POLYCARBONATE CONDUCTEUR D'ELECTRICITE

ELECTRICALLY CONDUCTIVE POLYCARBONATE

Abrégé anglais

ELECTRICALLY CONDUCTIVE POLYCARBONATE

Abstract of the Disclosure

An antistatic and electrically conductive moulding
composition comprising from 99 to 99.99 % by
weight of an aromatic polycarbonate and from 1 to
0.01 % by weight of carbon or graphite fibres
having a ratio of length to cross section of at
least 10:1.

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Revendications

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. An antistatic and electrically conductive moulding composition
comprising from 99 to 99.99% by weight of an aromatic polycarbonate and
from 1 to 0.01% by weight of carbon or graphite fibre having a ratio of
length to diameter of at least 10:1.


2. An antistatic and electrically conductive moulding composition
according to claim 1, wherein the aromatic polycarbonate is of a bisphenol
selected from the group consisting of bisphenol A, tetrachloro bisphenol A,
tetrabromo bisphenol A, tetramethyl bisphenol A and the corresponding
copolycarbonates and polycarbonates thereto which have been crosslinked
or branched by condensation of trivalent phenols.


3. An antistatic and electrically conductive moulding composition
according to claim 1, wherein the ratio of length to diameter of the fibre
is from 100:1 to 1000:1


4. An antistatic and electrically conductive moulding composition
according to claim 1, wherein the amount of carbon or graphite fibre
is 1 to 0.1% by weight.

Description

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This invention relates to an anti-static and electrically
conductive moulding composition composed of from 99 to 99.99% by weight
of an aromatic polycarbonate and from l to 0.01% by weight of carbon or
graphite fibres having a ratio of length to cross section of at least
10:1 .
The ratio of length to cross section of the fibres is preferably
within a range of from 100:1 to 1000:1. The compositions may contain, in
~; addition to the aromatic polycarbonate and the carbon or graphite Eibres~
the usual additives for thermoplastic compounds, such as stabilizers,
fillers and pigments.
Aromatic polycarbonates within the context of this invention
include, in particular, the polycarbonates of bis-phenols such as bis-
~ phenol A, tetrachloro or tetrabromo bis-phenols A, tetramethyl bis-phenol
;~1 A, the corresponding copolycarbonates and po~ycarbonates which have been
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`~ crosslinked or branched by condensation with small quantitites of trivalent
phenols. They are generally high molecular weight products with the
properties of thermoplastic resins.
It is known to render synthetic products antistatic or electrically
conductive by the addition o finely-divided metals or of carbon black. The
quantity of electrically conductive material to be added is in most cases
more than 20% by weight if a sufficient effect is to be achieved. At the
same time, the mechanical properties of the polymer are in most cases so
deleteriously affected by this addition that the products become unusable
for many purposes. Carbon and graphite fibres have also been

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1~5S289

used for mechanically strengthening synthetlc materials ~ see. Japanese
Published unexamined Patent Application No. 50-001169). Here again,
quantities of over 10% by weight are required.
The present invention is based on the discovery that the electric
conductivity of aromatic polycarbonates can be conside~ably increased, i.e.
by several powers of 10 by mixing the aromatic polycarbonate as homogeneously
as possible with carbon or graphite fibres in which the proportion of length
to cross section is at least lO:l, preferably from 100:1 to 1000:1. The
quantity of fibres is from 0.01 to 1% by weight, based on the mixture.
Quantities of less than 1 % by weight are sufficient for obtaining antistatic
properties, so tha~ amounts of from 1 to 0.1 % by wt. are preferred. The
quantity required depends on the geometrical shape of the fibres, that is,
- the longer and thinner the fibres, the smaller the quantity required. The
mechanical properties of the aromatic polycarbonate are not impaired by the
addition of carbon or graphite fibres but on the contrary are frequently
improved.
The carbon or graphite fibres can be incorporated in the polycar-
bonate by known methods, either during or after preparation of the polycar-
bonate. Methods of incorporation which do not alter the ~orphology of the
fibres are preferred. If the ratio of length to cross section is a]tered
in the process of incorporation due to breakage of the fibres, the quantity
of fibres may have to be adjusted. Aromatic polycarbonates reinforced with
fibres can be further treated by the usual methods of thermoplastic processing,
e.g. by injection moulding, extrusion or blow moulding, generally at
temperatures of from 2^5 C to 350 C. The manufacture

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1 15~289


of foils containing carbon fibres ~rom solutions of the
aromatic polycarbonates is preferred. Foils with
excellent antistatic properties and high transparency
are obtained by the addition o~ carbon or graphite
fibres in quantities of from 0.1 up to about 1% by
weight. The addition of carbon black in the same
quantities has virtually no ef~ect although it
considerably reduces the transparency.
The carbon or graphite ~ibres may also be
orientated in a preferential direction in the
polycarbonate by suitable methods. The resulting
products, for example moulded articles or foils, have
increased conducti-~ity in a given direction.
The moulding compounds according to the inven-
tion may advantageously be used wherever electros-
tatic charging must be completely prevented.
~` Examples include their use in mining underground,
in order to avoid -the risk of explosion, or in
electrical or electronic instruments, e.g. a~
housings for high sensitive MOS units.
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E~amples of Practical Application
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A 20% by weight solution of bisphenol A
- polycarbonate (molecular weight 28,000) was
;~ mixed with the quantities of carbon or
graphite fibres indicated in the following
Table. The resulting solution was used to
cast oils in thicknesses of from 0.01 to
0.1 mm. The results are shown in the follow-
ing Table 1.




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Example % by Average Average Electric Electro-
-: Number weight length dia- conduct- static
;~ by (mm) meter ivity charg~e
~-~ fibres (/um) (~ -1Cm-1) (V.cm

1 pure PC ~ o-18 ~5000
. 2 1,0 3.0 12.5 10-5 ~ 100
3 .5 3.0 12.,~ 10-7 ~200
~: 4 1.0 6.o 1l~.5 10~ C 100
. 5 0.5 6.0 1~.5 10-5 , C 100
. .6 0.1 600 14.5 10 ~3
: 7 0,5 10.0 1~ 10~5 ~ 100
0.1 25.0 1 L~. 5 1o-56 ~ 100
9 0,]. 100,0 1~,~ 10- ~200
1.0 0.13 12.5 1o~6 __
11 0.05 0.13 ~.2.5 10~9 --
I2 1.0 . 0.20 12.5 10-5
. 13 : 0~,1 :0,20 : 12,5 ; 10-7 __
~ ~ 14 1,0 0.37 14.5 10
:: 15 ~ o.o5 : 0.37 14.5 6
16 1.0 ~ 0,70 1~.5 10- --
17 0 1 0 70 14,5: : 10 : --
: : ~ *) Frict;on partners: Dralol~ 50 rubbings, 23~CJ

:~- 50% r~elative humid~ity,

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