Incremental printing of symbolic information – Light or beam marking apparatus or processes
Reexamination Certificate
1998-11-11
2001-07-10
Le, N. (Department: 2861)
Incremental printing of symbolic information
Light or beam marking apparatus or processes
Reexamination Certificate
active
06259465
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to a laser thermal imaging media, and more particularly to a media which has improved abrasion resistance.
BACKGROUND OF THE INVENTION
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 one of 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 and binder at the spot where the laser beam hits the element. 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.
There is a problem with the scratch and abrasion resistance of such an ablative element. One way to improve it is to use lamination. However, lamination is expensive and air pockets may be trapped during the laminating step causing image defects.
Another way to improve abrasion resistance is to apply a liquid overcoat. However, this method requires the handling of liquids and the use of environmentally undesirable solvents.
This invention overcomes the aforementioned problems and provides a novel approach to obtain a more abrasion resistant single sheet ablation material.
DESCRIPTION OF RELATED ART
U.S. Pat. No. 5,429,909 describes the use of an overcoat layer on a laser ablative element. However, there is a problem with this approach in that more power is required to remove the added protective overcoat layer.
U.S. Pat. No. 5,300,398 relates to the use of a cushion layer for use in a two sheet process for producing a laser transfer image. The cushion layer is on an intermediate sheet to which the dye is first transferred. This intermediate sheet is then used to transfer the dye image to a final receiver and the cushion layer was found to improve gloss control. However, a two-sheet process is inherently more complicated and expensive than a one-sheet process.
It is an object of this invention to provide a single sheet ablation element which has an improved abrasion and scratch resistance. It is another object of this invention to provide a method for producing an ablation image which can significantly reduce its susceptibility to scratches and abrasion while not requiring a post-processing step. It is still another object of the invention to provide an ablation element which has improved abrasion and scratch resistance while having little impact on its speed and efficiency.
SUMMARY OF THE INVENTION
These and other objects are achieved in accordance with the invention which relates to a laser ablative recording element comprising a support having a certain Young's modulus and having thereon an image layer comprising an image dye or pigment dispersed in a polymeric binder, the image layer having a near infrared-absorbing material associated therewith to absorb at a given wavelength of the laser used to expose the element, the image dye or pigment absorbing in the region of from about 250 to about 700 nm, the element having a compliant layer between the support and the image layer, the compliant layer having a Young's modulus lower than that of the support, and the compliant layer having a thickness of between about 2 &mgr;m and about 200 &mgr;m.
Another embodiment of the invention relates to a process of forming a single color, ablation image having improved abrasion resistance comprising:
a) imagewise-heating, by means of a laser, an ablative recording element comprising a support having a certain Young's modulus and having thereon an image layer, the imagewise-heating causing the image layer to ablate imagewise, the image layer comprising an image dye or pigment dispersed in a polymeric binder, the image layer having a near infrared-absorbing material associated therewith to absorb at a given wavelength of the laser used to expose the element, the image dye or pigment absorbing in the region of from about 250 to about 700 nm, the element having a compliant layer between the support and the image layer, the compliant layer having a Young's modulus lower than that of the support, and the compliant layer having a thickness of between about 2 &mgr;m and about 200 &mgr;m; and
b) removing the ablated material to obtain an image in the ablative recording element.
Use of the invention provides an element with an improved abrasion and scratch resistance without sacrificing speed or efficiency since the layer which provides the improvement is underneath the image layer and not on top like other methods.
DETAILED DESCRIPTION OF THE INVENTION
Compliant layers useful in the invention can be virtually any polymer as long as it has the Young's modulus relationship with the support as described above. For example, there can be used silicones, polyolefins, polyacrylates, polymethacrylates, polyimides, polybutylenes, polyesters, etc. In particular, the following materials can be used with a support having a Young's modulus of 2.6 Gigapascals (Gpa) such as poly(ethylene terephthalate):
Polymer A A 80/20 mixture of low density (branched) and high density polyethylene which can be hot melt extruded onto a support (0.1 Gpa)
Polymer B A linear polyester derived from terephthalic acid, ethyle
Heetderks James P.
Tutt Lee W.
Cole Harold E.
Eastman Kodak Company
Feggins K.
Le N.
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