Film stacks for thin circular polarizers

Abstract

The film stack includes a quarter wave retarder and a transparent aliphatic cross-linked polyurethane layer disposed on a major surface of the quarter wave retarder. The transparent aliphatic cross-linked polyurethane layer has a glass transition temperature in the range of 11°C to 27°C and a Tan δ peak in the range of 0.5 to 2.5.

Description

Technical Field

[0001] The present invention relates to a film stack that can be used for circular polarizers and a method for preparing the film stack. Background Art

[0002] Emissive displays such as organic light emitting diode (OLED) displays typically utilize circular polarizers as anti-reflective films. Typically, circular polarizers include film components that are laminated together and are relatively thick. With the development of new form factors such as bendable and rollable emissive displays, thinner display components are needed. Conventional thick film stack circular polarizers cannot withstand the tight bending radius required for bendable and rollable displays. Past attempts to prepare thin (e.g., less than 50 μm thick) circular polarizers have resulted in problems with the mechanical integrity of the film, and cracking or breaking during bending and folding. Summary of the invention

[0003] In view of the foregoing, we recognize the need for thin and mechanically robust circular polarizers.

[0004] In one aspect, the present invention provides a film stack comprising a quarter wave retarder and a transparent aliphatic cross-linked polyurethane layer disposed on a major surface of the quarter wave retarder. The transparent aliphatic cross-linked polyurethane layer has a glass transition temperature in the range of 11°C to 27°C and a Tan δ peak in the range of 0.5 to 2.5.

[0005] In another aspect, the present invention provides a film stack, the film stack comprising: a film including a strain hardened polyester layer; an alignment layer comprising polyvinyl alcohol disposed on the strain hardened polyester layer; and a transparent aliphatic cross-linked polyurethane layer having a thickness of 100 μm or less, the transparent aliphatic cross-linked polyurethane layer being disposed on the alignment layer comprising polyvinyl alcohol opposite to the strain hardened polyester layer. The transparent aliphatic cross-linked polyurethane has a glass transition temperature in the range of 11° C. to 27° C. and a Tan δ peak in the range of 0.5 to 2.5.

[0006] The film stacks of the present invention enable circular polarizers having a total thickness of less than 35 μm, 25 μm, 20 μm, 15 μm, 10 μm, 5 μm or 3 μm which are mechanically robust and therefore useful in highly curved, foldable or rollable displays.

[0007] In another aspect, the present invention provides a method for preparing a film stack, the method comprising (a) coating a layer comprising polyvinyl alcohol on a film comprising a strain hardened polyester layer, (b) orienting the coated film in a first direction, and (c) coating the layer comprising polyvinyl alcohol with a transparent aliphatic cross-linked polyurethane layer having a thickness of 100 μm or less. The transparent aliphatic cross-linked polyurethane layer has a glass transition temperature in the range of 11° C. to 27° C. and a Tan δ peak in the range of 0.5 to 2.5. BRIEF DESCRIPTION OF THE DRAWINGS

[0008] Figure 1 is a cross-sectional view of a membrane stack.

[0009] Figure 2A-2F is a cross-sectional view of a film stack prepared according to the process. DETAILED DESCRIPTION

[0010] The present invention enables very thin circular polarizers, which include a dyed polyvinyl alcohol (PVOH) layer, a polyurethane primer, and a quarter wave retarder. In some embodiments, the thickness of the PVOH layer is less than 10 μm, the thickness of the primer is less than 20 μm, 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.

[0011] The film stack of the present invention includes a urethane primer layer that bonds the polyvinyl alcohol layer and the quarter wave retarder. Surprisingly, the urethane primer layer allows for very thin constructions that resist cracking of the polyvinyl alcohol layer. The urethane primer material also resists staining during the polyvinyl alcohol dyeing process. In addition, the urethane primer layer allows the use of aggressive solvents for many liquid crystal polymers without increasing haze.

[0012] In some embodiments, the thickness of the urethane primer layer is less than 100 μm, 50 μm, 30 μm, 20 μm, 10 μm, or 5 μm. In some embodiments, the thickness of the urethane primer is 4 μm to 10 μm.

[0013] The urethane primer layer comprises a transparent aliphatic cross-linked polyurethane, such as those described in US 2017 / 0165950. "Polyurethane" refers to a polymer prepared by step-growth polymerization of a hydroxyl-functional material (a material comprising a hydroxyl group -OH) and an isocyanate-functional material (a material comprising an isocyanate group -NCO) and thus comprises a urethane bond (-O(CO)-NH), wherein (CO) refers to a carbonyl group (C=O). The term may include "polyurethane urea", in which both urethane bonds and urea bonds are present.

[0014] The transparent aliphatic cross-linked polyurethane layer may have a glass transition temperature in the range of 11 to 27 degrees Celsius or 17 to 22 degrees Celsius. The phrase "glass transition temperature" herein refers to the "set" glass transition temperature of DSC and is measured according to ASTM E1256-08 2014.

[0015] The transparent aliphatic cross-linked polyurethane layer may have a Tan δ peak in the range of 0.5 to 2.5, or 1 to 2, or 1.4 to 1.8. The Tan δ peak and peak temperature are measured according to the DMA analysis described in the examples. The transparent aliphatic cross-linked polyurethane layer may have a cross-linking density in the range of 0.34 mol / kg to 0.65 mol / kg.

[0016] The transparent aliphatic cross-linked polyurethane layer can be coated and then cured or cross-linked to form a thermosetting polyurethane layer. Polyurethane is a polymer composed of organic units bonded by urethane (ethyl carbamate) chains. The polyurethane described herein is a thermosetting polymer that does not melt when heated. The polyurethane polymer can be formed by reacting a diisocyanate or polyisocyanate with a polyol. Both the isocyanate and the polyol used to prepare the polyurethane contain an average of two or more functional groups per molecule. The polyurethane described herein may have a functionality greater than 2.4 or 2.5.

[0017] Various polyols can be used to form aliphatic crosslinked polyurethane layers. The term polyol includes hydroxyl functional materials, which usually contain at least 2 terminal hydroxyl groups. Polyols include diols (materials with 2 terminal hydroxyl groups) and higher polyols, such as triols (materials with 3 terminal hydroxyl groups), tetraols (materials with 4 terminal hydroxyl groups) etc. Usually, the reaction mixture contains at least some diols, and can also contain higher polyols. Higher polyols are especially useful for forming crosslinked polyurethane polymers. Diols can be described by the structure HO-B-OH usually, wherein the B group can be aliphatic, aromatic or a group comprising a combination of aromatic and aliphatic groups, and can contain various chains or functional groups (including additional terminal hydroxyl groups).

[0018] Polyester polyols are particularly useful. Among the available polyester polyols, linear and nonlinear polyester polyols are available, including, for example, polyethylene adipate, polybutylene succinate, polyhexanediol sebacate, polyhexanediol dodecane dicarboxylate, polyneopentyl adipate, polypropylene adipate, polycyclohexanedimethyl adipate, and poly-ε-caprolactone. Particularly useful are aliphatic polyester polyols, which can be obtained from King Industries, Norwalk, Conn. under the trade name "K-FLEX", such as K-FLEX 188 or K-FLEX A308.

[0019] A variety of polyisocyanates can be used to form aliphatic crosslinked polyurethane layers. The term polyisocyanate includes isocyanate functional materials, which usually contain at least 2 terminal isocyanate groups. Polyisocyanates include diisocyanates (materials with 2 terminal isocyanate groups) and higher polyisocyanates, such as triisocyanates (materials with 3 terminal isocyanate groups), tetraisocyanates (materials with 4 terminal isocyanate groups) etc. If difunctional polyols are used, the reaction mixture usually contains at least one higher isocyanate. Higher isocyanates are especially useful for forming crosslinked polyurethane polymers. Diisocyanates can be usually described by the structure OCN-Z-NCO, wherein the Z group can be an aliphatic group, an aromatic group or a group comprising a combination of an aromatic group and an aliphatic group.

[0020] Higher functional polyisocyanates (such as triisocyanates) are particularly useful for forming crosslinked polyurethane polymer layers. Triisocyanates include, but are not limited to, polyfunctional isocyanates, such as those prepared from biuret, isocyanurate, adducts, etc. Some commercially available polyisocyanates include parts of DESMODUR and MONDUR series purchased from Bayer Corporation (Bayer Corporation, Pittsburgh, PA.) in Pittsburgh, Pennsylvania, and PAPI series purchased from Dow Plastics (a conglomerate of Dow Chemical Company, Midland, Mich.). Particularly useful triisocyanates include those purchased from Bayer Corporation under the trade name DESMODUR N3300A and MONDUR 489. A particularly suitable aliphatic polyisocyanate is DESMODUR N3300A.

[0021] The reaction mixture for forming the transparent aliphatic cross-linked polyurethane layer also includes a catalyst. The catalyst promotes the step-by-step growth reaction between the polyol and the polyisocyanate. It is generally recognized that conventional catalysts used in urethane polymerization can be applicable to the present disclosure. For example, aluminum-based, bismuth-based, tin-based, vanadium-based, zinc-based or zirconium-based catalysts can be used. Tin-based catalysts are particularly useful. It has been found that tin-based catalysts can significantly reduce the amount of outgassing present in the polyurethane. Dibutyltin compounds are most ideal, such as dibutyltin diacetate, dibutyltin dilaurate, dibutyltin diacetylacetonate, dibutyltin dithiol, dibutyltin dioctoate, dibutyltin dimaleate, dibutyltin acetonyl acetonate and dibutyltin oxide. In particular, the dibutyltin dilaurate catalyst DABCO T-12 purchased from Air Products and Chemicals, Inc., Allentown, PA, in Allentown, Pennsylvania, is particularly suitable. The catalyst is typically included in an amount of at least 200 ppm or even 300 ppm or more.

[0022] The polyurethane composition described above can be used to prepare Figure 1 The film stack shown. The film stack 100 includes a quarter wave retarder 116, a polyurethane layer 120, and a layer 110 comprising PVOH. In some embodiments, the quarter wave retarder 116 has a thickness of 1 μm to 5 μm; the polyurethane layer 120 has a thickness of 4 μm to 10 μm; and the PVOH layer 110 has a thickness of less than 5 μm or less than 3 μm.

[0023] In some embodiments, the membrane stack 100 is prepared and used, for example, according to the following method. Figure 2A As shown, in step 1, PVOH layer 110 can be coated on orientation layer 102 and oriented. Orientation layer 102 can be, for example, a strain hardened polyester layer. Polyester has carboxylate subunits and diol subunits, which are generated by the reaction of carboxylate monomer molecules and ethylene glycol monomer molecules. Each carboxylate monomer molecule has two or more carboxylic acid or ester functional groups, and each diol monomer molecule has two or more hydroxyl functional groups. The carboxylate monomer molecules can all be the same, or can also be two or more different types of molecules. The same applies to diol monomer molecules. The properties of the polymer layer or film vary depending on the specific selected monomer molecules. An example of polyester is polyethylene naphthalate (PEN), which can be prepared by, for example, the reaction of naphthalene dicarboxylic acid with ethylene glycol.

[0024] Suitable carboxylate monomer molecules for forming the carboxylate subunits of the polyester layer include, for example, 2,6-naphthalene dicarboxylic acid and its isomers; terephthalic acid; isophthalic acid; phthalic acid; azelaic acid; adipic acid; sebacic acid; norbornene dicarboxylic acid; bis-cyclooctane dicarboxylic acid; 1,4-cyclohexane dicarboxylic acid and its isomers; tert-butyl isophthalic acid, trimellitic acid, sodium sulfonated isophthalic acid; 2,2'-biphenyl dicarboxylic acid and its isomers, and lower alkyl esters of these acids, such as methyl or ethyl esters. The term "lower alkyl" herein refers to a C1-C10 straight or branched alkyl group. The term "polyester" also includes polycarbonates derived from the reaction of diol monomer molecules with carbonates.

[0025] Suitable diol monomer molecules for forming the diol subunits of the polyester layer include ethylene glycol, propylene glycol, 1,4-butanediol and its isomers; 1,6-hexanediol, neopentyl glycol, polyethylene glycol; diethylene glycol, tricyclodecanediol, 1,4-cyclohexanedimethanol and its isomers, norbornanediol, bicyclooctanediol, trimethylolpropane; pentaerythritol; 1,4-benzenedimethanol and its isomers; bisphenol A, 1,8-dihydroxybiphenyl and its isomers; and 1,3-bis(2-hydroxyethoxy)benzene.

[0026] Examples of useful strain hardening polyesters include polyethylene terephthalate, mixed glycol substituted copolyethylene terephthalate, polyethylene naphthalate-2,6-dicarboxylate, mixed glycol substituted copolyethylene naphthalate-2,6-dicarboxylate, polyethylene terephthalate-co-naphthalene-2,6-dicarboxylate, mixed glycol substituted polyethylene terephthalate-co-naphthalene-2,6-dicarboxylate, polyethylene terephthalate-co-biphenyl-4,4'-dicarboxylate, mixed glycol substituted copolyethylene terephthalate-co-biphenyl-4,4'-dicarboxylate, and mixed glycol substituted copolyethylene terephthalate-co-biphenyl-4,4'-dicarboxylate. -dicarboxylates, polyethylene naphthalate-2,6-dicarboxylate-co-biphenyl-4,4'-dicarboxylates, mixed diol substituted polyethylene naphthalate-2,6-dicarboxylate-co-biphenyl-4,4'-dicarboxylates, polyethylene terephthalate-co-naphthalene-2,6-dicarboxylate-co-biphenyl-4,4'-dicarboxylates, and mixed diol substituted polyethylene terephthalate-co-naphthalene-2,6-dicarboxylate-co-biphenyl-4,4'-dicarboxylates, for example, the mixed diols may consist of straight, branched or cyclic chain lengths of two carbons C2 up to C10. Isophthalates such as sodium dimethyl sulfonate isophthalate ionomers may also replace terephthalate, 2,6-naphthalate and 4,4'-biphenyl dicarboxylates.

[0027] In some embodiments, the orientation layer 102 is PEN or low melting PEN. PEN can be described as a 0.48 IV 2,6-polyethylene naphthalate polymer. Low melting point PEN can be described as a 0.48 IV copolyester, which contains 90 mole % of polybutylene naphthalate parts and 10 mole % of terephthalate parts based on ester. Ethylene glycol contains glycols in the polymer. The orientation layer is used as a carrier, a supporting substrate, so that flat films can be produced during orientation and annealing. After annealing, the orientation layer is used to provide high modulus and dimensional stability. In some embodiments, the orientation layer 102 includes multiple layers.

[0028] Preferably, the oriented layer 102 has a Tg that is no less than 10°C lower than the Tg of the PVOH layer. The Tg of the PVOH layer can be suppressed based on the level of water present in the layer. The phrase "glass transition temperature" or "Tg" herein refers to the onset glass transition temperature determined by DSC and is measured according to ASTM E1256-08 2014.

[0029] The orientation layer 102 can be coated with a PVOH solution, dried, and then stretched, for example using a standard tenter frame, optionally with heat. Preferably, the orientation layer 102 is stretched in the length direction before coating with PVOH, so that the orientation layer 102 is biaxially oriented, while the PVOH is only uniaxially stretched. The biaxially oriented orientation layer 102 provides beneficial mechanical properties, making the film stack stronger and less prone to tearing.

[0030] The PVOH layer 110 can have any suitable thickness after orientation, preferably less than 5 μm thick. In some embodiments, the PVOH layer can 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 can be coated or extruded on the above-mentioned multilayer film so that the multilayer film and the PVOH layer can be oriented together. The general process for producing PVOH film is described in, for example, U.S. Patent No. 6,096,375. The PVOH coating solution generally contains 2% to 20% of the polymer based on weight in water, and the preferred concentration is generally 5% to 15%. In some embodiments, the PVOH coating comprises water, PVOH and a surfactant. Kuraray 2899 from Kuraray America, Houston, TX, USA, is an example of a suitable PVOH. PVOH should have a degree of hydrolysis between 95% and 100%, preferably between 97% and 99.5%. The dry coating weight is typically in the range of 2 grams to 80 grams per square meter. The PVOH coated multilayer film can then be stretched at an elevated temperature to form an oriented PVOH layer 110 and a multilayer film 100. The temperature is preferably above the glass transition temperature of at least one of the components of the multilayer film 100. Generally, the temperature is 60°C to 160°C. In some embodiments, the temperature is 105°C to 120°C. After stretching, the film stack can be heat set, preferably at a temperature of 160°C to 220°C.

[0031] The film is typically stretched 2 to 10 times its initial dimension. Preferably, the film should be stretched to 3 to 6 times its initial dimension. The film may be allowed to relax in dimension in the transverse stretch direction from a natural decrease in the transverse stretch direction (equal to the square root of the stretch ratio) to being constrained (i.e., no significant change in the transverse stretch dimension). The film may be stretched in the longitudinal direction (e.g., using a length orienter) or in width (using a tenter frame), or optionally both (where the cast web is stretched in one direction prior to PVOH coating).

[0032] like Figure 2B As shown, in step 2, the oriented PVOH layer 110 is coated with a polyurethane layer 120. For example, a standard coating method is used, such as using a slot coater. Typically, the polyurethane layer is solvent coated, but in some embodiments, it can be 100% solid coated. In some embodiments, the PVOH layer is primed or corona treated to promote adhesion of the polyurethane layer.

[0033] like Figure 2CAs shown, in step 3, a quarter wave retarder 116 is coated on the polyurethane layer 120. The quarter wave retarder can be provided, for example, by an oriented polymer material such as polycarbonate, polyethylene terephthalate or polyvinyl alcohol or by a coated liquid crystal material. Suitable materials include, for example, linear photopolymerizable polymer (LPP) materials and liquid crystal polymer (LCP) materials described in U.S. patent application publications US 2002 / 0180916 (Schadt et al.), US2003 / 028048 (Cherkaoui et al.), and US 2005 / 0072959 (Moia et al.). Suitable LPP materials include ROP-131EXP306LPP, and suitable LCP materials include ROF-5185EXP 410LCP, both of which are available from Rolic Technologies, Allschwil, Switzerland. In some examples, the quarter wave retarder can be a quarter wave retarder at at least one wavelength within a predetermined wavelength range. Figure 2C , the quarter-wave retarder 116 is shown as one layer, but it may include multiple layers, such as an LPP layer, an LCP half-wave plate, and an LCP quarter-wave plate.

[0034] like Figure 2D As shown, in optional step 4, a pre-mask 118 is added to the quarter-wave retarder 116 to provide support in the dyeing step. The pre-mask 118 typically comprises polyethylene terephthalate. In some embodiments, the pre-mask 118 is optically transparent, for example, to facilitate defect measurement or transmission measurement to measure the dyeing level without removing the pre-mask. The pre-mask 118 typically includes a pressure-sensitive adhesive (PSA) layer, preferably an optically transparent PSA to adhere the pre-mask. The PSA is selected to withstand the dyeing step and remain and be removable. In some embodiments, a thicker polyurethane layer (e.g., thicker than 25 μm) can be used to provide support in the dyeing step.

[0035] Next, if Figure 2E As shown, in step 5, the alignment layer 102 is removed to expose the PVOH layer 110 for dyeing.

[0036] In step 6, if Figure 2FAs shown, PVOH layer 110 is dyed with iodine solution to form an absorbing polarizer. The process includes iodine dyeing and boronization procedures. The dyeing bath is generally an aqueous solution of iodine. In some embodiments, the amount of iodine is 0.1 to 0.5 parts by weight relative to 100 parts by weight of water. In some embodiments, the aqueous solution of iodine is mixed 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., 80wt%), potassium iodide (e.g., 19.7%) and iodine (e.g., 0.3%).

[0037] The boronizing 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 generally 1 to 10 parts by weight relative to 100 parts by weight of water. In some embodiments, the boronizing bath may include, for example, water (e.g., 80 wt%), boric acid (e.g., 14%), and sodium borate (e.g., 6%).

[0038] The dyebath step is typically performed, for example, at a bath temperature of about 20° C. to 50° C. for about 5 seconds to 5 minutes.

[0039] In some embodiments, the dye bath step is performed at about 30°C for about 30 seconds to 40 seconds.

[0040] The boration step is typically performed at a bath temperature of, for example, about 40°C to 85°C for about 15 seconds to 5 minutes.

[0041] In some embodiments, the boronation step is performed at about 65°C for about 40-50 seconds.

[0042] After boronation, the film stack can be rinsed with water and dried, for example, in a 70°C oven for 5 minutes. The resulting film stacks are surprisingly crack-free and mechanically robust. They are ready to be integrated into devices such as bendable or foldable display devices for use as circular polarizing films to reduce reflectivity.

[0043] Example

[0044] 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.

[0045] Materials used in the examples

[0046]

[0047] Example 1 to Example 2

[0048] 120 parts by mass and 100 parts by mass of PD and HMDI were added to toluene at 10% solids in a plastic beaker at room temperature. Stir manually with a stirring rod until it is a uniform mixture. DTD catalyst was then added to this mixture at 150ppm and the final mixture was stirred manually with a stirring rod until fully mixed. The amount of catalyst is based on KFLEX 188 and Desmodur 3300.

[0049] The urethane mixture was coated through a slot die onto a moving web consisting of polyvinyl alcohol and a removable polyethylene terephthalate substrate at a speed of 10 feet per minute at target thicknesses of 7 μm, 10 μm, and heat cured in an oven at 210 degrees Fahrenheit for approximately three minutes. The coating was applied directly onto the polyvinyl alcohol surface.

[0050] Example 3 to Example 5

[0051] 110 parts by mass of PD and 100 parts by mass of HMDI were added to toluene at 10% solids in a plastic beaker at room temperature. Stir manually until it is a homogeneous mixture. DTD catalyst was then added to this mixture at 150 ppm and the final mixture was manually stirred with a stirring rod until fully mixed. The amount of catalyst is based on KFLEX 188 and Desmodur 3300.

[0052] The urethane mixture was coated through a slot die onto a moving web consisting of polyvinyl alcohol and a removable polyethylene terephthalate substrate at a speed of 10 feet per minute at target thicknesses of 4 μm, 7 μm, and 10 μm, and heat cured in an oven at 210 degrees Fahrenheit for approximately three minutes. The coating was applied directly onto the polyvinyl alcohol surface.

[0053] Example 6 to Example 8

[0054] 105 parts by mass and 100 parts by mass of PD and HMDI were added to toluene at 10% solids in a plastic beaker at room temperature. Stir manually with a stirring rod until it is a uniform mixture. DTD catalyst was then added to this mixture at 150ppm and the final mixture was stirred manually with a stirring rod until fully mixed. The amount of catalyst is based on KFLEX 188 and Desmodur 3300.

[0055] The urethane mixture was coated through a slot die onto a moving web consisting of polyvinyl alcohol and a removable polyethylene terephthalate substrate at a speed of 10 feet per minute at target thicknesses of 4 μm, 7 μm, and 10 μm, and heat cured in an oven at 210 degrees Fahrenheit for approximately three minutes. The coating was applied directly onto the polyvinyl alcohol surface. The coating was applied directly onto the polyvinyl alcohol surface.

[0056] Example 9 to Example 10

[0057] 80 parts by mass and 100 parts by mass of PD and HMDI were added to toluene at 10% solids in a plastic beaker at room temperature. Stir manually with a stirring rod until it is a uniform mixture. DTD catalyst was then added to this mixture at 150ppm and the final mixture was stirred manually with a stirring rod until fully mixed. The amount of catalyst is based on KFLEX 188 and Desmodur 3300.

[0058] The urethane mixture was coated through a slot die onto a moving web consisting of polyvinyl alcohol and a removable polyethylene terephthalate substrate at a speed of 10 feet per minute at target thicknesses of 7 μm, 10 μm, and heat cured in an oven at 210 degrees Fahrenheit for approximately three minutes. The coating was applied directly onto the polyvinyl alcohol surface.

[0059] Table 1

[0060]

[0061] Comparative Examples 1 to 4

[0062] 9 grams of PEGDA and 0.9 grams of PI were added to 290.1 ​​grams of MEK in a 500 mL amber glass jar at room temperature. The jar was capped and shaken until all components were evenly mixed into the solution.

[0063] The PEGDA mixture was coated through a slot die onto a moving web consisting of polyvinyl alcohol and a non-removable substrate, such as those mentioned in WO2019 / 003107, at a speed of 50 feet / minute at target thicknesses of 100 nm, 150 nm, 200 nm, 250 nm. Prior to UV curing, the solvent was removed from the coating by heating in an oven at 190 degrees Fahrenheit for about two minutes. The coating was applied directly onto the polyvinyl alcohol surface. Prior to coating, the coating was heated at 250 mJ / cm 2 The substrate surface is corona treated.

[0064] Comparative Examples 5 to 7

[0065] 72.7 g of PEGDA and 7.3 g of PI were added to 120 g of MEK in a 500 mL amber glass jar at room temperature. The jar was capped and shaken until all components were evenly mixed into the solution.

[0066] The PEGDA mixture was coated through a slot die onto a moving web consisting of polyvinyl alcohol and a removable substrate at a speed of 10 feet / minute at target thicknesses of 4 μm, 7 μm, and 10 μm. The solvent was removed from the coating by heating in an oven at 190 degrees Fahrenheit for about two minutes prior to UV curing. The coating was applied directly onto the polyvinyl alcohol surface.

[0067] Comparative Examples 8 to 11

[0068] 79.2 g of TICTA and 0.8 g of PI were added to 120 g of MEK in a 500 mL amber glass jar at room temperature. The jar was capped and shaken until all components were evenly mixed into the solution.

[0069] The TICTA mixture was coated through a slot die onto a moving web consisting of polyvinyl alcohol and a non-removable substrate, such as those mentioned in WO2019 / 003107, at a speed of 45 feet / minute at a target thickness of 210 nm. Prior to UV curing, the solvent was removed from the coating by heating in an oven at 165 degrees Fahrenheit to 180 degrees Fahrenheit for about 40 seconds. The coating was applied directly onto the polyvinyl alcohol surface. Prior to coating, the coating was heated at 0 mJ / cm 2 、250mJ / cm 2 、500mJ / cm 2 、750mJ / cm 2 The substrate surface is corona treated.

[0070] Comparative Example 12 to Comparative Example 14

[0071] 79.2 g of TICTA and 0.8 g of PI were added to 120 g of MEK in a 500 mL amber glass jar at room temperature. The jar was capped and shaken until all components were evenly mixed into the solution.

[0072] The TICTA mixture was coated through a slot die onto a moving web consisting of polyvinyl alcohol and a removable substrate at a speed of 10 feet per minute at target thicknesses of 4 μm, 7 μm, and 10 μm. The solvent was removed from the coating by heating in an oven at 190 degrees Fahrenheit for about two minutes prior to UV curing. The coating was applied directly onto the polyvinyl alcohol surface.

[0073] Comparative Examples 15 to 18

[0074] 79.2 g of AO and 0.8 g of PI were added to 120 g of MEK in a 500 mL amber glass jar at room temperature. The jar was capped and shaken until all components were evenly mixed into the solution.

[0075] The AO mixture was coated through a slot die onto a moving web consisting of polyvinyl alcohol and a non-removable substrate, such as those mentioned in WO2019 / 003107, at a speed of 45 feet / minute at a target thickness of 210 nm. Prior to UV curing, the solvent was removed from the coating by heating in an oven at 165 degrees Fahrenheit to 180 degrees Fahrenheit for about 40 seconds. The coating was applied directly onto the polyvinyl alcohol surface. Prior to coating, the coating was heated at 0 mJ / cm 2 、250mJ / cm 2 、500mJ / cm 2 、750mJ / cm 2 The substrate surface is corona treated.

[0076] Comparative Examples 19 to 21

[0077] 79.2 g of AO and 0.8 g of PI were added to 120 g of MEK in a 500 mL amber glass jar at room temperature. The jar was capped and shaken until all components were evenly mixed into the solution.

[0078] The AO mixture was coated through a slot die onto a moving web consisting of polyvinyl alcohol and a removable substrate at a speed of 10 feet / minute at target thicknesses of 4 μm, 7 μm, and 10 μm. The solvent was removed from the coating by heating in an oven at 190 degrees Fahrenheit for about two minutes prior to UV curing. The coating was applied directly onto the polyvinyl alcohol surface.

[0079] Comparative Examples 22 to 25

[0080] 79.2 g of PAO and 0.8 g of PI were added to 120 g of MEK in a 500 mL amber glass jar at room temperature. The jar was capped and shaken until all components were evenly mixed into the solution.

[0081] The PAO mixture was coated through a slot die onto a moving web consisting of polyvinyl alcohol and a non-removable substrate, such as those mentioned in WO2019 / 003107, at a speed of 45 feet / minute at a target thickness of 210 nm. The solvent was removed from the coating by heating in an oven at 165 to 180 degrees Fahrenheit for about 40 seconds prior to UV curing. The coating was applied directly onto the polyvinyl alcohol surface. Prior to coating, the coating was heated at 0 mJ / cm 2 、250mJ / cm 2 、500mJ / cm 2 、750mJ / cm 2 The substrate surface is corona treated.

[0082] Comparative Examples 26 to 28

[0083] 79.2 g of PAO and 0.8 g of PI were added to 120 g of MEK in a 500 mL amber glass jar at room temperature. The jar was capped and shaken until all components were evenly mixed into the solution.

[0084] The PAO mixture was coated through a slot die onto a moving web consisting of polyvinyl alcohol and a removable substrate at a speed of 10 feet per minute at target thicknesses of 4 μm, 7 μm, and 10 μm. The solvent was removed from the coating by heating in an oven at 190 degrees Fahrenheit for about two minutes prior to UV curing. The coating was applied directly onto the polyvinyl alcohol surface.

[0085] Comparative Example 29

[0086] 75 parts by mass of APETPU supplied at 40% solids in water were added to 925 parts by mass of water and mixed until homogeneous. The mixture was then applied manually by syringe to a moving cast polyester web and metered with a #18 Mayer rod. The cast web was then stretched in the transverse direction and dried in a tenter oven until the web was six times its starting width. The final coating thickness was less than 500 microns.

[0087] Comparative Example 30

[0088] 125 parts by mass of APETPU supplied at 40% solids in water was added to 875 parts by mass of water and mixed until homogeneous. The mixture was then applied manually by syringe to a moving cast polyester web and metered with a #18 Mayer rod. The cast web was then stretched in the transverse direction and dried in a tenter oven until the web was six times its starting width. The final coating thickness was less than 500 microns.

[0089] Comparative Example 31

[0090] 175 parts by mass of APETPU supplied at 40% solids in water was added to 825 parts by mass of water and mixed until homogeneous. The mixture was then applied manually by syringe to a moving cast polyester web and metered with a #18 Mayer rod. The cast web was then stretched in the transverse direction and dried in a tenter oven until the web was six times its starting width. The final coating thickness was less than 500 microns.

[0091] Comparative Example 32

[0092] 86 parts by mass of APCPU supplied at 35% solids in water were added to 914 parts by mass of water and mixed until homogeneous. The mixture was then applied manually by syringe onto a moving cast polyester web and metered with a #18 Mayer rod. The cast web was then stretched in the transverse direction and dried in a tenter oven until the web was six times its starting width. The final coating thickness was less than 500 microns.

[0093] Comparative Example 33

[0094] 143 parts by mass of APCPU supplied at 35% solids in water was added to 857 parts by mass of water and mixed until homogeneous. The mixture was then applied manually by syringe onto a moving cast polyester web and metered with a #18 Mayer rod. The cast web was then stretched in the transverse direction and dried in a tenter oven until the web was six times its starting width. The final coating thickness was less than 500 microns.

[0095] Comparative Example 34

[0096] 200 parts by mass of APCPU supplied at 35% solids in water were added to 800 parts by mass of water and mixed until homogeneous. The mixture was then applied manually by syringe onto a moving cast polyester web and metered with a #18 Mayer rod. The cast web was then stretched in the transverse direction and dried in a tenter oven until the web was six times its starting width. The final coating thickness was less than 500 microns.

[0097] Then, the steps of Examples 1-10 and Comparative Examples 1-4, 8-11, 15-18, 22-25, 29-37 were performed.

[0098] Next, a quarter wave plate is prepared. The material is solvent coated and UV cured on the urethane coating, with the slow optical axis oriented at 45 degrees relative to the pass direction of the integrated polarizer. The coating has a retardation of 138nm at a wavelength of 550nm. (The retardation is defined by Re = (ni-nj)*d, where ni-nj is the in-plane birefringence difference between the slow optical axis and the fast optical axis of the coating material, and d is the thickness of the coating layer.) The coating material utilized is similar to that described in US2002 / 0180916, US2003 / 028048 and US2005 / 0072959, wherein the linear photopolymerizable polymer (LPP) material is ROP-131EXP306LPP, and the liquid crystal polymer (LCP) material is ROF-5185EXP410LCP (both available from Rolic New Materials of Allschwil, Switzerland).

[0099] Measurement of Adhesion Test Method 1

[0100] The sample consisting of substrate, PVOH, primer and QWP was pasted to the glass panel above the linear polarizer and backlight with double-sided tape (3M 415, 3M Company, St. Paul, MN). The QWP was oriented upward toward the air. Next, the sample was carefully scored using an 11-tooth blade (Gardco PA-2053, Paul N.Gardner Company, Pompano Beach, FL, etc.), where the tooth spacing was 1 mm apart. The sample was then carefully scored again perpendicular to the first set of scoring marks to create a 10X10 square grid. A 1-inch tape (3M 8403) was pressed onto the scale grid at a 45-degree angle to the scale marks in a manner that completely covered the scale grid. Before removal, a 1-inch tape was applied for 30 seconds. The grid was visually observed through the linear polarizer, and the retention percentage was recorded.

[0101] Table 2

[0102]

[0103] Measurement of Adhesion Test Method 2

[0104] Adhesion is measured using a modified version of Test Method 1. This method was developed for situations where the primer coating is applied to a removable substrate. In situations where the substrate is removable, the adhesion between the substrate and the primer coating is insufficient to remove the tape, so the required substrate is removed first. In addition, the razor blade used in Adhesion Test Method 1 tears through the coating stack without a substrate for support. Therefore, a very sharp razor blade is required to score the cross-hatch grid. The test method is as follows:

[0105] First, two inches of double-sided tape (3M 415, 3M Company, St. Paul, MN) with paper lining is applied to the quarter wave plate side of the coated film in the longitudinal direction. Next, the removable substrate is removed from the coated film stack, leaving polyvinyl alcohol, urethane coating and a quarter wave plate adhered to the double-sided tape with paper lining. The paper lining is then taken out of the double-sided tape, and the tape / film stack is laminated to a glass plate with a rubber roller. The glass plate is located above a backlight with a linear polarizer (Sanritz HLC2-5618, Sanritz Corporation, Tokyo, JP, Japan), and the linear polarizer is located between the glass plate and the backlight plate. An aqueous iodine solution is applied to the exposed surface of the film stack by a cotton head applicator. If the film stack is stained with iodine, it indicates that all layers have been successfully transferred. If the film stack is not stained, it indicates that some or all layers have not been transferred. Five straight parallel lines spaced 2 mm apart and 2.5 inches long were scored into the film stack, with the razor blade guided by a template device. Five more parallel lines of equal size and oriented perpendicular to the first five lines were scored so that a 5×5 square grid was created. A 1-inch tape (3M8403, 3M Company, St. Paul, Minnesota) was pressed onto the scale grid at a 45-degree angle to the scale markings in a manner that completely covered the scale grid. The 1-inch tape was adhered to the grid for 30 seconds before removal. After removal, the grid was visually observed by a linear polarizer attached to a magnifying glass, which was oriented approximately 15 degrees from the block state to illuminate the quarter-wave plate and show any areas where polyvinyl alcohol was missing. The percentage of retention within the grid area was then recorded. If the complete film stack was not transferred, adhesion failure was indicated and was also noted. Alternatively, the grid can be stained with an iodine solution, visually observed without a linear polarizer, and the percentage of retention within the grid area is recorded.

[0106] Table 3

[0107]

[0108] Cracking test method

[0109] After the coating stack including PVOH, primer and QWP and the carrier substrate were subjected to iodine dye bath, boronization bath, rinsing and drying according to the above method, cracking was evaluated on a pass / fail basis. If any cracking was present, it was considered a failure, while the absence of cracking on the sample was considered a pass.

[0110] Iodine intake test method

[0111] According to the method described above, the primer is applied to a substrate without PVOH and immersed in an iodine dyeing bath, a boronization bath, rinsed and dried. Next, the primer layer is visually evaluated for yellow, and if any color is observed, a failure grade is given. If no color is found, it is considered qualified.

[0112] Table 4

[0113]

[0114]

[0115] *Not measured, but probably less than 0.5 μm

[0116] **ND=Not Data

[0117] The entire disclosure of the patent disclosures cited herein is incorporated herein in their entirety by reference, as if each patent disclosure were incorporated herein individually. Various modifications and alterations of the present invention will be apparent to those skilled in the art without departing from the scope and substance of the present invention. It should be understood that the present invention is not intended to be unduly limited to the exemplary embodiments and examples shown herein, and the above-described embodiments and embodiments are presented only by way of example, and the scope of the present invention is intended to be limited only by the claims shown herein below.

Claims

1. A membrane stack comprising: (a) Quarter-wave retarder, (b) a transparent aliphatic cross-linked polyurethane layer disposed on a major surface of the quarter-wave retarder, the transparent aliphatic cross-linked polyurethane layer having a glass transition temperature in the range of 11° C. to 27° C. and a Tan δ peak in the range of 0.5 to 2.5, and (c) a layer comprising polyvinyl alcohol, wherein the layer comprising polyvinyl alcohol is disposed on the polyurethane layer opposite to the quarter-wave retarder.

2. The film stack of claim 1, further comprising a pre-mask disposed on the quarter-wave retarder opposite the layer comprising polyvinyl alcohol.

3. The film stack of claim 2, wherein the pre-mask comprises polyethylene terephthalate.

4. The film stack according to any one of claims 1 to 3, wherein the layer comprising polyvinyl alcohol is provided on a film comprising a strain hardened polyester layer.

5. The film stack of claim 1, wherein the quarter wave retarder has a thickness of 1 μm to 5 μm. The film stack of claim 1 , wherein the polyurethane layer has a thickness of 4 μm to 10 μm.

7. The film stack of claim 1, wherein the layer comprising polyvinyl alcohol has a thickness of less than 5 μm.

8. The film stack of claim 7, wherein the layer comprising polyvinyl alcohol has a thickness of less than 3 μm.

9. The film stack of claim 1, wherein the film stack has a total thickness of less than 35 μm.

10. The film stack of claim 9, wherein the film stack has a total thickness of less than 20 μm. The film stack of claim 10 , wherein the film stack has a total thickness of less than 15 μm.

12. The film stack of claim 1, wherein the quarter wave retarder comprises an oriented polymer material or a coated liquid crystal material.

13. The film stack of claim 1, wherein the layer comprising polyvinyl alcohol is dyed with a composition comprising iodine.

14. The film stack according to claim 13 further includes a second transparent aliphatic cross-linked polyurethane layer with a thickness of 2 μm to 5 μm disposed on the iodine-dyed layer, the iodine-dyed layer containing polyvinyl alcohol, the second transparent aliphatic cross-linked polyurethane layer having a glass transition temperature in the range of 11° C. to 27° C. and a Tan δ peak in the range of 0.5 to 2.

5.

15. The film stack of claim 1 wherein the polyurethane layer is not stained with iodine.

16. A membrane stack comprising: (a) a film comprising a strain hardened polyester layer, (b) a layer comprising polyvinyl alcohol, the layer comprising polyvinyl alcohol being disposed on the strain hardened polyester layer, and A transparent aliphatic cross-linked polyurethane layer having a thickness of 100 μm or less and disposed on the layer containing polyvinyl alcohol opposite to the strain hardening polyester layer, the transparent aliphatic cross-linked polyurethane layer having a glass transition temperature in the range of 11° C. to 27° C. and a Tan δ peak in the range of 0.5 to 2.

5. 17 . The film stack of claim 16 , wherein the polyurethane layer has a thickness of 4 μm to 10 μm.

18. The membrane stack according to claim 16 or 17, wherein the layer comprising polyvinyl alcohol has a thickness of less than 5 μm.

19. The film stack of claim 18, wherein the layer comprising polyvinyl alcohol has a thickness of less than 3 μm.

20. The film stack of claim 16 or 17, wherein the film stack has a total thickness of less than 35 μm.

21. The film stack of claim 20, wherein the film stack has a total thickness of less than 20 μm.

22. The film stack of claim 21, wherein the film stack has a total thickness of less than 15 μm.

23. The membrane stack of claim 16 or 17, wherein the polyurethane layer is not dyed with iodine.

24. A method for preparing a membrane stack, comprising: (a) coating a layer comprising polyvinyl alcohol on a film comprising a strain-hardened polyester layer, (b) a film oriented along a first direction, and (c) coating the layer comprising polyvinyl alcohol with a transparent aliphatic cross-linked polyurethane layer having a thickness of 100 μm or less, the transparent aliphatic cross-linked polyurethane layer having a glass transition temperature in the range of 11° C. to 27° C. and a Tan δ peak in the range of 0.5 to 2.5, The method further includes orienting the film comprising the strain hardened polyester layer in a direction opposite to the first direction prior to applying the layer comprising polyvinyl alcohol.

25. The method of claim 24, further comprising coating a quarter wave retarder layer on the polyurethane layer.

26. The method of claim 24, further comprising removing the film comprising the strain hardened polyester layer from the film stack.

27. The method of claim 26, further comprising staining the layer comprising polyvinyl alcohol with iodine.

28. The method of claim 25, further comprising placing a pre-mask on the quarter-wave retarder layer.

29. The method of claim 24, wherein the polyurethane layer is not dyed with iodine.

Images