MULTILAYER FILTER MEDIUM Russian patent published in 1995 - IPC

FIELD: filter media. SUBSTANCE: multilayer filter medium consists of layer of coarse fibers on the side of air inlet, layer of fine fibers on the side of air outlet and intermediate layer of glued or thermally bonded nonwoven material. Inlet layer of material is made of positively charged fibers 6-50 mcm in diameter with surface density of 25-70 g/m² deposited on substrate in electrical field, and the second layer is made of negatively charged fibers 0.1-10 mcm in diameter with surface density of 10-30 g/m² deposited in electric field to reverse side of substrate with opposite polarity. Fibers with negative charge come to depth of intermediate layer through 0.4-1.2 of its thickness. Filter medium layers are made with their thickness ratio of (1-7):1:(1-3). The second layer of ultrafine fibers has density of unipolar charge of fibers not less than 7,5·10⁸ kl/m². EFFECT: higher efficiency. 3 cl