JPS6311992B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a thermal recording head, and particularly to a thermal recording head suitable for having a silicon-containing heating resistor made of chromium-silicon.

The heat-sensitive recording head includes a heating resistor and an electrode for supplying power to the heating resistor, which is provided on an electrically insulating substrate, and the heating resistor is made to generate heat by supplying electricity to the electrode.
A predetermined image is printed on the thermal recording paper that passes over the head. A heat-sensitive recording head is also called a thermal head.

Conventionally, the electrode materials of thermal recording heads are generally pure metals with good conductivity such as aluminum (Al) and gold (Au), or nickel (Ni)-chromium (Cr).
It has been made up of alloys like this.

However, because the electrode material and the constituent material of the heat-generating resistor interdiffuse and the electrode material reaches the heat-generating resistor, the performance of the heat-sensitive recording head gradually deteriorates, for example, the density unevenness of the printed image gradually becomes more severe. It was hot. The concentration unevenness is thought to be caused by mutual diffusion between the electrode and the heating resistor, which causes the resistance value of the heating resistor to fluctuate.

SUMMARY OF THE INVENTION An object of the present invention is to provide a thermal recording head in which diffusion of electrode material into a heating resistor is prevented.

In the present invention, the electrode material of the heat-sensitive recording head is made of a nickel-aluminum intermetallic compound, and the heating resistor is made of a silicon-containing heating resistor made of chromium-silicon.

In the present invention, the electrodes of the thermal recording head are made of nickel.
Those composed of aluminum intermetallic compounds are
This was done after investigating the fact that the material of the electrode is difficult to diffuse into the heating resistor made of chromium-silicon.

The intermetallic compound used for the electrode material must satisfy two requirements: it is solid at the heating temperature of the heating resistor, and it has a specific resistance lower than that of the constituent material of the heating resistor. A material that melts at the heating temperature of the heating resistor is not suitable because the shape of the electrode cannot be maintained due to melting. Since the heating temperature of the heating resistor is high, around 450°C, it is possible to apply it as long as it has a melting temperature of 500°C or higher. Furthermore, if the specific resistance of the electrode material is greater than the specific resistance of the heat generating resistor, even parts of the thermal recording paper that do not require printing will develop color, resulting in a significant deterioration in the quality of the printing. Therefore, it is unsuitable as an electrode material. If a material with a high specific resistance has to be used as the electrode material, one possible countermeasure is to increase the thickness of the electrode to lower the resistance value, but it is also possible to increase the distance between the heating resistor and the thermal recording paper. As a result, the overall print becomes thin and unclear. Therefore, it is not an effective countermeasure. Therefore, it is necessary to use an electrode material having a specific resistance lower than that of the constituent material of the heating resistor, and the smaller the specific resistance, the more desirable it is.

Examples of intermetallic compounds that can be used as electrode materials include nickel aluminum (NiAl), nickel 3 aluminum (Ni ₃ Al),
Cobalt/aluminum (CoAl), iron/cobalt (FeCo), iron/aluminum (FeAl), nickel/gallium (NiGa), cobalt/gallium (CoAl), beryllium/copper (BeCu), gold/magnesium (AuMg), silver・Magnesium (AgMg),
Gold/zinc (AuZn) and gold/cadmium (AuCd)
and so on. Intermetallic compounds include NiAl and CoAl
There are those with an atomic ratio of 1:1, such as Ni ₃ Al, and those with a non-1:1 atomic ratio, such as Ni 3 Al, but intermetallic compounds with an atomic ratio of 1:1 are better as electrode materials. desirable. This is because intermetallic compounds with an atomic ratio of 1:1 generally have a smaller specific resistance than other intermetallic compounds.

Among the various intermetallic compounds mentioned above, NiAl
has the lowest specific resistance, less than 10μΩ・cm at room temperature. Therefore, it is most suitable as an electrode material.

Conventionally, silicon-tantalum (Si-Ta) has been generally used as a constituent material for the heating resistor of a thermal recording head.
and tantalum nitride (Ta ₂ N). In addition, we have recently developed chromium-silicon (Cr-
We are conducting research and development on thermal recording heads with a focus on Si). Heat generating resistors containing silicon, such as Si-Ta and Cr-Si, have a higher resistivity than Ta ₂ N and the like, but on the other hand, aluminum and gold are easily diffused. Therefore, conventionally, silicon-containing heating resistors have not been fully utilized as heating resistors for thermal recording heads. However, the electrode material
By using NiAl, a silicon-containing heating resistor made of Cr--Si can be effectively used as a heating resistor of a thermal recording head. because,
NiAl does not substantially diffuse into the silicon-containing heating resistor made of Cr--Si, and therefore does not lower the resistance value of the silicon-containing heating resistor or cause a local change in the resistance value.

The electrode can have a single layer structure or a multilayer structure. When forming a multilayer structure, at least the heating resistor side should be formed of an intermetallic compound to prevent elements from other layers from diffusing into the heating resistor. By having a single layer structure or a multilayer structure, the following effects can be obtained compared to the other methods.

In the case of an electrode with a single layer structure, it is easier to form the electrode than with a multilayer structure. In the case of a multilayer structure, the power applied to the heating resistor can be increased by forming part of the layers from conductive gold or aluminum. In a multilayer electrode, if a pure metal or an alloy such as gold or aluminum is used for a part of the layer, a part of the pure metal or alloy will come out during use, and the electrode on the surface of the heating resistor may A phenomenon may occur in which the electrode material adheres to areas where it is not provided, and the adhered electrode material may further diffuse into the heating resistor. However, if the intermetallic compound has a single layer structure, such a phenomenon will not occur. Therefore, it is possible to prevent local fluctuations in the resistance value of the heating resistor caused by part of the electrode material protruding from the electrode, adhering to the surface of the heating resistor, and diffusing.

The intermetallic compound electrode can be easily formed on the surface of the heating resistor by applying a well-known sputtering technique. Specifically,
It can be formed by preparing a sample having a predetermined intermetallic compound shape in advance and sputtering it onto the heating resistor.

Example 1 NiAl was formed to a thickness of 3 μm on the heating resistor of an alumina substrate having a Cr-Si heating resistor by sputtering, and then heated at 500°C in the atmosphere.
was heated for 70 minutes. The weight ratio of chromium and silicon in the heating resistor is 20% chromium and 80% silicon, and the thickness of the heating resistor is 1000 Å. When the vicinity of the interface between the electrode and the heating resistor was observed under a microscope to examine the progress of diffusion, no mutual diffusion phenomenon was observed at the interface. Further, no phenomenon was observed in which part of the electrode material jumped out and adhered to the surface of the heating resistor. The results of the continuity test showed no problems at all.

Example 2 A heat-sensitive recording head having the structure shown in Fig. 1 was manufactured,
A sample was taken from this and the rate of change in resistance of the heating resistor was measured.

The thermal recording head shown in FIG. 1 comprises an electrically insulating substrate 1, a heating resistor 5, an electrode 6, a protective layer 7 for the heating resistor, and an insulating layer 10. The electrically insulating substrate 1 consists of an alumina plate 2, a glaze layer 3, and a Ta ₂ O ₅ layer 4, and the protective layer 7 includes a SiO ₂ layer 8 with excellent oxidation resistance and a Ta 2 O ₅ layer with excellent wear resistance. O ₅ layer 9
It consists of two layers. The heating resistor 5 is made of Cr-
Si has a ratio of 20% by weight of Cr and 80% by weight of Si.
Electrode 6 is NiAl. The heating resistor 5, electrode 6, and protective layer 7 are all formed by sputtering. The thickness of each layer is approximately 1 mm for the electrically insulating substrate, 1000 Å for the heating resistor 5, and 100 Å for the heating resistor 5.
The electrode 6 is 3 μm, the SiO ₂ layer 7 is 1 μm, and the Ta ₂ O ₅ layer 8 is
It is 2 μm.

The rate of change in resistance of the heating resistor can be determined by raising and lowering the temperature of the sample taken in the temperature range from room temperature to 500°C, and comparing the resistance value of the heating resistor at each temperature with the resistance value at room temperature. I asked for it. The formula for the rate of change in resistance is expressed as ΔR/R ₀ ×100. R ₀ is the resistance value of the heating resistor at room temperature, and ΔR is the value obtained by subtracting the resistance value R ₀ at room temperature from the resistance value at the measurement temperature. The temperature was raised and lowered twice, and the temperature was raised and lowered at a rate of 2° C./min in both cases. After the temperature was raised to 500°C, the temperature was maintained for 30 minutes the first time and 40 minutes the second time. A graph of the relationship between resistance change rate and temperature is shown in FIG. As is clear from FIG. 2, in the thermal recording head of the present invention, during the first temperature rise, the rate of change in resistance gradually decreases as shown in (1) until the temperature reaches around 250°C. It is clear that the temperature increases as the temperature increases, and that it increases in the opposite direction when the temperature exceeds 250℃. When the temperature is lowered, the resistance change rate is gradually increased until the temperature reaches room temperature, as shown by 1a. During the second temperature increase, the resistance change rate decreases roughly along the curve of the resistance change rate during the first temperature decrease, and when the temperature begins to decrease, the resistance change rate becomes slightly larger than the previous temperature decrease. The resistance change rate gradually increases with a curve similar to the first time.

Comparative Example 1 In order to compare the resistance change rate of the heating resistor in the thermal recording head of Example 2, a head without electrodes was prepared. Its structure is the same as in FIG. 1 except that there are no electrodes. A sample was taken from this, and the rate of change in resistance of the heating resistor was determined in the same manner as in Example 2. The holding time after the first temperature increase was 25 minutes, which was slightly shorter than in Example 2. The relationship between the rate of change in resistance and temperature is shown in a graph in FIG. Since this sample does not have electrodes, it is possible to determine the rate of change in resistance inherent in the heating resistor. It is clear that the graph of FIG. 3 is very similar to the graph of FIG.

A comparison between Example 2 and Comparative Example 1 revealed that the NiAl electrode did not substantially affect the resistance value of the heating resistor.

Example 3 Cr containing 20% by weight of Cr and 80% by weight of Si for the heating resistor
A thermal recording head with a structure similar to that shown in Fig. 1 was fabricated using Si and NiAl for the electrodes. In addition,
The thickness of the electrode was 2 μm. A step stress test was conducted on this heat-sensitive recording head to determine the relationship between the rate of change in resistance of the heating resistor and the applied power. In the step stress test, a pulse of appropriate power is applied to the heating resistor for a certain period of time, and the change in resistance from the initial resistance value is measured.The applied power is gradually increased until the heating resistor is burned out, and each step is This method measures the rate of change in resistance of a heating resistor, and is used to evaluate the thermal stability of a heating resistor. It is said that the larger the value of the applied power when the rate of change in resistance increases rapidly, the more stable the heating resistor is thermally. This step stress test was conducted under the conditions of a pulse width of 0.9 ms, a period of 10 ms, and an application time of 10 minutes. FIG. 4 shows the relationship between the resistance change rate of the heating resistor and the applied power. A is according to this embodiment.

Comparative Example 2 In the heat-sensitive recording head having the structure shown in FIG. 1, the electrode 6 had a two-layer structure of Ni--Cr alloy and Al. Ni-
The thickness of Cr alloy and Al are both approximately 1 μm,
Both were formed by vapor deposition. The Ni-Cr alloy was placed on the heating resistor side.

A step stress test was conducted on this heat-sensitive recording head, and the characteristics shown in B in FIG. 4 were obtained.

From FIG. 4, it is clear that the product A according to the present invention has better thermal stability than the product B according to the comparative example.

Example 4 Cr20wt%-Si80wt% on electrically insulating substrate
A heat-generating resistor layer made of the same material and an electrode made of a two-layer structure of NiAl and Al were formed. NiAl was provided on the heating resistor side. Cr-Si and NiAl were formed by sputtering, and Al was formed on NiAl by vapor deposition. The thickness of Cr-Si is 1000 Å, and the thickness of NiAl and Al is about 1 μm.

After heating at 500°C for 70 minutes and cooling to room temperature, the vicinity of the interface between the electrode and the heating resistor was observed using a microscope. As a result, as is clear from the photograph in FIG.
Although a very small diffusion layer 6c was observed at the NiAl interface shown in b, no diffusion layer was observed at the interface between NiAl and the heating resistor 5. In other words,
It has been revealed that NiAl does not interdiffuse with the material of the heating resistor and has a damping effect that prevents Al from diffusing into the heating resistor.

As is clear from the above description, according to the present invention, the electrode material is prevented from diffusing into the heating resistor. Therefore, it is possible to prevent the resistance value of the heating resistor from decreasing or locally varying due to the influence of the electrode material.

[Brief explanation of the drawing]

FIG. 1 is a perspective view showing an embodiment of the present invention, FIG. 2 is a graph showing the relationship between resistance change rate and temperature for a thermal recording head according to an embodiment of the present invention, and FIG. 3 is a comparison diagram. Regarding the example, the graph showing the relationship between the rate of resistance change and the temperature as in Figure 2, Figure 4 shows the step stress test results, and the graph showing the relationship between the rate of resistance change and the applied power, and Figure 5, This is a microscopic photograph of the vicinity of the interface between the heating resistor and the electrode. 1... Electrical insulating substrate, 5... Heat generating resistor, 6...
...Electrode, 6a...Al, 6b...NiAl, 6c...
Diffusion layer, 7...protective layer.

Claims (1)

[Claims] 1. A device having a heating resistor and an electrode for supplying power to the heating resistor on an insulating substrate, wherein the electrode is made of a nickel-aluminum intermetallic compound NiAl, and the heating resistor is made of silicon made of chromium-silicon. A heat-sensitive recording head comprising a heating resistor.