Improvements in and relating to aqueous phenol-formaldehyde resin emulsions and impregnating fibrous material therewith

摘要

An aqueous emulsion of a thermo-hardening phenol-formaldehyde condensation product is prepared by reacting together in water in the presence of a basic-reacting substance a mixture of monohydroxybenzene compounds and a molar excess of formaldehyde or a compound generating formaldehyde during the reaction at a temperature between room temperature and the reflux point, inclusive, until a low molecular weight product is obtained, suitable for impregnating fibrous materials, the mixture of monohydroxybenzene compounds having a mean functionality (towards formaldehyde) of 2.4-2.8 and being composed of a mixture consisting predominantly of xylenols containing not more than 60 mol per cent of trifunctional and not more than 25 mol per cent of monofunctional phenols, and added trifunctional monohydroxybenzene such that the mean functionality of the whole mixture is 2.4-2.8 and the monoalkylphenol content does not exceed 25 mol per cent. The phenol mixture may be obtained by adding to technical xylenol phenol itself or m-cresol or a mixture of cresols of average functionality greater than 2.4. After the preparation of the low molecular weight resin the mixture may be acidified by addition of an acid-reacting compound which will be incorporated into the resin, and which will form with the basic-reacting compound a non-dissociated compound or insoluble salt. The basic-reacting compound may be e.g. NaOH, KOH, Ba(OH)2, Ca(OH)2, Na2CO3, K2CO3, (C4H9)3N or (C2H5)4NOH. Loosening agents and softeners, e.g. stearamide, oleamide and waxes, may be added to the composition. In Examples 1 and 2 mixtures of technical xylenol and technical phenol of mean functionality 2.60 and 2.55 are reacted i.p.o. triethylamine with formalin in molar ratios of 1:1.35 and 1:1.50 respectively. In Example 3 a hard paper is prepared from a kraft paper impregnated with the product.ALSO:Kraft paper is impregnated with an aqueous formaldehyde-xylenol resin, the average functionality of which has been increased to 2.4-2.8 by addition of phenol or m-cresol, dried and compressed.