Introduction
Photoinitiator 1173 (chemical name: 2-Hydroxy-2-methyl-1-phenyl-1-propanone, CAS No. 7473-98-5) is one of the most widely used Type I radical photoinitiators in the UV curing industry. As a colorless to pale yellow transparent liquid, 1173 plays an important role in wood coatings, plastic varnishes, printing inks, and adhesives due to its efficient initiation performance and excellent yellowing resistance. This article provides a comprehensive overview of this classic photoinitiator, covering its product characteristics, application areas, and usage recommendations.
Product Characteristics
Physical Properties and Solubility
1173 is liquid at room temperature with a boiling point of 102–103°C (0.53kPa) and a molecular weight of 164.20. Its low-viscosity liquid form allows for easy dispersion in formulations without heating, enabling uniform mixing with acrylates, toluene, polyester, and other resin systems-significantly simplifying the production process. Product purity is typically ≥99%, and light transmittance at 425nm can reach ≥98%, ensuring high transparency of the cured coating.
Photoinitiation Performance
As a Norrish Type I cleavable photoinitiator, 1173 rapidly decomposes upon UV irradiation to generate benzoyl radicals and α-hydroxyalkyl radicals, both of which effectively initiate the polymerization of acrylate monomers and oligomers. Its UV absorption wavelengths cover 244nm, 278nm, and around 330nm, matching well with the spectral output of medium-pressure mercury lamps. Studies indicate that adding 5% 1173 in resin systems achieves optimal photocuring rates.
Key Advantages
Non-yellowing: 1173 produces almost no colored residues after photolysis, making it particularly suitable for transparent coatings and light-colored systems with strict color stability requirements.
Storage Stability: When sealed and stored in a cool, dry place, the product remains effective for up to 12 months, demonstrating good thermal and chemical stability.
Compatibility: It can be used in combination with other photoinitiators such as TPO and 184 to meet different curing needs.
Main Application Areas
1. UV Coatings
1173 is commonly used in wood varnishes, plastic coatings, metal finishing coats, and paper overprint varnishes. In transparent coating systems, it achieves a balance between fast surface curing and deep curing, imparting good gloss, surface hardness, and weather resistance to the coating. The recommended dosage is 1.0%–5.0% of the total formulation, depending on coating thickness and resin system.
2. UV Inks
In the printing ink sector, 1173 is frequently used in overprint varnishes, screen printing inks, and gravure inks. Its high initiation efficiency meets the instant curing requirements of high-speed printing lines, reducing the risk of blocking during stacking. For white or light-colored ink systems, 1173 typically needs to be combined with long-wavelength photoinitiators (such as TPO) to overcome the shielding effect of pigments.
3. Adhesives and Electronic Materials
1173 also performs well in UV-curable adhesives, suitable for applications such as ABS plastic bonding, electronic component fixing, and photoresist dry films. For example, in epoxy acrylate UV adhesives for ABS bonding, the addition amount of 1173 is usually 3–7 parts, combined with appropriate reactive diluents and leveling agents to achieve good bonding strength and surface drying performance.
4. Other Applications
Additionally, 1173 can be used in unsaturated polyester systems, water-based UV resin systems, and precision manufacturing of optical-grade materials. In PCB solder masks and electronic product coatings, it enhances coating adhesion and double bond conversion rate.
Usage Recommendations and Precautions
Formulation Design
Recommended Dosage: In conventional systems, 1%–4% (by weight) is recommended; for thicker coatings or demanding applications, it can be appropriately increased to 5%.
Combination Suggestions: In pigmented systems or thick coatings, it is advisable to combine with long-wavelength photoinitiators (such as TPO, 819) to ensure deep curing effectiveness.
Oxygen Inhibition: During thin film curing, attention should be paid to the inhibition of surface curing by oxygen. This can be improved by increasing light intensity or adding anti-oxidants to enhance surface drying.
Limitations
Odor Issues: The photolysis products of 1173 may generate trace amounts of formaldehyde and acetone. In applications sensitive to odor, such as food packaging, careful consideration is needed, or low-migration polymeric derivatives may be preferred.
Migration: As a small molecule photoinitiator, small amounts of residual extractable substances may remain in the cured film. High conversion rates effectively reduce residual levels.
Storage and Handling
1173 should be stored in a cool, ventilated warehouse, away from fire and heat sources, and kept separate from oxidizers. Standard packaging includes 20kg or 200kg plastic drums. Once opened, it should be used promptly and containers kept sealed.
Technical Specifications Summary
| Parameter | Specification |
|---|---|
| Appearance | Colorless to pale yellow transparent liquid |
| Assay | ≥99.0% |
| Absorption Wavelengths | 244nm, 278nm, 330nm |
| Volatile Content | ≤0.5% |
| Ash Content | ≤0.1% |
| Transmittance (425nm) | ≥98.0% |
| Recommended Dosage | 1.0%–5.0% |
Data sources: [Insert references/supplier data sheets as appropriate]
Conclusion
Photoinitiator 1173, with its excellent non-yellowing properties, good solubility, and stable initiation efficiency, has become an indispensable basic material in the UV curing field. Whether used in transparent varnishes, printing inks, or precision adhesives, 1173 provides reliable and economical curing solutions. With the increasing adoption of UV-LED light sources and water-based UV systems, the combined applications of 1173 continue to expand, and it will continue to play an important role in environmentally friendly photocurable materials in the future.