Composite filtering medium and method for production thereof

A method for producing a composite filtering medium comprising a base fabric, of the type with weft and warp of threads or monofilaments of polyether ether ketone and a nanofibre layer comprising nanofibres of polyimide deposited on the base fabric, wherein the method comprises:

• forming a solution by dissolving polyimide in a solvent mixture comprising dimethyl acetamide and N-methyl-2-pyrrolidone with N-methyl-2-pyrrolidone comprising an amount greater than or equal to 50% by weight in the solvent mixture,
• applying a difference of potential between a nozzle and the base fabric and
• injecting the solution through the nozzle to form the nanofibres and to spread the nanofibres on the base fabric, with the nanofibres contacting the threads or monofilaments at surfaces of contact of the threads or monofilaments,
• wherein the nanofibres are formed as a result of evaporation of the mixture of solvents, an electrical field created by the difference of potential, and stretching of the nanofibres deposited on the base fabric,
• wherein swellings of the threads or monofilaments are formed on the surfaces of contact when the nanofibers are spread on the base fabric,
• wherein the nanofibres adhere to the base fabric at the swellings without the aid of glues or adhesive agents applied to the base fabric or the nanofibre layer.