Process for the preparation of phenol-formaldehyde foams

Process for the preparation of phenol-formaldehyde foam which consisting of introducing a resol phase and a liquid anhydrous novolac phase into a mixer, mixing the resol phase and the novolac phase for a period of between about 5 and about 90 seconds to obtain a resin mixture, and subsequently spraying the resin mixture produced out of said mixer to obtain the foam, wherein

• the resol phase is homogeneous, has a viscosity, measured at 20.degree., of between 8 and 60 poises, and has a solids content of between 70 and 95% by weight, the resol contained in the said phase being obtained by polycondensation, by means of a basic catalyst, of phenol and formaldehyde in a molar ratio of between 1:1.5 and 1:3;
• the liquid novolac phase is a homogeneous and anhydrous essentially uncured liquid mixture which has a viscosity, measured at 20.degree. C., of between about 5 and about 300 poises and contains
• from 10 to 35% by weight of a blowing agent which is a halogenated hydrocarbon selected from the group consisting of methylene chloride, chloroform, 1,1,1-trichloroethane, trichloroethylene, dichloroethane and mixtures thereof or a mixture of said halogenated hydrocarbon with ethanol, and
• from 70 to 90% by weight of a mixture comprising
• a true novolac resin obtained by polycondensation, by means of an acid catalyst, of a mixture of phenol and formaldehyde in a molar ratio of 2:1 to 6:1,
• phenolsulphonic acid in an amount of between 5 and 10% by weight relative to the resin mixture of resol phase and novolac phase and
• optionally, free phenol representing at most 30% by weight of the novolac phase;
• the relative amounts by weight of resol phase and of novolac phase being such that the resol phase represents 45 to 75% by weight of the resin mixture.