Radiation imagery chemistry: process – composition – or product th – Silver halide colloid tanning process – composition – or product
Reexamination Certificate
2001-08-10
2002-09-03
Letscher, Geraldine (Department: 1752)
Radiation imagery chemistry: process, composition, or product th
Silver halide colloid tanning process, composition, or product
C430S373000, C430S375000, C430S449000, C430S573000, C430S578000, C430S591000, C430S593000, C430S607000, C430S613000, C430S614000, C430S615000, C430S598000
Reexamination Certificate
active
06444392
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to black and white graphic arts films, and to photographic silver halide emulsions therefor.
BACKGROUND OF THE INVENTION
Black and white graphic arts films are often used with either a helium-neon (HN) or laser diode (LD) light source. The wavelength of HN light is 633 nm, while the wavelength of LD light is 670 nm and the installed base of image-setters with the different light sources varies from country to country.
In photographic films, spectral sensitising dyes are commonly used, the dyes being adsorbed to grains of silver halide in the emulsion layers. A sensitising dye induces sensitivity of the silver halide grains to longer wavelengths. In general, when a dye is used in an emulsion layer of a photographic film, the spectral region of sensitisation corresponds to the absorption spectrum of the adsorbed dye. For a given dye, a particular spectral speed is achieved. The spectral speed is related to the absorptance characteristics of the dye.
Fogging describes a phenomenon in the photographic process whereby localised areas of silver halide grains become reduced in the developing process, even when they have not been exposed to light. Antifoggants are chemicals which may be added to the emulsion layer of photographic film to decrease the rate of development of the photographic image in a selective manner.
A group of compounds which act as antifoggants (or stabilisers) are tetraazaindenes. These have been studied extensively (E. J. Birr,
Stabilisation of Photographic Silver Halide Emulsions
, Focal Press, London, 1974, Chapter IV). In particular, it has been found that 4-hydroxy-6-alkyl-1,3,3a,7-tetraazaindenes are useful stabilisers. The 6-methyl compound has been studied most extensively. U.S. Pat. No. 5,221,604 describes a silver halide photographic material comprising a support having thereon at least one silver halide emulsion layer. The silver halide is chemically sensitised by a chemical sensitiser promoter comprising at least one silver halide solvent and an adsorbable compound. The adsorbable compound may be selected from various tetraazaindenes, including 2-methylthio-4-hydroxy-6-methyl-1,3,3a,7-tetraazaindene (hereinafter sometimes referred to as “SMe-TAI”).
U.S. Pat. No. 5,370,986 describes a photographic material comprising a silver halide emulsion layer. The emulsion layer comprises a water-soluble nonionic polyhydroxyalkyl compound, such as an oligosaccharide, and a co-stabilising agent, such as 2-methylthio-4-hydroxy-6-methyl-1,3,3a,7-tetraazaindene (SMe-TAI). This combination was found to be effective in reducing storage fog in the emulsion layer.
Neither of the above-mentioned Patents is directed to black and white graphic arts films.
PROBLEM TO BE SOLVED BY THE INVENTION
It is an object of the present invention to provide a black and white graphic arts film that is suitable for use on any LD or HN exposing device.
SUMMARY OF THE INVENTION
Accordingly, the present invention provides a black and white graphic arts film comprising a support having thereon at least one emulsion layer, said emulsion layer comprising:
(a) a trinuclear merocyanine spectral sensitising dye;
(b) 2-methylthio-4-hydroxy-6-methyl-1,3,3a,7-tetraazaindene; and
(c) a photosensitive silver halide.
The present invention further provides a photographic silver halide emulsion suitable for preparing a black and white graphic arts film comprising (a), (b) and (c).
The present invention even further provides a photographic silver halide emulsion melt comprising (a), (b) and (c).
ADVANTAGEOUS EFFECT OF THE INVENTION
It has been found that this specific combination of ingredients in the emulsion layer provides significant advantages.
Hitherto, it was believed that the concentration of antifoggant or stabiliser in the emulsion layer had an insignificant effect on the absorptance characteristics of the sensitising dye. However, surprisingly it has now been found that SMe-TAI has a dramatic effect on the absorptance characteristics of a trinuclear merocyanine sensitising dye. In particular, the concentration of SMe-TAI in the emulsion layer has been found to affect the absorptance characteristics of the trinuclear merocyanine dye. Since the absorptance characteristics of a given dye are related to its spectral speed, this combination of ingredients allows the spectral speed of a trinuclear merocyanine dye to be modulated by adjusting the concentration of SMe-TAI in the emulsion layer.
In addition, it has been found that the concentration of SMe-TAI in the emulsion layer has an effect on the relationship between the HN and LD speeds for a trinuclear merocyanine dye. Hitherto, it was believed that the relationship between the HN and LD speeds is generally consistent for a particular spectral sensitising dye. Previously, the HN and LD speeds could be changed in absolute terms by the use of various antifoggants, but their relative speeds could not be altered. However, in the present invention, it has been found that the relative HN and LD speeds can now be changed. Accordingly, the ability to change the relative HN and LD speeds for the same spectral sensitising dye finds numerous applications. Most notably, it will allow the same spectral sensitising dyes to be used in a single film for both HN and LD applications when the speed requirements of the film might otherwise be unachievable due to the inability to change the relative HN and LD speeds. This has the advantages of greater convenience and lower production costs.
A further advantage of the present invention is experienced in the production process. When an emulsion layer for a photographic film is prepared, the emulsion is held in a melt at approximately 40° C., before it is coated onto a photographic support. The emulsion may be held in the melt for up to 12 hours. However, it has been observed that the characteristics of the melt can change over time. This change in melt characteristics is termed “emulsion melt drift”. In particular, it has been observed that the spectral speed of the melt increases with time. An increase in spectral speed in an emulsion melt is undesirable, since the films produced will have inconsistent speeds, even when they are produced from the same emulsion melt. In the present invention, it has been found that the combination of SMe-TAI and a trinuclear merocyanine dye has an effect in reducing speed increases in the melt.
Various stabilisers have been proposed to control speed changes during long-term storage of undeveloped photographic films. However, a combination of chemicals which control speed changes in the emulsion melt has not been disclosed. Thus, the unique combination of a trinuclear merocyanine dye and SMe-TAI also has the advantage of producing films with a more consistent spectral speed from the same melt.
DETAILED DESCRIPTION OF THE INVENTION
Preferably, the amount of SMe-TAI in the emulsion melt is in the range of 0.05 to 0.2 g/Ag mole. It has been found that this concentration of SMe-TAI in the melt is very effective in controlling emulsion melt drift.
Preferably, the trinuclear merocyanine dye is a red sensitising dye. Trinuclear merocyanine dyes are known in the art (F. Hamer,
The Cyanine Dyes and Related Compounds
, Wiley-Interscience, 1964). All of the nuclei generally used in merocyanine dyes can be used for the basic heterocyclic nuclei in dyes of the present invention. The nuclei may be selected from a pyrroline nucleus, an oxazoline nucleus, a thiazoline nucleus, a pyrrole nucleus, an oxazole nucleus, a thiazole nucleus, a selenazole nucleus, an imidazole nucleus, a tetrazole nucleus or a pyridine nucleus; a nucleus in which one of these nuclei is fused with an aliphatic hydrocarbyl ring, or a nucleus in which one of these nuclei is fused with an aromatic hydrocarbyl ring, for example, an indolenine nucleus, a benzindolenine nucleus, an indole nucleus, a benzoxazole nucleus, a naphthoxazole nucleus, a benzothiazole nucleus, a naphthothiazole nucleus, a benzoselenazole nucleus, a benzimidazole nucleus or a quinoline nucleus. These nuclei may be s
Eastman Kodak Company
Letscher Geraldine
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