JPH08267808A - Thermal head - Google Patents

Abstract

(57) [Summary] [Purpose] To provide a thermal head with high thermal efficiency that can function well for a long period of time. A heat storage layer 2 is deposited on a ceramic substrate 1, and a heating resistor 3 and a pair of electrodes 4 are formed on the heat storage layer 2.
In the thermal head formed by depositing the
Is made of a composite material of a resin material and an inorganic material, and the content ratio of the inorganic material in the upper part and the lower part of the heat storage layer 2 is 80% or more, and the content ratio of the inorganic material in the middle part is 50% or less. This makes it possible to improve the heat storage characteristics of the heat storage layer 2 and improve the thermal efficiency without lowering the heat resistance of the heat storage layer 2.

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. 3, a thermal head incorporated as a printer mechanism of a word processor or the like has a ceramic substrate 1 made of alumina ceramics or the like.
A heat storage layer 12 made of borosilicate glass is deposited on the heat storage layer 12, and a heating resistor 13 made of tantalum nitride or the like, a pair of electrodes 14 made of aluminum or the like, and a protective film 15 are formed on the heat storage layer 12. And a predetermined power is applied between the pair of electrodes 14 based on a print signal from the outside to selectively cause the heating resistor 13 to generate Joule heat. The generated heat is conducted to a recording medium such as thermal paper to form a predetermined print image on the recording medium, thereby functioning as a thermal head.

The protective film 15 is made of a highly dense material such as silicon nitride. By covering the heating resistor 13 and the pair of electrodes 14 with the protective film 15, the heating resistor 13 is formed. Etc. are protected from abrasion due to sliding contact of the recording medium and oxidative corrosion due to contact with moisture contained in the atmosphere.

[0004]

However, in this conventional thermal head, the heat storage layer 12 has a relatively high thermal conductivity of borosilicate glass (thermal conductivity: about 2 × 10 ⁻³ ca).
(1 / cm · ° C.), most of the heat generated by the heating resistor 13 is absorbed by the ceramic substrate 11 via the heat storage layer 12, and the heat from the heating resistor 13 can be efficiently transferred. It cannot contribute to printing. As a result, the thermal efficiency of the thermal head is poor.

In order to solve the above drawbacks, it has been proposed to form the heat storage layer 12 with a resin material such as epoxy resin. Since such a resin material has a smaller thermal conductivity than borosilicate glass, It is possible to satisfactorily accumulate the heat generated by the heating resistor 13 and improve the thermal efficiency of the thermal head.

However, when the heat storage layer 12 is formed of a resin material such as epoxy resin, the heat generating resistor 13 is 30
When printing with Joule heat generation at a temperature of 0 to 400 ℃,
The epoxy resin forming the heat storage layer 12 is thermally decomposed in the vicinity of the interface with the heating resistor 13, gas is generated in association therewith, or the resin material is deteriorated so that predetermined heat storage characteristics cannot be obtained. Is triggered.

Further, since the thermal expansion coefficient of the epoxy resin or the like which forms the heat storage layer 12 and the alumina ceramics which forms the ceramic substrate 11 are greatly different from each other, when repeatedly printing at a high printing rate, the heat storage layer 12 and the ceramic are formed. There is a risk that a large thermal stress is generated between the substrate 11 and the joint between the two and the substrate 11 is destroyed.

[0008]

SUMMARY OF THE INVENTION The present invention has been devised in view of the above-mentioned drawbacks, and an object of the present invention is to provide a thermal head having a high thermal efficiency and capable of functioning well for a long period of time.

[0009]

A thermal head of the present invention is a thermal head comprising a ceramic substrate, a heat storage layer deposited on the ceramic substrate, and a heating resistor and a pair of electrodes deposited on the heat storage layer. The heat storage layer is formed of a composite material of a resin material and an inorganic material, and the inorganic content ratio of the upper and lower parts of the heat storage layer is 80% or more, and the inorganic content ratio of the middle part is
It is characterized by being 50% or less.

Further, the thermal head of the present invention is characterized in that a concentration gradient is provided in the content ratio of the inorganic substances above and below the heat storage layer.

[0011]

Embodiments of the present invention will now be described in detail with reference to the accompanying drawings. FIG. 1 is a cross-sectional view showing an embodiment of a thermal head of the present invention, in which 1 is a ceramic substrate, 2 is a heat storage layer, 3 is a heating resistor, 4 is a pair of electrodes, and 5 is a protective layer.

The ceramic substrate 1 is made of a ceramic material such as alumina ceramics and has a heat storage layer 2 on the upper surface thereof.
It also functions to support the heating resistor 3 and the like.

The ceramic substrate 1 is formed into a sludge form by adding and mixing an appropriate organic solvent and solvent to ceramic raw material powder such as alumina, silica, magnesia and the like, and is formed by a conventionally known doctor blade method or calender roll method. A ceramic green sheet is formed by adopting it, and thereafter, the ceramic green sheet is punched into a predetermined shape and fired at a high temperature.

A heat storage layer 2 is formed on the upper surface of the ceramic substrate 1 to a thickness of about 50 μm.

The heat storage layer 2 is formed of a composite material in which an inorganic substance such as silicon oxide or silicon nitride and a resin material such as an epoxy resin or a polyimide resin are mixed substantially uniformly at the molecular level. The thermal conductivity of the layer 2 can be lowered (for example, 9 × 10 ⁻⁴ cal / cm · ° C.) to improve the thermal storage characteristics of the thermal storage layer 2. As a result, the thermal efficiency of the thermal head is improved.

The heat storage layer 2 has an inorganic content of 80% or more in the upper and lower portions of the heat storage layer 2 and 50% in the middle portion.
The following is done.

FIG. 2 is a graph showing the ratio of the inorganic substance (silicon oxide) contained in the heat storage layer 2 having a thickness of 50 μm. The ratio of the inorganic substance contained in the heat storage layer 2 is the same as that of the ceramic substrate 1. 0 to 5 μm near the interface of (lower part)
In the vicinity of the interface with the heating resistor 3, 45 to 50 μm (upper part), 80 to 100%, and 19 μm to 30 μm, 20%. The upper and lower parts of the heat storage layer 2 and the thickness of 19 μm to 30 μm
A concentration gradient is provided in the content ratio of the inorganic substance between the region m and the region m, so that the ratio of the resin material contained in the heat storage layer 2 is 50% of the whole.

Since the content ratio of the inorganic substances in the heat storage layer 2 is 80% or more in the upper portion of the heat storage layer 2 as described above, even if the heat generating resistor 3 generates Joule heat during printing, The heat storage layer 2 in the vicinity of the body 3 is never decomposed by heat, and the decomposition of the heat storage layer 2 effectively prevents generation of gas or deterioration of the resin material in the heat storage layer 2. To be done. Thereby, the heat storage characteristics of the heat storage layer 2 can be maintained at a predetermined value.

When the content ratio of the inorganic substance is smaller than 80% in the upper part of the heat storage layer 2, a large amount of resin material is contained in the heat storage layer 2 near the heat generating resistor 3, so that the heat storage near the heat generating resistor 3 is accumulated. There is a risk that the layer 2 will be decomposed by heat. Therefore, the content ratio of the inorganic substance needs to be 80% or more in the upper portion of the heat storage layer 2.

In the heat storage layer 2, the content ratio of the inorganic substances is
Since it is 80% or more in the lower portion of the heat storage layer 2, the coefficient of thermal expansion of the heat storage layer 2 near the ceramic substrate 1 and the ceramic substrate 1 are close to each other, and the adhesion between them is extremely good. Therefore, even if Joule heat is generated in the heating resistor 3 during printing, no large thermal stress is applied between the heat storage layer 2 and the ceramic substrate 1, and the heat storage layer 2 and the ceramic substrate 1 are not applied.
And can be well bonded.

At this time, the content ratio of the inorganic substances is such that the heat storage layer 2
If it is less than 80% in the lower part of the, the thermal expansion coefficient between the heat storage layer 2 near the ceramic substrate 1 and the ceramic substrate 1 is greatly different, and the risk of the adhesion between the heat storage layer 2 and the ceramic substrate 1 being deteriorated. Have Therefore, the content ratio of the inorganic substance needs to be 80% or more in the lower portion of the heat storage layer 2.

Further, the composite material forming the heat storage layer 2 is
By setting the content ratio of the inorganic substances contained therein to 20% or more of the entire heat storage layer, the rigidity of the heat storage layer 2 can be secured to a sufficient level, and the sliding contact of the recording medium during printing can be achieved. Even if an external force is applied to the heat storage layer 2 due to, for example, the heat storage layer 2 is not easily broken, and the heat storage layer 2 can be maintained in a predetermined shape. Therefore, the composite material forming the heat storage layer 2 is
It is preferable that the content ratio of the inorganic substances contained therein be 20% or more of the entire heat storage layer.

The heat storage layer 2 is formed by a conventionally known sputtering method, vacuum deposition method, ion plating method, CVD method.
When a sputtering method is adopted, a sputtering target made of silicon oxide and a sputtering target made of epoxy resin are provided on two cathode electrodes provided in a film forming chamber of the sputtering apparatus. The ceramic substrate 1 is arranged so as to face each other, and then the film formation chamber is filled with argon gas, and predetermined electric power is intermittently applied to the above-mentioned two cathode electrodes to apply inorganic particles and resin from each target. By depositing the material on the surface of the ceramic substrate 1, the inorganic particles and the resin material are mixed at the molecular level. At this time, the ratio of the inorganic material to the resin material of the composite material forming the heat storage layer 2 can be adjusted by changing the magnitude of the electric power applied to each cathode electrode.
As a result, the specified thermal conductivity (5 × 10 ^-4 cal / cm ・ ° C ~ 2
A heat storage layer 2 having a density of × 10 ^-3 cal / cm · ° C) is formed.

A plurality of heating resistors 3 made of tantalum nitride or the like are deposited and arranged on the upper surface of the heat storage layer 2, and a pair of electrodes 4 are connected to both ends of each heating resistor 3. ing.

The heat generating 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 electrodes 4. , Joule heat is generated at a predetermined temperature necessary for forming a printed image on a recording medium, for example, a temperature of 300 ° C to 400 ° C.

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

The plurality of heat generating resistors 3 and the pair of electrodes 4 are formed on the upper surface of the heat storage layer 2 in a predetermined pattern and a predetermined thickness (0.01% for the heat generating resistor 2) by adopting the conventionally known sputtering method and photolithography technique. ~ 0.5 μm
The thickness of the pair of electrodes 3 is 0.5 to 2.0 μm).

A protective film 5 is also deposited on the upper surfaces of the heating resistor 3 and the pair of electrodes 4.

The protective film 5 is made of silicon nitride or the like, and protects the heat generating resistor 3 and the pair of electrodes 4 from corrosion due to contact of moisture contained in the atmosphere and abrasion due to sliding contact of the recording medium. To act.

The protective film 5 is formed with a predetermined thickness by a conventionally known sputtering method or the like.

Thus, the above-mentioned thermal head applies a predetermined electric power between the pair of electrodes 4 based on the print signal,
While selectively heating the heating resistor 3 by Joule,
The generated heat is conducted to the recording medium to form a predetermined print image on the recording medium, thereby functioning as a thermal head.

The present invention is not limited to the above embodiments, and various modifications and improvements can be made without departing from the gist of the present invention.

[0033]

According to the thermal head of the present invention, the heat storage layer is formed of a composite material of a resin material and an inorganic material, and the content ratio of the inorganic material in the upper part and the lower part of the heat storage layer is 80% or more, and the inorganic material in the middle part. Since the content ratio is 50% or less, it is possible to improve the heat storage characteristics of the heat storage layer and improve the thermal efficiency without lowering the heat resistance of the heat storage layer.

According to the thermal head of the present invention, even if the heating resistor is heated by Joule heat during printing, the heat storage layer in the vicinity of the heating resistor is never decomposed by heat, and the decomposition of the heat storage layer causes gas And the resin material in the heat storage layer is effectively prevented from being deteriorated. Thereby, the heat storage layer can be kept to have a predetermined heat storage characteristic.

Further, according to the thermal head of the present invention, the adhesion between the heat storage layer and the ceramic substrate is extremely good. No large thermal stress is applied to the heat storage layer, and the heat storage layer and the ceramic substrate can be firmly bonded to each other.

[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 graph showing a content ratio of an inorganic substance contained in the heat storage layer.

FIG. 3 is a sectional view of a conventional thermal head.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Ceramic substrate 2 ... Heat storage layer 3 ... Heating resistor 4 ... A pair of electrodes 5 ... Protective film

Claims (2)

[Claims] 1. A thermal head comprising a ceramic substrate on which a heat storage layer is deposited, and a heat generating resistor and a pair of electrodes deposited on the heat storage layer, wherein the heat storage layer is a composite material of a resin material and an inorganic material. And a content ratio of the inorganic material in the upper part and the lower part of the heat storage layer is 80% or more and a content ratio of the inorganic material in the middle part is 50% or less. 2. The thermal head according to claim 1, wherein a concentration gradient is provided in the content ratio of the inorganic substances above and below the heat storage layer.