JP2000158690A - Thermal head - Google Patents

Abstract

PROBLEM TO BE SOLVED: To form a print dot of sufficient density from the start of writing by heating a heat storage layer itself and setting the temperature thereof at a level suitable for printing so that the majority of heat generated from a heating resistor contributes efficiently to printing. SOLUTION: A heat storage layer 2 is applied in stripe onto an insulating substrate 1 and a plurality of heating resistors are arranged linearly thereon. Each heating resistor has one end connected with a common electrode 5a and the other end connected with a ground electrode 5c through a discrete electrode and a driver IC. The heating resistors are heated selectively while carrying a recording medium thereon thus forming a print. In such a thermal head, the heat storage layer 2 is formed of glass having electric resistivity of 250-3000 μΩcm under normal temperature and connected, respectively, with the common electrode 5a and the ground electrode 5c at the opposite ends in the longitudinal direction thereof. The heat storage layer 2 is heated by conducting these electrode 5a-5c.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a thermal head incorporated as a printer mechanism for a word processor, a facsimile, or the like.

[0002]

2. Description of the Related Art As shown in FIG. 5, for example, a conventional thermal head has an insulating substrate 11 made of alumina ceramics or the like.
A heat storage layer 12 having a mountain-shaped cross section is attached to the upper surface of the heat storage layer, and a plurality of heating resistors 13 are attached and arranged near the top of the heat storage layer 12, and a common electrode 14a is provided at one end of each of the heating resistors 13. It has a structure in which a ground electrode 14c is connected to each other end via an individual electrode 14b and a driver IC 15, and a predetermined power is applied between the common electrode 14a and the individual electrode 14b with the driving of the driver IC 15. By applying the applied heat, the heating resistors 13 are individually selectively heated to generate Joule heat, and the generated heat is conducted to a recording medium such as thermal paper to form a predetermined print on the recording medium, thereby functioning as a thermal head.

A switching element and a logic circuit are provided on the circuit forming surface of the driver IC 15 so as to correspond to the heating resistor 13. The switching element is connected between the individual electrode 14b and the ground electrode 14c. By turning this on and off on the basis of print data from the outside, energization to each heating resistor 13 is controlled.

The heat storage layer 12 is for keeping the thermal response characteristics of the thermal head good by accumulating and dissipating the heat generated by the heat generating resistor 13 during the printing operation. It is made of an electrically insulating material having both heat conductivity and low thermal conductivity, for example, glass or polyimide resin.

[0005]

However, according to the above-described conventional thermal head, when printing is to be started, the temperature of the heat storage layer 12 is almost equal to room temperature in many cases. When printing is started, initially, much of the heat generated by the heating resistor 13 is absorbed by the heat storage layer 12 side, and does not contribute much to printing. For this reason, during the period from the start of printing until the heat storage layer 12 warms to some extent (so-called writing start period), it is not possible to form printing dots of a sufficient density, and the printing becomes unclear. Had.

In order to solve the above-mentioned drawback, it has been proposed to control the power applied to the heating resistor 13 so that the heating value of the heating resistor 13 during the writing start period is increased.

However, such control of the applied power requires a memory or the like for storing past printing information, so that the control circuit and the like of the thermal head become complicated and large. There is a drawback, and such control is performed by estimating the temperature state at the time of printing the next line from past printing information, so that accuracy is relatively low and sufficient printing quality is obtained. Not in.

[0008]

SUMMARY OF THE INVENTION The present invention has been devised in view of the above-mentioned drawbacks. A thermal head according to the present invention has a heat storage layer formed in a strip shape on an insulating substrate and a plurality of heat storage layers formed on the heat storage layer. A plurality of heating resistors arranged linearly, one end of each heating resistor connected to a common electrode, and the other end connected to a ground electrode via an individual electrode and a driver IC. A thermal head for forming a print by selectively causing a heating resistor to heat while being transported upward, wherein the thermal storage layer has an electrical resistivity of 25 at room temperature.
The common electrode is connected to one end in the longitudinal direction of the heat storage layer and the ground electrode is connected to the other end of the heat storage layer, and the heat storage layer is heated by applying a current between these electrodes. A thermal head characterized by the following.

The thermal head according to the present invention is characterized in that the thermal storage layer has a temperature coefficient of resistance (TCR) of 1 × 10 ⁻⁶ / ° C. or more.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, a thermal head according to the present invention will be described in detail with reference to the accompanying drawings. FIG. 1 is a cross-sectional view of a thermal head according to one embodiment of the present invention, FIG. 2 is a plan view of an insulating substrate used in the thermal head of FIG. 1, and FIG.
FIG. 4 is an enlarged view of a portion A of FIG. 2, FIG. 4 is an enlarged view of a portion B of FIG. 2, 1 is an insulating substrate, 2 is a heat storage layer, 3 is an electric insulating layer, 4 is a heating resistor, 5a is a common electrode, and 5b is an individual electrode. , 5c is the ground electrode,
6 is a driver IC.

The insulating substrate 1 has a thickness of 0.5 to 1.5 mm.
The upper surface thereof functions as a supporting base material for supporting a heat storage layer 2, an electric insulating layer 3, a heating resistor 4, and the like, which will be described later.

When the insulating substrate 1 is made of, for example, alumina ceramics, an appropriate organic solvent and a suitable solvent are added to and mixed with a ceramic raw material powder such as alumina, silica, magnesia, etc. A ceramic green sheet is formed by using a blade method or a calendar roll method, and then
It is manufactured by punching the green sheet into a predetermined shape and firing at a high temperature.

On the upper surface of the insulating substrate 1, a heat storage layer 2 having a mountain-shaped cross section is attached in a strip shape. Near the top of the heat storage layer 2, a heating resistor array 4a is formed via an electric insulating layer 3. It is arranged.

The heat storage layer 2 is formed of glass having a desired heat resistance, and is 1.0 × 10 ^{−3 to} 5.0 × 1.
Since it has a thermal conductivity of 0 ⁻³ cal / cm · sec · ° C., it functions to accumulate and dissipate the heat generated by the heating resistor 4 during the printing operation, thereby maintaining a good thermal response characteristic of the thermal head. Do

Since the heat storage layer 2 is formed to have a mountain-like cross section as described above, the heating resistor array 4a disposed thereon is projected upward to press the recording medium against the recording medium. (Printing pressure) is also effectively increased.

The heat storage layer 2 contains 5 to 40% by weight of metal fine particles such as Ag (silver), Ti (titanium) and Cr (chromium) so that the electrical resistivity at room temperature is 250 to 3000 μΩcm. %, And has a positive temperature coefficient of resistance (TCR), specifically 2
It is set to a value of × 10 ⁻³ / ° C. or more.

Therefore, when a predetermined voltage is applied to the heat storage layer 2 via the common electrode 5a and the ground electrode 5c connected to both ends in the longitudinal direction, the heat storage layer 2 generates Joule heat according to its TCR, and The heat retention state of the layer 2 is changed by its own heat generation.

That is, when the TCR of the heat storage layer 2 is set to a positive value, the heat generation amount of the heat storage layer 2 is relatively large at 1 W when the heat storage layer 2 is not sufficiently warm, for example, immediately after the start of printing. However, when the heat storage layer 2 has warmed to a temperature of, for example, 75 ° C. to 80 ° C. after some time has elapsed from the start of printing, the heat storage layer 2
2, the electric resistance value increases, the amount of electricity decreases, and the heat value of the heat storage layer 2 also decreases.

Therefore, even if the temperature of the heat storage layer 2 is almost equal to the room temperature when printing is to be started,
By causing the heat storage layer 2 to generate heat in advance as described above, the temperature of the heat storage layer 2 can be set to a temperature suitable for printing, thereby efficiently contributing much of the heat generated by the heating resistor 4 to printing, so-called Printing dots of sufficient density can be formed from the start of writing.

In a state where the heat storage layer 2 is sufficiently warmed, if the TCR is 2 × 10 ⁻³ / ° C. or more, the amount of electricity supplied to the heat storage layer 2 is controlled by using a control circuit or the like using a temperature detecting element. Even without control, the amount of electricity supplied to the heat storage layer 2 naturally decreases as described above, so that the temperature of the heat storage layer 2 can be effectively prevented from becoming excessively high.

Therefore, the thermal storage layer 2 of the thermal head can be maintained at a temperature optimum for printing, and a clear and excellent print can always be formed on a recording medium.

The heat storage layer 2 is formed by, for example, printing a predetermined glass paste obtained by adding and mixing an organic solvent and a solvent to glass powder and Ag powder on the upper surface of the insulating substrate 1 by screen printing or the like. It is applied and then baked at a temperature of 500 to 800 [deg.] C. to form a mountain having a cross section of 1.0 to 3.0 mm in width and 50 to 100 [mu] m in height.

On the other hand, the heating resistor array 4a arranged near the top of the heat storage layer 2 is constituted by a plurality of heating resistors 4 arranged linearly at a dot density of, for example, 300 dpi.

The heating resistors 4 are each made of TaSiO.
₂ or TiSiO _2, TiCSiO ₂ like the electrical resistance material (volume resistivity: 100Myuomegacm higher) are formed by the common electrode 5a on one end, the other end individual electrode
The ground electrode 5c is electrically connected via the driver IC 6 and the driver 5b.

The common electrode 5a is connected to a positive terminal (potential: 24 V) of an external power supply, and the ground electrode 5c is connected to a negative terminal (potential: 0 V) of the external power supply. And individual electrode 5b-ground electrode
The switching element of the driver IC 6 is connected between 5c. That is, the heating resistor 4, the individual electrode 5b, and the switching element are connected in parallel with the above-described heat storage layer 2.

On the circuit forming surface of the driver IC 6, a switching element and a logic circuit are provided with a heating resistor 4.
The switching element is turned on / off based on print data supplied from the outside.

When the switching element is turned on, a predetermined electric power is applied to the heating resistor 4 via the common electrode 5a and the individual electrode 5b, and the heating resistor 4 can form a predetermined dot on the recording medium. Joule heating to temperature.

Since the above-described heat storage layer 2 is also connected between the common electrode 5a and the ground electrode 5c in addition to the heating resistor 4, the potential difference between the two electrodes 5a and 5c is reduced to 24V. If set, a voltage corresponding to this potential difference is also applied to the heat storage layer 2. Therefore, when it is desired to set the voltage applied to the heat storage layer 2 to be smaller than the voltage applied to the heating resistor 4, a resistor is connected to one end or the other end of the heat storage layer 2 in the longitudinal direction or the like. The voltage applied to the layer 2 may be adjusted. In this case, if the resistor is formed on the insulating substrate 1 using the same resistance material as the heating resistor 4, the resistor can be formed at the same time as the patterning of the heating resistor 4. It becomes a more preferable form also from a viewpoint.

The electric insulating layer 3 interposed between the heating resistor 4 and the heat storage layer 2 is for preventing the heat storage layer 2 and the heating resistor 4 from being electrically short-circuited. It is made of glass, Si ₃ N ₄ (silicon nitride), SiAlON (Sialon), SiO ₂ (silicon oxide), SiON, etc. Among these materials, it is preferable to use a material containing Si (silicon) and O (oxygen). It is particularly preferable in terms of adhesion to the heat storage layer 2 and the like.

The electric insulating layer 3 is applied and formed with a thickness of, for example, 0.7 to 1.2 μm by a conventionally known sputtering method, plasma CVD method, or the like so as to completely cover the surface of the heat storage layer 2. The heating resistor 4 and the electrodes 5a, 5b, 5c are deposited and formed in a predetermined pattern and a predetermined thickness by employing a conventionally known thin-film method, that is, a sputtering method, a photolithography technique, an etching technique, or the like.

The driver IC 6 is attached and mounted on the upper surface of the insulating substrate 1 by employing conventionally known face-down bonding or the like. In this case, a large number of output terminals provided on the lower surface of the driver IC 6 are connected to the corresponding individual electrodes 5b, and the ground terminals are connected to the ground electrode 5c via the solder 7, respectively.

Thus, in the above-described thermal head of the present invention, a predetermined power is applied between the common electrode 5a and the individual electrode 5b with the driving of the driver IC 6 while the recording medium such as thermal paper is conveyed onto the heating resistor 4. By applying the heat, the heating resistors 4 are individually selectively Joule-heated in accordance with the print data, and the generated heat is conducted to the recording medium to form a predetermined print on the recording medium, thereby functioning as a thermal head. .

The present invention is not limited to the above-described embodiment, and various changes and improvements can be made without departing from the gist of the present invention.

For example, in the above-described embodiment, the surfaces of the heating resistor 4, the common electrode 5a, the individual electrode 5b and the like are protected from the same material as the electric insulating layer 3 such as Si ₃ N ₄ (silicon nitride) or SiAlON (SiAlON). When covered with the film 8, the heating resistor 4, the common electrode 5a, and the individual electrode 5b are well protected from oxidative corrosion due to contact with moisture and the like contained in the air and wear due to sliding contact of the recording medium. In addition to this, since the thermal stress applied to the upper surface and the lower surface of the heating resistor 4 becomes substantially equal, there is an advantage that the peeling of the heating resistor 4 and the protective film 8 is effectively prevented. Therefore, the surfaces of the heating resistor 4, the common electrode 5a, the individual electrode 5b, and the like are made of Si ₃ N ₄
It is preferable to cover with a protective film 8 made of the same material as the electric insulating layer 3 such as N.

In the above embodiment, if the content ratio of the metal fine particles contained in the heat storage layer 2 is made to gradually increase from the lower region toward the upper region, the thermal efficiency of the thermal head and the surface of the heating resistor are reduced. There is an advantage that flatness can be improved. Therefore, it is preferable that the content ratio of the metal fine particles contained in the heat storage layer 2 is gradually increased from the lower region toward the upper region.

[0036]

According to the thermal head of the present invention, even when the temperature of the heat storage layer is substantially equal to the room temperature when printing is to be started, the heat storage layer itself is heated to print the temperature of the heat storage layer. By setting the temperature to a temperature suitable for printing, most of the heat generated by the heat generating resistor can be efficiently contributed to printing, so that a printing dot having a sufficient density can be formed from the beginning of so-called writing.

According to the thermal head of the present invention, the temperature coefficient of resistance (TCR) of the heat storage layer is set to a positive value, preferably 2 ×.
By setting the temperature to 10 ⁻³ / ° C. or more, when the heat storage layer is sufficiently warmed, the amount of electricity supplied to the heat storage layer can be reduced according to the temperature state. Therefore, the heat storage layer can be maintained at a temperature suitable for printing without using any control circuit or the like using a temperature detecting element, whereby a clear and good print is always formed. It becomes possible.

Further, according to the thermal head of the present invention, by providing an electric insulating layer between the heat storage layer and the heating resistor, an electrical short circuit between the heat storage layer and the heating resistor is ensured. Can be prevented.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view of a thermal head according to one embodiment of the present invention.

FIG. 2 is a plan view of an insulating substrate used in the thermal head of FIG.

FIG. 3 is an enlarged view of a portion A in FIG. 2;

FIG. 4 is an enlarged view of a portion B in FIG. 2;

FIG. 5 is a sectional view of a conventional thermal head.

[Explanation of symbols]

1 ... insulating substrate, 2 ... heat storage layer, 3 ... electric insulating layer, 4 ... heating resistor, 5a ... common electrode, 5b ...
Individual electrode, 5c: Ground electrode, 6: Driver IC, 8: Protective film

Claims (2)

[Claims] 1. A heat storage layer is applied in a strip shape on an insulating substrate, and a plurality of heating resistors are linearly arranged on the heat storage layer, and one end of each heating resistor is connected to a common electrode. A thermal head for forming a print by selectively heating the heating resistor while transporting a recording medium onto said heating resistor, the end being connected to a ground electrode via an individual electrode and a driver IC. The electrical resistivity of the heat storage layer at room temperature is 250 to 300.
The heat storage layer is formed of glass having a thickness of 0 μΩcm, the common electrode is connected to one end of the heat storage layer in the longitudinal direction, and the ground electrode is connected to the other end. Thermal head. 2. The thermal storage layer has a temperature coefficient of resistance (TCR) of 2
The thermal head according to claim 1, wherein the thermal head is at least ^10-3 / ° C.