JPS6168264A - Thermal head - Google Patents

Abstract

PURPOSE:To enable printing with high resolving power even if high speed printing is performed, by making the heat generated in a certain heat generating element hard to conduct to the adjacent other heat generating element. CONSTITUTION:The size R of each of heat generating elements 31 in a main scanning direction is reduced to the half or less of the arrangement pitch of the heat generating elements 31, that is, the center-to-center distance P between both electrodes 12, 13. When the heat generating density of this thermal head is 300 SPI, the distance P is about 84.7mum and the size Q in a sub-scanning direction is about 130mum. The width D between both electrodes 12, 13 is about 45mum and, therefore, the size R in the main scanning direction is about 39.7mum. Because of this, the interval between mutually adjacent heat generating elements 31 is same to the width D between both electrodes 12, 13 and about 45mum being a relatively large size and, as a result, the heat generated in a certain heat generating element 31 is hardly conducted to the adjacent other heat generating element 31 especially through a heat generating resistor 11. Therefore, for example, even if black image information is printed every one dot, the element 31 corresponding to white image information is not heated to a degree performing printing operation.

Description

DETAILED DESCRIPTION OF THE INVENTION "Field of Industrial Application" The present invention relates to a thermal head used in electronic equipment that performs thermal recording or display.

"Prior Art" In the recording sections of printers and facsimile machines, recording devices that utilize a thermal transfer recording method or a thermosensitive color recording method are widely used. These recording devices often use a thermal head as a means for applying heat pulses.

Further, some types of display devices that display images using latent magnetization images also use thermal heads as means for applying heat pulses.

FIG. 2 shows an example of such a conventional thermal head. A long and narrow heating resistor 11 is formed on the substrate of this thermal head. Two types of electrodes 12 and 13 are attached alternately to this heating resistor 11 at predetermined intervals. One of these electrodes is alternately divided into first and second electrodes 12a and 12b, the former being connected to the first common line CI through a diode 14a, and the latter being connected to the second common line CI through a diode 14b. Connected to line C2. These common lines C1, C
2, a predetermined voltage is alternately applied from a power supply circuit (not shown) via a switch circuit 15.

The other electrodes 13 are each connected to an output terminal of a NAND circuit 16.

Each NAND circuit 16 has two input terminals.

One of these input terminals is connected to each output terminal of the latch circuit 17, and each input terminal of the latch circuit 17 is connected to each output terminal of the shift register 18. The other input terminal of each NAND circuit 16 is connected to a strobe terminal 19.

A print signal 22 is supplied one pit at a time to the shift register 18 of this thermal head in synchronization with the feed lock 21. This print signal 22 is a print signal that has been recomposed by a signal processing circuit (not shown) in order to control the heat generation of the heat generating resistor 11 every two bits in units of two bits. In other words, in this thermal head, when a voltage is applied to the first common line C3, heat is generated every two bits at a time, as shown by circles, and then a voltage is applied to the second common line C2. When the voltage is applied, the remaining two bits each perform a heating operation as indicated by the X mark. Therefore, the print signal 22 has a data format in which every two bits are thinned out by two bits.

The print signal 22 set in the shift register 18 is serial-parallel converted and held in the latch circuit 17. When the switch circuit 15 selects the first common line CI at a predetermined timing, a strobe signal is supplied to the strobe terminal 19, and the heating elements indicated by circles of the heating resistor 11 selectively generate heat. When the first stage of heat generation is completed, the switch circuit I5 switches to the second common line C2.
is selected, and based on the print signal newly set in the shift register 18, the heating element indicated by the X mark of the heating resistor 11 is selectively heated. This is how the heat generation of this thermal head is controlled.

By the way, in such a thermal head, since image information is expressed in the form of dots, it is said that it is desirable that the shape of the printed dots be a square or a shape close to this. For example, in a thermal head with a heat generation density of 3003 PI, as shown in FIG. It is said that it is desirable to set it to 84.7μ square. The size of the printed dot depends on the size of the heating element 31 (the shaded area in FIG. 5). Therefore, if the size Q of the heating element 31 in the sub-scanning direction is set to about 130μ, the size of the printed dot in the same direction can be set to about 847μ. On the other hand, the size R of the heating element 31 in the main scanning direction depends on the width of the electrode 12.13, and the smaller this is, the closer the size of the printed dot in the same direction can be to 84.7μ. For this reason, efforts are being made to make the width of the electrodes 12, 13 as small as possible, and for example, widths of about 30 μm have been put into practical use.

However, in such a thermal head, the electrode 12.1
The smaller the width of heating elements 3, the more adjacent heating elements 3
The interval between 1 also becomes small.

Therefore, a relatively large amount of heat generated by one heating element 31 is conducted to other heating elements 31 adjacent thereto, particularly through the heating resistor 11. As a result, for example, when black image information is printed every other dot, the heating element 31 corresponding to white image information is also heated considerably, resulting in a substantial printing operation. In particular, when performing high-speed printing, the time applied to the heating element 31 is shortened and the applied power is increased, so if black image information is printed every other dot using N heat, it will become almost completely black. Something happened.

``Problems to be solved by the invention'' As described above, conventional thermal heads have a problem in that the reproducibility of white image information is poor, resulting in poor resolution, which is especially noticeable in high-speed printing. .

In view of these circumstances, an object of the present invention is to provide a thermal head that can print with high resolution even when printing at high speed.

"Means for Solving the Problem" In the present invention, the size of the heating element in the main scanning direction is set to approximately half or less of the arrangement pitch of the heating element, so that the heat generated by one heating element generates heat in the adjacent pond. This makes it difficult for conduction to the element.

"Example" The present invention will be described in detail below with reference to Examples.

FIG. 1 shows the main parts of a thermal head in one embodiment of the present invention. In this figure. 5, the same reference numerals are given to the same parts as in FIG. 5, and the explanation thereof will be omitted as appropriate.

The size R in the main scanning direction of the heating element 31 (the shaded area in FIG. 1) of this thermal head is as follows:
1 arrangement pitch, that is, the distance P between the centers of both electrodes 12 and 13
It is less than half of that. When the heat generation density of this thermal head is 30.0 S P I, both electrodes 12
．． The distance P between the centers of 13 is about 84.7μ,
Further, the size Q of the heating element 31 in the sub-scanning direction is approximately 130μ. The width of both electrodes 12 and 13 is, for example, 45
Therefore, the size R of the heating element 31 in the main scanning direction is about 39.7μ.

In this thermal head, heating elements 31 adjacent to each other
Since the spacing between the two electrodes 12 and 13 is relatively large at 45 μm, which is the same as the width of both electrodes 12 and 13, the heat generated in one heating element 31 is particularly transferred to other adjacent heating elements 31 via the heating resistor 11. This makes it difficult for conduction to occur. Therefore, even if black image information is printed every other dot, for example, the heating element 31 corresponding to white image information will not be heated up to the point where the actual printing operation is performed.

FIG. 2 schematically shows an example of printing by this thermal head. Of these, FIG. 2A shows a print signal, in which the diagonal-lined ◯ marks represent black image information and the open ◯ marks represent white image information.

FIG. 5(b) shows the printing state of this thermal head based on the print signal shown in FIG. 4(a).

In this figure (b), the dotted square represents the exact 84.7μ angle, which is said to be the ideal shape of the printed dot.
The shaded area represents the actual dots printed by this thermal head.

As is clear from FIG. 2, when the print signal of black image information is isolated, the size S of the print dot in the main scanning direction is about 40 to 50 microns.

When two print signals of black image information are consecutive, the print dots are also continuous due to heat diffusion, and the size T in the main scanning direction is about 120 to 130 μ. Even when three or more print signals of black image information are consecutive, the print dots are consecutive.

In this way, with this thermal head, the size of an isolated printed dot is smaller than 84.7 μ square, but if two or more printing signals of black image information are consecutive, the printed dots are continuous, and also isolated This means that the white image information that has been created will also be reproduced satisfactorily. Therefore, when looking at the recording surface as a whole,
Even if the size of the isolated printed dot is smaller than 84.7 μ square, it will give a clearer impression.

FIG. 3 shows the relationship between the size R of the heating element 31 in the main scanning direction and the size of the printed dot in the same direction. Assuming that the ideal shape of the printed dot is exactly 84.7μ square, it can be said that the size of the printed dot is within a good range of about 65μ to 95μ, and 35μ
If it is about 65μ, it can be said that it is within a fairly acceptable range.

As is clear from FIG. 3, when the printed dot is isolated, if the size R of the heating element 31 is about 80 μm or more, the printed dot size will be about 95 μm or more,
On the other hand, if it is about 33μ or less, it becomes about 35μ or less. Also, if black image information is printed every other dot,
If the size R of the heating element 31 is about 42μ or more, the size of the printed dot will be about 95μ or more, while if it is about 23μ or less, it will be about 35μ or less. Therefore, in both the case where the printed dot is isolated and the case where black image information is printed every other dot, a reasonably acceptable range is a range in which the size R of the heating element is around 40 μm. If this is expressed in a general formula, if the arrangement pitch of the heating elements 31 is P, then the size R in the main scanning direction is roughly expressed by the following formula.

R≦P/2' The size R of the heating element 31 in the main scanning direction does not need to be exactly half or less of the arrangement pitch P, and there is no problem even if it is slightly larger than half.

For example, it may be as expressed by the following equation.

R≦(1,1 to 1.2) Of course there are scales.

FIG. 4 shows an example in which the present invention is applied to a thin film type thermal head. In this thermal head, a large number of heating resistors 41 are arranged parallel to each other at a constant pitch, one electrode 42 and the other electrode 43 are laminated on both sides of the upper surface of each heating resistor 41, and both electrodes It has a structure in which a heating element 51 is formed by the heating resistor 41 exposed in between. In the thermal head of this example, the arrangement pitch P of the heating elements 51 is about 8487μ, and the size QXR is about 84.7μ×42μ.

"Effects of the Invention" As explained above, according to the present invention, heat generated by a certain heating element is difficult to conduct to other heating elements adjacent to it, so that other heating elements adjacent to it are not necessary. No printing operation is performed, so even if high-speed printing is performed, it is possible to print with high resolution.

[Brief explanation of drawings]

Fig. 1 is a plan view showing the main parts of a thermal head according to an embodiment of the present invention, Fig. 2 is a schematic diagram shown to explain an example of printing by a gutter on the thermal head, and Fig. 3 is a schematic diagram of the thermal head. A diagram showing the relationship between the size of the heating element in the main scanning direction and the size of the printed dot in the same direction, FIG. 4 is a plan view showing the main parts of a thermal head in another embodiment of the present invention, and FIG. 5 is a conventional one. FIG. 6 is a block diagram showing an example of the thermal head, and FIG. 6 is a plan view showing a part of the thermal head. 11.41... Heating resistor, 12.13.42.43... Electrode, 31.51
...Heating element. Applicant: Fuji Xerox Co., Ltd. Representative
Patent Attorney Ume Yu Yamauchi 1st
Figure 2 (a) ■ ○ ○ ooo. Figure 3: The size and weight of the heating element in the main direction ≠) Figure 4 Figure 6 Figure 5

Claims (1)

[Claims] It is equipped with a large number of heating elements linearly arranged on a substrate, and electrodes provided on both sides of these heating elements in the sub-scanning direction for applying a voltage to each heating element. A thermal head characterized in that the size in the scanning direction is approximately half or less of the arrangement pitch of heating elements.