In the field of radiation curing, the evolution of light sources is redefining material performance. With the widespread adoption of LED curing equipment, 405nm long‑wavelength light has become a mainstream choice for thick coatings, three‑dimensional structural parts, and highly filled systems, primarily due to its excellent penetration capability.
Traditional photoinitiators optimized for short‑wave ultraviolet light (e.g., 365nm) often show insufficient absorption efficiency at 405nm, leading to limited cure depth. Simply increasing the photoinitiator loading can cause yellowing and other appearance defects. Uyracure‑504, developed by Shenzhen Youyang Technology Co., Ltd., is a targeted solution to this technological challenge.
Molecular Design Precisely Matched to 405nm
Uyracure‑504 is a free‑radical photoinitiator of the bisacylphosphine oxide type, with its absorption maximum precisely aligned to 405nm. It is designed as a composite system to balance surface cure and deep‑section cure. The product is supplied as a low‑viscosity liquid at room temperature, with an appearance of light yellow liquid, a molecular weight of 202, a viscosity of 180 mPa·s at 25°C, and a recommended addition level of 1%–5% by weight.
Its low‑viscosity liquid form allows easy blending with various high‑solid resin systems, avoiding the dissolution difficulties and agglomeration often encountered with solid photoinitiators. At 405nm wavelength, Uyracure‑504 exhibits high molar extinction coefficient and efficient photoreactivity, converting light energy into initiating radicals that can be delivered to the bottom of a coating or the interior of a fabricated part.
Low Yellowing and Thermal Stability
Yellowing remains a major concern for many UV‑cured materials. Conventional photoinitiators can generate coloured chromophores upon photolysis, causing transparent or light‑coloured substrates to turn yellow, which adversely affects appearance and service life. Through careful molecular structure optimisation, Uyracure‑504 produces photolysis by‑products with an extremely low tendency to form chromophores. In various resin systems, test results show no significant yellowing.
This stability is not limited to the curing stage. Even during post‑cure baking or high‑temperature service, the cured material maintains good colour stability and physical integrity. In addition, Uyracure‑504 is free from benzene‑type substances and exhibits very low migration, making it suitable for sensitive applications where environmental and safety standards are strict, such as food‑contact packaging and precision electronic encapsulation.
Deep‑Section Curing Capability
Thick coatings and complex structural parts are often plagued by the "surface‑cured but under‑cured interior" gradient defect, especially in highly pigmented and black formulations. Uyracure‑504 achieves deep‑section curing through uniform photoreactivity: under 405nm LED illumination, the generation of free radicals is distributed evenly along the entire depth of the material, ensuring simultaneous crosslinking from the surface to the bottom.
This feature allows high‑density circuit boards with deep trenches and narrow line spacing to achieve excellent through‑cure with only a low photoinitiator loading. For white, black, or high‑pigment‑load ink systems, the strong penetration of 405nm light combined with the deep‑cure characteristics of Uyracure‑504 also delivers thorough and uniform curing, effectively solving the common problem of poor adhesion at the bottom caused by premature surface skinning.
Applications in 3D Printing
In the field of photopolymer 3D printing, 405nm LED light sources are widely used in desktop DLP and LCD printers. Uyracure‑504 shows good compatibility with mainstream 3D printing photopolymer resins and equipment. Under 405nm illumination, it rapidly triggers photopolymerisation, reducing single‑layer curing time.
In DLP/LCD processes, the uniform photoreactivity of Uyracure‑504 helps to improve crosslinking uniformity in the Z‑direction, reducing model warping and cracking caused by incomplete internal curing. For transparent or lightly coloured models, the material maintains high light transmittance and a smooth surface finish. Its low‑viscosity liquid form also ensures even dispersion in the resin system, avoiding local concentration variations that can lead to uneven curing.
PCB Solder Mask and Automotive UV‑Curable Coatings
In multilayer PCB solder mask applications, high‑density interconnect (HDI) boards face challenges such as deep trench filling and coverage over high‑density traces. Uyracure‑504 enables complete curing in shadowed areas and deep sections, providing reliable insulation protection and interlayer adhesion.
In automotive UV‑curable coatings – for instance, headlamp lens coatings and thick‑film clearcoats – it is essential to achieve the required film thickness and cure depth while preserving optical clarity, so that yellowing does not interfere with light output. Uyracure‑504 satisfies both the demands for cure depth and appearance quality in these applications.
Conclusion
Uyracure‑504 is a high‑performance photoinitiator specifically developed for 405nm long‑wavelength LED curing. Its balanced design – combining deep‑section curing capability, low yellowing, good thermal stability, and favourable environmental properties – offers a reliable material solution for high‑end manufacturing scenarios such as 3D printing photopolymer resins, PCB solder mask inks, and automotive UV coatings. By enabling consistent crosslinking inside complex geometries and thick layers, Uyracure‑504 helps manufacturers eliminate the gradient defects of traditional initiators and achieve durable, high‑quality finished parts.