Method and embossing structure for maximizing pressure buildup at rotational embossing of foils

Abstract

An embossing method allowing to emboss a material on both sides comprises feeding the foil material into a roll nip between a pair of a first roll and a second roll, providing the first roll and the second roll each with a plurality of positive projections and a plurality of negative projections of identical shaped polyhedral structures, a first subset of the plurality of positive projections being disposed with a first periodicity on a first grid in axial direction and a second periodicity on the first grid in circumferential direction on the first roll, and a second subset of the plurality of negative projections being disposed with the first periodicity in axial direction and the second periodicity in circumferential direction on the first grid intertwined with the positive projections, in axial and circumferential directions respectively, and projections complementary to the first grid, on the second roll, each of the positive projections and the negative projections on the first roll during operation of the rolls and in the roll nip being surrounded on all sides by positive projections and negative projections on the second roll, the positive projections of the first roll together with alternating corresponding negative projections on the second roll forming during the operation of the rolls and in the roll nip, a first straight line substantially parallel to the axial direction, and the negative projections of the first roll together with alternating corresponding positive projections on the second roll forming during the operation of the rolls and in the roll nip, a second straight line substantially parallel to the axial direction. The positive projections and the negative projections are such that in the axial direction on the first roll each positive projection shares a lateral base border with at least one negative projection adjacent to the positive projection, and during the operation of the rolls and in the roll nip, all lateral oblique surfaces of the positive and negative projections of the first roll are just above the surface in full faced view with the corresponding lateral oblique surfaces of the respective negative and positive projections of the second roll, thereby enabling a homogeneous distribution of pressure to the material.