JPH0667632B2 - Thermal head - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a thermal head for printing by selectively heating a large number of heating portions.

2. Description of the Related Art An example of a conventional thermal head is shown in FIG. This thermal head 1 is formed by sequentially laminating a glass glaze layer 3 and a heating resistance layer 4 on an alumina substrate 2, and further laminating an electrode layer 5 and a protective layer 6 in this order. The electrode layer 5 is made of aluminum (hereinafter referred to as Al). As the protective layer 6, the structure shown below is often used. That is, it has a structure such as a single-layer thin film of SiO ₂ and Ta ₂ O ₅ laminated single-layer thin film of Si ₃ N ₄ single-layer thin film of SiC single-layer thin film of Al ₂ O ₃ . FIG. 2 shows the cross-sectional shape of one dot of the thermal head. In practice, the electrode layer 5 is etched into a predetermined pattern, so that such a laminated structure has a large number of dots. It is formed continuously.

Note that FIG. 2 shows a state in which the thermal head 1 is in contact with the platen 8 via the recording paper 7 as an example of actually using the thermal head 1.

In the case of such a structure, a heat sensitive paper or a thermal transfer paper is used as the recording paper 7, and the heating resistance layer 4 in the portion where the dots are to be formed is heated. The heat generation of the heating resistance layer 4 is performed by energizing the electrode layer 5. As a result, dots are formed on the recording paper 7 at the portions that come into contact with the heat generating resistance layer 4 that has generated heat. Therefore, if the recording paper 7 and the thermal head 1 are relatively moved by rotating the platen 8 and dots are selectively formed in the process, the recording paper 7 is printed.

Problems to be Solved by the Invention In recent years, in a printing apparatus using the thermal head 1,
Higher densities, color printing, multiple printing, gradation printing, etc. are being advanced. In any of these printings, it is necessary to increase the printing speed. For this reason,
Friction between the protective layer 6 and the recording paper 7 increases. at the same time,
When high-speed printing is performed, the time margin provided for forming one dot is naturally small. Therefore,
In order to form a clear dot in a short time, it is necessary to increase the applied voltage applied to the heating resistance layer 4. Therefore, the temperature of the thermal head 1 rises.

Further, the recording paper 7 to be printed by the thermal head 1 is not always ideal one. Due to various circumstances on the user side, special ones such as those having poor color development sensitivity or low smoothness, and thermal paper in which a color former is applied to thick paper may be used. Therefore, in order to perform high-quality printing on such a special recording paper 7 without print unevenness or print blurring, the thermal head 1 is pressed with a platen 8 with a pressing force about twice as high as usual.
Need to be pressed. Therefore, the friction between the protective layer 6 and the recording layer 7 increases. At the same time, cracks are likely to occur in the protective layer 6 at the cut portions of the electrode layer 5.

Therefore, the material used as the protective layer 6 must be capable of supporting high-speed printing and strong pressing force on the platen 8 and maintaining the initial performance. However, the above-mentioned structures (1) to (3) exemplified as the protective layer 6 cannot completely deal with various situations that occur when such high speed printing or printing corresponding to a special recording paper is performed. It has the drawback. The drawbacks of the structures (1) to (3) will be individually described below.

The SiO ₂ / Ta ₂ O ₅ laminated thin film has the drawbacks of low hardness and poor wear resistance. Therefore, it is not suitable for high-speed printing or printing on special recording paper.

The Si ₃ N ₄ single-layer thin film has a drawback that cracks are likely to occur at the cut portion of the electrode layer 5. This is because Al, which is commonly used as the electrode layer 5 is soft, high hardness Si ₃ N ₄
This is because the internal stress of the protective layer 6 is increased. Therefore, it is not suitable for printing corresponding to a special recording paper which needs to be strongly brought into contact with the platen 8.

The SiC single-layer thin film is chemically unstable and easily reacts with the color former on the recording paper 7, resulting in abnormal wear. Such bad habit becomes more prominent when the thermal head 1 is heated to a high temperature. It also has the drawback of being poor in crack resistance. Therefore, it is not suitable for high-speed printing or printing on special recording paper.

The Al ₂ O ₃ single-layer thin film has a drawback of being inferior in moisture resistance. Moreover, the higher the temperature of the thermal head 1, the worse the moisture resistance becomes. Therefore, Al, which is usually used as the electrode layer 5, is easily corroded by evaporation of water contained in the recording paper 7 and ions, so-called electrolytic corrosion. When the electric field corrosion occurs in this way, the resistance value of the electrode layer 5 rises, which causes dot dropout during printing. Therefore, it is not suitable for high speed printing.

Means for Solving the Problems In the present invention, the protective layer formed as the uppermost layer on the substrate is formed of a mixture of Al ₂ O ₃ and SiO ₂ containing Al ₂ O ₃ as a main component.

Action Such a protective layer exhibits a predetermined performance with respect to wear resistance, crack resistance, chemical stability, moisture resistance and the like. Therefore, even if high-speed printing is performed, the wear is small and the inconvenience caused by high temperature is negligible. Further, even if the pressure contact force to the platen is increased in order to deal with a special recording paper, it is possible to prevent the occurrence of cracks in the cut portion of the electrode layer, as well as the wear.

Embodiment An embodiment of the present invention will be described with reference to FIG. This embodiment shows a film structure corresponding to one dot in the thermal head 10. That is, the substrate 11 made of Al ₂ O ₃ is provided, and the glass glaze layer 12 is provided on the substrate 11.
Are formed. Further, the heating resistance layer 13, the electrode layer 14, and the protective layer 15 are sequentially laminated.

The heat generating resistance layer 13 is a 1000 Å thin film formed of BaRuO ₃ by the RF sputtering method.

The electrode layer 14 is made of aluminum (hereinafter referred to as Al) DC
It is a 1 μm thin film formed by the sputtering method.
The electrode layer 14 is formed into a predetermined shape by a fine processing technique such as photo-etching, and the heat generating resistor layer 13 in the removed portion serves as a heat generating resistor 16. This heating resistor
The thermal head 10 has a large number of 16 arranged in an array, and the size of one dot is 100 μm × 120 μm and 1 m.
Eight dots are formed per m ² .

The protective layer 15 is a 5 μm thin film formed by forming a mixture of Al ₂ O ₃ and SiO ₂ by RF sputtering or electron beam evaporation. The mixing ratio is 65 mol% for Al ₂ O _{3 and 3} for SiO _2.
It is 5 mol%.

In such a configuration, the printing operation by the thermal head 10 is the same as that described as a conventional example, and the description thereof is omitted. On the other hand, the protective layer 15 in the present embodiment
Has a wear resistance, a crack resistance, a chemical stability, and a moisture resistance, all of which exceed predetermined standards. Therefore, high-speed printing and printing corresponding to special recording paper can be performed without inconvenience. Below, this will be verified based on the measured values.

First, in order to examine wear resistance, Vickers hardness was measured. For comparison, the protective layer having the following structure described in the section of the prior art was also measured at the same time.

Thin film of SiO ₂ and Ta ₂ O ₅ laminated Single layer thin film of Si ₃ N ₄ Single layer thin film of SiC Single layer thin film of Al ₂ O ₃ These protective layers are the same as the protective layer 15 in this example and the conditions. In order to make the same, the thin film was 5 μm in thickness. As a result of the experiment, the measured values shown in Table 1 were obtained. As is clear from Table 1 In addition, the protective layer 15 which is a mixture of Al ₂ O ₃ and SiO ₂ does not have particularly high hardness in comparison with other materials, but has a Vickers hardness of 500 to 700 km / mm ^2. ₂ / Ta ₂
It is superior in hardness to the protective layer formed by the laminated thin film of O ₅ . here,
When performing high speed printing or printing corresponding to special recording paper,
When the Vickers hardness is about 500 to 700 km / mm ² , it wears out quickly and cannot be used in actual use. However, when the Vickers hardness is 1000 to 1200 km / mm ² , the wear resistance is tentatively obtained. Therefore, it can be said that even the protective layer 15 of the present embodiment has sufficiently secured abrasion resistance for high-speed printing and the like.

Then, in order to examine the moisture resistance, a pre-tackiness tester test was conducted. The test objects are all the ones obtained by measuring the above-mentioned Vickers hardness. The test conditions are 120 ° C and 2 atm.
Leave for 8 hours. As a result, only the protective layer formed of the Al ₂ O ₃ single-layer thin film generated stripes or stains that seemed to be affected by the chemical, and no abnormality occurred in the other. Therefore, it was confirmed that only the protective layer made of Al ₂ O ₃ had poor moisture resistance.

Furthermore, the thermal head 10 was actually attached to the printing device to perform an experiment. For comparison, those having the protective layers having the above structures 1 to 3 were also tested under the same conditions. The experiment was conducted under the condition of high-speed printing corresponding to a special recording paper. Specifically, as the recording paper (not shown), a special paper having a low color development sensitivity in which a white agent or a color developing agent is applied to a thick paper is used. Therefore, the pressing force of the thermal head 10 against the platen (not shown) is 900 to 1000 g / cm ^{2, which} is about twice the normal pressure. The applied energy was set to 50 mJ / sec, and the recording paper feed speed was increased to 75 mm / sec. The experimental results for the protective layer 15 and the other four types of protective layers are shown below.

First, the protective layer consisting of a laminated thin film of SiO ₂ / Ta ₂ O ₅ is about 3
There were numerous large scratches on the surface when the vehicle was driven for km. It is presumed that this is because foreign matter such as hard particles and dust in the air contained in the recording paper was caught in the pressure contact portion with the platen. After that, when running for about 18 km, the scratches were generated on the heating resistance layer 12
And the printing was defective. Therefore, it was also referred to as the measured value of Vickers hardness, and it was proved that such a protective layer was inferior in abrasion resistance.

Next, in the protective layer made of a single-layer thin film of Si ₃ N ₄ , the protective layer film swells in the central portion of the heating resistor 16 after traveling for about 3 km,
After running for about 5 km, the part was missing and printing failure occurred. It is considered that cracking occurred in the cut portion of the electrode layer 14.

Next, the protective layer made of a single layer of SiC was cracked after running for about 3 km, and the heating resistance layer 13 was scratched, resulting in defective printing.

Next, the protective layer consisting of a single-layer thin film of Al ₂ O ₃ is about 10 km.
At the time of running, the resistance value of the electrode layer 14 increased by several%, and
At the time of traveling 16 km, the resistance value of the electrode layer 14 increased by several tens of percent, and the dot omission occurred. This is because the electrode layer 14 was galvanically corroded, which was also in agreement with the test results of the Prescler-Kutker test, and it was proved that such a protective layer was inferior in moisture resistance.

Then, regarding the protective layer 15 in this embodiment, 30 km
After running, there is no crack or swelling of the film, and the electrode layer 14
The change in the resistance value was stable from the initial state to about 1%.
This proves that the hardness is tentative as confirmed by Vickers hardness measurement and that there is no problem in moisture resistance as confirmed by the Prescler-Kutker test.
It was also proved to be excellent in crack resistance and chemical stability.

On the other hand, Al used as the electrode layer 14 is an inexpensive material that has been generally used in the past, and since it has high flexibility, it is easy to increase the internal stress in the protective layer 15, which is considered to be a cause of cracking. Was there. However, it has been confirmed by experiments that cracking does not occur in the protective layer 15 even if such an electrode layer 14 is used.

Regarding the mixing ratio of SiO ₂ in the protective layer 15, if it is 60 mol% or more, the hardness decreases and the wear resistance is poor, and if it is 5 mol% or less, the crack resistance and the chemical stability are poor. I was confirmed. Therefore, in practice, it is desirable to form the protective layer 15 mainly composed of Al ₂ O ₃ having a mixing ratio of SiO ₂ of 20 mol% to 45 mol%.

EFFECTS OF THE INVENTION The present invention provides that the uppermost protective layer of the laminated structure on the substrate is made of Al.
Since it is formed of a mixture of Al ₂ O ₃ and SiO ₂ containing ₂ O ₃ as a main component, it is possible to obtain a protective layer having excellent wear resistance, crack resistance, moisture resistance and chemical stability. High-speed printing and printing compatible with special recording paper are possible, providing high density and color printing, multiple printing and gradation printing, and recording paper with poor color development sensitivity and low smoothness It has the effect of enabling printing on special objects such as objects and contributing to the expansion of printability.

[Brief description of drawings]

FIG. 1 is a vertical sectional side view of one dot showing an embodiment of the present invention, and FIG. 2 is a vertical sectional side view of one dot showing an example of the prior art. 11 …… Substrate, 13 …… Heating resistance layer, 14 …… Electrode layer, 15 ……
Protective layer

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Claims (2)

[Claims] 1. A thermal head comprising a heating resistor layer, an electrode layer having a predetermined pattern, and a protective layer, which are sequentially laminated on an insulating substrate, wherein the protective layer contains Al ₂ O ₃ as a main component. A thermal head formed by a mixture of Al ₂ O ₃ and SiO ₂ . 2. The thermal head according to claim 1, wherein the electrode layer is formed of aluminum or an alloy containing aluminum as a main component.