| 摘要 |
PROBLEM TO BE SOLVED: To prevent the breaking of a window plate material due to a thermal shock and dynamic stress by using transparent glass ceramics as the window plate material. SOLUTION: A xenon lamp 3 and a reflecting plate 4 are built in a housing 2 disposed above recording paper 1 and a window plate material 5 made of transparent glass ceramics is fitted to the under surface opening of the housing 2 with pressing plates. An air intake 6 is formed at one end of the housing 2 in the longitudinal direction and an exhaust fan 7 is fitted to the other end. The window plate material 5 is produced by polishing both faces of a thin plate material made of transparent glass ceramics cut in prescribed dimensions to have a prescribed thickness, further polishing the peripheral face and developing the peripheral edges. The transparent glass ceramics has -10×10<7> to +10×10<7> / deg.C average coefft. of linear thermal expansion in the temp. range of 50-300 deg.C.
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