GB690698A - Improvements in or relating to adhesives - Google Patents

Abstract

An adhesive composition comprises between 70 and 90 per cent of a powdered mineral filler, between 5 and 12 per cent of a heat-hardenable phenol-aldehyde resin, a plastizer therefor, and between 0.05 and 5 per cent of a silicone, the percentages being by weight of the composition. The phenolic resin may either be a resol formed, e.g. by reacting a phenol such as cresol with a molecular excess of formaldehyde in the presence of an alkaline catalyst, or a mixture of hexamethylenetetramine and a novolak formed, e.g. by reacting a phenol with less than an equimolecular amount of formaldehyde in the presence of an acidic catalyst. Mineral fillers specified are marble dust, calcite, lithopone and barium sulphate. The plasticizer may comprise a liquid such as dibutyl phthalate or other high boiling liquid, or a material which itself is resinous or a mixture of such liquid and resinous material, e.g. rosin, shellac or ester gum, or it may consist of or include a thermoplastic or thermosetting synthetic resin, or it may be a fatty oil combined with a hardenable synthetic resin, e.g. the oil may be combined with a portion of the heat-hardenable resin (or other synthetic resin) and the product may be incorporated with the adhesive or with the basic resin of the adhesive. The plasticizer may be used in amount between 2 and 12 per cent by weight of the composition. The silicones, preferably those having thermosetting properties, may be added at any stage of the manufacture of the adhesive or be added to the paste formed by mixing the adhesive composition with solvent. In examples: (1) a resin made by dehydrating a mixture of a toluol solution of a silicone and a novolak obtained by refluxing phenol, aqueous formaldehyde and oxalic acid, was grouped and mixed with hexamethylenetetramine, calcite and colophony. The adhesive was made into a paste by mixing the alcohol; (2) the novolak of example (1) was modified by refluxing with blown castor oil and sulphuric acid, and the resulting resin was ground and mixed with hexamethylenetetramine, lithopone and ground marble and finally made into a paste with alcohol and mixed with a toluol solution of a silicone; (3) a castor-oil modified novolak resin, a mixture of a novolak resin, and a silicone resin, hexamethylenetetramine and p ground marble were ground in a ball mill and the mixture was formed into a paste by mixing with a solution of dibutylphthalate in alcohol. The adhesives are used for fixing moulded or metallic caps to electric lamp bulbs and radio valves.