Multilayer Optical Films

Abstract

The multilayer optical film includes a plurality of optical repeating units that may total less than about 175 and may have a total average thickness of less than about 20 micrometers. Each of the optical repeating units includes at least four individual layers that may include at least one polymer A layer, at least two B layers, and at least one polymer C layer. At least one layer of the at least four individual layers may have an average thickness of less than about 50 nm. The interlayer adhesion of the individual layers in the plurality of optical repeating units may be at least about 14 grams / inch when measured at a 90 degree peel angle. The multilayer optical film may be a reflective polarizer or a multilayer optical mirror.

Description

[Background technology]

[0001] A multilayer optical film can include a stack of polymer layers arranged into an optical repeating unit. A multilayer optical film can be a reflective polarizer or mirror. Summary of the Invention

[0002] This specification generally relates to multilayer optical films. The optical film can include a plurality of optical repeat units, each optical repeat unit including at least four individual layers. The optical repeat units can be configured so that the optical film has a desired reflective intensity at a low total thickness (e.g., less than about 24 micrometers or less than about 20 micrometers) and / or has high interlayer adhesion (e.g., at least about 14 grams / inch or at least about 20 grams / inch when measured at a 90 degree peel angle). The multilayer optical film can be, for example, a reflective polarizer or an optical mirror.

[0003] In some embodiments herein, a reflective polarizer is provided that includes a plurality of optical repeat units disposed between a first skin layer and a second skin layer. Each optical repeat unit can include at least one polymer A layer, at least two B layers, and at least one polymer C layer, with each pair of adjacent A and C layers having at least one of the two B layers disposed between the adjacent A and C layers. The total number of A and C layers in the plurality of optical repeat units disposed between the first and second skin layers can be less than about 400. Each of the A and C layers can have an average thickness of about 50 nm to about 500 nm, and each of the B layers can have an average thickness of less than about 50 nm. Each of the first and second skin layers has an average thickness of more than about 500 nm. The reflective polarizer can have an average thickness of less than about 20 micrometers. The reflective polarizer can be such that for light incident on the reflective polarizer at the plane of incidence, for each of a first angle of incidence less than about 5 degrees and a second angle of incidence greater than about 40 degrees, and for a visible wavelength range spanning from about 420 nm to about 680 nm, the plurality of optical repeating units have an average optical transmittance of less than about 10% for the s-polarized state when the in-plane first direction of the reflective polarizer is in the plane of incidence, and an average optical transmittance of more than about 65% for the p-polarized state when the in-plane orthogonal second direction of the reflective polarizer is in the plane of incidence.

[0004] In some embodiments herein, a multilayer optical film is provided that includes a plurality of optical repeat units. The optical repeat units in the plurality of optical repeat units may total less than about 175 in number and may have a total average thickness of less than about 20 micrometers. Each of the optical repeat units includes at least four individual layers. At least a first and a second individual layer of the at least four individual layers of each of the optical repeat units have the same respective refractive indices nx1 and nx2 along an in-plane x-direction, respective refractive indices ny1 and ny2 along an in-plane y-direction perpendicular to the x-direction, and respective refractive indices nz1 and nz2 along a z-direction perpendicular to the x-direction and y-direction. For at least one wavelength in the visible wavelength range spanning from about 420 nm to about 680 nm, nx1 may be at least 0.15 greater than at least one of ny1 and nz1, and the magnitude of the maximum difference between nx2, ny2, nz2 may be less than 0.15, and nx1 may be at least 0.15 greater than nx2. At least a third layer of the at least four individual layers of each of the optical repeating units can have an average thickness of less than about 50 nm. The interlayer adhesion of the individual layers in the plurality of optical repeating units can be at least about 14 grams / inch when measured at a 90 degree peel angle.

[0005] In some embodiments herein, a multilayer optical film is provided that includes a plurality of optical repeat units. The optical repeat units in the plurality of optical repeat units may total less than about 175 in number and may have a total average thickness of less than about 20 micrometers. Each of the optical repeat units includes at least four individual layers. At least a first and a second individual layer of the at least four individual layers of each of the optical repeat units have the same respective refractive indices nx1 and nx2 along an in-plane x-direction, respective refractive indices ny1 and ny2 along an in-plane y-direction perpendicular to the x-direction, and respective refractive indices nz1 and nz2 along a z-direction perpendicular to the x-direction and y-direction. For at least one wavelength in the visible wavelength range spanning from about 420 nm to about 680 nm, nx1 may be at least 0.15 greater than at least one of ny1 and nz1, and nx2 may be less than at least one of ny2 and nz2, and nx1 may be at least 0.15 greater than nx2. The interlayer adhesion of the individual layers in the multiple optical repeating units may be at least about 14 grams / inch when measured at a 90 degree peel angle.

[0006] In some embodiments herein, a multilayer optical film is provided that includes a plurality of optical repeating units. The optical repeating units in the plurality of optical repeating units may total less than about 175 in number and may have a total average thickness of less than about 20 microns. Each of the optical repeating units includes at least four individual layers. At least a first and a second individual layer of the at least four individual layers of each of the optical repeating units have the same respective refractive indices nx1 and nx2 along an in-plane x-direction, respective refractive indices ny1 and ny2 along an in-plane y-direction perpendicular to the x-direction, and respective refractive indices nz1 and nz2 along a z-direction perpendicular to the x-direction and y-direction. For at least one wavelength in the visible wavelength range spanning from about 420 nm to about 680 nm, the magnitude of the maximum difference between nx1, ny1, and nz1 may be less than 0.05, nx2 may be less than at least one of ny2 and nz2, and nx1 may be at least 0.07 greater than nx2. At least a third layer of the at least four individual layers of each of the optical repeating units can have an average thickness of less than about 50 nm. The interlayer adhesion of the individual layers in the plurality of optical repeating units can be at least about 14 grams / inch when measured at a 90 degree peel angle.

[0007] In some embodiments herein, a multilayer optical mirror is provided that includes a plurality of optical repeat units. The optical repeat units in the plurality of optical repeat units may total less than about 200 in number and may have a total average thickness of less than about 20 micrometers. Each of the optical repeat units includes at least four sequentially arranged first to fourth individual layers. The first individual layer and the third individual layer of each of the optical repeat units have the same respective refractive indices nx1 and nx2 along an in-plane x direction, respective refractive indices ny1 and ny2 along an in-plane y direction perpendicular to the x direction, and respective refractive indices nz1 and nz2 along a z direction perpendicular to the x direction and the y direction. For at least one wavelength in the visible wavelength range spanning from about 420 nm to about 680 nm, nx1 and ny1 may be at least 0.1 greater than nx2 and ny2, respectively, and nz2 may be at least 0.05 greater than nz1. The multilayer optical mirror can have an average optical transmittance T1 for a first angle of incidence less than about 5 degrees and an average optical transmittance T2 for a second angle of incidence greater than about 40 degrees for each of mutually orthogonal first and second polarization states for light incident on the multilayer optical mirror, and for a visible wavelength range, such that T1 / T2≧1.2.

[0008] These and other aspects will become apparent from the following detailed description, but in no way should this brief summary be construed as limiting the claimed subject matter. [Brief description of the drawings]

[0009] [Figure 1A] 1 is a schematic cross-sectional view of an optical film according to some embodiments. [Figure 1B] 1 is a schematic cross-sectional view of a portion of an optical film according to some embodiments. [Figure 2A] 1A-1D are schematic cross-sectional views of light incident on an optical film at different planes of incidence. [Figure 2B] 1A-1D are schematic cross-sectional views of light incident on an optical film at different planes of incidence. [Diagram 3] 1 is a schematic perspective view of exemplary layers of an optical film. [Figure 4A] 1 is a schematic plot of the optical transmission of multiple optical repeat units of a reflective polarizer according to some embodiments. [Figure 4B] 1 is a schematic plot of the optical transmission of multiple optical repeat units of a reflective polarizer according to some embodiments. [Diagram 5] 1 is a layer thickness profile of a first exemplary reflective polarizer. [Figure 6A] 1 is a plot of the optical transmission of multiple optical repeat units of a first exemplary reflective polarizer. [Figure 6B] 6B is a portion of the light transmittance plot of FIG. 6A. [Figure 7] 4 is a layer thickness profile of a second exemplary reflective polarizer. [Figure 8] 1 is a plot of the optical transmission of multiple optical repeat units of a second exemplary reflective polarizer. [Figure 9A] 1 is a schematic plot of optical transmission of multiple optical repeating units of an optical mirror, according to some embodiments. [Figure 9B] 1 is a schematic plot of optical transmission of multiple optical repeating units of an optical mirror, according to some embodiments. [Figure 10] 1 is a layer thickness profile of a first exemplary optical mirror. [Figure 11] 1 is a plot of optical transmission of multiple optical repeating units of a first exemplary optical mirror. [Figure 12] 4 is a layer thickness profile of a second exemplary optical mirror. [Figure 13] 11 is a plot of optical transmission of multiple optical repeating units of a second exemplary optical mirror. [Figure 14] 11 is a layer thickness profile of a third exemplary optical mirror. [Figure 15] 13 is a plot of optical transmission of multiple optical repeating units of a third exemplary optical mirror. [Figure 16]FIG. 1 is a schematic diagram of testing a multilayer optical film for interlayer adhesion. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] In the following description, reference is made to the accompanying drawings, which form a part hereof, 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 are contemplated and may be made without departing from the scope or spirit of the present disclosure. Accordingly, the following detailed description is not to be taken in a limiting sense.

[0011] Multilayer optical films comprising alternating polymer layers can be used to provide desired reflection and transmission in desired wavelength ranges by appropriately selecting layer thicknesses and refractive index differences, as generally described, for example, in U.S. Pat. Nos. 5,882,774 (Jonza et al.), 6,179,948 (Merrill et al.), 6,783,349 (Neavin et al.), 6,967,778 (Wheatley et al.), and 9,162,406 (Neavin et al.). The alternating polymer layers typically comprise alternating high and low refractive index layers, which can be described as optical layers that transmit and reflect light primarily by optical interference. Multilayer optical films comprising alternating high and low refractive index layers can be described as comprising a plurality of optical repeat units, each optical repeat unit comprising a high and low refractive index layer. An optical repeat unit is generally the smallest discrete unit of an optical layer that repeats along the thickness direction of an optical film. Each optical repeat unit may include one or more layers in addition to the high and low refractive index layers, as described, for example, in U.S. Pat. Nos. 5,103,337 (Schrenk et al.), 5,540,978 (Schrenk), and 6,207,260 (Wheatley et al.). The high refractive index layer is often selected to be a positively birefringent material so that when the cast film is stretched, the refractive index of the high refractive index layer increases in the stretch direction. Increasing the difference in refractive index between the high and low refractive index layers can result in stronger reflections, thereby reducing the total number of layers and resulting film thickness required to achieve a desired reflection intensity. The difference in refractive index can be increased by selecting a negatively birefringent material for the low refractive index layer and a positively birefringent material for the high refractive index layer, so that the refractive index of the low refractive index layer decreases and the refractive index of the high refractive index layer increases in the stretch direction. For example, polyethylene naphthalate (PEN) is a suitable positively birefringent material, and syndiotactic polystyrene (sPS) is a suitable negatively birefringent material.However, the bonding between PEN and sPS is low when these materials are coextruded and / or stretched together, which results in multilayer optical films formed from alternating PEN and sPS layers that have been found to produce interlayer adhesion that is too low for many applications (e.g., delamination or partial delamination of the layers may occur when the optical film is processed or formed or applied to a device or other optical element, which may degrade the performance of the optical film).

[0012] According to some embodiments, a polymeric multilayer optical film having a low total average thickness (e.g., less than about 20 micrometers) and / or a low total number of optical repeat units (e.g., less than about 200 optical repeat units or less than about 175 optical repeat units) achieves high reflectance (e.g., greater than about 90%) or correspondingly low transmission (e.g., less than about 10%) for at least one polarization state while maintaining suitable interlayer adhesion (e.g., at least about 14 grams / inch or at least about 20 grams / inch when measured at a 90 degree peel angle). In some embodiments, the optical film also has improved transmission in the pass polarization state. In some embodiments, the pass state transmission is improved at high (e.g., greater than about 40 degrees) angles of incidence. In some embodiments, the desired properties of the optical film are achieved by including a positively birefringent high index layer, a negatively birefringent low index layer, and an additional layer between each of the high and low index layers. The additional layer can be selected to increase the interlayer adhesion between the layers of the optical film. In some embodiments, the additional layer is an isotropic polymer layer. In some embodiments, the desired properties of the optical film are achieved by using a positively birefringent high refractive index layer, a substantially isotropic low refractive index layer (e.g., a low refractive index layer containing fluorine groups) that has poor bonding with the high refractive index layer when directly bonded to the high refractive index layer, and an additional layer between each of the high and low refractive index layers to improve interlayer adhesion. In some embodiments, the desired properties of the optical film are achieved by using an optical repeat unit that includes a substantially isotropic high refractive index layer, a negatively birefringent low refractive index layer, and an additional layer between each of the high and low refractive index layers. For example, such an optical repeat unit can be used to provide a collimating optical mirror as further described elsewhere herein.

[0013] FIG. 1A is a schematic cross-sectional view of a multilayer optical film 300 according to some embodiments. The optical film 300 can be adapted to selectively reflect and transmit light based on wavelength and / or polarization state. The optical film 300 can be, for example, a reflective polarizer or an optical mirror. The optical film 300 includes a plurality of optical repeat units 10, each of which includes at least four individual layers. In the illustrated embodiment, the at least four individual layers include an A layer, a B1 layer, a C layer, and a B2 layer. The optical film 300 can include more optical repeat units 10 than are shown diagrammatically in FIG. 1A. FIG. 1B is a schematic cross-sectional view of a portion of a multilayer optical film 300 according to some embodiments, showing a number of optical repeat units 10.

[0014] In some embodiments, the multilayer optical film 300 includes a plurality of optical repeat units 10 disposed between the first skin layer 20 and the second skin layer 21, each optical repeat unit including at least one polymer A layer, at least two B layers (e.g., at least B1 and B2 layers), and at least one polymer C layer. Each pair of adjacent A and C layers can have at least one of the two B layers disposed between the adjacent A and C layers. The total number of A and C layers in the plurality of optical repeat units disposed between the first skin layer 20 and the second skin layer 21 can be less than about 400. For example, the total number of A and C layers can be in the range of about 10 or about 20 to about 400 or about 350. The total number of optical repeat units in the plurality of optical repeat units refers to the total number of distinct optical repeat units (no layer of the film is in more than one distinct optical repeat unit). In some embodiments, the multilayer optical film 300 includes a plurality of optical repeat units, where the optical repeat units in the plurality of optical repeat units total less than about 200, or less than about 175, or less than about 150, or less than about 130, or less than about 120, or less than about 115, or less than about 110, or less than about 105, or less than about 100, or less than about 95, or less than about 90. The total number of optical repeat units in the plurality of optical repeat units can be, for example, at least about 10, or at least about 15, or at least about 20, or at least about 25, or at least about 30, or at least about 40, or at least about 50, or at least about 60, or at least about 70, or at least about 75. The plurality of optical repeat units can have a total average thickness of, for example, less than about 20 micrometers, or less than about 19 micrometers, or less than about 18 micrometers, or less than about 17 micrometers, or less than about 16 micrometers, or less than about 15 micrometers. The total average thickness of the optical repeating units may be, for example, greater than about 5 micrometers, or greater than about 8 micrometers, or greater than about 10 micrometers.

[0015] In some embodiments, each optical repeat unit 10 is defined by four distinct layers (e.g., A, B1, C, B2). In other words, in some embodiments, each optical repeat unit 10 includes only four distinct layers. In other embodiments, each optical repeat unit 10 includes more than four distinct layers.

[0016] Each of the A and C layers can have an average thickness of about 50 nm to about 500 nm, or about 75 nm to about 400 nm, or about 100 nm to about 300 nm. The average thickness of a layer is an unweighted average over the area of ​​the layer of the thickness of the layer. In some embodiments, the B layer is used primarily to promote adhesion between the A and C layers and may be thin enough not to substantially affect the optical properties of the optical film. In some embodiments, the B layer can promote adhesion between the A and C layers and also substantially affect the optical properties of the optical film. In some embodiments, each of the B layers has an average thickness of less than about 50 nm, or less than about 40 nm, or less than about 30 nm, or less than about 20 nm, or less than about 15 nm, or less than about 10 nm, or less than about 7.5 nm. In some such embodiments, or in other embodiments, each of the B layers has an average thickness of at least about 0.5 nm, or at least about 1 nm, or at least about 2 nm, or at least about 3 nm. For example, in some embodiments, each of the B layers has an average thickness ranging from about 1 nm to about 30 nm, or from about 3 nm to about 20 nm. In some embodiments, for each of the optical repeating units 10, the average thickness of each of the B layers (e.g., the B1 and B2 layers) is at least 2 times, or at least about 2.25 times, or at least about 2.5 times, or at least about 2.75 times, or at least about 3 times, or at least about 3.25 times less than the average thickness of each of the A and C layers. In some such embodiments, or in other embodiments, for each of the optical repeating units 10, the average thickness of each of the B layers (e.g., the B1 and B2 layers) is at least up to about 100 times, or up to about 50 times, or up to about 40 times less than the average thickness of each of the A and C layers. In some embodiments, each of the B layers is a polymer layer.

[0017] In some embodiments, the first skin layer 20 and the second skin layer 21 each have an average thickness greater than about 500 nm, or greater than about 750 nm, or greater than about 1000 nm, or greater than about 1250 nm, or greater than about 1500 nm. In some such embodiments, or in other embodiments, the first skin layer 20 and the second skin layer 21 each have an average thickness less than about 8 micrometers, or less than about 5 micrometers, or less than about 4 micrometers. The optical film 300 may include additional layers, such as protective boundary layers 120, 121 used to protect packets of optical repeat units, or additional layers 129, 131 disposed between the protective boundary layers 120, 121, or additional layer(s) 132 between the optical repeat units, as known in the art. The additional layers 129, 131, 132, if included, can each have an average thickness less than about 500 nm, or the average thickness can be within any of the ranges described for any of the A, B1, B2, or C layers. The protective boundary layers 120, 121, if included, can each have an average thickness ranging from, for example, about 500 nm or about 750 nm to about 2 micrometers. In some embodiments, the optical film 300 has an average thickness t that is less than about 24 micrometers, or less than about 22 micrometers, or less than about 20 micrometers, or less than about 19 micrometers, or less than about 18 micrometers, or less than about 17 micrometers, or less than about 16 micrometers, or less than about 15 micrometers. In some such embodiments, or in other embodiments, the average thickness t is, for example, greater than about 5 micrometers, or greater than about 8 micrometers, or greater than about 10 micrometers. The average thickness t can be described as the total average thickness of the optical repeating units plus the average thickness of the skin layers 20, 21 plus the average thickness of any additional layers that may be included (eg, 120, 121, 129, 131, 132).

[0018] In some embodiments, each of the B layers (e.g., the B1 and B2 layers) has the same composition. In other embodiments, the B1 and B2 layers have different compositions. In some embodiments, for each optical repeat unit in the optical film 300, or for each optical repeat unit in at least a majority of the optical repeat units of the optical film 300, the B1 and B2 layers in the optical repeat unit have substantially the same thickness (e.g., the layers can have thicknesses within 10% of each other or within 5% of each other). In some embodiments, each B1 and B2 layer in the optical film 300, or each B1 and B2 layer in at least a majority of the optical repeat units of the optical film 300, have substantially the same thickness. In some embodiments, the B1 and B2 layers have an average thickness that generally increases from one side of the optical film 300 to the opposite side of the optical film 300. In some embodiments, for each optical repeat unit in optical film 300, or for each optical repeat unit in at least a majority of the optical repeat units of optical film 300, the B1 and B2 layers in the optical repeat unit have different thicknesses. In some embodiments, for each optical repeat unit in optical film 300, or for each optical repeat unit in at least a majority of the optical repeat units of optical film 300, the A and C layers have the same composition and have substantially different thicknesses (e.g., differ in thickness by more than 10%). In some embodiments, the A and C layers have different compositions.

[0019] In some embodiments, the optical film 300 is integrally formed. As used herein, a first element "integrally formed" with a second element means that the first and second elements are manufactured together, rather than being manufactured separately and then bonded. Integral forming includes manufacturing the first element and then manufacturing the second element on the first element. An optical film including multiple layers is integrally formed when the layers are manufactured together (e.g., combined as a melt stream and then cast on a chill roll to form a cast film having each layer, and then orienting the cast film) rather than being manufactured separately and then bonded.

[0020] Light 130 and light 230 are shown in FIG. 1A as being incident on optical film 300 at respective angles of incidence θ1 and θ2. The angle of incidence is the angle of the direction of the light incident on a surface relative to the normal of that surface, and ranges from 0 degrees to 90 degrees. FIGS. 2A-2B show a schematic of light 30, which may correspond to light 130 or light 230, incident on optical film 300 at an angle of incidence θ. In FIG. 2A, a first in-plane direction (x-direction) of optical film 300 is in the plane of incidence 40 (a plane defined by the direction of the incident light and the plane normal). In FIG. 2B, a second in-plane direction (y-direction) of optical film 300 is in the plane of incidence 40. The second in-plane direction is orthogonal to the first in-plane direction. For example, the first direction may correspond to a block axis of a reflective polarizer, and the second direction may correspond to a pass axis of the reflective polarizer. The p-polarization state 31 (electric field in the plane of incidence) and the s-polarization state 32 (electric field perpendicular to the plane of incidence) are shown.

[0021] In some embodiments, the optical film 300 is a reflective polarizer such that for each of a first angle of incidence θ1 of less than about 5 degrees and a second angle of incidence θ2 of more than about 40 degrees for light 30 incident on the reflective polarizer at the plane of incidence 40, and for a visible wavelength range spanning from about 420 nm to about 680 nm, the plurality of optical repeating units 10 have an average light transmittance of less than about 10% for an s-polarized state 32 when the in-plane first direction (x-direction) of the reflective polarizer is in the plane of incidence 40, and an average light transmittance of more than about 65% for a p-polarized state 31 when the in-plane orthogonal second direction (y-direction) of the reflective polarizer is in the plane of incidence 40. The first angle of incidence θ1 may be, for example, less than about 4 degrees, or less than about 3 degrees, or less than about 2 degrees. For example, the first angle of incidence θ1 may be about 0 degrees. The second angle of incidence θ2 may be greater than about 45 degrees, or greater than about 50 degrees, or greater than about 55 degrees. For example, the second angle of incidence may be about 60 degrees. In some embodiments, for each of the first angle of incidence θ1 and the second angle of incidence θ2, for the visible wavelength range, the plurality of optical repeating units 10 have an average light transmission for the s-polarization state 32 of less than about 10%, or less than about 8%, or less than about 6%, or less than about 4%, or less than about 2% when the in-plane first direction of the reflective polarizer is in the plane of incidence 40. In some such embodiments, or in other embodiments, for each of the first angle of incidence θ1 and the second angle of incidence θ2 and for the visible wavelength range, the plurality of optical repeating units 10 have an average light transmission for the p-polarization state 31 of more than about 65%, or more than about 70%, or more than about 75%, or more than about 80%, or more than about 85% when the in-plane second direction of the reflective polarizer is in the plane of incidence 40.

[0022] The transmittance of the optical repeat units of the optical film, including the outermost skin layer, can be determined, for example, by measuring the transmittance of the optical film, measuring the refractive index of the outermost skin layer of the optical film, using the measured refractive index in the Fresnel equation to determine the reflectance from the outermost major surface, and then calculating the transmittance of the optical repeat units from the measured transmittance and the reflectance from the outermost major surface. This ignores typically small additional Fresnel reflections at the interfaces between the optical repeat units and any other layers of the optical film. Any such additional Fresnel reflections can be taken into account by determining the refractive index of the layers adjacent to these interfaces and making appropriate corrections using the Fresnel equation. Alternatively, the transmittance of the optical repeat units can be determined from conventional optical modeling calculations, for example, by determining the material properties of the individual layers and measuring the thicknesses of the individual layers of the optical film using atomic force microscopy (AFM). In some embodiments, the optical film 300 has optical transmittance in any of the ranges described for multiple optical repeat units for the s and / or p polarization states and for a first in-plane direction and / or a second in-plane direction of the reflective polarizer in the plane of incidence 40.

[0023] In some embodiments, the plurality of optical repeat units has an optical transmittance for an s-polarization state 32 when the reflective polarizer's first in-plane direction is in the plane of incidence 40 within any of the ranges described for a p-polarization state 31 when the reflective polarizer's first in-plane direction is in the plane of incidence 40. In some embodiments, the plurality of optical repeat units has an optical transmittance for a p-polarization state 31 when the reflective polarizer's second in-plane direction is in the plane of incidence 40 within any of the ranges described for an s-polarization state 32 when the reflective polarizer's second in-plane direction is in the plane of incidence 40. In some embodiments, the optical film 300 is a reflective polarizer such that for p-polarized light incident on the reflective polarizer at the incident plane 40, for each of a first incident angle θ1 less than about 5 degrees and a second incident angle θ2 greater than about 40 degrees, and for a visible wavelength range spanning from about 420 nm to about 680 nm, the multiple optical repeating units 10 have an average light transmittance of less than about 10% when the in-plane first direction (x-direction) of the reflective polarizer is in the incident plane 40, and an average light transmittance of more than about 65% when the in-plane orthogonal second direction (y-direction) of the reflective polarizer is in the incident plane 40.

[0024] Suitable materials for the various layers of the multilayer optical film 300 include, for example, polyethylene naphthalate (PEN), coPEN (copolyethylene naphthalate terephthalate copolymer), polyethylene terephthalate (PET), polyhexylethylene naphthalate copolymer (PHEN), glycol modified PET (PETG), glycol modified PEN (PENG), syndiotactic polystyrene (sPS), THV (terpolymer of tetrafluoroethylene, hexafluoropropylene, and vinylidene fluoride), polymethyl methacrylate (PMMA), coPMMA (methyl methacrylate), and the like. Examples of suitable A layers include styrene block copolymers (block copolymers containing styrene blocks), such as linear triblock copolymers based on styrene and ethylene / butylene, acrylic block copolymers (block copolymers containing acrylate or methacrylate blocks), such as linear triblock copolymers based on methyl methacrylate and n-butyl acrylate, anhydride-modified ethylene vinyl acetate polymers, ketone ethylene ester terpolymers, polyolefin-based thermoplastic elastomers, or blends thereof. For example, in some embodiments, each A layer comprises polyethylene naphthalate, polyethylene terephthalate, or polyhexylethylene naphthalate copolymer, and each C layer comprises syndiotactic polystyrene; terpolymers of tetrafluoroethylene, hexafluoropropylene, and vinylidene fluoride; polymethyl methacrylate; copolymers of methyl methacrylate and ethyl acrylate; or copolymers of polyethylene naphthalate terephthalate. In some embodiments, each B layer comprises a styrene block copolymer, an acrylic block copolymer, a glycol modified polyethylene terephthalate, a glycol modified polyethylene naphthalate, a polymethyl methacrylate, a copolymer of methyl methacrylate and ethyl acrylate, an anhydride modified ethylene vinyl acetate polymer, a ketone ethylene ester terpolymer, a polyolefin based thermoplastic elastomer, or a copolyethylene naphthalate terephthalate copolymer, and each B layer has a different composition than each of the A and C layers.In some embodiments, each A layer comprises polyethylene naphthalate, polyethylene terephthalate, or polyhexylethylene naphthalate copolymer, each B layer comprises a styrene block copolymer, an acrylic block copolymer, a glycol-modified polyethylene terephthalate, a glycol-modified polyethylene naphthalate, an anhydride-modified ethylene vinyl acetate polymer, or a ketone ethylene ester terpolymer, and each C layer comprises a syndiotactic polystyrene; a terpolymer of tetrafluoroethylene, hexafluoropropylene, and vinylidene fluoride; polymethyl methacrylate; a copolymer of methyl methacrylate and ethyl acrylate; or a copolyethylene naphthalate terephthalate copolymer. In some embodiments, each polymer A layer comprises polyethylene naphthalate, polyethylene terephthalate, or a polyhexylethylene naphthalate copolymer, each B layer comprises polymethyl methacrylate or a copolymer of methyl methacrylate and ethyl acrylate, and each polymer C layer comprises syndiotactic polystyrene; a terpolymer of tetrafluoroethylene, hexafluoropropylene, and vinylidene fluoride; or a copolyethylene naphthalate terephthalate copolymer.

[0025] In some embodiments where each C layer comprises syndiotactic polystyrene (sPS), each B layer may comprise, for example, a styrene block copolymer, an acrylic block copolymer, a glycol modified polyethylene terephthalate, or a glycol modified polyethylene naphthalate. In some embodiments where each A layer comprises a polyester (e.g., PET, PEN, or PHEN), each B layer may comprise, for example, a styrene block copolymer. Styrene block copolymers have been found to be particularly useful for providing high bond strength with polyesters (e.g., PET, PEN, or PHEN) and / or sPS. In some embodiments where each C layer comprises a terpolymer of tetrafluoroethylene, hexafluoropropylene, and vinylidene fluoride (THV), each B layer may comprise, for example, polymethyl methacrylate (PMMA) or a copolymer of methyl methacrylate and ethyl acrylate (coPMMA). Acrylates (e.g., PMMA or coPMMA or acrylic block copolymers or blends thereof) have been found to be particularly useful for providing high bond strength with fluoropolymers (e.g., THV). As an example, the A layer may include PEN, the C layer may include THV, and the B layer may include PMMA. As another example, the A layer may include PET, the C layer may include THV, and the B layer may include coPMMA. Interlayer adhesion between fluoropolymers (e.g., THV) and acrylates or other materials is described, for example, in U.S. Patent Application Publication Nos. 2019 / 0369314 (Hebrink et al.) and 2019 / 0111666 (Hebrink et al.). In some examples, the interlayer adhesion between PEN and PMMA was about 30 grams / inch when measured at a 90 degree peel angle, which is substantially higher than the interlayer adhesion between many fluoropolymers and PEN. In some examples, the interlayer adhesion between PET and coPMMA was about 50 grams / inch when measured at a 90 degree peel angle, which is substantially higher than the interlayer adhesion between many fluoropolymers and PET.

[0026] In some embodiments, each optical repeat unit 10 includes at least one fluoropolymer layer (e.g., one or more THV layers). In some embodiments, at least one layer of each optical repeat unit has a refractive index of 1.4 or less at a wavelength of 633 nm in at least one direction. In some embodiments, at least one layer of each optical repeat unit has a refractive index of 1.4 or less at a wavelength of 633 nm in each of three mutually orthogonal directions. In other embodiments, the optical repeat unit 10 does not include a fluoropolymer layer. In some embodiments, each layer of each optical repeat unit has a refractive index of at least 1.45 at a wavelength of 633 nm in at least one direction. In some embodiments, each layer of each optical repeat unit has a refractive index of at least 1.45 at a wavelength of 633 nm in each of three mutually orthogonal directions.

[0027] According to some embodiments, B layers formed from polymers having low glass transition temperatures, or block copolymers containing (e.g., soft) polymer blocks having low glass transition temperatures, or blends thereof, have been found to provide improved bonding with the A and C layers described herein. For example, the B layer can be formed from a styrene block copolymer, an acrylic block copolymer, PMMA, or coPMMA, or a blend of any of the latter three. The glass transition temperature (of the B layer or the soft block of the B layer) can be, for example, less than 105°C, or less than 100°C, or less than 90°C, or less than 80°C, or less than 70°C, or less than 60°C, or less than 50°C, or less than 40°C, or less than 30°C, or less than 20°C, or less than 10°C, or less than 0°C, or less than -10°C, or less than -20°C, or less than -30°C, or less than -40°C, or less than -50°C. The glass transition temperature of the polymer blocks of the copolymer can be determined as the glass transition temperature of the homopolymer of the monomer units of the polymer block. The block copolymer may also include other (e.g., hard) blocks, for example, for mechanical properties (e.g., for material handling and / or low creep). The (e.g., hard) blocks for mechanical properties may have, for example, a glass transition temperature of more than 50°C, or more than 60°C, or more than 70°C, or more than 80°C, or more than 90°C, or more than 100°C, or more than 105°C. In some embodiments, each B layer is a chemically inert or substantially chemically inert polymer layer. That is, in some embodiments, the polymer of the B layer does not form covalent bonds with the material of the A layer or the material of the C layer, or forms only covalent bonds that have a negligible effect on the bond with any of the adjacent layers.

[0028] Atactic polystyrene (aPS) can optionally be blended with sPS (e.g., at about 5 to about 30 weight percent aPS) to adjust the refractive index of the resulting layer and / or reduce the haze of the layer (e.g., by reducing the crystallinity of the layer). Suitable THV polymers include those described, for example, in U.S. Patent Application Publication No. 2019 / 0369314 (Hebrink et al.) and available under the tradename DYNEON THV from 3M Company (St. Paul, MN). In some embodiments, the THV can contain about 35 to about 75 mole percent tetrafluoroethylene, about 5 to about 20 mole percent hexafluoropropylene, and about 15 to about 55 mole percent vinylidene fluoride. Suitable styrenic block copolymers include KRATON G1645 and KRATON G1657 available from KRATON Polymers (Houston, TX). Suitable acrylic block copolymers include those available under the trade name KURARITY from Kuraray Co., Ltd. (Tokyo, JP). PETG can be described as PET in which some of the glycol units of the polymer have been replaced with different monomer units, typically monomer units derived from cyclohexanedimethanol. PETG can be produced, for example, by replacing a portion of the ethylene glycol used in the transesterification reaction to produce the polyester with cyclohexanedimethanol. Suitable PETG copolyesters include GN071 available from Eastman Chemical Company (Kingsport, TN). PEN and coPEN can be produced, for example, as described in U.S. Pat. No. 10,001,587 (Liu). A low melting PEN is a coPEN containing about 90 mole percent naphthalene dicarboxylate groups based on the total carboxylate groups, also known as coPEN 90 / 10.Another useful coPEN is coPEN 70 / 30, which contains about 70 mole percent naphthalene dicarboxylate groups and about 30 mole percent terephthalate dicarboxylate groups based on the total carboxylate groups. More generally, coPEN Z / 100-Z may be used, where coPEN Z / 100-Z contains Z mole percent naphthalene dicarboxylate groups (typically greater than 50 mole percent and up to about 90 mole percent) and 100-Z mole percent terephthalate dicarboxylate groups based on the total carboxylate groups. Glycol-modified polyethylene naphthalates (PENGs) can be described as PENs in which a portion of the glycol units of the polymer are replaced with different monomer units, and can be prepared, for example, by replacing a portion of the ethylene glycol used in the transesterification reaction to produce the polyester with cyclohexanedimethanol. PHENs can be prepared, for example, as described for PENs in U.S. Pat. No. 10,001,587 (Liu), except that a portion (e.g., about 40 mole percent) of the ethylene glycol used in the transesterification reaction is replaced with hexanediol. Suitable PET can be obtained, for example, from Nan Ya Plastics Corporation, America (Lake City, SC). Suitable sPS can be obtained, for example, from Idemitsu Kosan Co., Ltd. (Tokyo, Japan). Suitable PMMA can be obtained, for example, from Arkema Inc. (Philadelphia, PA). Suitable anhydride modified ethylene vinyl acetate polymers include, for example, those available under the trade name BYNEL from Dow Chemical (Midland, MI). Suitable ketone ethylene ester terpolymers include, for example, those available under the trade name BYNEL from Dow Chemical (Midland, MI). Suitable polyolefin-based thermoplastic elastomers include those available under the trade name ADMER from Mitsui Chemicals (Tokyo, Japan).

[0029] PEN, PET, and PHEN are examples of positively birefringent thermoplastic polymers, and sPS is an example of a negatively birefringent thermoplastic polymer. Whether a polymer exhibits positive or negative birefringence may depend on the geometry of the crystallites formed when the polymer is oriented, as described, for example, in U.S. Pat. No. 9,069,136 (Weber et al.). Suitable positively birefringent thermoplastic polymers include those that form crystallites with an axis of symmetry substantially aligned with the stretch direction, while suitable negatively birefringent thermoplastic polymers include those that form crystallites with a disk-shaped unit cell structure with the minimum unit cell dimension substantially aligned with the stretch direction. Styrene block copolymers, PMMA, coPMMA, THV, acrylic block copolymers, coPEN, and PETG are examples of thermoplastic polymers that may be substantially isotropic after orientation. Substantially isotropic polymers typically either do not substantially form crystallites when oriented, or form crystallites that melt away when a film containing the polymer is heat set. Further examples of positively and negatively birefringent thermoplastic polymers and isotropic thermoplastic polymers are described, for example, in U.S. Patent No. 9,069,136 (Weber et al.). Other suitable materials for the various layers in the multilayer optical film 300 include those described, for example, in U.S. Patent Nos. 5,103,337 (Schrenk et al.), 5,540,978 (Schrenk), 5,882,774 (Jonza et al.), 6,179,948 (Merrill et al.), 6,207,260 (Wheatley et al.), 6,783,349 (Neavin et al.), 6,967,778 (Wheatley et al.), 9,069,136 (Weber et al.), and 9,162,406 (Neavin et al.).

[0030] The various layers of the optical film 300 can be characterized by their refractive indices along a first in-plane direction (e.g., x-direction), an orthogonal second in-plane direction (e.g., y-direction), and / or a thickness direction (z-direction) orthogonal to the in-plane direction. In embodiments where the refractive indices of multiple layers are specified, the refractive indices along the x-, y-, and z-directions may be represented as nxi, nyi, nzi, respectively, where "i" is 1, 2, etc. FIG. 3 is a schematic perspective view of the layers of a multilayer optical film. The refractive indices nxi, nyi, nzi along the x-, y-, and z-directions are shown for layer "i," which may correspond, for example, to any of layers A, B1, C, B2 shown in FIGS. 1A-1B. For example, in some embodiments, the multilayer optical film 300 includes a plurality of optical repeating units 10, each of which includes at least four individual layers (e.g., A, B1, C, B2), and at least a first (e.g., one of A and C) and a second (e.g., the other of A and C) individual layer of the at least four individual layers of each of the optical repeating units have the same respective refractive indices nx1 and nx2 along an in-plane x-direction, respective refractive indices ny1 and ny2 along an in-plane y-direction perpendicular to the x-direction, and respective refractive indices nz1 and nz2 along a z-direction perpendicular to the x-direction and y-direction.

[0031] The following table lists the refractive index at a wavelength of about 633 nm for various exemplary materials that can be used for the layers of the optical film 300 according to some embodiments. Birefringent materials are typically uniaxially oriented for reflective polarizers and biaxially oriented for optical mirrors. Materials such as styrene block copolymers, THV, PMMA, coPMMA, acrylic block copolymers, coPEN, and PETG are typically isotropic, regardless of whether other layers in the multilayer optical film are biaxially or uniaxially oriented. For example, multilayer optical films including layers of such materials can be heat set at temperatures above the glass transition temperatures of the materials used in these layers to obtain isotropic layers. Layers of some materials (e.g., PHEN) can be uniaxially oriented, biaxially oriented, or isotropic, depending on the stretching conditions and heat setting temperatures. For example, PHEN layers can be biaxially or uniaxially oriented, or PHEN layers can be heat set at temperatures above the glass transition temperature of PHEN to obtain isotropic layers even after the layers are uniaxially or biaxially stretched.

[0032] [Table 1]

[0033] In some embodiments, each individual layer of each optical repeating unit has a refractive index in the range of about 1.3 to about 1.9 in each of the x, y, and z directions for at least one wavelength in the visible wavelength range of about 420 nm to about 680 nm. In some embodiments, each individual layer of each optical repeating unit has a maximum refractive index difference in any two of the x, y, and z directions of less than about 0.4, or less than about 0.36, for at least one wavelength in the visible wavelength range of about 420 nm to about 680 nm. In some embodiments, the maximum refractive index difference of the individual layers in the optical repeating unit along each of the x, y, and z directions for at least one wavelength is less than about 0.55, or less than about 0.5, or less than about 0.45. In some embodiments, the maximum refractive index difference of individual layers in an optical repeat unit along the same direction (e.g., one of the x, y, and z directions) for at least one wavelength is greater than about 0.05, or greater than about 0.07, or greater than about 0.1, or greater than about 0.15, or greater than about 0.2, or greater than about 0.22, or greater than about 0.25. In some embodiments, when a refractive index difference (e.g., the difference in refractive index of the same layer in different directions, or the difference in refractive index along the same direction for different layers) is said to be greater than a specified value for at least one wavelength, the difference may be, for example, up to about 0.55, or up to about 0.5, or up to about 0.45, or up to about 0.4, or up to about 0.35, or up to about 0.3.

[0034] In some embodiments, each optical repeat unit includes at least four individual layers including a more birefringent first individual layer (e.g., one of the A and C layers) and a less birefringent second individual layer (e.g., the other of the A and C layers). For example, in some embodiments, the first individual layer includes polyethylene naphthalate (PEN) or polyhexylethylene naphthalate copolymer (PHEN) and the second individual layer includes syndiotactic polystyrene (sPS), polymethyl methacrylate (PMMA), a copolymer of methyl methacrylate and ethyl acrylate (coPMMA), a copolyethylene naphthalate terephthalate copolymer (coPEN), or a terpolymer of tetrafluoroethylene, hexafluoropropylene, and vinylidene fluoride (THV). As another example, in some embodiments, the first individual layer comprises polyethylene terephthalate (PET) and at least a second individual layer comprises a terpolymer of tetrafluoroethylene, hexafluoropropylene and vinylidene fluoride (THV). The at least four individual layers can include at least a third layer that can include, for example, a styrene block copolymer, an acrylic block copolymer, or a glycol-modified polyethylene terephthalate (PETG). Any layer described as including a polymeric material can be a layer of that polymeric material. For example, a layer including PEN can be a PEN layer.

[0035] In some embodiments, for at least one wavelength in the visible wavelength range spanning from about 420 nm to about 680 nm, nx1 is at least 0.15 greater than at least one of ny1 and nz1, the magnitude of the maximum difference between nx2, ny2, and nz2 is less than 0.15, and nx1 is at least 0.15, or at least 0.17, or at least 0.2, or at least 0.22, or at least 0.25, or at least 0.28, or at least 0.3, or at least 0.32 greater than nx2. In some such embodiments, or in other embodiments, for at least one wavelength, nx1 is, for example, at most about 0.45, or at most about 0.4, or at most about 0.35 greater than nx2. In some embodiments, for at least one wavelength, nx1 is at least 0.15 greater than each of ny1 and nz1. In some embodiments, for at least one wavelength, nx1 is at least 0.15 greater than one of ny1 and nz1, but not greater than the other. The maximum difference between the three quantities is the maximum of the three quantities minus the minimum of the three quantities. In some embodiments, nx2 is smaller than at least one of ny2 and nz2 (e.g., at least 0.005, or at least 0.01, or at least 0.02, or at least 0.03). In some embodiments, the magnitude of the maximum difference between nx2, ny2, and nz2 is less than 0.1, or less than 0.05, or less than 0.02. In some embodiments, for at least one wavelength, nx1 is at least 0.17, or at least 0.2, or at least 0.22, or at least 0.25, greater than at least one of ny1 and nz1. In some embodiments, for at least one wavelength, nx1 is, for example, at most about 0.45, or at most about 0.4, or at most 0.35, greater than at least one of ny1 and nz1. For example, in some embodiments, the first individual layer is a uniaxially oriented PEN layer having refractive indices nx1, ny1, nz1 of about 1.85, 1.60, and 1.50, respectively, at 633 nm, and the second individual layer is a uniaxially oriented sPS layer having refractive indices nx2, ny2, nz2 of about 1.51, 1.62, and 1.62, respectively, at 633 nm.As another example, in some embodiments, the first individual layer is a biaxially oriented PEN layer having refractive indices nx1, ny1, nz1 of about 1.76, 1.74, and 1.49 at 633 nm, respectively, and the second individual layer is a biaxially oriented sPS layer having refractive indices nx2, ny2, nz2 of about 1.57, 1.57, and 1.62 at 633 nm, respectively. In some embodiments, at least a third layer (e.g., B1 and / or B2) has respective refractive indices nx3, ny3, and nz3 along the respective x-, y-, and z-directions, where nx2 is at least 0.005, or at least 0.01, or at least 0.02, or at least 0.05 greater than nx3 for at least one wavelength. For example, the first layer and the second layer may be as described above, and the third layer may be a styrene block copolymer layer having a refractive index of about 1.49 in each direction at 633 nm. In some embodiments, for at least one wavelength, nx3 is at least 0.05 or at least 0.1 greater than nx2. For example, the first layer and the third layer may be as described above, and the second layer may be a THV layer having a refractive index of about 1.36 in each direction at 633 nm. In some embodiments, for at least one wavelength, |nx2-nx3| is less than 0.02, or less than 0.01, or less than 0.007, or less than 0.005. For example, the third layer may be a styrene block copolymer layer having a refractive index of about 1.49 in each direction at 633 nm, and the second layer may be a PMMA or coPMMA layer having a refractive index of about 1.49 in each direction at 633 nm.

[0036] In some embodiments, for each optical repeat unit, the first individual layer (e.g., one of the A and C layers) is positively birefringent (refractive index increases in the stretch direction) and the second individual layer (e.g., the other of the A and C layers) is negatively birefringent (refractive index decreases in the stretch direction). For example, in some embodiments, the first individual layer comprises polyethylene naphthalate (PEN), polyethylene terephthalate (PET), or polyhexylethylene naphthalate copolymer (PHEN), and in some such embodiments or other embodiments, the second individual layer comprises syndiotactic polystyrene (sPS).

[0037] In some embodiments, for at least one wavelength in the visible wavelength range spanning from about 420 nm to about 680 nm, nx1 is at least 0.15 greater than at least one of ny1 and nz1, and nx2 is less than at least one of ny2 and nz2, and nx1 is at least 0.15, or at least 0.17, or at least 0.2, or at least 0.22, or at least 0.25 greater than nx2. In some embodiments, for at least one wavelength, nx1 is at least 0.15 greater than each of ny1 and nz1, and nx2 is at least 0.05 less than each of ny2 and nz2. In some embodiments, for at least one wavelength, nx1 is at least 0.15 greater than one of ny1 and nz1, but not greater than the other. In some embodiments, for at least one wavelength, nx2 is at least 0.03 less than nz2, and |nx2-ny2|<0.005. In some embodiments, for at least one wavelength, nx2 is at least 0.04 less than nz2, and |nx2-ny2|<0.003. In some embodiments, for at least one wavelength, nx1 is at least 0.17, or at least 0.2, or at least 0.22, or at least 0.25 greater than at least one of ny1 and nz1. In some embodiments, for at least one wavelength, nx1 is, for example, at most about 0.45, or at most about 0.4, or at most about 0.35 greater than at least one of ny1 and nz1. For example, the first discrete layer may be a PEN, PHEN, or PET layer uniaxially stretched along the x direction or biaxially stretched along the x and y directions, and the second discrete layer may be an sPS layer uniaxially stretched along the x direction or biaxially stretched along the x and y directions. In some embodiments, for at least one wavelength, nx2 is at least 0.005, or at least 0.01, or at least 0.02, or at least 0.05, or at least 0.1 less than ny2. In some embodiments, for at least one wavelength, the magnitude of the difference between nx2 and ny2 is less than 0.005, or less than 0.003, or less than 0.002.In some embodiments, for at least one wavelength, nz2 is at least 0.005, or at least 0.01, or at least 0.02, or at least 0.05, or at least 0.1 greater than nz1.

[0038] In some embodiments, for each optical repeat unit, the first individual layer (e.g., one of the A and C layers) is substantially isotropic and the second individual layer (e.g., the other of the A and C layers) is negatively birefringent. For example, in some embodiments, the first individual layer comprises copolyethylene naphthalate terephthalate copolymer (coPEN) or polyhexylethylene naphthalate copolymer (PHEN) and the second individual layer comprises syndiotactic polystyrene (sPS).

[0039] In some embodiments, for at least one wavelength in the visible wavelength range spanning from about 420 nm to about 680 nm, the magnitude of the maximum difference between nx1, ny1, and nz1 is less than 0.05, nx2 is smaller than at least one of ny2 and nz2, and nx1 is at least 0.07, or at least 0.08, or at least 0.09, or at least 0.1, greater than nx2. In some embodiments, for at least one wavelength, nx1 is, for example, at most 0.25, or at most 0.2, or at most 0.15, greater than nx2. In some embodiments, for at least one wavelength, nx2 is at least 0.05, or at least 0.06, or at least 0.07, less than each of ny2 and nz2. In some embodiments, for at least one wavelength, nx2 is, for example, at most 0.2, or at most 0.15, or at most 0.12, less than each of ny2 and nz2. In some embodiments, for at least one wavelength, nx2 is at least 0.03 less than nz2, and |nx2-ny2|<0.005. In some embodiments, for at least one wavelength, nx2 is at least 0.04 less than nz2, and |nx2-ny2|<0.003. For example, the first individual layer can be a coPEN layer, and the second individual layer can be a uniaxially or biaxially stretched sPS layer. As another example, the first individual layer can be an isotropic PHEN layer, and the second individual layer can be a uniaxially or biaxially stretched sPS layer. In some embodiments, for at least one wavelength, the magnitude of the maximum difference between nx1, ny1, and nz1 is less than 0.04, or less than 0.03, or less than 0.02, or less than 0.01, or less than 0.005. In some embodiments, for at least one wavelength, nx2 is at least 0.005, or at least 0.01, or at least 0.02, or at least 0.05, or at least 0.1 less than at least one of ny2 and nz2.

[0040] In some embodiments, the optical film 300 is a multilayer optical mirror. In some such embodiments, or in other embodiments, each of the optical repeating units 10 includes at least four sequentially arranged first through fourth individual layers. The first through fourth individual layers may be labeled sequentially, for example, in the plus or minus z direction of FIG. 1B, and the starting (first) layer may be, for example, layer A or layer C. For example, A, B1, C, B2 may be identified as an optical repeating unit including sequentially arranged first through fourth individual layers, or A, B2, C, B1 may be identified as an optical repeating unit including sequentially arranged first through fourth individual layers, or C, B2, A, B1 may be identified as an optical repeating unit including sequentially arranged first through fourth individual layers, or C, B1, A, B2 may be identified as an optical repeating unit including sequentially arranged first through fourth individual layers. The total number of optical repeating units 10 may be any of the ranges described elsewhere herein, and the total average thickness of the optical repeating units 10 may be any of the ranges described elsewhere herein. The at least four sequentially arranged first through fourth individual layers may have any of the respective ranges described elsewhere herein. In some embodiments, for each of the optical repeating units 10, the average thickness of each of the second and fourth individual layers (B1 and B2) is less than about 30 nm, or less than about 20 nm, or less than about 15 nm, or less than about 10 nm, or less than about 7.5 nm. In some embodiments, for each of the optical repeating units 10, the average thickness of each of the second and fourth individual layers (e.g., B1 and B2) is within a range of, for example, about 1 nm to about 30 nm, or about 3 nm to about 20 nm.

[0041] The first (e.g., one of A and C) and third (e.g., the other of A and C) individual layers of each of the optical repeating units 10 can have respective refractive indices nx1 and nx2 along the same in-plane x-direction, respective refractive indices ny1 and ny2 along an in-plane y-direction orthogonal to the x-direction, and respective refractive indices nz1 and nz2 along a z-direction orthogonal to the x-direction and y-direction. In some embodiments, nx1 and ny1 are at least 0.1 greater than nx2 and ny2, respectively, and nz2 is at least 0.05 greater than nz1, for at least one wavelength in the visible wavelength range spanning from about 420 nm to about 680 nm. In some embodiments, the first individual layer comprises polyethylene naphthalate (PEN), polyethylene terephthalate (PET), or polyhexylethylene naphthalate copolymer (PHEN), and in some such embodiments, or in other embodiments, the third individual layer comprises syndiotactic polystyrene (sPS). For example, in some embodiments, the first individual layer is a biaxially oriented PEN layer having refractive indices nx1, ny1, nz1 of about 1.76, 1.74, and 1.49 at 633 nm, respectively, and the third individual layer is a biaxially oriented sPS layer having refractive indices nx2, ny2, nz2 of about 1.57, 1.57, and 1.62 at 633 nm, respectively. In some such embodiments, or in other embodiments, the second and fourth layers are styrene block copolymer layers having a refractive index of about 1.49 in each direction at 633 nm. In some embodiments, nx1 and ny1 are at least 0.12, or at least 0.14, or at least 0.16, or at least 0.18 greater than nx2 and ny2, respectively, for at least one wavelength. In some embodiments, for at least one wavelength, nx1 and ny1 are, for example, up to about 0.45, or about 0.4, or about 0.35, or about 0.3, greater than nx2 and ny2, respectively. In some embodiments, for at least one wavelength, nz2 is at least 0.06, or at least 0.07, or at least 0.08, or at least 0.09, or at least 0.1, or at least 0.11, or at least 0.12 greater than nz1.In some embodiments, for at least one wavelength, nz2 is, for example, up to about 0.3, or up to about 0.25, greater than nz1. In some embodiments, optical film 300 is a multilayer optical mirror that utilizes a negative birefringent layer (e.g., sPS) to achieve a collimating effect (see, e.g., FIG. 9A) by reducing the transmission for larger angles of incidence (e.g., θ2) relative to the transmission at smaller angles of incidence (e.g., θ1).

[0042] The at least one wavelength in the range of 420 nm to 680 nm may be, for example, at least one wavelength in the range of 430 nm to 670 nm, or in the range of 450 nm to 650 nm, or in the range of 480 nm to 640 nm, or may include them. The at least one wavelength in the range of 420 nm to 680 nm may be, for example, 633 nm, or may include them.

[0043] In some embodiments, the optical film 300 is a reflective polarizer. Figures 4A-4B are schematic plots of optical transmission through multiple optical repeat units of a reflective polarizer for light 30 incident on the reflective polarizer at a plane of incidence 40 (see, e.g., Figures 2A-2B), according to some embodiments. Optical transmissions 50 and 60 are for a first angle of incidence θ1 and a second angle of incidence θ2 (see, e.g., Figure 1A) for the s-polarization state 32 when the first in-plane direction (x-direction) of the reflective polarizer is in the plane of incidence 40. Optical transmissions 150 and 160 are for a first angle of incidence θ1 and a second angle of incidence θ2 for the p-polarization state 31 when the second in-plane direction (y-direction) of the reflective polarizer is in the plane of incidence 40. The light transmittances 150, 160 have respective average values ​​T1 and T2 in a visible wavelength range spanning λ1 (e.g., about 400 nm, or about 420 nm, or about 450 nm) to λ2 (e.g., about 650 nm, or about 680 nm, or about 700 nm). The visible wavelength range spanning λ1 to λ2 may be, for example, about 420 nm to about 680 nm. The light transmittances 150, 160, 50, and 60 have respective average values ​​T3, T4, T5, and T6 in an infrared wavelength range spanning λ3 (e.g., about 720 nm, or about 750 nm, or about 800 nm) to λ4 (e.g., about 1150 nm, or about 1200 nm, or about 1250 nm, or about 1300 nm). The infrared wavelength range spanning λ3 to λ4 may be, for example, about 750 nm to about 1200 nm. In some embodiments, when the second in-plane direction of the reflective polarizer is in the plane of incidence 40, for a visible wavelength range spanning λ1 to λ2 (e.g., about 420 nm to about 680 nm), for the p-polarization state 31, the multiple optical repeating units 10 have average optical transmittances T1 and T2 for respective first and second angles of incidence θ1 and θ2, where T2 is at least 5% or at least 7% greater than T1.In some embodiments, for each of the first and second angles of incidence θ1 and θ2, for an s-polarization state 32 and a first direction in the plane of incidence, and for a p-polarization state and a second direction in the plane of incidence, and for an infrared wavelength range spanning λ3 to λ4 (e.g., about 750 nm to about 1200 nm), the multiple optical repeat units have an average optical transmittance (e.g., T3, T4, T5, T6) of greater than about 40%, or greater than about 45%, or greater than about 50%, or greater than about 55%, or greater than about 60%.

[0044] The optical transmittances 50' and 60' in FIG. 4B are for a first angle of incidence θ1 and a second angle of incidence θ2 (see, e.g., FIG. 1A) for the p-polarized state 31 when the first in-plane direction (x-direction) of the reflective polarizer is in the plane of incidence 40. The optical transmittances 150' and 160' are for a first angle of incidence θ1 and a second angle of incidence θ2 for the s-polarized state 32 when the second in-plane direction (y-direction) of the reflective polarizer is in the plane of incidence 40. The optical transmittances 150' and 160' have respective average values ​​T1' and T2' in the visible wavelength range spanning λ1 to λ2. The optical transmittances 150', 160', 50', and 60' have respective average values ​​T3', T4, T5', and T6' in the infrared wavelength range spanning λ3 to λ4. T1', T2', T3', T4', T5', and T6' may be any of the respective ranges described for T1, T2, T3, T4, T5, and T6. In some embodiments, for each of the first and second angles of incidence θ1 and θ2, for each of the s and p polarization states, for each of the first and second directions in the plane of incidence 40, and for an infrared wavelength range spanning from about 750 nm to about 1200 nm, the plurality of optical repeating units have an average optical transmittance (e.g., T3, T4, T5, T6, T3', T4', T5', T6') of greater than about 40%, or greater than about 45%, or greater than about 50%, or greater than about 55%, or greater than about 60%.

[0045] In some embodiments, for a first direction in the plane of incidence 40 and for the s-polarization state 32, the plurality of optical repeating units 10 have first and second optical transmittances 50 and 60 versus wavelength for respective first and second angles of incidence θ1 and θ2, the first and second optical transmittances 50 and 60 having respective first and second transmission band edges 51 and 61. In some embodiments, the band edges 51 and / or 61 have a sharp slope (e.g., greater than about 1.3% / nm). The band edge slope can be made sharp by including a layer having a substantially graded thickness profile at the edge of the stack of optical repeating units, as generally described, for example, in U.S. Pat. No. 6,967,778 (Wheatley et al.). However, according to some embodiments, it has been found that by using an optical repeating unit having at least four individual layers as described herein, a sharp band edge can be obtained without including a layer having a substantially graded thickness profile. In some embodiments, the best linear fit (52 and 62) to each of the first and second band edges (51 and 61, respectively), at least over the wavelength range along the transmission band edges where the light transmission increases from about 10% to about 50%, has a positive slope (S1 and S2, respectively) of greater than about 1.3% / nm, or greater than about 1.4% / nm, or greater than about 1.5% / nm, or greater than about 1.6% / nm, or greater than about 1.7% / nm, or greater than about 1.8% / nm, or greater than about 1.9% / nm, or greater than about 2% / nm. In some embodiments, each of the best linear fits 52 and 62 has an r-squared value greater than about 0.7. In some embodiments, at least one of the best linear fits 52 and 62 has an r-squared value greater than about 0.8. The best linear fits described herein may be linear least squares fits, as known in the art. Such fits minimize the sum of the squares of the residuals, where the residuals are the difference between the data and the fitted line. Least squares analysis allows the determination of an r-squared value, sometimes called the coefficient of determination.

[0046] The thickness of the optical repeat unit determines the wavelengths reflected by the optical repeat unit, and the refractive index difference between the layers in the optical repeat unit determines the intensity of the reflection. Thus, the optical transmission of Figures 4A-4B can be achieved, for example, by appropriate selection of layer materials to define the refractive index difference, and appropriate selection of layer thickness profile. In some embodiments, the A layer is a uniaxially oriented PEN layer, the C layer is a uniaxially oriented sPS layer, and the B1 and B2 layers are styrene block copolymer layers. Figure 5 is a plot of layer thickness versus optical repeat unit number for a reflective polarizer that can be formed from these materials. Alternatively, the layer thickness profile of Figure 5 may be used for optical mirrors or other multilayer optical films. The B1 and B2 layers have a thickness of 5 nm in each optical repeat unit, while the A and C layers generally increase in thickness over the thickness of the reflective polarizer. In some embodiments, when the optical repeat units are numbered sequentially from one side of the optical film to the other side of the optical film, the layer thickness versus optical repeat unit number has a generally upwardly concave shape for the A and C layers, while the B layer has a substantially constant thickness (e.g., varies by less than 10% or less than 5% across the thickness of the optical film). The optical repeat units of the reflective polarizer of Figure 5 have a total average thickness of about 14 micrometers.

[0047] Given the refractive indices and layer thicknesses of the layers of a multilayer optical film, the optical transmission spectrum of the optical film can be calculated using conventional optical modeling techniques. Figure 6A is a plot of the calculated optical transmission of multiple optical repeat units of a reflective polarizer having the layer thickness profile shown in Figure 5 for light 30 incident on the reflective polarizer at the incident surface 40 (see, for example, Figures 2A-2B) when the A layer is a uniaxially oriented PEN layer, the C layer is a uniaxially oriented sPS layer, and the B1 and B2 layers are styrene block copolymer layers. Similar optical transmissions can be obtained, for example, when the B1 and B2 layers are acrylic block copolymer layers, PMMA layers, or coPMMA layers. The optical transmissions of 50, 60, 150, and 160 are for the polarization states and incident angles described for the corresponding optical transmissions in Figure 4A, where in Figure 6A the first incident angle θ1 and the second incident angle θ2 are 0 degrees and 60 degrees, respectively. For a visible wavelength range spanning from about 420 nm to about 680 nm, the multiple optical repeating units have average light transmittances of 87.7% and 96.5% for the first and second angles of incidence θ1 and θ2 for p-polarization state 31 when the second in-plane direction of the reflective polarizer is within the plane of incidence 40, and have average light transmittances of 1.4% and 0.0% for the first and second angles of incidence θ1 and θ2 for s-polarization state 32 when the first in-plane direction of the reflective polarizer is within the plane of incidence 40. For an infrared wavelength range spanning approximately 750 nm to approximately 1200 nm, the multiple optical repeating units have average light transmittances of 90.0% and 99.8% for the first and second angles of incidence θ1 and θ2 for the p-polarization state 31 when the second in-plane direction of the reflective polarizer is within the plane of incidence 40, and have average light transmittances of 62.1% and 53.1% for the first and second angles of incidence θ1 and θ2 for the s-polarization state 32 when the first in-plane direction of the reflective polarizer is within the plane of incidence 40.

[0048] Figure 6B is a portion of the plot of Figure 6A expanded to show the region where the light transmission increases from about 10% to about 50%. Best linear fits 52 and 62 to the respective first and second band edges 51 and 61 over the wavelength range along the transmission band edges where the light transmission increases from about 10% to about 50% have respective positive slopes S1 and S2 of about 2.01% / nm and 2.08% / nm, respectively.

[0049] In some embodiments, the A layer is a uniaxially oriented PHEN layer, the C layer is a THV layer, and the B1 and B2 layers are coPMMA layers. FIG. 7 is a plot of layer thickness versus optical repeat unit number for a reflective polarizer that can be formed from these materials. Alternatively, the layer thickness profile of FIG. 7 may be used for an optical mirror or other multilayer optical film. The B1 and B2 layers each have a thickness of 5 nm in each optical repeat unit, while the A and C layers generally increase in thickness across the thickness of the reflective polarizer. The optical repeat units of the reflective polarizer have a total average thickness of 15 micrometers. FIG. 8 is a plot of the calculated light transmission of the optical repeat units of a reflective polarizer having the thickness profile shown in FIG. 7 for light 30 incident on the reflective polarizer at the incident surface 40 (see, for example, FIGS. 2A-2B) when the A layer is a uniaxially oriented PHEN layer, the C layer is a THV layer, and the B1 and B2 layers are coPMMA layers. Similar light transmittances can be obtained, for example, when the B1 and B2 layers are styrene block copolymer layers, acrylic block copolymer layers, or PMMA layers. The light transmittances of 50, 60, 150, and 160 are for the polarization states and incidence angles described for the corresponding light transmittances in FIG. 4A, where the first incidence angle θ1 and the second incidence angle θ2 are 0 degrees and 60 degrees, respectively, in FIG. 8. The reflective polarizer of FIG. 8 has a substantially lower average light transmittance in the visible wavelength range of 420 nm to 680 nm compared to the reflective polarizer of FIG. 6A for each of the first incidence angle θ1 and the second incidence angle θ2.

[0050] In some embodiments, the optical film 300 is a multilayer optical mirror. Figures 9A-9B are plots of optical transmittance for incident light 30, 130, or 230 incident on a multilayer optical mirror. Optical transmittance 250, 250', 250'' is for a first angle of incidence θ1, which may be less than about 5 degrees or within any range described elsewhere herein for θ1, and optical transmittance 260, 260', 260'' is for a second angle of incidence θ2, which may be greater than about 40 degrees or within any range described elsewhere herein for θ2. Optical transmittance 250 and 260 may be for any specified polarization state or for unpolarized incident light. Optical transmittance 250' and 260' is for s-polarized light, and optical transmittance 250'' and 260'' is for p-polarized light. In some embodiments, the optical transmittance is approximately the same for each of the mutually orthogonal first and second polarization states (e.g., for each of the p-polarization state 31 and the s-polarization state 32, or for each of two mutually orthogonal linear combinations of the p-polarization state 31 and the s-polarization state 32). In some embodiments, for light 30 incident on the multilayer optical mirror, for each of the mutually orthogonal first and second polarization states, and for a visible wavelength range spanning λ1 to λ2 (e.g., about 420 nm to about 680 nm), the plurality of optical repeating units 10 have an average optical transmittance T1 for a first angle of incidence θ1 and an average optical transmittance T2 for a second angle of incidence θ2, where T1 / T2≧1.2, or T1 / T2≧1.4, or T1 / T2≧1.6, or T1 / T2≧1.8, or T1 / T2≧2, or T1 / T2≧2.2, or T1 / T2≧2.4, or T1 / T2≧2.6. T1 / T2 may be, for example, up to 10, or up to 8, or up to 6, or up to 5.

[0051] In some embodiments, T1 is greater than T2 because the A layer has an in-plane index greater than the corresponding in-plane index of the C layer, while the C layer has a through-thickness index greater than the A layer. In some embodiments, this is achieved using a negatively birefringent C layer. For example, the A layer may be a biaxially oriented PEN layer with refractive indices nx1, ny1, nz1 of about 1.76, 1.74, and 1.49 at 633 nm, respectively, and the C layer may be a biaxially oriented sPS layer with refractive indices nx2, ny2, nz2 of about 1.57, 1.57, and 1.62 at 633 nm, respectively. In other embodiments, T1 may be approximately equal to T2, or T1 may be less than T2. In some embodiments, for light 30 incident on the multilayer optical mirror, for each of first and second orthogonal polarization states and for an infrared wavelength range spanning λ3 to λ4 (e.g., about 750 nm to about 1200 nm), the plurality of optical repeating units 10 have an average optical transmittance T3 for a first angle of incidence θ1 and an average optical transmittance T4 for a second angle of incidence θ2, where T3 and T4 are greater than about 40%, or greater than about 45%, or greater than about 50%, or greater than about 55%, or greater than about 60%, respectively.

[0052] The optical transmittance of Figures 9A-9B can be achieved, for example, by appropriate selection of layer materials to define the refractive index difference and appropriate selection of layer thickness profile. In some embodiments, the A layer is a biaxially oriented PEN layer, the C layer is a biaxially oriented sPS layer, and the B1 and B2 layers are styrene block copolymer layers. Figure 10 is a plot of layer thickness versus optical repeat unit number for an optical mirror that can be formed from these materials. Alternatively, the layer thickness profile of Figure 10 may be used for a reflective polarizer or other multilayer optical film. The B1 and B2 layers have a thickness of 5 nm in each optical repeat unit, while the A and C layers generally increase in thickness over the thickness of the optical mirror. The optical repeat units of the optical mirror have a total average thickness of about 14 micrometers. FIG. 11 is a plot of the calculated optical transmission of multiple optical repeat units of an optical mirror having the thickness profile shown in FIG. 10 for unpolarized light incident on the optical mirror at the incident surface 40 (see, e.g., FIGS. 2A-2B) where the A layer is a biaxially oriented PEN layer, the C layer is a biaxially oriented sPS layer, and the B1 and B2 layers are styrene block copolymer layers. Similar optical transmission can be obtained, for example, where the B1 and B2 layers are acrylic block copolymer layers, PMMA layers, or coPMMA layers. The optical transmissions 250 and 260 are for respective first and second angles of incidence θ1 and θ2 as generally described for FIG. 9A, where the first and second angles of incidence θ1 and θ2 are 0 degrees and 60 degrees, respectively, for FIG. 11.

[0053] In some embodiments, the A layer is an isotropic PHEN layer, the C layer is a biaxially oriented sPS layer, and the B1 and B2 layers are styrene block copolymer layers. FIG. 12 is a plot of layer thickness versus optical repeat unit number for an optical mirror that can be formed from these materials. Alternatively, the layer thickness profile of FIG. 12 may be used for a reflective polarizer or other multilayer optical film. The B1 and B2 layers have a thickness of 5 nm in each optical repeat unit, while the A and C layers generally increase in thickness across the thickness of the optical mirror. The optical repeat unit of the optical mirror has a total average thickness of 28 micrometers. FIG. 13 is a plot of the calculated optical transmission of multiple optical repeat units of an optical mirror having the thickness profile shown in FIG. 12 for unpolarized light incident on the mirror at the input surface 40 (see, for example, FIGS. 2A-2B) when the A layer is an isotropic PHEN layer, the C layer is a biaxially oriented sPS layer, and the B1 and B2 layers are styrene block copolymer layers. Similar light transmissions can be obtained, for example, when the B1 and B2 layers are acrylic block copolymer layers, PMMA layers, or coPMMA layers. Light transmissions 250 and 260 are for respective first and second angles of incidence θ1 and θ2 as generally described for FIG. 9A, where in FIG. 13 the first and second angles of incidence θ1 and θ2 are 0 degrees and 60 degrees, respectively. In the embodiment of FIG. 12-13, the average transmission within the visible wavelength range of 420 nm to 680 nm is greater at normal incidence than at a 60 degree angle of incidence.

[0054] In some embodiments, the A layer is a biaxially oriented PHEN layer, the C layer is a THV layer, and the B1 and B2 layers are coPMMA layers. FIG. 14 is a plot of layer thickness versus optical repeat unit number for an optical mirror that can be formed from these materials. Alternatively, the layer thickness profile of FIG. 14 may be used for a reflective polarizer or other multilayer optical film. The B1 and B2 layers have a thickness of 5 nm in each optical repeat unit, while the A and C layers generally increase in thickness across the thickness of the optical mirror. The optical repeat unit of the optical mirror has a total average thickness of about 15 micrometers. FIG. 15 is a plot of the calculated optical transmission of multiple optical repeat units of an optical mirror having the thickness profile shown in FIG. 14 for unpolarized light incident on the optical mirror at the incident surface 40 (see, for example, FIGS. 2A-2B) when the A layer is a biaxially oriented PHEN layer, the C layer is a THV layer, and the B1 and B2 layers are coPMMA layers. Similar light transmissions can be obtained, for example, when the B1 and B2 layers are styrene block copolymer layers, acrylic block copolymer layers, or PMMA layers. Light transmissions 250 and 260 are for respective first and second angles of incidence θ1 and θ2 as generally described for FIG. 9A, where in FIG. 15 the first and second angles of incidence θ1 and θ2 are 0 degrees and 60 degrees, respectively. In the embodiment of FIGs. 14-15, the average transmission at normal incidence in the visible wavelength range of 420 nm to 680 nm is less than about 5%, while the optical repeat unit has a total average thickness of only about 15 micrometers.

[0055] Any of the multilayer optical films, reflective polarizers, and multilayer optical mirrors described herein can have an interlayer adhesion of the individual layers in the optical repeating units of at least about 14 grams / inch (at least about 5.5 g / cm) when measured at a 90 degree peel angle. In some embodiments, the interlayer adhesion of the individual layers in the optical repeating units is at least about 16, 18, 20, 22, 25, 27, 30, 32, 35, 37, 40, 45, 50, or 55 grams / inch when measured at a 90 degree peel angle. In some embodiments, the interlayer adhesion can be, for example, up to about 400 grams / inch, or up to about 200 grams / inch, or up to about 150 grams / inch, or up to about 120 grams / inch. In some embodiments, the interlayer adhesion can be, for example, in the range of about 14 grams / inch to about 400 grams, or about 20 grams / inch to about 200 grams / inch. The peel force can be increased by appropriately selecting the materials of the A, B1, C, and B2 layers. For example, the B1, B2 layers can be selected to have suitable bonding to the A and C layers even if the A and C layers have poor direct bonding to each other. In some embodiments, the B1, B2 layers can be copolymers of the polymers used for the A and C layers. Suitable materials for the A, B1, C, and B2 layers are further described elsewhere herein. According to some embodiments, it has been found that the interlayer adhesion can be further increased by decreasing the temperature at which the film is stretched (e.g., from about 135°C to about 120°C or about 115°C) and / or by increasing the stretch ratio used in stretching the film (e.g., from a stretch ratio of about 5 along the stretch direction to a stretch ratio of about 6 along the stretch direction).

[0056] FIG. 16 is a schematic diagram of testing a multilayer optical film 300 for interlayer adhesion. The multilayer optical film 300 is bonded to a substrate 360 ​​(e.g., a rigid glass substrate) via double-sided tape 151. A cut 170 is then formed in the optical film 300, for example, using a razor blade. Another piece of tape 152 is then used to peel an end 333 of a portion 331 of the optical film 300 adjacent the cut 170 from the remaining portion 332 of the optical film 300. The peel force can then be measured by pulling the tape 152 in a direction (z-direction) away from the substrate 360 ​​that defines a peel angle φ of 90 degrees. The peel force per unit width (dimension in the x-direction) of the optical film 300 is the interlayer adhesion force. In some embodiments, the peel force is determined by using a pull speed (also called crosshead speed) of 12 inches / minute and averaging the measured force over a time period of at least about 5 seconds. In some embodiments, the peel force per unit width is the average peel resistance strength determined according to ASTM D6862-11 (reapproved 2016) testing standard, except that a crosshead speed of 12 inches / minute is used. In some embodiments, the interlayer adhesion of the individual layers in the plurality of optical repeating units is at least about 14 grams / inch, or the interlayer adhesion may be in any range described elsewhere herein, and the interlayer adhesion is determined as the average peel resistance strength measured according to ASTM D6862-11 (reapproved 2016) testing standard, except that a crosshead speed of 12 inches / minute is used to pull the top portion 331 of the multilayer optical film 300 from the bottom portion 332 of the multilayer optical film 300 at a 90 degree peel angle while the bottom portion 332 is bonded to the substrate 360. EXAMPLES

[0057] [Table 2]

[0058] A 151-layer feedblock and die were used to make a multilayer optical film containing 37 A layers, 76 B layers, and 38 C layers. The A, B, and C layers were optical layers arranged in an ABCB repeating unit. In addition, an outermost skin layer was added by extruding the resins shown in the table below for the A layers through a 25 mm twin screw extruder (TSE) at a feed rate of 20 pounds per hour through a neck tube and gear pump. The melt train used a progressive temperature extrusion profile with a peak temperature of 280°C. The A layers were made by extruding the resins shown in the table below through a 27 mm TSE at the feed rate shown in the table below through a neck tube and gear pump into the corresponding A layers of the 151-layer feedblock and die with a progressive temperature profile peaking at 280°C, except that approximately 20% of the material listed for the A layers was used to form a protective boundary layer between the optical layers and the skin layers. The B layers were produced by extruding the resins shown in the table below through a neck tube and gear pump at the feed rate shown in the table below through a TSE of 18 mm into the corresponding B layer of a 151 layer feedblock using a progressive temperature profile with a peak temperature of 260°C. The C layers were produced by extruding the resins shown in the table below through a neck tube and gear pump at the feed rate shown in the table below through a TSE of 27 mm into the corresponding C layer of a 151 layer feedblock and die using a progressive temperature profile that peaks at or near 280°C. The feedblock used gradient plates such that the A and C layers were approximately 2.5 times thicker on one side of the film than the other side of the film, while the B layer had a nominally constant thickness across the thickness of the film. The feedblock and die were held at a target temperature of 285°C. The extruded layers were cast onto a casting wheel operated at approximately 50°C to produce a cast web.

[0059] [Table 3]

[0060] These cast webs were then oriented using a KARO batch orienter (available from Bruckner Maschinenbau GmbH & Co. KG, Siegsdorf, Germany) at the stretch temperatures and stretch rates of 50 percent / second indicated in the table below. Substantially uniaxially oriented films were made with a stretch ratio of 1.5 (machine direction) x 5 or 6 (transverse direction), and biaxially oriented films were made with a stretch ratio of 3 x 3. The stretch ratios used for the various optical films are shown in the table below.

[0061] The interlayer adhesion of each of the optical films shown in the table below was measured as generally described in FIG. 16. The optical films were cut into 1 inch wide samples and laminated to a glass substrate 360 ​​using double-sided tape (SCOTCH Double-Sided Tape available from 3M Company, St. Paul, MN) 151. A razor blade was then used to create a cut 170 in the optical film 300. A piece of tape 152 was used to peel an edge 333 of a portion of the optical film 300 adjacent to the cut 170 from the remainder of the optical film 300. The interlayer adhesion was then measured using an IMASS SP-2100 (IMASS, inc., Accord, MA) using a 10 pound load cell to measure the 90 degree peel. The pull speed was set at 12 inches / minute and the peel force was averaged for 5 seconds after a 2 second delay. This was repeated 4 times. The average was taken and reported as the interlayer adhesion. The results are set forth in the table below. Web W7 utilized low melt PEN as both the A and C layers and sPS as the B layer to test the interlayer adhesion between low melt PEN and sPS.

[0062] [Table 4]

[0063] Terms such as "about" will be understood by those of skill in the art in the context in which they are used and described herein. Unless otherwise clear to one of skill in the art in the context in which the use of "about" as applied to quantities describing feature sizes, quantities, and physical properties is used and described herein, "about" will be understood to mean within 10 percent of a particular value. A quantity given as about a particular value may be exactly that particular value. For example, unless otherwise clear to one of skill in the art in the context in which it is used and described herein, an amount having a value of about 1 means that the amount has a value between 0.9 and 1.1, and may even be 1.

[0064] All references, patents, or patent applications referenced above are hereby incorporated by reference in their entirety. In the event of any inconsistency or contradiction between any of the incorporated references and this application, the information in the foregoing description shall prevail.

[0065] Descriptions of elements in the drawings should be understood to apply equally to corresponding elements in other drawings unless otherwise indicated. Although specific embodiments have been illustrated and described herein, those skilled in the art will appreciate that the specific embodiments illustrated and described may be replaced by various alternative and / or equivalent embodiments without departing from the scope of the present disclosure. The present application is intended to cover any adaptations, or variations, or combinations of the specific embodiments discussed herein. Accordingly, the present disclosure is intended to be limited only by the claims and the equivalents thereof.

Claims

1. A reflective polarizer comprising a plurality of optical repeat units disposed between a first skin layer and a second skin layer, each optical repeat unit comprising at least one polymer A layer, at least two B layers, and at least one polymer C layer, each pair of adjacent A and C layers having at least one of the two B layers disposed between the adjacent A layer and the C layer, a total number of the A layers and the C layers in the plurality of optical repeat units disposed between the first skin layer and the second skin layer being less than about 400, each of the A and C layers has an average thickness of about 50 nm to about 500 nm, each of the B layers has an average thickness less than about 50 nm, each of the first and second skin layers has an average thickness greater than about 500 nm, and the reflective polarizer has an average thickness less than about 20 micrometers; and for each of a first angle of incidence less than about 5 degrees and a second angle of incidence greater than about 40 degrees for light incident on the reflective polarizer at an incidence plane, and for a visible wavelength range spanning from about 420 nm to about 680 nm, the plurality of optical repeating units when the in-plane first direction of the reflective polarizer is in the plane of incidence, the polarization state is less than about 10% for an s-polarized state; and when the in-plane orthogonal second direction of the reflective polarizer is in the plane of incidence, the polarization state is greater than about 65% for a p-polarized state. A reflective polarizer having an average light transmission.

2. 2. The reflective polarizer of claim 1 , wherein when the second in-plane direction of the reflective polarizer is in the plane of incidence, for the visible wavelength range and the p-polarization state, the plurality of optical repeating units have average optical transmissions T1 and T2 for the respective first and second angles of incidence, where T2 is at least 5% greater than T1.

3. 2. The reflective polarizer of claim 1, wherein the plurality of optical repeating units have an average light transmission of greater than about 40% for each of the first angle of incidence and the second angle of incidence, for the s polarization state and the first direction in the plane of incidence and for the p polarization state and the second direction in the plane of incidence, and for an infrared wavelength range spanning from about 750 nm to about 1200 nm.

4. 2. The reflective polarizer of claim 1, wherein the plurality of optical repeating units have an average light transmission of greater than about 40% for each of the first and second angles of incidence, for each of the s and p polarization states, for each of the first and second directions in the plane of incidence, and for an infrared wavelength range spanning from about 750 nm to about 1200 nm.

5. 2. The reflective polarizer of claim 1, wherein for the first direction in the plane of incidence and for the s-polarization state, the plurality of optical repeat units have first and second optical transmittances versus wavelength for the respective first and second angles of incidence, the first and second optical transmittances including respective first and second transmission band edges, and a best linear fit to each of the first and second band edges over at least a range of wavelengths along the transmission band edges where the optical transmittance increases from about 10% to about 50% has a positive slope of greater than about 1.3% / nm.

6. Each polymer A layer comprises a polyethylene naphthalate, polyethylene terephthalate, or polyhexylethylene naphthalate copolymer, and each polymer C layer comprises syndiotactic polystyrene, terpolymers of tetrafluoroethylene, hexafluoropropylene and vinylidene fluoride; Polymethyl methacrylate, a copolymer of methyl methacrylate and ethyl acrylate, or Copolyethylene naphthalate terephthalate copolymer, The reflective polarizer of any one of claims 1 to 5, comprising:

7. 1. A multilayer optical film comprising a plurality of optical repeating units, the optical repeating units in the plurality of optical repeating units totaling less than about 175 in number and having a total average thickness of less than about 20 micrometers, each of the optical repeating units comprising at least four individual layers, at least a first and a second individual layer of the at least four individual layers of each of the optical repeating units having the same respective refractive indices nx1 and nx2 along an in-plane x-direction, respective refractive indices ny1 and ny2 along an in-plane y-direction orthogonal to the x-direction, and respective refractive indices nz1 and nz2 along a z-direction orthogonal to the x-direction and the y-direction, and for at least one wavelength in a visible wavelength range spanning from about 420 nm to about 680 nm: nx1 is at least 0.15 greater than at least one of ny1 and nz1; The magnitude of the maximum difference between nx2, ny2, and nz2 is less than 0.15; nx1 is at least 0.15 greater than nx2; at least a third layer of the at least four individual layers of each of the optical repeating units has an average thickness of less than about 50 nm, and an interlayer adhesion of the individual layers in the plurality of optical repeating units is at least about 14 grams / inch when measured at a 90 degree peel angle. Multilayer optical films.

8. 8. The multilayer optical film of claim 7, wherein the at least the third layer has respective refractive indices nx3, ny3, and nz3 along the respective x, y, and z directions, and wherein nx2 is at least 0.005 greater than nx3 or nx3 is at least 0.05 greater than nx2 for the at least one wavelength.

9. 1. A multilayer optical film comprising a plurality of optical repeating units, the optical repeating units in the plurality of optical repeating units totaling less than about 175 in number and having a total average thickness of less than about 20 micrometers, each of the optical repeating units comprising at least four individual layers, at least a first and a second individual layer of the at least four individual layers of each of the optical repeating units having the same respective refractive indices nx1 and nx2 along an in-plane x-direction, respective refractive indices ny1 and ny2 along an in-plane y-direction orthogonal to the x-direction, and respective refractive indices nz1 and nz2 along a z-direction orthogonal to the x-direction and the y-direction, and for at least one wavelength in a visible wavelength range spanning from about 420 nm to about 680 nm: nx1 is at least 0.15 greater than at least one of ny1 and nz1; nx2 is smaller than at least one of ny2 and nz2; nx1 is at least 0.15 greater than nx2; the interlayer adhesion of the individual layers in the plurality of optical repeating units is at least about 14 grams / inch when measured at a 90 degree peel angle; Multilayer optical films.

10. 10. The multilayer optical film of claim 9, wherein for the at least one wavelength, nx2 is at least 0.005 less than ny2.

11. 10. The multilayer optical film of claim 9, wherein for the at least one wavelength, the magnitude of the difference between nx2 and ny2 is less than 0.

005.

12. 1. A multilayer optical film comprising a plurality of optical repeating units, the optical repeating units in the plurality of optical repeating units totaling less than about 175 in number and having a total average thickness of less than about 20 micrometers, each of the optical repeating units comprising at least four individual layers, at least a first and a second individual layer of the at least four individual layers of each of the optical repeating units having the same respective refractive indices nx1 and nx2 along an in-plane x-direction, respective refractive indices ny1 and ny2 along an in-plane y-direction orthogonal to the x-direction, and respective refractive indices nz1 and nz2 along a z-direction orthogonal to the x-direction and the y-direction, and for at least one wavelength in a visible wavelength range spanning from about 420 nm to about 680 nm: The magnitude of the maximum difference between nx1, ny1, and nz1 is less than 0.05; nx2 is smaller than at least one of ny2 and nz2; nx1 is at least 0.07 greater than nx2; at least a third layer of the at least four individual layers of each of the optical repeating units has an average thickness of less than about 50 nm, and an interlayer adhesion of the individual layers in the plurality of optical repeating units is at least about 14 grams / inch when measured at a 90 degree peel angle. Multilayer optical films.

13. 13. The multilayer optical film of claim 12, wherein the interlayer adhesion of the individual layers in the plurality of optical repeating units is greater than about 20 grams / inch when measured at a 90 degree peel angle.

14. 1. A multilayer optical mirror comprising a plurality of optical repeating units, the optical repeating units in the plurality of optical repeating units totaling less than about 200 in number and having a total average thickness of less than about 20 micrometers, each of the optical repeating units including at least four sequentially arranged first through fourth discrete layers, the first discrete layer and the third discrete layer of each of the optical repeating units having the same respective refractive indices nx1 and nx2 along an in-plane x-direction, ny1 and ny2 respectively along an in-plane y-direction orthogonal to the x-direction, and nz1 and nz2 respectively along a z-direction orthogonal to the x-direction and the y-direction, and for at least one wavelength in a visible wavelength range spanning from about 420 nm to about 680 nm: nx1 and ny1 are at least 0.1 greater than nx2 and ny2, respectively; nz2 is at least 0.05 greater than nz1; For light incident on the multilayer optical mirror, for each of mutually orthogonal first and second polarization states, and for the visible wavelength range, the plurality of optical repeating units have an average optical transmittance T1 for a first angle of incidence less than about 5 degrees, and an average optical transmittance T2 for a second angle of incidence greater than about 40 degrees, such that T1 / T2≧1.

2. Multilayer optical mirror.

15. 15. The multilayer optical mirror of claim 14, wherein for each of said optical repeating units, the average thickness of each of said second discrete layers and said fourth discrete layers is less than about 20 nm.

Images