Device and method for dot-matrix thermal recording

Provided is a device which can form favorable perforated images corresponding to the resolution of the thermal head, reproduce faithful printed images for all kinds of original picture images, avoid ink transfer, and adapt itself to different environmental conditions, and is suitable for use with different thermal recording materials such as thermal recording paper, OHP TP sheets, and thermal stencil master plates. In the device of the present invention, a thermal head 4 consisting of a plurality of heat emitting elements 5 arranged in a single row in the primary scanning direction is directly contacted to the recording surface of a thermal recording material such as thermal recording paper, and the thermal recording material 1 is moved relative to the thermal head 4 in the secondary scanning direction which is perpendicular to the direction of the row of the heat emitting elements so that picture images may be formed with a dot matrix by selectively heating the thermal heat emitting elements at an appropriate timing in relation to the movement of the thermal recording material in the secondary scanning direction, the ratios of the length of each heat emitting element 5 in the primary and secondary scanning directions to the pitches of the primary and secondary scanning are set 30 to 70% and 60 to 95%, respectively.

TECHNICAL FIELD 
The present invention relates to a thermal recording device for forming an 
image with a dot matrix by applying a thermal head to a heat-sensitive 
recording material such as heat-sensitive printing paper, thermal transfer 
ribbon, and to thermal stencil master plates made by laminating a 
thermo-plastic film over a porous support. 
BACKGROUND OF THE INVENTION 
The thermal recording device which forms images with a dot matrix by using 
a thermal head is conventionally known, and such a thermal recording 
device forms images by applying a thermal head consisting of a plurality 
of heat emitting elements onto thermal recording paper, an OHP coloring TP 
sheet, an OHP frosted TP sheet, recording paper in conjunction with the 
use of thermal transfer ribbon, or a recording surface of heat sensitive 
recording material such as a thermal stencil master plate, and by 
selectively heating the heat emitting elements. Such thermal recording 
devices are widely used as facsimiles, printers for ticket dispensers, 
hand-held copiers, OHP transparency making devices, and thermal master 
plate making devices. 
In facsimiles, the feed speed of the thermal recording paper in the 
longitudinal direction or in the secondary scanning direction is 
determined by a unified standard, and the size of each heat emitting 
element is determined according to the feed speed in the secondary 
scanning direction. Further, the aspect ratio of each heat emitting 
element is determined to be a/b=1/2 by a communication standard where a 
and b are the lengths of each heat emitting element in the primary and 
secondary scanning directions, respectively, the primary direction 
corresponding to the lateral direction of the paper or the direction of 
the row of the heat emitting elements. 
Therefore, in the high resolution mode (fine mode) of the facsimile 
standard in which Pa=Pb where the dot pitch in the primary scanning 
direction is Pa and the dot pitch in the secondary scanning direction is 
Pb, b&gt;Pa=Pb holds, and there will be some overlapping in the heat emitting 
regions of the heat emitting elements for each small distance along the 
secondary scanning direction. 
If a thermal stencil master plate is processed or made by forming stencil 
images on a thermo-plastic film of a thermal stencil master plate with a 
thermal head for a facsimile of the above described kind in a mode 
equivalent to the high resolution mode of the facsimile standard, 
continuous openings will be formed in the thermo-plastic film of the 
thermal stencil master plate along the secondary scanning direction due to 
the above-mentioned overlapping. This causes not only the thickening and 
blurring of the lines of printed character and line images but also 
excessive deposition of ink onto the printing paper in solid areas of the 
picture images which could in turn cause conspicuous smearing of the 
reverse surface of the printing paper by ink transfer in continuous 
printing. 
To overcome this problem, it has been proposed to make a thermal stencil 
master plate with a thermal head using heat emitting elements each of 
which is shorter in length along the secondary scanning direction than the 
pitch of the secondary scanning, and to ensure formation of unaffected 
parts between the perforations along the secondary scanning direction as 
disclosed in Japanese patent laid open publication No. 2-67133. 
According to this proposal, since the perforations formed in the 
thermoplastic resin film of the thermal stencil master plate are formed so 
as to be independent from each other in both primary and secondary 
scanning directions, it is possible to faithfully reproduce character 
images by printing, and to control excessive deposition of ink and reduce 
ink transfer from one sheet to another. 
However, images formed by perforation of a film of a thermal stencil master 
plate are inferior in quality as compared to those formed by using thermal 
coloring type media, such as thermal recording paper, in terms of 
reproducibility (resolution) as compared to the original images, in 
particular the evenness of fine lines and small characters, legibility of 
small outlined characters, the sharpness of fine black and white patterns 
such as halftone screen images, and digitally reproduced photographic 
gradations. 
Further, in a high temperature environment, the perforation of the 
thermo-plastic resin film of the thermal stencil master plate, due to 
melting, tends to be excessive, and, combined with the lowering of the 
viscosity of the ink, the thickening and blurring of lines of character 
images become more pronounced, as compared to the original images, than in 
a normal or low temperature environment. Additionally, the smearing or the 
ink transfer of the printing paper tends to be more pronounced due to 
increase in the amount of ink deposition, and the acceptable temperature 
range becomes narrower. 
Thus, it has not heretofore been possible to provide a thermal recording 
device which can achieve the picture quality equivalent or comparable to 
those of the picture images produced by the coloring of thermal recording 
paper in the picture images produced by using the thermal stencil master 
plate, and achieving a desired uniformity in picture quality even when 
thermal recording materials having different recording properties are 
used. 
BRIEF SUMMARY OF THE INVENTION 
In view of such problems of the prior art, a primary object of the present 
invention is to eliminate such problems and to provide a thermal stencil 
master plate making device which can form favorable stencil images for a 
given resolution of the thermal head, reproduce faithful printed images 
for all kinds of original picture images, prevent ink transfer, and adapt 
itself to various environmental conditions. 
A second object of the present invention is to provide a thermal recording 
device which is suitable for use with a wide range of thermal recording 
materials having different recording properties, such as thermal recording 
paper, OHP TP sheets, and thermal stencil master plates. 
These and other objects of the present invention can be accomplished by 
providing a thermal recording device for forming an image with a dot 
matrix, comprising: a thermal recording material; a thermal head, 
including a plurality of heat emitting elements arranged in a single row 
at a first pitch along a primary scanning direction; thermal head applying 
means for applying the thermal head onto a surface of the thermal 
recording material; thermal recording material moving means for moving the 
thermal recording material relative to the thermal head in a secondary 
scanning direction perpendicular to the primary scanning direction; and 
heating means for selectively heating the heat emitting element in 
synchronism with a movement of the thermal recording material in the 
secondary scanning direction, wherein, a ratio of a first length of each 
of the heat emitting elements of the thermal head in the primary scanning 
direction to the first pitch is 30 to 70%, and a ratio of a second length 
of each of the heat emitting elements of the thermal head in the secondary 
scanning direction to the second pitch is 60 to 95%, and wherein, a dot 
matrix pitch of an image formed on the thermal recording material in the 
primary scanning direction is determined by the first pitch of the heat 
emitting elements and in the secondary scanning direction by a heat 
emitting timing of the heat emitting elements relative to a movement of 
the thermal recording material in the secondary scanning direction. 
The present invention also provides a method for forming a dot matrix image 
on a thermal recording material comprising the steps of: applying a 
thermal head onto a surface of the thermal recording material; moving the 
thermal recording material relative to the thermal head in a secondary 
scanning direction; and selectively heating a plurality of heat emitting 
elements of the thermal head along a primary scanning direction by heating 
the heat emitting elements at an appropriate timing in relation to a 
movement of the thermal recording material in the secondary scanning 
direction; wherein, ratio of a first length of each of the heat emitting 
elements of the thermal head in the primary scanning direction to the 
first pitch is 30 to 70%, and a ratio of a second length of each of the 
heat emitting elements of the thermal head in the secondary scanning 
direction to the second pitch is 60 to 95%, and wherein, a dot matrix 
pitch of an image formed on the thermal recording material in the primary 
scanning direction is determined by the first pitch of the heat emitting 
elements and in the secondary scanning direction by a heat emitting timing 
of the heat emitting elements relative to a movement of the thermal 
recording material in the secondary scanning direction. The dot matrix 
pitch of an image formed on the thermal recording material in the 
secondary scanning direction may also be determined by controlling heat 
emission of the heat emitting elements relative to a movement of the 
thermal recording material in the secondary scanning direction, or, 
alternatively, the dot matrix pitch of an image formed on the thermal 
recording material in the secondary scanning direction may also be 
determined according to a heat emitting response property of the heat 
emitting elements relative to a moving speed of the thermal recording 
material in the secondary scanning direction. 
In the thermal recording device of the present invention, since the size of 
each of the heat emitting elements of the thermal head is determined such 
that: 
length in the primary scanning direction 
.fwdarw.30 to 70% of the pitch of the primary scanning 
length in the secondary scanning direction 
.fwdarw.60 to 95% of the pitch of the secondary scanning 
not only each of the dots selectively formed in the thermo-plastic resin 
film is independent from others, but also the quality of the picture 
images which may be evaluated in terms of the evenness of fine lines and 
small characters, legibility of small outlined characters, the sharpness 
of fine black and white patterns such as halftone screen images, and 
digitally reproduced photographic gradations, which has been considered to 
be inferior to that of the images formed on thermal recording paper, can 
be improved to a comparable level. 
The primary reason which makes the quality of the picture images formed by 
thermal stencil master plate printing less favorable to that by thermal 
recording paper printing is found in the fact that the shape of the 
perforated dots in the film of the thermal stencil master plate are not so 
uniform as the colored dots of the thermal recording paper and, even 
though they may form independent dots, for instance, when three 
consecutive heat emitting elements along the secondary scanning direction 
are heated at the same time to form an image by perforation, the heat 
emitting elements are affected by the adjacent ones and the behavior of 
the melting and shrinking of the part of the perforated thermo-plastic 
resin film which directly contacts the heat emitting elements depend on 
the way the film is supported by the porous support fibers. In particular, 
when there is no support fibers under the thermo-plastic resin film upon 
which the heat emitting elements are pressed, the melting and shrinking of 
the film tends to be excessive. If such an area not supported by fibers 
extends over a number of heat emitting elements and is heated by several 
of the heat emitting elements at the same time, the dots may excessively 
expand or clog adjacent ones by expansion with the result that the 
adjacent dots are affected and the sizes of the perforated dots become 
uneven. 
Further, in the process of preparing a thermal stencil master plate in high 
temperature environment, the thermal effect from adjacent heat emitting 
elements becomes so pronounced that the thickening and blurring of fine 
lines tends to be significant, the quality of picture images become even 
more inferior to those of the thermal recording paper, and the excessive 
deposition of printing ink onto the printing paper through the expanded 
dots increases the possibility of ink transfer or the smearing of the 
reverse surface of the printing paper. 
On the other hand, according to the thermal recording device of the present 
invention, since the length of each heat emitting element of the thermal 
head in the primary scanning direction is 30 to 70% of the pitch of the 
primary scanning and the length in the secondary scanning direction is 60 
to 95% of the pitch of the secondary scanning to the end of avoiding the 
deterioration of the quality of the picture images due to the unevenness 
of the shape of the perforated dots, each of the dots would not be 
affected by the heating of the dots adjacent thereto along the primary 
scanning direction, and stable perforation may be achieved on the 
thermo-plastic resin film of the thermal stencil master plate so that the 
evenness of the perforated dots can be improved, and the quality of the 
printed images becomes comparable to that of the thermal recording paper. 
Further, in carrying out the process of plate making in high temperature 
environment, perforations may be formed in a stable fashion to an extent 
which has not heretofore been attainable, and the quality of picture 
images may be improved with the added advantage of eliminating ink 
transfer. 
Since each of the perforated dots is independent from each other, and the 
shape of the dots is highly uniform, the part remaining between the 
perforated dots of the thermo-plastic resin film of the thermal stencil 
master plate is made uniform, and the strength of the film is improved so 
that the number of sheets of paper that can be printed with the same 
master plate may be increased. 
The thermal recording device of the present invention offers a significant 
advantage over the method of making a recorded article with a number of 
steps such as the method involving the steps of processing a thermal 
stencil master plate and making printed materials, and the method of 
processing printing paper by using such thermal recording media as thermal 
transfer ribbon, and can be used in conjunction with the method of making 
recorded materials with a single step by using such materials as thermal 
recording paper and OHP coloring TP sheets. According to the thermal 
recording device of the present invention, the printed records (printed 
characters) are formed by independent dots, and the density of the printed 
characters (colored images) may become slightly less dark due to the 
reduction in the area of each printed (colored) dot. But, it is not 
significant, and the reproducibility and legibility of small characters 
and images actually improve.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
FIG. 1 shows the general structure of an example of thermal recording 
device according to the present invention. In the illustrated thermal 
recording device, thermal recording material 1 is conveyed in the 
direction indicated by the arrow A (secondary scanning direction) by a 
platen roller 3 which is rotatively driven by a stepping motor described 
hereinafter. The platen roller 3 which may consist of a resilient material 
such as rubber or other polymer material applies the thermal recording 
material 1 against a thermal head 4. Then, heat emitting elements 5 
provided in the thermal head 4 are placed in direct contact with a 
recording surface (surface 1a in the drawing) of the thermal recording 
material 1, and recorded images are formed on the recording surface 1a of 
the recording material 1 by selectively heating the heat emitting elements 
5. 
Thus, the heat emitting elements 5 of the thermal head 4 are brought into 
direct contact with the recording surface 1a of the thermal recording 
material 1, and are selectively heated to form a single line of an image 
while the thermal recording material 1 is conveyed by a distance 
corresponding to a single line of the image by the rotation of the platen 
roller 3. Optionally, the conveying rollers 2 may be rotatively driven by 
power means such as a stepping motor instead of driving the platen roller 
3. In either case, the movement of the thermal recording material 1 may be 
carried out either in a continuous manner or in a step-wise manner. 
The recording surface 1a of the thermal recording material 1 corresponds to 
the surface carrying the coloring layer of thermal printing paper or 
coloring type TP sheet, or the thermo-plastic resin film of a thermal 
stencil master plate, or the base film of thermal transfer ribbon. 
FIG. 2 is a schematic plan view of the thermal head 4. As shown in this 
drawing, the heat emitting elements 5 of this thermal head 4, each having 
a rectangular shape, are arranged in a single row, at a pitch of Pa, along 
a primary scanning direction which is perpendicular to the secondary 
scanning direction given as a direction in which the thermal recording 
material 1 is conveyed or as the direction of the relative movement. The 
two ends along the secondary scanning direction of each of the heat 
emitting elements 5 are connected to electrodes 6, respectively, so that 
electric power may be supplied individually to each of the heat emitting 
elements 5. 
FIG. 9 is a block diagram for illustrating the control arrangement for 
forming an image on the thermal recording material 1. Image data (VDATA) 
read by an image sensor such as a CCD is fed to an image processing 
circuit 31 which carries out desired editing of the data, and assigning of 
desired attributes to the data. The data is then converted into a binary 
signal, and supplied to a data managing circuit 32. The data managing 
circuit 32 produces various signals required for driving a thermal head 
drive circuit 33 (which is illustrated in FIG. 10) in synchronism with a 
reference clock signal (DCLK) from a timing generator circuit 34. The 
timing generator circuit 34 also supplies synchronized drive pulses (MCLK) 
to a motor control circuit 35 to actuate the stepping motor 36 in a 
stepwise manner. The timing related to the operation of the data managing 
circuit 32 is illustrated in FIG. 11. The heat emitting elements 5 of the 
thermal head 4 are thus heated in synchronism with the operation of the 
stepping motor 36 regulated by the motor control circuit 35 to carry out 
the recording for each line of the recorded image. 
FIG. 10 shows the thermal head drive circuit 33 in more detail. A shift 
register 41 stores recorded data (DAT) for a single line. The data is 
transferred to this shift register 41 as a serial signal in synchronism 
with the reference clock signal (DCLK), and the recorded data (DAT) stored 
in the shift register 41 and corresponding to a single line of the 
recorded image is supplied to a latch circuit 42 as a parallel signal. The 
latch circuit 42 stores the data (DAT) corresponding to a single line of 
the recorded image which is to be applied to the heat emitting elements 5, 
and receives the data from the shift register 41 in synchronism with the 
application of a latch signal (LAT) thereto. The recorded data (DAT) 
produced from this latch circuit 42 is supplied to gate circuits 43 as a 
parallel signal. One of a pair of inputs of each gate circuit 43 receives 
the signal for the recorded data (DAT) from the latch circuit 42, and the 
other input of the gate circuit 43 receives one of the strobe signals STB1 
to STB4 for driving the thermal head 4 consisting of four segments in a 
time sharing arrangement. A switching circuit 44 consists of a plurality 
of switching devices provided in association with the heat emitting 
elements 5 and adapted to turn on and off according to the signal supplied 
from the gate circuit 43. Each of the switching devices which has turned 
on will supply electric power to the associated heat emitting element 5. 
Therefore, when an associated strobe signal STB1 to STB4 is present, and 
the gate circuit 43 corresponding to the part of the latch circuit 42 
storing the recorded data (black data) is turned on, the switching circuit 
44 corresponding to this position is closed, and the corresponding heat 
emitting element 5 receives electric power. As a result, the heat emitting 
element 5 is heated, and a record or a dark dot is formed on the 
corresponding position of the thermal recording material 1. 
The interval of the drive pulses (MCLK) for driving the stepping motor 36 
in a stepwise manner is determined to be more than required for completing 
the recording of a single line of the image on the thermal recording 
material 1. 
The action of recording a single line with the thermal head drive circuit 
33 having the above described structure is now described in the following 
with reference to the time chart given in FIG. 11. 
For example, the recorded data for the (n-1)-th line of the record is 
stored in the shift register 41, and a latch signal (LAT) is produced from 
the data managing circuit 32 (refer to FIG. 11(c)) so that the recorded 
data for the (n-1)-th line of the image stored in the shift register 41 is 
stored in the latch circuit 42. 
Then, the stepping motor 36 is actuated by a single step by a stepping 
motor drive pulse (MCLK) from the timing generator circuit 34 supplied to 
the motor control circuit 35 (refer to FIG. 11(d)). As a result, the 
thermal recording material 1 is conveyed by prescribed length 
corresponding to a single line of the image. Thus, the thermal recording 
material 1 is conveyed by a distance corresponding to the dot pitch Pb in 
the secondary scanning direction of the dot matrix image which is to be 
recorded on the thermal recording material 1. 
Upon completion of the conveying action of the thermal recording material 
1, the strobe signals STB1 to STB4 are sequentially supplied according to 
a prescribed time sharing scheme (refer to FIGS. 11(e) to 11(h)), and the 
heat emitting elements 5 receive electric power and are heated according 
to the arrangement of the recorded data (DAT) so that a line of the image 
corresponding to the single line recorded data (DAT) is formed on the 
thermal recording material 1. 
Then, the recorded data (DAT) for the n-th line is transferred to and 
stored in the shift register 41 in synchronism with the reference clock 
signal (DCLK) produced from the timing generator circuit 37. This process 
is repeated thereafter, and the recorded data of the n-th line is recorded 
on the thermal recording material 1. Upon completion of the recording of 
the n-th line of the image, the stepping motor 36 is actuated by an 
additional step, and the thermal recording material 1 is conveyed by a 
distance corresponding to the dot pitch Pb in the secondary scanning 
direction. This process is repeated until the entire desired image is 
recorded on the thermal recording material 1. 
The dot pitch Pa of the dot matrix of the images formed on the recording 
surface 1a of the thermal recording material 1 in the primary scanning 
direction is determined by the pitch Pa of the heat emitting elements 5 in 
the primary scanning direction, and the dot pitch Pb of the dot matrix in 
the secondary scanning direction is determined by the heat emitting timing 
of the heat emitting elements 5 of the thermal head 4 in relation to the 
movement of the thermal recording material 1 in the secondary scanning 
direction. 
In other words, the dot pitch Pb in the secondary scanning direction 
determined by the feed of the thermal recording material 1 corresponding 
to a single line of a recorded image and the timing of the heat emission 
of the heat emitting elements 5 of the thermal head 4 is dictated by the 
actual conveying speed of the thermal recording material 1 caused by the 
rotation of the platen roller 3 and the actual timing of energizing the 
heat emitting elements 5. In this conjunction, it is desirable to take 
into account the heat emitting response property of the heat emitting 
elements 5 or to directly evaluate the actual emission of heat from the 
heat emitting elements 5 to accurately control the manner in which an 
image is formed in the thermal recording material 1 typically by 
perforation. 
In this case, the dot pitch of the dot matrix of the images formed on the 
recording surface 1a of the thermal recording material 1 in the primary 
scanning direction is determined by the pitch Pa of the heat emitting 
elements 5 in the primary scanning direction, and the dot pitch of the 
matrix in the secondary scanning direction is determined by the heat 
emitting response property of the heat emitting elements 5 of the thermal 
head 4 in relation with the moving speed of the thermal recording material 
in the secondary scanning direction. In the thermal recording device of 
the present invention, various parameters are so selected that the dot 
pitch of the dot matrix of the images formed by the heat from the heat 
emitting elements 5 of the thermal head 4 in the secondary scanning 
direction is made to be equal to the dot pitch in the primary scanning 
direction. 
According to the present invention, to the end of achieving a balance of 
the image formed by a dot matrix, the dot pitch Pb in the secondary 
scanning direction is made equal to the dot pitch Pa in the primary 
scanning direction. Therefore, if the resolution of the thermal head 4 is 
400 dots/inch, the dot pitches in the primary and secondary directions Pa 
and Pb are both made equal to 63.5 .mu.m (Pa=Pb=63.5 .mu.m). If the 
resolution of the thermal head 4 is 300 dots/inch, the dot pitches in the 
primary and secondary directions Pa and Pb would be made equal to 84.6 
.mu.m (Pa=Pb=84.6 .mu.m). The outer diameter of the platen roller 3 and 
various parameters of the stepping motor 36 and the power transmission 
mechanism (not shown in the drawings) for transmitting the rotation of the 
stepping motor 36 to the platen roller 3 is determined in such a manner 
that the feed of the thermal recording material 1 by each rotative step of 
the stepping motor 36 is made equal to the dot pitch Pb in the secondary 
scanning direction. 
If the lengths of each of the heat emitting elements 5 in the primary and 
secondary scanning directions are a and b, respectively, the thermal 
recording device of the present embodiment is characterized by the size of 
each of the heat emitting elements 5 being as follows: 
0.30 Pa.ltoreq.a.ltoreq.0.70 Pa, 
0.60 Pa.ltoreq.b.ltoreq.0.95 Pa, and 
Pa=Pb. 
Thus, as mentioned earlier, the dot pitch (secondary scanning pitch Pb) of 
the dot matrix of the images formed by the heat from the heat emitting 
elements 5 in the secondary scanning direction is equal to the dot pitch 
in the primary scanning direction which is equal to the pitch (primary 
scanning pitch) Pa of the heat emitting elements 5 in the primary scanning 
direction. 
Therefore, when the lengths of each of the heat emitting elements 5 in the 
primary and secondary scanning directions are short as compared to the 
corresponding dot pitches, the region of heat generation of each of the 
heat emitting elements will not be affected by the heat from the adjacent 
heat emitting elements 5, and the recorded traces or, in the case of 
thermal recording paper, the colored dots, the perforated dots in the case 
of the thermal stencil master plate, and the frosted dots in the case of 
the OHP frost type TP sheet will be independent from each other both in 
the primary and secondary directions, leaving gaps of unrecorded regions 
between the recorded dots. The size of these dots depends on the size of 
the heat emitting elements, the sensitivity of the thermal recording 
material or the medium, the coloring properties in the case of the thermal 
recording paper, the perforation property of the thermo-plastic resin film 
in the case of the thermal stencil master plate, and the melting and 
transferring properties of the ink sheet onto the printing paper in the 
case of the transfer ribbon. 
The gaps between the recorded dots are particularly useful for such thermal 
recording materials as thermal stencil master plate and thermal transfer 
ribbon which can rely on the seeping of ink, and the plate making or the 
printing by the device of the present invention can produce optimum gaps 
in the recording material. 
Meanwhile, in the case of the thermal recording paper and the OHP coloring 
type TP sheets, the expansion of the colored parts corresponding to the 
seeping of ink cannot be expected as much as in the case of the thermal 
stencil master plate, but when characters (records) are printed by the 
device of the present invention, solid areas will be slightly light in 
gradation as compared to the characters (records) printed by the 
conventional thermal head (although the density of each colored dot may 
have reached a saturated density level, the gaps extending between the 
dots reduce the area of each dot in the high density regions). However, it 
is not visually discernible, and actually achieves some improvement in the 
reproducibility and legibility of small character images. 
When the used device is such that the ratio of the length of each of the 
heat emitting elements 5 in the primary scanning direction to the scanning 
pitch in the primary scanning direction does not satisfy the conditions 
defined for the device of the present invention, in particular when the 
ratio is greater than that of the device of the present invention, the 
perforated dots are connected in both the secondary and primary scanning 
directions particularly under a high temperature condition, and 
unfavorable results such as the thickening and blurting of the lines of 
images and the ink transfer from one sheet of the printing paper to 
another tend to occur. If the ratio related to the dot pitch is smaller 
than that of the device of the present invention, the distance between 
adjacent perforated dots becomes excessive, and the thinning of picture 
images and lowering of gradation level in solid areas tend to occur. 
Now, embodiments of the present invention and examples for comparison are 
now described in the following. The results of evaluating the embodiments 
and the examples for comparison are summarized in Tables 1 and 2. 
EMBODIMENT 1 
A thin film type thermal head of a 400 dots/inch (abbreviated as DPI 
hereinafter) resolution with the following specifications was mounted on a 
digital stencil master plate making and printing device (sold by Riso 
Kagaku Kogyo KK under the tradename of Risograph RC115D), and a thermal 
stencil master plate (tradename: RC Master 55) was processed by using an 
original containing character images and solid images. The ink used in 
this embodiment had a spread meter reading of one minute value of 33, and 
the printing device was the same as above (the same thing applies to the 
subsequent embodiments). The processing of the thermal recording paper 
(tradename: Riso thermal paper sheet type C-197) and OHP TP sheet 
(tradename: Riso TP film T-113) was also carried out with the single copy 
mode of the aforementioned device. The ambient temperature was 23.degree. 
C. 
Length of each heat emitting element in the primary scanning direction 
.fwdarw.a=25 .mu.m 
Length of each heat emitting element in the second scanning direction 
.fwdarw.b=60 .mu.m 
Dot pitch (primary and secondary scanning directions) 
.fwdarw.Pa=Pb=63.5 .mu.m 
Heat emitting energy 
.fwdarw.68.8-50.0 .mu.J/dot 
The thermal stencil master plate was fabricated by laminating a polyester 
film (2 .mu.m in thickness) and a porous support (9.5 g/m.sup.2, manila 
hemp thin paper) with a bonding agent, and applying a release agent on the 
surface of the film facing the thermal head. 
The thermal recording paper consisted of base paper carrying a layer of 
heat sensitive coloring agent with a density of 57 g/m.sup.2. 
The OHP TP film consisted of a polyester film (50 .mu.m in thickness) 
provided with a layer of a coloring agent. 
As indicated by the microscopic photographs in FIGS. 3 and 4, the 
perforated dots which formed solid parts of the picture image were 
independent from each other, and formed a uniform dot matrix so that the 
unprocessed gaps between the adjacent dots may extend in both the primary 
and secondary scanning directions uniformly in the manner of a grid. 
When the quality of the character image on the thermal recording paper and 
the picture image formed on the OHP TP sheet were evaluated by using a 
microscope, it was found that the unprocessed gaps existed between colored 
dots, but they were visually indiscernible enough for the solid parts to 
be regarded as such. In regards to character images consisting of fine 
lines, they were also faithfully reproduced from the original. The 
projected images of the processed TP sheet were also quite satisfactory. 
When prints were made by using such a processed thermal stencil master 
plate, the parts corresponding to the unprocessed gaps between perforated 
dots observed in the master plate were filled by the seeping of the ink, 
and the printed solid parts were quite favorable. In regards to character 
images also, printed images faithful to the original were obtained without 
involving any thinning, thickening or blurring. In particular, favorable 
reproduction of minute character images was achieved. The images were 
comparable to those obtained by using thermal recording paper. 
A prescribed number of prints were made by operating the aforementioned 
recording device at the rate of 60 to 130 sheets per minute, and the 
reverse surface of each of the printed sheets piled into a stack showed 
substantially no smearing by ink or no ink transfer. 
The durability of the master plate was found to be favorable. 
EMBODIMENT 2 
The same operation as that of the first embodiment was carried out at the 
ambient temperature of 10.degree. C. 
The perforated dots of the thermal stencil master plate and the colored 
dots of the thermal recording paper and the OHP TP sheet had a tendency to 
be slightly smaller than those of the first embodiment, but a required 
picture quality was ensured in each case without creating any problem. 
EMBODIMENT 3 
The same operation as that of the first embodiment was carried out at the 
ambient temperature of 35.degree. C. 
The perforated dots of the thermal stencil master plate and the colored 
dots of the thermal recording paper and the OHP TP sheet had a tendency to 
be slightly larger than those of the first embodiment, but a required 
picture quality was ensured in each case without creating any problem. 
EMBODIMENT 4 
The recordability of the thermal recording materials (thermal stencil 
master plate, thermal recording paper and OHP TP sheet) was investigated 
by using a thin film type thermal head of 400 DPI which was set up as 
described above and the same device and original as the first embodiment. 
The ambient temperature was 23.degree. C. 
Length of each heat emitting element in the primary scanning direction 
.fwdarw.a=35 .mu.m 
Length of each heat emitting element in the second scanning direction 
.fwdarw.b=60 .mu.m 
Dot pitch (primary and secondary scanning directions) 
.fwdarw.Pa=Pb=63.5 .mu.m 
Heat emitting energy 
.fwdarw.75.0-55.0 .mu.J/dot 
When a pan of the thermal stencil master plate obtained in this embodiment 
was observed with a scanning electron microscope, the condition of the 
plate in the solid regions was found to be favorable as shown in the 
microscopic photographs of FIGS. 5 and 6. In other words, the perforated 
dots forming the solid areas were independent from each other, and formed 
a uniform dot matrix by defining unprocessed gaps between consecutive dots 
in both the primary and secondary directions in the manner of a grid. 
When the quality of the character images on the thermal recording paper and 
the picture image formed on the OHP TP sheet was evaluated by using a 
microscope, it was found that the unprocessed gaps existed between colored 
dots in the solid regions, but they were visually indiscernible enough for 
the solid parts to be regarded as such in regards to both solid images and 
character images. 
When prints were made by using a processed thermal stencil master plate, 
the parts corresponding to the unprocessed gaps between perforated dots 
observed in the master plate were filled by the seeping of the ink, and 
the printed solid parts were quite favorable. In regards to character 
images also, printed images faithful to the original were obtained without 
involving any thinning, thickening or blurring. In particular, favorable 
reproduction of minute character images was achieved. The images were 
comparable to those obtained by using thermal recording paper. 
A prescribed number of prints were made by operating the aforementioned 
recording device at the rate of 60 to 130 sheets per minute, and the 
reverse surface of each of the printed sheets piled into a stack showed 
substantially no smearing by ink. 
The durability of the master plate was found to be satisfactory. 
EMBODIMENT 5 
The same operation as that of the fourth embodiment was carried out at the 
ambient temperature of 10.degree. C. 
The perforated dots of the thermal stencil master plate and the colored 
dots of the thermal recording paper and the OHP TP sheet had a tendency to 
be slightly smaller than those of the fourth embodiment, but a required 
picture quality was ensured in each case without creating any problem. 
EMBODIMENT 6 
The same operation as that of the fourth embodiment was carried out at the 
ambient temperature of 35.degree. C. 
The perforated dots of the thermal stencil master plate and the colored 
dots of the thermal recording paper and the OHP TP sheet had a tendency to 
be slightly larger than those of the fourth embodiment, but a required 
picture quality was ensured in each case without creating any problem. 
EMBODIMENT 7 
The recordability of the thermal recording materials (thermal stencil 
master plate, thermal recording paper and OHP TP sheet) was investigated 
by using a thin film type thermal head of 400 DPI which was set up as 
described above and the same device and original as the first embodiment. 
The ambient temperature was 23.degree. C. 
Length of each heat emitting element in the primary scanning direction 
.fwdarw.a=44 .mu.m 
Length of each heat emitting element in the second scanning direction 
.fwdarw.b=60 .mu.m 
Dot pitch (primary and secondary scanning directions) 
.fwdarw.Pa=Pb=63.5 .mu.m 
Heat emitting energy 
.fwdarw.81.5-60.0 .mu.J/dot 
In this case, the perforated dots forming the solid areas were independent 
from each other, and formed a uniform dot matrix by defining unprocessed 
gaps between consecutive dots in both the primary and secondary directions 
in the manner of a grid. 
When the quality of the character images on the thermal recording paper and 
the picture image formed on the OHP TP sheet was evaluated by using a 
microscope, it was found that the unprocessed gaps existed between colored 
dots in the solid regions, but they were visually indiscernible enough for 
the solid parts to be regarded as such in regards to both solid images and 
character images. 
When prints were made by using a processed thermal stencil master plate, 
the parts corresponding to the unprocessed gaps between perforated dots 
observed in the master plate were filled by the seeping of the ink, and 
the print quality of the solid parts was quite favorable. In regards to 
character images also, printed images faithful to the original were 
obtained without involving any thinning, thickening or blurring. There was 
no smearing of the reverse surface of the printing paper. 
EMBODIMENT 8 
The same operation as that of the seventh embodiment was carried out at the 
ambient temperature of 10.degree. C. 
The perforated dots of the thermal stencil master plate and the colored 
dots of the thermal recording paper and the OHP TP sheet had a tendency to 
be slightly smaller than those of the seventh embodiment, but a required 
picture quality was ensured in each case without creating any problem. 
EMBODIMENT 9 
The same operation as that of the seventh embodiment was carried out at the 
ambient temperature of 35.degree. C. 
The perforated dots of the thermal stencil master plate and the colored 
dots of the thermal recording paper and the OHP TP sheet had a tendency to 
be slightly larger than those of the seventh embodiment, but a required 
picture quality was ensured in each case without creating any problem. 
EXAMPLE 1 FOR COMISON 
The recordability of the thermal recording materials (thermal stencil 
master plate, thermal recording paper and OHP TP sheet) was investigated 
by using a thin film type thermal head of 400 DPI which was set up as 
specified below and the same device and original as the first embodiment 
for the purpose of comparing it to those of the embodiments 1 through 9. 
The ambient temperature was 23.degree. C. 
Length of each heat emitting element in the primary scanning direction 
.fwdarw.a=53 .mu.m 
Length of each heat emitting element in the second scanning direction 
.fwdarw.b=60 .mu.m 
Dot pitch (primary and secondary scanning directions) 
.fwdarw.Pa=Pb=63.5 .mu.m 
Heat emitting energy 
.fwdarw.87.5-65.0 .mu.J/dot 
As shown in the microscopic photographs of FIGS. 7 and 8 taken with a 
scanning electron microscope and showing a solid picture image formed in a 
thermal stencil master plate, the perforated dots forming the solid areas 
were expanded in the primary or secondary scanning direction, and are 
merged with the adjacent ones, demonstrating the thermal influences from 
adjacent heat emitting elements. Therefore, the unprocessed gaps between 
consecutive dots were extremely small in some areas as compared to the 
above described embodiments, and the perforated dot matrix forming the 
solid regions was found to be inferior in terms of uniformity as compared 
with the above described embodiments. 
When prints were made by using a processed thermal stencil master plate, 
the character images involved substantial thickening and blurring, and the 
solid areas contained a substantial amount of imprints of the fibrous 
support. This was caused by the pails of the film corresponding to those 
dots which were thermally affected by adjacent heat emitting elements and 
excessively melted, and the fluidized film which entangled with the fibers 
of the porous support and formed resolidified film or lumps. Further, the 
perforated dots became uneven in size, and the height of the ink deposited 
on the printing paper became uneven thereby causing unevenness in the 
density of the picture image. 
There was a substantial amount of ink transfer because the expansion and 
blurring of the perforated dots became excessive, and the amount of ink 
deposition was accordingly great, thereby slowing the process of drying 
the printing ink. 
As for the printing durability, the unprocessed gaps between the perforated 
dots are less than those of the embodiments, and the mechanical strength 
of the film was diminished, thus producing generally less favorable 
results than those of the above mentioned embodiments. 
As for the coloring performances of the thermal recording paper and the OHP 
TP sheet, the colored dots forming solid regions were continuous, and a 
sufficient density was obtained. However, small character images involved 
thickening and blurring of lines, and legibility was diminished as 
compared to the above described embodiments. 
EXAMPLE 2 FOR COMISON 
The same operation as the first example for comparison was carried out at 
the ambient temperature of 10.degree. C. 
The extent to which the perforated dots of the thermal stencil master plate 
and the colored dots of the thermal recording paper and the OHP TP sheet 
expanded and merged with the adjacent ones was eased as compared to the 
first example, and the thickening and merging of the lines in the 
character images was reduced. However, the sensitivity of the perforation 
and coloring was reduced as compared to that of the first example, and 
generation of unperforated dots and reduction in the area of each colored 
dot caused whitening or reduction in the density of solid areas. 
EXAMPLE 3 FOR COMISON 
The same operation as the first example for comparison was carried out at 
the ambient temperature of 35.degree. C. 
The extent to which the perforated dots of the thermal stencil master plate 
and the colored dots of the thermal recording paper and the OHP TP sheet 
expanded and merged with the adjacent ones became even worse as compared 
to the first example, and the thickening and merging of the lines in the 
character images was more pronounced, resulting in a poor picture quality. 
In particular, the perforated dots forming solid images became more random 
in terms of size, shape and arrangement. It was presumably because each of 
the perforated dots was affected by the heat front adjacent heat emitting 
elements. The condition of perforation did not reflect the resolution of 
the thermal head (400 DPI) at all, and the prints produced by the 
processed master plate involved excessive ink transfer. 
EXAMPLE 4 FOR COMISON 
The recordability of the thermal recording materials (thermal stencil 
master plate, thermal recording paper and OHP TP sheet) was investigated 
by using a thin film type thermal head of 400 DPI which was set up as 
specified below and the same device and original as the first embodiment. 
The ambient temperature was 23.degree. C. 
Length of each heat emitting element in the primary scanning direction 
.fwdarw.a=44 .mu.m 
Length of each heat emitting element in the second scanning direction 
.fwdarw.b=85 .mu.m 
Dot pitch (primary and secondary scanning directions) 
.fwdarw.Pa=Pb=63.5 .mu.m 
Heat emitting energy 
.fwdarw.100.0-75.0 .mu.J/dot 
In regards to the coloring and recordability of the thermal recording paper 
or the OHP TP sheet, the density of the coloring in the solid areas was 
sufficiently high, and a microscopic observation revealed some continuity 
in the colored dots. The picture images were generally favorable except 
for some thickening and merging of the lines of small characters. 
However, the perforations in the thermal stencil master plate were 
continuous in both the primary and secondary scanning directions, and the 
picture images contained more imprints of the fibrous support than the 
first example for comparison with the added disadvantages of more severe 
ink transfer and increased ink consumption. 
EXAMPLE 5 FOR COMISON 
The same operation as the fourth example for comparison was carried out at 
the ambient temperature of 10.degree. C. 
The perforations of the thermal stencil master plate were continuous in 
both the primary and secondary scanning directions in some areas, but 
there were also areas where perforations were not produced (due to 
insufficient sensitivity). The prints contained excessive unevenness in 
density. 
The character images of the OHP TP film involved thinning (breaks in fine 
lines) due to the insufficiency in sensitivity. 
EXAMPLE 6 FOR COMISON 
The same operation as the fourth example for comparison was carried out at 
the ambient temperature of 35.degree. C. 
A majority of the perforated dots of the thermal stencil master plate were 
continuous in both the primary and secondary scanning directions, and the 
printability was extremely poor with severe thickening of character images 
and ink transfer. 
In regards to the thermal recording paper and the OHP TP sheet, the density 
of solid areas was favorably high, but excessive merging and thickening of 
the lines of the character images prevented reproduction of clear images. 
The results of evaluating the above described embodiments and examples for 
comparison are given in Tables 1 and 2. 
TABLE 1 
__________________________________________________________________________ 
Size of heat emitting element 
a: primary area ratio of heat emitting 
Embodiments 
b: secondary dot pitch 
element to dot pitch 
ambient temp. 
__________________________________________________________________________ 
#1 a = 25 .mu.m 63.5 .mu.m above 
primary 39.4% 
23.degree. C. 
b = 60 .mu.m secondary 94.5% 
#2 same as above same as above 
same as above 
10.degree. C. 
#3 same as above same as above 
same as above 
35.degree. C. 
#4 a = 35 .mu.m same as above 
primary 55.1% 
23.degree. C. 
b = 60 .mu.m secondary 94.5% 
#5 same as above same as above 
same as above 
10.degree. C. 
#6 same as above same as above 
same as above 
35.degree. C. 
#7 a = 44 .mu.m same as above 
primary 69.3% 
23.degree. C. 
b = 60 .mu.m secondary 94.5% 
#8 same as above same as above 
same as above 
10.degree. C. 
#9 same as above same as above 
same as above 
35.degree. C. 
__________________________________________________________________________ 
Recordability of thermal recording materials 
thermal recording 
paper OHP TP film 
Thermal stencil master plate 
coloring 
character 
coloring 
character 
perfor- 
print 
offset- 
dura- 
ink con- 
of solid 
reprodic- 
of solid 
reprodic- 
Embodiments 
ation 
quality 
ing bility 
sumption 
region 
ibility 
region 
ibility 
__________________________________________________________________________ 
#1 OO OO OO OO OO O OO O OO 
#2 OO OO OO OO OO O OO O OO 
#3 OO OO OO OO OO O OO O OO 
#4 OO OO OO OO OO O OO O OO 
#5 OO OO OO OO OO O OO O OO 
#6 OO OO OO OO OO OO OO OO OO 
#7 OO OO OO OO OO OO O OO O 
#8 OO OO OO OO OO OO OO OO OO 
#9 O O O O O OO O OO O 
__________________________________________________________________________ 
TABLE 2 
__________________________________________________________________________ 
Size of heat emitting element 
Examples for 
a: primary area ratio of heat emitting 
Comparison 
b: secondary dot pitch 
element to dot pitch 
ambient temp. 
__________________________________________________________________________ 
#1 a = 53 .mu.m same as above 
primary 83.5% 
23.degree. C. 
b = 60 .mu.m secondary 94.5% 
#2 same as above same as above 
same as above 
10.degree. C. 
#3 same as above same as above 
same as above 
35.degree. C. 
#4 a = 44 .mu.m same as above 
primary 69.3% 
23.degree. C. 
b = 85 .mu.m secondary 133.9% 
#5 same as above same as above 
same as above 
10.degree. C. 
#6 same as above same as above 
same as above 
35.degree. C. 
__________________________________________________________________________ 
Recordability of thermal recording materials 
thermal recording 
paper OHP TP film 
Thermal stencil master plate 
coloring 
character 
coloring 
character 
Examples for 
perfor- 
print 
offset- 
dura- 
ink con- 
of solid 
reprodic- 
of solid 
reprodic- 
Comparison 
ation 
quality 
ing bility 
sumption 
region 
ibility 
region 
ibility 
__________________________________________________________________________ 
#1 .DELTA. 
.DELTA. 
.DELTA. 
O .DELTA. 
OO O OO .DELTA. 
thin- merging 
ning 
#2 O .DELTA. 
O OO O O .DELTA. 
O .DELTA. 
thin- thinning merging 
ning 
#3 X X XX .DELTA. 
X OO X OO X 
thicken- thicken- 
ing ing 
#4 X X X .DELTA. 
X OO .DELTA. 
OO .DELTA. 
thick- merging merging 
ening 
#5 .DELTA. 
X .DELTA. 
O .DELTA. 
OO O OO .DELTA. 
un- thinning 
even- 
nes 
#6 XX XX XX X XX OO X OO X 
thick- thicken- thicken- 
ening ing ing 
__________________________________________________________________________ 
In Tables 1 and 2, "OO" denotes "very good", "O" denotes good, ".DELTA." 
denotes fair, "X" denotes poor, and "XX denotes "very poor". The criteria 
for each item of evaluation are as given in the following: 
1. Evaluation of the thermal stencil master plate 
1) Condition of the perforation 
OO--The perforation dots are independent from each other and define a 
uniform dot matrix. 
O--The arrangement of the perforation dots is uneven, but are independent 
from each other. 
.DELTA.--The perforation dots are partly continuous. 
X--A substantial part of the perforation dots are continuous. 
XX--Expansion and merging of the perforation dots are severe. 
2) Condition of the prints 
OO--The uniformity of solid areas and the reproducibility of character 
images are both favorable. 
O--The quality is generally acceptable, but the lines of character images 
are partly thickened. 
.DELTA.--Thinning or merging of the lines of character images can be seen. 
X--Thickening of images is conspicuous. 
XX--Thickening of images is severe, and the images are blurred as a whole. 
3) Ink transfer 
OO--There is almost no ink transfer. 
O--There is a slight ink transfer. 
.DELTA.--The solid areas give rise to ink transfer. 
X--There is a significant ink transfer. 
XX--There is a severe ink transfer. 
4) Plate durability 
OO--More than 5,000 prints. 
O--About 5,000 prints. 
.DELTA.--About 4,000 prints. 
X--Less than 4,000 prints. 
5) Ink consumption 
(The number of prints of B4 paper with an image ratio of 20% that can be 
made with 1,000 cc of printing ink) 
OO--More than 10,000 prints. 
O--More than 9,000 prints. 
.DELTA.--More than 8,000 prints. 
X--More than 7,000 prints 
XX--Less than 7,000 prints. 
2. Evaluation of the thermal printing paper 
1) Coloring of solid areas 
OO--Particularly favorable with a sufficient density. 
O--Solid areas are in a favorable condition. 
2) Reproducibility of character images 
OO--Legibility of even the small characters is favorable. 
O--There are some merging of lines in parts of the small characters 
.DELTA.--There are thinning or merging of lines, and the images lack 
evenness. 
X--There are conspicuous merging and thickening of the lines of the 
character images. 
3. Evaluation of the OHP TP sheet 
The same as the thermal recording paper. 
Since the ratios of the lengths of each heat emitting element in the 
primary and secondary scanning directions are 30 to 70% and 60 to 95%, 
respectively, to the dot pitches in the corresponding directions in the 
thermal plate making device of the present invention, faithful 
reproduction is possible for all kinds of images including small character 
images and solid images, and one can obtain other advantages such as a 
favorable ink transfer prohibiting properly, a high plate durability, a 
favorable print capability with controlled ink consumption, and an 
expanded environmental adaptability which can cover a wide temperature 
range. 
Further, the thermal recording device is suitable for use with thermal 
recording paper and OHP TP sheets, and is particularly advantageous in 
reproducing minute character images. 
Although the present invention has been described in terms of preferred 
embodiments thereof, it is obvious to a person skilled in the art that 
various alterations and modifications are possible without departing from 
the scope of the present invention which is set forth in the appended 
claims.