Polarizing plate, method for manufacturing the same, and display apparatus

Abstract

The application discloses a polarizer and a preparation method thereof, and a display device. The preparation method comprises the following steps: setting a first iodine dyeing and stretching groove, first dyeing and first stretching PVA material in the first iodine dyeing and stretching groove to obtain a first intermediate product; setting a second iodine dyeing and stretching groove, second dyeing and second stretching the first intermediate product in the second iodine dyeing and stretching groove to obtain a second intermediate product; after drying the second intermediate product, coating an adhesive, and laminating a TAC film to obtain the polarizer; the solution used for the first dyeing does not comprise boric acid, the solution used for the second dyeing comprises boric acid, the stretching ratio of the PVA film in the first dyeing and stretching is 1.6-2.5, and the total stretching ratio of the PVA film in the whole stretching process is 3.5-5. The polarizer provided by the application has excellent anti-curling performance.

Description

Technical Field

[0001] This invention relates to the field of liquid crystal displays, specifically to a polarizer and its preparation method, and a display device. Background Technology

[0002] In organic light-emitting diode (OLED) display technology, polarizers are used to suppress interference from ambient light reflection. OLEDs are widely used in flexible and foldable displays, requiring the thin films used to achieve a very thin profile, which places stringent demands on their anti-warping capabilities. To obtain high optical performance, polarizers are fabricated using thin polyvinyl alcohol (PVA) optical films, which require stretching the PVA optical film to a large stretch ratio.

[0003] However, polarizers prepared by stretching PVA material to a large stretch ratio are prone to warping under high temperature and high humidity conditions. Summary of the Invention

[0004] In view of the shortcomings of the prior art, the present invention proposes a polarizer and its preparation method, as well as a display device, aiming to solve the problem that polarizers prepared by stretching PVA material to a large stretch ratio are prone to warping under high temperature and high humidity environments.

[0005] To achieve the above objectives, the present invention proposes a method for preparing a polarizer, comprising the following steps: setting up a first iodine dyeing and stretching tank, dyeing and stretching PVA material for the first time in the first iodine dyeing and stretching tank to obtain a first intermediate product; setting up a second iodine dyeing and stretching tank, dyeing and stretching the first intermediate product for the second time in the second iodine dyeing and stretching tank to obtain a second intermediate product; drying the second intermediate product, coating it with an adhesive, and bonding it with a TAC film to obtain a polarizer; wherein, the solution used for the first dyeing does not include boric acid, and the solution used for the second dyeing includes boric acid.

[0006] Optionally, in the step of “setting up a first iodine dyeing and stretching tank, dyeing and stretching the PVA material for the first time in the first iodine dyeing and stretching tank to obtain a first intermediate product”, the stretching ratio of the first stretching is 1.6-2.5.

[0007] Optionally, in the step of “setting up a second iodine staining stretching tank, staining the first intermediate product for the second time and stretching it for the second time in the second iodine staining stretching tank to obtain a second intermediate product”, the solution used for the second staining includes boric acid, and the concentration of the boric acid is 1.0-3.5%.

[0008] Optionally, in the step of “setting up a second iodine dyeing stretching tank, dyeing the first intermediate product for the second time and stretching it for the second time in the second iodine dyeing stretching tank to obtain a second intermediate product”, the temperature of the second dyeing is 40-60℃.

[0009] Optionally, in the step of “setting a second iodine dyeing stretching tank, dyeing the first intermediate product a second time and stretching it a second time in the second iodine dyeing stretching tank to obtain a second intermediate product”, the total stretching ratio of the second intermediate product relative to the PVA material is 3.5-5.

[0010] To achieve the above objectives, the present invention also proposes a polarizer prepared by the above preparation method.

[0011] To achieve the above objectives, the present invention also proposes a display device comprising the aforementioned polarizer.

[0012] The beneficial effects of this invention are as follows: The method for preparing a polarizer provided by this invention involves two iodine dyeing and stretching tanks, performing two dyeing processes and two stretching processes. Boric acid is not added during the first dyeing process to avoid competition with iodine for complexation, resulting in a stretching ratio of 1.6-2.5 times. This allows the PVA film to initially form a complex with iodine. The second stretching process achieves a total stretching ratio of 3.5-5 times, further orienting the PVA molecules and forming a cross-linked structure with boric acid, which is beneficial for inducing the formation and orientation of polyiodide ions. This preparation method stretches the PVA material at a relatively small stretching ratio, preventing film warping in harsh environments (such as high temperature and high humidity environments) while simultaneously ensuring the thin profile and excellent optical performance of the polarizer. Detailed Implementation

[0013] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below. It should be understood that the following embodiments are only used to explain the present invention and are not intended to limit the present invention.

[0014] Unless otherwise specified, all technical and scientific terms used herein have their usual meaning within the field to which the subject matter is claimed.

[0015] To facilitate understanding of this embodiment, the following explanations are provided for the symbols and terms:

[0016] PVA stands for polyvinyl alcohol.

[0017] TAC stands for Triacetyl Cellulose.

[0018] In Organic Light Emitting Diode (OLED) display technology, polarizers are used to suppress interference from ambient light reflection. OLEDs are widely used in flexible and foldable displays, which places stringent requirements on the thinness of the various thin films used, including the polarizer itself. This also imposes strict requirements on the anti-warping capabilities of each film. To obtain high optical performance, polarizers are fabricated using thin polyvinyl alcohol (PVA) optical films, which requires stretching the PVA optical film to a large stretch ratio.

[0019] However, polarizers prepared by stretching PVA material to a large stretch ratio are prone to warping under high temperature and high humidity conditions.

[0020] To address the above problems, this invention proposes a method for preparing a polarizer, comprising the following steps:

[0021] A first iodine dyeing and stretching tank is set up. PVA material is dyed and stretched for the first time in the first iodine dyeing and stretching tank to obtain a first intermediate product.

[0022] In one embodiment of the present invention, the PVA material is a PVA film. The PVA film is immersed in a dyeing water bath in a first iodine dyeing stretching bath. The concentration of elemental iodine in the iodine dyeing bath is 0.5%, and the concentration of potassium iodide is 2%. A first stretching is performed at a certain stretching ratio. The first dyeing causes the PVA material to absorb iodine molecules bidirectionally. Subsequently, through stretching, the iodine molecules are arranged in an orderly manner on the PVA film. Because the PVA crystal structure serves as a physical cross-linking point during the first stretching, the stability of the internal polymer network structure of the PVA is maintained, so the slippage of the PVA chains during the stretching process can be ignored. Since the complexation reaction between PVA and boric acid and iodine both involve its hydroxyl structure, boric acid is not added to the first iodine dyeing stretching bath to avoid competition with iodine for complexation. The first intermediate product is the product after PVA has fully complexed with iodine and undergone sufficient dyeing.

[0023] A second iodine staining and stretching tank is set up, and the first intermediate product is stained and stretched for a second time in the second iodine staining and stretching tank to obtain a second intermediate product; the solution used for the second staining includes boric acid;

[0024] In one embodiment of the present invention, the PVA film, after being dyed for the first time, is dyed a second time and immersed in a second dyeing water bath containing 3% boric acid, 0.2% elemental iodine, and 0.8% potassium iodide. A second stretching is then performed at a certain multiple. This second stretching of 3.5-5 times further orients the PVA molecules and forms a cross-linked structure with boric acid, which is beneficial for inducing the formation and orientation of polyiodide ions. The formation of numerous dynamic chemical cross-linked structures between PVA and boric acid allows for effective stretching of the PVA molecular chains. The addition of boric acid improves the aging resistance of the iodine-dyed polarizer.

[0025] After drying the second intermediate product, an adhesive is applied, and a TAC film is bonded to it to obtain a polarizing film. In one embodiment of the present invention, the second intermediate product is dried in an air-floating oven, then PVA adhesive is applied to both sides, and then a TAC film is bonded and dried again to obtain a polarizing film. This ensures that the TAC and PVA contact surfaces are firmly bonded together, which facilitates the effective protection of the PVA adhesive and the TAC film. Since the polarizing layer made of PVA film is prone to absorbing water and fading, thus losing its polarizing performance, a layer of optically uniform and transparent TAC film is needed on both sides of the PVA film to isolate moisture and air and protect the polarizing layer.

[0026] Furthermore, in the step of "setting up a first iodine dyeing stretching tank, dyeing and stretching the PVA material for the first time in the first iodine dyeing stretching tank to obtain a first intermediate product", the stretching ratio of the first stretching is 1.6-2.5. For example, it can be 1.6 times stretching, 1.8 times stretching, 2.0 times stretching, 2.2 times stretching, or 2.5 times stretching. After the PVA optical film is stretched to a stretching ratio of 1.6-2.5, the crystal is damaged during the stretching process, and the PVA molecular chains begin to slip relative to each other, resulting in a weakening effect of stretching on the orientation of the PVA molecular chains.

[0027] Furthermore, in the step of "setting up a second iodine staining and stretching tank, and staining and stretching the first intermediate product a second time in the second iodine staining and stretching tank to obtain a second intermediate product", the solution used for the second staining includes boric acid, and the concentration of the boric acid is 1.0-3.5%. PVA undergoes a complexation reaction with boric acid, allowing the PVA molecules to be further effectively stretched.

[0028] Furthermore, in the step of "setting up a second iodine dyeing and stretching tank, and dyeing and stretching the first intermediate product a second time in the second iodine dyeing and stretching tank to obtain a second intermediate product", the temperature of the second dyeing is 40-60℃. By increasing the temperature, the chain mobility is improved, thereby improving the stretchability of PVA.

[0029] Furthermore, in the step of "setting up a second iodine dyeing and stretching tank, and dyeing and stretching the first intermediate product a second time in the second iodine dyeing and stretching tank to obtain a second intermediate product", the total stretching ratio of the second intermediate product relative to the PVA material is 3.5-5. At this low stretching ratio of 3.5-5, high PVA orientation can be achieved, ensuring complete complexation. Under the action of boric acid, polyiodide ions are further generated, ultimately yielding a thin, anti-warping polarizer.

[0030] To address the aforementioned problems, this invention also proposes a polarizer prepared by the above-described method. The prepared polarizer exhibits low stretching during the manufacturing process, thus reducing the likelihood of warping even in harsh environments.

[0031] To address the aforementioned problems, this invention also proposes a display device comprising the aforementioned polarizer. The polarizer serves to block external natural light and, due to its good anti-warping properties, prevents display defects such as light leakage from occurring in the display device.

[0032] Example 1:

[0033] Preparation of the first intermediate product: A 20 μm PVA film was immersed in a first dyeing water bath at 30 °C and dyed for 5 minutes. The concentration of elemental iodine in the dyeing water bath was 0.5% and the concentration of potassium iodide was 2%. Then the PVA film was stretched to a stretch ratio of 2.0 to obtain the first intermediate product.

[0034] Preparation of the second intermediate product: The PVA film dyed in the first step was immersed in a second dyeing and crosslinking water bath at 40°C for 2.5 minutes. The dyeing and crosslinking water bath contained 3% boric acid, 0.2% iodine and 0.8% potassium iodide. The film was then stretched to a total stretch ratio of 4.5 times to obtain the second intermediate product.

[0035] Preparation of polarizer: After drying the second intermediate product in an air-floating oven at 80°C for 5 minutes, PVA adhesive is applied to both sides of the second intermediate product and TAC film is attached. The product is then dried in an air-floating oven at 80°C for another 5 minutes to obtain the polarizer.

[0036] Example 2:

[0037] Preparation of the first intermediate product: A 20 μm PVA film was immersed in a first dyeing water bath at 30 °C and dyed for 5 minutes. The concentration of elemental iodine in the dyeing water bath was 0.5% and the concentration of potassium iodide was 2%. Then the PVA film was stretched to a stretch ratio of 2.2 times to obtain the first intermediate product.

[0038] Preparation of the second intermediate product: The PVA film dyed in the first step was immersed in a second dyeing and crosslinking water bath at 40°C for 2.5 minutes. The dyeing and crosslinking water bath contained 3% boric acid, 0.2% iodine and 0.8% potassium iodide. The film was then stretched to a total stretch ratio of 4.5 times to obtain the second intermediate product.

[0039] Preparation of polarizer: After drying the second intermediate product in an air-floating oven at 80°C for 5 minutes, PVA adhesive is applied to both sides of the second intermediate product and TAC film is attached. The product is then dried in an air-floating oven at 80°C for another 5 minutes to obtain the polarizer.

[0040] Example 3:

[0041] Preparation of the first intermediate product: A 20 μm PVA film was immersed in a first dyeing water bath at 30 °C and dyed for 5 minutes. The concentration of elemental iodine in the dyeing water bath was 0.5% and the concentration of potassium iodide was 2%. Then the PVA film was stretched to a stretch ratio of 2.0 to obtain the first intermediate product.

[0042] Preparation of the second intermediate product: The PVA film dyed in the first step was immersed in a second dyeing and crosslinking water bath at 40°C for 2.5 minutes. The dyeing and crosslinking water bath contained 2.5% boric acid, 0.2% iodine and 0.8% potassium iodide. The film was then stretched to a total stretch ratio of 4.5 times to obtain the second intermediate product.

[0043] Preparation of polarizer: After drying the second intermediate product in an air-floating oven at 80°C for 5 minutes, PVA adhesive is applied to both sides of the second intermediate product and TAC film is attached. The product is then dried in an air-floating oven at 80°C for another 5 minutes to obtain the polarizer.

[0044] Example 4:

[0045] Preparation of the first intermediate product: A 20 μm PVA film was immersed in a first dyeing water bath at 30 °C and dyed for 5 minutes. The concentration of elemental iodine in the dyeing water bath was 0.5% and the concentration of potassium iodide was 2%. Then the PVA film was stretched to a stretch ratio of 2.0 to obtain the first intermediate product.

[0046] Preparation of the second intermediate product: The PVA film dyed in the first step was immersed in a second dyeing and crosslinking water bath at 50°C for 2.5 minutes. The dyeing and crosslinking water bath contained 3% boric acid, 0.2% iodine and 0.8% potassium iodide. The film was then stretched to a total stretch ratio of 4.5 times to obtain the second intermediate product.

[0047] Preparation of polarizer: After drying the second intermediate product in an air-floating oven at 80°C for 5 minutes, PVA adhesive is applied to both sides of the second intermediate product and TAC film is attached. The product is then dried in an air-floating oven at 80°C for another 5 minutes to obtain the polarizer.

[0048] Example 5:

[0049] Preparation of the first intermediate product: A 20 μm PVA film was immersed in a first dyeing water bath at 30 °C and dyed for 5 minutes. The concentration of elemental iodine in the dyeing water bath was 0.5% and the concentration of potassium iodide was 2%. Then the PVA film was stretched to a stretch ratio of 2.0 to obtain the first intermediate product.

[0050] Preparation of the second intermediate product: The PVA film dyed in the first step was immersed in a second dyeing and crosslinking water bath at 40°C for 2.5 minutes. The dyeing and crosslinking water bath contained 3% boric acid, 0.2% iodine and 0.8% potassium iodide. The film was then stretched to a total stretch ratio of 3.8 times to obtain the second intermediate product.

[0051] Preparation of polarizer: After drying the second intermediate product in an air-floating oven at 80°C for 5 minutes, PVA adhesive is applied to both sides of the second intermediate product and TAC film is attached. The product is then dried in an air-floating oven at 80°C for another 5 minutes to obtain the polarizer.

[0052] Example 6:

[0053] Preparation of the first intermediate product: A 20 μm PVA film was immersed in a first dyeing water bath at 30 °C and dyed for 5 minutes. The concentration of elemental iodine in the dyeing water bath was 0.5% and the concentration of potassium iodide was 2%. Then the PVA film was stretched to a stretch ratio of 1.6 times to obtain the first intermediate product.

[0054] Preparation of the second intermediate product: The PVA film dyed in the first step was immersed in a second dyeing and crosslinking water bath at 40°C for 2.5 minutes. The dyeing and crosslinking water bath contained 3% boric acid, 0.2% iodine and 0.8% potassium iodide. The film was then stretched to a total stretch ratio of 4.5 times to obtain the second intermediate product.

[0055] Preparation of polarizer: After drying the second intermediate product in an air-floating oven at 80°C for 5 minutes, PVA adhesive is applied to both sides of the second intermediate product and TAC film is attached. The product is then dried in an air-floating oven at 80°C for another 5 minutes to obtain the polarizer.

[0056] Example 7:

[0057] Preparation of the first intermediate product: A 20 μm PVA film was immersed in a first dyeing water bath at 30 °C for 5 minutes and dyed. The concentration of elemental iodine in the dyeing water bath was 0.5% and the concentration of potassium iodide was 2%. Then the PVA film was stretched to a stretch ratio of 2.5 times to obtain the first intermediate product.

[0058] Preparation of the second intermediate product: The PVA film dyed in the first step was immersed in a second dyeing and crosslinking water bath at 40°C for 2.5 minutes. The dyeing and crosslinking water bath contained 3% boric acid, 0.2% iodine and 0.8% potassium iodide. The film was then stretched to a total stretch ratio of 4.5 times to obtain the second intermediate product.

[0059] Preparation of polarizer: After drying the second intermediate product in an air-floating oven at 75°C for 5 minutes, PVA adhesive is applied to both sides of the second intermediate product and TAC film is attached. The product is then dried in an air-floating oven at 75°C for another 5 minutes to obtain the polarizer.

[0060] Example 8:

[0061] Preparation of the first intermediate product: A 20 μm PVA film was immersed in a first dyeing water bath at 30 °C and dyed for 5 minutes. The concentration of elemental iodine in the dyeing water bath was 0.5% and the concentration of potassium iodide was 2%. Then the PVA film was stretched to a stretch ratio of 2.0 to obtain the first intermediate product.

[0062] Preparation of the second intermediate product: The PVA film dyed in the first step was immersed in a second dyeing and crosslinking water bath at 40°C for 2.5 minutes. The dyeing and crosslinking water bath contained 1% boric acid, 0.2% iodine and 0.8% potassium iodide. The film was then stretched to a total stretch ratio of 4.5 times to obtain the second intermediate product.

[0063] Preparation of polarizer: After drying the second intermediate product in an air-floating oven at 80°C for 5 minutes, PVA adhesive is applied to both sides of the second intermediate product and TAC film is attached. The product is then dried in an air-floating oven at 80°C for another 5 minutes to obtain the polarizer.

[0064] Example 9:

[0065] Preparation of the first intermediate product: A 20 μm PVA film was immersed in a first dyeing water bath at 30 °C and dyed for 5 minutes. The concentration of elemental iodine in the dyeing water bath was 0.5% and the concentration of potassium iodide was 2%. Then the PVA film was stretched to a stretch ratio of 2.0 to obtain the first intermediate product.

[0066] Preparation of the second intermediate product: The PVA film dyed in the first step was immersed in a second dyeing and crosslinking water bath at 40°C for 2.5 minutes. The dyeing and crosslinking water bath contained 3.5% boric acid, 0.2% iodine and 0.8% potassium iodide. The film was then stretched to a total stretch ratio of 4.5 times to obtain the second intermediate product.

[0067] Preparation of polarizer: After drying the second intermediate product in an air-floating oven at 85°C for 5 minutes, PVA adhesive is applied to both sides of the second intermediate product and TAC film is attached. The product is then dried in an air-floating oven at 85°C for another 5 minutes to obtain the polarizer.

[0068] Example 10:

[0069] Preparation of the first intermediate product: A 20 μm PVA film was immersed in a first dyeing water bath at 30 °C and dyed for 5 minutes. The concentration of elemental iodine in the dyeing water bath was 0.5% and the concentration of potassium iodide was 2%. Then the PVA film was stretched to a stretch ratio of 2.0 to obtain the first intermediate product.

[0070] Preparation of the second intermediate product: The PVA film dyed in the first step was immersed in a second dyeing and crosslinking water bath at 60°C for 2.5 minutes. The dyeing and crosslinking water bath contained 1% boric acid, 0.2% iodine and 0.8% potassium iodide. The film was then stretched to a total stretch ratio of 4.5 times to obtain the second intermediate product.

[0071] Preparation of polarizer: After drying the second intermediate product in an air-floating oven at 80°C for 5 minutes, PVA adhesive is applied to both sides of the second intermediate product and TAC film is attached. The product is then dried in an air-floating oven at 80°C for another 5 minutes to obtain the polarizer.

[0072] Example 11:

[0073] Preparation of the first intermediate product: A 20 μm PVA film was immersed in a first dyeing water bath at 30 °C and dyed for 5 minutes. The concentration of elemental iodine in the dyeing water bath was 0.5% and the concentration of potassium iodide was 2%. Then the PVA film was stretched to a stretch ratio of 2.0 to obtain the first intermediate product.

[0074] Preparation of the second intermediate product: The PVA film dyed in the first step was immersed in a second dyeing and crosslinking water bath at 40°C for 2.5 minutes. The dyeing and crosslinking water bath contained 1% boric acid, 0.2% iodine and 0.8% potassium iodide. The film was then stretched to a total stretch ratio of 3.5 times to obtain the second intermediate product.

[0075] Preparation of polarizer: After drying the second intermediate product in an air-floating oven at 80°C for 5 minutes, PVA adhesive is applied to both sides of the second intermediate product and TAC film is attached. The product is then dried in an air-floating oven at 80°C for another 5 minutes to obtain the polarizer.

[0076] Example 12:

[0077] Preparation of the first intermediate product: A 20 μm PVA film was immersed in a first dyeing water bath at 30 °C and dyed for 5 minutes. The concentration of elemental iodine in the dyeing water bath was 0.5% and the concentration of potassium iodide was 2%. Then the PVA film was stretched to a stretch ratio of 2.0 to obtain the first intermediate product.

[0078] Preparation of the second intermediate product: The PVA film dyed in the first step was immersed in a second dyeing and crosslinking water bath at 40°C for 2.5 minutes. The dyeing and crosslinking water bath contained 1% boric acid, 0.2% iodine and 0.8% potassium iodide. The film was then stretched to a total stretch ratio of 5 times to obtain the second intermediate product.

[0079] Preparation of polarizer: After drying the second intermediate product in an air-floating oven at 80°C for 5 minutes, PVA adhesive is applied to both sides of the second intermediate product and TAC film is attached. The product is then dried in an air-floating oven at 80°C for another 5 minutes to obtain the polarizer.

[0080] Comparative Example 1:

[0081] Preparation of the first intermediate product: A 20 μm PVA film was immersed in a first dyeing water bath at 30 °C and dyed for 5 minutes. The concentration of elemental iodine in the dyeing water bath was 0.5% and the concentration of potassium iodide was 2%. Then the PVA film was stretched to a stretch ratio of 2.8 times to obtain the first intermediate product.

[0082] Preparation of the second intermediate product: The PVA film dyed in the first step was immersed in a second dyeing and crosslinking water bath at 40°C for 2.5 minutes. The dyeing and crosslinking water bath contained 3% boric acid, 0.2% iodine and 0.8% potassium iodide. The film was then stretched to a total stretch ratio of 4.5 times to obtain the second intermediate product.

[0083] Preparation of polarizer: After drying the second intermediate product in an air-floating oven at 80°C for 5 minutes, PVA adhesive is applied to both sides of the second intermediate product and TAC film is attached. The product is then dried in an air-floating oven at 80°C for another 5 minutes to obtain the polarizer.

[0084] Comparative Example 2:

[0085] Preparation of the first intermediate product: A 20 μm PVA film was immersed in a first dyeing water bath at 30 °C and dyed for 5 minutes. The concentration of elemental iodine in the dyeing water bath was 0.5% and the concentration of potassium iodide was 2%. Then the PVA film was stretched to a stretch ratio of 2.0 to obtain the first intermediate product.

[0086] Preparation of the second intermediate product: The PVA film dyed in the first step was immersed in a second dyeing and crosslinking water bath at 40°C for 2.5 minutes. The dyeing and crosslinking water bath contained 0.5% boric acid, 0.2% iodine and 0.8% potassium iodide. The film was then stretched to a total stretch ratio of 4.5 times to obtain the second intermediate product.

[0087] Preparation of polarizer: After drying the second intermediate product in an air-floating oven at 80°C for 5 minutes, PVA adhesive is applied to both sides of the second intermediate product and TAC film is attached. The product is then dried in an air-floating oven at 80°C for another 5 minutes to obtain the polarizer.

[0088] Comparative Example 3:

[0089] Preparation of the first intermediate product: A 20 μm PVA film was immersed in a first dyeing water bath at 30 °C and dyed for 5 minutes. The concentration of elemental iodine in the dyeing water bath was 0.5% and the concentration of potassium iodide was 2%. Then the PVA film was stretched to a stretch ratio of 2.0 to obtain the first intermediate product.

[0090] Preparation of the second intermediate product: The PVA film dyed in the first step was immersed in a second dyeing and crosslinking water bath at 30°C for 2.5 minutes. The dyeing and crosslinking water bath contained 3% boric acid, 0.2% iodine and 0.8% potassium iodide. The film was then stretched to a total stretch ratio of 4.5 times to obtain the second intermediate product.

[0091] Preparation of polarizer: After drying the second intermediate product in an air-floating oven at 80°C for 5 minutes, PVA adhesive is applied to both sides of the second intermediate product and TAC film is attached. The product is then dried in an air-floating oven at 80°C for another 5 minutes to obtain the polarizer.

[0092] Comparative Example 4:

[0093] Preparation of the first intermediate product: A 20 μm PVA film was immersed in a first dyeing water bath at 30 °C and dyed for 5 minutes. The concentration of elemental iodine in the dyeing water bath was 0.5% and the concentration of potassium iodide was 2%. Then the PVA film was stretched to a stretch ratio of 2.0 to obtain the first intermediate product.

[0094] Preparation of the second intermediate product: The PVA film dyed in the first step was immersed in a second dyeing and crosslinking water bath at 40°C for 2.5 minutes. The dyeing and crosslinking water bath contained 3% boric acid, 0.2% elemental iodine and 0.8% potassium iodide. The film was then stretched to a total stretch ratio of 5.5 times to obtain the second intermediate product.

[0095] Preparation of polarizer: After drying the second intermediate product in an air-floating oven at 80°C for 5 minutes, PVA adhesive is applied to both sides of the second intermediate product and TAC film is attached. The product is then dried in an air-floating oven at 80°C for another 5 minutes to obtain the polarizer.

[0096] Furthermore, optical performance tests were conducted on Examples 1-5 and Comparative Examples 1-4, according to the national standard GB_T 25275-2010, specifically testing the transmittance and polarization degree. Simultaneously, the warp resistance of Examples 1-5 and Comparative Examples 1-4 under harsh conditions was tested. The specific procedures were as follows: 1) The polarizers to be tested were placed in a damp heat aging chamber for aging at 80°C and 80% RH for 500 hours; 2) Warp testing was performed. The warp detection method involved cutting out a 15mm diameter circular square film, fixing it to a 1.6×38mm needle tip, and placing it in an environment of 23°C and 50% RH for equilibration for 5 hours, then measuring the warp angle of the circle.

[0097] The final results were assessed as follows: a warp change of less than 90° indicates excellent warp resistance; a warp change of less than 120° indicates average warp resistance; and a warp change of more than 120° indicates poor warp resistance. These were denoted as: √ for good warp resistance, O for average warp resistance, and X for no warp resistance.

[0098] The test results are summarized in Table 1.

[0099] Table 1. Optical performance test experiments of Examples 1-5 and Comparative Examples 1-4

[0100] Transmission rate polarization degree warpage Example 1 43.2％ 99.95％ √ Example 2 43.0％ 99.91％ √ Example 3 43.4％ 99.90％ √ Example 4 43.2％ 99.95％ √ Example 5 43.1％ 99.90％ O Comparative Example 1 42.2％ 99.40％ O Comparative Example 2 42.0％ 99.33％ O Comparative Example 3 42.1％ 99.20％ O Comparative Example 4 43.5％ 99.99％ X

[0101] Through the above experiments, it can be clearly seen that the polarizer preparation method provided by the present invention in Examples 1-4 involves setting up two iodine dyeing and stretching tanks, performing two dyeing processes and two stretching processes. Boric acid is not added during the first dyeing to avoid competition with iodine for complexation, resulting in a stretching ratio of 1.6-2.5 times, allowing the PVA film to initially form a complex with iodine. The second stretching achieves a total stretching ratio of 3.5-5 times, further orienting the PVA molecules and forming a cross-linked structure with boric acid, which is beneficial for inducing the formation and orientation of polyiodide ions. This preparation method stretches the PVA material at a relatively small stretching ratio, preventing the prepared polarizer from warping under harsh environments (such as high temperature and high humidity), while simultaneously ensuring the thin profile and excellent optical performance of the polarizer. However, the warping resistance of Examples 5 and Comparative Examples 1-3 decreased after changing the stretching ratio, iodine concentration, boric acid concentration, and dyeing water bath temperature. The polarizer in Comparative Example 4 exhibited poor warping resistance at a high stretching ratio.

[0102] The above are merely preferred embodiments of the present invention and do not limit the patent scope of the present invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the patent protection scope of the present invention.

Claims

1. A method for producing a polarizing plate, characterized by, The method comprises the following steps: a first iodine dyeing and stretching tank is arranged, in which the PVA material is dyed and stretched for the first time to obtain a first intermediate product, and the stretching ratio after the first time is 1.6-2.5; the first iodine dyeing and stretching tank contains elemental iodine and potassium iodide; a second iodine dyeing and stretching tank is arranged, in which the first intermediate product is dyed and stretched for the second time to obtain a second intermediate product; the temperature of the second time of dyeing is 40-60℃; the total stretching ratio of the second intermediate product relative to the PVA material is 3.5-5; the second iodine dyeing and stretching tank contains elemental iodine and potassium iodide; the second intermediate product is dried, coated with an adhesive, and laminated with a TAC film to obtain a polarizing plate; wherein the solution used for the first time of dyeing does not contain boric acid, the solution used for the second time of dyeing contains boric acid, and the concentration of the boric acid is 1.0%-3.5%.

2. A polarizing sheet characterized by comprising: The polarizing plate is prepared by the preparation method of claim 1.

3. A display device, characterized by comprising: The polarizing plate comprises the polarizing plate of claim 2.