Reflective polarizer and lens assembly including same

Abstract

A biaxially stretched reflective polarizer includes a plurality of biaxially stretched polymer layers in a total of at least 10, wherein each of the polymer layers has an average thickness of less than about 500 nm. The reflective polarizer is stretched in orthogonal first and second directions by respective S1 and S2 percentages, where S2 > = 2% and S2 / S1 < = 10, such that for at least one location on the reflective polarizer, substantially normal incident light at the at least one location and a visible wavelength range extending from about 420 nm to about 680 nm, the incident light is substantially normal incident light at the at least one location and the visible wavelength range extending from about 420 nm to about 680 nm. The plurality of polymer layers: have an average reflectance of greater than about 60% when the incident light is polarized in the first direction; and having an average transmittance greater than about 60% and an average reflectance less than about 1% when the incident light is polarized in the second direction.

Description

Technical Field

[0001] This specification generally relates to reflective polarizers that can be stretched and / or bent. Background Art

[0002] The reflective polarizer may include a plurality of alternating first and second polymer layers. Summary of the Invention

[0003] In some aspects, the present disclosure provides a biaxially stretched reflective polarizer comprising a plurality of biaxially stretched polymer layers totaling at least 10, wherein each of the biaxially stretched polymer layers can have an average thickness of less than about 500 nm. The biaxially stretched reflective polarizer is stretched in first and second in-plane, mutually orthogonal directions by respective S1 and S2 percentages, wherein S2 ≥ 2% and S2 / S1 ≤ 10, such that, for at least one location on the biaxially stretched reflective polarizer, for substantially normally incident light at the at least one location, and for a visible wavelength range extending from about 420 nm to about 680 nm, the plurality of biaxially stretched polymer layers: have an average reflectivity greater than about 60% when the incident light is polarized in the first direction; and have an average transmittance greater than about 60% and an average reflectivity less than about 1% when the incident light is polarized in the second direction.

[0004] In some aspects, the present disclosure provides a curved reflective polarizer comprising a plurality of curved polymer layers totaling at least 10, wherein each of the curved polymer layers has an average thickness of less than about 500 nm, the curved reflective polarizer having a first radius of curvature and a second radius of curvature along mutually orthogonal first and second directions, wherein each of the first and second radii of curvature can be greater than about 1 mm and less than about 500 mm, such that, for at least one location on the curved reflective polarizer, for substantially normally incident light at the at least one location, and for a visible wavelength range extending from about 420 nm to about 680 nm, the plurality of curved polymer layers: when the incident light is polarized in the first direction, has an average reflectivity greater than about 60%; and when the incident light is polarized in the second direction, has an average transmittance greater than about 60% and an average reflectivity less than about 1%.

[0005] In some aspects, the present description provides a curved reflective polarizer comprising a plurality of curved polymer layers totaling at least 10, wherein each of the curved polymer layers has an average thickness of less than about 500 nm. The curved reflective polarizer has a first radius of curvature and a second radius of curvature along mutually orthogonal first and second directions, wherein each of the first radius of curvature and the second radius of curvature may be greater than about 1 mm and less than about 500 mm, such that for at least one location on the curved reflective polarizer, for substantially normally incident light at the at least one location, a blue wavelength range extending from about 420 nm to about 480 nm, a green wavelength range extending from about 490 nm to about 560 nm, and a red wavelength range extending from about 590 nm to about 670 nm, when the incident light is polarized along the second direction, the plurality of curved polymer layers have average reflectivities R2b, R2g, and R2r in the respective blue, green, and red wavelength regions, wherein 2.2% ≥ R2b–R2g ≥ 0.1% and 2.5% ≥ R2b–R2r ≥ −0.1%.

[0006] In some aspects, the present specification provides a method comprising: providing a reflective polarizer that is substantially uniaxially oriented along a first direction and includes a plurality of polymer layers totaling at least 10, wherein each of the polymer layers has an average thickness of less than about 500 nm, such that for substantially normally incident light and for a visible wavelength range extending from about 420 nm to about 680 nm, the plurality of polymer layers of the reflective polarizer that are substantially uniaxially oriented: have an average reflectivity greater than about 60% when the incident light is polarized along the first direction; and have an average reflectivity Rp1 and an average transmittance greater than about 60% when the incident light is polarized along a second direction orthogonal to the first direction. The method includes biaxially stretching the reflective polarizer in the first direction and the second direction by respective S1 percentages and S2 percentages, wherein S2 ≥ 2% and S2 / S1 ≤ 10, such that for at least one location on the biaxially stretched reflective polarizer, for substantially normally incident light at the at least one location, and for a visible wavelength range, when the incident light at the at least one location is polarized in the second direction, the plurality of polymer layers of the biaxially stretched reflective polarizer have an average reflectivity Rp2 of less than about 1%. Rp2 may be no greater than about 3 times Rp1.

[0007] In some aspects, the present specification provides a method comprising: providing a reflective polarizer that is substantially uniaxially oriented along a first direction and includes a plurality of polymer layers totaling at least 10, wherein each of the polymer layers has an average thickness of less than about 500 nm, such that for substantially normally incident light and for a visible wavelength range extending from about 420 nm to about 680 nm, the plurality of polymer layers of the reflective polarizer that are substantially uniaxially oriented: have an average reflectivity greater than about 60% when the incident light is polarized along the first direction; and have an average reflectivity Rp1 and an average transmittance greater than about 60% when the incident light is polarized along a second direction orthogonal to the first direction. The method includes forming the reflective polarizer into a curved reflective polarizer such that the curved reflective polarizer has a first radius of curvature and a second radius of curvature along mutually orthogonal first and second directions, wherein each of the first radius of curvature and the second radius of curvature may be greater than about 1 mm and less than about 500 mm, such that for at least one location on the curved reflective polarizer, for substantially normally incident light at the at least one location, and for a visible wavelength range, when the incident light at the at least one location is polarized along the second direction, the plurality of polymer layers of the curved reflective polarizer have an average reflectivity Rp2 of less than about 1%, and Rp2 is no greater than about 3 times Rp1.

[0008] These and other aspects will become apparent from the detailed description that follows.This brief summary, however, should not be construed in any way as limiting the claimed subject matter. BRIEF DESCRIPTION OF THE DRAWINGS

[0009] Figure 1 is a schematic cross-sectional view of a reflective polarizer according to some embodiments.

[0010] Figure 2 is a graph of reflectivity and transmittance versus wavelength for multiple layers of a reflective polarizer for substantially normally incident light, according to some embodiments.

[0011] Figure 3 is a scatter plot showing the average reflectivity of multiple layers of a reflective polarizer for substantially normally incident light by polarization state and various stretching conditions, according to some embodiments.

[0012] Figure 4A is a graph of the difference in average through-state reflectivity in the blue and green wavelength ranges as a function of stretch ratio for substantially normally incident light, according to some embodiments.

[0013] Figure 4B Shown Figure 4A An enlarged portion of the diagram.

[0014] Figure 5A is a graph of the difference in average through-state reflectivity in the blue wavelength range and the red wavelength range as a function of stretch ratio for substantially normally incident light, according to some embodiments.

[0015] Figure 5B Shown Figure 5A An enlarged portion of the diagram.

[0016] Figure 6 is a scatter plot of average transmittance of a reflective polarizer for substantially normally incident light for the blocking polarization state and various stretching conditions, according to some embodiments.

[0017] Figure 7 is a schematic cross-sectional view of a curved reflective polarizer according to some embodiments.

[0018] Figure 8 is a schematic perspective view of a curved reflective polarizer according to some embodiments.

[0019] Figure 9 is a schematic perspective view of a lens assembly according to some embodiments. DETAILED DESCRIPTION

[0020] In the following description, reference is made to the accompanying drawings, which form a part of this disclosure and in which various embodiments are shown by way of illustration. The drawings are not necessarily drawn to scale. It should be understood that other embodiments may be envisioned and implemented without departing from the scope or spirit of this description. Therefore, the following detailed description should not be construed in a limiting sense.

[0021] For example, in various optical system applications, such as head-mounted display applications, it is often desirable to bend a reflective polarizer (e.g., via thermoforming) so that it can conform to a curved surface, such as an optical lens. Optical systems utilizing curved reflective polarizers are described, for example, in U.S. Patent Nos. 9,835,777 (Ouderkirk et al.); 10,564,427 (Ouderkirk et al.); and 11,262,565 (Etter et al.). Reflective polarizers are typically bent about two orthogonal axes to form a compound curved shape. Thermoforming a reflective polarizer into such a shape includes stretching the reflective polarizer. Here, stretching a reflective polarizer (e.g., biaxially) refers to stretching a previously fabricated reflective polarizer. The previously fabricated reflective polarizer may have been fabricated by (e.g., uniaxially) stretching multiple polymer layers. It has been found that when a reflective polarizer is formed (e.g., thermoformed) and stretched into a desired curved shape using conventional forming processes, stretching the reflective polarizer can result in an undesirable increase in the through-state reflectivity of the reflective polarizer. Without intending to be limited by theory, it is believed that this increase in through-state reflectivity stems from a shift in the refractive index of the layers of the reflective polarizer during conventional forming processes, which can involve stretching the film, at least partially, in one in-plane direction significantly more than in an orthogonal in-plane direction. This asymmetric stretching can be due to intentionally stretching the film primarily along one in-plane direction, or can be due to different moduli of the reflective polarizer in different in-plane directions, resulting in, for example, greater stretching in the lower modulus direction.

[0022] According to some embodiments of the present specification, it has been found that when the forming process is modified to provide similar strains along orthogonal in-plane directions (e.g., the blocking direction and the pass direction), any increase in through-state reflectivity when forming can be significantly reduced compared to conventional forming processes. According to some embodiments, it has been found that providing similar strains can be achieved by controlling the stretching ratios along the blocking direction S1 and the pass-through direction S2, respectively, so that S2 / S1 does not exceed, for example, 10 or 9 or 8 or 7 or 6 or 5 or 4. In order to keep the strains similar while achieving a desired degree of stretchability / formability, S2 / S1 can be, for example, at least 0.4, 0.5, 0.6, 0.7, 0.8, 0.9 or 1. In addition, according to some embodiments, it has been found that the difference between the average through-state reflectivity in the blue (R2b), red (R2r) and green (R2g) wavelength ranges can be approximately maintained or increased by a desired or acceptable amount by the stretching / forming processes described herein. For example, in some embodiments, 2.2% ≥ R2b - R2g ≥ 0.1% and 2.5% ≥ R2b - R2r ≥ -0.1% before and after stretching / forming the reflective polarizer. In contrast, conventional processes can result in increased variance such that, for example, R2b - R2g is undesirably greater than 2.2% and R2b - R2r is undesirably greater than 2.5%.

[0023] The reflective polarizer can be a multilayer optical film. As is known in the art, multilayer optical films comprising alternating polymer layers can be used to provide desired reflection and transmission within a desired wavelength range and polarization state by appropriately selecting layer thicknesses and refractive index differences. Multilayer optical films and methods of making multilayer optical films are described, for example, in U.S. Patent No. 5,882,774 (Jonza et al.); U.S. Patent No. 6,783,349 (Neavin et al.); U.S. Patent No. 6,949,212 (Merrill et al.); U.S. Patent No. 6,967,778 (Wheatley et al.); U.S. Patent No. 9,162,406 (Neavin et al.); and U.S. Patent No. 11,493,677 (Haag et al.).

[0024] Figure 1 is a schematic cross-sectional view of a reflective polarizer 200 according to some embodiments. Reflective polarizer 200 includes a plurality of polymer layers 10, 11 totaling at least 10, or 25, or 50, or 100, or 200, or 300, or 400, or 500, or 600, or 700. For example, the number of polymer layers 10, 11 can be as many as 3,000, or 2,000, or 1,500, or 1,200. Each of polymer layers 10, 11 has an average thickness of less than about 500 nm, or 400 nm, or 300 nm, or 200 nm. For example, each of polymer layers 10, 11 can have an average thickness greater than about 10 nm, or 20 nm, or 30 nm, or 40 nm, or 50 nm. The plurality of polymer layers 10, 11 can be arranged as a plurality of alternating first and second polymer layers 10, 11, wherein the first and second polymer layers 10, 11 have different compositions. In some embodiments, a plurality of polymer layers 10, 11 are disposed between a first skin layer 24 and a second skin layer 25. In some embodiments, each of the first skin layer 24 and the second skin layer 25 has an average thickness greater than about 500 nm, 600 nm, 700 nm, 800 nm, 900 nm, 1000 nm, 1250 nm, 1500 nm, 1750 nm, or 2000 nm. For example, the average thickness of each of the skin layers can be up to about 150 microns, 100 microns, 50 microns, 30 microns, 20 microns, or 10 microns. In some embodiments, skin layers 24 and 25 can have, for example, the same composition as layer 10 or layer 11.

[0025] Suitable materials for the various layers of reflective polarizer 200 include polyethylene naphthalate (PEN), polyethylene terephthalate (PET), polycarbonate, copolyesters (such as glycol-modified PET), and blends or copolymers thereof. Other suitable materials are described in the multilayer optical film references provided elsewhere herein.

[0026] The reflective polarizer 200 can be a biaxially stretched reflective polarizer, and the plurality of polymer layers 10, 11 can be a plurality of biaxially stretched polymer layers. The biaxially stretched reflective polarizer has been biaxially stretched after the reflective polarizer was initially prepared. The initial process for making the reflective polarizer may involve other stretching processes. For example, the reflective polarizer 200 can be initially made by substantially uniaxially orienting a plurality of extruded polymer layers and then the resulting reflective polarizer can be subsequently biaxially stretched. For example, a subsequent (biaxial) stretching step can be applied to form the reflective polarizer into a curved shape. The biaxial stretching of the reflective polarizer typically changes the molecular orientation of the initially uniaxially oriented layers, which can affect optical and / or mechanical properties, such as, for example, modulus along orthogonal directions. The biaxially stretched reflective polarizer can be stretched along first and second directions in a plane orthogonal to each other (e.g., the x-direction and the y-direction, respectively, with reference to the xyz coordinate system shown) by respective S1 percentages and S2 percentages, which in Figure 1 In some embodiments, the in-plane direction may be a direction in the tangential plane. In some embodiments, S2 ≥ 2% or 3% or 4% or 5% or 6% or 7% or 8%. In some embodiments, for example, S2 ≤ 20% or 18% or 16% or 14% or 12% or 10%. In some embodiments, for example, 14% ≥ S2 ≥ 3%, or 12% ≥ S2 ≥ 4%, or 10% ≥ S2 ≥ 5%. In some embodiments, S2 / S1 ≤ 10 or 9 or 8 or 7 or 6 or 5 or 4 or 3.5 or 3. In some embodiments, for example, S2 / S1 ≥ 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1, 1.1 or 1.2. In some embodiments, for example, 0.5 ≤ S2 / S1 ≤ 8 or 0.8 ≤ S2 / S1 ≤ 6 or 1 ≤ S2 / S1 ≤ 5. In some embodiments, for example, S1 ≥ 0.1% or 0.2% or 0.4% or 0.6% or 8% or 1% or 1.2%. In some embodiments, for example, 14% ≥ S2 > S1 ≥ 0.6%. Biaxial stretching of a reflective polarizer typically modifies the molecular orientation of an initially uniaxially oriented layer, which can affect optical and / or mechanical properties, such as, for example, modulus in orthogonal directions. Different S1 percentages and S2 percentages typically result in different modifications to the molecular orientation of an initially uniaxially oriented layer.

[0027] Biaxial stretching can be applied during the process of thermoforming a reflective polarizer into a curved shape. For example, useful methods for thermoforming a reflective polarizer are described in U.S. Patent No. 11,543,572 (Jennings et al.) and U.S. Patent No. 11,358,355 (Jennings et al.). The stretch ratio S2 / S1 can be controlled, for example, by using a clamp or other fixture around the edges of the reflective polarizing film as the film is thermoformed, to control the tension in the film in the first and second directions during the thermoforming process. For example, U.S. Patent No. 11,358,355 (Jennings et al.) Figure 6 The process can be modified to provide the tension required to produce the desired stretch ratio S2 / S1 by modifying the tension generated by the clamps in the x-direction and the y-direction. The reflective polarizer 200 can be a curved reflective polarizer (see, e.g., Figures 7 to 9 ), and the plurality of polymer layers 10, 11 can be a plurality of curved polymer layers. For example, when the film is stretched against a curved surface, tension can be applied in orthogonal directions to control S1 and S2. For example, the curved surface can be the surface of an optical lens, and due to the stretching process (e.g., at a temperature greater than the glass transition temperature of at least one layer of the reflective polarizer), the film can become bonded to the optical lens. Alternatively, the curved surface can be the surface of a (e.g., heated) mold (e.g., a release-treated) mold, and the reflective polarizer can be peeled from the mold surface after being bent into the desired shape.

[0028] It has been discovered that when a reflective polarizer is stretched with a stretch ratio within these ranges, starting with a reflective polarizer having multiple layers 10, 11 with low through-state reflectivity, a biaxially stretched and / or bent reflective polarizer with low through-state reflectivity can be produced. In contrast, conventional forming processes can result in significantly increased through-state reflectivity. Low through-state reflectivity of the starting reflective polarizer can be achieved by closely matching the refractive indices of the first and second layers 10, 11 along the second (through) direction. For example, the first layer 10 can be a birefringent layer, the second layer 11 can be a substantially optically isotropic layer, and by selecting a blended polymer or copolymer for the second layer 11 (e.g., an amorphous blend of polycarbonate and glycol-modified PET, such as PCTg available from Eastman Chemical Company, Knoxville, TN) to achieve refractive index matching, the refractive index of the second layer 11 can be matched to that of the first layer 10 along the second direction for at least one wavelength within the visible wavelength range. Suitable reflective polarizers that can be stretched / formed as described herein and having multiple layers 10, 11 with low pass-state reflection include those available from 3M Company, St. Paul, MN under the trade designation 3M Image Quality Polarizer Enhanced (IQP E).

[0029] In some embodiments, the thickness variation of a biaxially stretched and / or bent reflective polarizer is less than the thickness variation of a reflective polarizer stretched and / or formed, for example, in a conventional thermoforming process. In some embodiments, the maximum thickness variation over the maximum optically active area of ​​the reflective polarizer is less than about 25% or 20% or 15% or 10% or 8% or 6% or 5% or 4% or 3% or 2%. The maximum active area of ​​a reflective polarizer is generally the largest area of ​​the reflective polarizer intended to be utilized when the reflective polarizer is incorporated into an optical system. The maximum active area can comprise at least 60%, 70%, 80%, 85%, 90%, or 95% of the total area of ​​the reflective polarizer.

[0030] The optical properties of the biaxially stretched and / or bent reflective polarizer (e.g., pass and / or block state reflectivity and / or transmittance) can be specified for at least one location 211 of the reflective polarizer. The at least one location 211 can be or include every location over at least 60%, 70%, 80%, 85%, 90%, or 95% of the total area of ​​the reflective polarizer. For example, the at least one location 211 can be or include every location within the maximum optically active area of ​​the reflective polarizer.

[0031] Figure 1, substantially normally incident light 20 is schematically shown incident on a reflective polarizer 200. In some embodiments, the angle of incidence θ of the substantially normally incident light 20 is less than about 20 degrees, or 15 degrees, or 12 degrees, or 10 degrees, or 9 degrees, or 8 degrees, or 7 degrees, or 6 degrees, or 5 degrees, or 4 degrees, or 3 degrees, or 2 degrees, or 1 degree. The angle of incidence θ can be, for example, about 8 degrees (e.g., to facilitate reflectivity measurements). The reflectivity and transmittance of the reflective polarizer or multiple layers 10, 11 can be determined as a function of wavelength for the incident light 20 and for a first polarization state (e.g., polarized along the x-axis with reference to the xyz coordinate system shown) and for an orthogonal second polarization state (e.g., polarized along the y-axis). The reflectivity and transmittance of the multiple layers 10, 11 can be determined from the reflectivity and transmittance of the reflective polarizer 200 by subtracting the Fresnel reflection from the outer surface of the reflective polarizer 200, as will be understood by one of ordinary skill in the art. The resulting reflectivity and transmittance may be referred to as immersed or internal reflectivity and immersed or internal transmittance, respectively.The reflectivity and transmittance of reflective polarizer 200 in air include surface reflections at the outer surfaces of the skin and may be referred to as the external reflectivity and external transmittance, respectively, of reflective polarizer 200.

[0032] Figure 2 is a graph of reflectivity and transmittance versus wavelength for multiple layers 10, 11 of reflective polarizer 200 according to some embodiments for substantially normally incident light 20. Reflectivity, Rs, and transmittance, Tp, are shown along the left axis for a first (e.g., x-axis, blocking) polarization state and a second (e.g., y-axis, passing) polarization state, respectively, while reflectivity, Rp, of the second polarization state is shown along the right axis.

[0033] In some embodiments, the reflective polarizers 200, 210 (see e.g. Figure 1 and Figures 7 to 9) such that for at least one location on the reflective polarizer (e.g., location 211), substantially normally incident light 20 at the at least one location, and a visible wavelength range 30 extending from about 420 nm to about 680 nm, the plurality of (e.g., biaxially stretched and / or bent) polymer layers 10, 11: have an average reflectivity greater than about 60% when the incident light 20 is polarized in a first direction; and have an average transmittance greater than about 60% and an average reflectivity Rp less than about 1% (or 0.9% or 0.8% or 0.7% or 0.6% or 0.5% or 0.4% or 0.3% or 0.2%) when the incident light 20 is polarized in a second direction. In some embodiments, the average reflectivity when the incident light 20 is polarized in the first direction is greater than about 70% or 80% or 90% or 95%. In some embodiments, the average transmittance when the incident light 20 is polarized in the second direction is greater than about 70% or 80% or 90% or 95%. In some embodiments, the average reflectivity is less than about 0.9% or 0.8% or 0.7% or 0.6% or 0.5% or 0.4% or 0.3% or 0.2% when incident light 20 is polarized in the second direction. The reflectivity and / or transmittance can be within any of these ranges before and / or after the reflective polarizer is biaxially stretched and / or bent.

[0034] Figure 3 is a scatter plot showing average reflectivity of multiple layers 10, 11 of reflective polarizers 200, 210 for substantially normally incident light 20 polarized along the second direction for various stretch percentages S2 along the second direction and various values ​​of the ratio S2 / S1, according to some embodiments. Figure 3 Each exemplary reflective polarizer is represented by a solid circle defining an S2 / S1 value and a solid diamond representing an S2 value. For example, reflective polarizer 210a has an S2 of about 7.21%, an S2 / S1 of about 4.90, and a pass state reflectivity of about 0.56%. For comparison, comparative reflective polarizer 210c has an S2 of about 7.16%, an S2 / S1 of about 59.7, and a pass state reflectivity of about 1.44%. For example, comparative reflective polarizer 210c can be thermoformed in a conventional thermoforming process, wherein the reflective polarizer is stretched significantly more in the second (pass) direction than in the first (blocking) direction during thermoforming. Moreover, prior to biaxial stretching, the average reflectivity of the multiple layers 10, 11 of the reflective polarizer for substantially normally incident light polarized in the second direction is about 0.1%. Figure 3 The average reflectivities of the plurality of layers 10, 11 of the reflective polarizer for substantially normally incident light polarized in the second direction before and after biaxial stretching and / or forming can be denoted as Rp1 and Rp2, respectively. Figure 4Ais the wavelength in the blue wavelength range 31b and the green wavelength range 31g (see, e.g., Figure 2 ) is a graph showing the difference in average through-state reflectivity within . Figure 4B Shown Figure 4A An enlarged portion of the diagram. Figure 5A is the wavelength range in the blue wavelength range 31b and the red wavelength range 31r (see e.g. Figure 2 ) is a graph showing the difference in average through-state reflectivity within . Figure 5B Shown Figure 5A . The reflectivity in these figures is for the various layers 10, 11 of the reflective polarizer and for substantially normally incident light. The solid circles in these figures show exemplary data for various S2 / S1 ratios. The open squares along the ordinate show the results for an unstretched reflective polarizer sample. The reflectivity difference of the unstretched reflective polarizer sample over different wavelength ranges can be selected by appropriately selecting the layer thicknesses and refractive index differences, as will be understood by one of ordinary skill in the art.

[0035] In some embodiments, the (e.g., curved) reflective polarizers 200, 210 (see e.g. Figure 1 and Figures 7 to 9) such that for at least one location 211 on the (e.g., curved) reflective polarizer, substantially normally incident light 20 at the at least one location 211, a blue wavelength range extending from about 420 nm to about 480 nm, a green wavelength range extending from about 490 nm to about 560 nm, and a red wavelength range extending from about 590 nm to about 670 nm, when the incident light is polarized in a second direction (y-direction), the plurality of (e.g., curved) polymer layers 10, 11 have average reflectivities R2b, R2g, and R2r in the respective blue, green, and red wavelength regions. In some embodiments, R2b-R2g is ≥ 0.1%, 0.15%, 0.2%, 0.25%, or 0.3%. In some such embodiments, or in other embodiments, R2b-R2g is ≤ 2.2%, 2.0%, 1.8%, 1.6%, 1.5%, or 1.4%. In some such embodiments, or in other embodiments, R2b-R2r≥-0.1% or 0% or 0.05% or 0.1% or 0.2% or 0.3%. In some such embodiments, or in other embodiments, R2b-R2r≤2.5% or 2.25% or 2.0% or 1.75% or 1.6% or 1.5% or 1.4%. For example, in some embodiments, 2.2%≥R2b-R2g≥0.1% and 2.5%≥R2b-R2r≥-0.1%; or 2.0%≥R2b-R2g≥0.15% and 2.25%≥R2b-R2r≥0%; or 1.6%≥R2b-R2g≥0.15% and 1.75%≥R2b-R2r≥0%. In some embodiments, the difference in average reflectivity of the plurality of layers 10, 11 of the biaxially stretched / bent reflective polarizer and the reflective polarizer before biaxially stretching / bending in the blue wavelength region, the green wavelength region, and the red wavelength region is within any of these ranges. The average reflectivity of the plurality of layers 10, 11 of the reflective polarizer before being biaxially stretched / bent in the blue wavelength region, the green wavelength region, and the red wavelength region can be referred to as R1b, R1g, and R1r, respectively.

[0036] Figure 6is a scatter plot of the average transmittance of a reflective polarizer (in air) for substantially normally incident light for blocking polarization states and various stretching conditions according to some embodiments. According to some embodiments, it has been found that the stretching process described herein does not significantly increase the transmittance of substantially normally incident light in the blocking polarization state. The average transmittance (T_block) in each of the blue wavelength range of 420nm to 480nm, the green wavelength range of 490nm to 560nm, the red wavelength range of 590nm to 670nm, and the visible wavelength range of 420nm to 680nm is shown. The average transmittance of the reflective polarizer sample before stretching is provided along the axis below S2 / S1=0. In some embodiments, for at least one location 211 on the (e.g., bent and / or biaxially stretched) reflective polarizer 200, 210, substantially normally incident light 20 at the at least one location, and the visible wavelength range 30, the reflective polarizer: has an average transmittance of less than about 1% or 0.9% or 0.8% or 0.7% or 0.6% or 0.5% or 0.4% or 0.3% or 0.25% or 0.2% or 0.15% or 0.12% or 0.1% when the incident light is polarized along a first direction (x-direction, blocking direction). In some embodiments, for at least one location 211 on the (e.g., bent and / or biaxially stretched) reflective polarizer 200, 210 and for substantially normally incident light 20 at the at least one location: when the incident light is polarized along a first direction, the reflective polarizer has an average transmittance of less than about 1% or 0.9% or 0.8% or 0.7% or 0.6% or 0.5% or 0.4% or 0.3% or 0.25% or 0.2% or 0.15% or 0.12% or 0.1% in each of the blue wavelength region 31b, the green wavelength region 31g, and the red wavelength region 31r.

[0037] In some embodiments, a method of biaxially stretching and / or shaping a reflective polarizer is provided. In some embodiments, the method includes providing a reflective polarizer that is substantially uniaxially oriented along a first direction (e.g., the x-direction) and includes a plurality of polymer layers 10, 11 totaling at least 10 (or within the ranges described elsewhere herein), wherein each of the polymer layers 10, 11 has an average thickness of less than about 500 nm (or within the ranges described elsewhere herein). The substantially uniaxially oriented reflective polarizer may include a birefringent layer having a refractive index n1x in the first direction (x-direction) that is significantly higher than a refractive index n1y in the second direction (y-direction), and the refractive index in the second direction may be approximately equal to the refractive index n1z in the thickness direction. For example, the absolute value of the difference between the refractive index in the second direction and the thickness direction may be less than 0.02 or less than 0.01, and the absolute value of the difference between the refractive index in the first direction and the second direction may be greater than 0.05 or greater than 0.10. For example, the refractive index may be determined for a wavelength of 532 nm or 633 nm. For example, substantially uniaxially oriented multilayer optical films are described in U.S. Patent Application Publication No. 2010 / 0254002 (Merrill et al.). Suitable substantially uniaxially oriented reflective polarizers include those available from 3M Company, St. Paul, Minnesota, under the trade designation 3M Image Quality Polarizer Enhanced (IQPE). In some embodiments, the plurality of polymer layers 10, 11 of the substantially uniaxially oriented reflective polarizer have: an average reflectivity greater than about 60% (or within the range described elsewhere herein for the reflective polarizer 200) when the incident light is polarized in a first direction (x-direction) and an average reflectivity Rp1 (see, e.g., FIG1 ) when the incident light is polarized in a second direction (y-direction) that is orthogonal to the first direction) for substantially normally incident light 20 and for a visible wavelength range 30 extending from about 420 nm to about 680 nm. Figure 3 ) and an average transmittance greater than about 60% (or within the range described elsewhere herein for reflective polarizer 200). Rp1 can be less than about 1% or can be within any range described elsewhere herein for Rp2.

[0038] In some embodiments, the method includes biaxially stretching the reflective polarizer in a first direction and a second direction by respective S1 percentages and S2 percentages, wherein S2 ≥ 2% (or within a range described elsewhere herein) and S2 / S1 ≤ 10 (or within a range described elsewhere herein), such that for at least one location on the biaxially stretched reflective polarizer, for substantially normally incident light 20 at the at least one location, and for a visible wavelength range, when the incident light at the at least one location is polarized in the second direction, the plurality of polymer layers 10, 11 of the biaxially stretched reflective polarizer have an average reflectivity Rp2 of less than about 1% (or within a range described elsewhere herein) (see, e.g., Figure 3 In some embodiments, for example, 1≤S2 / S1≤5 and 12%≥S2≥4%.

[0039] In some embodiments, the method includes shaping (e.g., thermoforming) the reflective polarizer into a curved reflective polarizer such that the curved reflective polarizer has a first radius of curvature rc1 and a second radius of curvature rc2 along first and second directions that are orthogonal to each other (see, e.g., Figure 8 ), wherein each of the first radius of curvature rc1 and the second radius of curvature rc2 is greater than about 1 mm and less than about 500 mm (or each of rc1 and rc2 may be within the ranges described elsewhere herein), such that for at least one location on the biaxially stretched reflective polarizer, for substantially normally incident light 20 at the at least one location, and for the visible wavelength range, when the incident light at the at least one location is polarized in the second direction, the plurality of polymer layers 10, 11 of the biaxially stretched reflective polarizer have an average reflectivity Rp2 of less than about 1% (or within the ranges described elsewhere herein) (see, e.g., Figure 3 ).

[0040] In some embodiments, the biaxial stretching and / or forming process results in substantially no increase or only a modest increase in Rp1 to Rp2. In some embodiments, Rp2 is no greater than about 3 times, or 2.75 times, or 2.5 times, or 2.25 times, or 2 times, or 1.75 times, or 1.6 times, or 1.5 times, or 1.4 times, or 1.3 times Rp1. In some embodiments, 1% ≥ Rp2 ≥ Rp1, or 0.8% ≥ Rp2 ≥ Rp1, or 0.6% ≥ Rp2 ≥ Rp1.

[0041] In some embodiments, for at least one location on the resulting curved and / or biaxially stretched reflective polarizer, substantially normally incident light 20 at the at least one location, a blue wavelength range extending from about 420 nm to about 480 nm, a green wavelength range extending from about 490 nm to about 560 nm, and a red wavelength range extending from about 590 nm to about 670 nm, when the incident light is polarized along the second direction, the multiple polymer layers of the curved and / or biaxially stretched reflective polarizer have average reflectivities R2b, R2g, and R2r in the corresponding blue wavelength region, green wavelength region, and red wavelength region, wherein 2.2% ≥ R2b–R2g ≥ 0.1% and 2.5% ≥ R2b–R2r ≥ -0.1% (or these differences may be in any ranges described elsewhere herein). In some embodiments: when incident light is polarized along the second direction, the plurality of polymer layers 10, 11 of the substantially uniaxially oriented reflective polarizer have average reflectivities R1b, R1g, and R1r in the respective blue, green, and red wavelength regions, wherein 2.2% ≥ R1b–R1g ≥ 0.1% and 2.5% ≥ R1b–R1r ≥ -0.1% (or these differences may be within any ranges described elsewhere herein).

[0042] In some embodiments, biaxial stretching and / or forming is performed at an elevated temperature. For example, biaxial stretching and / or forming can be performed at a temperature greater than the glass transition temperature of at least one layer of the reflective polarizer. In some embodiments, for example, biaxial stretching and / or forming is performed at a temperature of about 100° C. to about 200° C., or 160° C., or 140° C.

[0043] Figure 7 is a schematic cross-sectional view of a curved reflective polarizer 210 according to some embodiments. For example, reflective polarizer 210 can correspond to reflective polarizer 200. Figure 7 The cross section of the polarizer 210 is in the x'z plane (orthogonal to the y' direction). For example, the x' direction may correspond to the x direction or the y direction. The curved reflective polarizer 210 may appear similarly in each of the xz plane and the yz plane (see, for example, Figure 8In some embodiments, the curved reflective polarizer 210 has an arc length AL and a chord length CL in each of a first (xz plane) and a second (yz plane) cross-sectional plane that are substantially parallel to the thickness direction (z direction) of the reflective polarizer and include the respective first and second directions. In some embodiments, (AL - CL) / CL (expressed as a percentage) is greater than about 0.02% or 0.03% or 0.04% or 0.05% or 0.07% or 0.1% or 0.2% or 0.5% or 1%. In some such embodiments, or in other embodiments, (AL - CL) / CL (expressed as a percentage) is less than about 20% or 15% or 12% or 10%. In some embodiments, for example, 0.02%≤(AL-CL) / CL×100%≤20% or 0.05%≤(AL-CL) / CL×100%≤15% or 0.1%≤(AL-CL) / CL×100%≤12% or 0.5%≤(AL-CL) / CL×100%≤10%.

[0044] Figure 8 2 is a schematic perspective view of a curved reflective polarizer 210 according to some embodiments. In some embodiments, the curved reflective polarizer 210 has a first radius of curvature rc1 and a second radius of curvature rc2 along mutually orthogonal first and second directions (e.g., x-direction and y-direction). In some embodiments, each of the first radius of curvature rc1 and the second radius of curvature rc2 is greater than about 1 mm or 2 mm or 3 mm or 4 mm or 5 mm. In some such embodiments, or in other embodiments, each of the first radius of curvature rc1 and the second radius of curvature rc2 is less than about 500 mm or 450 mm or 400 mm or 350 mm or 300 mm or 250 mm or 200 mm or 150 mm or 100 mm. In some embodiments, each of the first radius of curvature and the second radius of curvature is in the range of, for example, about 1 mm to about 500 mm or about 2 mm to about 400 mm or about 3 mm to about 350 mm or about 4 mm to about 300 mm or about 5 mm to about 250 mm.

[0045] Figure 9is a schematic perspective view of a lens assembly 300 according to some embodiments. In some embodiments, the lens assembly 300 includes an optical lens 40 having a curved first major surface 41; and a reflective polarizer 210 (e.g., curved and / or biaxially stretched) bonded to the curved first major surface 41 and substantially conforming to the curved first major surface. The reflective polarizer 210 can be bonded to the major surface 41 via an optically clear adhesive layer, or the reflective polarizer 210 can be bonded to the major surface 41 by means of the optical lens 40 being directly molded onto the reflective polarizer, which can result in, for example, diffusion bonding of the optical lens to the reflective polarizer. The optical lens 40 can be a polymer optical lens (e.g., formed from polymethyl methacrylate or a cyclic olefin polymer or copolymer). In some embodiments, the lens assembly 300 is formed by thermoforming the reflective polarizer 210 into a curved reflective polarizer 200, wherein the thermoforming process biaxially stretches the reflective polarizer as described elsewhere herein, and then injection molding the optical lens 40 onto the curved reflective polarizer 210. For example, injection molding an optical lens onto a curved reflective polarizer is generally described in U.S. Patent Application Publication No. 2021 / 0208320 (Ambur et al.).

[0046] Example

[0047] Samples of reflective polarizing film (available from 3M Company, St. Paul, Minnesota, under the trade designation IQP E) were two-dimensionally stretched at 120° C. using a laboratory film stretcher (KARO IV from Brückner Maschinenbau GmbH & Co. KG, Siegsdorf, Germany). A two-dimensional reference pattern was applied to each film sample to record the elongation in the block and pass directions (x and y directions) and used to calculate the corresponding strain percentages S1 and S2. In the film stretcher, the film samples were preheated at 120° C. for 30 seconds and then stretched to the desired strain level at a stretching rate of 1% strain / second. To test the stretched film samples, each film sample to be tested was laminated to a glass substrate with an optically clear adhesive layer, and then a black tape layer was laminated on top of the film. Reflection spectra from the reflective polarizer samples were collected using a Lambda 1050 spectrophotometer (available from PerkinElmer, Waltham, MA). The reflections from the glass, film surface layer, and black tape were also measured and used to subtract the surface reflections from the reflective polarizing film sample to obtain the reflectance spectra of the multiple layers 10, 11 and the reflective polarizer. For various values ​​of S1 and S2, the results are given in Figure 3 、 Figures 4A to 4B 、 Figures 5A to 5B and Figure 6 Shown in.

[0048] For comparison, a reflective polarizer sample was stretched with an S1 of about 0% and an S2 of about 9%.The through-state reflectivity of the plurality of layers 10, 11 for substantially normally incident light increased from about 0.15% before stretching to about 1.75% after stretching.

[0049] Terms such as "about" will be understood by one of ordinary skill in the art in the context of their use and description in this specification. If it is not clear to one of ordinary skill in the art in the context of their use and description in this specification that "about" should be used to express quantities of feature sizes, quantities, and physical properties, then "about" will be understood to mean within 10% of the specified value. A quantity given as about a specified value may be exactly the specified value. For example, if it is not clear to one of ordinary skill in the art in the context of their use and description in this specification, a quantity having a value of about 1 means that the quantity has a value between 0.9 and 1.1, and that the value may be 1.

[0050] Those of ordinary skill in the art will understand terms such as "substantially" in the context of use and description in this specification. If the use of "substantially" with respect to a property or characteristic in the context of use and description in this specification is not clear to those of ordinary skill in the art, and when the opposite meaning of the property or characteristic is clear to those of ordinary skill in the art, the term "substantially" will be understood to mean that the property or characteristic is exhibited to a greater extent than the opposite meaning of the property or characteristic.

[0051] All references, patents, and patent applications cited above are hereby incorporated by reference in their entirety in a consistent manner. In the event of inconsistencies or conflicts between an incorporated reference portion and this application, the information in the foregoing description shall prevail.

[0052] Unless otherwise indicated, descriptions of elements in the accompanying drawings should be understood to apply equally to corresponding elements in other drawings. Although specific embodiments have been illustrated and described herein, those skilled in the art will appreciate that a variety of alternative and / or equivalent implementations may be substituted for the specific embodiments shown and described without departing from the scope of the present disclosure. This application is intended to cover any modifications, variations, or combinations of the specific embodiments discussed herein. Therefore, the present disclosure is intended to be limited only by the claims and their equivalents.

Claims

1. A biaxially stretched reflective polarizer, comprising a plurality of biaxially stretched polymer layers totaling at least 10, each of the biaxially stretched polymer layers having an average thickness of less than about 500 nm, the biaxially stretched reflective polarizer being stretched in first and second in-plane orthogonal directions by respective S1 percentages and S2 percentages, S2 ≥ 2%, S2 / S1 ≤ 10, such that, for at least one location on the biaxially stretched reflective polarizer, for substantially normally incident light at the at least one location, and for a visible wavelength range extending from about 420 nm to about 680 nm, the plurality of biaxially stretched polymer layers: When the incident light is polarized along the first direction, the reflectivity thereof is greater than about 60%; and When the incident light is polarized along the second direction, it has an average transmittance greater than about 60% and an average reflectance less than about 1%.

2. The biaxially stretched reflective polarizer of claim 1, wherein the angle of incidence of the substantially normally incident light is less than about 10 degrees. The biaxially stretched reflective polarizer of claim 1 , wherein S2 / S1≧0.

5. The biaxially stretched reflective polarizer of claim 1 , wherein 1≤S2 / S1≤5. The biaxially stretched reflective polarizer of claim 1 , wherein 12% ≥ S2 ≥ 4%.

6. A lens assembly, comprising: an optical lens comprising a curved first major surface; as well as The biaxially stretched reflective polarizer of any one of claims 1 to 5, bonded to and substantially conforming to the curved first major surface.

7. A curved reflective polarizer comprising a plurality of curved polymer layers totaling at least 10, each of the curved polymer layers having an average thickness of less than about 500 nm, the curved reflective polarizer having a first radius of curvature and a second radius of curvature along mutually orthogonal first and second directions, each of the first radius of curvature and the second radius of curvature being greater than about 1 mm and less than about 500 mm, such that, for at least one location on the curved reflective polarizer, for substantially normally incident light at the at least one location, and for a visible wavelength range extending from about 420 nm to about 680 nm, the plurality of curved polymer layers: When the incident light is polarized along the first direction, the reflectivity thereof is greater than about 60%; and When the incident light is polarized along the second direction, it has an average transmittance greater than about 60% and an average reflectance less than about 1%.

8. The curved reflective polarizer of claim 7 , wherein in each of a first cross-sectional plane and a second cross-sectional plane of the curved reflective polarizer that are substantially parallel to a thickness direction of the reflective polarizer and that include the first direction and the second direction, respectively, the curved reflective polarizer has an arc length AL and a chord length CL, and wherein (AL-CL) / CL is greater than approximately 0.02% and less than approximately 20%.

9. A curved reflective polarizer, the curved reflective polarizer comprising a plurality of curved polymer layers totaling at least 10, each of the curved polymer layers having an average thickness of less than about 500 nm, the curved reflective polarizer having first and second radii of curvature along mutually orthogonal first and second directions, each of the first and second radii of curvature being greater than about 1 mm and less than about 500 mm, such that for substantially normally incident light at at least one location on the curved reflective polarizer, when the incident light is polarized in the second direction, the plurality of curved polymer layers have average reflectivities R2b, R2g, and R2r in the blue, green, and red wavelength regions, respectively, of 2.2% ≥ R2b − R2g ≥ 0.1% and 2.5% ≥ R2b − R2r ≥ −0.1%.

10. The curved reflective polarizer of claim 9, wherein for the substantially normally incident light at the at least one location and for a visible wavelength range extending from about 420 nm to about 680 nm, the plurality of curved polymer layers: When the incident light is polarized along the first direction, the reflectivity thereof is greater than about 60%; and When the incident light is polarized along the second direction, it has an average transmittance greater than about 60% and an average reflectance less than about 1%.

11. A lens assembly, comprising: an optical lens comprising a curved first major surface; as well as The curved reflective polarizer of any one of claims 7 to 10, bonded to and substantially conforming to the curved first major surface.

12. A method comprising: A reflective polarizer is provided, the reflective polarizer being substantially uniaxially oriented along a first direction and comprising a plurality of polymer layers totaling at least 10, each of the polymer layers having an average thickness of less than about 500 nm, such that for substantially normally incident light and for a visible wavelength range extending from about 420 nm to about 680 nm, the plurality of polymer layers of the reflective polarizer being substantially uniaxially oriented: When the incident light is polarized along the first direction, the reflectivity thereof is greater than about 60%; as well as When the incident light is polarized along a second direction orthogonal to the first direction, it has an average reflectivity Rp1 and an average transmittance greater than about 60%; as well as The reflective polarizer is biaxially stretched along the first direction and the second direction with corresponding S1 percentages and S2 percentages, S2≥2%, S2 / S1≤10, so that for at least one position on the biaxially stretched reflective polarizer, for substantially normally incident light at the at least one position and for the visible wavelength range, when the incident light at the at least one position is polarized along the second direction, the multiple polymer layers of the biaxially stretched reflective polarizer have an average reflectivity Rp2 of less than about 1%, wherein Rp2 is not greater than about 3 times Rp1. The method according to claim 12 , wherein 0.5≤S2 / S1≤8 and 14%≥S2≥3%.

14. A method comprising: A reflective polarizer is provided, the reflective polarizer being substantially uniaxially oriented along a first direction and comprising a plurality of polymer layers totaling at least 10, each of the polymer layers having an average thickness of less than about 500 nm, such that for substantially normally incident light and for a visible wavelength range extending from about 420 nm to about 680 nm, the plurality of polymer layers of the reflective polarizer being substantially uniaxially oriented: When the incident light is polarized along the first direction, the reflectivity thereof is greater than about 60%; as well as When the incident light is polarized along a second direction orthogonal to the first direction, it has an average reflectivity Rp1 and an average transmittance greater than about 60%; as well as The reflective polarizer is formed as a curved reflective polarizer so that the curved reflective polarizer has a first radius of curvature and a second radius of curvature along mutually orthogonal first and second directions, each of the first radius of curvature and the second radius of curvature being greater than about 1 mm and less than about 500 mm, so that for at least one location on the curved reflective polarizer, for substantially normally incident light at the at least one location and for the visible wavelength range, when the incident light at the at least one location is polarized along the second direction, the multiple polymer layers of the curved reflective polarizer have an average reflectivity Rp2 of less than about 1%, wherein Rp2 is no greater than about 3 times Rp1.

15. The method of any one of claims 12 to 14, wherein Rp2 is no greater than about 2.5 times Rp1.

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