Ozone application to an extrudate web has been used for over a decade to enhance adhesion of polymer to the substrate in the extrusion coating process. However, to date, ozone’s effectiveness has not been quantified by published statistical data. A two level fractional factorial design consisting of 64 experimental runs was utilized to study the effects of ozonation and other variables (nine total variables) thought to affect adhesion and heat seal strength in the extrusion coating process.
The 64 experimental runs were performed by coating LDPE (0.923 g/cc, 10 g/10 min) onto a 40-pound Natural Kraft paper. Logistic regression was utilized to study the factors affecting adhesion in extrusion coating and ordinary linear regression techniques were used to quantify the affects of the variables on heat seal strength. The coating line variables found to have a statistically significant effect on adhesion and heat seal strength were corona treatment of the substrate, melt temperature, air gap, line speed, coating weight and ozone treatment of the extrudate. The most striking adhesion results were observed for the combination of ozone treatment of the extrudate and corona treatment of the substrate. This combination provided acceptable adhesion at conditions which otherwise could not be utilized in extrusion coating. Besides these adhesion results, heat seal strength was higher for samples utilizing both corona treatment and ozone treatment compared to samples where only the substrate was treated.