Preparation method and device of EVA hot melt adhesive for packaging

Abstract

The invention discloses a preparation method and device of an EVA hot melt adhesive for packaging, the device comprises a pretreatment drying unit, a precision metering and feeding unit and a multi-stage reactive extrusion unit, the pretreatment drying unit comprises a high-speed mixer, and an inner cavity of the high-speed mixer is provided with a heating module and a vacuum drying module; the precise metering and feeding unit comprises at least three bins arranged on one side of the high-speed mixer in an array mode, precise metering scales are arranged at the bottoms of the bins, and feeders are arranged on one sides of the precise metering scales; the multi-stage reaction extrusion unit comprises a double-screw extruder, and the double-screw extruder is sequentially divided into a melt blending section, a first lateral feeding section, a reaction crosslinking section and a second lateral feeding section in the material conveying direction. The efficient and stable preparation of the high-performance EVA hot melt adhesive is realized, and the bonding strength, heat resistance and comprehensive performance of the product are improved.

Description

Technical Field

[0001] This invention relates to the field of polymer material processing technology, specifically to a method and apparatus for preparing EVA hot melt adhesive for packaging. Background Technology

[0002] Hot melt adhesive is a thermoplastic adhesive that is solid at room temperature and melts into a liquid state when heated. Its core characteristic is that it is applied by heating and cured by cooling: when used, it is heated and melted by a special glue gun, applied to the bonding surface, and then quickly solidified within a few seconds to tens of seconds when cooled to room temperature, forming a tough solid adhesive layer, thus generating strong adhesion. Because it is solvent-free, has a fast curing speed, is applicable to a wide range of substrates (such as wood, plastic, and fabric), and is easy to store, it is widely used in many fields such as handicrafts, product packaging, woodworking, and home repair.

[0003] In the packaging industry, EVA hot melt adhesive is widely used due to its good bonding performance and processing adaptability, but there are still many technical pain points in its preparation process that need to be solved. Currently, traditional EVA hot melt adhesive preparation equipment often uses single mixing and drying devices, which makes it difficult to simultaneously achieve efficient mixing and deep drying of raw materials. This can easily lead to problems such as bubbles and reduced adhesive strength in the final product due to excessive moisture content in the raw materials. In the feeding stage, most devices use a single hopper or simple metering method, which cannot achieve precise staged feeding based on the characteristics of different additives (such as graft compatibilizers, nano-reinforcing fillers, and reactive heat-resistant additives). This can easily cause deviations in the additive addition ratio, affecting the stability of product performance. In the reactive extrusion process, traditional twin-screw extruders are mostly single-temperature control sections, which cannot meet the differentiated temperature requirements of different process stages such as melt blending and reactive crosslinking. Moreover, some heat-sensitive additives are prone to degradation at high temperatures, reducing the heat resistance and service life of the product. In addition, in existing preparation methods, the raw material ratio control precision is insufficient, and there is a lack of synergistic control mechanisms between various process parameters. As a result, the produced EVA hot melt adhesives cannot simultaneously achieve good performance in terms of adhesive strength, temperature resistance, and storage stability, and cannot fully meet the stringent requirements of the high-end packaging industry for hot melt adhesive performance.

[0004] Therefore, a method and apparatus for preparing EVA hot melt adhesive for packaging are proposed to solve the problems mentioned above. Summary of the Invention

[0005] The purpose of this invention is to provide a method and apparatus for preparing EVA hot melt adhesive for packaging, in order to solve the problems mentioned in the background art, such as insufficient mixing and drying, low accuracy of additive feeding, poor temperature control adaptability and insufficient process coordination, which lead to products with bubbles, unstable performance and reduced heat resistance, making it difficult to meet the requirements of high-end packaging.

[0006] To achieve the above objectives, the present invention provides the following technical solution: a method and apparatus for preparing EVA hot melt adhesive for packaging, comprising a pretreatment drying unit, a precision metering and feeding unit, and a multi-stage reactive extrusion unit. The pretreatment drying unit includes a high-speed mixer, and the inner cavity of the high-speed mixer is equipped with a heating module and a vacuum drying module; The precision metering and feeding unit includes at least three hoppers arranged in an array on one side of the high-speed mixer. Each hopper is equipped with a precision metering scale at its bottom and a feeder is provided on one side of the precision metering scale. The multi-stage reactive extrusion unit includes a twin-screw extruder, which is divided into a melt blending section, a first side feeding section, a reactive cross-linking section, and a second side feeding section along the material conveying direction. The inlet of the melt blending section is connected to the outlet of the high-speed mixer. The first side feeding section, the reactive cross-linking section, and the second side feeding section are respectively connected to different feeders through pipelines. The melt blending section and the reaction crosslinking section are each equipped with an independent temperature control module; the first lateral feeding section and the second lateral feeding section are equipped with cooling jackets; The device also includes a central control system, which is electrically connected to the heating module, vacuum drying module, precision weighing scale, feeder, twin-screw extruder and its temperature control module and cooling jacket.

[0007] Preferably, the silo includes at least a first silo for holding the grafted compatibilizer, a second silo for holding the nano-reinforced filler, and a third silo for holding the reactive heat-resistant additive; the first lateral feeding section is connected to the feeder of the first silo, the reactive crosslinking section is connected to the feeder of the second silo, and the second lateral feeding section is connected to the feeder of the third silo.

[0008] Preferably, the discharge end of the twin-screw extruder is equipped with an underwater pelletizing device.

[0009] A method for preparing EVA hot melt adhesive for packaging using the apparatus as described in any one of claims 1-3, comprising the following steps: S1. Pretreatment and initial mixing: Ethylene-vinyl acetate copolymer, composite tackifying resin and modified microcrystalline wax are added to a high-speed mixer and initially mixed and deeply dried under heating and vacuum conditions; S2. Staged precision feeding and reactive extrusion: a) The premixed material obtained in S1 is conveyed to the melt blending section of a twin-screw extruder for melt blending; b) The molten material enters the first side feeding section, where the grafted compatibilizer is precisely added through a precision metering and feeding unit; c) Subsequently, the material enters the reaction cross-linking section, where nano-reinforced fillers are precisely added through a precision metering and feeding unit and the reaction proceeds. d) After that, the material enters the second side feeding section, where reactive heat-resistant additives are precisely added through precision metering and feeding unit; S3. The molten material after S2 treatment is extruded from a twin-screw extruder, cooled, and pelletized to obtain EVA hot melt adhesive products.

[0010] Preferably, in step S1, the heating and vacuum conditions are: temperature 100°C-120°C, vacuum degree -0.08MPa~-0.1MPa, and processing time 1-3 hours.

[0011] Preferably, in step S2, the temperature of the melt blending section is controlled at 100°C-120°C; the temperature of the reaction crosslinking section is controlled at 110°C-125°C; and the temperatures of the first lateral feeding section and the second lateral feeding section are controlled at 80°C-90°C by a cooling jacket.

[0012] Preferably, in step S2, the screw speed of the twin-screw extruder is 200 r / min-400 r / min.

[0013] Preferably, in step S3, the cooling pelletizing is underwater pelletizing.

[0014] Preferably, the raw materials, by weight, include: 85-100 parts of ethylene-vinyl acetate copolymer; 12-18 parts of composite tackifying resin; 4-8 parts of modified microcrystalline wax; 2-5 parts of graft compatibilizer; 5-10 parts of nano-reinforcing filler; and 4-7 parts of reactive heat-resistant additive.

[0015] Preferably, the composite tackifying resin is a mixture of hydrogenated petroleum resin and terpene phenolic resin in a mass ratio of 2:1; the modified microcrystalline wax is a product of Fischer-Tropsch wax grafted with maleic anhydride; the nano-reinforcing filler is nano-talc powder surface-treated with a silane coupling agent; and the reactive heat-resistant additive is a modified polymer obtained by reacting epoxy-terminated EPDM rubber with aminoquinoxaline.

[0016] Compared with the prior art, the beneficial effects of the present invention are as follows: This method and apparatus for preparing EVA hot melt adhesive for packaging, through modular integration, automated control devices, and staged fine processes, achieves efficient and stable preparation of high-performance EVA hot melt adhesive, improving the product's bonding strength, heat resistance, and overall performance. The specific details are as follows: Firstly, the pretreatment drying unit, precision metering and feeding unit, and multi-stage reactive extrusion unit are organically integrated through modular design, and each unit is electrically connected to the central control system, achieving fully automated control and precise regulation of the entire process. This effectively avoids errors caused by manual operation and improves production efficiency and ease of operation. Specifically, the high-speed mixer in the pretreatment drying unit integrates both a heating module and a vacuum drying module, enabling deep drying while initially mixing materials. This eliminates the need for separate drying equipment, simplifying the overall structure of the device, saving floor space and investment costs, and preventing secondary moisture absorption or contamination of materials during transfer, thus ensuring the quality of raw material pretreatment. The precision metering and feeding unit employs at least three independent hoppers with precision weighing scales and feeders, allowing for individual storage, precise metering, and on-demand delivery of different functional additives (such as graft compatibilizers, nano-reinforced fillers, and reactive heat-resistant additives). This solves the problem of additive proportioning issues in traditional mixing and feeding methods. The issues of easy deviation and functional interference are significantly improved in terms of metering accuracy and feeding stability. The multi-stage reactive extrusion unit divides the twin-screw extruder into sections along the material conveying direction: a melt blending section, a first side feeding section, a reaction crosslinking section, and a second side feeding section. Each functional section is equipped with an independent temperature control module or cooling jacket, which can precisely control the temperature according to the process requirements of different reaction stages. For example, the melt blending section ensures that the substrate is fully melted, the reaction crosslinking section provides a suitable temperature for the reaction between the nano-reinforced filler and the substrate, and the side feeding section avoids high-temperature decomposition of additives through the cooling jacket. Each section has a clear function and works in synergy, providing a stable equipment foundation for the subsequent preparation of high-performance EVA hot melt adhesive. In addition, the underwater pelletizing device at the discharge end of the twin-screw extruder can achieve rapid cooling and uniform pelletizing of molten material. Compared with the traditional air-cooled pelletizing method, the pellet forming quality is better, the particle size distribution is more uniform, and dust pollution is effectively reduced, further improving product quality and environmental friendliness. Secondly, based on the preparation method of the aforementioned device, through a phased and refined process design, the performance advantages of the device were fully utilized, achieving high efficiency and high quality in the EVA hot melt adhesive preparation process. In the pretreatment and initial mixing stage, the ethylene-vinyl acetate copolymer, composite tackifying resin, and modified microcrystalline wax were treated at 100°C-120°C and a vacuum of -0.08MPa to -0.1MPa for 1-3 hours. This not only achieved preliminary mixing and dispersion of the materials through heating, but also thoroughly removed moisture and low-molecular-weight volatiles from the raw materials using the high vacuum environment. This prevented the generation of bubbles due to the presence of moisture during subsequent melt extrusion, or the impact of low-molecular-weight substances on the product's adhesive performance and stability, thus laying a good raw material foundation for subsequent reactive extrusion. In the staged precision feeding and reactive extrusion, a process route of "melting the substrate first and then adding additives in stages" is adopted. First, the premixed material is fully melted in the melt blending section (100°C-120°C). Then, the grafted compatibilizer is precisely added in the first lateral feeding section to ensure uniform mixing of the compatibilizer and the molten substrate, thereby improving the compatibility between the subsequent additives and the substrate. Subsequently, nano-reinforcing fillers are added and reacted in the reaction crosslinking section (110°C-125°C). The appropriate temperature conditions can promote the full reaction and crosslinking of the nano-reinforcing fillers and the substrate, maximizing the reinforcing effect of the nano-fillers. Finally, reactive heat-resistant additives are added in the second lateral feeding section, and the temperature is controlled at 80°C-90°C by a cooling jacket. This effectively avoids the decomposition or performance degradation of the heat-resistant additives at high temperatures, ensuring that their heat-resistant function is fully utilized. Meanwhile, the twin-screw extruder's screw speed design of 200r / min-400r / min ensures appropriate residence time for materials in each stage, guaranteeing sufficient reaction and uniform mixing, while maintaining high production efficiency. This avoids prolonged production cycles due to excessively low speeds or excessive shearing and performance degradation caused by excessively high speeds. Furthermore, the underwater pelletizing process used in step S3 is compatible with the underwater pelletizing device in the apparatus, achieving a continuous preparation process and further improving production efficiency and product particle quality. Finally, the EVA hot melt adhesive for packaging prepared by the apparatus and method of the present invention has better overall performance than EVA hot melt adhesive prepared by traditional methods, thanks to the dual guarantees of raw material ratio and process control. In terms of raw material ratio, 85-100 parts of ethylene-vinyl acetate copolymer are used as the base material, combined with 12-18 parts of composite tackifying resin (hydrogenated petroleum resin and terpene phenolic resin compounded in a 2:1 ratio), 4-8 parts of modified microcrystalline wax (Fischer-Tropsch wax grafted with maleic anhydride), and supplemented with 2-5 parts of graft compatibilizer, 5-10 parts of nano-reinforcing filler (nano-talc powder surface-treated with silane coupling agent), and 4-7 parts of reactive heat-resistant additive (prepared by reacting epoxy-terminated EPDM rubber with aminoquinoxaline). The ratio of each raw material is scientific and reasonable, and each functional additive specifically addresses the performance shortcomings of traditional EVA hot melt adhesives—the composite tackifying resin can improve the product's bonding strength and applicability, the modified microcrystalline wax can improve the product's fluidity and low-temperature flexibility, the graft compatibilizer improves the compatibility of each component, the nano-reinforcing filler enhances the product's mechanical properties and aging resistance, and the reactive heat-resistant additive significantly improves the product's heat resistance temperature and long-term heat resistance stability. From a process control perspective, precise temperature control, accurate metering, and staged reactions throughout the entire process ensure that the functions of each raw material are fully utilized, avoiding product performance fluctuations caused by deviations in process parameters. The resulting EVA hot melt adhesive has advantages such as high bonding strength, good flexibility, excellent heat resistance, and strong stability, which can meet the diverse and high-quality requirements of the packaging industry for hot melt adhesives. It has a wide range of applications and a promising market prospect. Attached Figure Description

[0017] Figure 1 This is a schematic diagram of the overall device structure of the present invention.

[0018] In the diagram: 1. High-speed mixer; 101. Heating module; 102. Vacuum drying module; 2. Hopper; 3. Precision weighing scale; 4. Feeder; 5. Twin-screw extruder; 501. Melt blending section; 502. First side feeding section; 503. Reaction crosslinking section; 504. Second side feeding section; 6. Central control system. Detailed Implementation

[0019] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0020] Please see Figure 1This invention provides a technical solution: a preparation device for EVA hot melt adhesive for packaging, the overall structure of which follows the process flow design of "pretreatment-precision feeding-multi-stage reactive extrusion", and each unit works together to achieve efficient and precise preparation of hot melt adhesive. The specific structural details are as follows: The pretreatment drying unit is centered around a high-speed mixer 1, whose internal cavity integrates a heating module 101 and a vacuum drying module 102. The heating module 101 employs an array of electric heating tubes, enabling precise temperature control between 100°C and 120°C to meet the requirements for initial melting and moisture evaporation of the raw materials. The vacuum drying module 102 is equipped with a high-vacuum pump, which can stably control the vacuum level within the high-speed mixer 1 cavity at -0.08MPa to -0.1MPa, effectively preventing oxidation of the raw materials during heating and accelerating moisture removal, thus ensuring the purity of the raw materials for subsequent melt blending processes. The precision metering and feeding unit includes at least three hoppers 2 arrayed on one side of the high-speed mixer 1, namely the first hopper for holding grafted compatibilizer, the second hopper for holding nano-reinforced filler, and the third hopper for holding reactive heat-resistant additives. Each hopper 2 is equipped with a precision weighing scale 3 and a feeder 4 at its bottom. The precision weighing scale 3 uses a high-precision electronic weighing sensor with a weighing accuracy of ±0.1g. It can monitor the output of raw materials in the hopper 2 in real time and feed the data back to the central control system 6. The feeder 4 adopts a screw-type feeding structure. The screw speed is adjusted by the central control system 6 to realize the quantitative delivery of raw materials and ensure that each additive is accurately added to the corresponding section of the twin-screw extruder (5) according to the preset ratio. The core of the multi-stage reactive extrusion unit is a twin-screw extruder 5, which is divided into a melt blending section 501, a first side feeding section 502, a reactive cross-linking section 503, and a second side feeding section 504 along the material conveying direction. The functions and parameter controls of each section are as follows: Melt blending section 501: The inlet is connected to the outlet of high-speed mixer 1 through a pipeline. An independent temperature control module is set up inside. The temperature is stably controlled at 100°C-120°C by electric heating and air cooling in combination, so as to ensure that the premixed materials such as ethylene-vinyl acetate copolymer, composite tackifying resin, and modified microcrystalline wax are fully melted and uniformly mixed. First side feeding section 502: It is connected to the feeder 4 of the first silo through a pipeline, and is wrapped with a cooling jacket. The temperature is controlled at 80°C-90°C by circulating water cooling to prevent the grafted compatibilizer from reacting or clumping in advance during the addition process, and to ensure its uniform dispersion with the molten material. The reaction crosslinking section 503 is connected to the feeder 4 of the second hopper through a pipeline. It is equipped with an independent temperature control module, and the temperature is controlled at 110°C-125°C. This temperature range can promote the crosslinking reaction between the nano-reinforced filler and the molten material. At the same time, the shearing action of the twin screw further improves the material dispersion. The second lateral feeding section 504 is connected to the feeder 4 of the third silo via a pipeline. It is also equipped with a cooling jacket, and the temperature is controlled at 80°C-90°C to prevent the reactive heat-resistant additive from decomposing at high temperatures and to ensure that it can stably exert its heat-resistant modification effect. In addition, the discharge end of the twin-screw extruder 5 is equipped with an underwater pelletizing device, which includes a circulating cooling water tank, a high-speed rotating cutter and a pellet separation component. This device can instantly cool the extruded molten material to room temperature and cut it into pellets with uniform particle size, while achieving rapid separation of pellets and cooling water, thus improving product molding efficiency. The central control system 6 employs a PLC programmable logic controller, which is electrically connected via data cables to the heating module 101, vacuum drying module 102, precision weighing scale 3, feeder 4, twin-screw extruder 5 and its temperature control module, cooling jacket, and underwater pelletizing device. Its core functions include: real-time acquisition of parameters such as temperature, vacuum level, weighing data, and screw speed of each unit; automatic adjustment of the operating status of each module according to preset programs, such as automatically activating the heating module 101 to compensate for temperature when the internal temperature of the high-speed mixer 1 is below 100°C; automatically adjusting the screw speed of the feeder 4 when the precision weighing scale 3 detects a deviation in raw material delivery exceeding ±0.5%; and parameter storage, fault alarm, and historical data query functions to ensure the stability and traceability of the production process. Preparation method examples Example

[0021] This embodiment uses the above-described apparatus to prepare EVA hot melt adhesive for packaging. The specific steps are as follows: S1. Pretreatment and Initial Mixing Weigh the following raw materials by weight: 85 parts of ethylene-vinyl acetate copolymer, 12 parts of composite tackifying resin (hydrogenated petroleum resin and terpene phenolic resin compounded at a mass ratio of 2:1), and 4 parts of modified microcrystalline wax (Fischer-Tropsch wax modified by maleic anhydride grafting). Add the above raw materials to high-speed mixer 1, start heating module 101 to raise the temperature to 100°C, start vacuum drying module 102 to stabilize the vacuum degree of the inner cavity at -0.08MPa, and continue stirring under these conditions for 3 hours to complete the preliminary mixing and deep drying of the raw materials and obtain the premixed material. S2. Staged precision feeding and reactive extrusion Step a: The premixed material obtained in S1 is transported to the melt blending section 501 of the twin-screw extruder 5 through the pipeline. The twin-screw extruder 5 is started and the screw speed is adjusted to 200 r / min. At the same time, the temperature of the melt blending section 501 is controlled at 100°C through the temperature control module. The premixed material is continuously melt blended in this section for 15 minutes to form a uniform melt material. Step b: The molten material enters the first side feeding section 502. The central control system 6 starts the feeder 4 of the first hopper and accurately adds 2 parts of graft compatibilizer by weight. At the same time, the temperature of the first side feeding section 502 is controlled at 80°C by the cooling jacket. The material and graft compatibilizer are mixed evenly under the shearing action of the twin screws. Step c: The mixed material enters the reaction crosslinking section 503. The central control system 6 starts the feeder 4 of the second hopper and accurately adds 5 parts by weight of nano-reinforced filler (nano-talc powder with silane coupling agent surface treatment). The temperature of the reaction crosslinking section 503 is raised to 110°C by the temperature control module and the screw speed is kept at 200 r / min. The material undergoes a crosslinking reaction in this section, and the reaction time lasts for 20 minutes. Step d: The reacted material enters the second side feeding section 504. The central control system 6 starts the feeder 4 of the third hopper and accurately adds 4 parts by weight of reactive heat-resistant additive (modified polymer obtained by reacting terminal epoxy group EPDM rubber with aminoquinoxaline). The temperature of the second side feeding section 504 is controlled at 80°C by the cooling jacket, and the material and heat-resistant additive are further mixed evenly. S3. Cooling and pelletizing Start the underwater pelletizing device at the discharge end of the twin-screw extruder 5 to extrude the molten material after S2 treatment from the extruder die. The extruded material immediately enters the circulating cooling water tank (water temperature controlled at 25°C) to cool to room temperature. Then, it is cut into particles with a particle size of 2mm by a high-speed rotating cutter (speed 3000r / min). After separation by the particle separation component, EVA hot melt adhesive product for packaging is obtained. Example

[0022] The apparatus in this embodiment is the same as that in Embodiment 1, with only slight adjustments to the raw material ratio and process parameters, as detailed below: S1. Pretreatment and Initial Mixing Raw material weight parts: 92 parts ethylene-vinyl acetate copolymer, 15 parts composite tackifying resin, 6 parts modified microcrystalline wax; High-speed mixer 1 parameters: temperature 110°C, vacuum degree -0.09MPa, processing time 2 hours. S2. Staged precision feeding and reactive extrusion Twin-screw extruder with 5 screws and a speed of 300 r / min; The temperature of the melt blending section 501 is 110°C, and the melt blending time is 12 minutes. In the first lateral feeding section 502, 3.5 parts of graft compatibilizer are added at a temperature of 85°C. The reaction crosslinking segment 503 was mixed with 7.5 parts of nano-reinforced filler, the temperature was 118°C, and the reaction time was 18 minutes. In the second lateral feeding section 504, 5.5 parts of a reactive heat-resistant additive are added at a temperature of 85°C. S3. Cooling and pelletizing The underwater pelletizing device has a cutter speed of 3500 r / min and a product particle size of 2.5 mm. Example

[0023] This embodiment represents the optimal parameter combination, as detailed below: S1. Pretreatment and Initial Mixing Raw material weight parts: 100 parts ethylene-vinyl acetate copolymer, 18 parts composite tackifying resin, 8 parts modified microcrystalline wax; High-speed mixer parameters: temperature 120°C, vacuum degree -0.1MPa, processing time 1 hour. S2. Staged precision feeding and reactive extrusion Twin-screw extruder with 5 screws and a speed of 400 r / min; The temperature of the melt blending section 501 is 120°C, and the melt blending time is 10 minutes. In the first lateral feeding section 502, add 5 parts of graft compatibilizer and keep the temperature at 90°C; Ten parts of nano-reinforced filler were added to the cross-linking segment 503 during the reaction at 125°C for 15 minutes. In the second lateral feeding section 504, 7 parts of a reactive heat-resistant additive are added at a temperature of 90°C. S3. Cooling and pelletizing The underwater pelletizing device has a cutter speed of 4000 r / min and a product particle size of 3 mm.

[0024] Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. An apparatus for preparing EVA hot melt adhesive for packaging, comprising a pretreatment drying unit, a precision metering and feeding unit, and a multi-stage reactive extrusion unit, characterized in that: The pretreatment drying unit includes a high-speed mixer (1), and the inner cavity of the high-speed mixer (1) is provided with a heating module (101) and a vacuum drying module (102). The precision metering and feeding unit includes at least three hoppers (2) arranged in an array on one side of the high-speed mixer (1), each hopper (2) is equipped with a precision metering scale (3) at its bottom, and a feeder (4) is provided on one side of the precision metering scale (3). The multi-stage reactive extrusion unit includes a twin-screw extruder (5), which is divided into a melt blending section (501), a first side feeding section (502), a reactive cross-linking section (503), and a second side feeding section (504) in sequence along the material conveying direction. The inlet of the melt blending section (501) is connected to the outlet of the high-speed mixer (1). The first side feeding section (502), the reactive cross-linking section (503), and the second side feeding section (504) are respectively connected to different feeders (4) through pipelines. The melt blending section (501) and the reaction crosslinking section (503) are each equipped with an independent temperature control module; the first lateral feeding section (502) and the second lateral feeding section (504) are equipped with cooling jackets; The device also includes a central control system (6), which is electrically connected to the heating module (101), the vacuum drying module (102), the precision weighing scale (3), the feeder (4), the twin-screw extruder (5), its temperature control module, and the cooling jacket.

2. The apparatus for preparing EVA hot melt adhesive for packaging according to claim 1, characterized in that: The silo (2) includes at least a first silo for holding grafted compatibilizer, a second silo for holding nano-reinforced filler and a third silo for holding reactive heat-resistant additive; the first lateral feeding section (502) is connected to the feeder (4) of the first silo, the reactive crosslinking section (503) is connected to the feeder (4) of the second silo, and the second lateral feeding section (504) is connected to the feeder (4) of the third silo.

3. The apparatus for preparing EVA hot melt adhesive for packaging according to claim 1, characterized in that: The discharge end of the twin-screw extruder (5) is equipped with an underwater pelletizing device.

4. A method for preparing EVA hot melt adhesive for packaging using the apparatus as described in any one of claims 1-3, characterized in that: Includes the following steps: S1. Pretreatment and initial mixing: Ethylene-vinyl acetate copolymer, composite tackifying resin and modified microcrystalline wax are added to a high-speed mixer (1) and initially mixed and deeply dried under heating and vacuum conditions; S2. Staged precision feeding and reactive extrusion: a) The premixed material obtained in S1 is conveyed to the melt blending section (501) of the twin-screw extruder (5) for melt blending; b) The molten material enters the first lateral feeding section (502), where the grafted compatibilizer is precisely added through a precision metering and feeding unit; c) Subsequently, the material enters the reaction crosslinking section (503), where nano-reinforced fillers are precisely added through precision metering and feeding unit and the reaction takes place; d) After that, the material enters the second side feeding section (504), where reactive heat-resistant additives are precisely added through precision metering and feeding unit; S3. The molten material after S2 treatment is extruded from the twin-screw extruder (5), and after cooling and pelletizing, EVA hot melt adhesive product is obtained.

5. The method according to claim 4, characterized in that, In step S1, the heating and vacuum conditions are: temperature 100°C-120°C, vacuum degree -0.08MPa~-0.1MPa, and processing time 1-3 hours.

6. The method according to claim 4, characterized in that, In step S2, the temperature of the melt blending section (501) is controlled at 100°C-120°C; the temperature of the reaction crosslinking section (503) is controlled at 110°C-125°C; and the temperatures of the first side feeding section (502) and the second side feeding section (504) are controlled at 80°C-90°C by a cooling jacket.

7. The method according to claim 4, characterized in that, In step S2, the screw speed of the twin-screw extruder (5) is 200r / min-400r / min.

8. The method according to claim 4, characterized in that, In step S3, the cooling pelletizing is underwater pelletizing.

9. The method according to claim 4, characterized in that, The raw materials, by weight, include: 85-100 parts of ethylene-vinyl acetate copolymer; 12-18 parts of composite tackifying resin; 4-8 parts of modified microcrystalline wax; 2-5 parts of graft compatibilizer; 5-10 parts of nano-reinforcing filler; and 4-7 parts of reactive heat-resistant additive.

10. The method according to claim 9, characterized in that, The composite tackifying resin is a mixture of hydrogenated petroleum resin and terpene phenolic resin in a mass ratio of 2:1; the modified microcrystalline wax is a product of Fischer-Tropsch wax grafted with maleic anhydride; the nano-reinforcing filler is nano-talc powder surface-treated with silane coupling agent; and the reactive heat-resistant additive is a modified polymer obtained by reacting epoxy-terminated EPDM rubber with aminoquinoxaline.

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