JPH08207332A - Thermal head - Google Patents

Abstract

(57) [Summary] [Object] To provide a thermal head having a simple structure and capable of forming a good printed image for a long period of time. [Structure] A plurality of heating resistors 3 are provided on an electrically insulating substrate 1.
An individual electrode 4 and a common electrode 5 connected to each heating resistor 3, and each heating resistor 3 connected to the individual electrode 4.
Driving IC 6 for selectively driving heat generation of the
6, a power supply line 7a for supplying power from a power source, a protective film 8 for covering at least the heating resistor 3 and a part of the power supply line 7a, and a conductive film deposited on the protective film 8. 9
And a through hole Z is provided in the protective film 8 on the power supply line 7a, and the conductive film 9 and the power supply line 7a are connected via the through hole Z.

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. 4, a thermal head incorporated as a printer mechanism such as a word processor has a plurality of heating resistors 32 and a plurality of heating resistors 32 on an electrically insulating substrate 31 made of alumina ceramics. The individual electrode 33 and the common electrode 34, which are connected to 32, and the protective film 35 that covers the surface of the heating resistor 32 and the like are sequentially deposited. A predetermined electric power is applied between the heat generating resistors 32 to selectively generate Joule heat, and the generated heat is conducted to the heat sensitive recording medium 36 to form a predetermined print image on the heat sensitive recording medium 36. Functions as a head.

The protective film 35 protects the heating resistor 32, the individual electrode 33, etc. from corrosion due to contact of moisture contained in the atmosphere and abrasion due to sliding contact of the thermosensitive recording medium 36. It is formed by applying a thin film method such as sputtering and depositing silicon nitride or the like on the upper surface of the heating resistor 32 or the like.

At one end of the electrically insulating substrate 31,
A flexible printed wiring board (hereinafter abbreviated as FPC) 37 having a plurality of wiring conductors 37a is attached, and the wiring conductors 37a of the FPC 37 are connected to the individual electrodes 33 and the common electrode 34 by soldering or the like. Electric power or the like from the power source is supplied to the heating resistor 32 or the like.

[0005]

However, in this conventional thermal head, the protective film 35 is formed by a thin film method such as sputtering, and foreign matter adheres to the protective film 35 during the film forming process. A large number of pinholes (holes having a diameter of several μm to several tens of μm) are formed by the above. Therefore, when the thermal recording medium 36 is conveyed onto the heating resistor 32 and printing is performed, sodium ions (Na ⁺ ), potassium ions (K ⁺ ) and magnesium ions (Mg) contained in the thermal recording medium 36 are contained. ²⁺ ) and other metal ions pass through the pinholes of the protective film 35 to generate the heating resistor 3
When the heat generating resistor 32 comes into contact with and corrodes it, the electric resistance value of the heat generating resistor 32 is largely changed in a relatively short time. As a result, the heating resistor 32 cannot generate Joule heat at a predetermined temperature, and it is impossible to form a desired printed image on the thermal recording medium 36.
Therefore, in order to solve the above drawbacks, a conductive film 38 made of tungsten chrome or the like is deposited on the protective film 35, and the conductive film 38 is connected to the wiring conductor 37a of the grounded FPC 37. It has been proposed that metal ions contained in the thermal recording medium 36 be captured by the Coulomb force of the conductive film 38 to prevent the metal ions from coming into contact with the heating resistor 32.

However, when the conductive film 38 on the electrically insulating substrate 31 is connected to the wiring conductor 37a of the FPC 37, it is necessary to connect the conductive film 38 and the wiring conductor 37a with the lead wire 39 or the like. In addition to the connection between the electrically insulating substrate 31 and the FPC 37, there is a drawback that complicated work such as soldering is involved and a connecting member such as the lead wire 39 is separately required.

[0007]

SUMMARY OF THE INVENTION The present invention has been devised in view of the above drawbacks, and an object thereof is to provide a thermal head capable of forming a good printed image for a long period of time with a simple structure. .

[0008]

A thermal head according to the present invention comprises a plurality of heating resistors, an individual electrode and a common electrode connected to each heating resistor, and an individual electrode on an electrically insulating substrate. A driving IC that selectively drives each heating resistor to generate heat, a power supply line that supplies electric power from a power source to the driving IC, and at least a portion of the heating resistor and the power supply line. A thermal head comprising: a protective film for coating; and a conductive film deposited on the protective film,
A through hole is provided in the protective film on the power supply line, and the conductive film and the power supply line are connected through the through hole.

[0009]

Embodiments of the present invention will now be described in detail with reference to the accompanying drawings.

FIG. 1 is a plan view showing an embodiment of a thermal head of the present invention, FIG. 2A is a sectional view taken along line XX of FIG.
2B is a cross-sectional view taken along the line YY of FIG. 1. 1 is an electrically insulating substrate, 2 is a glaze layer, 3 is a heating resistor, 4 is an individual electrode, 5 is a common electrode, and 6 is for driving. IC, 7a is a power supply line, 7b is a control signal line, 8a is a first protective film, and 8b is a second protective film.
A protective film, a conductive film 9 and an FPC 10.

The electrically insulating substrate 1 is made of alumina ceramics or the like, and has a glaze layer 2, a heating resistor 3, individual electrodes 4 and a common electrode 5, a driving IC on the upper surface thereof.
6, the power supply line 7a, the control signal line 7b, etc. are supported.

The electrically insulating substrate 1 has a rectangular shape, and a glaze layer 2 having an arcuate cross section is formed on the upper surface of the electrically insulating substrate 1 in a strip shape along one side of the substrate 1.

The glaze layer 2 is made of glass, polyimide resin or the like, and accumulates and dissipates the heat generated by the heating resistor 3 attached to the upper surface of the glaze layer 2 to maintain good thermal response characteristics of the thermal head. To act.

On the glaze layer 2, a plurality of heating resistors 3 linearly arranged along the glaze layer 2 and individual electrodes 4 and common electrodes 5 connected to the heating resistors 3 are formed. And are respectively applied.

Since the heating resistor 3 is made of an electric resistance material such as tantalum nitride, when a predetermined power is applied through the individual electrode 4 and the common electrode 5, a printed image is printed on the thermal recording medium 11. It acts to generate Joule heat to the temperature required for formation.

Further, 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, and the individual electrode 4 is set to the ground potential GND by the control of the driving IC 6 described later. The common electrode 5 is connected to a potential of 25 V, and a predetermined power is applied to the heating resistor 3 arranged between the two.

Further, on the electrically insulating substrate 1, a plurality of driving ICs are arranged substantially in parallel with the arrangement of the heating resistors 3.
6 is mounted on the lower surface of the IC 6, and the individual electrode 4
Is provided with a plurality of output terminals.

The driving IC 6 has a function of selectively supplying electric power to the heating resistor 3 based on a control signal such as a print signal, and is formed on the electrically insulating substrate 1 by a conventionally known face-down bonding method or the like. It will be installed.

A plurality of input terminals are provided on the lower surface of each of the driving ICs 6, and the input ICs have a power supply line 7a for supplying electric power from a power source to the heating resistor 3 and the driving ICs 6. A plurality of control signal lines 7b for supplying control signals to internal logic circuits and the like are connected to each other via solder.

The power supply line 7a has three portions, that is, a strip portion A arranged substantially parallel to the arrangement of the heating resistors 3.
And a first lead-out portion B led out from the strip-shaped portion A between the individual electrodes 4 on the heating resistor 3 side, and a second lead-out portion led out in a direction opposite to the lead-out direction of the first lead-out portion B. C, and is connected to the input terminal of the driving IC 6 at the strip portion A.

The control signal line 7b is connected to the driving IC 6
Is for inputting various control signals necessary for operating the drive IC 6, such as a print signal, a strobe signal, a clock signal, a latch signal, etc., to one end of each signal line 7b. The second derivation unit C of the power supply line 7a
In addition, they are juxtaposed along the end of the electrically insulating substrate 1.

The power supply line 7a and the control signal line 7b are connected to the wiring conductor 10b of the FPC 10 at the end of the electrically insulating substrate 1 via a brazing material such as solder.

The FPC 10 has a structure in which a plurality of wiring conductors 10b made of copper or the like and a cover film 10c made of polyimide resin or the like are sequentially deposited on a base film 10a made of polyimide resin or the like. The power supply line 7a on the electrically insulating substrate 1 is connected to the ground potential GND by a plurality of wiring conductors 10b, and the control signal line 7b is connected.
Is connected to the control signal supply means in the printer.

On the other hand, on the upper surface of the heating resistor 3, the individual electrode 4, the common electrode 5 and the power supply line 7a attached on the electrically insulating substrate 1, the heating resistor 3 and the like are contained in the atmosphere. A protective film 8 is applied to protect from corrosion due to contact with water and the like.

The protective film 8 is composed of a first protective film 8a and a second protective film 8b.
a is deposited so as to cover a part of the heating resistor 3, the common electrode 5 and the individual electrode 4, and the second protective film 8b is a region where the first protective film 8a is not deposited, that is, It is attached so as to cover the individual electrode 4 and a part of the power supply line 7a.

As the first protective film 8a, a material suitable for protecting the heat generating resistor 3 and the like from abrasion due to sliding contact of the thermosensitive recording medium 11, for example, silicon nitride or sialon is used, and the second protective film 8a is used. A material that can be easily handled, such as an epoxy resin or a polyimide resin, is used as 8b.

The first protective film 8a is formed by a thin film method such as a sputtering method, and the second protective film 8b is formed by a conventionally known coating method.

Further, TaSiO is formed on the upper surface of the protective film 8.
₂ , a conductive film 9 made of a conductive material such as TaN, TiSiO ₂ , CrSiO ₂ or the like is deposited. If the conductive film 9 is grounded at the time of printing, the first protective film 8a can be formed by a sputtering method or the like. When forming by the thin film method, even if a large number of pinholes are formed in the first protective film 8a due to adhesion of foreign matter or the like, metal ions (Na ⁺ , (K ⁺ , Mg ^2+, etc.) can be captured by the Coulomb force, and the metal ions can be effectively prevented from coming into contact with the heating resistor 3 via the pinhole in the first protective film 8a. As a result, the electric resistance value of the heating resistor 3 does not fluctuate significantly, and it is possible to form a good printed image on the thermal recording medium 11 for a long period of time.

The second protective film 8 on the power supply line 7a
A through hole Z filled with a conductor is provided in b, and the conductive film 9 and the power supply line 7a are electrically connected via the conductor filled in the through hole Z.

As described above, since the through hole Z is provided in the second protective film 8b on the power supply line 7a and the conductive film 9 and the power supply line 7a are connected via the through hole Z, If the power supply line 7a is grounded via the FPC 10, it is not necessary to separately perform a complicated work such as soldering other than the connection between the electrically insulating substrate 1 and the FPC 10, and a connecting member such as a lead wire. Is unnecessary.
This simplifies the construction of the thermal head, facilitates its assembly work, and further requires the provision of a cover member for protecting the connecting portion between the connecting member and the head substrate or the like from the application of external force. Also disappears.

The conductive film 9 is formed by depositing a conductive material such as TaSiO _{2 on} the upper surfaces of the first protective film 8a and the second protective film 8b to a thickness of several hundred Å to 1 μm by a conventionally known sputtering method or the like. The second protective film 8b is formed by depositing the conductive film 9 at a predetermined position, that is, the second protective film 8b on the first lead-out portion B of the power supply line 7a by etching or the like. By forming the through hole Z in advance, the conductive material can be filled into the through hole Z at the same time, and thus the electric connection between the power supply line 7a and the conductive film 9 can be performed very easily. You can The thermal head applies a predetermined electric power between the individual electrode 4 and the common electrode 5 based on the print signal to selectively cause the heating resistor 3 to generate Joule heat, and the generated heat is applied to the thermal recording medium 11 as well. To form a predetermined print image on the thermal recording medium 11 to function as a thermal head.

Next, another embodiment of the present invention will be described.

3 (a) and 3 (b) are sectional views showing another embodiment of the thermal head of the present invention, in which 12 is a head cover and 13 is a conductive tape. Incidentally, the same parts as those in the first embodiment shown in FIGS. 1 and 2 are designated by the same reference numerals, and the description thereof will be omitted.

The thermal head of this embodiment shown in FIG. 3 is different from the thermal heads of FIGS. 1 and 2 in that the connecting portion between the electrically insulating substrate 1 and the FPC 10 and the driving IC.
6 is covered with a head cover 12 for guiding the thermal recording medium 11 onto the heating resistor 3, and a conductive tape 13 having one end connected to the conductive film 9 on the protective film 8 is attached to the head cover 12. Another point is that the conductive tape 13 on the head cover 12 comes into contact with the thermal recording medium 11 on the upstream side in the transport direction of the thermal recording medium 11 during printing.

In this case, in addition to the effects similar to those of the above-described embodiment, there is an effect that the protective film 8 can be adhered to the heating resistor 3 in a good condition. That is, even if the surface of the thermosensitive recording medium 11 is charged to several thousand volts by friction or the like, the charged thermosensitive recording medium 11 comes into contact with the conductive tape 13 before being conveyed onto the heating resistor 3, and the surface thereof is contacted. The electric charges of the above are released to the ground potential GND through the conductive film 9 and the power supply line 7a, and the discharge is effectively prevented from occurring between the thermal recording medium 11 and the heating resistor 3, thereby protecting. It is possible to deposit the film 8 on the heating resistor 3 in good condition.

[0036]

According to the present invention, the conductive film on the protective film is connected to the power supply line. Therefore, if the power supply line is grounded via FPC or the like, the protective film can be formed into a thin film such as by sputtering. When forming by the method, even if many pinholes are formed in the protective film due to adhesion of foreign matter, the metal ions in the thermal recording medium transported onto the heating resistor are captured by the Coulomb force of the conductive film, Corrosion of the heating resistor due to contact with ions is effectively prevented. As a result, the electric resistance value of the heating resistor does not fluctuate significantly, and a good printed image can be formed on the thermosensitive recording medium for a long period of time.

Further, according to the present invention, since the conductive film is directly applied to the power supply line, if the power supply line is grounded, the conductive film is soldered to connect to the ground potential. It is not necessary to separately perform a complicated work such as the above, and a connecting member such as a lead wire is not necessary, which simplifies the configuration of the thermal head and facilitates its assembling work.

[Brief description of drawings]

FIG. 1 is a plan view showing an embodiment of a thermal head of the present invention.

2A is a sectional view taken along line XX of FIG. 1, and FIG. 2B is FIG.
3 is a sectional view taken along line YY of FIG.

FIG. 3 is a sectional view showing another embodiment of the thermal head of the present invention.

FIG. 4 is a sectional view of a conventional thermal head.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Electrically insulating substrate 2 ... Glaze layer 3 ... Heating resistor 4 ... Individual electrode 5 ... Common electrode 6 ... Driving IC 7a ... Power supply line 7b ... Control signal line 8 ... Protective film 9 ... Conductive film 10 ... Flexible printed wiring board 11 ... Thermal recording medium 12 ... Head cover 13 ... Conductive tape

Claims (1)

[Claims] 1. A plurality of heating resistors, an individual electrode and a common electrode connected to each of the heating resistors, and an individual electrode connected to the individual electrodes on an electrically insulating substrate to selectively select each heating resistor. A driving IC for driving heat generation, a power supply line for supplying electric power from a power source to the driving IC, a protective film covering at least the heating resistor and a part of the power supply line, and a protective film on the protective film. A thermal head comprising a conductive film deposited on the power supply line, wherein a through hole is provided in the protective film on the power supply line, and the conductive film and the power supply line are connected via the through hole. A thermal head characterized by that.