During the last years, the use of polycrystalline transparent ceramics in optical components has constantly increased. By integrating the transparent ceramics division of the CeramTec-ETEC GmbH (PERLUCOR®) Fraunhofer IKTS significantly expands its existing competencies in the development of transparent ceramics.
A research and development center for transparent ceramics at IKTS is built up (funded by the Free State of Thuringia). Among others the research work is focused on the lamination of transparent ceramic with other material. Transparent spinel ceramics represent a wear-resistant alternative for protective components instead of commercially available materials such as polycarbonate, tempered or surface hardened glass. Transparent ceramics are characterized by excellent material properties and are superior in comparison to glass, sapphire, or gorilla glass and within this suitable for many applications like optical scanners, mobile displays or optical sensors require a lamination of the spinel ceramic with optical quality.
For this purpose, Fraunhofer IKTS has developed technologies for laminating transparent ceramics with thicknesses from 0.2 to 5 mm with glass, such as borofloat glass, or plastics, such as PET or PVC, using acrylate and epoxy adhesives. To avoid dust particle inclusions, lamination takes place in partially enclosed glass boxes with a supply of filtered air with slight overpressure in a specially insulated clean room.
The final technological step includes the curing of the adhesive. If acrylate adhesive is used, this is accomplished through irradiation with UV light. If two-component epoxy resins are used, especially when joining with plastics, curing at room temperature is preferable to thermal curing at 60–80 °C, to avoid distortion of the composite laminates and coloring effects.
Defined dispensing patterns of the adhesive in dependence on size of the surface to be joined were developed. Complete and bubble-free wetting without adhesive transfer beyond the edges of the laminate structure was possible. Systematic investigations have shown that the lowest error rates and best reproducibility can be achieved with bonding layer thicknesses between 50 and 100 µm.
Favorable mechanical properties of the composites, such as adhesive tensile strength, tensile shear strength and biaxial bending strength, were shown through characterization in accordance with the relevant test standards. Based on the produced laminated samples the optical qualities of the composites are determined and their suitability for specific applications is assessed.