Compositions: coating or plastic – Coating or plastic compositions – Proteinaceous material containing
Reexamination Certificate
2001-08-23
2002-10-22
Brunsman, David (Department: 1755)
Compositions: coating or plastic
Coating or plastic compositions
Proteinaceous material containing
C106S154110, C430S449000, C430S451000, C430S496000, C430S539000
Reexamination Certificate
active
06468339
ABSTRACT:
FIELD OF THE INVENTION
The present invention involves photographic emulsions, particularly filled gelatin based emulsions that confer wet scratch resistance when coated on a support.
BACKGROUND OF THE INVENTION
In the photographic industry, gelatin based emulsions are often used to coat layers on a support. A gelatin based emulsion consists of a gelatin matrix and various photographic fillers or inclusions are present to perform the imaging capabilities of the coating. The gelatin is used as the matrix due to its properties in the dry and wet state. One of the key properties of gelatin that makes it a useful material for a photographic emulsion, is its ability to swell with water or a developing solution. This property of the coating is critical to allow the emulsion to be wet processed. To resist complete dissolution of the coating when swollen, chemical hardeners such as bis vinyl sulfonyl methane are often added.
When the coating is swollen, the material is a soft gel. Due to the soft nature of the coating, durability of the coating can be a problem during handling and transport through high speed processing units. One method to quantify the durability of an emulsion based coating is by measuring the wet scratch resistance. This is done by determining the load required to form a scratch of continuous plow in a fully swollen coating. To understand the problem, it must be realized that (i) a photographic emulsion is a gelatin matrix composite material, and (ii) the modulus (or the material's ability to withstand deformation) is very low in the swollen state. A high modulus material is stiff and glassy like, while a low modulus material is soft, compliant, and rubber like. A swollen gelatin based coating behaves as a low modulus rubber.
It would be advantageous to create a coating that would have high resistance to wet scratch, thus allowing for fewer defects during processing as well as allowing for processing labs to relax on the stringent care and maintenance in a processing unit.
SUMMARY OF THE INVENTION
The present invention increases the scratch resistance of a gelatin based coating which, as described above, becomes soft and rubbery when wet. Thus, the present invention discloses a coating composition comprising at least gelatin and colloidal alumina particles, the particles being less than 0.2 micrometers. The composition can be used in an imaging element comprising a support and at least one imaging layer, wherein the element contains, in any gelatin containing layer, colloidal alumina particles less than 0.2 micrometers. Also disclosed is a method of increasing the wet strength of a coated gelatin layer comprising the steps of: providing alumina particles having an average size of less than 0.2 micrometers; adding the alumina particles to gelatin at a pH between 3.5 and 7.0 to form a coating composition; adjusting the pH of the composition to a level required for coating; and coating the composition on a support.
The gelatin based photographic coating of the invention contains at least gelatin and colloidal alumina particles. Optionally, the coating may contain any photographic addenda that may be important to a photographic product, as well as a chemical hardening agent that will form crosslinks in the gelatin. The coating, when swollen with water or a photo processing solution, shows an increase in wet durability as demonstrated by increased wet scratch resistance. It is expected that the colloidal alumina may be placed throughout the entire coating package, or in selected layers that would require mechanical reinforcement in a scratch environment.
DETAILED DESCRIPTION OF THE INVENTION
Wet scratch resistance of a flexible coating, in particular a multilayer coating, will relate to two parameters. The first is the stress in the coating as a result of the scratching stylus or asperity. This stress is frequently found in the bottom layers of the package, and is primarily due to the mismatch in modulus between the glassy support or substrate, and the soft gelatin coating. To minimize this stress, it is advantageous to decrease the mismatch in modulus by increasing the modulus of the (bottom layer) swollen coating. This can be done by incorporation of a hard material or high modulus filler. The other parameter of importance to wet scratch is the failure strength. This failure occurs cohesively in the coating. High modulus fillers in a gelatin based coating should help to minimize the stresses in the coating; however, if the chemical interactions between the gelatin matrix and rigid filler are weak, these inclusions will simply lower the failure strength of the material. Therefore, it is important to find a high modulus filler with strong chemical interactions at the filler/matrix interface.
One such filler material is alumina particles. In the swollen state, alumina particles will maintain a high modulus and increase the overall modulus of the entire coating. Additionally, it is known that at the polar aluminum oxide surface, carboxylic acid containing molecules exchange for the surface hydroxyl groups to form strong bonds (Environmental Science and Technology 1988, 22(1), 37-41). Since gelatin contains a high number of carboxylic acid groups, the interfacial interaction between gelatin and alumina should be high.
Alumina particles used in the practice of this invention as reinforcing filler particles have a median diameter less than 0.2 micrometers, preferably less than 0.15 micrometers and most preferably less than 0.1 micrometers. As a practical matter, the minimum median diameter is 0.04 micrometers. The filler particles preferably have a Mohs hardness greater than 6 and are present in an amount of from 5 to 60 percent by weight and preferably from 10 to 50 percent and most preferably from 20 to 45 percent based on the weight of the binder. A specific example of the filler particles is &ggr;-alumina. These can also be pre-dispersed in water with or without a dispersant using media milling and then incorporated into the coating composition.
In accordance with a preferred embodiment of this invention, the gelatin containing alumina samples were prepared by first media milling the alumina in water until the appropriate size (less than 0.2 micrometers) was obtained. The resulting slurry was next added to gelatin at a pH of 3.5 and 7.0, preferably 4.0, at a ratio of 1:1 gelatin:alumina to ensure good interaction between gelatin and alumina. Ideally, the pH should be less 4.5.
As used herein the term “gelatin” includes gelatin and gelatin derivatives such as gelatin derivatized with aromatic sulfonyl chlorides, carboxylic acid chlorides, carboxylic acid anhydrides, aryl isocyanates, etc. Gelatin may be any of so-called alkali treated (lime treated) gelatin which was immersed in an alkali bath prior to extraction thereof, an acid treated gelatin which was immersed in an acid bath prior to extraction thereof, an acid treated gelatin that was immersed in both baths and enzyme treated gelatin.
The alumina filled gelatin layer of the present invention is preferably hardened. Hardeners usable for hardening gelatin layers include, for example, aldehyde compounds such as formaldehyde and glutaraldehyde; ketone compounds such as diacetyl and cyclopentanedione; compounds having reactive halogens such as bis(2-chloroethylurea), 2-hydroxy-4,6-dichloro-1,3,5-trizine and those described in U.S. Pat. Nos. 3,288,775 and 2,732,303 and British Patent Nos. 974,723 and 1,167,207; divinylsulfone, 5-acetyl-1,3-diacrylolhexahydro-1,3,5-triazine and reactive olefin-containing compounds such as divinylsulfone, 5-acetyl-1,2-diacryloyl-hexahydro-1,3,5-triazine, and the compounds such as divinylsulfone, 5-acetyl-1,3-diacryloyl-hexahydro-1,3,5-triazine, and the compounds disclosed in U.S. Pat. Nos. 3,635,718 and 3,232,763, and British Patent 994,869; N-hydroxymethylothalimide; N-methylol compounds such as N-hydroxymethylphthalimide and those described in U.S. Pat. Nos. 2,732,316 and 2,586,168; isocyanates described in U.S. Pat. Nos. 3,103,437; the aziridines disclosed in U.S. Pat. Nos. 3,017,28
Nair Mridula
Taylor Jeffrey F.
Brunsman David
Eastman Kodak Company
Wells Doreen M.
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