Coating industry:
I、Terms and definitions photoinitiator (photoinitiator), according to GB/T 41764-2022 ‘Determination of the content of photoinitiators in radiation-curing coatings Gas Chromatography-Mass Spectrometry Method’ in 3.1 described as: a substance that can absorb radiant energy, and undergoes chemical changes by excitation, generating reactive intermediates (free radicals or cations) with the ability to initiate polymerisation.
II、Relevant standards GB/T 41764-2022 ‘Determination of photoinitiator content in radiation curing coatings Gas Chromatography-Mass Spectrometry’ HG/T 5778-2020 ‘Ultraviolet (UV) curing coatings for cosmetic packaging materials’ SN/T 4317-2015 ‘Detection of migration of 7 photoinitiators in exported food Liquid Chromatography-Mass Spectrometry/Mass Spectrometry’.
IV、The mechanism and classification of photoinitiators in the direct or indirect absorption of light energy, the initiator molecules from the base state jumped to the excited single-linear state, through the inter-systems scurry jump to the excited three-linear state. In the excited unilinear state or trilinear state after a single molecule or bimolecular chemical action, the production of monomer polymerisation can be triggered by the active fragments (free radicals, cations, anions, etc.), thus triggering monomer polymerisation crosslinking curing. There are many types of photoinitiators. According to the different triggering mechanisms, photoinitiators can be divided into cationic photoinitiators and free radical photoinitiators, of which free radical photoinitiators have the widest range of applications.
4. Several mainstream photoinitiators and their application areas
907 and ITX or DETX photoinitiators used in conjunction with the coloured system, the main application areas for home decoration, etc.; 1173 and TPO with better curing effect, the main application areas for furniture and wood varnish, floor coatings, home decorations, The main application areas are: furniture wood varnish, floor coating, 3C electronic coating, automobile interior, home decoration, plastic products, etc. 184 can be used with TPO and other low-yellowing photoinitiators in the white system, mainly used in: furniture wood varnish, floor coating, 3C electronic coating, automobile interior, home decoration, plastic products, etc.
1. 184
The maximum absorption wavelength is 333 nm, mainly used to initiate the rapid curing of acrylate and methacrylate systems, reference dosage of 2% to 4%, curing time of 190 s and 140 s, respectively.
Alias: 1-Hydroxycyclohexyl phenyl ketone
English name: 1-Hydroxycyclohexyl phenyl ketone
CAS No.: 947-19-3
Appearance: White or off-white crystal
Transmittance: 425nm≥98.0%, 500nm≥99.0% (1g/10mL toluene)
Absorption peak: 246nm, 280nm, 333nm (in methanol solution)
Solubility: 20℃ (g/100g solution)
2. 907
907 can be in the ink curing process, the absorption of UV radiation energy and the formation of free radicals or cations, triggering the monomer and oligomer polymerisation, crosslinking and grafting reactions, in a very short period of time to make the ink curing into a three-dimensional mesh structure of polymers.
Alias: 2-methyl-1-(4-methylthiophenyl)-2-morpholinyl-1-propanone
CAS No.: 71868-10-5
Appearance: White crystalline powder
Transmittance: 425nm≥90.0%, 500nm≥95.0% (1g/10mL toluene)
Absorption peak: 230nm, 304nm (in methanol solution)
Solubility: 20℃ (g/100g solution)
V、The development trend of photoinitiators photoinitiators in addition to meeting environmental requirements such as some standards (such as food-grade coatings) on the residue of photoinitiators have strict limits, in terms of performance need to have a high molar extinction coefficient, low toxicity, good solubility and other characteristics, and spectral match with the light source.
With the improvement of public safety awareness, the safety of food and drug packaging is more and more important, such as Europe on food and drug packaging ink developed strict. Globally, macromolecule photoinitiators will be more and more used in packaging inks due to their advantages of low toxicity and low migration, so the development of more types of macromolecule photoinitiators is the development trend of the industry’s products.
Formulated products consisting of cationic photoinitiators and supporting resins and monomers have the advantages of anti-oxidation and polymerisation blocking, low shrinkage of the system, which can complement the free radical curing system. The future application of cationic curing products or mixed use with free radical curing products have development prospects, so the cationic photoinitiator is also one of the product and technology development direction.