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Mehner A.,IWT - Foundation Institute of Materials Engineering | Dong J.,IWT - Foundation Institute of Materials Engineering | Hoja T.,IWT - Foundation Institute of Materials Engineering | Prenzel T.,IWT - Foundation Institute of Materials Engineering | And 4 more authors.
Key Engineering Materials | Year: 2010

The demand for high precision optical elements as micro lens arrays for displays increases continually. Economic mass production of such optical elements is done by replication with high precision optical molds. A new approach for manufacturing such molds was realized by diamond machinable and wear resistant sol-gel coatings. Crack free silica based hybrid coatings from base catalyzed sols from tetraethylorthosilicate (TEOS: Si(OC2H 5)4) and methyltriethoxysilane (MTES: Si(CH 3)(OC2H5)3) precursors were deposited onto pre-machined steel molds by spin coating process followed by a heat treatment at temperatures up to 800°C. Crack-free multilayer coatings with a total thickness of up to 18 μm were achieved. Micromachining of these coatings was accomplished by high precision fly cutting with diamond tools. Molds with micro-structured coatings were successfully tested for injection molding of PMMA optical components. The wear resistance of the coatings was successfully tested by injection molding of 1000 PMMA lenses. Hardness and elastic modulus of the coatings were measured by nano indentation. The chemical composition was measured by X-ray photo electron spectroscopy (XPS) as a function of the sol-gel processing parameters. © (2010) Trans Tech Publications. Source


In many cases, residual stresses have to be considered during the strength analysis of fibre reinforced plastics. These result from the different contraction of the singe layers in case of the change of temperature or moisture. Furthermore, changing stresses in the different layers are caused by non-linear stress-strainrelations, by reduced layer stiffness due to tolerable inter-fibre fractures and by changing of the fibre direction under load. In order to consider these effects at the same time, a calculation scheme has been developed, which provides a realistic prediction of the laminate behaviour till final fracture in one single calculation step. The implementation of the calculation sheme into a programme enables the strength calculation of fibre-reinforced plastics corresponding to the VDI-guideline 2014 Part 3. Source


Holters S.,Fraunhofer Institute for Laser Technology | Overbeck J.,Institute For Kunststoffverarbeitung Ikv | Ederleh L.,Institute For Kunststoffverarbeitung Ikv | Michaeli W.,Institute For Kunststoffverarbeitung Ikv | And 2 more authors.
Coating International | Year: 2010

The Fraunhofer Institute for Laser Technology (ILT) and the Institute of Plastics Processing (1KV) in Aachen, Germany, are collaborating to develop a precise measurement technology for complex multilayer films. The project has been undertaken by them as part of the IRIS project funded by the German ministry of economics and technology (BMWi). The project aims at developing a laser sensor that can measure individual layer thicknesses in the micrometer range on production lines. It is observed that such inline measurement ensures high process reliability in the film manufacturing process, enabling the implementation of a control concept in film processing plants and equipment. The laser sensor utilizes light in the near-infrared range to optically measure individual layer thicknesses and its light is nonhazardous and operates without the need for safety measures. An optical fiber and a compact measuring head are also used to aim the measurement radiation at the film from a distance of a few centimeters. Source


Michaeli W.,Institute For Kunststoffverarbeitung Ikv | Bahroun K.,Institute For Kunststoffverarbeitung Ikv | Fragstein F.V.,Institute For Kunststoffverarbeitung Ikv
Polymers from Renewable Resources | Year: 2010

Having worked intensely on plasma-assisted barrier coating (plasma enhancedchemical vapor deposition, PECVD) of polymers, a technique already usedcommercially to enhance shelf-life performance of PET bottles, for the last twodecades, it seemed to be obvious to investigate the transfer of this existingtechnique to novel beverage materials such as PLA and PP. As a result of theirhigh oxygen and carbon dioxide permeability the market potential of PP and PLAis still restricted in the beverage packaging sector. On the one hand, the use of plasma coatings to improve the barrier propertiesof these materials shows advantages. For example, these coatings are lesslikely to interfere with PLA-bottle biodegradability. On the other hand, materialssuch as PP and PLA put higher demands on plasma coating processes due totheir different surface properties that make it much more difficult to establishan adequate adhesion between coating and bulk material and their increasedsensitivity to high temperature. By using a pre-treatment specific to the materials, we succeeded in applying effectivebarrier coatings by plasma polymerization using both hydrocarbons as well as siliconorganic monomers. For PLA the pre-treatment process can be integrated directlyinto the plasma polymerization process, whereas for PP it was necessary to use aLF-plasma in an external facility to enable a good coating adhesion. The barrier properties against oxygen could be increased by a factor of about 12for PP and 4 for PLA. Hydrocarbon-based coatings proved to be more effectivecompared to HMDSO-based coatings. These first evaluations show that it ispossible to raise the barrier performance of PP and PLA bottles to match thelevels obtained with uncoated monolayer PET types. Our current researchconcentrates on improving the processes in order to increase the barrierperformance and the efficiency of the process. © Smithers Rapra Technology, 2010. Source

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