Thin film laminate for circular polarizers

Abstract

The film laminate comprises an oriented first layer comprising polyvinyl alcohol disposed on an oriented second layer comprising a naphthalene dicarboxylate containing copolyester resin, the oriented second layer having an in-plane birefringence Δnxy of less than 0.02.

Description

[Technical Field]

[0001] The present invention relates to a film laminate useful in a circular polarizer and a method for making the film laminate. [Background technology]

[0002] Light-emitting displays, such as organic light-emitting diode (OLED) displays, often utilize circular polarizers as anti-reflection films. Typically, circular polarizers comprise film components laminated together and are relatively thick. The development of new form factors, such as bendable and wrappable light-emitting displays, requires thinner display components. Conventional thick film laminate circular polarizers cannot withstand the tight bending radii required for bendable and wrappable displays. Past attempts to create thin (e.g., less than 50 μm thick) circular polarizers have had mechanical integrity issues and resulted in films that crack or break during bending and folding. Summary of the Invention

[0003] In view of the foregoing, the present inventors have recognized a need for thin yet mechanically robust circular polarizers.

[0004] In one aspect, the present invention provides a film laminate comprising an oriented first layer comprising polyvinyl alcohol disposed on an oriented second layer comprising a naphthalene dicarboxylate containing copolyester resin, the oriented second layer having an in-plane birefringence Δnxy of less than 0.02.

[0005] In another aspect, the invention provides a film laminate comprising: (a) a carrier film including a release layer disposed between an oriented second layer including a naphthalene dicarboxylate containing copolyester resin having an in-plane birefringence Δnxy of less than 0.02 and a layer of strain-hardened polyester having a glass transition temperature at least 5° C. higher than the glass transition temperature of the naphthalene dicarboxylate containing polyester resin of the oriented second layer; and (b) an oriented first layer including polyvinyl alcohol disposed on the second layer on the opposite side of the release layer.

[0006] The film stacks of the present invention enable circular polarizers with total thicknesses of less than 35 μm, 25 μm, 20 μm, 15 μm, 10 μm, 5 μm, or 3 μm that are mechanically robust and therefore useful for highly curved, foldable, or wrappable displays.

[0007] In yet another aspect, the present invention provides a method for making a film laminate, comprising: (a) providing a carrier film comprising a release layer disposed between a second layer comprising a naphthalene dicarboxylate containing copolyester resin having an in-plane birefringence Δnxy of less than 0.02 and a layer of strain-hardened polyester having a glass transition temperature at least 5°C higher than the glass transition temperature of the naphthalene dicarboxylate containing polyester resin of the oriented second layer; (b) coating a first layer comprising polyvinyl alcohol onto the strain-hardened polyester; and (c) orienting the resulting coated carrier film in a second direction. [Brief explanation of the drawings]

[0008] [Figure 1] FIG. 2 is a cross-sectional view of a film laminate. [Figure 2] FIG. 2 is a cross-sectional view of a film laminate. [Figure 3A] 1 is a cross-sectional view of a film stack being made according to the process. [Figure 3B]1 is a cross-sectional view of a film stack being made according to the process. [Figure 3C] 1 is a cross-sectional view of a film stack being made according to the process. [Figure 3D] 1 is a cross-sectional view of a film stack being made according to the process. [Figure 3E] 1 is a cross-sectional view of a film stack being made according to the process. [Figure 3F] 1 is a cross-sectional view of a film stack being made according to the process. [Figure 4] 1 is a magnified photograph of a comparative iodine-dyed PVOH coating. [Figure 5] 1 is a scanning electron microscope (SEM) image of a cross section of a circular polarizer. [Figure 6] 1 is an SEM image of a cross section of a circular polarizer. DETAILED DESCRIPTION OF THE INVENTION

[0009] The present invention enables very thin circular polarizers comprising a dyed polyvinyl alcohol (PVOH) layer, a substrate, and a quarter-wave retarder. In some embodiments, the PVOH layer is less than 10 μm thick, the substrate is less than 20 μm thick, the quarter-wave retarder is less than 5 μm, and the total thickness of the thin circular polarizer is less than 35 μm, 25 μm, 20 μm, 15 μm, 10 μm, 5 μm, or 3 μm.

[0010] The inventors recognized that several problems must be overcome to fabricate such thin circular polarizers from thin PVOH layers. For example, a quarter-wave retarder, including an oriented polymer material or a coated liquid crystal material, must adhere to the PVOH coating. PVOH is typically processed in water, while liquid crystals are typically processed in organic solvents. The resulting film structure must also be mechanically robust, but PVOH is susceptible to cracking and damage due to stress during iodine dyeing and optional boronization. Additionally, the optical performance of the circular polarizer must not be distorted by birefringence from other layers or by disturbances to the polarization efficiency of the dyed PVOH.

[0011] To provide mechanical integrity to the thin PVOH layer, the present invention utilizes a coextruded tough film layer to carry the PVOH throughout the process. This tough film layer has many constraints. For example, it must be able to be coextruded with the carrier layer and have a similar rheology. The PVOH must adhere to the tough film layer. The tough film layer must be stretched under conditions suitable for both the strain-hardening polyester (e.g., polyethylene terephthalate, polyethylene naphthalate, or copolyesters thereof) and the PVOH. The tough film layer must have little or no birefringence and be resistant to liquid crystal solvents (i.e., not develop haze or craze). The tough film layer must be dimensionally stable throughout the PVOH dyeing process.

[0012] It has been found that naphthalene dicarboxylate containing copolyester resins with an in-plane birefringence Δnxy of less than 0.02 meet all the necessary constraints for a tough film layer. The birefringence can be calculated from refractive index measurements of the resin layer. The refractive index can be measured in the MD, TD, and TM directions using a Metricon Prism coupler (Metricon Corporation, Pennington, NJ), typically using a red laser (i.e., 635 nm). MD and TD are in-plane directions, and TM is perpendicular to the film surface. The refractive indices for TD, MD, and TM are, respectively, n x , n y , and n z is labeled as

[0013] In-plane birefringence Δn in : In-plane birefringence is used to measure the birefringence of uniaxially stretched films.

[0014] In-plane birefringence is the refractive index in the orthogonal in-plane direction (n x and n y ) More specifically for uniaxially stretched films, in-plane birefringence refers to the difference between the stretched and unstretched directions. For example, assuming the film is uniaxially stretched in the TD direction, the in-plane birefringence can be expressed as: Δn in =n x -n y =Δn xy In the formula, n x is the refractive index in the stretching direction (MD in this case), and n y is the refractive index in the non-stretch direction (TD in this case).

[0015] For biaxially stretched films, the in-plane birefringence is relatively small, and can be nearly zero when balanced. Instead, the out-of-plane birefringence is a more pronounced indicator of the birefringence of the stretched film.

[0016] Out-of-plane birefringence Δn out: Out-of-plane birefringence is used to measure the birefringence of biaxially oriented films.

[0017] Out-of-plane birefringence is related to the difference between the average in-plane (MD and TD) refractive index and the refractive index normal to the film (TM). It can be expressed as:

number

[0018] Out-of-plane birefringence can also be used to measure the birefringence of uniaxially stretched films.

[0019] Preferably, the naphthalene dicarboxylate containing copolyester resin has an in-plane retardance of less than 100 nm when oriented. Retardance can be measured with a polarimeter from Axometric, Inc. (Huntsville, AL). Examples of naphthalene dicarboxylate-containing copolyesters include mixed diol-substituted copolyethylene naphthalene-2,6-dicarboxylate, polyethylene terephthalate-conaphthalene-2,6-dicarboxylate, mixed diol-substituted polyethylene terephthalate-conaphthalene-2,6-dicarboxylate, polyethylene naphthalene-2,6-dicarboxylate-cobiphenyl-4,4'-dicarboxylate, mixed diol-substituted polyethylene naphthalene-2,6-dicarboxylate-cobiphenyl-4,4'-dicarboxylate, polyethylene terephthalate-conaphthalene-2,6-dicarboxylate-cobiphenyl-4,4'-dicarboxylate, and mixed diol-substituted polyethylene terephthalate-conaphthalene-2,6-dicarboxylate-cobiphenyl-4,4'-dicarboxylate. The mixed diols can have linear, branched, or cyclic chain lengths ranging from two carbons C2 to up to ten carbons C10. Isophthalates, such as dimethylsulfosodium isophthalate ionomer, can also be substituted for terephthalate, 2,6-naphthalenedicarboxylate, and 4,4'-biphenyldicarboxylate. Copolymer of polyethylene naphthalate (coPEN), known as PENg30, is a coPEN polyester. Its manufacturing method and material composition (100% dimethyl-2,6-naphthalenedicarboxylate (NDC) on the ester, 70 mol% ethylene glycol, and 30 mol% cyclohexanediol (CHDM) on the diol basis) are described, for example, in WO 2019 / 032635. PENg40 and PENg50 are also coPEN polyesters with 40 mol% and 50 mol% CHDM on the diol basis, and are also described in WO 2019 / 032635. Preferably, the Tg is higher than the maximum temperature of the dyeing process.

[0020] PENg materials are heat-set or annealed after stretching to "melt out" any birefringence caused by stretching. However, PVOH is known to lose optical performance when heat-set or annealed. Surprisingly, the inventors have discovered that conditions can be found to provide sufficiently low birefringence in PENg while still maintaining good optical properties in the PVOH layer.

[0021] In one embodiment, a coextruded multilayer film, such as that shown in Figure 1, is useful. Multilayer film 100 comprises an orientation layer 102, an optional tie layer 104, a release layer 106, and a PENg toughness layer 108. Orientation layer 102 provides strain hardening and supports the film during orientation. Tie layer 104 and release layer 106 are designed to release with orientation layer 102 when peeled from PENg toughness layer 108.

[0022] The orientation layer 102 is a layer of strain-hardened polyester having a glass transition temperature (Tg) at least 5° C. higher than the glass transition temperature of the naphthalene dicarboxylate containing polyester resin of the oriented second layer. The phrase “glass transition temperature” or “Tg” herein refers to the onset glass transition temperature by DSC, measured in accordance with ASTM E1256-08 2014.

[0023] Preferably, the alignment layer 102 is PEN, low-melt PEN, or PET. PEN can be described as a 0.48 IV polyethylene 2,6-naphthalate polymer. Low-melt PEN can be described as a 0.48 IV copolyester, containing 90 mole % naphthalate and 10 mole % terephthalate on an ester basis. Ethylene glycol is included as the diol in this polymer. The alignment layer functions as a carrier vehicle, allowing for the creation of a flat film during both the alignment and annealing processes. After annealing, the alignment layer functions to provide high elasticity and dimensional stability. Preferably, the alignment layer 102 has a Tg higher than the dyeing temperature.

[0024] The tie layer 104 is optional. The tie layer material(s) are preferably an elastomeric olefin or olefin blend that exhibits excellent adhesion (>300 gli) to polyester. These olefins should be capable of being coextruded and coordinating with the other layers. Exemplary elastomeric olefins include Kraton G1645 and Kraton G1657, available from Kraton Corporation. These materials can also be blended with low levels of other materials, such as SR549M or Pelestat 230, to tailor the physical and adhesive properties and / or improve electrostatic pinning performance.

[0025] The material of the peel layer 106, also referred to as the strippable layer, is preferably a polypropylene or copolypropylene blend that can be coextruded and cooriented with the following materials: the orientation layer, the PENg toughening layer, and the tie layer. An example of this material is Pro-Fax SR549M copolypropylene (7% polyethylene) available from Lyondell-Basell. These polypropylenes constitute 70% or more by weight of the peel layer and are blends with one or more SEBS / SEPS block copolymers that can be coextruded and cooriented with the orientation layer, the PENg toughening layer, and the tie layer. Examples of these materials include Kraton G1645 and Kraton G1657 available from Kraton Corporation. The peel layer may also contain an olefin-based antistatic agent that can be coextruded and cooriented with the orientation layer, the PENg toughening layer, and the tie layer to improve electrostatic pinning during the film casting process. An exemplary antistatic resin is Pelestat 230 available from Sanyo Chemical Industries. The release layer is designed to provide about 5-40 gli of adhesion to the PENg toughening or orientation layer.

[0026] As shown in Figure 2, multilayer film 100 can be coated with a polyvinyl alcohol (PVOH) solution, dried, and then stretched, for example, using a standard tenter, optionally with heat. Preferably, multilayer film 100 is stretched lengthwise before coating with PVOH, such that multilayer film 100 is biaxially oriented and the PVOH is stretched only uniaxially. Biaxially oriented multilayer film 100 provides beneficial mechanical properties, resulting in a film laminate that is stronger and less likely to tear.

[0027] The PVOH layer 110 may be of any suitable thickness, preferably less than 5 μm after orientation. In some embodiments, the PVOH layer may be 0.5 μm, 0.8 μm, or 1.2 μm to 1.5 μm, 2 μm, or 3 μm thick after orientation. The PVOH layer may be coated or extruded onto the multilayer film described above so that the multilayer film and PVOH layer can be oriented together. A typical process for manufacturing PVOH films is described, for example, in U.S. Pat. No. 6,096,375. PVOH coating solutions typically contain 2 to 20% polymer in water by weight, with a preferred concentration typically being 5 to 15%. In some embodiments, the PVOH coating comprises water, PVOH, and a surfactant. Kuraray 2899 from Kuraray America (Houston, TX) is an example of a suitable PVOH. The PVOH should have a degree of hydrolysis of 95 to 100%, preferably 97 to 99.5%. The coating dry weight typically ranges from 2 to 80 grams per square meter. The PVOH-coated multilayer film can then be stretched at an elevated temperature to create an oriented PVOH layer 110 and multilayer film 100. This temperature is preferably higher than the glass transition temperature of at least one of the components of multilayer film 100. Generally, the temperature is between 80 and 160°C. In some embodiments, the temperature is between 105 and 120°C. After stretching, the film laminate can be heat-set, preferably at a temperature between 160 and 220°C.

[0028] The film is typically stretched 2 to 10 times its original dimensions. Preferably, the film is stretched 3 to 6 times its original dimensions. The film may be allowed to relax dimensionally in the transverse direction from natural contraction in the transverse direction (equal to the square root of the stretch ratio) to being restrained (i.e., no substantial change in the transverse dimension). The film may be stretched in the machine direction, as with a length orienter, or may be stretched in the width direction using a tenter.

[0029] A series of lamination / delamination steps can be used to prepare an oriented film laminate for quarter-wave coating and dyeing. For example, in step 1 shown in FIG. 3A, a premask 312 can be laminated to the oriented PVOH layer 310 of the oriented multilayer film 300. In addition to the PVOH layer 310, the multilayer film 300 includes a PENg toughness layer 308, a release layer 306, a tie layer 304, an orientation layer 302, and an optional premask 314. The premask 312 protects the PVOH layer 310 throughout the dyeing process and handling. The premask 312 typically comprises polyethylene terephthalate. In some embodiments, the premask 312 is optically transparent, for example, to facilitate optical inspection. The premask 314 protects the orientation layer 302 and, optionally, provides additional support. In some embodiments, the premask 314 is provided by Tredegar Corporation (Richmond, VA).

[0030] 3B, the PENg tough layer 308 is separated from the release layer 306. The carrier layer is removed, exposing the PENg tough layer 308.

[0031] In step 3, shown in Figure 3C, a quarter-wave retarder 316 is coated onto the PENg toughness layer 308. The quarter-wave retarder may be provided, for example, from an oriented polymer material such as polycarbonate, polyethyl terephthalate, or polyvinyl alcohol, or from a coated liquid crystal material. Suitable materials include, for example, linear photopolymerizable polymer (LPP) and liquid crystal polymer (LCP) materials described in U.S. Patent Application Publication Nos. 2002 / 0180916 (Schadt et al.), 2003 / 028048 (Cherkaoui et al.), and 2005 / 0072959 (Moia et al.). A suitable LPP material includes ROP-131 EXP 306 LPP, and a suitable LCP material includes ROF-5185 EXP 410 LCP, both available from Rolic Technologies, Allschwil, Switzerland. In some embodiments, the quarter-wave retarder may be a quarter-wave retarder at at least one wavelength within a predetermined wavelength range. While shown in FIG. 3C as a single layer, the quarter-wave retarder 316 may include multiple layers, such as an LPP layer, an LCP half-wave plate, and an LCP quarter-wave plate.

[0032] In step 4, shown in FIG. 3D, a pre-mask 318 is added to the quarter-wave retarder 316 to provide support during the dyeing step. The pre-mask 318 typically comprises polyethylene terephthalate. In some embodiments, the pre-mask 318 is optically clear to facilitate transmittance measurements, for example, to accurately measure defect measurements or dye levels without removing the pre-mask. The pre-mask 318 typically includes a pressure-sensitive adhesive (PSA) layer, preferably an optically clear PSA, to adhere the pre-mask. The PSA is selected to withstand the dyeing step and be removable.

[0033] In step 5 shown in FIG. 3E, the pre-mask 312 is removed to expose the PVOH layer 310 for dyeing.

[0034] In step 6, shown in FIG. 3F, the PVOH layer 310 is dyed with an iodine solution to form an absorptive polarizer. This process includes iodine dyeing and an (optional) boronization step. The dye bath is typically an aqueous solution of iodine. In some embodiments, the amount of iodine is 0.1 to 0.5 parts by weight per 100 parts by weight of water. In some embodiments, the aqueous solution of iodine is blended with an iodide, for example, to increase the solubility of iodine in water. Examples of useful iodides include potassium iodide, lithium iodide, sodium iodide, zinc iodide, aluminum iodide, lead iodide, copper iodide, barium iodide, calcium iodide, tin iodide, and titanium iodide. The composition can include, for example, water (e.g., 80% by weight), potassium iodide (e.g., 19.7%), and iodine (e.g., 0.3%).

[0035] The boration bath composition is an aqueous solution of boric acid. The composition can be obtained by dissolving boric acid and / or a borate in water as a solvent. The concentration of boric acid is typically 1 part by weight to 10 parts by weight per 100 parts by weight of water. In some embodiments, the boration bath can include, for example, water (e.g., 80% by weight), boric acid (e.g., 14%), and sodium borate (e.g., 6%).

[0036] The dye bath step is typically carried out for, for example, about 5 seconds to 5 minutes at a bath temperature of about 20-50° C. In some embodiments, the dye bath step is carried out at about 30° C. for about 30-40 seconds.

[0037] The optional boriding step is typically carried out for about 15 seconds to 5 minutes, for example, at a bath temperature of about 40-85° C. In some embodiments, the boriding step is carried out at about 65° C. for about 40-50 seconds.

[0038] After boronization, the film stacks can be rinsed with water and dried, for example, in an oven at 70°C for 5 minutes. The resulting film stacks are remarkably crack-free and mechanically robust. They are ready for integration into devices such as bendable or foldable display devices for use as circular polarizing films to reduce reflectance. [Example]

[0039] The objects and advantages of this invention are further illustrated by the following examples, but the particular materials and amounts thereof recited in these examples, as well as other conditions and details, should not be construed to unduly limit this invention.

[0040] A typical process for producing PVOH film is described in U.S. Patent No. 6,096,375. Cast films may often be primed for adhesion to PVOH, in which case they are not primer-coated. The polyvinyl alcohol coating solution should contain 2-20% polymer in water by weight, with a preferred concentration of 5-15%. The polyvinyl alcohol should have a degree of hydrolysis of 95-100%, preferably 97-99.5%. The coating dry weight should be in the range of 2-80 grams per square meter. The polyvinyl alcohol-coated cast film is then stretched at an elevated temperature to produce oriented polyvinyl alcohol and an oriented base film. This temperature is preferably higher than the glass transition temperature of at least one of the components of the base cast film. Generally, the temperature should be 80-160°C, preferably 100-160°C. The film should be stretched to 2-10 times its original dimensions. In Comparative Example 1, the cast film was three-layered, with two outer layers of 90 / 10 coPEN, a polymer consisting of 90% polyethylene naphthalate (PEN) and 10% polyethylene terephthalate (PET), and an inner layer of copolyester Eastar GN071 (Eastman Chemical, Kingsport, Tenn.).

[0041] The film is preferably stretched to 3 to 6 times its original dimensions. The film may be allowed to relax dimensionally in the cross-stretch direction from natural cross-stretch contraction (equal to the square root of the stretch ratio) to restrained (i.e., no substantial change in cross-stretch dimension). The film may be stretched in the machine direction, as with a length orienter, or in the width direction using a tenter, or optionally in both directions if the cast web is stretched in one direction prior to PVOH coating.

[0042] Comparative Example A general process for producing PVOH films is described in US Pat. No. 6,096,375.

[0043] Polyethylene 2,6-naphthalenedicarboxylate-coterophthalate was fed into a first twin-screw extruder at 50 pph, conveyed, melted (530°F melt), mixed, and passed through a 30-disc filter with 7 μm media. Eastar copolyester GN071 (Eastman Chemical, Kingsport, TN)

[0044] GN071 (Eastman Chemicals, Kingsport, TN) was fed into a second twin-screw extruder at 220 pph, conveyed, melted (530°F melt), mixed, and passed through a 30-disc filter with 7 μm media. The copolyester GN071 was fed into the core of a three-layer feedblock, and polyethylene 2,6-naphthalenedicarboxylate-coterophthalate was fed into the skin plate.

[0045] The three layers were then extruded through a die and cast by electrostatic pinning against a chilled wheel.

[0046] The film was coated with PVOH in a solution consisting of 89 wt% water, 11 wt% PVOH, and 0.01 wt% surfactant. The PVOH was Kuraray 2899 from Kuraray America (Houston, TX). The surfactant was Dynol 604 available from Air Products (Allentown, PA).

[0047] The PVOH coated film was stretched in the transverse direction to a stretch ratio of about 6.0 at a temperature of 283° F. The final thickness of the film was about 72.6 um.

[0048] The material was solvent coated and UV cured onto a PVOH layer with its optical slow axis oriented at 45 degrees to the pass direction of the integrated polarizer. The coated layer had a retardation of 138 nm at a wavelength of 550 nm. (Retardation is defined as Re = (n-n) * d, where n-n is the in-plane birefringence difference between the optical slow and fast axes of the coated material, and d is the thickness of the coated layer.) The coating materials utilized were similar to those described in U.S. Patent Application Publication Nos. 2002 / 0180916, 2003 / 028048, and 2005 / 0072959, with the linear photopolymerizable polymer (LPP) material being ROP-131 EXP 306 LPP and the liquid crystal polymer (LCP) material being ROF-5185 EXP 410 LCP (both available from Rolic Technologies, Allschwil, Switzerland).

[0049] The oriented polyvinyl alcohol coating with the quarter-wave coating was then removed from the oriented base film. A PET premask with adhesive was laminated to the oriented polyvinyl alcohol coating with the quarter-wave layer and then peeled off the oriented base film.

[0050] The oriented polyvinyl alcohol coating and quarter wave coating with attached PET premask were then dyed with an iodine-based dye solution and then boronized to fix the coating.

[0051] The iodine dyeing and borining procedures included the following components: The dye bath composition was 80 wt. % water, 19.7 wt. % potassium iodide, and 0.3 wt. % iodine. The boric acid bath composition was 80 wt. % water, 14 wt. % boric acid, and 6.0 wt. % sodium borate. The dyeing process step used a dye bath temperature of 30°C and an exposure time of 34 seconds. The borining process step used a borining bath temperature of 65°C and an exposure time of 42 seconds. After borining, the samples were rinsed with water at 23°C for 24 seconds and then dried in an oven at 70°C for 5 minutes.

[0052] After drying, the PVOH coating had significant cracking in the fibers, as shown in Figure 4, and was unusable as an optical film.

[0053] Many process conditions were tested during the dyeing and drying process to prevent cracking, as shown in Table 1. All of the structures in Comparative Example 1 had unacceptable cracking.

[0054] [Table 1]

[0055] Example Experimental samples were prepared using a four layer feedblock having a 2 mil LmPEN layer, a 0.25 mil tie layer, a 0.25 mil release layer, and a 0.5 mil PENg layer.

[0056] Polyethylene 2,6-naphthalenedicarboxylate-co-terephthalate was fed into the first twin-screw extruder at 475 pph, conveyed, melted (530°F melt), mixed, and passed through a 30-disc filter with 7 μm media. Kraton G1657 (Kraton Corporation, Houston, TX) and PP9074MED (Exxon Mobil Corporation, Irving, TX) were fed into the second twin-screw extruder at 29 and 12 pph, respectively, conveyed, melted (530°F melt), mixed, and passed through a 15-disc filter with 7 μm media. Kraton G1657 (Kraton Corporation, Houston, TX) and PP9074MED (Exxon Mobil Corporation, Irving, TX) were fed into the third twin-screw extruder at 4.6 and 33.5 pph, respectively. PENG30 was fed into the fourth twin screw extruder at 50 pph.

[0057] Four melt streams were fed into a four-layer feedblock, with a first melt train feeding one outer layer, a second melt train feeding an inner layer adjacent to the first melt train, a third melt train feeding an inner layer adjacent to the second melt train, and a fourth melt train feeding an outer layer adjacent to the third melt train.

[0058] The outermost layer and alternating inner layers, as well as the remainder of the alternating inner layers, are provided by a second melt train. The four layers are extruded through a die, cast by electrostatic pinning against a chilled wheel, and then stretched in the machine direction to a stretch ratio of about 3.3 at a temperature of about 250°F.

[0059] PENG30 was coated with PVOH in a solution consisting of 89 wt% water, 11 wt% PVOH, and 0.01 wt% surfactant. The PVOH was Kuraray 2899 from Kuraray America (Houston, TX). The surfactant was Dynol 604 available from Air Products (Allentown, PA). A primer layer of sulfonated polyester was coated between the PVOH solution and the PENG30 layer.

[0060] The PVOH coated film was stretched in the transverse direction to a stretch ratio of about 5.0 at a temperature of 290° F. and then heat set at a temperature of 325° F. The final thickness of the film was about 72.6 um.

[0061] A second PVOH-coated film was made in a similar manner, except that the PENG extrusion rate was 100 pph. The total thickness of this film was 78.9 um.

[0062] A series of lamination steps was used to remove the toughening film layer and PVOH and prepare the film for the liquid crystal quarter-wave coating. In step 1, an optically clear PET premask NSA33T from Sun-a-Kaken (Japan) was added to the PVOH side of the film. In step 2, the release layer, tie layer, and LmPEN carrier layer were removed to expose the PENg. In step 3, an LPP layer and an LCP layer were coated onto the PENg to form an achromatic quarter-wave plate. The material was solvent coated and UV cured onto the PENg layer with its optical slow axis oriented at 45 degrees to the pass direction of the integrated polarizer. The coated layer had a retardation of 138 nm at a wavelength of 550 nm. (Retardation is defined as Re = (n-nj) * d, where n-nj is the in-plane birefringence difference between the optical slow and fast axes of the coated material, and d is the thickness of the coated layer.) The coating materials used were similar to those described in U.S. Patent Application Publication Nos. 2002 / 0180916, 2003 / 028048, and 2005 / 0072959. The linear photopolymerizable polymer (LPP) material was ROP-131 EXP 306 LPP, and the liquid crystal polymer (LCP) material was ROF-5185 EXP 410 LCP (both available from Rolic Technologies, Allschwil, Switzerland). The PENg layer remained haze-free after coating with LCP, despite the LCP coating process containing the aggressive solvent n-butyl acetate.

[0063] An optically clear PET pre-mask was laminated to the LPP and LCP coated side to provide support during the dyeing step. The optically clear PET on the PVOH side was removed. The PVOH was dyed with an iodine solution to form an absorbing polarizer. The film was immersed in the iodine solution at 30°C for 32 seconds, then immersed in a boronizing tank at 65°C for 42 seconds, and then rinsed in a water bath at 23°C. The film was dried in an oven at 70°C for 5 minutes. The resulting film was crack-free and mechanically robust after drying.

[0064] SEM cross sections (Figures 5 and 6) were taken to measure the thickness of the ultrathin circular polarizer.

[0065] The complete disclosures of the publications cited herein are incorporated by reference in their entireties, as if each were individually incorporated. Various modifications and alterations to the present invention will become apparent to those skilled in the art without departing from the scope and spirit of the present invention. It is understood that this invention is not intended to be unduly limited by the illustrative embodiments and examples described herein, which examples and embodiments are presented by way of example only, and that the scope of the present invention is intended to be limited only by the claims set forth herein below. In the following, exemplary embodiments are presented. [Item 1] 1. A film laminate comprising: an oriented first layer comprising polyvinyl alcohol disposed on an oriented second layer comprising a naphthalene dicarboxylate containing copolyester resin, the oriented second layer having an in-plane birefringence Δnxy of less than 0.02. [Item 2] Item 10. The film stack of item 1, wherein the oriented second layer has an in-plane retardance of less than 100 nm. [Item 3] 3. The film laminate of claim 1 or 2, wherein the oriented second layer is biaxially oriented. [Item 4] 4. The film stack of any one of items 1 to 3, further comprising a quarter wave retarder disposed on the oriented second layer opposite the oriented first layer. [Item 5] Item 5. The film stack of item 4, wherein the quarter wave retarder comprises an oriented polymer material or a coated liquid crystal material. [Item 6] 6. The film laminate of any one of items 1 to 5, wherein the oriented first layer is dyed with iodine. [Item 7] 7. The film stack of any one of items 4 to 6, further comprising a pre-mask positioned on the quarter wave retarder opposite the oriented second layer. [Item 8] 6. The film laminate of any one of items 1 to 5, further comprising a pre-mask disposed on the oriented first layer opposite the oriented second layer. [Item 9] Item 9. The film laminate of item 7 or 8, wherein the pre-mask comprises polyethylene terephthalate. [Item 10] 10. The film laminate according to any one of items 1 to 9, wherein the film laminate has a total thickness of less than 35 μm. [Item 11] Item 11. The film laminate of item 10, wherein the film laminate has a total thickness of less than 20 μm. [Item 12] Item 12. The film laminate of item 11, wherein the film laminate has a total thickness of less than 15 μm. [Item 13] 13. The film laminate of any one of items 1 to 12, wherein the oriented first layer has a thickness of less than 5 μm. [Item 14] Item 14. The film laminate of item 13, wherein the oriented first layer has a thickness of less than 3 μm. [Item 15] (a) a carrier film including a release layer disposed between an oriented second layer including a naphthalene dicarboxylate containing copolyester resin having an in-plane birefringence Δnxy of less than 0.02 and a layer of strain-hardened polyester having a glass transition temperature at least 5° C. higher than the glass transition temperature of the naphthalene dicarboxylate containing polyester resin of the oriented second layer; (b) an oriented first layer comprising polyvinyl alcohol disposed on the oriented second layer opposite the release layer; and A film laminate comprising: [Item 16] (a) providing a carrier film including a release layer disposed between a second layer including a naphthalene dicarboxylate containing copolyester resin having an in-plane birefringence Δnxy of less than 0.02 and a layer of strain-hardened polyester having a glass transition temperature at least 5° C. higher than the glass transition temperature of the naphthalene dicarboxylate containing polyester resin of the oriented second layer; (b) coating a first layer comprising polyvinyl alcohol onto the strain-hardening polyester; (c) orienting the resulting coated carrier film in a second direction; A method for producing a film laminate, comprising: [Item 17] Item 17. The method of item 16, comprising orienting the carrier layer in a first direction before coating the first layer. [Item 18] Item 18. The method of item 17, wherein orienting the carrier layer is performed by heat. [Item 19] 19. The method of any one of items 16 to 18, further comprising heat-setting the film laminate. [Item 20] 20. The method of any one of items 16 to 19, further comprising removing the release layer and the layer of strain-hardened polyester to expose the second layer. [Item 21] 21. The method of claim 20, further comprising coating a quarter wave retarder layer on the exposed second layer. [Item 22] 22. The method of claim 21, further comprising staining the first layer with iodine.

Claims

1. 1. A film laminate comprising: an oriented second layer containing a copolyester resin; and an oriented first layer comprising polyvinyl alcohol disposed on the oriented second layer, wherein the copolyester resin is mixed diol-substituted copolyethylene naphthalene-2,6-dicarboxylate, and the oriented second layer has an in-plane birefringence Δnxy of less than 0.

02.

2. 10. The film stack of claim 1, wherein the oriented second layer has an in-plane retardance of less than 100 nm.

3. 3. The film laminate of claim 1 or 2, wherein the oriented second layer is biaxially oriented.

4. 4. The film stack of claim 1, further comprising a quarter wave retarder disposed on the oriented second layer opposite the oriented first layer.

5. 5. The film stack of claim 4, wherein the quarter wave retarder comprises an oriented polymer material or a coated liquid crystal material.

6. The film laminate of any one of claims 1 to 5, wherein the oriented first layer is dyed with iodine.

7. The film stack of any one of claims 4 to 6, further comprising a pre-mask positioned on the quarter wave retarder opposite the oriented second layer.

8. The film laminate of any one of claims 1 to 5, further comprising a pre-mask disposed on the oriented first layer opposite the oriented second layer.

9. 9. The film laminate of claim 7 or 8, wherein the pre-mask comprises polyethylene terephthalate.

10. The film laminate of any one of claims 1 to 9, wherein the film laminate has a total thickness of less than 35 μm.

11. 11. The film laminate of claim 10, wherein the film laminate has a total thickness of less than 20 μm.

12. 12. The film laminate of claim 11, wherein the film laminate has a total thickness of less than 15 μm.

13. The film laminate of any one of claims 1 to 12, wherein the oriented first layer has a thickness of less than 5 μm.

14. (a) a carrier film including a release layer disposed between an oriented second layer containing a copolyester resin having an in-plane birefringence Δnxy of less than 0.02 and a layer of strain-hardened polyester having a glass transition temperature at least 5° C. higher than the glass transition temperature of the oriented second layer; (b) an oriented first layer comprising polyvinyl alcohol disposed on the oriented second layer opposite the release layer; and Equipped with A film laminate wherein the copolyester resin is a mixed diol-substituted copolyethylene naphthalene-2,6-dicarboxylate.

15. (a) providing a carrier film including a release layer disposed between an oriented second layer containing a copolyester resin having an in-plane birefringence Δnxy of less than 0.02 and a layer of strain-hardened polyester having a glass transition temperature at least 5° C. higher than the glass transition temperature of the oriented second layer; (b) coating a first layer comprising polyvinyl alcohol onto the strain-hardening polyester; (c) orienting the resulting coated carrier film in a second direction; Including, The method for producing a film laminate, wherein the copolyester resin is a mixed diol-substituted copolyethylene naphthalene-2,6-dicarboxylate.

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