Radiation imagery chemistry: process – composition – or product th – Imaging affecting physical property of radiation sensitive... – Readily visible image formation
Reexamination Certificate
1999-05-19
2001-01-30
McPherson, John A. (Department: 1756)
Radiation imagery chemistry: process, composition, or product th
Imaging affecting physical property of radiation sensitive...
Readily visible image formation
C430S017000, C430S293000, C430S346000, C430S945000
Reexamination Certificate
active
06180318
ABSTRACT:
TECHNICAL FIELD
The present invention generally relates to a method of imaging an article comprising a metal/metal oxide imageable layer with a laser beam, and more particularly to such a method for imparting a color image on the article.
BACKGROUND OF THE INVENTION
Many techniques are commercially available for imparting images or information onto labels, tapes, and like articles. This includes various printing techniques such as flexography, lithography, and electrophotography. It is also known to use a laser to impart images or information onto materials which can be imaged by laser. For example, U.S. Pat. No. 5,766,827 discloses a process for forming an image on a substrate comprising the steps of providing an imageable element comprising a film having a coating of a black metal on one surface thereof, directing radiation in an imagewise distributed pattern at said black metal layer with sufficient intensity to substantially increase the light transmissivity of the medium in the irradiated region in an imagewise distributed pattern, said element having no layers comprising a thermally activated gas-generating composition. The image comprises residual black metal on the film base, and may be used for overhead transparencies, contact negatives/positives, and the like. A preferred embodiment of the black metal layer comprises a black aluminum layer comprising from at least 19 atomic percent of oxygen to less than 58 atomic percent oxygen.
SUMMARY OF THE INVENTION
It is desirable to further improve the performance of laser-imageable metal/metal oxide articles, such as by providing the ability to impart one or more colors to the imageable layers, by providing the ability to quickly and efficiently impart the image with a low power laser, and by avoiding significant ablation of the imageable layer to reduce contamination concerns. It is also desirable to provide durable imaged articles.
One aspect of the present invention provides a method for imaging an article. The method comprises the steps of: a) providing an article including a substrate and an imageable layer, the imageable layer comprising a metal/metal oxide layer; b) imagewise applying a laser beam to the article; and c) in the portion of the article having the laser applied thereto, imparting a color to the metal/metal oxide layer different from the color in the non-imaged portion.
In one preferred embodiment of the above method, step b) further includes changing the distribution of metal oxidation states within the metal/metal oxide layer. In one aspect, this can occur by any one or combination of oxidation, reduction, and disproportionation.
In another preferred embodiment of the above method, step b) includes changing the size distribution of at least one of the phases of the metal/metal oxide layer.
In another preferred embodiment of the above method, the imageable layer comprises an aluminum/aluminum oxide layer. In one aspect of this embodiment, step b) further includes changing the distribution of aluminum oxidation states within the aluminum/aluminum oxide layer. In one aspect, this can occur by any one or combination of oxidation and reduction. In another aspect of this embodiment, step b) includes changing the size distribution of at least one of the phases of the aluminum/aluminum oxide layer.
In another preferred embodiment of the above method, the percent of oxygen atoms in the metal/metal oxide layer comprises a gradient, and wherein the percent of oxygen atoms varies from one surface to the opposite surface by at least 10 percentage points, and in another preferred embodiment, by at least 40 percentage points.
In another preferred embodiment of the above method, the imageable layer includes a reflective layer at one surface thereof.
In another preferred embodiment of the above method, step b) comprises applying no more than 3 J/cm
2
; in another, no more than 500 mJ/cm
2
; and in yet another, no more than 200 mJ/cm
2
.
In another preferred embodiment of the above method, step b) comprises applying the laser beam for between 30 nanoseconds and 30 milliseconds to each respective imaged portion.
In another preferred embodiment of the above method, step c) includes imparting a visually perceptible color. In one aspect of this embodiment, step c) includes imparting at least two different visually perceptible colors.
In another preferred embodiment of the above method, step c) includes imparting a color sufficiently distinct from the non-imaged portion so as to impart a machine-readable image, such as a bar code.
In another preferred embodiment of the above method, step c) includes imparting a color having a different hue than the non-imaged portion.
In another preferred embodiment of the above method, step b) causes essentially no ablation in the imaged portion.
In another preferred embodiment of the above method, the imageable article further includes a protective layer on the metal/metal oxide layer. The protective layer may be laminated to the metal/metal oxide layer with a pressure sensitive adhesive.
In another preferred embodiment of the above method, the imageable article includes an adhesive layer for attaching the imageable article to a surface. The imageable article may include a release liner temporarily attached to the adhesive layer, and/ or a low adhesion backsize layer opposite the adhesive layer.
The present invention also provides an article imaged by any of the preferred methods described herein.
The present invention also provides the preferred imageable articles described herein, and the preferred imaged articles described herein. The articles are useful for applications such as tapes, labels, decorative articles, and the like.
Certain terms are used in the description and the claims that, while for the most part are well known, may require some explanation. In describing the application of a laser beam to a substrate for a period of time, the terms Power, Irradiance and Fluence are often used. Power (P) is an expression of the rate at which work (W) is done:
P=W/t
where
t=
time
and is expressed in Joules/sec or its equivalent, Watts. Alternatively, the application of power for a period of time:
P·t=W=&Dgr;E
results in Work or its equivalent, change in energy, which is expressed in Joules. When the laser beam, having a specific Power (or rate of work) is applied to an Area (A), the ratio:
P/A=I
defines a level of Irradiance, expressed in Watts/m
2
. Finally, the product of Irradiance and time:
I·t=
(
P·t
)/
A=W/A=F
gives the Fluence which is Work per unit Area (expressed as Joules/m
2
). For applying the above to this application, it is assumed that the imaged area is the same as the area irradiated by the laser beam.
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Fitzer Robert C.
Huang Haitao
LePere Pierre H.
McCarthy-Pohl Theresa A.
Waid Robert D.
3M Innovative Properties Company
McPherson John A.
Trussell James J.
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