JP2000218840A - Thermal head - Google Patents

Abstract

PROBLEM TO BE SOLVED: To effectively prevent generation of printing failures caused by excessive supply of ink or the like by setting a sheet resistance value of each heating resistor to be small at a peripheral area and large at a central area. SOLUTION: A heating resistor 3 is formed of a TaSiO-based electric resistance material or the like in a single layer in a schematically rectangular shape. The heating resistor 3 has a predetermined electric resistivity by itself and therefore generates a Joule heat when electricity is applied from an external power source via a pair of conductive layers 4 and 4. A plurality of heating resistors 3 and the pair of conductive layers 4 and 4 are provided and formed by adopting a thin film form method such as etching or the like in a predetermined pattern and a predetermined thickness to an upper face of a glaze layer (the heating resistors 3 are approximately 0.01-0.5 μm thick, and the pair of conductive layers 4 and 4 are approximately 0.5-2.0 μm). Each of the plurality of heating resistors 3 has a larger sheet resistance value at a central area than at a peripheral area.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a thermal head incorporated as a printer mechanism in a thermal plate making apparatus or the like.

[0002]

2. Description of the Related Art Conventionally, a thermal head incorporated as a printer mechanism of a thermal plate making apparatus or the like has a plurality of heating resistors attached and arranged on an insulating substrate made of alumina ceramic or the like via a glass glaze layer or the like. It has a structure.

The heating resistors are arranged linearly at a dot density (linear density) of, for example, 300 dpi over the longitudinal direction of a rectangular insulating substrate, and usually employ a thin film technique such as sputtering, photolithography, and etching. Thereby, each is formed so as to form a predetermined rectangular shape. In this case, the sheet resistance value of each heating resistor is substantially constant over the entire area, and the temperature distribution when the heating resistor is caused to generate Joule heat has a gentle mountain shape with a relatively small temperature difference between the peripheral area and the central area. (See FIG. 6). Incidentally, the temperature distribution in FIG. 6 shows the result of measuring the surface temperature with an infrared thermometer when 0.14 W of power is applied to the heating resistor having an electric resistance of 4000Ω.

In the case where a predetermined pattern of perforations is formed in, for example, a heat-sensitive stencil sheet (a porous support made of Japanese paper or the like and a resin layer of wax or the like) applied using the above-described thermal head, A predetermined power is applied to the heating resistors based on the image data, and the heating resistors are individually and selectively subjected to Joule heat generation, and the generated heat is conducted to the heat-sensitive stencil sheet to form a resin layer of the heat-sensitive stencil sheet. A partial pattern of perforations is formed in the heat-sensitive stencil sheet by partially dissolving it.

The heat-sensitive stencil sheet having perforations of a predetermined pattern is used as a printing stencil for a stencil printing machine or the like. Specifically, the printing ink is arranged on one main surface side of the heat-sensitive stencil sheet, and the printing material is arranged on the other main surface side, and the ink is attached to the printing material through the perforations of the heat-sensitive stencil paper. Predetermined characters and images are printed on the printing substrate.

[0006]

By the way, expectations for high-density recording in recent years are also increasing in the above-described thermal plate making apparatus, and it is required to form a perforation pattern on a thermal stencil sheet at a dot density of 600 dpi or more. I have.

However, wax or the like used as a resin layer of a heat-sensitive stencil sheet generally has a property that when heat from a thermal head is applied, the wax or the like melts at once if it exceeds the glass transition point even slightly. From that
As described above, when trying to form perforations in the heat-sensitive stencil sheet with a heating resistor having a relatively small temperature difference between the peripheral area and the central area,
The diameter of each perforation becomes excessively large, and may lead to the main scanning direction (a direction parallel to the arrangement direction of the heating resistors) as shown in FIG. 7 (perforation: h). When such a heat-sensitive stencil sheet m is used as a printing stencil, ink is excessively supplied from a place where the perforations h are connected, and printing defects such as "smearing" and "character collapse" occur. . Therefore, it is important to make the perforation h of the heat-sensitive stencil sheet m an appropriate size. However, in order to realize this using the above-described conventional thermal head, the heat generation amount of the heat-generating resistor and the like are required. Is required to be adjusted with extremely high precision, and in that case, there is a disadvantage that the driving device of the thermal head becomes complicated.

[0008]

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned drawbacks, and a thermal head according to the present invention has a plurality of substantially rectangular heating resistors attached and arranged on an insulating substrate. The thermal head is characterized in that the sheet resistance value of each heating resistor is small in the peripheral area and large in the central area.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described in detail with reference to the accompanying drawings. 1 is a perspective view of a thermal head according to an embodiment of the present invention, FIG. 2 is a cross-sectional view of the thermal head of FIG. 1, 1 is an insulating substrate, 2 is a glaze layer, 3 is a heating resistor, and 4 and 4 are A pair of conductive layers, 5 is a protective layer. Note that the perspective view of FIG. 1 does not show the glaze layer 2 and the protective layer 5.

The insulating substrate 1 is made of a ceramic material such as alumina ceramics and has an upper surface serving as a supporting base material for supporting the glaze layer 2, the heating resistor 3, the conductive layers 4, 4, the protective layer 5, and the like. Make

The insulating substrate 1 is made of an organic solvent suitable for a ceramic raw material powder such as alumina, silica, magnesia, or the like.
A ceramic green sheet is formed by adding and mixing a solvent to form a slurry and adopting a conventionally known doctor blade method, calender roll method, or the like.
Thereafter, the ceramic green sheet is manufactured by stamping into a predetermined shape and firing at a high temperature.

A glaze layer is provided on the upper surface of the insulating substrate 1.
2 having a thickness of 20 to 60 μm.

The glaze layer 2 is formed of a low thermal conductive material such as glass or polyimide resin, and accumulates and dissipates heat therein so that the heat generated by the heat generating resistor 3 becomes an appropriate temperature. It works to maintain the thermal response characteristics of the head in a good state.

When the glaze layer 2 is formed of, for example, glass, a predetermined glass paste obtained by adding and mixing an appropriate organic solvent and a solvent to glass powder is formed on the upper surface of the insulating substrate by a conventionally known screen printing. The whole or part of the substrate is printed and applied with a predetermined thickness, and then is baked at a high temperature (approximately 900 ° C.) to be attached and formed on the upper surface of the insulating substrate 1.

On the glaze layer 2, a plurality of heating resistors 3 are attached and arranged at a dot density of, for example, 600 dpi, and a pair of conductive layers 4, 4 are provided at both ends of the heating resistors 3. It is electrically connected.

The heating resistor 3 is made of TaSiO or TaS.
iNO, TiSiO, TiSiCO, NbSiO
Since each heating resistor 3 itself has a predetermined electric resistivity, each of the heating resistors 3 is formed of a single layer so as to form a substantially rectangular shape by a system electric resistance material. ,Four
When electric power from an external power supply is applied through the device, Joule heat is generated, and Joule heat is generated at a predetermined temperature required for forming a print on a recording medium such as the heat-sensitive stencil sheet m, for example, a temperature of 280 ° C. to 320 ° C. . When a thermal head for a thermal plate making device is constructed, the size of each heating resistor 3 is, for example, 36 μm × 36 μm, and the electric resistance value is 2000Ω.
The film thickness is set so that For example, heating resistor 3
Is made of a TaSiO-based resistance material, the heating resistor 3
Is set to 0.05 μm.

A pair of conductive layers 4 and 4 connected to both ends of the heating resistor 3 are made of a metal material such as aluminum. The conductive layers 4 and 4 are used to cause the heating resistor 3 to generate Joule heat. It acts to apply necessary predetermined power.

The plurality of heat generating resistors 3 and the pair of conductive layers 4 are formed on the upper surface of the glaze layer 2 by a predetermined pattern and a predetermined thickness by employing a conventionally known thin film technique such as sputtering, photolithography, and etching. (The heating resistor 3 has a thickness of 0.01 μm to 0.5 μm, and the pair of conductive layers 4, 4 has a thickness of 0.5 μm to 2.0 μm).

The plurality of heating resistors 3 described above are:
As shown in FIG. 3, each sheet resistance is adjusted so as to be larger in the central region than in the peripheral region.

In the present embodiment, the sheet resistance in the peripheral area of each heating resistor 3 is 1850 Ω / □ to 1950 Ω / □, and the sheet resistance in the central area is 120% of the sheet resistance in the peripheral area.
It is set to 2220 Ω / □ to 2535 Ω / □ corresponding to １３０130%, and the sheet resistance is adjusted so as to gradually increase from the peripheral region toward the central region. The rate of change of the sheet resistance value along the main scanning direction is adjusted so as to change, for example, from 0.5% to 1.0% per 1 μm from the peripheral area to the central area. The central area has a protruding mountain shape as shown in FIG.

The temperature distribution when the heating resistor 3 generates Joule heat has a steep mountain-like shape with the central region as the top as shown in FIG. 4, whereby the temperature difference between the peripheral region and the central region is relatively large. Therefore, even when a perforation pattern is formed on the thermosensitive stencil sheet m at a dot density of 600 dpi or more, it is easy to control the diameter of each perforation h to an appropriate size. That is, although the wax or the like generally used as the resin layer r of the heat-sensitive stencil m has the property of being melted at once if its temperature slightly exceeds the glass transition point, the high-temperature portion of the heating resistor 3 has By concentrating the ink in the central area, the individual perforations h can be formed independently in the main scanning direction as shown in FIG. 5, whereby the excessive supply of ink can be performed without complicating the driving device of the thermal head. As a result, it is possible to manufacture a good printing original plate for a stencil printing apparatus, which can effectively prevent the occurrence of printing defects caused by the above-mentioned factors.

Incidentally, the temperature distribution in FIG.
This shows the results of measuring the surface temperature with an infrared thermometer when Joule heat is generated in the heating resistor 3 by applying, for example, 0.14 W of electric power to the heating resistor 3.

The heating resistor 3 having such a sheet resistance value distribution has a substantially constant thickness (± 5) by the thin film method described above.
% Of the heating resistor 3 is formed.
Is formed by performing pulse trimming under predetermined conditions. More specifically, a trimming pulse of several milliseconds is applied to the heating resistors 3 in the atmosphere to raise the temperature of the central region of each heating resistor 3 and bring the heating resistors 3 to the temperature state. By oxidizing accordingly, the sheet resistance value is adjusted. As a result,
The oxidation of the surface of the heating resistor proceeds to a deeper region in the central region of the heating resistor 3, and the sheet resistance value of the heating resistor 3 is adjusted to be small in the peripheral region and large in the central region. It should be noted that the above-described adjustment of the sheet resistance value is simultaneously performed on the plurality of heating resistors 3 so that the processing time can be reduced.

The heating resistor 3 and the conductive layers 4, 4
A protective layer 5 made of Si ₃ N ₄ (silicon nitride) or the like is further adhered on the upper surface of the substrate.
3 and at least a part of the conductive layer 4.

The protective layer 5 includes a heating resistor 3 and a conductive layer 4.
For protecting the recording medium from corrosion caused by contact with moisture or the like contained in the atmosphere and abrasion caused by sliding contact of the recording medium such as the heat-sensitive stencil sheet m. It is deposited and formed to a thickness of ２０20 μm. Therefore, when performing thermal recording using a thermal head, the recording medium such as the heat-sensitive stencil m is provided with a protective layer.
5 is slid in contact with the surface of the protective layer 5, and the heat conducted in the protective layer 5 is conducted to the recording medium.

Thus, in the above-described thermal head, for example, when the heat-sensitive stencil sheet m is used as a recording medium, a predetermined electric power is applied to the heating resistor 3 between the pair of conductive layers 4 based on image data from the outside. Then, the heat generating resistors 3 are individually selectively heated to generate Joule heat, and the generated heat is conducted to the heat-sensitive stencil sheet m, thereby forming the resin layer r of the heat-sensitive stencil sheet m.
Is partially dissolved to form perforations h of a predetermined pattern in the thermosensitive stencil m.

The resin layer r of the heat-sensitive stencil sheet m used as a recording medium in the present embodiment is applied to one main surface of a porous support b made of, for example, Japanese paper so as to have a thickness of 1 μm to 2 μm. The heat-sensitive stencil sheet m on which perforations h of a predetermined pattern are formed through the above-described heat-sensitive recording process is used as a printing stencil for a stencil printing apparatus or the like. That is, the printing ink is arranged on one main surface side of the heat-sensitive stencil m, and the printing material is arranged on the other main surface side, and the ink is attached to the printing material through the perforations h of the heat-sensitive stencil m. Predetermined characters and images are printed on the printing substrate.

The present invention is not limited to the above-described embodiment, and various changes and improvements can be made without departing from the gist of the present invention.

For example, in the above-described embodiment, a case has been described in which perforations having a predetermined pattern are formed in the heat-sensitive stencil sheet. It is also effective in the case of doing.

In the above-described embodiment, the heating resistor 3 is formed by a conventionally known sputtering method. However, the heating resistor 3 may be formed by another forming method, for example, a plasma CVD method or a thick film printing method. Absent.

[0031]

According to the thermal head of the present invention, the sheet resistance value of each heating resistor is made larger in the central region than in the peripheral region. The temperature distribution has a steep mountain shape with the central area of each heating resistor at the top, whereby the temperature difference between the peripheral area and the central area becomes relatively large. This gives 6
Even when a perforation pattern is formed on a heat-sensitive stencil sheet with a dot density of 00 dpi or more, it is easy to control the diameter of each perforation to an appropriate size, and each perforation is independent in the main scanning direction. Can be formed. Therefore, when the thermal head of the present invention is adopted as a printer mechanism for a thermal plate making apparatus, it is possible to effectively prevent the occurrence of printing defects due to excessive supply of ink and the like without complicating the driving device of the thermal head. It is possible to manufacture a printing stencil for a stencil printing apparatus that is capable of performing the printing.

[Brief description of the drawings]

FIG. 1 is a perspective view of a thermal head according to one embodiment of the present invention.

FIG. 2 is a cross-sectional view of the thermal head of FIG.

FIG. 3 is a view showing a sheet resistance value distribution of a heating resistor of the thermal head of FIG. 1;

FIG. 4 is a diagram showing a temperature distribution when the heating resistor of the thermal head of FIG. 1 generates Joule heat.

FIG. 5 is a view showing an example of a perforation pattern when perforations are formed in a thermosensitive stencil sheet using the thermal head of FIG. 1;

FIG. 6 is a diagram showing a temperature distribution when a heating resistor of a conventional thermal head generates Joule heat.

FIG. 7 is a diagram showing an example of a perforation pattern when perforations are formed in a thermosensitive stencil sheet using a conventional thermal head.

[Explanation of symbols]

1 ... insulating substrate, 2 ... glaze layer, 3 ... heating resistor, 4 ... conductive layer, 5 ... protective layer, m ... heat-sensitive stencil paper, r ... resin layer , B ... porous support

Claims (1)

[Claims] 1. A thermal head comprising a plurality of substantially rectangular heating resistors attached and arranged on an insulating substrate, wherein the sheet resistance of each heating resistor is small in a peripheral region,
Thermal head characterized by a large central area.