GB582448A - Improvements relating to the manufacture of synthetic resins - Google Patents

Abstract

Permanently fusible dihydric-phenol-aldehyde resins are made by heating together a dihydric phenol and an aldehyde in the absence of an acidic or basic catalyst in the proportion of less than one mol. of aldehyde to one mol. of dihydric phenol, adding said catalyst when the preliminary condensation is substantially complete, continuing the heating, and dehydrating, e.g. to a water-content of less than 1 per cent, preferably .5-.75 per cent. Phenols specified are resorcinol, hydroquinone and catechol, and a portion thereof may be replaced by phenol, cresylic acid, or other monohydric phenol, e.g. in an amount of 20-25 per cent. Aldehydes specified are formaldehyde, propionaldehyde and furfuraldehyde. In an example, formaldehyde solution is added gradually to resorcinol in a steam-heated vessel, and after the initial reaction has subsided, oxalic acid is added, refluxing is resumed for a short time, and water is then distilled off. The preferred molecular ratio of formaldehyde to resorcinol is .9 : 1 and preferably greater than .5 : 1. Other catalysts specified are hydrochloric, sulphuric, citric and tartaric acids, ammonium chloride, sodium and potassium hydroxides and carbonates, trisodium phosphate, triethanolamine, aniline, azoxy-toluidine, ethylenediamine. The preferred amount of catalyst based on the weight of resorcinol is .1-.3 per cent if the resin is to be used for bonding abrasive articles, and .6 per cent for other purposes. Hardening agents specified are hexamethylene tetramine, the oxymethylenes, para formaldehyde, polymethylol phenols and polymethylol melamines. The products are used in the manufacture of laminated products from cloth, e.g. cotton, paper, asbestos, or wood, abrasive articles, moulded articles, cold-setting adhesives, coating compounds, impregnating and reinforcing compounds, and in the bonding of nylon, leather and synthetic rubber.