JP3410227B2 - Thermal head and manufacturing method thereof - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a thermal head used for heat-sensitive recording or thermal transfer recording and a manufacturing method thereof, and more particularly to a structure of a heat storage layer and a forming method thereof.

[0002]

2. Description of the Related Art In the conventional thermal head, generally, as shown in FIG. 5A, an insulating material such as alumina or a substrate 1 formed by applying an insulating coating to a metal plate is used. A heat storage layer 2 made of glass is formed on the surface, a heating resistor layer 3 is formed thereon, and a large number of lead electrodes 4a and common electrodes 4b connected to a driving circuit are formed thereon, and heat is generated between them. The part 5 is formed, and these are covered with a heat-resistant and wear-resistant protective film 6.

As described above, glass has been conventionally used as the heat storage layer 2, but this glass has a thermal conductivity of 0.7.
It is about W / m · K, and it is necessary to use a material having a low thermal conductivity in order to increase the printing efficiency (that is, reduce the power consumption in the heat generating part 5), and therefore polyimide with the intention of reducing the power consumption. Like the resin, a heat-resistant resin having a low thermal conductivity (general polyimide resin has a thermal conductivity of about 0.15 W / m · K) is used for the heat storage layer 2, and the heat storage layer 2 has a thickness of about 20 μm. Is formed.

However, in the case of the planar structure shown in FIG. 5 (A), since the contact pressure with the thermal paper or the transfer film is low, the polyimide resin having a low thermal conductivity as described above is used as the heat storage layer 2. Even when used, the printing efficiency could not be improved so much. Further, when a general polyimide resin having a low thermal conductivity is used, if the heat storage layer 2 is formed to have a thickness of 20 μm or more, the heat storage effect becomes excessive, resulting in deterioration of print quality such as “tailing” or “bleeding”. There were also points. Further, it is necessary to bend the print medium (paper) for printing.

On the other hand, as described in JP-A-63-64767 or JP-A-1-93375, there is a heat storage layer in which a polyimide resin is formed to have an R-shaped cross section. Such a resin is generally prepared by coating a solution of a polyimide resin or its precursor in a solvent (hereinafter referred to as a solution of a polyimide resin) on a substrate, heating it to evaporate the solvent, and curing the reaction. Formed by.

However, when the solution of the polyimide resin is applied to the substrate, it is difficult to apply it on the substrate in an orderly and constant width so that the cross-sectional shape is R-shaped, and the heat storage function may vary. There was a problem.

As a means for solving such a problem, the applicant of the present invention forms a linear convex portion 1a on a substrate 1 as shown in FIG. 5 (B), and a fluid state on the convex portion 1a. The polyimide resin solution described above was applied using surface tension, heated and reacted to develop a heat storage layer 2 having an R-shaped cross section, and proposed as Japanese Patent Application No. 5-52867. did.

As described above, when the fluid of the polyimide resin having fluidity is applied to the linearly formed convex portion 1a, the coating width is regulated by the width of the convex portion 1a due to the surface tension of the solution, and the accurate heat storage is achieved. The width of the layer can be set, and both ends of the cross section of the heat storage layer 2 are rounded due to surface tension, but the center part becomes flat with the evaporation of the solvent, and the heat storage layer 2 having an R-shaped cross section close to a trapezoid is formed. Since the formed heating element has a larger radius of curvature than the thermal head having the conventional partial glaze heat storage layer 2, there is room for improvement in terms of printing efficiency in terms of the contact pressure of the platen during printing. It was

In view of the above problems, the present invention provides a thermal head using a polyimide resin as a heat storage layer,
An object of the present invention is to provide a thermal head in which a heat storage layer can be regularly formed with a constant width and whose cross-sectional shape is formed into an arc shape that is closer to a perfect circle, and a manufacturing method thereof.

[0010]

In order to achieve the above object, the present invention provides a thermal head in which a heat generating portion is formed on a substrate through a heat storage layer, and a polyimide resin is formed on the convex portion formed on the substrate. And a circular heat storage layer having a circular cross-sectional shape with a circularity tolerance of 10 μm or less is formed by laminating a solution obtained by dissolving the resin in a solvent a plurality of times.

The method of manufacturing a thermal head according to the present invention is the method of manufacturing a thermal head in which a heat generating portion is formed on a substrate via a heat storage layer, and the first coating is applied on the convex portion formed on the substrate. A solution obtained by dissolving a polyimide resin as a layer in a solvent is applied, and after the application of the solution, the reaction solution is heated at a temperature not higher than the reaction curing temperature, and the solution after application is heated and dried at a temperature at which it can be partially redissolved. A solution prepared by dissolving a polyimide resin of the same material in a solvent as the second coating layer is applied onto the dried layer, heated and dried at a reaction curing temperature or lower as described above, and then heated at a reaction curing temperature or higher. Thus, the heat storage layer is formed so that the cross-sectional shape is an arc shape having a circularity tolerance of 10 μm or less.

[0012]

According to the present invention, a heat storage layer made of a polyimide resin is formed by applying a solution of the resin a plurality of times. The formation surface is the upper surface of the convex portion, so that the cross-sectional shape of the heat storage layer is round. It is easily formed in an arc shape with a tolerance of 10 μm or less.

Further, in the method of the present invention, by coating a solution of a polyimide resin on the upper surface of the convex portion of the substrate, the solution remains on the upper surface of the convex portion due to surface tension, and the coating width is regularly arranged within the width of the convex portion of the substrate. Fits. In addition, the solution after coating is heated at a temperature not higher than the reaction curing temperature and at a temperature at which it can be partially redissolved to dry it, to form a first coating layer, and then a solution of a polyimide resin to be a second coating layer is formed in advance. The second coating layer remains on the upper surface of the previous layer due to the surface tension of the solution when it is coated so as not to overflow the layer. At this time, since the underlying coating layer is partially redissolved, the applied solution, that is, the second coating layer, has a higher concentration than the solution before coating, and this is at a temperature below the reaction curing temperature and at which partial dissolution is possible. By heating and drying with, a shape in which the central portion of the heat storage layer rises in an arc shape can be formed.

As described above, the first coating layer is formed on the top of the convex portion and the second coating layer is formed thereon, so that the second coating layer is formed as compared with the case where one heat storage layer is formed. After the application of the solution, the concentration of the second coating layer becomes high, the R-shape after the coating of the second coating layer is easily maintained, and the heat storage layer is more likely to be formed into a round cross-sectional shape.

[0015]

1A is a sectional view showing an embodiment of a thermal head according to the present invention, and FIG. 1B is an enlarged view thereof.
(C) is a block diagram showing the cross-sectional shape of the heat storage layer. In FIG. 1, reference numeral 1a denotes a convex portion formed by cutting or integral molding on a substrate 1 made of ceramic such as alumina, which is formed to be long in the heating element row forming direction, that is, the direction perpendicular to the paper surface. In the example, the height h1 is 500 μm, and the width W1 of the top of the protrusion 1a is 1.0 mm. Both sides of the convex portion 1a are formed as inclined surfaces 1b instead of vertical surfaces in consideration of film formation. That is, the convex portion 1a is formed to have a trapezoidal cross section. Reference numeral 2a denotes a first coating layer formed of a polyimide resin provided on the convex portion 1a according to the present invention, and 2b is formed on the first coating layer by a resin of the same material so that its cross-sectional shape is R-shaped. It is the second coating layer. First coating layer 2a, second coating layer 2b
After heating and reaction hardening, they become an integrated heat storage layer, and their boundaries disappear.

Specifically, a polyimide resin was dissolved in N-methyl-pyrrolidone as a solvent at a concentration of about 30 wt% to form a solution having a viscosity of about 10,000 cps, which was applied onto the convex portion 1a using a dispenser. In this way, when the solution of the polyimide resin is applied on the convex portion 1a,
An angle α formed by the upper surface of the convex portion 1a and the inclined surfaces 1b on both sides (see FIG.
(See (B)) exceeds 180 degrees, it does not flow down the inclined surface 1b due to surface tension, stays at the corners, has roundness on both sides of the upper surface, and the top of the convex portion located between the corners on both sides. A first coating layer 2a having a film thickness of 35 μm and having a flattened sectional shape was formed. The thus coated solution of the polyimide resin was heated at 60 ° C. for 30 minutes to remove the solvent and dried. FIG. 2 (A) shows the cross-sectional film thickness distribution of the first coating layer thus formed, measured with a surface roughness meter, and the vertical axis is shown to be about 10 times larger than the horizontal axis. It is a graph. The difference in radius between the concentric circles when the curve of the measured values was surrounded by two concentric circles consisting of the inscribed circle a and the circumscribed circle b was determined. However, the smaller inscribed circle a was a circle passing through the points at both ends of the coating layer. The difference between the radii of these two concentric circles is 4.504-4.49.
1 = 13 (μm), and the roundness tolerance was 13 μm.

Next, a solution of a polyimide resin of the same material as that for forming the first coating layer 2a for forming the second coating layer 2b is formed on the first coating layer 2a dried as described above in the same manner as described above. It was applied by the method described above, and heated at 60 ° C. for 30 minutes to be dried. At this time, as shown in FIG. 1C, the first coating layer 2a
Is formed to have a narrower width (W1> W2) than the top of the convex portion 1a, and the second coating layer 2b is formed thereon, so that the cross-sectional shape is R as compared with the case where one heat storage layer is formed. Easier to form. Further, the first coating layer 2a is the second coating layer 2
By partially re-dissolving after applying b, the second coating layer 2b has a high concentration and high viscosity, and the second coating layer 2b has a shape after coating, that is, a shape in which the central portion is raised in an arc shape. To be done. This is heated at 60 ° C for 30 minutes and then 2
It was heated at 00 ° C. for 40 minutes and further heated at 400 ° C. for 60 minutes to be cured by reaction, thereby forming the heat storage layer 2 in which the first and second coating layers 2a and 2b were integrated.

FIG. 2B shows the cross-sectional thickness distribution of the heat storage layer 2 formed of the first and second coating layers thus formed, measured with a surface roughness meter, and the vertical axis represents the horizontal axis. It is a graph enlarged to approximately 10 times the axis, and the maximum film thickness h2 is 70 μm.
Became. The difference in radius of the concentric circles when the curve of the measured values was surrounded by two concentric circles of the inscribed circle c and the circumscribed circle d was determined. However, the smaller circle c was a circle passing through the points at both ends of the coating layer. The difference between the radii of the two concentric circles was 1.777-1.771 = 6 (μm), and the roundness tolerance was 6 μm. The polyimide resin used had a thermal conductivity of about 0.4 W / m · K, which was higher than that of the conventional one, by crosslinking with —Si—O—.

After that, the heating resistor layer 3, the electrode layers 4a, 4
b is laminated by vapor deposition (may be sputtering, CVD method or the like), and the heating resistor layer 3, the lead electrode 4a, and the common electrode 4b are formed by photolithography, and the protective layer 6 is formed thereon. The connecting portions of the lead electrode 4a and the common electrode 4b with the external circuit were exposed.

A heating element driving IC (not shown) is mounted on the substrate 1 or a substrate different from the substrate 1 and the IC and the exposed portion of the lead electrode 4a are connected by wire bonding or the like. A thermal head was manufactured by mounting various components.

FIG. 3A shows the relationship between the electric power and the optical density when the planar shape of the heating element is formed so that the vertical and horizontal dimensions are 350 μm × 167 μm, and a polyimide resin is used as the heat storage layer 2. FIG. 5 (A) shows a comparison between the conventional product and the product of the present invention shown in FIG.
The electric power could be reduced to about 52% of that of the conventional product in order to obtain the same concentration as that of the conventional example. In addition, Japanese Patent Application No. 5 filed earlier
Compared to the case where the convex portion of the structure shown in -52867 is formed in the same width and the heat storage layer is formed by one-layer coating,
The power could be reduced to about 85%.

Further, FIG. 3 (B) is a diagram showing the results of temperature measurement by the infrared radiation thermometer when driving the heat generating part, comparing the case where glass is used as the heat storage layer and the product of the present invention. Was the same as when glass was used as the heat storage layer, and no image deterioration such as "tailing" or "bleeding" was observed.

In the present invention, the width W1 of the bottom of the first coating layer 2a shown in FIG. 1A is preferably set to 0.8 mm to 4 mm. If the width W is less than 0.8 mm, the cross-sectional shape of the second coating layer 2b cannot be formed in the R shape,
If it exceeds 4 mm, the upper surface of the second coating layer 2b tends to be flattened, and a desired shape cannot be obtained. If the roundness tolerance is 10 μm or less, the required contact pressure of the platen can be obtained. Further, the thermal conductivity of these heat storage layers 2 is 0.2 W / m · K to 0.6 W / m · K depending on the material selection so as to increase printing efficiency and prevent excessive heat storage.
The maximum film thickness h2 is preferably 20 μm to 120 μm in order to obtain an appropriate heat storage effect.

In the above embodiment, the heat storage layer 2 was formed by applying twice, but the heat storage layer 2 was formed by applying three times or more.
Can also be formed.

The examples shown in FIGS. 4A and 4B are examples in which the present invention is applied to an end face type thermal head, and the example shown in FIG. 1a
4 is an example in which the heat storage layer 2 is formed on the
(B) is an example in which the heat storage layer 2 is formed by using the corners of the end face of the substrate 1 as protrusions to prevent resin from wrapping around.

[0026]

According to the first aspect of the present invention, a plurality of coating layers made of the same polyimide resin are laminated by applying and heating a resin solution, so that a single heat storage layer is formed. The contact surface of the heat storage layer or the platen of the thermal head with the platen can be formed on the R surface protruding further to the platen side, the contact pressure with the platen is increased, and the printing efficiency can be further improved. Moreover, it is possible to easily realize a thermal head that can be used without bending the print medium. Moreover, since the width and height of the heat storage layer are made uniform by the convex portions, the heat storage function can be made uniform in the direction of the heating element array. In addition, the degree of freedom in designing the width and height of the heat storage layer having a circular cross section is greater than that in the case where the heat storage layer is formed as a single layer.

According to the second and third aspects, it is possible to form a heat storage layer that can obtain a preferable heat storage effect.

According to the fourth aspect, by setting the thermal conductivity to a suitable value, it is possible to form a heat storage layer that can obtain a suitable heat storage effect.

According to a fifth aspect of the present invention, in manufacturing the thermal head, the first coating layer of the polyimide resin is formed on the convex portion formed on the substrate by heating and drying at a temperature at which it can be redissolved. Since the polyimide resin solution is applied as the second coating layer on the first coating layer, the resin concentration of the second coating layer increases after the coating, and the shape of the second coating layer after coating is maintained even after being dried by heating. This facilitates formation of a heat storage layer made of a polyimide resin having an arc-shaped cross section with a circularity tolerance of 10 μm or less.

[Brief description of drawings]

FIG. 1A is a sectional view showing an embodiment of a thermal head according to the present invention, FIG. 1B is a partially enlarged view thereof, and FIG. 1C is a configuration diagram showing a sectional shape of a heat storage layer thereof.

FIG. 2A is a cross-sectional film thickness distribution diagram of the first coating layer after heating and drying in one embodiment of the present invention, and FIG. 2B is a cross-sectional view after forming the second coating layer, heating and drying, and reacting and curing. It is a surface film thickness distribution chart.

FIG. 3A is a diagram showing the relationship between the electric power and the print density of the product of the present invention and the conventional product in comparison, and FIG. 3B is the temperature change during driving of the heating element of the product of the present invention. It is a figure shown in contrast.

4A and 4B are cross-sectional views showing another embodiment to which the present invention is applied to an end face type thermal head.

5A is a sectional view showing an example of a conventional thermal head, and FIG. 5B is a sectional view showing an example of a thermal head previously filed by the present applicant.

[Explanation of symbols]

1: substrate, 1a: convex portion, 1b: inclined surface, 2: heat storage layer, 2
a: first coating layer, 2b: second coating layer, 3: resistor layer, 4
a: lead electrode, 4b: common electrode, 5: heat generating part, 6:
Protective layer

─────────────────────────────────────────────────── --- Continuation of the front page (56) Reference JP-A-6-320771 (JP, A) JP-A-59-146870 (JP, A) JP-A-4-288244 (JP, A) JP-A-58- 59865 (JP, A) JP-A-6-115130 (JP, A) (58) Fields investigated (Int.Cl. ⁷ , DB name) B41J 2/335

Claims (5)

(57) [Claims] 1. A thermal head having a heat generating portion formed on a substrate via a heat storage layer, wherein an arc shape made of a polyimide resin and having a circularity tolerance of 10 μm or less is formed on a convex portion formed on the substrate. A thermal head comprising a heat storage layer formed by laminating a solution obtained by dissolving the resin in a solvent a plurality of times by heating. 2. The thermal head according to claim 1, wherein the width of the top of the convex portion is 0.8 mm to 4.0 mm. 3. The thermal head according to claim 1, wherein the thickness of the thickest part of the central portion of the resin is 20 μm to 120 μm. 4. The method according to any one of claims 1 to 3,
A thermal head, wherein the resin has a thermal conductivity of 0.2 to 0.6 W / m · K. 5. A method of manufacturing a thermal head in which a heat generating portion is formed on a substrate via a heat storage layer, wherein a polyimide resin as a first coating layer is dissolved in a solvent on the convex portion formed on the substrate. The applied solution, and after the application of the solution, the solution after application is heated and dried at a temperature not higher than the reaction curing temperature and at which the solution can be partially redissolved, and a second coating layer is formed on the dried layer. As a solution of a polyimide resin of the same material dissolved in a solvent as above, and dried by heating below the reaction curing temperature in the same manner as above, and then heating above the reaction curing temperature, the cross-sectional shape roundness tolerance A method of manufacturing a thermal head, characterized in that the heat storage layer is formed so as to form an arc shape of 10 μm or less.