In the rapidly evolving world of UV-curing technology, Photoinitiator 907 stands out as a high-performance Type I α-amino ketone photoinitiator. Renowned for its exceptional deep-curing capability and remarkable oxygen inhibition resistance, it has become an indispensable component in demanding industrial coatings and advanced electronic chemicals. This comprehensive guide explores its properties, technical advantages, synergistic combinations, and practical application tips.
Product Snapshot
Photoinitiator 907 (also known as Irgacure 907, Omnirad 907, or by its chemical name 2-methyl-1-[4-(methylthio)phenyl]-2-morpholinopropan-1-one, CAS 71868-10-5) is a white to off-white crystalline powder with the molecular formula C₁₅H₂₁NO₂S and a molecular weight of 279.4.
| Parameter | Specification | Typical Value |
|---|---|---|
| Appearance | White to off-white crystalline powder | Conforms |
| Assay | ≥ 99.0% | 99.21% (GC) |
| Melting Point | 72.0 – 75.0°C | 72.8 – 73.5°C |
| Ash Content | ≤ 0.10% | 0.05% |
| Volatiles | ≤ 0.2% | 0.11% |
| Absorption Maxima | 230 nm, 303–325 nm (in methanol) | – |
| Transmittance (425 nm) | ≥ 40% (or ≥ 90% in certain solvents) | Solvent dependent |
| Solubility | Easily soluble in organic solvents and acrylate monomers | Soluble in acetone, toluene, acrylates at 20°C |
Storage: Keep in a cool, well-ventilated warehouse, away from oxidizers and ignition sources. Keep container tightly closed.
Packaging: Typically 20 kg cartons; custom packaging available upon request.
Three Core Technical Advantages
1. Deep Penetration & Through-Cure in Pigmented Systems
As a Type I (cleavage-type) photoinitiator, 907 undergoes Norrish Type I cleavage upon UV exposure, generating highly reactive free radicals without the need for a co-initiator (amine synergist). Its absorption extends into the longer UV range (peaks at ~330–385 nm with tailing), allowing UV light to penetrate through heavily pigmented layers. This makes it the go-to choice for high-opacity systems such as white, black, or metallic inks, ensuring complete bottom cure and excellent adhesion – solving the common problem of tacky surfaces in colored formulations.
2. Superior Chemical Resistance & High Resolution for Electronics
The morpholine radical generated during photolysis contributes to the formation of a densely crosslinked polymer network. This feature provides exceptional resistance to chemical etching (acids, alkalis, nickel/gold plating baths) and maintains sharp edge definition, making 907 the preferred photoinitiator for PCB solder masks (green oil) and dry-film photoresists in the electronics industry. It meets the stringent requirements of high-resolution imaging and reliability in subsequent manufacturing processes.
3. Synergy with Thioxanthone Sensitizers (ITX, DETX)
907 is frequently combined with thioxanthone photosensitizers like ITX (Isopropylthioxanthone) or DETX (Diethylthioxanthone) to achieve remarkable synergistic effects. Thioxanthones absorb strongly in the long-wave UV/visible region (380–420 nm), where 907 itself has weak absorption. Upon excitation, ITX transfers energy to ground-state 907 via an energy transfer mechanism, enabling 907 to generate free radicals. This not only broadens the spectral response of the formulation but also enhances photospeed and overcomes oxygen inhibition, significantly boosting overall curing efficiency.
Recommended Formulations & Dosage Guidelines
Based on industry practice and technical data from major suppliers like IGM Resins (Omnirad 907), here are typical addition levels for various applications:
| Application | Recommended Addition | Synergist Suggestions |
|---|---|---|
| Offset Inks | 4.0 – 6.0% | Can be used alone or with ITX/DETX |
| Screen Inks | 2.0 – 4.0% | + 0.2 – 0.5% ITX or DETX |
| Clear Coatings | 0.1 – 1.0% | + 2.0 – 3.0% of a Type II initiator like 184 (for surface cure) |
| Photoresists / Solder Masks | 3.0 – 6.0% | Often combined with ITX/DETX |
Formulation Tips:
High-pigment systems (white, black, metallic): Use higher end of dosage (4–6%) and pair with ITX/DETX for optimal through-cure.
Balance surface & through-cure: In clear coats, combine with a surface-curing photoinitiator like 184 to ensure tack-free surfaces while maintaining depth cure.
LED compatibility: 907 shows moderate compatibility with LED curing (rated 3 by IGM), suitable for hybrid mercury/LED systems.
Key Application Areas
1. High-Pigment UV Inks
UV offset and screen inks: Ensures complete cure beneath opaque pigments, enhancing adhesion and rub resistance on substrates like paper, metal, and plastics.
Metallic and white inks: Penetrates through reflective or high-load pigment layers.
2. Electronic Chemicals
PCB solder masks (green oil): Delivers the chemical resistance needed for PCB fabrication (resistance to etching, plating, and soldering processes).
Dry-film photoresists: Provides high sensitivity for fast exposure and high resolution for fine-line circuitry.
3. Industrial Coatings
Wood, plastic, and metal coatings: Suitable for both pigmented and clear systems, offering reliable curing performance.
Overprint varnishes: Enhances gloss and scratch resistance.