Impact resistant photographic element

Radiation imagery chemistry: process – composition – or product th – Radiation sensitive product – Structurally defined

Reexamination Certificate

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Details

C430S523000, C430S533000, C430S534000, C430S531000, C430S536000

Reexamination Certificate

active

06348304

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 prior art photographic papers comprising high strength biaxially oriented polypropylene layers, great care needs to be taken in handling the materials after exposure and development of the image. Prior art silver halide photographic papers are sensitive to some compressive forces. Dot matrix printers are commonly used to conveniently add various types of useful data to the opposite side of photographic materials. If sufficient localized force is applied from the back to the opposite side photosensitive layers, permanent surface deformation of the imaging side may create undesirable disturbances to the quality of the normally smooth surface of the image. It has been found that the small diameter (250 micrometers) print heads of some dot matrix printers are accelerated at a rate to impact the printed area to cause local stresses of more than 8 MPa, these have been found to permanently deform the emulsion and imaging side components if not sufficiently cushioned. This is particularly true for special photographic materials described in U.S. Pat. Nos. 5,853,965; 5,866,282; 5,888,643; 5,888,682; 5,888,683; and 5,902,720. These photographic materials include substantial replacement of prior art typical soft, thick polyethylene layers with high modulus oriented polypropylene layers which effectively reduce the cushioning effect when printed on the backside with high pressure dot matrix printers. It would be desirable to have a photographic base material that has a degree of compressibility in a location in the element that will not affect the quality of the imaging side, thus cushioning the pressure sensitive photographic layers. This will provide a photographic base material that has increased resistance to showing the effects of localized forces that may be applied to it on the side opposite the image after 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 after exposure to create an image 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 concentrated backside compressive loads.
It is another object to provide photographic elements with reduced imaging side deformation caused by compressive loads after development.
It is a further object to provide photographic elements that have improved resistance to defects caused by high pressure dot matrix printers.
These and other objects of the invention are accomplished by a photographic element comprising at least one layer of photosensitive silver halide, a base material wherein said base material comprises at least one bottom sheet of biaxially oriented polymer sheet and deformable tie layer material, wherein said deformable tie layer material yield stress of between 6 and 10 MPa in compression which is less than 10% the yield stress of any of the other layers in the element.
ADVANTAGEOUS EFFECT OF THE INVENTION
The invention provides photographic base materials that have resistance to compressive load after exposure which results in fewer image defects in the print after 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 image side surface deformation caused by backside high pressure printing head compression during photofinishing of said elements. The flat surface will, therefore, present a pleasing image in the product without undesirable surface streaks. It will also help to reduce image discoloration caused by damage to pressure sensitive silver halide grains which results in undesirable image errors. 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.
The photographic element that provides improved resistance to high pressure forces on the backside comprises at least one silver halide and dye forming coupler containing imaging layer and a cushioning layer below at least one side imaging layer having a deformable tie layer material, wherein said deformable material having a yield stress in compression less than 10% of any of the other layers in the element. The deformable material suitably has a plastic deformation stress of between 6 and 10 MPa. The other image base materials have a plastic deformation of between about 60 and 100 MPa. The most preferred deformable material has plastic deformation stress of 8 MPa and comprises a medium density polyethylene (density 0.926) at least 20 &mgr;m thick. Medium density polyethylene is hereby defined as having a density range, before extrusion, of 0.926 to 0.940. Other polyolefin layers having a plastic deformation stress below 10 MPa are also suitable. These may include polyethylene, polypropylene, ethylene-vinyl acetate, polybutylene, polymethylpentene, and polydicyclopentadiene. The cushioned layer, as incorporated in this invention, allows the backside compressive forces to be applied to a deformable layer that, once deformed, reduces the pressure on the silver grains and significantly reducing the deformation of the emulsion and any deformable tie layers on the emulsion side, thereby preventing surface imperfections. It is important that the cushioning layer undergoes an inelastic deformation and does not rebound or recover from the applied load.
The preferred location of deformable layer is below the oriented voided polyolefin sheet and under the photographic emulsion and as far as possible from the emulsion. This location is preferred because the deformable layer is most effective when it is located near the applied pressure. In this situation the force being applied to the emulsion can be more effectively dissipated. It is also possible to either add a second cushioning layer to the bottom side of a photographic element or to use the backside location as the sole cushion layer. Additional improvements may be realized with additional layers on the same side or in combination on the top and bottom sides of the base substrate.
The photographic element containing a biaxially oriented voided polyolefin sheet is normally adhered to a paper base by a lamination process. The preferred embodiment of this invention uses a melt extrudable polyolefin polymer to adhere the sheet to the paper base. Melt extrudable polyolefin polymers are used because of their relative low cost, stability, chemical inertness, and general ease of handling. Depending on the end use of the photographic element, it may be desirable to use a polyester base substrate in place of paper. In this case, a laminated cushion layer is critical because the polyester base has little or no compressibility in the thickness direction, and there is a greater need to have a force reducing layer to minimize pressure induced imperfections.
The sensitivity of a photographic emulsion layer containing silver halide may be impacted by a variety of parameters such as silver grain size, the ratio of silver grains to binder, as well as the addition of chemical addenda.
A deformable layer may also be formed by chemical or physical blowing agents. Typical materials comprise one or more from the list of azodicarbonamide, zeolite or molecular sieves, gases such as nitrogen, carbon dioxide or liquids that turn to gas at atmospheric pressure.
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