Shadow mask for cathode ray tube

Abstract

A shadow mask for a cathode ray tube has an effective screen portion having a plurality of beam passage holes arranged in a predetermined pattern, and an inactive portion with no beam passage holes. The length of a beam passage hole at a column adjacent to a division between the effective screen portion and the inactive portion in the long-sided direction is set to be smaller than the length of a beam passage hole placed at the short-sided center of the column. The length a of the beam passage hole adjacent to the division between the effective screen portion and the inactive portion at columns which are even-numbered from the long-sided center of the effective screen portion is established to satisfy the condition of 1>a/A≧0.45, compared to the length A of the beam passage hole placed at the short-sided center of relevant columns. The length b of the beam passage hole adjacent to the division between the effective screen portion and the inactive portion at columns which are odd-numbered from the long-sided center of the effective screen portion is established to satisfy the condition of 1>b/B≧0.35, compared to the length B of the beam passage hole placed at the short-sided center of relevant columns.

Dependencies are inferred from the claim text.