JPH0499654A - Manufacture of thermal head for accurately making surface temperature of heat generating resistor protective layer uniform - Google Patents

Abstract

PURPOSE:To make the surface temperature of a protective layer uniform, to eliminate density irregularity of a printing quality and to obtain a thermal head of high quality by measuring variation in the surface temperature of a heat generating resistor protective layer by an infrared ray radiation microscope at the time of applying a rated printing pulse to a thermal head heat generating resistor, and applying a voltage pulse until a predetermined surface temperature and a thermal response characteristic are obtained to vary heat generating resistor characteristics. CONSTITUTION:A conductor, electrodes, a heat generating resistor are formed on a glazed board, a heat generating resistor protective layer is further formed, and polished to flatten the surface. Then, a rated printing pulse is applied to the generator, and variation in the surface temperature of the protective layer is measured by an infrared ray radiation microscope. If the surface temperature is deviated from a predetermined value, sensitivity of a heat response curve is deviated from a predetermined value, a voltage pulse is applied. This operation is repeated to obtain predetermined surface temperature and response characteristics at the time of applying a printing pulse.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method of manufacturing a thermal head mainly used in facsimiles, printers, etc.

[Prior Art] Thermal heads, which do not require development or fixing, do not require maintenance, are noiseless, and are highly reliable, have become popular as the quality of thermal recording paper improves.

Among the thermal heads of Korera, the general manufacturing method conventionally used for thick film thermal heads is as follows.

That is, (1) a conductor is printed and fired on an insulating substrate such as a glazed substrate. (2) Form electrodes by photolithography or the like. (3) Print and bake the resistor pattern. (4) Print and bake the heating resistor protective layer (wear-resistant layer). (5) Adjust the resistance value by applying a voltage pulse to control the heating element temperature. (B) Perform resistor stabilization treatment.

In this manufacturing method, there were the following problems, particularly in (5) resistance value adjustment step.

The surface temperature of the heating element of a thick film thermal head is controlled by changing the resistance value of the heating element by applying a voltage pulse, adjusting it to the desired resistance value, suppressing the variation in resistance value, and using the resistance value as a substitute characteristic value for the surface temperature. Therefore, the main focus has been on adjusting surface temperature variations for the purpose of equalizing the resistance value of the heating resistor.

[Problems to be Solved by the Invention] However, in order to form the heating resistor and its protective layer using the thick film printing method, variations in film thickness inevitably occur.
Even if the resistance value of the heating resistor is adjusted, due to variations in film thickness, there will be differences in the heat transfer path from the heating resistor to the surface of the protective layer when a printing pulse is applied, and the resistance that ultimately comes into contact with the thermal paper will vary. There is a problem in that the surface temperature of the body protection layer is not uniform, resulting in uneven density when printed. The cause of this problem lies in the width of the resistor, the thickness of the resistor, the shape of the resistor, and the thickness of the resistor protective layer. Especially when it comes to resistor shapes, the viscosity of printing paste,
The shape depends on the printing conditions (snap distance, squeegee angle, squeegee speed, squeegee hardness, printing pressure), and the cross-sectional shape immediately after printing the resistor is either convex or concave, or Both are printed in a mixed state. A schematic cross-sectional view of the resistor portion of such a thermal head is shown in FIGS. 1(a) and 1(b).
Shown below. In addition, in the same figure, 1 is a heating resistor protective layer,
2 is a heating resistor, 3 is a conductor, 4 is a glaze layer, and 5 is an alumina substrate.

Therefore, the shape of the resistor after firing depends on the shape of the resistor immediately after printing. In order to form a protective layer on the resistor formed in this way, the protective layer formed by the thick film printing method takes into account variations in the film thickness and shape of the lower resistor layer in addition to the original variations, making it difficult to resist. Even if the values were adjusted to be uniform, there was a problem in that it was not possible to equalize the surface temperature of the heating resistor protective layer that came into contact with the thermal paper.

In addition, since the heating resistor protective layer is formed into a thick film by screen printing, etc., the surface roughness is rough in the as-fired state.
There was insufficient ideal contact with the thermal paper, and even if a uniform resistance value was achieved, sufficient printing quality could not be expected.

Therefore, it is difficult to use it for printers with high-quality, fine gradation expression.

It is an object of the present invention to solve the problems of the prior art, and to achieve uniformity of the surface temperature of the protective layer of the heating resistor, which could not be achieved only by adjusting the resistance value uniformity, and to improve the density of the printed image quality. An object of the present invention is to provide a method for manufacturing a thermal head that eliminates unevenness and provides high-quality printing.

[Means for Solving the Problems] The above objects of the present invention are achieved by the following manufacturing method.

That is, in the method for manufacturing a thermal head of the present invention, changes in the surface temperature of the heating resistor protective layer when a rated printing pulse is applied to the thermal head heating resistor are measured using an infrared radiation microscope, and a predetermined surface temperature and thermal response characteristics are determined. It is characterized in that the heating resistor characteristics are changed by applying a voltage pulse until the rated printing pulse is applied, and the surface temperature and thermal response characteristics are adjusted when the rated printing pulse is applied.

Hereinafter, the manufacturing method of the present invention will be explained in detail.

First, in the present invention, as shown in FIGS. 1(a) and 1(b), a conductor, an electrode, and a heating resistor are formed on a glazed substrate, and a heating resistor protective layer is further formed.

Next, the heating resistor protective layer is polished. As is done in the prior art, the surface is polished to a surface roughness of Ra-2 μD or less using a lapping machine or the like. As a result, the surface of the heating resistor protective layer becomes flat, and the contact with the thermal paper becomes uniform.

Next, a rated printing pulse is applied to the heating resistor, and the change in surface temperature of the heating resistor protective layer at that time is measured using an infrared radiation microscope.

That is, by applying infrared radiation temperature measurement technology that applies the theory of black body radiation, thermal response characteristics are monitored while measuring surface temperature changes of the heating resistor protective layer due to printing pulses. InSb, Hg Cd Te, etc. are used as a detector, and the detection wavelength range is 1.8 to 5.
By widening the range from 5 μm to 6 to 14 μm for Hg Cd Te, a signal is detected that is not disturbed by infrared rays that pass through the glass film, which is a wear-resistant layer. It is said that the smaller the pitch of the heating resistors of the thermal head, the better the resolution.

Therefore, a technique for measuring infrared radiation temperature in a minute area of 200 μm or less is required.

Based on this detected signal, a voltage pulse is applied if the surface temperature of the heat generating resistor protective layer deviates from a predetermined value or if the sensitivity of the thermal response curve deviates from a predetermined value. The voltage of the voltage pulse to be applied is calculated in advance based on the initial surface temperature when the first rated pulse is applied, the sensitivity of the thermal response curve, the rate of change in the surface temperature when the voltage pulse is applied, and the rate of change in the sensitivity of the thermal response curve.

A specific example is as follows. A 24 V printing pulse with a pulse width of 0.5 μs is printed, and the surface temperature of the heating resistor protective layer is measured. Next, a voltage pulse with a pulse width of 1 μs is applied. The voltage is 50V. Next, a printing pulse is applied and the surface temperature is measured. Furthermore, a voltage pulse of 1 μs is applied. The voltage is 100V. Apply a printing pulse and measure the surface temperature. In this way,
Create a table of the relationship between pulse voltage and surface temperature change rate. Create a table of pulse voltage and surface temperature in advance,
After measuring the initial surface temperature, the pulse voltage to be applied can be automatically calculated. FIG. 2 shows a graph showing the relationship between the rate of change in surface temperature and applied pulse energy, and FIG. 3 shows a graph showing the relationship between pulse voltage and surface temperature.

This applied voltage pulse has a bus width of 0.1 to 10 μs. The voltage pulse width for adjusting the resistance value is as small as 1/100th to 1000th of the printing pulse width. Application of a voltage pulse changes the resistance value, and in many cases the resistance value decreases. Therefore, the Joule heat generated when a printing pulse is applied changes. Next, a printing pulse is applied again and the surface temperature is measured using an infrared radiation microscope.

Further, if it is necessary to adjust the surface temperature of the heating resistor protective layer, the voltage of the voltage pulse is increased and applied.

Such operations are repeated to obtain a predetermined surface temperature and thermal response characteristics when a printing pulse is applied. FIG. 4 shows an outline of the apparatus used in the present invention. In the figure, 11 is a thermal head board, 2 is a probe, 13 is an infrared copying microscope, 14 is a detector, and 15 is a pulse generator 1
6 represents a CPU, and 17 represents a monitor. Further, a flowchart of the manufacturing method of the present invention is shown in FIG.

In this way, while the conventional technique attempts to achieve uniform surface temperature from the relationship between voltage pulse and resistance value, the present invention attempts to achieve uniform surface temperature from the relationship between voltage pulse and surface temperature. It is something.

[Function] In the present invention, changes in the surface temperature of the heat generating resistor protective layer due to rated printing pulses are monitored using an infrared radiation microscope, etc., and if the surface temperature is outside the predetermined surface temperature and predetermined thermal response sensitivity, the heat generating resistor is removed by applying a voltage pulse. By changing the resistance value, applying the rated printing pulse again, checking the surface temperature and thermal response characteristics, and repeating the above steps until the specified surface temperature is achieved, the surface temperature can be made uniform. This makes it possible to reduce density unevenness in printed image quality.

[Example] Examples of the present invention will be described below.

Example First, a conductor film was formed using gold resinate on a glazed substrate. Next, a fine pattern for the electrode lead portion of the conductor layer was formed by photolithography. Next, a common electrode was formed by printing and firing, and then screen printing and firing were performed using a resistance paste containing ruthenium oxide and glass as main components to form a resistor. Furthermore, a resistor protection layer (wear-resistant layer) was formed using glass paste. Next, after forming a heating resistor protective layer, the protective layer was polished using a lapping machine or the like. At this time, the surface roughness Ra-
It was set to 2 μm or less.

The surface temperature of the resistor protective layer of the thus obtained thermal head was measured using an infrared radiation microscope when a rated printing pulse was applied. Next, in order to obtain a predetermined surface temperature and thermal response sensitivity, a voltage pulse of a predetermined voltage value is selected from a pulse voltage surface temperature table created in advance and applied. After changing the heating resistor characteristics, the rated printing pulse was applied again.

These steps were repeated until a predetermined surface temperature and thermal response characteristics were obtained.

After repeating these steps, it was confirmed using an infrared radiation microscope that a predetermined surface temperature and thermal response sensitivity had been achieved.

In this way, a thick film thermal head was obtained in which the surface temperature of the resistor protective layer was uniform when the rated printing pulse was applied. After the heat generating resistor was treated with this method, the resistance value was measured. Although the surface temperature was uniform when the rated printing pulse was applied, the variation in the resistance value was larger than the variation in the surface temperature.

In contrast, the conventional pulse trimming method measures the resistance value and adjusts it to a predetermined resistance value by applying a voltage pulse. Local non-uniformity is observed.

When comparing the print image quality of the two, a clear improvement in image quality is recognized.

[Effects of the Invention] Since the thermal head obtained by the manufacturing method of the present invention has little variation in the surface temperature of the heating resistor protective layer, unevenness in print density of the thermal head is eliminated and high quality printing can be obtained.

[Brief explanation of the drawing]

Figures 1 (a) and (b) are schematic cross-sectional views of the resistor portion of the thermal head. Figure 2 is a graph showing the relationship between the surface temperature change rate and applied pulse energy. Figure 3 is a graph showing the relationship between the pulse voltage and the surface temperature. A graph showing the relationship between temperatures; FIG. 4 is a schematic diagram of the apparatus used in the present invention; and FIG. 5 is a flowchart of the manufacturing method of the present invention.

Claims (1)

[Claims] 1. The change in the surface temperature of the heating resistor protective layer when a rated printing pulse is applied to the thermal head heating resistor is measured using an infrared radiation microscope, and voltage pulses are applied until the predetermined surface temperature and thermal response characteristics are obtained. A method for manufacturing a thermal head, characterized by changing body characteristics and adjusting surface temperature and thermal response characteristics when a rated printing pulse is applied.