CN116615675A - Reflective polarizer - Google Patents

Abstract

The present disclosure provides a reflective polarizer comprising a plurality of polymer first layers and a plurality of polymer second layers. The average layer thickness versus layer number curve for the plurality of polymer first layers but not for the plurality of polymer second layers includes an inflection point region separating a left region comprising at least 50 sequences Lay out the first layer of polymer. The polymeric first layer has a lower number of layers and the average layer thickness increases with increasing number of layers from a right region comprising at least 5 sequentially arranged polymeric first layers. The polymeric first layer has a greater number of layers, and the average layer thickness increases with increasing number of layers such that a linear fit for the at least 50 sequentially arranged polymeric first layers and for the at least 5 The linear fit of the first layer of sequentially arranged polymers has corresponding positive slopes S1 and S2, S2/S1≥5.

Description

reflective polarizer

technical field

The present disclosure relates generally to reflective polarizers, and in particular to reflective polarizers for use in optical devices.

Background technique

Multilayer optical films are commonly used to make reflective polarizers. Reflective polarizers are widely used in optical devices such as virtual reality (VR) headsets, display devices, and the like. Conventional reflective polarizers can produce optical artifacts when used with such optics.

Contents of the invention

In a first aspect, the present disclosure provides a reflective polarizer. The reflective polarizer includes a plurality of polymer first layers and a plurality of polymer second layers. The plurality of polymeric first layers are disposed along a first portion of the thickness of the reflective polarizer. The plurality of polymeric first layers includes a polymeric first end layer at each end of the plurality of polymeric first layers. Each layer between the polymeric first end layer and the polymeric first end layer has an average layer thickness of less than about 300 nanometers (nm). The plurality of polymeric second layers are disposed along a second portion of the thickness of the reflective polarizer. The plurality of polymeric second layers includes a polymeric second end layer at each end of the plurality of polymeric second layers. Each layer between the polymeric second end layer and the polymeric second end layer has an average layer thickness of less than about 300 nm. The average layer thickness versus layer number curve for the plurality of polymer first layers but not for the plurality of polymer second layers includes an inflection region separating a left region from a right region. The left region includes at least 50 sequentially arranged polymeric first layers. The polymer first layer in the left region has a lower number of layers, and the average layer thickness increases with increasing number of layers. The right side region includes at least 5 sequentially arranged polymeric first layers. The polymer first layer in the right region has a greater number of layers, and the average layer thickness increases with increasing number of layers such that for the at least 50 sequentially arranged polymers in the left region The linear fit of the first layer and the linear fit of the at least 5 sequentially arranged polymer first layers in the right region have corresponding positive slopes S1 and S2, and S2/S1 > 5.

In a second aspect, the present disclosure provides a reflective polarizer. The reflective polarizer includes a plurality of polymeric first layers, a plurality of polymeric second layers, and at least one intermediate layer. The plurality of polymeric first layers is disposed between a pair of polymeric first end layers. The plurality of polymeric second layers is disposed between a pair of polymeric second end layers. Each layer between the pair of polymeric first end layers and each layer between the pair of polymeric second end layers has an average thickness of less than about 300 nm. The at least one intermediate layer has an average thickness greater than about 500 nm and is disposed between the plurality of polymeric first layers and the plurality of polymeric second layers. For a first wavelength range extending from about 400 nm to about 700 nm and for a first polarization state and an angle of incidence less than about 5 degrees, the plurality of polymer first layers and the plurality of polymer second layers in combination have a wavelength greater than about An average optical reflectance of 95%, an average optical transmission of less than about 1%, and an average optical absorptivity of less than about 1%. For a first wavelength range extending from about 400 nm to about 700 nm and for an orthogonal second polarization state and an angle of incidence between about 55 degrees and about 65 degrees, the plurality of polymer first layers and the plurality of polymer second layers The two layers in combination have an average optical transmission of greater than about 95%, an average optical reflectance of less than about 1%, and an average optical absorptivity of less than about 1%. The plurality of polymer first layers and the plurality of polymer second layers combine for a first wavelength range extending from about 400 nm to about 700 nm and for a first polarization state and an angle of incidence between about 55 degrees and about 65 degrees The ground has an average optical reflectance of greater than about 85%.

The details of one or more examples of the disclosure are set forth in the accompanying drawings and the description below. Other features, objects, and advantages of the disclosure will be apparent from the description and drawings, and from the claims.

Description of drawings

The exemplary embodiments disclosed herein may be more fully understood from consideration of the following detailed description when taken in conjunction with the accompanying drawings. The figures are not necessarily drawn to scale. Like numbers are used in the figures to refer to like parts. It should be understood, however, that the use of numbers to refer to components in a given figure is not intended to limit components labeled with the same number in another figure.

Figure 1 shows a schematic cross-sectional view of a reflective polarizer according to an embodiment of the present disclosure;

Figure 2 shows a schematic cross-sectional view of a reflective polarizer according to another embodiment of the present disclosure;

FIG. 3A shows a graph including a curve between the average layer thickness and the number of layers of a polymer first layer and a polymer second layer of a reflective polarizer;

Figure 3B shows another graph illustrating an enlarged portion of the curve of Figure 3A;

Figure 4A shows a graph including a linear fit to a sequential arrangement of polymer first layers of reflective polarizers;

Figure 4B shows a graph including a linear fit to a sequential arrangement of polymeric second layers of reflective polarizers;

5A-5B show graphs of average layer thickness versus number of layers for a polymer first layer and a polymer second layer of a reflective polarizer;

6A-6C illustrate graphs of the refractive index of the "A" polymer layer and the "B" polymer layer of a reflective polarizer versus the wavelength of incident light in a first wavelength range;

Figure 7A shows a graph of the optical transmittance of a reflective polarizer versus the wavelength range of a second polarization state; and

Figure 7B shows a graph of the optical transmission of a reflective polarizer versus the wavelength range of the first polarization state.

Detailed ways

In the following description, reference is made to the accompanying drawings which form a part hereof, and in which are shown by way of illustration various embodiments. It is to be understood that other embodiments can be conceived and made without departing from the scope or spirit of the present disclosure. Therefore, the following detailed description should not be considered as limiting.

As used herein, the term "blocked polarization state" refers to a polarization state when an optical device reflects or absorbs a relatively large amount of incident light.

As used herein, the term "transmission polarization state" refers to the polarization state when an optical device transmits a relatively large amount of incident light.

The present disclosure provides a reflective polarizer. Exemplary applications of the reflective polarizers of the present disclosure include display devices such as liquid crystal displays (LCDs) in mobile phones, personal digital assistants (PDAs), computers, televisions, and other optical devices. The reflective polarizers of the present disclosure may also be used in virtual reality (VR) headsets.

In some examples, optical films can be produced by coextrusion. The manufacturing method may include: (a) providing at least a first resin stream and a second resin stream corresponding to the first polymer and the second polymer to be used in the finished film; (b) separating the first stream and the second stream into layers using a suitable feedblock, such as a feedblock comprising (i) a gradient plate having a first flow channel and a second flow channel, wherein the cross-sectional area of the first channel changes from a first position to a second position along the flow channel, (ii) a feed tube sheet having a flow channel in fluid communication with the first flow channel A first plurality of conduits and a second plurality of conduits in fluid communication with the second flow channel, each conduit feeding its own corresponding slot die, each conduit having a first end and a second end, the first of the conduits One end is in fluid communication with the flow channel, and the second end of the conduit is in fluid communication with the slot die, and (iii) optionally an axial rod heater positioned close to the conduit; (c) compounding the flow of material through an extrusion die to form a multi-layer web, wherein each layer is substantially parallel to the major surfaces of adjacent layers; and (d) casting the multi-layer web onto chilled rolls (sometimes called casting wheels or drum) to form a cast multilayer film. The cast film can have the same number of layers as the finished film, but the layers of the cast film are usually much thicker than the layers of the finished film.

After cooling, the multilayer web can be preheated and drawn or stretched to produce a nearly finished multilayer optical film. Drawing or stretching accomplishes two goals: it thins the layers to their desired final thickness profile; and it orients the layers such that at least some of the layers become birefringent. Orientation or stretching can be accomplished in the crossweb direction (eg, via a tenter frame), in the downweb direction (eg, via a length orienter), or any combination thereof, whether simultaneously or sequentially. If stretched in only one direction, the stretching can be "unconstrained" (in which the film is allowed to relax dimensionally in the in-plane direction perpendicular to the stretching direction) or "constrained" (in which the film is constrained , and thus does not allow dimensionally relaxation in the in-plane direction perpendicular to the stretching direction). If stretched in two in-plane directions, the stretch may be symmetrical (ie, equal in orthogonal in-plane directions) or asymmetrical. Alternatively, the film can be stretched by a batch process. In any event, subsequent or simultaneous draw reduction, stress or strain equalization, heat setting, and other processing operations may also be applied to the film.

Preferably, the polymers of the various layers are selected to have similar rheological properties (eg, melt viscosity) such that they can be coextruded without significant fluid disturbance. Extrusion conditions can be chosen so that the respective polymers are adequately fed, melted, mixed and pumped as a feed or melt stream in a continuous and stable manner. The temperature used to form and maintain each molten stream can be selected within a range that avoids freezing, crystallization, or undue high pressure drop at the low end of the range and avoids Material degradation.

Multilayer optical films can be made using any suitable light transmissive material, but in many cases it is beneficial to use low absorbing polymeric materials. Using such materials, the absorption of the microlayer stack at visible and infrared wavelengths can be small or negligible, so that at any given wavelength and for any specified angle of incidence and polarization state, the stack (or the The sum of reflectance and transmittance of an optical film) is about 100%, that is, R+T≈100% or R≈100%−T. Exemplary multilayer optical films are composed of polymeric materials and can be fabricated using coextrusion, casting, and orientation processes. Reference is made to U.S. Patent 5,882,774 (Jonza et al.) "Optical Film (optical film)", U.S. Patent 6,179,948 (Merrill et al.), "Optical Film and Process for Manufacture Thereof (optical film and its preparation method)", U.S. Patent 6,783,349 (Neavin et al) "Apparatus for Making Multilayer Optical Films (apparatus for making multilayer optical films)", and patent application publication US 2011/0272849 (Neavin et al) "Feedblock for Manufacturing Multilayer Polymeric Films (for making multilayer polymeric films) film feed block)".

Multilayer optical films have also been demonstrated by coextrusion of alternating polymer layers. See, eg, US Patents 3,610,729 (Rogers), 4,446,305 (Rogers et al.), 4,540,623 (Im et al.), 5,448,404 (Schrenk et al.), and 5,882,774 (Jonza et al.). In these kinds of polymeric multilayer optical films, polymeric materials are used primarily or exclusively in the preparation of the individual layers. These films are suitable for high-volume manufacturing processes and are available in large sheets and rolls.

Multilayer optical films include individual microlayers with different refractive index characteristics such that some light is reflected at interfaces between adjacent microlayers. The microlayers are sufficiently thin such that light reflected at multiple interfaces undergoes constructive or destructive interference in order to impart the desired reflective or transmissive properties to the multilayer optical film. For multilayer optical films designed to reflect light at ultraviolet, visible, or near-infrared wavelengths, each microlayer typically has an optical thickness (physical thickness times refractive index) of less than about 1 μm. Thicker layers may also be included, such as skin layers at the outer surfaces of the multilayer optical film, or protective boundaries disposed within the multilayer optical film that separate coherent groupings of microlayers (referred to herein as "layer packs") layer (PBL).

For polarizing applications, such as reflective polarizers, at least some of the optical layers are formed using birefringent polymers in which the polymers have different values of refractive index along orthogonal Cartesian axes of the polymers. Typically, birefringent polymer microlayers have orthogonal Cartesian axes defined by the normal to the layer plane (z-axis), with the x- and y-axes lying within the layer plane. Birefringent polymers can also be used in non-polarizing applications.

In some cases, the microlayers have thicknesses and refractive index values corresponding to 1/4 wavelength stacks, i.e., arranged in optical repeating units or cells, each optical repeating unit or cell having two phases of equal optical thickness. Adjacent to the microlayer (f ratio = 50%), such optical repeat units efficiently reflect light by constructive interference at a wavelength λ that is twice the overall optical thickness of the optical repeat unit. Other layer arrangements are also known, such as multilayer optical films with dual microlayer optical repeat units having an f ratio different from 50%, or films in which the optical repeat unit comprises more than two microlayers. These optical repeat unit designs can be configured to reduce or increase certain higher order reflections. See , eg, US Patent No. 5,360,659 (Arends et al.) and US Patent No. 5,103,337 (Schrenk et al.). A thickness gradient along a film thickness axis (e.g., the z-axis) can be used to provide a broadened reflection band, such as one that extends throughout the human visual field and into the near-infrared region, such that when the band is viewed at an oblique angle of incidence When shifting to shorter wavelengths, the microlayer stack continues to reflect throughout the visible spectrum. Sharpening the bandedge (ie, the wavelength transition between high reflection and high transmission) by adjusting the thickness gradient is discussed in US Patent 6,157,490 (Wheatley et al.).

Additional details of multilayer optical films and related design and construction are found in US Pat. , and entitled "Giant Birefringent Optics in Multilayer Polymer Mirrors", Science, Vol. 287, March 2000 (Weber et al.) ("Giant Birefringent Optics in Multilayer Polymer Mirrors", Science, Vol. 287 , discussed in the publication of March 2000 (Weber et al.). Multilayer optical films and related articles can include additional layers and coatings selected for their optical, mechanical, and/or chemical properties. For example, a UV absorbing layer can be added on the incident side of the film to protect the part from degradation caused by UV light. The multilayer optical film can be attached to the mechanical reinforcement layer using a UV curable acrylate adhesive or other suitable material. Such reinforcement layers may comprise polymers such as PET or polycarbonate, and may also comprise structured surfaces providing optical functions such as light diffusion or light collimation, eg by using beads or prisms. Additional layers and coatings may also include anti-scratch coatings, anti-tear layers and hardeners. See, eg, US Patent 6,368,699 (Gilbert et al.). Methods and apparatus for making multilayer optical films are discussed in US Patent 6,783,349 (Neavin et al.).

The reflective and transmissive properties of a multilayer optical film are a function of the refractive index of the corresponding microlayer, as well as the thickness and thickness distribution of the microlayer. Each microlayer (at least at local locations of the film) can be characterized by the in-plane refractive index _nx , _ny , and the refractive index _nz associated with the thickness axis of the film. These indices of refraction represent, respectively, the indices of refraction of the material in question for light polarized along mutually orthogonal x-, y-, and z-axes. For ease of description in this patent application, unless otherwise indicated, the x-, y-, and z-axes are assumed to be local Cartesian coordinates applicable to any point of interest on a multilayer optical film, where the microlayers extend parallel to the xy plane, and where the x-axis is oriented in the plane of the film to maximize the magnitude of Δn _x . Thus, the magnitude of Δn _y may be equal to or less than (but not greater than) the magnitude of Δn _x . Furthermore, which material layer to choose (to start calculating the differences Δn _x , _Δny , Δn _z ) is determined by the need for Δn _x to be non-negative. In other words, the refractive index difference between the two layers forming the interface is Δn _j =n _1j –n _2j , where j=x, y or z, and where layer numbers 1, 2 are chosen such that n _1x ≥ n _2x , that is, Δn _x ≥ 0.

In practice, the refractive index is controlled through judicious material selection and processing conditions. Multilayer films are prepared by coextruding a large number (eg, tens or hundreds) of layers of two alternating polymers A, B, sometimes followed by passing the multilayer extrudate through one or more multiplying machine, and the extrudate is then stretched or otherwise oriented to form the final film. The resulting films are typically composed of hundreds of individual microlayers whose thickness and refractive index are tuned to provide one or more reflectance spectra in one or more desired spectral regions, such as the visible or near-infrared regions. bring. To achieve a specific target reflectivity with an appropriate number of layers, adjacent microlayers generally exhibit a difference in refractive index (Δn _x ) of at least 0.04 for light polarized along the x-axis. In some embodiments, the materials are selected such that the difference in refractive index for light polarized along the x-axis is as high as possible after orientation. Adjacent microlayers can also be made to exhibit a refractive index difference ( _Δny ) of at least 0.05 for light polarized along the y-axis if high reflectivity for two orthogonal polarizations is desired.

Optical modeling of multilayer optical films is computationally intensive, but is well understood when the refractive index and thickness of each layer are known. From a set of known refraction values and thicknesses, the transmitted and reflected optical spectra for each polarization state can be rigorously calculated based on well-known optical principles and a multilayer modeling technique commonly referred to as the transfer matrix method. By comparing the calculated optical spectrum with the measured optical spectrum from the fabricated multilayer optical film, corrections to the layer parameters can be determined iteratively until the modeled optical spectrum best matches the experimentally measured optical spectrum. spectrum. With this iterative modeling approach, the optical parameters of refractive index and layer thickness can be determined with high confidence from the measured optical spectrum of the multilayer optical film.

Among other things, the '774 (Jonza et al.) patent cited above describes how the difference in refractive index ( _Δnz ) between adjacent microlayers can be adjusted for anti-oblique incidence for light polarized along the z-axis. Desired reflectivity properties for the p-polarized component of light. To maintain high reflectivity for p-polarized light at oblique incidence angles, the z-axis refractive index mismatch Δn _z between microlayers can be controlled to be substantially smaller than the maximum value of the in-plane refractive index difference Δn _x such that Δn _z ≤0.5*Δn _x , or Δn _z ≤0.25*Δn _x . A z-index mismatch of zero or nearly zero magnitude creates an interface between microlayers whose reflectivity for p-polarized light is constant or nearly constant with angle of incidence. Furthermore, the z-axis refractive index mismatch Δn _z can be controlled to have an opposite polarity compared to the in-plane refractive index difference Δn _x , ie Δn _z <0. This condition produces an interface whose reflectivity increases for p-polarized light with increasing angle of incidence, as well as for s-polarized light.

The '774 (Jonza et al.) patent also discusses certain design considerations associated with multilayer optical films configured as polarizers (referred to as multilayer reflective or reflective polarizers). In general, the transmission of any reflective polarizer depends on the polarization of the incident light and the azimuthal orientation of that light relative to the major axis of the polarizer. In many applications, an ideal reflective polarizer has high reflectivity along one axis (the "extinction" or "blocking" axis) and zero reflectance along the other axis (the "transmission" or "transmission" axis). For the purposes of this patent application, light whose polarization state is substantially aligned with the pass or transmission axis is referred to as transmitted light, and light whose polarization state is substantially aligned with the block or extinction axis is referred to as Light blocking. Unless otherwise specified, transmitted light at 60° incidence is measured in p-polarized transmitted light along the transmission axis of the reflective polarizer. If some reflectivity occurs along the transmission axis, the contrast of the polarizer at off-perpendicular angles can be reduced; and if the reflectivity is different for multiple wavelengths, color can be introduced into the transmitted light. In addition, in some multilayer systems, it may not be possible to exactly match the two y-axis indices and the two z-axis indices, and when the z-axis indices are mismatched, it may be desirable for the in-plane indices n1y and n2y to yield slight mismatch. Specifically, by arranging the y-axis index mismatch to have the same sign as the z-axis index mismatch, the Brewster effect is generated at the microlayer interface to minimize the off-axis reflectance along the transmission axis of the multilayer reflective polarizer , and thus minimize off-axis colors.

The reflective polarizers of the present disclosure include a plurality of polymeric first layers and a plurality of polymeric second layers. The plurality of polymeric first layers are disposed along a first portion of the thickness of the reflective polarizer. The plurality of polymeric first layers includes a polymeric first end layer at each end of the plurality of polymeric first layers. Each layer between the first end layer and the first end layer has an average layer thickness of less than about 300 nanometers (nm). The plurality of polymeric second layers are disposed along a second portion of the thickness of the reflective polarizer. The plurality of polymeric second layers includes a polymeric second end layer at each end of the plurality of polymeric second layers. Each layer between the second end layer and the second end layer has an average layer thickness of less than about 300 nm. The average layer thickness versus layer number curve for the plurality of polymer first layers but not for the plurality of polymer second layers includes an inflection region separating a left region from a right region. The left region includes at least 50 sequentially arranged polymeric first layers. The right side region includes at least 5 sequentially arranged polymeric first layers. The polymer first layer in the left region has a lower number of layers, and the average layer thickness increases with increasing number of layers. The polymeric second layer in the right region has a higher number of layers, and the average layer thickness increases with increasing number of layers. The linear fit of the at least 50 sequentially arranged polymer first layers in the left region and the linear fit of the at least 5 sequentially arranged polymer first layers in the right region have corresponding Positive slopes S1 and S2, S2/S1≥5.

During the process of making the reflective polarizer, the plurality of polymeric first layers and the plurality of polymeric second layers can be coextruded and co-stretched in the transverse direction (TD). When the plurality of polymer first layers and the plurality of polymer second layers are stretched in TD, the plurality of polymer first layers and the plurality of polymer second layers can be in the machine direction (MD) and the normal direction ( ND) or may have zero tension. Each of the plurality of first polymer layers and the plurality of second polymer layers forms alternating layers of A polymer and B polymer. Relaxation in a non-stretch direction (such as MD and ND) can cause the refractive indices of alternating A and B polymer layers to match very closely in MD and ND. The close matching of the refractive indices of alternating A and B polymer layers in MD and ND provides very low reflectivity in the transmitted polarization state, and alternating A and B polymer layers in TD A large difference between the refractive indices on can provide very low transmission in the blocking polarization state of the reflective polarizer. Matching of the refractive indices of the alternating A and B polymer layers in MD and ND can also provide very low reflectivity in transmitted polarization states of obliquely incident or off-axis light.

A major problem with using conventional reflective polarizers in optical setups is ghosting. Ghosting refers to the generation of "ghost images" in the observed image. Ghost images usually appear as secondary images that are slightly displaced from the primary image in the observed image. Additionally, conventional optical devices may have low contrast ratios and low efficiencies.

Reflective polarizers of the present disclosure having very low reflectivity in the pass polarization state and very low transmittance in the block polarization state can significantly reduce optical artifacts, such as ghosting, in optical devices. A reflective polarizer having very low reflectivity in the transmitting polarization state and very low transmission in the blocking polarization state can also increase the contrast ratio of the optical device. Very low reflectivity in the transmitted polarization state and very low transmittance in the blocked polarization state can also increase the efficiency of the optical device.

Another problem with using conventional reflective polarizers in optical devices is wrinkling of the conventional reflective polarizers. Wrinkling of conventional reflective polarizers occurs when the first polymer layers and the second polymer layers are stretched in the TD direction. Wrinkle-free reflective polarizers with very low reflectivity in the pass polarization state and very low transmittance in the block polarization state can be used in high performance optical applications, such as in VR headsets.

Referring now to the drawings, FIG. 1 is a schematic cross-sectional view of an exemplary reflective polarizer 200 . Reflective polarizer 200 includes a plurality of polymer first layers 10 and a plurality of polymer second layers 20 .

Reflective polarizer 200 defines three mutually orthogonal axes x, y and z. The x- and y-axes are in-plane axes of reflective polarizer 200 , while the z-axis is a transverse axis disposed along the thickness of reflective polarizer 200 . In other words, the x-axis and y-axis lie along the plane of the reflective polarizer 200 , while the z-axis is perpendicular to the plane of the reflective polarizer 200 .

In some embodiments, the thickness t of reflective polarizer 200 may be greater than about 50 micrometers (μm), greater than about 100 μm, greater than about 200 μm, greater than about 300 μm, or greater than about 400 μm. However, the thickness t of reflective polarizer 200 may vary depending on the desired application properties.

A plurality of polymeric first layers 10 are arranged along the first portion 13 of the thickness t of the reflective polarizer 200 . The plurality of polymer first layers 10 comprises alternating polymer first layers 11 , 12 . The plurality of polymeric first layers 10 further comprises a polymeric first end layer 10a, 10b at each end of the plurality of polymeric first layers. In other words, the plurality of polymeric first layers 11, 12 are arranged between a pair of polymeric first end layers 10a, 10b. As shown in FIG. 1 , a polymer first end layer 10a is disposed at one end of a plurality of polymer first layers 10, and a polymer first end layer 10b is disposed at one end of a plurality of polymer first layers 10. At the other end opposite to one end.

Each layer 11 , 12 between the first end layers 10a, 10b and the first end layer 10a, 10b has an average layer thickness t1 of less than about 300 nm. The average layer thickness t1 is interchangeably referred to herein as "average thickness t1". In particular, each of the first end layers 10a, 10b has an average thickness t1 of less than 300 nm. Furthermore, each layer 11 , 12 between the pair of polymeric first end layers 10a, 10b has an average thickness t1 of less than about 300 nm. In some embodiments, the average thickness t1 may be less than about 250 nm, less than about 200 nm, or less than about 100 nm. However, the average thickness t1 can vary depending on the desired application properties. In some cases, an atomic force microscope can be used to measure the average thickness t1.

A plurality of polymeric second layers 20 are arranged along a second portion 23 of thickness t of reflective polarizer 200 . The plurality of polymeric second layers 20 comprises alternating polymeric second layers 21 , 22 . The plurality of polymeric second layers 20 also includes a polymeric second end layer 20a, 20b at each end of the plurality of polymeric second layers. In other words, the plurality of polymeric second layers 21 , 22 are arranged between a pair of polymeric second end layers 20a, 20b. As shown in FIG. 1 , a polymer second end layer 20a is disposed at one end of a plurality of polymer second layers 20, and a polymer second end layer 20b is disposed at one end of a plurality of polymer second layers 20. At the other end opposite to one end.

Each layer 21 , 22 between the second end layers 20a, 20b and the second end layer 20a, 20b has an average layer thickness t2 of less than about 300 nm. The average layer thickness t2 is interchangeably referred to herein as "average thickness t2". In particular, each of the polymeric second end layers 20a, 20b has an average thickness t2 of less than about 300 nm. Furthermore, each layer 21 , 22 between the pair of polymeric second end layers 20a, 20b has an average thickness t2 of less than about 300 nm. In some embodiments, the average thickness t2 can be less than about 250 nm, less than about 200 nm, or less than about 100 nm. However, the average thickness t2 can vary depending on the desired application properties. In some cases, an atomic force microscope can be used to measure the average thickness t2.

In some embodiments, reflective polarizer 200 also includes at least one intermediate layer 60 , 61 disposed between first plurality of polymeric layers 10 and second plurality of polymeric layers 20 . At least one intermediate layer 60, 61 may join the plurality of polymeric first layers 10 and the plurality of polymeric second layers 20 to each other.

In some embodiments, at least one intermediate layer 60, 61 has an average thickness t3. In some embodiments, the average thickness t3 is greater than about 500 nm. In some embodiments, at least one intermediate layer 60, 61 has an average thickness t3 greater than about 550 nm, greater than about 575 nm, or greater than about 600 nm. However, the average thickness t3 may vary according to application properties. In some embodiments, the materials used in the at least one intermediate layer 60, 61 can vary depending on the application properties. In some embodiments, each of the at least one intermediate layer 60, 61 is made of an isotropic material. In some embodiments, each of the at least one intermediate layer 60, 61 comprises polyethylene terephthalate (PET). In some cases, an atomic force microscope can be used to measure the average thickness t3.

In some embodiments, reflective polarizer 200 also includes at least one skin layer 62 , 63 . In some embodiments, each skin layer 62 , 63 is disposed on the same side of the plurality of polymeric first layers 10 and the plurality of polymeric second layers 20 . At least one skin layer 62 , 63 may serve as a protective boundary layer (PBL) for the reflective polarizer 200 . In some embodiments, at least one skin layer 62 , 63 can be coextruded on one or both major surfaces of reflective polarizer 200 . In the embodiment shown in FIG. 1 , reflective polarizer 200 includes two skin layers 62 , 63 . In particular, the skin layer 62 is disposed adjacent to the polymeric first end layer 10a and the skin layer 63 is disposed adjacent to the polymeric second end layer 20b. In other words, reflective polarizer 200 includes one skin 62 , 63 on both major surfaces of reflective polarizer 200 . However, in some other embodiments, reflective polarizer 200 may include only one skin layer. For example, reflective polarizer 200 may include either of skin layers 62,63.

In some embodiments, each skin layer 62, 63 has an average thickness greater than about 500 nm. In some embodiments, each skin layer 62, 63 has an average thickness greater than about 550 nm, greater than about 575 nm, or greater than about 600 nm. However, the average thickness of the skin layers 62, 63 may vary depending on the desired application properties.

In some embodiments, each of the skin layers 62, 63 is made of an isotropic material. In some embodiments, each of the skin layers 62, 63 comprises polyethylene terephthalate (PET). In some embodiments, the skin layers 62, 63 may be substantially similar to each other. In some other embodiments, the skin layers 62, 63 may be different from each other.

Skin layers 62, 63 are optional, and in some cases reflective polarizer 200 may not include any additional skin layers.

Figure 1 also shows incident light 80 incident on the outer surface (air-polymer interface) of reflective polarizer 200 at an angle of incidence Θ. Specifically, incident light 80 is incident on surface layer 62 of reflective polarizer 200 at an angle of incidence θ. The angle of incidence θ is measured relative to the normal 100 of the reflective polarizer 200 . In some embodiments, the angle of incidence Θ can range from about 0 degrees to about 90 degrees. In some implementations, the angle of incidence Θ may be less than about 5 degrees. In some implementations, the angle of incidence Θ may be between about 55 degrees and about 65 degrees.

In some embodiments, each of the plurality of polymeric first layers 10 and the plurality of polymeric second layers 20 includes at least 200 layers. Each of the polymeric first layer 10 and the polymeric second layer 20 has an average thickness t1 or t2 of less than 300 nm. In some embodiments, the plurality of polymeric first layers 10 can include at least 200 polymeric first layers 11 , 12 and the plurality of polymeric second layers 20 can include at least 200 polymeric second layers 21 , 22 . In some other embodiments, each of the plurality of polymeric first layers 10 and the plurality of polymeric second layers 20 can include at least 325 layers. In some other embodiments, each of the plurality of polymeric first layers 10 and the plurality of polymeric second layers 20 can include at least 350 layers.

In some embodiments, reflective polarizer 200 may include equal numbers of polymeric first layers 11 , 12 and polymeric second layers 21 , 22 . In some other embodiments, reflective polarizer 200 may include different numbers of polymeric first layers 11 , 12 and polymeric second layers 21 , 22 . The number of polymeric first layers 11, 12 and the number of polymeric second layers 21, 22 in reflective polarizer 200 may vary depending on the desired application properties.

In some embodiments, the plurality of polymeric first layers 10 and the plurality of polymeric second layers 20 are integrally formed with one another. However, in some other embodiments, the plurality of polymeric first layers 10 and the plurality of polymeric second layers 20 may be formed separately from each other. In some embodiments, the plurality of polymeric first layers 10 and the plurality of polymeric second layers 20 are coextruded. In some embodiments, the plurality of polymeric first layers 10 and the plurality of polymeric second layers 20 are coextruded and codrawn.

In some embodiments, the plurality of polymeric first layers 10 and the plurality of polymeric second layers 20 may be co-stretched in the transverse direction (TD) during the process of manufacturing reflective polarizer 200 . When the plurality of polymer first layers 10 and the plurality of polymer second layers 20 are stretched in TD, the plurality of polymer first layers 10 and the plurality of polymer second layers 20 can be stretched in the machine direction (MD) and Relaxed or may have zero tension in the normal direction (ND). TD, MD, and ND can be arranged along the x-axis, y-axis, and z-axis, respectively. MD can be the general direction along which the plurality of polymeric first layers 10 and the plurality of polymeric second layers 20 travel during the stretching process. TD may be a second axis in the plane of the plurality of polymer first layers 10 and the plurality of polymer second layers 20 and may be orthogonal to MD. ND can be orthogonal to both MD and TD and generally corresponds to the average thickness t1 , t2 of the plurality of polymeric first layers 10 and the plurality of polymeric second layers 20 . The plurality of polymeric first layers 10 and the plurality of polymeric second layers 20 may be relaxed or unstretched in the MD and ND directions.

In some embodiments, each of the plurality of polymeric first layers 10 and the plurality of polymeric second layers 20 form alternating "A" polymer layers and "B" polymer layers. In some embodiments, the alternating "A" polymer layers and "B" polymer layers are interleaved. In some embodiments, polymeric first layer 11 and polymeric second layer 21 are "A" polymeric layers, and polymeric first layer 12 and polymeric second layer 22 are "B" polymeric layers.

The "A" polymer layer and the "B" polymer layer have a refractive index nx along a first polarization state, a refractive index ny along an orthogonal second polarization state, and a refractive index ny along an orthogonal to the first polarization state and the second polarization state The refractive index nz of the z-axis. The refractive index nx is defined along the x-axis, the refractive index ny is defined along the y-axis, and the refractive index nz is defined along the z-axis. In some embodiments, the first polarization state is defined along the x-axis and the second polarization state is defined along the y-axis. Thus, the z-axis is orthogonal to the first and second polarization states. In some embodiments, the first polarization state can be a P polarization state and the second polarization state can be an S polarization state. In some other embodiments, the first polarization state can be the S polarization state and the second polarization state can be the P polarization state. In some embodiments, the first polarization state can be a blocking polarization state (BS). Additionally, the second orthogonal polarization state may be a pass polarization state (PS).

Each "A" polymer layer is isotropic. In other words, each "A" polymer layer is substantially index matched along the x-axis, y-axis, and z-axis, respectively. In other words, the "A" polymer layers have substantially matched refractive indices nx, ny, and nz. Two indices of refraction are considered to be substantially matched if the difference between the two indices of refraction is less than about 0.05, less than about 0.02, or less than about 0.01. Therefore, each pair of refractive indices of each "A" polymer layer does not differ by more than 0.05.

In some embodiments, each of the "A" polymer layers has a refractive index of about 1.57. In some embodiments, nx, ny, nz of each "A" polymer layer is substantially less than or equal to 1.57 ± 0.05.

Each "B" polymer layer is birefringent. In other words, each "B" polymer layer has at least one of the indices of refraction along the x-axis, y-axis, and z-axis, respectively, different from the others. In other words, at least one of the indices of refraction nx, ny, and nz of the "B" polymer layer is different from the other indices of refraction. Accordingly, at least one pair of refractive indices of each "B" polymer layer differs by more than 0.05.

In some embodiments, the "A" polymer layer comprises polycarbonate (PC) and copolyester (coPET). Each of the "A" polymer layers may comprise a copolymer of polycarbonate and copolyester. In some embodiments, the "A" polymer layer comprises a blend of polycarbonate and copolyester (PC:coPET) in a molar ratio of 42.5 mole % PC and 57.5 mole % coPET. However, the "A" polymer layer may comprise any other isotropic material based on the desired application properties. In some embodiments, the "A" polymer layer can comprise any isotropic material that remains substantially isotropic when uniaxially oriented.

In some embodiments, the "B" polymer layer comprises polyethylene naphthalate (PEN) and polyethylene terephthalate (PET). Each "B" polymer layer may comprise a copolymer of polyethylene naphthalate and polyethylene terephthalate. In some embodiments, the "B" polymer layer comprises a blend of polyethylene naphthalate and polyethylene terephthalate in a molar ratio of 90 mole percent PEN and 10 mole percent PET, also It is called low melting point polyethylene naphthalate (LMT PEN). Other polymers suitable for use in the "B" polymer layer may include, for example, 2,6-polybutylene naphthalate (PBN) and copolymers thereof. However, the "B" polymer layer may comprise any other birefringent material based on the desired application properties.

Each of the "A" polymer layer and the "B" polymer layer has an average thickness of less than about 300 nm. The average thickness of each of the "A" polymer layer and the "B" polymer layer was measured by using an AFM for each "A" polymer layer and "B" polymer layer pair (also referred to as an optical repeating unit (ORU). )) and assuming that the "A" polymer layer and the "B" polymer layer have the same thickness for each "A" polymer layer and "B" polymer layer pair. Specifically, the average thickness of each of the "A" polymer layer and the "B" polymer layer was determined to be half the thickness of each "A" polymer layer and "B" polymer layer pair, i.e. ( t _A +t _B )/2, where t _A and t _B are the thicknesses of the "A" polymer layer and the "B" polymer layer of the "A" polymer layer and "B" polymer layer pair, respectively. Relaxation in non-stretch directions (such as MD and ND) can cause the plurality of polymer first layers 10 and the plurality of polymer second layers 20 forming alternating A polymer layers and B polymer layers to have a refractive index between Very closely matched on MD and ND. The close matching of the refractive indices of alternating A and B polymer layers in MD and ND provides very low reflectivity in the transmitted polarization state, and alternating A and B polymer layers in TD A large difference between the refractive indices on can provide very low transmission in the blocking polarization state of the reflective polarizer. Matching of the refractive indices of the alternating A and B polymer layers in MD and ND can also provide very low reflectivity in the transmitted polarization state of off or oblique incident or off-axis light.

The isotropic material of the "A" polymer layer can be selected such that after stretching the "A" polymer layer and the "B" polymer layer, the "A" polymer layer is in both non-stretch directions (e.g., MD and ND) remain substantially matched to the corresponding refractive indices ny and nz of the birefringent material of the "B" polymer layer in the non-stretch direction. In addition, the "A" polymer layer and the "B" polymer layer have a significant mismatch in the refractive index nx in the direction of stretching, such as TD.

FIG. 2 shows a schematic cross-sectional view of another exemplary reflective polarizer 200'. Reflective polarizer 200' is substantially similar to reflective polarizer 200 shown in FIG. 1 . Similar to reflective polarizer 200 , reflective polarizer 200 ′ includes a plurality of polymer first layers 10 and a plurality of polymer second layers 20 , and at least one skin layer 62 , 63 . However, reflective polarizer 200' includes at least two intermediate layers 60,61. Each of the at least two intermediate layers 60, 61 has an average thickness t3 greater than about 500 nm. At least two intermediate layers 60 , 61 are disposed between the plurality of first polymer layers 10 and the plurality of second polymer layers 20 . The reflective polarizer 200' also includes a polymeric third layer 70 disposed between at least two intermediate layers 60,61. In some embodiments, reflective polarizer 200' includes between one and ten polymeric third layers 70 disposed between at least two intermediate layers 60, 61 . In some embodiments, the number of polymeric third layers 70 disposed between at least two intermediate layers 60, 61 can be between 2 and 5, between 4 and 7, between 6 and 9, or as desired. Depends on the application properties. Each polymeric third layer 70 has an average thickness t4 of less than about 300 nm. In some embodiments, each polymeric third layer 70 can have an average thickness t4 of less than about 270 nm, less than about 250 nm, less than about 200 nm, or less than about 150 nm. In some cases, an atomic force microscope may be used to measure the average thickness t4 of each third polymeric layer 70 of reflective polarizer 200'.

In some embodiments, each polymeric third layer 70 is made of an isotropic material. In some embodiments, each third polymeric layer 70 comprises polyethylene terephthalate (PET).

1 and 2, the average layer thickness t1 and t2 of the polymer first layer 11, 12 and the polymer second layer 21, 22 may depend on the polymer first layer 11, 12 and the polymer second layer 21, 22 layers. Exemplary variations between the average layer thickness t1 and t2 and the number of layers of the polymer first layer 11, 12 and the polymer second layer 21, 22 are shown in FIGS. 3A-3B and 4A-4B and in It is explained in detail below.

FIG. 3A shows an exemplary graph 30A. Graph 30A shows the average layer thickness from 40 nm to 140 nm on the axis of ordinate and the number of layers from 0 to 350 on the axis of abscissa. Graph 30A includes curve 40 and curve 50 .

FIG. 3B shows an exemplary graph 30B. Graph 30B shows an enlarged portion of graph 30A. Specifically, graph 30B shows the average layer thickness from 70 nm to 140 nm on the axis of ordinate and the number of layers from 300 to 325 on the axis of abscissa.

Referring to FIG. 1 and FIGS. 3A-3B , curve 40 is the average layer thickness t1 of a plurality of polymeric first layers 10 versus the number of layers. The curve 40 includes an inflection point region 41 , a left region 42 and a right region 43 . An inflection point area 41 separates a left area 42 from a right area 43 . An inflection point region 41 can be defined as a certain region of the curve 40 beyond which the average layer thickness t1 of the plurality of polymer first layers 10 increases with respect to the number of layers at a significantly greater rate than for a plurality of polymeric first layers 10 prior to the inflection point region 41. The rate of increase of the average layer thickness t1 of the first layer 10 of the object.

The left region 42 comprises at least 50 polymeric first layers 11 , 12 arranged in succession. In some embodiments, the left region 42 may include at least 100 sequentially arranged polymeric first layers 11 , 12 . In some embodiments, the left region 42 may include at least 150, at least 200, at least 250, or at least 300 sequentially arranged polymeric first layers 11 , 12 .

The polymeric first layers 11 , 12 in the left region 42 have a smaller number of layers, and the average layer thickness t1 of the polymeric first layers 11 , 12 in the left region 42 increases with increasing layer number.

The right region 43 comprises at least 5 sequentially arranged layers of the polymeric first layer 11 , 12 . In some embodiments, the right side region 43 may comprise at least 10, at least 15, at least 20, at least 25, or at least 30 sequentially arranged layers of the polymeric first layer 11 , 12 . The polymeric first layers 11 , 12 in the right region 43 have a greater number of layers, and the average layer thickness t1 of the polymeric first layers 11 , 12 in the right region 43 increases with increasing layer number.

Curve 50 is the average layer thickness t2 of a plurality of polymeric second layers 20 versus the number of layers. Curve 50 does not include an inflection point region. In this embodiment, curve 50 is substantially linear. Curve 50 also depicts the gradual increase in average layer thickness t2 as the number of layers of the plurality of polymeric second layers 20 increases.

FIG. 4A shows a graph 40A comprising linear fits 44 , 45 to sequentially arranged polymer first layers 11 , 12 in curve 40 . Graph 40A includes average thicknesses from 80 nm to 135 nm on the axis of ordinate and number of layers from 1 to 351 on the axis of abscissa. The graph 40A includes a linear fit 44 to at least 50 sequentially arranged polymer first layers 11 , 12 in the region 42 on the left. The graph 40A also includes a linear fit 45 to at least 5 sequentially arranged layers of the polymeric first layer 11 , 12 in the region 43 on the right.

Linear fits 44, 45 have corresponding positive slopes S1 and S2. In particular, the linear fit 44 to the at least 50 sequentially arranged polymer first layers 11 , 12 in the left region 42 has a slope S1. Furthermore, the linear fit 45 to the at least 5 sequentially arranged layers of the polymer first layer 11 , 12 in the right region 43 has a slope S2. According to Equation 1 provided below, the ratio between slope S2 and slope S1 is at least about 5.

Therefore, the slope S2 is greater than the slope S1. In particular, the slope S2 is at least 5 times greater than the slope S1. In some embodiments, the ratio between slope S2 and slope S1 can be at least about 7, at least about 10, at least about 12, at least about 15, or at least about 18, or at least about 19.

In some embodiments, a linear fit 44 to at least 50 sequentially arranged polymer first layers 11 , 12 in the left region 42 and a linear fit 44 to at least 5 sequentially arranged polymer first layers in the right region 43 The linear fit 45 of the layers 11, 12 has corresponding r-squared values R1 and R2. In particular, a linear fit 44 to at least 50 sequentially arranged polymer first layers 11 , 12 in the left region 42 has an r-squared value R1. Furthermore, a linear fit 45 to the at least 5 sequentially arranged polymer first layers 11 , 12 in the right region 43 has an r-squared value R2. Each of the r-squared values R1, R2 may also be referred to as a coefficient of determination or multiple coefficient of determination for multiple regression. Each of the r-squared values R1, R2 is a statistical measure for determining how closely the curve 40 fits to the linear fits 44, 45, respectively. In some embodiments, each of the r-squared values R1, R2 is greater than about 0.8. In some embodiments, each of the r-squared values R1, R2 may be greater than about 0.9. In some embodiments, each of the r-squared values R1, R2 may be greater than about 0.95.

In one example, the linear fit 44 is according to Equation 2 provided below.

y = 0.1105x + 81.537 [equation 2]

In Equation 2, y represents the average layer thickness t1, and x represents the number of layers. In this example, S1 = 0.1105, and R1 = 0.998.

In one example, the linear fit 45 is according to Equation 3 provided below.

y = 2.1359x - 561.55 [Equation 3]

In Equation 3, y represents the average layer thickness t1, and x represents the number of layers. In this example, S2 = 2.1359, and R2 = 0.9992. Therefore, S2/S1=19.3294.

FIG. 4B shows a graph 40B including a linear fit 51 to the sequentially arranged polymeric second layers 21 , 22 in the curve 50 . In some embodiments, the plurality of polymeric second layers 20 includes at least 100 sequentially arranged polymeric second layers 21 , 22 . However, in some other embodiments, the plurality of polymeric second layers 20 includes at least 150, at least 200, at least 250, or at least 300 sequentially arranged polymeric second layers 21 , 22 . Graph 40B includes average layer thicknesses from 40 nm to 90 nm on the axis of ordinate and number of layers from 0 to 350 on the axis of abscissa. In some embodiments, the linear fit 51 to the sequentially arranged polymeric second layers 21 , 22 has a positive slope S3. Slope S3 has a magnitude greater than about 0.04 nm/number of layers. In some embodiments, the linear fit 51 has an r-squared value R3 greater than about 0.8. The r-squared value R3 is a statistical measure used to determine how closely the curve 50 fits the linear fit 51 . In some embodiments, the linear fit 51 has an r-squared value R3 of greater than about 0.85, greater than about 0.90, or greater than about 0.95.

In one example, the linear fit 51 is according to Equation 4 provided below.

y = 0.1044x + 48.987 [equation 4]

In Equation 4, y represents the average layer thickness t2, and x represents the number of layers. In this example, S3 = 0.1044, and R3 = 0.9998.

As noted above, the values of S1 , S2 , S3 , R1 , R2 and R3 are exemplary in nature and these values may vary based on the properties of the polymeric first layer 10 and polymeric second layer 20 .

5A-5B illustrate exemplary graphs 50A, 50B, respectively. Each graph 50A, 50B includes the average layer thickness on the axis of ordinate and the number of layers on the axis of abscissa. Graph 50A shows the average layer thickness from 40 nm to 90 nm on the axis of ordinate and the number of layers from 0 to 50 on the axis of abscissa. Graph 50B shows the average layer thickness from 50 nm to 110 nm on the axis of ordinate and the number of layers from 100 to 200 on the axis of abscissa.

Both graphs 50A, 50B include curve 46 and curve 56 . Curve 46 is the average layer thickness t1 of a plurality of polymer first layers 10 versus the number of layers. Curve 56 is a plot of the average layer thickness t2 of the plurality of polymeric second layers 20 versus the number of layers. In some embodiments, the curve 46 , 56 includes at least 50 sequentially arranged polymer layers in the plurality of first polymer layers 10 and the plurality of second polymer layers 20 . In some embodiments, the curves 46, 56 include at least 100, at least 150, at least 200, at least 250, or at least 300 sequences of the plurality of polymeric first layers 10 and the plurality of polymeric second layers 20 Arranged polymer layers.

Both graphs 50A, 50B also include linear fit 47 and linear fit 57 . A linear fit 47 to at least 50 sequentially arranged polymer first layers 11 , 12 in the curve 46 has a positive slope D1. As shown in FIGS. 3A and 4A , the linear fit 47 corresponds to the linear fit 44 to the sequentially arranged polymer first layers 11 , 12 in the area 42 to the left of the inflection point area 41 . A linear fit 57 to the curve 56 for at least 50 sequentially arranged polymeric second layers 21 , 22 has a positive slope D2.

In some embodiments, slopes D1, D2 are within about 20% of each other. In some embodiments, slopes D1, D2 may be within about 15% or within about 10% of each other.

In the embodiment shown in Figure 5A, the positive slopes Dl, D2 are within about 6% of each other. In the embodiment shown in Figure 5B, the positive slopes Dl, D2 are within about 2.2% of each other.

Linear fits 47 and 57 have corresponding r-squared values P1, P2. In some embodiments, the r-squared value P1, P2 is greater than about 0.8. In some embodiments, r-squared values P1, P2 may be greater than about 0.85, greater than about 0.90, or greater than about 0.95.

In one example, the linear fit 47 from layer numbers 1 to 50 is according to Equation 5 provided below.

y = 0.0848x + 82.488 [Equation 5]

In Equation 5, y represents the average layer thickness t1, and x represents the number of layers. In this example, D1 = 0.0848, and P1 = 0.9657.

In one example, the linear fit 57 from layer numbers 1 to 50 is according to Equation 6 provided below.

y = 0.0902x + 49.474 [equation 6]

In Equation 6, y represents the average layer thickness t2, and x represents the number of layers. In this example, D2 = 0.0902, and P2 = 0.9978. Furthermore, for layer numbers 1 to 50, D1, D2 are within about 6% of each other.

In one example, the linear fit 47 from layer number 100 to 200 is according to Equation 7 provided below.

y = 0.1084x + 81.534 [Equation 7]

In Equation 7, y represents the average layer thickness t1, and x represents the number of layers. In this example, D1 = 0.1084, and P1 = 0.9657.

In one example, the linear fit 57 from layer number 100 to 200 is according to Equation 8 provided below.

y = 0.1061x + 48.722 [Equation 8]

In Equation 8, y represents the average layer thickness t2, and x represents the number of layers. In this example, D2 = 0.1061, and P2 = 0.9998. Furthermore, for layer numbers 100 to 200, D1, D2 are within about 2.2% of each other.

As noted above, the values of D1 , D2 , P1 and P2 are exemplary in nature and these values may vary based on the properties of the polymeric first layer 10 and polymeric second layer 20 .

As can be seen from FIGS. 5A and 5B , before the inflection point region 41 (as shown in FIG. 3A ), the rate of change of the average layer thickness of the polymer first layer 10 with respect to the number of layers and the average layer thickness of the polymer second layer 20 The rate of change of thickness versus number of layers is within a specified range of each other (eg, within about 20% of each other).

FIG. 6A shows an exemplary graph 60A. Graph 60A includes refractive index on the axis of ordinate and wavelength on the axis of abscissa. The wavelength is in the range extending from 400nm to 700nm.

Graph 60A includes curve 81 , curve 82 , curve 84 , and curve 86 . Curve 81 depicts the average refractive index navg for each "A" polymer layer. The average refractive index navg corresponds to the average of the refractive indices nx, ny and nz of each "A" polymer layer. For a given wavelength, navg=(nx+ny+nz)/3. Consider the average refractive index navg of each "A" polymer layer, since each "A" polymer layer is made of an isotropic material. Thus, the maximum variation between the refractive indices nx, ny, nz of each "A" polymer layer is very small (eg, less than about 0.05) over the wavelength range of 400 nm to 700 nm. Curve 82 depicts the refractive index nx of each "B" polymer layer along the x-axis. Curve 84 depicts the refractive index ny of each "B" polymer layer along the y-axis. Curve 86 depicts the refractive index nz of each "B" polymer layer along the z-axis. Curves 82, 84, 86 show that the refractive indices ny and nz are lower than the refractive index nx. Curves 84, 86 are close to each other. In other words, the refractive indices ny and nz of each "B" polymer layer substantially match each other. Stretching the "A" and "B" polymer layers and simultaneously relaxing the "A" and "B" polymer layers can cause the refractive indices in the "A" and "B" polymer layers to be in non-stretched directions such as MD and ND) match very well. Thus, the refractive indices ny and nz of the "A" and "B" polymer layers in two non-stretch directions (such as MD and ND) can substantially match each other. Referring to Figure 6A, the average refractive index navg of the "A" polymer layer substantially matches the refractive indices ny and nz of the "B" polymer layer. In some embodiments, curve 84 and curve 86 may coincide with each other. Furthermore, curve 82 does not match curves 84 , 86 . Thus, the refractive index nx of the "B" polymer layer in the direction of stretch (eg, TD) is substantially mismatched or mismatched with the indices of refraction ny and nz of the "B" polymer layer in the direction of stretch (eg, TD) . Thus, there is a substantial mismatch between the refractive index nx of the "A" polymer layer and the refractive index nx of the "B" polymer layer in the stretching direction (eg, TD). Referring to FIG. 6A, the average refractive index navg of the "A" polymer layer does not match the refractive index nx of the "B" polymer layer.

FIG. 6B shows an exemplary graph 60B. Graph 60B includes the refractive index to the left of the axis of ordinates, and the magnitude of the difference between the indices of refraction ny and nz of the "B" polymer layer to the right of the axis of ordinates. Graph 60B includes wavelength on the axis of abscissa.

Figure 60B includes corresponding curves 84, 86 for the refractive indices ny and nz of the "B" polymer layer. Graph 60B also includes curve 88 , which plots the magnitude of the difference between the refractive indices ny and nz of the "B" polymer layer. As is clear from graph 60B of FIG. 6B , the magnitude of the difference between the refractive indices ny and nz of the "B" polymer layer is less than about 0.0051 (ie, |nx-ny| _B <0.0051). In other words, the refractive indices ny and nz of each "B" polymer layer substantially match each other. Furthermore, as shown in Figure 6B, the magnitude of the difference between the refractive indices ny and nz of the "B" polymer layer decreases with increasing wavelength. In other words, |ny-nz| _B is inversely proportional to wavelength.

FIG. 6C shows an exemplary graph 60C. Graph 60C includes the refractive index to the left of the axis of ordinates, and the magnitude of the difference between the indices of refraction nx and ny of the "B" polymer layer to the right of the axis of ordinates. Graph 60C includes wavelength on the axis of abscissa.

Graph 60C includes a curve 82 corresponding to the refractive index nx and a curve 84 corresponding to the refractive index ny of the polymer "B" layer. Graph 60C also includes curve 90, which depicts the difference between the refractive indices nx and ny of the "B" polymer layer. As is clear from graph 60C of FIG. 6C , the difference between the refractive indices nx and ny of the "B" polymer layer is at least 0.2 (ie, (nx-ny) _B > 0.2). Specifically, the difference between the indices of refraction nx and ny of the "B" polymer layer is greater than about 0.24 and less than about 0.36. Furthermore, as shown in Figure 6C, the difference between the refractive indices nx and ny of the "B" polymer layer decreases with increasing wavelength. In other words, (nx-ny) _B is inversely proportional to wavelength.

1 and 6A-6C, each of the "A" polymer layer and the "B" polymer layer has a refractive index nx, a refractive index ny, and a refractive index nz such that for a predetermined At least a first wavelength in the wavelength range, the maximum refractive index in the set of refractive indices formed by the refractive indices nx, ny, and nz of the "A" polymer layer, and the refractive indices ny and nz of the "B" polymer layer is related to the The magnitude of the difference between the smallest refractive indices in the set of refractive indices is less than about 0.02.

|[max(refractive index group)]-[min(refractive index group)]|≤0.02[equation 9]

Wherein the set of refractive indices includes the refractive indices nx, ny and nz of the "A" polymer layer, and the refractive indices ny and nz of the "B" polymer layer, as described below.

(refractive index group) = [(nx, ny, nz) A + (ny, nz) B] [equation 10]

In some embodiments, for at least a first wavelength within a predetermined wavelength range extending from about 400 nm to about 600 nm, the refractive indices nx, ny, and nz of the "A" polymer layer and the "B" polymer layer The magnitude of the difference between the largest refractive index in the set of refractive indices formed by ny and nz and the smallest refractive index in that set is less than about 0.01, less than about 0.007, less than about 0.006, or less than about 0.005.

In some embodiments, the magnitude of the difference between the refractive index ny and the refractive index nz of the "B" polymer layer at a second wavelength greater than the first wavelength within the predetermined wavelength range is less than that at the first wavelength "B" "The magnitude of the difference between the refractive index ny and the refractive index nz of the polymer layer. In other words, the magnitude of the difference between the refractive indices ny and nz of the "B" polymer layer is smaller at the second wavelength than at the first wavelength.

In some embodiments, the difference between the refractive index nx of the "B" polymer layer and the refractive index nx of the "A" polymer layer for at least a first wavelength within a predetermined wavelength range extending from about 400 nm to about 600 nm Values greater than about 0.1. However, in some embodiments, the magnitude of the difference between the refractive index nx of the "B" polymer layer and the refractive index nx of the "A" polymer layer can be greater than about 0.15 or greater than about 0.2.

7A and 7B illustrate exemplary graphs 70A and 70B, respectively. Graphs 70A and 70B include optical transmittance on the axis of ordinate and wavelength on the axis of abscissa. In FIG. 7A , the optical transmittance is represented on a scale from 0.8 to 1 in the axis of ordinate. In FIG. 7B , the optical transmittance is represented on a scale from 10 ⁻⁶ to 1 in the axis of ordinates.

Referring now to FIGS. 1 and 7A-7B , graphs 70A and 70B depict the optical transmittance of light incident on the plurality of polymer first layers 10 and the plurality of polymer second layers 20 versus wavelength.

Graph 70A includes two curves 102 , 104 . Curves 102 , 104 depict the optical transmission of the plurality of first polymer layers 10 and the plurality of second polymer layers 20 . In particular, curve 104 shows the optical transmission of the plurality of polymer first layers 10 and the plurality of polymer second layers 20 for a second polarization state or pass polarization state, and for incident light at an angle of incidence of about 60 degrees. Rate. Curve 102 shows the optical transmission of the polymeric first layer 10 and the polymeric second layer 20 for the second polarization state or the transmitted polarization state, and for normally incident light. In this example, the plurality of polymer first layers 10 and the plurality of polymer second layers 20 have a high optical transmittance for incident light having an incident angle of about 60 degrees and a second polarization state (eg, P polarization state) Depends on the optical transmittance of the polymer first layer 10 and the second layer 20 for normally incident light having the second polarization state. This is because the incident light reflectance varies with the incident angle at the air-polymer interface (for example, as shown in FIG. The reflectivity of the plurality of polymeric second layers 20 varies. As is clear from plot 104 of graph 70A, for a first wavelength range extending from about 400 nm to about 700 nm and for a second polarization state and an angle of incidence θ between about 55 degrees and about 65 degrees, the plurality of polymers The one layer 10 and the plurality of polymeric second layers 20 in combination have an average optical transmission of greater than about 95%. In some other embodiments, the plurality of polymeric first layers 10 and the plurality of polymeric second layers 20 are combined for a first wavelength range and for a second polarization state and an angle of incidence θ between about 55 degrees and about 65 degrees The earth has an average optical transmission of greater than about 96%, greater than about 97%, greater than about 98%, or greater than about 99%. Furthermore, the plurality of polymer first layers 10 and the plurality of polymer second Layer 20 in combination has an average optical reflectance of less than about 1% and an average optical absorptivity of less than about 1%. In some embodiments, the plurality of first polymer layers 10 and second polymer layers 20 in combination have less than about 0.5%, less than about An average optical reflectance of 0.3% or less than about 0.2%. An angle of incidence θ between about 55 degrees and about 65 degrees may correspond approximately to an angle of incidence of about 60 degrees. Furthermore, for a first wavelength range extending from about 400 nm to about 700 nm and for a second polarization state and an angle of incidence θ less than about 5 degrees, the plurality of polymer first layers 10 and the plurality of polymer second layers 20 in combination Has an average optical transmission greater than about 85%. In some other embodiments, the plurality of polymeric first layers 10 and the plurality of polymeric second layers 20 in combination have a wavelength greater than about An average optical transmission of 86%, greater than 87%, or greater than about 88%. An angle of incidence Θ of less than about 5 degrees may approximately correspond to an angle of incidence of about 0 degrees.

Graph 70B includes curve 108 . Curve 108 depicts the optical transmission of the plurality of polymer first layers 10 and the plurality of polymer second layers 20 for a first polarization state or a blocking polarization state, and for normally incident light. Optical reflectance is substantially complementary to optical transmittance, ie, optical reflectance = (1 - optical transmittance).

As is clear from graph 70B, the optical transmission of the plurality of polymer first layers 10 and the plurality of polymer second layers 20 is very low for the first polarization state and normal incident light. Specifically, for a first wavelength range extending from about 400 nm to about 700 nm and for a first polarization state and an angle of incidence θ less than about 5 degrees, the plurality of polymer first layers 10 and the plurality of polymer second layers 20 combine The earth has an average optical reflectance of greater than about 95%, an average optical transmission of less than about 1%, and an average optical absorptivity of less than about 1%. In some other embodiments, the plurality of polymeric first layers 10 and the plurality of polymeric second layers 20 in combination have a wavelength greater than about An average light reflectance of 97%, greater than about 98%, or greater than about 99%. In some embodiments, the plurality of polymeric first layers 10 and the plurality of polymeric second layers 20 in combination have less than about 0.2%, less than about 0.1% Or an average optical transmission of less than about 0.05%. In addition, the plurality of polymer first layers 10 and the plurality of polymer second Layers 20 combined have an average optical reflectance of greater than about 85%. In some other embodiments, the plurality of polymeric first layers 10 and the plurality of polymeric second layers 20 are combined for a first wavelength range and for a first polarization state and an angle of incidence θ between about 55 degrees and about 65 degrees The ground has an average optical reflectance of greater than about 87%, or greater than about 88%, or greater than about 90%. An angle of incidence θ of less than about 5 degrees may be substantially perpendicular to reflective polarizer 200 . Furthermore, an angle of incidence θ between about 55 degrees and about 65 degrees may correspond approximately to an angle of incidence of about 60 degrees.

Thus, the reflective polarizer 200, 200' has very low transmission in the blocking polarization state and very low reflectivity in the transmitting polarization state. These optical properties of reflective polarizers 200, 200' can help achieve high contrast ratios in display devices, and can also help reduce optical artifacts such as "ghosting". Wrinkle-free reflective polarizers with very low reflectivity in the pass polarization state and very low transmittance in the block polarization state can be used in high performance optical applications, such as in VR headsets.

Unless otherwise indicated, all numbers expressing characteristic dimensions, quantities and physical properties used in the specification and claims are to be understood as modified by the term "about". Accordingly, unless indicated to the contrary, the numerical parameters set forth in the foregoing specification and attached claims are approximations that can be calculated based on the desired properties sought to be obtained by those skilled in the art utilizing the teachings disclosed herein. And change.

While specific embodiments have been illustrated and described herein, those of ordinary skill in the art will recognize that various alternative and/or equivalent implementations may be used in place of the embodiments shown without departing from the scope of the present disclosure. Specific embodiments shown and described. This application is intended to cover any adaptations or variations of the specific embodiments discussed herein. Accordingly, it is intended that this disclosure be limited only by the claims and the equivalents thereof.

Claims (10)

1. A reflective polarizer comprising: a plurality of polymer first layers disposed along a first portion of the thickness of the reflective polarizer and comprising a polymer first layer at each end of the plurality of polymer first layers a terminal layer, each layer between the polymeric first terminal layer and the polymeric first terminal layer having an average layer thickness of less than about 300 nanometers (nm); and a plurality of polymeric second layers disposed along a second portion of the thickness of the reflective polarizer and comprising at each end of the plurality of polymeric second layers a polymeric second end layer, each layer between the polymeric second end layer and the polymeric second end layer having an average layer thickness of less than about 300 nm; wherein said average layer thickness versus number of layers of said plurality of polymer first layers but not said plurality of polymer second layers includes an inflection point region separating a left side region from a right side region , the left region includes at least 50 sequentially arranged polymer first layers, wherein the polymer first layer has a smaller number of layers, and the average layer thickness increases with an increase in the number of layers, so The right side region includes at least 5 polymer first layers arranged sequentially, wherein the polymer first layer has a greater number of layers, and the average layer thickness increases with the number of layers, so that for all The linear fit of the at least 50 sequentially arranged polymer first layers in the left region and the linear fit of the at least 5 sequentially arranged polymer first layers in the right region have Corresponding positive slopes S1 and S2, S2/S1≥5. 2. The reflective polarizer of claim 1 , wherein the linear fit for the at least 50 sequentially arranged polymer first layers in the left region is the same as for the at least 50 sequentially arranged polymer first layers in the right region Said linear fit of said at least 5 sequentially arranged polymeric first layers has corresponding r-squared values R1 and R2, said R1 and said R2 each being greater than about 0.8. 3. The reflective polarizer of claim 1 , wherein in said average layer thickness versus number of layers of said plurality of polymer second layers, for at least 100 sequentially arranged polymer second layers The linear fit has a positive slope with a magnitude greater than about 0.04 nm/number of layers, and an r-squared value greater than about 0.8. 4. The reflective polarizer of claim 1 , wherein in said average layer thickness versus number of layers of said plurality of polymer first layers and said plurality of polymer second layers, for at least 50 The linear fit of the sequentially arranged polymer layers has positive slopes within about 20% of each other. 5. The reflective polarizer of claim 1, wherein the plurality of polymeric first layers and the plurality of polymeric second layers are coextruded and co-stretched. 6. A reflective polarizer comprising: a plurality of polymer first layers disposed between a pair of polymer first end layers and a plurality of polymer second layers disposed between Between a pair of polymeric second end layers, each layer between the pair of polymeric first end layers and each layer between the pair of polymeric second end layers has a thickness of less than about an average thickness of 300 nanometers (nm); and at least one intermediate layer having an average thickness greater than about 500 nm disposed between the plurality of polymer first layers and the plurality of polymer second layers such that for A first wavelength range of about 700 nm, the plurality of polymer first layers and the plurality of polymer second layers in combination have: For the first polarization state and an angle of incidence of less than about 5 degrees: an average optical reflectance of greater than about 95%, an average optical transmission of less than about 1%, and an average optical absorptivity of less than about 1%; For an orthogonal second polarization state and an angle of incidence between about 55 degrees and about 65 degrees: an average optical transmittance of greater than about 95%, an average optical reflectance of less than about 1%, and an average optical absorptivity of less than about 1%; and For the first polarization state and an angle of incidence between about 55 degrees and about 65 degrees: an average optical reflectance of greater than about 85%. 7. The reflective polarizer of claim 6, wherein each of the plurality of polymer first layers and the plurality of polymer second layers form alternating A polymer layers and B polymer layers , the A polymer layer and the B polymer layer each have an average thickness of less than about 300 nm, a refractive index nx along the first polarization state, a refractive index ny along the second orthogonal polarization state, and The refractive index nz of the z-axis orthogonal to the first polarization state and said second polarization state such that for at least a first wavelength within a predetermined wavelength range extending from about 400 nm to about 600 nm: The maximum refractive index in the set of refractive indices formed by said refractive indices nx, ny and nz of said A polymer layer and said refractive indices ny and nz of said B polymer layer is different from that of said set of refractive indices the magnitude of the difference between the minimum indices of refraction is less than about 0.02; and The magnitude of the difference between the refractive indices nx of the A polymer layer and the B polymer layer is greater than about 0.1. 8. The reflective polarizer of claim 6 , wherein the curve of the average thickness versus layer number for the plurality of polymer first layers but not for the plurality of polymer second layers includes an inflection point region, wherein The inflection point region separates a left region comprising at least 50 sequentially arranged polymer first layers, wherein the polymer first layers have a lower number of layers, and the average The thickness increases with the number of layers, the right region includes at least 5 sequentially arranged polymer first layers, wherein the polymer first layer has a greater number of layers, and the average thickness increases with the number of layers increases with increasing numbers such that a linear fit for the at least 50 sequentially arranged polymer first layers in the left region and a linear fit for the at least 5 sequentially arranged in the right region The linear fit of the polymer first layer has corresponding positive slopes S1 and S2, S2/S1≥5, wherein in the curve of said average thickness versus number of layers of said plurality of polymer second layers, for at least 100 A linear fit of sequentially arranged polymeric second layers has a positive slope with a magnitude greater than about 0.04 nm/number of layers, and an r-squared value greater than about 0.8. 9. The reflective polarizer of claim 6, wherein for the second polarization state and an angle of incidence between about 55 degrees and about 65 degrees, the plurality of polymer first layers and the plurality of polymer The second layers combined have an average optical transmission of greater than about 99%. 10. The reflective polarizer of claim 6 , wherein for the second polarization state and an angle of incidence between about 55 degrees and about 65 degrees, the plurality of polymer first layers and the plurality of polymer The second layers combined have an average optical reflectance of less than about 0.5%.