A process for producing a foamed EVA sheet
By introducing branched adamantane and cyclodextrin-modified resin into EVA materials to form soft crosslinking points, the problem of balancing wear resistance and flexibility in EVA materials is solved, achieving a balance between the two.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- GUANGDONG RONGJUN NEW MATERIALS TECHNOLOGY CO LTD
- Filing Date
- 2025-04-24
- Publication Date
- 2026-07-31
AI Technical Summary
Existing technologies struggle to improve the wear resistance of EVA materials without sacrificing their flexibility, making it difficult to achieve both in modification.
By introducing branched adamantane and cyclodextrin to modify the resin, soft crosslinking points are formed by utilizing the host-guest recognition effect of adamantane and cyclodextrin, which improves wear resistance while maintaining flexibility. The modified resin is blended with EVA using a blending modification process.
While improving the wear resistance of EVA materials, it maintains their good toughness, thus achieving a balance between wear resistance and flexibility.
Abstract
Description
Technical Field
[0001] This invention relates to the field of foam material preparation technology, specifically to a foamed EVA sheet production process. Background Technology
[0002] EVA, short for Ethylene Vinyl Acetate, is a thermoplastic copolymer of ethylene and vinyl acetate. Compared to polyethylene, EVA incorporates vinyl acetate monomers into its molecular chain, reducing crystallinity and improving flexibility, impact resistance, filler compatibility, and heat-sealing properties. Therefore, EVA is widely used in footwear, automotive interior packaging, sporting goods, and wire and cable, among other fields. EVA foam, on the other hand, uses EVA resin as a base material and employs physical or chemical foaming agents to generate numerous tiny air bubbles within the resin, creating a foam material with excellent cushioning, softness, thermal insulation, and water resistance. This material, with its unique lightweight, softness, and shock-absorbing properties, has found widespread application in many fields.
[0003] However, EVA materials themselves have limitations in terms of wear resistance and mechanical properties. Therefore, modifying EVA materials has become a common practice in the industry, such as blending modification or crosslinking modification. By blending EVA with other polymers or fillers, or by crosslinking it, its wear resistance can be improved. However, improving wear resistance usually comes at the cost of flexibility, making it difficult to balance flexibility and wear resistance in the modification process. Summary of the Invention
[0004] To address the above problems, this invention provides a process for producing foamed EVA sheets.
[0005] The objective of this invention is achieved through the following technical solution:
[0006] A process for producing foamed EVA sheets includes the following steps:
[0007] EVA and modified resin are dried, mixed and thoroughly kneaded until uniform. Foaming agent and additives are added, and kneaded again until uniform. The mixture is then molded into a sheet, which is then foamed and extruded to obtain the foamed EVA sheet.
[0008] The method for preparing the modified resin includes the following steps:
[0009] (1) Preparation of modified monomers
[0010] Weigh out hydroxyethyl methacrylate and dissolve it in dichloromethane solvent. Add triethylamine, stir and mix, then add 1-adamantane acetyl chloride. Stir and react at room temperature for 6-12 h. Add p-acetamidobenzenesulfonyl azide and 1,8-diazabicyclo[5.4.0]undec-7-ene, and continue stirring and reacting at room temperature for 12-24 h. After the reaction is complete, remove the insoluble matter, concentrate under reduced pressure, purify by silica gel column chromatography, and evaporate the solvent to obtain the modified monomer.
[0011] (2) Polymer preparation
[0012] Weigh low molecular weight branched polyethylene and add it to toluene solvent. Heat the mixture until it is completely dissolved, then cool it. Add the modified monomer and stir thoroughly. Heat the mixture to 100-110°C and reflux for 1-4 hours with stirring. After the reaction is complete, cool it and add vinyl cyclodextrin and an initiator. Mix the mixture and heat it again to 100-110°C and reflux for 1-4 hours with stirring. After the reaction is complete, cool it and dilute the reaction system with acetone. Separate the precipitate, wash and dry it to obtain the polymer, which is the modified resin.
[0013] In some preferred embodiments, the EVA contains 20-40% vinyl acetate by mass.
[0014] In some preferred embodiments, the additive is one or more of the following: foaming agent, antioxidant, crosslinking agent, dispersant, lubricant, and filler.
[0015] More preferably, the foaming agent is one or more of zinc oxide, stearic acid, zinc stearate, and calcium stearate; the antioxidant is one or more of antioxidant 1010, antioxidant 1076, antioxidant 1035, antioxidant 2103, antioxidant 168, antioxidant 164, and antioxidant 626; the crosslinking agent is a peroxide, such as dicumyl peroxide or di-tert-butyl peroxide; the dispersant may be naphthenic oil; the lubricant may be oxidized polyethylene wax; and the filler may be talc.
[0016] In some preferred embodiments, the foaming agent is azodicarbonamide, 4,4-oxodiphenylsulfonyl hydrazine, or calcium carbonate. The foaming agent is an azo compound, such as azodicarbonamide; or a sulfonyl hydrazine compound, such as 4,4-oxodiphenylsulfonyl hydrazine; or a carbonate, such as calcium carbonate.
[0017] In some preferred embodiments, the mass ratio of the EVA to the modified resin, the foaming agent, and the additives is 100:(12-55):(1-5):(0.5-10).
[0018] In some preferred embodiments, the mass ratio of hydroxyethyl methacrylate to triethylamine, 1-adamantane acetyl chloride, p-acetaminobenzenesulfonyl azide, and 1,8-diazabicyclo[5.4.0]undec-7-ene in step (1) is 10:(7.8-9):(15-18):(18-23):(11.5-14.5).
[0019] In some preferred embodiments, the number average molecular weight of the low molecular weight branched polyethylene in step (2) is 200-5000.
[0020] In some preferred embodiments, the initiator is benzoyl peroxide, dicumyl peroxide, di-tert-butyl peroxide, azobisisobutyronitrile, or azobisisoheptanenitrile.
[0021] In some preferred embodiments, the mass ratio of the low molecular weight branched polyethylene to the modified monomer, the vinyl cyclodextrin, and the initiator in step (2) is 10:(0.15-0.5):(1.7-2.8):(0.02-0.06).
[0022] In some preferred embodiments, the mixing temperature is 100-150°C, the mixing time is 5-30 min, and the rotation speed is 120-500 rpm.
[0023] In some preferred embodiments, the foaming temperature is 170-240°C and the foaming time is 1-20 minutes.
[0024] The beneficial effects of this invention are as follows:
[0025] To address the problem that existing technologies for modifying EVA materials struggle to simultaneously achieve both flexibility and abrasion resistance, this invention provides a process for producing foamed EVA sheets. This process involves introducing branched adamantane and cyclodextrin into the system through blending modification, thereby improving the material's abrasion resistance while maintaining good toughness. Specifically, this invention uses hydroxyethyl methacrylate as a raw material, which is acylated with 1-adamantane acetyl chloride to form an ester, which then serves as an active methylene compound. Under alkaline-promoted conditions, this compound undergoes an azide transfer reaction with a sulfonyl azide to obtain a modified monomer with an α-diazocarbonyl structure. Using low-molecular-weight branched polyethylene as a matrix, the modified monomer is grafted onto the branched polyethylene using diazo insertion. This monomer is then copolymerized with vinyl cyclodextrin to obtain a modified resin. This invention, through blending modification, introduces a modified resin with a polyolefin main chain and simultaneously grafted with adamantane and cyclodextrin into the EVA system. This not only exhibits good compatibility with the EVA system but also forms soft crosslinking points based on the host-guest recognition interaction between adamantane and cyclodextrin, thus improving both abrasion resistance and toughness. Detailed Implementation
[0026] The present invention will be further described in conjunction with the following embodiments.
[0027] Example 1
[0028] A process for producing foamed EVA sheets includes the following steps:
[0029] EVA and modified resin are dried, mixed, and thoroughly kneaded until homogeneous. A foaming agent and a foaming aid are added, and the mixture is kneaded again until homogeneous. The mixture is then molded into sheets, foamed, and extruded to obtain the foamed EVA sheet.
[0030] The EVA contains 29% vinyl acetate by mass.
[0031] The method for preparing the modified resin includes the following steps:
[0032] (1) Preparation of modified monomers
[0033] Hydroxyethyl methacrylate was weighed and dissolved in dichloromethane solvent. Triethylamine was added, and after stirring and mixing, 1-adamantane acetyl chloride was added. The mixture was stirred and reacted at room temperature for 8 hours. Acetaminobenzenesulfonyl azide and 1,8-diazabicyclo[5.4.0]undec-7-ene were added, and the mixture was stirred and reacted at room temperature for another 16 hours. After the reaction was completed, the insoluble matter was removed, the mixture was concentrated under reduced pressure, and purified by silica gel column chromatography. The modified monomer was obtained by elution with a mixed solvent of ethyl acetate and petroleum ether (v / v = 1:20) and evaporation of the solvent. The mass ratio of hydroxyethyl methacrylate to triethylamine, 1-adamantane acetyl chloride, acetaminobenzenesulfonyl azide, and 1,8-diazabicyclo[5.4.0]undec-7-ene was 10:8.46:16.35:20.77:13.15.
[0034] (2) Polymer preparation
[0035] Weigh low molecular weight branched polyethylene and add it to toluene solvent. Heat to ensure complete dissolution, then cool. Add the modified monomer and mix thoroughly. Heat to 100-110℃ and maintain the temperature under stirring and reflux for 2 hours. After the reaction is complete, cool. Add maleic anhydride-grafted β-cyclodextrin and an initiator and mix. Heat again to 100-110℃ and maintain the temperature under stirring and reflux for 2 hours. After the reaction is complete, cool. Add acetone to dilute the reaction system. Separate the precipitate, wash, and dry to obtain the polymer, which is the modified resin. The mass ratio of the low molecular weight branched polyethylene to the modified monomer, the maleic anhydride-grafted β-cyclodextrin, and the initiator is 10:0.22:2.22:0.055.
[0036] The low molecular weight branched polyethylene has a number average molecular weight of 2400 (BPE, Mn = 2400, Baker Hughes industrial grade).
[0037] The initiator is benzoyl peroxide;
[0038] The foaming agent is azodicarbonamide;
[0039] The foaming agent is zinc oxide and stearic acid in equal mass ratio;
[0040] The mass ratio of the EVA to the modified resin, the foaming agent, and the foaming aid is 100:27:3.4:0.5.
[0041] The mixing temperature is 145℃, the mixing time is 8 minutes, and the rotation speed is 120-150 rpm.
[0042] The foaming temperature is 220℃ and the foaming time is 5 minutes.
[0043] Example 2
[0044] A process for producing foamed EVA sheets includes the following steps:
[0045] EVA and modified resin are dried, mixed, and thoroughly kneaded until homogeneous. A foaming agent and a foaming aid are added, and the mixture is kneaded again until homogeneous. The mixture is then molded into sheets, foamed, and extruded to obtain the foamed EVA sheet.
[0046] The EVA contains 29% vinyl acetate by mass.
[0047] The method for preparing the modified resin includes the following steps:
[0048] Weigh low molecular weight branched polyethylene and add it to toluene solvent. Heat the mixture until completely dissolved, then cool it. Add maleic anhydride-grafted β-cyclodextrin and an initiator and mix. Heat the mixture again to 100-110℃ and maintain the temperature under stirring and reflux for 2 hours. After the reaction is complete, cool the mixture and add acetone to dilute the reaction system. Separate the precipitate, wash and dry it to obtain the polymer, which is the modified resin. The mass ratio of the low molecular weight branched polyethylene to the maleic anhydride-grafted β-cyclodextrin and the initiator is 10:2.22:0.055.
[0049] The low molecular weight branched polyethylene has a number average molecular weight of 2400 (BPE, Mn = 2400, Baker Hughes industrial grade).
[0050] The initiator is benzoyl peroxide;
[0051] The foaming agent is azodicarbonamide;
[0052] The foaming agent is zinc oxide and stearic acid in equal mass ratio;
[0053] The mass ratio of the EVA to the modified resin, the foaming agent, and the foaming aid is 100:27:3.4:0.5.
[0054] The mixing temperature is 145℃, the mixing time is 8 minutes, and the rotation speed is 120-150 rpm.
[0055] The foaming temperature is 220℃ and the foaming time is 5 minutes.
[0056] Example 3
[0057] A process for producing foamed EVA sheets includes the following steps:
[0058] EVA and modified resin are dried, mixed, and thoroughly kneaded until homogeneous. A foaming agent and a foaming aid are added, and the mixture is kneaded again until homogeneous. The mixture is then molded into sheets, foamed, and extruded to obtain the foamed EVA sheet.
[0059] The EVA contains 29% vinyl acetate by mass.
[0060] The method for preparing the modified resin includes the following steps:
[0061] (1) Preparation of modified monomers
[0062] Hydroxyethyl methacrylate was weighed and dissolved in dichloromethane solvent. Triethylamine was added, and after stirring and mixing, 1-adamantane acetyl chloride was added. The mixture was stirred and reacted at room temperature for 8 hours. Acetaminobenzenesulfonyl azide and 1,8-diazabicyclo[5.4.0]undec-7-ene were added, and the mixture was stirred and reacted at room temperature for another 16 hours. After the reaction was completed, the insoluble matter was removed, the mixture was concentrated under reduced pressure, and purified by silica gel column chromatography. The modified monomer was obtained by elution with a mixed solvent of ethyl acetate and petroleum ether (v / v = 1:20) and evaporation of the solvent. The mass ratio of hydroxyethyl methacrylate to triethylamine, 1-adamantane acetyl chloride, acetaminobenzenesulfonyl azide, and 1,8-diazabicyclo[5.4.0]undec-7-ene was 10:8.46:16.35:20.77:13.15.
[0063] (2) Polymer preparation
[0064] Weigh low molecular weight branched polyethylene and add it to toluene solvent. Heat to dissolve completely, then cool. Add the modified monomer and mix thoroughly. Heat to 100-110℃ and reflux with stirring for 2 hours. After the reaction is complete, cool. Add dimethyl maleate and initiator and mix. Heat again to 100-110℃ and reflux with stirring for 2 hours. After the reaction is complete, cool. Add acetone to dilute the reaction system. Separate the precipitate, wash, and dry to obtain the polymer, which is the modified resin. The mass ratio of the low molecular weight branched polyethylene to the modified monomer, dimethyl maleate, and initiator is 10:0.22:2.22:0.055.
[0065] The low molecular weight branched polyethylene has a number average molecular weight of 2400 (BPE, Mn = 2400, Baker Hughes industrial grade).
[0066] The initiator is benzoyl peroxide;
[0067] The foaming agent is azodicarbonamide;
[0068] The foaming agent is zinc oxide and stearic acid in equal mass ratio;
[0069] The mass ratio of the EVA to the modified resin, the foaming agent, and the foaming aid is 100:27:3.4:0.5.
[0070] The mixing temperature is 145℃, the mixing time is 8 minutes, and the rotation speed is 120-150 rpm.
[0071] The foaming temperature is 220℃ and the foaming time is 5 minutes.
[0072] Example 4
[0073] A process for producing foamed EVA sheets includes the following steps:
[0074] EVA and modified resin are dried, mixed, and thoroughly kneaded until homogeneous. A foaming agent and a foaming aid are added, and the mixture is kneaded again until homogeneous. The mixture is then molded into sheets, foamed, and extruded to obtain the foamed EVA sheet.
[0075] The EVA contains 29% vinyl acetate by mass.
[0076] The modified resin is low molecular weight branched polyethylene, and the number average molecular weight of the low molecular weight branched polyethylene is 2400 (BPE, Mn=2400, Baker Hughes industrial product).
[0077] The foaming agent is azodicarbonamide;
[0078] The foaming agent is zinc oxide and stearic acid in equal mass ratio;
[0079] The mass ratio of the EVA to the modified resin, the foaming agent, and the foaming aid is 100:27:3.4:0.5.
[0080] The mixing temperature is 145℃, the mixing time is 8 minutes, and the rotation speed is 120-150 rpm.
[0081] The foaming temperature is 220℃ and the foaming time is 5 minutes.
[0082] Example 5
[0083] A process for producing foamed EVA sheets includes the following steps:
[0084] After drying, EVA is thoroughly mixed until homogeneous. A foaming agent and a foaming aid are added, and the mixture is mixed again until homogeneous. The mixture is then molded into sheets, which are then foamed again before being extruded to obtain the foamed EVA sheet.
[0085] The EVA contains 29% vinyl acetate by mass.
[0086] The foaming agent is azodicarbonamide;
[0087] The foaming agent is zinc oxide and stearic acid in equal mass ratio;
[0088] The mass ratio of EVA to the foaming agent and the foaming aid is 100:3.4:0.5;
[0089] The mixing temperature is 145℃, the mixing time is 8 minutes, and the rotation speed is 120-150 rpm.
[0090] The foaming temperature is 220℃ and the foaming time is 5 minutes.
[0091] The wear resistance and mechanical properties of the foamed EVA materials prepared in Examples 1-5 were determined. Tensile strength and elongation at break were measured according to GB / T 528-2008 using an electronic tensile testing machine. The sample shape was dumbbell type 2, and the moving speed of the electronic tensile testing machine fixture was 500 mm / min ± 50 mm / min. Impact resilience was measured on a JH-7042-RE elastic testing machine. Compression set was measured according to HG / T2876-2009. The test results are shown in the table below.
[0092] Tensile strength / MPa 3.47 1.92 1.83 3.13 1.75 Elongation at break / % 295.7 279.5 268.7 207.2 288.4 Impact rebound rate / % 38 32 33 31 32 Compression set rate / % 16.4 18.6 19.7 17.3 19.5 <![CDATA[DIN wear / mm 3 > 179 344 355 321 358
[0093] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit the scope of protection of the present invention. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the essence and scope of the technical solutions of the present invention.
Claims
1. A process for producing foamed EVA sheets, characterized in that, Includes the following steps: After drying, EVA and modified resin are mixed and thoroughly kneaded until homogeneous. Foaming agent and additives are added and kneaded again until homogeneous. The mixture is then molded into a sheet, which is then foamed and extruded to obtain the foamed EVA sheet. The mass ratio of EVA to modified resin, foaming agent and additives is 100:(12-55):(1-5):(0.5-10). The method for preparing the modified resin includes the following steps: (1) Preparation of modified monomers Weigh out hydroxyethyl methacrylate and dissolve it in dichloromethane solvent. Add triethylamine, stir and mix, then add 1-adamantane acetyl chloride. Stir and react at room temperature for 6-12 h. Add p-acetamidobenzenesulfonyl azide and 1,8-diazabicyclo[5.4.0]undec-7-ene, and continue stirring and reacting at room temperature for 12-24 h. After the reaction is complete, remove the insoluble matter, concentrate under reduced pressure, purify by silica gel column chromatography, and evaporate the solvent to obtain the modified monomer. (2) Polymer preparation Weigh low molecular weight branched polyethylene and add it to toluene solvent. Heat the mixture until completely dissolved, then cool it. Add the modified monomer and stir thoroughly. Heat the mixture to 100-110°C and reflux for 1-4 hours. After the reaction is complete, cool it. Add vinyl cyclodextrin and initiator and mix them. Heat the mixture again to 100-110°C and reflux for 1-4 hours. After the reaction is complete, cool it. Add acetone to dilute the reaction system. Separate the precipitate, wash and dry it to obtain the polymer, which is the modified resin. The mass ratio of the low molecular weight branched polyethylene to the modified monomer, the vinyl cyclodextrin and the initiator is 10:(0.15-0.5):(1.7-2.8):(0.02-0.06).
2. The foamed EVA sheet production process according to claim 1, characterized in that, The mass fraction of vinyl acetate in the EVA is 20-40%.
3. The foamed EVA sheet production process according to claim 1, characterized in that, The additive is one or more of the following: foaming agent, antioxidant, crosslinking agent, dispersant, lubricant, and filler.
4. The foamed EVA sheet production process according to claim 1, characterized in that, The foaming agent is azodicarbonamide or 4,4-oxodibenzenesulfonylhydrazine.
5. The foamed EVA sheet production process according to claim 1, characterized in that, The mass ratio of hydroxyethyl methacrylate, triethylamine, 1-adamantane acetyl chloride, p-acetaminobenzenesulfonyl azide, and 1,8-diazabicyclo[5.4.0]undec-7-ene in step (1) is 10:(7.8-9):(15-18):(18-23):(11.5-14.5).
6. The foamed EVA sheet production process according to claim 1, characterized in that, The number average molecular weight of the low molecular weight branched polyethylene mentioned in step (2) is 200-5000.
7. The foamed EVA sheet production process according to claim 1, characterized in that, The mixing temperature is 100-150℃, the mixing time is 5-30 min, and the rotation speed is 120-500 rpm.
8. The foamed EVA sheet production process according to claim 1, characterized in that, The foaming temperature is 170-240℃, and the foaming time is 1-20 minutes.