JPH0890808A - Thermal print head - Google Patents

Abstract

PURPOSE: To sufficiently supply heat quantity from a heat generating resistor to the side of a matter to be printed by covering a board with a protective film having higher thermal conductivity than that of the board on the resistor. CONSTITUTION: A heat generator 5 for heating a heat-sensitive medium is so linearly formed on common and individual electrodes 3, 4 as to cross the ends 3a, 4a of the electrodes 3, 4. The common and individual electrodes 3, 4 are covered with a protective film 6 formed with the resistor 5 on the surface of a glazed layer 2 formed with the resistor 5 and the individual and common electrodes 3, 4. A protective film 7 of high thermal conductivity made of overcoating glass in which the thermal conductivity is largely improved is formed on the area formed with the resistor 5. At the time of using a thermal print head, the heat generated from the resistor 5 is mostly not radiated via a board 1 and the layer 2 but contributes to the heating of the matter to be printed via the film 7 of the high thermal conductivity.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a heating resistor and a thermal print head having a protective film formed on common and individual electrode wirings.

[0002]

2. Description of the Related Art Conventionally, printers for office automation equipment such as facsimiles, printers for ticket vending machines, label printers, etc.
2. Description of the Related Art Thermal print heads that form necessary image information by applying heat to thermal paper are widely used. The conventional thermal print head will be described by taking a thick film type as an example. As shown in the figure, the substrate 21 is formed by sintering alumina or the like, and is partially or entirely formed on the surface of the substrate 21. A glaze layer 22 made of glass or the like as a heat storage material, a common electrode wiring 23 formed in a comb shape on the glaze layer 22 from one surface of the substrate 21, and a glaze layer 22 from the other side of the substrate 21. The individual electrode wiring 24 extending between the tip portions of the common electrode wiring 23 toward the common electrode wiring 2
3 and a heating resistor 25 formed so as to cross over the respective tip portions of the individual electrode wiring 24.

These conventional thermal print heads generally have heating resistors 25 and common and individual electrode wirings 2.
A protective film 26 made of heat-resistant and abrasion-resistant glass is formed so as to cover Nos. 3 and 24. This protective film 26
Is to protect the heating resistor 25, the electrode wirings 23, 24, and the like from mechanical wear due to a heat-sensitive medium, or to cause electrical damage due to a short circuit between these elements or through an external substance. It is provided for the purpose of preventing

In such a conventional thermal print head, the substrate 21 is generally made of a sintered body containing alumina as a main component (about 96% alumina), and its thermal conductivity is about 20.
It is known that it is about w / m · k, and the thermal conductivity of the glaze layer 22 formed on this surface is relatively low to give a heat storage effect to some extent, about 0.8-1.0 w.
/ M · k. On the other hand, the glaze layer 22
Alternatively, a so-called overcoat glass of about 1-1.5 w / m · k is generally used for the heating resistor 25 on the surface of the substrate 21 and the protective film 26 for covering the common and individual electrode wirings 23, 24. .

[0005]

However, in the conventional thermal print head, since the thermal conductivity of the protective film 26 is significantly smaller than that of the substrate, the amount of heat generated from the heating resistor 25 is used for printing. It is generally considered that about 70% of the heat is radiated through the substrate 21 without being fully utilized for heating.

On the other hand, in recent years, along with the miniaturization and high performance of various OA equipment, the trend toward smaller and lighter thermal print heads has been increasing, and in particular, battery-powered and portable type. There is also a strong demand for the development of the thermal print heads. Under these circumstances, conventionally, in order to save power in the thermal print head, attempts have been made to use a polyimide film instead of using the glaze layer, but when polyimide is used, the heat resistance is poor. However, it has not yet been put into practical use because of problems such as lack of mechanical strength.

It is also possible to reduce the heat dissipation to the substrate side by increasing the thickness of the glaze layer, but if it is thicker than a certain level, the thermal response will decrease due to the heat storage effect and good printing will be achieved. There is a problem that is difficult to obtain. Therefore, it is an object of the present invention to provide a thermal print head which can supply a sufficient amount of heat generated from a heating resistor to the printed material side and has a good thermal response.

[0008]

In order to achieve the above object, according to the present invention, a substrate, a heating resistor formed on the substrate, a common electrode wiring electrically connected to the heating resistor, and What is claimed is: 1.A thermal printhead comprising individual electrode wirings and a heating film and a protective film formed on the substrate so as to cover the common and individual electrode wirings, wherein the protective film heats the heating resistor from the substrate. Thermal purine characterized by being formed so as to have high conductivity The protective film is formed from glass and is constituted by containing a substance having a higher thermal conductivity than the substrate as a filler on at least the heating resistor. be able to.

The upper front substrate may be configured to form a hollow region below the heating resistor.

[0010]

[Operation and effect] Since the protective film is formed on the heating resistor so as to have a higher thermal conductivity than the substrate, most of the heat generated from the heating resistor when the thermal print head is used is It is used for heating a printing medium that is pressed and moved to the upper surface through the protective film without being released to the outside through the substrate. For this reason, it is possible to improve the heat generation efficiency for a thermal print head of a certain size and design, and to obtain good thermal response, and to reduce the power supply of the thermal print head with a certain heat generation characteristic. Will be possible.

Further, by providing a hollow region in the substrate below the heat-generating resistor, the hollow region acts so as to prevent heat from the heat-generating resistor and its transmission, so that it is dissipated to the outside through the substrate. The amount of heat generated is greatly reduced, and the heat generation efficiency can be further improved.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A thermal print head according to an embodiment of the present invention will now be described in detail with reference to the drawings. FIG. 1 shows a cross section of a main part of a thermal print head according to the first embodiment of the present invention. In the figure, reference numeral 1 indicates a sintered substrate made of alumina, and a glaze layer 2 made of glass is formed on the entire surface of the substrate 1.

On the surface of the glaze layer 2 on one side of the substrate 1,
The common electrode 3 having a substantially comb-shaped pattern in plan view is formed. The common electrode 3 includes a common connection portion 3a extending in the longitudinal direction of the substrate 1 and electrically connected in common, and a plurality of tip portions 3b extending from the common connection portion to the other side. A plurality of individual electrodes 4 each having a tip portion 4a facing each tip portion 3a of the common electrode 3 are formed.
A heating resistor 5 for heating a heat-sensitive medium (not shown) is linearly formed on the common and individual electrodes 3 and 4 so as to cross over the respective tip portions 3a and 4a of the electrodes 3 and 4. Has been formed.

On the surface of the glaze layer on which the heating resistor 5 and the individual and common electrodes 3 and 4 are formed, the protective film 6 is common and individual except for the region where the heating resistor 5 is formed. It is formed so as to cover the electrodes 3 and 4. The protective film 6 is generally made of a material containing silicate glass as a main component and is of a type commercially available as overcoat glass.

On the other hand, in the region where the heat generating resistor 5 is formed, a high thermal conductive protective film 7 made of overcoat glass having a greatly improved thermal conductivity is formed. Here, the thermal conductivity of the substrate 1 made of alumina is about 20 w / m · k as in the conventional case, and the thermal conductivity of the first protective film 6 is about 1.3 w / m · k. . On the other hand, the protective film 7 having a high thermal conductivity is formed on the upper portion of the heating resistor 5 by a glass paste prepared by mixing a conventional overcoat glass material containing silicate glass as a main component with a substance having a high thermal conductivity as a filler. It is adhered and formed by coating and baking.

Alumina (100% alumina) having a thermal conductivity of about 36 w / m · k is known as a material having a high thermal conductivity of this type. Is about 60 w / m · k MgO, about 60-250 w
/ M · k AlN, about 260 w / m · k SiC, etc. can be used. By using these substances as filler in overcoat glass, about 30-50 w / m ·
It is possible to obtain a protective film having a thermal conductivity of k.

According to the thermal print head of this embodiment, as described above, the thermal conductivity is relatively high, about 20 w / m.
A relatively low thermal conductivity on the ceramic substrate 1 of k,
The heating resistor 5 is formed on the surface of the glaze layer 2 having a thickness of about 0.9 w / m · k, and the upper portion of the heating resistor 5 has a higher thermal conductivity than the substrate, for example, about 30-50 w / m · k. Since the protective film 7 made of coated glass has a high thermal conductivity, most of the heat generated from the heating resistor 5 is dissipated through the substrate and the glaze layer when the thermal print head is used. Instead, it effectively contributes to the heating of the material to be printed through the protective film 7 having a high thermal conductivity on the upper side.

The protective film 7 thus improved in thermal conductivity
May be formed so as to cover the entire surface of the substrate or the glaze layer, but in such a case, as shown in FIG. 2A, the heat from the heating resistor 5 is common and individual. Since it is diffused through the electrodes 3, 4 and the protective film having a uniform composition, that is, a uniform thermal conductivity, to the entire protective film, the heating temperature from the heating resistor becomes diffuse as shown in the graph of the figure. It is not possible to obtain sharp printing characteristics. On the other hand, when the protective film having a higher thermal conductivity than the substrate is formed only on the upper portion of the heating resistor as in the above-described embodiment, the heat from the heating resistor has a higher thermal conductivity than the substrate. Since it is effectively transmitted to the printed material side through the conductivity protective film, sharper printing characteristics can be obtained.

The method of manufacturing the thermal print head of this embodiment will be described. First, as in the case of the conventional thermal print head, the gold is formed on the glaze layer 2 formed on the entire surface of the substrate 1 to a thickness of about 60 μm. The conductor paste made of (1) is screen-printed, and after firing, common and individual electrodes 3 and 4 having a required pattern are formed by etching. Next, the heating resistor 5 is formed by linearly printing and firing a resistor paste made of ruthenium oxide so as to traverse the respective tip portions 3a, 4a of the common and individual electrodes 3, 4. .

Next, a glass paste for ordinary overcoating is printed and fired on the surface of the glaze layer 2 excluding the region where the heating resistor 5 is formed, and about 4 μm except for the region where the heating resistor 5 is formed. The first protective film 6 having a thickness of 1 is formed by screen printing, and then a glass paste mixed with the above-mentioned substance having a high thermal conductivity as a filler is applied so as to cover the exposed upper surface of the heating resistor 5. Then, this is fired to form a protective film having a high thermal conductivity with a thickness of about 6 μm, whereby the thermal print head of this embodiment is obtained.

Next, a second embodiment of the present invention will be described with reference to FIG. In the thermal print head of this embodiment, no glaze layer is formed on the surface of the substrate 1, and a hollow region 8 extending in the longitudinal direction of the substrate 1 is provided in the substrate below the heating resistor 5. It is similar to the first embodiment except that it is present. In this embodiment, since a glass glaze layer having a relatively low thermal conductivity, which is generally used as a heat storage body, is not provided, a part of the heat generated from the heating resistor 5 immediately enters the lower substrate 1. Although transmitted, since the hollow region 8 provided in the substrate 1a below the heating resistor 5 acts to prevent further heat conduction, the amount of heat conducted or dissipated to the entire substrate 1a is suppressed to a small amount. To be On the other hand, since a protective film having a high thermal conductivity higher than that of the substrate 1a is formed on the heating resistor 5 as in the above-described embodiment, most of the heat generated from the heating resistor 5 is formed. Will be used to heat the substrate. Therefore, the configuration of the present embodiment, when it is applied to a small and portable thermal print head, for example, of a battery drive type, which has been more and more developed in recent years, has good printing characteristics with low power consumption. The resulting thermal print head can be manufactured.

In the manufacture of the thermal print head of this embodiment, the heating resistor 5 and the common and individual electrodes 3 and 4 are directly formed without forming a glaze layer on the surface of the substrate 1a,
Also, it can be manufactured by the same method as in the first embodiment except that the hollow region 8 is provided in the substrate 1a below the heating resistor 5. The substrate 1a having such a hollow region 8 therein is, for example, about 35% by weight of powdered alumina, about 35% of borosilicate glass, and about 3% by weight.
It can be obtained by stacking and heating / baking a plurality of green sheets, each of which is made of 0% thermoplastic resin and partially provided with slits, and divided if necessary.
After the substrate 1a is formed in this way, the thermal print head can be manufactured by forming necessary elements on the substrate 1a as in the first embodiment.

In the above embodiment, the present invention is applied to the thick film type thermal print head.
It goes without saying that the same can be applied to a thin film type thermal print head. Further, without being limited to the above-mentioned examples, for example, the kind and the mixing amount of the filler mixed in the glass material for forming the protective film having high thermal conductivity are appropriately changed according to the application of the thermal print head and the required printing characteristics. Alternatively, the region where the glaze layer is formed, the thickness, and the like can be changed as appropriate.

[Brief description of drawings]

FIG. 1 is a sectional view of an essential part of a thermal print head according to a first embodiment.

FIG. 2 is a diagram showing a relationship between heating characteristics of a protective film and an object to be printed.

FIG. 3 is a cross-sectional view of essential parts of a thermal print head according to a second embodiment.

FIG. 4 is a cross-sectional view of a conventional thermal printhead.

[Explanation of symbols]

 1 substrate 2 glaze layer 3 common electrode wiring 4 individual electrode wiring 5 heating resistor 6 protective film 7 protective film with high thermal conductivity 8 hollow area

Claims (3)

[Claims] 1. A substrate, a heating resistor formed on the substrate, common electrode wirings and individual electrode wirings electrically connected to the heating resistor, the heating resistor and the common and individual electrodes. A thermal printhead comprising a protective film formed on the substrate so as to cover the wiring,
The thermal print head according to claim 1, wherein the protective film has a higher thermal conductivity on the heating resistor than the substrate. 2. The thermal print head according to claim 1, wherein the protective film is made of glass and contains a substance having a higher thermal conductivity than the substrate on at least the heating resistor as a filler. 3. The thermal print head according to claim 1, wherein a hollow region is formed on the substrate below the heating resistor.