Thermal transfer sheet

Details Thermal transfer sheet Thermal transfer sheet

1999-06-28

2001-07-24

Hess, Bruce H. (Department: 1774)

Record receiver having plural interactive leaves or a colorless

Having plural interactive leaves

C428S913000

Reexamination Certificate

active

06265345

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a thermal transfer sheet for use in sublimation thermal transfer recording, and more particularly, to a thermal transfer sheet that yields a picture image having an improved light-resistant colorfastness.
2. Discussion of the Related Art
A sublimation thermal transfer recording method has been known in the art as a simple method for producing full-color picture images. In the sublimation thermal transfer recording method, a sublimating dye of yellow, cyan, or magenta and an appropriate binder resin are coated on one face of a base film, such as a polyester film, to form a dye layer with the corresponding hue. The thus produced three thermal transfer sheets bearing respective colors are used to produce full color images on an image-receiving sheet. A chromophil thermal-transfer image-receiving sheet is alternately overlaid with the thermal transfer sheets bearing the respective three colors (and black, if necessary), and each dye on the respective thermal transfer sheet is sublimated and transferred onto a dye-receiving layer of the image-receiving sheet by a thermal head printer, thereby enabling regeneration of a full color picture image from an original.
Although the dyes for use in the thermal transfer sheets for respective colors should be selected from yellow, magenta, and cyan dyes having ideal huse—the dyes used in other printing methods such as offset printing, for example—in order to precisely reproduce the colors in the original picture, it is practically difficult to generate an ideal hue using merely one kind of dye. Conventionally, a plurality of dyes are blended for each color to produce acceptable hues.
Among the three thermal transfer sheets bearing respective colors, the cyan thermal transfer sheet is particularly difficult to regenerate an ideal cyan color if only one kind of cyan dye is used. A nearly ideal cyan is obtained by blending two or more kinds of cyan dyes. However, when the picture is formed by using such a conventional cyan thermal transfer sheet, the quality of the resulting full-color picture image degrades as time elapses; i.e., a light resistance is not sufficient. It is considered that this degradation occurs because of photo decomposition or photodegradation of the constituent dyes, which in turn occurs because the cyan dyes transferred from such a cyan thermal transfer sheet to the dye receiving layer exert catalytic effects on each other in the dye receiving layer under external light irradiation. When the cyan color fades or changes in the full-color picture image, the overall quality of the full-color picture image suffers considerably.
SUMMARY OF THE INVENTION
Accordingly, the present invention is directed to a thermal transfer sheet that substantially obviates the problems due to limitations and disadvantages of the related art.
An object of the present invention is to provide a thermal transfer sheet capable of forming a picture image with an excellent light resistance without causing catalytic color changes or fading.
Additional features and advantages of the invention will be set forth in the description that follows, and in part will be apparent from the description, or may be learned by practice of the invention. The objectives and other advantages of the invention will be realized and attained by the structure particularly pointed out in the written description and claims hereof.
To achieve these and other advantages and in accordance with the purpose of the present invention, as embodied and broadly described, the present invention provides a thermal transfer sheet comprising a base sheet and a dye layer coated on the base sheet, wherein the dye layer comprises a binder resin; at least one dye of the following formula (1); and at least one dye of the following formula (2):
wherein R
1
, R
2
, R
1
′ and R
2
′ in the formulae independently represent a substituted or non-substituted alkyl group, a substituted or non-substituted cycloalkyl group, a substituted or non-substituted aralkyl group, or a substituted or non-substituted aryl group; R
3
represents a hydrogen atom, a halogen atom, a cyano group, a hydroxyl group, a substituted or non-substituted alkyl group, a substituted or non-substituted alkoxy group, a substituted or non-substituted cycloalkyl group, a substituted or non-substituted aralkyl group, a substituted or non-substituted aryl group, a substituted or non-substituted acyl group, a substituted or non-substituted acylamino group, or a substituted or non-substituted sulfonylamino group; R
4
represents a hydrogen atom or a halogen atom; R
5
represents a hydrogen atom or a substituted or non-substituted alkyl group; R
6
represents a substituted or non-substituted alkyl group, a substituted or non-substituted cycloalkyl group, a substituted or non-substituted aralkyl group, a substituted or non-substituted aryl group, or a substituted or non-substituted alkoxy group; and R
7
and R
8
each represent a substituted or non-substituted alkyl group, a substituted or non-substituted cycloalkyl group, a substituted or non-substituted alkoxycarbonyl group, a substituted or non-substituted alkylaminosulfonyl group, a substituted or non-substituted alkoxy group, a substituted or non-substituted alkylaminocarbonyl group, a cyano group, a nitro group, or a halogen atom. R
9
represents a substituted or non-substituted alkyl group, a substituted or non-substituted amino group, a substituted or non-substituted alkoxy group, a substituted or non-substituted alkoxycarbonyl group, or a halogen atom; and R
10
represents a substituted or non-substituted aryl group, a substituted or non-substituted aromatic heterocyclic group, a cyano group, a nitro group, a halogen atom, or other electro-negative group. The symbol n represents an integer of 1 or 2. Preferably, each of the alkyl, cycloalkyl, aralkyl, aryl, alkoxy, acyl, acylamino, alkoxycarbonyl, alkylaminosulfonyl, alkylaminocarbonyl, and aromatic heterocyclic groups contains from 1 to 10 carbon atoms. In a particularly preferred embodiment, R
1
and R
2
each are C
2
H
5
; R
1
′ and R
2
′ are independently C
2
H
5
or C
4
H
9
; R
3
is H or CH
3
, preferably at the three position of the phenyl ring as indicated in formula (1); R
4
is H or Cl; R
5
is H, CH
3
, C
2
H
5
, or NHCOC
4
H
9
; R
6
is CH
3
, C
3
H
7
, preferably iso-C
3
H
7
, OC
2
H
5
, or phenyl; R
7
is CN; R
8
is CH
3
; R
9
is C
2
H
5
or C
7
H
15
; and R
10
is phenyl.
In another aspect, the present invention provides a method for forming an image on an image-receiving sheet using the thermal transfer sheet described above, the method comprising the steps of coupling the thermal transfer sheet described above with the image-receiving sheet, and heating a portion of the thermal transfer sheet from the back of the thermal transfer sheet to form the image corresponding to the heated portion of the thermal transfer sheet onto the image-receiving sheet.
It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory and are intended to provide further explanation of the invention as claimed.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
A dye layer of a thermal transfer sheet according to the present invention contains at least two dyes represented by forgoing general formulae (1) and (2) above. Although any dyes represented by general formulae (1) and (2) can be used in the present invention, examples of particularly preferable dyes represented by the general formula (1) include, but are not limited to, those listed in Table 1. The dyes in Table 1 are represented according to their substituents.
TABLE 1
Example
No.
R
1
R
2
R
3
R
4
R
5
R
6
1
—C
2
H
5
—C
2
H
5
CH
3
*
—Cl
—CH
3
—CH
3
2
—C
2
H
5
—C
2
H
5
CH
3
*
—Cl
—C
2
H
5
—OC
2
H
5
3
—C
2
H
5
—C
2
H
5
CH
3
*
—H
-H
Phenyl
4
—C
2
H
5
—C
2
H
5
—H
—H
—NHCOC
4
H
9
—C
3
H
7
(i)
*The methyl group is located at the C3 position of the phenyl ring, as indicated in formula (1).
Examples of partic

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