In recent years the increase in consumption of silver halide photographic materials has led to a strong request for a reduction of the processing times.
A reduction in the exposure dose and, at the same time a reduction of the processing time for silver halide medical imaging elements have been strongly demanded in medical circles.
Tabular silver halide grains are crystals possessing two major faces that are substantially parallel. The average diameter of said faces is at least three times the distance separating them (the thickness).
Silver halide photographic emulsions containing a high proportion of tabular grains have advantages of good developability, improved covering power and increased useful adsorption of sensitizing dye per weight of silver due to the high surface area-to-volume ratio of the grains. The use of such emulsions in photographic elements is disclosed in U.S. Pat. Nos. 4,425,425, 4,425,426, 4,433,048, 4,435,499, 4,439,520, and other related patents.
The use of automatic processors for the rapid processing (i.e., for a processing of from 45 to 90 sec) of light-sensitive silver halide elements including tabular silver halide grains, in particular light-sensitive silver halide elements for photographic use, is known. Such elements generally include a support (usually provided with a very thin subbing layer) having coated on at least one side a silver halide gelatin emulsion layer coated in turn with a gelatin protective layer. These elements are transported through machine processing units (developing, fixing, washing and drying) by means of opposed or staggered rollers (as described, for example, in U.S. Pat. No. 3,025,779) which also have the function of squeezing liquid from the film prior to drying.
If rapid processing of a film takes place, several problems occur, such as an inadequate image density (i.e. insufficient sensitivity, contrast and maximum density), insufficient fixing, insufficient washing, and insufficient film drying. Insufficient fixing and washing of a film can cause reduced image quality and modification of the silver tone. In order to reduce the time taken by the element to pass through the processing machine to 0.5 to 2 minutes, as particularly required in rapid processing of photographic elements, the processing is performed at relatively higher temperatures, usually higher than 30.degree. C., preferably between 35.degree. C. and 45.degree. C., such as 38.degree. C., and the gelatin content of the silver halide emulsions is considerably reduced as compared to that of emulsions for manual processing.
Under such conditions, the physical and photographic properties of the elements processed in an automatic processor tend to be worse. With high temperatures and such low gelatin content, for instance, the intrinsic sensitivity to pressure of the silver halide grains gets higher and the elements processed in the automatic processor show repeated marks caused by the pressure of the transporting rollers. Such pressure marks look like higher density regions and reduce the image faithfulness.
In order to prevent pressure marking, various methods have been described in the art. To this purpose, U.S. Pat. No. 2,960,404 describes the use in the photographic elements of glycerine, ethylene glycol and the like, Japanese Pat. No. 5316/1972 describes the use of 1,4-cyclohexane dimethanol and the like, and Japanese Pat. No. 4939/1978 describes the use of trimethylol propane. Another possible method of preventing pressure marking is increasing the degree of hardening of the gelatin layers, in particular of the external protective layers. Also, as another method, photographic elements are known wherein an intermediate gelatin layer is interposed between the support and the emulsion layer. For example, U.S. Pat. No. 3,637,389 describes a rapid processing photographic element wherein gradation, density and sensitivity are improved by applying such an intermediate gelatin layer between the support and the emulsion layer.
However, known methods of preventing pressure marking when used in photographic elements including tabular silver halide grains have proved less effective. In particular, when the hardening degree is increased to achieve a very low swelling index and to improve its resistance to pressure desensitization, the photographic characteristics are reduced. Accordingly, the problem still remains of preventing pressure marking in photographic elements including light-sensitive tabular silver halide emulsions.
EP 238,271 discloses a silver halide photographic material comprising at least one hydrophilic colloidal layer on a support, showing a melting time of from 8 to 45 minutes, and a water content of from 10 to 20 g/m.sup.2 upon completion of the washing step. The material is preferably processed in a developing solution comprising indazole and benzotriazole derivatives. The preferred processing time is 45 sec.
U.S. Pat. No. 4,647,528 discloses a method of increasing both covering power and scratching resistance by using a particular polymeric hardener in a photographic material comprising a support coated with at least one silver halide emulsion layer containing tabular silver halide grains with an aspect ratio higher than 5:1. This material is processed in developing and fixing solutions containing hardeners.
U.S. Pat. No. 4,847,189 discloses a silver halide photographic material comprising a silver halide emulsion having tabular silver halide grains with an aspect ratio not lower than 5:1 and showing a melting time of from 8 to 45 minutes. Also disclosed is a method for processing this material in processing solutions containing hardeners in a preferred time of 45 seconds.
EP 341,637 discloses a processing solution for the rapid processing of silver halide photographic material. The processing solution comprises a compound capable of reducing the molecular extinction coefficient at 624 nm of an aqueous solution of a specific carbocyanine sensitizing dye. The processing solution reduces the residual stain and improves photographic characteristics of the processed photographic material.
EP 327,133 discloses a developing solution comprising a thiadiazole derivative. This compound prevent sludge and provides a processed photographic material having good photographic and physical qualities.
EP 321,948 discloses a method to reduce the fixing time by employing a silver halide photographic material comprising a subbing layer which contains an aqueous polymeric latex.
EP 428,455 discloses a developing solution substantially free of both aldehydic hardening agents and silver halide solvents and containing a pyrazolidinone derivative, for use in the development of fore-hardened radiographic films.
However, when performing a super-rapid processing of less than 45 sec the above mentioned disadvantages can not be overcome by these techniques, and thus there is still the need for a method of processing a silver halide photographic material which shows good photographic and physical characteristics when processed in a super-rapid processing.