Photocurable Compositions Containing Photobleachable Ionic Dye Complexes

The aforementioned related application, which corresponds to European Application Publication No. 0233587, relates to photocurable compositions containing ionic dye complexes as photoinitiators. These complexes are characterized in that they directly or indirectly yield free radicals upon exposure to actinic radiation and particularly visible light.

By nature, compositions which are sensitive to visible light appear colored to the human eye. There are applications in which it would be desirable to use the compositions which can be cured upon exposure to visible light but for the colored appearance of these compositions. For example, in laminating glass, if the composition is colored it imparts a tint to the glass which may be undesirable. Similarly, a visible initiator would be advantageous in coating optical fibers but for its colored appearance. In these applications, photobleachable ionic dye complexes would be particularly useful. In some of the compositions disclosed in the related application, the dye has been observed to be photobleachable.

The present invention particularly relates to visible light sensitive photocurable compositions containing a photobleachable ionic dye complex as an initiator.

Another manifestation of the present invention is a process for coating a substrate with a visible light curable composition wherein the process is characterized in that the composition contains a photobleachable ionic dye complex as a photoinitiator.

The compositions and process of the present invention are useful in applications in which essentially colorless (e.g., clear, transparent or white) radiation cured coatings are desired. Typical examples of such applications are in laminating glass, coating optical fibers or in coating compositions containing white pigments such as titanium dioxide.

The ionic dye complexes used in the present invention are generally described in U.S. Pat. No. 4,772,530. Xanthane dye complexes are more particularly described in commonly assigned U.S. application Ser. No. 057,544, filed June 3, 1987.

The ionic dye complexes used in the present invention are characterized in that they are photobleachable.

The polymerizable or crosslinkable materials described in the aforementioned applications are useful herein. The photoinitiator systems described in the aforementioned applications are also useful herein with the requirement that the ionic dye-counter ion compounds be photobleachable. Of the dye complexes disclosed in U.S. application Ser. No. 944,305 corresponding to European Application Publication No. 0233587, all of the cyanine dye complexes are photobleachable with varying efficiency and speed. Some of the more efficient photobleachable complexes are: ##STR1## The azine dye complex of Methylene Blue and triphenylbutylborate is one of the most efficient complexes in terms of photobleachability. Its structure is ##STR2## Rose Bengal-onium dye complexes are also photobleachable. Of these complexes of Rose Bengal and its benzylester with diphenyliodonium ions (including di(4-t-butylphenyl)iodonium ions) are photobleachable with high efficiency.

Herein, the photobleachable dye complexes may bleach upon exposure to visible light upon curing the compositions, or they may be bleached upon post-exposure to a bleaching radiation such as ultraviolet radiation.

Having described the invention in detail and by reference to preferred embodiments thereof, it will be apparent that modifications and variations are possible without departing from the scope of the invention defined in the appended claims.