Corona‐discharge treatment of polyethylene films. I. Experimental work and physical effects

Abstract

AbstractCorona treatment of films, mainly polyethylene, was studied at commercial levels in a small continuous treater. Degree of treatment was characterized by measuring polar and dispersion components of surface energy, ASTM Wipe and ASTM Adhesion Ratio (“peel adhesion”). The chief factors studied were corona current, applied frequency, web speed, dielectric thickness and air‐gap thickness between electrode and film. Other factors less intensively investigated were type of film, film additives, aging time after treatment, humidity and corona atmosphere. The polar component of surface energy, γ, is the key to understanding the changes in adhesive behavior of the films during treatment. We found that, for the equipment used, γ is accurately given by the equation where D = dielectric thick ness and G = air gap, both in mils; S = web speed, ft/min; I = corona current, ma, and γ is in dyne‐cm/cm2. A similarly structured equation describes ASTM Wipe. Using measured surface‐energy components for the pressure‐sensitive tape used in the peel adhesion test, it was possible to calculate an adhesion interaction for each film on which peel adhesion was measured and to show that it closely correlates with peel strength. Humidity changes in the moderate‐humidity range, number of electrodes used and corona frequency had little effect on properties. Slip additives inhibited development of adhesion until treatment levels became high; adhesion properties gradually diminished upon aging of films stored at ambient conditions.