Cycloaliphatic Epoxy Resins: UV-LED Curing Solutions and Uses

Cycloaliphatic Epoxy Resins for UV-LED Curing Applications

Light sources are an indispensable component of radiation curing. UV radiation curing, which mainly uses mercury lamps, has been widely applied commercially. However, it has issues such as mercury pollution. The emergence of ultraviolet light-emitting diodes (UV-LEDs) has brought revolutionary changes to the UV radiation curing industry. Comparing the two, the emission spectrum of mercury lamps is continuous, with wavelength ranges of UV-C: 100–280nm; UV-B: 280–315nm; UV-A: 315–400nm; visible light 400–700nm; and infrared 700–3000nm, with a concentration of light intensity from UV-B to short-wave UV-A. In contrast, ultraviolet light-emitting diodes (UV-LEDs) have a narrow spectral output concentrated at a specific wavelength, with typical commercial LED lamps emitting at 365nm, 385nm, 395nm, or 405nm wavelengths.

Key Features of UV-LED Curing for Cycloaliphatic Epoxy Resins

From the table above, it can be seen that UV-LED has advantages such as consistent light intensity, excellent temperature control, and being environmentally friendly and non-polluting. However, there are also issues such as the mismatch between the photoinitiator's absorption and the light source wavelength. Cationic photoinitiators generally have the drawback of short UV absorption wavelengths. The maximum absorption wavelength of sulfonium salts is generally around 300nm, and it is even shorter for iodonium salts, mostly around 250nm. Therefore, it is necessary to sensitize cationic photoinitiators to improve their utilization of UV-LED light sources. For example, the commercial cationic photoinitiators diaryliodonium salts and triarylsulfonium salts can achieve UV-LED curing by adding photosensitizers (photosensitizers are substances that can broaden the spectral response range of photoinitiators).

Compared to free radical systems, cationic systems dominated by cycloaliphatic epoxy resins have advantages such as oxygen inhibition resistance and low viscosity, making them more suitable for UV-LED curing. They are widely used in coatings, inks, adhesives, electronic packaging, 3D printing, and other fields. As a professional supplier of cycloaliphatic epoxy resins, TETRA offers a rich variety of cycloaliphatic epoxy resins. The following will explore the UV-LED solution of cycloaliphatic epoxy resins using TTA21 as an example.

Results of UV-LED Curing Solution for Cycloaliphatic Epoxy Resins

• When cycloaliphatic epoxy resins TTA21 are paired with sulfonium salt (UVR692), they easily cures at 365nm, and the curing speed is accelerated by the photosensitizer. At 395nm, they are difficult to cure, but curing can be achieved with the photosensitizer, and the curing speed is affected by the performance of the photosensitizer.

• When cycloaliphatic epoxy resins TTA21 are paired with iodonium salt (UVR301), they cannot cure at either 365nm or 395nm. However, curing can be achieved with the photosensitizer, and the curing speed is affected by the performance of the photosensitizer.

TETRA is a world-leading supplier of high-performance specialty epoxy resins. Our products not only meet domestic market demands but are also sold to over 50 countries worldwide. Our application fields now permeate various industrial sectors, such as UV-curable coatings/inks, composites, adhesives, electronic and electrical insulation, semiconductor packaging materials, and 3D printing additive manufacturing. We are committed to becoming the benchmark for the application of new chemical materials in China, focusing on guiding China's demand and promoting the upgrading of the epoxy resin industry.