Process for forming an ablation image

Details Process for forming an ablation image Process for forming an ablation image

2000-02-29

2001-09-04

McPherson, John A. (Department: 1756)

Radiation imagery chemistry: process, composition, or product th

Visible imaging using radiation only other than heating by...

C430S292000, C430S945000

Reexamination Certificate

active

06284441

ABSTRACT:

FIELD OF THE INVENTION
This invention relates to a process of forming an ablation image using, a barrier layer in a laser ablative recording element.
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. Accordingly 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. 4,621,1271, 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 substantially all of 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. The transmission density serves as a measure of the completeness of image dye removal by the laser.
U.S. Pat. No. 5,468,591 relates to a barrier layer, such as a vinyl polymer and an IR-dye, for laser ablative imaging. There is a problem with that barrier layer, however, in that the imaging efficiency is not as high as one would like.
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 topcoat. Examples of the dynamic release layer include thin films of metals. An image is transferred to a receiver in contiguous registration therewith. However, there is a problem with this process in that it requires a separate receiving element which is more expensive.
It is an object of this invention to provide a single-sheet process of forming a single color, ablation image which does not require a separate receiving element. It is still another object of this invention to provide a single-sheet process of forming a single color, ablation image which has improved efficiency.
SUMMARY OF THE INVENTION
These and other objects are achieved in accordance with the invention which comprises a process of forming a single color, ablation image comprising imagewise heating by means of a laser in the absence of a separate receiving element, an ablative recording element comprising a support having thereon, in order, a barrier layer and a colorant layer comprising a colorant dispersed in a polymeric binder, the colorant layer having an infrared-absorbing material associated therewith, the laser exposure taking place through the colorant side of the element and removing the ablated colorant to obtain the image in the ablative recording element, wherein the barrier layer comprises a thin metal film having a UV optical density up to about 3.0.
By use of the invention, a more scratch-resistant element is obtained that has a practical Dmax and exposure level, i.e., greater efficiency, than the prior art.
DETAILED DESCRIPTION OF THE INVENTION
In a preferred embodiment of the invention, the metal is a transition metal or a group III, group IV or group V metal. In another preferred embodiment, the metal is titanium, nickel or iron.
While any coverage of the thin metal barrier layer may be employed which is effective for the intended purpose, good results have been obtained at a thickness of from about 500 Å to about 5,000 Å.
The ablation elements of this invention can be used to obtain medical images, reprographic masks, printing masks, etc. The image obtained can be a positive or a negative image.
The invention is especially useful in making reprographic masks which are used in publishing and in the generation of printed circuit boards. The masks are placed over a photosensitive material, such as a printing plate, and exposed to a light source. The photosensitive material usually is activated only by certain wavelengths. For example, the photosensitive material can be a polymer which is crosslinked or hardened upon exposure to ultraviolet or blue light but is not affected by red or green light. For these photosensitive materials, the mask, which is used to block light during exposure, must absorb all wavelengths which activate the photosensitive material in the Dmax regions and absorb little in the Dmin regions. For printing plates, it is therefore important that the mask have high UV Dmax. If it does not do this, the printing plate would not be developable to give regions which take up ink and regions which do not.
The dye removal process can be by either continuous (photographic-like) or halftone imaging methods.
The higher efficiency achieved in accordance with the invention greatly expands the UV contrast of these ablative elements, which enhances their usefulness when exposing UV-sensitive printing plates with UV radiation.
Any polymeric material may be used as the binder in the recording element employed in the process of the invention. For example, there may be used cellulosic derivatives, e.g., cellulose nitrate, cellulose acetate hydrogen phthalate, cellulose acetate, cellulose acetate propionate, cellulose acetate butyrate, cellulose triacetate, a hydroxypropyl cellulose ether, an ethyl cellulose ether, etc., polycarbonates; polyurethanes; polyesters; poly(vinyl acetate); poly(vinyl halides) such as poly(vinyl chloride) and poly(vinyl chloride) copolymers; poly(vinyl ethers); maleic anhydride copolymers; polystyrene; poly(styrene-co-acrylonitrile); a polysulfone; a poly(phenylene oxide); a poly(ethylene oxide); a poly(vinyl alcohol-co-acetal) such as poly(vinyl acetal), poly(vinyl alcohol-co-butyral) or poly(vinyl benzal); or mixtures or copolymers thereof. The binder may be used at a coverage of from about 0.1 to about 5 g/m
2
.
In a preferred embodiment, the polymeric binder used in the recording clement employed in process of the invention has a polystyrene equivalent molecular weight of at least 100,000 as measured by size exclusion chromatography, as described in U.S. Pat. 5,330,

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