EP1954495A1

EP1954495A1 - Plastic-metal composite material with metal wire mesh

Info

Publication number: EP1954495A1
Application number: EP06792357A
Authority: EP
Inventors: Christian Farhumand; Georgios Tziovaras; Matthias Boll
Original assignee: Bayer MaterialScience AG
Current assignee: Covestro Deutschland AG
Priority date: 2005-10-15
Filing date: 2006-10-04
Publication date: 2008-08-13
Also published as: US20070087209A1; KR20080050613A; CN101287600A; JP2009511299A; WO2007045354A1; DE102005049447A1

Abstract

A description is given of a plastic-metal composite material, in particular a transparent material, based on a thermoplastic polymer with a metal wire mesh of super-fine wire, in particular to be used for electromagnetic shielding or for mechanically reinforced viewing windows.

Description

Plastic-metal composite material with metal wire net

The invention relates to a particularly transparent plastic-metal composite material based on a thermoplastic polymer with a metal wire mesh made of superfine wire, in particular for use for electromagnetic shielding or for the mechanical reinforcement of components with high optical quality.

In many areas of everyday life, it is important to use components that on the one hand ensure mechanical protection and on the other hand ensure optical transparency. Examples are the shot or splinterproof car or building glazings, goggles for sophisticated protection claims or ATMs and vending machines, where the goods must be visible and at the same time protected against theft and vandalism.

Thus, it is basically known to use transparent glass sheets, e.g. To equip safety glass with a coarse wire mesh, which gives the disc a higher breaking strength and avoids splintering into large sharp-edged pieces of glass in order to minimize the risk of injury in the event of a disc breakage. Disadvantage of such safety glass panes is the disturbance of the review by the wiring and the high weight.

Other previously offered solutions consist of thick laminated glass (a sequence of glass panes with intermediate transparent plastic film), are therefore very difficult in principle, and due to the thickness of the materials, optical distortions can hardly be avoided. Despite these obvious disadvantages, these discs are used in the automotive industry, if a use of the vehicles is provided in crisis areas.

In such safety discs, which are to allow a clear and clear as possible, the break glass in the event of damage by the embedded film together. Typical applications are car windows, the glazing of trains and security windows in banks. To reduce the weight, plastic safety washers are sometimes used, especially in applications such as safety sights or the like. Protective shields of the police and military are relatively heavy with moderate safety effect, so here lighter shields with improved protection are needed. By using this new development, they are designed to be thinner and at the same time offer greater protection and thus become lighter and safer. However, the mechanical stability of safety visors is often regarded as still not sufficient, and efforts are therefore being made to find solutions which combine mechanical stability, optical transparency and a lower weight.

In the field of electromagnetic shielding or reflection, plastic components could not be used due to their low electrical conductivity. Plastics doped with conductive materials (for example conductive carbon black) have electrical conductivity that is a few orders of magnitude too low to provide effective electromagnetic shielding. They are used to avoid electrostatic charge. The object of electromagnetic shielding or reflection at present is solved by the use of metallic lattices, metallic sheets or metallic paints which have optically disturbing properties (i.e., are only partially transparent or completely non-transparent). In the area of the microwave oven, glass is currently used substantially, is incorporated into the perforated plate or applied to the strip or other pattern with a conductive paste and baked.

Enclosures of electrical equipment that are sensitive to the spread of electromagnetic radiation (for example, due to adjacent, strong alternating electrical fields) must currently be made of metal or provided with an electrically conductive paint, which disadvantages in design, in weight and in the Price and possibly also in environmental protection entails. Also, the reflection of electromagnetic radiation (for example, the field of view of a microwave oven) could not previously be realized by plastics. Changes in the design, which can also lead to technical advantages (bending of the windscreen to focus the radiation on the turntable, etc.) are difficult or impossible.

Parabolic antennas, which are used, for example, for the transmission and reception in the microwave range for radio and television in the home, are currently almost exclusively produced using metal sheets that are bent or punched into the appropriate shapes. The use of sheet metal has optical disadvantages: The built-in satellite dishes disturb the visual impression of the buildings on or on which they are attached quite considerably. It should be possible to combine an extremely high transparency and excellent functionality (reflection of microwaves) as well as high impact resistance and good weather resistance by the plastic used. The visually disturbing impression of the parabolic mirror should be able to be reduced.

In order to render the surface of plastics conductive (to prevent electrostatic charging, as is necessary in explosion-proof areas), hitherto, electrically conductive ones have always been used Materials (such as Leitruße) added to the plastics. Thus, a low electrical conductivity can be achieved, but sufficient to dissipate the electrical surface charge. The plastics used, however, are always intransparent due to the filling with Leitruß and usually black.

The object of the present invention is therefore to provide a composite material, in particular for reflexia or mechanically reinforced viewing windows or for the electromagnetic shielding of optically transparent components, which can be produced in a simple manner and combines good mechanical properties with a light weight and in particular optical transparency ,

The object is achieved in that conventional plastic material, in particular transparent plastic films, plastic moldings or film laminates are provided with a visually hardly noticeable Drahtnetifaus Feinstdraht.

The invention relates to a plastic-metal composite material based on a thermoplastic polymer with a metal wire mesh made of very fine wire, wherein the composite material is at least partially optically transparent.

The wire mesh may be a woven or knitted fabric of superfine or a crossed composite of at least two layers of parallel to each other arranged fine wires, wherein the layers are glued, welded or sintered at the intersection points of the wires.

The solution of the weight problem is achieved by the use of e.g. Polycarbonate instead of glass realized. For mechanical reinforcement, for example, a fine, thin fabric made of a metal or a metal alloy is used. The mesh size is z. B. about lOOμm, the wire thickness is z. B. at about 20μm. This results in one for the human

Eye virtually unresolvable, close-meshed wire mesh, which only weakens passing light, without the structures of the wires can be individually optically resolved.

For example, the wire net is applied to a polycarbonate sheet by being fixed by an adhesive or by softening the underlying PC sheet by solvents that can dissolve polycarbonate.

Preferably, the plastic-metal composite material comprises at least one plastic film. In a preferred variant of the plastic-metal composite material, the metal wire net is embedded in the polymer or adhered to the surface of the polymer, in particular the plastic film.

The wire mesh can also be by lamination z. B. between two PC films, even at elevated temperature, are fixed. After fixing the wires, the film thus obtained can still be mechanically deformed within certain limits (eg by deep drawing).

Particularly preferred is a plastic-metal composite material, which is characterized in that the plastic-metal composite material is multilayered with at least two plastic films and the metal wire mesh between two plastic films enclosed, in particular laminated.

Another variation of the _^ plastic-metal composite material is characterized in that the plastic-metal composite material as a whole is deep-drawable through one or more plastic sheets is formed and that the plastic-metal composite material.

The film thus obtained can be further treated by an injection molding process ("injection molding", preferably on the side facing away from the plastic film). In suitable machines, the back injection process can even be carried out without the wire mesh being directly connected to the film.

Alternatively, plates or profiles may also be laminated to the wire net by means of extrusion extrusion techniques.

By using a fine wire mesh of metal or a metal alloy and incorporation of the same in plastic, such as polycarbonate or another, preferably optically transparent plastic, the plastic can be strengthened mechanically. Depending on the mesh size and wire thickness, the effect is different pronounced.

In a further preferred embodiment, the plastic-metal composite material therefore additionally has at least one section of injection-molded plastic.

Another preferred embodiment of the plastic-metal composite material has both injection-molded sections of transparent and non-transparent plastic.

As the thermoplastic polymer for the plastic film and / or the injection-molded plastic, a polymer is preferably selected from the series: polycarbonate, polyacrylate, in particular Polymethyl methacrylate, polyester, especially Pqlyethylenterephthalat, polyalkylene, in particular polypropylene used.

Iron wire, in particular steel wire, or tungsten wire is preferably used as the material for the ultrafine wire.

The ultrafine wire preferably has a diameter of at most 100 μm, preferably 5 to 50 μm, particularly preferably 10 to 30 μm.

The mesh size of the wire mesh is preferably from 50 .mu.m to 20 mm, more preferably from 80 .mu.m to 5 mm, most preferably from 80 .mu.m to 1 mm.

Due to the above-mentioned selection results in a virtually no longer dissolvable to the human eye wire mesh, which only weakens passing light, without the structures of the wires can be visually resolved in detail.

The metal wire net is preferably sintered prior to bonding to the polymer.

As binding forms for the wire mesh all known binding forms in question, in particular the known types of fabric, preferably the canvas weave, tress, armor, twill and Köpertresse.

In order to minimize light reflections on the shiny metal surface of the wire mesh, the metal wire to be incorporated should first be matted. This can be achieved in various ways, for example by an etching process, which precedes the actual incorporation into the plastic or the injection molding process, or else by thermal treatment of the wire mesh under air, so that forms a thin layer of metal oxide on the wire, which scatters the incoming light diffused and not directed.

A particularly well-suited preferred arrangement is the wave-shaped, in particular regularly wavy or meandering arrangement of the wires in the wire composite. This arrangement can be realized by the use of special, programmable wire laying machines.

The invention also provides for the use of the plastic-metal composite material according to the invention as a mechanically reinforced viewing window, in particular for vehicle windows, safety helmets and protective shields or as a mechanically reinforced insert, in particular for equipping safety clothing. By using a fine electrically conductive wire mesh, for example made of metal or a metal alloy and incorporation into the plastic, the plastic-metal composite material can also be used for shielding or for reflecting electromagnetic radiation. Depending on the mesh size, different wavelengths can be reflected here. The mesh size should be of the order of magnitude or below the desired wavelength in order to ensure the most effective reflection of the electromagnetic radiation. For electromagnetic shielding, a fine, thin fabric made of a metal or a metal alloy is preferably used, preferably made of stainless steel or tungsten.

Another object of the invention is the use of the plastic-metal composite material according to the invention as an optically transparent, electromagnetic shielding or as an electromagnetic reflector, in particular for household appliances, eg. As microwave ovens and for Parabo lantennen.

Examples

example 1

Between two 375 micron thick polycarbonate films (type Makrofol ^®, manufactured by Bayer Material Science AG), a stainless steel mesh (stainless steel type 1.4306) is inserted with a wire thickness of 20 microns and a mesh size of lOOμm and at 185 ⁰ C for 10 minutes at a pressure of 300 N / cm ² laminated. The film composite thus obtained is back-injected with polycarbonate, so that 2 mm thick plates were obtained.

The plates show an improvement in puncture resistance compared to the unmodified PC plate of the same density.

Example 2

On a 375 micron thick polycarbonate film (Makrofol ^® ) wires of tungsten (with a diameter of 20 microns) are arranged in parallel in two mutually perpendicular layers. The wires lying on the film are first fixed on the film by applying small drops of dioxalane to the intersections of the individual wires. The dioxalane initially dissolves the polycarbonate on the surface of the film, but then evaporates again, so that a thin layer of polycarbonate remains on the wires, which ensures a sufficiently stable bond to the film.

A UV-curing polyurethane-based paint was used to fix the wires to the film while providing mechanical protection of the wires. The wires showed a good adhesion to the surface, which was sufficient to insert the film in a back injection mold and back-injected with polycarbonate. The wires were so completely enclosed by polycarbonate and the workpiece shows little distortion of the background in the see-through. The back molding can also be done without previous painting.

The film can, as described above, either back directly on the wire-coated side or on the side facing away from the wire or treated with different paint systems.

In another experiment, the application of the wires is not in a position straight to each other, but in a wavy manner, because this results in further optical advantages:

As a result of the arrangement, the wires are only very difficult to see and are hardly perceived by the human eye. Even the, by using the Fine wires only small, disturbing optical influence when viewing omitted due to the wavy arrangement practically completely.

Example 3

A composite of two films with a wire mesh as shown in Example 1 was examined for its properties and compared with a wireless film and a composite with a wider meshed wire mesh.

The foils were installed in a waveguide section and the material-dependent attenuation of microwave radiation was determined.

The transmission through the foils is in the considered frequency range (microwaves of the frequency 2,2 to 2,7 GHz) independent of the frequency (within the measuring accuracy of + - 5%)

The pure PC film gave a mean transmission of 95%.

A film laminate of two films with a coarse mesh (mesh size 5 mm) of tungsten wire (20 μm) between the two films showed a transmission of averaged 25%.

A polycarbonate (5 mm) back-injected film with a fine mesh (mesh size 100 μm) of tungsten wire (20 μm) had a transmission of 0% (+ noise).

Example 4

A sample prepared according to Example 1 and then back-injected, as well as two samples made according to Example 2 and then back-injected, were examined for reflectance at higher microwave frequencies, which correspond approximately to the commercial satellite emission frequency. The signal of a microwave wave detector was recorded with a change in distance between sensor and sample (measurement of the standing wave)

The signal curves of the samples to be examined were compared with the reflection on metal and on a blank sample. Samples and blank are sealed on the back with absorber material to provide optimal measurement conditions. The frequencies used were 12.5 GHz and 15 GHz. The reproducibility was investigated for all samples at 15 GHz.

For this purpose, 10 different, arbitrarily selected measurement positions were compared.

The location and polarization direction of the microwaves were varied.

For all samples a very good reproducibility was found.

The first pattern with an inserted metal wire mesh with a mesh size of 200 μm and a wire thickness of 20 μm showed a reflection that is directly comparable with the reflection on a metal sheet in the wavelength range used.

A second and a third sample, each prepared according to Example 2 with a mesh size of 1 mm with a wire thickness of 19 microns, was also measured by the above method. The wires used were made of stainless steel. Both patterns showed very good reflective properties, suggesting suitability as starting material for the use of transparent satellite dishes.

Claims

claims

A plastic-metal composite material based on a thermoplastic polymer with a metal wire mesh made of ultra-fine wire, wherein the composite material is at least partially optically transparent.

2. Plastic-metal composite material according to claim 1, characterized in that the plastic-metal composite material comprises at least one plastic film.

3. plastic-metal composite material according to any one of claims 1 or 2, characterized in that the metal wire network is embedded in the polymer or adhered to the surface of the polymer, in particular the plastic film.

4. Plastic-metal composite material according to one of claims 1 to 3, characterized in that the plastic-metal composite material is constructed in multiple layers and the metal wire mesh between two plastic films enclosed, in particular laminated.

5. Plastic-metal composite material according to one of claims 1 to 4, characterized in that the plastic-metal composite material is formed by one or more plastic films and is thermoformable.

6. plastic-metal composite material according to one of claims 1 to 5, characterized in that the plastic-metal composite material additionally comprises at least a portion of injection-molded plastic.

7. plastic-metal composite material according to one of claims 1 to 6, characterized in that the plastic-metal composite material injection-molded sections made of transparent and non-transparent plastic.

8. Plastic-metal composite material according to one of claims 1 to 7, characterized in that as thermoplastic polymer for the plastic film and / or the injection-molded plastic a polymer selected from the series: polycarbonate, polyacrylate, in particular polymethyl methacrylate, polyester, in particular Polyethylene terephthalate, polyalkylene, especially polypropylene is used.

9. plastic-metal composite material according to one of claims 1 to 8, characterized in that as the material for the ultrafine iron wire, in particular steel wire, or tungsten wire is used.

10. plastic-metal composite material according to one of claims 1 to 9, characterized in that the ultrafine has a diameter of at most 100 .mu.m, preferably 5 to 50 .mu.m, more preferably 10 to 30 microns.

11. plastic-metal composite material according to one of claims 1 to 10, characterized in that the mesh size of the wire mesh of 50 microns to 20 mm, preferably from

80 microns to 5 mm, more preferably from 80 microns to 1 mm.

12. Use of the plastic-metal composite material according to one of claims 1 to 11 as an optically transparent, electromagnetic shielding, or as an electromagnetic reflector, in particular for household appliances and parabolic antennas.

13. Use of the plastic-metal composite material according to one of claims 1 to 1 1 as a mechanically reinforced window, in particular for vehicle windows, safety helmets and shields.

14. Use of the plastic-metal composite material according to one of claims 1 to 11 as a mechanically reinforced insert, in particular for safety clothing.