Anti-shrinkage rubber foamed material and preparation method and application thereof

Abstract

The present application relates to a kind of anti-shrinkage rubber foamed material and its preparation method, application.NR / BR is as rubber main matrix, POE / EPDM is as rubber auxiliary component, select the mixture of polyethylene glycol and paraffin oil as rubber mixing dispersant, select the mixture of polyethylene glycol dimethyl methacrylate and silane coupling agent as rubber foaming control agent, with blowing agent AC, crosslinking agent DCP, stearic acid and other additives are mixed and mixed after, it is molded and foamed above 170 DEG C, finally, a kind of ultra-light, high elastic, low compression permanent deformation foamed shoe rubber new material is obtained.The composite foaming control agent and composite mixing dispersant selected in the present application can make rubber be better dispersed in the process of mixing, while ensuring that rubber material slowly foams when vulcanization foaming, obvious shrinkage will not be caused after being made into finished product, and the foamed shoe rubber material obtained has more advantages compared with EVA.

Description

Technical Field

[0001] This invention relates to the field of footwear materials technology, specifically to an anti-shrinkage rubber foam material, its preparation method, and its application. Background Technology

[0002] Ethylene-vinyl acetate copolymer (EVA) foam material for footwear has long been criticized by consumers for its low mechanical properties, poor elasticity, and poor compression resistance. In recent years, especially after the price of EVA raw materials has continuously risen above the price of rubber, industry experts hope to replace foamed EVA materials with foamed rubber to overcome the shortcomings of EVA footwear materials. Currently, commonly used rubbers on the market include natural rubber (NR), styrene-butadiene rubber (SBR), butadiene rubber (BR), nitrile rubber (NBR), isoprene rubber (IR), chloroprene rubber (CR), and ethylene propylene diene monomer (EPDM), all of which, after foaming, are expected to replace foamed EVA materials.

[0003] While foamed rubber boasts advantages such as light weight, good elasticity, softness, heat insulation, and sound absorption, making it widely used in aerospace, automotive, instrumentation, home appliances, and packaging, it also has some drawbacks. Firstly, foamed rubber materials are prone to shrinkage, exhibiting high shrinkage rates and poor dimensional stability. Secondly, the high Mooney viscosity of rubber hinders injection molding. Furthermore, when using chemical foaming agents to prepare foamed rubber materials, the pressure difference between the inside and outside of the cells causes gas to permeate into the polymer, leading to continuous volume shrinkage over time. This increases the difficulty of matching the vulcanization and foaming processes, resulting in uneven cell structure and significant shrinkage deformation during foaming. More importantly, foaming systems with rubber as the primary component are difficult to foam at temperatures exceeding 170°C.

[0004] To address these issues, some researchers have used a rubber-EVA compound foaming system to obtain foamed rubber with a shrinkage rate of 1%. However, this approach sacrifices the tensile properties and elasticity of the foamed material. Others have used natural rubber as the main material and foaming agent H to conduct foaming studies, obtaining foamed rubber that can be vulcanized at 150℃. Still others have studied the separate foaming of EPDM rubber, concluding that foaming is best performed at low temperatures. Therefore, preparing foamed rubber at temperatures above 170℃ remains a significant challenge in the industry. Summary of the Invention

[0005] This invention aims to obtain a low-compression, high-elasticity, and lightweight rubber foam material. Using NR / BR as the main matrix and POE (ethylene and butene polymer) / EPDM as the auxiliary system, rubber foaming is performed using foaming agent AC (azodicarbonamide) at 172°C through a vulcanization foaming process. The foaming process is adjusted by dispersing the rubber-plastic system with a rubber dispersant and regulating the foaming process with a foaming control agent to match the vulcanization and foaming systems. Ultimately, a new type of foamed rubber material for shoes with slow foaming, low shrinkage, ultra-lightweight, high elasticity, and low compression set is developed. To achieve the above objectives, the technical solution adopted by this invention is as follows:

[0006] A method for preparing an anti-shrinkage rubber foam material mainly includes the following steps: mixing and mixing the rubber matrix and rubber auxiliary components, then adding processing aids and continuing to mix, and finally foaming and crosslinking.

[0007] Furthermore, the rubber matrix is ​​specifically a mixture of NR and BR, wherein the weight ratio of NR to BR is 80-50:20-50, preferably 60:40.

[0008] Furthermore, the rubber auxiliary component is specifically a mixture of POE and EPDM, wherein the weight ratio of POE to EPDM is 80-50:20-50, preferably 70:30.

[0009] Furthermore, the weight ratio of the rubber matrix to the rubber auxiliary components is 50-40:50-60, preferably 50:50.

[0010] Furthermore, the processing aids include rubber mixing dispersants, rubber foaming control agents, foaming agents, crosslinking agents, and other additives. The amount of rubber mixing dispersant added is equivalent to 1.5%-3.0% of the total rubber and plastic composition (i.e., the sum of the rubber matrix and rubber auxiliary components), preferably 2%; the amount of rubber foaming control agent added is equivalent to 4%-8% of the total rubber and plastic composition, preferably 6%; the amount of foaming agent added is equivalent to 2%-4% of the total rubber and plastic composition, preferably 2.5%; the amount of crosslinking agent added is equivalent to 0.6%-1.2% of the total rubber and plastic composition, preferably 1%; and the amount of other additives added is equivalent to 10%-16% of the total rubber and plastic composition, preferably 12.5%.

[0011] Furthermore, the rubber mixing dispersant is specifically a mixture of polyethylene glycol and paraffin oil, with a weight ratio of 5-2:1, preferably 3:1.

[0012] Furthermore, the rubber foaming control agent is specifically a mixture of polyethylene glycol dimethacrylate and a silane coupling agent, with a weight ratio of 4-1:1, preferably 3:1.

[0013] Furthermore, the foaming agent is specifically foaming agent AC (azodicarbonamide), the crosslinking agent is specifically dicumyl peroxide (DCP), and the other additives include stearic acid, zinc oxide, zinc stearate, and talc.

[0014] Furthermore, during processing, the rubber matrix and rubber auxiliary components are first mixed and kneaded. Then, rubber kneading dispersant, rubber foaming control agent, and other additives are added in sequence and kneaded again. Next, foaming agent and crosslinking agent are added and kneaded again. Finally, the mixture is molded, foamed, and vulcanized.

[0015] Furthermore, the mixing temperature is 100-115℃, preferably 105℃; the molding foaming temperature is 168-175℃, preferably 172℃; the molding foaming pressure is 8-12MPa, preferably 10MPa; and the molding foaming time is 260s-320s.

[0016] A second objective of this invention is to provide a shrinkage-resistant rubber foam material prepared according to the above method, which has a resilience of 58%-67% and a density of 0.25-0.75 g·cm³. -3 The compression tolerance should not exceed 28%, and the best result can be controlled below 16%.

[0017] The third objective of this invention is to provide the application of the above-mentioned anti-shrinkage rubber foam material in shoemaking.

[0018] The main rubber compound chosen for the rubber foaming system of this invention is NR / BR, primarily due to the improved feel of the foamed product. Compared to SBR (styrene-butadiene rubber) / BR, this combination produces a smoother, silky feel to the surface of the foamed product. The POE / EPDM rubber foaming auxiliary compound system selected in this invention exhibits excellent flowability and significantly superior elasticity compared to EVA auxiliary compound, allowing it to work well with the NR / BR system to achieve highly elastic foamed shoe materials.

[0019] Both polyethylene glycol (PEG) and paraffin oil have good interpenetration capabilities with rubber systems. PEG, in particular, has inherent lubricating properties and disperses easily into the rubber system during internal mixing. More importantly, PEG molecules contain hydroxyl groups, making them polar; during dispersion, PEG molecules surround rubber macromolecules, resulting in better dispersion. Paraffin oil also primarily increases lubrication between rubber molecules, aiding in the dispersion of the rubber system; its effect is even better when used in conjunction with PEG.

[0020] The control principle of the rubber foaming control agent mixture of polyethylene glycol dimethacrylate and silane coupling agent is as follows: polyethylene glycol dimethacrylate itself has hydroxyl and ester groups. After these groups are dispersed into the rubber system, hydrogen bonds are formed between the active groups of the molecules during rubber foaming. The attraction between molecules slows down the foaming speed of the rubber, thus producing a slow foaming effect in the rubber system. The silane coupling agent has the ability to combine with inorganic fillers after interacting with the rubber, which improves the crystallinity of the composite material. When the rubber system is impacted by foaming gas, it can also constrain the foaming speed of the rubber to a certain extent and reduce the resilience of the rubber during the foaming process.

[0021] Compared with the prior art, the advantages of this invention are reflected in the following aspects:

[0022] (1) The present invention uses a two-component rubber mixing dispersant composed of polyethylene glycol and paraffin oil to ensure that the rubber is more evenly dispersed during mixing and will not shrink significantly during foaming. In particular, it will not shrink significantly after foaming and molding. As a result, the product has a smooth surface, uniform and dense pores, and good elasticity and compression resistance.

[0023] (2) By optimizing the raw material formula and improving the process, the present invention can foam rubber at temperatures above 170°C, and the product is free of bubble defects, which basically solves the problems of rubber foaming process such as poor high temperature resistance and excessive shrinkage ratio.

[0024] (3) The rubber elastomer prepared by the present invention has the advantages of high elasticity, light weight and compression resistance after foaming, and has obvious natural rubber touch (i.e. good hand feel), providing consumers with a comfortable shoe midsole material.

[0025] (4) The foamed rubber shoe material provided by the present invention does not contain EVA material and is expected to replace the more expensive EVA material.

[0026] Instruction manual illustrations

[0027] Figure 1 Photographs of the rubber composite foam samples prepared in Example 1(a) and Comparative Example 1(b);

[0028] Figure 2 Photographs of the rubber composite foam samples prepared in Example 2(a) and Comparative Example 2(b);

[0029] Figure 3 Photographs of the rubber composite foamed insoles prepared in Example 2(a) and Comparative Example 2(b). Detailed Implementation

[0030] To enable those skilled in the art to fully understand the technical solution and beneficial effects of the present invention, the following detailed description is provided in conjunction with specific embodiments.

[0031] Example 1

[0032] First, add 35 parts NR, 15 parts BR, 30 parts POE, and 20 parts EPDM (totaling 100 parts) to a mixer and mix the resulting mixture at 105°C for 3 minutes. Then add 2 parts of rubber dispersant (a mixture of polyethylene glycol and paraffin oil in a 3:1 mass ratio) and continue mixing for 3 minutes. Next, add 6 parts of rubber foaming control agent (a mixture of polyethylene glycol dimethacrylate and silane coupling agent KH550 in a 3:1 mass ratio) and continue mixing for 3 minutes. Add 0.8 parts of stearic acid, 0.9 parts of zinc oxide, 0.8 parts of zinc stearate, and 10 parts of talc powder, and continue mixing for 4 minutes. Add 2.5 parts of foaming agent azodicarbonamide (foaming agent AC) and 1 part of crosslinking agent dicumyl peroxide (crosslinking agent DCP) and mix again for 4 minutes. After mixing, discharge the material and transfer all the material to a granulator to granulate, obtaining rubber foam granules suitable for shoe materials. A certain amount of material granules is placed in a mold for vulcanization and compression molding foaming. The relevant process parameters are as follows: time 260s-320s, temperature 172℃, pressure 10MPa. After completion, the pressure is reduced and the mold is opened to obtain rubber composite foamed shoe material.

[0033] Example 2

[0034] First, add 40 parts NR, 10 parts BR, 30 parts POE, and 20 parts EPDM (totaling 100 parts) to a mixer and mix the resulting mixture at 110°C for 3 minutes. Then add 2.5 parts of rubber dispersant (a mixture of polyethylene glycol and paraffin oil in a 3:1 mass ratio) and continue mixing for 3 minutes. Next, add 6 parts of rubber foaming control agent (a mixture of polyethylene glycol dimethacrylate and silane coupling agent KH550 in a 2:1 mass ratio) and continue mixing for 3 minutes. Then add 0.9 parts of stearic acid, 1.2 parts of zinc oxide, 0.8 parts of zinc stearate, and 9 parts of talc and continue mixing for 4 minutes. Finally, add 2.5 parts of foaming agent azodicarbonamide (foaming agent AC) and 0.9 parts of crosslinking agent dicumyl peroxide (crosslinking agent DCP) and mix again for 4 minutes. After the mixing process is completed, the material is discharged and transferred to a granulator for granulation to obtain rubber foam granules suitable for shoe materials. A certain amount of granules is placed in a mold for vulcanization and compression molding foaming. The relevant process parameters are as follows: time 260s-320s, temperature 172℃, pressure 10MPa. After completion, the pressure is reduced and the mold is opened to obtain rubber composite foam shoe materials.

[0035] Comparative Example 1

[0036] First, add 35 parts NR, 15 parts BR, 30 parts POE, and 20 parts EPDM (totaling 100 parts) to a mixer and mix the resulting mixture at 105°C for 3 minutes. Then add 2 parts of rubber dispersant (paraffin oil) and continue mixing for 3 minutes. Next, add 6 parts of rubber foaming control agent (made from polyethylene glycol dimethacrylate and silane coupling agent KH550 mixed in a 2:1 mass ratio) and continue mixing for 3 minutes. Add 0.8 parts of stearic acid, 0.9 parts of zinc oxide, 0.8 parts of zinc stearate, and 10 parts of talc powder, and continue mixing for 4 minutes. Add 2.5 parts of foaming agent azodicarbonamide (foaming agent AC) and 1 part of crosslinking agent dicumyl peroxide (crosslinking agent DCP) and mix again for 4 minutes. After mixing, discharge the material and transfer it to a granulator to granulate, obtaining rubber foam granules. A certain amount of material granules is placed in a mold for vulcanization and compression molding foaming. The relevant process parameters are as follows: time 260s-320s, temperature 172℃, pressure 10MPa. After completion, the pressure is reduced and the mold is opened to obtain rubber composite foamed shoe material.

[0037] Comparative Example 2

[0038] First, add 40 parts NR, 10 parts BR, 30 parts POE, and 20 parts EPDM (totaling 100 parts) to a mixer and mix the resulting mixture at 110°C for 3 minutes. Then add 2.5 parts of rubber dispersant (made from a 3:1 mass ratio of polyethylene glycol and paraffin oil) and continue mixing for 3 minutes. Next, add 6 parts of silane coupling agent KH550 and continue mixing for 3 minutes. Then add 0.9 parts of stearic acid, 1.2 parts of zinc oxide, 0.8 parts of zinc stearate, and 9 parts of talc and continue mixing for 4 minutes. Finally, add 2.5 parts of foaming agent azodicarbonamide (foaming agent AC) and 0.9 parts of crosslinking agent dicumyl peroxide (crosslinking agent DCP) and mix again for 4 minutes. After mixing, discharge the material and transfer it to a granulator to granulate, obtaining rubber foam granules. A certain amount of material granules is placed in a mold for vulcanization and compression molding foaming. The relevant process parameters are as follows: time 260s-320s, temperature 172℃, pressure 10MPa. After completion, the pressure is reduced and the mold is opened to obtain rubber composite foamed shoe material.

[0039] To fully understand the various properties of the rubber foam materials prepared in the embodiments and comparative examples of the present invention, samples were taken and tested respectively, and the results are shown in the table below.

[0040] Table 1. Comparison of the properties of different foamed rubber specimens

[0041]

[0042] As can be seen from the table, the foaming ratio, resilience, and compression resistance of the foamed rubber material described in Example 1 are significantly better than those of Comparative Example 1. The test results also show that the choice of dispersant has a significant impact on the foaming ratio of the rubber, resulting in a significantly lower foaming ratio, significantly higher density, higher hardness, lower resilience, and greater thermal shrinkage in Comparative Example 1. Furthermore, due to the poor dispersion effect in Comparative Example 1, bubbles also appeared in the product's appearance, such as… Figure 1 As shown.

[0043] The table also shows that the foaming ratio, resilience, and compression resistance of the foamed rubber material described in Example 2 are significantly better than those of Comparative Example 2. The test results indicate that the choice of foaming control agent has a significant impact on the foaming ratio and thermal shrinkage of the rubber system, resulting in a significantly smaller foaming ratio and significantly larger thermal shrinkage in Comparative Example 2. Furthermore, because the foaming speed in Comparative Example 2 is faster than in Example 2, more bubbles appear on the product's appearance, such as… Figure 2 As shown. The finished insoles obtained in Example 2 and Comparative Example 2 are shown in the image. Figure 3 Due to the failure to properly control the foaming speed and heat shrinkage, the small holes at the bottom of the insole in Comparative Document 2 were completely filled during the foaming process, which no longer met the product quality requirements.

Claims

1. A method for preparing an anti-shrinkage rubber foam material, characterized in that, The method includes the following steps: mixing and internally mixing a rubber matrix and rubber auxiliary components, then adding processing aids and continuing internal mixing, and finally foaming and crosslinking; the rubber matrix is ​​specifically a mixture of NR and BR, wherein the weight ratio of NR to BR is 80-50:20-50; the rubber auxiliary components are specifically a mixture of POE and EPDM, wherein the weight ratio of POE to EPDM is 80-50:20-50; the weight ratio of the rubber matrix to the rubber auxiliary components is 50-40:50-60; the processing aids include rubber mixing components. The mixture includes a dispersant, a rubber foaming control agent, a foaming agent, a crosslinking agent, and other additives. Specifically, the rubber mixing dispersant is a mixture of polyethylene glycol and paraffin oil in a weight ratio of 5-2:1, and the amount added is equivalent to 1.5%-3.0% of the total rubber and plastic content. The rubber foaming control agent is specifically a mixture of polyethylene glycol dimethacrylate and a silane coupling agent in a weight ratio of 4-1:1, and the amount added is equivalent to 4%-8% of the total rubber and plastic content. The other additives include stearic acid, zinc oxide, zinc stearate, and talc.

2. The method as described in claim 1, characterized in that: The weight ratio of NR to BR is 60:40, the weight ratio of POE to EPDM is 70:30, the weight ratio of rubber matrix to rubber auxiliary components is 50:50, the amount of foaming agent added is equivalent to 2%-4% of the total amount of rubber and plastic, the amount of crosslinking agent added is equivalent to 0.6%-1.2% of the total amount of rubber and plastic, and the amount of other additives added is equivalent to 10%-16% of the total amount of rubber and plastic.

3. The method as described in claim 2, characterized in that: The amount of rubber mixing dispersant added is equivalent to 2% of the total amount of rubber and plastic, the amount of rubber foam control agent added is equivalent to 6% of the total amount of rubber and plastic, the amount of foaming agent added is equivalent to 2.5% of the total amount of rubber and plastic, the amount of crosslinking agent added is equivalent to 1% of the total amount of rubber and plastic, and the amount of other additives added is equivalent to 12.5% ​​of the total amount of rubber and plastic.

4. The method as described in claim 1, characterized in that: The weight ratio of polyethylene glycol to paraffin oil in the rubber mixing dispersant is 3:1, and the weight ratio of polyethylene glycol dimethacrylate to silane coupling agent in the rubber foaming control agent is 3:

1.

5. The method as described in claim 1, characterized in that: The foaming agent is specifically foaming agent AC, and the crosslinking agent is specifically crosslinking agent DCP.

6. The method as described in claim 1, characterized in that: During processing, the rubber matrix and rubber auxiliary components are first mixed and kneaded. Then, rubber kneading dispersant, rubber foaming control agent, and other additives are added in sequence and kneaded again. Next, foaming agent and crosslinking agent are added and kneaded again. Finally, the mixture is molded, foamed, and vulcanized. The kneading temperature is 100-115℃, the molding and foaming temperature is 168-175℃, the molding and foaming pressure is 8-12MPa, and the molding and foaming time is 260s-320s.

7. The method as described in claim 6, characterized in that: The mixing temperature for each cycle is 105℃, the molding and foaming temperature is 172℃, and the molding and foaming pressure is 10MPa.

8. A shrinkage-resistant rubber foam material, characterized in that: The material has a resilience of 58%-67% and a density of 0.25-0.75 g·cm³. -3 The compression resistance does not exceed 28%.

9. A shrinkage-resistant rubber foam material, characterized in that: The material has a compressibility of less than 16%.

10. The use of the anti-shrinkage rubber foam material of claim 8 or 9 in shoemaking.

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