JPH0692163B2 - Thermal head - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a thermal head used in a printer, and more particularly to a thermal head that is small and lightweight and has excellent thermal efficiency.

Conventional technology The conventional thermal head is a thin film type,
The thick film method is classified, and the scan method is classified into a line type and a serial type. FIG. 6 shows the basic structure of the thin film system. That is, the heating resistance layer 42 such as Ta-Si is provided on the alumina ceramic substrate 41 having the glass glaze layer 40, and the conductive electrodes 43 and 44 are provided on the heating resistance layer. Further, an oxidation resistant layer 45 and a wear resistant layer 46 are provided. All layers below the heating resistance layer are thin films obtained by a method such as sputtering or vapor deposition.

On the other hand, FIG. 7 shows a sectional view of a typical thick film type thermal head. That is, as in the case of the thin film method, the glass glaze layer 51 on the alumina ceramic substrate 50 and the Ru formed by screen printing and firing on this layer.
The resistance heating layer 52 made of O ₂ or the like, conductive electrodes 53, 54 similarly formed by printing and firing, and an oxidation resistant layer 55 and a wear resistant layer 56 formed by a thick film technique are basically formed. A thermal head composed of both thick and thin films has also been devised.

Generally, the thin-film type is suitable for high-speed printing, but the equipment required for manufacturing is expensive. Further, the thick film type has a relatively low manufacturing equipment cost and can easily make a large size one, but it is difficult to perform high speed printing due to the heat capacity and thickness of the heat generating layer.

The biggest development point of such a thermal head is how much input power to the heating layer is used for heat generation,
It is how much this heat is transmitted to the paper to obtain clear and high-density printing. Specifically, when the above-mentioned heating resistors 42, 52 are pulse-energized through the lead electrodes 43, 44, 53, 54, the resistors generate heat, but for high-speed printing, the resistors rapidly generate heat. Therefore, the heat insulating glass glaze layers 40 and 51 are provided for this purpose to improve the heat rising characteristics at the time of pulse-on. However, if the temperature of the paper heating resistance layers 42 and 52 after the pulse energization is stopped is quickly lowered to return to room temperature, a so-called tailing phenomenon occurs and the cost cost of printing becomes worse. Therefore, the heat storage glaze layer preferably has a small thickness in order to quickly dissipate the heat through alumina, which has good heat conductivity of the substrate. In the conventional thermal head, the thickness of the heat storage glass glaze layer is controlled in order to optimize the rising and falling speeds of the temperature at the time of pulse on / off. FIG. 8 shows the relationship between the thickness of the glass glaze layer and the temperature rising / falling characteristics of the resistance layer. The optimum printing characteristics are shown when the thickness of the glass glaze layer is 30 to 100 μm.

The heater materials, Ta-Si, TaN, NiCr , etc. RuO _2, 10 ¹
A film with a specific resistance of ~ 10 ^-6 Ωcm is used as a film with a thickness in the range of several 100Å to several μm, and the film resistance is several tens of ~.
Several hundred Ω / resistive element.

In addition, since 0.1 to 1 W of energy is input per resistance element, one thermal head can be used for several hundred W
Generates 1W of heat. To dissipate this more efficiently,
Heat sink 90 made of aluminum block as shown in FIG.
Is bonded to the above-described alumina substrate 91 using an adhesive 92.

There are various types of conventional thermal heads such as the material thickness, but basically, the heating resistance layer on the insulating substrate,
The electrodes and the heat sink are its constituent elements, and the glass glaze layer largely controls the energy characteristics of the device.

From the above, the thermal efficiency of the head, that is, the ratio of the input energy to the print density, the high-speed printability, the weight, the size, and the like are considered as problems to be solved in the conventional thermal head.

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention The present invention provides a small and lightweight thermal head that has high energy efficiency, exhibits excellent print quality even in high-speed printing.

Means for Solving Problems The thermal head of the present invention has a specific resistance of 10 ⁻⁶ to 10 ² Ω · cm.
Basically, it is composed of a base body and opposing electrodes formed on the base body.

More specifically, it is a thermal head in which a base made of carbon such as glassy carbon is used also as a heating element or a heating element, a substrate, and a heat dissipation plate, and an opposing electrode is formed on the surface of the base. .

Effect According to the present invention, since the base body made of carbon or the like having a relatively low electric resistance is used as the heating element, the heat generation efficiency per unit input energy is good. Thermal conductivity about 10 times (Al ₂ O ₃ :
0.5 to 2 kcal / m ・ hr ・ ℃, glassy carbon: 4 to 10 kcal / m ・ hr
・ ℃), density is about 1/3 (Al ₂ O ₃ : 4g / cc, glassy carbon: 1.5g
/ cc), the glass-like carbon has a small heat capacity and high thermal conductivity, so when it is also used as a substrate,
The rising and falling speeds of the temperature of the heating element are also very excellent, and excellent printing quality can be obtained.

Further, the weight of the entire head is light, and since it can also serve as a heat dissipation plate, the overall size can be reduced. Further, the carbon material is an excellent wear-resistant material, and it is possible to obtain a material having excellent wear-resistant characteristics by sliding on paper.

Embodiment FIG. 1 shows the basic structure of a thermal head according to the present invention. ^Reference numeral 1 is a substrate having a specific resistance of 10 ⁻⁶ to 10 ² Ω · cm, and, for example, glassy carbon is used in a plate-like shape having a certain thickness. Reference numerals 2 and 3 are electrodes provided on the base 1 and facing each other.
When a current is applied between the electrode 2 and the electrode 3, a current flows as indicated by an arrow 4 along the shortest distance between both electrodes near the surface of the substrate 1.
Then, the vicinity 5 of the surface of the portion sandwiched between both electrodes generates heat at a low applied voltage and becomes high in temperature.

Since the substrate 1 is made of a material having an electric resistivity of 10 ⁻⁶ to 10 ² Ω · cm, the heat generation efficiency per unit input watt is very large. As such a material, glassy carbon, amorphous carbon, graphite, recrystallized graphite, pyrolytic graphite, impermeable graphite and the like are suitable. Since the thermal conductivity of these materials becomes lower as the temperature becomes higher, the heat storage property by voltage application is improved and the heat radiation property is improved by voltage interruption. The heat flow shown by arrow 6 in the figure is used as a thermal head material. Works optimally. By utilizing this property, these carbon material substrates can be used alone as a heating element, a substrate, and a radiator, but if necessary, they can be bonded to a good heat conductor such as a metal block, ceramics, carbon, or on the back surface. It is sufficient to form a metal film having a low emissivity.

Among the above-mentioned substrate materials, glassy carbon is particularly effective in terms of its electrical resistance, surface smoothness, thermal conductivity, mechanical strength and the like. This glassy carbon plate is obtained by carbonizing a phenol resin, a furfural resin, a vinyl resin, an acrylic resin, a cellulose resin, or a mixture thereof, and its electric resistance value is an arbitrary value by controlling the firing temperature. You can get

Further, when a material having directivity to electric conductivity and thermal conductivity such as graphite is used as the substrate, in order to further enhance the effect of the present invention, heat treatment is performed in parallel with the line connecting the counter electrodes 2 and 3. It is preferable to install a shaft having high conduction and electric conduction, and arrange a shaft having low heat conduction and electric conduction (C axis) in a direction directly below the shaft.

When the electric resistance of the base body 1 is sufficiently low, the current 4 in FIG. 1 flows not only between the tip portions 2a and 3a of the electrodes 2 and 3 but also between the root portions 2b and 3b as shown by 7 and heat is generated. It does not occur concentratedly between the electrodes. Since this is prevented and the electric current is concentrated between the electrodes, it is effective to provide an electrically insulating layer between the electrodes 2 and 3 and the substrate 1. However, no electrical insulating layer is provided in the portion 5;
Alternatively, the electrical resistance of the electrode (value measured by the four-point probe method) a ₁
It is also possible to achieve current concentration between the electrodes by making A sufficiently lower than the electric resistance a ₂ of the substrate. In this case, a ₂ / a ₁ > 2 is appropriate.

As the material used for the electrodes 2 and 3, gold, copper, etc. are suitable, but by using a conductive material having wear resistance such as monel metal, it becomes possible to omit the wear resistant layer and improve the thermal efficiency. Further improve.

By treating the surface of the substrate in an atmosphere of high energy such as ozone or ultraviolet rays, the adhesion between the substrate and the electrode becomes stronger and a sufficient effect can be obtained.

As a wear resistant layer, when using a carbonaceous material for the substrate,
Using the same carbon-based diamond-like carbon, SiC, etc., they have good adhesiveness and excellent heat conduction, so that large thermal efficiency and high wear resistance can be obtained.

As the substrate, a flat plate, a round bar, a square bar, a foil, or the like may be used depending on the application, and glassy carbon is particularly excellent in processability and is industrially very advantageous in this respect.

Specific examples will be described below.

Example 1 Specific resistance 10 ⁻⁴ obtained by carbonizing a molded product of a phenol resin
As shown in FIG. 2, an electrode pattern 1 made of copper was formed on one surface of a substrate 10 made of a glassy carbon plate having a thickness of Ω · cm and a thickness of 1 mm.
Form 1,12. 11 is a common electrode, 12 is a segment electrode, and the pitch between the electrodes 11 and 12 is 100 μm. The segment electrodes each have a width of 100 μm, and the pitch with the adjacent electrodes is 100 μm. Reference numeral 13 is an oxidation resistant layer made of SiO ₂ provided between the electrodes 11 and 12.

The above thermal head is designated as a, and the thermal heads constructed by using glass substrates having the same glassy carbon plate thicknesses of 2 mm and 10 mm are designated as b and c, respectively.

Example 2 The same glassy carbon plate as in Example 1 having a thickness of 2 mm was used as a substrate, and a slit having a width of 150 μm was left on the substrate to give a thickness of 200.
A 0N TaN layer 14 is formed (Fig. 3). On top of this, the copper electrode
Form 11,12. The center between both electrodes and the center of the slit are made to coincide with each other. Further, an oxidation resistant layer 13 made of SiO ₂ is formed.

Example 3 A heat dissipation plate made of aluminum and having a thickness of 5 mm is bonded to the back surface of the substrate of the thermal head a of Example 1 with a conductive adhesive.

Example 4 An aluminum layer is provided on the back surface of the substrate of the thermal head c of Example 1 by vapor deposition or sputtering.

Example 5 After the surface of the glassy carbon having a thickness of 2 mm of Example 1 is treated with one or both of ozone and ultraviolet rays, a thermal head is prepared in the same manner as in Example 1.

Example 6 A thermal head is manufactured in the same manner as in Example 1 using an amorphous carbon plate having a specific resistance of 10 ⁻⁴ Ω · cm and a thickness of 2 mm as a substrate.

Example 7 A thermal head is manufactured in the same manner as in Example 1 using a graphite plate having a specific resistance of 10 ⁻⁵ Ω · cm and a thickness of 2 mm as a substrate. The electrodes are formed so that the C-axis directions of the graphite crystals are at right angles to the line connecting the electrodes facing each other.

Example 8 A thermal head is manufactured in the same manner as in Example 1 using a recrystallized graphite plate having a specific resistance of 10 ⁻⁶ Ω · cm and a thickness of 2 mm as a substrate.

Example 9 In glassy carbon having a structure in which a tetrahedral crystallite and a graphite crystallite are mixed, the graphite crystallite is fired so that its C axis is aligned at right angles to the plate thickness direction. Similar to Example 1, copper opposite electrode layers are formed. The electrodes are formed so that the direction parallel to the line connecting the electrodes facing each other is perpendicular to the C axis of the graphite-type crystallite.

Example 10 Phenolic resin and SiC powder having a particle size passing through a 325 mesh sieve were mixed in a weight ratio of 100/1, and this was molded into a plate and carbonized to form amorphous carbon containing SiC. Board (thickness 2m
m, specific resistance 10 ² Ω · cm) is obtained. Using this as a substrate, electrodes are formed in the same manner as in Example 1.

The thermal heads obtained in the above examples are connected to a drive power source and tested, and the results are shown in the table in comparison with the conventional example.

Example 11 Glass-like carbon having a specific resistance of 10 ⁻⁴ Ω · cm and a thickness of 1 mm and a size of 5 mm
Cut to × 8 mm. Copper electrodes 21 and 22 are patterned on the substrate 20 as shown in FIG. 5 on this whole surface
A SiC layer with a thickness of μm covers and wears. Reference numeral 21 is a common electrode, 22 is a segment electrode, and the electrode interval and width are the same as in the first embodiment.

When this was used as a head for a serial printer, the printing characteristics, energy efficiency, etc. of the head were found in Example 1.
It was the same as In particular, when used as a serial head, glassy carbon is light and has excellent heat dissipation, so its effect is great.

Example 12 Electrode patterning was performed on the surface of glassy carbon having a specific resistance of 10 ⁻⁴ Ω · cm and a thickness of 2 mm by using monel metal having abrasion resistance. All the conditions were the same as in Example 1, but since Monel metal had wear resistance, a good head was obtained without using a wear resistant layer, and the energy efficiency was further improved.

Example 13 A glassy carbon round bar having a diameter of 2 mm is used as a substrate. This base 3
As shown in FIG. 5, a copper common electrode 31 and a segment electrode 32 are formed on a part of the surface of 0 by sputtering. The common electrode has a width of 2 mm and the segment electrode has a width of 100 μm. The pitch between the segment electrodes, the common electrode and the adjacent segment electrodes is 100 μm. The printing characteristics and energy efficiency are the same as the results in Example 1. Since it is a round bar, it has excellent adhesion to printing paper and can be made compact and lightweight.

The specific resistance of the heat-generating substrate used in the present invention can be selected in a wide range depending on its thickness, width, etc., but considering the actual dimensions of the heat-generating portion, that is, the pitch between electrodes, and the dot density, 10 ⁻⁶ to 10 −10. ² Ω · cm is suitable, and the electrode pitch should be determined within this range so that an appropriate heat generation temperature can be obtained in consideration of the material's resistivity, heat dissipation due to thermal conductivity, and heat storage. . The glassy carbon used for the substrate is
For example, it is possible to obtain an electric resistance value in the range of 10 ⁻⁶ Ω · cm to 10 ² Ω · cm by varying the firing temperature of the phenol resin molded plate.

EFFECTS OF THE INVENTION According to the present invention, it is possible to obtain a thermal head which has a high temperature rise at the time of pulse application and a high temperature drop rate at the time of pulse erase, that is, an excellent thermal response. In addition, the material is light in weight and can be used as a heat generating layer, a substrate and a heat sink by itself, so the energy efficiency is greatly improved compared to the conventional one.

[Brief description of drawings]

FIG. 1 is a schematic sectional view showing the basic structure of a thermal head of the present invention, FIGS. 2 and 3 are longitudinal sectional views of an embodiment, and FIGS. 4 and 5 are perspective views of other embodiments. 6 and 7 are longitudinal sectional views of a conventional thermal head, and FIG. 8 is a diagram showing the relationship between the pulse application time to the thermal head and the temperature rising and falling speeds. 1,10 ... Base, 2,3,11,12 ... Electrodes.

 ─────────────────────────────────────────────────── ─── Continuation of front page (72) Inventor ▲ Yoshi ▼ Nobuyuki Ike 1006 Kadoma, Kadoma City, Osaka Prefecture Matsushita Electric Industrial Co., Ltd. (72) Ichiro Tanahashi 1006 Kadoma, Kadoma City, Osaka Matsushita Electric Industrial Co., Ltd. In the company

Claims (8)

[Claims] 1. A thermal head comprising a heat-generating / heat-radiating substrate having a specific resistance of 10 ⁻⁶ to 10 ² Ω · cm, and opposing current-carrying electrodes formed on the substrate. 2. The thermal head according to claim 1, wherein an electrically insulating film is provided between the base and the electrode in a portion other than the heat generating portion. 3. The substrate has high heat conduction and electric conductivity in a direction parallel to a line connecting electrodes facing each other, and low heat conduction and electric conductivity in a direction perpendicular to the heat conduction. The thermal head according to claim 1, wherein the thermal head is an anisotropic substance. 4. The thermal head according to claim 1, wherein the base body contains carbon as a main component. 5. The substrate is glassy carbon, amorphous carbon,
The thermal head according to claim 4, which is graphite, recrystallized graphite, pyrolytic graphite or impermeable graphite. 6. An electric resistance value of the electrode measured by a four-point probe method.
The thermal head according to claim ₁ , wherein a ₁ is smaller than the electric resistance value a ₂ of the substrate. 7. The a ₂ and a ₁ for the ratio a ₂ / a ₁ is larger claims thermal head ranges sixth claim of than 2. 8. The thermal head according to claim 1, wherein the base is bonded to a good heat conductor.