Method of manufacture of polytetrafluoroethylene stretched film, and polytetrafluoroethylene stretched film

摘要

A method of manufacturing a PTFE stretched film that has higher tensile strength at its breaking point. In the method, a resin composition is obtained by mixing an emulsion of PTFE (A) with a number average molecular weight of 5×106 or more and an emulsion of PTFE (B) with a number average molecular weight of 1×106 to 4×106 so that the solid content ratio (A/B) of the PTFE (A) and the PTFE (B) is 99/1 to 10/90. The mixed emulsion is subjected to compression molding in a melted state under a reduced-pressure atmosphere to obtain a film.

主权项

1. A method of manufacture of polytetrafluoroethylene stretched film having the following steps (I) and (II),
(I) A step in which a resin composition obtained by mixing an emulsion of polytetrafluoroethylene (A) with a number average molecular weight of 5×106 or more and an emulsion of polytetrafluoroethylene (B) with a number average molecular weight of 1×106 to 4×106 so that the solid content ratio (A/B) of the polytetrafluoroethylene (A) and the polytetrafluoroethylene (B) is 99/1 to 10/90, and obtaining a resin composition powder in which polytetrafluoroethylene (A) and polytetrafluoroethylene (B) are mixed on the secondary particle level, by mixing the emulsion of polytetrafluoroethylene (A) and the emulsion of polytetrafluoroethylene (B), and by subsequently aggregating and drying the mixed emulsion, and where the resin composition powder is subjected to compression molding in a melted state under a reduced-pressure atmosphere to obtain a film, wherein said polytetrafluoroethylene (A) and said polytetrafluoroethylene (B) are polytetrafluoroethylene obtained by emulsion polymerization, and (II) A step in which said film is melt stretched, wherein said melt stretching is biaxial stretching, said step (I) comprises step (I-1) in which said resin composition powder is pressed at a first pressure V1 in a range of 0.01-100 MPa for 1-100 minutes in a state where it has been heated to a temperature T1 in a range of 15-150° C. under a reduced-pressure atmosphere, and step (I-2) in which the heated and pressed resin composition in said step (I-1) is further heated at a temperature T2 in a range of 330-420° C. to a melted state, and compression molded at a second pressure V2 in a range of 0.01-100 MPa for 1-100 minutes under a reduced-pressure atmosphere, said reduced-pressure atmosphere in said steps (I-1) and (I-2) is 10 Torr or less, and the difference of said second pressure V2 and said first pressure V1 (V2−V1) ranges between about 0.1-99 MPa.