Method and apparatus for reducing non-normal incidence distortion in glazing films
A method of manufacturing a polymer film includes melting a resin, extruding the melted resin through a die to produce a polymer film, shaping the polymer film, cooling the polymer film, illuminating a surface with a light source, capturing an image of a shadow cast by the polymer film on the surface while the polymer film is between the light source and the surface, calculating a frequency spectrum of at least a portion of the captured image, and adjusting a process parameter of the melting, the extruding, the shaping, or the cooling based on the frequency spectrum.
1 . A polymer film having a density variation such that a maximum value of a frequency spectrum calculated from grayscale image data of a transverse cross-section of a shadow cast by the polymer film at 60 degrees angle of incidence with respect to a light source is at a spatial frequency greater than 2 cycles per millimeter, wherein the polymer film is a multi-layer film, wherein the multi-layer film comprises an adhesive, wherein the adhesive comprises a pressure sensitive adhesive (PSA).
2 . The polymer film of claim 1 , wherein the maximum value of the frequency spectrum is at a spatial frequency greater than 4 cycles per millimeter.
3 . The polymer film of claim 1 , wherein the multi-layer film is 3-ply.
4 . A polymer film having a density variation such that a maximum value of a frequency spectrum calculated from grayscale image data of a transverse cross-section of a shadow cast by the polymer film at 60 degrees angle of incidence with respect to a light source is at a spatial frequency greater than 2 cycles per millimeter, wherein the polymer film comprises biaxially-oriented polyethylene terephthalate.
5 . The polymer film of claim 4 , wherein the maximum value of the frequency spectrum is at a spatial frequency greater than 4 cycles per millimeter.
6 . The polymer film of claim 4 , wherein the polymer film is a multi-layer film.
7 . The polymer film of claim 6 , wherein the multi-layer film is 3-ply.
8 . The polymer film of claim 6 , wherein the multi-layer film comprises an adhesive.
9 . A polymer film having a density variation such that a maximum value of a frequency spectrum calculated from grayscale image data of a transverse cross-section of a shadow cast by the polymer film at 60 degrees angle of incidence with respect to a light source is at a spatial frequency outside of 0.5-2 cycles per millimeter, wherein the polymer film is a multi-layer film, wherein the multi-layer film comprises an adhesive, wherein the adhesive comprises a pressure sensitive adhesive (PSA).
10 . The polymer film of claim 9 , wherein the maximum value of the frequency spectrum is at a spatial frequency of between 4 and 6 cycles per millimeter.
11 . The polymer film of claim 9 , wherein the multi-layer film is 3-ply.
12 . A polymer film having a density variation such that a maximum value of a frequency spectrum calculated from grayscale image data of a transverse cross-section of a shadow cast by the polymer film at 60 degrees angle of incidence with respect to a light source is at a spatial frequency outside of 0.5-2 cycles per millimeter, wherein the polymer film comprises biaxially-oriented polyethylene terephthalate.
13 . The polymer film of claim 12 , wherein the maximum value of the frequency spectrum is at a spatial frequency of between 4 and 6 cycles per millimeter.
14 . The polymer film of claim 12 , wherein the polymer film is a multi-layer film.
15 . The polymer film of claim 14 , wherein the multi-layer film is 3-ply.
16 . The polymer film of claim 14 , wherein the multi-layer film comprises an adhesive.
17 . A polymer film having a density variation such that a maximum value of a frequency spectrum calculated from grayscale image data of a transverse cross-section of a shadow cast by the polymer film at 60 degrees angle of incidence with respect to a light source is at a spatial frequency between 2 and 6 cycles per millimeter, wherein the polymer film is a multi-layer film, wherein the multi-layer film comprises an adhesive, wherein the adhesive comprises a pressure sensitive adhesive (PSA).
18 . The polymer film of claim 17 , wherein the multi-layer film is 3-ply.
19 . A polymer film having a density variation such that a maximum value of a frequency spectrum calculated from grayscale image data of a transverse cross-section of a shadow cast by the polymer film at 60 degrees angle of incidence with respect to a light source is at a spatial frequency between 2 and 6 cycles per millimeter, wherein the polymer film comprises biaxially-oriented polyethylene terephthalate.
20 . The polymer film of claim 19 , wherein the polymer film is a multi-layer film.
21 . The polymer film of claim 20 , wherein the multi-layer film is 3-ply.
22 . The polymer film of claim 20 , wherein the multi-layer film comprises an adhesive.