For injection molding in modern plastics industry tool life, cycle time, and quality of the produced part-surfaces are of great importance for economic profitability. Friction plays a decisive role in this draft process. In this diploma thesis, the systematic investigation of surface energy as a function on surface roughness was done for various materials. Steels of different composition, coatings and plastic specimen manufactured under different process conditions were studied. A contact angle measuring instrument was used to determine the surface energy, whereas the surface roughness was measured by atomic force microscopy and with a confocal white light microscope. Both, the strong dependence of the surface energy on the surface roughness and the clear influence of the production process on each examined sample could be revealed. Typically, the surface energy diminishes with decreasing roughness. In the injection molding of thermoplastic materials, first the hot polymer melt is injected under pressure in a colder cavity formed of steel. The melt is then cooled down to a solid part which finally is separated under friction from the steel surface, as the part is ejected. The so-called interfacial tension is a main value which could describe the separation behavior of a solid from another solid. The aim of this work was to determine whether the interfacial tension can be used as a prediction parameter for the real demolding behavior. To calculate this, the interfacial tension of various combinations of plastics, coatings and steels was calculated from the measured surface energy and compared to results from previous process-related friction tests. A good correlation could be identified between calculated trends (high interfacial tension) and measured values (low friction). On closer examination for the systems polycarbonate – steels and polycarbonate – coatings, the calculated values for coatings where generally higher (γCrN = 4.23 mN/m) than those for steels (γsteel = 1.23 mN/m). This agrees with know-how acquired in practice, since in industry coatings are generally used for friction reduction instead of steel.