Werkzeugentwicklung für das Heissprägen beidseitig mikrostrukturierter Formteile

Abstract

In the present dissertation, a tool and process concept for double-sided hot embossing of microstructured molded parts was described. Studies focused on the manufacture of plastic substrates with large surface areas and thin residual layers, which are microstructured on both sides and considered for use in microoptics and microfluidics. Development of a cost-efficient process with short cycle times was deemed necessary to meet the demand for disposable components e.g. for microfluidic analysis chips. The tool and process concept covered the development of appropriate mechanisms for precise orientation of the tool halves, defect-free demolding of the large-area and usually flexible molded parts, and efficient temperature control of the tools to minimize cycle times. Based on the process technology requirements determined, a tool setup of two symmetrical tool halves and a positioning table was developed and implemented. The tool halves each consist of a tool frame of constant temperature, a tool insert of minimum mass that is subjected to thermal cycling, and a cooling block kept at constant temperature. During heating, the tool insert is thermally insulated from the cooling block. In this way, short heating times are reached. During the embossing and cooling phase, the tool insert is coupled thermally to the cooling block such that heat can be removed rapidly. As a result of the short times needed for heating and cooling the tool during embossing, cycle time is reduced considerably. The tool halves are additionally provided with plates, by means of which the semi-finished product is fixed during heating and cooling and shrinkage is avoided. By a demolding drive, the fixing plates can be moved precisely and independently of the tool opening movement. This allows to apply the semi-finished product to the mold inserts or to separate it from them for demolding. Via separate vacuum and pressurized air connections in the upper and lower tool, independent evacuation of the cavity or controlled separate pressurized gas supply to the upper or lower side of the semi-finished product is ensured. In this way, the large-area molded parts that have been microstructured on both sides can be demolded easily. The positioning table is equipped with an air bearing and flexible joints. Consequently, positioning is not influenced by friction or play of the joints. Precise orientation of the tool halves is achieved by piezoactuators driving the table and high-resolution sensors integrated in the tool frame. The tool and positioning table were taken into operation in a test facility. Microtiter plates were produced to demonstrate double-sided hot embossing of large-area microstructured molded parts. Cycle times of 4 minutes were reached.