Compositions: coating or plastic – Coating or plastic compositions – Proteinaceous material containing
Reexamination Certificate
2002-05-30
2003-07-08
Schilling, Richard L. (Department: 1752)
Compositions: coating or plastic
Coating or plastic compositions
Proteinaceous material containing
C430S621000, C430S622000, C430S642000, C430S449000, C530S354000, C530S355000
Reexamination Certificate
active
06589326
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to coating solutions comprising a hydrophilic colloid gelatin, which is prepared by the hydrolysis of ossein using sodium or potassium hydroxide, where the coating solution contains a gelatin hardener at a level of from 1-200 effective &mgr;mole hardener per gram of coating solution.
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.
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. Nos. 5,316,902, 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 be able to use less hardener.
Gelatin hardener is typically introduced into one or more hydrophilic colloid layer compositions coated together in a coating pack. Usually, the hardener solution is mixed with a fluid that contains gelatin immediately prior to the coating hopper. This mixture is referred to as a coating fluid, and may also contain other photographically-useful materials. While hardener may be added individually to each hydrophilic colloid layer coating fluid, it is commonly added only to a limited number of such layers, commonly to only a single layer coating solution for a multilayer coating pack. After passing through the coating hopper, the hardener molecules diffuse into the various layers of the coating pack, cross-link the gelatin molecules and thus form a chemical gel that acts as a permanent network or matrix. Fast-acting hardeners are preferably used to increase the rate of cross-linking thereby allowing the aim physical properties, and often the associated aim sensitometric properties, to be met at shorter times. The most preferred fast acting hardeners are vinylsulfonyl hardeners, which react with the ∈-amino function of lysine and hydroxylysine. The primary benefit from use of such hardeners is more rapid release of product to customers, with a consequent reduction in inventory.
The reaction of hardener with gelatin commences immediately on mixing in the coating fluid and continues throughout the coating process. The residence time of the coating fluid in the hopper is often on the order of a minute, but may be considerably longer in any regions of re-circulating flow in or on the hopper, e.g. because of surface imperfections. Cross-linking of gelatin by hardener molecules therefore takes place in the period between mixing and final coating of the pack onto the web. The cross-linking can give rise to large aggregates and, potentially, chemical gelation. The formation of “gel slugs” (microgels) within the hopper may cause coating defects, specifically lines and streaks, which leads to waste of coated product. This is a particular issue with delivery of fast-acting (i.e. rapidly cross-linking) hardeners, as if a coating fluid gels rapidly, the tendency to form coating defects increases. The time taken to gel generally decreases when the concentration and viscosity of the coating fluid increase, and thus is particularly potentially problematic in hardener-bearing coating fluids wherein hardener for all the hydrophilic colloid layers is delivered through only a single or only a limited number of hydrophilic colloid layers coating fluids.
One of the most expensive processes in manufacturing of multilayer photographic products is drying of water after coating. If the concentration of solids within a coating fluid can be increased, then less water is coated an
Howe Andrew M.
Lobo Lloyd A.
Santee Gary L.
Anderson Andrew J.
Eastman Kodak Company
Schilling Richard L.
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