JPH07186421A - Thermal head - Google Patents

Abstract

PURPOSE:To provide a thermal head which is capable of preventing effectively a heat storage layer from being destroyed by great stress and allowing to func tion extending for a long period and has high thermal efficiency. CONSTITUTION:A thermal head is comprised by allowing a heat storage layer 2 possessing a large number of hollow parts 2a to adhere to the upper part of an electric insulating base 1 and a heating resistor 3 and a pair of conductive layers 4 to adhere to the upper part of the heat storage layer 2 and pressure in the hollow part 2a of the layer 2 is made below 400torr (room temperature). Hereby, at the time when the heating resistor is allowed to generate Joule heat at a fixed temperature at the time of printing, even if the temperature of the layer 2 becomes a high temperature by heat, pressure within the hollow part 2a is controlled to almost identical with atmospheric pressure or pressure lower than that and such greater stress that destroys the layer 2 can be prevented effectively from being generated.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an improvement of a thermal head incorporated in a printer mechanism such as a word processor and a facsimile.

[0002]

2. Description of the Related Art Conventionally, a thermal head incorporated in a printer mechanism such as a word processor is as shown in FIG.
A glass heat storage layer 12 containing a large number of bubbles 12a is deposited on an electrically insulating substrate 11 made of alumina ceramics or the like, and a plurality of heating resistors 13 made of tantalum nitride or the like are formed on the heat storage layer 12. It has a structure in which a pair of conductive layers 14 made of aluminum or the like are adhered,
Predetermined electric power is applied between the pair of conductive layers 14 in response to an external electric signal to selectively cause the heating resistor 13 to generate Joule heat, and the generated heat is conducted to thermal paper or the like to generate thermal paper or the like. It functions as a thermal head by forming a predetermined print image on the.

The large number of bubbles 12a contained in the heat storage layer 12 are provided to reduce the heat transfer rate in the heat storage layer 12 and reduce the heat capacity of the heat storage layer 12 to increase the thermal efficiency of the thermal head. This heat storage layer 12
Is formed by printing and coating a predetermined glass paste on the electrically insulating substrate 11 by screen printing and firing the paste under predetermined conditions.

Further, the large number of bubbles 12a contained in the heat storage layer 12 are mixed with the air interposed between the screen meshes in the glass paste at room temperature and normal pressure when the heat storage layer 12 is formed. By forming them, they are formed at the same time.

[0005]

However, in this conventional thermal head, when a large number of bubbles 12a contained in the heat storage layer 12 form the heat storage layer 12 by screen printing, the glass paste is kept at room temperature under normal pressure. The air present between the meshes of the screen is formed in the form of bubbles and mixed at the same time, and the large number of bubbles 12a are formed by air having substantially the same pressure as the atmosphere. . Therefore, when the heating resistor 13 is Joule-heated to a temperature of about 300 ° C. and printing is performed, when the heat is applied to the heat storage layer 12, the thermal expansion coefficient of the glass or the like forming the heat storage layer 12 and bubbles The bubbles 12a are caused by the large difference in the coefficient of thermal expansion of the air forming the bubbles 12a.
The pressure of the air that forms is extremely high (about 1452 torr)
r). As a result, a large stress is generated in the heat storage layer 12, and the heat storage layer 12 is relatively easily destroyed by the large stress, and the function as the thermal head is lost in a short time.

[0006]

DISCLOSURE OF THE INVENTION The present invention has been devised in view of the above-mentioned drawbacks, and an object thereof is to effectively prevent the heat storage layer from being destroyed by a large stress and to enable it to function well for a long period of time. To provide an efficient thermal head.

[0007]

In the thermal head of the present invention, a heat storage layer having a large number of hollow portions is deposited on an electrically insulating substrate, and a heating resistor and a pair of conductive layers are formed on the heat storage layer. A thermal head formed by deposition, wherein the pressure in the hollow portion of the heat storage layer is 400 torr (room temperature) or less.

[0008]

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

FIG. 1A is a perspective view showing an embodiment of the thermal head of the present invention, and FIG. 1B is a sectional view taken along line XX of FIG. 1A.
It is a line sectional view, 1 is an electrically insulating substrate, 2 is a heat storage layer, 2
a is a hollow part, 3 is a heating resistor, and 4 is a pair of conductive layers.

The electrically insulative substrate 1 is made of an electrically insulative material such as alumina ceramics, and has an upper surface for supporting the heating resistor 3 and the like.

The electrically insulating substrate 1 is formed into a sludge form by adding and mixing an appropriate organic solvent and a solvent to ceramic raw material powder such as alumina, silica, magnesia, etc., and is formed by a well-known doctor blade method or calender roll method. Etc. are used to form a ceramic green sheet, and then the ceramic green sheet is punched into a predetermined shape and fired at a high temperature.

On the electrically insulating substrate 1, a heat storage layer 2 made of a heat storage material such as glass or polyimide resin is formed.
It is deposited to a thickness of μm to 80 μm.

The heat storage layer 2 accumulates the heat generated by the heat generating resistor 3 so as to have an appropriate temperature, and serves to keep the thermal response characteristics of the thermal head good.

The heat storage layer 2 has a large number of hollow portions 2a, which are made of gas such as air, nitrogen, and argon, and which are uniformly distributed throughout the heat storage layer 2, inside the heat storage layer 2. Gases such as air, nitrogen, and argon that form 2a have extremely low thermal conductivity as compared with the heat storage material made of glass or the like, so that the heat transfer rate in the heat storage layer 2 is slowed and the heat storage layer 2 The thermal capacity of the thermal head can be increased by reducing the heat capacity.

Further, the pressure inside the hollow portion of the heat storage layer 2 is 400 torr or less at room temperature. Therefore, when the heating resistor 3 is made to generate Joule heat at a predetermined temperature during printing, the heat of the heat storage layer 2 is generated. Even if the temperature becomes high, the pressure inside the hollow portion 2a is suppressed to a pressure that is substantially the same as or lower than the atmospheric pressure, and is large enough to destroy the heat storage layer 2 inside the heat storage layer 2. It is possible to effectively prevent generation of stress. This allows the thermal head having high thermal efficiency to function well for a long period of time.

Further, if the pressure inside the hollow portion 2a of the heat storage layer 2 is kept at room temperature from 10 ⁻⁶ torr to 100 torr, even when the heat storage layer 2 reaches a high temperature of about 300 ° C. during printing, the hollow portion 2 a The internal pressure is suppressed to an extremely low pressure of 190 torr or less, and it is possible to very effectively prevent the heat storage layer 2 from being destroyed by stress. Therefore, the pressure inside the hollow portion 2a of the heat storage layer 2 is 10 ⁻⁶ torr at room temperature.
It is preferable to set it to -100 torr.

Further, if the volume of the hollow portion 2a is set to 10% or more of the volume of the heat storage layer 2, the heat transfer rate of the heat storage layer 2 is slowed and the heat capacity of the heat storage layer 2 is reduced to achieve thermal performance. The thermal efficiency of the head can be effectively increased, and if the volume of the heat storage layer 2 is 70% or less,
The mechanical strength of the heat storage layer 2 can be sufficiently secured.
Therefore, the volume of the hollow portion 2a is 10% to 10% of the volume of the heat storage layer 2.
It is preferable to make it 70%.

For the heat storage layer 2, first, an organic solvent applicable to glass powder having a softening point of 800 ° C. and a glass paste obtained by adding and mixing the organic solvent are printed and applied onto the electrically insulating substrate 1 by screen printing. This is baked at a predetermined temperature (for example, a temperature of about 1000 ° C.) to deposit a first heat storage material made of glass having a softening point of 800 ° C. on the electrically insulating substrate 1, and then the surface of the first heat storage material. A glass obtained by forming a large number of holes by etching on the first heat storage material, and then adding and mixing an organic solvent applicable to the glass powder having a softening point of 500 ° C. and an organic solvent on the first heat storage material. The paste is printed and applied by screen printing, and then the paste is placed in a vacuum device which is kept in a vacuum or a reduced pressure of several tens Torr or less and left for about 1 hour to soften the opening of the hole to a softening point 50. ℃ pressure of 10 ^-6 of the hollow portion 2a to form a hollow portion 2a between the first heat storage material and the second heat storage material closed with a second heat storage material comprising glass torr~
It is formed by setting the pressure to 100 torr and finally firing it at a predetermined temperature (a temperature of 550 ° C. to 700 ° C.). In this case, since the large number of hollow portions 2a are formed by etching, it becomes easy to control the size, distribution, etc. of the hollow portions 2a, and the heat storage characteristics of the heat storage layer 2 can be made uniform.

On the upper surface of the heat storage layer 2, a plurality of heating resistors 3 made of tantalum nitride and a pair of conductive layers 4 connected to both ends of each heating resistor 3 are adhered. .

The heating resistor 3 is made of, for example, tantalum nitride or the like, and has a predetermined electric resistivity, so that Joule heat is generated when electric power is applied through the pair of conductive layers 4. It is raised and heat is generated at a predetermined temperature necessary for forming a printed image, for example, a temperature of 200 ° C to 350 ° C.

The pair of conductive layers 4 connected to both ends of the heating resistor 3 are made of a metal such as aluminum, and the pair of conductive layers 4 are necessary for causing the heating resistor 3 to generate Joule heat. It acts to apply a predetermined power.

The plurality of heating resistors 3 and the pair of conductive layers 4 are formed on the upper surface of the heat storage layer 2 by a well-known sputtering thin film forming technique and photolithography technique. The resistor 3 has a thickness of 0.01 μm to 0.5 μm, and the pair of conductive layers 4 has a thickness of 0.5 μm to 2.0 μm.

A protective layer 5 made of silicon nitride, sialon or the like is further formed on the upper surfaces of the heating resistor 3 and the pair of conductive layers 4.
The protective layer 5 has a function of protecting the heat generating resistor 3 and the like from oxidative corrosion due to contact with moisture contained in the atmosphere and abrasion due to sliding contact with thermal paper or the like.

The protective layer 5 has a thickness of 3 μm or more on the upper surface of the heating resistor 3 or the like by a thin film forming technique such as a sputtering method.
It is deposited to a thickness of 8 μm.

Thus, in the above-mentioned thermal head, a predetermined electric power is applied between the pair of conductive layers 4 in accordance with an external electric signal to selectively cause the heating resistor 3 to generate Joule heat and the generated heat to the thermal paper. To function as a thermal head by forming a predetermined print image on thermal paper or the like.

(Experimental Example) Next, the operation and effect of the present invention will be described based on an experimental example.

First, a heat storage layer made of a polyimide resin having a large number of hollow portions whose internal pressure is set to 100 torr is formed on an electrically insulating substrate made of alumina ceramics (volume of hollow portions / volume of heat storage layer is 50). %) 70 μm
Of the present invention, which is formed by depositing a heating resistor made of tantalum nitride and a pair of conductive layers made of aluminum on the heat storage layer, and an electrical insulation made of alumina ceramics. On the flexible substrate, a heat storage layer made of glass having a large number of hollow parts whose internal pressure is set to 100 torr (volume of hollow parts /
The volume of the heat storage layer is 50%) and the thermal head sample H as a product of the present invention is formed by depositing it to a thickness of 70 μm and depositing a heating resistor and a pair of conductive layers on the heat storage layer.
2 and a heat storage layer made of only glass to a thickness of 70 μm on an electrically insulating substrate made of alumina ceramics, and a heating resistor made of tantalum nitride and a pair of conductive members made of aluminum on the heat storage layer. Comparative thermal head sample H as a conventional product formed by depositing layers
Prepare 3.

Next, for each of the three thermal head samples, 0.2 W of electric power was applied to each heating resistor for 2 msec to cause each heating resistor to generate Joule heat, and the heating resistors in each of the samples H1 to H3 were tested. The surface temperature was examined using an infrared thermometer. The result is shown in FIG.

According to the figure, the surface temperature of the conventional product H3 is 1
While the temperature rose only to 77 ° C, the product H1 of the present invention
Up to 370 ° C. and the product H2 of the present invention rises to 330 ° C., showing that all the products of the present invention have significantly improved thermal efficiency.

The present invention is not limited to the above embodiments, and various changes and improvements can be made without departing from the gist of the present invention. For example, in the above embodiments,
The hollow portions 2a are distributed uniformly over the entire heat storage layer 2, but instead of this, as shown in FIG.
Is distributed so that the heat generation region R1 has a high density and the other regions have a low density, or the hollow portions 2a are distributed only in the heat generation region R1 as shown in FIG. As shown in c), the hollow portions 2a may be distributed in all regions except the region R2 adjacent to the heat generating region R1.
In this case, in the thermal head shown in FIGS. 3 (a) and 3 (b), the heat dissipation characteristic in the area outside the heat generating area R1 becomes good, so that the temperature of the heat generating resistor 3 falls well, and In the thermal head shown in FIG. 3 (c), the heat dissipation characteristics in the area outside the heat generating area R1 are good, and the base portion is kept at a relatively high temperature because of the strong heat storage effect in the outer portion, and repeated printing is performed. The thermal efficiency will be higher when doing.

Further, as shown in FIG. 4, a large number of hollow portions 2a may be formed only in the heat generating region R1 of the heat storage layer 2 and a metal material 2b such as aluminum may be embedded in the outer region thereof. Since the heat dissipation characteristics in the area outside the area R1 are better than those of the thermal head shown in FIGS. 3 (a) to 3 (c), the temperature drop of the heating resistor 3 is extremely good and high-speed printing is possible. It becomes a suitable thermal head.

[0032]

According to the thermal head of the present invention, a heat storage layer having a large number of hollow portions is deposited on an electrically insulating substrate, and a heating resistor and a pair of conductive layers are deposited on the heat storage layer. In the thermal head, the pressure inside the hollow portion of the heat storage layer is 400 torr or less at room temperature. Therefore, when the heating resistor is joule-heated to a predetermined temperature during printing, the temperature of the heat storage layer is increased by the heat. Even if the temperature becomes high, the pressure in the hollow part is kept at a pressure almost equal to or lower than the atmospheric pressure, and a large stress that destroys the heat storage layer is generated inside the heat storage layer. Can be effectively prevented. This allows the thermal head having high thermal efficiency to function well for a long period of time.

[Brief description of drawings]

1A is a perspective view showing an embodiment of a thermal head of the present invention, and FIG. 1B is a sectional view taken along line XX of FIG.

FIG. 2 is a diagram showing a surface temperature of a heating resistor.

3A to 3C are cross-sectional views showing a modified example of the thermal head of the present invention.

FIG. 4 is a sectional view showing a modified example of the thermal head of the present invention.

FIG. 5A is a perspective view of a conventional thermal head,
(B) is a YY line sectional view of (a).

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Electrically insulating substrate 2 ... Heat storage layer 2a ... Hollow part 3 ... Heating resistor 4 ... A pair of conductive layers 5 ... Protective layer

Claims (1)

[Claims] 1. A thermal head comprising a heat storage layer having a large number of hollow portions deposited on an electrically insulating substrate, and a heating resistor and a pair of conductive layers deposited on the heat storage layer. The pressure in the hollow part of the heat storage layer is 400 torr (room temperature)
A thermal head characterized by the following.