1387241 Self-adhesive stamps N J WATERBURY 28 March 1973 [29 March 1972] 14947/ 73 Heading B2E [Also in Division B8] A postage or trading stamp has adhered by a non-tacky binder to its reverse face microencapsulated material, the microcapsules being adapted to rupture when the stamp is pressed against a recipient surface, resulting in the release or formation between the reverse face and the recipient surface of an adhesive. The microencapsulated material may be a solvent for a binder which is a solvent-sensitive adhesive, or the capsules may contain a solution of adhesive optionally with plasticiser. Suitable solvent-sensitive adhesives are (1) water-soluble gums, the solvent being water or aqueous alcoholic solvent, (2) elastomer based adhesive e.g. neoprene, nitrile rubber or SBR with hydrocarbon solvent such as petroleum spirit or toluene, (3) acrylic resin e.g. polymethyl methacrylate, polybutylmethacrylate, or methyl methacrylate/butyl methacrylate copolymer with aromatic hydrocarbon solvent such as white spirit, toluene or xylene, or (4) a vinyl resin such as polyvinyl acetate or polyvinyl butyral, the solvent being alcohol, ester or ketone. Preferably, the binder is water-based so the stamp can be adhered alternatively by licking or by pressure, and the materials of the coating are non-toxic. The capsule material may be gelatin, gum arabic, or, preferably, a thermoset material such ureaformaldehyde resin. The coating may cover the whole of the reverse of the stamp or may be arranged in spaced regions such as in the corners or in a crossed pattern. The binder is preferably sprayed onto the reverse face of the stamp in a solution which contains a dispersion of the microcapsules. The microcapsules may also be sprayed or scattered in the form of a powder while the binder is still liquid and tacky, or applied to the front face of the stamp or include an ink.
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