Radiation imagery chemistry: process – composition – or product th – Radiation sensitive product – Identified backing or protective layer containing
Reexamination Certificate
1998-06-09
2003-02-18
Baxter, Janet (Department: 1752)
Radiation imagery chemistry: process, composition, or product th
Radiation sensitive product
Identified backing or protective layer containing
C430S536000, C430S538000, C430S631000, C430S933000
Reexamination Certificate
active
06521399
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to imaging materials. In a preferred form it relates to base materials for photographic color papers.
BACKGROUND OF THE INVENTION
In the formation of color paper it is known that the base paper has applied thereto a layer of polymer, typically polyethylene. This layer serves to provide waterproofing to the paper, as well as providing a smooth surface on which the photosensitive layers are formed. The formation of a suitably smooth surface is difficult requiring great care and expense to ensure proper laydown and cooling of the polyethylene layers. It would be desirable if a more reliable and improved surface could be formed at less expense.
In photographic papers the polyethylene layer also serves as a carrier layer for optical brightener and other whitener materials, as well as tint materials. It would be desirable if the optical brightener, rather than being dispersed throughout the polyethylene layer, could be concentrated nearer the surface of the layer where it would be more effective optically.
Prior art photographic materials have suggested that the addition of an optical brightener in the photographic support converts ultraviolet radiation into emitted blue light. This allows the white areas of an image to have a slight blue hue which is preferred by consumers. In traditional photographic support materials, the addition of optical brightener presents some problems in that the optical brightener migrates from the polymer layer to form unacceptable crystals in the imaging layer which significantly reduces the commercial value of the image. Prior art photographic materials avoid this problem by using an expensive form of nonmigrating optical brightener and using less than optimum amounts of optical brightener to prevent unwanted migration. It would be desirable if a less expensive optical brightener could be used that would not migrate into the image layer. Further, it would be desirable to increase the amount of optical brightener to optimize the optical properties of an image without the migration of the optical brightener into the image layer.
It has been proposed in U.S. Pat. No. 5,244,861 to utilize biaxially oriented polypropylene in reflective receiver sheets for thermal dye transfer.
An example of coextruded thin layer technology improvements and limitations is explained in U.S. Pat. No. 5,476,708 where it is proposed that sharpness improvements in photographic systems can be achieved by an untinted, unpigmented, thin skin made to be used under a light sensitive emulsion. A correlation is made suggesting that, if the limits of coextrusion technology are pushed to the maximum, a clear layer of thickness as low as 1.5 &mgr;m is the optimum for optical photographic response.
PROBLEM TO BE SOLVED BY THE INVENTION
There is a need for more effective use of optical brighteners in imaging elements. There is a need for the ability to utilize lower cost optical brighteners. There is also a need to prevent migration of optical brightener into the image forming layers of photographic elements.
SUMMARY OF THE INVENTION
It is an object of the invention to provide improved optical brightening of image elements.
It is another object to provide optical brightening in imaging elements at lower cost.
It is a further object to substantially eliminate migration of optical brighteners into the imaging layers of photographic elements.
These and other objects of the invention are accomplished by an imaging element comprising at least one biaxially oriented sheet wherein said biaxially oriented sheet when viewed from a surface of said element emits light in the visible spectrum when exposed to ultraviolet radiation.
In a preferred embodiment, the invention comprises a photographic element comprising at least one layer comprising photosensitive silver halide and a color coupler and a composite photographic support comprising a paper having bonded to its upper and lower surfaces biaxially oriented polyolefin sheets wherein the biaxially oriented sheet bond to said upper paper surface has in its surface layer or in the layer adjacent to its surface layer an optical brightener.
ADVANTAGEOUS EFFECT OF THE INVENTION
The invention provides improved optical brightening in imaging elements. Further, the imaging elements may be lower in cost and do not exhibit image defects caused by migration of optical brighteners into imaging layers.
DETAILED DESCRIPTION OF THE INVENTION
The invention has numerous advantages over prior practices in the art. The invention provides more effective utilization of optical brighteners resulting in a saving in cost. The optical brighteners are present in thin layers in the biaxially oriented polyolefin sheet and, therefore, are more effective requiring less of the optical brightener to be utilized. Further, in a preferred form of the invention, the optical brightener is in a layer adjacent to the surface layer of the biaxially oriented sheet, thereby substantially eliminating the migration of the optical brighteners from the biaxially oriented sheet into the imaging layers of the imaging member. Another advantage is that the paper base may have the optical brightener removed, as the biaxially oriented sheets containing optical brightener and titanium dioxide have the effect of rendering the coloration and brightening ability of the base paper of little concern.
In present photographic color paper, it is necessary to utilize only anatase titanium dioxide in combination with optical brighteners because the lower cost rutile titanium dioxide interferes with the effectiveness of the optical brighteners that are used. It is surprising that rutile titanium dioxide, when combined with optical brighteners in the thin layer of a biaxially oriented sheet, is effective for the reflective whitening action of the titanium dioxide while the prior optical brighteners also maintain their effectiveness. These and other advantages will be apparent from the detailed description below.
The terms as used herein, “top”, “upper”, “emulsion side”, and “face” mean the side or toward the side of the photographic member bearing the imaging layers. The terms “bottom”, “lower side”, and “back” mean the side or toward the side of the photographic member opposite from the side bearing the photosensitive imaging layers or developed image.
Any suitable biaxially oriented polyolefin sheet may be utilized for the sheet on the top side of the laminated base of the invention. Microvoided composite biaxially oriented sheets are preferred and are conveniently manufactured by coextrusion of the core and surface layers, followed by biaxial orientation, whereby voids are formed around void-initiating material contained in the core layer. Such composite sheets are disclosed in, for example, U.S. Pat. Nos. 4,377,616; 4,758,462; and 4,632,869, the disclosure of which is incorporated by reference.
The core of the preferred composite sheet should be from 15 to 95% of the total thickness of the sheet, preferably from 30 to 85% of the total thickness. The nonvoided skin(s) should thus be from 5 to 85% of the sheet, preferably from 15 to 70% of the thickness.
The density (specific gravity) of the composite sheet, expressed in terms of “percent of solid density”, is calculated as follows:
Composite Sheet Density
Polymer Density
×
100
=
%
of
Solid
Density
should be between 45% and 100%, preferably between 67% and 100%. As the percent solid density becomes less than 67%, the composite sheet becomes less manufacturable due to a drop in tensile strength and it becomes more susceptible to physical damage.
The total thickness of the composite sheet can range from 12 to 100 &mgr;m, preferably from 20 to 70 &mgr;m. Below 20 &mgr;m, the microvoided sheets may not be thick enough to minimize any inherent non-planarity in the support and would be more difficult to manufacture. At thickness higher than 70 &mgr;m, little improvement in either surface smoothness or mechanical properties are seen, and so there is little justificat
Aylward Peter T.
Bourdelais Robert P.
Gula Thaddeus S.
Baxter Janet
Eastman Kodak Company
Leipold Paul A.
Walke Amanda C.
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