JP2645759B2 - Method for manufacturing thermal head for uniformizing surface temperature of heating resistor protective layer with high accuracy - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a method for manufacturing a thermal head mainly used for facsimile machines, printers, and the like.

[Prior Art] Thermal heads that do not require development and fixing, do not require maintenance, are noiseless, and have high reliability have become widespread as the quality of thermosensitive recording paper improves.

Among these thermal heads, a general method of manufacturing a thick-film thermal head that has been conventionally used is as follows.

That is, (1) a conductor is printed and fired on an insulating substrate such as a grace substrate. (2) An electrode is formed by photolithographic etching or the like. (3) Print and bake the resistor pattern. (4) The heating resistor protective layer (abrasion resistant layer) is printed and baked. (5) The resistance value is adjusted by applying a voltage pulse for controlling the temperature of the heating element. (6) Perform resistor stabilization processing.

In this manufacturing method, in particular, there is the following problem in the (5) resistance value adjusting step.

The surface temperature of the heating element of the thick film thermal head is controlled by changing the resistance value of the heating element by applying a voltage pulse, adjusting the target resistance value, suppressing the variation of the resistance value, and changing the resistance value to a substitute characteristic value of the surface temperature. Therefore, the main focus has been on adjusting the variation of the surface temperature mainly for the purpose of adjusting the resistance value of the heating resistor to be uniform.

[Problems to be Solved by the Invention] However, in order to form the exothermic antibody and its protective layer by the thick film printing method, the film thickness inevitably varies,
Even if the resistance value of the heating resistor is adjusted, there is a variation in the film thickness, so that a difference occurs in the heat transfer path from the heating resistor to the surface of the protective layer when a print pulse is applied, and the resistance that finally contacts the heating paper. There is a problem in that the surface temperature of the body protective layer is not uniform, and density unevenness occurs when printing. The cause of this problem is the resistor width, the resistor film thickness, the resistor shape, and the resistor protective layer film thickness. Especially in the resistor shape, the viscosity of the 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 a clean convex or concave shape, or both. Are printed in a mixed state. FIGS. 1A and 1B are schematic cross-sectional views of a resistor portion of such a thermal head.
Shown in In the drawing, reference numeral 1 denotes a heating resistor protective layer,
2 denotes a heating resistor, 3 denotes a conductor, 4 denotes a glaze layer, and 5 denotes an alumina substrate.

For this reason, the shape after firing the resistor depends on the shape of the resistor immediately after printing. Since the protective layer is formed on the resistor thus formed, the thickness of the protective layer formed by the thick-film printing method may vary from the conventional variation to the variation in the thickness of the lower resistor layer.
Due to the variation in shape, even if the resistance value is adjusted to be uniform, there is a problem that the surface temperature of the heating resistor protective layer in contact with the thermal paper cannot be made uniform.

In addition, since the heating resistor protection layer is also formed as a thick film by screen printing or the like, the surface roughness is rough in the as-fired state, the ideal contact with the thermal paper is not sufficient, and a uniform resistance value is achieved. However, sufficient print quality could not be expected.

Therefore, it is difficult to use it for a printer having a high-quality fine gradation surface.

An object of the present invention is to solve the problems of the related art, and achieves uniform heating of the surface of the heating resistor protective layer, which has not been achieved only by adjusting the uniformity of the resistance value, and achieves density unevenness of print image quality. It is an object of the present invention to provide a method of manufacturing a thermal head capable of achieving high quality printing by solving the problem.

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

That is, the method of manufacturing a thermal head of the present invention measures a change in the surface temperature of the heating resistor protective layer when a rated print pulse is applied to the thermal head heating resistor using an infrared radiation microscope, and determines the predetermined surface temperature and thermal response characteristics. Until a voltage pulse is obtained to change the heating resistor characteristics,
It is characterized in that the surface temperature and the thermal response characteristics when a rated printing pulse is applied are adjusted.

 Hereinafter, the production method of the present invention will be described 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 glaze substrate, and further, a heating resistor protection layer is formed.

Next, the heating resistor protection layer is polished. As is done in the prior art, the surface roughness Ra
= 2 μm or less. 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 print pulse is applied to the heating resistor, and a change in the surface temperature of the heating resistor protective layer at that time is measured by an infrared radiation microscope.

That is, the thermal response characteristic is monitored while measuring the surface temperature change of the heating resistor protective layer due to the printing pulse by applying the infrared radiation temperature measurement technology applying the blackbody radiation theory. As the detector, In Sb, Hg Cd Te, or the like is used, and the detection wavelength range is from 1.8 to 5.5 μm of In Sb to Hg Cd T
By extending e to 6 to 14 μm, a signal which is not disturbed by infrared rays transmitted through the glass film as the wear-resistant layer is detected. It is considered that the finer the pitch of the heating resistors of the thermal head, the better the resolution. Therefore, a technique of measuring infrared radiation temperature in a minute region of 200 μm □ or less is required.

Based on the detected signal, a voltage pulse is applied when the surface temperature of the heating resistor protective layer deviates from a predetermined value or when the sensitivity of the thermal response curve deviates from a predetermined value. The voltage of the applied voltage pulse is calculated in advance based on the initial surface temperature at the time of applying the first rated pulse, the sensitivity of the thermal response curve, the rate of change of the surface temperature at the time of applying the voltage pulse, and the rate of change of the thermal response curve.

A specific example is as follows. A printing pulse of 24 V having 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 having a pulse width of 1 μs is applied. The voltage is 50V. Next, a printing pulse is applied to measure the surface temperature, and a voltage pulse of 1 μs is applied. The voltage is 100V. A printing pulse is applied to measure the surface temperature. In this way, a table of the relationship between the pulse voltage and the rate of change of the surface temperature is created. A table of pulse voltage and surface temperature is created in advance, and after the initial surface temperature is measured, the pulse voltage to be automatically applied can be calculated. FIG. 2 is a graph showing the relationship between the surface temperature change rate and the applied pulse energy, and FIG. 3 is a graph showing the relationship between the pulse voltage and the surface temperature.

The applied voltage pulse is a change pulse having a pulse width of 0.1 to 10 μs. The voltage pulse width for adjusting the resistance value is as small as about 1/100 to 1/1000 of the print pulse width. The application of the voltage pulse changes the resistance value, and often decreases the resistance value. For this reason, Joule heat generated when a print pulse is applied changes. Next, a printing pulse is applied again and the surface temperature is measured by an infrared radiation microscope.

Further, when the surface temperature of the heating resistor protective layer needs to be adjusted, the voltage of the voltage pulse is increased and applied. Such operations are repeated to obtain a predetermined surface temperature and thermal response characteristics at the time of applying the printing pulse. FIG. 4 shows an outline of the apparatus used in the present invention. In the figure, 11 is a thermal head substrate, 12 is a probe, 13 is an infrared radiation microscope, 14 is a detector, 15 is a pulse generator, 16 is a CPU, and 17 is a monitor. FIG. 5 shows a flowchart of the manufacturing method of the present invention.

As described above, the prior art attempts to achieve a uniform surface temperature from the relationship between the voltage pulse and the resistance value, whereas the present invention seeks to achieve a uniform surface temperature from the relationship between the voltage pulse and the surface temperature. Things.

[Operation] In the present invention, the change in the surface temperature of the heating resistor protective layer due to the rated printing pulse is monitored by an infrared radiation microscope or the like. If the surface temperature deviates from the predetermined surface temperature and the predetermined thermal response sensitivity, the heating resistor is applied by applying a voltage pulse. Change the resistance value and again
By applying the rated print pulse and examining the surface temperature and thermal response characteristics, the above steps are repeated until the predetermined surface temperature is achieved, so that the surface temperature can be made uniform and the density unevenness of the print image quality can be reduced. Can be reduced.

EXAMPLES Examples of the present invention will be described below.

Example First, a conductor film was formed on a glaze substrate using gold resinate. Next, a fine pattern of an electrode lead portion of the conductor layer was formed by a photolithographic etching method. 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, using a glass paste, a resistor protection layer (abrasion resistant layer)
Was formed. Next, after forming the heating resistor protection layer, the protection layer was polished with a lapping machine or the like. At this time, the surface roughness Ra =
It was 2 μm or less.

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

After repeating these, it was confirmed by an infrared radiation microscope that the predetermined surface temperature and thermal response sensitivity were achieved.

Thus, a thick-film thermal head having a uniform surface temperature at the time of application of the rated printing pulse of the resistor protective layer was obtained. After treating the heating resistor by this method, when the resistance value was measured, the variation in the resistance value was larger than the variation in the surface temperature, even though the surface temperature at the time of application of the rated print pulse was uniform.

On the other hand, the conventional pulse trimming method measures a resistance value and applies a voltage pulse to adjust the resistance value to a predetermined value. In this method, however, the surface temperature of the resistor and the protective layer due to uneven film thickness is reduced. Local unevenness is observed.

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

[Effects of the Invention] A thermal head obtained by the manufacturing method of the present invention includes:
Since there is little variation in the surface temperature of the heating resistor protective layer, uneven printing density of the thermal head is eliminated, and high quality printing is obtained.

[Brief description of the drawings]

1 (a) and 1 (b) are schematic cross-sectional views of a resistor portion of a thermal head, FIG. 2 is a graph showing a relationship between a surface temperature change rate and a printing pulse energy, and FIG. FIG. 4 is a graph showing a temperature relationship, FIG. 4 is a schematic diagram of an apparatus used in the present invention, and FIG. 5 is a flowchart of a manufacturing method of the present invention.

Claims (1)

(57) [Claims] An infrared radiation microscope is used to measure the change in the surface temperature of the heat-generating resistor protective layer when a rated print pulse is applied to the heat-generating resistor of the thermal head, and a voltage pulse is applied until a predetermined surface temperature and thermal response characteristics are obtained. A method of manufacturing a thermal head, comprising: changing the characteristics of a heating resistor by applying the same to adjust a surface temperature and a thermal response characteristic when a rated print pulse is applied.