Thermoplastic molding materials based on highly effective...

Details Thermoplastic molding materials based on highly effective... Thermoplastic molding materials based on highly effective...

2001-01-08

2002-12-03

Mullis, Jeffrey (Department: 1711)

Synthetic resins or natural rubbers -- part of the class 520 ser

Synthetic resins

Processes of preparing a desired or intentional composition...

C525S063000, C525S066000, C525S067000, C525S071000, C525S193000

Reexamination Certificate

active

06489379

ABSTRACT:

The invention provides thermoplastic moulding compositions of the ABS type containing highly effective graft rubber components obtained by emulsion polymerisation while using special initiator systems and observing defined reaction conditions.
Moulding compositions of the ABS type are two-phase plastics materials consisting of
I) a thermoplastic copolymer of styrene and acrylonitrile in which the styrene can be replaced completely or partially by &agr;-methyl styrene or methyl methacrylate; this copolymer, also known as SAN resin or matrix resin, forms the external phase;
II) at least one graft polymer produced by graft reaction of one or more of the monomers mentioned under I on butadiene—homo—or copolymer (“graft base”). This graft polymer (“elastomer phase” or “graft rubber”) forms the dispersed phase in the matrix resin.
With an identical matrix, the viscosity of an ABS moulding composition is determined substantially by the graft rubber. However, the viscosity required for markedly stressed mouldings cannot always be achieved with the necessary reliability using conventional ABS moulding compositions, particularly if very high viscosities are demanded at low temperatures or if these requirements are met only at the cost of other properties also required, for example rigidity or processing behaviour.
There is therefore a need for graft rubbers on the basis of which ABS moulding compositions with very high viscosities at room temperature and at low temperature can be produced without impairing the other properties, in particular rigidity and processibility.
Furthermore, it should also be possible to produce these graft rubbers on the basis of more finely divided rubber bases so that mouldings with high surface lustre can also be obtained if necessary.
It has accordingly been found that moulding compositions of the ABS type with excellent viscosities at room temperature and low temperature are obtained without adversely affecting the other properties if the graft rubber employed is produced while using special combinations of initiator systems and while maintaining defined reaction conditions.
The production of graft rubbers using various initiator systems is known. Thus, numerous documents, for example EP-A 154 244, describe the use of potassium persulfate as initiator. Documents such as, for example, EP-A 745 623 (see also the literature quoted therein) describe the use of special redox systems or of azo initiators. Although initiator systems of this type lead to graft polymers which lead to good properties in thermoplastic moulding compositions for special requirements, good viscosities at high and low temperatures are not achieved to the adequate extent while maintaining the other properties.
The invention provides thermoplastic moulding compositions of the ABS type containing
A) at least one elastic/thermoplastic graft polymer obtained by radical emulsion polymerisation of resin-forming vinyl monomers, preferably of styrene or acrylonitrile, wherein styrene and/or acrylonitrile can be completely or partially replaced by &agr;-methyl styrene, methyl methacrylate or N-phenylmaleimide, in the presence of rubber existing in latex form with a glass transition temperature ≦0° using an initiator combination consisting of a redox initiator system and a persulfate compound and
B) at least one copolymer of styrene and acrylonitrile, wherein styrene and/or acrylonitrile can be completely or partially replaced by &agr;-methyl styrene or methyl methacrylate or N-phenylmaleimide,
characterised in that the graft polymer A) is produced by supplying the monomers to the rubber latex, the redox initiator components are added at the beginning of the graft polymerisation reaction in quantities of 0.1 to 2.5 wt. %, preferably of 0.2 to 2.0 wt. % and particularly preferably of 0.5 to 1.5 wt. % (based on the monomers added up to the moment of addition of persulfate compound in each case), a persulfate compound is added after an addition of monomers of 10 to 95 wt. %, preferably 20 to 85 wt. %, in particular 20 to 80 wt. % particularly preferably 30 to 75 wt. % and quite particularly preferably 35 to 70 wt. % (based on total quantity of monomer in each case), in quantities of 0.05 to 1.5 wt. %, preferably of 0.08 to 1.2 wt. % and particularly preferably of 0.1 to 1.0 wt. % (based on the monomers added from the moment of addition of persulfate compound in each case) and polymerisation is carried out until completion.
In principle, any rubber-like polymers existing in the form of an emulsion with a glass transition temperature lower than 0° C. are suitable as rubbers for producing the elastic/thermoplastic graft polymers according to the invention.
Examples of suitable polymers include
diene rubbers, i.e. homopolymers of conjugate dienes containing 4 to 8 carbon atoms such as butadiene, isoprene, chloroprene or copolymers thereof with up to 60 wt. %, preferably up to 30 wt. % of a vinyl monomer, for example acrylonitrile, methacrylonitrile, styrene, &agr;-methyl styrene, halogen styrenes, C
1
-C
4
alkyl styrenes, C
1
-C
8
alkyl acrylates, C
1
-C
8
alkyl methacrylates, alkyleneglycol diacrylates, alkyleneglycol dimethacrylates, divinyl benzene;
acrylate rubbers, i.e. homo- and copolymers of C
1
-C
10
alkyl acrylates, for example homopolymers of ethyl acrylate, butyl acrylate or copolymers containing up to 40 wt. %, preferably not more than 10 wt. % of monovinyl monomers, for example styrene, acrylonitrile, vinylbutylether, acrylic acid (ester), methacrylic acid (ester), vinyl sulfonic acid. It is preferable to use acrylate rubber homo- or copolymers which contain from 0.01 to 8 wt. % of divinyl or polyvinyl compounds and/or N-methylolacrylamide or N-methylolmethacrylamide or other compounds acting as crosslinking agents, for example divinylbenzene, triallylcyanurate.
Polybutadiene rubbers, SBR rubbers with up to 30 wt. % of styrene incorporated by polymerisation and acrylate rubbers, in particular those having a core/shell structure, for example as described in DE-OS 3 006 804, are preferred.
Latices having average particle diameters d
50
of 0.05 to 2.0 &mgr;m, preferably of 0.08 to 1.0 &mgr;m and particularly preferably of 0.1 to 0.5 &mgr;m can be used for producing the graft polymers according to the invention. The gel contents of the rubbers used can be varied in wide limits and preferably lie between 30 and 95 wt. % (determined by the wire cage method in toluene (cf. Houben-Weyl, Methoden der Organischen Chemie, Makromolekulare Stoffe, part 1, page 307 (1961) Thieme Verlag Stuttgart)).
Quite particularly preferred are mixtures of rubber latices having
a) average particle diameters d
50
≦320 nm, preferably 260 to 310 nm, and gel contents ≦70 wt. %, preferably 40 to 65 wt. % and
b) average particle diameters d
50
≧370 nm, preferably 380 to 450 nm, and gel contents ≦70 wt. %, preferably 75 to 90 wt. %.
The rubber latex (a) preferably has a particle size distribution range of 30 to 100 nm, particularly preferably of 40 to 80 nm, and the rubber latex (b) of 50 to 500 nm, particularly preferably of 100 to 400 nm (measured as d
90
-d
10
value from the integral particle size distribution in each case).
The mixtures contain the rubber latices (a) and (b) preferably in a ratio by weight of 90:10 to 10:90, particularly preferably 60:40 to 30:70 (based on the respective solids content of the latices in each case).
The average particle diameters are determined by ultracentrifuge (cf. W. Scholtan, H. Lange: Kolloid-Z. u Z. Polymere 250, pages 782 to 796 (1972).
The values given for the gel content are determined by the wire cage method in toluene (cf. Houben-Weyl, Methoden der Organischen Chemie, Makromolekulare Stoffe, part 1, page 307 (1961) Thieme Verlag Stuttgart).
The rubber latices used can be produced by emulsion polymerisation and the necessary reaction conditions, auxiliaries and production techniques are basically known.
It is also possible initially to produce a finely divided rubber polymer by known methods and then to agglomerate it in a known manner to adjust the necessar

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