The use of magenta couplers comprising 1-phenyl-3-anilino-pyrazolo-5-one couplers containing phenylthio coupling-off groups at the 4-position are well known in the art. See for example U.S. Pat. No. 4,853,319 of Krishnamurthy et al. and other patents cited therein. While elements employing such couplers have provided certain advantages, there remain several shortcomings in photographic elements relying on these types of magenta couplers.
These shortcomings relate to the dye-forming efficiency of the coupler, the speed with which the dye is formed, the dye hue, and the undesirable occurrence of staining during processing. Compositions disclosed in the mentioned U.S. Pat. No. 4,853,319 contain an ortho carbonamido substituent on the phenylthio coupling-off group of the magenta coupler. It has been found that compounds of this type provide disadvantages in terms of the speed of dye formation and staining.
The dye forming efficiency of the coupler is affected by many factors such as the extent to which the parent portion of the coupler is ballasted so as to retain its proper position in the photographic element in order to optimize the image recorded. If the coupler parent is not sufficiently ballasted, it is free to wander both horizontally and vertically during processing thereby adversely affecting both sharpness and color rendition. Moreover, the coupler is susceptible to being washed out of the element entirely and thus contributing no dye density to the image. Therefore, this problem is-to be avoided.
The dye efficiency can also be affected by the coupling-off group. If the coupling-off group is able to migrate upon release and if it is capable of interfering in the desired chain of reactions that allows the reduction of silver to transform a corresponding amount of coupler to dye, then the coupling-off group can itself cause a reduction in dye formation efficiency.
The speed with which the dye is formed can present added problems. When a coupler undergoes coupling with a color developer to form a dye, the coupler goes through an intermediate stage wherein the oxidized developer and the coupling-off group are both annexed to the coupler parent. This intermediate is a leuco dye which is uncolored until the coupling reaction is complete. In the ideal photographic element, the intermediate stage is essentially instantaneous so that the process of dye formation is completed during development. The presence of the semi-stable leuco dye can effectively reduce dye density and adversely affect color rendition in the printing step. Moreover the presence of the semi-stable leuco dye can lead to post processing density increases the extent of which cannot be predicted and this leads to the undesirable situation of having an image which changes with time. Thus, the formation of semi-stable leuco dyes needs to be avoided.
Of further concern is the hue of the dye obtained upon completion of the coupling reaction. This property is important because it affects the accuracy of color rendition and also impacts the printer's ability to produce an accurate print from the negative. The hue of the dye is a function of the compositional make-up of both the parent and the coupling-off group. Both the individual substituents and the combined effect of the different substituents selected can affect the hue. The parent substituents affect hue primarily through their affect on the chromophore of the dye while the coupling-off group substituents have a more indirect effect by influencing the local environment of the dye, particularly when the coupled-off group is not free to diffuse away from the hydrophobic oil droplet.
Finally, staining or nonimagewise coloration of the element is to be avoided. One way that staining can occur is through the phenomenon called continued coupling. Certain couplers are more prone than others to react with oxidized developer that is carried over with the film into the bleach bath. These couplers will thus form dye on a non-imagewise basis causing a magenta stain.
While various efforts have been made to provide improved couplers, none have succeeded in solving the foregoing problems.
U.S. Pat. Nos. 4,555,479; 4,463,085; 4,483,918; and 4,904,579, all deal with the suggestion of various additives to elements containing 1-phenyl-3-anilino-pyrazolo-5-one couplers containing phenylthio or other types of coupling-off groups at the 4-position in order to improve sensitivity, stability etc. The materials exemplified therein do not provide the desired properties such as diffusion resistance of both the parent and coupling-off group. U.K. Patent 1,494,777 suggests couplers having improved properties such as high dye yield without formation of undesirable fog and stain. The couplers therein are unsatisfactory since the formed dyes are either not sufficiently ballasted to prevent washout during processing or do not exhibit the improvements specified herein.
U.S. Pat. No. 4,952,487 relates to the use of alkylphenol coupler solvents for hue improvement and suggests certain elements containing 1-phenyl-3-anilino-pyrazolo-5-one couplers containing phenylthio or other types of coupling-off groups at the 4-position. These couplers do not, however, solve the problems mentioned since efficiency is adversely affected by the coupling-off groups present.
It is therefore a problem to be solved to provide photographic elements containing a magenta coupler which does not present problems associated with the dye-forming efficiency of the coupler, the speed with which the dye is formed, the dye hue, and the undesirable occurrence of staining during processing.