Bonded films substrate surface finish

The most important aspect of pre-treatment is to provide the optimum surface roughness to give mechanical "keying" of the film to the surface. It is generally accepted that the optimum surface finish is between 0.5 and 2.0//m c.I.a. Most of the published work on surface finish effects has been related to bonded films, and the subject is described in detail in Chapter 11, but similar surface finishes are also desirable for burnished films, especially on hard substrates. However, for sputtered films, which may be only 1//m thick, much smoother substrate surfaces give the maximum life. 

An optimum surface finish of 0.5 /vm c.I.a. is recommended for the substrate for a bonded film. The optimum roughness for a counterface for forming an effective transfer film has not been as well established, but if a similar surface finish is assumed, then the combined roughness parameter will be 0.7 m c.I.a. Under normal circumstances a typical bonded film will have a thickness of between 5 and 10//m, so initially at least there is no risk of asperity penetration. 

Coextrusion and lamination processes have been described extensively in the patent literature. The technology usually involves multilayer structures utilizing, as an adhesive layer, a compound of PVDF with another material, which provides the bonding to the substrate. In this way, the full benefits of a thin film of PVDF may be realized (121). Another approach using acrylic alloys with PVDF sometimes achieves adherence to various substrates without the tie layer necessary for the pure PVDF film (122). The full breadth of options available by these technologies to protect surfaces with weatherable PVDF surfaces has been reviewed (123). Surface PVDF layers on polyolefins has been a particular technology of interest with respect to suitable finishes in cost effective parts for exterior automotive and agricultural equipment applications (124). 

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