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
2002-04-15
2004-04-06
Buttner, David J. (Department: 1712)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Mixing of two or more solid polymers; mixing of solid...
C525S064000, C525S067000, C525S073000, C525S074000, C525S077000, C525S084000, C525S086000, C525S261000, C525S316000
Reexamination Certificate
active
06716916
ABSTRACT:
The present invention provides thermoplastic moulding compositions of the ABS type or of the ABS blend type containing improved graft rubber components which are obtained by emulsion polymerisation using specific initiator systems while defined reaction conditions are maintained.
Moulding compositions of the ABS type are two-phase plastics comprising
I) a thermoplastic copolymer in particular of styrene and acrylonitrile, in which the styrene may be replaced entirely or in part by &agr;-methylstyrene or methyl methacrylate; this copolymer, also known as SAN resin or matrix resin, forms the outer phase;
II) at least one graft polymer which has been produced by a graft reaction of one or more of the monomers stated in I onto butadiene homo- or copolymer (“grafting backbone”). The graft polymer (“elastomer phase” or “graft rubber”) forms the disperse phase in the matrix resin.
These blends of plastics may additionally contain further polymer components such as for example aromatic polycarbonate resins, polyestercarbonate resins, polyester resins or polyamide resins, so resulting in so-called ABS blend systems.
Graft rubbers produced using redox initiator systems have proved particularly effective as impact modifiers for both ABS moulding compositions and ABS blend systems (c.f. for example EP 482 451 and the literature cited therein), wherein good toughness properties are generally achieved. Disadvantageously, surface gloss, elongation at break and thermoplastic flow properties are often inadequate or are subject to major variation.
Moreover, graft rubbers produced by redox initiation tend to have an elevated content of unreacted monomers which, while the content may indeed be reduced by adding metal ions (for example Fe ions) to the reaction mixture, impairs other properties (for example thermal stability, polymer colour).
There is accordingly a requirement for graft rubbers which do not exhibit these disadvantages and for a process by means of which ABS and ABS blend moulding compositions without the stated disadvantages may be produced.
It has now been found that moulding compositions having very good surface gloss, elevated elongation at break and good melt processability may be obtained without any negative effects on other properties if the graft rubber used is produced using specific combinations of initiator systems while maintaining defined reaction conditions.
The invention provides thermoplastic moulding compositions of the ABS type or of the ABS blend type containing
A) at least one elastic/thermoplastic graft polymer obtained by free-radical emulsion polymerisation of resin-forming vinyl monomers, preferably of compounds of the formulae (I) and (II) described below, particularly preferably of styrene and/or acrylonitrile, wherein styrene and/or acrylonitrile may be replaced entirely or in part by &agr;-methylstyrene, methyl methacrylate or N-phenylmaleimide, in the presence of rubber present in latex form having a glass transition temperature of ≦0° C. using an initiator combination comprising a persulfate compound and a redox initiator system and
B) at least one copolymer of styrene and acrylonitrile, wherein styrene and/or acrylonitrile may be replaced entirely or in part by &agr;-methylstyrene or methyl methacrylate or N-phenylmaleimide and optionally
C) at least one resin selected from the group of polycarbonates, polyestercarbonates, polyesters and polyamides,
characterised in that at the beginning of the graft polymerisation reaction the persulfate compound is added 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. % (in each case relative to the monomers apportioned up to the time of addition of the redox initiator), after addition of 1 to 50 wt. %, preferably of 2.5 to 40 wt. %, particularly preferably of 5 to 30 wt. % and very particularly preferably of 7.5 to 25 wt. % of the monomers (in each case relative to the total quantity of monomers), the redox initiator components are added in quantities of 0.1 to 2.5 wt. %, preferably of 0.2 to 2 wt. % and particularly preferably of 0.5 to 1.5 wt. % (in each case relative to the monomers apportioned since the time of addition of the redox initiator).
Rubbers suitable for the production of the elastic/thermoplastic graft polymers according to the invention art in principle any rubbery polymers in emulsion form having a glass transition temperature of below 0° C.
The following may, for example, be used:
diene rubbers, i.e. homopolymers of conjugated dienes having 4 to 8 C atoms such as butadiene, isoprene, chloroprene or the copolymers thereof with up to 60 wt. %, preferably up to 30 wt. % of a vinyl monomer, for example acrylonitrile, methacrylonitrile, styrene, &agr;-methylstyrene, halostyrenes, C
1
-C
4
allylstyrenes, C
1
-C
8
alkyl acrylates, C
1
-C
8
alkyl methacrylates, alkylene glycol diacrylates, alkylene glycol dimethacrylates, divinylbenzene;
acrylate rubbers, i.e. homo- or copolymers of C
1
-C
10
alkyl acrylates, for example homopolymers of ethyl acrylate, butyl acrylate or copolymers with up to 40 wt. %, preferably no more than 10 wt. % of monovinyl monomers, for example styrene, acrylonitrile, vinyl butyl ether, acrylic acid (esters), methacrylic acid (esters), vinylsulfonic acid. The acrylate rubber homo- or copolymers which are preferably used are those which contain 0.01 to 8 wt. % of divinyl or polyvinyl compounds and/or N-methylolmethacrylamide or N-methylolacrylamide or other compounds which act as crosslinking agents, for example divinylbenzene, triallyl cyanurate.
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 considered for the production of the graft polymers according to the invention are those 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. The gel contents of the rubbers used may be varied within broad limits, preferably lying between 30 and 95 wt. % (determined using the wire cage method in toluene (c.f. Houben-Weyl,
Methoden der organischen Chemie, Makromolekulare Stoffe
, part 1, p. 307 (1961), Thieme Verlag Stuttgart)).
Mixtures of rubber latices having
a) average particle diameters d
50
of ≦320 nm, preferably of 260 to 310 nm, and gel contents of ≦70 wt. %, preferably of 40 to 65 wt. %, and
b) average particle diameters d
50
of ≦370 nm, preferably of 380 to 450 nm, and gel contents of ≦70 wt. %, preferably of 75 to 90 wt. %,
are very particularly preferred.
The rubber latex (a) here preferably has a width of the particle size distribution of 30 to 100 nm, particularly preferably of 40 to 80 nm, while that of the rubber latex (b) is of 50 to 500 nm, particularly preferably of 100 to 400 nm (in each case measured as the d
90-d
10
value of the overall particle size distribution).
The mixtures contain the rubber latices (a) and (b) preferably in a weight ratio of 90:10 to 10:90, particularly preferably of 60:40 to 30:70 (in each case relative to the particular solids content of the latices).
The average particle diameters are determined by ultracentrifugation (c.f. W. Scholtan, H. Lange,
Kolloid
-
Z. u Z. Polymere
250, pp. 782-796 (1972)).
The stated gel content values relate to determination using the wire cage method in toluene (c.f. Houben-Weyl,
Methoden der organischen Chemie. Makromolekulare Stoffe
, part 1, p. 307 (1961), Thieme Verlag Stuttgart).
The rubber latices used may be produced by emulsion polymerisation, the necessary reaction conditions, auxiliaries and working methods being known in principle.
It is also possible initially to produce a finely divided rubber polymer using known methods and then to agglomerate it in known manner to establish the required particle size. Relevant techniques have been described (c.f. EP-B 0 029 613; EP-B 0 007 810; DD-PS 144 415; DE-AS 12 33 131; DE-AS 12 58 076; DE-OS 21 0
Alberts Heinrich
Eichenauer Herbert
Sun Liqing-Lee
Bayer Aktiengesellschaft
Buttner David J.
Gil Joseph C.
Preis Aron
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