Optical films and optical laminates

Abstract

To solve a problem in which, when an optical laminate having an absorbing polarizer and a reflective polarizer is used in a display, micro-wrinkling occurs which refers to a corrugation / buckling in the layers of the film.SOLUTION: An optical film includes a plurality of alternating first polymeric layers and second polymeric layers. The first polymeric layers have a smaller average in-plane index of refraction than the second polymeric layers, and the first polymeric layers have a glass transition temperature of at least 107 degrees Celsius. An optical laminate includes a linear absorbing polarizer and a reflective polarizer disposed on an absorbing polarizer and bonded to the absorbing polarizer. The reflective polarizer has an optical reflectance of at least 60% for a first polarization state and an optical transmittance of at least 60% for an orthogonal second polarization state. When heated at 105 degrees Celsius for 15 minutes, the difference in shrinkage factor between the reflective polarizer and the absorbing polarizer along the first polarization state and second polarization state is greater than about zero and greater than about 0.2%, respectively.SELECTED DRAWING: Figure 1

Description

Background Art

[0001] A polarizer laminate may comprise an absorbing polarizer and a reflecting polarizer that are integrally bonded. Such a polarizer laminate can be used in display applications.

Summary of the Invention

[0002] In some aspects of the present specification, there is provided an optical laminate comprising a linear absorbing polarizer, and a reflecting polarizer disposed on and bonded to the linear absorbing polarizer. For substantially normally incident light and for at least a first wavelength in the visible wavelength range ranging from about 420 nm to about 650 nm, the reflecting polarizer has at least 60% light reflectance for a first polarization state and at least 60% light transmittance for an orthogonal second polarization state, and the linear absorbing polarizer has at least 60% light absorptance for the first polarization state and at least 60% light transmittance for the second polarization state. When heated at 105 degrees Celsius for 15 minutes, the difference in shrinkage between the reflecting polarizer and the linear absorbing polarizer along the first polarization state and the second polarization state is more than about zero and more than about 0.2%, respectively. The reflecting polarizer comprises a plurality of alternating first polymer layers and second polymer layers, and for at least the first wavelength, the first polymer layer has a smaller average in-plane refractive index than the second polymer layer. The first polymer layer has a glass transition temperature of at least 107 degrees Celsius.

[0003] In some embodiments of this specification, integrally formed optical films are provided. The integrally formed optical film comprises a plurality of alternating first and second polymer layers, totaling at least 50, arranged between two outermost polymer layers that are opposite each other. Each of the first and second polymer layers has a thickness of less than about 400 nm, and each outermost polymer layer has a thickness of more than about 500 nm. The first polymer layers have a glass transition temperature of at least 107 degrees Celsius and an average in-plane refractive index lower than that of the second polymer layers. The minimum average peel strength between two parts of the integrally formed optical film is greater than about 0.4 N / cm, and each of the two parts comprises one of the outermost polymer layers. In some embodiments, the optical laminate comprises a linear absorbing polarizer and an integrally formed optical film arranged on and coupled to the linear absorbing polarizer. [Brief explanation of the drawing]

[0004] [Figure 1] This is a schematic cross-sectional view of an optical laminate. [Figure 2] This is a schematic diagram of the axis of passage for a reflective polarizer and a linear absorbing polarizer. [Figure 3] This is a schematic cross-sectional view of an optical component. [Figure 4] This is a schematic cross-sectional view of an optical film. [Figure 5] This is a schematic diagram of the peel test. [Figure 6] This plot shows the layer thickness profile of a reflective polarizer. [Figure 7] Figure 6 shows a plot of transmittance versus wavelength for a reflecting polarizer. [Figure 8] This plot shows the layer thickness profile of another reflective polarizer. [Figure 9] Figure 8 shows a plot of transmittance versus wavelength for a reflecting polarizer. [Modes for carrying out the invention]

[0005] The following description refers to the accompanying drawings, which constitute part of this specification and illustrate various embodiments. The drawings are not necessarily to a constant scale. It should be understood that other embodiments may be conceived and implemented without departing from the scope or spirit of this specification. Therefore, the embodiments for carrying out the following inventions should not be construed as restrictive.

[0006] Optical laminates, comprising an absorbing polarizer and an optical film and / or reflective polarizer, are useful in a variety of display applications. For example, an internal polarizer (a polarizer facing away from the observer) in a liquid crystal display (LCD) may include an optical laminate comprising a reflective polarizer facing the backlight and an absorbing polarizer facing the display panel. Polarizer laminates and their use in display applications are outlined, for example, in U.S. Patent No. 6,025,897 (Weber et al.).

[0007] A problem with using optical laminates having an absorptive polarizer and a conventional reflective polarizer in displays is the phenomenon of micro-wrinkling, which refers to wavy / buckling in the film layers. Such micro-wrinkling can occur during the lamination of the optical laminate to its components or over time. For example, optical laminates may be used in automotive applications (e.g., LCD displays in automobiles), in which case the optical laminate may be exposed to high temperatures that can cause micro-wrinkling. Micro-wrinkling is characterized by adjacent surfaces or interfaces of the multilayer film not being parallel to each other. For example, as described in PCT International Publication No. 2017 / 205106 (Stover et al.) and the corresponding U.S. Patent Application No. 16 / 301106, micro-wrinkling can be reduced by increasing the shrinkage rate of the reflective polarizer film, thereby avoiding the formation of compressive stress in the reflective polarizer film due to the shrinkage of the absorptive polarizer when exposed to high temperatures.

[0008] Multilayer optical films (e.g., reflective polarizer films) typically include alternating high-refractive-index and low-refractive-index layers. According to this specification, it has been found that microwrinkles can be reduced by selecting a polymer for the low-refractive-index layer that has a higher glass transition temperature than conventional polymers selected for the low-refractive-index layer. Conventionally, it was considered that for a multilayer film to have sufficient delamination resistance or delamination strength between adjacent layers, the low-refractive-index layer should have a relatively low glass transition temperature (e.g., below 105 degrees Celsius). However, it has now been found that using a low-refractive-index layer with a higher glass transition temperature can provide acceptable delamination resistance and result in a reduction of microwrinkles. Furthermore, it has been found that the adhesive used to bond the multilayer optical film to the absorbing polarizer can be selected to reduce microwrinkles. For example, adhesives with a low storage modulus and / or a high tanδ have been found to reduce microwrinkles. Any combination of selecting the relative shrinkage rate between the reflective polarizer or optical film and the absorbing polarizer, selecting the glass transition temperature of the low-refractive-index layer, or selecting the adhesive can be used to reduce microwrinkles.

[0009] Figure 1 is a schematic cross-sectional view of an optical laminate 100, which includes a linear absorbing polarizer 110 and an optical film and / or reflective polarizer 110 disposed on and bonded to the linear absorbing polarizer 120. In the illustrated embodiment, the optical film and / or reflective polarizer 110 and the linear absorbing polarizer 120 are integrally bonded together with an adhesive 130. In some embodiments, the optical film and / or reflective polarizer 110 is an integrally formed optical film. In some embodiments, the integrally formed optical film is a reflective polarizer having a through axis substantially aligned with the through axis of the linear absorbing polarizer.

[0010] Figure 2 is a schematic diagram of the passing axis 112 of the reflective polarizer and the passing axis 122 of the linear absorbing polarizer. The angle θ between the passing axis 112 and the passing axis 122 is shown. The passing axes can be described as substantially aligned, for example, if the angle is less than about 30 degrees. In some embodiments, the angle θ is less than about 30 degrees, or less than about 10 degrees, or less than about 5 degrees, or less than about 3 degrees.

[0011] In some embodiments, the optical laminate 100 includes a reflective polarizer 110 and a linear absorbing polarizer 120, which are bonded together with an adhesive 130, the adhesive 130 having a storage modulus G' at 105 degrees Celsius of less than about 10 kPa and a loss modulus G'' at 105 degrees Celsius, such that the ratio (tanδ) of the loss modulus G'' to the storage modulus G' is at least about 0.4, or at least about 0.5, or at least about 0.6. In some such embodiments, or in other embodiments, the adhesive 130 has a storage modulus G' at 105 degrees Celsius of less than about 8 kPa. It has been found that microwrinkles in the optical laminate are reduced by using an adhesive having a low storage modulus (e.g., less than about 10 kPa or less than about 8 kPa) and / or a high tanδ (at least about 0.4, or at least about 0.5, or at least about 0.6). The moduli G' and G'' are determined, for example, by dynamic mechanical analysis. The modulus of elasticity G' and G'' may be determined using analysis (DMA). Unless otherwise specified, the modulus of elasticity G' and G'' are determined at a frequency of 1 Hz. The modulus of elasticity may be determined, for example, according to the ASTM D4065-12 test standard.

[0012] In some embodiments, when heated at 105 degrees Celsius for 15 minutes, the difference in shrinkage rates between the reflective polarizer 110 and the linear absorptive polarizer 120 along orthogonal first and second polarization states (for example, along directions parallel to the first polarization state 215 and second polarization state 219 shown in Figure 3) is about zero and about 0.2%, respectively (for example, about -0.01% and about 0.18%, or about 0% and about 0.2%, or about 0.01% and about 0.22%, respectively). For example, the linear absorptive polarizer 120 may have shrinkage rates of 0.1% and 0.3% along the through axis and the block axis, and the reflective polarizer may have shrinkage rates of 0.3% and 0.6% along the through axis and the block axis, thereby the difference in shrinkage rates between the reflective polarizer and the absorptive polarizer along the through axis and the block axis is 0.2% and 0.3%, respectively. In some embodiments, the difference in shrinkage rates between the reflective polarizer 110 and the linear absorptive polarizer 120 along a second polarization state is greater than about 0.25% or greater than about 0.3%. In some embodiments, the difference in shrinkage rates between the reflective polarizer 110 and the linear absorptive polarizer 120 along a first polarization state is greater than about 0.05% or greater than about 0.1% or greater than about 0.15%. The difference in shrinkage rates may be less than 5%, less than 3%, or less than 1% along each polarization state. It has been found that having a difference in shrinkage rates within these ranges results in a reduction of microwrinkles in the optical laminate, for example, during lamination of the optical laminate to other components or during aging at high temperatures. The difference in shrinkage rates can be controlled by controlling the shrinkage rate of the optical film and / or the reflective polarizer 110, as further described elsewhere in this specification.

[0013] Figure 3 is a schematic cross-sectional view of an optical component 250, which may correspond to, for example, an optical film 110 or a linear absorbing polarizer 120. The optical component 250 may be a linear absorbing polarizer, an optical film, a reflective polarizer, or one or more of a plurality of alternating first polymer layers and second polymer layers. A substantially perpendicular (e.g., within 30 degrees, or 20 degrees, or 10 degrees, or 5 degrees from the perpendicular) incident light 213 having a first wavelength λ1 and a first polarization state 215 is schematically shown. A portion 233 of the incident light 213 is reflected (light reflectance × incident energy), a portion 253 of the incident light 213 (indicated by a dashed line without an arrow) is absorbed (light absorptive × incident energy), and a portion 243 of the incident light 213 is transmitted (light transmittance × incident energy). A substantially normally incident light 217 having a first wavelength λ1 and a second polarization state 219 orthogonal to the first polarization state 215 is schematically shown. A portion 237 of the incident light 217 is reflected (light reflectance × incident energy), a portion 257 of the incident light 217 is absorbed (light absorptive × incident energy), and a portion 247 of the incident light 217 is transmitted (light transmittance × incident energy).

[0014] In some embodiments, for substantially perpendicularly incident light and for at least a first wavelength in the visible wavelength range from about 420 nm to about 650 nm, a reflective polarizer has a light reflectance of at least 60% for a first polarization state 215 and a light transmittance of at least 60% for an orthogonal second polarization state 219, and a linearly absorbing polarizer has a light absorptance of at least 60% for a first polarization state 215 and a light transmittance of at least 60% for a second polarization state 219. In some embodiments, a reflective polarizer includes a plurality of alternating first and second polymer layers. In some embodiments, for substantially perpendicularly incident light and for at least a first wavelength, the plurality of alternating first and second polymer layers have a light reflectance of more than about 80% for a first polarization state 215, a light transmittance of more than about 85% for a second polarization state 219, and a light transmittance of less than about 0.1% for a first polarization state 215. In some embodiments, the linear absorbing polarizer has at least 70% light absorption for a first polarization state 215 and at least 70% light transmittance for a second polarization state 219.

[0015] Multilayer optical films are known that provide at least partially desirable transmission and / or reflection properties by arranging microlayers having different refractive indices. Such optical films have been demonstrated, for example, by co-extruding alternating polymer layers, casting the layers onto chill rolls via a film die, and then stretching the cast web. See, for example, U.S. Patent No. 3,610,729 (Rogers), No. 4,446,305 (Rogers et al.), No. 4,540,623 (Im et al.), No. 5,448,404 (Schrenk et al.), No. 5,882,774 (Jonza et al.), No. 6,157,490 (Wheatley et al.), No. 6,783,349 (Neavin et al.), and No. 9,279,921 (Kivel et al.), as well as International Publication No. 2018 / 163009 (Haag et al.). In these polymer multilayer optical films, polymer materials may be used primarily or exclusively in the fabrication of individual layers. Such films are suitable for mass production processes and can be manufactured as large sheets and roll articles.

[0016] The shrinkage rate of a multilayer optical film can be controlled by controlling the stress during the cooling of the film after stretching. It has generally been found that higher stress during this cooling results in a greater shrinkage rate. In some embodiments, heat setting is applied after the film has been stretched. Heat setting may be carried out in the final zone of a tenter oven used to orient the film, as described in U.S. Patent No. 6,827,886 (Neavin et al.). Typically, such a heat setting process is used to reduce or minimize the shrinkage rate of the film if heat is subsequently applied to the film. If it is desired to minimize the subsequent shrinkage rate of the film, the heat setting temperature may be set to the highest temperature that does not result in film breakage in the tenter, and the film may be relaxed transversely near the heat setting zone, reducing the tension of the film. Higher shrinkage rates, particularly in the mechanical direction (typically along the through axis if the optical film is a reflective polarizer), can be achieved by reducing the heat setting temperature, reducing the duration of the heat setting process with respect to a given heat setting temperature, and / or eliminating the heat setting process. Higher shrinkage rates, particularly in the transverse direction (typically along the block axis if the optical film is a reflective polarizer), can be achieved by reducing the slack of the film in the block direction. This can be done, for example, by adjusting the spacing between the tenter rails after heat setting. Reducing this spacing is often referred to as toe-in. The effects of heat setting temperature and toe-in on film shrinkage rates are described, for example, in U.S. Patent Application No. 6,797,396 (Liu et al.). Therefore, by controlling the heat setting and toe-in conditions, desired shrinkage rates in the transverse and mechanical directions can be achieved when the optical film is heated at 105 degrees Celsius for 15 minutes. Optical shrinkage rates can be determined, for example, according to the ASTM D2732-14 test standard, "Standard Test Method for Unrestrained Linear Thermal Shrinkage of Plastic Film and Sheeting."

[0017] Figure 4 is a schematic cross-sectional view of an optical film 310 that may be a reflective polarizer, comprising a plurality of alternating first polymer layers 361 and second polymer layers 362 positioned between the outermost layers 366 and 368 on opposite sides of the optical film 310. The optical film 310 may be a integrally formed optical film, and the outermost layers 366 and 368 may be polymer layers. In some embodiments, the first polymer layer 361 has a smaller average in-plane refractive index (the average of refractive indices along two orthogonal in-plane directions, such as refractive indices along orthogonal first and second polarization states) than the second polymer layer 362. For example, the second polymer layer 362 may be an oriented layer having a larger refractive index along the first in-plane direction and a smaller refractive index along the second in-plane direction, and the first polymer layer 361 may have substantially the same refractive index along the first and second in-plane directions, respectively, which is substantially equal to the refractive index of the second polymer layer along the second in-plane direction. The refractive index may be specified, for example, at the first wavelength λ1 in Figure 3. If the wavelength is not specified otherwise, the refractive index may be understood as the refractive index determined at a wavelength of 532 nm. The in-plane direction refers to the direction in the plane of the film when the film is laid flat, or the direction in the plane to which the film touches when the film is curved.

[0018] In some embodiments, at least the second polymer layer 362 is substantially uniaxially oriented. For example, in some embodiments, the optical film 310 is substantially uniaxially oriented and is a reflective polarizer having a uniaxiality U of at least 0.7, or at least 0.8, or at least 0.85, where U = (1 / MDDR-1) / (TDDR 1 / 2 -1) where MDDR is defined as the mechanically oriented stretch ratio and TDDR is defined as the transversely oriented stretch ratio. Such substantially uniaxially oriented multilayer optical films are described, for example, in U.S. Patent Application Publication No. 2010 / 0254002 (Merrill et al.).

[0019] In some embodiments, each layer within the first polymer layer 361 and the second polymer layer 362 has a thickness of less than approximately 500 nm, or less than approximately 400 nm, or less than approximately 300 nm, or less than approximately 250 nm. The thicknesses of the first polymer layer 361 and the second polymer layer 362 may be selected to provide a desired reflectance for light of a given wavelength (for example, the total optical thickness of a pair of adjacent layers may be selected to be half of a given wavelength). The thicknesses of the first polymer layer 361 and the second polymer layer 362 may be varied across the thickness of the optical film to provide a desired reflectance over a predetermined wavelength range (for example, spanning approximately 450 nm to approximately 650 nm, or approximately 420 nm to approximately 650 nm, or approximately 400 nm to approximately 700 nm).

[0020] The total number of first polymer layers 361 and second polymer layers 362 may substantially exceed those schematically shown in Figure 4. In some embodiments, there are at least 50 alternating first polymer layers 361 and second polymer layers 362 in total (e.g., 100 to 500 layers in total), arranged between the outermost polymer layers 366 and 368 on opposite sides of the optical film 310, with each of the first polymer layers 361 and second polymer layers 362 having a thickness of less than approximately 400 nm, and each of the outermost polymer layers 366 and 368 having a thickness of more than approximately 500 nm. In some embodiments, the alternating first polymer layers 361 and second polymer layers 361 of the optical film 310 are arranged between the outermost layers 366 and 368 on opposite sides of the optical film 310, with each outermost layer 366, 368 having a thickness of approximately 0.5 microns to approximately 5 microns. In some embodiments, the outermost polymer layer 366 and the outermost polymer layer 368 are each less than approximately 2 micrometers thick, less than approximately 1.5 micrometers thick, or less than 1 micrometer thick. It has been found that using outermost layers of such thickness can improve the delamination resistance of the optical film.

[0021] In some embodiments, for substantially normal incident light in a predetermined wavelength range, the optical film 300, or the plurality of alternating first polymer layers 361 and second polymer layers 362, have an average light reflectance of more than about 80% for a first polarization state, an average light transmittance of more than about 85% for an orthogonal second polarization state, and an average light transmittance of less than about 0.2% or less than about 0.1% for the first polarization state. Optical films having such transmittance and reflectance are described, for example, in International Application Publication No. 2018 / 163009 (Haag et al.).

[0022] The optical film or reflective polarizer herein may be integrally formed. As used herein, a first element "integrally formed" with a second element means that the first element and the second element are manufactured together rather than being separately manufactured and then bonded subsequently. Integrally formed includes manufacturing the first element, followed by manufacturing the second element on the first element. An optical film comprising a plurality of layers is integrally formed when the layers are manufactured together rather than being separately manufactured and then bonded subsequently (e.g., combined as a melt stream, then cast onto a chill roll to form a cast film, and then the cast film is oriented). The integrally formed optical film or reflective polarizer may comprise one or more packets of alternating polymer layers, each of the alternating polymer layers in each packet having a thickness of less than about 400 nm. Adjacent packets may be separated by layers thicker than about 500 nm, and / or layers thicker than about 500 nm may be disposed on the outermost surface of one or more packets. Such layers can be protective boundary layers (PBL) included to prevent flow profiles in a coextruded web of alternating polymer layers from causing optical defects within the alternating polymer layers.

[0023] In some embodiments, the optical film comprises two packets of alternating polymer layers, and a plurality of (e.g., at least 3, or 3 to 20) thinner PBLs (e.g., less than 400 nm thick, or less than 300 nm thick) disposed between the two packets. It has been found that this improves delamination resistance between adjacent packets, as further described in commonly owned Provisional Patent Application No. 62 / 852112, filed May 23, 2019, and entitled "MULTILAYER OPTICAL FILM".

[0024] In some embodiments, the first polymer layer 361 has a glass transition temperature of at least 107 degrees Celsius, or at least 109 degrees Celsius, or at least 112 degrees Celsius, or at least 115 degrees Celsius. In some embodiments, the glass transition temperature of the first polymer layer 361 is 125 degrees Celsius or lower, or 120 degrees Celsius or lower. It has been found that using the first polymer layer 361 having a glass transition temperature falling within any of these ranges provides acceptable delamination resistance of the optical film 310 and reduction of micro-wrinkles. In some embodiments, the outermost layer 366 and the outermost layer 368 have a glass transition temperature falling within any of these ranges. In some embodiments, the outermost layer 366 and the outermost layer 368 are formed from the same material as the first polymer layer 361.

[0025] The glass transition temperature can be determined, for example, by differential scanning calorimetry (DSC). For example, the ASTM D3418-15 or ASTM E1356-08(2014) test standards can be used to determine the glass transition temperature by DSC. Alternatively, the glass transition temperature can be determined by dynamic mechanical analysis (DMA). For example, the ASTM E1640-18 test standard can be used to determine the glass transition temperature by DMA. A polymer having a desired glass transition temperature can be formed by blending different polymers having different glass transition temperatures in a ratio that yields the desired glass transition temperature, and / or by including different segments in a copolymer in a ratio that yields the desired glass transition temperature. For example, a blend of polycarbonate and copolyester can yield a glass transition temperature within a desired range. In some embodiments, the low refractive index layer (e.g., the first polymer layer 361) is formed from a blend of polycarbonate and PETG (a copolyester of polyethylene terephthalate (PET) and cyclohexanedimethanol used as a glycol modifier, available from Eastman Chemicals (Knoxville, TN)) and PCTG (a copolyester of PET and cyclohexanedimethanol used as a glycol modifier, in twice the amount compared to PETG, also available from Eastman Chemicals (Knoxville, TN)). The proportion of polycarbonate used may be selected to give a desired glass transition temperature. In some embodiments, the high refractive index layer (e.g., the second polymer layer 362) is formed from polyethylene naphthalate (PEN) or a PEN / polyethylene terephthalate (PET) copolymer. Other polymer materials known to be useful in polymer multilayer optical films may be used as alternatives.

[0026] Interlayer delamination resistance can be characterized in terms of the peeling force between portions of an optical film. Interlayer delamination resistance can be expressed, for example, in grams / inch (understood to be grams per inch) or N / cm. For example, in some embodiments, the minimum mean delamination strength between two portions of a integrally formed optical film 310 is greater than about 0.4 N / cm (e.g., greater than 0.36 N / cm, or greater than 0.38 N / cm), or greater than about 0.6 N / cm, or greater than about 0.8 N / cm, where each of the two portions includes one of the outermost polymer layers 366, 368. In some embodiments, the minimum mean delamination strength is determined using a substantial 90-degree delamination test at a delamination rate of about 1.5 m / min, and the minimum mean delamination strength is the minimum value of the averaged delamination strength over an averaging time of about 5 seconds.

[0027] Figure 5 schematically illustrates a peel test applied to a integrally formed optical film 410, which may correspond to, for example, optical film 310. The optical film 410 may be cut to a standard size for testing (e.g., a strip 1 inch (2.54 cm) wide x 12 inches (30 cm) long). Double-sided tape 458 (e.g., 3M 665 Double Sided Tape, available from 3M Company (St. Paul, MN)) is attached to a plate 455 (e.g., a metal plate), and the film 410 is attached to the double-sided tape 448. The film 410 is cut near the edge of the film (e.g., using a razor blade) along a cut line 444 that makes an angle α with the main surface of the plate 455, for example, in the range of 20 to 60 degrees or 30 to 45 degrees. The tape 459 is attached to the film 410 such that the tape 459 covers at least the cut portion of the film 410, and that the free end 479 of the tape 459 is usable in the peel test. For example, the tape 459 can be a strip of 3M 396 tape, available from 3M Company (St. Paul, MN), approximately 1.5 inches (4 cm). The free end 479, used for gripping during the peel test, can be folded over the free end 479 itself to form a non-adhesive tab (e.g., a tab of approximately 1 / 2 inch (1.3 cm)). A substantial 90-degree peel test is then performed by peeling from the free end 479. For example, the angle β between the pulling direction ( schematically shown by the applied force F in Figure 5) and the direction parallel to the upper surface of the plate 455 can be approximately 90 degrees. The peel test is performed at a peel speed (speed at the free end along the pulling direction) in the range of approximately 1.2 to 1.8 m / min (e.g., approximately 1.5 m / min). The peel test can be performed using, for example, an IMASS SP-2000 peel tester (IMASS Inc. (Accord, MA)). The peel strength is averaged over an averaging time of approximately 4 to 6 seconds (e.g., approximately 5 seconds). The average peel strength can be determined for each of multiple samples (e.g., five film samples) with a single averaging time, or for a single (e.g., longer) sample with averaging times at multiple intervals.The minimum of these average peel strengths is called the minimum average peel strength.

[0028] The peel strength is the peel strength between two portions 434 and 435 of the optical film 410, where each of the two portions 434 and 435 includes one of the outermost polymer layers (e.g., the outermost layer 366 or outermost layer 368 shown in Figure 4). For example, during a peel test, the optical film 410 may delaminate at the interface between one of the outermost layers and one of the alternating first and second layers (e.g., the first layer 361 and the second layer 362), thereby so that one of the two portions 434 and 435 includes the delaminated outermost layer, and the other of the two portions 434 and 435 includes the remainder of the optical film 410. As another example, the optical film 410 may delaminate at the interface between two internal layers, thereby so that each of the two portions 434 and 435 includes the outermost layer and at least one of the alternating first and second layers. As yet another example, delamination may begin at the interface between the outermost layer and one of the alternating first and second layers, and then propagate into the inner layers of the optical film 410, so that each of the portions 434 and 435 includes a portion of the inner layer. [Examples]

[0029] Peel strength test method Film samples were prepared and cut into 1-inch (2.54 cm) x 12-inch (30 cm) strips. Double-sided tape (3M 665 Double Sided Tape, available from 3M Company (St. Paul, MN)) was attached to a metal plate, and the sample strips were attached to the double-sided tape. Excess film was cut from one end of the plate so that the film aligned with this edge of the plate, and a notch was made at the other edge by cutting at an acute angle with a razor blade. One end of the approximately 1.5-inch (4 cm) strip of tape (3M 396 Tape, available from 3M Company (St. Paul, MN)) was folded over the strip itself to form a 1 / 2-inch (1.3 cm) non-adhesive tab. The other end of the tape was attached to the notched edge of the film sample. Next, a 90-degree peel test was performed using an IMASS SP-2000 peel tester (IMASS Inc. (Accord, MA)) at a peel rate of 60 inches / min (1.5 m / min) with an averaging time of 5 seconds. Five strips were tested for each film sample. With respect to the results given in the examples, minimum values ​​are reported to compare the weakest or lowest force required to delaminate the layers from each other.

[0030] Shrinkage rate testing method Shrinkage rates were determined as outlined in the ASTM D2732-14 test standard, except that an oven was used instead of a constant-temperature liquid bath. Samples were prepared for >24 hours in a drying chamber (<20% RH) prior to testing. Samples were tested at 105°C (oven setting point) for 15 minutes.

[0031] Comparative Example C1 A birefringent reflective polarizer optical film was prepared as follows: Two multilayer optical packets were co-extruded, with each packet consisting of 325 alternating layers of polyethylene naphthalate (PEN) and a low refractive index isotropic layer. The low refractive index isotropic layer was made from a polycarbonate-copolyester blend (PC:coPET) with a refractive index of approximately 1.57, remaining substantially isotropic in uniaxial orientation. The PC:coPET weight ratio was approximately 41 wt% PC and 59 wt% coPET, with a Tg of 105.8 degrees Celsius. This isotropic material was selected such that, after stretching, the refractive index of the isotropic material in two unstretched directions remained substantially consistent with the refractive index of the birefringent material in the unstretched direction, while in the stretched direction, there was a substantial mismatch in refractive index between the birefringent and non-birefringent layers. The PEN and PC / coPET polymers were fed from separate extruders to a multilayer co-extrusion feed block, where the PEN and PC / coPET polymers were combined to form 661 layers in total: two packets of 325 alternating optical layers, plus a thicker protective boundary layer of PC / coPET on the outside of the laminated optical packets, and nine alternating internal protective boundary layers between the packets that have optical thickness but lack coherence. The multilayer molten material was then cast onto chill rolls via a film die in the conventional manner for polyester films and quenched upon casting. The cast web was then stretched in a parabolic tenter at a temperature of 320°F in a transverse ratio of approximately 6:1, as described in U.S. Patent No. 6,916,440 (Jackson et al.).

[0032] The layer thickness profile for the optical film of Comparative Example 1 is shown in Figure 6. The transmittance for passing and blocking under normal incidence was determined and is shown in Figure 7. The average transmittance for blocking and passing polarization at 450-650 nm was 0.011% and 86.7%, respectively. The film of Comparative Example 1 had a total thickness of approximately 58.9 μm, as measured by capacitance gauge. The shrinkage rate at 105°C for 15 minutes was approximately 1.01% in the machine direction (MD) and approximately 0.15% in the transverse direction (TD). The minimum average peel force was 256.7 g / inch.

[0033] An optical laminate was provided by laminating a Sanritz 5518 absorbing polarizer, which included an adhesive layer, onto an optical film using the adhesive on the Sanritz polarizer.

[0034] Example 1 A birefringent reflective polarizer optical film was prepared as follows: Two multilayer optical packets were co-extruded, with each packet having 325 alternating layers of 90 / 10coPEN, a polymer composed of 90% polyethylene naphthalate (PEN) and 10% polyethylene terephthalate (PET), and a low refractive index isotropic layer. The low refractive index isotropic layer was made from a blend of polycarbonate and copolyester (PC:coPET) such that the refractive index was approximately 1.57, and remained substantially isotropic in uniaxial orientation. The weight ratio of PC:coPET was approximately 61% PC and 39% coPET, and it had a Tg of 116.4 degrees Celsius. This isotropic material was selected such that, after stretching, the refractive index of the isotropic material in two non-stretching directions remained substantially the same as that of the birefringent material in the non-stretching direction, while in the stretching direction, there was a substantial mismatch in refractive index between the birefringent and non-birefringent layers. The PEN and PC / coPET polymers were fed from separate extruders to a multilayer co-extrusion feed block, where the PEN and PC / coPET polymers were combined to form a total of 661 layers, consisting of two packets of 325 alternating optical layers, plus a thicker protective boundary layer of PC / coPET on the outside of the laminated optical packets, and nine alternating internal protective boundary layers between the packets that had optical thickness but lacked coherence. The multilayer molten material was then cast onto chill rolls via a film die, in the conventional manner for polyester films, and quenched upon casting. The cast web was then stretched in a parabolic tenter at a temperature of 300°F at a transverse ratio of approximately 6:1, as described in U.S. Patent No. 6,916,440 (Jackson et al.).

[0035] The layer thickness profile for the optical film of Example 1 is shown in Figure 8. The transmittance for passing and blocking under normal incidence was determined and is shown in Figure 9. The average transmittances for blocking and passing polarization at 450-650 nm were 0.021% and 89.2%, respectively. The film of Example 1 had a total thickness of approximately 58.7 μm, as measured by capacitance gauge. The shrinkage rates at 105°C for 15 minutes were 0.31% and 0.57% for MD and TD, respectively. The minimum average peel force was 226.9 g / inch.

[0036] An optical laminate was provided by laminating an optical film with a Sanritz 5518 absorbing polarizer containing an adhesive layer (available from Sanritz Co., Ltd. (Japan)) using the adhesive on the Sanritz polarizer. The shrinkage rates of the Sanritz polarizer at 105°C for 15 minutes were 0.10% and 0.30% along the through axis and block axis, respectively.

[0037] Examples 2-8 Examples 2-8 were prepared in the same manner as Example 1, except for the modifications shown in Table 1. The glass transition temperature (Tg) of the low-index optical (LIO) layer was calculated from the glass transition temperatures of the PC and coPET used in the blend. The amounts of PC and coPET added, the calculated Tg, the shrinkage rates of the pass-through and blocked states at 105°C for 15 minutes, the difference Δ between the shrinkage rates of the pass-through and blocked states for the sample and the Sanritz polarizer at 105°C for 15 minutes, and the minimum mean peeling force are reported in Table 1. [Table 1]

[0038] Microwrinkle test 3M 8171 adhesive (available from 3M Company (St. Paul, MN)) was laminated to both sides of the optical laminates of Comparative Example C1 and Examples 1-8, and then laminated to glass slides.

[0039] Two samples from each laminate of Comparative Example C1 and Examples 1-3 were placed in an oven set to 105°C for 225 hours, and then placed in a thermal cycle oven for 20 cycles, ranging from 30 minutes at 105°C to 30 minutes at -40°C. After each oven condition, Comparative Example 1 had microwrinkles, while Examples 1-3 did not.

[0040] Two samples from each laminate of Comparative Example C1 and Examples 4-8 were placed in an oven set to 105°C for 24 hours. After 24 hours, they were removed from the oven, allowed to cool to room temperature, and inspected for microwrinkles. Comparative Example 1 had microwrinkles, while Examples 4-8 did not.

[0041] To test the effectiveness of adhesives between reflective and absorptive polarizers, various adhesives were used between the reflective polarizer of Comparative Example C1 and a Sanritz 5518 absorptive polarizer. The adhesive on the Sanritz polarizer was used to laminate the optical laminate onto a glass slide. To ensure good bonding, the samples were placed in an autoclave at 50°C and 0.5 MPa for 20 minutes. The bonded samples were then placed in an oven set to 105°C for 24 hours. The samples were then removed from the oven, allowed to cool to room temperature, and examined for microwrinkles. The results are reported in the table below. The adhesives were obtained from 3M Company (St. Paul, MN). The modulus of elasticity was determined at 105°C using DMA. [Table 2]

[0042] Terms such as "about" will be understood by those skilled in the art in the context in which they are used and described herein. Where the use of "about" in relation to quantities representing the size, volume, and physical properties of a feature is not clear to those skilled in the art in the context in which it is used and described herein, "about" will be understood to mean within 10 percent of the specified value. Where the use of "about" in relation to differences in quantities representing the size, volume, and physical properties of a feature is not clear to those skilled in the art in the context in which it is used and described herein, "about" in relation to differences will be understood to mean within 10 percent of the smaller quantity. For example, where "about zero" in relation to the difference between a quantity with a value of 0.275 and a quantity with a value of 0.3 is not clear to those skilled in the art in the context in which it is used and described herein, the difference is about zero because the difference is less than 10 percent of 0.275 and different from zero. A quantity given as an approximately specified value may be exactly the specified value. For example, where it is not clear to a person skilled in the art in the context in which it is used and described herein, a quantity having a value of about 1 means that the quantity has a value between 0.9 and 1.1, and that the value can be 1.

[0043] All references, patents, or patent applications cited above are incorporated herein by reference in their entirety. In the event of any inconsistency or conflict between any portion of an incorporated reference and this application, the information in the preceding description shall prevail.

[0044] Descriptions of elements in the figures should be understood to apply equally to corresponding elements in other figures unless otherwise indicated. While specific embodiments are illustrated and described herein, it will be understood by those skilled in the art that these specific embodiments can be replaced by various alternative and / or equivalent embodiments without departing the scope of this disclosure. This application is intended to encompass any adaptation or modification of any specific embodiment discussed herein. Therefore, this disclosure is intended to be limited only by the claims and their equivalents. The following are examples of exemplary embodiments. [Item 1] Linear absorbing polarizer and, A reflective polarizer is disposed on the linear absorbing polarizer and coupled to the linear absorbing polarizer, For substantially perpendicularly incident light, and for at least a first wavelength in the visible wavelength range of approximately 420 nm to approximately 650 nm, The reflective polarizer has a light reflectance of at least 60% for a first polarization state and a light transmittance of at least 60% for a second polarization state that is orthogonal to it. The linear absorbing polarizer has a light absorption rate of at least 60% for the first polarization state and a light transmittance of at least 60% for the second polarization state. When heated at 105 degrees Celsius for 15 minutes, the difference in shrinkage rates between the reflective polarizer and the linear absorbing polarizer along the first polarization state and the second polarization state is greater than approximately zero and greater than approximately 0.2%, respectively. The optical laminate comprising a plurality of alternating first polymer layers and second polymer layers, wherein, with respect to at least the first wavelength, the first polymer layer has a lower average in-plane refractive index than the second polymer layer, and the first polymer layer has a glass transition temperature of at least 107 degrees Celsius. [Item 2] The optical laminate according to item 1, wherein the first polymer layer has a glass transition temperature of at least 109 degrees Celsius. [Item 3] The optical laminate according to item 1, wherein the first polymer layer has a glass transition temperature of at least 115 degrees Celsius. [Item 4] An optical laminate according to any one of items 1 to 3, wherein each layer within the first polymer layer and the second polymer layer has a thickness of less than approximately 500 nm. [Item 5] The optical laminate according to item 4, wherein the plurality of alternating first polymer layers and second polymer layers of the reflective polarizer are arranged between two outermost layers on opposite sides of the reflective polarizer, and each outermost layer has a thickness of about 0.5 microns to about 5 microns. [Item 6] An optical laminate according to any one of items 1 to 5, wherein at least the second polymer layer is substantially uniaxially oriented. [Item 7] An optical laminate according to any one of items 1 to 6, wherein, with respect to substantially perpendicularly incident light and with respect to at least the first wavelength, the plurality of alternating first polymer layers and second polymer layers have a light reflectance of more than about 80% for the first polarization state, a light transmittance of more than about 85% for the second polarization state, and a light transmittance of less than about 0.1% for the first polarization state. [Item 8] The optical laminate according to any one of items 1 to 7, wherein the reflective polarizer and the linear absorbing polarizer are integrally bonded together with an adhesive, and the adhesive has a storage modulus G' at 105 degrees Celsius of less than about 10 kPa, and a loss modulus G'' at 105 degrees Celsius, wherein the ratio of the loss modulus G'' to the storage modulus G' is at least about 0.5. [Item 9] An integrally formed optical film comprising a plurality of alternating first and second polymer layers, totaling at least 50, arranged between two outermost polymer layers on opposite sides of each other, wherein each of the first and second polymer layers has a thickness of less than approximately 400 nm, each outermost polymer layer has a thickness of more than approximately 500 nm, the first polymer layer has a glass transition temperature of at least 107 degrees Celsius and an average in-plane refractive index smaller than that of the second polymer layer, the minimum average peel strength between two portions of the integrally formed optical film is greater than approximately 0.4 N / cm, and each of the two portions includes one of the outermost polymer layers. [Item 10] The optical film according to item 9, wherein the minimum average peel strength is greater than approximately 0.6 N / cm or greater than approximately 0.8 N / cm. [Item 11] The optical film according to item 9 or 10, wherein each outermost polymer layer has a thickness of less than approximately 2 micrometers. [Item 12] An optical film according to any one of items 9 to 11, wherein, with respect to substantially perpendicularly incident light and with respect to at least a first wavelength in the visible wavelength range from about 420 nm to about 650 nm, the plurality of alternating first polymer layers and second polymer layers have a light reflectance of more than about 80% for a first polarization state, a light transmittance of more than about 85% for an orthogonal second polarization state, and a light transmittance of less than about 0.1% for the first polarization state. [Item 13] Linear absorbing polarizer and, An optical film according to any one of items 9 to 12, which is placed on and coupled to the linear absorbing polarizer, An optical laminate comprising the above features. [Item 14] The optical laminate according to item 13, wherein the optical film includes a reflective polarizer having a through axis substantially aligned with the through axis of the linear absorbing polarizer. [Item 15] The optical laminate according to item 13 or 14, wherein the optical film and the linear absorbing polarizer are integrally bonded together with an adhesive, and the adhesive has a storage modulus G' at 105 degrees Celsius of less than about 10 kPa and a loss modulus G'' at 105 degrees Celsius, wherein the ratio of the loss modulus G'' to the storage modulus G' is at least about 0.5.

Claims

1. An integrally formed optical film which is a birefringent reflective polarizer comprising a total of at least 50 alternating first polymer layers and second polymer layers arranged between two outermost polymer layers on opposite sides of each other, wherein each of the first polymer layer and the second polymer layer has a thickness of less than 440 nm, each outermost polymer layer has a thickness of more than 450 nm, the first polymer layer is isotropic and has a glass transition temperature of at least 107 degrees Celsius and 120 degrees Celsius or less, and has an average in-plane refractive index smaller than that of the second polymer layer, the minimum average peel strength between two portions of the integrally formed optical film is greater than 0.36 N / cm, and each of the two portions includes one of the outermost polymer layers.

2. The optical film according to claim 1, wherein the minimum average peel strength is greater than 0.54 N / cm.

3. The optical film according to claim 1 or 2, wherein each outermost polymer layer has a thickness of less than 2.2 micrometers.

4. The optical film according to any one of claims 1 to 3, wherein, with respect to perpendicularly incident light and with respect to at least a first wavelength in the visible wavelength range from 378 nm to 715 nm, the plurality of alternating first polymer layers and second polymer layers have a light reflectance of more than 72% for a first polarization state, a light transmittance of more than 76.5% for an orthogonal second polarization state, and a light transmittance of less than 0.11% for the first polarization state.

5. Linear absorbing polarizer and, An optical film according to any one of claims 1 to 4, which is arranged on and coupled to the linear absorbing polarizer, An optical laminate comprising the above features.

6. The optical laminate according to claim 5, wherein the optical film includes a reflective polarizer having a through axis aligned with the through axis of the linear absorbing polarizer.

7. The optical laminate according to claim 5 or 6, wherein the optical film and the linear absorbing polarizer are integrally bonded together with an adhesive, and the adhesive has a storage modulus G' at 105 degrees Celsius of less than 11 kPa and a loss modulus G'' at 105 degrees Celsius, wherein the ratio of the loss modulus G'' to the storage modulus G' is at least 0.45.

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