JP3117243B2 - 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 a thermal head incorporated in a printer mechanism such as a word processor and a facsimile.

[0002]

2. Description of the Related Art As shown in FIG. 2, a thermal head conventionally incorporated in a printer mechanism such as a word processor has a heat storage layer 12 made of a polyimide resin on a substrate 11 having good thermal conductivity made of an Fe alloy or the like. A heat relaxation layer 13 made of silicon oxide or the like and preventing the heat storage layer 12 from being softened and deformed by heat generated by the heating resistor 14, a heating resistor 14 made of tantalum nitride or the like, and a pair of conductive layers made of aluminum or the like 15a and 15b and a protective layer 16 made of silicon nitride or the like are sequentially applied. A predetermined power is applied between the pair of conductive layers 15a and 15b, and the heating resistor 14 is turned on. Joule heat is generated at a predetermined temperature, and the generated heat is conducted to the thermal paper 17 to form a print image on the thermal paper 17, thereby functioning as a thermal head.

However, in this conventional thermal head, the thermal relaxation layer 13 is made of silicon oxide, which has low hardness (Vickers hardness: about 60).
0Hv), when stress is applied to the thermal relaxation layer 13 by sliding of the thermal paper 17 during printing, cracks 13a are easily formed in the thermal relaxation layer 13, and as a result, the thermal relaxation layer 13 is deposited on the thermal relaxation layer 13. Heating resistor 14 or conductive layer 15a,
There was a drawback that a disconnection occurred at 15b and the function as a thermal head was lost.

Therefore, in order to solve the above-mentioned disadvantage, it is conceivable to use, for example, silicon nitride having a high Vickers hardness of about 1500 Hv instead of silicon oxide having a low hardness for the thermal relaxation layer 13.

However, in the thermal head using this silicon nitride as the thermal relaxation layer, the silicon nitride forming the thermal relaxation layer is not well compatible with the polyimide resin forming the thermal storage layer.
The disadvantage is that the bonding strength between the two is weak, and the thermal relaxation layer peels off from the heat storage layer when the frictional force accompanying the sliding of the thermal paper is applied between the two during printing, and the function as a thermal head is lost. Induces.

[0006]

SUMMARY OF THE INVENTION The present invention has been devised in view of the above-mentioned disadvantages, and a thermal head according to the present invention has a heat storage layer made of a polyimide resin on a substrate having good thermal conductivity. In a thermal head having a heat generating resistor and a conductive layer disposed on the heat storage layer, between the heat storage layer and the heat generating resistor, silicon nitride is used as a main component, and an oxygen content ratio is increased from the heat storage layer side. It is characterized in that a heat relaxation layer gradually decreasing toward the heating resistor side is interposed.

In the thermal head according to the present invention, the heating resistor and the conductive layer are covered with a protective layer made of silicon nitride.

[0008]

Embodiments of the present invention will be described below with reference to the accompanying drawings. FIG. 1 is a sectional view showing an embodiment of the present invention, wherein 1 is a substrate, 2 is a heat storage layer, 3 is a thermal relaxation layer, 4 is a heating resistor, 5a and 5b are conductive layers, and 6 is a protective layer. , Substrate 1
Heat storage layer 2, thermal relaxation layer 3, heating resistor 4, conductive layer 5
a, 5b and a protective layer 6 are sequentially applied.

The substrate 1 is made of a good heat conductive material such as an Fe alloy, supports the heating resistor 4 and the like on the upper surface, and sets the temperature of the thermal head to a temperature required for forming a good printed image on the thermal paper. It acts to control.

The substrate 1 is formed by forming an Fe alloy or the like into a plate shape by employing a conventionally known rolling method or the like.

On the upper surface of the substrate 1, a heat storage layer 2 is adhered. The heat storage layer 2 accumulates the heat generated by the heat generating resistor 4 so as to have an appropriate temperature, so that the thermal response characteristic of the thermal head is obtained. Works to keep the good.

The heat storage layer 2 is made of a heat-resistant polyimide resin, and a varnish serving as a polyimide resin is applied on the substrate 1 by a conventionally known spin coating method.
This is thermally cured at a temperature of about 350 [deg.] C., so that a thickness of 20 to 30 [mu] m is deposited on the substrate 1.

On the upper surface of the heat storage layer 2, a heat relaxation layer 3 mainly composed of silicon nitride is applied.
Can effectively prevent the softening deformation of the heat storage layer 2 by diffusing and relaxing the heat generated by the heat-generating resistor 4 attached thereon and transmitting the heat of the diffused relaxation to the heat storage layer 2 made of a polyimide resin. Works.

The thermal relaxation layer 3 containing silicon nitride as a main component has an oxygen content in the range of, for example, 40 to 5% from the heat storage layer 2 side to the heating resistor 4 side. Since the portions of the heat relaxation layer 3 that are in contact with the heat storage layer 2 have a high oxygen content, the familiarity between the heat relaxation layer 3 and the heat storage layer 2 is greatly improved, and the two are bonded very firmly. It becomes possible. Therefore, even if a frictional force accompanying the sliding of the thermal paper is applied between the thermal relaxation layer 3 and the thermal storage layer 2, they do not peel off at all, and the function of the thermal head is not lost.

The thermal relaxation layer 3 containing silicon nitride as a main component has an oxygen content ratio of oxygen contained in the thermal relaxation layer 2.
From the side toward the heating resistor 4 side, the Vickers hardness of the heat relaxation layer 3 can be maintained as high as about 1400 Hv. Even if stress is applied to the relaxation layer 3, the thermal relaxation layer 3 does not crack, and the heating resistor 4 and the conductive layers 5a and 5b that are deposited on the heat relaxation layer 3
No disconnection occurs.

The thermal relaxation layer 3 containing silicon nitride as a main component, in which the oxygen content ratio gradually decreases from the heat storage layer 2 side to the heating resistor 4 side, is formed by a sputtering method. A target made of silicon nitride and a substrate 1 on which a heat storage layer 2 is adhered is placed at a predetermined position in a sputtering apparatus, and the inside of the sputtering apparatus is evacuated to about 1 × 10 ⁻⁵ torr. Is filled with argon gas, high-frequency power is applied to the target while the oxygen content contained in the argon gas is gradually reduced, and silicon nitride scattered from the target is deposited on the heat storage layer 2 to deposit the gas. Is done.

On the upper surface of the heat relaxation layer 3, a heating resistor 4 is further adhered, and on the heating resistor 4, a pair of conductive layers 5a and 5b with a constant interval are adhered. Have been.

The heating resistor 4 is made of, for example, tantalum nitride or the like and has a predetermined electric resistivity. Therefore, when electric power is applied through the pair of conductive layers 5a and 5b, Joule heat is generated. And generates heat at a temperature required to form a printed image, for example, at a temperature of 250 to 400 ° C.

The pair of conductive layers 5a and 5b provided on the heating resistor 4 are made of a metal such as aluminum or silver, and the conductive layers 5a and 5b generate Joule heat in the heating resistor 4. It acts to apply a predetermined electric power necessary for the operation.

The heating resistor 4 and a pair of conductive layers 5a,
5b is sequentially deposited on the thermal relaxation layer 3 by employing a conventionally known sputtering method and photolithography technique.

The heating resistor 4 having the pair of conductive layers 5a and 5b on its upper surface is covered with a protective layer 6 made of silicon nitride, and the protective layer 6 is formed of the heating resistor 4 and the pair of conductive layers. The layers 5a and 5b serve to protect the layers 5a and 5b from abrasion due to sliding with the thermal paper and the like, and from corrosion by contaminants such as moisture in the atmosphere and chlorine ions and sodium ions contained in the thermal paper and the like.

In this case, the protective layer 6 is made of the same silicon nitride as the main component of the thermal relaxation layer 3, and when the thermal head is used, the heat generated by the heating resistor 4 generates heat.
Since a large thermal stress does not occur between the protective layer 6 and the protective layer 6, the protective layer 6 can be adhered to the base in a good condition without cracks. Is improved.

The protective layer 6 is formed by a conventionally known sputtering method or the like to form a pair of conductive layers 5a, 5a.
The heating resistor 4 is attached with a predetermined thickness to the upper surface of the heating resistor 4 having b.

Thus, in the above-described thermal head, power is applied between the pair of conductive layers 5a and 5b in response to an external electric signal to cause the heating resistor 4 to generate Joule heat to a predetermined temperature and to generate the generated heat. Conduction to thermal paper 7 etc.
By forming a predetermined print image on the thermal paper 7 or the like, it functions as a thermal head.

Next, the operation and effect of this embodiment will be described based on experimental examples.

First, in the thermal head having the structure shown in FIG. 1, as shown in Table 1, silicon nitride is used as a thermal relaxation layer as a main component, and the oxygen content ratio decreases gradually from the heat storage layer side to the heating resistor side. First, three types of thermal head samples, one made of silicon oxide and one made of silicon nitride containing no oxygen, were prepared, and then a predetermined power was applied between a pair of conductive layers to heat the heating resistor at 350 ° C.
The heat-sensitive paper was run at a speed of 13 mm / sec while generating heat, and the distance traveled by the heat-sensitive paper when cracks and peeling occurred in the heat relaxation layer and printing became impossible was examined. Table 1 shows the results.

[0027]

[Table 1]

According to such an experiment, when the conventional silicon oxide was used for the thermal relaxation layer, cracks occurred in the thermal relaxation layer when the thermal paper ran for printing for 0.5 km, and poor printing occurred.
Further, in the case of using silicon nitride, when the thermal paper travels for printing about 5 km, the thermal relaxation layer is peeled off, resulting in poor printing.

On the other hand, in the case of using the silicon nitride of the present invention as a main component and the oxygen content ratio decreasing gradually from the heat storage layer side to the heating resistor side, the thermal paper prints and runs for 10 km. Also, no cracks or peeling occurred in the thermal relaxation layer, which proved to be extremely useful as a thermal head.

It should be noted that the present invention is not limited to the above-described embodiment, and various changes and improvements may be made without departing from the scope of the present invention.

[0031]

According to the thermal head of the present invention, between the heat storage layer made of polyimide resin and the heating resistor, silicon nitride is used as the main component, and the oxygen content ratio is increased from the heat storage layer side toward the heating resistor side. Since the thermal relaxation layer is made smaller in order, there is no possibility of cracks in the thermal relaxation layer and disconnection of the heating resistor or conductive layer during printing, and the thermal head can function well for a long time. Will be able to

In the thermal head of the present invention,
Since the oxygen content ratio of the thermal relaxation layer at the interface between the polyimide resin thermal storage layer and the thermal relaxation layer containing silicon nitride as the main component is increased, the familiarity between the thermal storage layer and the thermal relaxation layer becomes better, and the heat storage The thermal relaxation layer does not peel off from the layer, and functions well as a thermal head.

Further, in the thermal head of the present invention,
By covering the heating resistor layer and the conductive layer with the protective layer made of the same silicon nitride as the main component of the thermal relaxation layer, a large thermal stress is generated between the thermal relaxation layer and the protective layer when the thermal head is used. Therefore, the protective layer can be adhered to the underlayer in a good condition without cracks, which also improves the reliability of the thermal head.

[Brief description of the drawings]

FIG. 1 is a sectional view 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 ... Substrate, 2 ... Thermal storage layer, 3 ... Thermal relaxation layer, 4
... heating resistor, 5a, 5b ... conductive layer, 6 ...
Protective layer, 7 ... thermal paper

Claims (2)

(57) [Claims] 1. A thermal head comprising a heat storage layer made of a polyimide resin deposited on a substrate having good thermal conductivity and a heating resistor and a conductive layer disposed on the heat storage layer.
Between the heat storage layer and the heating resistor, a heat relaxation layer containing silicon nitride as a main component and having an oxygen content ratio gradually decreasing from the heat storage layer side toward the heating resistor side was interposed. > A thermal head characterized by the following. 2. The heating resistor and the conductive layer are made of silicon nitride.
2. The method according to claim 1, wherein the protective layer comprises a protective layer.
The thermal head according to 1.