Radiation imagery chemistry: process – composition – or product th – Radiation sensitive product – Identified backing or protective layer containing
Reexamination Certificate
2002-05-30
2003-06-03
Schilling, Richard L. (Department: 1752)
Radiation imagery chemistry: process, composition, or product th
Radiation sensitive product
Identified backing or protective layer containing
C430S621000, C430S622000, C430S642000
Reexamination Certificate
active
06573037
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to imaging elements comprising a hydrophilic colloid gelatin, which is prepared by the hydrolysis of ossein using sodium or potassium hydroxide, where the gelatin is crosslinked with a hardener at a level of 70-120 effective &mgr;mole hardener per gram of gelatin.
BACKGROUND OF THE INVENTION
Imaging elements, particularly photographic silver halide imaging elements, commonly use a hydrophilic colloid as a film forming binder for layers thereof, most commonly ossein. The layers of such imaging elements are typically coated employing multilayer slide bead coating processes such as described in U.S. Pat. No. 2,716,419 and multilayer slide curtain coating processes such as described in U.S. Pat. No. 3,508,947. The binder of choice in most cases is gelatin, prepared from various sources of collagen (see, e.g., P. I. Rose, The Theory of Photographic Process, 4th Edition, edited by T. H. James (Macmillan Publishing Company, New York, 1977) p. 51-65). The binder is expected to provide several functions, primarily to provide an element with some level of mechanical integrity and contain all the materials within the imaging element, which are required to provide an image. In particular, in photographic elements, the binder is expected to facilitate the diffusion of materials into and out of the element during a wet processing step. Gelatin is particularly suitable to perform this function, since it can absorb water and swell during the processing steps. In addition, gelatin also forms a cross linked network below a critical setting temperature through non-covalent bonding, which prevents dissolution of the gelatin, when wet. However, most photoprocessing operations are carried out above the critical temperature, which would thereby melt the gelatin in a non-crosslinked form. In order to prevent the dissolution of the gelatin during the photoprocessing operation, the gelatin is crosslinked chemically, with a hardener, during the manufacture of the imaging element.
High purity gelatins are generally required for imaging applications. Currently the most commonly employed manufacturing process for obtaining high purity gelatins involves demineralization of a collagen containing material, typically cattle bone (ossein), followed by extended alkaline treatment (liming) and finally gelatin extractions with water of increasing temperature as described in U.S. Pat. Nos. 3,514,518 and 4,824,939. The gelatin produced by this process, commonly referred to as lime processed ossein gelatin, has existed with various modifications throughout the gelatin industry for a number of years. The liming step of this process requires up to 60 days or more, the longest step in the approximately 3 month process of producing gelatin. The hydrolyzed collagen is extracted in a series of steps to obtain several gelatin fractions with varying molecular weights. In order to obtain gelatin of desired molecular weight to provide suitable coating solution viscosities, these fractions can be further hydrolyzed by high temperature hydrolysis. The fractions are then blended to obtain the appropriate molecular weight for photographic use. U.S. Pat. No. 5,908,921 describes a relatively new process for the preparation of photographic grade gelatin, where the agent for hydrolysis is a strong alkali, such as sodium or potassium hydroxide. The reaction rate is disclosed to be from 10 to 120 hours (substantially faster than the prior lime processes), after which a single extraction step yields a single batch of gelatin, which is then purified and deionized. The characteristics of the gelatin produced are that it has a high gel strength and narrow molecular weight distribution compared to gelatins produced by the conventional process where lime is used as the agent for hydrolysis.
Performance of the binder system may also be altered via chemical modification of the gelatin employed, as well as the choice and level of the hardener. Most of the hardeners used in practice act by reacting moieties on the hardener with the free amine groups on the gelatin. Lysine and hydroxylysine are the two predominant amino acids in gelatin that contribute the primary amine groups. Chemical modification of gelatin by increasing the amount of free amine groups have been disclosed in U.S. Pat. No. 5,316,902; U.S. Pat. No. 5,439,791 and EP 614930 and EP 813,109. These patents disclose elements wherein the carboxylic acid containing amino acids are reacted with moieties that can further react with vinyl sulfonyl hardeners. These are directed towards providing differential hardening between layers of a multilayer coating. Modified gelatin has also been disclosed in U.S. Pat. No. 4,590,151 for use in a top layer of a multilayer coating to reduce the amount of reticulation during photoprocessing. While chemical modification of gelatin may increase the wet mechanical properties of the imaging element, it is not easy or inexpensive to carry out. It adds an extra step in the gelatin manufacturing process and includes additional cost of the reactants needed. Other methods of improving the wet mechanical properties are by including other polymers along with gelatin. These polymers may be in the form of latexes as disclosed in U.S. Pat. No. 4,495,273 or as gelatin substitutes as disclosed in U.S. Pat. No. 4,019,908. Other attempts to improve the mechanical properties of the element, in the wet state, are related to improving the adhesion of the gelatin element to the substrate on which it is coated. EP 727698 discloses the use of specific solvents in layer adjacent to the support. However, even if the adhesion problems are solved, the cohesive strength or the wet strength property still may need to be improved.
Optimization of chemical hardening properties of a coated layer comprising gelatin is critical. While some attempts to optimize performance of the binder system have been carried out via chemical modification of the gelatin employed as discussed above, most attempts to optimize the binder system have focused on the choice and level of the hardener. It is the chemical hardening that renders the coating insoluble, and provides the required durability. The amount of hardener used, relative to the amount of gelatin present, is typically primarily a compromise of the swell of the wet element, the mechanical integrity, and cost. If too much hardener is used, the imaging element will not swell much, thereby, reducing the mobility of the various species required to permeate the element during processing. If too little hardener is used, however, when the element is in the developing solution, and immediately after removal from the developing solutions, it may be easily scratched while wet as the amount of chemical crosslinking is less and the coating becomes mushy, and prone to damage if it comes into contact with the hardware of the photoprocessor. Such scratches to the surface of the element may cause an unacceptable image to be formed. The third factor is cost of the hardener. It is always desirable to use less hardener.
Another factor which may impact the wet mechanical properties of imaging elements such as photographic elements is the amount of dispersed non-binder materials that are present in layers thereof, such as dispersed photographically useful materials. As the ratio of the amount of non-binder material, relative to the binder, increases, the mushiness of the element also increases. Thus, elements which have a higher volume fraction of non-binder material typically require a higher level of hardener relative to elements with a low ratio in order to provide comparable wet mechanical strength. In addition, most photographic elements are comprised of more than one layer. In a multilayer photographic element each of the layers may have a different ratio of the non-binder materials to the binder. The weakest link in this multilayer element is the one with the highest volume fraction of non-binder to binder material. Thus it may be desirable to be able to selectively strengthen the layers which have such high vo
Hahm Paul T.
Honan James S.
Lobo Lloyd A.
Yau Hwei-Ling
Anderson Andrew J.
Schilling Richard L.
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