Mechanically stable ultrafiltration membrane, and method for producing same

An ultrafiltration membrane comprising

• a first polymer layer which penetrates at least 25% into a support layer, thereby forming a coated support layer, and
• a second polymer layer on the first polymer layer of the coated support layer, thereby forming a multiply coated support layer, wherein the first and second polymer layers comprise cellulose derivates, wherein the support layer is a nonwoven web, a woven fabric or an open microfilter membrane, and
• wherein the first and second polymer layers, taken together, have a complex structure wherein the pores initially widen from a first main surface within the second polymer layer, the pores in the interior of the membrane then taper on entry into the first polymer layer, and the pores in the course of the structure widen again toward a second main surface.