Optical article comprising curved optical film

Abstract

An optical article includes a curved optical film rolled about a central axis such that opposing first and second ends of the curved optical film are joined and a seam is formed between the first and second ends. The curved optical film has an average thickness of less than about 500 microns, and for substantially vertical incident light, for at least one polarization state and for a first wavelength in a wavelength range extending from about 420 nm to about 1550 nm, the curved optical film has an average optical transmittance of greater than about 40%. In a first cross-section of the curved optical film taken in a first plane including the central axis, the optical film has opposite first and second curved cross-section portions. The cross-sectional portion has a minimum radius of curvature R1min of less than about 15 cm across a middle 60% of at least one of the first curved cross-sectional portion and the second curved cross-sectional portion.

Description

Technical Field

[0001] This specification as a whole relates to articles including a curved optical film. Background Art

[0002] Optical films can be thermoformed into desired shapes. Summary of the Invention

[0003] In some aspects, this specification provides an optical article that includes a curved optical film that is rolled around a central axis such that opposite first and second ends of the curved optical film are joined and a seam is formed between the first and second ends. The seam extends between opposite top and bottom portions of the curved optical film that are spaced apart by a distance H. The curved optical film has an average thickness of less than about 500 microns and has an average optical transmittance of greater than about 40% for substantially perpendicularly incident light, for at least one polarization state, and for a first wavelength in a wavelength range extending from about 420 nm to about 1550 nm. The curved optical film is such that, in a first cross-section taken in a first plane including the central axis, the curved optical film has opposite first and second curved cross-section portions. Across at least 60% of the middle of at least one of the first and second curved cross-section portions, the cross-section portion: has a minimum radius of curvature R1min of less than about 15 cm; and for the first wavelength, has an average in-plane refractive index Navg and a maximum in-plane birefringence DN, where DN / Navg may not exceed about 0.04.

[0004] In some aspects, this specification provides an optical article that includes a curved optical film that is rolled such that opposite first and second ends of the curved optical film are joined and a seam is formed between the first and second ends. The seam extends from an open top of the curved optical film to an opposite open bottom. The open top and the open bottom include respective open top perimeters and open bottom perimeters. The curved optical film may have an average thickness of less than about 500 microns and has an average optical transmittance of greater than about 40% for substantially perpendicularly incident light, for at least one polarization state, and for a first wavelength in a wavelength range extending from about 420 nm to about 1550 nm such that: the minimum distance between the open top perimeter and the open bottom perimeter is S1min; and the shortest path between the open top perimeter and the open bottom perimeter on the curved optical film is S2min, where S2min / S1min ≥ 1.05.

[0005] In some aspects, this specification provides a method for forming an optical film. The method includes: cutting a substantially flat polymeric optical film into a first film having a substantially annular sector shape; rolling up the first film such that opposite first and second ends of the first film are joined and form a seam, where the seam extends from an open top of the rolled-up first film to an opposite open bottom, and where the open top and the open bottom include respective open top perimeters and open bottom perimeters; fixing the positions of the open top perimeter and the open bottom perimeter such that a minimum distance between the open top perimeter and the open bottom perimeter is S1min; heating the first film; and expanding the heated first film with the open top perimeter and the open bottom perimeter fixed to provide a curved optical film such that a shortest path between the open top perimeter and the open bottom perimeter on the curved optical film is S2min, where S2min / S1min may be greater than or equal to 1.05.

[0006] These and other aspects will become apparent from the following detailed description. However, in no event should this brief summary be construed as limiting the claimed subject matter. BRIEF DESCRIPTION OF THE DRAWINGS

[0007] Figures 1 to 2 are a schematic top perspective view and a bottom perspective view, respectively, of an optical article including a curved optical film according to some embodiments.

[0008] Figure 3 is a schematic side view of an optical film according to some embodiments.

[0009] Figure 4 is a schematic cross-sectional view of an optical film in a first plane according to some embodiments.

[0010] Figure 5 is a schematic cross-sectional view of an optical article in a second plane according to some embodiments.

[0011] Figure 6A is a schematic top view of an optical film according to some embodiments.

[0012] Figure 6B Schematically illustrates expanding a rolled-up optical film according to some embodiments.

[0013] Figure 6C is a schematic cutaway perspective view of a mold for forming an optical film according to some embodiments. DETAILED DESCRIPTION

[0014] Reference is made in the following description to the accompanying drawings, which form a part of the present disclosure and in which various embodiments are shown by way of illustration. The drawings are not necessarily to scale. It is to be understood that other embodiments may be envisioned and effected without departing from the scope or spirit of the present specification. Accordingly, the following detailed description should not be taken in a limiting sense.

[0015] According to some embodiments of the present specification, an optical article includes an optical film that has been rolled into a frustoconical shape and then radially expanded into a desired curved shape. According to some embodiments, it has been found that, for example, when the film has a low in-plane birefringence before formation, compared to when formed into a similar radius of mean curvature using other methods (such as expanding a flat film into a three-dimensional shape as described in U.S. Patent Application Publication No. 2020 / 0241187 (Jennings et al.)), the optical film formed in this manner can have a lower in-plane birefringence (which refers to the birefringence in the tangent plane). According to some embodiments, it has been found that the processes of the present specification can allow an optical film to be formed into geometric shapes that cannot be obtained by previous methods without degrading the desired properties of the optical film, such as by (locally) overstretching the film. Additionally, according to some embodiments, it has been found that, compared to when formed into a similar radius of mean curvature using previous methods, the curved optical film as described herein can have a lower thickness variation and / or a lower in-plane birefringence variation.

[0016] In some embodiments, a portion of the curved optical film is cut out from the optical article for use in another optical article. For example, the cut-out portion can be used as a cover for an optical component. In some embodiments, it is desirable for such a film to have a low in-plane birefringence such that the polarization state of light incident substantially perpendicularly does not change substantially when transmitted through the optical film. In some embodiments, the optical film is a reflective polarizer, and the cut-out portion can be disposed, for example, on an optical lens (e.g., the optical lens can be molded onto the cut-out portion) to provide an optical configuration that can be used in, for example, optical systems such as those of U.S. Patent No. 10,678,052 (Ouderkirk et al.).

[0017] Figures 1 to 2 are a schematic top perspective view and a bottom perspective view, respectively, of an optical article 200 including a curved optical film 10 according to some embodiments. Figure 3 is a schematic side view of an optical film 10 according to some embodiments. Figure 4 is a schematic cross-sectional view of an optical film 10 in a first plane P1 according to some embodiments. Figure 5Schematic cross-sectional view of an optical article 200 in accordance with some embodiments in a second plane P2 that is substantially orthogonal (e.g., within an orthogonal range of about 30 degrees, 20 degrees, 10 degrees, or 5 degrees) to a first plane P1.

[0018] In some embodiments, the optical article 200 includes a curved optical film 10 that is rolled up such that opposite first end 11 and second end 12 of the curved optical film 10 are joined and form a seam 13 therebetween. For example, in some embodiments, the curved optical film 10 is rolled around a central axis 20 such that opposite first end 11 and second end 12 of the curved optical film 10 are joined and form a seam 13 therebetween. The first end 11 and the second end 12 may be joined by, for example, a piece of tape to form the seam 13. In some embodiments, the seam 13 extends between opposite top 14 and bottom 14 and 15 of the curved optical film that are spaced a distance H apart. In some embodiments, the seam extends from an open top 14 of the curved optical film to an opposite open bottom 15, where the open top 14 and the open bottom 15 include respective open top perimeters 114 and open bottom perimeters 115 (see, for example Figure 1 ). The open top perimeter 114 and the open bottom perimeter 115 may correspond to, for example, creases in the top and bottom of the film 10 caused by a clamp, such as when the film is formed into a curved shape. The curved optical film 10 may be a polymeric optical film.

[0019] In some embodiments, the curved optical film 10 has an average thickness t that is less than about 500 microns, or 450 microns, or 400 microns, or 350 microns, or 300 microns, or 250 microns, or 200 microns, or 150 microns, or 100 microns, or 75 microns, or 50 microns, or 40 microns, or 30 microns, or 20 microns, or 10 microns. In some embodiments, the average thickness t is greater than about 1 micron, 5 microns, 10 microns, 20 microns, 30 microns, 40 microns, or 50 microns. In some embodiments, for example, the average thickness t is in the range of about 1 micron to about 500 microns, or about 5 microns to about 400 microns, or about 10 microns to about 300 microns, or about 20 microns to about 250 microns, or about 30 microns to about 200 microns.

[0020] In some embodiments, for light 30 incident at substantially normal incidence (e.g., within about 30 degrees, 20 degrees, 10 degrees, or 5 degrees of the normal), for at least one polarization state 131 and / or 132, and for a first wavelength λ in the wavelength range extending from about 420 nm to about 1550 nm (e.g., 532 nm, 550 nm, or 637 nm), the curved optical film 10 has an average (e.g., on the surface of the optical film 10) optical transmittance greater than about 40%, or 50%, or 60%, or 70%, or 80%. For example, the first wavelength λ can be a visible wavelength in the visible wavelength range from about 420 nm to about 700 nm or to about 680 nm, or can be a near-infrared wavelength in the near-infrared wavelength range from about 700 nm to about 1550 nm. In some embodiments, for example, for light 30 incident at substantially normal incidence, in the wavelength range extending from about 420 nm to about 1550 nm, or in the near-infrared wavelength range from about 700 nm to about 1550 nm, or in the visible wavelength range from about 420 nm to about 680 nm, for at least one polarization state 131 and / or 132, the curved optical film 10 has an average (e.g., over the wavelength and on the surface of the optical film 10) optical transmittance greater than about 40%, or 50%, or 60%, or 70%, or 80%. In some embodiments, the at least one polarization state is the first polarization state 131. In some embodiments, the at least one polarization state includes the orthogonal first polarization state 131 and second polarization state 132. In some embodiments, for light 30 incident at substantially normal incidence and unpolarized, in the wavelength range extending from about 420 nm to about 1550 nm, or in the near-infrared wavelength range from about 700 nm to about 1550 nm, or in the visible wavelength range from about 420 nm to about 680 nm, the curved optical film 10 has an average (e.g., over the wavelength, over the polarization state, and on the surface of the optical film 10) optical transmittance greater than about 40%, or 50%, or 60%, or 70%, or 80%. For example, the optical film can be a substantially transparent polymer film, such as a polyethylene terephthalate (PET) film. For example, the film can optionally be coated and / or surface treated. Exemplary surface treatments and coatings are described, for example, in U.S. Patent Application Publication No. 2022 / 0177303 (Thompson et al.). For example, such surface treatments and coatings can be used to provide a hydrophobic (or superhydrophobic or superoleophobic) outer surface to the curved optical film used as a protective cover for an electronic device.

[0021] In some embodiments, for substantially vertically incident light 30 and a visible wavelength range extending from about 420 nm to about 680 nm, the curved optical film 10 has an average (e.g., over wavelength and over the surface of the optical film 10) optical transmittance greater than about 40% for a first polarization state 131 and can have an average (e.g., over wavelength and over the surface of the optical film 10) optical reflectance greater than about 40% for a second polarization state 132 orthogonal to the first polarization state 131. The average optical transmittance for the first polarization state 131 can be greater than about 50%, or 60%, or 70%, or 80%. The average optical reflectance for the second polarization state 132 can be greater than about 50%, or 60%, or 70%, or 80%, or 90%. For example, in some embodiments, for substantially vertically incident light 30, the curved optical film 10 has an average optical transmittance greater than about 60% for the first polarization state 131 in the visible wavelength range and an average optical reflectance greater than about 60% for the second polarization state 132 orthogonal to the first polarization state 131 in the visible wavelength range. For example, the optical film can be a reflective polarizer film as generally described in the following documents: 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.); and U.S. Patent No. 9,162,406 (Neavin et al.).

[0022] In some embodiments, the curved optical film 10 is such that, in a first cross-section 10a (see, for example Figure 4 ) of the curved optical film taken in a first plane (P1 or the xz plane of the exemplary x - y - z coordinate system) including the central axis 20, the optical film 10 has opposite first and second curved cross-sectional portions 111 and 112, where at least 60% of a middle portion (e.g., middle portion 116) spanning at least one of the first curved cross-sectional portion 111 and the second curved cross-sectional portion 112 has a minimum radius of curvature R1min of less than about 15 cm, or 14 cm, or 13 cm, or 12 cm, or 11 cm, or 10 cm, or 9 cm, or 8 cm, or 7 cm, or 6 cm, or 5 cm. In some such embodiments, or in other embodiments, the minimum radius of curvature R1min is greater than about 0.5 cm, 0.75 cm, 1 cm, 1.25 cm, 1.5 cm, 1.75 cm, 2 cm, 2.5 cm, 3 cm, 3.5 cm, or 4 cm.

[0023] In some such embodiments, or in other embodiments, across at least 60% of the midsection (e.g., midsection portion 116) of the first curved cross-sectional portion 111 and the second curved cross-sectional portion 112, the cross-sectional portion: has an average in-plane refractive index Navg and a maximum in-plane birefringence DN, where DN / Navg does not exceed about 0.04. In some such embodiments, or in other embodiments, DN / Navg does not exceed about 0.035, 0.03, 0.025, 0.02, 0.019, 0.018, 0.017, 0.016, 0.015, 0.014, or 0.013. The refractive index can be evaluated at the same first wavelength (e.g., 532 nm, 550 nm, or 637 nm) in the wavelength range extending from about 420 nm to about 1550 nm used to characterize the optical transmittance of the optical film. The in-plane birefringence at a certain position of the optical film is the birefringence in the plane tangent to the optical film at that position.

[0024] In some embodiments, the optical film is a single-piece monolayer film, and the in-plane refractive index of the optical film is the in-plane refractive index of a single layer. In this case, even in the presence of a large out-of-plane birefringence (e.g., greater than about 0.1), the in-plane birefringence may be low (e.g., less than about 0.05). In some embodiments, the average (averaged over the cross-sectional portion and in the direction in the plane of the film) in-plane refractive index Navg is in the range of about 1.4 to 2, or about 1.5 to 1.8, or about 1.6 to about 1.75. In some such embodiments, or in other embodiments, the maximum (over the cross-sectional portion) in-plane birefringence DN is less than about 0.05, 0.045, 0.04, 0.035, 0.03, or 0.025.

[0025] In some embodiments, the optical film includes multiple layers, and the average in-plane refractive index of the optical film can refer to the average value averaged over each layer (e.g., the volume-weighted average over the layer), and the maximum in-plane birefringence can refer to the maximum in-plane birefringence over all layers. For example, the optical film can include a first layer and a second layer, the first layer is biaxially oriented and has an out-of-plane birefringence greater than about 0.1 and an in-plane birefringence less than about 0.05, and the second layer is, for example, a coating and has an isotropic refractive index. In this case, DN can refer to the maximum in-plane birefringence of the first layer, Navg can refer to the average in-plane refractive index averaged over the first layer and the second layer, and DN / Navg can be within any range described elsewhere herein (e.g., DN / Navg can be no more than about 0.04). In other embodiments, the multiple layers include substantially uniaxially oriented layers. For example, the substantially uniaxially oriented layer can have a substantially higher DN value (e.g., greater than 0.06, 0.08, or 0.1). In some such embodiments, or in other embodiments, DN / Navg can be greater than, for example, 0.04, 0.06, 0.08, or 0.1.

[0026] In some embodiments, R1min and / or DN / Navg are within any of the ranges described elsewhere herein for the middle 65%, or 70%, 75%, or 80%, or 85%, or 90%, or 95% of at least one of the first and second curved cross-sectional portions. For example, in some embodiments, in the first cross-section 10a, across the middle 70% of at least one of the first and second curved cross-sectional portions, the cross-sectional portion: has a minimum radius of curvature R1min’ less than about 12 cm; and for the first wavelength λ, has an average in-plane refractive index Navg’ and a maximum in-plane birefringence DN’, where DN’ / Navg’ does not exceed about 0.03 (the prime ’ can be used to distinguish quantities defined on different middle portions). As another example, in some embodiments, in the first cross-section 10a, across the middle 80% of at least one of the first and second curved cross-sectional portions, the cross-sectional portion: has a minimum radius of curvature R1min’ less than about 10 cm; and for the first wavelength λ, has an average in-plane refractive index Navg’ and a maximum in-plane birefringence DN’, where DN’ / Navg’ does not exceed about 0.02. The minimum radius of curvature R1min, Navg, and / or DN can be different in different middle portions (e.g., R1min’, Navg’, and / or DN’ in the middle 80% of at least one of the first and second curved cross-sectional portions can be different from R1min, Navg, and / or DN in the middle 60% of at least one of the first and second curved cross-sectional portions). For example, the middle 60% of a curved cross-sectional portion refers to the middle 60% in the height direction (z-direction) multiplied by the length of the cross-sectional portion.

[0027] The refractive index and birefringence can be determined using a prism coupler (such as a Metricon Model 2010 / M prism coupler). The in-plane birefringence can alternatively be determined by measuring the in-plane retardation using a polarimeter (such as an AXOMETRICS AXOSCAN Mueller matrix polarimeter) and dividing by the film thickness at the same location where the retardation is measured.

[0028] In some embodiments, the minimum distance between the open top perimeter and the open bottom perimeter of the curved optical film 10 is S1min; and the shortest path between the open top perimeter and the open bottom perimeter on the curved optical film is S2min, where S2min / S1min ≥ 1.05, 1.06, 1.07, 1.08, 1.09, or 1.1. In some embodiments, S2min / S1min ≤ 1.2, 1.19, 1.18, 1.17, 1.16, 1.15, 1.14, 1.135, or 1.13. For example, in some embodiments, S2min / S1min ranges from about 1.05 to about 1.2, or from about 1.06 to about 1.18, or from about 1.07 to about 1.16, or from about 1.08 to about 1.14.

[0029] In some embodiments, across at least one of the middle portions (e.g., the middle 60% or the middle 70% or another middle portion) of the first curved cross-sectional portion and the second curved cross-sectional portion, the cross-sectional portion has an average thickness T1 (see, for example Figure 4 ) and a thickness standard deviation ST1 (e.g., schematically represented by any difference between T1 and t in Figure 4 ), where ST1 / T1 ≤ 0.2, or 0.15, or 0.1, or 0.09, or 0.08, or 0.07, or 0.06, or 0.05, or 0.04, or 0.03, or 0.02, or 0.01.

[0030] In some embodiments, across at least one of the middle portions (e.g., the middle 60% or the middle 70% or another middle portion) of the first curved cross-sectional portion and the second curved cross-sectional portion, the cross-sectional portion has a minimum radius of curvature R1min, where H / R1min ≥ 0.2, or 0.25, or 0.3, or 0.35, or 0.375, or 0.4, or 0.45, or 0.55, or 0.6, or 0.7, or 0.8, or 0.9, or 1, or 1.1, or 1.2, or 1.3. In some embodiments, H / R1min ≤ 2, 1.9, 1.8, 1.7, 1.6, 1.5.

[0031] In some embodiments, H ≥ 5 mm, or 6 mm, or 7 mm, or 8 mm, or 9 mm, or 10 mm, or 15 mm, or 20 mm, or 25 mm, or 30 mm, or 40 mm, or 50 mm. In some such embodiments, or in other embodiments, H ≤ 200 mm, 150 mm, 100 mm, 90 mm, 80 mm, 70 mm.

[0032] In some embodiments, in a second cross-section 10b taken in a second plane (P2 or xy plane) that is perpendicular to the central axis 20 and that bisects the curved optical film 10 substantially (see, for example, Figure 5 ), the optical film 10 has an average radius of curvature R2 that is greater than about 5 mm, or 6 mm, or 7 mm, or 8 mm, or 9 mm, or 10 mm, or 15 mm, or 20 mm, or 25 mm, or 30 mm, or 40 mm, or 50 mm and less than about 400 mm, or 375 mm, or 350 mm, or 325 mm, or 300 mm, or 275 mm, or 250 mm, or 225 mm, or 200 mm, or 175 mm, or 150 mm, or 125 mm, or 100 mm, or 75 mm. In some embodiments, for example, R2 is in the range of about 5 mm to about 400 mm, or about 7 mm to about 350 mm, or about 10 mm to about 300 mm, or about 15 mm to about 250 mm, or about 20 mm to about 200 mm. When the second plane P2 is midway between the top 14 and the bottom 15 of the optical film 10 in the height direction (z-direction) of the optical film 10, the optical film 10 is bisected by the plane. When the second plane P2 is midway between the top 14 and the bottom 15 of the optical film 10 (e.g., at about 30%, 25%, 20%, 15%, 10%, or 5% of H), the optical film 10 is substantially bisected by the plane.

[0033] Figures 6A to 6C Schematically illustrated is a process for forming an initially unstretched first film 210a into a curved optical film 210 (e.g., corresponding to the optical film 10) according to some embodiments. The optical films 210a, 210 can have any of the optical properties described elsewhere herein. In some embodiments, a method for shaping an optical film includes: cutting a substantially flat polymeric optical film into a first film having a substantially ring-sector shape (see, for example, Figure 6A ); rolling up the first film 210a such that opposite first ends 211 and second ends 212 of the first film 210a are joined and form a seam 213 (see, for example, Figure 6B ), where the seam extends from the open top to the opposite open bottom of the rolled-up first film (e.g., corresponding to 14 and 15), and where the open top and the open bottom include respective open top perimeters 214 and open bottom perimeters 215; fixing the positions of the open top perimeter and the open bottom perimeter (e.g., in the Figure 6C schematically illustrated mold 300) such that the minimum distance between the open top perimeter and the open bottom perimeter is S1min (see, for example, Figure 4); heating the first film; and expanding the heated first film while fixed at the open top perimeter and the open bottom perimeter to provide a curved optical film such that the shortest path between the open top perimeter and the open bottom perimeter on the curved optical film is S2min (see, for example Figure 4 ), where S2min / S1min ≥ 1.05, or S2min / S1min can be within the ranges described elsewhere herein.

[0034] If the film nominally has a given geometry (e.g., flat, annular cross-section, frustoconical) or has a geometry that varies little compared to the largest dimension of the formed film (e.g., less than about 15%, 10%, or 5%), then the film can have a shape that is substantially that geometry.

[0035] Rolling up the first film can include substantially rolling up the first film into a frustoconical shape (frustum) without stretching the film. For example, the film can be rolled around the frustoconical portion 331 of the die platen 330 in the die 300. Expanding the film can include expanding the film radially away from the central axis 20 (see, for example Figure 3 ). Heating the first film 210a can include heating the die platen 330, which heats the film. The first film 201a can be heated to a temperature greater than the glass transition temperature Tg of the first film (e.g., greater than the Tg of at least one layer of the film or greater than the Tg of each layer in the layer). In some embodiments, the first film 201a is semi-crystalline and has a series of melting temperatures. The first film 201a can be heated to a temperature below the maximum melting point of the optical film. In some embodiments, the first film 201 is heated to a temperature approximately equal to or even greater than the lowest melting temperature in the melting temperature range of the first film 201a. In some embodiments, for example, the first film 210a can be a polyethylene terephthalate film having a glass transition temperature of about 70 °C and a melting point in the range of about 240 °C to about 260 °C, and the first film can be heated to a temperature of about 150 °C to about 250 °C or about 180 °C to about 220 °C. Air pressure can be applied to the outer side of the film 210a to press the film against the frustoconical portion 331 of the die platen 330 to assist in heating the film. For example, a porous insert 340 can be included in the die 300 to allow injection of air. After the film 201a has been heated, expanding the film can include applying air to the interior of the film through the die platen 330 in order to push the film outward, thereby stretching it against the curved die surface 345 into, for example, a desired geometry.

[0036] Embodiment

[0037] For example, using the process described for Figures 6A to 6C to thermoform a biaxially oriented polyethylene terephthalate (PET) film approximately 125 microns thick into Figures 1 to 5The shape schematically illustrated. Before forming, the film had an out-of-plane refractive index of 1.491, an average in-plane refractive index of 1.658, and an average in-plane birefringence of 0.031 at 637 nm, as measured using a Metricon Model 2010 / M prism coupler. The film was cut into an annular sector shape and rolled into a frustoconical shape. The ends of the film were taped together to form a seam. The film was inflated in a mold, as Figure 6C schematically illustrated. Before inflation, the film was heated to about 190 °C. Air was injected through the porous insert 340 to keep the film adjacent to the frustoconical portion 331 of the mold platen 330 to assist in heating the film. To inflate the film, air was injected through the mold platen 330 to press the film against the curved mold surface 345. After thermoforming, the curved optical film had an R1min of about 4.3 cm, an H of about 6.1 cm, an R2 of about 5.7 cm, an average thickness of about 109.5 microns, and a thickness standard deviation of about 0.941 microns. The thermoformed film had an out-of-plane birefringence of 1.488, an average in-plane refractive index of 1.659, an average in-plane birefringence of 0.0176, and a maximum in-plane birefringence of 0.0205 at 637 nm, as measured using a Metricon Model 2010 / M prism coupler. The thermoformed film had a maximum in-plane birefringence of 0.0232 at 550 nm, as determined using an AXOMETRICS AXOSCAN Mueller matrix polarimeter to determine the in-plane retardation and dividing the retardation by the thickness measurement of the layer at the location being measured. The polarimeter was used with a spectrally selective source, and Mueller matrices were collected at a series of wavelengths in the visible spectrum. The spectrum was then analyzed by the polarimeter software to solve for the absolute retardation at each wavelength. The maximum birefringence was determined using a prism coupler and a polarimeter in a region excluding the perimeter 114 and 115.

[0038] A film comprising a biaxially oriented PET film of about 63 microns thick and a coating of about 71 microns thick, generally described in U.S. Patent Application Publication No. 2022 / 0177303 (Thompson et al.), was thermoformed as described for a PET about 125 microns thick. The film was rolled up such that the coating faced the outside of the curved optical film. Before thermoforming, the PET layer of the film had an out-of-plane refractive index of 1.495, an average in-plane refractive index of 1.659, and an average in-plane birefringence of 0.023 at 637 nm, as measured using a Metricon Model 2010 / M prism coupler. After thermoforming, the PET layer of the film had an out-of-plane refractive index of 1.495, an average in-plane refractive index of 1.656, an average in-plane birefringence of 0.0198, and a maximum in-plane birefringence of 0.022 at 637 nm, as measured using a Metricon Model 2010 / M prism coupler.

[0039] Terms such as "about" will be understood in the context in which they are used and described by one of ordinary skill in the art in this specification. If the use of "about" applied to a quantity expressing the size, amount, and physical characteristics of a feature is not clear to one of ordinary skill in the art in the context in which it is used and described in this specification, then "about" will be understood to mean within 10% of the specified value. A quantity given as about a specified value can be exactly the specified value. For example, if it is not clear to one of ordinary skill in the art in the context in which it is used and described 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 the value can be 1.

[0040] One of ordinary skill in the art will understand terms such as "substantially" in the context in which they are used and described in this specification. If, in the context in which it is used and described in this specification, the use of "substantially" with respect to a property or characteristic is not clear to one of ordinary skill in the art, and when one of ordinary skill in the art is clear about the opposite meaning of the property or characteristic, the term "substantially" will be understood to mean that the degree of manifestation of the property or characteristic is greater than the opposite meaning of the property or characteristic.

[0041] All of the above-cited references, patents, and patent applications are hereby incorporated by reference in their entirety in a consistent manner. In the event of any inconsistency or conflict between the incorporated reference portion and this application, the information in the foregoing description shall prevail.

[0042] Unless otherwise indicated, the description of elements in the drawings shall be understood to apply equally to corresponding elements in other drawings. Although specific embodiments have been illustrated and described herein, one of ordinary skill in the art will recognize that, without departing from the scope of the present disclosure, many alternative and / or equivalent forms of specific implementation may be used in place of the specific embodiments shown and described. This application is intended to cover any modifications or variations or combinations of the specific embodiments discussed herein. Accordingly, the present disclosure is intended to be limited only by the claims and their equivalents.

Claims

1. An optical article, the optical article comprising a curved optical film wound around a central axis such that opposite first and second ends of the curved optical film are joined and a seam is formed between the first end and the second end, the seam extending between opposite top and bottom portions of the curved optical film spaced a distance H apart, the curved optical film having an average thickness of less than about 500 microns, and the curved optical film having an average optical transmittance of greater than about 40% for substantially vertically incident light, for at least one polarization state, and for a first wavelength in a wavelength range extending from about 420 nm to about 1550 nm. Such that, in a first cross-section of the curved optical film taken in a first plane including the central axis, the curved optical film has opposite first and second curved cross-section portions, wherein across at least 60% of the midportion of at least one of the first and second curved cross-section portions, the cross-section portion: has a minimum radius of curvature R1min of less than about 15 cm; and for the first wavelength, has an average in-plane refractive index Navg and a maximum in-plane birefringence DN, and DN / Navg does not exceed about 0.

04.

2. The optical article according to claim 1, wherein in the first cross-section, across at least 70% of the midportion of at least one of the first and second curved cross-section portions, the cross-section portion: has a minimum radius of curvature R1min' of less than about 12 cm; and for the first wavelength, has an average in-plane refractive index Navg' and a maximum in-plane birefringence DN', and DN' / Navg' does not exceed about 0.

03.

3. The optical article according to claim 1, wherein the top and bottom of the curved optical film include respective open top perimeters and open bottom perimeters such that: the minimum distance between the open top perimeter and the open bottom perimeter is S1min; and the shortest path between the open top perimeter and the open bottom perimeter on the curved optical film is S2min, and 1.2 ≥ S2min / S1min ≥ 1.

05.

4. The optical article according to claim 1, wherein the minimum radius of curvature R1min is greater than about 1 cm.

5. The optical article according to claim 1, wherein across at least 60% of the midportion of at least one of the first and second curved cross-section portions, the cross-section portion has an average thickness T1 and a thickness standard deviation ST1, and ST1 / T1 ≤ 0.

2.

6. The optical article according to claim 1, wherein H / R1min ≥ 0.

2.

7. The optical article according to claim 6, wherein H / R1min ≤ 2.

8. The optical article according to claim 1, wherein H ≥ 5 mm.

9. The optical article according to claim 8, wherein H ≤ 200 mm.

10. The optical article according to any one of claims 1 to 9, wherein in a second cross-section taken in a second plane perpendicular to the central axis and substantially bisecting the curved optical film, the curved optical film has an average radius of curvature R2 greater than about 5 mm and less than about 400 mm.

11. An optical article, the optical article comprising a curved optical film, the curved optical film being rolled up such that opposite first and second ends of the curved optical film are joined and a seam is formed between the first and second ends, the seam extending from an open top of the curved optical film to an opposite open bottom, the open top and the open bottom including respective open top perimeters and open bottom perimeters, the curved optical film having an average thickness of less than about 500 microns, and for substantially perpendicularly incident light, for at least one polarization state, and for a first wavelength in a wavelength range extending from about 420 nm to about 1550 nm, the curved optical film having an average optical transmittance greater than about 40%, such that: The minimum distance between the open top perimeter and the open bottom perimeter is S1min; and The shortest path between the open top perimeter and the open bottom perimeter on the curved optical film is S2min, and S2min / S1min ≥ 1.

05.

12. The optical article according to claim 11, wherein S2min / S1min ≤ 1.

15.

13. The optical article according to claim 11 or 12, wherein the at least one polarization state includes orthogonal first and second polarization states.

14. The optical article according to claim 11 or 12, wherein for the substantially perpendicularly incident light, the curved optical film has an average optical transmittance greater than about 60% for the first polarization state in a visible wavelength range from about 420 nm to about 680 nm and an average optical reflectance greater than about 60% for a second polarization state orthogonal to the first polarization state in the visible wavelength range.

15. A method for shaping an optical film, the method comprising: Cutting a substantially flat polymeric optical film into a first film having a substantially ring-sector shape; Rolling up the first film such that opposite first and second ends of the first film are joined and a seam is formed, the seam extending from an open top of the rolled-up first film to an opposite open bottom, the open top and the open bottom including respective open top perimeters and open bottom perimeters; Fixing the positions of the open top perimeter and the open bottom perimeter such that the minimum distance between the open top perimeter and the open bottom perimeter is S1min; Heating the first film; And Expanding the heated first film with the open top perimeter and the open bottom perimeter fixed to provide a curved optical film such that the shortest path between the open top perimeter and the open bottom perimeter on the curved optical film is S2min, and S2min / S1min ≥ 1.05.

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