WO2001038084A1

WO2001038084A1 - Electroconductive composite plastic, component of such a composite plastic and method for producing the same

Info

Publication number: WO2001038084A1
Application number: PCT/DE2000/003745
Authority: WO
Inventors: Riittas Taipalus
Original assignee: Fact Future Advanced Composites & Technology Gmbh
Priority date: 1999-11-23
Filing date: 2000-10-21
Publication date: 2001-05-31
Also published as: DE19956331A1; AU1692701A

Abstract

The invention relates to an electroconductive composite plastic (4) and to a method for producing the same. The inventive composite plastic (4) consists of a matrix (5) and a component (1), said component consisting of a carrier material that is coated or wetted with an electroconductive plastic. The invention provides a composite plastic (4) or a component (1) of a composite plastic (4) and a method for producing the same, said composite plastic (4) having an adjustable electroconductivity and at the same time good mechanical properties.

Description

Electrically conductive composite plastic, component of such a composite plastic and process for the production thereof

The present invention relates to an electrically conductive composite plastic and a method for the production thereof.

In solid state theory as well as in materials science and materials science, it is customary to classify materials with regard to their electrical conductivity into insulators, electrical semiconductors and conductors. Most plastics, such as Polypropylene, for example, often have unusual mechanical properties, for example in terms of weight, processability and economy, but they are generally insulators. This severely limits their usability in various areas. A major disadvantage of insulators is their tendency to electrostatic charges. In the field of electronics in particular, the abrupt discharge of such electrostatic charges is a major problem. For example, there is a great demand for packaging and housings that can distribute and dissipate the resulting charge. However, this is not possible with isolators.

A few plastics have a high intrinsic electrical conductivity. They are therefore often referred to as synthetic or organic metals. These show metallic behavior over a wide temperature range and some become superconducting even at low temperatures below about 35 Kelvin. These polymers generally consist of a molecular chain which has so-called conjugated double bonds. Appropriate doping enables electron transport along the molecular chain. The best-known polymers that have an intrinsically electrical conductivity are polyaniline (PANI), polypyrrole (PPY), polythiophene (PT), polyvinylpyridine (PVP) and polyacetylene (PAC). However, all these polymers have in common that they have insufficient mechanical properties, which severely limits their commercial replaceability.

In order to increase the electrical conductivity of normally electrically insulating polymers, these polymers are often mixed with electrically conductive particles such as e.g. B. particles of soot or aluminum filled. It is essential that the introduced conductive particles are arranged so densely that electron transport from one particle to the next particle is possible. Are added to a few particles, the particles are in their insulating matrix so far apart that the electric Leitfähi ^π ness this composite essentially by the conductibility Ability of the matrix polymer is formed. However, if the concentration of the filler particles rises above a critical level, continuous paths of conductive filler particles within the material along which the electrical charges can move are formed almost suddenly. These continuous paths then form partially coherent lines which penetrate the insulating matrix polymer. The electrical conductivity then increases almost suddenly by several orders of magnitude. A further increase in the filler concentration then only leads to a smaller increase in the electrical conductivity. If the electrical conductivity of such a composite is therefore plotted in a diagram over the concentration of the added conductive particles, a clearly non-linear course is observed. The concentration at which this curve has an inflection point is also referred to as the percolation threshold.

These electrically conductive polymers and their blends with conventional thermoplastics have many favorable properties, such as. B. a low density and an adjustable electrical conductivity, but do not match the insulating plastics in their mechanical properties, therefore, in addition to the increase in the electrical conductivity of the mixture, a deterioration in the advantageous mechanical properties of the matrix is also observed.

Plastics are generally used because of their diverse design options, their low weight and, above all, their low price. With the help of the injection molding process, these plastics can be brought into almost any shape. In the field of electrical engineering, for example, they have been used as housing material for a long time. Metal materials must generally be used for all conductive components. The combination of the electrically insulating housing and the electrically conductive conductor tracks, which are often directly connected to very sensitive electronic components, entails the risk of electrostatic discharge in the form of voltage flashovers and the possible destruction of the semiconductor components.

It is true that some plastics can be made conductive by suitable addition of metallic elements, but only by accepting a substantial deterioration in the favorable properties of the plastics, so that these plastics and metal composites have poor overall properties.

The present invention is therefore based on the object of providing a composite plastic or a component of a composite plastic and a method for producing the same, the composite plastic having an adjustable electrical conductivity and, at the same time, good mechanical properties. This object is achieved according to the invention by a component of a composite plastic, the component consisting of a carrier material which is coated or wetted with an electrically conductive plastic, and by a composite plastic consisting of a matrix of the component.

In contrast to the known methods, in order to achieve the conductivity of the plastic, no intrinsically conductive materials are introduced into the matrix, but the material to be introduced is itself a composite that consists of a mostly non-conductive or poorly conductive material and a conductive plastic.

The proportion of conductive plastic must be at least so large that the resulting component made of carrier material and conductive plastic becomes conductive. In this way, a conductive, network-like structure essentially forms on the surface of the carrier material.

The component is then introduced into the matrix instead of, for example, a metallic element. As a result, the proportion of the conductive substance that has to be introduced into the matrix in order to obtain the desired conductivity can be significantly reduced. The type of carrier material can be suitably selected so that the carrier material does not significantly impair the mechanical properties or, in the ideal case, even improve it.

For example, fibers, spheres or particles are used as the carrier material.

For example, a fiber can be impregnated with an electrically conductive plastic, which does not necessarily have to be an intrinsically conductive plastic, but can also be a so-called "filled plastic". The resulting composite (fiber - conductive plastic) is now coated with the actual matrix mixed and the entire composite part or the entire composite part produced for example by the injection molding process.

With regard to the fiber, both electrically insulating fibers, such as. B. glass fibers, polymer fibers (PP, PA, polyester) or aramid fibers, as well as electrically conductive fibers, such as carbon fibers or metal fibers, are used.

With regard to the sphere, both an electrically insulating sphere, for example made of glass, or an electrically conductive sphere, for example made of metal, can be used.

Likewise, the particles can be electrically insulating (e.g. talc or CaC0 ₃ ) or electrically conductive (e.g. made of carbon black, aluminum, graphite). The electrically conductive plastic does not necessarily have to have an intrinsic conductivity. Of course, plastics filled with metallic materials can also be used. In addition, intrinsically electrically conductive plastics can be mixed with filled plastics.

Materials with the desired mechanical properties, for example in terms of weight or processability, are preferred as the matrix. As matrix material z. B. polypropylene (PP), polyethylene (PE), polyamide (PA), polystyrene (PS), epoxy (EP) and polyester have been used successfully. The matrix elements are therefore not only limited to thermoplastics. For example, thermosets can also be used.

Fibers are particularly preferably used as the carrier material. In the first step, the fibers are covered in a net-like manner with an electrically conductive material. The wetted fibers are then introduced into the matrix. The elongated shape of the fibers results in the formation of the conductive paths described at the beginning with an even lower concentration of conductive materials. The percolation threshold has thus been significantly reduced. Due to the low proportion of foreign material, the matrix almost retains its original mechanical properties. The matrix also fixes the fibers and protects them from harmful environmental influences.

Depending on the fibers used, the mechanical properties of the matrix can be improved even further by introducing the impregnated fibers. Due to the fact that forces applied to the material are transferred to the fibers via the fiber matrix interfaces, increased strength and rigidity of the composite material can be achieved.

The composite plastic thus obtained can by means of the usual methods such. B. the extrusion, the injection molding, the heating press or the extrusion process.

For special applications it can be advantageous that a filled polymer is used as the electrically conductive material and the matrix is formed from the same but unfilled polymer. This enables particularly good mixing between the electrically conductive layer and the matrix.

The mechanical properties of the electrically conductive composite plastic can be significantly improved in particular through the use of fibers as the carrier material without the electrical properties being adversely affected.

A further reduction in the proportion of metallic elements can also be achieved in that the materials of the composite plastic are selected in such a way that the conductive mesh-like structure on the carrier material also diffuses at least partially into the matrix. The resulting free conductive particles can then provide the electrical connection between two closely adjacent but not overlapping carrier material particles.

With the help of the present invention, composite plastics can therefore be made electrically conductive without the mechanical properties being adversely affected. In addition, the electrical conductivity of known electrically conductive composite plastics can of course also be increased further. The mechanical properties of these composite plastics can be significantly improved, in particular when fibers are used as carrier material.

Further advantages, features and possible uses of the present invention will become clear from the following description of a preferred embodiment and the associated figures. Show it:

1 shows a section of a fiber as a carrier material and

Figure 2 is a schematic representation of the fibers introduced into the matrix.

A fiber 2 is shown in FIG. In addition to electrically conductive carbon fibers, glass fibers are particularly preferred. Both short and discontinuous long E glass fibers can be used. Short fibers of the type SGF 4242 from PGG Industries, which have a density of 2.5 g / cm ³ , have been successfully used as short fibers. The fibers are preferably provided with a silane size, so that good adhesion between the fibers and the matrix is achieved, and thus good processability of the fibers is made possible, for example by means of a twin-screw extruder.

A long glass fiber composite from FACT GmbH, Kaiserlautem (FACTOR PP-GF-40) with a density of 1.2 g / cm ^{3 was} successfully used as long fibers.

As already mentioned, conductive fibers, such as. B. Kunststoffasem can be used as a carrier material. The production of long and short fiber composites is also possible here.

In general, better mechanical properties of the composite plastic are achieved by using long fibers as the carrier material.

The fibers are then preferably coated in a melt impregnation process with the conductive material, so that a network-like conductive structure 3 forms on the surface of the fiber 2, as indicated schematically in FIG. These fibers 1 are finally embedded in a matrix. A polyaniline complex (PANI) has proven particularly useful as a conductive material. Since PANI generally shows only poor processability, it can be of distribution to use a mixture of a readily processable polymer and PANI as the conductive material, PANI preferably being present in highly concentrated form.

As shown schematically in FIG. 2, the fibers 1 with a network-like conductive surface overlap in the composite in such a way that they form conductive paths. In this way, a composite plastic 4 is produced which shows both good electrical conductivity and good mechanical processability. Polypropylene, for example, can be used as the matrix. Polypropylene, e.g. B. an ethylene-propylene block copolymer (type designation BC 145 B from Borealis, Denmark) has high impact strength even at low temperatures and is a particularly suitable material for injection molding. This material has a density of 0.9 g / cm ³ and a processing range between about 230 ° and about 260 ° C.

Claims

Patent claims

1. Component (1) of a composite plastic consisting of a carrier material (2) which is coated or wetted with an electrically conductive plastic (3).

2. Component (1) according to claim 1, characterized in that the carrier material (2) is a fiber, ball or a particle.

3. Component (1) according to claim 1 or 2, characterized in that the carrier material (2) with the electrically conductive plastic (3) is impregnated.

4. Component (1) according to any one of claims 2 to 3, characterized in that the carrier material (2) is a glass fiber or a carbon fiber.

5. Component (1) according to one of claims 2 to 4, characterized in that the electrically conductive plastic (3) is an intrinsically electrically conductive plastic.

6. Component (1) according to one of claims 2 to 4, characterized in that the electrically conductive plastic (3) is an electrically insulating polymer which is filled with electrically conductive particles.

7. Component (1) according to claim 4, characterized in that the average fiber length is at least 4mm, preferably at least 8mm.

8. Component (1) according to claim 5 or 7, characterized in that the conductive

Plastic (3) a polyaniline complex, i.e. H. is a solution of polyaniline and another substance.

9. Component (1) according to claim 8, characterized in that the further substance is a metal compound, preferably an organometallic compound.

10. Composite plastic (4) consisting of a matrix (5) and a component (1) according to one of claims 1 to 9.

11. Composite plastic (4) according to claim 10, characterized in that the matrix (5) consists of polypropylene.

12. Composite plastic (4) according to claim 10, characterized in that the matrix (5) consists of polyethylene, polyamide, polystyrene, epoxy or polyester.

13. A method for producing a conductive composite plastic (4), characterized in that it has the steps:

Impregnating the surface of a carrier material (2) with an electrically conductive

Plastic (3) and

Introducing the impregnated carrier material (2) into a matrix (5).

14. The method according to claim 13, characterized in that the method additionally comprises the step:

Manufacture of the composite plastic or the composite plastic part (4) with the help of the extrusion, the injection molding, the heating press or the extrusion process.