Water vapor-permeable composite material

A process for producing a composite material, comprising:

• providing a nonwoven layer (i) comprising fibers formed from a first thermoplastic polyurethane and having meshes with a mesh size in the range from 10 to 100 μm, determined by scanning electron microscopy;
• b) providing a membrane layer (ii) comprising a second thermoplastic polyurethane which is compatible with the first thermoplastic polyurethane of the nonwoven layer (i), wherein the membrane layer is porous and has pores with an average pore diameter of less than 2000 nm, determined by Hg porosimetry in accordance with DIN 66133;
• c) applying the membrane layer (ii) to the nonwoven layer (i) and joining (i) and (ii) in an interlocking manner by cold welding;
• to obtain a composite material;
• wherein
• cold welding according to (c) means that the fibers of the nonwoven layer (i) and the membrane (ii) in the contact area at least partly form an interlocking joint with one another, wherein on account of the presence of solvent firstly the nonwoven layer (i) and/or the membrane layer (ii) partly dissolve, and then the membrane layer (ii) hardens on the nonwoven layer (i) when the solvent is removed,
• wherein (b) comprises:
• b 1) providing a polymer solution comprising the second thermoplastic polyurethane, wherein the polymer solution further comprises at least one additive selected from the group consisting of polytetrahydrofuran and an ammonium compound, and wherein the polymer solution comprises the at least one additive in a weight-based mixing ratio of second thermoplastic polyurethane:
• additive of 1:10 to 10:1, and
• b 2) creating a membrane layer (ii) from the polymer solution provided according to (b 1) by phase inversion.