COMPOSITE, METHOD AND APPARATUS FOR MAKING SAME

摘要

Methods of compression molding powdered polytetrafluoro-ethylene (PTFE) resins to produce composite articles having at least two distinct layers of PTFE resin, with each layer containing a different type of PTFE resin, are disclosed. A first layer of resin (100), preferably including a filter, is placed in a compression mold (200) and partially compressed at a relatively low pressure. A second layer of resin (102), preferably virgin (unfilled) resin, is then added to the mold and both layers are simultaneously fully compressed. After compression, the resulting composite preform is preferably sintered and coined to create a finished PTFE material or product. In a preferred embodiment, the partial compression step is performed at pressures of less than 500 psi. It has been found that modified PTFE resins provide improved resistance to cold flow and also provide better blending between filled and unfilled layers.