Process for the production of chemically bonded non-woven sheet materials containing a binder of microheteroporous structure

A process for the production of a chemically bonded non-woven material containing a binder having a microheteroporous structure comprising the steps of

• impregnating a needle-punched preshrunk fiber fleece formed from cut fibers with an aqueous butadiene acrylonitrile copolymer dispersion containing from about 10 to 20 parts by weight of vulcanization agent and from about 0.5 to 10 parts by weight of a heat sensitizing agent, calculated on 100 parts by weight of the butadiene acrylonitrile copolymer dispersion, said dispersion further containing from about 1 to 20 parts by weight of a water soluble aliphatic bi- or trivalent alcohol, a water soluble aliphatic polyether glycol plasticizer or an aqueous emulsion of an alkoxybutyl acetate, the alkyl portion of which contains from 1 to 4 carbon atoms, and from about 10 to 30 parts by weight of a water soluble condensation product of a diarylsulfone derivative and an arylsulfonic acid, said dispersion having a solids content of about 20 to 40% by weight;
• coagulating the polymer dispersion at a temperature between about 40.degree. to 70.degree. C.,
• crosslinking the polymer at a temperature between about 110.degree. and 120.degree. C., and then
• drying the sheet at a temperature between about 100.degree. to 160.degree. C.