JPS61152467A - Thermal recording head - Google Patents

Abstract

PURPOSE:To provide a thermal recording head which enables widening of a color-forming area and is less susceptible of deterioration by flattening the temperature distribution of a heating resistance element. CONSTITUTION:A heating resistance element 2 has an energizing direction end formed in an arc shape so that the distance between electrodes1, 1' in an energizing direction (arrow) may become maximum in the middle of a width direction and shorter toward the end. Fig. 2 shows a distance between electrodes a and current density b between A and B crossing a single resistance element. The current concentration shows a moderate distribution curve, i.e. becoming denser toward the end in inverse proportion to an interelectrode distance. Be cause of such a moderate curve of the current density distribution, no localized hot area generates, contributing toward an improvement of the durability of a resistance element. Thus a long-lasting and highly reliable thermal head can be obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application of the Invention] The present invention relates to a thermal recording head used in a printer that prints single letters or characters, and particularly to a thermal head suitable for printing color images.

[Background of the invention]

When printing color art bonds, if there are white non-coloring areas such as horizontal or vertical streaks on the print screen, or if there are uneven density, the smoothness of the image will be impaired, and the image will have a rough, low-quality image. becomes. In order to obtain high image quality comparable to conventional photographic images @Ic, the colored area per dot should be made as wide as possible, the non-colored areas between dots should be reduced, and the heat generation temperature distribution within each dot should be minimized. It is necessary to set it to 5 so that it is flattened and the entire dot is colored with uniform density.

In addition, the lifespan of a thermal head largely depends on the peak temperature of the heating resistor element when it generates heat, so in order to ensure a lifespan that can withstand long-term use, it is necessary to flatten the temperature distribution inside the resistor element and It is necessary to prevent hot areas from forming.

However, in conventional thermal heads, the shape of the heating resistor that forms one dot is rectangular, and because there is a non-heating part between adjacent dots, the heating temperature distribution within one dot is centered. It had a mountain-like distribution, with the temperature being highest at the top and dropping rapidly at the ends. For this reason, only the center of the dot develops color, and the edges do not develop color, resulting in white streaks.If you try to develop color all the way to the edges, the heat generated at the center becomes extremely high, which accelerates the deterioration of the resistor element. There was a drawback.

As a method to flatten the heat generation temperature distribution within one dot,
For example, Japanese Patent Application Laid-Open No. 52-105841 discloses that the current density at the ends of the resistance element is larger than that at the center, and the temperature drop at the ends is reduced, such as by making the heating resistance element octagonal. However, since the shape of each heat-generating resistor element is formed in a straight line or in a step-like manner, the distance between the electrodes changes in a step-like manner, and the current density distribution within one dot becomes step-like. . For this reason, the temperature distribution within one dot is not completely flat, and local peaks and valleys of heat generation temperature occur.
It is difficult to avoid uneven density within one dot and non-colored areas between dots. In particular, since there is an equal distance between the electrodes with a constant width at the center, a peak in the heat generation temperature distribution tends to occur at the center of the dot where heat is likely to accumulate, which has the disadvantage of accelerating the deterioration of the resistance element.

[Purpose of the invention]

The purpose of the present invention is to completely flatten the temperature distribution of the heating resistor element in order to eliminate density unevenness and non-coloring areas, which are the drawbacks of conventional thermal recording heads, thereby increasing the coloring area and preventing deterioration. The purpose is to provide a busy thermal recording head.

[Summary of the invention]

In order to realize this purpose, the thermal recording head 11 of the present invention
5, the shape of one or more resistor elements forming one dot is determined so that the distance between the electrodes in the energizing direction is maximum at the center in the width direction of each resistor element, and gradually decreases as it approaches the ends. By forming a circular arc shape, the current density distribution inside one resistor element becomes gradually larger at the ends, and by generating larger Joule heat closer to the end with better heat dissipation, one dot The temperature distribution within the area is almost completely flattened.

[Embodiments of the invention]

An embodiment of the present invention is shown in FIG.

Figure 1: VC, 1 and 1' are electrodes made of thin or thick metal films, 2 is a heating resistor arranged in a straight line at a predetermined interval so that electricity can be selectively applied to each pixel, and 3 is a This is an insulating part between resistance elements. It is desirable that the width of the insulating portion 50 is as small as 20 μm or less. In addition,
A wear-resistant protective film (not shown) is formed on the heating resistor element.

The heating resistor element 2 has an electrode 1.1 in the current direction (arrow direction).
51C, the distance between the two ends is maximum at the center in the width direction, and gradually decreases as it approaches the ends.

Figure 2 shows the distance between the electrodes and the current density between A and 8 across the resistance element for one resistance element shown in Figure 1, and the current density increases in inverse proportion to the distance between the electrodes. has a gentle distribution that increases as it approaches the edge. Figure 3 shows the temperature distribution in the width direction of the heat generating resistor element. The ends where the current density is high generate more heat due to Joule heat than the central part, but the influence of the insulation part 3 at the ends is Since the heat dissipation is good, they cancel each other out and become almost the same temperature (T3) as the center part, making it possible to obtain a flat temperature distribution without peaks or valleys over the entire width of the heating resistor element. Therefore, if a current is supplied such that the temperature Ts is slightly higher than the coloring temperature To, the entire heating element will develop color in the width direction, and there will be almost no non-colored areas between adjacent dots, and excellent image quality with no density unevenness within the dots will be achieved. Obtainable. Also,
Because the current density has a gentle distribution, there are no localized high temperature areas, which improves the durability of the resistor element.
A highly reliable thermal head that can withstand long-term use can be obtained.

FIG. 4 shows another embodiment of the present invention.
The same parts as those in the figure are indicated by the same reference numerals. On the right side of FIG. 4, 1 dot is formed by two separated resistor elements 21112b, and 4 is an insulating part provided between resistor elements 2a and 2b. When one dot is formed of two resistor elements, the two resistor elements are heated when energized, but the insulating section 4 does not generate heat, so that the temperature of the center of the dot is lower. This has the advantage of extending the life of the resistor, reducing the temperature drop at the end of one dot, and improving coloring efficiency.However, if the resistor element is rectangular in shape, The temperature distribution becomes a bimodal temperature distribution as shown by the broken line in FIG. 5, and is not flat. In the embodiment shown in FIG. 4, since the ends of the two resistor elements in the current direction have an arc shape, the current density distribution within each resistor element becomes closer to the insulating parts 3 and 4. As a result, a flat temperature distribution as shown by the solid line in FIG. 5 can be obtained for the entire dot. Note that if the insulating parts 3 and 4 are made to have the same width, the heat dissipation characteristics will be made uniform, so that the flattest temperature distribution can be obtained.

FIGS. 6 and 7 show other embodiments of the present invention, in which the heating resistor element is tilted to avoid the non-colored portion between the dots from becoming a straight line. It is something to do. In this embodiment as well, the same effect as described above can be obtained by forming the ends of each resistor element in the current direction in an arc shape. In particular, in the embodiment shown in FIG. 7, since one dot is formed by two resistor elements having arc-shaped ends, the coloring efficiency is high, there is no streak-like non-coloring part, and one dot is It has great advantages such as being able to obtain excellent image quality with uniform density distribution within the dots.

Note that the number of resistor elements forming one dot may be three or more, and the shape of the end does not necessarily have to be a perfect circular arc, but may be circular so that the current density changes smoothly. Good to have.

〔Effect of the invention〕

As stated above, if the heating resistor element according to the present invention is used, the temperature distribution within the heating element can be made almost completely flat, there is almost no non-coloring part, and density unevenness within the dots can be eliminated. Smooth image quality can be obtained and the durability of the resistor element can be greatly improved since local high temperature areas are not generated.

Note that the thermal head according to the present invention is effective not only for color printers but also for monochrome or facsimile applications.

[Brief explanation of drawings]

FIG. 1 is a plan view showing a heat generating resistor element according to an embodiment of the present invention, FIG. 2 and TAS are explanatory views thereof, FIG. 4 is a plan view showing another embodiment, and FIG. FIGS. 6 and 7 are plan views showing still other embodiments. Pole 1.1'...Electric number, 2 (2a, 2b)...Heating resistor element. Figure 2 Figure 3

Claims (1)

[Claims] 1. In a thermal recording head in which a plurality of selectively energized heating resistive elements are arranged in a straight line at predetermined intervals,
The ends of the resistor elements in the conduction direction are arranged so that the distance between the electrodes in the conduction direction of each of one or more resistor elements forming one dot gradually decreases from the center in the width direction toward the ends. A thermal recording head characterized by an arcuate shape.