| 摘要 |
PROBLEM TO BE SOLVED: To solve the problem of a usual method of joining a pressurized film 2 to a fitting frame 3 over the whole part overlapping therewith, that the film 2 is apt to be torn off when it is pressed on an upper plate 20, since the film 2 is subjected not only to a tensile force in the radial direction of the surface thereof at the opening end face of the fitting frame 3 in particular, but also to the tensile force in the direction of the thickness of the film 2. SOLUTION: The pressurized film 2 is not joined to the fitting frame 3 in the vicinity of the opening end face 13 of the fitting frame 3. Besides, the opening end face 14 of a frame 6 is formed inward from the opening end face 13 of the fitting frame 3 at a distance three times or larger than the dimension of the film thickness of the film 2. Moreover, a stepped part 26 is provided at the outer peripheral end of the pressurized film 2 and the film 2 is joined to the fitting frame 3 on the whole surface of the stepped part so that the opening end face 13 of the fitting frame 3 comes into contact with the stepped part 26. |
