GB607635A - Improvements in or relating to heat-hardenable phenolic resins - Google Patents

Abstract

To prepare an alkali-resistant heat-hardenable phenol-formaldehyde resin, at least 50 per cent of the arylhydroxy groups of the resin are etherified and an acid or latent acid-hardening catalyst is added thereto. The products may be blended with urea-formaldehyde resins and are useful as plasticisers for non-etherified phenolic resins, polyvinyl resins, including copolymers and cellulose esters. They are also compatible with drying oils and may be reacted with furfural. A suitable starting material is phenol, m-cresol or m-xylenol or a mixture containing at least 40 per cent of one of these, resorcinol or mono-resorcinol ethers. Suitable catalysts for the initial condensation are oxides or hydroxides of light metals including alkali and alkaline earth metals, e.g. zinc, magnesium or aluminium oxide. The initial condensation may be acid provided the reaction mass is made alkaline, while some uncombined formaldehyde is still present. Suitable etherifying agents are diethyl sulphate, dimethyl sulphate, methyl hydrogen sulphate, benzyl chloride, o-chlorbenzoyl chloride, allyl chloride, methallyl chloride, p-nitrochlorbenzene, bromobenzene, chloracetic acid, chloracetone, benzene sulphonyl chloride, chloromethyl ether, ethylene chlorhydrin, p-dichlorbenzene, trimethylene bromide, dichloroethyl ether, triglycoldichloride or dichlorethylbenzene. Preferably the resin is employed as its sodium salts. Suitable acid-hardening catalysts or latent acid-hardening catalysts are sulphuric, phosphoric, benzene sulphonic, p-toluene sulphonic, ethyl sulphuric, oxalic or oxalic-boric acid, ethyl sulphate, ethyl-benzene sulphonate, sodium ethyl sulphate or ammonium ethyl sulphate. Usually sufficient is added to give a pH of 5 or less. It may be incorporated in the dried resin or in a solution. In the case of oxalic acid, for example, the catalyst may be carried in a stream of hot air or other fluid over the surface of a film or coating of the ether resin, e.g. on the inside of a tube. Solutions of the non-hardened resins may be stabilized by addition of water or alcohol. In the examples: (1) a resin prepared from phenol and formaldehyde in presence of magnesium oxide was dissolved in caustic soda and etherified with diethyl sulphate. Further diethyl sulphate was added as hardening catalyst and the mixture dissolved in toluene is then heated until it gelled. The gel was re-dissolved in butanol to yield a solution which formed films. In example (2), sodium hydroxide was used as the initial condensation catalyst, the resin was etherified with benzyl chloride and phosphoric acid was used as the hardening catalyst. In example (3), the resin was prepared as in example (1), but using excess phenol, etherified with diethyl sulphate and the hardening catalyst was a mixture of boric and oxalic acids. Example (4) was similar to example (1) with phosphoric acid as the hardening catalyst. In example (5), a resin prepared from urea, formaldehyde and ethylendiamine was dissolved in butyl alcohol, mixed with oxalic acid and blended with an alcoholic solution of the etherified resin of example (1). Specifications 409,397 and 511,511 are referred to.