Molded optical film

Abstract

A curved optical film is described, the optical film extending generally in a base plane, having a thickness of less than about 500 microns and an average optical absorptance of less than about 70% for unpolarized normally incident light within a predetermined wavelength range. A first cross-section of the optical film in a first plane perpendicular to the base plane has an actual first length AL1, a projected first length PL1, and a first stretch ratio S1 that is (AL1-PL1) / PL1. A second cross-section of the optical film in a second plane perpendicular to the first and base planes has an actual second length AL2, a projected second length PL2, and a second stretch ratio S2 that is (AL2-PL2) / PL2. The optical film can have a maximum thickness variation of less than 20% along each of the first and second cross-sections, where S1 can be at least 0.1, and S2 can be at least 0.01 and less than 0.8S1.

Description

[Background technology]

[0001] The optical film can be thermoformed into a shaped optical film that varies in thickness as a result of the thermoforming process. Summary of the Invention

[0002] In some embodiments of the present description, a curved optical film is provided that extends generally in a base plane and has an average thickness of less than about 500 microns and an average optical absorptance of less than about 70% for substantially unpolarized, substantially normally incident light within a predetermined wavelength range that includes at least 450 nm to 600 nm. A first cross-section of the optical film in a first plane perpendicular to the base plane has an actual first length AL1, a projected first length PL1 on the base plane, and a first stretch ratio S1 defined as (AL1-PL1) / PL1, where S1≧0.1. A second cross-section of the optical film in a second plane perpendicular to the first and base planes has an actual second length AL2, a projected second length PL2 on the base plane, and a second stretch ratio S2 defined as (AL2-PL2) / PL2, where 0.01≦S2<0.8S1. The optical film has a maximum thickness variation of less than about 20% along each of the first cross section and the second cross section. In some embodiments, 0.02≦S2<0.8S1. In some embodiments, the optical film has a maximum thickness variation of less than about 15% along each of the first cross section and the second cross section. In some embodiments, the optical film has a maximum thickness variation in the range of about 0.2S1 to about 0.8S1 along each of the first cross section and the second cross section.

[0003] In some aspects of the present description, there is provided a curved optical film that generally spreads in a base plane, having an average thickness less than about 500 microns, and an average light absorption rate of less than about 70% for substantially perpendicularly incident light that is substantially non-polarized within a predetermined wavelength range including at least 450 nm to 600 nm. A first cross-section of the optical film in a first plane perpendicular to the base plane has an actual first length AL1, a projected first length PL1 on the base plane, and a first elongation ratio S1 defined as (AL1 - PL1) / PL1. A second cross-section of the optical film in a second plane perpendicular to the first plane and the base plane has an actual second length AL2, a projected second length PL2 on the base plane, and a second elongation ratio S2 defined as (AL2 - PL2) / PL2 (where 0.01 ≦ S2 < 0.7S1). The optical film has a maximum thickness variation in the range of about 0.05S1 to about 0.8S1 along each of the first cross-section and the second cross-section. In some embodiments, the optical film has a maximum thickness variation in the range of about 0.2S1 to about 0.8S1 along each of the first cross-section and the second cross-section.

[0004] In some aspects of the present specification, there is provided an extended and shaped optical film that is extended and shaped along at least directions orthogonal to each other, having an average light absorption rate of less than about 70% for substantially perpendicularly incident light that is substantially non-polarized within a predetermined wavelength range including at least 450 nm to 600 nm. When the optical film is disposed on a flat surface, a first cross-section of the optical film in a first plane perpendicular to the flat surface has a maximum deviation D1 from a straight line connecting both ends of the first cross-section, and the first plane is selected to maximize D1. A second cross-section of the optical film in a second plane perpendicular to the first plane and the flat surface has a maximum deviation D2 from a straight line connecting both ends of the second cross-section, and the second plane is selected to maximize D2, and 0.1D1 < D2 < 0.7D1. The optical film has a maximum thickness variation of less than about 15% along each of the first cross-section and the second cross-section.

[0005] In some aspects of the present specification, an optical film is provided that includes a plurality of polymer layers that are stretched and formed along first and second orthogonal directions, with each layer having a thickness less than about 500 nm. When the optical film is placed on a flat surface, a first cross-section of the optical film in a first plane parallel to the first direction and perpendicular to the flat surface has an actual first length AL1, a projected first length PL1 on the flat surface, and a first stretch ratio S1 defined as (AL1 - PL1) / PL1 (where S1 ≥ 0.15), and a second cross-section of the optical film in a second plane parallel to the second direction and perpendicular to the flat surface has an actual second length AL2, a projected second length PL2 on the flat surface, and a second stretch ratio S2 defined as (AL2 - PL2) / PL2 (where 0.01 ≤ S2 < S1). For light incident substantially perpendicularly, each position on the optical film has a corresponding reflection band with a band-edge wavelength that varies less than 15% along each of the first and second cross-sections.

[0006] In some aspects of the present specification, a method of forming a stretched and formed optical film is provided. The method includes providing a flat optical film having an average thickness less than about 500 microns and an average light absorption rate of less than about 70% for light incident substantially perpendicularly that is substantially non-polarized within a predetermined wavelength range including at least 450 nm to 600 nm, forming an unstretched bent optical film including an unstretched bent central region having a first shape surrounded by a peripheral region by bending the flat optical film without stretching it, and stretching the central region rather than the peripheral region of the unstretched bent optical film along at least first and second directions orthogonal to each other to obtain a stretched and formed optical film.

Brief Description of the Drawings

[0007] [Figure 1A] It is a schematic perspective view of an optical film. [Figure 1B] It is a schematic cross-sectional view in a first plane of the optical film of FIG. 1A. [Figure 1C]1B is a schematic cross-sectional view of the optical film of FIG. 1A in a second plane. [Figure 1D] 1B is a schematic perspective view of a bent optical film that can be stretched and shaped to form the optical film of FIG. 1A. FIG. [Figure 2A] 1A and 1B are schematic cross-sectional views of an optical film in first and second planes that are orthogonal to each other. [Figure 2B] 1A and 1B are schematic cross-sectional views of an optical film in first and second planes that are orthogonal to each other. [Figure 3A] 1 is a schematic plot of a property of an optical film versus position at a first cross section and a second cross section. [Figure 3B] 1 is a schematic plot of a property of an optical film versus position at a first cross section and a second cross section. [Figure 4] 1 is a schematic plot of transmittance versus wavelength. [Figure 5] 1 is a schematic plot of reflectance versus wavelength. [Figure 6] 1 is a schematic graph of absorbance versus wavelength. [Figure 7A] FIG. 1 is a schematic perspective view of an optical film. [Figure 7B] 7B is a schematic perspective view of a portion of the optical film of FIG. 7A. [Figure 8A] FIG. 1 is a schematic top view of a flat optical film. [Figure 8B] FIG. 2 is a schematic cross-sectional view of an unstretched bent optical film. [Figure 8C] FIG. 2 is a schematic cross-sectional view of a molded optical film. [Figure 8D] 1 is a schematic cross-sectional view of a flat optical film including a liner. [Figure 9] FIG. 2 is a schematic cross-sectional view of an unstretched bent optical film. [Figure 10] FIG. 2 is a schematic cross-sectional view of an unstretched bent optical film. [Figure 11] FIG. 2 is a schematic top view of an unstretched bent optical film. [Figure 12] 1 is a schematic exploded perspective view of an apparatus for forming a stretched and shaped optical film. DETAILED DESCRIPTION OF THE INVENTION

[0008] In the following description, reference is made to the accompanying drawings, which form a part hereof, and in which are shown by way of illustration various embodiments. The drawings are not necessarily to scale. It is to be understood that other embodiments are contemplated and may be made without departing from the scope or spirit of the present disclosure. Accordingly, the following detailed description is not to be taken in a limiting sense.

[0009] According to some embodiments herein, a flat optical film is bent but not stretched to form an unstretched, bent optical film, and then a central region of the bent optical film is stretched to form a stretched and shaped optical film, resulting in an optical film with improved properties over a comparable optical film formed to the same shape directly from the flat optical film, or an optical film having a desired shape that cannot be achieved by conventional processes by directly stretching an optical film to the desired shape. For example, in some embodiments, the methods herein for forming stretched and shaped optical films result in optical films with reduced thickness variation or band edge wavelength variation compared to optical films formed to the same shape using conventional processes. In some embodiments, the methods herein for forming stretched and shaped optical films result in optical films with shapes that cannot be achieved by conventional processes by directly stretching an optical film to the shape, because the strain resulting from the conventional processes is greater than the maximum strain at break of the flat optical film.

[0010] The optical film can be any suitable type of optical film, such as, for example, a reflective polarizer, an absorptive polarizer, a hybrid reflective / absorptive polarizer, a visible light mirror, an infrared mirror, or a diffuser. The optical film can have a thickness of less than about 500 microns (e.g., a thickness ranging from about 10 microns to about 500 microns). The optical film can have relatively low optical absorptance for at least one polarization state for at least some wavelengths in the visible wavelength range (e.g., 400 nm to 700 nm). In some embodiments, the optical film has an average optical absorptance of less than about 70% for substantially unpolarized, substantially normally incident light within a predetermined wavelength range (e.g., including at least 450 nm to 600 nm).

[0011] FIG. 1A is a schematic perspective view of a curved optical film 100 extending generally in a base plane (x'-y' plane). In some embodiments, the curved optical film 100 has an average thickness of less than about 500 microns and an average optical absorptance of less than about 70% for substantially unpolarized, substantially normally incident light within a predetermined wavelength range that includes at least 450 nm to 600 nm (e.g., 430 nm to 650 nm). The x'-y'-z' axes in FIG. 1A are centered about the center of the optical film 100. X, y, and z axes parallel to the x'-y'-z' axes in FIG. 1A can also be used. FIG. 1B is a schematic diagram of a first cross-section of the optical film 100 in a first plane (x-z plane) perpendicular to the base plane. In the first plane, the optical film 100 has an actual first length AL1 and a projected first length PL1 on the base plane. The actual first length AL1 is the arc length ds1 between the ends 101 and 103 of the first cross section, and the projected first length PL1 is the length between the ends 101 and 103 of the first cross section of the optical film 100 projected onto the base plane. The first stretch ratio S1 can be defined as (AL1-PL1) / PL1. FIG. 1C is a schematic diagram of a second cross section of the optical film 100 in a second plane (yz plane) perpendicular to the first and base planes. In the second plane, the optical film 100 has an actual second length AL2 and a projected second length PL2 on the base plane. The actual second length AL2 is the arc length ds2 between the ends 102 and 104 of the second cross section, and the projected second length PL2 is the length between the ends 102 and 104 of the second cross section of the optical film 100 projected onto the base plane. The second draw ratio S2 may be defined as (AL2-PL2) / PL2.

[0012] In FIG. 1A , optical film 100 is placed on a flat surface 110. Flat surface 110 may be a base plane or may be parallel to the base plane. In some embodiments, when optical film 100 is placed on flat surface 110, a first cross-section of optical film 100 in a first plane (xz plane, see FIG. 1B ) perpendicular to flat surface 110 has a maximum deviation D1 from a line 105 connecting ends 101 and 103 of the first cross-section, and the first plane is selected to maximize D1. In other words, the maximum deviation of any cross-section in the plane perpendicular to flat surface 110 from a line connecting ends of the cross-section is no greater than the first cross-section in the first plane. In some embodiments, when the optical film 100 is placed on a flat surface 110, a second cross-section of the optical film 100 in a second plane (y-z plane, see FIG. 1B ) perpendicular to the first and flat surface 110 has a maximum deviation D2 from a line 106 connecting the ends 102 and 104 of the second cross-section, and the second plane is selected to maximize D2. In other words, the maximum deviation from a line connecting the ends of the cross-section is not greater for any cross-section in a plane perpendicular to the flat surface 110 and perpendicular to the first plane than for the second cross-section in the second plane. The first cross-section of the optical film 100 has a maximum tilt M with respect to the base plane or flat surface 110. The x-, y-, and z-axes in FIGS. 1B and 1C are parallel to the x'-, y'-, and z'-axes in FIG. 1A , but may be shifted so that the maximum displacements D1 and D2 occur in the x- and y-z planes, respectively.

[0013] The actual first length AL1 and second length AL2 can be determined in any suitable manner. For example, deviation from line 105 or 106 can be measured directly, e.g., with a ruler, to determine the displacement of the film from the line as a function of x or y, which can then be used to determine the arc length between measurement points, which, if a small spacing is used between them, can be summed to obtain an accurate measurement of the arc length. In some embodiments, a substrate (e.g., a lens) is molded (e.g., injection molded) onto the optical film, and lengths PL1, PL2, AL1, and AL2 can be determined from measurements of the optical film bonded to the substrate.

[0014] In some embodiments, the optical film 100 is formed by bending a flat optical film without stretching to form an unstretched bent optical film, and then stretching a central region (e.g., at least a portion of the inner region 130) of the bent optical film to form the optical film 100 of a desired shape. FIG. 1D is a schematic perspective view of a curved but unstretched optical film 102 that can be shaped to form the optical film 100. Forming an unstretched bent optical film by bending a flat optical film without stretching and then stretching the central region of the bent optical film to form an optical film having a desired shape can result in an optical film with reduced variation in physical properties compared to an optical film stretched directly to the desired shape from a flat optical film. The physical properties may be, for example, film thickness, band edge wavelength, or light absorption rate in a block polarization state. In this context, unstretched means unstretched after the flat optical film is fabricated. It will be understood that the flat optical film may be pre-stretched (e.g., to orient an interference layer) during the fabrication process of the optical film. The geometric shape of the shaped optical film can be characterized by stretch ratios S1 and S2 (e.g., in some embodiments, S1≧0.1, 0.01≦S2<0.8S1), and / or maximum deviations D1 and D2 (e.g., in some embodiments, 0.1D1<D2<0.7D1). Other useful parameters for characterizing the geometric shape include the maximum slope M (e.g., in some embodiments, M is at least 1.5), and relative values of various length scales (e.g., in some embodiments, 0.4PL1>D1≧0.05PL1). Combinations of these parameters can also be used to characterize the geometric shape (e.g., in some embodiments, M≧1.5, 0.2×PL1×M≧D1≧0.05×PL1). In some embodiments, the shaped optical film is formed using a conventional shaping process and has less variation in physical properties than the corresponding shaped optical film having the same S1 and S2, and / or D1 and D2, and / or M, and / or PL1 / PL2.In some embodiments, conventional molding processes cannot be used to produce corresponding molded optical films having the same S1 and S2, and / or D1 and D2, and / or M, and / or PL1 / PL2, because the conventional molding processes result in strains greater than the strain at break of the optical film.

[0015] In some embodiments, S1≥0.1, or S1≥0.15, or S1≥0.2 (for example, S1 in the range of 0.1, or 0.15, or 0.2 to 1, or 0.7, or 0.5). In some embodiments, 0.01≤S2<S1, or 0.01≤S2<S1, or 0.01≤S2<0.8S1, or 0.01≤S2<0.7S1, or 0.02≤S2<S1, or 0.02≤S2<0.8S1, or 0.02≤S2<0.7S1. In some embodiments, PL1≥1.5PL2, or PL1≥2PL2, or PL1≥2.5PL2. In some embodiments, 0.5PL1>D1, or 0.4PL1>D1, or 0.3PL1>D1, or 0.25PL1>D1. In some embodiments, D1≥0.05PL1, or D1≥0.1PL1, or D1≥0.15PL1. For example, in some embodiments, 0.4PL1>D1≥0.1PL1. In some embodiments, 0.1D1<D2≤0.7D1. In some embodiments, 0.2×PL1×M≥D1≥0.05×PL1, or 0.15×PL1×M≥D1≥0.05×PL1, or 0.1×PL1×M≥D1≥0.05×PL1. In some embodiments, M is at least 1, or at least 1.5, or at least 2, or at least 2.5, or at least 3. In some embodiments, S1≥0.1 and 0.01≤S2<0.8S1; and / or S1≥0.15 and 0.01≤S2<S1; and / or 0.01<S2<0.7S1; and / or 0.1D1<D2<0.7D1.In some such embodiments, the optical film 100 has a maximum thickness variation of less than about 20%, or less than about 15% along each of the first and second cross-sections (e.g., in the range of about 5% to about 20% or about 15%); or has a maximum thickness variation in the range of about 0.05S1 to about 0.8S1 along each of the first cross-section and the second cross-section (e.g., S1 can be about 0.24, and the maximum thickness variation can be about 0.12 (0.5×0.24), or equivalently, about 12%), or about 0.05S1 to about 0.9S1, or about 0.05S1 to about 0.7S1, or about 0.1S1 to about 0.8S1, or about 0.2S1 to about 0.8S1; or has a band-edge wavelength that varies by less than about 20% or less than about 15% along each of the first cross-section and the second cross-section (e.g., in the range of about 5% to about 20% or about 15%). For example, in some embodiments, S1≧0.1 and 0.01≦S2<0.8S1, and the optical film 100 has a maximum thickness variation of less than about 20% along each of the first cross-section and the second cross-section. As another example, in some embodiments, 0.01<S2<0.7S1, and the optical film 100 has a maximum thickness variation in the range of about 0.05S1 to about 0.8S1 along each of the first cross-section and the second cross-section (e.g., along the first cross-section, the maximum thickness variation is in the range of about 0.2S1 to about 0.8S1, and along the second cross-section, the maximum thickness variation is in the range of about 0.05S1 to about 0.4S1, or about 0.05S1 to about 0.5S1, or about 0.1S1 to about 0.5S1, or about 0.2S1 to about 0.8S1). As another example, in some embodiments, S1≧0.15 and 0.01≦S2<S1, and for light incident substantially vertically, each position on the optical film 100 has a corresponding reflection band with a band-edge wavelength, where the band-edge wavelength varies by less than about 15% along each of the first cross-section and the second cross-section. In some such embodiments, the optical film has a maximum band-edge wavelength variation in the range of about 0.2S1 to about 0.8S1 along each of the first cross-section and the second cross-section. As yet another example, in some embodiments, 0.1D1<D2<0.7D1, and the optical film 100 has a maximum thickness variation of less than about 15% along each of the first cross-section and the second cross-section.

[0016] In some embodiments, optical film 100 includes an interior region 130 surrounded by a peripheral region 135. In some embodiments, peripheral region 135 is not included in optical film 100. For example, peripheral region 135 may be a region that is included in a forming process to produce optical film 100, as further described elsewhere herein, and that is subsequently removed from the optical film (e.g., by a cutting process such as die-cutting). Figures 2A-2B are schematic cross-sectional views of optical film 200 in first and second orthogonal planes, respectively, that do not include a peripheral region corresponding to peripheral region 135.

[0017] Optical film 200 can have any of the geometries (e.g., S1 and S2, and / or D1 and D2, and / or M, and / or PL1 / PL2 can be in any of the ranges described for optical film 100), thicknesses, and / or bandedge wavelength attributes described for optical film 100. For example, in some embodiments, optical film 200 is a curved optical film extending generally in a base plane (xy plane) and having an average thickness of less than about 500 microns and an average optical absorptance of less than about 70% for substantially unpolarized, substantially normally incident light within a predetermined wavelength range that includes at least 450 nm to 600 nm, wherein a first cross-section of optical film 200 in a first plane (xz plane, see FIG. 2A ) perpendicular to the base plane has an actual first length AL1, a projected first length PL1 on the base plane, and a first stretch ratio S1 defined as (AL1-PL1) / PL1, S1≧0.1; The second cross-section (y-z plane, see Fig. 2B) of the optical film 200 in the first plane and the second plane perpendicular to the base plane has an actual second length AL2, a projected second length PL2 on the base plane, and a second elongation ratio S2 defined as (AL2 - PL2) / PL2, where 0.01 ≦ S2 < 0.8S1. The optical film 200 has a maximum thickness variation of less than about 20% along each of the first cross-section and the second cross-section. As another example, in some embodiments, the optical film 200 is a curved optical film that generally spreads in the base plane (x-y plane), has an average thickness of less than about 500 microns, and an average light absorption rate of less than about 70% for substantially perpendicularly incident light that is substantially non-polarized within a predetermined wavelength range including at least 450 nm to 600 nm. The first cross-section of the optical film 200 in the first plane (x-z plane, see Fig. 2A) perpendicular to the base plane has an actual first length AL1, a projected first length PL1 on the base plane, and a first elongation ratio S1 defined as (AL1 - PL1) / PLi. The second cross-section (y-z plane, see Fig. 2B) of the optical film 200 in the first plane and the second plane perpendicular to the base plane has an actual second length AL2, a projected second length PL2 on the base plane, and a second elongation ratio S2 defined as (AL2 - PL2) / PL2, where 0.01 < S2 < 0.7S1. The optical film 200 has a maximum thickness variation in the range of about 0.05S1 to 0.8S1, or 0.2S1 to about 0.8S1 along each of the first cross-section and the second cross-section.As another example, in some embodiments, the optical film 200 is a stretched and formed optical film that is stretched and formed along orthogonal first and second directions (x and y directions), and includes a plurality of polymer layers, each layer having a thickness less than about 500 nm. When the optical film is placed on a flat surface, a first cross-section of the optical film 200 in a first plane (x-z plane, see FIG. 2A) that is parallel to the first direction (x direction) and perpendicular to the flat surface has a first actual length AL1, a first projected length PL1 on the flat surface, and a first stretch ratio S1 defined as (AL1 - PL1) / PL1. A second cross-section of the optical film 200 in a second plane (y-z plane, see FIG. 2B) that is parallel to the second direction (y direction) and perpendicular to the flat surface has a second actual length AL2, a second projected length PL2 on the flat surface, and a second stretch ratio S2 defined as (AL2 - PL2) / PL2 (where S1 ≧ 0.15 and 0.01 ≦ S2 < S1). For light incident substantially perpendicularly, each position on the optical film 200 has a corresponding reflection band having a band-edge wavelength, and the band-edge wavelength varies less than 15% along each of the first and second cross-sections.As another example, in some embodiments, the optical film 200 is a stretched and formed optical film that is stretched and formed along at least two directions (x and y directions) orthogonal to each other, and has an average light absorption rate of less than about 70% for substantially non-polarized, substantially perpendicularly incident light within a predetermined wavelength range including at least 450 nm to 600 nm. When the optical film 200 is disposed on a flat surface, a first cross-section of the optical film 200 in a first plane (x-z plane, see FIG. 2A) perpendicular to the flat surface has a maximum deviation D1 from a straight line 205 connecting both ends 201 and 203 of the first cross-section, and the first plane is selected to maximize D1. A second cross-section of the optical film 200 in a second plane (y-z plane, see FIG. 2B) perpendicular to the first plane and the flat surface has a maximum deviation D2 from a straight line 206 connecting both ends 202 and 204 of the second cross-section, and the second plane is selected to maximize D2 such that 0.1D1 < D2 < 0.7D1. Here, the optical film 200 has a maximum thickness variation of less than about 15% along each of the first cross-section and the second cross-section.

[0018] 1A-1C, optical film 100 includes a first inflection point 120 and a second inflection point 122 in a first cross-section (see FIG. 1B). Optical film 100 is concave-up in the region to the left of first inflection point 120, concave-down between first inflection point 120 and second inflection point 122, and concave-up in the region to the right of the second inflection point. In the illustrated embodiment, optical film 100 includes one or more saddle points 125. At the saddle points, optical film 100 is concave-down in one cross-section (e.g., the first cross-section in FIG. 1B) and concave-up in another cross-section (e.g., the second cross-section in FIG. 1C). In some embodiments, the one or more saddle points are multiple saddle points (e.g., a continuum of saddle points along x=0 near y=0). In the first cross-section, saddle point 125 is located between first inflection point 120 and second inflection point 122. Similarly, in the embodiment shown in Figures 2A-2B, optical film 200 includes first inflection point 220 and second inflection point 222 in the first cross-section (see Figure 2A), and includes one or more saddle points 225. In the first cross-section, saddle point 225 is located between first inflection point 220 and second inflection point 222. In other embodiments, the optical film may be stretched and formed into a curved optical film that does not have an inflection point and / or does not have one or more saddle points in the first cross-section. Optical films having saddle points and / or inflection points and having S1 and S2, and / or D1 and D2, and / or M, and / or PL1 / PL2 in the ranges described elsewhere herein often cannot be formed by conventional forming methods without breaking the optical film (e.g., S1 may be greater than the maximum strain at break) or result in properties (e.g., thickness, band edge wavelength, optical absorptance) that have unacceptably large variations when made using conventional molding methods.

[0019] The optical film 100 or 200 may have an average optical absorbance of less than about 70% for substantially unpolarized, substantially normally incident light within a predetermined wavelength range including at least 450 nm to 600 nm, or at least 400 nm to 600 nm, or at least 450 nm to 650 nm, or at least 450 nm to 700 nm, or at least 400 nm to 700 nm. Substantially unpolarized light is light with a degree of polarization that is sufficiently small so that the transmittance, reflectance, and absorbance of normally incident substantially unpolarized light differ negligibly from the transmittance, reflectance, and absorbance of normally incident unpolarized light. The degree of polarization is the fraction of light (by intensity) that is polarized. In some embodiments, light described as substantially unpolarized has a degree of polarization of less than 10%. In some embodiments, light described as substantially unpolarized is unpolarized or nominally unpolarized. Substantially normally incident light is light that is sufficiently close to normal incidence so that the transmittance, reflectance, and absorbance of substantially normally incident unpolarized light differs negligibly from the transmittance, reflectance, and absorbance of normally incident unpolarized light. Substantially normally incident light may, in some embodiments, be within 20 degrees or within 10 degrees of normal incidence, or may be normal incidence or nominally normal incidence.

[0020] In some embodiments, optical film 100 or 200 is one or more of a multilayer optical film, a reflective polarizer, an absorptive polarizer, a mirror, an infrared mirror, or a substantially transmissive optical film (e.g., a diffuser).

[0021] 3A is a schematic plot of a physical property of an optical film versus position at a first cross-section. FIG. 3B is a schematic plot of a physical property of an optical film versus position at a second cross-section. The optical film has a projected first length PL1 at the first cross-section and a projected second length PL2 at the second cross-section, as further described elsewhere herein. The physical property may be any property of the optical film that varies with position. In some embodiments, the property is a thickness of the optical film. In some embodiments, the property is a bandedge wavelength of a reflection band of the optical film. In some embodiments, the property is an average absorbance over a predetermined wavelength range of the optical film for substantially normally incident light that is substantially unpolarized, polarized in a block state, or polarized in a pass state. In some embodiments, the optical film includes a plurality of alternating high refractive index polymer layers and low refractive index polymer layers, and the bandedge wavelength is approximately proportional to the thickness of the plurality of alternating high refractive index polymer layers and low refractive index polymer layers. In some embodiments, the optical film is an absorptive polarizer, and the variation in block-state transmittance varies (e.g., nonlinearly) with thickness variation of the optical film. The property varies from Min1 to Max1 along a first cross-section and from Min2 to Max2 along a second cross-section. The maximum variation in the property along the first cross-section, when expressed as a percentage, is (Max1-Min1) / Max1 x 100%, or equivalently, when expressed as a fraction, is (Max1-Min1) / Max1. The maximum variation in the property along the second cross-section, when expressed as a percentage, is (Max2-Min2) / Max2 x 100%, or equivalently, when expressed as a fraction, is (Max2-Min2) / Max2. Whether the maximum variation refers to a percentage variation or a fractional variation will be clear depending on how the value or range of the maximum variation is specified. For example, a maximum variation of 0.1 refers to a maximum fractional variation of 0.1 (corresponding to a maximum percentage variation of 10%), and a maximum variation of 15% refers to a maximum percentage variation of 15% (corresponding to a maximum fractional variation of 0.15).In some embodiments, the maximum variation in a property (e.g., thickness, or band edge wavelength, or optical absorptance) along each of the first and second cross sections is in the range of about 0.05 S1 to about 0.9 S1, or about 0.05 S1 to about 0.8 S1, or about 0.05 S1 to about 0.7 S1, or about 0.1 S1 to about 0.8 S1, or about 0.2 S1 to about 0.8 S1. In some embodiments, the maximum variation in a property (e.g., thickness, or band edge wavelength, or optical absorptance) along the first cross section is in the range of about 0.2 S1 to about 0.9 S1, or about 0.2 S1 to about 0.8 S1, or about 0.05 S1 to about 0.7 S1, and the maximum variation in the property along the second cross section is in one of these ranges, or in the range of about 0.05 S1 to about 0.4 S1, or about 0.05 S1 to about 0.5 S1. In some embodiments, the optical film has a maximum thickness variation and / or a maximum bandedge wavelength variation of less than about 20% or less than about 15% along each of the first cross-section and the second cross-section.

[0022] 4 is a schematic plot of the transmittance of an optical film or of multiple alternating high and low refractive index polymer layers included in an optical film for orthogonal first and second polarization states for substantially normally incident light. The average transmittance over wavelengths within a predetermined wavelength range from λ1 to λ2 is T1 for the first polarization state and T2 for the second polarization state. In some embodiments, λ1 is in the range of about 400 nm to about 450 nm, and λ2 is in the range of about 600 nm to about 700 nm.

[0023] 5 is a schematic plot of the reflectivity of an optical film or a plurality of alternating high and low refractive index polymer layers included in an optical film for orthogonal first and second polarization states for substantially normally incident light. The average reflection / transmission over wavelengths within a predetermined wavelength range from λ1 to λ2 is R1 for the first polarization state and R2 for the second polarization state.

[0024] 6 is a schematic plot of the absorbance of an optical film or of multiple alternating high and low refractive index polymer layers contained in an optical film for orthogonal first and second polarization states for substantially normally incident light. The average absorbance over wavelengths within a predetermined wavelength range from λ to λ is A1 for the first polarization state and A2 for the second polarization state.

[0025] The transmittance, reflectance, and absorbance shown in Figures 4-6 may be for locations on a molded optical film, and each location on the film may have a corresponding transmittance, reflectance, and absorbance that may vary from location to location. For example, each location may have a corresponding reflection band, as generally shown in Figure 5, but the bandedge wavelengths λ and / or λ may vary with location (e.g., as shown in Figures 2A-2B). Average transmittance, reflectance, and absorbance refer to simple averages over a given wavelength range. An optical film can be said to have an average transmittance, reflectance, and / or absorbance within a specified range if at least one location on the optical film has an average transmittance, reflectance, and / or absorbance within the specified range. In some embodiments, each location in at least a majority of the area of ​​the optical film, or each location in all or substantially all of the area of ​​the optical film, may have a specified average transmittance, reflectance, and / or absorbance.

[0026] 4 and 5 show the long-wavelength bandedge λ3, and FIG. 5 shows the short-wavelength bandedge λ0. Reflection bands typically have both long-wavelength and short-wavelength bandedges where reflectivity drops off sharply. In the illustrated embodiment, the short-wavelength bandedge λ0 is less than λ1, and the long-wavelength bandedge λ3 is greater than λ2. The bandedges are determined for substantially normally incident light. The exact wavelength of the bandedge can be defined using several different criteria. The bandedge wavelength may be, for example, the wavelength where reflectivity for normally incident light having the second polarization state drops to ½R2, or the wavelength where transmission for normally incident light having the second polarization state increases to 10%.

[0027] The transmittance of an optical film generally refers to the transmitted light intensity divided by the incident light intensity (for light of a given wavelength, incident direction, etc.), but is sometimes expressed as the "external transmittance" or "internal transmittance." The external transmittance of an optical film is the transmittance of the optical film when the surrounding air is used and no correction is made for Fresnel reflections at the air / element interface in front of the element or for Fresnel reflections at the element / air interface behind the element. The internal transmittance of an optical film is the transmittance of the film when the Fresnel reflections at its front and rear surfaces are removed. Removing the front and rear Fresnel reflections can be done either by calculation (e.g., by subtracting the appropriate function from the external transmission spectrum) or by experiment. For many types of polymer and glass materials, Fresnel reflections are approximately 4-6% (for normal or near-normal incidence) at each of the two external surfaces, which shifts the external transmittance downward by approximately 10% compared to the internal transmittance. When reference is made herein to transmittance without specifying internal or external, the transmittance may be taken to refer to external transmittance unless the context dictates otherwise.

[0028] In some embodiments, an optical film (e.g., optical film 100 or 200) includes a plurality of alternating high and low refractive index polymer layers, wherein for substantially normally incident light within a predetermined wavelength range, the plurality of alternating high and low refractive index polymer layers have an average light transmittance T1 for a first polarization state that is greater than about 70% and an average light reflectance R2 for an orthogonal second polarization state that is greater than about 70%.

[0029] In some embodiments, an optical film (e.g., optical film 100 or 200) includes a plurality of alternating high and low refractive index polymer layers, wherein for substantially normally incident light within a predetermined wavelength range, the plurality of alternating high and low refractive index polymer layers have average optical reflectivities R1, R2 greater than about 70% for first and second mutually orthogonal polarization states, respectively. For example, in the embodiment shown in FIG. 5, R2 can be 95% or greater, and R1 can be greater than about 70% but less than R1. In other embodiments, R1 and R2 are approximately equal. For example, in some embodiments, R1 and R2 are each greater than about 90%.

[0030] In some embodiments, an optical film (e.g., optical film 100 or 200) has an average optical absorptance of less than about 70% for substantially unpolarized, substantially normally incident light within a predetermined wavelength range that includes at least 450 nm to 600 nm, where, for substantially normally incident light within the predetermined wavelength range, the optical film has an average optical transmittance T1 of greater than about 70% for a first polarization state and an average optical absorptance A2 of greater than about 70% for an orthogonal second polarization state. For example, the optical film may include a dichroic dye in an oriented layer that provides optical absorptance for the second polarization state. In some embodiments, the optical film is or includes an absorptive polarizer including an iodine-dyed polyvinyl alcohol layer. In other embodiments, an optical film having an average optical absorptance of greater than about 70% for the second polarization state includes multiple alternating high refractive index polymer layers and low refractive index polymer layers. For example, the high refractive index layer may include one or more dichroic dyes that provide light absorptance for the second polarization state, or the skin layer may include one or more dichroic dyes that provide light absorptance for the second polarization state. In some embodiments, the average light absorptance A2 of the optical film for the second polarization state varies by less than about 20%, or less than about 15%, or less than about 10% along each of the first and second cross sections (e.g., the cross sections of FIGS. 1B-1C or 2A-2B). In some embodiments, for substantially normally incident light within a predetermined wavelength range, the optical film has an average light transmittance T2 for the second polarization state that varies by less than about 50%, or less than about 40%, or less than about 30% along each of the first and second cross sections. In some embodiments, for substantially normally incident light within a predetermined wavelength range having the second polarization state, the optical film has an average light transmittance T2 of less than 1% at each location along each of the first and second cross sections.

[0031] In some embodiments, the optical film (e.g., optical film 100 or 200) has an average optical absorptance of less than about 70% for substantially unpolarized, substantially normally incident light within a predetermined wavelength range that includes at least 450 nm to 600 nm (e.g., 400 nm to 700 nm), and wherein for substantially normally incident light within the predetermined wavelength range, the optical film has an average optical transmittance of greater than about 50%, or greater than about 60%, or greater than about 70% for each of orthogonal first and second polarization states. For example, in some embodiments, the optical film may be a substantially transparent film having, for example, a desired optical clarity or optical haze. In some embodiments, the optical film has an average light transmittance of greater than about 50%, or greater than about 60%, or greater than about 70% for each of orthogonal first and second polarization states within a predetermined wavelength range that includes at least 450 nm to 600 nm, and an average light reflectance of greater than about 50%, or greater than about 60%, or greater than about 70% for each of orthogonal first and second polarization states within a second predetermined wavelength range that does not overlap with the predetermined wavelength range that includes at least 450 nm to 600 nm. For example, the optical film may be substantially transparent in the wavelength range of 450 nm to 600 nm, but reflective in the near-infrared wavelength range. Near-infrared wavelengths generally include wavelengths from about 700 nm to about 2500 nm. In some embodiments, the predetermined infrared wavelength range includes, for example, at least 850 nm to 900 nm (e.g., 800 nm to 950 nm), or at least 800 nm to 1000 nm, or at least 793 nm to 1064 nm. A predetermined infrared wavelength range useful for laser safety eyewear can span, for example, at least 793 nm to 1064 nm, because some types of laser diodes produce wavelengths around 793 nm and neodymium-doped yttrium aluminum garnet (Nd:YAG) lasers produce wavelengths around 1064 nm.

[0032] In some embodiments, an optical film (e.g., optical film 100 or 200) includes a plurality of alternating high refractive index polymer layers and low refractive index polymer layers, wherein for substantially normally incident light within a predetermined wavelength range, the optical film has an average optical transmittance of greater than about 50% for each of orthogonal first and second polarization states, and wherein for substantially normally incident light within a predetermined infrared wavelength range that does not overlap with the predetermined wavelength range, the plurality of alternating high refractive index polymer layers and low refractive index polymer layers have an average optical reflectance of greater than about 70% for each of the first and second polarization states.

[0033] In some embodiments, an optical film (e.g., optical film 100 or 200) includes multiple alternating high and low refractive index polymer layers. FIG. 7A is a schematic perspective view of an optical film 3100, which may correspond to optical film 100 or 200 prior to molding of optical film 100 or 200, or may correspond to a portion of optical film 100 or 200 where no curvature of the optical film is visible in FIG. 7A. FIG. 7B is a schematic perspective view of a portion of optical film 3100. Optical film 3100 includes multiple polymer interference layers 3102, having a total of (N) interference layers 3102. FIG. 7B is a schematic perspective view of a portion of optical film 3100 showing alternating high refractive index polymer layers 3102a (A layers) and low refractive index polymer layers 3102b (B layers). Optical film 3100 has an average thickness t of less than about 500 microns. Average thickness refers to the thickness average over the area of ​​the optical film. In some embodiments, the thickness of the optical film is substantially equal to the average thickness t, such that the thickness is substantially uniform prior to stretching and forming the optical film.

[0034] During use, light incident on a major surface (e.g., film surface 3104) of the optical film 3100, depicted as incident light 3110, enters a first layer of the optical film 3100, can propagate through the multiple interference layers 3102, and undergoes selective reflection or transmission due to optical interference, depending on the polarization state of the incident light 3110. The incident light 3110 may include a first polarization state (a) and a second polarization state (b) that are orthogonal to each other. In some embodiments, the optical film 3100 is a polarizing element, and the first polarization state (a) can be considered a "pass" state, while the second polarization state (b) can be considered a "block" state. In some embodiments, the optical film 3100 is a polarizer that is oriented along the stretch axis 3120 and not along the orthogonal axis 3122. In such embodiments, the polarization state of normally incident light with an electric field along axis 3122 is a first polarization state (a), and the polarization state of normally incident light with an electric field along axis 3120 is a second polarization state (b). In some embodiments, as incident light 3110 propagates through the plurality of interference layers 3102, portions of the light in the second polarization state (b) are reflected by adjacent interference layers, resulting in the second polarization state (b) being reflected by optical film 3100, while portions of the light in the first polarization state (a) are transmitted through optical film 3100 en masse.

[0035] In some embodiments, the high refractive index layer 3102a includes one or more dichroic dyes that absorb some or substantially all of the light in the second polarization state (b) that would otherwise be reflected by the optical film 3100. Suitable dichroic dyes include those available from, for example, Mitsui Chemicals Fine, Inc. (Japan). Reflective polarizers including dichroic dyes in the high refractive index layer are described, for example, in U.S. Patent Application Publication No. 2016 / 0306086 (Haag et al.). In some embodiments, the multilayer optical film includes a dichroic dye in a skin layer, as described, for example, in U.S. Patent No. 6,096,375 (Ouderkirk et al.). In some embodiments, the molded optical film includes an absorptive element having a first major surface and a second major surface, a first reflective polarizer disposed on the first major surface of the absorptive element, and a second reflective polarizer disposed on the second major surface of the absorptive element, as described, for example, in U.S. Patent No. 7,826,009 (Weber et al.). Each of the first and second reflective polarizers may correspond to optical film 3100, for example.

[0036] An interference layer may be described as reflecting and transmitting light primarily through optical interference if the reflectance and transmittance of the interference layer can be reasonably explained by, or reasonably accurately modeled as the result of, optical interference. Adjacent pairs of interference layers with different refractive indices reflect light through optical interference when the pair has a combined optical thickness (refractive index along the block axis times the physical thickness) of half the wavelength of light. The interference layers typically have a physical thickness of less than about 500 nm or less than about 200 nanometers. In some embodiments, each polymer interference layer has an average thickness (unweighted average of the physical thickness across the layer) in the range of about 45 nanometers to about 200 nanometers. Non-interference layers have an optical thickness that is too large to contribute to the reflection of visible light through interference. Non-interference layers typically have a physical thickness of at least 1 micrometer or at least 5 micrometers. The interference layer 3102 can be a plurality of polymer interference layers that reflect and transmit light primarily through optical interference in a predetermined wavelength range. The average thickness of the optical film, including the interference and non-interference layers, can be less than about 500 microns.

[0037] Methods for making optical films comprising alternating polymeric interference layers are known in the art and are described, for example, in U.S. Pat. Nos. 5,882,774 (Jonza et al.), 6,179,948 (Merrill et al.), 6,783,349 (Neavin et al.), and 9,162,406 (Neavin et al.).

[0038] 8A-8C schematically illustrate steps in a method of forming stretched and shaped optical film 800, starting with flat optical film 801 including flat central region 841 and flat peripheral region 836. In some embodiments, the method of forming stretched and shaped optical film 800 includes the steps of providing flat optical film 801, bending but not stretching flat optical film 801 to form unstretched bent optical film 802 including unstretched bent central region 842 (e.g., corresponding to flat central region 841 or a portion of flat central region 841) having a first shape surrounded by peripheral region 837 (e.g., corresponding to flat peripheral region 836), and stretching the central region, but not the peripheral region, of unstretched bent optical film 802 along at least mutually orthogonal first (x-direction) and second (y-direction) directions to obtain stretched and shaped optical film 800. FIG. 8A is a schematic top view of flat optical film 801, FIG. 8B is a schematic cross-sectional view of unstretched bent optical film 802, and FIG. 8C is a schematic cross-sectional view of formed optical film 800. Formed optical film 800 can correspond to optical film 100 and may have, for example, the shape shown in FIGS. 1A-1C. Unstretched bent optical film 802 can have the shape shown schematically in FIG. 8B along each cross section parallel to the xz plane. In some embodiments, bending but not stretching flat optical film 801 causes flat optical film 801 to bend in a second direction rather than in a first direction. For example, the unstretched bent optical film 802 may be bent in the y-direction but not in the x-direction.

[0039] In some embodiments, stretching the central region, but not the peripheral region, of the unstretched bent optical film along at least first and second directions perpendicular to each other includes clamping the unstretched bent optical film 802 along at least a portion of the peripheral region 837 and then stretching the central region 842 to conform to the curved mold surface. The clamped region may be curved in the y-direction but not in the x-direction. For example, first and second fixtures including first and second portions, respectively, adapted to clamp the optical film between the first and second portions can be utilized, where the shapes of the first and second portions are selected to conform to the peripheral regions of the stretched and shaped optical film within the clamping region. In some embodiments, stretching the central region 842 is performed by forcing a curved mold surface into the optical film and stretching the film to conform to the shape of the curved mold surface. Such a forming process can be performed, for example, using a vacuum former manufactured by MAAC Machinery Corporation (Carol Stream, IL). In some embodiments, stretching the central region 842 is performed by applying pressure (e.g., air pressure) to the optical film to stretch the optical film until it contacts the curved mold surface (see, e.g., FIG. 12 ). Such a pressure application process can be performed using a forming machine manufactured by Hy-Tech Forming Systems (USA), Inc. (Phoenix, AZ).

[0040] FIG. 12 is a schematic exploded perspective view of an apparatus 1299 for forming a stretched and shaped optical film. The apparatus includes an upper platen 1251 and a lower platen 1252. The lower platen includes a mold insert 1255 having a surface with the desired shape of the stretched and shaped optical film. An unstretched, bent optical film 1202 is shown between the upper platen 1251 and the lower platen 1252. In some embodiments, a method for forming a stretched and shaped optical film utilizes the apparatus 1299 as follows: First, a flat optical film is placed on the upper surface of the lower platen 1252. The flat optical film is allowed to relax without being forced into the shape of the upper surface of the lower platen 1252. Next, the upper platen 1251 is moved downward toward the lower platen 1252 until the peripheral regions of the upper and lower platens contact the optical film within the peripheral region surrounding the mold insert 1255, clamping the peripheral region of the optical film. Before the upper and lower platens 1251, 1252 clamp the optical film, the optical film can slide against the upper and lower platens 1251, 1252. As a result, the optical film is bent, without being stretched, to conform to the peripheral portions of the upper and lower platens 1251, 1252 so as to have the shape of the unstretched bent optical film 1202 shown in FIG. 12 . In some embodiments, the upper platen 1251 has a recessed region so that the upper platen 1251 does not contact the interior portion of the unstretched bent optical film 1202 when the upper and lower platens 1251, 1252 initially clamp the optical film 1202. In some embodiments, the upper platen is heated. In some embodiments, the mold insert 1255 is porous (e.g., porous aluminum). In some embodiments, air pressure is applied through a mold insert (eg, through porous aluminum) to heat the optical film 1202 and press the optical film 1202 against the upper platen 1251 .The air pressure is then released and air pressure is applied above the optical film to press the optical film into contact with the curved mold surface of the mold insert 1255, which may be at a lower temperature and therefore allows the optical film to cool. This pressure step stretches and forms the optical film to the shape of the curved mold surface of the mold insert 1255. In other embodiments, the upper platen 1251 is replaced with a compression mold that can mechanically press the optical film against the lower platen 1252.

[0041] In some embodiments, stretching the central region, but not the peripheral regions, of the unstretched bent optical film 802 along at least mutually orthogonal first and second directions comprises stretching the unstretched bent optical film 802 more along the first direction (x-direction) and less along the second direction (y-direction). In some embodiments, stretching the central region, but not the peripheral regions, of the unstretched bent optical film 802 along at least mutually orthogonal first and second directions comprises stretching the unstretched bent optical film substantially equally along the first direction and the second direction. In this context, substantially equally stretched along the first and second directions may be understood to mean stretched to a strain in the first direction that is within 10% of the strain in the second direction.

[0042] Optical film 800 has a central region 840 corresponding to unstretched, bent central region 842. Peripheral region 835 may correspond to a portion of optical film 800 adjacent the periphery of the optical film that can be removed prior to use, while central region 840 may correspond to the remainder of optical film 800. For example, central region 840 may correspond to optical film 200. Inner portion 830 may be or include a portion of the optical film that is not clamped during the forming process. Peripheral region 835 may include a portion of inner portion 830. In some embodiments, central region 840 is completely surrounded by peripheral region 835. In other embodiments, central region 840 may not be completely surrounded by peripheral region 835, such that a portion of the peripheral region is absent. For example, central region 840 may be surrounded by peripheral region 835 on each of the four sides of optical film 800, excluding the corners. In some embodiments, optical film 800 includes an inner portion 830 surrounded by an edge perimeter 845, where central region 840 is part of inner portion 830 and peripheral region 835 includes at least a portion of edge perimeter 845. In some embodiments, optical film 800 includes an inner portion 830 surrounded by edge perimeter 845, where central region 840 is part of inner portion 830 and at least a portion of peripheral region 835 is part of inner portion 830 and is spaced from edge perimeter 845.

[0043] In some embodiments, the flat optical film 801 has an average thickness of less than about 500 microns. The flat optical film 801 may have any of the optical properties described elsewhere herein for curved optical films. For example, the flat optical film 801 may have an average optical absorptance of less than about 70% for substantially unpolarized, substantially normally incident light within a predetermined wavelength range that includes at least 450 nm to 600 nm. The predetermined wavelength range may be any of the ranges further described elsewhere herein, such as at least 400 nm to 600 nm, or at least 450 nm to 650 nm, or at least 450 nm to 700 nm, or at least 400 nm to 700 nm.

[0044] In some embodiments, flat optical film 801 includes one or more liners, and the method further includes stretching the central region but not the peripheral regions of unstretched bent optical film 802, followed by removing the one or more liners to provide stretched and shaped optical film 800. For example, Figure 8D is a schematic cross-sectional view of flat optical film 1801 including liners 847 and 849 on both major surfaces of optical film 2801. In some embodiments, optical film 1801 is stretched and shaped to a desired shape, and then liners 847 and 849 are removed, leaving optical film 2801 formed to the desired shape.

[0045] In some embodiments, at least a portion of the first shape is cylindrical or parabolic. FIG. 9 is a schematic cross-sectional view of an unstretched bent optical film 902 having a central region 942 with a first shape, where the first shape is cylindrical. The cylindrical shape is the shape of a portion of a cylinder. The unstretched bent optical film 902 is bent in the y-direction but not in the x-direction. In the illustrated embodiment, the first shape is the shape of a portion of the outer surface of a cylinder 977. FIG. 10 is a schematic cross-sectional view of an unstretched bent optical film 1002 having a central region 1042 with a first shape, where the first shape is parabolic. The unstretched bent optical film 1002 is bent in the y-direction but not in the x-direction. In some embodiments, the first shape includes two or more cylindrical or parabolic portions. For example, in some embodiments, the first shape includes at least two spaced-apart, substantially parallel cylindrical or parabolic portions.

[0046] 11 is a schematic top view of an unstretched bent optical film 1102 having a central region 1142 and a peripheral region 1137. The central region 1142 includes a first central region 1142a and a second central region 1142b that are spaced apart. The peripheral region 1137 includes a first peripheral region 1137a surrounding the first central region 1142a and a second peripheral region 1137b surrounding the second central region 1132b. In some embodiments, the first central region 1142a and the second central region 1142b are each cylindrical portions of the central region 1142. In some embodiments, the first central region 1142a and the second central region 1142b are each parabolic portions of the central region 1142. In some embodiments, the unstretched bent optical film 1102 is bent in the y-direction but not in the x-direction. [Example]

[0047] Example 1 A reflective polarizer film was prepared as follows: Two multilayer optical packets were coextruded, each containing 325 alternating layers of polyethylene naphthalate (PEN) and low-index isotropic layers. The low-index isotropic layers had a refractive index of approximately 1.57 and were made using a blend of polycarbonate and copolyester (PC:coPET) to maintain substantial isotropy in the uniaxial direction. The molar ratio of PC:coPET was approximately 42.5 mol % PC and 57.5 mol % coPET, and the PC:coPET had a Tg of 105°C. The isotropic material was selected so that its refractive index in the two non-stretch directions remained substantially matched to that of the birefringent material in the non-stretch direction after stretching, while there was a substantial refractive index mismatch between the birefringent and non-birefringent layers in the stretch direction. The PEN and PC / coPET polymers were fed from separate extruders to a multilayer coextrusion feedblock, where they were assembled into packets of 325 alternating optical layers, with thicker protective boundary layers of coPEN added to the outside of the stacked optical packets for a total of 652 layers. The thicker layers of one packet were adjacent to the thinner layers of the other packet, and the layer thickness ranges of the two packets were approximately the same. The film was substantially uniaxially stretched in a parabolic tenter as described in U.S. Patent No. 6,916,440 (Jackson et al.). The film was stretched to a draw ratio of about 6 at a temperature of about 150°C.

[0048] A reflective polarizer sheet was cut into several samples of the same size and shape, using samples taken from adjacent sections of the reflective polarizer sheet. One of the samples was used to measure thickness and spectra to establish the initial thickness and band edge wavelength, and the other samples were formed into the desired shape. A protective olefin liner was applied to one side of the reflective polarizer sample to be formed, and a low-adhesive polyester liner was applied to the olefin liner and the opposite side of the reflective polarizer film sample.

[0049] The pressing process was carried out in a Hy-Tech Forming Systems (USA), Inc. (Phoenix, AZ) molding machine using the apparatus shown in Figure 12. The film sample was placed on the molding machine on the lower platen (corresponding to lower platen 1252), which contained a female mold machined from porous aluminum (corresponding to mold insert 1255) and maintained at a temperature of 80°F. The side of the film with the olefin liner faced away from the lower platen. The block axis of the reflective polarizer was along the length of the optical film (the x-direction in Figure 1A). Next, an upper platen (corresponding to upper platen 1251), preheated to 350°F, was lowered onto the lower platen and closed, clamping the edges of the film in place. As the platens approached the film, the film slid against the upper and lower platens, bending the film; however, the film was only bent uniaxially and was not stretched. The film, at this point in the process, had the shape generally shown in Figures 1D and 12. Then, 60 psi of pressure was applied to the bottom side of the film (through the porous aluminum) to press the film against an upper, flat, heated platen. This pressure was maintained for 6 seconds. The pressure on the bottom side was released, and 475 psi of pressure was applied to the top side of the film to expand the film into the lower female mold. The pressure was maintained for 6 seconds, after which the formed part (with the formed liner) was removed from the machine. The result was a curved optical film having the shape generally shown in Figures 1A-1C.

[0050] Referring to the coordinate system of FIGS. 1B-1C, the resulting film had a projected length PL1 (see FIG. 1B) of 7.63 inches and an actual length AL1 of 9.24 inches along the x-direction, and the resulting film had a projected length PL2 (see FIG. 1C) of 4.63 inches and an actual length AL2 of 4.68 inches along the y-direction. Peripheral portions of the optical film can be removed to leave an optical film having the geometry shown generally in FIGS. 2A-2B. The resulting film had a projected length PL1 (see FIG. 2A) of 7.47 inches and an actual length AL1 of 8.96 inches, and a projected length PL2 (see FIG. 2B) of 2.86 inches and an actual length AL2 of 2.90 inches along the y-direction.

[0051] The liner was removed, and the thickness and band edge wavelength were measured for the formed and flat film samples. Thickness was measured using a capacitance meter. The band edge wavelength was determined as follows: Block state transmittance was measured at normal incidence as a function of wavelength using a Lambda 950 spectrophotometer (available from PerkinElmer, Waltham, MA). The right (longer) wavelength band edge was determined as the wavelength at which the block state transmittance reached 10%.

[0052] Referring to the coordinate system shown in FIG. 1A with x′=0, y′=0 at the center of the film, the thickness and bandedge wavelength were determined at y′=0 (vertical position 0 inches) for various x′ values ​​(horizontal position).

[0053] Separate measurements of thickness were performed for several fixed x' values ​​for various y' values.

[0054] Table 1 shows the results of thickness and band edge wavelength for x' values ​​(horizontal position) ranging from -4 inches to +4 inches, with y'=0 inches.

[0055] [Table 1]

[0056] Tables 2-5 show the results when the measured x' values ​​(horizontal position) were 0 inches, -2 inches, -3 inches, and -3.5 inches, respectively, and the y' values ​​(vertical position) ranged from 0 inches to 1.25 inches.

[0057] [Table 2]

[0058] [Table 3]

[0059] [Table 4]

[0060] [Table 5]

[0061] Example 2 An infrared-reflective multilayer optical film with greater than 99% reflectivity for normally incident light having wavelengths between 800 and 1300 nm was fabricated from two packets of 275 alternating microlayers of poly(ethylene naphthalate) (PEN) and poly(methyl methacrylate) (PMMA) with a layer thickness gradient, each packet having a boundary layer of PEN. The outer layer of this combined two-packet structure had a skin layer of XYLEX RESIN polycarbonate polyester / blend manufactured by Sabic IP (Dusseldorf, Germany). The film was prepared generally according to the method described in U.S. Patent No. 7,271,951 (B2) (Weber et al.).

[0062] The film was stretched and formed into a curved shape as described in Example 1. Measurements were performed as in Example 1, except that the left (shorter) wavelength band edge of the near-infrared reflectance band was determined as the wavelength at which the transmittance reached 10%.

[0063] Table 5 shows the results using the coordinate system shown in Figure 1A where x' = 0, y' = 0 at the center of the film and the x' value (horizontal position) measured at y' = 0 inches ranges from -4 inches to +4 inches.

[0064] [Table 6]

[0065] Tables 6-9 show the results when the measured x' values ​​(horizontal position) were 0 inches, -2 inches, -3 inches, and -3.5 inches, respectively, and the y' values ​​(vertical position) ranged from 0 inches to 1.25 inches.

[0066] [Table 7]

[0067] [Table 8]

[0068] [Table 9]

[0069] [Table 10]

[0070] Example 3 An absorptive polarizer containing a dichroic dye was fabricated as follows. The center layer of a coextruded three-layer film was prepared by feeding CoPEN 90 / 10 (a copolymer containing 90% polyethylene naphthalate (PEN) units and 10% polyethylene terephthalate (PET) units) along with a dichroic dye (Mitsui Chemicals Fine, Japan) into a twin-screw extruder in the following weight percentages: 0.190% PD-104, 0.364% PD-325H, 0.085% PD-335H, and 0.405% PD-318H. The total extrusion rate of the center layer was 22.7 kg / h. Outer film layers were coextruded with the center layer. The outer layers were made from a blend of polycarbonate and copolyester (PC:coPET). The PC:coPET molar ratio was approximately 42.5 mol% PC and 57.5 mol% coPET. The total extrusion rate of the two outer layers was 45.4 kg / hr. The coextruded three-layer film was fed through a 0.34 meter die to form a cast sheet at a rate of 6.7 ft / min. The cast sheet was stretched in a tenter at a temperature of 146°C to a draw ratio of about 6.

[0071] The films were stretched and formed into curved shapes as described in Example 1 with the block axis along the length of the optical film (x-direction in FIG. 1A), and the thickness was determined as in Example 1.

[0072] Table 10 shows the results using the coordinate system shown in Figure 1A where x' = 0, y' = 0 at the center of the film and the x' value (horizontal position) measured at y' = 0 inches ranges from -4 inches to +4 inches.

[0073] [Table 11]

[0074] Example 4 The optical film used in this example was a 0.040 mm thick polyvinyl alcohol (PVA) absorptive polarizer film available from YS America (Torrance, CA). Other PVA absorptive polarizers would be expected to produce similar results. The film was stretched and formed into a curved shape as described in Example 1, except that the upper platen was preheated to a temperature of 280°F during the pressing process. The pass axis was along the length of the optical film (the x-direction in FIG. 1A). Thickness was determined as in Example 1.

[0075] Table 11 shows the results using the coordinate system shown in Figure 1A, where x' = 0, y' = 0 at the center of the film and the x' value (horizontal position) measured at y' = 0 inches ranges from -4 inches to +4 inches.

[0076] [Table 12]

[0077] Where the use of "about" as applied to quantities describing the shape, quantity, and physical properties of features is not clear to a person skilled in the art in the context used and described in the present invention, "about" will be understood to mean within 10 percent of the specified value. A quantity given as about a specified value may be exactly that specified value. For example, where it is not clear to a person skilled in the art in the context used and described in the present invention, a quantity having a value of about 1 means a quantity having a value between 0.9 and 1.1, and that value may be 1.

[0078] If the use of "substantially parallel" is not clear to one of ordinary skill in the art in the context used and described herein, "substantially parallel" will mean within 30 degrees of parallel. Directions or surfaces described as being substantially parallel to one another may, in some embodiments, be within 20 degrees, or within 10 degrees of parallel, or may be parallel or nominally parallel.

[0079] Any of the foregoing references, patents, or patent applications are incorporated herein by reference in their entirety in a consistent manner. In the event of any inconsistency or contradiction between any portion of the incorporated reference and this application, the information in the foregoing statement shall prevail.

[0080] Descriptions of elements in the figures should be understood to apply equally to corresponding elements in other figures unless otherwise indicated. While specific embodiments have been illustrated and described herein, those skilled in the art will recognize that various alternative and / or equivalent implementations may be substituted for the specific embodiments shown and described without departing from the scope of the present disclosure. The present application is intended to cover any adaptations or variations of the specific embodiments described herein. Accordingly, the present disclosure is limited only by the claims and their equivalents. In the following, exemplary embodiments are presented. [Item 1] 1. A curved optical film extending generally in a base plane, having an average thickness of less than about 500 microns and an average optical absorptance of less than about 70% for substantially unpolarized, substantially normally incident light within a predetermined wavelength range including at least 450 nm to 600 nm, a first cross section of the optical film in a first plane perpendicular to the base plane has an actual first length AL1, a projected first length PL1 on the base plane, and a first stretch ratio S1 defined as (AL1-PL1) / PL1, S1≧0.1; a second cross section of the optical film in a second plane perpendicular to the first plane and the base plane has an actual second length AL2, a projected second length PL2 on the base plane, and a second stretch ratio S2 defined as (AL2-PL2) / PL2, 0.01≦S2<0.8S1; The optical film has a maximum thickness variation along each of the first cross section and the second cross section of less than about 20%. [Item 2] 2. The optical film according to item 1, wherein the maximum thickness variation is in the range of about 0.05 S1 to about 0.8 S1 along each of the first cross section and the second cross section. [Item 3] Item 2. The optical film according to item 1, wherein the first cross section of the optical film has a maximum slope M with respect to the base plane and a maximum deviation D1 from a straight line connecting both ends of the first cross section, and the maximum deviation D1 satisfies 0.2×PL1×M≧D1≧0.05×PL1. [Item 4] 4. The optical film according to any one of items 1 to 3, wherein the first cross section of the optical film has a maximum slope M relative to the base plane that is at least 1. [Item 5] 5. The optical film according to any one of items 1 to 4, wherein PL1≧1.5PL2. [Item 6] 1. A curved optical film extending generally in a base plane, having an average thickness of less than about 500 microns and an average optical absorptance of less than about 70% for substantially unpolarized, substantially normally incident light within a predetermined wavelength range including at least 450 nm to 600 nm, The first cross-section of the optical film in a first plane perpendicular to the base plane has a first actual length AL1, a first projected length PL1 on the base plane, and a first elongation ratio S1 defined as (AL1 - PL1) / PL1. The second cross-section of the optical film in a second plane perpendicular to the first plane and the base plane has a second actual length AL2, a second projected length PL2 on the base plane, and a second elongation ratio S2 defined as (AL2 - PL2) / PL2, where 0.01 < S2 < 0.7S1. The optical film has a maximum thickness variation in the range of about 0.05S1 to about 0.8S1 along each of the first cross-section and the second cross-section. [Item 7] The optical film according to item 6, wherein the maximum thickness variation is less than about 20% along each of the first cross-section and the second cross-section. [Item 8] The optical film according to item 6 or 7, wherein the second cross-section of the optical film has a maximum deviation D2 from a straight line connecting both ends of the second cross-section, and 0.1D1 < D2 < 0.7D1. [Item 9] A stretched and formed optical film stretched and formed along at least two mutually perpendicular directions, having an average light absorption rate of less than about 70% for substantially perpendicularly incident light that is substantially non-polarized within a predetermined wavelength range including at least 450 nm to 600 nm. When the optical film is disposed on a flat surface. The first cross-section of the optical film in a first plane perpendicular to the flat surface has a maximum deviation D1 from a straight line connecting both ends of the first cross-section, and the first plane is selected to maximize D1. The second cross-section of the optical film in a second plane perpendicular to the first plane and the flat surface has a maximum deviation D2 from a straight line connecting both ends of the second cross-section, and the second plane is selected to maximize D2 with 0.1D1 < D2 < 0.7D1. The optical film has a maximum thickness variation of less than about 15% along each of the first cross-section and the second cross-section. [Item 10] A stretched and formed optical film stretched and formed along orthogonal first and second directions, including a plurality of polymer layers each having a thickness less than about 500 nm. When the optical film is placed on a flat surface. The first cross-section of the optical film in a first plane parallel to the first direction and perpendicular to the flat surface has a first elongation ratio S1 defined as the actual first length AL1, the projected first length PL1 on the flat surface, and (AL1 - PL1) / PL1, where S1 ≥ 0.15. The second cross-section of the optical film in a second plane parallel to the second direction and perpendicular to the flat surface has a second elongation ratio S2 defined as the actual second length AL2, the projected second length PL2 on the flat surface, and (AL2 - PL2) / PL2, where 0.01 ≤ S2 < S1. For light incident substantially perpendicularly, each position on the optical film has a corresponding reflection band with a band-edge wavelength, and the band-edge wavelength varies by less than 15% along each of the first cross-section and the second cross-section. An optical film. [Item 11] The optical film according to any one of Items 1 to 10, wherein the first cross-section of the optical film has one or more inflection points. [Item 12] The optical film according to any one of Items 1 to 11, including at least one saddle point. [Item 13] A method of forming a stretched and shaped optical film, comprising: providing a flat optical film having an average thickness of less than about 500 microns and an average light absorption rate of less than about 70% for light incident substantially perpendicularly that is substantially non-polarized within a predetermined wavelength range including at least 450 nm to 600 nm; forming an unstretched and bent optical film including an unstretched and bent central region having a first shape surrounded by a peripheral region by bending the flat optical film without stretching; stretching the central region, but not the peripheral region, of the unstretched and bent optical film along at least a first direction and a second direction orthogonal to each other to obtain a stretched and shaped optical film. [Item 14] The method according to Item 13, wherein at least a part of the first shape is cylindrical or parabolic. [Item 15] The method according to Item 13, wherein the first shape includes at least two spaced-apart substantially parallel cylindrical or parabolic portions.

Claims

1. 1. A curved and stretched optical film extending in a base plane and having an average thickness of less than 500 microns and an average optical absorptance of less than 70% for unpolarized normally incident light within a predetermined wavelength range including at least 450 nm to 600 nm, a first cross section of the optical film in a first plane perpendicular to the base plane has an actual first length AL1, a projected first length PL1 on the base plane, and a first stretch ratio S1 defined as S1=(AL1-PL1) / PL1, S1≧0.15; a second cross section of the optical film in a second plane perpendicular to the first plane and the base plane has an actual second length AL2, a projected second length PL2 on the base plane, and a second stretch ratio S2 defined as S2=(AL2-PL2) / PL2, 0.01≦S2<0.8S1; The optical film is a polarizer and / or a mirror, and the absolute value of the maximum thickness variation along each of the first cross section and the second cross section is less than 15%.

2. 2. The optical film of claim 1, wherein the absolute value of the maximum thickness variation ranges from 0.05S1 to 0.8S1 along each of the first cross section and the second cross section.

3. 2. The optical film of claim 1, wherein the first cross section of the optical film has a maximum inclination M with respect to the base plane and a maximum deviation D1 from a straight line connecting both ends of the first cross section, where D1 is 0.2×PL1×M≧D1≧0.05×PL1.

4. The optical film according to any one of claims 1 to 3, wherein the first cross section of the optical film has a maximum slope M relative to the base plane that is at least 1.

5. 5. The optical film according to claim 1, wherein PL1≧1.5PL2.

6. 1. A curved and stretched optical film extending in a base plane and having an average thickness of less than 500 microns and an average optical absorptance of less than 70% for unpolarized normally incident light within a predetermined wavelength range including at least 450 nm to 600 nm, a first cross section of the optical film in a first plane perpendicular to the base plane has an actual first length AL1, a projected first length PL1 on the base plane, and a first stretch ratio S1 defined as S1=(AL1−PL1) / PL1; a second cross section of the optical film in a second plane perpendicular to the first plane and the base plane has an actual second length AL2, a projected second length PL2 on the base plane, and a second stretch ratio S2 defined as S2=(AL2-PL2) / PL2, 0.01<S2<0.7S1; The optical film is a polarizer and / or a mirror, and the absolute value of the maximum thickness variation along each of the first cross section and the second cross section is in the range of 0.05S1 to 0.8S1.

7. 7. The optical film of claim 6, wherein the absolute value of the maximum thickness variation is less than 20% along each of the first cross section and the second cross section.

8. An optical film as described in claim 6 or 7, wherein the first cross section of the optical film has a maximum deviation D1 from a straight line connecting both ends of the first cross section, and the second cross section of the optical film has a maximum deviation D2 from a straight line connecting both ends of the second cross section, and 0.1D1 < D2 < 0.7D1.

9. A stretched and shaped optical film that has been stretched and shaped along at least mutually orthogonal directions, the film having an average optical absorptance of less than 70% for unpolarized, normally incident light within a predetermined wavelength range that includes at least 450 nm to 600 nm; When the optical film is placed on a flat surface, a first cross section of the optical film in a first plane perpendicular to the flat surface has a maximum deviation D1 from a line connecting both ends of the first cross section, and the first plane is selected to maximize D1; a second cross section of the optical film in a second plane perpendicular to the first plane and the flat surface has a maximum deviation D2 from a line connecting both ends of the second cross section, and the second plane is selected to maximize D2, such that 0.1D1<D2<0.7D1; The optical film is a polarizer and / or a mirror, and the absolute value of the maximum thickness variation along each of the first cross section and the second cross section is less than 15%.

10. A stretched and shaped optical film that has been stretched and shaped along orthogonal first and second directions, the film comprising a plurality of polymer layers, each layer being less than 500 nm thick; the optical film is a polarizer and / or a mirror; When the optical film is placed on a flat surface, a first cross section of the optical film in a first plane parallel to the first direction and perpendicular to the flat surface has an actual first length AL1, a projected first length PL1 on the flat surface, and a first stretch ratio S1 defined as S1=(AL1-PL1) / PL1, S1≧0.15; a second cross section of the optical film in a second plane parallel to the second direction and perpendicular to the flat surface has an actual second length AL2, a projected second length PL2 on the flat surface, and a second stretch ratio S2 defined as S2=(AL2-PL2) / PL2, where 0.01≦S2<S1; 1. An optical film, wherein for normally incident light, each location on the optical film has a corresponding reflection band having a band edge wavelength, the band edge wavelength varying by less than 15% along each of the first cross section and the second cross section.

11. The optical film according to any one of claims 1 to 10, wherein the first cross section of the optical film has one or more inflection points.

12. The optical film of any one of claims 1 to 11, comprising at least one saddle point.

13. 1. A method of forming a stretched and formed optical film, comprising: providing a flat optical film having an average thickness of less than 500 microns and an average optical absorptance of less than 70% for unpolarized normally incident light within a predetermined wavelength range including at least 450 nm to 600 nm; bending but not stretching the flat optical film to form an unstretched, bent optical film including an unstretched, bent central region having a first shape surrounded by peripheral regions; stretching the central region but not the peripheral regions of the unstretched bent optical film along at least a first direction and a second direction that are perpendicular to each other to obtain a stretched and shaped optical film, wherein the optical film is a polarizer and / or a mirror.

14. The method of claim 13 , wherein at least a portion of the first shape is cylindrical or parabolic.

15. The method of claim 13 , wherein the first shape comprises at least two spaced apart parallel cylindrical or parabolic sections.

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