Radiation imagery chemistry: process – composition – or product th – Radiation sensitive product – Silver compound sensitizer containing
Reexamination Certificate
2000-11-17
2003-05-06
Chea, Thorl (Department: 1752)
Radiation imagery chemistry: process, composition, or product th
Radiation sensitive product
Silver compound sensitizer containing
C430S572000, C430S578000, C430S582000, C430S583000, C430S584000, C430S586000, C430S587000, C430S588000, C430S590000, C430S591000, C430S592000
Reexamination Certificate
active
06558893
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to silver halide photographic material containing at least one silver halide emulsion which has improved color reproduction and enhanced photographic sensitivity.
BACKGROUND OF THE INVENTION
A multicolor photographic material typically comprises a support bearing a cyan dye image-forming unit comprising at least one red-sensitive silver halide emulsion layer having associated therewith at least one cyan dye-forming coupler, a magenta dye image-forming unit comprising at least one green-sensitive silver halide emulsion layer having associated therewith at least one magenta dye-forming coupler, a yellow dye image-forming unit comprising at least one blue-sensitive silver halide emulsion layer having associated therewith at least one yellow dye-forming coupler. One of the challenges of preparing photographic materials is to have each of the red, green, and blue sensitive emulsions absorb light as close as possible to the wavelength of light sensitivity of the human eye in that color range of the spectrum.
The human eye is most sensitive to green light. Thus the green light sensitive layer of photographic materials can have a large impact on perceived color reproduction. This layer is generally sensitive to light within the wavelength region of 500 to 600 nm. In photographic materials, it is common practice to sensitize this layer with a sensitizing dye that has a maximum sensitivity at about 550 nm. However, the human eye has a peak sensitivity at about 540 nm, and still has substantial sensitivity at 500 nm. Additional efficient sensitization in the region of 500 to 540 nm would enable more accurate color reproduction for color negative films.
Benzimidazolooxacarbocyanines can provide spectral sensitivity in the region of 520 to 540 nm. Oxacarbocyanines are another class of dyes that afford efficient J-aggregate sensitization in the green region. Ikegawa et. al. (U.S. Pat. Nos. 5,198,332, 4,970,141, and 4,889,796) and Nakamura et. al. (U.S. Pat. No. 5,637,448) describe oxacarbocyanine dyes that provide spectral sensitivity below 545 nm. U.S. Pat. No. 5,523,203 describes another class of short green sensitizers. Commonly assigned co-pending application Ser. No. 09/259,992 filed Mar. 1, 1999 also discloses short green sensitizing dyes. Acetylenic dyes, described in U.S. Pat. No. 4,025,349 can also provide short green sensitization.
However, addition of any of the above mentioned short green dyes requires that some of the mid-green sensitizer be removed since there is only limited space on the silver halide grains. This results in an increased sensitivity in the short green wavelengths, but a decrease in sensitivity at the mid-green region. Thus it would be desirable if the short green sensitivity could be increased without significantly decreasing the mid-green sensitivity.
In many photographic products, for example, color negative films, the blue spectral region, 400-500 nm, has been often sensitized with a dye that has its maximum sensitivity at about 470 nm while the eye sensitivity has a peak at approximately 440 nm, and fluorescent lights have a peak emission at 435 nm. A broader blue sensitization envelope could improve the sensitivity of the film color balance to changes in illuminant, especially fluorescent light. This type of spectral envelope can be obtained by combining a dye that has a maximum sensitization at 470 nm with a dye that has a maximum peak at a shorter wavelength. Thus dyes that aggregate at a shorter wavelength, for example oxathiacyanine dyes, that aggregate in the region of 400-460 nm are desirable. However, adding a short blue dye requires that some of the mid-blue dye be removed because of the limited surface area on silver halide grains. This can result in a substantial decrease in mid-blue sensitivity. In the yellow layer it would be desirable to increase short-blue sensitivity while maintaining mid-blue sensitivity.
The red sensitivity of the human eye peaks at approximately 590 nm. However, the red wavelength region, 600 to 700 nm, in many photographic products, for example color negative films, has been often sensitized with a dye that has its maximum sensitivity at about 650 nm. A change in the red spectral sensitization from a maximum at 650 nm to a position closer to 600 nm, for example in the 620 to 640 nm region, has several advantages. This could improve the sensitivity of the film color balance to changes in illuminant, especially fluorescent light. Also, some colors that are difficult to reproduce because of high infrared reflectance, would be reproduced more accurately. Thus increasing the sensitivity in the short red region is desirable.
To achieve a broad green, a broad blue, or a broad red sensitization and increase photographic sensitivity it is necessary to increase the light absorption of the silver halide emulsions. 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. Nos. 2,518,731, 3,976,493, 3,976,640, 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 connected to one another. In this approach the dyes can be added sequentially and are less likely to interfere with one another. Miysaka et al. in EP 270 079 and EP 270 082 describe silver halide photographic material having an emulsion spectrally sensitized with an adsorable sensitizing dye used in combination with a non-adsorable luminescent dye which is located in the gelatin phase of the element. Steiger et al. in U.S. Pat. Nos. 4,040,825 and 4,138,551 describe silver halide photographic material having an emulsion spectrally sensitized with an adsorable sensitizing dye used in combination with second dye which is bonded to gelatin. The problem with these approaches is that unless the dye 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. The problem with prior art dye layering approaches was that the dye layers described produced a very broad sensitization envelope. This would lead to poor color reproduction since, for example, the silver halide grains in the same color record would be se
Andrievsky Andrei
Harrison William J.
Parton Richard L.
Penner Thomas L.
Chea Thorl
Eastman Kodak Company
Rice Edith A.
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