Method and apparatus for reducing non-normal incidence distortion in glazing films

1. A method of manufacturing a polymer film, the method comprising:

melting a resin;

extruding the melted resin through a die to produce a polymer film;

shaping the polymer film;

cooling the polymer film;

capturing an image of a test pattern through the polymer film;

calculating a modulation transfer function value from the image; and

adjusting a process parameter of the melting, the extruding, the shaping, or the cooling based on the calculated modulation transfer function value.

2. The method of claim 1 , wherein the process parameter is a temperature setting of a heater used in the melting.

3. The method of claim 1 , wherein the process parameter is a rotation speed of an extrusion screw used in the extruding.

4. The method of claim 1 , wherein the process parameter is a rotation speed of a roller used in the shaping or the cooling.

5. The method of claim 1 , further comprising:

capturing an additional image of the test pattern through the polymer film with the polymer film at a different angle relative to the test pattern; and

calculating an additional modulation transfer function value from the additional image,

wherein the adjusting is based on the calculated additional modulation transfer function value.

6. The method of claim 5 , wherein, during the capturing of the image, the polymer film is at an angle relative to the test pattern of 55-65 degrees and, during the capturing of the additional image of the test pattern through the polymer film, the polymer film is at an angle relative to the test pattern of 65-75 degrees.

7. The method of claim 1 , wherein the capturing of the image is performed by an imaging radiometer 10-30 meters from the test pattern.

8. The method of claim 7 , wherein the capturing of the image is performed with the test pattern 1-10 meters from the polymer film.

9. The method of claim 1 , wherein the test pattern comprises line pairs.

10. The method of claim 1 , further comprising:

capturing a baseline image of the test pattern that is not taken through the polymer film; and

calculating a baseline modulation transfer function value from the baseline image,

wherein the adjusting is based on a difference between the calculated modulation transfer function value and the calculated baseline modulation transfer function value.

11. The method of claim 10 , wherein, during the capturing of the image, the polymer film is at an angle relative to the test pattern of 55-65 degrees.

12. The method of claim 11 , wherein said adjusting is performed such that the difference between the calculated modulation transfer function value and the calculated baseline modulation transfer function value is kept below 0.12.

13. The method of claim 12 , further comprising:

capturing an additional image of the test pattern through the polymer film with the polymer film at an angle relative to the test pattern of 65-75 degrees;

calculating an additional modulation transfer function value from the additional image,

wherein said adjusting is performed such that the difference between the calculated additional modulation transfer function and the calculated baseline modulation transfer function is kept below 0.38.

14. The method of claim 13 , wherein, during the capturing of the image, the polymer film is at an angle relative to the test pattern of 60 degrees and, during the capturing of the additional image, the polymer film is at an angle relative to the test pattern of 70 degrees.

15. The method of claim 1 , wherein the polymer film is a biaxially-oriented polyethylene terephthalate film.

16. The method of claim 1 , wherein the process parameter affects a density variation of the polymer film.

17. The method of claim 1 , wherein the process parameter affects a refractive index variation in the polymer film.

18. The method of claim 17 , wherein the process parameter affects a frequency of refractive index changes on the order of 0.010 in the polymer film.