The present invention relates to novel radiation-curable ink and coating compositions, and more particularly, to radiation-curable ink and coating compositions containing an ionic dye-reactive counter ion complex as a photoinitiator.
Radiation-curable ink compositions are widely used. Compared to solvent-based ink compositions, radiation-curable ink compositions are advantageous because toxicological and environmental concerns are avoided. U.S. Pat. Nos. 3,661,614; 4,003,868; and 4,215,167, teach ultraviolet-curable ink compositions. These compositions comprise a polymerizable material such as a monomer, an initiator system, and a pigment or a dye.
While the most common examples of radiation curable inks are sensitive to ultraviolet radiation or blue light, compositions which are sensitive to longer wavelengths of visible light such as longer wavelength blue, red or green light would be desirable. Ultraviolet-sensitive photoinitiators often are suitable for cyan and magenta ink compositions because cyan and magenta pigments absorb little near ultraviolet or blue light. However, ultraviolet-sensitive photoinitiators are generally undesirable for yellow compositions because yellow pigments and dyes absorb strongly in the near ultraviolet-blue region. As such, yellow ultraviolet-curable ink compositions cure more slowly or require higher intensity radiation than cyan or magenta ultraviolet-curable ink compositions. Inks with a large yellow components, such as brown, black, green, or red also cure more slowly.
In addition to inks, there are other applications in which radiation curable compositions containing a colorant are useful. In particular, in coating paper, paperboard, and other sheet materials, such compositions are useful. They are also useful in printing simulated wood coatings.