Stabilization of thermal images
AssigneePolaroid Corporation
InventorsRita S. Shon Baker, Larry C. Takiff
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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 quinone or hydroquinone 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:
- ##STR13## and forming after its change in color a dye compound of the formula:
- ##STR14## 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 quinone or hydroquinone.
A process for forming an image, the process comprising:
- providing a thermal imaging medium having at one imaging layer, the imaging layer comprising a binder and a color-forming compound of the formula:
- ##STR16## and a quinone or hydroquinone;
- 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:
- ##STR17## 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:
- ##STR19## and the colored areas of the image comprising a binder and a dye compound of the formula:
- ##STR20## 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 quinone or hydroquinone.
Dependencies are inferred from the claim text.