Controlling in-line the energy level applied during the corona treatment

A method to corona treat a polymeric surface with a fixed and pre-set treatment energy level is proposed. In order to reduce the effect of humidity, the Corona Discharge Energy - CDE value was controlled during the corona treatment by an in-line monitoring apparatus, which indicates when the energy level is attained. The method was tested applying a negative corona treatment discharge on a polypropylene copolymer film. Chemical and morphological surface changes were examined by IR spectra, contact angle and morphology. Treated samples show the presence of carbonyl, hydroxyl and unsaturations, the first being less concentrated. The formation of polar groups on the film surface led to a reduction of the contact angle and an increase in the surface tension. Film surface morphology was also modified, showing a second phase granular structure which grows with the increase of the CDE level.