JPS60151070A - Thermal head - Google Patents

Abstract

PURPOSE:To obtain favorable heat response characteristics and enable to print images with high quality, by a method wherein a heat conduction controlling layer the heat conductivity of which is reduced at the time of passing an electric current to a heating resistor and is increased at other times is provided between a substrate and the heating resistor. CONSTITUTION:A thermal head comprises heating resistors 14 and a driving circuit for selectively heating the elements in accordance with image information. The heating element 14 is provided on an insulating ceramic substrate 11 through a semi-conductor layer 12 consisting of a P type indium-arsenic layer and an electrical insulating layer 13 consisting of silicon oxide. The heat conductivity KP of P type indium-arsenic constituting the layer 12 is decreased as the supplied current I is increased. Accordingly, the thermal efficiency at the time of passing the electric current becomes favorable, heat-radiating characteristics after completion of the passing of the electric current (at non-current-passing time) become favorable, and high-quality images can be printed.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a thermal head, and particularly to a thermal head that does not require a heat storage correction circuit.

(Prior art) The thermal recording method has the advantage of being able to record by simply heating the thermal recording paper with a high-temperature heating element, and does not require development or fixing processes.
In addition to printers, as a recording method in the hard copy field,
It has been attracting a lot of attention recently.

The heating element, or thermal head, uses the Geel heat of a small resistor, and as the recording density (dot density) increases, the thermal response characteristics of the thermal head become an important factor that affects the quality of recorded images. There is.

Normally, a thermal head has heating elements arranged one-dimensionally or two-dimensionally, and as shown in a cross section of a part of the thermal head in FIG. It has an arranged structure.

By adopting such a structure, when heating, due to the presence of the heat insulating layer, the heat can be efficiently heated, and the thermal response is good.
Conversely, during cooling, the presence of the heat insulating layer prevents heat radiation, resulting in poor heat radiation characteristics and heat accumulation. Therefore, when a thermal head having such a structure is used as it is for thermal recording, there is a problem that the quality of the printed image deteriorates.

Therefore, in order to improve the image quality, it was necessary to equip the drive circuit of the thermal head with a heat accumulation correction circuit and adjust the amount of power supplied.

[Purpose of the invention]

The present invention has been made in view of the above-mentioned circumstances, and provides a thermal head that improves the heat dissipation characteristics during cooling of the thermal head and is capable of forming printed images of high quality without performing heat accumulation correction. The purpose is to

[Structure of the invention]

In order to achieve the above object, the thermal head of the present invention includes:
A heating resistor is formed on a substrate with a heat conduction control layer interposed therebetween. Sometimes they are configured to have high thermal conductivity.

[Example] Hereinafter, a thermal head according to an example of the present invention will be described in detail with reference to the drawings.

As shown in FIG. 2 as a partial plan view, and as shown in FIG. 3 and a cross-sectional view taken along line A-A in FIG. Semiconductor layer 1 consisting of a type indium arsenide (inAs) layer
2 and an electrically insulating layer 13 made of silicon oxide (SiO□).
The heating element 14 is composed of a RuOz) layer, and a drive circuit (not shown) for selectively causing the heating element to generate heat according to image information.

Further, the P-type indium arsenide constituting the semiconductor layer 12 has a characteristic that the thermal conductivity Kp decreases as the supplied current I increases, as shown in FIG.

Further, the semiconductor layer 12 is connected to a current control circuit (not shown) configured to apply electricity only when the heating element is energized, based on a timing chart for energizing the heating element, as shown in FIG. , heating element (3) When energized, a pulse current flows through the semiconductor layer as shown in FIG. Therefore, the semiconductor layer has a low thermal conductivity and functions as a heat insulating layer. In addition, when the heating element is not energized, no current flows through the semiconductor layer, so the thermal conductivity increases and the heat dissipation characteristics of the heating element are significantly improved.

By using a thermal head with such a configuration, thermal efficiency during energization is improved, and after energization ends (when not energized)
The thermal head drive circuit has good heat dissipation characteristics and no heat storage effect even when driven at high speed.
There is no need for a heat accumulation correction circuit, and high-quality printed images can be obtained with a simple drive circuit.

In the examples, P-type indium arsenide was used as the semiconductor layer, but it is not necessarily limited to this, and other materials such as other ■-■ compound semiconductors can also be used. It is.

It is also possible to use other means than the semiconductor layer.

(4) [Effects of the Invention] As explained above, the thermal head of the present invention has a structure between the substrate and the heat generating resistor, which has a low thermal conductivity when the heat generating resistor is energized, and a low heat conductivity when the heat generating resistor is not energized. Since it includes a heat conduction control layer configured to have high conductivity, it has good thermal response, and it is possible to obtain high-quality printed images without correcting heat accumulation correction.

[Brief explanation of drawings]

Fig. 1 shows a conventional thermal head, and Fig. 2 shows a conventional thermal head.
FIG. 3 is a partial schematic diagram of the thermal head according to the present invention.
Fig. 2 is a cross-sectional view taken along line AA, Fig. 4 is a diagram showing the relationship between current and thermal conductivity of indium arsenide used as a semiconductor layer, and Fig. 5 is a timing chart for energizing the heating element. FIG. 6 is a diagram showing a timing chart of the current supplied to the semiconductor layer. 1... Insulating substrate, 2... Heat insulating layer, 3... Heating element,
11... Ceramic substrate, 12... Semiconductor layer, 13...
...Insulating layer, 14...Heating element.

Claims (2)

[Claims] (1) In a thermal head in which a heating resistor is formed on one substrate via a heat conduction control layer, the heat conduction control layer has a low thermal conductivity when electricity is applied to the heating resistor, and is non-conductive. A thermal head characterized in that it is configured to have a high thermal conductivity when energized. (2) The heat conduction control layer is comprised of a two-layer structure consisting of a semiconductor layer whose thermal conductivity changes when energized and an electrically insulating layer. The thermal head described in ).