Radiation imagery chemistry: process – composition – or product th – Radiation sensitive product – Two or more radiation-sensitive layers containing other than...
Reexamination Certificate
2002-02-21
2002-08-20
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...
C430S502000, C430S965000, C430S966000
Reexamination Certificate
active
06436621
ABSTRACT:
DESCRIPTION
1. Field of the Invention
The present invention relates to a light-sensitive silver halide photographic material having a multilayer composition of light-sensitive silver halide emulsion layers comprising negative image type tabular grain emulsions and the method to prepare said material.
2. Background and Object of the Invention
Light-sensitive silver halide photographic materials comprising silver halide emulsion layers having negative image type tabular grain emulsions have become more and more important during the last decade.
Tabular silver halide grains are crystals possessing two parallel faces with a ratio between the diameter of a circle having the same area as these faces, and the thickness, being the distance between the two major faces, equal to at least 2.
Tabular grains are known in the photographic art for quite some time. As early as 1961 Berry et al. described the preparation and growth of tabular silver bromoiodide grains in Photographic Science and Engineering, Vol 5, No 6. A discussion of tabular grains appeared in Duffin, Photographic Emulsion Chemistry, Focal Press, 1966, p. 66-72. Early patent literature includes Bogg, U.S. Pat. No. 4,063,951, Lewis U.S. Pat. No. 4,067,739 and Maternaghan U.S. Pat. Nos. 4,150,994; 4,184,877 and 4,184,878. However the tabular grains described therein cannot be regarded as showing a high diameter to thickness ratio, commonly termed aspect ratio. In a number of U.S. Patent Applications filed in 1981 and issued in 1984 tabular grains with high aspect ratio and their advantages in photographic applications are described. So Wilgus U.S. Pat. No. 4,434,226 discloses tabular silver bromoiodide grains having a thickness of less than 0.2 &mgr;m, a diameter of at least 0.6 &mgr;m and an average aspect ratio greater than 8:1 and accounting for at least 50 percent of the total projected area of all the emulsion grains. Kofron U.S. Pat. No. 4,439,520 discloses similar grains which are spectrally sensitized. Abbott U.S. Pat. No. 4,425,425 describes radiographic materials containing tabular grains with an aspect ratio of at least 8:1 and Abbott U.S. Pat. No. 4,425,426 discloses similar grains with an aspect ratio between 5:1 and 8:1. A survey on high aspect ratio silver halide emulsions appeared in Research Disclosure, Volume 225, January 1983, Item 22534.
For radiographic applications the main photographic advantages of tabular grains compared to normal globular grains are a high covering power at high forehardening levels, a high developability and higher sharpness, especially in double side coated spectrally sensitized materials. The thinner the tabular grains the greater these advantages.
In the references on tabular grains cited above especially silver bromide or silver iodobromide emulsions having a high sensitivity are disclosed whereas the use of e.g. emulsions with tabular grains rich in chloride has hitherto been considered to be disadvantageous with respect to sensitivity. For emulsions with crystals rich in chloride, applications in the field of less sensitive materials as e.g. graphic arts materials, duplicating materials, radiographic hardcopy materials, diffusion transfer reversal materials and black-and-white or color print materials are well-known. The advantages of said emulsions with crystals rich in chloride regarding higher development and fixing rates, are highly appreciated.
As nowadays the tendency is present to get materials processed in shorter processing times, it is highly appreciated to combine said advantages with a high sensitivity for application in high-sensitive materials, an object which can be realized as has been described in EP-A 0 678 772.
In spite of these important advantages, tabular grains, those rich in chloride as well as those rich in bromide, have two important disadvantages: they are highly susceptible to mechanical stress and the developed silver has an unacceptable reddish-brown color if compared with the desired cold-black color shown by more globular grains. Tabular grains rich in silver chloride even show a worse image tone than those rich in bromide having comparable dimensions (thickness and aspect ratio) after processing in classical processing solutions used in the processing of classical radiological materials.
This reddish-brown color can be corrected by increasing the optical density in the red region of the visible spectrum by adding suitable dyes to the undercoat layer, to the emulsion layer and/or to the protective layer. This non-image wise color correction method has been disclosed in references as e.g. JP-A's 03 100 645; 01 029 838; 01 312 536; 03 103 846; 03 094 249; 03 255 435; 61 285 445; EP-B 271 309 and U.S. Pat. No. 4,861,702. But this inevitably leads to an undesirable higher gross-fog of the photographic material and obviously the sensitivity to mechanical stress is not improved by this optical correction method.
A more suitable way consists in an image-wise color correction. This can be made by making use of color-forming developers, which are colored blue in their oxidized form. Examples thereof are summarized in JP-A's 03 153 234; 03 154 043; 03 154 046. In JP-A's 03 156 447 and 03 157 645 the adsorption of a blue colored dye as a function of exposure has further been disclosed.
Another way to overcome these disadvantages is to use tabular grains with an increased thickness. Methods to prepare thicker tabular grains have already been described in U.S. Pat. Nos. 4,801,522; 5,028,521 and 5,013,641 and EP-A 0 569 075. However the advantages obtained by making use of tabular grains as cited above disappear by making use of this method.
Therefore it is an object of this invention to prepare tabular grains having a thickness less than 0.2 &mgr;m and to coat them in a negative image type silver halide photographic material, overcoming the above disadvantages of unacceptable image tone and susceptibility to mechanical stress. Other objects will become apparent from the description hereinafter.
SUMMARY OF THE INVENTION
The objects of the present invention are attained by providing a multilayer negative image type material comprising on at least one side of a support a multilayer composition of at least two layers of negative image type silver halide emulsions adjacent to each other, wherein the emulsion layer closest to the said support comprises tabular emulsion crystals selected from the group consisting of silver chloride, silver chlorobromide, silver chloroiodide, silver chlorobromoiodide, having a {111} or {100} crystal habit and wherein the adjacent layer(s) farther from the said support comprise(s) essentially cubic emulsion crystals selected from the group consisting of silver chloride, silver chlorobromide and silver bromide, wherein the essentially cubic grains are less sensitive than the tabular grains and wherein the said tabular emulsion crystals having {111} or {100} major faces have at least 50 mole % of chloride.
Moreover a method has been described for preparing said light-sensitive silver halide photographic negative image type material by the steps of coating said multilayer composition on at least one side of a support and overcoating said composition(s) with at least one protective layer.
DETAILED DESCRIPTION OF THE INVENTION
Preferably in the preparation step of the silver halide crystals selected from the group consisting of silver chloride, silver chlorobromide and silver bromide for use in the layer(s) adjacent to the layer(s) containing tabular {100} or {111} grains in the multilayer material according to this invention, the pAg range for the precipitation thereof is chosen such that the said emulsions coated in the emulsion layer farthest from the support are emulsions having essentially cubic crystal habit. By “essentially cubic” is meant a grain which either is (a) perfectly cubic, or (b) cubic with rounded corners, or (c) cubic with small (111) faces on the corners so that in fact a tetradecahedrical emulsion is obtained, the total area of these (111) fa
Andriessen Hieronymus
Henderickx Freddy
Agfa-Gevaert
Breiner & Breiner L.L.C.
Schilling Richard L.
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