Method for welding membranes

A process for welding porous membranes, the process comprising:

• i) providing a first porous membrane and a second porous membrane;
• ii) at least partially superimposing the first and second porous membranes to obtain an at least partial superimposition region;
• iii) welding the first and second porous membranes at least in a portion of the at least one superimposition region at a temperature in the range from 100 to 300° C. and at a pressure in the range from 1 to 10 bar to obtain an at least partially welded composite of the first and second porous membranes;
• wherein a material of the first and second porous membranes comprises at least one thermoplastic elastomer selected from the group consisting of a polyurethane elastomer, a polyester elastomer, a polyetherester elastomer, a polyesterester elastomer, a polyamide elastomer, a polyetheramide elastomer, a polystyrene elastomer, and an ethylene-vinyl acetate elastomer
• the first and second porous membranes have pores having an average pore diameter of less than 2000 nm, determined by means of Hg porosimetry in accordance with DIN 66133 and
• said first porous membrane and said second porous membrane are at least partially superimposed and are joined to one another in the form of a weld seam at least in a portion of said at least one superimposition region,
• wherein said first and second porous membranes each have a pore size distribution between a first surface and a second surface of the respective membranes, wherein the pore size distribution is a gradient wherein a ratio of a pore diameter of pores at or close to the first surface to a pore diameter of pores at or close to the second surface is 1:5 to 1:10,000, and
• an area of said weld seam has a water vapor permeability of 75% to 100% of a water vapor permeability of said first porous membrane.