Radiation imagery chemistry: process – composition – or product th – Radiation sensitive product – Identified backing or protective layer containing
Reexamination Certificate
1998-11-20
2003-12-02
Baxter, Janet (Department: 1752)
Radiation imagery chemistry: process, composition, or product th
Radiation sensitive product
Identified backing or protective layer containing
C430S533000, C430S536000, C430S538000
Reexamination Certificate
active
06656671
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to photographic materials. In the preferred form it relates to base materials for photographic prints.
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. While the polyethylene does provide waterproofing to the paper, the melt extruded polyethylene layer used in color paper has very little dimensional strength and, as a result, cannot be used alone as a carrier of an image. It has been proposed in U.S. Pat. No. 5,244,861 to utilize biaxially oriented polypropylene in receiver sheets for thermal dye transfer. In U.S. Pat. No. 5,244,861 high strength biaxially oriented sheets are laminated to cellulose paper with low density polyethylene. The biaxially oriented sheet utilized in U.S. Pat. No. 5,244,861 is an efficient thermal dye transfer support for the thermal dye receiving layers. The materials disclosed in U.S. Pat. No. 5,244,861 for use as thermal dye receiving layers are not sensitive to compressive forces.
In prior art photographic papers, great care needs to be taken in handling the materials prior to exposure and development of the image. Prior art silver halide photographic papers are sensitive to compressive forces. If sufficient force is applied to the photosensitive layers, an unacceptable latent site on the silver grain may be created. Compressive forces are typically applied during the slitting of sensitized rolls of photographic paper and during photographic processing of images. If this occurs, an area of the photosensitive layer may actually form dye coupler density in an area that, under normal circumstances, would not form density. It would be desirable to have a photographic base material that has a degree of compressibility, thus cushioning the pressure sensitive photographic layers. This will provide a photographic base material that has increased resistance to force that may be applied to it prior to exposure and development.
Problem to Be Solved by the Invention
There is a continuing need for photographic base materials that have resistance to compressive load prior to exposure that results in fewer defects in the print after development.
SUMMARY OF THE INVENTION
It is an object of the invention to provide photographic elements having improved resistance to compressive loads.
It is another object to provide photographic elements with reduced yellow discoloration caused by compressive loads prior to development.
It is a further object to provide photographic elements that have improved resistance to defects caused by winding. These and other objects of the invention are accomplished by a photographic element comprising at least one silver halide containing imaging layer and a cushioning layer below said at least one imaging layer having a compression percentage of between 5 and 25%.
Advantageous Effect of the Invention
The invention provides photographic print elements having improved resistance to defects caused by compressive loads applied to said elements prior to their development.
DETAILED DESCRIPTION OF THE INVENTION
The invention has numerous advantages over prior practices in the art. The invention provides photographic elements that have less yellow edge, an imperfection caused by emulsion compression during slitting of photographic paper. The elements of the invention also are resistant to defects caused by compression during winding. During winding relatively small defects and variations in thickness of photographic base will become magnified and create ridges, gauge bands, and hard spots that result in compression of silver halide layers causing defects after development. The photographic elements of the invention have a cushioning layer below the silver halide and will not suffer from these defects, as the cushioning layer will compress during winding, thereby relieving strain on silver halide grains which will result in defects. Further, the cushioned elements of the invention will rebound somewhat after compression during winding or contact with compressive forces during processing, thereby resulting in a flat surface of the photographic element even after compression has been applied in winding or processing. The flat surface will, therefore, present a pleasing image in the product without undesirable surface streaks or discoloration caused by damage to silver halide grains which results in undesirable image errors.
Because silver halide grains tend to be pressure sensitive, the selection of grain size has been limited by the compressive forces that occur during manufacturing and photographic processing. By providing a compressive layer just below the pressure sensitive emulsion, pressure sensitive silver grain designs that perform better for printing speed and image sharpness can now be utilized because the compressive forces are absorbed by the support. 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 towards the side of an imaging member bearing the imaging layers. The terms “bottom”, “lower side”, and “back” mean the side or towards the side of the imaging member opposite from the side bearing the imaging layers or developed image. The term “tie layer” as used herein refers to a layer of material that is used to adhere biaxially oriented sheets to a base such as paper, polyester, fabric, or other suitable material for the viewing of images.
As used herein, the term “compression percentage” is defined as the percent that a material deforms under a load referenced to when there is no compressive load applied. Compressive percentage is measured by using an “optical” thickness reading vs. a high pressure caliper reading. The optical thickness is obtained by slicing the photographic element with a microtome to expose the thickness dimension perpendicular to a microscope suitable for making uncompressed thickness readings. A high pressure caliper is hereby defined as a device to measure the thickness, as it is compressed between two pads with an area of 0.317 cm
2
and a pressure of at least 70 newtons/cm
2
. The compression percentage is 1 minus the ratio of the high pressure caliper to the optical thickness.
As used herein, the term “recovery” is defined as the optical thickness of a material after the compressive load is removed. The recovery of a material after being subjected to a compressive load is related to the magnitude of the compressive load, the type of material, the elastic limit of the material, the humidity and temperature of the materials, and the dynamics of the compressive load. The recovery percentage is 1 minus the ratio of the optical thickness after the compressive load has been removed to the optical thickness before the compressive load has been applied. The compressive load used to determine recovery percentage is 1.0 MPa.
The cushioning layers of the invention have levels of voiding adjusted to provide optimum compression. When a sufficiently large compressive load is applied to unexposed prior art photographic paper, an undesirable latent image can form significantly reducing the commercial value of the image. It is well known in the field of silver halide imaging that silver emulsions tend to be pressure sensitive. By providing a voided layer, the compressive forces applied to the materials of the invention are relieved by the voided layer, reducing the undesirable formation of a latent image. An imaging layer having a compression percentage of between 5 to 25% has been found to eliminate unwanted latent image formation during manufacturing and photographic processing of images. Compression percentage less than 4% does not significantly improve pressure sensitivity of silver halide imaging layers. Compression percentage greater than 30% has been found to stress fracture, creating undesirable fracture lines i
Aylward Peter T.
Bourdelais Robert P.
Gula Thaddeus S.
Baxter Janet
Eastman Kodak Company
Leipold Paul A.
Walke Amanda C.
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