GB349599A - Improvements in or relating to varnishes and the like - Google Patents

Abstract

Relates to varnishes containing phenol-aldehyde, phenol-oil-aldehyde, urea-aldehyde or sulpho-urea-aldehyde resins. Varnishes which dry to a non-tacky film without baking comprise a dispersion in a volatile varnish solvent of the resin which has been advanced towards the C stage by heating the A-resin, with or without a solvent, until it has little or no penetrating power when applied to a test-paper. The varnish solvent is one in which the advanced resin is substantially insoluble. The non-tacky film formed by such a varnish may be baked to increase the hardness and resistivity. The dispersion may be formed by advancing the A-resin in solution in the varnish solvent, provided the latter has a sufficiently high boiling-point. The resin may be advanced in a high-boiling solvent such as butyl alcohol, and the product poured into a low-boiling solvent or solvent mixture; high-boiling solvents specified are amyl acetate, turpentine, the usual plasticizers such as di-amylphthalate, ethyl abietate, &c., and natural resins such as rosin and rosin ester. The resin may be advanced without solvents till a gel is formed, and the gel may be broken down in paint rolls and the product suspended in a solvent. In one example, phenol is reacted with formaldehyde, using hexamethylenetetramine as catalyst, and the reaction is stopped, when the mass is about to kick-over to the porous rubber-like, infusible and insoluble form, by adding a cold mixture of butyl alcohol and amyl acetate. Alternatively, a commercial A-resin may be brought to the same condition. The product is then heated under a reflux condenser for 12 hours until the viscosity is sufficiently increased by the further advancement of the resin, and the liquid is poured into acetone, alcohol, toluene, ethyl acetate or other low-boiling solvent or mixture. The resin may be advanced still further by again heating under a reflux condenser. The solvents may be added to the raw materials prior to the initial condensation. In another example, phenol is reacted with tung oil (raw, or "boiled" containing metallic driers) using phosphoric acid as catalyst; the product is heated with amyl acetate, butyl alcohol, and hexamethylenetetramine to form a resin; butyl alcohol and turpentine are added and the liquid heated for 16 hours to advance the resin towards the C-stage. In a further example, phenol is reacted as before with a larger quantity of tung oil, the product is heated with hexamethylenetetramine for 24 hours at 105 DEG C. to form a gel, and the gel is broken down on rolls and suspended in acetone or like solvent to form a lacquer with 30 per cent solid content. Specifications 275,604 and 295,335, [both in Class 95, Paints &c.], are referred to. The Specification as open to inspection under Sect. 91 (3) (a) comprises also the use of alkyd resins. This subject-matter does not appear in the Specification as accepted.