JP2007194147A - Fluorescent lamp, method of forming phosphor film, backlight unit, and liquid crystal display device equipped with backlight unit - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a fluorescent lamp in which phosphor particles in the phosphor film are arranged densely. <P>SOLUTION: The phosphor film 22 contains blue phosphor 23B of nearly spherical shape, and film density of the phosphor film 22 is 2.00 g/cm<SP>3</SP>or more, and a coating amount per unit inner surface area of a glass container 12 is 3.416 mg/cm<SP>2</SP>-4.117 mg/cm<SP>2</SP>. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a fluorescent lamp or the like, and more particularly to a mode of a phosphor film formed on the inner surface of a glass container.

  Among the fluorescent lamps, the cold cathode fluorescent lamp is suitable for reducing the diameter, and thus is suitably used as a light source for a backlight unit that is required to be thin. Such a cold cathode fluorescent lamp is formed by forming a phosphor layer on the inner surface side of a tubular glass container and providing cold cathodes as internal electrodes at both ends. Further, the phosphor layer is formed through steps of applying, drying, and firing the phosphor suspension.

As a light source application of the backlight unit, it is required to have particularly high luminance. As one measure for realizing high brightness, it is desirable to set the thickness of the phosphor layer in an optimum range.
This is because if the film thickness is too thin than the optimum range, the rate at which ultraviolet rays are converted into visible light decreases and sufficient luminance cannot be obtained, and conversely, if the film thickness is too thick, the visible light is blocked. Based on the reason (see Patent Document 1).
JP 2004-207073 A (Fig. 6)

In order to meet the demand for larger and thinner backlight units, the glass containers of cold cathode fluorescent lamps tend to be longer and thinner.
In such a long and thin glass tube, it is difficult to uniformly apply the phosphor suspension in the central portion and both ends of the glass tube and dry it. It has been clarified that such coating unevenness becomes more serious as the phosphor layer is thicker.

In order to avoid the deterioration of productivity due to the occurrence of such coating unevenness, the upper limit value of the film thickness must be set to a value lower than the optimum value (peak value) desirable for increasing the brightness.
By the way, when the thickness of the phosphor layer is set to a value lower than the peak value, higher luminance is expected when the phosphor particles are arranged more densely. The inventors of the present application are focusing on this point and studying a method for densely arranging phosphor particles.

  The present invention has been made in view of the above problems, and is a fluorescent lamp such as a cold cathode fluorescent lamp, in which fluorescent particles are arranged more densely than in the past, a method for forming a phosphor film, a back It is an object to provide a light unit and a liquid crystal display device including the backlight unit.

To achieve the above object, a fluorescent lamp according to claim 1 of the present invention is a fluorescent lamp having a glass container and a phosphor film formed on the inner surface side of the glass container, wherein the phosphor film Includes a substantially spherical blue phosphor, the phosphor film has a film density of 2.00 g / cm ³ or more, and the coating amount per inner surface area to the glass container is from 3.416 mg / cm ^{2 to} 4.117 mg / cm characterized in that it is a ^2.

The fluorescent lamp according to claim 2 of the present invention is characterized in that the substantially spherical blue phosphor has a ratio of a major axis to a minor axis of 1.0 to 1.3.
The fluorescent lamp according to claim 3 of the present invention is characterized in that the blue phosphor is a barium magnesium aluminate compound.
The fluorescent lamp according to claim 4 of the present invention is characterized in that the glass container has a tube length of 450 mm to 1500 mm and an inner diameter of 2.0 mm or less.

The fluorescent lamp according to claim 5 of the present invention is characterized in that the phosphor film includes a substantially spherical red phosphor and a substantially spherical green phosphor.
A backlight unit according to a sixth aspect of the present invention includes the fluorescent lamp according to the fifth aspect as a light source.
A liquid crystal display device according to a seventh aspect of the present invention includes a liquid crystal display panel and the backlight unit according to the sixth aspect.

Moreover, the method for forming a phosphor film according to claim 8 of the present invention includes a production step of producing a suspension containing a substantially spherical blue phosphor, and an inner surface of the glass tube using the produced suspension. The film density of the phosphor film after firing is 2.0 g / cm ³ or more, and the coating amount of the phosphor film per inner surface area on the glass tube is 3.416 mg / cm ^{2 to} 4.117 mg / cm ^2. And a forming step of forming a phosphor film.

According to the fluorescent lamp according to claim 1 of the present invention, since the blue phosphor is substantially spherical, the arrangement in the phosphor film can be formed more densely than before, and the film thickness is made thicker than before. It is possible to increase the coating amount without any problems.
Since the phosphor film has a high film density and a large amount of coating, which is not in the conventional range, it is possible to achieve high brightness while suppressing coating unevenness.

According to the fluorescent lamp according to claim 2 of the present invention, the blue phosphor is formed so that the ratio of the major axis to the minor axis is small and close to a true sphere, so that the arrangement in the phosphor film is formed more densely. can do.
According to the fluorescent lamp of claim 3 of the present invention, the shape of the barium magnesium aluminate compound is usually a distorted shape such as a hexagonal crystal, and a gap is likely to occur when arranged, so the shape is spherical. The effect of making the arrangement dense by the replacement is particularly great.

According to the fluorescent lamp of claim 4 of the present invention, a glass container having a tube length of 450 mm to 1500 mm and an inner diameter of 2.0 mm or less and a long tube length and a small inner diameter particularly causes uneven coating when the coating amount is increased. It is preferable to apply the present invention because it is easy.
According to the fluorescent lamp of claim 5 of the present invention, not only the phosphors other than blue, but also the red and green phosphors are substantially spherical in shape. Can be dense.

In the backlight unit according to claim 6 of the present invention, since the fluorescent lamp is provided as a light source, high luminance can be realized.
Further, according to the liquid crystal display device of the seventh aspect of the present invention, since the liquid crystal display panel and the backlight unit are provided, the display surface of the liquid crystal display panel can be increased in luminance.

  Further, according to the method for forming a phosphor film according to claim 8 of the present invention, since the blue phosphor is substantially spherical, the arrangement in the phosphor film can be formed more densely than in the prior art. It becomes possible to increase the coating amount without increasing the thickness. Further, it is possible to avoid the deterioration of productivity due to the increase of the film thickness.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
1. Configuration of Cold Cathode Fluorescent Lamp FIG. 1 is a longitudinal sectional view showing a schematic configuration of a cold cathode fluorescent lamp according to the present embodiment.
The cold cathode fluorescent lamp 10 has a straight glass container 12. The glass container 12 is made of hard borosilicate glass, and has a total length of 450 mm, an outer diameter of 3.0 mm, an inner diameter of 2.0 mm, and a wall thickness of 0.5 mm.

Lead wires 14 and 16 are sealed at both ends of the glass container 12.
The lead wire 14 (16) is a connecting line composed of an internal lead wire 14A (16A) made of tungsten and an external lead wire 14B (16B) made of nickel. Electrodes 18 and 20 are joined to the inner lead wires 14A and 16A on the inner side of the glass container 12 by laser welding or the like, respectively.

The electrodes 18 and 20 are so-called hollow electrodes having a bottomed cylindrical shape, and niobium is used as a material.
Since the electrodes 18 and 20 are hollow electrodes, the discharge during lamp operation proceeds mainly on the cylindrical inner surface. For this reason, it is possible to prevent a phenomenon in which mercury in the lamp is consumed by sputtering as compared with the case where a rod-type electrode is used (for details, see JP-A-2002-289138).

Inside the glass container, mercury (not shown) as a luminescent substance, rare gas such as argon, neon, etc. is sealed at a predetermined sealing pressure.
A phosphor layer 22 having a thickness of about 19.2 μm is formed on the inner surface of the glass container 12. The phosphor layer 22 is formed by applying a phosphor suspension on the inner surface of a glass tube, followed by drying and firing processes.

The phosphor layer 22 is formed by stacking particle groups of red phosphor particles 23R, green phosphor particles 23G, and blue phosphor particles 23B. The material of each particle is Y ₂ O ₃ : Eu ³⁺ (YOX) as red phosphor particles, and BaMg ₂ Al ₁₆ O ₂₇ : Mn ²⁺ , Eu ²⁺ (BAM: Mn ²⁺ , Eu) as green phosphor particles. ²⁺ : barium magnesium aluminate manganese / europium activated phosphor), blue phosphor particles BaMg ₂ Al ₁₆ O ₂₇ : Eu ²⁺ (BAM: Eu ²⁺ , barium magnesium aluminate europium activated phosphor) Is used. The chromaticity of the phosphor layer 22 is set to x = 0.265, y = 0.237 (x and y are values in chromaticity coordinates).

The surface of the blue phosphor particles 23B is coated with particles of rare earth metal oxides such as La and Y in order to prevent phosphor deterioration.
In addition, you may use what coat | covered the circumference | surroundings of the blue fluorescent substance particle 23B with the continuous film of a metal oxide as another aspect of coating (coating).
Here, the red and green phosphor particles 23R and 23G have a substantially spherical shape, and the blue phosphor particles 23B have a substantially spherical shape as well.

Conventionally, blue phosphor particles (BAM) are generally used in the form of hexagonal, hexagonal plate or flat plate. For this reason, the presence of the blue phosphor particles having such a shape causes a gap between the particles in the phosphor layer.
In the present embodiment, since the blue phosphor particles 23B are spherical, the phosphor particles 23R, 23G, and 23B in the phosphor layer 22 can be densely arranged.

Since the phosphor particles are clogged, the phosphor coating amount can be increased without increasing the thickness of the phosphor film, and it is possible to approach the optimum phosphor coating amount.
In addition, as the spherical blue phosphor particles, for example, spherical particles obtained by exposing an aluminum compound such as alpha alumina to a high temperature such as plasma and quenching can be used.

Further, as the “spherical” shape, the ratio of the major axis to the minor axis is preferably 1.0 to 1.3. This is because when the ratio is a distorted shape exceeding 1.3, it is difficult to obtain the effect of densely arranging the particles.
Even if all the particles of the blue phosphor particles do not necessarily fall within the range of the major axis / minor axis, the effect of dense arrangement can be obtained as long as about 80% or more is within the above range.
2, Method for Applying Phosphor Suspension Next, of the manufacturing steps of the cold cathode fluorescent lamp 10 having the above-described configuration, steps relating to the formation of the phosphor layer 22 will be described with reference to FIG.

The phosphor layer includes (1) an application step of applying a phosphor suspension to a glass tube, (2) a drying step of drying the glass tube on which the suspension is applied, and (3) a step of firing the glass tube. (Sinter process).
FIG. 2 is a diagram schematically showing the coating process / drying process.
First, as shown in FIG. 2A, a suspension 28 containing phosphor particles is attached to the inner surface of a glass tube 26 that is a material of the glass container 12.

Specifically, a tank 30 containing the suspension 28 is prepared. The suspension 28 is made of butyl acetate as an organic solvent, a predetermined amount of red, green, and blue phosphor particles, low melting point glass powder particles such as barium borate, and nitrocellulose (NC) as a thickener. Is added.
Then, the glass tube 26 is vertically held and held in a state where the lower end portion is immersed in the suspension 28. The inside of the glass tube 26 is exhausted from the upper end of the glass tube 26 by a suction force of a vacuum pump (not shown), and the suspension 28 is sucked up by making the inside of the glass tube 26 have a negative pressure. Suctioning is stopped while the liquid level in the glass tube 26 reaches the upper end (predetermined height), and the glass tube 26 is pulled up from the suspension 28. As a result, the suspension 28 adheres in a film form to a predetermined region on the inner periphery of the glass tube 26.

Subsequently, dry air is blown into the inside from the upper end while rotating the glass tube 26 in the hanging posture and discharging the excess suspension. Further, an infrared heater 32 is disposed in the vicinity of the glass tube 26, and the heater 32 is lowered at a predetermined speed from the upper end to the lower end of the glass tube 26 [FIGS. 2 (b) to 2 (d)].
As a result, the boundary portion 36 between the dried portion 35 and the undried portion 37 of the glass tube 26 gradually moves to the lower portion of the glass tube.

The flow rate of the dry air is in the range of 16 to 80 cm ³ / min per unit area 1 mm ^{2 of the} cross section perpendicular to the central axis of the glass tube 26. The temperature of the infrared heater 32 is set so that the ambient temperature of the heated portion 34 of the glass tube is 40 ° C to 45 ° C. Moreover, the ambient temperature of the part of the glass tube which is not heated is set to about 20 degreeC-30 degreeC.
As described above, the suspension of the glass tube 26 is dried from the upper part to the lower part, where a dried portion is locally generated in the lower portion of the glass tube, and the suspension is divided from the dried portion to cause uneven coating. This is to prevent the occurrence.

After the drying process, a firing process of the glass tube 26 is performed to form a phosphor film.
As described above, in the coating process / drying process according to the present embodiment described above, the occurrence of coating unevenness can be suppressed, so that the amount of phosphor applied can be relatively increased without reducing productivity.
The method of applying the phosphor capable of preventing the occurrence of uneven coating is not limited to the above-described example. For example, the fluorescent tube is rotated while the glass tube is rotated at the first rotation speed with the central axis in the longitudinal direction as the rotation axis. The suspension containing the body is applied to the inner surface of the glass tube, and then rotated at a second rotation speed higher than the first rotation speed, whereby the phosphor in the suspension is rotated by centrifugal force to the inner wall of the glass tube. There is a coating method in which the phosphors are pressed to close the arrangement of the phosphors. A similar method is detailed in JP-A-2002-208350.
3. Influence of phosphor particle shape The present inventors evaluated the influence of the difference in the shape of the phosphor particles on the phosphor film.

First, a suspension containing only blue phosphor particles as a phosphor and no red / green phosphor particles is prepared, and the shape of the blue phosphor particles is a hexagonal crystal as a conventional product and a substantially spherical shape as an invention product. Was used.
The same amount of this suspension was applied to a glass tube having the same dimensions as the glass container 26 to form a phosphor film.

FIG. 3 is a diagram schematically showing a cross section of the glass container 12.
FIG. 3A shows a conventional phosphor film 1022 and blue phosphor particles 1023B, and FIG. 3B shows an inventive phosphor film 22 and blue phosphor particles 23B.
The phosphor film 22 of the invention is densely packed because the phosphor particles are substantially spherical, and specifically, the film thickness is about 27% thinner than the conventional product (t ₁ = t ₀ × 0.73). ). The film density, which is the weight of the phosphor particles per unit volume of the phosphor film, was 2.00 g / cm ³ or more for the invention product (the conventional product was about 1.93 g / cm ³ ).
Considering this result, when three-color phosphor particles are used, the ratio of blue phosphor particles in the light source application of the backlight unit is usually about 60% at most, so the maximum is 16% (from 27 × 0.60) Is a calculation that can reduce the film thickness. FIG. 4 schematically shows a cross section of the glass container 12 when three-color phosphor particles are used (t ₃ = t ₂ × 0.84).

FIG. 5 is a graph showing the relationship between the reference coating amount ratio and the coating film thickness. FIG. 6 is a graph showing the relationship between the coating amount and the relative luminance of the cold cathode fluorescent lamp.
The coating amount is the weight of the suspension applied to the inner surface of the glass tube.
The reference application amount is an ideal value at which the luminance of the lamp is highest, and specifically, the luminance peak value in FIG. 6 is 4.6 mg / cm ² . The coating film thickness is the thickness of the phosphor film after the phosphor film is formed (after firing).

As shown in the graph of FIG. 5, the coating amount of the suspension and the coating film thickness are in a substantially proportional relationship. If the film thickness is reduced by 16% as described above, the slope of the conventional product (= 24.017) will drop by 16%, so the slope of the invention will be 24.017 × 0.84 [= (100-16) / 100]. Becomes 20.174.
In the cold cathode fluorescent lamp according to the present embodiment, the set value as the coating film thickness is 19.2 μm. In the invention product, the coating amount can be increased as compared with the conventional product even with the same coating film thickness of 19.2 μm. Inventions coating amount 4.117mg / cm ² can be realized 2.1% of the brightness enhancement compared with conventional coating amount 2.795mg / cm ^2.

FIG. 7 is a graph showing the relationship between the coating amount and the luminance variation.
As shown in the figure, in the conventional product, when the coating amount exceeds 3.415 mg / cm ² , the luminance variation (σ) becomes larger than ± 13%. Therefore, considering productivity, the value exceeds the coating amount of 3.415 mg / cm ² Could not be set.
In contrast, the invention product can increase the coating amount even with the same coating film thickness of 19.2 μm as the conventional product, so it can be set to a coating amount of 3.416 mg / cm ² or more which could not be achieved conventionally. it can. The upper limit value of the coating amount is, for example, 4.117 mg / cm ² .
4. Liquid crystal display device Since the cold cathode fluorescent lamp 10 according to the present embodiment has higher brightness than conventional ones, it is preferably used as a light source of a backlight for a liquid crystal display device.

FIG. 8 is a cross-sectional view showing the liquid crystal display device 50.
The liquid crystal display device 50 includes a liquid crystal display panel 60 and an edge light type backlight unit 70 disposed on the back surface thereof.
The backlight unit 70 includes a light-transmitting acrylic resin light guide plate 72, a cold cathode fluorescent lamp 10 provided on one end surface of the light guide plate 72, and light emitted from the cold cathode fluorescent lamp 10 on the light guide plate 72 side. And a brightness enhancement sheet 76 provided on the main surface of the light guide plate 72.
5. Others (1) Lamp type In the embodiment, the cold cathode fluorescent lamp has been described as an example. However, the present invention can also be applied to a hot cathode fluorescent lamp and an external electrode fluorescent lamp. is there.

(2) Type of phosphor In the embodiment, the phosphor particles are of the three-wavelength type, but for example, a four-wavelength type can also be used.
(3) Effect of blue phosphor particle shape Although details have not been described in the embodiment, if the shape of the blue phosphor particle is substantially spherical, the particles are densely arranged in the phosphor film. For this reason, improvement of the adhesion strength of the phosphor film and prevention of tube end color difference can be expected.

(4) Glass container dimensions It is preferable to apply the present invention to a lamp having a long tube length and a small glass container, since uneven application of the phosphor film is likely to occur. Specifically, it is preferable to apply to a lamp having a tube length of 450 mm to 1500 mm and an inner diameter of 2.0 mm or less.

  The fluorescent lamp according to the present invention is useful because the blue phosphor has a substantially spherical shape, so that the arrangement in the phosphor film can be formed more densely than in the prior art.

1 is a longitudinal sectional view showing a schematic configuration of a cold cathode fluorescent lamp 10. FIG. It is a figure which shows an application | coating process and a drying process typically. It is a figure which shows the cross section of the glass container 12 typically. It is a figure which shows the cross section of the glass container 12 typically. It is a graph which shows the relationship between a reference | standard coating amount ratio and a coating film thickness. It is a graph which shows the relationship between a coating amount and the relative luminance of a cold cathode fluorescent lamp. It is a graph which shows the relationship between a coating amount and a brightness variation. 4 is a cross-sectional view showing a liquid crystal display device 50. FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Cold cathode fluorescent lamp 12 Glass container 22 Phosphor film 23B Blue phosphor particle 26 Glass tube 28 Suspension 50 Liquid crystal display device 60 Liquid crystal panel 70 Backlight unit

Claims (8)

A fluorescent lamp having a glass container and a phosphor film formed on the inner surface side of the glass container,
The phosphor film includes a substantially spherical blue phosphor,
The phosphor film has a film density of 2.00 g / cm ³ or more,
Fluorescent lamp, the coating amount per inner surface area of the glass container is characterized in that it is a ^{3.416mg / cm 2 ~4.117mg / cm 2} . 2. The fluorescent lamp according to claim 1, wherein the substantially spherical blue phosphor has a major axis to minor axis ratio of 1.0 to 1.3. The fluorescent lamp according to claim 1 or 2, wherein the blue phosphor is a barium magnesium aluminate compound. The fluorescent lamp according to any one of claims 1 to 3, wherein the glass container has a tube length of 450 mm to 1500 mm and an inner diameter of 2.0 mm or less. The fluorescent lamp according to claim 1, wherein the phosphor film includes a substantially spherical red phosphor and a substantially spherical green phosphor.   A backlight unit comprising the fluorescent lamp according to claim 5 as a light source.   A liquid crystal display device comprising a liquid crystal display panel and the backlight unit according to claim 6. A production process for producing a suspension containing a substantially spherical blue phosphor;
Using the prepared suspension, on the inner surface of the glass tube, the film density of the phosphor film after firing is 2.0 g / cm ³ or more, and the coating amount of the phosphor film per inner surface area on the glass tube is And a forming step of forming the phosphor film so as to be 3.416 mg / cm ^{2 to} 4.117 mg / cm ² .

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