CA2048602C

CA2048602C - Process for making antistatic or electrically conductive polymer compositions

Info

Publication number: CA2048602C
Application number: CA002048602A
Authority: CA
Inventors: Bernhard Wessling; Holger Merkle; Susanne Blattner
Original assignee: Zipperling Kessler GmbH and Co
Current assignee: Zipperling Kessler GmbH and Co
Priority date: 1989-12-30
Filing date: 1990-12-22
Publication date: 1999-09-07
Anticipated expiration: 2010-12-22
Also published as: KR920701988A; JP3056247B2; DE59010761D1; WO1991010237A1; ES2108041T3; DK0461232T3; FI914077A0; ATE158438T1; DE3943420A1; EP0461232A1; JPH04505941A; KR100187568B1; CA2048602A1; FI114583B; EP0461232B1

Abstract

Polymeric compositions rendered antistatic or electrically conductive showing increased conductivity are obtained by incorporating into a matrix polymer a combination of A. a first finely divided conductive material, namely conductive carbon black with a BET surface area of more than 80 m2/g or an intrinsically conductive organic polymer in complexed form, and B. a second finely divided conductive material, namely intercalated graphite or an intrinsically conductive polymer in complexed form, which is different from the material used as material A, or a metal powder and/or C. a finely divided non conductive material having an average particle size below 50 microns.

Description

The plastics proce~;sing industry requires for various purposes (e. g. for elimination of electrostatic charges, for electromag-netic shielding or as electrodes) antistatic or electrically conductive modifications of conventional polymers.
Thermoplastic polymers are being used amongst others as polymers but also durop2asti~~ polymers and enamels are being made conduc-tive. Carbon black color pigment and so-called "conductive car-bon black" (carbon black with a specific surface area of > 80 m2/g), carbon fibe~_s, metal coated glass microspheres, metal fibers and metal flakes are used for this purpose; mixtures of conventional polymers with intrinsically conductive polymers are also already known ( EP-OS 168 620 ) . Such mixtures are frequently also referred to as "compounds" or "polymer blends".
The present invent~_on relates to a method of optimizing anti-static or electrically conductive polymers in which finely di-vided conductive materials, i.e. materials with a particle size of about 1 micron and below are used. Conductive carbon black and dispersable intrinsically conductive polymers, e.g. those described in EP-OS 329 768, have the advantage that the conduc-tivity is drastically increased already at a content of less than 20 vol.~, sometimes even at significantly below 10 vol.~.
This behavior is normally referred to as "percolation" and is described using the percolation theory; more recently an inter-pretation of this phenomenon as "flocculation process" has been advanced (compare B. Wel3ling, Mol. Cryst. Liqu. Cryst. 160, 205 (1988) and Synt. Met. 27, A83 (1988).
The optimization of polymers which have been made conductive is almost always concerned with lowering the cost and with improv-ing the mechanical and the processing properties while retaining the conductivity by lowering the amount of conductive additives -.2 _ and also by a parallel shift of the percolation curve (the plot of the conductivity vs. the percent content of conductive mate-rials) to lower coni~ents. For achieving this objective different proposals have been made in the literature:
~ According to the "percolation theory" it is recommended to disperse in the polymers highly structured conductive mate-rials (compare E. Sichel (ed.) "Carbon Black Polymer Composites", New York, 1982); apparently this is only suc-cessful when using larger particles (e. g. fibers).
~ The concentration of the conductive materials in so-called "conductive paths" (GB-OS 2 214 511 and EP-OS 181 587) has proved successful in many cases.
~ The improvement of the dispersibility of the conductive materials (EP-OS 329 768) allows to shift the necessary critical concentration for the increase of the conductivity to lower percentages.
All proposals are still having disadvantages, especially that the advantage of :Lower material cost is frequently counter balanced by increased production expenditures, or that the pos sible areas of ap~~lication are restricted. Two examples may illustrate this point:
~ The "conductiver paths" concept (EP-OS 181 587) is not appli-cable if - for whatever reasons - pure monophasic polymers are to be rendered conductive.
~ Polymerblends with intrinsically conductive polymers ex-hibited frequently the disadvantage of unsatisfactory me-chanical properrties if modifications are needed which are stiff and/or dimensionally stable upon heating.
It is therefore an object of the invention to develop a method which affords a further possibility of optimizing polymers which are antistatic or conductive, as an alternative and/or improve-ment over the "conductive paths" or "dispersion" concepts.
The invention is directed to a method for preparing polymeric compositions rendered antistatic or electrically conductive and showing increased conductivity from at least one non-conductive matrix polymer and at least two additives, which is charac-terized in that there is used as additives a combination of A. a first finely divided conductive material, namely con-ductive carbon black having a BET surface area of more than 80 m2/g or an intrinsically conductive organic polymer in complexed form, and B. a second finely divided conductive material, namely gra-phite or an intrinsically conductive polymer in complexed form, which is different from the material used as material A, or a metal powder and/or C. a finely divided non-conductive material having an average particle size below 50 microns.
Surprisingly it has been found that at a given additive content in the polymer matrix the conductivity of the compound is signi-ficantly increased if a finely divided (preferred average particle size <_ 1 micron) conductive material A is combined with another conductive material B consisting preferably of larger particles of > 0,5 microns, e.g. about l0 microns (1 to 50 mi-crons), and/or a non-conductive material C having an average particle size < 10 microns.
Surprisingly a conductivity synergism occurs, i.e. at identical weight or volume proportion of the finely divided conductive material A alone or the coarser material B alone a lower conduc-tivity results as when incorporating A and B together in the same weight or volume ratio. Accordingly one achieves a higher conductivity by combining A and B in comparison to A or B alone at the identical degree of filling.

2o~sso2 Equally surprising is the effect that at a given content of material A the conductivity increases by addition of material C
although material C: is non-conductive. This effect is in some cases so significani~ that at a concentration of material A below the critical threshold of the sudden conductivity increase(below the percolation point) practically no conductivity is measurable whereas the sudden conductivity increase occurs when the non conductive material C is added. When using the materials B and C in combination with material A the mentioned effects are ad ditive.
In both cases an improvement of the mechanical properties will surprisingly often :result. This is detectable primarily in con-centration ranges resulting in a particularly high conductivity, and when using intrinsically conductive polymers as material A
in combination with a suitable material C in rigid or heat stable polymers.
As material A carbon black ( conductive carbon black ) having a specific surface area of more than 80m2 g or powdery, preferably dispersible intrins:i.cally conductive polymers in complexed form can be used which d_Lsplay in the polymer matrix a particle size of _< 1 micron, prei:erably < 500 nanometer. Suitable intrinsi-cally conductive polymers are e.g. polyacetylene, polypyrrole, polyphenylenes, polythiophenes, polyphthalocyanines and other polymers with conjugated n-electron systems which can be ren-dered conductive (complexed) in a known manner with acids or by oxidation. Particularly preferred are complexed polyanilines.
Graphites are suitable as material B. Particularly preferred is intercalated graphite (compare Rompp, Chemie-Lexikon, 8th ed., p. 1540/41 (1981), e.g. graphite loaded with copper(III)-chlo-ride or with nickel(III)-chloride. Further electrode graphite or natural graphite ma:~r be used. Metal powders are also useful as material B. The particle size of material B is in each case preferably larger than that of material A.

As material C essentially all pigments, fillers and other non-conductive particu.Late materials which are non-fusible under processing conditions or materials which are insoluble in the polymer matrix and having an average particle size of about 50 microns or less may be used. Preferably the particle size of material C is in each case larger than that of material A. Limi-tations concerning the chemical composition of the particles have up to now not been found. Thus titanium dioxide, organic or inorganic pigments, fillers such as silica, chalk, talcum and others, but also th~a neutral (compensated) non-conductive forms of intrisically conductive polymers may be employed.
As matrix polymers all polymers are suitable such as thermo-plastic or duromeric: polymers or enamels. The invention may also be used in polymer blends, particularly successfully in those corresponding to thc~ teaching of EP-OS 168 620.
The volume ratio between the materials A and B or between A and C or between A and a combination of B and C may be varied within broad ranges betweer,~ about 20:1 and 1:20 and has to be optimized in each case. Prefer=red are the following values for ~ the combination of A with B 2:1 to 1:5 ~ the combination of A with C 2:1 to 10:1.
The examples show a representative selection of successful ex-periments and corresponding comparison experiments. The incor-poration of the materials A and B and/or C may be effected by conventional methods which are known per se; it is preferred to premix the material:c A and B and/or C prior to their incorpo-ration into the matrix polymer.
An explanation for the surprising effects achieved with the invention is not yet possible. They are completely incomprehen-sible in the light of the "percolation theory", or even inadmis-sible. In connection with the newer concepts (B. Wessling, loc.

v .,' - 6 cit.) of the sudden conductivity increase as a phase transition between the dispersed and flocculated state the effects are also not comprehensible but at least admissible if further, up to now unproven assumptions are included.
In the following examples the mentioned materials A, B and C
were incorporated into conventional polymer systems. PE is LUPO
LEN~ 2424H (BASF AG). PETG is a copolyester manufactures by Eastman Rodak. The enamel (examples 27 and 32) is a PVC/VA-co f polymer enamel comprising solvent.
The incorporation of the additives into PE and PETG was accom-plished in an internal mixer after pre-mixing of the materials A, B and optionally C in a laboratory mixer. The mixtures were hot pressed; the specific conductivity was determined on the pressed samples using the four point measuring technique.
The incorporation of the additives into the enamel system was achieved after premixing in a ball mill. The liquid enamel was applied to a support and dried.
All percentages are percent by weight.
In the table the following were used:
Ketjenblack EC - conductive carbon black, surface area about 800mz/g .
Graphite EP 1010 = electrode graphite, particle size about 10 microns.
Polyaniline-pTs = polyaniline complexed with p-toluene sulfonic acid.

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Claims

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

1. An antistatic or electrically conductive polymeric composition showing increased conductivity comprising; at least one non-conductive matrix polymer; and at least two additives, selected from the group consisting of additives i) A and B, ii) A and C; and iii) A and B and C, wherein A is a first finely divided conductive material, namely conductive carbon black with a BET surface area of more than 80m2/g or an intrinsically conductive organic polymer in complexed form;
B is a second finely divided conductive material, namely intercalated graphite or an intrinsically conductive polymer in complexed form, which is different from the material used as material A, or a metal powder, and C is a finely divided non-conductive material having an average particle size below 50 microns, being non-fusible under the processing conditions and insoluble in the matrix polymer, whereby B may not be an intrinsically conductive polymer and C may not be a transition metal oxide if A is a conductive carbon black.

2. A composition according to Claim 1 wherein graphite intercalated with copper chloride or nickel chloride is used as material B.

3. A composition according to Claim 1 wherein complexed polyaniline is used as material A or as material B.

4. A composition according to Claim 1 wherein inorganic or organic electrically non-conductive fillers or pigments are used as material C.

5. A composition according to Claim 4 wherein titanium dioxide is used as inorganic pigment.

6. A composition according to Claim 4 wherein pigment yellow 13 is used as organic pigment.

7. A composition according to Claim 1 wherein when the materials are selected from A and B, the volume ratio is from 20:1 to 1:20; when the materials are selected from A and C, the volume ratio of A:C is from 20:1 to 1:20; or when the materials are selected from A and B and C, the volume ratio of A:(B + C) is from 20:1 to 1:20.

8. A composition according to Claim 7 wherein the materials A and B are used in a volume ratio of 2:1 to 1:5.

9. A composition according to Claim 7 wherein the materials A and C are used in a volume ratio of 2:1 to 10:1.

10. A method of producing the compositions according to Claim 1, 2, 3, 4, 5, 6, 7, 8 or 9 comprising the steps of premixing the additives i) A and B or ii) A and C or iii) A, B and C, and then incorporating them into the matrix polymer.