| 摘要 |
A dope is produced from TAC and a mixture solvent whose main compound is dichloromethane. The dope is cast from a casting die onto a casting drum. In an upstream side from the casting die, a decompression chamber having air pipes is provided. The difference from the ordinate pressure to the pressure inside the decompression chamber is -2000 Pa to -10 Pa. An air is fed through the air pipes into the decompression chamber. Thus the pressure fluctuation in the decompression chamber is reduced, and the pressure becomes almost constant in the widthwise direction. Therefore, the entrained air and another air are prevented from entering into the decompression chamber, which makes the shape of the bead of the discharged casting dope stable. When having self-supporting properties, the casting film is peeled as a film from the casting drum and dried to be a TAC film without thickness unevenness.
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