Imaging member with tough binder layer

Details Imaging member with tough binder layer Imaging member with tough binder layer

1999-08-10

2001-02-13

Schilling, Richard L. (Department: 1752)

Radiation imagery chemistry: process, composition, or product th

Transfer procedure between image and image layer, image...

Imagewise heating, element or image receiving layers...

C430S531000, C430S533000, C430S534000, C430S536000, C430S538000, C347S105000, C503S227000

Reexamination Certificate

active

06187501

ABSTRACT:

FIELD OF THE INVENTION
This invention relates to imaging materials. In a preferred form it relates to imaging base materials with improved toughness.
BACKGROUND OF THE INVENTION
In the formation of color paper it is known that the base paper has applied thereto a layer of polymer, typically polyethylene. This layer serves to provide waterproofing to the paper, as well as providing a smooth surface on which the photosensitive layers are formed. The formation of a suitably smooth surface is difficult requiring great care and expense to ensure proper laydown and cooling of the polyethylene layers. The formation of a suitably smooth surface would also improve image quality as the display material would have more apparent blackness as the reflective properties of the improved base are more specular than the prior materials. As the whites are whiter and the blacks are blacker, there is more range in between and, therefore, contrast is enhanced. Layers of polyethylene while imparting waterproofness as well as a means to provide a white reflective base for added whiteness and image sharpness, adds very little to the overall durability of the base. It would be desirable if a more durable base was provided that is resistant to abrasions, scratches and was more resistant to tearing.
Prior art photographic reflective typically contain cellulose fiber paper to provide support for the imaging layers. While paper is an acceptable support for the imaging layers, providing a perceptually preferred feel and look to the photograph, paper is not very durable or tear resistant. It would be desirable to have a photographic base that has the look and feel of paper but has better durability.
In U.S. Pat. No. 5,888,714, Bourdelais et al., adhesive such as metallocene catalyzed ethylene plastomers are utilized to adhere biaxially oriented polymer sheets to a base material. While the melt extruded metallocene catalyzed ethylene plastomers are efficient in an melt extrusion process and create sufficient bond strength between the base material and the biaxially oriented polymers sheets, they are typically low in tear strength and therefore do not substantially increase the tear strength of a laminated support structure. In U.S. Pat. No. 5,888,714, Bourdelais et al, white pigments are added to the bonding layer to improve opacity, and image whiteness and sharpness. It is known that weight percent loading of white pigment beyond 24% causes problems such as extrusion die lines and melt curtain instability. It would be desirable to increase the weight percent loading of white pigments in the binder layer beyond 24%.
During the photographic processing of photographic images, photographic paper is typically punched and chopped as slit rolls of photographic paper are transformed into consumer images. It is known that reducing the energy to break for the bonding layer will improve the punching and chopping operations thereby improving the efficiency of photographic processing of images.
PROBLEM TO BE SOLVED BY THE INVENTION
There is a continuing need for imaging elements that are more durable and tear resistant to improve handling during the formation of images, and to improve consumer durability as images are viewed, stored, and shipped.
SUMMARY OF THE INVENTION
It is an object of the invention to overcome disadvantages of prior art and practices.
It is another object of the invention to provide a tear resistant imaging element.
It is another object to provide an imaging support with improved opacity and whiteness.
It is a further object to provide improved punching and chopping of imaging elements.
These and other objects of the invention are accomplished by an imaging member comprising a substrate, at least one oriented polymer sheet adhered to said substrate and a binder layer between said at least one oriented polymer sheet and said substrate, wherein said binder layer comprises a binder polymer that has an energy to break of between 9.0×10
5
J/m
3
and 3.5×10
7
J/m
3
.
ADVANTAGEOUS EFFECT OF THE INVENTION
The invention provides a photographic element that is more durable and has improved toughness. The tough binder layers of this invention in combination with the very durable biaxially oriented sheets on each side of a paper base, provides a very tough print that has superior durability. The tough binder layers also improve image whiteness and opacity.
DETAILED DESCRIPTION OF THE INVENTION
The invention has numerous advantages over prior practices in the art. The imaging member of this invention has superior durability and toughness. Imaging members often are subjected to a variety of environmental stresses and adverse physical handling conditions that can cause damage to imaging elements. In large formats when an image is being slid into a frame, it is easy to kink or tear an image. Often when young children handling images, they can severely abuse a image by subjecting the image to shear forces which tend to tear an image. Once a image is torn, it loses value and is often discarded. In prior practices, the negative would have to be found and sent out for reprinting. Often the negatives can not easily be located for the specific print that has been damaged and even when it is found, it is very inconvenient and costly to take the negative back to the photofinisher to have a new image made. The tough binder layers of this invention in combination with the very durable biaxially oriented sheets on each side of a paper base, provides a very tough print that has superior durability over prior practices.
The tough binder layers also improve the whiteness and opacity of the image by using higher weight loading of white pigments. By improving image whiteness and opacity, the quality of the image is improved. Additionally, a tough binder layer is more efficient to punch, chop and convert thereby reducing the mechanical wear of knives and punches. Improving the punching and chopping of images increases the efficiency of photographic processing equipment. These and other advantages will be apparent from the detailed description below.
The layers of the biaxially oriented polymer sheet of this invention have levels of voiding, TiO
2
and colorants adjusted to provide optimum optical properties when combined with a low cost cellulose paper base. Biaxially oriented sheets are attached to both the top and bottom of a cellulose paper base. While paper is low in cost, it may be desirable to use a base substrate of polyester or other suitable material to further enhance toughness and overall durability. The biaxially oriented sheets utilized in this invention are required to be attached to the base substrate. The material used to adhere the biaxially oriented sheet to the base substrate is referred to as a binder layer. The binder layer preferably is a melt extruable polymer. To improve the toughness and tear resistance of the imaging support, it is preferable to use high yield strength polymers. In particular, polypropylene, polyester, polycarbonates and polyamides are preferred over polyethylene because they are tougher polymers and, when combined with biaxially oriented polymer sheets, provide an imaging member with superior strength and tear resistance. A laminated imaging element with a tough binder layer is more tear resistant and can endure more physical abuse than prior art ethylene-based binder layers.
An imaging member comprising a substrate, at least one oriented polymer sheet adhered to said substrate and a binder layer between said at least one oriented polymer sheet and said substrate, wherein said binder layer comprises a binder polymer that has an energy to break of between 9.0×10
5
J/m
3
and 3.5×10
7
J/m
3
is preferred because when the invention is subjected to a shearing force, it will provide more mechanical resistance. Polymers such as polyester, polypropylene, polycarbonates and even polyamides are preferred. These tough binder layer polymers in combination with biaxially oriented sheets provide excellent durability. Polyester is most preferred as the polyester polymer pro

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