| 摘要 |
PROBLEM TO BE SOLVED: To reduce volatilized matters from a burner dirt or glass and to provide a glass capable of shortening fusion period and decreasing working temperature, by setting light transmissivity of a specific wavelength of infrared radiation to a specific ratio to a specific glass thickness. SOLUTION: Light transmissivity of 1,050 nm wavelength of infrared radiation is less than 70% in glass thickness. Preferably, this funnel glass contains 0.2-10 wt.% Fe2O3 and 0.015 wt.% Fe2+, has 0.08 weight ratio of Fe2+ to Fe3+, contains 10-30 wt.% PbO, and absorption coefficient to X-ray with 0.6 A deg. is higher than 40 cm-1. Preferably, this funnel glass contains SiO2: 48-58 wt.%, Al2O3: 0.5-6 wt.%, PbO: 10-30 wt.%, MgO: 0-5 wt.%, CaO: 0-6 wt.%, SrO: 0-9 wt.%, BaO: 0-9 wt.%, Na2O: 3-9 wt.%, K2O: 4-11 wt.%, Sb2O3: 0-1 wt.%, and Fe2O3: 0.2-10 wt.%.
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