JP2005011665A - Cold-cathode fluorescent lamp - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To secure a luminance maintenance rate of a cold-cathode fluorescent lamp to restrain a chromaticity variation. <P>SOLUTION: Particle surfaces of a phosphor are coated with lanthanum oxide. Therefore, the deterioration of a phosphor coating 3 is prevented, the luminance maintenance rate is secured and a chromaticity variation is restrained. The ratio of the weight of lanthanum oxide to that of a phosphor matrix is set to 0.1-5%. Thus, the chromaticity variation is improved while restraining degradation of luminance, and the coating formed of lanthanum oxide is prevented from being easily separated. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a cold cathode fluorescent lamp used as a light source for a liquid crystal display device or the like.
[0002]
[Prior art]
The basic structure of a cold cathode fluorescent lamp is that a phosphor coating is formed on the inner wall of a straight tube-type glass bulb, rare gas and mercury are hermetically sealed inside the glass bulb, and a pair of glass bulbs are paired at both ends. It is the structure by which the electrode is arrange | positioned.
[0003]
The cold cathode fluorescent lamp having such a configuration has been widely used as a light source in liquid crystal display devices such as notebook computers and car navigation systems, and has been required to have a lifetime of about 10,000 hours.
[0004]
However, in recent years, with the expansion of applications of liquid crystal display devices, cold cathode fluorescent lamps are required to have a longer life.
[0005]
For example, the lifetime of a cold cathode fluorescent lamp used for a monitor or a large TV is set to 40000 to 50000 hours.
[0006]
[Problems to be solved by the invention]
FIG. 16 is a graph showing a change in the luminance maintenance ratio with respect to the elapsed time of the conventional cold cathode fluorescent lamp. Here, a glass bulb having an inner diameter of 2.0 mm and an axial length of 400 mm was used, the phosphor coating was 15 μm to 25 μm thick, the driving voltage was a sine wave with a lighting frequency of 40 kHz, and the discharge current was 8 mA.
[0007]
The luminance maintenance rate is about 70% when 10000 hours have elapsed and about 55% when 50000 hours have elapsed. In general, the lamp life is when the luminance maintenance ratio is 50% or less of the initial value. If this cold cathode fluorescent lamp is used for a monitor or a large TV requiring a life of 50000 hours, the life of the lamp will be shortened. However, the luminance maintenance rate is considerably lowered.
[0008]
In addition, when a cold cathode fluorescent lamp is actually incorporated in a backlight device, the deterioration of the reflector and the light guide plate is included, so that after 50,000 hours, only a luminance less than half of the initial value can be obtained. is there.
[0009]
FIG. 17 is a graph when the amount of chromaticity x value change with respect to elapsed time is measured, and FIG. 18 is a graph that similarly shows the amount of chromaticity y value change. After 10,000 hours, the x value increases by 0.021 relative to the initial value, the y value increases by 0.027, and after 50000 hours, the x value increases by 0.040, and the y value is 0.050. Therefore, there is a problem that the chromaticity is completely different from the initial one at the end of the lifetime.
[0010]
The present invention has been made in view of the above, and an object of the present invention is to provide a cold cathode fluorescent lamp capable of ensuring a luminance maintenance rate and suppressing a chromaticity change amount.
[0011]
[Means for Solving the Problems]
A cold cathode fluorescent lamp according to a first aspect of the present invention includes a glass bulb, a phosphor coating formed on an inner wall of the glass bulb, a rare gas and mercury enclosed in the glass bulb, and the glass bulb. In the cold cathode fluorescent lamp provided with a pair of electrodes sealed at both ends, the phosphor coating is characterized in that the particle surface is coated with lanthanum oxide.
[0012]
In the present invention, by covering the phosphor particle surface with lanthanum oxide, it is possible to prevent deterioration of the phosphor coating, secure a luminance maintenance rate and suppress chromaticity variation, and improve lamp performance. I have to.
[0013]
In the second cold cathode fluorescent lamp, the weight of the lanthanum oxide is 0.1 to 5% with respect to the weight of the base material of the phosphor.
[0014]
In the present invention, the weight of lanthanum oxide is set to a ratio of 0.1 to 5% with respect to the weight of the phosphor matrix, so that the lamp performance is suppressed by suppressing the chromaticity change amount while suppressing the decrease in luminance. The lanthanum oxide coating is difficult to peel off.
[0015]
The third cold cathode fluorescent lamp is characterized in that a protective film is provided between the inner wall of the glass bulb and the phosphor film.
[0016]
In the present invention, by providing a protective film between the inner wall of the glass bulb and the phosphor film, the lamp performance based on the luminance maintenance rate and the chromaticity change amount can be further improved.
[0017]
DETAILED DESCRIPTION OF THE INVENTION
As shown in FIG. 1, in the cold cathode fluorescent lamp in the present embodiment, a phosphor film 3 that emits light by stimulation with ultraviolet rays is formed on the inner wall of a straight tube-type glass bulb 1, and neon or A noble gas 6 using mercury and mercury (not shown) are hermetically sealed. The bottomed cylindrical electrodes 4a and 4b are disposed at both ends of the glass bulb 1, and lead wires 5a and 5b connected to the bottoms of the electrodes 4a and 4b are respectively connected to the sealing portions 2a and 2b at both ends of the glass bulb 1. 2b is sealed.
[0018]
The present cold cathode fluorescent lamp has a problem of improving the luminance maintenance ratio and the chromaticity shift. The main cause of the decrease in the luminance maintenance ratio and the increase in the chromaticity change is the deterioration of the phosphor coating 3. This is the color change of the glass bulb 1.
[0019]
The deterioration factors of the phosphor include (1) deterioration due to ultraviolet rays, (2) mercury adsorption, and (3) deterioration due to the phosphor becoming non-crystalline due to ion collision.
[0020]
Therefore, in the present cold cathode fluorescent lamp, in order to prevent the phosphor coating 3 from being deteriorated, it is fundamental to use the phosphor coating 3 in which the phosphor particle surface is coated with a metal oxide which is a stable substance. The configuration.
[0021]
FIG. 2 shows the surface of the phosphor particles with lanthanum oxide (La ₂ O ₃ ), alumina (Al ₂ O ₃ ), and magnesium oxide (MgO), which are easy to coat the surface of the phosphor particles and are considered to be stable substances. The luminance maintenance rate with respect to the elapsed time of each cold cathode fluorescent lamp is shown. The cold cathode fluorescent lamp used here has an inner diameter of 2.0 mm and an axial length of 400 mm. The ambient temperature was 25 ° C., and the lamp current was constant at 7 mA. In the case of coating with lanthanum oxide, the luminance maintenance rate is improved by about 10% compared with the case of not coating with metal oxide. On the other hand, in the case of coating with another metal oxide, the luminance maintenance rate is lower than that in the case of not coating with a metal oxide.
[0022]
FIG. 3 is a graph when the x-value change amount of chromaticity with respect to elapsed time is measured in the same state as FIG. 2, and FIG. 4 is a graph that similarly shows the y-value change amount of chromaticity. 3 and 4, the numerical value in the parentheses indicates the value of the chromaticity change amount at the rightmost measurement point. When coated with lanthanum oxide, the amount of change in chromaticity is reduced to 2/3 to 1/2 compared to when not coated with metal oxide. On the other hand, in the case of coating with other metal oxides, the amount of change in chromaticity increases compared to the case of not coating with metal oxides.
[0023]
When a rare earth material other than lanthanum, for example, yttrium (Y) or gadmium (Gd), was also examined as a coating material, problems such as difficulty in coating the phosphor particle surface and inability to form a stable phosphor coating occurred. For this reason, lanthanum is the most suitable coating material among rare earth materials.
[0024]
Next, the amount of the coating material will be described. As shown in the graph of FIG. 5, the relationship between the weight ratio (%) of lanthanum oxide to the host weight of the phosphor and the luminance shows that when the lanthanum oxide amount is 5% or more, the metal oxide is not coated. The brightness is reduced by 3% or more with respect to the case (when the weight ratio is 0%). In addition, there is a problem that the coating material is easily peeled off from the surface of the phosphor particles, which makes manufacture difficult.
[0025]
In addition, as shown in the graph of FIG. 6, when the change in the luminance maintenance ratio with respect to the elapsed time when the weight ratio of lanthanum oxide was changed, the luminance maintenance ratio significantly decreased when the weight ratio became 0.1% or less. ing. Therefore, the weight ratio of lanthanum oxide is optimally in the range of 0.1% to 5%. In the figure, the comparative example shows the case where the weight ratio of lanthanum oxide is 0%, that is, the case where the phosphor particle surface is not coated.
[0026]
Next, examples of the present cold cathode fluorescent lamp will be described. In the embodiment, the configuration shown in FIG. 1 is used as a basic structure, and a straight tubular glass bulb using soda glass or borosilicate glass is used. The inner diameter is 2.0 mm, and the length in the tube axis direction is 400 mm. . The phosphor is coated on the inner wall of the glass bulb so that the particle surface is coated with lanthanum oxide, the weight ratio of lanthanum oxide to the phosphor matrix is 1%, and the thickness of the phosphor coating is in the range of 18 to 23 μm. did.
[0027]
In order to further improve the lamp performance based on the luminance maintenance ratio and the chromaticity change amount, in another embodiment, in addition to the coating with lanthanum oxide, a protective film layer is provided between the glass bulb and the phosphor film. It was. The protective film layer was mainly composed of yttrium oxide, and the film thickness was about 1 μm.
[0028]
In the comparative example, the phosphor particle surface was not covered at all, and other conditions were the same as in the example.
[0029]
As shown in the graph of FIG. 7, when the relationship between the elapsed time and the luminance maintenance rate is observed, the luminance maintenance rate is 76.9% when the phosphor particle surface is not coated when 5000 hours have elapsed. On the other hand, when it is coated with lanthanum oxide, it is 86.5%, and when it is coated with lanthanum oxide and a protective film is formed between the glass bulb and the phosphor film, it is improved to 88.7%. is doing.
[0030]
Further, as shown in the graphs of chromaticity change amounts in FIGS. 8 and 9, when 5000 hours have elapsed, the x value change amount and the y value change amount are obtained when the phosphor particle surface is not coated. Whereas x: 0.013 and y: 0.015, when coated with lanthanum oxide, x: 0.009, y: 0.009, coated with lanthanum oxide, and a glass bulb and phosphor coating When a protective film is formed between the two, x: 0.006 and y: 0.007.
[0031]
Therefore, according to the present embodiment, since the phosphor particle surface is coated with lanthanum oxide, it is possible to prevent deterioration of the phosphor coating, thereby ensuring a luminance maintenance rate and suppressing chromaticity variation. Can do.
[0032]
According to the present embodiment, since the weight of lanthanum oxide is set to a ratio of 0.1 to 5% with respect to the weight of the phosphor matrix, the amount of change in chromaticity can be suppressed while suppressing a decrease in luminance, and oxidation can be performed. Since the coating with lanthanum is difficult to peel off, a cold cathode fluorescent lamp can be easily manufactured.
[0033]
[Additional description of effect]
Next, another effect of the cold cathode fluorescent lamp of the present embodiment will be described. FIG. 10 is a diagram showing manufacturing steps from bulb cut to baking of a cold cathode fluorescent lamp. In this step, first, the glass bulb is cut to a length of 400 mm, and a phosphor film is formed on the inner wall of the glass bulb to a thickness of about 18 μm to 23 μm. Subsequently, neck cleaning is performed, and baking is performed at a predetermined temperature for 5 to 7 minutes.
[0034]
The most important function required for cold cathode fluorescent lamps is to improve brightness. In order to improve the brightness in the manufacturing process, the key points are how much the baking temperature can be lowered to prevent deterioration of the phosphor due to baking and how much residual carbon can be reduced.
[0035]
FIG. 11 is a graph showing the relationship between the baking time and the powder luminance for each of the blue, green and red single colors of the powdered phosphor according to the baking temperature. The chemical formulas of blue phosphor (BAM), green phosphor (LAP), and red phosphor (YOX) are as follows.
[0036]
BAM: BaMgAl ₁₀ O ₁₇ : Eu
LAP: LaPO ₄ : Ce, Tb
YOX: Y ₂ O ₃ : Eu
Referring to the graph in the figure, the red and green phosphors do not have much deterioration in powder brightness even when the baking temperature and time are changed, whereas in the blue phosphor, the powder brightness increases with increasing temperature and time. Degradation of is increasing. For example, when baking is performed at a temperature of 600 ° C. for 5 minutes, the powder brightness decreases by about 2 to 3%.
[0037]
FIG. 12 is a graph showing the relationship between the baking temperature and the luminance of the green phosphor, and shows the relative value assuming that the luminance when baking at 600 ° C. is 100%. When the baking temperature is lowered, the organic thickener cannot be completely decomposed, and the amount of residual carbon increases. On the other hand, baking at 450 ° C has a brightness of about 20% compared to 600 ° C. It will decline.
[0038]
Thus, if the baking temperature is lowered to prevent the phosphor from deteriorating, the phosphor can be prevented from degrading, but on the other hand, the carbon is not completely decomposed and the luminance is lowered instead. is there.
[0039]
The inventors paid attention to the phosphor as a countermeasure for this problem, and tried to prevent the adsorption of the carbon to the phosphor matrix by covering the particle surface of the phosphor with a substance that hardly adsorbs the carbon.
[0040]
FIG. 13 is a graph showing the relationship between the baking temperature and the total luminous flux when the substance covering the particle surface of the green phosphor is changed. As the material for covering the phosphor particle surface, lanthanum oxide of rare earth oxide, yttrium oxide, gadmium oxide, and lanthanum boride of rare earth compound were used. The baking temperature was set to 600 ° C., which is the conventional baking temperature, and 450 ° C. which can sufficiently reduce the deterioration of the phosphor. The total luminous flux is shown as 100% at 600 ° C.
[0041]
When the phosphor particle surface is not covered at all, if the baking temperature is lowered to 450 ° C., only about 85% of the total luminous flux can be obtained due to the influence of residual carbon. Similarly, when the phosphor particle surface is coated with yttrium oxide, gadmium oxide, or lanthanum boride, the total luminous flux is similarly reduced. On the other hand, when the phosphor particles were coated with lanthanum oxide, the total luminous flux was almost the same as that at 600 ° C. even when the baking temperature was 450 ° C. This is considered to be due to the fact that carbon adherence to the phosphor particle surface was suppressed by lanthanum oxide, and even if the baking temperature was kept low, carbon residue could be reduced. Such a lanthanum oxide-coated phosphor is baked in a state where the powder is coated with a lanthanum compound containing a hydroxyl group, whereby a lanthanum oxide-coated phosphor is obtained.
[0042]
Next, an appropriate amount of lanthanum oxide that is most effective as a coating material will be examined. FIG. 14 is a graph showing the relationship between the amount of lanthanum oxide and the relative luminance. When the weight ratio of lanthanum oxide is 6% or more with respect to the phosphor matrix, the luminance is reduced by 3% or more compared to the case where the coating is not performed (lanthanum oxide is 0%). Further, in this case, there is a problem that the coating material is easily peeled off or the manufacture becomes difficult. On the other hand, when the amount of lanthanum oxide is 0.1% or less, the effect on the luminance maintenance rate is hardly obtained. For these reasons, the amount of lanthanum oxide is optimally in the range of 0.1% to 5% with respect to the phosphor matrix.
[0043]
Next, examples of the present cold cathode fluorescent lamp will be described. In the embodiment, the structure shown in FIG. 1 is used as a basic structure, and a straight tubular glass bulb using soda glass or borosilicate glass is used. The inner diameter is 2.0 mm, and the length in the tube axis direction is 400 mm. . The phosphor is coated on the inner wall of the glass bulb so that the particle surface is coated with lanthanum oxide, the weight ratio of lanthanum oxide to the phosphor matrix is 1%, and the thickness of the phosphor coating is in the range of 18 to 23 μm. did. The baking temperature was 450 ° C. On the other hand, in the comparative example, the phosphor particle surface was not covered at all, the baking temperature was 600 ° C., and the other conditions were the same as in the example.
[0044]
FIG. 15 is a table showing the results when the initial luminance and the reflectance of the lamp surface are compared for the examples and comparative examples. The initial luminance and reflectance for the examples are relative values when the comparative example is 100%. In the embodiment, the initial luminance is improved by about 2% compared to the comparative example, and the reflectance of the lamp surface is also improved by 2% or more. Thus, in the examples, it was confirmed that even when baking was performed at a low temperature, there was little carbon residue and phosphor deterioration was reduced.
[0045]
Therefore, according to the present embodiment, since the phosphor particle surface is coated with lanthanum oxide, carbon is sufficiently decomposed even when the baking temperature is lowered in the lamp manufacturing process. A high-performance cold cathode fluorescent lamp suitable for a large TV can be provided.
[0046]
【The invention's effect】
As described above, according to the present invention, it is possible to provide a high-performance cold cathode fluorescent lamp suitable for a monitor or a large TV, which can secure a luminance maintenance ratio and suppress a chromaticity change amount.
[Brief description of the drawings]
FIG. 1A is an axial sectional view showing a configuration of a cold cathode fluorescent lamp according to an embodiment, and FIG. 1B is a radial sectional view thereof.
FIG. 2 is a graph showing the relationship between elapsed time and luminance maintenance rate when the type of phosphor coating is changed.
FIG. 3 is a graph showing the relationship between elapsed time and change in x value of chromaticity when the type of phosphor coating is changed.
FIG. 4 is a graph showing the relationship between the elapsed time and the amount of change in y value of chromaticity when the type of phosphor coating is changed.
FIG. 5 is a graph showing the relationship between the weight ratio of lanthanum oxide to the base weight of the phosphor and the luminance.
FIG. 6 is a graph showing the relationship between the elapsed time and the luminance maintenance ratio when the weight ratio of lanthanum oxide is changed.
FIG. 7 is a graph showing the relationship between the elapsed time and the luminance maintenance ratio when the presence or absence of coating with lanthanum oxide and the presence or absence of a protective film are changed.
FIG. 8 is a graph showing the relationship between the elapsed time and the amount of change in the x value of chromaticity when the presence or absence of coating with lanthanum oxide and the presence or absence of a protective film are changed.
FIG. 9 is a graph showing the relationship between the elapsed time and the change in y value of chromaticity when the presence or absence of coating with lanthanum oxide and the presence or absence of a protective film are changed.
FIG. 10 is a diagram showing manufacturing steps from bulb cut to baking of a cold cathode fluorescent lamp.
FIG. 11 is a graph showing the relationship between the baking time and the powder brightness for each of the blue, green, and red single colors of the powdered phosphor according to the baking temperature.
FIG. 12 is a graph showing the relationship between baking temperature and luminance for a green phosphor.
FIG. 13 is a graph showing the relationship between the baking temperature and the total luminous flux when the substance covering the particle surface of the green phosphor is changed.
FIG. 14 is a graph showing the relationship between the amount of lanthanum oxide and the relative luminance.
FIG. 15 is a table showing a comparison between initial luminance and reflectance for examples and comparative examples.
FIG. 16 is a graph showing a change in luminance maintenance rate with respect to an elapsed time of a conventional cold cathode fluorescent lamp.
FIG. 17 is a graph showing the relationship between the elapsed time of a conventional cold cathode fluorescent lamp and the amount of change in x value of chromaticity.
FIG. 18 is a graph showing the relationship between the elapsed time of a conventional cold cathode fluorescent lamp and the amount of change in y value of chromaticity.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Glass bulb 2a, 2b ... Sealing part 3 ... Phosphor film 4a, 4b ... Electrode 5a, 5b ... Lead wire 6 ... Noble gas

Claims (3)

A glass bulb, a phosphor coating formed on the inner wall of the glass bulb, a rare gas and mercury sealed inside the glass bulb, and a pair of electrodes sealed at both ends of the glass bulb In cold cathode fluorescent lamps,
The phosphor film is a cold cathode fluorescent lamp characterized in that the particle surface is coated with lanthanum oxide. 2. The cold cathode fluorescent lamp according to claim 1, wherein the weight of the lanthanum oxide is in a ratio of 0.1 to 5% with respect to the weight of the phosphor. The cold cathode fluorescent lamp according to claim 1 or 2, wherein a protective film is provided between an inner wall of the glass bulb and the phosphor film.

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