Stock material or miscellaneous articles – Ink jet stock for printing – Physical properties of support specified
Reexamination Certificate
2000-07-24
2004-02-17
Kelly, Cynthia H. (Department: 1774)
Stock material or miscellaneous articles
Ink jet stock for printing
Physical properties of support specified
C428S032110, C428S032200
Reexamination Certificate
active
06692798
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to imaging supports and media. In a preferred form, it relates to base materials for photographic papers.
BACKGROUND OF THE INVENTION
An imaging base such as a photographic paper typically comprises a raw paper base that is coated on both sides with a polyolefin resin waterproofing layer. An alternative waterproofing approach for imaging supports has been proposed in U.S. Pat. No. 5,866,282 (Bourdelais et al.), which utilizes a composite material made of cellulosic base paper laminated with biaxially oriented polyolefin sheets. For imaging applications using base paper that is thus resin coated or laminated, it is desired that the paper base 1) be strong or have a high tensile modulus, 2) be stiff or resist bending forces, 3) be bright and white, 4) be opaque, and 5) have a smooth surface.
A base paper with high tensile modulus and stiffness resists undesirable deformation and curl that results when certain handling and environmental conditions exist. For example, many photographic papers exhibit increased curl on being exposed to low humidity conditions. Stiffer papers that lie flat within the same plane regardless of existing handling and environmental conditions are perceived by the end-user to have greater quality due to a more substantial ‘feel’ and, therefore, higher value.
Pulps with brightness of 90% or greater are commonly used in imaging supports because consumers typically prefer a white paper appearance. Poor whiteness can degrade photographic Dmin values making certain images such as snow scenes and wedding dresses look gray. Both brightness and opacity are frequently enhanced through the use of inorganic filler materials such as titanium dioxide, calcium carbonate, etc.
As indicated in European Patent 952 483 A1 (DeVries et. al), a smooth surface is not only a customer requirement, but also has critical manufacturing implications, as it defines the amount and technique of application of polyolefin resin. Rougher papers tend to limit the speed of coating and/or cause pits to form in the resin layer. A smoother base paper improves the gloss of photographic paper, while also permitting the reduction of polyolefin used.
In order to achieve the properties listed above, imaging paper bases typically utilize bleached hardwood chemical kraft pulp as it provides high brightness, an acceptable surface, and good formation while maintaining strength and stiffness. To obtain an even smoother surface, it is common to machine calender the paper. Machine calendering, however, typically results in a decrease in stiffness. Machine calendering also typically results in a decrease in opacity necessitating the use of increased amounts of inorganic fillers, such as titanium dioxide. The increased use of inorganic fillers, however, results in a decrease in the strength (or internal bond) of the paper since such materials interfere with the inter-fiber hydrogen bonding in the cellulose fiber network. For papers of the same thickness, tensile modulus determines paper stiffness with the paper having a higher tensile modulus exhibiting the higher stiffness. Papers with higher tensile modulus are frequently derived from pulps with higher tensile modulus, so pulps with higher tensile modulus are preferred. It is also desirable to use a pulp source that imparts greater opacity since this will reduce the need for inorganic fillers and, in turn, increase the strength of the paper through improved cellulose fiber hydrogen bonding.
Generally bleached chemical pulps are expensive due to the extended harvest cycles, low yield per acre, and high handling equipment costs. In addition, as pulp mills open and close capacity, there are frequent and substantial market swings in pulp price causing unpredictability in material costs. It is, therefore, desirable to use a more renewable, more predictable, and potentially less expensive cellulose fiber source.
In U.S. Pat. No. 6,030,742 (Bourdelais et al) a premium photographic element suitable for consumer silver halide images is disclosed. The paper base utilized in U.S. Pat. No. 6,030,742 comprises wood pulp that has been refined and sized with internal chemistry to minimize edge penetration of photographic chemistry into the cut edges of the paper. Further, the paper has a mechanical modulus greater than 800,000 MPa and has a surface roughness less than 0.20 micrometers.
In U.S. Pat. No. 5,908,728 a recording paper formed mainly from a fibrous material with a cationic substance applied onto the surface thereof or impregnated therein contains non-wood fiber is disclosed. Further, disclosed in U.S. Pat. No. 5,908,728 is an image forming method comprising forming an image on the recording non-wood paper by the steps of developing an electrostatic image on a photosensitive member by a developing means with a toner, transferring the developed toner image from the photosensitive member onto the recording paper, and fixing the transferred toner image on the recording paper. The inventon in U.S. Pat. No. 5,908,728 is directed toward the use of non-wood papers for ink jet and toner printing of images taking advantage of the excellent ink absorbency and large ink absorbing capacity of non-wood paper, particularly Kenaf fiber. While the invention in U.S. Pat. No. 5,908,728 is suitable for an ink jet printing base, it fails to meet the quality and performance expectations of a silver halide base material because of problems such as edge penetration of processing solution, surface roughness, and mechanical stiffness of the base.
PROBLEM TO BE SOLVED BY THE INVENTION
The use of hardwood pulps as the source of cellulose fiber in the manufacture of imaging base forces a compromise between paper smoothness, strength, stiffness, and opacity. Pulps that will yield papers of higher stiffness, higher opacity, and higher strength at comparable smoothness and colorimetry are desirable. Hardwood pulp is also a less-renewable, expensive source of cellulose fiber making alternate more-renewable, less-expensive sources desirable.
SUMMARY OF THE INVENTION
It is an object of the invention to provide an imaging support that has superior stiffness.
It is another object to provide an imaging support that has superior strength.
It is a further object to provide an imaging support that has superior opacity.
It is another object of the invention to accomplish superior strength, opacity, and whiteness.
These and other objects of the invention are accomplished by an imaging member comprising an image layer and a paper base comprising a mixture of vegetable fibers and wood fibers wherein said vegetable fibers comprise between 5 and 25 percent by weight of said paper base.
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 stiffer, have higher internal bond, are more opaque at comparable smoothness, and are made from more-renewable cellulose fiber sources.
DETAILED DESCRIPTION OF THE INVENTION
The invention has numerous advantages over prior practices in the art. The invention provides an imaging element that, for the same caliper, is stiffer. This increases the commercial value of the imaging element or instead allows for increased calendering of the paper base improving paper smoothness without excessive loss in paper stiffness. By improving the smoothness of the paper, the contrast range of the image is improved as the blacks appear blacker and the whites appear whiter. The invention provides an imaging element that is stronger as measured by Huygen internal bond. This also provides increased commercial value of the imaging element since it reduces undesirable curl. The invention also provides an imaging element that is more opaque. By improving the opacity of the paper, the amount of undesirable show through when images are viewed by consumers is reduced. While the preferred embodiment of this invention relates to silver halide images, this invention is useful as a base material for other imaging technologies such as ink je
Aylward Peter T.
Bourdelais Robert P.
Dagan Sandra J.
Sunderrajan Suresh
Whittaker Patrick J.
Kelly Cynthia H.
Leipold Paul A.
Shewareged B.
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