Patent ID: 7088035

Claim:
A glass bulb for a cathode ray tube comprising: a panel portion with a substantially rectangular face portion; and a funnel portion including a body portion with an opened end connected to the panel portion, wherein: glass constituting the funnel portion contains at least 60% of SiO 2 and at least 7% of PbO by molar percentage and satisfies 0.35≦WK/(WNa+WK)≦0.6 where WNa and WK indicate respectively a molar percentage of Na 2 O and K 2 O included therein; the glass bulb, when assembled in a cathode ray tube, has a region which generates a tensile vacuum stress by the application of an atmospheric pressure to an outer surface of the glass bulb inside of which is vacuumed, and a compressive stress layer is formed partly by ion exchanging in an at least a region in the funnel portion, which includes a portion in an outer surface of the body portion of the funnel portion, in which σ VF (MPa) is generated, where σ VF (MPa) is the maximum value of the tensile vacuum stress, and the concentration of potassium ions is distributed according to a substantially step function in a thickness direction of the glass in the compressive stress layer, and when the maximum value of a compressive stress in the compressive stress layer is a σcm(MPa), the relation between σ cm and σ VF is 0.03≦|σ VF /σ cm |≦0.5.