S064000, C525S067000, C264S102000
Reexamination Certificate
active
06639005
ABSTRACT:
This invention relates to thermoplastic moulding compositions to which antistatic properties are imparted and which exhibit improved colour stability during processing, and which are based on polymers, which are optionally modified with rubber, of aromatic vinyl compounds, e.g. styrene and/or &agr;-methylstyrene and acrylonitrile and/or acrylates, which contain a specially formulated combination comprising an antistatic agent and a phenolic antioxidant.
On account of their chemical constitution, most plastics are electrical insulators which exhibit a high electrical surface resistance. During the processing and use of compositions such as these, this readily results in electrostatic charging of the plastics surfaces. In practice this often leads to defects and contamination, e.g. to the rapid soiling of plastics parts and to the contamination thereof by dust, whereupon characteristic dust patterns are formed at the surface. This also applies in particular to polymers of aromatic vinyl compounds and acrylonitrile which are optionally modified with rubber and which are used as moulding compositions, e.g. styrene-acrylonitrile copolymers (SAN) and graft polymers of styrene and acrylonitrile on polybutadiene (ABS).
It is known that antistatic properties can be imparted to moulding compositions such as these. Examples of recommended antistatic agents include alkyl and aryl sulphonates (DE-OS 1 544 652), amines (DE-PS 1 258 083), quaternary amnonium salts, amides and phosphoric acids, as well as alkyl and aryl phosphonates and polyethers (DE-PS 1 244 398) and products produced by the graft polymerisation of styrene and acrylonitrile on to polyethers such as these (EP-A 61 692).
Polyethers modified with radical-formers have proved particularly useful (EP-A 278 349).
However, when these materials are used, just as when unmodified polyethers are used as antistatic agents, unsatisfactory colour stability of moulding compositions to which antistatic properties are imparted can occur during processing, despite the use of polymer starting materials which are stabilised in the optimum manner.
Surprisingly, it has now been found that a very good combination of an antistatic effect and a high level of colour stability is achieved, without a negative effect on other properties, if a specially formulated combination comprising an antistatic agent based on polyethers and a special phenolic antioxidant is used.
The present invention relates to thermoplastic moulding compositions containing
I.) 99.90 to 95 parts by weight, preferably 99.75 to 96 parts by weight, and most preferably 99.50 to 97 parts by weight, of a polymer, which is optionally modified with rubber, of aromatic vinyl compounds and optionally of other vinyl monomers, which consists of
A) 0 to 100 % by weight of one or more graft polymers formed from 10 to 95 % by weight (with respect to A) of rubber and 90 to 5 % by weight (with respect to A) of monomers which are graft-polymerised on to the rubber, wherein styrene, &agr;-methylstyrene, styrenes comprising a substituted nucleus, methyl methacrylate, (meth)acrylonitrile, maleic anhydride, N-substituted maleinimide or mixtures thereof are graft-polymerised as monomers and the rubbers have glass transition temperatures <10° C. and are 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 % by weight of one or more thermoplastic vinyl polymers, wherein the monomers are selected from the series comprising styrene, &agr;-methylstyrene, styrenes comprising a substituted nucleus, methyl methacrylate, acrylonitrile, methacrylonitrile, maleic anhydride, N-substituted maleinimide or mixtures thereof, and
II.) 0.10 to 5 parts by weight, preferably 0.25 to 4 parts by weight, and most preferably 0.5 to 3 parts by weight, of a mixture of
a) a component selected from at least one of the group comprising unmodified polyalkylene ethers, polyalkylene ethers modified with radical-formers, and polyalkylene ethers modified with acid groups (each with (number average) molecular weights between 500 and 20,000), and
b) a phenolic antioxidant selected from octadecyl-3-(3′, 5′-di-tert.-butyl-4-hydroxyphenyl) propionate and 2,4-di-methyl-6-(1-methylpentadecyl)-phenol or mixtures thereof, wherein the ratio by weight of (a):(b) is 20:1 to 1:1.
The present invention further relates to a process for producing improved polymers, which are optionally modified with rubber, of aromatic vinyl compounds and other vinyl monomers as described above, which is characterised in that 0.10 to 5 parts by weight of a mixture of a) a component selected from at least one of the group comprising unmodified polyalkylene ethers, polyalkylene ethers modified with radical-formers, and polyalkylene ethers modified with acid groups (each with (number average) molecular weights between 500 and 20,000), and b) a phenolic antioxidant selected from octadecyl-3-(3′, 5′-di-tert.-butyl-4-hydroxyphenyl) propionate and 2,4-di-methyl-6-(1-methylpentadecyl)-phenol or mixtures thereof, wherein the ratio by weight of (a):(b) is 20:1 to 1:1, is added to 99.90 to 95 parts by weight of polymer I.) and is mixed in the molten state.
In the sense of the present invention, copolymers (I), which are optionally modified with rubber, of aromatic vinyl compounds and other vinyl monomers are mixtures of A) 0 to 100 % by weight of one or more graft polymers and (B) 100 to 0 % by weight of one or more thermoplastic vinyl polymers. Graft polymers (A) in the sense of the invention are those in which either styrene, &agr;-methylstyrene, methyl methacrylate or a mixture of 95 to 50 % by weight styrene, &agr;-methylstyrene, styrenes comprising a substituted nucleus, methyl methacrylate or mixtures thereof and 5 to 50 % by weight (meth)acrylonitrile, maleic anhydride, N-substituted maleimide or mixtures thereof are graft-polymerised on to a rubber.
Suitable rubbers include practically all rubbers which have glass transition temperatures <10° C. Examples comprise polybutadiene, polyisoprene, styrene-butadiene copolymers, acrylonitrile-butadiene copolymers, acrylate rubbers, EPM rubbers, (ethylene-propylene rubbers), and EPDM rubbers (ethylene-propylene-diene rubbers) which contain, as the diene, an unconjugated diene such as 1,5-hexadiene or norbornadiene in small amounts. Diene rubbers are preferred.
Graft polymers (A) contain 10 to 95 % by weight, particularly 20 to 70 % by weight, of rubber and 90 to 5 % by weight, particularly 80 to 30 % by weight, of graft-copolymerised monomers. In these graft copolymers, the rubbers are present in the form of at least partially crosslinked particles with an average particle diameter (d
50
) from 0.05 to 20 &mgr;m, preferably from 0.1 to 2 &mgr;m, and most preferably from 0.1 to 0.8 &mgr;m.
The average particle diameter d
50
is the diameter above and below which 50 % by weight of the particles are to be found in each case. It can be determined by means of ultracentrifuge measurements (W. Scholtan, H. Lange, Kolloid-Z. and Z. Polymere 250 (1972), 782-796).
Graft copolymers of this type can be produced by the radical-initiated graft copolymerisation of styrene, &agr;-methylstyrene, styrenes comprising a substituted nucleus, (meth)acrylonitrile, methyl methacrylate, maleic anhydride or N-substituted maleinimide in the presence of the rubber on to which grafting is to occur. The preferred methods of production are emulsion, solution, bulk or suspension polymerisation.
Copolymers (B) can be synthesised by polymerisation from the graft monomers for (A) or from similar monomers, and can be synthesised in particular from styrene, &agr;-methylstyrene, styrenes comprising a substituted nucleus, acrylonitrile, (meth)acrylonitrile, methyl methacrylate, maleic anhydride, vinyl acetate, N-substituted maleinimide or mixtures thereof. These copolymers are preferably copolymers which are formed from 95 to 50 , preferably 60 to 80 % by weight styrene, &agr;-methylstyrene, methyl methacrylate or mixtures thereof with 5 to 50, pref
Alberts Heinrich
Eichenauer Herbert
Willenberg Bernd
Hu Henry
Preis Aron
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