In this article, we will briefly describe the structure and characteristics of various photoinitiators in the category of pyrolysis photoinitiators.
4. -Hydroxyalkylbenzone.
Hydroxyalkylbenzone photoinitiators generally have high photoinitiation activity and are representative of successful application development. Here are the main structures:
2-Hydroxy-2-methyl-1-phenyl-1 acetone (HMPP), trade name Darocur1173. It is a colorless liquid or yellowish, with a maximum absorption wavelength of 331nm, which is widely used in the domestic light-curing industry.
1-Hydroxy-cyclohexylbenzone (HCPK), trade name Irgacure184. This is a colorless powdery crystal, with a melting point of 45 49 and a maximum absorption wavelength of 333nm, which also has high photoinitiation activity and is also commonly used in China.
Both are favored for their excellent photoinitiation performance, good thermal stability, and other comprehensive properties. In addition, photolysis in the acrylic ester system does not produce free radicals that are easy to cause yellowing.
Compared with benzenyl ethers, DMPA, DEAP and acylphosphine oxides, -hydroxyalkylbenzone has a longer excitation triplet life and is easily quenched by monomers such as styrene, so its photoinitiation efficiency may be inferior to that of traditional photoinitiators in unsaturated polyester and styrene systems.
V. - Aminoalkyl benzone.
Amethylbenzone is a newer class of highly reactive photoinitiators, usually with strong electron-pushing groups in the para-position of the benzene ring, such as methylmercaptol or morpholino. Notable representatives include:
2-Methyl-1-(4-methylmercaptophenyl)-2-morpholino-1-propanone (MMMP, trade name Irgacure907, maximum absorption wavelength 307 nm).
2-Phenyl-2-dimethylamino-1-(4-morpholinophenyl)-1-butanone (BDMP, trading name Irgacure369, maximum absorption wavelength 324 nm).
Although their photochemical kinetic parameters may not always be favorable for initiation activity, they remain highly efficient in most light-curing systems. In most cases, the maximum absorption wavelength and absorbance are increased. It is often used in combination with thiasanthone photosensitizer to enhance light absorption. It is particularly excellent in pigment coloring systems, and is also a recommended photoinitiator for high value-added light-curing ink formulations.
6. Acylphosphine oxide.
Aryl phosphine oxide and aryl phosphonate can be regarded as photoinitiators with high activity and good comprehensive performance, especially suitable for systems with poor light transmittance, such as pigment coloring systems and lamination compounds. They have a longer absorption wavelength of 350 380 nm, and the absorption wavelength blue shift of photolysate products has a photobleaching effect and is suitable for thick coating curing. Note that these photoinitiators are sensitive to sunlight or short-wave visible light and should be stored and transported away from light.
For example, bisbenzoylphenylphosphine oxide (BAPo1, formerly known as CIBA Irgacure 819) is a highly effective new photoinitiator. It is a yellow powder, with a melting point of about 130 and a maximum absorption wavelength of 405nm, which is often used in combination with other initiators, and the actual dosage is low. In order to improve the compatibility of BAPo1 in resin, a long-chain alkyl group can be introduced into the phosphorus atom of its phosphine oxide to prepare BAPo2, which reduces the melting point and greatly improves the compatibility.