GB612108A - Improvements in or relating to pressure sensitive adhesive sheets or tapes - Google Patents

Abstract

A pressure-sensitive adhesive composition is made by heating together rubber that has been degraded or depolymerised by heating or mechanical working or both to a tacky and liquid or pasty state, and an oil-soluble, heat-reactive phenol-aldehyde resin. The depolymerisation of the rubber is effected by prolonged mechanical working in the presence of heat and air or oxygen. The process may be shortened by the addition of small quantities of copper or its salts, succinic acid, the zinc chloride double salt of phenyl hydrazine, naphthyl or xylyl mercaptan. Alternatively scrap rubber, such as red inner tube scrap, may be heated and stirred until it remains a heavy sticky liquid. The oil-soluble phenolaldehyde resins are made from alkyl- or aryl-substituted phenols such as ptert-, amyl- or butyl phenol, p-sec-octyl phenol, and o- or p-phenyl phenol, reacted with 1-2 mols. formaldehyde. The oil-soluble phenol-aldehyde resin and the depolymerized rubber are heated while being mixed, and other ingredients such as hydrogenated indene-coumarone resin, ester gum, rosin, clay, carbon black, zinc or magnesium oxide or resinate, titanium oxide, mineral oil, beta-naphthol may be added during the mixing and heating stage. A petroleum solvent with if desired a small ethyl alcohol content may be added on cooling. The adhesive may be used as an aqueous dispersion. Alternatively the depolymerised rubber and the oil-soluble phenol-aldehyde resin may be mixed cold, applied to a backing, and then heated to promote the reaction between the rubber and resin. The resin may be made by heating together under reflux p-tert.-butyl phenol, aqueous formaldehyde, and ammonia until the free formaldehyde content of the aqueous phase is reduced to 8 per cent. The resulting heavy fluid resin is dehydrated, e.g. by heating under vacuum and then heated at 110 DEG C. until a test drop forms a brittle pill on cooling. Alternatively formaldehyde and sodium hydroxide solutions are mixed and reacted with p-tert.-amyl phenol until the free formaldehyde content is 1 per cent or less. Dilute sulphuric acid is added to reduce the pH value to 1 or 2 when the resin separates. The resin is then washed, dehydrated, and heated.ALSO:A pressure-sensitive adhesive composition is made by heating together rubber that has been degraded or depolymerized by heating or mechanical working or both to a tacky and liquid or pasty state, and an oil soluble, heat-reactive phenol-aldehyde resin. The depolymerization of the rubber is effected by prolonged mechanical working in the presence of heat and air or oxygen. The process may be shortened by the addition of small quantities of copper or its salts, succinic acid, the zinc chloride double salt of phenyl hydrazine, napthyl or xylyl mercaptan. Alternatively scrap rubber, such as red inner tube scrap, may be heated and stirred until it remains a heavy sticky liquid. The oil-soluble phenolaldehyde resins are made from alkyl- or aryl-substituted phenols such as p. tert. amyl or butyl phenol, p. sec. octyl phenol, and o or h phenyl phenol, reacted with 1-2 mols formaldehyde. The oil soluble phenol-aldehyde resin and the depolymerized rubber are heated while being mixed, and other ingredients such as hydrogenated indenecoumarone resin, ester gum, rosin, clay carbon black, zinc or magnesium oxide or resinate, titanium oxide, mineral oil, beta-naphthol may be added during the mixing and heating stage. A petroleum solvent with if desired a small ethyl alcohol content may be added on cooling. The adhesive may be calendered on to the backing without solvents, or may be used as an aqueous dispersion. Alternatively the depolymerized rubber and the oil-soluble phenolaldehyde resin may be mixed cold, applied to a backing, and then heated to promote the reaction between the rubber and resin.