EVA composite waterproof sheet and preparation method thereof

Abstract

The invention relates to the technical field of thermoplastic polyolefin, in particular to an EVA composite waterproof sheet and a preparation method thereof. The sheet is of a five-layer structure and sequentially comprises a weather-proof surface layer, a first reaction transition layer, a reinforcing layer, a second reaction transition layer and a filling bottom layer from top to bottom. The core of the composite material is that an EVA base layer is connected with a chain-extended and carboxyl-terminated regenerated polyester reinforcing layer through a reaction transition layer (containing ethylene-glycidyl methacrylate copolymer) with specific components, and modified montmorillonite is introduced into the reinforcing layer, so that stable chemical bonding and physical entanglement are formed between the layers. According to the design, the high-temperature-resistant size stability, the creep resistance and the long-acting interlayer bonding strength of the sheet are synergistically improved, and the problem of interlayer stripping and deformation synergistic degradation of a traditional material under thermo-oxidative aging is effectively solved.

Description

Technical Field

[0001] This invention relates to the field of thermoplastic polyolefin technology, and in particular to an EVA composite waterproof sheet and its preparation method. Background Technology

[0002] Thermoplastic polyolefin (TPO) waterproofing materials, especially those represented by ethylene-vinyl acetate copolymer (EVA), have been widely used in the field of building waterproofing due to their excellent flexibility, low-temperature resistance, and ease of construction. However, with the increasing demand for long-term service in harsh environments such as roofs and underground projects, the inherent limitations of these materials are becoming increasingly apparent, posing a serious challenge to the long-term reliability of waterproofing systems.

[0003] First, as a thermoplastic resin, this type of material has a relatively low glass transition temperature, resulting in insufficient resistance to heat deformation. Under sustained high-temperature environments such as long-term exposure to sunlight on roofs or underground thermal storage, the movement of molecular chain segments intensifies, making it prone to irreversible creep and stress relaxation. This not only causes dimensional shrinkage, wrinkling, or sagging, compromising the integrity and sealing of the waterproof layer, but is also a key bottleneck restricting its application in high-temperature and high-stress scenarios.

[0004] Secondly, to compensate for the shortcomings of the aforementioned bulk materials, existing technologies typically employ the introduction of inorganic fillers or reinforcement through multi-layer co-extrusion of high-modulus polymer layers (such as polyester). However, simple physical blending or lamination often introduces new interfacial problems. Significant differences in polarity and surface energy exist between the EVA matrix and the inorganic fillers, as well as between EVA and the highly polar polyester reinforcing layer, leading to poor interfacial compatibility. Under the long-term synergistic effects of heat, oxygen, and water, these poor interfaces easily become stress concentration points and failure initiation points, triggering interlayer delamination, significantly reducing the reinforcement effect, and even accelerating the failure of the overall waterproof structure.

[0005] Furthermore, regarding interface modification, conventional techniques such as treating fillers with silane coupling agents or introducing compatibilizers, while improving adhesion in the initial stage, often fail to maintain stable modification effects under long-term humid and hot aging environments. For example, some organic modification methods relying on ion bonding may degrade under high temperature and high humidity conditions, leading to the failure of interface modification and severe degradation of material properties. Simultaneously, a single interface modification strategy is insufficient to effectively prevent the intrusion of water vapor and other media while providing strong interfacial adhesion, failing to synergistically withstand the long-term stresses of complex environments.

[0006] Furthermore, in multilayer composite structures, if there is a lack of effective chemical bonding and modulus gradient transition between functional layers, the internal stress generated by the mismatch in thermal expansion coefficients of the materials in each layer cannot be effectively dissipated and transferred. Under dynamic thermodynamic cycling or external forces, these internal stresses continuously accumulate in the interface region, easily inducing delamination failure. In existing technologies, the bonding between the reinforcing layer and the matrix layer mostly relies on physical-mechanical interlocking or limited polar interactions. This bonding method is not strong and durable enough under long-term harsh thermodynamic environments. Summary of the Invention

[0007] In view of this, the purpose of this invention is to propose an EVA composite waterproof sheet and its preparation method, so as to solve the problem of synergistic deterioration of interlayer delamination and creep deformation caused by insufficient interfacial bonding strength and poor thermal dimensional stability of the reinforcing phase in existing EVA waterproof materials under long-term thermo-oxidative aging and humid heat cycling environment.

[0008] To achieve the above objectives, the present invention provides an EVA composite waterproof sheet, comprising a weather-resistant surface layer, a first reactive transition layer, a reinforcing layer, a second reactive transition layer, and a filling underlayer, which are sequentially stacked from the upper surface to the lower surface; the weather-resistant surface layer and the filling underlayer are respectively located on both sides of the sheet, and the first reactive transition layer and the second reactive transition layer are respectively located on both sides of the reinforcing layer; The weather-resistant surface layer, by weight, is prepared from the following raw materials: 100 parts ethylene-vinyl acetate copolymer resin, 22-30 parts ultrafine heavy calcium carbonate, 7-10 parts rutile titanium dioxide, 0.35-0.50 parts light stabilizer 944, and 0.20-0.30 parts ultraviolet absorber 328. The filling substrate is prepared from the following raw materials: 100 parts of ethylene-vinyl acetate copolymer resin and 22-30 parts of ultrafine heavy calcium carbonate; Both the first reaction transition layer and the second reaction transition layer are prepared from the following raw materials: 65-75 parts of ethylene-vinyl acetate copolymer resin and 25-35 parts of ethylene-glycidyl methacrylate copolymer; The reinforcing layer is prepared from the following raw materials: 100 parts polyethylene terephthalate-1,4-cyclohexanediethanol ester copolyester resin, 0.4-0.8 parts polyfunctional epoxy chain extender, 0.1-0.3 parts succinic anhydride, 4-6.5 parts ethylene-glycidyl methacrylate copolymer, and 0.8-1.5 parts modified montmorillonite powder.

[0009] Preferably, the thickness of the weather-resistant surface layer is 380-450 μm, the thickness of the first reaction transition layer is 80-120 μm, the thickness of the reinforcing layer is 740-800 μm, the thickness of the second reaction transition layer is 80-120 μm, and the thickness of the filling substrate is 380-450 μm.

[0010] Preferably, by weight, the weather-resistant surface layer further comprises 0.15 parts of antioxidant 1010, 0.10 parts of antioxidant 168, and 0.10 parts of ethylene bis-stearamide; the filling bottom layer further comprises 0.15 parts of antioxidant 1010, 0.10 parts of antioxidant 168, and 0.10 parts of ethylene bis-stearamide; the first reaction transition layer and / or the second reaction transition layer further comprises 0.10 parts of antioxidant 1010, 0.10 parts of antioxidant 168, and 0.10 parts of ethylene bis-stearamide; and the reinforcing layer further comprises 0.15 parts of antioxidant 1010, 0.10 parts of antioxidant 168, and 0.10 parts of ethylene bis-stearamide.

[0011] Preferably, the glycidyl methacrylate content of the ethylene-glycidyl methacrylate copolymer is 6wt%-8wt%; the type of the ethylene-vinyl acetate copolymer resin of the weather-resistant surface layer is 14J2, and the type of the ethylene-vinyl acetate copolymer resin of the first reaction transition layer, the second reaction transition layer and the filling bottom layer is 18J3.

[0012] Preferably, the polyethylene terephthalate-1,4-cyclohexanediol copolyester resin has a glass transition temperature of 75-80°C and a density of 1.2-1.4 g / cm³. 3 .

[0013] Preferably, the multifunctional epoxy chain extender has an epoxy equivalent of 270-300 g / eq and a functionality of 8-10.

[0014] Further, the preparation steps of the modified montmorillonite powder are as follows: Sodium-based montmorillonite is dispersed in an ethanol-water system and glacial acetic acid is added. Then, a pre-hydrolyzed solution A1 containing γ-glycidoxypropyltrimethoxysilane is added sequentially and reacted at 60°C for 60-70 min, a low water activity solution A2 containing γ-glycidoxypropyltrimethoxysilane is reacted at 70°C for 30-40 min, and a pre-hydrolyzed solution B containing n-octyltriethoxysilane is reacted at 70°C for 60-70 min. The mixture is then filtered, washed, and dried to obtain the modified montmorillonite powder.

[0015] Preferably, the mass ratio of sodium-based montmorillonite, γ-glycidoxypropyltrimethoxysilane in pre-hydrolyzed solution A1, γ-glycidoxypropyltrimethoxysilane in low water activity solution A2, and n-octyltriethoxysilane is 500:10-12:5-6:10-12.

[0016] Preferably, the pre-hydrolyzed solution A1 is prepared by mixing anhydrous ethanol, deionized water, glacial acetic acid and γ-glycidoxypropyltrimethoxysilane in a mass ratio of 200-220:20-22:2-2.2:10-12.

[0017] Preferably, the low water activity solution A2 is prepared by mixing anhydrous ethanol, deionized water, glacial acetic acid and γ-glycidoxypropyltrimethoxysilane in a mass ratio of 100-110:2-2.2:1-1.1:5-6.

[0018] Preferably, the pre-hydrolyzed solution B is prepared from anhydrous ethanol, deionized water, glacial acetic acid and n-octyltriethoxysilane in a mass ratio of 200-220:20-22:2-2.2:10-12.

[0019] Furthermore, the present invention also provides a method for preparing an EVA composite waterproof sheet, comprising the following steps: S1: Using polyethylene terephthalate-1,4-cyclohexanediethanol ester copolyester resin as the matrix, reactive extrusion is carried out. First, a multifunctional epoxy chain extender is added for chain extension, then succinic anhydride is added to regenerate the end carboxyl groups, followed by the addition of ethylene-glycidyl methacrylate copolymer and modified montmorillonite powder. The mixture is then extruded and granulated to obtain a special masterbatch for the reinforcing layer. S2: Ethylene-vinyl acetate copolymer resin and ethylene-glycidyl methacrylate copolymer are melt-extruded and granulated to obtain reaction transition layer granules; S3: Ethylene-vinyl acetate copolymer resin, ultrafine heavy calcium carbonate, rutile titanium dioxide, light stabilizer 944 and ultraviolet absorber 328 are melt-extruded and granulated to obtain weather-resistant surface granules. S4: Ethylene-vinyl acetate copolymer resin and ultrafine heavy calcium carbonate are melt-extruded and granulated to obtain the filler bottom granule material; S5: The reinforcing layer masterbatch, the reaction transition layer granule, the weather-resistant surface layer granule, and the filler bottom layer granule are melt-co-extruded to form a five-layer co-extruded sheet with the following structure: weather-resistant surface layer / reaction transition layer / reinforcing layer / reaction transition layer / filler bottom layer. The co-extruded sheet is then heat-set and cooled to obtain an EVA composite waterproof sheet.

[0020] Preferably, step S1 uses a co-rotating twin-screw extruder for reactive extrusion. The temperatures of each zone of the extruder from the feed section to the die head are 200℃, 220℃, 235℃, 245℃, 245℃, 240℃, 235℃, and 230℃, respectively. The vacuum degree at the vacuum exhaust port is set to 80 kPa, and the screw speed is 190-220 rpm. A multifunctional epoxy chain extender is added to the side feed in the 3rd temperature zone, succinic anhydride is added to the side feed in the 6th temperature zone, ethylene-glycidyl methacrylate copolymer is added to the side feed in the 7th temperature zone, and modified montmorillonite powder is added to the side feed in the 8th temperature zone.

[0021] Preferably, step S2 uses a co-rotating twin-screw extruder for granulation, with extruder temperatures ranging from 160°C, 170°C, 180°C, 190°C, 190°C, 185°C, and 180°C from the feed section to the die head. The vacuum level at the vacuum exhaust port is set to 60 kPa, and the screw speed is 150-170 rpm. Step S3 uses a twin-screw extruder for granulation, with extruder temperatures ranging from 150°C, 160°C, 170°C, 180°C, 185°C, and 180°C from the feed section to the die head. The screw speed is 180 rpm. Step S4 uses a twin-screw extruder for granulation, with extruder temperatures ranging from 150°C, 160°C, 170°C, 180°C, 185°C, and 180°C from the feed section to the die head. The screw speed is 180 rpm.

[0022] Preferably, in step S5, the die temperature of the co-extrusion is 220°C, the temperature of the calendering roller is 60-65°C, and the linear speed is 2-3 m / min; and the extruder temperature for the weather-resistant surface layer is set to 150-185°C, the extruder temperature for the reaction transition layer is 160-200°C, and the extruder temperature for the reinforcing layer is 210-245°C.

[0023] Preferably, the heat setting temperature in step S5 is 105-120℃, held for 1.5-3 minutes, and then cooled in a 20℃ cooling zone for 2 minutes.

[0024] The beneficial effects of this invention are: This invention constructs a five-layer symmetrical gradient structure consisting of a surface layer, a transition layer, a reinforcing layer, another transition layer, and a bottom layer. It employs in-situ reactive co-extrusion and tension heat setting processes, resulting in a stable interface formed between the functional layers through a combination of chemical bonding and physical entanglement. Specifically, the reinforcing layer of polyethylene terephthalate-1,4-cyclohexanediethanol ester copolyester is designed using a reactive extrusion sequence that first expands the adhesiveness of the epoxy chain and then regenerates the terminal carboxyl groups with the anhydride. This design achieves a high molecular weight skeleton to ensure high-temperature dimensional stability while retaining active terminal carboxyl groups that can react with the transition layer, thus forming a robust covalent bond network at the co-extrusion interface. This design overcomes the traditional trade-off between heat resistance and adhesion in modification processes, achieving a simultaneous and significant improvement in the overall mechanical properties and dimensional stability of the material.

[0025] The sheet material of this invention exhibits excellent high-temperature resistance and resistance to long-term creep. The copolyester reinforcing layer in the middle, after chain extension and end-carboxyl group regeneration modification, shows significantly improved molecular chain regularity and molecular weight, forming a rigid framework resistant to heat deformation. Simultaneously, montmorillonite nanosheets, modified with specific silane sequential grafting, are uniformly dispersed in the reinforcing layer and matrix, effectively pinning the molecular chains and preventing slippage and relaxation under external force or heat. This allows the sheet material to maintain shape and dimensional stability for extended periods under continuous high temperatures or loads, greatly extending its service life in high-temperature roofing and other similar applications.

[0026] Thanks to the chemical bonding and flexible transition design at the interface, the sheet of this invention exhibits excellent and long-lasting interlayer adhesion stability. Ethylene-glycidyl methacrylate copolymer is simultaneously introduced into both the reactive transition layer and the reinforcing layer. Under the high temperature of the co-extrusion die, its epoxy groups undergo in-situ ring-opening esterification with the regenerated terminal carboxyl groups of the reinforcing layer, forming a robust covalent interface. Simultaneously, the ethylene segments in this copolymer have good compatibility with the EVA matrix, forming a flexible transition layer at the interface. This rigid-flexible interface structure not only withstands high peel stress but also possesses excellent stress dissipation capabilities, making the sheet less prone to brittle peeling or shear failure under thermal cycling or external impact.

[0027] This invention effectively prevents premature failure or migration of weather-resistant additives (such as rutile titanium dioxide, specific light stabilizers, and UV absorbers) during high-temperature reactive extrusion by confining the weather-resistant additive system (such as rutile titanium dioxide, specific light stabilizers, and UV absorbers) to a low-temperature processed surface layer and using inorganically encapsulated pigments. The surface layer thus acquires durable resistance to UV radiation and thermo-oxidative aging, slowing down surface chalking, cracking, and other aging phenomena. This not only directly protects the waterproof substrate but also indirectly eliminates the additional stress driving interfacial peeling caused by surface aging shrinkage by maintaining the integrity of the surface layer, thereby enhancing the overall weather resistance and durability of the waterproof system. Detailed Implementation

[0028] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to specific embodiments.

[0029] Raw material source and specifications: The polyethylene terephthalate-1,4-cyclohexanediethanol ester copolyester resin used in this embodiment is selected from the SKYGREEN series polyester of SK Chemicals (specifically SKYGREEN K2012 grade, which is a terephthalate copolyester modified with ethylene glycol and 1,4-cyclohexanediethanol, suitable for extrusion applications, with a glass transition temperature of approximately 78°C and a density of approximately 1.27 g / cm³). 3 The multifunctional epoxy chain extender selected was BASF's Joncryl ADR-4368-C (a multifunctional epoxy group acrylic oligomer chain extender with an epoxy equivalent of approximately 285 g / eq and a functionality of approximately 9); the ethylene-glycidyl methacrylate copolymer selected was Arkema's LOTADER AX8840 (6wt%-8wt% glycidyl methacrylate content, melt flow rate of 4-6 g / 10 min, test conditions of 190℃ / 2.16 kg, melting point of 104-108℃, and density of approximately 0.94 g / cm³). 3The montmorillonite used was CLOISITE-Na+ (sodium-based montmorillonite) from BYK Chemical Company; the ethylene-vinyl acetate copolymer resin used was Sinopec Beijing Yanshan Branch's ethylene-vinyl acetate copolymer resin 14J2 (vinyl acetate content 14wt%, melt flow rate 2g / 10min, test conditions 190℃ / 2.16kg) and 18J3 (vinyl acetate content 18wt%, melt flow rate 3g / 10min, test conditions 190℃ / 2.16kg); the rutile titanium dioxide used was BILLIONS BLR-895 (chlorination process, TiO2 content 94%, inorganic coating of alumina and zirconium oxide, oil absorption 16g / 100g, specific gravity approximately 4.1g / cm³) from Longbai Group. 3 The calcium carbonate used is Omyacarb 2 series ultrafine heavy calcium carbonate from Omya Company (D50 approximately 3μm, calcium carbonate content greater than 97%).

[0030] Example 1: Step S1: Weigh 200g anhydrous ethanol, 20g deionized water, and 2g glacial acetic acid into a beaker, stir at 600rpm and maintain a constant temperature of 25℃, then add 10g γ-glycidoxypropyltrimethoxysilane dropwise and continue stirring for 20min to obtain pre-hydrolyzed solution A1; then weigh 100g anhydrous ethanol, 2g deionized water, and 1g glacial acetic acid into a beaker, stir at 600rpm and maintain a constant temperature of 25℃, then add 5g γ-glycidoxypropyltrimethoxysilane and stir for 5min to obtain low water activity solution A2; weigh 200g anhydrous ethanol, 20g deionized water, and 2g glacial acetic acid into a beaker, stir at 600rpm and maintain a constant temperature of 25℃, then add 10g n-octyltriethoxysilane and stir for 15min to obtain pre-hydrolyzed solution B. Step S2: Weigh 9000g of anhydrous ethanol and 500g of deionized water and add them to the reaction vessel. Heat the mixture to 50℃ and stir at 1000rpm. Then add 500g of sodium-based montmorillonite and maintain stirring for 30min. Add 20g of glacial acetic acid and continue stirring for 30min to obtain a montmorillonite dispersion slurry. Heat the mixture to 60℃ and maintain stirring at 800rpm. First, add all of the pre-hydrolyzed solution A1 obtained in step S1 and react for 60min. Then heat the mixture to 70℃ and add all of the low water activity solution A2 obtained in step S1 and react for 30min. Then add all of the pre-hydrolyzed solution B obtained in step S1 and react for 60min. Cool the mixture to 30℃ and filter. Wash the filter cake twice with 500g of anhydrous ethanol. Place the filter cake in a vacuum oven and dry it at 80℃ and 80kPa for 12h to obtain modified montmorillonite powder. Step S3: Weigh 10000g of polyethylene terephthalate-1,4-cyclohexanedimethyl ester copolyester resin, 15g of antioxidant 1010, 10g of antioxidant 168, and 10g of ethylene bis-stearamide. Premix them in a mixer for 5 minutes and use as the main feed. Add the above main feed to the main feed port of the co-rotating twin-screw extruder. Set the temperature from the feed section to the die head as follows: 200℃, 220℃, 235℃, 245℃, 245℃. The temperature ranges are 240℃, 235℃, and 230℃, with a vacuum exhaust port and a vacuum degree of 80kPa. The screw speed is 200rpm. 60g of multifunctional epoxy chain extender is added to the side feed in the 3rd temperature zone, 20g of succinic anhydride is added to the side feed in the 6th temperature zone, 500g of ethylene-glycidyl methacrylate copolymer is added to the side feed in the 7th temperature zone, and 100g of modified montmorillonite powder is added to the side feed in the 8th temperature zone. The mixture is then extruded, water-cooled, and pelletized to obtain a special masterbatch for the reinforcing layer. Step S4: Weigh 7000g of ethylene-vinyl acetate copolymer resin 18J3, 3000g of ethylene-glycidyl methacrylate copolymer, 10g of antioxidant 1010, 10g of antioxidant 168 and 10g of ethylene bis-stearamide, mix them evenly and add them to a co-rotating twin-screw extruder. The temperature from the feed section to the die head is 160℃, 170℃, 180℃, 190℃, 190℃, 185℃ and 180℃ respectively. The vacuum exhaust port is set with a vacuum degree of 60kPa and the screw speed is 150rpm. Extrusion, water cooling and pelletizing are performed to obtain the reaction transition layer granules. Step S5: Weigh 10000g of ethylene-vinyl acetate copolymer resin 14J2, 2500g of ultrafine heavy calcium carbonate, 800g of rutile titanium dioxide, 40g of light stabilizer 944, 25g of UV absorber 328, 15g of antioxidant 1010, 10g of antioxidant 168 and 10g of ethylene bis-stearamide, mix them evenly and add them to a twin-screw extruder. The temperature from the feed section to the die head is 150℃, 160℃, 170℃, 180℃, 185℃ and 180℃ respectively. The screw speed is 180rpm. Extrusion, water cooling and pelletizing are performed to obtain weather-resistant surface granules. Step S6: Weigh 10000g of ethylene-vinyl acetate copolymer resin 18J3, 2500g of ultrafine heavy calcium carbonate, 15g of antioxidant 1010, 10g of antioxidant 168 and 10g of ethylene bis-stearamide, mix them evenly and add them to a twin-screw extruder. The temperature from the feed section to the die head is 150℃, 160℃, 170℃, 180℃, 185℃ and 180℃ respectively. The screw speed is 180rpm. Extrusion, water cooling and pelletizing are performed to obtain the filler bottom granules. Step S7: Add 25kg of weather-resistant surface granules, 6kg of reaction transition layer granules, 38kg of reinforcing layer masterbatch, 6kg of reaction transition layer granules, and 25kg of filler bottom layer granules to the hoppers of five extruders respectively. Adjust the speed of each extruder so that the thickness of each layer after co-extrusion is 400μm for the surface layer, 100μm for the transition layer, 800μm for the reinforcing layer, 100μm for the transition layer, and 400μm for the bottom layer, with a total thickness of 1800μm. Set the temperature of each extruder as follows: 150-185℃ for the surface layer extruder, 160-200℃ for the transition layer extruder, and 210-245℃ for the reinforcing layer extruder. Set the co-extrusion die temperature to 220℃ and the calendering roller temperature to 60℃ while maintaining a linear speed of 2m / min to obtain a composite waterproof sheet. Heat the composite waterproof sheet in the heat setting zone at 110℃ for 2 minutes and then cool it in the 20℃ cooling zone for 2 minutes to obtain an EVA composite waterproof sheet.

[0031] Example 2: The difference from Example 1 is as follows: In step S3, the screw speed is set to 190 rpm, 50 g of multifunctional epoxy chain extender is added to the third temperature zone, 25 g of succinic anhydride is added to the sixth temperature zone, 450 g of ethylene-glycidyl methacrylate copolymer is added to the seventh temperature zone, and 80 g of modified montmorillonite powder is added to the eighth temperature zone; in step S4, the amounts of ethylene-vinyl acetate copolymer resin 18J3 and ethylene-glycidyl methacrylate copolymer are 7500 g and 2500 g, respectively, and the screw speed is set to 160 rpm. m; In step S5, the amount of ultrafine heavy calcium carbonate is 2200g, the amount of rutile titanium dioxide is 700g, the amount of light stabilizer 944 is 35g, and the amount of UV absorber 328 is 20g; In step S6, the amount of ultrafine heavy calcium carbonate is 2200g; In step S7, by adjusting the speed of each extruder, the thickness of each layer after co-extrusion is 420μm for the surface layer, 90μm for the transition layer, 780μm for the reinforcing layer, 90μm for the bottom layer, and 420μm for the bottom layer, with a total thickness of 1800μm. The heat setting temperature is set to 115℃ and held for 2min. The remaining conditions are the same as in Example 1.

[0032] Example 3: The difference from Example 1 is as follows: In step S3, the screw speed is set to 220 rpm, 80g of multifunctional epoxy chain extender is added to the third temperature zone, 30g of succinic anhydride is added to the sixth temperature zone, 650g of ethylene-glycidyl methacrylate copolymer is added to the seventh temperature zone, and 150g of modified montmorillonite powder is added to the eighth temperature zone; In step S4, the amounts of ethylene-vinyl acetate copolymer resin 18J3 and ethylene-glycidyl methacrylate copolymer are 6500g and 3500g, respectively, and the screw speed is set to 170 rpm; In step S7, the linear speed of the calendering roller is set to 2.5m / min, and by adjusting the speed of each extruder, the thickness of each layer after co-extrusion is 380μm for the surface layer, 120μm for the transition layer, 800μm for the reinforcing layer, 120μm for the transition layer, and 380μm for the bottom layer, with a total thickness of 1800μm. The heat setting zone is maintained at 118℃ for 2min. The remaining conditions are the same as in Example 1.

[0033] Example 4: The difference from Example 1 is that: in step S1, the pre-hydrolyzed solution A1 is formulated with 220g anhydrous ethanol, 22g deionized water, 2.2g glacial acetic acid, and 12g γ-glycidoxypropyltrimethoxysilane; the low water activity solution A2 is formulated with 110g anhydrous ethanol, 2.2g deionized water, 1.1g glacial acetic acid, and 6g... γ-glycidoxypropyltrimethoxysilane; the pre-hydrolysis solution B was formulated with 220g anhydrous ethanol, 22g deionized water, 2.2g glacial acetic acid, and 12g n-octyltriethoxysilane; in step S2, after adding sodium montmorillonite, stirring was maintained for 40 min; when adding glacial acetic acid, the amount of glacial acetic acid was 25g and stirring was continued for 40 min; after adding pre-hydrolysis solution A1, the reaction was carried out for 70 min; after adding low water activity solution A2, the reaction was carried out for 40 min; after adding pre-hydrolysis solution B, the reaction was carried out for 70 min; the vacuum oven drying conditions were 85℃, vacuum degree 85kPa, and drying for 10 h; in step S3, 15g succinic anhydride was added to the side of the 6th temperature zone, and 120g modified montmorillonite powder was added to the side of the 8th temperature zone; in step S7, the heat setting temperature was set to 105℃ and held for 3 min. The remaining conditions were the same as in Example 1.

[0034] Example 5: The difference from Example 1 is as follows: In step S3, the screw speed is set to 210 rpm; 40g of multifunctional epoxy chain extender is added to the feed in the third temperature zone; 10g of succinic anhydride is added to the feed in the sixth temperature zone; 400g of ethylene-glycidyl methacrylate copolymer is added to the feed in the seventh temperature zone; and 90g of modified montmorillonite powder is added to the feed in the eighth temperature zone. In step S4, the amounts of ethylene-vinyl acetate copolymer resin 18J3 and ethylene-glycidyl methacrylate copolymer are 6800g and 3200g, respectively. In step S5, the amount of ultrafine heavy calcium carbonate is 3000g. The following steps were performed: 1000g of rutile titanium dioxide, 50g of light stabilizer 944, and 30g of UV absorber 328; 3000g of ultrafine heavy calcium carbonate was used in step S6; in step S7, the temperature of the calendering roller was set to 65℃ and the linear speed was maintained at 3m / min. By adjusting the speed of each extruder, the thicknesses of each layer after co-extrusion were made as follows: surface layer 450μm, transition layer 80μm, reinforcing layer 740μm, bottom layer 80μm, and bottom layer 450μm, with a total thickness of 1800μm. The heat setting zone was maintained at 120℃ for 1.5min. The remaining conditions were the same as in Example 1.

[0035] Comparative Example 1: The difference from Example 1 is that succinic anhydride is not added in step S3 during the feeding in the 6th temperature zone; the other conditions are the same as in Example 1.

[0036] Comparative Example 2: The difference from Example 1 is that: in step S3, no ethylene-glycidyl methacrylate copolymer is added to the side feed in the 7th temperature zone; the other conditions are the same as in Example 1.

[0037] Comparative Example 3: The difference from Example 1 is that in step S4, 3000g of ethylene-glycidyl methacrylate copolymer is replaced with 3000g of ethylene-vinyl acetate copolymer resin 18J3; the other conditions are the same as in Example 1.

[0038] Comparative Example 4: The difference from Example 1 is that in step S2, the pre-hydrolyzed solution A1 obtained in step S1 and the low water activity solution A2 are added to the montmorillonite dispersion slurry at 60°C and reacted for 90 min. Then, the pre-hydrolyzed solution B obtained in step S1 is added at 70°C and reacted for 60 min. The remaining conditions are the same as in Example 1.

[0039] Comparative Example 5: The difference from Example 1 is that the low water activity solution A2 is not added in step S2; the other conditions are the same as in Example 1.

[0040] Comparative Example 6: The difference from Example 1 is that in step S3, 100g of sodium-based montmorillonite is added to the side feed in the 8th temperature zone, replacing the 100g of modified montmorillonite powder in Example 1; the other conditions are the same as in Example 1.

[0041] Comparative Example 7: The difference between Comparative Example 7 and Example 1 is that the 6 kg reaction transition layer granules located between the reinforcing layer and the bottom layer in step S7 are replaced with 6 kg filler bottom layer granules; the other conditions are the same as in Example 1.

[0042] Performance testing: Sample preparation and conditioning: EVA composite waterproof sheets were prepared according to Examples 1-5 and Comparative Examples 1-7. The prepared sheets were placed at (23±2)℃ and (50±5)% relative humidity for 24 hours before cutting the samples. For samples involving joint testing, two (200mm×50mm) rectangular strips of the same sheet were overlapped with an overlap width of 50mm and an overlap length of 70mm. The joints were prepared by hot air welding at a hot air temperature of 380℃, a welding speed of 3m / min, and a pressure roller of 0.30MPa. After welding, the joint samples were placed at (23±2)℃ and (50±5)% relative humidity for 24 hours before cutting the joint test pieces.

[0043] Tensile properties: Tensile properties were tested according to GB / T 328.9-2007 using method A. Rectangular specimens (50mm×200mm) were cut from each sheet along both the longitudinal and transverse directions. The specimens were placed at (23±2)℃ and (50±5)% relative humidity for at least 20 hours as required by the standard before testing. The clamp spacing was set at 120mm on the universal testing machine. The initial gauge length of 100mm was marked on the specimens. The clamp moving speed was set to 100mm / min. The tensile-displacement curves were continuously recorded throughout the test. The maximum tensile force (N / 50mm) and the elongation (%) at the maximum tensile force were obtained. Five specimens were tested in each direction, and the arithmetic mean was taken.

[0044] Joint peel performance: The joint peel performance of polymer waterproof membrane was tested according to GB / T 328.21-2007. After preparing the joint strip, a (200mm×50mm) joint peel specimen was cut from each joint strip, ensuring that the joint was located in the center of the specimen and the overlap width was consistent at 50mm. The test was carried out at (23±2)℃, with a distance of 100mm between the clamps and a clamp moving speed of 100mm / min. The tensile force and failure mode during the peeling process were continuously recorded. The average peel force F (N) of the stable peeling section was taken, and the joint peel strength (N / mm) was calculated by converting F / 50. Five specimens were tested for each number and the arithmetic mean was taken.

[0045] Dimensional change rate (dimensional stability) after heat treatment: The dimensional change rate of polymer waterproof membrane after heat treatment was tested according to GB / T 328.13-2007. Two (200mm×200mm) specimens were cut from each sheet. A 100mm measurement baseline was marked on the specimens along the longitudinal and transverse directions, and the initial length L0 was accurately measured. The specimens were placed flat on a glass plate and treated in a forced-air oven at (80±2)℃ for 6 hours (allowable deviation ±15min). After being removed, they were placed at (23±2)℃ for 2 hours, and the length L1 after treatment was measured again. The dimensional change rate (%) in the longitudinal and transverse directions was calculated as (L1-L0) / L0×100%, and the average value of the two specimens was taken as the result.

[0046] Impermeability: The impermeability test shall be conducted in accordance with GB / T 328.10-2007 and Method B shall be adopted. A specimen that meets the clamping requirements shall be cut from each sheet and the surface shall be fixed on the 7-hole plate of the impermeability test device as the water-facing side. The pressure shall be gradually increased to 0.30 MPa and held for 120 min. During the test, observe whether water seepage or water droplets appear on the water-repellent side of the specimen and at each hole. If water seepage occurs in any hole, it shall be deemed unqualified. Three specimens shall be tested for each number and all of them shall be qualified as the result of impermeability judgment.

[0047] Performance retention rate after hot air aging: Hot air aging test was conducted according to GB / T 7141-2008; 6 strip specimens (200mm×50mm) were cut from each sheet and placed in a forced-air drying oven at 120℃ for 168h. During the aging period, the specimens were suspended and did not contact each other; after aging, they were placed at (23±2)℃ and (50±5)% relative humidity for 24h, and then the maximum tensile force and elongation at the maximum tensile force were determined according to the tensile performance test method and the retention rate was calculated.

[0048] Tensile creep: Tensile creep test was performed according to GB / T 11546.1-2008; 5 specimens (100mm×10mm) were cut from the reinforcing layer area of ​​each sheet and the thickness was measured. After the specimens were placed at (23±2)℃ and (50±5)% relative humidity for 24h, they were clamped in the tensile creep testing machine. The test temperature was set to 80℃ and held for 30min. Then a constant tensile stress of 0.20MPa was applied and held for 24h. The creep strain (%) at 24h was calculated.

[0049] Low-temperature bending performance: The low-temperature bending performance of polymer waterproof membranes shall be tested in accordance with GB / T 328.15-2007. Six specimens (100mm×50mm) shall be cut from each sheet and placed in a low-temperature chamber at -25℃ for 2 hours. The bending test shall be carried out immediately afterward. The bending shall be performed by bending a 30mm diameter round bar into a 180° bend in one go and holding it for 5 seconds. The specimens shall then be removed and observed at room temperature for cracks or delamination. Any specimen showing cracks or delamination shall be deemed unqualified.

[0050] Table 1 Performance test results of the examples and comparative samples Data Analysis: As can be seen from the data in Table 1, the ethylene-vinyl acetate copolymer composite waterproof sheet prepared by the present invention maintains a high maximum tensile strength and a high level of seam peel strength, and the lateral and longitudinal dimensional change rates after heat treatment are small, showing good thermal dimensional stability. It can still maintain a high mechanical retention rate after hot air aging and exhibits a low strain growth under tensile creep conditions at 80℃, indicating that the material is not prone to continuous deformation under high temperature loads and is suitable for long-term heat and stress conditions in roofing and underground engineering. The possible reasons are as follows: the end groups of polyethylene terephthalate-1,4-cyclohexanediethanol copolyester treated with succinic anhydride in the reinforcing layer are restored, and react with the epoxy groups of ethylene-glycidyl methacrylate copolymer to form a stable chemical anchor; the transition layer uses a blend of ethylene-glycidyl methacrylate copolymer and ethylene-vinyl acetate copolymer to form a polar gradient, so that stress is transferred stepwise between layers and the stress concentration at the interface is reduced; montmorillonite treated stepwise with silane coupling agent forms a nano-reinforcement and micro-barrier structure in the matrix, which synergistically improves creep resistance and aging stability; at the same time, the heat setting process releases the extrusion internal stress and fixes the sheet size, which further improves the dimensional stability of heat treatment.

[0051] As can be seen from the data in Example 1 and Comparative Example 1 in Table 1, when the reinforcing layer system no longer restores the copolyester end-group activity through succinic anhydride, the joint peel strength and mechanical retention rate after hot air aging of the material decrease simultaneously, accompanied by an increase in the dimensional change rate after heat treatment. The main reason is that after the number of reactive sites on the copolyester end groups decreases, the epoxy groups of the ethylene-glycidyl methacrylate copolymer are difficult to form a sufficiently dense chemical anchoring network, and the interface relies more on physical entanglement, resulting in the interface being more prone to relaxation under heat treatment and aging.

[0052] As can be seen from the data in Example 1 and Comparative Example 2 in Table 1, when the ethylene-glycidyl methacrylate copolymer was removed from the reinforcing layer system, the seam peel strength, mechanical retention rate after hot air aging, and tensile creep performance at 80°C all deteriorated significantly, and interlayer delamination occurred during low-temperature bending. The possible reason is that the lack of epoxy-based reactive bridging between the reinforcing layer and the transition layer makes it difficult for the surface-treated montmorillonite to establish a stable interface with the copolyester matrix. Local agglomeration and micro-defects are amplified under thermo-mechanical cycling, leading to more pronounced interfacial slip and structural relaxation.

[0053] As can be seen from the data in Table 1 for Example 1 and Comparative Example 3, when the transition layer was changed from an ethylene-glycidyl methacrylate copolymer / ethylene-vinyl acetate copolymer system to a single ethylene-vinyl acetate copolymer, although the elongation at maximum tensile force increased, the seam peel strength, heat treatment dimensional stability, and tensile creep at 80°C all showed significant deterioration. The main reason is that the polarity and reactivity of the single ethylene-vinyl acetate copolymer transition layer are insufficient, making it difficult to form a continuous chemical anchoring and gradient modulus transition with the reinforcing layer. This leads to easier chain segment relaxation and more pronounced stress concentration at high temperatures.

[0054] As can be seen from the data in Table 1 for Example 1 and Comparative Examples 4 and 5, when the surface treatment process of montmorillonite no longer uses a step-by-step low-water-activity system but instead involves a one-time mixing or omitting of key treatment steps, the material exhibits varying degrees of decline in joint peel strength, retention rate after hot air aging, and creep performance. Simultaneously, the dimensional change rate after heat treatment increases, and water seepage occurs due to impermeability issues. The possible reason is that insufficient control of water activity can induce the self-condensation of the silane coupling agent in solution, resulting in a decrease in effective grafting density and the introduction of agglomerated particles, causing the nano-reinforcement to transform from interfacial reinforcement into a defect source.

[0055] As can be seen from the data in Example 1 and Comparative Example 6 in Table 1, when unmodified sodium-based montmorillonite directly replaces montmorillonite treated with silane coupling agent, water seepage occurs due to impermeability, and the joint peel strength, aging resistance retention rate, and creep performance are all at their worst. Furthermore, cracks appear during low-temperature bending. The main reason for this is that sodium-based montmorillonite has strong hydrophilicity and poor compatibility with ethylene-vinyl acetate copolymers and copolyesters, easily forming interlayer micropores and interfacial voids. Under water pressure and heat treatment conditions, these voids evolve into seepage channels, inducing crack propagation during low-temperature bending.

[0056] As can be seen from the data in Example 1 and Comparative Example 7 in Table 1, when the transition layer between the reinforcing layer and the lower surface layer is removed and directly replaced by a high-fill surface layer, both the joint peel strength and creep performance decrease, and delamination occurs during low-temperature bending. The possible reason is that the absence of a transition layer on one side disrupts the symmetrical gradient structure of the upper and lower interfaces, making it difficult to release residual stress evenly after heat setting. This makes the interface more prone to shear slip and peeling propagation under low temperature and continuous load.

[0057] Those skilled in the art should understand that the discussion of any of the above embodiments is merely exemplary and is not intended to imply that the scope of the invention is limited to these examples; within the framework of the invention, the technical features of the above embodiments or different embodiments can also be combined, the steps can be implemented in any order, and there are many other variations of the different aspects of the invention as described above, which are not provided in detail for the sake of brevity.

Claims

1. An EVA composite waterproof sheet, characterized in that, It includes a weather-resistant surface layer, a first reactive transition layer, a reinforcing layer, a second reactive transition layer, and a filler underlayer, which are stacked sequentially from the top surface to the bottom surface; the weather-resistant surface layer and the filler underlayer are located on both sides of the sheet, and the first reactive transition layer and the second reactive transition layer are located on both sides of the reinforcing layer; The weather-resistant surface layer, by weight, is prepared from the following raw materials: 100 parts ethylene-vinyl acetate copolymer resin, 22-30 parts ultrafine heavy calcium carbonate, 7-10 parts rutile titanium dioxide, 0.35-0.50 parts light stabilizer 944, and 0.20-0.30 parts ultraviolet absorber 328. The filling substrate is prepared from the following raw materials: 100 parts of ethylene-vinyl acetate copolymer resin and 22-30 parts of ultrafine heavy calcium carbonate; Both the first reaction transition layer and the second reaction transition layer are prepared from the following raw materials: 65-75 parts of ethylene-vinyl acetate copolymer resin and 25-35 parts of ethylene-glycidyl methacrylate copolymer; The reinforcing layer is prepared from the following raw materials: 100 parts polyethylene terephthalate-1,4-cyclohexanediethanol ester copolyester resin, 0.4-0.8 parts polyfunctional epoxy chain extender, 0.1-0.3 parts succinic anhydride, 4-6.5 parts ethylene-glycidyl methacrylate copolymer, and 0.8-1.5 parts modified montmorillonite powder.

2. The EVA composite waterproof sheet according to claim 1, characterized in that, The thickness of the weather-resistant surface layer is 380-450 μm, the thickness of the first reaction transition layer is 80-120 μm, the thickness of the reinforcing layer is 740-800 μm, the thickness of the second reaction transition layer is 80-120 μm, and the thickness of the filling substrate is 380-450 μm.

3. The EVA composite waterproof sheet according to claim 1, characterized in that, By weight, the weather-resistant surface layer further comprises 0.15 parts of antioxidant 1010, 0.10 parts of antioxidant 168, and 0.10 parts of ethylene bis-stearamide; the filler bottom layer further comprises 0.15 parts of antioxidant 1010, 0.10 parts of antioxidant 168, and 0.10 parts of ethylene bis-stearamide; the first reaction transition layer and / or the second reaction transition layer further comprises 0.10 parts of antioxidant 1010, 0.10 parts of antioxidant 168, and 0.10 parts of ethylene bis-stearamide; the reinforcing layer further comprises 0.15 parts of antioxidant 1010, 0.10 parts of antioxidant 168, and 0.10 parts of ethylene bis-stearamide.

4. The EVA composite waterproof sheet according to claim 1, characterized in that, The glycidyl methacrylate copolymer of the ethylene-glycidyl methacrylate has a glycidyl methacrylate content of 6wt%-8wt%; the ethylene-vinyl acetate copolymer resin of the weather-resistant surface layer is of type 14J2, and the ethylene-vinyl acetate copolymer resin of the first reaction transition layer, the second reaction transition layer and the filling bottom layer is of type 18J3.

5. The EVA composite waterproof sheet according to claim 1, characterized in that, The preparation steps of the modified montmorillonite powder are as follows: Sodium-based montmorillonite is dispersed in an ethanol-water system and glacial acetic acid is added. Then, a pre-hydrolyzed solution A1 containing γ-glycidoxypropyltrimethoxysilane is added sequentially and reacted at 60°C for 60-70 min, a low water activity solution A2 containing γ-glycidoxypropyltrimethoxysilane is reacted at 70°C for 30-40 min, and a pre-hydrolyzed solution B containing n-octyltriethoxysilane is reacted at 70°C for 60-70 min. The mixture is then filtered, washed, and dried to obtain the modified montmorillonite powder.

6. The EVA composite waterproof sheet according to claim 1, characterized in that, The mass ratio of sodium-based montmorillonite, γ-glycidoxypropyltrimethoxysilane in pre-hydrolyzed solution A1, and γ-glycidoxypropyltrimethoxysilane and n-octyltriethoxysilane in low water activity solution A2 is 500:10-12:5-6:10-12.

7. The EVA composite waterproof sheet according to claim 1, characterized in that, The pre-hydrolyzed solution A1 was prepared by mixing anhydrous ethanol, deionized water, glacial acetic acid, and γ-glycidoxypropyltrimethoxysilane in a mass ratio of 200-220:20-22:2-2.2:10-12; the low water activity solution A2 was prepared by mixing anhydrous ethanol, deionized water, glacial acetic acid, and γ-glycidoxypropyltrimethoxysilane in a mass ratio of 100-110:2-2.2:1-1.1:5-6; and the pre-hydrolyzed solution B was prepared by mixing anhydrous ethanol, deionized water, glacial acetic acid, and n-octyltriethoxysilane in a mass ratio of 200-220:20-22:2-2.2:10-12.

8. A method for preparing an EVA composite waterproof sheet according to any one of claims 1-7, characterized in that, Includes the following steps: S1: Using polyethylene terephthalate-1,4-cyclohexanediethanol ester copolyester resin as the matrix, reactive extrusion is carried out. First, a multifunctional epoxy chain extender is added for chain extension, then succinic anhydride is added to regenerate the end carboxyl groups, followed by the addition of ethylene-glycidyl methacrylate copolymer and modified montmorillonite powder. The mixture is then extruded and granulated to obtain a special masterbatch for the reinforcing layer. S2: Ethylene-vinyl acetate copolymer resin and ethylene-glycidyl methacrylate copolymer are melt-extruded and granulated to obtain reaction transition layer granules; S3: Ethylene-vinyl acetate copolymer resin, ultrafine heavy calcium carbonate, rutile titanium dioxide, light stabilizer 944 and ultraviolet absorber 328 are melt-extruded and granulated to obtain weather-resistant surface granules. S4: Ethylene-vinyl acetate copolymer resin and ultrafine heavy calcium carbonate are melt-extruded and granulated to obtain the filler bottom granule material; S5: The reinforcing layer masterbatch, the reaction transition layer granule, the weather-resistant surface layer granule, and the filler bottom layer granule are melt-co-extruded to form a five-layer co-extruded sheet with the following structure: weather-resistant surface layer / reaction transition layer / reinforcing layer / reaction transition layer / filler bottom layer. The co-extruded sheet is then subjected to tension heat setting and cooling to obtain an EVA composite waterproof sheet.

9. The method for preparing the EVA composite waterproof sheet according to claim 8, characterized in that, Step S1 employs a co-rotating twin-screw extruder for reactive extrusion. The temperatures of each zone of the extruder, from the feed section to the die head, are 200℃, 220℃, 235℃, 245℃, 245℃, 240℃, 235℃, and 230℃, respectively. The vacuum degree at the vacuum exhaust port is set at 80 kPa, and the screw speed is 190-220 rpm. A multifunctional epoxy chain extender is added to the side feed in the 3rd temperature zone, succinic anhydride is added to the side feed in the 6th temperature zone, ethylene-glycidyl methacrylate copolymer is added to the side feed in the 7th temperature zone, and modified montmorillonite powder is added to the side feed in the 8th temperature zone.

10. The method for preparing the EVA composite waterproof sheet according to claim 8, characterized in that, In step S5, the die temperature of the co-extrusion is 220℃, the temperature of the calendering roller is 60-65℃, and the linear speed is 2-3m / min; and the extruder temperature for the weather-resistant surface layer is set to 150-185℃, the extruder temperature for the reaction transition layer is 160-200℃, and the extruder temperature for the reinforcing layer is 210-245℃.