| 摘要 |
PROBLEM TO BE SOLVED: To prevent distortion of the principal plane of a shadow mask after the mask and the mask frame were fixed. SOLUTION: By disposing a plurality of nearly rectangular grooves or nearly circular hollows on a buffer portion at the skirt of the shadow mask, flexural strength of the skirt in the circular direction is made larger than that in the direction parallel to the tube axis and deformation on the principal plane of the shadow mask is avoided.
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