A high-barrier multilayer coated PET film and its preparation process

Abstract

This invention relates to the field of multilayer polyester film technology, specifically to a high-barrier-performance multilayer coated PET film and its preparation process. This invention overcomes the problem in existing multilayer coated PET films where adhesion and barrier performance cannot be simultaneously achieved. The polyester-coated film of this invention uses copolymerized modified polyester as the substrate layer, and sequentially integrates a base layer, a reactive barrier layer, and a surface protective layer through a single-sided multilayer coating method; wherein the barrier layer includes nano-montmorillonite and nano-cellulose; the substrate layer is subjected to online corona treatment to achieve interfacial anchoring with the base layer. The multilayer polyester film obtained by this invention possesses both ultra-high barrier properties and excellent interlayer adhesion, and can be applied in the field of high-precision pharmaceutical packaging.

Description

Technical Field

[0001] This invention relates to the field of multilayer polyester film technology, specifically to a high-barrier-performance multilayer coated PET film and its preparation process. Background Technology

[0002] Currently, research on high-barrier polyester films mainly focuses on vacuum metallization, silica coating, and polyvinylidene chloride (PVDC) coating. However, vacuum coating is prone to micro-cracks during the folding process of flexible packaging, leading to barrier failure. PVDC coating, due to its chlorine content, does not conform to environmental protection trends. Although existing coating technologies exhibit good oxygen barrier properties, the presence of numerous hydrophilic hydroxyl groups in their molecular chains makes them highly susceptible to water absorption and swelling in high-humidity environments. This significantly reduces the tortuosity of the gas permeation path, resulting in a precipitous deterioration of barrier performance. Furthermore, the interfacial bonding between traditional PET substrates and polar coatings is weak. After high-temperature sterilization or thermal shock, the coating often undergoes physical detachment or delamination, severely affecting the reliability and service life of the packaging.

[0003] Improving the barrier properties of multilayer polyester films typically requires constructing a dense crystalline structure or introducing inorganic fillers with a high aspect ratio. However, this often leads to increased coating brittleness. Due to the low surface energy and lack of active sites in the polyester substrate, brittle coatings are prone to micro-delamination at the interface under the stress generated by biaxial stretching and subsequent heat treatment. In existing technologies, the silane crosslinking agents added to improve barrier properties often reduce the coating's flexibility, while the flexible components introduced to improve adhesion increase the free volume of the molecular chains, weakening the barrier network.

[0004] In summary, in the prior art, the overall performance of multilayer polyester films can be improved by adding components during coating. However, there is still a problem that interlayer adhesion and barrier properties cannot be simultaneously achieved during the multilayer coating process.

[0005] To address this, a high-barrier-resistant multilayer coated PET film and its preparation process are proposed. Summary of the Invention

[0006] The purpose of this invention is to provide a high-barrier-performance multilayer coated PET film and its preparation process. The polyester-coated film of this invention uses copolymer-modified polyester as the substrate layer, and sequentially integrates a base layer, a reactive barrier layer, and a surface protective layer through a single-sided multilayer coating method. The barrier layer is composed of a mixture of silicone-modified polyvinyl alcohol, nano-montmorillonite, and nano-cellulose. After online corona treatment, the substrate layer forms an interfacial anchor with the base layer. The barrier layer undergoes silanol condensation in a high-temperature region to form a glassy network and lock the nanosheets. The multilayer polyester film obtained by this invention possesses both ultra-high barrier properties and excellent interlayer adhesion, and can be applied in the field of high-precision pharmaceutical packaging.

[0007] To achieve the above objectives, the present invention provides the following technical solution: This invention discloses a process for preparing a high-barrier, multilayer coated PET film, comprising the following steps: subjecting the modified polyester layer to online corona treatment with a corona power of 5-7 kW to ensure a surface tension of 50-58 mN / m, thereby obtaining a polyester film; feeding the polyester film into a first-stage micro-grooved roller coating station at a linear velocity of 20 m / min, coating it with a primer, achieving a single-sided dry film thickness of 0.2-0.4 μm, and then drying it in a zone 1 oven at 80°C for 6 seconds to obtain a base coating layer, maintaining the coating in a slightly tacky state to facilitate... Interlayer penetration; interfacial anchoring is achieved by the isocyanate groups in the primer component and the sulfonic acid groups and hydroxyl groups on the modified substrate surface; then, the barrier liquid is applied through a second slit extrusion coating head, with the dry film thickness controlled at 1.2-1.8 μm. The film passes through three key gradient oven zones in sequence to obtain the barrier layer; the second zone has a temperature of 120℃ for initial moisture evaporation and directional alignment; the third zone has a temperature of 142-155℃ as the core reaction zone, with a residence time of no less than 15s, at which temperature the silanol condensation is triggered to form a three-dimensional network; the fourth zone has a temperature of 110℃ for cooling and shaping. In the high-temperature region, Si-PVA undergoes a deep silanol condensation reaction to form a Si-O-Si glassy network. Simultaneously, citric acid induces esterification crosslinking between PVA molecular chains, resulting in initial coating shaping and a non-adhesive state. The subsequent curing process further refines the crosslinking network, eliminates internal stress, and ultimately locks in the nanostructure. Immediately afterward, a surface protective liquid is coated onto the barrier layer surface using an anilox roller, resulting in a dry film thickness of 0.3-0.5 μm. The treated film is then wound up at a tension of 80-120 N / m and immediately transferred to a curing chamber at 55°C, where it is stored under constant temperature conditions for 48-96 hours. Through this precision coating process, a multilayer coated PET film with a total thickness ranging from 14.2-27.7 μm is finally obtained.

[0008] This invention employs a single-sided multi-layer coating method, concentrating the three functional layers—primer, main layer, and protective layer—on a single side. This maximizes the utilization of barrier properties while saving expensive nano-barrier components. The single-sided coating layer is typically used as the inner layer, while the uncoated PET surface is more convenient for outer layer lamination.

[0009] Preferably, the preparation of the modified polyester layer includes the following steps: By weight, 90 parts terephthalic acid, 40 parts ethylene glycol, 3.0-4.0 parts SIPA, 4.0-5.0 parts CHDM, and IPA are mixed. 1.5-2.5 parts of antimony trioxide were added to the reactor, along with 0.03 parts of antimony trioxide. An esterification reaction was carried out at 220-240℃ under normal pressure. When the water yield reached over 95% of the theoretical value, a vacuum pump was turned on to reduce the pressure to below 100Pa. 0.05 parts of zinc acetate were added, and a polycondensation reaction was carried out at 270-285℃ for 4-5 hours to obtain polyester pellets. The polyester pellets were then processed through a melt extruder, with the extrusion temperature controlled at 270-285℃ in each zone to ensure uniform melt distribution. The resulting melt was water-cooled, pelletized, and dried to obtain polyester cast sheets, with an intrinsic viscosity of 0.65-0.68 dL / g. Subsequently, the sheets were stretched longitudinally by 3.5 times and transversely by 3.8 times at 100-110℃ to obtain a modified polyester layer with a thickness of 12-25 μm.

[0010] Preferably, the preparation of the barrier liquid includes the following steps: 100 parts of PVA were added to deionized water at 95℃ and stirred at 500 rpm for 120 min to dissolve. After complete dissolution, the temperature was lowered to 80℃ at a rate of 0.5℃ / min. 6.5 parts of glycidyl etheroxypropyltrimethoxysilane were slowly added dropwise, and the pH was adjusted to 4.5 with 10% dilute hydrochloric acid. The grafting reaction was carried out at a constant temperature for 2 h to obtain a silanized PVA solution. During the reaction, the silane hydrolysis endpoint was determined by detecting the solution viscosity when it reached 100-150 mPa·s. 25.2-30.5 parts of OMMT and CNF were then added... 5.5-9.4 parts of deionized water (350-400 parts) are added and mixed and dispersed. The mixture is then subjected to strong exfoliation at 10,000 rpm for 60 minutes using a high-shear disperser to obtain a mixture. Under stirring conditions, the mixture is slowly added dropwise to the silanized PVA solution, and 2 parts of citric acid are added. The mixture is stirred at 800 rpm for 30 minutes to adjust the solid content to 12-18%, thereby obtaining a barrier liquid with a viscosity of 150-300 mPa·s.

[0011] Preferably, the preparation of the primer includes the following steps: 100 parts (wet weight) of WPU dispersion are added to a beaker, the stirring speed is 300 rpm, 4-5.8 parts of KH-560 and 2.1-2.9 parts of isocyanate crosslinking agent are slowly added, the stirring speed is maintained for 40-60 min to allow it to fully mature, and then deionized water is added to adjust the solid content to 10-15% to obtain a primer with a viscosity of 20-50 mPa·s.

[0012] Preferably, the preparation of the surface protective liquid includes the following steps: 5 parts of nano-zirconia are slowly added to 100 parts of perfluoroalkyl acrylate emulsion, and the mixture is treated at 2000 rpm for 30 min in a high-speed disperser to ensure uniform distribution of inorganic particles, thereby obtaining a surface protective liquid with a solid content of 20-22% and a viscosity of 15-35 mPa·s; wherein the nano-zirconia is a monoclinic phase nano-zirconia aqueous dispersion with an average particle size of 20-50 nm modified with epoxy silane.

[0013] Preferably, in this invention, the thickness of the modified polyester layer is 12-25 μm; the thickness of the base coating layer is 0.2-0.4 μm; the thickness of the barrier layer is 1.2-1.8 μm; and the thickness of the surface protective layer is 0.3-0.5 μm.

[0014] The present invention also provides a multilayer coated PET film with high barrier properties, wherein the raw materials for preparing the multilayer coated PET film include terephthalic acid, ethylene glycol, 1,4-cyclohexanediethanol, isophthalic acid, sodium dimethyl isophthalate sulfonate, WPU dispersion and perfluoroalkyl acrylate emulsion.

[0015] Compared with the prior art, the beneficial effects of the present invention are as follows: 1. This invention achieves a perfect balance between mechanical toughness and surface activity in the substrate layer by precisely introducing SIPA, CHDM and IPA monomers during the polyester substrate synthesis stage. The introduction of the asymmetric cyclic structure of CHDM effectively inhibits excessive crystallization of polyester molecules, increases the free volume between molecular chains, and ensures that the substrate will not undergo brittle fracture when the film is subjected to subsequent multi-coating and biaxial stretching processes. At the same time, it provides microscopic space for interlayer molecular penetration, ensuring the structural stability of the laminated product during deep processing.

[0016] 2. This invention utilizes KH-560 silane coupling agent and aqueous isocyanate crosslinking agent to construct a strong interlayer chemical bridge. Unlike traditional physical adsorption, it forms a stable Si-OC covalent bond at one end and reacts with polar groups at the other end. The isocyanate groups then anchor at the interface with the polar functional groups on the substrate surface, forming a molecular stitching effect. This chemical bonding strength is significantly better than physical entanglement. The semi-interpenetrating network formed after curing effectively solves the problem of polar coatings easily detaching from the surface of non-polar PET substrates.

[0017] 3. This invention constructs a highly regular brick-and-mortar structure by synergistically using Si-PVA matrix with high aspect ratio OMMT and CNF. Through high shear treatment, the montmorillonite sheets are completely exfoliated and the mechanical support of CNF is used to prevent their aggregation. The Si-O-Si hybrid network formed by the reaction significantly reduces the free volume of the polymer at the molecular scale, making the oxygen molecule permeation path exhibit extremely high tortuosity and achieving an ultra-high oxygen barrier effect in the quasi-glassy state.

[0018] 4. This invention modifies PVA by silanization, utilizing the silanol polycondensation reaction that occurs during the drying process of Si-PVA to form a highly water-resistant inorganic silicon-oxygen crosslinked framework inside the coating, locking the PVA molecular chains and preventing them from swelling significantly in humid and hot environments. This gives the reactive modification technology of this invention a significant technical advantage in dealing with extremely high humidity environments.

[0019] 5. This invention introduces CNF as a three-dimensional network framework into the barrier liquid, which assists OMMT to achieve uniform and parallel directional arrangement at the nanoscale. Through the synergistic system of Si-PVA and CNF, this invention effectively inhibits the secondary agglomeration of fillers and ensures that visible light can penetrate at a high proportion. While significantly improving barrier and adhesion performance, this invention successfully maintains the high transparency of polyester film, meeting the packaging requirements for visualization of internal contents. Attached Figure Description

[0020] Figure 1 This is a flowchart illustrating the preparation process of the multilayer coated PET film obtained in an embodiment of the present invention. Detailed Implementation

[0021] 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.

[0022] In this invention, PTA is terephthalic acid, CAS number 100-21-0, with an acid value of 675±2 mgKOH / g; EG is ethylene glycol, CAS number 107-21-1, with a color ≤5Pt-Co; CHDM is 1,4-cyclohexanediethanol, with a cis:trans ratio of 3:7, CAS number 105-08-8; IPA is isophthalic acid, with a meta-content ≥99.8%; SIPA is sodium dimethyl isophthalate sulfonate, specifically named sodium 5-sulfonate dimethyl isophthalate, CAS number 3965-55-7; and the WPU dispersion is an anionic polyester-based aqueous polyurethane dispersion with a solid content of 30-40%, a particle size of 50-150 nm, an elongation at break >300%, and a viscosity of 50-200 μL. mPa·s, number average molecular weight of 15000-20000; KH-560 is glycidyl etheroxypropyltrimethoxysilane, CAS number 2530-83-8; PVA is polyvinyl alcohol, CAS number 9002-89-5, degree of hydrolysis 98.5-99.5%; OMMT is nano-montmorillonite, average flake diameter of 300-500nm, CAS number 1318-93-0; CNF is nanocellulose, derived from softwood pulp, crystal diameter 10-20nm, aspect ratio 100-300, CAS number 9004-34-6; the isocyanate crosslinking agent is water-based blocked isocyanate, specifically Trixene Aqua BI. 220, the sealing agent type is 3,5-dimethylpyrazole, the NCO content is 3.5%-4.5%, and the curing temperature is 110-120℃; the perfluoroalkyl acrylate copolymer emulsion is a commercially available perfluoroalkyl acrylate copolymer aqueous emulsion, which is a copolymer aqueous dispersion system formed by emulsion polymerization of fluorinated acrylate monomers and other functional monomers, with a solid content of 20%-30%, a fluorine content ≥15%, and an emulsion particle size of 80-120nm; the average degree of polymerization of the PVA is 1700-2400.

[0023] Please see Figure 1 This invention provides a high-barrier-resistant multilayer coated PET film and its preparation process, the technical solution of which is as follows: Example 1

[0024] By mass, 90 parts of terephthalic acid, 40 parts of ethylene glycol, 3.5 parts of SIPA, 4.5 parts of CHDM, and 2.0 parts of IPA were added to a reactor, along with 0.03 parts of antimony trioxide. An esterification reaction was carried out at 230°C under normal pressure. When the water content reached more than 95% of the theoretical value, a vacuum pump was turned on to reduce the pressure to below 100 Pa, and a polycondensation reaction was carried out at 280°C for 4 hours to obtain polyester pellets. The polyester pellets were then processed in a melt extruder, with the melt temperature controlled at 270-285°C to obtain a melt. After water cooling, pelletizing, and drying, polyester castings were obtained. Subsequently, the mixture was stretched longitudinally by 3.5 times and transversely by 3.8 times at 110°C to obtain a modified polyester layer with a thickness of 12 μm. Add 100 parts of WPU dispersion to a beaker and stir at 300 rpm. Slowly add 4.5 parts of KH-560 and 2.5 parts of isocyanate crosslinking agent, and stir for 40-60 minutes to allow it to fully mature. Then add deionized water to adjust the solid content to 12% to obtain a primer with a viscosity of 20-50 mPa·s.

[0025] 100 parts of PVA were added to deionized water at 95°C and stirred at 500 rpm for 60 min to dissolve. After complete dissolution, the temperature was lowered to 80°C at a rate of 0.5°C / min. 6.5 parts of glycidyl etheroxypropyltrimethoxysilane were slowly added dropwise, and 10% dilute hydrochloric acid was added to adjust the pH to 4.5. The grafting reaction was carried out at a constant temperature for 2 h to obtain a silanized PVA solution. 27.5 parts of OMMT and 7.5 parts of CNF were added to 360 parts of deionized water and mixed and dispersed. The mixture was then subjected to strong exfoliation at 10,000 rpm for 60 min using a high-shear disperser to obtain a mixture. Under stirring conditions, the mixture was slowly added dropwise to the silanized PVA solution, and 2 parts of citric acid were added. The mixture was stirred at 800 rpm for 30 min to adjust the solid content to 15% to obtain a barrier liquid.

[0026] Five parts of nano-zirconia were slowly added to 100 parts of perfluoroalkyl acrylate emulsion, and the mixture was treated at 2000 rpm for 30 minutes in a high-speed disperser to ensure uniform distribution of inorganic particles, thus obtaining a surface protective liquid with a solid content of 20%.

[0027] The modified polyester layer was subjected to online corona treatment with a corona power of 6kW to obtain a polyester film. The polyester film was then fed into the first micro-grooved roller coating station at a linear speed of 20m / min to coat with a primer. The dry film thickness on one side was 0.3μm. Subsequently, it entered the first-zone oven for drying and dehydration at 80℃ for 6s. Then, it was coated with a barrier liquid through the second slit extrusion coating head, with the dry film thickness controlled at 1.5μm. The film passed through three key gradient oven zones in sequence: Zone 2, at a temperature of 120℃, for initial moisture evaporation and directional alignment; Zone 3, at a temperature of 150℃, served as the core reaction zone, with a residence time of no less than 15s, at which temperature the silanol polycondensation was triggered to form a three-dimensional network; Zone 4, at a temperature of 110℃, was used for cooling and shaping. Next, a surface protective liquid is coated onto the barrier layer surface using an anilox roller, resulting in a dry film thickness of 0.4 μm. The treated film is then wound up and immediately transferred to a curing chamber at 55°C, where it is stored at a constant temperature for 72 hours. Through this precision coating process, a multilayer coated PET film with a total thickness of 14.2 μm is finally obtained.

[0028] Examples 2-5 follow the same preparation method and parameters as Example 1, with differences shown in Table 1.

[0029] Table 1. Parameter variations in Examples 1-5 Example Example 1 Example 2 Example 3 Example 4 Example 5 SIPA dosage / part 3.5 3.2 3.8 3.1 3.9 CHDM dosage / part 4.5 4.9 4.1 4.7 4.3 IPA dosage / part 2 1.8 2.2 2.1 1.9 Corona treatment power / kW 6 5.5 6.5 5.2 6.8 KH-560 dosage (per serving) 4.5 5.2 4 5.8 4.2 Mass of isocyanate crosslinking agent used / part 2.5 2.8 2.1 2.9 2.3 OMMT nanosheet mass usage / part 27.5 25.2 30.5 26.4 28.6 CNF nanocellulose dosage / parts 7.5 6.2 8.8 5.5 9.4 Maximum temperature in the main drying zone / °C 150 142 158 145 155 Barrier layer dry film thickness / μm 1.5 1.3 1.7 1.4 1.6 Curing time / h 72 48 96 60 84 Modified polyester layer thickness / μm 12.0 15.1 18.2 20.3 25.4 Undercoat thickness / μm 0.3 0.2 0.4 0.2 0.3 Barrier layer thickness / μm 1.5 1.3 1.7 1.4 1.6 Surface protective layer thickness / μm 0.4 0.3 0.5 0.3 0.4

[0030] Comparative Example 1: Refer to Example 1, except that SIPA and CHDM monomers are not added to the substrate. The substrate is synthesized using only terephthalic acid, ethylene glycol and sodium isophthalate 5-sulfonate, while the amounts of other components remain unchanged.

[0031] Comparative Example 2 is the same as Example 1, except that SIPA is not added to the substrate. The substrate is synthesized using only terephthalic acid, ethylene glycol, CHDM and sodium isophthalate, while the amounts of other components remain unchanged.

[0032] Comparative Example 3 is the same as Example 1, except that CHDM is not added to the substrate. The substrate is synthesized using only terephthalic acid, ethylene glycol, SIPA and sodium isophthalate, while the amounts of other components remain unchanged.

[0033] Comparative Example 4 is the same as Example 1, except that the content of the barrier layer OMMT is increased to 50 parts, while the amount of other components remains unchanged.

[0034] Comparative Example 5 is the same as Example 1, except that the modified substrate is not subjected to online corona treatment, while the amounts of the other components remain unchanged.

[0035] Comparative Example 6 is the same as Example 1, except that the primer does not contain KH-560 silane coupling agent, while the amounts of the other components remain unchanged.

[0036] Comparative Example 7 is the same as Example 1, except that the primer does not contain an isocyanate crosslinking agent, while the amounts of the other components remain the same.

[0037] Comparative Example 8 is the same as Example 1, except that the modified substrate is coated without curing and the performance is tested directly.

[0038] Comparative Example 9 is the same as Example 1, except that the maximum temperature of the gradient temperature control oven is set to 100°C.

[0039] Comparative Example 10 is the same as Example 1, except that the barrier layer uses a regular PVA solution that has not been modified by silanization.

[0040] Comparative Example 11 is the same as Example 1, except that OMMT is not added to the barrier layer, while the amounts of the other components remain the same.

[0041] Comparative Example 12 is the same as Example 1, except that CNF is not added to the barrier layer, while the amounts of the other components remain the same.

[0042] Comparative Example 13 is the same as Example 1, except that no surface protective layer is coated, while the amounts of the remaining components remain unchanged.

[0043] Comparative Example 14 is the same as Example 1, except that dimethyl isophthalate sodium 5-sulfonate is not added to the modified substrate layer, while the amounts of the other components remain unchanged.

[0044] Example 1 Mechanical property testing

[0045] The mechanical properties of the multilayer coated PET films prepared in Examples 1-5 and Comparative Examples 1-4 were tested. According to the test standard of GB / T 1040.3-2006, strips with a width of 15 mm and a length of not less than 150 mm were cut from both the longitudinal and transverse directions of the film. Tensile strength and elongation at break were tested using a universal testing machine with an initial gauge length of 100 mm and a tensile speed of 50 mm / min. The test results are shown in Table 2.

[0046] Table 2 Test results of the examples and comparative examples Example Tensile strength / MPa Elongation at break / % Example 1 215.1 105.2 Example 2 212.3 108.4 Example 3 218.5 102.6 Example 4 210.7 110.8 Example 5 220.9 98 Comparative Example 1 204.6 82.7 Comparative Example 2 208.8 95.1 Comparative Example 3 213.2 89.3 Comparative Example 4 222.3 70.4

[0047] As shown in Table 2, the multilayer coated PET film prepared in the examples exhibits excellent mechanical properties, showing a significant improvement compared to the comparative example. This is because the functional monomers SIPA, CHDM, and IPA were introduced through copolymerization during the preparation of the modified substrate layer. CHDM, as a monomer with an asymmetric cyclic structure, effectively inhibits the crystallization rate of polyester molecules, increases the free volume between molecular chains, and endows the film with excellent toughness and flexibility. The sodium sulfonate groups introduced by SIPA enhance the polar interaction between molecular chains, further improving the cohesive strength of the substrate through ionic crosslinking. Furthermore, the brick-and-mortar structure formed by OMMT and CNF in the barrier layer achieves high barrier properties while also synergistically improving the overall mechanical strength of the film through the reinforcing effect of inorganic sheets. In Comparative Example 1, since no SIPA and CHDM monomers were added to the substrate for copolymerization modification, the resulting substrate layer mainly consists of highly regular polyester segments, lacking the perturbation of the lattice by the flexible cyclic structure and the polar support of the polar functional groups, resulting in the film exhibiting poor biaxial properties. During the stretching process, excessive internal stress significantly reduces flexibility and results in a low elongation at break. Comparative Examples 2-3 show that SIPA, as an ionic comonomer, has highly polar side chain groups that can form ionic aggregation regions, acting as anchors between molecular chains. Its absence causes the disappearance of ionic bonding forces within the film, reducing the cohesive energy of the substrate and leading to a significant decline in tensile strength. The absence of CHDM results in excessively high regularity of the polyester chains, making it easier for the film to form large-sized grains during the hot stretching process, reducing the material's deformation capacity. This excessive rigidity leads to brittleness under mechanical loads, resulting in a reduced elongation at break. In Comparative Example 4, increasing the content of the rigid inorganic component OMMT in the barrier layer slightly improves tensile strength due to the increased high-hardness filler. However, excessive nanosheets in the PVA matrix easily generate stress concentration effects. During stretching, the high filler density disrupts the continuity of the polymer matrix, making microcracks easily propagate at the interface, leading to a sharp increase in film brittleness and a significant decrease in elongation at break.

[0048] Experiment Example 2 Adhesion Performance Test

[0049] The adhesion properties of the multilayer coated PET films prepared in Examples 1-5, Comparative Examples 1, Comparative Examples 5-9, and Comparative Example 14 were tested according to GB / T 8808-1988. The coated side of the film was laminated with a standard heat-sealing film, and a 15 mm wide sample was cut. The laminated layer was peeled off at a speed of 300 mm / min at 180° on a peeling machine, and the average peel force value was recorded. In addition, the laminated sample was placed in a pressure steam sterilizer and kept at 121°C for 30 min. After cooling, the peel strength was tested again according to the above method. The test results are shown in Table 3.

[0050] Table 3 Test Results of Examples and Comparative Examples Example Initial peel strength (N / 15mm) Peel strength under boiling conditions / (N / 15mm) Example 1 8.5 7.2 Example 2 8.1 6.8 Example 3 8.9 7.6 Example 4 7.7 6.3 Example 5 9.2 8 Comparative Example 1 1.8 0.5 Comparative Example 5 3.4 1.9 Comparative Example 6 4.6 0.9 Comparative Example 7 5.3 2.1 Comparative Example 8 6 4.4 Comparative Example 9 3.2 1.1 Comparative Example 14 2.5 0.7

[0051] As shown in Table 3, the adhesion performance of the multilayer coated PET 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 strongly polar sodium sulfonate groups provided by SIPA significantly enhance the intrinsic surface energy of the substrate, while CHDM effectively reduces the crystallinity of the PET surface through its asymmetric ring structure, providing microscopic space for the penetration and entanglement of the primer liquid molecular chains. The KH-560 silane coupling agent and the aqueous isocyanate crosslinking agent introduced into the primer layer act as a chemical bridge. One end of KH-560 forms a Si-OC covalent bond with the activated substrate surface through the silanol group generated by hydrolysis, and the other end reacts with the hydroxyl groups in the main barrier layer. At the same time, the isocyanate groups anchor the hydroxyl, carboxyl, and sulfonic acid groups on the substrate surface, forming a cross-interface molecular stitching effect. During the curing process, the interlayer molecules undergo microscopic migration and interpenetration, ultimately bonding the layers tightly, so that the film can still maintain extremely high peel strength after high-temperature cooking. Comparative Examples 1 and 14 show that the lack of highly polar sulfonate monomers results in extremely low chemical activity on the substrate surface, preventing the primer from establishing effective initial adsorption through ion coupling or strong polar interactions. Furthermore, the absence of CHDM leads to excessively high substrate crystallinity and overly dense molecular chain packing, hindering the micro-diffusion and penetration of the primer components. This results in poor interfacial adhesion from the initial state and rapid failure under moisture attack. In Comparative Example 5, the lack of high-energy electron bombardment to remove the weak boundary layer and generate activation sites on the substrate surface resulted in insufficient oxygen-containing free radical density, limiting the effective collision and reaction probability between the silane coupling agent and isocyanate, leading to a significant decline in initial peel strength. Comparative Examples 6 and 7 show that without the crucial chemical bridge of KH-560, the substrate and barrier layer rely solely on weak physical adsorption bonding, which is insufficient during biaxial stretching and subsequent heat treatment. The interfacial stress generated during the process easily causes physical entanglement to slip, especially during cooking, where water molecules rapidly break the interfacial hydrogen bonds, leading to reduced adhesion. In addition, the lack of isocyanate results in insufficient cohesive strength within the undercoat, making it impossible to form a dense three-dimensional cross-linked network between the substrate and the main layer, thus weakening the overall peel strength. As shown in Comparative Example 8, the absence of the curing process, due to the lack of long-term molecular chain rearrangement and deep chemical cross-linking driven by heat, prevents the formation of a complete semi-interpenetrating network at the interface, resulting in stress concentration within the film, unstable initial peel strength, and poor resistance to environmental stress. In Comparative Example 9, below the reaction temperature, Si-PVA cannot form silanol polycondensation, and the cross-linking rate of isocyanate is also significantly reduced, resulting in the failure to form dense covalent bonds between the barrier layer and the undercoat. The coating structure is loose and the interfacial bonding is weak, exhibiting obvious interlayer delamination under high-temperature cooking.

[0052] Experiment Example 3 Barrier Performance Test

[0053] The barrier properties of the multilayer coated PET films prepared in Examples 1-5 and Comparative Examples 9-14 were tested according to GB / T 19789-2005, with the environment set at 23°C and 0% RH (dry state). The isobaric method was used, with high-purity nitrogen as the carrier gas, and the amount of oxygen permeating through the film per unit time was recorded. The test was also conducted according to GB / T 26253-2010, with the environment set at 38°C and 90% RH (high humidity). An infrared sensor was used to detect the concentration of water molecules permeating through the film. The test results are shown in Table 4.

[0054] Table 4 Test Results of Examples and Comparative Examples Example Oxygen permeability / cm³ / (m²·24h·0.1MPa) Water vapor transmission rate / g / (m²·24h) Example 1 0.021 0.11 Example 2 0.032 0.12 Example 3 0.013 0.09 Example 4 0.044 0.14 Example 5 0.015 0.08 Comparative Example 9 2.536 4.82 Comparative Example 10 1.157 15.64 Comparative Example 11 0.818 1.25 Comparative Example 12 0.429 0.63 Comparative Example 13 0.063 0.61 Comparative Example 14 0.054 0.22

[0055] As shown in Table 4, the barrier properties of the polyester multilayer composite functional membrane obtained in the comparative example, through adjustments to the components and process, are significantly different from those in the example. In the example, the barrier layer uses silanized modified PVA as the matrix, combined with exfoliated nano-montmorillonite and nano-cellulose with a high flake-to-diameter ratio. In the high-temperature reaction zone of 150°C, Si-PVA undergoes a deep silanol condensation reaction, forming a three-dimensional Si-O-Si glassy network in situ. Simultaneously, citric acid induces esterification crosslinking between PVA molecular chains, firmly locking the nanosheets in the matrix through chemical bonds. This highly ordered structure greatly prolongs the permeation of oxygen and water vapor molecules. The modified substrate layer, through the introduction of SIPA and CHDM, enhances surface energy and interfacial bonding, ensuring the integrity of the coating during biaxial stretching and preventing microcracks from compromising its barrier properties. In Comparative Example 9, at reaction thresholds far below the threshold, the silanol groups in Si-PVA cannot obtain sufficient activation energy for deep polycondensation, and the degree of esterification and crosslinking of PVA is also severely insufficient. This results in the failure to form a dense crosslinked network structure within the barrier layer, leading to numerous micropores and a large space for molecular thermal motion, making it easy for oxygen and water vapor to penetrate and significantly degrading the barrier performance. In Comparative Example 10, the barrier layer uses unmodified silanized substrate. Ordinary PVA solutions, lacking the support of the Si-O-Si inorganic hybrid network, exhibit strong hydrophilicity in humid and hot environments, readily absorbing moisture and swelling. This increases the free volume between polymer chains, providing channels for rapid diffusion of gas molecules and reducing barrier performance. In Comparative Example 11, with the physical barrier OMMT completely removed from the barrier layer, although the Si-PVA network possesses cohesive barrier properties, the absence of the tortuous path effect provided by the high aspect ratio nanosheets significantly reduces the permeation resistance of gas molecules, making the permeation path tend to be linear, thus reducing barrier performance. Combined with Comparative Example 12, it can be seen that the absence of CNF leads to excessive shrinkage of OMMT during coating drying. During the process, local agglomeration or disordered arrangement occurs, and the coating becomes more brittle, making it prone to micro-fractures under tension, thus weakening the overall barrier consistency. In Comparative Example 13, without the surface protective layer, the barrier layer is directly exposed to a humid and hot environment, and moisture easily seeps into and penetrates the Si-PVA layer, resulting in local network loosening and increasing the risk of later performance degradation. In Comparative Example 14, no SIPA was added to the modified substrate layer, which reduced the surface energy of the substrate layer and weakened the chemical anchoring force between the base coating and the substrate. During biaxial stretching, micro-peeling or displacement easily occurs at the interface between the barrier coating and the substrate, forming extremely small interfacial leakage channels, resulting in a significant reduction in barrier performance compared to the examples.

[0056] Experiment Example 4: Optical Performance Testing

[0057] The optical properties of the multilayer coated PET films prepared in Examples 1-5 and Comparative Examples 12-14 were tested. According to GB / T 2410-2008, the samples were placed in the optical path of an integrated spherical haze meter, and the total light transmittance and scattered light flux were read in sequence to calculate the haze value. The test results are shown in Table 5.

[0058] Table 5 Test Results of Examples and Comparative Examples Example Total light transmittance / % Haze / % Example 1 91.2 1.1 Example 2 91.5 1.3 Example 3 90.8 1.5 Example 4 91.7 1 Example 5 90.4 1.8 Comparative Example 12 88.3 4.6 Comparative Example 13 91.6 1.2 Comparative Example 14 90.9 1.4

[0059] As shown in Table 5, the optical properties of the polyester multilayer composite functional film obtained in the comparative example, through adjustments to the components and processes, are significantly different from those in the examples. In the examples, the synergistic system of nanocellulose and silanized modified PVA was introduced into the barrier layer preparation, which played a role in steric hindrance and mechanical support, preventing secondary agglomeration of nanofillers during the coating and drying process. This highly regular and uniform dispersion state allows visible light to pass through smoothly, reducing reflection and scattering caused by large-sized particles, and ensuring the excellent optical properties of the film. In contrast, Comparative Example 12 lacks the nanoscale spatial framework support of CNF. The high content of OMMT sheets is easily agglomerated due to intermolecular van der Waals forces and hydrogen bonds during the solvent evaporation stage, resulting in a significant deterioration in the haze and transmittance of the film. Combined with the results of Comparative Example 13, it can be seen that although reducing the coating layer improves the total light transmittance, the lack of protection from the low surface energy material makes the film more susceptible to physical / chemical erosion by fine particles or moisture in the test environment, potentially adversely affecting its long-term optical stability. In Comparative Example 14, the absence of SIPA reduces the surface affinity and wettability between the substrate layer and the primer. During the coating process, due to the low surface free energy, the spreading dynamics of the primer on the substrate surface deteriorate, making it easy to form defect interfaces with uneven thickness or poor local wetting at the microscopic level. The structural inhomogeneity at these microscopic interfaces interferes with the coherent propagation of light, resulting in slight fluctuations in transmittance and a slight increase in interface haze, indicating the implicit contribution of intrinsic substrate modification to improving the optical integration of multilayer structures.

[0060] 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 process for preparing a multilayer coated PET film with high barrier properties, characterized in that, Includes the following steps: A modified polyester layer is subjected to online corona treatment to obtain a polyester film; a primer is coated on one side of the polyester film and dried to obtain a base layer; a barrier liquid is coated onto the base layer and dried in stages with controlled temperature to obtain a barrier layer; a surface protective liquid is coated on the surface of the barrier layer to obtain a treated film; the treated film is wound up and cured to obtain the multilayer coated PET film. The modified polyester layer is obtained by terephthalic acid, ethylene glycol, 1,4-cyclohexanediethanol, sodium dimethyl isophthalate sulfonate, and esterification polycondensation of isophthalate; the primer is obtained by mixing WPU dispersion, KH-560, and isocyanate crosslinking agent; the barrier liquid is obtained by reacting polyvinyl alcohol, glycidyl etheroxypropyltrimethoxysilane, nano-montmorillonite, and nano-cellulose; and the surface protective liquid is obtained by dispersing nano-zirconia and perfluoroalkyl acrylate emulsion.

2. The preparation process of a high-barrier multilayer coated PET film according to claim 1, characterized in that, The preparation of the modified polyester layer includes the following steps: The terephthalic acid, ethylene glycol, sodium dimethyl isophthalate sulfonate, 1,4-cyclohexanediethanol, and isophthalic acid are added to a reactor, and antimony trioxide is added for esterification. Polyester pellets are obtained through polycondensation reaction. Polyester sheets are then obtained by melt extrusion, water cooling pelletizing, and drying. The sheets are then subjected to longitudinal stretching and transverse stretching to obtain the modified polyester layer.

3. The preparation process of a high-barrier multilayer coated PET film according to claim 1, characterized in that, The preparation of the barrier liquid includes the following steps: adding the polyvinyl alcohol to deionized water, stirring to dissolve, adding the glycidyl etheroxypropyltrimethoxysilane dropwise, adjusting the pH value with hydrochloric acid, and reacting to obtain a silanized solution; adding the nano-montmorillonite and the nano-cellulose to the deionized water, and shearing and dispersing to obtain a mixture; under stirring conditions, adding the mixture dropwise to the silanized solution, adding citric acid, and stirring to mix to obtain the barrier liquid.

4. The preparation process of a high-barrier multilayer coated PET film according to claim 1, characterized in that, The preparation of the primer includes the following steps: adding the WPU dispersion to a beaker, adding the KH-560 and the isocyanate crosslinking agent under stirring, stirring and mixing, and then adding deionized water to adjust and obtain the primer.

5. The preparation process of a high-barrier multilayer coated PET film according to claim 1, characterized in that, The preparation of the surface protective liquid includes the following steps: adding the nano-zirconia to the perfluoroalkyl acrylate emulsion and stirring to disperse it to obtain the surface protective liquid.

6. The preparation process of a high-barrier multilayer coated PET film according to claim 1, characterized in that, The modified polyester layer has a thickness of 12-25 μm; the base coating layer has a thickness of 0.2-0.4 μm; the barrier layer has a thickness of 1.2-1.8 μm; and the surface protective layer has a thickness of 0.3-0.5 μm.

7. A multilayer coated PET film with high barrier properties, characterized in that, The raw materials for preparing the multilayer coated PET film include terephthalic acid, ethylene glycol, 1,4-cyclohexanediethanol, isophthalic acid, sodium dimethyl isophthalate sulfonate, WPU dispersion, nano-montmorillonite, nano-cellulose, and perfluoroalkyl acrylate emulsion; the multilayer coated PET film is prepared by the preparation process described in any one of claims 1-6.

Images