Radiation imagery chemistry: process – composition – or product th – Radiation sensitive product – Silver compound sensitizer containing
Reexamination Certificate
2001-04-16
2003-09-23
Baxter, Janet (Department: 1752)
Radiation imagery chemistry: process, composition, or product th
Radiation sensitive product
Silver compound sensitizer containing
C430S569000
Reexamination Certificate
active
06623916
ABSTRACT:
This invention relates to tabular silver chloride-iodide or silver chloride-bromide-iodide emulsions with a chloride content of at least 90 mol %, an iodide content of 0.01 to 5 mol % and a cubic habit, to a process for producing these emulsions and to photographic materials which contain said emulsions.
It is known from U.S. Pat. No. 5,320,938 that (100) AgCl tab grains with an aspect ratio of up to 20 can be produced, wherein the tab grains occupy at least 50% of the projected area. As illustrated in an electron microscope photograph, however, the emulsion contains a high proportion of cubes and thus does not exhibit sufficient homogeneity of the (100) AgCl tab grains for use in practice.
In U.S. Pat. No. 5,663,041 and U.S. Pat. No. 5,641,620, attempts are made to increase the homogeneity and aspect ratio of(100) AgCl tab grains by the re-dissolution of micrate. This costly process is beset by the difficulty that at the commencement of the growth phase of the (100) AgCl tab grains the differences in solubility between micrate and (100) AgCl crystal nuclei are not large, and high degrees of supersaturation have to be ensured at the end of the growth phase in order to re-dissolve the entire micrate. This also results in a large proportion of cubes or in a population of micrate in the batch which is not re-dissolved if the degree of supersaturation at the end of the growth phase was set too low.
These difficulties associated with the micrate dissolution process were recognized by P. Verrept, who at the IS+T's 50th Annual Conference (1997) proposed a process for producing Ag(Cl,I) (100) tab grains in which crystal growth was effected by employing a double inflow technique. In this process, however, it is essential that physical ripening of the (100) Ag(Cl,I) tab grains is effected, and this has to be carried out in a prescribed manner. However, since the only driving force for crystal growth of the relatively large crystals is provided by local statistical fluctuations of the supersaturation in the precipitation medium, physical ripening also results in the formation of a large proportion of cubes, i.e. there is insufficient differentiation between crystal faces with and without dislocation lines.
The known chloride-rich (100) tab grain emulsions, which are particularly suitable for photographic materials which are capable of being processed rapidly, exhibit an unsatisfactory spectral sensitivity. Moreover, their stability on storage is unsatisfactory at elevated temperatures and is particularly unsatisfactory at high atmospheric humidities.
None of the known processes of production are successful in producing chloride-rich (100) tab grain emulsions with a very large proportion of tab grains. However, a large proportion of tab grains is a prerequisite for achieving the advantages which are known for crystals such as these, such as a higher spectrally sensitized film speed and improved sharpness. Chemical ripening and spectral sensitization of the crystals can only effectively be optimized if a substantially uniform crystal population is present. This necessity becomes increasingly pronounced with increasing aspect ratio, and in particular is increasingly difficult to achieve for (100) tab grains with increasing aspect ratio. At an identical proportion of the projected area, cubes possess seven times the volume of cubic platelets with an aspect ratio of 8. Even small proportions of cubes, expressed as usual with respect to the projected area of all the crystals, thus make up a large proportion of the total volume of the crystals. Due to their very much smaller surface area, cubes constitute a costly waste of silver halide which scarcely contributes to the spectrally sensitized film speed.
Furthermore, these known processes are costly to carry out and are particularly difficult to scale up from small test batches to larger batch volumes, which makes their use on a production scale very difficult.
The underlying object of the present invention is thus to produce chloride-rich (100) tab grain emulsions which exhibit a high spectral sensitivity and good stability on storage at elevated temperatures, and particularly at high atmospheric humidities.
Surprisingly, it has now been found that this object is achieved for chloride-rich (100) tab grain emulsions if, with respect to the projected area of all the crystals, at least 80% of the crystals have an average aspect ratio of at least 8, a maximum crystal thickness distribution width of 15% and a maximum particle size distribution width of 25%.
A further underlying object of the invention is to provide a new production process which is simple to carry out, which can readily be employed in batch installations of different sizes, and which results in chloride-rich (100) tab grain emulsions which comprise a very large proportion of tab grains with a high aspect ratio as measured on the projection surface of all the crystals and which are distinguished by a high spectral sensitivity and good stability on storage at elevated temperatures and particularly at high atmospheric humidities.
It has now surprisingly been found that this is achieved if the supersaturation of silver halide in the reaction medium satisfies defined conditions during the crystal growth which follows the formation of nuclei.
The present invention therefore relates to a tabular silver chloride-iodide or silver chloride-bromide-iodide emulsion with a chloride content of at least 90 mol %, an iodide content of 0.01 to 5 mol % and a cubic habit, characterized in that, with respect to the projected area of all the crystals, at least 80% of the crystals have an average aspect ratio of at least 8, a maximum crystal thickness distribution width of 15% and a maximum particle size distribution width of 25%.
In particular, the emulsions employed are those for which the aspect ratio is at least 10.
In a further preferred embodiment, the maximum particle size distribution width is 20%.
Emulsions with a chloride content of at least 95 mol % are particularly preferred.
FIG. 1
is a scanning electron microscope photograph of a (100) Ag(Cl,I) tab grain emulsion according to the invention with an iodide content of 0.2%, wherein 94% of the crystals, with respect to the projected area, have an average aspect ratio of 10, a crystal thickness distribution width of 12% and a particle size distribution width of 18% (emulsion example Em-4).
Values of the average aspect ratio, of the crystal thickness distribution width and of the particle size distribution width are obtained by analyzing electron microscope photographs of obliquely shaded emulsion samples. In order to examine a representative cross-section of the emulsion, the number of photographs evaluated is such that at least 1000 emulsion crystals per emulsion are assessed as regards their particle size, aspect ratio and crystal thickness.
The particle size is defined as the diameter of a sphere of equivalent volume to that of a crystal.
The aspect ratio AV of tab grains is defined as
AV=D/H,
where D represents the diameter of the circle with the same area as the projected area of the individual tab grains, H represents the crystal thickness of the tab grains, and the crystal thickness H is measured perpendicularly to the major face.
The particle size distribution width V of an emulsion is defined as
V
[
%
]
=
standard
deviation
of
the
particle
size
distribution
×
100
average
particle
size
The crystal thickness distribution width K of an emulsion is defined as
K
[
%
]
=
standard
deviation
of
the
crystal
thickness
distribution
×
100
average
crystal
thickness
The present invention further relates to a process for producing said emulsions according to the invention, consisting at least of the precipitation of nuclei and of crystal growth, c
Agfa-Gevaert
Baxter Janet
Connolly Bove & Lodge & Hutz LLP
Walke Amanda C.
LandOfFree
Photographic silver halide emulsion does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Photographic silver halide emulsion, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Photographic silver halide emulsion will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3017394