Radiation imagery chemistry: process – composition – or product th – Radiation sensitive product – Silver compound sensitizer containing
Reexamination Certificate
2001-06-20
2003-02-04
Schilling, Richard L. (Department: 1752)
Radiation imagery chemistry: process, composition, or product th
Radiation sensitive product
Silver compound sensitizer containing
C430S567000, C430S599000, C430S603000
Reexamination Certificate
active
06514682
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to photographic elements. It particularly relates to an improved silver halide obtained by surface treatment with formate.
BACKGROUND OF THE INVENTION
The photographic industry is constantly experimenting with methods of increasing film speed and at the same time reducing granularity. The most direct approach to increasing photographic speed in a silver halide based system is to increase the light sensitivity of the silver halide grains by making the grains larger. However, such an approach leads directly to increased granularity which the customer can find objectionable. If, on the other hand, the inherent photoefficiency of the emulsion grains can be increased without changing grain size, greater speeds can be obtained without added granularity.
Another important aspect of utilizing an addendum to alter emulsion speed is the point of addition. If the emulsion can be treated after it is prepared and fully sensitized, the building of a particular color record in a film is greatly simplified. Photographic film contains many chemical elements that can interact in unpredictable ways making film building very much an empirical or “trial and error” process. It is often impossible to predict the exact photographic speed required of a given emulsion. Rather, the emulsion must first be manufactured and placed in the complex milieu of the multi-layered photographic film to determine its effect. For instance, in the development of a new film much effort is expended in obtaining a linear response to light over a wide exposure latitude. Under these conditions it is critical to be able to obtain an emulsion with exactly the right photographic speed to combine with either a slower or faster emulsion or both and extend the exposure range. This process is called “knitting the curve” and relates to the shape of the curve obtained when optical density is plotted versus the log of the exposure for the color record of interest. The aim here is to produce a linear transition between the effective ranges of the individual emulsions and thereby provide consist tone reproduction. If one is able to alter the speed of an emulsion without remaking or resensitizing it, the cost of developing a new film is greatly reduced.
Many materials have been examined for their ability to increase photoefficiency. Notable examples are thioureas (U.S. Pat. No. 3,458,318), sulfonic acid derivatives (U.S. Pat. Nos. 2,937,089 and 3,706,567), triazine compounds (U.S. Pat. Nos. 2,875,058 and 3,695,888), mercapto compounds (U.S. Pat. No. 3,457,078), pyrmidine derivatives (U.S. Pat. No. 3,615,632), dihyrodpyridine compounds (U.S. Pat. No. 5,192,654), aminotriazoles (U.S. Pat. No. 5,306,612), hydrazines (U.S. Pat. Nos. 2,419,975, 5,459,052 and 4,971,890 and EP Application No. 554,856 A1, propargyl and butynyl benzoxazoles (U.S. Pat. Nos. 4,378,426, 4,451,557, and 5,500,333), fragmentable electron donors (U.S. Pat. Nos. 5,747,235, 5,747,236, and 6,010,841), and organic hole-trapping dopants (EP Application 0922994 A2). Disadvantages in the use of these compounds include relatively small speed effects, fog increases, loss in emulsion stability, exorbitant cost, the need to treat the emulsion either during making or during sensitizing, and undesirable interactions resulting from the relatively complex chemical structure of the addendum.
PROBLEM TO BE SOLVED BY THE INVENTION
Thus, there continues to be a need for more photoefficient emulsions that can be obtained utilizing an inexpensive, readily available, chemically simple addendum. The addendum should produce substantial speed gains with minimal fog effects and few undesirable interactions. Further benefits can be realized if the emulsion can be treated after it is fully prepared and spectrally sensitized.
SUMMARY OF THE INVENTION
It is an object of the invention to provide more photoefficient emulsions through the use of an inexpensive, readily available, chemically simple addendum.
It is another object to provide an addendum that has few undesirable side effects such as increased fog or poorer keeping properties of the emulsion.
It is a further object to provide an addendum that can be utilized with a fully prepared and spectrally sensitized emulsion.
These and other objects of the invention are accomplished by an emulsion comprising chemically and spectrally sensitized silver halide grains having formate on the surface of said grains.
ADVANTAGEOUS EFFECT OF THE INVENTION
The invention provides a means of obtaining silver halide emulsions with increased photoefficiency. This is accomplished through the use of an addendum that is inexpensive, readily available, and chemically simple. The addendum can be used after the emulsion is made and spectrally sensitized thereby simplifying and reducing the cost of producing a new film. The increased photoefficiency of the emulsion is accompanied by minimal side effects such as increased fog or degraded keeping.
DETAILED DESCRIPTION OF THE INVENTION
The invention has numerous advantages over prior methods of preparing photographic emulsions. The invention provides emulsions with increased photoefficiency that can be used to manufacture photographic film having greater photographic speed and/or improved granularity. The addendum producing the increased photoefficiency is added to fully made and spectrally sensitized emulsions which simplifies the building of film layers containing multiple emulsions. Because of the empirical or “trial and error” method of selecting emulsions with the correct speed, the ability to alter the speed of an emulsion without having to remake and resensitize it provides a great savings in the cost of building a new photographic film. Furthermore, the addendum is inexpensive and readily available. It is one of the simplest of all organic chemicals leading one to expect few unwanted and unpredictable interactions with the many chemical components found in photographic film. These and other advantages will be apparent from the detailed description below.
The invention utilizes the addition of formate following the addition of silver ion to a previously spectrally sensitized emulsion of a type commonly employed in color negative applications.
Other approaches to this problem such as that described by Mydlarz et al in U.S. Pat. No. 5,849,470 use materials which slow the emulsion speed with the consequence of a loss of photoefficiency. Furthermore, these materials like those described by De Keyzer et al must be utilized prior to or during the sensitization process. In contrast, the present invention provides a means of altering photographic speed by increasing the photoefficiency of a sensitized emulsion fully prepared for use. By using lesser or greater amounts of the addenda, the speed of a fully sensitized emulsion can be tuned to the correct speed thereby providing a linear curve shape. This approach teaches away from that of De Keyzer et al in EP Application 0922994 A2 in which formate is utilized as a dopant and is added to the emulsion during its formation.
The photographic emulsions of this invention are generally prepared by precipitating silver halide crystals in a colloidal matrix by methods conventional in the art. The colloid is typically a hydrophilic film forming agent such as gelatin, alginic acid, or derivatives thereof. The silver halide emulsions may consist of chloride, bromide, and iodide and combinations thereof with the most useful emulsions consisting of silver bromoiodide since this combination generally produces the most efficient photographic emulsion.
The crystals formed in the precipitation step are washed and then chemically and spectrally sensitized by adding spectral sensitizing dyes and chemical sensitizers, and by providing a heating step during which the emulsion temperature is raised, typically from 40° C. to 70° C., and maintained for a period of time. The precipitation and spectral and chemical sensitization methods utilized in preparing the emulsions employed in the invention can be those methods known in the art.
Spectral sensitizat
Blank Lynne M.
Eastman Kodak Company
Leipold Paul A.
Schilling Richard L.
LandOfFree
Speed addendum for photographic emulsions does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Speed addendum for photographic emulsions, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Speed addendum for photographic emulsions will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3126063