JPH048236B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a ceramic thermal head, and more particularly to a ceramic thermal head in which an insulator material, a heating element material, an electric conductor material, and a heat conductive material are integrated and sintered.

Traditionally, thermal heads for heat-sensitive recording have been produced using the thick film method.
By thin film method or thin film/thick film mixed method, etc.
It is formed on a ceramic substrate and has been put into practical use.

The thermal heads conventionally used are thick film type.
Each thin film type had advantages and disadvantages. In other words, in the case of the thick film type, large dimensions can be produced relatively inexpensively, but since the electrodes and heating elements are printed using a thick film printing method, the resolution is limited to 8 dots/mm. Furthermore, when attempting to increase the resolution using the thick film method, it is necessary to miniaturize the wiring pattern, which necessitates the use of gold as a conductor, which also has the disadvantage of extremely high costs.
Furthermore, high-density multilayer wiring leads to poor yields and increased costs.

Furthermore, with thick film types, the resistance variation of the heating element becomes large because it is difficult to control the printing thickness.
Resistance variation is ±20% even if it is very good.
There were some problems with the recording quality when used as a head.

In addition, thermal heads using the thin film method can form fine patterns and have good resolution, but they are difficult to make with large dimensions.
The manufacturing process was complicated, resulting in high costs, and the thin surface layer formed caused problems in wear resistance. In addition, multilayer wiring is difficult for thermal heads manufactured using the thin film method, resulting in lower yields due to the occurrence of pinholes in the multilayer wiring, higher wiring resistance in the multilayer wiring, and problems with element heat generation and drive circuits.

The present invention solves all of these problems and provides a thermal head that is small, low cost, has excellent resolution, and is highly reliable.

A thermal head must have at least 1,000 resistors with uniform shapes and resistance values arranged horizontally in a single row at minute intervals, and it must also have the same number of lead wires as resistors wired at the same density. . Furthermore, if any one of these resistors or lead wires becomes defective, it becomes unusable as a head.

In addition, in conventional thermal heads, the thickness of the resistor layer formed by either thick-film or thin-film methods ranges from several thousand Å to several tens of microns, resulting in poor wear resistance and poor wear resistance. The resistor layer often wore out.

For this reason, in conventional thermal heads, a wear-resistant layer of abrasion-resistant glass, Ta ₂ O ₅ , or the like is formed on the surface to a thickness of several tens of microns.

However, when these wear-resistant layers are formed, when heat from the resistance heating element is conducted to the wear-resistant layer, heat diffusion occurs in the lateral direction and in the thickness direction at the same time, which causes resolution to deteriorate.

In this way, conventional thermal heads are thick film type,
Both the thin film method and the mixed method have their own problems.

The present invention solves these problems by using a structure completely different from conventional ones, and provides a high-performance, low-cost thermal head that can be mass-produced.

That is, in the present invention, one or more high thermal conductors are formed inside an insulating ceramic body, a part of each high thermal conductor is exposed to a part of the surface of the ceramic body, and a high thermal conductor is formed inside the ceramic body. A heat generating resistor is formed according to the number of ceramic bodies, and is connected to the high heat conductor, and further includes a surface portion other than the surface of the ceramic body from which a part of the high heat conductor is exposed, or a surface portion of the other body. The ceramic thermal head is characterized in that a conductor is formed on the surface portion and inside the ceramic body, and the heating resistor and the conductor are connected on the surface or inside the ceramic body.

The details of the present invention will be explained below with reference to the drawings and examples.

FIG. 1 is a perspective view showing an embodiment of the structure of a thermal head according to the present invention, in which 1 is a high heat conductor layer exposed on the surface, 2 is an insulating ceramic body, and 3 is for inputting electrical signals from the outside. Shows electrodes for external connections. FIG. 2 shows a cross section of the thermal head of the present invention, where a represents the cross section taken along the dotted line in FIG. 1, and b represents the cross section taken along the dashed line in FIG. . In FIG. 2a, 1 is a high heat conductor, 2 is an insulating ceramic body, 3 is a resistor, and 4 in FIG. 2b is an internal conductor.

As is clear from FIGS. 1 and 2, in the thermal head according to the structure of the present invention, the heating resistor and the high thermal conductor are embedded in the insulator, and the high thermal conductor is on the surface. Since the resistor is exposed, there is no wear on the resistor at all, and since the heat conductive layer protected by the insulator is exposed on the surface, it can be sufficiently wear resistant even without providing a wear resistant layer on the surface. It has a certain structure. Furthermore, since the resistor is embedded in a metal insulator, the structure is such that the resistor never becomes disconnected. Therefore, since there is no diffusion of heat through the wear-resistant layer, a resolution approximately equal to the thickness of the high thermal conductor can be obtained. moreover,
In conventional thermal heads, when current flows inside the resistor and generates heat, the amount of heat generated changes depending on the location due to the width of the resistor and variations in the thickness of the resistor within that width, resulting in the recorded image being There were many cases where unevenness occurred.

According to the structure of the present invention, since the thickness direction of the resistor is exposed at the surface, the heat within the same dot becomes uniform and density unevenness is reduced. Furthermore, since the thermal head of the present invention forms a uniform resistor on a uniform insulating raw sheet and also forms a heat conductive layer, the thickness of the highly heat conductive layer exposed on the surface depends on the resistance value. The thickness of the high thermal conductor layer can be formed uniformly from a few microns to a few hundred microns, and the thickness and pitch of the high thermal conductor layer can be extremely controlled. It can be made finely,
The recording resolution can be dramatically improved from the conventional 6 to 8 dots/mm to several tens of dots/mm.

The method for manufacturing the structure shown in FIGS. 1 and 2 is as follows.

An alumina-crystalline glass mixture was used as the insulator material. Powders of 50 wt% alumina and 50 wt% borosilicate lead crystallized glass were wet mixed in a ball mill, and then filtered and dried to obtain insulating powder.

A ruthenium oxide-insulator mixture was used as the resistor material. 30wt% of ruthenium oxide powder with a purity of 99.9% or higher and 70wt% of insulator powder were weighed, wet-mixed, filtered and dried to obtain resistor powder.

The insulator powder and the resistor powder are each dispersed in an organic vehicle to form a slurry, which is then cast to a film thickness of 20 μm or more using a doctor blade.
A 500 μm insulator raw sheet and a resistor raw sheet were prepared. Note that polyvinyl butyral was used as the binder of the organic vehicle, and polyhydric alcohol ester was used as the solvent.

Punch out the outer shape of the raw insulator sheet using a mold,
A wiring pattern and a highly thermally conductive layer were printed on this by screen printing using a silver-palladium alloy paste. Next, make a resistor raw sheet 3mm x 2mm.
It was punched out to the dimensions of , and pasted onto an insulating green sheet.

A predetermined number of raw insulating sheets on which the resistor sheets thus produced were attached and conductors were formed, and raw insulating sheets on which only conductors were formed were placed in molds, laminated, and thermocompression bonded.

After lamination, the raw laminate was cut into a size of 5 mm x 10 mm, and after removing the binder at 500°C, it was sintered at a temperature of 800°C to 1000°C.

After firing, external electrodes were baked on the sintered laminate, and the surface in contact with the thermal paper was polished to a mirror finish, and then lead wires were attached to form a thermal head.

When the completed thermal head was set in a thermal printer and an operation test was performed, a resolution of 10 dots/mm to 30 dots/mm was obtained, making it fully practical, and moreover, compared to conventional thermal heads.
It was found to exhibit significantly improved resolution.

Thermal heads manufactured by other methods include the following.

An alumina-crystalline glass mixture was used as the insulator material. Weighed 56wt% alumina with a purity of 99.9% or higher and 44wt% lead borosilicate crystallized glass,
Wet mixing was performed in a ball mill, and after drying, an insulator powder was obtained.

This insulating powder was dispersed in an organic vehicle to form a slurry, and a green insulating sheet having a thickness of 20 μm to 500 μm was prepared by casting the slurry using a doctor blade. Note that polyvinyl alcohol was used as the binder of the organic vehicle, and water was used as the solvent.

Using a mold, punch out the outline of the raw insulator sheet,
On top of this, a wiring pattern and a thermally conductive layer pattern were printed using gold paste by a screen printing method.

Next, a ruthenium-based resistor paste was further used on the insulator raw sheet on which the conductor was formed, and a resistor layer was formed at a predetermined position by screen printing. The thickness of the resistor layer was 6 μm to 100 μm, and when the resistor layer was thick, overprinting was performed.

The resistor layer thus produced, the conductor layer, the insulating raw sheet on which the high heat conductive layer is formed, the insulating raw sheet on which only the conductor is formed, and the insulating raw sheet on which only through holes are formed, if necessary, are prepared as specified. The number of sheets was put into a mold, and laminated thermocompression bonding was performed.

After lamination, the raw laminate is cut into 5 mm x 10 mm dimensions, and the binder is removed at 500°C, followed by heating at 800°C.
Sintered at a temperature of 1000℃.

After firing, external electrodes were baked on the sintered laminate, and the surface in contact with the thermal paper was polished to a mirror finish, and then lead wires were attached to form a thermal head.

When the completed thermal head was set in a thermal printer and an operation test was performed, 10 dots/print was obtained.
It has been found that a resolution of mm to 50 dots/mm can be obtained, which is sufficient for practical use, and also shows a significantly improved resolution compared to conventional thermal heads.

As described above, the ceramic thermal head with the structure of the present invention has a resolution that cannot be achieved with conventional thermal heads, is compact and highly reliable, can be mass-produced, and can reduce costs. It turned out to be a thermal head.

In this example, a silver-palladium alloy and gold were used as the heat conductor layer, but the high heat conductor layer may also be made of gold, platinum, silver, palladium, etc., or an alloy of two or more of these. It was found that similar effects can be obtained using metals and alloys such as .

Furthermore, it has been found that similar results can be obtained by using metal oxides, metal nitrides, and metal carbides that have good thermal conductivity in addition to these metals. Among these, beryllium oxide, silicon carbide, and silicon nitride had particularly good wear resistance and good effects were obtained.

[Brief explanation of drawings]

FIG. 1 is a perspective view of an embodiment of the laminated ceramic thermal head of the present invention, and FIG. 2 is a sectional view of the laminated ceramic thermal head of the present invention, where a is a cross section taken along the broken line in FIG. b shows a cross section taken along the dashed line in FIG. In these figures, 1 is a high heat conductor, 2 is an insulating ceramic body, 3 is an external connection terminal, 4 is a conductor, and 5 is a conductor.
is a heating resistor.

Claims (1)

[Claims] 1. One or more high thermal conductors are formed inside an insulating ceramic body, and a part of each high thermal conductor is exposed to a part of the surface of the ceramic body,
Further, heat generating resistors are formed inside the ceramic body in accordance with the number of high heat conductors, and are connected to the high heat conductors, and further connect to the surface of the ceramic body where a part of the high heat conductors is exposed. is characterized in that a conductor is formed on another surface portion or on the other surface portion and inside the ceramic body, and the heating resistor and the conductor are connected on the surface or inside the ceramic body. Ceramic thermal head.