The Fraunhofer Institute for Applied Polymer Research (IAP) in Teltow carried out a two‑year research project (2017‑2019) funded by the German Federal Ministry of Education and Research (BMBF, project code 03ZZ0127A) to develop ultraviolet light‑emitting diode (UV‑LED)‑curable resins for pultrusion and large‑area composite manufacturing. The work was part of the UV‑Co‑Light initiative and involved a consortium of partners, notably the Haase Group, which supplied the LED modules and assisted in combining two wavelength ranges for optimal curing.
The technical objectives were to optimise existing UV‑curable reactive resins for use with UV‑LEDs, to formulate new flame‑retardant systems that are halogen‑free and UV‑transparent, and to demonstrate their applicability in continuous pultrusion of glass‑fiber‑reinforced polymer (GFRP) profiles and in the production of wide composite plates. The project built on earlier findings from a predecessor study (FKZ 03ZZ0111A) that compared conventional mercury lamps with efficient UV‑LEDs for curing and deep‑cure of composites.
Key scientific results include the successful design and fabrication of UV‑LED modules that deliver the required spectral output for curing the new resin formulations. By integrating two LED wavelengths at the Haase partner site, the curing efficiency was maximised, allowing the resin to reach full cross‑linking within the residence time of the pultrusion line. The flame‑retardant resins were engineered with environmentally friendly, halogen‑free additives that remain transparent to UV light, thereby enabling energy‑efficient curing while meeting stringent fire‑smoke‑toxicity (FST) standards required for transportation and construction applications.
Performance data demonstrate significant process improvements. For pultrusion, the production speed increased by a factor of two to four, depending on the profile geometry, compared with the baseline mercury‑lamp process. For large‑area laminate manufacturing, the throughput rose by up to 33 %. In both cases, the curing speed using UV‑LEDs was maintained at least 80 % of the speed achieved with mercury lamps, confirming that the new LED system does not compromise productivity. Additionally, the flame‑retardant formulation required a lower concentration of UV initiator, offsetting the higher material cost of the additives and reducing overall energy consumption.
The project also addressed the critical issue of volume shrinkage during curing. By characterising shrinkage as a function of the curing method, the partners were able to calculate the necessary wet lay‑up thickness for each composite geometry, ensuring dimensional accuracy and reducing defects in the final parts.
The consortium’s collaborative effort extended beyond resin development to include the design of the curing system, the integration of the LED modules into existing manufacturing lines, and the validation of the new materials in real‑world production settings. The project concluded on schedule, with all objectives met or exceeded, albeit with a six‑month delay relative to the original plan. The results provide a robust foundation for the adoption of UV‑LED curing in the composite industry, offering weight savings, energy efficiency, and compliance with modern fire‑safety regulations.