Patent GB-1074896-A (GB)
Title: Non-metallic packing material with interference absorption for electromagnetic waves
IPC: B32B27/00
Filed: 1958-01-06
Abstract: 1,074,896. Laminates. ELTRO G.m.b.H. Jan. 6, 1958 [Jan. 15, 1957], No. 530/58. Heading BSN. [Also in Division H4] A laminated packaging material for radar camouflage by absorption of radiated energy of 0À1 to 50 cm. wavelength comprises a fibrous packing material 11 having a dielectric constant between 1À5 and 10, metallized on its inward surface and coated on its outward surface with a radiation-absorbing layer consisting of coatings of a resin base material filled with an inorganic powder to raise the apparent dielectric constant of the layer to a multiple of that of the packing material. The fibrous material 11 represents about half the total thickness which may be 6 to 8 mm., and consists of cellulosic material, polyvinylchloride, polyethylene or plywood or of wood fibres bonded together with polyvinylchloride. The metallized layer 10 is formed by spraying a lacquer containing aluminium, bronze, copper, silver or zinc powder. The fibrous material 11 effects phase shift of waves reflected by the layer 10, alternatively a further layer 12 is used for this purpose. The layer 13 comprises a number of coatings of a base material with fillers that differ in successive coatings. Fillers described are carbon black, high-frequency iron powder with an average grain size of 1 to 10 microns, foaming agents, semi-conductor material, dipoles of aluminium or carbon paper or of polyethylene, polyvinylchloride or polyamide coated with carbon black or graphite. For the outermost coating of this layer an infra-redreflective pigment is used as a filler. The foaming agents are magnesium carbonate, titanates, silicates, sulphates, phosphates and corundum. The iron powders are of iron pentacarbonyl, iron oxalate, ferriferous oxide, gammaferric oxide, and ferrites in which the iron oxide may be substituted by an oxide of nickel, zinc, manganese, or a rare earth metal or an alkali earth metal. The semi-conductor material comprises zinc oxide, beryllia or germanium. The infra-red-reflective pigments are magnesium or calcium-magnesium silicates, oxychlorides, phosphates, pyrophosphates and phthalocyanius. The base materials described for this layer 13 are Dismodur/Desmophen polyurethanes, polyisobutylene, polyvinylchloride, polybutadiene butadiene-acrylonitrile copolymer phenolformaldehyde, anilinformaldehyde, nylon, polyvinylidenechloride, polyvinylalcoholacetate, polyvinylacetate, polyvinylbutyral, polyethylenemethacrylate, polyester, alkyd resin, cyclized rubber, nitrile rubber, neoprene, silicon rubber, urea formaldehyde, cellulose acetate, polyethylene, polychlortrifluorethylene, polytetrafluorethylene, polyisobutylmethacrylate, polyvinylcyclohexane, natural rubber, bitumen, polystyrene. The Desmodur/Desmophen materials are described as having a Desmodur component of diisocyanate, and the Desmophen consisting of adipic acid and Butantriol with phthalic acid, xylene formaldehyde resin or butylene glycol. A delustering layer 14 may be applied outside the layer 13 and comprises a lacquer coating or a perforated lacquer film with perforations having a diameter less than one fifth of the wavelength to be absorbed. This delustering layer is suitably coloured and has a filling of infra-redreflective pigments. An outer layer 15 affords mechanical protection. The packaging material may be used as a basket weave, the apertures therein not exceeding one fifth of the wavelength to be absorbed.