Radiation imagery chemistry: process – composition – or product th – Imaging affecting physical property of radiation sensitive...
Reexamination Certificate
1994-08-24
2001-04-17
Angebranndt, Martin (Department: 1756)
Radiation imagery chemistry: process, composition, or product th
Imaging affecting physical property of radiation sensitive...
C430S945000, C430S201000, C430S200000, C503S227000, C428S195100, C428S206000
Reexamination Certificate
active
06218071
ABSTRACT:
This invention relates to single-sheet, monocolor elements for laser-induced, dye-ablative imaging and, more particularly, to scratch- and abrasion-resistant matte overcoats for such elements.
In recent years, thermal transfer systems have been developed to obtain prints from pictures which have been generated electronically from a color video camera. According to one way of obtaining such prints, an electronic picture is first subjected to color separation by color filters. The respective color-separated images are then converted into electrical signals. These signals are then operated on to produce cyan, magenta and yellow electrical signals. These signals are then transmitted to a thermal printer. To obtain the print, a cyan, magenta or yellow dye-donor element is placed face-to-face with a dye-receiving element. The two are then inserted between a thermal printing head and a platen roller. A line-type thermal printing head is used to apply heat from the back of the dye-donor sheet. The thermal printing head has many heating elements and is heated up sequentially in response to the cyan, magenta and yellow signals. The process is then repeated for the other two colors. A color hard copy is thus obtained which corresponds to the original picture viewed on a screen. Further details of this process and an apparatus for carrying it out are contained in U.S. Pat. No. 4,621,271, the disclosure of which is hereby incorporated by reference.
Another way to thermally obtain a print using the electronic signals described above is to use a laser instead of a thermal printing head. In such a system, the donor sheet includes a material which strongly absorbs at the wavelength of the laser. When the donor is irradiated, this absorbing material converts light energy to thermal energy and transfers the heat to the dye in the immediate vicinity, thereby heating the dye to its vaporization temperature for transfer to the receiver. The absorbing material may be present in a layer beneath the dye and/or it may be admixed with the dye. The laser beam is modulated by electronic signals which are representative of the shape and color of the original image, so that each dye is heated to cause volatilization only in those areas in which its presence is required on the receiver to reconstruct the color of the original object. Further details of this process are found in GB 2,083,726A, the disclosure of which is hereby incorporated by reference.
In one ablative mode of imaging by the action of a laser beam, an element with a dye layer composition comprising an image dye, an infrared-absorbing material, and a binder coated onto a substrate is imaged from the dye side. The energy provided by the laser drives off the image dye at the spot where the laser beam hits the element and leaves the binder behind. In ablative imaging, the laser radiation causes rapid local changes in the imaging layer thereby causing the material to be ejected from the layer. This is distinguishable from other material transfer techniques in that some sort of chemical change (e.g., bond-breaking), rather than a completely physical change (e.g., melting, evaporation or sublimation), causes an almost complete transfer of the image dye rather than a partial transfer. Usefulness of such an ablative element is largely determined by the efficiency at which the imaging dye can be removed on laser exposure. The transmission Dmin value is a quantitative measure of dye clean-out: the lower its value at the recording spot, the more complete is the attained dye removal.
Laser-ablative elements are described in detail in co-pending U.S. Ser. No. 99,969, filed Jul. 30, 1993, by Chapman et al., the disclosure of which is hereby incorporated by reference. There is a problem with these elements in that they are subject to physical damage from handling and storage.
U.S. Pat. No. 5,171,650 relates to an ablation-transfer image recording process. In that process, an element is employed which contains a dynamic release layer which absorbs imaging radiation which in turn is overcoated with an ablative carrier overcoat which contains a “contrast imaging material”, such as a dye. An image is transferred to a receiver in contiguous registration therewith. However, there is no disclosure in that patent that the process should be conducted in the absence of a receiver, or that there should be an overcoat layer on the element which does not contain an image dye.
In co-pending application Ser. No. 08/283,880 of Kaszczuk et al. filed Aug. 1, 1994, a polymeric protective overcoat is applied to the surface of a laser ablative imaging element prior to the laser-writing process. There is a problem with this element, however, in that the scratch and abrasion resistance could be improved.
It is an object of this invention to provide an ablative recording element which has improved scratch resistance and a matte finish to reduce fingerprinting and glare. It is another object of this invention to provide an ablative single-sheet process which does not require a separate receiving element.
These and other objects are achieved in accordance with the invention which relates to a laser dye-ablative recording element comprising a support having thereon, in order, a dye layer comprising an image dye dispersed in a polymeric binder and a polymeric overcoat which contains spacer beads but which does not contain any image dye, the dye layer having an infrared-absorbing material associated therewith to absorb at a given wavelength of the laser used to expose the element, the image dye absorbing in the region of the electromagnetic spectrum of from about 300 to about 700 nm and not having substantial absorption at the wavelength of the laser used to expose the element.
It has been found unexpectedly that an overcoat containing spacer beads for a single-sheet, monocolor, laser ablative imaging element will render such an element scratch- and abrasion-resistant and provide a matte finish to reduce fingerprinting and glare. The spacer beads do not interfere in the ablation process of the image layer and, surprisingly, they may even remain on the imaged element after the ablation process. The beads serve as spacers by providing a protective gap between films stacked on top of one another.
The protective overcoat containing spacer beads applied to the surface of the ablation sheet prior to laser writing still allows the dye to be removed as well as improves the scratch-resistance and abrasion-resistance of the sheet. This is important, for example, in reprographic mask and printing mask applications where a scratch can remove fine line detail creating a defect in all subsequently exposed work. The dye removal process can be either continuous (photographic-like) or half-tone. For purposes of this invention, monocolor refers to any single dye or dye mixture used to produce a single stimulus color. The resulting single-sheet medium can be used for creating medical images, reprographic masks, printing masks, etc., or it can be used in any application where a monocolored transmission sheet is desired. The image obtained can be positive or negative.
The spacer beads employed in the overcoat layer may be employed in any concentration or particle size effective for the intended purpose. In general, the spacer beads should have a particle size ranging from about 1 to about 100 &mgr;m, preferably from about 5 to about 50 &mgr;m. The coverage of the spacer beads may range from about 0.005 to about 5.0 g/m
2
, preferably from about 0.05 to about 0.5 g/m
2
. The spacer beads do not have to be spherical and may be of any shape.
The spacer beads may be formed of polymers such as polystyrene, phenolic resins, melamine resins, epoxy resins, silicone resins, polyethylene, polypropylene, polytetrafluoroethylene, polyesters, polyimides, etc.; metal oxides such as silica; minerals; inorganic salts; organic pigments; waxes such as Montan wax, candelilla wax, polyethylene wax, polypropylene wax, etc. In general, the spacer beads should be inert and insensitive to heat at the temperature of use.
In a pref
Tutt Lee William
Weber Sharon Wheten
Angebranndt Martin
Cole Harold E.
Eastman Kodak Company
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