Optical antistatic polyester multilayer composite functional film and preparation method thereof

Abstract

The invention relates to the technical field of multi-layer polyester functional films, in particular to an optical antistatic polyester multi-layer composite functional film and a preparation method thereof. The problem that in the prior art, the optical performance and the antistatic performance of a polyester multilayer composite functional film cannot be considered at the same time is solved. The preparation method comprises the following steps: by adopting a surface layer-middle layer-surface layer three-layer structure, by taking terephthalic acid and ethylene glycol as raw materials, adding 1, 4-cyclohexanedimethanol and isophthalic acid for copolymerization, so as to prepare a copolymerized polyester base material; wherein the surface layer consists of a copolymerized polyester base material and an antistatic functional master batch; the middle layer is composed of a copolymerized polyester base material, an ultraviolet-resistant functional master batch and a chain extension toughening agent, and the three layers of materials are subjected to co-extrusion, two-way stretching and heat setting processes to prepare the polyester multi-layer composite functional film; the optical performance and the antistatic performance are cooperatively optimized through the multi-layer function partition design, and the liquid crystal display panel can be applied to the high-end optical fields such as liquid crystal display, touch panels and photovoltaic backboards.

Description

Technical Field

[0001] This invention relates to the field of multilayer polyester functional film technology, specifically to an antistatic polyester multilayer composite functional film for optical applications and its preparation method. Background Technology

[0002] Multilayer polyester composite functional films, with their excellent mechanical strength, chemical stability, processing adaptability, and cost advantages, have become core basic materials in high-end optical fields such as liquid crystal displays, touch panels, photovoltaic packaging, electronic devices, and automotive central control screens. Their performance directly affects the display effect, service life, and operational stability of end products. However, in practical applications, the synergistic optimization of optical performance and antistatic performance remains a core technical bottleneck for the industry. Existing technical solutions have many insurmountable defects, severely limiting the large-scale application of multilayer polyester composite functional films in high-end scenarios.

[0003] Traditional modification schemes for multilayer antistatic polyester films have significant drawbacks: First, while physically blending conductive fillers can improve antistatic properties, it can also disrupt the optical uniformity of the film, leading to decreased light transmittance and increased haze, failing to meet the high transparency requirements of high-end optical devices. Second, although adding small-molecule antistatic agents has little impact on optical performance, they are prone to migration and precipitation, causing not only a short-term decline in antistatic properties but also contaminating the contact interface and affecting product reliability. Third, some multilayer structures lack functional zoning optimization, resulting in a mixed distribution of antistatic components with UV-resistant and reinforcing components, which not only interferes with each other's performance but also exacerbates the risk of interlayer delamination due to compatibility issues.

[0004] In summary, existing modification schemes for multilayer polyester composite functional films often compromise on one aspect while neglecting the simultaneous protection of optical performance. This results in a situation where optical and antistatic properties cannot be simultaneously achieved, further restricting their large-scale application in high-end optical fields.

[0005] To this end, an antistatic polyester multilayer composite functional film for optical applications and its preparation method are proposed. Summary of the Invention

[0006] The purpose of this invention is to provide an antistatic polyester multilayer composite functional film for optical applications and its preparation method. This invention employs a three-layer structure: a surface layer, an intermediate layer, and another surface layer. Using terephthalic acid and ethylene glycol as raw materials, 1,4-cyclohexanediethanol and isophthalic acid are added for copolymerization to prepare a copolyester base material. The surface layer consists of the copolyester base material and an antistatic functional masterbatch. The intermediate layer consists of the copolyester base material, a UV-resistant functional masterbatch, and a chain extender / toughening agent. The three layers are co-extruded, biaxially stretched, and heat-set to obtain the polyester multilayer composite functional film. Through multilayer functional partitioning design, the optical and antistatic properties are synergistically optimized, making it applicable to high-end optical fields such as liquid crystal displays, touch panels, and photovoltaic backsheets.

[0007] To achieve the above objectives, the present invention provides the following technical solution: This invention provides a method for preparing an antistatic polyester multilayer composite functional film for optical applications, comprising the following steps: By mass, the copolyester base material was fed into a dehumidifying drying tower and dried at 150℃ for 6 hours. The antistatic and UV-resistant masterbatches were vacuum dried at 100℃ for 6 hours, with the dew point controlled below -45℃ and the moisture content <20ppm to obtain the dried material. The dried material was then added to a three-layer co-extrusion system, in a layered manner of surface layer-intermediate layer-surface layer. The surface layer consisted of 90 parts copolyester base material and 8-15 parts antistatic masterbatch, while the intermediate layer consisted of 95 parts copolyester base material, 3-6 parts UV-resistant masterbatch, and 0.15 parts ADR. The screw speed of the surface layer extruder was 45 rpm, and the barrel temperature was 265℃. The screw speed of the intermediate layer extruder was 120 rpm, and the barrel temperature was 280℃. The melt was distributed through a three-layer symmetrical distributor, and the actual flow ratio was adjusted to 1:10:1 before entering the T-die, with a die lip gap of 1.5 mm. The melt is subjected to electrostatic bonding at 10kV on a 30℃ quenching roller to obtain a polyester sheet. The polyester sheet is then sequentially fed into a biaxial stretching unit, where the longitudinal stretching section is preheated at 85℃, stretched at 95-105℃, and stretched by 3.0-3.8 times; the transverse stretching section is preheated at 100℃, stretched at 115-135℃, and stretched by 3.5-4.8 times. The stretched film is then placed in a heat-setting zone and treated at 220-240℃ for 20-40 seconds. Finally, after cooling, trimming, and winding, a composite functional film with a final thickness of 50μm-100μm is obtained.

[0008] Preferably, the preparation of the copolyester base material includes the following steps: Add 100 parts of terephthalic acid, 50 parts of ethylene glycol, 3-5.5 parts of 1,4-cyclohexanediethanol, and 1.5-4 parts of isophthalic acid to a reactor, start stirring at 80 rpm, and carry out the esterification reaction at 0.25 MPa pressure and 240-250℃. The temperature of the distillate is maintained at 100-105℃ by temperature control using a fractionation column. After the water yield reaches 96% of the theoretical value, the pressure is released to atmospheric pressure. Then add 0.04 parts of antimony glycolate and 0.015 parts of trimethyl phosphate, and proceed to the pre-condensation stage. In the first stage, the temperature is raised to 260℃-270℃, and the pressure is reduced from atmospheric pressure to 2kPa within 60 minutes. Then, the polycondensation stage begins, with the temperature raised to 280-285℃, the vacuum reduced to 80Pa, and the stirring speed reduced from 80rpm to 20rpm as the melt viscosity increases. The polycondensation reaction is then carried out, followed by nitrogen pressing, water cooling, and pelletizing to obtain a copolyester base material with an intrinsic viscosity of 0.68-0.72dL / g. The weight-average molecular weight of the copolyester base material is 36800-40200, and the melting point is 243-249℃.

[0009] Preferably, the preparation of the antistatic functional masterbatch includes the following steps: Add 10-30 parts of polyetheramine, 20 parts of copolyester base material, and 0.05 parts of dicumyl peroxide to a reactor, heat to 90-100℃, and slowly add 5-12 parts of glycidyl methacrylate dropwise over 30 minutes while stirring at 500 rpm. After the addition is complete, continue the pre-reaction mixing at this temperature for 2.5 hours to obtain the antistatic precursor. Feed 50 parts of copolyester base material into the main feed port of a twin-screw extruder through a loss-in-weight feeder. Add the antistatic precursor through the fourth zone of the extruder, and simultaneously add the chain extender and toughening agent ADR through the side feed port in the sixth zone. 0.25 parts of a twin-screw compressor with an L / D ratio of 48:1 and a screw speed of 450 rpm were prepared. The barrel temperature distribution was as follows: Zone 1 240℃, Zones 2 to 5 265℃, Zones 6 to 10 260℃. After the melt was fully sheared and dispersed, it was filtered through a 10μm filter membrane, water-cooled, air-dried and pelletized to obtain antistatic functional masterbatch.

[0010] Preferably, in the pre-reaction stage of this invention, the long-chain antistatic center PEA is pre-coupled with the monomer GMA with unsaturated double bonds through chemical bonds, forming an antistatic precursor that has both antistatic function and subsequent reactivity. Under the high temperature and high shear environment of the twin-screw extruder, the antistatic precursor undergoes a grafting reaction with the copolyester matrix. The epoxy functionalized chain extender and toughening agent added to the system contains multiple active epoxy groups, which further enhances the interfacial compatibility and chemical bond strength between the antistatic component and the polyester matrix.

[0011] Preferably, the preparation of UV-resistant functional masterbatch includes the following steps: 85 parts of copolyester base material and 15 parts of triazine absorber are mixed in a high-speed mixer at 1000 rpm for 5 minutes, and then fed into a twin-screw extruder. The extrusion temperature is set to 260-275℃ and the screw speed is 300-400 rpm. After fully melt extrusion and pelletizing, UV-resistant functional masterbatch is obtained.

[0012] The present invention also provides an antistatic polyester multilayer composite functional film for optical applications. The raw materials for preparing the multilayer composite functional film include terephthalic acid, ethylene glycol, 1,4-cyclohexanediol, isophthalic acid, polyetheramine, glycidyl methacrylate, ADR, and triazine absorbers.

[0013] Compared with the prior art, the beneficial effects of the present invention are as follows: 1. This invention introduces CHDM and IPA into the polyester base material for copolymerization modification, which disrupts the regularity of the molecular chain and reduces the crystallization rate. At the same time, chain extender and toughening agent ADR is added to the surface layer and the intermediate layer to improve the interlayer molecular chain entanglement strength through chemical bonding. This solves the problem that traditional modified polyester films cannot achieve both strength and flexibility, and meets the stringent requirements of high-end optical devices for the mechanical stability of the film material.

[0014] 2. This invention introduces chain extender and toughening agent ADR into both the surface layer and the intermediate layer. Its epoxy groups can undergo ring-opening addition reactions with the carboxyl and hydroxyl groups at the polyester chain ends, forming molecular bridges between the layers to achieve chemical bonding. At the same time, the grafted polar segments in the antistatic masterbatch improve the interfacial compatibility between the surface layer and the intermediate layer, ensuring the long-term stability of the multilayer structure. Compared with the existing technology where the multilayer polyester film layers rely solely on the physical entanglement of molecular chains, this invention avoids the deterioration of optical and mechanical properties caused by delamination.

[0015] 3. This invention disrupts the regularity of polyester molecular chains through CHDM, avoiding the formation of large-sized spherulites during biaxial stretching and reducing light scattering; it fine-tunes the refractive index of the polyester chains through IPA to match the refractive index of the antistatic components grafted onto the surface layer, reducing interlayer light reflection loss; at the same time, the antistatic masterbatch adopts an in-situ grafting process to avoid component agglomeration, achieving a perfect balance between high light transmittance and low haze compared to using physically blended conductive fillers.

[0016] 4. This invention concentrates triazine absorbers in the intermediate layer and uses a thick-layer design to efficiently intercept ultraviolet rays, protecting the surface layer and the substrate; the antistatic component is chemically grafted and anchored to the polyester main chain to prevent migration and precipitation; the addition of ADR enhances the hydrolysis resistance of the molecular chain, solves the problem of insufficient aging resistance of traditional polyester films, and extends the service life of the product in outdoor or long-term light exposure environments.

[0017] 5. This invention prepares an antistatic precursor by pre-reacting PEA and GMA, and then grafts it in situ with a copolyester base material to firmly anchor the conductive long chain onto the polyester main chain, forming a stable conductive path; the surface layer ensures that the antistatic function reaches the surface directly, solving the pain points of traditional antistatic polyester films that have short-lasting antistatic properties and are easily contaminated, and meeting the long-term requirements of electronic devices and optical displays for cleanliness and electrostatic protection. Attached Figure Description

[0018] Figure 1 The graph shows the change in tensile strength retention rate of the polyester multilayer composite functional films prepared in Examples 1-3 and Comparative Examples 6-10 of this invention before and after aging. Detailed Implementation

[0019] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. 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.

[0020] In this invention, PTA is terephthalic acid, CAS number 100-21-0, and acid value 675±2 mgKOH / g; CHDM is 1,4-cyclohexanediethanol, with a cis:trans ratio of 3:7, and CAS number 105-08-8; IPA is isophthalic acid, with a meta-position content ≥99.8%; PEA is polyetheramine, specifically amino-terminated polyoxypropylene ether, with a weight-average molecular weight of 2000-3000 and an amino-terminated content ≥1.0 mmol / g; GMA is glycidyl methacrylate; the chain extender and toughening agent is ADR 4468, which belongs to epoxy-functionalized styrene-acrylate copolymer, wherein the epoxy equivalent is 280-310 g / mol, and the Mw is 7000-9000; the triazine absorber is UV-1577, CAS number 147315-50-2.

[0021] Please see Figure 1 This invention provides an antistatic polyester multilayer composite functional film for optical applications and its preparation method. The technical solution is as follows: Example 1

[0022] 100 parts of terephthalic acid, 50 parts of ethylene glycol, 4.2 parts of 1,4-cyclohexanediethanol and 2.8 parts of isophthalic acid were added to a reactor. The stirring was started at 80 rpm, and the esterification reaction was carried out at 0.25 MPa and 240℃. The temperature of the distillate was kept between 100-105℃ by temperature control using a fractionating column. After the water output reached 96% of the theoretical value, the pressure was released to atmospheric pressure. Then, 0.04 parts of antimony glycolate and 0.015 parts of trimethyl phosphate were added to enter the pre-condensation stage. The temperature was raised to 260℃, and the pressure was reduced from atmospheric pressure to 2 kPa within 60 minutes. Then, the condensation stage was entered. The temperature was raised to 280℃, the vacuum was reduced to 80 Pa, and the stirring speed was reduced from 80 rpm to 20 rpm as the melt viscosity increased. The condensation reaction was carried out, and the product was discharged under nitrogen, water-cooled and pelletized to obtain a copolyester base material with an intrinsic viscosity of 0.69 dL / g.

[0023] 20 parts of polyetheramine, 20 parts of copolyester base material, and 0.05 parts of dicumyl peroxide were added to a reactor and heated to 90°C. Under high-speed stirring at 500 rpm, 8 parts of glycidyl methacrylate were slowly added dropwise over 30 minutes. After the addition was completed, the reactor was kept at the temperature for a pre-reaction of 2.5 hours to obtain an antistatic precursor. 50 parts of copolyester base material were fed into the main feed port of a twin-screw extruder through a loss-in-weight feeder. The antistatic precursor was added in the fourth zone of the extruder, and 0.25 parts of chain extender and toughening agent ADR were added at the side feed port. The twin-screw had an L / D ratio of 48:1, a screw speed of 450 rpm, and a barrel temperature distribution of 240°C in zone 1, 265°C in zones 2-5, and 260°C in zones 6-10. After the melt underwent a fully sheared in-situ grafting reaction, it was filtered through a 10 μm filter membrane, water-cooled, air-dried, and pelletized to obtain an antistatic functional masterbatch.

[0024] 85 parts of copolyester base material and 15 parts of triazine absorbent were mixed in a high-speed mixer at 1000 rpm for 5 minutes. Then the mixture was fed into a twin-screw extruder, and the extrusion temperature was set to 260-275℃ and the screw speed was 350 rpm. After fully melt extrusion and pelletizing, UV-resistant functional masterbatch was obtained.

[0025] The copolyester base material was fed into a dehumidifying drying tower and dried at 150℃ for 6 hours. The antistatic and UV-resistant masterbatches were vacuum dried at 100℃ for 6 hours, with the dew point controlled below -45℃ and the moisture content <20ppm to obtain the dried material. The dried material was then added to a three-layer co-extrusion system, in a layered manner of surface layer-intermediate layer-surface layer. The surface layer consisted of 90 parts copolyester base material and 10 parts antistatic masterbatch; the intermediate layer consisted of 95 parts copolyester base material, 4 parts UV-resistant masterbatch, and 0.15 parts ADR. The surface layer extruder screw speed was 45 rpm, and the surface layer barrel temperature was 265℃. The intermediate layer extruder screw speed was 120 rpm, and the intermediate layer barrel temperature was 280℃. The melt was distributed through a three-layer symmetrical distributor, with the actual flow ratio adjusted to 1:10:1, and entered the T-die, with a die lip gap of 1.5 mm. The melt is subjected to electrostatic bonding at 10kV on a 30℃ quenching roller to obtain a polyester sheet. The polyester sheet is then sequentially fed into a biaxial stretching unit, where the longitudinal stretching section has a preheating temperature of 85℃, a stretching temperature of 98℃, and a stretching ratio of 3.3 times; the transverse stretching section has a preheating temperature of 100℃, a stretching temperature of 125℃, and a stretching ratio of 4.2 times. The stretched film is then placed in a heat-setting zone and treated at 230℃ for 30 seconds. Finally, after cooling, edge trimming, and winding, a composite functional film with a final thickness of 50μm is obtained.

[0026] Examples 2-5 follow the same preparation method and parameter conditions as Example 1, with differences shown in Table 1.

[0027] Table 1. Parameter variations in Examples 1-5

[0028] Comparative Example 1 differs from Example 1 in that CHDM and IPA are not added in the preparation of the copolyester base material, only PTA and EG are used, and the amounts of other components remain unchanged.

[0029] Comparative Example 2 differs from Example 1 in that CHDM is not added in the preparation of the copolyester base material; only PTA, EG, and IPA are used for ternary copolymerization, while the amounts of other components remain unchanged.

[0030] Compared to Example 1, Comparative Example 3 differs in that IPA is not added in the preparation of the copolyester base material; only PTA, EG, and CHDM are used for ternary copolymerization, while the amounts of other components remain unchanged.

[0031] Compared to Example 1, Comparative Example 4 differs in that the amount of antistatic masterbatch added to the surface layer is increased to 30 parts.

[0032] Compared to Example 1, Comparative Example 5 differs in that the heat setting temperature is set at 250°C, which is close to the melting point of the resin base.

[0033] Comparative Example 6 differs from Example 1 in that no ADR is added to either the surface layer or the intermediate layer.

[0034] Compared to Example 1, Comparative Example 7 differs in that the thickness ratio of the surface layer-intermediate layer-surface layer is adjusted to 1:2:1, while the amounts of other components remain unchanged.

[0035] Compared to Example 1, Comparative Example 8 differs in that no triazine absorbent is added to the intermediate layer, while the amounts of the remaining components remain unchanged.

[0036] Comparative Example 9 differs from Example 1 in that it uses PEA directly physical blended and extruded with the copolyester base material without adding grafting agent GMA.

[0037] Compared to Example 1, Comparative Example 10 differs in that PEA and GMA are not pre-reacted in the preparation of the antistatic functional masterbatch, but are directly fed into the extruder for blending.

[0038] Comparative Example 11 differs from Example 1 in that the raw material drying temperature is set at 100°C and the moisture content is >500ppm.

[0039] Comparative Example 12 differs from Example 1 in that the surface layer extrusion screw speed is set to 5 rpm to maintain extremely low shear force.

[0040] Comparative Example 13 differs from Example 1 in that the lateral stretching ratio is set to 3.0 times.

[0041] Experimental Example 1: Mechanical Property Testing The polyester multilayer composite functional films prepared in Examples 1-5 and Comparative Examples 1-5 were subjected to mechanical property tests. The tensile strength and elongation at break were tested according to GB / T 1040.3-2006, and the hardness was tested according to GB / T 2411-2008. The test results are shown in Table 2.

[0042] Table 2 Test Results of Examples and Comparative Examples

[0043] As shown in Table 2, the mechanical properties of the polyester multilayer composite functional film obtained in the comparative examples, through adjustments to the components and processes, are significantly different from those in the examples. The examples, by introducing 1,4-cyclohexanediethanol and isophthalic acid into the polyester base material, disrupted the regularity of the pure polyester chain, reduced the crystallization rate, and thus significantly improved the film's flexibility and elongation at break while maintaining high strength. Furthermore, the addition of ADR chain extender and toughening agent acted as a molecular bridge at the interface between the surface and intermediate layers, improving interlayer adhesion and the overall mechanical stability of the film. In Comparative Examples 1-3, the pure PET molecular chain exhibited extremely high regularity, resulting in a very fast crystallization rate during processing. Without the addition of CHDM and IPA, the polyester molecular chain was extremely regular, leading to rapid thermal crystallization in the stretching thermal field. While this high crystallinity results in high hardness, it also leads to extreme brittleness of the film, reduced elongation at break, and tensile strength limited by brittle fracture in the crystalline region. The lack of steric hindrance and flexible segments provided by the CHDM alicyclic structure limits the effectiveness of crystallization suppression, making the film prone to secondary crystallization in the heat-setting region, resulting in insufficient toughness improvement and reduced elongation. The absence of IPA causes the disappearance of the irregular interpositional structure of the molecules, leading to uneven distribution of orientation stress in the film. Although hardness and strength are still acceptable, under high-ratio biaxial stretching, the lack of IPA-mediated crystallization rate regulation makes it easy for microscopic particles to accumulate inside the film. Stress leads to a low final elongation. In Comparative Example 4, when the surface layer antistatic masterbatch increases, the proportion of low molecular weight PEA grafted segments in the polyester matrix is ​​too large, which destroys the integrity of the PET continuous phase. These heterogeneous components are prone to forming stress concentration points when stretched, resulting in a significant deterioration in both tensile strength and elongation. In Comparative Example 5, the excessively high setting temperature is close to the melting point of the base material, which easily induces severe thermal over-crystallization and coarse grains. The formation of large-sized spherulites causes the film to completely lose its flexibility, exhibiting high hardness and low elongation. Furthermore, the tensile strength is impaired due to numerous internal defects.

[0044] Experiment Example 2: Optical Performance Testing The polyester multilayer composite functional films prepared in Examples 1-5 and Comparative Examples 1-8 were subjected to optical performance tests. The total light transmittance and haze were tested according to GB / T 2410-2008. The test results are shown in Table 3.

[0045] Table 3 Test Results of Examples and Comparative Examples

[0046] As shown in Table 3, the optical properties of the polyester multilayer composite functional film obtained in the comparative examples, through adjustments to the components and processes, are significantly different from those in the examples. Combined with Experimental Example 1, it can be seen that the introduction of CHDM disrupts the regularity of polyester molecules, significantly reducing the induced crystallization rate of the film during biaxial stretching, avoiding the formation of large-sized spherulites, and thus minimizing scattering. Furthermore, the addition of IPA fine-tunes the refractive index of the polyester chains, making it highly compatible with the refractive index of the antistatic component grafted onto the surface layer, reducing light reflection loss at the interlayer interface. Combined with the results of Comparative Examples 1-3, it can be seen that… Using only PTA and EG, the polyester chain is highly regular, leading to intense crystallization during stretching. The formation of large-sized grains causes severe Mie scattering of light, resulting in increased haze and decreased transmittance. The alicyclic structure of CHDM has significant steric hindrance; its absence weakens the crystallization inhibition effect, making the film prone to secondary crystallization in the heat-setting region, affecting optical clarity and flexibility. The lack of IPA to regulate the crystallization rate makes the film prone to accumulating micro-stress, impairing optical uniformity and resulting in significantly higher haze compared to the previous example. In Comparative Example 4, the excessively high antistatic masterbatch... The excessive addition of low-molecular-weight grafted components and amorphous regions resulted in an excessively high proportion, leading to significant micro-phase separation. These heterogeneous regions formed numerous light scattering centers, significantly reducing total transmittance and resulting in the highest haze. In Comparative Example 5, the excessively high setting temperature triggered severe secondary crystallization and grain coarsening. The excessive grain growth caused the film to exhibit a white haze phenomenon, and transmittance was significantly suppressed. In Comparative Example 6, the lack of ADR chain extender led to a decrease in rheological compatibility and molecular chain entanglement strength at the surface layer-intermediate layer interface. During high-speed stretching, fine voids or unevenness may occur at the interface, increasing light scattering. The haze increased. In Comparative Example 7, the surface layer-intermediate layer-surface layer thickness ratio was adjusted to 1:2:1, which means that the surface layer containing functional additives became significantly thicker. Since the surface layer contains more grafted antistatic components, its volume scattering is higher than that of the pure base material layer. The increased thickness accumulates more scattering effects, resulting in increased haze. In Comparative Example 8, no UV absorber was added to the intermediate layer, but it lacked a high-energy UV light capture center. Since there was no additive to affect the absorption of specific wavelengths, its initial haze and transmittance were acceptable, but after actual UV aging, it will undergo severe yellowing and turbidity.

[0047] Experiment Example 3 Adhesion Test The adhesion properties of the polyester multilayer composite functional films obtained in Examples 1-5 and Comparative Examples 6-8 were tested. The interlayer peel force was tested according to GB / T 8808-1988. Samples with a width of 15 mm and a length of 200 mm were cut and peeled continuously at a speed of 300 mm / min using the T-method. The average value of the stable force during peeling was taken as the peel force of the sample. The surface wetting tension was tested according to GB / T 14216-2008. A standard wetting test solution composed of formamide and ethylene glycol ethyl ether was used to coat a liquid film of approximately 6 cm² on the surface of layer A. The shrinkage or rupture of the liquid film within 2 seconds was observed, and the liquid value that could maintain wetting for exactly 2 seconds was found. The test results are shown in Table 4.

[0048] Table 4. Results of the Example and Comparative Tests

[0049] As shown in Table 4, the adhesion performance of the polyester multilayer composite functional film obtained in the comparative example, through adjustments to the components and process, is significantly different from that in the example. In the example, the chain extender and toughening agent ADR was introduced into both the surface layer and the intermediate layer. ADR can undergo ring-opening addition with the carboxyl or hydroxyl groups at the ends of the polyester chain through chemical reaction, forming a cross-interfacial molecular stitching effect at the melt interface of co-extrusion, tightly bonding the surface layer and the intermediate layer together. In addition, the antistatic functional components PEA and GMA underwent an in-situ grafting reaction during extrusion. The grafted polar segments not only endow the film with antistatic properties, but the polar groups in their molecular structure also significantly increase the free energy of the film surface, which is beneficial to the subsequent bonding process. In Comparative Example 6, without the interfacial chemical bridge of ADR, the surface-intermediate layer relies solely on physical molecular chain entanglement during co-extrusion. Due to the huge interfacial shear stress generated during biaxial stretching, the physical entanglement is insufficient to maintain structural integrity, resulting in layer... The adhesion between layers is extremely low, making delamination very easy. In Comparative Example 7, when the layer thickness ratio is adjusted to 1:2:1, the proportion of the surface layer increases significantly. In the co-extrusion channel, due to the presence of more grafted and modified antistatic components in the surface layer material, its rheological properties do not fully match those of the intermediate layer. The thicker surface layer will generate more complex and unstable flow when the distributor merges. Furthermore, in the subsequent biaxial stretching, due to the greater deformation resistance of the thick functional area, the stress concentration at the interface is severe, thus weakening the overall peel strength. In Comparative Example 8, although the main function of the absorbent is aging resistance, it exists in the intermediate layer, and the base material ratio has been slightly adjusted. The absence of UV absorbent means that the proportion of pure polyester component in the intermediate layer is higher. The crystallization rate and melt viscosity of the intermediate layer change slightly, resulting in a difference in the molecular chain diffusion depth when it comes into contact with the surface sensitive layer compared to when it contains additives. This has a slight impact on the initial peel strength, but its main risk lies in the performance degradation caused by photo-oxidative degradation in the later stage.

[0050] Experiment Example 4: Aging Resistance Test The polyester multilayer composite functional films obtained in Examples 1-5 and Comparative Examples 6-10 were subjected to aging resistance tests. The yellow index before and after aging was measured using a spectrophotometer with a D65 light source and a 10° observer angle, according to GB / T 16422.2-2022. The samples were fixed in a xenon arc lamp aging test chamber, and the irradiation intensity was set to 0.51 W / (m²) at 340 nm. 2 The blackboard temperature was 65℃, the relative humidity was 50%, and the exposure was continuous for 1000 hours. The change in yellowing index was calculated. The longitudinal tensile strength was tested according to GB / T 1040.3-2006. The tensile strength before and after aging was tested, and the tensile strength retention rate before and after aging was calculated. The test results are shown in Table 5. The changes in tensile strength retention rate before and after aging of the polyester multilayer composite functional films prepared in Examples 1-3 and Comparative Examples 6-10 are shown in Table 5. Figure 1 As shown.

[0051] Table 5 Test Results of Examples and Comparative Examples

[0052] Through Table 5, Figure 1The results show that the aging resistance of the polyester multilayer composite functional film obtained in the comparative example, through adjustments to the components and processes, is significantly different from that of the example. In the example, the strategy of anchoring the antistatic component to the polyester molecular chain through chemical grafting fundamentally locks in easily migrating small molecules. Simultaneously, the UV absorber is concentrated in the thicker intermediate layer, utilizing a layered structure to achieve efficient UV interception and protection of the functional layer, allowing the film to maintain extremely high mechanical strength even after long-term exposure. In Comparative Example 6, the lack of the chain extender and toughening agent ADR resulted in weak interlayer adhesion between the surface layer and the intermediate layer. Under aging conditions, moisture easily penetrated along the weakly bonded interface, inducing local hydrolysis or micro-delamination, leading to a significantly lower tensile strength retention rate after aging compared to the example, exhibiting poor aging resistance. In Comparative Example 7, although the intermediate layer contained a UV absorber, its insufficient absolute thickness shortened the UV penetration path. The reduced protective ability of the substrate leads to a significant increase in the yellowing index and impaired mechanical strength retention. Combined with the results of Comparative Example 8, it is evident that without the addition of a UV absorber, long-term UV irradiation causes severe photo-oxidative degradation of the polyester molecular chains, generating a large number of chromophores that result in severe yellowing. Simultaneously, molecular chain breakage leads to brittleness of the film material and a decrease in tensile strength retention. Comparative Examples 9-10 show that without the grafting agent GMA, the antistatic component PEA only undergoes physical blending with the matrix material and cannot form chemical bonds. Under aging conditions, small-molecule PEA rapidly migrates to and aggregates on the surface, accompanied by small molecule loss. Although the polyester matrix is ​​slightly less damaged, the continuity of the internal structure is compromised due to component loss, resulting in a significant decrease in tensile strength retention. Without a pre-reaction process, a large number of unreacted small molecules and unevenly dispersed reactants remain in the system. During aging, these unstable components undergo localized degradation or phase separation, leading to a significant reduction in tensile properties after aging.

[0053] Experimental Example 5: Antistatic Performance The antistatic properties of the polyester multilayer composite functional films prepared in Examples 1-5 and Comparative Examples 9-13 were tested. Following GB / T 31838.2-2019, using a high-resistivity meter, the composite films were cut into 100mm × 100mm square samples, ensuring the test surface was clean. The samples were pretreated for 24 hours at 23℃ and 50% relative humidity. The samples were then placed under electrodes in a shielded box, and a test voltage of 100V was applied. The resistance value was read 60 seconds after the voltage was applied. Subsequently, the samples were treated at 85℃ / 85%RH for 500 hours, then removed and equilibrated under standard conditions for 24 hours before the resistivity change was measured again. Following GB / T31838.4-2019, using an electrostatic decay tester, the samples were fixed on a test frame, and a high-voltage discharge was applied to the film surface through electrodes, causing the surface voltage to instantaneously reach 5000V. The power was then cut off, and the time required for the surface voltage to decay from the initial 5000V to 50V was recorded. The test results are shown in Table 6.

[0054] Table 6 Test Results of Examples and Comparative Examples

[0055] As shown in Table 6, the antistatic properties of the polyester multilayer composite functional film obtained in the comparative examples, through adjustments to the components and processes, are significantly different from those in the examples. In the examples, the precursor formed by the pre-reaction of PEA and GMA allows for grafting between the epoxy groups of GMA and the carboxyl groups at the ends of the copolyester during extrusion. This chemical bonding firmly anchors the conductive long chains to the polyester backbone, preventing them from moving freely and precipitating under humid heat aging, thus ensuring the long-term stability of resistivity. In Comparative Example 9, without the grafting agent GMA, PEA and the polyester matrix are only physically mixed, lacking chemical binding. Under humid heat, PEA small molecules are rapidly migrated to the surface driven by moisture and are washed away, leading to the loss of the surface conductive network function. In Comparative Example 10, without pre-reaction, the reaction efficiency in the extruder is low, resulting in… The system contains a large number of free small molecules, which aggregate locally during aging, resulting in an optical haze, and the initial charge dissipation efficiency is significantly lower than that of the examples. In Comparative Example 11, the high water content causes severe thermal hydrolysis of the polyester, leading to molecular weight collapse. Although there is an antistatic component, the degradation of the substrate structure causes the conductive pathway to be interrupted due to microcracks during aging. In Comparative Example 12, the low shear force cannot produce a rheology-induced gradient enrichment effect. The grafted component is uniformly distributed in the thickness direction of the surface layer, resulting in a significant reduction in the density of the surface charge dissipation center and a prolonged electrostatic decay time. At the same time, the low stretching in Comparative Example 13 is insufficient to induce sufficient orientation of the molecular chains, and it is even more impossible to stretch the dispersed conductive segments and connect them to form a network, thus failing to form a stable conductive pathway. Since the conductive pathway is in a broken state, the resistivity is high.

[0056] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A method for preparing an antistatic polyester multilayer composite functional film for optical applications, characterized in that, Includes the following steps: Polyester sheets are obtained by melt extrusion of a layered structure of surface layer-intermediate layer-surface layer and rapid cooling roll; then, the multilayer composite functional film is obtained by biaxial stretching and heat setting. The surface layer is obtained by mixing copolyester base material and antistatic functional masterbatch. The intermediate layer is obtained by mixing the copolyester base material, UV-resistant functional masterbatch, and epoxy-functionalized styrene-acrylate copolymer. The copolyester base material is obtained by esterification and polycondensation reaction of terephthalic acid, ethylene glycol, 1,4-cyclohexanediol, and isophthalic acid. The antistatic functional masterbatch is obtained by melt extrusion of polyetheramine, glycidyl methacrylate, epoxy-functionalized styrene-acrylate copolymer, and copolyester base material. The UV-resistant functional masterbatch is obtained by melt extrusion of the copolyester base material and triazine absorber.

2. The method for preparing an antistatic polyester multilayer composite functional film for optical applications according to claim 1, characterized in that, The preparation of the copolyester base material includes the following steps: adding the terephthalic acid, the ethylene glycol, the 1,4-cyclohexanediethanol and the isophthalic acid into a reaction vessel and performing an esterification reaction under stirring; then adding antimony glycolate and trimethyl phosphate, and obtaining the copolyester base material through a polycondensation reaction.

3. The method for preparing an antistatic polyester multilayer composite functional film for optical applications according to claim 1, characterized in that, The preparation of the antistatic functional masterbatch includes the following steps: adding the polyetheramine and the copolyester base material to a reactor, adding the glycidyl methacrylate dropwise under stirring conditions, and mixing under heat to obtain an antistatic precursor; adding the copolyester base material to a twin-screw extruder, adding the antistatic precursor through the fourth zone, adding the epoxy functionalized styrene-acrylate copolymer through the side feed port, melt extruding, filtering, water cooling, air drying, and pelletizing to obtain the antistatic functional masterbatch.

4. The method for preparing an antistatic polyester multilayer composite functional film for optical applications according to claim 1, characterized in that, The preparation of the UV-resistant functional masterbatch includes the following steps: mixing the copolyester base material and the triazine absorbent in a high-speed mixer, then feeding it into a twin-screw extruder, and obtaining the UV-resistant functional masterbatch through melt extrusion and pelletizing.

5. The method for preparing an antistatic polyester multilayer composite functional film for optical applications according to claim 1, characterized in that, The surface layer contains 8-15 parts by weight of the antistatic masterbatch; the intermediate layer contains 3-6 parts by weight of the UV-resistant masterbatch.

6. The method for preparing an antistatic polyester multilayer composite functional film for optical applications according to claim 1, characterized in that, The biaxial stretching and heat setting process includes the following steps: longitudinal stretching temperature is 90-105℃, stretching ratio is 3.0-3.8 times; transverse stretching temperature is 115-135℃, stretching ratio is 3.5-4.8 times; then the heat setting process is carried out at 220-240℃, followed by cooling, edge trimming, and winding to obtain the multilayer composite functional film.

7. An antistatic polyester multilayer composite functional film for optical applications, characterized in that, The raw materials for preparing the multilayer composite functional membrane include terephthalic acid, ethylene glycol, 1,4-cyclohexanediol, isophthalic acid, polyetheramine, glycidyl methacrylate, epoxy-functionalized styrene-acrylate copolymer, and triazine absorbent; the multilayer composite functional membrane is prepared by the preparation method according to any one of claims 1-6.

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