Technical Field

This invention relates to a combined infra-red and visible light camouflage system.

The basic principles of camouflaging an object to hinder visual observation of it are generally well known, and basically involve colouring the surface of the object in some way to match its background, or marking the object in a manner which breaks up its shape as seen by the eye. In either way, objects can be made to be virtually indis¬ tinguishable visually from their background.

There is also a need for materials which provide both visual camouflage and infra-red camouflage. The main requirements of an infra-red camouflage material are that it must be able to reflect radiant heat incident on the material, have a low emissivity and be able to re-emit conducted heat at a specific level in keeping with the surroundings. For camouflage to be effective at thermal wavelengths the main requirement is that it must control the radiation of heat from the object to be concealed to a level in keeping with the local environment. In the case of the present invention, this is achieved by means of an assembly which will reflect radiant heat from the object to be camouflaged back into the camouflaging enclosure and will also provide effective concealment of the outer surface of the camouflage assembly by virtue of an emis¬ sivity which is sufficiently low such that conducted heat is re-emitted at a level similar to that of the surround- ings.

In particular, there is a need for "thermal" camou¬ flage which controls the reflection and emittance of infra¬ red wavelengths in the region of 3 to 14 microns (i.e. the far infra-red wavelengths). The present invention is

particularly concerned with providing camouflage for the 3 to 14 micron wavelengths whereas many in-service camouflage materials are more concerned with controlling the reflec¬ tion and emissivity of wavelengths of 0.7 to 1.2 micron (i.e. near infra-red wavelengths).

It is difficult to produce a fabric having good visual camouflage and good infra-red camouflage properties. One method of manufacturing such a fabric is disclosed in EP-A- 0329320 which discloses a method of manufacturing a thermal camouflage fabric by weaving metal-coated flat tapes to form the fabric. The tapes may comprise two layers of aluminium sandwiched between two layers of high density polyethylene or may comprise a single layer of high density polyethylene sandwiched between aluminium layers. These "metallised" tapes are woven either with similarly metal¬ lised tapes or with non-metallised tapes of polyethylene to make up the fabric. The fabric is then overcoated (usually by an extrusion coating method) with polyethylene which may contain pigments that absorb radiation in the visible region of the electromagnetic spectrum.

We are aware of GB-A-1605261 which discloses an infra¬ red and visible camouflage system that comprises the combination of two materials, one being a selective absor¬ ber of visible light and the other a reflector of infra-red radiation. This British patent discloses manufacturing a laminated sheet comprising a layer of pigmented poly¬ ethylene which has a metal coating applied to it. The metal coated polyethylene sheet is then adhesively bonded to each side of a fabric material. The pigmented poly- ethylene layers are formed as an extrusion coating.

An object of the present invention is to provide a combined infra-red and visible light camouflage material and a method of manufacturing such material.

Summary of the Invention

According to one aspect of the present invention there is provided a laminated combined visible and infra-red camouflage material comprising a first layer which com- prises an infra-red reflector material, a second layer which is translucent to visible light applied to the first layer, and a layer of visible light-absorbing pigment or pigments located at the interface between the first and second layers.

Preferably the pigment or pigments is/are applied to one or both of the surfaces at the interface between the first and second layers. The pigment or pigments may be painted, printed, or coated on one or both of the surfaces.

The pigment may be a single colour or a plurality of colours if desired.

The first layer is preferably a metal layer which may be in the form of a metal foil or formed as a vapour- deposition of metal. The metal may be vapour-deposited onto a surface of the second layer or directly on to a substrate. If the metal is a foil or is vapour-deposited on to a substrate, the layer of pigment or pigments may be applied to the metal layer. Alternatively, or addition¬ ally, the pigment or pigments may be applied by painting, printing or coating onto a surface of the second layer prior to bringing the first layer into contact with the second layer.

In a further embodiment, a substrate has a first layer in the form of a layer of plastics material such as a polyolefin or a polyester which has a metal coating applied to it. In this embodiment the second layer comprises a clear polyolefin layer which has the pigment, or pigments applied to a surface of the second layer that contacts the first layer.

It is preferred that both surfaces of a substrate are

provided with the first and second layers, however, if desired, only one surface of the substrate may be provided with the first and second layers in which case such a material will not be reversible and will exhibit different visual and infra-red camouflage properties when viewed from different sides.

According to a further aspect of the present invention there is provided a method of manufacturing a laminated combined visible and infra-red camouflage material which comprises forming a first layer which comprises an infra¬ red reflector material, applying to the first layer a second layer which is translucent to visible light, and locating a layer of at least one visible light-absorbing pigment at the interface between the first and second layers.

Desirably the first layer is a metal layer which is applied to the second layer prior to contacting the first layer with a substrate, and the pigment is applied to one or both of the surfaces at the interface between the first and second layers prior to contacting the first layer with the second layer.

The camouflage material can be cut into strips and the strips woven to form a sheet of fabric either as one of the warp or weft or as both warp and weft.

Brief Description of the Drawing

The present invention will now be described by way of example with reference to the accompanying drawing, in which:

Figures 1 to 4 show in schematic cross-section four fabrics constructed in accordance with the present inven¬ tion, and

Figure 5 is a plan of a fifth fabric of woven con-

struction also constructed in accordance with the inven¬ tion.

Description of Preferred Embodiments

Referring to Figure 1 there is shown a flexible optically-translucent polyolefin (e.g. polyethylene) film 10 which has a thin layer of aluminium 11 bonded to it. Preferably the inner surface of the polyolefin film 10 is printed with a visible light-absorbing pigment prior to applying the metal layer 11. Alternatively, or additional- ly, the aluminium layer 11 may be printed with suitable visible light absorbing pigments 12 to produce the desired visual camouflage appearance prior to bonding it to the film 10. The flexibility introduced by the printing step enables one to apply the visual camouflage pigment rela- tively easily. The aluminium layer 11 is laminated to the polyolefin film 10 so that this gives a tough layer which cannot readily be delaminated and protects the pigments.

Two pieces of laminated outer layer 30 (comprising integers 10, 11, 12) are then bonded, one on each side of a flexible non-woven scrim 13 made of a polyester. It is preferred to bond each outer layer 30 to the scrim 13 using heat and pressure but one may use an adhesive instead. The scrim comprises, typically an open network of warp and weft filaments. Each layer 30 is bonded to the scrim 13 with its metal layer 11 in contact with the substrate scrim 13. A primer coat may be applied to the scrim prior to bonding to improve the bond.

In the further embodiment of the invention shown in Figure 2 we prefer to use a metallised clear polypropylene sheet 14, such as that manufactured by Courtaulds Films & Packaging Limited under the trade name "Shorko M", as used for packaging. The "Shorko M" sheet 14 comprises a central core of polypropylene homopolymer film which has copolymer layers of propylene and ethylene on each of its surfaces. This polypropylene triple-layer sheet 14 is stretched

preferentially more length ways than width ways to produce a highly oriented sheet of desired thickness. The sheet 14 is subjected to a Corona discharge treatment to ionise one of the surfaces of the sheet. The ionised surface of the sheet is then metallised with a thin aluminium layer 15 using a vacuum-deposition technique. The "Shorko" sheet 14 so formed is laminated with a further clear polyolefin (such as polypropylene) layer 16 which has a layer 17 of visible light-absorbing pigment printed on that surface of the layer 16 that contacts the "Shorko" sheet 14. Two pieces of laminated layer 31, comprising components 14, 15, 16 and 17 and produced by the technique described, are bonded to respective opposite sides of a non-woven support¬ ing scrim 18 with the aluminised surface layers 15 of the "Shorko" sheets 14 each in contact with the supporting scrim 18.

In a further embodiment of the invention shown in Figure 3 a substrate 20 may have a metal layer 21 applied directly ..to it, either in the form of a foil, or as a vapour-deposited coating. A visible light-absorbing pigment 22 may either be painted, printed or coated on the metal layer 21 or on the inside surface of an outer poly¬ thene or polypropylene layer 23.

In yet a further embodiment shown in Figure 4, a metal layer 24 is formed either as a foil, or a vapour-deposited coating, on to a layer 25 which may be a polyolefin or a polyester sheet. A layer 28 of visible light-absorbing pigment is applied to either, or both, of the outer surface of the metal layer 24 or to the inside surface of an outer polyolefin layer 26 which is transparent to visible light. The laminate 33 formed from component layers 24, 25, 26 is applied to one side of a non-woven scrim 27, which could be a polyester scrim, by bonding the layer 25 on to the scrim using heat and pressure or by use of an adhesive. This produces a non-reversible camouflage material but a rever¬ sible material can be made by applying the laminate 33 to

both sides of the scrim 27.

In yet further embodiments of the invention further visible light-absorbing pigments may be applied to the outer surface of the outer layers of the structures shown in Figures 1, 2, 3 or 4.

If a non-reversible material is acceptable, the sandwiching of the substrates 13, 18 and 20 between identi¬ cal laminates 30, 31 and 32 will not be necessary and the one-sided laminates so produced represent further embodi- ments of the invention.

In operation, the thermal camouflage material is placed between an object to be screened and a potential observer. Other screens such as canopy netting which simulate foliage or trees are used between the camouflage material of the present invention and the observer. Radiation from the object to be screened, in the wavelength range 3 to 14 microns, passes readily through the outer layer 10, 16, 23, 26 which faces the object to be screened and is reflected back towards the object by the metal layers. Good thermal transparency of the outermost layer(s) 10, 16, 23, 26, is required in order that thermal energy is not readily absorbed by the outer layers and can be reflected efficiently by the metal layer. Olefin polymers are especially good in this respect and whilst polythene is particularly good, polypropylene is generally adequate for use as an outer layer.

Preferably the substrate is a polyester scrim, how¬ ever, it may be possible to use other types of scrim and indeed other woven or non-woven fabrics or nets made from other materials or other polymers such as nylon or poly¬ propylene. It should be noted, however, that polyester has limited transparency to infra-red wavelengths whereas polypropylene has good transparency at these wavelengths.

In the absence of a pigment, both the thermal and visual reflectivity of the metal layer would be very large making it highly visible and of little use for concealment purposes. Use of a pigment therefore provides visual colouration and desirably reduces thermal reflectivity (and correspondingly increases emissivity) to a level consistent with providing minimum thermal contrast with the surround¬ ings. Pigmentation systems in general have poor transpar¬ ency to thermal wavelengths which tends to prevent achieve- ment of the required reflectivity and emissivity levels. It is therefore essential that the polymer chosen for the outer layer 10, 16, 23, 26 has good transparency to thermal wavelengths in order to provide the maximum latitude in pigment choice and concealment effectiveness.

The fabrics described above in connection with Figures 1 to 4 are fairly flexible and offer good thermal camou¬ flage. If desired, a more flexible screen may be made by taking one of the fabrics described above in relation to Figures 1 to 4 and cutting the fabric into thin strips to form tapes which are then woven to form a thermal camou¬ flage fabric as shown schematically in Figure 5.

In Figure 5 the tapes are shown as an open weave for clarity but it is to be understood that the fabric is woven so that there are no gaps between the tapes.

Referring to Figure 5, both weft tapes 34 and warp tapes 35 are made from one of the fabrics shown in Figures 1 to 4. However if desired, the warp tapes 35 could be strips of a plastics material such as a polyolefin, or polyester which is not coated with a metal coating. The fabric which is woven from the tapes could be further coated on one or both sides with a layer of optically- translucent polyolefin (e.g. polyethylene). In some circumstances the polyolefin film 10 of the fabric of Figure 1 could be omitted prior to cutting the fabric into strips to form tapes for weaving, and the polyolefin film

applied to a fabric which is woven from the tapes after it has been woven.

It will be appreciated that if the substrate is a scrim, the cutting of the fabric into strips may leave little in the way of a substrate and will reveal exposed ends of the fibres making up the scrim. In these cir¬ cumstances it may be desirable to omit the scrim and thus produce tapes that do not incorporate a substrate.