A halogen-free expandable flame-retardant EVA foam, its preparation method, and its application in lithium battery packaging.

Abstract

This invention relates to the field of EVA foam technology, and discloses a halogen-free intumescent flame-retardant EVA foam, its preparation method, and its application in lithium battery packaging. The raw materials of this halogen-free intumescent flame-retardant EVA foam include 100 parts by weight of ethylene-vinyl acetate copolymer, 10-20 parts by weight of polyvinyl acetate imidazole phosphate, and 5-12 parts by weight of sulfonated phenolic resin, etc. Polyvinyl acetate imidazole phosphate and sulfonated phenolic resin form an intumescent flame retardant, reducing the peak heat release rate and total heat release, and improving flame-retardant performance. Polyvinyl acetate imidazole phosphate has good compatibility with EVA and improves the compatibility between sulfonated phenolic resin and EVA, allowing the foam material to maintain good tear strength, thus enabling better practical applications in lithium battery packaging shells for new energy vehicles.

Description

Technical Field

[0001] This invention relates to the field of EVA foam technology, specifically to a halogen-free expandable flame-retardant EVA foam, its preparation method, and its application in lithium battery packaging. Background Technology

[0002] EVA (ethylene-vinyl acetate copolymer) foam has good thermal insulation properties, excellent elasticity, and strong impact resistance, making it suitable for applications in footwear, insulation materials, and battery pack casings. However, EVA foam has poor flame retardancy and is easily ignited, limiting its practical application in new energy vehicles and lithium battery packaging. Intumescent flame retardants are environmentally friendly flame retardants with important applications in polymer materials such as foams, plastics, and rubber.

[0003] Traditional intumescent flame retardants are added to materials such as foam through blending. However, the poor compatibility between flame retardants and materials can affect the mechanical properties of the materials. Phenolic resins have excellent mechanical properties, good high-temperature resistance, and high char formation, making them a high-performance flame retardant precursor. However, phenolic resins have poor compatibility with EVA foam, which can affect the mechanical strength of the foam material. Summary of the Invention

[0004] To address the shortcomings of existing technologies, this invention provides a halogen-free intumescent flame-retardant EVA foam, which solves the problem of poor flame-retardant performance of EVA foam material while maintaining good mechanical properties.

[0005] The technical solution of the present invention is: a halogen-free expandable flame-retardant EVA foam and its preparation method, the raw materials including 100 parts by weight of ethylene-vinyl acetate copolymer, 10-20 parts by weight of polyvinyl acetate imidazole phosphate, 5-12 parts by weight of sulfonated phenolic resin, 2.6-4.5 parts by weight of foaming agent, 1.2-1.7 parts by weight of crosslinking agent, 1-1.6 parts by weight of accelerator, and 0.8-1.2 parts by weight of additives.

[0006] The preparation methods of EVA foam include:

[0007] (1) In a nitrogen atmosphere, vinyl acetate imidazole phosphate and azobisisobutyronitrile were added to ethanol, stirred and reacted, filtered and washed with ethanol, and dried to obtain polyvinyl acetate imidazole phosphate.

[0008] (2) Ethylene-vinyl acetate copolymer, polyvinyl acetate imidazole phosphate, sulfonated phenolic resin, accelerator and additives are added to a two-roll mill for blending, then foaming agent is added and the mixture is blended at 80-90℃, then crosslinking agent is added and blended, the mixture is cut into pieces and molded in a foaming machine at a pressure of 10-20MPa, a temperature of 170-180℃ and a time of 6-10min to obtain halogen-free expandable flame-retardant EVA foam.

[0009] Furthermore, in (1), the amount of vinyl acetate imidazole phosphate is 100 parts by weight, and the amount of azobisisobutyronitrile is 0.8-1.2 parts by weight.

[0010] Furthermore, the reaction in (1) is carried out at 65-75℃ for 4-6 hours.

[0011] Furthermore, the foaming agent in (2) includes azodicarbonamide.

[0012] Furthermore, in (2), the crosslinking agent includes dicumyl peroxide.

[0013] Furthermore, the accelerator in (2) includes zinc oxide.

[0014] Furthermore, the additives in (2) include any one or combination of stearic acid and zinc stearate.

[0015] Furthermore, the preparation method of vinyl acetate imidazole phosphate includes: adding 100 parts by weight of neopentyl glycol phosphoryl imidazole and 58-66 parts by weight of vinyl chloroacetate to acetonitrile, heating to 70-80℃ and stirring for 24-36 h, and recrystallizing the crude product in an aqueous ethanol solution after vacuum distillation to obtain vinyl acetate imidazole phosphate. The reaction formula is: .

[0016] Furthermore, halogen-free expandable flame-retardant EVA foam is used in lithium battery packaging.

[0017] The beneficial technical effects of this invention are as follows: Vinyl acetate imidazole phosphate undergoes a self-polymerization reaction to obtain polyvinyl acetate imidazole phosphate, which is then foamed and crosslinked with ethylene-vinyl acetate copolymer, sulfonated phenolic resin, azodicarbonamide, dicumyl peroxide, etc., to obtain halogen-free intumescent flame-retardant EVA foam. Polyvinyl acetate imidazole phosphate contains phosphate ester and imidazole groups, which serve as the acid and gas source, while sulfonated phenolic resin acts as the carbon source, forming an intumescent flame retardant. During combustion, the imidazole groups pyrolyze to generate gases such as nitrogen, and the phosphate ester generates phosphoric acid, causing the phenolic resin to dehydrate and char, forming an intumescent char layer on the surface of the EVA foam. This layer provides heat insulation, oxygen barrier, and smoke suppression, reducing the peak heat release rate and total heat release, and improving flame-retardant performance.

[0018] The polyvinyl acetate imidazole phosphate of this invention contains polyvinyl acetate molecules similar to EVA, giving it good compatibility with EVA and minimal impact on the mechanical properties of EVA foam. Simultaneously, the polyvinyl acetate imidazole phosphate contains cationic groups, which form electrostatic interactions with the sulfonic acid anions of sulfonated phenolic resin. This enhances the compatibility between sulfonated phenolic resin and EVA, reduces the influence of phenolic resin on the mechanical properties of EVA foam, and maintains good tear strength in the foam. The resulting EVA foam exhibits good mechanical properties and high flame retardancy, making it more suitable for practical applications in lithium battery packaging shells for new energy vehicles. Detailed Implementation

[0019] The technical solutions in the embodiments of the present invention will be clearly and completely described below. 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] The following ethylene-vinyl acetate copolymer, model UL15028, is from Guangzhou Binlong Chemical Co., Ltd. The sulfonated phenolic resin, model kmkSMP, is from Wuhan Kamico Technology Co., Ltd. The phenolic resin, model XT-356, is from Dongguan Xiangteng Plastics Co., Ltd.

[0021] Neopentyl glycol phosphoryl imidazole was prepared according to the method described in patent publication number CN113248541B, "A phosphorus-nitrogen type flame retardant and its preparation method and application." Under a nitrogen atmosphere, 50 mL of dichloromethane and 50 mmol of imidazole were added to a flask, followed by dropwise addition of 50 mmol of neopentyl glycol phosphoryl chloride (CAS number 4090-55-5). After stirring, the mixture was heated to 60 °C and reacted for 5 h. After cooling, the mixture was filtered, and the filtrate was distilled under reduced pressure, washed with petroleum ether, and the product was recrystallized in dichloromethane to obtain neopentyl glycol phosphoryl imidazole. The structural formula is as follows: .

[0022] Example 1:

[0023] (1) Add 50g of neopentyl glycol phosphoryl imidazole and 29g of vinyl chloroacetate to 500mL of acetonitrile, heat to 75℃ and stir for 36h. After vacuum distillation, recrystallize the crude product in an aqueous ethanol solution to obtain vinyl acetate imidazole phosphate.

[0024] (2) In a nitrogen atmosphere, add 80g of vinyl acetate imidazole phosphate and 0.82g of azobisisobutyronitrile to 500mL of ethanol, heat to 65℃, stir for 6h, filter, wash with ethanol, and dry to obtain polyvinyl acetate imidazole phosphate.

[0025] (3) 1 kg of ethylene-vinyl acetate copolymer, 100 g of polyvinyl acetate imidazole phosphate, 50 g of sulfonated phenolic resin, 12 g of zinc oxide, 5.6 g of stearic acid and 4.5 g of zinc stearate were added to a two-roll mill for blending. Then 30 g of azodicarbonamide was added and the mixture was blended at 80 °C. Then 12 g of dicumyl peroxide was added and blended. The blend was cut into pieces and molded in a foaming machine at a pressure of 10 MPa, a temperature of 170 °C and a time of 10 min to obtain halogen-free expandable flame-retardant EVA foam.

[0026] Example 2:

[0027] (1) Add 50g of neopentyl glycol phosphoryl imidazole and 33g of vinyl chloroacetate to 600mL of acetonitrile, heat to 70℃ and stir for 36h. After vacuum distillation, recrystallize the crude product in an aqueous ethanol solution to obtain vinyl acetate imidazole phosphate.

[0028] (2) In a nitrogen atmosphere, add 80g of vinyl acetate imidazole phosphate and 0.64g of azobisisobutyronitrile to 500mL of ethanol, heat to 75℃, stir for 4h, filter, wash with ethanol, and dry to obtain polyvinyl acetate imidazole phosphate.

[0029] (3) 1 kg of ethylene-vinyl acetate copolymer, 150 g of polyvinyl acetate imidazole phosphate, 120 g of sulfonated phenolic resin, 10 g of zinc oxide, 7 g of stearic acid and 5 g of zinc stearate were added to a two-roll mill for blending. Then 26 g of azodicarbonamide was added and the mixture was blended at 90 °C. Then 17 g of dicumyl peroxide was added and blended. The blend was cut into pieces and molded in a foaming machine at a pressure of 15 MPa, a temperature of 180 °C and a time of 6 min to obtain halogen-free expandable flame-retardant EVA foam.

[0030] Example 3:

[0031] (1) Add 50g of neopentyl glycol phosphoryl imidazole and 29g of vinyl chloroacetate to 600mL of acetonitrile, heat to 80℃ and stir for 24h. After vacuum distillation, recrystallize the crude product in an aqueous ethanol solution to obtain vinyl acetate imidazole phosphate.

[0032] (2) In a nitrogen atmosphere, add 80g of vinyl acetate imidazole phosphate and 0.96g of azobisisobutyronitrile to 600mL of ethanol, heat to 70℃, stir for 4h, filter, wash with ethanol, and dry to obtain polyvinyl acetate imidazole phosphate.

[0033] (3) 1 kg of ethylene-vinyl acetate copolymer, 200 g of polyvinyl acetate imidazole phosphate, 80 g of sulfonated phenolic resin, 16 g of zinc oxide, 4.6 g of stearic acid and 3.4 g of zinc stearate were added to a two-roll mill for blending. Then 45 g of azodicarbonamide was added and the mixture was blended at 80 °C. Then 14 g of dicumyl peroxide was added and blended. The blend was cut into pieces and molded in a foaming machine at a pressure of 20 MPa, a temperature of 170 °C and a time of 8 min to obtain halogen-free expandable flame-retardant EVA foam.

[0034] Comparative Example 1:

[0035] (1) 1 kg of ethylene-vinyl acetate copolymer, 50 g of sulfonated phenolic resin, 12 g of zinc oxide, 5.6 g of stearic acid and 4.5 g of zinc stearate were added to a two-roll mill for blending. Then 30 g of azodicarbonamide was added and the mixture was blended at 80 °C. Then 12 g of dicumyl peroxide was added and blended. The blend was cut into pieces and molded in a foaming machine at a pressure of 10 MPa, a temperature of 170 °C and a time of 10 min to obtain EVA foam.

[0036] Comparative Example 2:

[0037] (1) Add 50g of neopentyl glycol phosphoryl imidazole and 29g of ethyl chloride acrylate (CAS No. 2206-89-5) to 500mL of acetonitrile, heat to 75℃ and stir for 36h. After vacuum distillation, recrystallize the crude product in an aqueous ethanol solution to obtain ethyl acrylate imidazole phosphate, with the structural formula: .

[0038] (2) In a nitrogen atmosphere, add 80g of ethyl acrylate imidazole phosphate and 0.82g of azobisisobutyronitrile to 500mL of ethanol, heat to 65℃, stir for 6h, filter, wash with ethanol, and dry to obtain ethyl acrylate imidazole phosphate.

[0039] (3) 1 kg of ethylene-vinyl acetate copolymer, 100 g of polyethyl acrylate imidazole phosphate, 50 g of sulfonated phenolic resin, 12 g of zinc oxide, 5.6 g of stearic acid and 4.5 g of zinc stearate were added to a two-roll mill for blending. Then 30 g of azodicarbonamide was added and the mixture was blended at 80 °C. Then 12 g of dicumyl peroxide was added and blended. The blend was cut into pieces and molded in a foaming machine at a pressure of 10 MPa, a temperature of 170 °C and a time of 10 min to obtain halogen-free expandable flame-retardant EVA foam.

[0040] Comparative Example 3:

[0041] (1) In a nitrogen atmosphere, add 80g of vinyl acetate (CAS No. 108-05-4) and 0.82g of azobisisobutyronitrile to 500mL of ethanol, heat to 65℃, stir for 6h, filter, wash with ethanol, and dry to obtain polyvinyl acetate.

[0042] (2) 1 kg of ethylene-vinyl acetate copolymer, 100 g of polyvinyl acetate, 50 g of sulfonated phenolic resin, 12 g of zinc oxide, 5.6 g of stearic acid and 4.5 g of zinc stearate were added to a two-roll mill for blending. Then 30 g of azodicarbonamide was added and the mixture was blended at 80 °C. Then 12 g of dicumyl peroxide was added and blended. The blend was cut into pieces and molded in a foaming machine at a pressure of 10 MPa, a temperature of 170 °C and a time of 10 min to obtain EVA foam.

[0043] Comparative Example 4

[0044] (1) Polyvinyl acetate imidazole phosphate was prepared according to the method of Example 1.

[0045] (2) 1 kg of ethylene-vinyl acetate copolymer, 100 g of polyvinyl acetate imidazole phosphate, 50 g of phenolic resin, 12 g of zinc oxide, 5.6 g of stearic acid and 4.5 g of zinc stearate were added to a two-roll mill for blending. Then 30 g of azodicarbonamide was added and the mixture was blended at 80 °C. Then 12 g of dicumyl peroxide was added and blended. The blend was cut into pieces and molded in a foaming machine at a pressure of 10 MPa, a temperature of 170 °C and a time of 10 min to obtain halogen-free expandable flame-retardant EVA foam.

[0046] The combustion performance of EVA foam was tested using a cone calorimeter, with a radiant power of 35 kW / m². 2 Tear strength was tested according to GB / T529-2008 standard.

[0047] Table 1 Performance of EVA Foam

[0048]

[0049] In each embodiment, polyvinyl acetate imidazole phosphate containing phosphate ester and imidazole groups was added to ethylene-vinyl acetate copolymer EVA foam. This phosphate served as both an acid and gas source, while sulfonated phenolic resin acted as a carbon source, forming an intumescent flame retardant. During combustion, the imidazole groups pyrolyzed to generate gases such as nitrogen, and the phosphate ester produced phosphoric acid compounds. This caused the phenolic resin to dehydrate and char, forming an expanded char layer on the surface of the EVA foam. This layer provides heat insulation, oxygen barrier, and smoke suppression, reducing the peak heat release rate and total heat release. Furthermore, the polyvinyl acetate imidazole phosphate contains polyvinyl acetate molecular chains similar to those of EVA (…). The process of adding polyvinyl acetate imidazole phosphate (PVC) to EVA ensures good compatibility with EVA and has minimal impact on the mechanical properties of EVA foam. Furthermore, PVC imidazole phosphate contains cationic groups that form electrostatic interactions with the sulfonate anions of sulfonated phenolic resin. This allows PVC imidazole phosphate to improve the compatibility between sulfonated phenolic resin and EVA, reducing the impact of phenolic resin on the mechanical properties of EVA foam and maintaining good tear strength in the foam material.

[0050] Compared with Example 1, Comparative Example 1 did not add polyvinyl acetate imidazole phosphate. The peak heat release rate and total heat release of the EVA foam material were very large, resulting in poor flame retardant properties. Furthermore, the added sulfonated phenolic resin had poor compatibility with EVA, which had a significant impact on the mechanical properties of the foam material, leading to low tear strength.

[0051] Comparative Example 2's polyethyl acrylate imidazole phosphate contains only polyacrylate molecular chains, and its compatibility with EVA is lower than that of polyvinyl acetate imidazole phosphate, which contains polyvinyl acetate molecular chains. This results in polyethyl acrylate imidazole phosphate and sulfonated phenolic resin having a significant impact on the mechanical properties of the EVA foam material, and the tear strength of the material is lower than that of Example 1.

[0052] The polyvinyl acetate added in Comparative Example 3 does not contain phosphate esters or imidazole groups, and therefore does not form an intumescent flame retardant. The flame retardancy of the foam material is poor. Furthermore, since polyvinyl acetate does not contain cationic groups, it cannot form electrostatic interactions with the sulfonic acid anions of sulfonated phenolic resin, and thus cannot improve the compatibility between sulfonated phenolic resin and EVA. Sulfonated phenolic resin has a significant impact on the mechanical properties of EVA foam material, and the tear strength of the foam material is lower than that in Example 1.

[0053] The phenolic resin added in Comparative Example 4 does not contain sulfonic acid groups and cannot form an electrostatic interaction with polyvinyl acetate imidazole phosphate. As a result, polyvinyl acetate imidazole phosphate cannot improve the compatibility between sulfonated phenolic resin and EVA. Phenolic resin has a significant impact on the mechanical properties of EVA foam material, and the tear strength of the foam material is lower than that in Example 1.

[0054] The preferred embodiments of the present invention disclosed above are merely illustrative of the invention. These preferred embodiments do not exhaustively describe all details, nor do they limit the invention to specific implementations. Clearly, many modifications and variations can be made based on the content of this specification. This specification selects and specifically describes these embodiments to better explain the principles and practical applications of the invention, thereby enabling those skilled in the art to better understand and utilize the invention. The invention is limited only by the claims and their full scope and equivalents.

Claims

1. A halogen-free intumescent flame-retardant EVA foam, characterized in that, The raw material of the halogen-free intumescent flame-retardant EVA foam includes 100 parts by weight of ethylene-vinyl acetate copolymer, 10-20 parts by weight of polyvinyl acetate imidazole phosphate, 5-12 parts by weight of sulfonated phenolic resin, 2.6-4.5 parts by weight of foaming agent, 1.2-1.7 parts by weight of crosslinking agent, 1-1.6 parts by weight of accelerator, and 0.8-1.2 parts by weight of auxiliary agent. The preparation method of the polyvinyl acetate imidazole phosphate includes the following steps: adding vinyl acetate imidazole phosphate and azobisisobutyronitrile into ethanol under nitrogen atmosphere, stirring and reacting, filtering, washing, drying, and obtaining polyvinyl acetate imidazole phosphate. The structural formula of the vinyl acetate imidazole phosphate ester is: .

2. The halogen-free intumescent flame-retardant EVA foam according to claim 1, characterized in that, The amount of the vinyl acetate imidazole phosphate is 100 parts by weight, and the amount of the azobisisobutyronitrile is 0.8-1.2 parts by weight.

3. The halogen-free intumescent flame-retardant EVA foam according to claim 1, wherein, The reaction is carried out at 65-75℃ for 4-6h.

4. The halogen-free intumescent flame-retardant EVA foam according to claim 1, wherein, The foaming agent includes azodicarbonamide, and the crosslinking agent includes dicumyl peroxide.

5. The halogen-free intumescent flame-retarded EVA foam according to claim 1, wherein, The accelerator includes zinc oxide, and the auxiliary agent includes any one or combination of stearic acid and zinc stearate.

6. The halogen-free intumescent flame-retarded EVA foam according to claim 1, wherein, The preparation method of the vinyl acetate imidazole phosphate includes: adding neopentyl glycol phosphoryl imidazole and vinyl chloroacetate into acetonitrile, stirring and reacting at 70-80℃ for 24-36h, distilling under reduced pressure, recrystallizing the crude product, and obtaining vinyl acetate imidazole phosphate.

7. The halogen-free intumescent flame-retarded EVA foam according to claim 6, characterized in that, The amount of the neopentyl glycol phosphoryl imidazole is 100 parts by weight, and the amount of the vinyl chloroacetate is 58-66 parts by weight.

8. A process for the preparation of halogen-free intumescent flame- retarded EVA foam according to any one of claims 1 to 7, characterized in that, The preparation method includes: adding ethylene-vinyl acetate copolymer, polyvinyl acetate imidazole phosphate, sulfonated phenolic resin, accelerator, and auxiliary agent into an open mill for blending, then adding foaming agent, mixing at 80-90℃, adding crosslinking agent for mixing, cutting the mixed material, and molding and foaming in a foaming machine to obtain halogen-free intumescent flame-retardant EVA foam, with a pressure of 10-20MPa, a temperature of 170-180℃, and a time of 6-10min.

9. Application of the halogen-free intumescent flame-retardant EVA foam obtained by the preparation method of claim 8 in lithium battery packaging.

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