GB2038712A - Absorbant and/or reflecting shield - Google Patents

Abstract

Shield which absorbs and/or reflects electromagnetic radiation. This shield is made from a composite material constituted by a mass-coloured polyvinyl fluoride film, a pigmented, non-flammable, organic foam layer and at least one other layer selected from polyvinyl fluoride, metallised polyester, polyvinyl chloride or a synthetic support sandwiched between two polyvinyl chloride layers. Application to the camouflage of military objects.

Description

SPECIFICATION Absorbant and/or reflecting shield Background of the invention The present invention relates in general terms to the detection or protection of objects, particularly military objects, in which electromagnetic radiation phenomena are involved.

The detection by visual, photographic, radar or thermal means of certain objects which can be located due to the fact that they emit electromagnetic and in particular infrared radiation in a standard method used for monitoring the industrial or military activities of certain countries. Such operations are regularly carried out by the large industrial countries using high flying aircraft or observation satellites.

Hitherto, the optical camouflage means used did not make it possible to provide security against the observation of electromagnetic radiation and in particular infrared radiation emitted by industrial or military objects, which it is desired to hide from the observation of third parties.

Summary of the invention The present invention relates to a shield which absorbs andior reflects electromagnetic radiation permitting, on the basis of simple means, such a protection to be given by reducing, disturbing or obliterating visual and electromagnetic information coming from a particular object.

According to the invention, this shield comprises a composite material constituted by a mass-coloured polyvinyl flouride film, a pigmented, non-flammable, organic foam layer and at least one other layer selected from polyvinyl fluoride, metallised polyester, polyvinyl chloride and a synthetic support sandwiched between two polyvinyl chloride layers.

The organic foam used in the absorbant shield according to the invention can be a flexible foam constituted for example by a material selected from the group including polyester, polyurethane and polyvinyl chloride, or a phenol-type rigid foam. This foam is pigmented and made non-flammable by means of substances such as antimony sulphide, antimony trioxide or halogen compounds such as for example zinc borate and calcium borate.

If for a specific purpose, it is desired tq increase the absorption or diffusion effectiveness of the shield according to the invention, the organic foam is also filled with balls of absorbant and diffusing materials, such as graphite, glass, silica and the like having a diameter preferably between 30 and 80 micrometres. In certain cases, these balls can also be mixed with metallic pigments or particles, particularly constituted by alumina trihydrate or barium ferrite.

As a result of its construction, the absorbant and/or reflecting shield according to the invention divides up the space into two areas, namely an inner area containing the objects or installation to be concealed or protected and an outer area in which functions the locating or detection apparatus. It makes it possible to reduce in a variable proportion or even totally prevent the transmission of signals and electromagnetic radiation from one of these areas into the other. Thus, it is able to protect from detection, both by day and night military objects by reflecting, diffusing, refracting and absorbing electromagnetic radiation and in particular optical radiation emitted by the objects to be concealed. If appropriate, it is also able to protect said objects from dangerous radiation, possibly coming from the outside.

The absorbant and/or reflecting shield according to the invention can be used as it is, as a camouflage or simulating device, or as a component of protective camouflage or simulation equipment, mainly in one of the following forms: 1) Tarpaulins, protective coverings, canvas, sheltertents, loose covers, overalls, battle dress.

2) Self-adhesive coverings resting on outer surfaces of moving or stationary military objects, which may or may not have metal surfaces, replacing painted motifs distorting colour schemes, as on helmets, wheeled or tracked vehicles, guns, blockhouses, etc.

3) Ground or floor coverings for concealing or distorting after its passage the stationary or parking of a moving object or for disguising after its passage the stationing or parking of a moving object or for simulating a passage of objects, a parking of objects (own and cast shadows) simulating a dummy mine field, a dugout shelter or a structure in the field.

4) Hood fittings, screens, netting etc.

Means 1 and 2 make it possible to adapt and conceal the object in the environment by reducing or obliterating the image and by distorting the silhouette of the stationary object in the environment or during movement at low speed, whilst also simulating a dummy object to form a trap.

Means 3 make it possible to reduce, obliterate or distort the thermal image or impression left by moving objects after parking, or to simulate false parking, ortho disguise a parked object, or to simulate fortifications, shelters or barrages such as trenches, mine fields, etc.

In certain cases, electric strips heated by low temperature radiation can be incorporated into the material to better simulate the occupation of the ground by motorised objects or personnel.

Whilst harmonising with the environment, means 4 give day and night protection from detection of moving or stationary military objects by covering, screening or shielding.

The material, which is transformed into strips or rings after appropriate cutting for the intended camouflaging purpose is fixed by clips, tied or secured by adhesion to a metal or synthetic meshed support, whose geometry is that of a grating or fishing net. The strips or rings can cover one surface of the support or can be distributed over both surfaces thereof in accordance with a density suitable for the sought camouflaging (harmonisation, relief, colours, reduction, absorption, diffusion, protection, etc).

Detailed description of the drawings and embodiments The invention will be better understood from the following description of a number of embodiments of the absorbant andior reflecting shield with reference to the attached Figures 1 to 11 showing in an illustrative and non-limitative manner the embodiments according to the invention. In the drawings, the composite material has been shown in "blown up" form to facilitate understanding, but it is obvious that in actual fact the different constituent layers are stuck to one another and compressed to give a fabric which is as thin as possible.

Example 1- Figure 1 In this embodiment, the shield according to the invention comprises three separate layers joined in pairs by a suitable known adhesive. Layer 1 is a polyvinyl chloride film, layer 2 a polester film and layer 3 a foam constituted for example by polyester, polyurethane or polyvinyl chloride. At least one of the two faces of polyester foam 2 is metallised by means of a coating of for example aluminium, nickel, silver or gold. This coating is of great importance for the reflection of electromagnetic waves and in particular infrared radiation, which in this way cannot completely through the shield.

Example 2- Figure 2 In this embodiment, the shield has three layers which are stuck to one another in pairs. The assembly has two polyvinyl fluoride films 1 and 4 confining a thermally compressed, pigmented and non-flammable foam 3. The foam 3 is pigmented and made non-flammable by means of antimony sulphide, antimonytrioxide and various halogen compounds, for example zinc or calcium borates.

Example 3- Figure 3 In this embodiment, the shield according to the invention comprises four layers. Thus, there are two polyvinyl fluoride outer layers 1 and 4, a metallised polyester layer 2 adhered and sandwiched with layer 3 formed by a previously pigmented, filled and fire-proofed, thermally compressed foam. The filling which is carried out serves to increase the dispersing and reflecting power of the shield relative to electromagnetic radiation and is brought about by means of very small balls of graphite, glass or silica, which are optionally mixed with metal pigments or particles, such as alumina trihydrate or barium ferrite. In standard realisations of the invention the diameter of the balls used for filling the foam layer 3 is between preferably 30 and 80 micrometres.Obviously, foam layer 3 is only filled with small balls of reflecting material when the need is considered to arise and this filling is therefore optional. Thus, it only increases the reflecting and dispersing action of the shield, but can be decisive in certain applications.

Example4-Figure4 In this embodiment, the shield is formed from five superimposed layers, stuck together in pairs by means suitable, per se known adhesive means. It is readilyapparentfrom Figure 5 that the thus formed shield is directly derived from that of the previous embodiment by adding a second polyester film 5 between foam layer 3 and the polyvinyl fluoride film 4.

Example 5 - Figure 5 In this embodiment, the shield has a polyvinyl fluoride film 1 adhered and sandwiched with a synthetic support 8, each of whose faces is coated with polyvinyl chloride films 6 and 7, which have been pigmented and fire-proofed in the same way as the foam of examples 3,4 and 5.

Example6-Figure6 In this embodiment, which is derived directly from the previous embodiment, a polyester film 2 has been added between the polyvinyl fluoride film 1 and the synthetic support 8, whose two faces are coated with polyvinyl chloride. One face of the polyester film 2 is metallised and is adhered to and sandwiched with the synthetic support 8. The polyvinyl chloride of layers 6 and 7 is treated with a cross-linking agent.

Example 7- Figure 7 It is derived from the previous example by adding the non-flammable, thermally compressed foam layer 3 adhered and sandwiched with the synthetic support 8.

Example8-Figure8 It is derived from the previous example by eliminaating the polyester layer 2. The foam 3 is thermally compressed, non-flammable, pigmented and filled as in Figure 4. The synthetic support 9, with which the foam 3 is adhered and sandwiched, is coated with polyurethane or polyvinyl chloride, whose faces 6 and 7 are treated with a cross-linking agent.

Example9-Figure9 This embodiment is directly derived from the previous example by the fact that the non-woven synthetic support 8 is adhered to a detachable, silicone-coated paper 9.

Example 10-Figure 10 The thermally compressed foam 3 is sandwiched between two polyvinyl fluoride films 1 and 4, the latter film being adhered to a detachable siliconecoated paper 9.

Example 11-Figure 11 This example relates to a constructional of the foam material which has a honeycomb structure.

The foam layer 3, after expanding in a mould in honeycomb form, is constituted by hexagonal cells geometrically arranged in the same way as the wax cells made by bees. After cooling, the complex is cut and sawed into portions. Films of polyvinyl fluoride 1 and 4, polyamide films or polyester films 2 and 10 are superimposed on and stuck to layer 3, whereby said films are metallised and one or both their faces are after being previously corrugated and/or moulded. The rigid or non-rigid foam chosen is previously filled and rendered non-flammable at the time of manufacture, as in the previous examples.

In all the examples described hereinbefore, the polyvinyl fluoride films are obtained by extrusion.

The polyvinyl fluoride is pigmented throughout in the mass with coloured pigments of various types such as, for example, alpha and beta phthalocyanine blues or greens or yellows, reds or browns of ferric oxide or fine aluminium powder.

The polyester films obtained by extrusion are colourless or opaque and are metallised on one or both their faces by a metal generally chosen from the group containing aluminium, nickel, gold and silver.

The polyester, polyurethane, polyvinyl chloride or phenol foam is coloured and fire-proofed and is then filled with balls of graphite, glass or silica, magnesia, carbon black or barium ferrite. The balls are distributed in varying percentages as a function of the sought objective, whereby the diameter of the balls can vary between 30 and 80 micrometres. They are incorporated into the mixtures before expansion (graphite and/or glass andor silica balls). Their function is to absorb or reduce electromagnetic waves, or absorb hyperfrequencies and the flow of waves or thermal reflections. For the same purpose or to vary the dispersion (squattering) it is possible to add to the non-flammable mixture a certain percentage (5 to 20%) of metal fibres, e.g. brass, steel, iron or aluminium, bronze, copper or silver powders.

The foam is produced by the method using one or two components with fluorine gas or an expanding agent using standard two-headed spray guns, pouring the two mixtures, mixing with the spray gun or pouring the layers one on top of the other onto a teflon-coated or silicone-coated kraft paper carrying strip or into moulds. After cooling, the foam is cut into two to five cm portions and its thickness is compressed at a temperature which can exceed 200 C, with a view to reducing the overall dimensions and to make it non-tearable. In the method involving cutting into strips, a synthetic grating can be used, whose two faces are rendered adhesive and is then placed between two foam portions, after which the assembly is thermally compressed.

The foam alone can be compressed and corrugated or the complex material is compressed and corrugated so as to obtain the texture like corrugated board or a pyramidal or conical texture, with a view to modifying the reflection of waves (scattering).

The invention is not limited to the embodiments described and represented hereinbefore and various modifications can be made thereto without passing beyond the scope of the invention.

Claims (7)

1. A shield which absorbs and/or reflects electromagnetic radiation, wherein it comprises a composite material constituted by a mass-coloured polyvinyl fluoride film, a pigmented, non-flammable, organic foam layer and at least one other layer selected from polyvinyl fluoride, metallised polyester, polyvinyl chloride and a synthetic support sandwiched between two polyvinyl chloride layers.

2. A shield according to claim 1, wherein the oraanic foam is a non-riqid foam constituted by a substance from the group including polyester, polyurethane and polyvinyl chloride.

3. A shield according to claim 1, wherein the organic foam is a rigid phenolic foam.

4. A shield according to claim 1, wherein the fire-proofing and pigmenting of said foam are carried out by means of a substance chosen from among antimony sulphide, antimony trioxide, halogen compounds, zinc borate and calcium borate.

5. A shield according to claim 1, wherein the foam is also filled with graphite and/or glass and/or silica balls having a diameter preferably between 30 and 80 rtm.

6. A shield according to claim 5, wherein the balls are mixed with metallic pigments or particles, particularly aluminium trihydrate and/or barium ferrite.

7. An absorbant and/or reflecting shield substantially as described hereinbefore with reference to the drawings.