Investigations into the production of achromatic lenses by two-component injection compression molding of transparent plastics

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Compared to many optical grades of glass, plastics have a high dispersion. This means that the refractive index of the material decreases more strongly with increasing wavelength. As a result, different wavelengths of light (light colors), which are focused by an optical lens, have different focal positions. This leads to image errors and blurred images, which is why imaging optics are usually composed of several combined lenses. In illumination optics, the dispersion is shown by a color veil on the edge of the light cone.By combining two lenses made of materials with different dispersions to form an achromatic lens, this chromatic aberration, can be reduced, resulting in a significant increase in imaging performance. To improve image quality, plastic lens systems are usually assembled from several lenses. This requires the production of several components, exact positioning and further assembly steps.The project therefore focuses on injecting a second component onto a preform with low warpage and shrinkage to produce an achromatic lens from different transparent plastics. Possible plastics for the combination are polycarbonate (PC) and poly(methyl methacrylate) (PMMA). In addition to reducing further processing and assembly steps, two-component injection molding also increases transmission by reducing reflections at the interfaces.From the application of an achromatic lens, the general derivation of a production strategy for low-shrinkage and low-warpage two-component injection compression molding with large contact surfaces is to be carried out in the research project. In addition to optics, this knowledge is relevant for numerous other applications. Nevertheless, the prerequisites for this two-component injection moulding of optical components are particularly challenging. The second component must be injected onto the preform with very little shrinkage, the injection process of the second component should not deform the first component surface and sufficient adhesion of the two plastics over a large surface must be ensured. These points are to be achieved by an adapted injection compression molding process. An adapted compression of the melt in the process by means of embossing should reduce subsequent shrinkage of the injected component as far as possible. The influences of the process parameters on adhesion, shrinkage, the shape of the interface and the refractive index as well as the component properties are systematically investigated.