Image receiving sheet

The image receiving sheet according to the present invention is an image receiving sheet which receives dye migrated by heat from a heat transfer sheet, wherein the image receiving sheet includes a substrate (3), a dye receiving layer (3) provided on one surface of the substrate and a curl prevention layer. The curl prevention layer includes a non-heat stretchable and shrinkable resin having a heating stretching or shrinking ratio within the range from -1.0 to 1.5% in JIS-K-6734 provided on the surface of the substrate on the side opposite to the above dye receiving layer, or between the substrate and the dye receiving layer. In the present invention, by having such a curl prevention layer as mentioned above, generation of curl by heat during image formation can be prevented to provide an image receiving sheet excellent in both conveyability of sheet and printing quality.

TECHNICAL FIELD 
This invention relates to an image receiving sheet for heat transfer 
recording, more particularly to an image receiving sheet for heat transfer 
recording which is excellent in curl preventability and slippability 
(conveyability) in a printer, without printing trouble, and capable of 
forming an image of high image quality. 
BACKGROUND ART 
In the prior art, various heat transfer methods have been known. Among 
them, there has been proposed a method in which a sublimable dye is used 
as the recording material, which is carried on a substrate sheet such as a 
paper or a plastic sheet to provide a heat transfer sheet. Various 
full-color images are formed on an image receiving sheet dyeable with a 
sublimable dye, for example, an image receiving sheet having a dye 
receiving layer provided on the surface of a paper or a plastic film. 
For this method, a thermal head of a printer is used as the heating means, 
and a large number of color dots of 3 colors or 4 colors are transferred 
onto an image receiving sheet by heating for a very short time, thereby 
reproducing the full-color image of the original by color dots of multiple 
colors. 
The image thus formed is very sharp and also excellent in transparency, 
because the colorants used are dyes, and therefore the image obtained is 
excellent in reproducibility and gradation of the intermediate color, and 
is similar to an image obtained by conventional offset printing or gravure 
printing. It has also become possible to form an image of high quality 
comparable with full-color photographic image. 
The heat transfer image receiving sheet to be used in the sublimation type 
heat transfer system, when a reflected image is required as in the printed 
matters or photography, one having a dye receiving layer comprising a 
resin having good dyeability provided on the surface of an opaque 
substrate sheet such as paper or synthetic paper is used, while when a 
light-transmissive image is required as used in OHP (overhead projector), 
one having a dye receiving layer provided on a transparent substrate sheet 
such as polyester film is used. 
In any case, when image formation is effected by use of these image 
receiving sheets, as the result of heating of the surface of the image 
receiving sheet during transfer, warping (curl) tends to occur on the 
image receiving sheet, whereby slippability of the image receiving sheet 
after printing becomes worse and causes the problem of paper jamming. 
Also, since it is necessarily unavoidable to heat the whole printer to a 
certain temperature, curl is generated within the printer also before 
printing, whereby conveyability of the image receiving sheet is worsened 
to generate a problem such as double delivery, etc. 
Further, in the case of forming a multi-color image, since printing is 
performed for 3 to 4 times on the same image receiving sheet, curl becomes 
excessive and generates non-matching of the printed dots and lower image 
quality. Particularly in the case of a light-transmissive image for OHP, a 
lowering in the image quality becomes further marked, because the printing 
image is projected with enlargement to several fold. 
The present invention has been accomplished in view of the above-mentioned 
problem. The object of the present invention is to provide an image 
receiving sheet, which does not curl due to the heat applied thereto by a 
thermal head during image transfer, can make delivery of the sheet better 
during image transfer, and will not give rise to color slippage or 
deformation of the image transferred on the receiving layer. 
DISCLOSURE OF THE INVENTION 
The image receiving sheet according to the present invention is an image 
receiving sheet for receiving the dye migrated from a heat transfer sheet 
by heat, characterized in that the image receiving sheet comprises a 
substrate, a dye receiving layer provided on one surface of said 
substrate, and a curl prevention layer provided on the surface of the 
substrate opposite to the dye receiving layer, said curl prevention layer 
comprising a non-heat shrinkable and stretchable resin having a heating 
shrinkage or stretchability in JIS-K-6734 within the range of from -1.0 to 
1.5%.

BEST MODE FOR PRACTICING THE INVENTION 
FIG. 1 shows an example of the image receiving sheet 1, and the sheet 1 is 
constituted by providing a dye receiving layer 3 on one surface of a 
substrate 2, and further providing a curl prevention layer 5 comprising a 
resin with small heating shrinkage through a primer layer 4 on the surface 
of the substrate 2 on the opposite side to the side where the dye 
receiving layer 3 is provided. 
As the above substrate 2, films, sheets of plastics, synthetic papers, 
cellulose fiber papers, etc. may be used. As the plastic film or sheet, 
for example, there can be used films, sheets comprising polyethylene 
terephthalate, polyolefin, polyvinyl chloride, polyvinylidene chloride, 
polystyrene, polycarbonate, polyphenylene sulfane, polyether sulfone, 
polyether ether ketone, polyether imide, polyarylate, acrylic resins such 
as polymethyl methacrylate, etc., and also these white films, sheets added 
with fillers and formed into white films, sheets, or foamed films obtained 
by effecting fine foaming can be used, but in the case for use in OHP, 
those having high transparency and further those with high heat resistance 
are preferable and polyethylene terephthalate film is generally employed. 
As the synthetic paper, there may be included those comprising a 
polyolefin resin or another synthetic resin as the resin component mixed 
by addition of an inorganic filler, etc. thereto and extrusion molded into 
shapes of films, sheets, or those prepared by coating an extender pigment 
on resin films, sheets such as polystyrene, polyester, polyolefin, etc. As 
the cellulose fiber paper, pure paper, coated paper, cast coated paper, 
paper impregnated etc. may be included. The thickness of the substrate 2 
may be preferably 30 to 200 .mu.m, particularly 50 to 150 .mu.m. 
As the material constituting the dye receiving layer 3, one which can 
receive a dye migrated from the heat transfer sheet, for example, an image 
of a sublimable disperse dye, and maintain the image formed by reception 
is used, but any of those which have been used in the prior art for the 
receiving layer of this kind of image receiving sheet may be available. 
Examples of such material may include either one or mixtures of two or 
more kinds of the following synthetic resins (a) to (e). 
(a) Those having ester bond: 
polyester, polyacrylate, polycarbonate, polyvinyl acetate, styrene-acrylate 
resin, vinyl toluene-acrylate resin, etc. 
(b) Those having urethane bond: polyurethane, etc. 
(c) Those having amide bond: polyamide (nylon, etc.). 
(d) Those having urea bond: urea resin, etc. 
(e) Those having other bonds with high polarity: 
polycaprolactone, polystyrene, polyvinyl chloride, polyacrylonitrile, etc. 
Also, the dye receiving layer 3 can be constituted of a mixed resin of a 
saturated polyester and a vinyl chloride-vinyl acetate copolymer. In this 
case, the vinyl chloride-vinyl acetate copolymer should be preferably one 
having a content of vinyl chloride component of 85 to 97% by weight and a 
polymerization degree of about 200 to 800. It is not limited to the case 
consisting of a copolymer only of vinyl chloride and vinyl acetate, but 
also those containing vinyl alcohol component, maleic acid component may 
be employed. 
Further, the dye receiving layer 3 can be also constituted of a styrene 
type resin other than polystyrene as mentioned above. As such styrene type 
resin, there may be included homopolymers or copolymers of styrene type 
monomers such as styrene, .alpha.-methylstyrene, vinyl toluene and the 
like, or copolymers of these monomers with other monomers, for example 
acrylic or methacrylic monomers such as acrylates, methacrylates, 
acrylonitrile, methacrylonitrile and the like, and maleic anhydride, etc. 
In the present invention, in the above dye receiving layer 3, a UV-absorber 
can be also added, if necessary. By addition of a UV-ray absorber, 
weathering resistance of the dye dyed on the receiving layer by migration 
from the heat transfer sheet can be improved. As the UV-ray absorber, 
benzophenone type, hindered amine type, benzotriazole type may be 
included. Its amount added may be about 0.05 to 5 parts by weight based on 
100 parts by weight of the resin constituting the receiving layer 3. 
In the above dye receiving layer 3, it is also possible to incorporate a 
release agent for the purpose of improving the peel-off characteristic 
from the heat transfer sheet, if necessary. As the release agent, solid 
waxes such as polyethylene wax, amide wax, Teflon powder, etc., 
surfactants such as fluorine type or phosphoric acid ester type or 
silicone oils may be employed, but silicone oils are preferred. As 
silicone oils, oily ones may be employed, but cured type oils are 
preferred. As the cured type silicone oil, the reaction cured type, the 
photocured type, the catalyst cured type, etc. may be included, but 
silicone oils of the reaction cured type are particularly preferred. As 
the reaction cured type silicone oil, those cured by the reaction between 
amino-modified silicone oils and epoxy-modified silicones are preferred. 
The amount of these cured type silicone oils added may be preferably 0.5 
to 30 parts by weight based on 100 parts of the resin constituting the dye 
receiving layer 3. Addition of the release agent is not limited to 
incorporating into the dye receiving layer 3, but a release agent layer 
may be also formed by coating and drying a solution or a dispersion of a 
release agent in an appropriate solvent on the surface of the dye 
receiving layer 3. As the release agent constituting the release agent 
layer, the reaction cured product of amino-modified silicone oil and 
epoxy-modified silicone oil as mentioned above is particularly preferred. 
The release agent layer should be preferably formed to a thickness of 0.01 
to 5 .mu.m, particularly 0.05 to 2 .mu.m. The release agent layer may be 
provided either on a part of the surface of the dye receiving layer 3 or 
the whole surface, but when the release agent layer is provided on a part 
of the surface of the dye receiving layer 3, recording by dot impact 
recording, heat-sensitive melt transfer recording or pencil, etc. can be 
performed on the portion where no release agent layer is provided, and 
sublimation transfer recording is performed on the portion where the 
release agent is provided, while recording according to another recording 
system is performed on the portion where no release agent is provided. 
Thus, the sublimation transfer recording system and another recording 
system can be used in combination. 
When the substrate 2 comprises a resin such as vinyl chloride, polyester, 
vinyl chloride-vinyl acetate copolymer, vinyl chloride-acrylic polymer, 
etc., since the surface of these resins has dye receptivity and 
releasability, no dye receiving layer 3 may be separately provided. 
The curl prevention layer 5, comprising a non-heat stretchable and 
shrinkable resin having small heating shrinkage and being provided through 
the primer layer 4 on the surface of the substrate 2 on the opposite side 
to the side where the dye receiving layer 3 is provided, comprises a 
heat-resistant or semi-heat-resistant resin having a heat shrinkage of 
-1.0 to 1.5% and a softening temperature of 90.degree. C. or higher in 
JIS-K-6734 (100.degree. C., 10 minutes). Examples of such resins may 
include polyacryl, polyurethane, polycarbonate, vinylidene chloride, 
epoxy, polyamide, polyester, etc. The thickness of the curl prevention 
layer 5 should be preferably 1 to 10 .mu.m, particularly 3 to 10 .mu.m. 
The curl prevention layer 5 can be formed by the method in which a melted 
resin or a resin dissolved in a solvent is coated, the method in which 
these resins are formed into films, sheets, and adhered, etc. The primer 
layer 4 is provided for the purpose of improving adhesiveness between the 
substrate 2 and the curl prevention layer 5, and as the resin constituting 
the primer layer 4, polyurethane, polyacryl, polyester, epoxy, etc. may be 
included. The primer layer 4 is not necessarily required to be provided 
depending on the materials of the substrate 2 and the curl prevention 
layer 5, when adhesiveness between both is good. 
The image receiving sheet 1 of the present invention can also provide the 
curl prevention layer 5 between the substrate 2 and the dye receiving 
layer 3 as shown in FIG. 2, and also, although not particularly shown, can 
provide it both between the substrate 2 and the dye receiving layer 3 and 
on the backside of the substrate 2. 
The image receiving sheet 1 can also have a support sheet 7 for improving 
paper passage characteristic of the image receiving sheet 1 within the 
transfer device adhered on the backside of the curl prevention layer 5 or 
the substrate 2 freely peelably through a tackifier layer 6 as shown in 
FIG. 3, FIG. 4. As the support sheet 7, either transparent or opaque sheet 
may be used, and as its material, for example, synthetic paper, cellulose 
fiber paper, synthetic resin sheet, etc. may be employed. As the synthetic 
paper, there may be employed those of the type of a polyolefin resin 
filled with a filler, which is extruded and stretched, those of the type 
of a sheet of a polyolefin, polystyrene, polyester, coated with a mixture 
comprising a filler and a binder, etc. As the cellulose fiber paper, pure 
paper, coated paper, art paper, cast coated paper, converted paper, 
impregnated.coated or internally added with a synthetic resin or a rubber, 
converted paper extrusion laminated with polyethylene, etc. can be used. 
As the synthetic resin sheet, there may be employed transparent films of 
polyethylene terephthalate, polypropylene, rigid vinyl chloride, etc. 
alone, sheets obtained by extrusion of these materials added with fillers 
such as clay, calcium carbonate, titanium oxide, etc. or laminated papers 
of the above resin or the resin containing the filler extruded on a pure 
paper, etc., or these papers having formed fine unevenness on the surface 
by the sand blast method, the emboss method, etc. 
By providing further a lubricating layer on the back of the support sheet 
7, paper passage characteristic can be further improved. The lubricating 
layer can be formed by coating a methacrylate resin such as methyl 
methacrylate or a corresponding acrylate resin, a vinyl type resin such as 
vinyl chloride-vinyl acetate copolymer, etc. 
The tackifier layer 6 can be constituted of a conventional tackifier such 
as polyacrylic acid ester, an acrylic copolymer, natural rubber, a 
synthetic rubber, petroleum resin, a block copolymer such as SIS, SBR, 
etc., but a weakly tacky tackifier is preferable for making peel-off of 
the support sheet 7 easier. As the weak tackifier, one having property of 
weak tackiness to the curl prevention layer 5 or the substrate 2 may be 
selected and employed, or a conventional tackifier as mentioned above in 
which inorganic particles are kneaded or a release agent is mixed to 
impart releasability thereto may be employed. 
On the back of the image receiving sheet 1 of the present invention, a 
detection mark for registration in a transfer device during transfer can 
be also printed (the surface on which the detection mark is provided may 
include the case of the back of the substrate 2, the back of the curl 
prevention layer, or the case of the support sheet 7, etc. 
Direct formation of Curl Prevention Layer 
Whereas, as described above, in the heat transfer method by use of 
sublimable dyes, since the colorants used are dyes, image formation with 
excellent transparency is possible, whereby formation of an image having 
resolution, gradation and color reproducibility, etc. approximate to 
silver salt photography is possible. For example, the uses are not limited 
for viewing of reflected light images, but the method has characteristics 
which are very useful in the field utilizing images by transmitted light, 
such as formation of OHP images. 
As the transferable material, namely image receiving sheet to be used for 
formation of OHP images as mentioned above, polyethylene terephthalate 
sheet or film excellent in transparency has been employed, but since said 
film has high crystallinity and insufficient dyeability, a dye receiving 
layer has been required to be formed on the film surface from a resin 
having excellent dye dyeability. 
The present inventor has made investigations about dyeability of various 
transparent films, and found that polyvinyl chloride (hereinafter called 
PVC) resin films, particularly PVC sheets containing a certain extent of 
plasticizers have good dye dyeability, and formation of the dye receiving 
layer can be omitted. However, soft PVC sheets involve the problem that 
curl is liable to be formed by the heater of the printer during heat 
transfer or the light source of OHP, whereby there is the problem that 
correct formation of transferred images and projected images can be 
effected only with difficulty. 
Such problem can be solved by forming a transparent resin layer (for 
example, an acrylic resin layer) subjected little to stretching and 
shrinkage by heat on the back of a PVC sheet (namely on the opposite 
surface of the image forming surface), but since adhesiveness between the 
PVC sheet and the acrylic resin is inferior, cumbersomeness is involved 
that a primer layer or an adhesive layer is required to be formed on the 
surface of the PVC sheet, whereby there is the problem that transparency 
must be sacrificed to some extent by formation of the primer layer or the 
adhesive layer. 
In the present invention in forming a non-heat stretchable and shrinkable 
resin layer (curl prevention layer) on one surface of a PVC sheet, by 
forming a non-heat stretchable and shrinkable resin solution dissolved in 
a solvent which swells or dissolves the above PVC sheet, an image 
receiving sheet excellent in transparency and curl prevention 
characteristic can be economically provided without forming a primer layer 
or an adhesive layer. 
The PVC sheet per se to be used in the embodiment of the present invention 
as mentioned above has been well known in the art, but in the present 
invention, a semi-rigid or soft PVC sheet containing a plasticizer may be 
preferably used. As the plasticizer, there may be employed all of those 
known in the art such as dibutyl phthalate, di-n-octyl phthalate, 
di-(2-ethylhexyl) phthalate, dinonyl phthalate, dilauryl phthalate, butyl 
lauryl phthalate, butyl benzyl phthalate, di-(2-ethylhexyl) adipate, 
di-(2-ethylhexyl) sebacate, tricresyl phosphate, tri-(2-ethylhexyl) 
phosphate, polyethylene glycol ester, epoxy fatty acid ester, etc. The 
amount of these plasticizers employed may be 5 to 80 parts by weight, 
particularly preferably within the range of from 10 to 50 parts by weight, 
per 100 parts by weight of the above PVC. If the amount of the plasticizer 
used is too small, dyeability for a sublimable dye is insufficient, while 
if it is too much, rigidity of the sheet is deficient to make the sheet 
too soft, and also blurring occurs in the printed image during sublimation 
transfer so that a sharp image undesirably cannot be obtained. Such 
plasticizer not only imparts softness and dye dyeability to the sheet, but 
also exhibits the effect of preventing adhesion between the PVC sheet and 
the heat transfer sheet during heat transfer. 
Also, in the preferred embodiment of the present invention, it has been 
also found that there is no blocking with the heat transfer sheet during 
transfer, and also the dyeability with a sublimable dye is further 
improved, even when a plasticizer may be included in PVC in a relatively 
larger amount, for example, at a ratio of 30 to 80 parts by weight, by 
including further 0.1 to 10 parts by weight of a lubricant per 100 parts 
by weight of PVC in addition to the above plasticizer. 
As such lubricant, all of the lubricants known in the art such as fatty 
acids, fatty acid amides, waxes, paraffins, etc. can be used. If the 
amount of these lubricants added is too small, there is no effect by 
addition, while if it is too much, surface roughening with the PVC resin 
sheet obtained will undesirably occur. Also, by use of these lubricants, 
not only dyeability of a sublimable dye is improved, but also adhesion 
between the sublimation heat transfer sheet and the PVC resin sheet is 
little even by use of a relatively higher temperature during sublimation 
transfer, whereby an image of high density can be formed further 
efficiently. The main components of the PVC sheet to be used in the 
present invention are as described, but of course in the present 
invention, further UV-ray absorbers, antistatic agents, heat stabilizers, 
antioxidants, fluorescent brighteners, fillers, etc. can be also used as 
desired. 
The PVC resin sheet to be used in the present invention is obtained by 
blending the necessary components as described above, and molding the 
blended product by the known formation method such as the calendering 
method, the extrusion method, etc. into a sheet with a thickness of, for 
example, about 10 to 300 .mu.m. 
The curl prevention layer to be formed on one surface of the PVC sheet as 
described above is formed from a resin which is relatively hard, low in 
stretchability and shrinkability by heating and also excellent in 
transparency. Suitable as such resin which is hard, low in stretchability 
and shrinkability and excellent in transparency may be acrylic resins, 
polystyrene type resins, polycarbonate type resins, polyester type resins, 
etc., and particularly useful resins are acrylic resins. As acrylic 
resins, there have been widely known thermoplastic, thermosetting, 
catalyst curable, UV-ray curable, electron beam curable resins, etc., all 
of which can be used in the present invention. All of these resins are 
available on the market and can be used in the present invention. 
The curl prevention layer is formed by preparing a coating material or an 
ink having a suitable resin as described above in an organic solvent and 
coating and drying the solution on one surface of the PVC sheet. 
In the embodiment as described above, the organic solvent as used above is 
particularly important, and it is necessary to select an organic solvent 
which swells or dissolves the above-mentioned PVC sheet. More 
specifically, when a coating material or an ink is coated, by swelling or 
dissolution of at least a part of the surface of the PVC sheet with the 
organic solvent in the coating material or the ink, the curl prevention 
layer formed is integrated with the PVC sheet, whereby adhesiveness 
between both becomes markedly higher and formation of the primer layer or 
the adhesive layer as in the prior art can be omitted, and for the reason 
which is not clear, transparency of the PVC sheet itself has been markedly 
improved. 
As described above, as the organic solvent which swells or dissolved the 
PVC sheet, aromatic solvents such as benzene, toluene, xylene, 
chlorobenzene, etc. or halogenated hydrocarbons such as chloroform, 
methylene chloride, trichloroethylene, perchloroethylene, etc. are useful, 
and these solvents can be also used by controlling swellability or 
solubility for the PVC sheet by mixing with other solvents in general for 
coating material or ink such as methyl ethyl ketone, methyl isobutyl 
ketone, ethyl acetate, butyl acetate, isopropyl alcohol, butanol, 
petroleum spirit, etc. 
The above-mentioned solvent dissolves the resin as described above, gives 
printing or coating material adaptability by control of the concentration 
and the viscosity, and is coated and cured by drying on the surface of the 
above PVC sheet according to conventional means such as the gravure 
printing method, the bar coating method, the screen printing method, the 
gravure off-set printing method, the gravure coating method, etc. to form 
a curl prevention layer. The thickness of these curl prevention layers may 
be about 1 to 20 .mu.m. 
Slippable Curl Prevention Layer 
The present inventor, as described above, has previously obtained an 
excellent effect by forming a curl prevention layer in a heat transfer 
image receiving sheet as the method of solving the problem of curl. 
However, the above-mentioned image receiving sheet provided with the curl 
prevention layer, when set in a plurality of sheets piled up in a paper 
feeding unit of a printer, there ensues the problem of double delivery due 
to great frictional coefficient of the upper curl prevention layer of the 
image receiving sheet and the dye receiving layer of the image receiving 
sheet therebeneath. Such problem can be solved by plastering a tacky sheet 
having excellent slip characteristic every time, but such method has the 
problem that it is very cumbersome. 
In the present invention, by forming the curl prevention layer of the image 
receiving sheet with a resin having little heating stretching degree and 
shrinkage containing a specific filler, an image receiving sheet excellent 
in curl prevention characteristic and slip characteristic, without 
printing trouble and capable of forming an image of high image quality is 
provided. 
The image-receiving sheet in the above-mentioned embodiment of the present 
invention comprises a substrate sheet, a dye receiving layer formed on the 
surface of the substrate sheet and a slippable curl prevention layer 
formed on the back of the substrate sheet. 
The slippable curl prevention layer in this embodiment has the objects to 
prevent curl of the image receiving sheet by the heat of the thermal head 
during heat transfer, and to lower the frictional coefficient with the dye 
receiving layer when superposed, thereby improving slippability, and is 
formed from a resin with low heating stretchability and shrinkability and 
a filler. 
Preferable examples of the resin with low heating stretchability and 
shrinkability may include acrylic resins, polyurethane resins, 
polycarbonate resins, vinylidene chloride resins, epoxy resins, polyamide 
resins, polyester resins, etc., and among them, although resins having 
various thermal characteristics may exist, particularly preferable resins 
are those having a heating shrinkage within the range of from -1.0 to 
1.5%, and a softening temperature of 90.degree. C. or higher in JIS-K-6734 
(100.degree. C., 10 min.). 
As the filler to be used, there may be included plastic pigments such as 
fluorine resin, polyamide resin, styrene resin, styrene.acrylic 
crosslinked resin, phenol resin, urea resin, melamine, resin, aryl resin, 
polyimide resin, benzoguanamine resin, etc., and inorganic fillers such as 
calcium carbonate, silica, clay, talc, titanium oxide, magnesium 
hydroxide, zinc oxide, etc. Among them, particularly particles having high 
heat resistance are preferred, and the particle size may be suitably about 
0.5 to 30 .mu.m. 
These fillers can be used either alone or in a mixture, and selection of 
the filler employed may be selected and determined depending on the use 
purpose of the image receiving sheet to be obtained. For example, in the 
case of an image receiving sheet for reflection image, since the curl 
prevention layer may become opaque, inorganic fillers with low 
transparency such as titanium oxide, zinc oxide, etc. may be employed. 
However, for light transmissive image, it is preferable to use a plastic 
segment with high transparency or an inorganic filler with small particle 
size. As to the amount used, which also depends on the filler to be used, 
may be generally 0.02 to 10% by weight of the filler in the slippable curl 
prevention layer, and a preferable range may be from 0.05 to 2% by weight. 
If the amount of the filler is less than the above range, the improvement 
effect of slippability is insufficient, while if it exceeds the above 
range, scattering of transmitted light becomes excessive in transparent 
uses such as OHP, etc., and also light transmittance is undesirably 
lowered. 
The method for forming the slippable curl prevention layer is a method in 
which a solution of the resin as described above added with the 
above-mentioned filler, and further added with necessary additives is 
dissolved in an appropriate solvent, or a dispersion thereof in an organic 
solvent or water is formed by coating and drying according to formation 
means such as gravure printing, screen printing method, reverse roll 
coating method by use of gravure plate, and the thickness of the curl 
prevention layer formed is generally about 1 to 10 .mu.m. In forming the 
curl prevention layer, when adhesiveness between the curl prevention layer 
and the substrate sheet is not good, it is preferable to form a primer 
layer from a polyurethane resin, a polyester resin, an acrylic resin, an 
epoxy resin, etc. 
Further, the image receiving sheet of the present invention can provide a 
cushioning layer between the substrate sheet and the dye receiving layer, 
if necessary, and by provision of such a cushioning layer, the noise 
during printing is reduce and images corresponding to image informations 
can be transfer recorded with good reproducibility. 
Further, a detection mark can be also provided. Detection marks are 
extremely convenient in effecting registration between the heat transfer 
sheet and the image receiving sheet, etc., and for example, a detection 
mark detectable by a photoelectric tube detecting device can be provided 
by printing, etc. on the back of the substrate sheet, etc. Of course, 
these detection marks may be freely peelable. 
The heat transfer sheet to be used in performing heat transfer by use of 
the image receiving sheet of the present invention as described above has 
a dye layer containing a sublimable dye provided on a paper or a polyester 
film, and all of heat transfer sheets known in the prior art are available 
as such in the present invention. 
For the means for imparting heat energy during heat transfer, all of known 
imparting means known in the prior art can be used. For example, by means 
of a recording device such as a thermal printer (for example, Video 
Printer VY-100, Hitachi Seisakusho K.K.), etc. by controlling the 
recording time to impart heat energy of about 5 to 10 mJ/mm.sup.2, the 
desired object can be sufficiently accomplished. 
The present invention is described in more detail by referring to Examples 
and Comparative Examples. In the sentences, parts or % are based on weight 
unless particularly otherwise noted. 
EXAMPLE A1, COMATIVE EXAMPLE A1 
By use of a transparent PET with a thickness of 75 .mu.m (Toray K.K., 
Japan: T-75) as the substrate, an ink composition for formation of dye 
receiving layer shown below was coated by a bar coater to a coated amount 
on drying of 5 g/m.sup.2 and dried by a dryer, followed by drying in an 
oven at 80.degree. C. for 10 minutes, to form a dye receiving layer. 
______________________________________ 
Ink composition for formation of receiving layer 
______________________________________ 
Polyester (Vylone 600: Toyo Boseki K.K., Japan) 
4.0 parts 
Vinyl chloride-vinyl acetate copolymer 
6.0 parts 
(#1000 A: Denki Kagaku Kogyo K.K., Japan) 
Amino-modified silicone (X-22-3050C: 
0.2 part 
Shin-etsu Kagaku Kogyo K.K., Japan) 
Epoxy-modified silicone (X-22-3000E: 
0.2 part 
Shin-etsu Kagaku Kogyo K.K., Japan) 
Solvent (MEK: Toluene = 1:1) 
89.6 parts 
______________________________________ 
Next, on the surface on the opposite side to the side where the dye 
receiving layer was provided, a primer having the following composition 
was coated by a bar coater to a coated amount on drying of 1 g/m.sup.2 and 
dried by a dryer, then an ink composition for formation of a curl 
prevention layer with a composition shown below was coated to 3 g/m.sup.2 
on drying and dried by a dryer, followed further by drying in an oven at 
80.degree. C. for 10 minutes, to obtain an image-receiving sheet. 
______________________________________ 
Primer composition 
Polyester polyol (Adcoat AD335AE: Toyo Morton 
15 parts 
K.K., Japan) 
Solvent (MEK: dioxane = 2:1) 
85 parts 
Ink composition for formation of curl prevention layer 
Acrylic resin (BR-85: Mitsubishi Rayon K.K., Japan) 
10 parts 
Solvent (MEK) 90 parts 
______________________________________ 
On the other hand, with a polyester film with a thickness of 4.5 .mu.m 
provided on one surface with a heat-resistant lubricating layer comprising 
a thermosetting acrylic resin (Toray K.K.: Lumilar 5AF53) as the 
substrate, a heat transfer layer was formed on the surface on the opposite 
side to the side where the heat-resistant lubricating layer was provided 
by coating an ink composition for heat transfer formation with the 
composition shown below to a coated amount after drying of 1 g/m.sup.2 to 
obtain a heat transfer sheet. 
______________________________________ 
Yellow ink composition for formation of heat transfer layer 
______________________________________ 
Disperse dye (Macrolex Yellow 6G: Bayer) 
5.5 parts 
(Disperse Yellow 201) 
Polyvinyl butyral (Ethlec BX-1, Sekisui Kagaku K.K.) 
4.5 parts 
Methyl ethyl ketone 45 parts 
Toluene 45 parts 
______________________________________ 
By use of the above heat transfer sheet and the image receiving sheet, 
transfer was effected under the following conditions and the extent of 
curl was examined. Similarly, by use of a transparent PET with a thickness 
of 100 .mu.m (T-100: Toray), a transparent PET with a thickness of 125 
.mu.m (T-125: Toray) as the substrate, the same image receiving layer and 
curl prevention layer as described above were formed thereon, and by use 
of these image receiving sheets, and also by use of the image receiving 
sheets having only receiving layers similarly provided as described above 
on the three kinds of transparent PET as described above, transfer was 
effected and the extents of curl were examined. The results are listed 
together in Table A1. 
Transfer Conditions 
Transfer printer: VY-50 (Hitachi Seisakusho K.K., Japan) 
Printing energy: 90 mJ/mm.sup.2 
One color high density solid printing 
TABLE A1 
______________________________________ 
Substrate Curl *1 (cm) 
______________________________________ 
Example 
T-75 75 .mu.m 
1.0 
T-100 100 .mu.m 
1.2 
T-125 125 .mu.m 
1.2 
Comparative Example 
T-75 75 .mu.m 
7.3 
T-100 100 .mu.m 
6.2 
T-125 125 .mu.m 
6.1 
______________________________________ 
*1: Method of testing extent of curl 
The sheet after transfer was placed on a flat place, the distances from the 
flat surface to the four corners of the sheet were measured, and the 
average value was 
EXAMPLE A2, COMATIVE EXAMPLE A2 
On the backside of each curl prevention layer of the same image receiving 
sheets as in Example A1 (three kinds substrates with thicknesses of 75 
.mu.m, 100 .mu.m, 125 .mu.m), white PET (E-20, Toray K.K.) with a 
thickness of 38 .mu.m was further laminated with a tackifier (SDyne AE349: 
Sekisui Kagaku, thickness 3 .mu.m), and by use of the image receiving 
sheets obtained, and the three kinds of the image receiving sheets having 
white PET laminated similarly as described above on the back surface of 
the same three kinds of the substrates of image receiving sheets as in 
Comparative Example A1 (Comparative Example A2), transfer was effected 
under the same conditions as in Example A1 and the extents of curl were 
examined. The results are shown in Table A2. 
TABLE A2 
______________________________________ 
Substrate Curl *1 (cm) 
______________________________________ 
Example 
T-75 75 .mu.m 
0.9 
T-100 100 .mu.m 
1.2 
T-125 125 .mu.m 
1.0 
Comparative Example 
T-75 75 .mu.m 
6.9 
T-100 100 .mu.m 
6.0 
T-125 125 .mu.m 
5.7 
______________________________________ 
EXAMPLE A3, COMATIVE EXAMPLE A3 
On the back surface of two kinds of vinyl chloride sheets with a thickness 
of 150 .mu.m (C-3033 and C-0436: Mitsubishi Jushi K.K., Japan) and two 
kinds of vinyl sheets with a thickness of 200 .mu.m (C-3033 and C-4020: 
Mitsubishi Jushi K.K., Japan) were coated by a bar coater an ink 
composition for formation of curl prevention layer the .composition shown 
below to 3 g/m.sup.2 on drying and dried by a dryer, followed by drying in 
an oven at 50.degree. C. for 5 minutes, to obtain image receiving sheets 
(since the substrate itself had dye receptivity, no receiving layer was 
provided). On each of the four kinds of image receiving sheets obtained, 
and the four kinds of the image sheets formed into image receiving sheets 
as such without provision of the curl prevention layer on the back surface 
of each of the above substrates as Comparative Examples, transfer was 
effected under the same conditions as the respective Examples A1, and the 
extents of curl were examined. The results are shown in Table A3. 
______________________________________ 
Ink composition for formation of curl prevention layer 
______________________________________ 
Acrylic resin (BR-85: Mitsubishi Rayon K.K.) 
10 parts 
Solvent (Toluene: ethyl acetate = 1:1) 
90 parts 
______________________________________ 
TABLE A3 
______________________________________ 
Substrate Curl *1 (cm) 
______________________________________ 
Example 
C-3033 150 .mu.m 
0 
C-3033 200 .mu.m 
0 
C-0436 150 .mu.m 
0.2 
C-4020 200 .mu.m 
0.3 
Comparative Example 
C-3033 150 .mu.m 
4.2 
C-3033 200 .mu.m 
4.5 
C-0436 150 .mu.m 
5.6 
C-4020 200 .mu.m 
5.3 
______________________________________ 
EXAMPLE A4, COMATIVE EXAMPLE A4 
On the curl prevention layer side of each of the same image receiving 
sheets as in Example A3, Comparative Example A3 was further laminated a 
white PET with a thickness of 38 .mu.m (E-20: Toray) to provide an image 
receiving sheet. By use of these respective image receiving sheets, 
transfer was effected under the same conditions as in Example A1, and the 
extent of curl was examined. The results are shown in Table A4. 
TABLE A4 
______________________________________ 
Substrate Curl *1 (cm) 
______________________________________ 
Example 
C-3033 150 .mu.m 
0 
C-3033 200 .mu.m 
0 
C-0436 150 .mu.m 
0.1 
C-4020 200 .mu.m 
0 
Comparative Example 
C-3033 150 .mu.m 
3.2 
C-3033 200 .mu.m 
3.6 
C-0436 150 .mu.m 
5.3 
C-4020 200 .mu.m 
4.9 
______________________________________ 
EXAMPLE A5, COMATIVE EXAMPLE A5 
On one surface of the same substrate as in Example A1, an ink composition 
for formation of a curl prevention layer with small heating shrinkage 
having the composition shown below was coated by a bar coater to 5 
g/m.sup.2 on drying and dried by a dryer, and then the same ink 
composition for formation of receiving layer as in Example A1 was coated 
on the resin layer surface to 5 g/m.sup.2 on drying and dried, followed 
further by drying in an oven at 80.degree. C. for 10 minutes to form a 
receiving layer to provide an image receiving sheet. By use of these 
respective image receiving sheets, transfer was effected under the same 
conditions and the extent of curl was examined. The results are shown in 
Table A5. Also, in Table A5, the results of Comparative Example A1 are 
also shown together for comparison. 
______________________________________ 
Ink composition for formation of curl prevention layer 
______________________________________ 
Polyurethane (Takelac E-360: Takedayakuhin 
15 parts 
Kagaku K.K.) 
Solvent (MEK: Toluene: = 1:1) 
85 parts 
______________________________________ 
TABLE A5 
______________________________________ 
Substrate Curl *1 (cm) 
______________________________________ 
Example 
T-75 75 .mu.m 
5.3 
T-100 100 .mu.m 
4.5 
T-125 125 .mu.m 
3.8 
Comparative Example 
T-75 75 .mu.m 
7.3 
T-100 100 .mu.m 
6.2 
T-125 125 .mu.m 
6.1 
______________________________________ 
EXAMPLE B1 
On one surface of a soft PVC sheet (C-3033, thickness 150 .mu.m, Mitsubishi 
Jushi K.K.) was coated a 10% toluene solution of an acrylic resin (BR-85, 
Mitsubishi Rayon K.K.) by a bar coater at a ratio of 3 g/m.sup.2 based on 
solids, dried on air, followed by drying in a heating furnace of 
50.degree. C. for 5 minutes to form a curl prevention layer, thus 
obtaining an image receiving sheet of the present invention. 
EXAMPLE B2 
An image receiving sheet of the present invention was obtained in the same 
manner as in Example B1 except for using a soft PVC sheet (C-0436, 
thickness 150 .mu.m, Mitsubishi Jushi K.K.) in place of the PVC sheet in 
Example B1, BR-100 (Mitsubishi Rayon K.K.) as the acrylic resin, and 
xylene as the solvent. 
EXAMPLE B3 
In place of the soft PVC sheet in Example B1, a soft PVC sheet (C-0633, 
thickness 200 .mu.m, Mitsubishi Jushi K.K.) was used, and as the acrylic 
resin, a UV-ray softenable resin coating material 2% benzophenone (Allonix 
5700, Toa Gosei K.K.) was coated by a bar coater at a ratio of 3 
g/m.sup.2, and cured by a high pressure mercury lamp to form a curl 
prevention layer, thus obtaining an image receiving sheet of the present 
invention. 
EXAMPLE B4 
On the same PVC sheet as in Example B1 was coated as an acrylic resin an 
electron beam curable resin coating material (dipentaerythritol 
hexaacrylate) by a bar coater at a ratio of 3 g/m.sup.2, and cured by an 
electron beam irradiating device to form a curl prevention layer, thus 
obtaining an image receiving sheet of the present invention. 
COMATIVE EXAMPLE B1 
An image receiving sheet of Comparative Example was obtained in the same 
manner as in Example B1 except for using methyl ethyl ketone in place of 
toluene in Example B1. 
COMATIVE EXAMPLE B2 
An image receiving sheet of Comparative Example was obtained in the same 
manner as in Example B2 except for using isopropyl alcohol in place of 
xylene in Example B2. 
Printing was performed on the image receiving sheets of the present 
invention and Comparative Examples, and comparison was made as to 
generation of curl immediately after printing, adhesion strength of curl 
prevention layer and whole transparency, to give the results shown below 
in Table B1. 
TABLE B1 
______________________________________ 
Adhesion Dot 
Curl strength Trnaparency 
slippage 
______________________________________ 
Example B1 
.largecircle. 
.largecircle. 
.largecircle. 
.largecircle. 
Example B2 
.largecircle. 
.largecircle. 
.largecircle. 
.largecircle. 
Example B3 
.largecircle. 
.largecircle. 
.largecircle. 
.largecircle. 
Example B4 
.largecircle. 
.largecircle. 
.largecircle. 
.largecircle. 
Comparative 
X X X X 
Example B1 
Comparative 
X X X X 
Example B2 
______________________________________ 
Curl: judged from manner of warping when placed on a flat plane 
.largecircle.: warping of 1 mm or less for A4 size 
X: warping of 100 mm or more for A4 size 
Adhesion strength: peeloff strength with Cellotape 
.largecircle.: no peeloff 
X: 50% or more peeled off 
Transparency: judged by light transmittance 
.largecircle.: 90% or more 
X: 80% or less 
Slippage of dot: judged by the following method 
.largecircle.: 1 mm or less 
X: 5 mm or more 
An ink composition for formation of a dye carrying layer having the 
following composition was prepared, coated by a wire bar and dried on a 
polyethylene terephthalate film with a thickness of 6 .mu.m applied with a 
heat-resistant treatment on the back to a dry coating amount of 1.0 
g/m.sup.2 to obtain heat transfer sheets of yellow and black colors. 
______________________________________ 
Yellow dye (black dye) 1.0 part 
Polyvinyl butyral resin 10.0 parts 
Methyl ethyl ketone/toluene (weight ratio 1/1) 
90.0 parts 
______________________________________ 
The above yellow heat transfer sheet and each of the image receiving sheets 
of Examples and Comparative Examples as described above were superposed 
with the respective dye layer and dye receiving layer being opposed to 
each other, and yellow printing was performed with a thermal head from the 
back of the heat transfer sheet under the conditions of a head application 
voltage of 12.0 V, a pulse width of 16 m.sec., a dot density of 6 
dots/line, subsequently printing was performed on the same position, and 
the slippage between the yellow dot and the black dot was examined by 
enlarged projection by OHP to 50-fold, to give the results shown in the 
above Table B1. 
EXAMPLE C1 
By use of a transparent polyethylene terephthalate film (T-75, thickness 75 
.mu.m, Toray K.K.) as the substrate sheet, a coating solution having the 
following composition was coated on one surface by a bar coater at a ratio 
to 5.0 g/m.sup.2 on drying, dried by a dryer, and then further dried in an 
oven of 80.degree. C. for 10 minutes to form a dye receiving layer. 
______________________________________ 
Composition for dye receiving layer: 
______________________________________ 
Polyester (Vylone 600: Toyobo K.K.) 
4.0 parts 
Vinyl chloride/vinyl acetate copolymer 
6.0 parts 
(#1000 A: Denki Kagaku Kogyo K.K.) 
Amino-modified silicone (X-22-3050C, 
0.2 part 
Shin-etsu Kagaku Kogyo K.K.) 
Epoxy-modified silicone (X-22-3000E, 
0.2 part 
Shin-etsu Kagaku Kogyo K.K.) 
Methyl ethyl ketone/toluene (weight ratio 1/1) 
89.6 parts 
______________________________________ 
On the back of the above film was coated a coating solution for primer 
layer having the following composition at a ratio to 1.0 g/m.sup.2 on 
drying, dried by a dryer, and further a coating solution for curl 
prevention layer having the following composition was coated at a ratio to 
3.0 g/m.sup.2 on drying, simply dried by a dryer, followed further by 
drying in an oven of 80.degree. C. for 10 minutes to form a curl 
prevention layer, thus obtaining an image receiving sheet of the present 
invention. 
______________________________________ 
Composition for primer layer: 
Polyester polyol (Adcoat, Toyo Morton K.K.) 
15.0 parts 
Methyl ethyl ketone/dioxane (weight ratio 2/1) 
85.0 parts 
Composition for curl prevention layer: 
Acrylic resin (BR-85, Mitsubishi Rayon K.K.) 
10.0 parts 
Filler (Orgasol 2002D, Nippon Lilsan K.K.) 
0.1 part 
Methyl ethyl ketone/toluene (weight ratio 1/1) 
89.9 parts 
______________________________________ 
EXAMPLE C2 
An image receiving sheet of the present invention was obtained in the same 
manner as in Example Cl except for using a transparent polyethylene 
terephthalate film (T-100, thickness 100 .mu.m, Toray K.K.) in place of 
the substrate sheet in Example C1. 
EXAMPLE C3 
An image receiving sheet of the present invention was obtained in the same 
manner as in Example C1 except for using a transparent polyethylene 
terephthalate film T-125, thickness 125 .mu.m, Toray K.K.) in place of the 
substrate sheet in Example C1. 
EXAMPLES C4 TO C9 
Image receiving sheets of the present invention were obtained in the same 
manner as in Example C1 except for using a transparent polyethylene 
terephthalate film (T-100, thickness 100 .mu.m, Toray K.K.) in place of 
the substrate sheet in Example C1, and using the following fillers. 
EXAMPLE C4 
Orgasol 2002 D (nylon resin)=0.1 part 
EXAMPLE C5 
Orgasol 2002 UL-D (nylon resin)=0.1 part 
EXAMPLE C6 
Siloid 244 (Fuji Davidson K.K. (microsilica))=0.1 part 
EXAMPLE C7 
Lublon L-5 (Daikin Kogyo K.K. (Teflon resin))=0.1 part 
EXAMPLE C8 
Magster #5 (Tateho Kagaku K.K. (magnesium hydroxide))=0.1 part 
EXAMPLE C9 
Orgasol 2002 D (nylon resin)=0.1 part+Lublon L-5 (Teflon resin))=0.02 part 
COMATIVE EXAMPLES C1 TO C3 
In the curl prevention layer coating solutions in Examples C1 to C3, no 
filler was used, and 90.0 parts of the solvent were used, following 
otherwise the same procedure as in Examples C1 to C3, to obtain image 
receiving sheets of Comparative Examples C1 to C3. 
USE EXAMPLE 
A yellow sublimation type heat transfer sheet (Dainippon Insatsu K.K.) and 
each of the image receiving sheets of the present invention and 
Comparative Examples as described above were superposed with the 
respective dye layer and dye receiving layer being opposed to each other, 
and printing was performed with a thermal head from the back of the heat 
transfer sheet with a printing energy of 90 mJ/mm.sup.2 by means of a 
heat-sensitive sublimation transfer printer (VY-50, Hitachi Seisakusho 
K.K.) to obtain a printed matter. 
EVALUATION METHODS 
(1) Printing Curl Degree 
The printed matter obtained was cut into A4 size, this was placed on a flat 
place, and the curl of the printed matter was evaluated by measuring the 
distance from the flat surface. The measuring places were 4 corners of 
the printed matter, and the value was shown by an average value. 
(2) Paper Feeding and Discharging Characteristics 
In carrying out printing in the above use example, continuous printing was 
performed by setting the image sheets piled up in 50 sheets in a printer 
paper feeding unit. However, for giving sensor adaptability, the tip end 
and the both sides of the image receiving sheet were coated with white 
ink, and further a mark was provided with black ink. The above evaluation 
was repeated for 5 times, and when the image receiving sheets were 
delivered as overlapped in two or more sheets or when paper jamming of the 
printed image receiving sheet occurred during paper discharging, 
evaluation was made as N.G., while evaluation was made as O.K. when there 
is no problem. 
The results shown below in Table C1 were obtained. 
As is apparent from Table C1 shown below, by addition of a filler in the 
curl prevention layer, excellent slip characteristic can be obtained 
together with having curl prevention effect, whereby the problem of 
conveyability during paper feeding and paper discharging has been solved. 
TABLE C1 
______________________________________ 
Printing 
Paper feeding and 
curl (cm) 
discharging characteristic 
______________________________________ 
Example C1 1.0 O.K. 
Comparative 1.1 N.G. 
Example C1 
Example C2 1.2 O.K. 
Comparative 1.2 N.G. 
Example C2 
Example C3 1.2 O.K. 
Comparative 1.2 N.G. 
Example C3 
Example C4 1.1 O.K. 
Example C5 1.3 O.K. 
Example C6 1.0 O.K. 
Example C7 1.1 O.K. 
Example C8 1.2 O.K. 
Example C9 1.1 O.K. 
______________________________________ 
FIELD OF UTILIZATION IN INDUSTRY 
The image receiving sheet of the present invention can be used widely for 
image formation according to the heat-sensitive transfer system by use of 
dot-shaped heating printing means such as a thermal head.