Effect of Surface Free Energy of Film Laminated Steel Sheets on Content Release Properties

Polyethylene terephthalate (PET) sheets that are now widely used in beverage cans have excellent properties of formability, corrosion resistance and adhesion to steel sheets. To expand their application, we have sought to develop a new PET film laminated steel sheet for use in food cans. Content release properties are necessary for easy removal of the can contents in food can applications. However, PET film laminated steel sheets have poor content release properties. Investigations of these properties have revealed dependence on the strength of adhesion between the films and can contents. The surface free energy of PET films has been inferred to be the main factor in poor content release properties. Therefore, using films with widely diverse surface free energy values, we studied the effects of surface free energy on the content release properties of materials in contact with cans. The results showed that these properties are closely related to the surface free energy of the film material, and that materials with surface free energy of less than 23 mN/m or greater than 44 mN/m show excellent properties for processed meat products with high protein content. The material with PET film coated with mixture of polyester resin and fatty acid is the most promising material for use in food cans in this study. The work has also shown that content release properties can be expressed as a function of adhesion in water between a material and protein. Reducing adhesion can significantly improve content release properties.