Radical Photoinitiator Jiuri New Material 184 (CAS 947-19-3, 1-hydroxycyclohexyl phenyl ketone) functions as a Norrish Type I free-radical photoinitiator in acrylate, methacrylate, and unsaturated polyester/styrene photopolymerization. The powder has a reported melting range of 45–49 °C, and its UV absorption covers the 240–350 nm region with a major n–π* band near 330 nm; this spectral profile makes it suitable for medium-pressure mercury arc and selected UV-A sources, but it limits stand-alone efficiency under 385–405 nm LED arrays because the absorption tail above 380 nm is weak. In practice, loading is set by film thickness, oxygen inhibition, pigment UV screening, lamp spectrum, and any downstream migration limit; commercial formulations normally range from 0.5 wt% in clear thick-film adhesives to 5 wt% in high-speed offset inks. The following downstream applications are limited to documented industrial cure regimes and material compatibility boundaries.

When 184 Is Selected for Clear Polycarbonate Glazing Hardcoats

In automotive headlamp lens refurbishment and polycarbonate glazing overcoats, the hardcoat formulation is based on a solvent-borne aliphatic urethane acrylate oligomer, hexanediol diacrylate (HDDA) or isobornyl acrylate (IBOA) as reactive diluent, and 2–3 wt% 184 based on total resin solids. A typical spray-applied composition contains 55–65 wt% oligomer, 30–40 wt% reactive diluent, 0.1–0.3 wt% polyether-modified polydimethylsiloxane flow additive, and 2–3 wt% photoinitiator; the solvent blend of methoxypropanol and butyl acetate is reduced to an application viscosity of 18–22 s DIN cup 4. The coated polycarbonate sheet passes through an infrared flash-off tunnel at 60–70 °C for 3–5 min to prevent solvent popping, then through a medium-pressure mercury arc lamp at 100–120 W/cm and a web speed of 5–8 m/min. Surface tack is assessed qualitatively at line speed, and adhesion is checked per ASTM D3359 using crosshatch tape peel; after thermal stress and 1000 h exposure in ISO 4892-3 fluorescent UV weathering, yellowing index measured by ASTM E313 should not shift more than 2 units on a 5 mm thick polycarbonate plaque. The use of 184 as the sole photoinitiator is restricted to clear topcoats with low UV screening pigments; if a pigment or UV absorber is present above 0.5 wt%, through cure must be supplemented with a longer-wavelength photoinitiator, otherwise surface cure is high but the lower layer remains undercrosslinked. Published data for this specific polycarbonate topcoat configuration are limited regarding long-term UV stabilizer interaction, so migration and crosslink density should be verified by gel fraction measurement on a representative production batch.

Offset Ink Cure Windows and Migration Control

In sheetfed lithographic ink for folding carton and label work, 184 is dissolved into the ink vehicle at 3–5 wt% relative to UV-curable resin and reactive diluent; however in dense black or reflex blue inks, 1.5–2.5 wt% of the same Type I photoinitiator is replaced by an acylphosphine oxide or thioxanthone co-initiator to overcome absorption competition from the pigment. The vehicle comprises a polyester acrylate or epoxidised soy oil acrylate oligomer at 60–75 wt%, trimethylolpropane triacrylate (TMPTA) or di-trimethylolpropane tetraacrylate at 15–25 wt%, and a small amount of amine-modified acrylate as an oxygen-scavenging co-synergist in order to raise surface gloss and reduce ink tack after the second UV lamp. Press runs at 7,000–15,000 sheets/h use lamp outputs in the 160–200 W/cm range and reflector geometries that deliver 400–600 mJ/cm² per station; the low absorbance of 184 at wavelengths above 370 nm makes it necessary to position a gallium-doped or iron-doped lamp after the first mercury lamp when high pigmentation reduces through cure. Residual 184 in printed matter intended for indirect food packaging remains a regulatory variable; compliance under Regulation (EC) No 1935/2004 and Regulation (EU) No 10/2011 must be based on migration testing under the intended time-temperature contact conditions, and conformance with the EuPIA low-migration suitability list alone does not establish legal compliance. Rub resistance per ASTM D5264 and yellowness index per ASTM E313 are routinely measured on the printed stock after 24 h dark storage, and residual acrylate monomer content is monitored by liquid chromatography to remain below the specification set by the brand owner or converter.

Solvent-free UV laminating adhesives for clear PET-PET and PET-PVC film structures are formulated with 184 at 0.5–1.5 wt% on total oligomer/monomer content when optical clarity and absence of yellowing after high-dose irradiation are primary acceptance criteria. In a roll coater running at 30–80 m/min, the adhesive layer is applied at 3–10 g/m² but not exposed to air until after nip lamination to the second film; this closed-film configuration is critical because oxygen inhibition at the adhesive surface otherwise consumes benzoyl radicals and leaves an uncured monolayer at the interface. The resin base is usually an aliphatic urethane diacrylate with a low glass transition temperature, combined with 20–30 wt% monofunctional or difunctional acrylic diluents to obtain a Newtonian coating viscosity of 800–1500 mPa·s at 40 °C. Fusion UV systems using mercury vapor lamps with an H-bulb spectrum are positioned after the laminating nip, and the UV dose is adjusted between 300 and 600 mJ/cm² to reach full peel adhesion; overdosing above 1200 mJ/cm² can lead to post-cure cracking in rigid films and a measurable increase in yellowness index. Adhesion performance is recorded as N/25 mm peel force per ASTM D903 or ISO 11339 and shear strength per ASTM D1002 for rigid bonded coupons. Residues of unreacted 184 and its photolysis by-products in food-packaging laminates must be evaluated by extraction and GC-MS against the applicable migration limit in Regulation (EU) No 10/2011; if the adhesive is used for indirect contact, the converter usually requires the coating supplier to state that the photoinitiator addition does not exceed the formulation-specific threshold validated by migration kinetics testing.

What Limits 184 in 405 nm LED-Cured Stereolithography Resins?

In stereolithography (SLA) and digital light processing (DLP) resins for dental models and rapid tooling, 184 is rarely used as the sole photoinitiator, because its molar absorptivity in the 385–405 nm LED emission band is too weak to generate sufficient radicals at the build layer interface at typical layer exposure times of 1–6 s. A practical DLP formulation uses 1–2 wt% 184 combined with 0.4–0.8 wt% phenylbis(2,4,6-trimethylbenzoyl)phosphine oxide or ethyl (2,4,6-trimethylbenzoyl) phenylphosphinate to extend the absorption envelope to 405 nm; the 184 fraction improves the top-surface cure and reduces tack, while the long-wavelength Type I co-initiator drives the depth of conversion. The base resin is commonly an ethoxylated bisphenol A diacrylate or polyester acrylate with 20–40 wt% methacrylate diluent to reduce brittleness, and the filled mixture is maintained below 1000 cP at 35 °C for DLP recoating speed. To dissolve 184 crystals into the oligomer, the vessel is preheated above 50 °C and mixed under vacuum; storage below its melting range can reseed crystalline material and produce batch-to-batch variation, particularly in formulations with low diluent content. Tensile bars made under these conditions are compared to ASTM D638 Type IV specimens and ISO 527-2 for ultimate tensile strength and elongation at break; impact strength is measured by ASTM D256 notched Izod. A process boundary exists at 40 µm build-layer thickness: if 184 is increased above 2.5 wt% to improve surface cure, overcure and lateral scatter can enlarge the xy dimensional error beyond the intended ±100 µm tolerance, and the printed part may require post-cure at 60 °C under 395 nm LED flood light for 15–30 min to stabilize residual monomer below the specified limit.

In optical fiber draw towers, primary and secondary UV-curable coatings are dispensed onto the freshly drawn glass fiber in a wet-on-wet sequence, and 184 is introduced into the inner primary acrylate coating at 1–2 wt% to provide rapid surface cure before the secondary coating is applied. The draw tower operates with multi-lamp cylindrical quartz irradiators, typically rated at 3–8 kW each and delivering UV-A and UV-B energy in an inert atmosphere with residual oxygen held below 50 ppm; this inerting is mandatory because the outer surface of the primary coating is highly sensitive to oxygen inhibition. The inner primary coating base consists of a low-modulus aliphatic urethane acrylate oligomer with a glass transition temperature below −20 °C, diluted with hydroxyethyl acrylate or isobornyl acrylate to control viscosity in the 2000–6000 cP range at line temperature. The outer secondary coating, by contrast, is usually formulated with a dual photoinitiator package where 184 contributes less than 1 wt% and a long-wavelength photoinitiator such as acylphosphine oxide provides through cure at higher line speeds. Fiber geometry and coating concentricity are tested according to IEC 60793-1-20 or GR-20-CORE methods, and the force required to strip the coating over a 10 mm length is compared with the fiber specification; coating strippability must remain within the supplier-defined acceptance window after thermal aging at 85 °C and 85% RH for 30 days. Because 184 has a melting point near 45–49 °C, cold storage of premixed primary coating can produce crystal seeds that plug fine filtration units, so holding tanks are normally maintained at 40–50 °C with recirculation and 1 µm absolute filtration. Published data on the specific effect of 184 on optical fiber coating delamination are limited, so manufacturers rely on full-scale draw trials and fast gas chromatographic monitoring of residual initiator rather than extrapolating from flat-film testing.

Acrylated urethane conformal coatings for printed circuit board assemblies are formulated with 184 at 2–3.5 wt% on resin solids when the selective coating process includes a UV-cure step followed by a secondary moisture cure for shadow zones under components. The coating is applied by selective spray or needle dispensing at a controlled thickness of 25–75 µm wet film; after a short solvent flash, UV exposure with a 365 nm mercury source is set to 500–1000 mJ/cm² to convert the exposed film to a tack-free state, while hidden areas continue curing through isocyanate or silane condensation over 24–72 h at 25–30 °C and 50–70% RH. The use of 184 as the main initiator in this dual-cure system fixes the UV trigger dose because its α-cleavage reaction is independent of hydrogen-donating amine additives, which could otherwise react with free isocyanate groups and reduce pot life. Adhesion to the solder mask and component surfaces is tested by IPC-TM-650 Method 2.4.1 or crosscut tape adhesion per ISO 2409; electrical insulation resistance is evaluated under IPC-CC-830B conditions after 168 h at 85 °C/85% RH with a 50 V DC bias. The cured coating is also subjected to flammability classification under UL 94 V-0 at the required minimum thickness and to reworkability testing by selective hot-air solder reflow; high retained photoinitiator concentration above the design level can reduce reworkability because thermal decomposition products may leave dark residues on solder lands. The processing boundary for this application is the low absorption of 184 at 395 nm and longer wavelengths: if the coating line is converted from mercury arc to LED cure without reformulation, surface tack after the UV step can fail inspection, especially in high-humidity environments above 60% RH where moisture condensation competes with radical cure.