Thermoplastic molding compounds

Details Thermoplastic molding compounds Thermoplastic molding compounds

2001-12-07

2004-08-10

Wu, David W. (Department: 1713)

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

Synthetic resins

Processes of preparing a desired or intentional composition...

C524S231000, C524S394000, C524S504000, C525S064000, C525S233000, C525S316000

Reexamination Certificate

active

06774166

ABSTRACT:

ABS moulding compositions have already been employed in large amounts for many years as thermoplastic resins for the production of all types of mouldings. The spectrum of properties of these resins here ranges from relatively brittle to very tough.
A specific field of use of ABS moulding compositions is the production of mouldings by injection moulding (e.g. housings, toys, motor vehicle components), where very good flowability of the polymer material is particularly important. In addition, the mouldings produced in this way must as a rule have a good notched impact strength.
There is the object of achieving the highest possible toughness values at a given rubber content, given rubber particle size and given matrix resin molecular weight, while retaining the good thermoplastic flowability. The high toughness values should be obtained here as far as possible independently of the type of matrix resin employed, especially when the styrene/acrylonitrile copolymers and &agr;-methylstyrene/acrylonitrile copolymers typical of ABS are used.
One possibility of increasing the toughness of ABS polymers at a given rubber content, given rubber particle size and given matrix molecular weight is the addition of special silicone oil compounds (cf. EP-A 6521); however, disadvantages such as poor paintability, inadequate printability or impaired yield stress values (risk of white fracture) may occur here. The addition of small amounts of EPDM rubber (cf. EP-A 412 370) or AES polymer (cf. EP-A 412 371) has also been described. However, both methods require relatively expensive additive components employed in considerable amounts.
It has now been found that by employing special additive mixtures, ABS products with a very good combination of notched impact strength (both at room temperature and at a low temperature) and thermoplastic processability are obtained.
The invention relates to thermoplastic moulding compositions comprising
A) 5 to 95 wt. %, preferably 10 to 90 wt. %, and particularly preferably 20 to 75 wt. % of one or more thermoplastic homo-, co- or terpolymers of styrene, &agr;-methylstyrene, styrene substituted on the nucleus, methyl methacrylate, acrylonitrile, methacrylonitrile, maleic anhydride, N-substituted maleimide or mixtures thereof
B) 5 to 95 wt. %, preferably 10 to 90 wt. %, and particularly preferably 25 to 80 wt. % of one or more graft polymers of
B.1) 5 to 90 parts by wt., preferably 20 to 80 parts by wt., and particularly preferably 25 to 60 parts by wt. styrene, &agr;-methylstyrene, styrene substituted on the nucleus, methyl methacrylate, acrylonitrile, methacrylonitrile, maleic anhydride, N-substituted maleimide or mixtures thereof on
B.2) 95 to 10 parts by wt., preferably 80 to 20 parts by wt., and particularly preferably 75 to 40 parts by wt. of at least one rubber with a glass transition temperature of ≦10° C.
and
C) 0.1 to 8 parts by wt., preferably 0.5 to 6 parts by wt., and particularly preferably 1 to 5 parts by wt., in each case per 100 parts by wt. of A)+B), of a combination of at least 3 components chosen from compounds I), II), III) and IV), where I) represents a compound with at least one structural unit
where
M=a metal, preferably Mg, Ca, Zn
n=the valency of the metal M, preferably 1 or 2,
II) represents a compound with at least one structural unit
III) represents a compound with at least one structural unit
and
IV) represents a compound with none of the structural units contained in compounds (I) to (III),
wherein each of the compounds I) to IV) preferably contains at least one terminal aliphatic C
6
-C
32
-hydrocarbon radical.
Thermoplastic polymers A) which are suitable according to the invention are those of styrene, &agr;-methylstyrene, p-methylstyrene, vinyltoluene, halogenostyrenes, methyl acrylate, methyl methacrylate, acrylonitrile, maleic anhydride, N-substituted maleimide or mixtures thereof.
The polymers A) are resinous, thermoplastic and rubber-free. Particularly preferred polymers A) are those of styrene, methyl methacrylate, styrene/acrylonitrile mixtures, styrene/acrylonitrile/methyl methacrylate mixtures, styrene/methyl methacrylate mixtures, acrylonitrile/methyl methacrylate mixtures, &agr;-methylstyrene/acrylonitrile mixtures, styrene/&agr;-methylstyrene/acrylonitrile mixtures, &agr;-methylstyrene/methyl methacrylate/acrylonitrile mixtures, styrene/&agr;-methylstyrene/methyl methacryl ate mixtures, styrene/&agr;-methylstyrene/methyl methacrylate/acrylonitrile mixtures, styrene/maleic anhydride mixtures, methyl methacrylate/maleic anhydride mixtures and styrene/methyl methacrylate/maleic anhydride mixtures.
The polymers A) are known and can be prepared by free-radical polymerization, in particular by emulsion, suspension, solution or bulk polymerization. They preferably have molecular weights {overscore (M)}
w
of 20,000 to 200,000 or limiting viscosities [&eegr;] of 20 to 110 ml/g (measured in dimethylformamide at 25° C.).
Rubbers which are suitable for the preparation of the graft polymers B) are, in particular, polybutadiene, butadiene/styrene copolymers, butadiene/acrylonitrile copolymers, polyisoprene or alkyl acrylate rubbers based on C
1
-C
8
-alkyl acrylates, in particular ethyl, butyl or ethylhexyl acrylate.
The acrylate rubbers can optionally comprise up to 30 wt. % (based on the rubber weight) of copolymerized monomers, such as vinyl acetate, acrylonitrile, styrene, methyl methacrylate and/or vinyl ethers. The acrylate rubbers can also comprise a small amount, preferably up to 5 wt. % (based on the rubber weight), of polymerized-in, ethylenically unsaturated monomers having a crosslinking action. Crosslinking agents are e.g. alkylene diol diacrylates and -methacrylates, polyester diacrylates and -methacrylates, divinylbenzene, trivinylbenzene, triallyl cyanurate, allyl acrylate and methacrylate, butadiene and isoprene. The graft base can also be acrylate rubbers having a core/jacket structure with a core of crosslinked diene rubber of one or more conjugated dienes, such as polybutadiene, or a copolymer of a conjugated diene with an ethylenically unsaturated monomer, such as styrene and/or acrylonitrile.
Preferred rubbers for the preparation of graft polymers B) are diene rubbers and alkyl acrylate rubbers.
The rubbers are present in the graft polymer B) in the form of at least partly crosslinked particles of average particle diameter (d
50
) of 0.05 to 20.0 &mgr;m, preferably of 0.1 to 2.0 &mgr;m, and particularly preferably of 0.1 to 0.8 &mgr;m. The average particle diameter d
50
is determined by ultracentrifuge measurements by the method of W. Scholtan et al., Kolloid-Z. u.Z. Polymere 250 (1972), 782-796.
The polymers B) can be prepared by free-radical grafting polymerization of monomers B.1) in the presence of the rubbers B.2) to be grafted onto.
Preferred preparation processes for the graft polymers B) are emulsion, solution, bulk or suspension polymerization, and combinations of these processes which are known per se. Particularly preferred graft polymers B) are ABS polymers.
Especially preferred polymers B) are products which have been obtained by free-radical polymerization of mixtures of styrene and acrylonitrile, preferably in a weight ratio of 10:1 to 1:1, particularly preferably in a weight ratio of 5:1 to 2:1, in the presence of a rubber which is built up predominantly from diene monomers (preferably polybutadiene) and has an average particle diameter (d
50
) of 100 to 450 nm, especially preferably in the presence of two rubbers which have been built up predominantly from diene monomers (preferably polybutadiene) and have a) an average particle diameter (d
50
) of 150 to 300 nm and b) an average particle diameter (d
50
) of 350 to 450 nm, in a weight ratio of (a):(b)=10:90 to 90:10, preferably 30:70 to 60:40.
The rubber content of the polymers B) is preferably 40 to 95 wt. %, particularly preferably 50 to 90 wt. %, and especially preferably 55 to 85 wt. %.
Suitable individual components of the additive mixture C) are e.g.:
Component I): Magnesium stearate, calcium steara

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