Fluorescent lamp, backlight unit, and liquid crystal display device

Abstract

A backlight unit has an external electrode fluorescent lamp in a housing. The external electrode fluorescent lamp includes a glass bulb having a discharge space inside, and electrodes around both ends of the glass bulb. A protective layer and a phosphor layer are formed on an internal surface of the glass bulb in this order. The glass bulb is made of soda glass, and sodium oxide precipitated from this soda glass appears on part of the internal surface of the glass bulb where the protective layer is not formed, so as to be exposed to the discharge space.

1 . A cold cathode fluorescent lamp comprising:
 a glass bulb having a discharge space inside; and   electrodes provided at both ends of the glass bulb,   wherein a protective layer is formed on an inner surface of the glass bulb, except a part of the inner surface at least one of the ends,   a phosphor layer is formed on the protective layer, and   an alkaline metal precipitated from the glass bulb appears on the part of the inner surface where the protective layer is absent.   
   
   
       2 . The cold cathode fluorescent lamp of  claim 1 ,
 wherein the glass bulb contains sodium oxide in a range of 3 wt % to 20 wt %.   
   
   
       3 . The cold cathode fluorescent lamp of  claim 1 ,
 wherein the glass bulb contains sodium oxide in a range of 5 wt % to 20 wt %, and   the alkaline metal includes sodium.   
   
   
       4 . The cold cathode fluorescent lamp of  claim 1 ,
 wherein the electrodes are external electrodes provided outside the glass bulb at both ends.   
   
   
       5 . The cold cathode fluorescent lamp of  claim 1 ,
 wherein the protective layer is composed of an aggregate of metal oxide particles, and has an average thickness of no more than 2 μm and a surface roughness of no more than 1 μm.   
   
   
       6 . The cold cathode fluorescent lamp of  claim 5 ,
 wherein the protective layer contains an electron emissive material selected from the group consisting of a cesium compound, a lithium compound, and a barium compound.   
   
   
       7 . The cold cathode fluorescent lamp of  claim 1 ,
 wherein the protective layer is composed of an aggregate of metal oxide particles, and has an average thickness of no more than 2 μm, and   an average cross sectional area of each closed hole between the metal oxide particles in the protective layer is no more than 0.1 μm 2 .   
   
   
       8 . The cold cathode fluorescent lamp of  claim 7 ,
 wherein the protective layer contains an electron emissive material selected from the group consisting of a cesium compound, a lithium compound, and a barium compound.   
   
   
       9 . The cold cathode fluorescent lamp of  claim 7 ,
 wherein a number of closed holes per unit area of cross section in the protective layer is no more than four in 1 μm 2 .   
   
   
       10 . The cold cathode fluorescent lamp of  claim 2 ,
 wherein the glass bulb is flattened in cross section, with an internal diameter on a minor axis being in a range of 1.6 mm to 4.0 mm.   
   
   
       11 . The cold cathode fluorescent lamp of  claim 3 ,
 wherein the glass bulb is flattened in cross section, with an internal diameter on a minor axis being in a range of 1.6 mm to 4.0 mm.   
   
   
       12 . The cold cathode fluorescent lamp of  claim 1 ,
 wherein the phosphor layer is formed entirely between inner ends of the electrodes, and   the protective layer is formed entirely between outer ends of the electrodes.   
   
   
       13 . The cold cathode fluorescent lamp of  claim 10 ,
 wherein the phosphor layer is formed entirely between inner ends of the electrodes, and   the protective layer is formed entirely between outer ends of the electrodes.   
   
   
       14 . A cold cathode fluorescent lamp comprising:
 a glass bulb having a discharge space inside; and   electrodes provided at both ends of the glass bulb,   wherein a phosphor layer is formed on an inner surface of the glass bulb, except at least one part of the inner surface, and   an alkaline metal precipitated from the glass bulb appears on the at least one part of the inner surface.   
   
   
       15 . A backlight unit comprising a cold cathode fluorescent lamp of  claim 1  as a light source. 
   
   
       16 . A liquid crystal display device comprising a backlight unit,
 the backlight unit including a plurality of cold cathode fluorescent lamps of  claim 1  and one high-frequency electronic ballast which illuminates the plurality of cold cathode fluorescent lamps.   
   
   
       17 . The cold cathode fluorescent lamp of  claim 1 ,
 wherein the electrodes are cold cathodes provided inside the glass bulb at both ends, and   an end of the phosphor layer is closer to a center of the glass bulb than an end of the protective layer is, in a longitudinal direction of the glass bulb.   
   
   
       18 . The cold cathode fluorescent lamp of  claim 17 ,
 wherein the electrodes are tubular, and   a part of the inner surface of the glass bulb facing tubular parts of the electrodes has an area where the protective layer is formed and the phosphor layer is not formed.   
   
   
       19 . The cold cathode fluorescent lamp of  claim 1 ,
 wherein the phosphor layer contains a phosphor that absorbs the ultraviolet light of 313 nm,   and a total weight proportion of the phosphor that absorbs ultraviolet light of 313 nm in a composition of the phosphor layer is larger than 50%.   
   
   
       20 . The cold cathode fluorescent lamp of  claim 6 ,
 wherein the protective layer is formed from by mixing a protective layer suspension with an electron emissive material selected from the group consisting of a cesium compound, a lithium compound, and a barium compound.   
   
   
       21 . The cold cathode fluorescent lamp of  claim 20  wherein the protective layer is formed from by mixing a protective layer suspension with a cesium compound, and wherein the cesium compound is less than 3 wt %. 
   
   
       22 . The cold cathode fluorescent lamp of  claim 1 , wherein the phosphor layer has a thickness in a range of 14 μm to 25 μm