Photoresins are plastics that are produced by irradiation with light - mostly ultraviolet (UV) - from liquid starting materials. In >90% of cases, they consist of acrylates and methacrylates. To make these mixtures reactive when irradiated with light, a photoinitiator must be added. In practice, photoresins are usually called photoresists, UV coatings and, if printable with inkjet technology, UV inks. In recent decades the use of UV inks in industrial printing processes has been growing worldwide. One major reason for this is their operating principle: while solvent-based inks dry by evaporating the solvent - which is 80-90% of their mass - UV inks cure through a photochemical reaction that converts them completely into solid plastic. This means greater material efficiency, fewer harmful emissions and greater occupational safety by avoiding solvent-air mixtures. In addition, after curing, photoresins form solid films that provide additional protection for the imprint or enhance the surface. Of course, the formulation must be adapted to the respective substrate in order to achieve this effect. However, this is made possible by the large chemical diversity of available components. This diversity is also an advantage of the technology - after all, it allows many new applications.
Task 1: Development of inkjet-compatible mixtures that can be used as inks in the colours white, black, cyan, magenta and yellow in commercially available industrial printers. The relevant substrates at the moment are glass, textiles and plastics (customer enquiries). A separate product line must be developed for each of these three substrates because their surface chemistry is very different and consequently no universal formulation that adheres to all materials is possible. A key challenge here is setting a target viscosity of below 30 mPas, ideally 10-15 mPas. The other, and additional, challenge arises in textile printing - the cured photoresin should be rubber elastic. However, the acrylate-based photoresins are usually rather brittle resins.
Task 2: Development of photoresins that can be used in 3D printers that work according to the stereolithography principle. While the viscosity requirements are less restrictive in this case, and values of 100 - 300 mPas are acceptable, the task is challenging in other ways. For successful printing, a balance of adhesion and cohesion must be maintained, the photoinitiator must match the 405 nm wavelength at which most stereolithographic 3D printers operate, and the finished workpieces must also be easy to remove from the device.