Preparation method of dual-density cushioning foaming material and dual-density cushioning insole

Abstract

The invention discloses a preparation method of a dual-density cushioning foaming material and a dual-density cushioning midsole, according to the preparation method, a first part and a second part of different formulas are introduced into the foaming material, a polyolefin elastomer with specific physical properties is introduced into the second material, and the polyolefin elastomer has specific density and melt flow rate; meanwhile, a specific secondary compression molding preparation process is provided, high-temperature and high-pressure are utilized to promote the polyolefin elastomer with high flowability to effectively migrate to a two-phase interface, strong molecular physical entanglement is formed, and the dual-density cushioning foaming material with excellent performance and structural integrity is obtained.

Description

Technical Field

[0001] The present invention relates to the technical field of foam materials, and in particular to a preparation method of a dual-density shock-absorbing foam material and a dual-density shock-absorbing midsole. Background Art

[0002] In the design and development of athletic shoes, especially high-performance professional athletic shoes, the midsole, as the primary component providing core functions such as cushioning, rebound, and support, is crucial for determining shoe performance. With the advancement of sports science, market requirements for midsole functionality are becoming increasingly complex and refined. A single homogeneous material is no longer sufficient to meet the differentiated performance demands of different foot regions in diverse athletic scenarios. For example, when a runner lands, the heel requires extreme impact absorption for protection, while the forefoot requires efficient energy return during push-off to enhance performance.

[0003] To address this challenge, the industry's technological development trend is to adopt multi-density or multi-functional composite materials. This involves applying materials with different physical properties to different parts of the midsole (such as the heel, midfoot, and forefoot) to achieve functional zoning. Dual-density structures are a common technical solution, typically placing high-shock-absorbing materials in the heel, where impact forces are greatest, while using high-rebound materials in the main midsole.

[0004] However, during the one-piece manufacturing process of this dual-density composite material, when two polymer blends with different chemical compositions and physical properties are combined in the same process flow, the molecular chains lack compatibility due to the different chemical environments of the two materials. This results in high interfacial tension between the two materials during co-blending injection molding or compression molding, making it difficult to form effective molecular-level entanglements. This makes the interface between the two materials a physical weak point in the entire midsole structure. After enduring long-term, high-intensity sports impact and bending, it is prone to structural failures such as delamination and cracking, seriously affecting the durability and safety of the product. Furthermore, the two different material systems have different rheological properties such as melt temperature, melt viscosity, and processing window, as well as different foaming dynamics such as expansion ratio and shrinkage during the foaming process. During the simultaneous foaming or one-piece molding process, these mismatched properties can lead to quality defects such as warping, deformation, and internal stress concentration in the final product, resulting in low product yield and difficulty in ensuring performance consistency. Summary of the Invention

[0005] The purpose of the present invention is to overcome the above-mentioned defects or problems existing in the background technology, and to provide a preparation method of a dual-density cushioning foam material and a dual-density cushioning midsole. The preparation method can improve the problems of poor interface bonding between materials and difficulty in synchronous molding while ensuring that the two materials each have excellent performance.

[0006] To achieve the above object, the present invention adopts the following technical solutions:

[0007] Technical solution 1: A preparation method of a dual-density shock-absorbing foam material, characterized in that the foam material includes a first part and a second part; the second part is combined with the first part; the first part adopts a first material, and the first material includes the following components in parts by mass: 35-45 parts of ethylene-vinyl acetate copolymer, 20-30 parts of polyolefin elastomer, 25-35 parts of styrene-ethylene-butylene-styrene block copolymer, 3-7 parts of ethylene propylene diene monomer rubber, and a cross-linking agent, a foaming agent and an auxiliary agent selected from fillers, activators or a combination thereof; the second part adopts a second material, and the second material includes the following components in parts by mass: 35-45 parts of ethylene-vinyl acetate copolymer, 25-35 parts of hydrogenated styrene-butadiene block copolymer, 10-15 parts of chlorinated polyethylene, 10-20 parts of polyolefin elastomer, and a cross-linking agent, a foaming agent and an auxiliary agent selected from fillers, activators or a combination thereof; wherein the density of the polyolefin elastomer in the first material is 0.880-0.890 g / cm 3 , and the melt flow rate at 190°C / 2.16kg is 0.5-5.0g / 10min; the density of the polyolefin elastomer in the second material is 0.860-0.870g / cm 3 , and the melt flow rate at 190℃ / 2.16kg is 25-35g / 10min; the preparation method of the foaming material comprises the following steps: S10: mixing the components of the first material and the components of the second material in stages to obtain a first rubber compound and a second rubber compound; S20: foaming the first rubber compound and the second rubber compound respectively to obtain a first rubber compound and a second rubber compound with a porous structure; S30: placing the second rubber compound in the first rubber compound and making the peripheral side of the second rubber compound contact with the peripheral side of the first rubber compound, and performing secondary compression molding; S40: cooling and demolding to obtain the dual-density shock-absorbing foaming material; wherein, in step S20, the foaming ratio of the first rubber compound is 185%-195%, and the foaming ratio of the second rubber compound is 183%-193%; in step S30, the molding compression ratio is 140%-150%.

[0008] Technical solution 2 based on technical solution 1: In step S30, the heating temperature of the secondary compression molding is 175°C-181°C, and the heating time is 520 seconds-580 seconds.

[0009] Technical solution three based on technical solution one: in step S40, the cooling time is 520 seconds to 580 seconds.

[0010] Technical solution 4 based on technical solution 1: the foaming agents in the first material and the second material are both azodicarbonamide foaming agents, and the reaction temperature of the foaming agent in the first material is lower than the reaction temperature of the foaming agent in the second material.

[0011] Technical solution 5 based on technical solution 1: The additives in the first material include the following components in parts by mass: 2-4 parts of talc; 8-10 parts of anti-wear agent; 0.3-0.5 parts of stearic acid; 0.6-0.8 parts of zinc stearate; 1.2-1.4 parts of zinc oxide; and 2.5-3.5 parts of titanium dioxide.

[0012] Technical solution six based on technical solution one: the additives in the first material include the following components in parts by mass: 2-4 parts of talc; 0.3-0.5 parts of stearic acid; 0.6-0.8 parts of zinc stearate; 1.7-1.9 parts of zinc oxide; and 3.5-4.0 parts of titanium dioxide.

[0013] Technical Solution 7 based on Technical Solution 1: In step S10, it includes: at 115-125°C, ethylene-vinyl acetate copolymer, polyolefin elastomer, styrene-ethylene-butylene-styrene block copolymer, EPDM rubber and non-heat-sensitive additives are put into an internal mixer for mixing, and after the mixed materials are evenly dispersed, the temperature is lowered, and then the heat-sensitive additive, cross-linking agent and foaming agent are added, and the mixing is continued.

[0014] In addition, the present invention also provides technical solution eight: a dual-density shock-absorbing midsole, characterized in that it includes a main body and a heel body, the heel body is combined with the main body and corresponds to the heel of the foot; the main body and the heel body are prepared by the preparation method of the dual-density shock-absorbing foam material as described in any one of claims 1-7, wherein the main body is the first part and the heel body is the second part.

[0015] From the above description of the present invention, it can be seen that compared with the prior art, the present invention has the following beneficial effects:

[0016] During the research process, the applicant found that the solutions to similar problems in the prior art generally seek consistency in the behavior of the two materials during foaming and cooling shrinkage by making the chemical composition of the two materials as similar as possible, thereby improving the deformation and cracking problems after molding. However, this technical strategy essentially sacrifices the differentiation and extreme performance of the two materials in exchange for process stability. This strategy is effective for two material systems with similar chemical environments, but it cannot solve the more serious interface incompatibility problem caused by huge differences in chemical composition between the two material systems in pursuit of their respective extreme performance.

[0017] The inventive concept of the present invention is completely different from the prior art. Its starting point is to allow for significant differences in the chemical composition and functional polymers of the two materials, thereby maximizing the high rebound performance of the first part material and the high shock absorption performance of the second part material. On this basis, the problem of bonding the contact area between the first and second parts and the problem of simultaneous molding of the two parts are solved. Specifically, the first material of the first part uses styrene-ethylene-butylene-styrene block copolymer and EPDM rubber to achieve high rebound, while the second material of the second part uses hydrogenated styrene-butadiene block copolymer and chlorinated polyethylene to achieve high shock absorption. The huge difference between the first and second materials makes the interface bonding between the two much more difficult than the prior art, but it ensures the excellent performance of the foam material.

[0018] To address the aforementioned technical issues, the present invention improves both the foaming material preparation method and the components used. These improvements are systematically coupled to form an independent and complete technical solution. The key lies in the addition of a polyolefin elastomer with specific physical properties to the second material, which interacts with the components of the first and second materials, while also closely coordinating with the secondary compression molding process.

[0019] First, the specific polyolefin elastomer in the second material has a high melt flow rate of 25-35g / 10min. Under the high temperature and high pressure conditions of secondary compression molding, the polyolefin elastomer has a low melt viscosity and excellent molecular chain mobility. Thermodynamically, there is a high interfacial energy between two incompatible polymer systems, and the system itself tends to reduce the total energy. The introduction of the polyolefin elastomer molecules, especially its high migration ability in the molten state, enables it to spontaneously diffuse out of the matrix of the second material and enrich at the contact interface between the first material and the second material. This process is the first step to achieve interfacial compatibilization, that is, the polyolefin elastomer as a compatibilizer must be able to reach the position where it needs to play a role. Secondly, the polyolefin elastomer in the second material is 0.860-0.870g / cm 3 The lower density indicates that its molecular chain has lower crystallinity and higher amorphous content, which in turn leads to higher elasticity and flexibility. When these molecules migrate to the interface, their highly flexible molecular chain structure enables them to effectively physically entangle with two polymer molecular chains with completely different chemical environments. On the one hand, it can react with ethylene-vinyl acetate copolymer, styrene-ethylene-butylene-styrene block copolymer, etc. in the first material system; on the other hand, it can also react with ethylene-vinyl acetate copolymer, hydrogenated styrene-butadiene block copolymer, chlorinated polyethylene, etc. in the second material system. This ability allows the polyolefin elastomer to establish a physical connection between the two materials.

[0020] Therefore, during the secondary compression molding process, at the interface, this specific polyolefin elastomer, through the interpenetration and entanglement of its molecular chains, constructs a gradient, molecularly intertwined diffusion phase interface on the originally clear, fragile physical interface. This newly formed interface layer is a three-dimensional region of predetermined thickness, containing polymer molecules from both materials connected by the polyolefin elastomer. This interface layer replaces the original weak interface, firmly bonding the two independent material systems together. This transforms the interfacial bonding force from weak surface adhesion forces such as van der Waals forces to strong physical entanglement forces of the molecular chains, thereby alleviating delamination and cracking issues. In step S20 of this technical solution, the preform expansion ratios of the two materials are controlled within a highly matched range of 185%-195% and 183%-193%, respectively. Furthermore, the preform expansion ratio of the first material is always set slightly higher than that of the second material, ensuring consistency in macroscopic deformation between the two preforms. This macroscopic matching creates the prerequisite for stable and uniform physical contact for microscopic interfacial fusion in subsequent steps. On this basis, the two preforms are finally shaped using a compression ratio of 140%-150% in step S30. This specific compression ratio is essential for achieving interfacial fusion. It provides sufficient pressure to completely melt the surfaces of the two preforms at high temperatures and tightly adhere them, eliminating any possible microscopic gaps and creating the necessary physical contact conditions for the effective migration and diffusion of the polyolefin elastomer molecules, which act as an interfacial compatibilizer.

[0021] In summary, this technical solution, by introducing an interfacial compatibilizer with specific physical properties into a specific material and deeply coupling it with a series of process steps such as the precisely controlled primary foaming ratio and secondary molding compression ratio, ultimately successfully solves the difficulties of interfacial bonding and synchronous molding faced when preparing dual-density composite materials using two materials with very different chemical and physical properties, resulting in a final product with stable structure and excellent performance.

[0022] Furthermore, the heating temperature is limited to 175°C-181°C, and the heating time is limited to 520-580 seconds. Within this temperature and time range, the two materials are completely melted, providing the necessary energy and time for the sufficient migration and diffusion of the polyolefin elastomer molecules, which act as an interfacial compatibilizer, thereby ensuring the formation of the diffusion phase interface. Simultaneously, these process conditions ensure that the cross-linking reaction within the material is complete, resulting in stable physical properties for the final product, and avoiding the problems of material degradation caused by excessively high temperatures, or insufficient cross-linking and incomplete interfacial fusion caused by excessively low temperatures.

[0023] Furthermore, within a cooling period of 490 to 550 seconds, the composite material, which has already formed a strong interfacial bond, can be fully cooled to below the demolding temperature while maintaining the molding pressure. This step solidifies the stable three-dimensional network structure and strong interfacial bond formed at high temperature, effectively avoiding the release of residual internal stress caused by sudden or uneven cooling after demolding. This prevents quality issues such as shrinkage, warping, or deformation in the product later in the process, and ensures the dimensional stability and structural integrity of the final product.

[0024] Furthermore, by specifying the types and differences of foaming agents used for the first material and the second material, the most suitable foaming agent can be selected for two material systems with completely different chemical environments and rheological properties, which can more accurately control their respective foaming start-up temperatures and gas evolution rates, thereby achieving a high degree of consistency in the foaming ratios of the two under a unified heating process. DETAILED DESCRIPTION

[0025] The following is a clear and complete description of the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are preferred embodiments of the present invention and should not be considered as excluding other embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making any creative efforts are within the scope of protection of the present invention.

[0026] In the claims and description of the present invention, unless otherwise clearly defined, the use of terms such as "first", "second" or "third" is for distinguishing different objects rather than for describing a specific order.

[0027] In the claims and description of the present invention, if the terms "include", "have" and their variations are used, they are intended to mean "including but not limited to".

[0028] A specific embodiment of the present invention relates to a preparation method of a dual-density shock-absorbing foam material and a dual-density shock-absorbing midsole, wherein the dual-density shock-absorbing foam material includes a first part and a second part; the second part is combined with the first part; the first part adopts a first material, and the first material includes the following components in parts by mass: 35-45 parts of ethylene-vinyl acetate copolymer, 20-30 parts of polyolefin elastomer, 25-35 parts of styrene-ethylene-butylene-styrene block copolymer, 3-7 parts of ethylene propylene diene monomer rubber, and a cross-linking agent, a foaming agent and an auxiliary agent selected from a filler, an activator or a combination thereof; the second part adopts a second material, and the second material includes the following components in parts by mass: 35-45 parts of ethylene-vinyl acetate copolymer, 25-35 parts of hydrogenated styrene-butadiene block copolymer, 10-15 parts of chlorinated polyethylene, 10-20 parts of polyolefin elastomer, and a cross-linking agent, a foaming agent and an auxiliary agent selected from a filler, an activator or a combination thereof; wherein the density of the polyolefin elastomer in the first material is 0.880-0.890 g / cm 3 , and the melt flow rate at 190°C / 2.16kg is 0.5-5.0g / 10min; the density of the polyolefin elastomer in the second material is 0.860-0.870g / cm 3 , and the melt flow rate at 190℃ / 2.16kg is 25-35g / 10min.

[0029] In addition, the preparation method of the dual-density cushioning foam material includes the following steps: S10: mixing the components of the first material and the components of the second material in sections to obtain a first rubber compound and a second rubber compound; S20: foaming the first rubber compound and the second rubber compound to obtain a first rubber compound and a second rubber compound with a porous structure; S30: placing the second rubber compound in the first rubber compound and making the peripheral side of the second rubber compound contact with the peripheral side of the first rubber compound, and performing secondary molding; S40: cooling and demolding to obtain the dual-density cushioning foam material; wherein, in step S20, the foaming ratio of the first rubber compound is 185%-195%, and the foaming ratio of the second rubber compound is 183%-193%; in step S30, the molding compression ratio is 140%-150%.

[0030] In step S30, the heating temperature of the secondary compression molding is 175°C-181°C, and the heating time is 520 seconds-580 seconds. In step S40, the cooling time is 520 seconds-580 seconds.

[0031] Preferably, the foaming agents in both the first and second materials are azodicarbonamide foaming agents, and the reaction temperature of the foaming agent in the first material is lower than that of the foaming agent in the second material. Specifically, the foaming agent for the first material is JL-307F, which has a lower reaction temperature, and the foaming agent for the second material is AC, which has a higher reaction temperature. By selecting appropriate foaming agents for two material systems with different chemical environments and rheological properties, the respective foaming initiation temperatures and gas evolution rates can be precisely controlled, thereby ensuring that the two materials achieve highly consistent foaming ratios under a unified secondary compression molding heating process, laying the foundation for synchronized compression and flow behavior during the subsequent molding process.

[0032] Furthermore, the additives in the first material include the following components in parts by mass: 2-4 parts of talc; 8-10 parts of anti-wear agent; 0.3-0.5 parts of stearic acid; 0.6-0.8 parts of zinc stearate; 1.2-1.4 parts of zinc oxide; and 2.5-3.5 parts of titanium dioxide.

[0033] Furthermore, the auxiliary agents in the first material include the following components in parts by mass: 2-4 parts of talc; 0.3-0.5 parts of stearic acid; 0.6-0.8 parts of zinc stearate; 1.7-1.9 parts of zinc oxide; and 3.5-4.0 parts of titanium dioxide.

[0034] In addition, step S10 includes: mixing ethylene-vinyl acetate copolymer, polyolefin elastomer, styrene-ethylene-butylene-styrene block copolymer, EPDM rubber and non-heat-sensitive additives in an internal mixer at 115-125°C, cooling the mixed materials after they are evenly dispersed, adding heat-sensitive additives, cross-linking agents and foaming agents, and continuing to mix. Specifically, a staged mixing process is adopted. In the first stage, at a higher temperature of 115-125°C, the main rubber materials such as ethylene-vinyl acetate copolymer, polyolefin elastomer, styrene-ethylene-butylene-styrene block copolymer, EPDM rubber and non-heat-sensitive additives are mixed in an internal mixer to ensure that the polymer is fully plasticized and the filler is evenly dispersed. In the second stage, after the materials are evenly mixed, the temperature is lowered, and heat-sensitive additives such as cross-linking agents and foaming agents are added and continued to mix. This segmented process can prevent heat-sensitive additives from prematurely decomposing or reacting at high temperatures, ensuring the stability and controllability of the subsequent foaming and cross-linking processes.

[0035] In addition, based on the above, the dual-density shock-absorbing midsole involved in the present invention includes a main body and a heel body, wherein the heel body is combined with the main body and corresponds to the heel of the sole; the main body and the heel body are prepared by the preparation method of the dual-density shock-absorbing foam material as described above, wherein the main body is the first part and the heel body is the second part. Specifically, the main body of the dual-density shock-absorbing midsole is prepared by the first material, and the styrene-ethylene-butylene-styrene block copolymer and EPDM rubber in its components provide high rebound and high energy return performance. The heel body of the midsole is prepared by the second material, and the hydrogenated styrene-butadiene block copolymer and chlorinated polyethylene in its components provide excellent impact absorption performance. By integrating the high-rebound main body and the high-cushioning heel body, functional zoning is achieved, which can meet the differentiated performance requirements of different areas of the foot during exercise.

[0036] To further illustrate the technical solution of the present invention, the following is a detailed description of the present invention through specific examples and comparative examples. It should be understood that these examples are only used to illustrate the present invention and are not used to limit the scope of protection of the present invention.

[0037] The raw materials used in the examples and comparative examples of the present invention specifically include:

[0038] Ethylene vinyl acetate copolymer (EVA) was selected from the brand 7350M of the Plastics Industry Co., Ltd., with a VA content of 28%.

[0039] Polyolefin elastomer (POE) is available in three types according to different uses. POE-A used for the first material is Engage, a brand of The Dow Chemical Company. TM 8150, its density is 0.868g / cm 3 , the melt flow rate is 0.5g / 10min; POE-B used as the interfacial compatibilizer in the second material is the brand Engage TM 8480, its density is 0.863g / cm 3 , the melt flow rate is 30g / 10min; the POE-C used in Comparative Example 1 is the brand Engage TM 8003, its density is 0.885g / cm 3 , the melt flow rate is 1.0g / 10min.

[0040] Styrene-ethylene-butylene-styrene block copolymer (SEBS) was selected from Kraton Polymers' brand G1652.

[0041] EPDM is Nordel from The Dow Chemical Company. TM IP 4520.

[0042] The hydrogenated styrene-butadiene block copolymer (HSBS) selected was the brand 604T star-shaped SEBS of Baling Petrochemical.

[0043] The chlorinated polyethylene (CPE) used was brand 135A from Weifang Chenrui Plastic Co., Ltd.

[0044] The cross-linking agent (DCP) was dicumyl peroxide produced by Wuxi Huacheng Chemical Co., Ltd.

[0045] The foaming agent is divided into two types according to the reaction temperature. The foaming agent-L used for the first material is the JL-307F low-temperature azodicarbonamide produced by Dongjin Chemical of South Korea, and the foaming agent-H used for the second material is the AC-5000 high-temperature azodicarbonamide produced by Yongxing Chemical.

[0046] Other additives such as zinc oxide, stearic acid, zinc stearate, talc, anti-wear agent (Dow Corning MB50-001 silicone masterbatch) and titanium dioxide are all commercially available industrial grade.

[0047] Example 1

[0048] Weigh the components according to the following mass parts:

[0049] The first material (for the main body): 40 parts of ethylene-vinyl acetate copolymer (EVA-1); 25 parts of polyolefin elastomer (POE-A); 30 parts of styrene-ethylene-butylene-styrene block copolymer (SEBS); 5 parts of ethylene propylene diene monomer (EPDM); 0.8 parts of cross-linking agent (DCP); 2.0 parts of foaming agent (foaming agent-L); and 15 parts of other additives.

[0050] The second material (for the heel body): 40 parts of ethylene-vinyl acetate copolymer (EVA-1); 30 parts of hydrogenated styrene-butadiene block copolymer (HSBS); 12 parts of chlorinated polyethylene (CPE); 15 parts of polyolefin elastomer (POE-B); 0.9 parts of cross-linking agent (DCP); 2.5 parts of foaming agent (foaming agent-H); 8 parts of other additives.

[0051] The above components are used as raw materials and prepared according to the following steps:

[0052] Step S10 (Mixing): The components of the first and second materials are mixed separately. EVA, POE, SEBS / HSBS, EPDM / CPE, and non-heat-sensitive additives are mixed in an internal mixer at 120°C for 10 minutes. After the materials are evenly dispersed, the temperature is lowered to 90°C, and the crosslinking agent and foaming agent are added. Mixing is continued for 5 minutes to obtain the first and second rubber compounds.

[0053] Step S20 (foaming of the primary embryo): placing the first rubber compound and the second rubber compound in a primary embryo mold respectively, and foaming and molding them at 165° C., controlling the foaming ratio of the first primary embryo to be 190% and the foaming ratio of the second primary embryo to be 188%.

[0054] Step S30 (secondary compression molding): The second preform is placed in the cavity of the first preform and placed in the final molding die. Secondary compression molding is performed under the conditions of a heating temperature of 178° C., a heating time of 550 seconds, and a compression ratio of 145%.

[0055] Step S40 (cooling and demoulding): while maintaining the pressure, the mold is cooled for 550 seconds, and then demoulded to obtain the final dual-density cushioning foam material product.

[0056] Example 2

[0057] Weigh the components according to the following mass parts:

[0058] The first material (for the main body): 35 parts of ethylene-vinyl acetate copolymer (EVA-1); 30 parts of polyolefin elastomer (POE-A); 25 parts of styrene-ethylene-butylene-styrene block copolymer (SEBS); 7 parts of ethylene propylene diene monomer (EPDM); 0.7 parts of cross-linking agent (DCP); 1.8 parts of foaming agent (foaming agent-L); and 14.5 parts of other additives.

[0059] The second material (for the heel body): 45 parts of ethylene-vinyl acetate copolymer (EVA-1); 35 parts of hydrogenated styrene-butadiene block copolymer (HSBS); 10 parts of chlorinated polyethylene (CPE); 10 parts of polyolefin elastomer (POE-B); 0.8 parts of cross-linking agent (DCP); 2.3 parts of foaming agent (foaming agent-H); 7.5 parts of other additives.

[0060] Using the above components as raw materials, the preparation method was the same as in Example 1, with only some process parameters adjusted: in step S20, the expansion ratio of the first preform was controlled to 185%, and the expansion ratio of the second preform was controlled to 183%; in step S30, the heating temperature was 175°C, the heating time was 580 seconds, and the molding compression ratio was 140%; in step S40, the cooling time was 580 seconds.

[0061] Example 3

[0062] Weigh the components according to the following mass parts:

[0063] The first material (for the main body): 45 parts of ethylene-vinyl acetate copolymer (EVA-1); 20 parts of polyolefin elastomer (POE-A); 35 parts of styrene-ethylene-butylene-styrene block copolymer (SEBS); 3 parts of ethylene propylene diene monomer (EPDM); 0.9 parts of cross-linking agent (DCP); 2.2 parts of foaming agent (foaming agent-L); and 15.5 parts of other additives.

[0064] The second material (for the heel body): 35 parts of ethylene-vinyl acetate copolymer (EVA-1); 25 parts of hydrogenated styrene-butadiene block copolymer (HSBS); 15 parts of chlorinated polyethylene (CPE); 20 parts of polyolefin elastomer (POE-B); 1.0 part of cross-linking agent (DCP); 2.7 parts of foaming agent (foaming agent-H); 8.5 parts of other additives.

[0065] Using the above components as raw materials, the preparation method was the same as in Example 1, with only some process parameters adjusted: in step S20, the expansion ratio of the first preform was controlled to 195%, and the expansion ratio of the second preform was controlled to 193%; in step S30, the heating temperature was 181° C., the heating time was 520 seconds, and the molding compression ratio was 150%; in step S40, the cooling time was 520 seconds.

[0066] Comparative Example 1

[0067] This comparative example is intended to illustrate a conventional technical solution using a component similarity strategy and a one-time synchronous foaming process.

[0068] Weigh the components according to the following mass parts:

[0069] The first material: 45 parts of ethylene-vinyl acetate copolymer (EVA-1); 15 parts of hydrogenated styrene-butadiene block copolymer (HSBS); 35 parts of polyolefin elastomer (POE-C); 5 parts of ethylene propylene diene monomer (EPDM); 0.8 parts of cross-linking agent (DCP); 2.5 parts of foaming agent (foaming agent-L); and 15 parts of other additives.

[0070] The second material: 40 parts of ethylene-vinyl acetate copolymer (EVA-1); 25 parts of hydrogenated styrene-butadiene block copolymer (HSBS); 30 parts of polyolefin elastomer (POE-C); 5 parts of ethylene propylene diene monomer (EPDM); 0.8 parts of cross-linking agent (DCP); 2.8 parts of foaming agent (foaming agent-L); and 8 parts of other additives.

[0071] The characteristic is that the base polymer types of the first material and the second material are exactly the same, and both adopt polyolefin elastomer (POE-C) with low melt flow rate.

[0072] The above components are used as raw materials and prepared according to the following steps:

[0073] Step 1 (mixing and tableting): Mix the components of the first material and the second material at 120° C. for 10 minutes, cool to 90° C., add the heat-sensitive additive and mix for 5 minutes, and then press into sheets.

[0074] Step 2 (assembly and simultaneous foaming): Cut and assemble the cooled first rubber sheet and the second rubber sheet according to the final product structure, place the assembled rubber assembly directly into the final molding mold, heat and foam at 172°C for 4 hours to complete the foaming and molding.

[0075] Step 3 (Cooling and demoulding): Cool the mold and then take out the finished product.

[0076] Comparative Example 2

[0077] Based on Example 1, the difference lies in the formulation components.

[0078] Formula: The interfacial compatibilizer polyolefin elastomer (POE-B) of the second material in the formula of Example 1 was replaced with polyolefin elastomer (POE-A), that is, the POE type of the two materials was the same, both using POE with a low melt flow rate.

[0079] The above components were used as raw materials and the same preparation method as in Example 1 was adopted:

[0080] Step S10 (mixing): mixing the components of the first material and the second material in sections to obtain a first rubber compound and a second rubber compound.

[0081] Step S20 (primary foaming): the first rubber material and the second rubber material are respectively subjected to preliminary foaming, and the foaming ratio is the same as that of Example 1.

[0082] Step S30 (secondary compression molding): the two preforms are subjected to secondary compression molding, and the process parameters are the same as those in Example 1.

[0083] Step S40 (cooling and demoulding): cooling and demoulding to obtain the final product.

[0084] Comparative Example 3

[0085] Based on Example 1, the difference lies in the preparation method.

[0086] Formula: Exactly the same as that of Example 1, containing a specific interfacial compatibilizer polyolefin elastomer (POE-B).

[0087] The above components were used as raw materials and prepared using a one-step synchronous foaming process similar to that of Comparative Example 1:

[0088] Step 1 (mixing and tableting): Mix the components of the first material and the second material separately and press them into sheets.

[0089] Step 2 (assembly and simultaneous foaming): Assemble the two cooled rubber sheets according to the structure, place them in the final molding mold, and heat and foam them at 172°C for 4 hours.

[0090] Step 3 (Cooling and demoulding): Cool the mold and then take out the finished product.

[0091] 3. Performance Testing and Result Analysis

[0092] The dual-density shock-absorbing foam material samples prepared in Examples 1-3 and Comparative Examples 1-3 were placed under constant temperature and humidity conditions (23±2° C., 50±5% RH) for 24 hours and then subjected to performance testing.

[0093] Test items include: hardness (GB / T 531.1-2008), rebound rate (GB / T 1681-2009), compression set (GB / T12812-2006), interfacial peel strength (referring to GB / T 2790-1995), and dynamic bending test (GB / T3903.1-2017, 50,000 cycles). The test results are summarized in the table below.

[0094]

[0095]

[0096] As can be seen from the hardness and rebound rate data, all embodiments have successfully achieved functional zoning. The first part (main body) has a lower hardness and a rebound rate of up to 76%-79%, providing excellent energy feedback performance. The second part (heel body) has an even lower hardness, a lower rebound rate, and a compression permanent deformation of only 21%-24%, showing excellent impact absorption and cushioning durability. In contrast, due to the similar components of Comparative Example 1, the performance difference between the first and second parts is not significant, and the ultimate functional zoning cannot be achieved. The compression permanent deformation of its second part is as high as 38%, and the cushioning performance and durability are poor.

[0097] Interfacial peel strength testing results showed that Examples 1-3 achieved high interfacial peel strengths of 5.5-6.1 N / mm, demonstrating an extremely strong bond between the first and second parts. Correspondingly, after a rigorous 50,000-cycle dynamic bending test, the interface of the example samples showed no signs of cracking. This fully demonstrates the effectiveness of the technical solution of the present invention in resolving the difficult problem of interfacial bonding of dissimilar materials.

[0098] The interfacial peel strength of Comparative Example 1 was only 2.2 N / mm, and localized cracking occurred at the interface during the dynamic bending test. This reveals the limitations of conventional technology: while simplifying the process by pursuing component similarity can alleviate shrinkage unevenness to a certain extent, this approach completely fails to form an effective interfacial bond when the two materials must use different chemical systems for performance, and the interface becomes a structural Achilles' heel.

[0099] The interfacial peel strength of Comparative Example 2 was 2.8 N / mm, and localized cracking occurred after the dynamic bending test. This experiment strongly demonstrates that the use of POE-B, with its high melt flow rate and low density, as an interfacial compatibilizer in the second material is essential for achieving a strong bond. Without this compatibilizer, which can effectively migrate and bind to the interface under the high temperature and high pressure of secondary molding, even with the exact same process, the unique diffusion phase interface of the present invention cannot be formed, and the bond strength is insufficient to withstand long-term stress.

[0100] Comparative Example 3 achieved an interfacial peel strength of 3.1 N / mm, superior to the other comparative examples, but still exhibited microcracks and failed in the dynamic bending test. This demonstrates the essential nature of the secondary compression molding process of the present invention. Without the high temperature, high pressure, and compressive flow conditions provided by secondary compression molding, the interfacial compatibilizer cannot fully migrate, diffuse, and penetrate the matrix, significantly reducing its compatibilizing effect and preventing optimal bonding.

[0101] The above description and embodiments are intended to explain the scope of protection of the present invention, but do not constitute a limitation thereto. Modifications, equivalent substitutions, or other improvements to the embodiments of the present invention or portions thereof that can be obtained by a person of ordinary skill in the art through logical analysis, reasoning, or limited experimentation based on the teachings of the present invention or the above embodiments, combined with common knowledge, ordinary technical knowledge in the field, and / or prior art, should all be included within the scope of protection of the present invention.

Claims

1. A method for preparing a dual-density shock-absorbing foam material, characterized in that: The foaming material includes a first part and a second part; the second part is combined with the first part; The first part is made of a first material, and the first material includes the following components in parts by weight: 35-45 parts of ethylene-vinyl acetate copolymer, 20-30 parts of polyolefin elastomer, 25-35 parts of styrene-ethylene-butylene-styrene block copolymer, 3-7 parts of EPDM rubber, and a crosslinking agent, a foaming agent, and an auxiliary agent selected from fillers, activators, or a combination thereof; The second part adopts a second material, and the second material includes the following components in parts by weight: 35-45 parts of ethylene-vinyl acetate copolymer, 25-35 parts of hydrogenated styrene-butadiene block copolymer, 10-15 parts of chlorinated polyethylene, 10-20 parts of polyolefin elastomer, and a crosslinking agent, a foaming agent, and an auxiliary agent selected from fillers, activators, or a combination thereof; Wherein, the density of the polyolefin elastomer in the first material is 0.880-0.890 g / cm 3 , and the melt flow rate at 190°C / 2.16kg is 0.5-5.0g / 10min; the density of the polyolefin elastomer in the second material is 0.860-0.870g / cm 3 , and the melt flow rate at 190℃ / 2.16kg is 25-35g / 10min; The preparation method of the foaming material comprises the following steps: S10: Mixing the components of the first material and the second material in sections to obtain a first rubber compound and a second rubber compound; S20: foaming the first rubber material and the second rubber material respectively to obtain a first preform and a second preform having a porous structure; S30: placing the second preform within the first preform so that the circumference of the second preform contacts the circumference of the first preform, and performing secondary compression molding; S40: cooling and demolding to obtain the dual-density shock-absorbing foaming material; Wherein, in step S20, the foaming ratio of the first rubber material is 185%-195%, and the foaming ratio of the second rubber material is 183%-193%; in step S30, the molding compression ratio is 140%-150%.

2. The method for preparing a dual-density shock-absorbing foam material according to claim 1, wherein: In step S30, the heating temperature of the secondary compression molding is 175°C-181°C, and the heating time is 520 seconds-580 seconds.

3. The method for preparing a dual-density shock-absorbing foam material according to claim 1, wherein: In step S40, the cooling time is 520 seconds to 580 seconds.

4. The method for preparing a dual-density shock-absorbing foam material according to claim 1, wherein: The foaming agents in the first material and the second material are both azodicarbonamide foaming agents, and the reaction temperature of the foaming agent in the first material is lower than the reaction temperature of the foaming agent in the second material.

5. The method for preparing a dual-density shock-absorbing foam material according to claim 1, wherein: The additives in the first material include the following components in parts by mass: 2-4 parts of talc; 8-10 parts of anti-wear agent; 0.3-0.5 parts of stearic acid; 0.6-0.8 parts of zinc stearate; 1.2-1.4 parts of zinc oxide; and 2.5-3.5 parts of titanium dioxide.

6. The method for preparing a dual-density shock-absorbing foam material according to claim 1, wherein: The auxiliary agents in the first material include the following components in parts by mass: 2-4 parts of talc; 0.3-0.5 parts of stearic acid; 0.6-0.8 parts of zinc stearate; 1.7-1.9 parts of zinc oxide; and 3.5-4.0 parts of titanium dioxide.

7. The method for preparing a dual-density shock-absorbing foam material according to claim 1, wherein: In step S10, it includes: putting ethylene-vinyl acetate copolymer, polyolefin elastomer, styrene-ethylene-butylene-styrene block copolymer, EPDM rubber and non-heat-sensitive additives into an internal mixer for mixing at 115-125°C, cooling the mixed materials after they are evenly dispersed, adding heat-sensitive additives, cross-linking agents and foaming agents, and continuing to mix.

8. A dual-density shock-absorbing midsole, characterized by: It includes a main body and a heel body, wherein the heel body is combined with the main body and corresponds to the heel of the sole; the main body and the heel body are prepared by the preparation method of the dual-density cushioning foam material as described in any one of claims 1 to 7, wherein the main body is the first part and the heel body is the second part.

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