Abstract
Mechanism of sealed postcards is discussed based on contact mechanics, i.e., elastic adhesion theory. Their adhesive interface is assumed as a semi-infinite elastic body contacting on a rigid body which has a two-dimensional sinusoidal surface roughness. Their equilibrium state is obtained as a function of the external pressure and the surface roughness using material constants of the postcards. It is found that after the initial line contact the interface is snaped to the area contact. There exists a critical external pressure which snap the interface from the partial contact to the perfect contact. After the perfect contact, the interface can not return to the area contact, even if the tensile external stress is applied. The necessary condition for the function of the sealed postcard is expressed using the parameter of surface roughness and the material constants.
