Radiation imagery chemistry: process – composition – or product th – Radiation sensitive product – Two or more radiation-sensitive layers containing other than...
Reexamination Certificate
2003-01-17
2004-11-02
Letscher, Geraldine (Department: 1752)
Radiation imagery chemistry: process, composition, or product th
Radiation sensitive product
Two or more radiation-sensitive layers containing other than...
C430S509000, C430S600000, C430S611000, C430S613000, C430S615000, C430S505000, C430S558000, C430S570000, C430S572000, C430S574000, C430S581000
Reexamination Certificate
active
06811963
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to a silver halide photographic material containing at least one silver halide emulsion that has enhanced light absorption. The invention is directed in particular to a color photographic material with high sensitivity, reduced granularity and radiation sensitivity.
BACKGROUND OF THE INVENTION
Increasing the sensitivity of silver halide based imaging composites to reflected scene information offers the potential for improved photographic performance. Examples of how increased response to light within the visible spectrum can provide system specific benefits include: (i) shorter exposure times which in turn enables “stop-action” image capture; (ii) increased depth of field enabled by the use of a smaller effective aperture; (iii) or improved penetration of artificial illuminants (so-called “flash distance”).
However, as executed to date, examples of silver halide based image capture media which display increased sensitivity have suffered from at least two major problems. The first relates to increased noise (or ‘graininess’) associated with the conventional tactic of increasing detector (emulsion crystal) size to elevate sensitivity. The second area of dissatisfaction related to existing highly light sensitive photographic materials is the rapid and significant reduction in signal-to-noise {S/N} response as these composites are exposed to normal background radiation outside the visible spectrum. The combination of these two facets of existing high speed emulsions can yield inferior results under normal usage conditions, severely compromising the utility described above.
In general, useful photographic sensitivity is correlated with the size of the most light sensitive silver halide detector (emulsion) employed. For tabular emulsions, the operative size variable is surface area per crystal, which in turn is a direct function of the equivalent circular diameter (ECD). Unfortunately, noise, as measured by micro-scale density variation or granularity, is also directly correlated with ECD. Equally distressing is the observation that sensitivity to radiation (outside the visible spectrum) is also a direct function of ECD, with larger ECD having greater sensitivity to and increased damage from radiation. Typical damage imparted from radiation exposure includes: (i) reduced discrimination due to increased minimum density (D-min); (ii) reduction in intended sensitivity to visible light and (iii) increased granularity.
Conceptually, one potential solution which simultaneously addresses both concerns associated with high speed photography would be to provide equivalent sensitivity (or speed) with silver halide crystals of smaller ECD. Central to this goal involves enhancing the amount of spectrally specific light absorbed by the crystal.
J-aggregating cyanine dyes are used in many photographic systems. It is believed that these dyes adsorb to a silver halide emulsion and pack together on their “edge” which allows the maximum number of dye molecules to be placed on the surface. However, a monolayer of dye, even one with as high an extinction coefficient as a J-aggregated cyanine dye, absorbs only a small fraction of the light impinging on it per unit area. The advent of tabular emulsions allowed more dye to be put on the grains due to the increased surface area per mole of silver. However, in most photographic systems, it is still the case that not all of the available light is being collected.
The need is especially great in the blue spectral region where a combination of low source intensity and relatively low dye extinction results in a deficient photo response. The need for increased light absorption is also great in the green sensitization of the magenta record of multilayer color film photographic elements. The eye is most sensitive to the magenta image dye and this layer has the largest impact on color reproduction. Higher speed in this layer can be used to obtain improved color and image quality characteristics. The cyan layer could also benefit from increased red-light absorption that could allow the use of smaller emulsions with less radiation sensitivity and improved color and image quality characteristics. For certain applications, it may be useful to enhance infrared light absorption in infrared sensitized photographic elements to achieve greater sensitivity and image quality characteristics.
One way to achieve greater light absorption is to increase the amount of spectral sensitizing dye associated with the individual grains beyond monolayer coverage of dye (some proposed approaches are described in the literature, G. R. Bird,
Photogr. Sci. Eng
., 18, 562 (1974)). One method is to synthesize molecules in which two dye chromophores are covalently connected by a linking group (see U.S. Pat. No. 2,518,731, U.S. Pat. No. 3,976,493, U.S. Pat. No. 3,976,640, U.S. Pat. No. 3,622,316, Kokai Sho 64(1989)91134, and EP 565,074). This approach suffers from the fact that when the two dyes are connected they can interfere with each other's performance, e.g., not aggregating on or adsorbing to the silver halide grain properly.
In a similar approach, several dye polymers were synthesized in which cyanine dyes were tethered to poly-L-lysine (U.S. Pat. No. 4,950,587). These polymers could be combined with a silver halide emulsion, however, they tended to sensitize poorly and dye stain (an unwanted increase in D-min due to retained sensitizing dye after processing) was severe in this system and unacceptable.
A different strategy involves the use of two dyes that are not covalently linked to one another. In this approach the dyes can be added sequentially and are less likely to interfere with each other. Miyasaka et al. in EP 270 079 and EP 270 082 describe silver halide photographic material having an emulsion spectrally sensitized with an adsorbable sensitizing dye used in combination with a non-adsorbable luminescent dye that is located in the gelatin phase of the element. Steiger et al. in U.S. Pat. No. 4,040,825 and U.S. Pat. No. 4,138,551 describe a silver halide photographic material having an emulsion spectrally sensitized with an adsorbable sensitizing dye used in combination with a second dye that is bonded to gelatin. The problem with these approaches is that unless the dye that is not adsorbed to the grain is in close proximity to the dye adsorbed on the grain (less than 50 angstroms separation) efficient energy transfer will not occur (see T. Förster,
Disc. Faraday Soc
., 27, 7 (1959)). Most dye off-the-grain in these systems will not be close enough to the silver halide grain for energy transfer, but will instead absorb light and act as a filter dye leading to a speed loss. A good analysis of the problem with this approach is given by Steiger et al. (
Photogr. Sci. Eng
., 27, 59 (1983)).
A more useful method is to have two or more dyes form layers on the silver halide grain. Penner and Gilman described the occurrence of greater than monolayer levels of cyanine dye on emulsion grains,
Photogr. Sci. Eng
., 20, 97 (1976); see also Penner,
Photogr. Sci. Eng
., 21, 32 (1977). In these cases, the outer dye layer absorbed light at a longer wavelength than the inner dye layer (the layer adsorbed to the silver halide grain). Bird et al. in U.S. Pat. No. 3,622,316 describe a similar system. A requirement was that the outer dye layer absorb light at a shorter wavelength than the inner layer. A problem with previous dye layering approaches was that the dye layers described produced a very broad sensitization envelope. This may be desirable for some black and white photographic applications, but in a multilayer color film element this would lead to poor color reproduction since, for example, the silver halide grains in the same color record would be sensitive to both green and red light.
Yamashita et al. (EP 838 719 A2, U.S. Pat. No. 6,117,629) describes the use of two or more cyanine dyes to form more than one dye layer on silver halide emulsions. The dyes are required to have at least one aromatic or heteroaromatic substituent
Foster David R.
Friday James A.
Johnston Sharon G.
Michno Drake M.
Singer Stephen P.
Eastman Kodak Company
Letscher Geraldine
Meeks Roberts Sarah
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