Laser thermal imaging process, dye, and element

Details Laser thermal imaging process, dye, and element Laser thermal imaging process, dye, and element

2001-10-25

2004-03-09

Hess, Bruce H. (Department: 1774)

Stock material or miscellaneous articles

Structurally defined web or sheet

Discontinuous or differential coating, impregnation or bond

C503S227000

Reexamination Certificate

active

06703111

ABSTRACT:

FIELD OF THE INVENTION
This invention relates to the use of IR-absorbing dyes for laser imaging, and more particularly to the field of laser thermal dye transfer imaging.
BACKGROUND OF THE INVENTION
In recent years, thermal transfer systems have been developed to obtain prints from pictures that 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 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 or 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 that 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.
U.S. Pat. No. 5,219,823 relates to the use of stabilizers for polymethine (also known as cyanine) IR dyes in a donor element for thermal dye transfer. However, there is a problem with these stabilizers in that they are not effective as one would like, as will be shown hereafter.
U.S. Pat. No. 4,950,639 relates to infrared-absorbing polymethine dyes in a donor element for thermal dye transfer. However, there is a problem with these dyes in that they are not effective as one would like, as will be shown in the examples hereafter.
It is a problem to be solved to provide a laser-induced thermal recording element, a dye, and a process where the element contains an IR dye exhibiting improved stability.
SUMMARY OF THE INVENTION
The invention provides a laser-induced thermal recording element comprising a support having thereon a colorant layer comprising a colorant dispersed in a polymeric binder, said colorant layer having associated therewith a laser light-absorbing dye absorbing at the wavelength of a laser used to expose said element, said laser light-absorbing dye comprising a polymethine (cyanine) dye having covalently bonded thereto a phenylenediamine moiety.
Other embodiments of the invention relate to the IR dye itself and to a process of forming a laser-induced thermal dye transfer image. Embodiments of the invention exhibit improved stability.
DETAILED DESCRIPTION OF THE INVENTION
The laser light-absorbing dye comprising a polymethine or cyanine dye described in this invention has the following formula:
wherein:
X
1
, X
2
and X
3
each independently represents hydrogen, halogen, cyano, an alkyl group having 1 to 12 carbon atoms, a cycloalkyl group having 5 to 10 carbon atoms in the carbocyclic ring, an aryl group having 6 to 10 carbon atoms in the carbocyclic ring, or any two of said X
1
, X
2
, and X
3
may be joined together to complete a 5- to 7-membered carbocyclic or heterocyclic ring group, and m is 1-3;
each R independently represents hydrogen or a substituent with at least one such group being a phenylenediamine moiety group, where each of R
1
, R
2
, R
3
, R
4
, and R
5
, independently represents an alkyl group having 1 to 12 carbon atoms a cycloalkyl group having 5 to 10 carbon atoms in the carbocyclic ring, an aryl group having 6 to 10 carbon atoms in the carbocyclic ring, or a heterocyclic or polymeric backbone group; provided R
1
and R
2
or R
3
and R
4
may be joined together to form a 5- to 7-membered heterocyclic ring group and;
each of r
1
, r
2
, and r
3
independently represents a substituent group and each n is 0-4; and
W is a monovalent counter anion to balance the charge on the dye.
In a preferred embodiment of the invention, the laser light-absorbing dye comprising a polymethine dye described in this invention has m=1. Suitably, the dye has the following formula:
The phenylenediamine moiety “R” in the light-absorbing dye acts as a stabilizer.
Examples of laser light-absorbing dyes within the above formula the following:
Dye
R
1
R
2
R
3
R
4
R
5
1
Me
Me
Me
Me
Me
2
Me
n-Butyl
Me
Me
Me
3
Me
Phenyl
Ethyl
Ethyl
Ethyl
4
Butyl
Butyl
Methyl
Methyl
Methyl
5
Phenyl
Phenyl
Methyl
Methyl
Methyl
6
Butyl
Butyl
Methyl
Phenyl
Methyl
7
C
2
H
4
OH
Butyl
Phenyl
Methyl
Methyl
8
C
2
H
4
OH
C
2
H
4
OH
Methyl
Phenyl
Methyl
9
4-pyridyl
Butyl
Butyl
4-pyridyl
butyl


In a preferred embodiment of the invention, the amount of the laser light-absorbing dye can be, for example, from about 0.01 g/m
2
to about 0.500 g/m
2
. In another preferred embodiment, the dye layer also has associated therewith an image dye or pigment.
The dye layer of the recording element of the invention may also contain an ultraviolet-absorbing dye, such as a benzotriazole, a substituted dicyanobutadiene, an aminodicyanobutadiene, or any of those materials disclosed in Patent Publications JP 58/62651; JP 57/38896; JP 57/132154; JP 61/109049; JP 58/17450; or DE 3,139,156, the disclosures of which are hereby incorporated by reference. They may be used in an amount of from about 0.05 to about 1.0 g/m
2
.
Any polymeric material may be used as the binder in the recording element employed in 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); 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 typically 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 element 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. No. 5,330,876, the disclosure of which is hereby incorporated by reference.
A barrier layer may be employed in the laser recording element of the invention if desired, as described in U.S. Pat. No. 5,459,017.
To obtain a laser-induced, dye image according to the invention, an infrared diode laser is preferably employed since it offers substantial advantages in terms of its small size, low cost, stability, reliability, ruggedness, and ease of modulation.
The laser radiation is then absorbed into the dye layer and converted to heat by a molecular process known as internal conve

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