JP4036243B2 - Cold cathode fluorescent lamp and backlight unit - Google Patents

Description

  The present invention relates to a cold cathode fluorescent lamp having electrodes at both ends of a tubular glass bulb and a backlight unit having the cold cathode fluorescent lamp as a light source, and more particularly to a technique for improving dark starting characteristics.

  In recent years, the size of liquid crystal display screens has increased, and the demand for backlight units for large screens has increased. As a lamp used in this backlight unit, for example, a fluorescent lamp having an electrode outside a glass bulb (so-called external electrode type fluorescent lamp), or a fluorescent lamp having an electrode inside a glass bulb (so-called cold cathode). Type fluorescent lamp) is under development.

By the way, in the dark state, these fluorescent lamps are not immediately turned on even when a starting voltage is applied, that is, the dark starting characteristic that it takes a long time to turn on is bad, and the technology for improving this characteristic. For example, an electron-emitting material having a high secondary electron emission coefficient, for example, a cesium compound applied to the inner surface of the end of the glass bulb has been proposed. According to this technique, secondary electrons are emitted from the applied cesium compound, and the secondary electrons are liable to cause a starting discharge, resulting in an improvement in the dark starting characteristics (Patent Document 1).
JP 2001-15065 A

  However, although the dark start-up characteristics can be improved by the above technique, there is a problem that it is necessary to apply a cesium compound in the glass bulb, which is troublesome.

  The present invention has been made in view of the above-described problems, and an object thereof is to provide a cold cathode fluorescent lamp and a backlight unit that can easily improve the dark starting characteristics without performing troublesome work. .

In order to achieve the above object, a cold cathode fluorescent lamp according to the present invention is a fluorescent lamp provided with electrodes at both ends of a glass bulb having a discharge space therein, and the glass bulb is made of soda glass. , on the inner surface of the glass bulb has a protective layer and a phosphor layer are formed in this order from the inner surface side leaving one or more regions where the protective layer and the phosphor layer is not formed, the region is said It exists in an electrode opposing part .

  The region only needs to be on the inner surface of the glass bulb, and the shape, size, number, etc. of the region are not particularly limited, but it is better that the region is close to the electrode from the viewpoint of improving the dark starting characteristics. .

  Furthermore, in the cold cathode fluorescent lamp according to the present invention, it is preferable that there is a portion where the protective layer is formed and the phosphor layer is not formed in the facing portion of the electrode.

In the cold cathode fluorescent lamp according to the present invention, it is preferable that the glass bulb has a Na content of 5 wt % or more and 20 wt % or less.

  On the other hand, in the cold cathode fluorescent lamp according to the present invention, it is preferable that an alkali metal precipitated from the soda glass exists in the region. Here, the “alkali metal” is a concept including an alkali metal (Group 1) and an alkaline earth metal (Group 2).

  The form of the alkali metal is not particularly limited, and may be precipitated from glass and present in the form of a film, or may be present in the form of particles. Of course, both may exist in a mixed form.

  In the cold cathode fluorescent lamp according to the present invention, the protective layer preferably contains a cesium compound.

  In the cold cathode fluorescent lamp according to the present invention, the glass bulb preferably has a flat cross-sectional shape and an inner diameter in the minor axis direction of 1.6 mm or more and 4.0 mm or less. The “inner diameter in the minor axis direction” as used herein refers to a dimension between two points where the imaginary line segment in the minor axis direction passing through the center of the glass bulb intersects the inner surface of the glass bulb (or , The maximum value of the dimension in the direction parallel to the minor axis direction), and the inner diameter is the inner diameter of the glass bulb even if the cross-sectional shape is not circular.

  On the other hand, in order to achieve the above object, a backlight unit according to the present invention includes the cold cathode fluorescent lamp described above as a light source.

  According to the cold cathode fluorescent lamp according to the present invention, since soda glass contains an alkali metal, an alkaline system is formed in a region where a protective layer is not formed in the discharge space, for example, when the phosphor layer is fired. Metal is likely to precipitate. The alkali metal deposited in this region is exposed to the discharge space, and the dark start-up characteristics can be improved.

  Moreover, since soda glass contains more alkali metal than borosilicate glass, the amount deposited is also larger than borosilicate glass, and the dark start-up characteristics can be improved more effectively than a lamp using borosilicate glass.

Further, according to the cold cathode fluorescent lamp of the present invention, the glass bulb is made of glass having a Na content of 5 wt % or more and 20 wt % or less, and thus no protective layer is formed in the discharge space. For example, an alkali metal is likely to be deposited in the region when the phosphor layer is fired. The alkali metal deposited in this region is exposed to the discharge space, and the dark start-up characteristics can be improved.

  In addition, since the alkali metal is precipitated from soda glass by heating, for example, the alkali metal is precipitated by using heat at the time of firing the phosphor layer or sealing the end of the glass bulb. There is no need to provide a special heating process.

  Furthermore, the alkali metal deposited from the soda glass exists in the region. This alkali metal usually has a lower electronegativity than a glass material, but has a higher electron emission coefficient than a glass material. For this reason, an alkaline metal can be easily deposited.

  Further, the protective layer contains a cesium compound. Thereby, the cesium compound which is an electron emission substance with a high secondary electron emission coefficient can be easily arranged in a glass bulb.

  The glass bulb has a flat cross-sectional shape and an inner diameter in the minor axis direction of 1.6 mm to 4.0 mm. For this reason, lamp efficiency can be improved.

  The phosphor layer is formed between the inner ends of both electrodes, and the protective layer is formed between the outer ends of both electrodes. For this reason, direct contact between the alkali metal deposited from the glass and the phosphor layer can be prevented. Thereby, the chemical reaction between the two can be prevented, and deterioration of the phosphor layer can be suppressed.

  Hereinafter, an external electrode fluorescent lamp (hereinafter simply referred to as “lamp”) and a backlight unit according to an embodiment of the present invention will be described with reference to the drawings. In addition, since the invention which concerns on this application is a thing about a cold cathode type | mold fluorescent lamp, what is applicable only about an external electrode type | mold fluorescent lamp among the following description is made into a reference example.

<Configuration of backlight unit>
First, the configuration of the backlight unit will be described. FIG. 1 is a schematic perspective view showing a configuration of a backlight unit 1 for a liquid crystal television according to the present embodiment. In the figure, in order to show the internal structure, a part of the front panel 16 is cut away. 1, 2, 4 to 6 for explaining the present invention are schematic diagrams for facilitating understanding of the configuration of the backlight unit and the lamp, and the dimensions and ratios thereof are different from the actual ones.

  As shown in FIG. 1, the backlight unit 1 has, for example, straight tubular lamps 20 arranged in 16 rows at intervals in a predetermined direction (Y direction in the drawing), and openings. A housing 10 that houses the lamp 20 and a front panel 16 that covers an opening of the housing 10 are provided.

  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 thereof.

  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, and foreign matter such as dust and dust does not enter inside. So that it is sealed.

  The diffusing plate 13 and the diffusing sheet 14 in the front panel 16 scatter and diffuse the light emitted from the lamp 20, and the lens sheet 15 arranges 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.

  The lamp 20 utilizes dielectric barrier discharge, and in the present embodiment, 16 lamps 20 are electrically connected in parallel. In FIG. 1, the lamps 20 are arranged so that the axis thereof is oriented in the direction along the long side of the casing 10 (the X direction in the figure), but the axis is short of the casing 10. You may arrange so that it may face the direction (Y direction) along a side.

<Lamp configuration>
Next, the configuration of the lamp 20 will be described. 2A and 2B are diagrams showing the configuration of the lamp 20 according to the present embodiment, in which FIG. 2A is a plan view of the lamp 20, and FIG. 2B is an axial center of the lamp 20 at the end of the lamp 20. FIG. It is a longitudinal cross-sectional enlarged view when it cut | disconnects in the plane containing, (c) is a cross-sectional enlarged view.

  As shown in FIG. 2A, the lamp 20 includes a glass bulb 21 in which both ends of a straight cylindrical glass tube are sealed, and electrodes 31 and 32 provided on both ends of the glass bulb 21. With.

The glass bulb 21 is made of, for example, soda glass having a Na content of about 16 ( wt %), and a cross section (cross section) cut along a plane perpendicular to the axis is as shown in FIG. Furthermore, it has a substantially elliptical shape. The lamp 20 is housed inside the housing 10 in a state in which the extending direction of the long axis of the ellipse having a cross-sectional shape thereof is parallel to the main surface of the front panel 16.

  Inside the glass bulb 21, for example, a discharge medium such as mercury or a rare gas (for example, argon or neon) is sealed at a predetermined sealing pressure. These discharge media are filled in a reduced pressure state.

  As shown in FIG. 2 (b), on the inner surface of the glass bulb 21, one or more regions (one location) of the glass bulb 21 (regions according to the present invention, here two regions on both ends of the glass bulb 21). And the protective layer 22 and the phosphor layer 23 are formed in this order from the glass bulb 21 side.

  The protective layer 22 is composed of, for example, a metal oxide compound such as yttrium oxide excluding a metal compound precipitated from the glass bulb, Na deposited from the glass, mercury enclosed in the glass bulb 21, and glass This is to prevent the phosphor layer 23 formed on the inner surface of the bulb from reacting and deteriorating. In addition, when it reacts with Na, mercury will be consumed and the life will be shortened, and the phosphor layer 23 will be deteriorated, resulting in a decrease in efficiency and luminance.

On the other hand, the phosphor layer 23 is for converting ultraviolet rays radiated from mercury into predetermined visible light, and is composed of rare earth phosphor particles, for example. As the rare earth phosphor particles, for example, in the case of three wavelengths, Y ₂ O ₃ : Eu ³⁺ as red, LaPO ₄ : Ce ³⁺ , Tb ³⁺ as green, and BaMg ₂ Al ₁₆ O ₂₇ : Eu ² as blue. ⁺ Can be used.

In addition to the above red, green, and blue phosphor particles, phosphor particles with high color reproducibility may be used. Specifically, YVO ₄ : Eu ³⁺ as red, BaMg ₂ Al ₁₆ O ₂₇ : Eu ²⁺ , Mn ²⁺ as green, and (Sr, Ca, Ba) ₅ (PO ₄ ) ₃ Cl: Eu as blue ²⁺ and phosphor particles of Sr ₁₀ (PO ₄ ) ₆ Cl ₂ : Eu ²⁺ may be used.

  As shown in FIGS. 2A and 2B, the phosphor layer 23 is between the inner ends (corresponding to position B) of the electrodes 31 and 32 (corresponding to BB in the figure). For example, the inner surface of the glass bulb 21 corresponding to the portion covered with the electrodes 31 and 32 (the position A in each electrode) It is not formed at the position B).

  On the other hand, as shown in FIGS. 2A and 2B, the protective layer 22 is between the outer ends (corresponding to the position A) of the electrodes 31 and 32 (corresponding to AA in the figure). It is formed outside the outer ends of the electrodes 31 and 32 (corresponding to the range from the outer end of each electrode to the end of the lamp in the lamp).

In a portion where the protective layer 22 is not formed, sodium oxide (Na ₂ O) 24 precipitated from soda glass constituting the glass bulb is present. Since this sodium oxide 24 has a high secondary electron emission coefficient, if it is formed in the vicinity of the electrodes 31 and 32 in the glass bulb 21, the secondary electrons emitted from this sodium oxide 24 will easily cause a discharge. The dark starting characteristics can be improved.

  In the sodium oxide 24, an alkali metal contained in the glass bulb 21, for example, Na (sodium) is deposited on the portion where the protective layer 22 is not formed when the phosphor layer 23 is fired. This is because Na has a lower electronegativity than soda glass constituting the glass bulb 21. In other words, the portion where Na is deposited is the portion of the inner surface of the glass bulb 21 that faces the discharge space 25.

  Na reacts with mercury or the phosphor layer as described above. Originally, in order to prevent these reactions, the protective layer 22 is formed, but if it is the inner surface of the glass bulb 21 outside the outer ends of the electrodes 31, 32, it is enclosed in the glass bulb 21. The reaction with mercury and the phosphor layer 23 formed on the inner surface of the glass bulb 21 is small, and its adverse effect is small.

  The sodium oxide 24 is formed by precipitation of Na by heat when firing the phosphor layer 23 or heat when sealing the end of the glass bulb.

<Dark start characteristics>
The dark starting characteristics of the lamp having the above configuration were investigated.

  First, the following two types of lamps were used for measuring the dark starting characteristics.

Conventional product ・ Cross sectional shape: Circle ・ Dimensions: Outer diameter 4 (mm), Inner diameter 3 (mm), Total length 300 (mm)
・ Material: Borosilicate glass (Na content: 1.4 wt %)
・ Other: No emitter (electron emitting material) Invented product ・ Cross-sectional shape: ellipse ・ Dimensions: major axis outer diameter 10.3 (mm), inner diameter 9.1 (mm)
Short axis outer diameter 4.0 (mm), inner diameter 2.8 (mm)
Total length 300 (mm)
・ Material: Soda glass (Na content: 16 wt %)
-Others: Precipitation sodium oxide, no emitter No dark starting characteristics were measured by starting and lighting under dark conditions using the above two types of lamps. The conditions for starting the lamp were that it was left in the dark at room temperature for 24 hours and then lit in a dark state under 0.1 (Lux). Then, the time (dark start time) from the start of applying a voltage to the lamp until the current flows through the lamp was measured with an oscilloscope.

  The measurement results in the above test are shown in FIG.

  In the “dark start time” column in FIG. 3, “no point” is a case where the lighting did not light even when the start time was 30 seconds. In the “evaluation” column, “x” represents a case where the dark start time was 1 second or longer, and “◯” represents a case where the dark start time was within 1 second. Finally, the “result” column indicates the number of evaluations of “◯” relative to the number of tests. Note that the dark start-up time under dark conditions is preferably shorter regardless of the application of the lamp. For example, when used as a backlight unit for a TV, the performance of “within 1 second” is required. Is done.

  As shown in the figure, in the conventional product, one of the four test samples was inconsequential (No. 4), there was no dark start time within 1 second, and “×” in all The result is “0/4”.

  This is because the conventional product does not provide an emitter in the glass bulb, and the glass bulb is made of borosilicate glass, so that the alkali metal does not precipitate when the phosphor layer is baked. This is probably because there is no such thing as an emitter.

  On the other hand, there were no inconvenient products after 30 seconds, and there were four products with a dark start time within 1 second, and the result was “4/4”. This is presumably because the glass bulb 21 is made of soda glass, so that Na was deposited during the firing of the phosphor layer 23, and this deposited Na was substituted for the emitter.

  From the above results, it was found that by using soda glass for the glass bulb and carrying out the phosphor layer firing step and the glass end sealing step, the alkali metal is deposited and the dark start-up characteristics can be improved.

<Modification>
1. About the content rate of Na In the said embodiment, soda glass containing about 16 ( wt %) of Na was used as the glass bulb, but the glass bulb of the present invention contained about 16 ( wt %) of Na. It is not limited to.

In other words, the present invention improves the dark starting characteristics by depositing an alkali metal contained in the glass constituting the glass bulb and utilizing the deposited metal. Accordingly, it is sufficient that the alkali metal can be deposited to such an extent that the dark starting characteristics can be improved. In consideration of the workability of glass, the alkali metal content is preferably in the range of 5 ( wt %) to 20 ( wt %).

This is because when the alkali metal content is less than 5 ( wt %), the probability that the dark start-up time under dark conditions exceeds 1 second increases, and conversely, the alkali metal content is 20 ( wt). %), The glass bulb becomes white due to long-term use, resulting in a decrease in luminance, and the strength of the glass bulb itself is reduced.

In consideration of environmental measures, a soda glass having an alkali metal content in the above range and a lead content of 0.1 ( wt %) or less is preferable (so-called “lead”). In addition, a glass having a lead content of 0.01 ( wt %) or less is more preferable.

2. Alkali metal In the embodiment, Na (precisely sodium oxide) is precipitated, but for example, a metal belonging to Group 1 such as Na or K, or a metal belonging to Group 2 such as Ba or Ca. There may be. That is, any alkali metal may be used.

  This is because alkali metals usually have a lower electronegativity than glass materials, and have a higher electron emission coefficient than glass materials. As a result, it is possible to easily deposit an alkali metal, and it is possible to effectively improve the dark start-up characteristics in an external electrode type lamp having no electrode inside.

  If soda glass is simply used as the material of the glass bulb, an alkali metal (for example, Na) precipitates and the precipitate and phosphor particles react to cause deterioration of the phosphor layer. As described in the embodiment, since the protective layer for preventing these reactions is formed between the soda glass and the phosphor layer, deterioration of the phosphor layer can be prevented.

3. Formation region of phosphor layer In the embodiment, the phosphor layer is formed in a region (between BB in FIG. 2) between the inner ends of both electrodes 31 and 32. This is for maximizing the light extraction area, and when ultraviolet rays that have not been converted into visible light by the phosphor layer are emitted to the outside of the lamp 20, the housing 10 and the like are deteriorated. It is. In addition, although the fluorescent substance layer is not formed in the edge part (part in which sodium oxide exists), since discharge generate | occur | produces between a pair of electrodes 31 and 32 fundamentally, it is from this part. The emission of ultraviolet rays is less than that between the electrodes 31 and 32 and can be ignored.

4). Regarding the formation region of the protective layer and the phosphor layer In the above embodiment, the phosphor layer is formed between the inner ends of both electrodes, and the protective layer is formed between the outer ends of the electrodes. Has been. However, if the protective layer is wider than the region where the phosphor layer is formed, it is possible to prevent the alkali metal precipitated from the soda glass from reacting with the phosphor layer.

  Therefore, if the protective layer is formed wider than the phosphor layer, deterioration of the phosphor layer can be suppressed. From this point of view, the protective layer formation region is not necessarily formed in the entire region extending between the outer ends of the electrodes as described in the embodiment.

  FIG. 4 is a diagram illustrating a modification of the protective layer formation region in the embodiment.

  As shown in FIG. 4A, the formation region of the protective layer 122a is more outward than the outer end (position A) of the electrode 31 (in the axial direction of the glass bulb 21). May be on the end) side. That is, the protective layer 122a formation region may be wider than the distance between the outer ends (between A and A) of the electrode 31 (32).

  In addition, as shown in FIG. 4B, the region where the protective layer 122b is formed has an end that is inward (center of the glass bulb 21) than the outer end (position A) of the electrode 31. Part) side. That is, the region where the protective layer 122b is formed is narrower than the outer end of the electrode 31 (32) (between A and A) and wider than the inner end of the electrode 31 (32) (between BB). Also good.

  Even if the protective layers 122a and 122b are formed in such a region, the direct contact between the alkali metal precipitated from the soda glass and the phosphor layer 23 can be prevented. Thereby, the chemical reaction between the two can be prevented, and the deterioration of the phosphor layer 23 can be suppressed.

  The protective layer (22, 122a, 122b) is preferably formed in a region corresponding to the region where the electrodes 31, 32 are present. This is because electrons in the discharge space (25) are attracted to the electrodes 31 and 32 and collide with the inner surface of the glass bulb 21. At this time, if the protective layer (22, 122a, 122b) is formed on the inner surface of the glass bulb 21, electrons in the discharge space 25 directly collide with the inner surface of the glass bulb 21 in the region where the electrodes 31, 32 are present. It is possible to suppress the occurrence of pinholes or the like due to electron collisions on the inner surface of the glass bulb 21 corresponding to the region where the electrodes 31 and 32 are present.

  In particular, the protective layer (22, 122a, 122b) has an end of its formation region located outward (position) from the approximate center between the outer end (position A) and the inner end (position B) of the electrodes 31, 32. It is preferable to be on the A) side. This is because the electric field increases as it moves from the approximate center between the outer end and the inner end of the electrodes 31 and 32 (approximately the center between the position A and the position B in the electrode 31) to the inner end (position B). It is. Where the electric field is high, the energy of electrons increases and pinholes are likely to occur when they collide with the inner surface of the glass bulb 21. That is, the inner surface of the glass bulb 21 can be reliably protected by covering the portion where the electric field is increased with the protective layer.

5. About a protective layer (1) About the formation location of a protective layer Although the protective layer in the said embodiment was formed between the glass bulb | bulb and the fluorescent substance layer, it seems to coat | cover at least 1 type of fluorescent substance particle, for example It may be formed. That is, the phosphor particles may be coated with, for example, yttrium oxide, which is a metal oxide, and the phosphor layer may be formed on the inner surface of the glass bulb using the coated phosphor particles.

  When the protective layer is formed on the phosphor particles in this way, the protective layer between the glass bulb and the phosphor layer as in the embodiment is not necessary. In this case, the “one or more regions” according to the present invention are regions in which the phosphor layer is not formed, that is, the glass bulb is exposed to the discharge space. If only the improvement of the dark start-up characteristics is considered and the reaction between the phosphor layer and mercury in the discharge space is not considered, the protective layer or phosphor particles described in the above embodiment and this example are coated. There may be no metal oxide.

  Hereinafter, a method for forming the protective layer on the phosphor particles will be described. In addition, it has been found from the inventors' investigation that mercury in the discharge space adheres to the phosphor particles when the phosphor particles contain alumina. A process of coating the phosphor particles with a protective layer (metal oxide) will be described.

As materials, blue phosphor particles (BaMg ₂ Al ₁₆ O ₂₇ : Eu ²⁺ ) powder, yttrium caprylate [Y (C ₇ H ₁₅ COO) ₃ ], and butyl acetate are prepared.

  Blue phosphor particle powder and yttrium caprylate are charged into a container containing butyl acetate and stirred. After sufficiently stirring, the container is allowed to stand at room temperature for a sufficient time to spontaneously evaporate butyl acetate in the solution.

  Next, the powder remaining in the beaker is fired at 600 ° C. for 5 minutes. Since the powder obtained by baking is agglomerated and the particle size is not uniform, it is pulverized by a ball mill to adjust the particle size. Through the above steps, blue phosphor particles having a surface coated with a protective layer can be obtained.

In addition, instead of Y (C ₇ H ₁₅ COO) ₃ described above, Y (OC ₂ H ₅ ) ₃ or lanthanum (La (C ₇ H ₁₅ COO) ₃ ) is used to protect the blue phosphor particles as a protective layer. It is also possible to coat with. When coating is performed using such a material, the phosphor particles are densely coated, so that mercury does not easily adhere to the phosphor particles.

  Next, a process for preparing a suspension for forming a phosphor layer will be described.

As the materials, red phosphor particles (Y ₂ O ₃ : Eu, not containing alumina) and green phosphor particles (LaPO ₄ : Ce, Tb, non-alumina) not having a metal oxide as a protective layer attached to the surface Containing), a blue phosphor particle coated with a protective layer of yttrium oxide by the above-mentioned process, a binder mainly composed of each oxide of calcium-barium-boron-phosphorus, a thickener, a dispersant, and Prepare butyl acetate.

  First, a predetermined amount of butyl acetate, a binder, a thickener, and a dispersant are put in a beaker and mixed. Then, red phosphor particles, green phosphor particles, and blue phosphor particles coated with a protective layer are put into this solution and sufficiently stirred. Thereby, a suspension for forming the phosphor layer is obtained.

  Then, using a known technique, this suspension is applied to the inside of the glass bulb to form a phosphor layer, so that only blue phosphor particles (alumina-containing phosphor particles) are covered with yttrium oxide. A phosphor layer can be obtained.

  Here, the protective layer is formed on the blue phosphor particles, but naturally, other color phosphor particles may be formed on the protective layer, and all red, blue, and green phosphor particles may be formed. You may coat | cover with a protective layer.

(2) Protective layer material In the embodiment, the protective layer is made of a metal oxide compound such as yttrium oxide, but the protective layer can be made of cesium that can improve the dark start-up characteristics in addition to yttrium oxide. May be included. In this case, it is preferable that a protective layer is formed on the inner surface including the end portion of the glass bulb, and the phosphor layer is formed on the protective layer so that the formed protective layer faces the discharge space.

  According to this configuration, the cesium is exposed to the discharge space without the need to bother the application of cesium to the inner surface of the glass bulb, so that the dark starting characteristics can be improved.

6). Regarding Glass Bulb Ends (1) End Shape In the embodiment, the shape of the inner surface of the end 21a of the glass bulb 21 (surface facing the discharge space) is flat so as to be substantially orthogonal to the axis of the glass bulb 21. However, other shapes may be used.

  FIG. 5 is a diagram showing a second modification of the end shape of the glass bulb in the embodiment.

  As shown in FIGS. 5A and 5B, the inner surface shapes of the end portions 221a and 226a of the glass bulbs 221 and 226 are such that the inner surfaces of the end portions 221a and 226a of the glass bulbs 221 and 226 are on the discharge space 228 side. It may be a shape that bulges.

(2) End part structure In embodiment, the pinch seal method is used for sealing of the edge part of a glass bulb. When sealed by this method, the inner surface of the end portion 21a of the glass bulb 21 becomes flat as shown in FIG. 2B and FIG. In addition, in the figure, it pinches from the direction orthogonal to a paper surface.

  However, the end sealing method may be performed by a method other than the pinch sealing method described above. As another method, there is a chip-off method. When sealed by this method, the shape of the end portion 226a of the glass bulb 226 bulges toward the discharge space 228 as shown in FIG.

  As a method other than the above, sealing may be performed using a bead at the end.

  FIG. 6 shows a schematic diagram of a modification in which the end of the glass bulb is sealed with a bead.

  In this sealing method, after a bead 330 having an outer diameter close to the inner diameter of the glass bulb 321 (glass tube 321a) is inserted into the end of the glass tube 321a, the portion of the glass tube 321a into which the bead 330 is inserted ( 321b) is heated to fuse the glass tube 321a and the bead 330 together. When sealed by this method, the shape of the end (including the bead) facing the discharge space 325 in the glass bulb 321 can be made a desired shape. In other words, when a spherical bead is used, it swells in a hemispherical shape toward the discharge space 325, and when a bead with a flat end surface is used, it can be made flat as shown in FIG.

(3) About inner diameter In embodiment, the cross-sectional shape of the glass bulb | bulb was elliptical shape, and the internal diameter (short diameter) was 2.8 (mm). However, the inner diameter of the glass bulb is preferably 8 (mm) or less. This is because, when the inner diameter is larger than 8 (mm), the heat radiation effect due to the surface area of the glass bulb is too large, and the rise in luminance is delayed.

  The inner diameter of the glass bulb is particularly the distance between the axis of the glass bulb and the inner surface located on the side from which light is mainly extracted (the front panel side when used in a backlight unit) (twice the distance). Is equivalent to the “inner diameter in the end axis direction” in the present invention.) Is preferably within the range of 0.8 (mm) or more and 2.0 (mm) or less regardless of the cross-sectional shape. . That is, when the cross-sectional shape is circular, the inner diameter may be in the range of 1.6 (mm) to 4.0 (mm), and the cross-sectional shape of the glass bulb as in the embodiment. Is an elliptical shape, the inner diameter of the minor axis may be 1.6 (mm) or more and 4.0 (mm) or less.

  The reason why the distance between the axis of the glass bulb and the inner surface located on the light extraction side is within the above range is that high lamp efficiency tends to be obtained.

(4) Cross-sectional shape As described above, the cross-sectional shape of the glass bulb in the embodiment is an elliptical shape, but may be another shape, for example, a circular shape.

  In particular, if the glass bulb is made into a thin tube using soda glass, the mechanical strength will be weaker than borosilicate glass if the dimensions are the same, but if the cross section is made flat, the dimensions are the same as the diameter in the short axis direction, for example. Compared to a circular cross section having a diameter, the diameter in the major axis direction is larger than a circular one. For this reason, the glass tube (glass bulb) having a flat cross section can have higher rigidity (second moment of cross section) than the glass tube (glass bulb) having a circular cross section. Mechanical strength can be increased.

  In addition, there is a possibility that the glass bulb will be enlarged by making the cross section flat, but for example, when a lamp using such a flat glass bulb is used for the backlight unit, the backlight unit The thickness direction of the backlight unit can be prevented from being increased by matching the thickness direction of the glass bulb with the minor axis direction of the glass bulb.

  In addition to the “elliptical shape” in the embodiment, the “flat shape” mentioned here includes an ellipse shape, a polygonal shape (for example, a rectangular shape), and a shape with rounded corners, etc. included.

7). Regarding the electrodes (1) Position In the embodiment, that is, in the example shown in FIG. 2, the outer ends (position A) of the electrodes 31 and 32 are positioned closer to the center of the glass bulb 21 than the inner ends of the glass bulb 21. However, the outer end of the electrode 31 may be positioned closer to the end side (outer side) of the glass bulb 221 than the inner end of the glass bulb 221 as shown in FIG. Furthermore, the outer end of the electrode may be positioned so as to substantially coincide with the inner surface end of the glass bulb.

(2) Shape The electrodes 31 and 32 in the embodiment are provided in a strip shape on the outer periphery of the glass bulb 21, but electrodes having other shapes may be used. As other shapes, for example, a cap shape that covers the entire end of the glass bulb may be used.

8). Phosphor layer and protective layer The protective layer 22 is made of yttrium oxide, but may be made of other materials. Examples of other materials include metal oxides, specifically, titania and magnesium oxide having a high relative dielectric constant in order to increase the dielectric constant of a member in contact with the electrode.

  Furthermore, in the embodiment, the protective layer is formed over a larger area than the phosphor layer, but the protective layer only needs to be formed in a range where the phosphor layer and the inner surface of the glass tube do not contact each other. For example, a state in which the end surface of the protective layer and the end surface of the phosphor layer substantially coincide with each other may be employed.

9. Kinds of lamps In the embodiment, an external electrode type having an electrode outside a glass bulb has been described as a fluorescent lamp. However, the present invention is also applied to a cold cathode type having a (cold cathode) electrode inside a glass bulb. it can.

  FIG. 7 is a schematic view of a cold cathode fluorescent lamp according to the present invention.

  The cold cathode fluorescent lamp 400 includes a glass bulb 401 and electrodes 403 sealed at both ends of the glass bulb 401 (only one side is shown in FIG. 7).

  The glass bulb 401 is made of soda glass as in the above embodiment, and a protective layer 405 and a fluorescent film layer 407 are formed on the inner surface from the inner surface side. The electrode 403 includes, for example, a bottomed cylindrical hollow electrode 409 and an electrode shaft 411 attached to the bottom of the hollow electrode 409. The electrode 403 is sealed to the glass bulb 401 with an electrode shaft 411.

  Also in the cold cathode fluorescent lamp 400, the protective layer 405 is formed in a region excluding the end portion of the glass bulb 401, and the phosphor layer 407 is in a region narrower than the region where the protective layer 405 is formed. Is formed. Specifically, in the longitudinal direction of the glass bulb 401, the end of the phosphor layer 407 is located closer to the center than the end of the protective layer 405.

  In the region where the protective layer 405 is not formed, which is the end of the glass bulb 401, the sodium oxide 413 is deposited during the firing of the phosphor layer 407, for example, as in the embodiment. ing.

  Even in such a configuration, the dark start-up characteristics can be improved because the sodium oxide 413 faces the discharge space 415 in the glass bulb 401. Moreover, since this sodium oxide 413 precipitates efficiently at the time of baking of the fluorescent substance layer 407 or an electrode sealing, it can be implemented easily.

10. The shape of the lamp In the embodiment and the above-described modification, the lamp has been described as having a straight tube shape, but the lamp may have another shape such as a U shape or a W shape.

11. Regarding the backlight In the embodiment, the backlight unit has been described as being a direct type as shown in FIG. 1, but the lamp according to the present invention may be used as the light source of the edge type backlight unit. In the case of the edge type, the lamp has a straight tube shape, an L shape, or a U shape.

12. Others In the embodiment, the case where the lamp is used as the light source of the backlight unit has been described. However, the lamp may be used as a light source other than the backlight unit such as general illumination.

  The present invention can be used for a cold cathode fluorescent lamp capable of improving the dark starting characteristics without performing a complicated process.

Schematic perspective view showing a configuration of a backlight unit for a liquid crystal television according to the present embodiment The figure which shows the structure of the lamp | ramp which concerns on this Embodiment. The figure which shows the result which measured the dark starting characteristic The figure which shows the modification which concerns on the formation area of the protective layer in embodiment The figure which shows the modification 2 which concerns on the edge part shape of the glass bulb in embodiment Schematic of a modified example in which the end of the glass bulb is sealed with a bead Schematic of a cold cathode fluorescent lamp according to the present invention

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Backlight unit 10 Housing | casing 16 Front panel 20 Fluorescent lamp 21 Glass bulb 22 Protective layer 23 Phosphor layer 24 Sodium oxide 31, 32 External electrode

Claims (8)

A fluorescent lamp having electrodes at both ends of a glass bulb having a discharge space therein, the glass bulb is made of soda glass, and a protective layer and a phosphor layer are not formed on the inner surface of the glass bulb. A cold cathode fluorescent lamp , wherein a protective layer and a phosphor layer are formed in this order from the inner surface side, leaving one or more regions, and the regions exist in the electrode facing portion . 2. The cold cathode fluorescent lamp according to claim 1, wherein an end of the phosphor layer is located closer to a center side than an end of the protective layer in a longitudinal direction of the glass bulb. In the opposing portion of the electrode, the protective layer is formed, and the cold cathode fluorescent lamp according to claim 2, characterized in that the phosphor layer is not formed moiety is present. The cold cathode fluorescent lamp according to claim 1 or 2, wherein the glass bulb has a Na content of 5 wt % or more and 20 wt % or less. The cold cathode fluorescent lamp according to any one of claims 1 to 3, wherein an alkali metal precipitated from the glass is present in the region. The cold cathode fluorescent lamp according to claim 1, wherein the protective layer contains a cesium compound. The cold cathode fluorescent lamp according to claim 1, wherein the glass bulb has a flat cross-sectional shape. A backlight unit comprising the cold cathode fluorescent lamp according to claim 1 as a light source.

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