Light-Curing Technology Series — Light Source 3

UVC LEDs are currently in the nascent stage of development within the field of photopolymerization technology, with no formal commercial applications yet. However, given the current trajectory of UVC LED advancements, it is highly likely that they will achieve commercial deployment in certain niche markets over the next few years.

I. What can UVC bring to photopolymerization technology?

It is worth noting that the UVC wavelength range (200–280 nm) serves as an effective light source for conventional photoinitiators, which恰恰 addresses the two major challenges currently hindering UV‑LED curing formulations:

Surface drying issues and yellowing problems

Currently, UVA LED light sources are widely used in photopolymerization technologies, and the corresponding photoinitiators include TPO, TPOL, 819, ITX, DETX, 369/379, among others. Among these, TPO and TPOL exhibit relatively low yellowing; however, their resistance to oxygen‑induced inhibition is comparatively poor. Consequently, using only these two photoinitiators often leads to diminished surface cure performance in coatings or ink layers. The remaining photoinitiators all offer some degree of resistance to oxygen‑induced inhibition and deliver satisfactory surface curing, but they tend to cause more pronounced yellowing—particularly DETX, 369, and 379. As a result, developing a formulation that combines low yellowing with excellent surface drying while being compatible with UVA LED light sources remains quite challenging. Conventional short‑wavelength photoinitiators (such as 173/184, 127, 1960, MBF, BP, OMBB, etc.) outperform TPO and TPOL in terms of surface drying and show significantly reduced yellowing before and after curing compared with DETX, 369, and 379. Therefore, if UVC LEDs can be commercialized, the issues of surface drying and yellowing should improve with the incorporation of short‑wavelength photoinitiators.

In 2021, the UV LED industry achieved a record-high total revenue, approaching RMB 3 billion for the first time, and is projected to reach RMB 10.75 billion by 2025. Driven by concerted efforts across the sector, the UV LED market has transitioned from an explosive growth phase in 2020 to a period of steady expansion, with substantial untapped potential. In particular, UVC LEDs are increasingly replacing mercury lamps, leading to an expanding range of applications and deeper penetration into diverse industries. According to TrendForce, the UVC LED market in 2022 encompasses home appliances, public‑space and manufacturing applications, flowing‑water sterilization, startup ventures, automotive air sterilization, as well as medical, life‑science, and agricultural sectors. With ongoing improvements in UVC LED optical output and product lifespan, coupled with broader adoption in disinfection applications, UVC LEDs are poised for rapid uptake in photopolymerization technologies as well.

The widespread adoption of UVC LED light sources in photopolymerization technology, in addition to improving existing UV‑LED curing formulations with respect to surface drying and yellowing, will also impact photopolymerization in the following two areas:

Comprehensive cost and green environmental protection

Conventional short‑wavelength photoinitiators are generally much less expensive than long‑wavelength ones (e.g., 1173/184, BP). Therefore, if UVC LED light sources become widely adopted in UV curing applications, low‑cost short‑wavelength photoinitiators can play a more significant role in formulations, while the dosage of higher‑cost long‑wavelength photoinitiators can be reduced accordingly. This, in turn, helps formulation manufacturers lower their raw‑material cost pressures.

Traditional mercury‑lamp light sources emit across the ultraviolet and visible spectral ranges, with UVC and UVA being the primary wavelength bands currently utilized in photopolymerization formulations. From a technical standpoint, if UVC LEDs and UVA LEDs can be seamlessly integrated, they could potentially replace existing mercury‑lamp sources without altering the original formulation. Mercury‑lamp systems are highly energy‑intensive, generate ozone, and pose mercury‑contamination risks; by contrast, UV LEDs (covering UVA, UVB, and UVC) offer an ideal solution to both of these challenges.

II. Several Issues with UVC-LEDs in Photocuring Applications

1. Energy

Although the power of UVC LEDs has improved significantly compared to earlier models, their performance in photopolymerization applications remains relatively limited, and further advances are needed in irradiance levels. Notably, UVC LEDs can now deliver irradiance fluxes exceeding 200 mW (e.g., Nichia’s NC4U334BR UVC LED, 280 nm, 200 mW), and ongoing development is focused on even higher‑power UVC/B LED chips. According to our laboratory tests, an irradiance of 200 mW is already sufficient for certain photopolymerization processes; however, to expand their use across a broader range of photopolymerization technologies, additional improvements in irradiance are still required.

2. Lifespan

Currently, UVC LEDs have relatively low photoelectric conversion efficiency and generate substantial heat, making thermal management particularly critical for UVC chips and directly impacting their service life. Additionally, due to the short wavelength of UVC light, conventional packaging technologies are no longer suitable (leading to rapid aging), so developing more advanced inorganic封装 techniques is essential for extending the lifespan of UVC chips. Some companies have already conducted aging tests on UVC and UVB LEDs, observing no degradation over 1,000 hours. Compared with the comparatively short lifetime of existing UVA LEDs, this performance already surpasses that of traditional mercury lamps. With continued technological advancements, the operational life of UVC LEDs is expected to improve further.

3. Cost

Since the outbreak of the pandemic in 2019, UVC LEDs have demonstrated unique advantages in disinfection, and major chip and packaging manufacturers have been continuously introducing new products. However, due to patent constraints and limited production volumes, their cost remains relatively high compared to UVA LED chips. Meanwhile, the entry into force of the Minamata Convention is accelerating the phase-out of mercury lamps, making UVC+UVA LEDs the optimal choice. Let’s first examine the UVC LED market. Taking a 1020‑mil chip emitting at 275 nm as an example, as of June, UVC LED chip prices have fallen by more than 80% from their peak during the pandemic, with the market median now below RMB 0.5 per unit. Low‑brightness versions are already priced at RMB 0.3–0.4 per unit, representing roughly a 70% decline compared to pre‑pandemic levels in 2019. We believe that as UVC applications in sterilization continue to expand, costs will improve significantly, paving the way for photopolymerization technologies to fully replace existing mercury‑based light sources with UVC+UVB+UVA solutions.

4. Distance

The longer the wavelength of light, the greater its penetration ability in air; by contrast, shorter‑wavelength UVC is significantly attenuated in air. Current UVC LEDs, due to their relatively low power, typically achieve an effective working distance of around 3 cm—or even less—when used in photopolymerization applications. Beyond this range, light attenuation becomes pronounced, leading to incomplete curing and compromising the performance of cured products. As UVC LED power continues to increase, the effective working distance in photopolymerization is expected to improve further. With the implementation of specialized protective measures, long‑distance photopolymerization may become feasible.

III. UVC   Potential application scenarios of LEDs in light-curing technology

Due to the relatively weak UVC energy and significant photodegradation in air, this technology may find applications in industries where the light source is positioned close to the substrate, such as UV flatbed printing, screen printing, and flexographic printing.

The pandemic has spurred advances in UVC LED light sources while also offering fresh avenues for development in the UV curing industry. Persistent challenges in UV curing technology may well be overcome with the integration of UVC LEDs. Based on these considerations, manufacturers capable of producing UV LED light sources could devote part of their resources to combining UVC, UVB, and UVA into a single solution for UV curing applications. This would accelerate the phase-out of mercury lamps from the UV curing market, making the technology more environmentally friendly and energy‑efficient by eliminating mercury and ozone emissions, and further expanding its range of applications.