JPH08207331A - Thermal head - Google Patents

Abstract

PURPOSE: To provide a thermal head with excellent resistances to corrosion which can effectively prevent a resistance change of a heat-generating resistance body and form a predetermined image for a long time. CONSTITUTION: A heat-generating resistance body 2 is set on an electrically insulating substrate 1, and an Si3 N4 thin film layer 4, an SiO2 thin film layer 5, and a baked glass layer 6 are sequentially layered on the heat-generating resistance body 2. Although the oxygen in the baked glass layer 6 would come into touch with the heat-generating resistance body 2 when the baked glass layer 6 is formed, this is effectively prevented by the Si3 N4 thin film layer 4 and SiO2 thin film layer 5. Moreover, since the Si3 N4 thin film layer 4 itself does not include oxygen, a value of the electric resistance of the heat-generating resistance body 2 hardly changes even when the thermal head is used for a long time. Accordingly, printing images can be always formed good to heat- sensitive recording papers.

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 for a word processor, a facsimile or the like.

[0002]

2. Description of the Related Art Conventionally, as shown in FIG. 2, a thermal head incorporated as a printer mechanism such as a word processor has an electrically insulating substrate 1 made of alumina ceramics or the like.
1 has a structure in which 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 layer 14 made of baked glass are sequentially laminated. A predetermined electric power is applied between the layers 13 based on a print signal to selectively cause the heating resistor 12 to generate Joule heat, and the generated heat is conducted to the thermosensitive recording paper pressed by a platen roller or the like to generate thermosensitive recording. It functions as a thermal head by forming a predetermined print image on paper.

The protective layer 14 protects the heating resistor 12 and the pair of conductive layers 13 from abrasion due to sliding contact of the thermal recording paper and oxidative corrosion due to contact with moisture contained in the atmosphere. Yes, thick film methods such as screen printing low softening point glass containing PbO (lead oxide), SiO ₂ (silicon oxide), B ₂ O ₃ (boron oxide), BaO (barium oxide), CaO (calcium oxide), etc. It was formed by coating and baking (about 500 ° C.). The reason why the low softening point glass is used for forming the protective layer 14 is that there is a risk that the heating resistor 12 or the like is deformed by heat if the glass is burned at an excessively high temperature. The layer 14 is formed by a thick film technique so that the surface of the protective layer 14 deposited on the heat-generating resistor 12 is made flat so that the thermal recording paper can be well adhered to the protective layer 14 during printing. This is because

[0004]

However, in this conventional thermal head, the protective layer 14 is formed by coating and baking glass by a thick film technique such as screen printing. When heat is applied to the glass coated on the heating resistor 12 during formation, oxygen contained in the protective layer 14 diffuses to the heating resistor 12 side at the interface between the heating resistor 12 and the protective layer 14. However, the heating resistor 12 is largely oxidized and corroded. As a result, the electric resistance value of the heating resistor 12 fluctuates significantly, and it is impossible to form a predetermined print image on the thermal recording paper.

In order to solve the above-mentioned drawbacks, therefore, an inorganic material, such as SiO ₂ (silicon oxide), which is chemically stable even when heat is applied, is provided between the heating resistor 12 and the protective layer 14. It is conceivable to intervene and prevent the oxygen in the protective layer 14 from diffusing into the heating resistor 12 by this SiO ₂ .

However, the heating resistor 12 and the protective layer 1
The interposition of SiO ₂ between the above and 4 did not completely prevent oxidative corrosion of the heating resistor 12.

That is, when SiO ₂ is interposed between the heating resistor 12 and the protective layer 14, oxygen in the protective layer 14 can be prevented from diffusing into the heating resistor 12. Oxygen forming SiO ₂ diffuses little by little near the interface with the heating resistor 12, and if the thermal head is used for a long time, a part of the heating resistor 12 is oxidized and corroded by the diffusion of oxygen near the interface. As a result, the electric resistance value of the heating resistor 12 changes, and there is a drawback that unevenness in the printed image is formed on the thermosensitive recording paper.

It is also possible to interpose an oxygen-free inorganic material such as Si ₃ N ₄ between the heating resistor 12 and the protective layer 14. In this case, the protective layer 14 is used.
When heat is applied during the formation of Si, the Si ₃ N ₄ itself is oxidized by the diffusion of oxygen contained in the protective layer 14, and the denseness thereof is lowered. As a result, the diffusion of oxygen from the protective layer 14 cannot be blocked by Si ₃ N ₄ , and it is impossible to form a predetermined print image on the thermal recording paper as in the conventional thermal head described above. It was

Further, in this case, when heat is applied during formation of the protective layer 14, PbO in the glass forming the protective layer 14 is formed.
And Si ₃ N ₄ partially react with each other to generate a bubble of nitrogen, and when the bubble remains in the protective layer 14, a convex portion corresponding to the shape of the bubble is formed on the surface of the protective layer 14. As a result, the surface flatness of the protective layer 14 is greatly impaired. As a result, the thermal recording paper cannot be brought into close contact with the thermal head in a good manner, which causes a defect that unevenness in the printed image is formed.

[0010]

SUMMARY OF THE INVENTION The present invention has been devised in view of the above-mentioned drawbacks, and an object thereof is to provide a thermal head having excellent corrosion resistance capable of forming a predetermined printed image for a long period of time. It is in.

[0011]

A thermal head according to the present invention comprises a heating resistor provided on an electrically insulating substrate and
It is characterized in that a Si ₃ N ₄ thin film layer, a SiO ₂ thin film layer, and a baked glass layer are sequentially laminated on the heating resistor.

[0012]

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

FIG. 1 is a sectional view showing an embodiment of a thermal head of the present invention. 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 Si.
₃ N ₄ thin film layer, 5 is a SiO ₂ thin film layer, and 6 is a baked glass layer.

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 2 and the like.

The electrically insulative 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 employed to form a ceramic green sheet, which is then punched into a predetermined shape and fired at a high temperature.

A glaze layer 1a made of glass or the like is deposited on the upper surface of the electrically insulating substrate 1 to a thickness of 15 μm to 60 μm. The glaze layer 1a appropriately generates heat generated by the heating resistor 2. It accumulates so that it will reach a certain temperature and keeps the thermal response characteristics of the thermal head in good condition.

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

A plurality of heating resistors 2 made of tantalum nitride or the like are deposited and arranged on the upper surface of the glaze layer 1a, and a pair of conductive layers 3 are provided at both ends of each heating resistor 2.
Is connected.

The heat generating resistor 2 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 3. When it is raised, heat is generated at a predetermined temperature necessary for forming a printed image on the thermosensitive recording paper, for example, a temperature of 200 ° C to 350 ° C.

The pair of conductive layers 3 connected to both ends of the heating resistor 2 are made of a metal material such as aluminum, and the pair of conductive layers 3 cause Joule heat generation in the heating resistor 2. It has the function of applying the required predetermined electric power.

The plurality of heating resistors 2 and the pair of conductive layers 3 are formed on the upper surface of the glaze layer 1a with a predetermined pattern and a predetermined thickness (the heating resistors 2 are 0.0
1 μm to 0.5 μm thick, the pair of conductive layers 3 is 0.5
(μm to 2.0 μm thick).

On the upper surfaces of the heating resistor 2 and the pair of conductive layers 3, a Si ₃ N ₄ thin film layer 4, a SiO ₂ thin film layer 5,
The fired glass layers 6 are sequentially laminated, and these layers shield the heating resistor 2 and the like from the atmosphere.

Since the Si ₃ N ₄ thin film layer 4 has an extremely dense film quality and contains no oxygen, Si
_The heating resistor 2 is not oxidized and corroded by the components in the ₃ N ₄ thin film layer 4.

Further, SiO ₂ on the Si ₃ N ₄ thin film layer 4 is
Since the thin film layer 5 has the property of being chemically stable even when heat is applied when forming the fired glass layer 6, Si ₃
It is hardly oxygen SiO ₂ thin film layer 5 are diffused into N ₄ thin film layer 4, also be heat is applied during the formation of the sintered glass layer 6, Si ₃ N ₄ thin film layer 4 is oxidized It does not significantly reduce the precision. If the thermal head is used for a long period of time, the oxygen in the SiO ₂ thin film layer 5 will become S
Although a little diffused in the i ₃ N ₄ thin film layer 4, these oxygens only slightly oxidize the vicinity of the surface of the Si ₃ N ₄ thin film layer 4,
It has no effect on the electric resistance value of the heating resistor 2.
Therefore, the antioxidation function of the Si ₃ N ₄ thin film layer 4 can be favorably maintained for a long period of time.

[0025] The Si ₃ N ₄ thin film layer 4 and the SiO ₂ thin-film layer 5, by employing a thin film method such as a sputtering method, on the upper surface of such heat generating resistor 2, 0.1, respectively
The layers are sequentially laminated with a thickness of 2.0 μm.

The sintered glass layer 6 on the SiO ₂ thin film layer 5 is made of PbO (lead oxide), SiO ₂ (silicon oxide), B.
aO (barium oxide), B ₂ O ₃ (boron oxide), CaO
It is formed of a low softening point glass containing (calcium oxide) or the like in a predetermined ratio, and has an inorganic particle having a hardness higher than that of the low softening point glass, for example, A
1 ₂ O ₃ particles are contained in a predetermined ratio.

The baking glass layer 6 has a function of protecting the heat generating resistor 2 and the pair of conductive layers 3 from abrasion due to sliding contact of the thermal recording paper and corrosion due to contact with moisture in the atmosphere, and the above baking. The inorganic particles in the glass layer 6 have the function of improving the wear resistance of the thermal head by making the sintered glass layer 6 have high hardness.

Further, if the thermal conductivity of the inorganic particles is substantially equal to or larger than that of the low melting point glass which is the main component of the sintered glass layer 6, the heating resistor 2
The heat that is transmitted from the thermal recording paper to the thermal recording paper 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 that of the low melting point glass which is the main component of the baked glass layer 6.

The baked glass layer 6 is made of PbO.
70% by weight, SiO ₂ 15% by weight, BaO, B ₂ O
₃ , powder of low softening point glass (softening point: about 450 ° C) containing 5% by weight each of CaO and an appropriate organic solvent and solvent are added and mixed to prepare a glass paste, and a predetermined amount of alumina is added thereto. A thick film method such as a screen printing method is applied to the electrically insulating substrate 1 on which the heating resistor 2 and the pair of conductive layers 3 are adhered by adding particles (particle diameter: about 1 μm). While applying to a thickness of 4 μm,
It is formed by firing it at a temperature of about 500 ° C.

At this time, the SiO ₂ thin film layer 5 is interposed between the PbO contained in the sintered glass layer 6 and the Si ₃ N ₄ thin film layer 4, and bubbles (nitrogen) are generated between them. Since a chemical reaction that accompanies the occurrence does not occur, the surface flatness of the baked glass layer 6 is high, and the thermal recording paper can be brought into good contact with the thermal head during printing. This makes it possible to form a clear printed image on the thermosensitive recording paper.

As described above, S is placed on the heating resistor 2.
iO ₂ thin film layer 5, Si ₃ N ₄ thin film layer 4, baked glass layer 6
If the layers are sequentially laminated, some chemical adsorption force acts between the Si ₃ N ₄ thin film layer 4 and the SiO ₂ thin film layer 5 in addition to the physical adsorption force between the layers. The SiO ₂ thin film layer 5 and the calcined glass layer 6 are firmly bonded together by the SiO ₂ contained in the calcined glass layer 6, so that the SiO ₂ thin film layer 5 and the calcined glass layer 6 are laminated on the heating resistor 3. The adhesion between layers is extremely high, and even if a heat pulse is repeatedly applied to each of these layers, peeling does not easily occur between the layers.

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

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 thermal head of the above embodiments, the baked glass is used. A wear resistant layer made of a hard material having a Vickers hardness of 1000 kg / mm ² or more, for example, silicon nitride, silicon carbide, sialon or the like may be deposited on the layer 6 to have a thickness of, for example, 3 μm. In this case, In addition to the same effects as those of the above embodiment, the wear resistance of the thermal head is further improved.

[0034]

According to the present invention, when forming a fired glass layer, it is effective that oxygen in the fired glass layer tries to contact the heating resistor by the SiO ₂ thin film layer and the Si ₃ N ₄ thin film layer. Since the Si ₃ N ₄ thin film layer itself is shielded and does not contain oxygen itself, the electric resistance value of the heating resistor does not change significantly even if the thermal head is used for a long period of time, and the thermal recording paper It is possible to form a good printed image without density unevenness over a long period of time.

Further, according to the present invention, since the SiO ₂ thin film layer has the characteristic of being chemically stable even at a high temperature when forming the fired glass layer, oxygen in the SiO ₂ thin film layer becomes Si. It hardly diffuses into the ₃ N ₄ thin film layer, and Si ₃
The denseness of the N ₄ thin film layer is kept high, and the oxidation preventing function of the Si ₃ N ₄ thin film layer is maintained well.

Further, according to the present invention, the PbO contained in the fired glass layer and the Si ₃ N ₄ thin film layer are shielded by the SiO ₂ thin film layer, and the Si ₃ N ₄ thin film layer and the fired glass layer are separated from each other. Since a chemical reaction involving generation of bubbles does not occur between them, the surface flatness of the baked glass layer is kept high, and the thermal recording paper can be brought into good contact with the thermal head during printing.

[Brief description of drawings]

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

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

[Explanation of symbols]

1 ... insulating substrate 2 ... heating resistor 3 ... pair of conductive layers 4 ... Si ₃ N ₄ thin film layer 5 ... SiO ₂ thin-film layer 6 ... fired glass layer

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Kosho Kusawa 999-3 Hayato-cho, Aira-gun, Kagoshima Prefecture Kyocera Corporation Hayato factory

Claims (1)

[Claims] 1. A heating resistor is provided on an electrically insulating substrate, and a Si ₃ N ₄ thin film layer, SiO 2 is formed on the heating resistor.
_A thermal head consisting of _two thin-film layers and a laminated glass layer, which are laminated in this order.