Optical-grade polyester film for polaroid release film and preparation method of optical-grade polyester film

Abstract

The invention relates to the technical field of polaroid release films, and discloses an optical-grade polyester film for a polaroid release film and a preparation method of the optical-grade polyester film. 5%-10% of bisphenol A polyester; 8%-12% of an N-alkylamide comonomer, the carbon chain length of the N-alkylamide comonomer is C6-C18, and the molecular structure of the N-alkylamide comonomer comprises at least one carbonyl group and an amide group; the substituent group of the pyridine derivative is alkyl, fluoro, carboxyl or hydroxyl, and the carbon chain length of the substituent group is C1-C6; and 0.3%-0.6% of an organophosphate nucleating agent, wherein the nucleating agent is polyphosphate, phosphate or pyrophosphate. And an optimized rheology induced directional crystallization process is adopted, so that molecular chains of the thin film are more orderly arranged in the stretching process, and the technical effect of remarkably improving optical transparency is achieved.

Description

Technical Field

[0001] The invention relates to the technical field of polarizer release films, in particular to an optical-grade polyester film for a polarizer release film and a preparation method thereof. Background Art

[0002] With the rapid development of the flat panel display industry, polarizers, as one of the important components, have also been widely used and developed. The polarizer release film is one of the key factors to ensure the stable performance of the polarizer. It not only requires good transparency and mechanical strength, but also requires excellent surface flatness and low friction coefficient. In recent years, researchers have continuously optimized polymer formulas, processing conditions and other aspects to improve product quality, but there is still much room for improvement.

[0003] There are two common practices in the market: one is to use the traditional biaxial stretching process to produce PET film. Although this method can obtain a higher transmittance, it has certain limitations in thickness uniformity control; the other is to introduce new material modifications such as nm particles or microporous structures to improve the surface quality and mechanical properties of the film. However, these methods are often accompanied by the problem of increased costs, and their stability in large-scale industrial production has yet to be verified.

[0004] Although the above two methods have their own advantages, they also expose many problems. For example, the PET film produced by the traditional biaxial stretching method is difficult to achieve the goal of ultra-thinness, and there is a risk of fracture due to stress concentration; while the new material modification strategy can significantly enhance certain specific properties, it may sacrifice other aspects of performance, such as reduced flexibility or reduced durability. Summary of the invention

[0005] In view of the deficiencies in the prior art, the present invention provides an optical-grade polyester film for a polarizer release film and a preparation method thereof, which solves the problem in the prior art that it is difficult to balance light transmittance, tear strength and surface flatness.

[0006] To achieve the above objectives, the present invention is implemented by the following technical scheme: an optical grade polyester film for a polarizer release film, comprising the following components: Polyethylene terephthalate 80%-90%; Bisphenol A polyester 5% to 10%; 8% to 12% of N-alkylamide comonomer, wherein the carbon chain length of the N-alkylamide comonomer is C6 to C18 and the molecular structure contains at least one carbonyl group and an amide group; 3% to 6% of a pyridine derivative, wherein the substituent is an alkyl group, a fluoro group, a carboxyl group or a hydroxyl group, and the carbon chain length of the substituent is C1 to C6; 0.3% to 0.6% of an organic phosphate nucleating agent, wherein the nucleating agent is a polyphosphate, a phosphate or a pyrophosphate; Sulfonate comonomer 0.5% to 1.5%; Antioxidant 0.2% to 0.5%; The residual solvent content does not exceed 0.1%.

[0007] Mechanism analysis shows that polyethylene terephthalate (PET) is the main matrix material of the film. PET has good transparency, mechanical strength and chemical stability, and can provide the basic structure and performance requirements of the film. The polymer chain enhances the tensile strength and tear resistance of the film through proper orientation and aggregation.

[0008] Bisphenol A polyester BPA-PES as a comonomer can enhance the flexibility and heat resistance of the film. The introduction of BPA helps to increase the structural stability of the film, and by adjusting its ratio, the mechanical properties of the film can be optimized.

[0009] N-alkylamide comonomers introduce hydrogen bonding structures and intermolecular interactions, thereby improving the mechanical strength of the film, while controlling the flexibility and tear resistance of the film under different alkyl chain lengths.

[0010] Pyridine derivatives provide π-π interactions in the molecular structure, which helps to align the molecular chains and thus optimize the surface flatness and optical properties of the film.

[0011] The organic phosphate nucleating agent promotes the formation of crystal nuclei during the crystallization process, helps control the grain size of the film, avoids coarse grains during the crystallization process, and effectively improves the surface smoothness and uniformity of the film.

[0012] Preferably, the molecular weight of the polyethylene terephthalate (PET) is 50,000 to 1,000,000 g / mol, and the molecular chain is a highly oriented structure.

[0013] Mechanistic analysis shows that the molecular weight range of polyethylene terephthalate (PET) has an important influence on the physical properties of the film. A higher molecular weight helps to improve the strength, durability and thermal stability of the PET film. By adjusting the molecular weight of PET, the transparency and mechanical strength of the film can be balanced. At the same time, by controlling the orientation of the molecular chain, the tensile strength, tear resistance and surface smoothness of the PET film are enhanced.

[0014] Preferably, the surface roughness Ra of the film is 2.5 to 3.0 nm, the light transmittance is 93% to 95%, and the tensile strength is 220 to 260 MPa.

[0015] Mechanism analysis shows that the surface roughness and transmittance of the film are the key factors affecting the performance of the polarizer. By adjusting the composition and process conditions of the film, a low Ra value (2.5-3.0nm) can be achieved while maintaining a high transmittance. A surface roughness of less than 3nm helps reduce light scattering, optimize the optical properties of the polarizer, and enhance its fit. The increase in transmittance ensures the clarity of the display effect, while the tensile strength is an important indicator of the durability and strength of the film. A tensile strength of 220-260MPa ensures the mechanical stability of the film.

[0016] A method for preparing an optical grade polyester film for a polarizer release film comprises the following steps: Blending and granulation: Add polyethylene terephthalate PET, bisphenol A polyester BPA-PES, N-alkylamide comonomer, pyridine derivative, and sulfonate comonomer to a twin-screw extruder in proportion, melt blend at 250-280°C, control the shear rate at 90-110r / min, granulate after extrusion, and control the particle size at 1-3mm; Extrusion casting: The blended pellets are extruded at 260-290°C, and a T-die is used for casting. The temperature of the cooling roller is set at 90-110°C, the pulling speed is 8-12m / min, and the film thickness is controlled at 20-50μm. Rheology-induced directional crystallization: In a constant temperature stretching device, the cast film is heated to 120-160°C for 3000-4000 seconds. 2 Orientation stretching is performed at a shear rate of 3 to 5 times, and the heat preservation time is 30 to 90 seconds; Metastable crystallization regulation: using an organic phosphate nucleating agent, annealing treatment is carried out at 60-100°C, the annealing time is controlled at 2-6h, and the grain size is controlled at 5-15nm; Solvent annealing: at 90-110° C., solvent vapor diffusion treatment is performed using dimethylacetamide DMAc, tetrahydrofuran THF and dichloromethane DCM, with the volume ratio of DMAc:THF:DCM controlled at 6-7:3-4:0.5-1, and the treatment time controlled at 15-25 min.

[0017] Mechanism analysis, blending and granulation: Through high-temperature melt blending, each component is ensured to be completely dissolved and evenly mixed, which improves the mechanical strength and uniformity of the film. Controlling the shear rate helps to achieve a stable polymer distribution.

[0018] Extrusion casting: During the casting process, by controlling the temperature and pulling speed, the thickness and surface flatness of the film can be controlled to ensure the optical properties of the film.

[0019] Rheology-induced directional crystallization: This step induces directional arrangement of molecular chains through shear force and heating treatment, thereby improving the mechanical strength and surface smoothness of the film.

[0020] Metastable crystallization regulation: Using nucleating agents to promote crystallization, improve the mechanical properties and durability of the film, and control the grain size, which helps to reduce surface irregularities.

[0021] Solvent annealing: Solvent annealing is used to adjust the hydrogen bonds and molecular structure of the film, thereby optimizing the optical properties and mechanical stability of the film.

[0022] Preferably, the shear rate of the rheology-induced directional crystallization step is controlled at 2500-4000 s 2 , the holding time is 30 to 90 seconds, and the molecular chain orientation degree reaches 80% to 95%.

[0023] Mechanism analysis shows that during the rheologically induced directional crystallization process, by controlling the shear rate and holding time, the orientation of the molecular chains in the film can be accurately adjusted to improve the tensile strength and tear resistance of the film. Appropriate molecular chain orientation helps to improve the overall performance of the film, especially its mechanical strength and durability.

[0024] Preferably, in the solvent annealing step, the volume ratio of DMAc, THF and DCM is 6.5-7: 3.2-4: 0.8-1, and the solvent action time is 15-25 min.

[0025] Mechanism analysis shows that the solvent annealing process can optimize the hydrogen bond network structure of the film by adjusting the solvent ratio and treatment time, so that the film surface can achieve the best optical and mechanical properties. Precise control of the solvent ratio and action time can help reduce surface defects and improve the transparency and optical uniformity of the film.

[0026] Preferably, the organic phosphate nucleating agent in the metastable crystallization regulating step is a phosphate ester, and a gradual temperature increase method is adopted during the annealing process, and the heating rate is 1 to 5°C / min.

[0027] Mechanism analysis shows that the organic phosphate nucleating agent promotes the crystallization process of the film during annealing. The introduction of phosphate can effectively control the crystallization rate and prevent the grains from being too large, thereby improving the uniformity of the film. The gradual temperature increase process can ensure the smooth progress of the crystallization process and further optimize the physical properties of the film.

[0028] Preferably, the extrusion temperature in the blending and granulation step is controlled at 250-280° C. and the shear rate is 90-110 r / min to ensure that the components are fully mixed.

[0029] Mechanism analysis shows that appropriate extrusion temperature and shear rate can ensure the complete melting and uniform dispersion of polyester materials and other comonomers, thereby obtaining a uniform mixture and improving the overall performance and stability of the film.

[0030] Preferably, the temperature of the cooling roller in the extrusion casting step is 90-110° C., and the pulling speed is 8-12 m / min to control the film thickness and surface smoothness.

[0031] Mechanism analysis shows that in the casting process, the control of cooling speed and pulling speed is crucial to the thickness and surface quality of the film. By adjusting the temperature of the cooling roller and the pulling speed, the uniform thickness of the film can be ensured, surface defects can be reduced, and optical properties can be improved.

[0032] Preferably, the mechanical property of the film is further manifested in a tear strength of 1.0 to 1.2 N / mm.

[0033] Mechanism analysis shows that tear strength is an important indicator for measuring film durability. By optimizing the composition and processing technology of the film, its tear resistance can be significantly improved, and the stability and life of the film in practical applications can be enhanced.

[0034] The present invention provides an optical grade polyester film for polarizer release film and a preparation method thereof. It has the following beneficial effects: 1. The present invention adopts an optimized rheology-induced directional crystallization process to make the molecular chains of the film more orderly arranged during the stretching process, achieving the technical effect of significantly improving the optical transparency. Compared with the light scattering problem caused by uneven grain size distribution in the prior art, it solves the problem of decreased light transmittance.

[0035] 2. The present invention optimizes the surface quality of the film through precise control of the solvent annealing process, thereby achieving the effect of improving the tear strength. Compared with the film brittleness problem caused by uneven annealing treatment in the prior art, it solves the problem of decreased mechanical properties caused by microscopic defects.

[0036] 3. The present invention uses a phosphate nucleating agent to regulate metastable crystallization, making the grain size of the film more uniform, achieving the technical effect of enhancing the uniformity of the material. Compared with the uneven strength distribution caused by the unstable grain structure in the prior art, it solves the problem of local fragility and easy damage of the film.

[0037] 4. The present invention utilizes optimized solvent ratios and steam annealing parameters to achieve efficient regulation of the internal structure of the film, achieving the effect of taking both transmittance and mechanical properties into consideration. Compared with the solutions in the prior art that are difficult to take both optical and mechanical properties into consideration, this solves the problem of increased strength accompanied by decreased transparency. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] Figure 1The present invention is a flow chart of the method. DETAILED DESCRIPTION

[0039] The following will be combined with the drawings in the specification of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0040] Please see attached Figure 1 : Embodiment 1: Components: Polyethylene terephthalate PET: 85% Bisphenol A polyester BPA-PES: 7% N-Alkylamide comonomer (C12): 6% Pyridine derivatives: 2% Organic phosphate nucleating agent: 0.3% Sulfonate comonomer: 1% Antioxidants: 0.5% Residual solvent: <0.1% Process steps: Blending and granulation: the above components were put into a twin-screw extruder, the temperature was set to 265°C, the shear rate was 100 r / min, and the mixture was uniformly blended. The particle size after extrusion was 2 mm.

[0041] Extrusion casting: heating to 270°C, using a T-die for casting, the cooling roller temperature is 95°C, the pulling speed is 10m / min, and the film thickness generated in this step is 40μm.

[0042] Rheology-induced directional crystallization: The film was heated to 130 °C and heated for 3000 s 2 The sample was stretched at a shear rate of 4 times and the holding time was 50 s.

[0043] Metastable crystallization regulation: The film was annealed at 80 °C for 4 h and treated with a phosphate nucleating agent, and the grain size was controlled at 10 nm.

[0044] Solvent annealing: The film was placed in the solvent vapor of DMAc:THF:DCM (6:3:1) at 95 °C for 20 min to ensure a smooth surface with good optical properties.

[0045] This embodiment successfully improves the surface quality of the film by reasonably adjusting the ratio of the blend and the process conditions, reducing the Ra value to ~2.8nm, achieving a transmittance of 94%, and a tensile strength of 250MPa, solving the problem of the difficulty in balancing mechanical properties and surface smoothness in traditional technologies.

[0046] Embodiment 2: Components: Polyethylene terephthalate PET: 80% Bisphenol A polyester BPA-PES: 8% N-Alkylamide comonomer (C10): 9% Pyridine derivatives: 3% Organic phosphate nucleating agent: 0.4% Sulfonate comonomer: 1.5% Antioxidants: 0.1% Residual solvent: <0.1% Process steps: Blending and granulation: Add each component into the twin-screw extruder according to the proportion, set the temperature to 260°C, and mix at a shear rate of 95r / min. The particle size after granulation is controlled to be 2.5mm.

[0047] Extrusion casting: The blended pellets were cast through a T-die at a temperature of 270°C, the cooling roller temperature was 100°C, the pulling speed was set to 9m / min, and the film thickness was controlled at 35μm.

[0048] Rheology-induced directional crystallization: The film was heated to 140°C for 3500 seconds. 2 The film was stretched at a shear rate of 3.5 times and the holding time was 60 s.

[0049] Metastable crystallization regulation: Annealing at 75 °C for 3 h, phosphate nucleating agent was used for crystallization to ensure that the grain size was controlled at 12 nm.

[0050] Solvent annealing: DMAc:THF:DCM (6.5:3:1) solvent ratio was used, the temperature was 100 °C, and the processing time was set to 18 min to achieve the best optical uniformity and surface quality.

[0051] The light transmittance of the film in this embodiment is 93%, the surface roughness Ra is 2.9nm, and the tensile strength reaches 245MPa. The tear strength of the film is 1.1N / mm, indicating that the process effectively improves the strength and surface smoothness of the film and avoids the trade-off between mechanical properties and optical properties of traditional films.

[0052] Embodiment 3: Components: Polyethylene terephthalate PET: 87% Bisphenol A polyester BPA-PES: 5% N-Alkylamide comonomer (C14): 6% Pyridine derivatives: 3% Organic phosphate nucleating agent: 0.5% Sulfonate comonomer: 1% Antioxidants: 0.2% Residual solvent: <0.1% Process steps: Blending and granulation: Add PET, BPA-PES, N-alkylamide comonomers, etc. into a twin-screw extruder, set the temperature to 275°C, and the shear rate to 100r / min to ensure uniform mixing. The particle size is controlled at 2mm.

[0053] Extrusion casting: The pellets were extruded at 275°C and cast through a T-die. The cooling roller temperature was set at 105°C, the pulling speed was 8m / min, and the film thickness was controlled at 40μm.

[0054] Rheology-induced directional crystallization: Heat the film to ~150°C for 3500 seconds 2 The sample was stretched at a shear rate of 4 times and the holding time was 50 s.

[0055] Metastable crystallization regulation: annealing at 85 °C for 5 h, adding phosphate nucleating agent, and controlling the grain size at 8 nm.

[0056] Solvent annealing: using DMAc:THF:DCM (7:3:1) solvent ratio, treating at 105°C for 20 min.

[0057] The surface roughness Ra of the film in this embodiment is 2.7nm, the light transmittance is 94.5%, the tensile strength is 230MPa, and the tear strength is increased to 1.2N / mm. Compared with the traditional technology, the tear resistance and optical properties of the film are significantly improved.

[0058] Embodiment 4: Components: Polyethylene terephthalate PET: 83% Bisphenol A polyester BPA-PES: 6% N-Alkylamide comonomer (C8): 9% Pyridine derivatives: 2% Organic phosphate nucleating agent: 0.3% Sulfonate comonomer: 1% Antioxidants: 0.2% Residual solvent: <0.1% Process steps: Blending and granulation: All components were put into a twin-screw extruder, the temperature was set to 270°C, the shear rate was 95r / min, and uniformly mixed particles were obtained. The particle size was controlled to be 2.5mm.

[0059] Extrusion casting: The temperature during the casting process was set at 275°C, a T-die was used for casting, the cooling roller temperature was 100°C, the pulling speed was 10 m / min, and the film thickness was 35 μm.

[0060] Rheology-induced directional crystallization: Heat the film to 140 °C and use 3000 s 2 The film was stretched at a shear rate of 3.5 times and the holding time was 60s.

[0061] Metastable crystallization regulation: The film was annealed at 80 °C for 3 h and a phosphate nucleating agent was used to ensure that the grain size was controlled at 10 nm.

[0062] Solvent annealing: DMAc:THF:DCM (6.5:3.5:1) solvent ratio was used, the temperature was 100°C, and the treatment time was set to 18 min.

[0063] This embodiment significantly improves the tear strength of the film (1.1N / mm), and the surface roughness Ra is reduced to 2.6nm, and the light transmittance is 94%. The comprehensive performance of the film is better than the existing technology, especially in terms of tear resistance and surface flatness, solving the problems of traditional films.

[0064] Comparative Example 1: Comparison point: film surface roughness and transparency Embodiment 1: Surface roughness: Ra = 2.5nm Light transmittance: 94% Process parameters: Blending granulation: shear rate 100r / min, temperature 270℃ Extrusion casting: cooling roller temperature 100℃, pulling speed 10m / min Rheology-induced directional crystallization: shear rate 3000s 2 , stretching ratio 4 times, heat preservation 50s Comparative Example 1: Surface roughness: Ra = 6.0nm (unoptimized process) Light transmittance: 90% (transparency not optimized) Process parameters: Blending granulation: shear rate 100r / min, temperature 260℃ Extrusion casting: cooling roller temperature 95°C, pulling speed 9m / min Rheology-induced directional crystallization: shear rate 2000s 2 , stretching ratio 3 times, heat preservation 60s Process Description: Blending granulation: polyethylene terephthalate PET, bisphenol A polyester BPA-PES, and N-alkylamide comonomer are put into a twin-screw extruder in proportion for mixing. The temperature is set at 260° C. and the shear rate is 100 r / min to obtain a particle size of about 2.5 mm.

[0065] Extrusion casting: During the casting process, the film thickness was set to 35 μm, the pulling speed was 9 m / min, and the cooling roller temperature was set to 95 °C.

[0066] Rheology-induced directional crystallization: The cast film was heated to 130 °C and the shear rate was set to 2000 s 2 , stretching, stretching ratio is 3 times, keep warm for 60s.

[0067] Solvent annealing: The solvent ratio of DMAc:THF:DCM was 6:3:1, and the solvent vapor treatment time was 20 min.

[0068] Comparative Example 2: Comparison point: Crystallization control and tear strength Embodiment 2: Tear strength: 1.1N / mm Process parameters: Metastable crystallization control: annealing temperature 75℃, treatment time 3h Solvent annealing: solvent ratio DMAc:THF:DCM (6.5:3:1), treatment time 18 min Comparative Example 2: Tear strength: 0.8N / mm (without optimized nucleating agent) Process parameters: Metastable crystallization control: annealing temperature 70℃, treatment time 2h Solvent annealing: solvent ratio DMAc:THF:DCM (7:3:1), treatment time 15 min Process Description: Blending granulation: The raw material ratio is the same as that in Example 2, but the temperature is set to 265° C., the shear rate is 100 r / min, and the particle size after granulation is 2 mm.

[0069] Extrusion casting: the pulling speed was 8 m / min, the cooling roller temperature was set to 100°C, and the thickness of the cast film was 40 μm.

[0070] Rheology-induced directional crystallization: heating to 135°C, stretching ratio 3 times, holding time 45s.

[0071] Solvent annealing: solvent ratio DMAc:THF:DCM (7:3:1), solvent action time was 15 min.

[0072] Comparative Example 3: Comparison point: Molecular chain orientation and tensile strength Embodiment 3: Tensile strength: 230MPa Process parameters: Rheology-induced directional crystallization: shear rate 3500s 2 , stretch ratio 4 times Metastable crystallization regulation: annealing temperature 85°C, phosphate nucleating agent used Solvent annealing: temperature 105°C, treatment time 20 min Comparative Example 3: Tensile strength: 200MPa (without rheology-induced crystallization optimization) Process parameters: Rheology-induced directional crystallization: shear rate 2500s 2 , stretching ratio 3 times Metastable crystallization control: annealing temperature 80℃, no nucleating agent used Solvent annealing: temperature 95°C, treatment time 18 min Process Description: Blending granulation: PET, BPA-PES, N-alkylamide comonomer, etc. are put into a twin-screw extruder in proportion, the temperature is set to 270°C, the shear rate is 100r / min, and the particle size is 2.5mm.

[0073] Extrusion casting: The cooling roll temperature was set to 100°C, the pulling speed was 9 m / min, and the film thickness was 35 μm.

[0074] Rheology-induced directional crystallization: heating ~140°C, shear rate 2500s 2 , stretching ratio is 3 times, and holding time is 60s.

[0075] Solvent annealing: DMAc:THF:DCM solvent ratio (6:3:1) was used, the temperature was 95°C, and the treatment time was 18 min.

[0076] Comparative Example 4: Comparison point: film thickness and surface quality Embodiment 4: Surface roughness: Ra = 2.6nm Light transmittance: 94% Process parameters: Extrusion casting: traction speed 10m / min, cooling roller temperature 100℃, film thickness 35μm Solvent annealing: solvent ratio DMAc:THF:DCM (6.5:3:1), treatment time 20 min Comparative Example 4: Surface roughness: Ra = 5.0nm (without optimized cooling control) Light transmittance: 90% (surface flatness not optimized) Process parameters: Extrusion casting: traction speed 8m / min, cooling roller temperature 95℃, film thickness 40μm Solvent annealing: solvent ratio DMAc:THF:DCM (7:3:1), treatment time 18 min Process Description: Blending and granulation: After mixing the components, set the extruder temperature to 260°C, the shear rate to 100 r / min, and the particle size to 2.5 mm.

[0077] Extrusion casting: film thickness is 40 μm, pulling speed is 8 m / min, and cooling roller temperature is 95 °C.

[0078] Rheology-induced directional crystallization: heating ~130°C, shear rate 2000s 2 , stretching ratio 3 times, holding time 60s.

[0079] Solvent annealing: carried out in a solvent ratio of DMAc:THF:DCM (7:3:1), a treatment temperature of 95°C, and a time of 18 min.

[0080] Experiment 1: Surface roughness comparison experiment Experimental description: Purpose: This experiment aims to test the difference in surface roughness of films prepared under different process conditions in order to verify the advantages of the present invention in terms of surface flatness.

[0081] Experimental Group: Example 1: Ra = 2.5 nm Comparative Example 1: Ra = 6.0 nm (unoptimized process) Experimental steps: Blending and granulation: A mixture of polyethylene terephthalate PET (85%), bisphenol A polyester BPA-PES (7%), N-alkylamide comonomer (6%), pyridine derivative (2%), organic phosphate nucleating agent (0.3%), sulfonate comonomer (1%), antioxidant (0.5%) and solvent residue (<0.1%) was put into a twin-screw extruder for uniform blending. The blending temperature was set at 270°C and the shear rate was 100r / min to ensure uniform mixing.

[0082] Extrusion Casting: The blended pellets were extruded through a T-die, the temperature was set at 270°C, the temperature of the cooling roll was set at 100°C, the pulling speed was 10 m / min, and the film thickness was maintained at 40 μm.

[0083] Rheology-induced directional crystallization: In a constant temperature stretching device, the cast film was heated to 130 °C and the shear rate was set to 3000 s 2 The stretching treatment was performed with a stretching ratio of 4 times and a heat preservation time of 50s to improve the orientation degree of the molecular chain.

[0084] Solvent Annealing: The film was placed in a DMAc:THF:DCM (6:3:1) mixed solvent with the temperature set at 95 °C and the steam treatment time was 20 min to optimize the surface quality and reduce the roughness.

[0085] Surface roughness measurement: Use an optical profilometer (such as Bruker ContourGT-K1) to measure the film surface. Select different areas of the film surface, measure them three times respectively, and finally take the average value.

[0086] Experimental data: Table Name: Table 1: Comparison of surface roughness and related performance data of films of Example and Comparative Example Summarize: From the experimental results, the surface roughness Ra value of the film of Example 1 is about 2.5nm, which is significantly better than 6.0nm of Comparative Example 1, and the light transmittance is higher and the tensile strength is stronger, indicating that the optimized process has significant advantages in film surface quality and mechanical properties. In the experiment, the fine adjustment of the pulling speed and the temperature of the cooling roller during the casting process is crucial to controlling the surface quality. In contrast, Comparative Example 1 did not make corresponding optimizations in the process settings, resulting in a rougher film surface and lower light transmittance. Obviously, the present invention successfully reduces the surface roughness and improves the light transmittance by optimizing the steps of solvent annealing, rheology-induced directional crystallization, etc., and solves the problem that it is difficult to balance surface flatness and mechanical strength in traditional technologies.

[0087] Furthermore, the surface roughness of the film is not only affected by the cooling rate and the pulling speed, but the solvent annealing process also plays a crucial role. By selecting a suitable solvent ratio and steam treatment time, the present invention can effectively improve the surface flatness and optical properties of the film. Experimental data show that under the optimized process, the surface roughness of the film is significantly reduced, and the optical properties are improved. Compared with traditional technologies, the surface quality control of the present invention is obviously more sophisticated, especially in terms of film transmittance and tensile strength, which show a higher level.

[0088] In the film preparation process, the directional orientation of the molecular chains plays a vital role. The rheologically induced directional crystallization process ensures the uniformity and surface smoothness of the film by adjusting the shear rate and stretching ratio. By controlling these parameters, the molecular chains can be arranged more evenly, thereby improving the mechanical properties and optical transparency of the film. Experimental data further verified that these processes improve the film properties, especially in terms of tear strength and light transmittance. The present invention provides an effective method to address the shortcomings of traditional films in this regard.

[0089] Experiment 2: Tensile strength comparison experiment Experimental description: Purpose: This experiment aims to verify the effect of the present invention in improving the mechanical properties of the film by comparing the tensile strength of the film of the embodiment and the comparative example.

[0090] Experimental Group: Example 2: Tensile strength = 245 MPa Comparative Example 2: Tensile strength = 200 MPa (unoptimized rheology-induced directional crystallization process) Experimental steps: Blending and granulation: The components were added into a twin-screw extruder in proportion for blending. The blend included: polyethylene terephthalate PET (80%), bisphenol A polyester BPA-PES (8%), N-alkylamide comonomer (9%), pyridine derivative (3%), organic phosphate nucleating agent (0.4%), sulfonate comonomer (1.5%), antioxidant (0.1%) and solvent residue (<0.1%). The temperature was set at 260°C and the shear rate was 100r / min to ensure uniform material flow. The particle size after granulation was 2.5mm.

[0091] Extrusion Casting: The blended particles were extruded through a T-die, the temperature was set at 270°C, the cooling roller temperature was 95°C, the pulling speed was set at 9m / min, and the film thickness was controlled at 35μm. This step ensures the uniformity and mechanical properties of the film.

[0092] Rheology-induced directional crystallization: In a constant temperature stretching device, the cast film was heated to 140 °C and the shear rate was set to 3500 s 2 , and then stretched to 3.5 times with a holding time of 60 seconds. This process helps the film's molecular chains to be more oriented, significantly improving the film's mechanical strength.

[0093] Metastable crystallization regulation: The phosphate nucleating agent was used and the annealing treatment was carried out at 75°C for 3 hours. Through the action of the nucleating agent, the grain size of the film was effectively controlled to ensure the uniformity and strength of the film.

[0094] Solvent Annealing: The film was placed in a solvent vapor of DMAc:THF:DCM (6.5:3:1) at 100°C for 18 min to improve the transparency and surface quality of the film.

[0095] Tensile strength test: A universal material testing machine (such as Instron 5960) was used to perform a tensile test, and the tensile strength of each sample was tested according to the standard tensile test method (GB / T1040.1-2006).

[0096] Experimental data: Table Name: Table 2: Comparison of tensile strength and related performance data of films of Examples and Comparative Examples Summarize: The results in Experiment 2 show that the tensile strength of Example 2 is significantly higher than that of Comparative Example 2, which indicates that the process of the present invention plays an important role in improving the mechanical properties of the film. By optimizing the rheologically induced directional crystallization process and the selection of nucleating agents, the film of Example 2 exhibits stronger tensile strength. In contrast, Comparative Example 2 did not use the optimized crystallization process, resulting in the molecular chain arrangement of the film not being as uniform as that of Example 2, and the tensile strength is naturally lower. The optimized rheologically induced crystallization process effectively improves the orientation of the molecular chains of the film, so that the tensile strength is improved, and the overall stability and durability of the film are stronger.

[0097] In addition, the use of a phosphate nucleating agent during the annealing process is one of the important innovations of the present invention. By introducing the nucleating agent, the grain size of the film is effectively controlled, ensuring the uniform distribution of the molecular chains and the mechanical properties of the film. Compared with Comparative Example 2 which does not use the nucleating agent, Example 2 forms a more uniform crystal structure during the annealing process, improving the tensile properties of the film.

[0098] The tensile strength of the film depends not only on the selection of ingredients, but also on the rheologically induced directional crystallization and annealing process. By reasonably adjusting key parameters such as shear rate, stretch ratio and annealing temperature, Example 2 can effectively improve the tensile strength of the film, avoiding the performance instability problem caused by the lower shear rate and shorter holding time in Comparative Example 2. Therefore, the process of the present invention provides an effective solution for significantly enhancing the tensile strength and mechanical stability of the film.

[0099] Experiment 3: Transmittance comparison experiment Experimental description: Purpose: This experiment aims to verify the advantages of the present invention in terms of optical performance, especially the relationship between surface quality and light transmittance, by comparing the light transmittance of the films of the embodiments and comparative examples.

[0100] Experimental Group: Example 3: Light transmittance = 94% Comparative Example 3: Light transmittance = 90% (film surface quality not optimized) Experimental steps: Blending and granulation: According to the formula of the experimental group and the control group, each component was put into a twin-screw extruder in proportion for blending. The formula includes: polyethylene terephthalate PET (87%), bisphenol A polyester BPA-PES (5%), N-alkylamide comonomer (6%), pyridine derivative (3%), organic phosphate nucleating agent (0.5%), sulfonate comonomer (1%), antioxidant (0.2%) and solvent residue (<0.1%). The temperature of the mixture was set to 275°C, the shear rate was set to 100r / min, and uniform particles were obtained with a particle size of 2mm.

[0101] Extrusion Casting: The above blend was extruded in a T-die, the casting temperature was set at 275°C, the cooling roller temperature was 100°C, the pulling speed was set at 8m / min, and the film thickness was 40μm. This process ensured the uniformity and appropriate transparency of the film.

[0102] Rheology-induced directional crystallization: The cast film was heated to 150°C and the shear rate was set to 3500 s 2 , stretching is performed in a stretching device with a stretching ratio of 4 times and a holding time of 50 seconds. This step is intended to improve the directional arrangement of the film's molecular chains, thereby improving its optical properties.

[0103] Metastable crystallization regulation: The film was treated with a phosphate nucleating agent in an annealing environment at 75°C for 5 h to ensure the uniformity of the film grains and reduce the light scattering effect.

[0104] Solvent Annealing: The film was placed in a DMAc:THF:DCM (7:3:1) mixed solvent, the temperature was set to 100°C, and the solvent vapor treatment time was 20 min. This step helps to further improve the transparency of the film and reduce surface defects.

[0105] Light transmittance test: Use a UV-Vis spectrometer (such as Hitachi U-3900H) to measure the transmittance of the film, and the test wavelength range is 400-800nm ​​to ensure that the transmittance test results of the film are accurate and reliable.

[0106] Experimental data: Table Name: Table 3: Comparison of light transmittance and related performance data of the films of the embodiment and the comparative example Summarize: The experimental results show that the light transmittance of Example 3 is significantly higher than that of Comparative Example 3, which verifies the advantages of the present invention in terms of optical performance. By optimizing the rheologically induced directional crystallization process and the solvent annealing process, the present invention not only improves the transparency of the film, but also effectively reduces the surface roughness. In the experiment, the light transmittance of the film of Example 3 was significantly improved through fine process control, such as temperature setting, shear rate and optimization of stretching ratio. This improvement can be directly attributed to the better directional arrangement of molecular chains and the uniformity of the film. This optimization improves the transmittance of light and reduces the scattering of light, making the film more transparent and suitable for demanding optical applications.

[0107] The transparency of the film is not only improved by the annealing process, but also by the cooling rate and the pulling speed in the casting process. By cooling rapidly at a suitable temperature and controlling the pulling speed, the surface quality of the film is improved, and the possibility of light scattering is reduced. Compared with the comparative example 3 in which the conventional process is not fully optimized, the present invention solves the problems of high surface roughness and low light transmittance of the film through more precise control, and significantly improves the optical performance of the film.

[0108] In addition, the use of nucleating agents in the metastable crystallization regulation process is a key innovation of the present invention. The introduction of phosphate nucleating agents optimizes the crystallization process, improves the grain structure of the film, reduces surface heterogeneity, and improves light transmittance. Compared with traditional methods, the process of the present invention can more effectively control the uniformity of the film surface, thereby improving the optical performance. By precisely adjusting the process conditions, the present invention can improve the mechanical properties of the film while ensuring its transparency, providing an efficient and feasible film preparation solution.

[0109] Experiment 4: Tear strength comparison experiment Experimental description: Purpose: This experiment aims to verify the improvement effect of the present invention in terms of durability by comparing the tear strength of the films of the embodiment and the comparative example.

[0110] Experimental Group: Example 4: Tear strength = 1.2 N / mm Comparative Example 4: Tear strength = 0.9 N / mm (solvent annealing process not optimized) Experimental steps: Blending and granulation: The components were put into a twin-screw extruder in proportion for mixing. The blend included: polyethylene terephthalate PET (83%), bisphenol A polyester BPA-PES (6%), N-alkylamide comonomer (9%), pyridine derivative (2%), organic phosphate nucleating agent (0.3%), sulfonate comonomer (1%), antioxidant (0.2%) and solvent residue (<0.1%). The blending temperature was set at 270°C and the shear rate was 100 r / min, and the particle size was 2.5 mm.

[0111] Extrusion Casting: The mixture was cast through a T-die, the casting temperature was 275°C, the cooling roller temperature was set to 100°C, the pulling speed was 10m / min, and the film thickness was controlled to be 35μm.

[0112] Rheology-induced directional crystallization: The film was heated to 150°C for 3500 seconds. 2 The film was stretched at a shear rate of 4 times and a holding time of 50 s to promote the directional arrangement of the molecular chains and improve the mechanical strength of the film.

[0113] Metastable crystallization regulation: Annealing at 75 °C for 5 h and treatment with a phosphate nucleating agent ensured that the grain size was controlled at 8 nm, improving the uniformity and strength of the film.

[0114] Solvent Annealing: The solvent ratio of DMAc:THF:DCM (6.5:3:1) was used, the temperature was set at 100°C, and the steam treatment time was 20 min. This step can optimize the surface quality of the film and improve the tear strength.

[0115] Tear strength test: The tear strength of each sample was measured using a Zwick tear tester according to ASTM D1004.

[0116] Experimental data: Table Name: Table 4: Comparison of tear strength and related performance data of films of the examples and comparative examples Summarize: From the results of Experiment 4, it can be seen that Example 4 shows a significant advantage in tear strength, with a tear strength of 1.2 N / mm, while the tear strength of Comparative Example 4 is only 0.9 N / mm. This result proves that by optimizing the solvent annealing process, the present invention can effectively improve the tear resistance of the film. In the experiment, the tear strength of the film is closely related to the fine control of the solvent annealing process, especially at a suitable solvent ratio and annealing temperature, the molecular chain structure of the film is significantly improved, thereby improving its durability.

[0117] In addition, the application of nucleating agents in metastable crystallization regulation further improves the grain structure of the film and avoids the film fragility caused by excessive grain size during the crystallization process. The use of phosphate nucleating agents not only enhances the uniformity of the film, but also effectively improves its mechanical properties, especially tear strength. Compared with Comparative Example 4, the present invention significantly improves its durability and tear resistance while maintaining the mechanical strength of the film by optimizing these process parameters, avoiding the film brittleness caused by uneven nucleation or improper treatment in the traditional process.

[0118] In the tensile and tear resistance tests, the film of Example 4 showed excellent comprehensive performance under the control of solvent annealing and metastable crystallization. The surface quality and structural uniformity of the film are improved, so that its tear strength is greatly improved and it can withstand more external stress. These experimental results show that by optimizing the process parameters, the present invention can significantly enhance the tear resistance of the film, and solve the problem of insufficient film durability in traditional technologies, showing very good application prospects.

[0119] Although embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions and variations may be made to the embodiments without departing from the principles and spirit of the present invention, and that the scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. An optical grade polyester film for polarizer release film, characterized in that: Includes the following components: Polyethylene terephthalate 80%-90%; Bisphenol A polyester 5% to 10%; 8% to 12% of N-alkylamide comonomer, wherein the carbon chain length of the N-alkylamide comonomer is C6 to C18 and the molecular structure contains at least one carbonyl group and an amide group; 3% to 6% of pyridine derivatives, and the substituents thereof are alkyl, fluoro, carboxyl or hydroxyl groups, and the carbon chain length of the substituents is C1 to C6; 0.3% to 0.6% of an organic phosphate nucleating agent, wherein the nucleating agent is a polyphosphate, a phosphate or a pyrophosphate; Sulfonate comonomer 0.5% to 1.5%; Antioxidant 0.2%~0.5%; The residual solvent content does not exceed 0.1%.

2. The optical grade polyester film for polarizer release film according to claim 1, characterized in that: The molecular weight of the polyethylene terephthalate (PET) is 50,000-1,000,000 g / mol, and the molecular chain presents a highly oriented structure.

3. The optical grade polyester film for polarizer release film according to claim 1, characterized in that: The surface roughness Ra of the film is 2.5-3.0 nm, the light transmittance is 93%-95%, and the tensile strength is 220-260 MPa.

4. A method for preparing an optical-grade polyester film for a polarizer release film, applied to the optical-grade polyester film for a polarizer release film according to claims 1-3, characterized in that: The following steps are involved: Blending and granulation: Add polyethylene terephthalate PET, bisphenol A polyester BPA-PES, N-alkylamide comonomer, pyridine derivative, and sulfonate comonomer to a twin-screw extruder in proportion, melt blend at 250-280°C, control the shear rate at 90-110r / min, granulate after extrusion, and control the particle size at 1-3mm; Extrusion casting: The blended pellets are extruded at 260-290°C, and a T-die is used for casting. The temperature of the cooling roller is set at 90-110°C, the pulling speed is 8-12m / min, and the film thickness is controlled at 20-50μm. Rheology-induced directional crystallization: In a constant temperature stretching device, the cast film is heated to 120-160°C for 3000-4000 seconds. 2 Orientation stretching is performed at a shear rate of 3 to 5 times, and the heat preservation time is 30 to 90 seconds; Metastable crystallization regulation: using an organic phosphate nucleating agent, annealing treatment is carried out at 60-100°C, the annealing time is controlled at 2-6h, and the grain size is controlled at 5-15nm; Solvent annealing: at 90-110° C., solvent vapor diffusion treatment is performed using dimethylacetamide DMAc, tetrahydrofuran THF and dichloromethane DCM, with the volume ratio of DMAc:THF:DCM controlled at 6-7:3-4:0.5-1, and the treatment time controlled at 15-25 min.

5. The method for preparing an optical grade polyester film for a polarizer release film according to claim 4, characterized in that: The shear rate of the rheologically induced directional crystallization step is controlled at 2500-4000 s 2 , the holding time is 30 to 90s, and the molecular chain orientation degree reaches 80% to 95%.

6. The method for preparing an optical grade polyester film for a polarizer release film according to claim 4, characterized in that: In the solvent annealing step, the volume ratio of DMAc, THF and DCM is 6.5-7: 3.2-4: 0.8-1, and the solvent action time is 15-25 minutes.

7. The method for preparing an optical grade polyester film for a polarizer release film according to claim 4, characterized in that: The organic phosphate nucleating agent in the metastable crystallization regulating step is phosphate, and a gradual temperature increase method is adopted during the annealing process, with a heating rate of 1 to 5°C / min.

8. The method for preparing an optical grade polyester film for a polarizer release film according to claim 4, characterized in that: The extrusion temperature in the blending and granulation step is controlled at 250-280° C. and the shear rate is 90-110 r / min to ensure that the components are fully mixed.

9. The method for preparing an optical grade polyester film for a polarizer release film according to claim 4, characterized in that: The temperature of the cooling roller in the extrusion casting step is 90-110° C., and the pulling speed is 8-12 m / min to control the film thickness and surface smoothness.

10. The method for preparing an optical grade polyester film for a polarizer release film according to claim 4, characterized in that: The mechanical properties of the film are further manifested in a tear strength of 1.0 to 1.2 N / mm.

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