Anti-ultraviolet PMMA (polymethyl methacrylate) protective film and preparation method thereof

Abstract

The invention discloses an anti-ultraviolet PMMA protective film and a preparation method thereof.The preparation method of the anti-ultraviolet PMMA protective film comprises the steps that a PMMA-BBP compound is synthesized and mixed with linear PMMA in proportion, the PMMA protective film with the adjustable birefringence is achieved, and the birefringence of the PMMA protective film has the linear change characteristic under the strain effect; under the tensile deformation, the birefringence of the prepared PMMA protective film is approximately linearly changed along with the deformation quantity, and the PMMA protective film has an application prospect in the field of flexible display; by mixing a certain proportion of the ultraviolet light absorber in the processing process, the prepared PMMA film has better ultraviolet resistance so as to meet the display requirement of being exposed in an ultraviolet environment for a long time.

Description

Technical Field

[0001] The present invention relates to the technical field of film materials, and particularly to an anti-ultraviolet PMMA protective film and a preparation method thereof. Background Art

[0002] Liquid crystal displays (LCDs) are widely used in electronic devices such as smartphones, tablets, TVs, and monitors. One of the core components is the polarizer, which is responsible for adjusting the polarization direction of light to enhance image clarity and color performance. The polarizer usually consists of a multi-layer structure, including a polarizing substrate layer (such as a PVA film) and optical protective films on both sides. Traditionally, cellulose triacetate (TAC) is the mainstream optical protective film material due to its excellent transparency and ultraviolet absorption properties. However, the thermal stability of TAC is relatively poor, and it is prone to degradation in the high-temperature environment of the LCD backlight module, resulting in deterioration of the polarization performance and thus affecting the image quality.

[0003] In recent years, polymethyl methacrylate (PMMA) has gradually become a preferred material to replace the TAC film due to its excellent optical transparency, weather resistance, and chemical stability. Compared with TAC, PMMA has higher heat resistance and mechanical strength, and also has environmental protection advantages. However, due to its birefringence characteristics, traditional PMMA films perform inadequately in wide-view displays. Especially in In-Plane Switching (IPS) liquid crystal panels, the PMMA film cannot effectively compensate for the birefringence effect of liquid crystal molecules, resulting in problems such as yellow light leakage and color shift in the display at wide viewing angles, affecting the overall display effect. IPS panels rely on the stable arrangement of liquid crystal molecules to achieve high dynamic clarity and wide-view display, so higher requirements are put forward for the refractive index matching and optical compensation of the polarizer. Summary of the Invention

[0004] The main object of the present invention is to provide a preparation method of an anti-ultraviolet PMMA protective film, aiming to solve the color shift phenomenon of the liquid crystal display at a specific viewing angle and the aging and yellowing phenomenon that occurs when exposed to the ultraviolet light environment for a long time, thereby solving the problem of narrow color viewing angle of the display and extending the service life.

[0005] To achieve the above object, the present invention proposes a preparation method of an anti-ultraviolet PMMA protective film, and the preparation method of the anti-ultraviolet PMMA protective film includes the following steps: S1. In a glove box, methyl methacrylate MMA (15 g, 150 mmol) and deoxygenated toluene (15 mL) are added to a 150 mL high-pressure container, and an argon environment is maintained; S2. Add CuBr (0.22 g, 1.5 mmol) and pentamethyldiethylenetriamine PMDETA (0.31 mL, 1.5 mmol). After stirring and dissolving, add 2-hydroxyethyl 2-bromoisobutyrate HEBiB (1.09 mL, 7.5 mmol) as the initiator for atom transfer radical polymerization; S3. After sealing the container, react in an oil bath at 70 °C for 2 hours. Then cool the reaction mixture to the ice-water temperature and expose it to air to terminate the reaction; S4. Filter through an alumina column to remove the copper complex. After concentration, precipitate in n-hexane (1000 mL) at room temperature and dry in a vacuum oven at 50 °C for 72 hours; S5. Under an argon atmosphere, add exo-5-norbornene carboxylic acid (2.16 g, 15.7 mmol) and deoxygenated toluene (10.9 mL) to a 250 mL two-necked flask. Add oxalyl chloride (1.34 mL, 15.7 mmol) and stir at room temperature for 30 minutes; S6. Stir the mixture at 60 °C for 1 hour, then stir in an oil bath at 70 °C for another 1 hour. Cool to room temperature and remove the remaining oxalyl chloride under vacuum; S7. In another 250 mL two-necked flask, mix PMMA-OH (6.0 g, 3.0 mmol) and triethylamine (2.24 mL, 16.0 mmol) with deoxygenated toluene (27.2 mL). After stirring in an oil bath at 60 °C for 30 minutes, perform three freeze-pump-thaw cycles for degassing; S8. Transfer the solution obtained in step S7 to the original flask by syringe. After stirring at 100 °C for 12 hours, precipitate the sample in cold methanol (-70 °C, 1000 mL) and dry in a vacuum oven at 50 °C for 72 hours; S9. Dissolve PMMA-NB (2.0 g) in deoxygenated tetrahydrofuran THF (30 mL). After degassing using three freeze-pump-thaw cycles, transfer it to a glove box under an argon atmosphere; S10. Quickly add the third-generation Grubbs catalyst (1.47 mg) to the PMMA-NB solution, stir and react for 21 hours, and avoid light exposure; S11. After the reaction, add vinyl ether (2.0 mL) to terminate the reaction. Precipitate the mixture in methanol (1000 mL) and dry in a vacuum oven at 50 °C for 72 hours; S12. Mix linear PMMA and PMMA-BBP in a specific mass ratio; S13. Take 2 g of the linear PMMA and PMMA-BBP mixture, weigh the ultraviolet absorber with a preset mass ratio, and add it to a 200 mL round-bottom flask; S14. Add 38 g of dichloromethane (DCM) as a solvent and stir with a magnetic stirrer at room temperature for 1 hour until the mixture is uniformly mixed and completely dissolved; S15. Slowly pour the uniformly stirred solution into 800 mL of cold methanol (-70 °C) to quickly precipitate the mixture as a white powder. During the precipitation process, keep the solution constantly stirred to ensure uniform precipitation; S16. After collecting the precipitate by filtration or centrifugation, transfer it to a drying container and dry it in a vacuum oven at 50 °C for 72 hours to remove the residual solvent; S17. Weigh 0.6 g of the sample from the dried mixture and sandwich the sample between two layers of polyethylene terephthalate (PET) films. Place it in a compression molding machine and press it at 180 °C and 8 MPa for 5 minutes to keep the film thickness at 0.3 mm; S18. After pressing is completed, take out the film and let it cool naturally to room temperature.

[0006] The present invention also provides an anti-ultraviolet PMMA protective film, which is obtained by the preparation method of the anti-ultraviolet PMMA protective film described above.

[0007] The beneficial effects of the present invention are as follows: The PMMA-BBP molecular brush polymer is prepared by the preparation method of the anti-ultraviolet PMMA protective film. After being mixed with linear PMMA in a certain proportion, different birefringences can be achieved. After further testing, under tensile deformation, the birefringence of the prepared PMMA changes nearly linearly with the strain, showing application prospects in the field of flexible displays. By mixing a certain proportion of ultraviolet absorber during the processing, the prepared PMMA film can have better anti-ultraviolet ability, meeting the display requirements for long-term exposure to ultraviolet environment. Description of the Drawings

[0008] Att Figure 1 It is a process schematic diagram of the synthesis of PMMA-BBP for the preparation method of the anti-ultraviolet PMMA protective film of the present invention; Att Figure 2 It is a graph of the change in birefringence under tensile strain for Examples 1-5; Att Figure 3 It is a graph of the change in transmittance under ultraviolet irradiation for Example 1, Comparative Example 1 and Comparative Example 2. Detailed Embodiments

[0009] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts belong to the scope of protection of the present invention.

[0010] In addition, in the present invention, descriptions such as "first" and "second" are only for descriptive purposes, and cannot be construed as indicating or implying their relative importance or implicitly indicating the quantity of the indicated technical features. Thus, features defined with "first" and "second" may explicitly or implicitly include at least one such feature. In addition, the technical solutions between various embodiments can be combined with each other, but it must be based on the ability of those of ordinary skill in the art to implement. When the combination of technical solutions is contradictory or cannot be implemented, it should be considered that such a combination of technical solutions does not exist and is not within the scope of protection required by the present invention.

[0011] The following will specifically describe the embodiments of the present invention in conjunction with the accompanying drawings.

[0012] As Figures 1-3 shown, the preparation method of the anti-ultraviolet PMMA protective film includes the following steps: I. Synthesis of PMMA-OH (hydroxyl-terminated PMMA) S1. In a glove box, MMA (15 g, 150 mmol) and deoxygenated toluene (15 mL) are added to a 150 mL high-pressure vessel, and an argon environment is maintained. S2. CuBr (0.22 g, 1.5 mmol) and PMDETA (0.31 mL, 1.5 mmol) are added, and after stirring and dissolving, HEBiB (1.09 mL, 7.5 mmol) is added as an initiator for atom transfer radical polymerization (ATRP). S3. After sealing the container, the reaction is carried out in an oil bath at 70 °C for 2 hours, and then the reaction mixture is cooled to the ice-water temperature and exposed to air to terminate the reaction. S4. The copper complex is removed by filtration using an alumina column, concentrated, precipitated with n-hexane (1000 mL) at room temperature, and dried in a vacuum oven at 50 °C for 72 hours. II. Synthesis of PMMA-NB (norbornene-terminated PMMA) S5. Under an argon atmosphere, 5-norbornene-2-carboxylic acid (2.16 g, 15.7 mmol) and deoxygenated toluene (10.9 mL) are added to a 250 mL two-necked flask, oxalyl chloride (1.34 mL, 15.7 mmol) is added, and the mixture is stirred at room temperature for 30 minutes. S6. Stir the mixture at 60 °C for 1 hour, then stir it in an oil bath at 70 °C for another 1 hour. Subsequently, cool it to room temperature and remove the remaining oxalyl chloride under vacuum; S7. In another 250 mL two-necked flask, mix PMMA-OH (6.0 g, 3.0 mmol) and triethylamine (2.24 mL, 16.0 mmol) with deoxygenated toluene (27.2 mL). Stir in an oil bath at 60 °C for 30 minutes, and then perform three freeze-pump-thaw cycles for degassing; S8. Transfer this solution to the original flask through a syringe, stir at 100 °C for 12 hours. Finally, precipitate the sample in cold methanol (about -70 °C, 1000 mL) and dry it in a vacuum oven at 50 °C for 72 hours; III. Synthesis of PMMA-BBP (molecular brush polymer) S9. Dissolve PMMA-NB (2.0 g) in deoxygenated THF (30 mL). After degassing using three freeze-pump-thaw cycles, transfer it to a glove box under an argon atmosphere; S10. Quickly add the third-generation Grubbs catalyst (1.47 mg, dissolved in THF) to the PMMA-NB solution, stir the reaction for 21 hours, and avoid light exposure; S11. After the reaction is completed, add vinyl ether (2.0 mL) to terminate the reaction. Precipitate the mixture in methanol (1000 mL) and dry it in a vacuum oven at 50 °C for 72 hours to obtain the PMMA-BBP polymer; Subsequently, use the prepared PMMA-BBP and linear PMMA to prepare an anti-UV PMMA compensation film:

[0013] Example 1: S12. Mix linear PMMA and PMMA-BBP in a mass ratio of 73:27; S13. Take 2 g of the linear PMMA and PMMA-BBP mixture, weigh 3% of the mixture mass of benzotriazole ultraviolet absorber (0.06 g), and add it to a 200 mL round-bottom flask; S14. Add 38 g of dichloromethane (DCM) as a solvent, and stir with a magnetic stirrer at room temperature for 1 hour until it is evenly mixed and completely dissolved; S15. Slowly pour the well-stirred solution into 800 mL of cold methanol (about -70 °C) to quickly precipitate the mixture into a white powder. During the precipitation process, keep the solution stirring continuously to ensure uniform precipitation; S16. After collecting the precipitate by filtration or centrifugation, transfer it to a drying container and dry it in a vacuum oven at 50 °C for 72 hours to remove the residual solvent; S17. Weigh approximately 0.6 g of the sample from the dried mixture, sandwich the sample between two layers of polyethylene terephthalate (PET) films, and place it in a compression molding machine. Press it at 180 °C and 8 MPa for 5 minutes. The final film thickness is maintained at approximately 0.3 mm; S18. After the pressing is completed, take out the film and let it cool naturally to room temperature.

[0014] Example 2: Different from Example 1, the mass ratio of PMMA:PMMA - BBP used in S12 is 90:10.

[0015] Comparative Example 3: Different from Example 1, the mass ratio of PMMA:PMMA - BBP used in S12 is 80:20.

[0016] Example 4: Different from Example 1, the mass ratio of PMMA:PMMA - BBP used in S12 is 60:40.

[0017] Example 5: Different from Example 1, the mass ratio of PMMA:PMMA - BBP used in S12 is 100:0, that is, pure linear PMMA.

[0018] Comparative Example 1: Different from Example 1, the type of ultraviolet absorber added in S13 is triazine - type ultraviolet absorber; Comparative Example 2: Different from Example 1, no ultraviolet absorber is added in S13.

[0019] As Figure 2 shown, measure the birefringence of Examples 1 to 5 under different stretching states. It can be seen from the figure that as the proportion of PMMA - BBP in the PMMA / PMMA - BBP mixture increases, the birefringence of the prepared PMMA film gradually increases; for the PMMA:PMMA - BBP = 73:27 mixture used in Example 1, it has a birefringence close to 0, and under strain, the birefringence remains unchanged, having a stable birefringence. As Figure 3 shown, measure the ultraviolet resistance of Example 1, Comparative Example 1, and Comparative Example 2, and it is found that for Example 1 with benzotriazole - type ultraviolet absorber added, the transmittance decreases the least under ultraviolet light irradiation, while for Comparative Example 2 without ultraviolet absorber added, the transmittance decreases significantly.

[0020] The present invention also proposes an ultraviolet - resistant PMMA protective film, and the ultraviolet - resistant PMMA protective film is obtained by the preparation method of the above - mentioned ultraviolet - resistant PMMA protective film.

[0021] In summary, the present invention synthesizes the PMMA-BBP compound and mixes it with linear PMMA in proportion to achieve a PMMA protective film with adjustable birefringence, and its birefringence has a linear variation characteristic under the action of strain; compared with the traditional cellulose acetate (TAC) film, the PMMA film adopted in the present invention has higher optical transparency, dimensional stability, weather resistance and mechanical strength, and lower cost. In particular, we point out that when the mass ratio of linear PMMA:PMMA-BBP is 73:27, the prepared PMMA protective film has zero birefringence, and the birefringence remains stable under the action of strain. These birefringence characteristics are all beneficial to the PMMA protective film applied to liquid crystal displays, especially the PMMA protective film for flexible liquid crystal displays, avoiding the color difference phenomenon during large-angle observation caused by birefringence. The present invention adds a certain proportion of ultraviolet absorber to the PMMA film, making it have a high transmittance, and under ultraviolet light irradiation, the attenuation of the transmittance is significantly lower than that of the PMMA film without adding ultraviolet absorber, which is suitable for application in display devices used outdoors for a long time.

[0022] The above are only the preferred embodiments of the present invention. It should be noted that for those of ordinary skill in the art, without departing from the technical principle of the present invention, several improvements and refinements can still be made, and these improvements and refinements should also be regarded as the protection scope of the present invention.

Claims

1. A preparation method of an anti-ultraviolet PMMA protective film, characterized in that, The preparation method of the anti-ultraviolet PMMA protective film comprises the following steps: S1. In a glove box, methyl methacrylate MMA (15 g, 150 mmol) and deoxygenated toluene (15 mL) are added to a 150 mL high-pressure vessel, and an argon environment is maintained; S2. CuBr (0.22 g, 1.5 mmol) and pentamethyldiethylenetriamine PMDETA (0.31 mL, 1.5 mmol) are added. After stirring and dissolving, 2-hydroxyethyl 2-bromoisobutyrate HEBiB (1.09 mL, 7.5 mmol) is added as an initiator for atom transfer radical polymerization; S3. After sealing the container, the reaction mixture is reacted in an oil bath at 70 °C for 2 hours, then cooled to the ice-water temperature and exposed to air to terminate the reaction; S4. The copper complex is removed by filtration using an alumina column, concentrated, precipitated with n-hexane (1000 mL) at room temperature, and dried in a vacuum oven at 50 °C for 72 hours; S5. Under an argon environment, exo-5-norbornene carboxylic acid (2.16 g, 15.7 mmol) and deoxygenated toluene (10.9 mL) are added to a 250 mL two-necked flask, and oxalyl chloride (1.34 mL, 15.7 mmol) is added, and stirred at room temperature for 30 minutes; S6. After stirring the mixture at 60 °C for 1 hour, it is further stirred in an oil bath at 70 °C for 1 hour, cooled to room temperature, and the remaining oxalyl chloride is removed under vacuum; S7. In another 250 mL two-necked flask, PMMA-OH (6.0 g, 3.0 mmol), triethylamine (2.24 mL, 16.0 mmol) and deoxygenated toluene (27.2 mL) are mixed. After stirring in an oil bath at 60 °C for 30 minutes, three freeze-pump-thaw cycles are carried out for degassing; S8. The solution obtained in step S7 is transferred to the original flask through a syringe. After stirring at 100 °C for 12 hours, the sample is precipitated in cold methanol (-70 °C, 1000 mL) and dried in a vacuum oven at 50 °C for 72 hours; S9. PMMA-NB (2.0 g) is dissolved in deoxygenated tetrahydrofuran THF (30 mL). After degassing using three freeze-pump-thaw cycles, it is transferred to a glove box under an argon environment; S10. The third-generation Grubbs catalyst (1.47 mg) is quickly added to the PMMA-NB solution, and stirred and reacted for 21 hours, and light exposure is avoided; S11. After the reaction is completed, vinyl ether (2.0 mL) is added to terminate the reaction. The mixture is precipitated in methanol (1000 mL) and dried in a vacuum oven at 50 °C for 72 hours; S12. Linear PMMA and PMMA-BBP are mixed in a specific mass ratio; S13. Take 2 g of the linear PMMA and PMMA-BBP mixture, weigh the ultraviolet absorber in a preset mass ratio, and add it to a 200 mL round-bottom flask; S14. 38 g of dichloromethane (DCM) is added as a solvent, and stirred with a magnetic stirrer at room temperature for 1 hour until evenly mixed and completely dissolved; S15. Slowly pour the well-stirred solution into 800 mL of cold methanol (-70 °C) to rapidly precipitate the mixture into a white powder. During the precipitation process, keep the solution constantly stirred to ensure uniform precipitation; S16. After collecting the precipitate by filtration or centrifugation, transfer it to a drying container and dry it in a vacuum oven at 50 °C for 72 hours to remove the residual solvent; S17. Weigh 0.6 g of the sample from the dried mixture and sandwich the sample between two layers of polyethylene terephthalate (PET) film. Place it in a compression molding machine and press it at 180 °C and 8 MPa for 5 minutes to keep the film thickness at 0.3 mm; S18. After pressing is completed, take out the film and let it cool naturally to room temperature.

2. The preparation method of the anti-ultraviolet PMMA protective film according to claim 1, wherein In the step S12, when the ratio of PMMA to PMMA-BBP is 73:27, a birefringence close to 0 is observed.

3. The preparation method of the anti-ultraviolet PMMA protective film according to claim 1, characterized in that, The ultraviolet absorber in the step S13 is a benzotriazole ultraviolet absorber or a triazine ultraviolet absorber.

4. The preparation method of the anti-ultraviolet PMMA protective film according to claim 3, wherein, The addition ratio of the ultraviolet absorber is 3% by mass ratio.

5. An anti-ultraviolet PMMA protective film, characterized in that The anti-ultraviolet PMMA protective film is obtained by the preparation method of the anti-ultraviolet PMMA protective film according to any one of claims 1-4.

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