CA1155289A

CA1155289A - Electrically conductive polycarbonate

Info

Publication number: CA1155289A
Application number: CA000368411A
Authority: CA
Inventors: Jurgen Hocker; Rolf Dhein; Wolfgang Cohnen; Peter-Rolf Muller
Original assignee: Bayer AG
Current assignee: Bayer AG
Priority date: 1980-01-15
Filing date: 1981-01-13
Publication date: 1983-10-18
Also published as: EP0032379A2; JPS56104960A; EP0032379A3; DE3001204A1

Abstract

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.

Le A 20 076 -

Description

11~52~

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 i'l `~ 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 '.`: ~:
:~, ,~

. :

: ` , . .: , - , , 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 ~;', .
~: `

:::
.

., , ~ . .
' '' , ' ~' .. ' . ~ : ' . I

. .

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.
'' ~ .

~`~
~`' ' Le A 20 076 ` ~', :-'.
:, ` ' , , ' ~' : I
`' ' 1 ~528 E~amples of Practical Application _______.___________________ ______ 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.

~:`

~"

''~ .

.- ,'.
~ Le A 20 07~
, ~.
`: :

- . : , -. . ~ . ,:: : .
.. . . ~ ' j , :
, , , ., , ~'' ' ' - . :

.~ ' .
.~ .

~ Table 1 . . .
.
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, ~ Le A 20 076 .,, . , , . , .. :
, i , 1, :
.

Claims

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.