Improvement of the surface of polyethylene foamed sheet by irradiation

The manufacturing methods of cross-linked polyethylene foams are classified into two categories based on a type of cross-linking. One is chemical cross-linking by using peroxide as a cross-linking agent. The other method is cross-linking by irradiation. As for chemical cross-linking, a fairly thick foam sheet can be produced, and a comparatively high degree of cross-linking can be achieved. This means chemical cross-linking excels in thermo-forming but, due to a rough surface, the product is lacking in adhesive property and printability. We studied how to improve the surface condition of foam sheet without damaging the features proceeding from chemical cross-linking. As a result, it has been revealed that at the pre-stage of foaming, and by irradiating the surface at low voltage, the resultant foamed sheet with smooth surfaces and excelling in mechanical properties can be produced.