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The observation and origin of micro flow marks in the precision injection molding of polycarbonate
Author(s) -
Yoshii Masaki,
Kuramoto Hiroki,
Kawana Takeshi,
Kato Kazunori
Publication year - 1996
Publication title -
polymer engineering and science
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.503
H-Index - 111
eISSN - 1548-2634
pISSN - 0032-3888
DOI - 10.1002/pen.10469
Subject(s) - mold , polycarbonate , materials science , transfer molding , molding (decorative) , composite material , flow (mathematics) , thermal diffusivity , heat transfer , heat flow , polymer , melt flow index , thermal , mechanics , thermodynamics , physics , copolymer
Micro flow marks have been found to occur in injection molding of polycarbonate. Their minimum depth is ˜ 5 nm on the mold smooth surface. Such marks seem to be formed when the molten polymer near the mold wall at the advancing front is cooled to the no‐flow temperature of resin before it comes into contact with the mold wall, preventing the precision transcription of the mold smooth surface. We investigated the molding factors affecting their occurrence by heat transfer analysis. It was found that the size of micro flow marks is related to the melt temperature, mold temperature, no‐flow temperature, thermal diffusivity of the resin, and time pitch formation of flow mark ridges and valleys. The relationships between those factors and the sizes of micro flow marks are clarified quantitatively, and the guidelines for precision transcription in injection molding are formulated.