A method for manufacturing a polarizing film for improving the hygrothermal stability of an iodine-based polarizing plate and a polarizing plate

Abstract

The application discloses a polarizing film manufacturing method for improving the damp-heat stability of an iodine polarizing film and a polarizing film, and the method comprises the following steps: taking gaseous phase nano-silicon dioxide as a base body, reacting with N-trimethoxy silicon propyl-N, N, N-trimethyl ammonium chloride in an ethanol-water mixed solvent, and centrifugally washing and drying to obtain quaternary ammonium salt functionalized nano-silicon dioxide microspheres; after the microspheres are prepared into a colloidal dispersion liquid, iodine-potassium iodide dyeing solution is added to dye a conventional polymeric degree PVA original film; then, the functionalized microspheres are fixed in the amorphous region of the PVA base body through uniaxial wet stretching, boric acid solution crosslinking and hot air drying; the quaternary ammonium salt cationic groups anchor polyiodine anions through coulomb electrostatic attraction, and the space clamping of the PVA chain segment and the three-dimensional blocking of the boric acid crosslinking network cooperatively form a triple constraint structure, so that the diffusion and migration of iodine ions under the damp-heat condition are effectively inhibited, and the damp-heat stability of the polarizing film is significantly improved.

Description

Technical Field

[0001] This invention relates to a method for manufacturing a polarizing film and a polarizing film for improving the damp heat stability of iodine-based polarizing films, belonging to the field of polarizing film technology. Background Technology

[0002] Iodine-based polyvinyl alcohol (PVA) polarizers are currently the most widely used polarizing optical elements in the flat panel display industry. Their polarization function relies on the highly oriented molecular chain structure formed after the PVA film is uniaxially stretched, and the dichroic absorption of the polyiodide ion complexes adsorbed between the PVA chains.

[0003] In the manufacturing process of iodine-based polarizing films, the PVA substrate undergoes a series of steps including swelling, iodine-potassium iodide solution dyeing, uniaxial wet stretching, boric acid solution crosslinking fixation, and hot air drying to form the polarizing film. The stability of iodide ions in the PVA matrix mainly depends on two mechanisms: firstly, the physical confinement effect of the crystallinity and orientation of the PVA molecular chains on iodide ions; and secondly, the blocking effect of the boron ester bond crosslinking network formed between boric acid and PVA hydroxyl groups on the migration path of iodide ions. Both mechanisms can maintain the optical performance stability of the polarizing film under normal temperature and humidity conditions, but both exhibit significant defects under high temperature and high humidity conditions.

[0004] Under high temperature and high humidity conditions, the boron ester bond undergoes hydrolysis under the nucleophilic attack of water molecules, resulting in local relaxation of the cross-linked network. The free volume of the PVA amorphous region increases accordingly, the iodine ion diffusion channel is opened, and polyiodine anions migrate and flow to the film surface along the concentration gradient, causing the polarization degree and transmittance of the polarizing film to deteriorate. Summary of the Invention

[0005] The purpose of this invention is to overcome the shortcomings of the prior art. In the case of existing iodine-based PVA polarizing films, the boron ester bonds are hydrolyzed under high temperature and high humidity conditions, which leads to the relaxation of the cross-linking network, the increase of the free volume of the PVA amorphous region, and the migration and loss of polyiodide anions to the film surface along the concentration gradient, resulting in the deterioration of the polarization performance of the polarizing film.

[0006] To solve the above-mentioned technical problems, the present invention is implemented using the following technical solution: In one aspect, a method for manufacturing a polarizing film that improves the damp heat stability of iodine-based polarizers is provided, comprising the following steps: The silica matrix was added to a mixed solvent of ethanol and deionized water in a volume ratio of 9:1, and after ultrasonic dispersion, N-trimethoxysilylpropyl-N,N,N-trimethylammonium chloride was added dropwise under stirring conditions. The mixed solvent containing N-trimethoxysilylpropyl-N,N,N-trimethylammonium chloride was refluxed at 60-70°C for 4-6 hours. The product after reflux reaction was centrifuged to discard the supernatant, and the precipitate was washed with anhydrous ethanol and then dried under vacuum at 60°C for 12 h to obtain quaternary ammonium salt functionalized nano silica particles. The obtained quaternary ammonium salt functionalized nano silica particles were dispersed in deionized water with a conductivity of no more than 1.0 μS / cm, and then ultrasonically treated to obtain a colloidal dispersion with a solid content of 1.0–5.0 wt%, a Z-average particle size of no more than 30 nm, and a PDI of no more than 0.25. Add colloidal dispersion to iodine-potassium iodide staining solution, mix and set solution temperature to 25-35℃; and allow PVA film to pass through the staining tank at a linear velocity of 3-8 m / min for 60-180 s. The treated PVA film was subjected to uniaxial wet stretching in a 2-4 wt% boric acid aqueous solution, with a stretching ratio of 4.5-6.0 times and a stretching temperature of 40-55℃. The stretched PVA film was then immersed in a crosslinking solution with a boric acid concentration of 3-6 wt% and a potassium iodide concentration of 3-8 g / L. The crosslinking temperature was 50-65℃ and the crosslinking time was 120-300 s. The PVA film was then dried with hot air to obtain a PVA polarizing film.

[0007] The chemical formula of the N-trimethoxysilylpropyl-N,N,N-trimethylammonium chloride is: ; The mass ratio of N-trimethoxysilylpropyl-N,N,N-trimethylammonium chloride to nano-silica is set between 0.15:1 and 0.25:1.

[0008] The iodine-potassium iodide staining solution has an iodine concentration of 0.3–0.8 g / L, a potassium iodide concentration of 15–30 g / L, and a dry basis mass concentration of quaternary ammonium salt functionalized nano-silica microspheres of 0.01–0.08 g / L.

[0009] The silica matrix has a primary particle size of 7–15 nm, a specific surface area of ​​150–300 m² / g, a SiO₂ mass fraction of not less than 99.5%, and a surface silanol group density of 2.0–4.6 groups / nm².

[0010] The solid-liquid ratio of the silica matrix to the mixed solvent is 1:20; The ultrasonic dispersion power is 300W, the frequency is 40kHz, and the time is 30min; The dropping rate of the N-trimethoxysilylpropyl-N,N,N-trimethylammonium chloride was 1-2 mL / min; the stirring speed was 200-400 rpm.

[0011] The centrifugation speed after the reflux reaction was completed was 8000 rpm, and the centrifugation time was 15 min.

[0012] The precipitate was washed with anhydrous ethanol three times.

[0013] The degree of polymerization of the PVA original film is 1700-1800, and the degree of saponification is not less than 99.5 mol.

[0014] The dyeing tank is equipped with a circulation pump, and the circulation flow rate is 2 to 4 times the tank volume per hour.

[0015] In a second aspect, an iodine-based polarizing film is provided, which is prepared by the polarizing film manufacturing method for improving the damp heat stability of iodine-based polarizers as described in the first aspect.

[0016] Compared with the prior art, the beneficial effects achieved by the present invention are as follows: 1. This invention introduces quaternary ammonium salt functionalized nano-silica microspheres into the dyeing process, which adds coulombic electrostatic bonding constraints between quaternary ammonium salt cations and polyiodide anions in the PVA matrix. Through the mechanical clamping of PVA chain segments in the stretching process and the three-dimensional coating of boric acid crosslinking network in the crosslinking process, iodide ions are ultimately subject to triple synergistic constraints of electrostatic bonding force, steric hindrance effect of nano-microspheres, and blockade by boric acid crosslinking network, which effectively inhibits the diffusion and migration of iodide ions under humid and hot conditions.

[0017] 2. Under the premise of using conventional degree of polymerization PVA film, the present invention achieves wet heat stability comparable to or even better than high degree of polymerization PVA polarizing film, significantly reducing raw material costs, while eliminating the process risks of high interruption rate and decreased film uniformity in wet stretching of high degree of polymerization PVA. Attached Figure Description

[0018] Figure 1 The diagram shows a flowchart of a method for manufacturing a polarizing film to improve the damp heat stability of an iodine-based polarizer, as provided by the present invention. Detailed Implementation

[0019] The present invention will now be described in further detail with reference to specific embodiments and the accompanying drawings. Unless otherwise specified, the experimental methods described in this invention are all conventional methods; the materials used are all commercially available. Example 1:

[0020] like Figure 1 As shown in this embodiment, a method for manufacturing a polarizing film to improve the damp heat stability of an iodine-based polarizer is provided, specifically including: The nano-silica matrix uses industrial-grade fumed silica powder with a primary particle size of 7-15 nm, a specific surface area of ​​150-300 m² / g, and a purity of not less than 99.5%. The surface silanol group density of the fumed silica product is 2.0-4.6 groups / nm², which serve as anchoring points for subsequent silane coupling agent grafting reactions.

[0021] The silane coupling agent selected is N-trimethoxysilylpropyl-N,N,N-trimethylammonium chloride, with the chemical formula: The trimethoxy end of the silane coupling agent molecule can undergo hydrolysis and condensation reaction with the silanol groups on the surface of nano-silica to form Si-O-Si covalent bonds; the quaternary ammonium salt end carries a permanent positive charge in aqueous solution and is not affected by changes in solution pH.

[0022] The reaction solvent is a mixture of anhydrous ethanol and deionized water in a volume ratio of 9:1. Anhydrous ethanol is used as the main solvent to disperse nano-silica and dissolve the coupling agent, while deionized water provides the necessary water molecules for the hydrolysis of methoxy groups.

[0023] Nano-silica powder was added to the above-mentioned ethanol-water mixed solvent at a solid-liquid ratio of 1:20 and ultrasonically dispersed for 30 min using an ultrasonic disperser with a power of 300W and a frequency of 40kHz to eliminate powder agglomerates and form a uniform suspension. Then, under stirring conditions of 200-400 rpm, a silane coupling agent was added at a dropping rate of 1-2 mL / min, and the mass ratio of coupling agent to nano-silica was controlled between 0.15:1 and 0.25:1. After the addition was completed, the temperature was raised to 60-70℃ and stirred and refluxed continuously for 4-6 h. During this period, the methoxy group of the silane coupling agent was gradually hydrolyzed and dehydrated and condensed with the silanol group on the surface of silica, covalently grafting the quaternary ammonium salt organic chain onto the particle surface.

[0024] After the reaction was completed, the product was centrifuged at 8000 rpm for 15 min to discard the supernatant. The precipitate was washed three times with anhydrous ethanol, and centrifuged again after each wash. Finally, the precipitate was dried in a vacuum drying oven at 60°C for 12 h to obtain quaternary ammonium salt functionalized nano-silica microspheres. The nano-silica particles have an average hydrated particle size of 15-25 nm and a Zeta potential of +30 mV to +50 mV.

[0025] The quaternary ammonium salt functionalized silica nanospheres prepared above were formulated into an aqueous dispersion for precise addition in liquid form during the dyeing process. Deionized water was used as the dispersion medium, with a conductivity not exceeding 1.0 μS / cm. Excessive ionic strength would compress the electric double layer on the microsphere surface, weakening the electrostatic interaction range of the quaternary ammonium salt cations and thus reducing subsequent anchoring efficiency. The solid content of the dispersion was 1.0-5.0 wt%.

[0026] The specific preparation steps are as follows: After adding the powder to deionized water, pre-disperse it for 10 minutes using a mechanical stirrer at 500 rpm, and then sonicate it for 20-30 minutes using an ultrasonic cell disruptor to fully deagglomerate the functionalized microspheres, obtaining a transparent to semi-transparent colloidal dispersion. The prepared dispersion, measured by dynamic light scattering, has a Z-average particle size of no more than 30 nm, a PDI of no more than 0.25, and no visible precipitation or flocculation. It is stable for at least 7 days when stored in a sealed container at 20°C to 25°C.

[0027] In the staining process containing functionalized nanospheres, electrostatic adsorption assembly between polyiodide anions and functionalized nanospheres is completed, forming a "molecular anchor" structure; the staining solution composition is as follows: iodine( The concentration of iodine in the staining solution is 0.3–0.8 g / L. It reacts with potassium iodide as an iodine source to generate polyiodide ions.

[0028] Potassium iodide (KI), at a concentration of 15–30 g / L, is used to promote the dissolution of iodine and the formation of... and .

[0029] Functionalized microsphere dispersions, at concentrations of 0.01–0.08 g / L in staining solutions, are used to provide cationic anchoring sites.

[0030] Deionized water is used as a solvent.

[0031] When the added amount of functionalized microspheres is below 0.01 g / L, the total number of quaternary ammonium salt cation sites per unit volume of staining solution is insufficient to effectively anchor and cover polyiodide anions, resulting in no significant improvement in iodide ion stability. When the added amount exceeds 0.08 g / L, the excessive quaternary ammonium salt cation sites preferentially capture a large number of free polyiodide anions in the staining solution, reducing the total amount of polyiodide anions that can diffuse into the PVA membrane and form PVA-iodine complexes, thus decreasing the polarization degree. Simultaneously, the accumulation of excessive nanospheres in the PVA membrane also leads to a decrease in transmittance.

[0032] The temperature of the dyeing solution is controlled at 25-35℃. This range ensures that the solubility of iodine, the rate of polyiodide ion generation, and the dispersion stability of functionalized microspheres are at a reasonable level. The PVA membrane passes through the dyeing tank continuously at a linear velocity of 3-8 m / min and is immersed for 60-180 s to ensure that iodide ions fully penetrate into the PVA membrane and that the functionalized microspheres complete effective adsorption.

[0033] In addition, a circulation pump needs to be installed in the dyeing tank, with a circulation flow rate of 2-4 times the tank volume per hour, to prevent microspheres from settling and maintain concentration uniformity.

[0034] After adding the functionalized microsphere dispersion to an iodine-potassium iodide solution, the quaternary ammonium salt cationic groups on the surface of the microspheres ( ) and polyiodide anions in the solution ( and Coulombic electrostatic attraction is generated between them. The permanent positive charge of the quaternary ammonium salt group makes this electrostatic attraction unaffected by pH and temperature fluctuations of the staining solution. Under the drive of electrostatic attraction, polyiodide anions spontaneously adsorb and accumulate on the surface of the microspheres, forming a core-shell assembly structure with the nanospheres as the core and the polyiodide anions as the shell, i.e., the "molecular anchor" structure.

[0035] After the PVA membrane is immersed in the dyeing solution, the hydroxyl groups of the PVA molecular chain complex with the polyiodide anion, and the iodide ion diffuses into the interior of the PVA membrane. The functionalized microspheres form multiple interactions with the iodide ion and the hydroxyl groups on the PVA chain through the positive charge on their surface. During the dyeing process, they are adsorbed on the surface and shallow region of the swollen PVA membrane and fixed in the PVA matrix with subsequent stretching and cross-linking processes.

[0036] After dyeing, the "molecular anchor" structure of the PVA film is further solidified into the microstructure of the PVA polarizing film in subsequent processes. The stretching is performed using a uniaxial wet stretching method with a stretch ratio of 4.5-6.0 times, a stretching temperature of 40-55℃, and a stretching medium of 2-4 wt% boric acid aqueous solution. During the stretching process, the PVA molecular chains are highly oriented along the stretching direction, and the inter-fiber network space in the amorphous region shrinks along a dimension perpendicular to the stretching direction. The functionalized microspheres embedded within are mechanically held in place by the surrounding PVA chain segments.

[0037] The crosslinking process uses a boric acid aqueous solution with a boric acid concentration of 3-6 wt% and a potassium iodide concentration of 3-8 g / L; the crosslinking temperature is 50-65℃, and the crosslinking time is 120-300 s. The boron ester bond crosslinking network formed by the reaction of boric acid and PVA hydroxyl groups forms a three-dimensional network coating structure around the functionalized microspheres, further preventing the displacement of polyiodide ions adsorbed on the functionalized microspheres and their surfaces; the iodide ions are simultaneously subjected to a triple constraint force: the electrostatic bonding force of quaternary ammonium salt cations on the surface of the functionalized microspheres, the steric hindrance effect of the nanospheres themselves, and the physical blocking effect of the boric acid crosslinking network. These three forces work together to form the aforementioned "charge trap" structure.

[0038] The drying process uses hot air drying at a temperature of 60-80℃ for 120-240 seconds. During the drying process, moisture evaporates from the PVA film, the crystallinity of the PVA molecular chains is further improved, the free volume of the amorphous region shrinks, and the interfacial contact between the functionalized microspheres and the PVA chain segments becomes tighter. After drying, the moisture content of the PVA polarizing film is no higher than 4.0 wt%. Example 2:

[0039] This embodiment also provides an iodine-based polarizing film, which is prepared using the polarizing film manufacturing method for improving the damp heat stability of iodine-based polarizers as described in Embodiment 1.

[0040] The above description is merely a preferred embodiment of the present invention, but is not intended to limit the implementation of the present invention. Those skilled in the art should understand that any modifications, equivalent substitutions, and improvements made based on the present invention without departing from the inventive concept of the present invention are within the scope of protection of the present invention.

Claims

1. A method for manufacturing a polarizing film to improve the damp heat stability of iodine-based polarizers, characterized in that, Includes the following steps: The silica matrix was added to a mixed solvent of ethanol and deionized water in a volume ratio of 9:1, and after ultrasonic dispersion, N-trimethoxysilylpropyl-N,N,N-trimethylammonium chloride was added dropwise under stirring conditions. The mixed solvent containing N-trimethoxysilylpropyl-N,N,N-trimethylammonium chloride was refluxed at 60-70°C for 4-6 hours. The product after reflux reaction was centrifuged to discard the supernatant, and the precipitate was washed with anhydrous ethanol and then dried under vacuum at 60°C for 12 h to obtain quaternary ammonium salt functionalized nano silica particles. The obtained quaternary ammonium salt functionalized nano silica particles were dispersed in deionized water with a conductivity of no more than 1.0 μS / cm, and then ultrasonically treated to obtain a colloidal dispersion with a solid content of 1.0–5.0 wt%, a Z-average particle size of no more than 30 nm, and a PDI of no more than 0.

25. Add colloidal dispersion to iodine-potassium iodide staining solution, mix and set solution temperature to 25-35℃; and allow PVA film to pass through the staining tank at a linear velocity of 3-8 m / min for 60-180 s. The treated PVA film was subjected to uniaxial wet stretching in a 2-4 wt% boric acid aqueous solution, with a stretching ratio of 4.5-6.0 times and a stretching temperature of 40-55℃. The stretched PVA film was then immersed in a crosslinking solution with a boric acid concentration of 3-6 wt% and a potassium iodide concentration of 3-8 g / L. The crosslinking temperature was 50-65℃ and the crosslinking time was 120-300 s. The PVA film was then dried with hot air to obtain a PVA polarizing film.

2. The method for manufacturing a polarizing film to improve the damp heat stability of an iodine-based polarizer according to claim 1, characterized in that, The chemical formula of the N-trimethoxysilylpropyl-N,N,N-trimethylammonium chloride is: ; The mass ratio of N-trimethoxysilylpropyl-N,N,N-trimethylammonium chloride to nano-silica is set between 0.15:1 and 0.25:

1.

3. The method for manufacturing a polarizing film to improve the damp heat stability of an iodine-based polarizer according to claim 1, characterized in that, The iodine-potassium iodide staining solution has an iodine concentration of 0.3–0.8 g / L, a potassium iodide concentration of 15–30 g / L, and a dry basis mass concentration of quaternary ammonium salt functionalized nano-silica microspheres of 0.01–0.08 g / L.

4. The method for manufacturing a polarizing film to improve the damp heat stability of an iodine-based polarizer according to claim 1, characterized in that, The silica matrix has a primary particle size of 7–15 nm, a specific surface area of ​​150–300 m² / g, a SiO₂ mass fraction of not less than 99.5%, and a surface silanol group density of 2.0–4.6 groups / nm².

5. The method for manufacturing a polarizing film to improve the damp heat stability of an iodine-based polarizer according to claim 1, characterized in that, The solid-liquid ratio of the silica matrix to the mixed solvent is 1:20; The ultrasonic dispersion power is 300W, the frequency is 40kHz, and the time is 30min; The dropping rate of the N-trimethoxysilylpropyl-N,N,N-trimethylammonium chloride was 1-2 mL / min; the stirring speed was 200-400 rpm.

6. The method for manufacturing a polarizing film to improve the damp heat stability of an iodine-based polarizer according to claim 1, characterized in that, The centrifugation speed after the reflux reaction was completed was 8000 rpm, and the centrifugation time was 15 min.

7. The method for manufacturing a polarizing film to improve the damp heat stability of an iodine-based polarizer according to claim 1, characterized in that, The precipitate was washed with anhydrous ethanol three times.

8. The method for manufacturing a polarizing film to improve the damp heat stability of an iodine-based polarizer according to claim 1, characterized in that, The degree of polymerization of the PVA original film is 1700-1800, and the degree of saponification is not less than 99.5 mol.

9. The method for manufacturing a polarizing film to improve the damp heat stability of an iodine-based polarizer according to claim 1, characterized in that, The dyeing tank is equipped with a circulation pump, and the circulation flow rate is 2 to 4 times the tank volume per hour.

10. An iodine-based polarizing film, characterized in that, The polarizing film is prepared using the method for improving the damp heat stability of iodine-based polarizers as described in any one of claims 1-9.

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