A laminated polarizing film and a method for manufacturing the same

Abstract

This application relates to the field of functional thin films and discloses a stacked polarizing film and its preparation method. The stacked polarizing film includes alternately stacked high-refractive-index functional layers and low-refractive-index functional layers, and a protective boundary layer. The high-refractive-index functional layer is a PET layer, and its refractive index at a wavelength of 550 nm satisfies: n x The value is 1.67–1.70, n y For 1.52-1.55, n z It is 1.52-1.55, and |n y -n z |≤0.004, in-plane birefringence|n x -n y |≥0.12; The low-refractive-index functional layer is optically isotropic at 550nm wavelength, and its three-dimensional refractive index n x '、n y '、n z Both are between 1.53 and 1.55, and the in-plane birefringence |n x '-n y '|≤0.005; where the x-axis is the polarization function direction of the stacked polarizing film, the y-axis is perpendicular to the x-axis and lies in the film plane, and the z-axis is perpendicular to the film plane. This application solves the problem of three-dimensional refractive index imbalance of PET caused by a single stretching process, and achieves high-precision matching between it and isotropic low refractive index materials in the y-axis and z-axis directions.

Description

Technical Field

[0001] This application relates to the field of functional thin film technology, and in particular to a multilayer polarizing film and its preparation method. Background Technology

[0002] Reflective polarizing films, as core optical components in fields such as liquid crystal displays, lighting, and energy-efficient buildings, function based on the principle of birefringence interference. They achieve the reflection and transmission of light in a specific polarization direction through alternating stacks of high- and low-refractive-index polymer layers. The core of their optical performance lies in the precise matching of the refractive indices of the high- and low-refractive-index materials across three spatial dimensions. Ideally, a sufficient refractive index difference must be maintained along the unpolarized light separation direction (x-axis, i.e., the polarization function direction) to achieve efficient reflection, while the other two directions should be matched as closely as possible to eliminate polarization state disorder and dispersion under oblique incident light, thereby ensuring optical uniformity and color fidelity over a wide viewing angle.

[0003] Polyethylene terephthalate (PET) is widely used as the preferred material for high-refractive-index functional layers due to its excellent mechanical strength, thermal stability, and inherent birefringence. However, traditional PET-based multilayer polarizing film fabrication processes have fundamental flaws. The industry commonly employs unidirectional stretching (usually longitudinal, i.e., the film's forward direction) to achieve PET molecular chain orientation and birefringence. While this process effectively increases the x-axis refractive index (n... x However, this results in the molecular chains being arranged almost entirely along the longitudinal direction (y-axis), while the molecular chain density in the thickness direction (z-axis) is extremely low, leading to a severe imbalance in the three-dimensional refractive index distribution, typically manifested as: n x The value is relatively high, approximately 1.63-1.68, n y The next value is approximately 1.55-1.57, n. z The value is the lowest, approximately 1.49-1.52, i.e., n y With n z Significant differences exist.

[0004] The aforementioned refractive index imbalance leads to a series of key performance issues. Firstly, biaxial fitting accuracy is low. Commonly used low-refractive-index materials, such as methyl methacrylate-styrene copolymers, cyclic olefin copolymers, and novel bio-based polyesters (such as PEFG), are mostly isotropic materials with a balanced and stable three-dimensional refractive index of approximately 1.53-1.55. In contrast, traditional PET films have an n... y high, n zThe low refractive index of PET materials results in a refractive index difference of 0.02-0.05 along the z-axis. When light is incident at a large angle, this mismatch in the yz plane causes drastic fluctuations in the reflectivity of p-polarized light, leading to significant visual color difference and severely impacting the image quality of displays viewed from the side. Secondly, optical performance stability is poor. The single stretching process introduces a large amount of uneven residual stress within the film, which is easily released under thermal conditions, causing dimensional changes and interlayer distortion, manifested as a significant increase in haze and a decrease in transmittance. Finally, long-term stagnation in process innovation, with traditional technological thinking confined to a single longitudinal stretching mode, prevents fundamental control over the three-dimensional spatial arrangement of PET molecular chains, limiting further improvements in polarization film performance.

[0005] Therefore, a new method for designing and fabricating polarizing film structures is urgently needed to solve the problem of three-dimensional refractive index imbalance in PET caused by a single stretching process, and to achieve high-precision matching between PET and isotropic low refractive index materials in the y-axis and z-axis directions, thereby producing a multilayer polarizing film with excellent wide viewing angle performance, high thermal stability and high reliability. Summary of the Invention

[0006] To address the issue of three-dimensional refractive index imbalance in PET caused by a single stretching process and to achieve high-precision matching between PET and isotropic low-refractive-index materials in the y-axis and z-axis directions, this application provides a multilayer polarizing film and its preparation method. This polarizing film exhibits excellent wide-viewing-angle performance, high thermal stability, and high reliability.

[0007] In a first aspect, this application provides a multilayer polarizing film, employing the following technical solution:

[0008] A multilayer polarizing film includes an alternating stacked structure formed by alternating stacked high-refractive-index functional layers and low-refractive-index functional layers, and a protective boundary layer disposed on both sides of the alternating stacked structure.

[0009] The high refractive index functional layer is a polyethylene terephthalate layer, whose three-dimensional refractive index at a wavelength of 550 nm satisfies: the refractive index n along the x-axis x The refractive index n along the y-axis is 1.67-1.70. y The refractive index n along the z-axis of the thickness direction is 1.52-1.55. z It is 1.52-1.55, and |n y -n z |≤0.004, in-plane birefringence|n x -n y |≥0.12;

[0010] The low-refractive-index functional layer is optically isotropic at a wavelength of 550 nm, and its three-dimensional refractive index n x'、n y '、n z Both are between 1.53 and 1.55, and the in-plane birefringence |n x '-n y '|≤0.005;

[0011] Wherein, the x-axis is the polarization direction of the stacked polarizing film, the y-axis is perpendicular to the x-axis and lies in the film plane, and the z-axis is perpendicular to the film plane.

[0012] By employing the above technical solution, a high-refractive-index PET layer with a novel three-dimensional refractive index distribution was constructed. The core of this achievement lies in the precise control of the PET layer to realize n... y With n z Achieving a balance while maintaining a high n x This value allows the high-refractive-index layer to exhibit near-isotropic characteristics in the yz plane, thus enabling near-perfect refractive index matching with isotropic low-refractive-index materials in the non-polarization functional directions (y-axis and z-axis). This fundamentally solves the problem of refractive index mismatch in traditional uniaxial stretched polarization films. y ≠n z This leads to problems such as large visual scattering and reflectivity fluctuations.

[0013] Optionally, along the y-axis, the refractive index difference between the high-refractive-index functional layer and the low-refractive-index functional layer is no greater than 0.005; along the z-axis, the refractive index difference between the high-refractive-index functional layer and the low-refractive-index functional layer is no greater than 0.005.

[0014] Optionally, the material of the low refractive index functional layer is selected from at least one of methyl methacrylate-styrene copolymer, polyethylene furanate dicarboxylate copolydiol modifier, and cyclic olefin copolymer.

[0015] Optionally, the protective boundary layer is made of polyethylene terephthalate with a thickness of 2-6 μm.

[0016] By adopting the above technical solution and using PET as the protective boundary layer, whose material is the same as that of the high refractive index functional layer, it is ensured that the protective boundary layer and the functional layer have similar thermodynamic and rheological behaviors in the subsequent synchronous stretching-shrinking process. This avoids edge stress concentration, interlayer delamination or uneven thickness caused by material mismatch, significantly improves process stability and mechanical integrity of the finished film edge, reduces edge trimming loss and improves product yield.

[0017] Optionally, the total number of high-refractive-index functional layers and low-refractive-index functional layers is 120-320 layers, and the total thickness of the finished laminated polarizing film is 22-36 μm with a thickness deviation of ≤2.5%.

[0018] Optionally, the transmitted light color difference ΔE of the stacked polarizing film in the 0°-85° viewing angle range is ≤0.8; and / or, after aging at 105°C for 1000 hours, its haze increase value is ≤0.1%; and / or, its interlayer peel strength is ≥6.0N / 25mm.

[0019] Secondly, this application provides a method for preparing a multilayer polarizing film, which adopts the following technical solution:

[0020] A method for preparing a multilayer polarizing film includes the following steps:

[0021] S1. Raw material pretreatment: Dry polyethylene terephthalate chips to a moisture content of ≤45ppm and dry low refractive index functional layer raw materials to a moisture content of ≤28ppm.

[0022] S2. Multilayer co-extrusion casting: Dried polyethylene terephthalate and low refractive index functional layer raw materials are melted separately and co-extruded through a multilayer distribution module to form an alternating layered melt flow. A polyethylene terephthalate protective layer is then laminated on both sides. The mixture is extruded through a die, cast, and quenched by a cooling roller to obtain the casting.

[0023] S3. Synchronous Stretching and Shrinkage Treatment with Clamping Grippers: After preheating the casting, clamp its two edges with grippers and simultaneously perform transverse stretching and longitudinal shrinkage operations at a temperature of 105-115℃; wherein, the transverse stretching direction is the width direction of the casting, and the stretching rate V X The shrinkage rate is 0.2-0.5 m / s, the longitudinal shrinkage direction is the length direction of the casting, and the shrinkage rate V y The speed is 0.05-0.2 m / s, and the time deviation between the completion of lateral stretching and longitudinal contraction is ≤0.5 seconds;

[0024] S4. Post-processing: The castings processed in step S3 are heat-set, cooled, and trimmed to obtain the laminated polarizing film.

[0025] By adopting the above technical solution and employing a gripper-synchronous lateral stretching-longitudinal shrinking process, physical and mechanical means are used to induce PET to align along the x-axis during lateral stretching, while simultaneously applying longitudinal shrinking force to promote molecular chain rearrangement in the yz plane, thereby achieving n in one step. y ≈n z The method of three-dimensional refractive index equalization control has a clear process logic and is significantly superior to the traditional single stretching mode.

[0026] Optionally, in step S3, a synchronization coordination factor F=V is defined. x / V y The value of F is controlled to be between 1.0 and 10.0.

[0027] By adopting the above technical solution and precisely controlling the F-value, the process can be optimized for low-refractive-index materials with different properties, and the orientation and relaxation degree of PET molecular chains can be adjusted in real time to ensure that n can be obtained stably and repeatedly in any production batch. y ≈n z The ideal refractive index distribution enables precision and standardization of the process.

[0028] Optionally, step S3 further includes layer thickness compensation control: defining a layer thickness compensation coefficient C=(d1' / d2') / (d1 / d2), where d1 and d2 are the initial design thicknesses of the high and low refractive index functional layers set in step S2, and d1' and d2' are the actual thicknesses of the corresponding layers after step S3. By adjusting the melt flow rate ratio in the co-extrusion stage, the value of C is controlled to be 0.95-1.05.

[0029] By adopting the above technical solution, a layer thickness compensation coefficient C is introduced as a closed-loop control parameter. During the synchronous bidirectional force process, the thickness change behavior of different materials may be different. By monitoring and adjusting the extrusion flow ratio to control the C value between 0.95 and 1.05, this non-uniform deformation can be actively compensated, ensuring that the actual thickness ratio of each functional layer in the final product meets the optical design expectations, thereby ensuring that the theoretical optical performance is accurately realized in production.

[0030] In summary, this application includes at least one of the following beneficial technical effects:

[0031] 1. By precisely controlling the PET layer, n was achieved. y With n z Numerical balance, while maintaining a high n x This value allows the high-refractive-index layer to exhibit near-isotropic characteristics in the yz plane, thus enabling near-perfect refractive index matching with isotropic low-refractive-index materials in the non-polarization functional directions (y-axis and z-axis). This fundamentally solves the problem of refractive index mismatch in traditional uniaxial stretched polarization films. y ≠n z This leads to problems such as large visual scattering and reflectivity fluctuations;

[0032] 2. Employing a gripper-synchronous transverse stretching-longitudinal shrinking process, this method uses physical and mechanical means to induce PET orientation along the x-axis through transverse stretching while actively applying longitudinal shrinking force to promote molecular chain rearrangement in the yz plane, thereby achieving n-axis orientation in one step. y ≈n z The method of three-dimensional refractive index equalization control has a clear process logic and is significantly superior to the traditional single stretching mode. Detailed Implementation

[0033] This application provides a multilayer polarizing film and its preparation method. The multilayer polarizing film is prepared by a clamp-based synchronous lateral stretching-longitudinal shrinking process. This process simultaneously introduces lateral (x-axis) molecular chain orientation and longitudinal (y-axis) molecular chain rearrangement into the high-refractive-index polyethylene terephthalate layer, thereby achieving a three-dimensional refractive index that satisfies: n x (1.67-1.70)>n y ≈n z (1.52-1.55). This high-low refractive index distribution can achieve precise matching (difference ≤0.005) with isotropic low refractive index materials (refractive index 1.53-1.55) in the y-axis and z-axis directions, while maintaining a high difference (≥0.1) in the x-axis. This not only achieves high polarization efficiency, but also completely solves the dispersion problem at large viewing angles and significantly improves the thermal stability and mechanical properties of the product.

[0034] Example

[0035] An embodiment of this application discloses a method for preparing a multilayer polarizing film, comprising the following steps:

[0036] S1. Raw material pretreatment: Vacuum dry PET chips at 125-145℃ for 5-7 hours to make the moisture content ≤45ppm. Vacuum dry low refractive index materials (such as MS resin, PEFG, COC) at 85-105℃ for 3-5 hours to make the moisture content ≤28ppm.

[0037] S2, Multi-layer co-extrusion casting: The dried PET is fed into the first extruder (260-265℃, 16-26MPa), and the low refractive index material is fed into the second extruder (temperature depends on the material, 250-265℃, 13-21MPa).

[0038] Two melts are alternately stacked at a preset layer thickness ratio (d1 / d2=1.2-2.0) using a multilayer distributor and gear pump, and a PET protective layer with a thickness of 2-6μm is laminated on both sides.

[0039] The composite melt is extruded through a T-die (die lip gap 0.6-1.1mm) and cast onto a cooling roller at 30-45℃ for quenching at a rate of ≥55℃ / s to obtain a casting with a thickness of 160-320μm and a layer thickness deviation of ≤3%.

[0040] S3. Synchronous Lateral Stretching-Longitudinal Shrinkage Processing with Grippers: The cast sheet is preheated at 95-105℃ for 40-60 seconds. After preheating, the cast sheet is gripped by the grippers of a gripper-type bidirectional tenter frame, with both edges held together, and simultaneously enters the stretching-shrinkage zone. Within this zone, the gripper system is mechanically linked and simultaneously performs the following actions:

[0041] Lateral stretching: The grippers open uniformly in the transverse direction (perpendicular to the extrusion direction), with a stretching rate V.X The tensile force should be controlled at 0.2-0.5 m / s, the tensile temperature at 105-115℃, and the transverse tension at 8-12 N / m.

[0042] Longitudinal stretching: While opening laterally, the grippers uniformly close along the longitudinal direction (extrusion direction), achieving active longitudinal contraction, with a contraction rate V. y Controlled within 0.05-0.2 m / s;

[0043] Cooperative control: Define the synchronization coordination factor F=V x / V y By adjusting in real time, the F value is kept within the range of 1.0-10.0 to ensure the dynamic balance between lateral stretching and longitudinal contraction. The time deviation between the completion of lateral stretching and longitudinal contraction must be ≤0.5 seconds.

[0044] After the synchronization operation is completed, the casting is held at 105-115℃ for 20-30 seconds to relax the stress, and then the jaws release the casting.

[0045] S4. Post-processing: The casting is heat-set at 180-220℃ for 45-75s, then cooled to room temperature in three stages, and finally laser edge cutting and corona treatment are performed to obtain the finished laminated polarizing film.

[0046] Example 1

[0047] Example 1: A stacked polarizing film with bio-based polyester PEFG as the low refractive index functional layer was prepared.

[0048] raw material:

[0049] High refractive index functional layer: PET chips (Mitsubishi FN110, intrinsic viscosity 0.68 dL / g), moisture content after drying 38 ppm;

[0050] Low refractive index functional layer: PEFG (melt flow rate 8 g / 10 min, three-dimensional refractive index 1.54), water content after drying 25 ppm;

[0051] Protective boundary layer: Same as the high refractive index functional layer, designed with a thickness of 3μm.

[0052] Preparation process:

[0053] Co-extrusion casting: First extruder (high refractive index functional layer PET) 260℃ / 21MPa, second extruder (PEFG) 255℃ / 17MPa, third extruder (protective boundary layer PET) 260℃ / 20MPa. A total of 200 layers of high and low refractive index functional layers (100 layers of PET / PEFG) are formed, alternating between the two layers for 100 cycles. Within each cycle, the layer thickness ratio of the high and low refractive index functional layers is set to 1.6:1, and the gear pump flow ratio is also set to 1.6:1. After extrusion casting, the wafer is quenched at 36℃ using cooling rollers (cooling rate 62℃ / s) to obtain a 190μm thick wafer.

[0054] Gripper synchronous processing: Preheat at 102℃ for 48s, longitudinal tension 3.2N / m, set transverse stretching rate V x =0.30m / s (stretch ratio 3.8), initial width 1m, stretching time 9.3s, longitudinal shrinkage rate V y =0.04m / s (shrinkage rate S≈0.1), both completed synchronously in 9.3 seconds, stretching temperature 114℃, synchronization synergy factor F=V x / V y =7.5.

[0055] Post-processing: After stress relaxation, the product is heat-set at 210℃ for 60 seconds, cooled, trimmed, and subjected to corona treatment to obtain the finished product.

[0056] Online monitoring: PET n x =1.69, n y =1.55, n z =1.55; C=1.01;

[0057] Performance testing: Color difference ΔE = 0.75 (at a 60° viewing angle), light transmittance 92.8%, light-blocking reflectance 98.2%;

[0058] After aging at 105℃ for 1000 hours, the haze was 1.22% (initially 1.2%).

[0059] Interlaminar peel strength 6.2N / 25mm, tensile strength 159 / 163MPa (longitudinal / transverse).

[0060] The finished product has a thickness of 28.5μm and an interlayer peel strength of 6.4N / 25mm.

[0061] Example 2

[0062] Example 2: A stacked polarizing film with MS resin as a low refractive index functional layer was prepared.

[0063] raw material:

[0064] High refractive index functional layer: PET chips (Eastman EASTAPAK® 7352, intrinsic viscosity 0.70 dL / g), moisture content 35 ppm after drying;

[0065] Low refractive index functional layer: MS resin (melt flow rate 10g / 10min, three-dimensional refractive index 1.53), water content after drying 25ppm;

[0066] Protective boundary layer: Same as the high refractive index functional layer, designed with a thickness of 3μm.

[0067] Preparation process:

[0068] Co-extrusion casting: First extruder 265℃ / 20MPa, second extruder 260℃ / 18MPa, third extruder 260℃ / 20MPa. A total of 220 layers of high-refractive-index and low-refractive-index functional layers were formed, with an initial layer thickness ratio of 1.4 and a gear pump flow ratio of 1.4:1. After extrusion casting, the wafer was quenched on a cooling roller at 38℃ (cooling rate 58℃ / s) to obtain a 200μm thick wafer.

[0069] Gripper synchronous processing: Preheat at 100℃ for 45s, longitudinal tension 3N / m, set V x =0.40m / s (stretch ratio 4.0), initial width 1m, stretching time 7.5s, V y =0.067m / s (S≈0.125), synchronization time 7.5 seconds, F=5.97, tensile temperature 112℃.

[0070] Online monitoring: PET n x =1.68, n y =1.55, n z =1.55; C=1.02;

[0071] Performance testing: Color difference ΔE = 0.8 (at a 60° viewing angle), light transmittance along the light axis 91.5%, and light-blocking reflectance 97.2%;

[0072] After aging at 105℃ for 1000 hours, the haze was 1.1% (initially 1.05%).

[0073] Interlaminar peel strength 6.4N / 25mm, tensile strength 155 / 164MPa (longitudinal / transverse).

[0074] The finished product has a thickness of 28.5μm.

[0075] Example 3

[0076] Example 3: A stacked polarizing film with COC as a low refractive index functional layer was prepared.

[0077] raw material:

[0078] High refractive index functional layer: PET chips (DuPont Selar® PET5453, intrinsic viscosity 0.65 dL / g), moisture content 40 ppm after drying;

[0079] Low refractive index functional layer: COC (T g =85℃, three-dimensional refractive index 1.535), moisture content after drying 20ppm;

[0080] Protective boundary layer: Same as the high refractive index functional layer, designed with a thickness of 3μm.

[0081] Preparation process:

[0082] Co-extrusion casting: First extruder 260℃ / 22MPa, second extruder 255℃ / 15MPa, third extruder 260℃ / 20MPa. A total of 180 layers of high-refractive-index and low-refractive-index functional layers are formed, with an initial layer thickness ratio of 1.5 and a gear pump flow ratio of 1.5:1. After extrusion casting, the wafer is quenched on a cooling roller at 35℃ (cooling rate 60℃ / s) to obtain a 185μm thick wafer.

[0083] Gripper synchronization processing: Preheat at 98℃ for 42s, longitudinal tension 2.8N / m, set V X =0.35m / s (stretch ratio 3.6), initial width 1m, stretching time 7.43s, V y =0.073m / s (S≈0.15), synchronization time 7.4 seconds, F=4.79, tensile temperature 112℃.

[0084] Online monitoring: PET n x =1.67, n y =1.54, n z =1.54; C=1.00;

[0085] Performance testing: Color difference ΔE = 0.7 (at a 60° viewing angle), light transmittance along the light axis 90.9%, and light-blocking reflectance 96.2%;

[0086] After aging at 105℃ for 1000 hours, the haze was 0.925% (initially 0.92%).

[0087] Interlaminar peel strength 6.2N / 25mm, tensile strength 152 / 165MPa (longitudinal / transverse);

[0088] The finished product has a thickness of 28.5μm.

[0089] Comparative Example

[0090] Comparative Example 1

[0091] Comparative Example 1: A uniaxial stretched laminated polarizing film with PETG as a low refractive index functional layer was prepared.

[0092] Raw material selection:

[0093] PET chips (DuPont Selar® PET5453, intrinsic viscosity 0.65 dL / g), moisture content after drying 40 ppm;

[0094] PETG (Eastman 6763, refractive index 1.56), moisture content after drying is 20 ppm;

[0095] Co-extruded castings:

[0096] The first extruder operates at 260℃ / 22MPa, and the second extruder operates at 260℃ / 15MPa. A total of 250 layers (125PET+125PETG) of high-refractive-index functional layer and low-refractive-index functional layer are used. The initial layer thickness ratio is 1.4, the gear pump flow ratio is 1.4:1, and the extruded sheet is quenched on a cooling roller at 30℃ (cooling rate 50℃ / s) to obtain a 230μm thick sheet.

[0097] Gripper synchronization processing: Preheat at 80℃ for 40 seconds, set V x =1m / s (stretch ratio 4), initial width 1m, temperature 88℃, tension 9.5N / m.

[0098] Performance testing: Color difference ΔE = 5.4 (at a 60-degree viewing angle), light transmittance along the light axis is 85%, and light-blocking reflectance is 94.2%.

[0099] After aging at 105℃ for 1000 hours, the haze was 3.46% (initially 1.2%).

[0100] Interlaminar peel strength 6.3N / 25mm, tensile strength 165 / 124MPa (longitudinal / transverse).

[0101] The finished product has a thickness of 30μm.

[0102] Comparative Example 2

[0103] Comparative Example 2: A uniaxial stretched laminated polarizing film with PMMA as a low refractive index functional layer was prepared.

[0104] Raw material selection:

[0105] PET chips (DuPont Selar® PET5453, intrinsic viscosity 0.65 dL / g), moisture content after drying 40 ppm;

[0106] PMMA (Wanhua, refractive index 1.49), moisture content after drying is 20ppm;

[0107] Co-extruded castings:

[0108] The first extruder operates at 260℃ / 22MPa, and the second extruder operates at 255℃ / 15MPa. A total of 200 layers (100PET + 100PMMA) of high-refractive-index functional layer and low-refractive-index functional layer are used. The initial layer thickness ratio is 1.35, the gear pump flow ratio is 1.35:1, and the extruded sheet is quenched on a cooling roller at 30℃ (cooling rate 50℃ / s) to obtain a 220μm thick sheet.

[0109] Gripper synchronization processing: Preheat at 90℃ for 40 seconds, set V x =1m / s (stretch ratio 4), initial width 1m, temperature 98℃, tension 9.5N / m.

[0110] Performance testing: Color difference ΔE = 4.2 (at a 60-degree viewing angle), light transmittance along the light axis 82%, and light-blocking reflectance 97.2%;

[0111] After aging at 105℃ for 1000 hours, the haze was 4.26% (initially 1.1%).

[0112] Interlaminar peel strength 5.0 N / 25 mm, tensile strength 167 / 136 MPa (longitudinal / transverse).

[0113] The finished product has a thickness of 32μm.

[0114] The performance test results of Examples 1-3 and Comparative Examples 1-2 are shown in Table 1 below:

[0115] Table 1

[0116]

[0117] Combining Examples 1-3 and Comparative Examples 1-2 with Table 1, it can be seen that Examples 1-3, through simultaneous processes, enable the n-value of high refractive index functional layer PET to increase. y ≈n z Thus, the refractive index difference between the isotropic low refractive index functional layer and the isotropic low refractive index functional layer on the y / z axis is ≤0.005, achieving biaxial matching, which is impossible to achieve in the comparative example (difference as high as 0.075). Therefore, Examples 1-3 reduce the large viewing angle difference ΔE from ≥4.2 to ≤0.8, solving the core problem of wide viewing angle blur.

[0118] The synchronous process effectively reduced the residual stress in the membrane, resulting in minimal haze changes (≤0.05%) in Examples 1-3 after high-temperature aging, which is far superior to the significant degradation (≥2.26%) in Comparative Examples 1-2, demonstrating excellent long-term reliability.

[0119] The synchronization synergy factor F and the layer thickness compensation coefficient C constitute a precise, adjustable, and universal process control system that can be successfully adapted to various materials such as MS, PEFG, and COC, breaking through the limitations of traditional single stretching processes and possessing application value.

[0120] The above are all preferred embodiments of this application, and are not intended to limit the scope of protection of this application. Therefore, all equivalent changes made in accordance with the structure, shape and principle of this application should be covered within the scope of protection of this application.

Claims

1. A method for preparing a multilayer polarizing film, characterized in that, Includes the following steps: S1. Raw material pretreatment: Dry polyethylene terephthalate chips to a moisture content of ≤45ppm and dry low refractive index functional layer raw materials to a moisture content of ≤28ppm. S2. Multilayer co-extrusion casting: Dried polyethylene terephthalate and low refractive index functional layer raw materials are melted separately and co-extruded through a multilayer distribution module to form an alternating layered melt flow. A polyethylene terephthalate protective layer is then laminated on both sides. The mixture is extruded through a die, cast, and quenched by a cooling roller to obtain the casting. S3. Synchronous Stretching and Shrinkage Treatment with Clamping Grippers: After preheating the casting, clamp its two edges with grippers and simultaneously perform transverse stretching and longitudinal shrinkage operations at a temperature of 105-115℃; wherein, the transverse stretching direction is the width direction of the casting, and the stretching rate V x The shrinkage rate is 0.2-0.5 m / s, the longitudinal shrinkage direction is the length direction of the casting, and the shrinkage rate V y The speed is 0.05-0.2 m / s, and the time deviation between the completion of lateral stretching and longitudinal contraction is ≤0.5 seconds; S4. Post-processing: The castings processed in step S3 are heat-set, cooled, and trimmed to obtain the laminated polarizing film.

2. The method for preparing a multilayer polarizing film according to claim 1, characterized in that: In step S3, the synchronization coordination factor F=V is defined. x / V y The value of F is controlled to be between 1.0 and 10.

0.

3. The method for preparing a multilayer polarizing film according to claim 1, characterized in that, Step S3 further includes layer thickness compensation control: defining a layer thickness compensation coefficient C=(d1' / d2') / (d1 / d2), where d1 and d2 are the initial design thicknesses of the high and low refractive index functional layers set in step S2, and d1' and d2' are the actual thicknesses of the corresponding layers after step S3. By monitoring d1' and d2' online, the melt flow ratio in the co-extrusion stage is adjusted in real time to control the value of C to be 0.95-1.

05.

4. A multilayer polarizing film, manufactured by the method for preparing a multilayer polarizing film according to any one of claims 1-3, characterized in that: It includes an alternating stacked structure formed by alternating stacked high-refractive-index functional layers and low-refractive-index functional layers, and protective boundary layers disposed on both sides of the alternating stacked structure; The high refractive index functional layer is a polyethylene terephthalate layer, whose three-dimensional refractive index at a wavelength of 550 nm satisfies: the refractive index n along the x-axis x The refractive index n along the y-axis is 1.67-1.

70. y The refractive index n along the z-axis of the thickness direction is 1.52-1.

55. z It is 1.52-1.55, and |n y -n z |≤0.004, in-plane birefringence|n x -n y |≥0.12; The low-refractive-index functional layer is optically isotropic at a wavelength of 550 nm, and its three-dimensional refractive index n x '、n y '、n z Both are between 1.53 and 1.55, and the in-plane birefringence |n x '-n y '|≤0.005; Wherein, the x-axis is the polarization direction of the stacked polarizing film, the y-axis is perpendicular to the x-axis and lies in the film plane, and the z-axis is perpendicular to the film plane.

5. A stacked polarizing film according to claim 4, characterized in that: Along the y-axis, the refractive index difference between the high-refractive-index functional layer and the low-refractive-index functional layer is no greater than 0.005; along the z-axis, the refractive index difference between the high-refractive-index functional layer and the low-refractive-index functional layer is no greater than 0.

005.

6. A stacked polarizing film according to claim 4, characterized in that: The material of the low refractive index functional layer is selected from at least one of methyl methacrylate-styrene copolymer, polyethylene furanate dicarboxylate copolydiol modified, and cyclic olefin copolymer.

7. A stacked polarizing film according to claim 4, characterized in that: The protective boundary layer is made of polyethylene terephthalate and has a thickness of 2-6 μm.

8. A stacked polarizing film according to claim 4, characterized in that: The total number of high-refractive-index functional layers and low-refractive-index functional layers is 120-320, and the total thickness of the finished laminated polarizing film is 22-36 μm with a thickness deviation of ≤2.5%.

9. A stacked polarizing film according to claim 4, characterized in that: The transmitted light color difference ΔE of the laminated polarizing film is ≤0.8 within the viewing angle range of 0°-85°; and / or, after aging at 105°C for 1000 hours, its haze increase value is ≤0.1%; and / or, its interlayer peel strength is ≥6.0N / 25mm.