Radiation imagery chemistry: process – composition – or product th – Radiation sensitive product – Silver compound sensitizer containing
Reexamination Certificate
1997-07-01
2003-03-18
Schilling, Richard L. (Department: 1752)
Radiation imagery chemistry: process, composition, or product th
Radiation sensitive product
Silver compound sensitizer containing
C430S603000, C430S605000, C430S622000
Reexamination Certificate
active
06534255
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to a light-sensitive silver halide photographic element and in particular, to a light-sensitive photographic element comprising tabular silver halide grains. The light-sensitive silver halide photographic elements of the present invention are advantageously developed without surface defects by super rapid processing in automatic processors which include transport rollers.
BACKGROUND OF THE INVENTION
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), this is generally described in the art as an aspect ratio of at least 3.
Silver halide photographic emulsions containing a high proportion of tabular Is grains have advantages of good developability, improved covering power and increased useful adsorption of sensitizing dye per weight of silver due to their high surface area-to-volume ratio. 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 rapid processing (i.e., for a processing of from 45 to 90 sec) of light-sensitive silver halide elements including tabular silver halide grains, and in particular for light-sensitive silver halide elements for radio-graphic use, is known. Such silver halide 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. In recent years the increased use of silver halide elements for radiography has increased the desire for a reduction of processing times. In rapid processing of films , several problems can occur, such as 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 cause a progressive worsening of the image quality and modification of the silver tone. To reduce the time taken by the element to pass through the processing machine to 0.5 to 2 minutes, as is particularly required in rapid processing of radiographic elements, processing is performed at relatively higher temperatures, usually higher than 30° C., preferably between 35-45° C., such as 38° 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, even with the changes in the emulsions, the physical and photographic properties of the elements processed in an automatic processor tend to be worse. With higher temperatures and in the presence of lower gelatin content, the intrinsic sensitivity to pressure of the silver halide grains tends to be higher and the elements processed in the automatic processor show marks caused by the pressure of the transporting rollers. Such pressure marks look like higher density regions and reduce the image faithfulness.
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 method of preventing pressure marking is by increasing the degree of hardening of the gelatin layers, in particular of the external protective layers. 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, photographic characteristics are reduced. Accordingly, the problem still remains of preventing pressure marking in photographic elements including light-sensitive tabular silver halide emulsions.
EP Patent Application No. 560,118 discloses a light-sensitive silver halide photographic element comprising a support and at least one silver halide emulsion layer containing tabular silver halide grains having an average diameter:thickness of at least 3:1 and highly deionized gelatin, said photographic element having a swelling index lower than 140% and a melting time of from 45 to 120 minutes. The above swelling index and melting time were obtained by hardening the gelatin with a vinylsulfonyl type hardener containing hydroxy group(s). The light-sensitive element disclosed in said EP application can be advantageously developed by high temperature super rapid processing in automatic processors which include transport rollers and provides good physical and photographic characteristics. Unfortunately, a defect in the form of white streaks has been evidenced on the surface of said films upon processing. The cause of such a defect has been extensively studied and attributed to the reaction of the vinylsulfonyl type hardener with a compound used in the chemical sensitization of the tabular silver halide grains.
To obtain the photographic characteristics (speed, minimum and maximum density, contrast, tone of the developed silver) required by the medical radiographic applications in EP 560,118, chemical sensitization of the tabular silver halide grains comprised the use of gold and thiosulfonate sensitizers in the presence of a sulfinate compound. The purpose of the sulfinate compound was to prevent fog (minimum density) during chemical ripening and retard chemical ripening to obtain a better speed/fog ratio. It has been, however, found that the vinylsulfonyl type hardeners are capable of reacting with sulfinate compounds and give water insoluble products which can create deposits in the form of white streaks on the surface of processed photographic films. By using hardeners different from vinylsulfonyl type hardeners or avoiding sulfinate compounds, the appearance of said white streaks is eliminated, but either rapid processability or photographic characteristics are negatively affected.
It is, therefore, one aspect of the present invention to provide a silver halide photographic element comprising tabular silver halide grains which can be developed by high temperature super rapid processing in automatic processors which include transporting rollers and have good photographic and physical characteristics and is free from surface defects.
U.S. Pat. No. 4,425,426 discloses radiographic elements comprising thin tabular silver halide grains. The preferred chemical sensitizers for tabular silver halide grains described in said patent are gold and sulfur sensitizers, gold and selenium sensitizers, and gold, sulfur and selenium sensitizers.
EP 348,934 discloses a silver halide color photographic material comprising tabular silver halide grains reduction-sensitized in the presence of a thiosulfonate compound and chemical sensitized, e.g., gold sensitized and/or sulfur and selenium sensitized.
EP 443,453 describes a silver halide photographic emulsion comprising tabular silver halide grains which have been subjected to chemical sensitization by at least one selenium sensitizer, at least one gold sensitizer and at least one sulfur sensitizer. A pal
Delfino Gerolamo
Ganduglia Roberta
Eastman Kodak Company
Schilling Richard L.
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