FR2511937A1 - Flexible, radar detectable sheet - comprises support coated with plastomer or elastomer compsn. contg. fine metal particles e.g. aluminium - Google Patents

Abstract

A flexible sheet for the prodn. of articles reflecting short electromagnetic waves of radar detector systems comprises a flexible support coated with a wave reflecting layer comprising a plastomer or elastomer based coated contg. fine metallic particles. The coating pref. contains 5-50% of the metal particles w.r.t the plastomer or elastomer and the particles may be Al powder of particle size 10-80 microns. The sheet is used for the prodn. of e.g. implantable rescue canoes, parachutes and the like. Use of the coating is cheaper than prior art metal vacuum deposition on the support.

Description

Soft articles detectable by radar, such as inflatable lifeboats, glider liners, parachutes, etc., are used to make fabrics coated with elastomeric or plastomeric material comprising a thin layer of a metallic deposit. likely to reflect waves from tracking radars. These fabrics are obtained by vacuum deposition of a thin layer of metal on a film of thermoplastic material such as polyester or polyethylene which is then laminated to the fabric coated with rubber or plastomer. This method of depositing the metal under vacuum is costly and the assembly operation on the previously coated fabric is poorly suited to the continuous manufacturing process of the coated fabric.

The invention proposes the production of flexible sheets for the manufacture of articles detectable by radar, in which the reflecting metal layer consists of fine particles which are incorporated within the layer based on plastomer or elastomer used for stretching the support sheet ensuring mechanical strength and which is generally a fabric or other flexible homogeneous sheet.

Examples of embodiments of the invention are described below with reference to the accompanying drawings in which the fig.1 and 2 schematically show in section two constitution of flexible sheets.

In the case of FIG. 1, the flexible sheet comprises a mechanical resistance support in fabric, for example in polyamide or polyester yarns i treated on one side with an adhesion layer 2 intended to obtain good adhesion with the coating layer. 3. The latter is carried out in the loom or by calendering one or more layers of a mixture based on plastomer or elastomer containing metallic particles intimately dispersed in the mass of this mixture. These metal particles may for example be aluminum powder having a particle size of 10 to 80 microns incorporated into the coating mixture at a rate of approximately 5 to 50% by weight per 100 parts of the elastomer or of the basic plastomer.

In the case of FIG. 2, the flexible sheet of fabric i is coated on both sides with a mixture based on elastomer or plastomer.

It is therefore treated on both sides with adhesion layers 2. On one of the faces the coating layer 3 is deposited a layer incorporating metallic pigments as in the previous example so as to form a reflective layer with regard to the short electromagnetic waves of radar systems. On the other face, the coating layer 4 based on plastomer or elastomer incorporates a fluorescent coloring material which serves to facilitate visual detection of the articles made from this flexible sheet. In this case, layer 4 forms the external face of the fabric and layer 3 its internal face.

As a variant, the reflective layer 3 of the preceding flexible sheets can incorporate both a metallic pigment and a fluorescent dyestuff. In the case of the double-sided fabric of FIG. 2, the layer 4 can be neutral or also fluorescent.

In another variant of the double-sided fabric, the two coating layers 3 and 4 can be reflective between incorporating the metallic pigment and either of these layers or both can be made more fluorescent by incorporating a suitable dye.

The basic composition of the coating layers 3 or 4 can, between one of the known formulas and used for the production of conventional coated fabrics and chosen to obtain the various properties desired for the articles to be made with these fabrics and such as impermeability to liquids and gases (if they are inflatable articles such as inflatable lifeboats) resistance to external agents, to light, to aging, to friction etc.
To this basic composition is added by mixing a metallic pigment and / or a fluorescent dye. The metallic pigment is preferably premixed and blended with a solvent or a plasticizer compatible with the composition and the degree of plasticity of this composition is adjusted according to the coating technique used, coating in the loom to be coated by scraping or coating by calendering - on cylinders.

 The composition of the coating layers may be based on a thermoplastic plastomer or a vulcanizable elastomer or a mixture of the two and the coated fabric is then subsequently treated accordingly.

A purely indicative formula based on a vulcanizable elastomer which can be used for coating with a roller calender is given below as a purely indicative example.

- Chlorosulfonated polyethylene 100 - Silica 20 - Di-Octyl-phthalate 10 - Polyglycol 1.5 - Antioxidant 0.7 - Resin 2 - Zinc oxide 1.5 - Stearic Acid 0.6 - Magnesia 4 - Sulfur 1 - TMTD 2 - Pentaerytritol 3 - Aluminum powder 20
empaté with 20% dioctyl phthalate

Claims (3)

Claims 10) Flexible sheet for making articles reflecting short electromagnetic waves of radar tracking systems, of the type comprising a flexible support layer and a thin metallic layer reflecting these waves, characterized in that the metallic layer consists of fine particles metallic intimately incorporated within the plastomer or elastomer coating layer of the flexible support layer to which it adheres. 20) Flexible sheet according to 10 in which the coating layer of the support sheet contains approximately 5 to 50% relative to the elastomer or the basic plastomer of fine metallic particles such as aluminum powder having a particle size of 10 to 80 microns.  30) Flexible sheet according to 10 or 20 in which the flexible support sheet coated on one side with a flexible layer with a reflective base of elastomer or plastomer incorporating metallic particles and on the other side with a flexible coating layer incorporating a material fluorescent. 40) flexible sheet according to one of claims 1 to 3 and wherein the reflective coating layer comprises both metallic particles and a fluorescent material.