A low alignment angle, high heat resistance release film base film for polarizers and its preparation method.

Abstract

This case relates to a low alignment angle, high heat resistance release film base for polarizers and its preparation method. The release film base uses optical-grade PET chips as the main material, with added modified PET and modified SiO2 fillers of a specific structure, and is manufactured through co-extrusion casting and a unique three-stage stretching process. The modified PET, by introducing 2-(pyridin-3-yl) terephthalic acid comonomer and ionic liquid intercalated montmorillonite, improves the rigidity and heat resistance of the molecular chain and provides heterogeneous nucleation sites. The modified SiO2 filler, through surface grafting of terpolymers, achieves good compatibility with the matrix and internal lubrication. The preparation method employs a three-stage stretching sequence of "transverse-vertical-transverse" and progressively increasing temperature control to synergistically regulate the orientation and crystallization of the molecular chains. Ultimately, an optical-grade polyester film with low alignment angle, low transverse heat shrinkage, and high surface adhesion is obtained, making it particularly suitable for manufacturing release films for high-end polarizers.

Description

Technical Field

[0001] This invention relates to the field of protective film technology for optical display equipment, specifically to a low alignment angle, high heat resistance release film 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 release film, as a protective layer for the pressure-sensitive adhesive, needs to be peeled off during use, but it must be peeled off without removing the adhesive along with it. Therefore, the release film requires controllable release force and cleanliness. Common raw materials in polarizer release film production include polyester base film and release agent, with the polyester base film being the key material. However, the alignment angle of currently used polyester films is relatively large. During quality monitoring of polarizers, a high alignment angle leads to phase delay and angular shift of light, easily affecting the final test results. Existing technologies address the alignment angle of polyester films by improving both process equipment and raw materials. Examples include patents CN106433502A, CN113752600A, and CN116694038B. These patented solutions effectively reduce the alignment angle, meeting the requirements for polarizer use. However, it also overlooks the fact that polyester film, as the base film for release film, also needs high thermal dimensional stability, i.e., low shrinkage rate, and high adhesion of the release agent. Summary of the Invention

[0004] To address the shortcomings of existing technologies, this invention starts with the raw materials themselves and combines process improvements to prepare a polyester film that meets the requirements of low heat shrinkage rate and high release agent adhesion for release film base films, while also satisfying the polarizer's requirement for a low alignment angle.

[0005] To achieve the above objectives, the present invention provides the following technical solution:

[0006] A low alignment angle, high heat-resistant release film base for polarizers is disclosed. The release film base is made primarily of optical-grade PET chips, with modified PET and modified SiO2 fillers added. The film is co-extruded, cast, and then subjected to three-stage stretching, heat setting, and corona treatment.

[0007] The modified PET is prepared by introducing 2-(pyridin-3-yl) terephthalic acid to replace part of the terephthalic acid during the PET polymerization process, and then blending it with 1-carboxyethyl-3-methylimidazolium chloride intercalated montmorillonite and melt extruding it after polymerization.

[0008] The modified SiO2 filler is obtained by free radical polymerization of a terpolymer of lauryl acrylate, glycidyl methacrylate and N-(4-vinylphenyl)acetamide on the surface of KH570 modified SiO2.

[0009] Furthermore, the weight fractions of the optical-grade PET chips, modified PET, and nanofillers are 100 parts, 8-15 parts, and 3-8 parts, respectively.

[0010] Furthermore, the preparation process of the 1-carboxyethyl-3-methylimidazolium chloride intercalated montmorillonite is as follows:

[0011] Add sodium montmorillonite and deionized water to a beaker, sonicate to disperse it evenly, then transfer it to a water bath and heat it to 60-70℃. While stirring, slowly add 20% by weight of 1-carboxyethyl-3-methylimidazolium chloride of sodium montmorillonite. After the addition is complete, keep it at the temperature for 2-3 hours, filter, wash with water, dry, and grind to obtain the final product.

[0012] Furthermore, the modified PET is prepared by the following method:

[0013] Ethylene glycol and 2-(pyridin-3-yl)terephthalic acid were added to a reactor, and tetrabutyl titanate was added as a catalyst. The temperature was raised to 200-230℃ for esterification. After reacting for 2-3 hours, terephthalic acid was added, and the temperature was raised to 250℃. After reacting for 2-4 hours, antimony glycolate was added as a catalyst. The pressure in the reactor was controlled at 0.3 MPa, and the temperature was raised to 270℃ for 2-3 hours. After the reaction was completed, the product was discharged after natural cooling to obtain poly(2-(pyridin-3-yl)terephthalic acid-ethylene glycol ester. Then, it was mixed with 1-carboxyethyl-3-methylimidazolium chloride intercalated montmorillonite in a high-speed mixer until homogeneous. The mixture was then melt-blended and granulated using a twin-screw extruder to obtain the final product.

[0014] Furthermore, the molar ratio of terephthalic acid, 2-(pyridin-3-yl)terephthalic acid, and ethylene glycol is 100:10~20:120; the mass ratio of poly(2-(pyridin-3-yl)terephthalic acid-ethylene glycol ester to 1-carboxyethyl-3-methylimidazolium chloride intercalated montmorillonite is 9~9.5:0.5~1.

[0015] Furthermore, the preparation steps of the modified SiO2 filler are as follows:

[0016] 1) A certain amount of nano-SiO2 particles were first activated with potassium hydroxide, then dispersed in deionized water and an equal mass of KH570 was added. The mixture was stirred at 50°C for 24 hours, filtered, washed, dried and ground to obtain KH570 modified SiO2 powder.

[0017] 2) KH570 modified SiO2 powder was dispersed in THF, and lauryl acrylate, glycidyl methacrylate and N-(4-vinylphenyl)acetamide were added in sequence. AIBN of 1% of the total monomer mass was added as an initiator. The reaction was carried out at 70℃ under nitrogen protection for 12 h. After the reaction was completed, the mixture was centrifuged and washed three times with THF to remove the homopolymer. After vacuum drying, the modified SiO2 filler was obtained.

[0018] Furthermore, the molar ratio of lauryl acrylate, glycidyl methacrylate, and N-(4-vinylphenyl)acetamide is 50~70:15~25:15~25; and their total mass is 80%~120% of the KH570 modified SiO2 powder.

[0019] The second objective of this invention is to provide a method for preparing a low alignment angle, high heat-resistant release film base film for polarizers as described above, comprising the following steps:

[0020] S1. Weigh and measure the optical-grade PET chips, modified PET, and modified SiO2 filler, place them in a high-speed mixer and mix them, then dry them under vacuum.

[0021] S2. The dried mixture is fed into a single screw extruder, and the extrusion temperature is set to 255~285℃. After being extruded through the die, it is rapidly cooled on the cooling roller to form a cast sheet.

[0022] S3. Preheat the cast film to 90℃ and perform a first transverse stretching with a stretching ratio of 1.5 to 2.5 times; then perform a longitudinal stretching with a stretching ratio of 3.2 to 5 times; perform a second transverse stretching on the longitudinally stretched film with a stretching ratio of 2.5 to 3.5 times; the three-stage stretching temperature increases step by step, with a total transverse stretching ratio of 3.75 to 6 times.

[0023] S4. Heat set the stretched film at 190~220℃ for 5~15s, slowly cool it down to 150℃ and keep it at that temperature for 10~30min, then cool it down to room temperature, and finally perform corona treatment; then pull and wind it up.

[0024] Furthermore, in step S2, the temperatures of each section of the extruder are set as follows: Zone 1: 255~270℃, Zone 2: 275~280℃, Zone 3: 280~285℃, Zone 4: 280~285℃, and Die head: 275~280℃.

[0025] Further, in step S3, the temperature for the first transverse stretching is set to 95~105℃; the temperature for the longitudinal stretching is set to 105~115℃; and the temperature for the second transverse stretching is set to 120~135℃.

[0026] Compared with the prior art, the beneficial effects of the present invention are as follows: 1. By introducing a rigid comonomer containing a pyridine ring and modified PET with intercalated montmorillonite, and working synergistically with the three-stage stretching process, a highly uniform orientation of the molecular chains in the plane is achieved, effectively reducing optical anisotropy and meeting the requirements of precision optical inspection of polarizers; 2. The montmorillonite and modified SiO2 filler added to the modified PET provide rigidity, improve the heat resistance of the film, and ensure dimensional stability during polarizer processing and use; the terpolymer grafted on the surface of the modified SiO2 filler improves the dispersion of the filler in the PET matrix, greatly enhancing the interfacial bonding force between the filler and the matrix; on the other hand, the abundant active sites can form stronger chemical bonds or hydrogen bonds, thereby strengthening the adhesion with the release agent and improving the surface adhesion between the film and the release agent coating. 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: A low alignment angle, high heat resistance release film base film for polarizers

[0032] The release film base film is made by co-extruding and casting 100 parts by weight of optical-grade PET chips as the main material, adding 8-15 parts by weight of modified PET and 3-8 parts by weight of modified SiO2 filler, followed by three-stage stretching, heat setting, and corona treatment.

[0033] The modified PET is prepared by the following method:

[0034] 1) Add sodium montmorillonite and deionized water to a beaker, sonicate to disperse it evenly, then transfer it to a water bath and heat it to 60-70℃. While stirring, slowly add 20% by weight of 1-carboxyethyl-3-methylimidazolium chloride of sodium montmorillonite. After the addition is complete, keep it at the temperature for 2-3 hours, filter, wash with water, dry, and grind to obtain 1-carboxyethyl-3-methylimidazolium chloride intercalated montmorillonite.

[0035] 2) Ethylene glycol and 2-(pyridin-3-yl)terephthalic acid were added to the reactor, and a catalytic amount of tetrabutyl titanate was added as a catalyst. The temperature was raised to 230°C for esterification. After 2 hours of reaction, terephthalic acid was added, and the temperature was raised to 250°C. After 4 hours of reaction, a catalytic amount of antimony glycolate was added as a catalyst. The pressure in the reactor was controlled at 0.3 MPa, and the temperature was raised to 270°C for 2 hours. After the reaction was completed, the product was discharged after natural cooling to obtain poly(2-(pyridin-3-yl)terephthalic acid-ethylene glycol ester. Then, it was mixed with 1-carboxyethyl-3-methylimidazolium chloride intercalated montmorillonite in a high-speed mixer. The mixture was then melt-blended and granulated using a twin-screw extruder to obtain the final product.

[0036] The molar ratio of terephthalic acid, 2-(pyridin-3-yl)terephthalic acid, and ethylene glycol is 100:10~20:120; the mass ratio of poly(2-(pyridin-3-yl)terephthalic acid-ethylene glycol ester) to 1-carboxyethyl-3-methylimidazolium chloride intercalated montmorillonite is 9~9.5:0.5~1.

[0037] The preparation steps of the modified SiO2 filler are as follows:

[0038] 1) A certain amount of nano-SiO2 particles were first activated with 2 mol / L potassium hydroxide, then dispersed in deionized water and an equal mass of KH570 was added. The mixture was stirred at 50℃ for 24 h, filtered, washed, dried and ground to obtain KH570 modified SiO2 powder.

[0039] 2) KH570 modified SiO2 powder was dispersed in THF, and lauryl acrylate, glycidyl methacrylate and N-(4-vinylphenyl)acetamide were added in sequence. AIBN of 1% of the total monomer mass was added as an initiator. The reaction was carried out at 70℃ under nitrogen protection for 12 h. After the reaction was completed, the mixture was centrifuged and washed three times with THF to remove the homopolymer. After vacuum drying, the modified SiO2 filler was obtained.

[0040] The molar ratio of lauryl acrylate, glycidyl methacrylate, and N-(4-vinylphenyl)acetamide is 50~70:15~25:15~25; the sum of their masses is 80%~120% of the KH570 modified SiO2 powder.

[0041] Example 1: A low alignment angle, high heat resistance release film base film for polarizers

[0042] S1. Weigh 100 parts by weight of optical grade PET chips, 8 parts by weight of modified PET, and 3 parts by weight of modified SiO2 filler and mix them in a high-speed mixer, then dry them under vacuum.

[0043] S2. The dried mixture is fed into a single-screw extruder, and the extrusion temperature is set to 255~285℃ (the temperature of each section of the extruder is set as follows: Zone 1: 255~270℃, Zone 2: 275~280℃, Zone 3: 280~285℃, Zone 4: 280~285℃, Die: 275~280℃). After being extruded through the die, it is rapidly cooled on the cooling roller to form a cast sheet.

[0044] S3. Preheat the cast film to 90℃, perform a first transverse stretching at 95℃ with a stretching ratio of 1.6 times; then perform a longitudinal stretching at 110℃ with a stretching ratio of 4.2 times; finally, perform a second transverse stretching at 125℃ with a stretching ratio of 2.5 times. The three-stage stretching temperature increases progressively, and the total transverse stretching ratio (the product of the two stretching ratios) is 4 times.

[0045] S4. Heat set the stretched film at 190°C for 15 seconds, slowly cool it down to 150°C and hold it for 30 minutes, then cool it down to room temperature and finally perform corona treatment; then pull and wind it up.

[0046] In the process of preparing the modified PET, the molar ratio of terephthalic acid, 2-(pyridin-3-yl)terephthalic acid, and ethylene glycol is 100:20:120; the mass ratio of poly(2-(pyridin-3-yl)terephthalic acid-ethylene glycol ester to 1-carboxyethyl-3-methylimidazolium chloride intercalated montmorillonite is 9:1.

[0047] In the preparation of the modified SiO2 filler, the molar ratio of lauryl acrylate, glycidyl methacrylate and N-(4-vinylphenyl)acetamide is 50:25:25; and their total mass is 80% of the KH570 modified SiO2 powder.

[0048] Example 2: A low alignment angle, high heat resistance release film base film for polarizers

[0049] S1. Weigh 100 parts by weight of optical grade PET chips, 12 parts by weight of modified PET, and 5 parts by weight of modified SiO2 filler and mix them in a high-speed mixer, then dry them under vacuum.

[0050] S2. The dried mixture is fed into a single-screw extruder, and the extrusion temperature is set to 255~285℃ (the temperature of each section of the extruder is set as follows: Zone 1: 255~270℃, Zone 2: 275~280℃, Zone 3: 280~285℃, Zone 4: 280~285℃, Die: 275~280℃). After being extruded through the die, it is rapidly cooled on the cooling roller to form a cast sheet.

[0051] S3. Preheat the cast film to 90℃, perform a first transverse stretching at 95℃ with a stretching ratio of 1.6 times; then perform a longitudinal stretching at 110℃ with a stretching ratio of 4.2 times; finally, perform a second transverse stretching at 125℃ with a stretching ratio of 2.5 times. The three-stage stretching temperature increases progressively, and the total transverse stretching ratio (the product of the two stretching ratios) is 4 times.

[0052] S4. Heat set the stretched film at 190°C for 15 seconds, slowly cool it down to 150°C and hold it for 30 minutes, then cool it down to room temperature and finally perform corona treatment; then pull and wind it up.

[0053] In the process of preparing the modified PET, the molar ratio of terephthalic acid, 2-(pyridin-3-yl)terephthalic acid, and ethylene glycol is 100:20:120; the mass ratio of poly(2-(pyridin-3-yl)terephthalic acid-ethylene glycol ester to 1-carboxyethyl-3-methylimidazolium chloride intercalated montmorillonite is 9:1.

[0054] In the preparation of the modified SiO2 filler, the molar ratio of lauryl acrylate, glycidyl methacrylate and N-(4-vinylphenyl)acetamide is 50:25:25; and their total mass is 80% of the KH570 modified SiO2 powder.

[0055] Example 3: A low alignment angle, high heat resistance release film base film for polarizers

[0056] S1. Weigh 100 parts by weight of optical grade PET chips, 15 parts by weight of modified PET, and 8 parts by weight of modified SiO2 filler and mix them in a high-speed mixer, then dry them under vacuum.

[0057] S2. The dried mixture is fed into a single-screw extruder, and the extrusion temperature is set to 255~285℃ (the temperature of each section of the extruder is set as follows: Zone 1: 255~270℃, Zone 2: 275~280℃, Zone 3: 280~285℃, Zone 4: 280~285℃, Die: 275~280℃). After being extruded through the die, it is rapidly cooled on the cooling roller to form a cast sheet.

[0058] S3. Preheat the cast film to 90℃, perform a first transverse stretching at 95℃ with a stretching ratio of 1.6 times; then perform a longitudinal stretching at 110℃ with a stretching ratio of 4.2 times; finally, perform a second transverse stretching at 125℃ with a stretching ratio of 2.5 times. The three-stage stretching temperature increases progressively, and the total transverse stretching ratio (the product of the two stretching ratios) is 4 times.

[0059] S4. Heat set the stretched film at 190°C for 15 seconds, slowly cool it down to 150°C and hold it for 30 minutes, then cool it down to room temperature and finally perform corona treatment; then pull and wind it up.

[0060] In the process of preparing the modified PET, the molar ratio of terephthalic acid, 2-(pyridin-3-yl)terephthalic acid, and ethylene glycol is 100:20:120; the mass ratio of poly(2-(pyridin-3-yl)terephthalic acid-ethylene glycol ester to 1-carboxyethyl-3-methylimidazolium chloride intercalated montmorillonite is 9:1.

[0061] In the preparation of the modified SiO2 filler, the molar ratio of lauryl acrylate, glycidyl methacrylate and N-(4-vinylphenyl)acetamide is 50:25:25; and their total mass is 80% of the KH570 modified SiO2 powder.

[0062] Example 4: A low alignment angle, high heat resistance release film base film for polarizers

[0063] S1. Weigh 100 parts by weight of optical grade PET chips, 12 parts by weight of modified PET, and 5 parts by weight of modified SiO2 filler and mix them in a high-speed mixer, then dry them under vacuum.

[0064] S2. The dried mixture is fed into a single-screw extruder, and the extrusion temperature is set to 255~285℃ (the temperature of each section of the extruder is set as follows: Zone 1: 255~270℃, Zone 2: 275~280℃, Zone 3: 280~285℃, Zone 4: 280~285℃, Die: 275~280℃). After being extruded through the die, it is rapidly cooled on the cooling roller to form a cast sheet.

[0065] S3. Preheat the cast film to 90℃, perform a first transverse stretching at 105℃ with a stretching ratio of 1.8; then perform a longitudinal stretching at 115℃ with a stretching ratio of 4.6; finally, perform a second transverse stretching at 125℃ with a stretching ratio of 2.5. The three-stage stretching temperature increases progressively, and the total transverse stretching ratio (the product of the two stretching ratios) is 4.5.

[0066] S4. Heat set the stretched film at 190°C for 15 seconds, slowly cool it down to 150°C and hold it for 30 minutes, then cool it down to room temperature and finally perform corona treatment; then pull and wind it up.

[0067] In the process of preparing the modified PET, the molar ratio of terephthalic acid, 2-(pyridin-3-yl)terephthalic acid, and ethylene glycol is 100:20:120; the mass ratio of poly(2-(pyridin-3-yl)terephthalic acid-ethylene glycol ester to 1-carboxyethyl-3-methylimidazolium chloride intercalated montmorillonite is 9:1.

[0068] In the preparation of the modified SiO2 filler, the molar ratio of lauryl acrylate, glycidyl methacrylate and N-(4-vinylphenyl)acetamide is 60:20:20; and the sum of their masses is 100% of the KH570 modified SiO2 powder.

[0069] Example 5: A low alignment angle, high heat resistance release film base film for polarizers

[0070] S1. Weigh 100 parts by weight of optical grade PET chips, 8 parts by weight of modified PET, and 3 parts by weight of modified SiO2 filler and mix them in a high-speed mixer, then dry them under vacuum.

[0071] S2. The dried mixture is fed into a single-screw extruder, and the extrusion temperature is set to 255~285℃ (the temperature of each section of the extruder is set as follows: Zone 1: 255~270℃, Zone 2: 275~280℃, Zone 3: 280~285℃, Zone 4: 280~285℃, Die: 275~280℃). After being extruded through the die, it is rapidly cooled on the cooling roller to form a cast sheet.

[0072] S3. Preheat the cast film to 90℃, perform a first transverse stretching at 105℃ with a stretching ratio of 1.8; then perform a longitudinal stretching at 115℃ with a stretching ratio of 4.6; finally, perform a second transverse stretching at 125℃ with a stretching ratio of 2.5. The three-stage stretching temperature increases progressively, and the total transverse stretching ratio (the product of the two stretching ratios) is 4.5.

[0073] S4. Heat set the stretched film at 190°C for 15 seconds, slowly cool it down to 150°C and hold it for 30 minutes, then cool it down to room temperature and finally perform corona treatment; then pull and wind it up.

[0074] In the modified PET preparation process, the molar ratio of terephthalic acid, 2-(pyridin-3-yl)terephthalic acid, and ethylene glycol is 100:10:120; the mass ratio of poly(2-(pyridin-3-yl)terephthalic acid-ethylene glycol ester to 1-carboxyethyl-3-methylimidazolium chloride intercalated montmorillonite is 9.5:0.5.

[0075] In the preparation of the modified SiO2 filler, the molar ratio of lauryl acrylate, glycidyl methacrylate and N-(4-vinylphenyl)acetamide is 70:15:15; and their total mass is 120% of the KH570 modified SiO2 powder.

[0076] Comparative Example 1: The process is similar to that of Example 4.

[0077] The difference is that no modified PET is added; its proportion is replaced by an equal amount of ordinary optical-grade PET chips.

[0078] Comparative Example 2: The process is similar to that of Example 4.

[0079] The difference lies in replacing the modified SiO2 filler with KH570 modified SiO2 powder.

[0080] Comparative Example 3: The raw materials are the same as those in Example 4.

[0081] The difference lies in the preparation process, which changes the three-stage stretching process to the conventional synchronous biaxial stretching (preheating temperature is 90℃, stretching temperature is 115℃, transverse stretching ratio is 3.3, and longitudinal stretching ratio is 3.5).

[0082] Comparative Example 4: The process is similar to that of Example 4.

[0083] The difference is that modified PET is obtained by directly mixing and melting PET chips with montmorillonite and then extruding; while modified SiO2 filler is only grafted with lauryl acrylate during the preparation process.

[0084] In the above preparation process, the thickness of the film is controlled at 40±2 μm; the obtained film is subjected to the following performance tests, and the results are recorded in Table 1.

[0085] Orientation angle: The orientation angle of the thin film at 50 mm intervals was measured using an automatic ellipsometry, and the maximum value was recorded.

[0086] Heat shrinkage rate: The film was placed in a 150°C forced-air oven for 30 minutes, and the change in transverse (TD) dimensions was measured.

[0087] Transmittance and haze: measured using a haze meter (BYK-Gardner, Haze-Gardi) in accordance with GB / T 2410-2008.

[0088] Release agent adhesion: A silicone release agent was applied, and a cross-cut adhesion test was performed on the resulting film. 0B was the worst, and 5B was the best.

[0089] Table 1

[0090]

[0091] As shown in Table 1, the technical solution provided in this application successfully prepared optical-grade PET films with low alignment angles and high heat resistance. The optical properties decreased slightly with increasing filler content, but the heat resistance and adhesion gradually improved. Therefore, the optimal formulation was 100 parts by weight of optical-grade PET chips, 12 parts by weight of modified PET, and 5 parts by weight of modified SiO2 filler. Furthermore, the three-stage stretching ratio and the composition of modified PET and modified SiO2 filler also had a certain impact on the performance. Ultimately, it can be seen that Example 4 exhibited the best performance. Based on the reaction conditions of Example 4, the effects of modified PET, modified SiO2 filler, and the three-stage stretching process on the film properties were further investigated. Comparative Example 1 shows that the application of modified PET has a significant impact on the alignment angle of the film. Due to the lack of rigid monomers and montmorillonite, the molecular chain orientation became uneven, resulting in a corresponding increase in the alignment angle. Comparative Example 2, lacking modified SiO2 filler, showed a significant decrease in release agent adhesion. Combined with Comparative Example 4, it was found that glycidyl methacrylate and N-(4-vinylphenyl)acetamide dominated adhesion performance, highlighting the decisive role of amide groups (hydrogen bonds) and epoxy groups (chemical reactivity) in improving adhesion. Meanwhile, the missing components in Comparative Examples 1 and 2 both resulted in decreased heat resistance. The results of Comparative Example 3 demonstrate the unique advantages of the three-stage stretching process in controlling molecular chain orientation.

[0092] 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 low alignment angle, high heat-resistant release film base film for polarizers, characterized in that, The release film base film is obtained by adding modified PET and modified SiO2 filler to optical grade PET chip as the main material, co-extrusion casting, three-stage stretching, heat setting, and corona treatment; wherein, The poly-2-(pyridine-3-yl) terephthalate-ethylene glycol ester is obtained by adding ethylene glycol and 2-(pyridine-3-yl) terephthalic acid into a reactor, adding tetrabutyl titanate as a catalyst, increasing the temperature to 200-230 DEG C for esterification, adding terephthalic acid after 2-3 hours of reaction, increasing the temperature to 250 DEG C, adding antimony ethylene glycol as a catalyst after 2-4 hours of reaction, controlling the pressure in the reactor to be 0.3 MPa, increasing the temperature to 270 DEG C for 2-3 hours of reaction, and naturally cooling the reactor to discharge the product; then the product is mixed with 1-carboxyethyl-3-methyl imidazole chloride intercalated montmorillonite in a high-speed mixer, and the mixture is melt blended and granulated by a twin-screw extruder to obtain the product. The molar ratio of the terephthalic acid, 2-(pyridine-3-yl) terephthalic acid, and ethylene glycol is 100:10-20:120; and the mass ratio of the poly-2-(pyridine-3-yl) terephthalate-ethylene glycol ester and 1-carboxyethyl-3-methyl imidazole chloride intercalated montmorillonite is 9-9.5:0.5-1. The modified SiO2 filler is obtained by grafting a terpolymer of lauryl acrylate, glycidyl methacrylate, and N-(4-vinylphenyl) acetamide onto the surface of KH570 modified SiO2 through radical polymerization; the molar ratio of the lauryl acrylate, glycidyl methacrylate, and N-(4-vinylphenyl) acetamide is 50-70:15-25:15-25; and the sum of the masses of the three is 80%-120% of the mass of the KH570 modified SiO2 powder. The weight fractions of the optical grade PET chip, modified PET, and nano filler are 100 parts, 8-15 parts, and 3-8 parts, respectively. The three-stage stretching process specifically includes first transverse stretching at a stretching ratio of 1.5-2.5 times, then longitudinal stretching at a stretching ratio of 3.2-5 times, and second transverse stretching of the film after longitudinal stretching at a stretching ratio of 2.5-3.5 times; the three-stage stretching temperature is increased step by step, and the total transverse stretching ratio is 3.75-6 times.

2. The low pretilt angle high heat-resistant release film base film for a polarizing plate according to claim 1, characterized by The preparation process of the 1-carboxyethyl-3-methyl imidazole chloride intercalated montmorillonite is as follows: Sodium-based montmorillonite and deionized water are added into a beaker, ultrasonically dispersed, and then transferred to a water bath and heated to 60-70 DEG C; 1-carboxyethyl-3-methyl imidazole chloride is slowly added dropwise while stirring, and the mixture is kept at the temperature for 2-3 hours after the addition is completed; the mixture is filtered, washed with water, and dried to obtain the product.

3. The low pretilt angle high heat-resistant release film base film for a polarizing plate according to claim 1, characterized by The preparation steps of the modified SiO2 filler are as follows: 1) A certain amount of nano SiO2 particles are first activated by potassium hydroxide, then dispersed in deionized water, and an equal amount of KH570 is added; the mixture is stirred at 50 DEG C for 24 hours, filtered, washed, dried, and ground to obtain KH570 modified SiO2 powder; 2) KH570 modified SiO2 powder was dispersed in THF, lauryl acrylate, glycidyl methacrylate and N-(4-vinylphenyl)acetamide were added in turn, 1% of the total mass of monomers AIBN was added as initiator, and the reaction was carried out at 70°C under nitrogen protection for 12h. After the reaction was completed, centrifugal separation was carried out, and THF was used for washing three times to remove homopolymer. After vacuum drying, the modified SiO2 filler was obtained.

4. The method for producing a low pretilt angle high heat-resistant release film base film for a polarizing plate according to any one of claims 1 to 3, characterized by, Comprise the following steps: S1, weigh the measured optical grade PET chips, modified PET, and modified SiO2 filler, mix them in a high-speed mixer, and then dry them under vacuum drying; S2, send the dried mixture into a single screw extruder, set the extrusion temperature to 255-285°C, extrude through the die, and then quickly cool on the cooling roller to form a cast sheet; S3, preheat the cast sheet to 90°C, perform a first transverse stretching with a stretching ratio of 1.5-2.5 times, then perform a longitudinal stretching with a stretching ratio of 3.2-5 times, and then perform a second transverse stretching on the longitudinally stretched film with a stretching ratio of 2.5-3.5 times; the three-stage stretching temperature gradually increases, and the total transverse stretching ratio is 3.75-6 times; S4, heat set the stretched film at 190-220°C for 5-15s, slowly cool to 150°C for 10-30min, then cool to room temperature, and finally perform a corona treatment; pull and wind up.

5. The method for producing a low-tilt-angle high-heat-resistant release film base film for a polarizing plate according to claim 4, characterized by, In the step S2, the temperature of each section of the extruder is set as follows: zone 1: 255-270°C, zone 2: 275-280°C, zone 3: 280-285°C, zone 4: 280-285°C, and die: 275-280°C.

6. The method for producing a low-tilt-angle high-heat-resistant release film base film for a polarizing plate according to claim 4, characterized by, In the step S3, the first transverse stretching temperature is set to 95-105°C, the longitudinal stretching temperature is set to 105-115°C, and the second transverse stretching temperature is set to 120-135°C.

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