JP2002059577A - Method of manufacturing thermal head and thermal recording apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method of manufacturing a thermal head of a common supply type to either end in which a difference of resistance value changes of heating elements generated in recording images is considerably small, and therefore high-quality images can be recorded for a long term without any image density irregularity caused by the difference, and a thermal recording apparatus using the same. SOLUTION: According to this method of manufacturing the thermal head of the common supply type to either end, a driving electricity is supplied from heating elements at the side of both ends in a horizontal scanning direction of the thermal head, and moreover, the resistance value of each heating element is changed beforehand by a predetermined value by applying a nearly uniform energy through a resistance value correction and a correction conforming to a voltage drop amount at a position in the horizontal scanning direction.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention belongs to the technical field of thermal recording using a thermal head, and in particular, obtains a high-quality image free from image density unevenness caused by a change in resistance even when used for a long time. The present invention relates to a method for manufacturing a thermal head and a thermal recording apparatus.

[0002]

2. Description of the Related Art Thermal recording is used as recording means in various printers, plotters, fax machines, recorders and the like. In addition, thermal recording does not require a wet development process and has advantages such as easy handling. Therefore, in recent years, large and high-quality images such as CT diagnosis, MRI diagnosis, and X-ray diagnosis have been demanded. In applications where this is used, use for image recording for medical diagnosis is also being studied.

[0003] As is well known, thermal recording uses a thermal head in which heating elements are arranged in one direction (main scanning direction), and a heating section of the thermal head is slightly pressed against a heat-sensitive material. While relatively moving in the sub-scanning direction orthogonal to the scanning direction, according to the recorded image, energy is applied to the heating element of each pixel to generate heat, thereby heating the heat-sensitive recording layer of the heat-sensitive material to record an image. I do.

[0004] Such a thermal head is generally
A heating element having a heating resistor and a switch element is connected in parallel between the power supply and the ground, so that the heating elements are arranged in the main scanning direction. For example, by turning on / off each switch element by a signal that is pulse width modulated according to the image data value (density data value) of each pixel, the corresponding heating element is equivalent to the pulse width of the pulse width modulated signal. Power is applied for a certain period of time to control thermal image recording by individual heat generating elements.

For connecting the power supply and the heating element in such a thermal head, a method of connecting a common electrode (common electrode) to the power supply using a flexible cable is known. This requires a flexible cable connection step and the like, and the configuration is complicated. On the other hand, as a configuration that has a small number of parts and a simple configuration and can be manufactured easily, as a result, the common electrode is formed by a wiring pattern to reduce the cost of the thermal head. A configuration in which a common electrode and a power supply are connected from both ends in the main scanning direction (hereinafter, referred to as a both-end common supply type) is known.

[0006]

However, in the thermal recording apparatus using such a thermal head, there is a problem that density unevenness occurs in a recorded image with the passage of time (image recording amount). The heating resistor constituting the heating element of the thermal head is annealed in accordance with the heating time and energy, and the resistance value decreases. The heating resistor, which is a heating element, generates a large amount of heat energy as the resistance value decreases, and the temperature of the heating element increases to increase the image density. The heat generation history of each heating element of the thermal head mounted on the thermal recording apparatus and performing image recording (how much heat is generated with respect to the recorded image = total heat generation = image recording amount) Therefore, the amount of change in the resistance value also differs for each heating element. Therefore, as the image recording is performed, a difference occurs in the amount of change in the resistance value of each heating element,
Image density unevenness occurs according to this difference.

As a method of preventing such image density unevenness caused by aging, the present applicant assigns a predetermined heating history to all the heating elements of an unused thermal head to thereby reduce the resistance value of the heating element in advance. A method of changing the amount by a predetermined amount has been developed, and this method has been previously proposed (see Japanese Patent Application Laid-Open No. 9-216395).

[0008] As disclosed in this publication, the change in the resistance value of the heating element of the thermal head is large at the beginning, but decreases at an accelerated rate as the total heat generation increases. for that reason,
By giving a uniform heating history to all the heating elements of the unused thermal head and changing the resistance values of the heating elements in advance, the change in resistance value can be greatly reduced thereafter, and each heating element can be reduced. The difference in resistance value change for each can be reduced, and as a result, there is no density unevenness caused by aging,
High-quality thermal image recording can be stably performed over a long period of time.

However, in the above-described thermal head of the common supply type at both ends, even when the method disclosed in the above-mentioned Japanese Patent Application Laid-Open No. 9-216395 is used, the resistance value of each heating element differs with the use (time) of the user. And as a result,
In some cases, image density unevenness due to this difference in resistance value occurs.

An object of the present invention is to solve the above-mentioned problems of the prior art, and to use a common electrode formed by a wiring pattern and to apply drive power from both ends in the main scanning direction to the arrangement of the heating elements. In a thermal head of the both ends common supply type, in which a power supply and a common electrode are connected so that power is supplied, the difference in resistance value change of each heating element due to the difference in the image recording amount of each heating element caused by use by the user is extremely large. A method for manufacturing a thermal head that is small, and therefore has no image density unevenness due to the difference in resistance value of each heating element, can perform high-quality image recording stably for a long time, and
It is an object of the present invention to provide a thermal recording apparatus using a thermal head manufactured by this manufacturing method.

[0011]

In order to achieve the above object, a method of manufacturing a thermal head according to the present invention includes a heating element arranged in a main scanning direction, and a common electrode connected to all heating elements. A method for manufacturing a thermal head that connects the common electrode and a power supply so as to supply drive power from heating elements on both ends in the main scanning direction, wherein the heating element is provided on both ends in the main scanning direction of the thermal head. Along with supplying the driving power, a substantially uniform energy is applied to each heating element, the resistance value of the heating element antibody being corrected and the correction corresponding to the voltage drop of the common electrode at the position in the main scanning direction. A method for manufacturing a thermal head, wherein the resistance of the heating element is changed by a predetermined value in advance.

In the method of manufacturing a thermal head according to the present invention, the application of the energy is performed by pulse width modulation, the position of the heating element in the main scanning direction is x, and the heating of the heating element after correcting the resistance value of each heating element. When the time is t _R (x), the correction term calculated by the quadratic expression of the position x is added to the heating time t _R (x) to calculate the heating time of each heating element. It is preferable to perform correction in accordance with the amount of voltage drop at the position in the main scanning direction. Further, when the total number of heating elements of the thermal head is N and the position x in the main scanning direction is indicated by 1 to N, When the total number N of heating elements is an even number, the heating element whose position x is 1 to N / 2 is represented by the following formula [1], and the heating element whose position x is (N / 2) +1 to N is The heating time t (x) is calculated by the equation [2], and the total heating elements are calculated. If N is an odd number, the position x. 1 to (N + 1) / 2 is the heat generating element by the following formula [1], the position x (N + 3) / heating elements 2~N the following formula [2]
It is preferable to calculate the heat generation time t (x). t (x) = t _R (x) + A (x−1) ² + B (x−1) + C Expression (1) t (x) = t _R (x) + A (N−x) ² + B (N− x) + C Equation [2] [In the above equations (1) and (2), A, B and C are constants]

Further, the thermal recording apparatus of the present invention provides a thermal recording apparatus equipped with a thermal head manufactured by the method of manufacturing a thermal head of the present invention.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, a method for manufacturing a thermal head and a thermal recording apparatus according to the present invention will be described in detail based on preferred embodiments shown in the accompanying drawings.

FIG. 1 is a conceptual diagram showing a cross section of an example of a thermal recording apparatus of the present invention, on which a thermal head manufactured by the manufacturing method of the present invention is mounted. The thermal recording device 10 is, for example,
A thermal image recording is performed on a thermal recording material such as a thermal recording film F (hereinafter, referred to as a film F) of a predetermined size such as a half-cut size. The film F is formed by a loading unit 14, a feeding and transporting unit 16, and a thermal head 18. A recording unit 20 for performing thermal image recording, and a discharge tray 22.

The film F has a heat-sensitive recording layer formed on one surface of a transparent polyethylene terephthalate (PET) support or the like.
A stack of about 0 sheets in a predetermined unit is accommodated in a dedicated magazine 24. The magazine 24 has a lid 26, is inserted into the inside of the thermal recording apparatus 10 from an insertion port 28 formed in the apparatus, and is positioned at a predetermined position of the loading unit 12 by a known means using a guide, a stopper, or the like. Will be loaded.

The supply and transport section 16 takes out the film F from the magazine 24 loaded in the loading section 14 and
0, and includes a sheet-feeding mechanism using a suction cup 30 for sucking the film F, a transport roller pair 32, a transport guide 34, a cleaning roller pair 36, an opening / closing mechanism (not shown), and the like.

In the thermal recording apparatus 10, when an instruction to start recording is issued, the opening / closing mechanism opens the cover 26 of the magazine 24, and one film F is taken out of the magazine 24 by the suction cup 34, and the transport roller pair 32. The film F supplied to the conveying roller pair 32 is conveyed to the cleaning roller pair 36 while being guided by the conveying guide 34, and while the dust and dirt adhering to the recording surface are removed by the upper cleaning roller in FIG. 20. When the film F to be used for recording is completely discharged from the magazine 24, the lid 26 is closed by the opening / closing means.

The recording section 20 includes a thermal head 18, a platen roller 38, conveyance guides 40 and 42, a discharge roller pair 44, a cooling fan (not shown) for the thermal head 18, and the like.

The thermal head 18 is, for example, 300d
The thermal image recording is performed at the recording (pixel) density of pi.
Heating element is in one direction (main scanning direction, perpendicular to the paper surface in Fig. 1)
And a heat sink fixed to the thermal head body. The platen roller 60 rotates at a predetermined speed while holding the film F at a predetermined position, sandwiches the film F together with the thermal head 18 (its glaze), and moves in a sub-scanning direction (arrow b direction) orthogonal to the main scanning direction. At a predetermined recording speed.

The film F transported from the cleaning roller pair 36 while being guided by the transport guide 40 is
With the glaze slightly pressed, the platen roller 60
And the thermal head 18 (glaze) and are conveyed. In parallel with this transport, the thermal head 18
By driving each heating element in accordance with the image data (recorded image), the heating resistor is heated, and the film F is heated accordingly to develop color and an image is recorded. The film F on which the image is recorded is conveyed to the discharge roller pair 44 while being guided by the conveyance guide 42, and is discharged to the discharge tray 22 as a hard copy on which the image is formed.

FIG. 2 conceptually shows a wiring diagram of the thermal head 18. The thermal head 18 has a common electrode (common electrode) common to all the heating elements, and connects the common electrode and a power supply such that driving power is supplied from the heating elements at both ends in the main scanning direction. (Hereinafter referred to as a common supply type at both ends).

In the illustrated example, as shown by hatching, a common wiring pattern constituting a common electrode is formed over the entire outer periphery of the main body of the thermal head 18 except for a part on the upstream side in the sub-scanning direction (the direction of arrow b in the figure). 46 (hereinafter, common pattern 4)
6) is formed. The heating element H includes a heating resistor R
And a switch element S such as an IC, which is used in a known thermal head. The common pattern 46 (that is, the power supply 48) and the ground G are connected in parallel, and N (H _{1 to} H _N ) are arranged in the main scanning direction (the direction of the arrow a). Note that the glaze is near the region indicated by the dotted line in the figure. In addition, the common pattern 46 and the power supply are located near the non-formed portion of the common pattern 46 on the outer periphery of the thermal head 18 (near both ends of the continuously formed common pattern 46 = near both ends of the common pattern 46 in the main scanning direction). And a connector 50 and 52 for connecting to the thermal head 18 of both ends common supply type.
Is composed.

The thermal recording apparatus 10 shown in FIG. 1 performs thermal image recording by pulse width modulation.
A signal that is pulse-width modulated according to image data (image density data) supplied from an image input device such as an RI,
By turning on / off the switch element S, the corresponding heating element H is energized for a time corresponding to the pulse width of the pulse-width-modulated signal, and a thermal image recording is performed by each heating element H.

Here, in the thermal recording apparatus 10 of the present invention, the thermal head 18 is made by the manufacturing method of the present invention, and gives a heating history to all the heating elements H in an unused state. Thus, the resistance values of all the heating elements H (the heating resistors R thereof) are changed by a predetermined amount in advance. Further, in the present invention, the heat generation history is substantially corrected by applying a resistance value correction of the heat generation low antibody R of each heat generation element H and correcting according to a voltage drop at a position of the heat generation element H in the main scanning direction. It is given by a uniform (hereinafter abbreviated) heat generation energy, thereby making the heat generation history of all the heat generation elements uniform and making the resistance value change uniform. In the illustrated example in which thermal recording is controlled by pulse width modulation, a constant driving current is supplied only for a time corrected according to the resistance value and the position in the main scanning direction, thereby making the heat generation history of all the heating elements uniform. I have.

Japanese Patent Application Laid-Open No. 9-216395 according to the present applicant
As disclosed in Japanese Unexamined Patent Publication, when a constant amount of heat is continuously supplied, the change in the resistance value of the heat element of the thermal head is substantially proportional to the logarithm of the heat generation time. That is, the change in the resistance value of the heating element is initially large, but decreases at an accelerated rate as time elapses, that is, as the total heat generation increases. Therefore, a predetermined heat generation history is uniformly given to all the heat generating elements by a method such as supplying a constant heat energy to all the heat generating elements of the unused thermal head for a predetermined time.
By changing the resistance value of the heating element by a predetermined amount, the subsequent change in resistance value can be greatly reduced, and the difference in resistance value change for each heating element can be reduced. In other words, by making a uniform change in the resistance value of all the heating elements of the thermal head in advance based on such a heating history, it is possible to reduce the change in the resistance value of each heating element caused by the use of the user and the disparity thereof. Thus, high-quality thermal image recording without density unevenness can be stably performed over a long period of time.

However, in the thermal head of the common supply type at both ends as in the present invention, even if all the heating elements generate heat under the same driving conditions, the applied heat energy, that is, the heating history is not uniform, that is, the resistance value change. Inconsistency. As a result, when the user
As the (thermal recording apparatus 10) is used, a different amount of resistance change occurs for each heating element in accordance with the difference in recording amount caused by aging, and as a result, a difference occurs in the resistance value of each heating element. Density unevenness may occur.

FIG. 3 shows an equivalent circuit of the thermal head 18. As described above, the thermal head 18 is a thermal head of the both ends common supply type, and the voltage V _H (hereinafter, referred to as a common voltage) at both ends of the common pattern 46 is equal. Here, the common pattern 46 has a resistance (hereinafter, referred to as a common resistance), and current flows to each heating element H according to the flow direction. That is, as indicated by the arrows in FIG. 3, the supplied current flows at both ends of the common pattern 46 in the main scanning direction, and the heating resistors R ₁ and R _N are applied to the common resistors r ₁ and r _N-1. A current decreased by an amount corresponding to the magnitude of the amount flowing into _N flows, and thereafter, similarly, as it goes to the center in the main scanning direction,
The current flowing through the common resistor r decreases.

Accordingly, in order to provide a uniform heating history to all the heating elements, it is necessary to correct the amount of energy to be supplied by the common voltage corresponding to the position in the main scanning direction, that is, the amount of energy drop. For example, in the illustrated example in which the heating element H is driven by pulse width modulation, it is necessary to correct the heating time according to this position.

Here, in order to estimate the current flowing through the common pattern 46, the following approximation is performed. In the case of a normal thermal head, the heating elements H are formed almost uniformly, and the resistance value of each heating resistor R (hereinafter, this resistance value is also R
(Shown by) is on the order of several percent. That is, R ₁ ≒ R ₂ ≒ R ₃ …... ≒ R _N-1 ≒ R _N ≒ R. The common pattern 46 is also formed uniformly over the entire area, and the resistance value r at each position can be considered to be equal. That is, r ₁近似 r ₂ ≒ r ₃ …... ≒ r _N-2 ≒ r _N-1 ≒ r.

Therefore, assuming that the common voltages V _{H at} both ends are equal, the heating elements H in the main scanning direction of the common pattern 46 are provided.
Is defined as x (hereinafter, referred to as position x), the distribution of the current flowing through the common pattern at this position x is symmetrical at the center as shown in the upper part of FIG. Can be approximated by a linear function as described below. I = ax + b (a and b are constants)

The amount of voltage drop ΔV (x) at the heating element H at each position x can be represented by the integral of the current I and the common resistance r. Therefore, as shown in the following equation and the lower part of FIG. , A quadratic function. ΔV (x) = ∫I (x) · rdx = (１ ／) arx ²
+ Brx + c (a, b and c are constants)

On the other hand, in the thermal head 18, the energy density E given to one dot by the heat generated by each heating element H can be expressed by the following equation. Here, t is the heat generation time, and L is the area of one dot. E = (V ² / R) × (t / L) In pulse width modulation, a heat-sensitive image corresponding to image data is usually recorded by changing the heat generation time t. In the thermal head 18 based on such pulse width modulation, performing the resistance value correction means performing correction so that the same amount of energy is applied to each heating element H (heating resistor R). That is, the energy density E is the voltage V
^Since it is proportional to ² , the resistance value of the low-pyrogenic antibody R is corrected by changing t in accordance with R so that t / R becomes constant.

However, as described above, in the thermal head 18 of the common supply type at both ends, a voltage drop occurs according to the position x. Therefore, the same energy cannot be applied only by resistance value correction.

Here, as is apparent from the above equation, the energy density E is proportional to the square of the voltage V. Therefore, considering the voltage drop ΔV (x), the energy density E becomes (V−ΔV (x) ) ² = V ² -2V · ΔV (x) + (Δ
V (x)) ² .

Since ΔV (x) is negligibly small as compared with the voltage V, the above equation can be considered as V ² −2V · ΔV (x). Therefore, the energy density E is 2V · ΔV (X) is considered to have decreased. From the above, in order to supply uniform heating energy to all the heating elements H and to provide a uniform heating history in the thermal head 18 of the common supply type at both ends, the resistance value of the heating resistor R must be corrected. , According to the position x of the heating element H, “2V · ΔV
(X) ", extra heat generation energy may be given.

As described above, in the thermal head of the both ends common supply type, the voltage drop ΔV at the position x
(X) can be represented by ΔV (x) = (１ ／) arx ² + brx + c. Therefore, in the case of the pulse width modulation, 2V · ΔV (x) = arVx ² + 2brVx + 2Vc, that is, = Ax ² + Bx + C... Is a constant).

In the both-end common supply type thermal head 18 driven by pulse width modulation, the voltage drop amount ΔV (x) at the position x of each heating element H increases from both ends in the main scanning direction to the center. What is necessary is just to increase the heat generation time t accordingly. Accordingly, assuming that the heating time of each heating element H after the resistance value correction is t _R (x), the heating element H at the position x (end to center) has the t _R as shown in the following equation [4]. If a predetermined current is supplied for a time t (x) obtained by correcting (x) according to the equation [3], a heat generation history can be given with uniform heat energy. t (x) = t _R (x) + Ax ² + Bx + C Equation [4]

Here, the common resistor r and the heating resistor R
Is uniform, the voltage drop Δ at the position x
V (x) is symmetric with respect to the center in the main scanning direction, that is, when x = i and x = N−i, the voltage drop amount ΔV
(X) is equal.

Therefore, when the total number of heating elements N is an even number using the above equation [4], the heating element H at the position x of 1 to N / 2 is expressed by the equation [1] t (x) = t _R (x) + A (x−1) ² + B (x−1) + C Expression (1), and the heating element H at the position x of (N / 2) +1 to N is obtained by the expression [2] t (X) = t _R (x) + A (N−x) ² + B (N−x) + C Equation (2) may be used to calculate the heat generation time t (x).

On the other hand, when the total number of heating elements N is an odd number,
Similarly, the heating element H whose position x is 1 to (N + 1) / 2 is
Formula [1] t (x) = t _R (x) + A (x−1) ² + B (x−1) + C Formula (1), and the position x is (N + 3) / 2 to N. H is calculated by the following equation: [2] t (x) = t _R (x)) + A (N−x) ² + B (N−x) + C (2) I just need.

In these equations, the constants A, B and C are the resistance of the common pattern 46 (common resistance),
It may be calculated in a design manner in accordance with the resistance of each heating resistor R, the voltage (common voltage) at both ends of the common pattern 46, and the like, and may be set experimentally using the calculated value.

In this way, by generating heat with a constant current for a time t (x) to all the heating elements H of the unused both-end common supply type thermal head 18, uniform energy is applied to all the heating elements H. The resistance value of the heating element can be changed by a predetermined amount by supplying a uniform heating history in advance. Therefore, according to the present invention, in the thermal head 18 of the common supply type at both ends, a difference in resistance value change of each heating element of the thermal head caused by use of the user can be reduced, and high image quality without density unevenness can be achieved. Thermal image recording can be stably performed over a long period of time.

In the present invention, there is no particular limitation on the amount of change in the resistance value (heating history) given to each heating element H of the thermal head 18 in advance, and the amount of change in the resistance value that can be caused by the user's use is the target. What is necessary is just to determine suitably so that it may become the predetermined range which can obtain the image of image quality. In other words, the amount of change in the resistance value to be given in advance, that is, the heat generation energy and the time to give it, may be determined from the relationship between the resistance change amount that causes the density unevenness and the time for maintaining the predetermined image quality. Since changing the resistance value of each heating element of the thermal head in advance leads to deterioration of the thermal head,
The amount of change must be determined in consideration of this, but the change in resistance value given to the heating element in advance is preferably about 3%.

In the manufacturing method of the present invention, such a heating history of the heating element may be given in a state where the thermal head is completed after all the protection layers and the like of the heating element are formed. The thermal head may be provided in an unfinished state, such as before forming the first layer. Also, when giving the heat generation history after the completion of the thermal head,
The heat generation history may be given after being mounted on the thermal recording apparatus 10.

Although the method of manufacturing a thermal head and the thermal recording apparatus of the present invention have been described in detail above, the present invention is not limited to the above embodiments, and various improvements and modifications can be made without departing from the gist of the present invention. Of course, you can do it.

[0047]

As described above in detail, according to the present invention, in a thermal recording apparatus using a thermal head of a common supply type at both ends, the change in the resistance value of the heating element (the resistance It is possible to prevent the occurrence of density unevenness of the image due to the change with time, and to output a high-quality image free of image density unevenness over a long period of time.

[Brief description of the drawings]

FIG. 1 is a conceptual diagram of an example of a thermal recording apparatus according to the present invention.

FIG. 2 is a view conceptually showing a wiring diagram of an example of a thermal head used in the thermal recording apparatus shown in FIG.

FIG. 3 is a diagram conceptually showing an example of an equivalent circuit of the thermal head shown in FIG.

FIG. 4 is a graph for explaining a voltage drop in each heating element of the thermal head.

[Explanation of symbols]

 REFERENCE SIGNS LIST 10 thermal recording device 14 loading unit 16 supply / transport unit 18 thermal head 20 recording unit 22 discharge tray 24 magazine 26 lid 28 insertion port 30 sucker 32, 40, 42 transport roller pair 34 transport guide 36 cleaning roller pair 38 platen roller 44 discharge Roller pair 46 Common (wiring) pattern 48 Power supply 50, 52 Connector S Switch element G Ground H Heating element R Heating resistor

Claims (4)

[Claims] 1. A heating element arranged in a main scanning direction and a common electrode connected to all heating elements. The common electrode is connected to the heating element at both ends in the main scanning direction so as to supply driving power. A method for manufacturing a thermal head for connecting to a power supply, comprising supplying drive power from heating elements on both ends of the thermal head in the main scanning direction, correcting the resistance value of a heating element antibody to each heating element, A thermal head characterized in that a substantially uniform energy is applied by performing a correction corresponding to a voltage drop of a common electrode at a position in a main scanning direction to change a resistance value of the heating element by a predetermined value in advance. Manufacturing method. 2. The method according to claim 1, wherein the application of the energy is performed by pulse width modulation, the position of the heating element in the main scanning direction is x, and the heating time after resistance value correction of each heating element is t _R (x). , The correction term calculated by the quadratic expression of the position x is calculated as the heating time t
_The method according to claim 1, wherein a correction according to a voltage drop at the position in the main scanning direction is performed by calculating a heating time of each heating element by adding the heating time to _R (x). 3. When the total number of heating elements of the thermal head is N and the positions x in the main scanning direction are 1 to N, if the total number of heating elements N is an even number, the position x is 1 ~ N
/ 2 is obtained by the following formula [1], and the position x is (N /
2) The heating elements of +1 to N are represented by the following formula [2], respectively.
The heat generation time t (x) is calculated, and when the total number of heat generation elements N is an odd number, the position x is 1 to
The heating element of (N + 1) / 2 is represented by the following equation [1], and the heating element having the position x of (N + 3) / 2 to N is represented by the following equation [2]:
The method for manufacturing a thermal head according to claim 2, wherein the heat generation time t (x) is calculated respectively. t (x) = t _R (x) + A (x−1) ² + B (x−1) + C Equation (1) t (x) = t _R (x) + A (N−x) ² + B (N− x) + C Equation [2] [In the above equations (1) and (2), A, B and C are constants] 4. A thermal recording apparatus equipped with a thermal head manufactured by the method for manufacturing a thermal head according to claim 1.