High performance eva rubber particles, process for their preparation and use

Abstract

The application relates to the technical field of EVA glue particle production, and is a high-performance EVA glue particle and a preparation method and application thereof; the former is prepared according to the following method: ethylene and vinyl acetate are mixed, pressure is increased, and preheating is carried out; polymerization reaction is initiated by an injected initiator in a first reactor, a second reactor, a third reactor and a fourth reactor to obtain a reaction product; after pressure reduction and cooling, high-pressure separation, low-pressure separation, extrusion granulation and degassing treatment are sequentially carried out on the reaction product to obtain the high-performance EVA glue particle. The preparation process is simple, the conversion rate of the polymerization reaction raw material is improved, the high-performance EVA glue particle prepared has high molecular chain branching degree, good compatibility with an additive, low small-molecular-weight polymer content and stable crystal point index; the high-performance EVA glue particle has good anti-aging yellowing performance, high peeling strength and moderate crosslinking speed when the high-performance EVA glue particle is used in a photovoltaic glue film, and has wide industrial application prospects.

Description

Technical Field

[0001] This invention relates to the field of EVA granule production technology, specifically a high-performance EVA granule, its preparation method, and its applications. Background Technology

[0002] EVA (ethylene-vinyl acetate copolymer) combines the advantages of polyethylene and polyvinyl acetate, primarily exhibiting good flexibility, transparency, adhesion, compatibility with fillers, and heat-sealing properties. It is widely used in photovoltaic films, foamed shoe materials, wires and cables, hot melt adhesives, and functional films. As one of the higher-end polyolefin resins, EVA is experiencing rapid development. EVA photovoltaic film is a photovoltaic encapsulation material made by melt extruding EVA particles with the addition of crosslinking agents, light stabilizers, antioxidants, tackifiers, and other additives, and then casting it. This material covers both sides of the solar cell (approximately 0.16 mm thick) and is bonded to the glass or backsheet using vacuum lamination technology to form a module. The film thickness is between 0.4 mm and 0.5 mm. The photovoltaic film protects the solar cells and improves power generation efficiency. The encapsulation of the solar cells is irreversible; once the photovoltaic film begins to yellow or crack, the photovoltaic module is prone to failure and scrapping. Although the cost of encapsulant film in photovoltaic modules is only about 6%, its quality (performance indicators such as light transmittance, shrinkage rate, peel strength, and resistance to heat / oxygen / UV aging) is crucial for modules to achieve a 25-year lifespan.

[0003] China currently has an EVA production capacity of approximately 3.1 million tons, with over 55% of it used in photovoltaic films. There are more than 10 EVA manufacturers, primarily employing high-pressure tubular polymerization. Leading companies include Sirbon Petrochemical, Zhejiang Petrochemical, Yulin Energy Chemical, and Tianli High-tech Petrochemical. The main physical properties of EVA granules used in photovoltaic films are: VA content of 26% to 30%, melt index (2.16 kg, 190℃) of 23 g / 10 min to 28 g / 10 min. The macroscopic properties and microstructures of the more than 10 commercially available photovoltaic-grade EVA granules vary, leading to different brand images in applications. High-quality photovoltaic-grade EVA should possess good additive compatibility, low shrinkage rate, low aging and yellowing, low crystal point count, no small bubbles, high volume resistivity, moderate cross-linking speed, normal end-face color, and stable quality indicators. In other words, high-quality photovoltaic-grade EVA granules require continuous quality optimization and upgrading based on feedback from downstream customers.

[0004] Chinese patent document CN105732871B discloses a method for preparing ethylene vinyl acetate copolymer for solar cell sealants and the resin obtained by this method. This method can provide EVA copolymer resin with low heat shrinkage and high transparency. The method specifies that the initiator consists of four peroxides, each with a non-zero content. It does not specify the number of tubular reactors used, but the initiator composition is the same in each reactor. The preparation of some products also requires the injection of the chain transfer agent propionaldehyde to adjust the melt index. Simultaneously, it is necessary to control the Z-average molecular weight and molecular weight distribution width of the EVA product to achieve low heat shrinkage and fisheye appearance. This method cannot comprehensively improve the main physical properties of EVA for photovoltaic films, and the low shrinkage rate can be effectively addressed in the downstream photovoltaic film preparation process.

[0005] Chinese patent document CN106916241B discloses a method for manufacturing an ethylene-vinyl acetate copolymer resin for solar cell sealing sheets and the resin manufactured by this method. This method provides a solar cell sealing material resin with excellent transparency and light transmittance, low moisture transmittance, low acetic acid generation level, high resistance, and excellent long-term durability. However, this method uses a tubular reactor without clear segmentation, and the initiator consists of three peroxides, with over 50% of the initiator being peroxide (A). The amount of initiator injected is related to the amount of raw materials; excessive initiator injection will produce a strong exothermic reaction, making it impossible to control the reaction temperature, especially without a clear understanding of the heat extraction effect of the reactor jacket's hot water. This method only focuses on controlling the reactor's process parameters, without specifying the process parameters of the separator or methods for adjusting product performance. It cannot comprehensively improve the main physical properties of EVA used in photovoltaic films, and the reduction of vinyl acetate content in the examples will inevitably lead to a decrease in product transparency.

[0006] Chinese patent document CN105669886B discloses an ethylene vinyl acetate copolymer resin for solar cell sealing sheets and a method for manufacturing the same. The EVA copolymer resin exhibits reduced shrinkage during sheet manufacturing and low shrinkage during thermal bonding in module manufacturing processes. This method, based on CN105732871B, focuses on protecting the rheological properties of EVA.

[0007] Authorization announcement number CN106916242B discloses a method for manufacturing ethylene vinyl acetate copolymer resin, the resin itself, and sheets for sealing materials in solar cells. The EVA resin described herein has a high crosslinking rate, increasing productivity and enabling mass production. The EVA resin for photovoltaic backsheets manufactured by this invention has a high crosslinking rate, preventing mixing with overlapping EVA sheets on the front panel during module manufacturing, thus preventing battery contamination. No additional crosslinking agent is required. The product has a melt index of 3–6 g / 10 min and is primarily used for white encapsulant films, meeting the processing performance requirements for EVA resin used in photovoltaic backsheets in smaller quantities.

[0008] Chinese patent document CN106928385B discloses a method for manufacturing polyethylene or polyethylene-vinyl acetate copolymer. This method involves limiting the free radical initiator fed into the reactor to manufacture polyethylene or polyethylene-vinyl acetate copolymer. The polyethylene and polyethylene-vinyl acetate copolymer resins manufactured in this way suppress the formation of fish eyes when processed at high temperatures, maintain a high appearance quality, and improve processability. This method injects the same proportion of initiator into multiple reactors, using a large amount of initiator, and only solves the problems of fish eyes and processing performance in the product.

[0009] Chinese patent document CN110563871B discloses a production apparatus and preparation method for EVA raw materials used in photovoltaic films. This method uses chain transfer agents such as propylene to adjust the melt index of the product, and uses the same ratio of initiator in four reactors. It does not adjust the initiator formulation stepwise according to the specific conditions of each reactor. The initiator has a high concentration of peroxide, and the pressure in the high-part and low-part tanks is relatively high. The product has the characteristics of good transparency, high volume resistivity, and good anti-PID performance. However, this method cannot comprehensively improve the main physical properties of EVA used in photovoltaic films.

[0010] Chinese patent document CN117209640A discloses an ethylene-vinyl acetate copolymer and its production method. This method, by optimizing the pressure of low-pressure separation, can significantly reduce the volatile content in the obtained ethylene-vinyl acetate copolymer while reducing energy and material consumption. The method involves injecting the same proportion of initiator into four reactors, with the polymerization reaction temperature of all four reactors below 215°C. Analysis of the polymerization process parameters suggests that the product is only suitable for white EVA resin 28-6, requiring a low polymerization temperature to achieve a low melt index.

[0011] It is evident that while the existing technologies mentioned above involve EVA production or have developed certain properties of EVA granules for photovoltaic films to address localized bottlenecks in applications, they do not comprehensively provide high-performance photovoltaic-grade EVA granules, their preparation methods, and applications. Therefore, there is an urgent need to develop a high-performance EVA granule to solve the aforementioned problems. Summary of the Invention

[0012] This invention provides a high-performance EVA granule, its preparation method, and its application, overcoming the shortcomings of the prior art. It can effectively solve the problems of insufficient compatibility of additives, poor stability of quality indicators, slow crosslinking speed, poor anti-aging and yellowing performance, and low peel strength after aging in the production of existing EVA granules.

[0013] One of the technical solutions of this invention is achieved through the following measures: a high-performance EVA granule, obtained by the following method:

[0014] Step S1: After mixing ethylene and vinyl acetate in a mass ratio of 70 to 73: 27 to 30, the mixture is pressurized and preheated to a pressure of 240 MPa to 260 MPa and a temperature of 136°C to 147°C. Initiators are then injected into the inlets of the first reactor, the second reactor, the third reactor, and the fourth reactor to carry out polymerization reactions and obtain reaction products.

[0015] The initiator comprises a peroxide and a solvent. The peroxide is two to four of the following: di(2-ethylhexyl) peroxydicarbonate, tert-butyl peroxypentanoate, tert-butyl peroxy-2-ethylhexanoate, tert-butyl peroxy-3,5,5-trimethylhexanoate, and di-tert-butyl peroxydicarbonate. The solvent is an isoalkanes with 10 to 18 carbon atoms. The peroxide content in the initiator is 5% to 18% by mass, and the remainder is the solvent.

[0016] After the initiator is injected, the temperature rise caused by the reaction of ethylene and vinyl acetate is 28°C to 109°C, and the highest temperature of the polymerization reaction is 239°C to 248°C. During the polymerization reaction, the heat of polymerization is removed by hot water in the reactor jacket. The temperature of the hot water is 130°C to 150°C, and the temperature rise after the heat of polymerization is removed by the hot water is 6°C to 10°C.

[0017] In step S2, after the reaction product is depressurized and cooled, it is subjected to high-pressure separation, low-pressure separation, extrusion granulation and degassing treatment in sequence to obtain high-performance EVA granules.

[0018] During the high-pressure separation, the pressure is 21.0 MPa to 23.0 MPa and the temperature is 190°C to 210°C. During the low-pressure separation, the liquid level of the reaction product is 40% to 53%.

[0019] The following are further optimizations and / or improvements to one of the above-mentioned technical solutions:

[0020] In step S1 above, the content of hydroquinone, the polymerization inhibitor, in the vinyl acetate is 10 ppm to 20 ppm.

[0021] When the initiator is injected into the inlets of the first reactor, second reactor, third reactor, and fourth reactor as described above, the components with the highest peroxide content in the injected initiator are di(2-ethylhexyl) peroxydicarbonate, tert-butyl peroxypentanoate, tert-butyl peroxy-3,5,5-trimethylhexanoate, and tert-butyl peroxy-3,5,5-trimethylhexanoate, with mass contents greater than 50%, 30%, 40%, and 50%, respectively; the solvent in the initiator is isododecane.

[0022] In the initiator injected into the inlet of the first reactor, the mass ratio of di(2-ethylhexyl) peroxide dicarbonate, tert-butyl peroxypentanoate, tert-butyl peroxy-2-ethylhexanoate, and tert-butyl peroxy-3,5,5-trimethylhexanoate is 9 to 10: 4 to 5: 2.5 to 3: 1.

[0023] In the initiator injected into the inlet of the second reactor, the mass ratio of di(2-ethylhexyl) peroxide dicarbonate, tert-butyl peroxypentanoate, tert-butyl peroxy-2-ethylhexanoate, and tert-butyl peroxy-3,5,5-trimethylhexanoate is 0.5 to 0.8: 1.2 to 1.5: 0.5 to 1.0: 1.

[0024] In the initiator injected into the inlet of the third reactor, the mass ratio of tert-butyl peroxypentanoate, tert-butyl peroxy-2-ethylhexanoate, and tert-butyl peroxy-3,5,5-trimethylhexanoate is 0.5 to 0.8: 0.5 to 0.8: 1.

[0025] In the initiator injected into the inlet of the fourth reactor, the mass ratio of tert-butyl peroxide-2-ethylhexanoate or di-tert-butyl peroxide to tert-butyl peroxide-3,5,5-trimethylhexanoate is 0.75 to 0.9:1.

[0026] In step S1 above, during the polymerization reaction, the highest temperature of the polymerization reaction is 241°C to 244°C, the polymerization reaction pressure is 245MPa to 254MPa, and the temperature of the hot water in the reactor jacket is 135°C to 145°C. After the hot water removes the heat of polymerization, the polymerization reaction temperature at the reactor outlet decreases by 30°C to 65°C.

[0027] In step S2 above, during high-pressure separation, the pressure is 21.6 MPa to 22.6 MPa and the temperature is 191°C to 205°C. During low-pressure separation, the liquid level of the reaction product is 40% to 48%. During extrusion granulation, 65 ppm to 135 ppm of hindered phenolic antioxidant 1076 is added to the reaction product. The extrusion granulation temperature is 186°C to 200°C, and the degassing time is 36 hours to 48 hours.

[0028] In the aforementioned high-performance EVA particles, the branching point of long-chain branches is 0.7 to 1.05 per 1000 carbons, the branching point of short-chain branches is 65 to 75 per 1000 carbons, the content of two consecutive vinyl acetates on the molecular chain is 0.54 mol% to 0.65 mol%, the content of three consecutive vinyl acetates is 0.4 mol% to 0.5 mol%, the content of low molecular weight polymers is low as determined by temperature gradient interaction chromatography (HGIC), and the soluble content at 30°C is 1.05% to 1.45%.

[0029] The aforementioned high-performance EVA granules contain 27.5% to 29.5% vinyl acetate, have a melt flow rate of 2.75 g / 10 min to 3.20 g / 10 min at 125°C and 2.16 kg, a weight-average molecular weight of 65,000 g / mol to 80,000 g / mol, a molecular weight distribution width of 4.4 to 5.2, a melting peak temperature of 69.5°C to 73.5°C, and a volume resistivity of 10 Ω·cm. 15 Ω·cm to 10 16 Ω·cm, number of crystal points of 0.3mm to 0.5mm ≤ 1 / 1200cm 2 .

[0030] The second technical solution of the present invention is achieved through the following measures: a method for preparing high-performance EVA particles, which is carried out according to the following method:

[0031] Step S1: After mixing ethylene and vinyl acetate in a mass ratio of 70 to 73:27 to 30, the mixture is pressurized and preheated to a pressure of 240 MPa to 260 MPa and a temperature of 136°C to 147°C. Initiators are then injected into the inlets of the first, second, third, and fourth reactors to initiate polymerization reactions and obtain the reaction products.

[0032] The initiator comprises a peroxide and a solvent. The peroxide is two to four of the following: di(2-ethylhexyl) peroxide dicarbonate, tert-butyl peroxypentanoate, tert-butyl peroxy-2-ethylhexanoate, tert-butyl peroxy-3,5,5-trimethylhexanoate, and di-tert-butyl peroxide. The solvent is an isoalkane with 10 to 18 carbon atoms. The peroxide content in the initiator is 5% to 18% by mass, with the remainder being the solvent.

[0033] After the initiator is injected, the temperature rise caused by the reaction of ethylene and vinyl acetate is 28°C to 109°C. During the polymerization reaction, the heat of polymerization is removed by hot water in the reactor jacket. The temperature of the hot water is 130°C to 150°C. After the heat of polymerization is removed by the hot water, the temperature rise is 6°C to 10°C.

[0034] In step S2, the reaction product is depressurized and cooled, and then subjected to high-pressure separation, low-pressure separation, extrusion granulation, and degassing treatment in sequence to obtain high-performance EVA granules.

[0035] During the high-pressure separation, the pressure is 21.0 MPa to 23.0 MPa and the temperature is 190°C to 210°C. During the low-pressure separation, the liquid level of the reaction product is 40% to 53%.

[0036] The third technical solution of the present invention is achieved through the following measures: the application of high-performance EVA particles in the field of photovoltaic films, wherein the high-performance EVA particles absorb liquid phase additives and then prepare photovoltaic films on a casting film machine, wherein the additive absorption time is 2.5 hours to 4 hours, the amount of precipitate from the casting film machine die head is 0.02 kg / day to 0.05 kg / day, the surface of the photovoltaic film is non-slip after 3 months of storage, and the crosslinking speed TC90 of the photovoltaic film is 560 seconds to 640 seconds.

[0037] The present invention has a simple preparation process, improves the conversion rate of polymerization reaction raw materials, and produces high-performance EVA particles with high molecular chain branching, good compatibility with additives, low content of low molecular weight polymers, and stable crystal point index. When high-performance EVA particles are used in photovoltaic films, they have good anti-aging and yellowing properties, high peel strength, moderate crosslinking speed, and broad prospects for industrial application. Attached Figure Description

[0038] Appendix Figure 1 This is a temperature distribution diagram inside the first reactor in Embodiment 12 of the present invention. Detailed Implementation

[0039] This invention is not limited to the following embodiments; specific implementation methods can be determined based on the technical solution of this invention and actual circumstances. Unless otherwise specified, all chemical reagents and chemical products mentioned in this invention are well-known and commonly used chemical reagents and chemical products in the prior art.

[0040] The present invention will be further described below with reference to embodiments:

[0041] Example 1: This high-performance EVA granules were obtained according to the following method:

[0042] Step S1: Ethylene and vinyl acetate are mixed in a mass ratio of 70 to 73:27 to 30 and then placed in a jacketed tubular reactor. The mixture is pressurized to 240 MPa to 260 MPa by at least two stages of compressors and preheated to 136°C to 147°C by two parallel or series preheaters. Initiators are then injected into the inlets of the first, second, third, and fourth reactors, which are connected in sequence, to carry out polymerization and generate a temperature rise, thereby obtaining the reaction product.

[0043] The initiator comprises a peroxide and a solvent. The peroxide is selected from two to four of the following: di(2-ethylhexyl) peroxydicarbonate (hereinafter referred to as PO1), tert-butyl peroxypentanoate (hereinafter referred to as PO2), tert-butyl peroxy-2-ethylhexanoate (hereinafter referred to as PO3), tert-butyl peroxy-3,5,5-trimethylhexanoate (hereinafter referred to as PO4), and di-tert-butyl peroxydioxide (hereinafter referred to as PO5). The solvent is an isoalkanes with 10 to 18 carbon atoms. The peroxide content in the initiator is 5% to 18% by mass, and the balance is isododecane. The purpose of diluting the peroxide with isododecane solvent is to improve the dispersibility of the peroxide in the polymerization reaction system and enhance the polymerization reaction efficiency.

[0044] After the initiator is injected, the temperature rise caused by the reaction of ethylene and vinyl acetate is 28°C to 109°C, and the highest polymerization temperature is 239°C to 248°C. During the polymerization process, the heat of polymerization is removed by hot water in the reactor jacket. The hot water temperature is 130°C to 150°C, and the temperature rise after the removal of the heat of polymerization is 6°C to 10°C. The number of reaction tubes in the first, second, third, and fourth reactors are 42, 36, 30, and 30, respectively, and each reaction tube is 17 meters long. The highest temperature rise in the first reactor is located in the 6th to 11th reaction tubes, with a temperature rise of 95°C to 108°C. The first reactor generates a higher temperature rise and controls the highest temperature point to be earlier. The purpose is, on the one hand, to increase the branching degree of the main molecular chain of the high-pressure polymer, improve the compatibility of EVA particles with additives in photovoltaic films, and on the other hand, to improve the efficiency of hot water removal of the reactor reaction heat, which is beneficial to improving the conversion rate of the polymerization reaction raw materials or the production efficiency.

[0045] In step S2, after the reaction product is depressurized and cooled, it is subjected to high-pressure separation, low-pressure separation, extrusion granulation and degassing treatment in sequence to obtain high-performance EVA granules.

[0046] During the high-pressure separation, the pressure is 21.0 MPa to 23.0 MPa and the temperature is 190°C to 210°C. During the low-pressure separation, the liquid level of the reaction product is 40% to 53%.

[0047] Example 2: As an optimization of the above example, in step S1, the content of hydroquinone, the polymerization inhibitor, in the vinyl acetate is 10 ppm to 20 ppm. The purpose of adding hydroquinone is to prevent the self-polymerization of vinyl acetate. Controlling its content is to reduce the negative impact of the polymerization inhibitor on the color and appearance of the EVA photovoltaic film end face.

[0048] Example 3: As an optimization of the above embodiment, when the initiator is injected into the inlet of the first reactor, the second reactor, the third reactor and the fourth reactor respectively, the components with the highest peroxide mass content in the injected initiator are PO1, PO2, PO4 and PO4, respectively, with mass contents greater than 50%, 30%, 40% and 50% respectively. Wherein, as needed, the mass content of peroxides PO1 and PO2 in the initiator injected into the inlet of the fourth reactor is 0.

[0049] The peroxides PO1 to PO5 are preferred from the top of the decomposition temperature gradient that initiates the polymerization reaction. PO1, with the lowest decomposition temperature, has the highest mass content in the initiator used in the first reactor. The purpose of this is to quickly initiate the polymerization reaction at a lower preheating temperature to generate a temperature rise and reduce the low-temperature polymerization reaction time. A higher polymerization temperature is conducive to the transfer of polymer molecular chains to form a highly branched molecular structure. PO4, with a relatively higher decomposition temperature, has a high mass content in the initiators used in the third and fourth reactors. On the one hand, this is conducive to the growth of polymer molecular chains and the increase of molecular weight. On the other hand, it is conducive to reducing the residue of peroxides in the reaction products and eliminating the harm of polymerization side reactions caused by residual peroxides.

[0050] Example 4: As an optimization of the above example, the composition of the peroxide in the initiator is adjusted according to the polymerization reaction characteristics initiated by each reactor. The mass ratio of PO1, PO2, PO3 and PO4 in the initiator injected into the inlet of the first reactor is 9 to 10: 4 to 5: 2.5 to 3: 1.

[0051] Example 5: As an optimization of the above example, the mass ratio of PO1, PO2, PO3, and PO4 in the initiator injected into the inlet of the second reactor is 0.5 to 0.8: 1.2 to 1.5: 0.5 to 1.0: 1.

[0052] Example 6: As an optimization of the above example, the mass ratio of PO2, PO3, and PO4 in the initiator injected into the inlet of the third reactor is 0.5 to 0.8: 0.5 to 0.8: 1.

[0053] Example 7: As an optimization of the above example, the mass ratio of PO3 or PO4 to PO4 in the initiator injected into the inlet of the fourth reactor is 0.75 to 0.9:1.

[0054] Example 8: As an optimization of the above example, in step S1, the highest polymerization temperature during the polymerization reaction is 241°C to 244°C. The highest polymerization temperature of each reactor is controlled by adjusting the amount of initiator injected. The highest polymerization temperature can also be finely adjusted according to the melt mass flow rate of the EVA particles. The hot water temperature in the reactor jacket is 135°C to 145°C. After the hot water removes the heat of polymerization, the polymerization temperature at the reactor outlet decreases by 30°C to 65°C. Further reducing the hot water temperature can remove more heat of reaction to improve the conversion rate of raw materials, but a thick layer of stagnant material will form on the inner wall of the reactor due to the large temperature difference, resulting in unstable or excessive crystal point indicators of the EVA product.

[0055] The polymerization reaction pressure is between 245 MPa and 254 MPa, controlled and regulated by a high-pressure pulse valve. The pulse pressure of the valve is between 140 MPa and 175 MPa, and the purpose of the pulse is to reduce the long-term retention of material adhering to the reactor walls. Narrowing the maximum polymerization temperature and reaction pressure aims to improve the stability of product quality indicators such as VA content and melt flow rate.

[0056] Example 9: As an optimization of the above example, in step S2, during high-pressure separation, the pressure is 21.6 MPa to 22.6 MPa and the temperature is 191°C to 205°C; during low-pressure separation, the liquid level of the reaction product is 40% to 48%; during extrusion granulation, 65 ppm to 135 ppm of hindered phenolic antioxidant 1076 is added to the reaction product; the extrusion granulation temperature is 186°C to 200°C; and the degassing treatment time is 36 hours to 48 hours.

[0057] In this process, unreacted raw materials and low-molecular-weight wax are separated from the reaction products in a high-pressure separation tank. The unreacted ethylene is circulated to the inlet of the secondary compressor via a high-pressure circulation pipeline, and the low-molecular-weight wax is condensed and removed in the heat exchanger of the high-pressure circulation pipeline. In a low-pressure separation tank, unreacted raw materials and light hydrocarbon impurities are separated from the reaction products. The vinyl acetate and light hydrocarbon impurities are condensed in a low-pressure circulation pipeline and then sent to a refining unit to remove the light hydrocarbon impurities before being reused. The unreacted ethylene is circulated to the inlet of the primary compressor.

[0058] The lower separation pressure and temperature of the high-pressure separator are conducive to improving gas-liquid separation efficiency. A large amount of low molecular weight wax and small molecular weight polymers are separated from the top of the high-pressure separator and condensed and removed in the high-pressure circulation pipeline. The purpose of controlling the liquid level of the low-pressure separator is to reduce the thickness of the material adhering to the separator wall, reduce the amount of material stuck to the wall and the risk of falling off. The material stuck to the wall for a long time will fall off irregularly after undergoing thermal cross-linking reaction, which will make the crystal point index of the product unstable.

[0059] The purpose of adding a small amount of the hindered phenolic antioxidant 1076 instead of other antioxidants is to reduce the conflict between the antioxidant and the liquid phase additives added during the photovoltaic film preparation process, and to reduce the impact of the type and amount of antioxidant added on the color and appearance of the photovoltaic film, such as the film end face color turning pink, bluish, or red. Adding a small amount of antioxidant can improve the stability of the melt flow rate index of EVA particles after degassing treatment.

[0060] Meanwhile, excessively low extrusion granulation temperature is not conducive to the extrusion of residues in the reaction products, resulting in products with strong odor and high volatile content; excessively high extrusion granulation temperature will cause micro-crosslinking of the reaction products, resulting in micro-crosslinked dead material in the products and unstable crystal point index of the products.

[0061] The degassing treatment is used to remove residual ethylene, vinyl acetate and low molecular weight polymers from EVA particles, reduce the impact of product volatiles on the application end, and eliminate the safety hazards of the residues.

[0062] Example 10: As an optimization of the above example, the high-performance EVA particles have abundant long and short branching. The branching points of long branched chains (LCBf) are 0.7 to 1.05 per 1000 carbons, and the branching points of short branched chains (SCB) are 65 to 75 per 1000 carbons. Vinyl acetate is evenly distributed in the ethylene molecular chain segments. The content of two consecutive vinyl acetates (VV) is 0.54 mol% to 0.65 mol%, and the content of three consecutive vinyl acetates (VVV) is 0.4 mol% to 0.5 mol%. The content of low molecular weight polymers is low. During the temperature gradient interaction chromatography (HGIC) process with o-dichlorobenzene as the mobile phase, the soluble content at 30°C is 1.05% to 1.45%. HGIC is used to characterize the content of low molecular weight polymers.

[0063] The purpose of controlling the low content of low molecular weight polymers in high-performance EVA particles is that low molecular weight polymers not only cause excessive changes in the yellow index and low peel strength after the EVA photovoltaic film ages, but also affect the improvement of the cross-linking speed during the cross-linking reaction of the photovoltaic film. The rate at which the cross-linking reaction of low molecular weight polymers forms a cross-linking network is relatively slow.

[0064] Meanwhile, the higher the content of two consecutive VV or three consecutive VVV, the stronger the polarity of the obtained high-performance EVA particles, and the better their absorption effect and compatibility with liquid phase additives.

[0065] Example 11: As an optimization of the above embodiment, the high-performance EVA granules contain 27.5% to 29.5% vinyl acetate, have a melt flow rate of 2.75 g / 10 min to 3.20 g / 10 min at 2.16 kg and 125 °C, a weight-average molecular weight (Mw) of 65,000 g / mol to 80,000 g / mol, a molecular weight distribution width (PDI) of 4.4 to 5.2, a melting peak temperature of 69.5 °C to 73.5 °C, and a volume resistivity of 10 Ω·cm. 15 Ω·cm to 10 16 Ω·cm, number of crystal points of 0.3mm to 0.5mm ≤ 1 / 1200cm 2 .

[0066] Example 12: The preparation method of this high-performance EVA granules is carried out according to the following method:

[0067] Step S1: Ethylene and vinyl acetate with a mass ratio of 72:28 are mixed, pressurized to 254 MPa, and preheated to 136.5 °C. Initiators are then injected into the inlets of the first reactor, the second reactor, the third reactor, and the fourth reactor, respectively, to carry out polymerization reactions. The highest temperature of the polymerization reaction is 242 °C, and the reaction products are obtained.

[0068] The temperature rises of the first, second, third, and fourth reactors were 105.5℃, 42℃, 39℃, and 30℃, respectively. The highest temperature rise in the first reactor was located in the ninth reaction tube. The temperature distribution within the first reactor was as follows: Figure 1 As shown;

[0069] The hot water temperature used to remove the heat of reaction in the reactor jacket is 141℃, and the temperature rise after the hot water removes the heat of reaction is 7℃. The mass ratio of PO1:PO2:PO3:PO4 in the initiator injected into the first reactor is 9.3:4.4:2.8:1, the mass ratio of PO1:PO2:PO3:PO4 in the initiator injected into the second reactor is 0.6:1.2:0.8:1, the mass ratio of PO2:PO3:PO4 in the initiator injected into the third reactor is 0.6:0.7:1, and the mass ratio of PO5:PO4 in the initiator injected into the fourth reactor is 0.78:1.

[0070] In step S2, the reaction product is depressurized by a pulse valve (pulse pressure of 155 MPa) and cooled by an aftercooler. Then, it is separated under high pressure in a high-pressure separator to remove unreacted raw materials and low-molecular-weight wax. Then, it is separated under low pressure in a low-pressure separator to remove unreacted raw materials and light hydrocarbon impurities (pressure of high-pressure separation is 22.5 MPa, temperature is 193°C, and liquid level of low-pressure separation is 40%). The amount of antioxidant 1076 added during the extrusion granulation process is 85 ppm, the extrusion granulation temperature is 195°C, and the extruded granules are degassed for 40 hours to obtain high-performance EVA granules.

[0071] The high-performance EVA granules obtained in Example 12 had a vinyl acetate content of 28.0%, a melt flow rate (2.16 kg, 125 °C) of 2.9 g / 10 min, a weight-average molecular weight (Mw) of 73000 g / mol, a molecular weight distribution width (PDI) of 4.96, a melting peak temperature of 71.5 °C, and a volume resistivity of 7 × 10⁻⁶. 15 Ω·cm. The branching point of long-chain LCBf is 0.90 branches / 1000 carbons, and the branching point of short-chain SCB is 69.4 branches / 1000 carbons; the VV content is 0.61 mol%, the VVV content is 0.46 mol%, and the soluble content at 30℃ is 1.28%.

[0072] Example 13: The only difference from Example 12 is that the raw material pressure is increased to 248 MPa, the highest polymerization temperature is 244°C, and the temperature rises of the first, second, third, and fourth reactors are 107.5°C, 46°C, 45°C, and 33°C, respectively. The highest temperature rise in the first reactor is located at the 8th reaction tube of the first reactor. The hot water temperature is 135°C, and the temperature rise after removing the heat of reaction is 9°C. The pulse pressure of the pulse valve is 175 MPa, the pressure in the high-pressure tank is 21.6 MPa, the temperature is 200°C, and the liquid level in the low-pressure tank is 48%. The amount of antioxidant 1076 added during granulation is 135 ppm, the extrusion granulation temperature is 186°C, and the extruded granules are degassed for 45 hours to obtain high-performance EVA granules.

[0073] The high-performance EVA granules contain 28.6% vinyl acetate, have a melt flow rate (2.16 kg, 125℃) of 3.1 g / 10 min, a weight-average molecular weight (Mw) of 68300 g / mol, a molecular weight distribution width (PDI) of 4.65, a melting peak temperature of 70.7℃, and a volume resistivity of 4.4 × 10⁻⁶. 15 Ω·cm. The branching point of long-chain LCBf is 1.01 branches / 1000 carbons, and the branching point of short-chain SCB is 72.3 branches / 1000 carbons; the VV content is 0.58 mol%, the VVV content is 0.43 mol%, and the soluble content at 30℃ is 1.4%.

[0074] Example 14: The only difference from Example 12 is that the raw material is pressurized to 245 MPa and preheated to 145°C, the highest temperature of the polymerization reaction is 241°C, and the temperature rises of the first reactor, second reactor, third reactor and fourth reactor are 96°C, 41°C, 35°C and 28°C respectively. The highest temperature rise of the first reactor is located at the 11th reaction tube of the first reactor; the hot water temperature is 145°C, and the temperature rise of the hot water after removing the heat of reaction is 6°C.

[0075] The mass ratio of PO1:PO2:PO3:PO4 in the initiator injected into the first reactor is 9.7:4.8:2.5:1; the mass ratio of PO1:PO2:PO3:PO4 in the initiator injected into the second reactor is 0.8:1.5:0.6:1; the mass ratio of PO2:PO3:PO4 in the initiator injected into the third reactor is 0.6:0.8:1; and the mass ratio of PO5:PO4 in the initiator injected into the fourth reactor is 0.9:1.

[0076] The pulse valve has a pulse pressure of 140 MPa, the high-pressure tank has a pressure of 22 MPa and a temperature of 205 °C, and the low-pressure tank has a liquid level of 45%. During the granulation process, the amount of antioxidant 1076 added is 70 ppm, the extrusion granulation temperature is 200 °C, and the extruded granules are degassed for 37 hours to obtain high-performance EVA granules.

[0077] The high-performance EVA granules contain 27.6% vinyl acetate, have a melt flow rate (2.16 kg, 125℃) of 2.78 g / 10 min, a weight-average molecular weight (Mw) of 77600 g / mol, a molecular weight distribution width (PDI) of 5.1, a melting peak temperature of 72.8℃, and a volume resistivity of 6.2 × 10⁻⁶. 15 Ω·cm. The branching point of long-chain LCBf is 0.79 branches / 1000 carbons, and the branching point of short-chain SCB is 67.0 branches / 1000 carbons; the VV content is 0.64 mol%, the VVV content is 0.47 mol%, and the soluble content at 30℃ is 1.13%.

[0078] Example 15: The only difference from Example 12 is that the raw material is pressurized to 248 MPa and preheated to 142°C, the highest temperature of the polymerization reaction is 244°C, and the temperature rises of the first reactor, second reactor, third reactor and fourth reactor are 102°C, 48°C, 43°C and 36°C respectively. The highest temperature rise of the first reactor is located at the 7th reaction tube of the first reactor; the hot water temperature is 135°C, and the temperature rise of the hot water after removing the heat of reaction is 8°C.

[0079] The mass ratio of PO1:PO2:PO3:PO4 in the initiator injected into the first reactor is 9.1:4.1:3.0:1; the mass ratio of PO1:PO2:PO3:PO4 in the initiator injected into the second reactor is 0.5:1.2:0.9:1; the mass ratio of PO2:PO3:PO4 in the initiator injected into the third reactor is 0.5:0.8:1; and the mass ratio of PO5:PO4 in the initiator injected into the fourth reactor is 0.9:1.

[0080] During the granulation process, the amount of antioxidant 1076 added was 135 ppm, and the extrusion granulation temperature was 186℃.

[0081] The high-performance EVA granules contain 27.6% vinyl acetate, have a melt flow rate (2.16 kg, 125℃) of 3.18 g / 10 min, a weight-average molecular weight (Mw) of 66000 g / mol, a molecular weight distribution width (PDI) of 4.7, a melting peak temperature of 73.2℃, and a volume resistivity of 4.0 × 10⁻⁶. 15 Ω·cm. The branching point of long-chain LCBf is 1.04 branches / 1000 carbons, and the branching point of short-chain SCB is 68.8 branches / 1000 carbons; the VV content is 0.58 mol%, the VVV content is 0.41 mol%, and the soluble content at 30℃ is 1.08%.

[0082] Example 16: Application of the high-performance EVA particles in the field of photovoltaic films. The high-performance EVA particles absorb liquid phase additives and are then used to prepare photovoltaic films on a casting machine. The additive absorption time is 2.5 hours to 4 hours, the amount of precipitate from the casting machine die head is 0.02 kg / day to 0.05 kg / day, there is no skinning that needs to be treated, and the surface of the photovoltaic film is not slippery after 3 months of storage. The high-performance EVA particles have good compatibility with the additives, and the crosslinking speed TC90 of the photovoltaic film is 560 seconds to 640 seconds.

[0083] The slightly faster crosslinking speed in this invention provides room for adjustment of the crosslinking speed. TC90 is the time it takes for the crosslinking degree of the photovoltaic encapsulant film to reach 90% during the encapsulation test (the crosslinking speed TC90 of the photovoltaic encapsulant film ranges from 550 seconds to 750 seconds).

[0084] After accelerated aging PCT (121℃, 48h) test, the yellow index change ΔYI of the photovoltaic film ranged from 1.0 to 2.6, and the peel strength ranged from 60N / cm to 100N / cm.

[0085] Comparative Example 1:

[0086] The only difference from Example 12 is that the raw material pressure was increased to 264 MPa, the highest polymerization temperature was 236°C, and the temperature rises of the first, second, third, and fourth reactors were 95.5°C, 37°C, 32°C, and 23°C, respectively. The highest temperature rise in the first reactor was located in the 7th reaction tube. After removing the heat of reaction with hot water, the temperature rise was 5°C. The obtained EVA granules had a vinyl acetate content of 27.8%, a melt flow rate (2.16 kg, 125°C) of 2.68 g / 10 min, a weight-average molecular weight (Mw) of 83200 g / mol, a molecular weight distribution width (PDI) of 4.7, a melting peak temperature of 69°C, and a volume resistivity of 1×10⁻⁶. 16 Ω·cm. The branching point of long-chain LCBf is 0.65 branches / 1000 carbons, and the branching point of short-chain SCB is 64.1 branches / 1000 carbons; the VV content is 0.56 mol%, the VVV content is 0.38 mol%, and the soluble content at 30℃ is 1.37%.

[0087] Comparative Example 2:

[0088] The only difference from Example 12 is that the raw materials were preheated to 130°C, and the temperature rises of the first, second, third, and fourth reactors were 112°C, 45°C, 41°C, and 33°C, respectively. The highest temperature rise in the first reactor was located at the 15th reaction tube. The hot water temperature was 130°C, and the temperature rise after removing the heat of reaction was 7°C. The melt flow rate of the EVA granules (2.16 kg, 125°C) was 2.95 g / 10 min; the weight-average molecular weight (Mw) was 72200 g / mol; the molecular weight distribution width (PDI) was 5.4; the melting peak temperature was 72.6°C; and the volume resistivity was 7 × 10⁻⁶. 14 Ω·cm. The branching point of long-chain LCB is 0.55 branches / 1000 carbons, and the branching point of short-chain SCB is 63.8 branches / 1000 carbons; the VV content is 0.54 mol%, the VVV content is 0.38 mol%, and the soluble content at 30℃ is 1.72%, with a high content of low molecular weight polymers.

[0089] Comparative Example 3:

[0090] The only difference from Example 12 is that: the mass ratio of PO1:PO2:PO3:PO4 in the initiator injected into the first reactor is 7.8:5.8:3.3:1; the mass ratio of PO1:PO2:PO3:PO4 in the initiator injected into the second reactor is 1.1:1.0:0.8:1; the mass ratio of PO2:PO3:PO4 in the initiator injected into the third reactor is 0.7:0.7:1; and the mass ratio of PO3:PO4 in the initiator injected into the fourth reactor is 0.8:1. The highest temperature rise point in the first reactor is located at the 15th reaction tube of the reactor, and the temperature distribution in the first reactor is as follows. Figure 1 As shown, the temperature distribution curve has poor smoothness, the composition ratio of PO1 to PO4 peroxides is unreasonable, and the effect of initiating the temperature rise relay of the polymerization reaction is poor; the weight average molecular weight Mw of EVA particles is 75000g / mol, the molecular weight distribution width PDI is 5.7, the soluble content at 30℃ is 1.93%, and the content of low molecular weight polymers is high.

[0091] Comparative Example 4:

[0092] The only difference from Example 14 is that the temperature rises of the first, second, third, and fourth reactors are 96°C, 37°C, 30°C, and 24°C, respectively, with the highest temperature rise in the first reactor located in the 10th reaction tube; the hot water temperature is 155°C, and the temperature rise after removing the heat of reaction is 3°C. The weight-average molecular weight (Mw) of the EVA particles is 78,000 g / mol, and the molecular weight distribution width (PDI) is 5.3; the branching point of long-chain LCB is 0.64 branches / 1000 carbons, and the branching point of short-chain SCB is 68 branches / 1000 carbons; the VV content is 0.6 mol%, the VVV content is 0.4 mol%, and the soluble content at 30°C is 1.46%.

[0093] Comparative Example 5:

[0094] The only difference from Example 14 is that the pressure in the high-precision tank is 26.5 MPa, the temperature is 185°C, and the extrusion granulation temperature is 186°C. The weight-average molecular weight (Mw) of the EVA granules is 75000 g / mol, the molecular weight distribution width (PDI) is 6.05, and the volume resistivity is 3 × 10⁻⁶. 14 Ω·cm, soluble content at 30℃ is 2.66%, with a high content of low molecular weight polymers.

[0095] Comparative Example 6:

[0096] The only difference from Example 14 is that the pulse pressure of the pulse valve is 75 MPa, the liquid level in the low-level tank is 45%, and after 33 days of production operation, a batch of EVA granules showed an excessive number of crystal points, with the highest number of 0.3-0.5 mm crystal points being 1.5 per 1200 cm³. 2 The product quality and stability deteriorated.

[0097] Comparative Example 7:

[0098] The only difference from Example 15 is that the amount of antioxidant 1076 added during granulation is 30 ppm, the extrusion granulation temperature is 195°C, and the degassing time of the extruded granules is 24 hours. The EVA granules have a VA content of 27.8%, a melt flow rate (2.16 kg, 125°C) of 3.5 g / 10 min, a molecular weight distribution width (PDI) of 5.3, a soluble content of 2.13% at 30°C, a strong acidic odor, and a melt flow rate (2.16 kg, 125°C) that decreases to 3.25 g / 10 min after being left at room temperature and under non-sealed conditions for 36 hours, indicating poor product quality stability.

[0099] The high-performance EVA particles prepared in Examples 12 to 15 and the EVA particles prepared in Comparative Examples 1 to 7 were used to further prepare photovoltaic films. After the EVA particles absorbed the liquid phase additives, the photovoltaic films were prepared on a casting film machine. The additives included crosslinking agents, crosslinking aids, coupling agents, antioxidants, light stabilizers, and tackifiers. The additive absorption time was 3.5 hours.

[0100] Performance testing:

[0101] The photovoltaic films prepared in the above examples and comparative examples were subjected to crosslinking performance (145℃, 15min), yellow index change ΔYI after PCT aging (121℃, 48h), and peel strength tests. The test results are shown in Table 1.

[0102] The testing instruments used for EVA granules and photovoltaic films are as follows: VA content: Infrared spectrometer, GB / T30925; GB / T1033.1; Melt flow rate (MFR): MP1200 melt indexer, GB / T3682.1; Molecular weight and its distribution: GPCV2000, ASTM D6474; Melting peak temperature: Differential scanning calorimeter, GB / T19466.3; Volume resistivity: HIOKISM7110 high-resistivity meter, GB / T31838.2; Branching point and segment distribution: Bruker 400 carbon NMR, SH / T1775; Temperature gradient interaction chromatography (HGIC): Polymer Char, IR5 detector, Hypercarb PGC column, mobile phase: o-dichlorobenzene; crosslinking performance (vulcanization curve): rotorless vulcanizer, GB / T16584; aging test: PCT test chamber, yellow index meter, tensile testing machine, GB / T29848.

[0103] The test results in Table 1 show that the present invention optimizes the composition of peroxides in the initiator, controls the temperature peak in the reactor to move forward, promotes the transfer rate of polymer molecular chains to form a molecular structure with a higher degree of branching, and improves the compatibility of the obtained high-performance EVA particles with additives in photovoltaic film applications. By reducing the content of low molecular weight polymers in the high-performance EVA particles, the product quality indicators are stabilized, and the problems of slow crosslinking speed, poor anti-aging and yellowing performance, and low peel strength after aging in photovoltaic films are solved.

[0104] In summary, the preparation process of this invention is simple, improves the conversion rate of polymerization reaction raw materials, and the prepared high-performance EVA particles have a high degree of molecular weight branching, good compatibility with additives, low content of low molecular weight polymers, and stable crystal point index. When high-performance EVA particles are used in photovoltaic films, they have good anti-aging and yellowing properties, high peel strength, moderate crosslinking speed, and broad prospects for industrial application.

[0105] The above technical features constitute the embodiments of the present invention, which have strong adaptability and implementation effect. Unnecessary technical features can be added or removed according to actual needs to meet the needs of different situations.

[0106] Table 1

[0107] .

Claims

1. A high performance EVA bead characterized in that The method is as follows: S1, the mixed mass ratio of ethylene and vinyl acetate is 70 to 73:27 to 30, and then the mixture is preheated to a pressure of 240 to 260 MPa and a temperature of 136 to 147 DEG C, and then initiators are injected into the inlets of the first reactor, the second reactor, the third reactor and the fourth reactor respectively to carry out polymerization reaction to obtain a reaction product; The initiator comprises peroxide and solvent, the peroxide is two to four of di(2-ethylhexyl)peroxydicarbonate, tert-butyl peroxypivalate, tert-butyl peroxy-2-ethylhexanoate, tert-butyl peroxy-3,5,5-trimethylhexanoate and di-tert-butyl peroxide, the solvent is isomeric alkane with carbon number of 10 to 18, the mass content of peroxide in the initiator is 5% to 18%, and the rest is solvent; Wherein, when the initiators are injected into the inlets of the first reactor, the second reactor, the third reactor and the fourth reactor respectively, the mass content of the component with the highest mass content of peroxide in the injected initiator is di(2-ethylhexyl)peroxydicarbonate, tert-butyl peroxypivalate, tert-butyl peroxy-3,5,5-trimethylhexanoate and tert-butyl peroxy-3,5,5-trimethylhexanoate, respectively more than 50%, 30%, 40% and 50%; In the initiator injected into the inlet of the first reactor, the mass ratio of di(2-ethylhexyl)peroxydicarbonate, tert-butyl peroxypivalate, tert-butyl peroxy-2-ethylhexanoate and tert-butyl peroxy-3,5,5-trimethylhexanoate is 9 to 10:4 to 5:2.5 to 3:1; In the initiator injected into the inlet of the second reactor, the mass ratio of di(2-ethylhexyl)peroxydicarbonate, tert-butyl peroxypivalate, tert-butyl peroxy-2-ethylhexanoate and tert-butyl peroxy-3,5,5-trimethylhexanoate is 0.5 to 0.8:1.2 to 1.5:0.5 to 1.0:1; In the initiator injected into the inlet of the third reactor, the mass ratio of tert-butyl peroxypivalate, tert-butyl peroxy-2-ethylhexanoate and tert-butyl peroxy-3,5,5-trimethylhexanoate is 0.5 to 0.8:0.5 to 0.8:1; In the initiator injected into the inlet of the fourth reactor, the mass ratio of tert-butyl peroxy-2-ethylhexanoate or di-tert-butyl peroxide to tert-butyl peroxy-3,5,5-trimethylhexanoate is 0.75 to 0.9:1; After the initiator is injected, the temperature rise caused by the reaction of ethylene and vinyl acetate is 28 to 109 DEG C, the highest temperature of the polymerization reaction is 239 to 248 DEG C, and in the polymerization reaction process, the heat of polymerization reaction is removed by hot water in the reactor jacket, the temperature of the hot water is 130 to 150 DEG C, and the temperature rise after the heat of polymerization reaction is removed by the hot water is 6 to 10 DEG C, and the highest point of the temperature rise of the first reactor is located in the 6th to 11th reaction tube of the first reactor, and the temperature rise is 95 to 108 DEG C; In the polymerization process, the highest temperature of the polymerization reaction is 241-244℃, the polymerization reaction pressure is 245-254MPa, the polymerization reaction pressure is controlled and adjusted by a high-pressure pulse valve, and the pulse pressure of the pulse valve is 140-175MPa; In step S2, after the reaction product is depressurized and cooled, high-pressure separation, low-pressure separation, extrusion granulation and degassing treatment are sequentially performed, and high-performance EVA particles are obtained. In the high-pressure separation, the pressure is 21.0-23.0MPa and the temperature is 190-210℃, and in the low-pressure separation, the liquid level of the reaction product is 40-53%. In the extrusion granulation, 65-135ppm of hindered phenolic antioxidant 1076 is added to the reaction product. The degassing treatment time is 36-48 hours.

2. The high performance EVA gelpart according to claim 1, characterized in that In step S1, the content of the polymerization inhibitor hydroquinone in the vinyl acetate is 10-20ppm.

3. The high performance EVA gelpart according to claim 1 or 2, characterized in that The solvent in the initiator is isododecane.

4. The high performance EVA gelpart according to claim 3, characterized in that The temperature of the hot water in the reactor jacket is 135-145℃, and after the hot water removes the polymerization heat, the polymerization temperature at the outlet of the reactor is reduced by 30-65℃.

5. The high performance EVA bead according to claim 1 or 2 or 4, characterized in that In step S2, in the high-pressure separation, the pressure is 21.6-22.6MPa and the temperature is 191-205℃, in the low-pressure separation, the liquid level of the reaction product is 40-48%, and the extrusion granulation temperature is 186-200℃.

6. The high performance EVA gumball of claim 5, wherein In the high-performance EVA particles, the long-chain branched point is 0.7-1.05 / 1000 carbons, the short-chain branched point is 65-75 / 1000 carbons, the content of two consecutive vinyl acetates on the molecular chain is 0.54-0.65mol%, the content of three consecutive vinyl acetates is 0.4-0.5mol%, and the 30℃ soluble content determined by high gradient interaction chromatography (HGIC) is 1.05-1.45%.

7. The high performance EVA gumball of claim 6, wherein The high-performance EVA particles have a content of vinyl acetate of 27.5% to 29.5%, a melt mass flow rate of 2.75 g / 10 min to 3.20 g / 10 min at 2.16 kg and 125 DEG C, a weight average molecular weight of 65,000 g / mol to 80,000 g / mol, a molecular weight distribution width of 4.4 to 5.2, a melting peak temperature of 69.5 DEG C to 73.5 DEG C, a volume resistivity of 10 15 Ω·cm to 10 16 Ω·cm, and a number of 0.3 mm to 0.5 mm crystal points of ≤1 / 1200 cm 2 .

8. A process for the preparation of high performance EVA gels as claimed in any one of claims 2 to 7, characterized by The method is as follows: In step S1, ethylene and vinyl acetate with a mixing mass ratio of 70-73:27-30 are mixed, and then preheated to a pressure of 240-260MPa and a temperature of 136-147℃, and initiators are injected into the inlets of the first reactor, the second reactor, the third reactor and the fourth reactor, respectively, to perform polymerization reaction and obtain a reaction product. The initiator includes peroxide and solvent, the peroxide is 2-4 of dicarbonic acid di(2-ethylhexyl) peroxide, tert-butyl peroxypivalate, tert-butyl peroxide-2-ethylhexanoate, tert-butyl peroxide-3,5,5-trimethylhexanoate and di-tert-butyl peroxide, the solvent is isomeric alkane with 10-18 carbon atoms, the mass content of peroxide in the initiator is 5-18%, and the rest is solvent. After the initiator is injected, the temperature rise caused by the reaction of ethylene and vinyl acetate is 28-109℃, the highest temperature of the polymerization reaction is 239-248℃, and in the polymerization process, the polymerization heat is removed by hot water in the reactor jacket, and the temperature rise after the hot water removes the polymerization heat is 6-10℃. In step S2, the reaction product is subjected to pressure reduction and cooling, high-pressure separation, low-pressure separation, extrusion granulation and degassing treatment to obtain high-performance EVA particles. In the high-pressure separation, the pressure is 21.0-23.0 MPa and the temperature is 190-210℃, and in the low-pressure separation, the liquid level of the reaction product is 40-53%.

9. Use of the high performance EVA rubber granules according to any one of claims 1 to 7 in the field of photovoltaic encapsulants, characterized in that The high-performance EVA particles are subjected to liquid-phase auxiliary agent absorption, and then used to prepare photovoltaic adhesive film on a casting film machine, wherein the auxiliary agent absorption time is 2.5-4 hours, the amount of casting film machine die precipitates is 0.02-0.05 kg / day, the surface of the photovoltaic adhesive film is not slippery after being placed for 3 months, and the crosslinking speed TC90 of the photovoltaic adhesive film is 560-640 seconds.

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