JPH04152147A - Thermal head and manufacture thereof - Google Patents

Abstract

PURPOSE:To make heating resistors to heat under self-control to a constant temp., uniformize the heating temp. distribution of the heating resistors to improve a dot reproducibility, and prevent the thermal breakage of the heating resistors per se by a method wherein the heating resistors in use function to be rapidly increased in resistance value to suppress a temperature increase when reaching a Curie temp. CONSTITUTION:As a heating resistor 1, a BaTiO3 valence-control semiconductor is used. On an insulating substrate, a mixture of a organometallic material at least containing Ba and Ti is provide. The insulating substrate is burned and annealed and the grains are grown, whereby the BaTiO3 valence-control semiconductor is made polycrystalline. In this manner, with the application of a voltage, the BaTiO3 valence- control semiconductor is increased in temp. by self-heating. However, when reaching a Curie temp., it is rapidly increased in resistance value, whereby an electric current is so suppressed as to stop the temp. increase. If additive elements in the Basic, polycrystalline are uniformly dispersed, the heating temperatures of the resistors are never affected, and a variation in printing density is eliminated. Additionally, the BaTiO3 valence-control semiconductor is not heated more than a Curie temp., thus never being thermally broken if a large voltage is applied thereto by mistake.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a thermal head used in a printer as an output device of a word processor, a personal computer, etc., a recording section of a facsimile, and a method of manufacturing the same.

[Conventional technology]

In recent years, thermal heads have come to be widely employed in printers as output devices for word processors, personal computers, etc., and in heads constituting the recording section of facsimile machines.

The thermal head includes at least one pair of electrodes and a heating resistor provided to bridge the electrode pair to form a heating section, and applying a current to the electrode pair causes the heating resistor to generate heat; Characters, figures, etc. are formed on a recording medium by coloring heat-sensitive recording paper or by sublimating an ink donor film.

This type of thermal head is broadly classified into a thick film type and a thin film type depending on the manufacturing method.

Thick-film thermal heads are easier to manufacture and easier to mass-produce than thin-film thermal heads, which require large-scale film forming equipment. The disadvantage was that the printing quality was inferior to that of the conventional thermal head.

Examples of ways to solve this problem include the foot-off method and MO
D method is known.

An example of a prior art disclosure of a heating resistor of this type of thermal head and a method of manufacturing the same is disclosed in Japanese Patent Application Laid-Open No. 164301/1983.

[Problem to be solved by the invention]

However, both thick-film thermal heads and thin-film thermal heads have variations in resistance values inherent in the heating resistors.

This resistance value variation causes unevenness in the heat generation temperature on the printing surface of the resistor, which appears as unevenness in printing density.

In the conventional thermal head, the variation in resistance value between adjacent heating resistors is adjusted by pulse trimming in the thick film type.

On the other hand, in the thin film type, the variation in resistance value between adjacent heating resistors is small, but the distribution of resistance value has large undulations.
Pulse trimming, which locally adjusts the resistance value as in the thick film type, cannot be applied.

Furthermore, since the heating temperature distribution of the heating resistor is a mountain-shaped temperature distribution with a peak at the center of the heating resistor, there is a drawback that the shape of the printed dots becomes round.

As a countermeasure, it is possible to make the printed dot shape accurately reproduce the shape of the heating resistor by driving with a large current to raise the heating peak temperature, but increasing the temperature will accelerate the deterioration of the heating resistor. There is also the problem that the heating resistor is destroyed.

Deterioration and destruction of the heating resistor occur due to the heat generated by the heating resistor.

Therefore, the life of conventional thermal heads is generally specified as 10" passes (approximately 100,000 sheets for A4 size) at the maximum rated energy (approximately 0.43 mJ).

The purpose of the present invention is to solve the above-mentioned problems of the prior art, and (1) self-control the heating temperature of the heating resistor to generate heat at a constant temperature; and (2) uniformize the heating temperature distribution of the heating resistor to improve dot reproducibility. (3) An object of the present invention is to provide a thermal head that can self-prevent thermal destruction of a heating resistor, and a method for manufacturing the same.

[Means to solve the problem]

In order to achieve the above object, the present invention is characterized in that a polycrystalline BaTi0:+-based valence-controlled semiconductor is used as a heating resistor.

Further, by depositing a film of a metal-organic material mixture containing at least Ba and Ti on an insulating substrate, and baking the insulating substrate on which the printed metal-organic material mixture is deposited, and performing an annealing treatment to cause grain growth. B
aTi0. The method is characterized by including the step of making a polycrystalline valence-controlled semiconductor and using this as a heating resistor.

[Effect]

BaTiO3-based valence control semiconductor ceramics are generally PTC (Positive Temperature
This type of thermistor is widely used as a heater with a self-temperature control function, and its application products such as electronic hot water baths, electronic jars, and hot air blowers are known.

A part of Ba'' in B a Ti Oar is replaced with a metal (
Y3゛, La'', Ce'', Sd'', sbco'', Th'', etc.), or a part of Ti'' is replaced with a metal (Nb
", T a ", W &-, etc.) to form a valence-controlled semiconductor.

The amount of the above impurity added necessary for semiconductor formation is 0. 1~0.
It is about 5 at%.

FIG. 8 is a temperature characteristic diagram of a PTC thermistor in which a part of Ba is replaced with Pb.

B a T i 03 has Curie (
From this Tc, the resistivity is 2. It becomes expensive.

As shown in the figure, this Curie temperature can be shifted to a higher temperature side by replacing Ba with Pb. The temperature rate is 4°C/at% Pb.

This BaTi0. When a voltage is applied to the system valence control semiconductor, the temperature begins to rise due to self-heating, but Curi
When the temperature e is reached, the resistance value increases rapidly, the current is suppressed, and the temperature rise stops.

On the other hand, when the temperature of the heating element decreases due to heat leakage to the surroundings of the heating resistor, the resistance value decreases, and the current increases to try to raise the temperature again.

When this operation is repeated and an equilibrium state is reached, the heating element continues to maintain a constant temperature.

〔Example〕

Embodiments of the present invention will be described in detail below with reference to the drawings.

FIG. 1 is a perspective view of essential parts for explaining the first embodiment of the thermal head according to the present invention, in which 1 is a heating resistor, 2 is a common electrode, 3 is a drive electrode, 4 is a wear-resistant layer, and 5 is an underlayer. The glaze layer 6 is an insulating substrate such as a ceramic substrate.

FIG. 2 is a sectional view taken along line A--A in FIG. 1.

In FIGS. 1 and 2, an underglaze layer 5 is deposited on the surface of a ceramic substrate 6, and a heat generating resistor 1 is placed on the underglaze layer 5.
is formed.

The heating resistor 1 is formed discontinuously in the main scanning direction They are placed opposite each other.

A heat generating portion corresponding to one dot is formed by the common electrode 2, the drive electrode 3, and the portion of the heat generating resistor 1 bridging each electrode.

A wear-resistant layer 4 is formed covering each of the electrodes 3.3 and the exposed portions of the heat generating resistor 1 to smooth the sliding contact with the recording medium, protect the heat generating resistor 1 and each electrode, and protect the heat generating resistor 1. 1 is prevented from oxidizing.

In this embodiment, BaTiO3-based valence-controlled semiconductor ceramic is used as the heating resistor 1.

If the conventional thermal head is a thick-film type, there will be large variations in resistance between adjacent heads, and the resistance values were matched by pulse trimming. In the thin film type, the variation in resistance values between adjacent ones is small, but the resistance value distribution has large undulations, and pulse trimming cannot be performed as in the thick film type.

In the case of the heating resistor according to the present invention, the heating temperature is BaTio
Since the z-based valence control semiconductor generates heat at a constant temperature at the Curie temperature, if the dispersion state of the additive elements inside the BaTiO3 polycrystal is uniform, there will be variations in the resistance value depending on the shape and thickness of each resistor. Since it does not affect the heat generation temperature of the resistor, there is no variation in print density.

Figure 3 is an explanatory diagram of the transient response of the heat generation temperature and heat storage characteristics of the thermal head, and the transient response of the heat generation temperature is shown in the same figure (
As shown in (a), the temperature of the conventional heating resistor increases with time as shown in (a-1), but in the heating resistor of this embodiment, the Curie temperature increases as shown in (a-2). (T
c) becomes flat.

Then, a square wave voltage (b-1) as shown in the same figure (b)
As shown in (b-2), the conventional heating resistor has a high heat generation peak temperature, so the heat does not completely decrease by the next cycle and accumulates heat, and the peak temperature as shown by Pt increases, which increases the next exothermic temperature.

Furthermore, since the heat generated by adjacent dots also has the effect of increasing this peak temperature, it is necessary to control heat accumulation by some means.

On the other hand, since the heating resistor according to this embodiment generates heat at a constant temperature, it becomes flat at Curie temperatures T and c, and there is no influence of heat storage layer heat due to continuous printing or influence of adjacent bits, and no heat storage control is required. As shown in (b-3) of the same figure, the transient response of heat generation can be made to have a heat generation characteristic closer to a square wave by increasing the applied voltage.

FIG. 4 is an explanatory diagram of the heat generation temperature distribution of the thermal head and the shape of printed dots, where (a) is the heat generation temperature distribution by the conventional thermal head, (b) is the heat generation temperature distribution by the present invention's thermal head, and (C) is the heat generation temperature distribution by the thermal head of the present invention. (d) shows a printed dot shape by a conventional thermal head, and (d) shows a printed dot shape by a thermal head of the present invention.

When the shape of the heat generating resistor is rectangular as in the thermal head having the configuration explained in FIGS. 1 and 2, the heat generation temperature distribution of the conventional heat generating resistor is as shown in (a). It has a mountain-shaped distribution with a peak at the center of the heating resistor.

In reality, there is a temperature difference of 25 to 30% between the central part and the peripheral part of the resistor with respect to the heat generation peak.

Therefore, if the heating resistor of the conventional thermal head does not have enough applied power, the printed dot shape becomes round as shown in (C).

For this reason, in the past, sufficient printing power was applied to increase the heat generation temperature to make the printed dots rectangular, but this resulted in excessive thermal stress being applied to the center of the resistor compared to the periphery of the resistor. The central part of the resistor was prone to deterioration.

On the other hand, in the heat generating resistor of the thermal head of this embodiment, when the Curie temperature is reached, the resistance value increases by 2 to suppress the rise in temperature, so that local heat concentration is less likely to occur.

For example, if heat generation reaches a peak at the center of the resistor, the resistance value at the center of the resistor increases, and current flows on both sides of the resistor, which has a lower resistance value.

Although more heat is emitted from both sides of the resistor than from the center, the heating resistor tries to compensate for the drop in temperature due to the heat release by allowing a large amount of current to flow. The current continues to flow preferentially until the heat generation temperature on both sides of the resistor becomes the same as that in the center of the resistor.

When the transient state is reached in this way, the heating resistor has a uniform temperature distribution (b).

Therefore, the shape of the printed dots faithfully reproduces the rectangular shape of the resistor as shown in FIG. 2(d).

However, it is necessary to apply enough voltage so that the heat generation temperature reaches the Curie temperature.

and BaTi0. Since the valence control semiconductor does not reach a temperature higher than the Curie temperature, it will not be thermally destroyed even if a large voltage is accidentally applied.

Therefore, it has the function of self-preventing thermal destruction.

Next, a method for manufacturing a thermal head according to the present invention will be explained.

FIG. 5 is an explanatory diagram of a method for manufacturing a thermal head according to the present invention, in which the thermal head is manufactured in the order of steps (a) to (f).

The BaTiOs-based valence-controlled semiconductor, which is a heat-generating resistor, is made by printing and firing a mixture of metal-organic materials to obtain a thin film of metal oxide, the so-called MOD method (Meiall).
After forming a metal oxide film of a predetermined thickness by repeatedly performing organic deposition (Original Deposition), crystal grains of B a T i O:I can be grown by annealing.

The MOD method is characterized in that a uniform metal oxide compound film of any composition can be easily formed by mixing metal-organic substances, and that the film thickness can be freely controlled by repeating this process.

Hereinafter, a method for forming a heating resistor according to the present invention will be explained in detail.

In this example, as shown below, the main materials are Ba and Ti.
An organic material and additive materials such as Pb and Ta are used.

First, the specifications of the heat generation temperature of the heating resistor are determined, and the mixing ratio of Ba and Pb is determined based on the specifications. Ta is used as the additive element.

For example, assuming that the heating temperature of the heating resistor is 200°C, the mixing ratio of Ba and Pb is 0.8:0°2, and a portion of Ti is replaced by 0.3 at% (atomic %) of Ta. If it is made into a semiconductor, the chemical formula is (B ao, s P b
o, +t ) (T io, qqt Tao.

1103)03.

As the metal-organic material for the heating resistor by MOD, for example, solutions of N, E, and Metal Resinate (trade name) manufactured by Chemcat Co., Ltd. with the following numbers are mixed and used.

#137-C (Ba organic material) #207A (Pb organic material) #9428 (Ti organic material) #7522 (Ta organic material) That is, the atomic ratio after firing each of the above solutions is Ba:P.
b: Yi: Ta = O, sho, 2:0.997:0.003, and then mixed at a ratio of 2:0.997:0.003, and further adjusted to an appropriate viscosity using a solvent such as α-terpineol or butylcarpitol acetate. .

As shown in FIG. 5(a), this MOD heating resistor paste is deposited on a glazed ceramic substrate 6 with an underglaze layer formed on its surface by screen printing or spin cording.

After drying the substrate coated with the MOD heating resistor paste, heat it at 10 to 200"C/m in an infrared belt firing furnace, etc.
Raise the temperature to 600℃ at a heating rate of 600℃
After holding at 1 hour at 0.degree. C., it is cooled.

A MOD film of about 350 nm can be obtained in this one-time film deposition process. This process is repeated until the film thickness is 4 to 8 μm.

Finally, the temperature is raised to 1200°C at a heating rate of 5°/min, annealed at 1200°C for 1 hour, and cooled. 10 is obtained.

Next, as shown in (b), the surface of the substrate 60 on which the heating resistor 10 is formed is coated with, for example, D27 manufactured by Noritake Co., Ltd.
A metal organic gold paste such as (trade name) is printed solidly and fired to form a gold electrode film 20'.

Then, as shown in (C), a resist layer is coated on the surface of the gold electrode film 2, dried, a photomask for exposure is placed on top of the resist layer, exposed to light, and then exposed to light. Photolithography is performed to remove the resist by etching using a potassium solution to obtain the Au electrode film 20.

Next, as shown in (d), using the Au electrode film 20 as a mask, the MOD heating resistor layer 10 is etched using fluorine-nitric acid.

Then, when the exposed portion of the heating resistor is removed from the Au electrode film 20 again by photolithography and etching, it is possible to obtain the heating resistor 1 divided in the main scanning direction as shown in (e).

Finally, as shown in FIG. 1F, a wear-resistant layer 4 is formed on the surface of the substrate subjected to the above-described treatment, thereby completing a thermal head as shown in FIG.

The thermal head manufactured in this way has, for example, a length of 120 μm in the sub-scanning direction and a length of 10 μm in the main scanning direction.
When forming a 0μm resistor, the resistivity is at least 10Ω.
・Since it is about cm, the average resistance value is 15 to 30 Ω.

Therefore, the driving voltage for this thermal head becomes high.

FIG. 6 is a block diagram of a second embodiment of the thermal head according to the present invention, and the same reference numerals as in FIG. 1 correspond to the same parts.

The thermal head shown in the figure has an alternating electrode wiring structure in which a common electrode 2 and a drive electrode 3 are meshed in the sub-scanning direction, and a heating resistor 1 is formed by crossing this meshing portion in the main scanning direction. If the width of the heating resistor 1 in the sub-scanning direction is 130 μm and the width of the alternating electrodes is 20 μm, the average resistance value will be 2 to 4 Ω when the resistivity is 10 Ω・cm.
Therefore, it is possible to lower the driving voltage.

Further, FIG. 7 is a configuration diagram of a third embodiment of the thermal head according to the present invention, and the same reference numerals as in FIGS. 1 and 6 correspond to the same parts.

The thermal head shown in the figure has a structure in which a heating resistor 1 is sandwiched between a rectangular batch-type common electrode 2 and a drive electrode 3 from above and below. 100μm×100μm
By setting the size to , the resistivity of the heating resistor 1 becomes 10Ω.
・The average resistance value can be as small as 40 to 80Ω when the resistance is cm.

If it is desired to further increase this resistance value, the resistivity can be increased by 10 to 100 times the above value by reducing the amount of impurities added.

[Effects of the Invention] As explained above, according to the present invention, the heating resistor is
aTi0. By using a polycrystalline valence-controlled semiconductor, the Curie temperature can be shifted to the high temperature side, and the heat generation temperature is self-controlled to generate heat at a constant temperature, making the temperature distribution of the heat generation part uniform and improving the reproducibility of printed dots. improve the
Moreover, it is possible to provide a thermal head in which self-destruction of the heating resistor is prevented.

[Brief explanation of drawings]

FIG. 1 is a perspective view of a main part explaining a first embodiment of a thermal head according to the present invention, FIG. 2 is a sectional view taken along line A-A in FIG. 1, and FIG. 3 is a diagram showing the heat generation temperature of the thermal head. An explanatory diagram of transient response and heat storage characteristics, Fig. 4 is an explanatory diagram of the heat generation temperature distribution of the thermal head and the shape of printed dots, Fig. 5 is an explanatory diagram of the method of manufacturing the thermal head according to the present invention, and Fig. 6 is an explanatory diagram of the thermal head manufacturing method according to the present invention. FIG. 7 is a block diagram of a second embodiment of the thermal head, FIG. 7 is a block diagram of a third embodiment of the thermal head according to the present invention, and FIG. 8 is a temperature characteristic diagram of a PTC thermistor in which a part of Ba is replaced with Pb. . l...Heating resistor, 2...Common electrode, 3...
- Drive electrode, 4... wear-resistant layer, 5... underglaze layer, 6... insulating substrate such as ceramic.

Claims (2)

[Claims] (1) A thermal head characterized in that a BaTiO_3-based valence control semiconductor is used as a heating resistor. (2) A mixture of metal-organic materials containing at least Ba and Ti is deposited on an insulating substrate, and the insulating substrate coated with the mixture of metal-organic materials is fired and annealed to grow grains of BaTiO.
A method for manufacturing a thermal head, comprising a step of making a polycrystal of a _3-based valence-controlled semiconductor and using this as a heating resistor.