[0001] The present invention relates to a thermosensitive transfer recording sheet (which
has the same meaning as "thermal transfer recording sheet") for use in thermosensitive
transfer recording, particularly in sublimation-type thermosensitive transfer recording,
and to an ink composition for use in producing the thermosensitive transfer recording
sheet.
[0002] In the field of facsimile, copying machines, or printers, studies are conventionally
being made of color recording techniques based on electrophotographic printing, ink-jet
printing and thermosensitive transfer printing.
[0003] Among these, the thermosensitive transfer recording technique is more advantageous
than the others because the maintenance and operation of the apparatus are easy and
the apparatus and its expendable supplies are inexpensive.
[0004] There are two systems in the thermosensitive transfer recording: fusion-type transfer
in which a transfer recording sheet composed of a base film and formed thereon a thermally
fusible ink layer is heated with a thermal head to fuse the ink and transfer the fused
ink to an image-receiving surface, thereby recording an image on the receiving surface;
and sublimation-type transfer in which a transfer recording sheet composed of a base
film and formed thereon a colorant layer containing a sublimable dyestuff is heated
with a thermal head to sublimate and/or heat-diffuse the dyestuff and transfer the
dyestuff from the transfer recording sheet to an image-receiving surface, thereby
recording an image on the receiving surface. The sublimation-type transfer is particularly
advantageous to full-color recording over the fusion-type in that gradation recording
is easy since the transferred amount of the dyestuff can be controlled by changing
the energy fed to the thermal head.
[0005] In the thermosensitive transfer recording of the sublimation type, sublimable dyestuffs
used in transfer recording sheets and in ink compositions for producing transfer recording
sheets greatly affect the speed of transfer recording and the quality and storage
stability of prints. Therefore, the sublimable dyestuffs are highly important and
need to satisfy the following requirements:
(1) the dyestuffs should readily sublimate and/or heat-diffuse under operation conditions
for the thermorecording head;
(2) they should not undergo thermal decomposition under operation conditions for the
thermorecording head;
(3) they should possess tints favorable for color reproduction;
(4) they should have high molecular absorption coefficients;
(5) they should be stable to heat, light, moisture and chemicals;
(6) they should be able to be easily synthesized;
(7) they should have good suitability for use in preparing inks; and
(8) they should have no health and safety problems.
[0006] However, a dyestuff which meets all the above requirements has not been found so
far. Magenta dyestuffs, in particular, have various defects and satisfactory one has
not yet been developed.
[0007] Conventionally known magenta dyestuffs having suitability to thermosensitive transfer
recording of the sublimation type are disclosed, for example, in JP-A-60- 31563, JP-A-59-78896,
and JP-A-63-203393. (The term "JP-A" as used herein means an "unexamined published
Japanese patent application".) These magenta dyestuffs are tricyanovinyl dyestuffs
having the same basic structure as that of the dyestuff employed in the present invention.
However, even the dyestuffs whose structural formulae are specified in those references
have had still insufficient performances, particularly in light resistance.
[0008] An object of the present invention is to provide a thermosensitive transfer recording
sheet employing a magenta dyestuff which satisfies all of the above-listed requirements.
[0009] Another object of the present invention is to provide an ink composition for use
in manufacturing the thermosensitive transfer recording sheet.
[0010] In one aspect of the present invention, a thermosensitive transfer recording sheet
is provided which comprises a substrate having thereon a colorant layer, the colorant
layer comprising a binder and a dyestuff represented by the following general formula
(I):

wherein X and Y independently represent a hydrogen atom, a lower alkyl group, or a
lower alkoxyl group, provided that either of X and Y represents a lower alkoxyl group;
and R¹ and R² independently represent a hydrogen atom, a substituted or unsubstituted
alkyl group, a cycloalkyl group, an allyl group, or a substituted or unsubstituted
phenyl group, provided that in the case where both of X and Y represent a lower alkoxyl
group, R¹ represents a hydrogen atom.
[0011] In another aspect of the present invention, an ink composition for use in manufacturing
the above thermosensitive transfer recording sheet is provided which ink composition
comprises the tricyanovinyl dyestuff represented by general formula (I), a binder
resin, and a medium.
[0012] The dyestuff employed in the present invention is represented by general formula
(I) given above, and includes dyestuffs represented by general formula (II) given
below and dyestuffs represented by general formula (III) given next.

(In general formula (II), R³ and R⁴ independently represent a hydrogen atom, a substituted
or unsubstituted alkyl group, a cycloalkyl group, allyl group, or a substituted or
unsubstituted phenyl group; and X¹ and Y¹ independently represent a hydrogen atom,
a lower alkyl group, or a lower alkoxyl group, provided that either of X¹ and Y¹ represents
a lower alkoxyl group and the remaining one represents another group.)

(In general formula (III), R⁵ represents a substituted or unsubstituted alkyl group,
a cycloalkyl group, allyl group, or a substituted or unsubstituted phenyl group, and
X² and Y² independently represent a lower alkoxyl group.)
[0013] Specific examples of the substituted or unsubstituted alkyl group, cycloalkyl group,
allyl group, or substituted or unsubstituted phenyl group represented by R¹, R², R³,
R⁴, and R⁵ in general formulae (I), (II), and (III) given above are as follows.
[0014] Examples of the unsubstituted alkyl group include straight-chain or branched alkyl
groups having 1 to 8 carbon atoms. Examples of the substituted alkyl group include
hydroxy-substituted alkyl groups such as 2-hydroxyethyl group, 3-hydroxypropyl group,
4-hydroxybutyl group, and 2-hydroxypropyl group; carboxy-substituted alkyl groups
such as carboxymethyl group, 2-carboxyethyl group, and 3-carboxypropyl group; cyano-substituted
alkyl groups such as 2-cyanoethyl group and cyanomethyl group; amino-substituted alkyl
groups such as 2-aminoethyl group; halogen-substituted alkyl groups such as 2-chloroethyl
group, 3-chloropropyl group, 2-chloropropyl group, and 2,2,2-trifluoroethyl group;
alkyl groups substituted with phenyl group which may further be substituted, such
as benzyl group, p-chlorobenzyl group, and 2-phenylethyl group; alkoxy-substituted
alkyl groups such as 2-methoxyethyl group, 2-ethoxyethyl group, 2-n-propoxyethyl group,
2-isopropoxyethyl group, 2-n-butoxyethyl group, 2-isobutoxyethyl group, 2-(2-ethylhexyloxy)ethyl
group, 3-methoxypropyl group, 4-methoxybutyl group, and 2-methoxypropyl group; alkoxyalkoxy-substituted
alkyl groups such as 2-(2-methoxyethoxy)ethyl group, 2-(2-ethoxyethoxy)ethyl group,
2-(2-n-propoxyethoxy)ethyl group, 2-(2-isopropoxyethoxy)ethyl group, 2-(2-n-butoxyethoxy)ethyl
group, 2-(2-isobutoxyethoxy)ethyl group, and 2-(2-(2-ethylhexyloxy)ethoxy)ethyl group;
allyloxyethyl group; aryloxyalkyl groups such as 2-phenoxyethyl group; aralkyloxyalkyl
groups such as 2-benzyloxyethyl group; acyloxy-substituted alkyl groups such as 2-acetyloxyethyl
group, 2-propionyloxyethyl group, 2-n-butyryloxyethyl group, 2-isobutyryloxyethyl
group, and 2-trifluoroacetyloxyethyl group; alkyl groups substituted with a substituted
or unsubstituted alkoxycarbonyl group, such as methoxycarbonylmethyl group, ethoxycarbonylmethyl
group, n-propoxycarbonylmethyl group, isopropoxycarbonylmethyl group, n-butoxycarbonylmethyl
group, isobutoxycarbonylmethyl group, 2-ethylhexyloxycarbonylmethyl group, benzyloxycarbonylmethyl
group, furfuryloxycarbonylmethyl group, tetrahydrofurfuryloxycarbonylmethyl group,
2-methoxycarbonylethyl group, 2-ethoxycarbonylethyl group, 2-n-propoxycarbonylethyl
group, 2-isopropoxycarbonylethyl group, 2-n-butoxycarbonylethyl group, 2-isobutoxycarbonylethyl
group, 2-(2-ethylhexyloxycarbonyl)ethyl group, 2-benzyloxycarbonylethyl group, and
2-furfurylcarbonylethyl group; alkyl groups substituted with a substituted or unsubstituted
alkoxycarbonyloxy group, such as 2-methoxycarbonyloxyethyl group, 2-ethoxycarbonyloxyethyl
group, 2-n-propoxycarbonyloxyethyl group, 2-isopropoxycarbonyloxyethyl group, 2-n-butoxycarbonyloxyethyl
group, 2-isobutoxycarbonyloxyethyl group, 2-(2-ethylhexyloxycarbonyloxy)ethyl group,
2-benzyloxycarbonyloxyethyl group, and 2-furfuryloxycarbonyloxyethyl group; and heterocyclic
ring-substituted alkyl groups such as furfuryl group and tetrahydrofurfuryl group.
[0015] Examples of the cycloalkyl group include the cyclopentyl and cyclohexyl group.
[0016] Examples of the substituted phenyl group include phenyl group substituted with a
straight-chain or branched alkyl group having 1 to 8 carbon atoms; phenyl group substituted
with a straight-chain or branched alkoxyl group having 1 to 4 carbon atoms; phenyl
group substituted with a halogen atom such as fluorine atom, chlorine atom, or bromine
atom; and phenyl group substituted with nitro group, cyano group, trifluoromethyl
group.
[0017] Particularly preferred examples of the groups of R¹, R², R³, R⁴, and R⁵ include hydrogen
atom, straight-chain or branched alkyl groups having 1 to 8 carbon atoms, and alkoxyalkyl
groups having 3 to 8 carbon atoms, provided that R⁵ preferably represents groups other
than a hydrogen atom.
[0018] Among the dyestuffs represented by the above-described general formula (I), those
represented by the general formula (I) in which either of R¹ and R² is hydrogen atom
are particularly preferred from the standpoints of the tints of dyestuffs and the
light resistance of prints obtained therefrom, etc.
[0019] Examples of the lower alkyl group represented by X, Y, X¹, and Y¹ include straight-chain
or branched alkyl groups having 1 to 4 carbon atoms. Examples of the lower alkoxyl
group represented by X, Y, X¹, Y¹, X², and Y² include straight-chain and branched
alkoxyl groups, having 1 to 4 carbon atoms.
[0020] In the above general formulae (I) and (II), either of X and Y and either of X¹ and
Y¹ represent a lower alkoxyl group, and the remaining ones preferably represent a
lower alkyl group or a lower alkoxyl group. More preferably, both X and Y and both
X¹ and Y¹ are a lower alkoxyl group.
[0021] Therefore, the most preferred of the dyestuffs of general formula (I) which can be
used in the present invention are dyestuffs represented by general formula (III) given
hereinabove, from the standpoints of the tints of dyestuffs, and the light resistance
of prints obtained therefrom.
[0023] The tricyanovinyl dyestuff of general formula (I) to be employed in the present invention
can be produced according to conventionally known methods. For example, it may be
obtained by reacting tetracyanoethylene with a compound represented by the following
general formula (IV):

(wherein R¹, R², X and Y have the same meanings as in general formula (I) given hereinabove)
in an organic solvent.
[0024] In manufacturing the thermosensitive transfer recording sheet of the present invention,
methods for forming the colorant layer containing the dyestuff of general formula
(I) are not particularly limited. Generally, the dyestuff is dissolved or finely dispersed,
along with a binder, in a medium to prepare an ink, which is then applied on a substrate
and dried, thereby forming a colorant layer on the substrate.
[0025] The binder for use in the ink preparation should have good heat resistance for the
purpose of preventing the heat fusion-adhesion of the binder onto an image-receiving
surface at the time of transfer recording. Especially preferred binders are those
having softening points and/or heat deformation temperatures of 100°C or more.
[0026] Examples of the binder include water soluble resins such as cellulose resins, acrylic
acid-based resins, starches, polyvinyl alcohols, and polyethylene oxides, organic
solvent-soluble resins such as acrylic resins, methacrylic resins, polystyrenes, polycarbonates,
polysulfones, AS resins, polyethersulfones, epoxy resins, polyvinyl acetals, phenoxy
resins, polyvinyl butyrals, polyesters, ethyl cellulose, and acetyl celluloses.
[0027] According to the medium to be used for the ink preparation, a binder soluble or uniformly
dispersible into the medium may be suitably selected from the above resins.
[0028] The amount of such a binder resin used is generally in the range of from 1 to 40%
by weight, preferably from 5 to 30% by weight, based on the total amount of the ink
composition.
[0029] Besides water, examples of the medium for use in ink preparation are organic solvents
which include alcohols such as methyl alcohol, n-propyl alcohol, isopropyl alcohol,
n-butyl alcohol, and isobutyl alcohol, Cellosolves such as methyl Cellosolve, ethyl
Cellosolve and butyl Cellosolve, aromatics such as toluene, xylene, and chlorobenzene,
esters such as ethyl acetate and butyl acetate, ketones such as acetone, methyl ethyl
ketone, methyl isobutyl ketone, and cyclohexanone, chlorine-containing solvents such
as methylene chloride, chloroform, and trichloroethylene, ethers such as tetrahydrofuran
and dioxane, N,N-dimethylformamide, and N-methylpyrrolidone. These may be used alone
or as a mixture of two or more thereof.
[0030] In addition to the ingredients described above, organic or inorganic non-sublimable
fine particles, a dispersant, an anti-static agent, an anti-blocking agent, an anti-foaming
agent, an antioxidant, a viscosity modifier and a release agent may be incorporated
into the ink if required and necessary.
[0031] Preferred examples of the substrate on which the ink is to be applied for preparing
the thermosensitive transfer recording sheet include a sheet of paper such as capacitor
paper and glassine paper, and a film of heat-resistant plastics such as polyesters,
polycarbonates, polyamides, polyimides and polyaramides. The thickness of such a substrate
is generally in the range of from 1 to 50 µm.
[0032] Among the above substrates, polyethylene terephthalate film is particularly advantageous
because of its high mechanical strength, good solvent resistance and low cost. In
some cases, however, even the polyethylene terephthalate film is not always satisfactory
in heat resistance, resulting in insufficient running of the thermal head. Therefore,
a heat-resistant resin layer containing a surface-active agent or lubricating heat-resistant
particles may be provided on the side opposite to the colorant layer, thus providing
improved thermal head-running properties.
[0033] Coating of the ink on the substrate can be accomplished by use of a reverse-roll
coater, a gravure coater, a rod coater, or an air-doctor coater . The coating may
be performed so as to give an ink coating layer thickness in the range of from 0.1
to 5 µm on a dry basis. (Reference may be made to Yuji Harasaki,
Coating Techniques, published in 1979 by Maki Shoten, Japan.)
[0034] On the other hand, the ink composition for use in producing the thermosensitive transfer
recording sheet, which ink composition is provided according to another aspect of
the present invention, comprises a tricyanovinyl dyestuff represented by the above-described
general formula (I), a binder resin, and a medium that may be an organic solvent and/or
water.
[0035] The tricyanovinyl dyestuff is as described in detail hereinabove.
[0036] The binder to be used is suitably selected from the above-mentioned resins which
are soluble in water or organic solvents, according to the medium to be used.
[0037] Of the above-mentioned resins, those having heat deformation temperatures and/or
softening points of 100°C or more are particularly preferred. As the organic solvent,
any of the above-mentioned solvents may be used. In addition to these, non-sublimable
fine particles and additives such as a dispersant, anti-static agent, anti-blocking
agent, anti-foaming agent, antioxidant, viscosity modifier, and release agent may
be used as mentioned hereinabove.
[0038] The amount of the dyestuff of general formula (I) contained in the ink composition
of the present invention is generally from 1 to 30% by weight, preferably from 3 to
20% by weight, based on the total amount of the ink composition.
[0039] The ink composition of the present invention may be prepared as follows. In one method,
a liquid mixture composed of the dyestuff, a medium, and a resin is placed in a proper
vessel equipped with a stirrer and the dyestuff is dissolved in the medium, with heating
if required and with addition of additives if necessary, thereby to prepare an ink
composition. Alternatively, the liquid mixture may be treated with a paint conditioner,
a ball mill or a sand grinding mill to uniformly disperse the dyestuff into the medium,
with addition of additives if necessary, thereby to prepare an ink composition.
[0040] Because the tricyanovinyl dyestuff of general formula (I) which is employed in the
thermosensitive transfer recording sheet of the present invention possesses a vivid
magenta color, it is suited for use in combining it with suitable cyan color dyestuffs
and suitable yellow color dyestuffs to attain full-color recording with good color
reproduction. Further, because the dyestuff of general formula (I) readily sublimates
and/or heat-diffuses and has a high molecular absorption coefficient, recorded images
having high color densities can be obtained at a high speed without a heavy load on
the thermal head. The dyestuff also has good stability to heat, light, moisture and
chemicals, and, hence, it never undergoes thermal decomposition during transfer recording
and the permanence properties of the resulting recorded images are also good, particularly
in light resistance. In addition, because the dyestuff of general formula (I) has
good solubility in organic solvents and good dispersibility into water, it is easy
to prepare an ink composition in which the dyestuff has been uniformly dissolved or
dispersed at a high concentration, and by use of such an ink composition, a thermosensitive
transfer recording sheet having a colorant coating layer in which the dyestuff is
distributed uniformly at a high concentration can be obtained. Therefore, by use of
such a thermosensitive transfer recording sheet, printed images having good homogeneity
and color density can be obtained.
[0041] In practicing transfer recording using the thermosensitive transfer recording sheet
of the present invention, infrared rays or laser light as well as a thermal head may
be utilized as a heating means.
[0042] It is also possible to coat the ink composition of the present invention on a film
that is heated by application of electric current and to use the resulting sheet as
an electrically-heated thermosensitive sheet.
[0043] The present invention will be explained below in more detail by reference to the
following examples, which should not be construed to be limiting the scope of the
invention. In these examples, all parts are by weight.
EXAMPLE 1
(a) Preparation of Ink
[0044]

[0045] A mixture having the above composition was treated with a paint conditioner for 10
minutes, thereby preparing an ink.
(b) Preparation of Transfer Recording Sheet
[0046] The above-obtained ink was coated with a wire bar on a polyethylene terephthalate
film (6 µm thick) whose back side had undergone treatment for imparting heat resistance
and lubricating properties. The coating was then dried (coating layer dry thickness,
about 1 µm) to obtain a transfer recording sheet.
[0047] The above treatment for imparting heat resistance and lubricating properties to the
polyethylene terephthalate film was conducted by coating the film with a composition
consisting of 8 parts of a polycarbonate resin having the repeating unit of the formula

1 part of a phosphoric ester-type surfactant (trade name, "Plysurf A-208B"; manufactured
by Dai-ichi Kogyo Seiyaku Co., Ltd., Japan), and 91 parts of toluene, and drying the
coating (coating layer dry thickness, about 0.5 µm).
(c) Preparation of Image-Receiving Sheet
[0048] A composition consisting of 10 parts of a saturated polyester resin (trade name,
"TP-220"; manufactured by Nihon Gosei Co., Ltd., Japan), 0.5 part of an amino-modified
silicone (trade name, "KF 393"; manufactured by Shin-Etsu Chemical Co., Ltd., Japan),
15 parts of methyl ethyl ketone, and 15 parts of xylene was coated on a synthetic
paper (trade name, "Yupo FPG 150"; manufactured by Oji-Yuka Co., Ltd., Japan) with
a wire bar, and then dried (coating layer dry thickness, about 5 µm). The coated synthetic
paper was further heat-treated in an oven at 100°C for 30 minutes to prepare an image-receiving
sheet.
(d) Transfer Recording
[0049] The transfer recording sheet prepared in (b) above was superimposed on the image-receiving
sheet in such a manner that the ink coating side of the transfer recording sheet was
in contact with the receiving sheet, and recording was conducted by use of a thermal
head under the conditions shown below. As a result, a recorded image which was of
a vivid magenta color and had a uniform color density as shown in Table 3 could be
obtained.

[0050] Color density was measured with densitometer TR-927 manufactured by Macbeth Corporation,
U.S.A.
[0051] The light resistance of the recorded image obtained was examined by means of a carbon
arc fade meter (manufactured by Suga Testing Machine Co., Ltd., Japan) at a black
panel temperature of 63±2°C. The degree of discoloration through a 40-hour irradiation
in the light resistance test was shown in Table 3 in terms of
ΔE
* value. Further, the transfer recording sheet and the print obtained were found to
be stable to heat and moisture and show good storage stability in the dark.
[0052] The dyestuff used in this example had been synthesized by reacting 3-methoxy-N,N-di-isobutylaniline
with tetracyanoethylene in N,N-dimethylformamide. Its maximum absorption wavelength
in acetone was as shown in Table 3 and its melting point was 116-117°C.
EXAMPLES 2 TO 10
[0053] Inks and transfer recording sheets were prepared and transfer recording was conducted
in the same manner as in Example 1 except that in place of the dyestuff used in Example
1, the dyestuffs shown in Table 3 were used. As a result, recorded images which were
of a vivid magenta color and respectively had color densities shown in Table 3 could
be obtained, and the light resistance of each recorded image was good as shown in
Table 3.
EXAMPLE 11
[0054] An ink and a transfer recording sheet were prepared and transfer recording was conducted
in the same manner as in Example 1 except that dyestuff No. 4 in Table 2 given hereinabove
was used in place of the dyestuff used in Example 1. The results obtained are shown
in Table 3.
[0055] The dyestuff used in this example had been synthesized by reacting 2,5-dimethoxy-N-isobutylaniline
with tetracyanoethylene in N,N-dimethylformamide. Its maximum absorption wavelength
in acetone was as shown in Table 3 and its melting point was 181-182°C.
EXAMPLES 12 TO 20
[0056] Inks and transfer recording sheets were prepared and transfer recording was conducted
in the same manner as in Example 1 except that in place of the dyestuff used in Example
1, the dyestuffs shown in Table 3 were used. As a result, recorded images which were
of a vivid magenta color and respectively had color densities shown in Table 3 could
be obtained, and the light resistance of each recorded image was good as shown in
Table 3.
COMPARATIVE EXAMPLES 1 TO 8
[0057] Inks and transfer recording sheets were prepared and transfer recording was conducted
in the same manner as in Example 1 except that the dyestuffs shown below were used
in place of the dyestuff used in Example 1. The results obtained are summarized in
Table 3.
Dyestuffs used in Comparative Examples
Comparative Example 1 (Example 1 of JP-A-59-78896)
[0058]

Comparative Example 2 (Example 1 of JP-A-60-31563)
[0059]

Comparative Example 3 (Reference Example 1 of JP-A-63-203393)
[0060]

Comparative Example 4
[0061]

Comparative Example 5
[0062]

Comparative Example 6
[0063]

Comparative Example 7
[0064]

Comparative Example 8
EXAMPLE 21
[0066] A transfer recording sheet was prepared and transfer recording was conducted in the
same manner as in Example 1 except that an ink prepared according to the following
formulation was used in place of the ink used in Example 1. As a result, a recorded
image which was of a vivid magenta color and had a uniform color density of 2.15 could
be obtained. Further, the recorded image was subjected to a light resistance test
and the transfer recording sheet and recorded image were subjected to a storage stability
test in the dark. As a result, good results were obtained in each test.

EXAMPLE 22
[0067] A transfer recording sheet was prepared and transfer recording was conducted in the
same manner as in Example 21 except that in place of the dyestuff used in Example
21, the same dyestuff as that used in Example 11, i.e., dyestuff No. 4 in Table 2,
was used. As a result, a recorded image which was of a vivid magenta color and had
a uniform color density of 2.15 could be obtained. Further, the recorded image was
subjected to a light resistance test and the transfer recording sheet and recorded
image were subjected to a storage stability test in the dark. As a result, good results
were obtained in each test.
1. A thermal transfer recording sheet comprising a substrate having thereon a colorant
layer, said colorant layer comprising a binder and a dyestuff represented by the following
general formula (I):

wherein X and Y independently represent a hydrogen atom, a lower alkyl group, or
a lower alkoxyl group, provided that either of X and Y represents a lower alkoxyl
group; and R¹ and R² independently represent a hydrogen atom, a substituted or unsubstituted
alkyl group, a cycloalkyl group, an allyl group, or a substituted or unsubstituted
phenyl group, provided that in the case where both of X and Y represent a lower alkoxyl
group, R¹ represents a hydrogen atom.
2. A sheet as claimed in claim 1, wherein said dyestuff is represented by the following
general formula (II)

wherein R³ and R⁴ independently represent a hydrogen atom, a substituted or unsubstituted
alkyl group, a cycloalkyl group, allyl group, or a substituted or unsubstituted phenyl
group; and X¹ and Y¹ independently represent a hydrogen atom, a lower alkyl group,
or a lower alkoxyl group, provided that either of X¹ and Y¹ represents a lower alkoxyl
group and the remaining one represents another group.
3. A sheet as claimed in claim 1, wherein said dyestuff is represented by general formula
(I) in which R¹ represents a hydrogen atom.
4. A sheet as claimed in claim 1, wherein said dyestuff is represented by general formula
(I) in which one of X and Y is a lower alkoxyl group and the other is a lower alkoxyl
group or a lower alkyl group.
5. A sheet as claimed in claim 1, wherein said dyestuff is represented by the following
general formula (III)

wherein R⁵ represents a substituted or unsubstituted alkyl group, a cycloalkyl group,
allyl group, or a substituted or unsubstituted phenyl group, and X² and Y² independently
represent a lower alkoxyl group.
6. A sheet as claimed in claim 1, wherein said dyestuff is represented by general formula
(I) in which R¹ and R² independently represent a hydrogen atom; a straight-chain or
branched alkyl group which has 1 to 8 carbon atoms and which may be substituted with
a substituent selected from the group consisting of phenyl group which may be substituted
with hydroxyl group, carboxyl group, cyano group, amino group, or a halogen atom,
an alkoxyl group, an alkoxyalkoxyl group, allyloxy group, an aryloxy group, an aralkyloxy
group, an acyl group, a substituted or unsubstituted alkoxycarbonyl group, a substituted
or unsubstituted alkoxycarbonyloxy group, and a heterocyclic group; cyclohexyl or
cyclopentyl group; allyl group; or phenyl group which may be substituted with a substituent
selected from the group consisting of a straight-chain or branched alkyl group having
1 to 8 carbon atoms, a straight-chain or branched alkoxyl group having 1 to 4 carbon
atoms, a halogen atom, nitro group, cyano group, and trifluoromethyl group.
7. A sheet as claimed in claim 1, wherein said dyestuff is represented by general formula
(I) in which R¹ and R² independently represent a hydrogen atom, a straight-chain or
branched alkyl group having 1 to 8 carbon atoms, or an alkoxyalkyl group having 3
to 8 carbon atoms.
8. A sheet as claimed in claim 1, wherein said binder is a resin selected from the group
consisting of water-soluble resins which are cellulose resins, acrylic acid-based
resins, polyvinyl alcohols, polyethylene oxides, and starches and organic solvent-soluble
resins which are acrylic resins, methacrylic resins, polystyrenes, polycarbonates,
polysulfones, AS resins, polyethersulfones, epoxy resins, polyvinyl acetals, phenoxy
resins, polyvinyl butyrals, polyesters, ethyl celluloses, and acetyl celluloses.
9. A sheet as claimed in claim 1, wherein said substrate is a sheet of paper selected
from capacitor paper and glassine paper or a film of a heat-resistant plastic selected
from the group consisting of polyesters, polycarbonates, polyamides, polyimides, and
polyaramids, and has a thickness in the range of from 1 to 50 µm.
10. A sheet as claimed in claim 1, wherein said substrate is a polyethylene terephthalate
film.
11. A sheet as claimed in claim 1, wherein said substrate has a heat-resistant resin layer
on the side thereof opposite to the colorant layer.
12. An ink composition for use in producing a thermal transfer recording sheet, said ink
composition comprising a dyestuff represented by the following general formula (I),
a binder resin, and a medium:

wherein X and Y independently represent a hydrogen atom, a lower alkyl group, or
a lower alkoxyl group, provided that either of X and Y represents a lower alkoxyl
group; and R¹ and R² independently represent a hydrogen atom, a substituted or unsubstituted
alkyl group, a cycloalkyl group, an allyl group, or a substituted or unsubstituted
phenyl group, provided that in the case where both of X and Y represent a lower alkoxyl
group, R¹ represents a hydrogen atom.
13. An ink composition as claimed in claim 12, wherein said medium is water, an organic
solvent, or a mixture thereof.
14. An ink composition as claimed in claim 13, wherein said organic solvent is a single
compound or a mixture of two or more compounds, said compound and compounds being
selected from the group consisting of alcohols which are methyl alcohol, n-propyl
alcohol, isopropyl alcohol, n-butyl alcohol, and isobutyl alcohol, Cellosolves which
are methyl Cellosolve, ethyl Cellosolve and butyl Cellosolve, aromatics which are
toluene, xylene, and chlorobenzene, esters which are ethyl acetate and butyl acetate,
ketones which are acetone, methyl ethyl ketone, methyl isobutyl ketone, and cyclohexanone,
chlorine-containing solvents which are methylene chloride, chloroform, and trichloroethylene,
ethers which are tetrahydrofuran and dioxane, N,N-dimethylformamide, and N-methylpyrrolidone.
15. An ink composition as claimed in claim 12, wherein said binder is a resin selected
from the group consisting of water-soluble resins which are cellulose resins, acrylic
acid-based resins, polyvinyl alcohols, polyethylene oxides, and starches and organic
solvent-soluble resins which are acrylic resins, methacrylic resins, polystyrenes,
polycarbonates, polysulfones, AS resins, polyethersulfones, epoxy resins, polyvinyl
acetals, phenoxy resins, polyvinyl butyrals, polyesters, ethyl celluloses, and acetyl
celluloses.
16. An ink composition as claimed in claim 12, wherein the content of said binder is in
the range of from 1 to 40% by weight based on the total amount of the ink composition.
17. An ink composition as claimed in claim 12, wherein the content of said dyestuff of
general formula (I) is in the range of from 1 to 30% by weight based on the total
amount of the ink composition.
18. An ink composition as claimed in claim 12, which further contains organic or inorganic
non-sublimable fine particles, a dispersant, an anti-static agent, an anti-blocking
agent, an anti-foaming agent, an antioxidant, a viscosity modifier, and a release
agent.