| abstract |
A back-up pad is provided over an anvil surface of a back-up plate, and between the anvil surface and a sealing surface of a sealing die, in an apparatus for forming seals between layers of film material. The back-up pad has a slip layer on one side thereof and a firm polymeric support layer on an opposite side thereof, the slip layer opposing the sealing face of the die so that the layers of film material pass between the sealing die and the back-up pad during seal formation. The polymeric support layer may have a Shore-A hardness of at least 10 at 20° C. and a dynamic loss tangent of less than 0.1 from 20° C. to 80° C. An example of a support layer is a polycarbonate pad, and an example of slip layer is a glass cloth coated with Teflon™. The back-up pad is particularly useful for forming lap seals in relatively thick film materials, such as laminated films having multi-layered films laminated together. |