JPS59207270A - Thermal head - Google Patents

Abstract

PURPOSE:A thermal head of a heat-sensitive recording device and the like which enables the attainment of printing patterns of uniform density, by using a resistor having a positive temperature resistance characteristic as a heating resistor. CONSTITUTION:A resistor having a characteristic that a temperature-to-resistivity varies at a Curie point from a gently-sloping region to a steep region, that is, a positive temperature resistance characteristic (for example, a posistor which is a ceramic prepared by adding a very small quantity of an element, such as La or Ce, to barium titanate) is used as a heating resistor 3 (which is deposited on a glazed layer 2 of small thermal conductivity provided on a substrate 1 formed of ceramic or the like) of a thermal head. Printing is conducted by impressing a pulse voltage through an electrode 4 in response to a printing instruction. EFFECT:Since the heating resistor has its own upper limit value in the rise of temperature, a heating energy necessitated for printing operations is fixed constantly, and thus uniform density can be obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field] The present invention relates to a thermal head installed in a heat-sensitive recording device, etc., and relates to a thermal head that uses a positive characteristic resistor such as a ql (.
This paper relates to the structure of a thermal head.

<Prior art> A thermal printer using a thermal recording method/thermal transfer recording method is a non-innocent type that does not generate noise, has a simple structure, can be made compact, and can print images at low cost and power. Therefore, it is widely used in calculators, register facsimiles, computer terminals, and other information processing equipment. When recording, electric pulses are applied to the thermal head installed in a thermal printer to generate thermal energy, and this thermal energy can be used to record directly on thermal paper (or it can be used to melt ink and print on recording paper). The recording operation is performed by forming the entire print with this molten ink.However, if electric pulses are continuously applied to the thermal head, even if the electric pulses are constant, heat will accumulate in the heat generating part of the thermal head. Also, there are problems such as fluctuations in the density of the printed pattern (7) due to various factors such as increases in the head substrate or ambient temperature (7), and the recording quality is significantly reduced.Therefore, in conventional thermal printers, this thermal head In order to compensate for temperature changes and obtain a print pattern with uniform density, for example, the input energy of the electric pulse is gradually reduced depending on the number of times the electric pulse is applied.
A control circuit was installed to ensure that the amount of heat stored in the heat generating part and the total value of the heat generating part were always equal, and all vorticity compensation means were included, such as making the density of the printed pattern completely uniform.However, this Adding such a control circuit not only complicates the circuit configuration, but also causes problems when the device l"l becomes larger. In addition, due to the influence of ambient temperature, etc., the heat storage in the heat generating section may not respond consistently to the number of times electric pulses are applied, and the accuracy of temperature compensation deteriorates.

<Objective of the Invention> In view of the above-mentioned current situation, the present invention utilizes a positive characteristic resistance element such as a POSISTOR to make the printed pattern density uniform.
The purpose is to provide 3t and useful thermal treatment f.

<Embodiment> FIG. 1 is a sectional view of the main part of a thermal head showing an embodiment of the present invention.

A lace layer 2'ff having a low thermal conductivity is provided on a substrate 1 made of ceramic or the like, and a heating resistor 3 is deposited thereon. Electrodes 4 are connected to both ends of the heating resistor 3, and the electrodes 4 are connected to a drive circuit to apply a full pulse voltage to the heating resistor 3. Furthermore, the surfaces of the heating resistor 3 and the electrode 4 are covered with a protective film 5.

As shown in Fig. 2, the heating resistor 3 has a resistivity to 1 degree that ranges from a gentle region to a steep region with the cue point as the boundary.
It consists of a resistor, such as a positive characteristic thermistor, which has a characteristic that changes to .

POSISTOR is made of porcelain made by adding elements such as lanthanum and cerium to barium titanate in an amount of 20%, and exhibits a remarkable positive temperature resistance characteristic. The lithium titanate semiconductor porcelain body (which is the main body of POSISTOR) can be formed into any shape or size to a certain extent, just like general porcelain. By forming a pattern on the brace layer 2, the heat-generating part of the thermal helix is constructed.-Also, when it is used as a thermal hemorrhage, it is necessary to use it in a temperature range exceeding the cue point. , the Posister constant is set.

When a pulse voltage is applied from the drive circuit through the four electrodes in response to a printing command, heat is generated in the heat generating resistor 3, and printing is performed using the thermal energy of the heat generating resistor 3 using a thermal recording method or a thermal transfer recording method. The temperature change of the resistor 3 has a sawtooth waveform as shown by the characteristic curve in FIG. 3(A). The upper limit of the temperature (is always maintained constant against repeated application of pulse voltage. Set the upper limit value of the heating temperature required for immediate operation, and configure all the heating resistors 3 up to this upper limit value. If the conditions of the POSISTOR are adjusted so that its resistance value becomes extremely high when the POSISTOR is heated, the temperature of the heating resistor 3 in the standby state will be rapidly raised by the application of the pulse voltage. However, as the temperature approaches the upper limit value, the resistance of the heating resistor 3 suddenly increases, and the rate of temperature rise becomes extremely slow.Therefore, the temperature of the heating resistor 3 reaches just before the upper limit value. When the applied pulse is removed, the rise is suppressed and gradually approaches the upper limit value.When the applied pulse is removed, the temperature is exponentially cooled according to the thermal time constant of the heating resistor 3Vi, and approaches the ambient temperature. do.

Next, when the same full pulse voltage is applied again in response to the printing command, the temperature of the heating resistor 3 is rapidly raised in the same way as described above, and when the set throat/chip temperature approaches the upper limit temperature, the temperature increase rate suddenly slows down. Approaching upper temperature limit. When the applied pulse is released, the three heating resistors are cooled down, but if the same pulse voltage is repeatedly applied in a short cycle jυ1 due to heat accumulation, the cooling gradually becomes incomplete and the lower limit temperature of the heating resistor 3 (d rise However, since the upper limit temperature of the heating resistor 3 is set to a value determined by the crystal resistance of the POSISTOR, 1. It is always -'/L without being affected by the rise in the lower limit temperature.
Lk is maintained. Since the density of the print pattern is determined by the temperature limit of the heating resistor 3, a print pattern with uniform density can be obtained.
(B) is a thermal box diagram of a conventional heating resistor used for comparison. The temperature of the heating resistor increases in response to the application of a pulse voltage, but if When JUJ is repeatedly applied, heat is accumulated in the heating resistor and its surroundings, and the lower limit temperature of the heating resistor rises.In addition, the influence of this heat accumulation As a result, the density of the printed pattern is not constant, and the recording quality deteriorates.

<Effects of the Invention> As described in detail above, the present invention uses a resistor such as a POSISTOR having a positive temperature resistance characteristic diagram as a heating resistor of a thermal head, and the heating resistor itself has an upper limit at 4 temperatures. Because of this value, the heat generation energy required for printing operation is always constant, and a printing pattern with uniform density can be obtained.

[Brief explanation of drawings]

Figure 1 shows the main structure of a thermal head showing one embodiment of the present invention! FIG. FIG. 2 is a temperature vs. resistance characteristic diagram of the POSISTOR used in the thermal head of FIG. Third
Figures (A) and (B) are explanatory diagrams that completely explain the temperature changes between the thermal head shown in Figure 1 and the conventional thermal head.
;, I → r I 5 Hou @ Membrane agent Patent attorney Aihiko Fukushi (and 2 others) Figure 1 Figure 2 Bribery... Poetry and painting Figure 3

Claims (1)

[Claims] 1. A thermal head characterized in that the heating resistor is composed of a resistor having a positive temperature resistance characteristic. 2. A thermal head characterized in that the heating resistor is composed of a POSISTOR. thermal head,.