The present invention relates to a gas discharge tube in which a discharge gas is sealed, a manufacturing method of the gas discharge tube, and a display device which can display images (video images) such as moving images by arranging a large number of gas discharge tubes.
A large display device, which can display video images such as moving images by, for example, arranging a large number of gas discharge tubes, each of which is produced by providing a phosphor layer inside a thin glass tube with an external diameter of 1 mmφ and a thickness of 0.1 mm and sealing a discharge gas therein similarly to the light-emitting principle of PDP, is proposed. Since this display device is a self emission type display device, it is possible to display bright video images and realize a large screen more than 100 inches. Thus, this display device is suitable for applications where the entire surface of an indoor wall is made a display device.
By the way, for such a display device, it is necessary to use thin, long gas discharge tubes according to the size of the display screen. However, in order to manufacture gas discharge tubes longer than 1 m, such as 2 m- to 3 m-long gas discharge tubes, the manufacturing machine becomes larger and the manufacturing cost increases, and also there is a problem that it is extremely difficult to manufacture uniform and satisfactory gas discharge tubes. More specifically, in order to manufacture a gas discharge tube, it is necessary to form a secondary electron emitting film of magnesium oxide (MgO), etc. and a phosphor layer therein. However, a sintering process is necessary to form these secondary electron emitting film and phosphor layer, and therefore if a length in the tube axial direction increases, it becomes extremely difficult to form the secondary electron emitting film and phosphor layer in good condition inside the gas discharge tube. The reason for this is that if the gas discharge tube becomes longer, there will be a shortage of oxygen in the tube, necessary for decomposing organic components such as a resin, and consequently it will be difficult to form a uniform film.
Hence, a proposal is made to provide a display device 100 capable of realizing the display screen of desired size even when gas discharge tubes shorter than the length of one side of a display screen are used, by regularly arranging a plurality of gas discharge tubes of different emission colors, namely, red (R) gas discharge tubes 100a, green (G) gas discharge tubes 100b and blue (B) gas discharge tubes 100c, in a line direction X of the screen and arranging a plurality of gas discharge tubes of the same emission color, for example, red gas discharge tubes 100a and 100a, in a column (tube axial direction) Y of the screen as shown in FIG. 1. For such a display device 100, since short gas discharge tubes can be used, it is possible to form the secondary electron emitting film and phosphor layer uniformly in good condition inside the tubes.
However, in the case where a plurality of gas discharge tubes are arranged in the tube axial direction, the contact section between adjacent gas discharge tubes in the tube axial direction becomes a non-light-emitting region 110 where a discharge cell cannot be formed. It is therefore necessary to dispose a pair of sustain electrodes 130a and 130b so as to prevent a discharge cell 120 from being included in the non-light-emitting region 110.
By the way, main elements that specify the display quality of the display device include brightness and resolution. The brightness is determined by the occupancy of the discharge cells 120 (X1/(X1+X2))×(Y1/(Y1+Y2)), the resolution in the column direction of the screen is determined by the pitch length (X1+X2) of the gas discharge tubes, and the resolution in the line direction of the screen is determined by the pitch length (Y1+Y2) of the sustain electrodes. Here, X2 is an element concerning the thickness of the gas discharge tube, and determined by the gas discharge tube to be placed. Hence, in order to achieve a high-brightness, high-resolution display device, it is necessary to shorten Y2, that is, it is necessary to narrow the non-light-emitting region 110.
However, the end faces of conventional gas discharge tubes are semi-spherical as shown in FIG. 1 and have irregularity in shape because the gas discharge tubes are sealed by heating the ends of glass tubes, and therefore it is extremely difficult to make the non-light-emitting region 110 uniform over the entire surface of the display screen. Consequently, it is difficult to make the brightness of all the discharge cells uniform, and there is a possibility that the conventional display device may have uneven brightness.
Therefore, the present inventor et., al. proposed a display device which uses gas discharge tubes with flat end faces to decrease the volume of the contact section between the facing gas discharge tubes, thereby capable of ensuring a sufficient display area (see, for example, Japanese Patent Application Laid-Open No. 2003-203603). A gas discharge tube disclosed in the Japanese Patent Application Laid-Open No. 2003-203603 is obtained by placing a thin glass plate with an adhesive layer in contact with a glass tube and heating the thin glass plate with a heater or the like to adhere it to an end face of the glass tube.