GB1105538A - Preparation of solid foams from polymer emulsions - Google Patents

Abstract

A solid foam is made by preparing an aqueous dispersion of a natural rubber latex or a polymer or copolymer of an ethylenically unsaturated compound and a foaming agent containing not more than 45 weight per cent of volatile substances and which is film forming below 300 DEG F., converting the dispersion into a foam and drying the foam at elevated temperature. The amount of foaming agent must be sufficient to maintain a foam structure during the drying operation, usually 1.5-15% of the weight of the polymer. Foaming agents which may be used are alkyl sulphates of alkali metals where the alkyl radical has 12 to 14 carbon atoms; alkali metal salts of the following, sulphated condensation products of ethylene oxide with an aliphatic alcohol having 10-18 carbon atoms, palmitic acid, a -sulpho substituted fatty acids having 10-16 carbon atoms, unsaturated fatty acids having more than 14 carbon atoms, amphoteric surfactants, esters of sulphoacetic acid with an aliphatic alcohol having 10-18 carbon atoms, amides of sulpho-substituted fatty acids having 10-16 carbon atoms, alkyl isothionates where the alkyl radical has 10-18 carbon atoms, N-methyl taurates of fatty acids having 10-14 carbon atoms; tetra alkali metal salts of N-(1,2-dicarboxy ethyl) N-alkyl sulphosuccinamic acids; dialkali metal salts of N-alkyl sulpho succinamic acids; amphoteric surfactants. The foaming agent may include foam stabilizers or boosters. Polymer emulsions which can be used are those prepared from natural rubber and polymers and copolymers of dienes, styrene and its derivatives, derivatives of ethylenically unsaturated acids, vinyl or allyl esters, ketones, vinyl and vinylidene halides and vinyl ethers. A preferred emulsion is one prepared from a copolymer which contains a "copolymerized emulsifier" in an amount from 0.5-20% by weight of total monomer. This can be obtained by polymerizing one of the above monomers with an ethylenically unsaturated monomer having a pendant hydrophilic group or groups or which has a substituent group which can be converted to a hydrophilic group after polymerization. Examples are acids and their sulpho and amine esters, acid amides, the hydrochlorides of the esters, sulpho and sodio derivatives of styrene. Cross-linking agents, surfactants and catalysts may be incorporated. Many examples of polymer emulsions are given in the description. The emulsion is foamed by using a blowing agent or by mechanical frothing. After drying an open celled solid foam is obtained.ALSO:A foam coated material is obtained by foaming an aqueous emulsion of an ethylenically unsaturated polymer or copolymer or of natural rubber latex and a foaming agent, coating the wet froth onto a substrate and drying the froth at elevated temperature when it forms a solid foam. Substrates to which the foam will adhere are cloth, fabric, leather, wood, glass or metal. In Example 2 the foam is coated onto cotton sheeting. A preferred polymer emulsion is one prepared from a copolymer which contains a "copolymerised emulsifier" in an amount from 0.5-20 per cent. by weight of total monomer. This can be obtained by polymerising a monomer such as styrene or a vinyl halide for example, with an ethylenically unsaturated monomer having a pendant hydrophilic group or groups or which has a substituent group which can be converted to a hydrophilic group after polymerisation.