Dye image

For two-equivalent couplers where the conversion of the leuco dye to image dye is rapid, the experimentally observed second-order rate constant, k, can be equated with kj, the rate of nucleophilic attack of coupler anion on oxidized developer. Thus when the pH of the process is specified, two parameters, piC and k, can be convenientiy used to characterize the molecular reactivity of a large variety of photographically weU-behaved couplers (40,54). 

Although most DIR couplers are based on image dye-forming parents, universal DIR couplers have appeared in the Hterature. These materials react with oxidized developer to produce the inhibitor (or precursor) and either a colorless dye, an unstable dye, or a washout dye (100). Universal DIR couplers could be used in any layer with a need to match only image-modifying properties, not hue, to the given layer. 

Additional Chromophores. Other types of dyes that have been studied as chromophores in dye developers include rhodamine dyes, azamethine dyes, indophenol dyes, and naphthazarin dyes (21). Cyanine dyes, although not generally stable enough for use as image dyes, have also been incorporated in dye developers (31). 

A second approach utilizes the oxidation of alow mobiUty substituted 4-hydroxydiphenylamine to which an image dye is linked through a sulfonamide group. Oxidation and hydrolysis result in ting closure and release of the alkaU-soluble dye (eq. 2). 

Fig. 14. Schematic cross section of Spectra integral film. The 600 Plus film has a similar stmcture. In these films the yellow image is formed by silver-assisted cleavage of a yellow dye releaser. A colorless developer reduces exposed silver hahde in the blue-sensitive emulsion in unexposed areas dissolved silver diffuses to the dye releaser layer and triggers the release of the yellow image dye.

Stabilization image dyes photography, 6,112 silver halides photography, 6, 102 Stabilizers... 

Positive displacement pumps, 21 54-56 cavitation damage to, 21 86 types of, 21 70-74 Positive image dye-release system,... 

Subtractive hybridization, 73 354 Subtractive image dyes, 79 262 Subtractive instant color films, 79 296 Subtractive mixing, in color photography, 79 241-245... 

The required features of the image dyes for the successful operation of the process are appropriate hues and good stability to light, heat and moisture. Also, the dyes must not migrate from the layers in which they are formed. 

Certain dyes derived from somep-phenylenediamines satisfy the requirements of practical image dyes. For example, the developer of Scheme 5 gives yellow and magenta azamethine dyes, respectively, with benzoylacetanilides and 2-pyrazolin-5-ones as couplers, and cyan indoaniline dyes result from phenols and naphthols. 

Specific substituents with the p -phenylenediamine structure can influence the performance of the developing agent in several important ways. Thus, fine control of the solubility of the agent in the alkaline medium, rate of development of silver, rate of dye formation and the hue of the ultimate image dye can be achieved. 

Generally, the couplers should form the image dyes reasonably quickly and yield dyes with the desired characteristics. 

The naphthol (60) is a representative of a class of compounds termed development inhibitor release couplers. Phenylmercaptotetrazole is released from this coupler during dye formation. The thiol can then inhibit development within the layer in which it is formed thereby causing a beneficial effect which is displayed in the form of a sharper image. Where the thiol wanders into an adjacent layer and causes inhibition of development some correction for the unwanted absorption of the image dye can be achieved (69MI11401). 

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