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BACKGROUND OF THE INVENTION AND PRIOR ART
The synthesis, as well as the chemical, electrical and photoelectrical
characteristics of nonpolymeric and polymeric organic semiconductors and
conductors have formed the subject of intense research. The state of
present knowledge, as well as the in part differing opinions have been
discussed in numerous works, cf G. Wegner, Angew. Chem. Vol. 93, pp. 352
to 371, 1981; M. Hanack, Naturwiss, Vol. 69, pp. 266 to 275, 1982; A.
Heeger et al, Synthetic metals, Vol. 6, pp. 243 to 263, 1983; and K.
Seeger, Angew. Makromol. Chem., Vol. 109/110, pp. 227 to 251, 1982.
The term "conductive polymers" is understood to mean polyconjugate systems,
such as occur in polyacetylene (PAc), poly-1,3,5 . . . n-substituted
polyacetylenes, acetylene copolymers, as well as
1,3-tetramethylene-bridged polyenes, e.g. polymers resulting from the
polymerization of 1,6-heptadiene and similar polyacetylene derivatives. It
also includes the various modifications of polyparaphenylenes (PPP), the
different modifications of polypyrroles (PPy), the different modifications
of polyphthalocyanines (PPhc) and other polymeric conductors, such as
polyanilines, polyperinaphthalines etc. They can be present as such or as
polymers complexed ("doped") with oxidizing or reducing substances.
Complexing generally leads to an increase in the electrical conductivity
by several decimal powers and into the metallic range.
The term "organic conductors" is understood to mean nonpolymeric, organic
substances, particularly complex salts or charge transfer complexes, e.g.
the different modifications of tetracyanoquinodimethane (TCNQ) salts.
Conductive polymers are in part obtained as polycrystalline powders,
film-like agglomerates or lumps of primary particles. As e.g.
polyacetylene is neither soluble nor fusible, it constituted an important
advance when Shirakawa was able to produce self-supporting, but very thin
films by interfacial polymerization, whose characteristics are similar to
those of thin polymer films. Tests carried out on these films concerning
the morphology of polyacetylene led to a fibril theory, according to which
the polyacetylene is assembled to give elongated fibres through which
crystalline regions form in the fibre direction, in which the current
flows along the fibre axis following doping (complexing).
The general opinion is that the conductivity is brought about by the high
crystallinity and by the arrangement of the polyconjugate systems
(optionally in complexed form). However, it has not as yet been adequately
clarified whether the conductivity mechanism in polyenes and
polyphenylenes, as well as polypyrroles is determined by electron
transfers along the chain or at right angles to the chain direction,
particularly as the morphology of conductive polymers has also not yet
been clarified. In this connection, the inventor has proved that the
primary particles of polyacetylene are always extremely fine spherical
particles, which in part agglomerate to fibrillar secondary particles and
in part agglomerate to non-directed foil-like film, cf B. Wessling,
Makromol. Chem., Vol. 185, 1265-1275, 1984. By reference the contents of
this paper form part of the disclosure of the present description.
The literature provides the following information concerning the physical
characteristics and processability of conductive polymers and organic
conductors:
High crystallinity, e.g. polycrystalline powders, in individual cases long
needle-shaped crystals (for TCNQ, cf Hanack, 1982), or other macroscopic
crystal shapes, e.g. in the case of polyphthalocyanines. In the case of
polyacetylene, the size of the crystallites clearly does not exceed 100
.ANG. (D. White et al, Polymer, Vol. 24, p. 805, 1983).
Polyconjugate polymers, are, in their basic state, insulators, as opposed
to polymer-bridged charge transfer complexes, such as polyphthalocyanines
(cf Hanack, loc. cit, pp. 269/270).
Optical appearance generally matt black (glossy or shining only if the
synthesis was carried out on the smooth surfaces, cf the Shirakawa method
for producing self-supporting "films", in which the side facing the glass
is glossy and that remote from the glass matt). Polyphthalocyanines are
non-glossy powders, which appear blue.
If, as a result of the synthesis conditions, macroscopically larger
structures can be obtained, they are brittle (the exception being
cis-polyacetylene). Due to their crystalline structure, charge transfer
complexes are always very brittle substances, which are very difficult to
process mechanically (Hanack, loc. cit, pp. 269/270). Much the same
applies for uncomplexed and particularly complexed conductive polymers.
Conductive polymers and organic conductors are generally insoluble,
infusible and not shapable, whilst in most cases being unstable relative
to oxygen, moisture and elevated temperatures. If e.g. in the case of
nonpolymeric or polymeric charge transfer complexes (TCNQ or PPhc),
melting points can in fact be observed, they are close to the
decomposition point, so that decomposition-free melting is either
impossible or is only possible with great difficulty. To the extent that
soluble derivatives exist in the case of the different conductive
polymers, their conductivity is several decimal powers inferior compared
with the insoluble non-modified substances. A thermoplastic deformation of
conductive polymers and organic conductors has not as yet proved possible.
Polypyrrole and certain representatives of the polyphthalocyanines are
comparatively stable with respect to oxidative and thermal influences, cf
Hanack, loc. cit; K. Kanazawa et al, J. Chem. Soc., Chem. Comm. 1979, pp.
854/855.
Hanack's 1982 statement that most organic conductors and conductive
polymers were primarily produced under the standpoint of high
conductivity, whilst ignoring their mechanical properties, stability and
processability, still applies. The following statements are made regarding
the physical characteristics of organic conductors and conductive polymers
which are important for processability.
Insolubility
Whilst nonpolymeric organic conductors are crystallized from solutions of
the two participating components and are in part still soluble in
decomposition-free manner after their preparation, a solvent has not
hitherto been found for conductive polymers either in the untreated or
complexed form. The tests described by T. Matsumoto et al, J. Polym. Sci.
A-2, Vol. 10, p. 23, 1972 with polyacetylene from polymerization induced
by .gamma.-radiation clearly did not relate to polyacetylene with the
chemical uniformity as discussed here and as shown by IR-spectra, but
instead related to non-uniform mixtures of different types of substituted,
low molecular weight polyenes. The dissolving of polyacetylene in hot
sulphuric acid (S. Miyata et al, Polym. J., Vol. 15, pp. 557 to 558, 1983)
leads to strongly oxidized, chemically changed products (A. Pron, Polymer,
Vol. 24, p. 1294ff, 1983).
Solvents have also not hitherto been described for other conductive
polymers. Attempts have been made for polyphthalocyanines to increase the
solubility by introducing ring substituents, e.g. tert.butyl groups, but
the conductivity decreases by several decimal powers. T. Inabe et al, J.
Chem. Soc., Chem. Comm, 1983, pp. 1984-85 describe the dissolving of
polyphthalocyanine in trifluoromethane sulphonic acid, but give no
information on the characteristics of the raw material recovered
therefrom.
In addition, no solvents or processes are known enabling true,
deposition-stable dispersions to be prepared. Although EP-OS 62,211
describes polyacetylene suspensions these are in fact only suspended,
coarse polyacetylene particles, without deagglomeration of the tertiary or
secondary structure of the particles.
Melting behaviour
Both in the untreated and complexed forms, all conductive polymers cannot
be melted. Although differential thermal analysis of polyphthalocyanines
gives certain indications of a melting behaviour, this is accompanied by
immediate decomposition. Dynamoviscoelastic tests on polyacetylene
(Shox-an Chen et al., Makromol. Chem. Rapid Comm., Vol. 4, pp. 503-506,
1983) show that between -100.degree. and +350.degree. C. there is neither
a glass transition temperature nor a crystalline melting. Polyacetylene
decomposition starts from approximately 350.degree. C. The only phase
transition in this range takes place at above 150.degree. C. and is
attributed to cis/trans-isomerization.
Admittedly, meltable or fusible conductive polymers have occasionally been
described, but their conductivity was never satisfactory and was several
decimal powers lower than in the case of the polymers under discussion
here.
Stability
Numerous reports deal with the instability of conductive polymers.
Polyacetylene is particularly sensitive to oxygen and it was reported that
even when stored under an inert atmosphere and in the cold, the original
polyacetylene characteristics were lost. For example, after a certain time
it can no longer be stretched. Even when stored in an inert atmosphere,
complexed polyacetylenes almost completely lose their excellent electrical
properties after a short time. These phenomena are attributed to an
oxidative decomposition and to crosslinking processes, which also occur in
the case of cis/trans-isomerization (cf inter alia M. Rubner et al, J.
Polym. Sci., Polym. Symp. Vol. 70, pp. 45-69, 1983). The instability of
polymers from 1,6-heptadiene is described by H. Gibson, J. Am. Chem. Soc.,
Vol. 105, pp. 4417 to 4431, 1983. During heating in vacuo, this is
rearranged into undefined, no longer conjugate polymers and comparable
processes take place in the case of polyacetylene.
Formability
It has hitherto proved impossible to produce moulded articles from
conductive polymers or organic conductors by the masters forming and
shaping processes (Kunststoff-Taschenbuch, p. 58ff). This is directly
linked with the fact that the polymers are infusible and insoluble. It has
also proved impossible up to the present to produce true dispersions of
these substances in organic solvents or in viscous polymers.
Cis-polyacetylene to a certain extent would appear to represent an
exception in that immediately following production is to a limited extent
"ductile", as described by M. Druy et al, J. Polym. Sci., Polym. Phys.,
Vol. 18, pp. 429-441, 1980. However, the ductility and stretchability is
limited exclusively to the cis-isomer, the transisomer being brittle even
in the absence of oxygen. A. MacDiarmid and A. Heeger, proceedings of a
Nato ASI on Molecular Metals Les Arcs, 1979, plenary lecture, state that
fresh "films" of both cis and trans-polyacetylene are flexible and easily
stretchable, the latter being attributed to the partial orientation of the
fibres. Shortly after synthesis, the cis-isomer also loses the ductility
properties, even in the absence of oxygen, which have an extreme
accelerating action on embrittlement. This is inter alia due to the fact
that oxygen not only brings about an oxidative decomposition, but also
leads to cis/transisomerization (J. Chien et al, J. Polym. Sci., Polym.
Phys., Vol. 21, pp. 767 to 770, 1983). According to Druy, loc. cit., a
volume increase unexpectedly occurs during stretching, which can be
explained by the weak interfibrillar forces of attraction. It is also
concluded from the stress-strain curves and the time behaviour that, even
in the absence of oxygen, crosslinking processes take place, possibly due
to the appearance of free radicals during cis/transisomerization.
As a result of these difficulties, shaping involves the use of methods
which cannot be considered a master forming process. Thus, Shirakawa et al
in EP-OS 26,235 describe the shaping of a gel-like polyacetylene with a
solvent content of 5 to 95% by weight, which is moulded at temperatures
between ambient temperature and 100.degree. C., which leads to moulded
articles which are subsequently dried. The same procedure is adopted by
Kobayashi et al (GB-OS 2,072,197) whereby freshly polymerized
cis-polyacetylene with comparatively high solvent contents is moulded and
subsequently calendered. Before the drying process, the end product still
contains approximately 5% of solvent.
A production of moulded articles, once again not by the master forming
process, is described by Chien et al, Makromol. Chem. Rapid Comm., Vol. 4,
pp. 5-10, 1983, who produced macroscopic polyacetylene strips by special
polymerization methods.
J. Hocker et al (EP-OS 62,211) describe the production of moulded articles
from polyacetylene-containing polymers, which are dissolved in a solvent
containing macroscopic polyacetylene particles. Shaping takes place by
removing the solvent. For accelerating suspension formation, optionally an
Ultraturrax.RTM. stirrer is used, the fibrous structure of the particles
being retained. The thus obtained moulded articles have only a
comparatively low conductivity. The further EP-OS 84,330 of the same
inventors also deals with attempts to obtain moulded articles from
polyacetylene-containing plastics, without using a master forming process.
Attempts are made in the examples to produce laminates with a (doped)
polyacetylene layer, in that polyacetylene in the form of a suspension in
an easily evaporatably solvent, such as methylene chloride, is sprayed
onto a substrate. The thus obtained polyacetylene layer on a polymer or an
organic carrier is subsequently coated with a further protective layer.
In the case of polypyrrole, DE-OS 3,227,914 describes a process, in which
polypyrrole is moulded at temperatures of 150.degree. to 300.degree. C.
and pressures of 50 to 150 bar. According to the examples, this process is
suitable for producing multilayer laminates of nonconductive polymer films
and polypyrrole films (as are directly obtained from electrochemical
polymerization). Preferably, polypyrrole and the various copolymers
thereof are pressed in film form onto polyester, polyethylene or
polyacrylonitrile films or on polyurethane or polystyrene foam. There is
clearly no shaping of the conductive polypyrrole and instead the
thermoplastic flowability of the non-conductive polymer films permits the
use thereof as binders. Homogeneous moulded articles from a continuous
polypyrrole phase or moulded articles consisting solely of polypyrrole
cannot be produced this way. A further disadvantage is that the process
time under non-inert conditions is 2 to 10 minutes, non-conductive
coatings forming on the surface and it is not possible to exclude chemical
decomposition processes.
Polymer blends with conductive polymers
In order to obviate the aforementioned difficulties, many attempts have
been made to incorporate conductive polymers or organic conductors into a
polymer matrix and consequently achieve mouldability. Within the frame
work of the work leading to the present invention, it has however been
found that the subsequent incorporation of conductive polymers and organic
conductors causes serious problems, because a homogeneous distribution is
not obtained. In fact, the conductive polymers are present in the matrix
in the form of macroscopic agglomerates (black spots) and in this way
impair the mechanical characteristics thereof, without positively
influencing the electrical characteristics to the desired extent.
This can largely be attributed to difficulties in the dispersion and a lack
of compatibility between the conductive polymers or organic conductors and
the matrix polymer. This is indirectly confirmed by the fact that no
reference is made thereto in the technical literature. With the clear
intention of obviating these problems, attempts have also been made to
produce polymer blends by carrying out the polymerization of the
conductive polymer in the carrier polymer matrix or the polymerization of
the carrier polymer in a suspension containing conductive polymer
particles. M. Galwin and G. Wnek, J. Polym. Sci. Polym. Chem., Vol 21., pp
2727 to 2737, 1983 polymerized acetylene on and in a LDPE film, which was
impregnated with Ziegler-Natta catalysts. The mechanical characteristics
were interesting, the polymer blend obtained can be doped with iodine from
the gaseous phase, conductivity of >5 Siemens/cm being attainable with a
polyacetylene proportion of more than approximately 10%. However, no
information is given on the conductivity and other characteristics
following further processing of the films via the thermoplastic phase or
after processing the blend.
U.S. Pat. No. 4,359,411 has a similar objective and according to it TCNQ
salts in the form of a crown ether complex are incorporated into a
thermoplastic polymer matrix. Whilst the finished compound can be readily
shaped and has good mechanical characteristics, the conductivity of max.
10.sup.-6 Siemens/cm is far from adequate and is several decimal powers
below the value of the TCNQ salts.
Another procedure was adopted by T. Inabe et al, J. Chem. Soc. Chem. Comm.
1983, pp. 1084/1085 in that they prepared concentrated solutions of a
polyphthalocyanin in trifluoromethane sulphonic acid and aramide fibers
and spun the same in a water bath. This gave dopable fibres which, as
expected, were extremely brittle, because the strength of aramide fibres
is based on the special molecular orientation, which is disturbed by the
incorporation of foreign substances.
SUMMARY OF PRIOR ART AND OBJECTS OF THE INVENTION
Thus, conductive polymers and organic conductors together have a number of
restricting disadvantages (insolubility, poor dispersibility, inadequate
softening ranges or glass transition temperatures, non-existent melting
points and lack of stability relative to oxygen, heat and in part
crosslinking processes), which have hitherto prevented the industrial
utilization thereof. In the present state of the art, these disadvantages,
like the conductivity, are particularly due to the relatively high degree
of crystallinity of the conductive polymers and organic conductors, as
well as the in part considerable reactivity, particularly with respect to
oxygen.
It would constitute an advance, if it proved possible to obtain stable
dispersions of conductive polymers in thermoplastic polymers, because this
would permit the shapability and the obtaining of morphological polymer
blend structures optimizing the conductivity. The technical usability of
polyacetylene and most conventional conductive polymers is particularly
prevented by the fact that the electrical and in particular mechanical
characteristics decrease very rapidly after a short time and in particular
after complexing. It would therefore constitute an extraordinary advance,
if it proved possible to form or mould conductive polymers, whilst both
during and after the forming process achieving a stabilization against
degradation by oxygen, moisture, heat and internal crosslinking processes.
It would be of great practical significance if it would be possible to
disperse electrically conductive polymers and/or organic conductors in a
thermoplastic matrix resulting on the one hand in a homogeneous
distribution of the conductive polymer or organic conductor and on the
other hand a micromorphology of the incorporated conductive polymer
yielding the desired electrical properties of the entire polymer blend. It
is accordingly an object of the invention to find a possibility to convert
electrically conductive polymers and/or organic conductors such as PAc,
PPP, PPy, PPhc or TCNQ charge transfer complexes etc. into formable
polymer blends from which shaped bodies with good mechanical properties
and increased electrical conductivity can be made, and to achieve at the
same time a stabilisation against the various known degradation
mechanisms, especially oxidation and cross-linking.
SUMMARY OF THE INVENTION
The invention relates to a process for producing mouldable polymer blends
from electrically conductive organic polymers and/or organic conductors,
as well as a matrix polymer, which is characterized in that substantially
monomer-free, electrically conductive organic polymers and/or organic
conductors are dissolved or dispersed in a melt or solution of a
thermoplastic polymer or polymer mixture partially compatible therewith
and having a solubility parameter of >8.6 (cal/cm.sup.3).sup.1/2 until a
homogeneous material has formed which, when visually observed, has a
different colour from the conductive organic polymers and/or organic
conductors and matrix polymers used, and optionally the solvent is then
removed. The mass is called "homogeneous", if it appears homogeneous under
an optical microscope up to an approximately 200 X magnification. Blends
are considered to be homogeneous which, apart from a few rare coarser
particles to be looked upon as faults, have an average particle size below
20 microns, preferably below 5 microns and in optimum cases around and
below 1 microns e.g. 50 to 200 nm (electron-microscopically detectable).
Suitable matrix polymers are thermoplastic polymers with high solubility
parameter and a surface tension of >35 dyn/cm such as polyethers,
polyesters, polyvinylidene chloride or fluoride, polyamide,
polycaprolactone, polyurethane, cellulose partially esterified with
acetic, propionic or butyric acid, partially esterified polyvinyl alcohol
or partially esterified polyvinyl acetate, polyvinyl pyrrolidone,
polyvinyl butyral, water-soluble or water-swellable polymers such as e.g.
polyacrylic acid, liquid-crystalline polymers such as e.g. thermoplastic
liquid-crystalline polyesters, ionomers or polymers having polar
functional groups, polyacrylonitrile, copolymers thereof or mixtures of
the aforementioned polymers. It is also possible to use reactive monomer
and/or prepolymer mixtures, which can be completely polymerized to the
matrix polymer after producing the dispersion. Examples are caprolactam,
diol/dicarboxylic acid and diisocyanate/diol/polyester or polyether
mixtures or other suitable reaction (injection) moulding materials.
For obtaining an optimum dispersion, it is important that the secondary and
tertiary structures (agglomerates) obtained during the polymerization of
the conductive polymers are extensively disintegrated, i.e. preferably
down to the primary particles. It is important for producing the
electrically conductive polymer blends, that the conductive particles are
in contact and that for this purpose the concentration of the conductive
polymer or organic conductor is above the volume concentration critical
for the electrical conductivity, i.e. the so-called percolation point. A
description of the physical laws of percolation in connection with the
example of electrically conductive carbon black is given by K. Miyasaka J.
Mat. Sci., Vol. 17, pp. 1610 to 1616, 1982.
The concentration is preferably in the vicinity of the interfacial--energy
equilibrium, where the sum of the cohesion energy is equal to the sum of
the adhesion energy and occurs through chain formation. This means in
practice that the quantity of conductive polymers and/or organic
conductors in the polymer blend can be between 3 and 35% by weight, as a
function of the chosen material pairs and preferably the concentration is
at least 8% by weight. The concentration may be still lower, i.e. between
about 0.5 and 3% by weight, if it is desired to prepare antistatic
mixtures.
The dispersion of the conductive polymer and/or organic conductor in the
physical--chemical partially compatible matrix polymer according to the
invention is largely achieved through the high interfacial energy between
the participating substances. Thus, matrix polymers with a particularly
high surface tension are used. In order to facilitate dispersion the
matrix polymer is either melted accompanied by heating and shearing or is
dissolved in a suitable solvent, which is then removed.
Polymers with low solubility parameters, such as polyolefins or olefin
copolymers with a solubility parameter of <8.6 (cal/cm.sup.3).sup.1/2 are
less suitable according to the invention. Instead of a dispersion in the
matrix polymer, agglomeration occurs, so that polycrystalline microcrystal
needles or fibrils of approximately 5 to 50 microns form, which through
contact with one another can lead to a conductivity of the polymer blend.
Surprisingly, this is possible with amorphous powders of the conductive
polymers if, in place of matrix polymers with high solubility parameters,
those with low solubility parameters well below 8.6 (cal/cm.sup.3).sup.1/2
are used, e.g. polyethylene, and ultrasonics are applied to the melt, so
that the aforementioned microcrystal needles or fibrils form.
According to a further embodiment of the invention the organic conductor,
e.g. a TCNQ charge transfer complex, is dissolved in a suitable matrix
polymer, e.g. polycaprolactone, using solvents or applying a melt,
optionally assisting the dissolution by ultrasonics and/or heat; by slowly
cooling or tempering the conductor crystallizes in the form of thin
needles in the melt or the solidifying polymer, said needles preferably
contacting each other. Antistatic or electrically conductive moulded
articles are obtained in this manner.
Chain-like strings or spherical primary particles form in the continuous
polymer matrix and above the percolation point. This leads to a type of
interfacial-energy equilibrium through the formation of the same number of
contact points between the conductive polymer particles, as between the
latter and the matrix polymer. Thus, the conductive particles form
submicroscopic, widely branched conductor paths or a through conductor
network.
The electrical conductivity of the organic polymers can be significantly
increased by doping (complexing) before or after the production of the
polymer blend. Complexing agents which are suitable are known per se,
iodine, antimony or arsenic pentafluoride, tetrafluoro boric acid,
perchlorates, sulphurtrioxide, sulphonates or metal salts and in
particular iron(III)-chloride being particularly suitable for p-doping and
butyl lithium, triphenylhexyl-lithium, naphthalin-sodium and the like
being particularly suitable for n-doping.
In order to obtain special semiconductor characteristics, which can e.g. be
used for optical information storage and processing, it is advantageous to
incorporate into a polymer blend homogeneously p-doped and homogeneously
n-doped predispersed conductive polymers in such a way that each p-doped
particle, isolated by the matrix polymer is surrounded by n-doped
particles and vice versa. Through the use of external energy sources, e.g.
laser light, the particles can be excited in a clearly defined manner to
give conductive, three-dimensional structures.
According to the invention, a homogeneous doping can be obtained, if doping
(complexing) is performed with the doping agent (e.g. I.sub.2 or
FeCl.sub.3) in a solution and under ultrasonic action. Either the
completely polymerized and undoped conductive polymers, e.g. PAc or PPhc,
or the monomers, e.g. pyrrole are used. When monomers are used,
polymerization and doping simultaneously take place. It has been found
that the homogeneously doped polymers give products, which are much more
stable with respect to decomposition or distintegration (conductivity
reduction). Doping under ultrasonic action can be performed in the
presence or absence of the non-conducting matrix polymer.
The product is recovered by filtration, centrifugation and/or
lyophilization.
It has also proved possible to subsequently homogenize and predisperse
heterogeneously doped conductive polymers such as e.g. PPy powder
synthesized by known methods, in that they are suspended in a neutral,
alkaline or acid aqueous or organic suspension and exposed to the action
of ultrasonics.
The doping of e.g. polyacetylene under the action of ultrasonics in a
solution or dispersion leads to completely different characteristics
(particularly more uniform doping, higher conductivity and crystallinity
or greater extension of the crystallites, increased stability, improved
processability) of the conductive polymers compared with doping of e.g.
foils or films through gaseous complexing agents (J.sub.2, AsF.sub.5, etc)
or suspended, macroscopically large particles (cf e.g. EP-OS 62,221)
through dissolved complexing agents (e.g. FeCl.sub.3). If the latter
process is called a "heterogeneous" doping process, then the presently
found process can be called a "homogeneous" doping process. Homogeneously
doped PAc in polymer blends, e.g. with cellulose propionate forms
microscopically fine homogeneous, possibly liquid-crystalline particles or
fibres of below 20 microns, which under the microscope through a
polarization filter dark position appear bright and are highly conductive.
For increasing the processing stability, conventional antioxidants (e.g.
phenolic antioxidants) and/or crosslinking inhibitors (e.g. phosphonites)
can be added to the polymer blend in a quantity of preferably 0.01 to 0.5%
by weight, together with other processing aids in a quantity of 1 to 5% by
weight. Optionally, light-collecting, fluorescent dyes are added for
producing photoconducting polymer blends. For the protection of the
oxidation-sensitive conductive polymer, it is recommended to work under a
protective gas or in vacuo when producing the polymer blend. The polymer
blends produced according to the invention have the particular advantage
that the conductive polymer is very well protected against oxidative
decomposition and/or crosslinking both during dispersion and during the
subsequent shaping process, as a result of the dispersion in the matrix
polymer. This can be in particular optimized by the choice of matrix
polymers with particularly low O.sub.2 and H.sub.2 O permeability
coefficients.
The polymer blends according to the invention and the moulded articles
produced therefrom have a different colour compared with the pulverulent
starting substances or simple mechanical mixtures thereof. The colour is
characteristic of the particular conductive polymer and can be measured on
ultra-thin coatings. In the case of the polymer blend of polyacetylene and
polycaprolactone the polyacetylene colour e.g. changes from black to deep
blue, a sign of the conductive polymer being truly dispersed in the
polymer matrix. Polychromism occurs in the case of
poly-.mu.-cyano(phthalocyaninato)cobalt (III). For complete dispersion,
accompanied by deagglomeration of the secondary particles of the
conductive organic polymer in the thermoplastic matrix, either a
particularly suitable matrix polymer having an optimum compatibility with
the conductive polymer is used, or the melt or solution of the matrix
polymer is exposed to ultrasonics. Alternatively, it is also possible to
initially disperse the conductive polymer in the solvent under ultrasonic
action and to only then add the matrix polymer. Ultrasonics has the
advantage that the mixture is locally exposed to very high alternating
pressures without macroscopic shearing stress occurring, the latter
leading to a considerable mechano-chemical decomposition risk. Ultrasonics
are preferably used for dispersion purposes when the compatibility of the
carrier polymer with the conductive polymer to be dispersed or the
interfacial energy is not sufficient for wetting the primary particles in
this way alone and consequently break down the secondary and tertiary
structures.
It has been found that there are a few matrix polymer-conductive polymer
pairs, which lead to a satisfactory dispersion without additional
dispersion energy. These are undoped polyacetylene and polycaprolactone or
cellulose propionate, as well as poly-.mu.-cyano(phthalocyaninato)-cobalt
(III) and cellulose propionate. Other pairs, e.g. polypyrrole and
cellulose propionate or polyvinylpyrrolidone, doped polyacetylene and
cellulose propionate, poly-.mu.-cyano(phthalocyaninato) cobalt (III) and
polyvinylpyrrolidone require ultrasonics as an additional dispersing
energy source.
The conductive polymer should be free of monomer and preferably also free
of oligomer.
The invention also relates to an apparatus for performing the process
according to the invention using ultrasonics. It is an extruder
characterized in that one or more sonotrodes project into the
transformation zone through the barrel wall. The apparatus is illustrated
by the attached drawings, wherein show:
FIG. 1 a longitudinal section through a screw extruder according to the
invention.
FIG. 2 a section through a disk extruder according to the invention at
right angles to the driving shaft.
FIG. 3 a section through a kneader (internal mixer) with a die.
A sonotrode is immersed in free-swinging manner in the mass for carrying
out the inventive process of ultrasonics-supported dispersion of the
conductive organic polymer and/or organic conductor in a melt or solution
of the matrix polymer. A power supply, a converter, a booster (transducer)
and the actual sonotrode are required for ultrasonics generation. These
parts are matched to one another in such a way that the maximum
oscillation energy is roughly 20 kHz per sonotrode at the sonotrode end
face. The sonotrode can be made from aluminium or preferably titanium
steel. The total power provided by the sonotrode or sonotrodes should be 5
to 30% of the drive power of the extruder motor.
In an embodiment of the apparatus according to the invention, the 135 mm
long sonotrode 17 projects through the barrel wall 11 into the
transformation zone 16 of a screw extruder. In the vicinity of sonotrode
17, the screw flights 14 are partly ground away, so that reduced height
flights 15 are obtained, whilst a space is formed into which the sonotrode
can project. The end face 18 of sonotrode 17 is arranged at right angles
to the sonotrode axis.
At the booster end, the sonotrode is connected to the extruder, a barrier
on the sonotrode at the zero passage of the oscillations (e.g. with half
the length) prevents a possible advance of the melt to the booster.
On operating the apparatus, the starting materials are supplied under a
protective gas atmosphere to the extruder by means of the charging hopper
13. The extruder is either filled with inert gas or is operated in vacuo
in order to prevent oxidative decomposition of the conductive organic
polymers and/or organic conductors.
According to a further embodiment, the apparatus according to the invention
can also be a modified disk extruder. Such disk extruders are
fundamentally known, cf Z. Tadmor et al, Plastics Engineering, Part I, pp.
20-25, 1979 and part II, 11-34-39, 1979. Such a disk extruder comprises a
cylindrical casing 21 and a driven shaft 22, on which are arranged a
plurality of parallel disks 24. Normally, mixing fingers project into the
gaps between the disks and improve the thorough mixing of the components
by shearing.
According to the invention, one or more of these mixing fingers are
replaced by sonotrodes 27. It is advantageous in this case, if the end
faces 28 of the sonotrodes 27 are at an angle to the sonotrode axis.
Angles between 30.degree. and 60.degree., preferably an angle of
approximately 45.degree. are suitable.
Here again, charging takes place by means of the supply hopper 23 under a
protective gas atmosphere, whilst the actual apparatus can either be
operated under a protective gas atmosphere or in vacuo, in order to
exclude moisture and oxygen.
FIG. 3 shows another embodiment of the apparatus in the form of a pressure
arm-operated kneader or internal mixer. Within the casing (kneading
chamber) 31, the kneading blades 32 rotate in opposite directions about
their shafts 33. Sonotrode 37 projects from above into the kneading
chamber so that the sound pressure waves emanating from the end face 38
act on the material being kneaded.
The invention finally relates to the use of the polymer blends obtained
with the aid of the inventive process for producing moulded articles,
particularly for electrical components such as conductors, semiconductors
or photoconductors. Using the polymer blends, it is possible e.g. to
produce electrical components such as semiconductor relays, thyristors or
the like, as well as batteries. Photovoltaic uses. e.g. in solar
technology for directly producing electric power from light are also
possible. Other uses are permanent antistatic packagings or components for
information storage and processing.
It is not at present possible to provide an explanation for the invention
and the surprising effects thereof. The following hypotheses could provide
a possible explanation, without the invention being bound thereto:
All the conductive polymers form under conventional conditions of
hetergeneous polymerization, sphere-like primary particles, which
aggregate in an unordered manner.
These particles can only be reversibly separated under the specific
conditions according to invention and on exceeding the percolation point
re-agglomerate to give conductive, chain-like structures.
The conductivity mechanisms are the same in pure, unshaped crude conductive
polymers comprising aggregated primary particles alone as in the
homogeneous polymer blend above the percolation point.
Apart from the known causes of the instability, a further possibly decisive
cause is that the known methods of heterogeneous doping lead to
heterogeneous agglomerates which (e.g. by diffusion processes) attempt to
become homogeneous and thereby destroy the internal structures.
An optimum case for a conductive polymer blend is consequently a
homogeneously doped conductive polymer, which is homgeneously dispersed in
ultra-finely divided form in the matrix polymer, the latter also
exercising a protective function against possible oxygen attack.
The following examples serve to further illustrate the invention, without
restricting the latter thereto.
EXAMPLE 1
0.185 g of black trans-polyacetylene with 2 mg of a phenolic antioxidant
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