JPH02117854A - Thermal head - Google Patents

Abstract

PURPOSE:To restrict an abnormal increase in the temperature of a thermal resistor by providing a constitution in which the resistance of the thermal resistor increases suddenly, if its temperature rises beyond a specified level. CONSTITUTION:A thermal head 1 consists of thermal resistors 4a, 4b, 4c, 4d... spaced between them arranged on a substrate 3 of an electrically insulative material supported with a supporting plate 2. The thermal resistor 4 has almost a constant value at near a normal temperature, and is characteristic of a sudden twofold increase in the resistance value at near a particular temperature (curie temperature; C.P.) over a resistance value at normal temperature. Therefore, if the temperature of a particular part reaches the level of curie temperature due to a continuously pulsed drive across the same electrode corresponding to a single printing dot, the resistance value of the part increases suddenly to prevent the smooth run of an electric current. Consequently, any further temperature increase is restricted so that the thermal resistor 4 is maintained at a constant temperature level.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a thermal head of a thermal printing device used as a printer in a word processor, typewriter, etc., or also used in a facsimile receiver or the like.

Conventional technology A conventional thermal head has a structure in which a heating resistor and an electrode are sequentially laminated on a substrate made of an electrically insulating material.A constant voltage is applied to the heating resistor via the electrode, and the This causes the heating resistor to generate Joule heat to print on thermal recording paper.

Figure 9 is a graph showing the temperature characteristics of the heating resistor. The horizontal axis shows the temperature T, and the vertical axis shows the resistance value (RT) of the heating resistor at the temperature T and at room temperature (25°C). The ratio with the resistance value (R25) is taken. In No. 9 [21], lines 11, 12, and 13 show the resistance-temperature characteristics of three types of substances conventionally used as materials for heating resistors. As is clear from the figure, the resistance value of the conventional heat-generating resistor remains approximately constant against temperature changes.

Fig. 10 is a waveform diagram for explaining the conventional printing motion Y, and l2I (1) in the same figure shows the voltage waveform of the drive pulse applied between the electrodes corresponding to one printing dot of the heating resistor. The figure (2) shows the temperature change of the heating resistor to which this drive pulse is applied. In this conventional technology,
Drive pulses having the same pulse width W1 have a constant period W
The case where the voltage is applied repeatedly to the same telephone line is shown.

That is, when a driving pulse is repeatedly applied between the same electrodes, the corresponding portion of the heating resistor becomes the 101st
As shown in 1ffl (2>), the temperature gradually rises, and even during the non-printing period when no drive pulse is applied, the temperature does not drop to a level that does not discolor the thermal recording paper, resulting in undesired printing operations. Therefore, when performing continuous printing in which drive pulses are repeatedly applied between the same electrodes, it is necessary to consider the time required for the heating resistor to cool down sufficiently, making it impossible to perform high-speed printing. Ta.

In another conventional technique for solving such a problem, as shown in FIG. 11 (1), a voltage at a constant period W is applied to a drive pulse between the same electrodes corresponding to one printed dot. The number of voltage applications for each of a plurality of periods W immediately before the application period Wi is stored, and a driving pulse is applied such that the greater the number of voltage applications, the shorter the period Wi in which power is applied. Although this conventional technology can suppress the temperature rise of the heating resistor and shorten its cooling time, as described above, the semiconductor memory for storing the number of voltage applications and the pulse width of the drive pulse are determined. It is necessary to provide an arithmetic processing unit for performing arithmetic processing to perform the calculation, and the configuration thereof is complicated. Further, even though such a driving method is used, it is still not possible to avoid an increase in the temperature of the heating resistor as a whole, which is an obstacle to high-speed printing.

SUMMARY OF THE INVENTION An object of the present invention is to provide a thermal head that can suppress abnormal temperature rise of a heating resistor even when pulsed driving is performed continuously, and that can perform high-speed printing with a simple configuration. .

Means for Solving the Problems The present invention provides a thermal head in which a heating resistor is interposed between a pair of electrodes, and a pulse is applied between the electrodes to cause the heating resistor to generate heat. This thermal head is characterized by having a structure in which resistance increases rapidly when the resistance exceeds a predetermined value.

Effect According to the present invention, the heating resistor is configured such that its resistance increases rapidly when its temperature exceeds a predetermined value, so even if pulses are continuously applied between specific electrodes, no heating occurs. When the temperature of the resistor exceeds the predetermined value, it becomes difficult for current to flow, and further temperature rise can be suppressed.

Embodiment FIG. 1 is a perspective view showing the structure of a thermal head 1 according to an embodiment of the present invention, and FIG. 2 is an equivalent circuit diagram thereof. The thermal head 1 includes a plurality of heating resistors 4a and 4b spaced apart from each other on a substrate 3 made of an electrically insulating material supported by a support plate 2.

4c, 4d,... (hereinafter collectively referred to as heating resistor 4)
are arranged on this heating resistor 4, and an individual electrode 5 and a plurality of common electrodes 6a, 6b, 6c, 6d, . . . (hereinafter referred to as
(generally referred to as the common electrode 6) are laminated. Each of the common electrodes 6 is individually connected to an integrated circuit element 7, which is a driving circuit provided on the substrate 3.

FIG. 3 is a graph showing the resistance temperature characteristics of the heating resistor 4 used in the present invention. In the same figure, the horizontal axis is the temperature T
The vertical axis shows the ratio of the resistance value (RT) of the heating resistor 4 at temperature T to the resistance value (R25) at room temperature (25° C.).

As shown in FIG. 3, the heating resistor 4 of the present invention has a nearly constant resistance value near room temperature, and at a certain temperature (Curie temperature; C, P, >), the resistance value changes to the resistance value at room temperature. It has a characteristic that the heating resistor 4 rapidly increases to twice the size of the
When continuous pulse driving is performed between the same electrodes corresponding to two printed dots, and the temperature of a specific part approaches the above-mentioned cue temperature, the resistance value of that part increases rapidly, making it difficult for current to flow. Further temperature rise is suppressed, and the heating resistor 4 is kept at a constant temperature. The heating resistor 4 used has a specific resistance in the range of 0.5 to 35 Ωcm at room temperature.

FIG. 4 is a waveform diagram for explaining the operation.

FIG. 1 (1) shows the waveform of a driving pulse having the same pulse width W1 that is continuously applied at a fixed period W between the same electrodes corresponding to the same printed dot.

Even when driving pulses are continuously applied in this way, the temperature of the heating resistor 4 does not exceed a certain temperature because the heating resistor 4 has a resistance temperature characteristic as shown in FIG. (See Figure 4 (2)).

Further, FIG. 4(3) shows the relationship between time and temperature in case 6 using a heating resistor having a resistance temperature characteristic different from that of this embodiment. In this case as well, only the characteristic curves of temperature rise and temperature fall are different, and even if driving pulses are continuously applied, the temperature of the heating resistor does not exceed a certain level.

As a material having such resistance-temperature characteristics, for example, a barium titanate (BaTiO*)-based material is used. Also, the temperature range where the resistance value increases rapidly is
It is determined by the following conditions. In other words, the lower limit of this temperature range is a temperature suitable for printing, that is, the temperature that can change the color of thermal recording paper, and the upper limit is a temperature that is suitable for printing, that is, a temperature that can discolor thermal recording paper, and the upper limit is a temperature that is suitable for printing, that is, a temperature that can change the color of thermal recording paper. The temperature is chosen so that the recording paper can be immediately cooled to a temperature that does not cause it to turn brown.

When these conditions are met, even if driving pulses with the same pulse width and the same period are continuously applied between the same electrodes, the temperature will always remain constant during the period when the driving pulses are applied. During the period when no drive pulse is applied, the thermal recording paper is cooled to a temperature that does not cause discoloration. Therefore, even if such a driving method is used, it is possible to avoid an undesired temperature rise of the heat generating resistor, thereby extending its life. In addition, since the time required for cooling can be shortened, high-speed printing can be performed without the occurrence of thin vertical stripes known as trailing when printing is performed without sufficient cooling. Can be done.

FIG. 5 is a perspective view showing the main structure of a thermal head 11 according to another embodiment of the present invention, and FIG. 6 is an equivalent circuit diagram thereof. In the thermal head 11 of this embodiment, the individual electrodes 16
Electrode portions 15a of the common electrode 15 are alternately arranged between the electrode portions 15a and the individual electrodes 16, and the individual electrodes ff! 16 heating resistors 14 extending in the arrangement direction are laminated. With such a thermal head 11, is it individual? ! ! , a current flows through the heating resistor 14 between the pole 16 and the electrode portion 15a of the common electrode 15,
Printing is performed.

FIG. 7 is a perspective view showing the main structure of still another embodiment of the present invention, and FIG. 8 is an equivalent circuit diagram thereof. In the thermal head 21 of this embodiment, the heating resistor 24 extending along the arrangement direction of the individual electrodes 26 is laminated on the individual electrodes 26, and the electrode portion 25a of the common electrode 25 is stacked on the heating resistor 24 in m layers. and configured. This thermal head 2
1, the individual voltage VM is connected from the electrode portion 25a of the common electrode 25.
Current flows to 26, Joule heat is generated in this portion, and printing is performed.

The heating resistors 14 and 24 of the second and third embodiments also use materials having the same resistance temperature characteristics as those of the first embodiment.
The same effects as in the first embodiment can be obtained in this embodiment as well.

Effects of the Invention As described above, according to the present invention, one continuous pulse drive can be achieved.
Even if there is only one heating resistor, the temperature of the heating resistor will not rise above a predetermined temperature, so the cooling time can be shortened and high-speed printing can be easily achieved.

[Brief explanation of drawings]

The first (21 is a perspective view showing the main part configuration of the thermal head 1 according to an embodiment of the present invention, the second (2I is an equivalent circuit diagram thereof, and the third is a graph showing the resistance temperature characteristics of the heating resistor 4. Fourth
The figure is a waveform diagram for explaining the operation, FIG. 5 is a perspective view showing the main structure of a thermal head 11 according to another embodiment of the present invention, FIG. 6 is an equivalent circuit diagram thereof, and FIG. 7 is a diagram of the present invention. Further, FIG. 8 is a perspective view showing the main part configuration of the thermal head 21 of Ike's embodiment, FIG. 8 is an isometric circuit diagram thereof, and FIG. 9 shows the resistance temperature characteristics of the heating resistor used in the prior art thermal head. The graphs, FIGS. 10 and 11 are waveform diagrams showing the operations of the first and second prior art techniques, respectively. 1 11.21...Thermal head, 3.1323.
...Substrate, 4,14.24...Heating resistor, 5゜15
25...Common electrode, 6,16.26...Individual electrode agent Patent attorney Kei Saikyo Part-6 Note T Diagram B? IvI Jitsusuke Magozu Figure 8// Figure Figure Figure 8,” Kasaasa T.

Claims (1)

[Scope of Claims] In a thermal head in which a heating resistor is interposed between a pair of electrodes and a pulse is applied between the electrodes to cause the heating resistor to generate heat, the heating resistor is configured such that when the temperature of the heating resistor exceeds a predetermined value, A thermal head characterized by having a configuration in which resistance increases rapidly.