[0001] The present invention relates to an improved image-receiving sheet for thermal transfer
printing in which a thermally sublimable dye is used. More particularly, the present
invention relates to an improved image-receiving sheet for thermal transfer printing
which has an improved intermediate layer containing fine particles of thermosetting
resin and fine particles of polyolefin resin and which exhibits an improved recording
sensitivity and provides excellent printed images with no missing dot.
[0002] Thermal printing systems in which printed images are obtained upon reception of input
signals are made up of a relatively simple apparatus and are inexpensive and low in
noises. In view of this, they have increasing utility in various fields such as facsimiles,
terminal printers for electronic computers, printers for measuring instruments, video
printers, and the like.
[0003] As the recording medium to be used in these thermal printing systems, there has been
generally used a so-called spontaneous developing heat sensitive paper having a recording
layer capable of causing a physical or chemical change upon application of heat to
provide color development. However, the spontaneous developing heat sensitive paper
of the color developing type has disadvantages that it is liable to undesirably cause
color development during the fabrication process or during storage; and the images
printed on the paper are poor in storage stability and they are apt to fade on contact
with organic solvents or chemicals.
[0004] In order to improve the above situation, there has been proposed a printing system
wherein a recording medium in which a coloring material such as a dye or colorant
is utilized is used in stead of the foregoing spontaneous developing heat sensitive
paper, for example, as disclosed in JP-A-51(1976)-15446. In the printing system disclosed
in this publication, a sheet comprising a substrate such as a paper or polymer film
and a colorant layer containing the coloring material (which is in the solid or semi-solid
state at ordinally temperature) being formed on the substrate is firstly provided,
and this sheet and a recording sheet are superposed so as to make the colorant layer
contacted with the recording sheet and heated from the non-faced side of the former
sheet by a heating means such as a thermal head to transfer the coloring material
in the colorant layer on the recording sheet upon the electric signals provided by
the heating means, whereby images corresponding to image information are recorded
on the recording sheet.
[0005] In the above printing system, the coloring material in the colorant layer is caused
to melt, evaporate or sublimate by application of heat and transferred on the recording
sheet, thereby forming a record image by adhesion, adsorption or reception of the
coloring material on the recording sheet. In view of this, this printing system has
been evaluated as being advantageous with a view point that there can be used an ordinary
paper (wood free paper) as the recording sheet. Further, as for this printing system,
when a sublimable dye is used as the coloring material, there can be obtained a printed
image excelling in tone reproduction. In order to develop this advantage in the full-color
printing, various studies have been made.
[0006] However, there are disadvantages for the foregoing printing system wherein an ordinary
paper (wood free paper) is used as the recording sheet that sufficient dye-reception
hardly occur to cause such printed images which are poor in color density (optical
density) and those image will be markedly discolored as time lapses.
[0007] To avoid this, there has been proposed the use of an image-receiving sheet having
an image-receiving layer containing a thermosetting resin as the main constituent
which is formed on a substrate as disclosed in JP-A-57(1982)-107885 or US-A-3,601,484.
[0008] The use of this image-receiving sheet is effective in somewhat improving the recording
sensitivity and storage-ability. However, there still remains a problem that when
an ordinary paper (wood free paper) is used as the substrate, it is difficult to provide
a desirable image-receiving layer containing a thermosetting resin as the main constituent
of uniform thickness with the paper and thus, the resulting image-receiving sheet
unavoidably becomes such that is poor in the recording sensitivity and provides undesirable
images inferior in the quality.
[0009] In order to eliminate the above problem, there has been proposed another image-receiving
sheet having an intermediate layer comprising a thermosetting resin which is disposed
between a substrate and an image-receiving layer as disclosed in JP-A-60(1985)-236794
or JP-A-61(1986)-144394.
[0010] This image-receiving sheet is so designed that its image-receiving layer can be effectively
contacted with the dye layer of the dye transfer sheet to prevent occurrence of negative
phenomena such as air-gap upon printing, and it exhibits an improved recording sensitivity
and provides improved record images.
[0011] In addition, there has been proposed a further image-receiving sheet having an intermediate
layer containing fine particles of a specific polyolefin resin which is disposed between
a substrate and an image-receiving layer by, among others, four of the coinventors
of the present invention as disclosed in US-A-4,837,200. The use of this image-receiving
sheet is effective especially in obtaining desirable recorded images free of missing
transfer portion.
[0012] The present inventors have made various studies on the foregoing image-receiving
sheets having an intermediate layer in order to make further improvements therefor.
[0013] As a result, it has been found that any of said image-receiving sheets is still accompanied
with a disadvantageous point that it is necessary to use a sufficiently white sheet
as the substrate and otherwise, it is extremely difficult to obtain a sufficiently
white image-receiving sheet which is practically acceptable as a recording sheet,
since the intermediate layer is insufficient in the covering power particularly when
it is formed by the use of fine particles of a single resin, and because of this,
there is a limit for the kind of the substrate to be used in any of the foregoing
cases.
[0014] The present inventors have tried to incorporate into the intermediate layer an inorganic
pigment such as calcium carbonate, talc, kaolin, titanium oxide, aluminum hydroxide,
zinc oxide, etc., or an organic pigment, wherein an ordinary paper was used as the
substrate, in order to eliminate the foregoing disadvantageous point. As a result,
it has been found that the resulting image-receiving sheet rather becomes accompanied
with a further disadvantage of causing reduction in the optical density and also in
the quality of images as printed and this situation becomes significant as the amount
of such pigment to be incorporated in the intermediate layer increases.
[0015] Standing on the above findings, the present inventors have made further studies in
order to provide a desirably improved image-receiving sheet comprising a substrate,
an intermediate layer and an image-receiving layer for thermal transfer printing for
use in the printing system wherein a coloring material, particularly a sublimable
dye is thermally transferred.
[0016] As a result, it has been found that when the intermediate layer is formed by using
fine particles of a specific thermosetting resin and fine particles of a polyolefinic
resin in combination, there can be obtained a desirable image-receiving sheet having
an improved opacity for the intermediate layer. And as a result of evaluating the
image-receiving sheet thus obtained with various items required for an image-receiving
sheet to be practically applicable, it has been found that it is extremely high in
the recording sensitivity and provides high quality record images excelling in resolution,
clearness and optical density and which are not accompanied with any missing dots.
It has been also found that the foregoing image-receiving sheet is satisfactory in
whiteness and opacity even in the case where an ordinary paper (wood free paper) is
used as the substrate and it can be mass-produced with a reduced cost.
[0017] The present invention has been accomplished based on the above findings.
[0018] An object of the present invention is to provide an improved image-receiving sheet
for thermal transfer printing which is free of the foregoing problems which are found
on the known image-receiving sheet and which enables one to form beautiful record
images of high optical density.
[0019] Another object of the present invention is to provide an improved image receiving
sheet which is satisfactory in whiteness and opacity even upon using an ordinary paper
(wood free paper) as the substrate.
[0020] A further object of the present invention is to provide an improved image-receiving
sheet which exhibits an excellent recording sensitivity and provides high quality
record images excelling in resolution and clearness which are not accompanied with
any missing dots.
[0021] The present invention attains the above objects and it contemplates to provide an
improved image-receiving sheet for thermal transfer printing for use in the printing
system wherein a sublimable dye is thermally transferred.
[0022] Accordingly the present invention provides an image-receiving sheet for thermal transfer
printing comprising a substrate, an intermediate layer and an image-receiving layer,
said intermediate layer and said image-receiving layer being disposed in this order
on said substrate, which is characterized in that said intermediate layer comprises
a layer containing (a) fine particles of one or more kinds of thermosetting resins
and/or (b) fine particles of one or more kinds of other resins than said thermosetting
resins, having a softening point of higher than 150°C and (c) fine particles of a
polyolefin resin as the main constituents.
[0023] The image-receiving sheet of the present invention comprises a substrate, an intermediate
layer and an image-receiving layer, said intermediate layer and said image-receiving
layer being disposed in this order on said substrate, and said intermediate layer
containing fine particles of a thermosetting resin and/or fine particles of a resin
having a softening point of more than 150°C and fine particles of a polyolefin resin.
[0024] The image-receiving sheet of the present invention is characterized by having a specific
intermediate layer containing (a) fine particles of a thermosetting resin and/or (b)
fine particles of a resin having a softening point of higher than 150°C and (c) fine
particles of a polyolefin resin.
[0025] The fine particles of a thermosetting resin (a), the fine particles of a resin having
a softening point of higher than 150°C (b) and the fine particles of a polyolefin
resin (c) will be hereinafter abbreviated simply as "thermosetting resin fine particle",
"high softening point resin fine particle" and "polyolefin resin fine particle", respectively.
[0026] As for the polyolefin resin which is of a low softening point and flexible and which
is capable of contributing to improving the recording sensitivity and the quality
of an image printed when used in the image-receiving sheet, there can be mentioned,
for example, polyethylene, polypropylene, polybutene-1, polyisobutylene, polypentene-1,
polyhexene-1, poly-3-methylbutene-1, poly-4-methylpentene-1, poly 5-methylhexene-1,
etc., and copolymers of two or more of these polymers.
[0027] These polyolefin resins are commercially available in the form of fine particles.
[0028] These polyolefin resin fine particles are not soluble in organic solvents and because
of this, they can be desirably used in the formation of an intermediate layer not
only in the case where an image-receiving layer is formed in the organic solvent system
or in the aqueous system.
[0029] However, the softening point of any of the foregoing polyolefin resin fine particles
is in the range of 40 to 150°C. Therefore, they are problematic upon forming the intermediate
layer with the use of any of them since they are softened and finally melted with
the heat applied in the process of preparing an image-receiving sheet. Thus, the resulting
intermediate layer unavoidably becomes such that is inferior in the coverage.
[0030] In view of the above, in the present invention, at least a member selected from the
group consisting of thermosetting resins and high softening point resins respectively
in the form of fine particles (these resins will be collectively called "high softening
point resins" hereinafter) is used together with the polyolefin resin fine particle.
[0031] The high softening point resin fine particles and the thermosetting resin fine particles
are hardly softened or melted by the action of heat applied in the process of preparing
an image-receiving sheet. In addition to this, when it is used together with the polyolefin
resin fine particle for the formation of the intermediate layer, the resulting intermediate
layer becomes provided with a desirable whiteness and a desirable opacity. Further
in addition, the resulting intermediate layer becomes to have a such a layer structure
that contains a plurality of minute cavities. For these reasons, the resulting image-receiving
sheet such that have a intermediate layer becomes to have a desirable heat-resistance
and provide a significant effect of enhancing the printing density, whereby obtaining
extremely high quality printed images since it is free of such a disadvantage that
loss of energy occurs due to endothermal phenomenon caused by the melting of the constituent
fine particles upon printing, which is often found on the known image-receiving sheet.
[0032] As high softening point resin fine particles and thermosetting resin fine particles
which can be used in the present invention fine particles of various cross linked
resins and fine particles of various thermosetting resins can be mentioned. Specific
examples of the cross linked resin fine particles are, for example, fine particles
of cross linked styrenic resins, fine particles of cross linked styrene-acrylic resins,
etc. Specific examples of the thermosetting resin fine particle are phenol resin fine
particle, urea resin fine particle, melamine resin fine particle, aryl resin fine
particle, polyimide resin fine particle, benzoguanamine resin particle, etc.
[0033] The term "softening point" in the present invention denotes the temperature when
a high molecular material converts from the original solid state into a state of low
elastic modules i.e. a so-called gum state as the temperature heightens and then it
is softened and melted as the temperature further heightens.
[0034] In the present invention, the polyolefin resin fine particle and the high softening
point resin fine particle are mixed at an appropriate mixing ratio in the range where
the characteristics of the intermediate layer are not hindered.
[0035] However, in general, the amount of the high softening point resin fine particle to
be mixed with the polyolefin resin fine particle is desired to be preferably in the
range of from 5 to 90% by weight, more preferably in the range of from 10 to 60% by
weight, respectively versus the total of the high softening point resin fine particle
and the polyolefin resin fine particle. When it is less than 5% by weight, the resulting
intermediate layer becomes to have insufficient whiteness and opacity. On the other
hand, when it exceeds 90% by weight, negative reduction will be caused for the optical
density and the quality of an image as printed.
[0036] The intermediate layer according to the present invention may be formed as follows.
That is, firstly, an aqueous emulsion containing the foregoing high softening point
resin fine particle and the foregoing polyolefin resin fine particle is prepared.
Then, a synthetic polymer adhesive such as polyacrylic acid ester, styrene-butadiene
copolymer or polyvinyl acetate and/or a natural adhesive such as starch or casein
are dispersed into the foregoing aqueous emulsion to obtain a coating composition.
The coating composition thus obtained is applied onto the surface of a substrate in
a predetermined amount by known coating means such as wire-bar coater, air-knife coater,
blade coater, gravure-roll coater, curtain coater, etc., to thereby form a liquid
coat to be the intermediate layer, followed by air-drying.
[0037] Thus, there can be formed the intermediate layer as desired.
[0038] As for the amount of the foregoing coating composition to be applied onto the surface
of a substrate for forming the intermediate layer, it is desired to be preferably
1 g/m² or more, more preferably in the range of from 3 to 30 g/m² on a dry basis.
[0039] In a preferred embodiment, the intermediate layer thus formed is graduated with heat
or pressure using a proper graduation means such as super calender after or prior
to forming the image-receiving layer thereon. In this case, the recording sensitivity
of the resulting image-receiving sheet is markedly improved to provide a significantly
high quality printed image.
[0040] For the image-receiving layer to be formed on the intermediate layer in the present
invention, there is not any particular restriction. However, it is desired to be comprised
of a thermosetting resin layer capable of exhibiting an effective dye-receptivity
for a sublimable dye.
[0041] As the thermosetting resin to constitute the image-receiving layer, there can be
mentioned, for example, polymers of vinyl monomer such as styrene, vinyltoluene, acrylic
ester, methacrylic ester, acrylonitrile, vinyl chloride, vinyl acetate, etc.; copolymers
of these monomers; condensed polymers such as polyester, polyamide, polycarbonate,
polysulfone, epoxy resin, polyurethane, etc.; and cellose resins.
[0042] These thermosetting resins may be used alone or in combination of two or more of
them.
[0043] In case where necessary, the image-receiving layer in the present invention may contain
one or more of other resins selected from the group consisting of methyl cellulose,
ethyl cellulose, hydroxypropyl cellulose, starch, polyvinyl alcohol, polyamide resin,
phenol resin, melamine resin, urea resin, urethane resin, epoxy resin, silicone resin,
etc. in an amount in the range where the effects of the present invention are not
hindered.
[0044] Further, the image-receiving layer in the present invention may contain a reactive
compound such as polyvalent isocyanate compound, epoxy compound or organometallic
compound. In this case, the quality of the image-receiving layer is improved.
[0045] Further in addition, it is possible to incorporate a proper auxiliary into the image-receiving
layer aiming at providing it with an improved writeability. As such auxiliary, there
can be mentioned, for example, inorganic or organic pigments such as ground calcium
carbonate, precipitated calcium carbonate, talc, clay, natural or synthetic silicate,
titanium oxide, aluminum hydroxide, zinc oxide, urea-formaldehyde resin, etc.; ultraviolet
ray absorbing agents; antioxidants; antistatic additives; releasing agents; lubricants,
etc. These auxiliaries may be used alone or in combination of two or more kinds of
them.
[0046] The image-receiving layer in the present invention may be properly formed in the
manner similar to the foregoing manner of forming the intermediate layer. For instance,
the image-receiving layer is formed on the previously formed intermediate layer by
using a coating composition containing the foregoing thermosetting resin or a coating
composition containing, in addition to the foregoing thermosetting resin, the foregoing
pigment or/and the foregoing auxiliary, applying said coating composition onto the
surface of the previously formed intermediate layer in a predetermined amount by the
foregoing coating means to therby form a liquid coat and air-drying said liquid coat.
[0047] The amount of the foregoing coating composition to be applied to form the image-receiving
layer is properly determined depending upon the use purpose of the resulting image-receiving
sheet. However, in general, it is desired to be in the range of 2 to 15 g/m² on a
dry basis.
[0048] As the substrate of the image-receiving sheet according to the present invention,
a wood free paper, a synthetic paper or a polymer film can be selectively used. Among
these, the wood free paper is most preferred since it excels not only in heat resisting
property but also other thermal properties. The wood free paper used in the present
invention includes papers manufactured under acidic conditions, neutral conditions
or alkaline conditions which are comprised chiefly of cellulose pulp and added with
a wet strength agent, sizing agent, filler such as inorganic or organic pigment, etc.
[0049] The wood free paper also includes those papers manufactured by size-pressing the
above papers with oxidized starch or the like and other papers having an improved
surface physical property manufactured by providing the above papers with a precoat
layer containing a pigment such as clay as the main constituent.
[0050] Other than those above mentioned, a No. 1 grade coated paper, a coated paper or a
cast coated paper can be more suitably used as the substrate in the present invention.
[0051] In the present invention, such a thin heat-resistant protective layer containing
a silicone resin as the main constituent, capable of permeating a sublimable dye as
disclosed in Japanese Unexamined Patent Publication Sho. 59(1984)-165686 or Sho. 61(1986)-27290
may be disposed on the surface of the image-receiving layer. In this case, the dye
or the dye layer can be prevented from directly transferring to the image-receiving
layer.
[0052] As above described, the image-receiving sheet for thermal transfer printing to be
provided according to the present invention exhibits marked performances when used
in the thermal transfer printing system wherein a dye transfer sheet containing a
thermally sublimable dye is used.
[0053] The thermally sublimable dye in the present invention includes such dyes that do
not cause transfer even on contact with the image-receiving sheet under ordinary handling
conditions but cause transfer, for the first time, with application of heat of 60°C
or more by way of melting, vaporization, sublimation and the like.
[0054] As such dye, there can be mentioned, for example, disperse system dyes such as azo
series dyes, nitro series dyes, anthraquinone series dyes, quinoline series dyes,
etc.; basic dyes such as triphenylmethane series dyes, fluoran series dyes, etc.;
and oil soluble dyes.
[0055] The image-receiving sheet for thermal transfer printing to be provided according
to the present invention is usable not only in the thermal transfer printing system
wherein contact heat caused, for example, by a heating plate or thermal head of thermal
printing unit is utilized but also in other thermal printing system wherein indirect
contact heat with the use of infrared lamp, YAG laser or carbon dioxide gas laser
is utilized.
PREFERRED EMBODIMENTS OF THE INVENTION
[0056] The advantages of the present invention are now described in more detail by reference
to the following Examples and Comparative Examples, which are provided here for illustrative
purposes only, and are not intended to limit the scope of the present invention.
[0057] Unless otherwise indicated, parts and % signify parts by weight and % by weight respectively.
EXAMPLE 1
[0058] A coating composition having a solid content of 40% for the intermediate layer was
firstly prepared by mixing 250 parts of thermosetting benzoguanamine resin fine particles
of 2 µm in particle size (trade name: EPOSTAR-EPS-MS, produced by Nippon Syokubai
Kagaku Kogyo Co., Ltd.), 600 parts of polyolefin resin fine particles of 5 µm in particle
size (softening point: 54°C, solid content: 40%)(trade name: CHEMIPEARL A-100, produced
by Mitsui Petrochemical Industries Co., Ltd.) and 150 parts of styrene-butadiene copolymer
emulsion (solid content: 48%)(trade name: L-1690, produced by Asahi Chemical Industry
Co., Ltd.) as a binder to obtain a mixture and adding water to the mixture.
[0059] The coating composition thus obtained was applied onto a No. 1 grade coated paper
of 128 g/m² (trade name: SA-KINFUJI, produced by Kanzaki Paper Manufacturing Co.,
Ltd.) in an amount to be 15 g/m² when dried to form a liquid coat comprising said
coating composition on said paper by the use of a wire-bar coater, followed by air-drying,
to thereby form an intermediate layer.
[0060] Then, a coating composition for the image-receiving layer which was prepared by dissolving
20 parts of polyester resin (trade name: VYLON-200, produced by Toyobo Co., Ltd.)
in an solvent composed of 40 parts of methyl ethyl ketone, 40 parts of toluene and
20 parts of cyclohexanone to obtain a solution and adding to the solution 0.3 parts
of amino denatured silicone oil (trade name: KF-393, produced by Shinetsu Chemical
Co., Ltd.) and 0.3 parts of epoxy denatured silicone oil (trade name: X-33-343, produced
by Shinetsu Chemical Co., Ltd.) was applied onto the surface of the previously formed
intermediate layer in an amount to be 4 g/m² when dried in the same manner as in the
case of forming the intermediate layer to form a liquid coat. The liquid coat thus
formed was then subjected to air-drying and curing at 120°C for 5 minutes.
[0061] The resultant was graduated at a linear pressure of 200 kg/cm by means of a super
calender comprising a metal roll having a mirror ground surface and a elastic roll.
Thus, there was obtained an image-receiving sheet for thermal transfer printing of
the present invention.
EXAMPLE 2
[0062] The procedures of Example 1 were repeated, except that as the coating composition
for the intermediate layer, a coating composition having a solid content of 30% prepared
by mixing 35 parts of thermosetting urea formaldehyde resin fine particles of 5 to
6 µm in secondary particle size (trade name: PERGOPAK M2, produced by Ciba Geigy Co.,
Ltd.), 850 parts of polyolefin resin fine particles (trade name: CHEMIPEARL A-100)
and 115 parts of styrene-butadiene copolymer emulsion of 50% in a solid content (trade
name: JSR-0530, produced by Japan Synthetic Rubber Co., Ltd.) as a binder to obtain
a mixture and adding water to the mixture was used, to thereby an image-receiving
sheet for thermal transfer printing of the present invention.
EXAMPLE 3
[0063] The procedures of Example 1 were repeated, except that as the coating composition
for the intermediate layer, a coating composition having a solid content of 40% prepared
by mixing 570 parts of cross linked styrenic resin fine particles of 0.3 to 0.4 µm
in particle size and having a softening point of 156°C (solid content: 20%)(trade
name: GRANDOLL PP-5491, produced by Dainippon Ink & Chemicals Inc.), 285 parts of
polyolefin resin fine particles (trade name: CHEMIPEARL A-100) and as a binder, 145
parts of styrene-butadiene copolymer emulsion having a solid content of 48% (trade
name: L-1690) to obtain a mixture and adding water to the mixture, to thereby obtain
an image-receiving sheet for thermal transfer printing of the present invention.
Comparative Example 1
[0064] A comparative image-receiving sheet for thermal transfer printing was prepared by
repeating the procedures of Example 1, except that as the coating composition for
the intermediate layer, a coating composition composed of 890 parts of polyolefin
resin fine particles (trade name: CHEMIPEARL A-100) and 110 parts of styrene-butadiene
copolymer emulsion (trade name: JSR-0530) was used.
Comparative Example 2
[0065] A comparative image-receiving sheet for thermal transfer printing was prepared by
repeating the procedures of Example 1, except that as the coating composition for
the intermediate layer, a coating composition having a solid content of 40% prepared
by mixing 865 parts of thermosetting benzoguanamine resin fine particles (trade name:
EPOSTAR EPS-MS) and 135 parts of styrene-butadiene copolymer emulsion (trade name:
L-1690) to obtain a mixture and adding water to the mixture was used.
Comparative Example 3
[0066] A comparative image-receiving sheet for thermal transfer printing was prepared by
repeating the procedures of Example 1, except that as the coating composition for
the intermediate layer, a coating composition having a solid content of 40% prepared
by mixing 250 parts of anatase type titaium oxide fine particles (trade naem: FA-55W,
produced by Furukawa Mining Co., Ltd.), 600 parts of polyolefin resin fine particles
(trade name: CHEMIPEARL A-100) and 150 parts of styrene-butadiene copolymer emulsion
(trade name: L-1690) to obtain a mixture and adding water to the mixture was used.
Comparative Example 4
[0067] A comparative image-receiving sheet for thermal transfer printing was prepared by
repeating the procedures of Example 1, except that as the coating composition for
the intermediate layer, a coating composition having a solid content of 40% prepared
by mixing 445 parts of polyethylene resin fine particles of 3 µm in particle size
and having a softening point of 132°C (solid content: 40%) (trade name: CHEMIPEARL
W-300, produced by Mitsui Petrochemical Industries Co., Ltd.), 445 parts of polyolefin
resin fine particles (trade name: CHEMIPEARL A-100) and 110 parts of styrene-butadiene
copolymer emulsion (trade name: JSR-0530) to obtain a mixture and adding water to
the mixture was used.
EVALUATION
[0068] The seven image-receiving sheets obtained in Examples 1 to 3 and Comparative Examples
1 to 4 were evaluated.
[0069] In the evaluation of each of the image-receiving sheets, there was used a thermal
dye-transfer sheet which was prepared in the way as below described.
[0070] That is, 0.45 parts of a blue thermally sublimable disperse dye (trade name: KST-B-714,
produced by Nippon Kayaku Co., Ltd.) and 0.4 parts of polyvinyl butyral resin (trade
name: Eslec BX-1, produced by Sekisui Chemical Co., Ltd.) were dissolved in a solvent
composed of 4.6 parts of methyl ethyl ketone and 4.6 parts of toluene to obtain an
ink composition for the formation of a thermal dye-transfer layer. The composition
thus obtained was applied onto a 6 µm thick polyethylene terephthalate film whose
reverse side has been subjected to heat-resisting treatment, in an amount to be 1.0
g/m² when dried by means of a wire bar coater and dried to obtain a thermal dye-transfer
sheet.
[0071] The thermal dye-transfer sheet thus obtained was superposed on the image-receiving
sheet sample to be evaluated, followed by printing with application of heat through
a thermal head, where a voltage was impressed under conditions of 12 V and 2 to 8
m sec for evaluating the recording sensitivity of the image-receiving sheet sample
and the quality of an image as printed.
[0072] In addition, the opacity and whiteness were evaluated for each of the image-receiving
sheet samples.
[0073] The above evaluations were made in the following manners.
Evaluation of the recording sensitivity:
[0074] The image obtained was measured by Macbeth Reflection Densitometer (product of Macbeth
Corp., U.S.A.) with its optical density. The results obtained were evaluated with
reference to the previously provided standard curve of the recording sensitivity.
Evaluation of the quality of an image obtained:
[0075] This evaluation was conducted by observing the image obtained by eyes with the use
of a magnifier with a 25 times magnification.
Evaluation of the opacity:
[0076] The image-receiving sheet sample was measured in accordance with the manner of JIS-P-8138
to obtain a value. And its opacity was evaluated based on the resultant value.
Evaluation of the whiteness:
[0077] The image-receiving sheet sample was set to Elrepho Whiteness Measuring Device (product
of Karl Zweis Co., Ltd.) to thereby evaluate its whiteness.
[0078] The evaluated results were collectively shown in Table 1.
[0079] From the results shown in Table 1, it has been recognized that any of the image-receiving
sheets obtained in Examples 1 to 3 is good or excellent with respect to any of the
evaluation items and provides satisfactory results in practical use.