EP0129744B1 - Camouflage material for camouflaging military targets - Google Patents

Abstract

A camouflage material whose convective heat exchange pattern simulates the thermal properties of a natural background and having a non planar surface comprising a mesh support, a conductive layer on said support and an outer layer on said conductive layer containing metallic material and having an emissivity in the wave length of far infrared of about 20 to 70% and wherein said outer layer comprises a synthetic foam layer.

Description

The invention relates to a camouflage material for camouflaging military targets against reconnaissance in the near and far infrared wave range as well as in the millimeter and centimeter wave radar range, with a base material constructed from threads in a net-like manner, which is at least one side electrically conductive with a low specific surface resistance and an outer layer applied thereon which has an emission factor that changes over the surface in the far infrared wave range.

Military targets are usually covered with camouflage nets, which consist of a support net and camouflage material made of textile-like material applied to it. The camouflage material is colored in such a way that the best possible adaptation to the background is given in the visible wave range and in the near infrared range. In the far infrared wave range, ie in the spectral ranges 3 to 5 µm and 8 to 14 µm (atmospheric windows II and 111) and in the radar range, these camouflage networks had no protection, so that they could be located for thermal imaging and radar devices.

In order to obtain a broadband camouflage also in the areas of modern locating devices, i.e. in particular in the wavelength ranges in which thermal imaging and radar devices work, camouflage materials have been developed which consist of a base material, a metallic reflective layer on the base material and a camouflage paint on the reflective Layer exist (see. DE-A-27 59 657, DE-A-21 51 349). According to the teaching of the first-mentioned publication, the camouflage paint should be formed by camouflage colors, the binder of which has good transparency in the spectral ranges of the atmospheric windows II and 111 and the pigments in the visible and near IR range have a reflection similar to chlorophyll. In this area, the camouflage colors should have an emission factor that changes over their area and should preferably vary between 50 and 90% in the wavelength range from 3 to 5 μm and between 60 and 95% in the wavelength range from 8 to 14 μm. This variation in the emission factor gives the camouflage in the spectral range of the thermal imaging devices a structure which is matched to that of the natural background in this spectral range.

The camouflage in the radar spectral range is achieved in that the metallic layer has a specific surface resistance of at most a few ohms / square and that the camouflage material is in the form of a garnish with, for example, a sickle cut. Through the combination of garnish and low surface resistance, the radar waves are scattered like the leaves of trees, so that the targets behind remain invisible to radar.

One disadvantage of this type of camouflage material has been its sensitivity. The electrically conductive layer changes its resistance and thus its effectiveness due to the stress on the camouflage material in use so significantly that the camouflage properties suffer.

On the other hand, the previously known camouflage material has a tendency to heat up more than the natural environment, in particular natural foliage, as a result of solar radiation. The foliage partially uses the sun's rays for photosynthesis. In addition, part of the absorbed energy is released into the environment through water evaporation. Furthermore, many plants change the angle of incidence of the sun's rays by changing the leaf position in order to avoid excessive heating by the sun's rays. The warming of foliage does not depend solely on its emission coefficient, which means that a camouflaged target no longer fits into the image of the natural grasses and leaves in the background after prolonged exposure to the sun.

The invention is therefore based on the object of improving the known camouflage material described at the outset in such a way that the camouflage effect is retained as far as possible even in the case of prolonged exposure to the sun and that the camouflage properties also remain constant for a long time even under high usage stress.

This object is achieved in that the threads have free spaces between them and accordingly the electrically conductive design of the base material and the outer layer are limited to the threads themselves.

This design of the camouflage material is based on the idea already belonging to the invention of using the convection flow which forms on the camouflage material due to its heating for better heat dissipation to the air by considerably increasing the heat transfer area. Due to the free spacing of the threads, an exchange of the air flows is also possible. In this way, the warming of the camouflage material due to solar radiation remains within the limits within which the surrounding foliage material also heats up.

In addition, the camouflage material is not affected as quickly by its use because there is no closed electrically conductive layer that could tear.

According to the invention, the covering of the camouflage material is not complete due to the free spaces between the threads. A compromise must be made on the one hand with regard to the size of the free spaces between the threads and on the other hand, the need to cover the military target. Such a compromise can consist in that the free distances are at least one third of the thread thickness, better still about half the thread thickness. In this way enough space is created for the convective air flow, but on the other hand the coverage of the military target is still sufficient.

In one embodiment, the threads for forming the net-like structure of the camouflage material, for example in the form of a fabric, are provided with an electrically conductive layer. This expediently consists of a binder, for example a phenolic resin binder, with electrically conductive pigments, for example graphite or carbon black particles. The binder should contain about 10 to 50% of the pigments. Such an electrically conductive layer can be applied in a simple manner by spraying or brushing onto the threads of the base material. The layer causes camouflage in the radar area, because the radar beams are scattered in a wide variety of directions and thus create a picture similar to that of the foliage of trees.

Alternatively or in combination, it can be provided that at least some of the threads consist of metal. This can be done, for example, in that the threads are formed from plastic-laminated aluminum strips with a width of 0.2 to 0.5 mm. The thickness of the aluminum strips can vary from 6 to 20 mm, whereby they are laminated on both sides with the same thickness.

In both cases, the surface resistance should be in a range between 2 to 50 ohms / square, since the reflection of the radar waves is particularly pronounced in this range.

In an advantageous embodiment, the outer layer according to the invention consists of a synthetic, open-cell foam covering. As a result, the surface area which is effective for heat transfer is increased considerably, which also counteracts excessive heating of the camouflage material as a result of solar radiation.

In order to adjust the emissivity to the natural environment, the foam covering should contain about 5 to 25% flaky metal pigments, for example made of copper, zinc, steel or aluminum particles. In this way, an emission factor of 70 to 95% can be achieved, which is recommended for camouflage in summer. An emission factor of 40 to 60% is sufficient for camouflage in winter. The emissivity or the emission factor is synonymous with the absorbency.

Alternatively, the outer layer can also be a color layer which consists of a binder which is largely transparent in the infrared spectrum, such as, for example, cyclo-rubber, polyethylene or polypropylene, and platelet-shaped metal pigments, such as, for example, chromium oxides, iron oxides or titanium oxides, or mineral pigments, such as, for example, Sienna, lime or cobalt blue.

As an alternative or in combination with the first proposal according to the invention, the basic idea of the present invention can also be realized by providing the camouflage material of the type mentioned at the beginning with depressions and / or projections, which are preferably embossed, over the surface. This measure also considerably increases the heat transfer area for the convective air flow, as a result of which better heat transfer to the ambient air is achieved. The consequence of this is that the camouflage material heats up less when exposed to sunlight, even if the camouflage material is formed without free spaces between the threads. In the latter case, however, the electrically conductive design and the outer layer can then be designed in the same way as for the camouflage material with the free spaces between the threads.

The depressions or projections can be hemispherical and / or conical, for example. In both cases, an increase in the heat transfer area and a scattering of the reflected radar beams is achieved.

The depressions and / or the projections can have a depth or height of approximately 5 to 25 mm and a diameter of the same order of magnitude. The dimensions of the depressions or projections should expediently change distributed over the surface.

As an alternative to this, the projections can also be formed in the form of ribs by appropriate folding of the tamp material.

Finally, the invention provides that spots of the camouflage material are applied irregularly distributed on a support net, the support net should consist of the open-mesh camouflage material.

• Figur 1 eine teilweise Querschnittsansicht eines Tarnmaterials;
• Figur 2 eine teilweise perspektivische Ansicht des Tarnmaterials gemäß Figur 1;
• Figur 3 eine teilweise Querschnittsansicht eines anderen Tarnmaterials;
• Figur 4a eine perspektivische Teilansicht eines geprägten Tarnmaterials nach Figur 3;
• Figur 4b eine Querschnittsansicht des Tarnmaterials nach Figur 4a;
• Figur 5a ein anders geprägtes Tarnmaterial nach Figur 3 in perspektivischer Ansicht;
• Figur 5b eine Querschnittsansicht des Tarnmaterials nach Figur 5a;
• Figur 6 eine teilweise perspektivische Ansicht eines rippenförmigen Tarnmater als nach Figur 3 und
• Figur 7 eine teilweise schematische Ansicht eines Tarnnetzes mit Flecken des Tarnmaterials nach Figur 3.

In the drawing, the invention is illustrated in more detail using exemplary embodiments. Show it:

• Figure 1 is a partial cross-sectional view of a camouflage material;
• FIG. 2 shows a partial perspective view of the camouflage material according to FIG. 1;
• Figure 3 is a partial cross-sectional view of another camouflage material;
• Figure 4a is a partial perspective view of an embossed camouflage material according to Figure 3;
• FIG. 4b shows a cross-sectional view of the camouflage material according to FIG. 4a;
• 5a shows a differently shaped camouflage material according to FIG. 3 in a perspective view;
• FIG. 5b shows a cross-sectional view of the camouflage material according to FIG. 5a;
• Figure 6 is a partial perspective view of a rib-shaped camouflage mat as in Figure 3 and
• FIG. 7 shows a partially schematic view of a camouflage net with spots of the camouflage material according to FIG. 3.

The camouflage material 1 shown in Figures 1 and 2 is designed as a carrier fabric, which consists of crossing threads 2, 3. Plastic monofilaments are particularly suitable as the material for the threads 2, 3.

The threads 2, 3 are, as can be seen in particular from FIG. 1, surrounded by an electrically conductive layer 4 which has been applied by means of an impregnation technique. Their conductivity is brought about by electrically conductive pigments, such as graphite or carbon black. The graphite or carbon black particles are contained in an amount of 10 to 50% in a phenolic resin binder. The electrically conductive layer 4 appears black.

A synthetic, open-cell foam covering 5 is applied to this layer 4, namely by immersion in a corresponding bath and subsequent foaming and drying. The open cell structure of this foam covering increases the heat transfer area effective for air convection.

The foam covering 5 can consist, for example, of polyurethane, polyolefin, polyvinyl chloride, polyester, polyether, polystyrene or polyacrylate. About 5 to 25% of metal pigments, for example copper, zinc, steel or preferably aluminum flakes, are embedded in the foam covering 5 in order to achieve a desired emission factor. For summer camouflage, the emission factor or emissivity should be between 70 and 95% of the black body, while for winter camouflage an emissivity of 40 to 60% is sufficient. The emissivity should change continuously over the area within the aforementioned ranges in order to tear apart the representation in the thermal imaging device and to adapt it to the representation of the natural environment.

As can be seen in particular from Figure 2, the crossing threads 2, 3 run at a distance from each other, so that gaps 6 arise. This also contributes to the improvement of the heat transfer, since the heat transfer area for the convective air flow is thereby increased. This has the consequence that the camouflage material 1 is no longer heated by the solar radiation as much as was the case with the known material. It has proven to be a favorable compromise between the best possible coverage of the target to be camouflaged and the best possible air permeability to make the distance a between two adjacent threads 2 approximately half to one third as large as the thickness b of the thread 2 itself. A corresponding treatment, as is customary in the textile industry, can follow to fix the threads 2, 3.

Another embodiment of a camouflage material 7 is shown in FIG. This camouflage material 7 is also woven from threads 8.

In contrast to the camouflage material 1 shown in FIGS. 1 and 2, however, the camouflage material 7 shown here is not air-permeable. The threads 8 and the gaps between them are surrounded or filled with an electrically conductive layer 9, which can consist of the same material as the electrically conductive layer 4 in the embodiment according to FIGS. 1 and 2. On both sides of the electrically conductive Layer 9, color layers 10, 11 are applied, the color binder of which is transparent in the thermal infrared range, that is to say, for example, made of cyclo-rubber, polyethylene or polypropylene. In this color binder, just like in the foam covering 5 in the embodiment according to FIGS. 1 and 2, metal pigments are incorporated, with which the emissivity can be set in the desired range, with the aim of adapting as well as possible to the emissivity of the surrounding nature to reach. As an alternative to the color layers 10, 11, it is of course also possible to apply foam coverings of the type provided for the camouflage material 1 according to FIGS. 1 and 2.

The threads 8 of the camouflage material 7 can again consist of plastic, such as polyester, nylon, polyethylene, polypropylene or other filaments. However, the threads 8 of the camouflage material 7 - like the threads 2, 3 of the camouflage material 1 according to FIGS. 1 and 2 - can also be designed to be electrically conductive. The preparation of the yarns 2, 3, 8 takes place then such that a thin aluminum foil with a thickness of 6 to 20 is laminated to both sides with a thin polyester film may have a thickness of 6 to 20 _I lm. This material is then cut into endless threads with a width of 0.2 to 0.5 mm. The threads can then partially or completely replace the plastic threads 2, 3, 8 in the camouflage materials 1, 7.

In order that the camouflage material 7 according to FIG. 3 has an increased heat transfer surface for the passing convection air flow, its surface is additionally structured, as can be seen from FIGS. 4, 5 and 6. In the example according to FIGS. 4a and 4b, the camouflage material 7 'is provided with cup-shaped recesses 12. In the example according to FIGS. 5a and 5b, pyramid-shaped depressions 13 are provided. Both types of depressions 12, 13 have been impressed by appropriately engraved calenders or rollers. The depressions 12, 13 not only have the task of increasing the heat transfer area, but should also scatter the radar beams reflected by the respectively electrically conductive layer 9 in a wide variety of directions.

In the example according to FIG. 6, the camouflage material 7 ″ is folded in such a way that rib-shaped projections 14 are formed Projections 14 have the same effect as the depressions 12, 13 in the camouflage materials 7 'and 7 "in FIGS. 4 and 5.

FIG. 7 shows a camouflage net 15, which consists of a support net 16 and colored spots 17 applied thereon in irregular shape and at intervals. The spots 17 are cut out of the camouflage material 7 according to FIGS. 3 to 6. The support net 16 consists of the camouflage material 1 according to FIGS. 1 and 2.

For the conventional heat exchange, the support net 16 and / or the spots 17 - in the latter case before being applied to the support net 16 - can be provided with incisions.

example 1

A fabric made from polypropylene monofilaments with a diameter of approximately 0.5 mm is coated with an electrically conductive lacquer of approximately 50 g / m ² , the lacquer containing 12 to 20% carbon black or graphite or a mixture thereof. The electrically conductive paint can be applied by spraying, rolling or soaking. After the fabric has dried to remove the solvent, it is immersed in a solution of 55% PVC and 45% phthalate plasticizer, which contains color and metal pigments. After drying to form a foam covering, spots are clipped onto the fabric. These spots consist of a woven textile material of approximately 12 threads per cm, which is covered on both sides with an electrically conductive layer. Color layers are applied to both sides of this layer, which has a binder which is essentially transparent in the thermal infrared range and contains pigments reflecting heat radiation, the colors of which also have a camouflaging effect in the visible range. The textile material is provided with embossed recesses, which have been embossed using an appropriate embossing calender.

Example 2

For the fabric described in Example 1, polyester fibers are used instead of polypropylene monofilaments. The electrically conductive layer contains aluminum particles and the foam covering consists of a pre-expanded acrylic dispersion. In order to improve the conductivity in the high-frequency radar range, threads are woven into the textile material that are themselves electrically conductive, since they consist of plastic-laminated aluminum strips.

Claims (18)

1. Camouflage material for camouflaging military targets against observation in the close- range and distant infrared wave range and also in the millimetre and centrimetre wave radar range, with a basic material which is constructed in net-like manner from threads and which is made electrically conductive at at least one side with a low surface resistivity and has an outer layer applied to it, this layer having in the distant infrared wave range an emission factor which varies over the surface, characterised in that the threads (2, 3) have free spacings (a) between themselves and accordingly the electrically conductive formation of the basic material, and the outer layer (5), are restricted to the threads (2, 3) themselves.

2. Camouflage material according to claim 1, characterised in that the free spacings (a) amount to at least a third, especially a half approximately, of the thread thickness (b).

3. Camouflage material for the camouflaging of military targets against observation in the close- range and distant infrared range and also in the millimetre and centimetre wave radar range, with a basic material which is constructed in net-like manner from threads and which is made electrically conductive at at least one side with a low surface resistivity and has an outer layer applied to it, this layer having in the distant infrared wave range an emission factor which varies over the surface, according to claim 1 or 2 also, characterised in that the camouflage material (7) is provided with depressions (12, 13) and/or projections (14) distributed over the surface.

4. Camouflage material according to claim 3, characterised in that the depressions (12,13) and/or the projections (14) are formed by stamping.

5. Camouflage material according to claim 3 or 4, characterised in that the depressions (12, 13) or projections are formed to hemispherical and/or conical shapes.

6. Camouflage material according to claim 5, characterised in that the depressions (12, 13) and/or the projections (14) have a depth or height respectively of approx. 5 to 25 mm and a diameter in the same order of magnitude.

7. Camouflage material according to claim 5 or 6, characterised in that the dimensions of the depressions (12, 13) or projections (14) respectively vary throughout the surface.

8. Camouflage material according to one of claims 3 to 7, characterised in that the projections (14) are given a rib-form construction.

9. Camouflage material according to one of claims 1 to 8, characterised in that the threads (2, 3, 8) are provided with an electrically conductive layer (4, 9), made for example of a binder, especially phenolic resin binder with electrically conductive pigments, especially graphite, carbon black or aluminium particles.

10. Camouflage material according to claim 9, characterised in that the pigment content in the binder amounts to 10 to 50 %.

11. Camouflage material according to one of claims 1 to 10, characterised in that at least some of the threads consist of metal, for example plastic-coated aluminium strips having a width of 0.2 to 0.5 mm.

12. Camouflage material according to claim 11, characterised in that the aluminium strips have a thickness of 6 to 20 um and are plastic-coated at both sides to the same thickness.

13. Camouflage material according to one of claims 1 to 12, characterised in that the surface resistivity amounts to between 2 and 50 ohms per square.

14. Camouflage material according to one of claims 1 to 13, characterised in that the outer layer (5) consists of a synthetic, open-cell, foam covering, consisting for example of polyurethane, polyolefin, polyvinyl chloride, polyester, polyether, polystyrene, polyacrylate.

15. Camouflage material according to claim 14, characterised in that the foam covering (5) contains approximately 5 to 50 % lamellar metal pigments, for example copper, zinc, steel or aluminium particles.

16. Camouflage material according to one of claims 1 to 13, characterised in that the outer layer is a colour layer (10, 11) which consists of a binder substantially transparent in the infrared spectrum, such as for example cyclised rubber, polyethylene or polypropylene, and lamellar metal pigments for example chromium oxides, iron oxides or titanium oxides or mineral pigments, for example sienna, lime or cobalt blue.

17. Camouflage material according to one of claims 1 to 16, characterised in that patches of the camouflage material (7) are arranged, in an irregularly distributed arrangement, on a supporting net (16).

18. Camouflage material according to claim 17, characterised in that the supporting net (16) consists of the camouflage material (1) with threads (2, 3) situated at free spacings from one another.

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