Printing method and a printing apparatus for carrying out the same

An ink sheet (3) is wound around rollers (6), and a recording sheet (4) is placed with a space (d) between the ink sheet (3) and the recording sheet (4) and is advanced. The thickness of the space (d) is a value in the range of 1 to 100 .mu.m. The ink sheet (3) is irradiated with a laser beam (L) emitted by a laser (5) to transfer the dye contained in a dye layer formed on the ink sheet (3) from the ink sheet (3) to the recording sheet (4) for printing. The dye layer of the ink sheet (3) is replenished with the dye (30, 30A) heated and fused by a heater (9) by a dye supply unit (7) at a position other than a position where the ink sheet (3) is irradiated with the laser beam (L). Since the ink sheet and the recording sheet are held with the space (d) having a thickness in the range of 1 to 100 .mu.m, the dye once transferred to the recording sheet is not transferred from the recording sheet to the ink sheet, so that a clear picture having a comparatively high density can be printed. Since the dye layer of the ink sheet is replenished with the dye, the ink sheet can be repeatedly used, so that no waste is produced.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to a printing method and a printing apparatus 
for carrying out the same and, more specifically, to a thermal printing 
method and a thermal printing apparatus for carrying out the same. 
2. Description of the Related Art 
The recent progressive development of color image transmission and 
recording by television cameras, television systems and computer graphic 
systems have sharply increased need to print color images in color 
pictures on recording media, and color printers of various printing 
systems have been developed and applied to various fields. 
A color printer of a thermal dye-transfer printing system, which is one of 
the previously proposed color printers of various printing systems, 
presses an ink sheet formed by coating a sheet with a layer of ink 
prepared by dispersing a dye in a high density in a binder resin and a 
recording medium, such as a recording sheet formed by coating a sheet with 
a dye-accepting resin that accepts the dye, closely against each other, 
applies heat to the ink sheet according to image information with a 
thermal print head placed on the ink sheet or with a laser beam emitted by 
a laser light source so that a quantity of the dye proportional to the 
quantity of heat applied to the ink layer is transferred from the ink 
sheet to the recording medium. A thermal sublimable dye printing method 
employing a sublimable dye or a heat-diffusible dye can be carried out by 
a printing apparatus having a comparatively small size and requiring 
simple maintenance service. A printer of the so-called thermal printing 
system, which prints a full-color picture having continuous gradation 
corresponding to the amount of heat energy by repeating the foregoing 
printing cycle for image signals representing images of the three 
subtractive primaries, namely, yellow, magenta and cyan, has a capability 
of immediately printing a color picture in a high picture quality 
comparable to that of silver salt photographs. 
FIG. 17 is a schematic front view of an essential portion of a thermal 
printer of such a thermal printing system. A thermal print head 91 is 
disposed opposite to a platen roller 93. An ink sheet 92 formed by coating 
a base film 92b with an ink layer 92a, and a recording sheet 100 formed by 
coating a paper sheet 100b with a dyeing resin layer 100a are held between 
the thermal print head 91 and the platen roller 93 and pressed against the 
platen roller 93 by the thermal print head 91. The platen roller 93 is 
rotated to feed the ink sheet 92 and the recording sheet 100. Portions of 
the ink layer 92a are heated locally and selectively by the thermal print 
head 91 to transfer the ink, i.e., a printing material, contained in the 
ink layer 92a to the dye-accepting resin layer 100a of the recording sheet 
in dots for printing. Generally, such a thermal printer is of a line 
printing system provided with an elongate thermal print head disposed with 
its length extending perpendicularly to the direction of feed of the 
recording sheet. 
The ink sheet employed in the foregoing conventional thermal sublimable dye 
printing method is a throw-away ink sheet formed by coating a base sheet, 
such as a polyester film, with a dye layer of a mixture of a dye and a 
binder resin having a dye-to-resin weight ratio of about 1:1, having a 
thickness on the order of 1 .mu.m. Therefore, the use of this ink sheet 
entails problems in resources conservation and environmental protection. 
To improve the utilization of such an ink sheet by repeatedly using the 
same, there have been proposed, for example, a dye layer regenerating 
method which replenishes the used dye layer with the dye, a multidye layer 
forming method which forms a multidye layer consisting of a plurality of 
laminated dye layers, and a relative speed control method which controls 
the ink sheet feed speed relative to the recording sheet feed speed to 
increase the amount of prints which can be printed with a unit length of 
the ink sheet. 
All the conventional thermal printing methods press the dye layer of the 
ink sheet against the dye-accepting layer of the recording sheet and heat 
the dye layer of the ink sheet. For example, when printing a color picture 
by the conventional thermal printing method, an yellow ink sheet is 
superposed on a recording sheet with the yellow dye layer thereof in 
contact with the dye-accepting layer of the recording sheet and the yellow 
ink sheet is heated to form a yellow picture on the recording sheet, a 
magenta ink sheet is superposed on the recording sheet with the magenta 
dye layer thereof in contact with the dye-accepting layer of the recording 
sheet and the magenta ink sheet is heated to superpose a magenta picture 
and the yellow picture on the recording sheet, a cyan ink sheet is 
superposed on the recording sheet with the cyan dye layer thereof in 
contact with the dye-accepting layer of the recording sheet and the cyan 
ink layer is heated to superpose a cyan picture, the yellow picture and 
the magenta picture on the recording sheet, and, when need be, a black ink 
sheet is superposed on the recording sheet with the black ink layer 
thereof in contact with the dye-accepting layer of the recording sheet and 
the black ink sheet is heated to superpose a black picture, the yellow 
picture, the magenta picture and the cyan picture on the recording sheet 
to form a color picture. 
Thus, the conventional thermal printing method prints pictures respectively 
having different colors successively by pressing a dye layer having a 
color different from those of the previously printed pictures against the 
previously printed pictures when printing a color picture. Therefore, it 
occurs sometimes that the dyes previously printed on the recording sheet 
are transferred from the recording sheet to the dye layer of an ink sheet 
for printing the next picture to deteriorate the picture quality and to 
contaminate the dye layer of the ink sheet for printing the next picture. 
When the ink sheet is used repeatedly, the contamination of the dye layer 
thereof is a significant problem. 
OBJECT AND SUMMARY OF THE INVENTION 
The present invention has been made in view of the foregoing problems in 
the prior art and it is therefore an object of the present invention to 
provide a printing method capable of being carried out without producing 
any waste, such as used ink sheets, by a printing apparatus capable of 
operating at a high thermal efficiency and having a small, lightweight 
construction. 
Another object of the present invention is to provide a printing apparatus 
capable of operating at a high thermal efficiency without producing any 
waste, such as used ink sheets, and having a small, lightweight 
construction. 
The inventors of the present invention made zealous studies of thermal 
printing and have successfully made the present invention. According to 
the present invention, a full-color picture is formed by repeating a 
printing cycle having steps of disposing a recording medium having a 
dye-accepting layer opposite to a printing unit having a fusible dye layer 
with a minute space therebetween, and selectively evaporating or 
sublimating the dye stored on the printing unit by a suitable heating 
means, such as a thermal print head or a laser, to transfer the dye 
through the minute space from the printing unit to the recording medium so 
that a picture of one of the three subtractive primaries, i.e., yellow, 
magenta and cyan, having continuous gradation is formed on the recording 
medium for image signals representing separate images of the three 
subtractive primaries. 
Since the dye contains little binder resin, the dye can be fed continuously 
to the printing unit as the dye is consumed for printing by letting the 
fused dye flow from a dye tank into the printing unit or by continuously 
moving a suitable base sheet coated with the dye into the printing unit, 
and the printing unit does not produce used ink sheets. 
When an ink Sheet having a binderless dye layer is used, the fused dye 
spreads over the surface of the recording sheet to spoil the clearness of 
the printed picture. The fused dye is caused to spread by the surface 
tension of a nonheated portion of the binderless dye layer greater than 
that of the heated portion of the binderless dye layer. Such undesirable 
spread of the fused dye can be effectively prevented by adding a surface 
active agent to the dye to reduce the surface tension of the fused dye. 
When carrying out a thermal dye-sublimation printing method, the 
temperature of the heating medium for heating the dye must be considerably 
high to sublimate the dye at a sufficiently high rate. However, nothing 
about the boiling point of the dye is taken into consideration by the 
conventional thermal dye-sublimation printing method. This problem can be 
solved by using a dye having a boiling point not higher than the 
decomposition point. 
The present invention provides a printing method which uses a heating 
medium supporting printing materials and capable of heating the printing 
materials by applying heat generated by a heat source to the printing 
materials, comprising: holding the printing materials and a recording 
medium with a space having a thickness in the range of 1 to 100 .mu.m 
therebetween; and heating the printing materials by the heating medium to 
transfer the printing materials to the recording medium. It is desirable 
to heat portions of the dyes supported on the heating medium by 
irradiating the portions of the dyes selectively according to image 
signals with light. A full-color picture can be printed when the heating 
medium supports a plurality of dyes differing from each other in color. It 
is desirable to replenish the heating medium with dyes by a dye supply 
means to use the heating medium repeatedly. It is desirable to replenish 
the heating medium with the dye at a position other than a position where 
the dyes are irradiated with light. It is desirable that the dyes are 
heated when the same are supplied to the heating medium by the dye supply 
means, and the dyes do not contain any binder. It is still more desirable 
that a surface active agent is added to the dye, the surface active agent 
is an anionic surface active agent, and the surface active agent content 
of the dye layer is in the range of 0.001 to 10% by weight. It is still 
more desirable that the printing materials are gasified or sublimated so 
that the printing materials are transferred through the space between the 
printing materials and the recording medium to the recording medium for 
printing, each of the printing materials has a boiling point not higher 
than a temperature at which the same is decomposed, and each of the dyes 
as the printing materials has a boiling point in the range of 50.degree. 
to 600.degree. C. and, it is further desirable that each of the dyes has a 
boiling point in the range of 250.degree. to 450.degree. C. 
The present invention provides a printing apparatus comprising a heating 
medium, and a heating means for heating the printing materials, and 
capable of carrying out the foregoing printing method. 
According to the present invention, a printing material held by a heating 
medium, and a recording medium are held with a space having a thickness in 
the range of 1 to 100.mu.m, and the printing material is heated by the 
heating medium to transfer the printing material from the heating medium 
to the recording medium. Therefore, the present invention has the 
following effects. 
Since the printing material is separated from the recording medium, the 
printing material need not be carried by a carrying member. Therefore, the 
carrying member and the residual printing material remaining on the 
carrying member after printing need not be disposed of as waste. Since the 
printing apparatus need not be provided with any means for holding the 
printing material and the recording medium in contact with each other, the 
printing apparatus can be formed in a comparatively small, lightweight 
construction. 
When a plurality of printing materials are used for printing a multicolor 
picture by superposing a plurality of monochromatic color pictures of the 
plurality of printing materials, the previously printed printing material 
will not be transferred from the recording medium to the next printing 
material and hence the next printing material will not be contaminated. 
Since the thickness of the space between the printing material and the 
recording medium is 1 .mu.m or greater, the foregoing effects can be 
surely secured. Since the thickness of the space is 100 .mu.m or smaller, 
pictures can be printed clearly in a comparatively high print density.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
A printing method in accordance with the present invention holds a printing 
medium and a recording medium with a space having a thickness in the range 
of 1 to 100 .mu.m, preferably, in the range of 2 to 50 .mu.m, therebetween 
to transfer a dye from the printing medium to the recording medium. 
Reverse transfer, in which the dye transferred from the printing medium to 
the recording medium is transferred from the recording medium to the 
printing medium, will occur if the size of the space is less than 1 .mu.m, 
and the dye of the printing medium cannot be satisfactorily transferred 
from the printing medium to the recording medium if the size of the space 
is greater than 100 .mu.m. Since the printing medium and the recording 
medium are spaced apart by such a space, thermal energy supplied to the 
printing medium for printing is not transmitted to the recording medium 
and hence the dye previously printed on the recording medium is not heated 
and, consequently, the reverse transfer of the dye, i.e., the transfer of 
the dye from the recording medium to the printing medium, which is 
undesirable particularly when printing a color picture, does not occur. 
Since the thermal energy supplied to the printing medium is not 
transmitted to the recording medium, the dye layer of the printing medium 
can be concentratedly heated, which enables printing a sharp picture. A 
printing method of the present invention having those advantages is 
particularly suitable for printing a color picture by using a plurality of 
dye layers. 
The printing medium and the recording medium may be held with the given 
space therebetween by any suitable means. For example, when a thermal 
print head is employed for heating the printing medium, the dye-accepting 
layer of the recording medium may contain beads to make the surface of the 
dye-accepting layer irregular so that the space having the given size in 
the range of 1 to 100 .mu.m is formed between the dye layer of the 
printing medium and the recording medium when the thermal printing head is 
pressed against the dye layer of the printing medium. For example, a dye 
layer, i.e., the dye layer of the printing medium, may be formed so that 
the same sinks beneath the surface of the heating medium. 
The composition of the printing method of the present invention may be the 
same as that of the conventional thermal printing method except for 
securing a given space between the printing medium and the recording 
medium, and the printing method of the present invention may employ 
printing materials, heating means for heating the printing materials, and 
a recording medium which are employed in carrying out the conventional 
thermal printing method. For example, a printing medium having a dye layer 
containing a dye and a binder or a binderless dye layer may be used. The 
printing method of the present invention, similarly to the conventional 
printing method, may use a thermal print head or a laser beam for heating 
the printing medium. It is preferable to use a laser beam capable of 
instantly applying thermal energy in a high energy density to the dye 
layer of the printing medium to transfer the dye from the dye layer 
through the space to the recording medium. When a laser beam is used for 
heating the dye layer, it is preferable to use a heating medium containing 
a substance that generates heat upon the absorption of the laser beam, 
such as carbon black or platinum black, or a heating medium provided with 
a thin layer of a substance that generates heat upon the absorption of the 
laser beam, such as a cobalt-nickel alloy. 
It is preferable to regenerate the dye layer of the printing medium to use 
the printing medium repeatedly. The printing method of the present 
invention is particularly advantageous for repeatedly using the printing 
medium by regenerating the dye layer of the same. Transfer of the dye of 
the dye layer of the printing medium from the printing medium to the 
recording medium and the regeneration of the dye layer of the printing 
medium can be achieved by various means. 
Means for transferring the dye of the dye layer of the printing medium from 
the printing medium to the recording medium and means for regenerating the 
dye layer of the printing medium will be described hereinafter on an 
assumption that the printing medium is a printing tape and a laser beam is 
used as heating means. 
As shown in FIGS. 3(a) and 3(b), a tape-shaped printing medium 3 has a base 
tape 1 formed of polyester or the like, an yellow dye layer Y, a magenta 
dye layer M and a cyan dye layer C formed in stripes on one of the major 
surface of the base tape 1, and thin platinum black layers 2, which absorb 
a laser beam and generate heat, formed in stripes on the other major 
surface of the base tape 1 so as to correspond to the yellow dye layer Y, 
the magenta dye layer M and the cyan dye layer C, respectively, as best 
shown in FIG. 3(b) 
A printing method that uses the printing medium 3 shown in FIGS. 3(a) and 
3(b) uses a printing apparatus as shown in FIG. 1(a). A recording sheet 4 
is placed opposite to the printing medium 3 with a predetermined space d 
therebetween, and then the printing medium 3 is irradiated with a laser 
beam L indicated by the arrow A emitted by a laser 5 to heat the recording 
medium 3 for printing. Since the printing medium 3 and the recording sheet 
4 are separated from each other by the space d, the reverse transfer of 
the dye does not occur and a picture can be printed in a high picture 
quality on the recording sheet 4. After one printing cycle has been 
completed, a roller 6 is rotated to turn the printing medium 3 and the dye 
layer of the printing medium 3 is replenished with the dye by a dye supply 
unit 7 at a position other than the position where the printing medium 3 
is irradiated with the laser beam L to regenerate the dye layer of the 
printing medium 3. Thus, the printing medium 3 can be repeatedly used. As 
shown in FIG. 1(b), the dye supply unit 7 has a dye tank 8 for containing 
the powdered dye 30, and a heater 9 for heating the powdered dye 30 when 
the powdered dye 30 is supplied to the printing medium 3. When supplying 
the powdered dye 30, the printing medium 3 is passed through the dye 
supply unit 7, and at least a portion of the powdered dye 30 contained in 
the dye tank 8 and covering the surface of the printing medium 3 is fused 
by the heat generated by the heater 9 so that a dye film 30A is formed on 
the surface of the printing medium 3. 
FIG. 2 shows cylindrical printing medium 10. The printing medium 10 is 
disposed opposite to a recording sheet 4 with a predetermined space d 
therebetween, and the printing medium 10 is irradiated with a laser beam 
emitted by a laser 5 as indicated by the arrow to heat the printing medium 
10 for printing. Since the printing medium 10 and the recording sheet 4 
are separated by the space d, the reverse transfer of the dye does not 
occur and a picture can be printed on the recording sheet 4 in a 
satisfactory picture quality. After one printing cycle has been completed, 
the printing medium 10 is rotated in the direction of the arrow B, and the 
printing medium 10 is replenished with the dye by a dye supply unit 7 
disposed at a position other than the position where the printing medium 
10 is irradiated with the laser beam to regenerate the dye layer of the 
printing medium 10. Thus, the printing medium 10 can be repeatedly used. 
The dye supply unit 7 may be the same as that shown in FIG. 1(b). 
FIG. 4 shows a disk-shaped printing medium 11. The printing medium 11 has a 
disk-shaped base sheet 12, a circular yellow dye layer Y, a circular 
magenta dye layer M and a circular cyan dye layer C, which are concentric 
with each other, formed on one of the major surfaces of the base sheet 12, 
and concentric circular platinum black thin layers 2 formed on the other 
major surface of the base sheet 12 so as to correspond to the yellow dye 
layer Y, the magenta dye layer M and the cyan dye layer C, respectively. 
When printing a picture on a recording sheet 4, the printing medium 11 is 
disposed opposite to the recording sheet 4 with a predetermined space d 
therebetween, and the printing medium 11 is irradiated with laser beams 
emitted by lasers to heat the printing medium 11 for printing. Since the 
printing medium 11 and the recording sheet 4 are separated from each other 
by the predetermined space d, the reverse transfer of the dyes will not 
occur and a picture can be printed on the recording sheet 4 in a 
satisfactory picture quality. After one printing cycle has been completed, 
the printing medium 11 is rotated and the yellow dye layer Y, the magenta 
dye layer M and the cyan dye layer C are replenished with the 
corresponding dyes by dye supply units 7 at positions other than the 
positions where the yellow dye layer Y, the magenta dye layer M and the 
cyan dye layer C are irradiated with the laser beams, respectively, to 
regenerate the yellow dye layer Y, the magenta dye layer M and the cyan 
dye layer C. Thus, the printing medium 11 can be repeatedly used. The dye 
supply units 7 may be the same as that shown in FIG. 1(b). 
The foregoing printing method of the present invention can be carried out 
by using any suitable printing medium, such as the printing medium 3, 10 
or 11. It is also possible to carry out the printing method of the present 
invention by using the following printing medium. 
The printing medium is featured by a dye layer containing a dye and a 
surface active agent. The surface active agent contained in the dye layer 
suppresses the spread of the fused dye on a recording medium so that a 
picture can be clearly printed on the recording sheet. The surface active 
agent may be of any kind, provided that the surface active agent is 
capable of reducing the surface tension of the fused dye or the dependence 
of the surface of the dye on temperature. It is preferable that the 
surface active agent is stable at temperatures in the range of 100.degree. 
to 200.degree. C., has a low volatility and is noncombustible. 
Possible surface active agents are, for example, anionic surface active 
agents including fatty acids respectively having carbon numbers in the 
range of six to twenty-four, alkali salts of those fatty acids, higher 
alcohol ester phosphate salts and higher alcohol sulfonates, cationic 
surface active agents including higher carboxyl amine salts, quaternary 
ammonium salts and alkyl pyridium salts, nonionic surface active agents 
including polyoxyethylene alkyl esters, polyoxyethylene alkyl esters and 
polyoxyethylene phenol ethers, and silicone surface active agents 
including dimethyl polysiloxanes and copolymers of dimethyl polysiloxanes 
and polyoxyethylene. 
Above all, anionic surface active agents are preferable because the acid 
residues of anionic surface active agents have high affinity for the amine 
residues of the dyes. These surface active agents may be used individually 
or in combination. Although dependent on the types of the dye and the 
surface active agent, generally, the surface active agent content of the 
dye layer is in the range of 0.001 to 10% by weight. The dye of the 
printing medium may be a heat-diffusive dye, such as a sublimable dye. The 
dye layer of the printing medium may contain a binder and various 
additives. However, to enable the printing medium to function properly for 
repeated use, it is preferable that the dye layer of the printing medium 
does not contain any binder and contain the dye in a large amount of dye 
per unit area of the dye layer so that the dye can be quickly supplied 
when heated. There is no particular restriction on the morphology of the 
printing medium of the present invention, provided that the dye layer of 
the printing medium contains a dye and a surface active agent. For 
example, the printing medium may be an ink ribbon, similar to the 
conventional ink ribbon, having a base sheet and a dye layer formed on the 
base sheet or may be a printing chip having a base plate, such as a glass 
plate, and a dye layer formed on the portion of the surface of the base 
plate. 
Although there is no particular restriction on the printing method that 
uses the printing medium, a transfer printing method that places a 
printing medium and a recording medium in contact with each other is not 
suitable for using the printing medium of the present invention because 
the dye of the dye layer not containing any binder of the printing medium 
of the present invention is fused for transfer. Therefore, the thermal 
sublimation transfer printing method of the present invention that holds 
the printing medium and the recording medium with a space of a given 
thickness therebetween is suitable for using the printing medium of the 
present invention. 
Since the printing method of the present invention holds the printing 
medium and the recording medium with a space having a thickness in the 
range of 1 to 100 .mu.m therebetween during printing, the heat supplied to 
the printing medium for thermal transfer is not diffused in the recording 
medium and unnecessary heating of the dye previously transferred from the 
printing medium to the recording medium can be avoided. Accordingly, 
reverse transfer of dyes, which is a significant problem in printing a 
color picture, can be prevented. Since portions of the dye layer of the 
printing medium can be concentratedly heated, a sharp picture can be 
printed. 
Since the printing medium of the present invention has a dye layer 
containing a surface active agent, the surface tension of the fused dye or 
the temperature dependence of the surface tension of the fused dye can be 
reduced. Accordingly, when portions of the dye layer to be transferred to 
the recording medium are heated to fuse the dye in the heated portions of 
the dye layer, the dye in the heated portions of the dye layer will not be 
caused to spread by the nonheated portions of the dye layer. Consequently, 
the reduction of the dye density of the heated portions of the dye layer 
can be prevented. This effect is particularly conspicuous when the dye 
layer is a binderless dye layer. 
In view of preventing the thermal deterioration of the heating medium, it 
is desirable that the dye, i.e., the printing material, for thermal 
sublimation transfer printing has a boiling point not higher than its 
decomposition point. It is desirable that the dye has a boiling point in 
the range of 50.degree. to 600.degree. C., more desirably in the range of 
80.degree. to 450.degree. C., most desirably in the range of 250.degree. 
to 450.degree. C. When a dye having such a comparatively low boiling point 
is used, the heating medium need not be heated at an excessively high 
temperature and whereby the thermal deterioration of the heating medium 
can be prevented. Possible dyes are dyes having dicyanostyryl groups, 
quinophthalone dyes and anthraquinone dyes. 
Dicyanostyryl Group 
##STR1## 
R: Hydrogen atom or a substituent, such as an alkyl group or a cyanogroup 
Quinophthalone Dye 
##STR2## 
X: A halogen atom 
The following dyes are exemplary possible dyes. 
Yellow dyes: 
HSY-2068 (Mitsubishi Kasei) 
Solvent-Yellow-56 
Magenta dyes 
HSR-2109 (Mitsubishi Kasei) 
HSR-2031 (Mitsubishi Kasei) 
HSR-2063 (Mitsubishi Kasei) 
Solvent-Red-19 
Cyan dyes 
HSB-2000-2 (Mitsubishi Kasei) 
Solvent-Blue-35 
Results of experiments obtained through experimental printing using the 
printing media shown in FIGS. 3(a), 3(b) and 4 and the printing apparatus 
shown in FIGS. 1(a), 1(b) and 2 will be described. 
EXPERIMENT 1 
An ink sheet similar to a printing medium shown in FIG. 3(b) was fabricated 
by forming three parallel grooves 1a, 1b and 1c having a depth of 5 .mu.m 
and a width of 100 .mu.m in one major surface of a titanium film 1 having 
a thickness of 10 .mu.m, forming a yellow dye layer containing an yellow 
dye Y (ESC151.RTM., Sumitomo Kagaku), a magenta dye layer containing a 
magenta dye M (ESC451.RTM., Sumitomo Kagaku) and a cyan dye layer 
containing a cyan dye C (Foron Blue.RTM., Sando) respectively in the three 
parallel grooves 1a, 1b and 1c, and forming thin platinum black layers 2 
having a width of 200 .mu.m and a thickness of 5 .mu.m on the other major 
surface of the titanium film 1 in areas respectively corresponding to the 
dye layers. 
Linear color pictures were formed on a recording sheet 4 (VPM-30STA.RTM., 
Sony Corp.) by using the ink sheet 3 in a manner as shown in FIG. 1(a), 
and the dye layers were replenished continuously with the corresponding 
dyes by dye supply units 7 as shown in FIG. 1(b). The ink sheet 3 was 
disposed with the surface provided with the dye layers facing the 
dye-accepting layer of the recording sheet 4 with a space d having a 
thickness of 10 .mu.m between the surface provided with the dye layers and 
the dye-accepting layer, the ink sheet 3 was moved at a speed of 4 cm/sec, 
the recording sheet 4 was fed at a speed of 2 cm/sec, and the ink sheet 
was irradiated with laser beams having a wavelength of 780 nm emitted by 
semiconductor lasers having an output capacity of 30 mW for continuous 
printing. During the printing process, powdered dyes 30 contained in the 
dye supply units were heated with heaters 9 to fuse the dyes 30 and the 
fused dyes 30A were supplied to the corresponding dye layers of the ink 
sheet 3. 
Linear color pictures having an optical density of 2.3 and a width of 85 
.mu.m were formed by the printing process, in which the reverse transfer 
of the dyes did not occur. The dye layers of the ink sheet 3 were 
replenished with the corresponding dyes and the printing process was 
carried out continuously without deteriorating picture quality. 
EXPERIMENT 2 
An ink cylinder 10, i.e., a printing medium, formed by wrapping the ink 
sheet 3 employed in the experiment 1 around a polyethylene terephthalate 
cylinder 10a having a wall thickness of 100 .mu.m was used. Linear color 
pictures were formed on a recording sheet 4 (VPM-30STA.RTM., Sony Corp.) 
by using the ink cylinder 10 in a manner as shown in FIG. 2, and the dye 
layers were replenished continuously with the corresponding dyes by dye 
supply units 7 as shown in FIG. 1(b). The ink cylinder 10 was disposed 
with the surface provided with the dye layers facing the dye-accepting 
layer of the recording sheet 4 with a space d having a thickness of 10 
.mu.m, the ink cylinder 10 was rotated at one turn per second, the 
recording sheet 4 was fed at a speed of 2 cm/sec, and the ink cylinder 10 
was irradiated with laser beams having a wavelength of 780 nm emitted by 
semiconductor lasers having an output capacity of 30 mW for continuous 
printing. During the printing process, the powdered dyes 30 contained in 
the dye supply units 7 were heated with heaters 9 to fuse the dyes and the 
fused dyes 30A were supplied to the corresponding dye layers of the ink 
sheet 3. 
Linear color pictures having an optical density of 2.3 and a width of 85 
.mu.m were printed by the printing process, in which the reverse transfer 
of the dyes did not occur. The dye layers of the ink sheet 3 were 
replenished with the corresponding dyes and the printing process was 
carried out continuously without deteriorating picture quality. 
EXPERIMENT 3 
An ink disk, i.e., a printing medium, was fabricated by forming a disk by 
mounting a circular titanium sheet 12 having a diameter of 20 mm and a 
thickness of 10 .mu.m on a glass disk having a diameter of 20 mm and a 
thickness of 100 .mu.m, forming three concentric grooves 12a, 12b and 12c 
having a depth of 5 .mu.m and a width of 100 .mu.m in one of the major 
surfaces, forming a yellow dye layer containing a yellow dye Y 
(ESC151.RTM., Sumitomo Kagaku), a magenta dye layer containing a magenta 
dye M (ESC451.RTM., Sumitomo Kagaku) and a cyan dye layer containing a 
cyan dye C (Foron Blue.RTM., Sando) respectively in the three concentric 
grooves 12a, 12b and 12c, and forming concentric thin platinum black 
layers 2 having a width of 200 .mu.m and a thickness of 5 .mu.m on the 
back surface of the titanium sheet 12 in areas corresponding to the dye 
layers. Linear color pictures were printed on a recording sheet 4 
(VPM-30STA.RTM., Sony Corp.) by using the ink disk. During the printing 
process, the dye layers of the ink disk were replenished continuously with 
the corresponding dyes by dye supply units 7, indicated by alternate long 
and two short dashes lines, as shown in FIG. 1(b). The ink disk was 
disposed with its dye layers facing the dye-accepting layer of the 
recording sheet 4 with a space having a thickness of 10 .mu.m, the ink 
disk was turned at one turn per second, the recording sheet 4 was fed at a 
speed of 2 cm/sec, the ink disk was irradiated with laser beams having a 
wavelength of 780 nm emitted by semiconductor lasers having an output 
capacity of 30 mW for continuous printing. During the printing process, 
the dyes 30 contained in the dye supply units 7 were heated by heaters 9 
to fuse the dyes 30 and the fused dyes 30A were supplied to the dye layers 
of the ink disk. 
Linear color pictures having an optical density of 2.2 and a width of 85 
.mu.m were formed by the printing process, in which the reverse transfer 
of the dyes did not occur. The dye layers of the ink disk were replenished 
with the corresponding dyes and the printing process was carried out 
continuously without deteriorating picture quality. 
COMATIVE EXPERIMENT 1 
A printing process for the comparative experiment 1 was the same as that 
for the experiment 1, except that an ink sheet provided with dye layers 
having a thickness of 10 .mu.m was employed and the ink sheet and the 
recording sheet were kept in contact with each other for the printing 
process for the comparative experiment 1. Reverse transfer of the dyes 
occurred and unclear linear color pictures were formed. 
The following experiments were conducted to verify the effect of the 
addition of a surface active agent to the ink layer. 
EXPERIMENT 4 
An ink sheet was fabricated by preparing a dye solution by dissolving a 
magenta dye (HSR 2030.RTM., Mitsubishi Kasei) in a concentration of 10 g/l 
and stearyl, i.e., a surface active agent, in a concentration of 10 mg/l 
in aceton, coating the surface of an aramide film provided with a Ni/Co 
alloy film, i.e., light-to-heat conversion layer, having a thickness of 
0.2 .mu.m formed by evaporation with the dye solution in a thickness of 
about 1 .mu.m by means of a wire bar, and evaporating aceton from the dye 
solution coating the surface of the aramide film in a thickness of about 4 
.mu.m. A linear picture was printed on a recording sheet (VPM-30STA.RTM. 
Sony Corp.) by an experimental printing apparatus shown in FIG. 6. 
FIG. 6 is an enlarged sectional view of the ink sheet. The ink sheet 17 is 
fabricated by sequentially forming a 0.2 .mu.m thick Ni-Co alloy film 17b 
by evaporation and a 1 .mu.m thick magenta dye layer 17c on a 4 .mu.m 
thick aramide film 17a. FIG. 5 is a schematic front view of an 
experimental printing apparatus. A standard 28 is set upright on a base 
plate 27, brackets 29A, 29B and 29C are fixed to the standard 28. Lenses 
15a and 15b, and a semiconductor laser chip (SV-203.RTM., Sony Corp.) 14A 
having an output capacity of 10 mW are supported respectively on the 
brackets 29C, 29B and 29A with their optical axes in alignment. The lenses 
15a and 15b constitute a focusing lens system 15. A recording sheet 4 is 
placed on an XY stage 16 mounted on the base plate 27, and an ink sheet is 
superposed on the recording sheet 4 for thermal printing. In this 
experiment, the ink sheet 17 is superposed on the recording sheet 4 with a 
spacer 21 therebetween. A laser beam was focused on the recording sheet 4 
in a spot of 20 .mu.m.times.30 .mu.m while the recording sheet 4 was fed 
at a liner speed of 1 cm/sec. A line having an optical density of 2.4 and 
a width of about 110 .mu.m was printed. 
COMATIVE EXPERIMENT 2 
An ink sheet used in the comparative experiment 2 was the same as that used 
in the experiment 4, except that the ink sheet used in the comparative 
experiment 2 is provided with an ink layer not containing any surface 
active agent. The experimental printing apparatus shown in FIG. 5 was 
used. A line having a small optical density of 1.2 and a width of about 30 
.mu.m was printed. The amount of the dye transferred from the ink sheet to 
the recording sheet 4 was about 1/3 of the amount of the dye transferred 
from the ink sheet to the recording sheet in the experiment 4. 
EXPERIMENT 5 
In the experiment 5, neither an ink sheet nor an ink film was used, and a 
printing chip, i.e., a heating medium, carrying a mixture of a dye and a 
surface active agent was used. FIG. 7 is a schematic front view of an 
experimental printing apparatus employed in the experiment 5. 
The printing apparatus shown in FIG. 7 is similar in construction to that 
shown in FIG. 5, except that the former has a bracket 29D fixed to a 
standard 28, and a printing chip 18 held on the bracket 29D in addition to 
the components of the latter. As shown in FIG. 7, a standard 28 is set 
upright on a base plate 27, brackets 29A, 29B, 29C and 29D are fixed to 
the standard 28, the printing chip 18, lenses 15a and 15b, and a 
semiconductor laser chip (SLD-203.RTM., Sony Corp.) 14B are held 
respectively on the brackets 29D, 29C, 29B and 29A with their optical axes 
in alignment. The lenses 15a and 15b constitute a focusing lens system 15. 
An XY stage 16 is fixedly mounted on the base plate 27, and a recording 
sheet 4 is placed on the XY stage 16. 
FIGS. 8(a) and 9 are an enlarged sectional view and an enlarged bottom 
view, respectively, of the printing chip 18. The printing chip 18 
comprises a glass plate 20, an ITO film (indium tin oxide film) 19 as a 
resistance heating element formed by evaporation on the lower surface of 
the glass plate 20, heat insulating spacers 21 put in contact with the ITO 
film 19, a 4 .mu.m thick polyimide film 22 coated with an evaporated 0.2 
.mu.m thick Ni/Co alloy film 23 as a light-to-heat conversion element and 
extended on the spacers 21, and a 10 .mu.m thick stainless steel sheet 24 
attached to the polyimide film 22 and provided with a dye pit 24h having a 
diameter of about 1 mm. During a printing process, the stainless steel 
sheet 24 is in contact with the recording sheet 4 (STA-30.RTM., Sony 
Corp.). 
In this experiment, the printing chip 18 was removed from the printing 
apparatus, the printing chip 18 was held with the dye pit 24 facing up in 
a state shown in 8(b), a mixture 25 of 1 g of a magenta dye (HSR2031.RTM., 
Mitsubishi Kasei) and 1 mg of a surface active agent was put in the dye 
pit 24 so as to fill about 1/3 of the depth thereof, energy was supplied 
to the resistance heating element 19 to fuse the mixture 25, and then the 
printing chip 18 was set in place on the bracket 29D. The printing chip 18 
was irradiated with a laser beam emitted by the semiconductor laser chip 
14B while the recording sheet 4 was fed at a linear speed of 1 cm/sec. A 
line having an optical density of 2.4 and a width of about 110 .mu.m was 
printed. 
COMATIVE EXPERIMENT 3 
The comparative experiment 3 is the same as the experiment 5, except that 
the former does not use any surface active agent. The printing chip 18 and 
the printing apparatus shown in FIG. 7 were used. Any picture could not be 
printed at all. 
Results of experiments conducted to examine the dependence of results of 
printing on the boiling point of the dye will be described hereinafter. 
EXPERIMENT 6 
FIG. 10 is a schematic front view of an experimental printing apparatus 
employed in the experiment 6. The printing apparatus shown in FIG. 10 is 
the same in construction as the printing apparatus shown in FIG. 7, except 
that the former has a printing chip 18 disposed opposite to a recording 
sheet 4 with a space d therebetween. 
A powdered yellow dye 26A (HSY-2068.RTM., Mitsubishi Kasei) having a 
melting point 103.degree. C. and boiling point of 378.degree. C. was put 
in the dye pit 24h formed in the stainless steel sheet 24 (FIG. 8(a)), and 
then energy was supplied to the resistance heating element 19 to heat the 
yellow dye at 120.degree. C. to fuse the same. The depth of the fused dye 
26B in the dye pit 24h was 4 .mu.m. The fused dye 26B on the Ni/Co alloy 
film 23 was irradiated continuously for sixty minutes with a laser beam 
emitted by the semiconductor laser 14B having an output capacity of 30 mW 
while the recording sheet 4 was fed at a speed of 10 cm/sec. The laser 
beam was focused in a spot of 20 .mu.m.times.30 .mu.m. 
A line having an optical density of 1.8 and a width of about 85 .mu.m was 
printed on the recording sheet 4. There was no thermal deterioration of 
the light-to-heat conversion layer consisting of the polyimide film 22 and 
the Ni/Co alloy film 23, and portions of the printing chip 18 around the 
light-to-heat conversion layer. 
EXPERIMENT 7 
A printing process similar to that carried out in the experiment 6 was 
carried out. Eyes shown in the following table were Used. The chemical 
constitution of the representative one of the dyes of each color is as 
follows. 
##STR3## 
The dyes shown in the table, similarly to the dye used in the experiment 6, 
were heated to temperatures above the corresponding melting points for the 
experimental printing. All the lines formed by printing the dyes had 
optical densities not lower than 1.8. There was no thermal deterioration 
of the light-to-heat conversion layer and portions of the printing chip 
around the light-to-heat conversion chip. 
TABLE 
______________________________________ 
Dyes m.p.(.degree.C.) 
b.p.(.degree.C.) 
______________________________________ 
Solvent Yellow-56(Y) 96 336 
Solvent Red-19 (M) 130 323 
HSR-2109 (Mitsubishi Kasei) (M) 
65 368 
HSR-2031 (Mitsubishi Kasei) (M) 
123 427 
HSR-2063 (Mitsubishi Kasei) (M) 
186 398 
Solvent Blue-35 (C) 121 398 
HSB-2000-2 (Mitsubishi Kasei) (C) 
157 358 
______________________________________ 
Note: 
(Y): Yellow dye, (M): Magenta dye, (C): Cyan dye 
COMATIVE EXPERIMENT 4 
A dye (MS Blue.RTM., Mitsui Toatsu) having a melting point of 117.degree. 
C., a decomposition point of 222.degree. C. and a boiling point higher 
than the decomposition point was used. A printing process exactly the same 
as those carried out in the experiments 6 and 7 was carried out. The 
light-to-heat conversion layer was perforated fifteen minutes after the 
start of irradiation with the laser beam, which made the transfer of the 
dye impossible. 
It is known from the results of the comparative experiment 4 and the 
experiments 6 and 7 that pictures can be satisfactorily printed when dyes 
having the boiling points not higher than their decomposition point are 
used. 
Dyes having boiling points not higher than their decomposition points other 
than those shown in the experiments 6 and 7 are as follows. 
##STR4## 
A printing apparatus in a preferred embodiment according to the present 
invention will be described hereinafter. The construction of the printing 
unit of the printing apparatus will be briefly described with reference to 
FIG. 14. 
A semiconductor laser chip 48 is disposed above a light-to-heat conversion 
layer 51, and a recording sheet 80 is placed under the light-to-heat 
conversion layer 51. The recording sheet 80 has a base sheet 80b, and a 
dye-accepting layer 80a formed on the upper surface of the base sheet 80b. 
A space d having a thickness in the range of 10 to 100 .mu.m is secured 
between the light-to-heat conversion layer 51 and the dye-accepting layer 
80a. In this embodiment, the thickness of the space d is 60 .mu.m. A dye 
layer 61 or a fused dye layer 62 is formed on the lower surface of the 
light-to-heat conversion layer 51. The light energy of a laser beam L 
emitted by the semiconductor laser chip 48 is converted into thermal 
energy by the light-to-heat conversion layer 51 to gasify or sublimate the 
dye of the dye layer 61 or the fused dye layer 62. The gasified or 
sublimated dye is transferred through the space d to the dye-accepting 
layer 80a and is fixed to the dye-accepting layer 80a for printing. 
FIG. 11 is a sectional view of the printing unit, FIG. 12 is an exploded 
perspective view of the printing apparatus and FIG. 13 is a schematic 
sectional view of the printing unit for assistance in explaining the 
printing mechanism of the printing apparatus. First the printing mechanism 
will be described with reference to FIGS. 12 and 13. Referring to FIGS. 12 
and 13, a laser sublimation transfer color video printer (laser 
sublimation transfer printer) 31 has a chassis 32 covered with a housing 
32a. A sheet cassette 33 containing recording sheets 80 and a flat platen 
34 are placed on the chassis 32. 
A sheet feed roller 36a, which is driven by a motor 35 or the like, is 
disposed near a sheet outlet 32b formed in the housing 32a, and a 
recording sheet 80 is pressed lightly against the sheet feed roller 36a by 
a pressure roller 36b. A printed-circuit board 37 having a head driving 
circuit and provided with a driving IC 78, and a dc power supply 38 are 
disposed above the sheet cassette 33 within the housing 32a. A print head 
supported in the flat platen 34 is connected to the printed-circuit board 
37 by a flexible harness 37a. 
The print head 40 comprises powdered-dye tanks 41Y, 41M and 41C (which will 
be inclusively indicated by a reference numeral "41") respectively 
containing a powdered yellow (Y) sublimable dye 61Y, a powdered magenta 
(M) sublimable dye 61M and a powdered cyan (C) sublimable dye 61C (which 
will be inclusively indicated by a reference numeral "61"); liquid-dye 
tanks 45 each having a protective plate 43 formed of a high-strength 
abrasion-resistant material, a base plate 44 formed of glass or a 
transparent ceramic material and joined to the protective plate 43 so as 
to form a narrow space for containing a liquid dye, and a heater 46 having 
an electric resistance element and attached to the base plate 44 to heat 
and fuse the powdered sublimable dye 61 contained in the corresponding 
powdered-dye tank 41; gasifying units 47 each for gasifying the liquid 
sublimable dye (liquid dispersed dye) 62 introduced therein from the 
corresponding liquid-dye tank 45; and semiconductor laser chips 48 (laser 
light sources) each attached to a support plate 49 fixed to the base plate 
44 to irradiate the gasifying unit with a laser beam L. 
Each gasifying unit 47 has a gasifying pit 47a. Disposed within the 
gasifying pit 47a are a transparent heat insulating layer 50 attached to 
the lower surface of the base plate 44, a light-to-heat conversion layer 
51, which absorbs a laser beam L and converts the light energy of the 
laser beam L into thermal energy, formed on the lower surface of the 
transparent heat insulating layer 50, an adhesive layer 53 formed on the 
lower surface of the light-to-heat conversion layer 51, and a dye holding 
layer 152 for holding the liquid sublimable dye 62, formed by adhesively 
attaching glass beads to the adhesive layer 53. The transparent heat 
insulating layer 50 is formed of a transparent PET resin. The 
light-to-heat conversion layer 51 is formed by spreading a mixture of a 
binder and carbon particles over the lower surface of the transparent heat 
insulating layer 50. The diameters of the glass beads forming the dye 
holding layer 152 are in the range of 5 to 10 .mu.m. The heater 46 heats 
and liquidize the powdered sublimable dye 61 so that the liquid sublimable 
dye 62 will diffuse into the dye holding layer 152. 
The recording sheets 80 contained in the sheet cassette 33 put on the laser 
sublimation transfer color video printer 31 are fed one at a time through 
the space between the flat platen 34 and the print head 40 to the feed 
roller 36a. The print head 40 is pressed lightly against the flat platen 
34 at a small pressure of about 50 g with a pair of weak springs 39 to 
press the recording sheet 80 against the flat platen 34. The semiconductor 
laser chips 48 are arranged on the print head 40 in three rows 
respectively for yellow pixels, magenta pixels and cyan pixels. The number 
of the semiconductor laser chips 48 in each row is equal to that of pixels 
on each printing line. The powdered dyes are fed from the powdered-dye 
tanks 41 (41Y, 41M, 41C) into the corresponding liquid-dye tanks 45, the 
powdered dyes are heated and liquidized, and then the liquidized dyes are 
supplied to the corresponding gasifying units 47. 
The powdered sublimable dye 61 fed from each powdered-dye tank 41 is heated 
to its melting point by the heater 46 to fuse (liquidize) the powdered 
sublimable dye, the liquid sublimable dye 62 is supplied by the capillary 
effect of the liquid-dye tank 45 to the gasifying unit 47, and a fixed 
amount of the liquid sublimable dye 62 is held by the dye holding layer 
152 formed in the gasifying pit 47a of the gasifying unit 47. In this 
state, when the recording sheet 80 is held between the feed roller 36a and 
the pressure roller 36b, an image signal representing dots of one of the 
three colors on one printing line is supplied to the printing head 40, and 
then the semiconductor laser chips 48 emits laser beams L according to the 
image signal. The laser beams L are converted into heat by the 
light-to-heat conversion layers 51, respectively. Consequently, the 
yellow, magenta and cyan liquid sublimable dyes 62 held by the dye holding 
layers 152 are gasified sequentially in order of the yellow liquid 
sublimable dye, the magenta liquid sublimable dye and the cyan liquid 
sublimable dye, and the yellow, magenta and cyan gasified dyes 63 are 
transferred sequentially in that order to the dye-accepting layer 80a of 
the recording sheet 80 held between the flat platen 34 and the protective 
plates 43 to print a color picture. 
FIG. 11 shows a print head 40 employed in a laser sublimation transfer 
color video printer 31. The print head 40 comprises powdered-dye tanks 
41Y, 41M and 41C (which will be inclusively indicated by a reference 
numeral "41") respectively containing a powdered yellow (Y) sublimable dye 
61Y, a powdered magenta (M) sublimable dye 61M and a powdered cyan (C) 
sublimable dye 61C (which will be inclusively indicated by a reference 
numeral "61"); liquid-dye tanks 45 each having a protective plate 43 
formed of a high-strength abrasion-resistant material, a base plate 44 
formed of glass or a transparent ceramic material and joined to the 
protective plate 43 so as to form a narrow space for containing a liquid 
dye, and a heater 46 having an electric resistance element and attached to 
the base plate 44 to heat and fuse the powdered sublimable dye 61 
contained in the corresponding powdered-dye tank 41; gasifying units 47 
each for gasifying the liquid sublimable dye (liquid dispersed dye) 62 
introduced therein from the corresponding liquid-dye tank 45; and 
semiconductor laser chips 48 (laser light sources) each attached to a 
support plate 49 fixed to the base plate 44 to irradiate the gasifying 
unit 47 with a laser beam L. This print head 40 is the same in 
construction as that shown in FIG. 13. 
A check valve 54 is disposed so as to close a dye passage 53 connecting the 
powdered-dye tank 41 and the liquid-dye tank 45. Each liquid-dye tank 45 
is provided therein with a dye feed element 55, such as a vibrator, 
opposite to the corresponding gasifying unit 47 to urge the liquid dye 62 
toward the gasifying unit 47. The dye feed element 55 is a bimorphic 
element or a piezoelectric elements. The dye feed element 55 is 
dispensable. The check valve 54 closes the dye passage 53 when the dye 
feed element 55 applies pressure to the dye and opens the dye passage 53 
when the dye feed element 55 applies negative pressure to the dye or the 
same is not in action. The powdered sublimable dye 61 contained in each 
powdered-dye tank 41 is heated an fused by the heater 46 while the check 
valve 54 is open and the liquid sublimable dye 62 is stored in the 
corresponding liquid-dye tank 45. Disposed within the gasifying pint 47a 
of each gasifying unit 47 are a light-transmissive, heat-resistant 
transparent layer 50 attached to the lower surface of the base plate 44, a 
light-to-heat conversion layer 51, which absorbs a laser beam L and 
converts the light energy of the laser beam L into thermal energy, formed 
on the lower surface of the heat-resistant transparent layer 50, and a 
liquid-dye holding layer 52 containing beads to hold the liquid sublimable 
dye 62 by capillary effect. 
The heat-resistant transparent layer 50 is a transparent film capable of 
withstanding high heat of 180.degree. C. or above and having a thermal 
conductivity of 1 W/m.multidot..degree.C. or below, a near infrared 
transmissivity of 85% or above (thickness: 10 .mu.m), a specific heat of 2 
J/g.multidot..degree.C. or below and a density of 3 g/cm.sup.3 or below. 
The heat-resistant layer 50 is formed on the lower surface of the base 
plate 44. The light-to-heat conversion layer 51 is a polyimide film. The 
liquid-dye holding layer 52 is formed by forming a metal thin film over 
the lower surface of the light-to-heat conversion layer 51 and etching the 
metal thin film in a mesh. 
In the laser sublimation color video printer 31, the powdered dye 61 
contained in each powdered-dye tank 41 is heated to its melting point to 
fuse (liquidize) the same by the heater 46. The liquid sublimable dye 62 
is supplied at a fixed high rate to the heat-resistant transparent layer 
50, the light-to-heat conversion layer 51 and the liquid-dye holding layer 
52 disposed in the gasifying pit 47a of the corresponding gasifying unit 
47 by the feed action of the dye feed element 55 and capillary effect. 
When printing a color picture on the recording sheet 80, an image signal 
representing dots of one of the three colors on one printing line is 
supplied to the print head 40, and the light energy of the laser beam L 
emitted by each semiconductor laser chip 48 is converted into heat by the 
corresponding light-to-heat conversion layer 51. Consequently, each liquid 
sublimable dye 62 held by each liquid-dye holding layer 52 is gasified, 
are transferred in that order to the dye-accepting layer 80a of the 
recording sheet held between the flat platen 34 and the protective plates 
43 to print a color picture. 
Since each liquid-dye tank 45 is provided with the vibrating element 55, a 
moderate pressure can be applied to the liquid sublimable dye 62 contained 
in the liquid-dye tank 45 to supply the liquid sublimable dye 62 at a 
fixed high rate to the light-to-heat conversion layer 51 and the 
liquid-dye holding layer 52. Since the dye passage 53 connecting the 
powdered-dye tank 41 and the liquid-dye tank 45 is provided with the check 
valve 54, the reverse flow of the liquid sublimable dye 62 from the 
liquid-dye tank 45 into the powdered-dye tank cam be surely inhibited. 
The heater 46 provided in the liquid-dye tank 45 heats the liquid 
sublimable dye 62 to maintain the sublimable dye in the liquid phase. The 
highly heat-resistant heat-resistant transparent layer 50 withstands 
continuous printing operation. A structure formed by laminating the 
light-to-heat conversion layer 51 and the heat-resistant transparent layer 
50 withstands continuous use, has a high thermal conductivity, enables 
rapid thermal diffusion in the surface of the light-to-heat conversion 
layer 51 and the light-to heat layer 51 can be heated in a uniform 
temperature distribution even if the light energy in the laser beam L is 
not distributed uniformly in a distribution like a Gaussian distribution 
and, consequently, uniform transfer of the dye can be achieved. 
Since the liquid-dye holding layer 52 is formed on the light-to-heat 
conversion layer 51, the liquid-dye holding layer 52 is formed by etching 
the metal thin film in a mesh having grooves arranged at an appropriate 
pitch and having an appropriate depth, the liquid-dye holding layer 52 is 
able to hold always an appropriate amount of the liquid sublimable dye 62 
and, consequently, an appropriate amount of the liquid sublimable dye 62 
necessary for printing can be gasified by the light-to-heat conversion 
layer 51. Since the liquid-dye holding layer 52 is formed directly on the 
light-to-heat conversion layer 51 to omit an adhesive layer, the heat 
capacity of the print head is smaller than that of an equivalent print 
head provided with an adhesive layer by the heat capacity of the adhesive 
layer and, consequently, the print head operates at a comparatively high 
thermal efficiency. 
The mode of transfer of the gasified sublimable dye from the light-to-heat 
conversion layer to the recording sheet will be described hereinafter. The 
laser beam L instantaneously emitted by each semiconductor laser chip 48 
travels through the glass base 44 and the heat-resistant transparent layer 
50 and reaches the light-to-heat conversion layer 51, and then the light 
energy of the laser beam L is converted into corresponding thermal energy 
by the light-to-heat conversion layer 51. The heat-resistant transparent 
layer 50 is caused to expand suddenly as shown in exaggerated views in 
FIGS. 15(e) to 15(g) by the heat generated by the light-to-heat conversion 
layer 51 to give kinetic energy to the liquid sublimable dye 62 so that 
the liquid sublimable dye 62 flies toward the dye-accepting layer 80a of 
the recording sheet 80 as shown in FIG. 15(g). Consequently, an amount of 
the gasified sublimable dye 63 proportional to that of the heat is 
transferred to the dye-accepting layer 80a of the recording sheet 80 as 
shown in FIG. 15(h)in a desired density to form a picture having a desired 
gradation. 
In FIG. 15(g), .o slashed..sub.1 (=100 .mu.m) is the diameter of a spot 
formed by the laser beam L, and .o slashed..sub.2 (=60 to 80 .mu.m) in 
FIG. 15(h) is the diameter of a dot (picture element). Thus, the yellow, 
magenta and cyan gasified sublimable dyes 63 are transferred sequentially 
in that order to the dye-accepting layer 80a of the recording sheet 80 
held between the flat platen 34 and the protective plates 43 to print a 
color picture. A heat-resistant transparent layer 50 formed of an aromatic 
polyamide has an excellent heat-resistant property and is capable of 
withstanding continuous use. The printing apparatus thus constructed is 
capable of stably and satisfactorily printing pictures by using the 
mixtures each of a surface active agent and a dye, or dyes having boiling 
points not higher than their decomposition temperature. 
Although the laser beam is emitted by the semiconductor laser chip disposed 
above the print head to print pictures on the recording sheet under the 
print head in the example shown in FIGS. 11 to 13, the respective 
positions of the semiconductor laser chip and the recording sheet may be 
reversed as shown in FIG. 16. A print head 90 shown in FIG. 16 has a base 
plate 44 provided with a heater 46, and heats the powdered dye 61 supplied 
from each powdered-dye tank 41 by the heater 46 to obtain the liquid 
sublimable dye 62. A heat-resistant transparent layer 50, a light-to-heat 
conversion layer 51 and a liquid-dye holding layer 52 are formed in that 
order in a laminated structure on the base plate 44. A semiconductor laser 
chip 48 is disposed under the babe plate 44. A laser beam L emitted by the 
semiconductor laser chip 48 is focused on liquid dye held by a liquid-dye 
holding layer 52 included in a gasifying unit 47 to gasify the liquid dye 
in order that the gasified dye is transferred from the gasifying unit 47 
to the dye-accepting layer 80a of a recording sheet 80 held over the print 
head 90. The print head 90 is the same in components and construction as 
the print head 40 shown in FIG. 11. Desirably, the light-to-heat 
conversion layer 51 is not formed of a polyimide resin. The light-to-heat 
conversion layer 51 is a Ni/Co alloy thin film formed by evaporation or 
sputtering over a heat-resistant transparent layer 50 and having a near 
infrared transmissivity of 0.9 or above, a thickness of 1 .mu.m or below, 
a specific heat of 0.5 J/g.multidot..degree.C. or above, a thermal 
conductivity of 20 W/m.multidot..degree.C. or above and a density of 20 
g/cm.sup.3 or below. The area of the Ni/Co alloy thin film may be equal to 
the area S shown in FIGS. 11 and 16 in which the gasified dye is printed. 
Thus, the heat resistance of the light-to-heat conversion layer is 
enhanced to enable the continuous use of the same. Having a very small 
thickness, the Ni/Co alloy thin film has a comparatively small heat 
capacity, and the light-to-heat conversion layer is heat-insulated by the 
liquid dye surrounding the same to improve the thermal efficiency. The 
powdered dye may be directly gasified, i.e., sublimated, for printing by 
irradiating the same With the laser beam instead of liquidizing the 
powdered dye and gasifying the liquid dye. 
Although the intention has been described specifically in terms of the 
preferred embodiments thereof, many modifications and variations of the 
present invention are possible in the light of the above teachings. For 
example, the printing layer and the print head may have may be formed in 
construction and shape other than those described above, and the materials 
of the components of the print head may have may be other than those 
described above. The printer of the present invention may be used for 
printing monochromatic color pictures or black-and-white pictures instead 
of printing full-color pictures using yellow, magenta and cyan dyes. The 
fusible dyes may be gasified or sublimated by using the energy of, for 
example, electromagnetic waves or electric discharge from styluses instead 
of the energy of a laser beam. A noncontact thermal print head may be 
employed instead of the foregoing print heads. 
Although the invention has been described in its preferred form with a 
certain degree of particularity, obviously many changes and variations are 
possible therein. It is therefore to be understood that the present 
invention may be practiced otherwise than as specifically described herein 
without departing from the scope and spirit thereof.