Imaging material with smooth cellulose base

Abstract

The invention relates to an imaging element comprising an imaging layer and a cellulose paper base wherein said base has an upper surface roughness of between 0.30 and 0.95 μm at a spatial frequency of between 200 cycles/mm and 1300 cycles/mm.

Description

FIELD OF THE INVENTION

This invention relates to imaging materials. In a preferred form it relates to base materials for photographic papers.

BACKGROUND OF THE INVENTION

In the formation of photographic paper it is known that the base paper has applied thereto a layer of polyolefin resin, typically polyethylene. This layer serves to provide waterproofing to the paper and provide a smooth surface on which the photosensitive layers are formed. The formation of the smooth surface is controlled by both the roughness of the chill roll where the polyolefin resin is cast, the amount of resin applied to the base paper surface and the roughness of the base paper. Since the addition of polyolefin resin to improve the surface adds significant cost to the product it would be desirable if a smoother base paper could be made to improve the gloss of the photographic paper.

Typical photographic grade cellulose paper base has a particularly objectionable roughness in the spatial frequency range of 0.30 to 6.35 μm. In this spatial frequency range, a surface roughness average greater than 0.50 micrometers can be objectionable to consumers. Visual roughness greater than 0.50 micrometers in usually referred to as “orange peel”. An imaging element with roughness less than 1.10 μm at a spatial frequency of between 200 cycles/mm and 1300 cycles/mm is considered smooth and is typically defined as a glossy image.

Traditional photographic papers contain chemistry to provide certain properties to the paper that are not inherent in the paper fiber. This chemistry includes materials known in the art to improve wet strength and dry strength. Since photographic paper that comprises laminated biaxially oriented polyolefin sheets laminated to base paper has greatly improved tensile strength over traditional photographic papers, the addition of wet and dry strength to the paper adds unwanted cost to the product. It would be desirable if a base paper could be made that was free of wet and dry strength resins.

It has been proposed in U.S. Pat. No. 5,866,282—Bourdelais et al., to utilize a composite support material with laminated biaxially oriented polyolefin sheets as a photographic imaging material. In U.S. Pat. No. 5,866,282, biaxially oriented polyolefin sheets are extrusion laminated to cellulose paper to create a support for silver halide imaging layers. The biaxially oriented sheets described in U.S. Pat. No. 5,866,282 have a microvoided layer in combination with coextruded layers that contain white pigments. The composite imaging support structure described in U.S. Pat. No. 5,866,282 has been found to be more durable, sharper and brighter than prior art photographic paper imaging supports that use cast melt extruded polyethylene layers coated on cellulose paper. The surface roughness of the paper base in U.S. Pat. No. 5,866,282 is replicated on the surface of the imaging element.

It has been proposed in U.S. Pat. No. 5,244,861 to utilize biaxially oriented polypropylene laminated to a base paper for use as a reflective imaging receiver for thermal dye transfer imaging. While the invention does provide an excellent material for the thermal dye transfer imaging process, this invention can not be used for imaging systems that are gelatin based such as silver halide and ink jet because of the sensitivity of the gel imaging systems to humidity. The humidity sensitivity of the gel imaging layer creates unwanted imaging element curl. One factor contributing to the imaging element curl is the ratio of base paper stiffness in the machine direction to the cross direction. Traditional photographic base papers have a machine direction to cross direction stiffness ratio, as measured by Young's modulus, of approximately 2.0. For a composite photographic material with laminated biaxially oriented polyolefin sheets to a base paper it would be desirable if the machine direction to cross direction stiffness ratio were approximately 1.6 to reduce imaging element curl.

A receiving element with cellulose paper support for use in thermal dye transfer has been proposed in U.S. Pat. No. 5,288,690 (Warner et al.). While the cellulose paper in U.S. Pat. No. 5,288,690 solved many of the problems existing with thermal dye transfer printing on a laminated cellulose paper, this cellulose paper is not suitable for a laminated cellulose photographic paper since this paper has undesirable surface roughness in the spatial frequency range of 0.30 to 6.35 mm and the pulp used in U.S. Pat. No. 5,288,690 is expensive compared to alternative pulps. It would be desirable if “orange peel” roughness could be minimized in the laminated photographic base paper.

PROBLEM TO BE SOLVED BY THE INVENTION

There remains a need for a more effective base paper to provide an improved smooth surface as well as provide a stronger photographic element.

SUMMARY OF THE INVENTION

An object of the invention is to provide an imaging material that has improved surface properties.

Another object of this invention is to provide an imaging material with a glossy surface.

A further object of this invention is to provide a base paper that provides a stronger photographic element.

These and other objects of the invention are generally accomplished by an imaging element comprising an imaging layer and an upper cellulose paper base wherein said base has a surface roughness of between 0.30 and 0.95 μm at a spatial frequency of between 200 cycles/mm and 1300 cycles/mm.

ADVANTAGEOUS EFFECT OF THE INVENTION

The invention provides an improved paper for imaging elements. It particularly provides an improved paper for imaging elements that are smoother, more opaque and are low cost.

DETAILED DESCRIPTION OF THE INVENTION

There are numerous advantages of the invention over prior practices in the art. The invention provides a imaging element that has a smoother surface, increasing the commercial value of the imaging element by providing a glossy photographic print material and eliminating the need for expensive smooth casting rolls that are typical of melt extruded photographic base materials. By improving the smoothness of the imaging element, the reflective print material has a more maximum black as the reflective properties of the improved surface are more specular that prior art materials. Further, as both the whites and blacks are improved, the contrast of the reflective photographic paper is improved. Improved contrast range has been shown to reduce unwanted fringing in digital optical printing applications. Another advantage is the significant reduction in dust generation as this base paper is cut in both the cross and machine directions in imaging converting applications such as the slitting of wide rolls of imaging support, punching of imaging elements as in photographic processing equipment and chopping as in photographic finishing equipment. A further advantage is the improvement in opacity for the imaging element, reducing back side show through that exists during the viewing of images allowing a higher density back side branding to be utilized. These and other advantages will be apparent from the detailed description below.

To accurately define a smooth surface for photographic grade cellulose base paper, the surface roughness of the cellulose paper is used to quantify the surface smoothness. A smooth surface is one that has a low surface roughness value. A non glossy surface or a rough surface is one that has a high surface roughness value. The Bourdelais surface roughness continuum is defined as surface roughness values from 0.30 to 0.95 micrometers at a spatial frequency of between 200 cycles/mm and 1300 cycles/mm. A surface roughness of 0.25 micrometers is approximately equal to the surface roughness of melt cast, oriented polyolefin. A surface roughness of approximately 1.1 micrometers is equal to prior art photographic cellulose paper bases. A spatial frequency of between 200 cycles/mm and 1300 cycles/mm has been selected for the Bourdelais roughness continuum because it represents a critical perceptual range of surface roughness. A spatial frequency greater than 1500 cycles/mm contributes haze to an image. A spatial frequency less than 180 cycles/mm is considered low frequency roughness or “orange peel” roughness.

In order to provide an imaging element with a smooth surface, a smooth paper base is preferred as the application of polymer layers to the cellulose paper, which is typical of imaging support materials, is not typically sufficient to cover the inherent roughness of the cellulose paper. An imaging element comprising an imaging layer and a cellulose paper base wherein said base has a surface roughness of between 0.30 and 0.95 μm at a spatial frequency of between 200 cycles/mm and 1300 cycles/mm is preferred as this range of roughness has been found to provide a perceptually preferred glossy surface on the imaging element. One preferred structure that has a surface roughness of between 0.30 and 0.95 μm at a spatial frequency of between 200 cycles/mm and 1300 cycles/mm is a cellulose paper base that contains spherical polymer beads. The spherical polymer beads create a smooth surface by filling the rough surface of the cellulose paper created during the formation of the paper. Additionally, the spherical beads also increase the opacity of the paper, reducing the back side show through during viewing of images.

The terms as used herein, “top”, “upper”, “emulsion side”, and “face” mean the side or toward the side of a imaging member bearing the imaging layers. The terms “bottom”, “lower side”, and “back” means the side or toward the side of the photographic member opposite from the side bearing the imaging layers or developed image. The term “face side” means the side opposite the side of cellulose paper formed on a fourdrinier wire. The term “wire side” means the side of cellulose paper formed adjacent to the fourdrinier wire.

The photographic base paper of the invention having a smooth surface provides a glossy image to images formed from photosensitive materials placed on the paper and then developed. In the photographic art, it is customary to provide a waterproof coating between the photosensitive layers and the photographic paper base. One way of doing this is to provide at least one coat of polyethylene on each side of the base paper. The polyethylene is coated with as smooth a surface as possible so as to form a glossy image when the photosensitive material is developed. It is also known to provide biaxially oriented polyolefin sheets on both sides of the paper base. Either of these methods of waterproofing paper is suitable for the instant invention and, in each instance, the smooth surface of the paper base material of the invention provides an improved surface for the image. While described above with reference to the formation of a base for photographic imaging using photosensitive materials, the base paper of the invention also could be utilized for formation of ink jet, thermal dye transfer, or electrostatic images. Even when utilized for these uses, it is generally desirable to provide a waterproofing layer to the paper to control humidity and provide additional strength. There is also in those instances an added layer that will receive the image and aid its inherence to the paper.

Any suitable biaxially oriented polyolefin sheet may be used for the sheet on the top side of the 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 U.S. Pat. Nos. 4,377,616; 4,758,462 and 4,632,869.

The core of the preferred top 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×100=% of Solid Density

Polymer Density

Percent 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. The sheet also becomes more susceptible to physical damage.

The total thickness of the top biaxially oriented composite sheet can range from 12 to 100 micrometers, preferably from 20 to 70 micrometers. Below 20 micrometers, 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 thicknesses higher than 70 micrometers, little improvement in either surface smoothness or mechanical properties are seen, and so there is little justification for further increase in cost for extra materials.

The top biaxially oriented sheets preferably have a water vapor permeability that is less than 0.85×10 −5 g/mm 2 /day/atm. This allows faster emulsion hardening, as the laminated support of this invention greatly slows the rate of water vapor transmission from the emulsion layers during coating of the emulsions on the support. The transmission rate is measured by ASTM F 1249.

“Void” is used herein to mean devoid of added solid and liquid matter, although it is likely the “voids” contain gas. The void-initiating particles which remain in the finished packaging sheet core should be from 0.1 to 10 micrometers in diameter, preferably round in shape, to produce voids of the desired shape and size. The size of the void is also dependent on the degree of orientation in the machine and transverse directions. Ideally, the void would assume a shape which is defined by two opposed and edge contacting concave disks. In other words, the voids tend to have a lens-like or biconvex shape. The voids are oriented so that the two major dimensions are aligned with the machine and transverse directions of the sheet. The Z-direction axis is a minor dimension and is roughly the size of the cross diameter of the voiding particle. The voids generally tend to be closed cells, and thus there is virtually no path open from one side of the voided-core to the other side through which gas or liquid can traverse.

The void-initiating material may be selected from a variety of materials, and should be present in an amount of about 5 to 50% by weight based on the weight of the core matrix polymer. Preferably, the void-initiating material comprises a polymeric material. When a polymeric material is used, it may be a polymer that can be melt-mixed with the polymer from which the core matrix is made and be able to form dispersed spherical particles as the suspension is cooled down. Examples of this would include nylon dispersed in polypropylene, polybutylene terephthalate in polypropylene, or polypropylene dispersed in polyethylene terephthalate. If the polymer is preshaped and blended into the matrix polymer, the important characteristic is the size and shape of the particles. Spheres are preferred and they can be hollow or solid. These spheres may be made from cross-linked polymers which are members selected from the group consisting of an alkenyl aromatic compound having the general formula Ar—C(R)═CH 2 , wherein Ar represents an aromatic hydrocarbon radical, or an aromatic halohydrocarbon radical of the benzene series and R is hydrogen or the methyl radical; acrylate-type monomers include monomers of the formula CH 2 ═C(R′)—C(O)(OR) wherein R is selected from the group consisting of hydrogen and an alkyl radical containing from about 1 to 12 carbon atoms and R′ is selected from the group consisting of hydrogen and methyl; copolymers of vinyl chloride and vinylidene chloride, acrylonitrile and vinyl chloride, vinyl bromide, vinyl esters having formula CH 2 ═CH(O)COR, wherein R is an alkyl radical containing from 2 to 18 carbon atoms; acrylic acid, methacrylic acid, itaconic acid, citraconic acid, maleic acid, fumaric acid, oleic acid, vinylbenzoic acid; the synthetic polyester resins which are prepared by reacting terephthalic acid and dialkyl terephthalics or ester-forming derivatives thereof, with a glycol of the series HO(CH 2 ) n OH wherein n is a whole number within the range of 2-10 and having reactive olefinic linkages within the polymer molecule, the above described polyesters which include copolymerized therein up to 20 percent by weight of a second acid or ester thereof having reactive olefinic unsaturation and mixtures thereof, and a cross-linking agent selected from the group consisting of divinylbenzene, diethylene glycol dimethacrylate, diallyl fumarate, diallyl phthalate and mixtures thereof.

Examples of typical monomers for making the crosslinked polymer include styrene, butyl acrylate, acrylamide, acrylonitrile, methyl methacrylate, ethylene glycol dimethacrylate, vinyl pyridine, vinyl acetate, methyl acrylate, vinylbenzyl chloride, vinylidene chloride, acrylic acid, divinylbenzene, acrylamidomethyl-propane sulfonic acid, vinyl toluene, etc. Preferably, the cross-linked polymer is polystyrene or poly(methyl methacrylate). Most preferably, it is polystyrene and the cross-linking agent is divinylbenzene.

Processes well known in the art yield non-uniformly sized particles, characterized by broad particle size distributions. The resulting beads can be classified by screening the beads spanning the range of the original distribution of sizes. Other processes such as suspension polymerization, limited coalescence, directly yield very uniformly sized particles.

The void-initiating materials may be coated with agents to facilitate voiding. Suitable agents or lubricants include colloidal silica, colloidal alumina, and metal oxides such as tin oxide and aluminum oxide. The preferred agents are colloidal silica and alumina, most preferably, silica. The cross-linked polymer having a coating of an agent may be prepared by procedures well known in the art. For example, conventional suspension polymerization processes wherein the agent is added to the suspension is preferred. As the agent, colloidal silica is preferred.

The void-initiating particles can also be inorganic spheres, including solid or hollow glass spheres, metal or ceramic beads or inorganic particles such as clay, talc, barium sulfate, calcium carbonate. The important parameter is that the material does not chemically react with the core matrix polymer to cause one or more of the following problems: (a) alteration of the crystallization kinetics of the matrix polymer, making it difficult to orient, (b) destruction of the core matrix polymer, (c) destruction of the void-initiating particles, (d) adhesion of the void-initiating particles to the matrix polymer, or (e) generation of undesirable reaction products, such as toxic or high color moieties. The void-initiating material should not be photographically active or degrade the performance of the photographic element in which the biaxially oriented polyolefin sheet is utilized.

For the biaxially oriented sheet on the top side toward the emulsion, suitable classes of thermoplastic polymers for the biaxially oriented sheet and the core matrix-polymer of the preferred composite sheet comprise polyolefins.

Suitable polyolefins for the biaxially oriented sheet on the top side toward the emulsion include polypropylene, polyethylene, polymethylpentene, polystyrene, polybutylene and mixtures thereof. Polyolefin copolymers, including copolymers of propylene and ethylene such as hexene, butene, and octene are also useful. Polypropylene is preferred, as it is low in cost and has desirable strength properties.

The nonvoided skin layers of for the biaxially oriented sheet on the top side toward the emulsion can be made of the same polymeric materials as listed above for the core matrix. The composite sheet can be made with skin(s) of the same polymeric material as the core matrix, or it can be made with skin(s) of different polymeric composition than the core matrix. For compatibility, an auxiliary layer can be used to promote adhesion of the skin layer to the core.

Addenda may be added to the core matrix and/or to the skins of the top biaxially oriented sheet to improve the whiteness of these sheets. This would include any process which is known in the art including adding a white pigment, such as titanium dioxide, barium sulfate, clay, or calcium carbonate. This would also include adding fluorescing agents which absorb energy in the UV region and emit light largely in the blue region, or other additives which would improve the physical properties of the sheet or the manufacturability of the sheet. For photographic use, a white base with a slight bluish tint is preferred.

The coextrusion, quenching, orienting, and heat setting for the biaxially oriented sheet on the top side toward the emulsion may be effected by any process which is known in the art for producing oriented sheet, such as by a flat sheet process or a bubble or tubular process. The flat sheet process involves extruding the blend through a slit die and rapidly quenching the extruded web upon a chilled casting drum so that the core matrix polymer component of the sheet and the skin components(s) are quenched below their glass solidification temperature. The quenched sheet is then biaxially oriented by stretching in mutually perpendicular directions at a temperature above the glass transition temperature, below the melting temperature of the matrix polymers. The sheet may be stretched in one direction and then in a second direction or may be simultaneously stretched in both directions. After the sheet has been stretched, it is heat set by heating to a temperature sufficient to crystallize or anneal the polymers while restraining to some degree the sheet against retraction in both directions of stretching.

The composite sheet for the biaxially oriented sheet on the top side toward the emulsion, while described as having preferably at least three layers of a microvoided core and a skin layer on each side, may also be provided with additional layers that may serve to change the properties of the biaxially oriented sheet. A different effect may be achieved by additional layers. Such layers might contain tints, antistatic materials, or different void-making materials to produce sheets of unique properties. Biaxially oriented sheets could be formed with surface layers that would provide improved adhesion, or appearance to the support and photographic element. The biaxially oriented extrusion could be carried out with as many as 10 layers if desired to achieve some particular desired property.

The composite sheets for the biaxially oriented sheet on the top side toward the emulsion may be coated or treated after the coextrusion and orienting process or between casting and full orientation with any number of coatings which may be used to improve the properties of the sheets including printability, to provide a vapor barrier, to make them heat sealable, or to improve the adhesion to the support or to the photo sensitive layers. Examples of this would be acrylic coatings for printability and coating polyvinylidene chloride for heat seal properties. Further examples include flame, plasma or corona discharge treatment to improve printability or adhesion.

By having at least one nonvoided skin on the microvoided core, the tensile strength of the sheet is increased thus making the sheet more manufacturable. It also allows the sheets to be made at wider widths and higher draw ratios then when sheets are made with all layers voided. Coextruding the layers further simplifies the manufacturing process.

The structure of a preferred top biaxially oriented sheet of the invention where the exposed surface layer is adjacent to the imaging layer is as follows:

Polyethylene exposed surface layer with blue tint, red tint and a fluoropolymer

Polypropylene layer containing 24% anatase TiO 2 , optical brightener and Hindered amine light stabilizer (HALS)

Polypropylene microvoided layer with 0.55 grams per cubic cm density

Polypropylene layer with 18% anatase TiO 2 and HALS

Polypropylene bottom layer

The sheet on the side of the base paper opposite to the emulsion layers may be any suitable biaxially oriented polymer sheet. The sheet may or may not be microvoided. It may have the same composition as the sheet on the top side of the paper backing material. Bottom biaxially oriented sheets are conveniently manufactured by coextrusion of the sheet, which may contain several layers, followed by biaxial orientation. Such biaxially oriented sheets are disclosed in, for example, U.S. Pat. No. 4,764,425.

Suitable classes of thermoplastic polymers for the bottom biaxially oriented sheet core and skin layers include polyolefins, polyesters, polyamides, polycarbonates, cellulosic esters, polystyrene, polyvinyl resins, polysulfonamides, polyethers, polyimides, polyvinylidene fluoride, polyurethanes, polyphenylenesulfides, polytetrafluoroethylene, polyacetals, polysulfonates, polyester ionomers, and polyolefin ionomers. Copolymers and/or mixtures of these polymers can be used.

Suitable polyolefins for the core and skin layers of the bottom biaxially oriented polymer sheet include polypropylene, polyethylene, polymethylpentene, and mixtures thereof. Polyolefin copolymers, including copolymers of propylene and ethylene such as hexene, butene and octene are also useful. Polypropylenes are preferred because they are low in cost and have good strength and surface properties.

Suitable polyesters for the bottom oriented sheet include those produced from aromatic, aliphatic or cycloaliphatic dicarboxylic acids of 4-20 carbon atoms and aliphatic or alicyclic glycols having from 2-24 carbon atoms. Examples of suitable dicarboxylic acids include terephthalic, isophthalic, phthalic, naphthalene dicarboxylic acid, succinic, glutaric, adipic, azelaic, sebacic, fumaric, maleic, itaconic, 1,4-cyclohexanedicarboxylic, sodiosulfoisophthalic and mixtures thereof. Examples of suitable glycols include ethylene glycol, propylene glycol, butanediol, pentanediol, hexanediol, 1,4-cyclohexanedimethanol, diethylene glycol, other polyethylene glycols and mixtures thereof. Such polyesters are well known in the art and may be produced by well known techniques, e.g., those described in U.S. Pat. No. 2,465,319 and U.S. Pat. No. 2,901,466. Preferred continuous matrix polyesters are those having repeat units from terephthalic acid or naphthalene dicarboxylic acid and at least one glycol selected from ethylene glycol, 1,4-butanediol and 1,4-cyclohexanedimethanol. Poly(ethylene terephthalate), which may be modified by small amounts of other monomers, is especially preferred. Other suitable polyesters include liquid crystal copolyesters formed by the inclusion of suitable amount of a co-acid component such as stilbene dicarboxylic acid. Examples of such liquid crystal copolyesters are those disclosed in U.S. Pat. Nos. 4,420,607, 4,459,402 and 4,468,510.

Useful polyamides include nylon 6, nylon 66, and mixtures thereof. Copolymers of polyamides are also suitable continuous phase polymers. An example of a useful polycarbonate is bisphenol-A polycarbonate. Cellulosic esters suitable for use as the continuous phase polymer of the composite sheets include cellulose nitrate, cellulose triacetate, cellulose diacetate, cellulose acetate propionate, cellulose acetate butyrate, and mixtures or copolymers thereof. Useful polyvinyl resins include polyvinyl chloride, poly(vinyl acetal), and mixtures thereof. Copolymers of vinyl resins can also be utilized.

The biaxially oriented sheet on the back side of the laminated base can be made with one or more layers of the same polymeric material, or it can be made with layers of different polymeric composition. In the case of a multiple layer system, when different polymeric materials are used, an additional layer may be required to promote adhesion between non-compatable polymeric materials so that the biaxially oriented sheets do not have layer fracture during manufacturing or in the final imaging element format.

The coextrusion, quenching, orienting, and heat setting of bottom biaxially oriented sheets may be effected by any process which is known in the art for producing oriented sheet, such as by a flat sheet process or a bubble or tubular process. The flat sheet process involves extruding or coextruding the blend through a slit die and rapidly quenching the extruded or coextruded web upon a chilled casting drum so that the polymer component(s) of the sheet are quenched below their solidification temperature. The quenched sheet is then biaxially oriented by stretching in mutually perpendicular directions at a temperature above the glass transition temperature of the polymer(s). The sheet may be stretched in one direction and then in a second direction or may be simultaneously stretched in both directions. After the sheet has been stretched, it is heat set by heating to a temperature sufficient to crystallize the polymers while restraining to some degree the sheet against retraction in both directions of stretching.

The surface roughness of bottom biaxially oriented sheet or R a is a measure of relatively finely spaced surface irregularities such as those produced on the back side of photographic materials by the casting of polyethylene against a rough chilled roll. The surface roughness measurement is a measure of the maximum allowable roughness expressed in units of micrometers and by use of the symbol R a . For the irregular profile of the back side of photographic materials of this invention, the roughness average, R a , is the sum of the absolute value of the difference of each discrete data point from the average of all the data divided by the total number of points sampled.

Biaxially oriented polyolefin sheets commonly used in the packaging industry are commonly melt extruded and then orientated in both directions (machine direction and cross direction) to give the sheet desired mechanical strength properties. The process of biaxially orientation generally creates a surface roughness average of less than 0.23 micrometers. While a smooth surface has value in the packaging industry, use as a back side layer for photographic paper is limited. Laminated to the back side of the base paper, the biaxially oriented sheet must have a surface roughness average (R a ) greater than 0.30 micrometers to ensure efficient transport through the many types of photofinishing equipment that have been purchased and installed around the world. At surface roughness less that 0.30 micrometers, transport through the photofinishing equipment becomes less efficient. At surface roughness greater than 2.54 micrometers, the surface would become too rough causing transport problems in photofinishing equipment and the rough back side surface would begin to emboss the silver halide emulsion as the material is wound in rolls.

The structure of a preferred backside biaxially oriented sheet of this invention wherein the skin layer is on the bottom of the photographic element is as follows:

Solid polypropylene core

Mixture of polypropylenes and a terpolymer of ethylene-propylene-butylene

Styrene butadiene methacrylate coating

Addenda may also be added to the biaxially oriented back side sheet to improve the whiteness of these sheets. This would include processes known in the art including adding a white pigment, such as titanium dioxide, barium sulfate, clay, or calcium carbonate. This would also include adding fluorescing agents which absorb energy in the UV region and emit light largely in the blue region, or other additives which would improve the physical properties of the sheet or the manufacturability of the sheet.

In order to successfully transport a photographic paper that contains a laminated biaxially oriented sheet with the desired surface roughness, on the opposite side of the image layer an antistatic coating on the bottom most layer is preferred. The antistat coating may contain any known materials known in the art which are coated on photographic web materials to reduce static during the transport of photographic paper. The preferred surface resistivity of the antistat coat at 50% RH is less than 10 −12 ohm/square.

These biaxially oriented sheets may be coated or treated after the coextrusion and orienting process or between casting and full orientation with any number of coatings which may be used to improve the properties of the sheets including printability, to provide a vapor barrier, to make them heat sealable, or to improve the adhesion to the support or to the photo sensitive layers. Examples of this would be acrylic coatings for printability and coating polyvinylidene chloride for heat seal properties. Further examples include flame, plasma or corona discharge treatment to improve printability or adhesion.

Photographic grade cellulose papers of the invention are preferred as a base for laminating biaxially oriented polyolefin sheets. In the case of silver halide photographic systems, suitable cellulose papers must not interact with the light sensitive emulsion layer. A photographic grade paper used in this invention must be “smooth” as to not interfere with the viewing of images. The surface roughness of cellulose paper or R a is a measure of relatively finely spaced surface irregularities on the paper. The surface roughness measurement is a measure of the maximum allowable roughness height expressed in units of micrometers and by use of the symbol R a at a specified frequency. For the smooth paper of this invention, long wave length surface roughness or orange peel is of interest. It has been found that by reducing the orange peel roughness of the paper, the image is perceptually preferred. For the irregular surface profile of the paper of this invention, a 0.95 cm diameter probe is used to measure the surface roughness of the paper and thus bridges all fine roughness detail. A preferred long wave length surface roughness of the paper is between 0.13 and 0.44 micrometers measured at a spatial frequency of between 20 cycles/mm and 180 cycles/mm. At surface roughness greater than 0.44 micrometers, little improvement in image quality is observed when compared to current photographic papers. A cellulose paper surface roughness less than 0.13 micrometers is difficult to manufacture and costly.

For a glossy image a base with a surface roughness of between 0.30 and 0.95 μm at a spatial frequency of between 200 cycles/mm and 1300 cycles/mm is preferred. Below 0.25 micrometers, a smooth surface is difficult to produce using cellulose fiber. Above 1.05 micrometers, there is little improvement over the current art. The surface roughness for spatial frequency of between 200 cycles/mm and 1300 cycles/mm can be measured by TAYLOR-HOBSON Surtronic 3 with 2 micrometers diameter ball tip. The output R a or “roughness average” from the TAYLOR-HOBSON is in units of micrometers and has a built in cut off filter to reject all sizes above 0.25 mm.

Spherical polymer beads in the paper sheet or coated onto the base paper sheet have been found to reduce the surface roughness of cellulose paper at a spatical frequency of between 200 cycles/mm and 1300 cycles/mm. Plastic, or polymeric, pigments are synthetic non-filming polymers used in paper coatings. Typical plastic pigments are composed of styrene, although plastic pigments can be made of any monomer of copolymer with a T g >50° C. There are two main types of plastic pigments, hollow sphere and solid bead. The pigments are classified by particle size, composition and core thickness (in the case of hollow sphere pigments). Generally, plastic pigments are spherical and quite uniform in size distribution. Particles are available in different sizes to allow for selection based on end use application or on the performance properties being sought.

When a coating made with plastic pigments is dried below the glass transition temperature of the polymer, the particle remains spherical and acts mainly as a light scattering agent. When the thermoplastic pigment is exposed to temperature and pressure, it deforms and flattens. The surface becomes smoother and glossier. Commercial producers of polystyrene beads in water include Dow Chemical, Morton-Thiakol and Rohm and Haas.

Hollow sphere pigments are preferred as the hollow sphere pigments reduce the roughness of the paper and provide desirable opacity to the paper base. Hollow sphere pigments have an air filled void, which distinguishes them from the solid bead pigments. Hollow sphere pigments can be supplied as an emulsion. The inner core is filled with water in the dispersion. This water is bound, that is, it does not interfere with the coating rheology. When the coating is dried, the water in inner core of the pigment diffuses out and leaves an air filled cavity. This air filled cavity allows more light scattering boundaries to increase opacity. Therefore, hollow sphere pigments can contribute more to opacity than solid bead pigments. A hollow sphere pigment comprising styrene-acrylic copolymer is most preferred because styrene-acrylic copolymer has been found to have excellent surface flow when subjected to heat and mechanical shearing during formation, drying and calendering. Additionally, it has been found that the styrene-acrylic copolymer can achieve a smoother surface at lower pressure and temperature compared to other polymer systems. Further, styrene-acrylic copolymer is low in cost compared to other polymers.

Using hollow sphere pigments, the coating smoothness can be accomplished at lower temperatures and/or pressures. This ease of finishing feature helps increase manufacturing latitude in finishing operations and can extend existing equipment capabilities. The amount of hollow sphere pigments needed depends on the formulation. Hollow sphere pigments can be used in combination with other pigments (such as clay), or by itself. A lower percentage of hollow sphere pigments are needed when used with other mineral pigments.

The smoothness of the paper may also be improved by the addition of fillers prior to calendering. Fillers, preferably clay, improve the smoothness of the paper sheet after calendering. A relationship exists between the hydrous properties of the clay and smoothness of the base paper. The blackening obtained with clay filled sheets is related to the plate like structure of the clay particles, since paper bases filled with pigments of cubic structures such as calcium carbonate do not blacken on calendering. Clay is usually mixed with water before adding to the stock. The preferred amount of clay is between 5 and 35%. Below 2% there is little improvement is smoothness. Above 40% the clay begins to suffer from dispersion problems such as non uniform particle size of the clay. Above 40% the clay filler also reduces the modulus of the paper, thereby causing a undesirable reduction in image support stiffness. An additional advantage of a clay filler is the improvement in opacity compared to a base paper that does not contain filler materials. The improvement in opacity is desirable as it reduces back side show through as images are viewed. Because clay tends to less expensive that polymer smoothing coatings, clay is preferred where a low cost smooth paper base is desired. Clay may also be used in the size coat prior to final calendering of the cellulose base paper. A clay size coating has been shown to improve the smoothness of the paper.

A preferred basis weight of the smooth cellulose paper is between 117.0 and 195.0 g/m 2 . A basis weight less than 117.0 g/m 2 yields an imaging support that does not have the required stiffness for transport through photographic processing equipment and digital printing hardware. Additionally, a basis weight less than 117.0 g/m 2 yields an imaging support that does not have the required stiffness for consumer acceptance. At basis weights greater than 195.0 g/m 2 , the imaging support stiffness, while acceptable to consumers, exceeds the stiffness requirement for efficient photographic processing. Problems such as the inability to be chopped and incomplete punches are common with a cellulose paper that exceeds 195.0 g/m 2 in basis weight. The preferred fiber length of the smooth paper is between 0.35 and 0.55 mm. Fiber Lengths are measured using a FS-200 Fiber Length Analyzer (Kajaani Automation Inc.). Fiber lengths less than 0.30 mm are difficult to achieve in manufacturing and as a result expensive. Because shorter fiber lengths generally result in an increase in paper modulus, paper fiber lengths less than 0.30 mm will result in a photographic paper that is very difficult to punch in photofinishing equipment. Paper fiber lengths greater than 0.62 mm do not show an improvement in surface smoothness.

The preferred density of the smooth cellulose paper of this invention is between 1.05 and 1.20 g/cc. A sheet density less than 1.05 g/cc would not provide the smooth surface preferred by consumers. A sheet density that is greater than 1.20 g/cc would be difficult to manufacture requiring expensive calendering and a loss in paper making machine efficiency.

The machine direction to cross direction modulus paper modulus ratio is critical to the quality of a biaxially oriented imaging support as the modulus ratio is a controlling factor in a laminated imaging element curl and a balanced stiffness in both the machine and cross directions. The preferred machine direction to cross direction base paper modulus ratio for a laminated support utilizing the smooth paper of this invention is between 1.4 and 1.9. A modulus ratio of less than 1.4 is difficult to manufacture since the cellulose fibers tend to align primarily with the stock flow exiting the paper machine head box. This flow is in the machine direction and is only counteracted slightly by fourdrinier parameters. A modulus ratio greater than 1.95 does not provide the desired curl and stiffness improvements to the laminated imaging support.

A smooth cellulose paper that contains TiO 2 is preferred as the opacity of the imaging support can be improved by the use of TiO 2 in the cellulose paper. The cellulose paper of this invention may also contain any addenda known in the art to improve the imaging quality of the paper. The TiO 2 used may be either anatase or rutile type. Examples of TiO 2 that are acceptable for addition of cellulose paper are Dupont Chemical Co. R101 rutile TiO 2 and DuPont Chemical Co. R104 rutile TiO 2 . Other pigments to improve photographic responses may also be used in this invention, pigments such as talc, kaolin, CaCO 3 , BaSO 4 , ZnO, TiO 2 , ZnS, and MgCO 3 are useful and may be used alone or in combination with TiO 2 .

A smooth cellulose paper substantially free of dry strength resin and wet strength resin is preferred when used in combination with biaxially oriented polymer sheets because the elimination of dry and wet strength resins reduces the cost of the cellulose paper and improves manufacturing efficiency. Dry strength and wet strength resins are commonly added to cellulose photographic paper to provide strength in the dry state and strength in the wet state as the paper is developed in wet processing chemistry during the photofinishing of consumer images. In this invention, dry and wet strength resin are no longer needed as the strength of the imaging support is the result of laminating high strength biaxially oriented polymer sheets to the top and bottom of the cellulose paper.

Any pulps known in the art to provide image quality paper may be used in this invention. Bleached hardwood chemical kraft pulp is preferred as it provides brightness, a good starting surface and good formation while maintaining strength. In general, hardwood fibers are much shorter than softwood by approximately a 1:3 ratio. Pulp with a brightness less than 90% Brightness at 457 nm is preferred. Pulps with brightness of 90% or greater are commonly used in imaging supports because consumers typically prefer a white paper appearance. A cellulose paper less than 90% Brightness at 457 nm is preferred as the whiteness of the imaging support can be improved by laminating a microvoided biaxially oriented sheet to the cellulose paper of this invention. The reduction in brightness of the pulp allows for a reduction in the amount of bleaching required thus lowering the cost of the pulp and reducing the bleaching load on the environment.

The smooth cellulose paper of this invention can be made on a standard continuous fourdrinier wire machine. For the formation of cellulose paper of this invention, it is necessary to refine the paper fibers to a high degree to obtain good formation. This is accomplished in this invention by providing wood fibers suspended in water bringing said fibers into contact with a series of disc refining mixers and conical refining mixers such that fiber development in disc refining is carried out at a total specific net refining power of 44 to 66 KW hrs/metric ton and cutting in the conical mixers is carried out at a total specific net refining power of between 55 and 88 KW hrs/metric ton, applying said fibers in water to a foraminous member to remove water, drying said paper between press and felt, drying said paper between cans, applying a size to said paper, drying said paper between steam heated dryer cans, applying steam to said paper, and passing said paper through calender rolls. The preferred specific net refining power (SNRP) of cutting is between 66 and 77 KW hrs/metric ton. A SNRP of less than 66 KW hrs/metric ton will provide an inadequate fiber length reduction resulting in a less smooth surface. A SNRP of greater than 77 KW hrs/metric ton after disc refining described above generates a stock slurry that is difficult to drain from the fourdrinier wire. Specific Net Refiner Power is calculated by the following formula:

(Applied Power in Kilowatts to the refiner−the No Load Kilowatts)/ (% consistency * flow rate in 1 pm * 0.907 metric tons/ton)

For the formation of cellulose paper of sufficient smoothness, it is desirable to rewet the paper surface prior final calendering. It has been found that the rewetting of the cellulose fibers prior to final hot calendaring improves the orange peel roughness of the paper. Papers made on the paper machine with a high moisture content calendar much more readily that papers of the same moisture content containing water added in a remoistening operation. This is due to a partial irreversibility in the imbition of water by cellulose. However, calendering a paper with high moisture content results blackening, a condition of transparency resulting from fibers being crushed in contact with each other. The crushed areas reflect less light and therefore appear dark, a condition that is undesirable in an imaging application such as a base for color paper. By adding moisture to the surface of the paper after the paper has been machine dried the problem of blackening can be avoided while preserving the advantages of high moisture calendering. The addition of surface moisture prior to machine calendering is intended to soften the surface fibers and not the fibers in the interior of the paper. Papers calendered with a high surface moisture content generally show greater strength, density, gloss and processing chemistry resistance, all of which are desirable for an imaging support and have been shown to be perceptually preferred to prior art photographic paper bases.

There are several paper surface humidification/moisturization techniques. The application of water either by mechanical roller or aerosol mist by way of a electrostatic field, are two techniques known in the art. The above techniques require dwell time, hence web length, for the water to penetrate the surface and equalize in the top surface of the paper. Therefore it is difficult for these above systems to make moisture corrections without distorting, spotting and swelling of the paper. The preferred method to rewet the paper surface prior final calendering is by use of a steam foil. A steam foil uses saturated steam in a controlled atmosphere to cause water vapor to penetrate the surface of the paper and condense. Prior to calendering, the steam foil allows a considerable improvement in gloss and smoothness due to the heating up and moisturizing the paper of this invention before the pressure nip of the calendering rolls. An example of a commercially available system that allows for controlled steam moisturization of the surface of cellulose paper is the “Fluidex System” manufacture by Pagendarm Corp.

The preferred moisture content of the smooth cellulose paper by weight after applying the steam and calendering is between 7% and 9%. A moisture level less than 7% is more costly to manufacture since more fiber is needed to reach a final basis weight. At a moisture level greater than 10% the surface of the paper begins to degrade. After the steam foil rewetting of the paper surface, the paper is calendered before winding of the paper. The preferred temperature of the calender rolls is between 76° C. and 88° C. Lower temperatures result in a poor surface. Higher temperatures are unnecessary, as they do not improve the paper surface and require more energy.

The Technical Association of the Pulp and Paper Industry literature suggests that the MD to CD modulus ratio predicts manufacturing efficiency in conversion processes, optimizing bending stiffness, monitors “draws” and the “jet/wire” ratio. An MSA (major strength angle) of a paper web or biaxially oriented polymer sheets is defined as the angle from the machine direction where the modulus of the paper web or biaxially oriented sheet is at its maximum. For example, a paper web with an MSA of 0 degrees has its modulus maximum aligned with the machine direction. A biaxially oriented polymer sheet with a MSA of 10 degrees has its modulus maximum 10 degrees away from the machine direction. The Technical Association of the Pulp and Paper Industry literature suggests that an MSA outside plus or minus 3 degrees predicts “stack lean”, dimensional stability, mis registration in printing due to differences in hygroexpansion, baggy edges and wrinkles. A MSA outside 5 degrees indicates that the paper making headbox is out of tune.

Stiffness in the plane of a sheet can be obtained from a Lorentzen & Wettre TSO gauge. This device can draw a polar plot of stiffness and it is also capable of estimating the major strength angle (MSA) by using sonic waves traveling though a sample in different directions. The sample may be analyzed repeatedly in a MD or CD pattern to map out the range of variation in the MD/CD profile and MSA.

In the absence of a TSO gauge, a tensile test can be done on a group of samples cut at angles from the MD to obtain the polar values. It is necessary take a large number of samples to be sure that the proper curve shape is obtained. The polar strength of a material can be modeled by the von Mises multimodal distribution equation below: $$ f ⁢ ( A , K , Θ , μ ) := A π · J0 ⁢ ( K ) · ⅇ K · ( cos ⁢ ( Θ_ ⁢   ⁢ μ ) ) 2

The parameter A is used to scale the size of the ellipsoid, K is a shape factor used in the term JO(K) which is a Bessel function of the first kind and zero order, Θ is the angle at which the strength is indicated, and μ is the MSA or major axis offset angle.

For assembled laminates, the polar stiffness data may either be elastic modulus readings or bending stiffness data. The bending stiffness of the sheet can be measured by using the LORENTZEN & WETTRE STIFFNESS TESTER, MODEL 16D. The output from this instrument is the force, in millinewtons, required to bend the cantilevered, unclamped end of a clamped sample 20 mm long and 38.1 mm wide at an angle of 15 degrees from the unloaded position. A typical range of stiffness that is suitable for photographic prints is 120 to 300 millinewtons. A stiffness greater than at least 120 millinewtons is required as the imaging support begins to loose commercial value below that number. Further, imaging supports with stiffness less than 120 millinewtons are difficult to transport in photographic finishing equipment or ink jet printers causing undesirable jams during transport. Supports with an MD stiffness greater than 280 millinewtons will also require too much force to transport a print around some metal guides because the coefficient of friction times the bending force is too high.

To better manage the curl of the smooth photographic grade cellulose paper replacing the low strength cast polyethylene layers with high strength biaxially oriented polymer sheets is useful. High strength plastic sheets are commonly made by biaxially orienting coextrusion cast thick (1025 micrometers) polyolefins. The sheets in-question may be labeled OPP for oriented polypropylene. Biaxially oriented polymer sheets are typically oriented 5× in the MD and then 8× in the CD. The final major strength properties are aligned with the CD and they are 1.8 times that of the MD. The MSA for biaxially oriented sheets can be aligned out of the exact CD direction by 10 degrees or more. For most purposes, a biaxially oriented sheet aligned out of the exact CD direction by 10 degrees or more is of no consequence. An MSA of 10 degrees or more is believed to be related to orientation of the polymer in the CD and then MD directions.

For a laminated imaging support material it has been found previously that to minimize curl in an imaging support material, the elastic modulus for high strength biaxially oriented polymer sheets should be the same order of magnitude as the cellulose paper base. High modulus biaxially oriented sheets therefore are superior to the weak polyethylene layers coated on prior art support materials. It has also been found that the primary strength axis for the biaxially oriented sheets should be approximately perpendicular to the cellulose paper base because it is possible to select combinations biaxially oriented sheets adhered to the cellulose paper base to obtain a combined bending stiffness that is equal in the MD and CD direction. It has been previously found that equal bending stiffness in the MD and CD tends to minimize image curl.

For a laminated imaging support it has been found that the condition of equal MD and CD strength is not, in itself, sufficient to keep a laminate from having optimum curling properties. Imaging supports made by laminating biaxially oriented sheets to cellulose paper and having a combined bending stiffness that is equal in the MD and CD direction have been shown to have “diagonal curl” which is curl where the axis of the cylinder of curvature is at an angle between the CD and MD. Diagonal curl, also known as “twist warp” makes the photographic print appear undesirable because the diagonal direction maximizes the total edge lift when the sample is laid on a table and the curl occurs along the line of maximum photo length. Perceptual testing showed that consumers seem to dislike the diagonal curl, even with small amounts of curl. A TSO angle for the base paper between −5 and 5 degrees is preferred, as this range of TSO has been shown to provide a perceptually acceptable twist warp in images.

When using a smooth cellulose fiber paper support in combination with high strength biaxially oriented sheets, it is preferable to extrusion laminate the microvoided composite sheets to the base paper using a polyolefin resin. Extrusion laminating is carried out by bringing together the biaxially oriented sheets of the invention and the base paper with application of an adhesive between them followed by their being pressed in a nip such as between two rollers. The adhesive may be applied to either the biaxially oriented sheets or the base paper prior to their being brought into the nip. In a preferred form the adhesive is applied into the nip simultaneously with the biaxially oriented sheets and the base paper. The adhesive may be any suitable material that does not have a harmful effect upon the photographic element. A preferred material is polyethylene that is melted at the time it is placed into the nip between the paper and the biaxially oriented sheet.

During the lamination process, it is desirable to maintain control of the tension of the biaxially oriented sheet(s) in order to minimize curl in the resulting laminated support. For high humidity applications (>50% RH) and low humidity applications (<20% RH), it is desirable to laminate both a front side and back side film to keep curl to a minimum. Also, during the lamination process, it is desirable to laminated the top sheet to the face side of the paper. Generally, the face side of the paper is a smoother surface than the wire side. Lamination of the top sheet to the face side of the paper will generally yield a image with better gloss than lamination of the top sheet to the wire side of the paper.

The support material may also comprise the smooth base paper of the invention with at least one waterproof layer to protect the cellulose paper during image development. The reflective support of the present invention preferably includes a resin layer with a stabilizing amount of hindered amine extruded on the top side of the imaging layer substrate. Hindered amine light stabilizers (HALS) originate from 2,2,6;6-tertramethylpiperidine. The hindered amine should be added to the polymer layer at about 0.01-5% by weight of said resin layer in order to provide resistance to polymer degradation upon exposure to UV light. The preferred amount is at about 0.05-3% by weight. This provides excellent polymer stability and resistance to cracking and yellowing while keeping the expense of the hindered amine to a minimum. Examples of suitable hindered amines with molecular weights of less than 2300 are Bis(2,2,6,6-letramethyl-4-piperidinyl)sebacate; Bis(1,2,2,6,6-pentamethyl-4-piperidinyl)sebacate; Bis(1,2,2,6,6-pentamethyl-4-piperidinyl)2-n-butyl-(3,5-di-tert-butyl-hydroxy-benzyl)malonate; 8-Acetly-3-dodecyl-7,7,9,9-tetramethly-1.3,8-triazaspirol(4,5)decane-2,4-dione; Tetra(2,2,6,6-tetramethyl-4-piperidinyl)1,2,3,4-butanetetracarboxylate; 1-(-2-[3,5-di-tert-butyl-4-hydroxyphenyl-propionyloxyl]ethyl)-4-(3,5-di-tert-butyl-4-hydroxyphenylpropionyloxy)-2,2,6,6-tetramethylpiperidine; 1,1′-(1,2-ethenadiyl)bis(3,3,5,5-tetramethyl-2-piperazinone). The preferred hindered amine is 1,3,5-triazine-2,4,6-triamine,N,N′″-[1,2-ethanediylbis[[[4,6-bis(butyl(1,2,2,6,6-pentamethyl-4-piperidinyl)amino]-1,3,5-triazine-2-yl]imino]-3,1 propanediyl]]-bis[N′,N″-dibutyl-N′, N″-bis(1,2,2,6,6-pentamethyl-4-piperidinyl) which will be referred to as Compound A. Compound A is preferred because when mixtures of polymers and Compound A are extruded onto imaging paper the polymer to paper adhesion is excellent and the long term stability of the imaging system against cracking and yellowing is improved.

Suitable polymers for the resin layer include polyethylene, polypropylene, polymethylpentene, polystyrene, polybutylene, and mixtures thereof. Polyolefin copolymers, including copolymers of polyethylene, propylene and ethylene such as hexene, butene, and octene are also useful. Polyethylene is most preferred, as it is low in cost and has desirable coating properties. As polyethylene, usable are high-density polyethylene, low-density polyethylene, linear low density polyethylene, and polyethylene blends. Other suitable polymers include polyesters produced from aromatic, aliphatic or cycloaliphatic dicarboxylic acids of 4-20 carbon atoms and aliphatic or alicyclic glycols having from 2-24 carbon atoms. Examples of suitable dicarboxylic acids include terephthalic, isophthalic, phthalic, naphthalene dicarboxylic acid, succinic, glutaric, adipic, azelaic, sebacic, fumaric, maleic, itaconic, 1,4-cyclohexanedicarboxylic, sodiosulfoisophthalic and mixtures thereof. Examples of suitable glycols include ethylene glycol, propylene glycol, butanediol, pentanediol, hexanediol, 1,4-cyclohexanedimethanol, diethylene glycol, other polyethylene glycols and mixtures thereof. Other polymers are matrix polyesters having repeat units from terephthalic acid or naphthalene dicarboxylic acid and at least one glycol selected from ethylene glycol, 1,4-butanediol and 1,4-cyclohexanedimethanol such as poly(ethylene terephthalate), which may be modified by small amounts of other monomers. Other suitable polyesters include liquid crystal copolyesters formed by the inclusion of suitable amount of a co-acid component such as stilbene dicarboxylic acid. Examples of such liquid crystal copolyesters are those disclosed in U.S. Pat. Nos. 4,420,607; 4,459,402; and 4,468,510. Useful polyamides include nylon 6, nylon 66, and mixtures thereof. Copolymers of polyamides are also suitable continuous phase polymers. An example of a useful polycarbonate is bisphenol-A polycarbonate. Cellulosic esters suitable for use as the continuous phase polymer of the composite sheets include cellulose nitrate, cellulose triacetate, cellulose diacetate, cellulose acetate propionate, cellulose acetate butyrate, and mixtures or copolymers thereof. Useful polyvinyl resins include polyvinyl chloride, poly(vinyl acetal), and mixtures thereof. Copolymers of vinyl resins can also be utilized.

Any suitable white pigment may be incorporated in the polyolefin layer, such as, for example, zinc oxide, zinc sulfide, zirconium dioxide, white lead, lead sulfate, lead chloride, lead aluminate, lead phthalate, antimony trioxide, white bismuth, tin oxide, white manganese, white tungsten, and combinations thereof. The preferred pigment is titanium dioxide because of its high refractive index, which gives excellent optical properties at a reasonable cost. The pigment is used in any form that is conveniently dispersed within the polyolefin. The preferred pigment is anatase titanium dioxide. The most preferred pigment is rutile titanium dioxide because it has the highest refractive index at the lowest cost. The average pigment diameter of the rutile TiO 2 is most preferably in the range of 0.1 to 0.26 μm. The pigments that are greater than 0.26 μm are too yellow for an imaging element application and the pigments that are less than 0.1 μm are not sufficiently opaque when dispersed in polymers. Preferably, the white pigment should be employed in the range of from about 10 to about 50 percent by weight, based on the total weight of the polyolefin coating. Below 10 percent TiO 2 , the imaging system will not be sufficiently opaque and will have inferior optical properties. Above 50 percent TiO 2 , the polymer blend is not manufacturable. The surface of the TiO 2 can be treated with an inorganic compounds such as aluminum hydroxide, alumina with a fluoride compound or fluoride ions, silica with a fluoride compound or fluoride ion, silicon hydroxide, silicon dioxide, boron oxide, boria-modified silica (as described in U.S. Pat. no. 4,781,761), phosphates, zinc oxide, ZrO 2 , etc. and with organic treatments such as polyhydric alcohol, polyhydric amine, metal soap, alkyl titanate, polysiloxanes, silanes, etc. The organic and inorganic TiO 2 treatments can be used alone or in any combination. The amount of the surface treating agents is preferably in the range of 0.2 to 2.0% for the inorganic treatment and 0.1 to 1% for the organic treatment, relative to the weight of the weight of the titanium dioxide. At these levels of treatment the TiO 2 disperses well in the polymer and does not interfere with the manufacture of the imaging support.

The polymer, hindered amine light stabilizer, and the TiO 2 are mixed with each other in the presence of a dispersing agent. Examples of dispersing agents are metal salts of higher fatty acids such as sodium palmitate, sodium stearate, calcium palmitate, sodium laurate, calcium stearate, aluminum stearate, magnesium stearate, zirconium octylate, zinc stearate, etc, higher fatty acids, higher fatty amide, and higher fatty acids. The preferred dispersing agent is sodium stearate and the most preferred dispersing agent is zinc stearate. Both of these dispersing agents give superior whiteness to the resin-coated layer.

For photographic use, a white base with a slight bluish tint is preferred. The layers of the waterproof resin coating preferably contain colorants such as a bluing agent and magenta or red pigment. Applicable bluing agents include commonly know ultramarine blue, cobalt blue, oxide cobalt phosphate, quinacridone pigments, and a mixture thereof. Applicable red or magenta colorants are quinacridones and ultramarines.

The resin may also include a fluorescing agent, which absorb energy in the UV region and emit light largely in the blue region. Any of the optical brighteners referred to in U.S. Pat. No. 3,260,715 or a combination thereof would be beneficial.

The resin may also contain an antioxidant(s) such as hindered phenol primary antioxidants used alone or in combination with secondary antioxidants. Examples of hindered phenol primary antioxidants include pentaerythrityl tetrakis [3-(3,5-di-tert-butyl-4-hydroxyphenyl)proprionate] (such as Irganox 1010), octadecyl 3-(3,5-di-tert-butyl-4-hydroxyphenyl)proprionate (such as Irganox 1076 which will be referred to as compound B), benzenepropanoic acid 3,5-bis(1,1-dimethyl)-4-hydroxy-2[3-[3,5-bis(1,1 -dimethylethyl)-4-hydroxyphenyl)-1-oxopropyl)hydrazide (such as Irganox MD1024), 2,2′-thiodiethylenebis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)proprionate] (such as Irganox 1035), 1,3,5-trimethyl-2,4,6-tri(3,5-di-tert-butyl-4-hydroxybenzyl)benzene (such as Irganox 1330), but are not limited to these examples. Secondary antioxidants include organic alkyl and aryl phosphites including examples such as triphenylphosphite (such as Irgastab TPP), tri(n-propylphenyl-phophite) (such as Irgastab SN-55), 2,4-bis(1,1-dimethylphenyl) phosphite (such as Irgafos 168).

The hindered amine light stabilizer, TiO 2 , colorants, slip agents, optical brightener, and antioxidant are incorporated either together or separately with the polymer using a continuous or Banburry mixer. A concentrate of the additives in the form of a pellet is typically made. The concentration of the rutile pigment can be from 20% to 80% by weight of the masterbatch. The master batch is then adequately diluted for use with the resin.

To form the water-proof resin coating according to the present invention, the pellet containing the pigment and other additives is subjected to hot-melt coating onto a running support of paper. If desired, the pellet is diluted with a polymer prior to hot melt coating. For a single layer coating the resin layer may be formed by lamination. The die is not limited to any specific type and may be any one of the common dies such as a T-slot or coat hanger die. An exit orifice temperature in heat melt extrusion of the water-proof resin ranges from 500-660° F. Further, before coating the support with resin, the support may be treated with an activating treatment such as corona discharge, flame, ozone, plasma, or glow discharge.

At least two melt extruded polymer layers applied to the base on each side is preferred. Two or more layers are preferred at different polymers systems can be used to improve image whiteness by using a higher weight percent of white pigments or by the use of a less expensive polymer located next to the base paper. The preferred method for melt extruding 2 or more layers is melt coextrusion from a slit die. Coextrusion is a process that provides for more than one extruder to simultaneously pump molten polymer out through a die in simultaneous yet discrete layers. This is accomplished typically through the use of a multimanifold feedblock which serves to collect the hot polymer keeping the layers separated until the entrance to the die where the discrete layers are pushed out between the sheet and paper to adhere them together. Coextrusion lamination is typically carried out by bringing together the biaxially oriented sheet and the base paper with application of the bonding agent between the base paper and the biaxially oriented sheet followed by their being pressed together in a nip such as between two rollers.

The thickness of the resin layer which is applied to a base paper of the reflective support used in the present invention at a side for imaging, is preferably in the range of 5 to 100 μm and most preferably in the range of 10 to 50 μm.

The thickness of the resin layer applied to a base paper on the side opposite the imaging element is preferably in a range from 5 to 100 μm and more preferably from 10 to 50 μm. The surface of the waterproof resin coating at the imaging side may be a glossy, fine, silk, grain, or matte surface. On the surface of the water-proof coating on the backside which is not coated with an imaging element may also be glossy, fine, silk, or matte surface. The preferred water-proof surface for the backside away from the imaging element is matte.

A melt extruded layer of polyester applied to the base paper is preferred as the melt extruded polyester provides mechanical toughness and tear resistance compared to typical melt extruded polyethylene. Further, a melt extruded layer of polyester is preferred as the weight percent of white pigment contained in polyester can be significantly increased compared to the weight percent of white pigment in polyolefin thus improving the whiteness of a polyester melt extruded imaging support material. Such polyester melt extruded layers are well known, widely used and typically prepared from high molecular weight polyesters prepared by condensing a dihydric alcohol with a dibasic saturated fatty acid or derivative thereof.

Suitable dihydric alcohols for use in preparing such polyesters are well known in the art and include any glycol wherein the hydroxyl groups are on the terminal carbon atom and contain from two to twelve carbon atoms such as, for example, ethylene glycol, propylene glycol, trimethylene glycol, hexamethylene glycol, decamethylene glycol, dodecamethylene glycol, 1,4-cyclohexane, dimethanol, and the like.

Suitable dibasic acids useful for the preparation of polyesters include those containing from two to sixteen carbon atoms such as adipic acid, sebacic acid, isophthalic acid, terephtalic acid and the like. Alkyl esters of acids such as those listed above can also be employed. Other alcohols and acids as well as polyesters prepared therefrom and the preparation of the polyesters are described in U.S. Pat. No. 2,720,503 and 2,901,466 which are hereby incorporated herein for reference. Polyethylene terephthalate is preferred.

Melt extrusion lamination of the polyester layer to the base paper is preferred. The thickness of the polyester layer is preferably from 5 to 100 micrometers. Below 4 micrometers the polyester layer begins to loose waterproof properties needed to survive a wet image development process. Above 110 micrometers, the melt extruded polyester layer becomes brittle and will show undesirable cracks under the image layers.

As used herein the phrase “imaging element” is a material that may be used as a imaging support for the transfer of images to the support by techniques such as ink jet printing or thermal dye transfer as well as a support for silver halide images. As used herein, the phrase “photographic element” is a material that utilizes photosensitive silver halide in the formation of images. The thermal dye image-receiving layer of the receiving elements of the invention may comprise, for example, a polycarbonate, a polyurethane, a polyester, polyvinyl chloride, poly(styrene-co-acrylonitrile), poly(caprolactone) or mixtures thereof. The dye image-receiving layer may be present in any amount which is effective for the intended purpose. In general, good results have been obtained at a concentration of from about 1 to about 10 g/m 2 . An overcoat layer may be further coated over the dye-receiving layer, such as described in U.S. Pat. No. 4,775,657 of Harrison et al.

Dye-donor elements that are used with the dye-receiving element of the invention conventionally comprise a support having thereon a dye containing layer. Any dye can be used in the dye-donor employed in the invention provided it is transferable to the dye-receiving layer by the action of heat. Especially good results have been obtained with sublimable dyes. Dye donors applicable for use in the present invention are described, e.g., in U.S. Pat. Nos. 4,916,112, 4,927,803 and 5,023,228.

As noted above, dye-donor elements are used to form a dye transfer image. Such a process comprises image-wise-heating a dye-donor element and transferring a dye image to a dye-receiving element as described above to form the dye transfer image.

In a preferred embodiment of the thermal dye transfer method of printing, a dye donor element is employed which compromises a poly-(ethylene terephthalate) support coated with sequential repeating areas of cyan, magenta, and yellow dye, and the dye transfer steps are sequentially performed for each color to obtain a three-color dye transfer image. Of course, when the process is only performed for a single color, then a monochrome dye transfer image is obtained.

Thermal printing heads which can be used to transfer dye from dye-donor elements to receiving elements of the invention are available commercially. There can be employed, for example, a Fujitsu Thermal Head (FTP-040 MCS001), a TDK Thermal Head F415 HH7-1089 or a Rohm Thermal Head KE 2008-F3. Alternatively, other known sources of energy for thermal dye transfer may be used, such as lasers as described in, for example, GB No. 2,083,726A.

A thermal dye transfer assemblage of the invention comprises (a) a dye-donor element, and (b) a dye-receiving element as described above, the dye-receiving element being in a superposed relationship with the dye-donor element so that the dye layer of the donor element is in contact with the dye image-receiving layer of the receiving element.

When a three-color image is to be obtained, the above assemblage is formed on three occasions during the time when heat is applied by the thermal printing head. After the first dye is transferred, the elements are peeled apart. A second dye-donor element (or another area of the donor element with a different dye area) is then brought in register with the dye-receiving element and the process repeated. The third color is obtained in the same manner.

The electrographic and electrophotographic processes and their individual steps have been well described in detail in many books and publications. The processes incorporate the basic steps of creating an electrostatic image, developing that image with charged, colored particles (toner), optionally transferring the resulting developed image to a secondary substrate, and fixing the image to the substrate. There are numerous variations in these processes and basic steps; the use of liquid toners in place of dry toners is simply one of those variations.

The first basic step, creation of an electrostatic image, can be accomplished by a variety of methods. The electrophotographic process of copiers uses imagewise photodischarge, through analog or digital exposure, of a uniformly charged photoconductor. The photoconductor may be a single-use system, or it may be rechargeable and reimageable, like those based on selenium or organic photorecptors.

In one form of the electrophotographic process of copiers uses imagewise photodischarge, through analog or digital exposure, of a uniformly charged photoconductor. The photoconductor may be a single-use system, or it may be rechargeable and reimageable, like those based on selenium or organic photoreceptors.

In one form of the electrophotographic process, a photosensitive element is permanently imaged to form areas of differential conductivity. Uniform electrostatic charging, followed by differential discharge of the imaged element, creates an electrostatic image. These elements are called electrographic or xeroprinting masters because they can be repeatedly charged and developed after a single imaging exposure.

In an alternate electrographic process, electrostatic images are created iono-graphically. The latent image is created on dielectric (charge-holding) medium, either paper or film. Voltage is applied to selected metal styli or writing nibs from an array of styli spaced across the width of the medium, causing a dielectric breakdown of the air between the selected styli and the medium. Ions are created, which form the latent image on the medium.

Electrostatic images, however generated, are developed with oppositely charged toner particles. For development with liquid toners, the liquid developer is brought into direct contact with the electrostatic image. Usually a flowing liquid is employed, to ensure that sufficient toner particles are available for development. The field created by the electrostatic image causes the charged particles, suspended in a nonconductive liquid, to move by electrophoresis. The charge of the latent electrostatic image is thus neutralized by the oppositely charged particles. The theory and physics of electrophoretic development with liquid toners are well described in many books and publications.

If a reimageable photoreceptor or an electrographic master is used, the toned image is transferred to paper (or other substrate). The paper is charged electrostatically, with the polarity chosen to cause the toner particles to transfer to the paper. Finally, the toned image is fixed to the paper. For self-fixing toners, residual liquid is removed from the paper by air-drying or heating. Upon evaporation of the solvent these toners form a film bonded to the paper. For heat-fusible toners, thermoplastic polymers are used as part of the particle. Heating both removes residual liquid and fixes the toner to paper.

The dye receiving layer or DRL for ink jet imaging may be applied by any known methods. Such as solvent coating, or melt extrusion coating techniques. The DRL is coated over the TL at a thickness ranging from 0.1-10 μm, preferably 0.5-5 μm. There are many known formulations which may be useful as dye receiving layers. The primary requirement is that the DRL is compatible with the inks which it will be imaged so as to yield the desirable color gamut and density. As the ink drops pass through the DRL, the dyes are retained or mordanted in the DRL, while the ink solvents pass freely through the DRL and are rapidly absorbed by the TL. Additionally, the DRL formulation is preferably coated from water, exhibits adequate adhesion to the TL, and allows for easy control of the surface gloss.

For example, Misuda et al, in U.S. Pat. Nos. 4,879,166; 5,264,275; 5,104,730; 4,879,166, and Japanese patents 1,095,091; 2,276,671; 2,276,670; 4,267,180; 5,024,335; 5,016,517 discloses aqueous based DRL formulations comprising mixtures of psuedo-bohemite and certain water soluble resins. Light, in U.S. Pat. Nos. 4,903,040; 4,930,041; 5,084,338; 5,126,194; 5,126,195; and 5,147,717 disclose aqueous-based DRL formulations comprising mixtures of vinyl pyrrolidone polymers and certain water-dispersible and/or water-soluble polyesters, along with other polymers and addenda. Butters et al, in U.S. Pat. Nos. 4,857,386 and 5,102,717, disclose ink-absorbent resin layers comprising mixtures of vinyl pyrrolidone polymers and acrylic or methacrylic polymers. Sato et al, in U.S. Pat. No. 5,194,317, and Higuma et al, in U.S. Pat. No. 5,059,983 disclose aqueous-coatable DRL formulations based on poly (vinyl alcohol). Iqbal in U.S. Pat. No. 5,208,092 discloses water-based IRL formulations comprising vinyl copolymers which are subsequently cross-linked. In addition to these examples, there may be other known or contemplated DRL formulations which are consistent with the aforementioned primary and secondary requirements of the DRL, all of which fall under the spirit and scope of the current invention.

The preferred DRL is a 0-10 μm DRL which is coated as an aqueous dispersion of 5 parts alumoxane and 5 parts poly (vinyl pyrrolidone). The DRL may also contain varying levels and sizes of matting agents for the purpose of controlling gloss, friction, and/or fingerprint resistance, surfactants to enhance surface uniformity and to adjust the surface tension of the dried coating, mordanting agents, antioxidants, UV absorbing compounds, light stabilizers, and the like.

Although the ink-receiving elements as described above can be successfully used to achieve the objectives of the present invention, it may be desirable to overcoat the DRL for the purpose of enhancing the durability of the imaged element. Such overcoats may be applied to the DRL either before or after the element is imaged. For example, the DRL can be overcoated with an ink-permeable layer through which inks freely pass. Layers of this type are described in U.S. Pat. Nos. 4,686,118; 5,027,131; and 5,102,717. Alternatively, an overcoat may be added after the element is imaged. Any of the known laminating films and equipment may be used for this purpose. The inks used in the aforementioned imaging process are well known, and the ink formulations are often closely tied to the specific processes, i.e., continuous, piezoelectric, or thermal. Therefore, depending on the specific ink process, the inks may contain widely differing amounts and combinations of solvents, colorants, preservatives, surfactants, humectants, and the like. Inks preferred for use in combination with the image recording elements of the present invention are water-based, such as those currently sold for use in the Hewlett-Packard Desk Writer 560C printer. However, it is intended that alternative embodiments of the image-recording elements as described above, which may be formulated for use with inks which are specific to a given ink-recording process or to a given commercial vendor, fall within the scope of the present invention.

This invention is directed to a silver halide photographic element capable of excellent performance when exposed by either an electronic printing method or a conventional optical printing method. An electronic printing method comprises subjecting a radiation sensitive silver halide emulsion layer of a recording element to actinic radiation of at least 10 −4 ergs/cm 2 for up to 100μseconds duration in a pixel-by-pixel mode wherein the silver halide emulsion layer is comprised of silver halide grains as described above. A conventional optical printing method comprises subjecting a radiation sensitive silver halide emulsion layer of a recording element to actinic radiation of at least 10 −4 ergs/cm 2 for 10 −3 to 300 seconds in an imagewise mode wherein the silver halide emulsion layer is comprised of silver halide grains as described above.

This invention in a preferred embodiment utilizes a radiation-sensitive emulsion comprised of silver halide grains (a) containing greater than 50 mole percent chloride, based on silver, (b) having greater than 50 percent of their surface area provided by {100} crystal faces, and (c) having a central portion accounting for from 95 to 99 percent of total silver and containing two dopants selected to satisfy each of the following class requirements: (i) a hexacoordination metal complex which satisfies the formula

[ML 6 ] n   (I)

wherein n is zero, −1, −2, −3 or −4; M is a filled frontier orbital polyvalent metal ion, other than iridium; and L 6 represents bridging ligands which can be independently selected, provided that least four of the ligands are anionic ligands, and at least one of the ligands is a cyano ligand or a ligand more electronegative than a cyano ligand; and (ii) an iridium coordination complex containing a thiazole or substituted thiazole ligand.

This invention is directed towards a photographic recording element comprising a support and at least one light sensitive silver halide emulsion layer comprising silver halide grains as described above.

It has been discovered quite surprisingly that the combination of dopants (i) and (ii) provides greater reduction in reciprocity law failure than can be achieved with either dopant alone. Further, unexpectedly, the combination of dopants (i) and (ii) achieve reductions in reciprocity law failure beyond the simple additive sum achieved when employing either dopant class by itself. It has not been reported or suggested prior to this invention that the combination of dopants (i) and (ii) provides greater reduction in reciprocity law failure, particularly for high intensity and short duration exposures. The combination of dopants (i) and (ii) further unexpectedly achieves high intensity reciprocity with iridium at relatively low levels, and both high and low intensity reciprocity improvements even while using conventional gelatino-peptizer (e.g., other than low methionine gelatino-peptizer).

In a preferred practical application, the advantages of the invention can be transformed into increased throughput of digital substantially artifact-free color print images while exposing each pixel sequentially in synchronism with the digital data from an image processor.

In one embodiment, the present invention represents an improvement on the electronic printing method. Specifically, this invention in one embodiment is directed to an electronic printing method which comprises subjecting a radiation sensitive silver halide emulsion layer of a recording element to actinic radiation of at least 10 −4 ergs/cm 2 for up to 100 μ seconds duration in a pixel-by-pixel mode. The present invention realizes an improvement in reciprocity failure by selection of the radiation sensitive silver halide emulsion layer. While certain embodiments of the invention are specifically directed towards electronic printing, use of the emulsions and elements of the invention is not limited to such specific embodiment, and it is specifically contemplated that the emulsions and elements of the invention are also well suited for conventional optical printing.

It has been unexpectedly discovered that significantly improved reciprocity performance can be obtained for silver halide grains (a) containing greater than 50 mole percent chloride, based on silver, and (b) having greater than 50 percent of their surface area provided by {100} crystal faces by employing a hexacoordination complex dopant of class (i) in combination with an iridium complex dopant comprising a thiazole or substituted thiazole ligand. The reciprocity improvement is obtained for silver halide grains employing conventional gelatino-peptizer, unlike the contrast improvement described for the combination of dopants set forth in U.S. Pat. Nos. 5,783,373 and 5,783,378, which requires the use of low methionine gelatino-peptizers as discussed therein, and which states it is preferable to limit the concentration of any gelatino-peptizer with a methionine level of greater than 30 micromoles per gram to a concentration of less than 1 percent of the total peptizer employed. Accordingly, in specific embodiments of the invention, it is specifically contemplated to use significant levels (i.e., greater than 1 weight percent of total peptizer) of conventional gelatin (e.g., gelatin having at least 30 micromoles of methionine per gram) as a gelatino-peptizer for the silver halide grains of the emulsions of the invention. In preferred embodiments of the invention, gelatino-peptizer is employed which comprises at least 50 weight percent of gelatin containing at least 30 micromoles of methionine per gram, as it is frequently desirable to limit the level of oxidized low methionine gelatin which may be used for cost and certain performance reasons.

In a specific, preferred form of the invention it is contemplated to employ a class (i) hexacoordination complex dopant satisfying the formula:

 [ML 6 ] n   (I)

where

n is zero, −1, −2, −3 or −4;

M is a filled frontier orbital polyvalent metal ion, other than iridium, preferably Fe +2 , Ru +2 , Os +2 , Co +3 , Rh +3 , Pd +4 or Pt +4 , more preferably an iron, ruthenium or osmium ion, and most preferably a ruthenium ion;

L 6 represents six bridging ligands which can be independently selected, provided that least four of the ligands are anionic ligands and at least one (preferably at least 3 and optimally at least 4) of the ligands is a cyano ligand or a ligand more electronegative than a cyano ligand. Any remaining ligands can be selected from among various other bridging ligands, including aquo ligands, halide ligands (specifically, fluoride, chloride, bromide and iodide), cyanate ligands, thiocyanate ligands, selenocyanate ligands, tellurocyanate ligands, and azide ligands. Hexacoordinated transition metal complexes of class (i) which include six cyano ligands are specifically preferred.

Illustrations of specifically contemplated class (i) hexacoordination complexes for inclusion in the high chloride grains are provided by Olm et al U.S. Pat. No. 5,503,970 and Daubendiek et al U.S. Pat. Nos. 5,494,789 and 5,503,971, and Keevert et al U.S. Pat. No. 4,945,035, as well as Murakami et al Japanese Patent Application Hei-2[1990]-249588, and Research Disclosure Item 36736. Useful neutral and anionic organic ligands for class (ii) dopant hexacoordination complexes are disclosed by Olm et al U.S. Pat. No. 5,360,712 and Kuromoto et al U.S. Pat. No. 5,462,849.

Class (i) dopant is preferably introduced into the high chloride grains after at least 50 (most preferably 75 and optimally 80) percent of the silver has been precipitated, but before precipitation of the central portion of the grains has been completed. Preferably class (i) dopant is introduced before 98 (most preferably 95 and optimally 90) percent of the silver has been precipitated. Stated in terms of the fully precipitated grain structure, class (i) dopant is preferably present in an interior shell region that surrounds at least 50 (most preferably 75 and optimally 80) percent of the silver and, with the more centrally located silver, accounts the entire central portion (99 percent of the silver), most preferably accounts for 95 percent, and optimally accounts for 90 percent of the silver halide forming the high chloride grains. The class (i) dopant can be distributed throughout the interior shell region delimited above or can be added as one or more bands within the interior shell region.

Class (i) dopant can be employed in any conventional useful concentration. A preferred concentration range is from 10 −8 to 10 −3 mole per silver mole, most preferably from 10 −6 to 5×10 −4 mole per silver mole.

The following are specific illustrations of class (i) dopants:

(i-1)  [Fe(CN)                                                                        6                                                                    ]                                                                        −4
(i-2)  [Ru(CN)                                                                        6                                                                    ]                                                                        −4
(i-3)  [Os(CN)                                                                        6                                                                    ]                                                                        −4
(i-4)  [Rh(CN)                                                                        6                                                                    ]                                                                        −3
(i-5)  [Co(CN)                                                                        6                                                                    ]                                                                        −3
(i-6)  [Fe(pyrazine)(CN)                                                                        5                                                                    ]                                                                        −4
(i-7)  [RuCl(CN)                                                                        5                                                                    ]                                                                        −4
(i-8)  [OsBr(CN)                                                                        5                                                                    ]                                                                        −4
(i-9)  [RhF(CN)                                                                        5                                                                    ]                                                                        −3
(i-10) [In(NCS)                                                                        6                                                                    ]                                                                        −3
(i-11) [FeCO(CN)                                                                        5                                                                    ]                                                                        −3
(i-12) [RuF                                                                        2                                                                    (CN)                                                                        4                                                                    ]                                                                        −4
(i-13) [OsCl                                                                        2                                                                    (CN)                                                                        4                                                                    ]                                                                        −4
(i-14) [RhI                                                                        2                                                                    (CN)                                                                        4                                                                    ]                                                                        −3
(i-15) [Ga(NCS)                                                                        6                                                                    ]                                                                        −3
(i-16) [Ru(CN)                                                                        5                                                                    (OCN)]                                                                        −4
(i-17) [Ru(CN)                                                                        5                                                                    (N                                                                        3                                                                    )]                                                                        −4
(i-18) [Os(CN)                                                                        5                                                                    (SCN)]                                                                        −4
(i-19) [Rh(CN)                                                                        5                                                                    (SeCN)]                                                                        −3
(i-20) [Os(CN)Cl                                                                        5                                                                    ]                                                                        −4
(i-21) [Fe(CN)                                                                        3                                                                    Cl                                                                        3                                                                    ]                                                                        −3
(i-22) [Ru(CO)                                                                        2                                                                    (CN)                                                                        4                                                                    ]                                                                        −1

When the class (i) dopants have a net negative charge, it is appreciated that they are associated with a counter ion when added to the reaction vessel during precipitation. The counter ion is of little importance, since it is ionically dissociated from the dopant in solution and is not incorporated within the grain. Common counter ions known to be fully compatible with silver chloride precipitation, such as ammonium and alkali metal ions, are contemplated. It is noted that the same comments apply to class (ii) dopants, otherwise described below.

The class (ii) dopant is an iridium coordination complex containing at least one thiazole or substituted thiazole ligand. Careful scientific investigations have revealed Group VIII hexahalo coordination complexes to create deep electron traps, as illustrated R. S. Eachus, R. E. Graves and M. T. Olm J. Chem. Phys ., Vol. 69, pp. 4580-7 (1978) and Physica Status Solidi A , Vol. 57, 429-37 (1980) and R. S. Eachus and M. T. Olm Annu. Rep. Prog. Chem. Sect. C. Phys. Chem ., Vol. 83, 3, pp. 3-48 (1986). The class (ii) dopants employed in the practice of this invention are believed to create such deep electron traps. The thiazole ligands may be substituted with any photographically acceptable substituent which does not prevent incorporation of the dopant into the silver halide grain. Exemplary substituents include lower alkyl (e.g., alkyl groups containing 1-4 carbon atoms), and specifically methyl. A specific example of a substituted thiazolc ligand which may be used in accordance with the invention is 5-methylthiazole. The class (ii) dopant preferably is an iridium coordination complex having ligands each of which are more electropositive than a cyano ligand In a specifically preferred form the remaining non-thiazole or non-substituted-thiazole ligands of the coordination complexes forming class (ii) dopants are halide ligands.

It is specifically contemplated to select class (ii) dopants from among the coordination complexes containing organic ligands disclosed by Olm et al U.S. Pat. No. 5,360,712, Olm et al U.S. Pat. No. 5,457,021 and Kuromoto et al U.S. Pat. No. 5,462,849.

In a preferred form it is contemplated to employ as a class (ii) dopant a hexacoordination complex satisfying the formula:

[IrL l 6 ] n′   (II)

wherein

n′ is zero, −1, −2, −3 or −4; and

L l 6 represents six bridging ligands which can be independently selected, provided that at least four of the ligands are anionic ligands, each of the ligands is more electropositive than a cyano ligand, and at least one of the ligands comprises a thiazole or substituted thiazole ligand. In a specifically preferred form at least four of the ligands are halide ligands, such as chloride or bromide ligands.

Class (ii) dopant is preferably introduced into the high chloride grains after at least 50 (most preferably 85 and optimally 90) percent of the silver has been precipitated, but before precipitation of the central portion of the grains has been completed. Preferably class (ii) dopant is introduced before 99 (most preferably 97 and optimally 95) percent of the silver has been precipitated. Stated in terms of the fully precipitated grain structure, class (ii) dopant is preferably present in an interior shell region that surrounds at least 50 (most preferably 85 and optimally 90) percent of the silver and, with the more centrally located silver, accounts the entire central portion (99 percent of the silver), most preferably accounts for 97 percent, and optimally accounts for 95 percent of the silver halide forming the high chloride grains. The class (ii) dopant can be distributed throughout the interior shell region delimited above or can be added as one or more bands within the interior shell region.

Class (ii) dopant can be employed in any conventional useful concentration. A preferred concentration range is from 10 −9 to 10 −4 mole per silver mole. Iridium is most preferably employed in a concentration range of from 10 −8 to 10 −5 mole per silver mole.

Specific illustrations of class (ii) dopants are the following:

(ii-1) [IrCl                                                                        5                                                                    (thiazole)]                                                                        −2
(ii-2) [IrCl                                                                        4                                                                    (thiazole)                                                                        2                                                                    ]                                                                        −1
(ii-3) [IrBr                                                                        5                                                                    (thiazole)]                                                                        −2
(ii-4) [IrBr                                                                        4                                                                    (thiazole)                                                                        2                                                                    ]                                                                        −1
(ii-5) [IrCl                                                                        5                                                                    (5-methylthiazole)]                                                                        −2
(ii-6) [IrCl                                                                        4                                                                    (5-methylthiazole)                                                                        2                                                                    ]                                                                        −1
(ii-7) [IrBr                                                                        5                                                                    (5-methylthiazole)]                                                                        −2
(ii-8) [IrBr                                                                        4                                                                    (5-methylthiazole)                                                                        2                                                                    ]                                                                        −1

In one preferred aspect of the invention in a layer using a magenta dye forming coupler, a class (ii) dopant in combination with an OsCl 5 (NO) dopant has been found to produce a preferred result.

Emulsions demonstrating the advantages of the invention can be realized by modifying the precipitation of conventional high chloride silver halide grains having predominantly (>50%) {100} crystal faces by employing a combination of class (i) and (ii) dopants as described above.

The silver halide grains precipitated contain greater than 50 mole percent chloride, based on silver. Preferably the grains contain at least 70 mole percent chloride and, optimally at least 90 mole percent chloride, based on silver. Iodide can be present in the grains up to its solubility limit, which is in silver iodochloride grains, under typical conditions of precipitation, about 11 mole percent, based on silver. It is preferred for most photographic applications to limit iodide to less than 5 mole percent iodide, most preferably less than 2 mole percent iodide, based on silver.

Silver bromide and silver chloride are miscible in all proportions. Hence, any portion, up to 50 mole percent, of the total halide not accounted for chloride and iodide, can be bromide. For color reflection print (i.e., color paper) uses bromide is typically limited to less than 10 mole percent based on silver and iodide is limited to less than 1 mole percent based on silver.

In a widely used form high chloride grains are precipitated to form cubic grains—that is, grains having {100} major faces and edges of equal length. In practice ripening effects usually round the edges and corners of the grains to some extent. However, except under extreme ripening conditions substantially more than 50 percent of total grain surface area is accounted for by {100} crystal faces.

High chloride tetradecahedral grains are a common variant of cubic grains. These grains contain 6 {100} crystal faces and 8 {111} crystal faces. Tetradecahedral grains are within the contemplation of this invention to the extent that greater than 50 percent of total surface area is accounted for by {100} crystal faces.

Although it is common practice to avoid or minimize the incorporation of iodide into high chloride grains employed in color paper, it is has been recently observed that silver iodochloride grains with {100} crystal faces and, in some instances, one or more {111} faces offer exceptional levels of photographic speed. In the these emulsions iodide is incorporated in overall concentrations of from 0.05 to 3.0 mole percent, based on silver, with the grains having a surface shell of greater than 50 Å that is substantially free of iodide and a interior shell having a maximum iodide concentration that surrounds a core accounting for at least 50 percent of total silver. Such grain structures are illustrated by Chen et al EPO 0 718 679.

In another improved form the high chloride grains can take the form of tabular grains having {100} major faces. Preferred high chloride {100} tabular grain emulsions are those in which the tabular grains account for at least 70 (most preferably at least 90) percent of total grain projected area. Preferred high chloride {100} tabular grain emulsions have average aspect ratios of at least 5 (most preferably at least >8). Tabular grains typically have thicknesses of less than 0.3 μm, preferably less than 0.2 μm, and optimally less than 0.07 μm. High chloride {100} tabular grain emulsions and their preparation are disclosed by Maskasky U.S. Pat. Nos. 5,264,337 and 5,292,632; House et al U.S. Pat. No. 5,320,938; Brust et al U.S. Pat. No. 5,314,798; and Chang et al U.S. Pat. No. 5,413,904.

Once high chloride grains having predominantly {100} crystal faces have been precipitated with a combination of class (i) and class (ii) dopants described above, chemical and spectral sensitization, followed by the addition of conventional addenda to adapt the emulsion for the imaging application of choice can take any convenient conventional form. These conventional features are illustrated by Research Disclosure , Item 38957, cited above, particularly:

III. Emulsion washing;

IV. Chemical sensitization;

V. Spectral sensitization and desensitization;

VII. Antifoggants and stabilizers;

VIII. Absorbing and scattering materials;

IX. Coating and physical property modifying addenda; and

X. Dye image formers and modifiers.

Some additional silver halide, typically less than 1 percent, based on total silver, can be introduced to facilitate chemical sensitization. It is also recognized that silver halide can be epitaxially deposited at selected sites on a host grain to increase its sensitivity. For example, high chloride {100} tabular grains with corner epitaxy are illustrated by Maskasky U.S. Pat. No. 5,275,930. For the purpose of providing a clear demarcation, the term “silver halide grain” is herein employed to include the silver necessary to form the grain up to the point that the final {100} crystal faces of the grain are formed. Silver halide later deposited that does not overlie the {100} crystal faces previously formed accounting for at least 50 percent of the grain surface area is excluded in determining total silver forming the silver halide grains. Thus, the silver forming selected site epitaxy is not part of the silver halide grains while silver halide that deposits and provides the final {100} crystal faces of the grains is included in the total silver forming the grains, even when it differs significantly in composition from the previously precipitated silver halide.

In the simplest contemplated form a recording element contemplated for use in the electronic printing method of one embodiment of the invention can consist of a single emulsion layer satisfying the emulsion description provided above coated on a conventional photographic support, such as those described in Research Disclosure , Item 38957, cited above, XVI. Supports. In one preferred form the support is a white reflective support, such as photographic paper support or a film support that contains or bears a coating of a reflective pigment. To permit a print image to be viewed using an illuminant placed behind the support, it is preferred to employ a white translucent support, such as a Duratrans™ or Duraclear™ support.

Image dye-forming couplers may be included in the element such as couplers that form cyan dyes upon reaction with oxidized color developing agents which are described in such representative patents and publications as: U.S. Pat. Nos. 2,367,531; 2,423,730; 2,474,293; 2,772,162; 2,895,826; 3,002,836; 3,034,892; 3,041,236; 4,883,746 and “Farbkuppler—Eine Literature Ubersicht,” published in Agfa Mitteilungen, Band III, pp. 156-175 (1961). Preferably such couplers are phenols and naphthols that form cyan dyes on reaction with oxidized color developing agent. Also preferable are the cyan couplers described in, for instance, European Patent Application Nos. 491,197; 544,322; 556,700; 556,777; 565,096; 570,006; and 574,948.

Typical cyan couplers are represented by the following formulas:

wherein R 1 , R 5 and R 8 each represent a hydrogen or a substituent; R 2 represents a substituent; R 3 , R 4 and R 7 each represent an electron attractive group having a Hammett's substituent constant σ para of 0.2 or more and the sum of the σ para values of R 3 and R 4 is 0.65 or more; R 6 represents an electron attractive group having a Hammett's substituent constant σ para of 0.35 or more; X represents a hydrogen or a coupling-off group; Z 1 represents nonmetallic atoms necessary for forming a nitrogen-containing, six-membered, heterocyclic ring which has at least one dissociative group; Z 2 represents —C(R 7 )═ and —N═; and Z 3 and Z 4 each represent —C(Rg)═ and —N═.

For purposes of this invention, an “NB coupler” is a dye-forming coupler which is capable of coupling with the developer 4-amino-3-methyl-N-ethyl-N-(2-methanesulfonamidoethyl) aniline sesquisulfate hydrate to form a dye for which the left bandwidth (LBW) of its absorption spectra upon “spin coating” of a 3% w/v solution of the dye in di-n-butyl sebacate solvent is at least 5 nm. less than the LBW for a 3% w/v solution of the same dye in acetonitrile. The LBW of the spectral curve for a dye is the distance between the left side of the spectral curve and the wavelength of maximum absorption measured at a density of half the maximum.

The “spin coating” sample is prepared by first preparing a solution of the dye in di-n-butyl sebacate solvent (3% w/v). If the dye is insoluble, dissolution is achieved by the addition of some methylene chloride. The solution is filtered and 0.1-0.2 ml is applied to a clear polyethylene terephthalate support (approximately 4 cm×4 cm) and spun at 4,000 RPM using the Spin Coating equipment, Model No. EC101, available from Headway Research Inc., Garland Tex. The transmission spectra of the so prepared dye samples are then recorded.

Preferred “NB couplers” form a dye which, in n-butyl sebacate, has a LBW of the absorption spectra upon “spin coating” which is at least 15 nm, preferably at least 25 nm, less than that of the same dye in a 3% solution (w/v) in acetonitrile.

In a preferred embodiment the cyan dye-forming “NB coupler” useful in the invention has the formula (IA)

wherein

R′ and R″ are substituents selected such that the coupler is a “NB coupler”, as herein defined; and

Z is a hydrogen atom or a group which can be split off by the reaction of the coupler with an oxidized color developing agent.

The coupler of formula (IA) is a 2,5-diamido phenolic cyan coupler wherein the substituents R′ and R″ are preferably independently selected from unsubstituted or substituted alkyl, aryl, amino, alkoxy and heterocyclyl groups.

In a further preferred embodiment, the “NB coupler” has the formula (I):

wherein

R″ and R′″ are independently selected from unsubstituted or substituted alkyl, aryl, amino, alkoxy and heterocyclyl groups and Z is as hereinbefore defined;

R 1 and R 2 are independently hydrogen or an unsubstituted or substituted alkyl group; and

Typically, R″ is an alkyl, amino or aryl group, suitably a phenyl group. R′″ is desirably an alkyl or aryl group or a 5-10 membered heterocyclic ring which contains one or more heteroatoms selected from nitrogen, oxygen and sulfur, which ring group is unsubstituted or substituted.

In the preferred embodiment the coupler of formula (I) is a 2,5-diamido phenol in which the 5-amido moiety is an amide of a carboxylic acid which is substituted in the alpha position by a particular sulfone (—SO 2 —) group, such as, for example, described in U.S. Pat. No. 5,686,235. The sulfone moiety is an unsubstituted or substituted alkylsulfone or a heterocyclyl sulfone or it is an arylsulfone, which is preferably substituted, in particular in the meta and/or para position.

Couplers having these structures of formulae (I) or (IA) comprise cyan dye-forming “NB couplers” which form image dyes having very sharp-cutting dye hues on the short wavelength side of the absorption curves with absorption maxima (λ max ) which are shifted hypsochromically and are generally in the range of 620-645 nm, which is ideally suited for producing excellent color reproduction and high color saturation in color photographic papers.

Referring to formula (I), R 1 and R 2 are independently hydrogen or an unsubstituted or substituted alkyl group, preferably having from 1 to 24 carbon atoms and in particular 1 to 10 carbon atoms, suitably a methyl, ethyl, n-propyl, isopropyl, butyl or decyl group or an alkyl group substituted with one or more fluoro, chloro or bromo atoms, such as a trifluoromethyl group. Suitably, at least one of R 1 and R 2 is a hydrogen atom and if only one of R 1 and R 2 is a hydrogen atom then the other is preferably an alkyl group having 1 to 4 carbon atoms, more preferably one to three carbon atoms and desirably two carbon atoms.

As used herein and throughout the specification unless where specifically stated otherwise, the term “alkyl” refers to an unsaturated or saturated straight or branched chain alkyl group, including alkenyl, and includes arykyl and cyclic alkyl groups, including cycloalkenyl, having 3-8 carbon atoms and the term ‘aryl’ includes specifically fused aryl.

In formula (I), R″ is suitably an unsubstituted or substituted amino, alkyl or aryl group or a 5-10 membered heterocyclic ring which contains one or more heteroatoms selected from nitrogen, oxygen and sulfur, which ring is unsubstituted or substituted, but is more suitably an unsubstituted or substituted phenyl group.

Examples of suitable substituent groups for this aryl or heterocyclic ring include cyano, chloro, fluoro, bromo, iodo, alkyl- or aryl-carbonyl, alkyl- or aryl-oxycarbonyl, carbonamido, alkyl- or aryl-carbonamido, alkyl- or aryl-sulfonyl, alkyl- or aryl-sulfonyloxy, alkyl- or aryl-oxysulfonyl, alkyl- or aryl-sulfoxide, alkyl- or aryl-sulfamoyl, alkyl- or aryl-sulfonamido, aryl, alkyl, alkoxy, aryloxy, nitro, alkyl- or aryl-ureido and alkyl- or aryl-carbamoyl groups, any of which may be further substituted. Preferred groups are halogen, cyano, alkoxycarbonyl, alkylsulfamoyl, alkyl-sulfonamido, alkylsulfonyl, carbamoyl, alkylcarbamoyl or alkylcarbonamido. Suitably, R″ is a 4-chlorophenyl, 3,4-di-chlorophenyl, 3,4-difluorophenyl, 4-cyanophenyl, 3-chloro-4-cyanophenyl, pentafluorophenyl, or a 3- or 4-sulfonamidophenyl group.

In formula (I), when R′″ is alkyl, it may be unsubstituted or substituted with a substituent such as halogen or alkoxy. When R′″ is aryl or a heterocycle, it may be substituted. Desirably it is not substituted in the position alpha to the sulfonyl group.

In formula (I), when R′″ is a phenyl group, it may be substituted in the meta and/or para positions with one to three substituents independently selected from the group consisting of halogen, and unsubstituted or substituted alkyl, alkoxy, aryloxy, acyloxy, acylamino, alkyl- or aryl-sulfonyloxy, alkyl- or aryl-sulfamoyl, alkyl- or aryl-sulfamoylamino, alkyl- or aryl-sulfonamido, alkyl-or aryl-ureido, alkyl- or aryl-oxycarbonyl, alkyl- or aryl-oxy-carbonylamino and alkyl- or aryl-carbamoyl groups.

In particular each substituent may be an alkyl group such as methyl, t-butyl, heptyl, dodecyl, pentadecyl, octadecyl or 1,1,2,2-tetramethylpropyl; an alkoxy group such as methoxy, t-butoxy, octyloxy, dodecyloxy, tetradecyloxy, hexadecyloxy or octadecyloxy; an aryloxy group such as phenoxy, 4-t-butylphenoxy or 4-dodecyl-phenoxy; an alkyl- or aryl-acyloxy group such as acetoxy or dodecanoyloxy; an alkyl- or aryl-acylamino group such as acetamido, hexadecanamido or benzamido; an alkyl- or aryl-sulfonyloxy group such as methyl-sulfonyloxy, dodecylsulfonyloxy or 4-methylphenyl-sulfonyloxy; an alkyl- or aryl-sulfamoyl-group such as N-butylsulfamoyl or N-4-t-butylphenylsulfamoyl; an alkyl- or aryl-sulfamoylamino group such as N-butyl-sulfamoylamino or N-4-t-butylphenylsulfamoyl-amino; an alkyl- or aryl-sulfonamido group such as methane-sulfonamido, hexadecanesulfonamido or 4-chlorophenyl-sulfonamido; an alkyl- or aryl-ureido group such as methylureido or phenylureido; an alkoxy- or aryloxy-carbonyl such as methoxycarbonyl or phenoxycarbonyl; an alkoxy- or aryloxy-carbonylamino group such as methoxy-carbonylamino or phenoxycarbonylamino; an alkyl- or aryl-carbamoyl group such as N-butylcarbamoyl or N-methyl-N-dodecylcarbamoyl; or a perfluoroalkyl group such as trifluoromethyl or heptafluoropropyl.

Suitably the above substituent groups have 1 to 30 carbon atoms, more preferably 8 to 20 aliphatic carbon atoms. A desirable substituent is an alkyl group of 12 to 18 aliphatic carbon atoms such as dodecyl, pentadecyl or octadecyl or an alkoxy group with 8 to 18 aliphatic carbon atoms such as dodecyloxy and hexadecyloxy or a halogen such as a meta or para chloro group, carboxy or sulfonamido. Any such groups may contain interrupting heteroatoms such as oxygen to form e.g. polyalkylene oxides.

In formula (I) or (IA) Z is a hydrogen atom or a group which can be split off by the reaction of the coupler with an oxidized color developing agent, known in the photographic art as a ‘coupling-off group’ and may preferably be hydrogen, chloro, fluoro, substituted aryloxy or mercaptotetrazole, more preferably hydrogen or chloro.

The presence or absence of such groups determines the chemical equivalency of the coupler, i.e., whether it is a 2-equivalent or 4-equivalent coupler, and its particular identity can modify the reactivity of the coupler. Such groups can advantageously affect the layer in which the coupler is coated, or other layers in the photographic recording material, by performing, after release from the coupler, functions such as dye formation, dye hue adjustment, development acceleration or inhibition, bleach acceleration or inhibition, electron transfer facilitation, color correction, and the like.

Representative classes of such coupling-off groups include, for example, halogen, alkoxy, aryloxy, heterocyclyloxy, sulfonyloxy, acyloxy, acyl, heterocyclylsulfonamido, heterocyclylthio, benzothiazolyl, phosophonyloxy, alkylthio, arylthio, and arylazo. These coupling-off groups are described in the art, for example, in U.S. Pat. Nos. 2,455,169; 3,227,551; 3,432,521; 3,467,563; 3,617,291; 3,880,661; 4,052,212; and 4,134,766; and in U.K. Patent Nos. and published applications 1,466,728; 1,531,927; 1,533,039; 2,066,755A, and 2,017,704A. Halogen, alkoxy and aryloxy groups are most suitable.

Examples of specific coupling-off groups are —Cl, —F, —Br, —SCN, —OCH 3 , —OC 6 H 5 , —OCH 2 C(═O)NHCH 2 CH 2 OH, —OCH 2 C(O)NHCH 2 CH 2 OCH 3 , —OCH 2 C(O)NHCH 2 CH 2 OC(═O)OCH 3 , —P(═O)(OC 2 H 5 ) 2 , —SCH 2 CH 2 COOH,

Typically, the coupling-off group is a chlorine atom, hydrogen atom or p-methoxyphenoxy group.

It is essential that the substituent groups be selected so as to adequately ballast the coupler and the resulting dye in the organic solvent in which the coupler is dispersed. The ballasting may be accomplished by providing hydrophobic substituent groups in one or more of the substituent groups. Generally a ballast group is an organic radical of such size and configuration as to confer on the coupler molecule sufficient bulk and aqueous insolubility as to render the coupler substantially nondiffusible from the layer in which it is coated in a photographic element. Thus the combination of substituent are suitably chosen to meet these criteria. To be effective, the ballast will usually contain at least 8 carbon atoms and typically contains 10 to 30 carbon atoms. Suitable ballasting may also be accomplished by providing a plurality of groups which in combination meet these criteria. In the preferred embodiments of the invention R 1 in formula (I) is a small alkyl group or hydrogen. Therefore, in these embodiments the ballast would be primarily located as part of the other groups. Furthermore, even if the coupling-off group Z contains a ballast it is often necessary to ballast the other substituents as well, since Z is eliminated from the molecule upon coupling; thus, the ballast is most advantageously provided as part of groups other than Z.

The following examples further illustrate preferred coupler of the invention. It is not to be construed that the present invention is limited to these examples.

Preferred couplers are IC-3, IC-7, IC-35, and IC-36 because of their suitably narrow left bandwidths.

Couplers that form magenta dyes upon reaction with oxidized color developing agent are described in such representative patents and publications as: U.S. Pat. Nos. 2,311,082; 2,343,703; 2,369,489; 2,600,788; 2,908,573; 3,062,653; 3,152,896; 3,519,429; 3,758,309; and “Farbkuppler-eine Literature Ubersicht,” published in Agfa Mitteilungen, Band III, pp. 126-156 (1961). Preferably such couplers are pyrazolones, pyrazolotriazoles, or pyrazolobenzimidazoles that form magenta dyes upon reaction with oxidized color developing agents. Especially preferred couplers are 1H-pyrazolo [5,1-c]-1,2,4-triazole and 1H-pyrazolo [1,5-b]-1,2,4-triazole. Examples of 1H-pyrazolo [5,1-c]-1,2,4-triazole couplers are described in U.K. Patent Nos. 1,247,493; 1,252,418; 1,398,979; U.S. Pat. Nos. 4,443,536; 4,514,490; 4,540,654; 4,590,153; 4,665,015; 4,822,730; 4,945,034; 5,017,465; and 5,023,170. Examples of 1H-pyrazolo [1,5-b]-1,2,4-triazoles can be found in European Patent applications 176,804; 177,765; U.S Pat. Nos. 4,659,652; 5,066,575; and 5,250,400.

Typical pyrazoloazole and pyrazolone couplers are represented by the following formulas:

wherein R a and R b independently represent H or a substituent; R c is a substituent (preferably an aryl group); R d is a substituent (preferably an anilino, carbonamido, ureido, carbamoyl, alkoxy, aryloxycarbonyl, alkoxycarbonyl, or N-heterocyclic group); X is hydrogen or a coupling-off group; and Z a , Z b , and Z c are independently a substituted methine group, ═N—, ═C—, or —NH—, provided that one of either the Z a —Z b bond or the Z b —Z c bond is a double bond and the other is a single bond, and when the Z b —Z c bond is a carbon-carbon double bond, it may form part of an aromatic ring, and at least one of Z a , Z b , and Z c represents a methine group connected to the group R b .

Specific examples of such couplers are:

Couplers that form yellow dyes upon reaction with oxidized color developing agent are described in such representative patents and publications as: U.S. Pat. Nos. 2,298,443; 2,407,210; 2,875,057; 3,048,194; 3,265,506; 3,447,928; 3,960,570; 4,022,620; 4,443,536; 4,910,126; and 5,340,703 and “Farbkuppler-eine Literature Ubersicht,” published in Agfa Mitteilungen, Band III, pp. 112-126 (1961). Such couplers are typically open chain ketomethylene compounds. Also preferred are yellow couplers such as described in, for example, European Patent Application Nos. 482,552; 510,535; 524,540; 543,367; and U.S. Pat. No. 5,238,803. For improved color reproduction, couplers which give yellow dyes that cut off sharply on the long wavelength side are particularly preferred (for example, see U.S. Pat. No. 5,360,713).

Typical preferred yellow couplers are represented by the following formulas:

wherein R 1 , R 2 , Q 1 and Q 2 each represents a substituent; X is hydrogen or a coupling-off group; Y represents an aryl group or a heterocyclic group; Q 3 represents an organic residue required to form a nitrogen-containing heterocyclic group together with the >N—; and Q 4 represents nonmetallic atoms necessary to from a 3- to 5-membered hydrocarbon ring or a 3- to 5-membered heterocyclic ring which contains at least one hetero atom selected from N, O, S, and P in the ring. Particularly preferred is when Q 1 and Q 2 each represent an alkyl group, an aryl group, or a heterocyclic group, and R 2 represents an aryl or tertiary alkyl group.

Unless otherwise specifically stated, substituent groups which may be substituted on molecules herein include any groups, whether substituted or unsubstituted, which do not destroy properties necessary for photographic utility. When the term “group” is applied to the identification of a substituent containing a substitutable hydrogen, it is intended to encompass not only the substituent's unsubstituted form, but also its form further substituted with any group or groups as herein mentioned. Suitably, the group may be halogen or may be bonded to the remainder of the molecule by an atom of carbon, silicon, oxygen, nitrogen, phosphorous, or sulfur. The substituent may be, for example, halogen, such as chlorine, bromine or fluorine; nitro; hydroxyl; cyano; carboxyl; or groups which may be further substituted, such as alkyl, including straight or branched chain alkyl, such as methyl, trifluoromethyl, ethyl, t-butyl, 3-(2,4-di-t-pentylphenoxy) propyl, and tetradecyl; alkenyl, such as ethylene, 2-butene; alkoxy, such as methoxy, ethoxy, propoxy, butoxy, 2-methoxyethoxy, sec-butoxy, hexyloxy, 2-ethylhexyloxy, tetradecyloxy, 2-(2,4-di-t-pentylphenoxy)ethoxy, and 2-dodecyloxyethoxy; aryl such as phenyl, 4-t-butylphenyl, 2,4,6-trimethylphenyl, naphthyl; aryloxy, such as phenoxy, 2-riethylphenoxy, alpha- or beta- naphthyloxy, and 4-tolyloxy; carbonamido, such as acetamido, benzamido, butyramido, tetradecanamido, alpha-(2,4-di-t-pentyl-phenoxy)acetamido, alpha-(2,4-di-t-pentylphenoxy)butyramido, alpha-(3-pentadecylphenoxy)-hexanamido, alpha-(4-hydroxy-3-t-butylphenoxy)-tetradecanamido, 2-oxo-pyrrolidin-1-yl, 2-oxo-5-tetradecylpyrrolin-1-yl, N-methyltetradecanamido, N-succinimido, N-phthalimido, 2,5-dioxo-1-oxazolidinyl, 3-dodecyl-2,5-dioxo-1-imidazolyl, and N-acetyl-N-dodecylamino, ethoxycarbonylamino, phenoxycarbonylamino, benzyloxycarbonylamino, hexadecyloxycarbonylamino, 2,4-di-t-butylphenoxycarbonylamino, phenylcarbonylamino, 2,5-(di-t-pentylphenyl)carbonylamino, p-dodecyl-phenylcarbonylamino, p-toluylcarbonylamino, N-methylureido, N,N-dimethylureido, N-methyl-N-dodecylureido, N-hexadecylureido, N,N-dioctadecylureido, N,N-dioctyl-N′-ethylureido, N-phenylureido, N,N-diphenylureido, N-phenyl-N-p-toluylureido, N-(m-hexadecylphenyl)ureido, N,N-(2,5-di-t-pentylphenyl)-N′-ethylureido, and t-butylcarbonamido; sulfonamido, such as methylsulfonamido, benzenesulfonamido, p-toluylsulfonamido, p-dodecylbenzenesulfonamido, N-methyltetradecylsulfonamido, N,N-dipropyl-sulfamoylamino, and hexadecylsulfonamido; sulfamoyl, such as N-methylsulfamoyl, N-ethylsulfamoyl, N,N-dipropylsulfamoyl, N-hexadecylsulfamoyl, N,N-dimethylsulfamoyl; N-[3-(dodecyloxy)propyl]sulfamoyl, N-[4-(2,4-di-t-pentylphenoxy)butyl]sulfamoyl, N-methyl-N-tetradecylsulfamoyl, and N-dodecylsulfamoyl; carbamoyl, such as N-methylcarbamoyl, N,N-dibutylcarbamoyl, N-octadecylcarbamoyl, N-[4-(2,4-di-t-pentylphenoxy)butyl]carbamoyl, N-methyl-N-tetradecylcarbamoyl, and N,N-dioctylcarbamoyl; acyl, such as acetyl, (2,4-di-t-amylphenoxy)acetyl, phenoxycarbonyl, p-dodecyloxyphenoxycarbonyl, methoxycarbonyl, butoxycarbonyl, tetradecyloxycarbonyl, ethoxycarbonyl, benzyloxycarbonyl, 3-pentadecyloxycarbonyl, and dodecyloxycarbonyl; sulfonyl, such as methoxysulfonyl, octyloxysulfonyl, tetradecyloxysulfonyl, 2-ethylhexyloxysulfonyl, phenoxysulfonyl, 2,4-di-t-pentylphenoxysulfonyl, methylsulfonyl, octylsulfonyl, 2-ethylhexylsulfonyl, dodecylsulfonyl, hexadecylsulfonyl, phenylsulfonyl, 4-nonylphenylsulfonyl, and p-toluylsulfonyl; sulfonyloxy, such as dodecylsulfonyloxy, and hexadecylsulfonyloxy; sulfinyl, such as methylsulfinyl, octylsulfinyl, 2-ethylhexylsulfinyl, dodecylsulfinyl, hexadecylsulfinyl, phenylsulfinyl, 4-nonylphenylsulfinyl, and p-toluylsulfinyl; thio, such as ethylthio, octylthio, benzylthio, tetradecylthio, 2-(2,4-di-t-pentylphenoxy)ethylthio, phenylthio, 2-butoxy-5-t-octylphenylthio, and p-tolylthio; acyloxy, such as acetyloxy, benzoyloxy, octadecanoyloxy, p-dodecylamidobenzoyloxy, N-phenylcarbamoyloxy, N-ethylcarbamoyloxy, and cyclohexylcarbonyloxy; amino, such as phenylanilino, 2-chloroanilino, diethylamino, dodecylamino; imino, such as 1 (N-phenylimido)ethyl, N-succinimido or 3-benzylhydantoinyl; phosphate, such as dimethylphosphate and ethylbutylphosphate; phosphite, such as dicthyl and dihexylphosphite; a heterocyclic group, a heterocyclic oxy group or a heterocyclic thio group, each of which may be substituted and which contain a 3 to 7 membered heterocyclic ring composed of carbon atoms and at least one hetero atom selected from the group consisting of oxygen, nitrogen and sulfur, such as 2-furyl, 2-thienyl, 2-benzimidazolyloxy or 2-benzothiazolyl; quaternary ammonium, such as triethylammonium; and silyloxy, such as trimethylsilyloxy.

If desired, the substituents may themselves be further substituted one or more times with the described substituent groups. The particular substituents used may be selected by those skilled in the art to attain the desired photographic properties for a specific application and can include, for example, hydrophobic groups, solubilizing groups, blocking groups, releasing or releasable groups, etc. Generally, the above groups and substituents thereof may include those having up to 48 carbon atoms, typically 1 to 36 carbon atoms and usually less than 24 carbon atoms, but greater numbers are possible depending on the particular substituents selected.

Representative substituents on ballast groups include alkyl, aryl, alkoxy, aryloxy, alkylthio, hydroxy, halogen, alkoxycarbonyl, aryloxcarbonyl, carboxy, acyl, acyloxy, amino, anilino, carbonamido, carbamoyl, alkylsulfonyl, arylsulfonyl, sulfonamido, and sulfamoyl groups wherein the substituents typically contain 1 to 42 carbon atoms. Such substituents can also be further substituted.

Stabilizers and scavengers that can be used in these photographic elements, but are not limited to, the following.

Examples of solvents which may be used in the invention include the following:

Tritolyl phosphate               S-1
Dibutyl phthalate                S-2
Diundecyl phthalate              S-3
N,N-Diethyldodecanamide          S-4
N,N-Dibutyldodecanamide          S-5
Tris(2-ethylhexyl)phosphate      S-6
Acetyl tributyl citrate          S-7
2,4-Di-tert-pentylphenol         S-8
2-(2-Butoxyethoxy)ethyl acetate  S-9
1,4-Cyclohexyldimethylene bis(2-ethylhexanoate) S-10

The dispersions used in photographic elements may also include ultraviolet (UV) stabilizers and so called liquid UV stabilizers such as described in U.S. Pat. Nos. 4,992,358; 4,975,360; and 4,587,346. Examples of UV stabilizers are shown below.

The aqueous phase may include surfactants. Surfactant may be cationic, anionic, zwitterionic or non-ionic. Useful surfactants include, but are not limited to, the following:

Further, it is contemplated to stabilize photographic dispersions prone to particle growth through the use of hydrophobic, photographically inert compounds such as disclosed by Zengerle et al in U.S. Pat. 5,468,604.

In a preferred embodiment the invention employs recording elements which are constructed to contain at least three silver halide emulsion layer units. A suitable full color, multilayer format for a recording element used in the invention is represented by Structure I.

STRUCTURE I
Red-sensitized
cyan dye image-forming silver halide emulsion unit
Interlayer
Green-sensitized
magenta dye image-forming silver halide emulsion unit
Interlayer
Blue-sensitized
yellow dye image-forming silver halide emulsion unit
///// Support /////

wherein the red-sensitized, cyan dye image-forming silver halide emulsion unit is situated furthest from the support; next in order is the green-sensitized, magenta dye image-forming unit, Followed by the lowermost blue-sensitized, yellow dye image-forming unit. The image-forming units are separated from each other by hydrophilic colloid interlayers containing an oxidized developing agent scavenger to prevent color contamination. Silver halide emulsions satisfying the grain and gelatino-peptizer requirements described above can be present in any one or combination of the emulsion layer units. Additional useful multicolor, multilayer formats for an element of the invention include structures as described in U.S. Pat. No. 5,783,373. Each of such structures in accordance with the invention preferably would contain at least three silver halide emulsions comprised of high chloride grains having al least 50 percent of their surface area bounded by {100} crystal faces and containing dopants from classes (i) and (ii), as described above. Preferably each of the emulsion layer units contains emulsion satisfying these criteria.

Conventional features that can be incorporated into multilayer (and particularly multicolor) recording elements contemplated for use in the method of the invention are illustrated by Research Disclosure , Item 38957, cited above:

XI. Layers and layer arrangements

XII. Features applicable only to color negative

XIII. Features applicable only to color positive

B. Color reversal

C. Color positives derived from color negatives

XIV. Scan facilitating features.

The recording elements comprising the radiation sensitive high chloride emulsion layers according to this invention can be conventionally optically printed, or in accordance with a particular embodiment of the invention can be image-wise exposed in a pixel-by-pixel mode using suitable high energy radiation sources typically employed in electronic printing methods. Suitable actinic forms of energy encompass the ultraviolet, visible and infrared regions of the electromagnetic spectrum as well as electron-beam radiation and is conveniently supplied by beams from one or more light emitting diodes or lasers, including gaseous or solid state lasers. Exposures can be monochromatic, orthochromatic or panchromatic. For example, when the recording element is a multilayer multicolor element, exposure can be provided by laser or light emitting diode beams of appropriate spectral radiation, for example, infrared, red, green or blue wavelengths, to which such element is sensitive. Multicolor elements can be employed which produce cyan, magenta and yellow dyes as a function of exposure in separate portions of the electromagnetic spectrum, including at least two portions of the infrared region, as disclosed in the previously mentioned U.S. Pat. No. 4,619,892. Suitable exposures include those up to 2000 nm, preferably up to 1500 nm. Suitable light emitting diodes and commercially available laser sources are known and commercially available. Imagewise exposures at ambient, elevated or reduced temperatures and/or pressures can be employed within the useful response range of the recording clement determined by conventional sensitometric techniques, as illustrated by T. H. James, The Theory of the Photographic Process , 4th Ed., Macmillan, 1977, Chapters 4, 6, 17, 18 and 23.

It has been observed that anionic [MX x Y y L z ] hexacoordination complexes, where M is a group 8 or 9 metal (preferably iron, ruthenium or iridium), X is halide or pseidohalide (preferably Cl, Br or CN) x is 3 to 5, Y is H 2 O, y is 0 or 1, L is a C—C, H—C or C—N—H organic ligand, and Z is 1 or 2, are surprisingly effective in reducing high intensity reciprocity failure (HIRF), low intensity reciprocity failure (LIRF) and thermal sensitivity variance and in in improving latent image keeping (LIK). As herein employed HIRF is a measure of the variance of photographic properties for equal exposures, but with exposure times ranging from 10 −1 to 10 −6 second. LIRF is a measure of the varinance of photographic properties for equal exposures, but with exposure times ranging from 10 −1 to 100 seconds. Although these advantages can be generally compatible with face centered cubic lattice grain structures, the most striking improvements have been observed in high (>50 mole %, preferably >90 mole %) chloride emulsions. Preferred C—C, H—C or C—N—H organic ligands are aromatic heterocycles of the type described in U.S. Pat. No. 5,462,849. The most effective C—C, H—C or C—N—H organic ligands are azoles and azines, either unsustituted or containing alkyl, alkoxy or halide substituents, where the alkyl moieties contain from 1 to 8 carbon atoms. Particularly preferred azoles and azines include thiazoles, thiazolines and pyrazines.

The quantity or level of high energy actinic radiation provided to the recording medium by the exposure source is generally at least 10 −4 ergs/cm , typically in the range of about 10 −4 ergs/cm 2 to 10 −3 ergs/cm 2 and often from 10 −3 ergs/cm 2 to 10 2 ergs/cm 2 . Exposure of the recording element in a pixel-by-pixel mode as known in the prior art persists for only a very short duration or time. Typical maximum exposure times are up to 100μ seconds, often up to 10μ seconds, and frequently up to only 0.5μ seconds. Single or multiple exposures of each pixel are contemplated. The pixel density is subject to wide variation, as is obvious to those skilled in the art. The higher the pixel density, the sharper the images can be, but at the expense of equipment complexity. In general, pixel densities used in conventional electronic printing methods of the type described herein do not exceed 10 7 pixels/cm and are typically in the range of about 10 4 to 10 6 pixels/cm 2 . An assessment of the technology of high-quality, continuous-tone, color electronic printing using silver halide photographic paper which discusses various features and components of the system, including exposure source, exposure time, exposure level and pixel density and other recording element characteristics is provided in Firth et al., A Continuous - Tone Laser Color Printer , Journal of Imaging Technology, Vol. 14, No. 3, June 1988, which is hereby incorporated herein by reference. As previously indicated herein, a description of some of the details of conventional electronic printing methods comprising scanning a recording element with high energy beams such as light emitting diodes or laser beams, are set forth in Hioki U.S. Pat. No. 5,126,235, European Patent Applications 479 167 A1 and 502 508 A1.

Once imagewise exposed, the recording elements can be processed in any convenient conventional manner to obtain a viewable image. Such processing is illustrated by Research Disclosure , Item 38957, cited above:

XVIII. Chemical development systems

XIX. Development

XX. Desilvering, washing, rinsing and stabilizing

In addition, a useful developer for the inventive material is a homogeneous, single part developing agent. The homogeneous, single-part color developing concentrate is prepared using a critical sequence of steps:

In the first step, an aqueous solution of a suitable color developing agent is prepared. This color developing agent is generally in the form of a sulfate salt. Other components of the solution can include an antioxidant for the color developing agent, a suitable number of alkali metal ions (in an at least stoichiometric proportion to the sulfate ions) provided by an alkali metal base, and a photographically inactive water-miscible or water-soluble hydroxy-containing organic solvent. This solvent is present in the final concentrate at a concentration such that the weight ratio of water to the organic solvent is from about 15:85 to about 50:50.

In this environment, especially at high alkalinity, alkali metal ions and sulfate ions form a su fate salt that is precipitated in the presence of the hydroxy-containing organic solvent. The precipitated sulfate salt can then be readily removed using ants suitable liquid/solid phase separation technique (including filtration, centrifugation or decantation). If the antioxidant is a liquid organic compound, two phases may be formed and the precipitate may be removed by discarding the aqueous phase.

The color developing concentrates of this invention include one or more color developing agents that are well known in the art that, in oxidized form, will react with dye forming color couplers in the processed materials. Such color developing agents include, but are not limited to, aminophenols, p-phenylenediamines (especially N,N-dialkyl-p-phenylenediamines) and others which are well known in the art, such as EP 0 434 097 A1 (published Jun. 26, 1991) and EP 0 530 921 A1 (published Mar. 10, 1993). It may be useful for the color developing agents to have one or more water-solubilizing groups as are known in the art. Further details of such materials are provided in Research Disclosure , publication 38957, pages 592-639 (September 1996). Research Disclosure is a publication of Kenneth Mason Publications Ltd., Dudley House, 12 North Street, Emsworth, Hampshire PO10 7DQ England (also available from Emsworth Design Inc., 121 West 19th Street, New York, N.Y. 10011). This reference will be referred 1:o hereinafter as “ Research Disclosure”.

Preferred color developing agents include, but are not limited to, N,N-diethylp-phenylenediamine sulfate (KODAK Color Developing Agent CD-2), 4-amino-3-methyl-N-(2-methane sulfonamidoethyl)aniline sulfate, 4-(N-ethyl-N-p-hydroxyethylamino)-2-methylaniline sulfate (KODAK Color Developing Agent CD-4), p-hydroxyethylethylaminoaniline sulfate, 4-(N-ethyl-N-2-methanesulfonylamiinoethyl)-2-methylphenylencdiamine sesquisulfate (KODAK Color Developing Agent CD-3), 4-(N-ethyl-N-2-methanesulfonylaminoethyl)-2-methylphenylenediamine sesquisulfate, and others readily apparent to one skilled in the art.

In order to protect the color developing agents from oxidation, one or more antioxidants are generally included in the color developing compositions. Either inorganic or organic antioxidants can be used. Many classes of useful antioxidants are known, including but not limited to, sulfites (such as sodium sulfite, potassium sulfite, ,;odium bisulfite and potassium metabisulfite), hydroxylamine (and derivatives thereof), hydrazines, hydrazides, amino acids, ascorbic acid (and derivatives thereof), hydroxamic acids, aminoketones, mono- and polysaccharides, mono- and polyamines, quaternary ammonium salts, nitroxy radicals, alcohols, and oxiines. Also useful as antioxidants are 1,4-cyclohexadiones. Mixtures of compounds from the same or different classes of antioxidants can also be used if desired.

Especially useful antioxidants are hydroxylamine derivatives as described for example, in U.S. Pat. Nos. 4,892,804; 4,876,174; 5,354,646; and 5,660,974, all noted above, and U.S. Pat. No. 5,646,327 (Burns et al). Many of these antioxidants are mono- and dialkylhydroxylamines having one or more substituents on one or both alkyl groups. Particularly useful alkyl substituents include sulfo, carboxy, amino, sulfonamido, carbonamido, hydroxy, and other solubilizing substituents.

More preferably, the noted hydroxylamine derivatives can be mono- or dialkylhydroxylamines having one or more hydroxy substituents on the one or more alkyl groups. Representative compounds of this type are described for example in U.S. Pat. No. 5,709,982 (Marrese et al), incorporated herein by reference, as having the structure I:

wherein R is hydrogen, a substituted or unsubstituted alkyl group of 1 to 10 carbon atoms, a substitute or unsubstituted hydroxyalkyl group of 1 to 10 carbon atoms, a substituted or unslibstituted cycloalkyl group of 5 to 10 carbon atoms, or a substituted or unsubstituted aryl group having 6 to 10 carbon atoms in the aromatic nucleus.

X 1 is —CR 2 (OH)CHR 1 — and X 2 is —CHR 1 CR 2 (OH)— wherein R 1 and R 2 are independently hydrogen, hydroxy, a substituted or unsubstituted alkyl group or 1 or 2 carbon atoms, a substituted or unsubstituted hydroxyalkyl group of 1 or 2 carbon atoms, or R 1 and R 2 together represent the carbon atoms necessary to complete a substituted or unsubstituted 5- to 8-membered saturated or unsaturated carbocyclic ring structure.

Y is a substituted or unsubstituted alkylene group having at least 4 carbon atoms, and has an even number of carbon atoms, or Y is a substituted or unsubstituted divalent aliphatic group having an even total number of carbon and oxygen atoms in the chain, provided that the aliphatic group has a least 4 atoms in the chain.

Also in Structure I, m, n and p are independently 0 or 1. Preferably, each of m and n is 1, and p is 0.

Specific di-substituted hydroxylamine antioxidants include, but are not limited to: N,N-bis(2,3-dihydroxypropyl)hydroxylamine, N,N-bis(2-methyl-2,3 -dihydroxypropyl)hydroxylamine and N,N-bis(1-hydroxymethyl-2-hydroxy-3-phenylpropyl)hydroxylamine. The first compound is preferred.

The following examples illustrate the practice of this invention. They are not intended to be exhaustive of all possible variations of the invention. Parts and percentages are by weight unless otherwise indicated.

EXAMPLES

Example 1

In this example an imaging grade cellulose paper base was coated with two coating solutions. One solution contained starch (coating 1), and the other contained a mixture of starch and hollow spherical polymer beads (coating 2). The invention was compared to a typical imaging grade cellulose paper base that is uncoated. This example will show that the addition of the hollow spherical beads to the surface of the paper significant improved the smoothness of paper base compared to the control paper. The imaging grade cellulose paper base used in the example:

A paper stock was produced for the imaged support using a standard fourdrinier paper machine and a blend of mostly bleached hardwood Kraft fibers. The fiber ratio consisted primarily of bleached poplar (38%) and maple/beech (37%) with lesser amounts of birch (18%) and softwood (7%). Fiber length was reduced from 0.73 mm length weighted average as measured by a Kajaani FS-200 to the levels listed in Table 1 using high levels of conical refining and low levels of disc refining. Fiber Lengths from slurry generated were measured using an FS-200 Fiber Length Analyzer (Kajaani Automation Inc.). Energy applied to the fibers using two conical refiners were used in series to provide the total conical refiners SNRP value. Neutral sizing chemical addenda, utilized on a dry weight basis, included alkyl ketene dimer at 0.20% addition, cationic starch (1.0%), polyaminoamide epichlorhydrin (0.50%), polyacrylamide resin (0.18%), diaminostilbene optical brightener (0.20%), and sodium bicarbonate. Surface sizing using hydroxyethylated starch and sodium chloride was also employed but is not critical to the invention. In the 3 rd Dryer section, ratio drying was utilized to provide a moisture bias from the face side to the wire side of the sheet. Sheet temperatures were raised to between 76° C. and 93° C. just prior to and during calendering. The paper was then calendered to an apparent density of 1.17. The paper base was produced at a basis weight of 178 g/mm 2 and thickness of 0.1524 mm, moisture levels after the calender were 7.0% to 9.0% by weight.

The above cellulose paper base was coated with aqueous coating 1 and 2 listed in Table 1 below. The hollow sphere pigments used in the invention (coating 1 and 2) were Rohm and Haas Ropaque HP-1055. The coating was applied utilizing a 2-mil knife. The Rohm and Haas Ropaque HP-1055 hollow sphere pigments had a mean core diameter of 0.82 micrometers and a mean shell thickness of 0.09 micrometers. Coating 1 and 2 were then dried at 100° C. for 2 minutes. The control sample was an uncoated sample of the above cellulose paper base.

TABLE 1
	Starch (% by	Hollow Sphere Pigments
Coating	Weight)	(% by Weight)
1	100	0
2	50	50

After coating 1 and 2 were applied to the base paper, the invention and control were calendered using a steel to steel calendar at the temperature of 80° C. at a pressure of 1900 MPa/cm. The invention and the control were calendered at 30 meters/minute.

The low frequency surface roughness of the base papers or orange peel was measured by a Federal Profiler. The Federal Profiler instrument consists of a motorized drive nip which is tangent to the top surface of the base plate. The sample to be measured is placed on the base plate and fed through the nip. A micrometer assembly is suspended above the base plate. The end of the mic spindle provides a reference surface from which the sample thickness can be measured. This flat surface is 0.95 cm diameter and, thus, bridges all fine roughness detail on the upper surface of the sample. Directly below the spindle, and nominally flush with the base plate surface, is a moving hemispherical stylus of the gauge head. This stylus responds to local surface variation as the sample is transported through the gauge. The stylus radius relates to the spatial content that can be sensed. The output of the gauge amplifier is digitized to 12 bits. The sample rate is 500 measurements per 2.5 cm. The roughness averages of 10 data points for each base variationn is listed in Table 1. The surface roughness for spatial frequency of between 200 cycles/mm and 1300 cycles/mm can be measured by TAYLOR-HOBSON Surtronic 3 with 2 micrometers diameter ball tip. The output Ra or “roughness average” from the TAYLOR-HOBSON is in units of micrometers and his a built-in, cutoff filter to reject all sizes above 0.25 mm. The roughness averages for 10 data points for each variation is listed in Table 2 below.

	TABLE 2
		Mean Low	Mean High
		Frequency	Frequency
		Roughness	Roughness
	Coating	(micrometers)	(micrometers)
	1	0.45	0.7
	2	0.34	0.55
	Control	1.22	1.01

The surface roughness results in Table 2 show that by coating the surface of the paper, the surface roughness of imaging grade paper can be significantly reduced. The hollow sphere pigments were able to substantially reduce the low frequency and high frequency roughness compared to the control (uncoated paper). The starch coating also reduced roughness to a lesser extent than the hollow sphere pigments but is still significant. The low frequency and high frequency surface roughness average reduction in the base paper resulted in perceptually preferred improvement in the gloss of the photographic paper when the hollow sphere pigment coated paper was coated with silver halide imaging layers. The surface roughness improvement is significant in that the gloss of an image has been improved beyond what is currently capable with traditional photographic paper bases. An imaging paper base with a low frequency surface roughness between 0.20 and 0.60 micrometers and a high frequency surface roughness between 0.30 and 0.95 has significant commercial value for consumers that prefer glossy images. Finally, because the smoothness of the base paper has been improved compared to prior art imaging quality base papers, the smooth base paper of the invention can also be utilized to improve the gloss of ink jet images, thermal dye transfer images and electrophotographic images.

The invention has been described in detail with particular reference to certain preferred embodiments thereof, but it will be understood that variations and modifications can be effected within the spirit and scope of the invention.

Claims

1. An imaging element comprising an imaging layer and a cellulose paper base wherein said base has an upper surface roughness of between 0.30 and 0.95 μm at a spatial frequency of between 200 cycles/mm and 1300 cycles/mm, wherein said paper base is provided on at least one surface with a biaxially oriented polyolefin sheet and said paper base comprises spherical polymer beads.

2. The imaging element of claim 1 wherein said at least one biaxially oriented polymer sheet comprises a top sheet below said imaging layer and above said paper and a bottom sheet below said paper.

3. The element of claim 1 wherein said beads comprise hollow spherical polymer beads.

4. The element of claim 3 wherein said beads comprise styrene acrylic copolymer.

5. The imaging member of claim 2 wherein said imaging layer comprises at least one layer comprising photosensitive silver halide and dye forming coupler.

6. The element of claim 1 wherein said paper base has an apparent density of greater than 1.05 g/cc.

7. The element of claim 1 wherein the fiber length of the cellulose fibers in said paper base has an average length of between 0.35 mm and 0.55 mm.

8. The element of claim 1 wherein said paper base has a stiffness of between 80 and 250 millinewtons.

9. The element of claim 2 wherein said paper base has a thickness of between 100 and 200 μm.

10. The element of claim 1 wherein said paper base has an opacity of at least 88.

11. The element of claim 1 wherein said paper base has a machine direction to cross direction modulus ratio of between 1.2 and 1.95.

12. The element of claim 1 wherein said paper base has a TSO angle of between −5 and 5 degrees.

13. The element of claim 1 wherein said paper base further comprises polymer fibers.

14. The element of claim 1 wherein said paper base has a clay coating on the upper surface.

15. The element of claim 1 wherein said paper base has a white pigment coating on the upper surface.

16. The element of claim 1 wherein said paper base has a brightness of at least 85.

17. The element of claim 1 wherein said imaging layer comprises at least one ink jet receiving layer or dye transfer receiving layer.

18. An imaging element comprising an imaging layer and a cellulose paper base wherein said base has an upper surface roughness of between 0.30 and 0.95 μm at a spatial frequency of between 200 cycles/mm and 1300 cycles/mm wherein the upper surface of said paper base comprises a surface that has been calendered and then coated with hollow spherical polymer beads and then calendered again to create a smooth surface by filling the rough surface of said paper.

19. The element of claim 18 wherein said beads comprise hollow spherical polymer beads.

20. The element of claim 18 wherein said beads comprise styrene acrylic copolymer.

21. The element of claim 18 wherein the fiber length of the cellulose fibers in said paper base has an average length of between 0.35 mm and 0.55 mm.

22. The element of claim 19 wherein said paper base has a stiffness of between 80 and 250 millinewtons.

23. The element of claim 18 wherein said paper base has a machine direction to cross direction modulus ratio of between 1.2 and 1.95.

24. The element of claim 18 wherein said paper base has a TSO angle of between −5 and 5 degrees.

25. The element of claim 18 wherein said paper base has a white pigment coating on the upper surface.

26. The element of claim 18 wherein said paper base is provided with at least one waterproof layer.

27. The element of claim 18 wherein said paper base is provided with at least one waterproof layer comprising polyethylene polymer.

28. The element of claim 18 wherein said paper base is provided with at least one waterproof layer comprising melt extruded polyester.

29. The element of claim 18 wherein said paper base is provided with at least one waterproof layer comprising at least two coextruded polymer layers.

30. The element of claim 18 wherein said imaging layer comprises at least one silver halide containing photosensitive layer.

31. The element of claim 18 wherein said imaging layer comprises at least one ink jet receiving layer or dye transfer receiving layer.

32. An imaging element comprising an imaging layer and a cellulose paper base wherein said base has an upper surface roughness of between 0.30 and 0.95 μm at a spatial frequency of between 200 cycles/mm and 1300 cycles/mm wherein the upper surface of said paper base comprises spherical polymer beads that have been calendered to create a smooth surface by filling the rough surface of said paper wherein said paper base is provided with at least one waterproof layer comprising melt extruded polyester.