| abstract |
The present invention is directed to composite filters and methods for preparing same. More specifically, it is directed to filter laminates of multiple discreet layers of material bonded together, with at least one of the layers being an asymmetric membrane. The laminates may be prepared using a lamination apparatus including an unwind (10) for, e.g., a low melting point polypropylene nonwoven material (12), a membrane unwind (14) for, e.g., a polyvinylidene difluoride membrane (16), and an unwind (18) for, e.g., a polyester nonwoven material (20). An adjustable, lateral spring force is applied to the unwind to maintain the stiffness of the material, thereby preventing formation of wrinkles in the laminate (22). Adjustable rollers (24) provide additional tension and also aid in wrinkle elimination. The layers (12, 16, 20) are pulled out from the unwinds (10, 14, 18) and over the heat shoe (26) by feeding the resulting laminate (22) between two drive rollers (30) situated after the heat shoe (26). A rewind (32) winds up the full width laminate (22). |