Patent ID: 7674412

Claim:
A method of forming a resin film from a first resin for a middle portion to form a resin film main body of the resin film and a second resin for edge portions to form both side edge portions in a crosswise direction of the resin film, the method comprising the steps of: joining the first resin and the second resin in such a manner as to enclose only both side edges in the crosswise direction of the first resin for the middle portion which is formed as a cross-section convex shape with the second resin for the edge portions which is formed as a cross-section concave shape and to form a boundary of the first resin and the second resin; and extruding the joined resins through an extruding die to form the resin film, wherein the first and second resins are joined by being fed through a feed block which includes a joining part having a specific cross-sectional shape in such a manner as to enclose only both side edges in the crosswise direction of the resin film main body which is formed as a cross-section convex shape with the resin for the edge portions which is formed as a cross-section concave shape, and wherein the joining part is formed so that the cross-sectional shape is shaped as a pair of recessed branch flow paths that are fitted on respective projecting edges of a trunk flow path.