JP2805447B2 - Thermal head, method and apparatus for manufacturing 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 and an apparatus for manufacturing a thermal head, and more particularly to a method and an apparatus for adjusting a resistance value of a heating resistor of a thermal head.

[0002]

2. Description of the Related Art A thermal head converts a current application into Joule heat by a heating resistor to form a print on a thermosensitive recording paper or a thermal transfer ink sheet. This technology is used in a wide range of fields such as facsimile machines and printers.

Here, the general structure of a thermal head will be described with reference to FIG. In FIG. 7, a thermal head 10 has a glaze layer 2 for heat storage formed on an insulating substrate 1 mainly composed of alumina or the like, and is formed on the glaze layer 2 with a conductive material such as aluminum or gold. The common electrode 5 including the individual electrode 3, the common electrode comb-like portion 5c, and the common electrode portion 5a is formed by photo-etching the conductive film.

Thereafter, a heating resistor 4 is formed on the individual electrode 3 and the common electrode comb 5c, and the heating resistor 4 is formed on the common electrode comb 5c.
A common electrode pattern 5b for increasing current capacity is formed on the common electrode portion 5a. Further, a protective film 6 is formed on these upper layers to form a thermal head substrate.

FIG. 7B is an enlarged top view of the heating resistor 4. The heating resistor 4 is electrically connected to the individual heating resistor dots 4 a by the individual electrodes 3 and the common electrode comb portion 5 c. Is divided. If a current flows between the common electrode 5 and any individual electrode, Joule heat is generated at the heating resistor portion. If thermal paper is brought into contact with the heating resistor 4 and pressed by a platen roller, Joule heat is transmitted to the thermal paper and printing is performed.

At this time, the surface temperature of the heating resistor 4 is proportional to Joule heat, that is, thermal energy, and the print color density on the thermal paper side is proportional to Joule heat. Generally, Joule heat of a thermal head is calculated by the following equation. P = V ² / RE = P × T Here, P: power (W) V: applied voltage R: resistance value (ohm) E: energy (mj) T: conduction time (ms). For this reason, when the voltage is fixed, the heat energy E is inversely proportional to the resistance value, and when the resistance value is high, the power decreases and the heat energy also decreases.

Generally, the applied voltage is a fixed condition, and the energizing time T is made variable according to the individual resistance value of the thermal head attached to the printing apparatus, so that the thermal energy is adjusted to be the same. At this time, when the resistance value of the thermal head, especially the variation of the average resistance value among the individual thermal heads is small, the adjustment of the power-on time is unnecessary, and the adjustment of the assembly of the printing apparatus is simplified. For this reason, there is an increasing demand for reducing the variation in the average resistance value between the individual thermal heads.

Further, regarding the variation of the resistance value of one heating resistor dot 4a in the thermal head, a difference occurs in thermal energy according to the resistance value of one heating resistor dot 4a. When printing is performed on thermal paper, this difference in thermal energy appears as unevenness in printing color density.

Hereinafter, the cause of the resistance value variation will be described. In the case of a thick-film thermal head, the heating resistor 4 is generally formed by printing and firing a resistance paste (JP-A-53-9544) mainly composed of a ruthenium oxide-based metal and glass. Formed by

The resistance value of the heating resistor formed by the sintered film is represented by the following equation. R = ρ × L / (W × t) (Ω), where R: resistance value of the heating resistor ρ: specific resistance of the resistor (Ω-cm) L: length (cm) of the resistor, W: The width (cm) of the resistor and t: the thickness (cm) of the resistor.

In the above equation, even if L, W, and t are physically formed with high precision, ρ varies between the respective dots of the resistor, so that the resistance value varies. The bonding material of the resistor material has a variation in particle size of the main material such as ruthenium oxide and glass.
Inevitably occurs at the 10 ^-5 mm ³ level. Therefore, after the heating resistor is formed, an adjustment (trimming) is performed to reduce the variation in the resistance value of the heating resistor dot 4a in which the variation has occurred.

In the trimming, the protective film 6 is formed after the heating resistor is formed, and thereafter, a voltage pulse is applied to the heating resistor to reduce the resistance value, thereby reducing the variation in the resistance value. . The voltage pulse is applied after the formation of the protective film because the firing at the time of forming the protective film is about 8 times.
Since the temperature is raised to 00 ° C., the resistance value changes before and after firing, so that it is general to adjust the resistance value by applying a voltage pulse after the final firing, that is, after forming the protective film.

As an example of the conventional example, Japanese Patent Publication No.
As described in No. 3 and Japanese Patent Publication No. 2-29506,
Measure the initial resistance value of each dot of the heating resistor made of a binding material of ruthenium oxide-based metal and glass paste,
From the result, a dot having a resistance value higher than the target resistance value is selected, and a voltage pulse is applied to the selected dot,
Further, the resistance value is measured again, and for the dots whose resistance value has not decreased below the target resistance value from the result, trimming is performed by applying a voltage pulse with a higher voltage pulse, and the initial resistance value is reduced. By stopping the application of the voltage pulse to the dots having a resistance value lower than the target resistance value, the resistance value of the heating resistor having a resistance value equal to or more than the target resistance value is reduced for a plurality of heating resistors. A method for manufacturing a thermal head and a manufacturing apparatus for a thermal head, characterized in that the thermal head is set within a certain range equal to or less than the value, have been proposed.

The above operation is repeated until the resistance value becomes equal to or less than the target resistance value. Finally, the average value, the maximum value, the minimum value, the standard deviation, etc. of the resistance values of all the dots in the thermal head are calculated and printed out. ing. In addition, the voltage pulse to be applied is generated using a monostable multi-circuit, and the trimming is performed by applying the voltage pulse to the resistor while changing the pulse width and the pulse number of the applied voltage pulse according to the applied voltage. As described above, in the thermal head in which the variation in the resistance value is adjusted to be small by applying the voltage pulse, the unevenness of the printing density is small even in the printing on the thermal paper, and the printing quality is at a practical level.

[0015]

The adjustment of the resistance value of the heating resistor in the conventional method and apparatus for manufacturing a thermal head is performed by applying a voltage pulse to reduce the variation in the resistance value of the heating resistor dot group. Although it can be made smaller, since the heating resistor dot to which the voltage pulse is applied is selected, the voltage pulse is not initially applied to the dot having the target resistance value or less, and the dot to which the voltage pulse is applied is not applied. On the other hand, a dot to which a voltage pulse is not applied has a problem that the life of the dot with respect to the print pulse is short in actual printing after being incorporated into the printing apparatus.

By the way, with respect to a thermal head which does not cause print unevenness in gradation printing, which has been required in the market due to a variation in the resistance value in the head after application of a voltage pulse as a thermal head, the variation in the resistance value in the head is small. Although further reduction is necessary, in the conventional method and apparatus for manufacturing a thermal head, as a result of first measuring a resistance value, a dot having a predetermined value or less is selected so that a voltage pulse is not applied. The inner variation is limited to about ± 15%, and it is very difficult to manufacture a thermal head of ± 5% or less that meets the above requirements.

Particularly, in a dot portion to which no voltage pulse is applied, there is a problem that the resistance value difference between adjacent dots is not adjusted while being large, and a density difference occurs when printing on thermal paper. . Furthermore, in the voltage pulse applying device described above, the voltage pulse when the peak value of the voltage pulse is increased requires variable adjustment of the number of pulses and the pulse width, and the voltage pulse applying device and the operation command are complicated. there were. In view of the above problems, the present invention extends the life of the printing dots, reduces the variation in the average resistance value of the heating resistor dots in the thermal head and between the thermal heads,
An object of the present invention is to provide a thermal head having no printing unevenness, a method and an apparatus for manufacturing a thermal head.

[0018]

In the thermal head of the present invention, the heating resistor is mainly composed of a ruthenium oxide-based metal and glass, and before the resistance value adjustment, the appearance resistance of all dots of the heating resistor is adjusted. The value (initial resistance value) is made higher than the upper limit of the product average resistance value standard. After applying a voltage pulse at the time of actual printing to all of the heating resistor dots of the thermal head, a voltage pulse for adjusting a resistance value is applied in order to reduce an appearance resistance value (initial resistance value) to a target resistance value. I do. When the resistance value of the heating resistor dot does not reach the target resistance value by applying the voltage pulse, the voltage value of the voltage pulse for resistance value adjustment is increased and applied again, and when the resistance value reaches the target resistance value, the adjustment is performed. finish. The voltage pulse applied to lower the resistance values of all the heating resistor dots of the thermal head to the target resistance value is CP
It is generated by a charge / discharge circuit whose charge / discharge is controlled by U control.

[0019]

DESCRIPTION OF THE PREFERRED EMBODIMENTS In a method for manufacturing a thermal head according to the present invention, a thermal glaze layer for heat storage is formed on an insulating substrate mainly composed of alumina or the like. An individual electrode pattern is formed on the conductive film by a photoetching process. Thereafter, a heating resistor is formed on the electrode, and a common electrode for increasing current capacity is formed on the common electrode portion. Further, a protective film is formed on these upper layers to constitute a thermal head substrate. The above is
There is no difference from the configuration of the thermal head 10 shown in FIG.

According to the present invention, there is provided a thermal head, a method for manufacturing a thermal head, and a manufacturing apparatus therefor, wherein all the heat generating resistor dots of the heat generating resistor are prepared in advance to have a resistance value higher than the upper limit of the product average resistance value standard. There is a special feature in that a head substrate is prepared in advance. More specifically, as the material of the heating resistor 4, a resistance paste containing a ruthenium oxide-based metal material and a glass material as main components is used.
The sheet resistance (Ω / □) of the resistance paste is determined by the mixing ratio of the ruthenium oxide-based metal material and the glass material in the resistance paste. Naturally, if the heating resistor is formed using a resistor paste having a high sheet resistance, the dot resistance of the thermal head also increases.

The present invention makes use of this fact so that the lowest resistance value in the thermal head of the resistance value appearing after the formation of the protective film 6 of the heating resistor 4 becomes larger than the upper limit value of the product average resistance value standard. The heating resistor 4 is formed using a resistance paste having a resistance value.

This will be described in detail in comparison with the conventional example.
FIG. 4 shows the appearance resistance value (initial resistance value) of each heating resistor dot in the conventional thermal head and the resistance value distribution after voltage pulse application. As is clear from this,
Among the initial resistance values, dots Ra, Rb, and R having resistance values lower than Rmax, which is the upper limit of the product average resistance value standard.
c exists.

On the other hand, in the thermal head of the present invention, as shown in FIG. 5, the initial resistance value of each heating resistor dot all shows a resistance value higher than the upper limit Rmax of the product average resistance value standard. It is manufactured in advance so as to have a higher resistance value than Rmax.

As described above, by setting the initial resistance value higher than the upper limit of the product average resistance value standard, the resistance value of the heating resistor dot is reduced by applying a voltage pulse.
If to reduce variations and, unlike the the conventional apparatus, the applying voltage pulses to all the heating resistors dots unconditionally. The initial average resistance value is
It is preferable to increase the upper limit of the product average resistance value standard by 20% to 100%, but it is desirable to aim at a resistance value of about 30% increase, and it is desirable to aim for a resistance value of about 30%. Is selected.

For example, in the case of a standard thermal head having an average thermal head resistance value standard of 3000Ω, a heating resistor film of 3 μm, and a dot density of 8 dots / mm, the resistance paste selected is, for example, Tanaka Kikinzoku. A GZ-based paste manufactured by International Co., Ltd. having a sheet resistance value of 20 to 40 KΩ / □ is obtained by blending resistance pastes having different sheet resistance values.

Next, a method and an apparatus for adjusting (trimming) and measuring each dot resistance value of the thermal head which has been manufactured in advance to the resistance value will be described. FIG. 1 is a circuit block diagram showing an example of the trimming apparatus of the present invention. In the voltage pulse applying apparatus for performing the trimming shown in FIG. 1, the main CPU 11 measures a resistance value, designates a target resistance value for decreasing the resistance value by applying a voltage pulse, and calculates the measured resistance value of each heating resistor dot. An average resistance value, a maximum resistance value, a minimum resistance value, a standard deviation, a variation in adjacent resistance values, and the like are calculated, and a printout instruction is issued to the printer 12. At this time, the target resistance value is arbitrarily input from outside as a setting condition.

The CPUs 13 to 16 are the main CPU 1
The sub CPUs 13 to 16 are provided with sub-CPUs 13 to 16 for measuring the eight circuits, applying a voltage pulse, and instructing the voltage value of the voltage pulse. Put out. The voltage pulse generating circuits 17 to 20, which are controlled by the sub CPUs 13 to 16, respectively, charge the capacitors from the high-voltage power supply 54 as described later, and then discharge the charged charges to each dot to perform trimming. Voltage pulse is applied. 22 is the thermal head 1
A probing device, for example, a probe card, for connecting an electrode unit connected to each dot of 0 to each terminal of the device.

Next, the respective functions of the CPU in the apparatus will be described. The main CPU 11 and the sub CPU 1
3 to 16, a CPU 23 of a control system for performing mechanical operation control such as movement of the thermal head 10, a contact needle of the probe card 22, and an electrode pattern.
Recognition system CP for optically recognizing and aligning at 5
The device is constituted by U24. Hereinafter, a device that performs trimming by applying a voltage pulse to a resistor in these devices is generically called a trimming device.

Next, the resistance trimming operation based on the circuit block diagram shown in FIG. 1 will be described with reference to the flowchart shown in FIG. First, a thermal head substrate prepared in advance so that the dot resistance value of the heating resistor 4 is higher than the upper limit value Rmax of the product average resistance value standard is set 30 in the trimming device, and the probe card 22 and the thermal head 10 After the electrodes are aligned by recognition of the video camera 25, the contact needle of the probe card 22 is brought into contact with the electrodes, and the resistance value measurement 31 is performed.
The resistance value measurement at this time is performed by the main CPU 11 and the resistance measurement circuit 21. A DC pulse (low-voltage pulse application) having a maximum rated power is applied 32 based on the measured resistance value. The low-voltage pulse is a maximum rated power that is a guaranteed value of the DC pulse applied to the thermal head 10 during actual printing. A voltage based on the power is calculated from the measured resistance value, and the same pulse width and pulse cycle as the actual printing conditions are applied.

The purpose of applying the low voltage pulse 32 is as follows.
By applying a printing pulse at the time of actual printing, there is an aim of detecting and rejecting an object having a weak heat-resistant energy characteristic with respect to the actual printing condition of the heating resistor dot. Since the resistance value of a dot having a weak heat-resistant energy characteristic changes by 10% or more when a low-voltage pulse having the maximum rated power is applied, the following resistance value measurement 33 is performed, and the resistance value is compared with the resistance value measurement 31. Then, it can be determined whether there is a dot whose resistance value has changed by 10% or more.

This determination is made in the resistance value determination 34, and the processing is stopped for the thermal head that has changed by 10% or more, and is rejected 48 as a defective product. The rejected defective product is also measured with a resistance value 4 if necessary.
Perform Step 6.

Thereafter, a resistance value measurement 35 by the sub CPUs 13 to 16 and the resistance measurement circuit 21 is performed.
The measurement result is compared with the resistance value of the resistance value measurement 33 in dot units. The comparison is made by the probe contact determination 36. If there is a difference in the resistance value, the probe card 22
It is determined that the contact of the probe is poor, and the position of the contact needle of the probe is slightly moved as the re-probe 37, and the resistance value measurement 35 is performed again. If the result of the probe contact determination 36 is good, the process proceeds to the next voltage pulse application 40. Here, the initial voltage of a preset voltage pulse is applied to all the heating resistor dots.

The low-voltage pulse application 41 is performed after the voltage pulse application 40. In this case, too, the same energy of the maximum rated power as described above is applied, and the energy is applied to confirm the stability of the dot resistance value after the voltage pulse application. Is done. If the resistance value of the resistor is in an unstable state due to the application 41 of the low-voltage pulse, the resistance value changes greatly by the application of the low-voltage pulse, and the unstable state can be detected. Then, the resistance value measurement 42 is performed. Here, the measurement is also performed by the sub CPUs 13 to 16 and the resistance measurement circuit 21.

Next, the measured resistance value is equal to the target resistance value R.
The judgment 43 as to whether or not it has decreased to 0
Perform at 6. As shown in FIG. 5, a target value between the center value R center and the upper limit value Rmax of the product average resistance value standard is set as the target resistance value R0. If the resistance value has not reached the target value, the process returns to the resistance value measurement 38, and after the resistance value measurement 38, the voltage pulse application determination 3
If the resistance value falls below the product standard at 9, it is rejected 47 as a defective product. Also in this case, the resistance value measurement 46 of the defective product is performed as necessary.

With respect to the other thermal heads, a voltage pulse of a voltage obtained by adding a preset voltage value to the voltage value of the voltage pulse applied first to the initial voltage is applied 40, and the above flow is repeated thereafter.

The above-mentioned flows 38 to 43 are repeated until the target resistance value R0 is reached. However, the voltage upper limit value of the voltage pulse is set in advance, and the voltage to be applied in the voltage pulse application judgment 39 reaches this voltage upper limit value. If so, reject 47 to end the trimming.

In these series of flows, the resistance measurement 3
8 to the resistance value determination 42, the sub CPUs 13 to 16 and the pulse generation circuit 17 are used to increase the processing speed of the apparatus.
20 are provided in one apparatus, and a plurality of resistor connection circuits are built in a set of sub CPUs and a pulse generation circuit at the same time. As a result, the voltage pulse application process can be performed on a plurality of heating resistors at the same time, so that the resistance value trimming can be completed in a very short time.

Next, the voltage value of the applied voltage pulse will be described. Since the heating resistor begins to decrease its resistance value linearly from the application of the voltage pulse of about 100 V, the voltage of the first applied voltage pulse is about 100 V. You have set. The voltage value of the voltage pulse is sequentially increased in accordance with the decrease in the resistance value. However, when the voltage becomes about 800 V or more, the resistance of the heating resistor changes not to decrease but to increase. This is because the oxidation of the ruthenium oxide-based metal material having an internal composition proceeds with respect to the voltage value of the voltage pulse in the resistor, and the resistance value of the particles themselves increases.

The target resistance value R is increased by sequentially increasing the voltage pulse.
When the value becomes O or less, the resistance value measurement 44 is performed. The resistance value measurement is processed by the main CPU 11, and thereafter, a low-voltage pulse application 45 is performed.
Here, the voltage value of the maximum rated power is set for the resistance value of the resistance value measurement 44, and a low voltage pulse is applied 45. Here, the number of applied low voltage pulses is larger than the number of applied low voltage pulses 41. Further, as a final step, a resistance value measurement 46 is performed by the main CPU 11, and an average resistance value, a maximum resistance value, a minimum resistance value, a standard deviation , a difference between adjacent resistance values, and the like are calculated from the resistance values, and are printed out to the printer 12. You.

Due to these trimmings, as shown in FIG. 5, the initial resistance values R1, R2, R3... Rn before the application of the voltage pulse for adjusting the resistance value are equal to the upper limit value Rmax of the product average resistance value standard. Since the number of heating resistor dots is larger than that, all the heating resistor dots are designated by the main CPU 11 as the heating resistor dots to which the voltage pulse is to be applied in the resistance value measurement 33. At this time, the target resistance value R0 is specified, and an intermediate value between the center value R center and the upper limit value Rmax of the product average resistance value standard is set as the target value.

As the voltage value of the applied voltage pulse for adjusting the resistance value, a voltage value to be added per one time is set in advance, and is fixed. For this reason, even when approaching the target resistance value, the voltage value under the fixed condition is added to the previous voltage value and a voltage pulse is applied. Since the resistance value is slightly lower, the target resistance value is set to the center value R center or more in this way. It is to be noted that the difference of the final resistance value from the target value can be further reduced by decreasing the value of the addition voltage value as the added voltage value approaches a target resistance value instead of being fixedly set.

Here, looking at the variation of the initial resistance value of the present invention and the conventional example, in the conventional method, as shown in FIG. 6, the initial resistance value of each thermal head is influenced by the variation of the resistance value in the thermal head. Since the variation in the resistance value after the application of the voltage pulse is determined, it is difficult to further reduce the variation in the resistance value in the thermal head.
On the other hand, in the present invention, as shown in FIG. 5, a fixed target resistance value is obtained irrespective of the initial resistance value, so that the variation in the resistance value in the thermal head can be made very small. Can also be reduced.

Thus, the product resistance value standard Rmax
The range width of -Rmin can be made smaller than that of the conventional method as shown in FIG. And
In the case of ± 15% variation in resistance value in the thermal head by the conventional trimming method, density unevenness during printing occurred.
According to the method of the present invention, it is possible to easily manufacture a product in which the resistance value variation in the thermal head required for gradation printing or the like is ± 5% or less.

Next, the problems concerning the life of the voltage pulse applied dot and the non-applied dot in the conventional system will be described, and the effectiveness of the system of the present invention will be clarified. The heating resistor is a binding material of a ruthenium oxide-based metal material and a glass material as described above, but in a sintered film state by firing,
The composition in the film is a state in which the glass material is filled between the ruthenium oxide particles, and the glass material is interposed between the ruthenium oxide particles and the sintered part so that the ruthenium oxide particles are in direct contact with each other. There are portions where contact resistance occurs between the particles.

Among these, the extremely thin portion of the glass material interposed between the ruthenium oxide particles is affected by the Joule heat between the particles due to the contact resistance between the particles when a direct current for printing is applied. Concentration occurs, the intervening glass material melts, and the contact resistance between the ruthenium oxide particles decreases. From this fact, the resistance value of the thermal head changes during actual printing, and if the resistance value changes by -10% or more, it is the same as the fact that the power of the applied printing DC pulse is increased by about 10%. As a matter of course, the applied heat energy increases, so that the life of the resistor is shortened. If the thermal energy is increased, the resistance value is greatly increased or the resistor is disconnected.

In the present invention, since the resistance value adjusting voltage pulse is applied unconditionally to all dots as described above, the composition inside the resistor is interposed by the application of the voltage pulse. Since the contact resistance between the ruthenium oxide particles is reduced in the very thin portion of the glass material by the application of the voltage pulse, the bonding between the particles is in a stronger state and can be extremely stabilized. Therefore, the service life is more stable than the conventional thermal head, and the service life can be extended.

Next, an example of the voltage pulse generating circuit will be described. As shown in FIG. 3, the voltage pulse generating circuit includes a charge / discharge capacitor 50, a discharge switch 51, and a charge switch 5.
2. Heating resistor dots 53 corresponding to the heating resistor dots 4a, and a high-voltage power supply 54.

In the voltage pulse generating circuit, the charge switch 52 is closed, and a DC voltage having a predetermined voltage value is connected from the high voltage power supply 54 to the charge / discharge capacitor 50 to charge the charge / discharge capacitor 50. The charging time at this time is to open the charging switch 52 by a timer circuit (not shown) and finish charging, then close the discharging switch 51 and discharge the heating resistor dots 53 through the contact needles of the probe card 22. Then, a voltage pulse is applied. When the voltage value of the voltage pulse is further increased and the resistance value of the heating resistor dot 53 is trimmed, the voltage at the time of charging the charging / discharging capacitor 50 is increased to increase the voltage of the voltage pulse. At this time, the capacity of the condenser 50 is suitably 100 to 200 pF, and optimally 150 pF.
Select a condenser.

The voltage V1 based on the discharge curve of the capacitor shown in FIG. 4 is applied to the discharge from the charge / discharge capacitor 50, that is, to the application of the voltage pulse to the heating resistor dot 53 as an example. Is obtained by the following equation. V1 = V × exp (−t / CR) where V1
Is the applied voltage (volt), V is the charge voltage (volt),
C is the capacitance of the capacitor (F), t is the time (second), and R is the resistance of the resistor (Ω). The above relationship is expressed as C = 150 pF,
FIG. 4 shows a discharge curve when R = 3000Ω. The time constant at the time of discharging is determined by C and R, and does not depend on the applied voltage. When the resistance value decreases, the time constant decreases, and the discharge time decreases.

On the other hand, regarding the applied energy of the voltage pulse, the energy stored in the capacitor is E = (１ ／) × QV = (１ ／) CV ² .
Here, E is energy (joules), Q is the amount of electricity (coulomb), C is the capacitance of the capacitor (farad), and the V applied voltage (volt).

Here, the energy increases in proportion to the square of the voltage. However, if the capacitance of the capacitor is reduced to a small value, the energy is not enough to damage the heating resistor. Generally, a thermal head used for a facsimile or the like generally has a resistance value of about 3000Ω, and the printing energy applied to the thermal head when printing is about 0.33 mj. In comparison, the discharge energy of the voltage pulse charged in the capacitor is
When the charging voltage is 400 V, it is 0.012 mj,
At 800 V, it is very small, 0.048 mj, which is about 1/7 or less of the applied energy during printing. Also, the upper limit of the voltage pulse applied at the time of resistor trimming does not exceed the above-mentioned 800 V, so that the resistor is not overloaded.

Further, since the energy of the voltage pulse is very small as described above, it is not necessary to change the capacity of the capacitor to change the discharge curve even if the voltage value of the voltage pulse at the time of trimming is increased. However, it is only necessary to increase the charging voltage of the capacitor and perform discharging sequentially, and a very simple configuration can be adopted as the voltage pulse applying device, and it is not necessary to control the voltage pulse waveform. The program is also simplified.

On the other hand, in the conventional method, the voltage pulse has a problem that the applied energy increases because a square wave from the monostable pulse generation circuit is applied to the resistor. Generally, a voltage pulse is applied 10 times in succession with a pulse having a pulse width of 1 μs. The energy applied to the resistor of the thermal head having a resistance of 3000Ω is when the voltage of the voltage pulse is 400 V (peak value). , The total energy for 10 pulses is 0.53 mj. This is 44 times (0.53 / 0.012 ≒ 44), which is much higher than the capacitor discharge method adopted in the present invention, and the applied energy value of 0.33 when printing with the thermal head is used.
It exceeds mj.

Therefore, if this voltage pulse is applied to the resistor, the heating resistor receives overload energy, and the resistor is destroyed, and the resistance value is greatly increased or the wire is disconnected. . For this reason, in the conventional method, when the voltage value is increased from several tens of volts of the initial application voltage of the voltage pulse application, the pulse width of the applied voltage pulse is reduced or the pulse width is reduced so that the applied energy is not increased. An essential condition is to make adjustments such as reducing the number so that the energy value does not increase. For this reason, the configuration of the trimming device is more complicated than that of the method of the present invention, and an additional processing program for changing the waveform of the voltage pulse is required. As described above, the difference between the method of the present invention and the conventional method is as described above, and the usefulness of the resistance value trimming of the method of the present invention is apparent.

[0055]

As described above, in the thermal head and the method and apparatus for manufacturing a thermal head according to the present invention, the thermal resistor in which the initial appearance resistance value of the heating resistor is made higher than the upper limit of the product average resistance value standard. In order to apply the voltage pulse for adjusting the resistance value unconditionally to all the heating resistor dots of the head, the variation of the average resistance value of the heating resistor inside the thermal head and between each thermal head can be made very small. In addition, it is possible to provide a thermal head free of uneven print density between resistor dots required for gradation printing.
Therefore, there is no need to adjust the print pulse width for each average resistance value of each thermal head when incorporating it into the printing device,
The work of assembling into the printing device is simplified.

When a voltage pulse is unconditionally applied to all the heating resistor dots from the beginning, the contact resistance between the ruthenium oxide particles is reduced even in a very thin portion of the glass material by applying the voltage pulse. The particle bonds between ruthenium oxides are in a strong state, and are stabilized without a change in resistance during actual printing. As a result, the printing life is stable without any difference between the resistor dots, and the life is prolonged.

Further, since the voltage pulse generation uses a capacitor charging / discharging method, even when the voltage value of the voltage pulse is increased and the resistance value is trimmed, the voltage pulse generation circuit structure is simplified and the trimming process is controlled. The method is also simple only by changing the voltage value, and the voltage pulse applying device can be simplified, so that the device price can be reduced, and as a result, the thermal head cost can be reduced.

[Brief description of the drawings]

FIG. 1 is a circuit block diagram of an embodiment of the present invention.

FIG. 2 is a flowchart of resistance value adjustment in the embodiment of the present invention.

FIG. 3 is an equivalent circuit diagram of a voltage pulse generation circuit used in the device of the present invention.

FIG. 4 is a diagram showing an example of a discharge curve of a voltage pulse generation circuit used in the device of the present invention.

FIG. 5 is a distribution diagram showing resistance value variations before and after application of a voltage pulse to the thermal head of the present invention.

FIG. 6 is a distribution diagram showing resistance value variations before and after applying a voltage pulse to a conventional thermal head.

FIG. 7 is a sectional view of a main part of a general thermal head and a plan view of a main part of a heating resistor part.

[Explanation of symbols]

4 Heating resistor 4a Heating resistor dot with higher initial resistance value than the upper limit of the product average resistance value standard 10 Thermal head 11 Main CPU 13, 14, 15, 16 Sub CPU 17, 18, 19, 20 Pulse generation circuit composed of discharge circuit 21 Resistance measurement circuit 22 Probe card

Claims (15)

(57) [Claims] In a thermal head having a heating resistor, the heating resistor is mainly composed of a ruthenium oxide-based metal and a glass material, and the appearance resistance value of all dots of the heating resistor is determined by a product average resistance value. A thermal head comprising a resistor paste having a sheet resistance value higher than a standard upper limit value. 2. A thermal head having a heating resistor, comprising a ruthenium oxide-based metal and a glass material as main components,
Further, a thermal head characterized in that at the stage before the resistance value adjustment, the appearance resistance value of all the dots of the heating resistor has a resistance value higher than the upper limit value of the product average resistance value standard. 3. A method of manufacturing a thermal head having a heating resistor, wherein a resistance paste containing a ruthenium oxide-based metal and a glass material as main components is used, and an appearance resistance value of all heating resistor dots is determined as a product average resistance value. A method for manufacturing a thermal head, comprising forming a heating resistor having a resistance value higher than a standard upper limit value. 4. The thermal head according to claim 3, wherein a resistance paste having a sheet resistance value giving an appearance resistance value having a resistance value higher than an upper limit of a product average resistance value standard is used as the resistance paste. Production method. 5. A voltage pulse at the time of actual printing is applied to all of the heating resistors, all resistance values of the dots are measured before and after the application, and a dot having a large variation is compared with each resistance value. The method for manufacturing a thermal head according to claim 3, wherein the detection is performed. 6. The method of manufacturing a thermal head according to claim 3, wherein a resistance value adjusting step of reducing an appearance resistance value to a target resistance value for all of the heating resistor dots is performed. 7. The method according to claim 6, wherein the resistance value adjusting step is a step of applying a voltage pulse for adjusting the resistance value. 8. The method of manufacturing a thermal head according to claim 6, wherein a voltage pulse for actual printing is applied to all of the heating resistor dots after the resistance value adjusting step. 9. The resistance value of the heating resistor dot is measured, and it is determined whether the measured resistance value has decreased to the target resistance value or has not reached the target resistance value. The thermal resistor according to claim 6, wherein the determined heating element dot finishes the resistance value adjustment, and the heating resistor dot determined to have not reached the target resistance value repeats the resistance value adjusting process again. Head manufacturing method. 10. The resistance value of the heating resistor dot is measured,
It is determined whether the measured resistance value has dropped to the target resistance value or the target resistance value has not been reached, and the heating element dot determined to have dropped to the target resistance value ends resistance value adjustment,
8. The thermal head manufacturing method according to claim 7, wherein the heating resistor dots determined to have not reached the target resistance value increase the voltage value of the voltage pulse for resistance value adjustment and repeat the resistance value adjustment process again. Method. 11. A thermal head manufacturing apparatus for performing the thermal head manufacturing method according to claim 3, wherein the resistance value of the heating resistor dot is measured and the resistance value of the heating resistor dot is measured. Resistance value measuring means,
Resistance value determination means for comparing the resistance value of the heating resistor dot whose resistance value has been adjusted with the target resistance value and determining whether the measured resistance value has decreased to the target resistance value or has not reached the target resistance value. A resistance value for controlling the resistance value adjusting means to act again on the heating resistor dots having a target resistance value or more, and controlling the resistance value adjusting means not to act on the heating resistor dots having a resistance value lower than the target resistance value. An apparatus for manufacturing a thermal head, comprising: an adjustment control unit. 12. The thermal head manufacturing apparatus according to claim 11, wherein the resistance value adjusting means comprises a resistance value adjusting voltage pulse generating means and a resistance value adjusting voltage pulse applying means. 13. The apparatus for manufacturing a thermal head according to claim 12, wherein the resistance value adjusting voltage pulse applying means is a probing device for contacting an electrode connected to the heating resistor. 14. A voltage pulse generating means for adjusting a resistance value,
14. The apparatus for manufacturing a thermal head according to claim 12, wherein the apparatus is a charge / discharge circuit that generates a voltage pulse. 15. The thermal head manufacturing apparatus according to claim 11, wherein a plurality of resistance value adjusting means for the heating resistor dots are provided.