JPS5968270A - Preparation of heat generating resistance body for thermal head - Google Patents

Abstract

PURPOSE:To eliminate the irregularity in the resistance values of dot shaped resistance bodies by a method wherein dot shaped heat generating resistance bodies are respectively subjected to anodic chemical conversion treatment to increase each electric resistance to a predetermined value and electric resistances of all dots are aligned to a predetermined value. CONSTITUTION:After electrodes 2a, 2b are coated with resist 3 and an electrolyte paste 4 containing a weak acid is placed on an exposed heat generating body 1, an anode is contacted with said paste 4. On the other hand, when a cathode is brought into contact with at least either one of pair of the electrodes 2a, 2b and DC voltage is applied to both electrodes, the heat generating body 1 is gradually oxidized to form oxide toward the depth direction from the surface thereof. Voltage to be applied for chemical conversion treatment is gradually increased while the resistance value between the electrodes 2a, 2b is monitored and said chemical conversion treatment is finished when the resistance value reaches a predetermined value. As mentioned above, when the dots are successively changed to perform anodic chemical conversion treatment, the resistance values of all dots can be aligned to a predetermined value.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for manufacturing a heating resistor for a thermal head.

Conventional thermal heads are roughly divided into two types depending on the printer type. The first type is called the serial type, and the number of heating element dots is small, 7 to 32 dots, and each dot is formed in a row in the vertical direction of the paper to be printed (in other words, in the column direction of the paper). ing. When printing, each dot first scans in the horizontal direction of the paper (that is, in the row direction of the paper) to print the first line, and then returns to its original position to print the second line. This type of head is small and has a small number of heating element dots, so it has the characteristic that it is easy to manufacture. However, this first type takes time to print because the number of dots that can be printed at one time is small, and is not suitable for high-speed printing.

For this reason, a so-called line printing method was developed with the aim of increasing speed, and has recently become popular. The second type of thermal head is used for this method, and the dot-shaped heating element is placed in the horizontal direction of the paper (that is, in the row direction of the paper). It is formed only in length.

This second type is called a di-in head type, and for example, a head for A4 size (210 mm x 296 m) requires a head length +-i of approximately 210 tones.

Therefore, if the resolution is 8 dots/mall, the total number of dots l for the - line will be 210 x 8 = 1680. However, with conventional manufacturing methods, it is very difficult to make the electrical resistances of the large number of dots required for such a large line head equal to a constant value.

If the resistance of each dot is not uniform, uneven density will occur in the print, resulting in a very unsightly print. The principle of thermal printing is that a predetermined amount of power is supplied to a heating resistor to generate Joule heat, and the heat is transmitted to, for example, heat-sensitive coloring paper to cause a chemical or physical change to occur, thereby causing the heating resistor to generate Joule heat. It visualizes the corresponding dots.

And, as a method of controlling the power injected into the heating element,
1. Conventionally, voltage control methods and current control methods have been proposed, but due to their ease of control, a method of varying the voltage or a method of controlling the energizing pulse width (time) while keeping the voltage constant has been put into practical use. In this case, the resistance value of the heating element is R and the current is I
If the voltage is V, the power energy Q supplied to the heating element is expressed as Q=iv=M2. Therefore, if the resistance value R of each heating element is different from each other, the amount of heat generated will be different even if a constant voltage is applied from the outside, and as a result, density unevenness will occur in printing.

In particular, recently there has been a demand for image printers that require gradation expression, and in the case of such types, -
In particular, all heating elements in the line must have the same resistance value.

However, as mentioned above, in the conventional manufacturing method of large line heads, it is very difficult to make the resistance values of the many dot-shaped heating resistors the same. Conventional methods for producing large line heads include a thick film method using screen printing and a thin film method using vacuum evaporation, sputtering, and the like. However, with the thick film method, the pattern accuracy is poor, so even now the resistance value variation within one line is ±20 to 30%.
There are so many. Furthermore, even with the thin film method, which has relatively good processing accuracy and can produce fine dots, the resistance value varies by a factor of ±7 due to, for example, unevenness in film thickness.

Furthermore, in the thin film method, the larger the line, the more uneven the film thickness becomes. However, if the resistance values vary as described above, it is impossible to obtain a larger printer with better gradation expression.

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to manufacture a heating resistor for a thermal head in which there is no or very little variation in the resistance value of the dot-shaped heating resistor even in the case of a large thermal head.

The inventor first considered improving the manufacturing process, but encountered near-impossible difficulties, and eventually focused on a method of correcting and equalizing the variation in resistance values in a post-process.

So far, as a method for correcting the resistance value of a heating element in a post-process, so-called laser trimming, in which a part of the heating element is removed using a laser, has been known. However, this method has the following drawbacks.

This is because the area and shape of the heating element dots change, and the image quality is undeniably degraded. Furthermore, the equipment is large and expensive, and the laser beam must be focused extremely minutely to match the fineness of the dot, but this focusing also requires difficult technology.

By the way, tantalum (TaN or TξN), Ta-8i cermet, and Ta-8i02 cermet are used as materials for the heating resistor because they are resistant to thermal shock, have a small temperature coefficient, are stable at high temperatures, and are easy to mass produce. has been done. The present inventors believe that most of these materials can be oxidized by anodization, and that the resulting oxides are electrical insulators, and that depending on the degree of oxidation, the electrical resistance value of the heating resistor can be increased (in the direction of increase). ) can be freely modified, and oxide formation occurs during anodization. It was discovered that the dots proceed in the depth direction from the surface of the dots that come into contact with the solution, and the substantial heat generating area of the dots does not change, and the present invention is based on this finding. That is, the present invention provides a method for manufacturing a heating resistor for a thermal head, which is composed of a large number of dot-shaped heating resistors and a pair of lead electrodes electrically connected to each dot. The above manufacturing method is characterized in that the dots are anodized in the transverse direction to increase the electrical resistance to a predetermined value, thereby making the electrical resistance of all the dots uniform within a certain range.

Hereinafter, the present invention will be specifically explained by examples with reference to the drawings.

Example I Dot-shaped heating resistor (1) and pair of lead electrodes (2a)
(2b) is a cross-sectional view of a heating resistor for a thermal head constructed from the above, and (B) is a plan view thereof.

The shape of the heating resistor (1) is not a so-called dot, but
As shown in diagram M2 (cross-sectional view), electrodes (2a), (2
b) It may be in the form of a band extending over the entire lower surface. In this case as well, the part that actually generates heat is the part sandwiched between the pair of electrodes (2a) and (2b), in other words, the part where the electrodes are not laminated, and can be said to be a dot-shaped heating resistor.

(S) is a glazed alumina substrate.

As shown in FIG. 3, the electrodes (2a), (2b
) is coated with resist (3). Next exposed heating element 1
As shown in FIG. 4, an electrolyte paste (4) containing a weak acid is placed on top of 1). In this way, electrolyte paste (
4) is brought into contact with an anode electrode (for example, platinum or tantalum metal), and a cathode electrode is brought into contact with at least one of the other pair of electrodes (2a) and (21)), and a DC voltage is applied to both electrodes. Then, the heating element (1) in contact with the electrolyte paste (4) is gradually oxidized to produce oxides from the surface toward the depth. Such an oxidation method is generally called an anodization method. The thickness of the oxide is proportional to the applied voltage. While monitoring the resistance value between the pair of electrodes (2a) and (2b), gradually increase the voltage applied to the chemical formation reservoir until the resistance value reaches a predetermined value (that of the dot with the highest resistance value or a value higher than that). When this is reached, chemical formation is terminated.

Since the rate of oxidation by anodization is proportional to the rate of increase in applied voltage, an appropriate rate of increase in voltage is selected.

In this way, by changing the dots and anodizing them one after another, the resistance values of all the dots can be made uniform to a predetermined value.

Finally, when the electrolyte paste (4) and the resist (3) are removed, a heating element (1) having an oxide layer (1a) on its surface is obtained as shown in FIG. 5 (cross-sectional view) K. This oxide (1a) has the chemical formula TaNz0ν, and since it is an electrical insulator and is very thin, it has no problem in conducting the generated heat. Thereafter, an anti-oxidation layer and an anti-wear layer are laminated on the heating element according to a conventional method.

In the heating resistor for a thermal head manufactured by the method of the present invention, the variation in resistance value between dots is ±0.01.
%.

The electrolyte paste (4) consists of carboxymethylcellulose, ethylene glycol, IJ phosphoric acid [water, and has a phosphoric acid content of 0.1 to 1% by weight.

Example 2 Glazed alumina 4& with a width of 5011 II 11 and a total length of 240 mm was coated with a thickness of 0.1 f by high frequency sputtering.
irn Ta2N thin film was formed, and this Ta2N thin film was used for effective recording at a dot density of 216111111, 8 dots/
1. Patterning is performed using 7-otolithography technology so that the total number of heating element dots is 1728. Ta2N etching is dry etching in plasma, and then
Heat treatment is performed in the air at 300°C for 5 hours. Next, Ni-C
Gold was deposited to a thickness of 1 μm on the soil with r of 50, and a pair of lead electrode patterns (
A piece J similar to that shown in FIG. 1(B) is formed. In this case, since it is desired to adopt a drive method using a well-known diode matrix for the heating resistor, three adjacent ones are connected from one end to the other.
The two dot ICs are divided into 54 groups in total, and within the 1 group, one of the pair of lead electrodes, for example, the (2a) side, is used as a common electrode and connected to one conductive wire.
On the remaining electrode (2b) side, those located at the same position (for example, nth from the left end) are connected to one conductive wire when compared between groups. In this way, fewer electrodes need to be drawn out to the outside, and the power supply to each dot can be controlled individually.

So, when we measured the resistance values of all 1728 dots, we found that
The average value is 120Ω, and the variation is about ±10%.

The relationship between the dot position and its resistance value was as shown in FIG. It is presumed that the cause of this variation in resistance value is mainly due to the non-uniformity of the film thickness during the production of the Th2N thin film by sputtering.

However, within one group of 32 adjacent dots mentioned above, the variation in resistance value is about ±0.5% even in the largest group. Therefore, with the idea that the resistance of the heating element dots in one group should be corrected at the same time, a resist pattern is formed on the entire surface except for the exposed heating element dots. Then, a lump of electrolyte paste is placed on all 1728 exposed soil dots, and a Ta or PT needle electrode is brought into contact with the paste. This situation is shown in FIG. 7 (cross-sectional view). In the figure, (S) is the substrate, (1) is 'l'a
2N% (2at) and (2bl) are Nl-Cr
, (2a2) and (2) is gold, (3) is resist,
(4) is an electrolyte-based electrode) and (5) is a needle-like electrode. In this way, the cathode of the chemical power supply is connected to the needle electrode (5), and the anode is connected to the side (2a) connected by the common electrode of the group.

Step 1 of chemical trimming is to calculate the average resistance value of each group in advance when the resistance values of all dots are measured, and let that value represent all the resistance values of that group.
The maximum value of the representative resistance values among all groups is determined as the trimming target value. Then, anodization is started, and while monitoring the representative resistance value of each group in a time-sharing manner, anodization is continued until the value reaches the trimming target value. In other words,
Although this is just an example, here the monitoring of the resistance value and the application of the formation voltage are performed by time-division driving with an appropriate time width. FIG. 8 shows the timing relationship between the two. As shown in FIG. 8, the resistance is measured during the rest time of the formation, but the pulse width of the formation voltage and the pulse width of the resistance measurement may be arbitrary. By the way, it is necessary to increase the formation voltage t4 with time, thereby increasing the formation of oxides. The resistance of the heating element increases with the formation of oxides, but
FIG. 9 shows the relationship between the increase in the formation voltage over time and the monitored resistance value. When the monitored resistance value reaches the target value, turn off the chemical power source.

Using the above method, the resistance values of each group are trimmed one after another. However, it goes without saying that groups that already have a representative resistance value equal to the target value are excluded.

As a result, the initial resistance value variation among the 32 dots in each group is within ±0.5%, but since each representative resistance value of the group is the same, the resistance value variation of all 1728 dots is also ±0.5%. Within %. FIG. 10 shows the relationship between the dot positions and the resistance values before and after trimming. However, FIG. 10 shows only some groups as an example.

As explained in Example 2 above, the present invention also divides a large number of dot-shaped heating elements into a plurality of groups, and the dots in one group are anodized at the same time, thereby controlling the resistance value of all the dots within a predetermined range. To provide a method for manufacturing a heating resistor for a thermal head, characterized in that the heating resistor is aligned within the same area.

As described above, according to the present invention, it is possible to manufacture a heat generating resistor for a thermal head in which the resistance value of the heat generating resistor is very uniform even in a large line head.

In addition, the trimming speed is fast, the processing capacity is large, and it is easy to trim minute parts. There are also advantages such as cheaper equipment.

Therefore, if the thermal head manufactured according to the present invention is used, a printed image with uniform print quality, especially print density, can be obtained. It is also applicable to color printers, which are printers that can reproduce multiple gradations, which are expected to be in demand in recent years.

[Brief explanation of the drawing]

FIG. 1 illustrates an example of a heating resistor for a thermal head, with FIG. 4 being a sectional view and FIG. 1B being a plan view. FIG. 2 is a sectional view of another example of a heating resistor for a thermal head. Figures 3 and 4 are according to Example 1! ! This is a cross-sectional view of a heating resistor for a thermal head that is being left behind. FIG. 5 is a sectional view of a heating resistor for a thermal head manufactured according to Example 1. Figure 6 is a graph showing the relationship between the dot positions and the resistance R of a general heating resistor for a thermal head. FIG. FIG. 8 is a timing chart. FIG. 9 is a graph showing the relationship between the monitor resistance value, the formation voltage, and the formation time. Figure 1O I-1: Position of the heating resistor/D dot for the thermal head molded according to Example 2 (only a portion is shown)
It is a graph which shows the relationship between and resistance value. [Explanation of symbols of main parts] S・・・・・・・・・・ Glazed alumina substrate ■・
・・・・・・Heating resistor 2a, 2b ・・・・・・・・・Pair of glue ~ electrode Applicant Nippon Kogaku Co., Ltd. Agent Takashi Watanabe (Picture 4) Spear 5 off-line drawing ＼,

Claims (1)

[Claims] 1. In a method for manufacturing a heating resistor for a thermal head, which is composed of a large number of dot-shaped heating resistors and a pair of lead electrodes electrically connected to each dot, each dot-shaped heating resistor is Each is anodized to increase the electrical resistance to a predetermined value,
The manufacturing method described above is characterized in that the electrical resistance of all dots is thereby adjusted to the predetermined value. 2. The manufacturing method according to claim 1, wherein the heating resistor is made of tantalum nitride (Ta2N) or tantalum-based cermet. 3. A large number of dot-shaped heating resistors are divided into a plurality of groups, and the dots in each group are anodized at the same time, thereby aligning the electrical resistance of all the dots within a predetermined range. The manufacturing method according to item 1 or 2.