JPH07314759A - Thermal recording method - Google Patents

Abstract

(57) [Abstract] [Purpose] To eliminate the conspicuous stripe-shaped density unevenness occurring in the main scanning direction and the sub scanning direction without significantly increasing the cost of the thermal printer. [Structure] The thermal heads H1, H2, H3 are arranged on the outer periphery of the platen drum 10 at intervals of distances L1, L2.
While rotating the platen drum 10 around which the thermosensitive recording material 1 is wound, each of the thermal heads H1, H2, and H3 once for the same thermosensitive coloring layer has a thermal energy lower than that required for the desired coloring density. Thermal recording is performed so that the thermal energy becomes higher and the thermal energy becomes higher successively. With these three thermal recordings, color is developed to the desired density of each pixel.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a thermal recording method,
More specifically, the present invention relates to a heat-sensitive recording method improved so that stripe-shaped density unevenness occurring in both the main and sub scanning directions is inconspicuous.

[0002]

2. Description of the Related Art In a thermal type thermal printer, a thermal recording material having at least one thermosensitive coloring layer is formed by using a thermal head having a heating element array in which a plurality of heating elements are arranged in a line in a main scanning direction. While being conveyed in the sub-scanning direction, thermal energy corresponding to image data is applied to the thermosensitive recording material to cause each pixel to develop a desired density. Such thermal printers include a platen drum system and a linear transport system depending on the method of transporting the thermal recording material. A platen-drum type thermal printer winds a heat-sensitive recording material around an outer peripheral surface of a platen drum and conveys it, and a thermal head extends in the axial direction on the outer periphery of the platen drum. Further, in a linear transport type thermal printer, a plurality of pairs of transport rollers are arranged along a straight transport path, and a thermal head is provided in this transport path.

In a thermal head, a cylindrical convex portion called a partial glaze is formed on a substrate made of alumina, for example, in order to make good contact with a heat-sensitive recording material. A plurality of heating elements (resistive elements) are linearly arranged on the upper side, and each heating element is provided with an electrode for energization. In order to form the partial glaze, for example, glass ink is screen-printed in a fine line shape on the substrate and heat-treated at a high temperature. As a result, the binder in the glass ink vaporizes, the glass melts and rises due to surface tension, and its cross section becomes an arc shape, forming a partial glaze.

[0004]

In the thermal printer as described above, the main scanning direction (the direction perpendicular to the paper feeding direction) and the sub-scanning direction (the direction perpendicular to the paper feeding direction) of the thermal recording material can be used in both the platen drum system and the linear transport system. Streaky uneven density may occur in the paper feeding direction). One of the causes of the stripe-shaped density unevenness in the main scanning direction is paper feed unevenness. For example, in a platen-drum thermal printer, if the drive system that rotates the platen drum has a non-uniform transmission system (for example, uneven machining accuracy of gears), uneven rotational speed always occurs at the same rotational position. Since the color density of the heat-recorded portion changes, streak-like density unevenness occurs on the heat-sensitive recording material. The same applies to a linear transport type thermal printer. In order to eliminate the stripe-shaped density unevenness that occurs in the main scanning direction, it is sufficient to improve the paper feeding accuracy, but it is technically extremely difficult to completely eliminate this paper feeding unevenness. If you try to do so, you can't avoid the high cost of a thermal printer.

Further, the cause of the stripe-shaped density unevenness in the sub-scanning direction is the unevenness of the resistance value of the heating element, and as shown in FIG. 10, the heating element array 10 of the thermal head 100.
This is because the height of the partial glaze 102 of No. 1 is not uniform. When the partial glaze 102 is formed, for example, when a material deviation occurs and a high portion A is formed, a low portion B is often formed next to it. In the high portion A, the contact pressure with the thermosensitive recording material 103 is high, and conversely, in the low portion B, the contact pressure with the thermosensitive recording material 103 is low, and an image is recorded lightly. Therefore, the color density of the portion thermally recorded by the portion A becomes relatively high, and streak-shaped density unevenness 104 occurs in the sub-scanning direction. Even in the case of uneven resistance values, the heat generating element having a small resistance value generates a large amount of thermal energy, so that the color density is high.

Such density unevenness 103 may be inconspicuous depending on the pattern of the image to be thermally recorded, but of the photographic pattern, the sky at cloudy weather is widely reflected or the wall is largely reflected. When recording such a thing with heat, it is very noticeable and annoying. In order to solve this problem, attempts are being made to make the partial glaze uniform and the resistance value uniform, but it is extremely difficult to completely eliminate this with the current technology.

Further, in Japanese Patent Application Laid-Open No. 5-116451, two thermal color-forming layers are colored simultaneously by using one thermal head and striking twice with thermal energy smaller than required thermal energy. A color thermosensitive recording method for preventing the occurrence of color mixture is described. However, even with this method, it is not possible to prevent streaky density unevenness.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a thermal recording method capable of making streak-shaped density unevenness occurring in the main scanning direction and the sub-scanning direction inconspicuous without significantly increasing the cost of the thermal printer. And

[0009]

In order to achieve the above object, a thermal recording method according to a first aspect of the present invention is such that a plurality of heating element arrays are arranged at predetermined intervals in the sub-scanning direction, and these heating elements are arranged. The array and the heat-sensitive recording material are moved relative to each other in the sub-scanning direction, and heat recording is performed with heat energy lower than the heat energy required for each heating element array to develop a desired density of color, and the heat recording is performed multiple times for the same pixel. The thermal recording causes this pixel to develop a desired density.

The respective heating element arrays are arranged with a distance such that they are not affected by heat. Further, only one heating element array may be formed for one thermal head, or a plurality of heating element arrays may be formed for one thermal head.

In the heat-sensitive recording method according to the second aspect, the heat-sensitive recording material is wound around a rotatable platen drum,
A plurality of heating element arrays are arranged so as to extend in the axial direction on the outer periphery of the platen drum.

In the heat-sensitive recording method according to the third aspect of the invention, the heat-sensitive recording material is reciprocated by a plurality of pairs of conveying rollers arranged in a substantially linear conveying path, and a plurality of heating element arrays are formed along the linear conveying path. It is arranged with an appropriate interval.

In the thermal recording method according to the fourth aspect, when the number of heating element arrays is N and the intended color density of the pixel is D, each heating element array develops a density of about D / N. As described above, the heat energy is increased in the heating element array on the downstream side.

In the heat-sensitive recording method according to the fifth aspect, each heating element array is used for cyan image recording, three for magenta image recording, and one for yellow image recording.

[0015]

While the heating element array and the heat-sensitive recording material are relatively moved in the sub-scanning direction, the first heat energy is lower than the heat energy required for heat recording at a desired density at one time. The heating element array is driven to perform the first thermal recording on each pixel. Next, the second heating element array, which is arranged at a predetermined distance from the first heating element array in the sub-scanning direction, heats the same pixel for the second time with the same low heat energy. Recording is done. Hereinafter, thermal recording is performed on the same pixels as the number of heating element arrays. As a result, each pixel has a desired density due to a plurality of times of color development.

Since a desired density is achieved by a plurality of thermal recordings using a plurality of heating element arrays, density unevenness is dispersed and the image quality is improved.

[0017]

In FIG. 2, a platen drum 10 holds a color thermosensitive recording material 1 on its outer peripheral surface 10a, and is rotated in a direction of an arrow by a pulse motor 12 during thermal recording.
The platen drum 10 is provided with a clamper 13 that presses and fixes the front end of the color thermosensitive recording material 1 against the outer peripheral surface 10 a of the platen drum 10. This clamper 13
Is attached to the platen shaft 15 through the long hole 13a. Then, the clamper 13 is shifted in the radial direction of the platen drum 10 by the cam mechanism 17.

In the color thermosensitive recording material 1, as shown in FIG. 3, a cyan thermosensitive coloring layer 3, a magenta thermosensitive coloring layer 4, a yellow thermosensitive coloring layer 5 and a protective layer 6 are sequentially laminated on a support 2. ing. As shown in FIG. 4, the uppermost yellow thermosensitive coloring layer 5 has the highest thermal recording sensitivity, and the lowermost cyan thermosensitive coloring layer 3 has the lowest thermal recording sensitivity. _Reference characters B _Y , B _M , and B _C in the figure are bias heat energy for heating to a temperature immediately before color development during recording of yellow, magenta, and cyan. _Y <B _M <B _C.

The cyan thermosensitive coloring layer 3 contains an electron-donating dye precursor and an electron-accepting compound as main components, and develops a cyan color when heated. The magenta thermosensitive coloring layer 4 contains, for example, a diazonium salt compound having a maximum absorption wavelength of 365 nm, and a coupler which thermally reacts with the diazonium salt compound to develop magenta. This magenta thermosensitive coloring layer 4
When irradiated with ultraviolet rays of 365 nm after thermal recording, the diazonium salt compound is photodegraded and the coloring ability is lost. The yellow thermosensitive coloring layer 5 has, for example, a maximum absorption wavelength of 420 nm.
And a coupler which thermally reacts with the diazonium salt compound to produce a yellow color. When this yellow thermosensitive coloring layer 5 is irradiated with near-ultraviolet rays of 420 nm, it is photo-fixed and the coloring ability is lost.

On the outer periphery of the platen drum 10, three thermal heads H1, H2, H3 are arranged at a distance L1, L2 from each other so as not to be thermally affected. The distances L1 and L2 are integer multiples of the length of the pixel in the sub-scanning direction in order to prevent pixel shift. The thermal head H1, H2, H3, are each heating element array h _1, h _2, h ₃ formed, each of the heat generating element array h _1, h _2, h _3, a main large number of heating elements They are arranged in a line in the scanning direction. Then, the yellow optical fixing device 2 is provided downstream of the thermal heads H1 to H3.
1, a magenta optical fixing device 22 is provided. The yellow light fixing device 21 has an emission peak of approximately 420 nm.
The ultraviolet lamp 24 and the reflector 25 each have a rod shape. Further, the magenta optical fixing device 22 includes an ultraviolet lamp 27 having a light emission peak of about 365 nm and a reflector 28.

A conveying roller pair 31 is arranged in the paper feeding / discharging passage 30, through which the color thermosensitive recording material 1 is conveyed. Further, on the platen drum side of the paper feeding / discharging passage 30, a separation claw 32 for guiding the rear end of the color thermosensitive recording material 1 to the paper feeding / discharging passage 30 at the time of discharging is provided.
In this embodiment, one passage is used as both the paper feed passage and the paper discharge passage, but they may be provided separately.

The heating elements of each of the heating element arrays h _{1 to} h ₃ generate bias heat energy B _Y , B _M , and B _C for each pixel during recording of yellow, magenta, and cyan, and color development. It is driven by a gradation pulse for adjusting the density. For example, in the case of 64 gradations, the drive data for one line of one color is read in 65 times including bias heating, and converted into 65 pulses by the strobe signal of 65 times. Each of the heating elements of the heating element array is selectively driven by the 65 times of pulses, and 64 gradations are expressed for one color.

FIG. 5 shows a pulse supplied to one heating element of the heating element array h ₁ to record one pixel. T1 is the time required for thermal recording of each pixel on one line, and is set shorter for a color having higher thermal recording sensitivity. T2 is the width of the bias pulse for performing bias heating, and is set narrower for colors having higher thermal recording sensitivity.
T3 is the ON period of the gradation pulse, and is set narrower as the thermal recording sensitivity is higher. These pulse widths T2, T3
Is determined by the strobe signal. T4 is the OFF period of the gradation pulse, which is the same for each thermosensitive coloring layer. T5 is a cooling time, which may be shorter for a color having higher thermal recording sensitivity. It should be noted that in a pixel having a small gradation level, the number of gradation pulses is small and the cooling time T5 is long.

Thermosensitive coloring of yellow, magenta and cyan
Each layer has three heating element arrays h.₁, H₂, H₃
Heat recording is carried out three times to develop the desired density. example
For example, when recording one pixel on the yellow thermosensitive coloring layer 5
And the heating element array h₁, H ₂, H₃By heat energy
-E₁, E₂, E₃Each of the colors develops to the desired density at one time
Lower than the heat energy used, and as described below, E
₁<E₂<E₃Will be decided. Therefore,
When thermally recording one pixel on the yellow thermosensitive coloring layer 5,
Heating element array h₁, H₂, H₃Each via supplied to
The width of the pulse is one when the color is developed to the desired density in one
Same as the width of the bias pulse, but the heating element array h
₁, H₂, H₃The width of each gradation pulse supplied to
Narrower than the width of the grayscale pulse when the desired density is developed.
Yes. Then, the heating element array h₁Width of gradation pulse T3
Is the narrowest and the heating element array h₃The width of the gradation pulse of
Is also wide.

The heating element arrays h ₁ , h ₂ and h ₃ are driven independently of each other, and come into contact with the color thermosensitive recording material 1 during thermal recording, and move away from the color thermosensitive recording material 1 during non-thermal recording. When the distances L1 and L2 are less than 1 mm, the heating element arrays h ₁ , h ₂ and h ₃ may be in contact with each other during operation, and may be affected by the heat of each other, resulting in the density to be recorded. The image may be recorded at a density different from that, which is not preferable. Therefore,
The distances L1 and L2 may be the same as or different from each other, but are set to 1 mm or more, preferably about 5 to about 50 mm.

The operation of the color thermal printer thus constructed will be described with reference to FIGS. 1 and 6. At the time of sheet feeding, the platen drum 10 is stopped with the clamper 13 being substantially vertical in FIG. The cam mechanism 17 sets the clamper 13 to the clamp release position. The conveying roller pair 31 nips and conveys the color thermosensitive recording material 1 supplied from a cassette (not shown) toward the platen drum 10. This conveying roller pair 31
Means that the tip of the color thermosensitive recording material 1 is the platen drum 10.
When it gets in between the clamper 13 and the clamper 13, it stops once. Then, the cam mechanism 17 shifts the clamper 13 to clamp the front end of the color thermosensitive recording material 1. After this clamping, the platen drum 10 and the conveying roller pair 31 rotate, so that the color thermosensitive recording material 1 is wound around the platen drum 10.

When the front end of the recording area of the color thermosensitive recording material 1 reaches the heating element array h ₁ by intermittently rotating the platen drum 10 by a certain number of steps, the heating element array h ₁ causes the _first heating of the yellow thermosensitive coloring layer 5. The thermal recording of is started. In this first thermal recording, each pixel to be recorded on the yellow thermosensitive coloring layer 5 has a target coloring density D.
_The thermal energy E is applied to the color thermosensitive recording material 1 by the heating element array h ₁ so that the color is developed to a density of about 1/3 of _Y
1 is given.

When the first line of the yellow image is recorded, the platen roller 10 is moved to 1 by the pulse motor 12.
The pixel is step-rotated, and at the same time, the second line of the yellow image is thermally recorded. Thereafter, in the same manner, the third and subsequent lines of the yellow image are thermally recorded on the color thermosensitive recording material 1. When the platen roller 10 rotates stepwise by a distance L1 and the tip of the recording area of the color thermosensitive recording material 1 reaches the heating element array h ₂ , the _second heating recording on the yellow thermosensitive coloring layer 5 is performed by the heating element array h ₂ . Be started. In this case, the heating element is driven to the same pixel by the drive data created from the same image data so that the pixel coincides with the first time.

By the way, in the yellow thermosensitive coloring layer 5, each pixel has a density of about D in the first recording by the heating element array h _{1.
The number of} unreacted couplers remaining in this layer after being colored _Y / 3 is smaller in the second recording by the heating element array h ₂ than in the first recording. Therefore, even if the same thermal energy E ₁ as that of the first recording is applied in the second recording, the color is developed to a density lower than the density of the first recording D _Y / 3. Therefore, in the second thermal recording by the heating element array h ₂ , the thermal energy E is added so that the yellow thermosensitive coloring layer 5 is added to the first density of about D _Y / 3 to develop the density of about 2D _Y / 3. _A thermal energy E ₂ greater than ₁ is applied to the color thermosensitive recording material 1.

Further, the platen roller 10 has a distance of L2.
When rotated stepwise, the recording image of the color thermosensitive recording material 1 is recorded.
The tip of the rear is the heating element array h₃Reaching yellow heat sensitivity
The third thermal recording on the coloring layer 5 is the heating element array h.₃
Started by This third yellow heat record
Concentration about 2D_YConcentration approx. D / 3_Y/ 3 is added
To the second heat energy E₂Greater heat energy
E₃Is applied to the color thermosensitive recording material 1. As a result,
Each pixel of the yellow thermosensitive coloring layer 5 has a target coloring density D _YFrom
To be colored. In this way, by performing the thermal recording three times, as shown in FIG.
As shown in, the characteristic curve is indicated by a dashed line from Y indicated by a solid line.
While changing to Y'shown and suppressing the color density of one time to a low level,
Color can be developed to a desired density. Also, streak
In addition to preventing yellow, the yellow thermosensitive coloring layer 5 and magenta
To prevent so-called color mixing, in which the thermosensitive coloring layer 4 is colored.
You can

In this way, the heating element arrays h ₁ , h ₂ ,
The heat energies E ₁ , E ₂ , E ₃ satisfying E ₁ <E ₂ <E ₃ are sequentially applied to the color thermal recording material 1 by h ₃ , but the actual heat energies E ₁ , E ₂ , E ₃ are Each value of is dependent on the color development characteristics of the color thermosensitive recording material 1 and the heat generation characteristics of the heating element arrays h ₁ , h ₂ and h ₃ , and is therefore determined by experiments.

When the portion on which the yellow image has been thermally recorded three times reaches the optical fixing device 21, the ultraviolet lamp 24 of the optical fixing device 21.
To near 420 nm from near UV to color thermosensitive recording material 1
The diazonium salt compound remaining in the yellow thermosensitive coloring layer 5 is photolyzed and the coloring ability is lost.

When the platen drum 10 makes one revolution and the recording area of the color thermosensitive recording material 1 reaches the position of the heating element array h ₁ again, the heating element array h ₁ is at the time of thermal recording of the yellow thermosensitive coloring layer 5. Similarly, the magenta thermosensitive recording layer 4
The first thermal recording for At this time, since the yellow thermosensitive coloring layer 5 has already been optically fixed, the yellow thermosensitive coloring layer 5 does not develop color.

When the platen roller 10 is step-rotated by the distance L1, the second thermal recording on the magenta thermosensitive coloring layer 4 is started by the heating element array h ₂ , and when the platen roller 10 is step-rotated by the distance L2. , The third thermal recording on the magenta thermosensitive coloring layer 4 is started by the heating element array h ₃ . When the color thermosensitive recording material 1 reaches the fixing device 22 during the third magenta recording, the color thermosensitive recording material 1 is irradiated with ultraviolet rays having a wavelength of about 365 nm, and the magenta thermosensitive coloring layer 4 is optically fixed.

When the platen drum 10 makes one further rotation and the recording area again reaches the position of the heating element array h ₁ , the first thermal recording of the cyan image is started. Thereafter, similarly to the thermal recording of the yellow and magenta images, the thermal recording of the cyan image for the second time and the third time is performed by the heating element arrays h ₂ and h ₃ . In the thermal recording of the cyan thermosensitive coloring layer 3,
The optical fixing devices 21 and 22 may be turned off.

After the thermal recording of the yellow image, the magenta image, and the cyan image is completed, the platen drum 10 and the conveying roller pair 31 are reversed. By the reverse rotation of the platen drum 10, the trailing end of the color thermosensitive recording material 1 is guided to the paper feeding / discharging path 30 by the separating claw 32 and is nipped by the conveying roller pair 31. After that, when the platen drum 10 reaches the sheet feeding position, the clamper 13 is shifted by the cam mechanism 17 to release the clamp of the leading end of the color thermosensitive recording material 1 and the platen drum 10 is stopped. Thereby, the heat-recorded color heat-sensitive recording material 1 is
The paper is discharged to the tray through the paper supply / discharge path 30.

As described above, the three heat-generating element arrays h ₁ , h ₂ and h ₃ separated by the distances L 1 and L _{2 respectively} cause low color development once for the same thermosensitive color forming layer of the color thermosensitive recording material 1. Thermal recording is performed at a density, and each pixel is finished to a target color density by a total of three thermal recordings. The rotation unevenness of the platen drum 10 occurs at the same position with respect to the platen shaft 15, but the position where the stripe-shaped density unevenness occurs in the main scanning direction due to this rotation unevenness is generated by the heating element arrays h ₁ and h. _It changes depending on the positions of ₂ , h ₃ and 1
It is not conspicuous because the density of unevenness of color developed by each thermal recording is about 1/3 of the target density at one time. Further, the streak-shaped density unevenness in the sub-scanning direction due to the uneven precision of the partial glazes of the heating element arrays h ₁ , h ₂ , and h ₃ is also not noticeable because it becomes about 1/3.

FIG. 7 shows a thermal printer for recording a full-color image with one rotation of the platen drum. On the outer circumference of the platen drum 10, yellow, magenta, and cyan thermal heads 41, 42, and 43 are arranged at a predetermined interval, and a yellow optical fixing device 21 and a magenta optical fixing device 22 are provided therebetween. It is arranged.
Each of the thermal heads 41, 42, and 43 has two heating element arrays H _Y1 , H _Y2 , and _{Y Y2} for recording a yellow image.
Heating element arrays H _M1 and H _M2 for magenta image recording and heating element arrays H _C1 and H _C2 for cyan image recording are provided. The heating element arrays H _Y1 and H _Y2 are the distance L _Y , the heating element arrays H _M1 and H _M2 are the distance L _M , and the heating element arrays H _C1 and H
_C2 is arranged at intervals of a distance L _C so as not to be affected by heat. Note that the distance L _Y ,
L _M and L _C may be the same or different.

After the yellow image is thermally recorded twice by the heating element arrays H _Y1 and H _Y2 , the yellow optical fixing device 2
1 is optically fixed. Then, the magenta image is thermally recorded twice by the heating element arrays H _M1 and H _M2 , and thereafter, the magenta image is optically fixed by the magenta light fixing device 22. Finally, the cyan image is thermally recorded twice by the heating element arrays H _C1 and H _C2 .

In this embodiment, thermal recording for pixels of the same color is performed once by two different heating element arrays, a total of two times, and a thermal head is used for each color. If the platen drum has uneven rotation, streak-like density unevenness always occurs at the same position with respect to the platen axis in the main scanning direction. The density varies depending on the position of the thermal head and is distributed to six places. The density of unevenness is about 1/2 of the target color density for each color, so that uneven density is not noticeable. Further, the stripe-shaped density unevenness in the sub-scanning direction due to the variation in the forming accuracy of each heating element array is not conspicuous because each density is about ½ of the target color density for each color.

In the embodiment shown in FIG. 8, while the color thermosensitive recording material 1 is conveyed linearly only once, yellow, magenta,
This is a linear-pass, single-pass color thermal printer that thermally records each cyan image and also performs optical fixing. The color thermal printer 45 includes a pair of conveyance rollers 4 arranged in a linear direction.
6, 47, 48 and 49 are provided with a conveying path for the color thermosensitive recording material 1. Along this transport path, yellow,
A total of six thermal heads 51 to 59 are arranged for recording magenta and cyan images, respectively, and a yellow optical fixing device is provided between the thermal heads 53 and 54 and between the thermal heads 56 and 57. 21, a magenta optical fixing device 22 is provided.

Each heat generation of the thermal heads 51, 52, 53
The element arrays 51a, 52a and 53a are respectively separated by distance.
L_Y1, L_Y2The thermal heads 5 are arranged at intervals of
4, 55, 56 heating element arrays 54a, 55a, 5
6a is the distance L_M1, L_M2Placed at intervals
Each of the heating elements of the thermal heads 57, 58, 59.
B 57a, 58a, and 59a are the distance L, respectively._C1, L_C2of
They are arranged at intervals. The thermal head 5
A well-known platen roller is provided at each position facing 1 to 59.
61 are arranged respectively. Also, the distance L_Y1，
L_Y2, L_M1, L_M2, L _C1, L_C2May all be different
I, L as shown_M1= L_M2<L_Y1= L_Y2<L_C1= L
_C2May be

The yellow image is thermally recorded three times by the heating element arrays 51a, 52a and 53a, and then the yellow image is optically fixed by the yellow optical fixing device 21. Next, the magenta image is thermally recorded three times by the heating element arrays 54a, 55a, 56a, and thereafter, the magenta image is optically fixed by the magenta light fixing device 22. Finally, the cyan image is thermally recorded three times by the heating element arrays 57a, 58a, 59a.

In this embodiment, the conveying roller pairs 46 to 49 are used.
When the paper feeding speed is uneven, streak-like density unevenness occurs in the main scanning direction, but the position of the density unevenness generated on the color thermosensitive recording material 1 differs depending on the positions of the thermal heads 51 to 59, and Since the density of unevenness is about 1/3 of the target color density for each color, the unevenness of density is not noticeable. Further, the stripe-shaped density unevenness in the sub-scanning direction due to the variation in the forming accuracy of the thermal heads 51 to 59 is not noticeable because the density becomes about 1/3 of the target color density for each color.

In the color thermal printer 70 shown in FIG. 9,
The conveying path for the color thermosensitive recording material 1 is constituted by the conveying roller pairs 64-69 arranged in the linear direction. Three thermal heads 71, 72, 73 are arranged along this transport path. An optical fixing device 21 for yellow and an optical fixing device 22 for magenta are arranged between them. Each of the thermal heads 71, 72, 73 is provided with a heating element array 75, 76 for recording a yellow image, a heating element array 77, 78 for recording a magenta image, and a heating element array 79, 80 for recording a cyan image. ing.

A well-known platen roller 81 is arranged at each position facing the thermal heads 75-80. The operation and effect of this embodiment are the same as those of the embodiment shown in FIG. 8 except that the density of the stripe-shaped density unevenness generated in the main and sub-scanning directions is about 1/2 of the target color density for each color. Therefore, the description is omitted.

Although the embodiment described above is a color thermal printer, the present invention can be applied to a monochrome thermal printer. In this case, a thermosensitive recording material having one thermosensitive coloring layer is used, and an optical fixing device can be omitted. Further, although the number of the heating element arrays for recording one color is two or three, the present invention only needs to be two or more. Also, the number of heating element arrays may be different for yellow, magenta, and cyan. For example, cyan unevenness is most noticeable, so 3 for cyan image recording.
It is also possible to print with one heating element array, one for magenta image recording, and one for yellow image recording. This combination requires a minimum number of heating element arrays and is practical in terms of cost.

[0048]

As described above, according to the thermosensitive recording method of the present invention, thermal recording is performed on the same thermosensitive coloring layer by a plurality of heating element arrays in a plurality of times. The stripe-shaped density unevenness that occurs in the main scanning direction is
The occurrence positions are dispersed in the sub-scanning direction, and the respective densities become low, so that they are not conspicuous. In addition, the stripe-shaped density unevenness that occurs in the sub-scanning direction due to the uneven formation accuracy of the heating element array is not noticeable because the respective density is low. Also, simply by increasing the number of heating element arrays,
Since the conventional paper feeding mechanism and the like can be used as they are, the cost of the thermal printer is not so high.

[Brief description of drawings]

FIG. 1 is a flowchart showing a thermal recording method of the present invention.

FIG. 2 is a schematic view of a specific example of a color thermal printer embodying the present invention.

FIG. 3 is an explanatory diagram showing an example of a layer structure of a color thermosensitive recording material.

FIG. 4 is a graph showing coloring characteristics of each thermosensitive coloring layer.

FIG. 5 is a waveform diagram showing each signal for driving the thermal head and the heat generation state of the heat generating element.

FIG. 6 is a graph showing the relationship between the number of thermal recordings and the color development characteristics of the yellow thermosensitive color development layer.

FIG. 7 is a schematic view showing a color thermal printer capable of recording a full-color image with one rotation of the platen drum.

FIG. 8 is a 1-pass type color thermal printer provided with three thermal heads for each color.

FIG. 9 is a schematic view showing a one-pass type color thermal printer in which one thermal head is provided with two heating element arrays.

FIG. 10 is an explanatory diagram showing a conventional recording method.

[Explanation of symbols]

1 color thermosensitive recording material 3 cyan coloring layer 4 magenta coloring layer 5 yellow thermosensitive coloring layer 10 platen drum 15 platen shaft 21 fixer for yellow fixer 22 Magenta D _Y target color density E _1, E _2, E ₃ Thermal energy H ₁ , H ₂ , H ₃ , 41, 42, 43, 51-59, 7
5-80 thermal head _{h 1, h 2, h 3} , H Y1, H Y2, H M1, H M2, H C1, H
_{C2, 51a~59a, 75~80} heating element array _{L 1, L 2, L 3} , L Y, L M, L C, L YM, L MC, L
_Y1 , L _Y2 , L _M1 , L _M2 , L _C1 , L _C2 , D _Y , D _M , D _C
distance

Continuation of the front page (51) Int.Cl. ⁶ Identification number Office reference number FI technical display location 7267-2H B41M 5/26 M

Claims (5)

[Claims] 1. A heat-sensitive recording method in which thermal energy is applied to a heat-sensitive recording material having at least one heat-sensitive color-developing layer formed thereon to color each pixel to a desired density, and a plurality of heating elements are linearly arranged in a main scanning direction. A plurality of heating element arrays arranged in the sub-scanning direction are arranged at a predetermined interval in the sub-scanning direction, and these heating element arrays and the heat-sensitive recording material are relatively moved in the sub-scanning direction, and each heating element array is set to a desired position. A heat-sensitive recording method, characterized in that heat recording is performed with a heat energy lower than that required to develop a color at a density, and this pixel is developed at a desired density by performing heat recording a plurality of times for one pixel. 2. The heat-sensitive recording material is wound around a rotatable platen drum, and the plurality of heating element arrays are arranged so as to extend in the axial direction on the outer periphery of the platen drum. The heat-sensitive recording method according to claim 1. 3. The heat-sensitive recording material is reciprocated by a plurality of pairs of conveying rollers arranged in a substantially linear conveying path, and a plurality of heating element arrays are arranged at appropriate intervals along the linear conveying path. The heat-sensitive recording method according to claim 1, wherein 4. When the number of the heating element arrays is N and the intended color density of the pixel is D, each heating element array is arranged on the downstream side so that the color density is about D / N. 4. The heat-sensitive recording method according to claim 1, wherein the heat energy is increased as the heating element array increases. 5. The number of the heating element array is set to three for cyan image recording, two for magenta image recording, and one for yellow image recording. The heat-sensitive recording method described.