JPH0429855A - Thermal head - Google Patents

Abstract

PURPOSE:To make the temperature of a heat-generating resistance body on each of lines of recording paper and the temperature of each of the heat-generating resistance bodies on each of the lines rise to the same level under the same conditions by a method wherein ferroelectric substance coat having positive temperature coefficient is added in specified quantity to a place near the heat-generating resistance body to which the addition is made in each of the heat-generating resistance bodies or in each of electrodes that supply electric current to the heat-generating resistance bodies. CONSTITUTION:As electric current is supplied from electrodes 4a, 4b to a heat-generating resistance body 3 at the time when recording is on a certain line of recording paper, the temperature in a temperature-sensitive variable resistance body 7 rises, together with the rise of the temperature in the heat-generating resistance body 3, heat conducted from the heat-generating resistance body 3. Therefore, with adjustments for positions where the resistance body 7 is added and for quantity and thickness of the addition made based on known data, heat value by electric current in the heat-generating resistance body 3 wherein the heat is accumulated decreases by the heat value equivalent to the heat accumulate. Ferroelectric substance coat in 50-300 deg.C Curie point is used as a material for the temperature- snesitive variable resistance body 7 that suddenly increases its resistivity at certain temperature. Such resistance bodies are formed respectively to specified positions with a manufacturing device.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a thermal head used in a thermal printer, a fused thermal transfer printer, or the like.

"Prior Art" Figures 2(a) and 2(b) are a schematic perspective view and a longitudinal side view, respectively, showing a conventional thermal head. In these figures, 1 is an aluminum substrate, and the top surface of this substrate 1 is A thermal insulating layer 2 is formed, and a plurality (hundreds) of heating resistors 3 are formed in parallel on two sides of the thermal insulating layer 2, and a first heating resistor 3 is formed on the upper surface of each heating resistor 3. An electrode 4a and a second electrode 4b are formed. (It is omitted in FIG. 1.) A protective film 5 covers the first electrode 4 a + the second electrode 4 b and the heating resistor 3 . Reference numeral 6 denotes a thermistor for temperature measurement, which is arranged at the center of the upper surface of the substrate 1 in the axial direction.

Note that one of the electrodes 4a and 4b is connected to a common electrode (not shown), and the other is connected to a power supply control section (not shown).

In the thermal head configured in this way, when a current is supplied from a power supply control unit (not shown) to the corresponding heat generating resistor 3 through the predetermined electrodes 4a and 4b, the heat generating resistor 3 generates heat, and the first electrode 4a and the first electrode 4a The heat of the exposed portion between the two electrodes 4b passes through the protective film 5 and causes heat-generating paper (not shown) to develop color, melts ink on an ink ribbon, and transfers the ink to the paper. Then, one page of paper is printed by selecting the heating resistor 3 that supplies current for each line of paper, but the temperature of the heating resistor 3 in each line (the temperature before supplying current) is the same. (Normally, it gradually increases each time one line of paper is printed due to heat accumulation.) If the same amount of current is applied to the heating resistor 3 in each line,
When the heating resistor 3 is storing heat, its temperature becomes higher than normal, causing a difference in printing density between each line. was measured, and the energization time to the heating resistor 3 was controlled according to a predetermined temperature table.

[Problem to be solved by the invention]

However, since the temperature measurement with the thermistor 6 described above is carried out only several times while printing one page of paper, it is not possible to control the temperature change of the heating resistor 3 for each line of the paper.
There is a problem in that there is a slight difference in printing density in each line, resulting in uneven printing in actual printers.

In addition, the heat generating resistor 3 that generated heat in a certain line in the paper accumulates some heat just before supplying current to the next line, so the heat generating resistor 3 that generates heat in a certain line in the paper
There is a difference in the temperature immediately before the current is supplied in the next line between the heating resistor 3 and the heating resistor 3 that did not generate heat, and when the current is supplied under the same conditions, the temperature of the former is higher, and this This also has the problem of uneven printing in actual printers, as in the case described above.

This invention was made to solve the above-mentioned problem, and it is possible to raise the temperature of the heating resistor in each line of paper and the temperature of each heating resistor in each line to the same temperature under the same conditions. The purpose of the present invention is to provide a thermal head that can provide stable quality without uneven printing when used in an actual printer.

[Means to solve the problem]

In order to achieve the above object, the thermal head of the present invention has a positive temperature coefficient characteristic in each heating resistor or in each electrode that supplies current to each heating resistor near the corresponding heating resistor. A predetermined amount of ferroelectric thin film having .

[Function] In the thermal head of the present invention, when a current is passed through a predetermined heating resistor to cause the heating resistor to generate heat, the temperature of the corresponding ferroelectric thin film also rises, so that while the heating resistor is storing heat, In this case, the corresponding ferroelectric thin film also accumulates heat and its resistance increases. At this time, when the same voltage as before is applied to the heating resistor for the same time again, the resistance of the ferroelectric thin film increases, so the current flowing through the heating resistor becomes smaller than before, and the amount of heat generated decreases. In other words, if there is heat stored in the heating resistor, the amount of heat generated by the heating resistor will decrease depending on the degree of heat storage, and as a result, the same voltage will be applied to the heating resistor for the same time regardless of the amount of heat stored in the heating resistor. When applied, the heating resistor rises to the same temperature.

[Embodiment 2] Next, an embodiment of the present invention will be described based on FIGS. 1(A) to 1(E). In addition, in these figures, Figures 2 (A) and (
Those with the same numbers as (b) have the same configuration as those in FIG. 2 (a) and (b).

Figures 1 (a) to (e) show different embodiments of the present invention, and in these figures, 7 is a temperature variable resistor whose resistance increases rapidly when the temperature reaches a certain temperature, and its material is Curie. Ferroelectric coatings with a point temperature of 50°C to 300°C, such as BaTiO3, SrTiO3, Pb
ZrO3 or the like is used and is formed at the following positions using a thin film forming apparatus such as evaporation, sputtering, or CVD.

In other words, the one shown in FIG.
What is shown in FIG. 1 (b) is a first electrode 4a and a second electrode 4.
b, one side of which is in the vicinity of the heating resistor 3 is a protective film 5.
It is formed with the same thickness as the electrodes 4a and 4b so as to be exposed on the side, and the one shown in FIG.
It is formed in the electrode 4b near the heating resistor 3 so as to protrude from the electrodes 4a and 4b so that one surface thereof is exposed to the protective film 5 side, and the one shown in FIG. The second electrode 4b is formed in the vicinity of the heating resistor 3 with the same thickness as the electrodes 4a and 4b so that one surface thereof is exposed to the protection 1 pattern 5 side. It is formed in the vicinity of the heating resistor 3 so as to protrude from the electrodes 4a and 4b so that one surface thereof is exposed to the protective film 5 side.

In each of the above thermal heads,
When a current is passed through the heating resistor 3 from the electrodes 4 a + 4 b at a certain line on the paper, the temperature of the heating resistor 3 rises by 1 cm (at this time, the temperature of the electrodes 4 a and 4 b also rises) and the temperature variable resistor 7 rises. The temperature also increases due to heat conduction of the heating resistor 3. Therefore, when the temperature of the heating resistor 3 increases due to heat storage every time one line of paper is printed, the temperature of the corresponding temperature variable resistor 7 and its resistance also increase. Therefore, even with the same applied voltage, the amount of current flowing through the heat generating resistor 3 gradually decreases, and the amount of heat generated by the current flowing through the heat generating resistor 3 gradually decreases.

Also, for the same reason, a certain line in the paper generated heat (
Even if the same voltage is applied in the next line to the heating resistor 3 (which stores heat) and the heating resistor 3 which does not generate heat (does not store heat), the amount of heat generated by the current will be smaller in the former.

Therefore, if the position, amount and thickness of the temperature variable resistor 7 are adjusted based on data known in advance, the amount of heat stored in the heating resistor 3 can be reduced by an amount corresponding to the amount of heat stored. Since the amount of heat generated by the current decreases, if the same voltage is applied to each heating resistor 3 for the same period of time in all lines of paper, each heating resistor 3 will rise to the same temperature regardless of the amount of heat stored. do.

[Effects of the Invention] As explained above, the thermal head according to the present invention has the following advantages:
If the same voltage is applied to each heating resistor for the same period of time, the heating resistor will rise to the same temperature regardless of the amount of heat stored, so it has the following advantages. It has a great effect.

■Printing unevenness does not occur in actual printers, and high-quality printing can be performed even when printing at high speeds.

■There is no need to install a temperature monitor such as a thermistor.

■There is no need to provide a thermal history control circuit section in the actual printer, and the printer can be made smaller.

[Brief explanation of drawings]

FIGS. 1(a) to 1(e) are longitudinal sectional side views showing a W-shaped embodiment of the present invention, and FIG. 2(a) is a longitudinal side view showing a W-shaped embodiment of the present invention, respectively. (B) is a perspective view showing a conventional thermal head;
FIG. DESCRIPTION OF SYMBOLS 1... Substrate, 2... Heat insulating layer, 3... Heat generating resistor, 4a... First electrode, 4b... Second electrode, 7... Temperature variable resistor.

Claims (1)

[Claims] In a thermal head equipped with a plurality of heat generating resistors provided on a substrate and a first electrode and a second electrode that supply current to each heat generating resistor, the first electrode in each heat generating resistor or each first electrode A thermal head characterized in that a predetermined amount of a ferroelectric thin film having positive temperature coefficient characteristics is added in the second electrode near the corresponding heating resistor.