High-temperature-resistant red-emitting polarizer and preparation method thereof

Abstract

The application provides a high-temperature-resistant red-free polarizing plate and a preparation method thereof. The preparation method comprises the following steps: first, swelling a polyvinyl alcohol film; then, dyeing the swollen polyvinyl alcohol film in a mixed solution of iodine solution and boric acid; then, cross-linking the polyvinyl alcohol film in a boric acid solution; then, stretching the cross-linked polyvinyl alcohol film in a mixed solution of potassium iodide and boric acid, and then, supplementing color of the stretched polyvinyl alcohol film in an aqueous solution of potassium iodide and boric acid; then, drying the polyvinyl alcohol film after the color supplementing; then, adhering inner protective films to upper and lower layers of the dried polyvinyl alcohol film through UV glue; and finally, drying the polyvinyl alcohol film, thereby preparing the high-temperature-resistant red-free polarizing plate. The prepared polarizing plate has an absorbance at 700 nm (A700) higher than 1.7, and satisfies a high-temperature five-hundred-hour durability test. The polarizing plate does not emit red light and has better weather resistance. Moreover, the preparation method is simple, does not need to add new processes or new substances, and has low cost.

Description

Technical Field

[0001] This invention belongs to the field of polarizer technology, and particularly relates to a high-temperature resistant red polarizer and its preparation method. Background Technology

[0002] A polarizer, also known as a light polarizer, is a key material in liquid crystal displays (LCDs). Attached to the LCD panel, it controls the passage and blocking of light, acting as a switch. Currently, LCD technology is mature, and its applications have expanded from indoor displays such as televisions, PC monitors, and laptops to outdoor mobile displays such as smartphones and tablets. In recent years, applications in automotive displays, smart wearables, and electronic tags have been gradually gaining traction, leading to increasing market demand and higher requirements for the heat resistance of polarizers used in LCDs. Therefore, polarizers need to possess excellent high-temperature resistance.

[0003] Polarizing films are typically manufactured by dyeing a polyvinyl alcohol (PVA) film with a dichroic substance, then uniaxially stretching and aligning it, and finally attaching two layers of optical protective films to the top and bottom to form a laminated structure. The performance of polarizing films mainly includes optical properties, basic physical properties, and durability. Optical properties primarily refer to the polarizer's monomer transmittance, degree of polarization, hue a value, and hue b value; basic physical properties mainly refer to the polarizer's peel strength, hardness, and abrasion resistance; durability, also known as reliability, includes resistance to damp heat, high temperatures, thermal shock, and low temperatures.

[0004] High-temperature reddening resistance mainly refers to the ability to withstand high-temperature environments. High temperatures affect the stability and lifespan of polarizers. Existing polarizers are prone to light leakage in the red band and exhibit a reddening phenomenon when exposed to 80°C for extended periods. Therefore, polarizers used in harsh outdoor or high-temperature environments should possess a certain degree of high-temperature resistance. Current industry research on the durability of polarizers mainly focuses on UV resistance and high-temperature resistance, but there are no reports on iodine-based polarizers with high-temperature reddening resistance. Summary of the Invention

[0005] To address the above technical problems, this invention discloses a high-temperature resistant red-emitting polarizing film and its preparation method, aiming to achieve the property of the polarizing film resisting heat and not turning red under high-temperature environments. Here, high temperature refers to above 80℃.

[0006] The technical solution adopted by this invention is as follows:

[0007] A method for preparing a high-temperature resistant red polarizing film includes the following steps:

[0008] Step S1: Swell the polyvinyl alcohol film at a swelling temperature of 20-35°C, a stretching ratio of 1.0-2.5 times, and a time of 50-150 seconds.

[0009] Step S2: Immerse the swollen polyvinyl alcohol film in a solution of iodine and a mixture of iodine for dyeing. The dyeing temperature is 25-35℃, the stretching ratio is 1.2-1.8 times, and the time is 100-400 seconds.

[0010] Step S3: Immerse the polyvinyl alcohol film in a boric acid solution to perform crosslinking on the dyed polyvinyl alcohol film. The crosslinking temperature is 30-50°C. In the boric acid solution, the mass percentage of boric acid is 2-6%, the stretching ratio is 1.2-1.8 times, and the time is 50-100 seconds.

[0011] Step S4: Immerse the polyvinyl alcohol film in a mixed solution of potassium iodide and boric acid, and stretch the cross-linked polyvinyl alcohol film at a stretching temperature of 50-60°C; wherein the potassium iodide and boric acid mixed solution has a mass percentage content of 3-4% and a mass percentage content of 3-6%, and a stretching ratio of 1.0-2.0 times.

[0012] Step S5: The stretched polyvinyl alcohol film is immersed in a mixed solution of potassium iodide and boric acid for color correction; the mass percentage of potassium iodide in the mixed solution of potassium iodide and boric acid is 3-3.5%, the color correction temperature is 10-40℃, and the stretching ratio is 1.0-1.8 times.

[0013] Step S6: Pre-dry the polyvinyl alcohol film after color correction in a drying oven;

[0014] Step S7: Use UV adhesive to bond the upper and lower layers of the PVA film with the inner protective film after color matching.

[0015] Step S8, drying, the drying temperature is 40~100℃, and the residence time is controlled to be 150-500 seconds.

[0016] Using this technical solution, the resulting polarizer exhibits minimal changes in transmittance, polarization degree, and hue under high-temperature conditions of 80℃×500hr, and does not turn red. Its high-temperature stability and weather resistance are significantly improved.

[0017] As a further improvement of the present invention, in the above steps, the total stretching ratio is 4.5 to 6.2 times. Further, the total stretching ratio is 5.0 to 6.0 times, implementing a segmented stretching ratio control method.

[0018] As a further improvement of the present invention, in step S1, the swelling temperature is 23-28°C. Furthermore, in step S1, the stretching ratio is 1.5-2.0 times.

[0019] As a further improvement of the present invention, in step S2, the dyeing temperature is 28–33°C. Furthermore, in step S2, the stretching ratio is 1.3–1.5 times.

[0020] As a further improvement of the present invention, in step S1, the iodine and the iodine mixture solution contains boric acid, and the mass percentage of the boric acid is no more than 2%. Further, the mass percentage of the boric acid is 0.5% to 1.0%.

[0021] As a further improvement of the present invention, in step S3, the bridging temperature is 35-45°C. Furthermore, in step S3, the boric acid in the boric acid solution has a mass percentage of 3-5%.

[0022] As a further improvement of the present invention, in step S3, the stretching ratio is 1.3 to 1.5 times.

[0023] As a further improvement of the present invention, in step S4, the cross-linked polyvinyl alcohol film is stretched at a stretching temperature of 55-60°C.

[0024] As a further improvement of the present invention, in step S4, the potassium iodide and boric acid mixed solution contains 3.5-4% by mass of potassium iodide and 4-5% by mass of boric acid.

[0025] As a further improvement of the present invention, in step S4, the stretching ratio is 1.3 to 1.8 times, and a gradient ratio distribution method is adopted.

[0026] As a further improvement of the present invention, in step S5, the temperature of the complementary color is 20-30℃.

[0027] As a further improvement of the present invention, in step S5, the stretching ratio is 1.0 to 1.5 times.

[0028] As a further improvement of the present invention, in step S6, the pre-drying temperature is 40-100°C, the residence time is 200-600 seconds, and circulating air is used for assisted drying. Further, the pre-drying temperature is 50-55°C.

[0029] As a further improvement of the present invention, in step S8, the drying temperature is 70-90℃, the residence time is controlled to be 200-400 seconds, and circulating air is used for assisted drying. Further, the drying temperature is 70-85℃.

[0030] The present invention also discloses a high-temperature resistant red polarizing film, which is prepared by the preparation method of the high-temperature resistant red polarizing film described in any one of the above claims.

[0031] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0032] By employing the technical solution of this invention, and through the selection of appropriate steps and process parameters, a polyvinyl alcohol (PVA) film is first swollen; the swollen PVA film is then immersed in a mixed solution of iodine and boric acid for dyeing; the dyed PVA film is then immersed in a boric acid solution for crosslinking; the crosslinked PVA film is then immersed in a mixed solution of potassium iodide and boric acid for stretching; the stretched PVA film is then immersed in an aqueous solution of potassium iodide and boric acid for color correction; the color-corrected PVA film is then dried; and the upper and lower layers of the dried PVA film are then bonded together with a UV adhesive to form a three-layer structure. This three-layer structure is then dried in a drying oven to produce a high-temperature resistant, non-red-emitting polarizer. Its absorbance (A700) at 700nm in the red light band is higher than 1.7, and it meets the 500-hour high-temperature durability test requirements. The polarizer does not turn red and exhibits better weather resistance. Moreover, this preparation method is simple, requires no additional steps or new substances, and is low in cost. Detailed Implementation

[0033] The preferred embodiments of the present invention will be described in further detail below.

[0034] A method for preparing a high-temperature resistant red-emitting polarizing film includes processes such as swelling, dyeing, cross-linking, stretching, color correction, pre-drying, inner protective film lamination, and drying to obtain the polarizing film. The most critical aspects are the control of swelling temperature and magnification, dyeing temperature, cross-linking potassium iodide concentration, stretching potassium iodide concentration, temperature, and magnification, and the control of color correction potassium iodide concentration and polarizing film drying temperature. Polarizing films prepared using this method have an absorbance (A700) value higher than 1.7 at 700nm in the red light band, and do not emit a red color after a 500-hour high-temperature durability test. Specifically, the method includes the following steps:

[0035] Swelling involves immersing a polyvinyl alcohol film (hereinafter referred to as PVA film) in an aqueous solution, preferably pure water, at a swelling temperature of 20–35°C, preferably 23–28°C, with a swelling ratio controlled at 1.0–2.5 times, preferably 1.5–2.0 times, for 50–150 seconds. This step mainly washes out the plasticizer from the PVA film, allowing the PVA film to swell and absorb water, thus eliminating the PVA crystalline areas and preparing for subsequent dyeing of the PVA film.

[0036] The swollen PVA film is immersed in a solution of iodine and a mixture of iodine to dye the film. The dyeing temperature is 25-35℃, preferably 28-33℃; the magnification ratio is controlled at 1.2-1.8, preferably 1.3-1.5; in this step, boric acid solution is added appropriately to improve the color fixing effect, and the boric acid mass percentage is controlled at 0-2%, preferably 0.5-1.0%; the time is controlled at 100-400 seconds.

[0037] Crosslinking is performed by immersing a polyvinyl alcohol (PVA) film in a boric acid solution to crosslink the dyed PVA film, thereby improving the color fixation effect. The temperature of this process is controlled at 30-50°C, preferably 35-45°C; the percentage content of boric acid is controlled at 2-6%, preferably 3-5%; the magnification ratio is controlled at 1.2-1.8 times, preferably 1.3-1.5; and the time is controlled at 50-100 seconds.

[0038] The stretching process involves immersing a polyvinyl alcohol (PVA) film in a mixed solution of potassium iodide and boric acid. The cross-linked PVA film is then stretched, causing iodine molecules to orient along the stretching direction. The potassium iodide solution alters the chemical balance of iodide ions within the PVA film, generating triiodide and pentaiodide ions. Stretching facilitates the flow of PVA molecular chains, creating numerous hollow tunnels that cause iodide ions to align in a single direction, resulting in a highly efficient polarization effect. The temperature in this process is controlled at 50–60°C, preferably 55–60°C; the percentage content of potassium iodide is controlled at 3–6%, preferably 3–4%; the percentage content of boric acid is controlled at 3–6%, preferably 4–5%; and the stretching ratio is controlled at 1.0–2.0 times, preferably 1.3–1.8, with a gradient ratio distribution method implemented.

[0039] For color correction, the stretched polyvinyl alcohol (PVA) film is immersed in a mixed solution of potassium iodide and boric acid. Potassium iodide alters the chemical equilibrium of polyiodide ions in the PVA, generating iodide ions. In this process, the percentage of potassium iodide is controlled at 2–6%, preferably 3–3.5%, the temperature is controlled at 10–40°C, preferably 20–30°C, and the magnification ratio is controlled at 1.0–1.8 times, preferably 1.0–1.5.

[0040] Pre-drying involves drying the polyvinyl alcohol (PVA) film after color correction in a drying oven at a temperature of 40–100°C and a dwell time of 200–600 seconds, while simultaneously using circulating air for assisted drying.

[0041] The bonding process involves using UV adhesive and polyvinyl alcohol adhesive to bond the upper and lower layers of the color-corrected polyvinyl alcohol film (PVA film) together with an inner protective film, forming a three-layer structure.

[0042] Drying: The polyvinyl alcohol film with the inner protective film is dried in a drying oven at a temperature of 40-100℃, preferably 70-90℃; the residence time is controlled at 150-500 seconds, preferably 200-400 seconds, while circulating air is used for auxiliary drying.

[0043] The overall magnification of the polarizer is controlled between 4.5 and 6.2 times, preferably between 5.0 and 6.0 times, and a segmented magnification control method is implemented.

[0044] The following detailed description is provided in conjunction with specific embodiments.

[0045] Example 1

[0046] A method for preparing a high-temperature resistant red polarizing film includes the following steps:

[0047] Swelling: The polyvinyl alcohol film (hereinafter referred to as PVA film) is immersed in a pure aqueous solution at a temperature of 23°C, with a magnification ratio of 1.80 times and a time of 100 to 130 seconds.

[0048] Staining: The swollen PVA film is immersed in iodine and a mixture of iodine and iodine for staining. The staining temperature is 30℃, the magnification ratio is controlled at 1.34, the boric acid mass percentage is controlled at 0.5%, and the time is controlled at 200-300 seconds.

[0049] Crosslinking: The dyed PVA film is immersed in a boric acid solution for crosslinking. The temperature is controlled at 40℃, the boric acid percentage content is controlled at 3%, the ratio is controlled at 1.38 times, and the time is controlled at 30-60 seconds.

[0050] Stretching: The cross-linked PVA film is immersed in a mixed solution of potassium iodide and boric acid and stretched. The temperature is controlled at 60℃, the percentage content of potassium iodide is controlled at 3.5-4.0%, the percentage content of boric acid is controlled at 4.5%, the stretching ratio is controlled at 1.75, and the total ratio is controlled at 5.8.

[0051] Color Complementation: The stretched PVA film is immersed in a mixed solution of potassium iodide and boric acid for color complementation, which generates iodide ions. In this process, the percentage content of potassium iodide is controlled at 3.0-3.5%, the temperature is controlled at 25℃, and the magnification ratio is controlled at 1.0.

[0052] Pre-drying: The PVA film after color correction is dried in a drying oven at a temperature of 50-55℃ and a dwell time of 300-400 seconds, while assisted drying with circulating air.

[0053] Bonding: By using UV adhesive, the upper and lower layers of the color-corrected PVA film are laminated with an inner protective film to form a three-layer structure.

[0054] Drying: The polyvinyl alcohol film with the inner protective film is dried in a drying oven at a temperature of 70-75℃ and a residence time of 300-400 seconds, while circulating air is used for auxiliary drying.

[0055] Example 2

[0056] A method for preparing a high-temperature resistant red polarizing film includes the following steps:

[0057] Swelling: The polyvinyl alcohol film (hereinafter referred to as PVA film) is immersed in a pure aqueous solution at a temperature of 23°C, with a magnification ratio of 1.8 times and a time of 100 to 130 seconds.

[0058] Staining: The swollen PVA film is immersed in iodine and a mixture of iodine and iodine for staining. The staining temperature is 30℃, the magnification ratio is controlled at 1.34, the boric acid mass percentage is controlled at 0.5%, and the time is controlled at 200-300 seconds.

[0059] Crosslinking: The dyed PVA film is immersed in a boric acid solution for crosslinking. The temperature is controlled at 40℃, the boric acid percentage is controlled at 2-3%, the magnification ratio is controlled at 1.38 times, and the time is controlled at 30-60 seconds.

[0060] Stretching: The cross-linked PVA film is immersed in a mixed solution of potassium iodide and boric acid and stretched. The temperature is controlled at 60℃, the percentage content of potassium iodide is controlled at 3.5-4.0%, the percentage content of boric acid is controlled at 4.5%, the stretching ratio is controlled at 1.75 times, and the total ratio is controlled at 5.8.

[0061] Color Complementation: The stretched PVA film is immersed in a mixed solution of potassium iodide and boric acid for color complementation, which generates iodide ions. In this process, the percentage content of potassium iodide is controlled at 3.0-3.5%, the temperature is controlled at 25℃, and the magnification ratio is controlled at 1.0.

[0062] Pre-drying: The PVA film after color correction is dried in a drying oven at a temperature of 50-55℃ and a dwell time of 300-400 seconds, while assisted drying with circulating air.

[0063] Bonding: By using UV adhesive, the upper and lower layers of the color-corrected PVA film are laminated with an inner protective film to form a three-layer structure.

[0064] Drying: The polyvinyl alcohol film with the inner protective film is dried in a drying oven at a temperature of 80-85℃ and a residence time of 300-400 seconds, while circulating air is used for auxiliary drying.

[0065] Comparative Example

[0066] This comparative example uses the following steps:

[0067] Swelling: The polyvinyl alcohol film (hereinafter referred to as PVA film) is immersed in a pure aqueous solution at a temperature of 23°C, with a magnification ratio of 1.8 times and a time of 100 to 130 seconds.

[0068] Staining: The swollen PVA film is immersed in iodine and a mixture of iodine and iodine for staining. The staining temperature is 30℃, the magnification ratio is controlled at 1.34, the boric acid mass percentage is controlled at 0.5%, and the time is controlled at 200-300 seconds.

[0069] Crosslinking: The dyed PVA film is immersed in a boric acid solution for crosslinking. The temperature is controlled at 40℃, the boric acid percentage content is controlled at 3%, the ratio is controlled at 1.38 times, and the time is controlled at 30-60 seconds.

[0070] Stretching: The cross-linked PVA film is immersed in a mixed solution of potassium iodide and boric acid and stretched. The temperature is controlled at 60℃, the percentage content of potassium iodide is controlled at 4.5-5.0%, the percentage content of boric acid is controlled at 4.5%, the stretching ratio is controlled at 1.75 times, and the total ratio is controlled at 5.8.

[0071] Color complementation: The stretched PVA film is immersed in a mixed solution of potassium iodide and boric acid for color complementation, which generates iodide ions. In this process, the percentage content of potassium iodide is controlled at 3.7-4.5%, the temperature is controlled at 25℃, and the magnification ratio is controlled at 1.0.

[0072] Pre-drying: The PVA film after color correction is dried in a drying oven at a temperature of 50-55℃ and a dwell time of 300-400 seconds, while assisted drying with circulating air.

[0073] Bonding: By using UV adhesive, the upper and lower layers of the color-corrected PVA film are laminated with an inner protective film to form a three-layer structure.

[0074] Drying: The polyvinyl alcohol film with the inner protective film is dried in a drying oven at a temperature of 70-75℃ and a residence time of 300-400 seconds, while circulating air is used for auxiliary drying.

[0075] The polarizers prepared in the examples and comparative examples were subjected to high-temperature testing, and the results are shown in Table 1 below.

[0076] Table 1

[0077] Experimental variables / high temperature test items Example 1 Example 2 Comparative Example Extended KI content / % 4 4 5 Corrected KI content / % 3.2 3.2 3.7 Main drying oven temperature / ℃ 73 85 73 105℃×0.5hr A700 value 1.8 2.0 1.5 Transmittance change at 80℃ for 500 hours 0.37 0.23 0.68 Polarization degree change at 80℃ for 500hr -0.024 -0.013 -0.043 Hue change at 80℃ for 500hr -0.34 -0.21 -0.66 Hue b change at 80℃ for 500 hours 1.2 0.9 1.7

[0078] Among them, 700nm is the representative wavelength of the red light band. The higher the absorbance of 700nm, i.e., the A700 value, the lower the transmittance of 700nm, which means that red light is not easily leaked. Macroscopically, it is not red. When A700>1.7, it is not red.

[0079] As shown in Table 1, the polarizers prepared in Examples 1 and 2 have A700 values ​​greater than 1.7. Compared with the comparative example, their transmittance, polarization degree, and hue change are smaller under long-term high-temperature conditions.

[0080] As described above, the polarizer prepared according to the present invention has better weather resistance than conventional polarizers, especially under high temperature conditions it is not prone to turning red, and can be used normally in harsh environments, especially high temperature environments.

[0081] The above description, in conjunction with specific preferred embodiments, provides a further detailed explanation of the present invention. It should not be construed that the specific implementation of the present invention is limited to these descriptions. For those skilled in the art, various simple deductions or substitutions can be made without departing from the concept of the present invention, and all such modifications and substitutions should be considered within the scope of protection of the present invention.

Claims

1. A method for preparing a high-temperature resistant red polarizing film, characterized in that: Includes the following steps: Step S1: Swell the polyvinyl alcohol film at a swelling temperature of 20-35°C, a stretching ratio of 1.0-2.5 times, and a time of 50-150 seconds. Step S2: Immerse the swollen polyvinyl alcohol film in a solution of iodine and a mixture of iodine for dyeing. The dyeing temperature is 25~35℃, the stretching ratio is 1.2~1.8 times, and the time is 100~400 seconds. Step S3: Immerse the polyvinyl alcohol film in a boric acid solution to perform crosslinking on the dyed polyvinyl alcohol film. The crosslinking temperature is 30~50℃. In the boric acid solution, the mass percentage of boric acid is 2~6%, the stretching ratio is 1.2~1.8 times, and the time is 50~100 seconds. Step S4: Immerse the polyvinyl alcohol film in a mixed solution of potassium iodide and boric acid, and stretch the cross-linked polyvinyl alcohol film at a stretching temperature of 50-60℃ to orient the iodine molecules along the stretching direction. The potassium iodide solution changes the chemical equilibrium of iodide ions in the PVA film, generating triiodide and pentaiodide ions. In the mixed solution of potassium iodide and boric acid, the mass percentage content of potassium iodide is 3.5-4.0%, the mass percentage content of boric acid is 4-5%, and the stretching ratio is 1.3-2.0 times. Step S5: The stretched polyvinyl alcohol film is immersed in a mixed solution of potassium iodide and boric acid for color correction; the mass percentage of potassium iodide in the mixed solution of potassium iodide and boric acid is 3~3.5%, the color correction temperature is 10~40℃, and the stretching ratio is 1.0~1.8 times. Step S6: Pre-dry the polyvinyl alcohol film after color correction in a drying oven; Step S7: Use UV adhesive to bond the upper and lower layers of the PVA film with the inner protective film after color matching. Step S8, drying, the drying temperature is 40~100℃, and the residence time is controlled to be 150-500 seconds; the high temperature refers to above 80℃.

2. The method for preparing the high-temperature resistant red polarizing film according to claim 1, characterized in that: In step S1, the swelling temperature is 23~28℃ and the stretching ratio is 1.5~2.0 times.

3. The method for preparing the high-temperature resistant red polarizing film according to claim 1, characterized in that: In step S2, the dyeing temperature is 28~33℃ and the stretching ratio is 1.3~1.5 times; the iodine and the iodine mixture solution contains boric acid, and the mass percentage of the boric acid is no more than 2%.

4. The method for preparing the high-temperature resistant red polarizing film according to claim 3, characterized in that: In step S2, the iodine and the iodine mixture solution contains boric acid, and the mass percentage of the boric acid is 0.5~1.0%.

5. The method for preparing the high-temperature resistant red polarizing film according to claim 1, characterized in that: In step S3, the bridging temperature is 35-45℃; the boric acid in the solution has a mass percentage of 3-5%; and the stretching ratio is 1.3-1.5 times.

6. The method for preparing the high-temperature resistant red polarizing film according to claim 1, characterized in that: In step S4, the cross-linked polyvinyl alcohol film is stretched at a stretching temperature of 55~60℃; the stretching ratio is 1.3~1.8 times, and a gradient ratio distribution method is adopted.

7. The method for preparing the high-temperature resistant red polarizing film according to claim 1, characterized in that: In step S5, the temperature of the complementary color is 20-30℃; the stretching ratio is 1.0 to 1.5 times.

8. The method for preparing the high-temperature resistant red polarizing film according to claim 1, characterized in that: In step S6, the pre-drying temperature is 40~100℃, the residence time is 200~600 seconds, and circulating air is used for assisted drying.

9. The method for preparing the high-temperature resistant red polarizing film according to claim 1, characterized in that: In step S8, the drying temperature is 70-90℃, the residence time is controlled to be 200-400 seconds, and circulating air is used for auxiliary drying.

10. A high-temperature resistant red polarizing film, characterized in that: It is prepared using the method for preparing high-temperature resistant red polarizing film as described in any one of claims 1 to 9.