High impact strength flame-retardant polycarbonate moulding compositions

The present invention relates to high impact strength flame-retardant polycarbonate moulding compositions, which are characterized in that they consist of halogen-free polydiorganosiloxane-polycarbonate block copolymers, halogen-free copolymers, halogen-free phosphorus compounds, tetrafluoroethylene polymers and, if appropriate, stabilizers, pigments, flow control agents, mould release agents and/or antistatics, and to processes for their preparation.

The present invention relates to high impact strength flame-retardant 
polycarbonate moulding compositions consisting of 
(A) 60 to 90 parts by weight of a halogen-free 
polydiorganosiloxane-polycarbonate block copolymer with an average 
molecular weight M.sub.w (weight average) of 10,000 to 200,000 and with a 
content of aromatic carbonate structural units of between 75 and 99% by 
weight, preferably between 75 and 97.5% by weight, and a content of 
diorganosiloxane units of between 25 and 1.0% by weight, preferably 
between 25 and 2.5% by weight, the block copolymers being prepared 
starting from polydiorganosiloxanes which contain 
.alpha.,.omega.-bishydroxyaryloxy end groups and have a degree of 
polymerization P.sub.n of 5 to 100, preferably of 20 to 80, 
(B) 10 to 40 parts by weight of a halogen-free thermoplastic copolymer of 
50 to 95% by weight of styrene, .alpha.-methylstyrene, nuclear-substituted 
styrene or mixtures thereof and 5 to 50% by weight of (meth)acrylonitrile, 
(C) 1 to 20 parts by weight, preferably 2 to 15 parts by weight, per 100 
parts by weight of the total weight of (A) and (B), of a halogen-free 
phosphorus compound of the formula (I); 
##STR1## 
wherein R.sub.1, R.sub.2 and R.sub.3 independently of one another are 
C.sub.1 -C.sub.8 -alkyl or optionally alkyl-substituted C.sub.6 -C.sub.20 
-aryl and 
"n" represents 0 or 1, and 
(D) 0.05 to 5 parts by weight, again per 100 parts by weight of the total 
weight of (A) and (B), and in particular 0.1 to 2 parts by weight, of a 
tetrafluoroethylene polymer with a density of 2.0 to 2.3 g/cm.sup.3 and a 
particle size of 100 to 1,000 .mu.m, and, if appropriate, effective 
amounts of stabilizers, pigments, flow control agents, mould release 
agents and/or antistatics. 
Component (A) can also be a mixture of polydiorganosiloxane-polycarbonate 
block copolymers with other siloxane-free thermoplastic halogen-free 
polycarbonates, the total content of diorganosiloxy units in the 
polycarbonate mixture in turn being between 1 and 25% by weight, 
preferably between 2.5 and 25% by weight. 
According to DE-OS (German Published Specification) 2,228,072, 
thermoplastic polycarbonates are rendered flame-retardant with a mixture 
of hexabromobenzene and an antimony compound, and can additionally contain 
a phosphate ester as a synergistic agent. The sole addition of 10 parts by 
weight of triphenyl phosphate to bisphenol A polycarbonate, however, has 
no anti-drip action in accordance with the ignition test of U.L. Subj. 94 
(see page 20 of DE-OS (German Published Specification) 2,228,072). 
British Patent Specification 1,459,648 describes flame-retardant, 
non-dripping polymers, for example of ABS polymers or of plycarbonates, to 
which a flameproofing additive, such as, for example, triphenyl phosphate, 
a non-combustible fibre material and polytetrafluoroethylene resin have 
been admixed. Example 2 of British Patent Specification 1,459,648 shows 
that polytetrafluoroethylene resin does not prevent dripping without the 
fibre additive. 
Thermoplastics which can be foamed are known from DE-OS (German Published 
Specification) 2,434,085, polycarbonates, polymers or mixtures thereof, 
inter alia, being mentioned as thermoplastics. Polymers which are 
mentioned are also those of butadiene, styrene and acrylonitrile or of 
styrene by itself. The plastics which can be foamed can contain phosphate 
esters as flameproofing agents, if appropriate in combination with halogen 
compounds. No polytetrafluoroethylene polymers are recommended as halogen 
compounds. 
DE-OS (German Published Specification) 2,921,325 describes the addition of 
pentaerythritol diphosphates and diphosphonates as flameproofing agents 
for polycarbonates, it also being possible for halogen compounds 
additionally to be used, and according to U.S. Pat. Specification 
3,392,136 cited on page 9 of DE-OS (German Published Specification) 
2,921,325, these can also be polyvinylidene fluorides. ABS copolymers can 
be admixed to the polycarbonates. 
Flame-retardant ABS polymers which contain polytetrafluoroethylenes are 
known, inter alia, from U.S. Pat. Specification 4,355,126 and 4,107,232. 
Triphenyl phosphate is the particularly preferred flameproofing agent. 
Flame-retardant mixtures of polycarbonates, ABS polymers and halogen 
compounds are known from DE-OS (German Published Specification) 2,903,100 
and 2,918,883. According to DE-OS (German Published Specification) 
2,903,100, the flame-retardant properties are achieved by special organic 
sulphonates. Fluorinated polyolefins can be added as drip-inhibiting 
agents. According to DE-OS (German Published Specification) 2,918,883, the 
flame-retardant properties are achieved by alkali metal or alkaline earth 
metal salts of acids in combination with anti-drip agents, the ABS 
polymers making up only a maximum of 10% by weight, based on the total 
mixture. 
Flame-retardant polymer mixtures which, in addition to 
polytetrafluoroethylenes and organic halogen compounds, contain 
polyphosphates with molecular weights M.sub.w of 1,600 to 150,000 in 
amounts of 1 to 35% by weight are also known (European Patent 
A-0,103,230). However, the polycarbonates of these moulding compositions 
are predominantly built up from tetramethylated diphenols. 
Flame-retardant thermoplastic moulding compositions which contain a. 
aromatic polycarbonates, b. SAN graft polymers, C. thermoplastic polymers, 
d. if appropriate halogen compounds, e. antimony trioxide, antimony 
carbonate, bismuth trioxide or bismuth carbonate and f. a fine-particled 
tetrafluoroethylene polymer, this being introduced into the moulding 
composition via an aqueous emulsion of the SAN graft polymer b. and, if 
appropriate, an aqueous emulsion of the thermoplastic polymer c., good 
surfaces of the moulding compositions thus being achieved, are known from 
DE-OS (German Published Specification) 3,322,260. 
High impact strength flame-retardant moulding compositions based on 
siloxane-free polycarbonates, copolymers of optionally substituted styrene 
and (meth)acrylonitrile, halogen-free phosphorus compounds and a 
tetrafluoroethylene polymer are known from German Patent Application P 35 
23 316.8 (Le A 23 927). 
In further development of these moulding compositions, it has now been 
found that these moulding compositions can be improved further in respect 
of their toughness, in particular their notched impact strength, if the 
polycarbonate component (A) consists of 
polydiorgano-siloxane-polycarbonate block copolymers or contains these. 
The moulding compositions according to the invention are distinguished by a 
good notched impact strength and good flame-retardant properties, without 
containing the halogen compounds and metal compounds used in customary 
fireproofing technology. 
Halogen-free polydiorganosiloxane-polycarbonate block copolymers of 
component (A) which are suitable according to the invention are those 
based on the halogen-free diphenols of the formula (II) and of the formula 
(IIa) 
##STR2## 
wherein A is a single bond, C.sub.1 -C.sub.5 -alkylene, C.sub.2 -C.sub.5 
-alkylidene, C.sub.5 -C.sub.6 -cycloalkylidene, --S-- or --SO.sub.2 --, 
n is 1 or zero, 
the symbols R are identical or different and are linear C.sub.1 -C.sub.20 
-alkyl, branched C.sub.3 -C.sub.20 -alkyl or C.sub.6 -C.sub.20 -aryl, 
preferably CH.sub.3, and 
m is an integer between 5 and 100, preferably between 20 and 80, 
the weight content of diphenols of the formula (IIa) in the 
copolycarbonates in each case being such that the content of 
diorganosiloxy units 
##STR3## 
in the copolycarbonate (A) is between 1 and 25% by weight, preferably 
between 2.5 and 25% by weight. 
Other siloxane-free thermoplastic halogen-free polycarbonates are 
preferably those which contain, as incorporated diphenols, only those of 
the formula (II). 
In the cases where components (A) is a mixture of siloxane-containing 
polycarbonates and siloxane-free polycarbonates, the siloxane-containing 
polycarbonates can also have a content of diorganosiloxy units of more 
than 25% by weight, as long as mixing with the siloxane-free 
polycarbonates gives a content in the polycarbonate mixture of in turn 
between 1 and 25% by weight. 
The halogen-free diphenols of the formula (II) are either known from the 
literature or can be prepared by processes which are known from the 
literature; polydiorganosiloxanes with hydroxyaryloxy end groups according 
to formula (Ia) are likewise known (see, for example, U.S. Pat. No. 
3,419,634), or they can be prepared by processes which are known from the 
literature. 
The preparation of the polycarbonates of component (A) which are suitable 
according to the invention is known from the literature and can be carried 
out, for example, with phosgene by the phase boundary process or with 
phosgene by the process in a homogeneous phase system (the so-called 
pyridine process), the molecular weight to be established in each case 
being achieved in a known manner by an appropriate amount of known chain 
stoppers. (In respect of polydiorganosiloxane-containing polycarbonates, 
see, for example, DE-OS (German Published Specification) 3,334,782 (Le A 
22 594)). 
Examples of suitable chain stoppers are phenol or p-tert.-butylphenol, and 
also long-chain alkylphenols such as 4-(1,3-tetramethyl-butyl)phenol 
according to DE-OS (German Published Specification) 2,842,005 (le A 19 
006) or monoalkylphenols or dialkylphenols with a total of 8 to 20 C atoms 
in the alkyl substituents, according to German Patent Application P 35 06 
472.2 (Le A 23 654), such as, for example, p-nonylphenol, 
2,5-di-tert.-butylphenol, p-tert.-octylphenol, p-dodecylphenol, 
2-(3,5-dimethylheptyl)-phenol and 4-(3,5-dimethylheptyl)-phenol. The 
amount of chain stoppers to be employed is in general between 0.5 and 10 
mol %, based on the sum of the diphenols (II) and (IIa) employed in each 
case. 
The polycarbonates of component (A) which are suitable according to the 
invention have mean weight-average molecular weights (M.sub.w, measured, 
for example, by ultracentrifugation or scattered light measurement) of 
10,000 to 200,000, preferably 20,000 to 80,000. 
Examples of suitable halogen-free diphenols of the formula (II) are 
hydroquinone, resorcinol, 4,4'-dihydroxydiphenyl, 
2,2-bis-(4-hydroxyphenyl)-propane, 
2,4-bis-(4-hydroxyphenyl)-2-methylbutane and 
1,1-bis-(4-hydroxyphenyl)-cyclohexane. 
Suitable diphenols of the formula (IIa) are those in which R is methyl, 
ethyl, propyl, n-butyl, tert.-butyl and phenyl. 
Preferred halogen-free diphenols of the formula (IIa) are those of the 
formula (IIb) 
##STR4## 
wherein the symbols R are identical and have the abovementioned meaning, 
that is to say denote methyl and the like and phenyl, and 
m in turn is an integer between 5 and 100, preferably between 20 and 80. 
The diphenols of the formula (IIa) can be prepared, for example, from the 
corresponding bi-chlorine compounds (III) 
##STR5## 
and the diphenols (II), for example in accordance with U.S. Pat. No. 
3,419,634, column 3, in combination with U.S. Pat. No. 3,182,662. 
In the bis-chlorine compounds (III), R and m have the meaning as for the 
diphenols (IIa) and (IIb). 
The polycarbonates of component (A) which are suitable according to the 
invention can be branched in a known manner, and in particular preferably 
by incorporation of 0.05 to 2.0 mol %, based on the sum of the diphenols 
employed, of compounds which are trifunctional or more than trifunctional, 
for example those with three or more than three phenolic OH groups. 
Preferred polydiorganosiloxane-polycarbonate block copolymers are 
copolycarbonates of the halogen-free diphenols of the formula (II) with 
diphenols of the formula (IIb). 
Halogen-free thermoplastic copolymers of component (B) which are suitable 
according to the invention are resinous, thermoplastic and free from 
rubber. Particularly preferred polymers (B) are those of styrene and/or 
.alpha.-methylstyrene with acrylonitrile. By nuclear-substituted styrenes 
there are to be understood nuclear-alkylated styrenes, such as, for 
example, p-methylstyrene. 
Particularly preferred weight ratios in the thermoplastic polymer (B) are 
60 to 80% by weight of styrene, .alpha.-methylstyrene, nuclear-substituted 
styrene or mixtures thereof and 40 to 20% by weight of acrylonitrile. 
The polymers of component (B) are known and can be prepared by free radical 
polymerization, in particular by emulsion, suspension, solution or bulk 
polymerization. The polymers of component (B) preferably have molecular 
weights M.sub.w (weight-average, determined by light scattering or 
sedimentation) of between 15,000 and 200,000. 
The halogen-free phosphorus compounds of component (C) which are suitable 
according to the invention are generally known (see, for example, Ullmann, 
Encyclopadie der technischen Chemie (Encyclopaedia of Industrial 
Chemistry), Volume 18, page 301 et seq., 1979; Houben-Weyl, Methoden der 
organischen Chemie (Methods of Organic Chemistry), Volume 12/1, page 43; 
and Beilstein, Volume 6, page 177). 
Phosphorus compounds of component (C), formula (I), which are suitable 
according to the invention are, for example, triphenyl phosphate, 
tricresyl phosphate, diphenyl 2-ethylcresyl phosphate, 
tri-(isopropylphenyl) phosphate, diphenyl methylphosphonate or diethyl 
phenylphosphonate. 
The tetrafluoroethylene polymers of component (D) which are suitable 
according to the invention are polymers with fluorine contents of 65 to 
76% by weight, preferably 70 to 76% by weight. Examples are 
polytetrafluoroethylene, tetrafluoroethylene-hexafluoropropylene 
copolymers and tetrafluoroethylene copolymers with small amounts of 
fluorine-free copolymerizable ethylenically unsaturated monomers. 
These polymers are known. They can be prepared by known processes, thus, 
for example, by polymerization of tetrafluoroethylene in an aqueous medium 
with a catalyst which forms free radicals, for example sodium peroxy 
disulphate, potassium peroxy disulphate or ammonium peroxy disulphate, 
under pressures of 7 to 71 kg/cm.sup.2 and at temperatures of 0.degree. to 
200.degree. C., preferably at temperatures of 20.degree. to 100.degree. C. 
(U.S. Pat. No. 2,393,967). The density of these materials is preferably in 
the range from 2.0 to 2.3 g/cm.sup.3, and the particle sizes are 
preferably in the range from 100 to 1,000 .mu.m. 
In particular, dripping of the moulding composition melt during the burning 
process is reduced or completely prevented by the addition of 
tetrafluoroethylene polymers. 
The thermoplastic moulding compositions according to the invention can 
contain other additives which are known for polycarbonates or for the 
thermoplastic polymers, such as stabilizers, pigments, flow control 
agents, mould release agents and/or antistatics. 
The moulding compositions according to the invention consisting of 
components (A), (B), (C) and (D) and if appropriate other known additives, 
such as stabilizers, pigments, flow control agents, mould release agents 
and/or antistatics, are prepared by mixing the particular constituents in 
a known manner and subjecting the mixture to melt compounding or melt 
extrusion at temperatures of 200.degree. to 330.degree. C. in customary 
units, such as internal kneaders or single- and twin-screw extruders, or 
by mixing solutions of the particular components in suitable organic 
solvents, for example in chlorobenzene, and evaporating the solution 
mixtures in customary units, for example in devolatilization extruders. 
The present invention thus also relates to a process for the preparation of 
thermoplastic moulding compositions consisting of components (A), (B), (C) 
and (D) and, if appropriate, stabilizers, pigments, flow control agents, 
mould release agents and/or antistatics, which is characterized in that 
components (A), (B), (C) and (D) and, if appropriate, stabilizers, 
pigments, flow control agents, mould release agents and/or antistatics, 
after being mixed, are subjected to melt compounding or melt extrusion at 
temperatures of 200.degree. to 330.degree. C. in customary units, or in 
that solutions of these components in suitable organic solvents, after 
being mixed, are evaporated in customary units. 
The moulding compositions of the present invention can be used to produce 
all types of mouldings. In particular, mouldings can be produced by 
injection moulding. Examples of mouldings which can be produced are all 
types of housing components (for example for domestic appliances, such as 
coffee machines or mixers) or cover plates for the building sector and 
components for the motor vehicle sector. They are also used in the field 
of electrical engineering, because they have very good electrical 
properties. 
Another form of processing is the production of mouldings by deep-drawing 
or thermoforming of sheets or foils produced beforehand by extrusion. 
Particle size always denotes average particle diameter d.sub.50, determined 
by ultracentrifuge measurements in accordance with the method of W. 
Scholtan et al., Kolloid-Z, u. Z. Polymere 250 (1972) 782 to 796.

EXAMPLES 
Blend components employed 
A. 1. A copolycarbonate based on bisphenol A and 5% by weight of 
polydimethylsiloxane of block length (P.sub.n) 40 with a relative solution 
viscosity of 1.31, measured in CH.sub.2 Cl.sub.2 at 25.degree. C., and at 
a concentration of 0.5% by weight, prepared using phenol as the chain 
stopper, according to DE-OS (German Published Specification) 3,334,782. 
A. 2. Homopolycarbonate based on bisphenol A with a relative solution 
viscosity of 1.32, measured in CH.sub.2 Cl.sub.2 at 25.degree. C. and at a 
concentration of 0.5% by weight, prepared using phenol as the chain 
stopper. 
B. Styrene/acrylonitrile copolymer with a styrene/acrylonitrile ratio of 
72:28 and a limiting viscosity of (.eta.)=0.55 dl/g (measured in 
dimethylformamide at 20.degree. C.). 
C. Triphenyl phosphate 
D. Tetrafluoroethylene polymer in powder form with a particle size of 500 
to 650 .mu.m and a density of 2.18 to 2.20 g/cm.sup.3, from Hoechst 
(Hostaflon TF 2026). 
Preparation of the moulding compositions according to the invention 
Components (A), (B), (C) and (D) were compounded on a 3 liter internal 
kneader at temperatures between 200.degree. and 220.degree. C. 
Mouldings were produced on an injection moulding machine at 260.degree. C. 
The burning properties of the samples were measured in accordance with 
UL-Subj. 94 V in test specimen thicknesses of 1.6 mm and 3.2 mm. The UL-94 
test is carried out as follows: 
Samples of substance are moulded to bars with dimensions of 
127.times.12.7.times.1.6 mm and 127.times.12.7.times.3.2 mm. The bars are 
mounted vertically so that the underside of the sample specimen is 305 mm 
above a strip of bandaging material. Each sample bar is ignited 
individually by means of two successive ignition operations lasting 10 
seconds; the burning properties after each ignition operation are observed 
and the sample is evaluated accordingly. A Bunsen burner with a 10 mm (3.8 
inches) high blue flame of natural gas with a thermal unit of 
3.73.times.10.sup.4 kJ/m.sup.3 (1000 BTU per cubic foot) is used to ignite 
the sample. 
The UL-94 V-0 classification comprises the properties described below for 
materials which have been tested in accordance with the UL-94 
specification. The polycarbonate moulding compositions in this class 
contain no samples which burn for longer than 10 seconds after each action 
of the test flame; they exhibit no total flaming time of more than 50 
seconds with the two flaming actions on each set of samples; they contain 
no samples which burn completely up to the holding clamp attached to the 
top end of the sample; they contain no samples which ignite cottonwool 
arranged below the sample by burning drips or particles; they also contain 
no samples which glow for longer than 30 seconds after the test flame is 
removed. 
Other UL-94 classifications describe samples which are less flame-retardant 
and self-extinguishing and which release flaming drips or particles. These 
classifications are designated UL-94 V-1 and V-2. F means "failed" and is 
the classification of samples which have an after-burn time of .gtoreq.30 
seconds. 
The notched impact strength was determined in accordance with the method of 
DIN 53 453/ISO R 179 on bars with dimensions of 50.times.6.times.4 mm, the 
bars being given a V-shaped notch of notch depth 2.7 mm, and by the Izod 
method on bars with dimensions of 2.5.times.1/2.times.1/8 in accordance 
with ASTM-D-256. The precise formulations of the moulding compositions 
tested and the test data obtained can be seen from the following table. 
It can be seen that when polydiorganosiloxanepolycarbonate block copolymers 
are used instead of polycarbonate, products with clearly improved notched 
impact strength and still with excellent flame-retardant properties 
result. 
TABLE 
__________________________________________________________________________ 
Components Notched impact strength 
Example 
A1 A2 
B C D DIN 53 453 
Izod UL-94 V 
No. (parts by weight) 
(kJ/m.sup.2) 
(J/m) 
3.2 mm 
1.6 mm 
__________________________________________________________________________ 
Examples according to 
the invention 
1 80 20 
10 0.3 
8.6 234 VO VO 
2 70 30 
10 0.3 
6.6 106 VI VI 
Comparison Examples 
3 80 
20 
10 0.3 
6.7 72 VO VO 
4 70 
30 
10 0.3 
5.8 62 VI VI 
__________________________________________________________________________