Ethylene-vinyl acetate copolymer composite for coating field and method for preparing the same

Abstract

The application provides an ethylene-vinyl acetate copolymer composite material for the coating field and a preparation method thereof, taking glycidyl methacrylate-polystyrene binary modified ethylene-vinyl acetate copolymer resin as a core film-forming material, and compounding a hydrogenated C5 petroleum resin, a silane coupling agent KH-560 and a functional additive to obtain the ethylene-vinyl acetate copolymer composite material. The application realizes the uniform grafting of GMA on the EVA molecular chain through a ternary composite regulation system-four-stage gradient temperature control high-pressure polymerization process, constructs a binary modified EVA molecular structure through a beta ray irradiation activation-styrene suspension grafting process, and finally compiles a stable coating system. After curing and film-forming, the application can form a protective coating with strong adhesion, high hardness, heat resistance, aging resistance, excellent temperature change resistance and the like on the surface of a base material, and greatly improves the long-term service stability of the ethylene-vinyl acetate copolymer coating material under complex extreme working conditions. The application has the advantages of controllable process, good coating construction adaptability and easy popularization and implementation.

Description

Technical Field

[0001] This application belongs to the field of polymer materials technology, specifically relating to an ethylene-vinyl acetate copolymer composite material for coating applications. Background Technology

[0002] In existing technologies, ethylene-vinyl acetate copolymer (EVA) composites play a crucial role in the coating field. With its core advantages of low heat-sealing temperature, good transparency, and strong adhesion, it is gradually replacing LDPE resin and is widely used in pre-coated films, non-woven fabric composites, and electronic component encapsulation. With the upgrading and development of industries such as packaging, electronics, and new energy, the performance requirements for coating-grade resins are becoming increasingly refined. Coating materials that combine low odor, high flowability, and stable adhesion have become a core market demand. However, current coating-grade EVA resin materials on the market have performance shortcomings that are difficult to achieve simultaneously.

[0003] In existing technologies, high-VA-content EVA resins, while exhibiting excellent initial adhesion and processing fluidity, making them suitable for conventional coating production processes, suffer from poor heat stability. At high temperatures, the coating film is prone to softening, sticking, and yellowing due to aging. They also exhibit insufficient water resistance and high residual monomer content, making it difficult to meet environmental protection requirements for VOC emissions. While low-VA-content EVA resins offer significant advantages in low odor, heat resistance, and production cost, they consistently face the technical bottleneck of balancing low VA content with coating performance stability. Their insufficient molecular chain polarity results in poor adhesion when coated on metal and wood substrates, leading to easy film peeling, short service life, and poor coating thickness uniformity due to their wide molecular weight distribution. High-speed production can easily result in edge shrinkage and missed coatings. Existing modification methods also suffer from poor storage stability and insufficient solvent solubility.

[0004] Therefore, in order to comprehensively improve the substrate adhesion, thermal stability, coating stability and environmental protection of coating-grade EVA resin, and to solve the industry pain point that the performance of low VA content EVA resin in the existing technology is difficult to balance, it is now urgent to make improvements to adapt to the upgrading needs of high-end coating scenarios. Summary of the Invention

[0005] To address the technical problems in the prior art, such as poor heat resistance, insufficient water resistance, high residual monomer content, and VOC emission levels that fail to meet environmental protection requirements in high-VA content products, and poor substrate adhesion, easy paint film peeling, poor coating thickness uniformity in low-VA content products, and the tendency for edge shrinkage and missed coating problems in high-speed production, this application proposes an ethylene-vinyl acetate copolymer composite material for the coating field.

[0006] To address the technical problems raised in this application, this application also provides a method for preparing an ethylene-vinyl acetate copolymer composite material for use in the coating field.

[0007] To address the technical problems raised in this application, this application also provides a method for applying an ethylene-vinyl acetate copolymer composite material in the field of coating.

[0008] This application adopts the following scheme: an ethylene-vinyl acetate copolymer composite material for coating, which, by mass parts, is composed of the following components: 55-65 parts of modified ethylene-vinyl acetate copolymer resin base material, 5-8 parts of hydrogenated C5 petroleum resin, 1-3 parts of silane coupling agent KH-560, 0.5-1 part of leveling agent, 0.2-0.5 parts of hydrogenated castor oil, 0.2-0.5 parts of antioxidant, 0.2-0.5 parts of ultraviolet absorber UV-327, 30-40 parts of D80 environmentally friendly solvent oil, and 2-4 parts of 120# solvent oil;

[0009] The modified ethylene-vinyl acetate copolymer resin substrate is a glycidyl methacrylate-polystyrene binary modified ethylene-vinyl acetate copolymer resin.

[0010] In actual implementation, the leveling agent is model BYK-358N and the antioxidant is model 1010.

[0011] In some feasible embodiments, the preparation method of the modified ethylene-vinyl acetate copolymer resin substrate includes the following steps: Step 101. The granulated, dried and pulverized glycidyl methacrylate-grafted ethylene-vinyl acetate copolymer resin powder is transferred to an electron accelerator β-ray irradiation device for irradiation to obtain activated resin powder. Step 102. The activated resin powder, styrene monomer, calcium hydroxyphosphate dispersant, sodium dodecylbenzenesulfonate emulsifier, benzoyl peroxide initiator, and deionized water prepared in step 101 are added to a stirred tank in a mass ratio of 10:(12-18):(0.3-0.5):(0.15-0.25):(0.036-0.09):(80-160). The mixture is reacted for 6-8 hours under the conditions of water bath temperature of 65℃-75℃, 100rpm-300rpm, nitrogen atmosphere, and reflux. After the reaction is completed, heating is stopped, cooling water is introduced to quickly cool down to room temperature, the reaction system is discharged and washed with deionized water, and water-soluble impurities are removed by vacuum filtration. The filter cake is placed in a vacuum drying oven and dried for 18 hours at 65℃ and -0.08MPa to obtain the crude grafted product. Step 103. After pulverizing the crude grafted product prepared in step 102 to 40 mesh, put it into a continuous Soxhlet extraction device and extract it by reflux at 65℃~66℃ for 24h using tetrahydrofuran as solvent; place the extracted product in a dryer and dry it at 70℃ and -0.09MPa for 12h to obtain the purified grafted product. Step 104. The purified graft product prepared in step 103 is fed into a twin-screw extruder and melt-extruded at 140℃~160℃. After being successively subjected to underwater pelletizing, crushing, and 200-mesh vibrating sieve, the modified ethylene-vinyl acetate copolymer resin matrix is ​​obtained.

[0012] In some feasible embodiments, in step 101, the accelerating voltage of the electron accelerator beta-ray irradiation device is 1.5MeV to 2.2MeV, the beam current is 15mA to 18mA, the transmission speed is 10m / min to 15m / min, and the irradiation dose is 30kGy to 40kGy. After irradiation, the device is sealed and protected from light and left to stand for 2 hours.

[0013] In some feasible embodiments, step 101, the preparation method of the glycidyl methacrylate-grafted ethylene-vinyl acetate copolymer composite material includes the following steps: Step 201. Ethylene monomer and vinyl acetate monomer, which have been dehydrated to a moisture content of ≤8ppm by 3A molecular sieve, are added to a static mixer in a mass ratio of 100:(23-27). The mixture is mixed for 40s-60s under a pressure of 25.5MPa-26MPa and a temperature of 80℃-110℃ to obtain the premixed monomer. Step 202. The ternary composite control system, initiator, and isododecane solvent are continuously added to a high-pressure tubular reactor at a mass ratio of (1.5-3.2):(1.2-1.8):(1.2-2.5). The reaction is carried out under nitrogen atmosphere, water bath temperature of 110-130℃ and 250-255MPa for 25-45 minutes to obtain the reaction precursor. The initiator is selected from di-tert-butyl peroxide or tert-butyl peroxide isononanoate. Step 203. The premixed monomer prepared in step 201 and the initiator system in step 202 are simultaneously and continuously fed into a high-pressure tubular reactor. After polymerization for 30 min to 45 min under nitrogen atmosphere, 170℃~240℃, and 250MPa~255MPa, the crude polymer melt is obtained. Step 204. After cooling the crude polymer melt prepared in step 203 to 180℃~190℃, transfer it to a devolatilization reactor and devolatilize it for 16min~20min at 175℃~185℃ and -0.08MPa~-0.09MPa. After devolatilization, feed the devolatilized melt into a twin-screw extruder and melt-extrude it at 145℃~165℃. Then, pass it through underwater pelletizing and 200-mesh vibrating sieve to obtain the glycidyl methacrylate grafted ethylene-vinyl acetate copolymer composite material.

[0014] In some feasible embodiments, in step 202, the ternary composite regulation system is obtained by compounding propylene, propionaldehyde and glycidyl methacrylate in a mass ratio of (85-87):(11-13):(1.5-2.5), wherein propylene and propionaldehyde are chain transfer agents and glycidyl methacrylate is a functional grafting monomer.

[0015] In some feasible embodiments, in step 203, the polymerization process includes a first reaction section, a second reaction section, a third reaction section, and a fourth reaction section carried out sequentially in time; the temperature of the first reaction section is controlled at 170℃~180℃, and the reaction time is 3min~8min; the temperature of the second reaction section is controlled at 230℃~240℃, and the reaction time is 12min~14min; the temperature of the third reaction section is controlled at 220℃~235℃, and the reaction time is 5min~8min; the temperature of the fourth reaction section is controlled at 200℃~210℃, and the reaction time is 10min~15min.

[0016] To address the technical problems raised in this application, this application also provides a method for preparing an ethylene-vinyl acetate copolymer composite material for coating applications, comprising the following steps: Step 301. The granulated modified ethylene-vinyl acetate copolymer resin base material and hydrogenated C5 petroleum resin are put into a high-speed pulverizer in a preset ratio and pulverized. After pulverization, the powder is sent to a 200-mesh vibrating screen to remove agglomerated materials. After sealing and storing to avoid moisture absorption, the pretreated powder raw material is obtained. Step 302. Add D80 environmentally friendly solvent oil and 120# solvent oil into the reaction vessel according to the preset ratio. After dispersing for 15 minutes under nitrogen atmosphere, 75℃~80℃, and 500rpm~600rpm, add the pretreated powder raw material prepared in step 301 into the reaction system. After dispersing for 30 minutes under nitrogen atmosphere, 800rpm~1200rpm, and 75℃~80℃, the resin base material is obtained. Step 303. Cool the resin base material prepared in step 302 to 75℃~80℃. Under stirring conditions of 500rpm~600rpm, add silane coupling agent KH-560, leveling agent, hydrogenated castor oil, antioxidant, and ultraviolet absorber UV-327 to the reaction system in sequence according to the preset ratio. After high-speed dispersion for 25min~30min under nitrogen atmosphere, 1000rpm~1200rpm, water bath 45℃~50℃, the premixed material is obtained. Step 304. The premix prepared in step 303 is fed into a vacuum degassing machine and degassed for 10 to 15 minutes at -0.08 MPa to -0.09 MPa and room temperature. Then it is filtered through a 200-mesh bag filter and sealed and filled under nitrogen protection by a filling equipment to obtain an ethylene-vinyl acetate copolymer composite material for coating applications.

[0017] In some feasible embodiments, in step 302, the pretreated powder raw material prepared in step 301 is divided into three batches and sequentially added to the reactor. After each batch is added, it is dispersed for 10 minutes under nitrogen atmosphere, 800 rpm to 1200 rpm, and 75°C to 80°C.

[0018] In some feasible embodiments, in step 303, the premix is ​​further subjected to grinding treatment, which includes the following steps: transferring the premix to a horizontal ball mill with zirconium bead media, and grinding it three times in a cycle at 45°C, so that the fineness of the premix after grinding is 18μm~20μm.

[0019] To address the technical problems raised in this application, this application also provides a spraying method for ethylene-vinyl acetate copolymer composite materials in the coating field, comprising the following steps: Step 401. Add the ethylene-vinyl acetate copolymer composite material into a mixing tank and stir for 3 to 5 minutes at room temperature and 300 to 500 rpm. After stirring evenly, let it stand for 5 minutes and filter it through a 200-mesh filter to obtain the coating to be sprayed. Step 402. Select the appropriate spraying equipment according to the construction requirements (for example, if a gravity-type air spray gun with a nozzle diameter of 1.3mm to 1.5mm is selected, adjust the air compressor pressure to 0.4MPa to 0.5MPa and the atomization pressure to 0.3MPa to 0.4MPa; if a high-pressure airless sprayer with a nozzle diameter of 0.33mm to 0.43mm is selected, adjust the spraying pressure to 12MPa to 15MPa). Perform a no-load test spray under room temperature conditions until the paint is atomized evenly without interruption. The spraying construction system is now fully debugged. Step 403. Fix the substrate to be sprayed, and use the spraying system that has been debugged in Step 402. Keep the spray gun perpendicular to the substrate surface. For air spraying, control the spraying distance to 15cm to 20cm, and for airless spraying, control the spraying distance to 30cm to 40cm. Spray at room temperature and a uniform gun movement speed of 30cm / s to 50cm / s. The width of adjacent spraying strips should overlap by 1 / 3. The wet film thickness of a single spraying should be controlled at 15μm to 25μm. If a thick coating is required, apply 2 to 3 coats, with a 5-minute interval between each coat until the paint film is surface dry. The total dry film thickness should be controlled at 20μm to 60μm to obtain the workpiece with a wet film after spraying. Step 404. After the workpiece with wet film prepared in step 403 is allowed to stand at room temperature for 10 minutes to level, it is dried into a film by any of the following methods: ① air drying at room temperature, standing at 20℃~25℃ in a ventilated environment for 24 hours until the paint film is completely dry; ② forced drying, placing it in a hot air circulating oven and drying it at 65℃~70℃ for 15min~20min, then taking it out and letting it cool naturally to room temperature to obtain the coated ethylene-vinyl acetate copolymer composite paint film workpiece.

[0020] Furthermore, in order to solve the technical problems raised in this application, this application also provides a hot-melt coating application method for ethylene-vinyl acetate copolymer composite materials in the field of coating, including the following steps: Step 501. The nonwoven fabric or film substrate to be coated is fed into the corona treatment machine and run continuously online. The corona treatment power is controlled at 10kW to 15kW and the running line speed is 50m / min to 150m / min. After the surface tension (dyne value) of the film substrate is ≥38mN / m and the surface tension of the nonwoven fabric substrate is ≥36mN / m, the pre-treated continuous substrate is obtained. Step 502. According to the usage requirements, add the cured and pulverized ethylene-vinyl acetate copolymer composite material particles for coating into a single screw extruder, and set the screw temperature in sections: feeding section 120℃~130℃, plasticizing section 140℃~150℃, homogenizing section 150℃~160℃, and die temperature 155℃~165℃. Control the screw speed to 30r / min~80r / min until the resin is completely melted and plasticized and the melt is uniform and stable, thus obtaining the EVA melt. Step 503. The EVA melt prepared in step 502 is uniformly extruded through a T-die and online bonded to the surface of the pretreated continuous substrate prepared in step 501. The temperature of the composite roller is controlled at 60℃~70℃, the composite pressure at 3MPa~5MPa, and the linear speed of the substrate running at 50m / min~150m / min. After the thickness of the dry film is controlled at 10μm~30μm, the coated composite substrate is obtained. Step 504. The coated composite substrate prepared in step 503 is cooled to below 35°C by a cooling roller at a temperature of 20°C to 25°C. After being wound up under constant tension, the finished ethylene-vinyl acetate copolymer composite material for coating is obtained.

[0021] Compared with the prior art, this application has the following beneficial effects: This application provides an ethylene-vinyl acetate copolymer composite material for coating applications and its preparation method. The core film-forming material is a glycidyl methacrylate-polystyrene binary modified ethylene-vinyl acetate copolymer resin, combined with hydrogenated C5 petroleum resin, silane coupling agent KH-560, and functional additives. This application achieves uniform grafting of GMA onto the EVA molecular chain through a ternary composite control system and a four-stage gradient temperature-controlled high-pressure polymerization process. Then, a binary modified EVA molecular structure is constructed through a β-ray irradiation activation-styrene suspension grafting process, ultimately forming a stable coating system. After curing, it forms a protective coating on the substrate surface with strong adhesion, high hardness, heat resistance, aging resistance, and excellent temperature change resistance, significantly improving the long-term service stability of the ethylene-vinyl acetate copolymer coating material under complex and extreme working conditions. This application has the advantages of controllable process, good adaptability to coating application, and ease of promotion and implementation. Attached Figure Description Figure 1 These are comparative diagrams of the Vicat softening points of the film-forming substrates in Examples 1 to 3 and Comparative Examples 1 to 6 of this application.

[0023] Figure 2 These are comparative diagrams showing the adhesion properties of the coatings of the ethylene-vinyl acetate copolymer composite materials prepared in Examples 1 to 3 and Comparative Examples 1 to 6 of this application.

[0024] Figure 3 This is a comparison chart of the adhesion retention rate of the coating film of the ethylene-vinyl acetate copolymer composite material prepared in Examples 1 to 3 and Comparative Examples 1 to 6 of this application under extreme working conditions.

[0025] Figure 4 This is a comparison diagram of the adhesion of the coating film of the ethylene-vinyl acetate copolymer composite material prepared in Examples 1 to 3 and Comparative Examples 1 to 6 of this application before and after thermal cycling.

[0026] Figure 5 This is a comparison chart of the storage stability of the coating films of the ethylene-vinyl acetate copolymer composite materials prepared in Examples 1 to 3 and Comparative Examples 1 to 6 of this application. Detailed Implementation

[0027] Combination Figures 1 to 5 Examples 1 to 3 and Comparative Examples 1 to 6 further illustrate the technical solutions proposed in this application.

[0028] Example 1 (1) The preparation method of the modified ethylene-vinyl acetate copolymer resin substrate includes the following steps: Step 101. The granulated, dried and pulverized glycidyl methacrylate-grafted ethylene-vinyl acetate copolymer resin powder is transferred to an electron accelerator β-ray irradiation device for irradiation to obtain activated resin powder. The accelerating voltage of the electron accelerator beta-ray irradiation device is 1.5 MeV, the beam current is 15 mA, the transmission speed is 10 m / min, and the irradiation dose is 30 kGy. After irradiation, the device is sealed and protected from light and left to stand for 2 hours. Step 102. The activated resin powder, styrene monomer, calcium hydroxyphosphate dispersant, sodium dodecylbenzenesulfonate emulsifier, benzoyl peroxide initiator, and deionized water prepared in step 101 are added to a stirred tank in a mass ratio of 10:12:0.3:0.15:0.036:80. The mixture is reacted for 6 hours under a water bath temperature of 65℃, 100 rpm, nitrogen atmosphere, and reflux. After the reaction is completed, heating is stopped, and cooling water is introduced to quickly cool the mixture to room temperature. The reaction system is discharged and washed with deionized water. Water-soluble impurities are removed by vacuum filtration. The filter cake is placed in a vacuum drying oven and dried for 18 hours at 65℃ and -0.08 MPa to obtain the crude grafted product. Step 103. After pulverizing the crude grafted product prepared in step 102 to 40 mesh, put it into a continuous Soxhlet extraction device and extract it by reflux at 65℃~66℃ for 24h using tetrahydrofuran as solvent; place the extracted product in a dryer and dry it at 70℃ and -0.09MPa for 12h to obtain the purified grafted product. Step 104. The purified graft product prepared in step 103 is fed into a twin-screw extruder and melt-extruded at 140°C. After being successively subjected to underwater pelletizing, crushing, and 200-mesh vibrating sieve, the modified ethylene-vinyl acetate copolymer resin matrix is ​​obtained.

[0029] (2) The preparation method of the glycidyl methacrylate-grafted ethylene-vinyl acetate copolymer composite material includes the following steps: Step 201. Ethylene monomer and vinyl acetate monomer, which have been dehydrated to a moisture content of ≤8ppm by 3A molecular sieve, are added to a static mixer in a mass ratio of 100:23. After mixing for 40s under a pressure of 25.5MPa and a temperature of 80℃, the premixed monomer is obtained. Step 202. The ternary composite control system, initiator, and isododecane solvent are continuously added to a high-pressure tubular reactor at a mass ratio of 1.5:1.2:1.2. After reacting for 25 minutes under a nitrogen atmosphere, at 110°C and 250MPa, the reaction precursor is obtained. The ternary composite regulatory system is obtained by compounding propylene, propionaldehyde and glycidyl methacrylate in a mass ratio of 85:11:1.5. Step 203. The premixed monomer prepared in step 201 and the initiator system in step 202 are simultaneously and continuously fed into a high-pressure tubular reactor. After polymerization under nitrogen atmosphere, 170°C and 250MPa, the crude polymer melt is obtained. The polymerization process includes a first reaction section, a second reaction section, a third reaction section, and a fourth reaction section, which proceed in chronological order. The temperature of the first reaction section is controlled at 170℃ for 3 minutes; the temperature of the second reaction section is controlled at 230℃ for 12 minutes; the temperature of the third reaction section is controlled at 220℃ for 5 minutes; and the temperature of the fourth reaction section is controlled at 200℃ for 10 minutes.

[0030] Step 204. After cooling the crude polymer melt prepared in step 203 to 180°C, transfer it to a devolatilization reactor and devolatilize it at 175°C and -0.08 MPa for 16 min. After the devolatilization is completed, feed the devolatilized melt into a twin-screw extruder and melt-extrude it at 145°C. Then, pass it through underwater pelletizing and 200-mesh vibrating sieve to obtain the glycidyl methacrylate-grafted ethylene-vinyl acetate copolymer composite material.

[0031] (3) A method for preparing ethylene-vinyl acetate copolymer composite materials for coating applications, comprising the following steps: Step 301. According to the component table shown in Table 1, the granulated modified ethylene-vinyl acetate copolymer resin base material and hydrogenated C5 petroleum resin are sequentially fed into a high-speed pulverizer for pulverization. After pulverization, the material is sent to a 200-mesh vibrating screen to remove agglomerated materials. After sealing and storing to avoid moisture absorption, the pretreated powder raw material is obtained. Step 302. According to the component table shown in Table 1, D80 environmentally friendly solvent oil and 120# solvent oil are added to the reaction vessel in sequence. After dispersing for 15 minutes under nitrogen atmosphere, 75°C and 500 rpm, the pretreated powder raw material prepared in step 301 is divided into three batches and added to the reaction system in sequence. After each batch is added, it is dispersed for 10 minutes under nitrogen atmosphere, 800 rpm and 75°C to obtain the resin base material. Step 303. Cool the resin base material prepared in step 302 to 75°C. Under stirring at 500 rpm, add silane coupling agent KH-560, leveling agent, hydrogenated castor oil, antioxidant, and ultraviolet absorber UV-327 to the reaction system in sequence according to the preset ratio. After high-speed dispersion at 1000 rpm and 45°C in a nitrogen atmosphere for 25 minutes, a premix is ​​obtained. Then transfer the premix to a horizontal ball mill with zirconium bead media and circulate and grind it three times at 45°C. The fineness of the premix after grinding is 18 μm. Step 304. The premix prepared in step 303 is fed into a vacuum degassing machine and degassed for 10 minutes at -0.08 MPa and room temperature. Then it is filtered through a 200-mesh bag filter and sealed and filled under nitrogen protection by a filling equipment to obtain an ethylene-vinyl acetate copolymer composite material for coating applications.

[0032] Example 2 (1) The preparation method of the modified ethylene-vinyl acetate copolymer resin substrate includes the following steps: Step 101. The granulated, dried and pulverized glycidyl methacrylate-grafted ethylene-vinyl acetate copolymer resin powder is transferred to an electron accelerator β-ray irradiation device for irradiation to obtain activated resin powder. The accelerating voltage of the electron accelerator beta-ray irradiation device is 1.8 MeV, the beam current is 16 mA, the transmission speed is 13 m / min, and the irradiation dose is 35 kGy. After irradiation, the device is sealed and protected from light and left to stand for 2 hours. Step 102. The activated resin powder, styrene monomer, calcium hydroxyphosphate dispersant, sodium dodecylbenzenesulfonate emulsifier, benzoyl peroxide initiator, and deionized water prepared in step 101 are added to a stirred tank in a mass ratio of 10:15:0.4:0.2:0.05:120. The mixture is reacted for 7 hours under a water bath at 70°C, 200 rpm, nitrogen atmosphere, and reflux. After the reaction is completed, heating is stopped, and cooling water is introduced to quickly cool the mixture to room temperature. The reaction system is discharged and washed with deionized water. Water-soluble impurities are removed by vacuum filtration. The filter cake is placed in a vacuum drying oven and dried for 18 hours at 65°C and -0.08 MPa to obtain the crude grafted product. Step 103. After pulverizing the crude grafted product prepared in step 102 to 40 mesh, put it into a continuous Soxhlet extraction device and extract it by reflux at 65℃~66℃ for 24h using tetrahydrofuran as solvent; place the extracted product in a dryer and dry it at 70℃ and -0.09MPa for 12h to obtain the purified grafted product. Step 104. The purified graft product prepared in step 103 is fed into a twin-screw extruder and melt-extruded at 150°C. After being successively subjected to underwater pelletizing, crushing, and 200-mesh vibrating sieve, the modified ethylene-vinyl acetate copolymer resin matrix is ​​obtained.

[0033] (2) The preparation method of the glycidyl methacrylate-grafted ethylene-vinyl acetate copolymer composite material includes the following steps: Step 201. Ethylene monomer and vinyl acetate monomer, which have been dehydrated to a moisture content of ≤8ppm by 3A molecular sieve, are added to a static mixer in a mass ratio of 100:25. After mixing for 50s under a pressure of 25.8MPa and a temperature of 100℃, the premixed monomer is obtained. Step 202. The ternary composite control system, initiator, and isododecane solvent are continuously added to a high-pressure tubular reactor at a mass ratio of 2:1.5:2.2. After reacting for 35 minutes under a nitrogen atmosphere, 120°C, and 252 MPa, the reaction precursor is obtained. The ternary composite regulatory system is obtained by compounding propylene, propionaldehyde and glycidyl methacrylate in a mass ratio of 86:12:2. Step 203. The premixed monomer prepared in step 201 and the initiator system in step 202 are simultaneously and continuously fed into a high-pressure tubular reactor. After polymerization under nitrogen atmosphere, 210°C and 253MPa, the crude polymer melt is obtained. In step 203, the polymerization process includes a first reaction section, a second reaction section, a third reaction section, and a fourth reaction section carried out in chronological order; the temperature of the first reaction section is controlled at 175℃ and the reaction time is 5 min; the temperature of the second reaction section is controlled at 235℃ and the reaction time is 13 min; the temperature of the third reaction section is controlled at 230℃ and the reaction time is 7 min; and the temperature of the fourth reaction section is controlled at 205℃ and the reaction time is 12 min.

[0034] Step 204. Cool the crude polymer melt prepared in step 203 to 185°C and transfer it to a devolatilization reactor. Devolatilize at 180°C and -0.09 MPa for 18 min. After devolatilization, feed the devolatilized melt into a twin-screw extruder and melt-extrude at 155°C. Then, pass it through underwater pelletizing and 200-mesh vibrating sieve to obtain the glycidyl methacrylate-grafted ethylene-vinyl acetate copolymer composite material.

[0035] (3) A method for preparing ethylene-vinyl acetate copolymer composite materials for coating applications, comprising the following steps: Step 301. According to the component table shown in Table 1, the granulated modified ethylene-vinyl acetate copolymer resin base material and hydrogenated C5 petroleum resin are sequentially fed into a high-speed pulverizer for pulverization. After pulverization, the material is sent to a 200-mesh vibrating screen to remove agglomerated materials. After sealing and storing to avoid moisture absorption, the pretreated powder raw material is obtained. Step 302. According to the component table shown in Table 1, D80 environmentally friendly solvent oil and 120# solvent oil are added to the reaction vessel in sequence. After dispersing for 15 minutes under nitrogen atmosphere, 78°C and 550 rpm, the pretreated powder raw material prepared in step 301 is divided into three batches and added to the reaction system in sequence. After each batch is added, it is dispersed for 10 minutes under nitrogen atmosphere, 1000 rpm and 78°C to obtain the resin base material. Step 303. Cool the resin base material prepared in step 302 to 78°C. Under stirring conditions of 550 rpm, add silane coupling agent KH-560, leveling agent, hydrogenated castor oil, antioxidant, and ultraviolet absorber UV-327 to the reaction system in sequence according to the preset ratio. After high-speed dispersion for 28 min under nitrogen atmosphere, 1100 rpm, water bath at 48°C, the premix material is obtained. Transfer the premix material to a horizontal ball mill with zirconium bead media and circulate and grind it three times at 45°C. The fineness of the premix material after grinding is 18μm~20μm. Step 304. The premix prepared in step 303 is fed into a vacuum degassing machine and degassed for 12 minutes at -0.085 MPa and room temperature. Then it is filtered through a 200-mesh bag filter and sealed and filled under nitrogen protection by a filling equipment to obtain an ethylene-vinyl acetate copolymer composite material for coating applications.

[0036] Example 3 (1) The preparation method of the modified ethylene-vinyl acetate copolymer resin substrate includes the following steps: Step 101. The granulated, dried and pulverized glycidyl methacrylate-grafted ethylene-vinyl acetate copolymer resin powder is transferred to an electron accelerator β-ray irradiation device for irradiation to obtain activated resin powder. The accelerating voltage of the electron accelerator beta-ray irradiation device is 2.2 MeV, the beam current is 18 mA, the transmission speed is 15 m / min, and the irradiation dose is 40 kGy. After irradiation, the device is sealed and protected from light and left to stand for 2 hours. Step 102. The activated resin powder, styrene monomer, calcium hydroxyphosphate dispersant, sodium dodecylbenzenesulfonate emulsifier, benzoyl peroxide initiator, and deionized water prepared in step 101 are added to a stirred tank in a mass ratio of 10:18:0.5:0.25:0.09:160. The mixture is reacted for 8 hours under a water bath at 75°C, 300 rpm, nitrogen atmosphere, and reflux. After the reaction is completed, heating is stopped, and cooling water is introduced to quickly cool the mixture to room temperature. The reaction system is discharged and washed with deionized water. Water-soluble impurities are removed by vacuum filtration. The filter cake is placed in a vacuum drying oven and dried for 18 hours at 65°C and -0.08 MPa to obtain the crude grafted product. Step 103. After pulverizing the crude grafted product prepared in step 102 to 40 mesh, put it into a continuous Soxhlet extraction device and extract it by reflux at 65℃~66℃ for 24h using tetrahydrofuran as solvent; place the extracted product in a dryer and dry it at 70℃ and -0.09MPa for 12h to obtain the purified grafted product. Step 104. The purified graft product prepared in step 103 is fed into a twin-screw extruder and melt-extruded at 160°C. After being successively subjected to underwater pelletizing, crushing, and 200-mesh vibrating sieve, the modified ethylene-vinyl acetate copolymer resin matrix is ​​obtained.

[0037] (2) The preparation method of the glycidyl methacrylate-grafted ethylene-vinyl acetate copolymer composite material includes the following steps: Step 201. Ethylene monomer and vinyl acetate monomer, which have been dehydrated to a moisture content of ≤8ppm by 3A molecular sieve, are added to a static mixer in a mass ratio of 100:27. After mixing for 60s under a pressure of 26MPa and a temperature of 110℃, the premixed monomer is obtained. Step 202. The ternary composite control system, initiator, and isododecane solvent are continuously added to a high-pressure tubular reactor at a mass ratio of 3.2:1.8:2.5. After reacting for 45 minutes under a nitrogen atmosphere, at 130°C and 255MPa, the reaction precursor is obtained. The ternary composite regulatory system is obtained by compounding propylene, propionaldehyde and glycidyl methacrylate in a mass ratio of 87:13:2.5. Step 203. The premixed monomer prepared in step 201 and the initiator system in step 202 are simultaneously and continuously fed into a high-pressure tubular reactor. After polymerization under nitrogen atmosphere, 240°C and 255MPa, the crude polymer melt is obtained. In step 203, the polymerization process includes a first reaction section, a second reaction section, a third reaction section, and a fourth reaction section carried out in chronological order; the temperature of the first reaction section is controlled at 180℃ and the reaction time is 8 min; the temperature of the second reaction section is controlled at 240℃ and the reaction time is 14 min; the temperature of the third reaction section is controlled at 235℃ and the reaction time is 8 min; and the temperature of the fourth reaction section is controlled at 210℃ and the reaction time is 15 min.

[0038] Step 204. After cooling the crude polymer melt prepared in step 203 to 190°C, transfer it to a devolatilization reactor and devolatilize it at 185°C and -0.09MPa for 20 minutes. After the devolatilization is completed, feed the devolatilized melt into a twin-screw extruder and melt-extrude it at 165°C. Then, pass it through underwater pelletizing and 200-mesh vibrating sieve to obtain the glycidyl methacrylate-grafted ethylene-vinyl acetate copolymer composite material.

[0039] (3) A method for preparing ethylene-vinyl acetate copolymer composite materials for coating applications, comprising the following steps: Step 301. According to the component table shown in Table 1, the granulated modified ethylene-vinyl acetate copolymer resin base material and hydrogenated C5 petroleum resin are sequentially fed into a high-speed pulverizer for pulverization. After pulverization, the material is sent to a 200-mesh vibrating screen to remove agglomerated materials. After sealing and storing to avoid moisture absorption, the pretreated powder raw material is obtained. Step 302. According to the component table shown in Table 1, D80 environmentally friendly solvent oil and 120# solvent oil are added to the reaction vessel in sequence. After dispersing for 15 minutes under nitrogen atmosphere, 80℃ and 600rpm, the pretreated powder raw material prepared in step 301 is divided into three batches and added to the reaction system in sequence. After each batch is added, it is dispersed for 10 minutes under nitrogen atmosphere, 1200rpm and 80℃ to obtain the resin base material. Step 303. Cool the resin base material prepared in step 302 to 80℃. Under stirring conditions of 600 rpm, add silane coupling agent KH-560, leveling agent, hydrogenated castor oil, antioxidant, and ultraviolet absorber UV-327 to the reaction system in sequence according to the preset ratio. After high-speed dispersion for 30 min under nitrogen atmosphere, 1200 rpm, water bath at 50℃, the premixed material is obtained. Transfer the premixed material to a horizontal ball mill with zirconium bead media and circulate and grind it three times at 45℃. The fineness of the premixed material after grinding is 18μm~20μm. Step 304. The premix prepared in step 303 is fed into a vacuum degassing machine and degassed for 15 minutes at -0.09 MPa and room temperature. Then it is filtered through a 200-mesh bag filter and sealed and filled under nitrogen protection by a filling equipment to obtain an ethylene-vinyl acetate copolymer composite material for coating applications.

[0040] Comparative Example 1 The difference between Comparative Example 1 and Example 2 is that: the glycidyl methacrylate-polystyrene binary modified ethylene-vinyl acetate copolymer in Example 2 was completely replaced with unmodified commercially available EVA resin (Yangzi Petrochemical EVA20-20), while the other components and processes remained unchanged.

[0041] Comparative Example 2 The difference between Comparative Example 2 and Example 2 is that steps 101-104 are omitted, and glycidyl methacrylate-grafted ethylene-vinyl acetate copolymer is directly used to replace the glycidyl methacrylate-polystyrene binary modified ethylene-vinyl acetate copolymer in Example 2, while the remaining components and processes remain unchanged.

[0042] Comparative Example 3 The difference between Comparative Example 3 and Example 2 is that the amount of styrene added in step 101 is reduced, and the mass ratio of activated resin powder, styrene monomer, calcium hydroxyphosphate dispersant, sodium dodecylbenzenesulfonate emulsifier, benzoyl peroxide initiator and deionized water prepared in step 101 is adjusted to 10:10:0.4:0.2:0.05:120, while the other components and processes remain unchanged.

[0043] Comparative Example 4 The difference between Comparative Example 4 and Example 2 is that the amount of styrene added in step 101 is increased, and the mass ratio of activated resin powder, styrene monomer, calcium hydroxyphosphate dispersant, sodium dodecylbenzenesulfonate emulsifier, benzoyl peroxide initiator and deionized water prepared in step 101 is adjusted to 10:19:0.4:0.2:0.05:120, while the other components and processes remain unchanged.

[0044] Comparative Example 5 The difference between Comparative Example 5 and Example 2 is that the silane coupling agent KH-560 in the composite material was removed, while the other components and processes remained unchanged.

[0045] Comparative Example 6 The difference between Comparative Example 6 and Example 2 is that: ordinary commercially available coated LDPE resin (Yanshan Petrochemical LDPE 1I2A-1) completely replaced the glycidyl methacrylate-polystyrene binary modified ethylene-vinyl acetate copolymer in Example 2, while the other components and processes remained unchanged.

[0046] Table 1. Composition of Ethylene-Vinyl Acetate Copolymer Composite Material

[0047] Continued from Table 1

[0048] The ethylene-vinyl acetate copolymer composite materials for coating applications prepared in Examples 1-3 and Comparative Examples 1-6 were then prepared into corresponding test specimens according to actual testing requirements (specifically, dilution, curing, and other operations were performed according to actual testing needs), and the following tests were conducted: Test 1: The Vicat softening point of the film-forming substrates in Examples 1-3 and Comparative Examples 1-6 was measured according to GB / T 1633-2000 "Determination of Vicat Softening Temperature (VST) of Plastics"; the melt flow rate (190℃ / 2.16kg, unit: g / 10min) of the test pieces made from the above film substrates was measured according to GB / T 3682.1-2018 "Determination of Melt Mass Flow Rate (MFR) and Melt Volume Flow Rate (MVR) of Thermoplastic Plastics - Part 1: Standard Methods"; the epoxy value was determined by hydrochloric acid-acetone titration, and the GMA grafting rate was calculated; the polystyrene grafting rate was determined by Soxhlet extraction-weight gain method to evaluate the influence of different modification methods on the core parameters of the substrate.

[0049] Test 2: The cross-cut adhesion of the ethylene-vinyl acetate copolymer composite materials prepared in Examples 1 to 3 and Comparative Examples 1 to 6 on tinplate metal substrates was measured according to GB / T 9286-1998 "Paints and Varnishes Cross-cut Adhesion Test". The pencil hardness of the paint film of each group of test pieces was measured according to GB / T 6739-2006 "Determination of Hardness of Paint Film by Pencil Method". The 180° peel strength (N / 15mm) of each group of test specimens was measured according to GB / T 2790-1995 "Test Method for 180° Peel Strength of Adhesives". According to GB / T 13452.2-2008 "Determination of film thickness of paints and varnishes - Part 2: Evaluation of the number of coating layers by measuring dry film thickness", the coating thickness uniformity error of the above test pieces was measured to comprehensively evaluate the influence of different formulations and modified substrates on the basic mechanical properties of the paint film and coating compatibility.

[0050] Test 3: Extreme Condition Simulation Experiment A: Test pieces (tinplate material) of the same size (30cm×30cm×2cm, dry film thickness 30±2μm) coated with ethylene-vinyl acetate copolymer composite materials of Examples 1 to 3 and Comparative Examples 1 to 6 were simultaneously placed in a 100℃ hot air circulating aging test chamber for 168h to simulate the thermal aging performance of the paint film under extreme high temperature use scenarios. After aging, the paint film adhesion of each group of test pieces was measured according to GB / T 9286-1998 "Cross-cut test of paints and varnishes" standard, and the adhesion retention rate after 168h of 100℃ heat aging was calculated to evaluate its heat aging resistance performance.

[0051] Test 4: Extreme Condition Simulation Experiment B. Test pieces (tinplate material) of the same size (30cm×30cm×2cm, dry film thickness 30±2μm) coated with ethylene-vinyl acetate copolymer composite materials of Examples 1 to 3 and Comparative Examples 1 to 6 were simultaneously immersed in an 80℃ constant temperature water bath for 168h to simulate the hot water resistance of the paint film under extreme humid conditions. After rinsing and drying, the paint film adhesion of each group of test pieces was measured according to GB / T 9286-1998 "Cross-cut Tests for Paints and Varnishes". The adhesion retention rate after 168h of hot water resistance at 80℃ was calculated to evaluate its water and heat resistance performance.

[0052] Test 5: The ethylene-vinyl acetate copolymer composite materials of Examples 1 to 3 and Comparative Examples 1 to 6 were sealed and stored at room temperature (23℃±2℃, protected from light) for 6 months in accordance with GB / T 6753.3-1986 "Test Method for Storage Stability of Coatings". The viscosity change was measured periodically using a Ford cup viscometer and the viscosity change rate was calculated to evaluate the influence of different formulations and substrates on the storage stability of the coatings.

[0053] Test 6: Extreme Condition Simulation Experiment C: Test specimens (wood substrates) of the same size (30cm×30cm×2cm, dry film thickness 30±2μm) coated with ethylene-vinyl acetate copolymer composite materials of Examples 1 to 3 and Comparative Examples 1 to 6 were simultaneously placed in a -20℃ to 80℃ thermal cycling test chamber for 20 cycles (each cycle included -20℃ for 1 hour, heating to room temperature at a rate of 5℃ / min for 10 minutes, heating to 80℃ at a rate of 5℃ / min for 1 hour, and cooling to room temperature at a rate of 5℃ / min to complete one cycle). This simulated the paint film adhesion of birch substrates under extreme temperature change usage scenarios. The initial and post-cycle paint film cross-cut adhesion was measured according to GB / T 9286-1998 "Paints and Varnishes Cross-cut Adhesion Test" standard to evaluate its temperature change adhesion performance. The test results are shown in Table 2 below.

[0054] Table 2 Test Results

[0055] Continued from Table 2

[0056] As shown in Table 2, in Examples 1-3, glycidyl methacrylate-grafted ethylene-vinyl acetate copolymer was first prepared, followed by activation by electron accelerator β-ray irradiation and styrene suspension grafting modification to obtain glycidyl methacrylate (GMA)-polystyrene binary modified ethylene-vinyl acetate copolymer resin substrate. This substrate was then used as the core film-forming material to prepare EVA composite materials for coating applications. Specifically, the GMA monomer contains both polymerizable carbon-carbon double bonds and highly reactive epoxy groups. Through the regulation of a propylene-propionaldehyde-GMA ternary complex chain transfer agent, during the four-stage gradient polymerization process in a high-pressure tubular reactor, the double bonds of GMA graft copolymerize with the EVA molecular chains, and the epoxy groups are completely preserved and uniformly distributed on the EVA backbone. Furthermore, the grafted epoxy groups are strongly polar functional groups. On the one hand, they can form hydrogen bonds with the hydroxyl and carboxyl groups on the substrate surface, and even undergo ring-opening chemical reactions to form chemical bonds, thereby improving the interfacial bonding between the resin and the substrate at the molecular level. On the other hand, they can significantly improve the compatibility of EVA with polar additives and solvents in the coating system, avoiding phase separation during film formation. The strong electron-withdrawing inductive effect of the GMA epoxy groups will significantly reduce the electron cloud density of α-H on the adjacent EVA main chain, making the CH bonds more prone to homolytic cleavage. This provides a structural basis for the efficient and controllable generation of macromolecular free radicals by subsequent electron beta-ray irradiation, while suppressing the degradation side reaction of C / C bond breakage in the EVA main chain during irradiation. In Examples 1-3, high-energy β-rays caused inelastic collisions with the molecular chains of 120-mesh GMA-grafted EVA powder, transferring electron kinetic energy to the atoms and chemical bonds of the polymer molecules. When the transferred energy exceeded the bond energy, homolytic cleavage of the bonds was initiated. Stable macromolecular free radicals were generated through two pathways: Primary Pathway: GMA-enhanced homolytic cleavage of CH bonds: The energy of β-rays preferentially acts on the adjacent low-bond-energy α-CH bonds of GMA, causing homolytic cleavage and generating large carbon free radicals in the EVA backbone. This pathway is the dominant free radical generation pathway. Thanks to the electron-withdrawing synergistic effect of GMA, the free radical yield is increased by more than 40% compared to native EVA under the same irradiation dose, and the free radical sites are evenly distributed on the EVA backbone without local concentration issues. Secondary Pathway: Activation of unsaturated double bonds: β-ray irradiation causes a small number of CH bonds on the EVA backbone to undergo dehydrogenation, generating carbon-carbon unsaturated double bonds. After being excited by high-energy electrons, these double bonds also form active free radical sites, serving as supplementary sites for subsequent styrene grafting.More specifically, in the preparation of glycidyl methacrylate-grafted ethylene-vinyl acetate copolymer, a propylene-propionaldehyde-GMA ternary composite control system, combined with a four-stage gradient temperature-controlled polymerization process in a high-pressure tubular reactor, can effectively control the grafting rate and distribution uniformity of GMA on the EVA molecular chain. This ensures that the epoxy groups of GMA are uniformly grafted onto the EVA molecular chain, providing stable active sites for subsequent styrene grafting and imparting strong polarity to the resin, effectively improving the interfacial bonding force between the resin and the substrate, as well as its compatibility with coating additives. Simultaneously, the high-pressure polymerization and gradient temperature control process can precisely control the molecular weight and molecular weight distribution of EVA, giving the resin excellent film-forming processing performance. The melt flow rate in Examples 1-3 of the test data is consistently between 18.8 g / 10 min and 19.5 g / 10 min, and decreases reasonably with increasing GMA and polystyrene grafting rates, conforming to the basic laws of polymer rheology and effectively adapting to various coating material systems.

[0057] More specifically, in the preparation process of binary modified EVA substrate, GMA-grafted EVA powder is activated by beta-ray irradiation using an electron accelerator. This allows for the formation of uniform free radical active sites on the EVA molecular chain without introducing residual chemical initiators, achieving stable grafting of styrene monomers onto the EVA molecular chain. This avoids the defects of uneven grafting rate and excessive homopolymer residue associated with traditional chemical grafting. By precisely controlling the feed ratio of styrene monomers and the irradiation and grafting process parameters, the polystyrene grafting rate is stably controlled at 34.9%~ Within the optimal range of 36.5%, sufficient and uniformly distributed rigid polystyrene segments were introduced into the flexible EVA matrix, constructing a molecular chain structure with synergistic rigidity and flexibility. On the one hand, this significantly improved the heat resistance of the resin matrix, stabilizing the Vicat softening point of Examples 1-3 at 101℃-103℃, far exceeding that of unmodified / single-grafted resins. On the other hand, it simultaneously achieved a synergistic improvement in film hardness and flexibility, with pencil hardness reaching H-2H and 180° peel strength reaching 4.2N / 15mm-4.8N / 15mm for Examples 1-3. Subsequent Soxhlet extraction purification and twin-screw extrusion granulation processes further removed homopolymer impurities, ensuring batch stability and film uniformity of the resin. The coating thickness uniformity error for Examples 1-3 was only ±2.1%-±2.8%, far superior to all comparative examples.

[0058] Meanwhile, in the preparation of the coated composite material, a stable coating system was constructed by using binary modified EVA as the core film-forming material, combined with hydrogenated C5 petroleum resin for thickening, KH-560 silane coupling agent for interface bridging, and functional additives for synergistic regulation. Specifically, the GMA epoxy groups in the binary modified EVA can synergistically interact with the epoxy groups in KH-560, forming stable chemical bonds and multi-hydrogen bond anchoring with the hydroxyl groups on the surfaces of metal and wood substrates, significantly improving the interfacial adhesion between the coating and the substrate. The initial cross-cut adhesion of the coating film in Examples 1-3 all reached level 0 (the optimal level). Simultaneously, the rigid-flexible resin matrix effectively mitigates interfacial stress caused by thermal expansion and contraction, maintaining excellent adhesion stability under extreme conditions. Example 2 showed a 94% adhesion retention rate after 168 hours of heat aging at 100℃, a 97% adhesion retention rate after 168 hours of hot water resistance at 80℃, and maintained level 0 adhesion after 20 cycles of thermal cycling from -20℃ to 80℃, far superior to all comparative groups. Furthermore, by precisely controlling the resin grafting structure and coating formulation, the viscosity change rate of Examples 1-3 after 6 months of sealing at room temperature is only 4.2%-5.7%, demonstrating both excellent coating application compatibility and long-term storage stability.

[0059] In Comparative Example 1, unmodified commercially available EVA resin completely replaced the glycidyl methacrylate-polystyrene binary modified ethylene-vinyl acetate copolymer of this patent, without any grafting modification of the EVA matrix. Firstly, the lack of rigid polystyrene segments in the resin system resulted in significantly insufficient heat resistance and structural rigidity of the resin matrix. Correspondingly, the Vicat softening point was only 73°C, far lower than the 101°C–103°C of the example, and the pencil hardness was only HB. This failed to provide stable mechanical support for the paint film, and the molecular chains were prone to thermal degradation and segment relaxation after 100°C heat aging, resulting in an adhesion retention rate of only 45%. Secondly, the absence of polar epoxy groups from glycidyl methacrylate (GMA) prevented the resin from forming strong chemical bonds and hydrogen bond anchoring with the surfaces of metal and wood substrates, relying only on weak van der Waals forces, leading to weak interfacial adhesion. The initial cross-cut adhesion of the coating film was only level 2, and the 180° peel strength was only 2.1 N / 15 mm, far lower than the 4.8 N / 15 mm of Example 2. At the same time, the unmodified EVA had poor compatibility with the solvents and additives in the coating system, resulting in poor coating film uniformity, with a thickness uniformity error of ±5.8%. The viscosity change rate after 6 months of storage at room temperature reached 12.6%, indicating poor storage stability. Under extreme thermal cycling conditions, the difference in thermal expansion coefficients between the resin and the substrate was large, and the interfacial stress could not be released through polar bonding, eventually leading to interfacial delamination. After thermal cycling, the adhesion dropped to level 4, which could not meet the coating requirements of complex working conditions.

[0060] In Comparative Example 2, the complete process of β-ray irradiation activation-styrene grafting modification (steps 101-104) was eliminated. Glycidyl methacrylate single-grafted ethylene-vinyl acetate copolymer was directly used to replace the binary modified EVA resin of this patent, and no rigid polystyrene grafted segments were introduced into the resin matrix. On the one hand, the lack of rigid polystyrene segments results in significantly insufficient heat resistance and structural rigidity of the resin matrix. With a Vicat softening point of only 75°C, the resin segments are prone to thermal creep and decreased intermolecular forces under high-temperature aging conditions. After 168 hours of heat aging at 100°C, the adhesion retention rate is only 72%, far lower than the 94% in Example 2. Furthermore, the compatibility between the single-grafted GMA EVA resin and the hydrogenated C5 petroleum resin and solvent system in the coating system is insufficient. Uneven resin segment arrangement occurs during film formation, resulting in a coating thickness uniformity error of ±4.2%. The paint film has a pencil hardness of only H and a 180° peel strength of only 3.2 N / 15 mm, significantly reducing mechanical properties and coating compatibility. Simultaneously, the lack of polystyrene segments to stabilize the resin molecular chains leads to hydrolysis and fatigue fracture of the molecular chains under hot water immersion and thermal cycling conditions. After 168 hours of hot water immersion at 80°C, the adhesion retention rate is only 75%, and after thermal cycling from -20°C to 80°C, the adhesion drops to level 3, indicating insufficient long-term service stability.

[0061] In Comparative Example 3, the amount of styrene monomer input was significantly reduced, and the final polystyrene grafting rate was only 11.8%, far lower than the 35.8% in Example 2, which failed to form a sufficient amount of rigid polystyrene grafted segments. On the one hand, the insufficient content of rigid grafted segments fails to effectively improve the heat resistance and structural rigidity of the resin matrix. The Vicat softening point is only 82℃, and the resin segments are prone to thermal deformation under high temperature conditions. The adhesion retention rate after 168 hours of heat aging at 100℃ is only 81%. On the other hand, the insufficient grafting rate of polystyrene limits the improvement of compatibility between the resin and petroleum resin and additives in the coating system. The film uniformity is poor, with a coating thickness uniformity error of ±4.5%. The pencil hardness is only HB, and the 180° peel strength is only 3N / 15mm, resulting in insufficient mechanical properties of the paint film. At the same time, the insufficient rigid segments lead to a decrease in the creep resistance and fatigue resistance of the resin molecular chains. Under the conditions of immersion in 80℃ hot water and thermal cycling, the molecular chains are prone to relaxation and the interfacial bonding force decreases. The adhesion retention rate after 168 hours of hot water resistance at 80℃ is only 83%, and the adhesion drops to level 3 after thermal cycling, which cannot meet the requirements of extreme working conditions.

[0062] In Comparative Example 4, the amount of styrene monomer added was significantly increased, and the final polystyrene grafting rate reached 42.3%, which was higher than 35.8% in Example 2. The excessive amount of rigid polystyrene segments led to an imbalance in the properties of the resin matrix. On the one hand, excessive rigid styrene segments significantly increase the brittleness of the resin matrix and reduce the flexibility of the molecular chains. Under stress, the segments cannot extend to relieve stress, resulting in a peel strength of only 2.2 N / 15 mm at 180°, far lower than the 4.8 N / 15 mm in Example 2, and a cross-cut adhesion rating of only 2. On the other hand, excessive polystyrene segments significantly reduce the compatibility with the EVA matrix and the coating solvent system, making phase separation easy to occur during film formation. The coating thickness uniformity error reaches ±5.2%, and the viscosity change rate is as high as 18.3% after 6 months of sealing at room temperature, indicating extremely poor storage stability. At the same time, excessive rigid segments lead to a decrease in the wettability of the resin and the substrate, resulting in insufficient interfacial bonding. Under hot water immersion and thermal cycling conditions, the interfacial stress cannot be effectively relieved. The adhesion retention rate after 168 hours of hot water resistance at 80°C is only 78%, and the adhesion drops to 4 after thermal cycling, significantly reducing the coating's service performance.

[0063] In Comparative Example 5, the silane coupling agent KH-560 in the coating system was removed, making it impossible to build a chemical bond bridge between the resin matrix and the substrate. On the one hand, the epoxy groups of KH-560 can form chemical bonds with the GMA epoxy groups in the binary modified EVA of this patent and the hydroxyl groups on the substrate surface. After removal, the resin and metal and wood substrates are only bonded by weak van der Waals forces, and the interfacial bonding force drops sharply. The initial cross-cut adhesion of the paint film is only grade 3, and the 180° peel strength is only 1.8N / 15mm. On the other hand, the lack of silane coupling agent to regulate the compatibility of inorganic-organic interface reduces the compatibility between powder fillers and resin matrix in the coating system, making agglomeration easy. The coating thickness uniformity error reaches ±3.8%. At the same time, there is no stable chemical bond at the interface. Under extreme conditions of thermal aging, hot water immersion, and thermal cycling, the interface is very prone to peeling failure. The adhesion retention rate after 168 hours of thermal aging at 100℃ is only 70%, and the adhesion retention rate after 168 hours of hot water resistance at 80℃ is only 65%. After thermal cycling, the adhesion drops to grade 5, which is completely unable to meet the long-term service requirements of complex working conditions.

[0064] In Comparative Example 6, the binary modified EVA resin of this patent was completely replaced by commercially available LDPE resin. LDPE is a non-polar polyolefin resin with no polar functional groups or rigid grafted segments in its molecular chain. On the one hand, non-polar LDPE has extremely poor compatibility with polar substrates and polar additives in coating systems, making it unable to form effective anchoring with the substrate surface. The initial cross-cut adhesion of the paint film is only level 4, and the 180° peel strength is only 1.5N / 15mm, the lowest among all groups. On the other hand, LDPE molecular chains lack rigid structural support and have poor heat resistance. Under high-temperature aging conditions, the molecular chains are prone to oxidative degradation and chain segment melting relaxation. The adhesion retention rate after 168 hours of heat aging at 100℃ is only 38%, and the adhesion retention rate after 168 hours of hot water aging at 80℃ is only 42%, both the worst among all groups. At the same time, LDPE has poor compatibility with solvent systems, and coatings are prone to stratification and sedimentation during storage. The viscosity change rate after 6 months of sealed storage at room temperature reaches 15.7%, and the coating thickness uniformity error reaches ±6.5%, indicating extremely poor coating compatibility. Under extreme thermal cycling conditions, the difference in thermal expansion coefficients between the resin and the substrate is extremely large, resulting in complete interface delamination. After thermal cycling, the adhesion drops to level 5, which cannot meet the basic usage requirements in the coating field.

[0065] In summary, this application provides an ethylene-vinyl acetate copolymer composite material for coating applications and its preparation method. It uses glycidyl methacrylate-polystyrene binary modified ethylene-vinyl acetate copolymer resin as the core film-forming material, combined with hydrogenated C5 petroleum resin, silane coupling agent KH-560, and functional additives. This application achieves uniform grafting of GMA onto the EVA molecular chain through a propylene-propionaldehyde-GMA ternary composite control system and a four-stage gradient temperature-controlled high-pressure polymerization process. Then, a binary modified EVA molecular structure is constructed through β-ray irradiation activation and styrene suspension grafting process, ultimately forming a stable coating system. After curing, it forms a protective coating with strong adhesion, high hardness, heat resistance, aging resistance, and excellent temperature change resistance on the substrate surface, significantly improving the long-term service stability of the ethylene-vinyl acetate copolymer coating material under complex and extreme working conditions. This application has the advantages of controllable process, good adaptability to coating application, and ease of promotion and implementation.

[0066] The embodiments provided by the present invention have been described in detail above. Specific examples have been used to illustrate the principles and implementation methods of the present invention. The descriptions of the embodiments above are merely for the purpose of helping to understand the method and core ideas of the present invention. It should be noted that those skilled in the art can make various improvements and modifications to the present invention without departing from its principles, and these improvements and modifications also fall within the protection scope of the claims of the present invention.

Claims

1. An ethylene-vinyl acetate copolymer composite material for use in the coating field, characterized in that, By weight, it consists of the following components: 55-65 parts modified ethylene-vinyl acetate copolymer resin base material, 5-8 parts hydrogenated C5 petroleum resin, 1-3 parts silane coupling agent KH-560, 0.5-1 part leveling agent, 0.2-0.5 parts hydrogenated castor oil, 0.2-0.5 parts antioxidant, 0.2-0.5 parts ultraviolet absorber UV-327, 30-40 parts D80 environmentally friendly solvent oil, and 2-4 parts 120# solvent oil; The modified ethylene-vinyl acetate copolymer resin substrate is a glycidyl methacrylate-polystyrene binary modified ethylene-vinyl acetate copolymer resin.

2. The ethylene-vinyl acetate copolymer composite material for coating applications according to claim 1, characterized in that, The preparation method of the modified ethylene-vinyl acetate copolymer resin substrate includes the following steps: Step 101. The granulated, dried and pulverized glycidyl methacrylate-grafted ethylene-vinyl acetate copolymer resin powder is transferred to an electron accelerator β-ray irradiation device for irradiation to obtain activated resin powder. Step 102. The activated resin powder, styrene monomer, calcium hydroxyphosphate dispersant, sodium dodecylbenzenesulfonate emulsifier, benzoyl peroxide initiator, and deionized water prepared in step 101 are sequentially added to a stirred tank. The mixture is reacted for 6 to 8 hours under the conditions of water bath temperature of 65℃~75℃, 100rpm~300rpm, nitrogen atmosphere, and reflux. After the reaction is completed, heating is stopped, cooling water is introduced to quickly cool down to room temperature, the reaction system is discharged and washed with deionized water, and water-soluble impurities are removed by vacuum filtration. The filter cake is placed in a vacuum drying oven and dried for 18 hours at 65℃ and -0.08MPa to obtain the crude grafted product. Step 103. After pulverizing the crude grafted product prepared in step 102 to 40 mesh, put it into a continuous Soxhlet extraction device and extract it by reflux at 65℃~66℃ for 24h using tetrahydrofuran as solvent; place the extracted product in a dryer and dry it at 70℃ and -0.09MPa for 12h to obtain the purified grafted product. Step 104. The purified graft product prepared in step 103 is fed into a twin-screw extruder and melt-extruded at 140℃~160℃. After being successively subjected to underwater pelletizing, crushing, and 200-mesh vibrating sieve, the modified ethylene-vinyl acetate copolymer resin matrix is ​​obtained.

3. The ethylene-vinyl acetate copolymer composite material for coating applications according to claim 2, characterized in that, In step 101, the accelerating voltage of the electron accelerator β-ray irradiation device is 1.5MeV to 2.2MeV, the beam current is 15mA to 18mA, the transmission speed is 10m / min to 15m / min, and the irradiation dose is 30kGy to 40kGy. After irradiation, the device is sealed and protected from light and left to stand for 2 hours.

4. The ethylene-vinyl acetate copolymer composite material for coating applications according to claim 2, characterized in that, In step 101, the preparation method of the glycidyl methacrylate-grafted ethylene-vinyl acetate copolymer composite material includes the following steps: Step 201. Ethylene monomer and vinyl acetate monomer, which have been dehydrated to a moisture content of ≤8ppm by 3A molecular sieve, are added to a static mixer in a mass ratio of 100:(23-27). The mixture is mixed for 40s-60s under a pressure of 25.5MPa-26MPa and a temperature of 80℃-110℃ to obtain the premixed monomer. Step 202. The ternary composite control system, initiator, and isododecane solvent are continuously added to a high-pressure tubular reactor at a mass ratio of (1.5-3.2):(1.2-1.8):(1.2-2.5). The reaction is carried out under nitrogen atmosphere, water bath at 110℃-130℃, and 250MPa-255MPa for 25 min-45 min to obtain the reaction precursor. Step 203. The premixed monomer prepared in step 201 and the initiator system in step 202 are simultaneously and continuously fed into a high-pressure tubular reactor. After polymerization for 30 min to 45 min under nitrogen atmosphere, 170℃~240℃, and 250MPa~255MPa, the crude polymer melt is obtained. Step 204. After cooling the crude polymer melt prepared in step 203 to 180℃~190℃, transfer it to a devolatilization reactor and devolatilize it for 16min~20min at 175℃~185℃ and -0.08MPa~-0.09MPa. After devolatilization, feed the devolatilized melt into a twin-screw extruder and melt-extrude it at 145℃~165℃. Then, pass it through underwater pelletizing and 200-mesh vibrating sieve to obtain the glycidyl methacrylate grafted ethylene-vinyl acetate copolymer composite material.

5. The ethylene-vinyl acetate copolymer composite material for coating applications according to claim 4, characterized in that, In step 202, the ternary composite control system is obtained by compounding propylene, propionaldehyde and glycidyl methacrylate in a mass ratio of (85-87):(11-13):(1.5-2.5).

6. The ethylene-vinyl acetate copolymer composite material for coating applications according to claim 4, characterized in that, In step 203, the polymerization process includes a first reaction section, a second reaction section, a third reaction section, and a fourth reaction section carried out sequentially in time. The temperature of the first reaction section is controlled at 170℃~180℃, and the reaction time is 3min~8min. The temperature of the second reaction section is controlled at 230℃~240℃, and the reaction time is 12min~14min. The temperature of the third reaction section is controlled at 220℃~235℃, and the reaction time is 5min~8min. The temperature of the fourth reaction section is controlled at 200℃~210℃, and the reaction time is 10min~15min.

7. The ethylene-vinyl acetate copolymer composite material for coating applications according to claim 2, characterized in that, In step 102, the mass ratio of activated resin powder, styrene monomer, calcium hydroxyphosphate dispersant, sodium dodecylbenzenesulfonate emulsifier, benzoyl peroxide initiator, and deionized water is 10: (12-18): (0.3-0.5): (0.15-0.25): (0.036-0.09): (80-160).

8. A method for preparing an ethylene-vinyl acetate copolymer composite material for coating applications according to any one of claims 1 to 7, characterized in that, Includes the following steps: Step 301. The granulated modified ethylene-vinyl acetate copolymer resin base material and hydrogenated C5 petroleum resin are put into a high-speed pulverizer in a preset ratio and pulverized. After pulverization, the powder is sent to a 200-mesh vibrating screen to remove agglomerated materials. After sealing and storing to avoid moisture absorption, the pretreated powder raw material is obtained. Step 302. Add D80 environmentally friendly solvent oil and 120# solvent oil into the reaction vessel according to the preset ratio. After dispersing for 15 minutes under nitrogen atmosphere, 75℃~80℃, and 500rpm~600rpm, add the pretreated powder raw material prepared in step 301 into the reaction system. After dispersing for 30 minutes under nitrogen atmosphere, 800rpm~1200rpm, and 75℃~80℃, the resin base material is obtained. Step 303. Cool the resin base material prepared in step 302 to 75℃~80℃. Under stirring conditions of 500rpm~600rpm, add silane coupling agent KH-560, leveling agent, hydrogenated castor oil, antioxidant, and ultraviolet absorber UV-327 to the reaction system in sequence according to the preset ratio. After high-speed dispersion for 25min~30min under nitrogen atmosphere, 1000rpm~1200rpm, water bath 45℃~50℃, the premixed material is obtained. Step 304. The premix prepared in step 303 is fed into a vacuum degassing machine and degassed for 10 to 15 minutes at -0.08 MPa to -0.09 MPa and room temperature. Then it is filtered through a 200-mesh bag filter and sealed and filled under nitrogen protection by a filling equipment to obtain an ethylene-vinyl acetate copolymer composite material for coating applications.

9. A method for preparing an ethylene-vinyl acetate copolymer composite material for coating applications according to claim 8, characterized in that, In step 302, the pretreated powder raw materials prepared in step 301 are divided into three batches and sequentially added to the reactor. After each batch is added, it is dispersed for 10 minutes under nitrogen atmosphere, 800 rpm to 1200 rpm, and 75℃ to 80℃.

10. A method for preparing an ethylene-vinyl acetate copolymer composite material for coating applications according to claim 8, characterized in that, In step 303, the premixed material is further subjected to grinding treatment. The grinding of the premixed material includes the following steps: transferring the premixed material to a horizontal ball mill with zirconium bead media, and grinding it three times in a cycle at 45°C. The fineness of the premixed material after grinding is 18μm~20μm.

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