Foaming EVA sheet production process

Abstract

The invention discloses a foaming EVA sheet production process, which belongs to the technical field of foaming material preparation, and comprises the following steps: drying EVA and modified resin, mixing, fully mixing to be uniform, adding a foaming agent and an auxiliary agent, mixing again to be uniform, carrying out mold pressing forming to obtain a sheet, foaming, and discharging to obtain the foaming EVA sheet. The modified resin is prepared by taking hydroxyethyl methylacrylate as a raw material, acylating the hydroxyethyl methylacrylate and adamantane acetyl chloride to form ester, then carrying out azide transfer reaction on the ester serving as an active methylene compound and sulfonyl azide to prepare a modified monomer with an alpha-diazocarbonyl structure, and preparing a modified monomer with an alpha-diazocarbonyl structure by taking low-molecular-weight branched polyethylene as a matrix. Grafting the modified monomer on branched polyethylene by diazo insertion, and then copolymerizing with vinyl cyclodextrin, so as to obtain the product, according to the production process of the foamed EVA sheet, the wear resistance of the material can be improved, and meanwhile, the good toughness of the material is kept.

Description

Technical Field

[0001] The present invention relates to the technical field of foaming material preparation, and particularly relates to a production process of foamed EVA sheets. Background Art

[0002] EVA, fully known as Ethylene Vinyl Acetate, is a thermoplastic plastic copolymerized from ethylene and vinyl acetate. Compared with polyethylene, vinyl acetate monomer is introduced into the molecular chain of EVA, thereby reducing the crystallinity and at the same time enhancing the flexibility, impact resistance, filler compatibility and heat-sealing performance. Therefore, EVA has a wide range of applications in many fields such as shoe materials, packaging, automotive interiors, sports equipment and wire and cable. EVA foaming material is a foaming material that uses EVA resin as the base material and generates a large number of tiny bubbles inside the EVA resin through the action of physical or chemical foaming agents, thereby forming a foaming material with excellent cushioning, softness, heat insulation and water resistance. This material has been widely used in many fields due to its unique light weight, softness and seismic resistance.

[0003] However, the EVA material itself has limitations in terms of wear resistance and mechanical properties. Therefore, it has become a common practice in the industry to modify the EVA material, such as blending modification or cross-linking modification. By blending EVA with other polymers or fillers, or cross-linking to improve its wear resistance, improving the wear resistance usually comes at the cost of sacrificing flexibility, making it difficult to balance flexibility and wear resistance in the modification. Summary of the Invention

[0004] In view of the above problems, the present invention provides a production process of foamed EVA sheets.

[0005] The object of the present invention is achieved by the following technical solutions:

[0006] A production process of foamed EVA sheets, comprising the following steps:

[0007] Dry and mix EVA and modified resin and fully knead until uniform, add foaming agent and additives, knead again until uniform, mold and form to obtain sheets, and then foam and take out the sheets to obtain the foamed EVA sheets;

[0008] Among them, the preparation method of the modified resin comprises the following steps:

[0009] (1) Preparation of modified monomer

[0010] Weigh 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 to stir and react at room temperature for 12 - 24 h. After the reaction is completed, remove the insoluble substances, concentrate under reduced pressure, and then purify by silica gel column chromatography. After evaporating the solvent, the modified monomer is obtained.

[0011] (2) Polymer preparation

[0012] Weigh low molecular weight branched polyethylene and add it to toluene solvent. Heat to dissolve completely and then cool. Add the modified monomer and stir well to mix. Heat to 100 - 110 °C and keep stirring and refluxing for 1 - 4 h. After the reaction is completed, cool, add vinyl cyclodextrin and initiator and mix. Heat up again to 100 - 110 °C and keep stirring and refluxing for 1 - 4 h. After the reaction is completed, cool, add acetone to dilute the reaction system, separate the precipitate, wash and dry to obtain the polymer, which is the modified resin.

[0013] In some preferred embodiments, the mass fraction of vinyl acetate in the EVA is 20 - 40%.

[0014] In some preferred embodiments, the auxiliary agent is one or more of a co-foaming agent, an antioxidant, a crosslinking agent, a dispersant, a lubricant, and a filler.

[0015] Further preferably, the co-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 and di-tert-butyl peroxide; the dispersant can be naphthenic oil; the lubricant can be polyethylene wax oxide; the filler can be talc powder.

[0016] In some preferred embodiments, the foaming agent is azodicarbonamide, 4,4'-oxybis(benzenesulfonyl hydrazide), or calcium carbonate. The foaming agent is an azo compound, such as azodicarbonamide; or a sulfonyl hydrazide compound, such as 4,4'-oxybis(benzenesulfonyl hydrazide); or a carbonate, such as calcium carbonate.

[0017] In some preferred embodiments, the mass ratio of the EVA, the modified resin, the foaming agent, and the auxiliary agent 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-acetamidobenzenesulfonyl 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, diisopropylbenzene peroxide, di-tert-butyl peroxide, azobisisobutyronitrile, or azodiisooctanenitrile.

[0021] In some preferred embodiments, the mass ratio of the low molecular weight branched polyethylene to the modified monomer, vinyl cyclodextrin, and initiator in step (2) is 10:(0.15 - 0.5):(1.7 - 2.8):(0.02 - 0.06).

[0022] In some preferred embodiments, the temperature of the mixing 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 temperature of the foaming is 170 - 240 °C, and the foaming time is 1 - 20 min.

[0024] The beneficial effects of the present invention are as follows:

[0025] Aiming at the problem that it is difficult to balance flexibility and wear resistance in the modification of EVA materials in the prior art, the present invention provides a production process for foamed EVA sheets. By blending modification, branched adamantane and cyclodextrin are simultaneously introduced into the system, maintaining good toughness while improving the wear resistance of the material. Specifically, the present invention uses hydroxyethyl methacrylate as a raw material, acylates it with 1-adamantane acetyl chloride to form an ester as an active methylene compound, and undergoes an azide transfer reaction with a sulfonyl azide under alkaline promotion conditions 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 by diazo insertion, and then copolymerized with vinyl cyclodextrin to obtain a modified resin. Through blending modification, the present invention introduces a modified resin with a polyolefin main chain and simultaneously grafted with adamantane and cyclodextrin into the EVA system. It not only has good compatibility with the EVA system but also forms soft crosslinking points based on the host-guest recognition between adamantane and cyclodextrin, achieving good toughness while improving wear resistance. Specific Embodiments

[0026] The present invention will be further described in conjunction with the following embodiments.

[0027] Embodiment 1

[0028] A production process of foamed EVA sheet includes the following steps:

[0029] After drying, EVA and modified resin are mixed and thoroughly kneaded until uniform. Then, a foaming agent and a co-foaming agent are added, and the mixture is kneaded again until uniform. The sheet is obtained by molding under pressure, and then foamed and taken out of the mold to obtain the foamed EVA sheet. Among them,

[0030] The mass fraction of vinyl acetate in the EVA is 29%;

[0031] The preparation method of the modified resin includes the following steps:

[0032] (1) Preparation of modified monomer

[0033] Weigh hydroxyethyl methacrylate and dissolve it in dichloromethane solvent. Add triethylamine, stir and mix, then add 1-adamantane acetyl chloride, and stir and react at room temperature for 8 h. Add p-acetamidobenzenesulfonyl azide and 1,8-diazabicyclo[5.4.0]undec-7-ene, and continue to stir and react at room temperature for 16 h. After the reaction is completed, remove the insoluble substances, concentrate under reduced pressure, and purify through a silica gel column. Elute with a mixed solvent of ethyl acetate and petroleum ether (v / v = 1:20), and evaporate the solvent to obtain the modified monomer. The mass ratio of hydroxyethyl methacrylate to triethylamine, 1-adamantane acetyl chloride, p-acetamidobenzenesulfonyl azide, and 1,8-diazabicyclo[5.4.0]undec-7-ene is 10:8.46:16.35:20.77:13.15;

[0034] (2) Preparation of polymer

[0035] Weigh low molecular weight branched polyethylene and add it to toluene solvent. Heat to dissolve completely and then cool. Add the modified monomer and stir and mix thoroughly. Heat to 100 - 110 °C and keep stirring and refluxing for 2 h. After the reaction is completed, cool, add maleic anhydride grafted β-cyclodextrin and initiator and mix. Heat again to 100 - 110 °C and keep stirring and refluxing for 2 h. After the reaction is completed, 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 low molecular weight branched polyethylene to the modified monomer, maleic anhydride grafted β-cyclodextrin, and initiator is 10:0.22:2.22:0.055;

[0036] The number average molecular weight of the low molecular weight branched polyethylene is 2400 (BPE, Mn = 2400, Baker Hughes industrial product);

[0037] The initiator is benzoyl peroxide;

[0038] The foaming agent is azodicarbonamide;

[0039] The co-foaming agent is zinc oxide and stearic acid with equal mass ratio;

[0040] The mass ratio of the EVA, the modified resin, the foaming agent, and the co-foaming agent is 100:27:3.4:0.5;

[0041] The temperature of the mixing is 145 °C, the mixing time is 8 min, and the rotation speed is 120 - 150 rpm;

[0042] The temperature of the foaming is 220 °C, and the foaming time is 5 min.

[0043] Example 2

[0044] A production process of foamed EVA sheet includes the following steps:

[0045] Dry and mix the EVA and the modified resin, and fully mix them until uniform. Then add the foaming agent and the co-foaming agent, and mix again until uniform. Press and form to obtain a sheet, and then foam and take out the sheet to obtain the foamed EVA sheet. Among them,

[0046] The mass fraction of vinyl acetate in the EVA is 29%;

[0047] The preparation method of the modified resin includes the following steps:

[0048] Weigh low molecular weight branched polyethylene and add it to toluene solvent. Heat up to complete dissolution and then cool. Add maleic anhydride grafted β-cyclodextrin and the initiator and mix. Heat up again to 100 - 110 °C and keep stirring and refluxing for 2 h. After the reaction is completed, 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, the maleic anhydride grafted β-cyclodextrin, and the initiator is 10:2.22:0.055;

[0049] The number average molecular weight of the low molecular weight branched polyethylene is 2400 (BPE, Mn = 2400, Baker Hughes industrial product);

[0050] The initiator is benzoyl peroxide;

[0051] The foaming agent is azodicarbonamide;

[0052] The co-foaming agent is zinc oxide and stearic acid with equal mass ratio;

[0053] The mass ratio of the EVA, the modified resin, the foaming agent, and the co-foaming agent is 100:27:3.4:0.5;

[0054] The temperature of the mixing is 145 °C, the mixing time is 8 min, and the rotation speed is 120 - 150 rpm;

[0055] The temperature of the foaming is 220 °C, and the foaming time is 5 min.

[0056] Example 3

[0057] A production process of foamed EVA sheet includes the following steps:

[0058] After drying, EVA and the modified resin are mixed and fully kneaded until uniform, the foaming agent and the co-foaming agent are added, and then kneaded again until uniform. The sheet is obtained by molding under pressure, and then the foamed EVA sheet is obtained after foaming and taking out the sheet. Among them,

[0059] The mass fraction of vinyl acetate in the EVA is 29%;

[0060] The preparation method of the modified resin includes the following steps:

[0061] (1) Preparation of modified monomer

[0062] Weigh 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 8 h, add p-acetamidobenzenesulfonyl azide and 1,8-diazabicyclo[5.4.0]undec-7-ene, and continue to stir and react at room temperature for 16 h. After the reaction is completed, insoluble substances are removed, concentrated under reduced pressure, and then purified by passing through a silica gel column, eluted with a mixed solvent of ethyl acetate and petroleum ether (v / v = 1:20), and the solvent is evaporated to obtain the modified monomer; the mass ratio of hydroxyethyl methacrylate, triethylamine, 1-adamantane acetyl chloride, p-acetamidobenzenesulfonyl azide, and 1,8-diazabicyclo[5.4.0]undec-7-ene is 10:8.46:16.35:20.77:13.15;

[0063] (2) Preparation of polymer

[0064] Weigh low molecular weight branched polyethylene and add it to toluene solvent. Heat it up to complete dissolution and then cool it. Add the modified monomer and stir well to mix. Heat it up to 100 - 110 °C and keep it warm with stirring and reflux for 2 h. After the reaction is completed, cool it. Add dimethyl maleate and initiator and mix. Heat it up again to 100 - 110 °C and keep it warm with stirring and reflux for 2 h. After the reaction is completed, 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 dimethyl maleate, and the initiator is 10:0.22:2.22:0.055;

[0065] The number average molecular weight of the low molecular weight branched polyethylene is 2400 (BPE, Mn = 2400, industrial product of Baker Hughes);

[0066] The initiator is benzoyl peroxide;

[0067] The foaming agent is azodicarbonamide;

[0068] The co - foaming agent is zinc oxide and stearic acid with an equal mass ratio;

[0069] The mass ratio of the EVA to the modified resin, the foaming agent, and the co - foaming agent is 100:27:3.4:0.5;

[0070] The temperature of the mixing is 145 °C, the mixing time is 8 min, and the rotation speed is 120 - 150 rpm;

[0071] The temperature of the foaming is 220 °C, and the foaming time is 5 min.

[0072] Example 4

[0073] A production process of foamed EVA sheet, comprising the following steps:

[0074] Dry EVA and the modified resin and then mix them and mix well until uniform. Add the foaming agent and the co - foaming agent, and mix again until uniform. Mold and form to obtain a sheet, and then foam and take out the sheet to obtain the foamed EVA sheet, where,

[0075] The mass fraction of vinyl acetate in the EVA is 29%;

[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, industrial product of Baker Hughes);

[0077] The foaming agent is azodicarbonamide;

[0078] The co - blowing agent is zinc oxide and stearic acid with an equal mass ratio;

[0079] The mass ratio of the EVA, the modified resin, the blowing agent, and the co - blowing agent is 100:27:3.4:0.5;

[0080] The temperature of the mixing is 145 °C, the mixing time is 8 min, and the rotation speed is 120 - 150 rpm;

[0081] The temperature of the foaming is 220 °C, and the foaming time is 5 min.

[0082] Example 5

[0083] A production process of foamed EVA sheet includes the following steps:

[0084] After drying the EVA, it is fully mixed until uniform, the blowing agent and the co - blowing agent are added, and then it is mixed again until uniform. The sheet is obtained by molding under pressure, and then the foamed EVA sheet is obtained after foaming and taking out the sheet. Among them,

[0085] The mass fraction of vinyl acetate in the EVA is 29%;

[0086] The blowing agent is azodicarbonamide;

[0087] The co - blowing agent is zinc oxide and stearic acid with an equal mass ratio;

[0088] The mass ratio of the EVA, the blowing agent, and the co - blowing agent is 100:3.4:0.5;

[0089] The temperature of the mixing is 145 °C, the mixing time is 8 min, and the rotation speed is 120 - 150 rpm;

[0090] The temperature of the foaming is 220 °C, and the foaming time is 5 min.

[0091] The abrasion resistance and mechanical properties of the foamed EVA materials prepared in Examples 1 - 5 are measured. Among them, the tensile strength and elongation at break are measured with reference to GB / T 528 - 2008, tested by an electronic tensile machine, the sampling shape is dumbbell - shaped type 2, and the moving speed of the experimental fixture of the electronic tensile machine is 500 mm / min ± 50 mm / min; the impact resilience rate is measured on a JH - 7042 - RE elastic testing machine; the compression set rate is measured with reference to HG / T2876 - 2009; the measurement results are shown in the following table:

[0092] Example 1 Example 2 Example 3 Example 4 Example 5 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 resilience / % 38 32 33 31 32 Compression set / % 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, rather than limiting the protection scope of the present invention. Although the present invention has been described in detail with reference to the preferred embodiments, those of ordinary skill in the art should understand that the technical solutions of the present invention can be modified or equivalently replaced without departing from the essence and scope of the technical solutions of the present invention.

Claims

1. A foamed EVA sheet production process, characterized in that: The following steps are involved: The EVA and modified resin are dried and mixed and fully kneaded until uniform, a foaming agent and an auxiliary agent are added, and the mixture is kneaded again until uniform, and a sheet is obtained by molding, and then the sheet is produced after foaming to obtain the foamed EVA sheet; Wherein, the preparation method of the modified resin comprises the following steps: (1) Preparation of modified monomers Weigh 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 hours, add 4-acetylaminobenzenesulfonyl azide and 1,8-diazabicyclo[5.4.0]undec-7-ene, continue to stir and react at room temperature for 12-24 hours, remove insoluble matter after the reaction is completed, concentrate under reduced pressure, purify through a silica gel column, and evaporate the solvent to obtain a modified monomer; (2) Polymer preparation Weigh low molecular weight branched polyethylene and add it to toluene solvent, heat it to dissolve completely and then cool it, add the modified monomer and stir and mix it thoroughly, heat it to 100-110° C. and keep it warm and stir and reflux for 1-4 hours, cool it after the reaction is completed, add vinyl cyclodextrin and initiator and mix them, heat it again to 100-110° C. and keep it warm and stir and reflux for 1-4 hours, cool it after the reaction is completed, add acetone to dilute the reaction system, separate the precipitate, wash it, and dry it to obtain a polymer, which is a modified resin.

2. A 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. A foamed EVA sheet production process according to claim 1, characterized in that: The auxiliary agent is one or more of a foaming agent, an antioxidant, a cross-linking agent, a dispersant, a lubricant, and a filler.

4. A foamed EVA sheet production process according to claim 1, characterized in that: The foaming agent is azodicarbonamide, 4,4-oxodibenzenesulfonylhydrazide or calcium carbonate.

5. A foamed EVA sheet production process according to claim 1, characterized in that: The mass ratio of the EVA to the modified resin, the foaming agent and the auxiliary agent is 100:(12-55):(1-5):(0.5-10).

6. A foamed EVA sheet production process according to claim 1, characterized in that: The mass ratio of the hydroxyethyl methacrylate to the triethylamine, the 1-adamantanacetyl chloride, the 4-acetamidobenzenesulfonyl azide, and the 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).

7. A foamed EVA sheet production process according to claim 1, characterized in that: The number average molecular weight of the low molecular weight branched polyethylene in step (2) is 200-5000.

8. A foamed EVA sheet production process according to claim 1, characterized in that: In step (2), 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).

9. A foamed EVA sheet production process according to claim 1, characterized in that: The mixing temperature is 100-150° C., the mixing time is 5-30 min, and the rotation speed is 120-500 rpm.

10. A foamed EVA sheet production process according to claim 1, characterized in that: The foaming temperature is 170-240° C., and the foaming time is 1-20 min.