JP4831481B2 - Alloys for cold cathode discharge tube electrodes - Google Patents

Description

  The present invention relates to an electrode alloy for a cold cathode discharge tube used as a light source for a backlight of a liquid crystal display device, for example.

  Conventionally, a backlight for illumination is incorporated in a liquid crystal display (LCD) used for a television or a personal computer, and a cold cathode discharge tube is used as a light source of the backlight. A cold cathode discharge tube generally has a structure in which a pair of electrodes are arranged opposite to each other inside a glass tube filled with a rare gas and mercury vapor, and an inner wall of the glass tube is covered with a fluorescent film. One end of a lead is connected to the pair of electrodes, and the other end of the lead is led out from both ends of the glass tube. When a voltage is applied between the pair of electrodes via the lead, electrons are emitted from one electrode, and the electrons collide with mercury atoms in the glass tube to generate ultraviolet rays. This ultraviolet ray is converted into visible light by a fluorescent film coated on the inner wall of the glass tube, and plays a role as illumination.

Since the cold cathode discharge tube electrode (hereinafter referred to as an electrode) often uses a thin plate-shaped material formed into a cup shape by cold plastic working such as deep drawing, Conventionally, a pure Ni thin plate that is soft and excellent in plastic workability has been used. However, there is a problem that an electrode composed of pure Ni is consumed by sputtering over a long period of time and reaches the end of its life. Since the life of this electrode depends on the sputtering resistance of the material constituting the electrode (difficult to be consumed by sputtering), proposals have been made to improve the sputtering resistance of the electrode material.
For example, Japanese Patent Laying-Open No. 2005-93119 (Patent Document 1) proposes to use, as an electrode, a Ni—Nb alloy containing Nb in an amount of 6% to less than 32% by mass and the balance being substantially Ni. ing. This proposal is superior in that an electrode superior in sputtering resistance to an electrode made of pure Ni can be provided by alloying Nb, which is less likely to be consumed by sputtering than Ni, with Ni.
JP 2005-93119 A

According to studies by the present inventors, the Ni—Nb alloy for electrodes disclosed in Patent Document 1 described above has an advantage that corrosion resistance is superior to pure Ni in addition to sputtering resistance. Corrosion resistance is one of the important characteristics of an electrode of a cold cathode discharge tube used for a long period of several years or more. Therefore, Nb is suitable as an element to be alloyed with Ni.
However, in the Ni—Nb alloy for electrodes disclosed in Patent Document 1, the Nb content is as high as 6% or more by mass%, and this range is where brittle intermetallic compound (Ni ₃ Nb) is generated, and the material is cupped. This is a region that has a problem of adversely affecting cold plastic workability in the process of forming a shaped electrode. Therefore, although the Ni—Nb alloy for electrodes disclosed in Patent Document 1 is excellent in spatter resistance, the plastic workability in the process of forming the material into a cup shape is poor, and it is difficult to produce the electrode itself. There is a drawback.
The object of the present invention is to solve the above-mentioned problem of plastic workability in the conventional Ni-Nb alloy for electrodes, and further provide an electrode alloy that has a sputter resistance equal to or higher than that of the conventional Ni-Nb alloy for electrodes. It is to be.

First, as a result of examining the problem of plastic workability in Ni—Nb alloys, the inventors of the present invention have a low Nb content (less than 6.0%) in a range in which Ni ₃ Nb, which is a brittle intermetallic compound, is not generated. It has been found that the plastic workability can be improved.
However, this Ni-Nb alloy having a low Nb content cannot provide the spatter resistance as high as that of a conventional alloy containing 6.0% or more of Nb. Therefore, Mo is selected as a third element that does not generate a brittle intermetallic compound even when it is contained up to a high concentration range and has an effect of improving the sputtering resistance, and finds an appropriate range of this Mo content. Thus, the present invention has been achieved.
That is, the present invention provides a cold cathode discharge tube electrode consisting of Nb: 1.0% to less than 6.0% by mass, Mo: 3.0 to 15.0%, the balance being substantially Ni and inevitable impurities. Alloy. Preferable Nb and Mo contents are Nb: 2.0 to 5.5% and Mo: 4.0 to 12.0%.

  The electrode alloy of the present invention has a plastic workability superior to that of a conventional Ni-Nb alloy in addition to having a sputtering resistance equivalent to or better than that of a conventional Ni-Nb alloy having excellent sputtering resistance. . Therefore, the electrode alloy of the present invention has an effect that it can be easily formed into a cup-shaped electrode in addition to the effect that a long life is obtained.

As described above, an important feature of the present invention is that the content of Nb alloyed with Ni for the purpose of improving the sputter resistance of pure Ni is within a range in which a brittle intermetallic compound (Ni ₃ Nb) is not generated. Mo is selected as a third element that has an effect of improving the sputtering resistance without generating an intermetallic compound with Ni up to a high concentration (content) region after setting to a low Nb content. We have found an appropriate range of quantities.
The reasons for defining chemical components in the electrode alloy of the present invention will be described below. Unless otherwise specified, the mass% is indicated.
Nb: 1.0% or more and less than 6.0% Nb is an essential element of the present invention that has the effect of improving the sputter resistance and the corrosion resistance by alloying with Ni. However, if less than 1.0%, any effect is small, and conversely in the range of 6.0% or more, plastic workability deteriorates due to the formation of brittle intermetallic compound (Ni ₃ Nb). . A more desirable upper limit is 5.5%, and even more desirably 5.0%. A desirable lower limit is 2.0%, and more desirably 3.0%.

Mo: 3.0-15.0%
Mo is an essential element of the present invention that has the effect of improving the sputtering resistance of the electrode alloy by alloying with Ni similarly to Nb. Therefore, a Ni—Nb—Mo alloy containing Nb in an amount of 1.0% to less than 6.0% and containing an appropriate amount of Mo contains 6.0% or more of Nb without deteriorating plastic workability. Sputtering resistance equivalent to that of a conventional Ni—Nb alloy can be obtained.
Further, the solid solubility limit of Mo in Ni is wide and theoretically does not produce a brittle intermetallic compound (Ni ₄ Mo) up to a high concentration (content) region of 25.0%, so this 25.0% With the following contents, there is no concern of significant deterioration in plastic workability due to the formation of intermetallic compounds. However, if the Mo amount exceeds 15.0%, the plastic workability deteriorates due to an increase in strength due to work hardening, so the upper limit of the Mo amount was set to 15.0%. Moreover, the lower limit of the amount of Mo is set to 3.0% because the effect of improving the sputtering resistance is small if it is less than 3.0%. The more desirable upper limit of Mo is 12.0%, more desirably 11.5%, and even more desirably 10.0%. A more desirable lower limit of Mo is 4.0%, and more preferably 5.0%.

The balance is Ni and unavoidable impurities. In the cold cathode discharge tube electrode alloy of the present invention, Ni is an essential element necessary for ensuring excellent workability and is the base that occupies the balance other than Nb and Mo described above. It is an element. Therefore, it is desirable that the balance has as little unavoidable impurity content as possible, but the following ranges are unavoidable as long as they do not adversely affect the sputtering resistance and plastic workability of the electrode alloy. It may be contained in.
C ≦ 0.10%, Si ≦ 0.50%, Mn ≦ 0.50%, P ≦ 0.05%, S ≦ 0.05%
In the electrode alloy of the present invention, the above-described structure ensures the spatter resistance equivalent to or better than that of the conventional Ni—Nb alloy having excellent spatter resistance, and the plastic working that has been a problem of the conventional Ni—Nb alloy. In addition to the effect that a long life can be obtained by excellent spatter resistance, it has the effect that plastic processing to a cup-shaped electrode is easy, and the electrode of the cold cathode discharge tube It is suitable as an alloy.

  Nine types of electrode alloys having chemical components shown in Table 1 were prepared in a vacuum melting furnace, 10 kg each. No. in Table 1 1-No. 6 is an alloy for electrodes of the present invention. On the other hand, no. 7-No. 9 is a comparative example. No. 9 corresponds to the electrode alloy disclosed in Patent Document 1.

Each alloy was heated to 1100 ° C. and subjected to hot forging and hot rolling to obtain a plate material having a thickness of 5 mm. Furthermore, the remainder of the hot rolled material was again heated to 1100 ° C. and hot rolled to obtain a plate material having a thickness of 2.5 mm. After removing the oxide scale generated during hot rolling by pickling, it was softened by annealing in a vacuum furnace maintained at 800 ° C. for 1 hour. These plate materials were repeatedly subjected to cold rolling and annealing at 800 ° C. to obtain thin plate materials having a thickness of 0.2 mm. In the final step, after cold rolling at a reduction rate of 80%, annealing was performed in a vacuum furnace maintained at 800 ° C. for 30 minutes, and then quenched with N ₂ gas.
After measuring the Vickers hardness of these annealed thin plates, a cold deep drawing test was performed. (The cold deep drawing test is performed with 10 test pieces, and is indicated as “No” when even one crack or crack occurs.) 1-No. Table 2 shows the results of 9 Vickers hardness and deep drawing test.

From Table 2, no. 1-No. No. 6 was able to be formed into a cup shape by a deep drawing test, but Nb and Mo were higher than the range of the present invention. 7, no. In No. 8, cracks occurred in the deep drawing test. No. In No. 9, although the hardness was low, a specimen having cracks in the deep drawing test was confirmed due to the formation of a brittle intermetallic compound (Ni ₃ Nb).

No. for which deep drawing was possible. 3, no. Sputtering resistance was evaluated for the alloy No. 4. No. as a comparative material. 9 was used.
No. 3, no. 4, no. A sputtering target having a diameter of 75 mm and a thickness of 3 mm was prepared from a 5 mm-thick plate material after hot rolling of No. 9 as a sample for evaluation of sputtering resistance. These targets are installed in a vacuum chamber of a magnetron sputtering apparatus, and continuously sputtered for 12 hours under conditions of Ar pressure of 0.8 Pa and input power of 300 W. Then, the target is taken out from the chamber, and the amount of consumption of the target by sputtering (weight) Change).
No. 3, no. 4, no. Table 3 shows the results of the sputtering rate of 9 (the smaller the value of the sputtering rate, the lower the consumption due to sputtering and the better the sputtering resistance).

No. No. 9 when the consumption amount of 9 is used as a reference (100%). 3 and no. No. 4 consumption is 99%. 3 and no. In No. 4, No. of the comparative example (conventional example). It can be seen that the spatter resistance almost equivalent to 9 is obtained.
From the above examples, the No. of the present invention. 3 and no. No. 4 is a comparative example (conventional example) No. No. 9 while maintaining spatter resistance almost equivalent to that of No. 9. From Fig. 9, it was found that molding into a cup shape (plastic processing) was easy, and it was shown that it was suitable as an electrode alloy for cold cathode discharge tubes.
In addition, No. of this invention. For 4 and pure Ni, the work function when electrons are emitted from the electrode (the smaller the value, the easier the electron emission occurs) was measured using atmospheric photoelectron spectroscopy. 0.08 eV (No. 4), 4.17 eV (pure Ni), which was superior to pure Ni. Therefore, no. It has been confirmed that the electrode consisting of 4 can be put to practical use from the viewpoint of electron emission characteristics as compared with a pure Ni electrode which has been mainly used so far.

  Since the electrode alloy of the present invention is excellent in spatter resistance and plastic workability, plastic processing into a cup shape is indispensable, and an electrode of a cold cathode discharge tube used for a long period of several years or more It can be applied as an alloy. For example, it is suitable for an electrode alloy of a cold cathode discharge tube used as a light source for a backlight of a liquid crystal display device.

Claims (2)

An alloy for a cold cathode discharge tube electrode, characterized in that Nb: 1.0% to less than 6.0% in mass%, Mo: 3.0 to 15.0%, and the balance consisting of Ni and inevitable impurities. The alloy for cold cathode discharge tube electrodes according to claim 1, wherein Nb is 2.0 to 5.5% and Mo is 4.0 to 12.0% by mass.