JPH11291525A - Thermal printing method and device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To make a surface of a recording paper smooth to improve gloss of the recording paper. SOLUTION: While a color thermal recording paper 10 as a recording paper is conveyed to a sub-scanning direction, an image is colored and recorded by driving a heating element 25. The heating element 25 is driven by an auxiliary driving pulse such that heating energy which does not color the color thermal recording paper is generated in the middle of a cooling time period after the heating element 25 is driven for recording a pixel of the image. A portion of a projection section 71 of a protection layer 15 is softened to be smoothed by virtue of the driving of the heating element 25 by the auxiliary driving pulse.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a thermal printing method and apparatus for recording an image on recording paper by causing a heating element of a thermal head to generate heat.

[0002]

2. Description of the Related Art A thermal printer employs a thermal recording system in which recording paper is heated by a thermal head to directly develop a color.
There is a thermal transfer recording system in which the back of an ink ribbon is heated by a thermal head to transfer ink on the ink ribbon to recording paper.

For example, in a thermal printer of a thermal recording system, a thermal recording paper in which a thermosensitive coloring layer and a transparent resin protective layer are provided on a support is used as a recording paper. At the time of recording an image, the thermal head and the thermal recording paper are relatively moved, and during this movement, the thermal recording paper is pressed and heated by the thermal head to color the thermal coloring layer, thereby performing color recording.

[0004] A thermal element array having a cylindrical shape is formed on the thermal head, and a plurality of heat elements are arranged in a line on the thermal element array. One heating element is driven by a driving pulse to generate heat, thereby heating the thermosensitive recording paper to form dots by virtually forming pixels partitioned into squares on the thermosensitive recording paper. Since each heating element becomes hot when it generates heat, the portion of the protective layer with which the heating element is in contact melts and softens, and then is cooled, so that the surface of the thermosensitive recording paper has irregularities corresponding to the shape of the heating element. Is formed. The irregularities become regular in accordance with the cycle of heat generation and cooling of the heating element, which causes a decrease in sharpness of a recorded image and a decrease in glossiness of a thermosensitive recording paper. Such a problem also occurs in a thermal transfer recording method in which the ink of the ink ribbon is transferred to an image receiving paper (recording paper).

In order to eliminate such irregularities, a smoothing device having a heat roller is conventionally used, and a smooth sheet is stacked on a printed color thermosensitive recording paper and passed through a pair of heat rollers. Pressing and heating of color thermosensitive recording paper have been performed. In addition, the heat roller is built into the printer, and after the printing process,
There is also proposed a device in which heat and pressure are applied by a heat roller (Japanese Patent Application Laid-Open No. 6-218968).

[0006]

In the case where the smoothing process is performed by the above-described method, a smoothing device must be prepared in addition to the thermal printer, or the printer must be heated. There is a problem that the roller must be built in and the cost increases. In addition, a smoothing process must be performed after the printing process, so that an extra time is required for the smoothing process in addition to the time for the printing process, and the actual printing time becomes longer. There is also.

On the other hand, if the recording density of dots recorded by the thermal head is increased, it is possible to reduce the unevenness and improve the glossiness.
It is necessary to further reduce the size of the heating element, and to finely control the driving of the heating element and the conveyance amount of the recording paper, so that the printer becomes expensive. Further, since the amount of data for recording an image is greatly increased, there arise problems that the recording speed is reduced and a large capacity memory is required.

SUMMARY OF THE INVENTION An object of the present invention is to provide a thermal printing method and apparatus capable of improving glossiness without substantially increasing the printing time and without increasing the recording density.

[0009]

According to a first aspect of the present invention, there is provided a thermal printing method for cooling a heating element after a heating period in which the heating element is driven by a recording drive pulse. During the period, an auxiliary driving pulse is generated for each heating element, and the heating element is driven by this auxiliary driving pulse, thereby giving heat energy of a size that does not form dots on the recording paper, thereby giving a heat energy to the surface of the recording paper. The smoothing process is performed.

In the thermal printing method according to the second aspect, the auxiliary drive pulse is generated for each heating element in the middle of the cooling period. Further, in the thermal printing method according to the third aspect, the auxiliary drive pulse is generated at a frequency that is an integral multiple of one energizing sequence from the start of the heating period to the end of the cooling period, and the auxiliary drive pulse is used for recording driving. The thermal printing method according to claim 4, wherein the heating element is driven during the cooling period by the auxiliary driving pulse by superimposing the heating element on the pulse. The frequency is different for each color. Further, claim 5
In the thermal printing method described above, the length of the heating element in the sub-scanning direction is longer than the length of the dot in the sub-scanning direction.

In the thermal printing apparatus according to the present invention, each heating element is heated during a cooling period for cooling the heating element after the heating period in which the heating element is driven by the recording drive pulse. An auxiliary driving pulse generating means for generating an auxiliary driving pulse based on the data; and a driving pulse synthesizing means for outputting a driving pulse obtained by superimposing the auxiliary driving pulse on the corresponding recording driving pulse. By driving the heating elements with the drive pulse, heat energy of such a size that dots are not formed on the recording paper in the middle of the cooling period is applied from the respective heating elements to the recording paper to smooth the surface of the recording paper. It is like that.

[0012]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 2 shows an example of a layer structure of a color thermal recording paper used as a recording paper of a color thermal printer embodying the present invention.
Are formed on a support 11 by a cyan thermosensitive coloring layer 12 and 365 n
magenta thermosensitive coloring layer 13 having photo-fixing property to ultraviolet rays of m
And a yellow thermosensitive coloring layer 14 having a light fixing property to ultraviolet light of 420 nm, and a transparent protective layer 15 are sequentially provided.

As the support 11, opaque coated paper or plastic film is used. When an OHP sheet is formed, a transparent plastic film is used. The thermosensitive coloring layers 12 to 14 are provided in the order of recording. For example, when thermal recording is performed in the order of magenta, yellow, and cyan, the yellow thermosensitive coloring layer 14 and the magenta thermosensitive coloring layer 13 are used. Is replaced. The protective layer 15 is made of a plastic resin, and is softened by being heated by a thermal head during printing.

FIG. 3 shows the coloring characteristics of the thermosensitive coloring layers 12 to 14. Each of the thermosensitive coloring layers 12 to 14 needs a large coloring heat energy to develop a color as it goes deeper. In the color thermosensitive recording paper 10, the coloring heat energy of the yellow coloring layer 14 is the lowest, and the cyan coloring layer 14 is the lowest. Twelve have the highest coloring heat energy. In the case of recording a yellow pixel, color thermal energy obtained by adding gradation thermal energy Egy to bias thermal energy Eby for yellow is applied to the color thermosensitive recording paper 10. The bias thermal energy Eby is thermal energy immediately before the yellow thermosensitive coloring layer 14 develops a color, and the grayscale thermal energy Egy is determined according to the color density of the pixel to be recorded, that is, the grayscale level of yellow. Since the same applies to magenta and cyan, symbols Ebm, Ebm
gm, Ebc and Egc are attached.

In FIG. 4, which schematically shows a color thermosensitive printer, a rotatable platen roller 20 is disposed on a transport path of the color thermosensitive recording paper 10, and a thermal head 21 is opposed to the platen roller 20. Is arranged. The color thermosensitive recording paper 10 is sent out from a paper feed cassette (not shown) on the upstream side (left side in the figure) of the conveyance path, and is sent toward the platen roller 20. On the transport path,
The color thermosensitive recording paper 10 is transported by a transport mechanism 2 driven by a pulse motor 23 driven by a motor driver 22.
The recording paper 4 is reciprocated by the recording paper 4, and is discharged from a paper discharge port (not shown) provided on the downstream side (right side in the figure) after the recording of the color image. Instead of transporting the color thermosensitive recording paper 10, the thermal head 21 may be moved.

A plurality of heating elements 25 (see FIG. 5) are linearly arranged below the thermal head 21 in the main scanning direction (the width direction of the color thermosensitive recording paper 10 and the direction perpendicular to the conveying direction). Heating element array 2
6 are formed. The thermal head 21 has a shaft 2
1a, the heating element array 26 is attached to the color thermosensitive recording paper 10 on the platen roller 20 to record an image.
Swings between a pressure contact position where the heat-generating element array 26 is separated from the color thermosensitive recording paper 10 and a retreat position where the heating element array 26 is separated from the color thermosensitive recording paper 10. The thermal head 21 is driven by a thermal head driving unit 27 and applies a bias heating and a gradation heating to the color thermosensitive recording paper 10 being transported from the upstream to the downstream of the transport path, that is, in the sub-scanning direction. To record one color image line by line. Then, by reciprocating the color thermosensitive recording paper 10 three times, a color image is color-recorded sequentially in three color planes.

Downstream of the thermal head 21, a yellow optical fixing device 28 and a magenta optical fixing device 29 are arranged. The light fixing unit 28 for yellow has an emission peak of 420
UV lamp 28a that emits UV light for yellow
And a reflector 28b. Magenta optical fuser 2
Reference numeral 9 includes an ultraviolet lamp 29a that emits magenta ultraviolet light having an emission peak of 365 nm and a reflector 29b.

The system controller 30 controls each part of the color thermal printer. The operation unit 31 can instruct an image capture or print by operating this, and sends a signal according to the operation to the system controller 30. During printing, the motor driver 22 supplies a motor drive pulse having a constant period to the pulse motor 23 based on a system clock generated by the system controller 30. Thereby, the pulse motor 23
Is rotated at a constant speed, and the color thermosensitive recording paper 10 is transported at a constant speed via the transport mechanism 24.

In this example, the color thermosensitive recording paper 10 is transported in the sub-scanning direction by a length of one line by four motor drive pulses, and one energizing sequence is performed during this time. One energizing sequence is from the start of heating by the heating element 25 to the end of the cooling period of the heating element 25 after this heating. In this example, one line is recorded in one energizing sequence.

An image to be recorded is subjected to three-color separation and photometry by a scanner or the like, converted into yellow, magenta, and cyan image data, and sent to an image memory 33 via a memory controller 32. The image memory 33 is composed of an image memory 33a for yellow (Y), an image memory 33b for magenta (M), and an image memory 33c for cyan (C). Is controlled. Yellow image data, magenta image data, and cyan image data of the corresponding color are written in the image memories 33a to 33c, respectively.

The image data of each color is, for example, 8 bits. When the gradation level is "0", the image data is "0". When the gradation level is "255", the image data is "0". 255 ". Memory controller 32
When printing, the image memories 33a to 33c for each color
, And sequentially reads out the image data of the three colors one line at a time and sends it to the print controller 34. In this example, the image data is the heat generation data. However, when the bias driving pulse for bias heating and the gradation driving pulse for gradation heating are created using the bias data and the image data, The bias data and the image data become heat generation data.

The print controller 34 performs image processing such as masking processing and γ correction using the image data of three colors, and sends processed image data of the color to be recorded to the thermal head driving section 27. The red image data, the green image data, and the blue image data are fetched into the image memory 33, and a complementary color conversion is performed by the print controller 34 at the time of printing, so that yellow image data, magenta image data,
You may create cyan image data.

The print controller 34 has a first
And second timing signal generation circuits 34a and 34b. The first timing signal generation circuit 34a includes:
A first count-up signal, a first shift clock, a first latch signal, and a strobe signal for generating a recording energizing pulse for image recording are generated. Further, the second timing signal generating circuit 34a generates a second count-up signal, a second shift clock, and a second latch signal for generating an auxiliary driving pulse for smoothing processing. Each of these signals is generated at a predetermined timing based on the system clock, and is sent to the thermal head driving unit 27.

A sensor 37 for detecting the leading end of the color thermosensitive recording paper 10 is provided in the vicinity of the thermal head 21. Based on the detection result of the sensor 37 and the number of motor drive pulses, a color sensor is provided. The transport position of the thermal recording paper 10 is specified.

FIG. 5 shows the structure of the thermal head driving section 27. The thermal head driving unit 27 is roughly divided into a line memory 40, a recording energizing unit 50 for generating a recording driving pulse for recording an image, and an auxiliary driving pulse for smoothing the surface of the color thermosensitive recording paper 10. And a drive pulse for superimposing (synthesizing) the auxiliary drive pulse on the recording drive pulse N
It comprises an OR gate array 41 and a switching array 42 for energizing each heating element 25 of the heating element array 26 only while a drive pulse is being generated.

Image data from the print controller 34 for one line is written in the line memory 40.
At the time of printing, one line of image data is sequentially read from the line memory 40 and the recording energizing unit 5 is read.
0 and the auxiliary power supply unit 60.
The reading of this image data is performed 256 times for one line.
However, only the first reading is sent to the auxiliary energizing unit 60.

The recording power supply unit 50 includes a first counter 51, a first comparator 52, and a first shift register 5.
3, a first latch array 54, and an AND gate array 55. The first counter 51 counts up the count value by “1” in response to the input of the first count-up signal, and outputs the count value as gradation comparison data. The first counter 51 sequentially generates gradation comparison data of “0” to “255” according to the gradation number 256 (gradation levels “0” to “255”).

The first comparator 52 includes a first counter 5
The gradation comparison data from No. 1 and the image data from the line memory 40 are compared to generate recording drive data. The first comparator 52 sequentially compares one line of image data for each gradation comparison data one by one, and creates one line of recording drive data. In each comparison, the first comparator 52 creates the recording drive data “1” when the image data is larger than or equal to the gradation comparison data, and creates the recording drive data “0” when the image data is smaller than the gradation comparison data. I do.

Therefore, in the recording of one line, "0"
Each image data for one line is compared 256 times using the gradation comparison data of “255” to “255”, and one image data is eventually converted into 256-bit recording drive data. The first comparator 52 serially outputs the recording drive data for one line and sends it to the first shift register 53.

The first shift register 53 takes in serial recording drive data for one line while sequentially shifting it by a first shift clock, converts the data into parallel recording drive data, and outputs it to the first latch array 54. . The parallel recording drive data from the first shift register 53 is latched by the first latch array 54 in response to the input of the first latch signal, and is output to the AND gate array 55. The AND gate array 55 is composed of a plurality of AND circuits, each of which receives a strobe signal and recording drive data, and outputs a result obtained by calculating a logical product of them as a recording drive pulse.

When printing one line, 256 first latch signals are output from the first timing signal generating circuit 34a. The interval at which the first latch signal is generated is determined from the coloring characteristics of the color thermosensitive recording paper 10. For example, when printing a yellow image, the first and second first
The interval between the latch signals is a conduction time required for the heating element 25 to generate the bias heat energy Eby of the yellow thermosensitive coloring layer 14. The interval between the second and third first latch signals is an energizing time required to cause the heating element 25 to continuously generate heat after the bias heating and to cause the yellow thermosensitive coloring layer 14 to develop the gray level "1". I have. Further, the generation interval of the first latch signal differs for each color to be recorded.

The strobe signal is kept at the "H level" only from the start of the bias heating to the end of the gradation heating for coloring at the gradation level "255" (hereinafter referred to as the maximum heating time). Since the maximum heating time varies depending on the color to be recorded, the strobe signal is set to the “H level” according to the color to be recorded, that is,
The pulse width of the strobe pulse is different.

Thus, the recording drive pulse ("H level") is continuously output only when the strobe pulse is input and the recording drive data from the first latch array 54 is "1". . First latch array 5
The recording drive data of No. 4 is sequentially updated at the generation timing of the first latch signal. As a result, a recording drive pulse having a pulse width corresponding to the image data is output.

The auxiliary energizing unit 60 includes an arithmetic circuit 61,
Line memory 62, second counter 63, second comparator 64, second shift register 65, second latch array 6
6. The arithmetic circuit 61 receives a color signal indicating a color to be recorded from the system controller 61 and image data from the line memory 40. The arithmetic circuit 61 performs arithmetic processing on each of the image data input from the line memory 40, creates one line of auxiliary energization timing data indicating the timing of generating an auxiliary drive pulse, and writes the data into the line memory 62. In this arithmetic processing, an intermediate timing of the cooling period of the corresponding heating element 25 is obtained from the input image data. This timing is represented by the number of second latch signals from the start of the energization sequence.

The generation cycle of the second latch signal is Ta, and the time from the start of bias heating of the heating element 25 to the end of gradation heating when the image data is the value D, that is, the time of the heating period is F.
(D), when the time of one energizing sequence is Ts,
The value P (D) of the auxiliary energization timing data can be obtained as in the following equation. P (D) = (Ts + F (D)) / (2 · Ta)

Since the energization time F (D) differs depending on the color to be recorded even when the size of the image data is the same, the value P (D) of the auxiliary energization timing data depends on the color to be recorded even when the size of the image data is the same. different. Instead of calculating the auxiliary energization timing data, a data table representing each auxiliary energization timing data for the image data “0” to “255” is created for each color, and the auxiliary energization timing data corresponding to the input image data is created. The energization timing data may be extracted from the data table.

The second counter 63 counts up the count value by "1" in response to the input of the second count-up signal, and outputs this count value as comparison data. When the maximum value of the auxiliary energization timing data is set to “Pmax−1”, the second counter 63 sets “1” to “Pmax”.
The comparison data of "x" is generated in order.

At the time of printing, 1
The auxiliary energization timing data for the lines is sequentially read and sent to the second comparator 64. The reading of the auxiliary energization timing data is performed by using “P
max ”times. The second comparator 64 receives the auxiliary energization timing data from the line memory 62 and the comparison data from the second counter 63, and compares them in the same manner as the first counter 51 to create auxiliary drive data. However, in this comparison, the second comparator 6
No. 4 creates auxiliary drive data of “1” only when the auxiliary energization timing data is the same as the comparison data, and creates auxiliary drive data of “0” otherwise.

Therefore, in the recording of one line, "1"
One piece of image data is converted into “Pmax” bits of auxiliary drive data using the comparison data of “〜Pmax”. The second comparator 64 serially outputs the auxiliary drive data for one line and sends it to the second shift register 65.

The second shift register 65 converts one line of serial auxiliary drive data into parallel data, and the second latch array 66 latches the parallel auxiliary drive data. At this time, the second shift register 65 takes in the auxiliary drive data every time the second shift clock is input, and
The latch array 66 latches the auxiliary drive data with the second latch signal. The second latch array 66 outputs an auxiliary drive pulse (“H level”) when the latched auxiliary drive data is “1”.

The second latch array 66 latches the "1" auxiliary drive data at the input of the second latch signal, and then latches the next "0" auxiliary drive data at the input of the next second latch signal. During this period, an auxiliary drive pulse is output from the corresponding output terminal. Therefore, the auxiliary drive pulse has the same pulse width as the period Ta of the second latch signal.

The second latch signal is generated at a constant cycle Ta from the start of the energizing sequence. “Pmax” second latch signals are generated during one energizing sequence. The cycle Ta determines the pulse width of the aforementioned auxiliary drive pulse. Then, the heating element 25 is driven by the auxiliary drive pulse to soften the protective layer 15 and smooth the surface of the color thermosensitive recording paper 10. Therefore, the cycle Ta is a size necessary to soften the protective layer 15 when the heating element 25 is energized for the time of the cycle Ta, and has such a size that the thermosensitive coloring layer of the color being recorded does not develop color. Energy is heating element 25
Is set to a value that is generated from In this example, the same cycle Ta is used for recording any color, and the cycle Ta is set so that the yellow thermosensitive coloring layer 14 having the highest thermal sensitivity is not colored. You may.

The NOR gate array 41 includes a plurality of NOR gates.
Each of the NOR circuits 41a receives a recording drive pulse from the recording power supply unit 50 and an auxiliary drive pulse from the auxiliary power supply unit 60 corresponding to each other. Find what negates the disjunction. As a result, a drive pulse (“L level”) in which the auxiliary drive pulse is superimposed on the recording drive pulse is generated.

The transistor 42a of the switching array 42 is connected to each NOR circuit 41a. Further, each transistor 42a is connected to the heating element 25 of the heating element array 26. Each transistor 42a
Turns ON while the drive pulse from the corresponding NOR circuit 41a is being input, and drives the heating element 25 connected thereto. Therefore, each heating element 25
Are energized for the pulse width of the recording drive pulse corresponding to the size of the corresponding image data, and energized for the pulse width Ta of the auxiliary drive pulse in the middle of the subsequent cooling period.

FIG. 6 shows a recording state of the color thermosensitive recording 10. As described above, a plurality of heating elements 25 are arranged in the heating element array 26 of the thermal head 21 in the main scanning direction. The thermal head 21 records an image of each color on the color thermosensitive recording paper 10 line by line. This one line extends in the main scanning direction, and one line is composed of a plurality of pixels PS which are virtually divided into squares on the color thermosensitive recording paper 10. The pixels PS are recorded by being colored by the application of heat generated by the heating element 25 driven by the recording drive pulse to form dots.

The length L1 of the heating element 25 in the main scanning direction is
For example, the length L2 of the heating element 25 in the sub-scanning direction is the same as the length L2 in the main scanning direction of the pixel PS to be recorded.
Is larger than the length (pixel pitch) L4 of the pixel PS in the sub-scanning direction, and the pixel PS is recorded with the length of the pixel PS in the sub-scanning direction being L4. This is because the temperature on both sides of the heating element 25 in the sub-scanning direction does not rise so much due to heat radiation. Further, by making the length L3 of the heating element 25 in the sub-scanning direction longer than the length L4 of the pixel PS in the sub-scanning direction, the protective layer 15 is heated even at both ends which do not contribute much to recording. Thus, the unevenness formed on the protective layer 15 is made as small as possible.

As shown in FIG. 7, a cross section of the heating element array 26 is formed below the thermal head 21 in a cylindrical shape as described above. The heating element 25 is formed along the shape of the heating element array 26. Actually, as shown in the figure, the surface of the heating element 25 is formed on the protective layer 25 having high thermal conductivity.
a is formed.

Next, the operation of the above configuration will be described with reference to FIG. By operating the operation unit 31, the image data of three colors of the image to be printed is fetched and written into the image memory 33. After the image data is captured, the operation unit 31 instructs a print start. In response to the print start instruction, the system controller 30 initializes each circuit, turns on the yellow optical fixing device 28, and
The color thermosensitive recording paper 10 is sent out from the paper feed cassette and fed.

When the color thermosensitive recording paper 10 reaches the transport path, the motor driver 22 outputs a motor drive pulse having a constant cycle. As a result, the pulse motor 23 is driven, and the color thermosensitive recording paper 10 is
Is conveyed toward the plastic roller 20. By this conveyance, when the leading end of the color thermosensitive recording paper 10 is detected by the sensor 37 after passing between the thermal head 21 at the retracted position and the platen roller 20, the thermal head 21
Is swung to the pressure contact position, and the heating element array 26 is pressed against the color thermosensitive recording paper 10.

The system controller 30 includes a sensor 37
The number of generated motor drive pulses from the time when the leading end of the color thermosensitive recording paper 10 is detected is monitored, and based on the number of motor drive pulses, the color thermosensitive recording paper 10 is conveyed by a predetermined amount and the color thermosensitive recording is performed. The leading end of a recording area for recording an image on the paper 10 is a thermal head 21.
When it is determined that the heating element array 26 has been reached, the recording of the yellow image is started.

When the recording of the yellow image is started, the memory controller 32 sets the image memories 33a to 33 of the respective colors.
The image data of yellow, magenta, and cyan of the first line are read from c, respectively, and are sent to the print controller 34. The print controller 34 writes one line of yellow image obtained by performing the masking process and the γ correction process using the three color image data from the memory controller 32 in the line memory 40. Thereafter, the yellow image data is sequentially read from the line memory 40 and sent to the first comparator 52 of the recording energizing unit 50 and the arithmetic circuit 61 of the auxiliary energizing unit 60, respectively.

In the recording energizing unit 50, the count value of the first counter 51 has been reset to "0" by the above initialization, so that the gradation comparison data of "0" is sent to the first comparator 52. The first comparator 52 compares the sequentially input yellow image data with the gradation comparison data of “0”, and outputs the recording drive data of “1” when the former is larger than or the same as the latter. At this time,
Since all the image data for one line is equal to or greater than "0", the recording drive data for one line, all of which is "1", is serially output based on the gradation comparison data of "0". Is done.

The serial recording drive data is generated by the first shift clock generated in synchronization with the output of the serial drive data.
The data is sequentially taken into the shift register 53. And 1
When the recording drive data for the line is converted into a parallel state, the first latch signal is input to the first latch array 54 from the first timing generation circuit 34a, and the strobe pulse is output to the AND gate array 55. Is entered.

As a result, the first parallel recording drive data is latched by the first latch array 54 and AND
The AND signal is output to the gate array 55. The AND gate array 55 calculates the logical product of each line of the recording drive data for one line and the strobe pulse. Since all the first recording drive data are “1”, the recording drive pulse is output to all the NOR circuits 41 a of the NOR gate array 41. Then, these recording drive pulses correspond to each NO
The driving pulse is output from the R circuit 41a. Therefore, all the transistors 4 of the switching array 42
2a is turned ON, all the heating elements 25 of the heating element array 26 are energized simultaneously, and bias heating is started.

After the first latch signal is generated, the first count-up signal is input to the first counter 51. As a result, the count value of the first counter 51 is incremented to “1”. The gradation comparison data of “1” is input to the first comparator 52. Then, the second reading of the yellow image data of the first line from the line memory 40 is started, and each yellow image data is sequentially compared with the gradation comparison data of “1” to obtain 2 bits.
The first drive data for recording is created for one line, and is taken into the first shift register 53. At this time, if the yellow image data is “1” or more, the corresponding recording drive data is “1”, but if the yellow image data is “0”, the corresponding recording drive data is “0”. ".

When the yellow bias heating time has elapsed since the first latch signal was generated, a second first latch signal is generated. In response to the second first latch signal, the second recording drive data output from the first shift register 53 is latched by the first latch array 54 instead of the first recording drive data.
Output to ND gate array 55.

As a result, the recording drive pulse is continuously output from the AND circuit of the AND gate array 55 in which the second recording drive data is "1", and the energization of the corresponding heating element 25 is continued. . Further, since the recording drive pulse is not output from the AND circuit whose recording drive data is “0”, the corresponding heating element 2
5 is stopped, and only the bias heating is performed.

The count value of the first counter 51 is set to "2" by a first count-up signal generated immediately after the second first latch signal. Third recording drive data for the line is created. Then, similarly to the above, when the third first latch signal is generated, the output of each recording drive pulse is controlled based on the third recording drive data. In the same manner, drive data is created using each of the gradation comparison data of “3” to “255”, the output of the recording drive pulse is controlled at the generation timing of the first latch signal, and from the start of the bias heating. When the maximum heating time of yellow elapses, the strobe pulse is stopped, so that all the recording drive pulses are stopped.

As a result, each heating element 2 in the heating element array 26
Reference numeral 6 denotes a coloring heat generated by being driven by a recording drive pulse having a pulse width corresponding to the yellow image data during the heating period and generating constant bias heat energy Eby and gradation heat energy Egy corresponding to the yellow image data. Generates energy. As a result, the first line of the yellow image is recorded on the color thermosensitive recording paper 10, and each pixel PS
The color is developed to a density corresponding to the yellow image data.

When the gradation heating is completed, the heating elements 25 are cooled until the heating period of the next second line starts, and the heating elements 25 are naturally cooled when the cooling period starts. Since the length of the gradation heating period of each heating element 25 differs depending on the width of the recording drive pulse, that is, the yellow image data, the length of this cooling period depends on the heating element 2.
It differs every five.

On the other hand, in the auxiliary energizing unit 60, the first readout from the line memory 40 in the first readout is performed.
The yellow image data of the line is sequentially input to the arithmetic circuit 61. The arithmetic circuit 61 calculates the auxiliary energization timing data for one line by applying each of the input yellow image data to the above equation. The obtained auxiliary energization timing data is sequentially sent to the line memory 62 and written therein.

When the auxiliary energization timing data for one line is written to the line memory 62, the auxiliary energization timing data is sequentially read from the line memory 62 and sent to the second comparator 64. The comparison data of “1” is sent from the initialized second counter 63 to the second comparator 64. The second comparator 64
Each auxiliary energization timing data is compared with the comparison data of “1”, and when the former is the same as the latter, the auxiliary drive data of “1” is output. At this time, since all the heating elements 25 perform the bias heating, the auxiliary drive data does not become “1”.

The serial auxiliary drive data from the second comparator 64 is the second auxiliary drive data generated in synchronization with the output of the second auxiliary drive data.
The data is sequentially taken into the second shift register 65 by the shift clock and converted into parallel auxiliary drive data.
After this conversion, the second timing generation circuit 34b generates the second latch signal simultaneously with the generation of the first first latch signal. The first parallel auxiliary drive data is latched in the second latch array 66 by the first second latch signal. Since the auxiliary drive data for one line is all “0”, the second latch array 66 does not output the auxiliary drive pulse.

After the generation of the first second latch signal,
The second count-up signal is input to the second counter 63, the count value is set to “2”, the comparison data of “2” is sent to the second comparator 64, and the auxiliary data of the first line is sent from the line memory 62. The second reading of the energization timing data is performed. The comparison data of “2” is compared with the auxiliary energization timing data of the first line in the same procedure as described above, and the second auxiliary drive data for one line is created, and is taken into the second shift register 65. When the time Ta elapses after the generation of the first second latch signal, the second second latch signal is generated, and the second auxiliary drive data is stored in the second latch array 66.
It is taken in. Hereinafter, similarly, “3” to “Pma
x "is used to generate auxiliary driving data,
The data is converted into a parallel by the second shift register 65. The second latch signal is latched by the second latch array 66 according to the second latch signal sequentially generated every time Ta.

As described above, when one line of auxiliary driving data is latched in the second latch array 66,
When the auxiliary drive data of “1” is included, an auxiliary drive pulse is output from the output terminal of the second latch array 66 corresponding to the auxiliary drive data.

For example, if auxiliary energization timing data having a value “P (D)” is created from yellow image data having a size “D”, when the comparison data is “P (D)”, Auxiliary drive data of "1" is created for the auxiliary energization timing data. The auxiliary drive data is generated by the “P (D)”-th second latch signal generated in the middle of the cooling period of the heating element 25 driven by the recording drive pulse based on the “D” yellow image data. The NOR circuit 41 of the NOR gate array 41 which is latched by the second latch array 66 and corresponds as an auxiliary drive pulse
is input to a. As a result, the auxiliary driving pulse is output as a driving pulse.
Is driven in the middle of the cooling period.

When the comparison data is set to "P (D) +1" by the next "P (D) +1" -th second count-up signal, the comparison data is compared with the auxiliary energization timing data. The auxiliary drive data of “0” is created. Then, when the time Ta elapses from the time when the “P (D)”-th second latch signal is generated and the “P (D) +1” -th second latch signal is generated, the “0” auxiliary driving is performed. The data is latched in the second latch array 66. Thus, the auxiliary drive pulse stops. As a result, the corresponding heating element 25 is driven for the time Ta by the auxiliary driving pulse generated for the time Ta in the middle of the cooling period corresponding to the yellow image data of the size “D”.

As described above, each heating element 25 is driven by the auxiliary drive pulse during the middle of the cooling period, and does not generate the yellow thermosensitive coloring layer 14 but softens the protective layer 15. The heat energy required for the recording is supplied to the color thermosensitive recording paper 10.

Immediately before the end of the cooling period of the first line, the memory controller 32 reads out the image data of three colors of the second line from the image memory 33 and sends it to the print controller 34. Print controller 34
Writes the second-line yellow image data subjected to the image processing into the line memory 40. Further, the first and second counters 51 and 63 are reset, and the count values are set to “0” and “1”, respectively.

Thereafter, the yellow image data of the second line is sequentially read from the line memory 40. As in the case of the first line, the recording unit 50 creates the first recording drive data using the yellow image data of the second line. Then, the driving data for recording is taken into the first shift register 53 and converted into parallel. Further, the auxiliary energizing unit 60 creates auxiliary energizing timing data for one line from each yellow image data of the second line and writes it in the line memory 62, and writes the auxiliary energizing timing data written in the line memory 62. The first auxiliary drive data is created using the first auxiliary drive data, and is taken into the second shift register 65.

When the cooling period of the first line, that is, the energizing sequence of the first line is completed, the generation of the strobe pulse is started in the same manner as described above, and the first and second strobe pulses are started.
A latch signal, a first count-up signal, and a second count-up signal are sequentially generated, and a driving pulse in which an auxiliary driving pulse is superimposed on a recording driving pulse is generated. By driving each of the heating elements 25 with this drive pulse, the second line of the yellow image is recorded, and heat energy for softening the protective layer 15 without generating color on the color thermosensitive recording paper 10 is generated. After the recording of the second line, the heating element 25 is driven by a drive pulse generated based on the yellow image data of the third and subsequent lines in the same manner, and the third and subsequent lines of the yellow image are sequentially recorded.

The portion of the color thermosensitive recording paper 10 on which the yellow image has been recorded is further conveyed downstream of the conveying path, and when it reaches the yellow light fixing unit 28, the yellow ultraviolet light from the yellow ultraviolet lamp 28a is discharged. Upon irradiation, the yellow thermosensitive coloring layer 14 is fixed, and the coloring ability is lost. Even after the last line of the yellow image is recorded, the color thermosensitive recording paper 10 is conveyed downstream until the rear end of the recording area passes through the yellow optical fixing device 28.

The rear end of the recording area is the optical fixing unit 2 for yellow.
8, the yellow ultraviolet lamp 28a is turned off and the pulse motor 23 is stopped once. Further, the thermal head 21 is swung to the retracted position. Thereafter, the pulse motor 23 is rotated in the reverse direction and the transport mechanism 2
At 4, the color thermosensitive recording paper 10 is transported toward the upstream of the transport path. When the leading end of the recording area reaches the position of the thermal head 21 during this conveyance, the conveyance of the color thermosensitive recording paper 10 is stopped, and the thermal head 21 is swung to the pressure contact position. Further, the magenta ultraviolet lamp 29a is turned on.

After the thermal head 21 is set at the pressure contact position, the pulse motor 23 is rotated forward again,
4 transports the color thermosensitive recording paper 10 downstream of the transport path. In the meantime, the heating element array 26 performs the bias heating for magenta and the gradation heating on the color thermosensitive recording paper 10 to record a magenta image line by line.

At the time of magenta recording, the image memory 33
The magenta image data that has been subjected to image processing is created using the three color image data read from the printer, and this magenta image data is sent to the thermal head drive unit 27 line by line. Recording unit 5 based on magenta image data
A recording drive pulse is created at 0, and an auxiliary drive pulse is created at the auxiliary energizing unit 60. Each heating element 25 is driven by a driving pulse in which an auxiliary driving pulse is superimposed on a recording driving pulse.

The portion of the color thermosensitive recording paper 10 on which the magenta image is recorded is irradiated with magenta ultraviolet rays from the magenta ultraviolet lamp 29a, and the magenta thermosensitive coloring layer 13 is formed.
Is light-fixed. When the rear end of the recording area passes through the magenta optical fixing unit 29, the color thermosensitive recording paper 10 is returned once and then conveyed downstream again in the same manner as described above. During this conveyance, the heating element array 26 driven by the driving pulse generated based on the cyan image data
, A cyan image is recorded line by line. The color thermosensitive recording paper 10 on which the last line of the cyan image is recorded is conveyed as it is, and is discharged through a paper discharge port.

FIG. 9 schematically shows the state of the surface of the protective layer 15 of the color thermosensitive recording paper 10 when the heating element 25 is driven only by the driving pulse on which the auxiliary driving pulse is not superimposed, that is, the recording driving pulse. Showing the protective layer 1
5 is an enlarged view of a cross section parallel to the sub-scanning direction.
Although the color thermosensitive recording paper 10 actually moves in the sub-scanning direction, the heating element 25 is drawn so as to move in the sub-scanning direction for convenience of explanation. When the heating element 25 is driven by a recording drive pulse to generate heat in order to record one pixel PS, the protection layer 1 in contact with the heating element 25 generates heat.
Part 5 softens. Since the color thermosensitive recording paper 10 is conveyed in the sub-scanning direction while the heating element 25 is generating heat, a concave portion 70 extending in the sub-scanning direction is formed in the protective layer 15. Since the heating element 25 is cooled in the cooling period,
The portion of the protective layer 15 that is in contact with the cooled heating element 25 is not softened. Further, when the heating element 25 generates heat to record the next pixel PS, the protection layer 15
Is softened and a new concave portion 70 is formed.

As described above, when the heating element 25 is driven only by the recording driving pulse, the recess 70 and the recess 70 are driven.
Between them, a convex portion 71 is formed in a portion of the protective layer 15 where the heating element 25 that has not generated heat has been in contact. The convex portion 71 becomes larger as the cooling period becomes longer, and becomes larger as the length of the heating element 25 in the sub-scanning direction becomes shorter. By forming the concave portions 70 and the convex portions 71 in this manner, the glossiness of the surface of the color thermosensitive recording paper 10 decreases, and the sharpness of the recorded image decreases.

However, in this color thermal printer, the auxiliary drive pulse is generated in the middle of the cooling period as described above. Thereby, as shown in FIG.
Is driven and heated by the auxiliary drive pulse when the portion of the protective layer 15 is to be the convex portion 71 of the protective layer 15.
5 is softened to form a concave portion 72. When the concave portion 72 is formed in this way, the convex portions 72a are formed on both sides of the concave portion 72, respectively.
Is extremely small in combination with the length L3 of the heating element 25 in the sub-scanning direction being longer than the length L4 of one pixel PS. As a result, the surface of the color thermosensitive recording paper 10 is smoothed, and the glossiness and the sharpness of the recorded image are improved.

Further, since the above-described processing for smoothing is performed using the thermal head 21, no mechanism for smoothing is required, and since the processing is performed during image printing, color image printing is performed. Since the smoothing process is completed simultaneously with the completion, no extra time is required for smoothing.

The number of pulses generated during the cooling period is not limited to one. For example, in the example shown in FIG. 10, two auxiliary driving pulses are generated during the cooling period, and the heating elements are driven and heated by a driving pulse that is superimposed on the recording driving pulse. This also has the effect of smoothing the protective layer.

In the example shown in FIG. 11, an auxiliary drive pulse is periodically generated at a frequency that is one time the energizing sequence, and the heating element is driven and generates heat by a drive pulse in which the auxiliary drive pulse is superimposed on a recording drive pulse. It is like that.
In such a case, the heating element is not driven / heated in the middle of the cooling period by the auxiliary driving pulse, but the same effect as in the first embodiment can be obtained. Further, the frequency of the auxiliary driving pulse can be set to an integral multiple of the energizing sequence. In the example shown in FIG. 12, the frequency of the auxiliary drive pulse is set to be three times the energizing sequence. Further, the frequency of the auxiliary driving pulse superimposed on the recording driving pulse may be changed for each recording color. For example, in the example shown in FIG. 13, the frequency of the auxiliary drive pulse is set to 1 time for yellow, 3 times for magenta, and 5 times for cyan, and the number of times the heating element is driven by the auxiliary drive pulse is changed for each color. .

In each of the above embodiments, the heating element is continuously driven to print one pixel. However, as shown in FIG. 14, a narrow recording drive pulse is generated intermittently. You may. In this example, one recording drive pulse is generated for bias heating, but it may be generated intermittently.

In each of the above embodiments, an auxiliary driving pulse is generated for recording of each color to smooth the protective layer. However, when the color to be recorded last is recorded, the cyan color is recorded in the first embodiment. Only by generating an auxiliary drive pulse to drive and generate heat, the protective layer can be satisfactorily smoothed.

Further, in each of the above embodiments, one line (1
Although the description has been given of the case where pixels are recorded in one energizing sequence, one line may be recorded in multiple energizing sequences. In this case, the heating element is driven and heated by the auxiliary drive pulse during the cooling period of each energization sequence.

In the above description, when recording an image, the color thermosensitive recording paper is reciprocated. However, a large-sized platen drum is used, and the color thermosensitive recording paper is wrapped around the platen drum, and one color per rotation is obtained. May be recorded. Further, a thermal head may be provided for each color, and a full-color image may be recorded by one transfer. Also, an example of a thermal printer of the heat-sensitive type has been described. However, in the present invention, the ink ribbon is heated by a heating element in a state where the ink ribbon is brought into close contact with the surface of an image receiving paper as a recording paper, so that the ink ribbon is heated. The present invention can also be used for a thermal printer of a fusion type or sublimation type thermal transfer system in which an ink containing a dye or a pigment is transferred to an image receiving paper, and the surface of the image receiving paper can be smoothed.

[0087]

As described above, according to the present invention, during the cooling period for cooling the heating elements, each of the heating elements is driven by the auxiliary driving pulse, and the size of the recording sheet is such that dots are not formed. By generating heat energy in each heating element, the recording paper is heated and subjected to a surface smoothing process, so that the glossiness of the recording paper is improved and the sharpness of the recorded image is also increased. Can be higher. Further, since smoothing is performed during recording of an image using a thermal head, no extra time is required for smoothing, and there is no need to provide a mechanism for smoothing.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram illustrating a state of a protective layer when a heating element is driven by an auxiliary driving pulse to perform smoothing.

FIG. 2 is an explanatory diagram showing a layer structure of a color thermosensitive recording paper.

FIG. 3 is an explanatory diagram showing color development characteristics of a color thermosensitive recording paper.

FIG. 4 is a schematic diagram showing a configuration of a color thermal printer of the present invention.

FIG. 5 is a block diagram illustrating a configuration of a thermal head driving unit.

FIG. 6 is an explanatory diagram showing a recording state of a color thermosensitive recording paper.

FIG. 7 is a cross-sectional view showing a cross section of the heating element array.

FIG. 8 is a timing chart showing signals for driving a heating element.

FIG. 9 is an explanatory diagram showing a state of a protective layer when an auxiliary driving pulse is not superimposed on a recording driving pulse.

FIG. 10 is a waveform diagram showing an example in which two auxiliary driving pulses are superimposed on a recording driving pulse during a cooling period.

FIG. 11 is a waveform diagram showing an example in which an auxiliary drive pulse generated at a frequency that is one time of the energization sequence is superimposed on a recording drive pulse.

FIG. 12 is a waveform diagram showing an example in which an auxiliary driving pulse generated at a frequency three times as high as that of an energizing sequence is superimposed on a recording driving pulse.

FIG. 13 is a waveform diagram showing an example in which the frequency of an auxiliary driving pulse superimposed on a recording driving pulse is changed for each color.

FIG. 14 is a waveform diagram showing an example in which gradation heating is performed with intermittent recording drive pulses.

[Explanation of symbols]

 Reference Signs List 10 color thermal recording paper 25 heating element 27 thermal head drive unit 41 NOR gate array 50 recording energizing unit 60 auxiliary energizing unit PS pixel

Claims (6)

[Claims] 1. A thermal head in which a large number of heating elements are formed in a line in a main scanning direction, and a heating element is generated by a recording drive pulse while relatively moving the thermal head and a recording paper in a sub-scanning direction. The ink is transferred by directly heating the heat-sensitive recording paper as the recording paper to form a dot by developing a color, or by heating the ink ribbon adhered to the receiving paper as the recording paper. In a thermal printing method for printing an image on recording paper by forming dots on the recording paper, the auxiliary driving is performed during a cooling period for cooling the heating element after the heating period for driving the heating element with the recording drive pulse. A pulse is generated for each heating element, and the heating element is driven by this auxiliary driving pulse, so that thermal energy of a size that does not form dots on recording paper is obtained. Thermal printing method being characterized in that so as to apply a smoothing treatment of the surface of the recording sheet giving. 2. The thermal printing method according to claim 1, wherein the auxiliary drive pulse is generated in the middle of a cooling period for each heating element. 3. The auxiliary driving pulse is generated at a frequency that is an integral multiple of one energizing sequence from the start of a heating period to the end of a cooling period, and the auxiliary driving pulse is superimposed on the recording driving pulse. 2. The thermal printing method according to claim 1, wherein the heating element is driven during a cooling period by an auxiliary driving pulse. 4. An image of each color is recorded on the recording paper in a color sequence, and a frequency of the auxiliary driving pulse superimposed on the recording driving pulse is different for each color. The thermal printing method according to claim 3. 5. The thermal device according to claim 1, wherein a length of the heating element in the sub-scanning direction is longer than a length of the dot in the sub-scanning direction. Printing method. 6. A thermal head in which a number of heating elements are formed in a line in the main scanning direction, moving means for moving at least one of the recording paper and the thermal head in the sub-scanning direction during printing, and a heating means based on the heating data. A recording drive pulse generating means for generating a recording drive pulse for driving the heating element by driving each heating element with a corresponding recording drive pulse, thereby directly directing the heat-sensitive recording paper as a recording paper. The image is printed on the recording paper by heating to form a dot by forming a color, or by heating an ink ribbon adhered to an image receiving paper as a recording paper and transferring the ink to form a dot. In the thermal printing apparatus, each heating is performed during the cooling period for cooling the heating element after the heating period in which the heating element is driven by the recording drive pulse. Auxiliary driving pulse generating means for generating an auxiliary driving pulse based on the heat generation data for each of the elements; and driving pulse synthesizing means for outputting a driving pulse in which the auxiliary driving pulse is superimposed on the corresponding recording driving pulse. By driving the heating elements with the driving pulse from the driving pulse synthesizing means, heat energy of such a size that dots are not formed on the recording paper in the middle of the cooling period is given from the respective heating elements to the recording paper, and A thermal printing apparatus characterized in that the surface is smoothed.