Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Mixing of two or more solid polymers; mixing of solid...
Reexamination Certificate
2001-01-08
2004-07-27
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...
C525S066000, C525S067000, C525S070000, C525S071000, C525S080000
Reexamination Certificate
active
06767963
ABSTRACT:
The present invention provides thermoplastic moulding compositions of the ABS type containing specific highly effective graft polymer components which are obtained by emulsion polymerization using specific initiator systems and observing defined reaction conditions.
Moulding compositions of the ABS type are two-phase plastics comprising
I) a thermoplastic copolymer comprising styrene and acrylonitrile, in which the styrene may be wholly or partially replaced by &agr;-methylstyrene or methyl methacrylate; this copolymer, also known as SAN resin or matrix resin, forms the external phase;
II) at least one graft polymer which has been produced by grafting 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 disperse phase in the matrix resin.
With identical matrix the strength of an ABS moulding composition is substantially determined by the graft rubber. For highly stressed moulded parts, however, the strength achievable with conventional ABS moulding compositions is not always sufficient with the necessary reliability, particularly when very high strengths at low temperature are also required or these requirements are only met at the expense of other equally desirable properties such as hardness or processing behaviour.
There is therefore a need for graft polymers on the basis of which ABS moulding compositions with very high strength values at room temperature and at low temperature can be produced without deterioration of the remaining properties, particularly hardness and processability.
Furthermore, it should also be possible to produce these graft rubbers on the basis of finer-particle rubber bases so that moulded parts with a high surface gloss may also be obtained if required.
It has now been found that moulding compositions of the ABS type with excellent strengths at room temperature and low temperature are obtained without serious losses as regards the other properties if the graft polymer used is produced using specific combinations of initiator systems and observing defined reaction conditions.
The production of graft rubbers using various initiator systems is known. Numerous documents including EP-A 154 244, for example, describe the use of potassium persulfate as initiator.
Documents such as EP-A 745 623 (see also the literature cited therein) describe the use of specific redox systems or azo initiators.
Although such initiator systems do indeed lead to graft polymers which lead to good properties for specific requirements in thermoplastic moulding compositions, good strength values at high and low temperatures while retaining the other properties are not, however, achieved to a sufficient extent.
The invention provides thermoplastic moulding compositions of the ABS type containing
A) at least one elastic-thermoplastic graft polymer obtained by radical emulsion polymerization of resin-forming vinyl monomers, preferably of styrene or acrylonitrile, wherein styrene and/or acrylonitrile may be wholly or partially replaced by &agr;-methylstyrene, methyl methacrylate or N-phenylmaleinimide, in the presence of rubber present in latex form with a glass transition temperature≦0° C. using an initiator combination comprising a specific azo compound and a persulfate compound and
B) at least one copolymer comprising styrene and acrylonitrile, wherein styrene and/or acrylonitrile may be wholly or partially replaced by &agr;-methylstyrene or methyl methacrylate or N-phenylmaleinimide,
characterized in that the graft polymer A) is produced by feed of the monomers to the rubber latex, at the start of the graft polymerization reaction the specific azo compound is added in quantities of 0.2 to 3 wt. %, preferably 0.3 to 2.5 wt. % and particularly preferably 0.5 to 2 wt. % (related to the monomers metered in up to the time of the persulfate compound addition in each case), after a monomer addition of 10 to 95 wt. %, preferably 20 to 85 wt. %, particularly preferably 20 to 80 wt. %, in particular 30 to 75 wt. % and most particularly preferably 35 to 70 wt. % (related to total monomer quantity in each case) a persulfate compound is added in quantities of 0.05 to 1.5 wt. %, preferably 0.08 to 1.2 wt. % and particularly preferably 0.1 to 1.0 wt. % (related to the monomers metered in from the time of the persulfate compound addition in each case) and the polymerization is brought to an end, wherein a compound of formula (IIl)
where R=CH
3
, C
2
H
5
, C
3
H
7
, C
4
H
9
,
wherein the isomer groups n-C
3
H
7
, i-C
3
H
7
, n-C
4
H
9
, i-C
4
H
9
, t-C
4
H
9
are included,
or a mixture thereof is used as azo compound.
In principle all rubber-like polymers present in emulsion form, with a glass transition temperature below 0° C. are suitable as rubbers for the production of the elastic-thermoplastic graft polymers according to the invention.
Examples of those which may be used are:
diene rubbers, i.e. homopolymers of conjugated dienes with 4 to 8 C atoms such as butadiene, isoprene, chloroprene or their copolymers with up to 60 wt. %, preferably up to 30 wt. %, of a vinyl monomer, e.g. acrylonitrile, methacrylonitrile, styrene, &agr;-methylstyrene, halogen styrenes, C
1
-C
4
alkyl styrenes, C
1
-C
8
alkyl acrylates, C
1
-C
8
alkyl methacrylates, alkylene glycol diacrylates, alkylene glycol dimethacrylates, divinyl benzene;
acrylate rubbers, i.e. homo and copolymers of C
1
-C
10
alkyl acrylates, e.g. homopolymers of ethyl acrylate, butyl acrylate or copolymers with up to 40 wt. %, preferably not more than 10 wt. %, of monovinyl monomers, e.g. styrene, acrylonitrile, vinyl butyl ether, acrylic acid (ester), methacrylic acid (ester), vinyl sulfonic acid. Those acrylate rubber homo and/or copolymers are preferably used which contain 0.01 to 8 wt. % of divinyl or polyvinyl compounds and/or N-methylolacrylamide and/or N-methylolmethacrylamide or other compounds which act as crosslinking agents, e.g. divinyl benzene, triallyl cyanurate.
Polybutadiene rubbers, SBR rubbers with up to 30 wt. % of styrene incorporated by polymerization and acrylate rubbers, particularly those which have a core/shell structure, such as are described in DE-OS 3 006 804 for example, are preferred.
Latices with average particle diameters d
50
of 0.05 to 2.0 &mgr;m, preferably 0.08 to 1.0 &mgr;m and particularly preferably 0.1 to 0.5 &mgr;m, are considered for producing the graft polymers according to the invention. The gel contents of the rubbers used may be varied in wide limits, preferably they are between 30 and 95 wt % (determined by the wire cage method in toluene, (cf. Houben-Weyl, Methoden der Organischen Chemie, Makromolekulare Stoffe, Part 1, p. 307 (1961), Thieme Verlag publishers, Stuttgart)).
Most particularly preferred are mixtures of rubber latices with
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 spread of the particle size distribution of 30 to 100 nm, particularly preferably 40 to 80 nm, the rubber latex (b) one of 50 to 500 nm, particularly preferably 100 to 400 nm (measured in each case as the d
90
−d
10
value from the integral particle size distribution).
The mixtures contain the rubber latices (a) and (b) preferably in the weight ratio 90:10 to 10:90, particularly preferably 60:40 to 30:70 (related in each case to the particular solids content of the latices).
The average particle diameter is determined by ultracentrifuge (cf. W. Scholtan, H. Lange: Kolloid-Z. u Z. Polymere 250, p. 782-796 (1972)).
The values quoted for the gel content relate to the determination by the wire cage method in toluene (cf. Houben-Weyl, Methoden der Organischen Chemie, Makromolekulare Stoffe, Part 1, p. 307 (1961), Thieme Verlag publishers, Stuttgart).
The rubber latices used may be produced by emulsion polymerization, the requisite
Bayer Aktiengesellschaft
Gil Joseph C.
Mullis Jeffrey
Preis Aron
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