Radiation imagery chemistry: process – composition – or product th – Radiation sensitive product – Identified backing or protective layer containing
Reexamination Certificate
2000-04-07
2002-05-21
Schilling, Richard L. (Department: 1752)
Radiation imagery chemistry: process, composition, or product th
Radiation sensitive product
Identified backing or protective layer containing
C430S536000, C430S538000, C162S090000, C162S181100
Reexamination Certificate
active
06391532
ABSTRACT:
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 provides 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 photographic paper. Sheet properties such as smoothness may be improved through the addition of inorganic particulate filler materials to paper making furnishes.
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 such as TiO
2
above and below the microvoided layer. 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 addition of inorganic particulate fillers such as clay, TiO
2
, calcium carbonate and talc, improves sheet properties because the particles fill in the void spaces within the fiber mat resulting in a denser, brighter, smoother, and more opaque sheet. In some instances, paper can also be made cheaper because the filler used is less expensive than cellulose fiber.
The substitution of fiber with filler in the sheet is, however, limited by the resultant reduction in strength, density, and sizing properties. As the proportion of filler is increased, fiber-to-fiber bonding is disrupted resulting in a reduction in sheet strength and stiffness properties. Due to the filling of sheet voids with increasing filler addition, sheet density is increased. The increased hydrophilicity of inorganic fillers over chemically-treated (sized) paper-making fibers also results in a reduction in sizing properties of the paper. All of the above undesirable changes limit the use of filler materials in various applications, particularly in photographic paper, where even a small change in any of the above properties can seriously affect effectiveness of the resulting image as a photograph. In addition to the above, the choice of filler is also limited because of it's impact on sheet properties or because of its undesired presence in processing steps. For example, the filler material should not be photographically active or degrade the performance of the photographic element in which it is utilized.
PROBLEM TO BE SOLVED BY THE INVENTION
The use of calcium carbonate as a filler in photographic base, though desirable in many ways, is problematic because of the tendency for calcium carbonate to leach out into developer solutions and subsequently precipitate in the form of calcium salts. Improved calcium carbonate retention is desirable to achieve a smoother and higher opacity photographic paper.
SUMMARY OF THE INVENTION
It is an object of the invention to provide an imaging material that has improved surface properties.
Another object of this invention is to provide an imaging material that is more opaque.
These and other objects of the invention are accomplished by a paper comprising between 2 and 8% calcium carbonate in a paper having a surface roughness average of between 0.10 and 0.44 &mgr;m, a fiber length of the individual fibers of said paper of between 0.4 and 0.6 mm, and a density of between 1.05 and 1.20 grams/cc. By proper mechanical development of the fibers and densification of the sheet, a fiber matrix is formed which makes it more difficult for the calcium carbonate to exit the fiber mass. This improved retention of calcium carbonate makes leaching of calcium carbonate in photofinishing less likely. It also leads to a reduction in dust levels during slitting. Better retention of the calcium carbonate makes its usage a feasible alternative to more conventional fillers such as titanium dioxide.
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, are more opaque, and are low cost.
DETAILED DESCRIPTION OF THE INVENTION
The invention has numerous advantages over prior practices in the art. The invention provides an imaging element that has a smoother surface, increasing the commercial value of the imaging element. By improving the smoothness of the paper, the contrast range of the paper in improved as the blacks appear blacker and the whites appear whiter. Further, the invention provides an imaging paper that is lower cost as the basis weight of the paper and the paper chemistry are reduced compared to traditional photographic paper bases. Another advantage is the improved knife-wear 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 reduction in imaging element curl over a wide range of relative humidity when compared to standard imaging element products. By improving the opacity of the paper, the amount of undesirable show through when images are viewed by consumers is reduced. These and other advantages will be apparent from the detailed description below.
The terms as used herein, “top”, “upper”, “emulsion side”, and “face” mean the side or toward the side of a photographic member bearing the imaging layers. The terms “bottom”, “lower side”, and “back” mean the side or toward the side of the photographic member opposite from the side bearing the photosensitive imaging layers or developed image. The term “face side” means the side opposite the side of cellulose paper formed on a Fourdriner wire. The term “wire side” means the side of cellulose paper formed adjacent to the Fourdriner wire.
For the cellulose paper of the invention, calcium carbonate is added to the paper fiber prior to the paper being formed on the Fourdriner wire. Calcium carbonate is preferred as it has been shown to lower cost as the basis weight of the paper and the paper chemistry are reduced compared to traditional high quality paper bases. Another advantage of the addition of the calcium carbonate is the improved knife-wear as the paper is cut in both the cross and machine directions. Examples include 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 paper comprising between 2 and 8% calcium carbonate in a paper having a surface roughness average of between 0.13 and 0.44 &mgr;m, a fiber length of the individual fibers of said paper of between 0.4 and 0.58 mm, and a density of between 1.05 and 1.20 grams/cc is preferred. This paper is preferred because it is smooth, strong and opaque providing a high quality cellulose paper for use in as a reflective imaging output media where smoothness, tear resistance and opacity are perceptually preferred by consumers. The calcium carbonate addition between 2 and 8% provides opacity to the high quality, smooth cellulose paper of the invention. Cal
Aylward Peter T.
Bourdelais Robert P.
Dagan Sandra J.
Sunderrajan Suresh
Leipold Paul A.
Schilling Richard L.
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