GB978623A - Cellular aminoplast resinous materials - Google Patents

Abstract

A cured cellular aminoplast has catalyst 5% of an intermixing agent, and at least one saccharide or a polyol containing at least four OH groups uniformly distributed throughout its cell walls. Suitable intermixing agents are sulphamic acid; ammonium sulphamate, chloride or bromide; o-, m- or pyrophosphoric acid or an ammonium, amine or salt, forming amide salt of one of the acids, e.g. monoammonium or urea orthophosphate. Suitable saccharides are cellulose, corn starch, inulin, dextrin, cold water soluble starch, water-soluble or dispersible cellulose ethers, hydroxyalkyl ethers of cellulose, carboxyalkyl celluloses, dextrose monohydrate, or a crude source of polysaccharide such as wood flour. Suitable polyols are pentaerythritol, mannitol and sorbitol. The intermixing agent, saccharide, blowing agent and thickeners, e.g. gum tragacanth, casein, glue, polyvinyl alcohol, or ammonium or alkali metal polyacrylate, if required, are uniformly dispersed into an aqueous solution or dispersions of an aminoplast pre-condensate and the mass blown out and cured at an acid pH. The aminoplast may be derived from formaldehyde and urea, thiourea, guaniline, dicyandiamide, guanamine, melamine, or mixtures of urea and melamine. Lower alkyl ethers of methylol melamines may be used. A minor proportion of phenol and formaldehyde or of phenol-formaldehyde novolak or resole may be included. Suitable blowing agents or volatile liquids e.g. methylol, acetaldehyde, propionaldehyde, glyoxal, acrolein, ethylamine, n- or isopropylamine, tert.-butylamine, allylamine, diethylamine, methyl or ethyl formate; alternatively a substance, e.g. a carbonate or bicarbonate which reacts with an acid to form gas may be used. The carbonate or bicarbonate may be soluble or insoluble in water. Coloured carbonates, e.g. nickel carbonate or manganese carbonates may be used to colour the reaction mixture. Acid curing agents, e.g. phosphonic, hydrochloric, trichloracetic or citric acid may be used. If desired a surface active agent, e.g. an alkali metal salt of a long chain alkyl sulphate or of an alkylated benzene sulphonate or of sulphosuccinic acid may be added to the composition of pre-condensate, and air, nitrogen or other unit gas whipped to make a foam which is then cured. In an example hydroxyethylcellulose (thickener), corn starch, monoammonium phosphate (curing and intermixing agent), heavy magnesium carbonate (blowing agent) and dicyandiamide (for centre strength) are mixed and added to a diluted aqueous urea-formaldehyde syrup. After 15 minutes the mixture reached the cellular gel point and was then warmed to 35 DEG C. It became rigid after 2 hours but is best left for 24 hours before use. Mixing may be effected in any convenient way, e.g. spray-mixing with a receptacle or on to a conveyor belt. Cellulose fillers, e.g. chopped cotton or wood flour may be added. The wood flour may be impregnated with n-dodecanoamide, n-octadecanoamide, chlorinated wax or chlorinated diphenyl to modify its water absorption properties. Other fillers, e.g. chopped spun glass fibres, asbestos film, asbestinie and micaceous materials may also be incorporated. Hydrophobic organic agents, e.g. paraffin wax, polyethylene or polystyrene may also be incorporated. A number of detailed examples are given of the preparation of cured cellular materials, which when exposed to a flame intermixed to give an outer layer of honeycombed carbonaceous char which prevented damage to the inner portions of the cellular material.