Research Reports: Printing technologies

Fraunhofer IOF develops optical and micro-optical components and systems for customers. In addition, we also work on the realization of new manufacturing processes in order to further develop and optimize optical components for various fields of application.

This includes, among others, the manufacturing process of inkjet printing. Its digital character makes it possible to produce highly individualized micro- and macro-optical components flexibly and cost-effectively and to integrate individualized functions.

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• 3D printing of optical elements
• Printing of functional materials
  

Below you will find research reports on our recent printing developments:

InkEye - 3D polymer printing of eyeglasses

Optical components are manufactured conventionally by milling, grinding, and polishing molded or replicated polymer- and glass preforms. For cost-effective production, such optics need to be fabricated with simple geometries in large lot sizes. However, in modern optics production, small lot sizes and even individual optics have become more and more important. This trend is established already in eyeglass manufacturing, where every glass is individualized to the person wearing it. With the inkjet printing of eyeglasses, an additive manufacturing strategy was developed at Fraunhofer IOF. Because of its digital character, this technique enables the cost-effective manufacturing of individualized freeform optics and even the deposition of further functional coatings. Within the “InkEye” project, the capabilities are demonstrated by fully inkjet printing eyeglasses with a scratch-resistant coating.

To manufacture the eyeglasses, a mixture of cross-linkable acrylates with low viscosity is deposited in a multilayer inkjet process. Each printed layer has to be UV-cured to crosslink the polymer ink and to guarantee the mechanical stability of the single layers. With each printing run, a 3 μm to 10 μm thick layer is applied. Thus, macroscopic optical components consist of many hundreds of layers. By tailoring the process management and the process parameters, the cross-linking reaction and thus the polymerization of the polymer can be controlled at the surface and interfaces. Therefore, highly precise and very homogeneous optics can be manufactured with inkjet printing.

As a final step, the scratch-resistant coating is printed onto the eyeglass. This increases abrasion resistance, which guarantees durability during mechanical cleaning. The dimensional accuracy of the surface achieved is in the range of PV < 150 nm with a surface roughness of < 3 nm RMS. The refractive index of the printed acrylate mixture was tailored to > 1.54 by achieving transmission of > 90 % of the resulting printed eyeglasses. In addition, the material has a glass transition temperature of > 80 °C. All these properties are essential requirements for the use of the material in eyeglass manufacturing.

The inkjet printing process developed enables the manufacturing of eyeglasses with high quality and properties comparable to modern requirements.

Authors: Falk Kemper, Erik Beckert, Maximilian Reif, Lisa Pohle, Thomas Schönfelder

3D-inkjet printing of optical components

Micro and macro optical components are conventionally manufactured using milling or molding techniques of polymers and glasses. The fabrication of medium and large lot sizes is very cost efficient with these techniques. However, for cost effective manufacturing of single individualized optics, they are not suitable. To overcome this issue, inkjet printing of Ormocers^® is being introduced at Fraunhofer IOF. This digital manufacturing technique is very flexible, provides a high freedom of design, and thus enables the fabrication of such highly individualized three-dimensional micro- and macro optical components.

For fully inkjet printing 3D-optical components, Ormocomp^®, a hybrid organic-inorganic polymer, is used. It combines beneficial properties of organic and inorganic materials. Its processability is comparable with conventional polymers. However, it has a higher chemical, mechanical, and thermal stability because of its inorganic components. In addition, it shows a very high optical transparency in the complete visible spectrum. Therefore, Ormocomp^® is highly suitable for the manufacturing of robust 3D-optics.

The 3D-Ormocomp^® components are manufactured using a commercial inkjet printer. The structures are sliced and printed layer-by-layer. Each printed layer of low viscous ink has to be UV-cured in order to crosslink the polymer ink and to guarantee mechanical stability of the single layers. With each printing run, a 3 μm to 10 μm thick layer is applied. Thus, macroscopic optical components consist of many thousands of layers.

By optimizing the resolution of the printed layers, the UV-curing conditions, and adapting the printed designs, high dimensional accuracies of the 3D-components could be achieved. The resulting surface roughness of macro optics is in the range of < 60 nm with a PV < 20 μm. With these parameters, the optics are suitable for the use in lighting applications. Figure 1 shows some examples of fully inkjet printed 3D-optical components made of Ormocomp^®.Because of the additive manufacturing approach, a further functionalization of the printed optics is possible. Figure 2 shows integrated LEDs with printed conductive tracks, integrated baffles and inkjet printed silver mirrors in fully inkjet printed three-dimensional optics.

The potential of the introduced technique lies in its use for rapid prototyping and the manufacturing of individualized components with very small lot sizes.

Authors: Falk Kemper, Maximilian Reif, Lisa Pohle, Thomas Schönfelder, Erik Beckert

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