Essentially anti-static polarizer protective film base film and preparation method thereof

Abstract

The application relates to an intrinsic anti-static polarizer protective film base film and a preparation method thereof, the preparation method comprising the following steps: synthesizing an ionic liquid dihydric alcohol first, then performing co-polycondensation on the ionic liquid dihydric alcohol, terephthalic acid, ethylene glycol and 1,4-cyclohexane dimethanol to obtain an antistatic master batch; taking nano silicon dioxide as a core, performing surface grafting on the core through a silane coupling agent and polyether amine in sequence, and performing a quaternary ammoniation reaction to obtain a hybrid functional filler; and drying, blending the PET master batch, the antistatic master batch and the functional filler, and performing a melting extrusion, bidirectional stretching and heat setting process to obtain the protective film base film. The ionic conductive structure is chemically bonded to the polymer main chain, and the functional filler with surface migration characteristics is supplemented, so that the obtained film has long-lasting and stable intrinsic antistatic performance, and simultaneously has good flame retardance, optical performance and mechanical strength, and the technical defects of the traditional surface coating method, such as poor durability and easy abrasion of the antistatic performance, are solved.

Description

Technical Field

[0001] This invention relates to the field of protective film technology for optical display equipment, specifically to an intrinsically antistatic polarizer protective film base film and its preparation method. Background Technology

[0002] Polarizing films are essential core components for LCD imaging. They consist of a multi-layered composite structure, with the innermost layer being a polyvinyl alcohol (PVA) core layer that polarizes light. On either side are protective layers of cellulose triacetate (TAC), forming the polarizing film substrate. Depending on the application, storage, or transportation requirements, a pressure-sensitive adhesive (PSA) of a certain thickness needs to be coated on one side of the polarizing film substrate, followed by a release film to protect the PSA. On the other side, depending on the product type, a protective film, a reflective film, and a semi-transparent reflective adhesive layer are laminated, thus forming the finished polarizing film.

[0003] Each layer of a polarizer has a specific function. The surface protective film, adhered to the outer surface of the polarizer, prevents surface contamination and scratches that may occur during subsequent processes such as testing, transportation, and storage. This requires the protective film to have a certain level of impact resistance and abrasion resistance. Furthermore, when the polarizer is assembled into a liquid crystal display device, a surface protective film is needed. Therefore, the surface protective film must have low adhesion and must not generate electrostatic voltage to avoid damaging the circuit components of the liquid crystal display.

[0004] In the existing technology, the main method for preparing antistatic polarizer protective films is the surface coating method, which involves coating the surface of a PET film with a polyurethane-acrylate coating containing an antistatic agent (such as CN118562402B, CN106675464B, etc.). While the antistatic coating can indeed provide a certain degree of antistatic effect, the external coating method often results in the coating migrating into the polymer due to friction or long-term exposure to air, thus gradually reducing the antistatic effect and making it not durable enough. Furthermore, the coating is easily worn and has poor durability. Summary of the Invention

[0005] In view of the shortcomings of the existing technology, the present invention aims to develop an inherently antistatic protective film base film that can meet the usage requirements of polarizers.

[0006] To achieve the above objectives, the present invention provides the following technical solution:

[0007] A method for preparing an intrinsically antistatic polarizer protective film base film includes the following steps:

[0008] S1. Preparation of antistatic masterbatch

[0009] S1-1. In a reaction flask, add N-methyldiethanolamine, Br(CH2)nCH3, and toluene, heat under reflux for 24 h, cool, wash with ethyl acetate, and dry.

[0010] S1-2. Dissolve the dried solid in deionized water, and then add an aqueous solution containing lithium bis(trifluoromethanesulfonyl)imide dropwise while stirring. After the addition is complete, stir at room temperature for 2 hours, then heat to 60°C and continue stirring for 4 hours. Extract the product with dichloromethane, collect the organic phase, dry it, and then distill it under reduced pressure to obtain the ionic liquid diol.

[0011] S1-3. Add terephthalic acid, ethylene glycol, 1,4-cyclohexanediethanol and catalyst to the reactor, and heat to 250℃ under nitrogen protection for 2-3 hours; then cool to 200℃, add ionic liquid diol and antimony trioxide condensation catalyst while stirring, and stir at 200℃ for 30 minutes; then heat to 270℃ and simultaneously evacuate to a vacuum degree of less than 100 Pa to carry out the condensation reaction. When the viscosity reaches 0.60-0.65 dL / g, stop the reaction, cool and discharge the material, and granulate to obtain antistatic masterbatch;

[0012] S2. Preparation of functional fillers

[0013] Nano-silica was dispersed in anhydrous toluene by ultrasonication until uniform dispersion. Then, KH560 was added, and the mixture was refluxed and stirred overnight under nitrogen protection. After cooling to room temperature, polyetheramine and a catalytic amount of triethylamine were added, and the mixture was heated to 110°C and reacted overnight. After cooling, the mixture was centrifuged, washed with toluene, and the resulting solid was dispersed in acetonitrile. Iodomethane was added and the mixture was heated to 60°C and reacted for 8 hours. After centrifugation, the solid was washed with ethanol, vacuum dried, and ground to obtain the final product.

[0014] S3. After vacuum drying the PET masterbatch, antistatic masterbatch and functional filler, mix them evenly in a certain proportion.

[0015] S4. The mixed materials are melted, extruded, cast, biaxially stretched, and heat-set to obtain a polyester film, which is the base film for the polarizer protective film.

[0016] Furthermore, in Br(CH2)nCH3, n is 2, 3, or 4; the molar ratio of Br(CH2)nCH3, N-methyldiethanolamine, and lithium bis(trifluoromethanesulfonylimide) is 1:1:1.1.

[0017] Furthermore, the molar ratio of terephthalic acid, ethylene glycol, and 1,4-cyclohexanediethanol is 1:1.5:0.05; the amount of ionic liquid diol added is 3~10 wt% of the total monomer mass.

[0018] Furthermore, the mass ratio of the nano-silica, KH560, polyetheramine, and iodomethane is 1:0.5~1:1.5~2:1; the polyetheramine is a polyoxyethylene-polyoxypropylene block copolymer monoamine with a number average molecular weight of 800~1200.

[0019] Furthermore, the mass ratio of the PET masterbatch, antistatic masterbatch, and functional filler is 100:10~20:2~10.

[0020] Furthermore, the preparation process in step S4 is specifically as follows:

[0021] The mixed materials are melted and extruded into sheets at 220~280℃. The sheets are cooled by a 45℃ cooling roller, then preheated at 90℃, stretched longitudinally at 100℃, stretched laterally at 115℃, and finally heat-set at 225℃ to obtain a polyester film with a thickness of 50±5μm, which is the base film for polarizer protective film.

[0022] Furthermore, the longitudinal stretching ratio is 3.2 to 3.6 times, and the transverse stretching ratio is 3.5 to 4.0 times.

[0023] The present invention further provides an intrinsically antistatic polarizer protective film base film prepared according to the preparation method described above.

[0024] This invention designs an intrinsically antistatic PET base film for protective films used in polarizers. This film is obtained by melt extrusion casting and biaxial stretching of PET masterbatch, antistatic masterbatch, and functional fillers, resulting in a simple manufacturing process. The antistatic masterbatch is a modified PETG material prepared by pre-esterification of terephthalic acid, ethylene glycol, and 1,4-cyclohexanediethanol, followed by polycondensation with an ionic liquid diol. The ionic liquid diol possesses high thermal stability and high ionic conductivity, thus remaining stable during the polycondensation of PETG and imparting antistatic properties. Compared to the traditional method of coating the film surface with an antistatic coating, this application directly polycondenses the antistatic agent with PETG to form an intrinsically antistatic masterbatch, fundamentally solving the problems of poor thermal stability and easy precipitation of traditional small-molecule antistatic agents. In actual production, the cost of preparing films entirely from modified PETG material is relatively high. Adding it as an antistatic masterbatch to the PET base material not only saves costs but also allows for adjustment of the film's surface resistance by regulating its addition amount. Because the main structure of the antistatic masterbatch (modified PETG material) remains highly consistent with that of the PET masterbatch, the two have good compatibility and do not require the addition of additional interfacial compatibilizers, thus reducing the surface resistivity of the film to 10. 9Ω. Meanwhile, unexpectedly, performance testing revealed that the antistatic masterbatch formed by the combination of quaternary ammonium salt and bis(trifluoromethanesulfonyl)imide imparts excellent flame retardant properties to the PET film, increasing the LOI to 29.5% in flame retardant performance tests. Furthermore, the antistatic masterbatch effectively disrupts the regularity of the PET molecular chains, inhibiting crystallinity and excessive orientation during stretching, thus ensuring good optical properties in the resulting film.

[0025] The functional filler uses nano-silica as its core, with KH560 forming a bridge between the inorganic and organic components, and grafting polyether segments to form a shell structure. The long-chain polyether forms a soft polymer brush-like layer on the SiO2 core surface, effectively isolating nanoparticles and preventing direct collision and aggregation. Simultaneously, the flexible chains are more easily wetted and entangled by the PET melt. Therefore, the functional filler exhibits good interfacial compatibility in PET masterbatch. Furthermore, the quaternary ammonium salt introduced through the quaternization reaction provides ionic carriers for conductivity. The polyether quaternary ammonium salt chains have moderate mobility. During the biaxial stretching of the PET film, the molecular chains orient themselves, and the flexible polyether chains surrounding the functional filler particles tend to migrate and accumulate towards the stress-relaxed, lower free energy film surface and amorphous regions, providing dynamic surface antistatic properties. Moreover, due to the presence of hydrophilic and hygroscopic polyether segments, the film's antistatic performance is significantly reduced to be dependent on environmental humidity. It complements the antistatic masterbatch, providing a permanent and stable bulk conductivity basis for the PET base film. Nano-SiO2 particles are classic inorganic reinforcing particles, and they also have a certain effect on improving the mechanical strength of thin films.

[0026] Compared with the prior art, the beneficial effects of the present invention are as follows: The present invention, by adding antistatic masterbatch and functional fillers similar to the main structure of PET to the PET masterbatch, enables the film to have durable and stable intrinsic antistatic properties, solving the problems of migration and attenuation, and has good aging resistance; at the same time, compared with traditional PET film materials, it also has a certain degree of flame retardant safety; while imparting antistatic and flame retardant properties to the film material, the mechanical properties and dimensional stability of the film are also improved, and excellent optical properties are maintained. Detailed Implementation

[0027] The technical solution of the present invention will be clearly and completely described below with reference to the embodiments. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0028] Furthermore, the technical features involved in the different embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0029] The raw materials used in this application are mostly bulk products that can be purchased on the market. The sources and models of some products are as follows:

[0030]

[0031] Example 1: Preparation of antistatic masterbatch A

[0032] S1-1. In a reaction flask, add 1 mol N-methyldiethanolamine, 1 mol 1-bromobutane and 100 mL toluene as solvent, heat to 60 °C, and reflux for 24 h; cool to room temperature, filter, wash thoroughly with ethyl acetate, and vacuum dry to obtain a solid powder;

[0033] S1-2. Dissolve the solid powder in deionized water, and then add an aqueous solution containing 1.1 mol of lithium bis(trifluoromethanesulfonyl)imide dropwise while stirring. After the addition is complete, continue stirring for 2 hours, then raise the temperature to 60°C and continue the reaction for 4 hours. Extract the product with dichloromethane, collect the organic phase, dry it, and then distill it under reduced pressure to obtain the ionic liquid diol.

[0034] S1-3. Add 166 g of terephthalic acid, 93 g of ethylene glycol, 7.2 g of 1,4-cyclohexanediethanol and 0.4 g of tetrabutyl titanate to the reactor. Under nitrogen protection, heat to 250℃ and react for 2.5 h. Then cool to 200℃, add 16 g of ionic liquid diol and 0.3 g of antimony trioxide condensation catalyst while stirring. Stir at 200℃ for 30 min. Then heat to 270℃ and simultaneously evacuate to a vacuum degree of less than 100 Pa to carry out the condensation reaction. When the viscosity reaches 0.65 dL / g, stop the reaction, cool and discharge the material, and granulate to obtain antistatic masterbatch.

[0035] Example 2: Preparation of functional filler B

[0036] 20g of nano-silica was dispersed in 700mL of anhydrous toluene by ultrasonication until uniform dispersion. Then, 16g of KH560 was added, and the mixture was refluxed and stirred overnight under nitrogen protection. After cooling to room temperature, 36g of polyetheramine and 0.4g of triethylamine were added, and the mixture was heated to 110℃ and reacted overnight. After cooling, the mixture was centrifuged and washed with toluene. The resulting solid was dispersed in acetonitrile, and 20g of iodomethane was added. The mixture was heated to 60℃ and reacted for 8 hours. After centrifugation, the solid was washed with ethanol, dried under vacuum, and ground to obtain the final product.

[0037] Example 3: Preparation of the base film

[0038] Optical-grade PET chips, antistatic masterbatch A, and functional filler B were vacuum dried at 120°C for 6 hours to remove moisture. They were then premixed at a mass ratio of PET:A:B = 100:18:2 and thoroughly mixed using a high-speed mixer.

[0039] The uniformly mixed material is fed into a twin-screw extruder, melted and plasticized at 240-260℃, extruded, and then cast into sheets on a cooling roller at 45℃ after passing through a metering pump and a T-die, resulting in unstretched thick sheets.

[0040] The thick film was preheated at 90℃ for 30 s, then longitudinally stretched at 100℃ with a stretch ratio of 3.4 times. Next, it was transversely stretched at 115℃ with a stretch ratio of 3.8 times. Finally, the biaxially stretched film was heat-set at 225℃ for 10 s, cooled, and then wound up to obtain an intrinsically antistatic polarizer protective film base film (sample 1) with a thickness of 50±5 μm.

[0041] Example 4: Preparation of the base film

[0042] Optical-grade PET chips, antistatic masterbatch A, and functional filler B were vacuum dried at 120°C for 6 hours to remove moisture. They were then premixed at a mass ratio of PET:A:B = 100:15:5 and thoroughly mixed using a high-speed mixer.

[0043] The uniformly mixed material is fed into a twin-screw extruder, melted and plasticized at 240-260℃, extruded, and then cast into sheets on a cooling roller at 45℃ after passing through a metering pump and a T-die, resulting in unstretched thick sheets.

[0044] The thick film was preheated at 90℃ for 30 s, then longitudinally stretched at 100℃ with a stretch ratio of 3.4 times. Next, it was transversely stretched at 115℃ with a stretch ratio of 3.8 times. Finally, the biaxially stretched film was heat-set at 225℃ for 10 s, cooled, and then wound up to obtain an intrinsically antistatic polarizer protective film base film (sample 2) with a thickness of 50±5 μm.

[0045] Example 5: Preparation of the base film

[0046] Optical-grade PET chips, antistatic masterbatch A, and functional filler B were vacuum dried at 120°C for 6 hours to remove moisture. They were then premixed at a mass ratio of PET:A:B = 100:10:10 and mixed evenly using a high-speed mixer.

[0047] The uniformly mixed material is fed into a twin-screw extruder, melted and plasticized at 240-260℃, extruded, and then cast into sheets on a cooling roller at 45℃ after passing through a metering pump and a T-die, resulting in unstretched thick sheets.

[0048] The thick film was preheated at 90℃ for 30 s, then longitudinally stretched at 100℃ with a stretch ratio of 3.4 times. Next, it was transversely stretched at 115℃ with a stretch ratio of 3.8 times. Finally, the biaxially stretched film was heat-set at 225℃ for 10 s, cooled, and then wound up to obtain an intrinsically antistatic polarizer protective film base film (sample 3) with a thickness of 50±5 μm.

[0049] Comparative Example 1: Preparation of Base Film

[0050] Optical-grade PET chips, antistatic masterbatch A, and functional filler B were vacuum dried at 120°C for 6 hours to remove moisture. They were then premixed at a mass ratio of PET:A:B = 100:20:0 and mixed evenly using a high-speed mixer.

[0051] The uniformly mixed material is fed into a twin-screw extruder, melted and plasticized at 240-260℃, extruded, and then cast into sheets on a cooling roller at 45℃ after passing through a metering pump and a T-die, resulting in unstretched thick sheets.

[0052] The thick film was preheated at 90℃ for 30 s, then longitudinally stretched at 100℃ with a stretch ratio of 3.4 times. Next, it was transversely stretched at 115℃ with a stretch ratio of 3.8 times. Finally, the biaxially stretched film was heat-set at 225℃ for 10 s, cooled, and then wound up to obtain sample 4.

[0053] Comparative Example 2: Preparation of Base Film

[0054] Optical-grade PET chips, antistatic masterbatch A, and functional filler B were vacuum dried at 120°C for 6 hours to remove moisture. They were then premixed at a mass ratio of PET:A:B = 100:0:20 and mixed evenly using a high-speed mixer.

[0055] The uniformly mixed material is fed into a twin-screw extruder, melted and plasticized at 240-260℃, extruded, and then cast into sheets on a cooling roller at 45℃ after passing through a metering pump and a T-die, resulting in unstretched thick sheets.

[0056] The thick film was preheated at 90℃ for 30 s, then longitudinally stretched at 100℃ with a stretch ratio of 3.4 times. Next, it was transversely stretched at 115℃ with a stretch ratio of 3.8 times. Finally, the biaxially stretched film was heat-set at 225℃ for 10 s, cooled, and then wound up to obtain sample 5.

[0057] Comparative Example 3: Preparation of Base Film

[0058] Same as Example 1, except that antistatic masterbatch A was replaced with a commercially available antistatic agent (Cleriane HS-1 from Germany) to prepare sample 6.

[0059] Performance testing:

[0060] System performance tests were performed on all thin film samples (samples 1-6). The test methods and standards are as follows:

[0061] Transmittance and haze: Tested using a haze meter in accordance with GB / T 2410-2008.

[0062] Tensile strength: The tensile properties of the film were tested in accordance with GB / T 1040.3-2006.

[0063] Limiting Oxygen Index (LOI): Refer to GB / T 2406.2-2009 to evaluate the flame retardancy of materials.

[0064] Surface resistivity: According to GB / T 33398-2016, it was tested using a high resistance meter under the conditions of 23±2℃ and 50±5%RH.

[0065] Surface resistance durability (resistance to damp heat aging): The sample was placed in a constant temperature and humidity aging chamber at 85℃ and 85%RH for 500 hours, and the surface resistance after aging was tested.

[0066] The results are recorded in Table 1.

[0067] Table 1

[0068]

[0069] The table above records the antistatic and optical properties of the films of samples 1-6. With the increase of functional filler B, the transmittance decreased slightly and the haze increased slightly, but the transmittance was above 90% and the haze was below 1%, maintaining excellent optical properties. The addition of antistatic masterbatch A significantly improved the limiting oxygen index and surface antistatic properties of the film.

[0070] Observing samples 4 and 5, using antistatic masterbatch A alone (sample 4) yields superior bulk antistatic and flame-retardant properties; while using functional filler B alone (sample 5) results in relatively weaker antistatic effects and durability. However, when the two are used in a specific ratio (sample 2), the film exhibits a synergistic enhancement effect: the surface resistance decreases by more than an order of magnitude, and the performance degradation after damp heat aging is minimal, while maintaining high light transmittance and high flame retardancy. This indicates that antistatic masterbatch A is the foundation for constructing a permanently conductive network, while functional filler B further optimizes the efficiency and stability of surface conductivity; the two are complementary and indispensable. Observing sample 6, the addition of a commercially available antistatic agent reduces the surface resistance of the film to 1.3 × 10⁻⁶. 9Ω has better antistatic properties than the antistatic masterbatch of this application. However, the excessive use of commercial antistatic agents will result in poor compatibility with the film, leading to interface separation and a significant decrease in optical and mechanical properties. In addition, it does not have excellent flame retardancy.

[0071] Although the embodiments of the present invention have been disclosed above, they are not limited to the applications listed in the specification and embodiments. They can be applied to various fields suitable for the present invention. For those skilled in the art, other modifications can be easily made. Therefore, without departing from the general concept defined by the claims and their equivalents, the present invention is not limited to the specific details.

Claims

1. A method for preparing an intrinsically antistatic polarizer protective film base film, characterized in that, Comprising the following steps: S1, preparing antistatic masterbatch S1-1, in a reaction bottle, add N-methyldiethanolamine, Br(CH2)nCH3, toluene, heat reflux for 24h, after cooling, wash with ethyl acetate and dry; n is 2, 3 or 4 in the Br(CH2)nCH3; S1-2, dissolve the dried solid in deionized water, then add lithium bis(trifluoromethanesulfonimide) aqueous solution while stirring, after the completion of dropwise addition, stir at room temperature for 2h, then heat to 60℃ and continue to stir for 4h, extract the product with dichloromethane, dry the organic phase and distill under reduced pressure to obtain ionic liquid diol; S1-3, add terephthalic acid, ethylene glycol, 1,4-cyclohexane dimethanol and catalyst to the reactor, heat to 250℃ under nitrogen protection for 2-3h; then cool to 200℃, add ionic liquid diol and polycondensation catalyst antimony trioxide under stirring, stir at 200℃ for 30min; then heat to 270℃ and simultaneously vacuumize, the vacuum degree is less than 100Pa, carry out polycondensation reaction, when the viscosity reaches 0.60-0.65 dL / g, stop the reaction, cool to discharge, pellet to obtain antistatic masterbatch; S2, preparing functional filler Disperse nano-silica in anhydrous toluene and ultrasonically disperse uniformly, then add KH560, reflux and stir overnight under nitrogen protection, cool to room temperature; add polyether amine and catalytic amount of triethylamine, heat to 110℃ and react overnight, centrifugalize after cooling, wash with toluene, disperse the obtained solid in acetonitrile, add iodomethane and heat to 60℃ and react for 8h, centrifugalize, wash with ethanol and vacuum dry, grind to obtain; S3, vacuum dry the PET masterbatch, antistatic masterbatch and functional filler respectively, then mix uniformly according to certain proportion; S4, melt extrude the mixed material, cast, biaxially stretch, heat set to obtain polyester film, which is the protective film base film of polarizing sheet.

2. The method of producing a base film for an antistatic polarizing plate protective film according to claim 1, characterized by, The molar ratio of Br(CH2)nCH3, N-methyldiethanolamine and lithium bis(trifluoromethanesulfonimide) is 1:1:1.

1.

3. The method of producing a base film for an antistatic polarizing plate protective film according to claim 1, characterized by, The molar ratio of terephthalic acid, ethylene glycol and 1,4-cyclohexane dimethanol is 1:1.5:0.05; the addition amount of ionic liquid diol is 3-10wt% of the total monomer mass.

4. The method of producing a base film for an antistatic polarizing plate protective film according to claim 1, characterized by, The mass ratio of nano-silica, KH560, polyether amine and iodomethane is 1:0.5-1:1.5-2:1; the polyether amine is polyoxyethylene-polyoxypropylene block copolymer monoamine with number average molecular weight of 800-1200.

5. The method of producing a base film for an antistatic polarizing plate protective film according to claim 1, characterized by, The mass ratio of the PET masterbatch, antistatic masterbatch and functional filler is 100:10-20:2-10.

6. The method of producing a base film for an antistatic polarizing plate protective film according to claim 1, characterized by, The preparation process of step S4 is specifically: Melt extrude the mixed material at 220-280℃ to cast, cool the cast by 45℃ cooling roll, then preheat at 90℃, stretch longitudinally at 100℃, then stretch transversely at 115℃, finally heat set at 225℃ to obtain polyester film with thickness of 50±5μm, which is the protective film base film of polarizing sheet.

7. The method of producing a base film for an antistatic polarizing plate protective film according to claim 6, wherein The longitudinal stretching ratio is 3.2-3.6 times, and the transverse stretching ratio is 3.5-4.0 times.

8. The base film for a protective film of a polarizing plate against static electricity prepared by the production method according to any one of claims 1 to 7.

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