Reflective polarizer, backlight, and display system

Abstract

A reflective polarizer includes a plurality of alternating first and second polymeric layers numbering at least 200 in total. Each of the first and second polymeric layers has an average thickness of less than about 500 nm. The first polymeric layers include at least about 90% by weight of polyethylene terephthalate (PET) and the second polymeric layers include at least about 90% by weight of copolyester (CoPET). For a substantially normally incident light and for each wavelength in a predetermined wavelength range from about 400 nm to about 700 nm, the plurality of alternating first and second polymeric layers reflects at least about 50% of the light having a first polarization state and transmits at least about 80% of the light having an orthogonal second polarization state.

Description

REFLECTIVE POLARIZER, BACKLIGHT, AND DISPLAY SYSTEMTechnical Field

[0001] The present disclosure relates to a reflective polarizer, a backlight including the reflective polarizer, and a display system including a display panel disposed on the backlight.Background

[0002] Reflective polarizers in display systems selectively reflect a light based on its polarization state. Conventional reflective polarizers may include materials which are not recyclable. In some cases, these conventional reflective polarizers may be stiff and may not be suitable for certain display systems, such as flexible display systems. Further, a delamination strength of the conventional reflective polarizers may be low. Therefore, the conventional reflective polarizers may have a short usable life.Summary

[0003] In a first aspect, the present disclosure provides a reflective polarizer. The reflective polarizer includes a plurality of alternating first and second polymeric layers numbering at least 200 in total. Each of the first and second polymeric layers has an average thickness of less than about 500 nanometers (nm). The first polymeric layers include at least about 90% by weight of polyethylene terephthalate (PET). The second polymeric layers include at least about 90% by weight of copolyester (CoPET). For a substantially normally incident light and for each wavelength in a predetermined wavelength range from about 400 nm to about 700 nm, the plurality of alternating first and second polymeric layers reflects at least about 50% of the light having a first polarization state and transmits at least about 80% of the light having an orthogonal second polarization state.

[0004] In a second aspect, the present disclosure provides a backlight for providing illumination to a display panel configured to display an image. The backlight includes an illumination source including one or more light sources and an emission surface and configured to emit light through the emission surface toward the display panel. The backlight further includes the reflective polarizer of the first aspect is disposed between the illumination source and the display panel.

[0005] In a third aspect, the present disclosure provides a display system. The display system includes a display panel disposed on the backlight of the second aspect. The display panel is configured to receive the light emitted through the emission surface and display an image. The reflective polarizer is disposed between the display panel and the emission surface.

[0006] In a fourth aspect, the present disclosure provides a reflective polarizer. The reflective polarizer includes a plurality of alternating first and second polymeric layers numbering at least 200 in total. Each of the first and second polymeric layers has an average thickness of less than about 500 nm. For a substantially normally incident light and for each wavelength in a predeterminedwavelength range from about 400 rnn to about 700 rnn, the plurality of alternating first and second polymeric layers reflects at least about 50% of the light having a first polarization state and transmits at least about 80% of the light having an orthogonal second polarization state. The first and second polymeric layers have respective refractive indices nxl and nx2 along a same in-plane first direction, respective refractive indices ny 1 and ny2 along a same in-plane second direction orthogonal to the first direction, and respective refractive indices nzl and nz2 along a same out-of-plane direction of the first and second polymeric layers orthogonal to the first and second directions. For at least one wavelength in the predetermined wavelength range, the refractive index nxl is in a range from about 1.62 to about 1.75. For the at least one wavelength in the predetermined wavelength range, the refractive index nyl is in a range from about 1.5 to about 1.6. For the at least one wavelength in the predetermined wavelength range, the refractive index nzl is in a range from about 1.45 to about 1.55. Furthermore, for the at least one wavelength in the predetermined wavelength range, each of the refractive indices nx2, ny2, and nz2 is in a range from about 1.47 to about 1.6.

[0007] 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.Brief Description of the Drawings

[0008] Exemplary embodiments disclosed herein may be more completely understood in consideration of the following detailed description in connection with the following figures. The figures are not necessarily drawn to scale. Like numbers used in the figures refer to like components. However, it will be understood that the use of a number to refer to a component in a given figure is not intended to limit the component in another figure labeled with the same number.

[0009] FIG. 1 shows a schematic sectional view of a display system, according to an embodiment of the present disclosure;

[0010] FIG. 2 shows a schematic detailed sectional view of a reflective polarizer, according to an embodiment of the present disclosure;

[0011] FIG. 3A shows a graph depicting an optical transmittance of a plurality of alternating first and second polymeric layers versus wavelength for a substantially normally incident light having a first polarization state, according to an embodiment of the present disclosure;

[0012] FIG. 3B shows a graph depicting an optical transmittance of the plurality of alternating first and second polymeric layers versus wavelength for the substantially normally incident light, having an orthogonal second polarization state, according to an embodiment of the present disclosure;

[0013] FIG. 4 shows a graph depicting an average optical transmittance of the plurality of alternating first and second polymeric layers versus total number of the alternating first and second polymeric layers for the substantially normally incident light and for a visible wavelength range, according to an embodiment of the present disclosure;

[0014] FIG. 5A shows a graph depicting an optical transmittance of the plurality of alternating first and second polymeric layers versus wavelength for an incident light incident at an oblique incident angle and having the first polarization state, according to an embodiment of the present disclosure;

[0015] FIG. 5B shows a graph depicting an optical transmittance of the plurality of alternating first and second polymeric layers versus wavelength for the incident light incident at the oblique incident angle having the second polarization state, according to an embodiment of the present disclosure;

[0016] FIG. 6 shows a graph depicting a relative axial brightness of a backlight including various samples and thickness of the various samples, according to an embodiment of the present disclosure;

[0017] FIG. 7A shows a graph depicting an on-axis brightness of a backlight including various samples, according to an embodiment of the present disclosure;

[0018] FIG. 7B shows a graph depicting an on-axis contrast ratio of a backlight including the various samples of FIG. 7 A, according to an embodiment of the present disclosure;

[0019] FIG. 7C shows a graph depicting an on-axis color of a backlight including the various samples of FIG. 7A, according to an embodiment of the present disclosure;

[0020] FIG. 8A shows a graph depicting color x of a backlight including the various samples of FIG. 7A versus horizontal viewing angle, according to an embodiment of the present disclosure;

[0021] FIG. 8B shows a graph depicting color y of a backlight including the various samples of FIG. 7A versus horizontal viewing angle, according to an embodiment of the present disclosure;

[0022] FIG. 8C shows a graph depicting color x of a backlight including the various samples of FIG. 7A versus vertical viewing angle, according to an embodiment of the present disclosure; and

[0023] FIG. 8D shows a graph depicting vertical color y of a backlight including the various samples of FIG. 7A versus vertical viewing angle, according to an embodiment of the present disclosure.Detailed Description

[0024] In the following description, reference is made to the accompanying figures that form a part thereof and in which various embodiments are shown by way of illustration. It is to be understood that other embodiments are contemplated and may be made without departing from the scope or spirit of the present disclosure. The following detailed description, therefore, is not to be taken in a limiting sense.

[0025] In the following disclosure, the following definitions are adopted.

[0026] As used herein, all numbers should be considered modified by the term “about”. As used herein, “a,” “an,” “the,” “at least one,” and “one or more” are used interchangeably.

[0027] As used herein as a modifier to a property or attribute, the term “generally”, unless otherwise specifically defined, means that the property or attribute would be readily recognizable by aperson of ordinary skill but without requiring absolute precision or a perfect match (e.g., within + / - 20 % for quantifiable properties).

[0028] The term “substantially”, unless otherwise specifically defined, means to a high degree of approximation (e.g., within + / - 10% for quantifiable properties) but again without requiring absolute precision or a perfect match.

[0029] The term “about”, unless otherwise specifically defined, means to a high degree of approximation (e.g., within + / - 5% for quantifiable properties) but again without requiring absolute precision or a perfect match.

[0030] As used herein, the terms “first” and “second” are used as identifiers. Therefore, such terms should not be construed as limiting of this disclosure. The terms “first” and “second” when used in conjunction with a feature or an element can be interchanged throughout the embodiments of this disclosure.

[0031] As used herein, “at least one of A and B” should be understood to mean “only A, only B, or both A and B”.

[0032] As used herein, the term “layer” generally refers to a thickness of material within a film that has a relatively consistent chemical composition. Layers may be of any type of material including polymeric, cellulosic, metallic, or a blend thereof. A given polymeric layer may include a single polymer-type or a blend of polymers and may be accompanied by additives. A given layer may be combined or connected to other layers to form films. A layer may be either partially or fully continuous as compared to adjacent layers or the film. A given layer may be partially or fully coextensive with adjacent layers. A layer may contain sub-layers.

[0033] Reflective polarizers in display systems selectively reflect a light based on its polarization state. Conventional reflective polarizers may include materials which are not recyclable. In some cases, these conventional reflective polarizers may be stiff and not suitable for certain display systems, such as flexible display systems. Further, a delamination strength of the conventional reflective polarizers may be low. Therefore, the conventional reflective polarizers may have a short usable life.

[0034] The present disclosure provides a reflective polarizer. The reflective polarizer includes a plurality of alternating first and second polymeric layers numbering at least 200 in total. Each of the first and second polymeric layers has an average thickness of less than about 500 nanometers (nm). The first polymeric layers include at least about 90% by weight of polyethylene terephthalate (PET). The second polymeric layers include at least about 90% by weight of copolyester (CoPET). For a substantially normally incident light and for each wavelength in a predetermined wavelength range from about 400 nm to about 700 nm, the plurality of alternating first and second polymeric layers reflects at least about 50% of the light having a first polarization state and transmits at least about 80% of the light having an orthogonal second polarization state.

[0035] Since the first and second polymeric layers substantially includes materials, such as PET and CoPET, which may be recyclable, the reflective polarizer of the present disclosure may be recyclable. Further, the reflective polarizer may be more flexible compared to the conventional reflective polarizers. In some cases, a delamination strength of the reflective polarizer of the present disclosure may be higher than the delamination strength of the conventional reflective polarizers. The reflective polarizer of the present disclosure may therefore have a longer usable life.

[0036] Referring now to figures, FIG. 1 is a schematic sectional view of a display system 300, according to an embodiment of the present disclosure.

[0037] The display system 300 defines mutually orthogonal x, y, and z-axes. The x and y-axes are in-plane axes of the display system 300, while the z-axis is a transverse axis disposed along a thickness of the display system 300. In other words, the x and y-axes are disposed along a plane of the display system 300, while the z-axis is perpendicular to the plane of the display system 300.

[0038] In the illustrated example of FIG. 1, the display system 300 includes a display panel 40 disposed on a backlight 200 for providing illumination 41 to the display panel 40. In some embodiments, the display system 300 includes the backlight 200. The display panel 40 is configured to display an image 42.

[0039] The backlight 200 includes an illumination source 21 including one or more light sources 20. The illumination source 21 further includes an emission surface 22. The illumination source 21 is configured to emit light 23 through the emission surface 22 toward the display panel 40. The backlight 200 further includes a reflective polarizer 100 disposed between the illumination source 21 and the display panel 40.

[0040] In some embodiments, the backlight 200 further includes a back reflector 27 disposed adjacent to the illumination source 21 opposite to the reflective polarizer 100. In some embodiments, the backlight 200 further includes a prismatic film 90 disposed between the reflective polarizer 100 and the emission surface 22. In some embodiments, the prismatic film 90 includes a plurality of prisms 91 extending along substantially a same longitudinal direction. In some embodiments, the longitudinal direction may extend along the y-axis.

[0041] In some embodiments, the backlight 200 further includes an absorptive polarizer 105 disposed between the reflective polarizer 100 and the display panel 40. In some embodiments, the backlight 200 further includes a bonding layer 44 disposed between the display panel 40 and the absorptive polarizer 105. In some embodiments, the display panel 40 and the absorptive polarizer 105 are bonded together using the bonding layer 44. In some embodiments, the bonding layer 44 may include an optically clear adhesive (OCA).

[0042] In some embodiments, the display panel 40 is configured to receive the light 23 emitted through the emission surface 22 and display the image 42. Furthermore, in some embodiments, the reflective polarizer 100 is disposed between the display panel 40 and the emission surface 22.

[0043] FIG. 2 is a schematic detailed sectional view of the reflective polarizer 100, according to an embodiment of the present disclosure.

[0044] In the illustrated example of FIG. 2, the reflective polarizer 100 includes a plurality of alternating first and second polymeric layers 43. The plurality of alternating first and second polymeric layers 43 includes first polymeric layers 31 and second polymeric layers 32. The plurality of alternating first and second polymeric layers 43 numbers at least 200 in total.

[0045] Each of the first and second polymeric layers 31, 32 has an average thickness t of less than about 500 nanometers (nm). The term “average thickness f ’, as used herein, refers to an average of thicknesses measured at multiple points across a plane (i.e. , the x-y plane) of each of the first and second polymeric layers 31, 32. In some embodiments, the alternating first and second polymeric layers 31, 32 are stacked along a thickness direction of the reflective polarizer 100. In some embodiments, the thickness direction extends substantially along the z-axis.

[0046] The first polymeric layers 31 include at least about 90% by weight of polyethylene terephthalate (PET). In some embodiments, the first polymeric layers 31 include at least about 99% by weight of PET.

[0047] The second polymeric layers 32 include at least about 90% by weight of copolyester (CoPET). In some embodiments, the second polymeric layers 32 include at least about 99% by weight of CoPET. In some embodiments, CoPET includes at least one of glycol-modified polyethylene terephthalate (PETG), glycol-modified poly cyclohexylenedimethylene terephthalate (PCTG), and poly(l,4 cyclohexylenedimethylene) terephthalate (PCTA).

[0048] In the illustrated example of FIG. 2, the reflective polarizer 100 further includes at least one skin layer 33 disposed on the plurality of alternating first and second polymeric layers 43. The at least one skin layer 33 has an average thickness st of greater than about 500 nm. The term “average thickness st”, as used herein, refers to an average of thicknesses measured at multiple points across a plane (i.e., the x-y plane) of each of the at least one skin layer 33. In some embodiments, the at least one skin layer 33 includes at least about 90% by weight of PET. In some embodiments, the at least one skin layer 33 includes at least about 99% by weight of PET.

[0049] In the illustrated example of FIG. 2, the at least one skin layer 33 includes a pair of skin layers 33. Further, the plurality of alternating first and second polymeric layers 43 is disposed between the pair of skin layers 33. Furthermore, the at least one skin layer 33 may protect the polymeric layers 43 and may also provide mechanical stability to the reflective polarizer 100. In some cases, the at least one skin layer 33 may act as protective boundary layer (PBL).

[0050] Since the first and second polymeric layers 31, 32 and the at least one skin layer 33 of the reflective polarizer 100 substantially includes materials, such as PET and CoPET, which may be recyclable, the reflective polarizer 100 may be recyclable. Further, the reflective polarizer 100 may be more flexible compared to conventional reflective polarizers. In some cases, a delaminationstrength of the reflective polarizer 100 may be higher than a delamination strength of the conventional reflective polarizers. The reflective polarizer 100 may therefore have a longer usable life.

[0051] Table 1 provided below summarizes test results of different experiments conducted on different test subjects for stiffness and delamination comparisons.Table 1

[0052] “DBEF-Qv2 and DBEF-Qv5” were used as the test subjects for the stiffness and delamination comparisons and are commercial reflective polarizer available from 3M Company (St. Paul, Minn.);

[0053] “PETRP (50um) and PETRP (70um)” were the test subjects for the reflective polarizer 100 having different thicknesses;

[0054] “ASTM D882” is a standard test method for measuring the tensile strength;

[0055] “DMA” is dynamic mechanical analysis;

[0056] “TMA” is thermo-mechanical analysis;

[0057] “D” is a flexural rigidity;

[0058] “E” is a young’s modulus of the test subjects;

[0059] “H” is a thickness of the test subjects;

[0060] “v” is a Poisson’s ratio of the test subjects;

[0061] “MD” is a machine direction MD; and

[0062] “TD” is a transverse direction.

[0063] The different experiments included mechanical, thermal, and delamination (or peel adhesion) experiments. The mechanical and thermal experiments were conducted for the stiffness comparison and the delamination experiments were conducted for the delamination comparison.

[0064] The mechanical experiments included different experiments for comparing tensile strength along the machine and transverse directions, storage modulus at different temperatures (i.e. , at 25°C, 85°C, and 105°C) along the machine and transverse directions, and bending stiffness different temperatures (i.e., at 25°C and 105°C) along the machine and transverse directions. The thermal experiments included different experiments for comparing coefficient of thermal expansion (0°C to 85°C) along the machine and transverse directions. The delamination experiments included different experiments for comparing delamination strength along the transverse direction.Delamination results aligned with the machine direction were not quantifiable (»TD) for all test subjects described. Thus, for purposes of testing, the TD results were measured and reported.

[0065] As is apparent from Table 1, the reflective polarizer 100 has a greater tensile strength and a greater storage modulus at the different temperatures than of the comparative test subjects, specially along the transverse direction. The greater storage modulus may provide better film handling and indevice stiffness to reduce a waviness of the film or laminates including the film within the device. Further, the reflective polarizer 100 has a greater delamination strength than of the comparative test subjects along the transverse direction.

[0066] FIG. 2 further illustrates a substantially normally incident light 35 incident on the reflective polarizer 100. In other words, the substantially normally incident light 35 is incident at an angle of about 0 degree on the reflective polarizer 100. FIG. 2 further illustrates an incident light 34 incident at an oblique incident angle al. The oblique incident angle al lies in a range from about 50 degrees to about 70 degrees.

[0067] FIG. 3 A is a graph 400 depicting an optical transmittance of the plurality of alternating first and second polymeric layers 43 (shown in FIG. 2) versus wavelength for the substantiallynormally incident light 35 (shown in FIG. 2) having a first polarization state, according to an embodiment of the present disclosure.

[0068] FIG. 3B is a graph 500 depicting an optical transmittance of the plurality of alternating first and second polymeric layers 43 (shown in FIG. 2) versus wavelength for the substantially normally incident light 35 (shown in FIG. 2) having an orthogonal second polarization state, according to an embodiment of the present disclosure.

[0069] In some embodiments, the first polarization state extends along the x-axis and the orthogonal second polarization state extends along the y-axis. In some embodiments, the first polarization state may correspond to a p-polarization state, while the second polarization state may correspond to an s-polarization state. In some other embodiments, the first polarization state may correspond to the s-polarization state, while the second polarization state may correspond to the p- polarization state.

[0070] Wavelength is expressed in nanometers (nm) in abscissa. Optical transmittance is expressed in percentage (%) in the left ordinate.

[0071] Referring to FIGS. 2 and 3A, the graph 400 includes a curve 402 depicting the optical transmittance of the plurality of alternating first and second polymeric layers 43 numbering about 275 in total for the substantially normally incident light 35 having the first polarization state. The graph 400 further includes a curve 404 depicting the optical transmittance of the plurality of alternating first and second polymeric layers 43 numbering about 305 in total for the substantially normally incident light 35 having the first polarization state. The graph 400 further includes a curve 406 depicting the optical transmittance of the plurality of alternating first and second polymeric layers 43 numbering about 650 in total for the substantially normally incident light 35 having the first polarization state. Furthermore, the graph 400 includes a curve 408 depicting the optical transmittance of the plurality of alternating first and second polymeric layers 43 numbering about 800 in total for the substantially normally incident light 35 having the first polarization state.

[0072] The graph 400 further includes a curve 410 depicting an optical transmittance of a comparative reflective polarizer including alternating polyethylene naphthalate (PEN) and cyclo olefin polyethylene naphthalate (CoPEN) layers numbering about 305 in total for the substantially normally incident light 35 having the first polarization state.

[0073] Referring to FIGS. 2 and 3B, the graph 500 includes a curve 502 depicting the optical transmittance of the plurality of alternating first and second polymeric layers 43 numbering about 275 in total for the substantially normally incident light 35 having the second polarization state. The graph 500 further includes a curve 504 depicting the optical transmittance of the plurality of alternating first and second polymeric layers 43 numbering about 305 in total for the substantially normally incident light 35 having the second polarization state. The graph 500 further includes a curve 506 depicting the optical transmittance of the plurality of alternating first and second polymeric layers 43 numbering about 650 in total for the substantially normally incident light 35 having thesecond polarization state. Furthermore, the graph 500 includes a curve 508 depicting the optical transmittance of the plurality of alternating first and second polymeric layers 43 numbering about 800 in total for the substantially normally incident light 35 having the second polarization state.

[0074] The graph 500 further includes a curve 510 depicting an optical transmittance of the comparative reflective polarizer including the alternating PEN and CoPEN layers numbering about 305 in total for the substantially normally incident light 35 having the second polarization state.

[0075] Referring to FIGS. 2, 3A, and 3B, for the substantially normally incident light 35 and for each wavelength in a predetermined wavelength range 50 from about 400 nm to about 700 nm, the plurality of alternating first and second polymeric layers 43 reflects at least about 50% of the light 35 having the first polarization state and transmits at least about 80% of the light having the orthogonal second polarization state. In some embodiments, for the substantially normally incident light 35 and for each wavelength in the predetermined wavelength range 50, the plurality of alternating first and second polymeric layers 43 reflects at least about 55%, at least about 60%, at least about 65%, at least about 70%, at least about 75%, at least about 80%, at least about 85%, or at least about 90% of the light 35 having the first polarization state and transmits at least about 85% of the light having the orthogonal second polarization state.

[0076] As is apparent from the curve 406, in some embodiments, the plurality of alternating first and second polymeric layers 43 number at least 600 in total, such that for the substantially normally incident light 35 and for each wavelength in the predetermined wavelength range 50, the plurality of alternating first and second polymeric layers 43 reflects at least about 75% of the light 35 having the first polarization state. In some embodiments, the plurality of alternating first and second polymeric layers 43 number at least 600 in total, such that for the substantially normally incident light 35 and for each wavelength in the predetermined wavelength range 50, the plurality of alternating first and second polymeric layers 43 reflects at least about 80%, or at least about 85% of the light 35 having the first polarization state.

[0077] As is apparent from the curve 408, in some embodiments, the plurality of alternating first and second polymeric layers 43 number at least 800 in total, such that for the substantially normally incident light 35 and for each wavelength in the predetermined wavelength range 50, the plurality of alternating first and second polymeric layers 43 reflects at least 85% of the light 35 having the first polarization state. In some embodiments, the plurality of alternating first and second polymeric layers 43 number at least 800 in total, such that for the substantially normally incident light 35 and for each wavelength in the predetermined wavelength range 50, the plurality of alternating first and second polymeric layers 43 reflects at least about 90% of the light 35 having the first polarization state.

[0078] Referring to FIGS. 2, 3 A, and 3B, in some embodiments, the first and second polymeric layers 31, 32 have respective refractive indices nxl and nx2 along a same in-plane first direction. In some embodiments, the first and second polymeric layers 31, 32 have respective refractive indices ny 1 and ny2 along a same in-plane second direction orthogonal to the first direction. Furthermore, insome embodiments, the first and second polymeric layers 31, 32 have respective refractive indices nzl and nz2 along a same out-of-plane direction of the first and second polymeric layers 31, 32 orthogonal to the first and second directions. In some embodiments, the in-plane first direction extends substantially along the x-axis, the in-plane second direction extends substantially along the y- axis, and the out-of-plane direction extends substantially along the z-axis.

[0079] In some embodiments, for at least one wavelength in the predetermined wavelength range 50, the refractive index nxl is in a range from about 1.62 to about 1.75. In some embodiments, for the at least one wavelength in the predetermined wavelength range 50, the refractive index ny 1 is in a range from about 1.5 to about 1.6. In some embodiments, for the at least one wavelength in the predetermined wavelength 50 range, the refractive index nzl is in a range from about 1.45 to about 1.55.

[0080] In some embodiments, for the at least one wavelength in the predetermined wavelength range 50, each of the refractive indices nx2, ny2, and nz2 is in a range from about 1.47 to about 1.6. In some embodiments, for the at least one wavelength in the predetermined wavelength range 50, the refractive indices nx2, ny2, and nz2 are substantially equal to each other.

[0081] In some embodiments, the first polymeric layers 31 are birefringent and the second polymeric layers 32 are substantially isotropic.

[0082] Furthermore, in some embodiments, for the at least one wavelength in the predetermined wavelength range 50, each of the refractive indices nx2, ny2, and nz2 is greater than the refractive index nzl and less than the refractive indices nxl and ny 1.

[0083] Table 2 provided below includes, for the at least one wavelength in the predetermined wavelength range 50, the refractive indices nxl, ny 1, and nzl of the first polymeric layers 31 that include PET and the refractive indices nx2, ny2, and nz2 of the second polymeric layers 32 that include CoPET, such as PETg.Table 2

[0084] FIG. 4 is a graph 600 depicting an average optical transmittance of the plurality of alternating first and second polymeric layers 43 versus total number of the alternating first and second polymeric layers 43 for the substantially normally incident light 35 in a visible wavelength range extending from about 380 nm to about 700 nm and having the first polarization state, according to an embodiment of the present disclosure.

[0085] Number of layers is expressed in abscissa. Optical transmitance is expressed in percentage (%) in the left ordinate.

[0086] In the illustrated example of FIG. 4, the graph 600 includes a point 602 depicting the average optical transmittance of the plurality of alternating first and second polymeric layers 43 numbering about 275 in total for the substantially normally incident light 35 in the visible wavelength range and having the first polarization state. The average optical transmittance of the plurality of alternating first and second polymeric layers 43 numbering 275 in total is about 26.7% for the substantially normally incident light 35 in the visible wavelength range and having the first polarization state.

[0087] The graph 600 further includes a point 604 depicting the average optical transmittance of the plurality of alternating first and second polymeric layers 43 numbering about 305 in total for the substantially normally incident light 35 in the visible wavelength range having the first polarization state. The average optical transmittance of the plurality of alternating first and second polymeric layers 43 numbering 305 in total is about 23.4% for the substantially normally incident light 35 in the visible wavelength range and having the first polarization state.

[0088] The graph 600 further includes a point 606 depicting the average optical transmittance of the plurality of alternating first and second polymeric layers 43 numbering about 650 in total for the substantially normally incident light 35 in the visible wavelength range and having the first polarization state. The average optical transmittance of the plurality of alternating first and second polymeric layers 43 numbering 650 in total is about 4.8% for the substantially normally incident light 35 in the visible wavelength range and having the first polarization state.

[0089] The graph 600 further includes a point 608 depicting the average optical transmittance of the plurality of alternating first and second polymeric layers 43 numbering about 800 in total for the substantially normally incident light 35 in the visible wavelength range and having the first polarization state. The average optical transmittance of the plurality of alternating first and second polymeric layers 43 numbering 800 in total is about 2.4% for the substantially normally incident light 35 in the visible wavelength range and having the first polarization state.

[0090] Table 3 provided below summarizes the number of layers of the plurality of alternating first and second polymeric layers 43 and their respective average optical transmitance for the substantially normally incident light 35 in the visible wavelength range and having the first polarization state.Table 3

[0091] FIG. 5A is a graph 700 depicting an optical transmittance of the plurality of alternating first and second polymeric layers 43 versus wavelength for the incident light 34 (shown in FIG. 2) incident at the oblique incident angle al (shown in FIG. 2) and having the first polarization state, according to an embodiment of the present disclosure.

[0092] FIG. 5B is a graph 800 depicting an optical transmittance of the plurality of alternating first and second polymeric layers 43 versus wavelength for the incident light 34 incident at the oblique incident angle al and having the orthogonal second polarization state, according to an embodiment of the present disclosure.

[0093] Wavelength is expressed in nanometers (nm) in abscissa. Optical transmittance is expressed in percentage (%) in the left ordinate.

[0094] Referring to FIGS. 2 and 5A, the graph 700 includes a curve 702 depicting the optical transmittance of the plurality of alternating first and second polymeric layers 43 numbering about 275 in total for the incident light 34 incident at the oblique incident angle al and having the first polarization state. The graph 700 further includes a curve 704 depicting the optical transmittance of the plurality of alternating first and second polymeric layers 43 numbering about 305 in total for the incident light 34 incident at the oblique incident angle al and having the first polarization state. The graph 700 further includes a curve 706 depicting the optical transmittance of the plurality of alternating first and second polymeric layers 43 numbering about 650 in total for the incident light 34 incident at the oblique incident angle al and having the first polarization state. Furthermore, the graph 700 includes a curve 708 depicting the optical transmittance of the plurality of alternating first and second polymeric layers 43 numbering about 800 in total for the incident light 34 incident at the oblique incident angle al and having the first polarization state.

[0095] The graph 700 further includes a curve 710 depicting an optical transmittance of a comparative reflective polarizer including the alternating PEN and CoPEN layers numbering about 305 in total for the incident light 34 incident at the oblique incident angle al and having the first polarization state.

[0096] Referring to FIGS. 2 and 5B, the graph 800 includes a curve 802 depicting the optical transmittance of the plurality of alternating first and second polymeric layers 43 numbering about 275 in total for the incident light 34 incident at the oblique incident angle al and having the second polarization state. The graph 800 further includes a curve 804 depicting the optical transmittance of the plurality of alternating first and second polymeric layers 43 numbering about 305 in total for the incident light 34 incident at the oblique incident angle al and having the second polarization state. The graph 800 further includes a curve 806 depicting the optical transmittance of the plurality of alternating first and second polymeric layers 43 numbering about 650 in total for the incident light 34incident at the oblique incident angle al and having the second polarization state. Furthermore, the graph 800 includes a curve 808 depicting the optical transmittance of the plurality of alternating first and second polymeric layers 43 numbering about 800 in total for the incident light 34 incident at the oblique incident angle al and having the second polarization state.

[0097] The graph 800 further includes a curve 810 depicting an optical transmittance of the comparative reflective polarizer including the alternating PEN and CoPEN layers numbering about 305 in total for the incident light 34 incident at the oblique incident angle al and having the second polarization state.

[0098] Referring to FIGS. 2, 5A, and 5B, for the incident light 34 incident at the oblique incident angle al (shown in FIG. 2) in the range from about 50 degrees to about 70 degrees and for each wavelength in the predetermined wavelength range 50, the plurality of alternating first and second polymeric layers 43 reflects at least about 70% of the light 34 having the first polarization state and transmits at least about 60% of the light 34 having the second polarization state.

[0099] As is apparent from the curve 806, in some embodiments, the plurality of alternating first and second polymeric layers 43 number at least 600 in total, such that for the incident light 34 incident at the oblique incident angle al and for each wavelength in a second wavelength range 54 from about 450 nm to about 650 nm, the plurality of alternating first and second polymeric layers 43 transmits at most about 85% of the light 34 having the second polarization state.

[0100] In some embodiments, the plurality of alternating first and second polymeric layers 43 number at least 600 in total, such that for the incident light 34 incident at the oblique incident angle al and having the second polarization state, and for the predetermined wavelength range 50, the plurality of alternating first and second polymeric layers 43 include a maximum optical transmittance Tlmax and a minimum optical transmittance Timin, Tlmax / Tlmin > 1.2.

[0101] In some embodiments, the plurality of alternating first and second polymeric layers 43 number at least 600 in total, such that for the incident light 34 incident at the oblique incident angle al and having the second polarization state, and for the predetermined wavelength range 50, the plurality of alternating first and second polymeric layers 43 has the maximum optical transmittance Tlmax and the minimum optical transmittance Timin, the minimum optical transmittance Timin and the maximum optical transmittance Tlmax lie in a wavelength range 52 from about 650 nm to about 700 nm, and a difference between the maximum optical transmittance Tlmax and the minimum optical transmittance Timin is at least 20%. In some embodiments, the plurality of alternating first and second polymeric layers 43 number at least 600 in total, such that for the incident light 34 incident at the oblique incident angle al and having the second polarization state, and for the predetermined wavelength range 50, the difference between the maximum optical transmittance Tlmax and the minimum optical transmittance Timin is at least 25%.

[0102] As is apparent from the curve 808, in some embodiments, the plurality of alternating first and second polymeric layers 43 number at least 800 in total, such that for the incident light 34incident at the oblique incident angle al and for each wavelength in the second wavelength range 54, the plurality of alternating first and second polymeric layers 43 transmits at most about 80% of the light 34 having the second polarization state.

[0103] In some embodiments, the plurality of alternating first and second polymeric layers 43 number at least 800 in total, such that for the incident light 34 incident at the oblique incident angle al and having the second polarization state, and for the predetermined wavelength range 50, the plurality of alternating first and second polymeric layers 43 has a maximum optical transmittance T2max and a minimum optical transmittance T2min, T2max / T2min > 1.3.

[0104] In some embodiments, the plurality of alternating first and second polymeric layers 43 number at least 800 in total, such that for the incident light 34 incident at the oblique incident angle al and having the second polarization state, and for the predetermined wavelength range 50, the plurality of alternating first and second polymeric layers 43 has the maximum optical transmittance T2max and the minimum optical transmittance T2min, the minimum optical transmittance T2min and the maximum optical transmittance T2max lie in the wavelength range 52 from about 650 nm to about 700 nm, and the difference between the maximum optical transmittance T2max and the minimum optical transmittance T2min is at least 25%. In some embodiments, the plurality of alternating first and second polymeric layers 43 number at least 800 in total, such that for the incident light 34 incident at the oblique incident angle al and having the second polarization state, and for the predetermined wavelength range 50, the difference between the maximum optical transmittance T2max and the minimum optical transmittance T2min is at least 30%.

[0105] As is apparent from the curves 806, 808, in some embodiments, the plurality of alternating first and second polymeric layers 43 number at least 600 in total, such that for the incident light 34 incident at the oblique incident angle al and having the second polarization state, and for the predetermined wavelength range 50, the plurality of alternating first and second polymeric layers 43 has the optical transmittance as a function of wavelength that includes a band edge 60 correlating the optical transmittance to wavelength at least across an increasing transition wavelength range where the optical transmittance decreases greater than about 10%, has a slope having a magnitude of greater than about 0.7% / nm.

[0106] Furthermore, in some embodiments, the plurality of alternating first and second polymeric layers 43 number at least 600 in total, such that for the incident light 34 incident at the oblique incident angle al and having the second polarization state, and for the predetermined wavelength range 50, the plurality of alternating first and second polymeric layers 43 has the optical transmittance as a function of wavelength that includes a band edge 70 correlating the optical transmittance to wavelength at least across an increasing transition wavelength range where the optical transmittance increases greater than about 20%, has a slope having a magnitude of greater than about 0.8% / nm.

[0107] FIG. 6 is a graph 900 depicting a relative axial brightness of a backlight including various samples with respect to an axial brightness of a backlight including the comparative reflective polarizer, according to an embodiment of the present disclosure. The graph 900 further depicts thickness of the samples, according to an embodiment of the present disclosure. The backlight is substantially similar to the backlight 200 shown in FIG. 1. However, the backlight includes one of the samples.

[0108] The samples are provided in abscissa. The relative axial brightness is expressed as bars and in percentage (%) in the left ordinate, while the thickness is expressed as points joined by a dashed line and in micrometers (um) in the right ordinate.

[0109] The graph 900 includes a sample 902 without any reflective polarizer. The graph 900 includes a sample 904 of the comparative reflective polarizer (i.e. , the comparative reflective polarizer including the alternating PEN and CoPEN layers numbering about 305 in total). The graph 900 further includes a sample 906 of the reflective polarizer 100 (shown in FIG. 1) having the plurality of alternating first and second polymeric layers 43 (shown in FIG. 2) numbering about 275 in total, a sample 908 of the reflective polarizer 100 having the plurality of alternating first and second polymeric layers 43 numbering about 305 in total, a sample 910 of the reflective polarizer 100 having the plurality of alternating first and second polymeric layers 43 numbering about 650 in total, and a sample 912 of the reflective polarizer 100 having the plurality of alternating first and second polymeric layers 43 numbering about 800 in total.

[0110] As discussed above, the relative axial brightness of the backlight including the samples 902, 906, 908, 910, 912 is with respect to the axial brightness of the backlight including the comparative reflective polarizer (i.e., the sample 904).

[0111] As is apparent from the graph 900, in some embodiments, each of the backlights including the reflective polarizer 100 have a relative axial brightness at least greater than 10% as compared to a backlight that has a same construction except that it does not include any reflective polarizer. In other words, the backlights including the samples 906, 908, 910, 912 have the relative axial brightness at least greater than 10% as compared to the backlight including the sample 902. In some embodiments, the backlight including the reflective polarizer 100 has the relative axial brightness at least greater than 15%, at least greater than 20%, or at least greater than 25% as compared to the backlight that has the same construction except that it does not include any reflective polarizer.

[0112] In some embodiments, when the backlight includes the samples 910, 912 (i.e., when the reflective polarizer 100 includes at least 650 layers) the backlight has the relative axial brightness greater than the axial brightness of the backlight including the sample 904 (i.e., the comparative reflective polarizer).

[0113] FIG. 7A is a graph 1000 depicting an on-axis brightness of a backlight including various samples, according to an embodiment of the present disclosure. Specifically, the graph 1000 depictsthe on-axis brightness of the backlights including samples 1002, 1004, 1006, 1008, 1010. For each sample 1002, 1004, 1006, 1008, 1010, three trials were performed and are shown in the graph 1000.

[0114] The graph 1000 includes a sample 1002 without any reflective polarizer. The graph 1000 includes a sample 1004 including APF-V3 (Advanced Polarizing Film, available from 3M Company, St. Paul, Minn.). The graph 1000 further includes a sample 1006 of the comparative reflective polarizer having skin layers of average thickness of about 18 microns. The graph 1000 further includes a sample 1008 of the reflective polarizer 100 (shown in FIG. 2) having the plurality of alternating first and second polymeric layers 43 (shown in FIG. 2) numbering about 275 in total. The graph 1000 further includes a sample 1010 of the comparative reflective polarizer having skin layers of average thickness of about 28 microns.

[0115] As is apparent from the graph 1000, the backlight 200 (including the reflective polarizer 100 or the sample 1008) has an on-axis brightness at least greater than 10% as compared to a backlight (not shown) that has a same construction except that it does not include the reflective polarizer 100 (for example, the sample 1002 does not include any reflective polarizer). In some embodiments, the backlight 200 has the on-axis brightness at least greater than 15%, at least greater than 20%, or at least greater than 25% as compared to the backlight 200 that has a same construction except that it does not include any reflective polarizer.

[0116] FIG. 7B is a graph 1001 depicting an on-axis contrast ratio of a backlight including the various samples of FIG. 7 A, according to an embodiment of the present disclosure. For each sample 1002, 1004, 1006, 1008, 1010, three trials were performed and are shown in the graph 1001.

[0117] As is apparent from the graph 1001, in some embodiments, the backlight 200 has an on- axis contrast ratio not less than 5% as compared to a backlight (not shown) that has a same construction except that it does not include the reflective polarizer 100.

[0118] FIG. 7C is a graph 1003 depicting an on-axis color of a backlight including the various samples of FIG. 7A, according to an embodiment of the present disclosure. For each sample 1002, 1004, 1006, 1008, 1010, three trials were performed and are shown in the graph 1003.

[0119] In some embodiments, light (e.g., the illumination 41 shown in FIG. 1) emitted by the backlight 200 and a backlight (not shown) that has a same construction except that it does not include the reflective polarizer 100 at zero degree with respect to a line (not shown) normal to the emission surface 22 (shown in FIG. 1) have respective color coordinates (xl, y 1) and (x2, y2) in Commission Internationale de FEclairage (CIE) 1931 chromaticity coordinate system in a white region.Furthermore, in some embodiments, each of a magnitude of difference between xl and x2 and a magnitude of difference between yl and y2 is less than about 0.01.

[0120] Table 4 provided below summarizes the graphs 1000, 1001, 1003 for the on-axis brightness, the on-axis contrast ratio, the on-axis color, respectively.Table 4

[0121] “Trial” refers to a number of trials carried out on the samples 1002, 1004, 1006, 1008,1010;

[0122] “Avg.” refers to an average of values obtained from the trails;

[0123] “White” refers to region;

[0124] “Y” refers to the on-axis brightness performance of the samplesl002, 1004, 1006, 1008,1010, measured in unit of ‘nit’;

[0125] “x” and “y” refer to the on-axis color coordinates;

[0126] “CR” refers to the on-axis contrast ratio; and

[0127] “White (vs no film)” refers to a comparison of Y, x, y, and CR performance of each of the samples 1004, 1006, 1008, 1010 with that of the sample 1002 with no film in the white region.

[0128] Referring to FIGS. 8A, 8B, 8C, and 8D, FIG. 8A is a graph 2000 depicting color x of a backlight including the various samples of FIG. 7A versus horizontal viewing angle, according to an embodiment of the present disclosure. FIG. 8B shows a graph 3000 depicting color y of a backlightincluding the various samples of FIG. 7 A versus horizontal viewing angle, according to an embodiment of the present disclosure. FIG. 8C shows a graph 4000 depicting color x of a backlight including the various samples of FIG. 7 A versus vertical viewing angle, according to an embodiment of the present disclosure. FIG. 8D shows a graph 5000 depicting color y of a backlight including the various samples of FIG. 7 A versus vertical viewing angle, according to an embodiment of the present disclosure. As is apparent from FIGS. 8A-8D, the sample 1008 (i.e., the reflective polarizer 100) has a similar performance to that of the samples 1004, 1006.

[0129] Unless otherwise indicated, all numbers expressing feature sizes, amounts, and physical properties used in the specification and claims are to be understood as being 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 vary depending upon the desired properties sought to be obtained by those skilled in the art utilizing the teachings disclosed herein.

[0130] 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 of the specific embodiments discussed herein. Therefore, it is intended that this disclosure be limited only by the claims and the equivalents thereof.

Claims

CLAIMS1. A reflective polarizer comprising: a plurality of alternating first and second polymeric layers numbering at least 200 in total, each of the first and second polymeric layers having an average thickness of less than about 500 nanometers (nm), the first polymeric layers comprising at least about 90% by weight of polyethylene terephthalate (PET), the second polymeric layers comprising at least about 90% by weight of copolyester (CoPET), such that: for a substantially normally incident light and for each wavelength in a predetermined wavelength range from about 400 nm to about 700 nm, the plurality of alternating first and second polymeric layers reflects at least about 50% of the light having a first polarization state and transmits at least about 80% of the light having an orthogonal second polarization state.

2. The reflective polarizer of claim 1, wherein the first polymeric layers comprise at least about 99% by weight of PET.

3. The reflective polarizer of claim 1, wherein the second polymeric layers comprise at least about 99% by weight of CoPET.

4. The reflective polarizer of claim 1, wherein CoPET includes at least one of glycol-modified polyethylene terephthalate (PETG), glycol-modified polycyclohexylenedimethylene terephthalate (PCTG), and poly(l,4 cyclohexylenedimethylene) terephthalate (PCTA).

5. The reflective polarizer of claim 1, wherein the first polymeric layers are birefringent, and wherein the second polymeric layers are substantially isotropic.

6. The reflective polarizer of claim 1, wherein the first and second polymeric layers have respective refractive indices nxl and nx2 along a same in-plane first direction, respective refractive indices nyl and ny2 along a same in-plane second direction orthogonal to the first direction, and respective refractive indices nzl and nz2 along a same out-of-plane direction of the first and second polymeric layers orthogonal to the first and second directions, such that for at least one wavelength in the predetermined wavelength range: the refractive index nxl is in a range from about 1.62 to about 1.75; the refractive index nyl is in a range from about 1.5 to about 1.6; the refractive index nzl is in a range from about 1.45 to about 1.55; and each of the refractive indices nx2, ny2, and nz2 is in a range from about 1.47 to about 1.6.

7. The reflective polarizer of claim 1, wherein the plurality of alternating first and second polymeric layers number at least 600 in total, such that for the substantially normally incident light and for each wavelength in the predetermined wavelength range, the plurality of alternating first and second polymeric layers reflects at least about 75% of the light having the first polarization state.

8. The reflective polarizer of claim 1, wherein for an incident light incident at an oblique incident angle in a range from about 50 degrees to about 70 degrees and for each wavelength in the predetermined wavelength, the plurality of alternating first and second polymeric layers reflects at least about 70% of the light having the first polarization state and transmits at least about 60% of the light having the second polarization state.

9. The reflective polarizer of claim 8, wherein the plurality of alternating first and second polymeric layers number at least 600 in total, such that for the incident light incident at the oblique incident angle and having the second polarization state, and for the predetermined wavelength range, the plurality of alternating first and second polymeric layers has a maximum optical transmittance Tlmax and a minimum optical transmittance Timin, Tlmax / Tlmin > 1.2.

10. The reflective polarizer of claim 8, wherein the plurality of alternating first and second polymeric layers number at least 800 in total, such that for the incident light incident at the oblique incident angle and having the second polarization state, and for the predetermined wavelength range, the plurality of alternating first and second polymeric layers has a maximum optical transmittance T2max and a minimum optical transmittance T2min, T2max / T2min > 1.3.

11. The reflective polarizer of claim 8, wherein the plurality of alternating first and second polymeric layers number at least 600 in total, such that for the incident light incident at the oblique incident angle and having the second polarization state, and for the predetermined wavelength range, the plurality of alternating first and second polymeric layers has an optical transmittance as a function of wavelength that comprises a band edge correlating the optical transmittance to wavelength at least across an increasing transition wavelength range where the optical transmittance decreases greater than about 10%, has a slope having a magnitude of greater than about 0.7% / nm.

12. The reflective polarizer of claim 8, wherein the plurality of alternating first and second polymeric layers number at least 600 in total, such that for the incident light incident at the oblique incident angle and having the second polarization state, and for the predetermined wavelength range, the plurality of alternating first and second polymeric layers has an optical transmittance as a function of wavelength that comprises a band edge correlating the optical transmittance to wavelength at least across anincreasing transition wavelength range where the optical transmittance increases greater than about 20%, has a slope having a magnitude of greater than about 0.8% / nm.

13. A backlight for providing illumination to a display panel configured to display an image, the backlight comprising: an illumination source comprising one or more light sources and an emission surface and configured to emit light through the emission surface toward the display panel; and the reflective polarizer of claim 1, wherein the reflective polarizer is disposed between the illumination source and the display panel.

14. The backlight of claim 13, wherein light emitted by the backlight and a backlight that has a same construction except that it does not include the reflective polarizer at zero degree with respect to a line normal to the emission surface have respective color coordinates (xl, yl) and (x2, y2) in CIE 1931 chromaticity coordinate system in a white region, wherein each of a magnitude of difference between xl and x2 and a magnitude of difference between yl and y2 is less than about 0.01.

15. A reflective polarizer comprising: a plurality of alternating first and second polymeric layers numbering at least 200 in total, each of the first and second polymeric layers having an average thickness of less than about 500 nanometers (nm), such that: for a substantially normally incident light and for each wavelength in a predetermined wavelength range from about 400 nm to about 700 nm, the plurality of alternating first and second polymeric layers reflects at least about 50% of the light having a first polarization state and transmits at least about 80% of the light having an orthogonal second polarization state, wherein the first and second polymeric layers have respective refractive indices nxl and nx2 along a same in-plane first direction, respective refractive indices nyl and ny2 along a same in-plane second direction orthogonal to the first direction, and respective refractive indices nzl and nz2 along a same out-of-plane direction of the first and second polymeric layers orthogonal to the first and second directions, such that for at least one wavelength in the predetermined wavelength range: the refractive index nxl is in a range from about 1.62 to about 1.75; the refractive index nyl is in a range from about 1.5 to about 1.6; the refractive index nzl is in a range from about 1.45 to about 1.55; and each of the refractive indices nx2, ny2, and nz2 is in a range from about 1.47 to about1.6.

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