JP3369012B2 - Color thermal printing method - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a color thermal printing method in which a plurality of thermal heads are used to record a full-color image in a single pass of the color thermal recording paper. The present invention relates to a color thermal printing method for preventing the occurrence of streak-like density unevenness caused by the above.

[0002]

2. Description of the Related Art In a color thermal printing method, a color thermal recording paper that develops color when heated is used. The thermal head presses and heats the color thermal recording paper while moving the thermal head and the color thermal recording paper relative to each other. Record full-color images. In this color thermosensitive recording paper, at least a cyan thermosensitive coloring layer, a magenta thermosensitive coloring layer, and a yellow thermosensitive coloring layer are sequentially formed on the base. In order to selectively develop the color of each thermosensitive coloring layer, the thermosensitive coloring layers have different thermal sensitivities, the cyan thermosensitive coloring layer in the lowermost layer has the lowest thermal sensitivity, and the yellow heating coloring layer in the uppermost layer has the thermal sensitivity. Highest sensitivity. Also, when recording the next thermosensitive coloring layer,
In order to prevent the recorded thermosensitive coloring layer thereon from being recorded again, the recorded thermosensitive coloring layer is irradiated with an electromagnetic ray specific to the recorded thermosensitive coloring layer and fixed.

A large number of heating elements are formed in a line on the thermal head, and an image of one color is recorded line by line. When recording this one line, each heating element applies coloring heat energy (mJ / mm ² ) based on the characteristic curve of the heat-sensitive color-forming layer to be recorded to the color heat-sensitive recording paper to virtually generate it on the color heat-sensitive recording paper. The dots are formed by coloring the inside of the pixels divided into squares. This coloring heat energy is
It consists of heat energy immediately before the color of the thermosensitive coloring layer to be recorded (hereinafter, this is referred to as bias heat energy) and heat energy for developing the color to a desired density (hereinafter, referred to as gradation heat energy). The bias heat energy is a constant value determined according to the type of the thermosensitive coloring layer, but the gradation heat energy changes according to the image data representing the gradation level.

In order to perform high-speed printing, three thermal heads are arranged in the passage area of the color thermal recording paper, and while each color thermal recording paper is passed once from the upstream side to the downstream side, a yellow color is produced by each thermal head. 1 pass 3 for sequentially recording images, magenta images, and cyan images to form full-color images
A head type color thermal printing method is known.

[0005]

When this one-pass, three-head type color thermal printing method is used, a line having a high density (called a black streak) or a line having a low density (called a white streak) is located at a specific position. I noticed that it contains. As a result of various studies on the cause of the density unevenness, it was found that it was due to the fluctuation of the transport load due to the behavior of the thermal head.

While a certain thermal head is recording,
Another thermal head presses against the color thermal recording paper,
Alternatively, when the color thermal recording paper is separated from the color thermal recording paper, the movement of the other thermal head changes the carrying load of the color thermal recording paper. When the transport load changes, the distortion of the platen drum, the expansion and contraction of the belt, the twisting of the rotating shaft, etc. increase or decrease according to the change. Also, when a pulse motor is used as the power source for the color thermal recording paper conveyance system, the rotor does not go out of step, but after step feed, the rotor does not stop at the normal position, It slightly shifts to a position where the magnetic force and the transport load are balanced. For the sake of convenience, these recoverable state changes are generically referred to as distortion of the transport system. Since the transport speed of the color thermosensitive recording paper temporarily changes according to the amount of change in the distortion of the transport system, density unevenness (black stripes, white stripes) occurs.

FIG. 12 is a 1-pass 3-head type color thermal printer in which the color thermal recording paper 90 is conveyed in the direction of the arrow while yellow (Y) and magenta (M) having a constant density.
It shows a state in which and are recorded in a strip shape. When the magenta thermal head goes down and presses against the color thermosensitive recording paper 90 during yellow recording, the color thermosensitive recording paper 90 is pressed.
The transporting load of is increased. When the carrying load increases, the amount of distortion of the carrying system increases by the amount of change, and the carrying speed of the color thermosensitive recording paper 90 temporarily decreases according to the amount of change in the amount of distortion. When the transport speed is temporarily reduced, the width of the line being recorded is reduced and the thermal energy (mJ / mm ² ) applied from the heating element is increased, so that the color density of this line is increased. For this reason, a high density line, a so-called black stripe 91, is generated.

Further, during the recording of magenta, when the thermal head for yellow which has finished recording rises and separates from the color thermosensitive recording paper 90, the carrying load of the color thermosensitive recording paper 90 decreases. Since the distortion is reduced by the reduction of the transportation load, the transportation speed of the color thermosensitive recording paper 90 is temporarily increased by the reduction of the distortion. When the transport speed temporarily increases,
Since the width of the line during printing becomes large and the thermal energy (mJ / mm ² ) given from the heating element becomes small, the color density of the line during printing becomes low and so-called white stripes 92 occur.

Each thermal head comprises a color thermosensitive recording paper 9
Recording is started when a predetermined time elapses after being pressed against 0. Further, the thermal head is separated from the color thermosensitive recording paper 90 after the recording of the image is finished and the energization is stopped. Therefore, the thermal head is used for the color thermal recording paper 9
When it is in pressure contact with 0, there are a state where it is not energized and remains cool, and a state where it is energized to generate heat. And
The transport load changes when one of these two states changes to the other. Since the distortion amount of the conveying system changes according to the change of the conveying load, the conveying speed of the color thermosensitive recording paper 90 temporarily changes.

The change of the carrying load depending on the energization state of the thermal head is caused by the thermal head and the color thermosensitive recording paper 90.
This is due to the coefficient of friction between and. That is, the friction coefficient between the thermal head and the color thermosensitive recording paper 90 is large when the thermal head is cold without being energized, but the color thermosensitive recording paper 90 is heated when the thermal head is energized and generating heat. Since the surface of is softened or melted by heat, the coefficient of friction becomes small. When this coefficient of friction increases, the load of carrying color thermal recording paper increases,
As the friction coefficient decreases, the transport load also decreases.

For example, when energization of the magenta thermal head is started during recording of the yellow thermal head,
The conveyance speed of the color thermosensitive recording paper is temporarily increased, and white stripes 93 are generated. Further, if the energization of the yellow thermal head is stopped during recording of the magenta thermal head, black streaks 94 occur.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a color thermal printing method capable of preventing the generation of white stripes or black stripes due to variations in the transport load of color thermal recording paper.

[0013]

In order to achieve the above object, in the color thermal printing method according to claim 1, another thermal head is pressed against the color thermal recording paper during recording of at least one thermal head. However, for lines in which streak-shaped density unevenness occurs due to separation from the color thermosensitive recording paper, the thermal energy generated by the thermal head is corrected so as to correct this density unevenness.

In the color thermal printing method according to the second aspect of the present invention, during the recording of at least one thermal head, a line in which streaky density unevenness occurs due to the start or stop of energization of another thermal head, The thermal energy generated by the thermal head is corrected so as to correct this density unevenness.

In a color thermal printing method according to a third aspect of the present invention, when one line consisting of a plurality of pixels is recorded on a specific thermosensitive coloring layer, bias thermal energy for heating each pixel until just before coloring, The gradation thermal energy corresponding to the color density of the pixel is applied, and the bias thermal energy is corrected according to the density unevenness in the line where the density unevenness occurs.

[0016]

The load fluctuation of the color thermosensitive recording paper is caused by the mechanical movement of the thermal head (whether the thermal recording paper is pressed against the color thermosensitive recording paper) and the energization state of the thermal head. When this transport load variation occurs, density unevenness occurs on the line being printed by the thermal head. Since the line in which the density unevenness occurs and the type and the degree of the density unevenness are known, the desired thermal energy is increased or decreased to prevent the occurrence of the density unevenness in the recording of this line. This modification of the thermal energy is simple because it is applied to the bias thermal energy having a constant value depending on the type of the thermosensitive coloring layer.

[0017]

EXAMPLE Referring to FIG. 2, a platen drum 10 comprises a metal shaft 10a and a black hard rubber drum 10b.
It consists of and. A pulley 11 is fixed to the shaft 10a. This pulley 11 and the pulse motor 12
A belt 14 is hung between the pulley 13 and the pulley 13. Pulse motor 12 with a motor drive pulse with a constant cycle
The platen drum 10 is continuously rotated by driving. The shaft 10a of the platen drum 10 may be directly connected to the output shaft of the pulse motor 12. Furthermore, if a rotary encoder is connected to the shaft 10a of the platen drum 10 and the rotational position of the platen drum 10 is detected by this rotary encoder, instead of the pulse motor 12,
A DC motor or the like can be used.

A color thermosensitive recording paper 16 is wound around the outer periphery of the platen drum 10 and is conveyed together with the platen drum 10 in the sub-scanning direction indicated by the arrow. The color thermosensitive recording paper 16 is pressed against the outer periphery of the platen drum 10 by a guide roller 17 arranged on the paper feed side (upstream side) and a guide roller 18 arranged on the paper discharge side (downstream side).

A sensor 19 for detecting the leading end of the color thermosensitive recording paper 16 is arranged beside the guide roller 17. This sensor 19 is provided with a light projecting section and a light receiving section, and due to the difference in reflectance between the black platen drum 10 and the white color thermosensitive recording paper, the color thermosensitive recording paper 1
The tip of 6 is detected optically. The motor drive pulse is counted from the time when the leading edge is detected, and the transport position of the color thermosensitive recording paper 16 is measured.

A yellow thermal head 20 for recording a yellow image, a magenta thermal head 21 for recording a magenta image, and a cyan thermal head 22 for recording a cyan image are arranged on the outer periphery of the platen drum 10. Has been done. Each thermal head 20-2
2 includes heating element arrays 20a, 21a, 22a in which a large number of heating elements are arranged in a line, and these extend in the axial direction (main scanning direction) of the platen drum 10. Further, each of the thermal heads 20 to 22 has a heating element array 2
0a, 21a, 22a move between a position where they are pressed against the color thermosensitive recording paper 16 and a position where they are retracted from the color thermosensitive recording paper 16.

A yellow fixing device 2 is provided between the yellow thermal head 20 and the magenta thermal head 21.
3 are arranged. The yellow fixing device 23 is composed of two ultraviolet lamps 24 that emit near-ultraviolet rays having an emission peak of 420 nm and a reflector 25.
Further, a magenta fixing device 26 is arranged between the magenta thermal head 21 and the cyan thermal head 22. The magenta fixing device 26 includes two ultraviolet lamps 2 that emit ultraviolet rays having an emission peak of 365 nm.
7 and a reflector 28.

As shown in FIG. 3, the system controller 30 controls the conveying section 31, the yellow recording section 32, the magenta recording section 33, and the cyan recording section 34 in a predetermined sequence. The system controller 30 commands the motor controller 36 of the transport unit 31 to start and stop the rotation of the pulse motor 12. The motor controller 36 sends a motor drive pulse having a constant cycle to the motor driver 37 to rotate the pulse motor 12 at a constant speed. The counter 38 starts counting from the time when the sensor 19 detects the front end of the color thermosensitive recording paper 16, and measures the transport position of the front end. The count value of the counter 38 is sent to the system controller 30 in order to determine the timing of movement and energization of each thermal head 20-22.

The system controller 30 includes a counter 3
A 1-line print start signal for instructing the yellow recording unit 32, the magenta recording unit 33, and the cyan recording unit 34 to up / down the thermal head and to start recording one line of an image based on the count value of 8 To send. The 1-line print start signal is sent to the recording units 32 to 34 at the same time.

The yellow recording section 32 is provided with a yellow (Y) print controller 42, and when the yellow print controller 42 receives a 1-line print start signal from the system controller 30, it prints 1 line of a yellow image. Start recording. Also this 1
A line to be recorded is specified by counting the line print start signal with a counter.

The memory 43 stores bias data and the like used for recording a yellow image. The bias data includes standard bias data, corrected bias data for preventing white lines, and corrected bias data for preventing black lines. Alternatively, the standard bias data alone may be stored in the memory 43, and the yellow print controller 42 may generate the corrected bias data by multiplying the correction coefficient according to the type of the density unevenness.

The bias data is commonly used for each heating element of the yellow thermal head 20, and one line of bias data read from the memory 43 produces one line of bias data. The bias line memory 44 is written only when the type of bias data used changes, and is commonly used for each line until the type changes. Each heating element has a variation in its resistance value, and even if it is driven by the same drive pulse, the amount of heat generated differs. Therefore, in order to correct the error of the heat generation amount, it is preferable to set the bias data for each heating element in consideration of the resistance value error.

Yellow image data fetched by a video camera, a scanner or the like is written in the yellow image memory 45. The yellow image memory 45 reads out the yellow image data line by line at the time of recording the yellow image and writes the read yellow image data in the image line memory 46.
Alternatively, the blue image data may be read into the image memory, and one line may be read at the time of recording and then converted into yellow image data.

When recording one line of the yellow image, the selector 47 first reads the bias data for one line from the bias line memory 44 for each pixel in order and sends it to the comparator 48. When the bias heating is completed, the selector 47 reads 1 from the image line memory 47.
The yellow image data for the line is read and sent to the comparator 48.

When the number of gradations is, for example, "256", the comparison data generating circuit 49 sequentially generates comparison data from "0" to "255" in both bias heating and gradation heating. The comparator 48 outputs 1 for each comparison data.
The line data is sequentially compared for each pixel, and drive data for one line is generated. In the comparison for each pixel,
When the bias data or the image data is larger than the comparison data, the drive data of "1" is generated, and when the bias data or the image data is smaller than the comparison data, the drive data of "0" is generated. Therefore, in the bias heating, each bias data of one line is compared 256 times, and one bias data is converted into 256-bit bias drive data as a result. Similarly, in the gradation heating, each line of yellow image data is compared 256 times, and one piece of yellow image data is eventually converted into 256-bit gradation driving data.

The comparator 48 serially outputs the drive data for one line and sends it to the drive circuit 50. The drive circuit 50 first converts serial drive data into parallel drive data for one line. Next, the logical product of each drive data for one line and the strobe signal from the strobe signal generation circuit 51 is obtained. That is, when the drive data is "1", a drive pulse having the width of the strobe signal is generated. When the drive data is "0", no drive pulse is generated. The width of the strobe signal is different between the bias heating and the gradation heating and is determined by the characteristic curve of the color thermosensitive recording paper 16, but generally the bias heating is wider.

The thermal head 20 for yellow is moved by the up-down mechanism 52 to a position where the heating element array 20a is in pressure contact with the color thermosensitive recording paper 16 and a position away from the color thermosensitive recording paper 16. The thermal head 20 for yellow heats the heating element after the color thermosensitive recording paper 16 is pressure-contacted and until the color thermosensitive recording paper 16 is stably conveyed, that is, after the color thermosensitive recording paper 16 is conveyed by a predetermined number of lines. Energization of the array 20a is started.
When the recording of the yellow image is completed, the heating element array 2
After the energization of 0a is stopped, the color thermal recording paper 16 is conveyed by a predetermined number of lines, and then the yellow thermal head 20 is retracted. The up / down mechanism 52 is composed of a cam mechanism, a solenoid, or the like, and swings the yellow thermal head 20 about the shaft 20b.

Since the magenta recording section 33 and the cyan recording section 34 have the same structure as the above-mentioned yellow recording section 32, a detailed block diagram and description thereof will be omitted.

FIG. 4 shows drive pulses for driving the heating elements of the three-color thermal head. For example, “240” is used as the standard bias data,
During the bias heating period, the drive circuit 50 creates 241 bias drive pulses. As shown in (A), one heating element of the yellow thermal head 20 is driven by 241 bias driving pulses to generate bias heat energy.

After the bias heating, the image data value becomes "2".
In the case of "55", the driving circuit 50 outputs 2 during the gradation heating period.
56 grayscale drive pulses are created. One heating element is driven by the 256 gradation driving pulses to generate gradation heat energy. In addition, depending on the value of the image data,
The number of gradation driving pulses changes. A period from the heating of the gradation to the start of recording of the next pixel is a cooling period, and the heat generating element is naturally cooled.

(B) is a drive pulse for driving the heating element of the magenta thermal head 21, and (C) is a drive pulse for driving the heating element of the cyan thermal head 22. Both show the state of bias heating with standard bias data.

FIG. 5 shows bias drive pulses for preventing the occurrence of density unevenness. (A) shows a bias drive pulse for preventing the generation of black stripes.
In this case, for example, the corrected bias data of "225" is used, and the heating element is driven by 226 bias driving pulses. In this case, the thermal energy at the time of bias heating becomes smaller than the bias thermal energy, and the color density decreases, so that the generation of black stripes is prevented.

(B) is a bias drive pulse for preventing the generation of white stripes, and the heating element is driven by 256 bias drive pulses created from the corrected bias data of "255", for example. In this case, the thermal energy at the time of bias heating becomes larger than the bias thermal energy and the color density becomes high, so that it is possible to prevent the occurrence of white stripes.

FIG. 6 shows an example of the layer structure of the color thermosensitive recording paper. On the support 55, a cyan thermosensitive coloring layer 56, a magenta thermosensitive coloring layer 57, and a yellow thermosensitive coloring layer 5
8 and a protective layer 59 are sequentially layered. Each thermosensitive coloring layer 5
6 to 58 have a thermal sensitivity depending on the distance from the surface. Further, each of the thermosensitive coloring layers 56 to 58 is layered from the surface in the order of thermal recording. For example, in the case of thermal recording in the order of magenta, yellow and cyan, the yellow thermosensitive coloring layer 58 and the magenta thermosensitive layer The position of the coloring layer 57 is exchanged. To make it easier to understand each thermosensitive coloring layer,
“Y” for the yellow thermosensitive coloring layer 58, “M” for the magenta thermosensitive coloring layer 57, and cyan thermosensitive coloring layer 56.
Is attached with “C”.

Although not shown in the drawing, an intermediate layer for adjusting the thermal sensitivity of the magenta thermosensitive coloring layer 57 and the cyan thermosensitive coloring layer 56 is formed between the thermosensitive coloring layers 56 to 58. An opaque coated paper or a plastic film is used as the support 55, and a transparent plastic film is used when an OHP sheet is prepared.

The cyan thermosensitive coloring layer 56 contains an electron-donating dye precursor and an electron-accepting compound as main components, and develops cyan when heated. Magenta thermosensitive coloring layer 5
No. 7 contains a diazonium salt compound having a maximum absorption wavelength of about 365 nm, and a coupler which thermally reacts with this compound to develop magenta color. When the magenta thermosensitive coloring layer 57 is irradiated with ultraviolet rays in the vicinity of 365 nm after thermal recording, the diazonium salt compound is photodecomposed and the coloring ability is lost. The yellow thermosensitive coloring layer 58 has a maximum absorption wavelength of about 42.
It contains a diazonium salt compound having a thickness of 0 nm and a coupler which thermally reacts with the compound to develop a yellow color. When the yellow thermosensitive coloring layer 58 is irradiated with near ultraviolet rays of 420 nm, the yellow thermosensitive coloring layer 58 is optically fixed and loses the coloring ability.

In FIG. 7 showing the color forming characteristics of each thermosensitive coloring layer, the yellow thermosensitive coloring layer 58 has the highest thermal sensitivity and the cyan thermosensitive coloring layer 56 has the lowest thermal sensitivity. Yellow "Y"
When the dots of 1 are recorded in one pixel on the color thermal recording paper 16, the color thermal energy obtained by adding the gradation thermal energy GY _J to the bias thermal energy BY is applied to the color thermal recording paper 16. This bias heat energy B
Y is thermal energy immediately before the yellow thermosensitive coloring layer 58 develops color, and is applied to the color thermosensitive recording paper 16 during the bias heating period. Further, the magnitude of the bias heat energy is determined by the number of bias pulses represented by the bias data.

The gradation thermal energy is determined according to the image data, and is applied to the color thermosensitive recording paper 16 during the gradation heating period following the bias heating period. Since magenta M and cyan C are the same, only reference numerals are attached.

In FIG. 8 showing the recording state, the thermal head 20 for yellow has a heating element array 20a extending in the main scanning direction M. This heating element array 2
0a is a large number of heating elements 62a arranged in a line,
62b, 62c, ... Each heating element has, for example, a length L1 in the main scanning direction M of 140 μm and a length L2 in the sub scanning direction S of 100 μm.

The yellow thermal head 20 records a yellow image line by line. This one line is
It extends in the main scanning direction, and its length L3 in the sub scanning direction is, for example, 156 μm. This one line consists of a plurality of pixels 63, and each pixel 63 is recorded by a corresponding heating element.

The pulse motor 12 for conveying the color thermosensitive recording paper 16 is provided with 20 motor drive pulses of a constant cycle while recording one line. With these 20 motor drive pulses, 15 pulses are continuously generated in the sub-scanning direction.
Move 6 μm. At the start of the bias heating period, for example, the heating element 62a is in the position indicated by reference numeral 64. Then, when the motor is moved to the position indicated by reference numeral 65 by the ten motor drive pulses, the bias heating is almost completed. During this bias heating period, when the heating element 62a is driven with standard bias data, no color is generated.

The gradation heating is started after the bias heating, and seven motor drive pulses are applied during this period, and the motor moves from the position indicated by the reference numeral 65 to the position indicated by the reference numeral 66. The pixel 63 develops color during this gradation heating period, and its density is related to the number of gradation driving pulses. After the gradation heating period, there is a cooling period in which the heating element 62a is not energized,
Three motor drive pulses are applied to this. Although the heating element 62a moves in the sub-scanning direction, in order to make the drawing easy to understand, the positions 64-66 are
The drawing is shifted in the main scanning direction.

Next, the operation of the above embodiment will be described. Import the 3-color image data of the image to be printed,
Write to the image memory provided for each color. After capturing the image data, a print start switch (not shown) is operated. When this print start switch is operated, the system controller 30 turns on the yellow fixing device 23 and the magenta fixing device 26, and also operates the paper feeding mechanism (not shown) to feed the color thermosensitive recording paper 16. Do the paper. The system controller 30 also instructs the motor controller 36 to rotate the motor. The motor controller 36 sends a motor drive pulse having a constant cycle to the driver 37 to rotate the pulse motor 12 at a constant speed. The rotation of the pulse motor 12 is transmitted to the platen drum 10 via the belt 14.

The fed color thermosensitive recording paper 16 is guided by the guide roller 17 and rotates the platen drum 10.
Is wrapped around the outer circumference of. And the platen drum 10
By the rotation of, the sheet is conveyed toward the guide roller 18 on the sheet discharge side. During this conveyance, the tip of the color thermosensitive recording paper 16 is detected by the sensor 19. The count operation of the counter 38 is started by the detection signal of the sensor 19, the number of motor drive pulses is counted, and the color thermal recording paper 1
The transport position of 6 is measured.

The system controller 30 uses the counter 3
8 is checked, and when it is detected that the tip of the color thermosensitive recording paper 16 has reached a predetermined position where the thermal head 20 for yellow has passed, the thermal head 20 for yellow is brought down and the print controller 42 for yellow is used. Instruct. The yellow print controller 42 operates the up-down mechanism 52 to swing the yellow thermal head 20 to generate the heating element array 20a.
Is pressed against the color thermosensitive recording paper 16.

After the yellow thermal head 20 is pressed, the yellow print controller 42 reads the yellow image data of the first line from the yellow image memory 45 for each pixel, and the read image data is read by the image line memory 46.
Write in. Further, the standard bias data having a value of “240” is read from the memory 43 and repeatedly transferred to the bias line memory 44, so that the standard bias data for one line is written in the bias line memory 44. Although the yellow thermal head is not energized and is in pressure contact with the color thermal recording paper 16 from the time when the yellow thermal head is down until the recording of the yellow image is started, the yellow thermal head is turned on during this period. Bias heating may be performed using bias data. By doing so, it is possible to eliminate fluctuations in the carrying load of the color thermosensitive recording paper 16 at the start of recording a yellow image.

In the memory of the system controller 30,
The distance between the front end of the color thermosensitive recording paper 16 and the front end of the recording area is input by a keyboard or written at the time of manufacturing the device. When the system controller 30 determines from the count value of the counter 38 that the leading end of the recording area has reached the heating element array 20a of the yellow thermal head 20, it instructs the yellow print controller 42 to start recording a yellow image. To do.

The yellow print controller 42
After the selector 47 is connected to the bias line memory 46, the reading of the bias line memory 46 is started. From this bias line memory 46, the numerical value is "2.
Bias data for one line of "40" is sequentially read one by one and sent to the comparator 48. On the other hand, the yellow print controller 42 resets the counter of the comparison data generation circuit 49. The comparison data generation circuit 49 compares the comparison data of “0” with the comparator 48.
Send to.

The comparator 48 compares the input bias data with the comparison data of "0" and outputs the bias drive data of "1" when the former is larger than the latter. Since the comparator 42 compares the standard bias data for one line with the comparison data of “0”, it outputs the bias drive data for one line in which all are “1” serially.

The serial bias drive data is sent to the drive circuit 50 and converted into parallel bias drive data by the shift register. Next, the bias drive data for one line and the bias heating strobe signal from the strobe signal generation circuit 51 are sent to the AND gate array to obtain the logical product. Since all the bias drive data are "1", the bias drive pulse for one line having the same pulse width as the width of the bias heating strobe signal is output. This bias drive pulse is labeled with “0” in FIG. The heating element array 20a is driven by a bias driving pulse for one line.
.. are simultaneously driven to generate heat.

When the heat generation by the 0th bias drive pulse is completed, the yellow print controller 42
The counter of the comparison data generation circuit 49 is incremented to generate the comparison data of "1". Next, the yellow print controller 42 starts the second reading from the bias line memory 44. The bias line memory 44 serially reads the standard bias data for one line again and sends it to the comparator 48. According to the procedure described above, the first bias drive pulse with "1" in FIG. 4A is created for one line, and the heating elements 62a and 62b of the heating element array 20a are generated.
... are driven simultaneously.

In the same manner, according to the comparison data of "2" to "255", the maximum is 25 during the bias heating period.
Six bias drive pulses can be created. But,
Since the standard bias data is "240", each of the heating elements 62a, 62b ... Generates heat 241 times by the 0th to 240th bias drive pulses. Therefore, when the comparison data is "240" to "255", the bias drive pulse is not generated.

As described above, each of the heating elements 62a, 62b, ... Of the heating element array 20a has two elements within the bias heating period.
By performing the heat generation 41 times, each heat generating element generates the bias heat energy BY immediately before the yellow thermosensitive coloring layer 35 develops color.

When the bias heating is completed, the gradation heating is started. First, the yellow print controller 42
Resets the counter of the comparison data generation circuit 49 to "0" and switches the selector 47 to connect the image line memory 46 to the comparator 48. Next, the yellow print controller 42 sequentially reads the yellow image data of the first line written in the image line memory 44 one by one and sends the yellow image data to the comparator 48.

The comparator 48 first sequentially compares the comparison data of "0" with each yellow image data which is serially input. When the yellow image data is larger than the comparison data, the comparator 42 outputs the gradation drive data of "1", and when it is small, it outputs the gradation drive data of "0". The comparator 48 serially generates gradation drive data for one line and sends them to the drive circuit 50.

In the drive circuit 50, the gradation drive data for one line is converted in parallel and then converted into gradation drive pulses using the strobe signal for gradation. Here, when the gradation drive data is "0", the gradation drive pulse is not generated. The heating elements 62a, 62b, ... Of the heating element array 20a are selectively driven by this one-line gradation driving pulse to generate heat. The first gradation drive pulse is labeled with “0” in FIG. 4 (A).

Similarly, the respective heating elements are selectively driven by using the comparison data from "1" to "255". As a result, each heating element is driven a number of times corresponding to the yellow image data within the range of 0 to 256 times to generate gradation thermal energy. Therefore, when recording the pixel with the highest density, the heating element is driven by the 0th to 255th gradation driving pulses. When recording the pixel of the lowest density, the gradation driving pulse is not given, and in this case, the gradation heating period becomes zero.

Each heating element generates coloring heat energy consisting of constant bias heat energy BY and gradation heat energy GY _J according to yellow image data. As a result, the yellow thermosensitive coloring layer 58 develops a color at a density corresponding to the yellow image data based on the characteristic curve of FIG. 7, so that yellow dots are formed in the rectangular pixels.

When the gradation heating is finished, each heating element is naturally cooled in a cooling period as shown in FIG. 4 (A). This cooling period becomes longer as the number of gradation driving pulses becomes smaller. It should be noted that the minimum value of the cooling period is as follows after supplying 256 gradation driving pulses to the heating element to generate heat.
It is determined from the time required for the heating element to drop to a predetermined temperature at room temperature.

After all the heating elements have entered the cooling period,
The yellow print controller 42 reads the yellow image data of the second line from the yellow image memory 45 and writes it in the image line memory 46. Also,
The selector 47 is switched to the bias line memory 44 side. In the bias line memory 44, the bias data is not written until the specific line,
The standard bias data already written is used.

At the end of the cooling period, the system controller 30 sends a 1-line print start signal to the yellow print controller 42 to start recording the second line. Also in the recording of the second line, first, the standard bias data is read from the bias line memory 44 to heat the bias, and then the gradation heating is performed using the second line of the yellow image data read from the image line memory 46. Hereinafter, in the same manner, the third and subsequent lines of the yellow image are sequentially recorded on the color thermosensitive recording paper 16 which is continuously moving.

When the portion on which the yellow image is recorded reaches the yellow fixing device 23 by the rotation of the platen drum 10, near-ultraviolet rays having an emission peak of 420 nm are irradiated, the yellow thermosensitive coloring layer 58 is fixed, and the coloring ability is improved. Will be lost.

The system controller 30 uses the counter 3
When it is detected from the count value of 8 that the color thermosensitive recording paper 16 has reached the magenta thermal head 21, the magenta recording unit 33 is instructed to turn down the magenta thermal head 21. The magenta recording unit 33 swings the magenta thermal head 21 and presses it against the color thermosensitive recording paper 16. After that, when it is detected that the leading end of the recording area has reached the magenta thermal head 21, the system controller 30 instructs the magenta recording unit 33 to print.

When recording the first line of the magenta image, each heating element of the thermal head 21 uses the standard bias data, as shown in FIG.
It is driven by the fifth bias driving pulse and generates bias heat energy BM. Here, the magenta thermosensitive coloring layer 5
Since the bias thermal energy BM of 7 is large, a strobe signal having a pulse width longer than that of recording a yellow image is used, and thereby a bias drive pulse having a wide pulse width is created.

Next, each heating element is driven by the number of gradation driving pulses corresponding to the magenta image data, and the magenta thermosensitive coloring layer 57 is heated to develop a color. As a result, the first line of the magenta image is recorded so as to overlap the first line of the yellow image. After the end of the cooling period, the second magenta image is recorded by the same procedure as the recording of the yellow image described above.
Line recording starts. Thus, bias heating,
By repeating gradation heating and cooling, magenta thermosensitive coloring layer 5
7 is heated and colored, and the third and subsequent lines of the magenta image are sequentially recorded.

When the portion on which the magenta image is recorded reaches the magenta fixing device 26, the magenta thermosensitive coloring layer 57 is fixed and the coloring ability is lost by irradiation with ultraviolet rays having an emission peak of 365 nm.

When the tip of the color thermosensitive recording paper 16 reaches the cyan thermal head 22, the system controller 30 instructs the thermal head 22 to go down and press it against the color thermosensitive recording paper 16. Thereafter, when it is detected that the leading end of the recording area has reached the cyan thermal head 22, the system controller 30 causes the cyan recording unit 34 to
Instruct to print.

As shown in FIG. 4C, the cyan recording section 34 drives each heating element with a fixed number of bias driving pulses and a number of gradation driving pulses according to the cyan image data to generate a cyan thermal image. The coloring layer 56 is heated and colored. As a result, the first line of the cyan image is recorded so as to overlap the first lines of the yellow image and the magenta image.
Similarly, the second color of the cyan image is printed on the color thermosensitive recording paper 16.
Sequentially record after the line.

The color thermosensitive recording paper 16 on which a full-color image is recorded by the three thermal heads 20 to 22 is
It is discharged onto a tray or the like via the guide roller 18.

During recording on the color thermosensitive recording paper 16, the three thermal heads 20 to 22 are moved up or down at predetermined positions with respect to the color thermosensitive recording paper 16, and the energization is started or stopped. Be seen. For example, during recording of the yellow thermal head 20, the magenta thermal head 21 is brought down (press contact), and then energization is started. On the contrary, during recording by the magenta thermal head 21, the energization of the yellow thermal head 20 is stopped,
After that, it is up (evacuated). Due to the behavior of these thermal heads, the transport load of the color thermosensitive recording paper fluctuates, which causes streaky density unevenness.

FIG. 9 shows variations in the carry amount due to the behavior of the yellow thermal head and the magenta thermal head. When the yellow thermal head 20 is up, a small carrying load acts on the carrying system. The color thermal recording paper 16 has a constant transport speed V
Be transported in.

If the yellow thermal head 20 goes down while the color thermosensitive recording paper 16 is being conveyed, the thermal head 20 comes into pressure contact with the color thermosensitive recording paper 16 and the conveyance load increases due to the frictional resistance between them. Due to this increase in the transportation load, distortion of the transportation system increases. The transport speed gradually decreases as the amount of distortion increases. Then, when the increase amount of the conveyance load and the distortion amount are balanced, the conveyance speed V is restored.

When energization of the yellow thermal head 20 is started, heat is generated and the temperature rises. Since the frictional resistance between the yellow thermal head 20 and the color thermal recording paper 16 is almost inversely proportional to the temperature, the heat generated by the yellow thermal head 20 reduces the carrying load. As a result, the strain amount of the transport system decreases, and the transport speed increases accordingly. When the transport load of the yellow thermal head 20 in the energized state and the strain amount of the transport system are balanced, the transport speed V is restored. Under this transport speed V, a yellow image is recorded line by line.

During the recording of the yellow image, the magenta thermal head 21 goes down and comes into pressure contact with the color thermosensitive recording paper 16. Since the transport system is distorted according to the variation of the transport load, the transport speed is temporarily reduced, and then returns to the constant transport speed V. When the transport speed of the color thermosensitive recording paper 16 is temporarily reduced, the line being recorded by the yellow thermal head 20 is narrowed and the thermal energy is increased, so that the yellow density is increased.

After that, when the magenta thermal head 21 is energized, the carrying load is reduced, so that the carrying speed of the color thermosensitive recording paper 16 is temporarily increased. As a result, the width of the line being recorded by the thermal head 20 for yellow becomes wider and the thermal energy becomes smaller, so that the yellow density becomes lower.

While the yellow thermal head 20 and the magenta thermal head 21 are recording the yellow image and the magenta image one line at a time, the recording of the yellow image is completed. When the recording of the yellow image is completed, the energization of the thermal head 20 for yellow is stopped, so that the carrying load is increased and the carrying speed is temporarily reduced. In this case, the line being recorded by the magenta thermal head 21 has a narrow width and a high magenta density.

After the yellow thermal head 20 is de-energized, the yellow thermal head 20 separates from the color thermosensitive recording paper 16, so that the conveying speed of the color thermosensitive recording paper 16 increases. For this reason, the line being recorded by the magenta thermal head 21 has a wide width and a low magenta density.

As described above, black streaks are generated when the thermal head is down and power supply is stopped, and white streaks are generated when the thermal head is up and power supply is started. Since the up / down operation of each thermal head and the start or stop of energization are performed according to the line position, the line in which white stripes and black stripes are generated is determined by the color. Therefore, each print controller stores the relationship between the line in which density unevenness occurs (this is called a correction line) and the correction bias data used for this line. This correction line is 1
Not only the book but also a plurality of continuous books.

For the correction line in which black streaks occur,
For example, the correction bias data of "225" is used, and "255" is used for the correction line in which white lines are generated.
The modified bias data of is used. FIG. 5 shows a bias drive pulse created from each corrected bias data.

As shown in FIG. 1, since the print controller of each of the recording units 32 to 34 counts the 1-line print start signal, the line to be recorded next can be determined. When the next line is a normal line, the standard bias data is read from the memory and written in the bias line memory. If the previous line is also a normal line, this writing is omitted. If it is a correction line, the correction bias data corresponding to the types of black stripes and white stripes is read from the memory and written in the bias line memory.

When the standard bias data is used, the bias heat energy immediately before the color development of the thermosensitive coloring layer is given within the bias heating period. When the corrected bias data is used, the thermal energy larger or smaller than the bias thermal energy is set within the bias heating period so that the desired color density corresponding to the image data can be obtained in consideration of the fluctuation of the transport speed. It is provided on the thermosensitive recording paper 16.

FIG. 10 shows an embodiment in which bias heating is performed by one bias driving pulse. In this case, the pulse width of the strobe signal is adjusted according to the bias heat energy, the presence / absence of density unevenness, and the type.

FIG. 11 shows a linear movement type color thermal printer. Three platen rollers 70-72
Are arranged at appropriate intervals. Instead of these platen rollers 70 to 72, a fixedly arranged plate template may be used. A yellow thermal head 73, a magenta thermal head 74, and a cyan thermal head 75 are arranged to face each platen roller 70 to 72, respectively. Each of the thermal heads 73 to 75 moves up and down by an up / down mechanism (not shown).

A plurality of pairs of conveying rollers 77 to 80 are arranged along the linear conveying path, and are rotated together with the platen rollers 70 to 72 by the pulse motor. A yellow fixing device 81 is arranged immediately before the magenta thermal head 74, and a magenta fixing device 82 is arranged immediately before the cyan thermal head 75. A sensor 84 for detecting the front end of the color thermosensitive recording paper 83 is arranged on the upstream side of the yellow thermal head 73.

When the color thermosensitive recording paper 83 is conveyed to the downstream side, the yellow thermal head 73 descends and presses the color thermosensitive recording paper 83, and then a yellow image is recorded line by line. When the portion on which the yellow image is recorded reaches the yellow fixing device 81, near-ultraviolet rays in the wavelength range of 420 nm are irradiated to fix the yellow image.

Next, after the magenta thermal head 74 descends, energization is started and a magenta image is recorded line by line. After recording the magenta image, the magenta fixing device 82 irradiates near-ultraviolet rays in the wavelength range of 420 nm to fix the magenta image. Then, the cyan thermal head 75 records a cyan image line by line.

The conveying path for the color thermosensitive recording paper 83 may be formed in a mountain or valley shape by shifting the position of the platen roller 71 up and down. Further, the platen roller 72 may be arranged below the platen roller 70 to form a U-shaped conveyance path.

As the color thermosensitive recording paper, in addition to printing one by one using a cut sheet, the same image is continuously printed a plurality of times by using a roll sheet, or a plurality of different images are continuously printed. It may be printed and finally cut by a cutter one by one. In addition, a black coloring layer is formed on a color thermosensitive recording paper to have a four-layer structure,
Furthermore, a thermosensitive coloring layer that develops a special color such as a skin color may be added to form a five-layer structure.

Although the bias heat energy is corrected to correct the uneven density, the heat energy for gradation heating may be corrected or both of them may be corrected. Also, during printing of an image, since the thermal energy is different for each line, the frictional resistance is different for each line. Therefore, the carrying load changes line by line, and the density of each line is slightly different from the expected value. Therefore, immediately before the recording of each line, the image data of the lines of each color that are simultaneously recorded may be examined, and the thermal energy generated by each thermal head may be corrected according to the total thermal energy or the average value thereof.

[0094]

As described above in detail, in the present invention, the heat energy is corrected for the line where the streak-like density unevenness due to the behavior of the thermal head is generated. Can be prevented. Further, since the thermal energy for bias heating is corrected, it is not necessary to perform a special calculation process on the image data, and the thermal energy can be easily corrected.

[Brief description of drawings]

FIG. 1 is a flow chart showing the method of the present invention.

FIG. 2 is a schematic diagram showing a drum-type color thermal printer for carrying out the present invention.

FIG. 3 is a block diagram showing an electrical configuration of a color thermal printer.

FIG. 4 is a waveform diagram of drive pulses when recording a line in which density unevenness does not occur.

FIG. 5 is a waveform diagram of drive pulses when recording a line in which density unevenness occurs.

FIG. 6 is a diagram showing an example of a layer structure of color thermosensitive recording paper.

FIG. 7 is a characteristic curve diagram showing color forming characteristics of color thermosensitive recording paper.

FIG. 8 is an explanatory diagram showing a recording state of color thermosensitive recording paper.

FIG. 9 is a graph showing a change in the transfer speed due to a change in the transfer load.

FIG. 10 is a waveform diagram when performing bias heating with one bias driving pulse.

FIG. 11 is a schematic view showing a linear transport type color thermal printer.

FIG. 12 is an explanatory diagram showing a color thermal recording paper printed by a conventional color thermal printing method.

[Explanation of symbols]

10 Platen drum 16 color thermal recording paper 20 Yellow thermal head 21 Thermal head for magenta 22 Cyan thermal head 23 Yellow fixing device 26 Magenta fuser 56 Cyan thermosensitive coloring layer 57 Magenta thermosensitive coloring layer 58 Yellow thermosensitive coloring layer 62a, 62b, 62c Heating element 63 pixels 70-72 Platen roller 73 Thermal head for yellow 74 Thermal head for magenta 75 Cyan thermal head 83 color thermal recording paper

Continuation of front page (58) Fields surveyed (Int.Cl. ⁷ , DB name) B41J 2/325 B41J 2/36

Claims (3)

(57) [Claims] 1. A color thermosensitive recording paper comprising at least three types of thermosensitive coloring layers, a yellow thermosensitive coloring layer, a magenta thermosensitive coloring layer, and a cyan thermosensitive coloring layer, which are laminated along a passage area of the color thermosensitive recording paper. At least three thermal heads, first to third, for recording the thermosensitive coloring layer of each line one by one are arranged in order from the upstream side, and when the color thermosensitive recording paper moves from the upstream side to the downstream side, it is on the upstream side. The first thermal head is pressed against the color thermosensitive recording paper in order, and then energization is started to record in order from the upper thermosensitive coloring layer having high heat sensitivity, and a full-color image is formed on the color thermosensitive recording paper by one movement. Immediately after recording by the first thermal head and immediately after recording by the second thermal head, the electromagnetic radiation peculiar to the thermosensitive coloring layer recorded by each thermal head is recorded by color thermosensitive recording. In a color thermal printing method of irradiating and fixing a recording paper, during recording of at least one thermal head, another thermal head is pressed against the color thermal recording paper or separated from the color thermal recording paper to form a streak density. For a line where unevenness occurs, a color thermal printing method is characterized in that the thermal energy generated by the thermal head is corrected so as to correct this uneven density. 2. A color thermosensitive recording paper having at least three kinds of thermosensitive coloring layers of a yellow thermosensitive coloring layer, a magenta thermosensitive coloring layer, and a cyan thermosensitive coloring layer is laminated, and is specified along a passage area of the color thermosensitive recording paper. At least three thermal heads, first to third, for recording the thermosensitive coloring layer of each line one by one are arranged in order from the upstream side, and when the color thermosensitive recording paper moves from the upstream side to the downstream side, it is on the upstream side. The first thermal head is pressed against the color thermosensitive recording paper in order, and then energization is started to record in order from the upper thermosensitive coloring layer having high heat sensitivity, and a full-color image is formed on the color thermosensitive recording paper by one movement. Immediately after recording by the first thermal head and immediately after recording by the second thermal head, the electromagnetic radiation peculiar to the thermosensitive coloring layer recorded by each thermal head is recorded by color thermosensitive recording. In the color thermal printing method of irradiating and fixing the recording paper, during the recording of at least one thermal head, for lines in which streaky density unevenness occurs due to start or stop of energization of other thermal heads, A color thermal printing method, characterized in that the thermal energy generated by the thermal head is corrected so as to correct this density unevenness. 3. The thermal head, when recording one line composed of a plurality of pixels on a specific thermosensitive coloring layer, has bias thermal energy for heating each pixel to immediately before coloring and coloring density of each pixel. 3. The color thermal print according to claim 1, wherein the bias thermal energy is corrected according to the density unevenness in a line in which density unevenness occurs in accordance with the gradation thermal energy. Method.