Multilayer optical film and display system including the same

Abstract

The invention discloses a multilayer optical film. The multilayer optical film comprises a plurality of optical repeating units. For an angle of incidence of less than about 10 degrees and for each of two mutually orthogonal polarization states, the multilayer optical film has a first order reflection band having an average reflectance of greater than about 70% in the infrared wavelength range and an average reflectance of less than about 15% in the visible wavelength range. For p-polarized incident light and a predetermined angle of incidence, the multilayer optical film has an average reflectance in the visible wavelength range in the range of about 18% to about 35%, where the standard deviation of the reflectance of the multilayer optical film in the visible wavelength range is less than about 0.15 times the average reflectance in the visible wavelength range. A display system includes an optical film and an image projector.

Description

TECHNICAL FIELD

[0001] This specification generally relates to multilayer optical films and display systems. BACKGROUND

[0002] The multilayer optical film can include a stack of polymer layers arranged into optical repeat units. The multilayer optical film can be a reflective polarizer or a mirror. The display system can include an image projector and a multilayer optical film. SUMMARY

[0003] In some aspects, this specification provides a multilayer optical film including a plurality of optical repeat units having a total number greater than about 10. Each optical repeat unit of the plurality of optical repeat units includes a plurality of polymer layers. Each polymer layer of each optical repeat unit can have an average thickness less than about 500 nm. The multilayer optical film is such that for incident light having an incident angle less than about 10 degrees and for each of two mutually orthogonal polarization states, the multilayer optical film has: a first-order reflection band having an average reflectivity greater than about 70% over an infrared wavelength range extending at least from about 1000 nm to about 1600 nm, wherein a standard deviation of the reflectivity of the multilayer optical film over the infrared wavelength range is less than about 0.05 times the average reflectivity over the infrared wavelength range; and an average reflectivity less than about 15% over a visible wavelength range from about 420 nm to about 680 nm. The multilayer optical film is such that for p-polarized incident light in an incident plane and for a predetermined incident angle in a range from about 45 degrees to about 75 degrees, the multilayer optical film has an average reflectivity in the visible wavelength range in a range from about 18% to about 35%, wherein a standard deviation of the reflectivity of the multilayer optical film over the visible wavelength range is less than about 0.15 times the average reflectivity over the visible wavelength range.

[0004] In some aspects, this specification provides a multilayer optical film comprising a plurality of optical repeating units in total greater than about 10. Each of the plurality of optical repeating units may have an average total thickness of less than about 1 micrometer and may include at least four first to fourth individual layers arranged sequentially. For each of the plurality of optical repeating units, the first to fourth individual layers may have corresponding f ratios f1 to f4 in the x-direction in the same plane for corresponding refractive indices nx1 to nx4, wherein each of f1 and f3 is in the range of about 0.28 to about 0.4, and each of f2 and f4 is in the range of about 0.1 to about 0.22. This multilayer optical film allows it to have, for p-polarized incident light in an incident plane including the x-direction and for incident angles less than about 10 degrees, a first-order reflection band having an average reflectivity greater than about 70% in an infrared wavelength range extending at least from about 1000 nm to about 1600 nm; and an average reflectivity less than about 15% in a visible light wavelength range from about 420 nm to about 680 nm. This multilayer optical film also allows it to have an average reflectivity in the visible light wavelength range of about 18% to about 35% for p-polarized incident light in an incident plane including the x-direction and for predetermined incident angles in the range of about 45 degrees to about 75 degrees.

[0005] In some aspects, this specification provides a display system including an automotive windshield and an image projector configured to project p-polarized image light toward the automotive windshield. The automotive windshield includes a multilayer optical film comprising a plurality of optical repeating units totaling more than about 10. Each of the plurality of optical repeating units includes at least four first to fourth individual layers arranged sequentially. Each of the first to fourth individual layers of each optical repeating unit may have an average thickness of less than about 500 nm. The central ray of the p-polarized image light is in the plane of incidence and forms a predetermined angle of incidence with respect to the automotive windshield. This predetermined angle of incidence may be in the range of about 45 degrees to about 75 degrees. For p-polarized incident light in the incident plane and for incident light incident on an automotive windshield at an incident angle of less than about 10 degrees, the multilayer optical film has: a first-order reflection band having an average reflectivity greater than about 70% in an infrared wavelength range extending at least from about 1000 nm to about 1600 nm; and an average reflectivity of less than about 15% in a visible light wavelength range from about 420 nm to about 680 nm. For p-polarized incident light in the incident plane and for incident light incident on an automotive windshield at a predetermined incident angle, the multilayer optical film has an average reflectivity in the visible light wavelength range of about 18% to about 35%.

[0006] These and other aspects will become apparent from the detailed description that follows. However, in no way should this brief overview be construed as limiting the subject matter for which protection may be claimed. Attached Figure Description

[0007] Figure 1 This is a schematic cross-sectional view of a multilayer optical film according to some implementation schemes.

[0008] Figures 2 to 4 It is a graph of the thickness of the optical repeating unit (ORU) versus the number of ORUs for various multilayer optical films according to some implementation schemes.

[0009] Figures 5 to 7 It is a graph of the reflectivity versus wavelength for various multilayer optical films according to some implementation schemes.

[0010] Figure 8 It is a schematic cross-sectional view of a display system based on some implementation schemes. Detailed Implementation

[0011] Reference is made in the following description to the accompanying drawings, which form part of this disclosure and in which various embodiments are illustrated by way of example. The drawings are not necessarily drawn to scale. It should be understood that other embodiments may be conceived and practiced without departing from the scope or spirit of this specification. Therefore, the following detailed description should not be considered limiting.

[0012] Vehicles may include digital information displays such as head-up displays (HUDs). HUDs present data on a transparent medium (e.g., a windshield), allowing the driver to view the displayed information without taking their eyes off the road. For example, information including vehicle status, environmental conditions, and / or navigation guidance can be displayed via a HUD to improve safety and driver comfort. To project an image onto the windshield, conventional HUD systems rely on Fresnel reflection from the air-glass interface of the windshield. Because the angle of incidence (typically around 60 degrees) is usually close to the Brewster angle, p-polarized reflection (reflection of light with a p-polarized state) is largely suppressed. Therefore, in conventional HUD systems, the image is formed by s-polarized reflection (reflection of light with a s-polarized state) from the windshield.

[0013] The disadvantages of this conventional construction include (1) ghosting reflections occur unless a wedge-shaped adhesive layer is used in the laminated windshield to reduce ghosting caused by double reflections; and (2) the projected s-polarized image is blocked by ordinary polarized sunglasses. To eliminate these disadvantages, a weakly reflective polarizer with an obscuring axis along p-polarized light can be incorporated into the windshield as a combiner film. Such reflective polarizers enable the projection of HUD images using p-polarized light, which does not cause ghosting reflections and can be used with conventional polarized sunglasses. However, conventional weakly reflective polarizers lack solar heat dissipation capabilities, which may be desired, for example, to reduce air conditioning energy consumption. Furthermore, it may be desirable to increase the vertical incident transmittance through the combiner film for each of the two mutually orthogonal polarization states.

[0014] According to some embodiments of this specification, a multilayer optical film is provided that provides p-polarized reflectivity for obliquely incident light and infrared reflectivity for solar energy blocking. Infrared reflectivity can be provided for at least one polarization state or two mutually orthogonal polarization states to further enhance solar energy blocking. In some embodiments, the multilayer optical film is substantially transmissive to visible light and substantially reflective to near-infrared light for substantially perpendicularly incident light and for each of the two mutually orthogonal polarization states. In some embodiments, the reflectivity is uniform for p-polarized incident light at a predetermined incident angle (e.g., corresponding to the incident angle used in a HUD system). For example, as further described elsewhere herein, the standard deviation of the reflectivity can be low to provide a reflective image with desired tinting. For example, the standard deviation of the near-infrared reflectivity for substantially perpendicular incident light can also be low to achieve uniform blocking of near-infrared solar radiation.

[0015] As is known in the art, multilayer optical films comprising multiple optical repeating units (e.g., alternating first and second polymer layers) can be used to provide desired reflection and transmission within a desired wavelength range by appropriately selecting layer thicknesses and refractive index differences. Multilayer optical films and methods of manufacturing multilayer optical films are described, for example, in U.S. Patent Nos. 5,882,774 (Jonza et al.); 6,783,349 (Neavin et al.); 6,949,212 (Merrill et al.); 6,967,778 (Wheatley et al.); 9,162,406 (Neavin et al.); and 11,493,677 (Haag et al.). The optical repeating units of a multilayer optical film are typically the smallest distinct units of an optical layer that repeats along the thickness direction of the optical film. Optical repeating units typically comprise at least two distinct layers (e.g., a first layer with a higher refractive index and a second layer with a lower refractive index) and may optionally include additional layers described, for example, in U.S. Patent Nos. 5,103,337 (Schrenk et al.); 5,360,659 (Arends et al.); 5,540,978 (Schrenk); and 6,207,260 (Wheatley et al.).

[0016] Figure 1 This is a schematic cross-sectional view of a multilayer optical film 300 according to some embodiments. The multilayer optical film 300 includes a plurality of optical repeating units 10. In some embodiments, each of the plurality of optical repeating units includes a plurality of polymer layers (e.g., 2 to 8 or 4 to 6 polymer layers). For example, each of the optical repeating units 10 may include at least four first to fourth individual layers A, C1, B, C2 arranged sequentially. The total number of optical repeating units in the plurality of optical repeating units may be greater than about 10. In some embodiments, the total number of optical repeating units is, for example, at least 10, 20, 40, 60, 80, or 90. In some embodiments, the total number of optical repeating units is, for example, up to 400, 300, 250, 200, 180, 170, 160, or 150. In some embodiments, the total number of optical repeating units is, for example, in the range of 80 to 150. Incident beams 230, 231, and 232 in the plane of incidence (the plane defined by the direction of the light and the surface normal) are schematically illustrated. Light 230 is incident substantially perpendicularly. Polarization states 131 and 132 are schematically illustrated. Light 232 has an s-polarization state 132 (an electric field orthogonal to the plane of incidence), and light 231 has a p-polarization state 131 (an electric field in the plane of incidence).

[0017] In some embodiments, the multilayer optical film 300 includes a plurality of optical repeating units 10, wherein each of the plurality of optical repeating units includes a plurality of polymer layers. In some embodiments, for each of the optical repeating units 10 of the plurality of optical repeating units, the plurality of polymer layers includes at least four sequentially arranged first to fourth individual layers A, C1, B, C2. In some embodiments, the first to fourth individual layers have corresponding first to fourth components. In some embodiments, the first component is different from the third component, and the second and fourth components are the same components different from each of the first and third components. In some embodiments, each polymer layer of each optical repeating unit 10 and / or each of the first to fourth individual layers of each optical repeating unit has an average thickness less than about 500 nm, 450 nm, 400 nm, 350 nm, 300 nm, or 250 nm. In some embodiments, each polymer layer of each optical repeating unit 10 has an average thickness greater than about 30 nm, 35 nm, 40 nm, 45 nm, or 50 nm. In some embodiments, each of the plurality of optical repeating units has an average total thickness of less than about 1 micrometer or less than about 900 nm, 850 nm, 800 nm, 750 nm, or 700 nm. The average total thickness of each optical repeating unit can be greater than, for example, about 100 nm, 150 nm, 200 nm, or 250 nm. The average thickness of a layer is the average of the thickness over the area of ​​that layer. The average total thickness of the optical repeating unit is the average of the sum of the thicknesses of the individual layers. The polymer layer of the optical repeating unit 10 may be referred to as an optical layer, a microlayer, or an interference layer.

[0018] In some embodiments, a plurality of optical repeating units 10 are disposed on at least one layer 20, 21 with an average thickness greater than about 500 nm, 750 nm, 1000 nm, 1500 nm, or 2000 nm. Such layers may be referred to as macroscopic layers. Each of the at least one layer 20, 21 may have a thickness, for example, less than about 20 micrometers, 10 micrometers, or 5 micrometers. In some embodiments, a plurality of optical repeating units 10 are disposed between macroscopic layers 20 and 21 with an average thickness within any of these ranges (e.g., greater than about 1000 nm and less than about 20 micrometers). In some embodiments, as will be understood by those skilled in the art, the multilayer optical film 300 includes an additional macroscopic layer (e.g., a protective boundary layer).

[0019] In some embodiments, the plurality of optical repeating units 10 includes a first plurality of optical repeating units and a second plurality of optical repeating units, wherein the first plurality of optical repeating units and the second plurality of optical repeating units are separated by at least one macroscopic layer. For example, the first plurality of optical repeating units and the second plurality of optical repeating units may be separated by one or more protective boundary layers. In some embodiments, each of the first plurality of optical repeating units and the second plurality of optical repeating units includes at least 10 optical repeating units. In some embodiments, each optical repeating unit of at least one of the first plurality of optical repeating units and the second plurality of optical repeating units includes at least four first to fourth separate layers A, C1, B, C2 arranged sequentially. In some embodiments, each optical repeating unit of the first plurality of optical repeating units includes at least four first to fourth separate layers arranged sequentially, and each optical repeating unit of the second plurality of optical repeating units includes at least two layers with different compositions (e.g., separate A and B layers). For example, a first plurality of optical repeating units can be used to reflect in the infrared wavelength range such that at least second-order and / or third-order harmonics (if present) will be within the visible range, while a second plurality of optical repeating units can be used to reflect in wavelength ranges in which the second-order and / or third-order harmonics will not be within the visible light range (e.g., different infrared wavelength ranges). In some embodiments, each optical repeating unit 10 of the multilayer optical film 300, or at least 60%, 70%, 80%, 85%, 90%, or 95% of all optical repeating units of the multilayer optical film 300, comprises at least four sequentially arranged first to fourth individual layers A, C1, B, C2.

[0020] In some embodiments, the multilayer optical film 300 has an average total thickness of less than about 100 micrometers, 95 micrometers, 90 micrometers, 85 micrometers, 80 micrometers, 75 micrometers, 70 micrometers, 65 micrometers, or 60 micrometers. In some embodiments, the average total thickness is greater than about 40 micrometers, 50 micrometers, or 60 micrometers. For example, in some embodiments, the average total thickness is in the range of about 40 micrometers to about 100 micrometers, or in the range of about 50 micrometers to about 90 micrometers. By increasing the number of optical repeating units and correspondingly increasing the total thickness, an average reflectance greater than 97%, 98%, or even 99% can be obtained in the desired near-infrared wavelength range. The desired near-infrared wavelength can be, for example, an infrared wavelength range extending at least from about 1000 nm to about 1600 nm. In some embodiments, the average reflectance in the desired near-infrared range can be slightly reduced so that the thickness of the optical film is within the desired range. For example, in some embodiments, the average reflectivity in the infrared wavelength range is less than about 98%, 97%, 96%, 95%, 94%, 93%, 92%, 91%, or 90% for p-polarized incident light, or for each of two mutually orthogonal polarization states, and for an incident angle of less than about 10 degrees. In some such embodiments, the multilayer optical film has an average thickness of less than about 100 micrometers or within the range described elsewhere herein.

[0021] Optical repeating units typically result in first-order reflection of perpendicularly incident light at twice the wavelength of the optical thickness of the repeating unit, while for integer n>1, higher-order harmonics correspond to reflections at 1 / n times the wavelength of that wavelength. For example, first-order reflection at a wavelength of 1000 nm can result in second-order reflection at a wavelength of 500 nm. An f-ratio can be selected to suppress this second-order reflection and other higher-order reflections of substantially perpendicularly incident light. For obliquely incident light (e.g., at a predetermined incident angle), second-order reflections may not be suppressed or may only be partially suppressed, such that a first-order reflection band in the near-infrared wavelength range at substantially perpendicular incident light forms a second-order reflection band in the visible light range for a predetermined incident angle. In some embodiments, for each of the plurality of optical repeating units: the first to fourth individual layers have corresponding f-ratios f1 to f4 in the x-direction in the same plane with respect to their respective refractive indices nx1 to nx4, where each of f1 and f3 is in the range of about 0.28 to about 0.4, and each of f2 and f4 is in the range of about 0.1 to about 0.22. For example, each of f1 and f3 can be approximately 1 / 3, while each of f2 and f4 can be approximately 1 / 6. These f-ratios within these ranges can be used to suppress higher harmonics in the first-order reflection band, such that the first-order reflection band in the near-infrared wavelength range has virtually no impact on visible light transmittance at perpendicular incidence. Other f-ratios can be selected to suppress even higher harmonics. Suppression of higher harmonics is described, for example, in U.S. Patent Nos. 5,103,337 (Schrenk et al.); 5,360,659 (Arends et al.); 5,540,978 (Schrenk); and 6,207,260 (Wheatley et al.), and, for example, in International Patent Application Publication No. WO 2022 / 195373 (Huseby et al.).

[0022] Suitable materials for the various layers of the multilayer optical film 300 include polyethylene naphthalate (PEN), polyethylene terephthalate (PET), polycarbonate, polymethyl methacrylate (PMMA), copolyesters, and blends or copolymers thereof. Other suitable materials are described elsewhere in the multilayer optical film references provided herein. For example, PEN can be used as a high refractive index layer (e.g., the first individual layer A), PMMA can be used as a low refractive index layer (e.g., the third individual layer B), and coPEN N / 100-N can be used as an intermediate refractive index layer (e.g., the second individual layer C1 and the third individual layer C2). Similarly, PET can be used as a high refractive index layer (e.g., the first individual layer A), coPMMA can be used as a low refractive index layer (e.g., the third individual layer B), and glycol-modified PET (PETg) can be used as an intermediate refractive index layer (e.g., the second individual layer C1 and the third individual layer C2). CoPEN N / 100-N can describe a copolyester in which the carboxylic acid ester units comprise N mol% of naphthalene dicarboxylate units and 100-N mol% of terephthalate units, and can be prepared as commonly described, for example, in U.S. Patent No. 6,946,188 (Hebrink et al.). N can be in the range of, for example, about 50 mol% to about 80 mol%. Diol-modified PET can be described as PET in which at least some of the diol units are replaced by different units, such as those derived from cyclohexanediethanol. Suitable PETg includes, for example, PCTg and EASTAR GN071 (both available from Eastman Chemical Company, Knoxville, TN).

[0023] In some embodiments, for each of the plurality of optical repeating units, the first to fourth individual layers have corresponding refractive indices nx1 to nx4 in the same plane along the x-direction. In some embodiments, the incident plane (e.g., the xz plane) includes the in-plane x-direction. In some embodiments, the first to fourth individual layers have corresponding refractive indices ny1 to ny4 in the same plane along the y-direction orthogonal to the in-plane x-direction, and corresponding refractive indices nz1 to nz4 in the same z-direction orthogonal to each of the in-plane x and y directions. In some embodiments, each of the first individual layers is birefringent. For example, in some embodiments, for at least one wavelength in the visible light wavelength range, |nx1 – nz1| > 0.05, 0.06, 0.07, 0.08, 0.09, 0.1, 0.11, 0.12, 0.13, 0.14, 0.15, 0.16, 0.17, 0.18, 0.19, or 0.2. For example, |nx1 – nz1| can be at most 0.3, 0.28, or 0.26. For a typical birefringent polymer, nx1 is greater than nz1. In some embodiments, each of the first individual layers is biaxially birefringent. For example, in some embodiments, for at least one wavelength in the visible light wavelength range, |nx1 – ny1| is less than 0.03, 0.025, 0.02, 0.015, or 0.01, while |nx1 – nz1| is greater than 0.05 or falls within any range described elsewhere herein. In some embodiments, each of the second, third, and fourth individual layers is substantially isotropic. For example, in some embodiments, for at least one wavelength in the visible light wavelength range and for each of the second, third, and fourth individual layers, the maximum birefringence of that layer (the maximum difference in refractive index of that layer in orthogonal directions) is less than 0.03, 0.025, 0.02, 0.015, or 0.01.

[0024] In some embodiments, for at least one wavelength in the visible light wavelength range, each of |nx1 - ny1|, |nx2 - ny2|, |nx3 - ny3|, and |nx4 - ny4| is less than 0.03; |nx1 - nx3| > 0.1; |nx2 - nx4| < 0.03; |nz1 - nz3| < 0.03; and |nz2 - nz1| > 0.05. In some embodiments, for at least one wavelength in the visible light wavelength range, each of |nx1 - ny1|, |nx2 - ny2|, |nx3 - ny3|, and |nx4 - ny4| is less than 0.025, 0.02, 0.015, or 0.01. In some embodiments, for at least one wavelength in the visible light wavelength range, |nx1 – nx3| > 0.1, 0.12, 0.14, 0.16, 0.18, or 0.2. For example, |nx1 – nx3| can be at most 0.45, 0.4, 0.35, or 0.3. In some embodiments, for at least one wavelength in the visible light wavelength range, |nx2 – nx4| < 0.025, 0.02, 0.015, or 0.01. In some embodiments, for at least one wavelength in the visible light wavelength range, |nz1 – nz3| < 0.025, 0.02, 0.015, or 0.01. In some embodiments, for at least one wavelength in the visible light wavelength range, |nz2 – nz1| > 0.06, 0.07, 0.08, 0.09, or 0.1. For example, |nz2 – nz1| can be at most 0.4, 0.35, 0.3, or 0.25. In some embodiments, for at least one wavelength in the visible light wavelength range, n1z and n3z are approximately equal (e.g., differing by less than 0.03), n2z and n4z are approximately equal, and the difference between n1z and n2z results in an increase in p-polarized reflectivity at a predetermined incident angle. In some embodiments, for at least one wavelength in the visible light wavelength range, nx2 and nx4 are each between nx1 and nx3. For example, each of nx2 and nx4 can be approximated (e.g., within 20%, 15%, 10%, or 5%) as the geometric mean of nx1 and nx3.

[0025] Figures 2 to 4This is a graph of the thickness of optical repeating units (ORUs) versus the number of ORUs for various multilayer optical films according to some embodiments. The optical thickness distribution can be selected to produce a desired reflectivity with desired uniformity (e.g., a low standard deviation of reflectivity) within a desired wavelength range. In some embodiments, when the optical repeating units are numbered sequentially from the optical repeating unit closest to the outermost first main surface 120 of the multilayer optical film 300 to the optical repeating unit closest to the opposite outermost second main surface 121 of the multilayer optical film, the graph of the thickness t of the optical repeating unit versus the optical repeating unit number n has the form t = an. 2 The best fit of +bn + c, where the coefficient of determination R 2 The values ​​should be at least 0.9, 0.92, 0.94, 0.95, 0.96, 0.97, 0.98, 0.99, 0.995, or 0.999, where a, b, and c are the fitting parameters. The best fit can be a least-squares fit that minimizes the sum of squared residuals, where the residuals are the differences between the data and the fitted curve (e.g., a polynomial). The coefficients of determination R can be obtained using the least-squares method. 2 . Figures 2 to 4 The form t = an is shown in the figure. 2 The equation for + bn + c (whose fitting parameters are determined by least squares fitting) and the coefficient of determination R 2 In some embodiments, the product of a / b and the total number of optical repeating units is at least about 0.45, 0.47, 0.49, 0.51, or 0.53. In some embodiments, the product of a / b and the total number of optical repeating units does not exceed about 0.67, 0.65, 0.63, 0.61, or 0.59. For example, the product of a / b and the total number of optical repeating units can be in the range of about 0.45 to about 0.67, or about 0.51 to about 0.61, or about 0.54 to about 0.58. Figures 2 to 4 In these embodiments, the product of a / b and the total number of optical repeating units is 0.55961, 0.56201, and 0.56199, respectively. In some implementations, the fitting parameter a is in the range of 0.003 nm to 0.012 nm, the fitting parameter b is in the range of 0.9 nm to 2.5 nm, and the fitting parameter c is in the range of 250 nm to 350 nm.

[0026] Figures 5 to 7 These are graphs showing the reflectivity versus wavelength for various multilayer optical films according to different implementation schemes. These graphs were determined using standard optical modeling techniques. Figures 5 to 7 The membranes respectively have Figures 2 to 4 The thickness distribution of the optical repeating unit is shown in the figure. Figure 2 and Figure 5In this model, the first through fourth individual layers are modeled as PET, PETg, coPMMA, and PETg, respectively. Figure 3 and Figure 6 In this model, the first through fourth individual layers are modeled as PEN, coPEN 75 / 25, PMMA, and coPEN 75 / 25, respectively. Figure 4 and Figure 7 In this model, the first through fourth individual layers are modeled as PEN, coPEN 55 / 45, PMMA, and coPEN 55 / 45, respectively. The films are modeled as biaxially stretched, such that the PET and PEN layers are biaxially birefringent, and the other layers are substantially isotropic. The table below provides the average reflectance Rpv0, Rpv60 for p-polarized light and Rsv0, Rsv60 for s-polarized light at incident angles of 0 degrees and 60 degrees, with visible wavelengths ranging from approximately 420 nm to approximately 680 nm; and the average reflectance Rpi0 for p-polarized light and Rsi0 for s-polarized light at an incident angle of 0 degrees, with infrared wavelengths ranging from approximately 1000 nm to approximately 1600 nm. Since these films are modeled as biaxially stretched, Rpv0 ≈ Rsv0 and Rpi0 ≈ Rsi0. The table below also provides the standard deviations Si0 of the reflectance of perpendicularly incident light in the infrared wavelength range (which are approximately equal for each of the two mutually orthogonal polarization states) and the standard deviations Sp and Ss of the reflectance of p-polarized and s-polarized light in the infrared wavelength range when the incident angle is 60 degrees.

[0027]

[0028] In some embodiments, the multilayer optical film 300 has a first-order reflection band 310 for incident light 230 at an angle of incidence less than about 10 degrees and for at least one polarization state, the first-order reflection band having an average reflectance greater than about 70%, 75%, 78%, or 80% in an infrared wavelength range extending at least from about 1000 nm to about 1600 nm. In some embodiments, the average reflectance in the infrared wavelength range is less than, for example, about 99%, 98%, 97%, 96%, 95%, 94%, 93%, 92%, 91%, or 90%. In some embodiments, for incident light at an angle of incidence less than about 10 degrees and for at least one polarization state, the multilayer optical film 300 has an average reflectance less than about 15%, 14%, 13%, 12%, 11%, 10%, or 9.5% in the visible light wavelength range from about 420 nm to about 680 nm. For example, the average reflectance in the visible light wavelength range can be in the range of about 5% to about 14%. In some embodiments, the incident light is p-polarized incident light (e.g., 231 or 230 having polarization state 131) in an incident plane (e.g., an incident plane including the x-direction, along which a refractive index for defining the f-ratio is specified). In this case, at least one polarization state can be p-polarized state 131 of the p-polarized incident light. In some embodiments, the incident light is s-polarized incident light (e.g., 232 or 230 having polarization state 132) in an incident plane (e.g., an incident plane including the x-direction, along which a refractive index for defining the f-ratio is specified). In this case, at least one polarization state can be s-polarized state 132 of the s-polarized incident light. In some embodiments, at least one polarization state comprises two mutually orthogonal polarization states.

[0029] In some embodiments, for p-polarized incident light 231 in the incident plane (e.g., the xz plane) and for a predetermined incident angle θ in the range of about 45 degrees to about 75 degrees, the multilayer optical film 300 has an average reflectivity in the visible light wavelength range of about 18% to about 35%. The predetermined incident angle θ can be at least about 50 degrees, 55 degrees, or 60 degrees. For example, the predetermined incident angle θ can be at most about 70 degrees or 65 degrees. The average reflectivity in the visible light wavelength range can be at least about 19%, 20%, 21%, 22%, or 23%. The average reflectivity in the visible light wavelength range can be at most about 34%, 33%, 32%, 31%, or 30%. In some embodiments, for p-polarized incident light and the predetermined incident angle, the multilayer optical film 300 has a second-order reflection band 320 of a first-order reflection band 310, wherein the second-order reflection band includes the average reflectivity in the visible light wavelength range.

[0030] In some embodiments, for p-polarized incident light (e.g., 230 having polarization state 131) in the incident plane (e.g., the xz plane including the x-direction): for incident angles less than about 10 degrees, the multilayer optical film 300 has a first-order reflection band 310 that has an average reflectivity greater than about 70% (or within the range described elsewhere herein) in an infrared wavelength range extending at least from about 1000 nm to about 1600 nm. In some such embodiments, or in other embodiments, for s-polarized incident light (e.g., 230 having polarization state 132) in the incident plane (xz plane) and for incident angles less than about 10 degrees, the multilayer optical film has an average reflectivity greater than about 70% (or within the range described elsewhere herein) in an infrared wavelength range. In some such embodiments, or in others, the multilayer optical film has an average reflectance of less than about 15% (or within the range described elsewhere herein) in the visible light wavelength range for s-polarized incident light (e.g., 230 with polarization state 132) in the incident plane and for an incident angle of less than about 10 degrees. In some such embodiments, or in others, the multilayer optical film has an average reflectance in the visible light wavelength range of about 18%, 19%, 20%, 21%, 22%, or 23% to about 50% for s-polarized incident light (e.g., 232) in the incident plane and for a predetermined incident angle θ. For example, the average reflectance in the visible light range can be at most about 45%, 40%, or 35% for s-polarized incident light and for a predetermined incident angle θ. For the predetermined incident angle θ and the visible light wavelength range, the average reflectance of the s-polarized incident light can be greater than the average reflectance of the p-polarized incident light (e.g., at least about 1.1 times, 1.2 times, 1.3 times, or 1.4 times greater).

[0031] The infrared wavelength range extends at least from about 1000 nm to about 1600 nm, and may extend below about 1000 nm and / or above about 1600 nm. In some embodiments, the infrared wavelength range extends at least from about 950 nm, 925 nm, or 900 nm to about 1700 nm. The infrared wavelength range may extend to, for example, about 1750 nm, 1800 nm, 1850 nm, or 1900 nm.

[0032] In some embodiments, for p-polarized incident light (e.g., 230 having polarization state 131) in the incident plane (e.g., the xz plane) and for incident angles less than about 10 degrees, or for incident angles less than about 10 degrees and for each of two mutually orthogonal polarization states, the first-order reflection band 310 has a first band edge 312, wherein the reflectivity of the multilayer optical film along this first band edge typically increases with increasing wavelength. The first band edge 312 has a first band edge wavelength λ1, wherein the reflectivity is about 50%. The first band edge wavelength λ1 can be in the range of, for example, about 880 nm to about 950 nm. In some embodiments, the reflectivity of the multilayer optical film 300 along the first band edge 312 increases with increasing wavelength from at least about 35%, 30%, or 25% to about 65%. The reflectivity along the first band edge 312 can be increased to, for example, at least about 70% or 75%.

[0033] In some embodiments, for p-polarized incident light in the plane of incidence and for an incident angle less than about 10 degrees, the first-order reflection band 310 has a second band edge 314, wherein the reflectivity of the multilayer optical film 300 along the second band edge 314 generally decreases with increasing wavelength, wherein the second band edge has a second band edge wavelength λ2, and wherein the reflectivity is about 50%. The second band edge wavelength λ2 can be in the range of about 1800 nm to about 2000 nm. In some embodiments, the reflectivity of the multilayer optical film 300 along the second band edge 314 decreases with increasing wavelength from at least about 65%, 70%, or 75% to about 35%. For example, the reflectivity along the second band edge 314 can be reduced to 30% or less, or reduced to 25% or less.

[0034] In some embodiments, for each of s-polarized incident light (e.g., 230 having polarization state 132) and p-polarized incident light (e.g., 230 having polarization state 131) in the incident plane and for incident angles less than about 10 degrees, the multilayer optical film 300 has a reflectance-wavelength relationship defining a first band edge 312 and a second band edge 314, wherein at the first band edge 312, the reflectance of the multilayer optical film 300 along the first band edge generally increases with increasing wavelength, and at the second band edge 314, the reflectance of the multilayer optical film 300 along the second band edge generally decreases with increasing wavelength. The first band edge 312 and the second band edge 314 have corresponding first band edge wavelengths λ1 and second band edge wavelengths λ2, wherein the reflectance is about 50%. In some embodiments, the first band edge wavelength λ1 is in the range of about 880 nm to about 950 nm. In some embodiments, the second band edge wavelength λ2 is in the range of about 1800 nm to about 2000 nm.

[0035] In some embodiments, the multilayer optical film 300 has a substantially uniform reflectance θ over a desired wavelength range (e.g., in the infrared range at incident angles less than 10 degrees and / or in the visible range at a predetermined incident angle). This uniformity can be achieved by appropriately selecting the layer thickness distribution, for example, as further described elsewhere herein. In some embodiments, for p-polarized incident light at a predetermined incident angle θ, the standard deviation (expressed as a percentage) of the reflectance of the multilayer optical film over the visible wavelength range is less than about 3%, 2.8%, 2.6%, 2.4%, or 2.2%. Here, since reflectance is expressed as a percentage, the standard deviation of reflectance is expressed in the same percentage "units". For example, a standard deviation of 10%, 12%, and 8% is 2% (the unbiased sample variance is obtained by using N-1 instead of the number of samples N in the denominator of the variance formula). In some embodiments, for a predetermined incident angle θ, the standard deviation of p-polarized visible light is less than the standard deviation of s-polarized visible light. In some embodiments, for a predetermined incident angle θ, the reflectivity of the multilayer optical film 300 in the visible light wavelength range has standard deviations Ss and Sp for the corresponding s-polarized and p-polarized incident light, where Sp / Ss < 1, 0.9, 0.8, 0.7, 0.6, 0.5, 0.4, or 0.35. In some embodiments, for p-polarized incident light at the predetermined incident angle, the standard deviation of the reflectivity of the multilayer optical film 300 in the visible light wavelength range is less than approximately 0.15, 0.14, 0.13, 0.12, 0.11, 0.1, 0.09, 0.08, 0.07, 0.06, or 0.05 times the average reflectivity in the visible light wavelength range. In some embodiments, for p-polarized incident light at an incident angle of less than about 10 degrees, the standard deviation of the reflectance of the multilayer optical film 300 in the infrared wavelength range is less than about 1.5%, 1.4%, 1.3%, 1.2%, 1.1%, 1%, or 0.9%. In some embodiments, for incident light at an incident angle of less than about 10 degrees and for each of two mutually orthogonal polarization states, the standard deviation of the reflectance of the multilayer optical film 300 in the infrared wavelength range is less than about 1.5%, 1.4%, 1.3%, 1.2%, 1.1%, 1%, or 0.9%. In some implementations, for p-polarized incident light at an incident angle of less than about 10 degrees, the standard deviation of the reflectivity of the multilayer optical film 300 in the infrared wavelength range is less than about 0.05, 0.045, 0.04, 0.035, 0.03, 0.025, 0.02, 0.018, 0.016, 0.014, 0.012, or 0.01 times the average reflectivity in the infrared wavelength range.In some implementations, for incident light with an angle of incidence less than about 10 degrees and for each of two mutually orthogonal polarization states, the standard deviation of the reflectivity of the multilayer optical film 300 in the infrared wavelength range is less than about 0.05, 0.045, 0.04, 0.035, 0.03, 0.025, 0.02, 0.018, 0.016, 0.014, 0.012, or 0.01 times the average reflectivity in the infrared wavelength range.

[0036] The standard deviation of reflectance over a wavelength range can be determined, for example, by measuring reflectance at 1 nm intervals within the wavelength range and determining the standard deviation of the resulting reflectance measurements. It has been found that a 1 nm interval can provide a substantially smooth reflectance-to-wavelength curve. Reflectance can be measured using, for example, a spectrophotometer. The spectrophotometer may have a spectral resolution of about 1 nm or less, or about 0.8 nm or less, or about 0.6 nm or less, or about 0.4 nm or less, or about 0.2 nm or less. Any noise introduced during the measurement process should be low enough that the standard deviation determined from the measurement reflects the characteristics of the film, rather than noise introduced by the measurement. For example, the spectrophotometer used for the measurement may have a sufficiently high signal-to-noise ratio so that any noise introduced by the spectrophotometer is negligible when determining the standard deviation. Suitable spectrophotometers include those available under the trade name LAMBDA from PerkinElmer, Inc., Waltham, MA, such as the LAMBDA 1050 spectrophotometer, which reportedly has an operating range of 175 nm to 3300 nm and a spectral resolution of ≤0.05 nm in the ultraviolet and visible wavelength range and ≤0.2 nm in the near-infrared wavelength range.

[0037] Figure 8 This is a schematic cross-sectional view of a display system 500 according to some embodiments. In some embodiments, the display system 500 includes a multilayer optical film 300 and an image projector 510 configured to project p-polarized image light 520 toward the multilayer optical film 300. In some embodiments, an automotive windshield 501 includes the multilayer optical film 300. For example, the multilayer optical film 300 may be disposed between and laminated onto a first and second glass layer of the automotive windshield.

[0038] In some embodiments, the display system 500 includes a vehicle windshield 501 and an image projector 510. The windshield includes a multilayer optical film 300 comprising a plurality of optical repeating units 10. The image projector is configured to project p-polarized image light 520 toward the vehicle windshield 501. Each optical repeating unit 10 may include at least four sequentially arranged first to fourth individual layers (A, C1, B, C2), wherein each of the first to fourth individual layers of each optical repeating unit has an average thickness of less than about 500 nm (or within the range described elsewhere herein). In some embodiments, the first to fourth individual layers may have an f-ratio within any range described elsewhere herein. The central ray of the p-polarized image light 520 is in the plane of incidence (xz plane) and forms a predetermined incident angle θ with the vehicle windshield. The predetermined incident angle θ may be in the range of about 45 degrees to about 75 degrees, or may be in another range described elsewhere herein. In some implementations, for p-polarized incident light in the plane of incidence: for incident light incident on the windshield at an angle of incidence less than about 10 degrees (e.g., corresponding to...) Figure 1 The light 230 shown in the figure), the multilayer optical film 300 has a first-order reflection band that has an average reflectivity greater than about 70% (or within the range described elsewhere in this document) in an infrared wavelength range of at least from about 1000 nm to about 1600 nm, and the multilayer optical film has an average reflectivity of less than about 15% (or within the range described elsewhere in this document) in a visible light wavelength range of about 420 nm to about 680 nm; and for incident light incident on the automotive windshield at a predetermined incident angle θ (e.g., corresponding to...) Figure 1 The light 231 shown herein), and the multilayer optical film 300 have an average reflectance in the visible light wavelength range of about 18% to about 35% (or within the range described elsewhere herein). In some embodiments, for p-polarized incident light at a predetermined incident angle, the standard deviation of the reflectance of the multilayer optical film in the visible light wavelength range is less than about 0.15 times the average reflectance in the visible light wavelength range (or within the range described elsewhere herein). In some embodiments, for p-polarized incident light at an incident angle of less than about 10 degrees, the standard deviation of the reflectance of the multilayer optical film in the infrared wavelength range is less than about 0.05 times the average reflectance in the infrared wavelength range (or within the range described elsewhere herein). The multilayer optical film 300 used in the display system 500 may have any of the characteristics described elsewhere herein.

[0039] In some embodiments, for s-polarized incident light incident on the automotive windshield 501 at an incident angle of less than about 10 degrees in the incident plane (see, for example...), Figure 1 The light 230 shown (with polarization state 132) has a first-order reflection band that has an average reflectivity greater than about 70% (or within the range described elsewhere herein) in the infrared wavelength range. In some embodiments, for s-polarized incident light incident on the windshield 501 at an incident angle of less than about 10 degrees in the incident plane, the multilayer optical film 300 has an average reflectivity of less than about 15% (or within the range described elsewhere herein) in the visible wavelength range. In some embodiments, for s-polarized incident light incident on the windshield 501 at a predetermined incident angle θ in the incident plane, the multilayer optical film has an average reflectivity in the visible wavelength range of about 18% to about 35% (or within the range described elsewhere herein).

[0040] Terms such as “about” will be understood in the context in which they are used and described in this specification by those skilled in the art. If the use of “about” to express quantities of characteristic size, quantity, and physical properties is unclear to those skilled 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 a specified value as “about” can be precisely the specified value. For example, if it is unclear to those skilled 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 that the value can be 1.

[0041] The term “substantially” will be understood by those skilled in the art in the context of its use and description in this specification. If, in the context of its use and description in this specification, the use of “substantially” regarding a property or characteristic is not readily apparent to those skilled in the art, and when the opposite meaning of such property or characteristic is clear to those skilled in the art, the term “substantially” will be understood to mean that the property or characteristic is more pronounced than its opposite meaning.

[0042] All cited references, patents, and patent applications are incorporated herein by reference in their entirety in a consistent manner. In the event of any inconsistency or contradiction between the incorporated references and this application, the information in the foregoing description shall prevail.

[0043] Unless otherwise indicated, the description of elements in the accompanying drawings should be understood to apply equally to corresponding elements in the other drawings. While specific embodiments have been illustrated and described herein, those skilled in the art will recognize that various alternative and / or equivalent embodiments may be used instead of the illustrated and described embodiments without departing from the scope of this disclosure. This application is intended to cover any modifications, variations, or combinations of the specific embodiments discussed herein. Therefore, this disclosure is intended to be limited only by the claims and their equivalents.

Claims

1. A multilayer optical film comprising a total number of optical repeat units greater than about 10, each of the optical repeat units comprising a plurality of polymeric layers, each polymeric layer of each optical repeat unit having an average thickness less than about 500 nm, such that: for incident light having an angle of incidence less than about 10 degrees and for each of two mutually orthogonal polarization states, the multilayer optical film has: a first order reflection band having an average reflectivity greater than about 70% over an infrared wavelength range extending at least from about 1000 nm to about 1600 nm, a standard deviation of reflectivity of the multilayer optical film over the infrared wavelength range being less than about 0.05 times the average reflectivity over the infrared wavelength range; and an average reflectivity less than about 15% over a visible wavelength range from about 420 nm to about 680 nm; and for p-polarized incident light in an incident plane and for a predetermined angle of incidence ranging from about 45 degrees to about 75 degrees, the multilayer optical film has an average reflectivity over the visible wavelength range ranging from about 18% to about 35%, a standard deviation of reflectivity of the multilayer optical film over the visible wavelength range being less than about 0.15 times the average reflectivity over the visible wavelength range.

2. The multilayer optical film of claim 1, wherein for each of the optical repeat units, the plurality of polymeric layers comprises at least four sequentially arranged first through fourth individual layers.

3. The multilayer optical film of claim 2, wherein the first through fourth individual layers have respective indices of refraction nx1 through nx4 in an in-plane x-direction, respective indices of refraction ny1 through ny4 in an in-plane y-direction orthogonal to the in-plane x-direction, and respective indices of refraction nz1 through nz4 in an out-of-plane z-direction orthogonal to each of the in-plane x-direction and the in-plane y-direction, the incident plane comprising the in-plane x-direction, wherein for at least one wavelength in the visible wavelength range: each of |nx1 - ny1|, |nx2 - ny2|, |nx3 - ny3|, |nx4 - ny4| is less than 0.03; |nx1 - nx3| > 0.1; |nx2 - nx4| < 0.03; |nz1 - nz3| < 0.03; and |nz2 - nz1| > 0.

05.

4. The multilayer optical film of claim 3, wherein for the at least one wavelength in the visible wavelength range, nx2 and nx4 are each between nx1 and nx3. ​ ​ ​ ​ ​ ​ ​ ​ ​ 5. The multilayer optical film of any of claims 2-4, wherein for each optical repeat unit of the plurality of optical repeat units, the first through fourth individual layers have respective f-ratios fl through f4 for respective indices nxl through nx4 in the same plane in the x-direction, each of fl and f3 is in a range from about 0.28 to about 0.4, and each of f2 and f4 is in a range from about 0.1 to about 0.

22.

6. The multilayer optical film of any of claims 1-5, wherein when the plurality of optical repeat units are sequentially numbered from the optical repeat unit nearest a first outermost major surface of the multilayer optical film to the optical repeat unit nearest an opposing outermost second major surface of the multilayer optical film, a plot of the thicknesses t of the optical repeat units versus optical repeat unit number n has a best fit of the form t = an + bn + c, where the coefficient of determination R2 is at least 0.95, a, b, and c are fit parameters, and the product of a / b and the total number of optical repeat units is in a range from about 0.45 to about 0.

67. 2 2 6. The multilayer optical film of any of claims 1-5, wherein when the plurality of optical repeat units are sequentially numbered from the optical repeat unit nearest a first outermost major surface of the multilayer optical film to the optical repeat unit nearest an opposing outermost second major surface of the multilayer optical film, a plot of the thicknesses t of the optical repeat units versus optical repeat unit number n has a best fit of the form t = an + bn + c, where the coefficient of determination R2 is at least 0.95, a, b, and c are fit parameters, and the product of a / b and the total number of optical repeat units is in a range from about 0.45 to about 0.

67. 2 2 7. The multilayer optical film of any of claims 1-6, wherein for s-polarized incident light in the plane of incidence and for the predetermined angle of incidence, the multilayer optical film has an average reflectivity in the visible wavelength range in a range from about 18% to about 50%.

8. The multilayer optical film of claim 7, wherein for the predetermined angle of incidence and the visible wavelength range, the average reflectivity for the s-polarized incident light is greater than the average reflectivity for the p-polarized incident light, and the reflectivity of the multilayer optical film in the visible wavelength range has standard deviations Ss and Sp for the respective s-polarized and p-polarized incident light, Sp / Ss < 0.

9.

9. A multilayer optical film comprising a plurality of optical repeat units having a total number greater than about 10, each optical repeat unit of the plurality of optical repeat units having an average total thickness less than about 1 micron and comprising at least four sequentially arranged first through fourth individual layers, wherein for each optical repeat unit of the plurality of optical repeat units, the first through fourth individual layers have respective f-ratios fl through f4 for respective indices nxl through nx4 in the same plane in the x-direction, each of fl and f3 is in a range from about 0.28 to about 0.4, and each of f2 and f4 is in a range from about 0.1 to about 0.22, such that for p-polarized incident light in a plane of incidence comprising the in-plane x-direction: for angles of incidence less than about 10 degrees, the multilayer optical film has: a first order reflection band having an average reflectivity greater than about 70% in an infrared wavelength range extending at least from about 1000 nm to about 1600 nm; and an average reflectivity less than about 15% in a visible wavelength range from about 420 nm to about 680 nm; and for a predetermined angle of incidence in a range from about 45 degrees to about 75 degrees, the multilayer optical film has an average reflectivity in the visible wavelength range in a range from about 18% to about 35%.

10. The multilayer optical film of claim 9, wherein for the p-polarized incident light at the predetermined angle of incidence, a standard deviation of the reflectivity of the multilayer optical film in the visible wavelength range is less than about 0.15 times the average reflectivity in the visible wavelength range.

11. The multilayer optical film of claim 9 or 10, wherein the multilayer optical film has an average reflectivity in the infrared wavelength range of greater than about 70% for s-polarized incident light in the plane of incidence and for angles of incidence less than about 10 degrees.

12. A display system comprising an image projector and the multilayer optical film of any one of claims 1 to 11, the image projector configured to project p-polarized image light toward the multilayer optical film.

13. A display system comprising an automotive windshield comprising a multilayer optical film comprising a total number of optical repeat units greater than about 10, each optical repeat unit of the plurality of optical repeat units comprising at least four sequentially arranged first through fourth individual layers, each of the first through fourth individual layers of each optical repeat unit having an average thickness less than about 500 nm; and an image projector configured to project p-polarized image light toward the automotive windshield, a central ray of the p-polarized image light being in a plane of incidence and at a predetermined angle of incidence to the automotive windshield, the predetermined angle of incidence being in a range of about 45 degrees to about 75 degrees, wherein for p-polarized incident light in the plane of incidence: for the incident light incident on the automotive windshield at an angle of incidence less than about 10 degrees, the multilayer optical film has: a first order reflection band having an average reflectivity in an infrared wavelength range extending at least from about 1000 nm to about 1600 nm of greater than about 70%; and an average reflectivity in a visible wavelength range of about 420 nm to about 680 nm of less than about 15%; and for the incident light incident on the automotive windshield at the predetermined angle of incidence, the multilayer optical film has an average reflectivity in the visible wavelength range in a range of about 18% to about 35%.

14. The display system of claim 13, wherein for s-polarized incident light in the plane of incidence incident on the automotive windshield at an angle of incidence less than about 10 degrees, the multilayer optical film has a first order reflection band having an average reflectivity in the infrared wavelength range of greater than about 70%.

15. The display system of claim 13 or 14, wherein for the p-polarized incident light at the predetermined angle of incidence, a standard deviation of reflectivity of the multilayer optical film in the visible wavelength range is less than about 0.15 times the average reflectivity in the visible wavelength range.

Images