JP2818509B2 - 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.

[0002]

FIG. 8 is a circuit diagram of a typical thermal head 1. As shown in FIG. The thermal head 1 forms a common electrode 3 and a plurality of individual electrodes 4 by patterning aluminum or the like on an insulating substrate 2 by a thin film technique. A plurality of heating resistors 5 are formed between the common electrode 3 and the individual electrodes 4 and linearly continuous in the left-right direction of FIG. The common electrode 3 includes an electrode portion 6 extending in parallel with the arrangement direction of the heating resistors 5, and an extending portion 7 extending from one end of the electrode portion 6 along the outer periphery of the insulating substrate 2. You. Further, a common ground conductor 8 extending in the same direction as the arrangement direction of the heating resistors 5 in the same step as the individual electrodes 4 and the like is formed in a band shape.

A drive circuit element 9 connected to a predetermined number of individual electrodes 4 and selectively driving the heating resistors 5 to generate heat is arranged on the common grounding conductor 8 along the arrangement direction of the heating resistors 5. A plurality is provided. An external wiring board 12 that supplies print data and various control signals to the drive circuit elements 9 is connected to the insulating substrate 2, and a common ground conductor 8 is connected to the external wiring board 12 for each drive circuit element 9. Connecting conductor 11
Is formed.

[0004] The common electrode 3 is supplied with energizing power of the heating resistor 5 by a circuit (not shown), and the switching element 10 built in the drive circuit element 9 is connected to any of the plurality of individual electrodes 4 connected thereto. By selectively connecting / disconnecting one or more of them to / from the common ground conductor 9, the heating resistor 5 is energized to perform thermal printing.

[0005]

In the thermal head 1 of the prior art, when a printing operation is performed using the thermal head 1, of the heating resistors 5 connected to one drive circuit element 9, the heating is driven. The current flowing through the common ground conductor 8 varies depending on the number of the heating resistors 5. For this reason,
The degree of the voltage drop in the common ground conductor 8 will be different. That is, as shown in FIG. 9, of the two adjacent drive circuit elements 9, one drive circuit element 9a supplies current to all the heating resistors 5 and the other drive circuit element 9b supplies 50
%, The greater the current flowing, the greater the degree of voltage drop in the common ground conductor 8, and therefore the voltage drop in the drive circuit elements 9a and 9b, and thus the voltage applied to the heat generating resistor 5. As shown in FIG. 10, a potential difference ΔV is generated between the two driving voltages.

Due to the potential difference ΔV, the driving circuit element 9a
Only the driving voltage lower than that of the heating resistor 5 on the side of the drive circuit element 9b is supplied to the heating resistor 5 on the side, and density unevenness occurs during printing operation. In the case of a sublimation transfer type printer, it is known that when this potential difference ΔV reaches about 0.7% of the drive voltage applied to the common electrode 3, it is recognized as a clear density unevenness.

In order to solve the density unevenness, conventionally, the resistance value of the heating resistor 5 is set to a value as high as possible to suppress the energizing current, so that the degree of the voltage drop in the common ground conductor 8 can be reduced. We try to suppress as much as possible. Such a conventional technique has the following problems.

[0008] An increase in the resistance value of the heating resistor 5 causes a reduction in the flowing current, and thus a reduction in the printing speed due to a reduction in the applied power.

If a large difference such as 100% or 30% occurs in the number of the heating resistors 5 driven by one driving circuit element 9 for example, the occurrence of density unevenness cannot be prevented. SUMMARY OF THE INVENTION An object of the present invention is to solve the above-mentioned technical problems and to provide a thermal head capable of significantly improving operation quality.

[0010]

According to the present invention, a plurality of heating elements arranged in a line on a substrate, a common electrode and individual electrodes connected to both ends of each heating element, and a connection to the individual electrodes are provided. A plurality of driving circuit elements arranged in a line having a plurality of switching elements, and a common ground formed over an arrangement region of the driving circuit elements and commonly connected to all switching elements via a ground terminal. A head substrate having a conductor attached thereto, and an external wiring substrate having a plurality of wiring conductors electrically connected to the common ground conductor and the common electrode, wherein the common electrode and the common ground conductor A thermal head for providing a predetermined potential difference therebetween and selectively energizing the heating element by a switching operation of the switching element, the thermal head comprising: The number of connections between parts wiring board of the wiring conductor, a thermal head is characterized in that the more than the number of driving circuit elements. Further, the invention is characterized in that the common ground conductor is connected to a wiring conductor of the external wiring board on at least both sides of each drive circuit element.

[0011]

According to the present invention, a common ground conductor formed over an array region of drive circuit elements and commonly connected to all switching elements connected to each drive circuit element via a ground terminal, The number of connections with the wiring conductor is larger than the number of drive circuit elements. As a result, the connection with the external wiring board is provided not only for each driving circuit element but also between each driving circuit element, and when each heating circuit element drives the heating element, each driving circuit element Thus, even if the number of heating elements driven to generate heat differs, the difference in the degree of voltage drop in the drive circuit element hardly occurs. In addition, the voltage between the adjacent drive circuit elements is changed smoothly, and a good print without density unevenness during the print operation can be formed.

According to the invention, the common ground conductor is connected to the wiring conductor of the external wiring board on at least both sides of each drive circuit element. As a result, during printing, the magnitude of the power applied to the heating elements connected to the adjacent drive circuit elements is made uniform, and the printing quality of the thermal head is further improved.

[0013]

FIG. 1 shows a thermal head 2 according to an embodiment of the present invention.
1 is a perspective view, FIG. 2 is a sectional view of the thermal head 21, and FIG. 3 is a plan view of the thermal head 21. The thermal head 21 includes an insulating substrate 22 formed of a ceramic such as aluminum oxide Al ₂ O _3, and a heat storage layer 23 such as glass is formed on the insulating substrate 22 and a thick film formed by printing a silver paste or the like. The common electrode 24 has a thickness t1
(For example, 15 μm). On top of this is Ta ₂
Several hundreds of N by thin film technology such as sputtering deposition
The resistor layer 25 is formed by forming a film having a thickness of Å. Further, a metal conductor layer of aluminum or the like formed by sputtering or vapor deposition is patterned on the outer periphery of the insulating substrate 22 as shown in FIG.
A common ground electrode 28 and a signal line 29 are formed.
A plurality of heating resistors 30 are constituted by the common electrode 26 and the plurality of strip-shaped individual electrodes 27.
Is obtained.

An abrasion-resistant layer 32 is formed by coating the common electrode 26 and the individual electrodes 27 in the vicinity thereof by a thin film technique such as sputtering. In addition, a plurality of drive circuit elements 33 that cover the individual electrodes 27, the common ground electrode 28, and the signal lines 29 and are electrically connected thereto are arranged along the direction in which the heating resistors 30 are arranged. For example, it is covered with a protective film 34 made of an epoxy resin or the like. On the other hand, the insulating substrate 22 is fixed on a heat sink 50 made of aluminum, and the signal lines 29 are connected to the external wiring substrate 35.
Connected to.

The common electrode 26 is supplied with drive power from the external wiring board 35 to the heating resistor 30 as an example, and the drive circuit element 33 converts each heating resistor 30 into print data from the external wiring board 35. Therefore, when selectively connected / cut off to the ground potential, a current flows from the selected heating resistor 30 to the common ground electrode 28. This common ground electrode 28
The connection conductors 36 a and 36 b are formed for connection to the external wiring board 35. This connection conductor 36a
As shown in FIG. 1, each drive circuit element 33 and the connection conductor 36 b are provided between each drive circuit element 33.

FIG. 4 is a perspective view showing the bottom surface of the drive circuit element 33. The drive circuit element 33 has a plurality of connection terminals 37, 38, and 39 connected to the individual electrode 27, the common ground electrode 28, and the signal line 29, respectively.

FIG. 5 is a circuit diagram of the thermal head 21 of this embodiment. Two adjacent drive circuit elements 3 shown in FIG.
3, one drive circuit element 33a as shown in FIG.
When current flows through all the heating resistors 30 and the other drive circuit element 33b passes through approximately 50% of the heating resistors 30, the larger the flowing current, the greater the voltage drop in the common ground conductor 28.

On the other hand, in the thermal head 21 of the present embodiment, when performing a thermal printing operation, the energizing power of the heating resistor 30 is supplied to the common electrode 26 by a circuit (not shown), and the common electrode 26 is built in the drive circuit element 33. The switching element 40 selectively connects / disconnects one or more of the plurality of connected individual electrodes 27 to / from the common ground conductor 28, so that the heating resistor 30 is energized, and thermal printing is performed. Will be At this time, due to the wiring resistance of the common ground electrode 28, a voltage drop occurs in the adjacent drive circuit elements 33a and 33b, and thus a potential difference ΔVG occurs in the drive voltage applied to the heating resistor 30.

In this embodiment, since the plurality of connection conductors 36 of the common ground electrode 28 are provided for each drive circuit element 33 and between each drive circuit element 33, At a portion corresponding to the common ground electrode 28, the ground potential is different between the adjacent drive circuit elements 33a and 33b.
As a result, the value of the ground potential becomes stable, the potential difference ΔVG between the drive circuit elements 33a and 33b becomes gentle, and the potential difference becomes negligible as density unevenness during printing operation.

As described above, in this embodiment, the printing quality of the thermal head 21 can be remarkably improved.

FIG. 7 is a perspective view of a thermal head 21a according to another embodiment of the present invention. This embodiment is similar to the previous embodiment, and corresponding parts are denoted by the same reference numerals. This embodiment is characterized in that the common ground electrode 40 is formed in a band shape near the end of the insulating substrate 22 toward the end, and the drive circuit element 33 is formed.
Are connected to the individual electrodes 27 by bonding wires 41,
The pair of common ground electrodes 40 are connected to connection pads 42 at both ends of the drive circuit element 33 in the arrangement direction of the heating resistors 30 by bonding wires 43.

With the thermal head 21a having such a configuration, the same effects as those described in the above embodiment can be achieved.

[0023]

As described above, according to the present invention, the common ground conductor formed over the arrangement region of the drive circuit elements and commonly connected to all the switching elements connected to each drive circuit element via the connection terminal. And the number of connections with the wiring conductors of the external wiring board was made larger than the number of drive circuit elements. As a result, even if the number of heating elements driven by each driving circuit element is different, a difference in the degree of voltage drop in each driving circuit element is less likely to occur, and a good print without density unevenness can be formed. Furthermore, if a common ground conductor is connected to the wiring conductor of the external wiring board on both sides of each drive circuit element,
The magnitude of the power applied to the heating elements connected to the adjacent drive circuit elements is made uniform, and the printing quality of the thermal head is further improved.

[Brief description of the drawings]

FIG. 1 is a perspective view of a thermal head 21. FIG.

FIG. 2 is a cross-sectional view of the thermal head 21.

FIG. 3 is a detailed plan view of the thermal head 21.

FIG. 4 is a perspective view showing a bottom portion of the drive circuit element 33.

FIG. 5 is a circuit diagram of the thermal head 21.

FIG. 6 is a diagram for explaining the operation of the thermal head 21.

FIG. 7 is a perspective view of a thermal head 21a according to another embodiment.

FIG. 8 is a plan view of a conventional thermal head 1.

FIG. 9 is a diagram for explaining the operation of the thermal head 1.

[Explanation of symbols]

 21, 21a Thermal head 30 Heating resistor 33 Drive circuit element 28 Common ground electrode 35 External wiring board 36a, 36b Connection conductor

Claims (2)

(57) [Claims] 1. A substrate comprises a plurality of heating elements arranged in a line, a common electrode and individual electrodes connected to both ends of each heating element, and a plurality of switching elements connected to the individual electrodes. A plurality of drive circuit elements arranged in a line, and a common ground conductor formed over the arrangement area of the drive circuit elements and commonly connected to all switching elements via ground terminals. A head substrate; and an external wiring substrate having a plurality of wiring conductors electrically connected to the common ground conductor and the common electrode, wherein a predetermined potential difference is provided between the common electrode and the common ground conductor. A thermal head for selectively energizing the heating element by a switching operation of the switching element, wherein the common ground conductor and a wiring conductor of the external wiring board are provided. Wherein the number of connections is greater than the number of drive circuit elements. 2. The thermal head according to claim 1, wherein the common ground conductor is connected to a wiring conductor of the external wiring board on at least both sides of each drive circuit element.