Optical film and optical system including same

Abstract

An optical film includes a plurality of alternating first and second layers. Differences of indices of refraction between the first and second layers along a first direction has a magnitude Dny. A dispersion of Dny as a function of wavelength has a valley within a blue-green wavelength range extending from about 420 nm to about 560 nm. The valley includes a minimum at a minimum wavelength. For a substantially normally incident light, a first wavelength range extending from about 420 nm to the minimum wavelength, and a second wavelength range extending from the minimum wavelength to about 750 nm, the plurality of alternating polymeric first and second layers has an optical reflectance Rp when the incident light is polarized along the second direction, where Rp has an average value of less than about 1% in the first wavelength range and less than about 0.5% in the second wavelength range.

Description

[0001] OPTICAL FILM AND OPTICAL SYSTEM INCLUDING SAME

[0002] TECHNICAL FIELD

[0003] The present description relates generally to optical films, such as reflective polarizer films, and optical systems including an optical film.

[0004] BACKGROUND

[0005] An optical film can include polymeric interference layers for providing reflection for at least one polarization state in a desired wavelength range. An optical system can include the optical film.

[0006] SUMMARY

[0007] In some aspects, the present description provides an optical film including a plurality of alternating polymeric first and second interference layers numbering greater than 10 in total, where each of the first and second interference layers can have an average thickness of less than about 500 nm. Differences of indices of refraction between the first and second interference layers along an in-plane same first direction and an orthogonal in-plane same second direction have respective magnitudes Dnx and Dny. A dispersion of Dny as a function of wavelength has a valley between a smaller first and a larger second wavelengths within a blue-green wavelength range extending from about 420 nm to about 560 nm. The valley includes a minimum at a minimum wavelength and a corresponding minimum value of less than about 0.002. Dny is greater than about 0.001 at each of the first and second wavelengths, such that, for a substantially normally incident light, a first wavelength range extending from about 420 nm to the minimum wavelength, and a second wavelength range extending from the minimum wavelength to about 750 nm, the plurality of alternating polymeric first and second interference layers has an optical reflectance Rp when the incident light is polarized along the second direction, where Rp has an average value of less than about 1% in the first wavelength range and less than about 0.5% in the second wavelength range.

[0008] In some aspects, the present description provides an optical film including a plurality of alternating polymeric different first and second layers. A difference of indices of refraction between the first and second layers along an in-plane same pass direction has a magnitude Dny, where a dispersion of Dny as a function of wavelength includes a global minimum at a minimum wavelength, such that, for a substantially normally incident light, a first wavelength range extending from about 400 nm to the minimum wavelength, and a second wavelength range extending from the minimum wavelength to about 750 nm, the plurality of alternating polymeric first and second layers has: an optical reflectance Rp when the incident light is polarized along the pass direction, where Rp can have a global maximum of greater than about 0.5% in the first wavelength range, and an average value of less than about 2% in the second wavelength range; and an optical transmittance Ts when the incident light is polarized along an in-plane block direction orthogonal to the pass direction, where Ts has an average value of less than about 1% in an extended wavelength range extending from about 400 nm to about 750 nm.

[0009] In some aspects, the present description provides an optical film including a plurality of alternating polymeric first and second layers numbering greater than 10 in total, where each of the first and second layers can have an average thickness of less than about 500 nm, such that for substantially normally incident light, the plurality of alternating polymeric first and second layers has: an average optical transmittance Ts for a first polarization state of less than about 2% in a blue-green wavelength range extending from about 420 nm to about 560 nm; and an optical reflectance Rp for a second polarization state orthogonal to the first polarization state, where Rp has a minimum in the blue-green wavelength range at a minimum wavelength. For a first wavelength range extending from about 420 nm to the minimum wavelength, a second wavelength range extending from the minimum wavelength to about 560 nm, and a third wavelength range extending from about 560 nm to about 750 nm, Rp can have an average value of less than about 0.9% in each of the first, second and third wavelength ranges.

[0010] In some aspects, the present description provides an optical system including a display, at least one lens, a partial reflector and a reflective polarizer defining an optical cavity therebetween, and a retarder layer disposed in the optical cavity. The optical system can be configured to form a virtual image of an image emitted by the display for viewing by a viewer. The reflective polarizer includes a plurality of alternating polymeric different first and second layers. A difference of indices of refraction between the first and second layers along an in-plane same pass direction has a magnitude Dny. A dispersion of Dny as a function of wavelength has a global minimum at a minimum wavelength disposed between about 420 nm and about 560 nm, such that for a substantially normally incident light, a first wavelength range extending from about 420 nm to the minimum wavelength, and a second wavelength range extending from the minimum wavelength to about 750 nm, the plurality of alternating polymeric first and second layers has an optical reflectance Rp when the incident light is polarized along the pass direction, wherein Rp has an average value of less than about 1% in the first wavelength range and less than about 0.5% in the second wavelength range.

[0011] These and other aspects will be apparent from the following detailed description. In no event, however, should this brief summary be construed to limit the claimable subject matter.

[0012] BRIEF DESCRIPTION OF THE DRAWINGS

[0013] FIG. 1 is a schematic cross-sectional view of an optical film, according to some embodiments.

[0014] FIG. 2 is a plot of refractive indices of first and second layers along a pass direction, according to some embodiments.

[0015] FIG. 3 is a plot of refractive indices of first and second layers along a block direction, according to some embodiments.

[0016] FIGS. 4-5 are plots of magnitudes of differences in refractive indices of first and second layers along pass and block directions, according to some embodiments. FIGS. 6-7 are plots of reflectance versus wavelength for substantially normally incident light polarized along a pass direction and of magnitudes of differences in refractive indices of first and second layers along the pass direction, according to some embodiments.

[0017] FIG. 8 is a plot of transmittance versus wavelength for substantially normally incident light polarized along a block direction and of magnitudes of differences in refractive indices of first and second layers along the block direction, according to some embodiments.

[0018] FIG. 9 is a schematic cross-sectional view of an optical film after it has been scored, according to some embodiments.

[0019] FIG. 10 is a schematic cross-sectional view of an optical construction, according to some embodiments.

[0020] FIG. 11 is a schematic cross-sectional view of an optical system, according to some embodiments.

[0021] DETAILED DESCRIPTION

[0022] In the following description, reference is made to the accompanying drawings that 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 description. The following detailed description, therefore, is not to be taken in a limiting sense.

[0023] As is known in the art, multilayer optical films including alternating polymeric layers can be used to provide desired reflection and transmission in desired wavelength ranges and polarization states by suitable selection of layer thicknesses and refractive index differences. Multilayer optical films and methods of making multilayer optical films are described in U.S. Pat. Nos. 5,882,774 (Jonza et al.); 6,783,349 (Neavin et al.); 6,949,212 (Merrill et al.); 6,967,778 (Wheatley et al.); 9,162,406 (Neavin et al.); and 11,493,677 (Haag et al ), for example. A multilayer optical film can be a reflective polarizer substantially reflecting a first polarization state (block state) and substantially transmitting a second polarization state (pass state).

[0024] An optical system can utilize a reflective polarizer and a partial reflector with a retarder therebetween to provide a folded optical path as generally described in U.S. Pat. No. 10,678,052 (Ouderkirk, et al ), for example. In such optical systems, it can be desired to minimize pass state reflectance of the reflective polarizer. It has been found that even a small pass state reflectance can result in undesired ghost images, for example. Further, it has been found that such problems caused by undesired pass state reflectance is particularly problematic when the reflective polarizer is disposed between bonded lenses. However, it has been found that it is difficult to achieve a very low pass state reflectance throughout a visible wavelength range, for example, due to a difference in dispersion of the refractive index with wavelength of the first and second layers of a plurality of alternating first and second layers of a reflective polarizer when conventional material choices are made for the first and second layers. The first layers can be higher index (higher refractive index along the block axis) optical (HIO) layers and the second layers can be lower index (lower index along the block axis) optical (LIO) layers.

[0025] According to some embodiments of the present description, it has been found that materials for the LIO layers can be selected to give a dispersion of pass state refractive indices versus wavelength that is closer to that of the HIO layers than conventional materials. This allows the refractive indices along the pass direction of the HIO and LIO layers to be substantially matched throughout a visible wavelength range. In some embodiments, this results in a plot of a magnitude of the difference in the refractive indices (Dny) along the pass direction having a valley in a blue-green wavelength range and / or results in a reflectance (Rp) of the plurality of HIO and LIO layers for substantially normally incident light having a minimum in the blue-green wavelength range. For example, the valley in Dny and / or the minimum in Rp can result from the refractive indices along the pass direction of the HIO and LIO layers crossing in a blue-green wavelength range. In some embodiments, a low pass state reflectance is achieved throughout at least a visible wavelength range. The low pass state reflectance can be characterized in low reflectance in at least one, two, or three different wavelength ranges, according to some embodiments. Another consequence of the approaches described for achieving the reduced overall pass state reflectance, according to some embodiments, is a global maximum of Rp occurring in a blue or blue-green wavelength range.

[0026] FIG. 1 is a schematic cross-sectional view of an optical film 200, according to some embodiments. The optical film 200 includes a plurality of alternating layers 10, 11. In some embodiments, the plurality of layers 10,11 may number greater than 10, 20, 30, 40, 50, 80, 100, 150, 200, 300, 400, 500, 600, or 700 in total. The total number of layers in the plurality of layers 10, 11 can be up to 10000, 5000, 2000, 1000, or 800, for example. Each of the layers in the plurality of layers 10, 11 can have an average thickness less than about 500, 450, 400, 350, 300, 250, 200, 150, or 100 nm, for example. The average thicknesses can be at least about 20, 30, 40, 50, or 60 nm, for example. The layers 10, 11 can be polymeric layers and / or can be interference layers which may be described as layers reflecting or transmitting light primarily by optical interference. Interference layers may be described as reflecting or transmitting light primarily by optical interference when the reflectance and transmittance of the interference layers can be reasonably described by optical interference or reasonably accurately modeled as resulting from optical interference.

[0027] In some embodiments, the plurality of layers 10, 11 are disposed between first and second skin layers 124 and 126. In some embodiments, each of the first and second skin layers 124 and 126 has an average thickness of greater than about 400, 500, 600, 700, 800, 900, 1000, 1250, 1500, 1750, or 2000 nm. The average thickness of each of the skin layers can be up to about 150, 100, 50, 30, 20, or 10 microns, for example. As would be appreciated by those of ordinary skill in the art, the optical film 200 may optionally include other layers (e.g., protective boundary layers) that may each have an average thickness in any of the ranges described for the skin layers 124, 126. In some embodiments, the optical film 200 is a reflective polarizer. In some embodiments, for substantially normally incident (e.g., within 30, 20, 10, or 5 degrees of normally incident) light 12 and for a wavelength range extending at least from about 420 nm to about 680 nm, the optical film 200, substantially reflects (e.g., an average optical reflectance of at least 60, 70, 80, 90, 95, 98, or 99%) a first polarization state 141 (block state) and substantially transmits (e.g, an average optical transmittance of at least 60, 70, 80, 85, or 90%) a second polarization state 142 (pass state). Reflectance for a pass polarization state for an optical film 200 or for a plurality of layers 10, 11 is schematically illustrated in FIGS. 6-7, for example. Transmittance for a block polarization state for an optical film 200 or for a plurality of layers 10, 11 is schematically illustrated in FIG. 8, for example. Optical absorption is often negligible, so that the transmittance and reflectance can be, to a good approximation, related as transmittance equals about 100 percent minus the reflectance. The first and second polarization states 141 and 142 of the substantially normally incident light 12 define respective first and second direction (x- and y-directions, respectively, referring to the illustrated x-y-z coordinate system) along which refractive indices may be specified. Reflectance and transmittance of an optical film can be understood to be immersed reflectance and transmittance as determined with the optical film immersed between layers (e.g., glass layers) having a refractive index of 1.51 (e.g., at a wavelength of 633 nm). The immersed reflectance and transmittance of the optical film is typically a good approximation for the reflectance and transmittance of the plurality of layers 10, 11.

[0028] Suitable materials for the various layers of the optical film 200 include polyethylene naphthalate (PEN), polyethylene terephthalate (PET), polycarbonate, copolyesters, and blends or copolymers thereof. Other suitable materials are described in the multilayer optical film references provided elsewhere herein. In some embodiments, the HIO layers (e.g., the first layers 10) can be coPEN 90 / 10 (also referred to as Low Melt PEN or LMPEN) layers as described in U.S. Pat. No. 6,946,188 (Hebrink et al.), for example, and the LIO layers (e.g., the second layers 11) can be a blend of coPEN 90 / 10 and at least one other polyester or other polymer, for example.

[0029] CoPEN 90 / 10 can be described a copolyester where carboxylate units of the copolyester comprises 90 mole percent naphthalate units and 10 mole percent terephthalate units. More generally, the copolyester can include other ratios of naphthalate and terephthalate units. For example, in some embodiments, carboxylate units of the copolyester can include about 80 to 95 mole percent naphthalate units and about 5 to 20 mole percent terephthalate units. Such copolyesters may be denoted coPEN N / 100-N where N is the mole percent naphthalate units and 100-N is the mole percent terephthalate units.

[0030] The at least one other polyester or other polymer of the LIO layers can include a first glycol- modified PET that can be selected to increase the dispersion of refractive index with wavelength of the LIO layers compared to that of convention films. Such first glycol-modified PETs generally have a different composition than PCTg and EASTAR GN071 (both available from Eastman Chemical Company, Knoxville, TN), for example. The at least one other polyester or other polymer of the LIO layers can optionally further include a second glycol-modified PET, such as PCTg or EASTAR GN071, and / or can include coPET 80 / 20. CoPET 80 / 20 can be described a copolyester where carboxylate units of the copolyester comprises 80 mole percent terephthalate units and 20 mole percent isophthalate units. More generally, the copolyester can include other ratios of terephthalate and isophthalate units. For example, in some embodiments, carboxylate units of the copolyester can include about 70 to 90 mole percent terephthalate units and about 10 to 30 mole percent isophthalate units. Such copolyesters may be denoted coPET M / 100-N where M is the mole percent terephthalate units and 100-M is the mole percent isophthalate units. Glycol-modified PET can be described as PET with at least some of the glycol units replaced with different units such as those derived from cyclohexanedimethanol. Suitable glycol-modified PETs for use as the first glycol-modified PET include those that include plant-derived biomass components (e.g., isosorbide) as such glycol-modified PETs have been found to result in increased dispersion compared to PCTg and EASTAR GN071, for example. Such glycol-modified PETs can include isosorbide-derived groups and can have glass transition temperatures (e.g., about 120 degrees C) higher than those of PCTg and EASTAR GN071 (e.g., about 80 degrees C), for example. Suitable such glycol-modified PETs include those available from SK Chemicals (Gyeonggi-do, South Korea) under the tradename ECOZEN, such as the ECOZEN T-series which includes ECOZEN T120.

[0031] In some embodiments, for at least one wavelength in a wavelength range of about 400 nm to about 750 nm, the first interference layers 10 have an in-plane birefringence of greater than about 0.05 and the second interference layers 11 have an in-plane birefringence of less than about 0.04. The first interference layers 10 can have an in-plane birefringence of greater than about 0.06, 0.07, 0.08, 0.09, 0.1, 0.12, 0.14, 0.16, 0.18, or 0.2 for the at least one wavelength. This in-plane birefringence forthe at least one wavelength can be up to about 0.45, 0.4, 0.35, or 0.3, for example. The second interference layers 11 have an in-plane birefringence of less than about 0.035, 0.03, 0.025, 0.02, 0.015, 0.01, or 0.005 forthe at least one wavelength.

[0032] In some embodiments, the second interference layers 11 comprise a blend of at least first and second copolyesters, where the first copolyester comprises a copolymer of polyethylene naphthalate (PEN) and polyethylene terephthalate (PET), and the second copolyester comprises a first glycol- modified PET (e.g., ECOZEN T120). In some embodiments, the blend of at least first and second copolyesters further comprises a second glycol-modified PET (e g., EASTAR GN071 or PCTg) having a different composition than the first glycol-modified PET. In some embodiments, the blend of at least first and second copolyesters comprises the first glycol-modified PET at a weight percent in a range of 50 to 95 weight percent. The weight percent of the first glycol-modified PET can be at least 55, 60, 76, or 70 weight percent. The weight percent of the first glycol-modified PET can be up to 90, 85, or 80 weight percent. In some embodiments, the first glycol-modified PET comprises isosorbide-derived groups. In some embodiments, the first glycol-modified PET, but not the second glycol-modified PET, comprises isosorbide-derived groups. In some embodiments, carboxylate units of the first copolyester comprises about 80 to 95 mole percent naphthalate units and about 5 to 20 mole percent terephthalate units. In some embodiments, the blend of at least first and second copolyesters further comprises a third copolyester, where the third copolyester comprises a copolymer of polyethylene terephthalate (PET) and polyethylene isophthalate (PEI). In some embodiments, carboxylate units of the third copolyester comprises about 70 to 90 mole percent terephthalate units and about 10 to 30 mole percent isophthalate units. In some embodiments, the second interference layers 11 comprise about 5 to about 25 weight percent isosorbide units based on a total weight of the second interference layers 11. It will be understood that blends of polymers and copolymers can be copolymerized blends (e.g., a blend of first and second copolyesters may undergo a transesterification reaction during an extrusion process resulting in a copolymer of the first and second copolyesters; such a blend may be referred to as a copolymerized blend).

[0033] In some embodiments, the first and second glycol-modified PETs have respective first and second glass transition temperatures, where the first glass transition temperature at least 5, 10, 15, 20, 25, 30 or 35 degrees C greater than the second glass transition temperature. In some embodiments, the first glass transition temperature is in a range of 110 to 130 degrees C and the second glass transition temperature is in a range of 70 to 90 degrees C. In some embodiments, the second interference layers 11 have a glass transition temperature of at least 100 degrees C. Glass transition temperature can be determined by Differential Scanning Calorimetry (DSC) according to ASTM E1356-08 (Reapproved 2014), “Standard Test Method for Assignment of the Glass Transition Temperatures by Differential Scanning Calorimetry”, for example.

[0034] FIG. 2 is a plot of refractive indices of first and second layers along a pass direction (e.g., y- direction or second direction), according to some embodiments. FIG. 3 is a plot of refractive indices of first and second layers along a block direction (e.g., x-direction or first direction), according to some embodiments, nxl and nyl are refractive indices along first (block) and second (pass) directions for HIO layers (e.g., first layers 10), and nx2 and ny2 are refractive indices along first (block) and second (pass) directions for LIO layers (e.g., second layers 11). The indices for second layers (labeled Coml) of a first comparative optical film are also shown. The exemplary and first comparative optical films utilize the same first layers 10 but utilize second layers 11 having different compositions. In the embodiment illustrated in FIG. 2, the curves for nyl and ny2 cross at a wavelength 24a of about 479 nm. In the embodiment illustrated in FIG. 3, the curves for nxl and nx2 are separated by at least about 0.2 throughout a wavelength range extending at least from about 400 nm to about 750 nm.

[0035] The shapes of the curves in FIG. 2, for example, can be characterized in terms of V-numbers which are related to Abbe numbers but can be defined using refractive indices at different wavelengths. V-numbers or Abbe numbers are commonly used to characterize the chromaticity of glass lenses, for example. V-numbers are defined herein as (nyb-l) / (nya-nyc), where nya, nyb and nyc are refractive indices along the second direction at respective wavelengths of 450 nm, 550 nm and 650 nm. In FIG. 2, nya, nyb, and nyc values are schematically illustrated as nyal, nybl, nycl and nya2, nyb2, nyc2 for the first and second layers 10 and 11 (having respective refractive index curves nyl and ny2), respectively. It has been found, according to some embodiments, that selecting materials for the HIO and LIO layers such that the V-numbers of the layers are closer to one another than for conventional films can result in improved (reduced) pass state reflectance over a visible wavelength range, for example. The HIO layers of conventional multilayer optical films often have a higher dispersion (lower V-number) than that of the LIO layers. Accordingly, in some embodiments, the material for the LIO layers is selected to result in higher dispersion (lower V-number) than that of conventional LIO materials. In some embodiments, the first and second (e.g., interference) layers 10 and 11 have respective first and second V-numbers VI and V2, where a magnitude of a difference between VI and V2 is less than about 5, 4.5, 4, 3.5, 3, 2.9, 2.8, 2.7, or 2.6. For example, forthe nyl and ny2 curves of FIG. 2, |V1 - V2| is about 2.58, while for the nyl and ny2(Coml) curves of FIG. 2, |V1 - V2| is about 5.19. In some embodiments, the second (e.g., interference) layers 11 (e g., LIO layers) have a V-number less than about 20, 19.8, 19.6, 19.4, 19.2, 19, 18.8, 18.7, 18.6, or 18.5. For example, the V-number forthe ny2 curve of FIG. 2 is about 18.4 while the V-number for the ny2(Coml) curve of FIG. 2 is about 21.0. The second layers 11 can have a V-number as low as about 10, 12, 14, or 15, for example.

[0036] FIGS. 4-5 are plots of magnitudes (Dny and Dnx) of differences in refractive indices of first and second layers along pass (Dny) and block (Dnx) directions, according to some embodiments. Curves for the exemplary and first comparative optical films of FIGS. 2-3 are shown and a curve Dny(Com2) for a second comparative (Com2) optical film is also shown. Dnx for the second comparative optical film can be the same or about the same as Dnx forthe first comparative optical film. Dny values are along the left axis and Dnx values are along the right axis.

[0037] FIGS. 6-7 are plots of reflectance versus wavelength for substantially normally incident light polarized along a pass direction and of magnitudes of differences in refractive indices of first and second layers along the pass direction, according to some embodiments. Reflectance values are along the left axes and Dny values are shown along the right axes.

[0038] FIG. 8 is a plot of transmittance versus wavelength for substantially normally incident light polarized along a block direction and of magnitudes of differences in refractive indices of first and second layers along the block direction, according to some embodiments. Transmittance values are along the left axis and Dnx values are shown along the right axis.

[0039] The reflectances and transmittances of FIGS. 7-8 are immersed reflectances and transmittance s determined for the optical film disposed between glass layers each having a refractive index of 1.51 for at least one wavelength in a range of about 420 nm to about 680 nm (e.g., a wavelength of about 633 nm). The immersed reflectance and immersed transmittance of the optical film typically correspond, to a good approximation, to reflectance and transmittance of the plurality of layers 10, 11 of the optical film.

[0040] The first and second comparative optical films (Coml and Com2) having properties illustrated in FIGS. 2-8 can be central end edge portions of a same optical film where manufacturing variations in the film between edge and center portions of the film account for the differences between the first and second comparative films. A third comparative film (Com3) can be a different edge portion of another film made similarly. These exemplary (Ex. 1 corresponding to curves not labeled with Com#) and comparative films (Coml, Com2, and Com3) each included a total of about 650 layers 10, 11 and included HIO layers composed of coPEN 90 / 10 and LIO layers composed of different blends of coPEN 90 / 10 and different glycol-modified PETs or other copolyesters as described further elsewhere herein. The blends for the LIO layers of these figures were selected to produce the refractive indices shown in FIGS. 2-3. For example, the exemplary optical fdm Ex. 1 included low index layers composed of about 75 weight percent ECOZEN T120, about 15 weight percent coPEN 90 / 10, and about 10 weight percent coPET 80 / 20. The layers of the optical fdm 200 can alternatively have any of the compositions described elsewhere herein and can include a total number of layers in any of the ranges described elsewhere herein.

[0041] The minimum wavelength 24a for these exemplary and comparative fdms are provided in the table below.

[0042] Average pass state reflectances (Rp) and block state transmittance s (Ts) in various wavelength ranges for the various films are provided in the table below.

[0043] In some embodiments, an optical film 200 includes a plurality of alternating polymeric first (10) and second (11) interference layers numbering greater than 10 in total (or in a range described elsewhere herein), where each of the first and second interference layers has an average thickness of less than about 500 nm (or in a range described elsewhere herein). In some embodiments, differences of indices of refraction between the first and second interference layers along an in-plane same first direction (e.g., x- direction) and an orthogonal in-plane same second direction (e.g., y-direction) have respective magnitudes Dnx and Dny. A dispersion 20 of Dny as a function of wavelength has a valley 21 between a smaller first (22a) and a larger second (22b) wavelengths within a blue-green wavelength range 23 extending from about 420 nm to about 560 nm (see, e.g., FIG. 5). The first wavelength 22a can be in a range of about 435 nm to about 475 nm, or about 445 nm to about 465 nm, for example. The second wavelength 22b can be in a range of about 500 nm to about 550 nm or about 510 nm to about 530 nm, for example. The valley 21 includes a minimum 24 at a minimum wavelength 24a and a corresponding minimum value 24b of less than about 0.002, or 0.0015, or 0.001, or 0.0005, or 0.0004, or 0.0003, or 0.0002, or 0.0001. The minimum value 24b can be zero. For example, the valley 21 can result from the curves ny 1 and ny2 crossing at the minimum wavelength 24a so that the minimum magnitude of the difference between the curves is zero at the minimum wavelength 24a. More generally, the valley 21 can result from the curves ny 1 and ny2 approaching one another, whether or not the curves cross. In some embodiments, Dny is greater than about 0.001, or 0.0012, or 0.0014, or 0.0016, or 0.0018, or 0.002 at each of the first and second wavelengths 22a and 22b. Dny can be greater than the minimum value 24b by at least about 0.001, or 0.0012, or 0.0014, or 0.0016, or 0.0018, or 0.002 at each of the first and second wavelengths 22a and 22b. Dny may be less than about 0.006, or 0.0055, or 0.005, or 0.0045, or 0.004, or 0.0035 at each of the first and second wavelengths 22a and 22b. In some embodiments, the minimum wavelength 24a is in a wavelength range of about 425 nm to about 550 nm, or about 430 to 540 nm, or about 435 to 530 nm, or about 440 to 520 nm, for example.

[0044] In some embodiments, Dnx is greater than about 0.05, 0.06, 0.07, 0.08, 0.09, 0.1, 0.12, 0.14, 0.16, 0.18, 0.2, or 0.25 at the minimum wavelength 24a. In some embodiments, Dnx is greater than about 0.04, 0.05, 0.06, 0.07, 0.08, 0.09, 0.1, 0.12, 0.14, 0.16, 0.18, or 0.2 for each wavelength in the blue-green wavelength range 23. Dnx at the minimum wavelength 24a, and / or for each wavelength in the blue-green wavelength range 23, can be up to about 0.45, 0.4, 0.35, or 0.3, for example. In some embodiments, the optical film 200 is such that, for a substantially normally incident light 12, a first wavelength range 25a extending from about 420 nm to the minimum wavelength 24a, and a second wavelength range 26b extending from the minimum wavelength 24a to about 750 nm (see, e.g., FIGS. 6-7), the plurality of alternating polymeric first and second interference layers 10, 11 has an optical reflectance Rp when the incident light is polarized along the second direction, where Rp has an average value of less than about 1% in the first wavelength range 25a and less than about 0.5% in the second wavelength range 26b. In some such embodiments, or in other embodiments, the average value of Rp in the first wavelength range 25a is less than about 0.9%, or 0.8%, or 0.7%, or 0.6%, or 0.5%, or 0.4%, or 0.3%. In some such embodiments, or in other embodiments, the average value of Rp in the second wavelength range 26b is less than about 0.45%, or 0.4%, or 0.35%, or 0.3%, or 0.25%, or 0.2%. The average value of Rp can alternatively, or in addition, be specified in other wavelength ranges (e.g., ranges 25a, 25b, and 25c; or ranges 26a and 26b; or range 28) as described further elsewhere herein.

[0045] In some embodiments, for the substantially normally incident light 12 having the minimum wavelength 24a and polarized along the first direction, the plurality of alternating polymeric first and second interference layers 10, 11 has an optical transmittance Ts of less than about 2%, or 1.75%, or 1.5%, or 1.25%, or 1%, or 0.75%, or 0.5%, or 0.25%, or 0.1%, or 0.075%, or 0.05% (see, e.g., FIG. 8). In some embodiments, for the substantially normally incident light 12 having the minimum wavelength 24a and polarized along the second direction, the optical reflectance Rp is less than about 2%, or 1.75%, or 1.5%, or 1.25%, or 1%, or 0.75%, or 0.5%, or 0.25%, or 0.2%, or 0.15% (see, e.g., FIG. 6-7). In some embodiments, for substantially normally incident light 12 polarized along the first direction, the plurality of alternating first and second polymeric layers 10, 11 has an average optical reflectance greater than about 60, 70, 80, 90, 95, 98, or 99 percent in each of the first and second wavelength ranges 25a and 26b. In some embodiments, for the substantially normally incident light 12 polarized along the first direction, the plurality of alternating polymeric first and second layers has an average optical reflectance of greater than about 60, 70, 80, 90, 95, 98, or 99 percent in a wavelength range extending from about 420 nm to about 680 nm. Since optical absorption is typically negligible, the optical reflectance of substantially normally incident light 12 polarized along the first direction is often 100% - Ts (see, e g., FIG. 8) to a good approximation. In some embodiments, for the substantially normally incident light 12 polarized along the second direction, the optical reflectance Rp has a global maximum 27 of greater than about 0.5%, or 0.6%, or 0.7%, or 0.8%, or 0.9%, or 1%, or 1.1% in a blue wavelength range extending from about 400 nm to about 450 nm. In FIGS. 6 and 7, the global maximum 27 occurs at the wavelength 47 which is in the blue wavelength range. The blue wavelength range can extend from about 400 nm to about 440, 430, or 420 nm. The global maximum in the blue wavelength range can result from the relative increase in ny 1 compared to ny2 in the blue wavelength range (see, e.g., FIG. 2).

[0046] In some embodiments, an optical film 200 includes a plurality of alternating polymeric different first and second layers 10, 11, where a difference of indices of refraction between the first and second layers along an in-plane same pass direction (y-direction) has a magnitude Dny. In some embodiments, a dispersion 20 of Dny as a function of wavelength has a global minimum 24 at a minimum wavelength 24a, such that, for a substantially normally incident light 12, a first wavelength range 26a extending from about 400 nm to the minimum wavelength 24a, and a second wavelength range 26b extending from the minimum wavelength 24a to about 750 nm, the plurality of alternating polymeric first and second layers 10, 11 has: an optical reflectance Rp when the incident light is polarized along the pass direction, where Rp has a global maximum 27 of greater than about 0.5% (or in a range described elsewhere herein), and an average value of less than about 2% in the second wavelength range 26b; and an optical transmittance Ts when the incident light is polarized along an in-plane block direction (x-direction) orthogonal to the pass direction, where Ts has an average value of less than about 1% in an extended wavelength range 28 extending from about 400 nm to about 750 nm. In some such embodiments, or in other embodiments, the optical reflectance Rp when the incident light 12 is polarized along the pass direction, has an average value of less than about 1.75%, or 1.5%, or 1.25%, or 1%, or 0.95%, or 0.9%, or 0.85%, or 0.8%, or 0.75%, or 0.7%, or 0.65%, or 0.6%, or 0.55, or 0.5%, or 0.45%, or 0.4%, or 0.35%, or 0.3%, or 0.25%, or 0.2%, or 0.15% in the second wavelength range 26b. In some such embodiments, or in other embodiments, the optical transmittance Ts when the incident light 12 is polarized along the block direction has an average value of less than about 0.75%, or 0.5%, or 0.25%, or 0.2%, or 0.1%, or 0.075%, or 0.05% in the extended wavelength range 28. In some such embodiments, or in other embodiments, the minimum wavelength 24a is in a blue-green wavelength range 23) extending from about 420 nm to about 560 nm (or in a range described elsewhere herein). In some such embodiments, or in other embodiments, for the substantially normally incident light 12 polarized along the pass direction and for each of a wavelength range 25a extending from about 420 nm to the minimum wavelength, a wavelength range 25b extending from the minimum wavelength to about 560 nm, and a wavelength range 25c extending from about 560 nm to about 750 nm, Rp has an average value of less than about 1%, or 0.95%, or 0.9%, or 0.85%, or 0.8%, or 0.75%, or 0.7%, or 0.65%, or 0.6%, 0.55%, or 0.5%, or 0.45%, or 0.4%, or 0.35%, or 0.3%. In some such embodiments, or in other embodiments, a difference of indices of refraction between the first and second layers 10 and 11 along the block direction (x-direction) has a magnitude Dnx, where Dnx is greater than about 0.05 (or in a range described elsewhere herein) at the minimum wavelength 24a. In some such embodiments, or in other embodiments, for the substantially normally incident light 12 polarized along the block direction, the plurality of alternating polymeric first and second layers 10, 11 has an average optical reflectance of greater than about 60% (or in a range described elsewhere herein) in a wavelength range extending from about 420 nm to about 680 nm.

[0047] In some embodiments, an optical film 200 includes a plurality of alternating polymeric first and second layers 10, 11 numbering greater than 10 (or in a range described elsewhere herein) in total, where each of the first and second layers 10, 11 has an average thickness of less than about 500 nm (or in a range described elsewhere herein), such that for substantially normally incident light 12, the plurality of alternating polymeric first and second layers has: an average optical transmittance Ts for a first polarization state of less than about 2% in a blue-green wavelength range 23 extending from about 420 nm to about 560 nm; and an optical reflectance Rp for a second polarization state orthogonal to the first polarization state, where Rp has a minimum in the blue-green wavelength range 23 at a minimum wavelength (e.g., at or about wavelength 24a), and where for a first wavelength range 25a extending from about 420 nm to the minimum wavelength, a second wavelength range 25b extending from the minimum wavelength to about 560 nm, and a third wavelength range 25c extending from about 560 nm to about 750 nm, Rp has an average value of less than about 0.9%, or 0.85%, or 0.8%, or 0.75%, or 0.7%, or 0.65%, or 0.6%, 0.55%, or 0.5%, or 0.45%, or 0.4%, or 0.35%, or 0.3% in each of the first, second and third wavelength ranges. In some such embodiments, or in other embodiments, the average optical transmittance Ts forthe first polarization state is less than about 1.75%, or 1.5%, or 1.25%, or 1%, or 0.75%, or 0.5%, or 0.25%, or 0.1%, or 0.075%, or 0.05% in the blue-green wavelength range 23. In some such embodiments, or in other embodiments, Rp is less than about 0.5%, or 0.45%, or 0.4%, or 0.35%, or 0.3%, or 0.25%, or 0.2% at the minimum wavelength. In some such embodiments, or in other embodiments, the minimum wavelength is in a range of about 425 nm to about 550 nm, or about 430 to 540 nm, or about 435 to 530 nm, or about 440 to 520 nm, for example. In some such embodiments, or in other embodiments, for substantially normally incident light 12, the plurality of alternating polymeric first and second layers 10, 11 has an average optical reflectance for the first polarization state of greater than about 60, 70, 80, 90, 95, 98, or 99 percent in a wavelength range extending from about 420 nm to about 680 nm. In some such embodiments, or in other embodiments, for substantially normally incident light 12 and the second polarization state, the optical reflectance Rp has a global maximum 27 of greater than about 0.5% (or in a range described elsewhere herein) in a blue wavelength range extending from about 400 nm to about 450 nm (or in a range described elsewhere herein).

[0048] In some embodiments, the optical film 200 comprises a plurality of polymeric layers comprising a plurality of alternating polymeric first and second interference layers and further comprising at least one macrolayer (e.g., 124 and / or 126) having an average thickness of greater than about 500 nm or greater than about 1000 nm (or in another range described from skin layers 124, 126). A marcolayer is generally a layer sufficiently thick that it does not reflect or transmit light primarily by optical interference. A macrolayer may be referred to as an optically thick layer or a non-interference layer, for example.

[0049] FIG. 9 is a schematic cross-sectional view of the optical film 200 after it has been scored (a score 342 that can be formed by cutting with a razor blade, for example, is schematically illustrated), according to some embodiments. The score may extend into the optical film at an angle of about 45 degrees with a normal (z -direction) of the optical film where the score may extend under a tape 344 attached to a major surface of the optical film and pulled in the peel test. A 90 degree peel test with peel force F is schematically illustrated. It has been found, according to some embodiments, that the materials used for the layers 10, 11 to achieve a low pass state reflectance can result in an improved interlayer bonding compared to conventional multilayer optical films. An interlayer bonding of the optical film 200 may be sufficiently strong that delamination via adhesive failure does not occur in a peel test even after the optical film has been scored (e.g., the film may fail via cohesive failure). In some embodiments, when the optical film is scored by cutting through at least some of the plurality of polymeric layers 10, 11, 124, 126 to result in a plurality of scored polymeric layers, then the scored optical film has a delamination resistance of no less than about 200, 300, 400, 500, 600, 700, 800, 900, or 1000 g / in under a 90 degree, 10 in / min peel test.

[0050] FIG. 10 is a schematic cross-sectional view of an optical construction 301, according to some embodiments. The optical construction includes at least first and second lenses 40 and 41 and a reflective polarizer 60 and a retarder layer 80 disposed therebetween. The reflective polarizer 60 can be an optical film 200 described elsewhere herein. The optical construction 301 can be a bonded optical construction where each layer of the construction is bonded to at least one adjacent layer. For example, an (e.g., optically clear) adhesive 45 may bond (e.g., indirectly through other layers) the first and second lenses 40 and 41 together. The optical construction 301 can be considered to be an optical system or can be a portion of an optical system.

[0051] FIG. 11 is a schematic cross-sectional view of an optical system 300, according to some embodiments. In some embodiments, the optical system 300 includes at least one lens 40, 41, a partial reflector 50 and a reflective polarizer 60 defining an optical cavity 70 therebetween, and a retarder layer 80 disposed in the optical cavity. The reflective polarizer 60 can be an optical film 200 described elsewhere herein. The optical system 300 can include a display 30 and can be configured to form a virtual image 32 of an image 31 emitted by the display 30 for viewing by a viewer 43. The display 30, the at least one lens 40, 41, the partial reflector 50, the reflective polarizer 60, and the retarder layer 80 can be disposed along an optical axis 111 of the optical system 300. In some embodiments, the at least one lens includes first and second lenses 40 and 41, and the reflective polarizer is disposed between, and bonded to, the first and second lens. The at least one lens, the reflective polarizer 60, the retarder layer 80 and optionally the partial reflector 50 can be included in a bonded optical construction (e.g., corresponding to optical construction 301, optionally with partial reflector 50 disposed on, and attached to, a major surface of lens 40 opposite lens 41). In some embodiments, the partial reflector 50 has an average optical reflectance in a range of about 20% to about 80%, or about 30% to about 70%, or about 40% to about 60% in a wavelength range extending from about 420 nm to about 680 nm. In some embodiments, the optical system 300 is substantially centered on an optical axis 111.

[0052] In some embodiments, the reflective polarizer 60 includes a plurality of alternating polymeric different first and second layers 10 and 11, where a difference of indices of refraction between the first and second layers 10 and 11 along an in-plane same pass direction (y-direction) has a magnitude Dny. A dispersion 20 of Dny as a function of wavelength can have a global minimum 24 at a minimum wavelength 24a disposed between about 420 nm and about 560 nm, such that for a substantially normally incident light 12, a first wavelength range 25a extending from about 420 nm to the minimum wavelength 24a, and a second wavelength range 26b extending from the minimum wavelength 24a to about 750 nm, the plurality of alternating polymeric first and second layers 10, 11 has an optical reflectance Rp when the incident light is polarized along the pass direction, where Rp has an average value of less than about 1% in the first wavelength range 25a and less than about 0.5% in the second wavelength range 26b. In some such embodiments, or in other embodiments, the average value of Rp is less than about 0.9%, or 0.8%, or 0.7%, or 0.6%, or 0.5%, or 0.4%, or 0.3% in the first wavelength range 25a. In some such embodiments, or in other embodiments, the average value of Rp less than about 0.45%, or 0.4%, or 0.35%, or 0.3%, or 0.25%, or 0.2% in the second wavelength range 26b. In some such embodiments, or in other embodiments, for the substantially normally incident light 12 polarized along the pass direction, the plurality of alternating polymeric first and second layers 10, 11 has global maximum 27 of greater than about 0.5% (or in a range described elsewhere herein) in a blue wavelength range extending from about 400 nm to about 450 nm (or in a range described elsewhere herein). In some such embodiments, or in other embodiments, for the substantially normally incident light 12 polarized along a block direction orthogonal to the pass direction, the plurality of alternating polymeric first and second layers has an average optical reflectance of greater than about 60% (or in a range described elsewhere herein) in a wavelength range extending from about 420 nm to about 680 nm. In some such embodiments, or in other embodiments, a difference of indices of refraction between the first and second layers 10, 11 along an inplane same block direction orthogonal to the pass direction has a magnitude Dnx, where Dnx is greater than about 0.05 (or in a range described elsewhere herein) at the minimum wavelength 24a. In some such embodiments, or in other embodiments, for V-numbers defined as (nyb-l) / (nya-nyc), where nya, nyb and nyc are refractive indices along the second direction at respective wavelengths of 450 nm, 550 nm and 650 nm, the first and second layers have respective first and second V-numbers VI and V2 where a magnitude of a difference between VI and V2 is less than 5 (or in a range described elsewhere herein). In some such embodiments, or in other embodiments, the second layers have a V-number (V2) less than 20 (or in a range described elsewhere herein).

[0053] Terms such as “about” will be understood in the context in which they are used and described in the present description by one of ordinary skill in the art. If the use of “about” as applied to quantities expressing feature sizes, amounts, and physical properties is not otherwise clear to one of ordinary skill in the art in the context in which it is used and described in the present description, “about” will be understood to mean within 5 percent of the specified value. A quantity given as about a specified value can be precisely the specified value. For example, if it is not otherwise clear to one of ordinary skill in the art in the context in which it is used and described in the present description, a quantity having a value of about 1, means that the quantity has a value between 0.95 and 1.05, and that the value could be 1.

[0054] Terms such as “substantially” will be understood in the context in which they are used and described in the present description by one of ordinary skill in the art. If the use of “substantially” with reference to a property or characteristic is not otherwise clear to one of ordinary skill in the art in the context in which it is used and described in the present description and when it would be clear to one of ordinary skill in the art what is meant by an opposite of that property or characteristic, the term “substantially” will be understood to mean that the property or characteristic is exhibited to a greater extent than the opposite of that property or characteristic is exhibited.

[0055] All references, patents, and patent applications referenced in the foregoing are hereby incorporated herein by reference in their entirety in a consistent manner. In the event of inconsistencies or contradictions between portions of the incorporated references and this application, the information in the preceding description shall control.

[0056] Descriptions for elements in figures should be understood to apply equally to corresponding elements in other figures, unless indicated otherwise. Although specific embodiments have been illustrated and described herein, it will be appreciated by those of ordinary skill in the art that a variety of alternate and / or equivalent implementations can be substituted for the specific embodiments shown and described without departing from the scope of the present disclosure. This application is intended to cover any adaptations, or variations, or combinations of the specific embodiments discussed herein. Therefore, it is intended that this disclosure be limited only by the claims and the equivalents thereof.

Claims

What is claimed is:

1. An optical film comprising a plurality of alternating polymeric first and second interference layers numbering greater than 10 in total, each of the first and second interference layers having an average thickness of less than about 500 nm, differences of indices of refraction between the first and second interference layers along an in-plane same first direction and an orthogonal in-plane same second direction having respective magnitudes Dnx and Dny, a dispersion of Dny as a function of wavelength having a valley between a smaller first and a larger second wavelengths within a blue-green wavelength range extending from about 420 nm to about 560 nm, the valley comprising a minimum at a minimum wavelength and a corresponding minimum value of less than about 0.002, Dny being greater than about 0.001 at each of the first and second wavelengths, such that, for a substantially normally incident light, a first wavelength range extending from about 420 nm to the minimum wavelength, and a second wavelength range extending from the minimum wavelength to about 750 nm, the plurality of alternating polymeric first and second interference layers has an optical reflectance Rp when the incident light is polarized along the second direction, wherein Rp has an average value of less than about 1% in the first wavelength range and less than about 0.5% in the second wavelength range.

2. The optical film of claim 1, wherein for the substantially normally incident light having the minimum wavelength and polarized along the first direction, the plurality of alternating polymeric first and second interference layers has an optical transmittance Ts of less than about 2%.

3. The optical film of claim 1, wherein for the substantially normally incident light polarized along the second direction, the optical reflectance Rp has a global maximum of greater than about 0.5% in a blue wavelength range extending from about 400 nm to about 450 nm.

4. The optical film of claim 1, wherein for V-numbers defined as (nyb-l) / (nya-nyc), nya, nyb and nyc being refractive indices along the second direction at respective wavelengths of 450 nm, 550 nm and 650 nm, the first and second interference layers have respective first and second V-numbers VI and V2, a magnitude of a difference between VI and V2 being less than 5.

5. The optical film of claim 1, wherein for at least one wavelength in a wavelength range of about 400 nm to about 750 nm, the first interference layers have an in-plane birefringence of greater than about 0.05 and the second interference layers have an in-plane birefringence of less than about 0.04.

6. The optical film of claim 5, wherein the second interference layers have a V-number less than 20, the V-number being (nyb-l) / (nya-nyc), nya, nyb and nyc being refractive indices of the second interference layers along the second direction at respective wavelengths of 450 nm, 550 nm and 650 nm.

7. The optical film of claim 5, wherein the second interference layers comprise a copolymerized blend of at least first and second copolyesters, the first copolyester comprising a copolymer of polyethylene naphthalate (PEN) and polyethylene terephthalate (PET), the second copolyester comprising a first glycol-modified PET comprising isosorbide-derived groups.

8. An optical film comprising a plurality of alternating polymeric different first and second layers, a difference of indices of refraction between the first and second layers along an in-plane same pass direction having a magnitude Dny, a dispersion of Dny as a function of wavelength comprising a global minimum at a minimum wavelength, such that, for a substantially normally incident light, a first wavelength range extending from about 400 nm to the minimum wavelength, and a second wavelength range extending from the minimum wavelength to about 750 nm, the plurality of alternating polymeric first and second layers has: an optical reflectance Rp when the incident light is polarized along the pass direction, Rp having a global maximum of greater than about 0.5% in the first wavelength range, and an average value of less than about 2% in the second wavelength range; and an optical transmittance Ts when the incident light is polarized along an in-plane block direction orthogonal to the pass direction, Ts having an average value of less than about 1% in an extended wavelength range extending from about 400 nm to about 750 nm.

9. The optical film of claim 8, wherein the minimum wavelength is in a blue-green wavelength range extending from about 420 nm to about 560 nm.

10. The optical film of claim 9, wherein for the substantially normally incident light polarized along the pass direction and for each of a wavelength range extending from about 420 nm to the minimum wavelength, a wavelength range extending from the minimum wavelength to about 560 nm, and a wavelength range extending from about 560 nm to about 750 nm, Rp has an average value of less than about 1%.

11. An optical film comprising a plurality of alternating polymeric first and second layers numbering greater than 10 in total, each of the first and second layers having an average thickness of less than about 500 nm, such that for substantially normally incident light, the plurality of alternating polymeric first and second layers has:an average optical transmittance Ts for a first polarization state of less than about 2% in a bluegreen wavelength range extending from about 420 nm to about 560 nm; and an optical reflectance Rp for a second polarization state orthogonal to the first polarization state, Rp having a minimum in the blue-green wavelength range at a minimum wavelength, wherein for a first wavelength range extending from about 420 nm to the minimum wavelength, a second wavelength range extending from the minimum wavelength to about 560 nm, and a third wavelength range extending from about 560 nm to about 750 nm, Rp has an average value of less than about 0.9% in each of the first, second and third wavelength ranges.

12. The optical film of claim 11, wherein for substantially normally incident light and the second polarization state, the optical reflectance Rp has a global maximum of greater than about 0.5% in a blue wavelength range extending from about 400 nm to about 450 nm.

13. An optical system comprising at least one lens, a partial reflector and a reflective polarizer defining an optical cavity therebetween, and a retarder layer disposed in the optical cavity, the reflective polarizer being an optical film according to any one of claims 1 to 12.

14. An optical system comprising a display, at least one lens, a partial reflector and a reflective polarizer defining an optical cavity therebetween, and a retarder layer disposed in the optical cavity, the optical system configured to form a virtual image of an image emitted by the display for viewing by a viewer, the reflective polarizer comprising a plurality of alternating polymeric different first and second layers, a difference of indices of refraction between the first and second layers along an in-plane same pass direction having a magnitude Dny, a dispersion of Dny as a function of wavelength comprising a global minimum at a minimum wavelength disposed between about 420 nm and about 560 nm, such that for a substantially normally incident light, a first wavelength range extending from about 420 nm to the minimum wavelength, and a second wavelength range extending from the minimum wavelength to about 750 nm, the plurality of alternating polymeric first and second layers has an optical reflectance Rp when the incident light is polarized along the pass direction, wherein Rp has an average value of less than about 1% in the first wavelength range and less than about 0.5% in the second wavelength range.

15. The optical system of claim 14, wherein for V-numbers defined as (nyb-l)Z(nya-nyc), nya, nyb and nyc being refractive indices along the second direction at respective wavelengths of 450 nm, 550 nm and 650 nm, the first and second layers have respective first and second V-numbers VI and V2, a magnitude of a difference between VI and V2 being less than 5.

Images