Radiation imagery chemistry: process – composition – or product th – Radiation sensitive product – Two or more radiation-sensitive layers containing other than...
Reexamination Certificate
2000-07-21
2001-11-13
Schilling, Richard L. (Department: 1752)
Radiation imagery chemistry: process, composition, or product th
Radiation sensitive product
Two or more radiation-sensitive layers containing other than...
C430S600000, C430S603000, C430S567000
Reexamination Certificate
active
06316176
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a method of preparing a highly photosensitive image-forming element and more particularly to a highly sensitive photographic silver halide emulsion having an improved speed in the presence of an organo-tellurium compound.
BACKGROUND OF THE INVENTION
In photographic industry there exists an ever lasting demand for photosensitive image-forming materials with increased sensitivity and image-quality. However both characteristics are often dependent on each other or inter-related which means that influencing one parameter will have its consequences for the other parameter and vice versa. This relationship can clearly be proved in testing silver halide photographic materials. So an increase of sensitivity or speed of a photographic silver halide material can be realized by an increase of the mean size of the silver halide emulsion crystals of the said material. This however normally results in a decrease of image quality. One way to solve this problem is to increase the efficiency of electron-trapping of the latent-image in the silver halide grains. This can be realized by chemical sensitization of the grains in the presence of a chemical compound which can enhance the electron-trapping efficiency as mentioned hereinbefore. Such compound may be a sulphur salt, a gold salt or a combination of both as normally used. In the recent years chemical sensitization in the presence of a labile selenium and even of a labile tellurium compound is increasingly used.
Examples of selenium compounds which were suggested for use in order to get an increased sensitivity were substituted selenourea (as described e.g. in EP-A 0 280 031, EP-A 0 458 278), selenoethers (e.g. in JP-A 2-132434, JP-A 4-271341, JP-A 6-175258, U.S. Pat. No. 5,532,120), diselenides (e.g. in EP-A 0 703 492), selenoesters (e.g. in U.S. Pat. No. 5,306,613), selenoketones (e.g. in EP-A 0 476 345), fosfineselenides (e.g. in EP-A 0 506 009), diselenides as in EP-A 0 889 354 and compounds grafted on an anchimeric long-chain group as in EP-A 0 895 121. Especially with the mentioned diselenides it has been shown that a suitable fog-speed relationship can be realized.
A variety of inorganic and organic tellurium complexes as chemically sensitizing compounds have been described as in CA 800,985 (elemental tellurium), sodium telluride and hydrogen telluride (GB 1,295,462) and sodium thiosulfatotelluride (GB 1,396,696). Specific complexes like stable palladium-tellurium complexes have been described in GB 2,316,184. Organo-tellurium compounds have been described in EP-A's 0 350 903, 0 572 662, 0 572 663, 0 573 649, 0 573 650, 0 619 515, 0 542 306, 0 661 589 and in U.S. Pat. Nos. 3,284,206; 4,076,537; 4,148,659; 4,188,218; 4,251,623; 5,215,880; 5,273,872; 5,273,874; 5,296,345, 5,340,695; 5,393,655; 5,395,745; 5,459,027; 5,561,033; 5,654,134; 5,677,120 and 5,759,760 and in DE-A's 1 96 16498, 1 96 19443, 1 96 48013 and 1 98 43081.
More recently synthesized tellurium compounds have been described in EP-A 0 809 137.
However tellurium sensitization easily tends to cause fog as a result of the depth of the electron trap(s) of the formed sensitivity speck(s) which is (are) larger than the depth of the sensitivity speck(s) created by selenium sensitization or sulphur sensitization. At the same time the stability and the gradation of a tellurium sensitized emulsion decreases if no precautions are taken. Special progress was announced by Yagihara M. in EP-A 0 585 787, describing chemical sensitization with sulphur, selenium or tellurium compounds like R
1
CO—Se—X—COR
2
where R
1
and R
2
equals alkyl, aryl or heterocycle and X equals S, Se or Te. Most of the patents dedicated to selenium sensitization like the ones mentioned hereinbefore are directed to the prevention of the described disadvantages. Moreover it is further known that sulphur or selenium sensitization carried out in the presence of a gold salt causes an increase in sensitivity but at the same time an unacceptable fog formation too. Particulary in comparison with gold-sulphur sensitization gold-selenium sensitization and even to a greater extent gold-tellurium sensitization causes a remarkable rise in fog. However until now the mechanism causing most of these effects is not fully understood yet and a lot of work has to be done in order to get fundamental improvements in the prevention of fogging or at least to get fog at an acceptable level in order to provide emulsions suitable for use in practical material applications. Accordingly there has been a strong demand for tellurium compounds offering a substantial speed increase while controlling fog to an acceptable low level. All the patents mentioned hereinbefore are to a certain extent more or less failing in disclosing a method for realizing highly sensitive silver halide emulsions with an acceptable fog level by using the tellurium compounds described therein.
OBJECTS OF THE INVENTION
It is therefore a first object of the present invention to provide a highly sensitive photographic element with an improved sensitivity-fog-relationship.
It is another object of the invention to provide a highly photosensitive silver halide emulsion comprising practically useful chemical tellurium sensitizers.
It is a further object of the invention to provide a method for chemically sensitizing a silver halide photographic emulsion with a tellurium compound in order to manufacture a highly sensitive photographic material suitable for use in practical applications.
Further objects and advantages of the invention will become apparent from the description hereinafter.
SUMMARY OF THE INVENTION
A method of chemically sensitizing a silver halide emulsion has thus been disclosed, wherein said emulsion has silver halide grains and a binder, said method comprising the steps of adding thereto, besides a chemically sensitizing agent providing sulphur, an organo-tellurium sensitizing compound providing tellurium in a molar ratio amount versus sulphur of less than 0.30.
A light-sensitive silver halide photographic element has also been provided which has been made highly sensitive by chemically sensitizing a silver halide emulsion by the method as described hereinbefore.
DETAILED DESCRIPTION OF THE INVENTION
While the present invention will hereinafter be described in connection with preferred embodiments thereof, it will be understood that it is not intended to limit the invention to those embodiments. On the contrary, it is intended to cover all alternatives, modifications, and equivalents as may be included within the spirit and scope of the invention as defined by the appending claims.
The present invention as described in the summary will now be explained in detail starting with an illustration of organo-tellurium compounds used in order to chemically sensitize silver halide emulsions crystals by the method of the present invention. Said organo-tellurium compounds are satisfying formula (I):
wherein each of R
1
and R
2
independently represents (C═S)OR
3
, (C═S)NR
4
R
5
or (P═S)R
6
R
7
;
wherein each of R
3
, R
4
and R
5
independently represents a (substituted or unsubstituted) alkyl, alkenyl, alkynyl, aryl or heteroaryl-group, wherein R
4
and R
5
may combine to form a ring
and wherein each of R
6
and R
7
independently represents a (substituted or unsubstituted) alkyl, alkenyl, alkynyl, aryl or heteroaryl group, OR
8
, NR
9
R
10
or SR
11
, wherein R
8
to R
11
are defined as R
3
and wherein R
9
and R
10
may combine to form a ring.
Another preferred group of compounds which are useful in the method of the present invention in order to get chemically sensitized silver halide emulsions having showing high speed is represented by formula (II):
wherein each of R′ and R″ independently represents a (substituted or unsubstituted) alkyl, alkenyl, alkynyl, aryl or heteroaryl group.
In a particular embodiment the compound according to the formula (III) is a preferred organo-tellurium compound for use in the method of the present invention:
The amount of the organ
Elst Kathy
Loccufier Johan
AGFA-GEVAERT
Breiner & Breiner L.L.C.
Schilling Richard L.
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