LOW PRESSURE VACUUM PLASMA TREATMENT OF NONWOVENS AND NEEDLEFELT FOR FILTRATION APPLICATIONS

摘要

Vacuum plasma treatment has found its way into industry since the 1980s.Initially it was used for cleaning printed circuit boards and later on as an activation for structural plastic parts prior to painting,flocking or gluing.Recently,however,the filtration industry has taken a sincere interest in the technology.Such interest has resulted in several plasma production systems having been installed in the industry.Plasma treatment is used either for activation of nonwovens or for coating of such products,for example needlefelts using plasma polymerization.In the case of activation,a process gas is used to graft functional groups on the surface of the fibres of the nonwoven.A typical example is the hydrophilization of nonwoven polypropylene (PP) for blood filters using carbonyl-groups.In the case of plasma polymerization,one or more precursor gases are (partially) decomposed in the plasma and react on the substrate surface to form a thin film.Such a process can be used for filtration media.Using precursors which contain fluorine,hydrophobic coatings can be deposited on the fibre surface.Such thin films substantially reduce the penetration of the filter medium,such as a nonwoven PP,with DOP aerosols (P and R type filters).Plasma treatments on nonwovens and needlefelts are typically carried out on roll-to-roll equipment.Such equipment allows multiple passages through the plasma zone so that web speeds of several tens of metres per minute can be used.At such speeds,a plasma coating costs typically less than 0.05 Euro/m2,the cost of a plasma activation is even lower.