Radiation imagery chemistry: process – composition – or product th – Radiation sensitive product – Silver compound sensitizer containing
Reexamination Certificate
2000-06-27
2001-09-18
Baxter, Janet (Department: 1752)
Radiation imagery chemistry: process, composition, or product th
Radiation sensitive product
Silver compound sensitizer containing
C430S569000, C430S966000
Reexamination Certificate
active
06291153
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to silver halide radiographic elements particularly adapted for use in dental imaging. More particularly, these radiographic elements contain lower silver than in conventional dental films.
BACKGROUND OF THE INVENTION
Roentgen discovered X-radiation by the inadvertent exposure of a silver halide photographic element. In 1913, Eastman Kodak Company introduced its first product specifically intended to be exposed by X-radiation (X-rays). Silver halide radiographic films account for the overwhelming majority of medical diagnostic images. It was recognized almost immediately that the high energy ionizing X-rays are potentially harmful, and ways were sought to avoid high levels of patient exposure. Radiographic films provide viewable silver images upon imagewise exposure followed by wet processing.
One approach, still in widespread practice is to coat a silver halide emulsion useful in radiographic films on both sides of the film support. Thus, the number of X-rays that can be absorbed and used for imaging are doubled, providing higher sensitivity. Dual-coated radiographic films are sold by Eastman Kodak Company under the trademark DUPLITIZED. Films that rely entirely on X-radiation absorption for image capture are referred in the art as “direct” radiographic elements, while those that rely on fluorescent intensifying screen light emission are referred to in the art as “indirect” radiographic elements.
Direct radiographic elements have various uses, such as in industrial applications where intensifying screens cannot be used for some reason (for example pipeline welds and turbine blades).
Another important application for direct radiographic elements is in dentistry where images of a patient's teeth and gums are made in order to provide desired diagnostic and preventative dental care. In dental diagnostic imaging a small piece of X-ray film, commonly referred to as “chip” mounted in a sealed opaque package is placed in a patient's mouth during X-ray exposure.
Copending and commonly assigned U.S. Ser. No. 09/007085 filed Jan. 14, 1998 by Baugher et al now U.S. Pat. No. 5,952,163, describes direct dental X-ray films that can be removed from the opaque packages after imagewise exposure and processed in room light. Those films are comprised of silver halide emulsion and protective layers that contain dye particles that can be decolorized during wet processing.
Copending and commonly assigned U.S. Ser. No. 09/087477 filed May 29, 1998, now U.S. Pat. No. 5,925,505, also describes and claims direct dental X-ray films that can be handled in ambient light.
Dental X-ray film is used worldwide in providing dental care. In many countries that are less industrialized or are considered “emerging” markets, cost of dental care is a great concern because of limited resources by dentists for purchasing materials and supplies. Many patients in those countries cannot pay for such services despite their need for them. As a result, there is a need to provide dental X-ray films that are less expensive, can be used with existing or lower cost processing systems, and that still provide desired sensitometric properties (for example, speed).
SUMMARY OF THE INVENTION
The problems noted above are overcome with a direct radiographic film comprising a support having disposed on one or both sides thereof, a silver halide emulsion unit comprising non-spectrally sensitized silver halide grains comprising at least 95 mol % bromide based on total silver and no more than 3 mol % iodide based on total silver, at least 50% of the silver halide grain projected area being provided by tabular grains having an average aspect ratio greater than 8, the coverage of silver in each silver halide emulsion unit being from about 30 to about 45 mg/dm
2
, and the coverage of gelatino-vehicle in each silver halide emulsion unit being from about 15 to about 30 mg/dm
2
.
The radiographic films of this invention are lower in cost because of the lowered coating of silver and gelatino vehicle, but the sensitometric results are very acceptable despite these unconventional changes. This was a surprise because it was expected that lowered silver coverage in the elements would result in lowered photographic sensitometric properties, for example lower photographic speed. That expectation is consistent with known teaching in the art that proposes that photographic speed in radiographic materials is largely influenced by the mass of the silver halide grains and silver coating coverage. The present invention achieves acceptable photographic speed despite having only about one-third the conventional amount of silver halide in each silver halide emulsion unit.
In addition, I found that it was important that the coating coverage of silver and gelatino-vehicle in each silver halide emulsion unit be carefully balanced. Thus, while the silver coverage has been lowered without loss of sensitometric results, the relationship of the gelatino-vehicle coverage to silver coverage is critical. If the gelatino-vehicle coverage is too high, a loss in speed is observed. If the coverage is too low, fog from drying can increase due to insufficient protection from the hydrophilic gelatino-vehicle.
DETAILED DESCRIPTION OF THE INVENTION
In the simplest possible construction a direct radiographic film according to the invention can take the following form:
Since flexible supports are much more common than rigid supports, usually two silver halide emulsion units are coated on the support, as shown in the following preferred embodiment:
The following represents a specifically preferred embodiment of the invention having broad general applicability as dental films:
The support can take the form of any conventional radiographic element support. It should be transmissive. A single silver halide emulsion unit is particularly compatible with rigid supports (for example, a glass or metal plates), since a rigid support can withstand the forces applied to the support. In all embodiments in which silver halide emulsion unit is coated on only one side of the support, the support can be either X-radiation transmissive or X-radiation absorbing.
In the preferred DXR-2 embodiment, the silver halide emulsion units can include one or more silver halide emulsion layers and additional gel layers. Coating physical property modifying addenda can be present in either or both units. In such embodiments, the support can be either flexible or rigid, but must be X-radiation and light transmissive.
In the more preferred embodiments, the silver halide emulsion unit can contain two or more layers, with at least one of these layers being a silver halide emulsion layer. For example, each silver halide emulsion unit described above can be divided into two or three silver halide emulsion layers. In a preferred form, each unit containing a silver halide emulsion is comprised of a silver halide emulsion layer and at least one overlying protective layer (as shown in DXR-3). Each silver halide emulsion layer can be sub-divided into two or more emulsion layers and each protective overcoat can be sub-divided into two or more individual layers. Protective overcoats are typically sub-divided into surface overcoats and interlayers.
The supports for the direct X-ray films of the invention can be chosen from among those disclosed by
Research Disclosure
, Item 38957, cited above, XV. Supports and
Research Disclosure
, Vol. 184, August 1979, Item 18431, XII. Film Supports. In the majority of applications the support is a transparent film support. In its simplest possible form the transparent film support consists of a transparent film chosen to allow direct adhesion of the hydrophilic colloid emulsion layers. More commonly, the transparent film is itself hydrophobic and subbing layers are coated on the film to facilitate adhesion of the hydrophilic emulsion layers. Typically the support is either colorless or blue tinted, tinting dye being present in one or both of the film and the subbing layers. Referring to
Research Disclosure
, Item 38957, Section X
Baxter Janet
Eastman Kodak Company
Tucker J. Lanny
Walla Amanda C.
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