Radiation imagery chemistry: process – composition – or product th – Luminescent imaging
Reexamination Certificate
1997-11-19
2001-02-20
Le, Hoa Van (Department: 1752)
Radiation imagery chemistry: process, composition, or product th
Luminescent imaging
C430S390000, C430S559000, C430S950000
Reexamination Certificate
active
06190821
ABSTRACT:
DESCRIPTION
1. Field of the Invention
This invention relates to photosensitive film materials and image-forming systems wherein said materials are forming an image by wet or dry processing after exposure to radiation.
2. Background of the Invention
Image forming systems wherein photosensitive silver halide film materials are processed after exposure are well-known. Processing of the said materials can be performed wet or dry, depending on the system used.
In radiology e.g. where classical screen-film systems still remain important, phosphors present in an intensifying screen convert X-ray radiation into visible light. The photons of visible light emitted from said phosphors are then absorbed by an adjacent radiographic film material containing light-sensitive silver halide emulsion crystals, whereafter the latent image becomes wet processed in order to give an image ready-for-examination by radiologists.
For applications, such as mammography and diagnosis of extremities, where radiographic images having high sharpness are required, suitable screen-film systems usually contain only one screen. Light-sensitive silver halide photographic layer(s) coated at only one side of a film support are used in this application, wherein the outermost layer of said film should be in close contact with the said screen in favour of sharpness.
For general applications wherein a higher sensitivity is preferred the screen-film system contains two screens. Between the said screens the film is positioned and comprises on each side of the support at least one light-sensitive silver halide photographic layer.
In the light-sensitive layers tabular silver halide emulsion crystals are frequently used nowadays. Tabular grains are disclosed e.g. in U.S. Pat. No. 4,414,304 for their high covering power (even at high hardening levels of the binder material, thus permitting the coating of lower amounts of silver halide) and developability, and in U.S. Pat. Nos. 4,425,425 and 4,425,426 for their lower cross-over. All these effects are the result of a higher surface to volume ratio characteristic for said tabular grains.
An unacceptable disadvantage of tabular grains is the brownish color of the developed silver after processing, especially when said grains have a thickness of less than 0.30 &mgr;m. For thinner tabular grains even a more tremendous deterioration from the desired black image tone is observed, especially when the image is examined in transparency (as radiologists perform their examinations), but also under reflected light conditions.
Another problem encountered when use is made of tabular grains having a higher surface to volume ratio is residual dye stain: although adsorption of higher amounts of spectrally sensitizing dyes offers the advantage of absorption of more incident light and of reduced cross-over, dye stain occurs after processing, due to incomplete removal of said dye(s) from the processed material.
A solution for these problems has been described in e.g. EP-A 0 468 211 and in EP-A 0 655 645. Therein a blue colored pigment is added to the photographic sensitive layer or another layer of the film in order to reduce residual dye stain but simultaneously to provide a black image tone. The blue pigment used in these EP-A's is characterized by an absorption maximum of from 570 to 630 nm and from 640 to 700 nm respectively. In the examples this pigment is added to the light-sensitive emulsion layer containing silver halide emulsion crystals and reduces dye stain after processing by deaggregation of the adsorbed spectral sensitiser, adsorbed at the crystal surface.
In U.S. Pat. No. 4,818,675 a dispersion of a dye having a maximum absorption wavelength of 520 to 580 nm is added to at least one layer on at least one side of a photographic material, such that the transmission density of green light is 0.03 or less after developing treatment of that material. This method leads to improvements surpassing other methods known before in order to improve image tone of developed tabular grains. As tone-regulating agents mercapto compounds are used. In the same document a review is given about methods of introducing dyes (and other additives) in emulsion and/or other layers of a silver halide photographic material: in the form of gelatinous dye dispersions, as an oilformer dispersion, as a polymer latex composition, in the form of a mordant together with a hydrophilic polymer having a charge opposite to that of the charged dye molecule, in dissolved form by using a suitable surfactant (an oligomer or a polymer), in a dispersion with a hydrophilic polymer together with or instead of an oilformer and in micro-capsule form employing therein a polymer having a carboxyl group, a sulphonic group etc.
A problem arising due to the presence of a blue pigment (besides image tone and dye stain) in a photographic element in operative association with an intensifying screen is the risk of staining of the surface of said screen so that artifacts can occur on the image formed after contact made with such stained screen. This phenomenon especially occurs after cleaning the screen surface with solvents used as screen-cleaners. Further blue pigment escaping from the film material often makes dirty the rollers in the automatic processing machine wherein the exposed film material is processed, thereby disturbing images generated on the following films processed therein.
3. OBJECTS OF THE INVENTION
Therefore it is a first object of the present invention to obtain, with classical silver halide photographic film materials, in particular those materials wherein use is made of thin tabular silver halide grains, images with a cold “blue-black” image tone by means of image-tone correcting blue dyes.
It is another object of the present invention to prevent in classical film-screen systems wherein the film comprises a blue dye that the intensifying screens in contact therewith become stained.
It is a further object of this invention to prevent staining of the rollers in automatic processing machines during wet processing of exposed film materials comprising blue dyes.
Other objects of this invention will become apparent from the description hereinafter.
4. SUMMARY OF THE INVENTION
The above objects are accomplished by a photosensitive silver halide film material comprising a support and on one or both sides thereof one or more layer(s) comprising a photosensitive silver halide emulsion, particularly a photosensitive silver halide emulsion having tabular silver halide crystals with an average thickness of less than 0.25 &mgr;m and an average aspect ratio of 2 or more; characterized in that said photosensitive layer(s) comprise(s) blue colored polymeric matting particles.
In particular said light-sensitive film material which is run in wet processing after exposure is used in an image-forming film-screen system for medical diagnostic imaging wherein said film material is used in operative association with one or two intensifying screens comprising on a support a layer of a visible light emitting luminescent phosphor, the said film material comprising a support and on one or both sides thereof a light-sensitive silver halide emulsion layer having spectrally sensitized tabular silver halide and a non-light-sensitive protective layer, characterised in that said light-sensitive silver halide emulsion layer(s) comprise(s) blue colored polymeric matting particles.
5. DETAILED DESCRIPTION OF THE INVENTION
The best results to improve the color of silver generated from developed thin tabular silver halide grains having an average thickness of less than 0.25 &mgr;m and an average aspect ratio of 2 or more, wherein said tabular grains are present in one or more photosensitive layer(s) of an exposed silver halide photographic material, and more particular in a radiographic film material or in an image recording film for medical diagnostic purposes, without increasing the minimum density of the said material, are obtained, when the blue dye is present in blue coloured (pigmented) polymeric matting paticles in one or more light-sensitive em
Agfa-Gevaert N.V.
Breiner & Breiner
Le Hoa Van
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