JPH04219257A - Thermal head - Google Patents

Abstract

PURPOSE:To reduce uneven density of printing image by providing individual electrodes with slits for adjusting their resistances, so that each of the heating resistances connected to each of the individual electtrodes will become equal in electric power consumption. CONSTITUTION:A printed board 7 is attached with an adhesive agent to the left side of the surface of a supporting body 1 and an external connection wiring 8 is made on the surface of the printed board 7. The external connection wiring 8 is connected at its input end to a socket 10 for functioning as a driving signal input terminal via a lead pin 9 passing through the printed board 7. A driving IC is provided at a part near the insulating base plate 2 of the printed board 7. A thermal head H is composed of components 1-14 and driving IC and a thermal recording (printing) is performed with each heating resistance 5 pressed against heat-sensitive recording paper P on a platen R through a wear resisting layer 6.

Description

DETAILED DESCRIPTION OF THE INVENTION A. OBJECTS OF THE INVENTION 1) Field of Industrial Application The present invention relates to a thermal head used in thermal printers, facsimile machines, etc. as output devices for word processors, personal computers, etc.

2) Conventional technology Conventionally, the thermal head has low noise during printing.
In addition, it has the advantage of being easy to handle because it does not require a developing/fixing process, and is widely used.

Next, an example of such a conventional thermal head is shown in Nos. 7 and 8.
This will be explained using figures.

FIG. 7 is a partial perspective view of the surface of the insulating substrate 02 of the thermal head, and FIG. 8 is a partial plan view of the surface of the insulating substrate 02.

In these figures, there is a main scanning direction X on the surface of the insulating substrate 02.
A heat generating resistor 05 is formed between the common electrode 03 extending in the main scanning direction and the tips of the plurality of individual electrodes 04 arranged in a row in the main scanning direction. A pad 04a for IC connection is formed at the base end of each individual electrode 04.

When a predetermined voltage V is applied between the pad 04a of the base end of the individual electrode and the common electrode 03, a current I is generated between the pad 04a of the individual electrode 04 and the common electrode 03. , and the magnitude of this current I is determined by the resistance value R of the heating resistor 05 between the common electrode 03 and the individual electrode tip 04a (see FIG. 8), and the individual resistance value R between the tip and base ends of the individual electrodes. It is determined by the resistance value r of the electrode 04 itself (see FIG. 8).

That is, In this case, the power W consumed by the heating resistor 05 is becomes.

As can be seen from equation (2), if there are variations in the resistance value R of each heat generating resistor 05 of the thermal head and the resistance value r of the individual electrode 04, the power consumed by each heat generating resistor 05 W
Variations occur.

By the way, the resistance value r of the individual electrode 04 and the resistance value R of the heating resistor 05 are, for example, r=30Ω,
R = on the order of 2000Ω, in which case r≪
It is R. The individual electrode 04 with r=30Ω is
This can be obtained by forming an electrode having a shape of 80 μm in width and 12 mm in length as shown in FIG. 2 using an electrode material having a sheet resistance of 200 mΩ/□. That is, the resistance value of the individual electrode 04 having this shape is as follows.

By the way, since electrodes are generally formed relatively uniformly,
Variations in the resistance values of the individual electrodes 04 are small. Moreover, as described above, since r<<R, the variation in the power W consumed by each heating resistor 05 of the thermal head is mainly caused by the variation in the resistance value R of each heating resistor 05.

Then, the resistance value R of each heating resistor 05 of the thermal head
If the electric power W consumed by each heat generating resistor 05 varies due to the variation, a difference occurs in the temperature of each heat generating resistor 05 that generates heat during printing. In this case, when printing is performed on thermal transfer paper or the like, density unevenness occurs in the printed "characters" or "figures".

Conventionally, in thermal heads manufactured using thick film technology,
In order to prevent the density unevenness from occurring, trimming for adjusting the resistance value is performed to make the resistance value of the heating resistor corresponding to each printed dot uniform.

This utilizes the property that when an electric field of a predetermined intensity is applied to the heating resistor within a range that does not cause resistance breakdown, the resistance value of the heating resistor decreases in accordance with the electric field strength.

As a conventional technique for making the resistance value of such a heating resistor uniform, for example, a pulse trimming method described in Japanese Patent Application Laid-open No. 83053/1983 is known.

In the pulse trimming method, a trimming pulse with a constant width and a different voltage value is applied to each heat generating resistor whose tips are arranged to face each other and connect between a plurality of individual electrodes and a common electrode, or a trimming pulse with a constant width and voltage value is applied to each heating resistor, or a trimming pulse with a constant width and voltage value is applied. Different trimming pulses are applied.

By this pulse trimming method, the resistance value of the heating resistor is made uniform within a range of ±3%.

As mentioned above, on the one hand, a technology has been developed to make the resistance values of each heating resistor formed using thick film technology uniform; Techniques for shaping the body are being developed.

Conventional MOD (M
etalo Organic Deposition)
A method (for example, see Japanese Patent Laid-Open No. 1-220402) has been proposed. In this conventional MOD method, the heating resistor is formed by firing a metal-organic resistor material coated on the surface of an insulating substrate by screen printing, roll coating, or other thick film technology. The variation in resistance value of the heating resistor formed by this MOD method is approximately ±3%.

3) Problems to be Solved by the Invention As mentioned above, even if the resistance value of each heating resistor is made uniform by the pulse trimming method, or even if the heating resistor is formed by the MOD method, each heating resistor There is a variation of about ±3% in the resistance value of the body, and this ±3%
Density unevenness occurs in the printed image due to variation in the amount of heat generated by the heating resistor due to variation in the resistance value.

However, in high-quality printing that displays high-quality halftones, in order to equalize the amount of heat generated by the heat-generating resistor, it is required that the variation in resistance value be within ±1%. As a means to meet this requirement, a laser trimming method can be considered in which the heating resistor is cut with a laser or a spot (hole) is made in the heating resistor to make the resistance value of the heating resistor uniform.

By using this laser trimming method, it is possible to reduce the variation in the resistance value of each heating resistor and make the amount of heat generated by each heating resistor uniform.

However, since the heating resistor is damaged by the laser, problems such as a decrease in the power resistance of the heating resistor and a change in the shape of printed dots arise.

Therefore, the inventors of the present invention have studied various ways to make the amount of heat generated by each heating resistor of the thermal head uniform.

That is, FIG. 9 is an equivalent circuit diagram of the common electrode 03, the individual electrodes 04, and each heating resistor 05 shown in FIG. In this FIG. 9, R1, R2, ... each heating resistor 0
5, the resistance values r1, r2, . . . are the resistance values of each individual pole arrangement 04.

When each heating resistor 05 in FIGS. 8 and 9 is adjusted to a range of 2000Ω±3% by pulse trimming, the maximum resistance value is 2060Ω, and the minimum resistance value is 1940Ω.
It is. Now, for example, among the resistance values of each heating resistor 05, R1 = 2060Ω, R2 = 1940Ω, and the individual heating resistor 05 with the maximum resistance value R1 = 2060Ω shown in Fig. 9 is connected. In this case, the resistance value of the electrode 04 is set to 1=30Ω, and the condition 2 is as follows in order for the amount of heat generated by the heat generating resistor 05 of each resistance value R1 and R2 to be constant.

In this formula, R1=2060, R2=1940, r
When 1=30 is substituted, r2=88 (Ω).

That is, the heating resistor 0 with the minimum resistance value R2 = 1940Ω
If the resistance value r2 of the individual electrode 04 connected to 5 is set to 88Ω, the heating resistor 05 with the maximum resistance value R1 = 2060Ω and the heating resistor 05 with the minimum resistance value R2 = 1940Ω have the same calorific value (i.e. power consumption is the same). Therefore, the maximum resistance value is 2060Ω and the minimum resistance value is 1940Ω.
Each heat generating resistor 05 having a resistance value intermediate between Ω and Ω can have a heat generation amount (
It should be possible to make all power consumption the same.

The present invention has been made in view of the above-mentioned circumstances, and even if there is variation in the resistance value of each heating resistor used for printing in a thermal head, the amount of heat generated by each heating resistor can be made uniform. , the objective is to reduce density unevenness in printed images.

B. Structure of the Invention 1) Means for Solving the Problems In order to solve the above problems, the thermal head of the present invention includes a plurality of individual electrodes and a common electrode arranged corresponding to the tips of the individual electrodes. and a heat-generating resistor connecting between the tips of the individual electrodes and the common electrode are formed on the surface of the insulating substrate, and are heated by a voltage selectively applied between the base end of each of the individual electrodes and the common electrode. In a thermal head configured such that the heat generating resistor generates heat, the resistance value of the individual electrode is set in the individual electrode so that the power consumption of each heat generating resistor connected to each of the individual electrodes becomes uniform. It is characterized by a slit for adjustment.

2) Function In the thermal head of the present invention described above, the individual electrodes include slits for adjusting the resistance values of the individual electrodes so that the power consumption in each heating resistor connected to each of the individual electrodes becomes uniform. Therefore, even if there is variation in the resistance value of each heating resistor, the amount of heat generated by each heating resistor is uniform.

3) Examples Next, one embodiment of the present invention will be described with reference to the drawings.

FIG. 1 is an overall explanatory diagram of an embodiment of the thermal head of the present invention, FIG. 2 is a perspective view of its main parts, FIG. 3 is an enlarged view of the portion shown by arrow III in FIG. 2, and FIG. 4A is the same. FIGS. 4B and 4C are plan views of essential parts of the embodiment taken along the IVA arrow in FIG. 3, and sectional views taken along the IVB-IVB and IVC-IVC lines in FIG. 4A.

As shown in FIG. 1, a thermal head H for performing thermal recording (printing) on a thermal recording paper P conveyed along the outer periphery of a platen roll R includes a support plate 1. As shown in FIG. An insulating substrate 2 is attached to the surface of the support plate 1 on the right side in FIG. 1 with an adhesive. It is composed of an underglaze layer 2b.

As shown in FIG.
A common electrode 3 having a large number of common electrode connecting portions 3b protruding in the sub-scanning direction Y in a comb-like shape, and a plurality of common electrode connecting portions 3b disposed at a predetermined distance from each other at a position facing the multiple common electrode connecting portions 3b. Individual electrodes 4 are formed. These electrodes 3 and 4 are made of, for example, metallo-organic (Meta
It is formed by coating gold paste, firing it, exposing it to light, and developing it. Each of the common electrode connecting portions 3b and the individual electrodes 4 are connected to each other by a large number of heating resistors 5 arranged in an island shape along the main scanning direction X on the surface of the insulating substrate 2. Further, the base end portion (the left end portion in FIG. 1) of the individual electrode 4 is connected to a driving IC, which will be described later.
Pad (i.e., IC connection terminal) 4 for connecting with
It is formed as a.

The common electrode 3, individual electrodes 4, heating resistor 5, etc. are covered with a wear-resistant layer 6 (see Figures 1, 3, 4A, 4B, etc.).

A printed wiring board 7 is attached to the surface of the support plate 1 on the left side in FIG. 1 with an adhesive, and external connection wiring 8 is formed on the surface of the printed wiring board 7. This external connection wiring 8 is connected at its input end side (on the left side in FIG. 1) to a socket 10 as a drive signal input terminal via a lead pin 9 passing through the printed wiring board 7. A driving IC is disposed in a portion of the printed wiring board 7 near the insulating substrate 2, and this driving IC is connected to the pad 4a of the individual electrode 4 and the external connection wiring 8 by bonding wires 11 and 12.
is connected to.

The IC and bonding wires 11 and 12 are covered with a protective resin 13, and the protective resin 13 is further protected by a cover 14 made of aluminum.

The thermal head H is composed of the components indicated by the numerals 1 to 14, the driving IC, and the like. Then, each heating resistor 5 is connected to the wear-resistant layer 6.
Thermal recording (printing) is performed while being pressed against the thermal recording paper P on the roller platen R via the roller platen R.

FIG. 5 shows a common electrode 3 formed on the surface of the insulating substrate 2.
, is an enlarged plan view of an individual electrode 4 and a heating resistor 5.

FIG. 6 is an equivalent circuit of FIG. 5.

In this FIG. 6, R1, R2,... are each heating resistor 5.
The resistance values r1, r2, . . . are the resistance values of each individual electrode 4. Each heating resistor 5 has a resistance of 200 by pulse trimming.
It is adjusted within the range of 0Ω±3%. In this case, the maximum resistance value is 2060Ω and the minimum resistance value is 1940Ω.

Each of the individual electrodes 4 has a sheet resistance value of 200 m.
Ω electrode material, width 80 μm, length (pad 4a
and the tip of the individual electrode) is formed at a distance of 12 mm.
This individual electrode 4 is formed with a slit 4b (described later) for adjusting power consumption in each heating resistor 5 having a different resistance value. Each of the individual electrodes 4 has a resistance value of 30Ω before the slit 4b is formed, but after the slit 4b is formed, the resistance value ri(i=1, 2, ) are adjusted to different values.

The shape of the slit 4b formed in each individual electrode 4 is determined, for example, as follows.

For example, in the resistance value Ri of each heating resistor 5, Ri=
When 2000Ω+2000Ω×3%=2060Ω (maximum resistance value), no slit is formed in the individual electrode 4 connected to the heating resistor 5 having this maximum resistance value R1. The resistance value r1 of the individual electrode connected to the heat generating resistor 5 which does not form a slit is 30Ω.

The conditions for making the power consumption uniform in each heating resistor 5 having the resistance value Ri (1940Ω≦Ri≦2060Ω) (that is, the condition for making the amount of heat generated uniform) are expressed by equation (4).

In this formula (4), R1=2060, R2=194
By substituting 0 and r1=30, r2=88 (Ω).

That is, the heating resistor 5 with the minimum resistance value R2=1940Ω
If the resistance value of the individual electrode 4 connected to 2 is set to 88Ω, the heat generating resistor 5 with the maximum resistance value R1 = 2060Ω and the heat generating resistor 5 with the minimum resistance value R2 = 1940Ω have the same calorific value (i.e. power consumption is the same). Also, the resistance value R between the maximum resistance value 2060Ω and the minimum resistance value 1940Ω
The resistance value ri of the individual electrode 4 connected to the heat-generating resistor 5 having i is between 30Ω and 88Ω. Therefore, by adjusting the resistance value of each individual electrode 4 to a value between 30Ω and 80Ω, the amount of heat generated by all the heating resistors can be made the same.

By the way, in order to make the resistance value r2 of the individual electrode 4 connected to the minimum resistance value R2 88Ω, as shown in FIG. 5, the electrode width is set to 24mm over a length of 10mm.
A slit 4b having a diameter of 1 μm is formed. This slit 4b is formed by a laser beam, and includes a horizontal slit portion with a length of 55.9 μm extending from one side of the individual electrode 4 in a direction across the individual electrode 4, and a vertical slit portion continuous with this horizontal slit portion. It has a longitudinal slit portion with a length of 10 mm. Due to the slit 4b having such a shape, the effective width (electrode width) of the individual electrode 4 is 24.1 μm. As a laser device for forming such a slit 4b, a laser device generally used for manufacturing hybrid ICs can be used.

Next, in order to make the resistance value of the individual electrode 4 88Ω,
The reason why the electrode width was set to 24.1 μm will be explained.

As mentioned above, the individual electrode 4 shown in FIG. 5 has a sheet resistance value of 200 mΩ, is formed to have a width of 80 μm, and a length of 12 mm, and its resistance value is 30Ω before the slit is formed. By narrowing the width of this individual electrode, it is possible to increase the resistance value from 30Ω to 88Ω, but within the length of this individual electrode of 12mm, the total 2mm portion at both ends is used as it is 80μm in width. That's it. Then, by narrowing the width of the 10 mm portion at the center in the length direction, the resistance value r2 of the individual electrode is set to 88Ω.

The resistance value of a portion having a total length of 2 mm at both ends of the individual electrode is as follows, and the resistance value of a portion having a total length of 10 mm at the center of this individual electrode before forming a slit is 25Ω. Therefore, if the width of the individual electrode at the central portion with a length of 10 mm is narrowed and its resistance value is increased from 25Ω to 83 (=88-5)Ω, the resistance value of this individual electrode is 2. Together with the value of 5Ω, it can be set to 88Ω.

Since the resistance value at the center of the individual electrode r2 is inversely proportional to its width, if the width is changed from 80 μm to B2 μm in order to increase the resistance value of the 25Ω to 83Ω, then B2 = 80 μm x (25/83). =24.1 μm.

As can be seen from the above explanation, when the resistance value of each individual electrode 4 is ri (i=1, 2,...), the width Bi (i=3, 4,...) of the individual electrode 4 is given by the following ( 5) Determined by the formula,
The amount of heat generated by each heating resistor 5 becomes uniform.

As mentioned above, ri in formula (5) is 30 to 8.
Since the value is between 8 (Ω), the value of Bi in equation (5) is 8
The value is between 0 μm and 24.1 μm.

That is, if the individual electrode 4 before slit formation is configured as explained in FIG.
By adjusting the width of the central portion between 80 μm and 24.1 μm, the amount of heat generated by each heating resistor 5 can be made uniform.

Although the embodiments of the thermal head according to the present invention have been described in detail above, the present invention is not limited to the above-described embodiments, and can be modified in various ways within the scope of the gist of the present invention as described in the claims. It is possible to make design changes.

For example, the invention can be applied to various thermal heads in which the heating resistor and the individual electrodes are formed using thick film or thin film technology. In addition, the specific resistivity, film thickness, etc. of the individual electrodes are set to appropriate values according to the average resistance value of each heating resistor, and the resistance value of the individual electrodes before slit formation is set to an appropriate value other than 30Ω. It is also possible to set it to a value.

C. Effects of the Invention The thermal head of the present invention described above has a slit in each of the individual electrodes for adjusting the resistance value so that the power consumption of each heating resistor connected to each of the individual electrodes becomes uniform. Therefore, even if there is variation in the resistance value of each heating resistor, the amount of heat generated by each heating resistor can be made uniform.

Therefore, since the temperature of each heating resistor becomes uniform during printing, density unevenness in the printed image can be reduced.

[Brief explanation of the drawing]

FIG. 1 is an overall explanatory diagram of an embodiment of the thermal head of the present invention, FIG. 2 is a perspective view of the main parts thereof, FIG. 3 is an enlarged view of the portion shown by arrow III in FIG. 2, and FIG. 3 is a view taken along the IVA arrow, FIG. 4B is a sectional view taken along the line IVB-IVB in FIG. 4A, and 5th
The figure is an explanatory diagram of the slit of the individual electrode of the same embodiment, FIG. 6 is an equivalent circuit of FIG. 5, and FIGS. 7 to 9 are explanatory diagrams of the prior art. 2...Insulating substrate, 3...Common electrode, 4...Individual electrode, 4b...Slit, 5...Heating resistor, Patent applicant Fuji Xerox Co., Ltd. agent Patent attorney Takahide Tanaka and two others

Claims (1)

[Claims] A plurality of individual electrodes (4), a common electrode (3) arranged corresponding to the tips of these individual electrodes, and a connection between the tips of the individual electrodes and the common electrode (3). Heat generating resistor (5)
are formed on the surface of the insulating substrate (2), and each of the individual electrodes (
4) in a thermal head configured such that the heating resistor (5) generates heat by a voltage applied between the base end portion of the heating resistor (5) and the common electrode (3), the heating resistor (5) being connected to each of the individual electrodes (4); Each heating resistor (5)
The individual electrodes (4)
, there is a slit (4b) for adjusting the resistance value of the individual electrode (4).
) is formed.