2001 Volume 58 Issue 9 Pages 462-471
The EVA content necessary to suppress the blooming in sheetings was determined. The content was higher than that in the case of injection moldings, and the appropriate blooming acceleration temperature was around 70°C being higher than that in the case of injection moldings. This is assumed to be because the amorphous region of PP in sheetings which can dissolve TBA-DB is less than that in injection moldings and because there exist skin layers where the transportation rate of additives is low in injection moldings. When a stimulation is applied to a part of surface of injection molding or sheeting by, for example, sucking operation and handling just after processing, a blooming generates at the part, and the necessary EVA content was determined to suppress it. TBA-DB has crystalline and amorphous forms, and the crystalline substance was observed as blooms while the transparent amorphous substance was not observed. Whether the crystalline substance is formed in the processed article or not unitarily determines the generation of blooming. When a stimulation was applied to the surface of a processed article at temperatures above the softening temperature of the amorphous substance (40°C), crystallization nuclei generated on it. By aging the processed article at temperatures above 40°C, the nuclei absorbed the amorphous substance, grew and became to be observed as blooms.
