JPH04259571A - Thermal head - Google Patents

Abstract

PURPOSE:To prevent the occurrence of a crack in a high-heat conductivity film which is provided in a protective film to reduce density unevenness in a thermal head used for a facsimile terminal equipment or a printer. CONSTITUTION:After a glaze layer 5, an electrode 4, and a resistor 3 are formed on an alumina substrate 6, a thin protective film 1 is formed so as to cover these layers. After that, a film 2 made of a mixture of a metal or metallic oxide with inorganic fine particle is provided correspondingly to a position substantially just above the resistor 3 on the protective film 1. Lastly, a protective film 1 is again formed so as to cover these layers.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a thermal recording device or a thermal transfer recording device used in a recording section of a facsimile or a printer, and more particularly to a thermal head.

0002

[Prior Art] A conventional thermal head has a structure in which a glaze layer, an electrode, a resistor, and a protective film are laminated on an insulating substrate.Due to the differences in the formation process of each film,
There are two types: thick film types, which are formed by printing and baking, and thin film types, which are formed by vapor deposition, sputtering, or CVD. In the thick film type thermal head, the electrode material is Au, the resistor material is RuO2, and the protective film material is SiO2/PbO (lead borosilicate glass).
However, each is commonly used. On the other hand, in thin film type thermal heads, Al is commonly used as the electrode material, metal compounds or metal oxides as the resistor material, and Ta2O5 or Si3N4 as the protective film material.

In thermal recording or thermal transfer recording using a thermal head, a predetermined voltage is applied to a resistor using the above-mentioned electrodes, and the Joule heat generated thereby is transmitted through a protective film on the resistor to the thermal recording paper. Alternatively, the ink reaches a thermal transfer ink film, and printing or printing is performed by transferring the ink from the film to the transfer paper by coloring by chemical reaction or melting or sublimation of the ink by heat. Therefore, when a protective film made of a material with high thermal conductivity is used, the thermal energy generated in the resistor is transmitted to the surface of the protective film in a short time, and the temperature distribution on the surface of the protective film is The temperature distribution will be similar to that on the body. On the other hand, when using a protective film made of a material with low thermal conductivity, the time it takes for the thermal energy generated in the resistor to be transmitted to the surface of the protective film is The temperature distribution on the surface of the protective film is different from the temperature distribution on the resistor, and the heat generation area is considerably reduced in the process of thermal energy propagating through the protective film. are doing.

[0004] The reduction of the heat generating area on the surface of the protective film due to the low thermal conductivity of the material used for the protective film reduces the area of the printed pixel corresponding to the resistor-element in thermal recording or thermal transfer recording. An uncolored area in the case of thermal recording or an untransferred area in the case of thermal transfer recording is generated between pixels of two adjacent prints or prints that should originally be continuous. Such uncolored or untransferred areas between pixels of two adjacent prints or prints appear as white streaks in the prints or prints output by a facsimile or printer, and can significantly reduce print quality. lower. Such deterioration in image quality is more noticeable in thermal transfer recording methods using sublimation ink, which are often used for output from high-quality printers such as video printers, than in thermal recording.

[0005] Also, in terms of the types of thermal heads,
Since the thermal conductivity of the protective film is smaller for SiO2 and PbO than for Ta2O5 and Si3N4, this phenomenon is more noticeable in thick-film type thermal heads.

[0006] Conventionally, as a method for preventing the deterioration of image quality due to the low thermal conductivity of the protective film, there has been proposed
As disclosed in Japanese Patent No. 111563, a structure in which a metal film is sandwiched inside a protective film has been proposed.

[0007]

However, the conventional structure in which a metal film is sandwiched inside a protective film has the following drawbacks. In other words, in order to sandwich a metal film inside the protective film, first, after forming the resistor, the protective film is formed by printing and baking, and then the metal film is formed on top of it in the same way. It is necessary to form a protective film by printing and baking so as to cover the protective film and metal film. However, when such a process is actually carried out, cracks may occur in the previously formed metal film when a protective film is printed and fired after the metal film is formed. When such cracks occur in the metal film, the temperature distribution on the surface of the protective film is greatly disturbed, resulting in a significant deterioration of image quality. The cause of this crack is that the adhesion of the metal film on the protective film made of glass that was first formed is not strong enough to this glass film, and when the protective film is fired on the metal film, the protective film on the metal film is The viscosity of the glass, which is the material of the membrane, becomes lower. As a result, although the metal film is sandwiched between upper and lower protective films made of glass, the binding force from these glass films becomes weaker during the above-mentioned firing process, and the metal film tends to shrink easily. This is thought to be because self-shrinkage occurs and cracks occur in areas where the film strength is weak. Considering the mechanism, the occurrence of such cracks is more pronounced as the viscosity of the glass material used for the protective film during firing is lower. The viscosity of the glass material during firing has a strong correlation with the surface smoothness of the protective film formed after firing, and the lower the glass viscosity during firing, the smoother the surface of the protective film formed after firing. The higher the glass viscosity during firing, the worse the surface smoothness of the protective film formed after firing. The smoothness of the surface of the protective film has a small effect on image quality in thermal recording used in facsimiles, etc.
In thermal transfer recording using sublimation ink, which is used in high-quality printers such as video printers, if the surface of the protective film is not smooth, density unevenness will occur, reducing print quality. It is necessary to use a glass material with good smoothness. In this way, in order to obtain a thermal head with high image quality that can be used in video printers, it is necessary to use a glass material with a good surface smoothness as the protective film material. It is necessary to use a material having a low glass viscosity, and when such a material is used, the above-mentioned cracks in the metal film are particularly likely to occur. Therefore, the metal film that was originally inserted into the protective film to improve the image quality actually deteriorated the image quality due to the occurrence of cracks.

One possible method for preventing the occurrence of such cracks is to make the thickness of the metal film sandwiched inside the protective film sufficiently thick to suppress self-shrinkage of the metal film. However, if the metal film is made too thick, most of the thermal energy generated in the resistor will propagate through the protective film made of glass, which has low thermal conductivity, and reach the surface of the protective film, rather than the metal film, which has high thermal conductivity. It propagates through the film and escapes in the main scanning direction, causing the density of a printed pixel corresponding to one resistor element to become faint and blurred, and two adjacent printed pixels to interfere with each other due to the metal film. This method had a major drawback in that it resulted in an output image with extremely poor resolution and sharpness of contours, so it could not be applied in practice.

An object of the present invention is to use a glass material with good surface smoothness and low viscosity during firing as a protective film, and to have a film thickness in the protective film that does not cause deterioration of the resolution of the output image. It is an object of the present invention to provide a thermal head capable of supporting high image quality, which is capable of sandwiching a thin metal film, and thereby can be applied to high image quality printers such as video printers.

0010

[Means for solving the problem] A method of improving image quality by sandwiching a metal film inside the protective film is possible when a glass material with a low viscosity during firing with good surface smoothness is used as the protective film. There was a problem in that cracks were generated in the metal film during firing of the protective film. Further, in order to avoid this problem, increasing the thickness of the metal film can suppress the occurrence of cracks in the metal film, but there is a drawback that the resolution of the output image is lost. Of course, if glass with high viscosity during firing is used as the protective film material, cracks in the metal film can be suppressed, but in this case, the surface of the protective film after firing is not smooth, resulting in unevenness of the surface. There was a drawback that density unevenness appeared in the output image. In this way, in the conventional technology, a glass material with good surface smoothness and low viscosity during firing is used as a protective film, and a thin metal film that does not cause deterioration of resolution is used in the protective film. It was difficult to insert it.

In order to solve this problem and achieve the above object, the present invention adds inorganic fine particles to a metal paste for forming a metal film sandwiched in a protective film. Of course, the metal film inserted into the protective film may be of any material as long as its thermal conductivity is higher than that of the glass used as the protective film material. The film is not limited to a metal film, but may be a metal oxide film. Further, the amount of the inorganic fine particles added is suitably between 0 wt % and 40 wt % so as not to deteriorate the surface smoothness of the metal film formed. Furthermore, for the same reason, it is appropriate that the average particle diameter of the inorganic fine particles added be 1 μm or less.

0012

[Operation] When inorganic fine particles are added to the metal paste to form the metal film sandwiched in the protective film, the inorganic fine particles are dispersed in the metal film formed using this paste. Since it acts as a reinforcing agent for the metal film itself, the breaking strength of the metal film is improved, and the tendency of the metal film to shrink is suppressed.

Therefore, if the metal film of the present invention, which is formed by printing and firing a metal paste to which inorganic fine particles are added, is used as the metal film sandwiched in the protective film, even if the metal film has a good surface smoothness during firing, Even if a glass material with a low viscosity is used as the protective film, shrinkage of the metal film during firing of the protective film and the occurrence of cracks in the metal film due to this can be avoided. Of course, if inorganic fine particles are added to the metal film as in the present invention, the breaking strength of the metal film is improved, so there is no need to increase the thickness of the metal film to prevent cracks in the metal film. Therefore, the thickness of the metal film can be designed with priority given to image quality, and the aforementioned deterioration in resolution due to an increase in the thickness of the metal film can be avoided.

[0014] As described above, by using a metal film to which inorganic fine particles are added as a metal film sandwiched between a protective film made of glass with low viscosity during firing and which has a good surface smoothness, there is no cracking and deterioration in resolution. It is possible to form a thin metal film in the protective film, and it is possible to obtain a thermal head compatible with high image quality that can be applied to high image quality printers such as video printers using a sublimation thermal transfer method.

[0015]

[Embodiment] An embodiment of the present invention will be described below with reference to FIG. In FIG. 1, a glaze layer 5 is formed on an alumina substrate 6. Then, on the glaze layer 5, an Au electrode film with a thickness of 0.6 μm made of a metal organic Au material is formed by printing and baking, and on the Au electrode film, a resistor film with a thickness of 3 to 10 μm made of RuO2 is formed. The body is formed by printing and firing. Thereafter, a protective film 1 made of a lead borosilicate glass material is formed to a thickness of about 3 μm by printing and baking so as to cover the resistor 3 and electrodes 4. After first forming the protective film 1 with a thickness of about 3 μm, as shown in FIGS. 1 and 2, a layer of Au as a material with higher thermal conductivity than the protective film is placed almost directly above the resistor 3. A paste containing fine particles of Al2O3 is printed and fired at a temperature of 700 to 900°C to form a film with a thickness of about 1 μm. This material has a thermal conductivity higher than that of the protective film 1 when approximately 20 wt% of Al2O3 fine particles are added to the Au paste, and a protective film 1 is added on top of the fired paste made by adding Al2O3 fine particles to the Au paste. Even if the thickness is about 3 μm, cracks 7 do not occur in a film formed by firing a paste in which Al2O3 fine particles are added to an Au paste, which is appropriate. By baking this Au paste with Al2O3 fine particles added, a film with better thermal conductivity than the protective film is formed, and by printing and baking a protective film 1 of about 3 μm over the entire surface including the film, the main A thermal head of the example is obtained.

FIG. 2 shows cracks 7 that occur in the film when Au paste, which is described in the prior art, is used as the material for the film 2. The thermal head is constructed by forming a glaze layer on an alumina substrate, as in the embodiment shown in FIG. After that, an Au film of about 1 μm is formed at a position almost directly above the resistor, and finally a protective film is formed to cover the entire resistor. When Au is used as a material with good thermal conductivity inside the protective film, cracks 7 are very likely to occur when the protective film printed to cover the entire surface is fired after the Au film is formed. many.

One possible method for preventing such cracks is to use glass, whose viscosity does not decrease significantly during firing, as the material for the protective film. FIG. 3 shows the relationship between temperature and viscosity for three types of glasses 8, 9, and 10 whose viscosities at the firing temperature To are η1, η2, and η3. The glass 10 has a very low viscosity η3 at the firing temperature To, and therefore easily generates cracks 7. However, if glass 8 having a very high viscosity η1 at the firing temperature To is used as the protective film material, the cracks 7 can be prevented from occurring. However, in this case, another problem occurs, which will be explained with reference to FIG. That is, FIG. 4 shows the relationship between the viscosity of glass at the firing temperature and the surface roughness of the glass film after firing. The glass 10 has a low viscosity η3 at the firing temperature To, and a very small surface roughness R3 after firing. Therefore, when a thermal head using the glass 10 as a protective film is used in a high-quality printer such as a video printer, density unevenness due to surface roughness is hardly observed. However, when a thermal head using glass 8 as a protective film is used in a similar high-quality printer, the viscosity η1 at the firing temperature To is high and cracks 7
Although this does not occur, the surface roughness R1 after firing becomes very large, and density unevenness caused by the surface roughness becomes noticeable.

In this example, Al is added to the Au paste as a material for the film provided inside the protective film and having better thermal conductivity than the protective film.
By using a paste containing about 20 wt% of 2O3 fine particles and baking the paste at 700 to 900°C to form a film with good thermal conductivity of about 1 μm in the protective film,
Since the film with good thermal conductivity has no cracks and the glass 10 with small surface roughness after firing can be used as the protective film material, it is possible to create a thermal head without density unevenness caused by surface roughness. Can be done. It is thought that the Al2O3 fine particles added to the Au paste have the effect of improving the strength of the Au film and making it difficult for cracks to occur.

[0019] When a paste obtained by adding Al2O3 fine particles to Au paste is used as a material for a film with better thermal conductivity than the protective film provided within the protective film, the film thickness is 2 μm.
Preferably the following: The reason for this will be explained with reference to FIG. FIG. 5 shows the relationship between the film thickness of a film with good thermal conductivity provided in the protective film and the sense of resolution. The resolution is evaluated subjectively, with the best resolution being rated 10 and the worst resolution being 0. As is clear from FIG. 5, the resolution during printing deteriorates rapidly as the thickness of the film with good thermal conductivity provided in the protective film is increased beyond 2 μm. This is because if the film with good thermal conductivity becomes too thick, the heat generating area on the surface of the protective film will expand, causing two adjacent prints or pixels of print to overlap.

[0020] Also, Al2O added to the Au paste
3. The amount of fine particles added is greater than 0 wt% and 40% by weight.
It is preferable to make it less than %. The reason for this will be explained using FIGS. 6 and 7. FIG. 6 shows the relationship between the amount of Al2O3 fine particles added to the Au paste and the number of cracks that occur when the paste is formed in the protective film. As is clear from this figure, when using Au paste to which no Al2O3 fine particles are added,
Although cracks were observed to occur at nine locations, the occurrence of cracks was completely suppressed in the Au paste containing 20 wt%. In this way, in order to suppress the occurrence of cracks, it is sufficient to add more than 0 wt % of Al2O3 fine particles. On the other hand, FIG. 7 shows the relationship between the amount of Al2O3 fine particles added to the Au paste and the surface roughness when the paste is printed and fired. As is clear from this figure, as the amount of Al2O3 fine particles added to the Au paste increases, the surface roughness increases when the paste is printed and fired. It can be seen that when the content exceeds 40 wt%, the surface roughness increases rapidly. If the amount of Al2O3 fine particles added to the Au paste added with Al2O3 fine particles provided in the protective film is kept below 40%, the deterioration of the surface roughness will not be so large and will be caused by surface irregularities. It can be seen that the density unevenness is also sufficiently small. In this way, Al2O3 added to Au paste
It can be seen that the amount of fine particles added is preferably greater than 0 wt % and less than 40 wt % from the viewpoint of preventing crack generation and reducing surface roughness.

In this example, Au paste with Al2O3 fine particles added is used as the material for the film with good thermal conductivity provided in the protective film, but of course the material is not limited to this material. Instead, Ag paste, Cu paste, Al paste, RuO2 paste, etc. may be used. In addition, the fine particles added are also Al2O
3 Not limited to fine particles, but also ZrO2, SiC, T
Any inorganic fine particles such as iC, BC, Si3N4, BN, etc. may be used.

[0022]Also, in this example, a thick film method is used for the material and film formation method, but the invention is not limited to this, and a thin film method using vapor deposition, sputtering, or CVD may also be used. .

Another embodiment of the present invention will be explained using FIG. The resistors up to the resistor 3 are formed by the same method as described in Example 1, and then the first layer protective film 10 is formed to a thickness of about 3 μm so as to cover the resistor and the electrodes. The material for the first layer protective film is a lead borosilicate glass material with a relatively high softening point of about 700°C. This is done by adding Al2O3 to the Au paste after forming the first protective film 1b.
A film 2 with good thermal conductivity made of a material containing fine particles,
This is to prevent the first layer protective film from flowing when firing the second layer protective film 1a. After forming the first protective film, Al
An Au paste added with 2O3 is printed at a position almost directly above the resistor 3 and fired at a temperature in the range of 700 to 900°C. Finally, an Au film containing Al2O3 fine particles,
The second protective film 1a is formed by printing and firing a material different from the first protective film, which is also a lead borosilicate glass material, so as to cover the first protective film. The second layer protective film material is a material with a relatively low softening point or Al2O
3. A material with no addition of fine particles or a material with a very small amount of addition is selected. This is effective in improving surface smoothness. Further, in order to suppress the generation of static electricity during printing, conductive fine particles may be added to the glass paste that is the material of the second layer protective film. The thermal head made in this way consists of an Au film doped with Al2O3 fine particles sandwiched between the first protective film 16 and the second protective film 1a.
This thermal head is ideal for high-quality printers such as video printers because it does not cause any cracks in the film and the surface of the head is extremely smooth. As in Example 1, instead of Au paste, Ag, Cu, A
Of course, pastes such as RuO2 and RuO2 may also be used. Further, the fine particles to be added do not need to be limited to Al2O3 fine particles, and ZrO2, SiC, TiC, BC, Si3N
4. Any inorganic fine particles such as BN may be used. Further, the film forming method is not limited to the thick film method, but may also be a thin film method.

[0024]

According to the present invention, by providing a film made of a mixture of metal or metal oxide and inorganic fine particles within the protective film as a film having better thermal conductivity than the protective film, a high thermal conductivity film can be obtained. It is possible to make a thermal head particularly suitable for high-quality printers, which has no cracks and has a small surface roughness of the protective film.

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional view of a thermal head having a metal film with inorganic fine particles added to the protective film.

FIG. 2 is a top view showing cracks in the metal film within the protective film.

FIG. 3 is a characteristic diagram showing the relationship between glass temperature and viscosity.

FIG. 4 is a characteristic diagram showing the relationship between the viscosity of glass during firing and the surface roughness after firing.

FIG. 5 is a characteristic diagram showing the relationship between the thickness of the metal film in the protective film and the resolution of the output image.

FIG. 6 is a characteristic diagram showing the number of cracks generated in an Al2O3-added Au film.

FIG. 7 is a characteristic diagram showing the surface roughness of an Al2O3-added Au film.

FIG. 8 is a cross-sectional view of a thermal head having a metal film in which inorganic fine particles are added to a double-layered protective film.

[Explanation of symbols]

1... Protective film, 2... Au film added with Al2O3 fine particles,
3...Resistor, 4...Electrode, 5...Glaze layer, 6...Alumina substrate.

Claims (10)

[Claims] Claim 1: A glaze layer, on a substrate having electrical insulation properties.
In a thermal head formed by laminating an electrode, a heating resistor, and a protective film, a film made of a material having a higher thermal conductivity than the protective film is provided inside the protective film, and the film is made of a metal or a metal oxide, A thermal head characterized by being made of a mixture with inorganic fine particles. [Claim 2] A glaze layer on a substrate having electrical insulation properties;
In a thermal head formed by laminating an electrode, a heating resistor, and a protective film, the protective film is configured in multiple layers, and a film made of a material having a higher thermal conductivity than the protective film is provided between the layers of the protective film, and the A thermal head characterized in that the film is made of a mixture of metal or metal oxide and inorganic fine particles. 3. A thermal head using one or more materials selected from Ag, Cu, Al, and RuO2 as the metal or the metal oxide according to claim 1. 4. The inorganic fine particles according to claim 1,
Al2O3, ZrO2, SiC, TiC, BC, Si3
A thermal head using one or more inorganic fine particles selected from N4 and BN. 5. A mixture of a metal or a metal oxide and inorganic fine particles is used as the film made of a material having a higher thermal conductivity than the protective film provided in the protective film according to claim 1; A thermal head with a mixed amount of fine particles of 40wt% or less. 6. The thermal head according to claim 1, wherein the protective film is made of a material having a higher thermal conductivity than the protective film and has a thickness of 2 μm or less. 7. The inorganic fine particles according to claim 2,
Al2O3, ZrO2, SiC, TiC, BC, Si3
A thermal head using one or more inorganic fine particles selected from N4 and BN. 8. The film provided between the plurality of multilayered protective films according to claim 2, which is made of a material having a higher thermal conductivity than the protective films, is made of a metal or metal oxide and inorganic fine particles. using a mixture of
Thermal head with 0wt% or less. 9. The thermal head according to claim 2, wherein a film made of a material having a higher thermal conductivity than the protective film provided between the plurality of multilayered protective films has a thickness of 2 μm or less. 10. A thermal facsimile using the thermal head according to claim 1 in a recording section.