JPH04250074A - Thermal head - Google Patents

Abstract

PURPOSE:To regulate the resistivity and temperature distribution of heating resistors without deteriorating the reproducibility of printing dots to prevent a heat spot by a method wherein a slit along a sub-scanning direction is formed on the center part of each of the heating resistors connecting between discrete electrodes and a common electrode. CONSTITUTION:On the surface of an insulating substrate 2, a thermal head is provided with a plurality of discrete electrodes 5 which extend in a sub- scanning direction Y and are arranged in a main scanning direction X; a common electrode 4 which is disposed apart from the discrete electrodes 5 in the sub-scanning direction Y correspondingly to tip end parts 5a of the discrete electrodes 5; and heating resistors 3 which are formed by burning an organic metallic resistant material so as to connect between the discrete electrodes 5 and the common electrode 4. In this construction, a slit 3a is provided on the center part of the heating resistor 3 along the sub-scanning direction. The slits 3a of the respective heating resistors 3 are made different in length, whereby the resistivities of the heating resistors 3 are regulated. Namely, the resistivities and heating values of the heating resistors 3 are uniformized.

Description

[Detailed Description of the Invention] A. OBJECTS OF THE INVENTION 1) Industrial Application Field 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.

In such a thermal head, a heating resistor is formed between a plurality of individual electrodes arranged in a row on an insulating substrate and a common electrode arranged corresponding to the tips of these electrodes. The thermal head is configured to supply power between the selected individual electrode and the common electrode to cause the heating resistor in that portion to generate heat, thereby performing thermal recording (printing).

As a method for forming a heating resistor on the insulating substrate,
Methods using thick film techniques such as screen printing and methods using thin film techniques such as sputtering are known.

Since the thin film technology described above can form a uniform heating resistor, when the heating resistor is formed using the thin film technology, it is possible to omit the trimming process to make the resistance value of the heating resistor constant. It is.

However, thin film technology has the problem of low productivity.

Although the thick film technology requires less expensive manufacturing equipment and has higher productivity than the thin film technology, it generally has a high dot density, making it difficult to form a uniform heating resistor.

If the resistance values of the heating resistors (that is, the heating resistors corresponding to each printed dot) formed on the surface of the insulating substrate of the thermal head are not uniform, a difference will occur in the temperature of the heating resistors when they generate heat. 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 can be made uniform within the 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 (Me
tallo-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. In the heating resistor formed by this MOD method, the variation in resistance value between adjacent heating resistors is as small as approximately ±2%, and there is little variation in shape, so dot reproducibility is good. It is difficult to keep the resistance value of the heating resistor within ±5% due to unevenness in film thickness during coating.

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% or more in the resistance value of the body, and the variation in the amount of heat generated by the heating resistor based on the variation of the resistance value of ±3% or more causes density unevenness in the printed image.

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, in the conventional laser trimming method, the resistance value is adjusted by sandwiching the width of the heating resistor, which may damage the heating resistor, lowering its power resistance, or changing the shape of the printed dots. Problems such as

Furthermore, although many conventional heat generating resistors are usually rectangular, the distribution of the amount of emission in each of these resistors is the same in each part. Therefore, the temperature distribution of each heating resistor is such that the temperature is high in the center and low in the peripheral part. Therefore, a heat spot is generated at the center of each heating resistor. If the temperature of this heat spot becomes too high, there is a problem that the life of the heating resistor will be shortened, and if the temperature of the heat spot is kept low, there is a problem that the temperature of the outer periphery of the heating resistor becomes too low. there were. If the temperature around the heating resistor becomes too low, when thermal recording (printing) is performed using thermal recording paper that develops color above a certain temperature, the thermal recording paper will come into contact with the center of the heating resistor. However, the areas that come into contact with the low-temperature surrounding areas do not develop color, resulting in poor reproducibility of printed dots.

By the way, as a result of research, the inventor of the present invention found that the direction of the current flowing through the central part of the heating resistor (sub-scanning direction) is
074(3) It has been discovered that when a slit is formed along the length of the heating resistor, the resistance value of the heating resistor changes in proportion to the length of the slit.

The present invention has been made in view of the above-mentioned circumstances and research results, and it is possible to adjust the resistance value of the heating resistor and at the same time adjust the temperature distribution of the heating resistor, without deteriorating the reproducibility of printed dots. The challenge is to prevent spots from occurring.

B. Structure of the Invention 1) Means for Solving the Problems In order to solve the above problems, the thermal head of the first invention of the present application includes a plurality of individual electrodes extending in the sub-scanning direction and arranged in rows in the main scanning direction. , a common electrode arranged apart in the sub-scanning direction corresponding to the tips of the individual electrodes,
In a thermal head formed by firing a metal-organic resistor material and having a heating resistor connecting between the individual electrodes and the common electrode formed on the surface of an insulating substrate, a heating resistor is formed in the central part of the heating resistor in the sub-scanning direction. It is characterized by a slit along the length.

Further, the thermal head of the second invention of the present application is characterized in that
The invention is characterized in that the distance between the individual electrodes and the common electrode arranged apart in the sub-scanning direction is shorter in the side portions than in the central portion in the main-scanning direction.

2) Effect The thermal heads of the first and second inventions of the present application having the above-mentioned features have a slit formed in the center of the heating resistor along the sub-scanning direction, and the length of the slit is The resistance value of the heating resistor is adjusted by varying the heating resistor. Therefore, the resistance value of each heating resistor becomes uniform.

Furthermore, since the slit is formed at the center of the heating resistor, the amount of heat generated at the center of the heating resistor is smaller than the amount of heat generated at both sides in the main scanning direction. Therefore, the slit functions to prevent heat spots from occurring. Then, the resistance value of the heating resistor is changed significantly (
(adjustment), the slit becomes long but has a narrow width, so a sufficient amount of heat flows into the slit portion from the heat generating portions on both sides thereof. Therefore, the temperature of the central portion of the heating resistor does not become too low.

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 the main parts thereof, Fig. 3 is an enlarged view of the part shown by arrow m in Fig. 2, and Fig. 4A is the same. A plan view of the main parts of the embodiment,
4B and 4C are cross-sectional views taken along lines IVB-IVB and IVC-IVC 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.

As shown in FIGS. 3 and 4A, a plurality of heating resistors 3 each having a width of 90 μm and a length of 300 μm are provided in an island shape along the main scanning direction X on the surface of the insulating substrate 2. , a width of 10 μm for adjusting the resistance value along the sub-scanning direction Y is provided at the center of most of these transmitting resistors 3.
m slits are formed. Note that the slit will be explained in detail later.

Further, on the surface of the insulating substrate 2, as shown in FIG. 3, a strip-shaped common electrode main body 4a and a large number of common electrode connection parts projecting in the sub-scanning direction Y in a comb-like shape from the common electrode main body 4a. 4b is formed. Further, on the surface of the insulating substrate 2, the plurality of common electrode connecting portions 4 are provided.
A large number of individual electrodes 5 are arranged in a row along the main scanning direction X, and are arranged at a predetermined distance (150 μm) from each other at positions facing the direction b. The common electrode connecting portions 4b and the tips of the individual electrodes 5 are connected by the heating resistors 3 arranged in rows along the main scanning direction X on the surface of the insulating substrate 2. As mentioned above, the distance between the electrodes 4 and 5 connected by the heating resistor 3 having a width of 90 μm and a length of 300 μm is 150 μm, so the length of the heating portion of the heating resistor 3 (the length of the heating resistor 3) is 150 μm. The effective length) is 150 μm. Further, the base end portion (the left end portion in FIG. 1) of the individual electrode 5 is a pad (i.e., an IC
It is formed as a connecting terminal) 5a. The heating resistor 3, common electrode 4, individual electrodes 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 to a socket 10 as a drive signal input terminal via a connector pin 9 passing through the printed wiring board 7 at its input end side (left side in FIG. 1). 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 IC connecting terminal 5a of the individual electrode 5 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 reference numerals 1 to 14, the driving IC, etc., and each of the heating resistors 3 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.

Next, an embodiment of the method for manufacturing the thermal head will be described with reference to FIGS. 5A to 9C.

First, a metal-organic material for forming a heating resistor (ie, a metal-organic resistor material) containing iridium Ir (or Ru) is printed all over the surface of the insulating substrate 2 by screen printing.

Next, the insulating substrate 2 coated with this metal-organic resistor material is dried and fired at 600° C. to form a resistor film 3L (see FIGS. 5A and 5B) on the surface of the insulating substrate 2. After a resist layer RI is formed on this resistor film 3L, an exposure mask M1 is placed thereon, and exposure and development are performed. Then, a resist pattern Rp for forming a heating resistor as shown in FIGS. 6A and 6B is obtained.

Next, the resistor film 3L is individually separated using an etching technique to form the heating resistor 3 shown in FIGS. 7A and 7B.

Next, a metallo-organic gold paste is applied to the surface of the insulating substrate 2 on which a large number of the heating resistors 3 are formed, and after baking, the common electrode 4 and individual electrodes 5 shown in FIGS. 8A to 8C are formed by photoisoetching technology.

The process of forming the heating resistor 3, the common electrode 4, and the individual electrodes 5 shown in FIGS. 5A to 8C is a type of thick film technology called MOD (Metallo-Organic Depo).
(location) method.

The heating resistor 3 of this example formed by the MOD method has a width of 90 μm and a length of the heating portion (the portion between the tips of the electrodes 4 and 5) of 150 μm, and the variation in resistance value is ±1.
It was within 0%.

Next, as shown in FIGS. 9A to 9C, a slit for adjusting the resistance value with a width of 10 μm is formed along the sub-scanning direction Y in the central part of the heat generating resistor 3 using a YAG laser. Make the resistance value uniform.

By the way, in the case of the heating resistor of this example, the relationship between the length of the slit and the resistance value change rate (resistance value increase rate) is the 10th
It was as shown in the figure. The relative standard deviation of the rate of change in resistance value at a certain slit length was as good as about 2%.

In order to equalize the resistance value of each of the silent resistors 3 by increasing the resistance value due to the slit, it is necessary to trim (adjust) the resistance value of each heating resistor 3 to match the largest resistance value. be. However, as mentioned above, since the variation in the resistance value of each heating resistor 3 is within ±10%,
When trimming the resistance value of each heating resistor 3 to match the heating resistor with the largest resistance value, the heating resistor 3 with the smallest resistance value forms a slit that increases its resistance value by approximately 20%. There is a need to. And, JP-A-4-2
50074(5) It is not necessary to form a slit in the heating resistor 3 having the maximum resistance value. Further, in trimming the resistance value of the other heating resistors 3 by forming the slit, the rate of increase in resistance value may be 20% or less. According to FIG. 10, the heat generating resistor 3 of this embodiment can obtain a resistance change rate of 20% due to the slit having a width of 10 μm and a length of 100 μm. Therefore, the resistance value of the other heating resistor 3 can be trimmed by a slit having a width of 10 μm and a length of 100 μm or less.

After forming a slit with a determined length as described above, the surface of the insulating substrate 2 is coated with an anti-wear layer, and the fourth A to
A thermal head having the configuration shown in Fig. 4C is manufactured.

Each heat-generating resistor 3 in which the slit 3a for trimming the resistance value described above is formed has a variation in its resistance value that is ±
We were able to keep it within 1%.

Next, the operation of the thermal head having the above-described configuration will be explained.

When a voltage is selectively applied between the individual electrodes 5 and the common electrode 4 via the driving IC shown in FIG. 1, a current flows through the heat generating resistor 3 and the heat generating resistor 3 generates heat. In this case, since the resistance values of the respective heating resistors 3 are made uniform by the slits, the power consumption and the amount of heat generated are approximately the same. The heat generation amount distribution h in the main scanning direction of the heating resistor 3 in which the slit for trimming the resistance value is formed is as follows:
The result is as shown in FIG. As can be seen from FIG. 11, the central portion A of the heating resistor 3 in the main scanning direction (corresponding to the position of the slit 3a) is different from the side portions B1 and B of the heating resistor 3.
Compared to 2, the amount of heat generated is less or zero. In this case, heat is conducted from the side portions B1 and B2 where the amount of heat generated is large to the center portion A where the amount of heat generated is small or zero, so the temperature distribution t of the heating resistor 3 (see FIG. 11) is approximately Equalized. Therefore, when thermal recording (printing) is performed using thermal recording paper that develops color at a temperature higher than the determined temperature To, substantially the entire surface (hatched area) of the heating resistor 3 appears as shown in the lower part of FIG.
reaches a predetermined color development temperature of to or higher without generating heat spots, and the heat-sensitive recording paper in contact with that surface develops color. Therefore, the reproducibility of printed dots can be improved without generating heat spots.

Next, a second embodiment of the thermal head of the present invention will be described with reference to FIG.

In this second embodiment, the center portions of the opposing electrodes 4 and 5 in the main scanning direction It differs from the first embodiment in that it is configured to be shorter at the end.

According to this second embodiment, both the electrodes 4 of the heating resistor 3
, 5 is larger at the center than at both sides in the main scanning direction. Therefore, compared to the first embodiment, the amount of heat generated at the center of the heating resistor 3 in the main scanning direction becomes less. In this case, it is possible to prevent heat spots from occurring even in the heating resistor 3 in which no slit is formed.

Next, a third embodiment of the thermal head of the present invention will be described with reference to FIG.

In this third embodiment, the tips of the opposing electrodes 4 and 5 are cut out in a triangular shape so that the distance between the tips of the electrodes 4 and 5 becomes shorter from the center in the main scanning direction toward both sides. This embodiment differs from the first embodiment in its configuration.

This third embodiment has the same effect as the second embodiment.

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, trimming the resistance value of the heating resistor by forming slits can be performed after pulse trimming. In that case, if the variation in resistance value is made uniform within the range of ±3% by pulse trimming, a maximum resistance change rate of 6% is required to make the resistance value even more uniform by forming slits. In order to obtain a resistance value change of 6% by forming the slit, the slit length should be about 30 μm, as can be seen from FIG.

Further, the tip portions of both electrodes are shaped so that the distance between each individual electrode arranged apart in the sub-scanning direction and the common electrode is shorter at the side portion than at the center portion in the main-scanning direction. As such, it is possible to adopt various shapes other than those shown in the embodiments. In this case, it is also possible to make the shapes of the tips of the two electrodes different from each other. Furthermore, the common electrode 4 can also be composed of only the strip-shaped common electrode main body portion 4a. Furthermore, it is also possible to thermally anneal the heating resistor after trimming it. It is also possible to form the heating resistor after forming electrodes on the surface of the insulating substrate.

C. Effects of the Invention In the thermal head of the present invention described above, a slit for adjusting the resistance value along the sub-scanning direction is formed in the center of the heating resistor, and the length of the slit is made different for each heating resistor. The resistance value of the heating resistor is adjusted. Therefore, each heat generating resistor has a uniform resistance value, so that the amount of heat generated is also uniform. Furthermore, since the slit is formed at the center of the heating resistor, the amount of heat generated at the center of the heating resistor is smaller than the amount of heat generated at both sides in the main scanning direction. Therefore, the slit functions to prevent heat spots from occurring. Therefore, the temperature distribution of the heating resistor is made uniform.

In addition, when the slit is formed by laser trimming, a part where the power resistance is reduced due to heat is generated in the central part of the heating resistor, but as mentioned above, the heat generation amount in the central part is reduced, so the power resistance is reduced. It is possible to reduce the effect of a decrease in

[Brief explanation of the drawing]

FIG. 1 is an overall explanatory diagram of an embodiment of the thermal head according to the present invention, FIG. 2 is a perspective view of the main parts thereof, FIG. 3 is an enlarged view of the part shown by arrow m 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
Figures A to 9C are explanatory diagrams of the method of forming a heating resistor and electrodes on the surface of the insulating substrate of the same thermal head, and Figure 10 shows the slit length and resistance when slits are formed in the heating resistor of the above example. A diagram showing the relationship with the rate of change, FIG. 11 is an explanatory diagram of the calorific value distribution and temperature distribution of a heating resistor with slits formed, FIG. 12 is an explanatory diagram of the second embodiment of the present invention, and FIG. 13 is an explanatory diagram of a third embodiment of the present invention. 2... Insulating substrate, 3... Heat generating resistor, 3a... Slit, 4...
Common electrode, 5...individual electrode. Patent applicant Fuji Xerox Co., Ltd. Agent Patent attorney Takashi Tanaka 2 people

Claims (2)

[Claims] 1. A plurality of individual electrodes (5) extending in the sub-scanning direction (Y) and arranged in a row in the main-scanning direction (X), and a plurality of individual electrodes (5) extending in the sub-scanning direction (X), corresponding to the tips (5a) of the individual electrodes in the sub-scanning direction. (Y
), and a common electrode (4) which is formed by firing a metal-organic resistor material and which is spaced apart from the individual electrodes (4).
5) and the common electrode (4).
) is formed on the surface of an insulating substrate (2), characterized in that a slit (3a) along the sub-scanning direction (Y) is formed in the center of the heating resistor (3). head. 2. The distance between each individual electrode (5) and the common electrode (4) arranged apart in the sub-scanning direction (Y) is greater in the side part than in the center part in the main scanning direction (X). 2. The thermal head according to claim 1, wherein the thermal head is formed short.