Thermal print head with double-row heating elements and multi-color printing method

Abstract

The present invention relates to the technical field of thermal print head manufacturing, and more specifically to a thermal print head with double-row heating elements and a multi-color printing method, wherein the heating resistors include double-row heating resistors parallel to each other, and the double-row heating resistors are arranged in parallel along a secondary scanning direction, wherein the area of ​​a row of heating resistors close to a paper feed side is larger than the area of ​​a heating resistor close to a paper discharge side; a control IC is used to control the on / off state of a single heating point in the heating resistor, and a control signal end of the control IC is connected to a multi-color printing time calculation and distribution unit, and the multi-color printing time calculation and distribution unit is provided with a theoretical duty cycle and color development time calculation module, a printing mode judgment module, a high color development temperature printing control logic signal generation module, and a low color development temperature printing control logic signal generation module.

Description

Technical Field

[0001] The present invention relates to the technical field of thermal print head manufacturing, and more specifically to a thermal print head with double-row heating elements and a multi-color printing method, which can overcome the problems of blurring and insufficient color development between different colors in high-energy and high-speed printing conditions such as multi-color printing while maintaining the printing speed, and effectively extend the service life of the thermal print head. Background Art

[0002] As is known to all, the thermal print head in the prior art includes an insulating substrate, a base glaze layer is provided on the surface of the insulating substrate, a common electrode and individual electrodes and a single row of heating resistors are provided on the surfaces of the insulating substrate and the base glaze layer, and the heating resistor is arranged between the two electrodes, one end of the common electrode is connected to the heating resistor, and the other end is connected to one end of the power supply; one end of the individual electrode is connected to the heating resistor, and the other end is connected to the IC, which is in turn connected to the other end of the power supply; the heating resistor, the individual electrode and the common electrode are provided with an insulating protective layer. During printing, driven by the control signal sent by the control IC, the heating resistor heats up and contacts with the thermal consumables, and the thermal consumables are heated to complete the color development.

[0003] Thermal multi-color printing uses a thermal print head to provide different color development temperatures to achieve different color development on thermal printing media. When performing multi-color printing, under high-temperature color printing conditions, if the contact time between the heating resistor of a single-row structure and the thermal consumables is insufficient, insufficient color development may occur. In order to overcome this problem, it is necessary to increase the heating rate of the heating resistor during the contact time between the heating resistor and the thermal consumables, so that it can output high printing energy in a short time, that is, to increase the heating power. However, this method significantly increases the energy consumption of the equipment, easily damages the print head, and may cause low-temperature smudging problems at the edges of patterns that develop colors at high temperatures. In the case of low-temperature color printing, if the pulse control signal of the print head is not adjusted accordingly, or because of the temperature accumulation of the single-row heating resistor after the high-temperature printing condition ends, the thermal printing medium may be overheated, causing the low-temperature color to show the high-temperature color.

[0004] The thermal print head in patent document JP2010-201693 is provided with a double-row heating resistor, which can print twice at the same position on the printing paper. Since the heating is carried out in two steps, heat concentration can be avoided and damage to the medium can be reduced. However, this technical solution essentially shortens the ON time required for printing and achieves high-speed printing without reducing the grayscale gradation. The two rows of heating resistors are of equal volume and specifications and are closely arranged side by side. When printing, the turn-on time of the two rows of heating resistors changes, but the power of the single row of heating resistors does not change. When applied to multi-color printing, it is still unable to overcome the multi-color blurring problem caused by heat accumulation. Summary of the invention

[0005] In view of the shortcomings and deficiencies in the prior art, the present invention proposes a thermal print head with double-row heating elements and a multi-color printing method thereof, which can overcome the problems of insufficient printing color or printing blurring in high-energy, high-speed printing processes such as multi-color printing, and effectively extend the service life of the thermal print head.

[0006] The present invention is achieved by the following measures:

[0007] A thermal print head with double-row heating elements is provided with a thermal printing assembly, wherein an insulating substrate is provided in the thermal printing assembly, a base glaze layer is provided on the surface of the insulating substrate, a common electrode and an individual electrode are provided on the surfaces of the insulating substrate and the base glaze layer, a heating resistor is arranged between the common electrode and the individual electrode, one end of the common electrode is connected to the heating resistor, and the other end is connected to one end of a power supply, one end of the individual electrode is connected to the heating resistor, and the other end is connected to a control IC, and the control IC is connected to the other end of the power supply, and is characterized in that the heating resistor includes double-row heating resistors parallel to each other, the double-row heating resistors are arranged in parallel along the secondary scanning direction, wherein the area of ​​a row of heating resistors close to the paper feed side is larger than that of the row of heating resistors close to the paper feed side. The area of ​​the heating resistor near the paper output side; the control IC is used to control the on / off state of a single heating point in the heating resistor, and the control signal end of the control IC is connected to the multi-color printing time calculation allocation unit, and the multi-color printing time calculation allocation unit is provided with a theoretical duty cycle and color development time calculation module, a printing mode judgment module, a high color development temperature printing control logic signal generation module, and a low color development temperature printing control logic signal generation module, wherein the theoretical duty cycle and color development time calculation module is connected to the color development time calculation module and the printing mode judgment module in sequence, and the output end of the printing mode judgment module is connected to the high color development temperature printing control logic signal generation module and the low color development temperature printing control logic signal generation module respectively.

[0008] In the present invention, the size of the heating resistor body near the paper feed side in the double-row heating resistor body is set according to normal specifications based on the resolution, and the area of ​​the heating resistor body near the paper outlet side is 60-90% of the size of the heating resistor body near the paper feed side. It is specifically determined according to the color superposition of the double-row printing. For example, the heat diffusion situation can be calculated based on the thermal conductivity, specific heat capacity, density and other parameters of the heating body material and thermal paper. It is preferable that the color temperature distribution area of ​​the double-row printing is equivalent to the required area.

[0009] In the double-row heating resistors of the present invention, the size (area) of the heating resistors close to the paper discharge side is 80% of the size of the heating resistors close to the paper feed side.

[0010] In the present invention, the spacing between the double-row heating resistors is L, which should be as small as possible, preferably L≤1mm. The larger the L value, the larger the size of the second row of heating elements, and the maximum size is the same as the first row of heating elements.

[0011] The multi-color printing time calculation and allocation unit of the present invention is also provided with a bad pixel energy compensation module, which is respectively connected to the high color development temperature printing control logic signal generation module and the low heating temperature printing control logic signal generation module.

[0012] The present invention also proposes a multi-color printing method of a thermal print head with double-row heating elements, characterized in that when the thermal print head with double-row heating elements as described above is applied to multi-color printing, the double-row printing time difference △T is calculated according to the spacing L of the double-row heating resistors and the printing speed V, △T=L / V, and the double-row heating elements are controlled by IC to print corresponding content, and the following steps are performed:

[0013] Step 1: According to the color temperature T at the current point, combined with the temperature differential formula, obtain the required theoretical color duty cycle α and color time t A , t A is the sum of the total opening time of multiple cycles of the current heating point, where the temperature rise and fall differential formula is: C dT + AT dt = Q dt; where C (Cth) is the heat capacity (J / K), T is the color temperature (K), A is the thermal diffusion coefficient Rth = 1 / A (W / K), t is the heating time of each cycle of the current heating point (s), that is, the voltage width in the pulse control signal, and Q is the heating power (W); the color duty cycle α is based on the temperature rise to the color temperature, and the color time t A The saturation of the printed color is used as the standard, which can be obtained based on the printing time and concentration curve;

[0014] Step 2: The printing mode determination module determines the current printing mode, which includes high color development temperature color printing and low color development temperature color printing. If the high color development temperature color printing is over 120°C, continue to step 3; otherwise, it is a low heating temperature printing mode, and continue to step 4;

[0015] Step 3: When printing with high color temperature, the pulse control signal output by the control IC adopts a large duty cycle α b At this time, under the pulse control signal, the heating temperature of a single heating point of the heating resistor is higher, but the opening time is shortened, which specifically includes the following steps:

[0016] Step 3-1: Determine the duty cycle α of the pulse control signal b , α b =N·α, the coefficient N is determined according to the color temperature, and N is based on the color temperature reached by a single pulse;

[0017] Step 3-2: Determine the duty cycle α b In this case, is the single-row printing time sufficient? If the duty cycle α bOutput single-row printing time t b ≤Actual printing cycle t c , it is judged that the time is sufficient, where t b is the total Ton time in the pulse, t c In order to meet the printing time required for printing saturation, at this time, two rows of alternating printing are adopted, that is, interlaced printing. At this time, the pulse control signal parameters of the two rows of heating resistors are the same. After one row of heating resistors receives the printing control data of odd rows, the other row of heating resistors receives the printing control data of even rows. The thermal efficiency of the thermal printing device is higher, which can avoid the damage of the heating element due to the accumulation of temperature at a single point, and can also effectively avoid the problem of blooming caused by temperature accumulation;

[0018] Step 3-3: If the single-row printing time is insufficient, t b >t c , then the double-row printing mode is adopted. At this time, the printing time t of the row of heating resistors close to the paper feeding side is d The total printing time t greater than this color temperature A 55% of which t d It is calculated based on the effective time in the pulse to avoid the blurring problem caused by temperature accumulation. At this time, the two rows of heating resistors correspond to the same area of ​​the printing paper and print repeatedly;

[0019] Step 4: When printing at low color temperature, the pulse control signal output by the control IC uses a small duty cycle α s , making the printing temperature lower and the time longer, α s =M·α, coefficients M, M are based on the color development temperature reached by a single pulse, and a double-row printing mode is adopted, that is, two rows of heating resistors are driven by the same printing data and print the same content in the same position one after another to complete the printing work, and the printing time of the row of heating resistors close to the paper feed side is greater than 50% of the total printing time of this color development temperature.

[0020] In step 3-3 of the present invention, if the energy for single-row printing is insufficient, double-row simultaneous printing is adopted. The printing time ratio of the double rows is such that the printing time of the front row (the heating resistor close to the paper feed side) is greater than 55% of the total printing time, and the duty cycle of the front-row pulse control signal is greater than the duty cycle of the rear-row pulse control signal. Furthermore, the duty cycle of the front-row pulse signal is set to 20%~70%, subject to a single pulse reaching the color development temperature; the rear row is set to 15%~60%, subject to no blurring.

[0021] When printing low color development temperature colors in step 4 of the present invention, the printing time ratio of the double rows makes the first row slightly greater than 55% of the total printing time, and the duty cycle of the pulse control signal of the first row is greater than the duty cycle of the pulse control signal of the rear row.

[0022] In the double-row printing mode described in step 3 and step 4 of the present invention, if the resistance of a heating element at a point in any one of the two rows of heating resistors increases or is damaged, the point at the corresponding position in the other row is used to perform energy compensation for the bad point, specifically: the output energy of the two rows of heating resistors is redistributed according to the increase in resistance, wherein the total output energy of the good points at the corresponding positions = the original output energy of the good points + the compensation energy, and the compensation energy = the output energy of the damaged point - the actual output energy of the damaged point, so as to avoid printing white streaks or white lines due to a bad point as much as possible.

[0023] The present invention can ensure that both high and low temperature color development can be fully achieved and multi-color blurring can be avoided under the premise of avoiding high energy and high speed destruction of the heating element. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Attached Figure 1 It is a structural schematic diagram of the present invention.

[0025] Attached Figure 2 : is a control pulse and temperature curve diagram of the heating resistor in the high temperature color printing mode in Example 1 of the present invention, wherein Figure 2 a and Figure 2 b is the curve diagram corresponding to the two rows of heating elements of the double-row heating resistor in the rotating printing state. Figure 2 c is the corresponding curve diagram when the double-row heating resistor performs double-row printing.

[0026] Attached Figure 3 It is a schematic diagram of pulse application and temperature curve for double-row printing in low-temperature color printing mode in Example 2 of the present invention.

[0027] Attached Figure 4 It is a flow chart of the present invention.

[0028] Attached Figure 5 Schematic diagram of temperature distribution used in the embodiment of the present invention.

[0029] Attached Figure 6 It is the printing time density saturation curve used in the embodiment of the present invention. DETAILED DESCRIPTION

[0030] The specific implementation modes of the invention will be further described below in conjunction with the accompanying drawings. Example

[0031] This example provides a thermal print head with double-row heating elements and a multi-color printing method. The thermal print head in this example is provided with an insulating substrate, a base glaze layer is provided on the surface of the insulating substrate, a common electrode and an individual electrode are provided on the surface of the insulating substrate and the base glaze layer, and a heating resistor is arranged between the common electrode and the individual electrode, one end of the common electrode is connected to the heating resistor, and the other end is connected to one end of a power supply; one end of the individual electrode is connected to the heating resistor, and the other end is connected to a control IC, and the control IC is connected to the other end of the power supply, wherein the control IC is used to control the on / off state of a single heating point in the heating resistor. The above structure is similar to the prior art and will not be described in detail here;

[0032] like Figure 1 As shown, in this example, the thermal print head is provided with two rows of heating resistors parallel to each other, and the two rows of heating resistors are arranged in parallel along the secondary scanning direction, wherein the area of ​​the heating resistor close to the paper feed side is larger than the area of ​​the heating resistor close to the paper discharge side;

[0033] In this example, a multi-color printing time calculation and allocation unit and two control ICs for respectively receiving logic control signals for heating control of two rows of heating elements are also provided. The multi-color printing time calculation and allocation unit is provided with a theoretical duty cycle and color development time calculation module, a printing mode judgment module, a high color development temperature printing control logic signal generation module, and a low color development temperature printing control logic signal generation module. The two control ICs generate switch control logic signals for each heating point by receiving CLK / DATA / LATCH / STROBE signals corresponding to the high color development temperature and the low color development temperature output by the multi-color printing time calculation and allocation unit;

[0034] In this example, the size of the heating resistor near the paper feed side of the double-row heating resistor is set according to the normal specifications based on the resolution, and the size (area) of the heating resistor near the paper outlet side is 80% of the size of the heating resistor near the paper feed side. It is specifically determined according to the color superposition of the double-row printing. For example, the heat diffusion can be calculated based on the parameters such as the thermal conductivity, specific heat capacity, and density of the heating element material and thermal paper using ansys software. It is appropriate to make the double-row printing color distribution area equal to the required area (see Figure 5 ).

[0035] This example also proposes a multi-color printing method for a thermal print head with double-row heating elements, wherein firstly, the printing time difference △T of the two rows is calculated according to the distance L (0.1 mm in this example) between the two rows of heating resistors in the double-row heating resistors and the printing speed V (200 mm / s in this example), △T=L / V, and then the following operations are performed:

[0036] The calculation unit for calculating the multi-color time allocation calculates the required coloring duty ratio and coloring time (the sum of the total opening time of multiple pulses in a single printing cycle) according to the coloring temperature of the current point combined with the temperature rise and fall differential formula. The coloring duty ratio α is based on the temperature rise to the coloring temperature, and the coloring time t A The saturation of the printed color is used as the standard, which can be obtained based on the printing time and concentration curve) (see Figure 6 );

[0037] The temperature differential formula is: C dT + AT dt = Q dt; where C (Cth) means heat capacity (J / K); T means temperature (K); A means thermal diffusion coefficient Rth = 1 / A (W / K); t means time (s); that is, the width of the voltage; Q means heating power (W);

[0038] In this example, the duty cycle α is 130°C when the color temperature is b is 60%, α b The coloring temperature reached by a single pulse is taken as the standard. The coloring time depends on the coloring saturation requirement (0.25mJ in this case. The power is calculated based on the resistance of the heating element and the printing voltage, and then the heating time is calculated based on the power. Ton=Energy / Power (Ton is the coloring time). The specific data needs to be obtained based on the theory combined with the experiment of the print head (material density, thermal conductivity, specific heat, etc.) and consumables (coloring temperature, thermal conductivity, specific heat, etc.) used.

[0039] If the current printing is of high color temperature (in this case: 130°C) or low color temperature (in this case: 80°C), if the current printing is of high color temperature, the pulse control signal output by the control IC adopts a larger duty cycle α b (Calculated according to step 1, the result is 60% in this example) Make the printing temperature higher and the time shorter, and judge whether the single-row printing time is sufficient. If the single-row printing time is sufficient (in this example, Ton<(0.625ms

[0040] *60%=0.375ms)), reference Figure 2 a and Figure 2 b. The two-row printing method is adopted, that is, interlaced printing, which has higher thermal efficiency. It can not only avoid the damage of the heating element due to single-point temperature accumulation, but also effectively avoid the blurring problem caused by temperature accumulation;

[0041] If the single-row printing time is insufficient, double-row printing can be used. Figure 2c. The printing time ratio of the double rows is such that the printing time of the front row (the heating resistor close to the paper feed side) is greater than 55% of the total printing time (for example, if the total Ton is 0.45ms, then the Ton of the front row is 0.45*55%=0.25ms, and the Ton of the back row is 0.2ms). The duty cycle of the front row is set to 60%, which is based on the color development temperature reached by a single pulse; the duty cycle of the back row is set to 45%. Taking into account the temperature accumulation, the duty cycle of the pulse control signal of the heating resistor in the back row is reduced to avoid the blurring problem caused by temperature accumulation and to avoid the mixing of low-temperature colors into high-temperature colors. Example

[0042] This example provides a thermal print head with a double row of heating elements, the structure of which is similar to that of Example 1. When the thermal print head of this example performs multi-color printing under low color development temperature conditions, for printing of low color development temperature colors (80°C in this example), refer to Figure 3 , using a smaller duty cycle α s (Calculated according to step 1, this example uses 30%) to make the printing temperature lower and the printing time longer. Use a double-row, time-sharing printing mode to print the same content at the same position. The duty cycle of the front row is set to 30%, based on the color development temperature reached by a single pulse; the duty cycle of the back row is set to 25%. Because there is a certain amount of temperature accumulation, the duty cycle is slightly reduced, and the printing time ratio of the double row makes the front row slightly greater than 55% of the total printing time (for example, the total Ton is 0.25ms, then the Ton of the front row is 0.225*55%=0.13ms, and the Ton of the back row is 0.12ms). This can avoid the mixing of high-temperature colors into low-temperature colors due to excessive temperature. Example

[0043] This example provides a method for performing multi-color printing in a thermal print head with double-row heating elements when there is a bad point in any row of heating resistors. If the resistance of the heating element at a certain point in one row increases or is damaged, it is necessary to use a resistance measuring circuit to measure the current resistance of each point. The resistance test method is to use CLK, LACH, and DATA signals to open the first point in the print head, insert a sampling resistor in the power supply circuit, and calculate the resistance of the current point through the voltage of the sampling resistor. Then, the data shift register goes to the next point and measures the resistance, and the cycle continues until the resistance of all points is measured.

[0044] According to the increase in resistance, the energy of the corresponding points in the two rows of heating elements is redistributed. In this example, the bad points still output energy according to the original printing time, and the energy difference of the bad points is compensated by the corresponding good points in the other row at the same printing position. The total energy of the good points = the original output energy of the bad points + the compensation energy. The calculation method of the difference compensation energy is: the compensation energy of the good points = the output energy of the damaged points - the actual output energy of the damaged points, which is obtained by the following formula:

[0045] EΔ =V 2 t / R0-V 2 t / R1,

[0046] Among them, E Δ : Energy difference, i.e. required compensation energy, V: voltage,

[0047] R0: normal resistance, R1: destruction resistance (usually Rup);

[0048] When the present invention is applied to situations where precise control of concentration or grayscale is required, precise control of printing time can also be achieved by using the method of multiple input data and multiple latching commonly used in general thermal history control. The above method takes into account the printing of high and low temperature colors, maintains speed, avoids smearing between different colors, reduces damage to the print head, and avoids printing white streaks or white lines due to a single defect.

Claims

1. A thermal print head with double-row heating elements, provided with a thermal printing assembly, wherein an insulating substrate is provided in the thermal printing assembly, an underglaze layer is provided on the surface of the insulating substrate, a common electrode and an individual electrode are provided on the surfaces of the insulating substrate and the underglaze layer, a heating resistor is arranged between the common electrode and the individual electrode, one end of the common electrode is connected to the heating resistor, and the other end is connected to one end of a power supply, one end of the individual electrode is connected to the heating resistor, and the other end is connected to a control IC, and the control IC is connected to the other end of the power supply, characterized in that: The heating resistors include double rows of heating resistors parallel to each other, and the double rows of heating resistors are arranged in parallel along the secondary scanning direction, wherein the area of ​​a row of heating resistors close to the paper feed side is larger than the area of ​​the heating resistors close to the paper discharge side; the control IC is used to control the on / off state of a single heating point in the heating resistors, and the control signal end of the control IC is connected to a multi-color printing time calculation allocation unit, and the multi-color printing time calculation allocation unit is provided with a theoretical duty cycle and color development time calculation module, a printing mode judgment module, a high color development temperature printing control logic signal generation module, and a low color development temperature printing control logic signal generation module, wherein the theoretical duty cycle and color development time calculation module is connected to the printing mode judgment module, and the output end of the printing mode judgment module is respectively connected to the high color development temperature printing control logic signal generation module and the low color development temperature printing control logic signal generation module; If the current printing is of a high color development temperature, the pulse control signal output by the control IC uses a larger duty cycle to make the printing temperature higher and the time shorter, and judge whether the single-row printing time is sufficient. If the single-row printing time is sufficient, the two-row rotation printing method is adopted. If the single-row printing time is insufficient, the double-row simultaneous printing method is adopted. When performing multi-color printing under low color development temperature conditions, a smaller duty cycle is used to make the printing temperature lower and the time longer.

2. A thermal print head with double-row heating elements according to claim 1, characterized in that: The size of the heating resistor near the paper feed side in the double row heating resistor is set according to normal specifications based on the resolution, and the area of ​​the heating resistor near the paper discharge side is 60-90% of the size of the heating resistor near the paper feed side.

3. A thermal print head with double-row heating elements according to claim 1, characterized in that: The area of ​​the heating resistors on the paper discharge side of the double-row heating resistors is 80% of the size of the heating resistors on the paper feed side.

4. A thermal print head with double-row heating elements according to claim 1, characterized in that: The spacing between the double-row heating resistors is L, L≤1mm, and the larger the L value is, the larger the size of the second row of heating elements is.

5. The thermal print head with double-row heating elements according to claim 1, characterized in that: The multi-color printing time calculation and allocation unit is also provided with a bad pixel energy compensation module, which is respectively connected to the high color development temperature printing control logic signal generation module and the low heating temperature printing control logic signal generation module.

6. A multi-color printing method using a thermal print head with double-row heating elements, characterized in that: When the thermal print head with double-row heating elements as claimed in any one of claims 1 to 5 is applied to multi-color printing, the double-row printing time difference △T is calculated according to the spacing L of the double-row heating resistors and the printing speed V, △T=L / V, and the double-row heating elements are controlled by IC to print corresponding content, and the following steps are performed: Step 1: According to the color temperature T at the current point, combined with the temperature differential formula, obtain the required theoretical color duty cycle α and color time t A , t A is the sum of the total opening time of multiple cycles of the current heating point, where the temperature rise and fall differential formula is: C dT + AT dt = Q dt; where C is the heat capacity (J / K), T is the color temperature (K), A is the thermal diffusion coefficient, A = 1 / Rth (W / K), t is the heating time of each cycle of the current heating point (s), that is, the voltage width in the pulse control signal, and Q is the heating power (W); the color duty cycle α is based on the temperature rise to the color temperature, and the color time t A The saturation of the printed color is used as the standard, which can be obtained based on the printing time and concentration curve; Step 2: The printing mode determination module determines the current printing mode, which includes high color development temperature color printing and low color development temperature color printing. If the high color development temperature color printing is over 120°C, continue to step 3; otherwise, it is a low heating temperature printing mode, and continue to step 4; Step 3: When printing with high color temperature, the pulse control signal output by the control IC adopts a large duty cycle α b At this time, under the pulse control signal, the heating temperature of a single heating point of the heating resistor is higher, but the opening time is shortened, which specifically includes the following steps: Step 3-1: Determine the duty cycle α of the pulse control signal b , α b =N·α, the coefficient N is determined according to the color temperature, and N is based on the color temperature reached by a single pulse; Step 3-2: Determine the duty cycle α b In this case, is the single-row printing time sufficient? If the duty cycle α b Output single-row printing time t b ≤Actual printing cycle t c , it is judged that the time is sufficient, where t b is the total Ton time in the pulse, t c In order to meet the printing time required for printing saturation, at this time, two rows of alternating printing are adopted, that is, interlaced printing. At this time, the pulse control signal parameters of the two rows of heating resistors are the same. After one row of heating resistors receives the printing control data of odd rows, the other row of heating resistors receives the printing control data of even rows. The thermal efficiency of the thermal printing device is higher, which can avoid the damage of the heating element due to the accumulation of temperature at a single point, and can also effectively avoid the problem of blooming caused by temperature accumulation; Step 3-3: If the single-row printing time is insufficient, t b >t c , then the double-row printing mode is adopted. At this time, the printing time t of the row of heating resistors close to the paper feeding side is d The total printing time t greater than this color temperature A 55% of which t d It is calculated based on the effective time in the pulse to avoid the blurring problem caused by temperature accumulation. At this time, the two rows of heating resistors correspond to the same area of ​​the printing paper and print repeatedly; Step 4: When printing at low color temperature, the pulse control signal output by the control IC uses a small duty cycle α s , making the printing temperature lower and the time longer, α s =M·α, coefficients M, M are based on the color development temperature reached by a single pulse, and a double-row printing mode is adopted, that is, two rows of heating resistors are driven by the same printing data and print the same content in the same position one after another to complete the printing work, and the printing time of the row of heating resistors close to the paper feed side is greater than 50% of the total printing time of this color development temperature.

7. A multi-color printing method using a thermal print head with double-row heating elements according to claim 6, characterized in that: In step 3-3, if the energy for single-row printing is insufficient, double-row simultaneous printing is adopted. The printing time ratio of the double rows is such that the printing time of the heating resistor of the front row, i.e., the side close to the paper feed, is greater than 55% of the total printing time, and the duty cycle of the front-row pulse control signal is greater than the duty cycle of the rear-row pulse control signal.

8. A multi-color printing method using a thermal print head with double-row heating elements according to claim 7, characterized in that: In step 3-3, the duty cycle of the front pulse signal is set to 20%~70%, based on the single pulse reaching the color development temperature; the duty cycle of the rear pulse signal is set to 15%~60%, based on no blurring.

9. The multi-color printing method of a thermal print head with a double-row heating element according to claim 6, characterized in that: When printing the color with low color development temperature in step 4, the printing time ratio of the double rows makes the first row slightly greater than 55% of the total printing time, and the duty cycle of the pulse control signal of the first row is greater than the duty cycle of the pulse control signal of the rear row.

10. The multi-color printing method of a thermal print head with a double-row heating element according to claim 6, characterized in that: In the double-row printing mode in step 3 or step 4, if the resistance of a heating element in any one of the two rows of heating resistors increases or is damaged, the point at the corresponding position in the other row is used to compensate the bad point for energy. Specifically, the output energy of the two rows of heating resistors is redistributed according to the increase in resistance, where the total output energy of the good point at the corresponding position = the original output energy of the good point + the compensation energy, and the compensation energy = the output energy of the damaged point - the actual output energy of the damaged point, so as to avoid printing white streaks or white lines due to a bad point as much as possible.

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