JP3026289B2 - Manufacturing method of thermal head - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of manufacturing a thermal head used for a thermal printer or a facsimile as an output device of a word processor, a personal computer or the like. The present invention relates to a method for manufacturing a thermal head.

[0002]

2. Description of the Related Art Conventionally, thermal heads have been widely used because they have advantages such as low noise during printing and easy handling because no developing and fixing steps are required. In such a thermal head, a heating element for connecting them is formed between a plurality of individual electrodes arranged in a row on an insulating substrate and a common electrode arranged corresponding to the tip of the individual electrodes. Then, electric power is supplied between the selected individual electrode and the common electrode to cause the heating element in that portion to generate heat, thereby performing thermal recording (printing). by the way,
If the resistance value of each heating element disposed between each of the individual electrodes and the common electrode (that is, the heating element corresponding to each print dot is not uniform, a difference occurs in the temperature of the heating element when heat is generated. When printing is performed on thermal transfer paper or the like, density unevenness occurs in the printed “character” or “figure.” In order to prevent the occurrence of the density unevenness, conventionally, the resistance of the heating element corresponding to each of the dots has been known. This method utilizes the property that when a predetermined electric field is applied within a range that does not cause resistance breakdown in the heating element, the resistance value of the heating element decreases according to the intensity of the electric field. As a conventional technique for equalizing the resistance value of such a heating element, for example, Japanese Patent Application Laid-Open No. 61-83053 is known. Is constant and the voltage In this publication, a trimming pulse having a constant width and a different voltage value is applied to a heating element as an example. What is done is described.

The device described in the embodiment measures the initial resistance value of the heating element corresponding to each dot on the insulating substrate, and when those initial resistance values are larger than the target resistance value, the heating element is measured. Is applied with a predetermined voltage VO to reduce the resistance value of the heating element. If this reduced resistance value is still greater than the target resistance value R0,
A voltage VO + Δ obtained by adding ΔV to the predetermined voltage VO.
By applying a V trimming pulse, the resistance value of the heating element is further reduced. If the further reduced resistance value is still larger than the target resistance value R0, the predetermined voltage V
A trimming pulse of a voltage VO + 2ΔV obtained by adding O to 2ΔV is applied to further reduce the resistance value of the heating element. Thus, the resistance value of the heating element becomes the target resistance value R0.
Until it falls below, the voltage VO + nΔ added by ΔV
A trimming pulse of V is applied.

However, even if the resistance values are made uniform by applying the trimming pulse to the heating elements as described above, the resistance values of the heating elements vary during the long-term use of the thermal head. Would. This is because the heating element immediately after being formed on the insulating substrate surface is unstable and its resistance value changes with time, but the heating element whose resistance value is uniformed by the trimming pulse still has the same resistance value. Probably because of instability.
Therefore, even with a thermal head that uses a heating element whose resistance value has been uniformed by precious trimming, the resistance value decreases over time, causing variations, and a portion printed with a heating element having a large reduction in resistance value has a reduced amount. The print density is higher than that of the portion printed by the small heating element. Then, density unevenness occurred on the printed matter. Therefore, a method of performing thermal annealing to suppress the resistance value fluctuation after trimming (JP-A-3-266650) and a method of performing trimming for each half dot (JP-A-63-5955).
5) have been proposed.

[0005]

However, even if the trimming is performed based on the above proposal and the trimming accuracy is reduced to ± 1% or less, each of them is effective for improving the image quality, but it is still effective. Density unevenness occurred for each bit (for each print dot). Thus, the present inventor has conducted research for the cause investigation, and found the fact shown in FIGS. In FIG. 9, the horizontal axis represents the sample number of the resistor trimmed to a predetermined target resistance value Ro.
The vertical axis indicates the temperature resistance coefficient TCR (unit: ppm). As shown in FIG. 9, even if trimming is performed to make the resistance values of the respective heating elements equal to the target resistance value Ro,
The temperature coefficient of resistance differs between samples. Therefore, even when the resistance values are uniform at room temperature, the resistance value differs for each sample at the temperature (220 ° C.) at which the heating element reaches the actual printing temperature (hereinafter referred to as “actual use temperature”), and the heating value varies. Has occurred. As described above, even if the resistance values of all the heating elements are aligned with high accuracy at room temperature, there is a difference between the resistance values of the heating elements at the actual use temperature ().
In this case, each heating element varies in the amount of generated heat,
The temperature also varies.

FIG. 10 shows a drop width (Ri-Rt) / Ri when a trimming pulse is applied to reduce the resistance value of a heating element from an initial resistance value Ri to a resistance value Rt after trimming, and a temperature resistance coefficient (hereinafter referred to as "TCR"). "Is also described)). In FIG. 10, the horizontal axis indicates the drop width (Ri−Rt) / Ri (unit is “%”), and the vertical axis indicates the temperature resistance coefficient (unit is “ppm”). That is, FIG. 10 shows that the temperature resistance coefficient TCR of the resistor without trimming is about -90 ppm on average and about -100 ppm on minimum, but the TCR linearly increases as the trimming width increases. Shows that the TCR of the resistor dropped by 50% by trimming becomes about 0 ppm.

As described above, even if the resistance values of all the heating elements are aligned with high accuracy at room temperature, there is a difference in resistance value at a high temperature in actual use. The difference is caused by a change in the temperature resistance coefficient TCR according to a drop width (Ri−Rt) / Ri when the resistance is reduced by trimming from the initial resistance Ri to the resistance Rt after trimming. I do. Therefore, even if the resistance values of all the heating elements are aligned with high accuracy at room temperature, the temperature resistance coefficient TCR is different, so that the actual use temperature state (the temperature state during actual printing;
(20 ° C.), the resistance value varies.
The amount of heat generated for each heating element changes significantly. (Please check the following)

[0008] Due to the variation of the resistance temperature coefficient, even if the resistance value of the heating element is set to the same resistance value at normal temperature, a resistance value difference occurs in an actual use temperature state. The maximum value of this resistance difference is empirically about 2.5%. 1% difference in resistance
In this case, the influence on the picture room starts to occur, so that the resistance value is not negligible. The approximate value of the resistance difference can be predicted by the following calculation. The initial resistance of the heating element is Ri, and the resistance at room temperature (20 ° C.) after trimming is R.
When t, the resistance value in the actual use temperature state (220 ° C.) after trimming is R, and the resistance temperature coefficient is TCR, the following equation is established. R = Rt (1 + TCR × 200) In this equation, Rt is constant and the maximum value of TCR is 0,
Assuming that the minimum value is -100 ppm, the value of R when TCR is 0 is R = Rt, and the value of R when TCR is -100 ppm is R = Rt (1-0.02) = 0.98 Rt Becomes Therefore, when the value of TCR is 0, -10
The difference in R at 0 ppm is 0.02 Rt. This 0.
The ratio of 02Rt to 0.98Rt is (0.02Rt /
0.98 Rt) = about 0.02 = about 2%. Therefore, Rt of the resistance value at room temperature after trimming is not made uniform,
In consideration of the drop width (Ri-Rt) / Ri, it is necessary to perform trimming so that the resistance value in an actual use temperature state becomes uniform.

The present invention has been made in view of the above circumstances and the results of consideration,
An object of the method of manufacturing a thermal head is to describe the following (A11). (A11) To reduce the density unevenness of the print image quality by making the resistance values of the heat generating elements of the thermal head uniform at the actual use temperature state.

[0010]

Next, the configuration of each invention of the present application devised to solve the above problem will be described.
In order to clarify the correspondence between the components of the present invention and the components of the embodiment described later, those of the components of the embodiment which are enclosed in parentheses are added. The reason why the present invention is described in correspondence with the reference numerals of the embodiments described below is to facilitate understanding of the present invention, and not to limit the scope of the present invention to the embodiments.

In order to solve the above-mentioned problem, the first application of the present application
The method of manufacturing a thermal head according to the present invention is a method of manufacturing a thermal head, comprising: a plurality of individual electrodes (4a) on a surface of an insulating substrate (4); a common electrode (4b) arranged corresponding to the tip of the individual electrodes; ) And a plurality of heating elements (4c1) connecting between the common electrode (4b) and each heating element connecting between the individual electrode (4a) and the common electrode (4b).
In the method for manufacturing a thermal head having a trimming step of applying a trimming pulse to (4c1) to lower each resistance value of each of the heating elements (4c1) and equalize the resistance values of the plurality of heating elements (4c1), (A1) each of the heating elements (4c
Applying the trimming pulse while measuring the resistance value of 1) in an actual use temperature state which is reached when it is actually used, and making the resistance values uniform.

A method of manufacturing a thermal head according to a second invention of the present application is characterized in that the method of manufacturing a thermal head according to the first invention has the following requirement (A2). (A2) The actual operating temperature condition is determined by the heating elements (4
To be realized by heating the insulating substrate (4) on which the c1) is formed.

Further, a method for manufacturing a thermal head according to a third invention of the present application is characterized in that the method for manufacturing a thermal head according to the first invention has the following requirement (A3). (A3) The actual use temperature state is determined by the heating elements (4
A pulse used in actual printing is applied to c1), and the temperature is increased by the heat generated by each heating element (4c1) at that time.

[0014]

Next, the operation of the present invention having the above-mentioned features will be described. The method for manufacturing a thermal head according to the first invention of the present application having the above-mentioned features is a method for manufacturing a plurality of individual electrodes (4a) on a surface of an insulating substrate (4) and a common electrode arranged corresponding to the tips of the individual electrodes. (4b) and a plurality of heating elements (4c1) connecting between the individual electrode (4a) and the common electrode (4b).
And are formed. Next, while measuring the resistance value of each heating element (4c1) connecting between each of the individual electrodes (4a) and the common electrode (4b) in an actual use temperature state reached when it is actually used, A trimming pulse is applied to each heating element (4c1) to make the resistance values uniform. Then, the resistance values of the respective heating elements (4c1) become uniform in the actual use temperature state even if they vary at room temperature. Therefore, printing with uniform density can be performed.

[0015] The second aspect of the present application having the above-mentioned features.
In the method for manufacturing a thermal head according to the invention, in the method for manufacturing a thermal head according to the first invention, the actual use temperature state is realized by heating an insulating substrate on which the heating elements () are formed. It is easy to realize.

Further, the method of manufacturing a thermal head according to the third invention of the present application having the above-described features is the same as the method of manufacturing a thermal head of the first invention, except that the heating elements (4c
A pulse used in actual printing is applied to 1), and the actual use temperature state is realized by a temperature rise due to heat generation of each heating element (4c1) at that time.

As described above, in each method of manufacturing the thermal head of the invention of the present application having the above-described features, the temperature of each heating element (4c1) is set at the actual operating temperature which is reached when it is actually used. The trimming pulse is applied while measuring the resistance value to make the resistance value equal to the target resistance value (target resistance value in the actual use temperature state) Ro. In this case, although the resistance value Rt of each heating element after trimming at room temperature varies, the resistance value in the actual use temperature state is almost equal to Ro. As described above, since the values of the heating elements (4c1) are substantially uniform (the target resistance value Ro in actual use),
The heating value of each heating element (4c1) is uniform. For this reason, the density unevenness of the print image quality can be reduced. In this case, the heat value Q of each heating element (4c1) is expressed by the following equation (1). Q = (V ² / Ro) × t (1) V: voltage Ro: target resistance value in actual use t: pulse application time

[0018]

【Example】

(Embodiment 1) Next, Embodiment 1 of the present invention will be described with reference to the drawings. In FIG. 1, a thermal head H for performing thermal recording (printing) on a thermosensitive recording paper B conveyed along the outer periphery of a platen roller A includes a support plate made of a metal material having a high thermal conductivity such as aluminum or cast iron. 1, an insulating substrate 4 made of ceramic and a printed wiring board 5 made of plastic are provided on the upper surface of the support plate 1 on the left and right portions in FIG. It is stuck. In FIG. 1, an IC is disposed on the upper surface of the printed wiring board 5 near the insulating substrate 4, and a wiring 5a is provided by printing on the right side of the IC in FIG. The input end side (the right side in FIG. 2) of the wiring 5a is connected to a socket 7 as a drive signal input terminal via a lead wire 6 penetrating the printed wiring board 5. The IC provided on the printed wiring board 5 is connected to wires 5 a of the printed wiring board 5 and individual electrodes 4 a of the insulating substrate 4 by wires 8 and 9.

As shown in detail in FIGS. 2 and 3, the insulating substrate 4 has a plurality of individual electrodes 4a on its surface (ie, upper surface) in the length direction of the insulating substrate 4 (ie, in the main scanning direction). They are arranged along X. A common electrode 4b is provided along the main scanning direction X. The common electrode 4b is provided with a main body 4b1 extending along the main scanning direction X and a sub-scanning sub-scanning from the main body 4b1. And a plurality of connecting portions 4b2 extending in the direction Y. The individual electrodes 4a and the connection portions 4b2 of the common electrodes 4b are alternately arranged along the main scanning direction X. These alternately arranged individual electrodes 4a and common electrode connection portions 4b2 are formed by heating elements 4c1 and 4c1 constituting heating resistors (heating units) for one print dot of a belt-shaped heating resistor 4c extending in the main scanning direction. 4c
1, ... (see FIG. 3). Figure 1 again
2, the IC and the wires 8 and 9 are sealed by a resin 10 and protected by a cover member 11. The thermal head H includes the reference numerals 1 to
The heating elements 4c1 are pressed against a thermosensitive recording paper B on the platen roller A to perform thermal recording.

Next, an embodiment of the method for manufacturing the thermal head will be described. As shown in FIG. 3, the electrodes 4a, 4b
The insulating substrate 4 on which the heating element 4c1 is formed is manufactured by a conventionally known manufacturing technique such as a screen printing technique. The resistance value of each of the heating elements 4c1 of the insulating substrate 4 is trimmed by a trimming device shown in a block diagram of FIG.

In FIG. 4, a prober 21a is in contact with an electrode pad (not shown) of the individual electrode 4a (connection terminal used for connection with the wire 9 when assembling a thermal head later). , 21a,... A multiplexer relay 22 is connected to the prober 21. The prober 21 and the multiplexer relay 22 are controlled by a computer 23, and the heating elements 4c1, 4c1,. .. Are configured to select one bit (a heating element for one print dot). The multiplexer relay 22 is configured to be selectively connected to an output terminal of a pulse generator 25 or an input terminal of a resistance measuring device 26 via a changeover switch 24 controlled by the computer 23. The insulating substrate 4 of the thermal head is maintained at 220 DEG C. by the heater 27, which is equal to the temperature during actual use.

Next, the operation of the trimming device shown in the block diagram of FIG. 4 will be described with reference to the flowchart of FIG. First, the insulating substrate 4 is heated by a heater 27, and the respective heating elements 4c1 formed on the surface thereof are heated to the actual use temperature (the temperature in the temperature state when actually used). This actual use temperature is 220 ° C. When a process (trimming flow) for trimming each of the heating elements 4c1 is started, the prober 21 is set in step S1.
Are brought into contact with the individual electrodes 4a, 4a,... And a number corresponding to the number of the probes 21 (for example, 128).
The initial resistance Ri of the heating element 4c1 is measured. Next, in step S2, n = 1 is set. Next, in step S3, a bit corresponding to n = 1 is selected. Next, in step S4, it is determined whether or not the resistance value is within a range of a predetermined target resistance value Ro. If no (N), the process moves to step S5. In step S5, the voltage value of the trimming pulse applied to the heating element 4c1 is calculated. The method of calculating this voltage value is described in, for example, the above-mentioned JP-A-61-83.
The method described in Japanese Unexamined Patent Application Publication No. 053 or Japanese Unexamined Patent Application Publication No. 1-271262 is adopted. Next, in step S6, a trimming pulse is applied to the heating element 4c1. Next, in step S7, the resistance value of the heating element 4c1 is measured, and the process returns to step S4. If the answer is yes (Y) in step S4, the process moves to step S8. In step S8, n = n + 1 is set. Next, in step S9, n
= No is determined. Where no is the individual electrode 4
This is a number obtained by adding 1 to the number of the probes 21a of the probe 21 contacting a. For example, if the number of the probes 21a is 128, no = 129. If no in step S9, the process returns to step S3. If yes, it is determined that the trimming of each heating element 4c1 connected to all the probes (for example, 128 probes) 21a has been completed, and the process returns to step S10. Move on. In step S10, it is determined whether the trimming of all bits (all the heating elements on the insulating substrate 4) has been completed. If no, the process returns to step S1, and if yes, the trimming ends.

When the thermal head of the above embodiment is actually used, each heating element 4c1 is kept at a substantially constant temperature during use.
Generates heat, for example, at 220 ° C. Although the resistance before use (resistance at room temperature) is different from the resistance during actual use,
In actual use, the resistance value obtained by the trimming, that is, the target resistance value Ro, is obtained, and the resistance value of each heating element 4c1 of the thermal head H is substantially uniform. Therefore, the heating value of each heating element 4c1 is also uniform. This is best shown in FIG. In FIG. 6, the numerical value on the horizontal axis indicates the sample number of the heating element 4c1, and the vertical axis indicates the measured value of the surface peak temperature (° C.) of the heating element 4c1. In the plot, white circles indicate examples of the present invention, and black circles indicate conventional products in which the resistance value after trimming was constant at room temperature. As can be seen from FIG. 6, the variation in the surface temperature was reduced to about half or less, and the density unevenness was significantly reduced when printing was actually performed. In the first embodiment, since the insulating substrate 4 is heated by the heater 27, the configuration of the heating means is easy.

(Embodiment 2) In Embodiment 1, the heater 27 is used to heat the heating element 4c1 to the temperature at the time of actual use. Next, Embodiment 2 in which the heating means is changed is shown in FIG. This will be described below. In FIG. 7, a prober 21 is a probe 21 that contacts an electrode pad (not shown) of the individual electrode 4a.
, and the prober 21 is connected to a multiplexer relay 22. The prober 21 and the multiplexer relay 22 are controlled by a computer 23, and are connected to the heating element through the probe 21a and the individual electrode 4a. Are configured to select one bit among 4c1, 4c1,..., And the multiplexer relay 22 is selectively connected to an output terminal of a pulse generator 25 via a changeover switch 24 controlled by the computer 23. The configuration is the same as that of the first embodiment, but the second embodiment does not use the heater 27 of the first embodiment but actually replaces the resistance measuring instrument 26 of the first embodiment. The difference is that a pulse current measuring device 28 is used. The actual pulse current measuring device 28 includes a measuring pulse generator for generating a pulse (the same pulse as a printing pulse) at the time of actual use (at the time of printing) and a current measuring device. The current measuring device uses a combination of a shunt resistor and an A / D converter.

In the second embodiment, since the actual printing pulse is used for heating, each heating element 4c1, 4c1 is used.
Are heated to the actual use temperature state, the current value at that time is measured, and based on the current value, each of the heating elements 4c1, 4c
The resistance values of c1... are measured, and heating elements 4c1, 4c1... having uniform resistance values are formed under the same conditions as in actual use. Therefore, it generates heat at a uniform temperature during actual use.
The heating element when the printing pulse is applied has a low temperature in the initial period of the printing pulse and a high temperature (actual operating temperature state) in the last period of the printing pulse. Therefore, the value in the last period of the print pulse is adopted as the current value for measuring the resistance value of the heating element. In this embodiment, each heating element 4c
The heating of 1,4c1 becomes the same as in the actual use, and the resistance value in the actual use temperature state can be made equal to the target resistance value Ro.

(Modification) The embodiment of the thermal head according to the present invention has been described in detail. However, the present invention is not limited to the first and second embodiments and is described in the claims. Various design changes can be made without departing from the invention. For example, the band-shaped heating element 4c1
8A and 8B, a plurality of individual heating elements 4c1, 4c1,... Are arranged in a row along the main scanning direction X, and the individual heating elements 4c are used.
The present invention can be applied to a thermal head in which a plurality of individual electrodes 4a, 4a... And a common electrode 4b are individually connected by 1, 4c1,. In Example 2, instead of using the print pulse as a heating element heating pulse and a resistance measurement pulse, a print pulse was used as a heating element heating pulse, and immediately after the print pulse, a separate resistance value measurement pulse was used. It is also possible to apply a pulse to the heating element.

The method of manufacturing a thermal head according to the present invention having the above-described structure has the following effect (A21). (A21) Since the trimming is performed so that the resistance value of each heating element becomes uniform in the actual use temperature state, the resistance value of each heating element in actual use becomes uniform. Therefore, the heating value of each heating element becomes uniform, the density unevenness of the printed matter is reduced, and the printing quality is improved.

[Brief description of the drawings]

FIG. 1 is a side sectional view showing a thermal head H manufactured according to a first embodiment of a method of manufacturing a thermal head of the present invention.

FIG. 2 is a perspective view of a main part of the thermal head according to the first embodiment.

FIG. 3 is a partially enlarged view of a main part of the thermal head according to the first embodiment.

FIG. 4 is an explanatory diagram of a trimming device used for manufacturing the thermal head.

FIG. 5 is a flowchart for explaining the operation of the trimming device of FIG. 4;

FIG. 6 is a diagram showing a surface peak temperature for each heating element.

FIG. 7 is a view showing another embodiment 2 of the trimming device.

FIG. 8 is a diagram showing another example of a thermal head to which the present invention can be applied. FIG. 8A shows a general individual facing type thermal head (in which a common electrode connection portion and an individual electrode facing the common electrode are individually heated). Thermal head connected with a resistor)
FIG. 8B shows a thermal head in which the common electrode connection portion is omitted.

FIG. 9 is a diagram generally showing a temperature resistance coefficient TCR of a heating element for each sample.

FIG. 10 is a graph showing the relationship between the resistance drop width of trimming and T.
It is a figure showing relation with CR (resistance temperature coefficient).

[Explanation of symbols]

4. Insulating substrate, 4a ... individual electrode, 4b ... common electrode, 4c1
... heating element, Ri ... initial resistance value, Ro ... resistance value in actual use.

──────────────────────────────────────────────────続 き Continuation of front page (56) References JP-A-4-80048 (JP, A) JP-A-2-214672 (JP, A) JP-A-63-157404 (JP, A) JP-A-63-157404 116870 (JP, A) JP-A-4-99654 (JP, A) JP-A-5-305722 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) B41J 2/335

Claims (3)

(57) [Claims] A plurality of individual electrodes and a common electrode disposed on the surface of the insulating substrate in correspondence with a tip of each of the individual electrodes;
After forming a plurality of heating elements that connect between the individual electrodes and the common electrode, a trimming pulse is applied to each heating element that connects between the individual electrodes and the common electrode, and the resistance value of each of the heating elements is adjusted. A method of manufacturing a thermal head having a trimming step of reducing the resistance values of the plurality of heating elements to equalize the resistance values of the plurality of heating elements, wherein the method includes the following requirement (A1): (A1) The trimming pulse is applied while measuring the resistance value at the actual use temperature state which is reached when it is actually used, and the resistance values are made uniform. 2. The method for manufacturing a thermal head according to claim 1, further comprising the following requirement (A2).
2) The actual use temperature state is realized by heating the insulating substrate on which the heating elements are formed. 3. The method for manufacturing a thermal head according to claim 1, further comprising the following requirement (A3).
3) The actual use temperature state is realized by applying a pulse used for actual printing to each of the heating elements, and increasing the temperature due to heat generation of each of the heating elements at that time.