JPH06183046A - Thermal printer - Google Patents

Abstract

PURPOSE:To obtain a thermal print head having high abrasion resistance by forming a heating resistor composed of a thin film resistor of specific alloy and a thin film conductor of specific metal on an alumina ceramic substrate applied with a glazed glass layer. CONSTITUTION:A glazed glass layer 1 having average coefficient of linear expansion of about 6.0X10<-6>/ deg.C at 30-700 deg.C is formed by firing on an alumina ceramic substrate 6 having average coefficient of linear expansion of about 7.6X10<-6>/ deg.C within same temperature range. Heating part is formed only of a thin film resistor 2 of Cr-Si-SiO2 alloy and a barrier metal thin film conductor 3 is formed of thin film of Cr. Furthermore, a thin film conductor 4 of Ni is formed and when the length of the thin film conductor 4 is short, thin film conductor 3 only of Cr may be employed and thereby fabrication process is shortened and cost is reduced. Ni, Mo, W or Ta may be used in place of Cr.

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 such as a facsimile or printer.

[0002]

It is well known that a thin film thermal print head is one of important parts for thermal recording and thermal transfer recording (hereinafter referred to as thermal recording) used in recording devices such as facsimiles and printers. The basic configuration example is shown in FIG.

The glaze glass layer 11 is composed of a glass layer having a thickness of 50 to 100 μm and poor in thermal conductivity provided on the alumina ceramic substrate 10, and the heat generation amount of the heat generation resistor 17 is as high as possible. It works adiabatically so as to conduct to the anti-oxidation layer 15 and the abrasion resistant layer 16 side,
The thickness is optimized so that heat can be quickly transferred to the substrate 10 side during cooling. The average coefficient of linear expansion of the alumina ceramic substrate 10 at 30 to 1300 ° C. is about 8.5 × 10 ⁶ / ° C.
A material in which the average linear expansion coefficient of the glazed glass layer fired at 300 ° C. is also adjusted to about 7.0 × 10 ⁶ / ° C. is used.

The thin film resistor 12 is heated to 250 to 300 ° C. by a pulsed current of 2 ms, for example, and then heated to 2 ° C.
The characteristic is that the extremely severe operation of dropping to the original temperature in a cooling time of 0 ms is repeated 10 ⁸ times or more, and the rate of change in resistance during that time must remain within ± 10% or less. There is. Further, since the practical thickness limit of the thin film is 500 to 1000 Å, there is a circumstance that it is difficult to use unless the specific resistance is about 1000 to 2000 μΩcm. Ta ₂ N, TiOx, B ₂ Hf, etc. are often used as the few resistor materials satisfying these conditions from old days. However, when they are heated in air, they will be oxidized and burned. The antioxidant layer 15 is indispensable as an oxygen barrier layer. Generally, a SiO ₂ sputtered film is used for the anti-oxidation layer 15, and the film thickness is 3-5.
μm. However, since the SiO ₂ film causes abrasion and breakage when it is pressed and passed through a thermal recording paper or the like,
A hard Ta ₂ O ₅ sputtered film as a wear resistant layer 16 is coated thereon with a thickness of 2 to 3 μm. The anti-oxidation layer 15 and the wear resistant layer 16 also serve as protective layers for the thin film conductor 14 made of a soft metal such as Al or Au.

On the other hand, a thin film conductor 1 made of a material such as Al
4 is formed directly on the thin film resistor 12, and when a voltage is applied and heated, electromigration occurs and the resistance value greatly changes. Usually to prevent this,
A refractory metal thin film made of Cr or the like having a thickness of 500 to 1000 Å is formed on the thin film resistor 12 and used as a barrier metal thin film 13 as a barrier layer. Further, the thin film conductor 14 has a film thickness of 1 to 2 μm in order to reduce the value of the wiring resistance, but the step due to this film thickness affects the contact between the heat sensitive recording paper and the heat generating portion (heat sensitive recording. In order to prevent the paper from hitting the heat generating part near the step) and to prevent the heat generation from escaping to the Al conductor side with good thermal conductivity, it is preferable to retract the paper by about 200 to 300 μm as shown in FIG. It is common. With such a receding amount, the resistance value of the barrier metal thin film 13 can be set to 1% or less of the resistance value of the thin film resistor 12, and the heat loss can be suppressed lower than when the thin film conductor is not receded. It is possible. That is, the Cr layer 13 substantially functions as a thin film conductor.

Conventionally, thermal printers have been commercialized by using the thermal print head having such a structure. Needless to say, however, there is a strong demand for improvement in the printing speed, and the energizing pulse width is as short as 1 ms. The repetition frequency has also been increased to 100 Hz or more (cooling time 10 ms or less). However, this increase in speed requires raising the heat-generating temperature of the heat-generating resistor, which increases thermal and mechanical strain to the periphery. As a result, generation of cracks in the anti-oxidation layer 15 and wear resistant layer 16 and burning of the thin-film resistor 12 by air intruding from the cracks have been a major development issue.

In response to this, Cr-Si-described in JP-A-58-82770 and JP-A-58-84401.
A SiO alloy thin film resistor material was developed. This can be said to be an oxide and is a material that is stabilized by heat treatment and can be used very stably even when heated in an oxidizing atmosphere as long as it is used at a temperature lower than that. As a result, products such as high-speed facsimiles have been provided with high reliability.

[0008]

As described above, a high-speed thermal printer has been commercialized, but its basic structure is, as shown in FIG. 3, an antioxidation layer having a thickness of 5 to 8 μm and poor thermal conductivity. 15 and the wear resistant layer 16 is actually used after being coated. However, if the bare thin-film resistor can be used as the heat-generating resistor without providing the antioxidation layer 15 and the abrasion resistant layer 16, the thermal recording paper or the like is heated through the antioxidation layer 15 and the abrasion resistant layer 16. In addition to being able to halve the conventional required amount of applied power, it is possible to speed up the heating of the heating resistor by eliminating the time delay, and it is also possible to significantly reduce the escape of heat to the substrate side. become able to. Therefore, it is an object of the present invention to provide a heating resistor without a protective layer that can achieve these.

[0009]

SUMMARY OF THE INVENTION The above object is to provide Cr--Si.
This can be achieved by forming a -SiO alloy thin film resistor and a heating resistor consisting only of Cr, Mo, Ni, W, or Ta thin film conductors on an alumina ceramic substrate on which a glaze glass layer is formed. In addition, if the glaze glass layer is made of low-temperature baking type glass having a low coefficient of thermal expansion, or if the heat-generating resistor is coated with a wear-resistant layer having a thickness of 0.5 μm or less, the durability will be improved. It is even more effective.

[0010]

The heating resistor constructed as described above is stable against heating in the air even without a protective layer (antioxidation layer, abrasion resistant layer), and as shown in the examples, its resistance in actual operation. It is possible to keep the rate of change in value within the required range. The high hardness of the thin-film resistor and the high-melting-point metal thin-film conductor shows excellent wear resistance, and also from this point, the rate of change in resistance value can fall within the required range. Further, since the formation of the protective layer is unnecessary or simplified, the head manufacturing process is simplified and the cost can be reduced.

On the other hand, as described above, the input energy required for recording can be halved, and the printing speed can be increased. That is, since the protective layer can be substantially eliminated, heat transfer to the thermal paper is dramatically improved, which is impossible with conventional thermal print heads having a pulse width of 0.2 to 0.3 ms. It enables extremely short pulse heating. This makes it possible to reduce the thickness of the glaze glass layer as a heat storage layer to about 10 to 30 μm, and it is possible to dramatically increase the cooling rate after pulse heating. That is, high-speed printing of 2 to 5 times can be easily realized without causing tailing development.

[0012]

EXAMPLES A detailed description will be given below based on examples.

[Embodiment 1] FIG. 1 is a sectional view showing a heating resistor of a thermal print head according to the present invention. 30-7
A glazed glass layer having an average linear expansion coefficient of about 6.0 × 10 ⁶ / ° C. in the same temperature range on an alumina ceramic substrate 6 having an average linear expansion coefficient of about 7.6 × 10 ⁶ / ° C. at 00 ° C. 1
(For example, GP-350 manufactured by Nichiden Glass) is fired at a thickness of 10 to 30 μm at about 720 ° C. Here, the glaze layer has a thickness of 20 μm.

The heat generating portion is a portion formed only of the Cr-Si-SiO alloy thin film resistor 2. Cr-Si-SiO
The film thickness of the alloy thin film resistor 2 is preferably 500 to 2000Å, but in the case of this embodiment, it is set to about 700Å. Further, the thickness of the Cr thin film of the barrier metal thin film 3 is preferably 500 to 1000 Å, but in the case of the present embodiment, it is about 1000 Å. Furthermore, N
The film thickness of the thin film conductor 4 of i is about 2 μm, and the resistance value of the heating resistor is about 2.5 kΩ. However, although the Cr thin film 3 is used in this embodiment, a hard metal thin film such as Mo, W, or Ta having a low electric resistance may be used instead of Cr. When the length of the thin film conductor 4 is short, only the Cr thin film 3 may be used as the conductor, and the manufacturing process can be shortened and the head can be manufactured at low cost. Of course, instead of Cr, Ni, Mo, W, or Ta
Needless to say, can be used.

Here, the reason why a material having a small linear expansion coefficient is used as the material of the substrate will be described. The thin film resistor expands when it is pulse-heated, but naturally, the vicinity of the surface of the substrate to which it is adhered is also heated and expands. Generally, when the expansion amount of the substrate is larger than that of the thin film resistor, the thin film resistor receives tensile stress and is broken. The average linear expansion coefficient of the conventional glazed alumina ceramic substrates 10 and 11 shown in FIG. 3 at 30 to 400 ° C. is as large as about 6.5 to 7 × 10 ⁶ / ° C., but in this case, the antioxidant layer 15 is used. SiO ₂ and wear resistant layer 1
The coefficient of linear expansion of Ta ₂ O ₅ of No. ⁶ was as small as about 1 × 10 ⁶ / ° C. or less, and since these always applied compressive stress to the thin film resistor 12, it was possible to prevent breakage.

However, if the amount of expansion on the substrate side is smaller than that of the thin film resistor 2, the thin film resistor 2 will be subjected to compressive stress, and the pulse life can be extended without the protective layer. Therefore, in the present invention, the average linear expansion coefficient at 30 to 400 ° C. on an alumina ceramic substrate is about 5 × 10 ⁶ /
A low temperature firing type glazed glass layer (eg GP-350 manufactured by Nichiden Glass Co., Ltd.) having a temperature of 20 ° C. was provided with a thickness of 20 μm. The temperature at which this glazed glass layer is fired is about 720 ° C. In this way, the firing temperature is set to 6
By lowering the temperature by 00 ° C., it becomes possible to form a glass layer having a low thermal expansion coefficient on the alumina ceramic substrate without breaking it.

A pulse voltage was applied to the head (8 dots / mm) having such a constitution, and recording was carried out on a thermosensitive recording paper by a usual method to evaluate printing. The print power under the condition that the print density is the same is 0 in the conventional head shown in FIG. 3 with a pulse width of 1 ms and a repetition cycle (cooling time) of 10 ms.
In contrast to 32 ± 0.02 W / dot, the head of this example has a half of 0.20 ± 0.02 W / dot. Furthermore, when a high-speed printing test was performed with the same print density, a pulse width of 0.3 ms and a repetition cycle of 3 ms,
Printing power of 0.60 ± 0.1 W / dot was achieved, and no tailing development was observed. Then, a continuous print life test was conducted under these conditions, and it was confirmed that the print could withstand 10 ⁸ times of printing. As a matter of course, it goes without saying that the power consumption of the thermal recording apparatus using this head is halved, and a facsimile or printer capable of high speed printing of 2 to 5 times can be manufactured. In addition, pulse width /
The optimum thickness of the glaze layer when the repetition period is 0.2 ms / 2 ms is about 10 μm, and when it is 1 ms / 10 ms, it is about 30 μm. It goes without saying that the biggest reason for the better thermal efficiency with such a thinner optimal glaze thickness than in the prior art is the elimination of the protective layer, and for this reason without tailing. It became a head that can realize high-speed printing.

[Embodiment 2] As a particularly severe test among the continuous printing life tests of Embodiment 1, a test was tried by entrapping the printing portion with dust. This is because even if it is installed in the office room, depending on the season, the dust entering through the window may be caught between the head and the thermal recording paper, causing a large mechanical strain to cause a breakage of the heating resistor. Because. As a result, it was found that the resistance value deviated from the specified range at about 10 ⁷ pulses, and it was found that the reliability of the head was problematic depending on the environment in which it was used. The countermeasure for this is the present embodiment.

In this embodiment, as shown in FIG. 2, a very thin scratch-resistant protective layer 5 on the heating resistor of the present invention, specifically, a Ta ₂ O ₅ layer having excellent wear resistance and Si. _{A 3} N ₄ layer was coated. In this case, the protective layer 5 only needs to protect the thin-film resistor 2 and the thin-film conductor 3 having a thickness of 500 to 1000 Å and the glaze glass layer 1 on which they are formed from scratches from dust or the like. Can be estimated to be sufficient in the range of 0.1 to 0.5 μm in consideration of the wear amount of Ta ₂ O ₅ of the conventional head. So actually 0.1, 0.2,
A head coated with 0.4 μm of Ta ₂ O ₅ or Si ₃ N ₄ protective layer 5 was made, and a life test was carried out while entraining the same dust as above, but a problem was found in the test up to 3 to 5 × 10 ⁷ pulses. No inconvenience was found. It goes without saying that the protective layer having such a thickness has a small increase in power consumption of 10% or less, and the effect of greatly improving the thermal efficiency is directly accepted.

[Embodiment 3] The thermal print head described in Embodiment 1 is an alumina provided with a low temperature firing type glazed glass layer having an average linear expansion coefficient at 30 to 400 ° C. of 5 × 10 ⁶ / ° C. or less. It was found that the printing life was 10 ⁸ dots or more using a ceramic substrate. On the other hand, most of the examples of actual use of the thermal facsimile use only the number of times of 1 to 3 × 10 ⁷ dot printing. That is, Examples 1 and 2 are of excessive quality in terms of life. Therefore, in this embodiment, the excessive quality is shortened and the cost is reduced. A specific way to achieve this is to use the most mass-produced, prior art, glazed alumina ceramic substrates. However, the thickness of the glaze layer is 30 μm or less for high-speed printing, which also contributes to cost reduction of the substrate. The same heating resistor as in Example 1 or 2 was formed on this substrate, and a step-up stress test was first performed. The results are shown in FIG. 4, in which not only Example 1 but also a thermal print head using Neoceram N-11 (manufactured by Nichiden Glass) for the substrate and no conventional protective layer for the substrate, and a conventional glazed alumina substrate for the substrate were used. The data (FIG. 3) in which a protective layer is provided by using is also described as data. In each case, the thin film resistor is a Cr-Si-SiO alloy thin film resistor under the same conditions. 30-40
The average coefficient of linear expansion at 0 ° C is about 0.7 for neoceram substrate.
× 10 to ⁶ / ° C., the conventional glaze layer is about 6.5 × 10
~ ⁶ / ℃ SiO ₂ and Ta ₂ O ₅ layer is about 1.0 × 10 ~ ⁶ / ℃ in
Therefore, the composite linear expansion coefficient is set to 3.75 × 10 ⁶ / ° C. The relationship between these linear expansion coefficients and the applied energy at ΔR / R = 10% in the SST characteristic shown in FIG. 4 is shown in FIG. 5, but the pulse resistance of the heating resistor depends on the substrate or the protective layer. It is well understood that it is determined by the magnitude of repeated stress. Needless to say, such a clear tendency has been clarified because the Cr-Si-SiO thin film resistor of the present invention which does not cause burnout rupture due to thermal oxidation is used. The head of the present invention having no protective layer capable of dramatically improving the thermal efficiency has the SST shown in FIG.
As can be estimated from the characteristics, even in the present embodiment in which the Cr-Si-SiO thin film resistor is formed on the conventional technology glazed alumina substrate, 2000 to 3 which is sufficiently practical.
The print life was 10 million dots. Of course, these results did not change when a protective layer having a thickness of 0.5 μm or less was formed on the heating resistor as in Example 2.

[0021]

According to the present invention, it is possible to print on a thermal paper or the like with an input power of about half that of the conventional one, the printing speed can be doubled or more, and the head manufacturing process can be greatly simplified. Low cost is also achieved. The reduction of the power supply capacity of the thermal recording device adopting this is also a great practical effect.

[Brief description of drawings]

FIG. 1 is a sectional view showing a heating resistor according to an embodiment of the present invention.

FIG. 2 is a sectional view showing a heating resistor according to another embodiment of the present invention.

FIG. 3 is a plan view and a sectional view showing a conventional heating resistor.

FIG. 4 is a diagram showing SST characteristics of the present invention and a conventional heating resistor.

FIG. 5 is a diagram showing the relationship between the magnitude of repeated stress applied to a heating resistor and SST characteristics.

[Explanation of symbols]

Reference numeral 1 is a glaze glass layer, 2 is a thin film resistor, 3 is a barrier metal thin film, 4 is a thin film conductor, 5 is a wear resistant layer, and 6 is an alumina ceramic substrate.

Claims (5)

[Claims] 1. A Cr-Si-SiO alloy thin film resistor,
A thermal print head comprising a heating resistor made of a Cr, Mo, Ni, W, or Ta thin film conductor formed on an alumina ceramic substrate on which a glaze glass layer is formed. 2. The glazed glass layer is 30-40.
2. The thermal print head according to claim 1, which is made of a low temperature baking type glass material having an average linear expansion coefficient at 0 ° C. of 5 × 10 ⁶ / ° C. or less. 3. The thickness of the glazed glass layer is 30 μm.
The thermal print head according to claim 1, wherein the thermal print head has a thickness of m or less. 4. The heat-generating resistor is coated with a wear-resistant layer having a thickness of 0.5 μm or less.
The thermal print head described. 5. A thermal recording device comprising the thermal print head according to claim 1.