JPH0569571A - Thermal head - Google Patents

Abstract

PURPOSE:To provide a thermal head of high reliability having a structure capable of making the damage of a head part hard to generate. CONSTITUTION:A flat plate-shaped heating resistor 19 is formed on an insulating substrate 6 and flat plate-shaped electrodes 20A, 20B are formed on the heating resistor 19 and, further, an insulating layer 18 is formed in a built-up chevron shape and a protective layer 21 is formed on all of them to constitute the head part of a thermal head 14.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a thermal head used in a thermal recording device.

[0002]

2. Description of the Related Art A thermal recording apparatus of a thermal transfer type or a color developing type uses a thermal head in which heating elements are arranged in an array in one direction. FIG. 3 shows an example of a thermal recording device provided with such a thermal head.

First, the recording paper 2 is attached to the drum-shaped platen 1.
The thermal head 4 thermally prints and prints a character image on the wound recording paper 2 via the ink sheet 3 wound on the winding side roll portion 3A.

FIG. 4 shows the thermal head 4 for performing such recording in an upside-down manner, in which an insulating substrate 6 made of, for example, ceramic is provided on a metal base 5 such as aluminum. A heating element array for recording 7 is provided on the top. The thermal head 4 illustrated here is a so-called line type head.

The recording heating element array 7 as described above has conventionally been constructed as follows.

FIG. 5 is an enlarged sectional view of a main part of a thermal head called a glaze type.

A glaze layer 8 is formed on the insulative substrate 6 so that the head can be uniformly pressed against the platen 1 with a sufficient force through the ink sheet and the recording paper. And is arranged along the axial direction of the platen 1. Heat generating resistors 9 are formed on the substrate 6 and the glaze layer 8 as thin films, which are arranged at regular intervals as shown in FIG. The heating resistor 9 is curved in a mountain shape so that the portion in contact with the glaze layer 8 follows the glaze layer.

On each heating resistor 9, electrodes 10A and 10B are formed on both sides of the heating resistor 9, leaving the top 9a of the heating resistor 9 raised in a mountain shape by the glaze layer 8. In this example, as shown in FIG.
Is an individual electrode, and the other electrode 10B is a common electrode.

On the substrate 6, each heating resistor 9 and electrode 10 are provided.
A protective layer 11 is formed which uniformly covers A, 10B and the like. The protective layer 11 protects the electrodes and the heating resistors and also improves the wear resistance of the head.
The protective layer 11 also enters the space 12 shown in FIG. 6 to insulate the electrodes from each other.

The heating resistor 9, the electrodes 10A and 10B, the protective layer 11 and the like are formed into a thin film by a vapor deposition method, a sputtering method or another thin film forming method. Of these, the top portion of the heating resistor 9 is formed. 9a is a heating element, which is arranged in the axial direction of the platen 1. That is, it becomes the heating element array for recording 7 (FIG. 4).

The electrodes 10A and 10B give a predetermined potential difference to the heating resistor 9. As a result, the heating resistor 9 having a predetermined electric resistance is brought into an energized state, Joule heat is generated in the heating resistor 9, and the above-mentioned heating element generates heat. As a thermal head provided with such a glaze layer, those disclosed in Japanese Utility Model Publication No. 62-102640 and Japanese Utility Model Publication No. 62-5940 have been already proposed.

By the way, in FIG. 5, when the protective layer 11 is formed into a thin film, for example, since the end portion 10B ₁ of the electrode 10B is depressed, a step 11a is formed on the top side of the protective layer 11. Part. Also, a step portion 11b is formed on the opposite side.

When printing is performed by using such a thermal head, the head usually applies a force of several kg to several tens of kg to pass through the ink sheet and the recording paper (only the recording paper in the case of the coloring type). It will be pressed against the platen 1. So to speak, such a force is relatively applied to the top side of the protective layer 11.

At this time, such a pressing force, a frictional force associated with the conveyance of the ink sheet, and a thermal stress due to the difference in the coefficient of thermal expansion act on the top. The place where such mechanical force and thermal stress act intensively is the A portion circled in FIG. Incidentally, since the heating resistor 9 has the highest temperature among the respective members, thermal expansion is most likely to occur, and the electrodes 10A and 10B are second only to the next one.
The protective layer 11 is most resistant to thermal expansion. Due to such a difference in the coefficient of thermal expansion, the above-mentioned thermal stress concentrates on the portion A, and the above-mentioned pressing force and frictional force also concentrate on the portion.

While such a head is used for a long period of time, there is a risk that the portion A will be broken by the action of such mechanical force and thermal stress. In particular, the F portion where the step portions 11a and 11b are located is cracked. If the protective layer portion between the cracks is peeled off due to this crack, the head function can no longer be performed.

[0016]

SUMMARY OF THE INVENTION It is an object of the present invention to have a structure that can prevent such damage to the head portion.
It is to provide a highly reliable thermal head.

[0017]

In order to achieve the above object, the present invention has an insulating substrate and a flat plate-shaped heat generating resistor formed on the substrate and arranged at regular intervals. And formed on each heating resistor,
This exposed part is left so that a part of the surface opposite to the substrate is exposed, and a pair of flat plate-shaped electrodes provided on both sides of this exposed part, the exposed part of the heating resistor and the electrode located on this exposed part. Insulation layer is formed by covering the extreme part side uniformly and forming a mountain shape in cross section so that the part located at the exposed part becomes the top part and forming a mountain shape following this insulating layer. The present invention proposes a thermal head having a layer and a protective layer that uniformly covers the electrodes, and the exposed portion of the heating resistor serves as a heating element.

It should be noted that it is particularly effective to use an insulating layer which has better thermal conductivity than the substrate.

[0019]

EXAMPLE FIG. 1 shows a thermal head 1 of this example.
4 has an insulating substrate 6 and a heating resistor 19 formed on the substrate 6. This heating resistor 19
As shown in FIG. 2, the plate-shaped elongated heat generating resistors are arranged at a constant pitch and spaced from each other, and the arrangement direction is the axial direction of the platen 1.

The thermal head 14 is formed on each heating resistor 19 and leaves the exposed portion 19a so that a part of the surface of the heating resistor opposite to the substrate 6 is exposed.
A pair of flat plate-shaped electrodes 20A, 20 provided on both sides
B, the exposed portion 19a of the heating resistor 19 and the electrode end side located on this exposed portion are evenly covered, and the insulation is formed in a mountain shape in cross section so that the portion located on the exposed portion 19a is the top. And layer 18. Regarding the electrodes, in this example, one electrode 20A is an individual electrode and the other electrode 20B is a common electrode.

Incidentally, in FIG. 2, such an insulating layer 18 is used.
Regarding the above, although not shown, in any case, this is formed in a convex shape so as to traverse the electrodes, and the electrodes are insulated from each other.

Further, the thermal head 14 has an insulating layer 18
Is formed in a mountain shape following the shape of
And a protective layer 21 that uniformly covers the electrodes 20A and 20B. The protective layer 21 also penetrates between the electrodes to insulate the electrodes from each other.

The functions of the various constituent elements are performed as described above, and the description thereof is omitted here.
In any case, the exposed portion 19a of the heating resistor 19 serves as a heating element, which is arranged in the axial direction of the platen 1. That is, the recording heating element array 7 (FIG. 4) is formed.

Conventionally, as shown in FIG. 5, the joint portion between the heating resistor 9 and the electrodes 10A and 10B is
The glaze layer 8 has a curved surface. On the other hand, in the thermal head of this example, as shown in FIG. 1, the mutual junction between the heating resistor 19 and the electrodes 20A and 20B is flat.

In the case of the conventional example, as shown in FIG. 5, for example, in the case of the common electrode 10B, the protective layer 11 is formed so as to cover the end portion 10B ₁ directly. The protection layer 11 inevitably has a step 11a.

On the other hand, in the case of this example, as shown in FIG. 1, the end portion 20B ₁ of the electrode 20B is covered with the insulating layer 18, but does not participate in the portion of the protective layer 21. As a result, the steps 11a and 11b of the protective layer 11 as shown in FIG. 5 are not generated.

Conventionally, such steps 11a, 1
Due to the presence of 1b and the fact that the A portion has a complicated multi-layer structure, the F portion and the like were likely to break, but in this example, the protective layer 21 does not have such a step portion. , End 20B
_Since the structure section that vertically cuts ₁ is simple, even if the above-mentioned mechanical force or thermal stress acts on the side of the top 21a of the protective layer 21, it is possible to prevent the stress from concentrating there. However, such breakage is less likely to occur.

By the way, in the conventional head, as shown in FIG. 5, the heat of the heating element 9a is transferred to the ink sheet 3 (FIG. 3) through the protective layer 11. On the other hand, in the case of this example, the heat of the heat generating element 19a is transmitted to the ink sheet via the insulating layer 18 and the protective layer 21.

In this type of thermal recording apparatus, the thermal efficiency of the thermal head is a problem. For example, if the density of the image obtained when a certain amount of energy is applied to the thermal head is high, the thermal efficiency is good, and in the opposite case, the thermal efficiency is bad.

In the case where the heat efficiency is deteriorated by passing the heat from the heat generating element 19a through the insulating layer 18, the insulating layer 18 may be made to have good thermal conductivity (heat conductivity). .. In addition, the thermal conductivity of the insulating layer 18 and that of the substrate 6 are made equal to each other, or preferably, relative to each other.
Is an insulating layer having better thermal conductivity than the substrate 6, so that heat from the heating element 19a is less likely to be transferred to the substrate 6 side and is preferentially transferred to the insulating layer 18. be able to. By doing so, the thermal efficiency can be further improved.

Further, in this embodiment, the insulating layer 18 is uniformly formed in the arrangement direction of the heat generating elements 19a so as to cross the heat generating elements. By making it good, the heat conduction between the heat generating elements becomes better than that of the conventional one, it is possible to suppress the phenomenon that the image density between pixels is lowered, and it is possible to further improve the image quality.

By the way, in the conventional example, as shown in FIG. 5, the portion indicated by B has a complicated multi-layer structure, and moreover, the heating resistor 9, the electrode 10B (electrode 10A), and the protective layer 11 are formed. Everything is in a strong bending state when standing up from the flat part.

As described above, when a frictional force or a pressing force is applied to the top side of the protective layer 11 by the ink sheet or the like, the stress also concentrates on the B portion and is easily damaged. When thermal stress acts on the B portion due to the difference in the coefficient of thermal expansion of each component, the portion is easily stretched and this portion is easily damaged.

On the other hand, in the case of this example, as shown in FIG. 1, the C portion has a simple structure in which only the protective layer 21 is bent. Therefore, also in this portion, the concentration of stress is suppressed, It is possible to make the damage less likely to occur.

The thermal head of the present invention can be generally used in a recording apparatus of a thermal transfer type, a color developing type or a type using this type of thermal head, such as a printer, a facsimile or a copying machine.

[0036]

According to the thermal head of the first aspect of the present invention, a structure in which mechanical force or thermal stress concentration is unlikely to occur in the head portion on which thermal recording is substantially performed. As a result, it is possible to prevent breakage of the head portion caused by those stresses, and it is possible to greatly improve the reliability of the head.

According to the thermal head of the second aspect, the heat of the heat generating element can be preferentially transferred to the side of the insulating layer rather than the substrate, so that the thermal efficiency of the thermal head can be improved and the image quality can be further improved. ,improves.

Further, it is possible to suppress the phenomenon that the image density between pixels is lowered, and it is possible to further improve the image quality.

[Brief description of drawings]

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

FIG. 2 is an enlarged perspective view showing a main part of a thermal head according to an embodiment of the present invention.

FIG. 3 is a schematic diagram of a thermal recording apparatus used to describe the configuration of a conventional thermal head.

FIG. 4 is a configuration perspective view of a conventional thermal head.

FIG. 5 is a cross-sectional view showing an enlarged principal part of a conventional thermal head.

FIG. 6 is a perspective view of a heating resistor portion of a conventional thermal head.

[Explanation of symbols]

 6 Substrate 14 Thermal Head 18 Insulating Layer 19 Heating Resistor 19a Exposed Part 20A Electrode 20B Electrode 21 Protective Layer

Claims (2)

[Claims] 1. An insulating substrate, formed on the substrate,
A flat plate-shaped heating resistor arranged at a constant pitch with a space between each other and formed on each heating resistor so that a part of the surface of the heating resistor opposite to the substrate is exposed. Except for the exposed portion, a pair of flat plate-shaped electrodes provided on both sides of the exposed portion, the exposed portion of the heating resistor and the electrode end side located on this exposed portion are evenly covered, and are located at the exposed portion. Has an insulating layer formed in a mountain shape in cross section so as to be the top, and a mountain shape is formed following this insulating layer, and has a protective layer that uniformly covers the insulating layer and the electrode with respect to the substrate, A thermal head comprising the exposed portion of the heating resistor as a heating element. 2. The thermal head according to claim 1, wherein the insulating layer is an insulating layer having better thermal conductivity than the substrate.