Einfluss der Herstellungsbedingungen von PP-Halbzeugen auf die Thermoformeigenschaften

Abstract

___________________________________________________________________________ 7 Abstract Variations in sheet material quality often lead to problems during the thermoform process of polymeric semi-finished products. Currently, these variations in quality are handled by a trial and error adjustment of the thermoforming process parameters. This leads not only to a loss in productivity but also results in unsatisfying quality of the thermoformed parts. The lack of knowledge about the thermoformability of semi-finished products constrains the development of new thermoformed products and restricts the use of thermoforming in new areas of application. The introduction of a test method to determine the quality of polymeric sheet materials can solve this problem. This test method must reliably detect changes in sheet quality and thereby facilitate a prediction of the thermoformability of the material. For this dissertation sheet materials of two different types of polypropylene have been extruded. HB205TF and HC205TF from Borealis have been used. Extrusion parameters like throughput, temperature and chill-roll-temperature have been varied based on a statistical design of experiments. In order to evaluate the thermoformability of the extruded material, the material was processed on an instrumented laboratory thermoforming machine using varying process parameters. The deformation characteristics and the optical appearance of the parts produced have been evaluated. Furthermore, the sheet characteristics of the materials such as rheological and morphological properties have been determined by experiments. The interrelationship of extrusion process settings and resulting thermoforming characteristics could be shown by a regression analysis. The main parameter influencing the thermoformability is the raw material used for sheet extrusion. Minor dependencies between deformation characteristics and extrusion-speed were observed, varying in intensity depending on the raw material used. The regression analysis also showed a relationship between extrusions process settings and resulting sheet properties. The sheet properties are mainly determined by the used raw material as well as by the extrusion-speed while crystalline structures are influenced by an interaction of extrusion-speed and chill-roll-temperature. The average molecular weight of the sheet material, as well as the reaction force during a biaxial deformation, depends on the interaction of extrusion temperature and extrusion speed. A main effect analysis displayed a correlation of sheet material properties and thermoformability. Sheet properties which are directly influenced by the processed raw