JP3329970B2 - Thermal head - Google Patents

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 as a printer mechanism of a word processor, a facsimile or the like.

[0002]

2. Description of the Related Art Conventionally, a thermal head incorporated as a printer mechanism of a word processor or the like is, as shown in FIG.
1, a heating resistor 12 made of tantalum nitride or the like, a pair of conductive layers 13 made of aluminum or the like, and a protective film 14 made of fired glass are sequentially applied. A predetermined power is applied between the conductive layers 13 based on a print signal to cause the heating resistor 12 to selectively generate Joule heat, and to conduct the generated heat to a heat-sensitive paper or the like pressed by a platen roller or the like, By forming a predetermined print image on thermal paper or the like, it functions as a thermal head.

The protective film 14 protects the heating resistor 12 and the pair of conductive layers 13 from abrasion due to sliding contact with thermal paper or the like and oxidation corrosion due to contact with moisture contained in the air. In addition, it was formed by applying a low softening point glass containing hard inorganic particles made of alumina or the like by a thick film method. The reason why the low softening point glass is used to form the protective film 14 is that if the firing temperature of the glass is too high, the heating resistor 12 and the like may be deformed by heat. The reason why the protective film 14 is formed by the thick film method is that a step corresponding to the thickness of the conductive layer 13 is not formed on the surface of the protective film 14 located on the heating resistor 12 so that the heating resistor 12 is formed. This is because the generated heat is transmitted well to the thermal paper or the like.

[0004]

However, in this conventional thermal head, since the protective film 14 is made of glass, the protective film 14 can be formed by a thick film method such as screen printing or printed. When heat is applied, for example, when the heat is applied, oxygen in the glass forming the protective film 14 diffuses into the heating resistor 12, and as a result, the heating resistor 1
2 has a drawback that it is oxidized and corroded in a very short time, making it impossible to form a predetermined printed image on thermal paper or the like.

Therefore, in order to solve the above-mentioned drawback, a diffusion preventing layer made of silicon nitride, sialon, or the like is interposed between the heating resistor 12 and the protective film 14, and the diffusion preventing layer is used to protect the protective film 14. It is conceivable to block oxygen from diffusing into the heating resistor 12.

However, the heating resistor 12 and the protective film 1
The interposition of the above-mentioned diffusion preventing layer between the heating resistor 12 and the heating resistor 4 was not enough to effectively prevent the oxidative corrosion of the heating resistor 12.

That is, when the diffusion preventing layer is made of silicon nitride, the diffusion preventing layer itself is oxidized by the oxygen in the protective film 14 and its density is reduced. Therefore, diffusion of oxygen is effectively prevented by the diffusion preventing layer. Can no longer be shut off,
There is a disadvantage that the function itself as a diffusion prevention layer is lost in a relatively short time.

When the diffusion preventing layer is made of sialon, although the function of blocking oxygen permeation is excellent, the sialon itself contains oxygen, so that the oxygen in the sialon generates heat. It diffuses near the interface with the resistor 12 and oxidizes and corrodes a part of the heating resistor 12. Also in this case, the electric resistance value of the heating resistor 12 changes,
There is a drawback that unevenness in the density of a printed image is formed on thermal paper or the like.

[0009]

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned drawbacks. It is an object of the present invention to effectively prevent a change in the resistance value of a heating resistor and form a predetermined print for a long period of time. An object of the present invention is to provide a thermal head having excellent corrosion resistance.

[0010]

According to the thermal head of the present invention, a heating resistor is provided on an electrically insulating substrate.
On the heating resistor, Si ₃ N ₄ or Si-Al-N
, A shielding layer made of Si-Al-ON, and a protective film made of fired glass are sequentially applied.

[0011]

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

FIG. 1 is a sectional view showing an embodiment of a thermal head according to the present invention, wherein 1 is an electrically insulating substrate, 1a is a glaze layer, 2 is a heating resistor, 3 is a pair of conductive layers, and 4 is a diffusion layer. The prevention layer, 5 is a shielding layer, and 6 is a protective layer.

The electrically insulating substrate 1 is made of an electrically insulating material such as alumina ceramics, and functions to support the heating resistor 2 and the like on its upper surface.

The electrically insulating substrate 1 is formed into a slurry by adding a suitable organic solvent and a solvent to a ceramic raw material powder such as alumina, silica, magnesia, etc., and forming the slurry into a slurry. A ceramic green sheet is formed by employing the method described above, and thereafter, the ceramic green sheet is punched into a predetermined shape and fired at a high temperature.

Further, a glaze layer 1a made of glass or the like is formed on the upper surface of the electrically insulating substrate 1 so as to have a thickness of 15 μm to 60 μm. The thermal head accumulates at a suitable temperature and acts to keep the thermal response characteristics of the thermal head good.

The glaze layer 1a is formed, for example, by applying a glass paste obtained by adding and mixing an appropriate organic solvent and an organic resin to a powder of a high softening point glass on the upper surface of the electrically insulating substrate 1 by screen printing or the like. Thereafter, this is baked at a high temperature of about 1000 ° C. to 1200 ° C. to be formed on the upper surface of the electrically insulating substrate 1.

On the upper surface of the glaze layer 1a, a plurality of heating resistors 2 made of tantalum nitride or the like are attached and arranged.
Is connected.

The heating resistor 2 is made of, for example, TaN, TaS.
It is made of a NO resistance material such as iO, TiSiO, TaSiNO, etc., and has a predetermined electric resistivity. Therefore, when power is applied through a pair of conductive layers 3, Joule heat is generated, and heat Heat is generated at a predetermined temperature required to form a print image on paper or the like, for example, a temperature of 200 to 350 ° C.

A pair of conductive layers 3 connected to both ends of the heating resistor 2 are made of a metal material such as aluminum. The pair of conductive layers 3 is used to cause the heating resistor 2 to generate Joule heat. It acts to apply necessary predetermined power.

The plurality of heat generating resistors 2 and the pair of conductive layers 3 are formed on the upper surface of the glaze layer 1a by a predetermined pattern and a predetermined thickness by employing a conventionally known sputtering method and photolithography technology. 0.0
A thickness of 1 μm to 0.5 μm, a pair of conductive layers 3 is 0.5
μm to 2.0 μm).

On the upper surfaces of the heat generating resistor 2 and the pair of conductive layers 3, a diffusion preventing layer 4, a shielding layer 5, and a protective layer 6 are sequentially adhered. These layers shield the atmosphere.

The diffusion preventing layer 4 is made of Si ₃ N ₄ or Si—Al—N, and has a dense film quality not containing oxygen, so that oxygen constituting the shielding layer 5 is contained in the heating resistor 2. The diffusion can be effectively prevented, and the heating resistor 2 can be effectively prevented from being oxidized by the components in the diffusion prevention layer 4.

[0023] In the case of forming the diffusion preventing layer 4 in Si ₃ N ₄ is a Si ₃ N ₄ employing a thin film method such conventionally known sputtering, the thickness of 0.2~2.0μm In the case of using Si—Al—N, a target material of AlN and a target material of Si ₃ N ₄ are prepared, and are formed by sputtering them simultaneously in an argon atmosphere.

The shielding layer 5 on the diffusion preventing layer 4 is made of S
Since it is made of i-Al-ON (SiAlON) and has excellent denseness and chemical stability, oxygen that is going to the diffusion preventing layer 4 and the heat generating resistor 2 side is highly dense shielding. The layer 5 is reliably shielded and does not come into contact with the heating resistor 2 or the like.

Further, the Si-Al-
O-N has a stable bonding state, and oxygen is rarely separated. Therefore, even if a small amount of oxygen is separated from the oxygen, the oxygen is slightly oxidized in the vicinity of the upper surface of the diffusion preventing layer 4. The heating resistor 2 is not affected at all. Therefore, the function of the diffusion preventing layer 4 is favorably maintained for a long time.

Further, the protective layer 6 on the shielding layer 5 is formed by a thick film method, and inorganic particles having a low softening point glass as a main component and having a higher hardness than the low softening point glass are contained therein. It is contained in the proportion of.

The protective layer 6 functions to protect the heating resistor 2 and the pair of conductive layers 3 from abrasion due to sliding contact with thermal paper or the like and corrosion due to contact with moisture or the like in the atmosphere.

The inorganic particles in the protective layer 6 are made of a hard inorganic material such as alumina, and have an effect of improving the wear resistance of the thermal head by making the protective layer 6 high in hardness.

Further, if the thermal conductivity of the inorganic particles is substantially equal to or higher than the low softening point glass which is a main component of the protective layer 6, the heat resistance from the heating resistor 2 to the heat sensitive paper or the like can be obtained. The heat to be conducted is not blocked by the inorganic particles, and the thermal efficiency of the thermal head can be improved. Therefore, it is preferable that the thermal conductivity of the inorganic particles is substantially equal to or higher than the low softening point glass which is the main component of the protective layer 6.

Incidentally, the protective layer 6 is formed such that the diffusion preventing layer 4 is made of Si.
-Al-N, the diffusion preventing layer 4
A glass paste obtained by adding and mixing a powder of low softening point glass (softening point: about 450 ° C.) and a predetermined amount of alumina particles (particle diameter: about 1 μm) with an appropriate organic solvent and a solvent is screen-printed. For example, it is formed by applying a thickness of about 4 μm and baking it at a temperature of about 500 ° C. by a thick film technique such as the above. At this baking, the interface between the diffusion prevention layer 4 and the glass paste is The atoms are mutually diffused by heat to form Si-Al-ON with a thickness of about 0.2 μm, that is, the shielding layer 5.

On the other hand, when the diffusion preventing layer 4 is made of Si ₃ N ₄ , the shielding layer 5 and the protective layer 6 are firstly formed on the diffusion preventing layer 4 by a well-known sputtering method.
₂ O ₃ is applied to a thickness of 0.2 to 2.0 μm, and then a glass paste obtained by adding and mixing an appropriate organic solvent and a solvent to the powder of low softening point glass and predetermined alumina particles is screened. For example, about 4
It is formed by applying a thickness of about μm and firing it at a temperature of about 500 ° C. Also in this case, at the interface between the diffusion preventing layer 4 and the Al ₂ O ₃ layer, the constituent atoms of the two diffuse at the interface between the diffusion preventing layer 4 and the Al ₂ O ₃ layer by heat (substitution of Si and Al and substitution of O and N). As a result, Si-Al-ON (shielding layer 5) having a thickness of about 0.2 μm is formed simultaneously with the protection layer 6. Since the Al ₂ O ₃ layer and the protective layer 6 are both oxides, and the Al ₂ O ₃ layer has excellent chemical stability, the Al ₂ O ₃ layer is likely to be brittle due to transformation at the interface region between them. Therefore, the mechanical strength in the interface region between the Al ₂ O ₃ layer and the protective layer 6 can be kept high.

Thus, in the above-described thermal head, a predetermined power is applied between the pair of conductive layers 3 based on a print signal to selectively cause the heating resistor 2 to generate Joule heat, and the generated heat is transferred to a platen roller or the like. The thermal head is made to conduct to thermal paper or the like pressed by the above, and forms a predetermined print image on the thermal paper or the like to function as a thermal head.

It should be noted that the present invention is not limited to the above embodiment, and various changes and improvements can be made without departing from the scope of the present invention. Vickers hardness of 1 on 6
A wear-resistant layer made of a hard material of 000 kg / mm ² or more, for example, silicon nitride, silicon carbide, sialon, or the like may be applied to a thickness of, for example, 3 μm. In this case, the same effect as in the above embodiment is obtained. And the wear resistance of the thermal head is further improved.

[0034]

According to the present invention, oxygen which is to be brought into contact with the heating resistor is surely shielded by the high-density shielding layer, and is contained in the diffusion preventing layer directly deposited on the heating resistor. Oxygen does not contain any oxygen, so that the oxidative corrosion of the heating resistor is extremely effectively prevented. Therefore, the corrosion resistance of the thermal head is significantly improved.

[Brief description of the drawings]

FIG. 1 is a sectional view showing an embodiment of a thermal head according to the present invention.

FIG. 2 is a sectional view of a conventional thermal head.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Electric insulating substrate 2 ... Heating resistor 3 ... A pair of conductive layers 4 ... Diffusion prevention layer 5 ... Shielding layer 6 ... Protective layer

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁷ , DB name) B41J 2/335

Claims (1)

(57) [Claims] A heating resistor is provided on an electrically insulating substrate, and Si ₃ N ₄ or Si—
An anti-diffusion layer made of Al-N, a shielding layer made of Si-Al-O-N, and a protective film made of fired glass are sequentially formed.
A thermal head characterized by being attached.