Kurt Dietliker

Recent developments in photoinitiators

Abstract A new photoinitiator, bis(2,6-dimethoxybenzoyl)-2,4,4-trimethylpentylphosphine oxide (1), has been developed for industrial applications. The absorption of this bisacylphosphine oxide (BAPO) compound in the near UV-Vis range is significantly higher than that of hitherto known photoinitiators for UV curing. Investigation of the photochemistry of 1 revealed the efficient formation of four radicals, which can all initiate polymerization. Since the photoreaction is accompanied by the destruction of the chromophore responsible for absorption in the near UV-Vis, photobleaching of the long wavelength absorption is observed and the photoinitiator does not impart yellowing in the cured lacquer. Studies using FTIR and RTIR techniques showed that these features result in a higher conversion of acrylic double bonds than obtained with other photoinitiators in formulations containing a high loading of rutile type titanium dioxide pigments. These findings were confirmed by application tests in different white pigmented coatings. Further, the new photoinitiator allows the fast curing of thick pigmented layers, which makes it suitable for use in pigmented furniture coating. This new class of high performance photoinitiators is expected to promote the development of UV curable white coatings of high opacity and other applications where light in the near UV-Vis range is essential for curing. A liquid containing 25 parts of the BAPO photoinitiator 1 and 75 parts of 2-hydroxy-2-methyl-l-phenyl-propan-l-one (2) is an excellent technical and economical solution for most applications.