Note: Descriptions are shown in the official language in which they were submitted.
2048602
- 1 -
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
208602
-.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
CA 02048602 1999-06-07
3
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
- 4 -
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.
2048602
- 5 -
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
CA 02048602 1999-06-07
.,' - 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.
204860
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