Shaped optical films and methods of shaping optical films

1. A method of shaping an optical film, the method comprising the steps of:

disposing the optical film adjacent first and second rollers such that a first portion of the optical film contacts the first roller and a second portion of the optical film contacts the second roller, the first and second rollers spaced apart along a first direction, the first portion of the optical film having a first width along a second direction orthogonal to the first direction;

securing opposing first and second ends of the optical film, the first and second ends spaced apart along the first direction, the first and second portions disposed between the first and second ends;

providing a curved mold surface; and

shaping the optical film by contacting the optical film with the curved mold surface while stretching the optical film along the first direction,

wherein the shaping step comprises keeping a threshold distance between closest first and second points less than about the first width, the first point on the optical film contacting the first roller, the second point on the optical film contacting the curved mold surface.

2. The method of claim 1 , wherein the shaping step comprises changing positions of the first and second ends of the optical film to control a tension in the optical film along the first direction.

3. The method of claim 2 , wherein the tension is controlled to produce a desired thickness variation in the optical film.

4. The method of claim 1 , further comprising heating the optical film to a temperature greater than a glass transition temperature of the optical film.

5. The method of claim 1 , wherein the method results in a shaped optical film having a first maximum sag along the first direction, and a second maximum sag along the second direction, the first maximum sag greater than or equal to the second maximum sag, the second maximum sag greater than zero, each location over at least 80% of a total area of the shaped optical film having a reflectance greater than about 80% for normally incident light having a same predetermined wavelength and a same first polarization state.

6. The method of claim 1 , wherein keeping the threshold distance between the closest first and second points less than about the first width comprises changing a separation distance between the first and second rollers along the first direction.

7. The method of claim 1 , further comprising disposing the optical film adjacent third and fourth rollers, the third roller adjacent the first roller, the fourth roller adjacent the second roller, wherein the shaping step further comprises changing a separation distance between the third and fourth rollers along the first direction.

8. The method of claim 7 , wherein the third roller is disposed to increase a contact angle of the optical film with the first roller, and the fourth roller is disposed to increase a contact angle of the optical film with the second roller.

9. A method of shaping an optical film, the method comprising the steps of:

disposing the optical film adjacent first and second rollers such that a first portion of the optical film contacts the first roller and a second portion of the optical film contacts the second roller, the first and second rollers spaced apart along a first direction, the first portion of the optical film having a first width along a second direction orthogonal to the first direction;

securing opposing first and second ends of the optical film, the first and second ends spaced apart along the first direction, the first and second portions disposed between the first and second ends;

providing a curved mold surface; and

shaping the optical film by contacting the optical film with the curved mold surface while stretching the optical film along the first direction,

wherein the shaping step comprises changing a separation distance between the first and second rollers along the first direction to reduce buckling of the optical film between the first and second rollers and along the second direction between and away from longitudinal edges of the optical film.

10. The method of claim 9 , wherein the optical film has no buckles between the first and second rollers during the shaping step.

11. The method of claim 9 , wherein the shaping step comprises keeping a threshold distance between closest first and second points less than about the first width, the first point on the optical film contacting the first roller, the second point on the optical film contacting the curved mold surface.

12. The method of claim 9 , wherein the shaping step comprises changing positions of the first and second ends of the optical film to control a tension in the optical film along the first direction.

13. The method of claim 12 , wherein the tension is controlled to produce a desired thickness variation in the optical film.

14. A method of shaping an optical film, the method comprising the steps of:

disposing the optical film adjacent first and second rollers such that a first portion of the optical film contacts the first roller and a second portion of the optical film contacts the second roller, the first and second rollers spaced apart along a first direction;

securing opposing first and second ends of the optical film, the first and second ends spaced apart along the first direction, the first and second portions disposed between the first and second ends;

securing opposing third and fourth ends of the optical film, the third and fourth ends spaced apart along a second direction orthogonal to the first direction;

providing a curved mold surface; and

shaping the optical film by contacting the optical film with the curved mold surface while stretching the optical film, resulting in a curved optical film curved along at least the first direction,

wherein stretching the optical film during the shaping step comprises stretching the optical film along the first direction greater than 3 times any stretching along the second direction.

15. The method of claim 14 , wherein the first portion of the optical film has a first width along the second direction, and wherein the shaping step comprises keeping a threshold distance between closest first and second points less than about the first width, the first point on the optical film contacting the first roller, the second point on the optical film contacting the curved mold surface.

16. The method of claim 14 , wherein the shaping step comprises changing a separation distance between the first and second rollers along the first direction to reduce buckling of the optical film between the first and second rollers and along the second direction between and away from longitudinal edges of the optical film.

17. The method of claim 14 , wherein prior to shaping the optical film, the optical film is generally cross shaped and comprises:

a central region disposed between the first and second ends and between the third and fourth ends;

first and second end regions extending from the central region to the first and second ends, respectively; and

third and fourth end regions extending from the central region to the third and fourth ends, respectively.