Patent GB-333194-A (GB)
Title: Improvements in films or sheets for adhesive purposes
IPC: C09J7/30
Filed: 1929-02-27
Abstract: 333,194. Arnot, R. Feb. 27, 1929. Adhesives.-A process for making films or sheets for adhesive purposes consists in combining synthetic resins in reactive state with carriers which may be initially solid or initially liquid and subsequently becoming solid, without the addition of solvents other than those present in, or resulting from the manufacture of, the components. The resins are mixed with the liquid carrier material or are allowed to penetrate the solid carrier. The hydrophile synthetic resins described in Specification 290,327 are particularly suitable. The solid carrier may be paper, sheets of woven paper strands, fabrics, asbestos paper or sheet, sheets prepared from wood pulp, cellulose, glasswool, or fine wire netting. The resin solution may be applied bv spraying or by drawing the material through the resin. In drying the sheets, the temperature must not exceed the setting point of the resin; a temperature of 60 C. is usually sufficient. Softeners or plasticisers such as tricresyl phosphate, butyl stearate, phthalic esters, or latex, may be added to the hydrophile resin in order to render articles joined by the adhesive film more flexible. Metal powder may be added to the resin to convert the film into a heat or electrical conductor. For instance, adhesive films rendered heat conducting may be used in making bearings from superposed sheets of parchementized fibre as described in Specification 251,814, [Class 12 (i), Bearings &c.]. Where asbestos, wire netting or glass wool are used as carriers, or fireproofing materials are added to the resin, the materials joined by means of the sheets may be used for preventing the spread of fire. A suitable synthetic resin may be prepared by dissolving 108 parts of cresylic acid in 60 parts of a solution containing 12 parts of caustic soda, and adding 125 parts of 30 per cent formaldehyde. The mixture is heated in a jacketed pan provided with a stirrer and a reflux cooler to about 80 C., and kept at this temperature for about a quarter of an hour. Other adhesives such as casein, albumen, glue, &c. may be added to the resin, either in their natural state or hydrolized as described in Specifications 225,953 and 306,168, or may be applied to the carrier material. The adhesive film or sheet forms an insoluble and infusible binder at temperatures between 100 and 150 C., or at lower temperatures if the materials to be joined are exposed to heat and pressure for a longer period. For making plywood, pressures of 200 lbs. per sq. in. for soft woods and 250 to 300 lbs. per sq.in. for hard woods are used. Adhesive films may also be made by mixing synthetic resins in the reactive state with liquids such as viscose, cellulose acetate or nitrocellulose which in their initial state contain agents which act as solvents for the resin, for instance, excess alkali in viscose, or excess acetic acid in acetyl-cellulose. Similarly nitro-cellulose or celluloid varnishes may be mixed with synthetic resins which will dissolve therein. These mixtures are formed into films in known manner. In one example, a condensation product is obtained by heating under reflux 94 parts of phenol with 94 parts of 40 per cent formaldehyde and 5 parts of ammonia. The oily product is separated, washed with warm water and mixed with 200 parts of a cellulose varnish such as that known under the Registered Trade Mark " Zapon." The mixture is termed into a film on a glass plate. In a second example 20 parts of viscose prepared in the usual way are mixed with 10 parts of mucilage containing 5 per cent of gum tragacanth, and to this mixture are added 5 parts of alkaline, cresol-formaldehyde condensation product as above described diluted with 10 parts of water. The liquid is poured on to glass plates coated with butylsteara,t.e, tricresyl phosphate or glycerine, dried and stripped off.