JP3109088B2 - Thick film type thermal head and method of manufacturing the same - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a thermal head of a thermal recording apparatus used as a print output unit of various information processing apparatuses such as a facsimile apparatus and a printer, and a method of manufacturing the same.

[Prior Art] This type of thermal head has a plurality of heating elements (resistance layers) arranged on an insulating substrate, and has electrodes for supplying current to these heating elements, and the heating elements are selected through the electrodes. By generating heat, the ink on the thermal recording paper or the ink donor film is melted or sublimated to record characters or graphics on a recording medium such as transfer paper, plain paper, or sublimation recording paper.

The thermal head is a thin-film thermal head that uses a thin-film forming technology such as evaporation or sputtering on an insulating substrate to form a heating element consisting of a resistive layer, and constituent layers such as power supply electrodes for heating this heating element. A paste of a resistive layer material or an electrode material constituting the heating element is applied on an insulating substrate by screen printing or the like, dried, and then patterned by a photolithography technique to form a heating element, an electrode, and other components. A thick film type thermal head for forming a layer is known.

The former thin-film type thermal head has the advantage that high-density and uniform film formation is possible, so that high-definition print dots can be obtained.On the other hand, the production equipment becomes large-scale, so the cost is high. There is a disadvantage that there is.

On the other hand, thick-film thermal heads apply a film-forming material as a paste and pattern it by photolithography technology (photolithography). Has the disadvantage of being non-uniform, but is attractive in that the cost is low.

In order to reduce the variation of the resistance value of the heating elements of the thick film type thermal head, for example, as disclosed in JP-A-61-131404, the resistance value of each heating element is adjusted by a pulse voltage trimming technique, Substantially uniform variation (for example, ± 3%
).

This trimming can reduce the unevenness of the print density.

FIG. 6 is a schematic diagram for explaining an example of the structure of this type of conventional thick film type thermal head, and shows a cross section in the sub-scanning direction when the thermal head is mounted on a recording apparatus.

In the drawing, a heat storage layer 22 made of a glass material is formed on an insulating substrate 21 made of a ceramic such as alumina, and a resistance layer 23 serving as a heating element and a common electrode for supplying power to the resistance layer 23 are provided. 24a and the individual electrode 24b are formed.

The common electrode 24a and the individual electrode 24b are connected by a well-known MOD method (Met
allo-Organic Deposition Method).

Then, on the upper surfaces of the resistance layer 23 and the electrodes 24a and 24b, the resistance layer 2
3 and an overcoat layer 25 for physically protecting the resistance layer 23 and the electrodes 24a and 24b and smoothing the contact sliding with the recording medium.

FIG. 7 is a schematic diagram for explaining another example of the structure of this kind of conventional thick film type thermal head, and shows a cross section in the sub-scanning direction when the thermal head is mounted on a recording apparatus.

6, a common electrode 34a, an individual electrode 34b, and a resistance layer 33 are formed on a heat storage layer 32 made of a glass material on an insulating substrate 31 made of alumina or the like, similarly to FIG.
Are formed.

After forming a thin metal layer to be the electrodes 34a and 34b, the resistive layer 33 is coated with a photosensitive resist (photoresist), dried, pattern-exposed through a photomask, and developed to form a resistive layer forming portion. Is removed by etching, and then a resistor material is applied, dried, and patterned to form a film using a so-called lift-off technique.

On the upper surfaces of the resistance layer 33 and the electrodes 34a and 34b, to prevent oxidation of the resistance layer 33, and to physically protect the resistance layer 33 and the electrodes 34a and 34b, and to facilitate the contact sliding with the recording medium. An overcoat layer 35 is provided.

[Problem to be Solved by the Invention] The thermal head according to the former MOD method has a resistance layer 23
Are located below the electrodes 24a and 24b, so that there is a step between the heating layer of the resistance layer 23 and the electrodes.

Therefore, the overcoat layer 25 formed on this upper surface
Has a depression as shown by arrow C.

Even if the resistance value of the resistance layer is equalized by the trimming due to the presence of the recess, a non-uniform gap is formed between the resistance layer and the recording medium, resulting in a problem that density unevenness occurs in a recording result.

The occurrence of the density unevenness is particularly remarkable in the halftone density.

On the other hand, in the latter thermal head by the lift-off technique, since the resistance layer 33 protrudes above the electrodes 34a and 34b,
Since the overcoat layer 35 is formed in a convex shape,
Due to the steps shown in D and E, undulation in the sub-scanning direction of the overcoat layer 35 occurs, and the contact with the recording medium is disturbed (uneven pressure due to variation in the contact area with the platen roller).
Occurs.

Due to the pressure unevenness, the contact pressure with the recording medium becomes uneven, resulting in a problem that the print density becomes non-uniform.

Also, in this type of thick film type thermal head, as the overcoat layer, a ceramic powder is added as a filler for increasing abrasion resistance to the glass powder, so that the surface smoothness of the film quality is not good. There is a problem that.

In order to improve the film quality of the overcoat layer, as disclosed in JP-A-63-9728, firing conditions at the time of forming the overcoat layer may be changed. The technology disclosed in this publication discloses that the temperature at which the overcoat layer is fired is set in two steps (for example, after firing for a predetermined time at 600 ° C., and then firing at 800 ° C., the voids generated in the glass paste are reduced). To improve the surface smoothness.

However, the conventional technique cannot eliminate the step between the resistance layer and the electrode layer.

In the thin-film type thermal head, partial glaze is adopted to improve the contact with the recording medium. However, when the partial glaze is applied to the thick-film type thermal head, the yield may be reduced. Is done.

SUMMARY OF THE INVENTION An object of the present invention is to provide a thick-film type thermal head and a method for manufacturing the same, which have solved the above-mentioned problems of the prior art, reduced non-uniform recording density, improved halftone reproducibility, and reduced manufacturing costs. To provide.

[Means for Solving the Problems] In order to achieve the above object, the present invention provides a heat storage layer (2, 2 in FIG. 1) on an insulating substrate (1, 1 in FIG. 1, 11 in FIG. 2). 12, a plurality of resistive layers arranged in the main scanning direction (3 in FIG. 1, 139 in FIG. 2, and electrodes for supplying power to the resistive layers (common electrode 4 in FIG. 1)).
a, an individual electrode 4b, 14a, 14b in FIG. 2, a plurality of resistive layers and an overcoat layer covering the electrodes, wherein the overcoat layer is a first overcoat layer. The first overcoat layer (5 in FIG. 1 and the second overcoat layer 15 in FIG. 2) and the second overcoat layer (6 in FIG. 1 and FIG.
16), wherein the second overcoat layer is formed by applying and firing a glass paste containing no filler, and is formed in a band shape in the main scanning direction with a width W in the sub-scanning direction covering the plurality of resistance layers. And the width W is a distance between the power supply electrodes respectively connected to the plurality of resistance layers, and the effective width of the resistance layers in the sub-scanning direction is U. It is characterized by 2U.

The width W may be a width sufficient to fill the concave portions generated in the first overcoat layer and form the second overcoat layer so as to have a convex shape slightly projecting from the first overcoat layer. .

Further, at least the second overcoat layer constituting the overcoat layer for manufacturing the thermal head is formed by screen printing of a glass paste.

[Operation] A resistive layer (3 in FIG. 1, 13 in FIG. 2) as a heating element and a common electrode (4a in FIG. 1,
14a) of FIG. 2 and individual electrodes (4b of FIG. 1, 14b of FIG. 2)
The first overcoat layer (5 in FIG. 1, 15 in FIG. 2) which covers the upper surface of the above has excellent abrasion resistance due to the filler, prevents oxidation of the resistance layer, and prevents the resistance layer from being oxidized. Is efficiently transferred upward (to the recording medium side).

The second overcoat layer (6 in FIG. 1 and 16 in FIG. 2) formed on the upper surface of the first overcoat layer has an effective width U in the sub-scanning direction of the resistance layer when the width is W. On the other hand, since U <W <2U and formed by screen printing of a glass paste containing no filler, the dents and undulations existing on the surface of the first overcoat layer are filled, and And provide a smooth surface.

Since the pressing force (the pressure contact force with the platen roller) between the recording medium and the heat generating portion (the surface facing the resistive layer) of the thermal head becomes uniform, the recording density does not become uneven.

Further, in the present invention, since the film layers constituting the thermal head employ a thick film forming technique such as screen printing, the manufacturing equipment is simplified.

〔Example〕

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

FIG. 1 is a schematic view for explaining the structure of a first embodiment of a thick film type thermal head according to the present invention, and shows a cross section in the sub-scanning direction when the thermal head is mounted on a recording apparatus.

In the figure, 1 is an insulating substrate, 2 is a storage layer made of a glass material, 3 is a resistance layer as a heating element, 4a is a common electrode,
4b is an individual electrode, 5 is a first overcoat layer, and 6 is a second overcoat layer.

A heat storage layer 2 is formed on an insulating substrate 1, and a resistance layer 3,
The structure up to the formation of the common electrode 4a and the individual electrode 4b is the same as the conventional example described in FIG.

The present embodiment is characterized in that the overcoat layer is composed of two layers, a first overcoat layer 5 and a second overcoat layer 6.

That is, the first overcoat layer 5 is provided to directly cover the upper surfaces of the resistance layer 3 and the common electrode 4a and the individual electrode 4b for supplying a heating current to the resistance layer 3.

The first overcoat layer 5 is formed by applying a paste obtained by mixing a ceramic powder to a glass powder using an organic solvent, followed by firing. By mixing the ceramic powder, an overcoat layer having excellent wear resistance can be formed.

Then, on the upper surface of the first overcoat layer 5, a second
An overcoat layer 6 is provided.

The second overcoat layer 6 is formed by applying and baking a glass paste having no ceramic powder, and has a substantially convex shape centered on the dent C so as to fill the dent C described in FIG. Is formed on the first overcoat layer 5 such that

The second overcoat layer 6 extends in a band shape in the main scanning direction, and has a width W larger than the effective width U of the resistance layer 3 and smaller than twice (2U) the width in the sub-scanning direction. I do.

When the width W of the second overcoat layer 6 is larger than 2U,
Since the second overcoat layer 6 has low wear resistance against sliding with the recording medium, the outer direction around the recessed portion of the first overcoat layer 5 wears out in a short time, and the first overcoat layer 5 Exposed.

Therefore, the width W of the second overcoat layer 6 is set to 2U.
It doesn't make much sense to do so.

For the above reason, the width W of the second overcoat layer 6 is
It is preferable to form in the range of U <W <2U.

By forming the second overcoat layer 6 in such a range, the dent of the first overcoat layer 5 is eliminated,
The first overcoat layer 5 maintains the abrasion resistance with the recording medium, and the second overcoat layer 6 smoothes the contact sliding between the recording medium facing the resistance layer 3 and the thermal head to achieve uniform recording. The concentration can be maintained.

FIG. 2 is a schematic diagram for explaining the structure of a second embodiment of the thick film type thermal head according to the present invention, and shows a cross section in the sub-scanning direction when the thermal head is mounted on a recording apparatus.

In the figure, 11 is an insulating substrate, 12 is a storage layer made of a glass-based material, 13 is a resistance layer as a heating element, 14a is a common electrode, 14b is an individual electrode, 15 is a first overcoat layer, and 16 is a second overcoat layer. It is an overcoat layer.

A heat storage layer 12 is formed on an insulating substrate 11 and a common electrode is formed thereon.
14a and the individual electrode 14b are formed, and the common electrode 14a and the individual electrode 14b are formed.
The structure up to the structure in which the resistance layer 13 is formed so as to bridge the above is the same as the conventional example described with reference to FIG.

In this embodiment, similarly to the first embodiment, the overcoat layer is formed by the first overcoat layer 15 and the second overcoat layer.
The feature is that it consists of 16 layers.

That is, the first overcoat layer 15 is provided so as to directly cover the upper surface of the resistance layer 13 and the common electrode 14a and the individual electrode 14b for supplying a heating current to the resistance layer 13.

The first overcoat layer 15 is formed by applying a paste obtained by mixing a glass powder with a ceramic powder or the like as a filler using an organic solvent, and applying and firing the paste.

Then, on the upper surface of the first overcoat layer 15, a second
An overcoat layer 16 is provided.

The second overcoat layer 16 is formed by applying and baking a glass paste having no filler such as a ceramic powder. The first overcoat layer 15 is formed so as to fill the depressions D and E described in FIG. The upper part is formed so as to have a substantially convex shape.

The second overcoat layer 16 extends like a band in the main scanning direction and has a width W larger than the width U of the resistance layer 13 in the sub-scanning direction, as described with reference to FIG. It is formed in the range of U <W <2U, which is narrower than double (2U).

As described with reference to FIG. 1, when the width W of the second overcoat layer 16 is smaller than the width U of the resistance layer 13, undulation in the sub-scanning direction indicated by arrows D and E in FIG. 6 occurs. If the step cannot be filled, and W is larger than 2U, the second overcoat layer 16 has low abrasion resistance against sliding with the recording medium, so that the first overcoat layer 15 cannot be moved in the sub-scanning direction. The outer direction of the wear of the first
The overcoat layer 15 is exposed.

Therefore, the width W of the second overcoat layer 16 is set to 2U.
It doesn't make much sense to do so.

For the above reason, the width W of the second overcoat layer 16 is
It is preferable to form in the range of U <W <2U.

By forming the second overcoat layer 16 in such a range, the undulation of the first overcoat layer 15 in the sub-scanning direction is eliminated, and the first overcoat layer 15 maintains the wear resistance with the recording medium. In addition, the second overcoat layer 16 allows the recording medium facing the resistive layer 13 to slide smoothly into contact with the thermal head, thereby maintaining a uniform recording density.

In each of the above embodiments, the second overcoat layer (6, 1
6) is extended in the main scanning direction in a belt shape, so that the sliding accompanying the relative movement between the thermal head and the recording medium is particularly smooth, and wrinkles are not generated on the recording medium, and more uniform recording is performed. Can be made.

It is preferable that the belt-like second overcoat layer has a flat surface in the main scanning direction.

FIG. 3 is an energy consumption-recording density characteristic diagram showing the effect of the thermal head according to the present invention in comparison with the effect of the thermal head according to the prior art.

In the figure, the horizontal axis represents the energy (mJ / dot) supplied to the thermal head, and the vertical axis represents the density of the recording dots (the minimum density of solid black is 1.0).

In the figure, the curve A shows the characteristics of the thermal head according to the present invention, and the curve B shows the characteristics of the thermal head according to the prior art.

As is apparent from this characteristic curve, according to the thermal head of the present invention, since the recording density is uniform over all gradations, it is possible to perform good recording with a small heating current.

FIG. 4 is a schematic process diagram for explaining a method of manufacturing a thick film type thermal head according to the present invention.

This figure relates to the manufacture of the thick-film type thermal head of the embodiment described with reference to FIG.

First, a so-called glass paste made of glass powder and an organic binder is applied and baked on an insulating substrate 1 made of alumina or the like to form a heat storage layer 2. (A) Next, the metal component ratio is Ir: Si: Bi = 1: 1: 1 (atomic ratio)
Solid printing of metal organic matter solution by screen printing,
This is dried at about 70 ° C. and baked at a peak temperature of 800 ° C. for 10 minutes to deposit the resistance layer film 30. (B) After applying and drying a photoresist on the resistive layer film 30, the resist layer film 30 is exposed through a photomask and developed to develop the resistive layer film.
The photoresist at 30 unnecessary portions is removed, and the photoresist is immersed in an etching solution such as an aqueous solution of hydrofluoric acid-nitric acid and melted.

The resistor 3 is formed by this photolithography-etching. (C) After the formation of the resistance layer 3, a metallo organic gold paste is printed on the entire upper surface of the resistance layer 3 by solid printing, followed by firing to form the gold film layer 40. ... (d) A photoresist is applied to cover the upper surface of the formed gold film layer 40, pattern exposure is performed using a mask, and this is developed to remove the photoresist except for a portion to be an electrode. I do.

Thereafter, the portion of the gold film layer from which the photoresist has been removed is etched using an etching solution such as an aqueous solution of iodine-potassium iodide, and a substantially heating portion (dot portion) of the resistance layer 3 is formed.
In addition, the gold film layer other than the part to be the electrode is separated and removed in the sub-scanning direction.

As a result, the common electrode 4a that is partially continuous and the individual electrodes 4b that are independent from each other are formed. (E) Next, the whole of the resistance layer 3, the common electrode 4a and the individual electrode
Except for the electrode connection pad forming portion of 4b, a ceramic paste as a filler was mixed with the glass powder, and the mixture was made into a paste with an organic solvent. For example, 15% by weight of LS201 (trade name) manufactured by Tanaka Massey Organic solvent: for example, diluted with α-terpineol) using a 400-mesh calendering screen.

This is fired at a peak temperature of 800 ° C. to form the first overcoat layer 5. (F) Then, on the upper surface of the first overcoat layer 5, a resistance layer 3
A 400 mesh calender screen having an opening that is not less than the width in the sub-scanning direction and less than twice the width in the sub-scanning direction of the resistive layer 3 and whose opening is continuous in the main scanning direction. Print the paste.

After printing, this is baked in the same manner as described above to obtain the resistance layer 3.
A second overcoat layer 6 having a convex shape above is formed. ... (g) Finally, the surface of the second overcoat layer 6 is 2,000 to 4,000.
Polishing and smoothing using a wrapping sheet of about number.

Through the above steps, a thick film type thermal head as shown in FIG. 1 is obtained.

FIG. 5 is a schematic process drawing for explaining another method of manufacturing a thick film type thermal head according to the present invention.

This figure relates to the manufacture of the thick-film type thermal head of the embodiment described with reference to FIG.

First, a so-called glass paste made of glass powder and an organic binder is applied and baked on an insulating substrate 11 made of alumina or the like to form a heat storage layer 12. (A) Then, a metallo-organic gold paste is printed on the entire upper surface of the heat storage layer 12 by solid printing, and baked to form the gold film layer 140. ... (b) A photoresist is applied to cover the upper surface of the formed gold film layer 140, pattern exposure is performed using a photomask, and this is subjected to a development treatment to remove the photoresist except for a part to be an electrode. Remove.

Thereafter, using an etching solution such as an aqueous solution of iodine-potassium iodide, the portion of the gold film layer 140 from which the photoresist has been removed is etched, and the gold film layer other than the portion serving as an electrode is separated and removed in the sub-scanning direction. I do.

As a result, the common electrode 14a that is partially continuous and the individual electrodes 14b that are independent from each other are formed. ...
(C) Next, the metal component ratio is Ir: Si: Bi = 1: 1: 1 (atomic number ratio)
The metal organic substance solution is solid printed by screen printing so as to fill the space between the common electrode 14a and the individual electrode 14b and to cover the upper surfaces of both electrodes, and is dried at about 70 ° C. and then 800 ° C.
The resist layer 130 is deposited by baking for 10 minutes at the peak temperature. (D) A photoresist is applied on the resistive layer film 130, dried, exposed through a photomask, developed, and removed to remove unnecessary portions of the resistive layer. It is immersed and melted in an etching solution such as a hydrofluoric acid-nitric acid aqueous solution.

By this photolithography etching, the common electrode 14a is formed.
And a plurality of resistance layers 13 bridging the individual electrodes 14b. (E) Next, ceramic powder as a filler is mixed with glass powder except for the entire resistive layer 13 and the portions where the electrode connection pads of the common electrode 14a and the individual electrode 14b are formed. A glass paste made into a paste with the same organic solvent is solid printed using a 400 mesh calendering screen.

This is fired at a peak temperature of 800 ° C. to form the first overcoat layer 15 extremely thin. (F) Then, on the upper surface of the first overcoat layer 15, a resistance layer 13 is formed.
A 400 mesh calender screen having an opening that is not less than the width in the sub-scanning direction and less than twice the width of the resistance layer 13 in the sub-scanning direction, and the opening is continuous in the main scanning direction. Print the paste.

After printing, this is subjected to the same baking as described above, and the resistance layer 13
A second overcoat layer 16 having a convex shape is formed on the second overcoat layer 16. ... (g) Finally, the surface of the second overcoat layer 16 is 2,000 to 4,000.
Polishing and smoothing using a wrapping sheet of about number.

Through the above steps, a thick film type thermal head as shown in FIG. 2 is obtained.

According to this thermal head, the contact area with the platen roller becomes uniform, and the occurrence of uneven recording density is avoided.

The first overcoat layer is formed by applying a mixture of a metal-containing organic compound, instead of the one formed by screen-printing a glass paste composed of glass powder and an organic solvent (organic binder). May be thermally decomposed into a thin layer to form an overcoat layer having good heat radiation characteristics.

The organic material of the resistance layer constituting material in the present invention includes various metal alkoxides, various carboxylate salts such as naphthenate salts and octylate salts, metal acetyl acetate, crown ether, thia crown ether, or cyclam vinegar, -An organic metal compound having a carbon bond.

〔The invention's effect〕

As described above, according to the present invention, it is possible to obtain a thermal head capable of performing uniform recording without unevenness in density, excluding the above-described disadvantages of the related art.
Energy consumption can be reduced as compared with the conventional thermal head.

Further, since the manufacturing equipment is simple, the manufacturing cost can be reduced.

[Brief description of the drawings]

FIG. 1 is a schematic diagram illustrating the structure of a first embodiment of a thick film type thermal head according to the present invention, FIG. 2 is a schematic diagram illustrating the structure of a second embodiment of a thick film type thermal head according to the present invention, FIG. 3 is a graph showing energy consumption vs. recording density characteristics showing the effect of the thermal head according to the present invention in comparison with the effect of the thermal head according to the prior art, and FIG. 4 explains a method of manufacturing a thick film type thermal head according to the present invention. FIG. 5 is a schematic process diagram, FIG. 5 is a schematic process diagram illustrating another method of manufacturing a thick film type thermal head according to the present invention, and FIG. 6 is a schematic diagram illustrating an example of the structure of a conventional thick film type thermal head. FIG. 7 is a schematic view for explaining another example of the structure of this type of conventional thick film type thermal head. 1 ... insulating substrate, 2 ... heat storage layer, 3 ... resistance layer, 4a ...
Common electrode, 4b: individual electrode, 5: first overcoat layer, 6: second overcoat layer.

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-61-135762 (JP, A) JP-A-63-216760 (JP, A) JP-A-3-219967 (JP, A) JP-A-4-1992 239657 (JP, A) (58) Field surveyed (Int. Cl. ⁷ , DB name) B41J 2/335

Claims (2)

(57) [Claims] A heat storage layer, a plurality of resistance layers arranged in the main scanning direction, electrodes for supplying power to the resistance layers, an overcoat layer for covering the plurality of resistance layers and the electrodes are laminated on an insulating substrate. Wherein the overcoat layer comprises a first overcoat layer and a second overcoat layer laminated on the first overcoat layer, wherein the second overcoat layer Is formed by applying and baking a glass paste containing no filler, and is formed in a band shape in the main scanning direction with a width W in the sub-scanning direction covering the plurality of resistance layers, and the width W When the effective width in the sub-scanning direction of the resistive layer is U, which is the distance between the power supply electrodes connected to the resistive layer, U <W <2U. Film type thermal head. 2. An insulating substrate comprising a heat storage layer, a plurality of resistance layers arranged in the main scanning direction, electrodes for supplying power to the respective resistance layers, an overcoat layer for covering the plurality of resistance layers and the electrodes. In the method for manufacturing a thick film type thermal head, after forming the first overcoat layer covering the plurality of resistive layers and the electrodes, screen printing of a filler-free glass paste is performed on the resistive layer. A method of manufacturing a thick-film type thermal head, comprising: forming a second overcoat layer that fills a dent of the first overcoat layer and is substantially convex on the first overcoat layer.