JP4426416B2 - Fluorescent lamp and backlight device - Google Patents

Description

  The present invention relates to a fluorescent lamp and a backlight device including the same, and more particularly to a technique for reducing a chromaticity difference in a fluorescent lamp.

  In recent years, various fluorescent lamps have been developed and used. Incidentally, mercury that obtains energy from electrons and emits ultraviolet rays is enclosed in a glass bulb that constitutes the arc tube of the fluorescent lamp, and this mercury reacts with the glass bulb (hereinafter referred to as the present specification). In this case, the glass bulb may be discolored or the mercury may be consumed, resulting in a short life.

In order to suppress the mercury reaction, it has been proposed to form a protective film between the glass bulb and the phosphor film (see, for example, Patent Document 1 and Patent Document 2). FIG. 10 is an enlarged photograph of a conventional arc tube cut along a plane passing through the tube axis, and shows a state in which a protective film 102 and a phosphor film 104 are laminated on a glass bulb 100.
By the way, the protective film 102 is made of metal oxide particles, and a gap A exists between the particles. The present inventors have found that when the air gap A exists in the protective film 102, visible light is irregularly reflected at the interface having different refractive indexes, so that the luminous flux of the arc tube decreases. In addition, from the viewpoint of suppressing the mercury reaction, it is necessary to sufficiently increase the thickness of the protective film 102. Here, if the protective film 102 is made thick in order to suppress the mercury reaction, the luminous flux is reduced due to the above-mentioned diffuse reflection, and conversely, if the protective film 102 is made thin in order to secure the luminous flux, the mercury reaction is sufficiently suppressed. There was a problem that it was not possible.

Therefore, the present inventors have proposed to increase the bulk density of the metal oxide particles in the protective film. As a result, voids between particles in the protective film 101 can be reduced to suppress irregular reflection, and the film thickness can be made thicker than before, so that the mercury reaction can be sufficiently performed without causing a decrease in luminous flux. It is thought that it can be suppressed.
Japanese Patent Laid-Open No. 1-112651 JP 2003-123691 A

The inventors of the present invention have made a prototype of a fluorescent lamp in which the bulk density of the particles forming the protective film 101 is increased. As a result, it has been confirmed that even if the film thickness is increased, the luminous flux does not decrease more than before. It was.
However, it has been found that the fluorescent lamp has a new problem that the distribution of the phosphors of each color is uneven and a chromaticity difference occurs in the entire arc tube.
The present invention has been made in view of the above-described problems, and an object of the present invention is to provide a fluorescent lamp and a backlight device that can suppress a chromaticity difference generated in the entire arc tube.

  The present inventors have investigated the cause of the occurrence of the chromaticity difference, and when the bulk density of the metal oxide particles forming the protective film is increased, the surface of the protective film to be adhered to the phosphor film becomes smooth. Because of this, when applying the phosphor suspension with the glass tube standing vertically, the distribution of phosphors can be uneven due to the difference in specific gravity of each color phosphor, resulting in chromaticity differences depending on the location of the arc tube It has been found. This is because if the surface of the protective film to be adhered to the phosphor film is smooth, the binder in the phosphor suspension can easily flow downward along the surface of the phosphor. The phosphors of the respective colors in the liquid are also likely to flow downward, but this is considered to be due to the fact that the falling speed differs depending on the specific gravity.

  Therefore, the fluorescent lamp according to the present invention is a fluorescent lamp in which a protective film is formed on the inner surface of a glass bulb, and the protective film is deposited on the protective film, and the fluorescent film in the protective film It is characterized in that a crack is formed on the adherend surface.

  In said structure, the crack is formed in the adherence surface with the fluorescent substance film of a protective film, and when apply | coating fluorescent substance suspension, the binder in fluorescent substance suspension enters into the said crack. Generally, since the binder has a high viscosity, it becomes difficult to flow downward when a part of the binder enters the crack. As a result, the phosphors of the respective colors covered by the binder are less likely to flow downward, the difference in the falling speed due to the difference in specific gravity of the phosphors of each color is less likely to occur, and the phosphor distribution tends to be non-uniform. It is thought to be reduced.

In the above configuration, the number of cracks in the tube axis direction of the adherend surface is desirably 20 / mm or more and 200 / mm or less.
When the number of cracks in the tube axis direction of the surface to be adhered to the phosphor film of the protective film is less than 20 [/ mm], the above-described action when the binder enters the cracks becomes insufficient, and the distribution of the phosphors This is because the amount of mercury entering the crack increases and mercury reaction may occur if the amount is more than 200 [pieces / mm].

The protective film is preferably composed mainly of metal oxide particles, and the bulk density of the metal oxide particles in the protective film is preferably 80% or more.
When the bulk density of the metal oxide particles is less than 70%, voids increase between the particles and the luminous flux is reduced due to irregular reflection. Therefore, the bulk density of the particles is preferably 80% or more. The “bulk density of the particles” is the percentage of the volume occupancy of the particles in the unit volume.

Here, the average particle diameter of the metal oxide particles is preferably 0.01 μm or more and 1 μm or less.
This is because if the average particle diameter of the metal oxide particles is 1 μm or more, the bulk density cannot be increased to 80% or more, and those having a particle diameter of less than 0.01 μm are difficult to manufacture.
The protective film preferably has a thickness of 0.5 μm or more and 5 μm or less. This is because if the thickness of the protective film is less than 0.5 μm, it is difficult to form a crack on the adherend surface, and if the thickness of the protective film is greater than 5 μm, the luminous flux of the lamp decreases.

In addition, the surface roughness of the deposition surface of the protective film is preferably 200 nm or less. This is because if the surface roughness is larger than 200 nm, the scattering of visible light increases and the luminance decreases.
The backlight device of the present invention is characterized by including the fluorescent lamp described above as a light source. Since the above-described fluorescent lamp is provided as a light source, a backlight device with little chromaticity difference can be provided.

Hereinafter, a cold cathode fluorescent lamp and a backlight device according to an embodiment of the present invention will be described with reference to the drawings.
<Configuration of backlight device>
First, the configuration of the backlight device according to this embodiment will be described. FIG. 1 is a schematic perspective view showing a configuration of a backlight device 1 for a liquid crystal television having an aspect ratio of 16: 9 according to the present embodiment. In the figure, a part of the front panel 16 is cut away to show the internal structure.

As shown in FIG. 1, the backlight device 1 includes a cold cathode fluorescent lamp (hereinafter referred to as “lamp”) 20, a housing 10 having an opening and housing these lamps 20, and the housing. And a front panel 16 covering the opening of the body 10.
The housing 10 is made of, for example, polyethylene terephthalate (PET) resin, and a reflective surface is formed by depositing a metal such as silver on the inner surface 11 thereof.

The lamp 20 has a straight tube shape, and in the present embodiment, 14 lamps 20 are arranged directly below in the housing 10 and are electrically connected in parallel. The configuration of the lamp 20 will be described later.
The opening of the housing 10 is covered with a translucent front panel 16 formed by laminating a diffusion plate 13, a diffusion sheet 14, and a lens sheet 15, so that foreign matters such as dust and dust do not enter inside. It is sealed.

The diffusion plate 13 and the diffusion sheet 14 in the front panel 16 scatter and diffuse the light emitted from the lamp 20, and the lens sheet 15 aligns the light in the normal direction of the sheet 15, Thus, the light emitted from the lamp 20 is configured to irradiate the front uniformly over the entire surface (light emitting surface) of the front panel 16.
<First Embodiment>
[Configuration of Lamp 20]
Next, the structure of the lamp 20 according to the first embodiment will be described with reference to FIG. FIG. 2 is a partially cutaway perspective view showing a schematic configuration of the lamp 20.

The lamp 20 includes a glass bulb 30 having a straight tube shape in which both end portions of a glass tube having a circular cross section are hermetically sealed at a lead wire 21 portion.
The glass bulb 30 is made of borosilicate glass. The glass bulb 30 has a length of 340 mm, an outer diameter of 4.0 mm, and an inner diameter of 3.0 mm. A protective film 32 for preventing a mercury reaction is formed on the inner surface of the glass bulb 30, and a phosphor film 34 is deposited on the protective film 32. The configuration of the protective film 32 will be described later.

The phosphor film 34 includes three kinds of rare earth phosphors such as red light emitting Y ₂ O ₃ : Eu, green light emitting LaPO ₄ : Ce, Tb, and blue light emitting BaMg ₂ Al ₁₆ O ₂₇ : Eu. The phosphor film 34 contains a binder.
The lead wire 21 is a connection between an internal lead wire made of tungsten and an external lead wire made of nickel, and both ends of the glass bulb 30 are hermetically sealed at the internal lead wire portion.

  An electrode 22 is joined to the end of the lead wire 21 inside the glass bulb 30 by laser welding or the like. The electrode 22 is a so-called hollow electrode having a bottomed cylindrical shape, and is obtained by processing a nickel rod or a niobium rod. The reason why the hollow electrode is used as the electrode 22 is that it is effective for suppressing sputtering in the electrode caused by the discharge when the lamp is turned on.

The glass bulb 30 is filled with a predetermined amount of, for example, mercury and a rare gas (Ar 5% Ne 95%) having a gas pressure of 60 Torr.
[Configuration of Protective Film 32]
The protective film 32 is made of yttria (Y ₂ O ₃ ) fine particles, and the bulk density of the particles is about 90%. Here, the bulk density is preferably 80% or more. If it is less than 80%, there are many voids between the particles, and the translucency of the protective film decreases due to irregular reflection.

The average particle size of the yttria particles is desirably 0.01 μm to 1 μm. This is because it is difficult to produce yttria particles less than 0.01 μm, and when the particles are larger than 1 μm, it is difficult to increase the bulk density of the particles to 80% or more.
A crack 50 is formed on the surface of the protective film 32 to be adhered to the phosphor film 34. FIG. 3 is an enlarged photograph of a cross section when the arc tube is cut in the tube axis direction. A protective film 32 is formed on the inner surface of the glass bulb 30, and a phosphor film 34 is attached to the protective film 32. Indicates the state.

The number of cracks 50 in the tube axis direction is about 100 [piece / mm] per unit length in the example of the photograph. The number of cracks 50 in the tube axis direction is obtained by taking a longitudinal section of the arc tube with a scanning electron microscope (SEM) (see, for example, FIG. 3) and counting how many cracks are present per unit length. Can be measured.
FIG. 4 is a photograph of the surface to be coated of the protective film 32 before the phosphor film 34 is applied, and shows a state in which a crack 50 is formed on the surface of the surface to be deposited. As shown in FIG. 4, many cracks 50 are formed in a turtle shell shape on the surface of the adherend surface.

In addition, from the viewpoint of suppressing a decrease in luminance due to scattering of visible light, it is preferable that the surface of the protective film 32 to be deposited has a surface roughness of 200 nm or less. The thickness is preferably 100 nm or less, more preferably 50 nm or less.
[Method of forming protective film and phosphor film]
Next, a method for forming the protective film 32 and the phosphor film 34 on the inner surface of the glass bulb 30 will be described with reference to FIGS. 5 and 6. FIG. 5 is a schematic diagram showing a process of forming the protective film 32, and FIG. 6 is a schematic diagram showing a process of forming the phosphor film 34.

First, a glass tube 30 made of borosilicate glass, a protective film solution 40, and a phosphor suspension 42 are prepared.
As the protective film solution 40, a solution obtained by dispersing yttria particles in an aqueous solution containing an appropriate surfactant is used.
As the phosphor suspension 42, a mixture of red, green and blue phosphors, a binder, a binder and an organic solvent is used.

  First, as shown in FIG. 5 (a), the protective film solution is drawn by a suction device (not shown) connected to the upper end opening in a state where the glass tube 30 is set up vertically and the lower end opening is applied to the surface of the protective film solution 40. 40 is sucked into the glass tube 30. When the liquid level reaches a predetermined height, the suction is stopped, the glass tube 30 is pulled up from the protective film solution 40 as shown in FIG. 5B, and the protective film solution 40 is discharged from the lower end opening of the glass tube 30. Thereby, the protective film solution 40 adheres to the inner surface of the glass tube 30 in the form of a film.

Subsequently, as shown in FIG. 5C, the protective film solution 40 adhering to the inner surface of the glass tube 30 is dried by ventilating dry air from the upper end opening of the glass tube 30. Next, as shown in FIG. 5D, the glass tube 30 is baked at a predetermined temperature to decompose organic components remaining in the protective film solution 40. Thereby, the protective film 32 is formed on the inner surface of the glass tube.
Here, for example, by adjusting the firing temperature from 630 ° C. to the firing temperature from room temperature to 1.7 to 2.0 ° C./sec, the surface of the protective film 32 (attachment to the phosphor film 34) As shown in FIG. 4, a crack 50 is formed on the entire surface.

Next, as shown in FIG. 6A, the lower end opening of the glass tube 30 is applied to the liquid surface of the phosphor suspension 42, and the phosphor suspension 42 is sucked into the glass tube 30. Next, the suction is stopped, and the glass tube 30 is pulled up from the phosphor suspension 42 as shown in FIG. 6B, and the phosphor suspension 42 is discharged. Thereby, the phosphor suspension 42 is attached to the surface of the protective film 32 in the form of a film.
Subsequently, as shown in FIG. 6C, by drying the air from the upper end of the glass tube 30, the phosphor suspension 42 attached to the protective film 32 is dried, so that the phosphor film 32 is protected. 30 is formed. Then, as shown in FIG. 6D, the unnecessary phosphor film 34 and protective film 32 on the lower end side are removed. Thereafter, the electrode 22 is disposed by a predetermined method, and a rare gas and mercury are enclosed, whereby the lamp 20 is obtained.

[Action]
Since the phosphor suspension 42 is applied with the glass tube 30 standing vertically as described above, conventionally, green or red having a large specific gravity is applied between the application of the phosphor suspension 42 and the drying. The phosphors tend to increase as they approach the lower end, and the blue phosphors having a lower specific gravity tend to increase as they approach the upper end, resulting in chromaticity differences at each part of the arc tube. In a cold cathode fluorescent lamp used as a light source of a backlight device such as a liquid crystal display, if the chromaticity difference is large, there is a problem that only one side of the screen is bluish, for example. This chromaticity difference needs to be particularly small. There is.

  The present inventors have investigated the cause of the occurrence of the chromaticity difference in the arc tube, and since the bulk density of the metal oxide particles forming the protective film was increased, the surface of the protective film to be adhered to the phosphor film was It is thought to be caused by smoothness. This is because if the surface of the protective film to be adhered to the phosphor film is smooth, the binder in the phosphor suspension can easily flow downward along the surface of the phosphor. The phosphors of the respective colors in the liquid are also likely to flow downward, but this is considered to be due to the fact that the falling speed differs depending on the specific gravity.

In the present embodiment, in the step of forming the protective film 32, the protective film 32 is applied and dried, and then baked under predetermined conditions (baking temperature, heating rate). A crack 50 is formed on the (attachment surface with the phosphor film). The reason for the uniform distribution of the phosphor due to the crack 50 will be described below.
If a crack 50 is formed on the surface of the protective film 32 to be adhered to the phosphor film 34, the binder in the phosphor suspension enters the crack 50 when the phosphor suspension 42 is applied. Generally, since the binder has a high viscosity, it becomes difficult to flow downward when a part of the binder enters the crack 50. As a result, the phosphors of the respective colors covered by the binder are less likely to flow downward, the difference in the falling speed due to the difference in specific gravity of the phosphors of each color is less likely to occur, and the phosphor distribution tends to be non-uniform. It is thought to be reduced.

The present inventors also examined how often the crack 50 should be present. Here, since the phosphor suspension 42 is applied to the vertically standing glass tube 30, attention was paid to the number of cracks 50 in the tube axis direction.
As a result of the examination, when the number of cracks 50 in the tube axis direction of the surface of the protective film 32 to be adhered to the phosphor film 34 is less than 20 [/ mm], the above-described action when the binder enters the crack 50 is achieved. It has been found that the distribution of the phosphor is not sufficient, and the distribution of the phosphor is difficult to be uniform, and if the number of cracks 50 is greater than 200 [/ mm], mercury may enter from the cracks 50 and a mercury reaction may occur. Therefore, the number of cracks 50 in the tube axis direction on the adherend surface of the protective film 32 is preferably 20 to 200 [/ mm]. The number of cracks can be adjusted by adjusting the heating rate and the firing temperature.

  The present inventors also examined the thickness of the protective film 32. As a result, when the thickness of the protective film 32 is less than 1 μm, it is presumed that it is difficult to form a crack because the protective film is thin relative to the particle size of the metal oxide forming the protective film. Further, it has been found that when the thickness is larger than 5 μm, the light transmittance is lowered and the luminous flux is lowered. Therefore, the thickness of the protective film 32 is preferably 1 μm or more and less than 5 μm.

Furthermore, the width of the crack is desirably 0.1 μm or more and 5 μm or less. This is because if the thickness is less than 0.1 μm, the above-described action of the binder is not sufficient, and if it is larger than 5 μm, mercury easily enters the crack 50.
[Example]
Examples of the present invention will be described below in comparison with comparative examples.

As an example, the thickness of the protective film 32 is 1.8 μm, the bulk density of the metal oxide particles in the protective film 32 is 90%, and cracks 50 are formed at 100 / mm in the tube axis direction. Was used.
As a comparative example, a protective film 32 having a thickness of 1 μm, a bulk density of metal oxide particles in the protective film 32 of 70%, and having no cracks was used.

  7 and 8 are chromaticity deviations at each position of the arc tube, the vertical axis of the graph is the chromaticity deviation in the x direction or y direction on the chromaticity diagram, and the horizontal axis is one end of the arc tube. Each position in the tube axis direction is indicated by the distance from the origin, where is the origin. The solid line in the graph is data of the example, and the broken line is data of the comparative example. The chromaticity deviation is obtained as a deviation on the chromaticity diagram from the chromaticity reference chromaticity at each position when the chromaticity at the center of the lamp (position 17 mm) is used as the reference chromaticity.

  From FIG. 7, the maximum chromaticity difference in the x direction on the chromaticity diagram in the entire lamp is about 0.0058 in the example and about 0.011 in the comparative example, and in the y direction on the chromaticity diagram from FIG. The maximum chromaticity difference is about 0.0117 in the example and about 0.0138 in the comparative example. That is, in both the x direction and the y direction, the maximum chromaticity difference is smaller in the example than in the comparative example, and the chromaticity difference is smaller in the entire arc tube in the example. From the above, it was confirmed by experiments that a chromaticity difference in the arc tube can be reduced as compared with a lamp having a conventional configuration by forming a crack in the surface to which the protective film is applied.

<Modification>
As described above, the present invention has been described based on the embodiments. However, the content of the present invention is not limited to the specific examples shown in the above embodiments. For example, the following modifications are possible. Can think.
(1) In the above description, the configuration in which the protective film is formed in one layer has been described. However, the protective film may be formed in a plurality of layers. FIG. 9 is a schematic view when the arc tube in the modified example is cut along a plane passing through the tube axis, and the first protective film 62A and the second protective film 62B are laminated on the inner surface of the glass bulb 30, and the protective film 62 is formed. ing.

  The protective film 62 has almost no cracks (for example, 10 pieces / mm in the tube axis direction) and the second protective film 62B has a surface formed with cracks of 200 pieces / mm, for example. And two layers. Accordingly, the distribution of each color phosphor is made uniform by the crack 50 formed in the protective film 62B, and the mercury that has entered the crack 50 by the first protective film 62A is prevented from reacting with the glass bulb. Thereby, even if the crack 50 is formed on the surface of the protective film 62 to be adhered to the phosphor film 34 in order to make the distribution of the respective color phosphors uniform, the mercury reaction can be effectively suppressed.

(2) In the above description, the case where yttria is used as the metal oxide for forming the protective films 32 and 62 has been described. Instead of yttria, titania (TiO ₂ ), ceria (CeO ₂ ), magnesia (MgO) ), Lantania (La ₂ O ₃ ), alumina (Al ₂ O ₃ ), or a mixture of two or more of these may be used. In particular, when titania is used as the metal oxide, it suppresses the mercury reaction and has the effect of blocking ultraviolet rays. Therefore, lamps equipped with a protective film made of titania often use plastic members that are susceptible to UV degradation. It is suitable as a light source for a backlight device.

(3) Although it has been described above that the crack is formed in a turtle shell shape, the crack may be formed in another shape, for example, a stripe shape.
(4) In the above embodiment, the size of the arc tube has been described as having a length of 340 mm, an outer diameter of 4.0 mm, and an inner diameter of 3.0 mm, but it is of course not limited to this size. The length of the arc tube in the tube axis direction may be about 720 mm. Further, the shape of the arc tube is not limited to a straight tube shape, and may be, for example, a bent shape.

  (5) In the above description, the cold cathode fluorescent lamp has been described. In the manufacturing process, a fluorescent lamp in which a glass tube is set up vertically and a phosphor suspension is applied, for example, an annular fluorescent lamp widely used as general illumination. The present invention can also be applied to the above.

  The present invention can be widely applied to fluorescent lamps. In particular, in a backlight device of a liquid crystal display or the like, if a fluorescent lamp used as a light source of the backlight device has a large chromaticity difference, color unevenness occurs when an image is displayed on the display. Since the chromaticity difference of the fluorescent lamp can be reduced, the present invention is optimal as a light source for a backlight device.

It is a schematic perspective view which shows the structure of the backlight apparatus for liquid crystal television which concerns on this Embodiment. It is a partially cutaway perspective view showing a schematic configuration of a cold cathode fluorescent lamp. It is the photograph which expanded and photographed the cross section when an arc tube was cut | disconnected in the tube-axis direction. It is the plane photograph which expanded and photographed the adhesion surface with the fluorescent substance film of a protective film. It is a schematic diagram which shows the process of forming a protective film. It is a schematic diagram which shows the process of forming a fluorescent substance film. It is a graph which shows the relationship between chromaticity deviation (DELTA) x and a lamp position in an Example and a comparative example. It is a graph which shows the relationship between chromaticity deviation (DELTA) y and a lamp position in an Example and a comparative example. It is a schematic diagram of the protective film in a modification. It is a photograph which shows the form of the protective film in the conventional fluorescent lamp.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Backlight apparatus 10 Case 13 Diffusion plate 20 Cold cathode fluorescent lamp 22 Electrode 30 Glass bulb 32, 62 Protective film 34 Phosphor film 40 Protective film solution 42 Phosphor suspension 50 Crack 62A 1st protective film 62B 2nd protection film

Claims (7)

A fluorescent lamp in which a protective film is formed on the inner surface of the glass bulb, and a phosphor film is attached to the protective film,
A fluorescent lamp characterized in that a crack is formed on a surface of the protective film to be adhered to the phosphor film. 2. The fluorescent lamp according to claim 1, wherein the number of cracks in the tube axis direction of the adherend surface is 20 / mm or more and 200 / mm or less. 3. The protective film according to claim 1, wherein the protective film is mainly composed of metal oxide particles, and the bulk density of the metal oxide particles in the protective film is 80% or more. A fluorescent lamp according to claim 1. 4. The fluorescent lamp according to claim 3, wherein an average particle diameter of the metal oxide particles is 0.01 μm or more and 1 μm or less. The fluorescent lamp according to claim 1, wherein the protective film has a thickness of 0.5 μm or more and 5 μm or less. The fluorescent lamp according to any one of claims 1 to 5, wherein the surface roughness of the deposition surface of the protective film is 200 nm or less. A backlight device comprising the fluorescent lamp according to any one of claims 1 to 6 as a light source.