Glass bulb for a cathode ray tube and a method for producing the same

A glass bulb for a cathode ray tube comprising a panel portion having a substantially rectangular face portion and a funnel portion including a body portion having an opened end connected to the panel portion, the glass bulb being characterized in that:

• glass constituting the funnel portion contains at least 60% of SiO2 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 Na2O and K2O included therein;
• that 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 σVF(MPa) is generated, where σVF(MPa) is the maximum value of the tensile vacuum stress, and
• that 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 cm(MPa), the relation between σcm and σVF is 0.03≦|σVF/σcm|≦0.5.