JP2534041Y2 - Thick film type thermal head - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial application field) The present invention relates to a thick film type thermal head used for a facsimile apparatus and a printer in a thermal recording system, and particularly to a thick film capable of performing gradation recording. The present invention relates to a thermal head.

(Prior art) The thermal recording apparatus has low noise during printing,
Since it does not require a fixing step, it has advantages such as easy handling and is more widely used than before.

FIG. 6 is a perspective view of a conventional thick film type thermal head, and FIG. 7 is a sectional view of the vicinity of the heating resistor. In the thick-film type thermal head, a glass glaze layer 22 is printed and fired on a ceramic substrate 21 for heat dissipation, and then the individual electrodes 23 and the common electrode 24 are printed and fired, and are patterned by photolithographic etching. Individual electrode 23 and common electrode
A heating resistor 25 is formed between the heating resistor 24 and the heating resistor 25, and a wear-resistant layer 26 further covers the heating resistor 25. The heating resistors 25 are individually formed using a ruthenium oxide-based thick film resistor, and the abrasion resistant layer 26 is also formed by printing and firing.

Instead of forming the heating resistors individually, see JP-A-63-319.
As in the thermal head described in Japanese Patent No. 161, there is a thermal head in which a heating resistor is formed in a line shape and an alternate lead type electrode arrangement is employed.

A thermal transfer recording system using these thermal heads will be described with reference to FIG. In the thermal transfer sheet (ink donor film) 27, an ink 27b is applied on a base film 27a. The heat-sensitive transfer sheet 27 and the recording paper 28 are superimposed and pass between the platen roller 29 and the top of the wear-resistant layer 26 of the thermal head. The platen roller 29 has a wear-resistant layer
Thermal transfer sheet 27 and thermal transfer sheet 27
The thermal transfer sheet 27 and the recording paper 28 are pressed against the top of the abrasion-resistant layer 26 so that the recording paper 28 and the recording paper 28 are in close contact with each other. When a voltage pulse is applied to the individual electrode 23 and the heating resistor 25 is selectively heated, the ink 27b applied to the thermal transfer sheet 27 is melted, and the ink 27b is applied to the recording paper 28 by the pressing force of the platen roller 29. 27b is transferred and recorded.

FIG. 9 shows a characteristic example of thermal transfer recording by a conventional thermal head. In thermal transfer recording, high-density areas are recorded stably with small variations. However, from the low density region to the medium density region, the gradient of the recording density D with respect to the supplied energy is large and the variation is large, so that it is difficult to record uniformly from the low density to the medium density. The reason is as follows. Since the heating resistor 25 has a constant thickness and width as shown in FIG. 6, the temperature distribution becomes high at the center of the heating resistor, but becomes substantially flat on the heating resistor. Therefore, when the temperature at which the ink melts is reached, the entire heating resistor is at that temperature, and it is difficult to reproduce dots smaller than the heating resistor.

Thus, in thermal transfer recording, high density is recorded,
However, it is suitable for binary recording of whether or not, but is not suitable for multi-level recording expressing halftone. Therefore, in the halftone expression in the conventional thermal transfer recording, an area gradation method such as a dither method in which one pixel is composed of a plurality of dots and the number of recording dots in one pixel is changed has been widely used.

However, in this method, since one pixel is composed of a plurality of dots, there are problems that the resolution of the pixel is lower than the resolution of the thermal head and that the driving circuit is complicated.

The thermal recording head described in Japanese Patent Application Laid-Open No. 60-58877 performs gradation expression by increasing the resistance value of the central portion of the heating resistor and lowering the resistance value nearer the electrode so that the resistance distribution has a gradient. Although it can solve the drawbacks of the dither method, it has problems in the production of the heating resistors, and also has a problem in the variation of the resistance value and resistance distribution characteristics of each heating resistor. Have.

(Issues to be solved by the present invention) The present invention has been made in view of the circumstances described above.
It is an object of the present invention to provide a thermal head that enables continuous gradation recording by changing the area of dots recorded in thermal transfer recording.

(Means for Solving the Problems) According to the present invention, in a thick film type thermal head having a common electrode and an individual electrode arranged to face the common electrode, a concave portion facing the individual electrode is formed in the common electrode. And providing a heat-generating resistor between the common electrode and the individual electrode to perform gradation recording by positioning the tip of the individual electrode near the center of an imaginary line connecting both ends of the concave portion. It is characterized by doing so.

The shape of the concave portion can be an appropriate shape such as a semicircle, a semiellipse, or a polygonal shape approximate thereto.

(Operation) The present invention provides a thick-film type thermal head having a common electrode and an individual electrode arranged to face the common electrode, wherein the common electrode is provided with a recess facing the individual electrode, and both ends of the recess are provided. The tip of the individual electrode is located near the center on an imaginary line connecting the portions, and a heating resistor is formed between the common electrode and the individual electrode, so that the resistance value between the individual electrode and the common electrode is reduced. The distribution is such that the resistance value is high near the tip of the individual electrode, and decreases as it approaches the common electrode. Therefore, in a region where the pulse width of the print pulse is small, heat is concentrated near the tip of the individual electrode, and printing is performed in the heat generation region. As the pulse width is increased, the heat generation region is directed toward the common electrode. The printing area is widened, and continuous gradation can be reproduced.

FIG. 5 is an example of printing by the thermal head of the present invention. In this example, print dots of 3 × 4 = 12 pixels are shown, and the pulse width of the voltage pulse applied to the individual electrode is increased.

In the area where the pulse width is small, small dots are independently recorded to reproduce low density, as shown in FIG.

When the pulse width is further increased, the dots become larger and the respective heating regions begin to connect with each other to reproduce the medium density as shown in FIG.

When the pulse width is further increased, the non-recording area between adjacent dots gradually decreases as shown in FIG.

As described above, according to the present invention, it is possible to continuously reproduce from a low density to a high density according to the pulse width, and it is possible to perform recording with excellent gradation characteristics.

(Embodiment) FIG. 1 is a plan view for explaining an electrode arrangement of an embodiment of the thermal head of the present invention. In the figure, 10 is a common electrode, 111, 112, 113,... Are individual electrodes, and 12 is a heating resistor. The common electrode 10 is provided with a semicircular cutout for each dot on the side facing the individual electrodes 111, 112, 113,.... Each of the individual electrodes 111, 112, 113,... Is provided such that its tip is located at the center of a semicircle. Heating resistor 12
Are provided so as to sufficiently cover the semicircular common electrode.

Therefore, in this embodiment, in the region where the pulse width is small, printing is performed in the heat generating region near the tip of the common electrode, recording is performed with each dot separated, and low density is reproduced. As the width is increased, the area of the heat generation region is increased, and adjacent dots start to connect with each other, thereby reproducing medium density. Further, as the pulse width is increased, the non-recording area between adjacent pixels gradually decreases, and high density can be reproduced.

Next, a method of manufacturing the thermal head of the embodiment described with reference to FIG. 1 will be described.

As shown in FIG. 2, a glass glaze layer 14 having a thickness of about 60 μm is formed on a ceramic substrate 13 by using a conventional thick film technique. A conductive film 15 of gold or the like is formed on this substrate with a thickness of about 1.0 μm, and the common electrode 10 and the individual electrodes 111, 112, 113,.
.. are formed.

The electrode structure is, as shown in FIG.
The individual electrodes are made semicircular for each dot, and the tips of the individual electrodes 111, 112, 113,... Are positioned at the center of the semicircle.

Next, a photosensitive resist 16 having a thickness of about 20 μm is applied on a substrate on which electrodes are formed by a roll coater, a spin coater, or the like, exposed and developed by a photomask, and an opening 17 is formed at a location where a heating resistor is provided. Form. In the present invention, in order to form a belt-like heating resistor having a length in the sub-scanning direction about the recording density, the opening 17 also has a belt-like shape having a length in the sub-scanning direction about the recording density. For example, since the recording density is 125 μm at 8 dots / mm, the length of the opening 17 in the sub-scanning direction is about 125 μm.

A resistor paste for forming a thick-film resistor is formed by screen printing on the opening 17 so as to be wider than the opening width and thicker than the opening, and then dried. Thereafter, the thick-film resistor on the photosensitive resist pattern is removed by polishing with, for example, a wrapping sheet or the like, and at the same time, the surface of the thick-film resistor at the opening is also removed so as to have the same thickness. Thick film resistor flattened in this way
It is baked at a high temperature of 800 to 900 ° C. to sinter the heating resistor 12 and burn and vaporize the photosensitive resist 16.

Finally, an overglaze as a wear-resistant layer is formed by screen printing or the like, and fired at a high temperature of 800 to 900C.

Through the above process, the thermal head of the present invention is manufactured.

In the above-described embodiment, the tip of the individual electrode has a rectangular shape. However, the shape of the heat generation distribution may be adjusted by making the tip of the individual electrode circular.

Further, the shape of the common electrode 10 is not limited to a semicircular shape, and may be an elliptical shape, a triangular shape, or a polygonal shape.

(Effects of the Invention) As is clear from the above description, according to the present invention, in thermal recording using a thick-film type thermal head, it is possible to continuously reproduce from a low density to a high density according to the pulse width. Thus, there is an effect that recording with improved gradation characteristics can be performed.

[Brief description of the drawings]

FIG. 1 is a plan view for explaining an electrode arrangement of one embodiment of the thick film type thermal head of the present invention, and FIGS. 2 to 4 are diagrams showing a method of manufacturing the thick film type thermal head of FIG. FIG. 5 is an explanatory view of the operation of gradation recording, FIG. 6 is a perspective view of a conventional thick film type thermal head, FIG. 7 is a cross-sectional view of the vicinity of the heating resistor, and FIG. Is an explanatory view of a thermal transfer recording method using a thermal head, and FIG. 9 is a diagram showing characteristics of thermal transfer recording by a conventional thermal head. 10 common electrodes, 111, 112, 113, individual electrodes, 12
...... Heating resistor.

Claims (1)

(57) [Scope of request for utility model registration] In a thick-film type thermal head having a common electrode and an individual electrode arranged so as to face the common electrode, a concave portion facing the individual electrode is provided in the common electrode, and both ends of the concave portion are formed. The tip of the individual electrode is located near the center of the imaginary line to be connected, and a heating resistor is formed between the common electrode and the individual electrode to perform gradation recording. Thick film type thermal head.