Polarized resin film and process for producing same

1. A polarized vinylidene fluoride/tetrafluoroethylene copolymer resin film having 560 or fewer spot defects per m 2 , the number of spot defects being measured by a defect measurement method;

the defect measurement method comprising reading defects of the film, using an surface inspection system in which a CCD camera is placed so as to detect defects at an angle of 45 degrees relative to an LED light source, within a rectangular range of 300 mm in a width direction, which is a direction perpendicular to a scanning direction, and 150 mm in a machine direction, which is the scanning direction, while the film is scanned under the camera at a rate of 20 m/min;

wherein,

first, defects having a bright area of 1.5 mm 2 or less and a dark area of 1.4 mm 2 or less are selected; and

next, in order to remove defects resulting from causes other than a corona treatment from the selected defects, a circumscribed rectangle of defect is set so as to have two sides along the scanning direction, and the number of only defects having a circumscribed width of 2.88 mm or less, a circumscribed length of 0.43 to 2.30 mm, an aspect ratio of −39 to +27, an occupancy area ratio in the circumscribing rectangle of 4,000 to 6,950, and an area ratio of −3,100 to +5,200, is automatically counted as spot defects by the surface inspection system.

2. The polarized vinylidene fluoride/tetrafluoroethylene copolymer resin film according to claim 1 , wherein the number of spot defects per m 2 is 50 or fewer.

3. A method for producing the polarized resin film of claim 1 , comprising:

step A of charging a non-polarized resin film directly placed on a ground electrode by a corona treatment using a first electrode while applying a voltage between the first electrode and the ground electrode, thereby attaching the non-polarized resin film to the ground electrode by static electricity; and

step B of polarizing the non-polarized resin film attached to the ground electrode by a corona treatment using a second electrode while applying a voltage between the second electrode and the ground electrode to obtain the polarized resin film of claim 1 .

4. The production method according to claim 3 , wherein step A is carried out while the non-polarized resin film directly placed on the ground electrode is moved relative to the first electrode, and

the first electrode comprises a plurality of needle electrodes arranged perpendicular to the moving direction.

5. The production method according to claim 3 , wherein the non-polarized resin film is an odd-chain nylon film or a polyvinylidene fluoride-based resin.

6. The production method according to claim 3 , wherein the non-polarized resin film is a polyvinylidene fluoride-based resin.

7. The production method according to claim 6 , wherein the polyvinylidene fluoride-based resin is a vinylidene fluoride/tetrafluoroethylene copolymer resin film.

8. An apparatus for producing the polarized resin film of claim 1 , comprising a first electrode and a second electrode;

wherein the first electrode is provided to face a ground electrode to be moved, and generates a corona discharge upon a voltage applied between the first electrode and the ground electrode, thereby charging a non-polarized resin film placed on the ground electrode so that the non-polarized resin film is attached to the ground electrode by static electricity; and

the second electrode is provided downstream of the first electrode to face the ground electrode, and generates a corona discharge upon a voltage applied between the second electrode and the ground electrode, thereby polarizing the non-polarized resin film attached to the ground electrode to obtain the polarized resin film of claim 1 .

9. The production apparatus according to claim 8 , wherein the first electrode comprises a plurality of needle electrodes arranged at predetermined intervals perpendicular to the moving direction of the ground electrode.

10. The production apparatus according to claim 9 , wherein the plurality of needle electrodes are arranged at intervals that are set so that a charged area of the non-polarized resin film that can be charged by a corona discharge overlaps at least part of a charged area of the non-polarized resin film charged by an adjacent needle electrode.

11. The production apparatus according to claim 8 , wherein the second electrode comprises a wire electrode extending perpendicular to the moving direction.

12. The polarized vinylidene fluoride/tetrafluoroethylene copolymer resin film according to claim 1 , which is for touch panels.

13. A touch panel having the polarized vinylidene fluoride/tetrafluoroethylene copolymer resin film according to claim 1 .

14. The production method according to claim 4 , wherein the non-polarized resin film is an odd-chain nylon film or a polyvinylidene fluoride-based resin.

15. The production method according to claim 4 , wherein the non-polarized resin film is a polyvinylidene fluoride-based resin.

16. The production method according to claim 15 , wherein the polyvinylidene fluoride-based resin is a vinylidene fluoride/tetrafluoroethylene copolymer resin film.

17. The production apparatus according to claim 9 , wherein the second electrode comprises a wire electrode extending perpendicular to the moving direction.

18. The production apparatus according to claim 10 , wherein the second electrode comprises a wire electrode extending perpendicular to the moving direction.

19. The polarized vinylidene fluoride/tetrafluoroethylene copolymer resin film according to claim 2 , which is for touch panels.

20. A touch panel having the polarized vinylidene fluoride/tetrafluoroethylene copolymer resin film according to claim 2 .