Halogen-free intumescent flame-retardant EVA foam as well as preparation method and application thereof in lithium battery packaging

Abstract

The invention relates to the technical field of EVA foam, and discloses halogen-free intumescent flame-retardant EVA foam as well as a preparation method and application thereof in lithium battery packaging. The halogen-free intumescent flame-retardant EVA foam comprises the following raw materials in parts by weight: 100 parts of ethylene-vinyl acetate copolymer, 10-20 parts of polyvinyl acetate imidazole phosphate, 5-12 parts of sulfonated phenolic resin and the like. Polyvinyl acetate imidazole phosphate and sulfonated phenolic resin form an intumescent flame retardant, so that the peak value of the heat release rate and the total heat release amount are reduced, and the flame retardant property is improved. The polyvinyl acetate imidazole phosphate has good compatibility with the EVA, and the compatibility of the sulfonated phenolic resin and the EVA is improved, so that the foam material keeps good tear strength, and the foam material has better practical application in the aspects of lithium battery packaging shells of new energy automobiles and the like.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of EVA foam, in particular to a halogen-free intumescent flame-retardant EVA foam, a preparation method thereof and application thereof in lithium battery packaging. BACKGROUND

[0002] EVA (ethylene-vinyl acetate copolymer) foam has good heat preservation performance, excellent elasticity and strong impact resistance, and is used in shoe materials, thermal insulation materials, battery package shells and the like. However, the flame retardancy of EVA foam material is poor, and it is easy to burn when exposed to fire, which limits its practical application in new energy vehicles, lithium battery packaging and the like. Intumescent flame retardant is a kind of green environmental protection flame retardant, and has important application in foams, plastics, rubbers and other high polymer materials.

[0003] Traditional intumescent flame retardant is added to foams and the like by blending, and the compatibility of the flame retardant with the material is poor, which affects the mechanical properties and the like of the material. Phenolic resin has excellent mechanical properties and good high temperature resistance, and has high char forming property, and is a kind of flame retardant precursor with excellent performance, but the compatibility of phenolic resin with EVA foam is poor, which affects the mechanical strength of the foam material. SUMMARY

[0004] In view of the deficiencies of the prior art, the present application provides a halogen-free intumescent flame-retardant EVA foam, which solves the problem of poor flame retardancy of EVA foam material and maintains good mechanical properties.

[0005] The technical scheme of the present application is: a halogen-free intumescent flame-retardant EVA foam and a preparation method thereof, the raw materials comprising 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.

[0006] The preparation method of the EVA foam comprises the following steps:

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

[0008] (2) The ethylene-vinyl acetate copolymer, polyvinyl acetate imidazole phosphate, sulfonated phenolic resin, accelerator and auxiliary agent are added to an open mill for blending, then the foaming agent is added for mixing at 80-90 DEG C, and then the crosslinking agent is added for mixing, the mixed material is cut into pieces, and the pieces are molded and foamed in a foaming machine at a pressure of 10-20 MPa, a temperature of 170-180 DEG C and a time of 6-10 min to obtain the halogen-free intumescent flame-retardant EVA foam.

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

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

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

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

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

[0014] Further, the auxiliary agent in (2) includes any one or a combination of stearic acid and zinc stearate.

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

[0016]

[0017] Further, the halogen-free intumescent flame-retardant EVA foam is applied to lithium battery packaging.

[0018] The application has the beneficial technical effects that: the vinyl acetate imidazole phosphate is subjected to self-polymerization 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. The polyvinyl acetate imidazole phosphate contains phosphate and imidazole groups, which are used as acid source and gas source, and the sulfonated phenolic resin is used as carbon source to form an intumescent flame retardant. When burning, the imidazole group pyrolyzes to generate nitrogen gas and the phosphate generates phosphoric acid substances, so that the phenolic resin is dehydrated to form carbon, and an intumescent carbon layer is formed on the surface of the EVA foam, which can play the effects of heat insulation, oxygen insulation, smoke suppression, etc., reduces the peak heat release rate and total heat release, and improves the flame-retardant performance.

[0019] The polyvinyl acetate imidazole phosphate of the present application contains polyvinyl acetate molecules similar to EVA, so that the polyvinyl acetate imidazole phosphate has good compatibility with EVA, and has little effect on the mechanical properties of the EVA foam material. At the same time, the polyvinyl acetate imidazole phosphate contains cationic groups, which form electrostatic interaction with the sulfonic acid anions of the sulfonated phenolic resin, so that the polyvinyl acetate imidazole phosphate can improve the compatibility of the sulfonated phenolic resin with EVA, reduce the influence of the phenolic resin on the mechanical properties of the EVA foam material, and make the foam material maintain good tear strength. The EVA foam has good mechanical properties and high flame retardant performance, and has better practical application in the packaging shell of lithium battery of new energy vehicles and the like. DETAILED DESCRIPTION

[0020] The technical solutions in the embodiments of the present application will be described clearly and completely below. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor fall within the scope of protection of the present application.

[0021] The following ethylene-vinyl acetate copolymer, model UL15028, is from Guangzhou Binlong Chemical Co., Ltd. The sulfonated phenolic resin, model kmk SMP, is from Wuhan Kamik Technology Co., Ltd. The phenolic resin, model XT-356, is from Dongguan Xiangteng Plastic Co., Ltd.

[0022] The neopentyl glycol phosphoryl imidazole is prepared according to the method of patent publication number CN113248541B “Phosphorus-nitrogen type flame retardant and preparation method and application thereof”. In a nitrogen atmosphere, 50 mL of dichloromethane, 50 mmol of imidazole are added to a flask, 50 mmol of neopentyl glycol phosphoryl chloride (CAS number 4090-55-5) is added dropwise, stirred and heated to 60℃, reacted for 5h, cooled and filtered, the filtrate is distilled under reduced pressure, washed with petroleum ether, and the product is recrystallized in dichloromethane to obtain neopentyl glycol phosphoryl imidazole. The structural formula is

[0023] Example 1:

[0024] (1) 50g of neopentyl glycol phosphoryl imidazole, 29g of vinyl chloroacetate are added to 500mL of acetonitrile, heated to 75℃ and stirred for 36h, distilled under reduced pressure, and the crude product is recrystallized in an ethanol aqueous solution to obtain vinyl acetate imidazole phosphate.

[0025] (2) In a nitrogen atmosphere, 80g of vinyl acetate imidazole phosphate, 0.82g of azobisisobutyronitrile are added to 500mL of ethanol, heated to 65℃, stirred for 6h, filtered, washed with ethanol, and dried to obtain polyvinyl acetate imidazole phosphate.

[0026] (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, 4.5 g of zinc stearate were added to an open mill and blended, then 30 g of azodicarbonamide was added and mixed at 80°C, and 12 g of dicumyl peroxide was added and mixed, the mixture was cut, and molded and foamed in a foaming machine at a pressure of 10 MPa, a temperature of 170°C, and a time of 10 min to obtain a halogen-free intumescent flame-retardant EVA foam.

[0027] Example 2:

[0028] (1) 50 g of neopentyl glycol phosphoric imidazole, 33 g of vinyl chloroacetate were added to 600 mL of acetonitrile, heated to 70°C and stirred for 36 h, and the crude product was recrystallized in an aqueous ethanol solution after distillation under reduced pressure to obtain vinyl acetate imidazole phosphate.

[0029] (2) 80 g of vinyl acetate imidazole phosphate, 0.64 g of azobisisobutyronitrile were added to 500 mL of ethanol under a nitrogen atmosphere, heated to 75°C and stirred for 4 h, filtered, washed with ethanol, and dried to obtain polyvinyl acetate imidazole phosphate.

[0030] (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, 5 g of zinc stearate were added to an open mill and blended, then 26 g of azodicarbonamide was added and mixed at 90°C, and 17 g of dicumyl peroxide was added and mixed, the mixture was cut, and molded and foamed in a foaming machine at a pressure of 15 MPa, a temperature of 180°C, and a time of 6 min to obtain a halogen-free intumescent flame-retardant EVA foam.

[0031] Example 3:

[0032] (1) 50 g of neopentyl glycol phosphoric imidazole, 29 g of vinyl chloroacetate were added to 600 mL of acetonitrile, heated to 80°C and stirred for 24 h, and the crude product was recrystallized in an aqueous ethanol solution after distillation under reduced pressure to obtain vinyl acetate imidazole phosphate.

[0033] (2) 80 g of vinyl acetate imidazole phosphate, 0.96 g of azobisisobutyronitrile were added to 600 mL of ethanol under a nitrogen atmosphere, heated to 70°C and stirred for 4 h, filtered, washed with ethanol, and dried to obtain polyvinyl acetate imidazole phosphate.

[0034] (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, 3.4 g of zinc stearate were added to an open mill and mixed, then 45 g of azodicarbonamide was added and mixed at 80°C, and 14 g of dicumyl peroxide was added and mixed, the mixed material was cut, and was molded and foamed in a foaming machine at a pressure of 20 MPa, a temperature of 170°C, and a time of 8 min to obtain a halogen-free intumescent flame-retardant EVA foam.

[0035] Comparative Example 1

[0036] (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, 4.5 g of zinc stearate were added to an open mill and mixed, then 30 g of azodicarbonamide was added and mixed at 80°C, and 12 g of dicumyl peroxide was added and mixed, the mixed material was cut, and was molded and foamed in a foaming machine at a pressure of 10 MPa, a temperature of 170°C, and a time of 10 min to obtain an EVA foam.

[0037] Comparative Example 2

[0038] (1) 50 g of neopentyl glycol phosphoric imidazole, 29 g of chloroethyl acrylate (CAS No. 2206-89-5) were added to 500 mL of acetonitrile and stirred at 75°C for 36 h, and after distillation under reduced pressure, the crude product was recrystallized in an aqueous solution of ethanol to obtain ethyl acrylate imidazole phosphate, the structural formula of which is

[0039] (2) 80 g of ethyl acrylate imidazole phosphate, 0.82 g of azobisisobutyronitrile were added to 500 mL of ethanol under a nitrogen atmosphere, heated to 65°C, stirred for 6 h, filtered, washed with ethanol, and dried to obtain polyethyl acrylate imidazole phosphate.

[0040] (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, 4.5 g of zinc stearate were added to an open mill and mixed, then 30 g of azodicarbonamide was added and mixed at 80°C, and 12 g of dicumyl peroxide was added and mixed, the mixed material was cut, and was molded and foamed in a foaming machine at a pressure of 10 MPa, a temperature of 170°C, and a time of 10 min to obtain a halogen-free intumescent flame-retardant EVA foam.

[0041] Comparative Example 3

[0042] (1) In a nitrogen atmosphere, 80 g of vinyl acetate (CAS No. 108-05-4) was added to 500 mL of ethanol, 0.82 g of azobisisobutyronitrile was added, heated to 65°C, stirred for 6 h, washed with ethanol after filtration, and dried to obtain polyvinyl acetate.

[0043] (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 an open mill and blended, then 30 g of azodicarbonamide was added and mixed at 80°C, and then 12 g of dicumyl peroxide was added and mixed to obtain an EVA foam.

[0044] Comparative Example 4

[0045] (1) Polyvinyl acetate imidazole phosphate was prepared according to the method of Example 1.

[0046] (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 an open mill and blended, then 30 g of azodicarbonamide was added and mixed at 80°C, and then 12 g of dicumyl peroxide was added and mixed to obtain an EVA foam.

[0047] The combustion performance of the EVA foam was tested by a cone calorimeter with a radiant power of 35 kW / m 2 The tear strength was tested according to GB / T529-2008 standard.

[0048] Table 1 Properties of EVA foam

[0049]

[0050] Each example added polyvinyl acetate imidazole phosphate containing phosphate and imidazole groups to ethylene-vinyl acetate copolymer EVA foam, which served as an acid source and a gas source, and sulfonated phenolic resin as a carbon source to form an intumescent flame retardant. During combustion, the imidazole group pyrolyzed to generate nitrogen gas and the phosphate generated phosphoric acid, which dehydrated the phenolic resin to form carbon, forming an expanded carbon layer on the surface of the EVA foam, which had the effect of heat insulation, oxygen insulation, and smoke suppression, reducing the peak heat release rate and total heat release. And the polyvinyl acetate imidazole phosphate contains a polyvinyl acetate molecular chain similar to EVA The polyvinyl acetate imidazole phosphate ester has good compatibility with EVA, has little influence on the mechanical properties of the EVA foam material, and contains cationic groups, which form electrostatic interaction with sulfonic acid anions of the sulfonated phenolic resin, so that the polyvinyl acetate imidazole phosphate ester can improve the compatibility of the sulfonated phenolic resin with EVA, reduce the influence of the phenolic resin on the mechanical properties of the EVA foam material, and make the foam material maintain good tear strength.

[0051] In comparison with Example 1, the peak heat release rate and total heat release amount of the EVA foam material of Comparative Example 1 are very large, the flame retardant performance is poor, and the sulfonated phenolic resin added has poor compatibility with EVA, has great influence on the mechanical properties of the foam material, and results in low tear strength.

[0052] The polyethyl acrylate imidazole phosphate ester of Comparative Example 2 only contains a polyethyl acrylate molecular chain, and has lower compatibility with EVA than the polyvinyl acetate imidazole phosphate ester containing a polyvinyl acetate molecular chain, so that the polyethyl acrylate imidazole phosphate ester and the sulfonated phenolic resin have great influence on the mechanical properties of the EVA foam material, and the tear strength of the material is lower than that of Example 1.

[0053] The polyvinyl acetate added in Comparative Example 3 does not contain phosphate ester and imidazole groups, does not form intumescent flame retardant, and has poor flame retardancy of the foam material, and the polyvinyl acetate does not contain cationic groups, cannot form electrostatic interaction with sulfonic acid anions of the sulfonated phenolic resin, cannot improve the compatibility of the sulfonated phenolic resin with EVA, has great influence on the mechanical properties of the EVA foam material, and the tear strength of the foam material is lower than that of Example 1.

[0054] The phenolic resin added in Comparative Example 4 does not contain sulfonic acid groups, cannot form electrostatic interaction with the polyvinyl acetate imidazole phosphate ester, so that the polyvinyl acetate imidazole phosphate ester cannot improve the compatibility of the sulfonated phenolic resin with EVA, the phenolic resin has great influence on the mechanical properties of the EVA foam material, and the tear strength of the foam material is lower than that of Example 1.

[0055] The preferred embodiments of the present application disclosed above are only used to help explain the present application. The preferred embodiments do not describe all the details, and do not limit the present application to the specific embodiments. Obviously, many modifications and changes can be made according to the contents of the present application. The embodiments are selected and specifically described in the present specification in order to better explain the principles and practical applications of the present application, so that those skilled in the art can well understand and utilize the present application. The present application 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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