Note: Descriptions are shown in the official language in which they were submitted.
s
Mixtures containing from 90 to 30~ by weight of a poly-
carbonate based on aromatic dihydroxy compounds and from 10 to 70%
by weight of a graft polymer prepared from polybutadiene and a
mixture of acrylonitrile and an aromatic vinyl hydrocarbon have
been disclosed in German Auslegeschrift No. l,170,141. These
moulding compounds are distinguished by their good processing
quality, but for some technical usages the strength of their
coalescence seams is insufficient. Special mixtures of aromatic
polycarbonates and ABS polymers in which the strength of the
coalescence seam is considerably improved have been disclosed in
German Offenlegungsschrift No. 2,259,565.
Since the above moulding compounds lose their impact
strength at low temperatures and bréak with splintering, they are
not suitable for use in, for example, mokor car manufacturing, in
spite o their other satisfactory properties. This is because, in
this field, they are required to be either resistant to breakage
at -30C or at least to break without splintering at this
temperature.
The present invention is based on the finding that the
~0 low temperature breakage characteristics of moulding compounds are
substantially improved by a combination of two ABS graft copolymers.
The present invention therefore provides a thermoplastic
moulding compound having a rubber content of from 10 to 25% by
weight which comprises:
(i) 70 to 30 parts by weight of a thermoplastic polycarbonate
of bisphenol-A; and
(ii) 30 to 70 parts by weight of a mixture of:
(a) 0 to 75~ by weight of a copolymer of 95 to
-2-
~9L6~95
50% by weight styrene, ~ -methylstyrene, methyl methacrylate or
mixtures thereof and 5 to 50% by weight of acrylonitrile,
methacrylonitrile, methyl methacrylate or mixtures thereof; and
(b) 100 to 25% by weight of graft polymers which
are a mixture of:
(I) a graft copolymer, having a degree of grafting of from
0.2 to 0.5, of from 50 to 95% by weight of a mixture of the
monomers styrene and acrylonitrile in respective propor~ions
by weight of from 50:95 to 95.5 on from 50 to 5% by weight of
polybutadiene having an average particle size of from 0.1 to 2~(;
and
(II) a graft copolymer, having a degree of grafting of from
0.7 to 0.9, of from 35 to 20% by weight of a mixture of the
monomers styrene and acrylonitrile in respective proportions
by weight of from 50:50 to 95:5 on from 65 to 80% by weight of
polybutadiene having an average particle size of fxom 0.1 to 2,4,
the graft copolymers (I) and (II) being present in proportions by
weight of from 1:3 to 3:1.
Preferably, the graft copolymer (I) is a graft copolymer
of from 50 to 70~ by weight of a mixture of the monomers styrene
and acrylonitrile in respective proportions by weight of from
50 : 50 to 95 : 5 on from 50 to 30% by weight of a rubber having
an average particle size of from 0.1 to 2)~. It is furthermore
preferred that the rubber of each of the graft copolymers (I)
and (II) has an average particle size of from 0.3 to 1~. A
further preferred embodiment of the invention is a moulding
compound as defined above wherein the rubber content is from
-3-
;29S
15 to 20% by weight. The thermoplastic polycarbonate preferably
has a moleculax weight of from 10,000 to 60,000, particularly
from 20,000 to 40,000.
Compared with the known mixtures of aromatic poly-
carbonates and ABS polymers, the moulding compounds according to
the present invention have improved tensile strength and a reduced
tendency to splinter at low ~emperatures. The high strength of the
-3a-
:
: . ~
: . : '
6~95
coalescence seam is unchanged. It was also unexpectedly found
that the dimensional stability under heat, determined according
to Vicat B, fell only insignificantly with increasing rubber
content.
Any thermoplastic polycarbonates preferably from bisphenol
A may in principle be used for the moulding compounds according to
the present invention. Polycarbonates are known. They are
prepared by the reaction of di- or polyhydroxyl compounds with
phosgene by known phase interface processes.
They may be prepared b~, for example, emulsion polymeri-
sation of the graft monomers with the aid of radical initiators
in a rubber latex. The rubber particles in this latex preferably
have average diameters of from O.3 to 1~ . The particles are not
substantially increased in size by the graft polymerisation of
the monomers, and the
-4-
~. .
~6Z~
particles of gra~t copolymer there~ore have the size given
above. The terms "particle size" and "particle diameter'
are always used herein to denote the average diameter
d50, which means that 50/0 of the particles under conside-
ration are larger and 50/0 are smaller than the d50. Theterm "degree of grafting" means the proportion of gr~t
polymerised monomers (i.e. chemically bound to the rubber)
to the total quantity of polymerised monomers.
The following rubbers are particularly suitable for
use as gra~t bases:- polybutadiene; butadiene/styrene
copolymers containing up to 30/0 by weight of styrene incorp-
orate~ by polymerisation; copolymers of butadiene and
acrylonitrile containing up to 20~ by weight o~ acrylonitrile;
and copolymers of butadiene containing up to 20~/o by weight
f a lower alkyl ester of acrylic or methacrylic acid (e.g~
methyl acrylatej ethyl acrylate, methyl methacrylate or
ethylmethacrylate).
In addition to the grait polymers, the moulding com-
pound may contain a copolymer of the graft monomers or
20 similar monomers. Copolymers of from 95 to 50/0 by weight
of styrene, a-methylstyrene, methyl methacrylate or
mixtures thereof and from 5 to 50/0 by weight of acrylo-
nitrile, methacrylonitrile, methyl methacrylate or mixtures
thereof are suitable. Copolymers of this type are fre-
quently formed as by-products of graft polymerisation,
especially when large quantities of monomers are grafted
on small quantities of rubber. The properties o~ the
material can therefore be influenced by the addition of
such copolymers.
The various constituents of the moulding compounds
of the present invention are generally prepared separately
and then mixed together in known mixing apparatus such as
mixing rollers, double screw extruders or internal mixers.
The constituents are generally melted in these mixing
processes. In cases where the constituents of the moulding
Le A 18 745
6;~5
compound are initially obtained as latices, the latices
may, of course, be mixed and then precipitated together.
The usual aggregates such as fillers, glass fibres, pig-
ments, stabilizers, flame retarding agents, ~luidizing
agents, lubricants, mould release agents and antistatic
agents may be added in the mixing processes. The moulding
compounds of the present invention may be used for the
production of all types of moulded articles, and in
particular the compounds may be worked up by injection
moulding Their main application lies in cases where
good low temperature breakage characteristics are required,
e.g. in dashboards, steering column casings, loudspeaker
cases and all types of internal parts in motor vehicles.
The present invention is further illustrated by the ~ollow-
ing Examples:
I. Graft polymer with 50 parts b~ weight of rubber
35 Parts by weight of styrene and 15 parts by weight
of acrylonitrile are grafted onto 50 parts by weight of a
coarse-particled rubber in which the polybutadiene graft
basis (which is in the latex form) has an average particle
diameter of from 0.3 to 0.4 p, using the process of
emulsion polymeri~ation according to German Auslegeschri~ten
Nos. l,247,665 and l,269,360.
II. Graft polymer with 80 parts by weight of rubber
14 Parts by weight of styrene and 6 parts by weight
of acrylonitrile are grafted onto 80 parts by weight of
a coarse-particled rubber in which the butadiene graft
basis present in the latex form has an average particle
diameter of from 0.3 to 0.4 p, using the process of
emulsion polymerisation~a~c,~Fding to German Auslegeschriften
A Nos. l,247,665 and ~
III. ~tyrene/acrylonitrile copolymer
72 Parts by weight of styrene are polymerised with
28 parts by weight of acrylonitrile by emulsion polymeri-
sation. The copolymer has an intrinsic viscosity of [~]
= 80.2 (determined in dim~th~l~uran (DMF) at 20C).
Le A 18 745
' '
.
6~95
IY. Aromatic ~ol~carbonate
A polycarbonate based on 4,4'-dihydroxy-diphenyl-
propane -2,2 is prepared by the phase interface process.
The relative solution viscogity was 1.30 (determined
in methylene chloride at 25C and at a concentration of
5 g/l).
The individual components are mixed in internal
kneaders at ca. 2600C and isolated, using a roller followed
by band granulating. Various characteri~tic compounds
are 9hown in the following Table.
The apparatus used in the test for determining the
splintering breakage at low temperatures is shown in Fig.
1, in which a molded body (1) formed from the compounds
shown in the Table measuring 163 mm in width, 105 mm in
depth~ 20 mm in height and 3 mm in thickness and cooled
to the test temperature, is pla oed in a support frame (2)
inside a refrigeration chamber. A falling hemispherical
body (3) 45 mm in diameter and weighing 29 kg is then
dropped on the test sample from a height of 2 metres.
The fracture pictures are assessed visually and
graded as follows:
0 no damage
l beginning of a single tear in any position (Fig.2)
2 breakage of body into two (Fig. 3)
3 breakage into two with additional crack (Fig. 4)
4 breakage through the body (Fig. 5)
t~aring breakage into several fragments still
hanging together (Fig. 6)
6 splinter breakage into a large number of parts no
longer joined together. (Fig. 7)
Le A 18 745
.~, .
. 8
TABLE
Example
Product
(~) 1 2 3 4 5
I 35.6 12.8 16.0 19.2 25
II -- 20.0 15.0 10.0 5
III 14.4 7.2 9.0 20.8 --
IV 50.0 60.0 60.0 5.0 70
Rubber (/0) 17.8 22.4 20.0 17.616.5
Low temperature breakage characteristics*
at -20~C 3.2 0 0 2.0 1.8
at -30C 5.0 0.8 2.6 1.8 2.6
at -40C -- 1.6 3.0 1.6 3.0
Vicat B** 117 120 119 116 127
*) average of assessment of breakage pictures
from five test samples (Figures 2 - 7)
**) DIN 53 460
Le A 18 745
.
:.
,
