Effect of pH on screen dot size from crosslinking reaction of Poly(vinyl alcohol) in phosphor slurry for cathode ray tube production

Abstract

Effect of pH of phosphor slurry in color display tube (CDT) processing on the screen dot size was investigated. A phosphate and carboxylate buffer solutions were used for pH control but they were not compatible with the slurry and generated poor pattern of phosphor adherence. Reduction of sodium polyacrylate solution (tamol), asurfactant, conld slightly reduce the slurry pH from 8.0 to 7.8 . The screen with best quality was found when tamol was reduced by 10%. Slurry pH 6.0-9.0 were investigated by adding sulfuric acid and ammonia solution. At pH 7.0-8.2, the slurries gave the optimum screen qualities while other pH gave poor screen qualities. For the pH 6.0, at which supposedly the highest concentration of bichromate ions is present, the larger screen dot sizes were observed but other screen qualities were unacceptable. At 115% of the current routine exposure amount, the dot sizes tended to be larger at lower pH, however at lower exposure, this trend became less obvious. The most preferred condition for phosphor slurry in CDT manufacturing was at the slurry pH 7.0 with exposure amount over 85% of the current routine exposure amount since this condition produced good controlled dot sizes, good sharpness, less pin holes, high white uniformity, and satisfied corner brightness.