Corrosion-resistant EVA (Ethylene Vinyl Acetate) foamed sheet and preparation method thereof

Abstract

The invention relates to the technical field of foaming materials, in particular to a corrosion-resistant EVA foaming sheet and a preparation method thereof. According to the invention, the problem of poor durability of the existing EVA foamed sheet is overcome. The synthetic raw materials comprise EVA, a polyurethane elastomer, a composite cross-linking agent, a modified foaming agent, a composite foaming aid, modified graphene, a composite lubricant, a modified coupling agent, zinc oxide, stearic acid and calcium propionate. The preparation method comprises the following steps: firstly, carrying out primary internal mixing on EVA and a polyurethane elastomer, and then adding the rest synthetic raw materials for secondary internal mixing to obtain a mixture; and pressing the mixture into a sheet, carrying out mold pressing foaming, and cooling to obtain the EVA foamed sheet. By preparing and adding the polyurethane elastomer, the modified foaming agent, the modified graphene, the modified coupling agent and other raw materials, the mechanical property, the rebound rate, the wear resistance and the corrosion resistance of the foamed sheet can be improved, so that the durability of the foamed sheet is improved, and the final foamed sheet can be used in multiple scenes.

Description

Technical Field

[0001] The present invention relates to the technical field of foaming materials, and particularly to a corrosion-resistant EVA foamed sheet and a preparation method thereof. Background Art

[0002] EVA (ethylene-vinyl acetate copolymer) resin is a thermoplastic elastomer copolymerized from ethylene and vinyl acetate. In EVA resin, the ethylene chain segment endows the material with flexibility, low-temperature resistance and mechanical strength, while the vinyl acetate chain segment provides good flexibility, transparency and chemical corrosion resistance. With the increase of the vinyl acetate content, the elasticity, softness and viscosity of EVA resin will also increase accordingly.

[0003] Since the 1960s, EVA resin has been industrially produced. With the continuous progress of production technology, the performance of EVA resin has been continuously improved and its application fields have been continuously expanded. In the 1980s, EVA foaming technology gradually matured, and EVA foamed sheets began to be widely used in fields such as shoemaking, packaging, and sports goods. Since then, with the continuous improvement of people's requirements for material performance, the production technology of EVA foamed sheets has been continuously innovated, and various high-performance EVA foamed sheet products have emerged.

[0004] In the traditional chemical foaming process, due to the poor performance of the foaming agent, the foam cells may deform, rupture, fuse, etc., forming an irregular foam cell morphology, reducing the elasticity and cushioning performance of the sheet; and because the hardness of EVA itself is relatively low, in some application scenarios with high wear resistance requirements, such as the parts of the sole that often rub against the ground, it is easy to wear, affecting the service life of the product. When the EVA foamed sheet is used as a packaging or protective material, organic solvents may penetrate into the interior of the sheet, destroying the regularity of its molecular chains and the foam cell structure, causing it to lose its original physical and protective properties, and ultimately reducing the product life.

[0005] In summary, the current EVA foamed sheets still have disadvantages such as poor corrosion resistance, poor mechanical properties and poor wear resistance, resulting in poor durability, which seriously hinders their production applications in various aspects.

[0006] Therefore, a corrosion-resistant EVA foamed sheet and a preparation method thereof are proposed. Summary of the Invention

[0007] The object of the present invention is to design a corrosion-resistant EVA foamed sheet and its preparation method. The synthetic raw materials of the present invention include EVA, polyurethane elastomer, composite cross-linking agent, modified foaming agent, composite foaming aid, modified graphene, composite lubricant, modified coupling agent, zinc oxide, stearic acid and calcium propionate; first, EVA and polyurethane elastomer are subjected to primary kneading, and then the remaining synthetic raw materials are added for secondary kneading to obtain a mixture; the mixture is pressed into a sheet and then subjected to mold pressing and foaming, and after cooling, an EVA foamed sheet is obtained. The present invention improves the mechanical properties of the EVA foamed sheet by preparing a polyurethane elastomer and synergistically with a composite cross-linking agent; the modified foaming agent can promote the formation of the foamed sheet together with the composite foaming aid and jointly improve its rebound rate; the added modified graphene and composite lubricant can improve the wear resistance of the EVA foamed sheet; the modified coupling agent, zinc oxide and stearic acid therein can synergistically improve the corrosion resistance of the EVA foamed sheet, and the final EVA foamed sheet can be used in multiple scenarios.

[0008] To achieve the above object, the present invention provides the following technical solutions:

[0009] On the one hand, the present invention provides a corrosion-resistant EVA foamed sheet. By weight, the synthetic raw materials of the EVA foamed sheet include:

[0010] EVA: 80 parts; polyurethane elastomer: 15 - 20 parts; composite cross-linking agent: 2 - 6 parts; modified foaming agent: 6 - 10 parts; composite foaming aid: 0.5 - 1 part; modified graphene: 1 - 4 parts; composite lubricant: 0.5 - 1 part; modified coupling agent: 1 - 5 parts; zinc oxide: 1.1 - 1.5 parts; stearic acid: 0.2 - 0.6 part; calcium propionate: 2 parts;

[0011] The polyurethane elastomer includes 4,4'-diphenylmethane diisocyanate, polycaprolactone diol and dibutyltin dilaurate;

[0012] The modified foaming agent includes azodicarbonamide, sodium hydroxide and ethanolamine;

[0013] The modified graphene includes graphene and cyclopentadiene;

[0014] The modified coupling agent includes γ-glycidoxypropyltrimethoxysilane, hydroquinone and triethylamine.

[0015] Preferably, the composite cross-linking agent is composed of a mixture of dicumyl peroxide and 1,4-bis(tert-butylperoxyisopropyl)benzene, and the weight ratio of dicumyl peroxide to 1,4-bis(tert-butylperoxyisopropyl)benzene is 2 - 4:1.

[0016] Preferably, the composite foaming aid is composed of a mixture of calcium carbonate and talcum powder, and the weight ratio of calcium carbonate to talcum powder is 1 - 4:2.

[0017] Preferably, the composite lubricant is formed by mixing butyl stearate and zinc stearate, and the weight ratio of butyl stearate to zinc stearate is 2:3-5.

[0018] On the other hand, the present invention provides a method for preparing a corrosion-resistant EVA foam sheet. By weight, the preparation method includes the following steps:

[0019] S1: Put 80 parts of EVA and 15-20 parts of polyurethane elastomer into a kneader for the first kneading. The temperature of the first kneading is 90°C-100°C, the time is 10 min-15 min, and the rotation speed is 40 rpm;

[0020] S2: Add 2-6 parts of a composite crosslinking agent, 6-10 parts of a modified blowing agent, 0.5-1 part of a composite blowing aid, 1-4 parts of modified graphene, 0.5-1 part of a composite lubricant, 1-5 parts of a modified coupling agent, 1.1-1.5 parts of zinc oxide, 0.2-0.6 part of stearic acid, and 2 parts of calcium propionate to the kneader for the second kneading. The temperature of the second kneading is 110°C-120°C, the time is 10 min, and the rotation speed is 30 rpm to obtain a mixture;

[0021] S3: Press the mixture on a mixing mill into a sheet with a thickness of 5 mm;

[0022] S4: Carry out mold pressing and foaming on the sheet. The temperature of the mold pressing and foaming is 175°C-185°C, the time is 8 min, and after cooling, an EVA foam sheet is obtained.

[0023] Preferably, the preparation method of the polyurethane elastomer is as follows: Add 6 parts of 4,4'-diphenylmethane diisocyanate and 10-14 parts of polycaprolactone diol to a reaction vessel, stir at 85°C for 30 min to obtain a prepolymer; after cooling the prepolymer to 50°C, add 1 part of dibutyltin dilaurate and 10 parts of ethylene glycol, then stir for 2 h. After the reaction is completed, wash the solid product and dry it in a vacuum drying oven at 50°C for 12 h to obtain the polyurethane elastomer.

[0024] Preferably, the preparation method of the modified blowing agent is as follows: Add 5-10 parts of azodicarbonamide and 10 parts of N,N-dimethylformamide to a reaction kettle, stir at 50°C for 30 min to obtain a mixed solution I; add 0.5 part of sodium hydroxide to the mixed solution I and continue to stir for 15 min to obtain a mixed solution II; slowly drop 5 parts of ethanolamine into the mixed solution II, raise the temperature of the reaction kettle to 75°C, and continue to stir and react for 4 h. After the reaction is completed, cool the reaction kettle to room temperature to obtain a mixed solution III; pour 30 parts of deionized water into the mixed solution III, then separate the precipitate through a suction filtration device, wash the precipitate with deionized water, and then put it into a drying oven and dry it at 60°C for 12 h to obtain the modified blowing agent.

[0025] Preferably, the preparation method of modified graphene is: dispersing 7-12 parts of graphene in 15 parts of toluene, stirring for 30 minutes to obtain a mixed solution A; adding 1 part of cyclopentadiene to the mixed solution A, stirring and reacting for 2 hours, and then transferring to a reactor, the reactor is reacted in an oven at a temperature of 160°C-180°C for 12 hours, and after the reaction is completed, the reaction solution is centrifuged to obtain a solid product, and the centrifugal speed is 8000rpm; the solid product is washed with ethanol 5 times, and vacuum dried at 60°C for 18 hours to obtain the modified graphene.

[0026] Preferably, the preparation method of the modified coupling agent is: add 3-8 parts of γ-glycidyloxypropyltrimethoxysilane and 10 parts of toluene into a four-necked flask, stir for 30 minutes, then add 0.1 parts of hydroquinone and 0.5 parts of triethylamine, and continue stirring for 30 minutes; slowly heat the four-necked flask to 70°C, slowly drop 1 part of acrylic acid into the four-necked flask, continue stirring and react for 4 hours, after the reaction is completed, adjust the pH value to 8 to obtain a reaction solution; perform reduced pressure distillation on the reaction solution, then wash with deionized water, and vacuum dry at 60°C for 12 hours to obtain the modified coupling agent.

[0027] Compared with the prior art, the present invention has the following beneficial effects:

[0028] 1. The present invention improves the mechanical properties of EVA foam sheet by preparing polyurethane elastomer and coordinating with a composite crosslinking agent. There is a strong interaction force between the molecular chains of the polyurethane elastomer, and it has a high cohesive energy. After the polyurethane elastomer is introduced into the EVA foam sheet, it can play the role of a "bridge" between the molecular chains of EVA, enhance the interaction between the molecular chains, and thus improve the overall mechanical properties of the foam sheet. When the polyurethane elastomer and the composite crosslinking agent act together, the molecular chains of the polyurethane elastomer can participate in the crosslinking reaction initiated by the composite crosslinking agent, and form a more complex and stable interpenetrating network structure with the EVA molecular chains. This interpenetrating network structure not only enhances the interaction between the molecular chains, but also makes the stress distribution inside the material more uniform, thereby further improving the mechanical properties of the EVA foam sheet, and its durability is also improved accordingly.

[0029] 2. In the present invention, the modified blowing agent and the composite blowing aid can promote the formation of the foamed sheet and jointly improve its resilience rate. Introducing hydroxyl groups to modify azodicarbonamide can make more effective use of the gas generated by its own decomposition, reduce the escape and waste of gas, and enable more gas to participate in the formation and expansion of the cells, thereby improving the foaming efficiency, making the foamed sheet have a lighter weight and better cushioning performance. The modified blowing agent reduces the stress concentration points between the cells by controlling the cell size and distribution, while the composite blowing aid further enhances the cell stability by forming a protective film on the bubble surface and adjusting the melt properties. The synergistic effect of the two enables the cells to better maintain their integrity and shape during the foaming process and subsequent use, and is not prone to problems such as rupture and collapse. Therefore, the foamed sheet can more effectively return to its original state after being compressed by an external force, significantly improving the resilience rate, and thus also improving the durability of the foamed sheet.

[0030] 3. The modified graphene and the composite lubricant added in the present invention can improve the wear resistance of the EVA foamed sheet. Graphene itself has extremely high strength and modulus. The modified graphene after the cycloaddition reaction can better combine with the EVA matrix. In the EVA foamed sheet, it is equivalent to a reinforcing framework, which can bear a part of the external applied friction and pressure, reduce the stress directly borne by the EVA matrix, and thus reduce the material loss caused by friction and improve the wear resistance. The modified graphene enhances the mechanical properties and barrier properties of the EVA matrix, and the composite lubricant improves the processing properties and interfacial bonding force. The combined action of the two makes the overall structure of the EVA foamed sheet more stable and uniform. During the friction process, the material can better withstand external forces and is not prone to local deformation and increased wear, and the wear resistance is synergistically enhanced, thereby improving the durability of the foamed sheet.

[0031] 4. The modified coupling agent, zinc oxide, and stearic acid in the present invention can synergistically improve the corrosion resistance of the EVA foamed sheet. One end of the modified coupling agent obtained by grafting modification can be tightly combined with the molecular chains in the EVA matrix through chemical bond action, and the other end can act on the surface of zinc oxide, thereby forming a good bridge between the EVA matrix and other components, making their combination more firm and reducing the interfacial damage caused by the intrusion of external corrosive media. The modified coupling agent promotes the combination between zinc oxide and the EVA matrix, enables zinc oxide to better play its role in the crosslinking reaction, increases the crosslinking density, and at the same time enhances the dispersion stability of zinc oxide in the EVA matrix, reducing the agglomeration phenomenon of zinc oxide, thereby more effectively blocking the corrosive media. Stearic acid helps the uniform dispersion of the modified coupling agent and zinc oxide in the EVA matrix, further improving their synergistic effect, improving the corrosion resistance of the sheet, and thus increasing the durability. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 This is the mass loss rate graph of Example 18 and Comparative Examples 20-25 in the present invention. Detailed implementation manners

[0033] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0034] Specifically refer to Figure 1 , the present invention provides a corrosion-resistant EVA foamed sheet and its preparation method, and the technical solution is as follows:

[0035] Example 1

[0036] The composite cross-linking agent is composed of dicumyl peroxide and 1,4-bis(tert-butylperoxyisopropyl)benzene, and the weight ratio of dicumyl peroxide to 1,4-bis(tert-butylperoxyisopropyl)benzene is 2:1; the composite foaming agent assistant is composed of calcium carbonate and talcum powder, and the weight ratio of calcium carbonate to talcum powder is 1:2; the composite lubricant is composed of butyl stearate and zinc stearate, and the weight ratio of butyl stearate to zinc stearate is 2:3.

[0037] Prepare polyurethane elastomer:

[0038] Add 6 parts of 4,4'-diphenylmethane diisocyanate and 10 parts of polycaprolactone diol into a reaction vessel, stir at 85°C for 30 min to obtain a prepolymer; after cooling the prepolymer to 50°C, add 1 part of dibutyltin dilaurate and 10 parts of ethylene glycol, then stir for 2 h. After the reaction is completed, wash the solid product and dry it in a vacuum drying oven at 50°C for 12 h to obtain a polyurethane elastomer.

[0039] Prepare modified foaming agent:

[0040] Add 5 parts of azodicarbonamide and 10 parts of N,N-dimethylformamide into a reaction kettle, stir at 50°C for 30 min to obtain a mixed solution I; add 0.5 part of sodium hydroxide into the mixed solution I, continue to stir for 15 min to obtain a mixed solution II; slowly drop 5 parts of ethanolamine into the mixed solution II, raise the temperature of the reaction kettle to 75°C, and continue to stir and react for 4 h. After the reaction is completed, cool the reaction kettle to room temperature to obtain a mixed solution III; pour 30 parts of deionized water into the mixed solution III, then separate the precipitate through a suction filtration device, wash the precipitate with deionized water, and then put it into a drying oven and dry it at 60°C for 12 h to obtain a modified foaming agent.

[0041] Preparation of modified graphene:

[0042] Disperse 7 parts of graphene in 15 parts of toluene, and obtain a mixed solution A after stirring for 30 min; add 1 part of cyclopentadiene to the mixed solution A, stir and react for 2 h, then transfer it to a reaction kettle, and the reaction kettle reacts in an oven at a temperature of 160 °C for 12 h. After the reaction is completed, the reaction solution is centrifuged to obtain a solid product, and the centrifugation speed is 8000 rpm; wash the solid product with ethanol 5 times and vacuum dry it at 60 °C for 18 h to obtain modified graphene.

[0043] Preparation of modified coupling agent:

[0044] Add 3 parts of γ-glycidoxypropyltrimethoxysilane and 10 parts of toluene into a four-necked flask, stir for 30 min, then add 0.1 part of hydroquinone and 0.5 part of triethylamine, and continue to stir for 30 min; slowly heat the four-necked flask to 70 °C, slowly drop 1 part of acrylic acid into the four-necked flask, and continue to stir and react for 4 h. After the reaction is completed, adjust the pH value to 8 to obtain a reaction solution; carry out vacuum distillation on the reaction solution, then wash it with deionized water, and vacuum dry it at 60 °C for 12 h to obtain a modified coupling agent.

[0045] Preparation of EVA foamed sheet:

[0046] S1 Put 80 parts of EVA and 15 parts of polyurethane elastomer into a mixer for the first mixing. The temperature of the first mixing is 90 °C, the time is 10 min, and the rotation speed is 40 rpm;

[0047] S2 Add 2 parts of composite cross-linking agent, 6 parts of modified foaming agent, 0.5 part of composite foaming assistant, 1 part of modified graphene, 0.5 part of composite lubricant, 1 part of modified coupling agent, 1.1 parts of zinc oxide, 0.2 part of stearic acid and 2 parts of calcium propionate into the mixer for the second mixing. The temperature of the second mixing is 110 °C, the time is 10 min, and the rotation speed is 30 rpm to obtain a mixture;

[0048] S3 Press the mixture into a sheet with a thickness of 5 mm on a mixing mill;

[0049] S4 Carry out mold pressing and foaming on the sheet. The temperature of the mold pressing and foaming is 175 °C, the time is 8 min, and the EVA foamed sheet is obtained after cooling.

[0050] Examples 2 - 5

[0051] Refer to the parameter conditions in Example 1, and the specific differences are shown in Table 1.

[0052] Table 1 Parameter conditions of Examples 1 - 5 Comparative Example 1

[0053] Refer to the parameter conditions in Example 1, with the difference that polyurethane is used instead of polyurethane elastomer.

[0054] Comparative Example 2

[0055] Refer to the parameter conditions in Example 1, with the difference that no polyurethane elastomer is added.

[0056] Comparative Example 3

[0057] Refer to the parameter conditions in Example 1, with the difference that only dicumyl peroxide is used as the crosslinking agent.

[0058] Comparative Example 4

[0059] Refer to the parameter conditions in Example 1, with the difference that only 1,4-bis(tert-butylperoxyisopropyl)benzene is used as the crosslinking agent.

[0060] Comparative Example 5

[0061] Refer to the parameter conditions in Example 1, with the difference that no composite crosslinking agent is added.

[0062] Comparative Example 6

[0063] Refer to the parameter conditions in Example 1, with the difference that the temperature of the first stage of internal mixing is 150 °C and the time is 1 h.

[0064] Comparative Example 7

[0065] Refer to the parameter conditions in Example 1, with the difference that the temperature of the first stage of internal mixing is 50 °C and the time is 1 min.

[0066] Experimental Example 1 Mechanical Property Test

[0067] Test the tensile strength and elongation at break of Examples 1 - 5 and Comparative Examples 1 - 7 according to the GB / T 3903.4 standard; test the Shore hardness of Examples 1 - 5 and Comparative Examples 1 - 7 according to the HG / T 2489 - 93 and GB 2411 - 80 standards. The results are shown in Table 2.

[0068] Table 2 Mechanical Property Test of Examples 1 - 5 and Comparative Examples 1 - 7

[0069]

[0070]

[0071] It can be found from Table 2 that in Comparative Examples 1-2, when polyurethane was used to replace the polyurethane elastomer or the polyurethane elastomer was not added, the mechanical properties of the foamed sheet were significantly lower than those of the Examples. This is because the polyurethane elastomer has a unique soft segment and hard segment structure. The soft segment endows it with good flexibility and elasticity. After combining it with the EVA foamed sheet, it can effectively enhance the interaction between molecular chains, improve the hard and brittle problems existing in EVA itself, enable the foamed sheet to better adapt to deformation when subjected to external force bending and stretching, and is not prone to situations such as rupture and breakage, thereby improving the overall mechanical properties of the foamed sheet. In Comparative Examples 3-5, when using a single crosslinking agent or not adding a composite crosslinking agent, the mechanical properties of the foamed sheet also showed a significant decrease compared to the Examples. Since the composite crosslinking agent can chemically react with the active groups on the EVA molecular chain to form a covalent bond crosslinking network between the EVA molecular chains, the formation of this crosslinking network can effectively restrict the relative movement of the EVA molecular chains, enabling the molecular chains to act synergistically and jointly bear the external force when the EVA foamed sheet is subjected to external force, thereby improving the mechanical properties of the material. When the polyurethane elastomer and the composite crosslinking agent act together, the molecular chains of the polyurethane elastomer can participate in the crosslinking reaction initiated by the composite crosslinking agent to form a more complex and stable interpenetrating network structure with the EVA molecular chains. This interpenetrating network structure not only enhances the interaction between molecular chains but also makes the stress distribution inside the material more uniform, thereby further improving the mechanical properties of the EVA foamed sheet, enabling it to exhibit better performance under various stress conditions such as tension, compression, and bending, and thus improving the durability of the foamed sheet. In Comparative Examples 6-7, too high or too low temperature or too long or too short time of the first-stage mixing will have an adverse impact on the mechanical properties of the foamed sheet. Too high mixing temperature will cause thermal degradation of materials such as the polyurethane elastomer, molecular chain breakage, resulting in a decrease in molecular weight, and the foamed sheet becoming prone to breakage and losing its due toughness; too low mixing temperature, the activity of the composite crosslinking agent is low, and it cannot fully initiate the crosslinking reaction, and the polyurethane elastomer cannot form a sufficient crosslinking network, and it is prone to damage during use; as the mixing time prolongs, the crosslinking reaction continues, the degree of crosslinking continuously increases, which may lead to the aging of the material, the elastic and flexible properties of the foamed sheet gradually lose, the hardness increases, and the brittleness increases; too short time results in insufficient crosslinking reaction and an incomplete and stable crosslinking network cannot be formed, and the mechanical properties of the foamed sheet will be significantly affected.

[0072] Examples 6-10

[0073] Referring to the parameter conditions in Example 3, the specific differences are shown in Table 3.

[0074] Table 3 Parameter Conditions of Example 3 and Examples 6-10

[0075]

[0076] Comparative Example 8

[0077] Referring to the parameter conditions in Example 3, the difference is that azodicarbonamide is used as the foaming agent.

[0078] Comparative Example 9

[0079] Referring to the parameter conditions in Example 3, the difference is that the modified foaming agent is not added.

[0080] Comparative Example 10

[0081] Referring to the parameter conditions in Example 3, the difference is that only calcium carbonate is used as the foaming aid.

[0082] Comparative Example 11

[0083] Referring to the parameter conditions in Example 3, the difference is that only talcum powder is used as the foaming aid.

[0084] Comparative Example 12

[0085] Referring to the parameter conditions in Example 3, the difference is that the composite foaming aid is not added.

[0086] Comparative Example 13

[0087] Referring to the parameter conditions in Example 3, the difference is that the temperature of the first stage of internal mixing is 180 °C.

[0088] Comparative Example 14

[0089] Referring to the parameter conditions in Example 3, the difference is that the temperature of the first stage of internal mixing is 50 °C.

[0090] Experimental Example 2 Rebound Rate Test

[0091] The rebound rates of Example 3, Examples 6 - 10 and Comparative Examples 8 - 14 were tested according to the standard of GB / T 1681 - 1991, and the results are shown in Table 4.

[0092] Table 4 Rebound Rate Test of Example 3, Examples 6 - 10 and Comparative Examples 8 - 14

[0093] Example Rebound rate / % Example 3 55 Example 6 57 Example 7 56 Example 8 59 Example 9 57 Example 10 57 Comparative Example 8 43 Comparative Example 9 31 Comparative Example 10 45 Comparative Example 11 46 Comparative Example 12 38 Comparative Example 13 42 Comparative Example 14 45

[0094] As can be seen from Table 4, in Comparative Examples 8-9, when only azodicarbonamide is used as the foaming agent or no modified foaming agent is added, the rebound rate of the foamed sheet is significantly lower than that of the Examples. This is because during the preparation of the modified foaming agent, the nitrogen atom on the amino group in the ethanolamine molecule attacks the carbonyl carbon atom in the azodicarbonamide molecule with its lone pair of electrons, forming an intermediate with a negative charge. However, the intermediate is unstable and will undergo a proton transfer. The hydrogen atom connected to the nitrogen atom in the intermediate will transfer to the oxygen anion connected to the carbonyl oxygen atom, forming a hydroxyl group. At this time, the intermediate transforms into a compound containing a hydroxyl group and an amino group, and the amino group and the hydroxyl group will undergo a condensation reaction, ultimately generating a product containing an amide bond. The modified foaming agent at this time can make more effective use of the gas generated by its own decomposition, reduce the escape and waste of gas, and enable more gas to participate in the formation and expansion process of the foam cells, thereby improving the foaming efficiency and making the foamed sheet have a lighter weight and better cushioning performance. In Comparative Examples 10-12, when a single foaming aid is used or no composite foaming aid is added, the rebound rate of the foamed sheet is lower than that of the Examples. Since the composite foaming aid can reduce the surface tension of EVA, making the gas generated by the decomposition of the foaming agent easier to form bubbles and making the bubbles easier to expand during the growth process. The lower surface tension helps the thinning and stretching of the bubble wall, which is beneficial to the formation of larger and more uniform foam cells and improves the foam cell quality of the foamed sheet, creating conditions for a good rebound rate. The modified foaming agent reduces the stress concentration points between the foam cells by controlling the size and distribution of the foam cells, while the composite foaming aid further enhances the stability of the foam cells by forming a protective film on the bubble surface and adjusting the melt properties. The two work together to enable the foam cells to better maintain their integrity and shape during the foaming process and subsequent use, and are not prone to problems such as rupture and collapse. As a result, the foamed sheet can more effectively return to its original state after being compressed by an external force, significantly improving the rebound rate, and thus also improving the durability of the foamed sheet. In Comparative Examples 13-14, too high or too low temperature in the secondary mixing will have an adverse effect on the rebound rate of the foamed sheet. Too high temperature will cause the cross-linking reaction to proceed too violently, resulting in a significant increase in the cross-linking density. Excessive cross-linking will significantly reduce the movement ability of the molecular chain segments of the foamed sheet, making the material become rigid, weakening the elastic deformation ability, and reducing the rebound rate. If the temperature of the secondary mixing is too low, the activity of the cross-linking agent is insufficient, and the cross-linking reaction cannot proceed fully. Insufficient cross-linking points cannot be formed between the polymer molecular chains, making it difficult to construct a complete and stable cross-linking network, and unable to effectively transfer and disperse the external force. As a result, the material cannot rely on the elastic restoring force of the cross-linking network to return to its original state after compression, and the rebound rate is reduced.

[0095] Examples 11-15

[0096] Referring to the parameter conditions in Example 8, the specific differences are shown in Table 5.

[0097] Table 5 Parameter Conditions of Example 8 and Examples 11 - 15

[0098]

[0099] Comparative Example 15

[0100] Refer to the parameter conditions in Example 8, with the difference that only graphene is added.

[0101] Comparative Example 16

[0102] Refer to the parameter conditions in Example 8, with the difference that modified graphene is not added.

[0103] Comparative Example 17

[0104] Refer to the parameter conditions in Example 8, with the difference that only butyl stearate is used as the lubricant.

[0105] Comparative Example 18

[0106] Refer to the parameter conditions in Example 8, with the difference that only zinc stearate is used as the lubricant.

[0107] Comparative Example 19

[0108] Refer to the parameter conditions in Example 8, with the difference that the composite lubricant is not added.

[0109] Experimental Example 3 Abrasion Resistance Test

[0110] The abrasion resistance of Example 8, Examples 11 - 15 and Comparative Examples 15 - 19 was tested according to the standard of GB / T 9867 - 2008, and the obtained results are shown in Table 6.

[0111] Table 6 Abrasion Resistance Test of Example 8, Examples 11 - 15 and Comparative Examples 15 - 19

[0112] Example <![CDATA[DIN Wear Resistance / mm 3 > Example 8 108 Example 11 105 Example 12 106 Example 13 103 Example 14 105 Example 15 106 Comparative Example 15 122 Comparative Example 16 145 Comparative Example 17 127 Comparative Example 18 124 Comparative Example 19 138

[0113] It can be found from Table 6 that in Comparative Examples 15-16, only graphene was used or modified graphene was not added, and the wear resistance of the foamed sheet was much lower than that of the Examples. This is because graphene itself has extremely high strength and modulus, and after modification, it can better combine with the EVA matrix. In the EVA foamed sheet, it is equivalent to a kind of reinforcing framework, which can bear a part of the externally applied friction and pressure, reduce the stress directly borne by the EVA matrix, thereby reducing the material loss caused by friction and improving the wear resistance. During the friction process, the modified graphene can also form a lubricating transfer film on the surface of the EVA foamed sheet. This film has an extremely low friction coefficient and can reduce the surface wear. In Comparative Examples 17-19, only a single lubricant was used or a composite lubricant was not used, and the wear resistance of the foamed sheet was also very low compared with the Examples. Since the composite lubricant can form a uniform lubricating film on the surface of the EVA foamed sheet, making the sheet surface smoother, reducing the friction coefficient when contacting other objects, and reducing the wear generated during the friction process, just like adding a "separator layer" between two friction surfaces, making it easier for them to slide relative to each other instead of scraping against each other. The modified graphene enhances the mechanical properties and barrier properties of the EVA matrix, and the composite lubricant improves the processing properties and interfacial bonding force. The combined action of the two makes the overall structure of the EVA foamed sheet more stable and uniform. During the friction process, the material can better withstand external forces and is not prone to local deformation, increased wear, etc., and the wear resistance is synergistically enhanced, thereby improving the durability of the foamed sheet.

[0114] Examples 16-20

[0115] Referring to the parameter conditions in Example 13, the specific differences are shown in Table 7.

[0116] Table 7 Parameter Conditions of Example 13 and Examples 16-20

[0117]

[0118] Comparative Example 20

[0119] Referring to the parameter conditions in Example 13, the difference is that only γ-glycidoxypropyltrimethoxysilane is added.

[0120] Comparative Example 21

[0121] Referring to the parameter conditions in Example 13, the difference is that the modified coupling agent is not added.

[0122] Comparative Example 22

[0123] Referring to the parameter conditions in Example 13, the difference is that zinc oxide is not added.

[0124] Comparative Example 23

[0125] Refer to the parameter conditions in Example 13, with the difference that stearic acid is not added.

[0126] Comparative Example 24

[0127] Refer to the parameter conditions in Example 13, with the difference that the temperature of compression molding and foaming is 230 °C.

[0128] Comparative Example 25

[0129] Refer to the parameter conditions in Example 13, with the difference that the temperature of compression molding and foaming is 100 °C.

[0130] Experimental Example 4 Corrosion Resistance Test

[0131] Cut 10-mm experimental samples from the foamed sheets prepared in Example 13, Examples 16 - 20, and Comparative Examples 20 - 25, and place them separately in a 5% (by mass) NaCl solution, a 10% (by mass) NaOH solution, and a 3% (by mass) HCl solution. The corrosion resistance of the coating was tested by calculating the mass loss rate (%) of the samples in the acid, alkali, and salt solutions after 30 days. The results are shown in Table 8. The mass loss rates of Example 18 and Comparative Examples 20 - 25 are as Figure 1 shown.

[0132] Table 8 Corrosion Resistance Test of Example 13, Examples 16 - 20, and Comparative Examples 20 - 25

[0133]

[0134]

[0135] From Table 8 and Figure 1It can be found that in Comparative Examples 20-21, when only γ-glycidoxypropyltrimethoxysilane is used or no modified coupling agent is added, the corrosion resistance of the foamed sheet is much lower than that of the Examples. This is because one end of the modified coupling agent obtained by graft modification can be tightly combined with the molecular chains in the EVA matrix through chemical bond action, and the other end can act on the surface of zinc oxide, thus forming a good bridge between the EVA matrix and other components, making their combination more firm and reducing the interfacial damage caused by the intrusion of external corrosive media. In the Examples, zinc oxide has a certain particle size and shape and can be evenly dispersed in the EVA matrix to form a physical barrier, which can block the penetration of corrosive media, extend the path for the corrosive media to reach the inside of the EVA matrix, and thus slow down the corrosion process. In Comparative Example 22, zinc oxide is not added, and its corrosion resistance is significantly poor. In Comparative Example 23, stearic acid is not added, and the corrosion resistance of the foamed sheet decreases. Since stearic acid molecules can form an isolation layer inside the EVA foamed sheet to prevent the diffusion and penetration of corrosive media inside the sheet; in an environment with acid-base corrosion, stearic acid can maintain a relatively stable pH value inside the sheet by neutralizing alkaline substances or inhibiting the dissociation of acidic substances, reducing the corrosion of the EVA matrix and other components by acid-base. There is a certain synergistic effect among the three. The modified coupling agent promotes the combination between zinc oxide and the EVA matrix, enabling zinc oxide to better play its role in the cross-linking reaction, increasing the cross-linking density, and at the same time enhancing the dispersion stability of zinc oxide in the EVA matrix, reducing the agglomeration phenomenon of zinc oxide, thereby more effectively blocking the corrosion media. Stearic acid helps the modified coupling agent and zinc oxide to be evenly dispersed in the EVA matrix, further improving their synergistic effect and the corrosion resistance of the sheet, thus improving the durability. In Comparative Examples 24-25, too high or too low molding and foaming temperature will have an adverse effect on the corrosion resistance of the foamed sheet. Too high molding and foaming temperature may cause excessive cross-linking or degradation of the polymer chains inside the foamed sheet. Excessive cross-linking will reduce the flexibility of the molecular chains, making the material hard and brittle, and more prone to cracks when exposed to chemical substances, providing channels for the penetration of corrosive media and accelerating the corrosion process; too low molding and foaming temperature will cause insufficient decomposition of the foaming agent and unable to generate enough gas to form a uniform and fine cell structure, resulting in a large amount of unreacted foaming agent or bubble nuclei inside the material. These defects will become channels and aggregation points for corrosive media, accelerating the corrosion of the material. Therefore, controlling the appropriate molding and foaming temperature can enable the foamed sheet to maintain good corrosion resistance and thus improve its durability.

[0136] Although embodiments of the present invention have been shown and described, those of ordinary skill in the art will appreciate that various changes, modifications, substitutions and variations can be made to these embodiments without departing from the principles and spirit of the present invention. The scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A corrosion-resistant EVA foam sheet, characterized in that: By weight, the synthetic raw materials of the EVA foam sheet include: EVA: 80 parts; polyurethane elastomer: 15-20 parts; composite cross-linking agent: 2-6 parts; modified foaming agent: 6-10 parts; composite foaming aid: 0.5-1 parts; modified graphene: 1-4 parts; composite lubricant: 0.5-1 parts; modified coupling agent: 1-5 parts; zinc oxide: 1.1-1.5 parts; stearic acid: 0.2-0.6 parts; calcium propionate: 2 parts; The polyurethane elastomer comprises 4,4'-diphenylmethane diisocyanate, polycaprolactone diol and dibutyltin dilaurate; The modified foaming agent includes azodicarbonamide, sodium hydroxide and ethanolamine; The modified graphene includes graphene and cyclopentadiene; The modified coupling agent includes gamma-glycidyloxypropyltrimethoxysilane, hydroquinone and triethylamine.

2. The corrosion-resistant EVA foam sheet according to claim 1, characterized in that: The composite crosslinking agent is prepared by mixing dicumyl peroxide and 1,4-di-tert-butyl peroxyisopropylbenzene, and the weight ratio of the dicumyl peroxide to the 1,4-di-tert-butyl peroxyisopropylbenzene is 2-4:

1.

3. The corrosion-resistant EVA foam sheet according to claim 1, characterized in that: The composite foaming agent auxiliary agent is a mixture of calcium carbonate and talcum powder, and the weight ratio of the calcium carbonate to the talcum powder is 1-4:

2.

4. The corrosion-resistant EVA foam sheet according to claim 1, characterized in that: The composite lubricant is prepared by mixing butyl stearate and zinc stearate, wherein the weight ratio of the butyl stearate to the zinc stearate is 2:3-5.

5. A method for preparing a corrosion-resistant EVA foam sheet, characterized in that: The EVA foam sheet according to claim 1 is prepared, and the preparation method comprises the following steps, measured by weight: S1: 80 parts of EVA and 15-20 parts of polyurethane elastomer are put into an internal mixer for a first internal mixing, wherein the temperature of the first internal mixing is 90°C-100°C, the time is 10min-15min, and the speed is 40rpm; S2: adding 2-6 parts of a composite crosslinking agent, 6-10 parts of a modified foaming agent, 0.5-1 parts of a composite foaming aid, 1-4 parts of modified graphene, 0.5-1 parts of a composite lubricant, 1-5 parts of a modified coupling agent, 1.1-1.5 parts of zinc oxide, 0.2-0.6 parts of stearic acid and 2 parts of calcium propionate into the internal mixer for secondary internal mixing, wherein the temperature of the secondary internal mixing is 110° C.-120° C., the time is 10 min, and the rotation speed is 30 rpm to obtain a mixture; S3 pressing the mixture into a sheet with a thickness of 5 mm on a mixer; S4: subjecting the sheet to compression foaming at a temperature of 175° C. to 185° C. for 8 minutes, and obtaining the EVA foamed sheet after cooling.

6. The method for preparing a corrosion-resistant EVA foam sheet according to claim 5, characterized in that: The preparation method of the polyurethane elastomer is as follows: 6 parts of 4,4'-diphenylmethane diisocyanate and 10-14 parts of polycaprolactone diol are added into a reaction container, and stirred at 85°C for 30 minutes to obtain a prepolymer; after cooling the prepolymer to 50°C, 1 part of dibutyltin dilaurate and 10 parts of ethylene glycol are added, followed by stirring for 2 hours, and after the reaction is completed, the solid product is washed and dried in a vacuum drying oven at 50°C for 12 hours to obtain the polyurethane elastomer.

7. The method for preparing a corrosion-resistant EVA foam sheet according to claim 5, characterized in that: The preparation method of the modified foaming agent is as follows: 5-10 parts of azodicarbonamide and 10 parts of N,N-dimethylformamide are added to a reactor, and stirred at 50°C for 30 minutes to obtain a mixed solution one; 0.5 parts of sodium hydroxide are added to the mixed solution one, and stirring is continued for 15 minutes to obtain a mixed solution two; 5 parts of ethanolamine are slowly added dropwise to the mixed solution two, the temperature of the reactor is increased to 75°C, and stirring is continued for 4 hours. After the reaction is completed, the reactor is cooled to room temperature to obtain a mixed solution three; 30 parts of deionized water are poured into the mixed solution three, and then the precipitate is separated by a suction filtration device, the precipitate is washed with deionized water, and then placed in a drying oven and dried at 60°C for 12 hours to obtain the modified foaming agent.

8. The method for preparing a corrosion-resistant EVA foam sheet according to claim 5, characterized in that: The preparation method of the modified graphene is as follows: 7-12 parts of graphene are dispersed in 15 parts of toluene, and a mixed solution A is obtained after stirring for 30 minutes; 1 part of cyclopentadiene is added to the mixed solution A, and the mixture is transferred to a reactor after stirring for 2 hours, and the reactor is reacted in an oven at a temperature of 160° C.-180° C. for 12 hours. After the reaction is completed, the reaction solution is centrifuged to obtain a solid product, and the centrifugal speed is 8000 rpm; the solid product is washed with ethanol for 5 times, and vacuum dried at 60° C. for 18 hours to obtain the modified graphene.

9. The method for preparing a corrosion-resistant EVA foam sheet according to claim 5, characterized in that: The preparation method of the modified coupling agent is as follows: 3-8 parts of γ-glycidyloxypropyltrimethoxysilane and 10 parts of toluene are added into a four-necked flask, and after stirring for 30 minutes, 0.1 parts of hydroquinone and 0.5 parts of triethylamine are added, and stirring is continued for 30 minutes; the four-necked flask is slowly heated to 70°C, 1 part of acrylic acid is slowly dripped into the four-necked flask, and stirring is continued for 4 hours. After the reaction is completed, the pH value is adjusted to 8 to obtain a reaction solution; the reaction solution is subjected to reduced pressure distillation, then washed with deionized water, and vacuum dried at 60°C for 12 hours to obtain the modified coupling agent.

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