Stable coating composition

Details Stable coating composition Stable coating composition

1999-09-30

2001-01-16

Schilling, Richard L. (Department: 1752)

Radiation imagery chemistry: process, composition, or product th

Dye image from radiation sensitive dye or dye former by dry...

Composition or product

C430S201000, C430S944000, C430S964000

Reexamination Certificate

active

06174652

ABSTRACT:

FIELD OF THE INVENTION
This invention relates to use of a complexing agent in a coating composition used in thermal dye transfer imaging which is used to obtain a color proof that accurately represents the hue of a printed color image obtained from a printing press.
BACKGROUND OF THE INVENTION
In order to approximate the appearance of continuous-tone (photographic) images via ink-on-paper printing, the commercial printing industry relies on a process known as halftone printing. In halftone printing, color density gradations are produced by printing patterns of dots or areas of varying sizes, but of the same color density, instead of varying the color density continuously as is done in photographic printing.
There is an important commercial need to obtain a color proof image before a printing press run is made. It is desired that the color proof will accurately represent at least the details and color tone scale of the prints obtained on the printing press. In many cases, it is also desirable that the color proof accurately represent the image quality and halftone pattern of the prints obtained on the printing press. In the sequence of operations necessary to produce an ink-printed, full-color picture, a proof is also required to check the accuracy of the color separation data from which the final three or more printing plates or cylinders are made. Traditionally, such color separation proofs have involved silver halide photographic, high-contrast lithographic systems or non-silver halide light-sensitive systems which require many exposure and processing steps before a final, full-color picture is assembled.
Colorants that are used in the printing industry are insoluble pigments. By virtue of their pigment character, the spectrophotometric curves of the printing inks are often unusually sharp on either the bathochromic or hypsochromic side. This can cause problems in color proofing systems in which dyes, as opposed to pigments, are being used. It is very difficult to match the hue of a given ink using a single dye.
In U.S. Pat. No. 5,126,760, a process is described for producing a direct digital, halftone color proof of an original image on a dye-receiving element. The proof can then be used to represent a printed color image obtained from a printing press. The process described therein comprises:
a) generating a set of electrical signals which is representative of the shape and color scale of an original image;
b) contacting a dye-donor element comprising a support having thereon a dye layer and an infrared-absorbing material with a first dye-receiving element comprising a support having thereon a polymeric, dye image-receiving layer;
c) using the signals to imagewise-heat by means of a diode laser the dye-donor element, thereby transferring a dye image to the first dye-receiving element; and
d) retransferring the dye image to a second dye image-receiving element which has the same substrate as the printed color image.
In the above process, multiple dye-donors are used to obtain a complete range of colors in the proof. For example, for a full-color proof, four colors: cyan, magenta, yellow and black are normally used.
By using the above process, the image dye is transferred by heating the dye-donor containing the infrared-absorbing material with the diode laser to volatilize the dye, the diode laser beam being modulated by the set of signals which is representative of the shape and color of the original image, so that the dye is heated to cause volatilization only in those areas in which its presence is required on the dye-receiving layer to reconstruct the original image.
In color proofing in the printing industry, it is important to be able to match the proofing ink references provided by the International Prepress Proofing Association. These ink references are density patches made with standard 4-color process inks and are known as SWOP® (Specifications Web Offset Publications) color aims. For additional information on color measurement of inks for web offset proofing, see “Advances in Printing Science and Technology”, Proceedings of the 19th International Conference of Printing Research Institutes, Eisenstadt, Austria, June 1987, J. T. Ling and R. Warner, p.55.
In U.S. Pat. No. 5,866,509, a magenta dye donor element comprising a mixture of magenta dyes and a yellow dye is described for color proofing. However, a problem has developed using the dye solutions when it is necessary to hold them for a period of time before coating in that the composition of the solutions changes. Thus when a comparison of coatings was made from the fresh solution and the aged solution, the donor made from the aged solution did not have the same speed. Analysis of the aged solution showed that the speed change was caused by decomposition of the IR-absorbing dye which is due to the presence of copper ion in one of the magenta dyes. Cuprous cyanide is used in the synthesis of one of the magenta dyes and it is difficult to remove all traces of copper from the final dye.
It is an object of this invention to provide a coating composition for color proofing which is stable over a period of time
SUMMARY OF THE INVENTION
This and other objects are achieved in accordance with the invention which relates to a stable coating composition comprising an image dye, an infrared-absorbing dye, a polymeric binder, an organic solvent and a complexing agent having the following formula:
wherein
Y
1
and Y
2
each independently represents an alkyl or fluoroalkyl group having from 1 to about 6 carbon atoms, such as methyl, ethyl, propyl, trifluoromethyl, pentafluoroethyl, etc.; an aryl group having from 6 to about 10 carbon atoms, such as phenyl, tolyl, etc., or a hetaryl group having from about 5 to about 10 atoms, such as thienyl, furyl, etc.
DETAILED DESCRIPTION OF THE INVENTION
In a preferred embodiment of the invention, Y
1
and Y
2
are each methyl. In another preferred embodiment, Y
1
is methyl and Y
2
is phenyl. In still another preferred embodiment, Y
1
and Y
2
are each phenyl. In yet still another embodiment, Y
1
is trifluoromethyl and Y
2
is 2-thienyl.
Specific examples of complexing agents useful in the invention include the following:
Virtually any image dye that is used in color proofing can be used in the stable coating composition of the invention. For example, there may be employed image dyes as shown in the following U.S. Pat. Nos. 5,079,213; 5,866,509; 5,866,510; 5,041,412 and 5,134,116. During the synthesis or handling of these dyes, unwanted metal impurities may be introduced.
In particular, magenta dyes used in color proofing applications may have copper impurities arising from the synthesis of the dye. In accordance with the invention, a small amount of complexing agent is added to the coating solution and has no deleterious effect on the coating solution. In general, the complexing agents may be used at a concentration of from about 0.1 to about 1% in the coating solution, which is equivalent to about 2 to about 20% by weight in the dry coating.
Magenta dyes that often bring copper impurities in the coating solution include the following:

Dye
R
1
R
2
R
3
R
4
R
5
X
J
M-1 
C
2
H
5
C
2
H
5
CH
3
CH
3
C
4
H
9
-t
OCH
3
CO
M-2 
C
2
H
5
C
2
H
5
CH
3
CH
2
CH—OHCH
3
C
4
H
9
-t
OCH
3
CO
M-3 
C
2
H
5
C
2
H
5
CH
3
CH
2
CH—OHC
6
H
5
C
4
H
9
-t
OCH
3
CO
M-4 
C
2
H
5
C
2
H
5
C
4
H
9
-t
CH
3
CH
3
OCH
3
CO
M-5 
C
2
H
5
C
2
H
5
CH
3
C
2
H
5
C
4
H
9
-t
OC
2
H
5
SO
2
M-6 
C
2
H
5
C
2
H
5
C
2
H
5
CH
3
CH
3
OC
2
H
5
CO
M-7 
C
2
H
5
C
3
H
7
CH
3
CH
3
C
4
H
9
-t
OCH
3
CO
M-8 
C
2
H
5
C
2
H
5
CH
3
CH
3
C
4
H
9
-t
OCH
3
CO
2
M-9 
C
2
H
5
C
2
H
5
C
6
H
5
C
3
H
7
C
4
H
9
-t
OC
2
H
5
SO
2
M-10
CH
2
═CH—CH
2
CH
2
═CH—CH
2
CH
3
CH
2
C
6
H
5
C
4
H
9
-t
OCH
3
CO
M-11
C
3
H
7
C
3
H
7
C
2
H
5
C
2
H
5
CH
3
OC
3
H
7
CO
M-12
C
3
H
7
C
3
H
7
C
2
H
5
C
2
H
5
CH
3
OC
3
H
7
SO
2
Other specific magenta dyes that often bring copper impurities in the coating solution include the following:

Compound No
R
6
R
7
R
8
R
9
R
10
M-13
NHCOCH
3
C
2
H
5
C
2
H
5
H
CH
3
M-14
NHSO
2

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