| 摘要 |
<p>This invention relates to leuco dyes, and more particularly, to stabilized leuco phenazine dyes. These dyes are suitable for use in thermographic imaging systems wherein the leuco dye is in composition containing a nitrate salt. <??>Although acylated (benzoylated) leuco azine dyes exhibit improved stability compared with the hydrogen leuco form thereof, and acylated (benzoylated) leuco forms of phenoxazines and phenothiazines often show extremely good stability, benzoylated leuco phenazine dyes are still far too unstable to be useful for most types of thermally imageable compositions. <??>This invention provides 3,7-diamino phenazine leuco dyes with acyl substituents in the 10-position, said substituents being themselves substituted with electron-withdrawing groups. Incorporation of electron-withdrawing groups on the acyl substituent at the 10-position of the leuco dye results in a dramatic improvement in the thermal and light stability of the leuco form, and, generally, the stronger the electron-withdrawing character of the electron-withdrawing substituent, the more stable is the leuco form. The dyes cover a wide range of colors when oxidized, including reds, yellows, and magentas, and they are readily capable of being incorporated into thermographic and photothermographic imaging systems. </p> |
