JPH0199860A - Thermal head - Google Patents

Abstract

PURPOSE:To control the size of a dot to be printed according to conduction time of a current passed to a heating resistor, by gradually increasing the width of the heating resistor from a first electrode toward a second electrode. CONSTITUTION:The smaller its width, the larger current density and heating quantity a heating resistor 3 has. When conduction time of current to the resistor 3 of which width increases as it approaches a second electrode 4b from a first electrode 4a or its peak value is small, the narrower portion of the resistor 3 only gives out heat enough to fuse ink and ink on an ink surface facing the upper heating portion only fuses to reduce the size of a dot to be printed. To increase the size, the conduction time of the current or peak value is increased and heat given off by a wider portion is increased accordingly to also fuse ink on an ink surface facing the portion.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a thermal head used in a thermal printer.

[Prior Art] FIG. 7 is a sectional view showing the structure of a conventional thermal head. In this figure, l is a substrate made of aluminum oxide, and a glass gelase layer 2 for thermal insulation is laminated on the upper surface of the substrate l.

A heating resistor 3 made of a resistive film is formed on the top surface of the glass gelatin layer 2, and electrodes 4a and 4b are formed on the top surface of the heating resistor 3 at a predetermined distance apart. here,
The surface of the heating resistor 3 exposed between the electrodes 4a and 4b becomes the heating portion 3h. Further, one of the electrodes 4a and 4b is connected to a common electrode, and the other is connected to an output end of a power supply control section (having a function of flowing current to the heating resistor 3), not shown.

5 is an oxidation-resistant film, and electrodes 4m, 4b and heat generating part 3h
It is formed to cover the Furthermore, a wear-resistant film 6 is formed on the upper surface of the oxidation-resistant film 5 . The oxidation-resistant film 5 and the wear-resistant film 6 constitute a protective film. The thermal heads described above are arranged facing the platen 10, and the ink 8 is placed between these thermal heads and the platen 10.
The ink film 7 and the paper 9 to be transferred are arranged.

FIG. 8 is a plan view of the above-mentioned thermal head, and as shown in this figure, the heat generating portion 3h of the heat generating resistor 3 has a rectangular shape.

In the thermal head configured in this manner, when a current flows through the heating resistor 3, the entire heated portion of the resistor 3 uniformly generates heat. As a result, the portion of the ink film placed on the thermal head facing the heat generating portion is heated, and the ink is melted.

As a result, dots having the shape shown by broken lines in FIG. 8 are printed on the transfer paper.

[Problems to be Solved by the Invention] Incidentally, in order to express the density gradation of an image using a thermal printer, it is desirable to control the size of printed dots. With the head, it was only possible to print dots in a shape based on the shape of the heat generating part of the heat generating resistor, and the size of the dots could not be controlled.

The present invention has been made in view of the above-mentioned circumstances, and an object of the present invention is to provide a thermal head that can control the size of printed dots.

[Means for Solving the Problems] In order to solve the above-mentioned problems, the present invention includes a heat insulating layer formed on the surface of the substrate, a heat generating resistor formed of a resistive film on the heat insulating layer, and
In a thermal head in which a first Tti electrode, a second electrode that supplies current to the heating resistor, and a protective layer that protects the surface are sequentially laminated, the width of the heating resistor is set to the first Tti electrode.
It is characterized in that it gradually widens as it approaches the second electrode from the electrode.

[Function] According to the above configuration, the width of the heating resistor is narrow, the current density is large, and the amount of heat generated is large. Therefore, if the current flow time or the peak value of the current flowing through the heating resistor is small, only the narrow part of the heating resistor will generate enough heat to melt the ink, so it should be placed above the heating resistor. Only the ink on the ink surface facing that area is melted, and if the current flow time or peak value of the current flowing through the heating resistor is increased, the amount of heat generated in the area with a wide resistance will increase accordingly. The ink on the ink side facing the section is also melted. Therefore, by controlling the duration of the current flowing through the heating resistor or its peak value, the size of the printed dots can be controlled.

[Examples] Examples of the present invention will be described below with reference to the drawings.

FIG. 1 is a plan view showing the configuration of an embodiment of the present invention, and FIG.
The figure is a sectional view taken along the line ■-■ in FIG.

Here, only the parts that are different from the above-mentioned FIG. 7 will be explained, and the same parts as in FIG. 7 will be given the same reference numerals and the explanation thereof will be omitted.

In FIG. 1 and FIG. 2, 3 is a heating resistor;
The resistance width is minimum La on the first electrode 4a side, and the resistance width monotonically increases linearly as it approaches the second electrode 4b.
On the b side, the width is Lb.

Here, La is less than half the size of Lb.

In such a configuration, when a current is passed from the first electrode 4a to the second electrode 4b via the heat generating resistor 3, the resistance width is smallest on the first electrode 4a side, so that the heat generating resistor 3 in the vicinity
The current density becomes the maximum, and the amount of heat generated also becomes the maximum. The closer the electrode is to the second electrode 4b, the larger the resistance width becomes, so the current density becomes smaller and the amount of heat generated becomes smaller.

By the way, a certain amount of thermal energy is required to melt ink. Therefore, when the current flow time or peak value of the current flowing through the heating resistor 3 is small, only the heat generated in the narrow part of the heating resistor 3 reaches the thermal energy that melts the ink, and the ink in this part Only the ink on the surface is melted, and when the current flow time or peak value of the current flowing through the heating resistor 3 is increased, the amount of heat generated in the wide part of the heating resistor 3 also reaches the thermal energy that melts the ink, and a wide area is melted. The ink is melted.

In other words, by changing the duration or peak value of the current flowing through the heating resistor 3, the melting range of the ink surface can be controlled, and the size of the dots transferred to the transfer paper can be controlled as shown in Figure 3. Sao (a), (b), (c)
, can be changed as shown in (a).

FIG. 4 is a diagram showing a plurality of heating resistors 3 arranged in a row. As shown in this figure, in an actual thermal head, it is desirable to alternately change the direction of the heating resistor 3. By doing this, when the dots to be thermally transferred are small, the dots are uniformly transferred without being biased upward or downward, and distortion of the characters can be prevented.

FIG. 5 shows a second embodiment of the invention, in which the heating resistor 3
, the second N-pole 4 is slightly away from the contact part with the first electrode 4a.
The resistance width is the smallest near the b side, and the resistance width becomes wider as it approaches the second electrode 4b side. Furthermore, FIG. 6 shows a third embodiment of the present invention, in which the resistance width of the heating resistor 3 at the contact portion with the first electrode 4a is the minimum, and from there the resistance width approaches the 27th [pole 4b side]. The resistance width increases monotonically in a curved manner. These second
Also in the third embodiment, the current density in the heating resistor can be changed according to the resistance width of each part, and the same effect as in the first embodiment can be obtained.

[Effects of the Invention] As explained above, according to the present invention, the width of the heating resistor is gradually increased from the first electrode to the second electrode, so that the current flow time or the waveform of the current flowing through the heating resistor is By controlling the high value, the melting range of the ink can be controlled,
Therefore, the size of the printed dots can be controlled.

[Brief explanation of the drawing]

FIG. 1 is a plan view showing the configuration of an embodiment of the present invention, and FIG.
The figure is a sectional view taken along the line ■-■ in Figure 1, Figure 3 is a diagram showing the shape of the dots thermally transferred in the thermal head of the present invention, and Figure 4 is the first electrode and heating resistor in the thermal head of the present invention. , a plan view showing the arrangement method of the second electrode, the fifth
The figure is a plan view showing the configuration of the second embodiment of the present invention.
The figure is a plan view showing the configuration of the third embodiment of the present invention.
The figure is a sectional view showing the structure of a conventional thermal head, and FIG. 8 is a plan view of the same thermal head. 1...Substrate, 2...Glass gelase layer (thermal insulation layer), 3...Heating resistor, 4a...
...First electrode, 4b... Second electrode, 5...
... Oxidation-resistant film, 6... Wear-resistant film (5 and 6 constitute a protective layer). Fig. 1 Fig. 2rR Fig. 3 To) Tbl ・Nose Crystal 2---\ , --1- (C) (d) Fig. 4 Fig. 5

Claims (1)

[Claims] A heat insulating layer is formed on the surface of the substrate, and a heat generating resistor made of a resistive film, a first electrode and a second electrode that supply current to the heat generating resistor, and a protective layer that protects the surface are sequentially laminated on the heat insulating layer. 1. A thermal head characterized in that the width of the heating resistor is gradually increased from the first electrode to the second electrode.