JPS58155974A - Thermal head - Google Patents

Abstract

PURPOSE:To eliminate the unevenness of temperature generated in the longitudinal direction of a thermal head and thereby to make a heat density uniform by a constitution wherein the resistance values of heating resistors are made high as they are located near to the central part in relation to said longitudinal direction. CONSTITUTION:A number of heating resistor patterns arranged in zigzag lines in the longitudinal direction of a thermal head are constituted so that the pattern width Wc of a pattern 1 located in the central part thereof is narrower than the pattern width We of heating resistors 2 located in the ends thereof and that the heating resistors located in the central part have narrower pattern widths. Thus, the resistance values becomes high as the patterns are located near to the central part, that is, the quantity of heat becomes little as the patterns are located near to the central part wherein the effect of heat accumulation is large. Therefore, the temperature of a heating part acting on thermal recording paper becomes uniform. The resistance values of the heating resistors in the central part can be increased either by increasing the length thereof, or by reducing the thickness of a resistor film.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a thermal head used in printers, facsimile machines, etc. for thermal recording.

A thermal head used in a line printer or the like has a large number of heat generating parts in its longitudinal direction.

The heat generating part is constructed by connecting a large number of heat generating resistors formed in a serpentine or rectangular pattern on the substrate, each of which is connected to an electrode terminal and a common terminal, or formed in a strip shape on the board along the longitudinal direction of the thermal head. Electrode terminals and common terminals are alternately provided in the direction perpendicular to the formed heating resistor, and a heating portion is formed between the two terminals. In order to record on thermal recording paper using a thermal head, the thermal recording paper is brought into contact with the thermal head, and a heating resistor at a predetermined position is energized to generate heat, thereby coloring the corresponding portion of the thermal recording paper.

In a conventional thermal head, the heat generating resistor is formed uniformly regardless of its position in the longitudinal direction, so the amount of heat generated at each heat generating portion is equal. However, the heat generated from the heating resistor is radiated to the thermal head support through the substrate, but the heat radiating effect is smaller at the center in the longitudinal direction of the thermal head and larger at the ends, so the accumulation effect is conversely at the center. Since it is large in size and becomes small at the edges, repetition of recording operations causes non-uniformity in substrate temperature, resulting in non-uniformity in color density.

In other words, even if electrical heating is performed under the same conditions at the center and ends of the thermal head in the longitudinal direction, the substrate temperature will be higher at the center, so the temperature of the heat-generating portion will be higher at the center than at the ends. The color density is darker in the center (lighter at the edges).

In view of the above-mentioned problems, the present invention aims to provide a thermal head that does not cause non-uniformity in color density in the longitudinal direction, and the resistance value of the heating resistor is adjusted to the central part of the thermal head in the longitudinal direction. By creating a distribution in the resistance value of the heating resistor so that the resistance value of the heating resistor increases as the resistance increases, the heating value of the heating resistor in the center can be reduced to reduce the temperature of the heating part that acts on the thermal recording paper. The purpose is to make the color density uniform by making it uniform in the longitudinal direction.

Next, embodiments will be described with reference to the drawings.

FIG. 1 shows a serpentine heating resistor pattern in a first embodiment of the present invention, where 1 is the pattern of the heating resistor at the center in the longitudinal direction of the thermal head, and 2 is the pattern of the heating resistor at the end. . Although not shown in the figure, a large number of heating resistors are also formed between these heating resistors. In this embodiment, the pattern width Wc of the heating resistor 1 at the center is narrower than the pattern width We of the heating resistor 2 at the end. The heating resistors between the heating resistors 1 and 2 are formed so that the closer they are placed to the center, the narrower the pattern width.

In this way, the pattern width of the heat generating resistor in the central portion becomes narrower, and as a result, the resistance value becomes higher in the central portion.

FIG. 2 shows a pattern of a meandering heating resistor according to a second embodiment of the present invention, in which numeral 3 is a pattern at the center and 4 is a pattern at an end. In this example, all the pattern widths are the same, but the lengths (Lc, Le) of the heat-generating portions of the patterns are formed so that the closer they are placed to the center, the longer they become. The resistor becomes taller.

In other embodiments, the pattern shape is the same as the conventional one, and is formed uniformly over the longitudinal direction of the thermal head, but the sheet resistance value of the heat generating resistor film such as a tantalum nitride thin film is located in the center of the longitudinal direction. The heating resistor arranged is a thermal head configured to be raised high. One way to create a distribution in the sheet resistance value is to change the target shape so that the area corresponding to the center of the substrate is small, and the area toward the edges is smaller when the heating resistor film is formed by sputtering. It is necessary to mold the material so that it becomes large. As a result, the sputtering speed in the central portion becomes slower, the thickness of the heat generating resistor film formed becomes thinner, and the sheet resistance value becomes higher.

In addition, by varying the sputtering discharge gas pressure between the center and the ends of the substrate in the longitudinal direction to create a distribution in the sputtering rate, or by distributing the substrate temperature in the longitudinal direction of the substrate to create a distribution in the film formation rate. It is also possible to give a distribution to the sheet resistance value.

FIG. 3 is a diagram showing a heating resistor pattern of another type of thermal head to which the present invention is applied.

Reference numeral 5 denotes a band-shaped heating resistor formed on the substrate along the longitudinal direction of the thermal head, and electrode terminals 6 and common terminals 7 are provided alternately from opposite directions at right angles to the longitudinal direction of the heating resistor 5. ing. The recording current i flows from the electrode terminal 6 to the common terminal 7, and the heating resistor in the area between them is energized to generate heat.

In the thermal head shown in FIG. 3, a thin film may be formed so that the sheet resistance of the heating resistor 5 is higher at the center as described above.

Further, in FIG. 3, the pattern width W of the band-shaped heating resistor 5 may be formed to be narrower at the center.

As described above, the present invention is configured such that the resistance value of the heating resistor is higher at the center in the longitudinal direction of the thermal head, so that it is possible to generate electricity and record on thermal recording paper in normal usage conditions. If this is done, the central part, which has a large heat storage effect, will generate less heat, and as a result of the interaction of the storage effect and the heat generation effect in the longitudinal direction, the temperature of the heat generation part that acts on the thermal recording paper will be uniform over the longitudinal direction of the thermal head. Then,
Color density becomes uniform.

[Brief explanation of drawings]

1 and 2 are diagrams each showing a heating resistor pattern in one embodiment of the present invention, and FIG. 3 is a diagram showing a heating resistor/N11 turn in another embodiment of the present invention. 1.3...Heating resistor pattern in the center, 2,4...
- Heating resistor pattern at the end, 5... Band-shaped heating resistor pattern. Patent applicant Ricoh Co., Ltd. Agent Patent attorney Aoyama Aoyama and two others Figure 1, Figure 2s

Claims (1)

[Claims] (1) In a thermal head in which a heating resistor is formed on a substrate so as to have a large number of heating parts in the longitudinal direction of the thermal head, the heating resistor is a heating resistor located in the center of the thermal head in the longitudinal direction. A thermal head characterized by having a resistance value distribution such that the resistance value of the body increases.