Heat transfer sheet

A heat transfer sheet according to the present invention includes a substrate sheet and a dye carrying layer formed on its one major side, and is characterized in that a dye included in the dye carrying layer is expressed by the following general formula (I) or (II): ##STR1## An image formed with such a heat transfer sheet shows excellent fastness properties, and excels in resistance to contamination in particular.

TECHNICAL FIELD 
The present invention relates to a heat transfer sheet and, more 
particularly, to a heat transfer sheet capable of easily providing a 
recording image excelling in various fastness properties. 
BACKGROUND ART 
Heretofore, various heat transfer techniques have been known in the art, 
including sublimation type transfer systems wherein a sublimable dye is 
carried on a substrate sheet such as paper to make a heat transfer sheet, 
which is then overlaid on an imageable material (image-receiving 
material), for instance, a woven fabric made of polyester to apply heat 
energy in the form of a pattern from the back side of the heat transfer 
sheet, thereby transferring the sublimable dye into the imageable 
material. 
With a sublimation textile printing system of the above sublimation 
transfer systems, in which the imageable material used is made of, e.g., a 
polyester textile, relatively satisfactory dye transfer is achieved, since 
heat energy is applied over a relatively extended period of time so that 
the imageable material per se can be heated by that heat energy. 
With an advance in recording techniques, however, fine characters or 
figures or photographic images could have been formed at high speeds on 
imageable materials made of, e.g., polyester or paper sheets having 
thereon a dye-receiving layer by means of a thermal head, etc. In this 
case, the application of thermal energy is required to be achieved within 
a time as short as fractions of a second. However, no image of sufficient 
density can be obtained, since the sublimable dyes and imageable materials 
are not well heated within such a short time. 
In order to cope with such high-speed recording, sublimable dyes excelling 
in sublimability have thus been developed. However, problems with such 
dyes of excellent sublimability are that after transfer, they transfer 
into the imageable materials or bleed onto their surfaces with time, 
generally because of their low molecular weight. In consequence, the 
images, once formed, become out of order or blurred, or otherwise 
contaminate surrounding articles. 
In the art of heat transfer using sublimable dyes, there is thus still 
strong demand for the development of a heat transfer sheet which provides 
a clear image of sufficient density by the application of thermal energy 
within such short a time as mentioned above and imparts improved fastness 
properties to the formed image. 
It is therefore an object of the present invention to satisfy the above 
demand. 
DISCLOSURE OF THE INVENTION 
Thus, the present invention provides a heat transfer sheet comprising a 
substrate sheet and a dye carrying layer formed on its one major side, 
characterized in that a dye included in said dye carrying layer is 
expressed by the following general formula (I): 
##STR2## 
wherein: R.sub.1 stands for a hydrogen atom, a halogen atom or a 
substituent such as an alkyl, aryl, cycloalkyl, arylalkyl, alkoxy, 
acylamino or aminocarbonyl group which may include a substituent, 
n is 1 or 2, 
R.sub.2 and R.sub.3 each denote an alkyl group which may or may not include 
a substituent, or may form a ring together, and 
X indicates a hydrogen atom or at least one substituent. 
According to another aspect of the present invention, there is provided a 
heat transfer sheet comprising a substrate sheet and a dye carrying layer 
formed on its major side, characterized in that a dye included in said dye 
carrying layer is expressed by the following general formula (II): 
##STR3## 
wherein: A stands for a cyano, alkoxycarbonyl, aryloxycarbonyl, carbamoyl, 
alkylcarbamoyl, arylcarbamoyl, alkylcarbonyl, arylcarbonyl, alkylsulfonyl, 
alkylsulfonylamino, arylsulfonyl or aryl group, 
R.sub.1 denotes a substituted or unsubstituted alkyl, aralkyl or aryl 
group, or an atom or atomic group which form a five- or six-membered ring 
together with Z, 
R.sub.2 indicates a substituted or unsubstituted alkyl, aralkyl or aryl 
group, 
said R.sub.1 and R.sub.2 may form a five- or six-membered ring which may 
include an oxygen or nitrogen atom, 
R.sub.3 stands for a hydrogen or halogen atom or an alkyl, alkoxy or 
acylamino group which may include a substituent, 
R.sub.4 denotes a hydrogen or halogen atom or an alkyl, alkoxy, nitro, 
cyano, acylamino or aryl group which may include a substituent, 
Z indicates a hydrogen atom or an atom or atomic group which forms a five- 
or six-membered ring together with R.sub.1, and 
n and m each are 1 or 2. 
Studies of the present inventors have revealed that it is an essential 
condition for conventional sublimation textile printing techniques using 
textiles or woven fabrics of polyester, etc. that the dye used is 
sublimable or vaporizable (i.e., has the property of being capable of 
transferring through a space present between a heat transfer sheet and a 
woven fabric), since the heat transfer sheet is unlikely to come into 
close contact with the woven fabric that is an imageable material due to 
the surface of the latter lacking smoothness. In the case of using as an 
imageable material a polyester sheet or surface-processed paper having a 
plain surface, etc., however, it has now been found that as the heat 
transfer sheet is brought into full contact with the imageable material at 
the time of heat transfer, what is of crucial importance is not only the 
sublimability and vaporizability but also the property of the dye that it 
can travel thermally across the interface between the two brought into 
close contact with each other, and that such a property is greatly 
affected by the chemical structure of the dye used, what substituent it 
has, or where that substituent is located. This leads to another finding 
that with selected dyes of suitable molecular structures, even if they 
have a molecular weight so high that they are considered unusable from a 
common sense standpoint, good thermal transfer is achievable. It has thus 
been found that by using a heat transfer sheet carrying such a dye, it is 
possible to make a record of an image of high density and improved 
fastness properties even with the application of thermal energy within a 
very short time, since the dye used transfers easily into an imageable 
material.

BEST MODE FOR CARRYING OUT THE INVENTION 
The present invention will now be explained in more detail with reference 
to the preferred embodiments. 
The dye used in the first aspect of the present invention may be prepared 
by the known coupling reaction of ziazonium compounds of 
2-aminobenzothiazole or their derivatives with couplers such as 
N,N-dialkylanilines or their derivatives. 
Of the thus prepared dyes according to the present invention, particular 
preference is given to those of the general formula (I) in which R.sub.1 
is a hydrogen atom or an alkoxy group such as methoxy, ethoxy, propoxy or 
butoxy, located at the 2-position with respect to the azo group, and 
R.sub.2 and R.sub.3 each are a C.sub.1 -C.sub.20 alkyl group such as 
methyl, ethyl, propyl, butyl, pentyl, hexyl, heptyl, octyl, nonyl, decyl, 
undecyl, dodecyl or hexadecyl, which may include a polar substitute such 
as a hydroxyl, amino, alkylamino, acylamino, sulfonylamino, aminocarbonyl, 
aminosulfonyl, alkoxycarbonyl, alkoxysulfonyl, cyano, alkoxy, phenyl, 
cycloalkyl or nitro group or a halogen atom, and X is a hydrogen atom or 
an alkoxy group such as methoxy, ethoxy, propoxy or butoxy, located at the 
6-position, and which have a selected molecular weight of at least 320, 
preferably at least 350. By far the most preference is given to dyes of 
the general formula (I) wherein at least one of R.sub.1 and X is a lower 
alkoxy group and at least one of R.sub.2 and R.sub.3 is an alkyl group 
having 1 to 20 carbon atoms, which is substituted by a hydroxyl or cyano 
group. 
By detailed studies of the present inventors, the dyes of the general 
formula (I) have their molecular weight increased to at least 320 or at 
least 350 by selecting for R.sub.1 -R.sub.3 and X groups other than 
hydrogen, e.g., substituted or unsubstituted alkyl groups, etc. Unlike 
generally well-established conceptions, however, it has now been found 
that the dyes having the above general formula are likely to decrease in 
their melting points, and that when such dyes are used as the dyes for 
heat transfer sheets, they transfer from the heat transfer sheets to 
imageable materials at an increased rate, even though they are heated by a 
thermal head, etc., within a very short time, and provide images improved 
in terms of fastness, esp., storability and light resistance. 
With thiazole dyes coming under the general formula (I) but having a 
molecular weight below 300, on the other hand, it has been found that the 
resulting images are satisfactory in the density of developed color, etc., 
but are not in terms of storability and light resistance. 
In addition, it has been found that the above preferable dyes are so 
improved in their solubility in general-purpose organic solvents used for 
the preparation of heat transfer sheets such as, for instance, methyl 
ethyl ketone, toluene, ethanol, isopropyl alcohol, cyclohexanone, ethyl 
acetate or their mixed solvents that they can be present on dye carrying 
layers formed on the heat transfer sheets in a non- or low-crystalline 
state, and so can easily transfer thermally into imageable materials in 
the quantity of heat applied that is much lower than that required in such 
a high-crystalline state as encountered with conventional dyes. 
Illustrative dyes suitable for the present invention will now be summarized 
in Table A1 showing illustrative examples of the substituents R.sub.1 
-R.sub.3, n and X in the general formula (I). 
TABLE A1 
__________________________________________________________________________ 
No. 
X n R.sub.1 R.sub.2 R.sub.3 
__________________________________________________________________________ 
1 CH.sub.3 
1 H C.sub.2 H.sub.5 
C.sub.2 H.sub.5 
2 CH.sub.3 
1 OC.sub.2 H.sub.5 
C.sub.2 H.sub.4 CN 
C.sub.2 H.sub.5 
3 CH.sub.3 
2 CH.sub.3 
C.sub.2 H.sub.4 NHSO.sub.2 CH.sub.3 
C.sub.2 H.sub.5 
4 OCH.sub.3 
1 H C.sub.2 H.sub.5 
C.sub.2 H.sub.5 
5 OC.sub.2 H.sub.5 
1 OC.sub.2 H.sub.5 
C.sub.2 H.sub.5 
C.sub.2 H.sub.5 
6 OC.sub.2 H.sub.5 
2 OC.sub.2 H.sub.5 
C.sub.2 H.sub.4 OH 
C.sub.2 H.sub.5 
7 OC.sub.2 H.sub.5 
1 H C.sub.2 H.sub.4 CN 
CH.sub.3 
8 OC.sub.2 H.sub.5 
1 NHCOCH.sub.3 
C.sub.2 H.sub.5 
C.sub.2 H.sub.5 
9 NO.sub.2 
1 H C.sub.2 H.sub.5 
C.sub.2 H.sub.5 
10 NO.sub.2 
2 CH.sub.3 
C.sub.2 H.sub.5 
C.sub.2 H.sub.5 
11 NO.sub.2 
1 * C.sub.2 H.sub.5 
CH.sub.3 
12 Cl 2 OC.sub.2 H.sub.5 
C.sub.2 H.sub.5 
C.sub.2 H.sub.5 
13 Cl 1 H --C.sub.2 H.sub.4 OC.sub.2 H.sub.4 -- 
14 Cl 1 CH.sub.3 
C.sub.2 H.sub.5 
C.sub.2 H.sub.5 
15 CH.sub.2 CN 
1 CH.sub.3 
C.sub.2 H.sub.5 
C.sub.2 H.sub.5 
16 N(CH.sub.3).sub.2 
2 OC.sub.2 H.sub.5 
C.sub.2 H.sub.4 OH 
C.sub.2 H.sub.5 
17 CH.dbd.CHCH.sub.3 
1 CH.sub.3 
C.sub.2 H.sub.4 OCH.sub.3 
C.sub.2 H.sub.5 
18 iso-C.sub.3 H.sub.7 
2 CH.sub.3 
CH.sub.3 CH.sub.3 
19 H 1 OC.sub.2 H.sub.5 
C.sub.8 H.sub.17 
C.sub.8 H.sub.17 
20 H 1 CH.sub.3 
C.sub.2 H.sub.4 Ph 
H 
21 Br 1 C.sub.4 H9 
C.sub.8 H.sub.17 
C.sub.8 H.sub.17 
22 NHCOCH.sub.3 
1 iso-C.sub.3 H.sub.7 
C.sub.2 H.sub.4 OH 
C.sub.2 H.sub.5 
23 CH.sub.3 
1 NHSO.sub.2 CH.sub.3 
C.sub.2 H.sub.5 
C.sub.2 H.sub.4 OH 
__________________________________________________________________________ 
*--CH.dbd.CH--CH.dbd.CHgroup forming a naphthalene ring. 
The second aspect of the present invention will then be explained. 
The dyes used according to the second aspect of the present invention are 
well-known in themselves, and may be easily prepared by the 
condensation-with-dehydration of dihydrobenzothiophene-1,1-dioxide 
derivatives expressed by the following general formula (III) with nitroso 
compounds expressed by the following general formula (IV) in the presence 
of solvents. 
##STR4## 
wherein R.sub.1 -R.sub.5, X and Z have the same meanings as defined above. 
In the second aspect of the present invention, preference is given to dyes 
which have a molecular weight of 400 or more, and in which the substituent 
Z is a hydrogen atom, R.sub.1 and/or R.sub.2 are an ethyl group which may 
have a hydroxyl group, R.sub.3 is an alkyl or alkoxy group located at the 
ortho-position with respect to the azomethyne group, R.sub.4 is a hydrogen 
atom, A is a cyano or alkoxycarbonyl group and m and n are both 1. 
Preference is also given to dyes in which at least one of the substituents 
R.sub.1 -R.sub.4 and A includes a polar group such as hydroxyl, amino, 
alkylamino, acylamino, sulfonylamino, aminocarbonyl, aminosulfonyl, 
alkoxycarbonyl, alkoxysulfonyl, cyano, alkoxy, phenyl, cycloalkyl or nitro 
group or a halogen atom. 
Illustrative dyes suitable for the present invention will now be summarized 
in Table B1 showing illustrative examples of the substituents R.sub.1 
-R.sub.4, A and Z, m and n in the general formula (II) as well as their 
molecular weight. 
TABLE B1 
__________________________________________________________________________ 
Molecular 
No. 
Z R.sub.1 R.sub.2 
m R.sub.3 
n R.sub.4 
A Weight 
__________________________________________________________________________ 
1 H C.sub.2 H.sub.5 
C.sub.2 H.sub.5 
1 OC.sub.2 H.sub.5 
1 H CN 434 
2 H C.sub.2 H.sub.5 
C.sub.2 H.sub.4 OH 
1 CH.sub.3 
1 H CN 420 
3 H C.sub.2 H.sub.5 
C.sub.2 H.sub.5 
2 OC.sub.2 H.sub.5 
1 H CN 478 
4 H CH.sub.3 
Ph 1 Cl 1 NO.sub.2 
CN 503.5 
5 H C.sub.2 H.sub.5 
C.sub.2 H.sub.4 Cl 
1 CH.sub.3 
1 NHCOCH.sub.3 
CN 495.5 
6 CHCH.sub.3 
CH.sub.2 C(CH.sub.3).sub.2 *.sup.1 
C.sub.2 H.sub.5 
1 CH.sub.3 
1 H CN 458 
7 H C.sub.6 H.sub.13 
C.sub.6 H.sub.13 
1 NHSO.sub.2 CH.sub.3 
1 H CN 596 
8 H *2 C.sub.2 H.sub.5 
1 H 1 OC.sub.2 H.sub.5 
CN 515 
9 H C.sub.2 H.sub.5 
C.sub.2 H.sub.4 OH 
1 OC.sub.2 H.sub.5 
1 H CN 450 
10 H C.sub.2 H.sub.5 
C.sub.2 H.sub.5 
2 CH.sub.3 
1 CN CN 444 
11 H C.sub.2 H.sub.5 
CH.sub.2 Ph 
1 H 1 H CN 452 
12 H C.sub.2 H.sub.5 
C.sub.2 H.sub.4 CN 
1 NHCOCH.sub.3 
1 Cl CN 506.5 
13 H CH.sub.3 
C.sub.2 H.sub.5 
1 CH.sub.3 
1 H CN 404 
14 H (CH.sub.2).sub.5 *.sup.3 
1 CH.sub.3 
1 H COOCH.sub.3 
463 
15 H C.sub.2 H.sub.5 
C.sub.2 H.sub.5 
1 CH.sub.3 
1 H COOCH.sub.3 
437 
16 H C.sub.2 H.sub.5 
C.sub.2 H.sub.5 
1 CH.sub.3 
2 CN COOCH.sub.3 
487 
17 H C.sub.2 H.sub.5 
C.sub.2 H.sub.4 OH 
1 C.sub.4 H.sub.9 
1 CH.sub.3 
COOC.sub.2 H.sub.5 
524 
18 H C.sub.2 H.sub.5 
C.sub.2 H.sub.5 
1 OC.sub.2 H.sub.5 
1 Cl COOC.sub.2 H.sub.5 
480 
19 H C.sub.2 H.sub.5 
C.sub.2 H.sub.5 
1 CH.sub.3 
1 H COPh 483 
20 H C.sub.2 H.sub.4 OH 
C.sub.2 H.sub.5 
1 CH 1 H CONHC.sub.3 H.sub.7 
480 
21 H C.sub.2 H.sub.4 OH 
C.sub.2 H.sub.5 
1 CH.sub.3 
1 H CONHPh 514 
22 H C.sub.2 H.sub.5 
C.sub.2 H.sub.5 
1 CH.sub.3 
1 H NHSO.sub.2 CH.sub.3 
472 
23 H C.sub.2 H.sub.4 OH 
C.sub.2 H.sub.5 
1 CH.sub.3 
1 H Ph 471 
__________________________________________________________________________ 
*.sup.1 Z forms a ring with R.sub.1. 
*2: C.sub.2 H.sub.4 NHSO.sub.2 CH.sub.3 
*.sup.3 Z forms a ring with R.sub.1. 
The heat transfer sheets according to the present invention are 
characterized in that such specific dyes as mentioned above are used, and 
may otherwise be identical with conventional known heat transfer sheets. 
As the substrate sheets used for the heat transfer sheets containing the 
above dyes according to the present invention, use may be made of any 
known material having some heat resistance and strength. By way of example 
alone, use may be made of paper sheets, various-processed paper sheets, 
polyester films, polystyrene films, polypropylene films, polysulfone 
films, polycarbonate films, aramide films, polyvinyl alcohol films, 
cellophane and so on, all having a thickness of about 0.5 to 50 .mu.m, 
preferably about 3 to 10 .mu.m. Particular preference is given to 
polyester films. 
The dye carrying layers formed on the surfaces of such substrate sheets as 
mentioned above may be obtained by carrying the dyes of the general 
formula (I) or (II) on any suitable binder resin. 
As the binder resins to carry thereon the above dyes, use may be made of 
any known resin. Preferable to this end are cellulosic resins such as 
ethyl cellulose, hydroxyethyl cellulose, ethylhydroxy cellulose, 
hydroxypropyl cellulose, methyl cellulose, cellulose acetate and cellulose 
acetate butyrate; and vinylic resins such as polyvinyl alcohol, polyvinyl 
acetate, polyvinyl butyral, polyvinyl acetal, polyvinyl pyrrolidone and 
polyacrylic amide. Of these resins, particular preference is given to 
polyvinyl butyral and polyvinyl acetal in view of heat resistance and 
dye-transfer properties. 
The dye carrying layers of the heat transfer sheets according to the 
present invention are basically formed of the above materials and, if 
required, may include various additives such as those heretofore known in 
the art. 
Preferably, such a dye carrying layer may be formed on the above substrate 
sheet by dissolving or dispersing the above dye, binder resin and any 
other components in a suitable solvent to prepare a coating or ink liquid 
for the formation of the dye carrying layer and, then, coating it on the 
substrate, followed by drying. 
Suitably, the carrying layer formed in this manner has a thickness of about 
0.2 to 5.0 .mu.m, preferably about 0.4 to 2.0 .mu.m and a dye content of 5 
to 70% by weight, preferably 10 to 60% by weight based on the weight 
thereof. 
The heat transfer sheets of the present invention may be successfully used 
as such for the purpose of heat transfer. By the provision of an anti-tack 
layer, i.e., a release coat on the surface of the dye carrying layer, 
however, it is possible to prevent the heat transfer sheet from sticking 
to an imageable material at the time of heat transfer and hence use a much 
more increased heat transfer temperature, thereby forming an image of much 
more improved density. 
Some anti-tack effect may be obtained by using only anti-tack inorganic 
powders for that release layer. However, more preferable results are 
obtained by forming a release layer of 0.01 to 5 .mu.m, preferably 0.05 to 
2 .mu.m in thickness from a resin having excellent releasability such as 
silicone polymers, acrylic polymers and fluorinated polymers. 
It is understood that such inorganic powders or releasable polymers as 
mentioned above produce a sufficient release effect, even if they are 
contained in the dye carrying layer. 
Further, such a heat transfer sheet may additionally be provided on its 
back side with a heat-resistant layer so as to prevent the heat of a 
thermal head from having an adverse influence thereon. 
The imageable material used for forming an image with such a heat transfer 
sheet as mentioned above may be any material having its recording surface 
capable of receiving the above dye. In the case of paper, metal, glass, 
synthetic resin or the like having the property of being incapable of 
receiving the dye, they may be provided on one of their major surfaces 
with a dye receiving layer. 
As the imageable materials which may not contain any dye receiving layer, 
use may be made of fibers, woven fabrics, films, sheets and formings 
formed of, for instance, polyolefinic resins such as polypropylene, 
halogenated polymers such as polyvinyl chloride and polyvinylidene 
chloride, vinylic polymers such as polyvinyl acetate and polyacrylic 
esters, polyester resins such as polyethylene terephthalate and 
polybutylene terephthalate, polystyrene resins, polyamide resins, 
copolymeric resins of olefins such as ethylene and propylene with other 
vinylic monomers, ionomers, cellulosic resins such as cellulose diacetate 
and polycarbonate. 
Particular preference is given to polyester sheets or films or processed 
paper having a polyester layer. Non-dyeable imageable materials such as 
paper, metal and glass may be formed into imageable materials by coating a 
solution or dispersion of such a dyeable resin as mentioned above on their 
recording surfaces, followed by drying, or laminating a film of such 
resins thereon. 
As is the case with the above paper, such a dyeable imageable material may 
additionally be formed on its surface with a dye receiving layer of a 
resin of much more improved dyeability. 
The dye receiving layer prepared in this manner may be formed of a single 
material or a plurality of materials. As a matter of course, it may 
contain various additives, provided that the desired object is achievable. 
Such a dye receiving layer may have any suitable thickness but may 
generally be 3 to 50 .mu.m in thickness. Although the dye receiving layer 
should preferably be provided in the form of a continuous coat, it may be 
provided in the form of a discontinuous coat by using a resin emulsion or 
dispersion. 
The imageable material is basically as mentioned above and may successfully 
be used as such. However, this imageable material or its dye receiving 
layer may contain inorganic powders for anti-tack purposes. In this way, 
much more improved heat transfer is achievable, since the heat transfer 
sheet is prevented from sticking to the imageable material even at 
elevated heat transfer temperatures. By far the most preference is given 
to finely divided silica. 
In place of or in combination with such inorganic powders as the above 
silica, such resins of improved releasability as already indicated may be 
added. By far the most preference is given to cured silicone compounds, 
typically, cured products comprising epoxy modified silicone oil and amino 
modified silicone oil. Such a release agent may preferably account for 
about 0.5 to 30% by weight of the dye receiving layer. 
In addition, the imageable material used may be either deposited on the 
surface of its dye receiving layer with such inorganic powders as already 
indicated so as to better its anti-tack effect or provided thereon with a 
layer consisting of such a release agent of improved releasability as 
already indicated. 
At a thickness of about 0.01 to 5 .mu.m, such a release layer produces an 
effect so sufficient that much more improvements can be introduced in dye 
acceptability, while preventing any sticking of the dye receiving layer of 
the heat transfer sheet to the imageable layer. 
As the thermal energy applying means used for carrying out heat transfer 
with such a heat transfer sheet of the present invention as already 
indicated and such an imageable material as already stated, any of 
conventional means hitherto known in the art may be used. For instance, 
the desired object is successfully achievable by the application of a heat 
energy of about 5 to 100 mJ/mm.sup.2 for a controlled recording time with 
such recording equipment as a thermal printer (e.g., Video Printer VY-100 
made by Hitachi Co., Ltd., Japan). 
According to the present invention as detailed above, although the dye used 
for the heat transfer sheet of the present invention is much higher in 
molecular weight than sublimable dyes used for conventional heat transfer 
sheets (having a molecular weight of about 150 to 250), it shows improved 
thermal transferability and excellent dyeability and color developability 
with respect to the imageable material due to its specific structure and 
its having a substituent at a specific position. Moreover, it is unlikely 
to transfer through, or bleed on, the heat transfer sheet after 
transferring. 
Thus, the image formed with the heat transfer sheet of the present 
invention is so high in its fastness properties and so particularly 
improved in its resistance to both transfer and contamination that it 
cannot possibly be blurred or contaminate other articles, thus making it 
possible to solve various problems of the prior art. 
Especially in the case of the dyes of the general formula (I) wherein at 
least one of R.sub.1 -R.sub.3 contains a polar group, or of the general 
formula (II) wherein at least one of R.sub.1 -R.sub.4, A and Z contains a 
polar group, such fastness properties as mentioned above are much more 
improved. Such effects as excellent as never anticipated from the prior 
art become marked especially when the dye receiving portion of the 
imageable material is formed of such a material as polyester. This appears 
to be because the polar group-containing dye is fixed into the polyester 
for some unknown reasons, but probably through a certain correlation 
between it and the ester bond that forms a polar group in the polyester. 
The present invention will now be explained more illustratively with 
reference to the following reference examples, examples and comparative 
examples. It is understood that unless otherwise stated, "parts" and "%" 
are given on weight basis and that the structural formulae of dyes are 
estimated ones. 
REFERENCE EXAMPLE A1 
Dissolved in a mixed solution of 20 ml of acetic acid and 50 ml of sulfuric 
acid are 18 g of 2-amino-6-methylbenzothiazole, with further addition of 
100 g of ice water. 
While the obtained solution is cooled down to 5.degree. C. or below, a 
solution of 5 g of sodium nitrite in 20 ml of water is slowly added 
thereto for diazotation. After stirring at 0.degree. to 5.degree. C. for a 
further 2 hours, a small amount of sulfamic acid is added to the solution, 
with subsequent filtration yielding a diazo solution. 
On the other hand, 15 g of diethylaniline are dissolved in a mixed solution 
of 30 g of hydrochloric acid with 400 ml of water. While this solution is 
ice-cooled under agitation to 0.degree. to 5.degree. C., small portions of 
the above diazotated solution are added thereto for coupling. After the 
completion of the coupling reaction, the reaction product is neutralized 
with sodium carbonate, and the precipitates are filtrated, washed with 
water and dried. Thus, 28.5 g of a dye expressed by the following 
structural formula were obtained in the form of purplish red crystals. 
##STR5## 
REFERENCE EXAMPLES A2 TO A22 
Reference Example A1 was repeated with the 2-aminobenzothiazole derivatives 
and P-phenylenediamine derivatives corresponding to Nos. 2 to 23 in Table 
A1 to obtain the thiazole-azo dyes set forth in Table A1. 
EXAMPLE A 
Prepared was an ink composition for the formation of a dye carrying layer, 
composed of the following ingredients, which was then coated a 
6-.mu.m-thick polyethylene terephthalate film subjected to heat-resistant 
treatment on its back side in a quantity of 1.0 g/m.sup.2 on dry basis. 
Subsequent drying gave the heat transfer sheets according to the present 
and comparative examples. 
______________________________________ 
Dyes set forth in Table A1 
3 parts 
Polyvinyl butyral resin 
4.5 parts 
Methyl ethyl ketone 46.25 parts 
Toluene 46.25 parts 
______________________________________ 
It is noted, however, that when the dyes were insoluble in the above 
composition, DMF, dioxane, chloroform, etc. were optionally used as the 
solvents. 
Next, a coating solution composed of the following ingredients was coated 
on one side of a substrate sheet formed of synthetic paper (Yupo FPG #150 
made by Oji Yuka Co., Ltd.) in an amount of 10.0 g/m.sup.2 on dry basis, 
which was then dried at 100.degree. C. for 30 minutes to obtain an 
imageable material. 
______________________________________ 
Polyester resin (Vylon 200 made 
11.5 parts 
by Toyobo Co., Ltd., Japan) 
Vinyl chloride/vinyl acetate 
5.0 parts 
copolymer (VYHH made by UCC9 
Amino modified silicone (KF-393 
1.2 parts 
made by the Shin-Etsu Chemical 
Co., Ltd., Japan) 
Epoxy modified silicone (X-22-343 
1.2 parts 
made by the Shin-Etsu Chemical 
Co., Ltd., Japan) 
Methyl ethyl ketone/toluene/cyclohexanone 
102.0 parts 
(4:4:2 in weight ratio) 
______________________________________ 
Each of the above heat transfer sheets according to the present invention 
and comparative examples was overlaid on the above imageable material with 
the dye-carrying and dye-receiving layers located in opposition to each 
other. Then, recording was carried out from the back side of the heat 
transfer sheet with a thermal head under the following conditions: at a 
voltage of 10 V applied to the head for a printing time of 4.0 msec. The 
results are summarized in Table A2. 
TABLE A2 
______________________________________ 
Density of Light Molecular 
Dyes Development Color 
Fastness Resistance 
Weight 
______________________________________ 
1 2.60 .DELTA. .largecircle. 
324 
2 1.95 .largecircle. 
.largecircle. 
393 
3 1.80 .largecircle. 
.largecircle. 
450 
4 2.13 .DELTA. .circleincircle. 
340 
5 2.50 .largecircle. 
.circleincircle. 
398 
6 2.13 .circleincircle. 
.largecircle. 
458 
7 2.04 .largecircle. 
.largecircle. 
365 
8 1.95 .largecircle. 
.largecircle. 
411 
9 1.75 .largecircle. 
.largecircle. 
355 
10 1.55 .largecircle. 
.largecircle. 
383 
11 1.53 .largecircle. 
.largecircle. 
377 
12 2.14 .largecircle. 
.circleincircle. 
432.5 
13 1.82 .largecircle. 
.largecircle. 
358.5 
14 2.17 .largecircle. 
.largecircle. 
358.5 
15 1.64 .largecircle. 
.largecircle. 
363 
16 1.81 .circleincircle. 
.largecircle. 
457 
17 1.96 .largecircle. 
.largecircle. 
394 
18 2.08 .largecircle. 
.largecircle. 
352 
19 1.63 .circleincircle. 
.largecircle. 
522 
20 1.92 .largecircle. 
.largecircle. 
372 
21 1.32 .largecircle. 
.largecircle. 
612.9 
22 1.72 .largecircle. 
.largecircle. 
425 
23 1.80 .circleincircle. 
.largecircle. 
433 
______________________________________ 
The hues of the dyes set forth in the above table are all red or purple. 
COMATIVE EXAMPLES A1 TO A4 
Example A1 was repeated, provided however that the dyes set forth in the 
following Table A3 were used in place of the dyes used therein. The 
results are shown in Table A3. 
TABLE A3 
______________________________________ 
Comparative Examples 
A1 A2 A3 A4 
______________________________________ 
Dyes AI AII AIII AIV 
Density of Developed Color 
1.76 0.66 1.03 0.40 
Fastness .DELTA. 
.DELTA. x .DELTA. 
Light resistance x x x x 
______________________________________ 
Dye AI = Disperse red 1 (with a molecular weight of 314) 
Dye AII = Disperse violet 1 (with a molecular weight of 238) 
Dye AIII = Disperse violet 4 (with a molecular weight of 252) 
Dye AIV = Disperse violet 28 (with a molecular weight of 305) 
It is noted that the density of developed color as referred to above was 
measured with Densitometer RD-918 made by Macbeth Co., Ltd., U.S.A. 
Storability was measured after the recorded images had been allowed to 
stand in an atmosphere of 50.degree. C. for an extended period of time, 
and was estimated as follows. 
Double circles indicate that the sharpness of the images underwent no 
change at all and that when the test pieces were rubbed with white paper, 
it was not altogether colored; circles indicate that the images lost 
sharpness with slight coloration of white paper; triangles indicate that 
the image lost sharpness with white paper being colored; and crosses 
indicate that the images became blurred with noticeable coloration of 
white paper. 
Light resistance was measured according to JIS L 0842 and estimated as 
follows. Double circles indicate the test pieces having an initial 
fastness of 3 or more, as determined according to the secondary exposure 
method provided by JIS L 0841; circles indicate the test pieces having a 
value something of the order of 3; and crosses indicate the test pieces 
having a value below 3. 
REFERENCE EXAMPLE B1 
Dissolved in toluene were 1.2 parts of the nitroso compound expressed by 
the following structural formula: 
##STR6## 
Then, a solution of 1.0 part of the dihydrobenzothiophene-1,1-dioxide 
derivative expressed by the following structural formula: 
##STR7## 
in toluene was added dropwise to the resulting solution under cooling 
conditions. After the completion of the dropwise addition, the reaction 
was continued for a further two hours. Afterwards, the precipitated 
crystals were filtrated for separation, and then recrystallized from ethyl 
acetate to obtain 0.7 parts of the dihydrobenzothiophene methyne dye 
expressed by the following structural formula: 
##STR8## 
The maximum absorption wavelength (ethyl acetate) of said dye was found at 
635 nm. 
REFERENCE EXAMPLES B2 TO B22 
With the nitroso compounds and dihydrobenzophenone-1,1-dioxide derivatives 
corresponding to Nos. 2 to 23 set forth in Table B1, Reference Example B1 
was repeated to obtain the azomethyne dyes set forth in Table B1. 
EXAMPLE B 
Prepared was an ink composition for the formation of a dye carrying layer, 
composed of the following ingredients, which was then coated a 
6-.mu.m-thick polyethylene terephthalate film subjected to heat-resistant 
treatment on its back side in a quantity of 1.0 g/m.sup.2 on dry basis. 
Subsequent drying gave the heat transfer sheets according to the present 
and comparative examples. 
______________________________________ 
Dyes set forth in Table B1 
3 parts 
Polyvinyl butyral resin 
4.5 parts 
Methyl ethyl ketone 46.25 parts 
Toluene 46.25 parts 
______________________________________ 
It is noted, however, that when the dyes were insoluble in the above 
composition, DMF, dioxane, chloroform, etc. were optionally used as the 
solvents. 
Next, a coating solution composed of the following ingredients was coated 
on one side of a substrate sheet formed of synthetic paper (Yupo FPG #150 
made by Oji Yuka Co , Ltd.) in an amount of 10.0 g/m.sup.2 on dry basis, 
which was then dried at 100.degree. C. for 30 minutes to obtain an 
imageable material. 
______________________________________ 
Polyester resin (Vylon 200 made 
11.5 parts 
by Toyobo Co., Ltd., Japan) 
Vinyl chloride/vinyl acetate 
5.0 parts 
copolymer (VYHH made by UCC9 
Amino modified silicone (KF-393 
1.2 parts 
made by the Shin-Etsu Chemical 
Co., Ltd., Japan) 
Epoxy modified silicone (X-22-343 
1.2 parts 
made by the Shin-Etsu Chemical 
Co., Ltd., Japan) 
Methyl ethyl ketone/toluene/cyclohexanone 
102.0 parts 
(4:4:2 in weight ratio) 
______________________________________ 
Each of the above heat transfer sheets according to the present invention 
was overlaid on the above imageable material with the dye-carrying and 
dye-receiving layers located in opposition to each other. Then, recording 
was carried out from the back side of the heat transfer sheet with a 
thermal head under the following conditions: at a voltage of 10 V applied 
to the head for a printing time of 4.0 msec. The results are summarized in 
Table B2. 
TABLE B2 
______________________________________ 
Density of 
Dyes Development Color 
Fastness Hue 
______________________________________ 
1 1.85 .largecircle. 
Indigo 
2 1.75 .circleincircle. 
Indigo 
3 1.80 .largecircle. 
Indigo 
4 1.60 .circleincircle. 
Indigo 
5 1.70 .circleincircle. 
Indigo 
6 1.75 .circleincircle. 
Indigo 
7 1.45 .circleincircle. 
Indigo 
8 1.80 .largecircle. 
Indigo 
9 1.70 .circleincircle. 
Indigo 
10 1.90 .largecircle. 
Indigo 
11 1.80 .circleincircle. 
Indigo 
12 1.65 .largecircle. 
Indigo 
13 2.10 .largecircle. 
Indigo 
14 1.80 .largecircle. 
Indigo 
15 2.05 .largecircle. 
Indigo 
16 1.80 .largecircle. 
Indigo 
17 1.60 .circleincircle. 
Indigo 
18 1.65 .largecircle. 
Indigo 
19 1.70 .largecircle. 
Indigo 
20 1.90 .circleincircle. 
Indigo 
21 1.55 .circleincircle. 
Indigo 
22 1.80 .largecircle. 
Indigo 
23 1.80 .circleincircle. 
Indigo 
______________________________________ 
COMATIVE EXAMPLES B1 to B4 
Example B1 was repeated, provided however that the dyes set forth in the 
following Table B3 were used in place of the dyes used therein. The 
results are shown in Table B3. 
TABLE B3 
______________________________________ 
Comp. Density of 
Ex. Developed Color Fastness Hue 
______________________________________ 
B1 0.99 x Indigo 
B2 1.16 .DELTA. Indigo 
B3 2.07 x Indigo 
B4 1.12 .DELTA. Indigo 
B5 1.02 x Purple 
______________________________________ 
B1: Disperse blue 14 
B2: Disperse blue 134 
B3: Solvent blue 63 
B4: Disperse blue 26 
B5: Disperse violet 4 
It is noted that the density of developed color as referred to above was 
measured with Densitometer RD-918 made by Macbeth Co., Ltd. U.S.A. 
Storability was measured after the recorded images had been allowed to 
stand in an atmosphere of 50.degree. C. for an extended period of time, 
and was estimated as follows. 
Double circles indicate that the sharpness of the images underwent no 
change at all and that when the test pieces were rubbed with white paper, 
it was not altogether colored; circles indicate that the images lost 
sharpness with slight coloration of white paper; triangles indicate that 
the images lost sharpness with white paper being colored; and crosses 
indicate that the images became blurred with noticeable coloration of 
white paper. 
Light resistance was measured according to JIS L 0842 and estimated as 
follows. Double circles indicate the test pieces having an initial 
fastness of 3 or more, as determined according to the secondary exposure 
method provided by JIS L 0841; circles indicate the test pieces having a 
value something of the order of 3; and crosses indicate the test pieces 
having a value below 3. 
INDUSTRIAL APPLICABILITY 
The heat transfer sheets of the present invention find wide applications as 
imaging materials in heat transfer systems with thermal heads.