GB1278378A - Improvements in or relating to the covering of foamed phenolic resins - Google Patents

Abstract

1278378 Foamed phenolic resin laminates. DYNAMIT NOBEL AG 30 July 1970 [30 July 1969] 37015/70 Heading B5N [Also in Division C3] A surface of a foamed phenolic resin is covered with a surface covering which is impervious to water vapour by impregnating a fibre-containing sheet structure which is pervious to water vapour, at least at the surface thereof which is to contact the foamed phenolic resin, with a liquid impregnant which consists of or comprises a synthetic polymer which renders the fibrecontaining sheet structure impervious to water vapour, and bringing this surface of the impregnated sheet structure into contact with a phenolic resin which is either in the course of being foamed or the foaming of which has been completed but the curing of which has not taken place, at the temperature at which foaming is taking/has taken place, and then curing the foamed phenolic resin, preferably while subjecting it to a limiting pressure of 0À01-2À0 Kp./cm.<SP>2</SP>. The phenolic resin in the foamable resin composition is produced by the condensation of 1 mol. of a phenol, alkylated phenol, polyhydric phenol or alkylated polyhydric phenol, e.g. resorcinol, pyrocatechol, a cresol or xylenol, with 1-3 mols. of an aldehyde, e.g. formaldehyde, para-formaldehyde, trioxane, acetaldehyde, furfural or hexamethylene tetramine, in an alkaline medium. The foamable phenolic resin composition contains a blowing agent, e.g. a chlorofluoromethane, n-pentane, petroleum ether, methylene dichloride, ethylene dichloride or an alkali or alkaline earth metal carbonate, and a hardener, e.g. p-toluene sulphonic, hydrochloric, sulphuric or phosphoric acid, and may also contain a modifying agent, e.g. a polyester, high-boiling ester, e.g. dibutylphthalate, or an addition product of ethylene oxide and phenol. The synthetic polymer used to impregnate the fibre-containing sheet structure may be a liquid condensation product of 1 mol. of a phenol, polyhydric phenol, alkylated phenol or alkylated polyhydricphenol with 1-3 mols. of an aldehyde, a solution or dispersion of a polyamide which may be a condensation product of a diamine and dicarboxylic acid or polymerization product of an #-aminocarboxylic acid or lactam thereof and/or a polymer of butadiene which is optionally substituted with chlorine or methyl in the 2-position and/or 3-position, or a solution or dispersion of a polyacetal. The fibre containing sheet material may be paper, e.g. millboard or soda-kraft paper, or a woven fabric or fleece comprising inorganic or organic synthetic or natural fibres. If the phenolic resin contains an anti-foaming agent, e.g. modified dimethyl polysiloxane, and two blowing agents operative in different temperature ranges the fibrous sheet structures may be impregnated with the phenolic resin which is to be foamed by introducing the phenolic resin composition into a mould lined with the fibrous sheet structures, allowing the resin composition to foam up quickly under the action of the lower boiling point blowing agent so that it wets at least the part of the fibrous sheet structure adjacent the interior of the mould and allowing the foam to collapse under the action of the anti-foaming agent and foam up again under the action of the second blowing agent. In a continuous process two webs of impregnated fibrous sheet material are fed through a double belt press and the foamable phenolic resin introduced between them.