JPS59225972A - Thermal head - Google Patents

Abstract

PURPOSE:To obtain a thermal head having steep temp. characteristics, forming a color image with good quality and having no possibility such that early stage abrasion and the feed-irregularity of heat-sensitive paper are generated, by providing grooves to both sides of a glass layer at a part where the glass layer is opposed to a heat generator. CONSTITUTION:A pair of grooves 7 are provided to both sides of the glass layer 2'' on an alumina substrate 1 at a part corresponding to a minute section (l) where a heat generator part 6'' must be constituted. Thus constituted thermal head is low in heat capacity at the part provided between the grooves 7, 7 because the glass layer 2'' in the vicinity of the heat generator part 6'' is separated from the peripheral part thereof through the grooves 7 and the heat conduction to said glass layer 2'' is suppressed and the temp. characteristics thereof become steep as shown by the curve C2. Therefore, a color image with good quality is obtained on heat-sensitive paper. In addition, the heat- sensitive part 9 is held between the thermal head and the protective layer 5'' of a platen roller 8 over the range W where the platen rooler 8 wider than the width (s) between the grooves 7 is crushed. As a result, there is no possibility of generating feed irregularity of the heat-sensitive paper 9 and early stage abrasion caused by local pressure.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application of the Invention] The present invention relates to a thermal head used in a thermal recording device such as a facsimile or a printer.

[Background of the invention]

The above thermal head requires the ability to rapidly heat and cool a minute area. For this reason, a structure as shown in FIG. 1 has conventionally been generally used.

1 is an alumina substrate, on which a glass layer 2 is provided,
Furthermore, a resistive layer 3 and a wiring layer 4 are formed on top of the resistive layer 3 in a suction pattern. 5 is a protective layer.

The minute section t of the wiring layer 4 is removed by etching. As a result, the portion of the resistance layer 3 corresponding to the t section constitutes the heating element section 6.

A part of the Joule heat generated in the heating element part 6 is conducted through the glass layer 2 and escapes, and a part is transferred to the wiring layer 4. The remaining portion conducts through the resistive layer 3 and escapes, and the remaining portion conducts through the protective layer 5 and contributes to color development of the thermal paper. The ratio of the amount of heat conducted to each of these paths is, for example, as follows.

Amount of heat contributing to color development: Approximately 15 Amount of heat escaping to wiring layer 4: Approximately 20% Amount of heat escaping to glass layer 2: Approximately 65% Above glass layer 2
For example, the thickness of the resistive layer 3 (for example, about 0 μm) is about 0 μm.
．． 1 μm), wiring layer (for example, about 1 μm).

Since it is thicker than the protective layer (for example, about 6 μm), it has a large heat capacity and absorbs most of the heat generated.

The fact that the glass layer 2 absorbs and wastefully dissipates the majority of the calorific value as described above is harmful not only in terms of energy consumption but also in terms of temperature characteristics.

FIG. 2 shows the temperature characteristics of the thermal head, with the horizontal axis representing time and the vertical axis representing the temperature on the surface of the thermal head.

T1 is the temperature required to color the thermal paper, tl is the temperature increase period up to T1, and t2 is the temperature fall period from T1.

In the conventional thermal head shown in FIG. 1, the generated heat is dissipated to the glass layer 2, etc., so that the temperature rise characteristic on the surface of the thermal head is relatively slow as shown by the solid line curve C1. Furthermore, as described above, since the heat capacity of the glass layer 2 is large, the rate of decline of the curve C1 is also relatively slow.

In order to eliminate the above-mentioned drawbacks and make the slope of the temperature characteristic curve steeper, the upper surface of the glass layer 2' is formed into a convex shape, as shown in FIG. An improved thermal head may also be considered in which the length is slightly larger than the t section.

The temperature characteristics of the improved thermal head (Fig. 3) in which the glass layer 2' with a small heat capacity is provided in this way are as shown by the broken line C2 in Fig. 2, compared to the curve C1 of the conventional type. It becomes extremely steep. Therefore, the electric power needed to raise the temperature TI necessary to color the thermal paper is small, and since the fall is steep, less heat is stored in the glass layer δ, and it is difficult to obtain the same exothermic temperature T1. Control is no longer required in practice. (When the heat generation temperature T1 goes up and -C, the recording density of the part printed on the thermal paper becomes darker and the image quality becomes better.) However, because the structure shown in Fig. 3 is adopted, the heat generation part 6' is placed upward. It forms a convex shape toward the
As a result, the pressure with which this thermal head presses the platen roller 8 against the heating element through the thermal paper 9 becomes locally high, causing a problem in that the heating element becomes susceptible to wear. For this reason, when the pressure with which the platen roller 8 is pressed against the heating element portion is reduced, a problem arises in that the thermal paper 9 is unevenly fed.

[Purpose of the invention]

The present invention has been made in view of the above-mentioned problems, and an object of the present invention is to provide a thermal head that has steep temperature characteristics and is free from premature wear and uneven feeding of thermal paper.

[Summary of the invention]

In order to achieve the above object, the present invention provides a thermal head in which a glass layer is provided between a heating element and a substrate, in which grooves are provided on both sides of the portion where the glass layer faces the heating element,
It is characterized in that it is designed to suppress heat conduction through the glass layer.

[Embodiments of the invention]

Next, one embodiment of the present invention will be described with reference to FIG.

A glass layer 2'' is fired on the alumina substrate 1. This glass layer 2 has a minute section t which is to constitute the heating element part 6.
A pair of grooves 7 are provided on both sides of the corresponding portion. In this embodiment, the bottom of the groove 7 reaches the top surface of the alumina substrate 1.

A resistive layer 3 is placed on the glass layer 2 provided with the grooves 7 as described above.
〃The wiring layer 4〃 is formed using a suction vine, and the wiring layer in the section is removed by etching to form the heating element portion 6〃, and then the protective layer 5〃 is formed using a suction vine.

The thermal head (Fig. 4) constructed as described above has heat conduction suppressed between the glass layer 2 near the heating element part 6 and the surrounding part through the groove 7, so that this part (The part near the heating element part 6, that is, the part sandwiched between the grooves 7, 7)
has a small heat capacity, and its temperature characteristics are shown by curve C2 in Figure 3.
It becomes steep as well. Therefore, a high quality colored image can be obtained on the thermal paper.

The above dimension t is approximately 2 in a normal thermal head.
It is 50 μm. In this example as well, the dimension t was 250 μm. In this example, the distance si between the grooves 7 is about 120 mm, and the width W in which the grating roller 8 is crushed is about 3 mm. For this reason, the grating roller 8
' is wider than the width t of the area provided, and the grooves 7, 7
A thermal paper 9 is sandwiched between the protective layer 5 and the protective layer 5 over a wider range W than the width S between them. Therefore, there is no risk of uneven feeding of the thermal paper 9, and there is no risk of premature wear due to local pressure.

〔Effect of the invention〕

As explained above, the thermal head of the present invention has a steep temperature characteristic, consumes little power, and can obtain high-quality colored images, and there is no risk of premature wear or uneven feeding of thermal paper. This has excellent practical effects.

[Brief explanation of drawings]

Fig. 1 is a sectional view of a conventional thermal head, Fig. 2 is a chart showing the temperature characteristics of the thermal head, Fig. 3 is a sectional view of an improved thermal head, and Fig. 4 is an embodiment of the thermal head of the present invention. FIG. 1...Alumina substrate, 2.2', 2"...Glass layer, 3°3', 3"...Resistance layer, "4.4", 4...
- Wiring layer, 5.5'. 5〃...Protective layer, 6.6', 6''...Heating element part, 7
...Groove formed in the glass layer, 8...Platen roller, 9...Thermal paper. Agent Patent Attorney Masami Akimoto

Claims (1)

[Claims] In a thermal head in which a glass layer is provided between a heating element and a substrate, grooves are provided on both sides of the portion where the glass layer faces the heating element to suppress heat conduction through the glass layer as much as possible. A thermal head featuring