Relationship between Fibrous Structure and Spunbond Process

The structure of spunbonded nonwovens is characterized by a filament orientation distribution function that is a length-weighted density. This density was defined according to the `Equivalent Pore Model' and was experimentally determined by an optical method. The method permits a description of the anisotropy and the main direction of the fibrous network on both faces of the webs. Despite the lesser thickness, the spunbonded nonwovens presented a different organization of the filaments on the two faces. The conveyor face was more anisotropic than the upper one. The filament lay down process in the Perfobond technology was analyzed. The combined action of the velocities of the filaments, of the belt and of the air suction, influenced the structure, causing two important effects: a rotation of the filaments and a shear stress. The air suction velocity appears to be the most important variable, which controls the action of the belt.