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
1999-03-25
2002-04-30
Mulcahy, Peter D. (Department: 1713)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Mixing of two or more solid polymers; mixing of solid...
C524S504000
Reexamination Certificate
active
06380306
ABSTRACT:
The present invention relates to thermoplastic molding materials containing, based on the total weight of the molding material,
A) from 72 to 88.5% by weight of a thermoplastic polymer of, based on A),
a1) from 50 to 100% by weight of styrene or &agr;-methylstyrene or mixtures thereof,
a2) from 0 to 50% by weight of acrylonitrile and,
a3) from 0 to 50% by weight of one or more further monoethylenically unsaturated monomers,
B) from 10 to 20% by weight of a first graft polymer having an average particle diameter d
50
from 400 to 600 nm, comprising, based on B),
b1) from 30 to 90% by weight of a rubber-elastic graft core of, based on b1),
b11) from 80 to 99.99% by weight of n-butyl acrylate,
b12) from 0.01 to 20% by weight of at least one crosslinking monomer and,
b13) from 0 to 40% by weight of one or more further monoethylenically unsaturated monomers, and
b2) from 10 to 70% by weight of a graft shell of, based on b2),
b21) from 50 to 100% by weight of styrene or &agr;-methylstyrene or mixtures thereof,
b22) from 0 to 50% by weight of acrylonitrile and
b23) from 0 to 50% by weight of one or more further monoethylenically unsaturated monomers,
C) from 1.5 to 8% by weight of a second graft polymer having a bimodal particle size distribution, the average particle diameter d
50
being from 25 to 200 nm on the one hand and from 350 to 550 nm on the other hand, comprising, based on C),
c1) from 30 to 90% by weight of a rubber-elastic graft core of, based on c1),
c11) from 50 to 100% by weight of butadiene or isoprene or mixtures thereof, and
c12) from 0 to 50% by weight of one or more further monoethylenically unsaturated monomers, and
c2) from 10 to 70% by weight of a graft shell of, based on c2),
c21) from 50 to 100% by weight of styrene or &agr;-methylstyrene or mixtures thereof,
c22) from 0 to 50% by weight of acrylonitrile and,
c23) from 0 to 50% by weight of one or more further monoethylenically unsaturated monomers and
D) from 0 to 50% by weight of lubricants or mold release agents, pigments, dyes, flameproofing agents, antioxidants, light stabilizers, fibrous or particulate fillers or reinforcing materials or antistatic agents or other additives, or mixtures thereof,
the sum of the graft polymers B) and C) accounting for from 11.5 to 25% by weight of the sum of the three components A), B) and C)
and the sum of the four components A) to D) being 100% by weight.
The present invention furthermore relates to the use of the thermoplastic molding materials for the production of special shaped articles and to the special shaped articles produced from the thermoplastic molding materials.
Shaped articles of ABS (polybutadiene rubber particles, grafted with polystyrene/acrylonitrile, in polystyrene/acrylonitrile matrix) are distinguished by good mechanical properties, in particular—due to the low glass transition temperature Tg of the polybutadiene—by good impact strengths even at low temperatures.
It has been found that it is advantageous for the production of shaped articles, in particular by injection molding process, if small and large rubber particles are present in the ABS molding material. Such molding materials are described, for example, in German laid-open application DOS 2,427,960. Injection molded articles which have complex geometries, for example housing parts and front panels for appliances, electric switches, switches and installation boxes, can particularly advantageously be produced from molding materials having such a bimodal particle size distribution of the rubber, owing to their good flowability.
The disadvantage of shaped articles of ABS is that their stability to light, oxygen and other weathering influences is not completely satisfactory, owing to the presence of double bonds in the polybutadiene. When exposed to the weather, ABS shaped articles therefore tend in some cases to exhibit discoloration of the surface due to yellowing and chalking. Furthermore, the mechanical properties, in particular the impact strength, may deteriorate.
Shaped articles of ASA (polyalkyl acrylate rubber particles, grafted with polystyrene/acrylonitrile, in a polystyrene/acrylonitrile matrix) do not have these disadvantages since acrylic rubber contains no double bonds sensitive to weatherings. Accordingly, shaped articles made of ASA are extremely stable to ageing and weathering. ASA molding materials are described, for example, in German laid-open application DOS 1,260,135.
The disadvantage of shaped articles of ASA is that their mechanical properties are inadequate for some applications, in particular the low-temperature impact strength, which is lower than that of shaped articles made of ABS (owing to the higher Tg of the Tg of the polyacrylate rubbers).
German laid-open application DOS 2,901,576 discloses molding materials which consist of an SAN matrix, or polybutadiene rubber grafted with SAN and having an average particle size d
50
of from 200 to 450 nm, and a small-particle polyalkyl acrylate rubber grafted with SAN and having an average particle size d
50
of from 50 to 150 nm. Such molding materials are not completely satisfactory with regard to their mechanical properties and in particular their stability to weathering (tendency to yellow).
EP-A 52 732 discloses molding materials comprising an SAN matrix, a course-particle polybutadiene rubber grafted with SAN and having an average particle diameter d
50
of from 500 to 5000 nm, and a polyalkyl acrylate or polybutadiene rubber grafted with SAN and having an average particle diameter d
50
of from 50 to 180 nm on the one hand and from 250 to 600 nm on the other. These molding materials, too, are not completely satisfactory with regard to their stability to weathering.
It is an object of the present invention to remedy the disadvantages described. In particular, it is intended to provide molding materials having good flowability, from which shaped articles having good mechanical properties and sufficient stability to ageing and to weathering can be produced, in particular shaped articles having a balanced ratio of impact strength and a tendency to yellow.
We have found that this object is achieved by the thermoplastic molding materials defined at the outset. We have also found the use of the molding materials for the production of special shaped articles, and special shaped articles consisting of the molding materials.
Component A) of the novel molding material is present in an amount of from 72 to 88.5, preferably from 73 to 85, particularly preferably from 75 to 83, % by weight, based on the sum of components A), B), C) and D). Component A) is a thermoplastic polymer which consists of
a
1
) from 50 to 100, preferably from 55 to 95, particularly preferably from 60 to 85, % by weight of styrene or &agr;-methylstyrene or mixtures thereof,
a
2
) from 0 to 50, preferably from 5 to 45, particularly preferably from 15 to 40, % by weight of acrylonitrile and
a
3
) from 0 to 50, preferably from 0 to 40, % by weight of one or more further monoethylenically unsaturated monomers,
the percentages in each case based on component A). The monomers stated further below for component b13) are suitable as further monomers a3), the monomers a1) and a2) of course being excluded from the list of the monomers b13).
The polymers A) which, owing to their main component styrene and acrylonitrile, are generally also referred to as SAN polymers, are known and some of them are also commercially available. They have, as a rule, a viscosity number VN (determined according to DIN 53 726 at 25° C., 0.5% by weight dimethylformamide) of from 40 to 160 ml/g, corresponding to a weight average molecular weight of from about 40000 to 2000000. They are obtained in a known manner by mass, solution, suspension, precipitation or emulsion polymerization. Details of these processes are described, for example in Kunststoffhandbuch, published by R. Vieweg and G. Daumiller, vol. V “Polystyrol”, Carl-Hanser-Verlag Munich 1969, page 118 et seq.
Component B) of the molding material is present in an amount of from 10 to 20, preferably from 12 to 18, particularly prefe
Ginss Christophe
Güntherberg Norbert
Ittemann Peter
Kötting Manfred
Meyer Christian
BASF - Aktiengesellschaft
Keil & Weinkauf
Mulcahy Peter D.
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