PURPOSE: To obtain a film without rough and large particles, to attain longer filter life and to make production of industrial scale possible, by filtering further a polyester raw material containing an ordinary carbon black under a specified filtering condition.
CONSTITUTION: A polyester resin containing 0.01W70wt% of carbon black based on wt. of the polyester is filtered through a unit with a built-in filter whose absolute filtering diameter is smaller than 10μ under a filtering speed of smaller than 500kg/hr.m2 and larger than 10kg/hr.m2 and the intrinsic viscosity of the polyester thereafter becomes larger than 0.20 and smaller than 0.60. The life of the filter for manufacturing the polyester raw material containing carbon black can be thereby lengthened. At the same time, it is possible to obtain a raw material which is suitable for manufacturing a high-density recording light-shielding film and whose no. of rough and large projection becomes smaller and the life of the filter for manufacturing the film also becomes longer, in a filmy state of this raw material.
UCHIUMI SHIGEO
TAKIZAWA TOSHIBUMI
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