In UV-curable systems, surface-cure photoinitiators govern the curing of the outermost film layer. They directly determine surface drying speed, surface dryness (tack-free finish), and resistance to oxygen inhibition — making them essential for thin-coat applications, printing inks, and overprint varnishes.
This article provides a comprehensive, side-by-side comparison of six dominant surface-cure photoinitiators — 184, 1173, BDK (651), BP, 127, and 2959 — analyzing differences in surface drying performance, application scenarios, and formulation selection strategies.
Photoinitiator | Chemical Type | CAS Number | Appearance | Cleavage Type | Key Characteristic |
light yellow transparent liquid | Liquid form, easy handling, low odor, general-purpose thin coats | ||||
Ultra-low cost, requires amine co-initiator, regulatory restrictions | |||||
1,1'-(Methylene-2,4-phenylene)bis[2-hydroxy-2-methyl-1-propanone] | |||||
Comparison Dimension | ||||||
Chemical Type | α-Hydroxy ketone (Type I) | α-Hydroxy ketone (Type I) | Benzoin ether (Type I) | Benzophenone (Type II) | Macromolecular modified Type I | Low-migration α-hydroxy ketone |
Appearance | Colorless / pale yellow liquid | White crystalline | White crystalline | White crystalline | White powder | White crystalline |
Surface Drying Speed | ★★★★ Very High | ★★★★ High | ★★★ Good | ★★★★ Highest | ★★★ Good | Moderate |
Odor Level | Medium | Low | Low-Medium | Strong, pungent | Near odorless (premium) | Very low |
Yellowing Resistance | Poor | Excellent | Poor | Very Poor | Excellent | Excellent |
Volatility | High | Medium | Medium | High | Very low | Low |
Migration Tendency | Medium | Low | Medium | High | Very low | Very low |
Typical Loading | 1.5% – 3.5% | 1.0% – 3.0% | 2.0% – 5.0% | 3.0% – 6.0% | 1.0% – 2.5% | 1.5% – 3.0% |
Solubility / Compatibility | Excellent (liquid, universal) | Excellent | Excellent | Moderate | Good | Excellent |
Price Tier | Most cost-effective, bulk commodity | Mid-to-high end | Mid-range | Ultra-low cost | Highest price, premium photo-curing material | / |
Curing Wavelength | Short-wave Hg lamp | Short-wave Hg lamp | Short-to-medium wave | Short-wave | Compatible with Hg / some LED | Short-wave |
Surface Drying Mechanism: Type I cleavage photoinitiator. Direct photolysis generates radicals — ultra-fast surface cure with high efficiency and strong resistance to oxygen inhibition. Thin films become tack-free instantly, with no residual stickiness — ideal for high-speed production lines.
Key Trade-off: Excellent cost-performance ratio, but yellowing is irreversible and migration tendency is high. Completely incompatible with LED curing systems. Do not use in light-colored coatings, white paints, or eco-label compliant applications.
Best Suited For: Mercury lamp curing, extremely thin films, cost-driven surface drying.
Surface Drying Mechanism: Excellent surface drying efficiency, second only to BDK. Being the only liquid surface-cure initiator in this group, it offers dust-free direct addition and uniform surface drying. The benchmark for low-odor surface cure.
Key Trade-off: Volatility and migration are relatively high. Weak deep-layer cure — in thick films, the surface may dry while the bottom layer remains under-cured.
Best Suited For: Automated production lines, low-odor applications, general thin-coat formulations.
Surface Drying Mechanism: Stable, balanced surface drying performance. Produces a smooth, defect-free cured surface. Serves as the universal reference standard among surface-cure initiators.
Key Trade-off: Yellowing resistance and general stability outperform BDK and 1173. Surface drying speed is slightly slower than BDK and 1173, but overall compatibility is the broadest.
Best Suited For: The vast majority of conventional surface-cure applications, light-colored thin coats, and volume manufacturing.
Surface Drying Mechanism: Surface drying efficiency comparable to BDK and 1173, with outstanding resistance to oxygen inhibition. Delivers rapid surface cure while maintaining extremely low yellowing.
Key Trade-off: Difunctional molecular structure. After surface curing, the coating exhibits superior yellowing resistance, low odor, and very low migration. Reserved for high-end applications. Unit price is higher.
Best Suited For: Premium white coatings, light-colored surface cure, low-odor systems, and weatherable thin films.
Surface Drying Mechanism: Exclusively designed for waterborne systems. Provides mild, uniform surface drying that solves common waterborne coating defects such as surface bloom and residual tack.
Key Trade-off: The only water-soluble surface-cure initiator in this group. Offers optimal compatibility with waterborne resins. In non-aqueous systems, surface drying performance is unremarkable.
Best Suited For: Waterborne UV coatings and inks, low-migration waterborne surface cure.
Surface Drying Mechanism: Type II hydrogen-abstraction initiator. Requires a tertiary amine co-initiator to function. Used alone, surface drying is slow and highly susceptible to oxygen inhibition. Can only serve as a surface "grab" booster. Cannot be used as the primary surface-cure initiator.
Key Trade-off: Low unit price, but low surface drying efficiency, strong odor, and heavy yellowing. Strictly an auxiliary role.
Best Suited For: Low-cost formulations requiring a secondary boost to surface grab. Must be combined with an amine synergist.
Application Goal | Recommended Choice | Rationale |
Maximum surface drying speed | BDK (651) | Ignore yellowing and eco-concerns — pure speed |
Fast cure + easy handling | 1173 | Liquid addition; balances surface drying with process efficiency |
Balanced performance, no mistakes | 184 | Stable and versatile; fits 90% of conventional surface-cure scenarios |
Low yellowing + premium appearance | 127 | Surface drying and yellowing resistance delivered together |
Waterborne system surface cure | 2959 | No real alternative for waterborne UV |
Cost reduction + auxiliary cure | BP (small addition) | Blend in small amounts; never use as the sole surface-cure initiator |
All six products are surface-cure dominant. Through-cure in thick films is inherently insufficient. For deep-layer curing, you must co-formulate with TPO or 819.
LED curing compatibility is poor across all six surface-cure initiators. For LED systems, co-formulate with a long-wavelength photoinitiator to boost surface drying efficiency.
For light-colored coatings, white paints, or weatherable surface-cure, eliminate BDK and BP outright. For waterborne surface cure, prioritize 2959.
All six products are purpose-built for surface curing in UV systems. The critical differences lie not in the presence or absence of surface drying capability, but in surface drying speed, appearance quality, eco-profile, system compatibility, and overall cost.
It is worth noting that photoinitiators may develop a slight yellowish tint during prolonged storage or if purity drops slightly — this is normal behavior and does not indicate product failure.
Quick Selection Reference:
Maximum speed → BDK
Easiest handling → 1173
Best all-rounder → 184
Premium low-yellowing → 127
Waterborne specialist → 2959
Auxiliary cost-saver → BP
For detailed technical data sheets (TDS), sample requests, or formulation guidance, contact Sinocure Chemical Group today.
