JPH0526661B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a method for manufacturing a thermal head used in facsimile machines and the like.

[Prior art]

A thermal head is generally used to record numbers, characters, symbols, etc. on thermal recording paper, and usually has a pair of electrodes formed on an insulating substrate and a heating resistor between the two electrodes. connected and configured. When recording using this thermal head, a voltage is applied to the heating resistor between both electrodes to cause the resistor to generate heat, and the heat is applied to the thermal recording paper. In this case, thermal recording is performed in accordance with the heat generated by the resistor.

Conventionally, this type of thermal head has been classified into thick-film type and thin-film type based on the difference in the manufacturing process, and the manufacturing process of the thick-film type thermal head is much easier than that of the thin-film type thermal head. It has the characteristics of being mass-producible, inexpensive, and strong.

However, in conventional thick-film thermal heads, the variation in the resistance value of the thick-film heating resistor is ±25%, whereas that of the thin-film type is as small as ±7% or less.
This is extremely large, and when an image is drawn, the image quality is poor, resulting in poor image quality due to this variation in resistance value. One possible method for resolving the poor image quality caused by variations in resistance in thick-film thermal heads is to increase the power supply capacity.

That is, the resistance value of the heating resistor is R, and the applied voltage is V.
Then, the power P ₀ applied to the heating resistor is
It is expressed as V ² /R. Here, the applied voltage V is assumed to be constant. However, if there is a deviation ±ΔR in the resistance value R, the applied power will fluctuate, and the minimum applied power will
PMIN and maximum applied power PMAX are each expressed by the following formulas.

PMIN=V ² /R(1+ΔR) =P ₀ /(1+ΔR) …(1) PMAX=V ² /R(1−ΔR) =P ₀ /(1−ΔR)…(2) And the above formula (1) If ΔR=±25%, which is a characteristic of a thick film resistor, is substituted into (2), the energy difference will be -20% to +30%. On the other hand, the print density D of thermal recording paper increases almost in proportion to the increase in applied power, but if the increase coefficient is k (k = 4D/W for ordinary thermal recording paper), then The concentration difference ΔD caused by the difference in applied power is expressed by the following equation.

ΔD=kP ₀ (1/1−ΔR−1/1+ΔR) =kP ₀ 2ΔR/1−ΔR ² …(3) Here, assuming k=4 and P ₀ =0.5W, using equation (3), When calculating the concentration difference ΔD, the concentration difference produced by a thin film thermal head with ΔR = ±7% is ΔD = 0.28.
On the other hand, in a thick film type thermal head with ΔR = ±25%, the concentration difference is ΔD = 1.07, which is 3.8 times larger than that of a thin film type. If printing is performed on thermal recording paper in this state, vertical streaks corresponding to the heating resistors will appear, and the image quality will be significantly impaired.

In addition, thermosensitive recording paper has the characteristic that it saturates at a density of about 1.3, but if you try to make all the dots' heat-generating low antibodies above the temperature corresponding to the minimum density value of 1.0, which is visually perceived as black, the heat-generating It is necessary to set the power applied to the resistor so that the average concentration becomes D=(1.0+ΔD/2). In this case, if the concentration difference ΔD is large as described above, the average concentration will naturally be set high, which will require an extremely large amount of extra energy compared to the thin film type.

[Summary of the invention]

Therefore, this invention was made to eliminate the above-mentioned drawbacks of the conventional devices, and by equalizing the variation in resistance values of the large number of thick-film heating resistors in a thermal head, the power supply capacity can be increased. It is an object of the present invention to provide a new method for manufacturing a thermal head that can significantly improve image quality without increasing the image quality.

That is, the method for manufacturing a thermal head according to the present invention is based on the fact that in a thermal head consisting of a large number of thick film heating resistors, the variation in resistance value is much larger than that of a thin film type. A group of heating resistors is electrically connected to a common electrode and a plurality of individual electrodes, one probe is brought into contact with the common electrode, the other probe is brought into contact with the individual electrodes, and each thick film heating resistor is detected by a resistance detector. The resistance value of the body is detected, and while the one probe is kept in contact with the common electrode, the other probe is moved to the predetermined thickness with respect to a predetermined thick film heating resistor whose resistance value is higher than the set value. The predetermined thick film heating is performed through the one and the other probes by applying a voltage within the range where the resistance value of the thick film heating resistor decreases by applying a voltage by contacting the individual electrodes connected to the film heating resistor. By lowering the resistance value of the predetermined thick-film heat generating resistor by applying it to the resistor, variations in the resistance values of the heat generating resistor group are made uniform.

[Embodiments of the invention]

Before explaining one embodiment of the present invention, the fundamental matters of the present invention will be explained first.

For thick film heating resistors, when one and the other probes are brought into contact with the common electrode and individual electrodes connected to the thick film heating resistor, respectively, and a voltage higher than the rated voltage is applied through these one and the other probes. The phenomenon in which the resistance value decreases is utilized. This is thought to be due to local dielectric breakdown occurring within the thick film heating resistor due to the application of voltage.

FIG. 1 shows the relationship between the resistance change rate ΔR/R on the vertical axis and the applied power on the horizontal axis. In Figure 1, the applied power P ₀ is the point set as the actual operating condition;
The range up to PB is the range in which deterioration progresses under long-term power application, and even further as the applied power
The range exceeding PB is the range in which deterioration and damage can occur with the application of power for an extremely short period of time. Of particular note in this characteristic curve is the range from applied power P ₀ to PB; in this range, if power is applied for an extremely short period of time, the resistance value will only decrease and no deterioration will occur. . Therefore, by applying power within this range, it is possible to trim the resistance value of the heating resistor. In this case, the applied voltage may be either a DC voltage or a pulse voltage.

Figure 2 shows the experimental results of the present inventor, which are the basis of the present invention.The vertical axis shows the resistance change rate ΔR/R, and the horizontal axis shows the pulse voltage.For example, the duty ratio is 1/50, the pulse width is 1μsec pulse voltage,
The figure shows the rate of change in resistance value when the voltage is applied while increasing it stepwise. According to FIG. 2, it can be seen that, for example, when trimming the resistance value by -30%, it is sufficient to apply a pulse voltage of 80V. Note that the application method may be such that the pulse voltage is increased in steps of 20 V, 40 V, and 60 V. If this method is used, the resistance value of the thick film heating resistor can be brought as close as possible to the desired value.

Further, when a DC voltage is used as the applied voltage, it is sufficient to apply a low voltage, for example, about 5 V, so that only the resistance value drifts and does not cause deterioration or damage.

Next, one embodiment of the present invention will be described with reference to the drawings.

3 and 4 illustrate a thermal head according to one embodiment of the invention. In the figure, 1 is an insulating substrate made of, for example, alumina, and 2 is an insulating substrate 1.
The common electrodes 31 to 3n formed on the insulating substrate 1 and having a plurality of protruding electrode portions 2a are arranged so as to fit between the electrode portions 2a of the common electrode 2, that is, an interdigitated type. A plurality of individual electrodes 4 are formed on the insulating substrate 1 and are electrically connected to the protrusion electrode portion 2a and the individual electrodes 31 to 3n of the common electrode 2, and between adjacent protrusion electrode portions 2a. Each part is a heating resistor 4 of 1 bit.
The resistance value of the heating resistor 4a is lowered by applying a pulse voltage when the resistance value of the heating resistor 4a is higher than the required resistance value. Reference numeral 5 indicates a 32-bit driver for controlling energization to the heating resistor 4a, and 61 to 632 indicate pads of the 32 drivers 5, which are provided at the other ends of the individual electrodes 61 to 632 and are considered to be included in the individual electrodes. shall be taken as a thing.

Next, the manufacturing method will be explained.

When manufacturing a thermal head, first, a common electrode 2, individual electrodes 31 to 3n, and pads 61 to 632 are formed on an insulating substrate 1 using a conventionally known thick film technique.
At the same time, a heating resistor group 4 is formed on the insulating substrate 1 by electrically connecting it to the common electrode 2 and the individual electrodes 31 to 3n using a conventionally known thick film technique. Next, one probe of the resistance detector is brought into contact with the common electrode 2, and the other probe is brought into contact with the pads 61 to 632 included in the individual electrodes in order to detect the resistance value of each thick film heating resistor 4a,
At that time, regarding the thick film heating resistor 4a (see the fifth part A and B) whose resistance value is higher than the set value _R0 ,
Connect the probe to common electrode 2 and individual electrode (pad) 61
632, remove the probe from the detector, and connect the two probes with a duty ratio of 1/50, a pulse width of 1 μsec, and a size according to the deviation of the resistance value (see Figure 2). A pulse voltage of is applied to lower the resistance value to near the set value R ₀ (see parts C and D in FIG. 5). Since such a thermal head has a large number of thick film heating resistors, in order to measure the resistance value of each thick film heating resistor, a common electrode and individual electrodes are provided, and both probes are brought into contact with these to measure the resistance value. In addition to making measurements quick and easy, the voltage is applied by keeping one probe in contact with the common electrode and the other probe in contact with the individual electrodes of a predetermined high-resistance thick-film heating resistor. Variation in values can also be easily adjusted. Finally, place the driver 5 on the insulating board 2.
Equipped with.

In the thermal head of the above embodiment, the variation in the resistance value of the thick film heating resistor can be suppressed to the same level as that of the thin film type thermal head, or less than that, and as a result, the power supply capacity can be reduced without increasing the power supply capacity. Image quality can be significantly improved. Particularly in thick film thermal heads, both probes are brought into contact with the common electrode and the individual electrodes, and a voltage is applied to the thick film heating resistor that has a resistance value higher than a predetermined value within a range in which the resistance value decreases. Since the variation in resistance value is adjusted by adjusting the variation in resistance value, it is possible to trim the resistance value by -30% at a relatively small voltage, for example 80V, and the variation can be improved to a level close to that of the thin film type.

However, as the voltage increases, the resistance value increases rapidly, which is generally referred to as a breakdown mode, and may involve a change in the shape of the heating resistor, but in a relatively small voltage range, this risk does not occur. do not have.

In this way, by equalizing the variations in the resistance values of a large number of thick film heating resistors, image quality deterioration can be significantly improved and the problem of insufficient density can also be solved.

Further, as a method of suppressing variations in resistance value, it may be possible to change the printing conditions of the heating resistor, for example, the width, but this method has the problem of causing variations in the size of printed dots. On the other hand, in the present invention, variations in resistance value are suppressed by applying a pulse voltage, so variations in the size of printed dots do not occur.

〔Effect of the invention〕

As described above, according to the method for manufacturing a thermal head according to the present invention, in order to measure the resistance values of a large number of thick film heating resistors, a common electrode and a plurality of individual electrodes are provided, and probes are attached to these electrodes. Measure the resistance value by contacting the electrode, and apply the desired voltage by keeping one probe in contact with the common electrode and touching the other probe with the individual electrode connected to the thick-film heating resistor whose resistance value is higher than the set value. This makes it possible not only to measure the resistance value but also to apply voltage to the large number of thick-film heating resistors in the thermal head easily and quickly. By lowering the resistance value by applying a relatively small voltage and making the variation in resistance uniform to the same level as the thin-film type, image quality deterioration is significantly improved without changing the shape of the thick-film resistor. be able to.

[Brief explanation of the drawing]

1 and 2 are both diagrams showing the relationship between applied power and resistance change rate for explaining matters necessary for understanding the present invention, and FIG. 4 is a partially enlarged view of FIG. 3, and FIG. 5 is a diagram for explaining the method of manufacturing the thermal head. 1... Insulating substrate, 2... Common electrode, 31-3n...
Individual electrode, 4... Heat generating resistor group, 4a... Thick film heat generating resistor. Note that the same reference numerals in the figures indicate the same or equivalent parts.

Claims (1)

[Claims] 1. A heating resistor group consisting of a large number of thick film heating resistors is electrically connected to a common electrode and a plurality of individual electrodes, one probe is brought into contact with the common electrode, and the other probe is brought into contact with the common electrode. The resistance value of each thick film heating resistor is detected by a resistance detector by contacting the individual electrodes, and one of the probes is connected to the common electrode for a predetermined thick film heating resistor whose resistance value is higher than the set value. While keeping the other probe in contact with the individual electrode connected to the predetermined thick film heating resistor, apply a voltage of a magnitude within the range where the resistance value of the thick film heating resistor decreases by applying the voltage. By lowering the resistance value of the predetermined thick film heating resistor by applying voltage to the predetermined thick film heating resistor through the one and the other probes, the variation in the resistance value of the heating resistor group is made uniform. 1. A method for manufacturing a thermal head, characterized in that: 2. When the applied voltage is a pulse voltage, the pulse voltage has a magnitude of several tens of V within a range where the resistance value of the thick film heating resistor decreases. A method of manufacturing a thermal head. 3. The method of manufacturing a thermal head according to claim 1, wherein when the applied voltage is a DC voltage, the DC voltage is approximately 5V.