The spreading of liquids on polyethylene film. The effect of preprinting treatments

A study has been made of the wettability of thin films of polyethylene by observing the equilibrium advancing contact angle formed by a drop of liquid on the surface. Treatment of polyethylene film by exposure to methane/oxygen flames of varying intensity produces a controllable increase in the polarity of the surface as measured by the contact angles with a series of solutions of ethyl alcohol in water. The surface tension lowering of water by ethyl alcohol required to give complete spreading was determined for each flaming condition and related to the adhesion of a polar printing ink. It is shown that an essential criterion for good ink adhesion is the complete wetting of the film surface by the ink. It is suggested that a simple measure of the efficacy of the preprinting treatment would be the contact angle of water with the film.