RECENT DEVELOPMENTS IN PHOTOINITIATORS

A new photoinitiator, 6-dimethoxybenzoyl)-2,4,4-trimethylpentylphosphi ne oxide (1), has been developed for industrial applications. The abso rption of this bisacylphosphine oxide (BAPO) compound in the near UV-V is range is significantly higher than that of hitherto known photoinit iators for UV curing. Investigation of the photochemistry of 1 reveale d the efficient formation of four radicals, which can all initiate pol ymerization. Since the photoreaction is accompanied by the destruction of the chromophore responsible for absorption in the near W-Vis, phot obleaching of the long wavelength absorption is observed and the photo initiator does not impart yellowing in the cured lacquer. Studies usin g FTIR and RTIR techniques showed that these features result in a high er conversion of acrylic double bonds than obtained with other photoin itiators in formulations containing a high loading of rutile type tita nium dioxide pigments. These findings were confirmed by application te sts in different white pigmented coatings. Further, the new photoiniti ator allows the fast curing of thick pigmented layers, which makes it suitable for use in pigmented furniture coating. This new class of hig h performance photoinitiators is expected to promote the development o f UV curable white coatings of high opacity and other applications whe re light in the near W-Vis range is essential for curing. A liquid con taining 25 parts of the BAPO photoinitiator 1 and 75 parts of 2-hydrox y-2-methyl-1-phenyl-propan-1-one (2) is an excellent technical and eco nomical solution for most applications. [GRAPHICS] rough coatings appl ied to a substrate is valuable for interpreting corrosion, blistering and delamination of organic coating systems, and for developing models for use in predicting the service lives of protective coatings.