Method of forming phosphor layer of gas discharge tube

1. A method of forming a phosphor layer of a gas discharge tube provided with the phosphor layer on an internal surface of an elongated tubular vessel forming a discharge space, comprising:

introducing a slurry of a phosphor powder and a binding resin dispersed in a medium into the tubular vessel;

holding the tubular vessel horizontally, in a sideways state, to deposit the phosphor powder and the binding resin in the tubular vessel; and

removing the medium from the tubular vessel, thereby forming a phosphor layer on a portion of the internal surface of the tubular vessel.

2. The method of claim 1 , wherein the binding resin is in a dispersion state in a dispersion medium when added to the medium.

3. The method of claim 2 , wherein the binding resin comprises polyvinyl alcohol and the dispersion medium comprises water.

4. The method of claim 1 , further comprising adding, to the slurry, a first solvent having a low viscosity for promoting the deposition of the phosphor powder and the binding resin immediately before introducing the slurry into the tubular vessel.

5. The method of claim 1 , further comprising, after removing the medium from the tubular vessel, passing through an inside of the tubular vessel a second solvent having a low viscosity which does not dissolve the binding resin but dissolves the medium, thereby removing the medium remaining in the tubular vessel.

6. The method of claim 4 , wherein the first solvents having a low viscosity comprises acetone or isopropyl alcohol.

7. The method of claim 1 , wherein a plurality of phosphor layers are formed on one portion of the internal surface of the tubular vessel by repeating, plural times, the introducing the slurry having the phosphor powder and the binding resin dispersed in the medium into the tubular vessel, the holding the tubular vessel sideways to deposit the phosphor powder and the binding resin in the tubular vessel and then removing the medium from the tubular vessel.

8. The method of claim 7 , wherein when repeating, plural times, the introducing the slurry having phosphor powder and the binding resin dispersed in the medium into the tubular vessel, the holding the tubular vessel sideways to deposit the phosphor powder and the binding resin in the tubular vessel and the removing the medium from the tubular vessel, the amount of the phosphor powder in the slurry is so changed that a plurality of phosphor layers having different thicknesses are formed on a portion of the internal surface of the tubular vessel.

9. The method of claim 1 , wherein the slurry is introduced into the tubular vessel in a specific amount such that a convex phosphor layer is formed in the tubular vessel.

10. The method of claim 1 , wherein, when introducing the slurry into the tubular vessel, air is introduced at regular intervals such that a plurality of convex phosphor layers are formed in the tubular vessel.

11. The method of claim 5 , wherein the second solvent having a low viscosity comprises acetone or isopropyl alcohol.

12. A method of forming a phosphor layer of a gas discharge tube provided with the phosphor layer on an internal surface of an elongated tubular vessel forming a discharge space, comprising:

introducing a slurry of a phosphor powder and a binding resin, emulsionized in a medium, into the tubular vessel;

holding the tubular vessel sideways to deposit the phosphor power and the binding resin in the tubular vessel; and

removing the medium from the tubular vessel, thereby forming a phosphor layer on a portion of the internal surface of the tubular vessel.

13. The method of claim 12 , further comprising adding, to the slurry, a first solvent having a low viscosity for promoting the deposition of the phosphor powder and the binding resin immediately before introducing the slurry into the tubular vessel.

14. The method of claim 12 , further comprising, after removing the medium from the tubular vessel, passing through an inside of the tubular vessel a second solvent having a low viscosity which does not dissolve the binding resin but dissolves the medium, thereby removing the medium remaining in the tubular vessel.

15. The method of claim 13 , wherein the first solvent having a low viscosity comprises acetone or isopropyl alcohol.

16. The method of claim 14 , wherein the second solvent having a low viscosity comprises acetone or isopropyl alcohol.