High-efficiency plasma treatment of polyolefins

Abstract

A method and apparatus are taught for treating polyolefin containing or polyolefin-coated webs or laminates for obtaining the proper surface characteristics to promote adhesion of photosensitive coating materials and/or layers typically coated thereon. The web is passed through a high-voltage sheath region or dark space of the plasma generated by a powered electrode residing in a discharge zone. The frequency of the driving voltage must be above a lower bound dictated by the properties of the paper support and the plasma, and it must be below an upper bound beyond which the sheath voltages drop significantly and it is observed that the benefits of this approach diminish. The dark space is generated by a treatment electrode in a treatment zone. There is a counter electrode having a surface area in said treatment zone which is at least as great as the surface area of the treatment electrode. A power supply is included for driving the treatment electrode with an oscillating high voltage at a frequency less than about 2 MHz and greater than 1/tc where tc is the charging time of a web surface exposed to a rms ion current in the plasma.

Dependencies are inferred from the claim text.