Moulded bodies containing carbon

This invention relates to carbon-containing moulded bodies based on thermoplastic polycarbonates and thermoplastic polyalkylene terephtalates with an addition of carbon black and graphite and to a process for the production of these moulded bodies.

This invention relates to carbon-containing moulded bodies produced by the 
extrusion process or by the injection moulding process, characterised in 
that they contain 
(a) 40 to 85% by weight of thermoplastic polycarbonates, 
(b) 35 to 5% by weight of thermoplastic polyalkylene terephthalates and 
(c) 35 to 10% by weight, preferably 30 to 15% by wieght of carbon black and 
graphite, 
in which the ratio by weight of carbon black to graphite is in the range of 
5:1 to 1:3, preferably from 3:2 to 2:3, and the sum of percentages of 
weight of components (a)+(b)+(c) is in all cases 100% by weight. 
The moulded bodies according to this invention include, for example, 
extrusion cast sheets and injection moulded articles of all kinds. They 
are distinguished by their antistatic behaviour up to a certain 
conductivity and by their great toughness, tensile strength at break and 
dimensional stability in the heat. The moulded products according to the 
invention are therefore suitable, for example, for the packaging of 
electronic measuring instruments or electronic structural parts, 
especially those which are at risk from the accumulation of electrostatic 
charges, for example, in computers, television receivers, etc. 
The invention also relates to a process for the production of moulded 
bodies containing carbon, characterised in that the thermoplastic 
polycarbonate is intimately mixed with the carbon black and graphite and 
the whole mixture is extruded or injection moulded after the addition of 
the thermoplastic polyalkylene terphthalate to produce the desired moulded 
article. 
The invention also relates to the carbon-containing moulded bodies 
obtainable by the process according to the invention. 
According to U.S. Pat. No. 3,218,372 mixture of polycarbonates with 
polyalkylene terephthalates are known. From these mixtures films can be 
obtained (Col. 4, line 9 of U.S. Pat. No. 3,218,372). The addition of 
carbon black or graphite is not mentioned. 
According to JA-PS No. 932,197 mixtures of 50 parts by weight or more of 
polycarbonates and 50 parts by weight or less of polybutylene 
terephthalates are known. Fillers like carbon black, TiO.sub.2, glass 
fibers etc. and other dyeing pigments can be added. The preparation of 
films is not mentioned. 
According to Japanese patent application No. 47/121,683 films from mixtures 
consisting of 100 parts by weight of polycarbonate produced from 
bisphenol-A and 10 to 70 parts by weight of polytetramethylene 
terephthalate are claimed. Pigments, dyestuffs or an inorganic or organic 
additive such as stabilizer, filler or the like can be added. Carbon black 
or graphite are not mentioned, neither as fillers nor as pigments. 
According to the U.S. Pat. No. 4,559,164 electrically conductive 
poly(butylene-terephthalate) mouldings and compositions therefor are 
known. The carbon used can be some type of carbon black or graphite or 
combinations thereof. (Col. 2, line 13 ff. of the U.S. Pat. No. 
4,559,164). The amount of carbon is between 10 and 25% by weight of the 
composition. (Col. 1, lines 65/67). Moreover, the total composition can 
contain 1 to 50% by weight of bisphenol-A-polycarbonate (claim 1 of U.S. 
Pat. No. 4,559,164). 
The thermoplastic polycarbonates used for the present invention may be 
polycondensates obtained by the reaction of diphenols, in particular 
dihydroxydiarylalkanes, with phosgenes or diesters of carbonic acid. The 
dihydroxydiarylalkanes used may be either the unsubstituted compounds or 
compounds in which the aryl groups carry methyl groups or halogen atoms in 
the ortho- and/or meta-position to the hydroxyl group. Branched chain 
polycarbonates are also suitable. 
The thermoplastic polycarbonates used here have average molecular weights 
M.sub.w in the range of from 22,000 to 50,000, preferably from 28,000 to 
40,000, determined by measurements of the relative viscosity in CH.sub.2 
Cl.sub.2 at 25.degree. C. and at a concentration of 0.5 g per 100 ml. 
The following are examples of suitable diphenols: Hydroquinone, resorcinol, 
4,4'-dihydroxydiphenyl, bis-(hydroxyphenl)-alkanes such as, for example, 
C.sub.1 -C.sub.8 -alkylene-bisphenols or C.sub.2 -C.sub.8 
-alkylidene-bisphenols, bis-(hydroxy-phenyl)-cycloalkanes such as C.sub.5 
-C.sub.15 -cycloalkylene-bisphenols or C.sub.5 -C.sub.15 
-cycloalkylidene-bisphenols and bis-(hydroxyphenyl)-sulphides, -ethers, 
-ketons, -sulphoxides and -sulphones; also, .alpha.,.alpha.'-bis 
(hydroxyphenyl)-diisopropylbenzene and the corresponding compounds which 
are alkylated or haloganted in the nucleus. It is preferred to use 
polycarbonates based on bis-(4-hydroxyphenyl)-propane-(2,2) (bisphenol A), 
bis-(4-hydroxy-3,5-dichlorophenyl)-propane-(2,2) (tetrachlorobisphenol A), 
bis-(4-hydroxy-3,5-dibromophenyl)-propane(2,2) (tetrabromobisphenol A), 
bis-(4-hydroxy-3,5-dimethylphenyl)-propane-(2,2) (tetramethylbisphenol A), 
bis-(4-hydroxyphenyl)-cyclohexane-(1,1) (bisphenol Z) and on 
trinuclearbisphenols such as 
.alpha.,.alpha.'-bis(4-hydroxy-phenyl)-p-diisopropylbenzene. 
Other diphenols suitable for the preparation of the polycarbonates are 
described in U.S. Pat. Nos. 2,970,131, 2,991,273, 2,999,835, 2,999,846, 
3,028,365, 3,062,781, 3,148,172, 3,271,367 and 3,275,601. 
The aromatic polycarbonates may be branched in known manner by the 
incorporation of small quantities, preferably from 0.05 to 2.0 mol-% 
(based on the quantity of diphenols) of trifunctional or higher functional 
compounds, in particular compouds containing three or more than three 
phenolic hydroxyl groups. 
Polycarbonates of this kind are described, for example, in German 
Offenlegungsschriften No. 1,570,533 and 1,595,762, British Pat. No. 
1,079,821, U.S. Pat. No. Re 27,682 and German Pat. No. 2,500,092. 
The following are some examples of suitable compounds containing three or 
more than three phenolic hydroxyl groups: 
2,4-Bis-(hydroxyphenyl-isopropyl)-phenol, 
2,6-bis-(2'-hydroxy-5'-methyl-benzyl)-4-methylphenol, 
2-(4-hydroxyphenyl)-2-(2,4-dihydroxyphenyl)-propane and 
1,4-bis(4,4"-dihydroxytriphenylmethyl)-benzene. 
The following are further examples of trifunctional compounds: 
2,4-dihydroxybenzoic acid, trimesic acid, cyanuric chloride and 
3,3-bis-(4-hydroxy-3-methylphenyl)-2-oxo-2,3-dihydroindole isatin-bis 
cresol). 
Thermoplastic polalkylene terephthalates within the meaning of this 
invention are polyesters of terephthalic acid and an aliphatic diol, 
preferably from the group of butane-1-4-diol, ethanediol and 
cyclohexane-1,4-dimethanol, especially butane-1,4-diol. 
In addition to the glycol groups mentioned above the aforesaid 
terephthalates may contain up to 30 mol-% of residues of other aliphatic 
diols containing 3 to 12 carbon atoms or cycloaliphatic diols containing 6 
to 21 carbon atoms, e.g. those based on propane-1,3-diol, neopentyl 
glycol, pentane-1,5diol, hexane-1,6-diol, 3-methylpentane-2,4-diol, 
2-methylpentane-2,4-diol and 2,2,4-trimethylpentane-1,3-diol. 
In addition to terephthalic acid esters, the products may contain up to 15 
mol-% of residues of other dicarboxylic acids, e.g. isophthalic acid, 
adipic acid, succinic acid, sebacic acid, naphthalene-2,6-dicarboxylic 
acid, diphenylcarboxylic acid, azelaic acid or cyclohexanediacetic acid. 
The polyalkylene glycol terephthalates may be prepared by known methods, 
for example from dialkyterephthalates and the corresponding diol by ester 
interchange (see e.g. U.S. Pat. Nos. 2,647,885, 2,643,989, 2,534,028, 
2,578,660, 2,742,494 and 2,901,466). A lower alkyl ester of terephthalic 
acid, preferably the dimethylester, may be used as starting material which 
may be reacted with an excess of diol in the presence of suitable 
catalysts for transesterification to the bishydroxyalkylester of 
terephthalic acid. In this process, the temperature is raised from 
140.degree. C. to 210.degree.-220.degree. C. and the alcohol liberated is 
distilled off. Condensation is then carried out at a temperature of 
210.degree.-180.degree. C. while the pressure is lowered stepwise to below 
1 Torr so that excess diol is distilled off. 
The molecular weights M.sub.w of the terephthalates are in the range of 
from 30,000 to 80,000 and the molecular weights M.sub.w of the 
copolyesters of terephthalic and isophthalic acid are also in the range of 
from 30,000 to 80,000. The M.sub.w is determined measuring the intrinsic 
viscosity (limiting viscosity number, value of the reduced specific 
viscosity extrapolated to 0) I.V. in phenyl/o-dichlorobenzene (1/1) at 
25.degree. C., using a 5% solution, or it may be determined from the 
RSV-value (reduced specific viscosity) which is the specific viscosisty 
divided by the concentration of the solution used for the measurement. The 
RSV-value is determined on a 23% solution in phenol/tetrachloroethane 
(60/40) at 20.degree. C. The I.V. values are generally in the region of 
0.85 to 1.25. 
Polybutylene terephthalates with M.sub.w values in the range of 30,000 to 
60,000 are particularly preferred aliphatic thermoplastic polyesters. The 
carbon blacks used for the purpose of this invention may be gas black, 
furnace black or flame black with average primary particle sizes below 200 
Nanometer (nm), preferably below 100 Nanometer (nm) and in particular with 
an average primary particle size of less than 50 Nanometer, generally 
determined by electron microscope. 
The graphites used for the purpose of this invention may be graphite powder 
or graphite dust which is available in a wide range of particle sizes with 
particles of up to 5 mm, for example as electrode graphite, while the 
graphite powder used generally has an average particle size of up to 1 mm, 
preferably up to 0.5 mm. 
The carbon blacks used are preferably so-called conductivity carbon blacks 
which not only have a very small primary particle size but also a large 
external and internal surface area, i.e., a high porosity and therefore 
high BET surfaces available for nitrogen adsorption and high 
dibutylphthalate (DBP) adsorption values. In addition, they are highly 
structured, i.e. they have a strong tendency to agglomeration or 
aggregation of individual particles to form larger structures, e.g. in the 
form of chains. The BET surface areas of the carbon blacks are generally 
greater than 20 m.sup.2 /g and the DBP adsorption is generally above 40 ml 
per 100 g of carbon black. Conductivity carbon blacks with BET surfaces 
above 50 m.sup.2 /g and DBP adsorptions greater than 80 ml/100 g and 
average primary particle sizes below 50 nanometers (nm) are particularly 
siutable. Electronically conductive carbon blacks of this kind are 
commercially available as special grade carbon blacks with a pronounced 
structure and high electrical conductivity. 
Mixing of the carbon black and graphite with the thermoplastic 
polycarbonate may be carried out, for example, by the usual methods of 
powder mixing employed in the art, e.e. the polycarbonate powder may be 
intimately mixed with carbon black and graphite at room temperature and 
then extruded through an extruder at about 250.degree. to about 
300.degree. C. to form a granulate. 
Alternatively, the polycarbonate may be mixed with the carbon black and 
graphite by putting measured quantities of the components through suitable 
kneaders and directly granulating the mixture obtained. The temperatures 
for this method are again maintained at about 250.degree. to 300.degree. 
C. but granulation must be carried out in a vacuum which is produced by 
means of a degassing apparatus. 
The mixtures of polycarbonate, carbon black and granphite, which are 
obtained in the form of granulates as described above, are generally 
extruded with the thermoplastic polyalkylene terphthalate in conventional 
degassing extruders to produce extrusion moulded parts such as extruded 
sheets, profiles, plates or blown articles. The extrusion process is 
generally carried out at a temperature in the range of about 220 .degree. 
to 280.degree. C. 
Injection moulding of the granulate of polycarbonat, carbon black and 
graphite described above with the thermoplastic polyalkylene terephthalate 
and optionally other thermoplastic polycarbonates is generally carried out 
at temperatures in the range of aobut 270.degree. C. to about 300.degree. 
C. in conventional injection moulding apparatus. 
The whole mixture should preferably contain at least 15% by weight of 
thermoplastic polyalkylene terphthalates, based on the total weight of 
components (a)+(b)+(c). 
The present invention therefore also relates to carbon-containing moulded 
bodies produced by the injection moulding process, characterised in that 
they contain 
(a) 40 to 75% by weight of thermoplastic polycarbonates, 
(b) 35 to 15% by weight of thermoplastic polyalkylene terephthalates and 
(c) 35 to 10% by weight, preferably 30 to 15% by weight, of carbon black 
and graphite, in which the ratio by weight of carbon black to graphite 
should be in the range of from 5:1 to 1:3, preferably from 3:2 to 2:3, and 
the sum of percentages by weight is 100. 
Alternatively, the polyalkylene terephthalate may be added to the mixture 
of polycarbonate, carbon black and graphite without a granulate being 
first formed from the mixture, and the compounds may then be directly 
extruded or injection moulded as described above. This method is, however, 
less convenient as regards the ease of handling the components. 
In another variation of the process, addition of the polyalkylene 
terphtalate may be carried out immediately after or even together with the 
process of mixing the polycarbonate with carbon black and graphite, and 
the resulting mixture may then be worked up into a granulate, either by 
means of extrusion as described above or by agglomeration in the known 
agglomerators, before the product is extruded to form the moulded products 
such as sheets or injection moulded as described above. In this variation 
of the process, therefore, thermoplastic processing of the polyalkylene 
terephthalate is carried out twice. 
Mixtures of thermoplastic polycarbonates and thermoplastic polyalkylene 
terephtalates and moulded articles and sheets produced from them are known 
(see, for example, EP-OS No. 0,120,394 (Le A No. 22,232-EP), EP-OS No. 
0,143,352 (Le A No. 22 591-EP) and EP-OS No. 0,106,225 (Le A No. 
21,855-EP) and the literature quoted in and for these European 
Offenlegungsschriften). 
Polycarbonate sheets containing carbon black or graphite are known (see, 
for example, EP-OS No. 0,143,352 (Le A No. 22,591) and EP-OS No. 0,141,310 
(Le A 22,590) and the literature quoted in and for these European 
Offenlegungschriften). 
The combined use of carbon black and graphite in polyether ester elastomers 
has been described in EP-OS No. 0,032,375. 
The known stabilizers against heat, moisture and air used for thermoplastic 
polycarbonates and thermoplastic polyalkylene terephtalates may be added 
to the thermoplastic polycarbonates and the thermoplastic polyalkylene 
terephtalates.

EXAMPLES 
Method of preparation of basic compounds 
From a bisphenol-A/polycarbonate granulate .eta..sub.rel 1300, stabilized 
with 0.07% by weight of tris-(2-ethyl-oxetanyl-2)-methyl-phophite, and 
conductive carbon black (the carbon blacks should have a very small 
primary particle size and a large external and internal surface area, i.e. 
high porosity and therefore large BET surfaces for N.sub.2 adsorption and 
high dibutylphthalate (DBP) adsorption values and they should be highly 
structured, i.e. they should have a strong tendency to agglomeration of 
individual particles to form larger structures, e.g. chains, and the BET 
surface area of the carbon blacks should generally be greater than 20 
m.sup.2 /g and the DBP adsorption should be above 40 ml per 100 g of 
carbon black) and graphite powder (the graphite powder should have an 
average particle size of up to 1 mm, preferably and especially up to 0.5 
mm), the basis compound is prepared in a compounding extruder by the dosed 
introduction of the polycarbonate, carbon black and graphite under 
degassing conditions. 
The temperature in the melting region of the compounding extruder is 
280.degree. C. 
The granulate obtained from this process, hereinafter referred to as basic 
compound 1.1 and basic compound 2.1, is used for the extrusion of sheets 
or for injection moulding. 
1. Production of an antistatic extruded sheet 
1.1 Preparation of the basic compound as described above from 
______________________________________ 
polycarbonate 80% by weight 
carbon black 12% by weight 
and 
graphite 8% by weight. 
______________________________________ 
1.2 For the preparation of a granulates mixture for the production of 
sheets, polybutylene terphthalate is added to this basic compound in 
proportions of 5:1 in suitable mixing apparatus (tumbler mixers or conical 
screw mixer) and after thorough mixing, the sheet is directly extruded 
from this granulate mixture. 
The extrusion temperature should be in the range of 230.degree.-260.degree. 
C. on account of the addition of polybutylene terephthalate. The 
temperature of the subsequent smoothing apparatus (applicator roller for 
sheet extrusion) should be kept at or below 60.degree. C. in order to 
avoid crystallisation in the sheet. The sheet obtained has the following 
composition: 
______________________________________ 
polycarbonate 66.66% by weight, 
polybutylene terephthalate 
16.66% by weight, 
conductive carbon black 
9.99% by weight and 
graphite 6.69% by weight. 
______________________________________ 
A. Mechanical characteristics of 1.2 
______________________________________ 
Tests Units Test regulation 
______________________________________ 
Tensile MPa ISO/R 527 66 
strength 
at break 
Elongation % DIN 53 455 6 
on tearing 
Tensile MPa DIN 53 455 69 
stress 
at yield 
Density g/cm.sup.2 1.28 
______________________________________ 
B. Electrical properties of 1.2 
______________________________________ 
Specific surface resistance pS 
10.sup.4 Ohm 
Specific volume resistance pD 
10.sup.2 Ohm.cm 
______________________________________ 
2. Production of a conductive extrusion sheet 
The starting material for the production of a conductive extrusion sheet is 
again a basic compound prepared by the method of preparation given for 
basic compounds. 
The proportions of polycarbonate, carbon black and graphite in the mixture 
were adjusted to the following composition: 
2.1 Preparation of the basic compound from 
______________________________________ 
polycarbonate 70% by weight 
conductive carbon black 
18% by weight 
graphite 12% by weight 
______________________________________ 
2.2 For the production of extrusion sheet, 80% by weight of basic compound 
2.1 are mixed with 20% by weight of polybutylene terephthalate and the 
mixture is extruded to a sheet as described under 1.2. 
The sheet obtained has the following composition: 
______________________________________ 
polycarbonate 56.00% by weight 
polybutylene terephthalate 
20.00% by weight 
conductive carbon black 
14.40% by weight 
graphite 9.60% by weight. 
______________________________________ 
3. Preparation of antistatic injection moulding compounds 
The starting materials used for the preparation of the antistatic injection 
moulding compounds are the two basic compounds 1:1 and 2.1 which are mixed 
with 20% by weight or 30% by weight of polybutylene terephtalate, 
depending on the antistatic properties required. Processing temperature: 
260.degree. C.-280.degree. C. 
3.1 Composition of the injection moulding compounds from basic compound 1.1 
______________________________________ 
polycarbonate 64.00% by weight, 
polybutylene terephthalate 
20.00% by weight, 
conductive carbon black 
9.60% by weight and 
graphite 6.40% by weight 
______________________________________ 
3.2 Composition of the injection moulding compound obtained from basic 
compound 2.1 (now outside the scope of the claims of the CIP) 
______________________________________ 
polycarbonate 49.00% by weight, 
polybutylene terephthalate 
30.00% by weight, 
conductive carbon black 
12.60% by weight and 
graphite 8.40% by weight. 
______________________________________ 
Especially the instant invention relates to carbon-containing moulded 
bodies produced by extrusion or by injection moulding and comprising 
(a) 55% by weight to 85% by weight of thermoplastic polycarbonate, 
(b) 30% by weight to 5% by weight of thermoplastic polyalkylene 
terephthalate and 
(c) 35% by weight to 10% by weight of carbon black and graphite, in which 
the ratio by weight of carbon black to graphite is in the range of from 
5:1 to 1:3 and the sum of percentages by weight of components (a)+(b)+(c) 
is 100% by weight. 
It is understood that if component (b) is 30% by weight, component (c) can 
be only up to 15% by weight; also it is understood that if component (c) 
is 35% by weight, component (b) can be only up to 10% by weight, referred 
always to 100% by weight of the sum of (a)+(b)+(c). 
The relationship of the carbon black and the graphite is of some importance 
for the properties of the bodies of the instant invention because, if the 
ratio carbon black to graphite is above 5:1, the incorporation into the 
polycarbonate becomes difficult, and if the ratio carbon black to graphite 
is below 1:3, the effect of the incorporated amount of carbon is reduced. 
It is understood that these latter specially mentioned moulded bodies 
comprising the components (a), (b) and (c) can be prepared by the same 
different processes mentioned in the body of instant specification.