R-gen® 919: Liquid Photoinitiator for Dark UV Inks | Overcoming Carbon Black Shielding & Curing Bottlenecks
Curing Challenges in Dark UV Systems: A Tug-of-War Between Aesthetic and Process Stability
In industrial inkjet printing, electronic marking, and premium packaging applications, achieving “deep and uniform black” is not only a visual requirement but also a significant formulation challenge. To obtain ideal opacity, black UV inks and coatings often require high carbon black loading. However, carbon black exhibits strong UV absorption, effectively blocking light penetration through the coating. This severely limits photoinitiator activation, resulting in incomplete curing, residual tackiness, surface defects, and compromised downstream processing.
Such issues can degrade product appearance, trigger customer complaints, and increase the risk of returns. These challenges are particularly critical in thick films, high-pigment, and deep-color formulations, placing triple pressure on formulation stability, production efficiency, and quality control.
Limitations of Conventional Photoinitiators: Poor Dispersion, Sedimentation, and Low Curing Efficiency
Conventional solid photoinitiators, such as Chivacure® 169, often face poor solubility and dispersion in dark, high-pigment systems, causing localized under-curing and sedimentation. This not only reduces coating uniformity and finished product quality but also significantly impacts formulation storage stability. In applications such as inkjet printing or precision coating, these issues can lead to nozzle clogging and production downtime, affecting yield, throughput, and delivery schedules, thereby disrupting the entire supply chain.
Key Considerations When Developing Dark UV Systems
First is the selection and dosage of pigments. Dark formulations often rely on carbon black to achieve high opacity; however, excessive use can severely block UV penetration, making it difficult for photoinitiators to trigger the curing reaction. Therefore, finding the optimal balance between opacity and light transmittance becomes the first step in formulation optimization.
Second, the solubility and dispersion stability of photoinitiators are equally critical. If photoinitiators are not fully dissolved or are unevenly dispersed within the system, it can lead to localized curing defects, reduced surface quality, and negatively impact production continuity and equipment efficiency.
R-gen® 919: A High-Performance Solution Engineered for Dark UV Systems
1. Liquid Design Optimized for Dark Systems – Overcoming Solubility Limitations
In dark UV inks and high-pigment coatings, carbon black’s high opacity severely hinders light penetration. Traditional solid photoinitiators (e.g., Chivacure® 169) exhibit extremely low solubility, resulting in poor formulation stability, incomplete curing, and unacceptable nozzle clogging due to early precipitation.
R-gen® 919, with its fully liquid design, completely eliminates the solubility limitations of solid p-morpholinoacetophenone photoinitiators. It is fully miscible with most acrylate resins, ensuring no separation, turbidity, or sedimentation, even in formulations with extremely high pigment content.
▶ Key Performance Data:
- Solubility: Fully miscible with acrylate resins; aqueous solubility: 3.37 ×10⁻³ g/L
- Viscosity & Density: 210,000 cps (20°C), 1.088 g/cm³, suitable for high-precision coating and inkjet systems
2. Excellent Photocuring Efficiency Under High Opacity – Compatible with Arc and LED Light Sources
R-gen® 919 delivers photoreactivity comparable to conventional high-performance photoinitiators. Even in highly opaque systems with severe UV absorption caused by carbon black, it consistently initiates polymerization, ensuring curing quality and system reliability.
• ARC lamps: Suitable for traditional formulations requiring a broad wavelength range, but associated with higher heat load and environmental restrictions.
• LED lamps: The mainstream technology today, particularly suitable for digital printing, low-temperature curing, and automated production processes.
Test data show that R-gen® 919 achieves a curing speed of 10–20 m/min under both ARC and 365 / 395 nm LED light sources, demonstrating excellent light source compatibility and stable photochemical reactivity.
Particularly suitable for high-performance processes such as high-speed inkjet printing, UV coatings, and precision electronic component marking, where production speed and consistent curing are critical.
In printed circuit board (PCB) manufacturing, each board must clearly display component models, batch traceability codes, customer markings, or anti-counterfeiting patterns. These markings are typically applied via UV inkjet printing, which requires sharp definition and rapid curing. R-gen® 919 maintains excellent photoreactivity even in dark, highly filled inks, enabling fast and complete curing—making it ideal for automated processes that demand both high productivity and precision.
▶ Key Performance Data:
- Curing speed: 10–20 m/min (high-opacity black formulation)
- UV absorption peak: 330–340 nm, corresponding to the main output wavelength of the D-bulb, effectively enhancing UV energy utilization
3. High Reactivity with Low Odor Performance
While traditional p-morpholinoacetophenone photoinitiators deliver high reactivity, they typically release strong ester or amine odors after curing due to their small-molecule structure.
R-gen® 919 achieves high curing efficiency with virtually no post-cure odor, making it ideal for odor-sensitive applications.
R-gen® 919 – Key Applications and Solutions
1. Black UV Inkjet
- Challenge: High carbon black loading blocks UV light; traditional photoinitiators have poor solubility, sedimentation issues, and risk of nozzle clogging.
- Solution: Fully liquid R-gen® 919 offers excellent miscibility with acrylate resins, enhancing formulation homogeneity and storage stability, significantly reducing sedimentation and clogging risks, and enabling high-speed, high-precision printing.
2. UV Inks for PCB Marking
- Challenge: High-opacity PCB inks suffer from UV attenuation and poor curing; solid photoinitiators sediment, reducing process stability and yield.
- Solution: R-gen® 919 maintains superior reactivity under high carbon black loading, enabling fast, tack-free curing and improved dispersion stability – ideal for electronic-grade, high-efficiency production.
3. High-Pigment UV Coatings
- Challenge: High pigment concentration reduces curing efficiency; traditional photoinitiators may precipitate or stratify, compromising coating quality.
- Solution: R-gen® 919 provides stable curing initiation under high-opacity conditions and is compatible with multiple resin systems, ensuring uniform, reliable film formation.
4. Non-CMR UV Systems
- Challenge: Many advanced markets (e.g., EU, North America) restrict CMR 1(b) substances, making traditional photoinitiators unsuitable.
- Solution: R-gen® 919 contains no CMR 1(b) substances, offering an ideal choice for globally compliant high-performance formulations.
CMR 1B = Substances presumed to be carcinogenic, mutagenic, or toxic to reproduction, classified as high-risk materials.
If a raw material is categorized as CMR 1B: it is restricted or banned in the EU market (especially in applications such as food contact materials, personal care products, and children’s products). Many formulation customers explicitly require that “no CMR 1B substances” be present. Regulations such as REACH, RoHS, and Ecolabel certifications also emphasize the exclusion of CMR substances.
For samples, application recommendations, and customized formulation consulting:
📧 sales@chitec.com
