Radiation imagery chemistry: process – composition – or product th – Radiation sensitive product – Antihalation or filter layer containing
Reexamination Certificate
2001-04-27
2002-09-24
Schilling, Richard L. (Department: 1752)
Radiation imagery chemistry: process, composition, or product th
Radiation sensitive product
Antihalation or filter layer containing
C430S531000, C430S533000, C430S536000, C430S539000, C430S935000, C430S961000, C427S420000
Reexamination Certificate
active
06455240
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to an improved method of coating multilayer liquid packs on moving webs involved in the manufacture of photographic elements. More particularly, the present invention involves the coating of a non-gelatin overcoat over a topmost gelatin layer in a photographic element. In one embodiment, a processing-solution-permeable overcoat is simultaneously coated with the emulsion layers onto a photographic substrate, which overcoat becomes water and stain resistant in the photochemically processed product.
BACKGROUND OF THE INVENTION
In many instances it is desired to coat the surface of an object with a plurality of distinct, superposed layers (collectively, the plurality of layers is also known as a coating pack). In the manufacture of photographic elements, such as photographic film, wherein a number of layers (up to ten or more) of different photographic coating compositions must be applied to a suitable support in a distinct layered relationship, the uniformity of thickness of each layer in the photographic element must be controlled within very small tolerances. Common methods of applying photographic coating compositions to suitable supports involve simultaneously applying the superposed layers to the support. Typically, a coating pack having a plurality of distinct layers in face-to-face contact is formed and deposited on the object so that all the distinct layers are applied in a single coating operation. In the photographic industry, several such coating operations may be performed to produce a single photographic element. Several methods and apparatus have been developed to coat a plurality of layers in a single coating operation. One such method is by forming a free falling, vertical curtain of coating liquid which is deposited as a layer on a moving support Exemplary “curtain coating” methods of this type are disclosed in U.S. Pat. No. 3,508,947 to Hughes, U.S. Pat. No. 3,632,374 to Grieller, and U.S. Pat. No. 4,830,887 to Reiter. “Bead coating” is another method of applying a plurality of layers to a support in a single coating operation. In typical bead coating techniques, a thin liquid bridge (a “bead”) of the plurality of layers is formed between, for example, a slide hopper and a moving web. The web picks up the plurality of layers simultaneously, in proper orientation, and with substantially no mixing between the layers. Bead coating methods and apparatus are disclosed, for example, in U.S. Pat. Nos. 2,681,294 and 2,289,798.
U.S. Pat. Nos. 5,306,527 and 5,310,637 disclose methods of reducing the tendency toward formation of ripple imperfections in the coating of multilayer photographic elements. In U.S. Pat. No. 5,310,637, it is stated that ripple or ripple imperfection is defined for the purposes of this invention as a layer thickness nonuniformity resulting from wave growth at the fluid-fluid interfaces of a plurality of layers due to a hydrodynamic instability of the gravity-induced flow of the plurality of layers on a coated web. The patent theorizes that ripple imperfections arise when there are viscosity differences between adjacent layers of multilayer coating packs. These viscosity differences can be introduced in a variety of ways, including initial viscosity differences between the various layers as delivered to the web or changes in relative layer viscosities from thermal effects after the layers are coated on a web. Another theorized cause was interlayer mass transport of solvent, for example, in the coating of photographic elements, where adjacent layers often contain varying amounts of gelatin. It was thought that these differences cause water diffusion between the layers which, in turn, can significantly alter the resulting viscosities of the individual layers after they are coated on the web. In this way, viscosity disparities between layers may be introduced on the web for layers which were originally coated at nominally equal viscosities. It was also stated that an osmotic pressure difference between adjacent layers drives interlayer water diffusion in gelatin-containing multilayer coating packs, such as commonly used in the photographic industry and that, in many cases, osmotic pressure differences may result from significant differences in the layer concentrations of gelatin and other addenda. The patent further teaches that the tendency toward the formation of ripple imperfections in multilayer coatings can be reduced by controlling the gelatin concentration of adjacent layers. For example, in a multilayer coating pack having upper, middle, and lower gelatin-containing layers, respectively, the patent concludes that the tendency toward the formation of ripple will be greatly reduced if the middle layer has a gelatin concentration within three weight percent of the gelatin concentration of each of the upper and lower layers and each of the layers has a viscosity which differs from a norm by no more than fifteen percent. U.S. Pat. No. 5,306,537 teaches methods of coating multilayer gelatin based coating packs in which the compositions are determined according to a given formula to keep the ripple value below 35. This formula includes maintaining certain viscosity ratios between adjacent layers. In a gelatin-based coating, maintaining similar viscosities is typically achieved by maintaining similar gelatin concentrations. As a result, inherently the osmotic pressures are naturally kept close and prevent instability problems.
In both bead coating and curtain coating methods, it is necessary to set and/or dry the layered coating after it has been applied to the support. To accomplish this, the web is typically conveyed from the coating application point to a chill section. Subsequently, the web is conveyed through a series of drying chambers after which it is wrapped on a winder roll. Space constraints for the coating machine, cost considerations, and flexibility of design may dictate that one or more inclined web paths be present in conveying the coated substrate from the coating point to the chill section and drying chambers.
Advancements in coating technology have led to increased numbers of layers coated at each coating station, increased total pack thickness per station, thinner individual layers, use of rheology-modifying agents, and the development of new, sophisticated chemistries. In addition, a multilayer photographic coating can consist of sensitizing layers and/or additional, non-imaging, layers. As a result, the chemical composition of the multilayer coating pack is often markedly different from one layer to the next.
A number of patents have been directed to water-resistant protective coatings that can be applied to a photographic element prior to development. For example, U.S. Pat. No. 2,706,686 describes the formation of a lacquer finish for photographic emulsions, with the aim of providing water- and fingerprint-resistance by coating the light-sensitive layer, prior to exposure, with a porous layer that has a high degree of water permeability to the processing solutions. After processing, the lacquer layer is fused and coalesced into a continuous, impervious coating. More recently, U.S. Pat. No. 5,853,926 to Bohan et al. discloses a protective coating for a photographic element, involving the application of an aqueous coating comprising polymer particles and a soft polymer latex binder. This coating allows for appropriate diffusion of photographic processing solutions, and does not require a coating operation after exposure and processing. Again, however, the hydrophobic polymer particles must be fused to form a protective coating that is continuous and water-impermeable.
U.S. Pat. No. 5,856,051 describes the use of hydrophobic particles with gelatin as the binder in an overcoat formulation. This invention demonstrated an aqueous coatable, water-resistant protective overcoat that can be incorporated into the photographic product, allows for appropriate diffusion of photographic processing solutions, and does not require a coating operation after exposure and processing. The hydropho
Adams Ryan B.
Boris David C.
Donovan Kevin M.
Lobo Lloyd A.
Nair Mridula
Eastman Kodak Company
Konkol Chris P.
Schilling Richard L.
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