A protective base film for a polarizing plate and a method for producing the same

Abstract

The application discloses a protective base film for a polarizing plate and a preparation method thereof, and belongs to the technical field of optical display device protective films; the protective base film comprises an antistatic PET base material layer and a self-adhesive layer; the antistatic PET base material layer is made of optical-grade PET chips and antistatic master batches; the master batches are prepared by taking ionic liquid dihydric alcohol as a comonomer, and the master batches endow the base film with long-lasting and stable intrinsic antistatic properties; the self-adhesive layer is formed by melt blending polyurethane acrylate prepolymer, modified montmorillonite fillers and other matrix materials and auxiliaries in a specific ratio, and through an online UV curing process. Through innovative material design and integrated forming process, the prepared protective base film has excellent optical transparency, long-lasting antistatic property, suitable adhesive strength, clean peelability and excellent moisture and heat aging resistance, and the comprehensive performance is significantly better than that of a traditional glue-coated protective film, and the production process is more environmentally friendly and efficient.

Description

Technical Field

[0001] This invention relates to the field of protective film technology for optical display equipment, specifically to a protective base film for polarizers 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 existing technologies, the main method for preparing antistatic polarizer protective films is surface coating, such as coating the surface of a PET film with a polyurethane-acrylate coating containing an antistatic agent (e.g., CN118562402B, CN106675464B). This achieves both antistatic properties and good peel strength. However, the surface coating method is complex, the coating may affect the original optical properties and thickness uniformity of the film, and there is a long-term risk of coating wear or peeling. CN105607176B provides a self-adhesive protective film for polarizers, comprising an adhesive layer, a core layer, and a surface layer for single contact. The adhesive layer ensures that the protective film will not develop bubbles or wrinkles after long-term use, adheres firmly, and is easy to peel off from the polarizer without leaving glue residue or dirt. This solution uses a three-layer co-extrusion process to prepare the self-adhesive protective film, which is simple and has good repeatability. However, this solution does not address the antistatic properties of the film and fails to solve the problem of antistatic properties of the PET base film. In this technical solution, the applicant attempted to add some conventional small molecule or high molecular weight antistatic agents. However, in actual production, it was found that after blending with the adhesive layer and extruding, the antistatic agent often faced problems such as poor compatibility with the matrix, easy migration and precipitation (leading to the decay of antistatic properties and the increase of haze), or high addition amount damaging mechanical properties. Summary of the Invention

[0005] To address the shortcomings of existing technologies, this invention designs an antistatic PET base film and forms a self-adhesive layer on its surface through melt extrusion casting combined with photocuring, ultimately obtaining a composite protective film with excellent comprehensive performance.

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

[0007] A protective base film for polarizers includes an antistatic PET substrate layer and a self-adhesive layer; the antistatic PET substrate layer comprises optical-grade PET chips and antistatic masterbatch; the self-adhesive layer is formed by melt extrusion and casting curing of the following materials in parts by weight:

[0008] 20-35 parts of polyurethane acrylate prepolymer;

[0009] 10-18 parts of hydrogenated styrene-isoprene-styrene block copolymer;

[0010] 10-25 parts of polypropylene;

[0011] 20-30 parts of metallocene polyethylene;

[0012] Photoinitiator 0.5-3 parts;

[0013] 2-5 parts compatibilizer;

[0014] 3-8 parts of modified montmorillonite filler;

[0015] Other additives: 0.2-1 part;

[0016] The preparation process of the antistatic masterbatch is as follows:

[0017] S1. In a reaction flask, add N-methyldiethanolamine, Br(CH2)nCH3, and toluene, heat under reflux and stir for 24 h, cool, wash with ethyl acetate and dry.

[0018] S2. 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.

[0019] S3. Add terephthalic acid, ethylene glycol, 1,4-cyclohexanediol, and tetrabutyl titanate to the reactor. Under nitrogen protection, heat to 250℃ and react for 2-3 hours. Then cool to 200℃, add ionic liquid diol and antimony trioxide as a polycondensation catalyst while stirring. Stir at 200℃ for 30 minutes. Then heat to 270℃ and simultaneously apply a vacuum of less than 100 Pa to carry out the polycondensation 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.

[0020] The polyurethane acrylate prepolymer is prepared by polycondensation of polycaprolactone polyol and isophorone diisocyanate followed by end-capping with hydroxyethyl methacrylate.

[0021] The modified montmorillonite filler is obtained by intercalation reaction of nano-montmorillonite with carboxyl-containing aromatic quaternary ammonium salts.

[0022] Furthermore, in the preparation process of the antistatic masterbatch, n in Br(CH2)nCH3 is 2, 3 or 4; the molar ratio of Br(CH2)nCH3, N-methyldiethanolamine and lithium bis(trifluoromethanesulfonylimide) is 1:1:1.1.

[0023] Furthermore, in the preparation process of the antistatic masterbatch, 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 3~10wt% of the total monomer mass.

[0024] Furthermore, the preparation process of the polyurethane acrylate is as follows:

[0025] The vacuum-dehydrated polycaprolactone polyol was added to the reactor, along with isophorone diisocyanate, a catalyst, and a polymerization inhibitor. Under nitrogen protection, the mixture was heated to 75-80°C and reacted for 2-3 hours. Hydroxyethyl methacrylate was mixed with acetone and added dropwise to the reactor, and the reaction was continued for 4-5 hours. The solvent was removed by rotary evaporation, and the resulting viscous liquid was the polyurethane acrylate prepolymer.

[0026] Furthermore, the polycaprolactone polyol has a number average molecular weight of 1000-2000, and its molar ratio with isophorone diisocyanate and hydroxyethyl methacrylate is 1:2.1-2.4:1.2-1.5.

[0027] Furthermore, the catalyst is dibutyltin dilaurate; the polymerization inhibitor is p-hydroxyanisole.

[0028] Furthermore, the preparation process of the modified montmorillonite filler is as follows:

[0029] 1) Preparation of carboxyl-containing aromatic quaternary ammonium salts

[0030] Add p-chloromethylbenzoic acid and N,N-dimethyloctadecylamine to a reaction flask, add anhydrous ethanol and stir until well mixed, heat to 75°C under nitrogen protection, reflux overnight, cool and evaporate by rotary evaporation, wash with ethyl acetate and dry under vacuum to obtain the product;

[0031] 2) Disperse sodium montmorillonite in deionized water using ultrasound to obtain a suspension with a solid content of 5%, and heat it to 70°C for later use. Dissolve the carboxyl-containing aromatic quaternary ammonium salt in ethanol solution, and then slowly add it dropwise to the suspension. After the addition is complete, continue stirring and reacting for 8 hours. Adjust the pH to 6~6.5 with sodium hydroxide solution. After the reaction is complete, filter while hot, rinse with 70°C hot water, wash with ethanol 2~3 times, vacuum dry, grind and sieve to obtain the final product.

[0032] Furthermore, the photoinitiator is TPO; the compatibilizer is an epoxy-based polyolefin elastomer; and the other additives include equal masses of antioxidant 1010 and leveling agent BYK-361.

[0033] The present invention further provides a method for preparing the protective base film for polarizers as described above, comprising the following steps:

[0034] S1. The metered modified montmorillonite filler and compatibilizer are premixed in a high-speed mixer for 5 minutes, then melt-extruded and granulated in a twin-screw extruder, and then initially mixed with all solid components except polyurethane acrylate prepolymer and photoinitiator.

[0035] S2. The initial mixture is fed into a twin-screw extruder equipped with a side liquid injection system. The polyurethane acrylate prepolymer is mixed with the photoinitiator and then injected into the middle section of the extruder through a liquid injection pump. The extruder temperature is set to 135~140℃. The extruded strip is water-cooled, pelletized and dried to obtain self-adhesive composite granules.

[0036] S3. The dried optical-grade PET chips and antistatic masterbatch are mixed in a high-speed machine at a mass ratio of 70~85:15~30. Then, the mixture is melt-extruded, cast, and biaxially stretched by a single-screw extruder to obtain a PET base film with a thickness controlled at 40~50μm.

[0037] S4. The PET base film is drawn to the composite roller and preheated to 50°C; then the obtained self-adhesive composite granules are melt-extruded and cast onto the surface of the PET base film through an extruder, with a composite pressure of 0.3-0.5 MPa.

[0038] S5. The composite film is immediately placed in a nitrogen-protected UV curing chamber for UV curing. A release film is then applied to its surface, and the film is cured at 35-40°C for 24-48 hours to obtain a protective base film for polarizers.

[0039] Compared with the prior art, the beneficial effects of the present invention are:

[0040] 1. By introducing ionic liquid diols into the PET backbone through copolymerization, an "intrinsic" antistatic system is formed, avoiding the migration and precipitation problems of small molecule antistatic agents and ensuring good durability. The use of 1,4-cyclohexanediethanol can improve the processability and optical properties of PET. The PET film made by mixing it with optical grade PET chips can maintain optical properties while having durable and stable antistatic properties.

[0041] 2. The modified montmorillonite used in the self-adhesive layer is obtained by intercalating sodium-based montmorillonite with an aromatic quaternary ammonium salt containing carboxyl groups. The long alkyl chain ensures compatibility, and the carboxyl groups after salt formation provide ion conduction sites to assist in antistatic properties. The aromatic structure can enhance the interaction with the hard segments in polyurethane acrylate. The compatibilizer is used to pre-blend the modified montmorillonite to enhance its compatibility with the self-adhesive layer system, effectively inhibiting phase separation and improving long-term resistance to humid heat aging.

[0042] 3. The composite film is prepared by using an integrated process of "melt co-extrusion casting + online UV curing", which avoids the complicated steps such as solvent recovery and multiple baking required by traditional coating processes. The interface is firmly bonded, no additional primer treatment is required, and there will be no glue residue or stains. Detailed Implementation

[0043] 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.

[0044] 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.

[0045] 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:

[0046]

[0047] Example: A protective base film for polarizers

[0048] A protective base film for polarizing films, characterized in that it comprises an antistatic PET substrate layer and a self-adhesive layer; the antistatic PET substrate layer comprises optical-grade PET chips and antistatic masterbatch; the self-adhesive layer is formed by melt extrusion and casting curing of the following materials in parts by weight:

[0049] 20-35 parts of polyurethane acrylate prepolymer;

[0050] SEPS 10-18 servings;

[0051] PP 10~25 portions;

[0052] 20-30 parts of mPE;

[0053] TPO 0.5~3 parts;

[0054] GMA-g-POE 2-5 parts;

[0055] 3-8 parts of modified montmorillonite filler;

[0056] Antioxidant 1010: 0.1-0.5 parts;

[0057] Leveling agent BYK-361, 0.1~0.5 parts;

[0058] The preparation process of the antistatic masterbatch is as follows:

[0059] S1. In a reaction flask, add 1 mol N-methyldiethanolamine, 1 mol 1-bromobutane and 100 mL toluene as solvent, heat to 60 °C, reflux for 24 h; cool to room temperature, filter, wash thoroughly with ethyl acetate, and vacuum dry to obtain a solid powder;

[0060] S2. 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.

[0061] S3. 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.

[0062] The preparation process of polyurethane acrylate prepolymer (PUA) is as follows:

[0063] 500g of vacuum-dehydrated polycaprolactone polyol was added to a reactor, along with 250g of isophorone diisocyanate, 0.85g of DBTDL, and 1.5g of MEHQ. The mixture was heated to 80℃ and reacted for 3 hours under nitrogen protection. 88g of hydroxyethyl methacrylate was mixed with 150g of acetone and added dropwise to the reactor, and the reaction was continued for 5 hours. The solvent was removed by rotary evaporation, and the resulting viscous liquid was the polyurethane acrylate prepolymer (viscosity approximately 11000 mPa·s, moisture ≤0.05%).

[0064] The preparation process of modified montmorillonite filler is as follows:

[0065] 1) Preparation of carboxyl-containing aromatic quaternary ammonium salts

[0066] Add 16.7g of p-chloromethylbenzoic acid and 31.3g of N,N-dimethyloctadecylamine to a reaction flask, add 150ml of anhydrous ethanol and stir until well mixed. Under nitrogen protection, heat to 75℃ and reflux overnight. After cooling, evaporate by rotary evaporation, wash with ethyl acetate and dry under vacuum to obtain the product.

[0067] 2) Disperse 100g of sodium montmorillonite in 2000ml of deionized water using ultrasonication to obtain a suspension with a solid content of 5%, and heat it to 70℃ for later use; dissolve 60g of carboxyl-containing aromatic quaternary ammonium salt in 500ml of ethanol solution, and then slowly add it dropwise to the suspension. After the addition is complete, continue stirring and reacting for 8 hours; adjust the pH to 6.5 with sodium hydroxide solution; after the reaction is complete, filter while hot, rinse with 70℃ hot water and then wash three times with ethanol, vacuum dry, grind and sieve to obtain the final product.

[0068] Example 1: A protective base film for polarizers

[0069] S1. The modified montmorillonite filler and GMA-g-POE are premixed in a high-speed mixer for 5 minutes, then melt-extruded and granulated in a twin-screw extruder, and then initially mixed with all solid components except polyurethane acrylate prepolymer and photoinitiator.

[0070] S2. The initial mixture is fed into a twin-screw extruder equipped with a side liquid injection system. The polyurethane acrylate prepolymer is mixed with the photoinitiator and then injected into the middle section of the extruder through a liquid injection pump. The extruder temperature is set to 135~140℃. The extruded strip is water-cooled, pelletized and dried to obtain self-adhesive composite granules.

[0071] S3. The dried optical-grade PET chips and antistatic masterbatch are mixed in a high-speed machine at a mass ratio of 70:30. Then, the mixture is melt-extruded, cast, and biaxially stretched by a single-screw extruder to obtain a PET base film with a thickness controlled at 40~50μm.

[0072] S4. The PET base film is drawn to the composite roller and preheated to 50°C; then the obtained self-adhesive composite granules are melt-extruded and cast onto the surface of the PET base film through an extruder, with a composite pressure of 0.3-0.5 MPa.

[0073] S5. The composite film is immediately placed in a nitrogen-protected UV curing chamber for UV curing. A release film is then placed on its surface and cured at 35°C for 48 hours to obtain a protective base film for polarizers.

[0074] The self-adhesive composite granules are composed of the following raw materials: 35 parts PUA, 10 parts SEPS, 15 parts PP, 23 parts mPE, 3 parts TPO, 5 parts GMA-g-POE, 8 parts modified montmorillonite filler, 0.5 parts antioxidant 1010, and 0.5 parts leveling agent BYK-361.

[0075] Example 2: A protective base film for polarizers

[0076] The preparation process is the same as in Example 1, except that the composition of each raw material in the self-adhesive composite granules is as follows: 30 parts PUA, 10 parts SEPS, 17.5 parts PP, 26 parts mPE, 2.5 parts TPO, 5 parts GMA-g-POE, 8 parts modified montmorillonite filler, 0.5 parts antioxidant 1010, and 0.5 parts leveling agent BYK-361.

[0077] Example 3: A protective base film for polarizers

[0078] The preparation process is the same as in Example 1, except that the composition of each raw material in the self-adhesive layer composite granules is as follows: 25 parts PUA, 13 parts SEPS, 18 parts PP, 28.5 parts mPE, 1.5 parts TPO, 5 parts GMA-g-POE, 8 parts modified montmorillonite filler, 0.5 parts antioxidant 1010, and 0.5 parts leveling agent BYK-361.

[0079] Example 4: A protective base film for polarizers

[0080] The preparation process is the same as in Example 1, except that the composition of each raw material in the self-adhesive composite granules is as follows: 20 parts PUA, 18 parts SEPS, 22 parts PP, 33 parts mPE, 1 part TPO, 2 parts GMA-g-POE, 3 parts modified montmorillonite filler, 0.5 parts antioxidant 1010, and 0.5 parts leveling agent BYK-361.

[0081] Example 5: A protective base film for polarizers

[0082] The preparation process is the same as in Example 2, except that the mass ratio of optical-grade PET chips to antistatic masterbatch is 80:20.

[0083] Example 6: A protective base film for polarizers

[0084] The preparation process is the same as in Example 2, except that the mass ratio of optical-grade PET chips to antistatic masterbatch is 85:15.

[0085] Comparative Example 1: A PET film

[0086] The preparation process is the same as in Example 2, except that the PET base film layer does not use antistatic masterbatch, but only pure optical grade PET; the self-adhesive layer formulation is the same as in Example 2.

[0087] Comparative Example 2: A PET film

[0088] The preparation process is the same as in Example 2, except that the composition of each raw material in the self-adhesive layer composite granules is as follows: 30 parts vinyl polyacrylate (refer to CN105607176B - a self-adhesive protective film for polarizing film), 10 parts SEPS, 18 parts PP, 28 parts mPE, 5 parts GMA-g-POE, 8 parts modified montmorillonite filler, 0.5 parts antioxidant 1010, and 0.5 parts leveling agent BYK-361.

[0089] Comparative Example 3: A PET film

[0090] The preparation process is the same as in Example 2, except that the modified montmorillonite filler in the self-adhesive composite granules is replaced with untreated sodium-based montmorillonite.

[0091] The PET film prepared above was subjected to performance testing. The release film was removed during the testing, and the testing standards are as follows:

[0092] Transmittance and haze: GB / T 2410-2008, tested using a haze meter.

[0093] 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.

[0094] Adhesion performance: The protective base film was cut into 300 mm × 25 mm size, attached to the surface of the polarizer, and the peel force was tested using an electronic universal testing machine at a test angle of 180° and a tensile speed of 300 mm / min.

[0095] Durability:

[0096] The protective base film adhesive layer is attached to the surface of the polarizer. After being placed at 100℃ and 90% humidity for 12 hours, the protective base film is observed to see if there are any wrinkles, delamination, or bubbles on the surface of the polarizer. If none are found, the high temperature and high humidity resistance is good and is recorded as good; otherwise, it is recorded as poor.

[0097] The test results are recorded in Table 1.

[0098] Table 1

[0099]

[0100] Note: The surface resistance of Comparative Example 1 is >10. 14 .

[0101] Based on the data in Table 1, analysis of Examples 1-4 shows that with the base film unchanged, the changes in optical performance and surface resistance are not significant. However, a reduction in the PUA content in the self-adhesive layer leads to a decrease in peel strength. Referring to patent CN105607176B, using vinyl polyacrylate instead of the PUA in this application, the peel strength of Comparative Example 2 is significantly lower than that of Example 2 at the same dosage, and its durability is also generally poor. This is because the self-adhesive layer system composed of a large amount of vinyl polyacrylate has poor compatibility and weak interface stability, resulting in insufficient heat resistance, and is also manifested in decreased light transmittance and increased haze. Combining Examples 5 and 6, it is concluded that the antistatic masterbatch in the PET base film plays a decisive role in the surface resistance of the final protective base film. The more antistatic masterbatch, the lower the surface resistance and the better the antistatic properties. Although the increase in antistatic masterbatch leads to a slight decrease in optical performance, the overall result is light transmittance >90% and haze <1%, indicating that the addition of antistatic masterbatch and the adhesion of the self-adhesive layer not only maintain excellent optical performance but also provide superior antistatic properties and peel strength. Observing Comparative Example 1, its base film layer is made of optical-grade PET, thus lacking excellent antistatic properties. Furthermore, due to the lack of modification, the pure PET film is more prone to adsorbing moisture on its surface during high-temperature and high-humidity testing, adversely affecting the self-adhesive layer and resulting in generally poor durability. Observing Comparative Example 3, unmodified montmorillonite tends to agglomerate in the matrix, leading to a significant decrease in durability even with the help of a compatibilizer. In addition, although the antistatic properties are mainly provided by the antistatic masterbatch in the PET base film, the modified montmorillonite filler also provides additional ion conduction sites, synergistically achieving efficient and long-lasting antistatic properties. Therefore, when using unmodified montmorillonite, its surface resistivity also increases accordingly.

[0102] 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 protective base film for polarizers, characterized in that, It comprises an antistatic PET substrate layer and a self-adhesive layer; the raw materials for preparing the antistatic PET substrate layer are optical grade PET chips and antistatic masterbatch; the self-adhesive layer is formed by melt extrusion, casting and curing of the following materials in parts by weight: Polyurethane acrylate prepolymer 20~35 parts; Hydrogenated styrene-isoprene-styrene block copolymer 10~18 parts; Polypropylene 10~25 parts; Metallocene polyethylene 20~30 parts; Photoinitiator 0.5~3 parts; Compatibilizer 2~5 parts; Modified montmorillonite filler 3~8 parts; Other auxiliaries 0.2~1 parts; In the preparation process of the antistatic masterbatch: S1, in a reaction bottle, add N-methyldiethanolamine, Br(CH2)nCH3, toluene, heat reflux and stir for 24 h, then wash with ethyl acetate and dry; n is 2, 3 or 4 in Br(CH2)nCH3; S2, dissolve the dried solid in deionized water, then add lithium bis(trifluoromethanesulfonimide) aqueous solution while stirring, stir at room temperature for 2 h after the addition is completed, then heat to 60℃ and continue to stir for 4 h, extract the product with dichloromethane, dry the organic phase and distill under reduced pressure to obtain ionic liquid diol; S3, add terephthalic acid, ethylene glycol, 1,4-cyclohexane dimethanol and tetrabutyl titanate 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 30 min; 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 and discharge, granulate to obtain the antistatic masterbatch; The polyurethane acrylate prepolymer is prepared by polycondensation of polycaprolactone polyol and isophorone diisocyanate, and then end-capped with hydroxyethyl methacrylate; The modified montmorillonite filler is obtained by intercalation reaction of carboxyl-containing aromatic quaternary ammonium salt on nano-montmorillonite.

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

1.

3. The protective base film for a polarizing plate according to claim 1, wherein In the preparation process of the antistatic masterbatch, the molar ratio of terephthalic acid, ethylene glycol and 1,4-cyclohexane dimethanol is 1:1.5:0.05; the amount of ionic liquid diol added is 3~10wt% of the total monomer mass.

4. The protective base film for a polarizing plate according to claim 1, wherein The preparation process of the polyurethane acrylate prepolymer is as follows: After vacuum dewatering, the polycaprolactone polyol is added to the reaction kettle, isophorone diisocyanate and catalyst and polymerization inhibitor are also added, under nitrogen protection, heat to 75~80℃ and react for 2~3h; mix hydroxyethyl methacrylate with acetone and add to the reaction kettle, continue to react for 4~5h; remove the solvent by rotary evaporation to obtain a viscous liquid, which is the polyurethane acrylate prepolymer.

5. The protective base film for a polarizing plate according to claim 4, wherein The number average molecular weight of the polycaprolactone polyol is 1000-2000, and the molar ratio of the polycaprolactone polyol, isophorone diisocyanate, and hydroxyethyl methacrylate is 1:2.1-2.4:1.2-1.

5.

6. The protective base film for a polarizing plate according to claim 4, wherein The catalyst is dibutyl tin dilaurate; and the polymerization inhibitor is p-hydroxyanisole.

7. The protective base film for a polarizing plate according to claim 1, wherein The preparation process of the modified montmorillonite filler is as follows: 1) Preparation of carboxyl-containing aromatic quaternary ammonium salt A reaction bottle is added with p-chloromethylbenzoic acid and N,N-dimethyloctadecylamine, anhydrous ethanol is added and stirred to mix uniformly, and then the temperature is raised to 75 DEG C under nitrogen protection, and refluxed overnight. After cooling, rotary evaporation is performed, washed with ethyl acetate, and then vacuum dried to obtain the product; 2) The sodium-based montmorillonite is ultrasonically dispersed in deionized water to obtain a suspension with a solid content of 5%, and then heated to 70 DEG C for standby use. The carboxyl-containing aromatic quaternary ammonium salt is dissolved in an ethanol solution, and then slowly added to the suspension. After the addition is completed, the stirring is continued for 8 hours. The pH is adjusted to 6-6.5 with a sodium hydroxide solution. After the reaction is completed, hot filtration is performed, washed with hot water at 70 DEG C, and then washed with ethanol for 2-3 times. Vacuum drying and sieving are performed to obtain the product.

8. The protective base film for a polarizing plate according to claim 1, wherein The photoinitiator is TPO; the compatilizer is an epoxy-based polyolefin elastomer; and the other auxiliary agents include equal mass of antioxidant 1010 and leveling agent BYK-361.

9. The preparation method of the protective film for polarizing plate according to any one of claims 1-8, comprising the following steps: S1, a measured amount of modified montmorillonite filler and compatilizer are premixed in a high-speed mixer for 5 minutes, and then melt-extruded and pelletized in a twin-screw extruder, and then all solid components except the polyurethane acrylate prepolymer and photoinitiator are initially mixed; S2, the initial mixture is fed into a twin-screw extruder equipped with a lateral liquid injection system, the polyurethane acrylate prepolymer and photoinitiator are mixed and then injected into the middle section of the extruder through a liquid injection pump, the temperature of the extruder is set to 135-140 DEG C, and the extruded strip is water-cooled, cut and dried to obtain self-adhesive layer composite pellets; S3, the dried optical-grade PET chip and antistatic masterbatch are mixed in a high-speed mixer according to a mass ratio of 70-85:15-30, and then melt-extruded, cast and bidirectionally stretched in a single-screw extruder to obtain a PET base film with a thickness of 40-50 μm; S4, the PET base film is pulled to a compounding roller and preheated to 50 DEG C; then the obtained self-adhesive layer composite pellets are melt-extruded and cast onto the surface of the PET base film through an extruder, and the compounding pressure is 0.3-0.5 MPa; S5, the compounded film immediately enters a UV curing box under nitrogen protection for UV light curing, and a release film is covered on the surface, and then aged at 35-40 DEG C for 24-48 hours to obtain the protective film for polarizing plate.

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