JPH10297013A - Thermal head - Google Patents

Abstract

PROBLEM TO BE SOLVED: To take a countermeasure against static electricity without causing any trouble even for lap finish and without limiting the range for selecting the material of a protective film by forming an insulation layer, a conductive layer and an abrasion resistant layer, constituting the protective film, sequentially on the upper layer of a heating element, an individual electrode and a common electrode. SOLUTION: A protective film 8 comprises an insulation layer 9 superposed on a heating element layer 3, a common electrode 4 and an individual electrode 5, a conductive layer 7 superposed on the insulation layer 9, and an uppermost abrasion resistant layer 10. The common electrode 4 and the individual electrode 5 are disposed oppositely through a gap G to form a heating part H. The common electrode 4 is partially formed in two layers in order to increase the current capacity and formed thicker than the individual electrode 5. Furthermore, an aluminum substrate 11 functioning as a heat sink and a holding member is provided beneath an alumina substrate 1. In order to enhance the effect for preventing electrostatic breakdown, the conductive layer 7 is grounded and held at a constant potential.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a thermal head for thermal recording or thermal transfer recording, and more particularly to a card printer, a bar code printer, a video printer, and the like.
The present invention relates to a thermal head applied to a ticket vending machine or the like.

[0002]

2. Description of the Related Art FIG. 6 is a sectional view of an essential part showing an example of a conventional thermal head. In FIG.
A heating resistor layer 3 is provided on the upper side via a heat storage layer, that is, a glaze 2. The gap G is formed on the heating resistor layer 3.
The common electrode 4 and the individual electrode 5 are provided so as to face each other, and a portion of the heating resistor layer 3 corresponding to the gap G between the common electrode 4 and the individual electrode 5 is provided with a heating element corresponding to the print dot. Area. A wear-resistant protective film 6 is formed on the heating resistor layer 3 and the electrodes 4 and 5. The protective film 6 is required to have various properties such as high hardness, crack resistance due to temperature change, stability against humidity, alkali, and the like, in addition to abrasion resistance in order to withstand sliding with the print medium.

Since a high-resistance material is generally used for the protective film 6, static electricity is generated when the print medium slides on the protective film 6. As a result, a large current flows through the heating resistor layer 3, and the heating resistor layer 3 may be altered or destroyed.

As a countermeasure against such a problem, there has been proposed a thermal head in which the protective film itself has conductivity or a conductive layer is laminated on the surface of the protective film. FIG.
This is an example in which a conductive layer 7 is laminated on the surface of the protective film 6. For example, the conductive layer 7 is a layer of tungsten having a thickness of 1 μm.
An example of a thermal head with a conductive layer laminated on the protective layer surface is
It is described in JP-A-5-286154.

[0005]

The above-mentioned conventional thermal head has the following problems. As described above, the protective film of the thermal head is required to have various characteristics such as abrasion resistance and high hardness. However, in order to make the protective film itself conductive as a countermeasure against static electricity, it is necessary to select a material that does not deteriorate the above characteristics, and as a result, the range of selection of materials that can be used as the protective film is narrowed. There is a problem that it is.

Further, in the case where the conductive layer is laminated on the protective film, there is a problem in that the conductive layer is worn out over a long period of use, and the effect of preventing static electricity is reduced. Furthermore, the surface of the thermal head, that is, the protective layer may be lap-finished on the assumption that the print medium is easily damaged, such as an OHP film. However, such a finish cannot be performed because the conductive layer is cut off. Problems arise.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a thermal head which solves the above-mentioned problems, and which can take a countermeasure against static electricity which does not cause a problem even by lapping without narrowing a material selection range of a protective film. And

[0008]

SUMMARY OF THE INVENTION In order to solve the above problems and achieve the object, the present invention provides a heating resistor disposed on an insulating substrate through a glaze, and a plurality of heating resistors provided on the heating resistor. An individual electrode and a common electrode for forming a region, and a protective film provided on the heating resistor and the individual electrode and the common electrode, and provided with an insulating layer, a conductive layer, and a wear-resistant layer in order from the lower layer. There is a first feature in that it is provided, and a second feature in that the insulating layer and the wear-resistant layer are made of the same material. The present invention has a third feature in that the present invention includes a means for maintaining the conductive layer at a constant potential.

According to the first to third features, since the wear-resistant layer is formed on the uppermost layer of the protective film, the lower conductive layer is protected. Then, the electric charge generated in the conductive layer corresponding to the electric charge generated in the wear-resistant layer is diffused into the conductive layer, and the electric charge is not concentrated on the heat generating region, so that the electrostatic breakdown can be prevented. In particular, according to the third feature, the conductive layer is kept at a constant potential by, for example, being grounded, so that the charge is not concentrated on the heat generation region and causes the electrostatic breakdown.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail with reference to the drawings. FIG. 1 is a cross-sectional view showing a heat generating portion of a thermal head according to the present invention, and FIG. 2 is a plan view showing the arrangement of electrodes. The same reference numerals as in FIGS. 6 and 7 denote the same or equivalent parts.
It should be noted that FIGS. 1 and 2 do not have the same drawing scale, and in particular, the thickness of FIG. 1 is exaggerated for easy understanding. The protective film 8 includes an insulating layer 9 overlaid on the heating resistor layer 3, the common electrode 4 and the individual electrode 5, a conductive layer 7 further overlaid on the insulating layer 9, and a wear-resistant layer provided on the uppermost layer. Consists of layer 10.

The insulating layer 9 is made of, for example, Si _X O _Y N _Z (X = 1, Y =
1 to 2, Z = 0 to 1.5), and the conductive layer 7 can be formed of, for example, aluminum. Ta ₂ O ₅ , Si
Well-known wear-resistant materials such as C, Al ₂ O ₃ and B ₄ C can be used. Abrasion resistant layer 10 is not necessarily be a material different from the insulating layer 9, for example, the same Si _X O _Y N and the insulating layer 9
_It may be formed of _Z.

The common electrode 4 and the individual electrode 5 are opposed to each other with a gap G to form a heating portion H.
The common electrode 4 is partially overlapped with two layers in order to increase the current capacity, and is thicker than the individual electrodes 5. Further, an aluminum substrate 11 functioning as a heat sink and a holding member is provided below the alumina substrate 1. The conductive layer 7 is preferably grounded and kept at a constant potential in order to enhance the effect of preventing electrostatic breakdown. In the present embodiment, the antistatic effect is enhanced by grounding, as described later. However, it is only necessary that the conductive layer 7 can be maintained at a constant potential, and the grounding is not necessarily required. For example, the conductive layer 7 may be connected to the high side (VH) of the digital control power supply.

FIG. 3 is a plan view of a main part showing a connecting portion between the heating unit and the control unit. FIG. 4 is a sectional view taken along line AA 'of FIG. 3, and FIG. 5 is a sectional view taken along line BB' of FIG. 3 to 5, a driving IC 13 and wiring patterns 14 and 15 are provided on a wiring substrate 12 fixed on an aluminum substrate 11 by bonding or the like. Although a plurality of driving ICs 13 are provided, only one is shown here.

On the terminal 5a of the individual electrode 5, a protective film 8
Has been removed, and the terminal 5a is exposed. A protrusion 7a is formed at an end of the conductive layer 7, and the wear-resistant layer 10 on the protrusion 7a is removed similarly to the terminal 5a of the individual electrode 5. The terminal 5a of the individual electrode 5 is a gold wire 1.
The driving IC 13 is connected to the wiring pattern 14 by a gold wire 17. On the other hand, the protrusion 7 of the conductive layer 7
a is a wiring pattern (land) 15 formed by a gold wire 18;
The land 15 is further grounded via a resistor 19. The resistor 19 functions to limit sudden high current, and is not an essential component and can be omitted.

[0015]

As is apparent from the above description, according to the first to fourth aspects of the present invention, since the conductive layer is provided, electric charges generated by sliding with the print medium are locally accumulated. This does not lead to electrostatic breakdown of the heating resistor. In addition, since the conductive layer is protected by the abrasion-resistant layer formed thereon, it does not wear out, and the antistatic effect is not impaired even by long-term use. When the smoothness of the wear-resistant layer protecting the conductive layer is required, for example, lapping or the like can be performed.

In the case where polycrystalline silicon is used for the heating resistor, if electric charges are accumulated on the protective film, the resistance of the heating resistor changes due to an electric field effect, and the heating temperature is affected. Degrades print quality. However, according to the present invention, since such an electric field effect does not occur, the resistance value of the heating resistor is stabilized, and the printing quality is stabilized. This effect is particularly remarkable in the third and fourth aspects of the invention.

[Brief description of the drawings]

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

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

FIG. 3 is a plan view of a main part showing a connecting portion between a heating unit and a control unit of the thermal head according to the embodiment of the present invention.

FIG. 4 is a cross-sectional view taken along line AA ′ of the connection portion.

FIG. 5 is a sectional view of the connection section taken along line BB ′. It is principal part sectional drawing.

FIG. 6 is a plan view of a main part of a conventional thermal head.

FIG. 7 is a sectional view of a main part of a conventional thermal head.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Alumina substrate, 2 ... Glaze, 3 ... Heating resistor, 4 ... Common electrode, 5 ... Individual electrode, 7 ... Conductive layer,
8: protective film, 9: insulating layer, 10: wear-resistant layer, 11
... Aluminum substrate, 12 ... Wiring board, 13 ... Drive IC, 14,15 ... Wiring pattern, 16,17,
18 ... gold wire, 19 ... resistance

Claims (4)

[Claims] 1. A heating resistor disposed on an insulating substrate via a glaze; an individual electrode and a common electrode connected to the heating resistor to form a plurality of heating regions in the heating resistor; A thermal head, comprising: a protective film provided on an upper layer of the heating resistor and the individual electrodes and the common electrode, and provided with an insulating layer, a conductive layer, and a wear-resistant layer in order from the lower layer. 2. The thermal head according to claim 1, wherein the insulating layer and the wear-resistant layer are made of the same material. 3. The thermal head according to claim 1, further comprising means for maintaining the conductive layer at a constant potential. 4. A thermal head according to claim 3, wherein a means for holding said conductive layer at a constant potential via a resistor is realized.