Compositions which produce a color change upon exposure to light or heat are of great interest in producing images on a variety of substrates. Optical disks represent a significant percentage of the market for data storage of software as well as of photographic, video, and/or audio data. Typically, optical disks have data patterns embedded thereon that can be read from and/or written to one side of the disk, and a graphic display printed on the other side of the disk.
In order to identify the contents of the optical disk, printed patterns or graphic display information can be provided on the non-data side of the disk. The patterns or graphic display can be both decorative and provide pertinent information about the data content of the disk. In the past, commercial labeling has been routinely accomplished using screen-printing methods. While this method can provide a wide variety of label content, it tends to cost ineffective for production of less than about 400 customized disks because of the fixed costs associated with preparing a stencil or combination of stencils and printing the desired pattern or graphic display.
In recent years, the significant increase in the use of optical disks for data storage by consumers has increased the demand to provide customized labels to reflect the content of the optical disk. Most consumer available methods of labeling are limited to either handwritten descriptions which lack professional appearance, quality and variety, or peripheral labels which may be affixed to the disk, but which can also adversely affect the disk performance upon spinning at high speeds.
In accordance with the present invention, a variety of leuco dye-containing compositions have been investigated for use on optical disks and other substrates. Leuco dye compositions thus far investigated often include a leuco dye along with an optional activator and an infrared absorber. However, many of these compositions are insufficiently stable under light exposure, and are not durable enough for practical use. Over a period of a short time, exposure to sunlight or fluorescent lights can reduce activity and absorbance of the infrared absorbers, thus reducing the quality of leuco dye development. Further, the leuco dye and/or other components have a tendency to cause browning during exposure to ambient light sources and/or UV light used during curing steps. For this and other reasons, the need still exists for leuco dye compositions which have improved stability, and which have improved image forming and developing characteristics.