| 摘要 |
PURPOSE:To enable a low-cost material to be used for a sealing plate by airtightly isolating the internal spaces of the inner and the outer tube bulbs from the external atmosphere by applying an airtightness maintenance part to the surface of the sealing plate surrounded by the open end of the outer tube bulb. CONSTITUTION:An airtightness maintenance part 22 is applied to the entire area on a sealing plate 21 surrounded by the open end of an outer tube bulb 1. Since the airtightness of the outer tube bulb 1 is maintained by the effect of the part 22 applied to the surface of the sealing plate 21, the sealing plate 21 for closing the open end of the bulb 1 is not required to be airtight and may be air permeable. Accordingly, it is possible to use a low-cost material for the sealing plate 21.
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