Soft foaming sole material and preparation method thereof

Abstract

The invention discloses a soft foaming sole material and a preparation method thereof, and relates to the technical field of polymer foaming materials. The material is prepared from the following components in parts by mass: 45 to 65 parts of an ethylene-vinyl acetate copolymer, 15 to 35 parts of a polyolefin elastomer, 3 to 10 parts of polyisobutene, 0.5 to 1.5 parts of an anti-aging agent, 0.4 to 0.8 part of dicumyl peroxide, 1.5 to 3.0 parts of azodicarbonamide, 1.0 to 2.0 parts of zinc oxide and 0.5 to 1.0 part of stearic acid, the anti-aging agent is a compound with a specific spatial configuration. According to the material, through multiphase blending of the ethylene-vinyl acetate copolymer and the polyolefin elastomer and the molecular anchoring effect of the anti-aging agent, a microscopic network structure with soft touch feeling and high resilience is constructed, and the defects that a conventional auxiliary agent is prone to migration blooming and a soft material is prone to collapse can be effectively overcome; the weather-resistant stability is excellent, and the foam structure is fine and compact.

Description

Technical Field

[0001] This invention relates to the field of polymer foaming materials technology, specifically to a soft foamed shoe sole material and its preparation method. Background Technology

[0002] Traditional EVA foam materials exhibit significant performance defects in practical applications. Due to the characteristics of the EVA molecular chain structure, this type of material is highly susceptible to photo-oxidative degradation when exposed to ultraviolet light, heat radiation, and oxygen for extended periods. This aging manifests macroscopically as irreversible yellowing and surface powdering of the shoe sole, accompanied by a sharp decline in key mechanical properties such as elongation at break and tear strength, severely shortening the lifespan of the shoe material and affecting the product's appearance quality.

[0003] While existing foaming formulations often incorporate light stabilizers or antioxidants to slow down the aging process, commercially available small-molecule additives frequently exhibit poor compatibility with the polymer matrix. During long-term storage or use, these additives can easily migrate from the matrix to the material surface, forming blooms. This not only significantly reduces anti-aging efficiency but also interferes with subsequent bonding processes between the sole and other components. Furthermore, with increasing market demands for wearing comfort, single-matrix EVA materials struggle to simultaneously meet the requirements of high resilience and low hardness for a comfortable "walking on clouds" feel. Simply adjusting filler or oil content to reduce hardness often leads to a deterioration in the material's compression set, causing the sole to collapse and fail under long-term load. At the manufacturing process level, achieving uniform nanoscale or microscale dispersion of functional additives in high-viscosity polymer melts remains a technical challenge. Traditional simple mixing processes are insufficient to effectively break up additive agglomerates, resulting in uneven dispersion within the system and the existence of localized concentration gradients. This inhomogeneity directly interferes with the matching balance between the subsequent chemical crosslinking and foaming reaction rates, resulting in a coarse cell structure, wide pore size distribution, and even appearance defects such as pinholes or dents on the surface of the foamed product. Conventional processing methods also have shortcomings in accurately controlling the thermal history of the rubber compound, which can easily lead to early scorching or incomplete plasticization due to the accumulation of shear heat, making it difficult to stably prepare shoe sole materials that combine excellent weather resistance, fine cell structure, and soft, highly elastic feel. Summary of the Invention

[0004] This invention addresses the problems existing in the prior art by providing a soft foamed shoe sole material and its preparation method, which features excellent weather resistance, high component compatibility, soft and comfortable touch, good resilience, and a fine and dense pore structure.

[0005] To achieve a soft foamed shoe sole material, which includes an anti-aging agent as shown in Formula 1: Formula 1: ; In Formula 1, R1 is selected from any one of alkyl, alkoxy, benzyloxy, and hydroxyl groups having 1-5 carbon atoms.

[0006] Further, the alkyl group having 1-5 carbon atoms is selected from methyl; the alkoxy group having 1-5 carbon atoms is selected from methoxy; and R1 is selected from any one of methyl, methoxy, benzyloxy, and hydroxyl. Further, the anti-aging agent is any one of the compounds shown in the following structures: ; ; ; .

[0007] Application as an anti-aging component in a soft foamed shoe sole material.

[0008] A soft foamed shoe sole material is made of the following components in parts by weight: 45 to 65 parts of ethylene-vinyl acetate copolymer, 15 to 35 parts of polyolefin elastomer, 3 to 10 parts of polyisobutylene, 0.5 to 1.5 parts of anti-aging agent, 0.4 to 0.8 parts of dicumyl peroxide, 1.5 to 3.0 parts of azodicarbonamide, 1.0 to 2.0 parts of zinc oxide, and 0.5 to 1.0 parts of stearic acid; wherein the anti-aging agent is the anti-aging agent according to any one of claims 1 to 3.

[0009] Furthermore, in the aforementioned soft foamed sole material, polyisobutylene (PIB) plays a key role primarily due to the high flexibility and high viscosity damping properties of its molecular chains. As a physical modifier, the long-chain molecules of PIB permeate the cross-linked network of EVA and POE, acting similarly to a macromolecular plasticizer. This effectively weakens the intermolecular forces and increases the free volume, thereby significantly reducing the material's hardness and modulus, resulting in an extremely soft feel for the sole. Simultaneously, utilizing its high damping coefficient, PIB can convert impact kinetic energy into heat dissipation when the foamed material is deformed under pressure, reducing excessive rebound and providing the wearer with a thick, shock-absorbing, and non-collapsed delicate foot feel.

[0010] Furthermore, the vinyl acetate content in the ethylene-vinyl acetate copolymer is 28% to 33% by mass; the melt index of the ethylene-vinyl acetate copolymer is 2 to 5 g / 10 min.

[0011] Furthermore, the polyolefin elastomer is an ethylene-octene copolymer; the density of the polyolefin elastomer is 0.86 to 0.88 g / cm³. 3 .

[0012] A method for preparing a soft foamed shoe sole material includes the following steps: a. The ethylene-vinyl acetate copolymer, polyolefin elastomer and polyisobutylene are added to a mixer and subjected to a first stage of plasticizing under pressure to obtain a melt mixture; b. Add the anti-aging agent, zinc oxide and stearic acid to the melt mixture, and carry out a second stage of mixing to obtain the base rubber compound; c. After the matrix rubber compound is discharged, it is thinly passed on a two-roll mill. After the temperature is reduced, dicumyl peroxide and azodicarbonamide are added, mixed evenly in a triangular bag, and then sheeted to obtain an unfoamed rubber sheet. d. After cutting the unfoamed rubber sheet, place it into a mold, pressurize and heat it for foaming and vulcanization, open the mold, and cool it to obtain a soft foamed shoe sole material.

[0013] Furthermore, in step a, the rotor speed of the internal mixer is 50 to 70 rpm, the temperature is 95 to 105°C, and the plasticizing time is 3 to 5 min; in step b, the rotor speed of the internal mixer is increased to 80 to 100 rpm, the temperature is controlled at 110 to 120°C, and the mixing time is 4 to 6 min.

[0014] Furthermore, in step c, the temperature when adding dicumyl peroxide and azodicarbonamide is 75 to 85°C; in step d, the temperature of pressurized heating foaming vulcanization is 165 to 175°C, the pressure is 15 to 18 MPa, and the time is 500 to 700 s.

[0015] This invention resolves the contradiction between tactile feel, mechanical stability, and weather resistance in flexible foam materials through multi-polymer network interpenetration technology and in-situ anchoring strategies for functional molecules. In terms of matrix structure, ethylene-vinyl acetate copolymer and polyolefin elastomer together form a bicontinuous phase framework that combines rigid support and elastic recovery. The long branched chains in the polyolefin elastomer molecular chains form physical cross-linking points, effectively bearing deformation and providing rebound driving force. Within this basic network, polyisobutylene fluid with high viscosity and damping properties utilizes the extremely high flexibility of its molecular chains to penetrate and fill the gaps in the cross-linked network, significantly increasing the free volume of the system and giving the material a soft, low-modulus feel. The introduction of polyisobutylene also utilizes its damping effect to convert the impact kinetic energy under pressure into heat dissipation, mitigating the vibration sensation of traditional high-resilience materials and achieving dynamic mechanical equilibrium at the microscopic level. Regarding weather resistance, the specific anti-aging agents selected in this invention have a large molecular skeleton and a special stereoconfiguration, generating significant steric hindrance and molecular entanglement effects within the polymer matrix. During processing and molding, this compound is stably retained deep within the amorphous network of the polymer, limiting its thermodynamic migration to the material surface and eliminating the risk of surface blooming. The internal retention mechanism ensures that active functional groups remain in regions prone to oxidative degradation for a long time, continuously blocking heat- and light-induced polymer chain breaking reactions, and maintaining the integrity of the cell wall structure and the stability of the appearance and color.

[0016] Compared with the prior art, the beneficial effects of the present invention are: 1. To solve the problems of additive migration and weather resistance, specific high molecular weight anti-aging agents are used to restrict their migration to the surface by utilizing steric hindrance, avoiding blooming phenomenon, so that the active center remains in the matrix for a long time, thereby improving the material's resistance to yellowing and mechanical properties.

[0017] 2. Improved soft touch and anti-collapse performance: Polyolefin elastomers provide physical support, while polyisobutylene utilizes high flexibility to increase free volume and dissipate impact energy, balancing a low-hardness feel with anti-collapse ability and reducing compression set.

[0018] 3. Optimize the cell structure and surface quality through a staged processing technology to promote the matching of cross-linking and foaming rates, form an independent and dense microporous structure, eliminate surface pinhole defects, and enhance the buffering and shock absorption performance by utilizing the stress dispersion effect of the pore walls. Attached Figure Description

[0019] Figure 1 This is a method for synthesizing the anti-aging agent described in this invention.

[0020] Figure 2 This is the infrared absorption spectrum of the anti-aging agent 1 described in this invention.

[0021] Figure 3This is the ultraviolet absorption spectrum of the anti-aging agent 1 described in this invention. Detailed Implementation

[0022] The technical solution of the present invention will now be clearly and completely described with reference to the accompanying drawings. Obviously, the described embodiments are merely some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0023] Preparation Example 1 Preparation of anti-aging agent 1: ; First, under a nitrogen atmosphere, 16.61 g of diisopropylethylamine and 15.00 g of raw material 1 were added to 180 mL of 1,4-dioxane, and 10.10 g of raw material 2 was dissolved in 50 mL of 1,4-dioxane. The solution was slowly added dropwise to the above solution while maintaining the temperature below -10℃. After the addition was complete, the solution was stirred at 40℃ for 12 h. After the reaction was completed, the reaction solution was slowly poured into 500 ml of saturated sodium bicarbonate aqueous solution at 4℃ and stirred until no more bubbles were generated. The pH of the system was adjusted to neutral with 0.1 mol / L hydrochloric acid. The mixture was separated, and the organic phase was retained. The organic phase was washed with water (50 mL × 2) and then with saturated saline (50 mL). The organic phase was dried with anhydrous sodium sulfate, concentrated, and purified by silica gel column chromatography. A mixed solvent of dichloromethane and ethanol was used as the eluent (DCM:MeOH = 20:1 v / v, with 0.5% ammonia added). The eluent was evaporated to dryness to obtain 14.34 g of intermediate 1. In the second step, under nitrogen protection, 10.12 g of raw material 3, 14.34 g of intermediate 1, and 90 ml of a toluene-water mixture (60 ml toluene and 30 ml water) were added sequentially to the dry reaction system. After purging the air with nitrogen, 0.9 g of 1,1-bis(diphenylphosphine)ferrocene palladium dichloride and 11.19 g of potassium carbonate were added sequentially. After purging the air with nitrogen again, the mixture was stirred until homogeneous, heated to 100 °C, and refluxed for 9 h. After the reaction was completed, the mixture was cooled to room temperature and allowed to stand for separation. The upper organic phase was retained and washed sequentially with water and saturated brine. After drying with anhydrous sodium sulfate, the mixture was filtered. The filtrate was purified by removing the solvent using a rotary evaporator and recrystallized with ethanol. After cooling and crystallization, the crystals were filtered and dried under vacuum to obtain 13.01 g of anti-aging agent 1.

[0024] Product structure identification: Mass spectrometry (MS) of intermediate 1 [M+H] + 354; Mass spectrometry (MS) [M+H] of anti-aging agent 1 + :480; NMR of intermediate 1: δ 7.90 (dd, 1H), 7.81 (dd, 1H), 7.52 (d, 1H), 5.20 (p, 1H), 2.38 (d, 3H), 1.99 (dd, 2H), 1.73 (dd, 2H), 1.37 (s, 1H), 1.27 (s, 6H), 1.14 (s, 6H); NMR of anti-aging agent 1: δ 7.97-7.85 (m, 2H), 7.52 (d, 1H), 7.35 (s, 2H), 5.65 (s, 1H), 5.20 (p, 1H), 2.42 (d, 3H), 1.99 (dd, 2H), 1.73 (dd, 2H), 1.49 (s, 18H), 1.37 (s, 1H), 1.27 (s, 6H), 1.14 (s, 6H); The infrared absorption spectrum of anti-aging agent 1 is as follows: Figure 2 As shown; Aging agent 1 was prepared into 10 -5 A mol / L propylene glycol methyl ether acetate (PMA) solution was tested for its UV absorption spectrum in the 250-400 nm range. Figure 3 As shown, it can absorb UV-B ultraviolet light.

[0025] Preparation Examples 2-4 In Preparation Examples 2-4, anti-aging agents 1-4 were synthesized sequentially, following the same synthesis method as in Preparation Example 1, except that raw material 1 was replaced, and all other conditions remained the same as in Preparation Example 1. Specific structures of raw material 1, anti-aging agents 2-4, and MS [MS+H] are described. + The data is shown in Table 1.

[0026] Table 1 Example 1 A method for preparing a soft foamed shoe sole material: 1. Raw material mass ratio: Ethylene-vinyl acetate copolymer: 60 parts, wherein the mass percentage of vinyl acetate (VA) is 30% and the melt index is 3 g / 10 min; Polyolefin elastomer: 30 parts, ethylene octene copolymer, density 0.87 g / cm³ 3 ; Polyisobutylene (PIB): 5 parts; Anti-aging agent: 1.0 part, using anti-aging agent 1 synthesized in Preparation Example 1; (Dicumyl peroxide): 0.6 parts; Azodicarbonamide: 2.0 parts; Zinc oxide: 1.5 parts; Stearic acid: 0.8 parts.

[0027] 2. Preparation method: a. First-stage plasticizing: Add the ethylene-vinyl acetate copolymer, polyolefin elastomer, and polyisobutylene in the above-mentioned proportions to a closed internal mixer, and start the internal mixer under pressure to carry out the first-stage plasticizing. Control the rotor speed of the internal mixer at 60 rpm and the plasticizing temperature at 100℃, and continue plasticizing for 4 minutes to allow the three-phase polymers to fully melt and form an interpenetrating network, resulting in a homogeneous melt mixture; b. Second stage mixing: While maintaining the internal mixer under pressure, add the formulated amount of anti-aging agent, zinc oxide and stearic acid to the melt mixture obtained in step a, increase the rotor speed of the internal mixer to 90 rpm, control the temperature at 115℃, and continue mixing for 5 minutes to fully disperse and blend the functional additives with the polymer matrix to obtain a uniform matrix rubber. c. Mixing and sheeting on an open mill: The base rubber compound obtained in step b is discharged from the internal mixer and transferred to an open mill for thin-pass processing. When the temperature of the rubber compound naturally drops to 80°C, dicumyl peroxide and azodicarbonamide are added in the prescribed amount. The crosslinking agent and foaming agent are evenly dispersed in the rubber compound by repeatedly making triangular wraps. Finally, the unfoamed rubber sheet with a thickness of 3mm is obtained. d. Foaming and vulcanization molding: The unfoamed rubber sheet obtained in step c is cut into the corresponding shape according to the mold size, placed into the mold of the flat vulcanizing machine, and subjected to pressure heating for foaming and vulcanization. The vulcanization temperature is controlled at 170℃, the vulcanization pressure at 16MPa, and the holding time is 600s. After vulcanization, the mold is opened, the product is taken out and placed at room temperature to cool naturally to room temperature, resulting in a soft foamed shoe sole material.

[0028] Examples 2-4 A method for preparing a soft foamed shoe sole material, referring to the preparation method of Example 1, except that the anti-aging agent is replaced in turn with the anti-aging agent synthesized in Preparation Examples 2-4, and the remaining raw materials, proportions and preparation steps are the same as in Example 1.

[0029] Comparative Example 1 The preparation of a soft foamed shoe sole material is carried out according to the preparation method of Example 1, except that the anti-aging agent 1 is not added, and the proportions of other raw materials and preparation steps are the same as those in Example 1.

[0030] Comparative Example 2 The preparation of a soft foamed shoe sole material is carried out by referring to the preparation method of Example 1, except that the anti-aging agent 1 is replaced with an equal mass of anti-aging agent UV-531 (2-hydroxy-4-n-octyloxybenzophenone), and the remaining raw material ratios and preparation steps are the same as in Example 1.

[0031] Comparative Example 3 The preparation of a soft foamed shoe sole material is carried out by referring to the preparation method of Example 1, except that the anti-aging agent 1 is replaced with antioxidant 1010, and the remaining raw material ratios and preparation steps are the same as in Example 1.

[0032] Comparative Example 4 The preparation of a soft foamed shoe sole material is carried out according to the preparation method of Example 1, except that polyisobutylene is not added, and the proportions of other raw materials and preparation steps are the same as in Example 1.

[0033] Performance testing: Test items and methods A1. Yellowing Resistance Test (ΔYI): The test was conducted according to the standard HG / T3689-2014 "Test Method for Yellowing Resistance of Footwear". Test conditions were set as follows: UVA-340 lamp, irradiance 0.89W / m². 2 The blackboard temperature was 60°C, and the samples were continuously exposed to light for 1000 hours. The yellowness index (YI) of the samples was measured using a colorimeter before and after the test, and the change in yellowing index (ΔYI = YI after - YI before) was calculated. The smaller the ΔYI value, the better the resistance to yellowing. The data are shown in Table 2.

[0034] A2. Elongation at break retention rate after aging (%): Refer to GB / T528-2009 "Determination of tensile stress-strain properties of vulcanized rubber or thermoplastic rubber". Test the initial elongation at break of the sample; then place the sample in a hot air aging chamber at 70℃ for 500 hours, remove it and cool it, and test its elongation at break after aging. The data are shown in Table 2.

[0035] A3. Compression set (%): Refer to GB / T6669-2008 "Determination of compression set of flexible foam polymer materials". Compress the sample to 50% of its original thickness, maintain it at 50℃ for 22 hours, and after decompression, allow it to recover at room temperature for 30 minutes. Measure the thickness change. The data are shown in Table 2.

[0036] Table 2 Examples 1-5 outperformed Comparative Examples 1-3 in both yellowing resistance index (ΔYI) and elongation at break retention after aging. Compared to Comparative Example 2, which only added conventional small-molecule additives, the performance advantages of the example groups indicate that the macromolecular anti-aging agent synthesized in this invention has excellent anti-migration stability in the polymer matrix. Its special spatial structure effectively prevents the precipitation of additives during high-temperature vulcanization and long-term light exposure, ensuring the effective concentration of active functional groups in the deep layers of the matrix, thereby permanently blocking the photo-oxidative aging reaction. Regarding the compression set performance of Comparative Example 4, which did not add polyisobutylene (PIB), its compression set rate was significantly higher than that of Example 1. This data difference verifies the key role of polyisobutylene in the ternary blend system: although polyisobutylene is mainly used to reduce modulus and improve softness, it fills the gaps in the crosslinking network of ethylene-vinyl acetate copolymer and polyolefin elastomer, dissipating the destructive internal energy during compression by utilizing its high damping characteristics. The presence of polyisobutylene effectively alleviates the structural collapse of soft foam materials caused by excessive slippage of molecular chains, enabling the material to maintain excellent dimensional stability and fatigue recovery ability while having a low hardness feel.

[0037] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. An anti-aging agent, characterized in that, The anti-aging agent is a compound represented by Formula 1; Formula 1: ； In Formula 1, R1 is selected from any one of alkyl, alkoxy, phenoxy, benzyloxy, and hydroxyl groups having 1-5 carbon atoms.

2. The anti-aging agent according to claim 1, characterized in that, The alkyl group having 1-5 carbon atoms is selected from methyl; the alkoxy group having 1-5 carbon atoms is selected from methoxy.

3. The anti-aging agent according to claim 1, characterized in that, The anti-aging agent is any one of the compounds shown in the following structures: ； ； ； 。 4. The use of the anti-aging agent according to any one of claims 1 to 3 as an anti-aging component in a soft foamed shoe sole material.

5. A soft foamed shoe sole material, characterized in that, It is made from the following components in parts by weight: 45 to 65 parts of ethylene vinyl acetate copolymer, 15 to 35 parts of polyolefin elastomer, 3 to 10 parts of polyisobutylene, 0.5 to 1.5 parts of anti-aging agent, 0.4 to 0.8 parts of dicumyl peroxide, 1.5 to 3.0 parts of azodicarbonamide, 1.0 to 2.0 parts of zinc oxide, and 0.5 to 1.0 parts of stearic acid; wherein the anti-aging agent is the anti-aging agent according to any one of claims 1 to 3.

6. The soft foamed shoe sole material according to claim 5, characterized in that, The ethylene-vinyl acetate copolymer has a vinyl acetate content of 28% to 33% by mass; the melt index of the ethylene-vinyl acetate copolymer is 2 to 5 g / 10 min.

7. The soft foamed shoe sole material according to claim 5, characterized in that, The polyolefin elastomer is an ethylene octene copolymer; the polyolefin elastomer has a density of 0.86 to 0.88 g / cm 3 .

8. A method for preparing a soft foamed shoe sole material according to any one of claims 5 to 7, characterized in that, Includes the following steps: a. The ethylene-vinyl acetate copolymer, polyolefin elastomer, and polyisobutylene are added to a mixer and subjected to a first-stage plasticizing under pressure to obtain a melt mixture; b. The anti-aging agent, zinc oxide, and stearic acid are added to the melt mixture and subjected to a second-stage mixing to obtain a base compound; c. After the matrix rubber compound is discharged, it is thinly passed on a two-roll mill. After the temperature is reduced, dicumyl peroxide and azodicarbonamide are added, mixed evenly in a triangular bag, and then sheeted to obtain an unfoamed rubber sheet. d. After cutting the unfoamed rubber sheet, place it into a mold, pressurize and heat it for foaming and vulcanization, open the mold, and cool it to obtain a soft foamed shoe sole material.

9. The method for preparing a soft foamed shoe sole material according to claim 8, characterized in that, In step a, the rotor speed of the internal mixer is 50 to 70 rpm, the temperature is 95 to 105°C, and the plasticizing time is 3 to 5 minutes; In step b, the rotor speed of the internal mixer is increased to 80 to 100 rpm, the temperature is controlled at 110 to 120°C, and the mixing time is 4 to 6 minutes.

10. The method for preparing a soft foamed shoe sole material according to claim 8, characterized in that, The temperature for adding dicumyl peroxide and azodicarbonamide in step c is 75 to 85°C; the temperature for pressurized heating and foaming vulcanization in step d is 165 to 175°C, the pressure is 15 to 18 MPa, and the time is 500 to 700 s.

Images