Lightweight flame-retardant EVA foam material and preparation method thereof

Abstract

The invention discloses a lightweight flame-retardant EVA foaming material and a preparation method thereof, and belongs to the technical field of flame-retardant foaming materials, and the lightweight flame-retardant EVA foaming material specifically comprises the following components in parts by weight: 80-90 parts of EVA, 15-20 parts of olefin modified EVA, 18-25 parts of boron modified polysiloxane, 4-6 parts of a phosphorus-aluminum flame retardant, 10-12 parts of activated supported silicon, 0.8-1.0 part of a cross-linking agent and 3-5 parts of an additive. Olefin modified EVA and EVA are mixed through boron modified polysiloxane and a phosphorus-aluminum flame retardant, then the mixture is mixed with activated loaded silicon and a cross-linking agent, and foaming is performed, so that the mechanical property and heat resistance of the foaming material are effectively improved, and the flame retardant property and the lightweight property of the foaming material are also improved.

Description

Technical Field

[0001] The invention relates to the technical field of flame-retardant foam material processing, and in particular to a lightweight flame-retardant EVA foam material and a preparation method thereof. Background Art

[0002] Foaming materials are materials that form a porous structure in a base material (such as plastic, rubber, resin, etc.) through physical or chemical methods. Ethylene-vinyl acetate copolymer (EVA) foaming materials are widely used in footwear, packaging, building insulation and other fields due to their light weight, flexibility and strong weather resistance.

[0003] In the prior art, the invention patent with publication number CN109161091A relates to a highly flame-retardant EVA foam material and a preparation method thereof. The material is prepared from 100 parts of a modified magnesium hydroxide-EVA composite material, 3-6 parts of a foaming agent, 1-3 parts of zinc oxide, 1-2 parts of stearic acid, 0.5-1.0 parts of a cross-linking agent, and 30-100 parts of a filler. The modified magnesium hydroxide-EVA composite material comprises magnesium hydroxide modified with a modified resin. The resulting foamed material has high flame retardancy, an oxygen index exceeding 35, and possesses superior tensile strength and a higher elongation at break.

[0004] However, when preparing traditional foaming materials, the foaming agent is directly mixed with the EVA material. During the preparation, the foaming agent is unevenly dispersed, resulting in excessive local foaming and causing large-diameter pores in the EVA foam material, resulting in its rebound performance and mechanical properties to be further improved. In addition, the foam material has abundant pores and is prone to shrinkage and deformation in a high-temperature environment, resulting in poor dimensional stability. In addition, in order to improve the flame retardant properties of the flame retardant EVA foam material, a large amount of flame retardant additives are added, which increases the density, resulting in the lightweight effect of the EVA foam material to be further improved. Summary of the Invention

[0005] The object of the present invention is to provide a lightweight flame-retardant EVA foam material and a preparation method thereof, so as to solve the technical problem in the prior art that the rebound performance, mechanical strength, dimensional stability and lightweight performance of the flame-retardant EVA foam material need to be further improved.

[0006] The object of the present invention can be achieved by the following technical solution: a lightweight flame-retardant EVA foam material, comprising the following components in parts by weight: 80-90 parts of EVA, 15-20 parts of olefin-modified EVA, 18-25 parts of boron-modified polysiloxane, 4-6 parts of phosphorus-aluminum flame retardant, 10-12 parts of activated loaded silicon, 0.8-1.0 parts of cross-linking agent and 3-5 parts of additives;

[0007] The preparation method of the activated loaded silicon comprises the following steps: mixing azodicarbonamide and dimethyl sulfoxide and stirring until the system is dissolved; adding porous silicon dioxide to the reaction system, ultrasonically dispersing the mixture for 40-60 minutes; dripping purified water into the reaction system, ultrasonically dispersing the mixture for 30-50 minutes after the dripping is complete, and performing post-processing to obtain the loaded porous silicon; mixing the loaded porous silicon and an ethanol solution, ultrasonically dispersing the mixture for 50-70 minutes, raising the temperature of the reaction system to 70-80°C, adding tetraethyl orthosilicate to the reaction system, preserving the reaction temperature for 90-100 minutes, lowering the temperature of the reaction system to 50-60°C, adding KH-560 to the reaction system, preserving the reaction temperature for 60-80 minutes, and performing post-processing to obtain the activated loaded silicon.

[0008] The synthetic reaction mechanism of activated supported silicon is:

[0009] During the reaction, ultrasonic dispersion is used to promote the entry of azodicarbonamide molecules into the pore structure of porous silica. The azodicarbonamide molecules enter the pores of porous silica through physical adsorption or filling. Purified water serves as a poor solvent for azodicarbonamide. Its addition reduces the solubility of azodicarbonamide, so that the azodicarbonamide is solidified and loaded on the porous silica to prepare loaded porous silicon. In an ethanol solution, ethyl orthosilicate is hydrolyzed into silanol and then condensed. Modified polysiloxane is coated on the loaded porous silicon, and then the surface is modified by KH-560 to prepare activated loaded silicon.

[0010] Furthermore, the additives are composed of zinc stearate, talc, ethylene bisstearamide, and antistatic agent SN in a weight ratio of 5:2:3:2, and the cross-linking agent is dicumyl peroxide.

[0011] Furthermore, in the preparation process of loaded porous silicon, the amount ratio of azodicarbonamide, dimethyl sulfoxide, porous silica and purified water is 1-1.5g:5mL:2-3g:40mL, and the post-treatment includes: after the completion of ultrasound, filtration, washing the filter cake with purified water twice and then drying, transferring the filter cake to a drying oven at a temperature of 50-60°C, and drying to constant weight to obtain loaded porous silicon; in the preparation process of activated loaded silicon, the loaded porous silicon, ethanol solution, positive The dosage ratio of ethyl silicate and KH-560 is 5g:50mL:2-3g:0.8-1.2g. The ethanol solution is composed of anhydrous ethanol, purified water and sodium hydroxide in a dosage ratio of 10mL:3mL:0.02g. The post-treatment includes: after the reaction is completed, the temperature of the reaction system is lowered to room temperature, filtered, the filter cake is washed with purified water until neutral and then dried, and the filter cake is transferred to a drying oven at a temperature of 50-60°C and dried to constant weight to obtain activated supported silicon.

[0012] Furthermore, the preparation method of the boron-modified polysiloxane comprises the following steps:

[0013] A1. Under an inert atmosphere, hydroxyl-terminated polysiloxane and toluene were mixed and stirred to dissolve, 3-isocyanate propylene was added to the reaction system, the temperature of the reaction system was raised to 50-60°C, the reaction was kept warm for 60-80 minutes, and post-treated to obtain modified polysilane;

[0014] A2. The modified polysiloxane and boric acid are mixed and stirred. The reaction system is evacuated to a vacuum and then heated to 175-185° C. The reaction is kept at this temperature for 120-150 minutes. The temperature of the reaction system is then lowered to room temperature and the material is discharged to obtain boron-modified polysiloxane.

[0015] The synthetic reaction mechanism of boron-modified polysiloxane is:

[0016]

[0017] During the reaction, the hydroxyl groups on the hydroxyl-terminated polysiloxane molecules undergo condensation reaction with the isocyanate groups on the 3-isocyanate propylene molecules to form olefin double bond modifications, thereby preparing modified polysiloxane. Under high temperature and negative pressure, the three hydroxyl groups of boric acid undergo dehydration condensation with the silanols at the ends of the polysiloxane to form silaboroxane bonds (≡Si-OBO-Si≡), constructing a three-dimensional cross-linked network. The vacuum environment accelerates the removal of the generated water, pushing the reaction toward the cross-linking direction, thereby preparing boron-modified polysiloxane.

[0018] Furthermore, in step A1, the molar ratio of the 3-isocyanate propylene to the hydroxyl group in the hydroxy-modified siloxane is 0.2:1, the amount ratio of the hydroxyl-terminated polysiloxane to toluene is 1 g:5 mL, and the post-treatment includes: raising the reaction temperature to 80°C, and removing low-boiling substances under reduced pressure to obtain a modified polysiloxane; in step A2, the molar ratio of the boric acid to the hydroxyl group in the modified siloxane is 1:1.

[0019] Furthermore, the preparation method of the phosphorus-aluminum flame retardant is as follows: 2-(aminomethyl)-2-methyl-1,3-propylenediamine, purified water, allylphosphinic acid and formaldehyde solution are mixed and stirred, the temperature of the reaction system is increased to the system reflux, the reaction is kept warm for 90-110 minutes, the temperature of the reaction system is reduced to room temperature, sodium hydroxide solution is added to the reaction system, the pH of the system is adjusted to 6, aluminum isopropoxide is added to the reaction system, the temperature of the reaction system is increased to the system reflux, the reaction is kept warm for 120-160 minutes, and post-processing is performed to obtain the phosphorus-aluminum flame retardant.

[0020] The synthetic reaction mechanism of phosphorus-aluminum flame retardant is:

[0021]

[0022] During the reaction, under reflux conditions, formaldehyde condenses with the amino group of the amine to generate an iminium cation intermediate, and then the PH bond of the allylphosphinic acid undergoes nucleophilic addition to the methylene group to form a PCN bond, releasing water molecules. Sodium hydroxide is added to neutralize the acidic byproducts generated by the reaction, while stabilizing the phosphonate structure and preventing the hydrolysis of the PO bond. At the same time, aluminum isopropoxide reacts with water under reflux conditions to generate hydroxyaluminum and isopropanol. The hydroxyl group on the hydroxyaluminum molecule condenses with the P-OH of the phosphorus-nitrogen polymer to form a PO-Al bond, thereby preparing an olefin double-bond modified phosphorus-aluminum flame retardant.

[0023] Furthermore, the amount ratio of the 2-(aminomethyl)-2-methyl-1,3-propylenediamine, purified water, allylphosphinic acid, formaldehyde solution and aluminum isopropoxide is 10g:100mL:54g:110mL:10g, the formaldehyde solution is composed of formaldehyde and water, and the mass fraction is 10%. The post-treatment includes: after the reaction is completed, the temperature of the reaction system is lowered to room temperature, filtered, the filter cake is washed three times with purified water and ethanol in sequence, and then dried, the filter cake is transferred to a drying oven at a temperature of 60-70°C, and dried to constant weight to obtain a phosphorus-aluminum flame retardant.

[0024] Furthermore, the preparation method of olefin-modified EVA comprises the following steps:

[0025] B1. EVA, 3-butene-1-ol and toluene were mixed, the reaction system temperature was raised to 80-90°C, and the mixture was stirred at this temperature until the system was dissolved. An initiator was added to the reaction system, and the mixture was reacted at this temperature for 3-5 hours. After post-treatment, hydroxyl-modified EVA was obtained.

[0026] B2. Under the protection of inert gas, hydroxyl-modified EVA and toluene were mixed, the temperature of the reaction system was raised to 50-60°C, and the mixture was stirred until the reaction system was dissolved. 3-isocyanate propylene was added to the reaction system, and the mixture was kept warm for 60-80 minutes. After post-treatment, olefin-modified EVA was obtained.

[0027] The synthetic reaction mechanism of olefin-modified EVA is:

[0028] During the reaction, AIBN decomposes under heating to generate isobutyronitrile free radicals, which attack the α-H in the EVA main chain to form EVA macromolecular free radicals. The EVA macromolecular free radicals react with the double bond of 3-butene-1-ol to introduce hydroxyl groups into the EVA side chain to prepare hydroxyl-modified EVA; then the hydroxyl groups on the hydroxyl-modified EVA molecules undergo condensation reaction with the isocyanate groups on the 3-isocyanate propylene molecules to form unsaturated olefin modifications to prepare olefin-modified EVA.

[0029] Furthermore, in step B1, the amount ratio of the EVA, 3-butene-1-ol, toluene and initiator is 10-12g:0.8-1.1g:30mL:0.05g, the initiator is azobisisobutyronitrile, and the post-treatment includes: after the reaction is completed, the temperature of the reaction system is reduced to room temperature, purified water is added to the reaction system, stirred and dispersed for 20-30min, allowed to stand for separation, the organic phase is washed twice with purified water and then dried, the organic phase is transferred to an evaporator at a temperature of 80-90°C, and low-boiling substances are removed by distillation under reduced pressure to obtain hydroxy-modified EVA; in step B2, the amount ratio of the hydroxy-modified EVA, toluene and 3-isocyanate propylene is 2g:10mL:0.8-1g, and the post-treatment includes: after the reaction is completed, the temperature of the reaction system is increased to 80-90°C, and low-boiling substances are removed by distillation under reduced pressure to obtain olefin-modified EVA.

[0030] The present invention also provides a method for preparing a lightweight flame-retardant EVA foam material, comprising the following steps:

[0031] S1. Add EVA, olefin-modified EVA, boron-modified polysiloxane, phosphorus-aluminum flame retardant and additives to an internal mixer, set the internal mixer temperature to 80-90° C., and mix for 15-20 min. Add activated loaded silicon and cross-linking agent to the internal mixer, raise the temperature of the internal mixer to 120-130° C. at a heating rate of 3-5° C. / min, and then discharge the material. Transfer the material to an open mixer at a temperature of 90-100° C., set the roller distance to 2-3 mm, and mix in a triangle bag for 3-5 min. Cool to room temperature, and discharge to obtain a mixed masterbatch.

[0032] S2. Evenly put the mixed masterbatch into the mold and close the mold. Set the molding pressure to 9-11MPa and the molding temperature to 190-200℃. Keep the heat and pressure for 10-12 minutes. After the mold cools down to room temperature, discharge the material to obtain the foaming material.

[0033] The present invention has the following beneficial effects:

[0034] 1. The present invention is to mix olefin-modified EVA with EVA by boron-modified polysiloxane and phosphorus-aluminum flame retardant, and then mix them with activated loaded silicon and a crosslinking agent. Under high temperature and high pressure environment, azodicarbonamide acts as a foaming agent to decompose gas while being restricted by high pressure to form a uniform closed-cell structure. By mixing olefin-modified EVA with EVA, unsaturated olefin modification is formed in EVA by utilizing the similarity and compatibility of molecular chains. The initiator diisopropylbenzene peroxide triggers the dynamic cross-linking of unsaturated olefin double bonds to absorb energy and recover, thereby improving the compression rebound performance of the foamed material. Boric acid condenses with polysiloxane to form Si-OB bonds, which can inhibit the relaxation of molecular chains at high temperatures and reduce thermal shrinkage. The boron cross-linking network is dispersed in the matrix, which helps to improve the dimensional stability of the material. At the same time, the three-dimensional boron cross-linking network disperses stress, reduces bubble collapse, and enhances compressive strength. The flexible chain segments of polysiloxane are compatible with EVA to form a "rigid and flexible" structure, thereby improving tear resistance.

[0035] 2. The present invention also uses 2-(aminomethyl)-2-methyl-1,3-propylenediamine and allylphosphinic acid in the presence of formaldehyde as a catalyst to prepare an olefin-modified phosphorus-aluminum flame retardant. The polyolefin modified on the molecule of the phosphorus-aluminum flame retardant can serve as a reaction active site to form a multi-crosslinked network under the action of a cross-linking agent. Moreover, the phosphorus and aluminum elements in the phosphorus-aluminum flame retardant can form a stable compound that is not easily decomposed at high temperatures, thereby helping to maintain the dimensional stability of the material. The Al-OP network in the phosphorus-aluminum flame retardant molecule can catalyze EVA into carbon, forming a dense carbon layer, inhibiting thermal degradation and shrinkage. Moreover, the phosphorus-aluminum flame retardant and the boron-modified polysiloxane form a "gas phase-condensed phase" double barrier, which improves the flame retardant properties of the material while maintaining the high-temperature resilience of the material.

[0036] 3. The present invention also uses porous silica as a carrier to load the foaming agent azodicarbonamide, and then modifies it with epoxy groups on the outside after coating with polysiloxane, so as to avoid the epoxy groups from contacting with the amino groups on the azodicarbonamide molecules to cause ring-opening condensation during the reaction, thereby maintaining the reactivity of the epoxy groups on the molecules. The epoxy groups modified on the surface can improve its dispersion performance and can also condense with active functional groups on other molecules under high temperature, so that the silica particles can be more evenly dispersed in the reaction system while improving the mechanical strength of the material. Moreover, after the foaming agent is evenly dispersed along with the silica particles, it decomposes in a high temperature environment to produce a large amount of gas, thereby forming uniform pores in the material, improving the foaming ratio while avoiding the formation of large voids and reducing the density of the material. DETAILED DESCRIPTION

[0037] The technical solutions of the present invention will be clearly and completely described below in conjunction with the embodiments. Obviously, the embodiments described are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0038] In the present invention, EVA is ethylene vinyl acetate, wherein the vinyl acetate content is 18-20%;

[0039] In the present invention, the hydroxyl-terminated polysiloxane is a hydroxy silicone oil with a viscosity of 22-25 mm 2 / s (25 ° C), hydroxyl content is 7.5-8.5%;

[0040] In the present invention, the porous silica is a mesoporous silica hollow sphere, which is selected from Qinghe Chaotai Metal Materials Co., Ltd., with a particle size of 200-900nm, a pore size of 2-3nm, and a specific area of ​​2400m 2 / g, pore volume 20.4m 2 / g;

[0041] In the present invention, the CAS number of phosphorous acid is 13598-36-2;

[0042] In the present invention, the CAS number of allylphosphinic acid is 66899-05-6;

[0043] In the present invention, KH-560 is γ-glycidyloxypropyltrimethoxysilane, and its CAS number is 2530-83-8.

[0044] Example 1

[0045] This embodiment provides a method for preparing a lightweight flame-retardant EVA foam material, comprising the following steps:

[0046] Step 1: Preparation of olefin-modified EVA

[0047] Weigh: 500g of EVA, 40g of 3-butene-1-ol and 1500mL of toluene are added to a reaction flask and mixed and stirred. The temperature of the reaction flask is raised to 80°C, and the mixture is stirred and maintained until the system is dissolved. 2.5g of azobisisobutyronitrile as an initiator is added to the reaction flask, and the mixture is kept warm for 3h. The temperature of the reaction flask is lowered to room temperature, 300mL of purified water is added to the reaction flask, and the mixture is stirred and dispersed for 20min. The mixture is allowed to stand for separation, and the organic phase is washed twice with purified water and then dried. The organic phase is transferred to an evaporator at a temperature of 80°C, and low-boiling substances are evaporated under reduced pressure to obtain hydroxyl-modified EVA;

[0048] Weigh: 400 g of hydroxyl-modified EVA and 2000 mL of toluene are added to a reaction flask protected by argon and stirred to mix. The temperature of the reaction flask is raised to 50°C and stirred until the system is dissolved. 160 g of 3-isocyanate propylene is added to the reaction flask and the reaction is kept warm for 60 minutes. The temperature of the reaction flask is raised to 80°C and low-boiling substances are evaporated under reduced pressure to obtain olefin-modified EVA.

[0049] Step 2: Preparation of boron-modified polysiloxane

[0050] Weigh: 100 mL of hydroxyl-terminated polysiloxane and 500 mL of toluene are added to a reaction flask protected by argon, mixed and stirred until dissolved, and the amount of 3-isocyanate added is calculated as 0.2 times the molar amount of hydroxyl groups in the hydroxyl-terminated polysiloxane in the reaction flask. The 3-isocyanate is added to the reaction flask and stirred. The temperature of the reaction flask is raised to 50° C. and the reaction is kept at this temperature for 60 minutes. The reaction temperature is then raised to 80° C. and low-boiling substances are evaporated under reduced pressure to obtain a modified polysiloxane;

[0051] Weigh: add the modified polysiloxane to a reaction flask and stir, calculate the amount of boric acid added based on the molar amount of hydroxyl groups in the modified polysiloxane, and add it to the reaction flask and stir, evacuate the reaction flask to a vacuum pressure of 0.1 MPa, heat the reaction flask to 175°C, keep the temperature for reaction for 120 minutes, lower the temperature of the reaction flask to room temperature, and discharge the material to obtain boron-modified polysiloxane.

[0052] Step 3: Preparation of phosphorus-aluminum flame retardant

[0053] Weigh: 100 g of 2-(aminomethyl)-2-methyl-1,3-propylenediamine, 1000 mL of purified water, 540 g of allyl phosphinic acid and 1100 mL of 10 wt% formaldehyde solution were added to a reaction flask and mixed and stirred. The temperature of the reaction flask was raised to reflux of the system, and the reaction was kept warm for 90 minutes. The temperature of the reaction flask was lowered to room temperature. 0.5 mol / L sodium hydroxide solution was added to the reaction flask to adjust the pH of the system to 6. 100 g of aluminum isopropoxide was added to the reaction flask, the temperature of the reaction flask was raised to reflux of the system, and the reaction was kept warm for 120 minutes. The temperature of the reaction flask was lowered to room temperature, and the filter cake was washed three times with purified water and ethanol in sequence and then dried. The filter cake was transferred to a drying oven at 60°C and dried to constant weight to obtain a phosphorus-aluminum flame retardant.

[0054] Step 4: Preparation of activated loaded silicon

[0055] Weigh: 50 g of azodicarbonamide and 250 mL of dimethyl sulfoxide are added to a reaction flask and stirred until the system is dissolved. 100 g of porous silica is added to the reaction flask and ultrasonically dispersed for 40 min. 2000 mL of purified water is added dropwise to the reaction flask. After the addition is complete, ultrasonically disperse for 30 min and filter. The filter cake is washed twice with purified water and then dried. The filter cake is transferred to a drying oven at 50°C and dried to constant weight to obtain loaded porous silicon.

[0056] Mix anhydrous ethanol, purified water, and sodium hydroxide in a ratio of 10 mL: 3 mL: 0.02 g to obtain an ethanol solution for later use.

[0057] Weigh: 200 g of loaded porous silicon and 2000 mL of ethanol solution are added to a reaction flask and mixed, ultrasonically dispersed for 50 minutes, the temperature of the reaction flask is raised to 70°C, 80 g of ethyl orthosilicate is added to the reaction flask, and the reaction is kept warm for 90 minutes. The temperature of the reaction flask is lowered to 50°C, 32 g of KH-560 is added to the reaction flask, and the reaction is kept warm for 60 minutes. The temperature of the reaction flask is lowered to room temperature, filtered, and the filter cake is washed with purified water until neutral and then dried. The filter cake is transferred to a drying oven at a temperature of 50°C and dried to constant weight to obtain activated loaded silicon.

[0058] Step 5: Prepare the foaming material.

[0059] Zinc stearate, talc, ethylene bisstearamide, and antistatic agent SN were mixed uniformly in a weight ratio of 5:2:3:2 to obtain an additive;

[0060] Weigh 80 parts of EVA, 15 parts of olefin-modified EVA, 18 parts of boron-modified polysiloxane, 4 parts of phosphorus-aluminum flame retardant, and 3 parts of additives in parts by weight and add them to an internal mixer. Set the internal mixer temperature to 80°C and mix for 15 minutes. Add 10 parts of activated loaded silicon and 0.8 parts of dicumyl peroxide, a cross-linking agent, to the internal mixer. Heat the internal mixer to 120°C at a heating rate of 3°C / min and then discharge the material. Transfer the material to an open mixer at 90°C, set the roller spacing to 2mm, and mix in a triangle bag for 3 minutes. Cool to room temperature and discharge to obtain a mixed masterbatch.

[0061] After the mixed masterbatch is evenly placed in the mold, the mold is closed, the molding pressure is set to 9 MPa, the molding temperature is 190°C, and the heat and pressure are kept for 10 minutes. After the mold is cooled to room temperature, the material is discharged to obtain a foamed material.

[0062] Example 2

[0063] This embodiment provides a method for preparing a lightweight flame-retardant EVA foam material, comprising the following steps:

[0064] Step 1: Preparation of olefin-modified EVA

[0065] Weigh: 550g of EVA, 48g of 3-butene-1-ol and 1500mL of toluene are added to a reaction flask and mixed and stirred. The temperature of the reaction flask is raised to 85°C, and the mixture is stirred and maintained until the system is dissolved. 2.5g of azobisisobutyronitrile as an initiator is added to the reaction flask, and the mixture is kept warm for 4h. The temperature of the reaction flask is lowered to room temperature, 300mL of purified water is added to the reaction flask, and the mixture is stirred and dispersed for 25min. The mixture is allowed to stand for separation, and the organic phase is washed twice with purified water and then dried. The organic phase is transferred to an evaporator at a temperature of 85°C, and low-boiling substances are evaporated under reduced pressure to obtain hydroxyl-modified EVA;

[0066] Weigh: 400 g of hydroxyl-modified EVA and 2000 mL of toluene are added to a reaction flask protected by argon and stirred to mix. The temperature of the reaction flask is raised to 55°C and stirred until the system is dissolved. 180 g of 3-isocyanate propylene is added to the reaction flask and the reaction is kept warm for 70 minutes. The temperature of the reaction flask is raised to 85°C and low-boiling substances are evaporated under reduced pressure to obtain olefin-modified EVA.

[0067] Step 2: Preparation of boron-modified polysiloxane

[0068] Weigh: 100 mL of hydroxyl-terminated polysiloxane and 500 mL of toluene are added to a reaction flask protected by argon, mixed and stirred until dissolved, and the amount of 3-isocyanate added is calculated as 0.2 times the molar amount of hydroxyl groups in the hydroxyl-terminated polysiloxane in the reaction flask. The 3-isocyanate is added to the reaction flask and stirred. The temperature of the reaction flask is raised to 55° C. and the reaction is kept at this temperature for 70 minutes. The reaction temperature is then raised to 80° C. and low-boiling substances are evaporated under reduced pressure to obtain a modified polysiloxane;

[0069] Weigh: add the modified polysiloxane to the reaction flask and stir, calculate the amount of boric acid added based on the molar amount of hydroxyl groups in the modified polysiloxane, and add it to the reaction flask and stir, evacuate the reaction flask to a vacuum pressure of 0.1 MPa, heat the reaction flask to 180°C, keep the temperature for reaction for 135 minutes, lower the temperature of the reaction flask to room temperature, and discharge the material to obtain boron-modified polysiloxane.

[0070] Step 3: Preparation of phosphorus-aluminum flame retardant

[0071] Weigh: 100 g of 2-(aminomethyl)-2-methyl-1,3-propylenediamine, 1000 mL of purified water, 540 g of allyl phosphinic acid and 1100 mL of 10 wt% formaldehyde solution were added to a reaction flask and mixed and stirred. The temperature of the reaction flask was raised to reflux of the system, and the reaction was kept warm for 100 minutes. The temperature of the reaction flask was lowered to room temperature. 0.5 mol / L sodium hydroxide solution was added to the reaction flask to adjust the pH of the system to 6. 100 g of aluminum isopropoxide was added to the reaction flask, the temperature of the reaction flask was raised to reflux of the system, and the reaction was kept warm for 140 minutes. The temperature of the reaction flask was lowered to room temperature, and the filter cake was washed three times with purified water and ethanol in sequence and then dried. The filter cake was transferred to a drying oven at 65° C. and dried to constant weight to obtain a phosphorus-aluminum flame retardant.

[0072] Step 4: Preparation of activated loaded silicon

[0073] Weigh: 63 g of azodicarbonamide and 250 mL of dimethyl sulfoxide are added to a reaction flask and stirred until the system is dissolved. 125 g of porous silica is added to the reaction flask and ultrasonically dispersed for 50 min. 2000 mL of purified water is added dropwise to the reaction flask. After the addition is complete, ultrasonically disperse for 40 min and filter. The filter cake is washed twice with purified water and then dried. The filter cake is transferred to a drying oven at 55°C and dried to constant weight to obtain loaded porous silicon.

[0074] Mix anhydrous ethanol, purified water, and sodium hydroxide in a ratio of 10 mL: 3 mL: 0.02 g to obtain an ethanol solution for later use.

[0075] Weigh: 200 g of loaded porous silicon and 2000 mL of ethanol solution are added to a reaction flask and mixed, ultrasonically dispersed for 60 minutes, the temperature of the reaction flask is raised to 75°C, 100 g of ethyl orthosilicate is added to the reaction flask, and the reaction is kept warm for 95 minutes. The temperature of the reaction flask is lowered to 55°C, 40 g of KH-560 is added to the reaction flask, and the reaction is kept warm for 70 minutes. The temperature of the reaction flask is lowered to room temperature, filtered, and the filter cake is washed with purified water until neutral and then dried. The filter cake is transferred to a drying oven at a temperature of 55°C and dried to constant weight to obtain activated loaded silicon.

[0076] Step 5: Prepare the foaming material.

[0077] Zinc stearate, talc, ethylene bisstearamide, and antistatic agent SN were mixed uniformly in a weight ratio of 5:2:3:2 to obtain an additive;

[0078] Weigh 85 parts of EVA, 17 parts of olefin-modified EVA, 22 parts of boron-modified polysiloxane, 5 parts of phosphorus-aluminum flame retardant, and 4 parts of additives in parts by weight and add them to an internal mixer. Set the internal mixer temperature to 85°C and mix for 17 minutes. Add 11 parts of activated loaded silicon and 0.9 parts of dicumyl peroxide, a cross-linking agent, to the internal mixer. Heat the internal mixer to 125°C at a heating rate of 4°C / min and then discharge the material. Transfer the material to an open mixer at 95°C, set the roller distance to 2.5 mm, pack the material in a triangle bag and mix for 4 minutes. Cool to room temperature and discharge the material to obtain a mixed masterbatch.

[0079] After the mixed masterbatch is evenly placed in the mold, the mold is closed, the molding pressure is set to 10 MPa, the molding temperature is 195°C, and the heat and pressure are kept for 11 minutes. After the mold is cooled to room temperature, the material is discharged to obtain a foamed material.

[0080] Example 3

[0081] This embodiment provides a method for preparing a lightweight flame-retardant EVA foam material, comprising the following steps:

[0082] Step 1: Preparation of olefin-modified EVA

[0083] Weigh: 600g EVA, 55g 3-butene-1-ol and 1500mL toluene are added to a reaction flask and mixed and stirred. The temperature of the reaction flask is raised to 90°C, and the mixture is stirred and maintained until the system is dissolved. 2.5g azobisisobutyronitrile as an initiator is added to the reaction flask, and the mixture is kept warm for 5h. The temperature of the reaction flask is lowered to room temperature, 300mL of purified water is added to the reaction flask, and the mixture is stirred and dispersed for 30min. The mixture is allowed to stand for separation, and the organic phase is washed twice with purified water and then dried. The organic phase is transferred to an evaporator at a temperature of 90°C, and low-boiling substances are evaporated under reduced pressure to obtain hydroxyl-modified EVA;

[0084] Weigh: 400 g of hydroxyl-modified EVA and 2000 mL of toluene are added to a reaction flask protected by argon and stirred to mix. The temperature of the reaction flask is raised to 60°C and stirred until the system is dissolved. 200 g of 3-isocyanate propylene is added to the reaction flask and the reaction is kept warm for 80 minutes. The temperature of the reaction flask is raised to 90°C and low-boiling substances are evaporated under reduced pressure to obtain olefin-modified EVA.

[0085] Step 2: Preparation of boron-modified polysiloxane

[0086] Weigh: 100 mL of hydroxyl-terminated polysiloxane and 500 mL of toluene are added to a reaction flask protected by argon, mixed and stirred until dissolved, and the amount of 3-isocyanate added is calculated as 0.2 times the molar amount of hydroxyl groups in the hydroxyl-terminated polysiloxane in the reaction flask. The 3-isocyanate is added to the reaction flask and stirred. The temperature of the reaction flask is raised to 60° C. and the reaction is kept warm for 80 minutes. The reaction temperature is then raised to 80° C. and low-boiling substances are evaporated under reduced pressure to obtain a modified polysiloxane;

[0087] Weigh: add the modified polysiloxane to the reaction flask and stir, calculate the amount of boric acid added based on the molar amount of hydroxyl groups in the modified polysiloxane, and add it to the reaction flask and stir, evacuate the reaction flask to a vacuum pressure of 0.1 MPa, heat the reaction flask to 185°C, keep the temperature for reaction for 150 minutes, lower the temperature of the reaction flask to room temperature, and discharge the material to obtain boron-modified polysiloxane.

[0088] Step 3: Preparation of phosphorus-aluminum flame retardant

[0089] Weigh: 100 g of 2-(aminomethyl)-2-methyl-1,3-propylenediamine, 1000 mL of purified water, 540 g of allyl phosphinic acid and 1100 mL of 10 wt% formaldehyde solution were added to a reaction flask and mixed. The temperature of the reaction flask was raised to reflux of the system, and the reaction was kept warm for 110 minutes. The temperature of the reaction flask was lowered to room temperature. 0.5 mol / L sodium hydroxide solution was added to the reaction flask to adjust the pH of the system to 6. 100 g of aluminum isopropoxide was added to the reaction flask, the temperature of the reaction flask was raised to reflux of the system, and the reaction was kept warm for 160 minutes. The temperature of the reaction flask was lowered to room temperature, and the filter cake was washed three times with purified water and ethanol in sequence and then dried. The filter cake was transferred to a drying oven at 70°C and dried to constant weight to obtain a phosphorus-aluminum flame retardant.

[0090] Step 4: Preparation of activated loaded silicon

[0091] Weigh: 75 g of azodicarbonamide and 250 mL of dimethyl sulfoxide are added to a reaction flask and stirred until the system is dissolved. 150 g of porous silica is added to the reaction flask and ultrasonically dispersed for 60 min. 2000 mL of purified water is added dropwise to the reaction flask. After the addition is complete, ultrasonically disperse for 50 min and filter. The filter cake is washed twice with purified water and then dried. The filter cake is transferred to a drying oven at 60°C and dried to constant weight to obtain loaded porous silicon.

[0092] Mix anhydrous ethanol, purified water, and sodium hydroxide in a ratio of 10 mL: 3 mL: 0.02 g to obtain an ethanol solution for later use.

[0093] Weigh: 200 g of loaded porous silicon and 2000 mL of ethanol solution are added to a reaction flask and mixed, ultrasonically dispersed for 70 minutes, the temperature of the reaction flask is raised to 80°C, 120 g of ethyl orthosilicate is added to the reaction flask, and the reaction is kept warm for 100 minutes. The temperature of the reaction flask is lowered to 60°C, 48 g of KH-560 is added to the reaction flask, and the reaction is kept warm for 80 minutes. The temperature of the reaction flask is lowered to room temperature, filtered, and the filter cake is washed with purified water until neutral and then dried. The filter cake is transferred to a drying oven at a temperature of 60°C and dried to constant weight to obtain activated loaded silicon.

[0094] Step 5: Prepare the foaming material.

[0095] Zinc stearate, talc, ethylene bisstearamide, and antistatic agent SN were mixed uniformly in a weight ratio of 5:2:3:2 to obtain an additive;

[0096] Weigh 90 parts of EVA, 20 parts of olefin-modified EVA, 25 parts of boron-modified polysiloxane, 6 parts of phosphorus-aluminum flame retardant, and 5 parts of additives in parts by weight and add them to an internal mixer. Set the internal mixer temperature to 90°C and mix for 20 minutes. Add 12 parts of activated loaded silicon and 1.0 part of dicumyl peroxide, a cross-linking agent, to the internal mixer. Heat the internal mixer to 130°C at a heating rate of 5°C / min and then discharge the material. Transfer the material to an open mixer at 100°C, set the roller distance to 3mm, roll the material into a triangle bag and mix for 5 minutes. Cool to room temperature and discharge the material to obtain a mixed masterbatch.

[0097] After the mixed masterbatch is evenly placed in the mold, the mold is closed, the molding pressure is set to 11 MPa, the molding temperature is 200°C, and the heat and pressure are kept for 12 minutes. After the mold is cooled to room temperature, the material is discharged to obtain a foamed material.

[0098] Comparative Example 1

[0099] The difference between this comparative example and the embodiment is that step one is omitted and olefin-modified EVA is not added in step five.

[0100] Comparative Example 2

[0101] The difference between this comparative example and the embodiment is that the boron-modified polysiloxane in step five is replaced by the modified polysiloxane in step two.

[0102] Comparative Example 3

[0103] The difference between this comparative example and the embodiment is that in step 3, allylphosphinic acid is replaced by phosphorous acid in an equimolar amount.

[0104] Comparative Example 4

[0105] The difference between this comparative example and the embodiment is that the activated supported silicon in step five is replaced by supported porous silicon in step four.

[0106] Performance testing:

[0107] The compressive strength and relative deformation of the foam material samples prepared in Examples 1-3 and Comparative Examples 1-4 were measured with reference to the standard GB / T 8813-2020 “Determination of compression properties of rigid foam plastics”;

[0108] The rebound resilience of the foam material samples prepared in Examples 1-3 and Comparative Examples 1-4 was measured with reference to the standard HG / T 4993-2016 “Test method for rebound resilience of microporous materials for footwear”;

[0109] The tear strength of the foam material samples prepared in Examples 1-3 and Comparative Examples 1-4 was measured with reference to the standard HG 2726-1995 "Test method for tear strength of microporous sole materials";

[0110] The vertical combustion grades of the foam material samples prepared in Examples 1-3 and Comparative Examples 1-4 were measured with reference to the standard GB / T 2408-2021 “Determination of combustion performance of plastics—Horizontal and vertical methods”;

[0111] The foam materials prepared in Examples 1-3 and Comparative Examples 1-4 were cut into test pieces with a size of 75 mm × 75 mm, and then a diagonal line was drawn, with the length marked as L1. The test pieces were then placed in a constant temperature oven at 70°C for 45 minutes, taken out, and cooled to room temperature. The diagonal length was measured as L2, and the formula was used to calculate the diagonal length. Calculate the thermal shrinkage of the sample. The specific test results are shown in Table 1 below.

[0112] Table 1-Performance test data of the sample

[0113]

[0114]

[0115] Data Analysis:

[0116] Comparing and analyzing the data in Table 1 above, the density of the foamed material prepared by the present invention is reduced to 0.179 g / cm 3 The compression strength reaches 2.3MPa, the relative deformation reaches 22.4%, the rebound resilience reaches 59.5%, the tear strength reaches 10.5N / cm, the thermal shrinkage rate is reduced to 2.2%, and the vertical burning grade reaches V-0. All performance test data are better than the comparative example, indicating that the present invention uses boron-modified polysiloxane and phosphorus-aluminum flame retardant to olefin-modified EVA and EVA, and then mixes them with activated loaded silicon and cross-linking agent for foaming, which not only effectively improves the mechanical properties and heat resistance of the foamed material, but also improves its flame retardant and lightweight properties.

[0117] The preferred embodiments of the present invention disclosed above are intended only to help illustrate the present invention. These preferred embodiments do not exhaustively describe all details, nor do they limit the present invention to specific embodiments. Obviously, many modifications and variations are possible based on the contents of this specification. These embodiments are selected and described in detail in this specification to better explain the principles and practical applications of the present invention, thereby enabling those skilled in the art to better understand and utilize the present invention. The present invention is limited only by the claims and their full scope and equivalents.

Claims

1. A lightweight flame-retardant EVA foam material, characterized in that: The invention comprises the following components in parts by weight: 80-90 parts of EVA, 15-20 parts of olefin-modified EVA, 18-25 parts of boron-modified polysiloxane, 4-6 parts of phosphorus-aluminum flame retardant, 10-12 parts of activated loaded silicon, 0.8-1.0 parts of crosslinking agent and 3-5 parts of additives; The preparation method of the activated loaded silicon comprises the following steps: mixing azodicarbonamide and dimethyl sulfoxide and stirring until the system is dissolved; adding porous silicon dioxide to the reaction system, ultrasonically dispersing the mixture for 40-60 minutes; dripping purified water into the reaction system, ultrasonically dispersing the mixture for 30-50 minutes after the dripping is complete, and performing post-processing to obtain the loaded porous silicon; mixing the loaded porous silicon and an ethanol solution, ultrasonically dispersing the mixture for 50-70 minutes, raising the temperature of the reaction system to 70-80°C, adding tetraethyl orthosilicate to the reaction system, preserving the reaction temperature for 90-100 minutes, lowering the temperature of the reaction system to 50-60°C, adding KH-560 to the reaction system, preserving the reaction temperature for 60-80 minutes, and performing post-processing to obtain the activated loaded silicon.

2. A lightweight flame-retardant EVA foam material according to claim 1, characterized in that: The additives are composed of zinc stearate, talc, ethylene bisstearamide, and antistatic agent SN in a weight ratio of 5:2:3:2, and the cross-linking agent is dicumyl peroxide.

3. The lightweight flame-retardant EVA foam material according to claim 1, characterized in that: During the preparation of loaded porous silicon, the usage ratio of azodicarbonamide, dimethyl sulfoxide, porous silica and purified water is 1-1.5g:5mL:2-3g:40mL; during the preparation of activated loaded silicon, the usage ratio of loaded porous silicon, ethanol solution, tetraethyl orthosilicate and KH-560 is 5g:50mL:2-3g:0.8-1.2g, and the ethanol solution is composed of anhydrous ethanol, purified water and sodium hydroxide in a usage ratio of 10mL:3mL:0.02g.

4. The lightweight flame-retardant EVA foam material according to claim 1, characterized in that: The preparation method of boron-modified polysiloxane comprises the following steps: A1. Under an inert atmosphere, hydroxyl-terminated polysiloxane and toluene were mixed and stirred to dissolve, 3-isocyanate propylene was added to the reaction system, the temperature of the reaction system was raised to 50-60°C, the reaction was kept warm for 60-80 minutes, and post-treated to obtain modified polysilane; A2. The modified polysiloxane and boric acid are mixed and stirred. The reaction system is evacuated to a vacuum and then heated to 175-185° C. The reaction is kept at this temperature for 120-150 minutes. The temperature of the reaction system is then lowered to room temperature and the material is discharged to obtain boron-modified polysiloxane.

5. A lightweight flame-retardant EVA foam material according to claim 4, characterized in that: In step A1, the molar ratio of the 3-isocyanate propylene to the hydroxyl group in the hydroxy-modified siloxane is 0.2:1, and the amount ratio of the hydroxyl-terminated polysiloxane to toluene is 1 g:5 mL; in step A2, the molar ratio of the boric acid to the hydroxyl group in the modified siloxane is 1:

1.

6. The lightweight flame-retardant EVA foam material according to claim 1, characterized in that: The preparation method of the phosphorus-aluminum flame retardant comprises the following steps: mixing and stirring 2-(aminomethyl)-2-methyl-1,3-propylenediamine, purified water, allylphosphinic acid and formaldehyde solution, raising the temperature of the reaction system to the system reflux, keeping the temperature to react for 90-110 minutes, lowering the temperature of the reaction system to room temperature, adding sodium hydroxide solution to the reaction system to adjust the pH of the system to 6, adding aluminum isopropoxide to the reaction system, raising the temperature of the reaction system to the system reflux, keeping the temperature to react for 120-160 minutes, and performing post-treatment to obtain the phosphorus-aluminum flame retardant.

7. A lightweight flame-retardant EVA foam material according to claim 6, characterized in that: The usage ratio of the 2-(aminomethyl)-2-methyl-1,3-propanediamine, purified water, allylphosphinic acid, formaldehyde solution and aluminum isopropoxide is 10g:100mL:54g:110mL:10g. The formaldehyde solution consists of formaldehyde and water with a mass fraction of 10%.

8. The lightweight flame-retardant EVA foam material according to claim 1, characterized in that: The preparation method of olefin-modified EVA comprises the following steps: B1. EVA, 3-butene-1-ol and toluene were mixed, the reaction system temperature was raised to 80-90°C, and the mixture was stirred at this temperature until the system was dissolved. An initiator was added to the reaction system, and the mixture was reacted at this temperature for 3-5 hours. After post-treatment, hydroxyl-modified EVA was obtained. B2. Under the protection of inert gas, hydroxyl-modified EVA and toluene were mixed, the temperature of the reaction system was raised to 50-60°C, and the mixture was stirred until the reaction system was dissolved. 3-isocyanate propylene was added to the reaction system, and the mixture was kept warm for 60-80 minutes. After post-treatment, olefin-modified EVA was obtained.

9. The lightweight flame-retardant EVA foam material according to claim 8, characterized in that: In step B1, the amount ratio of the EVA, 3-butene-1-ol, toluene and initiator is 10-12g:0.8-1.1g:30mL:0.05g, and the initiator is azobisisobutyronitrile; in step B2, the amount ratio of the hydroxyl-modified EVA, toluene and 3-isocyanate propylene is 2g:10mL:0.8-1g.

10. The method for preparing a lightweight flame-retardant EVA foam material according to any one of claims 1 to 9, characterized in that: The following steps are involved: S1. Add EVA, olefin-modified EVA, boron-modified polysiloxane, phosphorus-aluminum flame retardant and additives to an internal mixer, set the internal mixer temperature to 80-90° C., and mix for 15-20 min. Add activated loaded silicon and cross-linking agent to the internal mixer, raise the temperature of the internal mixer to 120-130° C. at a heating rate of 3-5° C. / min, and then discharge the material. Transfer the material to an open mixer at a temperature of 90-100° C., set the roller distance to 2-3 mm, and mix in a triangle bag for 3-5 min. Cool to room temperature, and discharge to obtain a mixed masterbatch. S2. Evenly place the mixed masterbatch into the mold and close the mold. Set the molding pressure to 9-11 MPa and the molding temperature to 190-200°C. Keep the temperature and pressure for 10-12 minutes. After the mold cools down to room temperature, discharge the material to obtain the foaming material.

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