Process for reinforcing nonwovens

A process for reinforcing nonwoven fiber material by a foaming process, comprising the steps of

• A. impregnating the nonwoven fiber material with an aqueous preparation containing a water-soluble or water-dispersible binding agent and a foaming assistant, wherein the binding agent is a reaction product obtained by reacting, in the presence of an organic solvent,
• a. an epoxide which contains at least 2 epoxide groups per molecule,
• b. a fatty amine having 12 to 22 carbon atoms, and
• c.sub.1. an aliphatic, saturated dicarboxylic acid containing 7 to 14 carbon atoms, and wherein the foaming assistant is a reactive surfactant which is convertable into the irreversibly insoluble state at elevated temperature and thereby loses its surface activity, the foaming assistant being a surface active methylolmelamine or methylolurea having methylol groups etherified with a monoalcohol of 4 to 22 carbon atoms and at least one member of the group consisting of an alkanolamine of 2 to 6 carbon atoms, a polyethyleneglycol having an average molecular weight of 1000 to 5000, an alkanol of the formula H--(OCH.sub.2 CH.sub.2).sub.m --OH where m is 1 to 25 and which contains an alkali metal sulfonate group bonded to carbon and an aliphatic-hydroxy-carboxylic acid containing 2 to 4 carbon atoms, and
• B. subsequently heating the impregnated non-woven fiber material at 60.degree. to 190.degree. C to convert the foaming assistant to an irreversibly insoluble state and to destroy the surface activity of the foaming assistant.