JP4674805B2 - Method for producing electrode material for cold cathode fluorescent lamp - Google Patents

Description

  The present invention relates to a manufacturing method of an electrode material for a cold cathode fluorescent lamp which is preferably used for a backlight of an illumination light source, a personal computer monitor, a liquid crystal television, a liquid crystal display for a car navigation system, and the like. The present invention relates to a technique for preventing peeling of an emitter layer when an electrode is deep-drawn with the emitter layer formed on a substrate.

  Conventionally, cold cathode fluorescent lamps have been used for various purposes, and recently, their application to backlights for liquid crystal displays has been actively studied. Since the equipment equipped with the liquid crystal display is mainly battery-powered, there is a strong demand for low power consumption for the cold cathode fluorescent lamp used for the backlight for the liquid crystal display. In order to realize the low power consumption, it is important to reduce the voltage drop of the electrode that does not contribute to light emission. In recent years, liquid crystal elements have begun to be used for TVs, so that a cold cathode fluorescent lamp having a longer life and higher brightness than the conventional one is desired.

  As shown in FIG. 1, the cold cathode fluorescent lamp has a structure in which electrodes 3 connected to the outside by terminals 2 are arranged at both ends in a glass tube 1. 4 and a sealed gas 5 made of an inert gas and a small amount of mercury are sealed. A high electric field is applied to the electrodes 3 at both ends to generate a glow discharge in a low-pressure mercury vapor. The mercury excited by the discharge generates ultraviolet rays, and the ultraviolet rays on the inner surface of the glass tube 1 are excited by the ultraviolet rays. To emit light. In recent years, the electrode 3 used here is formed in a cup shape. By forming the electrode in a cup shape, electrons are easily emitted from the inside of the electrode due to the hollow cathode effect resulting from the shape, the cathode voltage drop can be reduced, and it is effective for reducing power consumption. In addition, in order to reduce the electrode loss of the cold cathode fluorescent lamp to achieve high efficiency and low power consumption, the elements of Group 1 to Group 3 having a work function lower than that of other metals are used as the material of the electrode 3. Including emitter materials have been applied.

  A cup-shaped cathode electrode in which an emitter layer is formed by coating the emitter material as described above on or by ion plating to form an emitter layer is known, and a cold cathode fluorescent lamp using such a cup-shaped electrode is known. Has been reported that the voltage drop of the electrode can be reduced by about 40 V compared to that of the conventional bar-shaped metal electrode, and the power consumption can be reduced accordingly (for example, see Patent Documents 1 and 2).

  In addition, by using a refractory metal material such as Mo, Ta, or Nb as the emitter material, sputtering of the electrode during lamp operation is suppressed, the amount of mercury consumed in the lamp is reduced, and the life is extended. Has been reported (see Non-Patent Document 1). In this case, the Mo and Ta electrodes are expected to consume about 40% less mercury than the conventional Ni electrodes, and the lamp life is extended accordingly.

Japanese Patent Laid-Open No. 10-14425 JP 2000-11866 A (page 3) Journal of the Illuminating Society of Japan Vol. 1.87, no. 1 2003 15 pp. “Technology Trends of Liquid Crystal Display Cold Cathode Fluorescent Lamps”

  However, it is not easy to form the emitter layer on the inner surface of the metal substrate of the electrode processed into a cup shape with a uniform thickness and a strong adhesion strength. For example, when an emitter layer is formed on a cup-shaped metal electrode by coating, the thickness of the emitter layer is not uniform. In addition, the adhesion strength between the metal electrode and the emitter layer is weak, and the emitter layer is likely to fall off due to ion bombardment during the fluorescent lamp production process or during lighting. Further, when the emitter layer is formed by dipping, there is a disadvantage that the emitter layer is also applied to the outer peripheral surface of the electrode.

  In addition, when the emitter layer is formed by ion plating, an emitter layer having a high adhesion strength can be obtained, but the emitter material adheres to the inner surface of the plating apparatus other than the metal substrate, and the material yield is poor. There is. Furthermore, as is the case with coating, if the emitter layers are individually formed on the cup-shaped electrode substrate, there is a problem that the production efficiency is low and the manufacturing cost is high.

  The present invention has been made in view of the above circumstances, and it is possible to form an emitter layer on the inner surface of a cup-shaped electrode material with a uniform thickness and a strong adhesion strength, as well as production efficiency. The object of the present invention is to provide a method for producing an electrode material for a cold cathode fluorescent lamp, which is favorable and can reduce production costs.

  In order to improve the production efficiency of cold cathode fluorescent lamp electrodes, the present inventors formed a discharge layer (emitter layer) on a metal plate, and then formed a cup-shaped cold cathode fluorescent lamp electrode from the material. Considered manufacturing. However, if a severe plastic working such as deep drawing is performed after forming the discharge layer, it is inevitable that the discharge layer is strongly scratched and peeled off, and therefore, such a technique is not provided at present. Is the actual situation. In view of this, the present invention and the like have examined a method of firmly attaching the discharge layer to the metal material while densifying the discharge layer. As a result, it was found that by applying compression processing after applying the discharge layer to the metal substrate, the discharge layer adhered firmly to the metal substrate and did not peel even after deep drawing.

  The present invention has been made based on the above knowledge, and includes a metal substrate and a discharge layer formed on the metal substrate, and is used for a cold cathode fluorescent lamp processed into a discharge electrode of a cold cathode fluorescent lamp. A method for manufacturing an electrode material, in which a powder coating in which emitter powder is dispersed in a dispersion medium is applied onto a metal substrate to form a discharge layer, and the discharge layer is compressed toward the metal substrate. The first compression step, the removal step of removing components other than the emitter powder from the discharge layer after the first compression step, and the discharge layer from which components other than the emitter powder have been removed are compressed toward the metal substrate side. And a second compression step.

  A large number of pores exist inside the discharge layer formed by applying the powder coating material on the metal substrate. The pores include voids formed after evaporation of the solvent by drying, air particles entrained when mixing the powder paint, and the like. According to the present invention, the discharge layer formed in the coating process is compressed in the first compression process, so that the pores inside the discharge layer are crushed and become dense, and the discharge layer is firmly attached to the metal substrate. To do. Next, pores are generated by removing components other than the emitter powder such as the dispersion medium in the removal step, but the pores are crushed in the second compression step, and the discharge layer becomes dense again.

  Then, by performing the second compression step, the thickness of the discharge layer is made uniform and the discharge layer adheres more firmly to the metal substrate. A cup-shaped cold cathode fluorescent lamp electrode can be produced by subjecting such an electrode material for cold cathode fluorescent lamp to plastic processing such as deep drawing. In this case, since the discharge layer is densified and firmly adhered to the metal substrate, it is possible to prevent the emitter powder from dropping or peeling off during plastic working.

  Therefore, for example, a series of processes of the present invention can be performed while continuously unwinding a metal base material from a roll, and then fed to a press device to form an electrode by deep drawing, thereby enabling processing by a continuous line in a factory. . Therefore, according to the present invention, it is possible to form a discharge layer with uniform thickness and strong adhesion strength, as well as good production efficiency of cold cathode fluorescent lamp electrodes and reduced production costs. can do.

  The reason why the discharge layer adheres firmly to the metal substrate by the compression process is not clear. According to the study by the present inventors, it has been confirmed that a part of the emitter powder bites into the surface of the metal substrate, which is presumed to be one of the reasons. It is also conceivable that the emitter powders or the emitter powder and the metal substrate are in close contact with each other with the residue of the dispersion medium and are not separated from each other by atmospheric pressure. However, these are only estimates, and it goes without saying that the present invention is not limited by the presence or absence of such actions.

  When an electrode was formed from the material produced in the present invention and a cold cathode fluorescent lamp was prototyped and tested using this electrode, no outgas problem occurred in the glass tube. Therefore, it is confirmed that even if such a residue is present, the residue is rendered harmless.

  FIG. 2 is a cross-sectional view showing the steps of the present invention and the state of the discharge layer. In the figure, reference numeral 10 denotes a metal substrate, and reference numeral 11 denotes a discharge layer. As shown in FIG. 2, a powder paint in which emitter powder and a dispersion medium (which may contain a solvent) are mixed in a slurry state is applied to one side of a metal substrate 10 in a coating process, and the powder paint is applied by a drying or cooling process. Solidify. This forms pores after the solvent has evaporated. The pores are crushed by the first compression step, and the discharge layer is densified. Next, the dispersion medium evaporates in the removal step, and pores are formed thereafter. The pores are crushed by the second compression step, and the discharge layer is densified. Hereafter, each process of this invention is demonstrated in detail.

  As the metal substrate, nickel or a nickel alloy (for example, permalloy), an iron alloy (for example, stainless steel), chromium, molybdenum, tantalum, niobium pure metal, or an alloy of two or more of these metals can be used.

The emitter powder preferably contains an element having a low work function. For example, barium tungstate (Ba ₂ CaWO ₆ , BaWO ₄ ), calcium hexaboride (CaB ₆ ), strontium hexaboride (SrB ₆ ). , Barium hexaboride (BaB ₆ ), lanthanum hexaboride (LaB ₆ ), cerium hexaboride (CeB ₆ ), praseodymium hexaboride (PrB ₆ ), neodymium hexaboride (NdB ₆ ), samarium hexaboride (SmB ₆ ), europium hexaboride (EuB ₆ ), titanium carbide (TiC), vanadium carbide (VC), zirconium carbide (ZrC), niobium carbide (NbC), molybdenum carbide (MoC), hafnium carbide (HfC), One or more of tantalum carbide (TaC) and tungsten carbide (WC) are used. It is suitable.

  The emitter powder as described above is mixed with a dispersion medium to form a slurry-like powder paint, which is applied to a metal substrate. Examples of the dispersion medium include polyvinylidene fluoride, acrylic resins, phenol resins, melamine resins, polyethylene resins, polyimide resins, and other soluble resins, hydroxypropylcellulose, methylcellulose, gelatin and other natural or synthetic polysaccharides, and ethylene bisstearamide. What dissolved 1 type or 2 types or more of higher fatty acids, such as in a solvent, can be used. In this case, an organic solvent such as normal methyl pyrrolidone or water can be used as a solvent for dissolving the dispersion medium. The powder coating material is preferably prepared by mixing a dispersion medium containing a solvent and powder in a mass ratio of about 1: 1. In addition, it is desirable to perform the drying process which evaporates a solvent after an application | coating process.

  As the dispersion medium, one or more of a thermoplastic resin made into a molten state by heating, a natural or synthetic polysaccharide, a metal soap such as zinc stearate, and a higher fatty acid can be used. In this case, energy is saved because the dispersion medium is solidified when cooled to room temperature. In addition, it is desirable to perform the cooling process which solidifies a dispersion medium after an application | coating process.

  For the coating process, any of dipping, spraying, printing, brush coating, flow coating, and doctor blade method can be used. The doctor blade method is a method in which a powder coating is attached to a metal substrate, scraped to a certain thickness with a doctor blade, and applied, and is suitable because the thickness of the powder coating can be managed strictly. .

After applying the powder coating material to the metal substrate, the discharge layer is formed on one side of the metal substrate by drying or cooling and solidifying. Then, the 1st compression process which compresses a discharge layer toward the metal base material side is performed. The first compression step is performed by sandwiching the metal substrate and the discharge layer between a pair of rolls. Thereby, the discharge layer is compressed and densified, and the thickness of the discharge layer becomes uniform. Further, when the dispersion medium is dissolved by the solvent, pores are formed after the solvent is evaporated by drying, but the pores are crushed by the first compression step. The reduction ratio in the first compression step is desirably 20% or more in order to reliably achieve the object of the present invention. Here, the rolling reduction is expressed by (h ₀ −h ₁ ) / h ₀ × 100, where the plate thicknesses of the samples before and after compression are h ₀ and h ₁ .

  Next, the removal process which removes components other than emitter powder from a discharge layer is performed. In the removing step, heating is performed to evaporate the dispersion medium. The heating temperature and time are appropriately selected depending on the type and content of the dispersion medium. Since the heating temperature is several hundred degrees Celsius, it is desirable to perform the removal step in an inert atmosphere such as nitrogen gas in order to prevent the emitter powder from being oxidized.

  Next, a second compression step is performed in which the discharge layer is compressed again toward the metal substrate side. The second compression step is performed by sandwiching the metal substrate and the discharge layer between a pair of rolls. The pores are formed after the dispersion medium evaporates in the removing step, but the pores are crushed by the compression and the discharge layer becomes dense. Further, the thickness of the discharge layer is further uniformized by the second compression step. The reduction ratio in the second compression step is desirably 50% or more in order to reliably achieve the object of the present invention.

  The thickness of the discharge layer after the second compression step is preferably 0.005 to 0.05 mm. The thickness of the discharge layer needs to be 0.005 mm or more in order to ensure the discharge characteristics. However, if the thickness of the discharge layer exceeds 0.05 mm, peeling tends to occur during deep drawing.

  The cold cathode fluorescent lamp electrode material produced as described above has a discharge layer made of emitter powder formed on one side of a metal substrate. Since this discharge layer is densified and firmly adhered to the metal substrate, peeling of the discharge layer when formed on a cup-shaped electrode by deep drawing is prevented. In addition, since the thickness of the discharge layer is made uniform by the first and second compression steps, the discharge characteristics when the electrode is used in a cold cathode fluorescent lamp are good.

1. Production of Electrode A lanthanum hexaboride (LaB ₆ ) powder coating was applied to a thickness of 0.02 mm on one side of a 0.30 mm thick nickel plate. The powder coating used was a mixture of 47.6% by mass of lanthanum hexaboride, 2.4% by mass of hydroxypropylcellulose, and 50.0% by mass of normal methylpyrrolidone. This sample was heated in air at 120 ° C. for 15 minutes to evaporate normal methyl pyrrolidone and solidify the powder coating.

  Next, the sample was rolled with a rolling roll at a reduction rate of 25% or 53% (first compression step). The sample was then heated in nitrogen gas at 500 ° C. for 1 hour to evaporate hydroxypropylcellulose. Next, the sample was rolled with a rolling roll at a reduction rate of 53% (second compression step) to prepare Sample 1 which is an example of the present invention.

  For comparison, electrode materials for cold cathode fluorescent lamps were prepared under the same conditions as described above (Sample 2 and Sample 3) except that the first compression step or the strike 2 compression step was not performed. In Sample 2 in which the second compression step was performed without performing the first compression step, the discharge layer was peeled off from the metal substrate in the second compression step.

2. Tape peel test The electrode material for cold cathode fluorescent lamps produced as described above was cut to an appropriate size to produce a test piece, and a tape peel test was conducted to peel off after attaching a cellophane tape to the discharge layer. . The results are shown in Table 1. In Table 1, the case where a part of the discharge layer adhered to the cellophane tape and peeled was evaluated as “Δ”, and the case where the discharge layer was not peeled was evaluated as “◯”.

  As shown in Table 1, the discharge layer was not peeled in Sample 1 subjected to the first and second compression steps, but a part of the discharge layer was peeled off in Sample 3 where the second compression step was not performed. In Sample 2 in which the first compression step was not performed, the tape peeling test could not be performed because the discharge layer was peeled off in the second compression step.

3. 180 ° Bending Test Table 1 shows the results of a bending test in which the test piece was bent 180 ° with the discharge layer inside, and the state of peeling of the discharge layer was observed. As shown in Table 1, since neither the sample 1 that performed the first compression process nor the sample 3 that did not perform the second compression process peeled off the discharge layer, it was evaluated as “◯”.

4). Excitation test A test piece was placed in an ultrasonic cleaner into which methanol was injected, and ultrasonic cleaning was performed for 5 minutes. Table 1 shows the results of observation of the state of peeling of the discharge layer of the test piece after ultrasonic cleaning. As shown in Table 1, since neither the sample 1 that performed the first compression process nor the sample 3 that did not perform the second compression process peeled off the discharge layer, it was evaluated as “◯”.

  As described above, in Sample 2 where the first compression process was not performed, the discharge layer became porous due to the pores formed after the removed solvent and dispersion medium were removed, and the deformation in the second compression process was performed. The discharge layer collapsed and peeled off without being able to withstand. Moreover, in the sample 3 which was not subjected to the second compression, the bonding force between the emitter powders was reduced by the pores formed after the dispersion medium was removed, and the resistance to tape peeling was reduced. Therefore, it was confirmed that it is essential to perform the first and second compression steps in order to make the discharge layer dense and improve the adhesion strength to the metal substrate.

5. Internal Structure of Discharge Layer FIG. 3 is an SEM photograph showing a cross section of Sample 1. As can be seen from this photograph, the emitter powders are in close contact with each other, and the discharge layer is so dense that almost no pores can be confirmed. It can also be confirmed that part of the emitter powder bites into the surface of the metal substrate.

6). Discharge characteristics Sample 1 was deep-drawn to form a cup-shaped electrode indicated by reference numeral 3 in FIG. 1, and a cold cathode fluorescent lamp shown in FIG. 1 was produced using this electrode. As another example of the present invention, instead of hydroxypropylcellulose and normal methylpyrrolidone, an electrode was formed under the same conditions as in Sample 1 except that zinc stearate was mixed at the same mass% to obtain a cold cathode fluorescent lamp. Produced. Further, for comparison, an electrode was formed only from a nickel plate to produce a cold cathode fluorescent lamp. A current was supplied to the above cold cathode fluorescent lamp, and the relationship between the current and the voltage was investigated. The result is shown in FIG.

  As is apparent from FIG. 4, the cold cathode fluorescent lamp using the electrode produced through the manufacturing method of the present invention has a lower discharge voltage than that for a cold cathode fluorescent lamp using an electrode made only of a nickel plate. Good discharge characteristics were shown. Therefore, it can be seen that the effect of using the emitter powder having a low work function is exhibited in the present invention. This indicates that in the cold cathode fluorescent lamp electrode material produced according to the present invention, the discharge layer does not peel off by deep drawing.

It is sectional drawing which shows the structure of a cold cathode ray lamp. It is a figure which shows the process of embodiment of this invention in order. It is a SEM photograph which shows the cross section of the electrode material for cold cathode ray lamps. It is a graph which shows the relationship between the electric current and voltage of a cold cathode ray lamp in the Example of this invention.

Explanation of symbols

10 Metal substrate 11 Discharge layer

Claims (6)

A method for producing an electrode material for a cold cathode fluorescent lamp comprising a metal substrate and a discharge layer formed on the metal substrate, which is processed into a discharge electrode of a cold cathode fluorescent lamp,
A coating step in which a powder coating material in which an emitter powder is dispersed in a dispersion medium is coated on the metal substrate to form the discharge layer;
A first compression step of compressing the discharge layer toward the metal substrate;
A removal step of removing components other than the emitter powder from the discharge layer after the first compression step;
A method for producing an electrode material for a cold cathode fluorescent lamp, comprising: a second compression step of compressing the discharge layer from which components other than the emitter powder are removed toward the metal substrate side.   2. The electrode material for a cold cathode fluorescent lamp according to claim 1, wherein the metal substrate is a pure metal of nickel, iron, chromium, molybdenum, tantalum, niobium, or an alloy of two or more of these metals. Production method. The emitter powder includes barium tungstate (Ba ₂ CaWO ₆ , BaWO ₄ ), calcium hexaboride (CaB ₆ ), strontium hexaboride (SrB ₆ ), barium hexaboride (BaB ₆ ), lanthanum hexaboride ( LaB ₆ ), cerium hexaboride (CeB ₆ ), praseodymium hexaboride (PrB ₆ ), neodymium hexaboride (NdB ₆ ), samarium hexaboride (SmB ₆ ), europium hexaboride (EuB ₆ ), carbonized Of titanium (TiC), vanadium carbide (VC), zirconium carbide (ZrC), niobium carbide (NbC), molybdenum carbide (MoC), hafnium carbide (HfC), tantalum carbide (TaC), and tungsten carbide (WC) The electrode for a cold cathode fluorescent lamp according to claim 1 or 2, comprising one or more kinds. The method of production.   4. The dispersion medium according to claim 1, wherein one or more of a soluble resin, a natural or synthetic polysaccharide, a metal soap, and a higher fatty acid are dissolved in a solvent. A method for producing an electrode material for cold cathode fluorescent lamps according to claim 1.   The said dispersion medium consists of 1 type, or 2 or more types in the thermoplastic resin of a molten state, natural or a synthetic polysaccharide, metal soap, and a higher fatty acid, The Claim 1 characterized by the above-mentioned. Of manufacturing an electrode material for a cold cathode fluorescent lamp.   The said application | coating process is any one of the dipping method, the spraying method, the printing method, the brush coating method, the flow coating (flow coat) method, and a doctor blade method, The one in any one of Claims 1-5 characterized by the above-mentioned. A method for producing an electrode material for a cold cathode fluorescent lamp.

Images