JP3522064B2 - Thermal head - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an improvement in a thermal head incorporated as a printer mechanism in a word processor, a facsimile or the like. 2. Description of the Related Art Conventionally, a thermal head incorporated as a printer mechanism such as a word processor includes a plurality of heating resistors 13 on an insulating substrate 11 made of alumina ceramics, as shown in FIG. It has a structure in which an individual electrode 14 and a common electrode 15 connected to the resistor 13 and a protective layer 17 covering the surface of the heating resistor 13 and the like are sequentially applied. In the above thermal head, each individual electrode 14 is connected to a reference potential (for example, 0 V) via switching means (not shown), and the common electrode 15 is connected to an external power supply (for example, 24 V). The individual electrodes 14 are opened and closed based on the print signal.
Power is applied between the common electrode 15 and the heating resistors 13 to selectively and individually generate Joule heat, and the generated heat is conducted to a recording medium such as an ink ribbon or a thermosensitive recording paper, and a predetermined amount is applied to the recording medium. It functions as a thermal head by forming a print. The protective layer 17 protects the heating resistor 13, the individual electrodes 14 and the like from corrosion due to contact with moisture or the like contained in the air and abrasion due to sliding contact of the recording medium. The heating resistor 1 is made of a hard, high-resistance inorganic material such as silicon nitride by sputtering or the like.
It is formed by being attached to the upper surface such as 3. The common electrode 15 is a thick film common electrode 1.
5b, a portion of the thin film common electrode 15a is laminated on
The thin-film common electrode 15a is connected to each other end of the heating resistor 13, and the thick-film common electrode 15b allows a large current. [0006] However, in this conventional thermal head, a pinhole is formed inside the protective layer 17 formed by a sputtering method or the like due to adhesion of foreign matter in a film forming process. Many film defects such as p are formed. For this reason, when printing is performed by transporting the recording medium onto the heating resistor 13, sodium ions (Na ⁺ ), potassium ions (K ⁺ ),
Metal ions I such as magnesium ions (Mg ²⁺ ) come into contact with the heating resistor 13 and the like via film defects in the protective layer 17,
Causes corrosion. As a result, the electric resistance value of the heating resistor 13 fluctuates greatly in a short period of time, and has a drawback that it is impossible to form a desired print by causing the heating resistor 13 to generate Joule heat to a predetermined temperature. In order to solve the above-mentioned drawback, a conductive layer is deposited on the protective layer 17 and the conductive layer is connected to the common electrode 15 so that the metal ions contained in the recording medium can be removed. It has been proposed that I be captured by the Coulomb force of the conductive layer and escape to the outside via the common electrode 15. However, the common electrode 15 is normally kept at a potential of about 24 V, so that the charge removing effect is weak and the common metal ions I having a positive charge cannot be sufficiently captured. There are various metal parts inside a printer or the like in which the thermal head is incorporated, and most of them are grounded. Therefore, if paper dust or the like that absorbs moisture in the air adheres between the conductive layer and the grounded metal part, a potential difference occurs between the two and a leakage current flows, thereby corroding the conductive layer. There was also a disadvantage such as. SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned drawbacks. A plurality of heating resistors are provided on an insulating substrate, and each heating resistor is provided at one end of the heating resistor. An individual electrode individually connected to the resistor; a common electrode commonly connected to the heating resistor at the other end of the heating resistor; and protection for covering at least a part of the heating resistor and the common electrode. A thermal head comprising a layer and a conductive layer deposited on the protective layer, wherein the surface roughness is provided on the insulating substrate or the protective layer and outside the common electrode along the common electrode. Is provided with a ground electrode having a center line average roughness Ra set to 0.1 μm to 0.5 μm, and the conductive layer is applied on the ground electrode to be electrically connected, and the ground electrode and the ground electrode are provided. The end of the common electrode is led out to the one end of the heating resistor, and the And it is characterized in that the end portion of the common electrode and the individual electrodes are arranged along one side of the insulating substrate. Hereinafter, the present invention will be described in detail with reference to the accompanying drawings. FIG. 1 is a plan view showing one embodiment of the thermal head of the present invention, and FIG. 2 is a plan view of the thermal head of FIG. 1, wherein 1 is an insulating substrate, 3 is a heating resistor, 4 is an individual electrode, and 5 is a common electrode. An electrode, 7 is a protective layer, 8 is a conductive layer, and 9 is a ground electrode. The insulating substrate 1 is made of an electrically insulating material such as alumina ceramics or glass. On its upper surface, the glaze layer 2, the heating resistor 3, the individual electrodes 4 and the common electrode 5, the protective layer 7, the conductive layer 8, the ground electrode 9 and the like are supported. When the insulating substrate 1 is made of alumina ceramics, a ceramic material powder of alumina, silica, magnesia, or the like is mixed with an appropriate organic solvent and a solvent to form a slurry. The ceramic green sheet is formed by employing a method or the like, and thereafter, the ceramic green sheet is punched into a predetermined rectangular shape and fired at a high temperature. A glaze layer 2 having an arc-shaped cross section is formed on the upper surface of the insulating substrate 1 in a strip shape in the longitudinal direction of the insulating substrate 1. The glaze layer 2 is made of a low thermal conductive material such as glass or polyimide resin, and accumulates and dissipates heat generated by the heat generating resistor 3 attached to the upper surface thereof, thereby maintaining good thermal response characteristics of the thermal head. To act. When the glaze layer 2 is made of glass, a predetermined glass paste is printed and applied in a belt shape by a conventionally known screen printing or the like, and is baked at a high temperature, for example, to a height of 35 to 150 μm and a width of 0.8 to 0.8 μm. 3.0 mm,
It is adhered and formed to have an outer shape with a radius of curvature of 2.5 to 28.0 mm. On the glaze layer 2, a plurality of heating resistors 3 arranged in a straight line and individual electrodes 4 and common electrodes 5 connected to both ends of each heating resistor 3 are attached. Have been. Since the heating resistor 3 is made of an electric resistance material such as tantalum nitride, when power from an external power source is applied through the individual electrode 4 and the common electrode 5, it is necessary to form a print on a recording medium. It acts to generate Joule heat at a predetermined temperature. The individual electrode 4 and the common electrode 5 connected to the heating resistor 3 are formed of a metal such as aluminum or copper. The other end of the heating resistor 3 is commonly connected to an external power supply (for example, 24 V). These individual electrodes 4
The common electrode 5 applies a predetermined power to the heating resistor 3 by opening and closing switching means connected to the individual electrode 4 based on a printing signal. The common electrode 5 is formed by laminating a part of a thin film common electrode 5a formed by a thin film technique such as a sputtering method and a photolithography technique on a thick film common electrode 5b formed by a thick film technique such as screen printing. The thin-film common electrode 5a is connected to each other end of the heating resistor 3, and the thick-film common electrode 5b allows a large current to be applied to the common electrode 5. On the other hand, on the upper surfaces of the heating resistor 3, the individual electrode 4, the common electrode 5 and the like attached on the insulating substrate 1,
A protective layer 7 has been applied. The protective layer 7 is made of a hard (Vickers hardness Hv: 1500 or more) inorganic material having a high resistance (10 ¹² Ωcm or more), for example, silicon nitride. It functions to protect against corrosion due to contact and wear due to sliding contact of the recording medium. The protective layer 7 is deposited and formed with a thickness of about 4 to 10 μm by a thin film technique such as a sputtering method. As a result, a pin is formed inside the protective layer 7 due to adhesion of foreign matter in a film forming process. Hole p (several μm to several tens μm in diameter)
A large number of film defects such as holes (m) are formed. On the upper surface of the protective layer 7, a conductive layer 8 made of a conductive material is applied. The conductive layer 8 has a sheet resistance of, for example, 2 × 10 ² to 5 × 10 ⁶ Ω /.
In the range of □, preferably set to 2 × 10 ³ to 1 × 10 ⁶ Ω / □, and by being electrically connected to a ground electrode 9 described later, the sheet is conveyed onto the heating resistor 3 during printing operation. To capture metal ions (Na ⁺ , K ⁺ , Mg ^2+, etc.) in the recording medium by Coulomb force. This effectively prevents metal ions from coming into contact with the heating resistor 3 and the like via film defects in the protective layer 7. The conductive layer 8 is made of TiC
And TaSiO ₂ , TaN, TiSiO ₂ , CrSiO ₂
It is preferable to use a conductive material having a hardness of not less than Vickers hardness Hv300. On the upper surface of the insulating substrate 1 and outside the common electrode 5, a distance of 0.5 to 1.0 mm
The ground electrode 9 is provided so as to leave an interval. During the printing operation, the ground electrode 9 always has 0V.
And a part of the conductive layer 8 is adhered to the upper surface thereof, so that when printing is performed by transporting the recording medium onto the heating resistor 3, The metal ions contained therein can be satisfactorily captured by the conductive layer 8, and the charges of the metal ions can escape to the outside via the ground electrode 9. As a result, the electric resistance value of the heating resistor 3 does not fluctuate significantly, and a good print can be formed over a long period of time. In this case, even if paper dust or the like that absorbs atmospheric moisture adheres between the conductive layer 8 and the external metal part grounded, the conductive layer 8 and the metal part are not No potential difference occurs, and no leakage current or the like flows at all. As a result,
The electric resistance value of the conductive layer 8 can be kept substantially constant for a long time, and the metal layer contained in the recording medium can be reliably captured by the conductive layer 8. Further, the ground electrode 9 is formed outside the common electrode 5 along the common electrode 5, and the common electrode 5 is disposed between the ground electrode 9 and the individual electrode 4, so that the metal ion Even if a large current instantaneously flows through the ground electrode 9 as a result of the capture, no electromagnetic induction occurs in the individual electrode 4 and the potential of the individual electrode 4 can be kept substantially constant. Therefore, the current can be supplied to all the heating resistors 3 correctly, and the thermal head can always be operated accurately. The potential of the common electrode 5 may slightly change due to the above-described electromagnetic induction. However, since the common electrode 5 is connected to all the heating resistors 3, the influence on each heating resistor 3 can be ignored. And there is no substantial problem in forming a print. Such a ground electrode 9 is formed by employing a thick film method or the like, similarly to the above-mentioned thick film common electrode 5b. Specifically, a predetermined conductive paste produced using a copper powder or the like is printed by, for example, conventionally well-known screen printing with a width of 0.5 mm or more and a thickness of about 30 μm.
It is applied and formed by applying and baking it at a high temperature. At this time, if the pattern of the thick film common electrode 5b and the ground electrode 9 is formed on one screen and printing is performed simultaneously, the printing and printing process of the thick film common electrode 5b and the ground electrode 9 can be performed only once. In addition, the manufacturing process of the thermal head can be simplified. The conductive layer 8 is
A hard conductive material such as TiC is coated on the upper surfaces of the protective layer 7 and the ground electrode 9 by a known sputtering method or the like for several 300 Å.
The conductive layer 8 and the ground electrode 9 are connected at the same time by being deposited and formed by depositing to a thickness of about 3000 °. Thus, in the above-described thermal head, a predetermined power is applied between the individual electrode 4 and the common electrode 5 based on the print signal, and the heating resistors 3 are individually selectively heated to generate Joule heat. The generated heat is conducted to the recording medium, and a predetermined print is formed on the recording medium to function as a thermal head. (Experimental Example) Next, an experimental example relating to the thermal head of the present invention will be described. First, a protective layer 7 made of silicon nitride is applied to a thickness of about 5 μm on the upper surface of an insulating substrate on which a heating resistor or the like is applied, and a conductive layer made of a TaSiO ₂ -based conductive material is applied thereon. Forty-six thermal head samples were produced. Here, the thickness of the conductive layer of each sample is 10 steps in the range of 80 to 4,200 °, and the thermal conductivity is 7 by changing the composition ratio of Ta and SiO _2.
Stage, prepared. Next, the printing operation was actually performed using each sample (traveling distance: 30 km), and the sharpness of the printing dots recorded by each sample and the adhesion state of the conductive layer were observed. Table 1 shows the results. [Table 1] According to Table 1, the thickness of the conductive layer is 300 mm.
In the thinner sample, a part of the conductive layer was worn by sliding contact of the recording medium, and the surface of the protective layer was exposed. In the sample in which the thickness of the conductive layer was more than 3,000 mm, the conductive layer was peeled off in the middle, and the function of capturing metal ions was lost. This is probably because the thermal stress applied between the conductive layer and the protective layer increased with the thickness of the conductive layer. In a sample in which the thermal conductivity of the conductive layer was set to be larger than 0.005 (cal / seccm.degree.C), the heat generated by the heating resistor diffused through the conductive layer and the outline of the printing dot was likely to be blurred. Was. On the other hand, in a sample in which the thickness of the conductive layer is 300 to 3,000 mm and the thermal conductivity is 0.005 (cal / seccm.degree. C.) or less, the conductive layer is worn to expose the surface of the protective layer,
None of the conductive layers were peeled off, and clear printing dots without blurring were formed on the recording medium. From the above, the thickness of the conductive layer 8 is
300 ~ 3,0003,000, thermal conductivity 0.005 (cal / sec ・ cm ・
° C) It is understood that it is preferable to set the following. It should be noted that the present invention is not limited to the above-described embodiment, and various changes and improvements can be made without departing from the spirit of the present invention. Although the ground electrode is formed on the upper surface of the insulating substrate on which the body and the like are attached, the ground electrode may be formed on the end surface of the insulating substrate, or may be formed over a wide area from the end surface to the back surface. In this case, no space is required on the upper surface of the insulating substrate for disposing the ground electrode, and the thermal head can be reduced in size. The ground electrode is formed on the insulating substrate 1 in the above-described embodiment, but may be formed on the protective layer 7 instead. Further, in the above-described thermal head of FIG. 1, the surface roughness of the ground electrode 9 is defined as a center line average roughness Ra of 0.
If the thickness is 1 μm or more, the conductive layer 8 formed thereon can be firmly adhered to the surface of the ground electrode 9 by the anchor effect, and the reliability of the thermal head is improved. . When the surface roughness of the ground electrode 9 exceeds 0.5 μm in the center line average roughness Ra, at the time of printing operation,
In some cases, the recording medium sticks to lower the printing quality. Therefore, it is preferable that the surface roughness of the ground electrode 9 is in the range of 0.1 to 0.5 μm in center line average roughness Ra. According to the thermal head of the present invention, the conductive layer formed on the ground electrode can be firmly adhered to the surface of the ground electrode by the anchor effect by the above structure. It is possible to improve the reliability of the thermal head. According to the thermal head of the present invention, the ground electrode existing outside the common electrode can be replaced by the above structure.
Together with the individual electrodes and the common electrode, they can be collectively connected to the signal wiring and the like of the external wiring board, and the manufacturing process can be simplified.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a sectional view showing an embodiment of a thermal head according to the present invention. FIG. 2 is a plan view of the thermal head of FIG. FIG. 3 is a sectional view of a conventional thermal head. [Description of Signs] 1 Insulating substrate 3 Heating resistor 4 Individual electrode 5 Common electrode 7 Protective layer 8 Conductive layer 9 Ground electrode

Claims (1)

(57) Claims: 1. A plurality of heating resistors, an individual electrode individually connected to each heating resistor at one end of the heating resistor, on the insulating substrate , At the other end of the heating resistor,
A common electrode, a protective layer that covers at least the heating resistor and a part of the common electrode, and a conductive head that is provided on the protective layer. On the insulating substrate or the protective layer and outside the common electrode, along the common electrode , the surface roughness has a center line average roughness.
A ground electrode set to 0.1 μm to 0.5 μm in Ra is provided , and the conductive layer is deposited on the ground electrode to electrically
Connected to the ground electrode and the common electrode.
Part is led out to the one end side of the heating resistor, and the ground electrode and common
Edges of the electrodes and the individual electrodes along one side of the insulating substrate
A thermal head characterized by being arranged.