Compositions – Electrically conductive or emissive compositions
Patent
1998-04-09
1999-11-30
Kopec, Mark
Compositions
Electrically conductive or emissive compositions
H01B 120
Patent
active
059936967
DESCRIPTION:
BRIEF SUMMARY
The invention is related to electrically conductive elastomer alloys and their use as antistatic materials and/or EMI shielding materials.
A lot of research work in the area of electrically conductive polymers is done at the moment all around the world. These polymers make it possible to replace metallic conductors and semi-conductors in many applications like batteries, transducers, switches, solar cells, circuit boards, heating elements and in electrostatic discharge (ESD) and electromagnetic interference shielding (EMI) applications.
The advantages of electrically conductive polymers compared to metals are for instance their low weight, good mechanical properties, corrosion resistance and cheaper synthesis and processing methods.
Electrically conductive polymers can be roughly divided in two different categories: filled electrically conductive plastics, which are composed of thermoplastics or thermosets containing electrically conductive fillers like carbon black or soot, carbon fibres, metal powder, etc. and inherently electrically conductive plastics, which are based on polymers that are made electrically conductive by oxidation or reduction (doping).
The electrical conductivity of filled electrically conductive plastics depends on the physical contacts between the electrically conductive filler particles. In general one needs about 10-50 w-% of well dispersed fillers in order to obtain composites with good conductivity. However, there are problems with such conductive composites: their mechanical and some chemical properties disimprove considerably when increasing the filler content and the electrical conductivity is difficult to control especially in the semiconductive region when the polymer content decreases. Also a long lasting and homogenous dispersion of fillers into the matrix plastic is difficult to obtain.
Inherently electrically conductive plastics can be made from organic polymers, in which there are long chains with conjugated double bonds or double bonds and hetero-atoms. The stable .pi.- and .pi.-p-electron-systems in the double bonds and hetero-atoms can be disturbed by adding to the polymer certain doping agents or additives which either attract or repell electrons. In this way holes and/or excess electrons are obtained in the polymer chain, which make it possible for an electrical current to go along the conjugated chain.
An advantage with the inherently electrically conductive polymers is that their electrical conductivity is easily varied as a function of the doping time, which is especially seen in the case of low conductivities. It is difficult to obtain low conductivities for filled electrically conductive plastics. Examples of inherently electrically conductive polymers are polyacetylene, poly-p-phenylene, polypyrole, polythiophene and polyaniline.
One technically and commercially promising inherently electrically conductive polymer is polyaniline and its derivatives. The aniline polymer is based on an aniline unit, the nitrogen atom of which is bonded to the paracarbon of the benzene ring of the next unit. Non-substituted polyaniline can appear in many forms like the leukoemeraldine, protoemeraldine, emeraldine, nigraniline and tolu-protoemeraldine forms.
The so called basic emeraldine form of polyaniline is normally described by molecular model (I) ##STR1## in which X is about 0.5.
In patent applications EP-545 729 and EP-582 919 polyaniline and its derivatives have been obtained in an easily melt processable form by contacting polyaniline or its derivative and a protonic acid under high shear forces and a temperature of about 80-300.degree. C. Furthermore in the latter patent application EP-582919 the product based on polyaniline and a protonic acid has been improved by permanently adding a metal compound. In the same patent application it has also been suggested that the electrically conductive and melt processable polyaniline polymer obtained is mixed with a thermoplastic in order to form an electrically conductive plastic blend. Thermoplastic blends which have been mentio
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Hanhi Kalle
Lonnberg Viveca
Pyorala Keijo
Kopec Mark
Optatech Oy
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