Glass panel resistant to coloring when irradiated with electron rays.

摘要

A glass panel for a face plate of a cathode ray tube which is characterized in that said glass panel has the following glass composition: SiO2 64 -75% by weight Al2O3 1.5-2.0% by weight CaO 6.5-9.0% by weight MgO 0 -5.0% by weight Li2O 0.5-2.5% by weight Na2O 7.0-12% by weight K2O 2.1-5.0% by weight SrO + BaO + ZrO2 0 -10% by weight CeO2 0 -0.5% by weight and wherein part of the Na ion in at least the surface layer of the panel region to be irradiated with electron rays, is substituted with K ion by an ion exchange treatment in a K-containing molten salt and resultantly the molar ratio of Na ion and K ion expressed by Na2O/(Na2O + K2O) in at least the glass layer ranging from 0.5 mu m to 6.5 mu m in depth from the panel surface, of said panel region to be irradiated with electron rays is 0.3-0.75; and the glass panel has a shape of a tray comprising a rectangular top portion and side portions, the shorter side of said rectangular top having a length (L1) of 100 to 530 mm, the longer side having a length (L2) of 1.3 to 3 times L1 mm, the depth (H) of the tray being 20 to 40 mm, and the thickness (t) of the rectangular top expressed in mm and the length (L1) of said shorter side expressed in mm satisfying the relationship as defined below: $$