Stabilization of thermal images
AssigneePolaroid Corporation
InventorsRong C. Liang, William C. Schwarzel, Rita S. Shon Baker, Robert P. Short, Stephen R. Sofen, Michael A. Young
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Abstract
The addition, to a thermal imaging medium comprising a color-forming compound which undergoes a change of color upon heating above a color-forming temperature for a color-forming time, the color-forming compound being of the cyclic sulfonamide type described in U.S. Pat. Nos. 4,720,449 and 4,960,901, of a source of zinc, nickel, copper(II), cobalt(II) or aluminum(III) cations increases the sensitivity of the imaging medium and helps to prevent fading of images produced therefrom while the images are being projected.
Claims36
A thermal imaging medium comprising at least one imaging layer, the imaging layer comprising a binder and a color-forming compound which undergoes a change of color upon heating above a color-forming temperature for a color-forming time, the color-forming compound being of the formula:
- ##STR15## and forming after its change in color a dye compound of the formula:
- ##STR16## in which formulae:
- rings A and B are aromatic nuclei;
- Z and Z', which may be linked other than via the meso carbon atom, represent the moieties sufficient to complete the auxochromophoric system of a diarylmethane or a triarylmethane dye in the dye compound, Z and Z' being such that the dye compound has absorption in the visible region;
- L is a leaving group which is removed on heating;
- and
- the broken line between the SO.sub.2 group and ring B denotes that the sulfonamide ring in the color-forming compound may be 5- or 6-membered,
- the imaging layer further comprising a source of zinc, nickel, copper(II), cobalt(II) or aluminum(III) cations.
A process for forming an image, the process comprising:
- providing a thermal imaging medium having at least one imaging layer, the imaging layer comprising a binder and a color-forming compound of the formula:
- ##STR18## and a source of zinc, nickel, copper(II), cobalt(II) or aluminum(III) cations;
- imagewise heating the imaging layer above a color-forming temperature for a color-forming time, thereby causing, in heated regions of the image, at least part of the color-forming compound to be converted to a dye compound of the formula:
- ##STR19## in which formulae:
- rings A and B are aromatic nuclei;
- Z and Z', which may be linked other than via the intervening carbon atom, represent the moieties sufficient to complete the auxochromophoric system of a diarylmethane or a triarylmethane dye in the dye compound, Z and Z' being such that the dye compound has absorption in the visible region;
- L is a leaving group which is removed on heating;
- and
- the broken line between the SO.sub.2 group and ring B denotes that the sulfonamide ring in the color-forming compound may be 5- or 6-membered,
- thereby forming an image.
An imaged medium having imagewise colored and substantially uncolored areas, the substantially uncolored areas of the image comprising a binder and a color-forming compound which undergoes a change of color upon heating above a color-forming temperature for a color-forming time, the color-forming compound being of the formula:
- ##STR21## and the colored areas of the image comprising a binder and a dye compound of the formula:
- ##STR22## in which formulae:
- rings A and B are aromatic nuclei;
- Z and Z', which may be linked other than via the intervening carbon atom, represent the moieties sufficient to complete the auxochromophoric system of a diarylmethane or a triarylmethane dye, Z and Z' being such that the dye compound has absorption in the visible region;
- L is a leaving group which is removed on heating;
- and
- the broken line between the SO.sub.2 group and ring B denotes that the sulfonamide ring in the color-forming compound may be 5- or 6-membered,
- the colored and substantially uncolored areas further comprising a source of zinc, nickel, copper(II), cobalt(II) or aluminum(III) cations.
Dependencies are inferred from the claim text.